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Mar 1994

Volume 12, Issue 2, pp. 515-1311


Contributions of scanning probe microscopy and spectroscopy to the investigation and fabrication of nanometer‐scale structures@f|

R. Wiesendanger

J. Vac. Sci. Technol. B 12, 515 (1994); http://dx.doi.org/10.1116/1.587032 (15 pages) | Cited 11 times

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Scanning tunneling microscopy and related local probe methods have led to a novel perception of nanometer‐ and atomic‐scale structures and processes. Since the information is obtained directly in real space, the scanning probe techniques offer significant advantages for the investigation of nonperiodic structures at solid surfaces compared with diffraction techniques. Additionally, local probe methods allow the study of a large variety of physical properties of nanometer‐scale structures down to atomic resolution and even became useful for the fabrication of artificial nanometer‐scale structures. On the other hand, a large number of unresolved scientific and technological issues still remains. In this review, the focus is on two basic questions: what actually has been achieved and which fundamental physics issues need to be addressed further. The discussion will be restricted to topics in solid state physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Low damage etching of InGaAs/AlGaAs by the electron cyclotron resonance plasma with Cl2/He mixture for heterojunction bipolar transistors

S. Miyakuni, M. Sakai, R. Hattori, S. Izumi, T. Shimura, K. Sato, H. Takano, and M. Otsubo

J. Vac. Sci. Technol. B 12, 530 (1994); http://dx.doi.org/10.1116/1.587033 (6 pages) | Cited 1 time

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Low damage InGaAs/AlGaAs etching was realized by electron cyclotron resonance (ECR) plasma with a Cl2/He mixture for heterojunction bipolar transistors (HBTs) emitter mesa formation. By optimizing the etching pressure and the Cl2/He ratio, n‐InGaAs cap layer and n‐AlGaAs emitter layer are successively etched and the smooth surface morphology was obtained. An optical emission measurement reveals that the enhancement of the ionized Cl etching plays the essential role for etching of InGaAs. Raman scattering spectra and the base contact resistance measurements indicate that the etching induced damage is extremely low. Moreover, it was found that the etching rate of p‐AlGaAs base layer decreased down to two‐thirds of that for n‐AlGaAs emitter layer under the optimized etching condition. These results demonstrate the potentiality of ECR plasma etching with Cl2/He discharge providing degradation‐free dry etching for AlGaAs/GaAs HBTs.
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81.65.-b Surface treatments
85.30.Pq Bipolar transistors

Reactive ion etching of AlInGaP and GaAs in SiCl4/CH4/Ar‐based plasmas

C. V. J. M. Chang and J. C. N. Rijpers

J. Vac. Sci. Technol. B 12, 536 (1994); http://dx.doi.org/10.1116/1.587034 (4 pages)

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The reactive ion etching of AlInGaP and GaAs with a gas mixture of SiCl4, CH4, and Ar is examined. Process parameters such as gas flow composition and radio‐frequency power input are varied. The CH4 flow variation in particular has a substantial effect on the morphology of AlInGaP, while generally the effects on GaAs are less dramatic. The etch rates of AlInGaP and GaAs show similar trends. A suitable etching process was found and applied to an AlInGaP/InGaP index‐guided 675 nm laser structure.
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81.65.-b Surface treatments

Electron cyclotron resonance plasma oxidation studies of InP

Y. Z. Hu, J. Joseph, and E. A. Irene

J. Vac. Sci. Technol. B 12, 540 (1994); http://dx.doi.org/10.1116/1.587035 (7 pages) | Cited 2 times

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Electron cyclotron resonance plasma oxidation of InP was studied using both spectroscopic and single wavelength ellipsometry employed during the oxidation process. A two layer oxide was observed with the outer layer being In rich and the inner layer P rich as confirmed from x‐ray photoelectron spectroscopy and etch rate studies. Optical models and oxidation kinetics are analyzed. From positive substrate bias effects on oxidation rates, negative ion oxidant species were identified as dominant and oxide etching was observed at negative bias. Plasma oxidation, like thermal oxidation, yielded excess P near the semiconductor surface which would degrade electronic properties.
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81.65.-b Surface treatments
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Optimal surface cleaning of GaAs (001) with atomic hydrogen

E. J. Petit and F. Houzay

J. Vac. Sci. Technol. B 12, 547 (1994); http://dx.doi.org/10.1116/1.587388 (4 pages) | Cited 13 times

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Atomic hydrogen is commonly used to clean GaAs surfaces. The goals of this work are to optimize the cleaning process and to control surface reactions in order to avoid decomposition of GaAs. Chemically polished GaAs (001) surfaces have been cleaned by thermally generated atomic hydrogen and analyzed by surface sensitive techniques. We propose an optimal process involving two exposures. The first one at room temperature etches As oxides. The second one at 300 °C completes the reduction of Ga oxides. We demonstrate that the variations of the ionization energy, work function, and Fermi level are very sensitive to the completion of the cleaning reaction. These parameters can be used to monitor surface reactions on‐line in order to avoid excessive desorption of As and GaAs decomposition.
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81.65.-b Surface treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Arsenic capping and decapping of InyAl1−yAs(100) grown by molecular beam epitaxy

S. A. Clark, C. J. Dunscombe, D. A. Woolf, S. P. Wilks, and R. H. Williams

J. Vac. Sci. Technol. B 12, 551 (1994); http://dx.doi.org/10.1116/1.587389 (4 pages) | Cited 2 times

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A study of the surface of InyAl1−yAs, grown lattice matched on InP(100) by molecular beam epitaxy, protected by an As cap during storage in air and subsequently annealed in ultrahigh vacuum, is presented. The surface structure and stoichiometry of the layers are investigated by low energy electron diffraction and x‐ray photoemission spectroscopy. These investigations show that decapping may be achieved by annealing the sample at 390 °C to reveal an atomically clean, As‐stabilized surface, exhibiting a (3×1) symmetry. It is also shown that the relative population of In and Al on or near the surface is different from that of the underlying bulk InyAl1−yAs layer and that the overall surface symmetry and stoichiometry may be further adapted by annealing to higher temperatures.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.B- Structure of clean surfaces (and surface reconstruction)

Investigation of chemically assisted ion beam etching for the fabrication of vertical, ultrahigh quality facets in GaAs

Mats Hagberg, Björn Jonsson, and Anders G. Larsson

J. Vac. Sci. Technol. B 12, 555 (1994); http://dx.doi.org/10.1116/1.587390 (12 pages) | Cited 10 times

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Extensive theoretical and experimental investigation of the chlorine and argon chemically assisted ion beam etching process for the fabrication of vertical, ultrahigh quality facets in GaAs are reported. The dependence of etch rate and verticality of the etched profile on chlorine flow and ion flux have been studied and analytical expressions for the etch rate are presented. The analytical expressions are based on previously suggested surface‐reaction models as well as on a new model where the reactions are stimulated by the incident argon ions. Using this new surface‐reaction model together with ion trajectory simulations, computer programs were developed for the etch rate and etch profile which allow us to study the dependence on chlorine flow, argon ion current density, and argon ion energy. The dependence of the etch rate and the etch profile on the chlorine flow is explained by the combined effect of a saturation of the chlorine surface coverage and increased scattering of the high‐energetic argon ions with increasing chlorine flow. Furthermore, the importance of the etch‐mask profile as well as adequate heat sinking, for the verticality of the etched facets is demonstrated.
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81.65.-b Surface treatments

Damage to Si substrates during SiO2 etching: A comparison of reactive ion etching and magnetron‐enhanced reactive ion etching

Tieer Gu, R. A. Ditizio, S. J. Fonash, O. O. Awadelkarim, J. Ruzyllo, R. W. Collins, and H. J. Leary

J. Vac. Sci. Technol. B 12, 567 (1994); http://dx.doi.org/10.1116/1.587391 (7 pages) | Cited 5 times

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The damage and contamination effects present in silicon substrates from both reactive ion etching and magnetron‐enhanced reactive ion etching of SiO2 have been examined for various overetch percentages using spectroscopic ellipsometry (SE) and secondary ion mass spectroscopy (SIMS). The former method has shown that the thickness of the etch‐induced heavy damage layer in silicon decreases, but its damage density increases with magnetic field. In addition, a thinner fluorocarbon residue layer was detected by both SE and SIMS on the samples etched in the presence of a magnetic field. The high temperature annealing behavior of silicon surfaces after UV/O2 removal of this polymer layer was also compared for samples etched with and without the presence of a magnetic field. Almost complete surface recovery was observed for the samples etched with the presence of a magnetic field as a result of a 15 min anneal at 600 °C.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Cleaning of silicon surfaces by hydrogen multipolar microwave plasma excited by distributed electron cyclotron resonance

P. Raynaud and C. Pomot

J. Vac. Sci. Technol. B 12, 574 (1994); http://dx.doi.org/10.1116/1.587392 (7 pages) | Cited 1 time

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Hydrogen plasma produced by a microwave multipolar reactor has been used to clean a single crystal of silicon. The substrate is kept at room temperature and floating potential during the plasma treatment and then heated at 700 °C. The effect of atomic species created in the plasma on the silicon surface is studied by in situ analysis (spectroscopic ellipsometry, low energy electron diffraction, and Auger electron spectroscopy) and ex situ analysis (atomic force microscopy). Quasi‐instantaneous removal of carbon is demonstrated, showing the high efficiency of hydrogen plasma to remove carbon of the silicon surface. This cleaning treatment allows the obtainability of silicon surfaces exempt of contaminants (carbon and oxygen) and roughness (very low perturbed thickness). The peaks values of the imaginary part of dielectric function of Si surface cleaned by hydrogen plasma exceed those previously reported (values of ϵi at 4.25 eV=48.25). This process seems to be compatible with very large scale integrated and ultra‐large scale integration technology.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
52.50.Gj Plasma heating by particle beams

Silicon dioxide deposition by electron cyclotron resonance plasma: Kinetic and ellipsometric studies

M. J. Hernandez, J. Garrido, and J. Piqueras

J. Vac. Sci. Technol. B 12, 581 (1994); http://dx.doi.org/10.1116/1.587393 (4 pages) | Cited 10 times

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Silicon dioxide has been deposited from electron cyclotron resonance silane/oxygen plasmas at temperatures below 150 °C. Deposition rates over 4000 Å/min have been obtained. The refractive indexes in the measuring range of 1.5–4.5 eV were found to be almost insensitive to the different deposition rates and flux ratio regimes except in the near infrared region where small deviations from thermal oxide indexes were observed. Etch rates and refractive indexes were very close to the thermal oxide values for low silane/oxygen flow ratios 0.025, whereas the refractive index decreased and the etch rate increased for the largest flow ratios used (0.20). After a low temperature annealing, 500 °C in nitrogen ambient, the refractive indexes reached the best obtained values and were independent of the conditions under which the layers were deposited.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Nk Insulators

High temperature deposition of SiN films using low pressure chemical vapor deposition system for x‐ray mask application

Tsuneaki Ohta, Rakesh Kumar, Yoshio Yamashita, and Hirosi Hoga

J. Vac. Sci. Technol. B 12, 585 (1994); http://dx.doi.org/10.1116/1.587394 (4 pages) | Cited 2 times

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SiN films for x‐ray mask membranes were prepared using a low pressure chemical vapor deposition system designed for high temperature deposition and low impurity incorporation. The physical and optical properties of the films such as stress, uniformity, optical transmittance, and absorption were investigated. Film composition and impurities were also evaluated. The SiN film deposited at a substrate temperature of 1000 °C showed suitable properties for x‐ray mask membrane, such as well controlled tensile stress of about 5×107 Pa, high optical transmittance over 95% at 500 to 800 nm, and low impurity concentration.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Hp Lithography, masks and pattern transfer
68.60.Bs Mechanical and acoustical properties

Fundamental principles of phase shifting masks by Fourier optics: Theory and experimental verification

K. Ronse, M. Op de Beeck, L. Van den hove, and J. Engelen

J. Vac. Sci. Technol. B 12, 589 (1994); http://dx.doi.org/10.1116/1.587395 (12 pages) | Cited 1 time

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In this article, the imaging principles of projection steppers for optical lithography, using standard transmission masks, are reviewed, and compared with the image formation using various types of phase shifting masks (PSM), in order to get a better insight in the working principles of the various PSM techniques. The printability of periodic lines using a standard transmission mask is compared with the use of an alternating shifter PSM and the dependence of imaging on spatial coherence is discussed extensively. Furthermore the imaging of isolated lines is discussed, using a bright field standard transmission mask, a chromeless phase edge PSM, and a dark field rim PSM. The coherence dependence of an alternated shifter is verified experimentally. Experiments also confirm the superior performance of a chromeless phase edge PSM to print isolated lines.
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42.79.-e Optical elements, devices, and systems
85.40.Hp Lithography, masks and pattern transfer

Tungsten trench etching in a magnetically enhanced triode reactor

S. V. Pendharkar and J. C. Wolfe

J. Vac. Sci. Technol. B 12, 601 (1994); http://dx.doi.org/10.1116/1.587396 (4 pages) | Cited 2 times

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The problem of polymer contamination in W trench etching is studied for fluorocarbon plasmas. Polymer contamination of narrow trenches has been observed on samples where isolated positive‐relief structures (mesas) are clean. This effect is linked to sidewall sputtering by ions backscattered at low angles from the substrate: the sidewalls of a mesa are bombarded by reflected ions originating over a larger area of the substrate than the sidewalls of a trench. The presence of a blast of backscattered ions is confirmed (in an SF6/Br2 plasma) by images where sidewalls adjacent to large substrate areas etch isotropically while those in the shadow of an adjacent feature etch anisotropically. Finally, it is shown that ultrathin, durable polymer coatings which protect mesa sidewalls without contaminating nanometer‐scale trenches can be formed in a magnetically enhanced, triode etching system using a CF4/O2 source gas: 40 nm wide, 300 nm deep trenches are shown.
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81.05.Bx Metals, semimetals, and alloys

Effects of substrate temperature and angular position on the properties of ion beam sputter deposited Fe films on (100) GaAs substrates

S. D. Bernstein, T. Y. Wong, and R. W. Tustison

J. Vac. Sci. Technol. B 12, 605 (1994); http://dx.doi.org/10.1116/1.587397 (8 pages) | Cited 6 times

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The effects of substrate temperature and position on the properties of Fe films deposited onto (100) GaAs substrates by ion beam sputtering were studied. Films were deposited on substrates at angular positions from −20° to 66°, with respect to the target surface normal, at temperatures from 100 to 500 °C. The deposition rate was higher in the forward scattered direction but decreased for angles greater than 45°. The macroscopic film stress was compressive at low temperatures but underwent a compressive to tensile transition between 300 and 500 °C. Furthermore, the stress varied with substrate position. The stress predicted from thermal expansion mismatch is tensile. Both the low temperature compressive stress and the variation of stress with position are qualitatively accounted for by an energetic bombardment or ‘‘atomic peening’’ process. For optimum deposition conditions, the films are highly (200) oriented, with rocking curves as narrow as 0.5°. The resistivity of the films approaches that of bulk Fe, and the variations of resistivity with deposition conditions appear to be associated with the crystallographic perfection of the films.
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81.15.Cd Deposition by sputtering
68.60.Bs Mechanical and acoustical properties

Selective deposition of metals on submicron resist patterns

J. Petermann, T. Hoffmann, and J. Martinez‐Salazar

J. Vac. Sci. Technol. B 12, 613 (1994); http://dx.doi.org/10.1116/1.587398 (3 pages)

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A process to coat submicron structures in paraffin resists, selectively with metals in a single vacuum cycle (all‐dry process), is demonstrated. The process includes the evaporation of paraffin on to a support, the generating of crosslinked areas by irradiation with electrons, the developing of the structure by heating the resist film, and finally a selective coating with metal. The degree of crosslinking of the paraffin film has a remarkably influence on the nucleation density of the metal and allows us to control on a very fine scale the area on which the metal is deposited.
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85.40.Hp Lithography, masks and pattern transfer

Improvement in molecular‐beam epitaxy machine reliability using preventive maintenance

C. W. Ebert, L. J. Peticolas, C. L. Reynolds, and H. H. Vuong

J. Vac. Sci. Technol. B 12, 616 (1994); http://dx.doi.org/10.1116/1.587399 (4 pages)

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Abstract Unavailable
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Optical beam‐deflection scanning force microscope with easy cantilever‐laser beam alignment

Kazuyoshi Sugihara, Akira Sakai, Tetsuo Matsuda, Masao Toyosaki, Kuniyoshi Tanaka, Akira Matsuura, and Shirou Tsukada

J. Vac. Sci. Technol. B 12, 620 (1994); http://dx.doi.org/10.1116/1.587400 (2 pages)

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Abstract Unavailable
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
07.60.Pb Conventional optical microscopes

Arrays of gated field‐emitter cones having 0.32 μm tip‐to‐tip spacing

Carl O. Bozler, Christopher T. Harris, Steven Rabe, Dennis D. Rathman, Mark A. Hollis, and Henry I. Smith

J. Vac. Sci. Technol. B 12, 629 (1994); http://dx.doi.org/10.1116/1.587401 (4 pages) | Cited 39 times

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We have reduced the gate voltage required to achieve a given emission current density in field‐emitter arrays by scaling down the gate‐to‐tip and tip‐to‐tip spacing to the unprecedented levels of 0.08 and 0.32 μm, respectively. The submicrometer features of our arrays are patterned using interferometric lithography. Electrical tests of arrays we have fabricated have shown a record low turn‐on voltage of 8 V for cesiated molybdenum emitters. Emission current densities of 1600 A/cm2 have been obtained, which is also a record for such structures. These arrays provide large advantages for applications such as flat panel displays and microwave devices.
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption

Chemical vapor deposition and plasma‐enhanced chemical vapor deposition carbonization of silicon microtips ∗

V. V. Zhirnov and E. I. Givargizov

J. Vac. Sci. Technol. B 12, 633 (1994); http://dx.doi.org/10.1116/1.587402 (5 pages) | Cited 2 times

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Silicon microtips for field emission applications were coated with thin silicon carbide layers by chemical vapor deposition (CVD) and plasma‐enhanced CVD (PECVD) at temperatures of 800 to 1200 °C using propane or a methane/propane mixture as carbon sources. Coatings from 4 to 30 nm thick were obtained. Scanning electron microscopy and Auger electron spectroscopy were used to investigate the morphology and composition of the carbonized tips. Both silicon carbide and pure carbon coatings could be formed depending on the process parameters used. Sharp carbonized tips were obtained by PECVD using propane flow concentrations.  
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85.45.-w Vacuum microelectronics
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Process characterization and analysis of sealed vacuum microelectronic devices

Q. Mei, S. Zurn, and D. L. Polla

J. Vac. Sci. Technol. B 12, 638 (1994); http://dx.doi.org/10.1116/1.587403 (6 pages) | Cited 1 time

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Cold‐cathode microdiodes with tungsten and heavily doped polycrystalline silicon emitters have been fabricated using silicon planar processing and solid‐state surface micromachining techniques. This work has focused on building reliability into vacuum microelectronic devices and eliminating the need for external vacuum pumping as commonly used in these devices. The following technology advances have been incorporated into sealed microdiode devices: (1) recessed cavities with lateral chemical etch delivery channels, (2) electron beam‐evaporated vacuum enclosures, (3) the use of atomic force microscopy to analyze the fine grain emitter surface structure, (4) the use of soft x‐ray photoelectron spectroscopy to determine surface chemical composition of cathode and anode surfaces, and (5) the use of ultraviolet photoelectron spectroscopy to measure as‐processed work function.
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85.45.-w Vacuum microelectronics

Knife‐edge thin film field emission cathodes on (110) silicon wafers

Bo Lee, T. S. Elliott, T. K. Mazumdar, P. M. McIntyre, Y. Pang, and H. J. Trost

J. Vac. Sci. Technol. B 12, 644 (1994); http://dx.doi.org/10.1116/1.587404 (4 pages) | Cited 1 time

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In the effort to develop a high performance field emission cathode for application in microwave amplifiers, it is clear that the emitter structure should have a sharp emitter surface, a large emitter height, a small gate opening size, and a small emitter angle. We have developed a technique that fabricates knife‐edge field emission arrays (KEFEA) on (110) silicon wafers. KEFEA has an optimized structure meeting the requirements mentioned above. The emitter edge radius is about 250 Å or less, the emitter height is 8 μm, and the gate gap is ∼0.2 μm. Experiments have exhibited Fowler–Nordheim type field emission with gate‐to‐substrate bias voltage less than 50 V.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Silicon vacuum microdiode with on‐chip anode

Yeong J. Yoon, Yicheng Lu, B. Lalevic, and Robert J. Zeto

J. Vac. Sci. Technol. B 12, 648 (1994); http://dx.doi.org/10.1116/1.587405 (4 pages) | Cited 1 time

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A vacuum microdiode was fabricated with a silicon avalanche cathode and an on‐chip microanode. The image reverse process followed by proper heat treatment was employed to form a photoresist sacrificial layer in shaping a microanode. The distance of ∼3 μm between cathode and anode was achieved by adjusting the number of depositions of photoresist. On the top of the sacrificial layer, a multilayer (Al/TiW/Al) structure was deposited, which provided the microanode with good conductivity and mechanical strength. The dimension of the microanode was 8 (or 18) μm in width and more than 30 μm in length. The I–V characteristics of this vertical‐type microdiode demonstrated the enhancement of current emission due to a strong electric field at relatively low anode voltages.
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption

Oxidized amorphous silicon as gate insulator for silicon tips

D. Peters, I. Paulus, and D. Stephani

J. Vac. Sci. Technol. B 12, 652 (1994); http://dx.doi.org/10.1116/1.587406 (3 pages) | Cited 5 times

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Field emission cathode arrays of Betsui type [K. Betsui, Technical Digest of the International Vacuum of Microelectronics Conference, Nagahama, Japan, 1991 (unpublished)] need an intermediate spacer layer with excellent insulator properties, i.e., ultrahigh resistivity, high breakdown voltage, excellent adhesion both to substrate and gate layer, low roughness, low dielectric constant, and sufficient long term stability. This study reports on an investigation of various fabrication methods for this insulating film in order to optimize its properties. Silicon and some compounds (a:Si, SiO, SiO2, SiOxNy) have been deposited by e‐beam or thermal evaporation and plasma enhanced chemical vapor deposition, respectively. These layers have been annealed or oxidized before deposition of the extraction gate layer. The structures have been characterized by means of capacitance measurements. The best results have been obtained with the deposition of pure silicon by e‐beam evaporation followed by an oxidization process. The method described in detail results in an insulator consisting of SiO2 which exhibits excellent insulating properties (breakdown field strength 7 MV/cm). Field emission cathodes fabricated in this manner exhibit stable emission currents up to 1 μA/tip.
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption
81.65.-b Surface treatments

