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May 2013

Volume 31, Issue 3, Articles (03xxxx)

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Molecular beam epitaxial growth of ultralow absorption GaN high electron mobility transistor material on sapphire substrates for infrared transparent conductors

William E. Hoke, Amanda J. Kirchner, John J. Mosca, Daniel P. Resler, Theodore D. Kennedy, Michael Holz, Amanda J. Kerr, and Steven R. Collins

J. Vac. Sci. Technol. B 31, 03C101 (2013); http://dx.doi.org/10.1116/1.4769895 (5 pages)

Online Publication Date: 7 December 2012

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GaN HEMT structures have been grown on sapphire substrates that exhibit very low absorption loss at 1 μm and low sheet resistance, which are attractive properties for infrared transparent conductors. Initial GaN HEMT/sapphire films showed highly variable absorptions, which were determined to be caused by oxygen outdiffusion from the sapphire substrate into the AlN buffer layer. Growth conditions were modified enabling reproducible growth of low absorption and low sheet resistance material. Absorption losses as low as 0.1% with concomitant film conductivities of 350 Ω/sq or less were demonstrated. Consequently, free carriers in the GaN HEMT channel do not cause significant infrared absorption. The concomitant properties of low absorption and low sheet resistance exceed the properties of transparent conducting oxides. These properties of the GaN HEMT/sapphire structure are also more thermally stable compared to transparent conducting oxides. The low absorption characteristic of the GaN HEMT/sapphire structure is expected to extend into the visible spectrum enabling visible transparent conductor applications as well.
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85.30.Tv Field effect devices
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Molecular beam epitaxy of highly mismatched N-rich GaN1−xSbx and InN1−xAsx alloys

Sergei V. Novikov, Kin M. Yu, Alejandro Levander, Douglas Detert, Wendy L. Sarney, Zuzanna Liliental-Weber, Martin Shaw, Robert W. Martin, Stefan P. Svensson, Wladek Walukiewicz, and C. Thomas Foxon

J. Vac. Sci. Technol. B 31, 03C102 (2013); http://dx.doi.org/10.1116/1.4774028 (5 pages)

Online Publication Date: 8 January 2013

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GaN materials alloyed with group V anions form the so-called highly mismatched alloys (HMAs). Recently, the authors succeeded in growing N-rich GaN1−xAsx and GaN1−xBix alloys over a large composition range by plasma-assisted molecular beam epitaxy (PA-MBE). Here, they present first results on PA-MBE growth and properties of N-rich GaN1−xSbx and InN1−xAsx alloys and compare these with GaN1−xAsx and GaN1−xBix alloys. The enhanced incorporation of As and Sb was achieved by growing the layers at extremely low growth temperatures. Although layers become amorphous for high As, Sb, and Bi content, optical absorption measurements show a progressive shift of the optical absorption edge to lower energy. The large band gap range and controllable conduction and valence band positions of these HMAs make them promising materials for efficient solar energy conversion devices.
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88.40.J- Types of solar cells
71.20.Gj Other metals and alloys
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Metastable CdSe/MgSe quantum wells prepared by MBE with near IR intersubband absorption

Aidong Shen, Guopeng Chen, Kuaile Zhao, Jung-Tso Lai, and Maria C. Tamargo

J. Vac. Sci. Technol. B 31, 03C103 (2013); http://dx.doi.org/10.1116/1.4789478 (3 pages)

Online Publication Date: 30 January 2013

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The authors report, for the first time, the growth of a metastable CdSe/MgSe quantum well structure by molecular beam epitaxy. The structure was grown on InP substrate with thin ZnCdSe and InGaAs buffers. To maintain the zincblende structure of MgSe (which naturally favors rocksalt structure), a ZnCdSe spacer layer was inserted between CdSe/MgSe quantum wells. The structural and optical properties of the sample were characterized by high-resolution x-ray diffraction and photoluminescence measurements. Intersubband transitions in the near infrared region were observed.
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81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
78.67.De Quantum wells
81.05.Dz II-VI semiconductors

Structural and electrical characterization of InN, InGaN, and p-InGaN grown by metal-modulated epitaxy

Michael Moseley, Brendan Gunning, Jonathan Lowder, W. Alan Doolittle, and Gon Namkoong

J. Vac. Sci. Technol. B 31, 03C104 (2013); http://dx.doi.org/10.1116/1.4790865 (6 pages)

Online Publication Date: 8 February 2013

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InN, high indium content InGaN, and Mg-doped InGaN were grown by metal modulated epitaxy (MME). Transient reflection high-energy electron diffraction intensities were analyzed during the growth of InN and found to be similar to that previously reported for GaN and AlN. The x-ray diffraction rocking curve and background electron concentration of InN grown by MME were found to be respectable in comparison to recent reports in literature. InGaN alloys grown by MME were also investigated, and a method for detecting indium surface segregation was demonstrated. It was found that the shutter modulation scheme could be modified to prevent phase separation by indium surface segregation, and a range of single-phase InGaN samples with indium contents throughout the miscibility gap were grown. Using the discovered method of suppressing phase separation, several p-InxGa1 − xN samples were grown with indium contents from x = 0 to 0.22. A maximum hole concentration of 2.4 × 1019 cm−3 was detected by Hall effect characterization, demonstrating feasibility of these p-InGaN layers for use in several device applications.
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68.55.ag Semiconductors
68.35.Dv Composition, segregation; defects and impurities
73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
64.75.Bc Solubility

MBE grown GaAsBi/GaAs double quantum well separate confinement heterostructures

Dongsheng Fan, Perry C. Grant, Shui-Qing Yu, Vitaliy G. Dorogan, Xian Hu, Zhaoquan Zeng, Chen Li, Michael E. Hawkridge, Mourad Benamara, Yuriy I. Mazur, Gregory J. Salamo, Shane R. Johnson, and Zhiming M. Wang

J. Vac. Sci. Technol. B 31, 03C105 (2013); http://dx.doi.org/10.1116/1.4792518 (5 pages)

Online Publication Date: 14 February 2013

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GaAsBi/GaAs double quantum wells and double quantum well separate confinement heterostructures are grown at low temperatures using molecular beam epitaxy. Methods of achieving identical quantum wells in double quantum well structures without growth interruption are proposed and implemented. Cross-sectional transmission electron microscopy and room temperature photoluminescence measurements indicate that the samples have excellent structural and optical properties. The high optical quality of the samples is attributed to the surfactant effect of Bi throughout the low temperature growth of GaAs and AlGaAs layers. The proposed approach can be extended to grow laser diode structures with multiple quantum well separate confinement heterostructures containing more identical quantum wells.
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68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
78.67.De Quantum wells
81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.55.Px Semiconductor lasers; laser diodes

MBE growth of GaSb-based photodetectors on 6-inch diameter GaAs substrates via select buffers

Joel M. Fastenau, Dmitri Lubyshev, Yueming Qiu, Amy W. K. Liu, Edwin J. Koerperick, Jon T. Olesberg, and Dennis Norton, Jr.

