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Low resistance and thermally stable Ti/Al-based Ohmic contacts to N-face n-GaN for vertical light-emitting diodes by using Ti(Ga) solid solution and TiN layers

Joon-Woo Jeon, Woong-Sun Yum, Tae-Yeon Seong, Sang Youl Lee, and June-O Song

J. Vac. Sci. Technol. B 30, 020601 (2012); http://dx.doi.org/10.1116/1.3678490 (4 pages) | Cited 1 time

Online Publication Date: 24 January 2012

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The authors report on the formation of highly reliable Ti/Al-based ohmic contacts to N-face n-GaN for high-performance vertical light-emitting diodes by using Ti(Ga) solid solution and TiN layers. The Ti(Ga) solid solution layer is used to minimize the outdiffusion of Ga atoms from the n-GaN surface region. Unlike the Ti/Al contacts, the Ti(Ga)/Ti/Al and Ti(Ga)/TiN/Al samples exhibit ohmic behavior with contact resistivities of 3.9 – 4.8 × 10⁻⁴ Ωcm² after annealing at 250 °C. It was further shown that unlike the Ti(Ga)/TiN/Al samples, the Ti/Al and the Ti(Ga)/Ti/Al samples are largely electrically degraded when annealed at 300 °C in an oven. Based on x-ray photoemission spectroscopy and secondary ion mass spectrometry results, ohmic formation and degradation mechanisms are briefly described and discussed.

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85.60.Jb	Light-emitting devices
84.32.Dd	Connectors, relays, and switches

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Resistive switching of HfO₂ based flexible memories fabricated by low temperature atomic layer deposition

R. C. Fang, L. H. Wang, W. Yang, Q. Q. Sun, P. Zhou, P. F. Wang, S. J. Ding, and David W. Zhang

J. Vac. Sci. Technol. B 30, 020602 (2012); http://dx.doi.org/10.1116/1.3694003 (4 pages)

Online Publication Date: 22 March 2012

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HfO₂-based flexible memories were fabricated using a low temperature atomic layer deposition (LTALD) process to examine resistive switching performance. The devices exhibit typical bipolar resistive switching. The endurance and retention behaviors were also investigated. No significant degradation of the device was noted at either room temperature or 85 °C, and the current transport mechanism of the high- and low-resistance states are estimated to be Ohmic and trap-assisted current, respectively. The authors propose that this LTALD process will significantly improve fabrication of flexible memories.

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84.30.Sk	Pulse and digital circuits
84.32.Dd	Connectors, relays, and switches
07.20.Mc	Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
85.40.Sz	Deposition technology

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Characteristic comparison of AlGaN/GaN enhancement-mode HEMTs with CHF₃ and CF₄ surface treatment

C. H. Chen, C. W. Yang, H. C. Chiu, and Jeffrey. S. Fu

J. Vac. Sci. Technol. B 30, 021201 (2012); http://dx.doi.org/10.1116/1.3680115 (6 pages)

Online Publication Date: 1 February 2012

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In this study, enhancement-mode (E-mode) AlGaN/GaN HEMTs that underwent CHF₃ and CF₄ plasma treatment beneath the gate metal were fabricated. These treatments were applied because, although previous studies have formed AlF₃ compound layers after fluorine-based plasma treatment to suppress the polarization-induced charge density, the surface negative charges still influenced the device gate leakage current and trap density. In the device in this study, unlike in previous CF₄ plasma-treated GaN E-mode devices, the hydrogen atoms of the CHF₃ plasma were introduced to compensate for vacancies by donating an electron to a vacancy acceptor level, thereby reducing the number of vacancy induced traps. Based on the measured subthreshold slope (SS) and the effective interface state density (D_it) results, the SS value of a CHF₃-treated HEMT was 80 mV/decade and the D_it was 1.23 × 10¹² cm⁻². Moreover, the CHF₃-treated HEMT exhibited a current gain cut-off frequency, a maximum oscillation frequency, and an output power of 6.7, 26, and 14.8 dBm (302 mW/mm), respectively. The 1/f noise measurement results of the CHF₃-treated HEMT indicated that the flicker noise-induced generation-recombination noise and gate leakage-induced generation-recombination noise were also improved. Therefore, the CHF₃-treated HEMT has great potential for use in low-distortion power amplifiers and logic control circuits.

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85.30.Tv

Field effect devices

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Influence of hydrogen on the thermionic electron emission from nitrogen-incorporated polycrystalline diamond films

W. F. Paxton, M. Howell, W. P. Kang, and J. L. Davidson

J. Vac. Sci. Technol. B 30, 021202 (2012); http://dx.doi.org/10.1116/1.3684982 (3 pages) | Cited 3 times

Online Publication Date: 13 February 2012

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Although hydrogen has been shown to enhance the thermionic emission properties of nitrogen-incorporated diamond cathodes, the effect diminishes when these cathodes are heated to temperatures in excess of 700 °C, possibly due to the hydrogen desorbing from the diamond. In order to further examine this behavior, this work examines the thermionic emission properties of a nitrogen-incorporated diamond film grown by chemical vapor deposition in a hydrogen-methane-nitrogen plasma. The film was tested for thermally stimulated electron emission at temperatures ranging from 500 to 900 °C in an as-grown state and after exposure to a hydrogen plasma treatment. Emission current increased, as described by the Richardson equation for thermal emission up to ∼ 700 °C. Above ∼ 800 °C the thermionic emission current was observed to diminish, an effect attributed to the loss of hydrogen from the diamond. Recovery of the hydrogen effect was explored by exposing the diamond film to a low-energy hydrogen plasma. The thermionic emission current at temperatures below ∼700 °C after this hydrogen plasma exposure was observed to increase by four orders of magnitude over the thermionic emission current observed in the initial (as-grown) test. Possible explanations for this emission current increase are discussed.

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79.40.+z	Thermionic emission
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq	Plasma-based ion implantation and deposition

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Comparison of tunnel junctions for cascaded InAs/GaSb superlattice light emitting diodes

L. M. Murray, D. T. Norton, J. T. Olesberg, T. F. Boggess, and J. P. Prineas

J. Vac. Sci. Technol. B 30, 021203 (2012); http://dx.doi.org/10.1116/1.3692252 (6 pages) | Cited 2 times

Online Publication Date: 7 March 2012

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Tunnel junctions in cascaded structures must provide adequate barriers to prevent carriers from leaking from one emission region to the next without first recombining radiatively, while at the same time remain low in tunneling resistance for current recycling. In this study, a variety of tunnel junction designs are compared in otherwise identical four stage InAs/GaSb superlattice light emitting diodes, which past studies have found hole confinement to be problematic. Here we used GaSb on the p-side of the junction, while varying materials on the n-side. The authors find Al_0.20In_0.80As_0.73Sb_0.27 tunnel junctions function best due to the low set of the conduction band; Ga_0.75In_0.25As_0.23Sb_0.77 also works well, though is more resistive due to a reduced set of the conduction band; and GaSb, while giving good hole confinement, results in a very resistive junction. Graded superlattice junctions can also work well, though they show sensitivity to doping levels, and present some challenges in growing strain-free.

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85.60.Jb

Light-emitting devices

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Process effects of copper film over a step etched with a plasma-based process

Chi-Chou Lin and Yue Kuo

J. Vac. Sci. Technol. B 30, 021204 (2012); http://dx.doi.org/10.1116/1.3692251 (9 pages) | Cited 2 times

Online Publication Date: 6 March 2012

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The additive gas effect of a new plasma-based process for etching the copper film over a dielectric step has been investigated. The addition of different gases, such as Ar, N₂, and CF₄, affected the copper vertical and lateral conversion rates, which are critical to the attack of the cusp region and the sidewall as well as the residue formation. This is due to changes of plasma phase chemistry and ion bombardment energy. Excessive attacks of the cusp region and the sidewall were observed when the chlorine radical concentration was high except for the short plasma exposure time or the sidewall passivation condition. When the slope angle of the dielectric step was small, the cusp structure of the copper film was barely visible; therefore, the excessive plasma attack of the cusp region was negligible. A two step etch process that minimizes excessive attacks of the cusp region and the sidewall as well as the residue formation has been developed. This new process is critical to the practical application of copper in microelectronic products.

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81.65.Cf	Surface cleaning, etching, patterning
82.33.Xj	Plasma reactions (including flowing afterglow and electric discharges)
61.80.Jh	Ion radiation effects
81.65.Rv	Passivation
68.55.-a	Thin film structure and morphology
52.77.Bn	Etching and cleaning

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Electrical properties and radiation detector performance of free-standing bulk n-GaN

In-Hwan Lee, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, E. A. Kozhukhova, V. M. Zaletin, I. M. Gazizov, N. G. Kolin, and S. J. Pearton

J. Vac. Sci. Technol. B 30, 021205 (2012); http://dx.doi.org/10.1116/1.3690644 (7 pages) | Cited 1 time

Online Publication Date: 12 March 2012

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Electrical properties and deep electron and hole trap spectra were measured for undoped n-GaN cut from a thick boule grown by hydride vapor phase epitaxy (HVPE). The material is characterized by a very low concentration of residual donors (10¹³–10¹⁴cm⁻³) in the first 30 μm near the growth surface. The bulk electrical properties were similar to those of standard high quality undoped bulk HVPE n-GaN, with a net donor concentration of ∼10¹⁶cm⁻³ and mobility ∼1000 cm²/V s. The strong decrease of electron concentration in the surface region of the high resistivity GaN was caused by the compensation of shallow residual donors by a high density (∼6 × 10¹⁵cm⁻³) of hole traps with activation energy of 0.2 eV, confined to the compensated region. In addition, other hole traps H5 with activation energy 1.2 eV and concentration 5 × 10¹⁵cm⁻³ were present. These latter traps had similar concentrations in both the high resistivity and standard conducting HVPE GaN. Radiation detectors prepared on the high resistivity material showed charge collection efficiency (CCE) close to 100% for spectrometry of α-particles with energy up to 5.1 MeV. The CCE dependence on voltage indicated a strong trapping of holes in the active region of detectors by the H5 hole traps.

