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Sample records for gas-source molecular-beam epitaxy

  1. A safety system for gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Biswas, Dhrubes; Morkoç, Hadis

    1991-08-01

    Gas source molecular beam epitaxy (GSMBE) is one of the newest developments in epitaxial growth technology wherein the group V sources such as arsine and phosphine are gaseous and in the form of hydrides, while the Group III sources such as indium, aluminum, gallium are all solids. However, the gases involved are very hazardous, extremely toxic, highly inflammable and explosive at elevated temperatures. Adequate care must be taken for the safe use of these gases so that this attractive technique can be properly utilized. This paper discusses the salient safety features of one such GSMBE system (installed in the Epicenter at the University of Illinois) consisting of a gas delivery system with its robust piping assembly, gas manifold and a scrubber. The system is integrated with a Multiple Point Toxic Gas Monitor (MPTGM) acting as the central alarm command system based on the concept of fail safe total safety. This alarm system is equipped with audio-visual alarms for a variety of monitored conditions and interlocks for automatic shutdown. A well-designed air flow pattern has been incorporated to provide good air quality in the laboratory and in the gas storage facility. Additionally a set of good laboratory practices ensured by administrative and personal control are instituted to reduce the hazards to an acceptable risk level.

  2. Gas source molecular beam epitaxy of GaN with hydrazine on spinel substrates

    NASA Astrophysics Data System (ADS)

    Nikishin, S. A.; Temkin, H.; Antipov, V. G.; Guriev, A. I.; Zubrilov, A. S.; Elyukhin, V. A.; Faleev, N. N.; Kyutt, R. N.; Chin, A. K.

    1998-05-01

    Growth of high quality wurtzite-structure GaN layers on (111) MgAl2O4 by gas source molecular beam epitaxy is described. Hydrazine was used as a source of active nitrogen. In situ reflection high energy electron diffraction was used to monitor the growth mode. Two-dimensional growth was obtained at temperatures above 750 °C on multi-step GaN buffer layers. The resulting GaN films show excellent luminescence properties.

  3. InAs nanowire growth modes on Si (111) by gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Robson, M. T.; LaPierre, R. R.

    2016-02-01

    InAs nanowires (NWs) were grown on silicon substrates by gas source molecular beam epitaxy using five different growth modes: (1) Au-assisted growth, (2) positioned (patterned) Au-assisted growth, (3) Au-free growth, (4) positioned Au-assisted growth using a patterned oxide mask, and (5) Au-free selective-area epitaxy (SAE) using a patterned oxide mask. Optimal growth conditions (temperature, V/III flux ratio) were identified for each growth mode for control of NW morphology and vertical NW yield. The highest yield (72%) was achieved with the SAE method at a growth temperature of 440 °C and a V/III flux ratio of 4. Growth mechanisms are discussed for each of the growth modes.

  4. Effects of high source flow and high pumping speed on gas source molecular beam epitaxy / chemical beam epitaxy

    NASA Astrophysics Data System (ADS)

    McCollum, M. J.; Jackson, S. L.; Szafranek, I.; Stillman, G. E.

    1990-10-01

    We report the growth of GaAs by molecular beam epitaxy (MBE), gas source molecular beam epitaxy (GSMBE), and chemical beam epitaxy (CBE) in an epitaxial III-V reactor which features high pumping speed. The system is comprised of a modified Perkin-Elmer 430P molecular beam epitaxy system and a custom gas source panel from Emcore. The growth chamber is pumped with a 7000 1/s (He) diffusion pump (Varian VHS-10 with Monsanto Santovac 5 oil). The gas source panel includes pressure based flow controllers (MKS 1150) allowing triethylaluminum (TEA), triethylgallium (TEG), and trimethylindium (TMI) to be supplied without the use of hydrogen. All source lines, including arsine and phosphine, are maintained below atmospheric pressure. The high pumping speed allows total system flow rates as high as 100 SCCM and V/III ratios as high as 100. The purity of GaAs grown by MBE in this system increases with pumping speed. GaAs layers grown by GSMBE with arsine flows of 10 and 20 SCCM have electron concentrations of 1 × 10 15 cm -3 (μ 77=48,000 cm 2/V·) and 2 × 10 14 cm -3 (μ 77=78,000 cm 2/V·s) respectively. El ectron concentration varies with hydride injector temperature such that the minimum in electron concentration occurs for less than complete cracking. The effect of V/III ratio and the use of a metal eutectic bubbler on residual carrier concentration in GaAs grown by CBE is presented. Intentional Si and Be doping of CBE grown GaAs is demonstrated at a high growth rate of 5.4 μm/h.

  5. GaNAsP: An intermediate band semiconductor grown by gas-source molecular beam epitaxy

    SciTech Connect

    Kuang, Y. J.; Yu, K. M.; Walukiewicz, W.; Kudrawiec, R.; Luce, A. V.; Ting, M.; Tu, C. W.

    2013-03-18

    Dilute nitride GaNAsP thin films were grown via a GaAsP metamorphic buffer on GaP(100) substrate with gas-source molecular beam epitaxy. The compositions of this III-V-V-V compound were determined by channeling Rutherford backscattering spectroscopy and nuclear reaction analysis. Photoreflectance shows two distinctive transitions from the valence band to the split conduction bands due to N incorporation. Photoluminescence and optical absorption show the fundamental bandgap of Ga(N)AsP is largely tailored by the small amount of N. The observed multiband characteristics and the bandgap tunability of GaNAsP are two merits that fit into the intermediate-band solar cell roadmap, and GaNAsP of high crystal quality provides a strong candidate for intermediate band solar cell materials.

  6. GaNAsP: An intermediate band semiconductor grown by gas-source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kuang, Y. J.; Yu, K. M.; Kudrawiec, R.; Luce, A. V.; Ting, M.; Walukiewicz, W.; Tu, C. W.

    2013-03-01

    Dilute nitride GaNAsP thin films were grown via a GaAsP metamorphic buffer on GaP(100) substrate with gas-source molecular beam epitaxy. The compositions of this III-V-V-V compound were determined by channeling Rutherford backscattering spectroscopy and nuclear reaction analysis. Photoreflectance shows two distinctive transitions from the valence band to the split conduction bands due to N incorporation. Photoluminescence and optical absorption show the fundamental bandgap of Ga(N)AsP is largely tailored by the small amount of N. The observed multiband characteristics and the bandgap tunability of GaNAsP are two merits that fit into the intermediate-band solar cell roadmap, and GaNAsP of high crystal quality provides a strong candidate for intermediate band solar cell materials.

  7. Electron beam evaporated carbon doping of InGaAs layers grown by gas source molecular beam epitaxy

    SciTech Connect

    Salokatve, A.; Toivonen, M.; Asonen, H.; Pessa, M.; Likonen, J.

    1996-12-31

    The authors have studied carbon doping of GaInAs grown by gas-source molecular beam epitaxy. Graphite was used as a source material for carbon evaporation. GaInAs was studied due to its importance as a base layer in InP-based heterojunction bipolar transistors. They show that useful p-type acceptor concentrations can be achieved by evaporation from graphite source for GaInAs grown by gas-source molecular beam epitaxy. Secondary ion mass spectroscopy and Van der Pauw Hall measurements were used to characterize the carbon and net acceptor concentrations of their GaInAs layers. The effect of rapid thermal annealing on acceptor concentrations and Hall mobilities was also studied.

  8. Indium Gallium Arsenic Phosphide-Based Optoelectronics Grown by Gas Source Molecular Beam Epitaxy.

    NASA Astrophysics Data System (ADS)

    Shiau, Guang-Jye

    We have demonstrated the gas-source molecular beam epitaxy (GSMBE) growth of high purity rm In_{1-x}Ga_{x}As_ {y}P_{1-y.} with a background doping level as low as 5times10^{15 } {rm cm}^{-3}, and the precise lattice-matching control to within +/-5times10^{-4}. We found that exposure of freshly-grown InP to an As flux during growth interruption between layers of different compositions results in the substitution of surface P atoms by As atoms, thereby generating a strained transition layer at each interface. By assuring a group-III stabilized surface during interruption, As/P substitution can be avoided. Heterointerface abruptness was examined by double-crystal x-ray diffraction and photoluminescence. The results show that the interfaces grown with the modified sequence are considerably more abrupt than those obtained using conventional sequences where As/P interdiffusion extends over several monolayers. We have demonstrated the GSMBE growth of low-threshold 1.3mum and 1.55 mu m strained-layer rm In_{1 -x}Ga_{x}As_{y1}P _{1-y1}/ In_{1-x}Ga_ {x}As_{y2}P_{1-y2 } SCHMQW lasers. For 1.3mum lasers, threshold currents as low as 16mA were measured for 390times5mum ridge lasers, and a threshold current density of 370A/cm^2 was achieved for a 2000times50mu m broad-area device consisting of five 0.84% compressively strained QWs. To the best of our knowledge, these are the lowest values reported to date for GSMBE-grown 1.3 μm lasers, and are comparable to the best devices grown by other techniques such as chemical beam epitaxy and metalorganic vapor phase epitaxy. As for 1.55mum lasers, a threshold current density as low as 320A/cm^2 was achieved for a 2250times50mum broad-area device consisting of four 1.2% compressively strained QWs. This low threshold current density is apparently the same as the lowest reported value for 1.55 μm lasers with four QWs. We have demonstrated a 1.3mum wavelength, GSMBE-grown, strained InGaAsP MQW, folded-cavity surface emitting laser using a

  9. Gas source molecular beam epitaxy of scandium nitride on silicon carbide and gallium nitride surfaces

    SciTech Connect

    King, Sean W. Davis, Robert F.; Nemanich, Robert J.

    2014-11-01

    Scandium nitride (ScN) is a group IIIB transition metal nitride semiconductor with numerous potential applications in electronic and optoelectronic devices due to close lattice matching with gallium nitride (GaN). However, prior investigations of ScN have focused primarily on heteroepitaxial growth on substrates with a high lattice mismatch of 7%–20%. In this study, the authors have investigated ammonia (NH{sub 3}) gas source molecular beam epitaxy (NH{sub 3}-GSMBE) of ScN on more closely lattice matched silicon carbide (SiC) and GaN surfaces (<3% mismatch). Based on a thermodynamic analysis of the ScN phase stability window, NH{sub 3}-GSMBE conditions of 10{sup −5}–10{sup −4} Torr NH{sub 3} and 800–1050 °C where selected for initial investigation. In-situ x-ray photoelectron spectroscopy (XPS) and ex-situ Rutherford backscattering measurements showed all ScN films grown using these conditions were stoichiometric. For ScN growth on 3C-SiC (111)-(√3 × √3)R30° carbon rich surfaces, the observed attenuation of the XPS Si 2p and C 1s substrate core levels with increasing ScN thickness indicated growth initiated in a layer-by-layer fashion. This was consistent with scanning electron microscopy (SEM) images of 100–200 nm thick films that revealed featureless surfaces. In contrast, ScN films grown on 3C-SiC (111)-(3 × 3) and 3C-SiC (100)-(3 × 2) silicon rich surfaces were found to exhibit extremely rough surfaces in SEM. ScN films grown on both 3C-SiC (111)-(√3 × √3)R30° and 2H-GaN (0001)-(1 × 1) epilayer surfaces exhibited hexagonal (1 × 1) low energy electron diffraction patterns indicative of (111) oriented ScN. X-ray diffraction ω-2θ rocking curve scans for these same films showed a large full width half maximum of 0.29° (1047 arc sec) consistent with transmission electron microscopy images that revealed the films to be poly-crystalline with columnar grains oriented at ≈15° to the [0001] direction of the

  10. Single-crystalline BaTiO3 films grown by gas-source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Matsubara, Yuya; Takahashi, Kei S.; Tokura, Yoshinori; Kawasaki, Masashi

    2014-12-01

    Thin BaTiO3 films were grown on GdScO3 (110) substrates by metalorganic gas-source molecular beam epitaxy. Titanium tetra-isopropoxide (TTIP) was used as a volatile precursor that provides a wide growth window of the supplied TTIP/Ba ratio for automatic adjustment of the film composition. Within the growth window, compressively strained films can be grown with excellent crystalline quality, whereas films grown outside of the growth window are relaxed with inferior crystallinity. This growth method will provide a way to study the intrinsic properties of ferroelectric BaTiO3 films and their heterostructures by precise control of the stoichiometry, structure, and purity.

  11. Heteroepitaxy growth of GaAsBi on Ge(100) substrate by gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Pan, Wenwu; Wu, Xiaoyan; Cao, Chunfang; Wang, Shumin; Gong, Qian

    2016-04-01

    We have investigated the growth of GaAsBi single-crystal film on Ge substrate by gas source molecular beam epitaxy. A high-quality GaAsBi epilayer has been obtained. It has been found that the surfactant effect of Bi suppresses the interdiffusion of Ge at the GaAsBi/Ge interface and reduces the misfit dislocation density. The Bi atoms occupy the As sites, as indicated by the appearance of GaBi-like TO(Γ) and LO(Γ) phonon modes in Raman spectra. In addition, the redshift of the GaAs-like LO(Γ) phonon frequency has been observed in the Raman spectra, owing to the Bi-induced biaxial strain and the alloying effect as well.

  12. Tertiarybutylarsine (TBAs) and -phosphine (TBP) as group V-precursors for gas source molecular beam epitaxy for optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Mayer, B.; Reithmaier, J. P.; Forchel, A.

    2001-07-01

    Tertiarybutylarsine and -phosphine are used in a gas source molecular beam epitaxy system as alternative sources for the highly toxic hydrides arsine (AsH 3) and phosphine (PH 3). The growth parameters for binary and ternary (Al, Ga, In) (As, P) compounds on InP substrates were investigated. Heterostructures with good morphologies and optical properties were realized. AlGaInAs/GaInAs/InP long wavelength separate confinement heterostructure lasers with four compressively strained quantum wells were grown. They exhibit a transparency current density of 700 A/cm 2 and a threshold current density of 1.0 kA/cm 2 for 1 mm long broad area devices, respectively.

  13. Si(001):B gas-source molecular-beam epitaxy: Boron surface segregation and its effect on film growth kinetics

    NASA Astrophysics Data System (ADS)

    Kim, H.; Glass, G.; Spila, T.; Taylor, N.; Park, S. Y.; Abelson, J. R.; Greene, J. E.

    1997-09-01

    B-doped Si(001) films, with concentrations CB up to 1.7×1022cm-3, were grown by gas-source molecular-beam epitaxy from Si2H6 and B2H6 at Ts=500-800 °C. D2 temperature-programed desorption (TPD) spectra were then used to determine B coverages θB as a function of CB and Ts. In these measurements, as-deposited films were flash heated to desorb surface hydrogen, cooled, and exposed to atomic deuterium until saturation coverage. Strong B surface segregation was observed with surface-to-bulk B concentration ratios ranging up to 1200. TPD spectra exhibited β2 and β1 peaks associated with dideuteride and monodeuteride desorption as well as lower-temperature B-induced peaks β2* and β1*. Increasing θB increased the area under β2* and β1* at the expense of β2 and β1 and decreased the total D coverage θD. The TPD results were used to determine the B segregation enthalpy, -0.53 eV, and to explain and model the effects of high B coverages on Si(001) growth kinetics. Film deposition rates R increase by ⩾50% with increasing CB>˜1×1019 cm-3 at Ts⩽550 °C, due primarily to increased H desorption rates from B-backbonded Si adatoms, and decrease by corresponding amounts at Ts⩾600 °C due to decreased adsorption site densities. At Ts⩾700 °C, high B coverages also induce {113} facetting.

  14. Properties of Strain Compensated Symmetrical Triangular Quantum Wells Composed of InGaAs/InAs Chirped Superlattice Grown Using Gas Source Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Gu, Yi; Zhang, Yong-Gang

    2008-02-01

    We investigate the properties of symmetrical triangular quantum wells composed of InGaAs/InAs chirped superlattice, which is grown by gas source molecular beam epitaxy via digital alloy method. In the quantum well structure tensile AlInGaAs are used as barriers to partially compensate for the significant compressive strain in the wells, the strain compensation effects are confirmed by x-ray measurement. The photoluminescence spectra of the sample are dominated by the excitonic recombination peak in the whole temperature range. The thermal quenching, peak energy shift and line-width broadening of the PL spectra are analysed in detail, the mechanisms are discussed.

  15. Dilute Nitride GaNP Wide Bandgap Solar Cells Grown by Gas-Source Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Sukrittanon, Supanee

    Integration of III-V semiconductors and Si is a very attractive means to achieve low-cost high-efficiency solar cells. A promising configuration is to utilize a dual-junction solar cell, in which Si is employed as the bottom junction and a wide-bandgap III-V semiconductor as the top junction. The use of a III-V semiconductor as a top junction offers the potential to achieve higher efficiencies than today's best Si solar cell. Dilute nitride GaNP is a promising candidate for the top cell in dual-junction solar cells because it possesses several extremely important attributes: a direct-bandgap that is also tunable as well as easily-attained lattice-match with Si. As a first step towards integration of GaNP solar cells onto Si, the goal of this dissertation is to optimize and demonstrate GaNP solar cells grown by gas-source molecular beam epitaxy (GSMBE) on GaP (001) substrate. The dissertation is divided into three major parts. In the first part, we demonstrate ˜ 2.05 eV ([N]˜ 1.8%) dilute nitride GaNP thin film solar cells, in which the GaNP is closely lattice-matched to Si, on GaP substrates. From transmission electron microscopy (TEM), the device exhibits defects only at the GaNP/GaP interface, and no threading dislocations in an active layer are observed. Our best GaNP solar cell achieved an efficiency of 7.9% with anti-reflection (AR) coating and no window layer. This GaNP solar cell's efficiency is higher than the most efficient GaP solar cell to date and higher than other solar cells with similar direct bandgap (InGaP, GaAsP). Through a systematic study of the structural, electrical, and optical properties of the device, efficient broadband optical absorption and enhanced solar cell performance using GaNP are demonstrated. In the second part, we demonstrate the successful fabrication of GaP/GaNP core/shell microwires utilizing a novel technique: top-down reactive-ion etching (RIE) to create the cores and MBE to create the shells. Systematic studies have been

  16. A study of mixed group-V nitrides grown by gas-source molecular beam epitaxy using a nitrogen radical beam source

    SciTech Connect

    Bi, W.G.; Tu, C.W.; Mathes, D.; Hull, R.

    1997-12-31

    The authors report a study of N incorporation in GaAs and InP by gas-source molecular beam epitaxy using a N radical beam source. For GaNAs grown at high temperatures, phase separation was observed, as evidenced from the formation of cubic GaN aside from GaNAs. By lowering the growth temperature, however, GaNAs alloys with N as high as 14.8% have been obtained without showing any phase separation. For InNP, no phase separation was observed in the temperature range studied (310--420 C). Contrary to GaNAs, incorporating N in InP is very difficult, with only less than 1% N being achieved. Optical absorption measurement reveals strong red shift of bandgap energy with direct-bandgap absorption. However, no semimetallic region seems to exist for GaNAs and a composition, dependent bowing parameter has been observed.

  17. InP/InGaAs/InP DHBT structures with graded composition base grown by gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Teng, Teng; Ai, Likun; Xu, Anhuai; Sun, Hao; Zhu, Fuying; Qi, Ming

    2011-05-01

    A new InP/InGaAs/InP DHBT structure with graded composition base was optimized and grown successfully in this work. The gallium (Ga) composition increased gradually from 47% on the collector side to 55% on the emitter side. The InP/InGaAs/InP DHBT structures were grown by gas source molecular beam epitaxy (GSMBE). Characteristics of InP, InGaAs and InGaAsP materials were investigated. High quality InP/InGaAs/InP DHBT structural materials were obtained. The InP/InGaAs/InP DHBT device with emitter area of 100×100 μm2 was fabricated. The offset voltage of 0.2 V, BVCEO>1.2 V, current gain of ß=550 at VCE of 1.0 V were achieved. The reasons for the low breakdown voltage were analyzed.

  18. InP/InGaAs/InP DHBT structures with high carbon-doped base grown by gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Teng, Teng; Xu, Anhuai; Ai, Likun; Sun, Hao; Qi, Ming

    2013-09-01

    A new InP/InGaAs/InP DHBT structure with high carbon (C)-doped base was optimized and grown successfully by gas source molecular beam epitaxy (GSMBE) in this work. The C-doping concentration is 3×1019 cm-3 with carrier mobility of 66.3 cm2/V s. Characteristics of C-doped InGaAs materials were investigated. High quality InP/InGaAs/InP DHBT structural materials were obtained. The InP/InGaAs/InP DHBT device with emitter area of 100×100 μm2 was fabricated. The open base breakdown voltage (VBCEO) of 4.2 V and current gain of 60 at VCE of 3.0 V were achieved. All these results prove the material is suitable for DHBT device fabrication.

  19. Infrared reflectivity spectra of gas-source molecular beam epitaxy grown dilute InN{sub x}As{sub 1-x}/InP (001)

    SciTech Connect

    Talwar, Devki N.; Yang, Tzuen-Rong; Hsiung Lin, Hao; Chuan Feng, Zhe

    2013-02-04

    Vibrational spectra of gas-source molecular beam epitaxy grown dilute InN{sub x}As{sub 1-x}/InP (001) alloys are obtained using a Fourier-transform infrared (IR) spectroscopy. A triply degenerate N{sub As} local vibrational mode of T{sub d}-symmetry is observed near 438 cm{sup -1} corresponding to the In-N bond energy. The analysis of composition dependent infrared reflectivity spectra in InNAs has predicted a two-phonon-mode behavior. In In(Ga)-rich GaInNAs alloys the observed splitting of the N{sub As} local mode into a doublet for the N{sub As}-Ga{sub 1}(In{sub 1})In{sub 3}(Ga{sub 3}) pair-defect of C{sub 3v}-symmetry is consistent with our simulated results based on a sophisticated Green's function theory.

  20. Role of adsorption kinetics in the low-temperature Si growth by gas-source molecular beam epitaxy: In situ observations and detailed modeling of the growth

    SciTech Connect

    Murata, Takeshi; Nakazawa, Hideki; Tsukidate, Yoshikazu; Suemitsu, Maki

    2001-08-06

    The growth rate and surface hydrogen coverage during Si gas-source molecular beam epitaxy using disilane have been obtained as functions of both the growth temperature and the source-gas pressure. The activation energy of the low-temperature (<600{sup o}C) growth rate was found to increase with the source-gas pressure, indicating a contribution by the adsorption process in these low-temperature growth kinetics. Several growth models have been constructed based on the results, among which the two-site/four-site-adsorption model [M. Suemitsu Jpn. J. Appl. Phys., Part 236, L625 (1997)] showed the best fit to both the growth rate and the hydrogen coverage. {copyright} 2001 American Institute of Physics.

  1. InGaAs Photodetectors Cut-off at 1.9 μm Grown by Gas-Source Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Zhang, Yong-Gang; Hao, Guo-Qiang; Gu, Yi; Zhu, Cheng; Li, Ai-Zhen; Liu, Tian-Dong

    2005-01-01

    Using a linear graded InxGa1-xAs as the buffer layer, positive-intrinsic-negative wavelength-extended In0.6Ga0.4 As photodetectors with 50% cut-off wavelength of 1.9 μm at room temperature were grown by using gas-source molecular beam epitaxy, and their performance over a wide temperature range has been extensively investigated. The detectors show typical dark current at bias voltage 50 mV and the resistance-area product R0A of 7 nA/765 Ωcm2 and 31 pA/404 kΩcm2 at 290 K and 210 K, respectively. The thermal activation energy of the dark current in the temperature range 250-350 K is 0.488 eV.

  2. Gas source molecular-beam epitaxial growth of TlInGaAsN double quantum well light emitting diode structures and thallium incorporation characteristics

    NASA Astrophysics Data System (ADS)

    Matsumoto, T.; Krishnamurthy, D.; Fujiwara, A.; Hasegawa, S.; Asahi, H.

    2006-10-01

    TlInGaAsN/GaAs double quantum well (DQW) structures were grown on GaAs (1 0 0) substrates by gas source molecular-beam epitaxy. It has been found that high Tl flux is needed for the incorporation of Tl into the films. Reduction in the temperature variation of electroluminescence (EL) peak energy has been observed by the addition of Tl into quantum well (QW) layers; -0.62 meV/K for the InGaAsN/GaAs DQW light emitting diodes (LEDs) and -0.53 meV/K for the TlInGaAsN/GaAs DQW LEDs. By replacing GaAs barrier layers with TlGaAs barrier layers, further reduction could be obtained; -0.35 meV/K for TlInGaAsN/TlGaAs DQW LEDs. SIMS measurements indicated that this improvement is caused by the increased incorporation of Tl into the QW layers.

  3. Modelling, Design, Growth and Characterization of Strain Balanced Quantum Cascade Lasers (3-11mum), grown by Gas Source Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, Neelanjan

    Quantum Cascade Laser (QCL) is a compact room temperature (RT) source of mid-infrared radiation, which can be used for spectroscopic detection of trace amount of chemicals. The mid-infrared spectral range between (3-11 microm), has a dense array of absorption lines of numerous molecules, due to the presence of fundamental vibrational modes. The goal of this thesis can be subdivided into two parts. Firstly, short wavelength QCLs, emitting below 4microm, perform poorly at RT, due to inter-valley Gamma --- L carrier scattering, carrier escape to the continuum, heat removal from the core region at high power density corresponding to short wavelength operation, and large interface scattering due to highly strained materials. Secondly, it is desirable to have a single QCL based source emitting between 6-10microm, which be used to detect multiple molecules having their peak absorptions far apart, inside this spectral range. However, gain bandwidth of a single core QCL is relatively small, so laser emission cannot be tuned over a wide spectral range. This thesis describes the working principle of a QCL based on superlattice transport, rate equations, scattering mechanism, and waveguide design. The choice of the material system for this work and the fundamentals of band structure engineering has been derived. Gas source molecular beam epitaxy - growth optimization and characterization is one of the most important features of this work, especially for short wavelength QCLs, and has been explained in depth. Different strategies for design of active region design of short wavelength QCL and heterogeneous broadband QCL has been explored. The major milestones, of this research was the world's first watt level continuous wave (CW), RT demonstration at 3.76 microm, which was followed by another milestone of the first CW, RT demonstration at 3.39microm and 3.55microm, and finally the elusive result of QCL emitting at CW, RT at a wavelength as short as lambda ~3microm, a record. In

  4. Ultrahigh B doping ({<=}10{sup 22} cm{sup -3}) during Si(001) gas-source molecular-beam epitaxy: B incorporation, electrical activation, and hole transport

    SciTech Connect

    Glass, G.; Kim, H.; Desjardins, P.; Taylor, N.; Spila, T.; Lu, Q.; Greene, J. E.

    2000-03-15

    Si(001) layers doped with B concentrations C{sub B} between 1x10{sup 17} and 1.2x10{sup 22} cm{sup -3} (24 at %) were grown on Si(001)2x1 at temperatures T{sub s}=500-850 degree sign C by gas-source molecular-beam epitaxy from Si{sub 2}H{sub 6} and B{sub 2}H{sub 6}. C{sub B} increases linearly with the incident precursor flux ratio J{sub B{sub 2}}{sub H{sub 6}}/J{sub Si{sub 2}}{sub H{sub 6}} and B is incorporated into substitutional electrically active sites at concentrations up to C{sub B}{sup *}(T{sub s}) which, for T{sub s}=600 degree sign C, is 2.5x10{sup 20} cm{sup -3}. At higher B concentrations, C{sub B} increases faster than J{sub B{sub 2}}{sub H{sub 6}}/J{sub Si{sub 2}}{sub H{sub 6}} and there is a large and discontinuous decrease in the activated fraction of incorporated B. However, the total activated B concentration continues to increase and reaches a value of N{sub B}=1.3x10{sup 21} cm{sup -3} with C{sub B}=1.2x10{sup 22} cm{sup -3}. High-resolution x-ray diffraction (HR-XRD) and reciprocal space mapping measurements show that all films, irrespective of C{sub B} and T{sub s}, are fully strained. No B precipitates or misfit dislocations were detected by HR-XRD or transmission electron microscopy. The lattice constant in the film growth direction a{sub (perpendicular} {sub sign)} decreases linearly with increasing C{sub B} up to the limit of full electrical activation and continues to decrease, but nonlinearly, with C{sub B}>C{sub B}{sup *}. Room-temperature resistivity and conductivity mobility values are in good agreement with theoretical values for B concentrations up to C{sub B}=2.5x10{sup 20} and 2x10{sup 21} cm{sup -3}, respectively. All results can be explained on the basis of a model which accounts for strong B surface segregation to the second-layer with a saturation coverage {theta}{sub B,sat} of 0.5 ML (corresponding to C{sub B}=C{sub B}{sup *}). At higher C{sub B} (i.e., {theta}{sub B}>{theta}{sub B,sat}), B accumulates in the upper layer as

  5. A Reflection High Energy Electron Diffraction-Reflectance Anisotropy Spectroscopy Study of Silicon Growth Dynamics During Gas Source Molecular Beam Epitaxy from Silanes

    NASA Astrophysics Data System (ADS)

    Joyce, B. A.; Zhang, J.; Taylor, A. G.; Lees, A. K.

    Molecular beam epitaxy (MBE) provides an ideal experimental vehicle for the in situ study of thin film growth dynamics. By using a combination of reflection high energy electron diffraction (RHEED) and reflectance anisotropy (difference) spectroscopy [RA(D)S], it is possible to separate morphological (long range order) and local electronic structure effects, which we demonstrate with the growth of silicon films from disilane (Si2H6) on Si(001) (2 × 1)+(1 × 2) reconstructed surfaces. The rate-limiting step in Si growth from both monosilane (SiH4) and disilane is the desorption of molecular hydrogen and we have found using RAS that, over a significant range of temperature and coverage, hydrogen desorption follows zeroth order kinetics as the result of a step-mediated process. Finally, we show how this influences the growth rate on substrates of differing degrees of vicinality.

  6. In situ doping control for growth of n p n Si/SiGe/Si heterojunction bipolar transistor by gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Gao, F.; Huang, D. D.; Li, J. P.; Liu, C.

    2005-01-01

    N-p-n Si/SiGe/Si heterostructures have been grown by a disilane (Si 2H 6) gas and Ge solid sources molecular beam epitaxy system using phosphine (PH 3) and diborane (B 2H 6) as n- and p-type in situ doping sources, respectively. Adopting an in situ doping control technology, the influence of background B dopant on the growth of n-Si emitter layer was reduced, and an abrupt B dopant distribution from SiGe base to Si emitter layer was obtained. Besides, higher n-type doping in the surface region of emitter to reduce the emitter resist can be realized, and it did not result in the drop of growth rate of Si emitter layer in this technology.

  7. Silicon Holder For Molecular-Beam Epitaxy

    NASA Technical Reports Server (NTRS)

    Hoenk, Michael E.; Grunthaner, Paula J.; Grunthaner, Frank J.

    1993-01-01

    Simple assembly of silicon wafers holds silicon-based charge-coupled device (CCD) during postprocessing in which silicon deposited by molecular-beam epitaxy. Attains temperatures similar to CCD, so hotspots suppressed. Coefficients of thermal expansion of holder and CCD equal, so thermal stresses caused by differential thermal expansion and contraction do not develop. Holder readily fabricated, by standard silicon processing techniques, to accommodate various CCD geometries. Silicon does not contaminate CCD or molecular-beam-epitaxy vacuum chamber.

  8. Perspective: Oxide molecular-beam epitaxy rocks!

    SciTech Connect

    Schlom, Darrell G.

    2015-06-01

    Molecular-beam epitaxy (MBE) is the “gold standard” synthesis technique for preparing semiconductor heterostructures with high purity, high mobility, and exquisite control of layer thickness at the atomic-layer level. Its use for the growth of multicomponent oxides got off to a rocky start 30 yr ago, but in the ensuing decades, it has become the definitive method for the preparation of oxide heterostructures too, particularly when it is desired to explore their intrinsic properties. Examples illustrating the unparalleled achievements of oxide MBE are given; these motivate its expanding use for exploring the potentially revolutionary states of matter possessed by oxide systems.

  9. Materials issues in molecular beam epitaxy

    SciTech Connect

    Tsao, J.Y.

    1993-12-31

    The technology of crystal growth has advanced enormously during the past two decades; among those advances, the development and refinement of molecular beam epitaxy (MBE) has been among the most important. Crystals grown by MBE are more precisely controlled than those grown by any other method, and today form the basis for many of the most advanced device structures in solid-state physics, electronics and optoelectronics. In addition to its numerous device applications, MBE is also an enormously rich and interesting area of materials science in and of itself. This paper, discusses a few examples of some of these materials issues, organized according to whether they involve bulk, thin films, or surfaces.

  10. Perspective: Oxide molecular-beam epitaxy rocks!

    NASA Astrophysics Data System (ADS)

    Schlom, Darrell G.

    2015-06-01

    Molecular-beam epitaxy (MBE) is the "gold standard" synthesis technique for preparing semiconductor heterostructures with high purity, high mobility, and exquisite control of layer thickness at the atomic-layer level. Its use for the growth of multicomponent oxides got off to a rocky start 30 yr ago, but in the ensuing decades, it has become the definitive method for the preparation of oxide heterostructures too, particularly when it is desired to explore their intrinsic properties. Examples illustrating the unparalleled achievements of oxide MBE are given; these motivate its expanding use for exploring the potentially revolutionary states of matter possessed by oxide systems.

  11. Twenty years of molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Cho, A. Y.

    1995-05-01

    The term "molecular beam epitaxy" (MBE) was first used in one of our crystal growth papers in 1970, after having conducted extensive surface physics studies in the late 1960's of the interaction of atomic and molecular beams with solid surfaces. The unique feature of MBE is the ability to prepare single crystal layers with atomic dimensional precision. MBE sets the standard for epitaxial growth and has made possible semiconductor structures that could not be fabricated with either naturally existing materials or by other crystal growth techniques. MBE led the crystal growth technologies when it prepared the first semiconductor quantum well and superlattice structures that gave unexpected and exciting electrical and optical properties. For example, the discovery of the fractional quantized Hall effect. It brought experimental quantum physics to the classroom, and practically all major universities throughout the world are now equipped with MBE systems. The fundamental principles demonstrated by the MBE growth of III-V compound semiconductors have also been applied to the growth of group IV, II-VI, metal, and insulating materials. For manufacturing, the most important criteria are uniformity, precise control of the device structure, and reproducibility. MBE has produced more lasers (3 to 5 million per month for compact disc application) than any other crystal growth technique in the world. New directions for MBE are to incorporate in-situ, real-time monitoring capabilities so that complex structures can be precisely "engineered". In the future, as environmental concerns increase, the use of toxic arsine and phosphine may be limited. Successful use of valved cracker cells for solid arsenic and phosphorus has already produced InP based injection lasers.

  12. InPBi Single Crystals Grown by Molecular Beam Epitaxy

    PubMed Central

    Wang, K.; Gu, Y.; Zhou, H. F.; Zhang, L. Y.; Kang, C. Z.; Wu, M. J.; Pan, W. W.; Lu, P. F.; Gong, Q.; Wang, S. M.

    2014-01-01

    InPBi was predicted to be the most robust infrared optoelectronic material but also the most difficult to synthesize within In-VBi (V = P, As and Sb) 25 years ago. We report the first successful growth of InPBi single crystals with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InPBi thin films reveal excellent surface, structural and optical qualities making it a promising new III–V compound family member for heterostructures. The Bi concentration is found to be 2.4 ± 0.4% with 94 ± 5% Bi atoms at substitutional sites. Optical absorption indicates a band gap of 1.23 eV at room temperature while photoluminescence shows unexpectedly strong and broad light emission at 1.4–2.7 μm which can't be explained by the existing theory. PMID:24965260

  13. Dissociation of Al2O3(0001) substrates and the roles of silicon and oxygen in n-type GaN thin solid films grown by gas-source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Van Nostrand, J. E.; Solomon, J.; Saxler, A.; Xie, Q.-H.; Reynolds, D. C.; Look, D. C.

    2000-06-01

    Unintentionally doped and silicon doped GaN films prepared by molecular beam epitaxy using ammonia are investigated. Hall, secondary ion mass spectroscopy (SIMS), photoluminescence, and x-ray data are utilized for analysis of sources of autodoping of GaN epitaxial films in an effort to identify whether the n-type background electron concentration is of impurity origin or native defect origin. We identify and quantify an anomalous relationship between the Si doping concentration and free carrier concentration and mobility using temperature dependent Hall measurements on a series of 2.0-μm-thick GaN(0001) films grown on sapphire with various Si doping concentrations. SIMS is used to identify oxygen as the origin of the excess free carriers in lightly doped and undoped GaN films. Further, the source of the oxygen is positively identified to be dissociation of the sapphire substrate at the nitride-sapphire interface. Dissociation of SiC at the nitride-carbide interface is also observed. Finally, SIMS is again utilized to show how Si doping can be utilized to suppress the diffusion of the oxygen into the GaN layer from the sapphire substrate. The mechanism of suppression is believed to be formation of a Si-O bond and a greatly reduced diffusion coefficient of the subsequent Si-O complex in GaN.

  14. Growth and characterization of dilute nitride GaN{sub x}P{sub 1−x} nanowires and GaN{sub x}P{sub 1−x}/GaN{sub y}P{sub 1−y} core/shell nanowires on Si (111) by gas source molecular beam epitaxy

    SciTech Connect

    Sukrittanon, S.; Kuang, Y. J.; Dobrovolsky, A.; Chen, W. M.; Buyanova, I. A.; Kang, Won-Mo; Kim, Bong-Joong; Jang, Ja-Soon; Tu, C. W.

    2014-08-18

    We have demonstrated self-catalyzed GaN{sub x}P{sub 1−x} and GaN{sub x}P{sub 1−x}/GaN{sub y}P{sub 1−y} core/shell nanowire growth by gas-source molecular beam epitaxy. The growth window for GaN{sub x}P{sub 1−x} nanowires was observed to be comparable to that of GaP nanowires (∼585 °C to ∼615 °C). Transmission electron microscopy showed a mixture of cubic zincblende phase and hexagonal wurtzite phase along the [111] growth direction in GaN{sub x}P{sub 1−x} nanowires. A temperature-dependent photoluminescence (PL) study performed on GaN{sub x}P{sub 1−x}/GaN{sub y}P{sub 1−y} core/shell nanowires exhibited an S-shape dependence of the PL peaks. This suggests that at low temperature, the emission stems from N-related localized states below the conduction band edge in the shell, while at high temperature, the emission stems from band-to-band transition in the shell as well as recombination in the GaN{sub x}P{sub 1−x} core.

  15. Method of deposition by molecular beam epitaxy

    DOEpatents

    Chalmers, S.A.; Killeen, K.P.; Lear, K.L.

    1995-01-10

    A method is described for reproducibly controlling layer thickness and varying layer composition in an MBE deposition process. In particular, the present invention includes epitaxially depositing a plurality of layers of material on a substrate with a plurality of growth cycles whereby the average of the instantaneous growth rates for each growth cycle and from one growth cycle to the next remains substantially constant as a function of time. 9 figures.

  16. Method of deposition by molecular beam epitaxy

    DOEpatents

    Chalmers, Scott A.; Killeen, Kevin P.; Lear, Kevin L.

    1995-01-01

    A method is described for reproducibly controlling layer thickness and varying layer composition in an MBE deposition process. In particular, the present invention includes epitaxially depositing a plurality of layers of material on a substrate with a plurality of growth cycles whereby the average of the instantaneous growth rates for each growth cycle and from one growth cycle to the next remains substantially constant as a function of time.

  17. Induced base transistor fabricated by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chang, C.-Y.; Liu, W. C.; Jame, M. S.; Wang, Y. H.; Luryi, S.

    1986-09-01

    A novel three-terminal hot-electron device, the induced base transistor (IBT), has been fabricated by molecular beam epitaxy. Two-dimensional electron gas induced by the applied collector field in an undoped GaAs quantum well is used as the base of the IBT. The common-base current gain alpha has been achieved as high as 0.96 under a collector bias of 2.5 V and an emitter current of 3 mA.

  18. Applying CLIPS to control of molecular beam epitaxy processing

    NASA Technical Reports Server (NTRS)

    Rabeau, Arthur A.; Bensaoula, Abdelhak; Jamison, Keith D.; Horton, Charles; Ignatiev, Alex; Glover, John R.

    1990-01-01

    A key element of U.S. industrial competitiveness in the 1990's will be the exploitation of advanced technologies which involve low-volume, high-profit manufacturing. The demands of such manufacture limit participation to a few major entities in the U.S. and elsewhere, and offset the lower manufacturing costs of other countries which have, for example, captured much of the consumer electronics market. One such technology is thin-film epitaxy, a technology which encompasses several techniques such as Molecular Beam Epitaxy (MBE), Chemical Beam Epitaxy (CBE), and Vapor-Phase Epitaxy (VPE). Molecular Beam Epitaxy (MBE) is a technology for creating a variety of electronic and electro-optical materials. Compared to standard microelectronic production techniques (including gaseous diffusion, ion implantation, and chemical vapor deposition), MBE is much more exact, though much slower. Although newer than the standard technologies, MBE is the technology of choice for fabrication of ultraprecise materials for cutting-edge microelectronic devices and for research into the properties of new materials.

  19. Molecular Beam Epitaxy Growth of Iron Phthalocyanine Nanostructures

    SciTech Connect

    Debnath, A. K.; Samanta, S.; Singh, Ajay; Aswal, D. K.; Gupta, S. K.; Yakhmi, J. V.

    2009-06-29

    FePc films of different thickness have been deposited by molecular beam epitaxy (MBE) as a function of substrate temperature (25-300 deg. C) and deposition rate (0.02-0.07 nm/s). The morphology of a 60 nm alpha-phase film has been tuned from nanobrush (nearly parallel nanorods aligned normal to the substrate plane) to nanoweb (nanowires forming a web-like structure in the plane of the substrate) by changing the deposition rate from 0.02 to 0.07 nm/s. We propose growth mechanisms of nanoweb and nanobrush morphology based on the van der Waals (vdW) epitaxy. For air exposed FePc films I-V hysteresis was observed at 300 K and it is attributed to surface traps created by chemisorbed oxygen.

  20. Very high (> 1019 cm-3) in situ n-type doping of silicon during molecular beam epitaxy using supersonic jets of phosphine

    NASA Astrophysics Data System (ADS)

    Malik, R.; Gulari, E.; Bhattacharya, P.; Linder, K. K.; Rieh, J.-S.

    1997-03-01

    The use of supersonically injected pulses of phosphine to achieve uniform and high levels of n-type doping in Si during gas-source molecular beam epitaxy is demonstrated. Uniform n-type doping up to levels of 5×1019 cm-3 is obtained. SiGe/Si junction diodes made with this doping technique show good doping profiles and rectifying characteristics.

  1. Development of Crystal Al MKIDs by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Naruse, M.; Sekimoto, Y.; Noguchi, T.; Miyachi, A.; Nitta, T.; Uzawa, Y.

    2011-11-01

    We report here the effect of film qualities in superconductors on the properties of Microwave Kinetic Inductance Detectors (MKIDs). The sensitivity of MKIDs between crystal aluminum films and amorphous aluminum films is compared. The good quality and crystallized aluminum films have been prepared by using molecular beam epitaxy. We have confirmed that epitaxial Al(111) films were grown on Si(111) substrates with X-ray diffraction and in-situ reflection high-energy electron diffraction measurements. The amorphous aluminum films on the Si(111) wafers have been deposited by electron beam evaporation. We have measured transmission losses of MKIDs, noise spectrum and relaxation time against optical pulses, changing MKIDs' bath temperature from 0.11 K to 0.55 K in a dilution refrigerator. Despite of the improvement in normal resistivity, the quasiparticle decay time of both films are equivalent and 450 μs at 0.11 K. The electrical noise equivalent power of the both MKIDs are also comparable and around 10^{-17} W/sqrt{Hz}. Fabrication details and performance data of both films are presented.

  2. Molecular Beam Epitaxy of Layered Material Superlattices and Heterostructures

    NASA Astrophysics Data System (ADS)

    Vishwanath, Suresh; Liu, Xinyu; Rouvimov, Sergei; Furdyna, Jacek K.; Jena, Debdeep; Xing, Huili Grace

    2014-03-01

    Stacking of various layered materials is being pursued widely to realize various devices and observe novel physics. Mostly, these have been limited to exfoliation and stacking either manually or in solution, where control on rotational alignment or order of stacking is lost. We have demonstrated molecular beam epitaxy (MBE) growth of Bi2Se3/MoSe2 superlatticeand Bi2Se3/MoSe2/SnSe2 heterostructure on sapphire. We have achieved a better control on the order of stacking and number of layers as compared to the solution technique. We have characterized these structures using RHEED, Raman spectroscopy, XPS, AFM, X-ray reflectometry, cross-section (cs) and in-plane (ip) TEM. The rotational alignment is dictated by thermodynamics and is understood using ip-TEM diffraction patterns. Layered growth and long range order is evident from the streaky RHEED pattern. Abrupt change in RHEED pattern, clear demarcation of boundary between layers seen using cs-TEM and observation of Raman peaks corresponding to all the layers suggest van-der-waals epitaxy. In our knowledge this is a first demonstration of as grown superlattices and heterostuctures involving transition metal dichalcogenides and is an important step towards the goal of stacking of 2D crystals like lego blocks.