J. Vac. Sci. Technol. B 31, 03C106 (2013); http://dx.doi.org/10.1116/1.4792516 (6 pages)

Online Publication Date: 15 February 2013

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GaSb-based, 6.1 Å lattice-constant, infrared photodetector materials were grown on large diameter, 6-in. GaAs substrates by molecular beam epitaxy. Multiple metamorphic buffer architectures, including bulk GaSb nucleation, AlAsSb superlattices, and graded GaAsSb ternary alloys, were investigated to bridge the 7.8% mismatch gap between the GaAs substrates and the GaSb-based epitaxial layers. Unique surface morphologies and crystal structure properties, as revealed by atomic force microscopy and cross-section transmission electron microscopy, pointed to different relaxation mechanisms for different buffer architectures. GaSb nucleation results in a more island-like surface morphology with a mix of 90° misfit and 60°-type threading dislocations, while the graded ternary buffer results in a cross-hatch surface morphology with effective filtering of the threading dislocations. Low root-mean-square roughness values of 5–20 Å were obtained for this type of metamorphic epilayer growth. A generic InAsSb/AlAsSb nBn photodiode structure, where the first “n” is the contact layer, the “B” is the wide-bandgap barrier layer, and the second “n” is the n-type narrow bandgap absorber layer, with ∼4 μm cutoff wavelength was grown on 6 in. GaAs substrates using the different metamorphic buffers. Cross-wafer optical and structural measurements showed excellent epitaxial layer uniformity, with PL wavelength variation <0.1 μm. Dark currents of 2–3 × 10−6 A/cm2 were measured on devices fabricated from the photodiode material grown on GaAs. This was about 5-times higher than measured on the same structure grown on GaSb substrates. This work demonstrates a promising path to satisfy the increasing demand for even larger area focal plane array detectors in a commercial production environment.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.60.Dw Photodiodes; phototransistors; photoresistors

Three-dimensional GaN templates for molecular beam epitaxy of nonpolar InGaN/GaN coaxial light-emitting diodes

Ashwin K. Rishinaramangalam, Michael N. Fairchild, Stephen D. Hersee, Ganesh Balakrishnan, and Daniel F. Feezell

J. Vac. Sci. Technol. B 31, 03C107 (2013); http://dx.doi.org/10.1116/1.4792519 (7 pages)

Online Publication Date: 15 February 2013

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This work highlights the development of three-dimensional (3D) GaN templates grown by metal organic vapor phase epitaxy (MOVPE). These templates are ideally suited for the subsequent growth of nonpolar (1math00) m-plane InGaN-based coaxial wire/wall light-emitting diodes (LEDs) using molecular beam epitaxy (MBE). The use of MBE is expected to result in increased indium incorporation on the (1math00) m-plane, compared with growth using MOVPE, which provides an attractive approach for the development of nonpolar green LEDs. While planar free-standing m-plane GaN substrates are prohibitively expensive (approximately ∼$500 per cm2), the coaxial LED approach offers an attractive lower-cost alternative. These nonpolar nanoscale LED templates are also free from threading dislocations and are expected to provide a number of benefits, including higher light extraction and a larger effective active region area. Previous work in our group has demonstrated the controlled growth of GaN nanowires using a catalyst-free selective-area MOVPE growth method. The present work extends this method to grow 3D GaN templates in various aperture geometries, resulting in smooth m-plane GaN using a scalable and industrially viable high-quality GaN growth technique. In addition to m-plane sidewalls, the authors also demonstrate semipolar (1math01) inclined sidewalls. This orientation has been shown to incorporate indium at a higher rate during MOVPE growth, in comparison to both c-plane and m-plane.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.60.Jb Light-emitting devices
68.55.ag Semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Causes and elimination of pyramidal defects in GaSb-based epitaxial layers

Lee M. Murray, Asli Yildirim, Sydney R. Provence, Dennis T. Norton, Thomas F. Boggess, and John P. Prineas

J. Vac. Sci. Technol. B 31, 03C108 (2013); http://dx.doi.org/10.1116/1.4792515 (6 pages) | Cited 1 time

Online Publication Date: 20 February 2013

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Here, the authors report on the occurrence, cause, and elimination of pyramidal defects in layers of GaSb grown by molecular beam epitaxy on GaSb substrates. These defects are typically 3–8 nm high, 1–3 μm in diameter, and shaped like pyramids. Their occurrence in the growth of GaSb buffer layers can propagate into subsequent layers such as GaSb, GaInAsSb, and GaSb/InAs superlattices. Defects are nucleated during the early stages of growth after the thermal desorption of native oxide from the GaSb substrate. These defects grow into pyramids due to a repulsive Ehrlich–Schwoebel potential on atomic step edges leading to an upward adatom current. The defects reduce in density with growth of GaSb. The insertion of a thin AlAsSb layer into the early stages of the GaSb buffer increases the rate of elimination of the defects, resulting in a smooth surface within 500 nm. The acceleration of defect reduction is due to the temporary interruption of step-flow growth induced by the AlAsSb layer. This leads to a reduced isolation of the pyramids from the GaSb epitaxial layer and allows the pyramidal defects to smooth out.
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71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
64.60.qj Studies of nucleation in specific substances
68.55.ag Semiconductors
68.65.Cd Superlattices

Molecular beam epitaxial growth of high-reflectivity and broad-bandwidth ZnTe/GaSb distributed Bragg reflectors

Jin Fan, Xinyu Liu, Lu Ouyang, Richard E. Pimpinella, Margaret Dobrowolska, Jacek K. Furdyna, David J. Smith, and Yong-Hang Zhang

J. Vac. Sci. Technol. B 31, 03C109 (2013); http://dx.doi.org/10.1116/1.4793475 (4 pages)

Online Publication Date: 25 February 2013

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This paper reports the molecular beam epitaxial growth and characterization of high-reflectivity and broad-bandwidth distributed Bragg reflectors (DBRs) made of ZnTe/GaSb quarter-wavelength (λ/4) layers for optoelectronic applications in the midwave infrared spectral range (2–5 μm). A series of ZnTe/GaSb DBRs has been successfully grown on GaSb (001) substrates using molecular beam epitaxy (MBE). During the MBE growth, a temperature ramp was applied to the initial growth of GaSb layers on ZnTe to protect the ZnTe underneath from damage due to thermal evaporation. Post-growth characterization using high-resolution x-ray diffraction, atomic force microscopy, and transmission electron microscopy reveals smooth surface morphology, low defect density, and coherent interfaces. Reflectance spectroscopy results show that a DBR sample of seven λ/4 pairs has a peak reflectance as high as 99.0% centered at 2.56 μm with a bandwidth of 517 nm.
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42.79.Bh Lenses, prisms and mirrors
78.30.Fs III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.bg Semiconductors
68.55.ag Semiconductors