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73.61.Ey	III-V semiconductors
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.60.Gz	Photodetectors (including infrared and CCD detectors)
72.20.Jv	Charge carriers: generation, recombination, lifetime, and trapping

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Morphology of inkjet printed 6,13 bis(tri-isopropylsilylethynyl) pentacene on surface-treated silica

Xiang Hua Wang, Xian Feng Xiong, Long Zhen Qiu, and Guo Qiang Lv

J. Vac. Sci. Technol. B 30, 021206 (2012); http://dx.doi.org/10.1116/1.3693415 (6 pages)

Online Publication Date: 20 March 2012

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The soluble small molecule organic semiconductor, 6,13 bis(tri-isopropylsilylethynyl) pentacene, is inkjet printed on thermally grown silicon dioxide via an orthodichlorobenzene solvent. This paper studies the effect of surface treatment on the size and geometry of sessile drops, as well as the film growth and crystallization behavior on the substrate. The mechanism of morphology control of inkjet-printed arrayed isolating dots or thin film involves the interaction at the interface between the solute molecules and solid substrate. The size and geometry of microscale isolating dots depend on the substrate’s surface uniformity, while the thin film morphology is less affected by this uniformity. Crystallization of the semiconductor requires a relatively high solute concentration at the contact line and is usually accompanied by solute diffusion driven under a concentration gradient. The polar contribution of the surface energy enhances pinning interaction between the substrate and solute molecules and favors the formation of a continuous film.

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68.55.ag	Semiconductors
81.65.-b	Surface treatments
65.40.gp	Surface energy

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Probing temporal evolution of extreme ultraviolet assisted contamination on Ru mirror by x-ray photoelectron spectroscopy

A. Al-Ajlony, A. Kanjilal, M. Catalfano, M. Fields, S. S. Harilal, A. Hassanein, and B. Rice

J. Vac. Sci. Technol. B 30, 021601 (2012); http://dx.doi.org/10.1116/1.3680122 (6 pages) | Cited 2 times

Online Publication Date: 1 February 2012

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Extreme ultraviolet (EUV) radiation mediated carbon contamination and oxidation of the Ru mirror surface, and the corresponding impact on reflectivity were studied. In particular, time-dependent systematic decrease in EUV reflectivity with a 13.5 nm wavelength of light in high vacuum atmosphere was recorded and correlated with the change in chemical composition on the Ru surface as derived from in situ x-ray photoelectron spectroscopy (XPS). The contamination on Ru surface is caused by residual impurities of the test chamber. The recorded XPS spectra show a sudden increase in carbon concentration in the first 1 h followed by a slow but linear growth in the presence of EUV radiation. Further analyses show a slight increase in Ru oxide, whereas the concentration of water molecules decreases continuously. Moreover, the carbon monoxide level at the surface was stabilized after initial increase in concentration for an hour. The impact of water molecules and the accumulation of carbon atoms on the Ru surface are discussed in details.

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81.65.Mq	Oxidation
68.35.Dv	Composition, segregation; defects and impurities
79.60.-i	Photoemission and photoelectron spectra
82.80.Pv	Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.05.js	X-ray photoelectron diffraction
61.80.Ba	Ultraviolet, visible, and infrared radiation effects (including laser radiation)

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Wafer level critical dimension control in spacer-defined double patterning for sub-72 nm pitch logic technology

Ryoung-han Kim, Robert Watso, Youri van Dommelen, Jo Finders, Matthew E. Colburn, and Harry J. Levinson

J. Vac. Sci. Technol. B 30, 021602 (2012); http://dx.doi.org/10.1116/1.3684894 (8 pages)

Online Publication Date: 29 February 2012

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Optimization of critical dimension (CD) uniformity during a spacer-defined double patterning process was explored. Image log-slope (ILS) was used as a major metric in optimizing the CD uniformity as well as the vertical sidewall of the developed resist pattern, which was used as a core-mandrel. In aerial image optimization, mask CD, mask pitch, target CD, defocus, and illumination settings were identified as influential factors in the CD uniformity. An over-exposure from a large mask CD was discovered to be beneficial to the CD maintenance as was a vertical sidewall of the resist pattern, although the CD uniformity across the focus reversely deteriorates with an increase in the ILS. As for wafer-level CD uniformity control, ASML’s Spacer Controller was able to correct CD nonuniformity of post-etch patterns across the intra- and inter-fields of the wafer by adjusting the local dose during the lithographic exposure.

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85.40.Hp	Lithography, masks and pattern transfer
81.16.Nd	Micro- and nanolithography
81.16.Rf	Micro- and nanoscale pattern formation
42.82.Cr	Fabrication techniques; lithography, pattern transfer

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Magnetophoretic assembly and printing of nanowires

Andrew C. Wright and Michael Faulkner

J. Vac. Sci. Technol. B 30, 021603 (2012); http://dx.doi.org/10.1116/1.3683152 (7 pages)

Online Publication Date: 8 March 2012

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Nanowires are a well-established class of materials covering both metals and semiconductors. Although the synthesis of nanowires has been highly developed, their manipulation into specific device structures has lagged behind. Here we report a simple room temperature method for creating directly patterned structures out of nickel nanowires of submicron diameters as previously formed by electrotemplating. Specially shaped magnetic pole-pieces are used to form patterns of these ferromagnetic rods on thin flexible plastic foils, which were then fixed permanently into place either by electrodepositing an additional thin nickel coating or by a UV-curable polymer solution. It is shown that it is possible with oriented and patterned magnetic fields to create both vertically and, by using additional surface tension forces upon drying, horizontally aligned arrays of nickel rods. The authors show that linewidths down to 50 μm can easily be realized with this technique and also show that direct printing of these magnetophoretically assembled structures onto adhesive or rubber substrates is also possible. The simplicity and low-cost inherent in this lithography-free method suggests that it is suitable as a general manufacturing method for nanowire assembly. As an example, a simple field emission display device is demonstrated.

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75.75.Cd	Fabrication of magnetic nanostructures
81.16.Rf	Micro- and nanoscale pattern formation
81.15.Pq	Electrodeposition, electroplating
75.70.Ak	Magnetic properties of monolayers and thin films

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100 keV electron backscattered range and coefficient for silicon

David A. Czaplewski and Leonidas E. Ocola

J. Vac. Sci. Technol. B 30, 021604 (2012); http://dx.doi.org/10.1116/1.3693985 (6 pages) | Cited 1 time

Online Publication Date: 16 March 2012

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The authors have measured the range and intensity of backscattered electrons in silicon from a 100 keV source using a process independent method. Backscattered electrons contributed to the total dose of features written in a negative tone electron beam resist. Instead of measuring the height of the resist and using a contrast curve to convert the resist height to dose, the heights of the features were made equal by adjusting the backscattered contribution through dose assignments. Creating features of equal height eliminated the need to use a contrast curve to convert from resist height to total dose. Also, it allowed for measurements of the backscattered contribution from larger distances. Using a circularly symmetric torus pattern, the three-dimensional backscatter problem was reduced to a 1-dimensional Gaussian form. The authors measured the range of the backscattered electrons, β, to be 31.08 ± 0.06 μm. By varying the writing dose of the pattern, we determined the backscatter coefficient, η, to be 0.63 ± 0.03.

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79.20.Kz	Other electron-impact emission phenomena
81.16.Nd	Micro- and nanolithography
61.46.-w	Structure of nanoscale materials

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Nanoscale scratching of platinum thin films using atomic force microscopy with DLC tips

Xiaohong Jiang, Guoyun Wu, Zuliang Du, Keng-Jeng Ma, Jun-ichi Shirakashi, and Ampere A. Tseng

J. Vac. Sci. Technol. B 30, 021605 (2012); http://dx.doi.org/10.1116/1.3694242 (8 pages) | Cited 2 times

Online Publication Date: 20 March 2012

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Atomic force microscopy experiments were conducted to investigate the scratching characteristics of platinum thin-films for making microscale or nanoscale structures. The wear behavior of the diamond-like-carbon coated tip used was first studied to quantify the wear rate for scratching Pt films. The influences of the scratching parameters on the resulting geometries were then investigated. The scratching parameters to be considered included the applied tip force, number of scratch cycles, and scratch speed. All results indicated that the scratched groove size could be well correlated with and precisely controlled by the applied force and the scratch cycle number. With the aid of the correlation parameters and the known tip wear rate, the scratched geometry can be better controlled and fabricated. The associated scratchability, which is a measure of the easiness of the material to be removed by scratching, can also be determined.

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81.40.Pq	Friction, lubrication, and wear
62.20.Qp	Friction, tribology, and hardness
64.70.Nd	Structural transitions in nanoscale materials
68.37.Ps	Atomic force microscopy (AFM)
68.55.-a	Thin film structure and morphology

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Emission properties of carbon nanowalls on porous silicon

Stanislav A. Evlashin, Yuri A. Mankelevich, Vladimir V. Borisov, Andrey A. Pilevskii, Anton S. Stepanov, Victor A. Krivchenko, Nikolai V. Suetin, and Alexander T. Rakhimov

J. Vac. Sci. Technol. B 30, 021801 (2012); http://dx.doi.org/10.1116/1.3681287 (6 pages) | Cited 1 time

Online Publication Date: 1 February 2012

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For the past two decades various methods of carbon nanostructures growth have been proposed. Special substrate pretreatment methods are generally used to grow carbon nanowalls on silicon substrates and among them are mechanical and catalytic methods and ion bombardment in an rf discharge with bias. This work describes the possibility of growing carbon structures on porous silicon in a dc discharge without any additional pretreatment of the substrate surface. Carbon structures were grown on n- and p-type (100) porous silicon substrates produced by using standard photoelectrochemical etching. The analysis of these carbon structures revealed nanocrystalline carbon with multilayer carbon nanotubes and fibers. All samples demonstrated low field emission thresholds (E_tr < 3 V/μm) and high current densities, showing an achieved current density of more than 6 A/cm² for an electric field of E ∼ 15 V/μm. The authors investigated various modifications of porous silicon samples and carbon structures and demonstrated a practicable technique to create a reproducible uniform spot that varies in size from several millimeters to tens of millimeters. The authors propose a simplified and less expensive alternative to existing methods.