  3. Nanoengineering of Ruddlesden-Popper phases using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Haeni, Jeffrey Hewlett

    Epitaxial films including superlattices of the A n+1BnO3 n+1 Ruddlesden-Popper homologous series with A=Sr and Ba and B=Ti and Ru have been grown by reactive molecular beam epitaxy (MBE) on (LaAlO3)0.3--(SrAl0.5Ta 0.5O3)0.7 (LSAT), SrTiO3, DyScO 3 and Si substrates. The strict composition control necessary for the synthesis of these phases was achieved through the use of reflection high-energy electron diffraction (RHEED) intensity oscillations. The first five members of the Srn+1 TinO3n+1 and the Sr n+1RunO3 n+1 Ruddlesden-Popper homologous series, i.e., Sr 2TiO4, Sr3Ti2O7, Sr 4Ti3O10, Sr5Ti4O13 , and Sr6Ti5O16, and Sr2RuO 4, Sr3Ru2O7, Sr4Ru 3O10, Sr5Ru4O13, and Sr 6Ru5O16, respectively, were grown with layer-by-layer deposition. Dielectric measurements indicate that the dielectric constant tensor coefficient epsilon33 of the Srn +1TinO3n +1 series increases from a minimum of 44 +/- 4 in the n = 1 (Sr2TiO4) film to a maximum of 263 +/- 2 in the n = infinity (SrTiO3) film. XPS measurements on Sr2TiO4/SrTiO3 heterostructures indicate a type II interface between the two materials, with a valence band offset of -0.40 +/- 0.1 eV, and a conduction band offset of -0.2 +/- 0.1 eV. Epitaxial SrTiO3 thin films grown on DyScO3 and LSAT substrates show dramatically different dielectric properties, as measured with interdigitated electrodes. The film on DyScO3 is under biaxial tensile strain and shows significant room temperature tunability and a sharp Curie-Weiss peak at 293 K. Under biaxial compressive strain, the SrTiO 3 exhibits negligible room temperature tunability. Epitaxial SrTiO3/BaTiO3 short period superlattices were grown with nearly atomically-abrupt interfaces that are maintained even after annealing to high temperature. In addition, cross-sectional TEM reveals that all superlattice periods grown are coherently strained to the underlying (001) SrTiO3 and (001) LSAT substrates. Epitaxial SrRuO3 layers were grown on Si (100) on which a thin epitaxial (Ba,Sr)O/SrSi2

  4. Perspective: Rapid synthesis of complex oxides by combinatorial molecular beam epitaxy

    DOE PAGESBeta

    A. T. Bollinger; Wu, J.; Bozovic, I.

    2016-03-15

    In this study, the molecular beam epitaxy(MBE) technique is well known for producing atomically smooth thin films as well as impeccable interfaces in multilayers of many different materials. In particular, molecular beam epitaxy is well suited to the growth of complex oxides, materials that hold promise for many applications. Rapid synthesis and high throughput characterization techniques are needed to tap into that potential most efficiently. We discuss our approach to doing that, leaving behind the traditional one-growth-one-compound scheme and instead implementing combinatorial oxide molecular beam epitaxy in a custom built system.

  5. Perspective: Rapid synthesis of complex oxides by combinatorial molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bollinger, A. T.; Wu, J.; Božović, I.

    2016-05-01

    The molecular beam epitaxy (MBE) technique is well known for producing atomically smooth thin films as well as impeccable interfaces in multilayers of many different materials. In particular, molecular beam epitaxy is well suited to the growth of complex oxides, materials that hold promise for many applications. Rapid synthesis and high throughput characterization techniques are needed to tap into that potential most efficiently. We discuss our approach to doing that, leaving behind the traditional one-growth-one-compound scheme and instead implementing combinatorial oxide molecular beam epitaxy in a custom built system.

  6. Metallic impurities in gallium nitride grown by molecular beam epitaxy

    SciTech Connect

    McHugo, S.A.; Krueger, J.; Kisielowski, C.

    1997-04-01

    Transition metals are often encountered in trace amounts in semiconductors. They have been extensively studied in most elemental and compound systems, since they form deep donor and/or acceptor levels which usually degrade the electronic and optical material properties. Only very little is known about transition metals in recent III-V semiconducting materials, such as GaN, AlN and InN. These few studies have been done exclusively on Metal-Organic Chemical Vapor Deposition (MOCVD) or Hybrid Vapor Phase Epitaxy HVPE-grown GaN. Preliminary x-ray fluorescence studies at the Advanced Light Source, beamline 10.3.1, Lawrence Berkeley National Laboratory have revealed that GaN materials grown by Molecular Beam Epitaxy (MBE) have Fe, Ni and Cr as the dominant transition metal contaminants. This finding is commensurate with the extremely high concentrations of hydrogen, carbon and oxygen (up to 10{sup 20} cm{sup {minus}3}) measured by Secondary Ion Mass Spectroscopy (SIMS). Preliminary work using the mapping capabilities of the x-ray fluorescence microprobe revealed the metal impurities were inhomogeneously distributed over the film. Future work of this collaboration will be to find a correlation between the existence of transition metals in MBE films, as revealed by x-ray fluorescence, and Photoluminescence (PL) spectra taken in the infrared region. Also, the authors will make use of the 1 {mu}m spatial resolution of x-ray microprobe to locate the contaminants in relation to structural defects in the GaN films. Because of the large strain caused by the lattice mismatch between the GaN films and the substrates, the films grow in a columnar order with high densities of grain boundaries and dislocations. These structural defects offer preferential sites for metal precipitation or agglomeration which could degrade the optical properties of this material more so than if the impurities were left dissolved in the GaN.

  7. Creating Ruddlesden-Popper phases by hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Haislmaier, Ryan C.; Stone, Greg; Alem, Nasim; Engel-Herbert, Roman

    2016-07-01

    The synthesis of a 50 unit cell thick n = 4 Srn+1TinO3n+1 (Sr5Ti4O13) Ruddlesden-Popper (RP) phase film is demonstrated by sequentially depositing SrO and TiO2 layers in an alternating fashion using hybrid molecular beam epitaxy (MBE), where Ti was supplied using titanium tetraisopropoxide (TTIP). A detailed calibration procedure is outlined for determining the shuttering times to deposit SrO and TiO2 layers with precise monolayer doses using in-situ reflection high energy electron diffraction (RHEED) as feedback. Using optimized Sr and TTIP shuttering times, a fully automated growth of the n = 4 RP phase was carried out over a period of >4.5 h. Very stable RHEED intensity oscillations were observed over the entire growth period. The structural characterization by X-ray diffraction and high resolution transmission electron microscopy revealed that a constant periodicity of four SrTiO3 perovskite unit cell blocks separating the double SrO rocksalt layer was maintained throughout the entire film thickness with a very little amount of planar faults oriented perpendicular to the growth front direction. These results illustrate that hybrid MBE is capable of layer-by-layer growth with atomic level precision and excellent flux stability.

  8. On the Growth of Complex Oxides by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Fong, Dillon

    Functional materials based on complex oxides in thin film form offer new and exciting strategies for meeting many of our outstanding energy challenges through systematic control of layer sequencing, strain, etc. However, the synthesis of such oxide films can be a major challenge even when utilizing reactive molecular-beam epitaxy (MBE), a powerful deposition technique that allows the construction of materials atomic plane by atomic plane. To understand the fundamental physics of oxide growth by reactive MBE, we present in situ surface x-ray diffraction results on the growth of SrTiO3 and SrO-SrTiO3 thin films on (001)-oriented SrTiO3 substrates. For homoepitaxy, we compare sequential deposition (alternating Sr and Ti monolayer doses) with that of co-deposition of Sr and Ti, both in a background of oxygen pressure, and observe drastically different growth pathways due to the presence of a TiO2 double layer. For heteroepitaxial growth of Ruddlesden-Popper SrO-SrTiO3 films, we find that layers rearrange dynamically, resulting in layer sequences distinct from the shutter sequence. In general, the starting surface structure and composition, in combination with local thermodynamic considerations, strongly influence our ability to atomically construct new complex oxides.

  9. Quality of epitaxial InAs nanowires controlled by catalyst size in molecular beam epitaxy

    SciTech Connect

    Zhang, Zhi; Xu, Hong-Yi; Guo, Ya-Nan; Liao, Zhi-Ming; Lu, Zhen-Yu; Chen, Ping-Ping; Shi, Sui-Xing; Lu, Wei; Zou, Jin

    2013-08-12

    In this study, the structural quality of Au-catalyzed InAs nanowires grown by molecular beam epitaxy is investigated. Through detailed electron microscopy characterizations and analysis of binary Au-In phase diagram, it is found that defect-free InAs nanowires can be induced by smaller catalysts with a high In concentration, while comparatively larger catalysts containing less In induce defected InAs nanowires. This study indicates that the structural quality of InAs nanowires can be controlled by the size of Au catalysts when other growth conditions remain as constants.

  10. Quality of epitaxial InAs nanowires controlled by catalyst size in molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zhang, Zhi; Lu, Zhen-Yu; Chen, Ping-Ping; Xu, Hong-Yi; Guo, Ya-Nan; Liao, Zhi-Ming; Shi, Sui-Xing; Lu, Wei; Zou, Jin

    2013-08-01

    In this study, the structural quality of Au-catalyzed InAs nanowires grown by molecular beam epitaxy is investigated. Through detailed electron microscopy characterizations and analysis of binary Au-In phase diagram, it is found that defect-free InAs nanowires can be induced by smaller catalysts with a high In concentration, while comparatively larger catalysts containing less In induce defected InAs nanowires. This study indicates that the structural quality of InAs nanowires can be controlled by the size of Au catalysts when other growth conditions remain as constants.

  11. Superconductivity in oxygen doped iron telluride by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zheng, Mao

    Iron base superconductor have gained much attention in the research community. They offer great potentials to improve our understanding of the subject of superconductivity by having another family of high temperature superconductors to compare and contrast to the cuprates. Practically, the iron based superconductors seems to be even better candidates for applications in power generation and power transmission. Iron telluride is regarded as the parent compound of the "11" family, the family of iron chalcogenide that has the simplest structure. Iron telluride itself is not a superconductor, by can become one when doped with oxygen. In this investigation, we developed the growth recipe of thin film iron telluride by Molecular Beam Epitaxy (MBE). We found the growth to be self-regulated, similar to that of GaAs. The initial layers of growth seem to experience a spontaneous crystallization, as the film quickly go from the initial polycrystalline phase to highly crystalline in just a few unit cells. We studied oxygen doping to the iron telluride thin films and the resultant superconductivity. We characterized the sample with AFM, XRD, transport, and STEM-EELS, and we found that interfacial strain is not an essential ingredient of superconductivity in this particular case. We investigated the doping conditions for two candidate oxygen doping modes: substitution and interstitial. We found that substitution occurs when the film grown in oxygen, while interstitial oxygen is primarily incorporated during annealing after growth. The substitutional oxygen are concentrated in small local regions where substitution is around 100%, but does not contribute to superconductivity. We estimated substitutional oxygen to be about 5%, and is the proximate cause of superconductivity. Hall experiment on our sample showed a shift of dominant carrier type from holes to electrons around 35 K, but the transition was set in motion as early as the structural phase transition around 70 K. We

  12. Bismuth nano-droplets for group-V based molecular-beam droplet epitaxy

    NASA Astrophysics Data System (ADS)

    Li, C.; Zeng, Z. Q.; Fan, D. S.; Hirono, Y.; Wu, J.; Morgan, T. A.; Hu, X.; Yu, S. Q.; Wang, Zh. M.; Salamo, G. J.

    2011-12-01

    Self-assembly of bismuth droplets at nanoscale on GaAs(100) surface using molecular beam epitaxy was demonstrated. Fine control of density and size was achieved by varying growth temperature and total bismuth deposition. Droplet density was tuned by roughly 3 orders of magnitude, and the density-temperature dependence was found to be consistent with classical nucleation theory. These results may extend the flexibility of droplet epitaxy by serving as templates for group V based droplet epitaxy, which is in contrast to conventional group III based droplet epitaxy and may encourage nanostructure formation of bismuth-containing materials.

  13. Substrate temperature changes during molecular beam epitaxy growth of GaMnAs

    SciTech Connect

    Novak, V.; Olejnik, K.; Cukr, M.; Smrcka, L.; Remes, Z.; Oswald, J.

    2007-10-15

    Our band gap spectroscopy measurements reveal a remarkably big increase of the substrate temperature during the low-temperature molecular beam epitaxy growth of GaMnAs layers. With the help of numerical simulations we explain the effect as a consequence of changing absorption/emission characteristics of the growing epilayer. We discuss possibilities for reducing the substrate temperature variations during the growth.

  14. Growth of epitaxial ZnO films on sapphire substrates by plasma assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hyndman, Adam R.; Allen, Martin W.; Reeves, Roger J.

    2014-03-01

    Epitaxial layers of ZnO have been grown on c-plane, (0001) sapphire substrates by plasma assisted molecular beam epitaxy. The oxygen:zinc flux ratio was found to be crucial in obtaining a film with a smooth surface and good crystallinity. When increasing film thickness from ~80 to 220 nm we observed an increase in the streakiness of RHEED images, and XRD revealed a reduction in crystal strain and increase in crystal alignment. A film with surface roughness of 0.5 nm and a XRD rocking curve FWHM of 0.1 for the main ZnO peak (0002) was achieved by depositing a low temperature ZnO buffer layer at 450 °C and then growing for 120 minutes at 700 °C with a Zn-cell temperature of 320 °C and an oxygen partial pressure of 7e-7 Torr. We found novel structures on two samples grown outside of our ideal oxygen:zinc flux ratio. SEM images of a sample believed to have been grown in a Zn-rich environment showed flower like structures up to 150 um in diameter which appear to have formed during growth. Another sample believed to have been deposited in a Zn-deficient environment had rings approximately 1.5 um in diameter scattered on its surface.

  15. Growth of very large InN microcrystals by molecular beam epitaxy using epitaxial lateral overgrowth

    SciTech Connect

    Kamimura, J.; Kishino, K.; Kikuchi, A.

    2015-02-28

    Very thick InN (∼40 μm) was grown by molecular beam epitaxy using the epitaxial lateral overgrowth (ELO) technique. In some regions, the ELO of InN was observed as expected, indicating an important step toward fabricating quasi-bulk InN substrates. Interestingly, most parts of the sample consist of large flat-topped microcrystals and well-faceted microstructures. This is likely due to local growth condition variations during ELO, which is supported by an experiment where ELO of InN was performed on a substrate with various stripe mask patterns. TEM characterization of a flat top InN microcrystal revealed few stacking faults and only related threading dislocations. Defect-free small faceted microcrystals were also observed. The thick InN crystals show a narrow photoluminescence spectrum with a peak at 0.679 eV and linewidth of 16.8 meV at 4 K.

  16. Epitaxial Cd3As2 Thin Films Synthesized by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Schumann, Timo; Goyal, Manik; Stemmer, Susanne

    Cd3As2 is a three-dimensional (3D) Dirac semimetal, i.e. it possesses Dirac cones in a 3D bulk state where the band dispersion relation is linear near the Fermi energy. Cd3As2 is has raised considerable interest due to its high electron mobilities in bulk crystals and for novel quantum phenomena, such as chiral anomalies. However, few studies have been performed using thin films of Cd3As2. In this presentation, we report on the synthesis of Cd3As2 thin films by molecular beam epitaxy (MBE). Single phase, epitaxial films were grown on undoped GaSb(111)B substrates with the (112) facet of Cd3As2 parallel to the GaSb(111) surface. We report on the structural quality and orientation variants in the films. Electrical transport properties indicate electron mobilities exceeding 6000 cm2V-1s-1. We discuss the impact of the MBE growth parameters and substrate preparation on the structural and electrical properties of the films.

  17. Molecular-beam epitaxy of (Zn,Mn)Se on Si(100)

    SciTech Connect

    Slobodskyy, T.; Ruester, C.; Fiederling, R.; Keller, D.; Gould, C.; Ossau, W.; Schmidt, G.; Molenkamp, L.W.

    2004-12-20

    We have investigated the growth by molecular-beam epitaxy of the II-VI diluted magnetic semiconductor (Zn,Mn)Se on As-passivated Si(100) substrates. The growth start has been optimized by using low-temperature epitaxy. Surface properties were assessed by Nomarski and scanning electron microscopy. Optical properties of (Zn,Mn)Se have been studied by photoluminescence and a giant Zeeman splitting of up to 30 meV has been observed. Our observations indicate a high crystalline quality of the epitaxial films.

  18. Critical issues of complex, epitaxial oxide growth and integration with silicon by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lettieri, James

    Molecular beam epitaxy was used to grow epitaxial oxides on silicon substrates. The growth of BaO, SrO, EuO, and SrTiO3 are discussed with a focus on the general theme of integration of functional, epitaxial oxides into a silicon environment. Oxidation studies of various metal systems relevant for oxide on silicon epitaxy and integration are reported. Results demonstrate the catalytic nature of an alkaline earth metal at small concentrations to enable the oxidation of the poorly oxidizing metals at pressures lower than during deposition of the pure metal alone. Results from the deposition of various elements are presented. The aspects of the growth of alkaline earth oxides on silicon are explained. The transition from the silicon to the alkaline earth oxide as described through reflection high energy electron diffraction (RHEED) is presented and used to understand issues related to each stage of the growth. High quality, commensurate alkaline earth oxides are grown on silicon at room temperature and P O2 background ˜ 3 x 10-8 Torr. The growth of alkaline earth and rare earth oxide solid solutions and rare earth oxides (EuO) are described. The first reported epitaxial EuO on silicon is reported, enabled by the use of a thin buffer layer (13 A) of SrO. Using a strategy of transition from simple structures to the more complex, the growth of a perovskite (SrTiO3) on silicon is demonstrated. Growth of a structurally optimized perovskite structure entails the transformation of a thin interfacial alkaline earth oxide layer into the initial perovskite cells. SrTiO3 and La-doped SrTiO3 on silicon are used to integrate a piezoelectric relevant for microelectromechanical systems (MEMS) applications and a ferroelectric relevant for a ferroelectric random access memory (FRAM) architecture. A d33 value of over 400 pm/V under bias is measured for the piezoelectric (Pb(Mn1/3Nb 2/3)O3 -PbTiO3) and a remanent polarization of 25 muC/cm2 and fatigue free behavior (>1012 cycles) for a

  19. Laser Probing of Molecular Beam Epitaxy on SILICON(100) Surface.

    NASA Astrophysics Data System (ADS)

    Smilgys, Russell Victor

    The work presented here investigates the desorption kinetics of Ga and In from films of Ga, In, GaAs, and InAs on Si(100). Films a few monolayers (ML) thick are deposited from molecular beams under ultrahigh vacuum conditions. Laser induced fluorescence (LIF) is used to detect Ga and In in the gas phase. Using the techniques of temperature programmed desorption and isothermal desorption the desorption kinetics of each species are measured. The variation in the kinetic order and rate constant with temperature and coverage reflect the morphology and energetics of the film growth. Individually, Ga, In, and As each interact strongly with Si(100) at low coverages to form a two dimensional film. Above 1 ML for Ga and {1over2 } ML for In three dimensional islands form. For temperatures above 550 K, As coverage saturates at 1 ML. When As is codeposited with either Ga or In, As occupies the interfacial sites bound to Si. Ga and In atoms form three dimensional islands on top of the two dimensional As film. When the As coverage is below 1 ML, Ga and As strongly interact, probably to form a GaAs structure. Under the same conditions no comparable InAs structure is evident. The much larger lattice mismatch between InAs and Si(100) is proposed to explain this difference. The desorption kinetics and dynamics of the interfacial As film are also investigated. To measure As_2 desorption rates and vibrational populations, LIF detection of As_2 is developed. A result is that As_4 dissociates on Si(100) to yield chemisorbed As atoms. During desorption As atoms recombine to yield As_2. The vibrational populations of desorbed As_2 suggest a direct desorption mechanism in which the directionality of the covalent bonding to the substrate strongly influences the dynamics. To expand the detection capabilities to species not readily detected by LIF, a time-of-flight mass spectrometer is built. In the first studies nonresonant multiphoton ionization is used. As_4 is detected using 266 nm

  20. Carrier dynamics in ZnxCd1-xO films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Cheng, F. J.; Lee, Y. C.; Hu, S. Y.; Lin, Y. C.; Tiong, K. K.; Chou, W. C.

    2016-05-01

    In this work, the carrier dynamics in Zn1-xCdxO thin films with different Cd contents grown by molecular beam epitaxy system have been investigated using photoluminescence and time-resolved photoluminescence measurements. The carrier lifetime can be estimated from the PL decay curve fitted by triple exponential function. The emission energy dependence and temperature dependence of the PL decay time indicate that carrier localization dominate the luminescence mechanism of the ZnCdO alloy semiconductor.

  1. Mn2Au: body-centered-tetragonal bimetallic antiferromagnets grown by molecular beam epitaxy.

    PubMed

    Wu, Han-Chun; Liao, Zhi-Min; Sofin, R G Sumesh; Feng, Gen; Ma, Xiu-Mei; Shick, Alexander B; Mryasov, Oleg N; Shvets, Igor V

    2012-12-11

    Mn(2)Au, a layered bimetal, is successfully grown using molecular beam epitaxy (MBE). The experiments and theoretical calculations presented suggest that Mn(2)Au film is antiferromagnetic with a very low critical temperature. The antiferromagnetic nature is demonstrated by measuring the exchange-bias effect of Mn(2)Au/Fe bilayers. This study establishes a primary basis for further research of this new antiferromagnet in spin-electronic device applications. PMID:22996352

  2. Molecular Beam Epitaxial Growth of GaAs on (631) Oriented Substrates

    SciTech Connect

    Cruz Hernandez, Esteban; Rojas Ramirez, Juan-Salvador; Contreras Hernandez, Rocio; Lopez Lopez, Maximo; Pulzara Mora, Alvaro; Mendez Garcia, Victor H.

    2007-02-09

    In this work, we report the study of the homoepitaxial growth of GaAs on (631) oriented substrates by molecular beam epitaxy (MBE). We observed the spontaneous formation of a high density of large scale features on the surface. The hilly like features are elongated towards the [-5, 9, 3] direction. We show the dependence of these structures with the growth conditions and we present the possibility of to create quantum wires structures on this surface.

  3. (In,Mn)As quantum dots: Molecular-beam epitaxy and optical properties

    SciTech Connect

    Bouravleuv, A. D. Nevedomskii, V. N.; Ubyivovk, E. V.; Sapega, V. F.; Khrebtov, A. I.; Samsonenko, Yu. B.; Cirlin, G. E.; Ustinov, V. M.

    2013-08-15

    Self-assembled (In,Mn)As quantum dots are synthesized by molecular-beam epitaxy on GaAs (001) substrates. The experimental results obtained by transmission electron microscopy show that doping of the central part of the quantum dots with Mn does not bring about the formation of structural defects. The optical properties of the samples, including those in external magnetic fields, are studied.

  4. Antimony-assisted carbonization of Si(111) with solid source molecular beam epitaxy

    SciTech Connect

    Hackley, Justin; Richardson, Christopher J. K.; Sarney, Wendy L.

    2013-11-15

    The carbonization of an antimony-terminated Si (111) surface in a solid source molecular beam epitaxy system is presented. Reflection high-energy electron diffraction, atomic force microscopy, x-ray photoelectron spectroscopy, and cross-sectional transmission electron microscopy are used to characterize samples grown with and without antimony termination. It is shown that the antimony-terminated surface promotes the formation of thin, smooth and continuous SiC films at a relatively low temperature of 800 °C.

  5. Fabrication of precision high quality facets on molecular beam epitaxy material

    DOEpatents

    Petersen, Holly E.; Goward, William D.; Dijaili, Sol P.

    2001-01-01

    Fabricating mirrored vertical surfaces on semiconductor layered material grown by molecular beam epitaxy (MBE). Low energy chemically assisted ion beam etching (CAIBE) is employed to prepare mirrored vertical surfaces on MBE-grown III-V materials under unusually low concentrations of oxygen in evacuated etching atmospheres of chlorine and xenon ion beams. UV-stabilized smooth-surfaced photoresist materials contribute to highly vertical, high quality mirrored surfaces during the etching.

  6. Lutetium-doped EuO films grown by molecular-beam epitaxy

    SciTech Connect

    Melville, A.; Heeg, T.; Mairoser, T.; Schmehl, A.; Shai, D. E.; Monkman, E. J.; Harter, J. W.; Hollaender, B.; Schubert, J.; Shen, K. M.; Mannhart, J.; Schlom, D. G.

    2012-05-28

    The effect of lutetium doping on the structural, electronic, and magnetic properties of epitaxial EuO thin films grown by reactive molecular-beam epitaxy is experimentally investigated. The behavior of Lu-doped EuO is contrasted with doping by lanthanum and gadolinium. All three dopants are found to behave similarly despite differences in electronic configuration and ionic size. Andreev reflection measurements on Lu-doped EuO reveal a spin-polarization of 96% in the conduction band, despite non-magnetic carriers introduced by 5% lutetium doping.

  7. Site-controlled Ag nanocrystals grown by molecular beam epitaxy-Towards plasmonic integration technology

    SciTech Connect

    Urbanczyk, Adam; Noetzel, Richard

    2012-12-15

    We demonstrate site-controlled growth of epitaxial Ag nanocrystals on patterned GaAs substrates by molecular beam epitaxy with high degree of long-range uniformity. The alignment is based on lithographically defined holes in which position controlled InAs quantum dots are grown. The Ag nanocrystals self-align preferentially on top of the InAs quantum dots. No such ordering is observed in the absence of InAs quantum dots, proving that the ordering is strain-driven. The presented technique facilitates the placement of active plasmonic nanostructures at arbitrarily defined positions enabling their integration into complex devices and plasmonic circuits.

  8. In-situ epitaxial growth of graphene/h-BN van der Waals heterostructures by molecular beam epitaxy

    PubMed Central

    Zuo, Zheng; Xu, Zhongguang; Zheng, Renjing; Khanaki, Alireza; Zheng, Jian-Guo; Liu, Jianlin

    2015-01-01

    Van der Waals materials have received a great deal of attention for their exceptional layered structures and exotic properties, which can open up various device applications in nanoelectronics. However, in situ epitaxial growth of dissimilar van der Waals materials remains challenging. Here we demonstrate a solution for fabricating van der Waals heterostructures. Graphene/hexagonal boron nitride (h-BN) heterostructures were synthesized on cobalt substrates by using molecular beam epitaxy. Various characterizations were carried out to evaluate the heterostructures. Wafer-scale heterostructures consisting of single-layer/bilayer graphene and multilayer h-BN were achieved. The mismatch angle between graphene and h-BN is below 1°. PMID:26442629

  9. Molecular beam epitaxy and properties of GaAsBi/GaAs quantum wells grown by molecular beam epitaxy: effect of thermal annealing.

    PubMed

    Makhloufi, Hajer; Boonpeng, Poonyasiri; Mazzucato, Simone; Nicolai, Julien; Arnoult, Alexandre; Hungria, Teresa; Lacoste, Guy; Gatel, Christophe; Ponchet, Anne; Carrère, Hélène; Marie, Xavier; Fontaine, Chantal

    2014-01-01

    We have grown GaAsBi quantum wells by molecular beam epitaxy. We have studied the properties of a 7% Bi GaAsBi quantum well and their variation with thermal annealing. High-resolution X-ray diffraction, secondary ion mass spectrometry, and transmission electron microscopy have been employed to get some insight into its structural properties. Stationary and time-resolved photoluminescence shows that the quantum well emission, peaking at 1.23 μm at room temperature, can be improved by a rapid annealing at 650°C, while the use of a higher annealing temperature leads to emission degradation and blue-shifting due to the activation of non-radiative centers and bismuth diffusion from the quantum well. PMID:24636335

  10. Molecular beam epitaxy and properties of GaAsBi/GaAs quantum wells grown by molecular beam epitaxy: effect of thermal annealing

    PubMed Central

    2014-01-01

    We have grown GaAsBi quantum wells by molecular beam epitaxy. We have studied the properties of a 7% Bi GaAsBi quantum well and their variation with thermal annealing. High-resolution X-ray diffraction, secondary ion mass spectrometry, and transmission electron microscopy have been employed to get some insight into its structural properties. Stationary and time-resolved photoluminescence shows that the quantum well emission, peaking at 1.23 μm at room temperature, can be improved by a rapid annealing at 650°C, while the use of a higher annealing temperature leads to emission degradation and blue-shifting due to the activation of non-radiative centers and bismuth diffusion from the quantum well. PMID:24636335

  11. Low temperature growth of crystalline magnesium oxide on hexagonal silicon carbide (0001) by molecular beam epitaxy

    SciTech Connect

    Goodrich, T. L.; Parisi, J.; Cai, Z.; Ziemer, K. S.

    2007-01-22

    Magnesium oxide (111) was grown epitaxially on hexagonal silicon carbide (6H-SiC) (0001) substrates at low temperatures by molecular beam epitaxy and a remote oxygen plasma source. The films were characterized by reflection high-energy electron diffraction, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and atomic force microscopy. Crystal structure, morphology, and growth rate of the magnesium oxide (MgO) films were found to be dependent on the magnesium flux, indicating a magnesium adsorption controlled growth mechanism. The single crystalline MgO thin films had an epitaxial relationship where MgO (111) parallel 6H-SiC (0001) and were stable in both air and 10{sup -9} Torr up to 1023 K.

  12. High-mobility BaSnO{sub 3} grown by oxide molecular beam epitaxy

    SciTech Connect

    Raghavan, Santosh; Schumann, Timo; Kim, Honggyu; Zhang, Jack Y.; Cain, Tyler A.; Stemmer, Susanne

    2016-01-01

    High-mobility perovskite BaSnO{sub 3} films are of significant interest as new wide bandgap semiconductors for power electronics, transparent conductors, and as high mobility channels for epitaxial integration with functional perovskites. Despite promising results for single crystals, high-mobility BaSnO{sub 3} films have been challenging to grow. Here, we demonstrate a modified oxide molecular beam epitaxy (MBE) approach, which supplies pre-oxidized SnO{sub x}. This technique addresses issues in the MBE of ternary stannates related to volatile SnO formation and enables growth of epitaxial, stoichiometric BaSnO{sub 3}. We demonstrate room temperature electron mobilities of 150 cm{sup 2} V{sup −1} s{sup −1} in films grown on PrScO{sub 3}. The results open up a wide range of opportunities for future electronic devices.

  13. Conducting (Si-doped) aluminum nitride epitaxial films grown by molecular beam epitaxy

    SciTech Connect

    Kim, J.G.; Moorthy, M.; Park, R.M.

    1999-07-01

    As a member of the III-V nitride semiconductor family, AlN, which has a direct energy-gap of 6.2eV, has received much attention as a promising material for many applications. However, despite the promising attributes of AlN for various semiconductor devices, research on AlN has been limited and n-type conducting AlN has not been reported. The objective of this research was to understand the factors impacting the conductivity of AlN and to control the conductivity of this material through intentional doping. Prior to the intentional doping study, growth of undoped AlN epilayers was investigated. Through careful selection of substrate preparation methods and growth parameters, relatively low-temperature molecular beam epitaxial growth of AlN films was established which resulted in insulating material. Intentional Si doping during epilayer growth was found to result in conducting films under specific growth conditions. Above a growth temperature of 900 C, AlN films were insulating, however, below a growth temperature of 900 C, the AlN films were conducting. The magnitude of the conductivity and the growth temperature range over which conducting AlN films could be grown were strongly influenced by the presence of a Ga flux during growth. For instance, conducting, Si-doped, AlN films were grown at a growth temperature of 940 C in the presence of a Ga flux while the films were insulating when grown in the absence of a Ga flux at this particular growth temperature. Also, by appropriate selection of the growth parameters, epilayers with n-type conductivity values as large as 0.2 {Omega}{sup {minus}1} cm{sup {minus}1} for AlN and 17 {Omega}{sup {minus}1} cm{sup {minus}1} for Al{sub 0.75}Ga{sub 0.25}N were grown in this work for the first time.

  14. Growth of EuO/Si and EuO/SrO/Si heteroepitaxial structures by molecular-beam epitaxy

    SciTech Connect

    Teterin, P. E. Averyanov, D. V.; Sadofyev, Yu. G. Parfenov, O. E.; Likhachev, I. A.; Storchak, V. G.

    2015-01-15

    Epitaxial EuO thin films with thickness up to 60 nm have been grown by molecular beam epitaxy both on SrO sublayers and directly on Si (001) substrates. Crystal structure has been controlled in situ by reflection high energy electron diffraction. Ex situ studies by X-ray diffraction and Rutherford backscattering have confirmed high crystalline quality of the films.

  15. Formation of large-grain-sized BaSi2 epitaxial layers grown on Si(111) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Baba, M.; Toh, K.; Toko, K.; Hara, K. O.; Usami, N.; Saito, N.; Yoshizawa, N.; Suemasu, T.

    2013-09-01

    BaSi2 epitaxial films were grown on Si(111) substrates by a two-step growth method including reactive deposition epitaxy (RDE) and molecular beam epitaxy (MBE). To enlarge the grain size of BaSi2, the Ba deposition rate and duration were varied from 0.25 to 1.0 nm/min and from 5 to 120 min during RDE, respectively. The effect of post-annealing was also investigated at 760 °C for 10 min. Plan-view transmission electron micrographs indicated that the grain size in the MBE-grown BaSi2 was significantly increased up to approximately 4.0 μm, which is much larger than 0.2 μm, reported previously.

  16. Characterization of GaN microstructures grown by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Lo, Ikai; Pang, Wen-Yuan; Hsu, Yu-Chi; Hsieh, Chia-Ho; Shih, Cheng-Hung; Chou, Mitch M. C.; Chen, Wen-Yen; Hsu, Tzu-Min; Hsu, Gary Z. L.

    2013-06-15

    The characterization of GaN microstructures grown by plasma-assisted molecular beam epitaxy on LiAlO{sub 2} substrate was studied by cathodoluminescence and photoluminescence measurements. We demonstrated that the cathodoluminescence from oblique semi-polar surfaces of mushroom-shaped GaN was much brighter than that from top polar surface due to the reduction of polarization field on the oblique semi-polar surfaces. It implies that the oblique semi-polar surface is superior for the light-emitting surface of wurtzite nano-devices.

  17. New MBE (molecular beam epitaxy) buffer used to eliminate backgating in gaas mesfets

    SciTech Connect

    Smith, F.W.; Calawa, A.R.; Chen, C.L.; Manfra, M.J.; Mahoney, L.J.

    1988-02-01

    A new buffer layer has been developed that eliminates backgating between MESFET's fabricated in active layers grown upon it. The new buffer is grown by molecular beam epitaxy (MBE) at low substrate temperatures (150-300 C) using Ga and As4 beam fluxes. It is highly resistive, optically inactive, and crystalline, and high-quality GaAs active layers can be grown on top of the new buffer. MESFET's fabricated in active layers grown on top of this new buffer show improved output resistance and breakdown voltages; the dc and Rf characteristics are otherwise comparable to MESFET's fabricated by alternative means and with other buffer layers.

  18. Analysis of atomic force microscopic results of InAs islands formed by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Gong, Q.; Liang, J. B.; Xu, B.; Ding, D.; Li, H. X.; Jiang, C.; Zhou, W.; Liu, F. Q.; Wang, Z. G.; Qiu, X. H.; Shang, G. Y.; Bai, C. L.

    1998-09-01

    Atomic force microscopy (AFM) measurements of nanometer-sized islands formed by 2 monolayers of InAs by molecular beam epitaxy have been carried out and the scan line of individual islands was extracted from raw AFM data for investigation. It is found that the base widths of nanometer-sized islands obtained by AFM are not reliable due to the finite size and shape of the contacting probe. A simple model is proposed to analyze the deviation of the measured value from the real value of the base width of InAs islands.

  19. Luminescence characterization of CdTe:In grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bassani, F.; Tatarenko, S.; Saminadayar, K.; Bleuse, J.; Magnea, N.; Pautrat, J. L.

    1991-06-01

    We report on the incorporation of indium as a shallow donor in CdTe by molecular beam epitaxy. Using proper surface stoichiometry conditions, we demonstrate that it is possible to incorporate and activate up to 1018 cm-3 indium impurities. The doped layers have been characterized by secondary-ion mass spectroscopy, capacitance-voltage and Hall-effect measurements. Photoluminescence (PL) and resonant excitation of the PL clearly identify indium as the chemical dopant, acting as an effective mass donor with an energy of 14 meV. Incorrect stoichiometry conditions lead to a poor dopant activity and to complex centers formation.

  20. Growth of GaN with warm ammonia by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kawaharazuka, A.; Yoshizaki, T.; Ploog, K. H.; Horikoshi, Y.

    2009-03-01

    We demonstrate the growth of GaN by molecular beam epitaxy with warm ammonia as a nitrogen source. Ammonia gas is heated by the tungsten filament located at the open end of the gas-tube installed in the growth chamber. By using this simple structure, the multiple collisions of molecules within the heater, thus the generation of nitrogen molecule, can be suppressed. The crystalline quality of the grown GaN layer is significantly improved by introducing the warm ammonia. This effect can be explained by the enhancement of the two-dimensional growth due to the active nitrogen species such as radical NH2* generated by cracking ammonia molecule.

  1. Metastable GaAsBi Alloy Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Yoshimoto, Masahiro; Murata, Satoshi; Chayahara, Akiyoshi; Horino, Yuji; Saraie, Junji; Oe, Kunishige

    2003-10-01

    GaAs1-xBix has been grown at a substrate temperature (Tsub) between 350 and 410°C by molecular beam epitaxy. The relationship between GaBi molar fraction (x) evaluated by Rutherford backscattering spectroscopy and the lattice constant showed good linearity. To achieve Bi incorporation into the epilayer, As flux was adjusted in a limited range on the brink of As shortage on the growing surface. The Bi incorporation was saturated at a large Bi flux, probably due to a low miscibility of Bi with GaAs. The value of x increased up to 4.5% with decreasing Tsub to 350°C.

  2. Molecular beam epitaxy of GaBiAs on (311)B GaAs substrates

    SciTech Connect

    Henini, M.; Ibanez, J.; Schmidbauer, M.; Shafi, M.; Novikov, S. V.; Turyanska, L.; Molina, S. I.; Sales, D. L.; Chisholm, M. F.; Misiewicz, J.

    2007-12-17

    We report the growth by molecular beam epitaxy of GaBi{sub x}As{sub 1-x} epilayers on (311)B GaAs substrates. We use high-resolution x-ray diffraction (HRXRD), transmission electron microscopy, and Z-contrast imaging to characterize the structural properties of the as-grown material. We find that the incorporation of Bi into the GaBiAs alloy, as determined by HRXRD, is sizably larger in the (311)B epilayers than in (001) epilayers, giving rise to reduced band-gap energies as obtained by optical transmission spectroscopy.

  3. Molecular beam epitaxy of GaBiAs on (311)B GaAs substrates

    NASA Astrophysics Data System (ADS)

    Henini, M.; Ibáñez, J.; Schmidbauer, M.; Shafi, M.; Novikov, S. V.; Turyanska, L.; Molina, S. I.; Sales, D. L.; Chisholm, M. F.; Misiewicz, J.

    2007-12-01

    We report the growth by molecular beam epitaxy of GaBixAs1-x epilayers on (311)B GaAs substrates. We use high-resolution x-ray diffraction (HRXRD), transmission electron microscopy, and Z-contrast imaging to characterize the structural properties of the as-grown material. We find that the incorporation of Bi into the GaBiAs alloy, as determined by HRXRD, is sizably larger in the (311)B epilayers than in (001) epilayers, giving rise to reduced band-gap energies as obtained by optical transmission spectroscopy.

  4. Reflection mass spectrometry technique for monitoring and controlling composition during molecular beam epitaxy

    DOEpatents

    Brennan, T.M.; Hammons, B.E.; Tsao, J.Y.

    1992-12-15

    A method for on-line accurate monitoring and precise control of molecular beam epitaxial growth of Groups III-III-V or Groups III-V-V layers in an advanced semiconductor device incorporates reflection mass spectrometry. The reflection mass spectrometry is responsive to intentional perturbations in molecular fluxes incident on a substrate by accurately measuring the molecular fluxes reflected from the substrate. The reflected flux is extremely sensitive to the state of the growing surface and the measurements obtained enable control of newly forming surfaces that are dynamically changing as a result of growth. 3 figs.

  5. Reflection mass spectrometry technique for monitoring and controlling composition during molecular beam epitaxy

    DOEpatents

    Brennan, Thomas M.; Hammons, B. Eugene; Tsao, Jeffrey Y.

    1992-01-01

    A method for on-line accurate monitoring and precise control of molecular beam epitaxial growth of Groups III-III-V or Groups III-V-V layers in an advanced semiconductor device incorporates reflection mass spectrometry. The reflection mass spectrometry is responsive to intentional perturbations in molecular fluxes incident on a substrate by accurately measuring the molecular fluxes reflected from the substrate. The reflected flux is extremely sensitive to the state of the growing surface and the measurements obtained enable control of newly forming surfaces that are dynamically changing as a result of growth.

  6. Growth of atomically smooth MgO films on graphene by molecular beam epitaxy

    SciTech Connect

    Wang, W. H.; Han, W.; Pi, K.; McCreary, K. M.; Miao, F.; Bao, W.; Lau, C. N.; Kawakami, R. K.

    2008-11-03

    We investigate the growth of MgO films on graphene by molecular beam epitaxy and find that surface diffusion promotes a rough morphology. To reduce the mobility of surface atoms, the graphene surface is dressed by Ti atoms prior to MgO deposition. With as little as 0.5 ML (monolayer) of Ti, the MgO overlayer becomes atomically smooth. Furthermore, no aggregation of MgO is observed at the edges of the graphene sheet. These results are important for the fabrication of nanoscale electronic and spintronic devices.

  7. Low defect densities in molecular beam epitaxial GaAs achieved by isoelectronic In doping

    NASA Technical Reports Server (NTRS)

    Bhattacharya, P. K.; Dhar, S.; Berger, P.; Juang, F.-Y.

    1986-01-01

    A study has been made of the effects of adding small amounts of In (0.2-1.2 pct) to GaAs grown by molecular beam epitaxy. The density of four electron traps decreases in concentration by an order of magnitude, and the peak intensities of prominent emissions in the excitonic spectra are reduced with increase in In content. Based on the higher surface migration rate of In, compared to Ga, at the growth temperatures it is apparent that the traps and the excitonic transitions are related to point defects. This agrees with earlier observations by Briones and Collins (1982) and Skromme et al. (1985).

  8. Silicon sheet with molecular beam epitaxy for high efficiency solar cells

    NASA Technical Reports Server (NTRS)

    Allen, F. G.

    1983-01-01

    The capabilities of the new technique of Molecular Beam Epitaxy (MBE) are applied to the growth of high efficiency silicon solar cells. Because MBE can provide well controlled doping profiles of any desired arbitrary design, including doping profiles of such complexity as built-in surface fields or tandem junction cells, it would appear to be the ideal method for development of high efficiency solar cells. It was proposed that UCLA grow and characterize silicon films and p-n junctions of MBE to determine whether the high crystal quality needed for solar cells could be achieved.

  9. Perspective: Extremely fine tuning of doping enabled by combinatorial molecular-beam epitaxy

    SciTech Connect

    Wu, J.; Božović, I.

    2015-06-01

    Chemical doping provides an effective method to control the electric properties of complex oxides. However, the state-of-art accuracy in controlling doping is limited to about 1%. This hampers elucidation of the precise doping dependences of physical properties and phenomena of interest, such as quantum phase transitions. Using the combinatorial molecular beam epitaxy, we improve the accuracy in tuning the doping level by two orders of magnitude. We illustrate this novel method by two examples: a systematic investigation of the doping dependence of interface superconductivity, and a study of the competing ground states in the vicinity of the insulator-to-superconductor transition.

  10. Demonstration of molecular beam epitaxy and a semiconducting band structure for I-Mn-V compounds

    SciTech Connect

    Jungwirth, T.; Novak, V.; Cukr, M.; Zemek, J.; Marti, X.; Horodyska, P.; Nemec, P.; Holy, V.; Maca, F.; Shick, A. B.; Masek, J.; Kuzel, P.; Nemec, I.; Gallagher, B. L.; Campion, R. P.; Foxon, C. T.; Wunderlich, J.

    2011-01-15

    Our ab initio theory calculations predict a semiconducting band structure of I-Mn-V compounds. We demonstrate on LiMnAs that high-quality materials with group-I alkali metals in the crystal structure can be grown by molecular beam epitaxy. Optical measurements on the LiMnAs epilayers are consistent with the theoretical electronic structure. Our calculations also reproduce earlier reports of high antiferromagnetic ordering temperature and predict large, spin-orbit-coupling-induced magnetic anisotropy effects. We propose a strategy for employing antiferromagnetic semiconductors in high-temperature semiconductor spintronics.

  11. Gallium Arsenide Layers Grown by Molecular Beam Epitaxy on Single Crystalline Germanium Islands on Insulator

    NASA Astrophysics Data System (ADS)

    Takai, Mikio; Tanigawa, Takaho; Minamisono, Tadanori; Gamo, Kenji; Namba, Susumu

    1984-05-01

    Gallium arsenide (GaAs) layers have successfully been grown by molecular beam epitaxy on single crystalline germanium (Ge) islands, recrystallized by zone melting with SiO2 capping layers, on thermally-oxidized Si-wafers. The GaAs layers, grown on the single crystalline Ge islands, show smooth surfaces without any grain-boundaries, while those, grown on the Ge islands with grain-boundaries and on the SiO2, have grain-boundaries. The GaAs layers on the single crystalline Ge islands emit photoluminescence, the intensity of which is almost comparable to that of GaAs layers on bulk Ge crystals.

  12. Molecular-beam epitaxy of monolayer MoSe2: growth characteristics and domain boundary formation

    NASA Astrophysics Data System (ADS)

    Jiao, L.; Liu, H. J.; Chen, J. L.; Yi, Y.; Chen, W. G.; Cai, Y.; Wang, J. N.; Dai, X. Q.; Wang, N.; Ho, W. K.; Xie, M. H.

    2015-05-01

    Monolayer (ML) transition metal dichalcogenides (TMDs) are of great research interest due to their potential use in ultrathin electronic and optoelectronic applications. They show promise in new concept devices in spintronics and valleytronics. Here we present a growth study by molecular-beam epitaxy of ML and sub-ML MoSe2, an important member of TMDs, revealing its unique growth characteristics as well as the formation processes of domain boundary (DB) defects. A dramatic effect of growth temperature and post-growth annealing on DB formation is uncovered.

  13. Application of ellipsometry to crystal growth by organometallic molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Aspnes, D. E.; Quinn, W. E.; Gregory, S.

    1990-06-01

    We report the first use of ellipsometry as a real-time monitor of III-V semiconductor crystal growth by molecular beam epitaxy, specifically growth of GaAs and AlGaAs from arsine, triethylgallium, and triethylaluminum sources. Our results provide new insight into the oxide desorption process and show a sensitivity of ±0.03 in compositions x>0.2 for 10 Å thickness increments of AlxGa1-xAs during initial deposition on GaAs.

  14. The growth of high-quality AlGaAs by metalorganic molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hersee, S. D.; Martin, P. A.; Chin, A.; Ballingall, J. M.

    1991-07-01

    The electrical and optical properties of AlGaAs grown by metalorganic molecular-beam epitaxy using triethylaluminum, tri-isobutylaluminum, and trimethylamine-alane are compared. It is found that tri-isobutylaluminum yields the lowest residual carbon incorporation in the layers (Na - Nd = 4 × 1015 cm-3) and the highest electron and hole mobilities. Photoluminescence spectra for the higher-quality AlGaAs, grown using TiBAl, show excitonic luminescence. However, this luminescence appears to be defect related.