Space‐charge effects in Spindt‐type field emission cathodes

G. N. A. van Veen

J. Vac. Sci. Technol. B 12, 655 (1994); http://dx.doi.org/10.1116/1.587407 (7 pages) | Cited 15 times

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The field emission characteristic of a Spindt‐type cathode, cleaned extensively in a hydrogen atmosphere while emitting, is considered. The maximum emission reached is about 800 μA. At high current levels the I–V curve clearly deviates from a Fowler–Nordheim behavior. This can be explained by the occurrence of space charge. Several models are considered to simulate the experimental results. The fit to the data is good except at the highest emission levels. In this region the difference between the measured currents and the simulation results is due to the neglect of the variation of the field on top of the tip in the presence of space charge.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Field emission from pyramidal cathodes covered in porous silicon

P. R. Wilshaw and E. C. Boswell

J. Vac. Sci. Technol. B 12, 662 (1994); http://dx.doi.org/10.1116/1.587408 (4 pages) | Cited 6 times

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Square‐based pyramidal emitters formed by wet etching of p‐type silicon wafers have been anodized to give a thin surface layer of porous silicon. At the surface of such material are very small fibrils with widths ≤3 nm. Field emission measurements from pyramidal cathodes of plain and anodized silicon show a dramatic improvement, when the porous silicon is present. In this case, average peak emission currents of 25 μA have been obtained with the highest measured being 90 μA, improved uniformity between cathodes was produced and emission began at lower voltages. It was found that plain cathodes too blunt to emit did so when covered in porous silicon. The reasons why such silicon fibrils improve emission are discussed.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Improved monolithic vacuum field emission diodes

James D. Legg, Mark E. Mason, Roger T. Williams, and Mark H. Weichold

J. Vac. Sci. Technol. B 12, 666 (1994); http://dx.doi.org/10.1116/1.587366 (6 pages) | Cited 2 times

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Realization of an easily manufacturable field emission device has been widely recognized as one of the keys to the widespread acceptance of vacuum microelectronics technology. Working to achieve this goal, many researchers have investigated edge emission cathodes similar to those developed by Gray et al. These efforts include work in the area of nonplanar edge emission devices reported by Weichold et al. and devices reported by Itoh et al. Based on that concept, this paper describes an improved nonplanar edge emission diode, suitable for monolithic integration. The structure described by Weichold has several interesting qualities, including the ability to easily define, nonphotolithographically, the anode to cathode spacing during the fabrication process. Additionally, the unique device geometry provides several advantages over traditional structures. Unfortunately, this device does not lend itself well to integration, due to the difficulty of making electrical contact to the cathode. An improved nonplanar diode design which addresses this issue has been conceived and manufactured. The new design has the additional advantage of relying only upon standard manufacturing techniques for its construction. Preliminary device testing has shown current–voltage characteristics that follow the Fowler–Nordheim model for cold field emission over several orders of magnitude of current. In this work, various cathode sizes are investigated and several cathode array sizes are tested.
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption

Characterization of silicon field emission microtriodes

D. Liu and R. B. Marcus

J. Vac. Sci. Technol. B 12, 672 (1994); http://dx.doi.org/10.1116/1.587367 (4 pages)

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The properties of single silicon field emission microtriodes have been examined. Gate and collector currents were measured in a vacuum of 2×10−8 Torr, and current–voltage, current–time, Fowler–Nordheim (I/V2 versus 1/V), and triode characteristics were determined. The data showed that the electron emission followed Fowler–Nordheim behavior. Single emitters had turn‐on gate‐to‐cathode voltages (V) above 25 V (typically 50–90 V) and reproducible emission currents were measured in the range 5 pA–1 μA. Temporal fluctuations in emission current of 10%, 16%, and 40% were found for emission currents of 0.35, 50 nA, and 0.5 μA, respectively. The triode characteristics showed an Ig/Ic ratio of 0.25% and higher. Transconductances were found to be 3×10−8 Ω−1/tip. Electrostatic discharge and other device failure mechanisms have been observed and are described.
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption

Fabrication and characterization of silicon field emission diodes and triodes

Q. Li, M. Y. Yuan, W. P. Kang, S. H. Tang, J. F. Xu, D. Zhang, and J. L. Wu

J. Vac. Sci. Technol. B 12, 676 (1994); http://dx.doi.org/10.1116/1.587368 (4 pages) | Cited 6 times

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I–V characteristics of silicon field emission diode and triode were investigated. The maximum emission current of 17 μA and the lowest onset voltage of 60 V were obtained by an array of 245 silicon tips. The typical reverse recovery time of the diode was 350 ps. The typical transconductance of the triode was about 10−7 S. The fabrication processes for forming sharp silicon conical tips with a gate hole diameter 1 μm smaller than the corresponding oxide mask is described. The results of a high temperature activation process for improving emission characteristics of the device are presented. The stability and uniformity of the devices affected by the fabrication process and emission environment are also discussed in this paper.
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption

Gated chromium volcano emitters

J. E. Pogemiller, H. H. Busta, and B. J. Zimmerman

J. Vac. Sci. Technol. B 12, 680 (1994); http://dx.doi.org/10.1116/1.587369 (5 pages) | Cited 3 times

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By reversing the bias of a field emitter with a volcano‐shaped gate, it is demonstrated that emission occurs from the rim of the gate. The gate‐to‐emitter distance of this structure is defined by the thickness of the insulating film between the electrodes and not by expensive photolithographic techniques. By enlarging the gate diameter to printed circuit board‐type dimensions, in principle, low cost, large area field emitter arrays can be fabricated. The process is being demonstrated on a silicon substrates and initial emission data are being presented. The article concludes by demonstrating one transfer path of this technology onto an inexpensive glass substrate.  
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption

Stability of the emission of a microtip

C. Py and R. Baptist

J. Vac. Sci. Technol. B 12, 685 (1994); http://dx.doi.org/10.1116/1.587370 (4 pages) | Cited 7 times

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In order to evaluate the potential of microtips in novel electron optics applications, the emission stability of a single tip was studied. It was found that after a few hours of ‘‘self‐shaping,’’ a tip may emit a very stable spot (for 700 nA of global emission, 7 min is reported without any change over 1 nA, and a couple of hours with less than ±1% change). Unfortunately, a period of instability may follow a period of stability. It was observed that the spot is composed of several subspots, each one having a much greater stability than the whole spot. These subspots are very likely to be emitted from independent nanoprotrusions or atoms, and changes in the emission occur because of motions of atoms and/or adsorption–desorption processes. It was concluded that, though the stability of an electron beam cannot be ‘‘infinite’’ as a laser beam is, very long periods of stability (hours) and high coherence of wave packets can be obtained, if work was done under very high vacuum (several 10−11 mbar) and with a unique beam emitted from a single atomic site.
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79.70.+q Field emission, ionization, evaporation, and desorption

Scaling of emission currents and of current fluctuations of gated silicon emitter ensembles

H. H. Busta, J. E. Pogemiller, and B. J. Zimmerman

J. Vac. Sci. Technol. B 12, 689 (1994); http://dx.doi.org/10.1116/1.587371 (4 pages) | Cited 9 times

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The scaling of emission currents and of their corresponding current fluctuations of ensembles of gated, monocrystalline silicon emitters ranging from n=1 to n=20 800 emitters have been investigated. For randomly selected ensembles, the current scales approximately with n and the fluctuation with n−0.16. For selected ensembles of identical emission behavior, the current scales with n and the fluctuations with n−0.5 as is expected from theory. The discrepancy in the exponent for the scaling of the current fluctuations is caused by the poor participation of the emitters within an ensemble. Only a few emitters per ensemble contribute to the total current. The scaling behavior can thus be used as a diagnostic tool to evaluate a given process. The measurements were performed at room temperature and at pressures of approximately 1×10−8 Torr.  
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption

Bright‐field analysis of field‐emission cones using high‐resolution transmission electron microscopy and the effect of structural properties on current stability

W. D. Goodhue, P. M Nitishin, C. T. Harris, C. O. Bozler, D. D. Rathman, G. D. Johnson, and M. A. Hollis

J. Vac. Sci. Technol. B 12, 693 (1994); http://dx.doi.org/10.1116/1.587372 (4 pages) | Cited 6 times

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High‐resolution transmission electron microscopy has been used to analyze 150 nm diameter by 150 nm high polycrystalline molybdenum field‐emission cones. The analysis shows that the cones comprise 5 to 10 nm thick grains with tips having gross radii of curvature of about 5 nm and protrusions having radii of curvature of about 1 nm. Such small protrusions may explain why analysis of experimental emission data indicates that the effective emission area of such tips is only 0.1 to 0.5 nm.2 Furthermore, the fact that the structure is composed of small grains indicates that there is a substantial number of molybdenum atoms at grain boundaries and that many configurations of grains and boundaries are possible with minimal free energy. A qualitative model is proposed which links the structural properties to current stabilization and hydrogen passivation effects.
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

SiO2‐induced silicon emitter emission instability

W. J. Bintz and N. E. McGruer

J. Vac. Sci. Technol. B 12, 697 (1994); http://dx.doi.org/10.1116/1.587373 (3 pages) | Cited 13 times

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An emission instability attributed to an oxide layer on a silicon emitter tip surface has been characterized. The instability leads to a current runaway which often results in device failure. When device failure does not occur, the instability is a one time event while the device remains in a vacuum environment. The magnitude of the instability increases with increasing oxide thickness and can be effectively eliminated by etching in buffered HF immediately before testing or device packaging.
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption

Activation, stabilization degradation, and lifetime predictions of refractory thin films emitters operated in cold cathode magnetrons@f|

M. F. Kopylov

J. Vac. Sci. Technol. B 12, 700 (1994); http://dx.doi.org/10.1116/1.587374 (3 pages)

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Qualitative physical and chemical analysis of cold cathode magnetrons, field emitter activation process, and emission stabilization is described. The field emitter materials being presented are super thin films of Ta, Nb, W and their alloys and secondary electron emitters being presented by different kinds of emission active materials. Degradation processes of cold cathode magnetrons with field electron excitation are studied. Criteria for predicting of long (≳10 000 h) life, including individual life predictions are defined. Parameters of the lowest voltage state‐of‐the‐art cold cathode magnetron with 7.5 and 5 kW pulse output power in 3 cm wavelength range are tabulated.
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption

Diffusion on an elliptical field emission cathode@f|

D. V. Eremchenko and V. I. Makhov

J. Vac. Sci. Technol. B 12, 703 (1994); http://dx.doi.org/10.1116/1.587375 (2 pages)

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The stability limit for curvature of a charged elliptical surface is found beyond the Dyke et al. approximation.
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption

Atom probe analysis and field emission studies of silicon

R. A. King, R. A. D. Mackenzie, G. D. W. Smith, and N. A. Cade

J. Vac. Sci. Technol. B 12, 705 (1994); http://dx.doi.org/10.1116/1.587376 (5 pages) | Cited 6 times

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Single ungridded silicon tips have been studied by field emission current–voltage characterization, field emission imaging, field ion imaging, and pulsed laser atom probe (PLAP) analysis. Changes in field emission characteristics were observed as a thin contaminant layer (oxygen, hydrogen, carbon, and carbon monoxide) formed on the surface of clean field evaporated silicon tips. Removal of the contaminant layer by pulsed laser‐assisted field desorption restored the original field emission characteristics. Clean silicon tips that were oxidized in air began to emit at half the voltage required for unoxidized tips. As the voltage was increased, a sudden irreversible increase in field emission current was observed. PLAP analysis and field emission imaging showed that this effect was caused by the disruption of the oxide layer shortly after the onset of field emission. After the oxide disruption, field emission occurred from regions of sharp local geometry around the circumference of the tip. Removal of these regions by field evaporation or PLAP produced field emission characteristics very similar to those obtained from clean silicon tips. This explains a long‐standing problem in understanding the ‘‘switch‐on’’ behavior of silicon emitters.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.37.Vj Field emission and field-ion microscopy
85.45.-w Vacuum microelectronics

Investigation of the operating modes of gated vacuum field emitter arrays to reduce failure rates

S. Meassick, Z. Xia, C. Chan, and J. Browning

J. Vac. Sci. Technol. B 12, 710 (1994); http://dx.doi.org/10.1116/1.587377 (3 pages) | Cited 1 time

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The influence of the operating mode of arrays of gated vacuum field emitters on the intrinsic failure rate of emitter tips has been investigated. In particular, the failure rates of arrays of gated silicon vacuum field emitters operating in a dc and pulsed bias mode as a function of pulse duty cycle, pulse frequency, emitted current, and neutral gas pressure have been measured. There is a large reduction of the failure rate, per unit time that the array is emitting current, when emitters are operated in pulsed mode as compared to a dc mode of operation. This reduction in the failure rate is dependent on the duty cycle of the pulses that the array is operated at but is independent of the repetition frequency of the pulses. The failure rate is an exponential function of the emitted current, both for the dc bias and for the pulse bias case. The increase in failures with increasing current is more rapid for a dc bias than for a pulse bias. The failure rate of gated vacuum field emitters increases rapidly with the neutral gas pressure, with the rate of increase in failures identical for a dc and a pulsed bias.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Characterization of gridded field emitters

M. Huang, R. A. D. Mackenzie, T. J. Godfrey, and G. D. W. Smith

J. Vac. Sci. Technol. B 12, 713 (1994); http://dx.doi.org/10.1116/1.587378 (4 pages) | Cited 1 time

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A system combining field emission microscopy, field ion microscopy, atom probe, and current–voltage (I–V) measurement facilities has been developed to study gridded field emitter devices, either in the form of single tips or arrays. (I–V) measurement results, field emission images, and field ion images of a single tip and an array of 1500 tips are presented here, of which field ion images of the gridded emitters are reported for the first time. The first atom probe results from a gridded array are also given here, demonstrating that chemical composition analysis of gridded field emission cathodes is possible.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.37.Vj Field emission and field-ion microscopy
85.45.-w Vacuum microelectronics

Modification of Si field emitter surfaces by chemical conversion to SiC

J. Liu, U. T. Son, A. N. Stepanova, K. N. Christensen, G. J. Wojak, E. I. Givargizov, K. J. Bachmann, and J. J. Hren

J. Vac. Sci. Technol. B 12, 717 (1994); http://dx.doi.org/10.1116/1.587379 (5 pages) | Cited 6 times

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Silicon field emitters have been modified by coating with a thin SiC film through a chemical conversion process. Silicon carbide was formed on Si emitter surfaces by reacting with ethylene gas at temperatures between 850 and 950 °C using pressures as high as 5×10−3 Torr. The thickness of the coatings ranged from 2 to 500 nm, determined by a combination of reaction time, pressure, and temperature. Stable emission currents above 10 μÅ were measured from individual SiC coated emitters.  
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85.45.-w Vacuum microelectronics
79.70.+q Field emission, ionization, evaporation, and desorption

Transition metal carbides for use as field emission cathodes

William A. Mackie, Robert L. Hartman, Mark A. Anderson, and Paul R. Davis

J. Vac. Sci. Technol. B 12, 722 (1994); http://dx.doi.org/10.1116/1.587380 (5 pages) | Cited 21 times

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Field emission characteristics of clean ZrC, HfC, and TaC cathodes are reported. High current density emission, greater than 1×108 A/cm2, is discussed, and a method for determining the cathode changes leading to this high current emission condition is proposed. A close‐spaced triode designed for testing individual emitters is described, and results are reported. The effective thermionic work functions of clean and partially oxygen covered surfaces of ZrCx specimens of two different bulk compositions are reported and discussed. Clean values of 3.5 and 3.4 eV were observed for ZrC0.92 and ZrC0.86 specimens, respectively, at 1500 K. With adsorbed oxygen, values as low as 3.4 and 3.2 eV, respectively, were observed for these surfaces at 1500 K.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Energy exchange processes in electron emission at high fields and temperatures

M. S. Chung, P. H. Cutler, N. M. Miskovsky, and T. E. Sullivan

J. Vac. Sci. Technol. B 12, 727 (1994); http://dx.doi.org/10.1116/1.587381 (10 pages) | Cited 17 times

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A new more complete theory for energy exchange processes in electron emission is formulated. It is found that the tunneling contribution to the availability of vacant states is necessary to explain the replacement process occurring in the emitter region. The introduction of the tunneling states now makes it possible to obtain both the average energies of the emitted and replacement electrons using the same formalism. At T=0 K, the average energy of replacement electrons, 〈ϵr〉, is the same as the average energy of the emitted electrons, 〈ϵe〉. As T increases, 〈ϵr〉 increases rapidly until it reaches a maximum and then decreases slowly, while 〈ϵe〉 increases monotonically. When T equals the inversion temperature Ti, 〈ϵe〉=〈ϵr〉 and the energy exchange Δϵ=0. We have also calculated both Δϵ and Ti as a function of field F. For high temperature and fields, the value of Ti differs considerably from that obtained without the tunneling state contribution and Ti exhibits nonlinear behavior as a function of field. Tunneling state contributions are essential for explaining the steady state condition in the conduction process, especially at very low temperatures. These results are crucial for resolving the controversial problem of the replacement process in electron emission. Contrary to the assertion of Nottingham [Phys. Rev. 59, 907 (1941)] that the replacement energy is the Fermi energy, the current results indicate that the average value can be 10–102 meV less than the Fermi energy in agreement with Fleming and Henderson [Phys. Rev. 58, 887 (1940)]. Nonequilibrium effects evaluated within the relaxation time approximation are significant only for large fields.
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79.70.+q Field emission, ionization, evaporation, and desorption

Calculated I–V characteristics of a gold liquid metal ion source for a prototype emitter modeled as a cone–sphere

Shana Nicole Miskovsky, N. M. Miskovsky, and P. H. Cutler

J. Vac. Sci. Technol. B 12, 737 (1994); http://dx.doi.org/10.1116/1.587382 (8 pages)

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The operational properties of liquid metal ion sources (LMIS) have been studied extensively the last three decades. Nevertheless, debate still exists on the emitter shape and the mechanism(s) responsible for ion emission. It is generally believed that prior to onset, the applied electric field causes a (cuspidal) deformation of the liquid emitter surface. This study will use the cone–sphere as a prototype for the emitter surface. The advantage of the cone–sphere model is its ability to replicate analytically the emitter shapes seen experimentally, since one can independently choose the radius of curvature, R, the ‘‘form factor’’ k (which determines the amount of ‘‘necking’’) and the asymptotic cone angle. The I–V characteristics of a cone–sphere model of a Au LMIS were calculated using the image hump (IH) and charge exchange (CE) models for the field evaporation process. Field evaporation is assumed to be thermally activated and follow an Arrenhius expression of the form exp(−Qn/kT), where Qn is the activation energy. The multidimensionality of the source is accounted for in the calculation of the exact field variation on the three‐dimensional surface of the liquid emitter. The calculation of Qn in the image hump model follows a standard procedure. However, the evaluation of Qn for the charge exchange model differs from that done by others. First, the atomic energy curve for Au is calculated using the universal binding energy curve of Smith et al. [J. R. Smith, J. Ferrante, and J. H. Rose, Phys. Rev. B 25, 1149 (1982)]. The intersection of the atomic and ionic potential energy curves is determined as a function of field. The quantity Qn is then the energy difference between the minimum of the atomic energy curve and its value at the intersection. The I–V characteristics for Au obtained using the CE model are in better qualitative agreement with experimental results for Au and Cs than the IH model in the voltage range from 1 to 10 kV. In paricular, the calculated curves exhibit a definitive onset voltage, a sharp rapid rise, and saturation behavior.  
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79.40.+z Thermionic emission
85.45.-w Vacuum microelectronics

Calculations of capacitance and electric field of a vacuum field effect device

Z.‐H. Huang, P. H. Cutler, N. M. Miskovsky, and T. E. Sullivan

J. Vac. Sci. Technol. B 12, 745 (1994); http://dx.doi.org/10.1116/1.587383 (4 pages) | Cited 1 time

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Capacitance and transconductance are critical parameters determining the limiting operating frequency of a vacuum field effect transistor. We calculate the capacitance and the electric field of a vacuum field effect device using the charge density method. The cathode is modeled as a cone of half angle α with a rounded tip (a section of a sphere) of radius R, and the gate is represented by a thin circular disk of radius R2 with a concentric circular hole of radius R1, and placed a distance d above the tip. It is found that (1) The capacitance C is 0.2 fF for R=0.05 μm, R1=1 μm, R2=3 μm, d=0, and α=15°. (2) For fixed R1, C increases linearly with ΔR=R2−R1. (3) For fixed ΔR and d, C increases with increasing R1. (4) For fixed R1 and R2, C decreases with increasing d. (5) A significant field drop occurs close to the tip, as is expected. This strongly localized gradient focuses a majority of the electrons initially in the direction perpendicular to the plane of the gate.
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85.45.-w Vacuum microelectronics
85.30.Tv Field effect devices

Field emission diode characterization through model parameters extraction from current–voltage experimental data

Dan Nicolaescu and Viorel Avramescu

J. Vac. Sci. Technol. B 12, 749 (1994); http://dx.doi.org/10.1116/1.587384 (5 pages) | Cited 8 times

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Standard field emission diode and array modeling is based on the planar Fowler–Nordheim (FN) current density‐electric field J(E) relationship and the introduction of the field enhancement a and area b factors to relate E and J to the measurable quantities potential V and current I. This approach is questionable because E is not constant on the emitter and the b factor is V dependent. In this article, while still using the FN J(E) relationship, I(V) is obtained through J integration over the emitter surface, based on the ideal field emitter floating sphere model (FSM). The model parameters are the emitter’s height h, radius R, work function ϕ, and anode–cathode planes spacing d and the factors a and b are not used. A parameters extraction procedure (PEP) has been developed, in order to obtain the value of the parameters within the model framework ensuring the best fit to the experimental field emission data. The objective function to be minimized is the standard deviation between FSM and experimental field emission I(V) data. The nonlinear minimization routine used in PEP has been chosen after an extensive testing. The best set of searching variables is outlined. The PEP was applied to reported field emission data. An electric field reduction factor ρ was introduced allowing a physical explanation to be derived. Several ways of applying the PEP are suggested.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Use of boundary element methods in field emission computations

Robert L. Hartman, William A. Mackie, and Paul R. Davis

J. Vac. Sci. Technol. B 12, 754 (1994); http://dx.doi.org/10.1116/1.587385 (5 pages) | Cited 13 times

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The boundary element method is well suited to deal with some potential field problems encountered in the context of field emission. A boundary element method is presented in the specific case of three‐dimensional problems with azimuthal symmetry. As a check, computed results are displayed for well‐known theoretical examples. The code is then employed to calculate current from a field emission tip and from the same tip with a protrusion. Finally an extension of the boundary element code is employed to calculate space‐charge effects on emitted current.
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79.70.+q Field emission, ionization, evaporation, and desorption
02.70.-c Computational techniques; simulations

Technological parameters distribution effects on the current–voltage characteristics of field emitter arrays