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81.07.De	Nanotubes
81.65.Cf	Surface cleaning, etching, patterning
82.50.-m	Photochemistry
61.48.De	Structure of carbon nanotubes, boron nanotubes, and other related systems
73.63.Fg	Nanotubes
79.70.+q	Field emission, ionization, evaporation, and desorption

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Scanning tunneling microscope-based local electroluminescence spectroscopy of p-AlGaAs/i-GaAs/n-AlGaAs double heterostructure

Kentaro Watanabe, Masakazu Ichikawa, Yoshiaki Nakamura, Shigeyuki Kuboya, Ryuji Katayama, and Kentaro Onabe

J. Vac. Sci. Technol. B 30, 021802 (2012); http://dx.doi.org/10.1116/1.3684985 (6 pages)

Online Publication Date: 13 February 2012

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Local characterization of electroluminescence (EL) from working light-emitting devices is a key to developing and improving their EL properties. The authors developed a scanning tunneling microscope- (STM-) EL technique based on conductive optical fiber probe STM with homemade bipolar sample holder and we demonstrated spatially resolved STM-EL nanospectroscopy of p-AlGaAs/i-GaAs/n-AlGaAs double heterostructure (110) cross-sections. The lateral spatial resolution of the STM-EL measurement was evaluated to be about 0.9 μm, whose origin was attributed to far-field EL collection by the tapered core of the optical fiber probe. This lateral spatial resolution agrees with the estimated spatial resolution of 1.1 μm in lateral and 1.2 μm in depth.

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78.60.Fi	Electroluminescence
68.37.Ef	Scanning tunneling microscopy (including chemistry induced with STM)

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First-principles study of field-emission from carbon nanotubes in the presence of methane

Ali Kashefian Naieni, Parham Yaghoobi, and Alireza Nojeh

J. Vac. Sci. Technol. B 30, 021803 (2012); http://dx.doi.org/10.1116/1.3684980 (7 pages)

Online Publication Date: 17 February 2012

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Carbon nanotubes are promising candidates for field-emitters. It has been shown that the presence of various gases can enhance or degrade the performance of nanotube emitters. Small hydrocarbons are of particular interest because of their ability to enhance the emission properties. The authors report a simulation study of field-emission from a carbon nanotube exposed to methane in various configurations with an emphasis on calculating the emission current. The Hartree–Fock theory combined with a Green’s functions approach was used for the simulations. It was observed that the change in the emission current strongly depends on the particular arrangement of the methane molecules on the nanotube.

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79.70.+q	Field emission, ionization, evaporation, and desorption
73.63.Fg	Nanotubes

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Study of Ti etching and selectivity mechanism in fluorocarbon plasmas for dielectric etch

F. Weilnboeck, E. Bartis, S. Shachar, G. S. Oehrlein, D. Farber, T. Lii, and C. Lenox

J. Vac. Sci. Technol. B 30, 021804 (2012); http://dx.doi.org/10.1116/1.3690643 (10 pages) | Cited 1 time

Online Publication Date: 6 March 2012

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The authors studied the behavior of Ti hardmasks in CF₄/Ar and C₄F₈/Ar discharges using conditions relevant to pattern transfer processes into organosilicate glass (OSG), a reference low-k material investigated in parallel. The authors examined various material erosion stages and determined the dependencies of etch rates (ERs) and etching selectivities (ESs) on the following plasma parameters: self-bias voltage (50–150 V), processing pressure (20–60 mTorr) and %CF₄ (10–30 %) in CF₄/Ar discharges, and O₂ addition (0–10 %) and N₂ addition (0–20 %) to C₄F₈/Ar discharges. Erosion behavior and ERs were characterized by real-time ellipsometric measurements and multilayer optical modeling. These measurements were complemented by x ray photoelectron spectroscopy to study the surface composition. The impact of plasma parameter changes were investigated by comparing ERs and corresponding ESs (OSG ER/Ti ER). During the erosion of Ti, the initially oxidized film surface was transformed into a TiF_x layer (x ∼ 3) covered by a FC film. The FC film thickness strongly depended on the FC feed gas and was significantly thicker for the C₄F₈-based etch (1.5 nm) than for the CF₄-based etch (0.9 nm). Ti erosion was found to be dependent on the energy deposited on the film surface by ion bombardment and to exponentially decrease with increasing FC film thicknesses. For thin FC films (< 1 nm), erosion was ion driven, i.e., “chemical sputtering”, and, for thick FC films (> 1 nm), erosion was limited by the amount of F that could diffuse through the FC layer to the Ti interface. In contrast to organic masking materials, Ti hardmasks have lower ESs for the more polymerizing C₄F₈-based discharges than for CF₄-based discharges. This can be explained by the consumption of the limited supply of F at the OSG surface by C and H impurities, which form volatile CF₄ and HF etch products. For thin FC films and low ion energy deposition by ion bombardment, ESs up to 15 have been achieved.

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81.65.Cf	Surface cleaning, etching, patterning
82.80.Pv	Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.jd	Thickness
52.77.Bn	Etching and cleaning
68.35.Dv	Composition, segregation; defects and impurities
79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces

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Characterization of carbon nanotube film-silicon Schottky barrier photodetectors

Yanbin An, Hemant Rao, Gijs Bosman, and Ant Ural

J. Vac. Sci. Technol. B 30, 021805 (2012); http://dx.doi.org/10.1116/1.3690645 (5 pages) | Cited 1 time

Online Publication Date: 7 March 2012

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The authors fabricate vertical geometry single-walled carbon nanotube (CNT) film/p-type silicon Schottky barrier photodetectors, where the CNT film acts as the transparent metal and silicon as the active semiconductor. The authors experimentally characterize the current-voltage, spectral responsivity, and noise properties of these devices under reverse bias. The authors find that the CNT film–Si Schottky barrier photodetectors exhibit a large photocurrent-to-dark current ratio with responsivity as high as 0.10 A/W due to the high transmittance of the CNT film. The measured current noise spectral density shows a 1/f limited behavior and scales as the square of the reverse bias current. The noise equivalent power of the devices is found to be 1.4 × 10⁻¹⁰ W. A comparison between CNT film devices and devices based on conventional metal electrodes is also carried out. These results provide important insights into the properties and performance of CNT film–Si Schottky barrier photodetectors.

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85.60.Gz	Photodetectors (including infrared and CCD detectors)
85.35.Kt	Nanotube devices

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Dopant depletion in the near surface region of thermally prepared silicon (100) in UHV

Jason L. Pitters, Paul G. Piva, and Robert A. Wolkow

J. Vac. Sci. Technol. B 30, 021806 (2012); http://dx.doi.org/10.1116/1.3694010 (7 pages)

Online Publication Date: 20 March 2012

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Degenerately doped (arsenic) n-type hydrogen terminated silicon (100) samples were prepared using various heat treatments for ultrahigh vacuum scanning tunneling microscopy (STM) and spectroscopy (STS) analysis. Samples heat treated to 1050 °C were found to have a consistent level of doping throughout the bulk and near surface regions. STS revealed tunneling through dopant states consistent with degenerately doped samples. SIMS profiling and HREELS measurements confirmed dopant and carrier concentrations, respectively. Samples heated to 1250 °C were found to have a reduced concentration of dopants in the near surface region. STS measurements showed shifted I/V curves and the loss of tunneling through dopant states in the band gap, indicating reduced dopant concentrations. Observations were confirmed by SIMS and HREELS where depleted dopants and reduced carrier concentrations were measured. The effect of the varying surface dopant concentrations on the STM imaging characteristics of dangling bonds on hydrogen terminated surfaces was also investigated. Understanding the effect of thermal processing on near surface dopant atom concentrations will permit better control over equilibrium charge occupation and charging characteristics of dangling bond midgap states on H:silicon.

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81.20.-n	Methods of materials synthesis and materials processing
71.55.-i	Impurity and defect levels
81.40.Gh	Other heat and thermomechanical treatments
68.37.Ef	Scanning tunneling microscopy (including chemistry induced with STM)
61.72.U-	Doping and impurity implantation

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Behavioral model for electrical response and strain sensitivity of nanotube-based nanocomposite materials

Alborz Amini and Behraad Bahreyni

J. Vac. Sci. Technol. B 30, 022001 (2012); http://dx.doi.org/10.1116/1.3691654 (6 pages) | Cited 1 time

Online Publication Date: 6 March 2012

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An algorithm to study the electrical conductivity of nanocomposite layers, made by dispersing nanotubes inside a polymer structure, is proposed. Conduction is modeled by following the path of electric current through the nanotube network within the polymer. Based on this algorithm, a numerical simulator is developed to study the effect of nanoparticles and nanocomposite film dimensions and concentration on the conductance of a nanocomposite resistor. This simulator is also capable of predicting the behavior of nanocomposite resistors under mechanical strain for devices with different parameters. To verify the simulation results, several test devices with different filler concentrations are fabricated from a composite of SU-8 and multiwall carbon nanotubes. The experimental results agree with the performance anticipated by the simulator, as the applied strain and filler concentration are altered independently. The simulator is capable of illustrating the tradeoffs between conductivity, sensitivity, and repeatability and can be used as a powerful tool to pave the path for designing reliable electronic components from nanocomposite materials.