  15. Near-bandgap optical properties of pseudomorphic GeSn alloys grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    D'Costa, Vijay Richard; Wang, Wei; Yeo, Yee-Chia

    2016-08-01

    We investigated the compositional dependence of the near-bandgap dielectric function and the E0 critical point in pseudomorphic Ge1-xSnx alloys grown on Ge (100) substrate by molecular beam epitaxy. The complex dielectric functions were obtained using spectroscopic ellipsometry from 0.5 to 4.5 eV at room temperature. Analogous to the E1 and E1+Δ1 transitions, a model consisting of the compositional dependence of relaxed alloys along with the strain contribution predicted by the deformation potential theory fully accounts for the observed compositional dependence in pseudomorphic alloys.

  16. Electrical properties of nominally undoped silicon nanowires grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bauer, Jan; Fleischer, Frank; Breitenstein, Otwin; Schubert, Luise; Werner, Peter; Gösele, Ulrich; Zacharias, Margit

    2007-01-01

    Single undoped Si nanowires were electrically characterized. The nanowires were grown by molecular-beam epitaxy on n+ silicon substrates and were contacted by platinum/iridium tips. I-V curves were measured and electron beam induced current investigations were performed on single nanowires. It was found that the nanowires have an apparent resistivity of 0.85Ωcm, which is much smaller than expected for undoped Si nanowires. The conductance is explained by hopping conductivity at the Si -SiO2 interface of the nanowire surface.

  17. Acceptor states in heteroepitaxial CdHgTe films grown by molecular-beam epitaxy

    SciTech Connect

    Mynbaev, K. D.; Shilyaev, A. V. Bazhenov, N. L.; Izhnin, A. I.; Izhnin, I. I.; Mikhailov, N. N.; Varavin, V. S.; Dvoretsky, S. A.

    2015-03-15

    The photoluminescence method is used to study acceptor states in CdHgTe heteroepitaxial films (HEFs) grown by molecular-beam epitaxy. A comparison of the photoluminescence spectra of HEFs grown on GaAs substrates (CdHgTe/GaAs) with the spectra of CdHgTe/Si HEFs demonstrates that acceptor states with energy depths of about 18 and 27 meV are specific to CdHgTe/GaAs HEFs. The possible nature of these states and its relation to the HEF synthesis conditions and, in particular, to the vacancy doping occurring under conditions of a mercury deficiency during the course of epitaxy and postgrowth processing are discussed.

  18. Ge/GeSn heterostructures grown on Si (100) by molecular-beam epitaxy

    SciTech Connect

    Sadofyev, Yu. G. Martovitsky, V. P.; Bazalevsky, M. A.; Klekovkin, A. V.; Averyanov, D. V.; Vasil’evskii, I. S.

    2015-01-15

    The growth of GeSn layers by molecular-beam epitaxy on Si (100) wafers coated with a germanium buffer layer is investigated. The properties of the fabricated structures are controlled by reflection high-energy electron diffraction, atomic-force microscopy, X-ray diffractometry, Rutherford backscattering, and Raman scattering. It is shown that GeSn layers with thicknesses up to 0.5 μm and Sn molar fractions up to 0.073 manifest no sign of plastic relaxation upon epitaxy. The lattice constant of the GeSn layers within the growth plane is precisely the same as that of Ge. The effect of rapid thermal annealing on the conversion of metastable elastically strained GeSn layers into a plastically relaxed state is examined. Ge/GeSn quantum wells with Sn molar fraction up to 0.11 are obtained.

  19. GaAs Core/SrTiO3 Shell Nanowires Grown by Molecular Beam Epitaxy.

    PubMed

    Guan, X; Becdelievre, J; Meunier, B; Benali, A; Saint-Girons, G; Bachelet, R; Regreny, P; Botella, C; Grenet, G; Blanchard, N P; Jaurand, X; Silly, M G; Sirotti, F; Chauvin, N; Gendry, M; Penuelas, J

    2016-04-13

    We have studied the growth of a SrTiO3 shell on self-catalyzed GaAs nanowires grown by vapor-liquid-solid assisted molecular beam epitaxy on Si(111) substrates. To control the growth of the SrTiO3 shell, the GaAs nanowires were protected using an arsenic capping/decapping procedure in order to prevent uncontrolled oxidation and/or contamination of the nanowire facets. Reflection high energy electron diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were performed to determine the structural, chemical, and morphological properties of the heterostructured nanowires. Using adapted oxide growth conditions, it is shown that most of the perovskite structure SrTiO3 shell appears to be oriented with respect to the GaAs lattice. These results are promising for achieving one-dimensional epitaxial semiconductor core/functional oxide shell nanostructures. PMID:27008537

  20. Lattice constant and substitutional composition of GeSn alloys grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bhargava, Nupur; Coppinger, Matthew; Prakash Gupta, Jay; Wielunski, Leszek; Kolodzey, James

    2013-07-01

    Single crystal epitaxial Ge1-xSnx alloys with atomic fractions of tin up to x = 0.145 were grown by solid source molecular beam epitaxy on Ge (001) substrates. The Ge1-xSnx alloys formed high quality, coherent, strained layers at growth temperatures below 250 °C, as shown by high resolution X-ray diffraction. The amount of Sn that was on lattice sites, as determined by Rutherford backscattering spectrometry channeling, was found to be above 90% substitutional in all alloys. The degree of strain and the dependence of the effective unstrained bulk lattice constant of Ge1-xSnx alloys versus the composition of Sn have been determined.

  1. Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Liu, J. K.; Sadwick, L.; Wang, K. L.; Kao, Y. C.

    1987-01-01

    GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

  2. Cyan laser diode grown by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Turski, H. Muziol, G.; Wolny, P.; Cywiński, G.

    2014-01-13

    We demonstrate AlGaN-cladding-free laser diodes (LDs), operating in continuous wave (CW) mode at 482 nm grown by plasma-assisted molecular beam epitaxy (PAMBE). The maximum CW output power was 230 mW. LDs were grown on c-plane GaN substrates obtained by hydride vapor phase epitaxy. The PAMBE process was carried out in metal-rich conditions, supplying high nitrogen flux (Φ{sub N}) during quantum wells (QWs) growth. We found that high Φ{sub N} improves quality of high In content InGaN QWs. The role of nitrogen in the growth of InGaN on (0001) GaN surface as well as the influence of LDs design on threshold current density are discussed.

  3. GaN grown on (1 1 1) single crystal diamond substrate by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Dussaigne, A.; Malinverni, M.; Martin, D.; Castiglia, A.; Grandjean, N.

    2009-10-01

    GaN epilayers are grown on (1 1 1) oriented single crystal diamond substrate by ammonia-source molecular beam epitaxy. Each step of the growth is monitored in situ by reflection high energy electron diffraction. It is found that a two-dimensional epitaxial wurtzite GaN film is obtained. The surface morphology is smooth: the rms roughness is as low as 1.3 nm for 2×2 μm 2 scan. Photoluminescence measurements reveal pretty good optical properties. The GaN band edge is centred at 3.469 eV with a linewidth of 5 meV. These results demonstrate that GaN heteroepitaxially grown on diamond opens new rooms for high power electronic applications.

  4. Real-time reflectance-difference spectroscopy of GaAs molecular beam epitaxy homoepitaxial growth

    SciTech Connect

    Lastras-Martínez, A. E-mail: alastras@gmail.com; Ortega-Gallegos, J.; Guevara-Macías, L. E.; Nuñez-Olvera, O.; Balderas-Navarro, R. E.; Lastras-Martínez, L. F.; Lastras-Montaño, L. A.; Lastras-Montaño, M. A.

    2014-03-01

    We report on real time-resolved Reflectance-difference (RD) spectroscopy of GaAs(001) grown by molecular beam epitaxy, with a time-resolution of 500 ms per spectrum within the 2.3–4.0 eV photon energy range. Through the analysis of transient RD spectra we demonstrated that RD line shapes are comprised of two components with different physical origins and determined their evolution during growth. Such components were ascribed to the subsurface strain induced by surface reconstruction and to surface stoichiometry. Results reported in this paper render RD spectroscopy as a powerful tool for the study of fundamental processes during the epitaxial growth of zincblende semiconductors.

  5. Controlled in situ boron doping of short silicon nanowires grown by molecular beam epitaxy

    SciTech Connect

    Das Kanungo, Pratyush; Zakharov, Nikolai; Bauer, Jan; Breitenstein, Otwin; Werner, Peter; Goesele, Ulrich

    2008-06-30

    Epitaxial silicon nanowires (NWs) of short heights ({approx}280 nm) on Si <111> substrate were grown and doped in situ with boron on a concentration range of 10{sup 15}-10{sup 19} cm{sup -3} by coevaporation of atomic Si and B by molecular beam epitaxy. Transmission electron microscopy revealed a single-crystalline structure of the NWs. Electrical measurements of the individual NWs confirmed the doping. However, the low doped (10{sup 15} cm{sup -3}) and medium doped (3x10{sup 16} and 1x10{sup 17} cm{sup -3}) NWs were heavily depleted by the surface states while the high doped (10{sup 18} and 10{sup 19} cm{sup -3}) ones showed volume conductivities expected for the corresponding intended doping levels.

  6. Molecular beam epitaxial growth of a three-dimensional topological Dirac semimetal Na3Bi

    NASA Astrophysics Data System (ADS)

    Zhang, Yi; Liu, Zhongkai; Zhou, Bo; Kim, Yeongkwan; Hussain, Zahid; Shen, Zhi-Xun; Chen, Yulin; Mo, Sung-Kwan

    2014-07-01

    We report a molecular beam epitaxial growth of Na3Bi single-crystal thin films on two different substrates—epitaxial bilayer graphene terminated 6H-SiC(0001) and Si(111). Using reflection high-energy electron diffraction, we found that the lattice orientation of the grown Na3Bi thin film was rotated by 30° respect to the surface lattice orientations of these two substrates. An in-situ angle-resolved photoemission spectroscopy clearly revealed the 3-dimensional Dirac-cone band structure in such thin films. Our approach of growing Na3Bi thin film provides a potential route for further studying its intriguing electronic properties and for fabricating it into practical devices in future.

  7. In situ surface/interface x-ray diffractometer for oxide molecular beam epitaxy

    SciTech Connect

    Lee, J. H.; Tung, I. C.; Chang, S. -H.; Bhattacharya, A.; Fong, D. D.; Freeland, J. W.; Hong, Hawoong

    2016-01-01

    In situ studies of oxide molecular beam epitaxy by synchrotron x-ray scattering has been made possible by upgrading an existing UHV/molecular beam epitaxy (MBE) six-circle diffractometer system. For oxide MBE growth, pure ozone delivery to the chamber has been made available, and several new deposition sources have been made available on a new 12 in. CF (ConFlat, a registered trademark of Varian, Inc.) flange. X-ray diffraction has been used as a major probe for film growth and structures for the system. In the original design, electron diffraction was intended for the secondary diagnostics available without the necessity of the x-ray and located at separate positions. Deposition of films was made possible at the two diagnostic positions. And, the aiming of the evaporation sources is fixed to the point between two locations. Ozone can be supplied through two separate nozzles for each location. Also two separate thickness monitors are installed. Additional features of the equipment are also presented together with the data taken during typical oxide film growth to illustrate the depth of information available via in situ x-ray techniques.

  8. In situ surface/interface x-ray diffractometer for oxide molecular beam epitaxy.

    PubMed

    Lee, J H; Tung, I C; Chang, S-H; Bhattacharya, A; Fong, D D; Freeland, J W; Hong, Hawoong

    2016-01-01

    In situ studies of oxide molecular beam epitaxy by synchrotron x-ray scattering has been made possible by upgrading an existing UHV/molecular beam epitaxy (MBE) six-circle diffractometer system. For oxide MBE growth, pure ozone delivery to the chamber has been made available, and several new deposition sources have been made available on a new 12 in. CF (ConFlat, a registered trademark of Varian, Inc.) flange. X-ray diffraction has been used as a major probe for film growth and structures for the system. In the original design, electron diffraction was intended for the secondary diagnostics available without the necessity of the x-ray and located at separate positions. Deposition of films was made possible at the two diagnostic positions. And, the aiming of the evaporation sources is fixed to the point between two locations. Ozone can be supplied through two separate nozzles for each location. Also two separate thickness monitors are installed. Additional features of the equipment are also presented together with the data taken during typical oxide film growth to illustrate the depth of information available via in situ x-ray techniques. PMID:26827327

  9. Structural study and ferroelectricity of epitaxial BaTiO3 films on silicon grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Mazet, L.; Bachelet, R.; Louahadj, L.; Albertini, D.; Gautier, B.; Cours, R.; Schamm-Chardon, S.; Saint-Girons, G.; Dubourdieu, C.

    2014-12-01

    Integration of epitaxial complex ferroelectric oxides such as BaTiO3 on semiconductor substrates depends on the ability to finely control their structure and properties, which are strongly correlated. The epitaxial growth of thin BaTiO3 films with high interfacial quality still remains scarcely investigated on semiconductors; a systematic investigation of processing conditions is missing although they determine the cationic composition, the oxygen content, and the microstructure, which, in turn, play a major role on the ferroelectric properties. We report here the study of various relevant deposition parameters in molecular beam epitaxy for the growth of epitaxial tetragonal BaTiO3 thin films on silicon substrates. The films were grown using a 4 nm-thick epitaxial SrTiO3 buffer layer. We show that the tetragonality of the BaTiO3 films, the crystalline domain orientations, and SiO2 interfacial layer regrowth strongly depend on the oxygen partial pressure and temperature during the growth and on the post-deposition anneal. The ferroelectricity of the films, probed using piezoresponse force microscopy, is obtained in controlled temperature and oxygen pressure conditions with a polarization perpendicular to the surface.

  10. Epitaxial growth of SrTiO{sub 3} thin film on Si by laser molecular beam epitaxy

    SciTech Connect

    Zhou, X. Y.; Miao, J.; Dai, J. Y.; Chan, H. L. W.; Choy, C. L.; Wang, Y.; Li, Q.

    2007-01-01

    SrTiO{sub 3} thin films have been deposited on Si (001) wafers by laser molecular beam epitaxy using an ultrathin Sr layer as the template. X-ray diffraction measurements indicated that SrTiO{sub 3} was well crystallized and epitaxially aligned with Si. Cross-sectional observations in a transmission electron microscope revealed that the SrTiO{sub 3}/Si interface was sharp, smooth, and fully crystallized. The thickness of the Sr template was found to be a critical factor that influenced the quality of SrTiO{sub 3} and the interfacial structure. Electrical measurements revealed that the SrTiO{sub 3} film was highly resistive.

  11. Photodiode properties of molecular beam epitaxial InSb on a heavily doped substrate

    NASA Astrophysics Data System (ADS)

    Sun, Weiguo; Fan, Huitao; Peng, Zhenyu; Zhang, Liang; Zhang, Xiaolei; Zhang, Lei; Lu, Zhengxiong; Si, Junjie; Emelyanov, E.; Putyato, M.; Semyagin, B.; Pchelyakov, O.; Preobrazhenskii, V.

    2014-01-01

    Photodiodes of InSb were fabricated on an epitaxial layer grown using molecular beam epitaxy (MBE). Thermal cleaning of the InSb (0 0 1) substrate surface, 2° towards the (1 1 1) B plane, was performed to remove the oxide. Photodiode properties of МВЕ-formed epitaxial InSb were demonstrated. Zero-bias resistance area product (R0A) measurements were taken at 80 K under room temperature background for a pixel size of 100 μm × 100 μm. Values were as high as 4.36 × 104 Ω/cm2, and the average value of R0A was 1.66 × 104 Ω/cm2. The peak response was 2.44 (A/W). The epitaxial InSb photodiodes were fabricated using the same process as bulk crystal InSb diodes with the exception of the junction formation method. These values are comparable to the properties of bulk crystal InSb photodiodes.

  12. GaAs surface cleaning by thermal oxidation and sublimation in molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Saito, Junji; Nanbu, Kazuo; Ishikawa, Tomonori; Kondo, Kazuo

    1988-01-01

    GaAs surface cleaning by thermal oxidation and sublimation prior to molecular-beam-epitaxial growth has been investigated as a means of reducing the carrier depletion at the substrate and epitaxial layer interface. The carrier depletion between the substrate and epitaxial films, measured by a C-V carrier profiling technique, was shown to decrease significantly with an increase in the thickness of the thermal oxidation. The concentration of carbon contamination near the substrate-epitaxial interface was measured using secondary ion mass spectroscopy. The carbon concentration correlated very well with the carrier depletion. Therefore, the main origin of the carrier depletion is believed to be the carbon concentration of the initial growth surface. Based on these results, the thermal oxidation and sublimation of a semi-insulating GaAs substrate was successfully applied to improve the mobility and sheet concentration of the two-dimensional electron gas in selectively doped GaAs/N-Al0.3Ga0.7As heterostructures with very thin GaAs buffer layers.

  13. Molecular beam epitaxy control of the structural, optical, and electronic properties of ScN(001)

    SciTech Connect

    Smith, Arthur R.; AL-Brithen, Hamad A. H.; Ingram, David C.; Gall, Daniel

    2001-08-15

    Scandium nitride (001) oriented layers have been grown on magnesium oxide (001) substrates by molecular beam epitaxy using a rf-plasma source and a scandium effusion cell. The Sc/N flux ratio is found to be critical in determining the structural, optical, and electronic properties of the grown epitaxial layers. A distinct transition occurs at the point where the Sc/N flux ratio equals 1, which defines the line between N-rich and Sc-rich growth. Under N-rich conditions, the growth is epitaxial, and the surface morphology is characterized by a densely packed array of square-shaped plateaus and four-faced pyramids with the terraces between steps being atomically smooth. The films are stoichiometric and transparent with a direct optical transition at 2.15 eV. Under Sc-rich conditions, the growth is also epitaxial, but the morphology is dominated by spiral growth mounds. The morphology change is consistent with increased surface diffusion due to a Sc-rich surface. Excess Sc leads to understoichiometric layers with N vacancies which act as donors. The increased carrier density results in an optical reflection edge at 1 eV, absorption below the 2.15 eV band gap, and a drop in electrical resistivity. {copyright} 2001 American Institute of Physics.

  14. Plasma-assisted molecular beam epitaxy of SnO 2 on TiO 2

    NASA Astrophysics Data System (ADS)

    Tsai, M. Y.; White, M. E.; Speck, J. S.

    2008-08-01

    Epitaxial growth of SnO 2 on TiO 2 (1 1 0) substrates by plasma-assisted molecular beam epitaxy was studied under various growth conditions to explore the potential for high-quality single crystalline growth. Phase-pure (1 1 0)-oriented SnO 2 films with an optimum on-axis X-ray rocking curve scan full-width at half-maximum equal to 0.612° were grown. The film epitaxy proceeded in the Volmer-Weber growth mode. We identified different growth regimes by measuring growth rate variations correlated with increasing tin fluxes at a fixed oxygen pressure. Beginning in the oxygen-rich growth regime, growth rates increased linearly as the tin flux increased. Atomically flat surfaces were observed in the oxygen-rich regime. Continued tin flux increases resulted in a maximum growth rate of 470 nm/h. Further tin flux increases prevented SnO 2 formation on the growth surface and acted as a nucleation barrier of SnO 2 on the TiO 2 substrates identifying a metal-rich growth regime.

  15. Molecular beam epitaxy growth of SnO{sub 2} using a tin chemical precursor

    SciTech Connect

    Wang, Tianqi; Prakash, Abhinav; Jalan, Bharat; Warner, Ellis; Gladfelter, Wayne L.

    2015-03-15

    The authors report on the development of a molecular beam epitaxy approach for atomic layer controlled growth of phase-pure, single-crystalline epitaxial SnO{sub 2} films with scalable growth rates using a highly volatile precursor (tetraethyltin) for tin and rf-oxygen plasma for oxygen. Smooth, epitaxial SnO{sub 2} (101) films on r-sapphire (101{sup ¯}2) substrates were grown as a function of tin precursor flux and substrate temperatures between 300 and 900 °C. Three distinct growth regimes were identified where SnO{sub 2} films grew in a reaction-, flux-, and desorption-limited mode, respectively, with increasing substrate temperature. In particular, with increasing tin flux, the growth rates were found to increase and then saturate indicating any excess tin precursor desorbs above a critical beam equivalent pressure of tin precursor. Important implications of growth kinetic behaviors on the self-regulating stoichiometric growth of perovskite stannates are discussed.

  16. Epitaxial dysprosium phosphide grown by gas-source and solid-source MBE on gallium arsenide substrates

    NASA Astrophysics Data System (ADS)

    Sadwick, L. P.; Lee, P. P.; Patel, M.; Nikols, M.; Hwu, R. J.; Shield, J. E.; Streit, D. C.; Brehmer, D.; McCormick, K.; Allen, S. J.; Gedridge, R. W.

    1996-07-01

    We report the first known study of the growth of epitaxial dysprosium phosphide (DyP) grown on gallium arsenide (GaAs). DyP is lattice matched to GaAs, with the room-temperature mismatch being less than 0.01%. We have grown DyP on GaAs by gas-source and by solid-source molecular beam epitaxy using custom-designed group V thermal cracker cells and group III high temperature effusion cells. X-ray diffraction results show the DyP epilayer to be (001) single crystal on GaAs(001) substrate. Electrical and optical measurements performed to date are inconclusive as to whether DyP is a semi-metal or a semiconductor with a small band gap. The undoped films are n-type with measured electron concentrations on the order of 5 × 10 19-6 × 10 20cm -3 with mobilities of 1-10 cm 2/V · s. {DyP}/{GaAs} is stable in air with no apparent oxidation taking place, even after months of exposure to ambient untreated air. Material and surface science properties measured for {DyP}/{GaAs} include Hall measurements, 2ϑ and double-crystal X-ray diffraction spectra and photothermal deflection spectroscopy.

  17. Bismuth-induced phase control of GaAs nanowires grown by molecular beam epitaxy

    SciTech Connect

    Lu, Zhenyu; Chen, Pingping E-mail: luwei@mail.sitp.ac.cn; Shi, Suixing; Yao, Luchi; Zhou, Xiaohao; Lu, Wei E-mail: luwei@mail.sitp.ac.cn; Zhang, Zhi; Zhou, Chen; Zou, Jin

    2014-10-20

    In this work, the crystal structure of GaAs nanowires grown by molecular beam epitaxy has been tailored only by bismuth without changing the growth temperature and V/III flux ratio. The introduction of bismuth can lead to the formation of zinc-blende GaAs nanowires, while the removal of bismuth changes the structure into a 4H polytypism before it turns back to the wurtzite phase eventually. The theoretical calculation shows that it is the steadiest for bismuth to adsorb on the GaAs(111){sub B} surface compared to the liquid gold catalyst surface and the interface between the gold catalyst droplet and the nanowire, and these adsorbed bismuth could decrease the diffusion length of adsorbed Ga and hence the supersaturation of Ga in the gold catalyst droplet.

  18. Fe-doped InN layers grown by molecular beam epitaxy

    SciTech Connect

    Wang Xinqiang; Liu Shitao; Ma Dingyu; Zheng Xiantong; Chen Guang; Xu Fujun; Tang Ning; Shen Bo; Zhang Peng; Cao Xingzhong; Wang Baoyi; Huang Sen; Chen, Kevin J.; Zhou Shengqiang; Yoshikawa, Akihiko

    2012-10-22

    Iron(Fe)-doped InN (InN:Fe) layers have been grown by molecular beam epitaxy. It is found that Fe-doping leads to drastic increase of residual electron concentration, which is different from the semi-insulating property of Fe-doped GaN. However, this heavy n-type doping cannot be fully explained by doped Fe-concentration ([Fe]). Further analysis shows that more unintentionally doped impurities such as hydrogen and oxygen are incorporated with increasing [Fe] and the surface is degraded with high density pits, which probably are the main reasons for electron generation and mobility reduction. Photoluminescence of InN is gradually quenched by Fe-doping. This work shows that Fe-doping is one of good choices to control electron density in InN.

  19. Formation of GeSn alloy on Si(100) by low-temperature molecular beam epitaxy

    SciTech Connect

    Talochkin, A. B.; Mashanov, V. I.

    2014-12-29

    GeSn alloys grown on Si(100) by the low-temperature (100 °C) molecular beam epitaxy are studied using scanning tunneling microscopy and Raman spectroscopy. It is found that the effect of Sn as a surfactant modifies substantially the low-temperature growth mechanism of Ge on Si. Instead of the formation of small Ge islands surrounded by amorphous Ge, in the presence of Sn, the growth of pure Ge islands appears via the Stranski-Krastanov growth mode, and a partially relaxed Ge{sub 1−x}Sn{sub x} alloy layer with the high Sn-fraction up to 40 at. % is formed in the area between them. It is shown that the observed growth mode induced by high surface mobility of Sn and the large strain of the pseudomorphic state of Ge to Si ensures the minimum elastic-strain energy of the structure.

  20. Molecular beam epitaxy growth of free-standing plane-parallel InAs nanoplates

    NASA Astrophysics Data System (ADS)

    Aagesen, Martin; Johnson, Erik; Sørensen, Claus B.; Mariager, Simon O.; Feidenhans'l, Robert; Spiecker, Erdmann; Nygård, Jesper; Lindelof, Poul Erik

    2007-12-01

    Free-standing nanostructures such as suspended carbon nanotubes, graphene layers, III-V nanorod photonic crystals and three-dimensional structures have recently attracted attention because they could form the basis of devices with unique electronic, optoelectronic and electromechanical characteristics. Here we report the growth by molecular beam epitaxy of free-standing nanoplates of InAs that are close to being atomically plane. The structural and transport properties of these semiconducting nanoplates have been examined with scanning electron microscopy, transmission electron microscopy, X-ray diffraction and low-temperature electron transport measurements. The carrier density of the nanoplates can be reduced to zero by applying a voltage to a nearby gate electrode, creating a new type of suspended quantum well that can be used to explore low-dimensional electron transport. The electronic and optical properties of such systems also make them potentially attractive for photovoltaic and sensing applications.

  1. Microstructure of In x Ga1-x N nanorods grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Webster, R. F.; Soundararajah, Q. Y.; Griffiths, I. J.; Cherns, D.; Novikov, S. V.; Foxon, C. T.

    2015-11-01

    Transmission electron microscopy is used to examine the structure and composition of In x Ga1-x N nanorods grown by plasma-assisted molecular beam epitaxy. The results confirm a core-shell structure with an In-rich core and In-poor shell resulting from axial and lateral growth sectors respectively. Atomic resolution mapping by energy-dispersive x-ray microanalysis and high angle annular dark field imaging show that both the core and the shell are decomposed into Ga-rich and In-rich platelets parallel to their respective growth surfaces. It is argued that platelet formation occurs at the surfaces, through the lateral expansion of surface steps. Studies of nanorods with graded composition show that decomposition ceases for x ≥ 0.8 and the ratio of growth rates, shell:core, decreases with increasing In concentration.

  2. Investigation of Localized States in GaAsSb Epilayers Grown by Molecular Beam Epitaxy.

    PubMed

    Gao, Xian; Wei, Zhipeng; Zhao, Fenghuan; Yang, Yahui; Chen, Rui; Fang, Xuan; Tang, Jilong; Fang, Dan; Wang, Dengkui; Li, Ruixue; Ge, Xiaotian; Ma, Xiaohui; Wang, Xiaohua

    2016-01-01

    We report the carrier dynamics in GaAsSb ternary alloy grown by molecular beam epitaxy through comprehensive spectroscopic characterization over a wide temperature range. A detailed analysis of the experimental data reveals a complex carrier relaxation process involving both localized and delocalized states. At low temperature, the localized degree shows linear relationship with the increase of Sb component. The existence of localized states is also confirmed by the temperature dependence of peak position and band width of the emission. At temperature higher than 60 K, emissions related to localized states are quenched while the band to band transition dominates the whole spectrum. This study indicates that the localized states are related to the Sb component in the GaAsSb alloy, while it leads to the poor crystal quality of the material, and the application of GaAsSb alloy would be limited by this deterioration. PMID:27381641

  3. Ferromagnetic (Ga,Mn)As nanowires grown by Mn-assisted molecular beam epitaxy

    SciTech Connect

    Bouravleuv, Alexei; Cirlin, George; Sapega, Victor; Werner, Peter; Savin, Alexander; Lipsanen, Harri

    2013-04-14

    (Ga,Mn)As nanowires were grown by molecular beam epitaxy using Mn as a growth catalyst on GaAs(001) substrates at 485 Degree-Sign C, i.e., at intermediate temperatures higher than ones used for the growth of (Ga,Mn)As thin films, but lower than the ordinary temperatures of Au-assisted growth of GaAs nanowires. (Ga,Mn)As nanowires obtained with typical lengths between 0.8 and 4 {mu}m and diameters 50-90 nm do not have defects, such as dislocations or precipitates, except for the stacking faults lying parallel to the growth direction. The investigation of magnetic and optical properties has been carried out not only for as-grown samples with nanowires but also for peeled off nanowires from the host substrate. The results obtained demonstrate that (Ga,Mn)As nanowires exhibit ferromagnetic ordering around 70 K.

  4. Infrared electroluminescence from GeSn heterojunction diodes grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Gupta, Jay Prakash; Bhargava, Nupur; Kim, Sangcheol; Adam, Thomas; Kolodzey, James

    2013-06-01

    Infrared electroluminescence was observed from GeSn/Ge p-n heterojunction diodes with 8% Sn, grown by molecular beam epitaxy. The GeSn layers were boron doped, compressively strained, and pseudomorphic on Ge substrates. Spectral measurements indicated an emission peak at 0.57 eV, about 50 meV wide, increasing in intensity with applied pulsed current, and with reducing device temperatures. The total integrated emitted power from a single edge facet was 54 μW at an applied peak current of 100 mA at 100 K. These results suggest that GeSn-based materials maybe useful for practical light emitting diodes operating in the infrared wavelength range near 2 μm.

  5. Formation of GeSn alloy on Si(100) by low-temperature molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Talochkin, A. B.; Mashanov, V. I.

    2014-12-01

    GeSn alloys grown on Si(100) by the low-temperature (100 °C) molecular beam epitaxy are studied using scanning tunneling microscopy and Raman spectroscopy. It is found that the effect of Sn as a surfactant modifies substantially the low-temperature growth mechanism of Ge on Si. Instead of the formation of small Ge islands surrounded by amorphous Ge, in the presence of Sn, the growth of pure Ge islands appears via the Stranski-Krastanov growth mode, and a partially relaxed Ge1-xSnx alloy layer with the high Sn-fraction up to 40 at. % is formed in the area between them. It is shown that the observed growth mode induced by high surface mobility of Sn and the large strain of the pseudomorphic state of Ge to Si ensures the minimum elastic-strain energy of the structure.

  6. Molecular beam epitaxy of SrTiO3 with a growth window

    NASA Astrophysics Data System (ADS)

    Jalan, Bharat; Moetakef, Pouya; Stemmer, Susanne

    2009-07-01

    Many complex oxides with only nonvolatile constituents do not have a wide growth window in conventional molecular beam epitaxy (MBE) approaches, which makes it difficult to obtain stoichiometric films. Here it is shown that a growth window in which the stoichiometry is self-regulating can be achieved for SrTiO3 films by using a hybrid MBE approach that uses a volatile metal-organic source for Ti, titanium tetra isopropoxide (TTIP). The growth window widens and shifts to higher TTIP/Sr flux ratios with increasing temperature, showing that it is related to the desorption of the volatile TTIP. We demonstrate stoichiometric, highly perfect, insulating SrTiO3 films. The approach can be adapted for the growth of other complex oxides that previously were believed to have no wide MBE growth window.

  7. Investigation of Localized States in GaAsSb Epilayers Grown by Molecular Beam Epitaxy

    PubMed Central

    Gao, Xian; Wei, Zhipeng; Zhao, Fenghuan; Yang, Yahui; Chen, Rui; Fang, Xuan; Tang, Jilong; Fang, Dan; Wang, Dengkui; Li, Ruixue; Ge, Xiaotian; Ma, Xiaohui; Wang, Xiaohua

    2016-01-01

    We report the carrier dynamics in GaAsSb ternary alloy grown by molecular beam epitaxy through comprehensive spectroscopic characterization over a wide temperature range. A detailed analysis of the experimental data reveals a complex carrier relaxation process involving both localized and delocalized states. At low temperature, the localized degree shows linear relationship with the increase of Sb component. The existence of localized states is also confirmed by the temperature dependence of peak position and band width of the emission. At temperature higher than 60 K, emissions related to localized states are quenched while the band to band transition dominates the whole spectrum. This study indicates that the localized states are related to the Sb component in the GaAsSb alloy, while it leads to the poor crystal quality of the material, and the application of GaAsSb alloy would be limited by this deterioration. PMID:27381641

  8. Towards precise defect control in layered oxide structures by using oxide molecular beam epitaxy

    PubMed Central

    Baiutti, Federico; Christiani, Georg

    2014-01-01

    Summary In this paper we present the atomic-layer-by-layer oxide molecular beam epitaxy (ALL-oxide MBE) which has been recently installed in the Max-Planck Institute for Solid State Research and we report on its present status, providing some examples that demonstrate its successful application in the synthesis of different layered oxides, with particular reference to superconducting La2CuO4 and insulator-to-metal La2− xSrxNiO4. We briefly review the ALL-oxide MBE technique and its unique capabilities in the deposition of atomically smooth single-crystal thin films of various complex oxides, artificial compounds and heterostructures, introducing our goal of pursuing a deep investigation of such systems with particular emphasis on structural defects, with the aim of tailoring their functional properties by precise defects control. PMID:24995148

  9. Analysis of carbon in SrTiO{sub 3} grown by hybrid molecular beam epitaxy

    SciTech Connect

    Jalan, Bharat; Cagnon, Joeel; Mates, Thomas E.; Stemmer, Susanne

    2009-11-15

    Secondary ion mass spectroscopy (SIMS) was used to investigate carbon impurity concentrations in stoichiometric SrTiO{sub 3} films grown by a hybrid molecular beam epitaxy approach that uses an effusion cell to supply strontium, a rf plasma source for oxygen and a metal organic titanium source (titanium tetra isopropoxide). The carbon concentration in the films was measured as a function of growth parameters. At sufficiently high growth temperatures (>800 degree sign C), the films contain a few ppm of carbon. The challenges in accurately quantifying low carbon concentrations are discussed. A carbon-containing contamination layer is detected on the surfaces of SrTiO{sub 3} substrates and air-exposed films by SIMS and in scanning transmission electron microscopy. The contamination layer could be removed by high-temperature predeposition oxygen plasma cleaning.

  10. Surface energies for molecular beam epitaxy growth of HgTe and CdTe

    NASA Astrophysics Data System (ADS)

    Berding, M. A.; Krishnamurthy, Srinivasan; Sher, A.

    1991-10-01

    We present results for the surface binding energies for HgTe and CdTe that will serve as input for molecular beam epitaxy growth models. We have found that the surface binding energies are surface orientation dependent and are not simply proportional to the number of first-neighbor bonds being made to the underlying layer. Moreover, because of the possibility of charge transfer between cation and anion surface states, one may have large differences between the binding energy for the first and the last atom in a given layer, and these differences will be different for the narrow-gap, less ionic materials than for the wide gap, ionic materials. We also find that the surface states associated with an isolated surface atom or vacancy are extended in materials with small gaps and small effective masses, and thus call into question the modeling of surface binding by simple pair interactions.

  11. Raman measurements of substrate temperature in a molecular beam epitaxy growth chamber

    NASA Astrophysics Data System (ADS)

    Hutchins, T.; Nazari, M.; Eridisoorya, M.; Myers, T. M.; Holtz, M.

    2015-01-01

    A method is described for directly measuring the temperature of a substrate in a molecular-beam epitaxy (MBE) growth system. The approach relies on the establishment of the temperature dependence of Raman-active phonons of the substrate material using independently known calibration points across the range of interest. An unknown temperature in this range is then determined based on the Raman peak position with the substrate in situ the MBE chamber. The apparatus relies on conventional optics and Raman components. Shifting and broadening of the Raman spectrum are described based on the effects of thermal expansion and anharmonic decay. The choice of reference temperature is discussed. The method is qualified by examining the substrate temperature dependence, relative to that of a standard thermocouple, during a commonly used ramp procedure. Both temperature difference and time lag are obtained.

  12. Synthesis of atomically thin hexagonal boron nitride films on nickel foils by molecular beam epitaxy

    SciTech Connect

    Nakhaie, S.; Wofford, J. M.; Schumann, T.; Jahn, U.; Ramsteiner, M.; Hanke, M.; Lopes, J. M. J. Riechert, H.

    2015-05-25

    Hexagonal boron nitride (h-BN) is a layered two-dimensional material with properties that make it promising as a dielectric in various applications. We report the growth of h-BN films on Ni foils from elemental B and N using molecular beam epitaxy. The presence of crystalline h-BN over the entire substrate is confirmed by Raman spectroscopy. Atomic force microscopy is used to examine the morphology and continuity of the synthesized films. A scanning electron microscopy study of films obtained using shorter depositions offers insight into the nucleation and growth behavior of h-BN on the Ni substrate. The morphology of h-BN was found to evolve from dendritic, star-shaped islands to larger, smooth triangular ones with increasing growth temperature.

  13. Molecular beam epitaxy growth of GaAs1-xBix

    NASA Astrophysics Data System (ADS)

    Tixier, S.; Adamcyk, M.; Tiedje, T.; Francoeur, S.; Mascarenhas, A.; Wei, Peng; Schiettekatte, F.

    2003-04-01

    GaAs1-xBix epilayers with bismuth concentrations up to x=3.1% were grown on GaAs by molecular beam epitaxy. The Bi content in the films was measured by Rutherford backscattering spectroscopy. X-ray diffraction shows that GaAsBi is pseudomorphically strained to GaAs but that some structural disorder is present in the thick films. The extrapolation of the lattice constant of GaAsBi to the hypothetical zincblende GaBi alloy gives 6.33±0.06 Å. Room-temperature photoluminescence of the GaAsBi epilayers is obtained and a significant redshift in the emission of GaAsBi of ˜84 meV per percent Bi is observed.

  14. Novel InGaPBi single crystal grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Yue, Li; Wang, Peng; Wang, Kai; Wu, Xiaoyan; Pan, Wenwu; Li, Yaoyao; Song, Yuxin; Gu, Yi; Gong, Qian; Wang, Shumin; Ning, Jiqian; Xu, Shijie

    2015-04-01

    InGaPBi crystalline thin films with up to 2.1% bismuth concentration have been grown on GaAs substrates by molecular beam epitaxy. Rutherford backscattering spectrometry confirms that the majority of Bi atoms are located at substitutional lattice sites. The films exhibit good surface, structural, and interface quality, and their strains can be tuned from tensile to compressive by increasing the Bi content. InBi LO and GaBi LO vibrational modes in Raman spectroscopy were observed, and their intensities increased with Bi concentration. A weak photoluminescence signal was observed at 1.78 eV at room temperature for the sample with a Bi content of 0.5%.

  15. New Semiconductor GaNAsBi Alloy Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Yoshimoto, Masahiro; Huang, Wei; Takehara, Yuji; Saraie, Junji; Chayahara, Akiyoshi; Horino, Yuji; Oe, Kunishige

    2004-07-01

    GaNyAs1-x-yBix epilayers were grown on GaAs by molecular beam epitaxy for the first time. Multilayered samples consisting of GaAs1-xBix, GaNyAs1-y and GaNyAs1-x-yBix showed distinct X-ray diffraction (XRD) peaks ascribed to each layer. The GaBi molar fraction, x, estimated by the combination of Rutherford backscattering spectroscopy and XRD was controlled in a range up to 4.0%. The GaN molar fraction estimated from the angular spacing of the XRD peak between GaAs1-xBix and GaNyAs1-x-yBix increased up to 8.0% with increasing supply of activated nitrogen generated in rf plasma.

  16. Intense terahertz emission from molecular beam epitaxy-grown GaAs/GaSb(001)

    SciTech Connect

    Sadia, Cyril P.; Laganapan, Aleena Maria; Agatha Tumanguil, Mae; Estacio, Elmer; Somintac, Armando; Salvador, Arnel; Que, Christopher T.; Yamamoto, Kohji; Tani, Masahiko

    2012-12-15

    Intense terahertz (THz) electromagnetic wave emission was observed in undoped GaAs thin films deposited on (100) n-GaSb substrates via molecular beam epitaxy. GaAs/n-GaSb heterostructures were found to be viable THz sources having signal amplitude 75% that of bulk p-InAs. The GaAs films were grown by interruption method during the growth initiation and using various metamorphic buffer layers. Reciprocal space maps revealed that the GaAs epilayers are tensile relaxed. Defects at the i-GaAs/n-GaSb interface were confirmed by scanning electron microscope images. Band calculations were performed to infer the depletion region and electric field at the i-GaAs/n-GaSb and the air-GaAs interfaces. However, the resulting band calculations were found to be insufficient to explain the THz emission. The enhanced THz emission is currently attributed to a piezoelectric field induced by incoherent strain and defects.

  17. Nucleation mechanism of gallium-assisted molecular beam epitaxy growth of gallium arsenide nanowires

    SciTech Connect

    Fontcuberta i Morral, A.; Colombo, C.; Abstreiter, G.; Arbiol, J.; Morante, J. R.

    2008-02-11

    Molecular beam epitaxy Ga-assisted synthesis of GaAs nanowires is demonstrated. The nucleation and growth are seen to be related to the presence of a SiO{sub 2} layer previously deposited on the GaAs wafer. The interaction of the reactive gallium with the SiO{sub 2} pinholes induces the formation of nanocraters, found to be the key for the nucleation of the nanowires. With SiO{sub 2} thicknesses up to 30 nm, nanocraters reach the underlying substrate, resulting into a preferential growth orientation of the nanowires. Possibly related to the formation of nanocraters, we observe an incubation period of 258 s before the nanowires growth is initiated.

  18. Investigation of Localized States in GaAsSb Epilayers Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Gao, Xian; Wei, Zhipeng; Zhao, Fenghuan; Yang, Yahui; Chen, Rui; Fang, Xuan; Tang, Jilong; Fang, Dan; Wang, Dengkui; Li, Ruixue; Ge, Xiaotian; Ma, Xiaohui; Wang, Xiaohua

    2016-07-01

    We report the carrier dynamics in GaAsSb ternary alloy grown by molecular beam epitaxy through comprehensive spectroscopic characterization over a wide temperature range. A detailed analysis of the experimental data reveals a complex carrier relaxation process involving both localized and delocalized states. At low temperature, the localized degree shows linear relationship with the increase of Sb component. The existence of localized states is also confirmed by the temperature dependence of peak position and band width of the emission. At temperature higher than 60 K, emissions related to localized states are quenched while the band to band transition dominates the whole spectrum. This study indicates that the localized states are related to the Sb component in the GaAsSb alloy, while it leads to the poor crystal quality of the material, and the application of GaAsSb alloy would be limited by this deterioration.

  19. Antimony segregation in stressed SiGe heterostructures grown by molecular beam epitaxy

    SciTech Connect

    Drozdov, M. N.; Novikov, A. V.; Yurasov, D. V.

    2013-11-15

    The effects of the growth temperature, composition, and elastic strains in separate layers on the segregation of antimony are studied experimentally for stressed SiGe structures grown by molecular beam epitaxy. It is established that the growth conditions and parameters of the structures exert an interrelated influence on the segregation of Sb: the degree of the influence of the composition and elastic stresses in the SiGe layers on Sb segregation depends on the growth temperature. It is shown that usage of a method previously proposed by us for the selective doping of silicon structures with consideration for the obtained dependences of Sb segregation on the growth conditions and parameters of the SiGe layers makes it possible to form SiGe structures selectively doped with antimony.

  20. GaInP and AlInP grown by elemental source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Varriano, J. A.; Koch, M. W.; Johnson, F. G.; Wicks, G. W.

    1992-02-01

    We report on the use of a new, valved, solid phosphorus cracker source for the growth of phosphides by molecular beam epitaxy. The source avoids the relatively high expense and high level of toxicity associated with the use of phosphine gas and eliminates the problems commonly encountered in using conventional solid phosphorus sources. The source has been used to grow GaInP and AlInP lattice-matched to GaAs substrates. The quality of the materials reported here is comparable to the best materials grown by other techniques. Photoluminescence and Raman scattering measurements indicate that the resulting material has a high degree of disorder on the group III sublattice. The new source is shown to be a reliable and attractive alternative for the growth of these phosphide materials.

  1. High breakdown single-crystal GaN p-n diodes by molecular beam epitaxy

    SciTech Connect

    Qi, Meng; Zhao, Yuning; Yan, Xiaodong; Li, Guowang; Verma, Jai; Fay, Patrick; Nomoto, Kazuki; Zhu, Mingda; Hu, Zongyang; Protasenko, Vladimir; Song, Bo; Xing, Huili Grace; Jena, Debdeep; Bader, Samuel

    2015-12-07

    Molecular beam epitaxy grown GaN p-n vertical diodes are demonstrated on single-crystal GaN substrates. A low leakage current <3 nA/cm{sup 2} is obtained with reverse bias voltage up to −20 V. With a 400 nm thick n-drift region, an on-resistance of 0.23 mΩ cm{sup 2} is achieved, with a breakdown voltage corresponding to a peak electric field of ∼3.1 MV/cm in GaN. Single-crystal GaN substrates with very low dislocation densities enable the low leakage current and the high breakdown field in the diodes, showing significant potential for MBE growth to attain near-intrinsic performance when the density of dislocations is low.

  2. Towards precise defect control in layered oxide structures by using oxide molecular beam epitaxy.

    PubMed

    Baiutti, Federico; Christiani, Georg; Logvenov, Gennady

    2014-01-01

    In this paper we present the atomic-layer-by-layer oxide molecular beam epitaxy (ALL-oxide MBE) which has been recently installed in the Max-Planck Institute for Solid State Research and we report on its present status, providing some examples that demonstrate its successful application in the synthesis of different layered oxides, with particular reference to superconducting La2CuO4 and insulator-to-metal La2- x Sr x NiO4. We briefly review the ALL-oxide MBE technique and its unique capabilities in the deposition of atomically smooth single-crystal thin films of various complex oxides, artificial compounds and heterostructures, introducing our goal of pursuing a deep investigation of such systems with particular emphasis on structural defects, with the aim of tailoring their functional properties by precise defects control. PMID:24995148

  3. Optical properties of plasma-assisted molecular beam epitaxy grown InN/sapphire

    NASA Astrophysics Data System (ADS)

    Talwar, Devki N.; Liao, Ying Chieh; Chen, Li Chyong; Chen, Kuei Hsien; Feng, Zhe Chuan

    2014-11-01

    The optical properties of as-grown InN/sapphire films prepared by plasma assisted molecular beam epitaxy (PA-MBE) are characterized by photoluminescence (PL), Raman scattering (RS) and infrared (IR) reflectance techniques. The PL measurements have consistently exhibited lower values of InN band gaps providing clear indications of electron concentration dependent peak energy shifts and widths. The phonon modes identified by RS are found to be in good agreement with the grazing inelastic X-ray scattering measurements and ab initio lattice dynamical calculations. An effective medium theory used to analyze IR reflectance spectra of InN/sapphire films has provided reasonable estimates of free charge carrier concentrations.