Dan Nicolaescu

J. Vac. Sci. Technol. B 12, 759 (1994); http://dx.doi.org/10.1116/1.587386 (5 pages) | Cited 5 times

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Different applications require the development of field emitters arrays (FEA). The uniformity of the emitters is an important feature of FEA. The array technological parameters distribution effects on the FEA Fowler–Nordheim (FN) current–voltage I(V) plot has been investigated based on the ideal field emitter floating sphere model. The model parameters are emitter height h, radius R, work function ϕ, and anode–cathode planes distance d. The array FN I(V) plot is shown to be modified in a specific way when the parameters R and h vary according to a Gaussian distribution function (DF). The array representative emitter is defined and its parameters are obtained through a parameter extraction procedure. Several analytical results are presented for parabolic DF on R. Further modeling suggestions are given.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Simulations of fabricated field emitter structures

D. Hong, M. Aslam, M. Feldmann, and M. Olinger

J. Vac. Sci. Technol. B 12, 764 (1994); http://dx.doi.org/10.1116/1.587387 (6 pages) | Cited 11 times

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Five different single field emitters and emitter arrays with flat or nonflat collector structures were selected from the literature to simulate the actual emitting area of the tip. The Poisson’s equation was solved under two different assumptions of emitting behavior; uniform electron emission from the whole tip area, and electron emission from only small part of the tip area. It was observed that the geometry factor β of an array is larger than that of a single emitter, which is believed to be partly responsible for exceedingly small computed value of emitting area α for multiemitter structures. Finite element analysis of single and multiemitter structures indicates that the large β values are due to the interemitter interactions in an array.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Time dependent, self‐consistent simulations of field emission from silicon using the Wigner distribution function

K. L. Jensen and A. K. Ganguly

J. Vac. Sci. Technol. B 12, 770 (1994); http://dx.doi.org/10.1116/1.587344 (6 pages) | Cited 8 times

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Field emission current calculations from semiconductors typically rely on the assumptions that the emitted current is negligible and that the band bending at the surface may be calculated via Poisson’s equation with a Fermi–Dirac momentum distribution of electrons [the zero emitted current approximation (ZECA)]. This approach cannot take into account complications due to quantum confinement near the surface, and problems associated with scattering for large applied field. We have developed and applied a time‐dependent, self‐consistently calculated Wigner distribution function (WDF) approach for dealing with the semiconductor field emission problem, and have applied it to the case of silicon for the cases of 300 and 900 K. In particular, effects of self‐consistency and scattering on the density and potential profiles were examined, comparing the results to the ZECA approach to show when quantum and scattering effects become significant. At low fields, the WDF approach may be coupled with the transmission coefficient approach to yield reasonable current estimates. At high fields, it is shown that current saturation effects set in, in which the current no longer exponentially rises with applied field. Finally, the time dependence of the current and particle densities after a sudden shift in the applied field are examined.
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79.70.+q Field emission, ionization, evaporation, and desorption

Field emission from an elliptical boss: Exact and approximate forms for area factors and currents

K. L. Jensen and E. G. Zaidman

J. Vac. Sci. Technol. B 12, 776 (1994); http://dx.doi.org/10.1116/1.587345 (5 pages) | Cited 10 times

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Field emission from metallic or semiconductor tips, in comparison to planar surfaces, is complicated by current enhancement effects and changes in the image charge. It is shown that the approximations typically used for the calculation of the transmission coefficient, namely, a ‘‘linearized’’ Wentzel–Kramers–Brillouin approach and methods based upon the Fowler–Nordheim approach, are inappropriate for small spherical surfaces but adequate for elliptical surfaces. The derivation of the approximate approaches is given, as well as a simple analytical formula for the average emitting area, which may be derived based on the Fowler–Nordheim equation. By use of the elliptical approximation for the tip geometry, a simple scale factor is sufficient to deal with spherical and pointed tips.
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79.70.+q Field emission, ionization, evaporation, and desorption

New electron excited light emitting materials∗

A. Vecht, D. W. Smith, S. S. Chadha, C. S. Gibbons, James Koh, and David Morton

J. Vac. Sci. Technol. B 12, 781 (1994); http://dx.doi.org/10.1116/1.587346 (4 pages) | Cited 24 times

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A range of bright, multicolor phosphor systems for field emission displays is reported. These include the standard ZnO:Zn and newer, narrow band emitting systems based on green ZnGa2O4:Mn and red CaTiO3:Pr. A modified, blue emitting ZnO:(Zn/Mg) and thin films of ZnGa2O4:Mn have also been prepared.
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85.60.Pg Display systems
79.70.+q Field emission, ionization, evaporation, and desorption

Phosphor selection constraints in application of gated field‐emission microcathodes to flat panel displays

Andrei G. Chakhovskoi, W. Dawson Kesling, Johann T. Trujillo, and Charles E. Hunt

J. Vac. Sci. Technol. B 12, 785 (1994); http://dx.doi.org/10.1116/1.587347 (5 pages) | Cited 12 times

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The major issues and tradeoffs surrounding phosphor selection for field‐emission flat panel displays are identified. The two main classes of commercially available phosphors applicable to flat panel displays are contrasted, and the major physical, electrical, chemical and optical factors effecting phosphor selection are discussed. The implications of screen layering designs and cathode materials are described as they relate to phosphor characteristics. Resolution requirements for displays severely limits the maximum anode voltage, which in turn forces specific phosphor choices. Possible solutions to these limitations are explored.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.60.Pg Display systems

Deflection microwave and millimeter‐wave amplifiers

Cha‐Mei Tang, Y. Y. Lau, and T. A. Swyden

J. Vac. Sci. Technol. B 12, 790 (1994); http://dx.doi.org/10.1116/1.587348 (5 pages) | Cited 2 times

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A new class of microwave and millimeter‐wave amplifiers, called deflectron amplifiers, which are based on the deflection of low voltage electron beams in a microstructure were analyzed. This concept may be applied in two ways: as microelectronic amplifiers or as bunched beam cathodes to power conventional amplifier configurations such as klystrodes and traveling wave tubes. Estimates for gain and efficiency are obtained from a circuit analysis. Particle codes are used to test the viability of the concept. Frequencies of operation are projected up to a few tens of GHz for microelectronic amplifiers and up to ∼80 GHz for power amplifiers.
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85.45.-w Vacuum microelectronics
84.30.Le Amplifiers
79.70.+q Field emission, ionization, evaporation, and desorption

Study of the I–V characteristics of planar‐doped‐barrier electron emitters

Wei‐Nan. Jiang and Umesh K. Mishra

J. Vac. Sci. Technol. B 12, 795 (1994); http://dx.doi.org/10.1116/1.587349 (6 pages)

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Unlike conventional planar‐doped‐barrier (PDB) diodes which have relative low built‐in accelerating fields, tunneling of electrons through the energy band gap becomes an important, and at times dominant, current transport mechanism under the high accelerating field which is essential for high performance PDB electron emitters. Thermionic emission across the triangular barrier is also found to be important. A systematic study on the temperature dependent I–V characteristics of PDB diodes with high accelerating field has been carried out, and different carrier transport mechanisms across the PDB diodes will be discussed in this article.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Energy distribution of tunneling emission from Si‐gate metal–oxide–semiconductor cathode

Kuniyoshi Yokoo, Shinji Sato, Gen Koshita, Isato Amano, Junichi Murota, and Shoich Ono

J. Vac. Sci. Technol. B 12, 801 (1994); http://dx.doi.org/10.1116/1.587350 (5 pages) | Cited 11 times

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An Si‐gate metal–oxide–semiconductor (MOS) electron tunneling cathode was fabricated and its emission characteristics were examined. The emission occurred at a gate voltage higher than the work function of the Si gate by electron tunneling through the potential barrier in the MOS cathode and was stable in the Si‐gate cathode. The energy distribution of emitted electrons was measured and was confirmed to be mainly determined by the scattering process of hot electrons in the oxide. The emission current from the Si‐gate MOS cathode was nearly independent of pressure.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics

Metal plasma immersion ion implantation and deposition using vacuum arc plasma sources

André Anders, Simone Anders, Ian G. Brown, Michael R. Dickinson, and Robert A. MacGill

J. Vac. Sci. Technol. B 12, 815 (1994); http://dx.doi.org/10.1116/1.587351 (6 pages) | Cited 33 times

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Plasma source ion implantation (PSII) with metal plasma results in a qualitatively different kind of surface modification than with gaseous plasma due to the condensable nature of the metal plasma, and a new, PSII‐related technique can be defined: metal plasma immersion ion implantation and deposition (MPI). Tailored, high‐quality films of any solid metal, metal alloy, or carbon (amorphous diamond) can be formed by MPI using filtered vacuum arc plasma sources, and compounds such as oxides or nitrides can be formed by adding a gas flow to the deposition. Here we describe the plasma formation at cathode spots, macroparticle filtering of the vacuum arc plasma by magnetic ducts, the underlying physics of MPI, and present some examples of MPI applications.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.65.-b Surface treatments
52.75.-d Plasma devices

50‐kV pulse generator for plasma source ion implantation@f|

G. Böhm and R. Günzel

J. Vac. Sci. Technol. B 12, 821 (1994); http://dx.doi.org/10.1116/1.587352 (2 pages) | Cited 5 times

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The pulse generator has been especially designed by Puls‐Plasmatechnik GmbH for the application of the field of plasma source ion implantation. The maximum output voltage is −50 kV. The pulse frequency can be adjusted up to 100 Hz. A brief survey is given in this article.  
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52.75.-d Plasma devices
84.30.Ng Oscillators, pulse generators, and function generators

Metal ion implantation: Conventional versus immersion

I. G. Brown, A. Anders, S. Anders, M. R. Dickinson, and R. A. MacGill

J. Vac. Sci. Technol. B 12, 823 (1994); http://dx.doi.org/10.1116/1.587353 (5 pages) | Cited 9 times

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Vacuum‐arc‐produced metal plasma can be used as the ion feedstock material in an ion source for doing conventional metal ion implantation, or as the immersing plasma for doing plasma immersion ion implantation. The basic plasma production method is the same in both cases; it is simple and efficient and can be used with a wide range of metals. Vacuum arc ion sources of different kinds have been developed by the authors and others and their suitability as a metal ion implantation tool has been well established. Metal plasma immersion surface processing is an emerging tool whose characteristics and applications are the subject of present research. There are a number of differences between the two techniques, both in the procedures used and in the modified surfaces created. For example, the condensibility of metal plasma results in thin film formation and subsequent energetic implantation is thus done through the deposited layer; in the usual scenario, this recoil implantation and the intermixing it produces is a feature of metal plasma immersion but not of conventional energetic ion implantation. Metal plasma immersion is more suited (but not limited) to higher doses (≳1017 cm−2) and lower energies (Ei<tens of keV) than the usual ranges of conventional metal ion implantation. These and other differences provide these vacuum‐arc‐based surface modification tools with a versatility that enhances the overall technological attractiveness of both.
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52.75.-d Plasma devices
61.72.-y Defects and impurities in crystals; microstructure
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Plasma ion implantation technology for broad industrial application

Dipten Deb, John Siambis, and Robert Symons

J. Vac. Sci. Technol. B 12, 828 (1994); http://dx.doi.org/10.1116/1.587354 (5 pages) | Cited 3 times

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The recently invented Plasma Ion Implantation (PII) process (1987) [J. R. Conrad, U.S. Patent No. 764394 (August 16, 1988)] is currently under intense industrial engineering investigation and development. A critical component of PII for broad industrial utilization is the availability of an efficient modulator system that applies the high voltage pulse to the workpiece. A modulator technology assessment and selection is carried out. The requirements of the PII process favor the selection of a hard‐tube modulator. The PII process favors the application of beam switch tube technology such as the Litton L‐5012 and L‐5097. These Litton tubes have already been selected by LANL and utilized in their pilot engineering demonstration experiment with GM and the University of Wisconsin. The performance, physical operation, and potential enhancements of the Litton beam switch tubes L‐5012 and L‐5097 will be discussed in connection with the requirements of the emerging plasma ion implantation industrial modulator technology.
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52.75.-d Plasma devices
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

Analytical modeling of plasma immersion ion implantation target current using the SPICE circuit simulator

William En and Nathan W. Cheung

J. Vac. Sci. Technol. B 12, 833 (1994); http://dx.doi.org/10.1116/1.587355 (5 pages) | Cited 8 times

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Plasma immersion ion implantation applies a series of negative high‐voltage pulses to a target immersed in a plasma. An analytical model of the currents and potentials induced before, during, and after the negative bias in a planar geometry is presented. The effect of multiple pulses on the results is also studied. The model determines the time‐varying ion current, electron current, total current, total dose, and sheath thickness for a piecewise linear voltage pulse. The sheath collapse is found to be important for high repetition rate pulses. Implementation of the model is done in SPICE, a circuit simulator. Comparison with experimental data has demonstrated the accuracy of the model.
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52.40.Hf Plasma-material interactions; boundary layer effects
61.72.up Other materials

High power modulator for plasma ion implantation

Dan M. Goebel

J. Vac. Sci. Technol. B 12, 838 (1994); http://dx.doi.org/10.1116/1.587356 (5 pages) | Cited 4 times

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The treatment of metal and polymer materials by plasma ion implantation (PII) requires high‐voltage, high average‐power modulators to process relatively large‐size parts in a reasonable amount of time. CROSSATRON‐switch‐based modulators provide all of the features desired for large‐scale PII. The fast opening and closing capability of the switch eliminates the need for pulse‐forming networks and high‐voltage thyratrons, and allows arbitrary pulse width adjustment over the range of 2 to 100 μs of interest for PII. The CROSSATRON switch is capable of modulating high peak currents, which permits rapid charging of the relatively high capacitance of the PII load to provide fast switching times. The CROSSATRON switch requires only a low‐voltage (≤1 kV) pulsed biasing of the control grid to close and open, and has switching times of 1 μs or less. CROSSATRON switches are cold‐cathode, plasma discharge devices that also eliminate the need for large filament‐heater power supplies and higher grid‐drive power required for hard‐vacuum‐tube switches. A 100‐kV modulator, built at Hughes Research Laboratories for the PII program, has demonstrated reliable operation at up to 100 kW of average power, limited only by the existing power supply. The modulator is based on the 120‐kV, 8455H CROSSATRON switch, which provides hard‐tube‐like modulation at peak currents of up to 1000 A and pulse repetition frequencies (PRFs) of over 1 kHz.
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52.75.-d Plasma devices
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

Overview of plasma source ion implantation research at University of Wisconsin–Madison

Shamim M. Malik, K. Sridharan, R. P. Fetherston, A. Chen, and and J. R. Conrad

J. Vac. Sci. Technol. B 12, 843 (1994); http://dx.doi.org/10.1116/1.587357 (7 pages) | Cited 12 times

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In the last five years, plasma source ion implantation (PSII) research at the University of Wisconsin–Madison, has encompassed work in the areas of plasma physics, diagnostics, ion‐material interactions’ modeling, materials science issues, and a broad spectrum of industrial applications of PSII technology. The third generation PSII system is presently under construction. Three methods of plasma generation, namely, electron impact method, glow discharge, and radio frequency have been successfully employed. In the following article the highlights of the above facets of PSII research activities have been presented.
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61.72.up Other materials
52.40.Hf Plasma-material interactions; boundary layer effects
81.65.-b Surface treatments

Plasma ion implantation technology at Hughes Research Laboratories

Jesse N. Matossian

J. Vac. Sci. Technol. B 12, 850 (1994); http://dx.doi.org/10.1116/1.587358 (4 pages) | Cited 10 times

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The plasma ion implantation (PII) project at Hughes Research Laboratories (HRL) has as its main objective the evaluation and application of PII technology to improve the tribological properties of metal and nonmetal materials used in aerospace, defense, and commercial applications. The HRL PII facility consists of a 4‐ft‐diam×8‐ft‐long vacuum chamber capable of implanting objects weighing up to 7000 lbs, and a high‐power (100‐kW), high‐voltage (100‐kV) pulse modulator to provide voltage pulses for implantation. Advanced plasma sources have been developed to produce atomic, as well as molecular, nitrogen and oxygen ions, and PII processes have been developed to treat metal and nonmetal materials. The HRL PII facility has been operational since 1989 and has been used for prototype demonstrations of PII technology to achieve (1) a 2–3× improved wear life of Co/WC drill bits used for printed‐wiring‐board fabrication, (2) an 8× reduced wear rate for TiN‐coated cutting tools, and (3) a 2× increased surface hardness for a 7000‐lb polymer object, 3 ft by 5 ft by 1 ft.
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52.75.-d Plasma devices
61.72.up Other materials
81.40.Pq Friction, lubrication, and wear

Survey of high‐voltage pulse technology suitable for large‐scale plasma source ion implantation processes

William A. Reass

J. Vac. Sci. Technol. B 12, 854 (1994); http://dx.doi.org/10.1116/1.587359 (7 pages) | Cited 6 times

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Many new plasma processes ideas are finding their way from the research lab to the manufacturing plant floor. These require high voltage (HV) pulse power equipment, which must be optimized for application, system efficiency, and reliability. Although no single HV pulse technology is suitable for all plasma processes, various classes of high voltage pulsers may offer a greater versatility and economy to the manufacturer. Technology developed for existing radar and particle accelerator modulator power systems can be utilized to develop a modern large scale plasma source ion implantation (PSII) system. The HV pulse networks can be broadly defined by two classes of systems, those that generate the voltage directly, and those that use some type of pulse forming network and step‐up transformer. This article will examine these HV pulse technologies and discuss their applicability to the specific PSII process. Typical systems that will be reviewed will include high power solid state, hard tube systems such as crossed‐field ‘‘hollow beam’’ switch tubes and planar tetrodes, and ‘‘soft’’ tube systems with crossatrons and thyratrons. Results will be tabulated and suggestions provided for a particular PSII process.  
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61.72.uj III-V and II-VI semiconductors
52.40.Hf Plasma-material interactions; boundary layer effects
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
89.20.Bb Industrial and technological research and development

Magnetic insulation of secondary electrons in plasma source ion implantation

D. J. Rej, B. P. Wood, R. J. Faehl, and H. H. Fleischmann

J. Vac. Sci. Technol. B 12, 861 (1994); http://dx.doi.org/10.1116/1.587360 (6 pages) | Cited 11 times

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The uncontrolled loss of accelerated secondary electrons in plasma source ion implantation (PSII) can significantly reduce system efficiency and poses a potential x‐ray hazard. This loss might be reduced by a magnetic field applied near the workpiece. The concept of magnetically insulated PSII is proposed, in which secondary electrons are trapped to form a virtual cathode layer near the workpiece surface where the local electric field is substantially reduced. Subsequent electrons that are emitted can then be reabsorbed by the workpiece. Estimates of anomalous electron transport from microinstabilities are made. Insight into the process is gained with multidimensional particle‐in‐cell simulations.
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52.40.Hf Plasma-material interactions; boundary layer effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Development of plasma source ion implantation in China

Bao Yin Tang

J. Vac. Sci. Technol. B 12, 867 (1994); http://dx.doi.org/10.1116/1.587361 (3 pages) | Cited 1 time

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In recent years, the plasma source ion implantation (PSII) technique has been developed in China. It is called all orientation ion implantation. Experimental devices have been built in Harbin Institute of Technology, Southwestern Institute of Physics, Dalian University of Technology, Sichuan University, and China Textile University, respectively. In this article, two typical devices are described, preliminary results of the PSII‐ion beam enhanced deposition and production of diamondlike carbon films, and some computer simulation programs are reported briefly. Some experiments show that addition of rare‐earth metal ions, or heavy metal ions, or Xe+, Kr+ in the nitrogen plasma may make the effectiveness of the surface modification better. Future considerations are also described in the article.
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81.65.-b Surface treatments
61.72.up Other materials
52.40.Hf Plasma-material interactions; boundary layer effects
89.20.Bb Industrial and technological research and development

Initial operation of a large‐scale plasma source ion implantation experiment

B. P. Wood, I. Henins, R. J. Gribble, W. A. Reass, R. J. Faehl, M. A. Nastasi, and D. J. Rej

J. Vac. Sci. Technol. B 12, 870 (1994); http://dx.doi.org/10.1116/1.587362 (5 pages) | Cited 10 times

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In plasma source ion implantation (PSII), a workpiece to be implanted is immersed in a weakly ionized plasma and pulsed to a high negative voltage. Plasma ions are accelerated toward the workpiece and implanted in its surface. A large‐scale PSII experiment has recently been assembled at Los Alamos, in which stainless steel and aluminum workpieces with surface areas over 4 m2 have been implanted in a 1.5 m diam, 4.6 m length cylindrical vacuum chamber. Initial implants have been performed at 50 kV with 20 μs pulses of 53 A peak current, repeated at 500 Hz, although the pulse modulator will eventually supply 120 kV pulses of 60 A peak current at 2 kHz. A 1000 W, 13.56 MHz capacitively coupled source produces nitrogen plasma densities in the 1015 m−3 range at neutral pressures as low as 0.02 mTorr. A variety of antenna configurations have been tried, with and without axial magnetic fields of up to 60 G. Measurements of sheath expansion, modulator voltage and current, and plasma density fill‐in following a pulse are presented. We consider secondary electron emission, x‐ray production, workpiece arcing, implant conformality, and workpiece and chamber heating.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.up Other materials
52.50.Dg Plasma sources

Measurements of potentials and sheath formation in plasma immersion ion implantation

G. A. Collins and J. Tendys

J. Vac. Sci. Technol. B 12, 875 (1994); http://dx.doi.org/10.1116/1.587363 (5 pages) | Cited 4 times

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Collecting and emitting probes have been used to explore the distribution of potentials and the dynamic behavior of the cathodic sheath in the rf glow discharge plasmas used for plasma immersion ion implantation (PI3). On application of a negative voltage pulse, the sheath expands rapidly but comes to a steady‐state position within a few microseconds. The potential distribution then remains stable as long as there is sufficient plasma outside the sheath region to replace the ions lost to the cathode. The various dc potentials in the plasma that arise from rectification of the rf fields are also important. At power levels up to 500 W, the plasma potential is several hundred volts above the average dc potential of the antenna. The magnitude of this voltage difference depends on the antenna geometry, its insulation from the plasma and the dc potential that can exist between it and the chamber walls. The floating potential of a typical PI3 target can vary from 50 to 300 V below the plasma potential but in all cases the difference is sufficient to ensure that there is a sheath and presheath structure around the target before the application of the high voltage pulse.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.80.Hc Glow; corona
52.25.Jm Ionization of plasmas

Model for expanding sheaths and surface charging at dielectric surfaces during plasma source ion implantation

G. A. Emmert

J. Vac. Sci. Technol. B 12, 880 (1994); http://dx.doi.org/10.1116/1.587364 (4 pages) | Cited 19 times

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Plasma source ion implantation utilizes negative high voltage pulses applied to targets immersed in a plasma. This produces an expanding sheath which accelerates ions into the target. A model for expanding sheaths at dielectric surfaces is developed; the significant differences between this and metal targets are the finite dielectric constant of the material and accumulation of charge in the nonconducting material. A model is developed for an expanding sheath at a dielectric surface and applied to a polyethylene sheet as an example. The most significant effect is the reduction of the energy at which ions are implanted in the material because of charging at the surface of the polyethylene.
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61.72.up Other materials
52.40.Hf Plasma-material interactions; boundary layer effects