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73.61.Wp	Fullerenes and related materials
85.35.Kt	Nanotube devices
84.32.Ff	Conductors, resistors (including thermistors, varistors, and photoresistors)
73.63.Fg	Nanotubes
07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

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Simulation of the electron field emission characteristics of a flat panel x-ray source

Chrystian M. Posada, Carlos H. Castaño, Edwin J. Grant, and Hyoung K. Lee

J. Vac. Sci. Technol. B 30, 022201 (2012); http://dx.doi.org/10.1116/1.3680112 (9 pages) | Cited 1 time

Online Publication Date: 6 February 2012

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A distributed flat panel x ray source is designed as an alternative for medical and industrial imaging fields. The distributed x ray source corresponds to a two dimensional array of micro (93 μm) x ray cells similar in format to a field emission display. In this paper the field electron emission characteristics of a single micro x ray cell are presented. The field electron emission from a carbon-nanotube- (CNT-) based cold cathode is simulated using the particle-in-cell code oopic pro. The electron source is simulated as a triode structure, composed of an emitting cathode, extracting grid and anode. The possibility of using focusing lenses to control the trajectory of emitted electrons is also evaluated. The layer of CNT emitters is modeled as Fowler–Nordheim emitters. The field emission characteristics were analyzed for extracting voltages between 20 and 70 V and accelerating voltages between 30 and 120 kV. Under these conditions, J_FN-V curves, energy, and electron distributions at the anode surface were determined. Electron trajectories were determined as well. When no focusing structures were employed, electron trajectories were found to be divergent. When focusing lenses were included in the triode structure, the emitted electrons could be made to converge at the anode. In the cases where focusing structures were used, a dependency between the focal spot size and the extracting grid voltage was found. Results indicated an early feasibility of the proposed device to be employed as an electron source in the distributed flat panel x ray source.

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07.85.-m	X- and γ-ray instruments
85.45.Fd	Field emission displays (FEDs)

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Work function extraction of metal gates with alternate channel materials

Mary Coan, Derek Johnson, Jung Hwan Woo, Nivedita Biswas, Veena Misra, Prashant Majhi, and H. Rusty Harris

J. Vac. Sci. Technol. B 30, 022202 (2012); http://dx.doi.org/10.1116/1.3679412 (5 pages)

Online Publication Date: 8 February 2012

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The effects of a heterojunction on the effective work function in a metal/high κ gate stack are studied and a new structure developed for the extraction of the work function. It is found that when a Ge/Si heterostructure on silicon is low doped and sufficiently thin, then the work function can be extracted in a manner similar to that on a simple silicon substrate. Modifications to the terraced oxide structure are proposed to remove oxidation effects of the alternate channel materials. The extracted work function of thickness variation of TiN is found to be in agreement with that of TiN on a silicon substrate.

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81.05.Hd	Other semiconductors
73.30.+y	Surface double layers, Schottky barriers, and work functions
73.40.Lq	Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

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Stress mapping in strain-engineered silicon p-type MOSFET device: A comparison between process simulation and experiments

Christophe D. Krzeminski

J. Vac. Sci. Technol. B 30, 022203 (2012); http://dx.doi.org/10.1116/1.3683079 (8 pages) | Cited 1 time

Online Publication Date: 13 February 2012

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Strain engineering is the main technological booster used by semiconductor companies for the 65 and 45 nm technology nodes to improve the transistor channel mobility and the electrical performance of logic devices. For 32 and 22 nm nodes, intense research work focuses on the integration and optimization of these different techniques by accumulating the effects of different stressors. Estimating the level and the distribution of the stress field generated in the channel by the fabrication process is a complex issue. The process simulation has a key role to play in order to face the many challenges associated with the stress engineering approach in terms of scalability, yield, and design. The objective of this paper is first to evaluate the stress distribution generated by the two most usual processing steps: contact etch stop liner and embedded SiGe stressors. Next, the final stress field in nanoscale device resulting of these intentional stress sources are evaluated. Process simulation has been able to quantify the global trend observed in relatively close correlation with several experimental studies.

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85.30.Tv

Field effect devices

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Advanced nanodiamond emitter with pyramidal tip-on-pole structure for emission self-regulation

Anurat Wisitsora-at, Shao-Hua Hsu, Weng P. Kang, Jimmy L. Davidson, and Adisorn Tuantranont

J. Vac. Sci. Technol. B 30, 022204 (2012); http://dx.doi.org/10.1116/1.3684425 (6 pages)

Online Publication Date: 13 February 2012

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In this paper, we report an innovative nanodiamond field emitter structure consisting of an individual pyramidal tip sitting on top of a ballast resistor “pole.” The tip-on-pole nanodiamond structures are fabricated by a new mold transfer process that is comprised of reactive-ion-etching of 3.5 μm-thick thermal oxide on Si substrate, anisotropic etching of Si, tip sharpening by thermal oxidation and chemical vapor deposition of nanodiamond. The fabricated tip-on-pole nitrogen-incorporated nanodiamond emitter exhibits a low turn-on electric field of 3.5 V/um and a very high emission current density of ∼1.7 A/cm² at an electric field of ∼7.5 V/um. Analysis of the emission current based on Fowler–Nordheim theory indicates a current regulated regime due to the pole-structured ballast resistor with the resistance value of ∼140 kΩ. Thus, the diamond pole ballast resistor has proven to provide self-limiting of emission current that improves the total current density as well as the emission current stability of the pyramidal nanodiamond emitters. Therefore, the proposed tip-on-pole nanodiamond emitters show great promise for high current and power applications.

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81.16.-c	Methods of micro- and nanofabrication and processing
81.05.ug	Diamond
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Cf	Surface cleaning, etching, patterning

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Mechanism of Ohmic Cr/Ni/Au contact formation on p-GaN

Liubov Magdenko, Gilles Patriarche, David Troadec, Olivia Mauguin, Erwan Morvan, Marie-Antoinette di Forte-Poisson, Konstantinos Pantzas, Abdallah Ougazzaden, Anthony Martinez, and Abderrahim Ramdane

J. Vac. Sci. Technol. B 30, 022205 (2012); http://dx.doi.org/10.1116/1.3688486 (5 pages)

Online Publication Date: 1 March 2012

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Detailed investigation of Ohmic Cr/Ni/Au based contact formation to p-GaN was realized by scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy and compared to the Cr/Au bilayer metallization scheme. The authors found that it is essential to introduce a nickel film in Cr-based contacts and anneal the trilayer structure in air in order to suppress the Shottky barrier and thus obtain the Ohmic contact. Our findings also indicate that oxygen behaves as a dopant dispersed in chromium nitride matrix. Thus Ohmic trilayer Cr/Ni/Au contact to p-GaN annealed in air is formed by Ni–Ga–Au alloy mixed with Au–Ga-doped Cr₂N crystalline composites. Possible ways for improvement of such types of contact are discussed.

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73.40.Ns	Metal-nonmetal contacts
82.80.Ej	X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
85.40.Ls	Metallization, contacts, interconnects; device isolation
81.40.Gh	Other heat and thermomechanical treatments
73.30.+y	Surface double layers, Schottky barriers, and work functions
81.40.Ef	Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

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GaN surface electron field emission efficiency enhancement by low-energy photon illumination

Anatoli Evtukh, Oktay Yilmazoglu, Vladimir Litovchenko, Valery Ievtukh, Hans L. Hartnagel, and Dimitris Pavlidis

J. Vac. Sci. Technol. B 30, 022206 (2012); http://dx.doi.org/10.1116/1.3692253 (4 pages)

Online Publication Date: 7 March 2012

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The enhancement of electron field emission efficiency due to illumination by low energy photons has been investigated. Illumination of electron field emitting GaN cathodes with light energy lower than the bandgap caused an increase of the emission current and a change in the slope of the emission curves as evidenced by Fowler–Nordheim characteristics. The observed properties suggest a change of effective emission barrier due to charge carrier excitation. The influence of light modulation on the field emission current was also investigated with an increase of emission current only observed at lower light modulation frequencies. Two slopes were observed in the Fowler–Nordheim curves without illumination; namely, a larger slope at lower voltages and a smaller slope at higher voltages. Such behavior has been explained by emission from the Γ- and X-valley, respectively. Key field-emission parameters were determined from the Fowler–Nordheim plots and are reported. Another important peculiarity is the relative decrease of the ratio of illuminated to dark current under maximum voltage operation conditions.

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79.70.+q	Field emission, ionization, evaporation, and desorption
73.25.+i	Surface conductivity and carrier phenomena

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Electron emission Si-based resonant-tunneling diode

A. Evtukh, V. Litovchenko, N. Goncharuk, and H. Mimura

J. Vac. Sci. Technol. B 30, 022207 (2012); http://dx.doi.org/10.1116/1.3693977 (8 pages)

Online Publication Date: 20 March 2012

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A new type of field emission resonant tunneling diode has been proposed and investigated both theoretically and experimentally. The diode is based on an Si–SiO_x–Si multilayer cathode containing an SiO_x layer as the input potential barrier, an Si layer as the quantum well, and a vacuum layer as the output potential barrier of a double barrier quantum structure. The calculation predicted the existence of the resonant maxima (three or four depending on the input barrier height) of the current density–electric field dependencies. Frequency dependencies of the diode microwave impedance pointed to the existence of negative conductance resulting from resonant tunneling through an energy level in the quantum well (QW) at electron transit angle values in the interval from zero up to near 2π/3. Also found is a peak of negative conductance on the frequency dependence with the greatest peak value ∼57 S/cm at a frequency of 0.63 THz. The maximum upper frequency of the negative conductance band of more than 2 THz at a transit angle near 0.45π is reached when resonant tunneling occurs through the third resonant level in the QW. Experimental results confirmed the existence of the resonance peak in the investigated resonant-tunneling structure.