Growth and characterization of GaP/GaNP core/shell nanowires

Supanee Sukrittanon, YanJin Kuang (邝彦瑾), and Charles W. Tu

J. Vac. Sci. Technol. B 31, 03C110 (2013); http://dx.doi.org/10.1116/1.4793476 (4 pages)

Online Publication Date: 25 February 2013

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This paper reports on self-catalyzed vertical GaP nanowires (NWs) and GaP/GaNP core/shell NWs grown on Si(111) by gas-source molecular beam epitaxy. It was found that GaP NWs have a growth window from ∼585 °C to ∼615 °C. The low temperature limit is set by lack of adatom mobility, while the high temperature limit is set by unattainable supersaturation condition of vapor–liquid–solid growth. In the temperature window, the GaP NW diameter can be tailored by the growth temperature. A comparison of the photoluminescent spectrum between an ensemble GaP/GaNP core/shell NWs and a single NW shows that the broad and nearly identical width of the spectra probably does not originate from the variation of N composition among NWs but from the mechanism of light emission.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Uh Nanowires
81.07.Gf Nanowires
78.55.Cr III-V semiconductors

Molecular beam deposited zirconium dioxide as a high-κ dielectric for future GaN based power devices

Annett Freese, Matthias Grube, Andre Wachowiak, Marion Geidel, Barbara Adolphi, Stefan Schmult, and Thomas Mikolajick

J. Vac. Sci. Technol. B 31, 03C111 (2013); http://dx.doi.org/10.1116/1.4793764 (4 pages)

Online Publication Date: 27 February 2013

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Molecular beam deposited zirconium dioxide (ZrO2) was assessed as high-κ gate dielectric for future GaN based devices. To compare and study electrical and structural properties, thin ZrO2 films were deposited on three different substrates, n++-c-plane GaN, p-(100) Si, and TiN. The films were fabricated by electron beam evaporation from a single stoichiometric ZrO2 target. A substrate-independent phase transition from amorphous ZrO2 to the tetragonal/cubic phase was identified by gracing incidence x-ray diffractometry. Finally, monoclinic ZrO2 emerged with increasing film thickness. As found by x-ray photoelectron spectroscopy, ZrO2 formed an abrupt interface to both GaN and TiN without intermixture. Dielectric constants in the range of 14–25 were extracted from capacitance versus voltage measurements for as-deposited ZrO2 films. The leakage currents of ZrO2 on GaN resembled their counterparts on Si as well as on TiN.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
77.55.dj For nonsilicon electronics (Ge, III-V, II-VI, organic electronics)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Surface properties of c-plane GaN grown by plasma-assisted molecular beam epitaxy

Grzegorz Cywiński, Robert Kudrawiec, Łukasz Janicki, Jan Misiewicz, Caroline Chèze, Marcin Siekacz, Marta Sawicka, Paweł Wolny, Michał Boćkowski, and Czesław Skierbiszewski

J. Vac. Sci. Technol. B 31, 03C112 (2013); http://dx.doi.org/10.1116/1.4793765 (5 pages) | Cited 1 time

Online Publication Date: 28 February 2013

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Two series of GaN van Hoof structures with different thicknesses of an undoped GaN cap layer were grown under metal-rich conditions by plasma-assisted molecular beam epitaxy. These were then investigated by contactless electroreflectance (CER) to study the Fermi-level position of the (0001) GaN surface after growth as well as after chemical treatment using Piranha solution. The first and second series of samples were grown on GaN/sapphire templates and high-pressure bulk GaN crystals, respectively. A clear CER resonance followed by Franz–Keldysh oscillations (FKOs) of various periods was clearly observed for both sample series before and after chemical treatment. The Fermi-level position of the GaN surface was determined from the analysis of FKOs related to the built-in electric field in the undoped GaN layer. For the as-grown GaN surface, the Fermi level was found to be located 0.42 and 0.57 eV below the conduction band in samples grown on GaN/sapphire templates and high-pressure bulk GaN crystals, respectively. For the Piranha-etched GaN surfaces, the Fermi level was pinned at almost the same energy (0.49 and 0.48 eV) in each of the two sets of samples. This means that this cleaning procedure, which is commonly used before device processing, is able to saturate the surface states at a certain level of Fermi-level pinning.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning
68.55.ag Semiconductors
73.20.At Surface states, band structure, electron density of states
78.20.Jq Electro-optical effects
81.05.Ea III-V semiconductors

MBE growth of ZnCdSe/ZnCdMgSe quantum-well infrared photodetectors

Aidong Shen, Arvind Pawan Ravikumar, Guopeng Chen, Kuaile Zhao, Adrian Alfaro-Martinez, Thor Garcia, Joel de Jesus, Maria C. Tamargo, and Claire Gmachl

J. Vac. Sci. Technol. B 31, 03C113 (2013); http://dx.doi.org/10.1116/1.4794383 (3 pages)

Online Publication Date: 4 March 2013

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The authors report the growth of quantum well infrared photodetectors (QWIPs) made from wide band gap II-VI semiconductors. ZnCdSe/ZnCdMgSe QWIPs in both medium-wave infrared and long-wave infrared regions were grown by molecular beam epitaxy on InP substrates. High-resolution x-ray diffraction and photoluminescence measurements showed that the as-grown samples have high structural and optical quality. Spectral responses with peaks at 8.7 μm and 4.0 μm have been obtained.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
68.65.Fg Quantum wells
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
81.07.St Quantum wells
85.60.Gz Photodetectors (including infrared and CCD detectors)

In-rich InGaN thin films: Progress on growth, compositional uniformity, and doping for device applications

Mark A. Hoffbauer, Todd L. Williamson, Joshua J. Williams, Julia L. Fordham, Kin M. Yu, Wladek Walukiewicz, and Lothar A. Reichertz