  4. Raman measurements of substrate temperature in a molecular beam epitaxy growth chamber

    SciTech Connect

    Hutchins, T.; Nazari, M.; Eridisoorya, M.; Myers, T. M.; Holtz, M.

    2015-01-15

    A method is described for directly measuring the temperature of a substrate in a molecular-beam epitaxy (MBE) growth system. The approach relies on the establishment of the temperature dependence of Raman-active phonons of the substrate material using independently known calibration points across the range of interest. An unknown temperature in this range is then determined based on the Raman peak position with the substrate in situ the MBE chamber. The apparatus relies on conventional optics and Raman components. Shifting and broadening of the Raman spectrum are described based on the effects of thermal expansion and anharmonic decay. The choice of reference temperature is discussed. The method is qualified by examining the substrate temperature dependence, relative to that of a standard thermocouple, during a commonly used ramp procedure. Both temperature difference and time lag are obtained.

  5. Residual stress in AlN films grown on sapphire substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Rong, Xin; Wang, Xinqiang; Chen, Guang; Pan, Jianhai; Wang, Ping; Liu, Huapeng; Xu, Fujun; Tan, Pingheng; Shen, Bo

    2016-05-01

    Residual stress in AlN films grown by molecular beam epitaxy (MBE) has been studied by Raman scattering spectroscopy. A strain-free Raman frequency and a biaxial stress coefficient for E2(high) mode are experimentally determined to be 657.8 ± 0.3 cm-1 and 2.4 ± 0.2 cm-1 / GPa, respectively. By using these parameters, the residual stress of a series of AlN layers grown under different buffer layer conditions has been investigated. The residual compressive stress is found to be obviously decreased by increasing the Al/N beam flux ratio of the buffer layer, indicating the generation of tensile stress due to stronger coalescence of AlN grains, as also confirmed by the in-situ reflection high energy electron diffraction (RHEED) monitoring observation. The stronger coalescence does lead to improved quality of AlN films as expected.

  6. n{sup +}-GaN grown by ammonia molecular beam epitaxy: Application to regrown contacts

    SciTech Connect

    Lugani, L.; Malinverni, M.; Giraud, E.; Carlin, J.-F.; Grandjean, N.; Tirelli, S.; Marti, D.; Bolognesi, C. R.

    2014-11-17

    We report on the low-temperature growth of heavily Si-doped (>10{sup 20 }cm{sup −3}) n{sup +}-type GaN by N-rich ammonia molecular beam epitaxy (MBE) with very low bulk resistivity (<4 × 10{sup −4} Ω·cm). This is applied to the realization of regrown ohmic contacts on InAlN/GaN high electron mobility transistors. A low n{sup +}-GaN/2 dimensional electron gas contact resistivity of 0.11 Ω·mm is measured, provided an optimized surface preparation procedure, which is shown to be critical. This proves the great potentials of ammonia MBE for the realization of high performance electronic devices.

  7. Growth regimes during homoepitaxial growth of GaN by ammonia molecular beam epitaxy

    SciTech Connect

    Corrion, A. L.; Wu, F.; Speck, J. S.

    2012-09-01

    c-plane GaN films were grown by ammonia molecular beam epitaxy on metal-organic chemical vapor deposition templates for a wide range of NH{sub 3}:Ga flux ratios and growth temperatures, and the resulting films were characterized using atomic force microscopy, reflection high-energy electron diffraction, and transmission electron microscopy. Three distinct nitrogen-rich growth regimes - unstable layer-by-layer, quasi-stable step flow, and dislocation-mediated pitting - were identified based on the growth mode and film properties. In addition, step flow growth was observed under conditions of gallium droplet accumulation. The results indicate the existence of two regimes for step-flow growth of GaN by ammonia MBE - both gallium-rich and nitrogen-rich. Growth mode instabilities and mound formation were observed and are discussed in the context of a step-edge energy barrier to adatom diffusion over a terrace.

  8. Real-time control of the molecular beam epitaxy of nitrides

    NASA Astrophysics Data System (ADS)

    Massies, J.; Grandjean, N.

    1999-05-01

    Due to the peculiarities of the growth process of GaN and related alloys on sapphire substrates, reflection high-energy electron diffraction (RHEED) is not sufficient to correctly monitor all the different steps of molecular beam epitaxy growth (MBE). It is shown that laser reflectivity, which is a very simple method, is highly complementary to RHEED. However, RHEED remains an unrivaled tool for the precise control of the growth. In particular, the observation of RHEED intensity oscillations can be used, as for classical semiconductors, to determine the growth rate with monolayer precision and also the composition of ternary alloys such as Al xGa 1- xN. The accuracy of such a RHEED based control of MBE growth of nitrides is exemplified by the optical properties of GaN/Al xGa 1- xN quantum well structures.

  9. High reflectance III-nitride Bragg reflectors grown by molecular beam epitaxy

    SciTech Connect

    Ng, H.M.; Moustakas, T.D.

    2000-07-01

    Distributed Bragg reflector (DBR) structures based on AlN/GaN have been grown on (0001) sapphire by electron-cyclotron-resonance plasma-assisted molecular-beam epitaxy (ECR-MBE). The design of the structures was predetermined by simulations using the transmission matrix method. A number of structures have been grown with 20.5--25.5 periods showing peak reflectance ranging form the near-UV to the green wavelength regions. For the best sample, peak reflectance up to 99% was observed centered at 467 nm with a bandwidth of 45 nm. The experimental reflectance data were compared with the simulations and show excellent agreement with respect to peak reflectance, bandwidth of high reflectance and the locations of the sidelobes.

  10. Growth of Inclined GaAs Nanowires by Molecular Beam Epitaxy: Theory and Experiment

    PubMed Central

    2010-01-01

    The growth of inclined GaAs nanowires (NWs) during molecular beam epitaxy (MBE) on the rotating substrates is studied. The growth model provides explicitly the NW length as a function of radius, supersaturations, diffusion lengths and the tilt angle. Growth experiments are carried out on the GaAs(211)A and GaAs(111)B substrates. It is found that 20° inclined NWs are two times longer in average, which is explained by a larger impingement rate on their sidewalls. We find that the effective diffusion length at 550°C amounts to 12 nm for the surface adatoms and is more than 5,000 nm for the sidewall adatoms. Supersaturations of surface and sidewall adatoms are also estimated. The obtained results show the importance of sidewall adatoms in the MBE growth of NWs, neglected in a number of earlier studies. PMID:21076695

  11. Improved tunneling magnetoresistance at low temperature in manganite junctions grown by molecular beam epitaxy

    SciTech Connect

    Werner, R.; Kleiner, R.; Koelle, D.; Petrov, A. Yu.; Davidson, B. A.; Mino, L. Alvarez

    2011-04-18

    We report resistance versus magnetic field measurements for a La{sub 0.65}Sr{sub 0.35}MnO{sub 3}/SrTiO{sub 3}/La{sub 0.65}Sr{sub 0.35}MnO{sub 3} tunnel junction grown by molecular-beam epitaxy, that show a large field window of extremely high tunneling magnetoresistance (TMR) at low temperature. Scanning the in-plane applied field orientation through 360 deg., the TMR shows fourfold symmetry, i.e., biaxial anisotropy, aligned with the crystalline axis but not the junction geometrical long axis. The TMR reaches {approx}1900% at 4 K, corresponding to an interfacial spin polarization of >95% assuming identical interfaces. These results show that uniaxial anisotropy is not necessary for large TMR, and lay the groundwork for future improvements in TMR in manganite junctions.

  12. Concentration transient analysis of antimony surface segregation during Si(100) molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Markert, L. C.; Greene, J. E.; Ni, W.-X.; Hansson, G. V.; Sundgren, J.-E.

    1991-01-01

    Antimony surface segregation during Si(100) molecular beam epitaxy (MBE) was investigated at temperatures T(sub s) = 515 - 800 C using concentration transient analysis (CTA). The dopant surface coverage Theta, bulk fraction gamma, and incorporation probability sigma during MBE were determined from secondary-ion mass spectrometry depth profiles of modulation-doped films. Programmed T(sub s) changes during growth were used to trap the surface-segregated dopant overlayer, producing concentration spikes whose integrated area corresponds to Theta. Thermal antimony doping by coevaporation was found to result in segregation strongly dependent on T(sub s) with Theta(sub Sb) values up to 0.9 monolayers (ML): in films doped with Sb(+) ions accelerated by 100 V, Theta(sub Sb) was less than or equal to 4 x 10(exp -3) ML. Surface segregation of coevaporated antimony was kinematically limited for the film growth conditions in these experiments.

  13. High electron mobility in Ga(In)NAs films grown by molecular beam epitaxy

    SciTech Connect

    Miyashita, Naoya; Ahsan, Nazmul; Monirul Islam, Muhammad; Okada, Yoshitaka; Inagaki, Makoto; Yamaguchi, Masafumi

    2012-11-26

    We report the highest mobility values above 2000 cm{sup 2}/Vs in Si doped GaNAs film grown by molecular beam epitaxy. To understand the feature of the origin which limits the electron mobility in GaNAs, temperature dependences of mobility were measured for high mobility GaNAs and referential low mobility GaInNAs. Temperature dependent mobility for high mobility GaNAs is similar to the GaAs case, while that for low mobility GaInNAs shows large decrease in lower temperature region. The electron mobility of high quality GaNAs can be explained by intrinsic limiting factor of random alloy scattering and extrinsic factor of ionized impurity scattering.

  14. Accommodation mechanism of InN nanocolumns grown on Si(111) substrates by molecular beam epitaxy

    SciTech Connect

    Grandal, J.; Sanchez-Garcia, M. A.; Calleja, E.; Luna, E.; Trampert, A.

    2007-07-09

    High quality InN nanocolumns have been grown by molecular beam epitaxy on bare and AlN-buffered Si(111) substrates. The accommodation mechanism of the InN nanocolumns to the substrate was studied by transmission electron microscopy. Samples grown on AlN-buffered Si(111) show abrupt interfaces between the nanocolumns and the buffer layer, where an array of periodically spaced misfit dislocations develops. Samples grown on bare Si(111) exhibit a thin Si{sub x}N{sub y} at the InN nanocolumn/substrate interface because of Si nitridation. The Si{sub x}N{sub y} thickness and roughness may affect the nanocolumn relative alignment to the substrate. In all cases, InN nanocolumns grow strain- and defect-free.

  15. Molecular beam epitaxy of SrTiO{sub 3} with a growth window

    SciTech Connect

    Jalan, Bharat; Moetakef, Pouya; Stemmer, Susanne

    2009-07-20

    Many complex oxides with only nonvolatile constituents do not have a wide growth window in conventional molecular beam epitaxy (MBE) approaches, which makes it difficult to obtain stoichiometric films. Here it is shown that a growth window in which the stoichiometry is self-regulating can be achieved for SrTiO{sub 3} films by using a hybrid MBE approach that uses a volatile metal-organic source for Ti, titanium tetra isopropoxide (TTIP). The growth window widens and shifts to higher TTIP/Sr flux ratios with increasing temperature, showing that it is related to the desorption of the volatile TTIP. We demonstrate stoichiometric, highly perfect, insulating SrTiO{sub 3} films. The approach can be adapted for the growth of other complex oxides that previously were believed to have no wide MBE growth window.

  16. Characterization of homoepitaxial p-type ZnO grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Look, D. C.; Reynolds, D. C.; Litton, C. W.; Jones, R. L.; Eason, D. B.; Cantwell, G.

    2002-09-01

    An N-doped, p-type ZnO layer has been grown by molecular beam epitaxy on an Li-diffused, bulk, semi-insulating ZnO substrate. Hall-effect and conductivity measurements on the layer give: resistivity=4 x101 Omega cm; hole mobility=2 cm2/V s; and hole concentration=9 x1016 cm-3. Photoluminescence measurements in this N-doped layer show a much stronger peak near 3.32 eV (probably due to neutral acceptor bound excitons), than at 3.36 eV (neutral donor bound excitons), whereas the opposite is true in undoped ZnO. Calibrated, secondary-ion mass spectroscopy measurements show an N surface concentration of about 1019 cm-3 in the N-doped sample, but only about 1017 cm-3 in the undoped sample.

  17. Growth of high quality AlGaAs by metalorganic molecular beam epitaxy using trimethylamine alane

    NASA Astrophysics Data System (ADS)

    Abernathy, C. R.; Jordan, A. S.; Pearton, S. J.; Hobson, W. S.; Bohling, D. A.; Muhr, G. T.

    1990-06-01

    AlGaAs grown by metalorganic molecular beam epitaxy (MOMBE) has been problematic due to oxygen and carbon contamination, particularly when triethylaluminum (TEAl) has been used as the aluminum source. Consequently, we have investigated trimethylamine alane (TMAAl) as a potential replacement for the conventional metalorganic Al sources. AlGaAs films with excellent structural and optical properties have been grown with this source. Photoluminescence intensities from AlGaAs grown by MOMBE at 500 °C using TMAAl are comparable to those from material grown by metalorganic chemical vapor deposition at 675 °C using triethylaluminum (TMAl). Carbon and oxygen levels in MOMBE-grown AlGaAs are drastically reduced in comparison to similar films grown with TEAl.

  18. Preface of the 18th International Conference on Molecular Beam Epitaxy (MBE 2014)

    NASA Astrophysics Data System (ADS)

    Brown, April S.; Ptak, Aaron J.

    2015-09-01

    The first International Conference on Molecular Beam Epitaxy (IC-MBE) was held in Paris in 1978, chaired by Alfred Y. Cho. Every other year since, with the exception of a four-year break after the initial meeting, the IC-MBE has been held in European, Asian, and North American venues. The 18th and latest IC-MBE was held in Flagstaff, Arizona, USA, September 7-12, 2014, and was chaired by Yong-Hang Zhang (Arizona State University). MBE is an advanced crystal growth method that benefits areas from the study of fundamental physics, all the way through the production of devices used in countless fields. IC-MBE brings together researchers from all over the world, and is the premier forum for scientific and technological exchange among researchers investigating all types of materials growth using the MBE technique.

  19. Effects of substrate orientation on the growth of InSb nanostructures by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chou, C. Y.; Torfi, A.; Pei, C.; Wang, W. I.

    2016-05-01

    In this work, the effects of substrate orientation on InSb quantum structure growth by molecular beam epitaxy (MBE) are presented. Motivated by the observation that (411) evolves naturally as a stable facet during MBE crystal growth, comparison studies have been carried out to investigate the effects of the crystal orientation of the underlying GaSb substrate on the growth of InSb by MBE. By depositing InSb on a number of different substrate orientations, namely: (100), (311), (411), and (511), a higher nanostructure density was observed on the (411) surface compared with the other orientations. This result suggests that the (411) orientation presents a superior surface in MBE growth to develop a super-flat GaSb buffer surface, naturally favorable for nanostructure growth.

  20. AlN Nanowall Structures Grown on Si (111) Substrate by Molecular Beam Epitaxy.

    PubMed

    Tamura, Yosuke; Hane, Kazuhiro

    2015-12-01

    AlN nanowall structures were grown on Si (111) substrate using molecular beam epitaxy at substrate temperature of 700 °C with N/Al flux ratios ranging from 50 to 660. A few types of other AlN nanostructures were also grown under the nitrogen-rich conditions. The AlN nanowalls were ranged typically 60-120 nm in width and from 190 to 470 nm in length by changing N/Al flux ratio. The AlN nanowall structures grown along the c-plane consisted of AlN (0002) crystal with full-width at half maximum of the rocking curve about 5000 arcsec. PMID:26625884

  1. Effect of growth temperature on defects in epitaxial GaN film grown by plasma assisted molecular beam epitaxy

    SciTech Connect

    Kushvaha, S. S. Pal, P.; Shukla, A. K.; Joshi, Amish G.; Gupta, Govind; Kumar, M.; Singh, S.; Gupta, Bipin K.; Haranath, D.

    2014-02-15

    We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 10{sup 8} cm{sup −2} at 750 °C) than that of the low temperature grown sample (1.1 × 10{sup 9} cm{sup −2} at 730 °C). A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

  2. Direct growth of graphene on in situ epitaxial hexagonal boron nitride flakes by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Xu, Zhongguang; Zheng, Renjing; Khanaki, Alireza; Zuo, Zheng; Liu, Jianlin

    2015-11-23

    Hexagonal boron nitride (h-BN) single-crystal domains were grown on cobalt (Co) substrates at a substrate temperature of 850–900 °C using plasma-assisted molecular beam epitaxy. Three-point star shape h-BN domains were observed by scanning electron microscopy, and confirmed by Raman and X-ray photoelectron spectroscopy. The h-BN on Co template was used for in situ growth of multilayer graphene, leading to an h-BN/graphene heterostructure. Carbon atoms preferentially nucleate on Co substrate and edges of h-BN and then grow laterally to form continuous graphene. Further introduction of carbon atoms results in layer-by-layer growth of graphene on graphene and lateral growth of graphene on h-BN until it may cover entire h-BN flakes.

  3. Magnetotransport in MgO-based magnetic tunnel junctions grown by molecular beam epitaxy (invited)

    SciTech Connect

    Andrieu, S. Bonell, F.; Hauet, T.; Montaigne, F.; Lefevre, P.; Bertran, F.

    2014-05-07

    The strong impact of molecular beam epitaxy growth and Synchrotron Radiation characterization tools in the understanding of fundamental issues in nanomagnetism and spintronics is illustrated through the example of fully epitaxial MgO-based Magnetic Tunnel Junctions (MTJs). If ab initio calculations predict very high tunnel magnetoresistance (TMR) in such devices, some discrepancy between theory and experiments still exists. The influence of imperfections in real systems has thus to be considered like surface contaminations, structural defects, unexpected electronic states, etc. The influence of possible oxygen contamination at the Fe/MgO(001) interface is thus studied, and is shown to be not so detrimental to TMR as predicted by ab initio calculations. On the contrary, the decrease of dislocations density in the MgO barrier of MTJs using Fe{sub 1−x}V{sub x} electrodes is shown to significantly increase TMR. Finally, unexpected transport properties in Fe{sub 1−X}Co{sub x}/MgO/Fe{sub 1−X}Co{sub x} (001) are presented. With the help of spin and symmetry resolved photoemission and ab initio calculation, the TMR decrease for Co content higher than 25% is shown to come from the existence of an interface state and the shift of the empty Δ1 minority spin state towards the Fermi level.

  4. High response solar-blind MgZnO photodetectors grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Schoenfeld, Winston V.; Wei, Ming; Boutwell, R. Casey; Liu, Huiyong

    2014-03-01

    High quality w-MgxZn1-xO thin films were grown epitaxially on c-plane sapphire substrates by plasma-assisted Molecular Beam Epitaxy. ZnO thin films with high crystalline quality, low defect and dislocation densities, and subnanometer surface roughness were achieved by applying a low temperature nucleation layer. By tuning Mg/Zn flux ratio, wurtzite MgxZn1-xO thin films with Mg composition as high as x=0.46 were obtained without phase segregation. Metal- Semiconductor-Metal (MSM) photoconductive and Schottky barrier devices with interdigitated electrode geometry and active surface area of 1 mm2 were fabricated and characterized. Resultant devices showed ~100 A/W peak responsivity at wavelength of ~260nm. We also report on cubic rock salt c-MgxZn1-xO thin films, following a non-traditional approach on MgO substrates, to demonstrate solar-blind photoresponse in MSM photodetectors, realizing a peak responsivity of 460 A/W (@ 250 nm) and 12.6 mA/W (@ 240nm) for mixed phase and single crystal films, respectively. A specific focus of the work is on identifying the impact of various growth parameters on the performance of the c- MgZnO detectors.

  5. An ultra-compact, high-throughput molecular beam epitaxy growth system

    SciTech Connect

    Baker, A. A.; Hesjedal, T.; Braun, W. E-mail: fischer@createc.de; Rembold, S.; Fischer, A. E-mail: fischer@createc.de; Gassler, G.

    2015-04-15

    We present a miniaturized molecular beam epitaxy (miniMBE) system with an outer diameter of 206 mm, optimized for flexible and high-throughput operation. The three-chamber system, used here for oxide growth, consists of a sample loading chamber, a storage chamber, and a growth chamber. The growth chamber is equipped with eight identical effusion cell ports with linear shutters, one larger port for either a multi-pocket electron beam evaporator or an oxygen plasma source, an integrated cryoshroud, retractable beam-flux monitor or quartz-crystal microbalance, reflection high energy electron diffraction, substrate manipulator, main shutter, and quadrupole mass spectrometer. The system can be combined with ultrahigh vacuum (UHV) end stations on synchrotron and neutron beamlines, or equivalently with other complex surface analysis systems, including low-temperature scanning probe microscopy systems. Substrate handling is compatible with most UHV surface characterization systems, as the miniMBE can accommodate standard surface science sample holders. We introduce the design of the system, and its specific capabilities and operational parameters, and we demonstrate the epitaxial thin film growth of magnetoelectric Cr{sub 2}O{sub 3} on c-plane sapphire and ferrimagnetic Fe{sub 3}O{sub 4} on MgO (001)

  6. Strain-Engineered Graphene Grown on Hexagonal Boron Nitride by Molecular Beam Epitaxy

    PubMed Central

    Summerfield, Alex; Davies, Andrew; Cheng, Tin S.; Korolkov, Vladimir V.; Cho, YongJin; Mellor, Christopher J.; Foxon, C. Thomas; Khlobystov, Andrei N.; Watanabe, Kenji; Taniguchi, Takashi; Eaves, Laurence; Novikov, Sergei V.; Beton, Peter H.

    2016-01-01

    Graphene grown by high temperature molecular beam epitaxy on hexagonal boron nitride (hBN) forms continuous domains with dimensions of order 20 μm, and exhibits moiré patterns with large periodicities, up to ~30 nm, indicating that the layers are highly strained. Topological defects in the moiré patterns are observed and attributed to the relaxation of graphene islands which nucleate at different sites and subsequently coalesce. In addition, cracks are formed leading to strain relaxation, highly anisotropic strain fields, and abrupt boundaries between regions with different moiré periods. These cracks can also be formed by modification of the layers with a local probe resulting in the contraction and physical displacement of graphene layers. The Raman spectra of regions with a large moiré period reveal split and shifted G and 2D peaks confirming the presence of strain. Our work demonstrates a new approach to the growth of epitaxial graphene and a means of generating and modifying strain in graphene. PMID:26928710

  7. Growth kinetics and island evolution during double-pulsed molecular beam epitaxy of InN

    NASA Astrophysics Data System (ADS)

    Kraus, A.; Hein, C.; Bremers, H.; Rossow, U.; Hangleiter, A.

    2016-06-01

    The kinetic processes of InN growth using alternating source fluxes with sub-monolayer In pulses in plasma-assisted molecular beam epitaxy have been investigated. Growth at various temperatures reveals the existence of two growth regimes. While growth at low temperatures is solely governed by surface diffusion, a combination of decomposition, desorption, and diffusion becomes decisive at growth temperatures of 470 °C and above. At this critical temperature, the surface morphology changes from a grainy structure to a structure made of huge islands. The formation of those islands is attributed to the development of an indium adlayer, which can be observed via reflection high energy electron diffraction monitoring. Based on the growth experiments conducted at temperatures below TGrowth = 470 °C, an activation energy for diffusion of 0.54 ± 0.02 eV has been determined from the decreasing InN island density. A comparison between growth on metalorganic vapor phase epitaxy GaN templates and pseudo bulk GaN indicates that step edges and dislocations are favorable nucleation sites. Based on the results, we developed a growth model, which describes the main mechanisms of the growth.

  8. Strain-Engineered Graphene Grown on Hexagonal Boron Nitride by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Summerfield, Alex; Davies, Andrew; Cheng, Tin S.; Korolkov, Vladimir V.; Cho, Yongjin; Mellor, Christopher J.; Foxon, C. Thomas; Khlobystov, Andrei N.; Watanabe, Kenji; Taniguchi, Takashi; Eaves, Laurence; Novikov, Sergei V.; Beton, Peter H.

    2016-03-01

    Graphene grown by high temperature molecular beam epitaxy on hexagonal boron nitride (hBN) forms continuous domains with dimensions of order 20 μm, and exhibits moiré patterns with large periodicities, up to ~30 nm, indicating that the layers are highly strained. Topological defects in the moiré patterns are observed and attributed to the relaxation of graphene islands which nucleate at different sites and subsequently coalesce. In addition, cracks are formed leading to strain relaxation, highly anisotropic strain fields, and abrupt boundaries between regions with different moiré periods. These cracks can also be formed by modification of the layers with a local probe resulting in the contraction and physical displacement of graphene layers. The Raman spectra of regions with a large moiré period reveal split and shifted G and 2D peaks confirming the presence of strain. Our work demonstrates a new approach to the growth of epitaxial graphene and a means of generating and modifying strain in graphene.

  9. Magnetotransport in MgO-based magnetic tunnel junctions grown by molecular beam epitaxy (invited)

    NASA Astrophysics Data System (ADS)

    Andrieu, S.; Bonell, F.; Hauet, T.; Montaigne, F.; Calmels, L.; Snoeck, E.; Lefevre, P.; Bertran, F.

    2014-05-01

    The strong impact of molecular beam epitaxy growth and Synchrotron Radiation characterization tools in the understanding of fundamental issues in nanomagnetism and spintronics is illustrated through the example of fully epitaxial MgO-based Magnetic Tunnel Junctions (MTJs). If ab initio calculations predict very high tunnel magnetoresistance (TMR) in such devices, some discrepancy between theory and experiments still exists. The influence of imperfections in real systems has thus to be considered like surface contaminations, structural defects, unexpected electronic states, etc. The influence of possible oxygen contamination at the Fe/MgO(001) interface is thus studied, and is shown to be not so detrimental to TMR as predicted by ab initio calculations. On the contrary, the decrease of dislocations density in the MgO barrier of MTJs using Fe1-xVx electrodes is shown to significantly increase TMR. Finally, unexpected transport properties in Fe1-XCox/MgO/Fe1-XCox (001) are presented. With the help of spin and symmetry resolved photoemission and ab initio calculation, the TMR decrease for Co content higher than 25% is shown to come from the existence of an interface state and the shift of the empty Δ1 minority spin state towards the Fermi level.

  10. An ultra-compact, high-throughput molecular beam epitaxy growth system

    NASA Astrophysics Data System (ADS)

    Baker, A. A.; Braun, W.; Gassler, G.; Rembold, S.; Fischer, A.; Hesjedal, T.

    2015-04-01

    We present a miniaturized molecular beam epitaxy (miniMBE) system with an outer diameter of 206 mm, optimized for flexible and high-throughput operation. The three-chamber system, used here for oxide growth, consists of a sample loading chamber, a storage chamber, and a growth chamber. The growth chamber is equipped with eight identical effusion cell ports with linear shutters, one larger port for either a multi-pocket electron beam evaporator or an oxygen plasma source, an integrated cryoshroud, retractable beam-flux monitor or quartz-crystal microbalance, reflection high energy electron diffraction, substrate manipulator, main shutter, and quadrupole mass spectrometer. The system can be combined with ultrahigh vacuum (UHV) end stations on synchrotron and neutron beamlines, or equivalently with other complex surface analysis systems, including low-temperature scanning probe microscopy systems. Substrate handling is compatible with most UHV surface characterization systems, as the miniMBE can accommodate standard surface science sample holders. We introduce the design of the system, and its specific capabilities and operational parameters, and we demonstrate the epitaxial thin film growth of magnetoelectric Cr2O3 on c-plane sapphire and ferrimagnetic Fe3O4 on MgO (001).

  11. The competing oxide and sub-oxide formation in metal-oxide molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Vogt, Patrick; Bierwagen, Oliver

    2015-02-01

    The hetero-epitaxial growth of the n-type semiconducting oxides β-Ga2O3, In2O3, and SnO2 on c- and r-plane sapphire was performed by plasma-assisted molecular beam epitaxy. The growth-rate and desorbing flux from the substrate were measured in-situ under various oxygen to metal ratios by laser reflectometry and quadrupole mass spectrometry, respectively. These measurements clarified the role of volatile sub-oxide formation (Ga2O, In2O, and SnO) during growth, the sub-oxide stoichiometry, and the efficiency of oxide formation for the three oxides. As a result, the formation of the sub-oxides decreased the growth-rate under metal-rich growth conditions and resulted in etching of the oxide film by supplying only metal flux. The flux ratio for the exclusive formation of the sub-oxide (e.g., the p-type semiconductor SnO) was determined, and the efficiency of oxide formation was found to be the highest for SnO2, somewhat lower for In2O3, and the lowest for Ga2O3. Our findings can be generalized to further oxides that possess related sub-oxides.

  12. The competing oxide and sub-oxide formation in metal-oxide molecular beam epitaxy

    SciTech Connect

    Vogt, Patrick; Bierwagen, Oliver

    2015-02-23

    The hetero-epitaxial growth of the n-type semiconducting oxides β-Ga{sub 2}O{sub 3}, In{sub 2}O{sub 3}, and SnO{sub 2} on c- and r-plane sapphire was performed by plasma-assisted molecular beam epitaxy. The growth-rate and desorbing flux from the substrate were measured in-situ under various oxygen to metal ratios by laser reflectometry and quadrupole mass spectrometry, respectively. These measurements clarified the role of volatile sub-oxide formation (Ga{sub 2}O, In{sub 2}O, and SnO) during growth, the sub-oxide stoichiometry, and the efficiency of oxide formation for the three oxides. As a result, the formation of the sub-oxides decreased the growth-rate under metal-rich growth conditions and resulted in etching of the oxide film by supplying only metal flux. The flux ratio for the exclusive formation of the sub-oxide (e.g., the p-type semiconductor SnO) was determined, and the efficiency of oxide formation was found to be the highest for SnO{sub 2}, somewhat lower for In{sub 2}O{sub 3}, and the lowest for Ga{sub 2}O{sub 3}. Our findings can be generalized to further oxides that possess related sub-oxides.

  13. Strain-Engineered Graphene Grown on Hexagonal Boron Nitride by Molecular Beam Epitaxy.

    PubMed

    Summerfield, Alex; Davies, Andrew; Cheng, Tin S; Korolkov, Vladimir V; Cho, YongJin; Mellor, Christopher J; Foxon, C Thomas; Khlobystov, Andrei N; Watanabe, Kenji; Taniguchi, Takashi; Eaves, Laurence; Novikov, Sergei V; Beton, Peter H

    2016-01-01

    Graphene grown by high temperature molecular beam epitaxy on hexagonal boron nitride (hBN) forms continuous domains with dimensions of order 20 μm, and exhibits moiré patterns with large periodicities, up to ~30 nm, indicating that the layers are highly strained. Topological defects in the moiré patterns are observed and attributed to the relaxation of graphene islands which nucleate at different sites and subsequently coalesce. In addition, cracks are formed leading to strain relaxation, highly anisotropic strain fields, and abrupt boundaries between regions with different moiré periods. These cracks can also be formed by modification of the layers with a local probe resulting in the contraction and physical displacement of graphene layers. The Raman spectra of regions with a large moiré period reveal split and shifted G and 2D peaks confirming the presence of strain. Our work demonstrates a new approach to the growth of epitaxial graphene and a means of generating and modifying strain in graphene. PMID:26928710

  14. Hybrid molecular beam epitaxy for the growth of stoichiometric BaSnO{sub 3}

    SciTech Connect

    Prakash, Abhinav Dewey, John; Yun, Hwanhui; Jeong, Jong Seok; Mkhoyan, K. Andre; Jalan, Bharat

    2015-11-15

    Owing to its high room-temperature electron mobility and wide bandgap, BaSnO{sub 3} has recently become of significant interest for potential room-temperature oxide electronics. A hybrid molecular beam epitaxy (MBE) approach for the growth of high-quality BaSnO{sub 3} films is developed in this work. This approach employs hexamethylditin as a chemical precursor for tin, an effusion cell for barium, and a radio frequency plasma source for oxygen. BaSnO{sub 3} films were thus grown on SrTiO{sub 3} (001) and LaAlO{sub 3} (001) substrates. Growth conditions for stoichiometric BaSnO{sub 3} were identified. Reflection high-energy electron diffraction (RHEED) intensity oscillations, characteristic of a layer-by-layer growth mode were observed. A critical thickness of ∼1 nm for strain relaxation was determined for films grown on SrTiO{sub 3} using in situ RHEED. Scanning transmission electron microscopy combined with electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy confirmed the cube-on-cube epitaxy and composition. The importance of precursor chemistry is discussed in the context of the MBE growth of BaSnO{sub 3}.

  15. Growth of GaN nanowall network on Si (111) substrate by molecular beam epitaxy

    PubMed Central

    2012-01-01

    GaN nanowall network was epitaxially grown on Si (111) substrate by molecular beam epitaxy. GaN nanowalls overlap and interlace with one another, together with large numbers of holes, forming a continuous porous GaN nanowall network. The width of the GaN nanowall can be controlled, ranging from 30 to 200 nm by adjusting the N/Ga ratio. Characterization results of a transmission electron microscope and X-ray diffraction show that the GaN nanowall is well oriented along the C axis. Strong band edge emission centered at 363 nm is observed in the spectrum of room temperature photoluminescence, indicating that the GaN nanowall network is of high quality. The sheet resistance of the Si-doped GaN nanowall network along the lateral direction was 58 Ω/. The conductive porous nanowall network can be useful for integrated gas sensors due to the large surface area-to-volume ratio and electrical conductivity along the lateral direction by combining with Si micromachining. PMID:23270331

  16. Formation of Ga droplets on patterned GaAs (100) by molecular beam epitaxy

    PubMed Central

    2012-01-01

    In this paper, the formation of Ga droplets on photo-lithographically patterned GaAs (100) and the control of the size and density of Ga droplets by droplet epitaxy using molecular beam epitaxy are demonstrated. In extension of our previous result from the journal Physical Status Solidi A, volume 209 in 2012, the sharp contrast of the size and density of Ga droplets is clearly observed by high-resolution scanning electron microscope, atomic force microscope, and energy dispersive X-ray spectrometry. Also, additional monolayer (ML) coverage is added to strength the result. The density of droplets is an order of magnitude higher on the trench area (etched area), while the size of droplets is much larger on the strip top area (un-etched area). A systematic variation of ML coverage results in an establishment of the control of size and density of Ga droplets. The cross-sectional line profile analysis and root mean square roughness analysis show that the trench area (etched area) is approximately six times rougher. The atomic surface roughness is suggested to be the main cause of the sharp contrast of the size and density of Ga droplets and is discussed in terms of surface diffusion. PMID:23033893

  17. Growth and properties of GdTiO3 films prepared by hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Moetakef, Pouya; Ouellette, Daniel G.; Zhang, Jack Y.; Cain, Tyler A.; Allen, S. James; Stemmer, Susanne

    2012-09-01

    The paper reports on the thin film growth of a protoptype Mott insulator, ferrimagnetic GdTiO3, using shuttered molecular beam epitaxy. Substrates were (001) (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT), with and without epitaxial SrTiO3 buffer layers, respectively. It was found that on bare LSAT, the starting monolayer was crucial for stabilizing the GdTiO3 perovskite phase. The quality of the films was evaluated using structural, electric, optical and magnetic characterization. Structural characterization showed that the GdTiO3 layers were free of pyrochlore impurity phases and that the lattice parameter was close to what was expected for coherently strained, stoichiometric GdTiO3. The room temperature film resistivity was 7 Ωcm and increased with decreasing temperature, consistent with Mott insulating characteristics. The Curie temperature was 30 K and a small coercivity was observed at 2 K, in good agreement with bulk GdTiO3 properties reported in the literature.

  18. Molecular-beam-epitaxy-grown ZnMgS ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Sou, I. K.; Wu, Marcus C. W.; Sun, T.; Wong, K. S.; Wong, G. K. L.

    2001-03-01

    Epitaxial growth of Zn1-xMgxS alloy thin films on GaP(100) substrates was carried out using the molecular-beam-epitaxy technique. In situ reflection high-energy electron diffraction studies show that the alloys can be grown with a stable zinc-blende structure up to x around 30%. For x>30%, a structural transition will occur at a critical thickness which is sensitively dependent on the x composition. A near-band-edge peak with a full width at half maximum of about 10 nm was observed in room-temperature photoluminescence measurements made on as-grown alloy thin films. Several Zn1-xMgxS-based Schottky barrier photodetectors were fabricated. Room-temperature photoresponse measurements were performed on these detectors and abrupt long-wavelength cutoffs covering 325, 305, 295, and 270 nm were achieved for devices with Mg composition of 16%, 44%, 57%, and 75%, respectively. The response curve of the Zn0.43Mg0.57S device offers a close match to the erythemal action spectrum that describes human skin sensitivity to UV radiation.

  19. Molecular Beam Epitaxy of BaSi2 Films with Grain Size over 4 µm on Si(111)

    NASA Astrophysics Data System (ADS)

    Baba, Masakazu; Nakamura, Kotaro; Du, Weijie; Ajmal Khan, M.; Koike, Shintaro; Toko, Kaoru; Usami, Noritaka; Saito, Noriyuki; Yoshizawa, Noriko; Suemasu, Takashi

    2012-09-01

    100-nm-thick BaSi2 epitaxial films were grown on Si(111) substrates by a two-step growth method including reactive deposition epitaxy (RDE) and molecular beam epitaxy (MBE). The Ba deposition rate and duration were varied from 0.25 to 1.0 nm/min and from 5 to 120 min during RDE, respectively. Plan-view transmission electron micrographs indicated that the grain size in the MBE-grown BaSi2 was significantly dependent on the RDE growth conditions and was varied from approximately 0.2 to more than 4 µm.

  20. Epitaxial growth and optical properties of Al- and N-polar AlN films by laser molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chen, X. W.; Jia, C. H.; Chen, Y. H.; Wang, H. T.; Zhang, W. F.

    2014-03-01

    Epitaxial aluminum nitride (AlN) films with c-axis orientation were grown on both (1 1 1) MgO and c-sapphire substrates by laser molecular beam epitaxy. The in-plane epitaxial relationships were determined to be [1 1 \\bar{{2}} 0]AlN‖[0 \\bar{{1}} 1]MgO and [1 \\bar{{1}} 0 0]AlN‖[1 1 \\bar{{2}} 0]sapphire, and the lattice mismatch was 4.2% and 13.2% for AlN films on MgO and sapphire, respectively. The AlN films were shown to be Al- and N-polar on MgO and sapphire, respectively. The former is assumed to be caused by the centre of inversion symmetry of (1 1 1) MgO substrate, while the latter is due to the O polarity of sapphire. The full-width at half-maximum of the ω-scanning spectrum for AlN film on (1 1 1) MgO substrate is smaller than that on the c-sapphire substrate. The optical band-gap energies for AlN films grown on MgO and sapphire were found to be 5.93 and 5.84 eV, close to the standard band gap of 6.2 eV, and the calculated Urbach energies were 0.27 eV and 0.53 eV, respectively. These results indicate a lower amorphous content and/or less defects/impurities in Al-polar than N-polar AlN.

  1. Gas Source Melecular Beam Epitaxy Growth of High Quality AlGaAs Using Trimethylamine Alane as the Aluminum Source

    NASA Astrophysics Data System (ADS)

    Okamoto, Naoya; Ando, Hideyasu; Sandhu, Adarsh; Fujii, Toshio

    1991-12-01

    We investigated the dependence of the background impurity incorporation on growth conditions and optical properties of undoped AlGaAs grown by gas source molecular beam epitaxy using trimethylamine alane (TMAAl), triethylgallium, and arsine. The use of TMAAl enabled us to reduce the carbon concentration (7× 1016 cm-3) to over one order of magnitude less than that using triethylaluminum (TEAl). The 77 K photoluminescence spectrum of undoped AlGaAs grown using TMAAl was dominated by excitonic band-edge emission not observable in AlGaAs grown using TEAl. Furthermore, we report for the first time the doping characteristics of n-type AlGaAs grown using disilane (Si2H6) as an n-type gaseous dopant source together with TMAAl. The carrier concentration (5× 1017--3× 1018 cm-3) in n-AlxGa1-xAs (x{=}0.09--0.27) was reliably controlled and showed the same Si2H6 flow rate dependence as that of GaAs. The activation efficiency of silicon was more than 60%. We demonstrated the excellent n-type doping characteristics by uisng TMAAl.

  2. HgCdTe Molecular Beam Epitaxy Growth Temperature Calibration Using Spectroscopic Ellipsometry

    NASA Astrophysics Data System (ADS)

    Vilela, M. F.; Pribil, G. K.; Olsson, K. R.; Lofgreen, D. D.

    2012-10-01

    In this work, spectroscopic ellipsometry (SE) is demonstrated as a technique to calibrate growth temperature measurement devices (thermocouples and pyrometers) prior to real mercury cadmium telluride (HgCdTe) growth. A pyrometer is used to control the substrate temperature in molecular beam epitaxy (MBE) for the growth of HgCdTe-based material. It is known that a very narrow optimal growth temperature range exists for HgCdTe, typically ±5°C. A nonoptimal growth temperature will negatively impact on material quality by inducing growth defects, reducing composition uniformity, causing difficulty in controlling doping incorporation, promoting poor electronic properties, and having other adverse effects. Herein, we present a method for measuring and calibrating substrate temperature measurement equipment by using spectroscopic ellipsometry (SE) prior to real HgCdTe growth. This method is easy to implement, nondestructive, and reliable. The proposed method requires one substrate with a surface material with optical properties well known in the temperature range of interest, but not necessarily the same base material as the material to be grown. In the specific case of this work, we use epitaxial CdTe material on top of a Si substrate. This wafer was used to create a database of its optical properties as a function of temperature by using SE. From the collected optical parameters, a model is built and a fit is generated from the SE data collected. The temperature can then be determined by fitting the temperature-dependent SE measurements from this specific CdTe material. The angle offset and surface roughness parameters are also included in the model to account for changes in the average run-to-run angle variations and surface conditions over time. This work does not attempt to obtain an absolute temperature, but rather a reliable and repeatable relative temperature measurement.

  3. Chemical and molecular beam epitaxy of III-V nanowires on silicon for photovoltaic application

    NASA Astrophysics Data System (ADS)

    Radhakrishnan, Gokul

    Nanowires, due to their unique structure and carrier transport abilities, have sparked huge interest in the semiconductor industry. An array of nanometric size wires inserted between the p and n conductivity regions of a conventional solar cell or core shell type p-n junction nanowires synergized with semiconductor nanocrystals can lead to faster carrier collection, thereby improving device performance. This work investigates the growth of GaAs and InP semiconductor nanowires on silicon (111) using Chemical Beam Epitaxy (CBE) and Molecular Beam Epitaxy (MBE). Uniform gold nanoparticles acting as growth centers in the Vapor Liquid Solid mode of growth were generated by using the cheap and rapid technique called Nanosphere Lithography (NSL). Variation of the experimental parameters during NSL resulted in honeycomb and hexagonal patterns of gold nanoparticles. A high degree of selectivity was obtained for CBE grown nanowires whereas the MBE grown GaAs nanowires revealed the formation of a thick polycrystalline wetting layer at the interface. The CBE grown InP nanowires mostly maintained the honeycomb structure although they were found to be oriented contrary to the expected <111> direction. SEM analysis of GaAs nanowires grown by CBE showed that during growth, the nanowires may coalesce with each other resulting in unique structures such as bipods, tripods and multipods. High resolution TEM analysis of single GaAs nanowires revealed periodic formation of contrasting materials. Diffraction patterns recorded at these dark contrast areas confirmed the formation of hexagonal wurtzite single crystal structures interspaced with cubic zincblende single crystal structures. These nanowires can be used for photovoltaic applications or as light emitting devices. In addition, the formation of superlattices of different crystal structures can pave the way for novel quantum confined optoelectronic devices.

  4. Dynamic grazing incidence fast atom diffraction during molecular beam epitaxial growth of GaAs

    SciTech Connect

    Atkinson, P. Eddrief, M.; Etgens, V. H.; Khemliche, H. Debiossac, M.; Mulier, M.; Lalmi, B.; Roncin, P.; Momeni, A.

    2014-07-14

    A Grazing Incidence Fast Atom Diffraction (GIFAD) system has been mounted on a commercial molecular beam epitaxy chamber and used to monitor GaAs growth in real-time. In contrast to the conventionally used Reflection High Energy Electron Diffraction, all the GIFAD diffraction orders oscillate in phase, with the change in intensity related to diffuse scattering at step edges. We show that the scattered intensity integrated over the Laue circle is a robust method to monitor the periodic change in surface roughness during layer-by-layer growth, with oscillation phase and amplitude independent of incidence angle and crystal orientation. When there is a change in surface reconstruction at the start of growth, GIFAD intensity oscillations show that there is a corresponding delay in the onset of layer-by-layer growth. In addition, changes in the relative intensity of different diffraction orders have been observed during growth showing that GIFAD has the potential to provide insight into the preferential adatom attachment sites on the surface reconstruction during growth.

  5. In-situ spectral reflectance for improving molecular beam epitaxy device growth

    SciTech Connect

    Breiland, W.G.; Hammons, B.E.; Hou, H.Q.; Killeen, K.P.; Klem, J.F.; Reno, J.L.; Sherwin, M.

    1997-05-01

    This report summarizes the development of in situ spectral reflectance as a tool for improving the quality, reproducibility, and yield of device structures grown from compound semiconductors. Although initially targeted at MBE (Molecular Beam Epitaxy) machines, equipment difficulties forced the authors to test most of their ideas on a MOCVD (Metal Organic Chemical Vapor Deposition) reactor. A pre-growth control strategy using in situ reflectance has led to an unprecedented demonstration of process control on one of the most difficult device structures that can be grown with compound semiconductor materials. Hundreds of vertical cavity surface emitting lasers (VCSEL`s) were grown with only {+-} 0.3% deviations in the Fabry-Perot cavity wavelength--a nearly ten-fold improvement over current calibration methods. The success of the ADVISOR (Analysis of Deposition using Virtual Interfaces and Spectroscopic Optical Reflectance) method has led to a great deal of interest from the commercial sector, including use by Hewlett Packard and Honeywell. The algorithms, software and reflectance design are being evaluated for patents and/or license agreements. A small company, Filmetrics, Inc., is incorporating the ADVISOR analysis method in its reflectometer product.