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85.30.Kk	Junction diodes
85.30.Mn	Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Be	Quantum well devices (quantum dots, quantum wires, etc.)
85.35.Ds	Quantum interference devices

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Erratum: “Method to pattern etch masks in two inclined planes for three-dimensional nano- and microfabrication” [J. Vac. Sci. Technol. B 29(6), 061604 (2011)]

R. Willem Tjerkstra, Léon A. Woldering, Johanna M. van den Broek, Fred Roozeboom, Irwan D. Setija, and Willem L. Vos

J. Vac. Sci. Technol. B 30, 023401 (2012); http://dx.doi.org/10.1116/1.3683157 (1 page)

Online Publication Date: 15 February 2012

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Abstract Unavailable

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81.16.Rf	Micro- and nanoscale pattern formation
81.65.Cf	Surface cleaning, etching, patterning

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Planar-localized surface plasmon resonance device by block-copolymer and nanoimprint lithography fabrication methods

C. Y. Peter Yang, Elaine L. Yang, Chip A. Steinhaus, Chi-Chun Liu, Paul F. Nealey, and Jack L. Skinner

J. Vac. Sci. Technol. B 30, 026801 (2012); http://dx.doi.org/10.1116/1.3683475 (6 pages) | Cited 1 time

Online Publication Date: 8 February 2012

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The authors report on the integration of delocalized surface plasmon resonances (SPRs) and localized surface plasmon resonances (LSPRs) on a single device. The submicron SPR device was fabricated with nanoimprint lithography (NIL). Gold nanoparticles for LSPR generation were created and deposited via three methods and analyzed with rhodamine 6 G and surface-enhanced Raman spectroscopy (SERS). Compared to drop-cast and thin film annealing methods, gold nanoparticles fabricated from a diblock-copolymer NIL template produced the most significant effect on the charge-transfer component of the SERS enhancement mechanism due to near-field interactions at the 10 nm inter-particle separation region. The authors also report a 26% enhancement of optical resonance with an integrated SPR-LSPR plasmonic device consisting of a two-dimensional submicron aluminum grating fully coupled with gold nanoparticles measuring 20.4 nm in diameter in a water medium. If the 2D aluminum grating were coupled to an optimized nanoparticle SERS device fabricated from a DBCP NIL template, the coupled nanoparticle-grating device could exhibit an even higher enhancement and optical resonance performance.

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81.16.Nd	Micro- and nanolithography
85.40.Hp	Lithography, masks and pattern transfer

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Monolithic integration of silicon CMOS and GaN transistors in a current mirror circuit

W. E. Hoke, R. V. Chelakara, J. P. Bettencourt, T. E. Kazior, J. R. LaRoche, T. D. Kennedy, J. J. Mosca, A. Torabi, A. J. Kerr, H.-S. Lee, and T. Palacios

J. Vac. Sci. Technol. B 30, 02B101 (2012); http://dx.doi.org/10.1116/1.3665220 (6 pages) | Cited 2 times

Online Publication Date: 6 December 2011

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GaN high electron mobility transistors (HEMTs) were monolithically integrated with silicon CMOS to create a functional current mirror circuit. The integrated circuit was fabricated on 100 mm diameter modified silicon-on-insulator (SOI) wafers incorporating a resistive (111) silicon handle substrate and a lightly doped (100) silicon device layer. In a CMOS-first process, the CMOS was fabricated using the (100) device layer. Subsequently GaN was grown by plasma molecular beam epitaxy in windows on the (111) handle substrate surface without wire growth despite using gallium-rich growth conditions. Transmission lines fabricated on the GaN buffer/SOI wafer exhibited a microwave loss of less than 0.2 dB/mm up to 35 GHz. Direct current measurements on GaN HEMTs yielded a current density of 1.0 A/mm and transconductance of 270 mS/mm. At 10 GHz and a drain bias of 28 V, 1.25 mm long transistors demonstrated a small signal gain of 10.7 dB and a maximum power added efficiency of 53% with a concomitant power of 5.6 W. The silicon and GaN transistors were interconnected to form high yield test interconnect daisy chains and a monolithic current mirror circuit. The CMOS output drain current controlled the GaN transistor quiescent current and consequently the microwave gain.

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85.40.Ls	Metallization, contacts, interconnects; device isolation
85.30.Tv	Field effect devices
84.30.Le	Amplifiers

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InGaN laser diodes operating at 450–460 nm grown by rf-plasma MBE

C. Skierbiszewski, M. Siekacz, H. Turski, G. Muzioł, M. Sawicka, A. Feduniewicz-Żmuda, J. Smalc-Koziorowska, P. Perlin, S. Grzanka, Z. R. Wasilewski, R. Kucharski, and S. Porowski

J. Vac. Sci. Technol. B 30, 02B102 (2012); http://dx.doi.org/10.1116/1.3665223 (5 pages) | Cited 3 times

Online Publication Date: 6 December 2011

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This work demonstrates the first true blue laser diodes (LDs) grown by plasma assisted molecular beam epitaxy that operate at the region of 450–460 nm. The single quantum well LDs were grown on several types of c-plane bulk GaN substrates, with threading dislocation densities varying from 10⁴ to 10⁸cm⁻². The key factors that allowed the authors to achieve lasing in true-blue wavelengths are improvements in the growth technology of the InGaN quantum wells attributed to the high nitrogen flux used and the design of the LD structure, which reduced the light losses in the cavity. The authors discuss the influence of the diodes’ design on the parameters of LDs.

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85.35.Be	Quantum well devices (quantum dots, quantum wires, etc.)
42.55.Px	Semiconductor lasers; laser diodes
42.60.By	Design of specific laser systems

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Characterization of Bi₂Te₃ and Bi₂Se₃ topological insulators grown by MBE on (001) GaAs substrates

Xinyu Liu, David J. Smith, Helin Cao, Yong P. Chen, Jin Fan, Yong-Hang Zhang, Richard E. Pimpinella, Malgorzata Dobrowolska, and Jacek K. Furdyna

J. Vac. Sci. Technol. B 30, 02B103 (2012); http://dx.doi.org/10.1116/1.3668082 (4 pages) | Cited 3 times

Online Publication Date: 9 December 2011

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Films of pseudohexagonal Bi₂Te₃, Bi₂Se₃ and their alloys were successfully grown by molecular beam epitaxy on GaAs (001) substrates. The growth mechanism and structural properties of these films were investigated by reflection high-energy electron diffraction, atomic force microscopy, x-ray diffraction (XRD), high-resolution transmission electron microscopy, and Raman spectroscopy and mapping. The results indicate that the epitaxial films are highly uniform and are of high crystalline quality.

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81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
78.66.Nk	Insulators
78.30.Hv	Other nonmetallic inorganics
68.55.aj	Insulators

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Suppressed phase separation in thick GaInAsSb layers across the compositional range grown by molecular beam epitaxy for 1.7–4.9 μm infrared materials

Asli Yildirim and John P. Prineas

J. Vac. Sci. Technol. B 30, 02B104 (2012); http://dx.doi.org/10.1116/1.3668088 (7 pages) | Cited 1 time

Online Publication Date: 13 December 2011

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Thick 2 um Ga_1-xIn_xAs_ySb_1-y layers lattice-matched to (100)-GaSb were grown by molecular beam epitaxy across the compositional range x = 0 to 1. By lowering the growth temperature to the 410 – 450 C range, phase separation was suppressed throughout the miscibility gap, as evidenced in measurements such as photoluminescence, high-resolution x-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. Bright photoluminescence was recorded in the sample series ranging from 1.7 to 4.9 ums.

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81.05.Ea	III-V semiconductors
64.75.Qr	Phase separation and segregation in semiconductors
78.55.Cr	III-V semiconductors
81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy

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Structural and luminescent properties of bulk InAsSb

W. L. Sarney, S. P. Svensson, H. Hier, G. Kipshidze, D. Donetsky, D. Wang, L. Shterengas, and G. Belenky

J. Vac. Sci. Technol. B 30, 02B105 (2012); http://dx.doi.org/10.1116/1.3670749 (4 pages) | Cited 2 times

Online Publication Date: 21 December 2011

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The strong bandgap bowing in the InAs_xSb₁₋_x alloy system allows it to potentially be used for infrared photodetection in the middle and long wavelength range. The authors have used compositionally graded metamorphic buffer layers to accommodate the misfit strain between InAs_xSb₁₋_x alloys and GaSb and InSb substrates in order to reach the long wave infrared range. In this work, we present the characterization of metamorphically grown InAs_xSb₁₋_x films that demonstrate strong photoluminescence in the spectral range from 5 to 9 μm.

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81.05.Ea	III-V semiconductors
78.66.Fd	III-V semiconductors
78.55.Cr	III-V semiconductors
71.20.Nr	Semiconductor compounds

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Structural properties of InAs/InAs_1–xSb_x type-II superlattices grown by molecular beam epitaxy

Lu Ouyang, Elizabeth H. Steenbergen, Yong-Hang Zhang, Kalyan Nunna, Diana L. Huffaker, and David J. Smith

J. Vac. Sci. Technol. B 30, 02B106 (2012); http://dx.doi.org/10.1116/1.3672026 (5 pages)

Online Publication Date: 21 December 2011

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Strain-balanced InAs/InAs_1−xSb_x type-II superlattices (SLs) have been proposed for possible long-wavelength infrared applications. This paper reports a detailed structural characterization study of InAs/InAs_1−xSb_x SLs with varied Sb composition grown on GaSb (001) substrates by modulated and conventional molecular beam epitaxy (MBE). X-ray diffraction was used to determine the SL periods and the average composition of the InAs_1−xSb_x alloy layers. Cross-section transmission electron micrographs revealed the separate In(As)Sb/InAs(Sb) ordered-alloy layers within individual InAs_1−xSb_x layers for SLs grown by modulated MBE. For the SLs grown by conventional MBE, examination by high-resolution electron microscopy revealed that interfaces for InAs_1−xSb_x deposited on InAs were more abrupt, relative to InAs deposited on InAs_1−xSb_x: this feature was attributed to Sb surfactant segregation occurring during the SL growth. Overall, these results establish that strain-balanced SL structures with excellent crystallinity can be achieved with proper design (well thickness versus Sb composition) and suitably optimized growth conditions.

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81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
82.70.Uv	Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)

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Strain-balanced InAs/InAs_1−xSb_x type-II superlattices grown by molecular beam epitaxy on GaSb substrates

Elizabeth H. Steenbergen, Kalyan Nunna, Lu Ouyang, Bruno Ullrich, Diana L. Huffaker, David J. Smith, and Yong-Hang Zhang

J. Vac. Sci. Technol. B 30, 02B107 (2012); http://dx.doi.org/10.1116/1.3672028 (5 pages) | Cited 4 times

Online Publication Date: 21 December 2011

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Strain-balanced InAs/InAs_1−xSb_x type-II superlattices (SLs) on GaSb substrates with 0.27 ≤ x ≤0.33 were grown by molecular beam epitaxy and demonstrated photoluminescence (PL) up to 11.1 μm. The calculated SL bandgap energies agree with the PL peaks to within 5 meV for long-wavelength infrared samples (9.5, 9.9, and 11.1 μm) and to within 9 meV for a mid-wavelength infrared sample (5.9 μm). X-ray diffraction measurements reveal average SL mismatches of less than 0.2%, and the PL full-width-at-half-maximums increase with the mismatch, confirming the importance of strain-balancing for material quality.