J. Vac. Sci. Technol. B 31, 03C114 (2013); http://dx.doi.org/10.1116/1.4794788 (6 pages)

Online Publication Date: 8 March 2013

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A number of In-rich InGaN films with In contents in the 20–40% range have been grown at moderately low temperatures on sapphire and silicon substrates at high growth rates using a versatile molecular beam epitaxy-type technology that utilizes an energetic beam of N atoms called energetic neutral atom beam lithography and epitaxy to overcome reaction barriers in the group III-nitride system. Extensive characterization results on the crystalline, optical, and electrical properties of the In-rich InGaN materials are reported. It was found that N-rich growth conditions are required to produce materials that have excellent crystallinity, uniform compositions, and bright band edge photoluminescence. For In-rich InGaN growth on sapphire, electrical transport measurements show reasonably low carrier concentrations and high mobilities. Successful p-type doping of In-rich InGaN with ∼20% and ∼40% In contents is demonstrated, and preliminary results on the formation of a p–n junction are reported. For In-rich InGaN growth on Si, the film structural properties are somewhat degraded and carrier concentrations are considerably higher.
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68.55.ag Semiconductors
72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors

GaSb-based infrared detectors utilizing InAsPSb absorbers

John F. Klem, Samuel D. Hawkins, Jin K. Kim, Darin Leonhardt, Eric A. Shaner, Torben R. Fortune, and Gordon A. Keeler

J. Vac. Sci. Technol. B 31, 03C115 (2013); http://dx.doi.org/10.1116/1.4794381 (7 pages)

Online Publication Date: 11 March 2013

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InPSb and InAsPSb have been investigated for use as absorber materials in GaSb-based n-type/barrier/n-type (nBn) detectors with cutoff wavelengths shorter than 4.2 μm. The growth temperature window for high-quality InPSb lattice-matched to GaSb by molecular beam epitaxy is approximately 440–460 °C. InPSb films with thicknesses greater than approximately 1 μm or films grown outside this temperature window have high densities of large defects, with films grown at lower temperatures exhibiting evidence of significant phase separation. In contrast, InAsPSb films can be grown with excellent surface morphologies and no apparent phase separation over a wide temperature range. InAsPSb samples with low-temperature photoluminescence between 3.0 and 3.4 μm and lattice mismatch of less than 1 × 10−3 have been grown, although both photoluminescence and x-ray diffraction data exhibit peak splitting indicative of compositional nonuniformity. AlAsSb-barrier nBn detectors with InPSb and InAsPSb absorbers have been fabricated. At 160 K, InPSb-absorber devices have a photocurrent responsivity edge at approximately 2.8 μm and a dark current of approximately 1.4 × 10−7 A/cm2, and InAsPSb devices with responsivity edges of 3.1–3.2 μm have a dark current of 2.3 × 10−8 A/cm2. Both InPSb and InAsPSb devices require significant reverse bias for full photocurrent collection at low temperature, suggesting the existence of an undesirable valence band energy discontinuity. The temperature dependence of dark current indicates that it is dominated by a mechanism other than generation in the undepleted absorber region.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.A- Nucleation and growth

Closed cycle chiller as a low cost alternative to liquid nitrogen in molecular beam epitaxy

Ryan B. Lewis, James A. Mackenzie, Thomas Tiedje, Daniel A. Beaton, Mostafa Masnadi-Shirazi, Vahid Bahrami-Yekta, Keelan P. Watkins, and Patricia M. Mooney

J. Vac. Sci. Technol. B 31, 03C116 (2013); http://dx.doi.org/10.1116/1.4795512 (6 pages)

Online Publication Date: 14 March 2013

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The high cost of cooling the cryoshroud in a molecular beam epitaxy system has been greatly reduced by replacing liquid nitrogen (LN2) as a coolant with a silicone polymer heat transfer fluid cooled to as low as −80 °C by a closed cycle chiller. Gallium arsenide epitaxial layers have been grown with two different cooling configurations of the shroud: conventional LN2 cooling and cooling to −70 °C with the chiller. The partial pressure of water in the chamber is a factor of about 2.5 higher with the closed cycle chiller operating at −70 °C than with liquid nitrogen in the shroud. No significant difference is observed in the density of deep levels in the GaAs, as determined by deep level transient spectroscopy.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

Development of AlGaN-based graded-index-separate-confinement-heterostructure deep UV emitters by molecular beam epitaxy

Haiding Sun, Jeff Woodward, Jian Yin, Adam Moldawer, Emanuele F. Pecora, Alexey Yu. Nikiforov, Luca Dal Negro, Roberto Paiella, Karl Ludwig, Jr., David J. Smith, and Theodore D. Moustakas

J. Vac. Sci. Technol. B 31, 03C117 (2013); http://dx.doi.org/10.1116/1.4796107 (7 pages)

Online Publication Date: 21 March 2013

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The authors report on the growth, structure, and emission properties of AlGaN double heterostructures having a graded-index-separate-confinement-heterostructure design. These devices were grown on the Si-face of 6H-SiC substrates by plasma-assisted molecular-beam epitaxy. The active region of the device consists of 75-nm thick Al0.72Ga0.28N film, confined by two 50-nm thick compositionally graded AlxGa1−xN films (x = 1–0.8 and x = 0.8–1) and two AlN cladding layers. X-ray diffraction and transmission electron microscopy provide evidence that the compositionally graded AlGaN layer may also be serving as a strain transition buffer, by blocking threading defects in the vicinity of the AlN/AlGaN heterointerface. Polarization dependent photoluminescence studies indicate that the emission from these structures at 257 nm is transverse magnetic polarized. Simulation studies indicate that the vertical confinement of the optical mode in these structures is 32.5% and simulations of the band structure indicate the formation of a p-n junction resulting from polarization-induced doping. Electron-beam pumping of these structures provides evidence of the onset of stimulated emission at room temperature.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition
68.55.ag Semiconductors

Epitaxial growth of ZnTe on GaSb(100) using in situ ZnCl2 surface clean

Chihyu Chen, S. J. Kim, X. Q. Pan, and Jamie D. Phillips

J. Vac. Sci. Technol. B 31, 03C118 (2013); http://dx.doi.org/10.1116/1.4796108 (4 pages)

Online Publication Date: 21 March 2013

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The epitaxial growth of high-quality ZnTe on GaSb substrates is demonstrated by molecular beam epitaxy without the use of a group-V beam flux or intermediate GaSb buffer layer. A reduced surface cleaning temperature is achieved using a combination of HCl etching prior to loading into the growth chamber and use of a ZnCl2 flux during the thermal clean step. This procedure results in a surface clean temperature of approximately 440 °C, in comparison to 500 °C for an as-received GaSb substrate, providing a means to achieve a clean GaSb surface for ZnTe epitaxy without the requirement for a group-V flux to stabilize the surface to prevent noncongruent sublimation of GaSb. The resulting ZnTe epitaxial layers demonstrate good surface morphology and structural properties based on Nomarski microscope images, transmission electron microscopy images of the ZnTe/GaSb interface, and x-ray diffraction measurements demonstrating a rocking curve with a full width at half maximum of 40 arc sec for the ZnTe (004) reflection.
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68.55.ag Semiconductors
81.65.Cf Surface cleaning, etching, patterning
68.37.Lp Transmission electron microscopy (TEM)
68.35.bg Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Optimization of growth conditions of type-II Zn(Cd)Te/ZnCdSe submonolayer quantum dot superlattices for intermediate band solar cells