Application of particle‐in‐cell simulation to plasma source ion implantation

Rickey Faehl, Barbara De Volder, and Blake Wood

J. Vac. Sci. Technol. B 12, 884 (1994); http://dx.doi.org/10.1116/1.587365 (5 pages) | Cited 14 times

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The powerful numerical technique of particle‐in‐cell simulation has been used to study sheath formation and dynamics of plasma source ion implantation (PSII). Two‐dimensional cylindrical calculations permit us to study the process when sheath dimensions are large compared to feature scales of the implanted object, where conformality is not assured. Plasma chambers as large as the PSII system at Los Alamos have been modeled. Densities of 1014–15 m−3 are initialized in the numerical configuration. Voltages of −50 to −100 kV have been modeled, with rise times on this pulse of 0.1–1.0 μs. Calculations of the ambient electron/N+2 ion plasma are presented. The implantation flux and dose on a variety of different shapes, including long cylinders and bores in flat plates, have been investigated. Finally, magnetic fields have been added to the calculations. The effect of this field on the process is measured with and without the effect of secondary electron emission from the surface.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.65.-y Plasma simulation

Two‐dimensional fluid modeling of time‐dependent plasma sheath

MunPyo Hong and G. A. Emmert

J. Vac. Sci. Technol. B 12, 889 (1994); http://dx.doi.org/10.1116/1.587322 (8 pages) | Cited 31 times

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A two‐dimensional code is developed for simulating the nonuniformly expanding plasma sheath when a negative potential is applied to a two‐dimensional target immersed in a plasma. The code uses fluid equations for the cold, collisionless ions coupled with the Boltzmann relationship for the electrons and Poisson’s equation. The evolution of the sheath at a square target is simulated numerically. The nonuniformity of the incident dose and the angular distribution of the ions striking the surface near the corner are calculated. The incident dose is higher near the corner of the square target but has its maximum value at a slight distance from the corner. In addition, the angle at which the ions strike the surface is more oblique near the corner and the area over which the oblique angle occurs broadens as the sheath grows.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.65.-y Plasma simulation

Ion‐matrix sheath around a square bar

T. E. Sheridan and M. J. Alport

J. Vac. Sci. Technol. B 12, 897 (1994); http://dx.doi.org/10.1116/1.587323 (4 pages) | Cited 17 times

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The structure of the ion‐matrix sheath surrounding a square bar is calculated. Equipotentials and field lines are presented, and the sheath width and eccentricity are calculated as a function of the bar width.
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52.40.Hf Plasma-material interactions; boundary layer effects

Two ion fluid model for plasma source ion implantation

K. Thomas, M. J. Alport, and T. E. Sheridan

J. Vac. Sci. Technol. B 12, 901 (1994); http://dx.doi.org/10.1116/1.587324 (4 pages) | Cited 5 times

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For plasma source ion implantation in a nitrogen discharge, there is a mixture of atomic and molecular species N+ and N+2, respectively. A time dependent fluid model has been developed, which models a plasma consisting of two species of cold collisionless ion fluids, assuming that the electrons are in thermal equilibrium. Following the application of a large, negative voltage pulse to the metal target, the density and velocity of the two ion species, and the sheath evolution for a range of possible ion mixtures are calculated.
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52.40.Hf Plasma-material interactions; boundary layer effects

Energy and angle distributions of ions striking the spherical target∗ in plasma source ion implantation

Dezhen Wang, Tengcai Ma, and Xinlu Deng

J. Vac. Sci. Technol. B 12, 905 (1994); http://dx.doi.org/10.1116/1.587325 (5 pages) | Cited 1 time

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Plasma source ion implantation is a process in which a target is immersed in a plasma and a series of large negative‐voltage pulses are applied to it to extract ions from the plasma and implant them into the target. A Monte Carlo simulation model is developed to study the energy and angle distributions of ions striking the spherical target for high pressures of the neutral gas. The charge exchange and momentum transfer sections of ion‐neutral that depend on the ion energy are taken into account precisely. The energy and angle distributions of A+r at the spherical target during the sheath edge evolution for the different pressures are investigated in detail.
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52.40.Hf Plasma-material interactions; boundary layer effects
61.72.up Other materials

Target temperature prediction for plasma source ion implantation

James P. Blanchard

J. Vac. Sci. Technol. B 12, 910 (1994); http://dx.doi.org/10.1116/1.587326 (8 pages) | Cited 7 times

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Plasma source ion implantation (PSII) is a plasma‐based ion implantation technique which requires pulsed operation. Because the power incident on the implanted objects (targets) can be large, target temperatures can be quite high. Therefore, target temperature prediction can be quite useful, both in reaching high temperatures when they are desirable, and in avoiding high temperatures when they are undesirable. In this paper, a simple, time‐dependent, lumped‐capacity thermal model is developed for predicting temperatures in PSII targets. Two simple analytical models are used to justify the assumptions used in developing the lumped model. Comparison of the model with measured target temperatures is used to validate the assumptions of the model. The comparison is favorable.  
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52.75.-d Plasma devices
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Dose analysis of nitrogen plasma source ion implantation treatment of titanium alloys

A. Chen, J. Firmiss, and J. R. Conrad

J. Vac. Sci. Technol. B 12, 918 (1994); http://dx.doi.org/10.1116/1.587327 (5 pages) | Cited 5 times

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Dose analysis of plasma source ion implantation (PSII) treatment involves two issues: calculation of the delivered dose and measurement of the retained dose. This article discusses the delivered dose calculation method and the determination of constants used in this calculation, such as the secondary electron emission coefficient and average number of atoms per ion being implanted. Both can be measured experimentally at the University of Wisconsin PSII group. The retained dose is usually studied by Auger electron spectroscopy (AES). For nitrogen PSII treated titanium alloys, like all titanium nitrogen compounds, the chemical analysis by AES is complicated by two factors: (1) the Auger electron emission from nitrogen occurs at an energy that completely overlaps a transition from titanium; and (2) titanium oxide has a strong influence on the titanium transitions. In this study, a new technique that takes into account the influence of titanium oxide and solves the overlap problem has been developed to convert AES data to a concentration depth profile. A comparison of the concentration profile for nitrogen as observed in the AES data and calculated by the tamix code (computer simulation) shows good agreement.
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61.72.up Other materials

Nitrogen profiles of high dose, high temperature plasma source ion implantation treated austenitic stainless steel

C. B. Franklyn and G. Nothnagel

J. Vac. Sci. Technol. B 12, 923 (1994); http://dx.doi.org/10.1116/1.587328 (4 pages) | Cited 1 time

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Plasma source ion implantation over a period of 30 min, with actual ion implantation times of ∼15 s, has been studied. Estimates of steady‐state heat diffusion indicate bulk average temperatures of <50 °C. Experimental profiles show nitrogen diffusion up to ≳1 μm, indicating surface temperatures of ∼500 °C. Resultant implantation and diffusion profiles are compared with conventional plasma nitrided samples.
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61.72.up Other materials
81.05.Bx Metals, semimetals, and alloys

Plasma source ion implantation of oxygen and nitrogen in aluminum@f|

R. Günzel, E. Wieser, E. Richter, and J. Steffen

J. Vac. Sci. Technol. B 12, 927 (1994); http://dx.doi.org/10.1116/1.587329 (4 pages) | Cited 13 times

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In a preliminary study we compare the surface properties of oxygen and nitrogen implanted in aluminum by the plasma source ion implantation (PSII) technique with beam line implantation of these elements. The acceleration voltage was 35 keV. Using PSII at these energies the areal density of the implanted species saturates at about 2×1017 cm−2 for nitrogen and 4×1017 cm−2 for oxygen. In the case of PSII with nitrogen, a relatively high concentration of oxygen is detected which is explained as due to the strong surface interaction with the oxygen contamination of the plasma. During PSII from a steady state oxygen plasma, the plasma surface interaction predominates the implantation. A surface layer of Al2O3 with a rough topology is formed. The surface hardness is lowered by this treatment. All other implanted samples show an increased dynamic hardness in a thin surface near layer of about 50 nm thickness in comparison to a nonimplanted sample. A maximum increase of the dynamic hardness by a factor 1.2 has been estimated for PSII with nitrogen and for PSII with oxygen from the plasma of the Townsend discharge.
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61.72.up Other materials
52.75.-d Plasma devices
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Structure and wear behavior of nitrogen‐implanted aluminum alloys@f|

Lifang Xia, Rizhi Wang, Xinxin Ma, and Yue Sun

J. Vac. Sci. Technol. B 12, 931 (1994); http://dx.doi.org/10.1116/1.587330 (4 pages) | Cited 2 times

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Aluminum alloys L2, LD2, LF12, LY12, and Al‐4% Cu were implanted at room temperature with nitrogen ions at an energy of 80 keV and dose range of 1×1016–8.3×1017 N+ cm−2. The surface structure and chemical state of the implanted surface layer was investigated by x‐ray photoelectron spectroscopy, transmission electron microscopy and transmission electron diffraction. Hardness measurements were made using a Vickers microhardness tester, and wear tests were carried out using a pin‐on‐disk wear testing machine. The results reveal that implanted nitrogen combines with aluminum to form AlN precipitates at room temperature and nitrogen implantation accelerates the aging process of Al‐4% Cu alloys. The results also reveal that nitrogen implantation increases the hardness and sliding wear resistance of aluminum alloys. The improvements are mainly attributed to the formation of AlN precipitates.
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61.72.up Other materials
81.40.Pq Friction, lubrication, and wear

Significance of nitrogen mass transfer mechanism on the nitriding behavior of austenitic stainless steel

M. Samandi, B. A. Shedden, T. Bell, G. A. Collins, R. Hutchings, and J. Tendys

J. Vac. Sci. Technol. B 12, 935 (1994); http://dx.doi.org/10.1116/1.587331 (5 pages) | Cited 14 times

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Plasma immersion ion implantation (PIII), although originally developed as an alternative non‐line‐of‐sight ion implantation technique, is also capable of producing structures typical of thermochemical processing. In this work, the structure and properties of PIII and plasma nitrided AISI 316 austenitic stainless steel were characterized in order to establish the similarities and differences between PIII and plasma nitriding. A distinct difference between PIII and plasma nitriding has been identified with respect to the degree of nitrogen supersaturation of the austenite that can be achieved. It is proposed that the extent of supersaturation and the resultant microstructure are primarily controlled by the nitrogen mass transfer mechanism. For plasma nitrided stainless steel, a surface iron nitride layer is formed and limits the nitrogen content to less than 20 at. %. For PIII, where nitrogen is also directly implanted below the surface, nitrogen contents near the theoretical limit of 50 at. % can be achieved.
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61.72.up Other materials

Enhanced pitting corrosion resistance of 304L stainless steel by plasma ion implantation

Preston P. Smith, R. A. Buchanan, J. Reece Roth, and Sanjay G. Kamath

J. Vac. Sci. Technol. B 12, 940 (1994); http://dx.doi.org/10.1116/1.587332 (5 pages) | Cited 1 time

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High‐nitrogen, austenitic stainless steels combine a variety of superior mechanical properties with an increased resistance to localized pitting/crevice corrosion in halide environments. However, nitrogen content in the bulk is restricted during normal melt/solidification processes due to limited solubility, which, if exceeded, leads to nitride formation and possible sensitization. Plasma ion implantation (PII) techniques may result in much higher nitrogen contents via nonequilibrium surface modification. PII of nitrogen into 304L stainless steel, and its subsequent effect on the pitting corrosion of this alloy, has been investigated. The implantation process at the University of Tennessee Microwave Plasma Facility results from a large‐volume (206 l  ), steady‐state, uniform plasma, generated by up to 2 kW of 2.45 GHz microwave power. Samples were negative pulse biased to potentials of 10 and 20 kV, with doses ranging from 1014 to 1018 ions/cm2. Rutherford backscattering spectroscopy analyses of dose uniformity and depth profiling were also conducted. Potentiodynamic anodic polarization behaviors were determined in a deaerated 1.0 wt % NaCl solution. The highest pitting potentials, up to 1440 mV (standard hydrogen electrode) were measured at the lowest range of doses. These results indicate that nitrogen doses effective for tribological enhancement may be incompatible with those effective in resisting localized corrosion.
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61.72.up Other materials
81.05.Bx Metals, semimetals, and alloys

Nitrogen plasma source ion implantation of aluminum

K. C. Walter

J. Vac. Sci. Technol. B 12, 945 (1994); http://dx.doi.org/10.1116/1.587333 (6 pages) | Cited 5 times

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Nitrogen plasma source ion implantation has been applied to pure aluminum and aluminum alloy 7075 (Al–Cu–Mg–Zn). Nitrogen implantation modified the surface properties through transformation of the surface to aluminum–nitride (AlN). A uniformly thick (∼0.15 μm), polycrystalline (∼30 nm grain size) and continuous AlN layer was formed on both pure aluminum and 7075. Knoop microhardness tests showed an increase in surface hardness at low loads. Pin‐on‐disk wear tests showed nitrogen implantation decreased the wear rates by a factor of ∼10 for alloy 7075. This study demonstrates significant modification of the tribological properties of an aluminum surface can be accomplished using nitrogen plasma source ion implantation.
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61.72.up Other materials
81.05.Bx Metals, semimetals, and alloys
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties

Structural characterization of plasma‐doped silicon by high resolution x‐ray diffraction

D. L. Chapek, J. R. Conrad, R. J. Matyi, and S. B. Felch

J. Vac. Sci. Technol. B 12, 951 (1994); http://dx.doi.org/10.1116/1.587334 (5 pages) | Cited 3 times

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High resolution x‐ray diffraction methods have been used to characterize boron‐doped silicon fabricated using low energy plasma source ion implantation (PSII). Double‐crystal rocking curves recorded using the asymmetric (113) reflection show increasing intensity in the low‐angle tail as the ion dose was increased from 1.1×1015 to 4.4×1015 cm−2. Scans of the diffuse intensity around the 113 point in reciprocal space using triple crystal diffraction showed no significant differences in the magnitude of diffuse kinematic scattering from an unimplanted control sample and the plasma doped silicon; in all cases, negligible diffuse scattering was observed. This suggests that the doping by PSII is accompanied by negligible amount of crystallographic damage. Postimplant rapid thermal annealing was found to cause no change in the level of diffuse scattering; however, the asymmetry in the double‐crystal rocking curves switched to the high‐angle side. Dynamic simulation of the rocking curves has been used to estimate the strain distribution in the as‐implanted and annealed samples.
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61.72.uf Ge and Si

Anomalous behavior of shallow BF3 plasma immersion ion implantation

Erin C. Jones, William En, Shinichi Ogawa, David B. Fraser, and Nathan W. Cheung

J. Vac. Sci. Technol. B 12, 956 (1994); http://dx.doi.org/10.1116/1.587335 (6 pages) | Cited 4 times

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Plasma immersion ion implantation (PIII) with BF3 and SiF4 plasmas is used to fabricate shallow P+/N junctions in Si. Exposure to the plasma and accelerated ions can lead to simultaneous etching and deposition on the substrate during implantation. A simple mathematical model for this process is presented and applied to the case of shallow implantation of BF3. Etching rates of SiO2 are seen to vary with power and pressure of the process gas. Etching rates of Si, SiO2, and CoSi2 are studied by spectrophotometry and Rutherford backscattering spectrometry. The roughness of Si substrates and SiO2 and CoSi2 films before and after PIII is monitored by atomic force microscopy.  
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61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.65.-b Surface treatments
52.75.-d Plasma devices

Plasma immersion ion implantation doping experiments for microelectronics

Shu Qin and Chung Chan

J. Vac. Sci. Technol. B 12, 962 (1994); http://dx.doi.org/10.1116/1.587336 (7 pages) | Cited 19 times

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Using plasma immersion ion implantation (PIII), silicon has been doped with boron in a high voltage pulsed microwave multipolar bucket plasma system. In order to optimize the system design and predict the doping results, a collisional dynamic sheath model has been developed, which has been verified by measurements as well as simulations. Silicon devices, including diode, metal–oxide–semiconductor (MOS) capacitor, and PMOS transistor, were fabricated by PIII doping technique. B2H6 diluted in helium (1%) was used as the gas source. The reasonable contamination levels involved from PIII process were observed by the measurements of secondary ion mass spectrometry and characteristics of fabricated devices. Good quality of devices has been demonstrated including low reverse current of diode and reasonable lifetimes of the minority carrier.
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85.30.Kk Junction diodes
61.72.uf Ge and Si

Characteristics of a plasma doping system for semiconductor device fabrication

T. Sheng, S. B. Felch, and C. B. Cooper

J. Vac. Sci. Technol. B 12, 969 (1994); http://dx.doi.org/10.1116/1.587337 (4 pages) | Cited 9 times

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A plasma doping system for semiconductor ion implantation is described. The target to be implanted is placed directly in the plasma and then biased to a negative potential to accelerate the positive ions into the target. A wafer bias of up to −5 kV with a BF3 source gas are used to implant boron ions into 150 mm diameter Si wafers. Data are presented showing sub‐100 nm shallow p+–n junction with good sheet resistance uniformity and dose control repeatability. A high dose rate of ≳1015 cm−2 per minute at low energy (<5 keV) can be readily achieved. Excellent charging test device performance as well as surface contamination control are discussed. All of these results demonstrate the attractiveness of this unique alternate doping technique.  
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52.75.-d Plasma devices
85.30.-z Semiconductor devices
85.40.Hp Lithography, masks and pattern transfer

Plasma immersion ion implantation for semiconductor thin film growth

M. Tuszewski, J. T. Scheuer, I. H. Campbell, and B. K. Laurich

J. Vac. Sci. Technol. B 12, 973 (1994); http://dx.doi.org/10.1116/1.587338 (4 pages) | Cited 4 times

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A new experiment has been constructed to explore the potential of the plasma immersion ion implantation technique for thin film growth on semiconductor substrates. The experiment consists of an inductive plasma source, an ultrahigh vacuum vessel, and a 10 kV pulse generator. The first nitrogen and oxygen plasma results obtained with the inductive source are presented and analyzed.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Mechanical properties of Si‐diamondlike carbon films formed by ion beam assisted deposition

C. G. Fountzoulas, T. Z. Kattamis, J. D. Demaree, W. E. Kosik, W. Franzen, and J. K. Hirvonen

J. Vac. Sci. Technol. B 12, 977 (1994); http://dx.doi.org/10.1116/1.587339 (4 pages)

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This article reports on the composition, microhardness, cohesion, adhesion, and friction coefficients of Si‐diamondlike carbon coatings on M50 steel and silicon substrates prepared at room temperature by the ion beam assisted deposition process, using energetic Ar+ ions and tetraphenyl‐tetramethyl‐trisiloxane (Type 704 Dow–Corning silicone oil) as a precursor material. The thickness, microhardness, and friction coefficients of these films were investigated. The cohesion and adhesion failure loads of the films were also evaluated by automatic scratch testing in combination with optical and scanning electron microscopy observation of the scratch. Rutherford backscattering spectroscopy analysis showed that film stoichiometry is insensitive to deposition parameters including the relative arrival ratios of Ar+ ions and deposited silicon‐hydrocarbon molecules. Knoop microhardness values (at 25‐g load) were found to vary from 800 to 1600 kg/mm2, and the unlubricated friction coefficients ranged from 0.21 to 0.27, depending on deposition parameters.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.60.Bs Mechanical and acoustical properties
81.40.Pq Friction, lubrication, and wear

Carbonaceous surface layers deposited on TiN coatings by ion implantation

M. Franck, B. Blanpain, J. P. Celis, J. R. Roos, and H. Pattyn

J. Vac. Sci. Technol. B 12, 981 (1994); http://dx.doi.org/10.1116/1.587340 (5 pages) | Cited 2 times

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TiN coatings deposited by physical vapor deposition have been subjected to a postdeposition treatment involving beam line implantation with 80‐keV C+ ions at doses between 1×1017 and 3×1017 ions/cm2. Rutherford backscattering spectrometry measurements showed Gaussian‐like implantation‐depth profiles extending towards the surface which was found to be covered with carbon. The carbonaceous surface layer was characterized by Raman spectroscopy revealing the typical band features of diamondlike carbon. Simulations of the carbon depth profile indicate that the opaque carbon layer was formed from carbon in excess of the implanted dose. Further experiments suggest that the carbon layer resulted from an ion‐beam‐assisted deposition process. Fretting wear tests demonstrated lower friction and improved wear resistance of the TiN covered with the diamondlike carbon layer in comparison with as‐deposited TiN.
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61.72.up Other materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.40.Pq Friction, lubrication, and wear

Ion‐beam‐induced densification of sol‐gel ceramic thin films

Timothy E. Levine, Peter Revesz, Emmanuel P. Giannelis, and James W. Mayer

J. Vac. Sci. Technol. B 12, 986 (1994); http://dx.doi.org/10.1116/1.587341 (5 pages)

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Ion‐beam‐induced densification of sol‐gel zirconia thin films is examined here. Ion irradiation of sol‐gel zirconia films leads to microstructural and chemical changes (densification) in the films. Ion beam analysis indicates the loss of carbon, hydrogen, and oxygen as a result of implantation. Oxygen:zirconium ratios less than that predicted for stoichiometric ZrO2 for the higher dose implanted films were observed. The chemical and microstructural modifications were attributed to both electronic interactions and nuclear collisions between the energetic ions and the target atoms. Densification of only a near‐surface region of a sol‐gel zirconia thin film proved that the effects of beam heating on the observed densification are minimal.  
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Potential applications of fusion neutral beam facilities for advanced material processing

J. M. Williams, C. C. Tsai, W. L. Stirling, and J. H. Whealton

J. Vac. Sci. Technol. B 12, 991 (1994); http://dx.doi.org/10.1116/1.587342 (7 pages)

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Surface processing techniques involving high energy ion implantation have achieved commercial success for semiconductors and biomaterials. However, wider use has been limited in good part by economic factors, some of which are related to the line‐of‐sight nature of the beam implantation process. Plasma source implantation (or plasma immersion ion implantation) is intended to remove some of the limitations imposed by directionality of beam systems and also to help provide economies of scale. The present paper will outline relevant technologies and areas of expertise that exist at Oak Ridge National Laboratory in relation to possible future needs in materials processing. Experience in generation of plasmas, control of ionization states, pulsed extraction, and sheath physics exist. Contributions to future technology can be made either for the immersion mode or for the extracted beam mode. Existing facilities include the High Power Test Facility, which could conservatively operate at 1 A of continuous current at 100 kV delivered to areas of about 1 m2. Higher instantaneous voltages and currents are available with a reduced duty cycle. Another facility, the High Heat Flux Facility can supply a maximum at 60 kV and currents of up to 60 A for 2 s on a 10% duty cycle. Plasmas may be generated by use of microwaves, radio‐frequency induction, or other methods and plasma properties may be tailored to suit specific needs. In addition to ion implantation of large steel components, foreseeable applications include ion implantation of polymers, ion implantation of Ti alloys, Al alloys, or other reactive surfaces.  
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52.75.-d Plasma devices
61.72.up Other materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Ordered and randomly disordered AlAs/GaAs short‐period superlattices