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81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
68.65.Cd	Superlattices
71.20.Nr	Semiconductor compounds
78.55.Cr	III-V semiconductors

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Interface properties of (In,Ga)As/GaAs quantum wells grown by solid-phase epitaxy

E. Luna, R. Hey, and A. Trampert

J. Vac. Sci. Technol. B 30, 02B108 (2012); http://dx.doi.org/10.1116/1.3672022 (5 pages) | Cited 1 time

Online Publication Date: 27 December 2011

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(In,Ga)As/GaAs quantum wells (QWs) are successfully fabricated via a thermally induced structural transition from deposited amorphous material to epitaxial films, also known as solid-phase epitaxy (SPE). Although exact processes occurring during the epilayer formation are unknown, it is shown that the method allows the fabrication of high quality QWs with abrupt and symmetric composition profiles. As discussed here, the analysis of the chemical interface (composition profile) of the SPE-grown QWs, and its comparison with the element profiles of similar heterostructures grown by conventional molecular beam epitaxy (C-MBE) provides further insight into the SPE processes. In particular, we find that regardless of the fabrication method (SPE vs C-MBE), the smooth variation of the element concentration with the position across the interface is remarkably well described by a sigmoidal function. Such functional dependence is determined by fundamental processes occurring during the growth; thus suggesting that the basic mechanisms of interface formation are similar in SPE and C-MBE. Finally, the effect of self- and post-growth thermal annealing on SPE QWs is also discussed.

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81.15.Np	Solid phase epitaxy; growth from solid phases
68.55.ag	Semiconductors
68.65.Fg	Quantum wells
73.61.Ey	III-V semiconductors
78.66.Fd	III-V semiconductors

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Molecular beam epitaxy control and photoluminescence properties of InAsBi

S. P. Svensson, H. Hier, W. L. Sarney, D. Donetsky, D. Wang, and G. Belenky

J. Vac. Sci. Technol. B 30, 02B109 (2012); http://dx.doi.org/10.1116/1.3672023 (5 pages) | Cited 1 time

Online Publication Date: 27 December 2011

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Thick InAsBi layers were grown for photoluminescence (PL) characterization. The As to In overpressure ratio was carefully characterized and adjusted to achieve Bi-droplet-free surfaces. A closed loop feedback system was used to maintain the As overpressure during a 5-h deposition sequence. Despite a high degree of control of the growth parameters, evidence for local phase separation was observed in the PL spectra.

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81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag	Semiconductors
78.55.Cr	III-V semiconductors
78.66.Fd	III-V semiconductors

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Rare-earth-metal oxide buffer for epitaxial growth of single crystal GeSi and Ge on Si(111)

Rytis Dargis, Erdem Arkun, Andrew Clark, Radek Roucka, Robin Smith, David Williams, Michael Lebby, and Alexander A. Demkov

J. Vac. Sci. Technol. B 30, 02B110 (2012); http://dx.doi.org/10.1116/1.3673799 (6 pages)

Online Publication Date: 28 December 2011

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Ternary and binary rare-earth oxides that are used as a template buffer, which accommodates the crystal lattice mismatch between substrate and a semiconductor layer, are discussed here. The oxides were grown on Si(111) substrates and exhibit the cubic bixbyite crystal structure. Stabilization of the cubic bixbyite structure of ternary erbium-neodymium oxide and lanthanum oxide was analyzed using structural investigation of the epitaxially grown oxides and ab initio density functional theory calculations. The authors demonstrate that despite the more energetically favorable hexagonal structure of bulk lanthanum oxide a pseudomorphic single crystal cubic lanthanum oxide layer grows under nonequilibrium conditions of a molecular beam epitaxy process on gadolinium oxide. Growth of hexagonal lanthanum oxide begins when the critical thickness of the layer is reached. Germanium was epitaxially grown on the cubic bixbyite lanthanum sesquioxide. Due to a higher surface energy, germanium starts to grow in the form of twinned islands on the oxide layer that later merge, forming a closed layer. X ray diffraction reveals mostly single crystal structure of the germanium layer with stacking twins located only at the interface with the lanthanum oxide layer.

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68.55.ag	Semiconductors
61.72.Mm	Grain and twin boundaries
65.40.gp	Surface energy
81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy

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Photoluminescence study of self-assembled GaAs quantum wires on (631)A-oriented GaAs substrates

E. Cruz-Hernández, D. Vázquez-Cortés, A. Cisneros-de-la-Rosa, E. López-Luna, V. H. Méndez-García, and S. Shimomura

J. Vac. Sci. Technol. B 30, 02B111 (2012); http://dx.doi.org/10.1116/1.3673798 (4 pages)

Online Publication Date: 9 January 2012

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The authors report a low-temperature photoluminescence (PL) study of multiple GaAs layers grown between AlAs(0.6 nm)/GaAs(0.6 nm) short-period superlattice barriers (SLBs) simultaneously grown on both GaAs(631)A and (100) substrates. Five GaAs-layers of different nominal thicknesses (L_W, ranging from 12 to 2.4 nm) were grown by molecular beam epitaxy. By using (631)A-oriented substrates a self-organized and highly ordered corrugation is obtained in the growth of the GaAs layers, and at the end of the SLB growth, flat surfaces are found. Whereas, for the (100)-oriented sample, flat interfaces are confirmed after the growth of GaAs and SLB layers. By reducing L_W below ∼3.6 nm in the (631) sample, strong quantum wire (QWR)-like confinement is achieved as deduced from polarized PL spectroscopy where polarization degrees as large as 0.43 are obtained. The PL emission energy of the (631)-QWRs is redshifted, as compared with the transitions of the (100)-oriented quantum wells, when L_W is reduced. The authors explain this energy shift by the widening of the effective thickness of the confinement regions in the GaAs layers.

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78.55.Cr	III-V semiconductors
81.16.Dn	Self-assembly
81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
68.65.La	Quantum wires (patterned in quantum wells)
81.07.Vb	Quantum wires

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Analysis of defect-free GaSb/GaAs(001) quantum dots grown on the Sb-terminated (2 × 8) surface

Andrew J. Martin, Timothy W. Saucer, Kai Sun, Sung Joo Kim, Guang Ran, Garrett V. Rodriguez, Xiaoqing Pan, Vanessa Sih, and Joanna Millunchick

J. Vac. Sci. Technol. B 30, 02B112 (2012); http://dx.doi.org/10.1116/1.3675455 (5 pages) | Cited 4 times

Online Publication Date: 9 January 2012

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Multilayer and single layer GaSb/GaAs(001) quantum dot structures were grown on an Sb-terminated (2 × 8) surface reconstruction and compared to those grown on an As-terminated (2 × 4) surface reconstruction. Uncapped quantum dots grown on the (2 × 8) surface were approximately 25% smaller in diameter and had a larger width/height aspect ratio. Quantum dots grown on both surfaces were defect free at the quantum dot/spacer layer interface. The dots did not appear to be fully compact when imaged by transmission electron microscopy, which may be due to dissolution and/or quantum ring formation. The quantum dot photoluminescence peak for dots grown on the (2 × 8) surface was brighter but at the same energy as that of dots grown on the (2 × 4) surface. This was likely the result of a higher areal density of dots on the (2 × 8) surface and a lower tendency for them to intermix during capping, resulting in dots of similar size for both samples after capping. Quantum dots grown on the (2 × 8) surface also displayed greater morphological stability when quenched in the absence of Sb.

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68.65.Hb	Quantum dots (patterned in quantum wells)
68.47.Fg	Semiconductor surfaces
78.67.Hc	Quantum dots
78.67.Pt	Multilayers; superlattices; photonic structures; metamaterials
81.40.Gh	Other heat and thermomechanical treatments
68.35.bg	Semiconductors

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Homoepitaxial N-polar GaN layers and HEMT structures grown by rf-plasma assisted molecular beam epitaxy

D. F. Storm, D. J. Meyer, D. S. Katzer, S. C. Binari, Tanya Paskova, E. A. Preble, K. R. Evans, Lin Zhou, and David J. Smith

J. Vac. Sci. Technol. B 30, 02B113 (2012); http://dx.doi.org/10.1116/1.3676175 (7 pages) | Cited 3 times

Online Publication Date: 12 January 2012

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The authors have investigated the growth and structural and electrical properties of homoepitaxial GaN layers and GaN/AlGaN heterostructures grown on free-standing, hydride vapor phase epitaxy grown, N-polar GaN:Fe substrates by rf-plasma molecular beam epitaxy. Secondary-ion mass spectroscopic analysis of unintentionally doped and Be-doped N-polar GaN layers indicate that oxygen is the dominant impurity in all layers and is largely insensitive to growth temperature in the range investigated (675 °C < T_S < 760 °C). Transmission electron microscopy (TEM) indicates that threading dislocations are generated at the regrowth interface in these samples; in contrast to homoepitaxial growth on Ga-polar GaN, and that the density of threading dislocations diminishes as the growth temperature increases. However, examination by TEM indicates that threading dislocations are not generated at the regrowth interface of samples subjected to pregrowth substrate surface cleaning by gallium deposition and desorption and subsequent growth of ultrathin (15 Å) initial AlN layers. N-polar GaN/AlGaN heterostructures grown on Be-doped homoepitaxial N-polar GaN buffers exhibit low buffer leakage and Hall mobilities up to 1680 cm²/Vs at sheet densities of 1.3 × 10¹³cm⁻². High electron mobility transistors have been fabricated on these structures; drain current densities over 700 mA/mm and breakdown voltages as high as 70 V have been measured.