  6. Relevant characteristics of undoped GaMnN grown by using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lee, J. W.; Shon, Yoon; Subramaniam, N. G.; Park, C. S.; Kim, E. K.; Im, Hyunsik; Kim, H. S.

    2015-08-01

    GaN:Mn epilayers were grown on Al2O3 substrate by using molecular beam epitaxy (MBE). Xray diffraction (XRD) data showed intrinsic GaMnN and precipitates including MnGa and MnN. PL transitions (e, Mn) and (D, Mn) related to Mn were remarkably activated. Clear ferromagnetic hysteresis loops were obtained in both samples, which means a good formation of ferromagnetic coupling. The M-T curves revealed a curie temperature ( T c ) of 140 ~ 170 K which is intrinsic to GaMnN and a Tc of above 300 K which is due to the MnGa and the MnN precipitates. The samples clearly displayed a magnetic resonance at a field of around 200 - 400 mT. Electron spin resonance (ESR) data showed that the shift of (H center ) ( i. e., H center = 337 - H center [mT]) were greater than 20 mT for samples, and the appearance of a Hcenter with a positive H center is indicative of the samples having obvious ferromagnetism. The incorporated Mn ions are in a 2+ ionic state ( i. e., Mn2+) because Mn2+ with a spin state of S = 5/2 typically exhibits a magnetic resonance with g ≈ 2 when Mn is doped into semiconductors.

  7. Laser-assisted metalorganic molecular beam epitaxy of GaAs

    NASA Astrophysics Data System (ADS)

    Donnelly, V. M.; Tu, C. W.; Beggy, J. C.; McCrary, V. R.; Lamont, M. G.; Harris, T. D.; Baiocchi, F. A.; Farrow, R. C.

    1988-03-01

    We report preliminary studies of the growth of homoepitaxial GaAs by laser-assisted metalorganic molecular beam epitaxy, using triethylgallium (TEGa) and As4 sources and a 193 nm ArF excimer laser. Laser irradiation results in a high, selective-area growth rate at temperatures below 450 °C, where pyrolytic growth is very slow. The process is extremely efficient, with roughly unit probability for impinging TEGa molecules sticking and being dissociated by laser radiation to form GaAs. From the strong dependence on laser fluence, the growth enhancement process appears to be pyrolytic in nature (because of transient heating by the pulsed laser) and not photolytic. The cross section for photolysis must be at least ten times lower than the gas-phase value (9×10-18 cm2). The surface morphology of films grown at 400 °C is rough at threshold fluences (˜0.10 J/cm2), but becomes smooth at higher fluences (˜0.13 J/cm2). These regions with relatively smooth surfaces exhibit enhanced photoluminescence yields compared to areas receiving less intense laser radiation.

  8. Electrical and optical properties of Fe doped AlGaN grown by molecular beam epitaxy

    SciTech Connect

    Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Kozhukhova, E. A.; Dabiran, A. M.; Chow, P. P.; Wowchak, A. M.; Pearton, S. J.

    2010-01-15

    Electrical and optical properties of AlGaN grown by molecular beam epitaxy were studied in the Al composition range 15%-45%. Undoped films were semi-insulating, with the Fermi level pinned near E{sub c}-0.6-0.7 eV. Si doping to (5-7)x10{sup 17} cm{sup -3} rendered the 15% Al films conducting n-type, but a large portion of the donors were relatively deep (activation energy 95 meV), with a 0.15 eV barrier for capture of electrons giving rise to strong persistent photoconductivity (PPC) effects. The optical threshold of this effect was {approx}1 eV. Doping with Fe to a concentration of {approx}10{sup 17} cm{sup -3} led to decrease in concentration of uncompensated donors, suggesting compensation by Fe acceptors. Addition of Fe strongly suppressed the formation of PPC-active centers in favor of ordinary shallow donors. For higher Al compositions, Si doping of (5-7)x10{sup 17} cm{sup -3} did not lead to n-type conductivity. Fe doping shifted the bandedge luminescence by 25-50 meV depending on Al composition. The dominant defect band in microcathodoluminescence spectra was the blue band near 3 eV, with the energy weakly dependent on composition.

  9. Hollow-anode plasma source for molecular beam epitaxy of gallium nitride

    SciTech Connect

    Anders, A.; Newman, N.; Rubin, M.; Dickinson, M.; Thomson, A.; Jones, E.; Phatak, P.; Gassmann, A.

    1995-09-01

    GaN films have been grown by molecular beam epitaxy (MBE) using a hollow-anode nitrogen plasma source. The source was developed to minimize defect formation as a result of contamination and ion damage. The hollow-anode discharge is a special form of glow discharge with very small anode area. A positive anode voltage drop of 30--40 V and an increased anode sheath thickness leads to ignition of a relatively dense plasma in front of the anode hole. Driven by the pressure gradient, the ``anode`` plasma forms a bright plasma jet streaming with supersonic velocity towards the substrate. Films of GaN have been grown on (0001) SiC and (0001) Al{sub 2}O{sub 3} at a temperature from 600--800 C. The films were investigated by photoluminescence, cathodoluminescence, X-ray diffraction, and X-ray fluorescence. The film with the highest structural quality had a rocking curve with 5 arcmin, the lowest reported value for MBE growth to date.

  10. Molecular beam epitaxy of single phase GeMnTe with high ferromagnetic transition temperature.

    PubMed

    Hassan, M; Springholz, G; Lechner, R T; Groiss, H; Kirchschlager, R; Bauer, G

    2011-05-15

    Ferromagnetic Ge(1-x)Mn(x)Te is a promising candidate for diluted magnetic semiconductors because solid solutions exist over a wide range of compositions up to x(Mn)≈0.5, where a maximum in the total magnetization occurs. In this work, a systematic study of molecular beam epitaxy of GeMnTe on (1 1 1) BaF(2) substrates is presented, in which the Mn concentration as well as growth conditions were varied over a wide range. The results demonstrate that single phase growth of GeMnTe can be achieved only in a narrow window of growth conditions, whereas at low as well as high temperatures secondary phases or even phase separation occurs. The formation of secondary phases strongly reduces the layer magnetization as well as the Curie temperatures. Under optimized conditions, single phase GeMnTe layers are obtained with Curie temperatures as high as 200 K for Mn concentrations close to the solubility limit of x(Mn)=50%. PMID:21776175

  11. Positron annihilation studies of defects in molecular beam epitaxy grown III-V layers

    SciTech Connect

    Umlor, M.T.; Keeble, D.J.; Asoka-Kumar, P.; Lynn, K.G.; Cooke, P.W.

    1994-08-01

    A summary of recent positron annihilation experiments on molecular beam epitaxy (MBE) grown III-V layers is Presented. Variable energy positron beam measurements on Al{sub 0.32}Ga{sub 0.68}As undoped and Si doped have been completed. Positron trapping at a open volume defect in Al{sub 0.32}Ga{sub 0.68}:Si for temperatures from 300 to 25 K in the dark was observed. The positron trap was lost after 1.3 eV illumination at 25K. These results indicate an open volume defect is associated with the local structure of the deep donor state of the DX center. Stability of MBE GaAs to thermal annealing war, investigated over the temperature range of 230 to 700{degrees}C, Proximity wafer furnace anneals in flowing argon were used, Samples grown above 450{degrees}C were shown to be stable but for sample below this temperature an anneal induced vacancy related defect was produced for anneals between 400 and 500{degrees}C. The nature of the defect was shown to be different for material grown at 350 and 230{degrees}C. Activation energies of 2.5 eV to 2.3 eV were obtained from isochronal anneal experiments for samples grown at 350 and 230{degrees}C, respectively.

  12. Structural and Magnetic Characterization of EuTe/SnTe Superlattices Grown by Molecular Beam Epitaxy

    SciTech Connect

    Diaz, B.; Abramof, E.; Rappl, P. H. O.; Granado, E.; Chitta, V. A.; Henriques, A. B.; Oliveira, N. F. Jr.

    2010-01-04

    Here we investigate the structural and magnetic properties of 24 repetitions EuTe/SnTe superlattices (SLs), with 3 monolayers (ML) EuTe films and SnTe thicknesses between 13 and 36 ML. The SLs were grown by molecular beam epitaxy on 3 {mu}m SnTe buffer layers, grown on top of (111)BaF{sub 2} substrates. High resolution x-ray diffraction measurements indicated that the SLs with thicker SnTe layers have higher structural quality. This is due to the SnTe growth mode on EuTe, which starts in islands and evolves to layer-by-layer. The magnetic diffraction peak observed for the higher quality SLs proved the existence of antiferromagnetic order within the individual EuTe layers. Decreasing the width of the non-magnetic SnTe layers resulted in rougher interfaces, and the fading of the magnetic peak signal. The magnetization versus applied field curves indicated that the magnetic moments of SLs with thinner SnTe layers were also harder to align along the field direction. We interpret our results considering the loss of Eu neighbors, related with the increasing roughness of the SL interfaces.

  13. Polarity inversion of N-face GaN by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Wong, M.H.; Mishra, Umesh K.; Wu Feng; Mates, Thomas E.; Speck, James S.

    2008-11-01

    The polarity of GaN grown by plasma-assisted molecular beam epitaxy was inverted from N-face to Ga-face by simultaneously exposing the surface to Mg and activated N fluxes during a growth interruption at a reduced substrate temperature. Growth studies suggested that a Mg{sub x}N{sub y} compound was responsible for inverting the crystal. The change in polarity was verified in situ by reflection high energy electron diffraction via GaN surface reconstructions, and ex situ by convergent beam electron diffraction and KOH etch studies. The surface of the inverted material showed smooth step flow features. Ga-face high electron mobility transistors with good dc and small signal performance were fabricated on the inverted epilayers. A drain-source current of 0.84 A/mm was measured at a gate-source voltage of +1 V. Current-gain cutoff and maximum oscillation frequencies of 22 and 53 GHz, respectively, were measured in these devices. The device performance is similar to that of Ga-face transistors with comparable dimensions.

  14. Molecular-beam epitaxy of CdTe on large area Si(100)

    NASA Astrophysics Data System (ADS)

    Sporken, R.; Lange, M. D.; Faurie, J. P.; Petruzzello, J.

    1991-10-01

    We have grown CdTe directly on 2- and 5-in. diam Si(100) by molecular-beam epitaxy and characterized the layers by in situ reflection high-energy electron diffraction, double crystal x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and low-temperature photoluminescence. The films are up to 10-μm thick and mirror-like over their entire surface. Even on 5-in. diam wafers, the structural and thickness uniformity is excellent. Two domains, oriented 90° apart, are observed in the CdTe films on oriented Si(100) substrates, whereas single-domain films are grown on Si(100) titled 6° or 8° toward [011]. The layers on misoriented substrates have better morphology than those on oriented Si(100), and the substrate tilt also eliminates twinning in the CdTe layers. First attempts to grow HgCdTe on Si(100 with a CdTe buffer layer have produced up to 10-μm thick layers with cutoff wavelengths between 5 and 10-μm and with an average full width at half-maximum of the double-crystal x-ray diffraction peaks of 200 arc s.

  15. Coherent growth of superconducting TiN thin films by plasma enhanced molecular beam epitaxy

    SciTech Connect

    Krockenberger, Yoshiharu; Karimoto, Shin-ichi; Yamamoto, Hideki; Semba, Kouich

    2012-10-15

    We have investigated the formation of titanium nitride (TiN) thin films on (001) MgO substrates by molecular beam epitaxy and radio frequency acitvated nitrogen plasma. Although cubic TiN is stabile over a wide temperature range, superconducting TiN films are exclusively obtained when the substrate temperature exceeds 710 Degree-Sign C. TiN films grown at 720 Degree-Sign C show a high residual resistivity ratio of approximately 11 and the superconducting transition temperature (T{sub c}) is well above 5 K. Superconductivity has been confirmed also by magnetiztion measurements. In addition, we determined the upper critical magnetic field ({mu}{sub 0}H{sub c2}) as well as the corresponding coherence length ({xi}{sub GL}) by transport measurements under high magnetic fields. High-resolution transmission electron microscopy data revealed full in plane coherency to the substrate as well as a low defect density in the film, in agreement with a mean-free path length Script-Small-L Almost-Equal-To 106 nm, which is estimated from the residual resistivity value. The observations of reflection high energy electron diffraction intensity oscillations during the growth, distinct Laue fringes around the main Bragg peaks, and higher order diffraction spots in the reciprocal space map suggest the full controlability of the thickness of high quality superconducting TiN thin films.

  16. Structural and optical properties of dilute InAsN grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ibáñez, J.; Oliva, R.; De la Mare, M.; Schmidbauer, M.; Hernández, S.; Pellegrino, P.; Scurr, D. J.; Cuscó, R.; Artús, L.; Shafi, M.; Mari, R. H.; Henini, M.; Zhuang, Q.; Godenir, A.; Krier, A.

    2010-11-01

    We perform a structural and optical characterization of InAs1-xNx epilayers grown by molecular beam epitaxy on InAs substrates (x ≲2.2%). High-resolution x-ray diffraction (HRXRD) is used to obtain information about the crystal quality and the strain state of the samples and to determine the N content of the films. The composition of two of the samples investigated is also obtained with time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measurements. The combined analysis of the HRXRD and ToF-SIMS data suggests that the lattice parameter of InAsN might significantly deviate from Vegard's law. Raman scattering and far-infrared reflectivity measurements have been carried out to investigate the incorporation of N into the InAsN alloy. N-related local vibrational modes are detected in the samples with higher N content. The origin of the observed features is discussed. We study the compositional dependence of the room-temperature band gap energy of the InAsN alloy. For this purpose, photoluminescence and optical absorption measurements are presented. The results are analyzed in terms of the band-anticrossing (BAC) model. We find that the room-temperature coupling parameter for InAsN within the BAC model is CNM=2.0±0.1 eV.

  17. Molecular Beam Epitaxy Growth of GaBi, InBi and InGaBi

    NASA Astrophysics Data System (ADS)

    Keen, B.; Makin, R.; Stampe, P. A.; Kennedy, R. J.; Piper, L. F. J.; McCombe, B.; McConville, C. F.; Durbin, S. M.

    2014-03-01

    Recent interest in bismuth alloys of III-V semiconductors for infrared and far-infrared device applications, specifically GaAsBi and InAsBi, has indicated that further study of the III-Bi family of binary compounds would be of great help in improving the quality of these material systems. While immiscibility issues have so far frustrated the growth of GaBi and AlBi, InBi is less problematic, and we have grown it by molecular beam epitaxy on (001) GaAs substrates. However, regions of varying composition exist across the substrate due to poor wetting of the surface. In an effort to improve film quality we have continued to refine the growth parameters by adjusting substrate temperature, beam flux ratio, and deposition rate. Characterization of these films has been performed by x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Additionally, we have explored growth of GaBi and In1-xGaxBi at low Ga mole fractions, and modeled this using molecular dynamics simulations. This work is supported by the Research Foundation of the State University of New York Collaborations Fund.

  18. Growth Parameters for Thin Film InBi Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Keen, B.; Makin, R.; Stampe, P. A.; Kennedy, R. J.; Sallis, S.; Piper, L. J.; McCombe, B.; Durbin, S. M.

    2014-04-01

    The alloying of bismuth with III-V semiconductors, in particular GaAs and InAs thin films grown by molecular beam epitaxy (MBE), has attracted considerable interest due to the accompanying changes in band structure and lattice constant. Specifically, bismuth incorporation in these compounds results in both a reduction in band gap (through shifting of the valence band) and an increase in the lattice constant of the alloy. To fully understand the composition of these alloys, a better understanding of the binary endpoints is needed. At present, a limited amount of literature exists on the III-Bi family of materials, most of which is theoretical work based on density functional theory calculations. The only III-Bi material known to exist (in bulk crystal form) is InBi, but its electrical properties have not been sufficiently studied and, to date, the material has not been fabricated as a thin film. We have successfully deposited crystalline InBi on (100) GaAs substrates using MBE. Wetting of the substrate is poor, and regions of varying composition exist across the substrate. To obtain InBi, the growth temperature had to be below 100 °C. It was found that film crystallinity improved with reduced Bi flux, into an In-rich regime. Additionally, attempts were made to grow AlBi and GaBi.

  19. InGaP grown on Ge (100) by molecular beam epitaxy: a spectroscopic ellipsometry study

    NASA Astrophysics Data System (ADS)

    D'Costa, Vijay Richard; Khai Loke, Wan; Zhou, Qian; Fatt Yoon, Soon; Yeo, Yee-Chia

    2016-03-01

    We investigated the optical properties of disordered In0.52Ga0.48P alloys by spectroscopic ellipsometry in the far-infrared to ultraviolet energy range (0.037-5.1 eV). The alloys were grown on Ge (100) substrate by solid-source molecular beam epitaxy. The far-infrared dielectric function reveals two absorption peaks that can be attributed to InP- and GaP-like vibrational modes. The visible-UV dielectric function of In0.52Ga0.48P alloys nearly lattice-matched to Ge shows the critical points E 0, E 1, and E 2, energies of which are determined using a derivative analysis. A weak transition that can be identified as the E 1 + Δ1 critical point is revealed. The vibrational frequencies and the transition energies in In0.52Ga0.48P are lower relative to In0.49Ga0.51P lattice-matched to GaAs. The downward shifts in E 0 and phonons can be estimated using the compositional dependence of E 0 and phonons of bulk alloys.

  20. Usage of antimony segregation for selective doping of Si in molecular beam epitaxy

    SciTech Connect

    Yurasov, D. V.; Drozdov, M. N.; Murel, A. V.; Shaleev, M. V.; Novikov, A. V.; Zakharov, N. D.

    2011-06-01

    An original approach to selective doping of Si by antimony (Sb) in molecular beam epitaxy (MBE) is proposed and verified experimentally. This approach is based on controllable utilization of the effect of Sb segregation. In particular, the sharp dependence of Sb segregation on growth temperature in the range of 300-550 deg. C is exploited. The growth temperature variations between the kinetically limited and maximum segregation regimes are suggested to be utilized in order to obtain selectively doped structures with abrupt doping profiles. It is demonstrated that the proposed technique allows formation of selectively doped Si:Sb layers, including delta ({delta}-)doped layers in which Sb concentrations can be varied from 5 x 10{sup 15} to 10{sup 20} cm{sup -3}. The obtained doped structures are shown to have a high crystalline quality and the short-term growth interruptions, which are needed to change the substrate temperature, do not lead to any significant accumulation of background impurities in grown samples. Realization of the proposed approach requires neither too low (<300 deg. C), nor too high (>600 deg. C) growth temperatures or any special equipment for the MBE machines.

  1. Surface diffusion during shadow-mask-assisted molecular-beam epitaxy of III-V compounds

    SciTech Connect

    Schallenberg, T.; Brunner, K.; Borzenko, T.; Molenkamp, L.W.; Karczewski, G.

    2005-07-01

    We present a comprehensive discussion of molecular-beam epitaxy of III-V compound semiconductors through shadow masks. Based on model calculations and growth experiments, we examine how the surface diffusion and the incorporation of group-III adatoms depend on the growth configuration, group-III and group-V fluxes, and the crystal orientation. According to a macroscopic diffusion model, gradients of the group-V flux drive the unidirectional migration of group-III adatoms. Although this effect is generally observed in the experiments, the different growth profiles obtained for [110]- and [110]-oriented samples reflect the different roles of A-type and B-type steps in the incorporation of group-III adatoms. We also demonstrate that during the heteroepitaxial growth of InAs, the dissociation of the GaAs substrate is locally enhanced by the incidence of the In beam. This effect can be exploited for shadow-mask-assisted etching on selected areas. In addition, we show how the positions and sizes of III-V nanostructures can be controlled with high precision on a planar substrate by the usage of shadow masks with multiple nanoscale apertures.

  2. Multiferroic fluoride BaCoF4 Thin Films Grown Via Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Borisov, Pavel; Johnson, Trent; García-Castro, Camilo; Kc, Amit; Schrecongost, Dustin; Cen, Cheng; Romero, Aldo; Lederman, David

    Multiferroic materials exhibit exciting physics related to the simultaneous presence of multiple long-range orders, in many cases consisting of antiferromagnetic (AF) and ferroelectric (FE) orderings. In order to provide a new, promising route for fluoride-based multiferroic material engineering, we grew multiferroic fluoride BaCoF4 in thin film form on Al2O3 (0001) substrates by molecular beam epitaxy. The films grow with the orthorhombic b-axis out-of-plane and with three in-plane structural twin domains along the polar c-axis directions. The FE ordering in thin films was verified by FE remanent hysteresis loops measurements at T = 14 K and by room temperature piezoresponse force microscopy (PFM). An AF behavior was found below Neel temperature TN ~ 80 K, which is in agreement with the bulk properties. At lower temperatures two additional magnetic phase transitions at 19 K and 41 K were found. First-principles calculations demonstrated that the growth strain applied to the bulk BaCoF4 indeed favors two canted spin orders, along the b- and a-axes, respectively, in addition to the main AF spin order along the c-axis. Supported by FAME (Contract 2013-MA-2382), WV Research Challenge Grant (HEPC.dsr.12.29), and DMREF-NSF 1434897.

  3. Surface reconstructions in molecular beam epitaxy of SrTiO{sub 3}

    SciTech Connect

    Kajdos, Adam P.; Stemmer, Susanne

    2014-11-10

    We show that reflection high-energy electron diffraction (RHEED) can be used as a highly sensitive tool to track surface and resulting film stoichiometry in adsorption-limited molecular beam epitaxy of (001) SrTiO{sub 3} thin films. Even under growth conditions that yield films with a lattice parameter that is identical to that of stoichiometric bulk crystals within the detection limit of high-resolution x-ray diffraction (XRD), changes in surface reconstruction occur from (1 × 1) to (2 × 1) to c(4 × 4) as the equivalent beam pressure of the Ti metalorganic source is increased. These surface reconstructions are correlated with a shift from mixed SrO/TiO{sub 2} termination to pure TiO{sub 2} termination. The crossover to TiO{sub 2} surface termination is also apparent in a phase shift in RHEED oscillations observed at the beginning of growth. Comparison with prior results for carrier mobilities of doped films shows that the best films are grown under conditions of a TiO{sub 2}-saturated surface [c(4 × 4) reconstruction] within the XRD growth window.

  4. Growth of SrVO{sub 3} thin films by hybrid molecular beam epitaxy

    SciTech Connect

    Eaton, Craig; Brahlek, Matthew; Engel-Herbert, Roman; Moyer, Jarrett A.; Alipour, Hamideh M.; Grimley, Everett D.; LeBeau, James M.

    2015-11-15

    The authors report the growth of stoichiometric SrVO{sub 3} thin films on (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (001) substrates using hybrid molecular beam epitaxy. This growth approach employs a conventional effusion cell to supply elemental A-site Sr and the metalorganic precursor vanadium oxytriisopropoxide (VTIP) to supply vanadium. Oxygen is supplied in its molecular form through a gas inlet. An optimal VTIP:Sr flux ratio has been identified using reflection high-energy electron-diffraction, x-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy, demonstrating stoichiometric SrVO{sub 3} films with atomically flat surface morphology. Away from the optimal VTIP:Sr flux, characteristic changes in the crystalline structure and surface morphology of the films were found, enabling identification of the type of nonstoichiometry. For optimal VTIP:Sr flux ratios, high quality SrVO{sub 3} thin films were obtained with smallest deviation of the lattice parameter from the ideal value and with atomically smooth surfaces, indicative of the good cation stoichiometry achieved by this growth technique.

  5. Carbon doping in molecular beam epitaxy of GaAs from a heated graphite filament

    NASA Technical Reports Server (NTRS)

    Malik, R. J.; Nottenberg, R. N.; Schubert, E. F.; Walker, J. F.; Ryan, R. W.

    1988-01-01

    Carbon doping of GaAs grown by molecular beam epitaxy has been obtained for the first time by use of a heated graphite filament. Controlled carbon acceptor concentrations over the range of 10 to the 17th-10 to the 20th/cu cm were achieved by resistively heating a graphite filament with a direct current power supply. Capacitance-voltage, p/n junction and secondary-ion mass spectrometry measurements indicate that there is negligible diffusion of carbon during growth and with postgrowth rapid thermal annealing. Carbon was used for p-type doping in the base of Npn AlGaAs/GaAs heterojunction bipolar transistors. Current gains greater than 100 and near-ideal emitter heterojunctions were obtained in transistors with a carbon base doping of 1 x 10 to the 19th/cu cm. These preliminary results indicate that carbon doping from a solid graphite source may be an attractive substitute for beryllium, which is known to have a relatively high diffusion coefficient in GaAs.

  6. Photoluminescence of localized excitons in ZnCdO thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wu, T. Y.; Huang, Y. S.; Hu, S. Y.; Lee, Y. C.; Tiong, K. K.; Chang, C. C.; Shen, J. L.; Chou, W. C.

    2016-07-01

    We have investigated the luminescence characteristics of Zn1-xCdxO thin films with different Cd contents grown by molecular beam epitaxy system. The temperature-dependent photoluminescence (PL) and excitation power-dependent PL spectra were measured to clarify the luminescence mechanisms of the Zn1-xCdxO thin films. The peak energy of the Zn1-xCdxO thin films with increasing the Cd concentration is observed as redshift and can be fitted by the quadratic function of alloy content. The broadened full-width at half-maximum (FWHM) estimated from the 15 K PL spectra as a function of Cd content shows a larger deviation between the experimental values and theoretical curve, which indicates that experimental FWHM values are affected not only by alloy compositional disorder but also by localized excitons occupying states in the tail of the density of states. The Urbach energy determined from an analysis of the lineshape of the low-energy side of the PL spectrum and the degree of localization effect estimated from the temperature-induced S-shaped PL peak position described an increasing mean exciton-localization effects in ZnCdO films with increasing the Cd content. In addition, the PL intensity and peak position as a function of excitation power are carried out to clarify the types of radiative recombination and the effects of localized exciton in the ZnCdO films with different Cd contents.

  7. Influence of growth conditions on tin incorporation in GaAs grown by molecular beam epitaxy

    SciTech Connect

    Alexandre, F.; Raisin, C.; Abdalla, M.I.; Brenac, A.; Masson, J.M.

    1980-08-01

    Intentional perturbations applied to the growth parameters of Sn-doped GaAs layers grown by molecular beam epitaxy have been performed in order to investigate the tin incorporation mechanism. The start, the interruption, and the end of growth as well as a variation of fluxes or substrate temperature have been studied, using either the Auger electron spectroscopy (AES) measurement of tin accumulation on the surface, or C-V derived free-carrier concentration profile versus any of these growth parameters. The theoretical model proposed by Wood and Joyce, based on a time-delayed incorporation mechanism, has been found to fit the observed results, especially for As-rich surface, provided that an incorporation mechanism of second order is assumed. For Ga-rich conditions (T/sub s/>580 /sup 0/C), a new result has been recognized, i.e., a significant reduction of carrier concentration as T/sub s/ is increased. The assumption of a partially acceptor nature of tin incident atoms under these growth conditions does not seem to fully explain this result. On the other hand, this may be better understood assuming a certain amount of tin atoms being re-evaporated in the high substrate temperature range. This behavior induces a temporarily weaker accumulation at the surface, and hence a relatively smaller incorporation rate.

  8. Molecular beam epitaxy growth and magnetic properties of Cr-Co-Ga Heusler alloy films

    SciTech Connect

    Feng, Wuwei Wang, Weihua; Zhao, Chenglong; Van Quang, Nguyen; Cho, Sunglae; Dung, Dang Duc

    2015-11-15

    We have re-investigated growth and magnetic properties of Cr{sub 2}CoGa films using molecular beam epitaxy technique. Phase separation and precipitate formation were observed experimentally again in agreement with observation of multiple phases separation in sputtered Cr{sub 2}CoGa films by M. Meinert et al. However, significant phase separation could be suppressed by proper control of growth conditions. We showed that Cr{sub 2}CoGa Heusler phase, rather than Co{sub 2}CrGa phase, constitutes the majority of the sample grown on GaAs(001) at 450 {sup o}C. The measured small spin moment of Cr{sub 2}CoGa is in agreement with predicted HM-FCF nature; however, its Curie temperature is not as high as expected from the theoretical prediction probably due to the off-stoichiometry of Cr{sub 2}CoGa and the existence of the disorders and phase separation.

  9. Diffusion-driven growth of nanowires by low-temperature molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Rueda-Fonseca, P.; Orrò, M.; Bellet-Amalric, E.; Robin, E.; Den Hertog, M.; Genuist, Y.; André, R.; Tatarenko, S.; Cibert, J.

    2016-04-01

    With ZnTe as an example, we use two different methods to unravel the characteristics of the growth of nanowires (NWs) by gold-catalyzed molecular beam epitaxy at low temperature. In the first approach, CdTe insertions have been used as markers, and the nanowires have been characterized by scanning transmission electron microscopy, including geometrical phase analysis and energy dispersive electron spectrometry; the second approach uses scanning electron microscopy and the statistics of the relationship between the length of the tapered nanowires and their base diameter. Axial and radial growth are quantified using a diffusion-limited model adapted to the growth conditions; analytical expressions describe well the relationship between the NW length and the total molecular flux (taking into account the orientation of the effusion cells), and the catalyst-nanowire contact area. A long incubation time is observed. This analysis allows us to assess the evolution of the diffusion lengths on the substrate and along the nanowire sidewalls, as a function of temperature and deviation from stoichiometric flux.

  10. Growth and magnetic property of antiperovskite manganese nitride films doped with Cu by molecular beam epitaxy

    SciTech Connect

    Yu, Fengmei; Ren, Lizhu; Meng, Meng; Wang, Yunjia; Yang, Mei; Wu, Shuxiang; Li, Shuwei

    2014-04-07

    Manganese nitrides thin films on MgO (100) substrates with and without Cu-doping have been fabricated by plasma assisted molecular beam epitaxy. Antiperovskite compounds Mn{sub 3.6}Cu{sub 0.4}N have been grown in the case of Cu-doping, and the pure Mn{sub 3}N{sub 2} single crystal has been obtained without Cu-doping. The Mn{sub 3.6}Cu{sub 0.4}N exhibits ferrimagnetism, and the magnetization of Mn{sub 3.6}Cu{sub 0.4}N increases upon the temperature decreasing from 300 K to 5 K, similar to Mn{sub 4}N. The exchange bias (EB) effects emerge in the Mn{sub 3.6}Cu{sub 0.4}N films. The EB behavior is originated from the interfaces between ferrimagnetic Mn{sub 3.6}Cu{sub 0.4}N and antiferromagnetic metal Mn, which is verified to be formed by the data of x-ray photoelectron spectroscopy. The present results not only provide a strategy for producing functional antiperovskite manganese nitrides, but also shed promising light on fabricating the exchange bias part of spintronic devices.

  11. Molecular beam epitaxial growth of Bi{sub 2}Se{sub 3} nanowires and nanoflakes

    SciTech Connect

    Knebl, G. M. Gessler, J. R.; Kamp, M.; Höfling, S.

    2014-09-29

    Topological Insulators are in focus of immense research efforts and rapid scientific progress is obtained in that field. Bi{sub 2}Se{sub 3} has proven to be a topological insulator material that provides a large band gap and a band structure with a single Dirac cone at the Γ-point. This makes Bi{sub 2}Se{sub 3} one of the most promising three dimensional topological insulator materials. While Bi{sub 2}Se{sub 3} nanowires and nanoflakes so far were fabricated with different methods and for different purposes, we here present the first Bi{sub 2}Se{sub 3} nanowires as well as nanoflakes grown by molecular beam epitaxy. The nanostructures were nucleated on pretreated, silicon (100) wafers. Altering the growth conditions nanoflakes could be fabricated instead of nanowires; both with high crystalline quality, confirmed by scanning electron microscopy as well as transmission electron microscopy. These nanostructures have promise for spintronic devices and Majorana fermion observation in contact to superconductor materials.

  12. InAlN/GaN Bragg reflectors grown by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Gacevic, Z.; Fernandez-Garrido, S.; Calleja, E.; Estrade, S.

    2010-12-01

    We report on molecular beam epitaxy growth and characterization of ten-period lattice-matched InAlN/GaN distributed Bragg reflectors (DBRs), with peak reflectivity centered around 400 nm. Thanks to the well tuned ternary alloy composition, crack-free surfaces have been obtained, as confirmed by both optical and transmission electron microscopy (TEM). Their good periodicity and well-defined interfaces have been confirmed by both x-ray diffraction and TEM measurements. Peak reflectivity values as high as 60% with stop bands of 30 nm have been demonstrated. Optical measurements revealed that discrepancy between the obtained (60%) and the theoretically expected ({approx}75%) reflectivity is a consequence of significant residual absorption ({approx}35%). TEM measurements revealed the coexistence of zinc-blende and wurtzite phases, as well as planar defects, mainly in GaN. These defects are suggested as the potential source of the undesired absorption and/or scattering effects that lowered the DBRs' peak reflectivity.

  13. Structural and optical properties of dilute InAsN grown by molecular beam epitaxy

    SciTech Connect

    Ibanez, J.; Oliva, R.; De la Mare, M.; Zhuang, Q.; Godenir, A.; Krier, A.; Schmidbauer, M.; Hernandez, S.; Pellegrino, P.; Scurr, D. J.; Cusco, R.; Artus, L.; Shafi, M.; Mari, R. H.; Henini, M.

    2010-11-15

    We perform a structural and optical characterization of InAs{sub 1-x}N{sub x} epilayers grown by molecular beam epitaxy on InAs substrates (x < or approx. 2.2%). High-resolution x-ray diffraction (HRXRD) is used to obtain information about the crystal quality and the strain state of the samples and to determine the N content of the films. The composition of two of the samples investigated is also obtained with time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measurements. The combined analysis of the HRXRD and ToF-SIMS data suggests that the lattice parameter of InAsN might significantly deviate from Vegard's law. Raman scattering and far-infrared reflectivity measurements have been carried out to investigate the incorporation of N into the InAsN alloy. N-related local vibrational modes are detected in the samples with higher N content. The origin of the observed features is discussed. We study the compositional dependence of the room-temperature band gap energy of the InAsN alloy. For this purpose, photoluminescence and optical absorption measurements are presented. The results are analyzed in terms of the band-anticrossing (BAC) model. We find that the room-temperature coupling parameter for InAsN within the BAC model is C{sub NM}=2.0{+-}0.1 eV.

  14. Magneto-Transport Studies of Molecular Beam Epitaxial Grown Osmium Silicides

    NASA Astrophysics Data System (ADS)

    Cottier, Ryan; Zhao, Wei; Amir, Fatima; Hossain, Khalid; Anibou, Noureddine; Donner, Wolfgang; Golding, Terry

    2006-03-01

    Semiconducting transition metal silicides present a possible solution to on-chip integration of optical and electronic Si-based circuitry. Two phases of osmium silicide (OsSi2 and Os2Si3) are predicted to have promising optical characteristics but require additional development to fully determine their feasibility for high-quality devices. This study has been motivated by reports that OsSi2 has a bandgap between 1.4--1.8eV [1, 2] and Os2Si3 may have a direct bandgap of 0.95 eV [3] or 2.3 eV [1]. In this paper we will present temperature dependent (20 < T < 300 K) magneto Hall measurements of molecular beam epitaxial grown osmium silicide thin films. Os and Si were coevaporated onto Si(100) substrates at varying growth rates and temperatures. XRD was performed in order to identify the silicide phases present. We will discuss our results in relation to the known phase diagrams and our growth parameters. [1] L. Schellenberg et al., J. Less-Common Met. 144, 341 (1988). [2] K. Mason and G. Müller-Vogt, J. Appl. Phys. 63, 34 (1983). [3] A. B. Filonov et al., Phys. Rev. B 60(24), 16494 (1999).

  15. Thin film growth of CaFe2As2 by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hatano, T.; Kawaguchi, T.; Fujimoto, R.; Nakamura, I.; Mori, Y.; Harada, S.; Ujihara, T.; Ikuta, H.

    2016-01-01

    Film growth of CaFe2As2 was realized by molecular beam epitaxy on six different substrates that have a wide variation in the lattice mismatch to the target compound. By carefully adjusting the Ca-to-Fe flux ratio, we obtained single-phase thin films for most of the substrates. Interestingly, an expansion of the CaFe2As2 lattice to the out-of-plane direction was observed for all films, even when an opposite strain was expected. A detailed microstructure observation of the thin film grown on MgO by transmission electron microscope revealed that it consists of cube-on-cube and 45°-rotated domains. The latter domains were compressively strained in plane, which caused a stretching along the c-axis direction. Because the domains were well connected across the boundary with no appreciable discontinuity, we think that the out-of-plane expansion in the 45°-rotated domains exerted a tensile stress on the other domains, resulting in the unexpectedly large c-axis lattice parameter, despite the apparently opposite lattice mismatch.

  16. Cu-doped AlN: A possible spinaligner at room-temperature grown by molecular beam epitaxy?

    SciTech Connect

    Ganz, P. R.; Schaadt, D. M.

    2011-12-23

    Cu-doped AlN was prepared by plasma assisted molecular beam epitaxy on C-plane sapphire substrates. The growth conditions were investigated for different Cu to Al flux ratios from 1.0% to 4.0%. The formation of Cu-Al alloys on the surface was observed for all doping level. In contrast to Cu-doped GaN, all samples showed diamagnetic behavior determined by SQUID measurements.

  17. Mass transport and alloying during InN growth on GaN by molecular-beam epitaxy

    SciTech Connect

    Liu, Y.; Xie, M.H.; Wu, H.S.; Tong, S.Y.

    2006-05-29

    During Stranski-Krastanov (SK) growth of InN on GaN by molecular-beam epitaxy, a mass transport is noted from the two-dimensional wetting layer and/or the surface excess metal adlayers to the SK islands when the excess nitrogen flux is used for deposition. The extent of mass transport depends on the material coverage. For growth under the excess indium flux condition, no such mass transport is observed.

  18. Apparatus for producing ultraclean bicrystals by the molecular beam epitaxy growth and ultrahigh vacuum bonding of thin films

    SciTech Connect

    Amiri-Hezaveh, A.; Balluffi, R.W. )

    1993-10-01

    An apparatus has been designed and constructed which is capable of growing single-crystal thin films and then bonding them together face-to-face to produce bicrystals under ultrahigh vacuum (UHV) conditions. The films are grown in molecular beam epitaxy (MBE) system capable of growing well-characterized single-crystal thin films of metals, semiconductors, and high [ital T][sub [ital c

  19. Effect of substrate growth temperatures on H diffusion in hydrogenated Si/Si homoepitaxial structures grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Shao, Lin; Lee, J. K.; Wang, Y. Q.; Nastasi, M.; Thompson, Phillip E.; David Theodore, N.; Alford, T. L.; Mayer, J. W.; Chen, Peng; Lau, S. S.

    2006-06-01

    We have investigated hydrogen diffusion in hydrogenated <100> Si/Si homoepitaxial structures, which were grown by molecular beam epitaxy at various temperatures. The substrate growth temperature can significantly affect the H diffusion behavior, with higher growth temperatures resulting in deeper H diffusion. For the Si/Si structure grown at the highest temperature of 800 °C, H trapping occurs at the epitaxial Si/Si substrate interface, which results in the formation of (100) oriented microcracks at the interface. The mechanism of H trapping and the potential application of these findings for the development of a method of transferring ultrathin Si layers are discussed.

  20. Transition between wurtzite and zinc-blende GaN: An effect of deposition condition of molecular-beam epitaxy

    SciTech Connect

    Shi, B. M.; Xie, M. H.; Wu, H. S.; Wang, N.; Tong, S. Y.

    2006-10-09

    GaN exists in both wurtzite and zinc-blende phases and the growths of the two on its (0001) or (111) surfaces are achieved by choosing proper deposition conditions of molecular-beam epitaxy (MBE). At low substrate temperatures but high gallium fluxes, metastable zinc-blende GaN films are obtained, whereas at high temperatures and/or using high nitrogen fluxes, equilibrium wurtzite phase GaN epilayers resulted. This dependence of crystal structure on substrate temperature and source flux is not affected by deposition rate. Rather, the initial stage nucleation kinetics plays a primary role in determining the crystallographic structures of epitaxial GaN by MBE.

  1. X-ray diffractometry of AlN/c-sapphire templates obtained by plasma-activated molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ratnikov, V. V.; Nechaev, D. V.; Jmerik, V. N.; Ivanov, S. V.

    2016-04-01

    The structure of AlN/c-sapphire templates obtained by plasma-activated molecular beam epitaxy (PAMBE) has been studied by X-ray diffractometry techniques. The results show the advantages of using coarse-grained AlN nucleation layers prepared by high-temperature (780°C) adatom-migration-enhanced epitaxy. Using 3.5-nm-thick GaN inserts (obtained by three-dimensional growth under N-rich conditions), it is possible to obtain templates with insignificant residual macrostresses and relatively narrow widths (FWHM) of 0002 and 10bar 15 diffraction reflections.

  2. Optical control of growth of AlxGa1 - xAs by organometallic molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Aspnes, D. E.; Quinn, W. E.; Gregory, S.

    1990-12-01

    Using spectroellipsometry, we obtain information on the near-surface composition x of epitaxial AlxGa1-xAs layers during crystal growth by organometallic molecular beam epitaxy and use this information to regulate the flow of triethylaluminum to the growth surface. The resulting closed-loop control system maintains the imaginary part of the dielectric response of thick AlxGa1-xAs films constant to an equivalent compositional precision better than ±0.001 over extended periods of time.

  3. Epitaxial growth of HgCdTe 1.55-um avalanche photodiodes by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    de Lyon, Terence J.; Baumgratz, B.; Chapman, G. R.; Gordon, E.; Hunter, Andrew T.; Jack, Michael D.; Jensen, John E.; Johnson, W.; Johs, Blaine D.; Kosai, K.; Larsen, W.; Olson, G. L.; Sen, M.; Walker, B.

    1999-04-01

    Separate absorption and multiplication avalanche photodiode (SAM-APD) device structures, operating in the 1.1 - 1.6 micrometer spectral range, have been fabricated in the HgCdTe material system by molecular-beam epitaxy. These HgCdTe device structures, which offer an alternative technology to existing III-V APD detectors, were grown on CdZnTe(211)B substrates using CdTe, Te, and Hg sources with in situ In and As doping. The alloy composition of the HgCdTe layers was adjusted to achieve both efficient absorption of IR radiation in the 1.1 - 1.6 micrometer spectral range and low excess-noise avalanche multiplication. To achieve resonant enhancement of hole impact ionization from the split-off valence band, the Hg(subscript 1-x)Cd(subscript x)Te alloy composition in the gain region of the device, x equals 0.73, was chosen to achieve equality between the bandgap energy and spin-orbit splitting. The appropriate value of this alloy composition was determined from analysis of the 300 K bandgap and spin-orbit splitting energies of a set of calibration layers, using a combination of IR transmission and spectroscopic ellipsometry measurements. MBE-grown APD epitaxial wafers were processed into passivated mesa-type discrete device structures and diode mini-arrays using conventional HgCdTe process technology. Device spectral response, dark current density, and avalanche gain measurements were performed on discrete diodes and diode mini- arrays on the processed wafers. Avalanche gains in the range of 30 - 40 at reverse bias of 85 - 90 V and array-median dark current density below 2 X 10(superscript -4) A/cm(superscript 2) at 40 V reverse bias have been demonstrated.

  4. Electrical properties of scandium nitride epitaxial films grown on (100) magnesium oxide substrates by molecular beam epitaxy

    SciTech Connect

    Ohgaki, Takeshi; Watanabe, Ken; Adachi, Yutaka; Sakaguchi, Isao; Hishita, Shunichi; Ohashi, Naoki; Haneda, Hajime

    2013-09-07

    Scandium nitride (ScN) films were grown on (100) MgO single crystals by a molecular beam epitaxy method. The effects of growth conditions, including [Sc]/[N] ratio, growth temperature, and nitrogen radical state, on the electrical properties of the ScN films were studied. The ScN films comprised many small columnar grains. Hall coefficient measurements confirmed that the ScN films were highly degenerate n-type semiconductors and that the carrier concentration of the ScN films was sensitive to the growth temperature and the nitrogen radical states during the film growth. The carrier concentrations of the ScN films ranged from 10{sup 19}–10{sup 21} cm{sup −3} while the Hall mobilities ranged from 50–130 cm{sup 2}·V{sup −1}·s{sup −1} for undoped films. The temperature-dependent Hall coefficient measurements showed that the carrier concentration is nearly independent of temperature, indicating that the change in resistivity with temperature is explained by a change in the Hall mobility. The temperature-dependence of the Hall mobility was strongly affected by the growth conditions.

  5. Growth of amorphous and epitaxial alternative gate dielectrics on silicon by molecular-beam epitaxy and their characterization

    NASA Astrophysics Data System (ADS)

    Edge, Lisa Friedman

    The continued scaling of SiO2 in metal-oxide-semiconductor field-effect transistors (MOSFETs) is approaching its fundamental limit and in the next few years will have to be replaced with an alternative gate dielectric if Moore's law is to continue. In a search for suitable alternative dielectrics, I have investigated the growth of amorphous and epitaxial LaAlO3, LaScO3, La2O3, and Sc2O3 thin films by molecular-beam epitaxy (MBE) on silicon. A major challenge in the growth of alternative gate dielectrics on silicon is the formation of SiO2 at the interface between silicon and the high- K gate dielectric. In this dissertation, I have established deposition conditions that yielded abrupt interfaces (< 0.1 A of SiO2) between amorphous LaAlO3 or LaScO3 thin films and silicon. These results demonstrate the thinnest gate dielectrics ever produced that are free of interfacial SiO2, despite exposure to air. The thermal stability between silicon and the abrupt amorphous LaAlO 3 and LaScO3 thin films was established for the first time. By 900°C, crystallization is clearly observed, but the LaAlO3/Si interface remains sharp with no detectable interfacial SiO2. The thermal stability results establish key processing windows for the integration of amorphous LaAlO3 and LaScO3 thin films into silicon-based MOSFETs. In this work, the following critical physical properties of amorphous LaAlO3 thin films deposited on silicon have been determined: dielectric constant (K = 16 +/- 2), bandgap (Eg = 6.2 +/- 0.1 eV), and band alignment (DeltaEc = 1.8 +/- 0.2 for electrons and DeltaEv = 3.2 +/- 0.1 eV for holes). The following critical physical properties of amorphous LaScO3 thin films deposited on silicon have been determined: bandgap (Eg = 5.7 +/- 0.1 eV) and band alignment (DeltaEc = 2.0 +/- 0.1 eV for electrons and DeltaEv = 3.1 +/- 0.1 eV for holes). In this dissertation, epitaxial (0001) La2O3 thin films with the hexagonal crystal structure were grown on (111) Si for the first time

  6. Ultrafast structural dynamics of LaVO3 thin films grown by hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Brahlek, Matthew; Lapano, Jason; Stoica, Vladimir; Zhang, Lei; Zhang, Hai-Tian; Akamatsu, Hirofumi; Eaton, Craig; Gopalan, Venkatraman; Freeland, John; Wen, Haidan; Engel-Herbert, Roman

    LaVO3, with a partially full d-shell is expected to be metallic, but due to electron-electron interactions a gap emerges and the ground state is a Mott insulator. Such effects are a strong function of the bonding geometry, and particularly the V-O-V bond angle. Controlling these structural effects on the ultrafast time scale can lead to control over the underlying electronic ground state. Here we report the ultrafast structural dynamics of 25 and 50 nm thick LaVO3 thin films grown by the hybrid molecular beam epitaxy technique on SrTiO3 when excited across the bandgap by 800 nm light. Using time-resolved x-ray diffraction on the 100 ps time scale at Sector 7 of the Advanced Photon Source, we directly measured the structural changes with atomic accuracy by monitoring integer Bragg diffraction peaks and find a large out-of-plane strain of 0.18% upon optical excitation; the recovery time is ~1 ns for the 25 nm film and ~2 ns for the 50 nm film, consistent with the thermal transport from the film to the substrate. Further, we will discuss the response of the oxygen octahedral rotation patterns indicated by changes of the half-order diffraction peaks. Understanding such ultrafast structural deformation is important for optimizing optical excitations to create new metastable phases starting from a Mott insulator. This work was supported by the Department of Energy under Grant DE-SC0012375, and DE-AC02-06CH11357.