D. J. Arent, R. Alonso, G. Horner, M. Bode, J. M. Olson, X. Yin, M. C. DeLong, A. J. SpringThorpe, and A. Majeed

J. Vac. Sci. Technol. B 12, 1009 (1994); http://dx.doi.org/10.1116/1.587116 (4 pages) | Cited 1 time

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Unique optical signatures of different atomic arrangements of Al0.5Ga0.5As, deposited by molecular‐beam epitaxy and having nominally identical average composition, have been observed in steady‐state photoluminescence and photoluminescence excitation spectroscopies. Compared to the observations from a random pseudobinary alloy and a (AlAs)2(GaAs)2 ordered superlattice, intense photoluminescence emission is observed from disordered (AlAs)n(GaAs)4−n superlattices where n is randomly chosen from the sets 0≤n≤4 or 1≤n≤3. The photoluminescence peak energies of the randomly ordered superlattices are red‐shifted by 100–400 meV from the emission energy of the pseudobinary alloy, suggesting that a significant density of localized or band tail states exists at energies lower than the band gap, which are confirmed by photoluminescence excitation spectroscopy. We also measure greatly increased photoluminescence intensity from the randomly ordered superlattices at high temperatures indicating that these materials may be suitable for optoelectronic applications in previously unattainable energy regions.
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78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Growth optimization of molecular beam epitaxy grown InAlAs on InP

Woo‐Young Choi and Clifton G. Fonstad

J. Vac. Sci. Technol. B 12, 1013 (1994); http://dx.doi.org/10.1116/1.587117 (3 pages) | Cited 3 times

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The effects of different molecular beam epitaxy (MBE) growth conditions on material qualities of In0.52Al0.48As on InP were investigated. Investigated parameters were growth temperature and As overpressure. A range of these two parameters within which InAlAs grows under the As‐rich condition was first determined by reflection high‐energy electron diffraction. Five different InAlAs samples were grown within this range and characterized by double crystal x‐ray diffraction, Hall measurement, and photoluminescence. Based on the results of these characterizations, the optimal MBE growth condition for InAlAs was determined.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Modulated arsenic molecular‐beam epitaxial growth of In0.48Al0.52As

S. T. Chou and K. Y. Cheng

J. Vac. Sci. Technol. B 12, 1016 (1994); http://dx.doi.org/10.1116/1.587118 (3 pages) | Cited 1 time

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A modulated As molecular‐beam epitaxy method is utilized to grow high‐quality In0.48Al0.52As epilayer at a low substrate temperature, which is compatible to the optimal In0.47Ga0.53As growth condition. The reflection high‐energy electron diffraction intensity oscillations recorded during modulated As beam epitaxy shows that a persistent layer‐by‐layer growth mode is maintained throughout the epitaxy process. The high electron mobility, high photoluminescence (PL) intensity, and narrow PL linewidth have confirmed the low defect generation/incorporation during the modulated As beam epitaxy of the In0.48Al0.52As. The effect of interface smoothing is confirmed by the extremely narrow 77 K PL linewidth of an In0.47Ga0.53As/In0.48Al0.52As quantum well stack heterostructure grown by this method.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors

Growth studies on In0.5Ga0.5As/AlGaAs quantum wells grown on GaAs with a linearly graded InGaAs buffer

H. C. Chui and J. S. Harris

J. Vac. Sci. Technol. B 12, 1019 (1994); http://dx.doi.org/10.1116/1.587119 (4 pages) | Cited 8 times

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High indium content InGaAs/AlGaAs quantum wells (QWs) are useful for modulator and intersubband applications. Growth of these highly strained QWs on GaAs has been facilitated by the use of a linearly graded InGaAs buffer. We present here growth studies performed on these QW structures. Buffer parameters including buffer substrate temperature, buffer grading rate, and final buffer indium composition are studied. QW parameters including QW substrate temperature, the use of GaAs interface smoothing layers, and barrier substrate temperature are also investigated. Using near optimized growth conditions, narrow linewidth intersubband transitions are demonstrated.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors

Accurate measurements of transients and intentional rates of change in molecular beam epitaxy growth rate calibrations

Rouel Fernandez, Alex Harwit, and Don Kinell

J. Vac. Sci. Technol. B 12, 1023 (1994); http://dx.doi.org/10.1116/1.587120 (3 pages)

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Shuttering the arsenic flux off and on is known to induce reflection high‐energy electron diffraction (RHEED) intensity oscillations during continuous molecular beam epitaxy growth long after the regular oscillations have damped out. These RHEED intensity oscillations are shown to be useful for quantifying the flux variations from group III cells. Flux transients from opening the gallium and aluminum shutters, and intentional flux changes produced by changing cell temperatures have been accurately measured using this technique. After opening a group III shutter, two transients have been observed in this system. In the case of gallium, a relatively short‐time transient less than 300 s long is typically observed. This short time transient is characterized by a 3% drop in the flux. Sometimes, however, a longer transient with a time constant of about 20 min occurs. The longer transient usually gives a 3% to 4% rise in the growth rate. The aluminum cell consistently displays only a long‐time constant transient. Intentional rates of change in growth rates are also easily measured with the induced RHEED intensity oscillations. For example, near a 1 μm/h growth rate, linearly increasing the gallium cell temperature by 15 °C over 5 min results in a linear rate of change in the growth rate of 11.0±0.5 (Å/h)/s. Linearly ramping down the gallium cell temperature by 15 °C in 5 min results in a rate of change of −12.4±0.7 (Å/h)/s.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

External photoluminescence efficiency and minority carrier lifetime of (Al,Ga)As/GaAs multi‐quantum‐well samples grown by molecular beam epitaxy using both As2 and As4

C. T. Foxon, T. S. Cheng, P. Dawson, D. E. Lacklison, J. W. Orton, W. Van der Vleuten, O. H. Hughes, and M. Henini

J. Vac. Sci. Technol. B 12, 1026 (1994); http://dx.doi.org/10.1116/1.587078 (3 pages) | Cited 3 times

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We report the results of measurement of the external photoluminescence efficiency and minority carrier lifetime of a series of n‐ and p‐type (AlGa)As–GaAs multi‐quantum‐well samples grown by molecular beam epitaxy, as a function of growth temperature in the range 600 to 700 °C, using both As2 and As4. For equivalent growth conditions (substrate temperature and arsenic species) the minority carrier lifetimes in n‐ and p‐type samples are found to be the same. We suggest that the lifetimes are determined by recombination via deep centers (possibly oxygen‐related) close to the (AlGa)As/GaAs interface. For an individual sample there is a good correlation between the variations in lifetime and external efficiency across a wafer, the variation being ascribed to temperature differences resulting from poor wetting with In. A much weaker correlation is observed from sample to sample, suggesting that there are factors other than the internal photoluminescence efficiency that determine the light emitted from the surface. We tentatively suggest that morphology may be a factor.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Bonding and migration of 111In atoms on GaAs surfaces studied by perturbed‐angular‐correlation spectroscopy

Jianming Fu, James M. Adams, Gary L. Catchen, D. L. Miller, J. Kim, M. C. Gallagher, and R. F. Willis

J. Vac. Sci. Technol. B 12, 1029 (1994); http://dx.doi.org/10.1116/1.587079 (5 pages)

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The first application of perturbed‐angular‐correlation (PAC) spectroscopy to study the incorporation and diffusion of In atoms on GaAs surfaces is reported here. A PAC‐MBE system has been established to perform in situ PAC measurements on surfaces grown by molecular beam epitaxy. To define the surface conditions that the PAC experiments are based on, scanning tunneling microscopy is used to characterize the topography of similar surfaces grown under identical conditions. To perform the PAC surface experiments, 111In–111Cd radioactive probe nuclei are deposited onto the surface to be studied in trace quantities (10−4 ML). The measured physical quantity is the electric‐field‐gradient tensor at the probe site. Preliminary results show that In atoms are incorporated into several types of sites on (001) and (111)B surfaces. These surface sites are characterized by well‐defined electric‐field gradients. These results show that PAC spectroscopy is sensitive to the local atomic arrangement of surface atoms. Moreover, annealing experiments show that changes in electric‐field gradients associated with surface‐site conversion characterize surface processes on GaAs such as diffusion, desorption, and adsorption.  
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68.35.Fx Diffusion; interface formation
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.70.Jp Nuclear states and interactions

Structural properties of highly mismatched InGaAs‐based devices grown by molecular beam epitaxy on GaAs substrates

M. S. Goorsky, J. W. Eldredge, S. M. Lord, and J. S. Harris

J. Vac. Sci. Technol. B 12, 1034 (1994); http://dx.doi.org/10.1116/1.587080 (4 pages) | Cited 3 times

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We examined the structural properties of optical modulators consisting of multi‐quantum wells and InGaAs relaxed buffer layers grown on (001) GaAs substrates by MBE. The effects of different linearly graded buffer layers was a key component of this study. For all samples, high resolution x‐ray techniques determined that the buffer layers were completely relaxed in both 〈110〉 directions. The epitaxial layers did not possess any overall crystallographic tilt with respect to the substrate. The strained layer superlattices were pseudomorphic as well. We determined that the crystal quality of multiquantum wells grown on the InGaAs buffers decreases with increasing composition gradient in the underlying buffer layer. The improved material quality correlates with sharper exciton resonance from the more slowly graded samples and suggests that the proximity of the buffer layer strain fields to the active multi‐quantum wells plays a significant role in optical and structural properties.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.79.Hp Optical processors, correlators, and modulators

Interface analysis of dry etched and molecular beam epitaxial regrown AlGaAs

L. H. Grober, M. Hong, J. P. Mannaerts, R. S. Freund, H. S. Luftman, and S. N. G. Chu

J. Vac. Sci. Technol. B 12, 1038 (1994); http://dx.doi.org/10.1116/1.587081 (5 pages)

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Many novel optoelectronic devices can be realized by the technique of molecular beam epitaxy regrowth on etched surfaces. A smooth etched surface free from contaminants is necessary as this surface determines the success of the regrowth and the etched/regrown interface affects the performance and reliability of the devices. We have systematically studied the contaminants at the etched and regrown interface of Al0.4Ga0.6As for various steps of our in situ process. Using secondary ion mass spectroscopy, transmission electron microscopy, and mass spectroscopic analysis we have pinpointed what we believe to be the sources of carbon, oxygen, and silicon contamination in the etch chamber and have taken steps to eliminate them.
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68.35.Dv Composition, segregation; defects and impurities
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Extremely high uniformity of interfaces in GaAs/AlGaAs quantum wells grown on (411)A GaAs substrates by molecular beam epitaxy

S. Hiyamizu, S. Shimomura, A. Wakejima, S. Kaneko, A. Adachi, Y. Okamoto, N. Sano, and K. Murase

J. Vac. Sci. Technol. B 12, 1043 (1994); http://dx.doi.org/10.1116/1.587082 (4 pages) | Cited 20 times

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GaAs/AlGaAs quantum wells (QWs) were grown on (411)A‐oriented GaAs substrates by molecular beam epitaxy (MBE). Photoluminescence linewidths at 4.2 K are almost the same as the narrowest linewidths reported so far for GaAs/AlGaAs QWs grown on (100)‐oriented GaAs substrates with the growth interruption at the heterointerfaces. Furthermore, only one sharp peak was observed for each QW on the (411) substrate over the whole area of the wafer (10 mm×10 mm), in contrast with three splitted luminescence peaks for one kind of GaAs/AlGaAs QW grown on the (100) substrates by MBE with growth interruption. This result implies that effectively atomically flat interfaces over a macroscopic area (about 10 mm×10 mm) has been realized for the first time in GaAs/Al0.3Ga0.7As QWs grown on (411)A GaAs substrates by MBE. This is possibly due to the large migration of Ga and Al atoms on the (411)A plane during MBE growth and the step‐flow growth mode on the atomically corrugated (411)A plane.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors

In situ nonalloyed ohmic contacts to p‐GaAs

M. Hong, D. Vakhshoori, J. P. Mannaerts, F. A. Thiel, and J. D. Wynn

J. Vac. Sci. Technol. B 12, 1047 (1994); http://dx.doi.org/10.1116/1.587083 (3 pages) | Cited 2 times

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Very low resistivity, nonalloyed ohmic contacts to p‐GaAs are realized by in situ molecular beam epitaxy (MBE). Heavily Be‐doped GaAs either in a uniform doping or with a δ‐doping scheme was grown using MBE. Three different metals of Au, Ag, and Nb were in situ deposited on p‐GaAs, yielding contact resistance RC less than (1–4)×10−7 Ω cm2.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.30.-z Semiconductor devices

Effects of As4 flux on reflection high‐energy electron diffraction oscillations during growth of GaAs at low temperatures

J. P. Ibbetson, R. P. Mirin, U. K. Mishra, and A. C. Gossard

J. Vac. Sci. Technol. B 12, 1050 (1994); http://dx.doi.org/10.1116/1.587084 (3 pages) | Cited 11 times

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This article reports on the observation of reflection high‐energy electron diffraction oscillations during growth of GaAs by molecular beam epitaxy at temperatures as low as 60 °C. At low temperatures (<300 °C), the amplitude of the oscillations is shown to be sensitive to the As:Ga flux ratio. The largest amplitude oscillations are observed under stoichiometric conditions.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Quantum‐confined Stark shift observed by electroluminescence and circularpolarized luminescence excitation spectroscopy in GaAs/AlGaAs coupled quantum wells

Y. Kato, Y. Takahashi, S. Fukatsu, Y. Shiraki, and R. Ito

J. Vac. Sci. Technol. B 12, 1053 (1994); http://dx.doi.org/10.1116/1.587085 (3 pages)

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The quantum‐confined Stark effect in electroluminescence (EL) spectra was observed using Al0.3Ga0.7As/GaAs symmetric coupled quantum‐well (CQW) structures. The Stark shift of the transition between the ground electron state and heavy‐hole state was found to be symmetrical with regard to the flatband bias for EL and for photoluminescence (PL), in which the electric field was applied in reverse direction. Circularly polarized photoluminescence excitation (CPPLE) spectroscopy was also employed to clarify the origins of optical transitions. Six transitions between electrons and light and heavy holes in the CQWs were clearly identified by PL and by polarization of CPPLE measurement.
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78.66.Fd III-V semiconductors
78.60.Fi Electroluminescence
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Raman scattering study of the intermixing of AlAs monolayers in GaAs grown by molecular‐beam epitaxy

D. S. Katzer, B. V. Shanabrook, and D. Gammon

J. Vac. Sci. Technol. B 12, 1056 (1994); http://dx.doi.org/10.1116/1.587086 (3 pages) | Cited 1 time

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In this article we present results from a Raman scattering study of AlAs monolayers in GaAs grown by molecular beam epitaxy. A recent model for the LO phonons in AlxGa1−xAs developed by Molinari et al. [Appl. Surf. Sci. 56–58, 617 (1992); Phys. Rev. B 45, 4280 (1992)] gives excellent qualitative agreement with our measurements. We show that intermixing between AlAs and GaAs is reduced through the use of low substrate temperatures and migration‐enhanced epitaxy. We show the utility of the LO phonon model for obtaining quantitative information about the Al concentration in a monolayer. We also discuss the utility of using Raman scattering to help determine the optimum growth conditions to minimize intermixing of GaAs/AlAs interfaces and for mapping Al flux variations across a sample.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Fx Diffusion; interface formation
78.30.Fs III-V and II-VI semiconductors

Low‐temperature growth and characterization of GaAs epitaxial layer on (111)B GaAs substrates

G. H. Kim, J. L. Gray, H. M. Yoo, and F. S. Ohuchi

J. Vac. Sci. Technol. B 12, 1059 (1994); http://dx.doi.org/10.1116/1.587087 (4 pages)

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Unique properties of homoepitaxial (111) GaAs layers grown at low temperatures have not been realized mainly due to very narrow temperature range for the layer‐by‐layer growth. In this study, molecular‐beam epitaxy growth of GaAs (111) layers on a tilted (111)B substrate at 350 °C is reported. Reflective high‐energy electron diffraction observation during the low‐temperature growth shows an initial surface structure of (2 × 2) which changes to (1 × 1) at the beginning of the growth. Diffraction spots appear at the growth layer thickness of 75 nm. These extra spots are attributed to twins and stacking faults confirmed by transmission electron microscopy. GaAs (111) layers grown at 350 °C have a high density of twins and a specular surface. High‐temperature growth of (111) GaAs on a low‐temperature buffer layer leads to a tenfold increase in the surface roughness.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.J- Electron diffraction and scattering

Molecular‐beam epitaxy growth of quantum dots from strained coherent uniform islands of InGaAs on GaAs

D. Leonard, M. Krishnamurthy, S. Fafard, J. L. Merz, and P. M. Petroff

J. Vac. Sci. Technol. B 12, 1063 (1994); http://dx.doi.org/10.1116/1.587088 (4 pages) | Cited 55 times

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The two‐ (2D) to three‐dimensional (3D) growth mode transition during the initial stages of growth of highly strained InxGa1−xAs on GaAs is used to obtain quantum dot structures. Transmission electron micrographs (TEM) reveal that when the growth of InxGa1−xAs is interrupted exactly at the onset of this 2D–3D transition, dislocation‐free islands (dots) of InGaAs result. Size distribution measurements from TEM images indicate that these dots are less than 300 Å in diameter and remarkably uniform. A phase diagram is constructed, showing the growth conditions under which these strained coherent uniform dots form. Photoluminescence from layers containing these dots is observed and correlated with growth conditions and with structural data obtained from TEM images. We observe that the photoluminescence emitted from the dots and an underlying reference quantum well are nearly equal, indicating a high quantum efficiency for these quantum dots.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors

Molecular beam epitaxial growth of GaAs on CaF2/Si(111) substrate

Weidan Li, Takayoshi Anan, and Leo J. Schowalter

J. Vac. Sci. Technol. B 12, 1067 (1994); http://dx.doi.org/10.1116/1.587089 (4 pages) | Cited 2 times

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In this work, molecular beam epitaxial (MBE) growth of GaAs on CaF2/Si(111) substrates has been studied with both Rutherford backscattering spectroscopy and transmission electron microscopy. It has been observed that, under certain conditions, a chemical reaction between As adatoms and CaF2 layers can be induced, by which a more stable As layer on the CaF2 surface is formed. The existence of the As layer improves the Ga wettability on the CaF2 surface and, if properly controlled, leads to two‐dimensional (2D) nucleation of GaAs on the CaF2/Si(111) surface as opposed to the more commonly observed three‐dimensional growth. In subsequent growth, two kinds of twins have been observed. All samples were observed to have microtwins near the GaAs/CaF2 interface. These twins can be suppressed during the first 1000 Å, if the layer is grown in a narrow optimal growth window. Otherwise, the growth will be in a 3D mode at lower temperature, or, it will suffer from the formation of big rotational twins at higher temperature. It has been observed that growth on the vicinal substrates tilted to [1̄1̄2] azimuth is helpful in suppressing the development of rotational twins so that growth on these substrates have a wider optimal growth window.  
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Fx Diffusion; interface formation

Realization of three‐dimensionally confined structures via one‐step in situ molecular beam epitaxy on appropriately patterned GaAs(111)B and GaAs(001)

K. C. Rajkumar, A. Madhukar, P. Chen, A. Konkar, L. Chen, K. Rammohan, and D. H. Rich

J. Vac. Sci. Technol. B 12, 1071 (1994); http://dx.doi.org/10.1116/1.587090 (4 pages) | Cited 8 times

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The realization of three‐dimensionally confined GaAs/AlGaAs structures on GaAs (111)B and GaAs (001) substrates via one step in situ molecular beam epitaxy is reported. Growth is carried out on nonplanar patterned substrates with crystallographically equivalent mesa top edges. Equivalent side facets evolve during growth and completely surround the mesa top. Adatom migration from these facets to the mesa top result in shrinkage of the mesa top area leading to mesa pinch‐off. Scanning and transmission electron microscopy provide evidence for the realization of structures with lateral linear dimensions ≲500 Å. Cathodoluminescence images from the (111)B structures attest to their high optical quality.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Application of the digital alloy composition grading technique to strained InGaAs/GaAs/AlGaAs diode laser active regions

Jeffrey G. Cody, David L. Mathine, Ravi Droopad, George N. Maracas, Ramamurti Rajesh, and Ray W. Carpenter

J. Vac. Sci. Technol. B 12, 1075 (1994); http://dx.doi.org/10.1116/1.587091 (3 pages) | Cited 6 times

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Molecular‐beam epitaxy (MBE) growth, lasing performance, and transmission electron microscopy (TEM) of In0.25Ga0.75As asymmetric triangular quantum well (ATQW) active regions is reported. The digital alloy technique was utilized to form three active regions of widths 200, 300, and 400 Å. Each structure lased with a threshold current density of 313, 152, and 241 A/cm2, respectively. The lasing wavelength range was 979–1030 nm. This is the first demonstration that controlled, digitally graded quantum wells can be incorporated into laser diode active regions.
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42.55.Px Semiconductor lasers; laser diodes
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Determination of AlAs mole fraction in AlxGa1−xAs using Raman spectroscopy and x‐ray diffraction

G. S. Solomon, D. Kirillov, H. C. Chui, and J. S. Harris

J. Vac. Sci. Technol. B 12, 1078 (1994); http://dx.doi.org/10.1116/1.587092 (4 pages) | Cited 5 times

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High resolution x‐ray diffraction (HRXRD) is used to accurately determine the AlAs mole fraction in AlxGa1−xAs samples over the complete alloy range. The AlAs mole fraction error in the HRXRD measurement is estimated to be less than 0.0035. A small bowing in the variation of the alloy lattice constant with changing AlAs mole fraction is observed. The HRXRD characterized samples are used in Raman spectroscopy to calibrate the variation in the longitudinal optical (LO) GaAs and AlAs modes with varying alloy composition. Empirical expressions for the variation in the LO modes are found, with mole fraction errors of less than 0.03. Raman spectroscopy is a relatively simple nondestructive measurement and the expressions developed here allow for the fast determination of AlAs mole fraction in AlxGa1−xAs samples. The Raman data is compared to a theoretical dependence for a two phonon mode alloy crystal with excellent results.
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68.55.Nq Composition and phase identification
78.30.Fs III-V and II-VI semiconductors
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Random‐period superlattice quantum wells

Y. C. Albert Shih, K. Sadra, and B. G. Streetman

J. Vac. Sci. Technol. B 12, 1082 (1994); http://dx.doi.org/10.1116/1.587093 (4 pages) | Cited 1 time

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We report a study of a novel quantum well structure, the random‐period superlattice quantum well (RSLQW), consisting of an AlAs/GaAs superlattice (SL) sandwiched between two AlGaAs layers, where the periods in the SL are intentionally randomized. Photoluminescence (PL) measurements are performed to probe the optical properties of the RSLQW structures. Theoretical calculations are employed to correlate the type of transition and transition energy with the experimental observations. Phonon sidebands are identified in the PL spectra of RSLQWs, in which type II transitions are predicted by calculation results. Compared to the findings in periodic superlattice quantum wells, some RSLQWs show significantly stronger PL signals. However, all the RSLQW samples exhibit larger degradation of radiative recombination efficiency with increasing temperature.  
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors

Characterization and improvement of the layer uniformity for large‐area quantum well device arrays grown in an Intevac/Varian Gen II molecular beam epitaxy system

Stefan P. Svensson and Frederick J. Towner

J. Vac. Sci. Technol. B 12, 1086 (1994); http://dx.doi.org/10.1116/1.587094 (5 pages) | Cited 1 time

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The uniformity of GaAs, AlAs, and InAs grown in an Intevac/Varian Gen II molecular beam epitaxy system has been characterized using a quantum well (QW) structure and room‐temperature photoluminescence (PL) evaluation. Artifacts in the measured distributions have been identified through simulations and were proposed to originate from incomplete rotation averaging during growth of the QW and/or oscillations of the Al mole fraction in the growth direction. The first effect is an actual thickness variation while the second effect leads to shifts in the PL signal that will be incorrectly interpreted as thickness variations when Schrödinger’s equation is solved for wells with symmetric potential barriers. Modeling of the flux distribution predicted that an upward tilt of the substrate away from the group III cells is beneficial. This was confirmed experimentally with the best overall uniformity achieved for a tilt of ∼9 deg.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors

Molecular beam epitaxy of MnAs thin films on GaAs

M. Tanaka, J. P. Harbison, T. Sands, T. L. Cheeks, V. G. Keramidas, and G. M. Rothberg

J. Vac. Sci. Technol. B 12, 1091 (1994); http://dx.doi.org/10.1116/1.587095 (4 pages) | Cited 69 times

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We have successfully grown single‐crystalline ferromagnetic MnAs thin films on (001) GaAs substrates by molecular beam epitaxy. By reflection high energy electron diffraction and x‐ray measurements, the growth direction of the MnAs thin films was found to be [100] on (001) GaAs, and the epitaxial relationship was [0001] MnAs //[10] GaAs and [110] MnAs // [110] GaAs. Magnetization measurements at room temperature have revealed that the epitaxial MnAs thin films have strong magnetic anisotropy, and that the easy magnetization direction is in‐plane, along the [110] axis of the MnAs thin films which is parallel to the [110] axis of the GaAs substrate, with almost perfect square hysteresis loops, relatively high remanent magnetization, and low coercive field.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.Ak Magnetic properties of monolayers and thin films

Study of lattice‐mismatched (In,Ga)As/GaAs heterostructures on the unconventional (110) GaAs surface

Decai Sun, Elias Towe, and Brian R. Bennett

J. Vac. Sci. Technol. B 12, 1095 (1994); http://dx.doi.org/10.1116/1.587096 (4 pages)

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Structural and optical properties of strained (In,Ga)As/GaAs heterostructures grown on (110) GaAs substrates intentionally misoriented by 6° toward the (111)B surface have been investigated. Photoluminescence and double‐crystal x‐ray diffraction data show that high‐quality (In,Ga)As/GaAs quantum wells can be grown on the (110) vicinal surface.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
78.66.Fd III-V semiconductors

Growth of the (In,Al,Ga)As quaternary alloy system on GaAs at low substrate temperatures by molecular‐beam epitaxy

E. Towe, D. Sun, and B. R. Bennett

J. Vac. Sci. Technol. B 12, 1099 (1994); http://dx.doi.org/10.1116/1.587097 (3 pages) | Cited 2 times

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The III–V quaternary alloy system of (In,Al,Ga)As has been successfully grown on (100) GaAs substrates at low substrate temperatures. Visible photoluminescence emission spanning the wavelengths from 630 to 700 nm has been observed from material grown at substrate temperatures ranging from 300 to 500 °C. It is found that the emission intensity is influenced by the substrate temperature. Results are presented for the In0.10Al0.41Ga0.49As quaternary alloy.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors

Lateral variation of indium content in InGaAs grown on GaAs channeled substrates by molecular beam epitaxy

A. Wakejima, A. Inoue, T. Kitada, N. Tomita, S. Shimomura, S. Hiyamizu, M. Fujii, T. Yamamoto, K. Kobayashi, and N. Sano

J. Vac. Sci. Technol. B 12, 1102 (1994); http://dx.doi.org/10.1116/1.587098 (4 pages) | Cited 5 times

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Lateral variation of In content in a 1.5 μm thick InxGa1−xAs (x≂0.2) epilayer grown on channeled GaAs (100) substrates having (755)A or (411)A slope regions by molecular beam epitaxy (MBE) was studied by the energy dispersive x‐ray spectroscopy, with high spatial resolution (0.6 μm). Significantly peculiar migration of In atoms on the (411)A was observed. Experimental data of this work strongly suggest that In atoms migrate preferentially in one way, that is to say, they migrate much more in the [12̄2̄] direction than in the opposite [1̄22] direction on the (411)A plane during MBE growth. The migration length of In atoms on the (100) plane was 5 μm when InGaAs was grown at Ts=570 °C and V/III=30.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Electrical characteristics of InP grown by molecular beam epitaxy using a valved phosphorus cracking cell

J. N. Baillargeon, A. Y. Cho, R. J. Fischer, P. J. Pearah, and K. Y. Cheng

J. Vac. Sci. Technol. B 12, 1106 (1994); http://dx.doi.org/10.1116/1.587057 (4 pages) | Cited 6 times

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The electrical characteristics of InP grown by molecular beam epitaxy (MBE) using a valved phosphorus cracking cell are presented. Stoichiometric growth of InP was achieved with a beam equivalent pressure as low as 5×10−7 Torr and 1 μm/h InP growth rate. The efficiency of the solid source is high, consuming on average only ∼0.09 g of phosphorus per μm of InP growth with the beam equivalent pressure ∼1.5×10−6 Torr. The conductivity of the unintentionally doped layers is n‐type, with the electrical background concentration primarily dependent upon the valved cell cracking zone temperature. Electrical carrier concentrations at 300 K ranged from 2.9×1015 cm−3 to 3.3×1016 cm−3. The lowest backgrounds were achieved with the lowest cracking zone temperatures. Low temperature photoluminescence shows impurity related emission at 1.383 eV.
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73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Chemical beam epitaxy of strain balanced GaP/GaAs/InP/GaAs superlattices

A. H. Bensaoula, A. Freundlich, A. Bensaoula, V. Rossignol, and A. Ponchet

J. Vac. Sci. Technol. B 12, 1110 (1994); http://dx.doi.org/10.1116/1.587058 (3 pages) | Cited 2 times

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This work addresses the chemical beam epitaxy (CBE) growth and interface properties of a new type of GaP(n)/GaAs(m)/InP(n)/GaAs(k) pseudomorphically strained superlattice structures. The structural properties of these highly strained heterostructures are discussed in light of high‐resolution x‐ray diffraction and transmission electron microscopy observations. In spite of the large lattice mismatch between the individual GaP, GaAs, and InP layers in the superlattice structures, it is demonstrated that due to a nearly perfect strain balance between GaP (in extension) and InP (in compression) layers, GaP/GaAs/InP/GaAs superlattices with thicknesses up to 1 μm can be achieved with CBE.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Characterization of high quality GaInP/GaAs superlattices grown on GaAs and Si substrates by gas source molecular beam epitaxy

C. Jelen, S. Slivken, X. G. He, M. Razeghi, and S. Shastry

J. Vac. Sci. Technol. B 12, 1113 (1994); http://dx.doi.org/10.1116/1.587059 (3 pages) | Cited 6 times

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We report an analysis of the heteroepitaxial interfaces in high quality GaInP–GaAs superlattices grown simultaneously on GaAs and Si substrates by gas source molecular beam epitaxy. These two superlattices have been studied using high resolution x‐ray diffraction measurements. Sharp superlattice satellites, with very little broadening, are observed within a 6° range for the sample on GaAs. Photoluminescence peaks with full widths at half‐maximums of 5 and 7 meV are obtained at 4 K for samples with 58 Å wells on GaAs and Si, respectively. Room temperature exciton absorption is observed in the photovoltage measurements for a superlattice grown on Si substrate. The thicknesses determined by x‐ray analysis are consistent with those obtained by a Kronig–Penny model fitting of the photovoltage spectroscopy.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors

Structural and optical characterizations of InAsP/InP strained multiple quantum wells grown on InP (111)B substrates

H. Q. Hou, C. W. Tu, W. Shan, S. J. Hwang, J. J. Song, and S. N. G. Chu

J. Vac. Sci. Technol. B 12, 1116 (1994); http://dx.doi.org/10.1116/1.587060 (3 pages) | Cited 1 time

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InAsP/InP strained multiple quantum wells (MQWs) with specular surfaces were grown on InP (111)B substrates by gas‐source molecular beam epitaxy. Cross‐sectional transmission electron microscopy and high‐resolution x‐ray rocking curves show that the InAsP/InP (111)B MQW structures possess sharp and uniform interfaces, excellent periodicity, and crystalline quality. Structural parameters were extracted accurately from a dynamical‐theory simulation by considering the anisotropy of the (111) strain tensor. Low‐temperature photoluminescence and photoluminescence excitation measurements revealed interband excitonic transitions, and the energies agree with a calculation with an internal piezoelectric field taken into account.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Fd III-V semiconductors
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Operation of a molecular‐beam epitaxy machine employing a valved solid phosphorus source

G. W. Wicks, M. W. Koch, F. G. Johnson, J. A. Varriano, G. E. Kohnke, and P. Colombo

J. Vac. Sci. Technol. B 12, 1119 (1994); http://dx.doi.org/10.1116/1.587061 (3 pages) | Cited 4 times

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The use of an elemental source molecular‐beam epitaxy (MBE) machine for the growth of phosphides requires hardware and operating procedures different from those normally encountered in the growth of arsenides. The main hardware alterations are the use of valved group V cracker sources and different pumping schemes. Operating procedures must be developed to cope with higher operating pressures and flammable deposits. High‐quality phosphides and abrupt arsenide/phosphide interfaces are now possible using elemental source MBE.  
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Molecular beam epitaxy grown AlAsSb/GaAsSb distributed Bragg reflector on InP substrate operating near 1.55 μm

O. Blum, I. J. Fritz, L. R. Dawson, A. J. Howard, T. J. Headley, J. A. Olsen, J. F. Klem, and T. J. Drummond

J. Vac. Sci. Technol. B 12, 1122 (1994); http://dx.doi.org/10.1116/1.587062 (3 pages) | Cited 4 times

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Surface normal optoelectronic devices operating in the 1.3–1.5 μm wavelength range require distributed Bragg reflectors (DBRs) with a practical number (≤50) of mirror layers. This requirement implies a large refractive index difference between the mirror layers, which is difficult to achieve in the traditionally used phosphide compounds. For the first time, an AlAsSb/GaAsSb DBR grown nominally lattice matched to an InP substrate by molecular beam epitaxy is demonstrated. Reflectivity measurements indicate a stop band centered at 1.53 μm, which is well fitted by these theoretical predictions. Atomic force microscopy and transmission electron microscopy indicate reasonable crystal quality with some defects due to an unintentional lattice mismatch to the substrate.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.60.-q Optoelectronic devices

Reflection high energy electron diffraction observation of exchange reaction dynamics on InAs surfaces

D. A. Collins, M. W. Wang, R. W. Grant, and T. C. McGill

J. Vac. Sci. Technol. B 12, 1125 (1994); http://dx.doi.org/10.1116/1.587063 (4 pages) | Cited 4 times

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We have used time‐resolved reflection high energy electron diffraction (RHEED) measurements to study the dynamics of a surface, anion exchange reaction. In the experiment, InAs surfaces are exposed to Sbx fluxes and subsequent changes in the crystals’ RHEED patterns are examined. We find that when an InAs surface is initially exposed to an Sb flux the specular spot intensity first decreases, then recovers back toward its initial value. The shape of the intensity versus time curves is extremely reproducible if the absolute Sb flux and the Sb species are kept constant. The length of time required for the RHEED pattern to stabilize is much shorter for cracked Sb than for uncracked Sb. The RHEED dynamics are also faster if the total Sb flux increases. The behavior of the RHEED dynamics as a function of Sb flux and Sb species is consistent with the changes in the RHEED pattern being due to an Sb/As exchange reaction on the crystals’ surface. The RHEED data are compared to previously published x‐ray photoelectron spectroscopy (XPS) data which studied exchange reactions on InAs surfaces exposed to Sb fluxes. The XPS study confirmed that the incident Sb did indeed exchange with As in the epilayer and estimated the exposure time needed to complete the Sb/As exchange reaction. The time scales for exchange associated with the RHEED and XPS data are in good agreement, which further indicates that the observed RHEED dynamics are due to the Sb/As exchange reaction. Preliminary results from exposing GaSb surfaces to As fluxes show similar RHEED and XPS behavior. This suggests that RHEED could be generally applicable to the study of surface exchange reaction dynamics.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Recombination lifetime in InAs–Ga1−xInxSb superlattices

E. R. Youngdale, J. R. Meyer, C. A. Hoffman, F. J. Bartoli, R. H. Miles, and D. H. Chow

J. Vac. Sci. Technol. B 12, 1129 (1994); http://dx.doi.org/10.1116/1.587064 (4 pages) | Cited 4 times

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We report an experimental investigation of Shockley–Read and Auger lifetimes in InAs–Ga1−xInxSb and InAs–GaSb superlattices, based on measurements of the photoconductive response to excitation by a frequency‐doubled CO2 laser (4.63 μm) at intensities up to 100 kW/cm2. Results at 77 K for low excitation levels yield Shockley–Read lifetimes between 0.13 and 6 ns. The scaling of the lifetime with carrier concentration also provides the first determinations of Auger coefficients in narrow‐gap type II superlattices: γ3≊8×10−25 cm6/s at 300 K and γ3≊1.3×10−27 cm6/s at 77 K. The observed Auger lifetime at 77 K is two orders of magnitude longer than that in Hg1−xCdxTe with the same energy gap, which has highly favorable implications for InAs–Ga1−xInxSb superlattices in both IR detector and nonlinear optical applications.
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73.61.Ey III-V semiconductors
73.50.Pz Photoconduction and photovoltaic effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Reflection high‐energy electron diffraction study of the GaSb surface during molecular beam epitaxy

Mitsuaki Yano, Kazuhiko Yamamoto, Takashige Utatsu, and Masataka Inoue

J. Vac. Sci. Technol. B 12, 1133 (1994); http://dx.doi.org/10.1116/1.587065 (3 pages) | Cited 2 times

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Surface stoichiometry of GaSb during molecular beam epitaxy is studied by using the reflection high‐energy electron diffraction technique. This study has shown a desorption energy of 1.47 eV for excessively absorbed Sb atoms on the Sb‐stabilized surface. It is also shown that the Ga‐stabilized surface easily dissociates Ga atoms from the Sb sublayer to aggregate fine droplets. The activation energy is found to be 1.76 eV for the Ga droplet formation.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Molecular‐beam epitaxy growth of Bi epilayers and Bi–CdTe superlattices

A. DiVenere, X. J. Yi, C. L. Hou, H. C. Wang, J. Chen, J. B. Ketterson, G. K. Wong, J. R. Meyer, C. A. Hoffman, and F. J. Bartoli

J. Vac. Sci. Technol. B 12, 1136 (1994); http://dx.doi.org/10.1116/1.587066 (4 pages) | Cited 7 times

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The successful growth of Bi epilayers, and for the first time Bi–CdTe superlattices, by molecular‐beam epitaxy (MBE) on CdTe (111)B substrates is reported. X‐ray diffraction shows several orders of satellites indicative of the abruptness of the interfaces. Initial analysis by high‐resolution transmission electron microscopy shows sharp interfaces, although stacking faults are evident in the growth of CdTe on Bi. The growth of Bi layers exhibits streaked reflection high‐energy electron diffraction patterns with clear Kikuchi lines. This is the first direct evidence for the layer by layer growth of Bi on CdTe by MBE. A detailed characterization of the electron and hole densities and mobilities in epilayers with a range of thicknesses has been obtained from a hybrid mixed conduction analysis of the magneto‐transport data. Temperature dependences of the minority electron concentrations at ≥150 K have yielded the first convincing evidence for a semimetal to semiconductor transition in Bi thin films, at a thickness between 200 and 300 Å.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.61.-r Electrical properties of specific thin films

First indications of spontaneous ordering in ZnSe0.50Te0.50 alloy

H. Luo, N. Samarth, S. W. Short, S. H. Xin, J. K. Furdyna, P. Ahrenkiel, M. H. Bode, and M. M. Al‐Jassim

J. Vac. Sci. Technol. B 12, 1140 (1994); http://dx.doi.org/10.1116/1.587067 (3 pages) | Cited 7 times

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We describe our study of II–VI alloy ZnSe0.5Te0.5 in search of spontaneous ordering. Samples were prepared by molecular beam epitaxy in a variety of structure configurations and growth temperatures, in order to scan a wide range of parameters and identify a favorable condition for ordering. Transmission electron microscopy was carried out on these samples and revealed indications of spontaneous ordering in several samples, where regions with stacking of atoms that appear to be different from the zinc‐blende structure were observed. Preliminary study shows that such regions have the CuAu [i.e., the (100) superlattice] structure.  
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64.70.K- Solid-solid transitions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Migration enhanced epitaxy and optical properties of ZnSe/CdSe digital alloy quantum wells

S. W. Short, H. Luo, S. Xin, A. Yin, A. Pareek, M. Dobrowolska, and J. K. Furdyna

J. Vac. Sci. Technol. B 12, 1143 (1994); http://dx.doi.org/10.1116/1.587068 (3 pages) | Cited 2 times

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We report the growth of ZnSe/CdSe digital alloy quantum wells by migration enhanced epitaxy. The well regions are imbedded in barriers of ZnSe, and are composed of various periods of 1 monolayer (ML) of CdSe and 3 ML of ZnSe, thus having an effective Cd concentration of 25%. The time and sequence of successive shutter openings was varied during growth, and the effects on layer coverage were investigated using reflection high‐energy electron diffraction oscillations, photoluminescence, photoluminescence excitation, and optical absorption.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Hf II-VI semiconductors

Characteristic Zeeman patterns in novel graded gap II–VI quantum well structures

W. E. Hagston, S. J. Weston, M. O’Neill, T. Stirner, P. Harrison, J. H. C. Hogg, D. E. Ashenford, and B. Lunn

J. Vac. Sci. Technol. B 12, 1146 (1994); http://dx.doi.org/10.1116/1.587069 (4 pages)

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Novel methods of growing graded gap structures are described. In order to provide a check that the structures are indeed graded in the correct manner, magnetic ions in the structure have been employed. The good agreement between the predicted and observed Zeeman splitting of the corresponding light‐ and heavy‐hole exciton transitions, together with the magnetic field dependence of the Zeeman splittings and intensity of a forbidden heavy‐hole exciton transition, is taken as direct evidence that graded gap structures having the correct composition have indeed been fabricated.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Hf II-VI semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Exciton dynamics in multiquantum well CdTe–Cd1−xMnxTe systems

T. Stirner, W. E. Hagston, M. O’Neill, and P. Harrison

J. Vac. Sci. Technol. B 12, 1150 (1994); http://dx.doi.org/10.1116/1.587070 (3 pages) | Cited 2 times

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The exciton dynamics associated with the transfer of energy from the light‐hole state to both the heavy‐hole state and to a donor bound exciton (D0X) are investigated utilizing time‐resolved spectroscopy, in a multiquantum well sample of CdTe–Cd1−xMnxTe containing 75 Å wells and 150 Å barriers. The results show that the relaxation time of the light‐hole to the heavy‐hole state occurs, at low temperature, in a time ≤40 ps whereas the combined drift/diffusion of the excitons in the plane of the quantum well and their subsequent trapping at donor states occurs in a time ∼80 ps. Theoretical calculations show that the light‐hole–heavy‐hole carrier relaxation time is consistent with confined (acoustic) phonon relaxation and that the equivalent in‐plane mobility is consistent with interface roughness scattering.  
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78.66.Hf II-VI semiconductors
71.35.-y Excitons and related phenomena

Gas source molecular beam epitaxy growth of ZnSe on novel buffer layers

K. Lu, P. A. Fisher, J. L. House, E. Ho, C. A. Coronado, G. S. Petrich, L. A. Kolodziejski, G.‐C. Hua, and N. Otsuka

J. Vac. Sci. Technol. B 12, 1153 (1994); http://dx.doi.org/10.1116/1.587071 (3 pages) | Cited 2 times

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Thin films of ZnSe on pseudomorphic and partially relaxed (In,Ga)P buffer layers (on GaAs) have been examined; both epilayers were grown by gas source molecular beam epitaxy. The ZnSe layers were grown using elemental Zn and thermally decomposed H2Se. The II–VI nucleation occurred following an ex situ transfer in air of the As‐passivated (In,Ga)P buffer layers, grown using In, Ga, and cracked PH3. Microstructural characterization of the II–VI/III–V heterostructures was performed with high‐resolution x‐ray diffraction and transmission electron microscopy. The (511) reflection of the x‐ray rocking curves was used to measure the residual strain in the ZnSe/(In,Ga)P/GaAs structures, and to determine the alloy composition of the (In,Ga)P. The (400) reflection of the x‐ray diffraction rocking curves indicated peaks having full width at half‐maximum of 130 and 18 arcsec for the relaxed ZnSe on thin (1 μm) pseudomorphic (In,Ga)P buffer layers, respectively. Transmission electron microscopy confirmed the relaxed or pseudomorphic nature of each heterolayer. Thicker (≳4 μm) In0.52Ga0.48P buffer layers were still not completely relaxed, and exhibited a residual lattice mismatch of approximately 0.11% between the ZnSe layer and the In0.52Ga0.48P buffer layer. Relatively thick (1–2 μm) ZnSe films had surface morphologies that were featureless when examined by Nomarski microscopy and scanning electron microscopy. Low‐temperature photoluminescence spectra originating from the ZnSe films on the partially relaxed (In,Ga)P buffer layers were dominated by donor‐bound and free‐excitonic features with each exhibiting nearly the same intensity. Luminescence from extended defects (the Y0 and Iv transitions) within the ZnSe layer, and luminescence originating from the (In,Ga)P buffer layers, were also observed.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Hf II-VI semiconductors

Time‐of‐flight measurement of carrier transport and carrier collection in strained Si1−xGex/Si quantum wells

S. Fukatsu, A. Fujiwara, K. Muraki, Y. Takahashi, and Y. Shiraki

J. Vac. Sci. Technol. B 12, 1156 (1994); http://dx.doi.org/10.1116/1.587072 (4 pages) | Cited 6 times

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Carrier transport and collection was investigated in strained Si1−xGex/Si(100) double quantum wells (QWs) separated by a Si barrier. Steady‐state photoluminescence (PL) revealed a clear spectral dominance switch of PL between the two QWs as the Si barrier was systematically varied. Time‐of‐flight luminescence spectroscopy was used to estimate the mean drift velocity of carriers in terms of the luminescence rise time difference between the two QWs. Carrier collection efficiency was found to be dependent on the well width, which was obtained from the luminescence intensity difference.
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73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors

Room temperature photoluminescence in strained Si1−xGex/Si quantum wells

S. Fukatsu, H. Sunamura, and Y. Shiraki

J. Vac. Sci. Technol. B 12, 1160 (1994); http://dx.doi.org/10.1116/1.587073 (3 pages) | Cited 5 times

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Photoluminescence (PL) observation at room temperature is reported in strained Si1−xGex/Si multiple quantum wells (MQWs) grown by gas source Si molecular beam epitaxy. It was found that QW PL is enhanced when MQWs are arranged so that photogenerated carriers are trapped efficiently to QWs without significant loss. This was achieved by locating MQWs over the penetration depth of the excitation light. QW PL was found to develop with a power exponent of 1.8 for lower excitation. QW PL was observed at room temperature for MQW samples with x up to 0.69.
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78.66.Db Elemental semiconductors and insulators
78.55.Cr III-V semiconductors

Novel integration of a group IV electron‐beam deposition capability with a III–V molecular beam epitaxy system∗

H. P. Lee, F. J. Szalkowski, D. L. Sato, X. Liu, E. Ranalli, and T. George

J. Vac. Sci. Technol. B 12, 1163 (1994); http://dx.doi.org/10.1116/1.587074 (4 pages) | Cited 1 time

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A novel way of integrating epitaxial Si and carbon (C) doping capabilities within an existing solid‐source III–V molecular beam epitaxy system by means of electron‐beam evaporation is reported. By significantly increasing the Si evaporation rate over conventional effusion cells, this technique offers a practical way of growing high Si content (III–V)–Si alloys and superlattices. The use of GaAs–Si alloys with adjustable lattice constants for GaAs on Si growth with improved crystalline quality over previous methods is also demonstrated. Both uniform layer and delta‐doped C in GaAs (p‐type concentration up to the mid 1019/cm3 range) are demonstrated with carrier mobility comparable to other doping sources. These extended capabilities should find wide applications ranging from material synthesis to III–V devices and technology.
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85.40.Hp Lithography, masks and pattern transfer
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Study of interaction between incident silicon and germanium fluxes and SiO2 layer using solid‐source molecular beam epitaxy

Sun Jin Yun, Seung‐Chang Lee, Bo‐Woo Kim, and Sang‐Won Kang

J. Vac. Sci. Technol. B 12, 1167 (1994); http://dx.doi.org/10.1116/1.587075 (3 pages) | Cited 5 times

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The dependence on the substrate temperature and the flux rates of the behavior of impinging elemental Si and Ge fluxes on a SiO2 surface, including SiO2 etching and the deposition of polycrystalline Si and SiGe films, was investigated by using the solid source molecular beam epitaxy (MBE). Flux rates of the source beams and a substrate temperature were in the range of 1 to 5×1013 atoms/cm2 s and 710–810 °C, respectively. Under these experimental conditions, the Ge flux was not individually effective to etch the SiO2, but contributed to etching the oxide layer with an accompanying Si flux. The critical flux of Si for SiO2 etching at 740 °C was determined to be about 1×1013 atoms/cm2 s.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Atomic layer‐by‐layer epitaxy of cuprate superconductors

I. Bozovic, J. N. Eckstein, and G. F. Virshup

J. Vac. Sci. Technol. B 12, 1170 (1994); http://dx.doi.org/10.1116/1.587076 (4 pages) | Cited 1 time

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A technique for atomic layer‐by‐layer epitaxy of cuprate superconductors and other complex oxides has been developed at Varian. The samples are engineered by stacking molecular layers of different compounds to assemble multilayers and superlattices, by adding or omitting atomic monolayers to create novel compounds, and by doping within specified atomic monolayers. Apart from manufacturing trilayer Josephson junctions with IcRn≳5 mV, this technique enables one to address fundamental issues such as the dimensionality of HTSC state, existence of long‐range proximity effects, occurrence of resonant tunneling etc., as well as to synthesize novel metastable HTSC compounds.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
74.72.-h Cuprate superconductors

Growth morphologies of (001), (100), and (010) oriented Er5Ba7Cu12Oy high‐temperature superconductor thin films on various substrates

K. M. Choudhary, P. Seshadri, and M. Black

J. Vac. Sci. Technol. B 12, 1174 (1994); http://dx.doi.org/10.1116/1.587077 (4 pages)

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Er5Ba7Cu12Oy thin film is a high‐temperature superconductor material (Tc=93 K). The growth morphologies of Er5Ba7Cu12Oy thin films on various substrates were studied by scanning electron microscopy. The films were prepared by molecular beam deposition and postgrowth annealing. The Er5Ba7Cu12Oy thin films on LaAlO3 (100) [and SrTiO3 (100)] substrates showed small amount of (100) oriented grains on top of a (001) epilayer if the films were annealed in the 850–865 °C range (film thickness=0.4 μm). The (001) oriented Er5Ba7Cu12Oy/cubic‐ZrO2(100) thin films showed a ‘‘spherullite’’‐type growth morphology. On MgO (100) [and cubic‐ZrO2(100)] substrates, Er5Ba7Cu12Oy thin films with mixed (010) and (001) growth orientations were obtained.
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74.78.-w Superconducting films and low-dimensional structures
68.55.-a Thin film structure and morphology

Effects of oxygen on the sublimation of alkaline earths from effusion cells

E. S. Hellman and E. H. Hartford

J. Vac. Sci. Technol. B 12, 1178 (1994); http://dx.doi.org/10.1116/1.587036 (3 pages) | Cited 4 times

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The stability of the atomic flux from effusion cells is essential for the application of molecular‐beam epitaxy (MBE) to new materials systems. In particular, the possible effects of oxygen background pressure on source stability have been a concern to those applying MBE to the growth of oxides, such as the high Tc superconductors. We have studied the effects of oxygen exposure on the sublimation of the alkaline earth elements Mg, Ca, Sr, and Ba from effusion cells, using deposition rate measurements and quadrupole mass spectrometry. Sublimation of Mg, Ca, and Sr is suppressed exponentially by oxygen with a characteristic pressure comparable to the source equilibrium vapor pressure. Ba sublimation is increased linearly by oxygen background. A surprising finding is that immediately after an exposure to oxygen, Mg, Ca, or Sr flux from an effusion cell is increased over a period of several minutes. We suggest an explanation for this phenomenon in terms of changes in the emissivity of oxide coated source material. The implication is that the stability of these sources is better at moderate oxygen pressures than at low oxygen pressures.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
64.70.Hz Solid-vapor transitions

Atomically controlled growth of GaAs/NiAl/GaAs structures by molecular‐beam epitaxy

S. Hirono, M. Tanimoto, and N. Inoue

J. Vac. Sci. Technol. B 12, 1181 (1994); http://dx.doi.org/10.1116/1.587037 (3 pages)

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The morphology of molecular‐beam epitaxy (MBE) grown GaAs/NiAl/GaAs structures using scanning tunneling microscopy (STM) was investigated. Improving the flatness of the NiAl layer is achieved by improving the wettability of NiAl on GaAs by using a Ni template and increasing the island density by low‐temperature growth. This method gives a continuous, flat NiAl film with a mean roughness of one monolayer. A GaAs overlayer with a roughness of two monolayers or less is obtainable by using low‐temperature migration enhanced epitaxy (MEE).
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Stabilized α‐Sn grown at high temperature by molecular beam epitaxy

M. Kimata, T. Suzuki, K. Saino, K. Kawamura, and A. Hobbs

J. Vac. Sci. Technol. B 12, 1184 (1994); http://dx.doi.org/10.1116/1.587038 (2 pages)

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The first observation of lattice images of stabilized α‐Sn grown at 150 °C by high‐resolution transmission electron microscopy is reported here. A structure of CdTe/α‐Sn/InSb has been grown on an InSb buffer layer, which was grown on an InSb(100) substrate by molecular beam epitaxy at 220 °C. During the growth, cross doping was carefully avoided. In addition, by the energy‐dispersive x‐ray spectroscopy, it was found that the interdiffusion of In and Te, which usually occurs across the interface of CdTe/InSb, is prevented by the α‐Sn layer inserted at the interface.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Fx Diffusion; interface formation

Growth of group III nitrides on Si(111) by plasma‐assisted molecular beam epitaxy

K. S. Stevens, A. Ohtani, A. F. Schwartzman, and R. Beresford

J. Vac. Sci. Technol. B 12, 1186 (1994); http://dx.doi.org/10.1116/1.587039 (4 pages) | Cited 14 times

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Wurtzitic single‐crystal GaN and polycrystalline (columnar) InGaN have been grown on the Si(111) face in an electron cyclotron resonance plasma‐assisted molecular beam epitaxy process. Reflection high‐energy electron diffraction shows registry of the nitride basal‐plane triangular lattice with respect to the Si(111) substrate triangular network. Plan‐view transmission electron microscopy images reveal crystalline or polycrystalline GaN structure depending on growth temperature. High‐resolution x‐ray rocking curves of the (0002) peak were as narrow as 30 min for a 0.6‐μm GaN film grown on a thin AlN buffer layer at 750 °C.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Carbon p+ doping of molecular‐beam epitaxial GaAs films using carbon tetrabromide

P. J. Lemonias, W. E. Hoke, D. G. Weir, and H. T. Hendriks

J. Vac. Sci. Technol. B 12, 1190 (1994); http://dx.doi.org/10.1116/1.587040 (3 pages) | Cited 2 times

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Carbon‐doped GaAs films have been grown by molecular‐beam epitaxy using carbon tetrabromide as the carbon source. The films were doped up to 1.3 × 1020 cm−3 with mobilities which compare favorably to beryllium‐doped films. Secondary‐ion mass spectrometry measurements made on these films indicate sharp transitions and negligible memory effects as well as near unity doping incorporation. Room temperature photoluminescence intensities were equivalent to comparably beryllium‐doped films at 5.0 × 1019 cm−3. Photoluminescence intensities and hole concentrations were found to be dependent on both arsenic to gallium flux ratios and substrate temperature. Annealing studies on a film doped with carbon at 4.6 × 1019 cm−3 indicate good thermal stability of the carbon in the arsenic lattice site.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
78.66.Fd III-V semiconductors

Carbon doping of InGaAs in solid‐source molecular beam epitaxy using carbon tetrabromide

Wen‐Yen Hwang, D. L. Miller, Y. K. Chen, and D. A. Humphrey

J. Vac. Sci. Technol. B 12, 1193 (1994); http://dx.doi.org/10.1116/1.587041 (4 pages) | Cited 7 times

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Carbon tetrabromide was used to dope (In,Ga)As layers lattice matched to InP grown by solid‐source molecular beam epitaxy. The maximum hole density depended on substrate temperature. A hole concentration as high as 7.5×1019 cm−3 was achieved at a substrate temperature of 450 °C with reduced As2 flux. Variations in arsenic flux intensity were found to have little effect on the doping density. Hole mobility was comparable to the mobility of Be‐doped material grown in our MBE system and to the mobility of CCl4‐doped material grown elsewhere. We observed a short‐term doping memory effect which we attribute to desorption of CBr4 from growth chamber internal surfaces due to radiant heat from column III ovens. (In,Al)As/(In,Ga)As Npn heterojunction bipolar transistors fabricated using CBr4 doping for the (In,Ga)As base layer with p=2×1019 cm−3 exhibited a dc current gain of eight.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.30.Pq Bipolar transistors

Some doping results in ZnSe grown by molecular beam epitaxy

L. K. Li, W. I. Wang, J. M. Gaines, J. Petruzzello, and T. Marshall

J. Vac. Sci. Technol. B 12, 1197 (1994); http://dx.doi.org/10.1116/1.587042 (3 pages)

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Comparison studies of N‐doping of ZnSe for (100) and (311)A orientations have been performed. The C–V measurements indicated that the doping level of the samples grown on (311)A is higher than that of the samples on (100). Doping experiments using Zn3As2 as As‐doping source evaporated by a Knudsen effusion cell also have been performed. Low‐temperature photoluminescence measurements revealed evidence of shallow acceptor bound excitons, indicating that some of the As is being incorporated as shallow levels. It is also pointed out that group V monomers such as As and P are promising p‐type dopants.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Et II-VI semiconductors

Carbon doping by a compact electron beam source

J. M. Van Hove, P. P. Chow, M. F. Rosamond, G. L. Carpenter, and L. A. Chow

J. Vac. Sci. Technol. B 12, 1200 (1994); http://dx.doi.org/10.1116/1.587043 (3 pages) | Cited 5 times

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Carbon doping in III–V compounds has generated much attention because of applications in high temperature and high current devices. We present results using a novel electron beam carbon source for doping GaAs and GaSb. The source construction allows normal effusion cell geometry and utilizes electron bombardment for evaporation from a carbon rod. Mass spectrometer data showed the carbon flux contained C1, C2, and C3 species. For GaAs, controllable hole doping densities between 3×1015 cm−3 and 5×1019 cm−3 were obtained. For GaSb, carbon doping resulted in P‐type material with hole densities ranging from the background level of 2×1016 to 3×1020 cm−3 for specular film morphology. Hole mobility values for GaAs and GaSb are comparable to published data.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors

Boron delta doping in Si and SiGe and its application toward field‐effect transistor devices

T. K. Carns, X. Zheng, K. L. Wang, S. L. Wu, and S. J. Wang

J. Vac. Sci. Technol. B 12, 1203 (1994); http://dx.doi.org/10.1116/1.587044 (4 pages) | Cited 4 times

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The mobility behavior of boron delta (δ)‐doped Si, Si1−xGex(0≤x≤1) is investigated, which includes the first mobility measurements reported for B δ‐doped Si1−xGex and Ge. The expected mobility enhancement from δ doping is not realized in Si:B due to the heavy effective mass of holes. However, some enhancement may be possible at lower doping levels for narrower wells. Indications of mobility enhancement have been realized for δ‐doped Ge:B because of the relatively light effective mass. We also present the implementation of boron δ‐doped layers in the fabrication of (i) the first SiGe:B δ‐FET and (ii) the first coupled δ‐layer Si:B δ‐FET.
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73.50.Dn Low-field transport and mobility; piezoresistance
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.30.Tv Field effect devices

Pyrometric interferometry for real time molecular beam epitaxy process monitoring

F. G. Böbel, H. Möller, A. Wowchak, B. Hertl, J. Van Hove, L. A. Chow, and P. P. Chow

J. Vac. Sci. Technol. B 12, 1207 (1994); http://dx.doi.org/10.1116/1.587045 (4 pages) | Cited 8 times

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Pyrometric interferometry (PI) has recently been demonstrated for simultaneous real time wafer temperature and thickness measurement during the molecular beam epitaxy process. Both parameters of the thin film layer can be determined from the changing interference conditions in the layer. We used a reflection assisted version of PI to follow the thermal history of the wafer under different conditions and were able to resolve temperature to less than 1 °C. For thickness measurements, a parabolic fitting algorithm was used to accurately determine the endpoints of the GaAs/AlAs quarter wave stacks. Compared to other noncontact methods this technique can be used for very thick layers and is unaffected by the layer absorption and optical effects.  
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
07.20.Ka High-temperature instrumentation; pyrometers

Determination of molecular beam epitaxial growth parameters by ellipsometry

R. Droopad, C. H. Kuo, S. Anand, K. Y. Choi, and G. N. Maracas

J. Vac. Sci. Technol. B 12, 1211 (1994); http://dx.doi.org/10.1116/1.587046 (3 pages) | Cited 5 times

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The use of ellipsometry as an alternative technique for in situ determination of molecular beam epitaxial growth parameters has been demonstrated. Epitaxial growth has been monitored in real time using three discrete wavelengths to extract growth rates and alloy composition. The effect of substrate rotation on the measured growth rates has also been determined by this technique. From measurements of the GaAs growth rates versus substrate temperature, a value of 4.68±0.12 eV for the activation energy for Ga desorption during GaAs growth was obtained. This agrees with values obtained by other measurement techniques.
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07.60.Fs Polarimeters and ellipsometers
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Measurement of GaAs temperature‐dependent optical constants by spectroscopic ellipsometry

C. H. Kuo, S. Anand, R. Droopad, K. Y. Choi, and G. N. Maracas

J. Vac. Sci. Technol. B 12, 1214 (1994); http://dx.doi.org/10.1116/1.587047 (3 pages) | Cited 15 times

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Temperature‐dependent optical constants (30 °C<T<650 °C) of semi‐insulating GaAs in the range of 1.24–5.00 eV were measured using spectroscopic ellipsometry (SE) inside a specially designed molecular beam epitaxy chamber. Because of the lack of native oxides and surface adsorbates, a simple two‐phase model (vacuum/substrate) could be used to calculate optical constants from the ellipsometry data. A Lorentz oscillator model with seven oscillators was used to fit the ϵ1 and ϵ2 experimental data to determine the temperature‐dependent interband transition energies, E1 and E1+Δ1. Changes in the dielectric function at different surface temperatures would allow SE to be used as a tool to accurately measure the surface temperature of GaAs. Accurate knowledge of the temperature‐dependent optical constants is also useful for the design of optical devices.
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78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
07.60.Fs Polarimeters and ellipsometers

Dual beam atomic absorption spectroscopy for controlling thin film deposition rates

S. J Benerofe, C. H. Ahn, M. M. Wang, K. E. Kihlstrom, K. B. Do, S. B. Arnason, M. M. Fejer, T. H. Geballe, M. R. Beasley, and R. H. Hammond

J. Vac. Sci. Technol. B 12, 1217 (1994); http://dx.doi.org/10.1116/1.587048 (4 pages) | Cited 10 times

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We have developed a stable (<1% drift/h at 1 Å/s), fast (∼200 ms), sensitive (S/N∼10–200 at 1 Å/s) evaporation rate monitor for controlling electron beam sources. Based on dual beam atomic absorption spectroscopy (AAS), in which a reference arm compensates for drift in the light source and signal detection apparatus, this technique is very wavelength and hence element specific, allowing many elements to be simultaneously and independently monitored. Furthermore, the system can operate at very high background gas pressures, as well as under ultrahigh vacuum conditions. Also, because only the light must enter the vacuum chamber and pass through the evaporant, minimal periodic maintenance inside the chamber is necessary. The versatility and sensitivity of this AA system make it a viable candidate for in situ monitoring of various other thin film processes, including sputtering, ion milling, and reactive ion etching.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Rd Visible and ultraviolet spectrometers
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

In situ thickness monitoring and control for highly reproducible growth of distributed Bragg reflectors

Y. M. Houng, M. R. T. Tan, B. W. Liang, S. Y. Wang, and D. E. Mars

J. Vac. Sci. Technol. B 12, 1221 (1994); http://dx.doi.org/10.1116/1.587049 (4 pages) | Cited 9 times

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A theoretical model was developed to simulate the apparent substrate temperature oscillation during the growth of AlAs/AlxGa1−xAs, x=0 and 0.25, distributed Bragg reflectors (DBR) for 980‐ and 780‐nm vertical cavity surface emitting lasers, respectively. The simulated data were then used for in situ monitoring and feedback control of layer thickness by a simple pyrometric interferometry technique to obtain a highly reproducible DBR. These measurements can be performed with continuous substrate rotation and without any growth interruption. The reproducibility of the center wavelength and full width at half‐maximum of the reflectivity stop band with a variation of <±0.2% and <±0.4% for the AlAs/GaAs and AlAs/AlGaAs mirror stacks, respectively, were achieved.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
42.55.Px Semiconductor lasers; laser diodes

Factors affecting the temperature uniformity of semiconductor substrates in molecular‐beam epitaxy

S. R. Johnson, C. Lavoie, E. Nodwell, M. K. Nissen, T. Tiedje, and J. A. Mackenzie

J. Vac. Sci. Technol. B 12, 1225 (1994); http://dx.doi.org/10.1116/1.587050 (4 pages) | Cited 2 times

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The temperature of GaAs substrates is profiled in a molecular‐beam epitaxy system with a spatial resolution of 3 mm and a thermal resolution of 0.4 °C, respectively. The effects of substrate doping, back surface textures, thermal contact to the holder, and a pyrolytic boron nitride diffuser plate, on the temperature uniformity, are explored for indium‐free mounted substrates. Both positive and negative curvature temperature profiles are observed.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
07.20.-n Thermal instruments and apparatus

Efficient liquid nitrogen supply system for the cooling shroud in a molecular beam epitaxy system

J. W. Cook and J. F. Schetzina

J. Vac. Sci. Technol. B 12, 1229 (1994); http://dx.doi.org/10.1116/1.587051 (3 pages) | Cited 1 time

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The molecular beam epitaxy (MBE) process is generally surrounded by liquid nitrogen (LN2) cooled surfaces for optimum control of the environment in which the thin‐film deposition takes place. The design and operation of a LN2 supply system for feeding the cryogenicly cooled surfaces in a MBE system is described here. The supply system is based on modification of a standard 50‐l LN2 storage dewar. The reservoir gravity feeds liquid through a vacuum‐insulated line into the fill port of the MBE system. A solenoid‐operated vent valve activated by a temperature controller regulates the level of LN2 in the MBE system. The LN2 supply system is efficient and costs much less than other alternatives.
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Atomic nitrogen production in a molecular‐beam epitaxy compatible electron cyclotron resonance plasma source

R. P. Vaudo, J. W. Cook, and J. F. Schetzina

J. Vac. Sci. Technol. B 12, 1232 (1994); http://dx.doi.org/10.1116/1.587052 (4 pages) | Cited 29 times

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The first high‐resolution study of the optical emission from nitrogen plasmas produced by an ASTeX compact electron cyclotron resonance (ECR) microwave plasma source is reported. The spectroscopic results clearly show that the ECR plasma source generates an appreciable flux of nitrogen atoms, as indicated by strong atomic emission lines in the near‐infrared spectral region, in addition to various species of molecular nitrogen.
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52.50.Dg Plasma sources
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Reflection high‐energy electron diffraction intensity oscillations during molecular‐beam epitaxy on rotating substrates

Jan P. A. van der Wagt and James S. Harris

J. Vac. Sci. Technol. B 12, 1236 (1994); http://dx.doi.org/10.1116/1.587053 (3 pages) | Cited 6 times

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We report the gated detection of reflection high‐energy electron diffraction (RHEED) signal intensity oscillations during molecular‐beam epitaxy (MBE) while the wafer is being rotated at high speed (≳100 rpm). In general, a larger number of oscillation periods are observed with this technique than during stationary measurement because of the very high growth rate uniformity across the sample. We found that the average over all azimuths of the RHEED specular spot intensity shows the same growth induced oscillations. This allowed us to replace the gated detection by an averaging detection method: a low‐pass filter suppresses fast variations due to rapid changes in azimuth, while passing low‐frequency (<1 Hz) growth related oscillations. This simplifies the detection system and at the same time reduces noise related to wafer motion, 60 Hz, etc. These techniques have potential use for in situ monitoring of thickness and composition of device wafers.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Molecular beam epitaxial growth and properties of Si‐doped GaAs/AlGaAs quantum wells