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85.30.Tv	Field effect devices
85.75.Hh	Spin polarized field effect transistors
68.55.A-	Nucleation and growth

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Growth of GaSb_1−xBi_x by molecular beam epitaxy

Yuxin Song (宋禹忻), Shumin Wang, Ivy Saha Roy, Peixiong Shi, and Anders Hallen

J. Vac. Sci. Technol. B 30, 02B114 (2012); http://dx.doi.org/10.1116/1.3672025 (7 pages) | Cited 3 times

Online Publication Date: 18 January 2012

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Molecular beam epitaxy for GaSb_1−xBi_x is investigated in this article. The growth window for incorporation of Bi in GaSb was found. Strategies of avoiding formation of Bi droplets and enhancing Bi incorporation were studied. The Bi incorporation was confirmed by SIMS and RBS measurements. The Bi concentration in the samples was found to increase with increasing growth temperature and Bi flux. The position of GaSb_1−xBi_x layer peak in XRD rocking curves is found to be correlated to Bi composition. Surface and structural properties of the samples were also investigated. Samples grown on GaSb and GaAs substrates were compared and no apparent difference for Bi incorporation was found.

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81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
61.05.Np	Atom, molecule, and ion scattering (for structure determination only)
68.55.J-	Morphology of films
79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces

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Magnetic anisotropy of GaAs/Fe/Au core-shell nanowires grown by MBE

K. Tivakornsasithorn, R. E. Pimpinella, V. Nguyen, X. Liu, M. Dobrowolska, and J. K. Furdyna

J. Vac. Sci. Technol. B 30, 02B115 (2012); http://dx.doi.org/10.1116/1.3678203 (4 pages) | Cited 1 time

Online Publication Date: 24 January 2012

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GaAs/Fe/Au core-shell nanowires were grown on GaAs(111)B substrates by molecular beam epitaxy. Scanning electron microscopy images show that the Fe shell has successfully coated the sidewalls of GaAs nanowires. Magnetic anisotropy of GaAs/Fe core-shell nanowires was studied by ferromagnetic resonance and by superconducting quantum interference device magnetometer. The authors’ results show that the magnetic anisotropy of this novel core-shell nanowire system cannot be simply described by any known theory, as revealed by attempts to use micromagnetic simulation using the Object Oriented MicroMagnetic Framework. The observed features thus suggest the existence of a domain structure that is specific to this new system

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75.30.Gw	Magnetic anisotropy
76.50.+g	Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
81.07.Gf	Nanowires
75.75.Cd	Fabrication of magnetic nanostructures
75.75.Fk	Domain structures in nanoparticles

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Electrical properties of C₆₀ and Si codoped GaAs layers

Jiro Nishinaga and Yoshiji Horikoshi

J. Vac. Sci. Technol. B 30, 02B116 (2012); http://dx.doi.org/10.1116/1.3678205 (4 pages) | Cited 1 time

Online Publication Date: 24 January 2012

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C₆₀ uniformly doped GaAs and C₆₀, Si codoped GaAs layers are grown by a migration enhanced epitaxy method. C₆₀ doped GaAs layers show a single and sharp diffraction peak in x-ray diffraction and only an LO phonon peak is confirmed, indicating that the crystalline quality is fairly good. All of the C₆₀ doped GaAs layers have highly resistive characteristics, and C₆₀, Si codoped GaAs layers show n-type conductivity only when the Si concentration is of the same order or greater than the total carbon concentrations. At low temperatures the conductivity of the C₆₀, Si codoped GaAs layers increases with exposure to light whose energy is below the GaAs bandgap energy. The electron concentrations and mobilities of the layers are confirmed to be increased under illumination by wavelengths between 900 and 1100 nm. These results imply that the electron transitions from the valence band to the trap levels and from the trap levels to the conduction band occur simultaneously as if the traps act as intralevels. As a result, the carrier concentrations are enhanced in the same way they would be if the excitation was above the GaAs bandgap energy.

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73.61.Ey	III-V semiconductors
78.30.Fs	III-V and II-VI semiconductors
78.66.Fd	III-V semiconductors
81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag	Semiconductors
72.60.+g	Mixed conductivity and conductivity transitions

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Molecular beam epitaxial growth and characterization of nitrogen δ-doped AlGaAs/GaAs quantum wells

Shin-ichiro Furuse, Kengo Sumiya, Masato Morifuji, and Fumitaro Ishikawa

J. Vac. Sci. Technol. B 30, 02B117 (2012); http://dx.doi.org/10.1116/1.3678204 (5 pages)

Online Publication Date: 1 February 2012

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The authors carry out δ-doping at the middle of AlGaAs/GaAs quantum wells employing molecular beam epitaxy and varying the nitrogen coverage up to 0.5 monolayers. Transmission electron micrography and x ray diffraction indicate the introduction of a nitrogen δ-doped layer with precisely controlled position and nitrogen coverage. Photoluminescence spectra obtained for the samples show clear redshift of spectral peak positions depending on the amount of nitrogen, suggesting the band structure is modified by the δ-doping. The growth can be carried out at a substrate temperature of 560 °C. The growth temperature, which is high compared with that of standard dilute nitride compounds, could suppress the formation of growth-induced defects, resulting in the weak effect of post-growth thermal annealing on the characteristics of room-temperature photoluminescence.

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81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj	III-V and II-VI semiconductors
61.72.Cc	Kinetics of defect formation and annealing
78.55.Cr	III-V semiconductors
78.66.Fd	III-V semiconductors
78.67.De	Quantum wells

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InAs MOS devices passivated with molecular beam epitaxy-grown Gd₂O₃ dielectrics

C. A. Lin, M. L. Huang, P.-C. Chiu, H.-K. Lin, J.-I. Chyi, T. H. Chiang, W. C. Lee, Y. C. Chang, Y. H. Chang, G. J. Brown, J. Kwo, and M. Hong

J. Vac. Sci. Technol. B 30, 02B118 (2012); http://dx.doi.org/10.1116/1.3678206 (4 pages)

Online Publication Date: 1 February 2012

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InAs MOS devices passivated with molecular beam epitaxy (MBE)-grown Gd₂O₃ 2–3 monolayers thick followed by an Al₂O₃ cap have demonstrated excellent electrical performances and interfacial properties. Band offset energies of in situ atomic-layer-deposited (ALD)-Al₂O₃/MBE-Gd₂O₃/InAs and ALD-Al₂O₃/InAs were determined by in situ x-ray photoelectron spectroscopy in conjunction with Fowler–Nordheim tunneling current analysis. A conduction-band offset energy (ΔE_c) and a valence-band offset energy of 2.3 and 3.92 eV for ALD-Al₂O₃/InAs were determined, respectively. The insertion of a Gd₂O₃ layer increases the value of ΔE_c by nearly 0.1 eV as compared to the case for Al₂O₃ directly deposited on InAs. The distribution of interfacial density of states (D_it) within the InAs bandgap, deduced by the conductance method at 77 K, gives a low D_it value of 10¹² cm⁻² eV⁻¹ near the conduction-band edge. Moreover, with energy band engineering in the heterostructure, gate-first depletion channel InAs MOSFETs have produced drain current density of 46 μA/μm and transconductance of 17 μS/μm for 12-μm-gate-length devices at 300 K.

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85.30.Tv

Field effect devices

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Molecular beam epitaxy growth of AlGaN quantum wells on 6H-SiC substrates with high internal quantum efficiency

Wei Zhang, A. Yu. Nikiforov, C. Thomidis, J. Woodward, H. Sun, Chen-Kai Kao, D. Bhattarai, A. Moldawer, L. Zhou, D. J. Smith, and T. D. Moustakas

J. Vac. Sci. Technol. B 30, 02B119 (2012); http://dx.doi.org/10.1116/1.3678208 (5 pages) | Cited 5 times

Online Publication Date: 1 February 2012

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The authors report the development of high internal quantum efficiency AlN/AlGaN/AlN double heterostructures and AlGaN/AlN multiple quantum wells (MQWs) grown on 6H-SiC and 4H-SiC substrates of various miscuts by plasma-assisted molecular-beam epitaxy. The authors find that the luminescence spectra for identical MQWs show a single peak across the gap, with a wavelength that is redshifted by ∼20 nm as the excess Ga during growth of the wells increases. The internal quantum efficiency of the double heterostructures emitting at 250 nm is found to be 43%, and that of the multiple quantum wells emitting at 245 nm is 68%. These results suggest that AlGaN alloys on SiC substrates are capable of producing deep-ultraviolet emitters with high efficiency. The authors propose that these results can be accounted for by the introduction of lateral band structure potential fluctuations due to the changing of the growth mode from physical vapor phase epitaxy to liquid phase epitaxy (LPE) as the excess gallium increases. In this LPE mode the arriving active nitrogen species from the plasma source and aluminum atoms from the aluminum effusion cells dissolve in the excess liquid gallium and incorporate into the film from the liquid phase.

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81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
81.15.Lm	Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.65.Fg	Quantum wells
78.55.Cr	III-V semiconductors
81.05.Ea	III-V semiconductors
81.07.St	Quantum wells

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Shallow defect states in GaAs responsible for GaAs bandgap upconversion induced by electron beam during MBE growth

David M. Tex and Itaru Kamiya

J. Vac. Sci. Technol. B 30, 02B120 (2012); http://dx.doi.org/10.1116/1.3679547 (4 pages)

Online Publication Date: 1 February 2012

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Upconversion through excitation of bulk GaAs is investigated by change in crystal growth conditions with electron beam (e-beam). The upconverted photoluminescence intensity is enhanced several times by striking the source fluxes with e-beam during molecular beam epitaxy (MBE) growth. Experimental evidence for a shallow intermediate state being responsible for this upconversion is presented. It is suggested that the intermediate state may be formed by shallow exciton trap states induced by As anti-site defects, which can be increased with e-beam during MBE growth.