Siddharth Dhomkar, Igor L. Kuskovsky, Uttam Manna, I. C. Noyan, and Maria C. Tamargo

J. Vac. Sci. Technol. B 31, 03C119 (2013); http://dx.doi.org/10.1116/1.4797486 (7 pages)

Online Publication Date: 21 March 2013

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Intermediate band solar cells (IBSCs) have been predicted to be significantly more efficient than the conventional solar cells, but have not been realized to their full potential due to the difficulties related to the fabrication of practical devices. The authors report here on growth and characterization of Zn(Cd)Te/ZnCdSe submonolayer quantum dot (QD) superlattices (SLs), grown by migration enhanced epitaxy. These QDs do not exhibit formation of wetting layers, which is one of the culprits for the unsatisfactory performance of IBSCs. The ZnCdSe host bandgap is ∼2.1 eV when lattice matched to InP, while the Zn(Cd)Te-ZnCdSe valence band offset is ∼0.8 eV. These parameters make this material system an excellent candidate for a practical IBSC. The detailed structural analysis demonstrates that the process of desorption of Cd and the preferential incorporation of Zn facilitates the formation of unintentional strained ZnSe-rich layer at the QD-spacer interface. The growth conditions have been then optimized so as to obtain high crystalline quality lattice matched SL, by growing intentionally Cd-rich spacers, which strain balanced the SL. The excitation intensity dependent photoluminescence confirmed the type-II nature of these multilayer QD structures, which is expected to suppress nonradiative Auger recombination, and improve the carrier extraction process when implemented in an actual device.
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81.05.Dz II-VI semiconductors
88.40.hj Efficiency and performance of solar cells
88.40.jp Multijunction solar cells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.Ta Quantum dots
73.21.La Quantum dots

Energy splitting of CdSe quantum dots induced by intense femtosecond laser excitation

Shengkun Zhang, Iosif Zeylikovich, Taposh Gayen, Robert Alfano, and Maria Tamargo

J. Vac. Sci. Technol. B 31, 03C120 (2013); http://dx.doi.org/10.1116/1.4797485 (4 pages)

Online Publication Date: 22 March 2013

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Microscopic photoluminescence (PL) spectra of self-assembled CdSe quantum dots (QDs) grown by molecular beam epitaxy were investigated under excitation of intense femtosecond laser. Two samples with different QD sizes were fabricated. One had a single layer of larger CdSe QDs while the other had three layers of smaller QDs. The second harmonic radiation at 420 nm obtained from a mode-locked tunable Ti-Sapphire laser was used as the excitation source. The laser power density was in the order of kW cm−2 and the peak power density was in the order of GW cm−2 for the 150 fs laser pulse with a repetition rate of 78 MHz. The intense femtosecond laser pulses generated strong surface acoustic waves and modulated energy bands of electrons and holes of CdSe QDs. Increasing of the laser power resulted in the PL peak of the CdSe QDs splitting into four peaks for both QD samples: two peaks shifted to a lower energy side and the other two shifted to a higher energy side. The strong strain fields led to the mixing of heavy-hole state and light-hole state in the quantum dots. The strain fields further modulated the energy bands of electrons and holes and produced splitting of both electron–heavy hole (e-hh) transition and electron–light hole (e-lh) transition. For the sample with a single layer of smaller QDs, the energy splitting for both e-hh and e-lh transitions reached 23.5 meV at a peak power density of 0.32 GW cm−2. For the sample with three layers of larger QDs, the energy splitting was 19.9 meV for e-hh transition and 17.9 meV for e-lh transition at a peak power of 1.1 GW cm−2.
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78.67.Hc Quantum dots
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.47.J- Ultrafast spectroscopy (<1 psec)
68.35.Iv Acoustical properties
73.21.La Quantum dots
78.55.Et II-VI semiconductors

Epitaxial growth of engineered metals for mid-infrared plasmonics

Stephanie Law, Lan Yu, and Daniel Wasserman

J. Vac. Sci. Technol. B 31, 03C121 (2013); http://dx.doi.org/10.1116/1.4797487 (6 pages)

Online Publication Date: 22 March 2013

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The authors demonstrate the ability of high-quality epitaxial InAs films to be used as wavelength-flexible, low-loss, engineered plasmonic metals across the mid-infrared spectral range. Films are grown by molecular beam epitaxy and characterized by Hall effect measurements, atomic force microscopy, and infrared reflection and transmission spectroscopy. The losses of our plasmonic material are studied as a function of InAs doping density, growth rate, buffer layer type, and substrate type. High growth rates are shown to be integral to obtaining films with low losses and doping densities approaching 1×1020 cm−3.
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68.55.ag Semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.uj III-V and II-VI semiconductors

High performance long-wave type-II superlattice infrared detectors

Arezou Khoshakhlagh, Linda Höglund, David Z. Ting, Cory J. Hill, Sam A. Keo, Alexander Soibel, Jean Nguyen, and Sarath D. Gunapala

J. Vac. Sci. Technol. B 31, 03C122 (2013); http://dx.doi.org/10.1116/1.4798485 (4 pages)

Online Publication Date: 3 April 2013

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The authors report on growth, material characterization, and device performance of infrared photodetectors based on type II InAs/GaSb superlattices using the complementary barrier infrared detector (CBIRD) design. In this paper, control steps for improvement of material quality in terms of surface, structural, and optical properties of infrared detectors grown at Jet Propulsion Laboratory are described. For a specific CBIRD studied, these quality control steps indicate high structural and optical quality of the grown material. Furthermore, single-element detector from the optimized growth conditions exhibit dark current density less than 1 × 10−5 A/cm2 at applied biases up to Vb = 0.36 V (T = 77 K), so this material can be utilized for focal plane arrays development.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Type-II InAs/GaSb strained layer superlattices grown on GaSb (111)B substrate

Elena Plis, Brianna Klein, Stephen Myers, Nutan Gautam, Thomas J. Rotter, Ralph L. Dawson, Sanjay Krishna, Sang Jun Lee, and Young Heon Kim