  7. Study of optical properties of GaAsN layers prepared by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Pulzara-Mora, A.; Cruz-Hernández, E.; Rojas-Ramirez, J.; Contreras-Guerrero, R.; Meléndez-Lira, M.; Falcony-Guajardo, C.; Aguilar-Frutis, M. A.; López-López, M.

    2007-04-01

    We have grown GaAsN layers (with nitrogen concentration between 1.2% and 3.2%) on GaAs(1 0 0) substrates by molecular beam epitaxy (MBE) using a radio frequency (RF) plasma nitrogen source, and solid sources for Ga and As. The growth temperature was varied from 420 to 600 °C, and the GaAsN growth mode was in situ monitored by reflection high-energy electron diffraction (RHEED). The optical properties of the layers were studied by photoreflectance spectroscopy (PR) and phase modulated ellipsometry (PME). For the growth temperature of 420 °C the films grew in a three-dimensional (3D) mode as indicated by the appearance of transmission spots in the RHEED patterns. In contrast, GaAsN layers grown at higher temperatures presented a two-dimensional (2D) growth mode. These GaAsN layers are pseudomorphic according to high-resolution X-ray diffraction (HRXRD). The PR spectra of all samples exhibited Franz-Keldysh oscillations (FKO) above of the GaAs band gap energy. From these oscillations we obtained the built-in internal electric field intensity ( Fint) at the GaAsN/GaAs interface. In the low-energy region of the PR spectra we observed the transitions associated to fundamental band gap of the GaAsN layers. The variation of the GaAsN fundamental band gap obtained by PR as a function of the N content was explained according the band anti-crossing model (BAC). On the other hand, the E1 and E1+Δ E1 critical points were obtained from the analysis of spectra of the imaginary part of the dielectric function obtained by PME. We observed a shift of these critical points to higher energies with the increase of N content, which was explained by a combination of strain and alloying effects.

  8. Molecular-beam epitaxy and characteristics of GaNyAs1-x-yBix

    NASA Astrophysics Data System (ADS)

    Huang, Wei; Oe, Kunishige; Feng, Gan; Yoshimoto, Masahiro

    2005-09-01

    GaNyAs1-x-yBix alloys were grown by molecular-beam epitaxy using solid Ga, Bi, and As sources and nitrogen radicals generated from nitrogen gas in rf plasma. Changing the growth temperature is found to be a convenient method for controlling the GaBi molar fraction in the alloy reproducibly. The photoluminescence (PL) spectra show that the PL peak energy of GaNyAs1-x-yBix alloy decreased with increasing GaBi and GaN molar fractions. The redshift coefficients of ~62 meV/%Bi and ~130 meV/%N at the PL peak energy of GaNyAs1-x-yBix were observed at room temperature. The temperature dependence of the PL peak energy in the temperature range of 150-300 K is much smaller than the temperature dependence of the band gap of InGaAsP. The temperature coefficients of GaAs1-xBix and GaNyAs1-x-yBix band gaps are governed by the GaBi molar fraction and they decrease with increasing GaBi molar fraction. GaNyAs1-x-yBix alloys with different PL peak energies and lattice matched to GaAs substrates were obtained. The photoluminescence peak energy was located at a predicted wavelength for the sample lattice matched to GaAs which was found to have the structure of Ga(N0.33Bi0.67)zAs1-z.

  9. High Active Nitrogen Flux Growth of (Indium) Gallium Nitride by Plasma Assisted Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    McSkimming, Brian Matthew

    Plasma-assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) has evolved over the past two decades due to progress in growth science and in the active nitrogen plasma source hardware. The transition from electron cyclotron resonance (ECR) microwave plasma sources to radio frequency (RF) plasma sources has enabled higher growth rates, reduced ion damage and improved operation at higher growth chamber pressures. Even with further improvements in RF plasma sources, PAMBE has remained primarily a research tool partially due to limitations in material growth rates. This dissertation presents results based upon two modifications of a commercially available nitrogen plasma source. These modifications have resulted in record active nitrogen fluxes, and therefore record growth rates of more than 7.6 mum/h. For optimized growth conditions in the standard metal-rich growth regime, the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 mumx3 mum) on the order of 1 nm. Secondary ion mass spectroscopy (SIMS) impurity analysis demonstrates unintentional oxygen incorporation of ˜1x1016, comparable to the metal organic chemical vapor deposition (MOCVD) grown template layer. Additionally, a revised universal growth diagram is proposed allowing the rapid determination of the metal flux needed to grow in a specific growth regime for any and all active nitrogen fluxes available. High temperature nitrogen rich PAMBE growth of GaN has been previously demonstrated as a viable alternative to the challenges presented in maintaining the Ga bilayer required by metal rich growth of GaN. This dissertation also present results demonstrating PAMBE growth of GaN at a substrate temperature more than 150 °C greater than our standard Ga rich GaN growth regime and ˜100 °C greater than any previously reported PAMBE growth of GaN. Finally, a revised growth diagram is proposed highlighting a large growth window available at high temperatures.

  10. Minority carrier lifetime in iodine-doped molecular beam epitaxy-grown HgCdTe

    SciTech Connect

    Madni, I.; Umana-Membreno, G. A.; Lei, W.; Gu, R.; Antoszewski, J.; Faraone, L.

    2015-11-02

    The minority carrier lifetime in molecular beam epitaxy grown layers of iodine-doped Hg{sub 1−x}Cd{sub x}Te (x ∼ 0.3) on CdZnTe substrates has been studied. The samples demonstrated extrinsic donor behavior for carrier concentrations in the range from 2 × 10{sup 16} cm{sup −3} to 6 × 10{sup 17} cm{sup −3} without any post-growth annealing. At a temperature of 77 K, the electron mobility was found to vary from 10{sup 4} cm{sup 2}/V s to 7 × 10{sup 3} cm{sup 2}/V s and minority carrier lifetime from 1.6 μs to 790 ns, respectively, as the carrier concentration was increased from 2 × 10{sup 16} cm{sup −3} to 6 × 10{sup 17} cm{sup −3}. The diffusion of iodine is much lower than that of indium and hence a better alternative in heterostructures such as nBn devices. The influence of carrier concentration and temperature on the minority carrier lifetime was studied in order to characterize the carrier recombination mechanisms. Measured lifetimes were also analyzed and compared with the theoretical models of the various recombination processes occurring in these materials, indicating that Auger-1 recombination was predominant at higher doping levels. An increase in deep-level generation-recombination centers was observed with increasing doping level, which suggests that the increase in deep-level trap density is associated with the incorporation of higher concentrations of iodine into the HgCdTe.

  11. Atom probe tomography characterisation of a laser diode structure grown by molecular beam epitaxy

    SciTech Connect

    Bennett, Samantha E.; Humphreys, Colin J.; Oliver, Rachel A.; Smeeton, Tim M.; Hooper, Stewart E.; Heffernan, Jonathan; Saxey, David W.; Smith, George D. W.

    2012-03-01

    Atom probe tomography (APT) has been used to achieve three-dimensional characterization of a III-nitride laser diode (LD) structure grown by molecular beam epitaxy (MBE). Four APT data sets have been obtained, with fields of view up to 400 nm in depth and 120 nm in diameter. These data sets contain material from the InGaN quantum well (QW) active region, as well as the surrounding p- and n-doped waveguide and cladding layers, enabling comprehensive study of the structure and composition of the LD structure. Two regions of the same sample, with different average indium contents (18% and 16%) in the QW region, were studied. The APT data are shown to provide easy access to the p-type dopant levels, and the composition of a thin AlGaN barrier layer. Next, the distribution of indium within the InGaN QW was analyzed, to assess any possible inhomogeneity of the distribution of indium (''indium clustering''). No evidence for a statistically significant deviation from a random distribution was found, indicating that these MBE-grown InGaN QWs do not require indium clusters for carrier localization. However, the APT data show steps in the QW interfaces, leading to well-width fluctuations, which may act to localize carriers. Additionally, the unexpected presence of a small amount (x = 0.005) of indium in a layer grown intentionally as GaN was revealed. Finally, the same statistical method applied to the QW was used to show that the indium distribution within a thick InGaN waveguide layer in the n-doped region did not show any deviation from randomness.

  12. Growth mechanism of CuZnInSe2 thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tseng, Ya Hsin; Yang, Chu Shou; Wu, Chia Hsing; Chiu, Jai Wei; Yang, Min De; Wu, Chih-Hung

    2013-09-01

    CuZnInSe2 (CZIS) has potential application in solar cell for absorption layer, and give an advantage to change the band gap from CuInSe2 (1.02 eV) to ZnSe (2.67 eV). Using molecular beam epitaxy technology, the CZIS thin films were grown via CuInSe (CIS) and ZnSe base. In the case of CIS, thin films were grown on Mo-coated soda lime glass with various zinc flux. CIS was transformed into chalcopyrite and sphalerite coexisting CZIS easily but it is difficult to transform into the pure sphalerite CZIS. Zn/(Zn+In+Cu) ratio has limited to approximate 36 at% and the excess-Zn played a catalyst role. In the case of ZnSe base, which was grown on GaAs (001), various In and Cu flux defined as the TIn series and TCu series, respectively. There are four types of compound in the TIn series and TCu series, including ZnSe, InxSey, ZnIn2Se4 (ZIS) and CZIS. In the TIn series under the lowest In and Cu flux, selenium (Se) were randomly combined with cations to form the CZIS. When TIn is increased in this moment, the CZIS was transformed into ZIS. In the TCu series, CZIS demonstrated via In-rich ZIS (Zn(In, Cu)Se) and InxSey base ((Zn, Cu)InSe). It is chalcopyrite and sphalerite coexisting structure in the medium TCu region. In the high TCu region, it is transformed into the Zn-poor and Cu-rich CZIS.

  13. Molecular beam epitaxy of free-standing wurtzite AlxGa1-xN layers

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.; Staddon, C. R.; Martin, R. W.; Kent, A. J.; Foxon, C. T.

    2015-09-01

    Recent developments with group III nitrides present AlxGa1-xN based LEDs as realistic devices for new alternative deep ultra-violet light sources. Because there is a significant difference in the lattice parameters of GaN and AlN, AlxGa1-xN substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free-standing wurtzite AlxGa1-xN bulk crystals by plasma-assisted molecular beam epitaxy (PA-MBE). Thick wurtzite AlxGa1-xN films were grown by PA-MBE on 2-in. GaAs (111)B substrates and were removed from the GaAs substrate after growth to provide free standing AlxGa1-xN samples. X-ray microanalysis measurements confirm that the AlN fraction is uniform across the wafer and mass spectroscopy measurements show that the composition is also uniform in depth. We have demonstrated that free-standing wurtzite AlxGa1-xN wafers can be achieved by PA-MBE for a wide range of AlN fractions. In order to develop a commercially viable process for the growth of wurtzite AlxGa1-xN substrates, we have used a novel Riber plasma source and have demonstrated growth rates of GaN up to 1.8 μm/h on 2-in. diameter GaAs and sapphire wafers.

  14. Lead strontium telluride and lead barium telluride grown by molecular-beam epitaxy

    SciTech Connect

    Partin, D.L.; Thrush, C.M.; Clemens, B.M.

    1987-05-01

    Long wavelength diode lasers operating in the 3--10-..mu..m wavelength range are of interest as optical sources for future fiber optics communications and sensor systems. PbEuSeTe large optical cavity single quantum well diode lasers have so far attained the highest operating temperatures (174 K cw, 280 K pulsed) in this wavelength range. Two alternative materials systems PbSrTe and PbBaTe have now been grown for the first time by molecular-beam epitaxy. The choice of these ternaries was motivated by the fact that SrTe and BaTe have the same face-centered-cubic crystal structure as PbTe and roughly comparable lattice constants, but much larger energy band gaps. In the Pb/sub 1-//sub x/Sr/sub x/Te system, x-ray diffraction studies show clear evidence of phase segregation for x>0.15. The carrier mobilities decrease monotonically with strontium concentration in the single phase region, which suggests that disorder-related scattering is dominant. The energy band gap increases approximately as dEg/dx = 3.2 eV for small x, and the index of refraction decreases monotonically with increasing x. In the Pb/sub 1-//sub x/Sr/sub x/Te system, a combination of x-ray diffraction, energy band gap and other data clearly demonstrate that the solubility of BaTe in PbTe is limited to about 4%, possibly because of the relatively large difference in lattice constants between PbTe (6.460 A) and BaTe (7.001 A). These results imply that PbSrSeTe grown lattice matched to PbTe is a promising material system for long wavelength diode lasers and light emitting diodes.

  15. Lattice mismatched InGaAs on silicon photodetectors grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Papanicolaou, N. A.; Anderson, G. W.; Iliadis, A. A.; Christou, A.

    1993-02-01

    In0.5Ga0.5As on silicon photodetectors, including three types of interdigitated-finger devices as well as linear photoconductors, were fabricated and measured. The InGaAs/Si structure was grown by molecular beam epitaxy and utilized a 100 Å GaAs intervening nucleation layer between the silicon substrate and the InGaAs layers, step-graded InxGa1-xAs layers, and an in-situ grown 40 Å thick GaAs surface layer, which substantially enhanced the metal-semiconductor barrier height (Φb = 0.67 V) for the InGaAs. Schottky diodes fabricated independently of the photodetectors had nearly ideal characteristics with an ideality factor (n) of 1.02 and a reverse breakdown voltage of 40 V. The interdigitated Schottky photodetectors showed dark currents between <3nA and 54 μA at a 3 V bias and initial photoresponse rise times in the range of 600 to 725 ps, comparable to similar InGaAs metal-semiconductor-metal photodetectors grown lattice matched on InP. The photoconductors fabricated in the same material had rise times in the range of 575 to 1300 ps, thus being slightly slower, and had dark currents of 7 to 80 mA. The responsivity of the photoconductors was typically greater than that of the diodes by a factor of five to fifteen. The results show potential for monolithic integration of InGaAs photodetectors on silicon substrates.

  16. LaCrO3 heteroepitaxy on SrTiO3(001) by molecular beam epitaxy

    SciTech Connect

    Qiao, Liang; Droubay, Timothy C.; Bowden, Mark E.; Shutthanandan, V.; Kaspar, Tiffany C.; Chambers, Scott A.

    2011-08-09

    Stoichiometric, epitaxial LaCrO3 films have been grown on TiO2-terminated SrTiO3(001) substrates by molecular beam epitaxy using O2 as the oxidant. Film growth occurred in a layer-by-layer fashion, giving rise to structurally excellent films and surfaces which preserve the step-terrace structure of the substrate. The critical thickness is in excess of 500 Å. Near-surface Cr(III) is highly susceptible to further oxidation to Cr(V), leading to the formation of a disordered phase upon exposure to atomic oxygen. Recovery of the original epitaxial LaCrO3 phase is readily achieved by vacuum annealing.

  17. High-index Cu2O (113) film on faceted MgO (110) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Huo, Wenxing; Shi, Jin'an; Mei, Zengxia; Liu, Lishu; Li, Junqiang; Gu, Lin; Du, Xiaolong; Xue, Qikun

    2015-06-01

    We report the growth of single-oriented Cu2O (113) film on faceted MgO (110) substrate by radio-frequency plasma assisted molecular beam epitaxy. A MgO {100} faceted homoepitaxial layer was introduced beforehand as a template for epitaxy of Cu2O film. The epitaxial relationship is determined to be Cu2O (113)//MgO (110) with a tilt angle of 4.76° and Cu2O [ 1 1 bar 0]//MgO [ 1 1 bar 0] by the combined study of in-situ reflection high-energy electron diffraction and ex-situ X-ray diffraction and transmission electron microscopy. The film demonstrates a good p-type conductivity and excellent optical properties, indicating that this unique approach is potentially applicable for high-index film preparation and device applications.

  18. In silico carbon molecular beam epitaxial growth of graphene on the h-BN substrate: carbon source effect on van der Waals epitaxy.

    PubMed

    Lee, Jonghoon; Varshney, Vikas; Park, Jeongho; Farmer, Barry L; Roy, Ajit K

    2016-05-01

    Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon molecular beam epitaxy (CMBE) techniques using solid carbon sublimation have reported relatively poor quality of the graphene. In this article, the CMBE growth of graphene on the h-BN substrate is numerically studied in order to identify the effect of the carbon source on the quality of the graphene film. The carbon molecular beam generated by the sublimation of solid carbon source materials such as graphite and glassy carbon is mostly composed of atomic carbon, carbon dimers and carbon trimers. Therefore, the graphene film growth becomes a complex process involving various deposition characteristics of a multitude of carbon entities. Based on the study of surface adsorption and film growth characteristics of these three major carbon entities comprising graphite vapour, we report that carbon trimers convey strong traits of vdW epitaxy prone to high quality graphene growth, while atomic carbon deposition is a surface-reaction limited process accompanied by strong chemisorption. The vdW epitaxial behaviour of carbon trimers is found to be substantial enough to nucleate and develop into graphene like planar films within a nanosecond of high flux growth simulation, while reactive atomic carbons tend to impair the structural integrity of the crystalline h-BN substrate upon deposition to form an amorphous interface between the substrate and the growing carbon film. The content of reactive atomic carbons in the molecular beam is suspected to be the primary cause of low quality graphene reported in the literature. A possible optimization of the molecular beam composition towards the synthesis of better quality graphene films is suggested. PMID:27108606

  19. Molecular beam epitaxy and metalorganic chemical vapor deposition growth of epitaxial CdTe on (100) GaAs/Si and (111) GaAs/Si substrates

    NASA Technical Reports Server (NTRS)

    Nouhi, A.; Radhakrishnan, G.; Katz, J.; Koliwad, K.

    1988-01-01

    Epitaxial CdTe has been grown on both (100)GaAs/Si and (111)GaAs/Si substrates. A combination of molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) has been employed for the first time to achieve this growth: the GaAs layers are grown on Si substrates by MBE and the CdTe film is subsequently deposited on GaAs/Si by MOCVD. The grown layers have been characterized by X-ray diffraction, scanning electron microscopy, and photoluminescence.

  20. High active nitrogen flux growth of GaN by plasma assisted molecular beam epitaxy

    SciTech Connect

    McSkimming, Brian M. Speck, James S.; Chaix, Catherine

    2015-09-15

    In the present study, the authors report on a modified Riber radio frequency (RF) nitrogen plasma source that provides active nitrogen fluxes more than 30 times higher than those commonly used for plasma assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N{sub 2} gas flow rates between 5 and 25 sccm while varying the plasma source's RF forward power from 200 to 600 W. The highest growth rate, and therefore the highest active nitrogen flux, achieved was ∼7.6 μm/h. For optimized growth conditions, the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 × 3 μm) on the order of 1 nm. Secondary ion mass spectroscopy impurity analysis demonstrates oxygen and hydrogen incorporation of 1 × 10{sup 16} and ∼5 × 10{sup 17}, respectively. In addition, the authors have achieved PAMBE growth of GaN at a substrate temperature more than 150 °C greater than our standard Ga rich GaN growth regime and ∼100 °C greater than any previously reported PAMBE growth of GaN. This growth temperature corresponds to GaN decomposition in vacuum of more than 20 nm/min; a regime previously unattainable with conventional nitrogen plasma sources. Arrhenius analysis of the decomposition rate shows that samples with a flux ratio below stoichiometry have an activation energy greater than decomposition of GaN in vacuum while samples grown at or above stoichiometry have decreased activation energy. The activation energy of decomposition for GaN in vacuum was previously determined to be ∼3.1 eV. For a Ga/N flux ratio of ∼1.5, this activation energy was found to be ∼2.8 eV, while for a Ga/N flux ratio of ∼0.5, it was found to be ∼7.9 eV.

  1. Visible and Near-Infrared Quantum Well Laser Diodes Grown by Solid Source Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Varriano, John A.

    1993-01-01

    The growth of near infrared quantum well (QW) laser diodes in the AlGaAs material system and visible QW laser diodes in the AlGaInP material system by solid source molecular beam epitaxy (MBE) is investigated. Procedures for fabrication, measurement, and analysis are developed on the more easily grown GaAs QW lasers. Several studies are performed on the GaAs QW lasers. Doping of the laser core with a p-i-n profile improves laser performance. Low growth temperatures result in lasers with high threshold current densities due to the formation of traps caused by interface states and a deep level near the QW interface region. High growth temperatures also cause increases in threshold currents due to the effects of Ga desorption. Threshold current is not observed to depend strongly on the width of the laser waveguide core. Fabrication of lasers with tilted facets is facilitated by using misoriented substrates. The lasers exhibit higher threshold current densities due to decreased facet reflectivity. The benefits of compressively strained active layers are demonstrated in a GaInAs QW laser. Growth of visible AlGaInP lasers lattice matched to GaAs substrates is performed using a novel valved cracker cell for solid phosphorus. The cell avoids the expense and possible toxicity associated with the use of phosphine common in other growth techniques. It also alleviates the problems encountered when using solid phosphorus in a conventional effusion cell. High quality AlGaInP material is grown using the cell. The quality of the AlInP and GaInP ternaries is comparable to or better than that grown by other techniques based on photoluminescence and Raman spectroscopy measurements. The material is found to be highly disordered. Adequate doping levels for laser operation are obtained in the AlGaInP quaternary. Growth stops at the QW/barrier interfaces are proven to be detrimental to laser performance. Appropriate choices of barrier Al composition and QW Ga composition allow for the

  2. Hetero- and homo-epitaxial growth of III-nitride based junctions and devices by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sampath, Anand Venktesh

    2002-01-01

    The family of III-Nitrides semiconductors (InN, GaN, AlN and their alloys) is an area of intense interest for the development of power electronic, optoelectronic and mico-electromechanical systems (MEMS) based devices due to the unique properties of these materials. Presently, light emitting diodes (LEDs) and lasers emitting in the blue part or the electromagnetic spectrum have become available based on these wide band gap materials. Further interest exists in the development of p-n and Schottky based junctions for application as solar-blind ultraviolet (UV) detector arrays and power rectifiers. Solar blind UV detectors require the growth of high quality AlxGa1-x N alloys containing up to 60% AlN mole fraction. Both devices require the development of high-quality p-type doped material. This dissertation addresses the growth of GaN and AlxGa1-xN alloys by molecular beam epitaxy (MBE) as well as the processing of these materials for the fabrication of optoelectronic and power devices. The growth of III-Nitrides materials by MBE requires the development of an appropriate source of active nitrogen due to the large binding energy of molecular nitrogen (9.5 eV). Two methods for producing active N are the cracking of molecular nitrogen using a plasma source and the catalytic decomposition of ammonia on a heated substrate. The first method is explored using a compact electron cyclotron resonance (ECR) plasma source, and it is found that smooth films are grown by this technique under group-III rich conditions. The second method is explored using ammonia gas that enters the MBE system through an ammonia injector. In contrast to the plasma-assisted technique, smooth films can be grown under N-rich conditions. Due to the lack of native substrates for these materials, these films are generally deposited heteroepitaxially on c-plane sapphire or (0001) Si-face 6H-silicon carbide (SiC) substrates. The polarity of films grown on the former was observed to be dependent on the

  3. The thickness-dependent dynamic magnetic property of Co2FeAl films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Qiao, Shuang; Nie, Shuaihua; Zhao, Jianhua; Zhang, Xinhui

    2014-10-01

    Co2FeAl films with different thickness were prepared at different temperature by molecular beam epitaxy. Their dynamic magnetic property was studied by the time-resolved magneto-optical Kerr effect measurements. It is observed that the intrinsic damping factor of Co2FeAl for [100] orientation is not related to the film's thickness and magnetic anisotropy as well as temperature at high-field regime, but increases with structural disorder of Co2FeAl. The dominant contribution from the inhomogeneous magnetic anisotropy is revealed to be responsible for the observed extremely nonlinear and drastic field-dependent damping factors at low-field regime.

  4. (GaMn)As: GaAs-based III?V diluted magnetic semiconductors grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hayashi, T.; Tanaka, M.; Nishinaga, T.; Shimada, H.; Tsuchiya, H.; Otuka, Y.

    1997-05-01

    We have grown novel III-V diluted magnetic semiconductors, (Ga 1 - xMn x)As, on GaAs substrates by low-temperature molecular beam epitaxy using strong nonequilibrium growth conditions. When the Mn concentration x is relatively low (≲0.08), homogeneous alloy semiconductors, GaMnAs, are grown with zincblende structure and slightly larger lattice constants than that of GaAs, whereas inhomogeneous structures with zincblende GaMnAs (or GaAs) plus hexagonal MnAs are formed when x is relatively high. Magnetization measurements indicate that the homogeneous GaMnAs films have ferromagnetic ordering at low temperature.

  5. Improving stability of photoluminescence of ZnSe thin films grown by molecular beam epitaxy by incorporating Cl dopant

    NASA Astrophysics Data System (ADS)

    Wang, J. S.; Chen, W. J.; Yang, C. S.; Tsai, Y. H.; Wang, H. H.; Chen, R. H.; Shen, J. L.; Tsai, C. D.

    2011-01-01

    This investigation studies the effect of chlorine (Cl) dopant in ZnSe thin films that were grown by molecular beam epitaxy on their photoluminescence (PL) and the stability thereof. Free excitonic emission was observed at room-temperature in the Cl-doped sample. Photon irradiation with a wavelength of 404 nm and a power density of 9.1 W/cm2 has a much stronger effect on PL degradation than does thermal heating to a temperature of 150 °C. Additionally, this study shows that the generation of nonradiative centers by both photon irradiation and thermal heating can be greatly inhibited by incorporating Cl dopant.

  6. High electron mobility GaN grown under N-rich conditions by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Koblmueller, G.; Wu, F.; Mates, T.; Speck, J. S.; Fernandez-Garrido, S.; Calleja, E.

    2007-11-26

    An alternative approach is presented for the plasma-assisted molecular beam epitaxy of high-quality GaN. Under N-rich growth conditions, an unexpected layer-by-layer growth mode was found for a wide range of growth temperatures in the GaN thermal decomposition regime (>750 deg. C). Consequently, superior surface morphologies with roughness of less than 1 nm (rms) have been achieved. For lightly Si-doped GaN films, room-temperature electron mobilities exceeding 1100 cm{sup 2}/V s were measured, surpassing the commonly insulating nature of GaN grown under N-rich conditions at low temperature.

  7. Nucleation, Growth, and Bundling of GaN Nanowires in Molecular Beam Epitaxy: Disentangling the Origin of Nanowire Coalescence.

    PubMed

    Kaganer, Vladimir M; Fernández-Garrido, Sergio; Dogan, Pinar; Sabelfeld, Karl K; Brandt, Oliver

    2016-06-01

    We investigate the nucleation, growth, and coalescence of spontaneously formed GaN nanowires in molecular beam epitaxy combining the statistical analysis of scanning electron micrographs with Monte Carlo growth models. We find that (i) the nanowire density is limited by the shadowing of the substrate from the impinging fluxes by already existing nanowires, (ii) shortly after the nucleation stage, nanowire radial growth becomes negligible, and (iii) coalescence is caused by bundling of nanowires. The latter phenomenon is driven by the gain of surface energy at the expense of the elastic energy of bending and becomes energetically favorable once the nanowires exceed a certain critical length. PMID:27168127

  8. Heavily boron-doped Si layers grown below 700 C by molecular beam epitaxy using a HBO2 source

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Fathauer, R. W.; Grunthaner, P. J.

    1989-01-01

    Boron doping in Si layers grown by molecular beam epitaxy (MBE) at 500-700 C using an HBO2 source has been studied. The maximum boron concentration without detectable oxygen incorporation for a given substrate temperature and Si growth rate has been determined using secondary-ion mass spectrometry analysis. Boron present in the Si MBE layers grown at 550-700 C was found to be electrically active, independent of the amount of oxygen incorporation. By reducing the Si growth rate, highly boron-doped layers have been grown at 600 C without detectable oxygen incorporation.

  9. Lattice Distortion of GaAsBi Alloy Grown on GaAs by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Takehara, Yuji; Yoshimoto, Masahiro; Huang, Wei; Saraie, Junji; Oe, Kunishige; Chayahara, Akiyoshi; Horino, Yuji

    2006-01-01

    GaAs1-xBix alloys were grown on GaAs by molecular beam epitaxy (MBE). The lattice constants perpendicular and parallel to the surface of epilayers were estimated by high-resolution X-ray diffraction (XRD) analysis. The GaBi molar fraction was estimated by the Rutherford backscattering spectroscopy (RBS). GaAs1-xBix epilayers with GaBi molar fractions less than 5% were almost coherently grown on GaAs substrate with compressive strain. The lattice mismatch between GaAs1-xBix (x=5%) and GaAs was estimated to be approximately 0.5%.

  10. Insights in High-Temperature Superconductivity from the Study of Films and Heterostructures Synthesized by Molecular Beam Epitaxy

    SciTech Connect

    Bozovic,I.

    2009-01-09

    Using molecular beam epitaxy, we synthesize atomically smooth thin films, multilayers and superlattices of cuprate high-temperature superconductors (HTS). Such heterostructures enable novel experiments that probe the basicphysics of HTS. For example, we have established that HTS and antiferromagnetic phases separate on Ångstrom scale, while the pseudo-gap state apparently mixes with HTS over an anomalously large length scale ('Giant Proximity Effect'). Here, we briefly review our most recent experiments on such films and superlattices. The new results include an unambiguous demonstration of strong coupling of in-plane charge excitations to out-of-plane lattice vibrations and the discovery of interface HTS.

  11. Room temperature weak ferromagnetism in Sn1-xMnxSe2 2D films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Dong, Sining; Liu, Xinyu; Li, Xiang; Kanzyuba, Vasily; Yoo, Taehee; Rouvimov, Sergei; Vishwanath, Suresh; Xing, Huili G.; Jena, Debdeep; Dobrowolska, Margaret; Furdyna, Jacek K.

    2016-03-01

    We discuss growth and magnetic properties of high-quality two dimensional (2D) Sn1-xMnxSe2 films. Thin films of this 2D ternary alloy with a wide range of Mn concentrations were successfully grown by molecular beam epitaxy. Mn concentrations up to x ≈ 0.60 were achieved without destroying the crystal structure of the parent SnSe2 2D system. Most important, the specimens show clear weak ferromagnetic behavior above room temperature, which should be of interest for 2D spintronic applications.

  12. Chirped-pulse manipulated carrier dynamics in low-temperature molecular-beam-epitaxy grown GaAs

    SciTech Connect

    Lee, Chao-Kuei; Lin, Yuan-Yao; Lin, Sung-Hui; Lin, Gong-Ru; Pan, Ci-Ling

    2014-04-28

    Chirped pulse controlled carrier dynamics in low-temperature molecular-beam-epitaxy grown GaAs are investigated by degenerate pump-probe technique. Varying the chirped condition of excited pulse from negative to positive increases the carrier relaxation time so as to modify the dispersion and reshape current pulse in time domain. The spectral dependence of carrier dynamics is analytically derived and explained by Shockley-Read Hall model. This observation enables the new feasibility of controlling carrier dynamics in ultrafast optical devices via the chirped pulse excitations.

  13. Emission control of InGaN nanocolumns grown by molecular-beam epitaxy on Si(111) substrates

    SciTech Connect

    Albert, S.; Bengoechea-Encabo, A.; Sanchez-Garcia, M. A.; Calleja, E.; Jahn, U.; Trampert, A.

    2011-09-26

    This work studies the effect of the growth temperature on the morphology and emission characteristics of self-assembled InGaN nanocolumns grown by plasma assisted molecular beam epitaxy. Morphology changes are assessed by scanning electron microscopy, while emission is measured by photoluminescence. Within the growth temperature range of 750 to 650 deg. C, an increase in In incorporation for decreasing temperature is observed. This effect allows tailoring the InGaN nanocolumns emission line shape by using temperature gradients during growth. Depending on the gradient rate, span, and sign, broad emission line shapes are obtained, covering the yellow to green range, even yielding white emission.

  14. Ultraviolet light-emitting diodes grown by plasma-assisted molecular beam epitaxy on semipolar GaN (2021) substrates

    SciTech Connect

    Sawicka, M.; Grzanka, S.; Skierbiszewski, C.; Turski, H.; Muziol, G.; Krysko, M.; Grzanka, E.; Sochacki, T.; Siekacz, M.; Kucharski, R.

    2013-03-18

    Multi-quantum well (MQW) structures and light emitting diodes (LEDs) were grown on semipolar (2021) and polar (0001) GaN substrates by plasma-assisted molecular beam epitaxy. The In incorporation efficiency was found to be significantly lower for the semipolar plane as compared to the polar one. The semipolar MQWs exhibit a smooth surface morphology, abrupt interfaces, and a high photoluminescence intensity. The electroluminescence of semipolar (2021) and polar (0001) LEDs fabricated in the same growth run peaks at 387 and 462 nm, respectively. Semipolar LEDs with additional (Al,Ga)N cladding layers exhibit a higher optical output power but simultaneously a higher turn-on voltage.

  15. Room temperature infrared photoresponse of self assembled Ge/Si (001) quantum dots grown by molecular beam epitaxy

    SciTech Connect

    Singha, R. K.; Manna, S.; Das, S.; Dhar, A.; Ray, S. K.

    2010-06-07

    We report on the observation of intraband near infrared (approx3.1 mum) and mid infrared (approx6.2 mum) photocurrent response at room temperature using Ge/Si self-assembled quantum dots grown by molecular beam epitaxy. Due to the bimodal size distribution and SiGe intermixing, distinguishable photoluminescence transitions are observed at 10 K, below and above the optical band gap of bulk Ge. The observed redshift in photocurrent with increasing temperature has been explained by the excitonic electric field originated due to infrared excitation at low temperatures. A good correlation between the spectral photocurrent response and photoluminescence of the quantum dots has been established.

  16. Molecular-beam epitaxy and robust superconductivity of stoichiometric FeSe crystalline films on bilayer graphene

    SciTech Connect

    Song Canli; Jiang Yeping; Xue Qikun; Wang Yilin; Li Zhi; Wang Lili; He Ke; Ma Xucun; Chen Xi

    2011-07-01

    We report on molecular beam epitaxy growth of stoichiometric and superconducting FeSe crystalline thin films on double-layer graphene. Layer-by-layer growth of high-quality films has been achieved in a well-controlled manner by using Se-rich condition, which allow us to investigate the thickness-dependent superconductivity of FeSe. In situ low-temperature scanning tunneling spectra reveal that the local superconducting gap in the quasiparticle density of states is visible down to two triple layers for the minimum measurement temperature of 2.2 K, and that the transition temperature T{sub c} scales inversely with film thickness.

  17. Catalyst-free growth of Bi{sub 2}Te{sub 3} nanostructures by molecular beam epitaxy

    SciTech Connect

    Harrison, S. E.; Schönherr, P.; Hesjedal, T.; Huo, Y.; Harris, J. S.

    2014-10-13

    We present the catalyst-free growth of binary Bi{sub 2}Te{sub 3} topological insulator nanostructures on c-plane sapphire substrates by molecular beam epitaxy. Dense arrays of single-crystalline nanostructures, growing along the [110] direction, are obtained for substrate temperatures ranging from ∼180 °C to 260 °C. The growth rate and shape of the nanostructures are highly temperature-dependent. The microscopic study of the nanostructures and their relationship to the underlying Bi{sub 2}Te{sub 3} thin film gives an insight into the growth mechanism.

  18. Structural and Magnetic Phase Transitions in Manganese Arsenide Thin-Films Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Jaeckel, Felix Till

    Phase transitions play an important role in many fields of physics and engineering, and their study in bulk materials has a long tradition. Many of the experimental techniques involve measurements of thermodynamically extensive parameters. With the increasing technological importance of thin-film technology there is a pressing need to find new ways to study phase transitions at smaller length-scales, where the traditional methods are insufficient. In this regard, the phase transitions observed in thin-films of MnAs present interesting challenges. As a ferromagnetic material that can be grown epitaxially on a variety of technologically important substrates, MnAs is an interesting material for spintronics applications. In the bulk, the first order transition from the low temperature ferromagnetic alpha-phase to the beta-phase occurs at 313 K. The magnetic state of the beta-phase has remained controversial. A second order transition to the paramagnetic gamma-phase takes place at 398 K. In thin-films, the anisotropic strain imposed by the substrate leads to the interesting phenomenon of coexistence of alpha- and beta-phases in a regular array of stripes over an extended temperature range. In this dissertation these phase transitions are studied in films grown by molecular beam epitaxy on GaAs (001). The films are confirmed to be of high structural quality and almost purely in the A0 orientation. A diverse set of experimental techniques, germane to thin-film technology, is used to probe the properties of the film: Temperature-dependent X-ray diffraction and atomic-force microscopy (AFM), as well as magnetotransport give insights into the structural properties, while the anomalous Hall effect is used as a probe of magnetization during the phase transition. In addition, reflectance difference spectroscopy (RDS) is used as a sensitive probe of electronic structure. Inductively coupled plasma etching with BCl3 is demonstrated to be effective for patterning MnAs. We show

  19. Molecular beam epitaxy growth of indium nitride and indium gallium nitride materials for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Trybus, Elaissa

    The objective of the proposed research is to establish the technology for material growth by molecular beam epitaxy (MBE) and fabrication of indium gallium nitride/gallium nitride (InxGa1-xN/GaN) heterojunction solar cells. InxGa1-xN solar cells have the potential to span 90% of the solar spectrum, however there has been no success with high indium (In) incorporation and only limited success with low In incorporation InxGa1-xN. Therefore, this present work focuses on 15--30% In incorporation leading to a bandgap value of 2.3--2.8 eV. This work will exploit the revision of the indium nitride (InN) bandgap value of 0.68 eV, which expands the range of the optical emission of nitride-based devices from ultraviolet to near infrared regions, by developing transparent In xGa1-xN solar cells outside the visible spectrum. Photovoltaic devices with a bandgap greater than 2.0 eV are attractive because over half the available power in the solar spectrum is above the photon energy of 2.0 eV. The ability of InxGa1-xN materials to optimally span the solar spectrum offers a tantalizing solution for high-efficiency photovoltaics. This work presents results confirming the revised bandgap of InN grown on germanium (Ge) substrates and the effects of oxygen contamination on the bandgap. This research adds to the historical discussion of the bandgap value of InN. Using the metal modulated epitaxy (MME) technique in a new, ultra-clean refurbished MBE system, an innovative growth regime is established where In and Ga phase separation is diminished by increasing the growth rate for In xGa1-xN. The MME technique modulates the metal shutters with a fixed duty cycle while maintaining a constant nitrogen flux and proves effective for improving crystal quality and p-type doping. InxGa 1-xN/GaN heterojunction solar cells require p-type doping to create the p-n subcell collecting junction, which facilitates current collection through the electrostatic field created by spatially separated ionized

  20. Growth Optimization of III-N Electronic Devices by Plasma-Assisted Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Ahmadi, Elaheh

    InAlN has received significant attention due to its great potential for electronic and optoelectronic applications. In particular, In 0.18Al0.82N presents the advantage of being lattice-matched to GaN and simultaneously exhibiting a high spontaneous polarization charge, making In0.18 Al0.82N attractive for use as the barrier layer in high-electron-mobility transistors (HEMTs). However, in the case of InAlN growth by plasma-assisted molecular beam epitaxy (PAMBE), a strong non-uniformity in the in-plane In distribution was observed for both N-face and metal-face In0.18Al 0.82N. This compositional inhomogeneity manifests itself as a columnar microstructure with AlN-rich cores (5-10 nm in width) and InN-rich intercolumn boundaries. Because of the large differences between the bandgaps and polarization of InN and AlN, this non-uniformity in InAlN composition could be a source of scattering, leading to mobility degradation in HEMTs. In this work, the growth conditions for high quality lattice-matched InAlN layers on free-standing GaN substrates were explored by plasma-assisted molecular beam epitaxy (PAMBE) in the N-rich regime. The microstructure of N-face InAlN layers, lattice-matched to GaN, was investigated by scanning transmission electron microscopy and atom probe tomography. Microstructural analysis showed an absence of the lateral composition modulation that was previously observed in InAlN films grown by PAMBE. Using same growth conditions for InAlN layer, N-face GaN/AlN/GaN/InAlN high-electron-mobility transistors with lattice-matched InAlN back barriers were grown directly on SiC. A room temperature two-dimensional electron gas (2DEG) mobility of 1100cm2 V-1s-1 and 2DEG sheet charge density of 1.9 x1013 cm 2 was measured on these devices. However, the threading dislocation density (TDD) of GaN grown directly on SiC by PAMBE (≈2 x10 10 cm-2 ) is two orders of magnitude higher than GaN grown by MOCVD on SiC or sapphire (≈5 x10 8 cm-2). This high TDD can

  1. Molecular beam epitaxy deposition of Gd2O3 thin films on SrTiO3 (100) substrate

    NASA Astrophysics Data System (ADS)

    Wang, Jinxing; Hao, Jinghua; Zhang, Yangyang; Wei, Hongmei; Mu, Juyi

    2016-06-01

    Gd2O3 thin films are grown on the SrTiO3 (100) substrate by molecular beam epitaxy (MBE) deposition. X-ray diffraction (XRD) analysis, conventional transmission electron microscopy (TEM) and aberration-corrected scanning transmission electron microscopy (STEM) are performed to investigate the microstructure of deposited thin films. It is found that the as-deposited thin film possesses a very uniform thickness of ∼40 nm and is composed of single cubic phase Gd2O3 grains. STEM and TEM observations reveal that Gd2O3 thin film grows epitaxially on the SrTiO3 (100) substrate with (001)Gd2O3//(100)STO and [110]Gd2O3//[001]STO orientations. Furthermore, the Gd atoms are found to diffuse into the SrTiO3 substrate for a depth of one unit cell and substitute for the Sr atoms near the interface.

  2. Characterization of mismatched SiGe grown on low temperature Si buffer layers by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Linder, K. K.; Zhang, F. C.; Rieh, J.-S.; Bhattacharya, P.

    1997-05-01

    Several types of buffer layer structures, including superlattice and step-graded layers, have been employed to reduce the threading dislocation in SiGe epitaxial layers. A new technique, using a 0.1 μm thick Si buffer grown at 450°C by molecular beam epitaxy, provides the best results. For a 0.5 μm thick Si 0.85Ge 0.15 layer, the dislocation density is ⩽ 10 5cm -2. Hall measurements indicate an improvement in the hole mobility of a 1 μm thick Boron doped Si 0.7Ge 0.3 layer. A {SiGe}/{Si} heterojunction bipolar transistor has been fabricated exploiting the low temperature Si buffer. Transmission electron microscopy of the structure does not indicate any evidence of threading dislocations.

  3. Molecular beam epitaxy of thick InGaN(0001) films: Effects of substrate temperature on structural and electronic properties

    NASA Astrophysics Data System (ADS)

    Papadomanolaki, E.; Bazioti, C.; Kazazis, S. A.; Androulidaki, M.; Dimitrakopulos, G. P.; Iliopoulos, E.

    2016-03-01

    Indium gallium nitride films with compositions close to the middle of the miscibility gap and thickness approximately up to 0.5 μm were epitaxially grown on GaN(0001) by plasma-assisted molecular beam epitaxy at growth temperatures spanning a range of 400-590 °C. Epilayers were characterized by X-ray diffraction, transmission electron microscopy and Hall effect measurements. The effect of substrate temperature during growth, on the structural and electronic properties of the films, was studied. Single phase films, with record high electron mobilities were obtained at lower temperatures. Increased growth temperatures led to epilayers with higher defect densities and phase separation. Strain relaxation through sequestration layering and introduction of multiple basal stacking faults was observed at such temperatures.

  4. Mid-infrared to ultraviolet optical properties of InSb grown on GaAs by molecular beam epitaxy

    SciTech Connect

    D'Costa, Vijay Richard Yeo, Yee-Chia; Tan, Kian Hua; Jia, Bo Wen; Yoon, Soon Fatt

    2015-06-14

    Spectroscopic ellipsometry was used to investigate the optical properties of an InSb film grown on a GaAs (100) substrate, and to compare the optical properties of InSb film with those of bulk InSb. The film was grown by molecular beam epitaxy under conditions intended to form 90° misfit dislocations at the InSb-GaAs interface. The complex dielectric function obtained in a wide spectroscopic range from 0.06–4.6 eV shows the critical point transitions E{sub 0}, E{sub 1}, E{sub 1} + Δ{sub 1}, E{sub 0}{sup ′}, and E{sub 2}. The amplitudes, energy transitions, broadenings, and phase angles have been determined using a derivative analysis. Comparing film and bulk critical point results reveal that the epitaxial film is nearly relaxed and has bulk-like optical characteristics.