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71.55.Eq	III-V semiconductors
78.55.Cr	III-V semiconductors
81.05.Ea	III-V semiconductors
81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
61.80.Fe	Electron and positron radiation effects
71.20.Ps	Other inorganic compounds

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Growth of GaN_xAs_yP_1−x−y alloys on GaP(100) by gas-source molecular beam epitaxy

Yan-Jin Kuang (邝彦瑾), San-Wen Chen (陳尚文), Hua Li (李华), Sunil K. Sinha, and Charles Wuching Tu

J. Vac. Sci. Technol. B 30, 02B121 (2012); http://dx.doi.org/10.1116/1.3680603 (5 pages) | Cited 3 times

Online Publication Date: 8 February 2012

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The authors report epitaxial growth of dilute nitride GaN_xAs_yP_1−x−y on GaP(100) via a linearly graded GaAs_xP_1−x metamorphic buffer. The As content is in situ determined by group-V-induced reflection high energy electron diffraction intensity oscillation, while the N content is determined by x-ray diffraction. Room-temperature photoluminescence (PL) is observed for the top GaN_xAs_yP_1−x−y layer and in temperature dependent PL, the peak position shows S-shape curve, indicative of defect states in the bandgap. Room-temperature PL intensity is drastically increased after rapid thermal annealing (RTA) and the results suggest GaN_xAs_yP_1−x−y with different N content requires different optimal RTA temperature for optical performance.

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81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd	III-V semiconductors
78.55.Cr	III-V semiconductors
71.55.Eq	III-V semiconductors
61.72.Cc	Kinetics of defect formation and annealing

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Influence of temperature ramp on the materials properties of GaSb grown on ZnTe using molecular beam epitaxy

Jin Fan, Lu Ouyang, Xinyu Liu, Ding Ding, Jacek K. Furdyna, David J. Smith, and Yong-Hang Zhang

J. Vac. Sci. Technol. B 30, 02B122 (2012); http://dx.doi.org/10.1116/1.3681280 (5 pages) | Cited 3 times

Online Publication Date: 15 February 2012

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This paper reports high-quality GaSb grown on ZnTe using molecular beam epitaxy with a temperature ramp during growth, and investigates the influence of the temperature ramp on material properties. During growth, in situ reflection-high-energy electron diffraction shows rapid and smooth transition from ZnTe surface reconstruction to GaSb surface reconstruction. Post-growth structural characterization using x-ray diffraction and transmission electron microscopy reveals smooth interface morphology and low defect density. Strong photoluminescence emission is observed up to 200 K. The sample grown with a temperature ramp from 360 to 470 °C at a rate of 33 °C/min showed the narrowest bound exciton emission peak with a full width at half maximum of 15 meV.

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68.55.ag	Semiconductors
68.47.Fg	Semiconductor surfaces
78.55.Cr	III-V semiconductors
78.66.Fd	III-V semiconductors
81.05.Ea	III-V semiconductors
81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy

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Optimization of Ohmic metal contacts for advanced GaAs-based CMOS device

W. H. Chang, T. H. Chiang, T. D. Lin, Y. H. Chen, K. H. Wu, T. S. Huang, M. Hong, and J. Kwo

J. Vac. Sci. Technol. B 30, 02B123 (2012); http://dx.doi.org/10.1116/1.3687418 (4 pages)

Online Publication Date: 23 February 2012

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Ohmic contact resistivity of a nongold Pd/Ge/Ti/Pt on highly doped molecular beam epitaxy grown n-GaAs and In_0.2Ga_0.8As/GaAs (∼2 × 10¹⁸cm⁻³) has been investigated by varying Pd/Ge thicknesses and rapid thermal annealing (RTA) temperature/duration. An optimized Ohmic contact was obtained in the samples with Pd/Ge of 30 nm/30 nm, using RTA at 300 °C for 10 s. Low Ohmic contact resistivity of 5.4 × 10⁻⁷ Ω cm² on n-In_0.2Ga_0.8As has been achieved. The mechanism of the contact resistivity reduction has been studied using the energy-dispersive x-ray spectroscopy depth profile.

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73.40.Sx	Metal-semiconductor-metal structures
81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
81.40.Gh	Other heat and thermomechanical treatments
82.80.Ej	X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
73.40.Cg	Contact resistance, contact potential
73.40.Ns	Metal-nonmetal contacts

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MBE growth and characterization of Mn-doped InN

Jessica H. Chai, Thomas H. Myers, Young-Wook Song, Roger J. Reeves, Wojciech M. Linhart, Richard J. H. Morris, Timothy D. Veal, Mark G. Dowsett, Christopher F. McConville, and Steven M. Durbin

J. Vac. Sci. Technol. B 30, 02B124 (2012); http://dx.doi.org/10.1116/1.3687903 (5 pages) | Cited 1 time

Online Publication Date: 23 February 2012

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The majority of InN doping studies have primarily focused on Mg, as it has previously been used to successfully realize p-type GaN. Here, we consider an alternative dopant—Mn—as a possible acceptor candidate in InN. Magnetotransport, x ray photoelectron spectroscopy, and photoluminescence were used to investigate electrical and optical properties of a series of Mn-doped InN thin films grown using molecular beam epitaxy. Evidence of acceptor behavior was observed only for moderate (10¹⁷ cm⁻³) doping levels. At a doping level around 10¹⁷ cm⁻³, light hole features appear in the quantitative mobility spectrum analysis, the surface Fermi level shifts downwards towards the valence band, and low energy features appear in the low temperature photoluminescence spectra.

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81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag	Semiconductors
72.20.My	Galvanomagnetic and other magnetotransport effects
78.55.Cr	III-V semiconductors
79.60.Bm	Clean metal, semiconductor, and insulator surfaces

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Optical and electrical properties of Si-doped GaAs films grown on (631)-oriented substrates

D. Vázquez-Cortés, E. Cruz-Hernández, V. H. Méndez-García, S. Shimomura, and M. López-López

J. Vac. Sci. Technol. B 30, 02B125 (2012); http://dx.doi.org/10.1116/1.3687904 (4 pages) | Cited 1 time

Online Publication Date: 23 February 2012

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This work studies the Si-doping of GaAs on (631)-oriented substrates as a function of the As₄-beam equivalent pressure (P_As). The electrical properties obtained by Hall effect measurements show that the mobility of the layers grown on (631)-substrates present changes related to carrier compensation processes and the Si-doping changes from p- to n-type when P_As is increased. The optical properties of the samples, as observed by photoluminescence (PL) spectroscopy, modified according to the electrical characteristics. For (631)-samples, when P_As is increased the energy of the maximum intensity PL peak redshifts in the p-type region but, after the threshold of the conduction type conversion, the peak blueshifts in the n-type region. The variation of the PL excitation intensity also shifts the emission energy of the samples as a consequence of the increasing recombination rate for close pairs in donor acceptor pair recombination. Photoluminescence as a function of temperature shows that the activation energy of the PL lines transition is enhanced as P_As is increased.

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78.66.Fd	III-V semiconductors
61.72.uj	III-V and II-VI semiconductors
73.50.Jt	Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ey	III-V semiconductors
78.55.Cr	III-V semiconductors

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Successful growth of Cu₂Se-free CuGaSe₂ by migration-enhanced epitaxy

Miki Fujita, Tomohiro Sato, Tsuyoshi Kitada, Atsushi Kawaharazuka, and Yoshiji Horikoshi

J. Vac. Sci. Technol. B 30, 02B126 (2012); http://dx.doi.org/10.1116/1.3690456 (5 pages) | Cited 1 time

Online Publication Date: 29 February 2012

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CuGaSe₂ films were grown on GaAs (001) substrates by migration enhanced epitaxy, where Cu + Ga and Se are alternately deposited. The in situ reflection high energy electron diffraction observation during growth revealed that the segregation of Cu₂Se on CuGaSe₂ can be detected by anomalous diffraction patterns. When the Cu₂Se segregation takes place, a distorted pattern appears in both Cu + Ga and Se deposition periods. By optimizing the flux ratios, the anomalous diffraction disappears, and we succeeded in growing high quality CuGaSe₂ single crystal layers free from Cu₂Se segregation on GaAs (001) substrates. The authors also found that, in the CuGaSe₂/GaAs wafers with Cu₂Se segregation, a high density of voids is often observed at the substrate surface. These voids disappeared when the Cu₂Se-free growth conditions were employed. Ga atoms near the GaAs substrate surface were probably drawn out by excess Cu atoms in the growing layer to form CuGaSe₂, leading to the creation of voids with fairly large size.

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81.05.Hd	Other semiconductors
81.15.Hi	Molecular, atomic, ion, and chemical beam epitaxy
64.75.Qr	Phase separation and segregation in semiconductors
68.55.ag	Semiconductors
61.72.Qq	Microscopic defects (voids, inclusions, etc.)

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Application of GaInNAs for the gain medium of a photonic crystal microcavity

H. Nagatomo, K. Kukita, H. Goto, R. Nakao, K. Nakano, F. Ishikawa, M. Morifuji, and M. Kondow

J. Vac. Sci. Technol. B 30, 02B127 (2012); http://dx.doi.org/10.1116/1.3691651 (4 pages) | Cited 1 time

Online Publication Date: 6 March 2012

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The authors demonstrated the functionality of a circularly arranged submicron scale optical cavity with a GaInNAs gain medium and an AlO_x cladding layer within a two-dimensional photonic crystal slab. The GaInNAs gain has negligible optical degradations due to process damage, probably stemming from the suppressed diffusion carriers and the small surface recombination velocity of the material. The calculated spectrum when using a finite different time domain simulation provides a cavity mode containing a whispering gallery mode at a wavelength close to 1.3 μm. An observation of the tuned spectral peaks related to the cavity mode shows this cavity has promise for future device applications.

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78.67.Pt	Multilayers; superlattices; photonic structures; metamaterials
73.25.+i	Surface conductivity and carrier phenomena
72.20.Jv	Charge carriers: generation, recombination, lifetime, and trapping

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RHEED transients during InAs quantum dot growth by MBE

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Mar 2012

Volume 30, Issue 2, Articles (02xxxx)