J. Vac. Sci. Technol. B 31, 03C123 (2013); http://dx.doi.org/10.1116/1.4798650 (6 pages)

Online Publication Date: 8 April 2013

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In this paper, the authors report on the growth of InAs/GaSb type-II strained layer superlattice (T2SL) material on (111)B GaSb substrates. Both substrate temperature and V/III beam equivalent pressure ratio were varied to optimize the crystalline and optical quality of the T2SL material. Midwave infrared (λ100% cut-off ∼ 5.6 μm at 295 K) InAs/GaSb T2SL detectors were then grown on the same substrate orientation. After detailed radiometric characterization, the authors have measured, at 295 K and 4 μm, a dark current density of 0.53 A/cm2 (at −50 mV) and a Johnson noise limited specific detectivity (D*) of 8.5 × 109 Jones, which are superior values to the state-of-the-art T2SL detectors grown on conventional GaSb (100) substrates and operating in a similar wavelength range.
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81.05.Ea III-V semiconductors
68.65.Cd Superlattices
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.30.Fs III-V and II-VI semiconductors
72.70.+m Noise processes and phenomena
85.60.Gz Photodetectors (including infrared and CCD detectors)

Mercury cadmium selenide for infrared detection

Kevin Doyle, Craig H. Swartz, John H. Dinan, Thomas H. Myers, Gregory Brill, Yuanping Chen, Brenda L. VanMil, and Priyalal Wijewarnasuriya

J. Vac. Sci. Technol. B 31, 03C124 (2013); http://dx.doi.org/10.1116/1.4798651 (5 pages)

Online Publication Date: 8 April 2013

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Samples of HgCdSe alloys were grown via molecular beam epitaxy on thick ZnTe buffer layers on Si substrates. Two Se sources were used: an effusion cell loaded with 5N source material that produced a predominantly Se6 beam and a cracker loaded with 6N material that could produce a predominantly Se2 beam. The background electron concentration in as-grown samples was significantly reduced by switching to the Se cracker source, going from 1017–1018 cm−3 to 3–5 × 1016 cm−3 at 12 K. The concentration remained low even when the cracking zone temperature was lowered to produce a predominantly Se6 beam, which strongly suggests that a major source of donor defects is impurities from the Se source material rather than Se species. Secondary ion mass spectroscopy was performed. Likely donors such as F, Br, and Cl were detected at the ZnTe interface while C, O, and Si were found at the interface and in the top 1.5 μm from the surface in all samples measured. The electron concentration for all samples increased when annealed in a Cd or Hg overpressure and decreased when annealed under Se. This suggests the presence of native defects such as vacancies and interstitials in addition to impurities. Overall, by switching to higher purity Se material and then annealing under Se overpressures, the background electron concentration was reduced by an order of magnitude, with the lowest value achieved being 9.4 × 1015 cm−3 at 12 K.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
61.72.Cc Kinetics of defect formation and annealing
73.61.Ga II-VI semiconductors
61.72.jd Vacancies
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Strain- and kinetically induced suppression of phase separation in MBE-grown metastable and unstable GaInAsSb quaternary alloys for mid-infrared optoelectronics

Asli Yildirim and John P. Prineas

J. Vac. Sci. Technol. B 31, 03C125 (2013); http://dx.doi.org/10.1116/1.4799352 (9 pages)

Online Publication Date: 8 April 2013

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The authors have examined the dependence of phase separation in thick layers (1 μm) of molecular beam epitaxially grown, thermodynamically metastable Ga(0.25)In(0.75)As(0.22)Sb(0.78) and unstable Ga(0.50)In(0.50)As(0.44)Sb(0.56) alloys on growth kinetics and strain. For the metastable alloy, which emits at 2.8 μms, they found that phase separation does not occur for any growth temperature, and the alloy grows stoichiometrically, with step flow growth and with high optical output at around 400 °C and 440–480 °C. Moreover, optical quality is robust for alloys grown up to 30 times the critical thickness, with evidence of some improvement for compressive strain. Remarkably, no relaxation of layers occurs, as evidenced in atomic force microscopy or reciprocal space maps up to 12 times the critical thickness. The unstrained unstable alloy, which emits at 3.9 μms, can be grown with optimal optical output and a low degree of phase separation by limiting adatom diffusion length with lower temperature growth (400–440 °C) than metastable alloy. At 450 °C and hotter, severe spinoidal decomposition occurs; however, the authors show that compressive strain may be employed to dramatically suppress phase separation.
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64.75.Qr Phase separation and segregation in semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Ps Atomic force microscopy (AFM)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
64.75.St Phase separation and segregation in thin films

In situ Auger probe enabling epitaxy composition control of alloys by elemental surface analysis

W. Laws Calley, Jordan D. Greenlee, Walter E. Henderson, Jonathan Lowder, Michael W. Moseley, W. Alan Doolittle, and Philippe G. Staib

J. Vac. Sci. Technol. B 31, 03C126 (2013); http://dx.doi.org/10.1116/1.4798653 (5 pages)

Online Publication Date: 9 April 2013

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An in situ Auger probe (AP) is employed to monitor changes in growth surface chemistry of the component elements of Terfenol-D, a completely miscible alloy of DyFe2 and TbFe2. The AP's surface sensitivity is quantified by depositing Dy onto a layer of Tb in 0.01 monolayer increments. The AP is able to distinguish surface coverage changes as small as 2% of a monolayer when elements with similar Auger spectra are used. The AP also allowed the identification of oxygen contamination in the system. Additionally, the glancing angle incidence primary electrons result in enhanced surface sensitivity compared to a more traditional Auger electrons spectroscopy configuration.
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68.55.A- Nucleation and growth
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.20.Fv Electron impact: Auger emission
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Inducing a junction in n-type InxGa(1−x)N

Joshua J. Williams, Todd L. Williamson, Mark A. Hoffbauer, Alec M. Fischer, Stephen M. Goodnick, Nikolai N. Faleev, Kunal Ghosh, and Christiana B. Honsberg

J. Vac. Sci. Technol. B 31, 03C127 (2013); http://dx.doi.org/10.1116/1.4797489 (6 pages)

Online Publication Date: 10 April 2013

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The pseudo-binary alloy of indium(x)gallium(1−x)nitride has a compositionally dependent bandgap ranging from 0.65 to 3.42 eV, making it desirable for light emitting diodes and solar cell devices. Through modeling and film growth, the authors investigate the use of InxGa1−xN as an active layer in an induced junction. In an induced junction, electrostatics are used to create strong band bending at the surface of a doped material and invert the bands. The authors report modeling results, as well as preliminary film quality experiments for an induced junction in InGaN by space charge effects of neighboring materials, piezoelectric effects, and spontaneous polarization.
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68.55.ag Semiconductors
77.22.Jp Dielectric breakdown and space-charge effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
77.55.hn Other piezoelectric or electrostrictive films
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors

Evidence of long-wave-infrared excited state transition at high temperature (200 K) in 35-layer In0.50Ga0.50As/GaAs quantum dot infrared photodetector

Sourav Adhikary and Subhananda Chakrabarti

J. Vac. Sci. Technol. B 31, 03C128 (2013); http://dx.doi.org/10.1116/1.4801791 (4 pages)

Online Publication Date: 18 April 2013

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Fabricating quantum dot infrared photodetectors (QDIPs) operable under high temperatures has remained a challenge. The authors report the performance of multispectrum 35-layer In0.50Ga0.50As/GaAs QDIP at high temperatures. Results showed three photoresponse peaks at ∼5.6, 7.4, and 11.5 μm. The third peak is observed only at 200 K, possibly because of transition of electrons from the second excited state of the quantum dot to GaAs barrier state. Peak responsivity value (∼140 mA/W) and maximum D* value (∼1.25 × 1010 cm·Hz1/2/W) is reached at 1.5 V. Responsivity is higher (210 mA/W) at 150 K than 77 K, possibly because of better transport of carriers at higher temperatures. The D* values are ∼4.33 × 108 cm·Hz1/2/W at 150 K and ∼3.3 × 106 cm·Hz1/2/W at 200 K at 1.0 V bias.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.21.Ac Multilayers
63.22.Np Layered systems
81.05.Ea III-V semiconductors
73.21.La Quantum dots
85.60.Gz Photodetectors (including infrared and CCD detectors)

Epitaxial growth of elemental Sb quantum wells

Chomani K. Gaspe, Shayne Cairns, Lin Lei, Kaushini S. Wickramasinghe, Tetsuya D. Mishima, Joel C. Keay, Sheena Q. Murphy, and Michael B. Santos

J. Vac. Sci. Technol. B 31, 03C129 (2013); http://dx.doi.org/10.1116/1.4802212 (6 pages)

Online Publication Date: 18 April 2013

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An experimental study of growth, structural, and electronic properties of elemental Sb quantum wells with GaSb barriers was performed to explore their potential as topological insulators. A growth procedure on GaAs (111)A substrates was developed to realize ultrathin Sb layers with a thickness of ≤4 nm. Transmission electron microscopy and scanning electron microscopy were used to optimize growth conditions. Resistivity measurements indicated that Sb wells with a thickness above ∼2 nm were metallic (relatively temperature-independent resistivity) whereas thinner wells showed insulating or semiconducting behavior (resistivity increased with decreasing temperature).
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73.40.Vz Semiconductor-metal-semiconductor structures
73.63.Hs Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
73.21.Fg Quantum wells

Investigation on the origin of luminescence quenching in N-polar (In,Ga)N multiple quantum wells

Caroline Chèze, Marcin Siekacz, Grzegorz Muzioł, Henryk Turski, Szymon Grzanka, Marcin Kryśko, Jan L. Weyher, Michał Boćkowski, Christian Hauswald, Jonas Lähnemann, Oliver Brandt, Martin Albrecht, and Czesław Skierbiszewski

J. Vac. Sci. Technol. B 31, 03C130 (2013); http://dx.doi.org/10.1116/1.4802964 (7 pages)

Online Publication Date: 29 April 2013

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The growth of N-polar (In,Ga)N structures by plasma-assisted molecular beam epitaxy is studied. (In,Ga)N multiple quantum well samples with atomically smooth surface were grown and their good structural quality was confirmed by x-ray diffraction, scanning transmission electron microscopy, and defect selective etching. The In incorporation was higher in the N-polar than in the Ga-polar oriented crystal, consistent with previous reports. However, despite the good morphological and structural properties of these samples, no photoluminescence signal from the (In,Ga)N wells was detected. In contrast, a thick N-polar (In,Ga)N layer exhibited a broad peak at 620 nm in good agreement with the In content determined by x-ray diffraction. The potential source of the luminescence quenching in the N-polar (In,Ga)N multiple quantum wells is discussed and attributed either to a strong nonradiative recombination channel at the surface promoted by the electric field or to the high concentration of point defects at the interfaces of the quantum well structures.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors

Growth and spectroscopic ellipsometry evaluation of composite layers of ErAs and InAs nanoparticles

Kurt G. Eyink, Luke J. Bissell, Jodie Shoaf, David H. Tomich, Daniel Esposito, Madelyn Hill, Larry Grazulis, Andrew Aronow, and Krishnamurthy Mahalingam

J. Vac. Sci. Technol. B 31, 03C131 (2013); http://dx.doi.org/10.1116/1.4802965 (5 pages)

Online Publication Date: 6 May 2013

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Metal nanoparticles coupled to semiconductor quantum dots have been studied recently due to the enhancement in absorption, emission, and nonlinearities expected from these hybrid structures. These properties stem from the ability of the metal to focus light as well as shift the phase, which occurs at the metal–dielectric interface. To date, most quantum dots metal nanoparticle couples are formed by the attachment of a ligand to both particles. The extension of this idea to bulk semiconductor films is being attempted by the formation of a composite structure of ErAs, which forms semimetallic nanoparticles (SMNP) in GaAs, and InAs self-assembled quantum dots (SAQD). In this work, the authors analyze structures composed of periods of InAs SAQDs and ErAs SMNPs and analyze these with spectroscopic ellipsometry in the spectral region 0.7–4.0 eV with 0.02 eV steps. Initially, individual structures composed of InAs SAQD stacks or ErAs SMNP stacks, both capped with layers of GaAs, are analyzed. The authors have also analyzed the films with high-resolution x-ray diffraction. The structural parameters from x-ray models are used in conjunction with the spectroscopic ellipsometry data to extract the homogenized refractive index for the individual stacks. The properties of these films are then used to calculate the properties of a composite structure composed of eight repeats of periods, which contain a growth sequence used to form the stacks of InAs SAQDs and ErAs SMNPs. The authors find that this composite structure is best modeled with a Bruggeman effective medium mixture of the two component stacks and a thin intermediate layer of constant index of refraction to account for the reflections at the boundaries between the periods.
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81.07.Ta Quantum dots
81.16.Dn Self-assembly
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.72.Dd Experimental determination of defects by diffraction and scattering
68.65.Hb Quantum dots (patterned in quantum wells)

Dependence of structural and electrical properties of AlGaN/GaN HEMT on Si(111) on buffer growth conditions by MBE

Partha Mukhopadhyay, Subhra Chowdhury, Andrew Wowchak, Amir Dabiran, Peter Chow, and Dhrubes Biswas