  5. Critical thickness and strain relaxation in molecular beam epitaxy-grown SrTiO3 films

    NASA Astrophysics Data System (ADS)

    Wang, Tianqi; Ganguly, Koustav; Marshall, Patrick; Xu, Peng; Jalan, Bharat

    2013-11-01

    We report on the study of the critical thickness and the strain relaxation in epitaxial SrTiO3 film grown on (La0.3Sr0.7)(Al0.65Ta0.35)O3 (001) (LSAT) substrate using the hybrid molecular beam epitaxy approach. No change in the film's lattice parameter (both the in-plane and the out-of-plane) was observed up to a film thickness of 180 nm, which is in sharp contrast to the theoretical critical thickness of ˜12 nm calculated using the equilibrium theory of strain relaxation. For film thicknesses greater than 180 nm, the out-of-plane lattice parameter was found to decrease hyperbolically in an excellent agreement with the relaxation via forming misfit dislocations. Possible mechanisms are discussed by which the elastic strain energy can be accommodated prior to forming misfit dislocations leading to such anomalously large critical thickness.

  6. Growth of nonpolar ZnO Films on (100) β-LiGaO2 substrate by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lee, Chun-Yu; Chen, Chenlong; Chang, Liuwen; Chou, Mitch M. C.

    2014-12-01

    Nonpolar m-plane (11¯00) ZnO epitaxial films were grown on (100) β-LiGaO2 (LGO) substrates by plasma assisted molecular beam epitaxy (PAMBE). The dependence of growth characteristics on the growth temperatures was investigated. The surface morphologies of ZnO films were characterized by scanning electron microscopy and atomic force microscopy. Furthermore, the structural properties characterized by high resolution X-ray diffraction (HRXRD) indicated that the ZnO epilayers were grown in the nonpolar [11¯00] orientation. Detailed structural characterization and defect analysis of nonpolar ZnO epilayer on β-LiGaO2 substrate were studied by transmission electron microscope (TEM). Optical properties of m-plane ZnO films were investigated by Raman spectroscopy and photoluminescence analyses.

  7. Molecular beam epitaxial growth of a three-dimensional topological Dirac semimetal Na{sub 3}Bi

    SciTech Connect

    Zhang, Yi; Liu, Zhongkai; Shen, Zhi-Xun; Zhou, Bo; Kim, Yeongkwan; Hussain, Zahid; Mo, Sung-Kwan; Chen, Yulin

    2014-07-21

    We report a molecular beam epitaxial growth of Na{sub 3}Bi single-crystal thin films on two different substrates—epitaxial bilayer graphene terminated 6H-SiC(0001) and Si(111). Using reflection high-energy electron diffraction, we found that the lattice orientation of the grown Na{sub 3}Bi thin film was rotated by 30° respect to the surface lattice orientations of these two substrates. An in-situ angle-resolved photoemission spectroscopy clearly revealed the 3-dimensional Dirac-cone band structure in such thin films. Our approach of growing Na{sub 3}Bi thin film provides a potential route for further studying its intriguing electronic properties and for fabricating it into practical devices in future.

  8. LaCrO{sub 3} heteroepitaxy on SrTiO{sub 3}(001) by molecular beam epitaxy

    SciTech Connect

    Qiao, L.; Droubay, T. C.; Bowden, M. E.; Shutthanandan, V.; Kaspar, T. C.; Chambers, S. A.

    2011-08-08

    Stoichiometric, epitaxial LaCrO{sub 3} films have been grown on SrTiO{sub 3}(001) by molecular beam epitaxy using O{sub 2} as the oxidant. Films grew in a layer-by-layer fashion, giving rise to coherently strained, structurally excellent films and surfaces which preserve the step-terrace structure of the substrate. The critical thickness is in excess of 500 A. Cr(III) near the surface is easily oxidized to Cr(V) upon exposure to atomic oxygen and reduction back to Cr(III) is readily achieved by vacuum annealing, resulting in tunability of the charge state at the B-site cation.

  9. High temperature step-flow growth of gallium phosphide by molecular beam epitaxy and metalorganic chemical vapor deposition

    SciTech Connect

    Ratcliff, C.; Grassman, T. J.; Ringel, S. A.; Carlin, J. A.

    2011-10-03

    Post-growth surface morphologies of high-temperature homoepitaxial GaP films grown by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) have been studied. Smooth, stepped surface morphologies of MBE-grown layers, measured by atomic force microscopy, were found for a wide range of substrate temperatures and P{sub 2}:Ga flux ratios. A MOCVD-based growth study performed under similar conditions to MBE-grown samples shows a nearly identical smooth, step-flow surface morphology, presenting a convergence of growth conditions for the two different methods. The additional understanding of GaP epitaxy gained from this study will impact its use in applications that include GaP-based device technologies, III-V metamorphic buffers, and III-V materials integration with silicon.

  10. Interface kinetics in phase-field models: Isothermal transformations in binary alloys and step dynamics in molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Boussinot, G.; Brener, Efim A.

    2013-08-01

    We present a unified description of interface kinetic effects in phase-field models for isothermal transformations in binary alloys and steps dynamics in molecular-beam-epitaxy. The phase-field equations of motion incorporate a kinetic cross-coupling between the phase field and the concentration field. This cross-coupling generalizes the phenomenology of kinetic effects and was omitted until recently in classical phase-field models. We derive general expressions (independent of the details of the phase-field model) for the kinetic coefficients within the corresponding macroscopic approach using a physically motivated reduction procedure. The latter is equivalent to the so-called thin-interface limit but is technically simpler. It involves the calculation of the effective dissipation that can be ascribed to the interface in the phase-field model. We discuss in detail the possibility of a nonpositive definite matrix of kinetic coefficients, i.e., a negative effective interface dissipation, although being in the range of stability of the underlying phase-field model. Numerically we study the step-bunching instability in molecular-beam-epitaxy due to the Ehrlich-Schwoebel effect, present in our model due to the cross-coupling. Using the reduction procedure we compare the results of the phase-field simulations with the analytical predictions of the macroscopic approach.

  11. Interface kinetics in phase-field models: isothermal transformations in binary alloys and step dynamics in molecular-beam epitaxy.

    PubMed

    Boussinot, G; Brener, Efim A

    2013-08-01

    We present a unified description of interface kinetic effects in phase-field models for isothermal transformations in binary alloys and steps dynamics in molecular-beam-epitaxy. The phase-field equations of motion incorporate a kinetic cross-coupling between the phase field and the concentration field. This cross-coupling generalizes the phenomenology of kinetic effects and was omitted until recently in classical phase-field models. We derive general expressions (independent of the details of the phase-field model) for the kinetic coefficients within the corresponding macroscopic approach using a physically motivated reduction procedure. The latter is equivalent to the so-called thin-interface limit but is technically simpler. It involves the calculation of the effective dissipation that can be ascribed to the interface in the phase-field model. We discuss in detail the possibility of a nonpositive definite matrix of kinetic coefficients, i.e., a negative effective interface dissipation, although being in the range of stability of the underlying phase-field model. Numerically we study the step-bunching instability in molecular-beam-epitaxy due to the Ehrlich-Schwoebel effect, present in our model due to the cross-coupling. Using the reduction procedure we compare the results of the phase-field simulations with the analytical predictions of the macroscopic approach. PMID:24032848

  12. INSTRUMENTS AND METHODS OF INVESTIGATION: Atomic structures on a GaAs(001) surface grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bakhtizin, Raouf Z.; Hashizume, T.; Xue, Qi-Kun; Sakurai, Toshio

    1997-11-01

    A unique apparatus for in-situ atomic-resolution study of solid state structures grown by molecular beam epitaxy (MBE) is developed, in which a scanning tunneling microscope (STM) is combined with an MBE chamber within the same vacuum system. The utility of the apparatus is demonstrated by examining atomic structures on a molecular-beam-epitaxial GaAs(001) surface over a wide range of [As]/[Ga] ratios. By varying the As surface coverage, the 2×4 - α, β, γ and c(4×4) phases are examined in detail. High-resolution STM images indicate that 2×4 - α, β, and γ phases in the outermost surface layer have essentially the same unit cell consisting of two As dimers and two As dimer vacancies. Using the STM images, reflection high-energy electron diffraction (RHEED) patterns and dynamical RHEED calculations, the existing structural models for the 2×4 phases are analysed and a new model of the As-rich GaAs(001) surface is proposed, found to be consistent with most of the previous observations.

  13. Self-regulated growth of LaVO{sub 3} thin films by hybrid molecular beam epitaxy

    SciTech Connect

    Zhang, Hai-Tian; Engel-Herbert, Roman; Dedon, Liv R.; Martin, Lane W.

    2015-06-08

    LaVO{sub 3} thin films were grown on SrTiO{sub 3} (001) by hybrid molecular beam epitaxy. A volatile metalorganic precursor, vanadium oxytriisopropoxide (VTIP), and elemental La were co-supplied in the presence of a molecular oxygen flux. By keeping the La flux fixed and varying the VTIP flux, stoichiometric LaVO{sub 3} films were obtained for a range of cation flux ratios, indicating the presence of a self-regulated growth window. Films grown under stoichiometric conditions were found to have the largest lattice parameter, which decreased monotonically with increasing amounts of excess La or V. Energy dispersive X-ray spectroscopy and Rutherford backscattering measurements were carried out to confirm film compositions. Stoichiometric growth of complex vanadate thin films independent of cation flux ratios expands upon the previously reported self-regulated growth of perovskite titanates using hybrid molecular beam epitaxy, thus demonstrating the general applicability of this growth approach to other complex oxide materials, where a precise control over film stoichiometry is demanded by the application.

  14. Effect of GaN interlayer on polarity control of epitaxial ZnO thin films grown by molecular beam epitaxy

    SciTech Connect

    Wang, X. Q.; Sun, H. P.; Pan, X. Q.

    2010-10-11

    Epitaxial ZnO thin films were grown on nitrided (0001) sapphire substrates with an intervening GaN layer by rf-plasma-assisted molecular beam epitaxy. It was found that polarity of the ZnO epilayer could be controlled by modifying the GaN interlayer. ZnO grown on a distorted 3-nm-thick GaN interlayer has Zn-polarity while ZnO on a 20-nm-thick GaN interlayer with a high structural quality has O-polarity. High resolution transmission electron microscopy analysis indicates that the polarity of ZnO epilayer is controlled by the atomic structure of the interface between the ZnO buffer layer and the intervening GaN layer.

  15. Growth and phase transition characteristics of pure M-phase VO{sub 2} epitaxial film prepared by oxide molecular beam epitaxy

    SciTech Connect

    Fan, L. L.; Chen, S.; Wu, Y. F.; Chen, F. H.; Chu, W. S.; Chen, X.; Zou, C. W.; Wu, Z. Y.

    2013-09-23

    VO{sub 2} epitaxial film with large size has been prepared by oxide-molecular beam epitaxy method on Al{sub 2}O{sub 3} (0001) substrate. The VO{sub 2} film shows a perfect crystal orientation, uniformity, and distinct metal-insulator phase transition (MIT) characteristics. It is observed that the MIT character is closely associated with the crystal defects such as oxygen vacancies. By controlling the growth condition, the MIT temperature can be tuned through modifying the content of oxygen vacancies. The role of the oxygen vacancies on the phase transition behavior of this VO{sub 2} film is discussed in the framework of the hybridization theory and the valence state of vanadium.

  16. Direct growth of hexagonal boron nitride/graphene heterostructures on cobalt foil substrates by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Xu, Zhongguang; Khanaki, Alireza; Tian, Hao; Zheng, Renjing; Suja, Mohammad; Zheng, Jian-Guo; Liu, Jianlin

    2016-07-01

    Graphene/hexagonal boron nitride (G/h-BN) heterostructures have attracted a great deal of attention because of their exceptional properties and wide variety of potential applications in nanoelectronics. However, direct growth of large-area, high-quality, and stacked structures in a controllable and scalable way remains challenging. In this work, we demonstrate the synthesis of h-BN/graphene (h-BN/G) heterostructures on cobalt (Co) foil by sequential deposition of graphene and h-BN layers using plasma-assisted molecular beam epitaxy. It is found that the coverage of h-BN layers can be readily controlled on the epitaxial graphene by growth time. Large-area, uniform-quality, and multi-layer h-BN films on thin graphite layers were achieved. Based on an h-BN (5-6 nm)/G (26-27 nm) heterostructure, capacitor devices with Co(foil)/G/h-BN/Co(contact) configuration were fabricated to evaluate the dielectric properties of h-BN. The measured breakdown electric field showed a high value of ˜2.5-3.2 MV/cm. Both I-V and C-V characteristics indicate that the epitaxial h-BN film has good insulating characteristics.

  17. Room-temperature ferromagneticlike behavior in Mn-implanted and postannealed InAs layers deposited by molecular beam epitaxy

    SciTech Connect

    Gonzalez-Arrabal, R.; Gonzalez, Y.; Gonzalez, L.; Martin-Gonzalez, M. S.; Munnik, F.

    2009-04-01

    We report on the magnetic and structural properties of Ar- and Mn-implanted InAs epitaxial films grown on GaAs (100) by molecular beam epitaxy and the effect of rapid thermal annealing (RTA) for 30 s at 750 deg. C. Channeling particle induced x-ray emission (PIXE) experiments reveal that after Mn implantation almost all Mn atoms are substitutional in the In site of the InAs lattice, like in a diluted magnetic semiconductor. All of these samples show diamagnetic behavior. However, after RTA treatment the Mn-InAs films exhibit room-temperature magnetism. According to PIXE measurements the Mn atoms are no longer substitutional. When the same set of experiments was performed with Ar as implantation ion, all of the layers present diamagnetism without exception. This indicates that the appearance of room-temperature ferromagneticlike behavior in the Mn-InAs-RTA layer is not related to lattice disorder produced during implantation but to a Mn reaction produced after a short thermal treatment. X-ray diffraction patterns and Rutherford backscattering measurements evidence the segregation of an oxygen-deficient MnO{sub 2} phase (nominally MnO{sub 1.94}) in the Mn-InAs-RTA epitaxial layers which might be the origin of the room-temperature ferromagneticlike response observed.

  18. Theoretical and experimental studies of surface processes in the course of molecular-beam epitaxy of gallium nitride

    SciTech Connect

    Bobrovnikova, I. A. Ivonin, I. V.; Novikov, V. A.; Preobrazhenskii, V. V.

    2009-03-15

    The method of atomic-force microscopy has been used to experimentally study the effect of growth conditions on the structure of the surface of epitaxial GaN layers grown by molecular-beam epitaxy. Quantitative values of the density, height, and width of growth centers in relation to the conditions of epitaxy are obtained; the average length of the diffusion path of particles limiting the GaN growth rate have been estimated; and the activation energies and the surface-diffusion coefficients for these particles have been calculated. The equilibrium composition of adsorbed layers at the GaN (0001) surface in a wide range of deposition temperatures and pressures of gallium and nitrogen has been calculated with account taken of the following components: gallium atoms, nitrogen atoms, and NH molecules. On the basis of the comparison of experimental data on the structure of the GaN surface with results of calculations concerning the composition of adsorbed layers on the growth surface, it was assumed that the growth of GaN layers is limited by supply of gallium.

  19. Photoluminescence and bowing parameters of InAsSb/InAs multiple quantum wells grown by molecular beam epitaxy

    SciTech Connect

    Liu, P.-W.; Tsai, G.; Lin, H. H.; Krier, A.; Zhuang, Q. D.; Stone, M.

    2006-11-13

    Detailed studies are reported on the photoluminescence of InAsSb/InAs multiple quantum wells grown by molecular beam epitaxy on InAs substrates with the Sb mole fraction ranging from 0.06 to 0.13. From 4 K photoluminescence the band alignment was determined to be staggered type II. By comparing the emission peak energies with a transition energy calculation it was found that both the conduction and valence bands of InAsSb alloy exhibit some bowing. The bowing parameters were determined to be in the ratio of 4:6. For a sample with Sb composition {approx}0.12 in the quantum well the photoluminescence emission band covers the CO{sub 2} absorption peak making it suitable for use in sources for CO{sub 2} detection.

  20. GaN nanowires with pentagon shape cross-section by ammonia-source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lin, Yong; Leung, Benjamin; Li, Qiming; Figiel, Jeffrey. J.; Wang, George T.

    2015-10-01

    Ammonia-based molecular beam epitaxy (NH3-MBE) was used to grow catalyst-assisted GaN nanowires on (1 1 bar 02) r-plane sapphire substrates. Dislocation free [ 11 2 bar 0 ] oriented nanowires are formed with pentagon shape cross-section, instead of the usual triangular shape facet configuration. Specifically, the cross-section is the result of the additional two nonpolar { 10 1 bar 0 } side facets, which appear due to a decrease in relative growth rate of the { 10 1 bar 0 } facets to the { 10 1 bar 1 } and { 10 1 bar 1 } facets under the growth regime in NH3-MBE. Compared to GaN nanowires grown by Ni-catalyzed metal-organic chemical vapor deposition, the NH3-MBE grown GaN nanowires show more than an order of magnitude increase in band-edge to yellow luminescence intensity ratio, as measured by cathodoluminescence, indicating improved microstructural and optical properties.

  1. Growth morphology of MnAs epilayers on GaAs(1 1 1)-B substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Etgens, V. H.; Eddrief, M.; Demaille, D.; Zheng, Y. L.; Ouerghi, A.

    2002-04-01

    MnAs epilayers were grown by molecular beam epitaxy on GaAs(1 1 1)B substrates. The morphology of epilayers has been studied by coupling several in situ techniques. Two distinct growth regimes were distinguished as a function of the substrate temperature. For the growth at 320°C, the system shows an intriguing mechanism of relaxation that produces MnAs isolated islands (the so-called "blocks") with constant height. The explanation for this mechanism associates the large mobility of atoms at this temperature with the strain due to the important misfit. At lower temperature (200°C) the surface mobility is greatly reduced which results in a more homogeneous film.

  2. Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

    DOE PAGESBeta

    Ahmed, Adam S.; Wen, Hua; Ohta, Taisuke; Pinchuk, Igor V.; Zhu, Tiancong; Beechem, Thomas; Kawakami, Roland K.

    2016-04-27

    Here, we report the successful growth of high-quality SrO films on highly-ordered pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy. The SrO layers have (001) orientation as confirmed by X-ray diffraction (XRD) while atomic force microscopy measurements show continuous pinhole-free films having rms surface roughness of <1.5 Å. Moreover, transport measurements of exfoliated graphene, after SrO deposition, show a strong dependence between the Dirac point and Sr oxidation. As a result, the SrO is leveraged as a buffer layer for more complex oxide integration via the demonstration of (001) oriented SrTiO3 grown atop a SrO/HOPG stack.

  3. Growth of SrTiO{sub 3}(110) film by oxide molecular beam epitaxy with feedback control

    SciTech Connect

    Feng Jiagui; Yang Fang; Yang Yang; Gu Lin; Guo Jiandong; Wang Zhiming

    2012-12-15

    By controlling the growth of complex oxide films with atomic precision, emergent phenomena and fascinating properties have been discovered, and even been manipulated. With oxide molecular beam epitaxy (OMBE) we grow high-quality SrTiO{sub 3}(110) films by evaporating Sr and Ti metals with separate controls of the open/close timing of the shutters. The incident electron beam angle of the reflective high energy electron diffraction (RHEED) is adjusted to make the (01) beam sensitive to surface chemical concentration. By monitoring such an intensity, we tune the shutter timing to synchronize the evaporation amount of Sr and Ti in real-time. The intensity is further used as a feedback control signal for automatic growth optimization to fully compensate the possible fluctuation of the source flux rates upon extended growth. A 22 nm-thick film is obtained with the precision of metal cation stoichiometry better than 0.5%.

  4. X-ray diffraction study of GaSb grown by molecular beam epitaxy on silicon substrates

    NASA Astrophysics Data System (ADS)

    Rodriguez, J. B.; Madiomanana, K.; Cerutti, L.; Castellano, A.; Tournié, E.

    2016-04-01

    We report on the molecular beam epitaxy and characterization by X-ray diffraction techniques of GaSb layers grown on silicon substrates. AlSb and Al nucleation layers were used with different thicknesses and growth temperatures. Reciprocal space maps and a modified version of the Williamson-Hall analysis allowed for a characterization of the misfit dislocations properties. Finally, a post-growth annealing step is studied in order to further improve the material quality. Using this technique, a full-width-at-half-maximum of the GaSb peak of 235 arc sec was obtained for a layer thickness of 1 μm, which is comparable to the best results for GaAs or Ge on Si.

  5. Molecular beam epitaxial growth and characterization of Bi{sub 2}Se{sub 3}/II-VI semiconductor heterostructures

    SciTech Connect

    Chen, Zhiyi Zhao, Lukas; Krusin-Elbaum, Lia; Garcia, Thor Axtmann; Tamargo, Maria C.; Hernandez-Mainet, Luis C.; Deng, Haiming

    2014-12-15

    Surfaces of three-dimensional topological insulators (TIs) have been proposed to host quantum phases at the interfaces with other types of materials, provided that the topological properties of interfacial regions remain unperturbed. Here, we report on the molecular beam epitaxy growth of II-VI semiconductor–TI heterostructures using c-plane sapphire substrates. Our studies demonstrate that Zn{sub 0.49}Cd{sub 0.51}Se and Zn{sub 0.23}Cd{sub 0.25}Mg{sub 0.52}Se layers have improved quality relative to ZnSe. The structures exhibit a large relative upward shift of the TI bulk quantum levels when the TI layers are very thin (∼6nm), consistent with quantum confinement imposed by the wide bandgap II-VI layers. Our transport measurements show that the characteristic topological signatures of the Bi{sub 2}Se{sub 3} layers are preserved.

  6. Low-temperature growth of GaSb epilayers on GaAs (001) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Benyahia, D.; Kubiszyn, Ł.; Michalczewski, K.; Kębłowski, A.; Martyniuk, P.; Piotrowski, J.; Rogalski, A.

    2016-01-01

    Non-intentionally doped GaSb epilayers were grown by molecular beam epitaxy (MBE) on highly mismatched semi-insulating GaAs substrate (001) with 2 offcut towards [110]. The effects of substrate temperature and the Sb/Ga flux ratio on the crystalline quality, surface morphology and electrical properties were investigated by Nomarski optical microscopy, X-ray diffraction (XRD) and Hall measurements, respectively. Besides, differential Hall was used to investigate the hole concentration behaviour along the GaSb epilayer. It is found that the crystal quality, electrical properties and surface morphology are markedly dependent on the growth temperature and the group V/III flux ratio. Under the optimized parameters, we demonstrate a low hole concentration at very low growth temperature. Unfortunately, the layers grown at low temperature are characterized by wide FWHM and low Hall mobility.

  7. Low-temperature growth of GaSb epilayers on GaAs (001) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Benyahia, D.; Kubiszyn, Ł.; Michalczewski, K.; KĘbŁOwski, , A.; Martyniuk, P.; Piotrowski, J.; Rogalski, A.

    2016-01-01

    Non-intentionally doped GaSb epilayers were grown by molecular beam epitaxy (MBE) on highly mismatched semi-insulating GaAs substrate (001) with 2 offcut towards [110]. The effects of substrate temperature and the Sb/Gaflux ratio on the crystalline quality, surface morphology and electrical properties were investigated by Nomarski optical microscopy, X-ray diffraction (XRD) and Hall measurements, respectively. Besides, differential Hall was used to investigate the hole concentration behaviour along the GaSb epilayer. It is found that the crystal quality, electrical properties and surface morphology are markedly dependent on the growth temperature and the group V/III flux ratio. Under the optimized parameters, we demonstrate a low hole concentration at very low growth temperature. Unfortunately, the layers grown at low temperature are characterized by wide FWHM and low Hall mobility.

  8. High-efficiency Al sub 0. 22 Ga sub 0. 78 As solar cells grown by molecular beam epitaxy

    SciTech Connect

    Melloch, M.R. ); Tobin, S.P.; Bajgar, C. ); Keshavarzi, A.; Stellwag, T.B.; Lush, G.B.; Lundstrom, M.S. ); Emery, K. )

    1990-07-02

    The quality of {ital pn} junction photodetectors made of Al{sub 0.2}Ga{sub 0.8}As has been investigated as a first step in the optimization of tandem solar cells. We have obtained 1 sun AM1.5 efficiencies of 16.1% for 0.25 cm{sup 2} Al{sub 0.22}Ga{sub 0.78}As solar cells fabricated from molecular beam epitaxy (MBE) material. This efficiency is 3.2 percentage points higher than the previously best reported efficiency of 12.9% for an Al{sub 0.2}Ga{sub 0.8}As solar cell fabricated from MBE material.

  9. Electrical and Optical Studies of Defect Structure of HgCdTe Films Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Świątek, Z.; Ozga, P.; Izhnin, I. I.; Fitsych, E. I.; Voitsekhovskii, A. V.; Korotaev, A. G.; Mynbaev, K. D.; Varavin, V. S.; Dvoretsky, S. A.; Mikhailov, N. N.; Yakushev, M. V.; Bonchyk, A. Yu.; Savytsky, H. V.

    2016-07-01

    Electrical and optical studies of defect structure of HgCdTe films grown by molecular beam epitaxy (MBE) are performed. It is shown that the peculiarity of these films is the presence of neutral defects formed at the growth stage and inherent to the material grown by MBE. It is assumed that these neutral defects are the Te nanocomplexes. Under ion milling, they are activated by mercury interstitials and form the donor centers with the concentration of 1017 cm-3, which makes it possible to detect such defects by measurements of electrical parameters of the material. Under doping of HgCdTe with arsenic using high temperature cracking, the As2 dimers are present in the arsenic flow and block the neutral Te nanocomplexes to form donor As2Te3 complexes. The results of electrical studies are compared with the results of studies carried out by micro-Raman spectroscopy.

  10. Comparison of AlN films grown by RF magnetron sputtering and ion-assisted molecular beam epitaxy

    SciTech Connect

    Chan, J.; Fu, T.; Cheung, N.W.; Ross, J.; Newman, N.; Rubin, M.

    1993-04-01

    Crystalline aluminum nitride (AlN) thin films were formed on various substrates by using RF magnetron sputtering of an A1 target in a nitrogen plasma and also by ion-assisted molecular beam epitaxy (IAMBE). Basal-oriented AlN/(111) Si showed a degradation of crystallinity with increased substrate temperature from 550 to 770 C, while the crystallinity of AlN/(0001) A1{sub 2}O{sub 3} samples improved from 700 to 850 C. The optical absorption characteristics of the AlN/(0001) A1{sub 2}O{sub 3} films as grown by both deposition methods revealed a decrease in subbandgap absorption with increased substrate temperature.

  11. Molecular beam epitaxial growth of ultrathin CdTe-CdMnTe quantum wells and their characterization

    NASA Astrophysics Data System (ADS)

    Waag, A.; Schmeusser, S.; Bicknell-Tassius, R. N.; Yakovlev, D. R.; Ossau, W.; Landwehr, G.; Uraltsev, I. N.

    1991-12-01

    We report the growth and optical characterization of CdTe/CdMnTe single quantum wells with well thicknesses ranging from 60 down to 6 Å. The single quantum wells were grown by standard molecular beam epitaxy without growth interruption and investigated by reflection, photoluminescence (PL), and excitation PL. All structures including the 6-Å-thick quantum well exhibit extraordinarily narrow photoluminescence lines. From an analysis of linewidth and Stokes shift of the photoluminescence lines informations on the structure of the CdTe/CdMnTe interfaces are derived. The good quality of those structures made it possible to identify for the first time recombination of two-dimensional free exciton magnetic polarons.

  12. Optical characterization of Hg1-xCdxTe/CdTe/GaAs multilayers grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Liu, Weijun; Liu, Pulin; Shi, Guo L.; Zhu, Jing-Bing; He, Li; Xie, Qin X.; Yuan, Shixin

    1991-11-01

    The IR transmission spectra for HgCdTe/CdTe/GaAs multilayers grown by molecular-beam epitaxy were measured in the wavenumber region of 600 cm-1 - 4000 cm-1 at 300 K and 77 K. The transmission spectra were calculated taking the thickness d1 of MCT layer and the thickness d2 of CdTe layer as fitting parameters in the energy range from 600 cm-1 to 300 cm-1 below the energy gap Eg assuming the existence of abrupt interfaces between the neighboring layers. The values of d1 and d2 obtained by fitting the IR transmission spectra are in good agreement with that by transmission electron microscopy (TEM) measurement. The accurate absorption coefficient spectra were obtained and discussed in the energy region equivalent to 0.9 Eg to 4000 cm-1 taking into account the interference effects.

  13. Elemental boron-doped p(+)-SiGe layers grown by molecular beam epitaxy for infrared detector applications

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; George, T.; Jones, E. W.; Ksendzov, A.; Huberman, M. L.

    1992-01-01

    SiGe/Si heterojunction internal photoemission (HIP) detectors have been fabricated utilizing molecular beam epitaxy of p(+)-SiGe layers on p(-)-Si substrates. Elemental boron from a high-temperature effusion cell was used as the dopant source during MBE growth, and high doping concentrations have been achieved. Strong infrared absorption, mainly by free-carrier absorption, was observed for the degenerately doped SiGe layers. The use of elemental boron as the dopant source allows a low MBE growth temperature, resulting in improved crystalline quality and smooth surface morphology of the Si(0.7)Ge(0.3) layers. Nearly ideal thermionic emission dark current characteristics have been obtained. Photoresponse of the HIP detectors in the long-wavelength infrared regime has been demonstrated.

  14. Germanium doping of self-assembled GaN nanowires grown by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Schörmann, Jörg; Hille, Pascal; Schäfer, Markus; Müßener, Jan; Becker, Pascal; Klar, Peter J.; Hofmann, Detlev M.; Teubert, Jörg; Eickhoff, Martin; Kleine-Boymann, Matthias; Rohnke, Marcus; Mata, Maria de la; Arbiol, Jordi

    2013-09-14

    Germanium doping of GaN nanowires grown by plasma-assisted molecular beam epitaxy on Si(111) substrates is studied. Time of flight secondary ion mass spectrometry measurements reveal a constant Ge-concentration along the growth axis. A linear relationship between the applied Ge-flux and the resulting ensemble Ge-concentration with a maximum content of 3.3×10{sup 20} cm{sup −3} is extracted from energy dispersive X-ray spectroscopy measurements and confirmed by a systematic increase of the conductivity with Ge-concentration in single nanowire measurements. Photoluminescence analysis of nanowire ensembles and single nanowires reveals an exciton localization energy of 9.5 meV at the neutral Ge-donor. A Ge-related emission band at energies above 3.475 eV is found that is assigned to a Burstein-Moss shift of the excitonic emission.

  15. Role of native defects in nitrogen flux dependent carrier concentration of InN films grown by molecular beam epitaxy

    SciTech Connect

    Tangi, Malleswararao; Kuyyalil, Jithesh; Shivaprasad, S. M.

    2012-10-01

    We address the carrier concentration, strain, and bandgap issue of InN films grown on c-sapphire at different N-flux by molecular beam epitaxy using x-ray diffraction and x-ray photoelectron spectroscopy. We demonstrate that the strain in InN films arises due to point defects like nitrogen interstitials and nitrogen antisites. We report minimal biaxial strain due to relaxed growth morphology and a minimal hydrostatic strain arising due to interstitial nitrogen atoms being partially compensated by nitrogen antisites. We find that the variation in absorption edge can be attributed to defect induced carrier concentration and that nitrogen interstitials and nitrogen antisites act as donors that yield the respective absorption edge and Moss-Burstein shift. Our studies are a step towards the ability to form low carrier concentration strain-relaxed films and to determine the intrinsic band gap value for this technologically important material.

  16. Molecular beam epitaxy-grown wurtzite MgS thin films for solar-blind ultra-violet detection

    SciTech Connect

    Lai, Y. H.; He, Q. L.; Cheung, W. Y.; Lok, S. K.; Wong, K. S.; Sou, I. K.; Ho, S. K.; Tam, K. W.

    2013-04-29

    Molecular beam epitaxy grown MgS on GaAs(111)B substrate was resulted in wurtzite phase, as demonstrated by detailed structural characterizations. Phenomenological arguments were used to account for why wurtzite phase is preferred over zincblende phase or its most stable rocksalt phase. Results of photoresponse and reflectance measurements performed on wurtzite MgS photodiodes suggest a direct bandgap at around 5.1 eV. Their response peaks at 245 nm with quantum efficiency of 9.9% and enjoys rejection of more than three orders at 320 nm and close to five orders at longer wavelengths, proving the photodiodes highly competitive in solar-blind ultraviolet detection.

  17. High quality InAlN single layers lattice-matched to GaN grown by molecular beam epitaxy

    SciTech Connect

    Gacevic, Z.; Fernandez-Garrido, S.; Calleja, E.; Estrade, S.

    2011-07-18

    We report on properties of high quality {approx}60 nm thick InAlN layers nearly in-plane lattice-matched to GaN, grown on c-plane GaN-on-sapphire templates by plasma-assisted molecular beam epitaxy. Excellent crystalline quality and low surface roughness are confirmed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. High annular dark field observations reveal a periodic in-plane indium content variation (8 nm period), whereas optical measurements evidence certain residual absorption below the band-gap. The indium fluctuation is estimated to be {+-} 1.2% around the nominal 17% indium content via plasmon energy oscillations assessed by electron energy loss spectroscopy with sub-nanometric spatial resolution.

  18. Chemical Composition and Thermal Stability of Atomic Force Microscope-Assisted Anodic Oxides as Nanomasks for Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Cha, Kyu Man; Shibata, Kenji; Kamiko, Masao; Yamamoto, Ryoichi; Hirakawa, Kazuhiko

    2011-12-01

    We have investigated the thermal stability of GaAs-oxides grown by atomic force microscope (AFM)-assisted anodic oxidation to identify the conditions suitable for fabricating oxide nanomasks for molecular beam epitaxy (MBE). The oxides grown at bias voltages, Vox, less than 30 V were desorbed after standard thermal cleaning in MBE, while the oxide patterns fabricated at Vox ≥40 V survived on the GaAs surfaces. From X-ray photoemission spectroscopy, we have found that the better thermal stability of AFM-oxides grown at Vox > 40 V can be attributed to the formation of Ga2O3 and that Ga2O3 can be used as nanomasks for site-controlled MBE growth.

  19. Effects of growth temperature and device structure on GaP solar cells grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Vaisman, M.; Tomasulo, S.; Masuda, T.; Lang, J. R.; Faucher, J.; Lee, M. L.

    2015-02-01

    Gallium phosphide (GaP) is an attractive candidate for wide-bandgap solar cell applications, possessing the largest bandgap of the III-arsenide/phosphides without aluminum. However, GaP cells to date have exhibited poor internal quantum efficiency (IQE), even for photons absorbed by direct transitions, motivating improvements in material quality and device structure. In this work, we investigated GaP solar cells grown by molecular beam epitaxy over a range of substrate temperatures, employing a much thinner emitter than in prior work. Higher growth temperatures yielded the best solar cell characteristics, indicative of increased diffusion lengths. Furthermore, the inclusion of an AlGaP window layer improved both open-circuit voltage and short wavelength IQE.

  20. Effect of N2 microplasma treatment on initial growth of GaN by metal–organic molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Suzuki, Yohei; Kusakabe, Yasuhiro; Uchiyama, Shota; Maruyama, Takahiro; Naritsuka, Shigeya; Shimizu, Kazuo

    2016-08-01

    N2 atmospheric microplasma was applied to improve the yields and reproducibility of the initial growth of GaN by metal–organic molecular beam epitaxy (MOMBE). The plasma treatment was found to be effective in cleaning the surface, and excellent flat growth was achieved even in the early stage of the growth. The effect of the air exposure after plasma treatment was also studied, and the yield of the growth was found to be largely decreased by the air exposure even after the treatment. Therefore, the oxidation of the substrate is one of main causes of the poor initial growth and the installation of the microplasma equipment in the MBE loading chamber is useful for suppressing the oxidation after the treatment. Atomic force microscopy (AFM) measurement shows that the microplasma treatment is also effective for undoing the surface double steps through etching, which is helpful for a very smooth layer-by-layer growth in the early stage of growth.

  1. Effects of growth temperature and device structure on GaP solar cells grown by molecular beam epitaxy

    SciTech Connect

    Vaisman, M.; Tomasulo, S.; Masuda, T.; Lang, J. R.; Faucher, J.; Lee, M. L.

    2015-02-09

    Gallium phosphide (GaP) is an attractive candidate for wide-bandgap solar cell applications, possessing the largest bandgap of the III-arsenide/phosphides without aluminum. However, GaP cells to date have exhibited poor internal quantum efficiency (IQE), even for photons absorbed by direct transitions, motivating improvements in material quality and device structure. In this work, we investigated GaP solar cells grown by molecular beam epitaxy over a range of substrate temperatures, employing a much thinner emitter than in prior work. Higher growth temperatures yielded the best solar cell characteristics, indicative of increased diffusion lengths. Furthermore, the inclusion of an AlGaP window layer improved both open-circuit voltage and short wavelength IQE.

  2. Long-wavelength PtSi infrared detectors fabricated by incorporating a p(+) doping spike grown by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Park, J. S.; George, T.; Jones, E. W.; Fathauer, R. W.; Maserjian, J.

    1993-01-01

    By incorporating a 1-nm-thick p(+) doping spike at the PtSi/Si interface, we have successfully demonstrated extended cutoff wavelengths of PtSi Schottky infrared detectors in the long wavelength infrared (LWIR) regime for the first time. The extended cutoff wavelengths resulted from the combined effects of an increased electric field near the silicide/Si interface due to the p(+) doping spike and the Schottky image force. The p(+) doping spikes were grown by molecular beam epitaxy at 450 C, using elemental boron as the dopant source, with doping concentrations ranging from 5 x 10 exp 19 to 2 x 10 exp 20/cu cm. Transmission electron microscopy indicated good crystalline quality of the doping spikes. The cutoff wavelengths were shown to increase with increasing doping concentrations of the p(+) spikes. Thermionic emission dark current characteristics were observed and photoresponses in the LWIR regime were demonstrated.

  3. Compositional variations in In0.5Ga0.5N nanorods grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Cherns, D.; Webster, R. F.; Novikov, S. V.; Foxon, C. T.; Fischer, A. M.; Ponce, F. A.; Haigh, S. J.

    2014-05-01

    The composition of InxGa1 - xN nanorods grown by molecular beam epitaxy with nominal x = 0.5 has been mapped by electron microscopy using Z-contrast imaging and x-ray microanalysis. This shows a coherent and highly strained core-shell structure with a near-atomically sharp boundary between a Ga-rich shell (x ˜ 0.3) and an In-rich core (x ˜ 0.7), which itself has In- and Ga-rich platelets alternating along the growth axis. It is proposed that the shell and core regions are lateral and vertical growth sectors, with the core structure determined by spinodal decomposition.

  4. Formation of GaN quantum dots by molecular beam epitaxy using NH3 as nitrogen source

    NASA Astrophysics Data System (ADS)

    Damilano, B.; Brault, J.; Massies, J.

    2015-07-01

    Self-assembled GaN quantum dots (QDs) in AlxGa1-xN (0.3 ≤ x ≤ 1) were grown on c-plane sapphire and Si (111) substrates by molecular beam epitaxy using ammonia as nitrogen source. The QD formation temperature was varied from 650 °C to 800 °C. Surprisingly, the density and size of QDs formed in this temperature range are very similar. This has been explained by considering together experimental results obtained from reflection high-energy electron diffraction, atomic force microscopy, and photoluminescence to discuss the interplay between thermodynamics and kinetics in the QD formation mechanisms. Finally, possible ways to better control the QD optical properties are proposed.

  5. Spinel-structured metal oxide on a substrate and method of making same by molecular beam epitaxy

    DOEpatents

    Chambers, Scott A.

    2006-02-21

    A method of making a spinel-structured metal oxide on a substrate by molecular beam epitaxy, comprising the step of supplying activated oxygen, a first metal atom flux, and at least one other metal atom flux to the surface of the substrate, wherein the metal atom fluxes are individually controlled at the substrate so as to grow the spinel-structured metal oxide on the substrate and the metal oxide is substantially in a thermodynamically stable state during the growth of the metal oxide. A particular embodiment of the present invention encompasses a method of making a spinel-structured binary ferrite, including Co ferrite, without the need of a post-growth anneal to obtain the desired equilibrium state.

  6. Self-corrected Sensors Based On Atomic Absorption Spectroscopy For Atom Flux Measurements In Molecular Beam Epitaxy

    SciTech Connect

    Du, Yingge; Droubay, Timothy C.; Liyu, Andrey V.; Li, Guosheng; Chambers, Scott A.

    2014-04-24

    A high sensitivity atom flux sensor based on atomic absorption spectroscopy has been designed and implemented to control electron beam evaporators and effusion cells in a molecular beam epitaxy system. Using a high-resolution spectrometer and a two-dimensional charge coupled device (CCD) detector in a double-beam configuration, we employ a non-resonant line or a resonant line with lower absorbance from the same hollow cathode lamp as the reference for nearly perfect background correction and baseline drift removal. This setup also significantly shortens the warm-up time needed compared to other sensor technologies and drastically reduces the noise coming from the surrounding environment. In addition, the high-resolution spectrometer allows the most sensitive resonant line to be isolated and used to provide excellent signal-to-noise ratio.

  7. Self-corrected sensors based on atomic absorption spectroscopy for atom flux measurements in molecular beam epitaxy

    SciTech Connect

    Du, Y. E-mail: scott.chambers@pnnl.gov; Liyu, A. V.; Droubay, T. C.; Chambers, S. A. E-mail: scott.chambers@pnnl.gov; Li, G.

    2014-04-21

    A high sensitivity atom flux sensor based on atomic absorption spectroscopy has been designed and implemented to control electron beam evaporators and effusion cells in a molecular beam epitaxy system. Using a high-resolution spectrometer and a two-dimensional charge coupled device detector in a double-beam configuration, we employ either a non-resonant line or a resonant line with low cross section from the same hollow cathode lamp as the reference for nearly perfect background correction and baseline drift removal. This setup also significantly shortens the warm-up time needed compared to other sensor technologies and drastically reduces the noise coming from the surrounding environment. In addition, the high-resolution spectrometer allows the most sensitive resonant line to be isolated and used to provide excellent signal-to-noise ratio.

  8. Characterization of Si volume- and delta-doped InGaAs grown by molecular beam epitaxy

    SciTech Connect

    Fedoryshyn, Y.; Kaspar, P.; Jaeckel, H.; Beck, M.

    2010-05-15

    Bulk InGaAs layers were grown at 400 deg. C lattice-matched to InP semi-insulating substrates by molecular beam epitaxy. Si doping of the layers was performed by applying volume- and delta-doping techniques. The samples were characterized by capacitance-voltage, van der Pauw-Hall, secondary ion mass spectroscopy and photoluminescence measurements. Good agreement in terms of dependence of mobility and Burstein-Moss shift shift on doping concentration in samples doped by the two different techniques was obtained. Amphoteric behavior of Si was observed at doping concentrations higher than {approx}2.9x10{sup 19} cm{sup -3} in both delta- and volume-doped samples. Degradation of InGaAs crystalline quality occurred in samples with Si concentrations higher than {approx}4x10{sup 19} cm{sup -3}.

  9. Ferromagnetism in Ge{sub 1-x}Cr{sub x}Te epilayers grown by molecular beam epitaxy

    SciTech Connect

    Fukuma, Y.; Asada, H.; Taya, T.; Irisa, T.; Koyanagi, T.

    2006-10-09

    IV-VI ferromagnetic semiconductor Ge{sub 1-x}Cr{sub x}Te has been grown on BaF{sub 2} (111) by molecular beam epitaxy. The ferromagnetism was clearly established by direct magnetization and Hall measurements. The experimental correlation between the anomalous Hall resistivity {rho}{sub xy} and the resistivity {rho}{sub xx}, {rho}{sub xy}{proportional_to}{rho}{sub xx}{sup 1.76}, is understood from the semiclassical nature of the charge carrier dynamics, suggesting that the ferromagnetism gives rise to p-d exchange interaction. The Curie temperature increases systematically from the substrate temperature T{sub S} of 300 to 250 to 200 deg. C and with increasing the Cr composition along with each T{sub S}.

  10. Molecular beam epitaxy engineered III-V semiconductor structures for low-power optically addressed spatial light modulators

    NASA Technical Reports Server (NTRS)

    Larsson, Anders G.; Maserjian, Joseph

    1992-01-01

    Device approaches are investigated for optically addressed SLMs based on molecular-beam epitaxy (MBE) engineered III-V materials and structures. Strong photooptic effects can be achieved in periodically delta-doped multiple-quantum-well structures, but are still insufficient for high-contrast modulation with only single- or double-pass absorption through active layers of practical thickness. The asymmetric Fabry-Perot cavity approach is employed to permit extinction of light due to interference of light reflected from the front and back surfaces of the cavity. This approach is realized with an all-MBE-grown structure consisting of GaAs/AlAs quarter-wave stack reflector grown over the GaAs substrate as the high reflectance mirror and the GaAs surface as the low reflectance mirror. High-contrast modulation is achieved using a low-power InGaAs/GaAs quantum well laser for the control signal.

  11. Selective-area growth of heavily n-doped GaAs nanostubs on Si(001) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chang, Yoon Jung; Simmonds, Paul J.; Beekley, Brett; Goorsky, Mark S.; Woo, Jason C. S.

    2016-04-01

    Using an aspect ratio trapping technique, we demonstrate molecular beam epitaxy of GaAs nanostubs on Si(001) substrates. Nanoholes in a SiO2 mask act as a template for GaAs-on-Si selective-area growth (SAG) of nanostubs 120 nm tall and ≤100 nm in diameter. We investigate the influence of growth parameters including substrate temperature and growth rate on SAG. Optimizing these parameters results in complete selectivity with GaAs growth only on the exposed Si(001). Due to the confined-geometry, strain and defects in the GaAs nanostubs are restricted in lateral dimensions, and surface energy is further minimized. We assess the electrical properties of the selectively grown GaAs nanostubs by fabricating heterogeneous p+-Si/n+-GaAs p-n diodes.

  12. Molecular beam epitaxial growth of intermediate-band materials based on GaAs:N δ-doped superlattices

    NASA Astrophysics Data System (ADS)

    Suzuki, Tomoya; Osada, Kazuki; Yagi, Shuhei; Naitoh, Shunya; Shoji, Yasushi; Hijikata, Yasuto; Okada, Yoshitaka; Yaguchi, Hiroyuki

    2015-08-01

    We fabricated GaAs:N δ-doped superlattices (SLs) by molecular beam epitaxy and investigated their potential as an intermediate-band photoabsorber in high-efficiency solar cells. The N area concentration in a N δ-doped layer was well controlled by adjusting the fabrication conditions, and the SLs with the average N composition of up to 1.5% were obtained. The SL minibands related to the N-induced E+ and E- conduction subbands were formed with well-separated bottom energies of up to 0.4 eV, indicating the suitability of this material system for use in intermediate-band solar cells. A two-step photoabsorption process in a solar cell with the SL absorber was successfully demonstrated through external quantum efficiency measurements under additional infrared illumination at room temperature.