M. T. Asom, G. Livescu, V. Swaminathan, M. Geva, and L. Luther

J. Vac. Sci. Technol. B 12, 1239 (1994); http://dx.doi.org/10.1116/1.587054 (3 pages)

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We report on molecular beam epitaxial growth of Si doped, single and multiple quantum well structures. We have examined the effects of growth parameters such as substrate temperature, group V/III ratio, and intentional and unintentional impurities, on the electrical and optical properties of the quantum wells structures. Capacitance–voltage and secondary ion mass spectrometry analysis of the structures reveal that the net density of electrically active carriers in the wells is controlled by the number of acceptor states in the AlGaAs barrier. We have assigned the source of the acceptor state to the presence of oxygen in the AlGaAs barrier. We observe that the strength of the intersubband optical absorption from the quantum wells increases linearly with the Si‐doping in the well. Photoluminescence measurements indicate that for a given substrate temperature, a lower V/III ratio results in higher quality quantum well.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors

Electrical and optical properties of heavily n‐doped GaSb–AlSb multiquantum well structures for infrared photodetector applications

Berinder Brar, Lorene Samoska, Herbert Kroemer, and John H. English

J. Vac. Sci. Technol. B 12, 1242 (1994); http://dx.doi.org/10.1116/1.587055 (4 pages) | Cited 4 times

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A detailed analysis of the electrical and optical properties of GaSb–AlSb quantum well infrared photodetector structures is presented. Hall effect measurements were performed, and a two‐band conduction model was employed to extract the electron concentration in the L subband, indicating that at typical detector operating temperatures T=80 K there are at least 1012 cm−2 carriers in the L subband. Temperature‐dependent dark current measurements indicate that the dark current mechanism in detector structures consists of a tunneling regime for T<100 K, and a thermionic regime for T≳100 K. An activation energy of 170 meV is extracted from the temperature dependence of the thermionic dark current. Photoluminescence and absorption measurements were also used to obtain information on the subband levels relative to the bottom of the well, and to investigate the effect of doping on the quality of the GaSb quantum wells. We also report on a method to push the intersubband transition to longer wavelengths by growing center‐loaded structures in which a thin layer of AlSb is deposited in the center of the well in order to raise the energy of only the ground state in the well.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Growth of GaAs light modulators on Si by gas source molecular‐beam epitaxy for 850 nm optical interconnects

J. E. Cunningham, K. W. Goossen, J. A. Walker, W. Jan, M. Santos, and D. A. B. Miller

J. Vac. Sci. Technol. B 12, 1246 (1994); http://dx.doi.org/10.1116/1.587056 (5 pages) | Cited 2 times

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The growth of GaAs quantum well modulators on Si for photonic switching applications is reported. Comparison of modulator’s quantum confined Stark effect atop different miscut Si surfaces demonstrate the need for a highly ordered array of bilayer steps as an initial Si surface condition for heteroepitaxy. Proton implantation into the SiO2/Si system via an electron cyclotron resonance plasma to lower the Si oxide desorption temperature, while perserving step ordering of the surface, is explored.  
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42.79.Hp Optical processors, correlators, and modulators
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Chemical beam epitaxy of InP‐based solar cells and tunnel junctions

M. F. Vilela, V. Rossignol, A. Bensaoula, N. Medelci, and A. Freundlich

J. Vac. Sci. Technol. B 12, 1251 (1994); http://dx.doi.org/10.1116/1.587014 (3 pages)

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Chemical beam epitaxy has been utilized to demonstrate high efficiency InGaAs/InP tandem solar cells on InP substrates. The key development in achieving such tandems is the growth of high peak current density InGaAs tunnel junctions for use as interconnect between the top and bottom cells. The growth and performance of the InGaAs bottom cell, the InGaAs tunnel junction, and the InP top cell are first independently presented in the paper. Then the growth of an InP‐based tandem cell is described followed by a discussion of its performance.
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84.60.Jt Photoelectric conversion
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Pz Photoconduction and photovoltaic effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Molecular beam epitaxy growth of pseudomorphic II–VI multilayered structures for blue/green laser diodes and light‐emitting diodes

J. Han, L. He, D. C. Grillo, S. M. Clark, R. L. Gunshor, H. Jeon, A. Salokatve, A. V. Nurmikko, G. C. Hua, and N. Otsuka

J. Vac. Sci. Technol. B 12, 1254 (1994); http://dx.doi.org/10.1116/1.587015 (4 pages) | Cited 2 times

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This article reports results involving the molecular beam epitaxial growth of the quaternary (Zn,Mg)(S,Se) compound as well as the incorporation of this quaternary into a pseudomorphic separate confinement heterostructure laser diode configuration. It was found that the quaternary (Zn,Mg)(S,Se) can accommodate much more strain as compared to binary ZnSe; the films remained essentially pseudomorphic, with low defect densities, for strains in the studied range from −0.225% (tension) to 0.137% (compression) at room temperature. The relationship between the surface morphology and the strain is also described in this paper. Lasing was routinely obtained at room temperature under pulsed injection. A threshold lasing voltage of as low as 7 V was observed in index‐guided diode lasers.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
42.55.Px Semiconductor lasers; laser diodes
85.60.Jb Light-emitting devices

Buried heterostructure laser diodes fabricated using in situ processing

M. Hong, D. Vakhshoori, L. H. Grober, J. P. Mannaerts, M. T. Asom, J. D. Wynn, F. A. Thiel, and R. S. Freund

J. Vac. Sci. Technol. B 12, 1258 (1994); http://dx.doi.org/10.1116/1.587016 (4 pages) | Cited 5 times

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An in situ process which includes electron cyclotron resonance plasma etching and molecular beam epitaxial regrowth is applied to the fabrication of buried heterostructure vertical cavity surface‐emitting laser (SEL) diodes and edge‐emitting laser (EEL) diodes. The buried SEL with a 7.5 μm diameter has a pulsed laser threshold current of 1 mA, and a threshold voltage of 4 V with a peak power of 0.9 mW. The buried EEL with 2.5 μm stripe width and 800 μm cavity length has a threshold current density of 500 A/cm2.
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42.55.Px Semiconductor lasers; laser diodes
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Blue/green ZnSe–ZnCdSe light‐emitting diodes and photopumped laser structures grown by molecular beam epitaxy on ZnSe substrates

J. Ren, D. B. Eason, Z. Yu, B. Sneed, J. W. Cook, J. F. Schetzina, N. A. El‐Masry, X. H. Yang, J. J. Song, Gene Cantwell, and William C. Harsh

J. Vac. Sci. Technol. B 12, 1262 (1994); http://dx.doi.org/10.1116/1.587017 (4 pages) | Cited 5 times

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The first ZnSe–ZnCdSe double‐heterostructure light‐emitting diodes (LEDs) and photopumped laser structures on ZnSe substrates have been successfully grown by molecular beam epitaxy. The LEDs emit bright blue/green electroluminescence at room temperature, with the emission peak centered at 492 nm. Photopumped laser emission was also observed from ZnSe–ZnCdSe multiple‐quantum‐well structures grown on ZnSe substrates. The cleaved‐cavity devices display stimulated emission in the deep‐blue spectral region near 477 nm at 10 K and at 478.8 nm at 80 K.  
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42.55.Px Semiconductor lasers; laser diodes
85.60.Jb Light-emitting devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Molecular‐beam epitaxy growth of high‐performance midinfrared diode lasers

G. W. Turner, H. K. Choi, D. R. Calawa, J. V. Pantano, and J. W. Chludzinski

J. Vac. Sci. Technol. B 12, 1266 (1994); http://dx.doi.org/10.1116/1.587018 (3 pages) | Cited 19 times

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Recent advances in the performance of GaInAsSb/AlGaAsSb quantum‐well diode lasers have been directly related to improvements in the quality of the molecular‐beam epitaxy (MBE)‐grown epitaxial layers. These improvements have been based on careful measurement and control of lattice matching and intentional strain, changes in shutter sequencing at interfaces, and a generally better understanding of the growth of Sb‐based epitaxial materials. By using this improved MBE‐grown material, significantly enhanced performance has been obtained for midinfrared lasers. These lasers, which are capable of ∼2‐μm emission at room temperature, presently exhibit threshold current densities of 143 A/cm2, continuous wave powers of 1.3 W, and diffraction‐limited powers of 120 mW. Such high‐performance midinfrared diode lasers are of interest for a wide variety of applications, including eye‐safe laser radar, remote sensing of atmospheric contaminants and wind turbulence, laser surgery, and pumping of solid‐state laser media.
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42.55.Px Semiconductor lasers; laser diodes
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Photocontrolled double‐barrier resonant‐tunneling diode

H. S. Li, Y. W. Chen, K. L. Wang, D. S. Pan, L. P. Chen, and J. M. Liu

J. Vac. Sci. Technol. B 12, 1269 (1994); http://dx.doi.org/10.1116/1.587019 (4 pages) | Cited 1 time

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A photocontrolled InGaAs/AlAs double‐barrier resonant‐tunneling diode, for the first time, has been demonstrated. The photoinduced valley current in the resonant‐tunneling diode was optically controlled by varying the incident optical power level. With the incident optical power intense enough, the photogenerated valley current became dominant over the peak current. As a consequence, the negative differential resistance of the device was nullified. A photogeneration process, based on photogenerating carriers in the depletion region adjacent to the double barriers, is described and characterized. The device under illumination was modeled as a resonant‐tunneling diode in series integration with a photodetector. The quantum efficiency for the photogeneration was measured and found comparable with theoretical prediction. The demonstrated photocontrolled double‐barrier resonant‐tunneling diode can be useful in a variety of applications.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects

Studies of Si segregation in GaAs using current–voltage characteristics of quantum well infrared photodetectors

Z. R. Wasilewski, H. C. Liu, and M. Buchanan

J. Vac. Sci. Technol. B 12, 1273 (1994); http://dx.doi.org/10.1116/1.587020 (4 pages) | Cited 4 times

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Segregation of Si in molecular beam epitaxy grown GaAs quantum wells is investigated using current–voltage characteristics (I–V) of quantum well infrared photodetectors. Theoretical modeling is used to derive the extent of segregation from the measured ratio of dark currents through the device in forward and reverse directions. The segregation length, expressed in Å per decade of concentration decay, increases from 12 to 52 Å on increasing the growth temperature from 550 to 605 °C. The character of this increase indicates that Si segregation is kinetically limited in this temperature range, but approaches thermal equilibrium above 600 °C. The effect of arsenic overpressure on the segregation length at a growth temperature of 595 °C is also studied. An increased overpressure of arsenic suppresses Si segregation for both dimeric and tetrameric forms of As. The effect of As2 is very small, with the segregation length decreasing from 52 to 48 Å on increasing the arsenic flux by a factor of eight from its nominal value. The same increase in flux gives a much stronger suppression of Si segregation if As4 is used: the segregation length decreases from 51 to 40 Å.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.60.Gz Photodetectors (including infrared and CCD detectors)

One‐dimensional wire formed by molecular‐beam epitaxial regrowth on a patterned pnpnp GaAs substrate

J. H. Burroughes, M. P. Grimshaw, M. L. Leadbeater, D. A. Ritchie, M. Pepper, and G. A. C. Jones

J. Vac. Sci. Technol. B 12, 1277 (1994); http://dx.doi.org/10.1116/1.587021 (3 pages) | Cited 1 time

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We have grown high mobility one‐dimensional electron gases by molecular‐beam epitaxy (MBE) on etched GaAs pnpnp facets. By applying the appropriate bias to the p‐ and n‐GaAs layers which serve as a unique backgate, the electron gas width and mobility may be controlled. The width may be varied between about 400 and 100 nm. We also find that the mobility increases up to about 6×105 cm2/V s, rather than decreases with falling carrier concentration.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.61.Ey III-V semiconductors

High‐quality strained quantum wires grown by molecular beam epitaxy on (100) GaAs substrate

Y.‐P. Chen, J. D. Reed, W. J. Schaff, and L. F. Eastman

J. Vac. Sci. Technol. B 12, 1280 (1994); http://dx.doi.org/10.1116/1.587022 (3 pages)

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High‐radiative recombination efficiency arrays of InGaAs/GaAs strained quantum wires have been fabricated by a combination of e‐beam lithography, dry and wet etching, sidewall desorption, migration‐enhanced epitaxial and molecular beam epitaxial regrowth. The structure was evaluated by reflection high‐energy electron diffraction, cross‐sectional transmission electron microscopy, and photoluminescence spectroscopy. Transmission electron microscopy study showed that a defect‐free regrown layer and excellent sidewall coverage have been attained. From the photoluminescence measurement, the sample showed high‐radiative efficiency, and had strong photoluminescence for wire widths down to 190 nm.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Current‐controlled negative differential resistance in InAs/AlxGa1−xSb tunnel structures

D. H. Chow and J. N. Schulman

J. Vac. Sci. Technol. B 12, 1283 (1994); http://dx.doi.org/10.1116/1.587023 (3 pages)

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We report the design and demonstration of a novel resonant tunneling device which displays bistability in operating current over a range of applied voltages. The device is based on an InAs/AlxGa1−xSb double barrier heterostructure. Although similar in design to conventional resonant tunneling structures, the type‐II InAs/AlxGa1−xSb heterostructure permits the simultaneous accumulation of electrons and holes in the quantum well/barrier region under an applied bias. The steady‐state free‐charge distribution, and hence the device current, is strongly dependent upon the bias history of the device. This effect is manifested as a current‐controlled (S‐shaped) negative differential resistance under conditions in which the device current is specified while the device voltage is measured; a bistable (hysteretic) characteristic is observed under conditions in which the voltage is specified and the current is measured. We have observed current bistability for AlxGa1−xSb barrier compositions in the range 0.4<x<0.6, with high/low state separation in the 105 A/cm2 range. Under current‐controlled measurement conditions, peak‐to‐valley voltage ratios as high as 1.5 have been observed.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

50 nm GaAs/AlAs wire structures grown on corrugated GaAs

David J. Miller and James S. Harris

J. Vac. Sci. Technol. B 12, 1286 (1994); http://dx.doi.org/10.1116/1.587024 (4 pages)

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Electron beam lithography has been used to investigate the growth of GaAs wires in finely corrugated GaAs. Electron beam lithography was used to define 100 nm corrugations along the [110] and [11̄0] directions; anisotropic etching revealed grooves that were V‐shaped ([11̄0]) or dovetailed ([110]). Here, AlAs resharpens the groove profile during growth, provided the barrier thickness is not less than 30–40 nm. Also, GaAs exhibited an enhanced growth rate in both groove directions, with an increase of 60% over the nonpatterned growth rate for the [11̄0] direction. Growth in grooves along [11̄0] preserved the V shape of the groove, while [110] growth showed evidence of deposition masking and microvoiding.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.40.Hp Lithography, masks and pattern transfer

Effect of the proximity of an ex situ patterned interface on the quality of two‐dimensional electron gases at GaAs/AlGaAs heterojunctions

M. P. Grimshaw, D. A. Ritchie, J. H. Burroughs, and G. A. C. Jones

J. Vac. Sci. Technol. B 12, 1290 (1994); http://dx.doi.org/10.1116/1.587025 (3 pages) | Cited 6 times

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High‐quality two‐dimensional electron gases (2DEGs) were regrown onto ex situ patterned substrates and the effect of the distance between the 2DEG and the contaminated regrowth interface was investigated. At a separation of 220 nm mobilities of 7.1×105 cm2 V−1 s−1 in the dark and 1.3×106 cm2 V−1 s−1 after illumination with a red light‐emitting diode (LED) were measured with corresponding carrier concentrations of 2.4×1011 and 4.3×1011 cm−2. The quality of this 2DEG was equivalent to that attained in conventionally grown 2DEGs at the time, indicating that the 2DEG was not affected by presence of the regrowth interface in this case. For smaller separations a degradation in the 2DEG quality was observed. Thus, at a separation of only 60 nm, a mobility of 4.1×105 cm2 V−1 s−1 at a carrier concentration of 4.2×1011 cm−2 was measured after illumination. The use of an independently contacted n+ layer in the patterned substrate as a backgate was also demonstrated.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Pz Photoconduction and photovoltaic effects

Fabrication of independent contacts to two closely spaced two‐dimensional electron gases using molecular beam epitaxy regrowth and in situ focused ion beam lithography

K. M. Brown, E. H. Linfield, D. A. Ritchie, G. A. C. Jones, M. P. Grimshaw, and A. C. Churchill

J. Vac. Sci. Technol. B 12, 1293 (1994); http://dx.doi.org/10.1116/1.587026 (3 pages) | Cited 13 times

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Lateral patterning of a buried GaAs epilayer can be achieved during molecular beam epitaxy growth by in situ implantation with a high energy focused ion beam. Applying this technique, 30 keV Ga ions have been used to form small, highly resistive, regions in the backgate layer of a double two‐dimensional electron gas (2DEG) structure. Independent contacts to the two 2DEGs were then achieved by selectively depleting out regions of the upper and lower 2DEGs with potentials on patterned front and backgates. In the resulting devices, the magnetoresistance of the two 2DEG layers was measured both together and separately. It was demonstrated that a bias of up to ±50 mV could be applied, across the 20 nm AlGaAs barrier separating the 2DEGs, with leakage currents of <0.01 nA at 4.2 K. Finally, resonant tunneling between the two 2DEGs was observed when the barrier thickness was reduced to 7 nm. These results have demonstrated the success of this novel in situ fabrication route.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Optimization of high mobility two‐dimensional hole gases

M. Y. Simmons, D. A. Ritchie, I. Zailer, A. C. Churchill, and G. A. C. Jones

J. Vac. Sci. Technol. B 12, 1296 (1994); http://dx.doi.org/10.1116/1.587027 (4 pages) | Cited 3 times

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Modulation‐doped (Al,Ga)As two‐dimensional hole gas (2DHG) structures have been grown by molecular‐beam epitaxy (MBE) on the (311)A surface of GaAs using silicon as a p‐type dopant. Systematic variations of carrier density ps and mobility μ with undoped spacer thickness were observed at 1.7 K, with a peak mobility of 4.95×105 cm2 V−1 s−1 at a sheet carrier density of 2.2×1011 cm−2 occurring at a spacer thickness of 200 Å. The mobility and carrier density of all samples were also measured over the temperature range 300 mK to 4.2 K. These results lead to the conclusion that for samples with spacer thicknesses greater than 400 Å, acoustic phonon scattering limits the mobility at low temperatures, whereas for samples with spacer thicknesses less than this value, ionized impurity scattering was observed to be the dominant scattering mechanism. As observed with electron gases, an increase in mobility was achieved by using a thicker region of lightly doped (Al,Ga)As, giving a sample with a mobility of 7.2×105 cm2 V−1 s−1, at a carrier density of 8.7×1010 cm−2 measured at 300 mK. This value constitutes the highest mobility so far reported, at carrier densities below 1×1011 cm−2.  
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.61.Ey III-V semiconductors

AlGaAs/Ge/GaAs heterostructures grown by molecular beam epitaxy

Y. Wang, N. Baruch, W. I. Wang, M. E. Cheney, C. I. Huang, and R. L. Scherer

J. Vac. Sci. Technol. B 12, 1300 (1994); http://dx.doi.org/10.1116/1.587028 (3 pages)

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We report the comparison studies of molecular beam epitaxial growth of AlGaAs/Ge/GaAs heterostructures on differently oriented GaAs substrates. We have investigated the molecular beam epitaxial growth of Ge on GaAs, and GaAs and AlGaAs on Ge epitaxial layers with the aim of obtaining device‐quality interfaces of AlGaAs and GaAs epilayers on Ge which are free of antiphase domains. Our results show that the junctions grown on (311)B oriented substrates have better electrical characteristics than those grown on (100) oriented substrates. This is due to the absence of antiphase domains and less interface charge in heterostructures grown on (311)B substrates.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Observation of quantum mechanical reflections of electrons at an in situ grown GaAs/aluminum Schottky barrier

M. V. Weckwerth, Jan P. A. van der Wagt, and James S. Harris

J. Vac. Sci. Technol. B 12, 1303 (1994); http://dx.doi.org/10.1116/1.587029 (3 pages) | Cited 3 times

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The room temperature observation of quantum mechanical reflections of electrons at an aluminum/gallium arsenide Schottky barrier is reported here. Molecular‐beam epitaxy was used to grow an AlAs/GaAs/AlAs double barrier resonant tunneling diode (RTD) followed by an epitaxial in situ grown aluminum/gallium arsenide Schottky barrier. This RTD was used to inject a nearly monoenergetic beam of electrons towards the Schottky barrier. The measured I–V curves show resonances associated with the reflections of electrons at the Schottky interface. Understanding the transport properties of hot electrons at a Schottky barrier may prove important for understanding the physics of metal base transistors and other device structures that employ the use of epitaxial metals.
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73.30.+y Surface double layers, Schottky barriers, and work functions

Modulation‐doped InAlAs/InGaAs quantum well structures for high electron mobility transistors

W. Klein, G. Böhm, M. Sexl, S. Grigull, H. Heiss, G. Tränkle, and G. Weimann

J. Vac. Sci. Technol. B 12, 1306 (1994); http://dx.doi.org/10.1116/1.587030 (3 pages) | Cited 2 times

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Modulation‐doped InAlAs/InGaAs heterostructures were grown on InP substrates by solid source molecular beam epitaxy. Lattice matching within ±10−3 was reproducibly obtained. The high quality of the ternary compounds is demonstrated by narrow photoluminescence linewidths of full width at half‐maximum=2 and 13 meV for InGaAs and InAlAs, respectively. The transport properties are excellent, too, with a 4.2 K mobility of 84 000 cm2/Vs for two‐dimensional electron gas concentrations of 1.3×1012 cm−2 in conventional single heterostructures. Optimized single quantum‐well structures with high current carrying capacity due to modulation doping in both barriers have sheet carrier concentrations of 4.0×1012 cm−2 and 4.2 K mobilities of 28 000 cm2/Vs. Sub‐μm‐high electron mobility transistors processed from these structures show a maximum transconductance of 500 mS/mm at a drain current of 445 mA/mm. A very high maximum drain current of 1120 mA/mm is obtained, while maintaining cutoff frequencies of fT=118 GHz and fmax=191 GHz.  
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.61.Ey III-V semiconductors
85.30.Tv Field effect devices

Double quantum well charge transport in pseudomorphic Al0.3Ga0.7As/In0.15Ga0.85As/GaAs modulation doped heterostructures

A. P. Young, J. M. Fernandez, Jianhui Chen, and H. H. Wieder

J. Vac. Sci. Technol. B 12, 1309 (1994); http://dx.doi.org/10.1116/1.587031 (3 pages) | Cited 2 times

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The influence of the spacer thickness upon the apparent mobility and the efficiency of electron transfer between two closely spaced quantum wells has been measured. By decreasing the distance of the δ‐doped layer from the InGaAs channel below 100 Å, the efficiency of charge transfer into the InGaAs channel is increased. A dramatic drop is observed in the apparent mobility of the structure with the GaAs embedment when that distance is 50 Å. This indicates that the experimentally measured electron transport properties must be considered in terms of the parameters of two interacting channels, and are dominated by the properties of the embedded GaAs.
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73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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