J. Vac. Sci. Technol. B 31, 03C132 (2013); http://dx.doi.org/10.1116/1.4803836 (5 pages)

Online Publication Date: 6 May 2013

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Multiple AlGaN/GaN heterostructure has been grown on Si(111) substrate by molecular beam epitaxy with different buffer growth conditions. Its influence on physical and electrical properties of two-dimensional electron gas (2DEG) has been investigated. Correlation between growth temperature variation in AlN intermediate layer and thick GaN buffer layer on 2DEG transport property has been observed. Besides the variation in growth temperatures, dissimilar partial doping in the thick GaN buffer has also been studied. Impact of different silicon substrate doping has been examined to inspect the electrical properties of high electron mobility transistors (HEMT). DC characteristics of large area fabricated HEMT have been compared in terms of current, transconductance, and linearity for power amplifier applications.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
85.40.Ry Impurity doping, diffusion and ion implantation technology

Improved electrical properties and crystalline quality of II–VI heterostructures for quantum cascade lasers

Thor Axtmann Garcia, Songwoung Hong, Maria Tamargo, Joel de Jesus, Vasilios Deligiannakis, Arvind Ravikumar, Claire Gmachl, and Aidong Shen

J. Vac. Sci. Technol. B 31, 03C133 (2013); http://dx.doi.org/10.1116/1.4803837 (6 pages)

Online Publication Date: 7 May 2013

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The authors report on investigations of the doping, lattice mismatch, and interface quality for the molecular beam epitaxial growth of ZnCdSe/ZnCdMgSe/InP quantum cascade structures with improved electrical, structural, and spectral properties. An improved doping strategy, the control of the lattice mismatch to less than 0.25%, and the incorporation of growth interruptions have led to quantum cascade structures with good I–V characteristics and electroluminescence emission up to room temperature, with an emission energy of 230 meV (5.4 μm) and a full-width at half maximum of 41 meV at 80 K, the best device properties reported so far for this material system. It is expected that the addition of waveguide layers in the structure will lead to the observation of lasing.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
73.61.Ga II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.60.Fi Electroluminescence

Characterization of the three-well active region of a quantum cascade laser using contactless electroreflectance

Joel De Jesus, Thor A. Garcia, Siddharth Dhomkar, Arvind Ravikumar, Claire Gmachl, Guopeng Chen, Aidong Shen, Dino Ferizovic, Martin Muñoz, and Maria C. Tamargo

J. Vac. Sci. Technol. B 31, 03C134 (2013); http://dx.doi.org/10.1116/1.4803838 (5 pages)

Online Publication Date: 7 May 2013

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Quantum cascade (QC) lasers with emission at wavelengths below 4 μm are difficult to achieve from conventional III-V materials systems lattice matched to GaAs and InP due to the limited conduction band offset (CBO) of those materials that results from the presence of intervalley scattering. The II-VI materials ZnCdSe/ZnCdMgSe, with a CBO as high as 1.12 eV and no intervalley scattering, are promising candidates to achieve this goal. Using molecular beam epitaxy (MBE), the authors grew a QC laser structure with a three-well active region design made of ZnCdSe and ZnCdMgSe multilayers closely lattice matched to InP. A test structure, which contains only the active region of the QC laser separated by quaternary barrier layers, was also grown. The test structure was characterized by contactless electroreflectance (CER). Photoluminescence measurements and a model based on the transfer matrix method were used to identify the CER transitions. The energy levels obtained for the test structure were then used to predict the Fourier transform infrared (FTIR) absorption spectrum of the QC laser structure. Excellent agreement between the predicted values based on the test structure and the experimental FTIR absorption peaks of the full QC laser structure was observed.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.70.-a Optical materials
78.20.Jq Electro-optical effects
78.55.Cr III-V semiconductors
78.55.Et II-VI semiconductors

MBE growth optimization of InAs (001) homoepitaxy

Hao Ye, Lu Li, Robert T. Hinkey, Rui Q. Yang, Tetsuya D. Mishima, Joel C. Keay, Michael B. Santos, and Matthew B. Johnson

J. Vac. Sci. Technol. B 31, 03C135 (2013); http://dx.doi.org/10.1116/1.4804397 (6 pages)

Online Publication Date: 10 May 2013

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The optimal conditions for growth of homoepitaxial InAs layers by molecular beam epitaxy were investigated over a wide range of substrate temperatures and As2/In flux ratios at a growth rate of 0.66 monolayer/s. Material quality was investigated using a variety of techniques: differential interference contrast microscopy, scanning electron microscopy, and atomic force microscopy. The results indicated that the InAs layer grown at a temperature between 430 and 450 °C with an As2/In flux ratio of about 15:1 yielded the highest quality, with a defect density of 2 × 104 cm−2 and a root mean square roughness of 0.19 nm. The quality can be further improved by growth at a lower growth rate of 0.22 monolayer/s. The morphology of large oval hillock defects on the InAs layers suggested that these defects originated at the substrate surface.
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68.55.ag Semiconductors
68.35.bg Semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Comprehensive study on molecular beam epitaxy-grown InAs sub-monolayer quantum dots with different capping combinations

Saumya Sengupta, Arjun Mandal, Hemant Ghadi, Subhananda Chakrabarti, and Keshav Lal Mathur

J. Vac. Sci. Technol. B 31, 03C136 (2013); http://dx.doi.org/10.1116/1.4805018 (4 pages)

Online Publication Date: 16 May 2013

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Here the authors report a comprehensive study on InAs sub-monolayer quantum dots with different capping layers. After performing systematic optimization of InAs deposition and GaAs thickness, they grew three samples, namely A, B and C, using solid-state molecular beam epitaxy with identical architecture but different capping materials (2 nm of GaAs, InGaAs-GaAs, and InAlGaAs-GaAs, respectively). Photoluminescence emission peaks due to the ground state transition from the dots were observed at 898, 917, and 867 nm for samples A, B, and C, respectively. Narrow full-width half-maxima (19–32 meV) of the emission peaks indicates high uniformity of dot size distribution. Using the conventional Arrhenius plot, the authors calculated the thermal activation energies from temperature-dependent photoluminescence experiment for samples A, B, and C as 49, 112, and 109 meV, respectively. To complete the study, single-pixel photodetectors were fabricated from samples A, B, and C and temperature-dependent dark current variation with applied bias voltage was measured. Dark current was calculated to be in the range of 10−5–10−4 A/cm2 at a 0.5 V applied bias at 77 K. The activation energies calculated from temperature-dependent dark current measurement for samples A, B, and C were 75, 160, and 155 meV, respectively, and followed the trend observed in temperature-dependent photoluminescence measurements.
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78.67.Hc Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
73.63.Kv Quantum dots
78.55.Cr III-V semiconductors
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