  13. Formation of GaN quantum dots by molecular beam epitaxy using NH{sub 3} as nitrogen source

    SciTech Connect

    Damilano, B. Brault, J.; Massies, J.

    2015-07-14

    Self-assembled GaN quantum dots (QDs) in Al{sub x}Ga{sub 1−x}N (0.3 ≤ x ≤ 1) were grown on c-plane sapphire and Si (111) substrates by molecular beam epitaxy using ammonia as nitrogen source. The QD formation temperature was varied from 650 °C to 800 °C. Surprisingly, the density and size of QDs formed in this temperature range are very similar. This has been explained by considering together experimental results obtained from reflection high-energy electron diffraction, atomic force microscopy, and photoluminescence to discuss the interplay between thermodynamics and kinetics in the QD formation mechanisms. Finally, possible ways to better control the QD optical properties are proposed.

  14. Antimony incorporation in InAs quantum dots grown on GaAs substrate by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Rihani, J.; Sallet, V.; Christophe, H. J.; Oueslati, M.; Chtourou, R.

    2008-01-01

    We have grown InAs(Sb) quantum dots (QDs) on GaAs (0 0 1) substrates by molecular beam epitaxy (MBE) using two different antimony exposures ( ΦSb). Atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy were carried out to investigate the dot size evolution as function of the incorporated antimony content in InAs/GaAs QDs material. Anomalous asymmetric-band feature was observed in room temperature photoluminescence (RTPL) spectra of the investigated QD samples grown at relatively high temperature (490 °C). From the temperature-dependent PL measurements, it was found that the asymmetric-band feature is associated with the ground-states transitions from QDs with bimodal size distribution. The analysis of the pump power dependent PL spectra allows us to suggest a type II band lineup for the InAsSb/GaAs QDs materials system.

  15. Nanoclusters of CaSe in calcium-doped Bi2Se3 grown by molecular-beam epitaxy.

    PubMed

    Shang, Panju; Guo, Xin; Zhao, Bao; Dai, Xianqi; Bin, Li; Jia, Jinfeng; Li, Quan; Xie, Maohai

    2016-02-26

    In calcium (Ca) doped Bi2Se3 films grown by molecular beam epitaxy, nanoclusters of CaSe are revealed by high-angle annular dark field imaging and energy dispersive x-ray spectroscopy analysis using a scanning transmission electron microscope. As the interface between the ordinary insulator CaSe and topological insulator, Bi2Se3, can host topological nontrivial interface state, this represents an interesting material system for further studies. We show by first principles total energy calculations that aggregation of Ca atoms in Bi2Se3 is driven by energy minimization and a preferential intercalation of Ca in the van der Waals gap between quintuple layers of Bi2Se3 induces reordering of atomic stacking and causes an increasing amount of stacking faults in film. The above findings also provide an explanation of less-than-expected electrical carrier (hole) concentrations in Ca-doped samples. PMID:26808586

  16. Nanoclusters of CaSe in calcium-doped Bi2Se3 grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Shang, Panju; Guo, Xin; Zhao, Bao; Dai, Xianqi; Bin, Li; Jia, Jinfeng; Li, Quan; Xie, Maohai

    2016-02-01

    In calcium (Ca) doped Bi2Se3 films grown by molecular beam epitaxy, nanoclusters of CaSe are revealed by high-angle annular dark field imaging and energy dispersive x-ray spectroscopy analysis using a scanning transmission electron microscope. As the interface between the ordinary insulator CaSe and topological insulator, Bi2Se3, can host topological nontrivial interface state, this represents an interesting material system for further studies. We show by first principles total energy calculations that aggregation of Ca atoms in Bi2Se3 is driven by energy minimization and a preferential intercalation of Ca in the van der Waals gap between quintuple layers of Bi2Se3 induces reordering of atomic stacking and causes an increasing amount of stacking faults in film. The above findings also provide an explanation of less-than-expected electrical carrier (hole) concentrations in Ca-doped samples.

  17. Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

    NASA Astrophysics Data System (ADS)

    Ahmed, Adam S.; Wen, Hua; Ohta, Taisuke; Pinchuk, Igor V.; Zhu, Tiancong; Beechem, Thomas; Kawakami, Roland K.

    2016-08-01

    We report the successful growth of high-quality SrO films on highly-ordered pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy. The SrO layers have (001) orientation as confirmed by X-ray diffraction (XRD) while atomic force microscopy measurements show continuous pinhole-free films having rms surface roughness of <1.5 Å. Transport measurements of exfoliated graphene after SrO deposition show a strong dependence between the Dirac point and Sr oxidation. Subsequently, the SrO is leveraged as a buffer layer for more complex oxide integration via the demonstration of (001) oriented SrTiO3 grown atop a SrO/HOPG stack.

  18. p-type ZnO films with solid-source phosphorus doping by molecular-beam epitaxy

    SciTech Connect

    Xiu, F.X.; Yang, Z.; Mandalapu, L.J.; Liu, J.L.; Beyermann, W. P.

    2006-01-30

    Phosphorus-doped p-type ZnO films were grown on r-plane sapphire substrates using molecular-beam epitaxy with a solid-source GaP effusion cell. X-ray diffraction spectra and reflection high-energy electron diffraction patterns indicate that high-quality single crystalline (1120) ZnO films were obtained. Hall and resistivity measurements show that the phosphorus-doped ZnO films have high hole concentrations and low resistivities at room temperature. Photoluminescence (PL) measurements at 8 K reveal a dominant acceptor-bound exciton emission with an energy of 3.317 eV. The acceptor energy level of the phosphorus dopant is estimated to be 0.18 eV above the valence band from PL spectra, which is also consistent with the temperature dependence of PL measurements.

  19. Contactless electroreflectance studies of surface potential barrier for N- and Ga-face epilayers grown by molecular beam epitaxy

    SciTech Connect

    Kudrawiec, R.; Janicki, L.; Gladysiewicz, M.; Misiewicz, J.; Cywinski, G.; Boćkowski, M.; Muzioł, G.

    2013-07-29

    Two series of N- and Ga-face GaN Van Hoof structures were grown by plasma-assisted molecular beam epitaxy to study the surface potential barrier by contactless electroreflectance (CER). A clear CER resonance followed by strong Franz-Keldysh oscillation of period varying with the thickness of undoped GaN layer was observed for these structures. This period was much shorter for N-polar structures that means smaller surface potential barrier in these structures than in Ga-polar structures. From the analysis of built-in electric field it was determined that the Fermi-level is located 0.27 ± 0.05 and 0.60 ± 0.05 eV below the conduction band for N- and Ga-face GaN surface, respectively.

  20. High Growth Rate Metal-Organic Molecular Beam Epitaxy for the Fabrication of GaAs Space Solar Cells

    NASA Technical Reports Server (NTRS)

    Freundlich, A.; Newman, F.; Monier, C.; Street, S.; Dargan, P.; Levy, M.

    2005-01-01

    In this work it is shown that high quality GaAs photovoltaic devices can be produced by Molecular Beam Epitaxy (MBE) with growth rates comparable to metal-organic chemical vapor deposition (MOCVD) through the subsitution of group III solid sources by metal-organic compounds. The influence the III/V flux-ratio and growth temperatures in maintaining a two dimensional layer by layer growth mode and achieving high growth rates with low residual background impurities is investigated. Finally subsequent to the study of the optimization of n- and p doping of such high growth rate epilayers, results from a preliminary attempt in the fabrication of GaAs photovoltaic devices such as tunnel diodes and solar cells using the proposed high growth rate approach are reported.

  1. Photoluminescence enhancement in quaternary III-nitrides alloys grown by molecular beam epitaxy with increasing Al content

    SciTech Connect

    Fernandez-Garrido, S.; Pereiro, J.; Gonzalez-Posada, F.; Munoz, E.; Calleja, E.

    2008-02-15

    Room temperature photoluminescence and optical absorption spectra have been measured in wurtzite In{sub x}Al{sub y}Ga{sub 1-x-y}N (x{approx}0.06, 0.02molecular beam epitaxy. Photoluminescence spectra show both an enhancement of the integrated intensity and an increasing Stokes shift with the Al content. Both effects arise from an Al-enhanced exciton localization revealed by the S- and W-shaped temperature dependences of the photoluminescence emission energy and bandwidth, respectively. Present results point to these materials as a promising choice for the active region in efficient light emitters. An In-related bowing parameter of 1.6 eV was derived from optical absorption data.

  2. Polarity control and transport properties of Mg-doped (0001) InN by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Choi, Soojeong; Wu Feng; Bierwagen, Oliver; Speck, James S.

    2013-05-15

    The authors report on the plasma-assisted molecular beam epitaxy growth and carrier transport of Mg-doped In-face (0001) InN. The 1.2 {mu}m thick InN films were grown on GaN:Fe templates under metal rich conditions with Mg concentration from 1 Multiplication-Sign 10{sup 17}/cm{sup 3} to 3 Multiplication-Sign 10{sup 20}/cm{sup 3}. A morphological transition, associated with the formation of V-shape polarity inversion domains, was observed at Mg concentration over 7 Multiplication-Sign 10{sup 19}/cm{sup 3} by atomic force microscopy and transmission electron microscopy. Seebeck measurements indicated p-type conductivity for Mg-concentrations from 9 Multiplication-Sign 10{sup 17}/cm{sup 3} to 7 Multiplication-Sign 10{sup 19}/cm{sup 3}, i.e., as it exceeded the compensating (unintentional) donor concentration.

  3. Defect study in molecular beam epitaxy-grown HgCdTe films with activated and unactivated arsenic

    SciTech Connect

    Izhnin, I. I.; Dvoretsky, S. A.; Mikhailov, N. N.; Varavin, V. S.; Mynbaev, K. D.; Fitsych, O. I.; Pociask-Bialy, M.; Sheregii, E.; Voitsekhovskii, A. V.

    2014-04-28

    A defect study was performed on molecular beam epitaxy-grown HgCdTe films in situ doped with arsenic. Doping was performed from either effusion cell or cracker cell, and studied were both as-grown samples and samples subjected to arsenic activation annealing. Electrical properties of the films were investigated with the use of ion milling as a means of “stirring” defects in the material. As a result of the study, it was confirmed that the most efficient incorporation of electrically active arsenic occurs at the cracking zone temperature of 700 °C. Interaction between arsenic and tellurium during the growth was observed and is discussed in the paper.

  4. InGaN/GaN self-organized quantum dot lasers grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Banerjee, Animesh; Frost, Thomas; Jahangir, Shafat; Stark, Ethan; Bhattacharya, Pallab

    2013-09-01

    Blue-and green-emitting quantum dots have been characterized and ridge waveguide lasers incorporating such quantum dots into the active region have been realized. The laser heteroscturctures were grown by plasma assisted molecular beam epitaxy. Injected carrier lifetimes in the quantum dots have also been measured by temperature dependent and time resolved photoluminescence. A threshold current density of 930 A/cm2 in the blue-emitting lasers was measured under pulsed bias. A tunnel injection scheme to inject holes has been incorporated in the design of the green quantum dot lasers, and a threshold current density of 945 A/cm2 in the green-emitting lasers has been measured under pulsed bias. Slope efficiencies of 0.41 W/A and 0.25 W/A have been measured, corresponding to differential quantum efficiencies of 13.9% and 11.3%, in the blue and green lasers, respectively.

  5. Electrical performance of phase change memory cells with Ge3Sb2Te6 deposited by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Boschker, Jos E.; Boniardi, Mattia; Redaelli, Andrea; Riechert, Henning; Calarco, Raffaella

    2015-01-01

    Here, we report on the electrical characterization of phase change memory cells containing a Ge3Sb2Te6 (GST) alloy grown in its crystalline form by Molecular Beam Epitaxy (MBE). It is found that the high temperature growth on the amorphous substrate results in a polycrystalline film exhibiting a rough surface with a grain size of approximately 80-150 nm. A detailed electrical characterization has been performed, including I-V characteristic curves, programming curves, set operation performance, crystallization activation at low temperature, and resistance drift, in order to determine the material related parameters. The results indicate very good alignment of the electrical parameters with the current state-of-the-art GST, deposited by physical vapor deposition. Such alignment enables a possible employment of the MBE deposition technique for chalcogenide materials in the phase change memory technology, thus leading to future studies of as-deposited crystalline chalcogenides as integrated in electrical vehicles.

  6. Formation of strained interfaces in AlSb/InAs multilayers grown by molecular beam epitaxy for quantum cascade lasers

    SciTech Connect

    Nicolaï, J.; Warot-Fonrose, B.; Gatel, C. Ponchet, A.; Teissier, R.; Baranov, A. N.; Magen, C.

    2015-07-21

    Structural and chemical properties of InAs/AlSb interfaces have been studied by transmission electron microscopy. InAs/AlSb multilayers were grown by molecular beam epitaxy with different growth sequences at interfaces. The out-of-plane strain, determined using high resolution microscopy and geometrical phase analysis, has been related to the chemical composition of the interfaces analyzed by high angle annular dark field imaging. Considering the local strain and chemistry, we estimated the interface composition and discussed the mechanisms of interface formation for the different growth sequences. In particular, we found that the formation of the tensile AlAs-type interface is spontaneously favored due to its high thermal stability compared to the InSb-type interface. We also showed that the interface composition could be tuned using an appropriate growth sequence.

  7. High quality CuInSe2 films grown on pseudo-lattice-matched substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Niki, S.; Fons, P. J.; Yamada, A.; Kurafuji, T.; Chichibu, S.; Nakanishi, H.; Bi, W. G.; Tu, C. W.

    1996-07-01

    CuInSe2 films have been grown by molecular beam epitaxy on pseudo-lattice-matched substrates that consist of a 1-μm-thick In0.29Ga0.71As layer grown on a linearly composition-graded InxGa1-xAs buffer (0≤x≤0.29) grown in turn on GaAs (001). The properties of these films have been compared with those of the films grown directly on GaAs (001). High resolution x-ray diffraction analysis on CuInSe2 grown on pseudo-lattice-matched substrates indicated substantial reduction on residual strain in the CuInSe2 films. A photoluminescence spectrum dominated by sharp free exciton emissions has been observed for the first time from CuInSe2 films indicative of significant improvement in crystalline quality and substantial reduction in the point defect density.

  8. Growth of ErAs nanodots by molecular beam epitaxy for application to tunneling junctions in multijunction solar cells

    NASA Astrophysics Data System (ADS)

    Hung, Chao-Yu; Sogabe, Tomah; Miyashita, Naoya; Okada, Yoshitaka

    2016-02-01

    ErAs nanodots (NDs) grown on GaAs(001) substrates by using molecular beam epitaxy (MBE) were investigated. Atomic force microscope images indicate that the size of ErAs NDs increases with deposition time and growth temperature. A calibration was performed to determine the deposition rate of ErAs in order that the size of NDs can be accurately controlled and hence optimized. Local current flow images and surface profiles around ErAs NDs were simultaneously measured to clarify the local conductivity distribution corresponding to a real space profile. Furthermore, we also fabricated and characterized an ErAs-ND-embedded GaAs tunnel junction (TJ), which resulted in a voltage drop of 30 mV for 15 A/cm2 operation current equivalent to 1000 suns concentration, which is less than one-third of that of a conventional heavily doped tunnel junction.

  9. Characterization of deep acceptor level in as-grown ZnO thin film by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Asghar, M.; K., Mahmood; A. Hasan, M.; T. Ferguson, I.; Tsu, R.; Willander, M.

    2014-09-01

    We report deep level transient spectroscopy results from ZnO layers grown on silicon by molecular beam epitaxy (MBE). The hot probe measurements reveal mixed conductivity in the as-grown ZnO layers, and the current—voltage (I—V) measurements demonstrate a good quality p-type Schottky device. A new deep acceptor level is observed in the ZnO layer having activation energy of 0.49 ±0.03 eV and capture cross-section of 8.57 × 10-18 cm2. Based on the results from Raman spectroscopy, photoluminescence, and secondary ion mass spectroscopy (SIMS) of the ZnO layer, the observed acceptor trap level is tentatively attributed to a nitrogen-zinc vacancy complex in ZnO.

  10. Room temperature Ultraviolet B emission from InAlGaN films synthesized by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Kong, W. Jiao, W. Y.; Kim, T. H.; Brown, A. S.; Roberts, A. T.; Fournelle, J.; Losurdo, M.; Everitt, H. O.

    2015-09-28

    Thin films of the wide bandgap quaternary semiconductor In{sub x}Al{sub y}Ga{sub (1−x−y)}N with low In (x = 0.01–0.05) and high Al composition (y = 0.40–0.49) were synthesized on GaN templates by plasma-assisted molecular beam epitaxy. High-resolution X-ray diffraction was used to correlate the strain accommodation of the films to composition. Room temperature ultraviolet B (280 nm–320 nm) photoluminescence intensity increased with increasing In composition, while the Stokes shift remained relatively constant. The data suggest a competition between radiative and non-radiative recombination occurs for carriers, respectively, localized at centers produced by In incorporation and at dislocations produced by strain relaxation.

  11. Low-relaxation spin waves in laser-molecular-beam epitaxy grown nanosized yttrium iron garnet films

    NASA Astrophysics Data System (ADS)

    Lutsev, L. V.; Korovin, A. M.; Bursian, V. E.; Gastev, S. V.; Fedorov, V. V.; Suturin, S. M.; Sokolov, N. S.

    2016-05-01

    Synthesis of nanosized yttrium iron garnet (Y3Fe5O12, YIG) films followed by the study of ferromagnetic resonance (FMR) and spin wave propagation in these films is reported. The YIG films were grown on gadolinium gallium garnet substrates by laser molecular beam epitaxy. It has been shown that spin waves propagating in YIG deposited at 700 °C have low damping. At the frequency of 3.29 GHz, the spin-wave damping parameter is less than 3.6 × 10-5. Magnetic inhomogeneities of the YIG films give the main contribution to the FMR linewidth. The contribution of the relaxation processes to the FMR linewidth is as low as 1.2%.

  12. In silico carbon molecular beam epitaxial growth of graphene on the h-BN substrate: carbon source effect on van der Waals epitaxy

    NASA Astrophysics Data System (ADS)

    Lee, Jonghoon; Varshney, Vikas; Park, Jeongho; Farmer, Barry L.; Roy, Ajit K.

    2016-05-01

    Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon molecular beam epitaxy (CMBE) techniques using solid carbon sublimation have reported relatively poor quality of the graphene. In this article, the CMBE growth of graphene on the h-BN substrate is numerically studied in order to identify the effect of the carbon source on the quality of the graphene film. The carbon molecular beam generated by the sublimation of solid carbon source materials such as graphite and glassy carbon is mostly composed of atomic carbon, carbon dimers and carbon trimers. Therefore, the graphene film growth becomes a complex process involving various deposition characteristics of a multitude of carbon entities. Based on the study of surface adsorption and film growth characteristics of these three major carbon entities comprising graphite vapour, we report that carbon trimers convey strong traits of vdW epitaxy prone to high quality graphene growth, while atomic carbon deposition is a surface-reaction limited process accompanied by strong chemisorption. The vdW epitaxial behaviour of carbon trimers is found to be substantial enough to nucleate and develop into graphene like planar films within a nanosecond of high flux growth simulation, while reactive atomic carbons tend to impair the structural integrity of the crystalline h-BN substrate upon deposition to form an amorphous interface between the substrate and the growing carbon film. The content of reactive atomic carbons in the molecular beam is suspected to be the primary cause of low quality graphene reported in the literature. A possible optimization of the molecular beam composition towards the synthesis of better quality graphene films is suggested.Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon

  13. In silico carbon molecular beam epitaxial growth of graphene on the h-BN substrate: carbon source effect on van der Waals epitaxy

    NASA Astrophysics Data System (ADS)

    Lee, Jonghoon; Varshney, Vikas; Park, Jeongho; Farmer, Barry L.; Roy, Ajit K.

    2016-05-01

    Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon molecular beam epitaxy (CMBE) techniques using solid carbon sublimation have reported relatively poor quality of the graphene. In this article, the CMBE growth of graphene on the h-BN substrate is numerically studied in order to identify the effect of the carbon source on the quality of the graphene film. The carbon molecular beam generated by the sublimation of solid carbon source materials such as graphite and glassy carbon is mostly composed of atomic carbon, carbon dimers and carbon trimers. Therefore, the graphene film growth becomes a complex process involving various deposition characteristics of a multitude of carbon entities. Based on the study of surface adsorption and film growth characteristics of these three major carbon entities comprising graphite vapour, we report that carbon trimers convey strong traits of vdW epitaxy prone to high quality graphene growth, while atomic carbon deposition is a surface-reaction limited process accompanied by strong chemisorption. The vdW epitaxial behaviour of carbon trimers is found to be substantial enough to nucleate and develop into graphene like planar films within a nanosecond of high flux growth simulation, while reactive atomic carbons tend to impair the structural integrity of the crystalline h-BN substrate upon deposition to form an amorphous interface between the substrate and the growing carbon film. The content of reactive atomic carbons in the molecular beam is suspected to be the primary cause of low quality graphene reported in the literature. A possible optimization of the molecular beam composition towards the synthesis of better quality graphene films is suggested.Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon

  14. Structural and ferroelectric properties of BaTiO 3/YBa 2Cu 3O 7 heterostructures prepared by laser molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, H. S.; Liu, Y. W.; Ma, K.; Peng, Z. Q.; Cui, D. F.; Lu, H. B.; Zhou, Y. L.; Chen, Z. H.; Li, L.; Yang, G. Z.

    1997-08-01

    Heteroepitaxial BaTiO 3(BTO)/YBa 2Cu 3O 7(YBCO) thin films were grown on (100) SrTiO 3(STO) substrates by ozone assistant laser molecular beam epitaxy (L sbnd MBE). The results show that by using this technique, high quality ferroelectric/superconductor heterostructures with high crystalline quality and desirable device performance can be obtained.

  15. Fabrication of GeSn-multiple quantum wells by overgrowth of Sn on Ge by using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Oliveira, F.; Fischer, I. A.; Benedetti, A.; Zaumseil, P.; Cerqueira, M. F.; Vasilevskiy, M. I.; Stefanov, S.; Chiussi, S.; Schulze, J.

    2015-12-01

    We report on the fabrication and structural characterization of epitaxially grown ultra-thin layers of Sn on Ge virtual substrates (Si buffer layer overgrown by a 50 nm thick Ge epilayer followed by an annealing step). Samples with 1 to 5 monolayers of Sn on Ge virtual substrates were grown using solid source molecular beam epitaxy and characterized by atomic force microscopy. We determined the critical thickness at which the transition from two-dimensional to three-dimensional growth occurs. This transition is due to the large lattice mismatch between Ge and Sn (≈14.7%). By depositing Ge on top of Sn layers, which have thicknesses at or just below the critical thickness, we were able to fabricate ultra-narrow GeSn multi-quantum-well structures that are fully embedded in Ge. We report results on samples with one and ten GeSn wells separated by 5 and 10 nm thick Ge spacer layers that were characterized by high resolution transmission electron microscopy and X-ray diffraction. We discuss the structure and material intermixing observed in the samples.

  16. Fabrication of GeSn-multiple quantum wells by overgrowth of Sn on Ge by using molecular beam epitaxy

    SciTech Connect

    Oliveira, F.; Fischer, I. A.; Schulze, J.; Benedetti, A.; Zaumseil, P.; Cerqueira, M. F.; Vasilevskiy, M. I.; Stefanov, S.; Chiussi, S.

    2015-12-28

    We report on the fabrication and structural characterization of epitaxially grown ultra-thin layers of Sn on Ge virtual substrates (Si buffer layer overgrown by a 50 nm thick Ge epilayer followed by an annealing step). Samples with 1 to 5 monolayers of Sn on Ge virtual substrates were grown using solid source molecular beam epitaxy and characterized by atomic force microscopy. We determined the critical thickness at which the transition from two-dimensional to three-dimensional growth occurs. This transition is due to the large lattice mismatch between Ge and Sn (≈14.7%). By depositing Ge on top of Sn layers, which have thicknesses at or just below the critical thickness, we were able to fabricate ultra-narrow GeSn multi-quantum-well structures that are fully embedded in Ge. We report results on samples with one and ten GeSn wells separated by 5 and 10 nm thick Ge spacer layers that were characterized by high resolution transmission electron microscopy and X-ray diffraction. We discuss the structure and material intermixing observed in the samples.

  17. Molecular beam epitaxial growth and characterization of GaSb layers on GaAs (0 0 1) substrates

    NASA Astrophysics Data System (ADS)

    Li, Yanbo; Zhang, Yang; Zhang, Yuwei; Wang, Baoqiang; Zhu, Zhanping; Zeng, Yiping

    2012-06-01

    We report on the growth of GaSb layers on GaAs (0 0 1) substrates by molecular beam epitaxy (MBE). We investigate the influence of the GaAs substrate surface treatment, growth temperature, and V/III flux ratios on the crystal quality and the surface morphology of GaSb epilayers. Comparing to Ga-rich GaAs surface preparation, the Sb-rich GaAs surface preparation can promote the growth of higher-quality GaSb material. It is found that the crystal quality, electrical properties, and surface morphology of the GaSb epilayers are highly dependent on the growth temperature, and Sb/Ga flux ratios. Under the optimized growth conditions, we demonstrate the epitaxial growth of high quality GaSb layers on GaAs substrates. The p-type nature of the unintentionally doped GaSb is studied and from the growth conditions dependence of the hole concentrations of the GaSb, we deduce that the main native acceptor in the GaSb is the Ga antisite (GaSb) defect.

  18. Molecular Beam Epitaxial Growth and Properties of CoFe2O4 on MgO(001)

    SciTech Connect

    Chambers, Scott A.; Farrow, Robin F.; Maat, S.; Toney, M.; Folks, L.; Catalano, J.G.; Trainor, T.P.; Brown, G.E. Jr.

    2002-04-01

    We have grown single-crystal Co ferrite (CoFe2O4) on MgO(001) by oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE), and have characterized the composition, structure, surface morphology, and magnetic properties by a number of methods The as-grown OPA-MBE material forms a perfect inverse spinel, in which all Co is in the? formal oxidation state, and occupies octahedral sites within the cation sublattice. The OPA-MBE film surfaces are very flat, with mean roughnesses of only a few A, and exhibit large, stable magnetic domains. The measured moment per unit volume is 250 emu/cm3, and the saturation magnetization for films in the 1000A film thickness range is {approx}60% of that of bulk Co ferrite. The material also exhibits strain-dependent magnetic anisotropy that can be understood by considering the various contributions to the total magnetic energy. The overall quality of epitaxial Co ferrite grown on MgO by OPA-MBE is superior in every respect to that obtained using pulsed laser deposition as the growth method.

  19. NO2-assisted molecular-beam epitaxy of wustitelike and magnetitelike Fe oxynitride films on MgO(100)

    NASA Astrophysics Data System (ADS)

    Voogt, F. C.; Smulders, P. J.; Wijnja, G. H.; Niesen, L.; Fujii, T.; James, M. A.; Hibma, T.

    2001-03-01

    In an attempt to obtain wustite Fe1-xO as epitaxial films on MgO(100), NO2-assisted molecular-beam epitaxy was applied. At low NO2 fluxes, the low-energy electron diffraction and reflection high-energy electron diffraction images indeed indicate the formation of a rocksaltlike structure. In addition, Mössbauer spectroscopy provides evidence for the formation of a phase that is paramagnetic at room temperature. However, the layers are not pure oxides but are well-ordered oxynitrides with composition Fe1-xO1-yNy. The nitrogen atoms occupy substitutional sites on the oxygen-anion sublattice. Similarly, at slightly higher NO2 fluxes, magnetitelike oxynitride films with composition Fe3+δO4-yNy are obtained. By correlating x-ray photoelectron spectroscopy spectra with the intensity oscillation periods observed during reflection high-energy electron diffraction, it is possible to derive the complete stoichiometry of the films. We propose that the abrupt incorporation of nitrogen atoms only occurs if the atomic oxygen provided by the NO2 flux is insufficient to form a stoichiometric Fe3O4.

  20. Growth, nucleation, and electrical properties of molecular beam epitaxially grown, As-doped Ge on Si substrates

    SciTech Connect

    Sheldon, P.; Yacobi, B.G.; Asher, S.E.; Jones, K.M.; Hafich, M.J.; Robinson, G.Y.

    1986-05-01

    Epitaxial Ge is grown on (100)Si substrates by molecular beam epitaxy (MBE). The effect of various MBE growth conditions on both the nucleation and morphology of Ge grown on Si is studied by Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and reflection high-energy electron diffraction (RHEED). These studies indicate that, at the substrate temperatures examined (300--600 /sup 0/C), heteroepitaxy of Ge on Si favors three-dimensional growth, which is enhanced by both higher growth temperatures and substrate preparation techniques that leave residual surface contamination. Heavily doped n/sup +/ Ge layers are obtained using an elemental As source. The electrical properties of these films are evaluated by Hall--van der Pauw measurements. Growth temperatures of 250 /sup 0/C and optimum As:Ge flux ratios yield electron concentrations as high as 2.5 x 10/sup 20/ cm/sup -3/. Secondary ion mass spectroscopy (SIMS) and Hall effect data show that for As concentrations which exceed this optimum level, a decrease in both the electron concentration and drift mobility is observed, indicating the presence of electrically inactive As.

  1. Molecular beam epitaxial growth of high-quality InSb on InP and GaAs substrates

    NASA Technical Reports Server (NTRS)

    Oh, J. E.; Bhattacharya, P. K.; Chen, Y. C.; Tsukamoto, S.

    1989-01-01

    Epitaxial layers of InSb were grown on InP and GaAs substrates by molecular beam epitaxy. The dependence of the epilayer quality on flux ratio, J sub Sb4/J sub In, was studied. Deviation from an optimum value of J sub Sb4/J sub In (approx. 2) during growth led to deterioration in the surface morphology and the electrical and crystalline qualities of the films. Room temperature electron mobilities as high as 70,000 and 53,000 sq cm /V-s were measured in InSb layers grown on InP and GaAs substrates, respectively. Unlike the previous results, the conductivity in these films is n-type even at T = 13 K, and no degradation of the electron mobility due to the high density of dislocations was observed. The measured electron mobilities (and carrier concentrations) at 77 K in InSb layers grown on InP and GaAs substrates are 110,000 sq cm/V-s (3 x 10(15) cm(-3)) and 55,000 sq cm/V-s (4.95 x 10(15) cm(-3)), respectively, suggesting their application to electronic devices at cryogenic temperatures.

  2. Critical thickness and strain relaxation in molecular beam epitaxy-grown SrTiO{sub 3} films

    SciTech Connect

    Wang, Tianqi; Ganguly, Koustav; Marshall, Patrick; Xu, Peng; Jalan, Bharat

    2013-11-18

    We report on the study of the critical thickness and the strain relaxation in epitaxial SrTiO{sub 3} film grown on (La{sub 0.3}Sr{sub 0.7})(Al{sub 0.65}Ta{sub 0.35})O{sub 3} (001) (LSAT) substrate using the hybrid molecular beam epitaxy approach. No change in the film's lattice parameter (both the in-plane and the out-of-plane) was observed up to a film thickness of 180 nm, which is in sharp contrast to the theoretical critical thickness of ∼12 nm calculated using the equilibrium theory of strain relaxation. For film thicknesses greater than 180 nm, the out-of-plane lattice parameter was found to decrease hyperbolically in an excellent agreement with the relaxation via forming misfit dislocations. Possible mechanisms are discussed by which the elastic strain energy can be accommodated prior to forming misfit dislocations leading to such anomalously large critical thickness.

  3. Conduction-type control of Ge films grown on (NH 4) 2S-treated GaAs by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Inada, M.; Fujishima, T.; Umezu, I.; Sugimura, A.; Yamada, S.

    2001-07-01

    We have performed epitaxial growth of Ge films on (NH 4) 2S-treated GaAs (0 0 1) substrates under various growth temperatures using molecular beam epitaxy. We confirmed that this sulfur passivation is quite effective for preventing the oxidation of GaAs surface. Thus, the Ge films were grown epitaxially on GaAs substrate without thermal cleaning. The electric properties of Ge films were investigated using Hall measurement and it was found that the conduction type of Ge films can be controlled by growth temperature. The Ga-S bond is thought to be the key for conduction type control, although the details are not identified yet.

  4. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    SciTech Connect

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R.

    2014-04-15

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  5. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy.

    PubMed

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R

    2014-04-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  6. Crystal orientation mechanism of ZnTe epilayers formed on different orientations of sapphire substrates by molecular beam epitaxy

    SciTech Connect

    Nakasu, T. Yamashita, S.; Aiba, T.; Hattori, S.; Sun, W.; Taguri, K.; Kazami, F.; Kobayashi, M.

    2014-10-28

    The electrooptic effect in ZnTe has recently attracted research attention, and various device structures using ZnTe have been explored. For application to practical terahertz wave detector devices based on ZnTe thin films, sapphire substrates are preferred because they enable the optical path alignment to be simplified. ZnTe/sapphire heterostructures were focused upon, and ZnTe epilayers were prepared on highly mismatched sapphire substrates by molecular beam epitaxy. Epitaxial relationships between the ZnTe thin films and the sapphire substrates with their various orientations were investigated using an X-ray diffraction pole figure method. (0001) c-plane, (1-102) r-plane, (1-100) m-plane, and (11-20) a-plane oriented sapphire substrates were used in this study. The epitaxial relationship between ZnTe and c-plane sapphire was found to be (111) ZnTe//(0001) sapphire with an in-plane orientation relationship of [−211] ZnTe//[1-100] sapphire. It was found that the (211)-plane ZnTe layer was grown on the m-plane of the sapphire substrates, and the (100)-plane ZnTe layer was grown on the r-plane sapphire. When the sapphire substrates were inclined from the c-plane towards the m-axis direction, the orientation of the ZnTe thin films was then tilted from the (111)-plane to the (211)-plane. The c-plane of the sapphire substrates governs the formation of the (111) ZnTe domain and the ZnTe epilayer orientation. These crystallographic features were also related to the atom arrangements of ZnTe and sapphire.

  7. Crystal orientation mechanism of ZnTe epilayers formed on different orientations of sapphire substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Nakasu, T.; Yamashita, S.; Aiba, T.; Hattori, S.; Sun, W.; Taguri, K.; Kazami, F.; Kobayashi, M.

    2014-10-01

    The electrooptic effect in ZnTe has recently attracted research attention, and various device structures using ZnTe have been explored. For application to practical terahertz wave detector devices based on ZnTe thin films, sapphire substrates are preferred because they enable the optical path alignment to be simplified. ZnTe/sapphire heterostructures were focused upon, and ZnTe epilayers were prepared on highly mismatched sapphire substrates by molecular beam epitaxy. Epitaxial relationships between the ZnTe thin films and the sapphire substrates with their various orientations were investigated using an X-ray diffraction pole figure method. (0001) c-plane, (1-102) r-plane, (1-100) m-plane, and (11-20) a-plane oriented sapphire substrates were used in this study. The epitaxial relationship between ZnTe and c-plane sapphire was found to be (111) ZnTe//(0001) sapphire with an in-plane orientation relationship of [-211] ZnTe//[1-100] sapphire. It was found that the (211)-plane ZnTe layer was grown on the m-plane of the sapphire substrates, and the (100)-plane ZnTe layer was grown on the r-plane sapphire. When the sapphire substrates were inclined from the c-plane towards the m-axis direction, the orientation of the ZnTe thin films was then tilted from the (111)-plane to the (211)-plane. The c-plane of the sapphire substrates governs the formation of the (111) ZnTe domain and the ZnTe epilayer orientation. These crystallographic features were also related to the atom arrangements of ZnTe and sapphire.

  8. Au impact on GaAs epitaxial growth on GaAs (111)B substrates in molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Liao, Zhi-Ming; Chen, Zhi-Gang; Lu, Zhen-Yu; Xu, Hong-Yi; Guo, Ya-Nan; Sun, Wen; Zhang, Zhi; Yang, Lei; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2013-02-01

    GaAs growth behaviour under the presence of Au nanoparticles on GaAs {111}B substrate is investigated using electron microscopy. It has been found that, during annealing, enhanced Ga surface diffusion towards Au nanoparticles leads to the GaAs epitaxial growth into {113}B faceted triangular pyramids under Au nanoparticles, governed by the thermodynamic growth, while during conventional GaAs growth, growth kinetics dominates, resulting in the flatted triangular pyramids at high temperature and the epitaxial nanowires growth at relatively low temperature. This study provides an insight of Au nanoparticle impact on GaAs growth, which is critical for understanding the formation mechanisms of semiconductor nanowires.

  9. Epitaxial growth of Ruddlesden-Popper Lan+1NinO3n+1 series using reactive molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lee, June Hyuk; Tung, I.-Cheng; Moyer, Jarrett; Luo, Guangfu; Chang, Seo Hyoung; Morgan, Dane; Hong, Hawoong; Schiffer, Peter; Fong, Dillon; Freeland, John

    2014-03-01

    We report the growth of single crystalline Lan+1NinO3n+1 epitaxial thin films using reactive molecular-beam epitaxy. Ruddlesden-Popper Lan+1NinO3n+1 compounds, consisting of LaO+ and NiO2- layers, have been considered a potential candidate for solid-oxide fuel cell cathodes and thermoelectrics. However, the growth of higher order Lan+1NinO3n+1 single crystals has not been possible so far. We utilize synchrotron x-ray diffraction at the Advanced Photon Source during layer?by?layer deposition together with density functional theory calculations to understand how LaO+ and NiO2- oxide layers re-arrange dynamically during growth. Using this layer re-arrangement, epitaxial La2NiO4, La3Ni2O7,andLaSUB>4Ni3O10 films on (001)-oriented SrTiO3 have been synthesized with the proper nickel valance state and structure. Here we will discuss the connection between structure and electrical transport properties. Work at the APS, Argonne is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

  10. Study of structural properties of cubic InN films on GaAs(001) substrates by molecular beam epitaxy and migration enhanced epitaxy

    SciTech Connect

    Casallas-Moreno, Y. L.; Perez-Caro, M.; Gallardo-Hernandez, S.; Ramirez-Lopez, M.; Martinez-Velis, I.; Lopez-Lopez, M.; Escobosa-Echavarria, A.

    2013-06-07

    InN epitaxial films with cubic phase were grown by rf-plasma-assisted molecular beam epitaxy (RF-MBE) on GaAs(001) substrates employing two methods: migration-enhanced epitaxy (MEE) and conventional MBE technique. The films were synthesized at different growth temperatures ranging from 490 to 550 Degree-Sign C, and different In beam fluxes (BEP{sub In}) ranging from 5.9 Multiplication-Sign 10{sup -7} to 9.7 Multiplication-Sign 10{sup -7} Torr. We found the optimum conditions for the nucleation of the cubic phase of the InN using a buffer composed of several thin layers, according to reflection high-energy electron diffraction (RHEED) patterns. Crystallographic analysis by high resolution X-ray diffraction (HR-XRD) and RHEED confirmed the growth of c-InN by the two methods. We achieved with the MEE method a higher crystal quality and higher cubic phase purity. The ratio of cubic to hexagonal components in InN films was estimated from the ratio of the integrated X-ray diffraction intensities of the cubic (002) and hexagonal (1011) planes measured by X-ray reciprocal space mapping (RSM). For MEE samples, the cubic phase of InN increases employing higher In beam fluxes and higher growth temperatures. We have obtained a cubic purity phase of 96.4% for a film grown at 510 Degree-Sign C by MEE.

  11. Silicon sample holder for molecular beam epitaxy on pre-fabricated integrated circuits

    NASA Technical Reports Server (NTRS)

    Hoenk, Michael E. (Inventor); Grunthaner, Paula J. (Inventor); Grunthaner, Frank J. (Inventor)

    1994-01-01

    The sample holder of the invention is formed of the same semiconductor crystal as the integrated circuit on which the molecular beam expitaxial process is to be performed. In the preferred embodiment, the sample holder comprises three stacked micro-machined silicon wafers: a silicon base wafer having a square micro-machined center opening corresponding in size and shape to the active area of a CCD imager chip, a silicon center wafer micro-machined as an annulus having radially inwardly pointing fingers whose ends abut the edges of and center the CCD imager chip within the annulus, and a silicon top wafer micro-machined as an annulus having cantilevered membranes which extend over the top of the CCD imager chip. The micro-machined silicon wafers are stacked in the order given above with the CCD imager chip centered in the center wafer and sandwiched between the base and top wafers. The thickness of the center wafer is about 20% less than the thickness of the CCD imager chip. Preferably, four titanium wires, each grasping the edges of the top and base wafers, compress all three wafers together, flexing the cantilever fingers of the top wafer to accommodate the thickness of the CCD imager chip, acting as a spring holding the CCD imager chip in place.

  12. Epitaxial growth of M-plane GaN on ZnO micro-rods by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    You, Shuo-Ting; Lo, Ikai; Tsai, Jenn-Kai; Shih, Cheng-Hung

    2015-12-01

    We have studied the GaN grown on ZnO micro-rods by plasma-assisted molecular beam epitaxy. From the analyses of GaN microstructure grown on non-polar M-plane ZnO surface ( 10 1 ¯ 0 ) by scanning transmission electron microscope, we found that the ZnGa2O4 compound was formed at the M-plane hetero-interface, which was confirmed by polarization-dependent photoluminescence. We demonstrated that the M-plane ZnO micro-rod surface can be used as an alternative substrate to grow high quality M-plane GaN epi-layers.

  13. Au impact on GaAs epitaxial growth on GaAs (111){sub B} substrates in molecular beam epitaxy

    SciTech Connect

    Liao, Zhi-Ming; Chen, Zhi-Gang; Xu, Hong-Yi; Guo, Ya-Nan; Sun, Wen; Zhang, Zhi; Yang, Lei; Lu, Zhen-Yu; Chen, Ping-Ping; Lu, Wei; Zou, Jin; Centre for Microscopy and Microanalysis, The University of Queensland, St. Lucia, Queensland 4072

    2013-02-11

    GaAs growth behaviour under the presence of Au nanoparticles on GaAs {l_brace}111{r_brace}{sub B} substrate is investigated using electron microscopy. It has been found that, during annealing, enhanced Ga surface diffusion towards Au nanoparticles leads to the GaAs epitaxial growth into {l_brace}113{r_brace}{sub B} faceted triangular pyramids under Au nanoparticles, governed by the thermodynamic growth, while during conventional GaAs growth, growth kinetics dominates, resulting in the flatted triangular pyramids at high temperature and the epitaxial nanowires growth at relatively low temperature. This study provides an insight of Au nanoparticle impact on GaAs growth, which is critical for understanding the formation mechanisms of semiconductor nanowires.

  14. Crack healing during molecular-beam-epitaxy growth of GaP/GaAs thin films

    SciTech Connect

    Li, Y.; Weatherly, G.C.; Niewczas, M.

    2005-07-01

    A crack-healing phenomenon occurring during epitaxial growth of GaP films on a GaAs substrate was studied by transmission electron microscopy. The process is driven by a decrease in the surface energy of the cracked film. The results indicate that the fundamental mechanism operating during healing is the deposition and diffusion of Ga and P atoms onto the crack surface in the GaP lattice, combined with self-diffusion of GaAs within the crack tip in the GaAs substrate. This process is not fully completed in the GaP/GaAs system; unhealed crack tips located in the GaAs substrate always remain in the structure. Development of cracks and subsequent crack healing during film growth lead to a decrease in residual stress in the film. New cracks are formed at an equilibrium spacing which increases with increasing film thickness. A modified expression for predicting the relation between crack spacing and film thickness in epitaxial films is proposed.

  15. Two-step fabrication of self-catalyzed Ga-based semiconductor nanowires on Si by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Yu, Xuezhe; Li, Lixia; Wang, Hailong; Xiao, Jiaxing; Shen, Chao; Pan, Dong; Zhao, Jianhua

    2016-05-01

    For the epitaxial growth of Ga-based III-V semiconductor nanowires (NWs) on Si, Ga droplets could provide a clean and compatible solution in contrast to the common Au catalyst. However, the use of Ga droplets is rather limited except for that in Ga-catalyzed GaAs NW studies in a relatively narrow growth temperature (Ts) window around 620 °C on Si. In this paper, we have investigated the two-step growth of Ga-catalyzed III-V NWs on Si (111) substrates by molecular-beam epitaxy. First, by optimizing the surface oxide, vertically aligned GaAs NWs with a high yield are obtained at Ts = 620 °C. Then a two-temperature procedure is adopted to preserve Ga droplets at lower Ts, which leads to an extension of Ts down to 500 °C for GaAs NWs. Based on this procedure, systematic morphological and structural studies for Ga-catalyzed GaAs NWs in the largest Ts range could be presented. Then within the same growth scheme, for the first time, we demonstrate Ga-catalyzed GaAs/GaSb heterostructure NWs. These GaSb NWs are axially grown on the GaAs NW sections and are pure zinc-blende single crystals. Compositional measurements confirm that the catalyst particles indeed mainly consist of Ga and GaSb sections are of high purity but with a minor composition of As. In the end, we present GaAsSb NW growth with a tunable Sb composition. Our results provide useful information for the controllable synthesis of multi-compositional Ga-catalyzed III-V semiconductor NWs on Si for heterogeneous integration.For the epitaxial growth of Ga-based III-V semiconductor nanowires (NWs) on Si, Ga droplets could provide a clean and compatible solution in contrast to the common Au catalyst. However, the use of Ga droplets is rather limited except for that in Ga-catalyzed GaAs NW studies in a relatively narrow growth temperature (Ts) window around 620 °C on Si. In this paper, we have investigated the two-step growth of Ga-catalyzed III-V NWs on Si (111) substrates by molecular-beam epitaxy. First, by

  16. Structural and optical properties of InGaN--GaN nanowire heterostructures grown by molecular beam epitaxy

    SciTech Connect

    Limbach, F.; Gotschke, T.; Stoica, T.; Calarco, R.; Sutter, E.; Ciston, J.; Cusco, R.; Artus, L.; Kremling, S.; Hofling, S.; Worschech, L.; Grutzmacher, D.

    2011-01-01

    InGaN/GaN nanowire (NW) heterostructures grown by plasma assisted molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multifaceted InGaN cap wrapping the top part of the GaN NW. High-resolution transmission electron microscopy (HRTEM) images taken from different parts of a InGaN/GaN NW show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it, while additional crystallographic domains are observed whithin the InGaN cap region. Large changes in the lattice parameter along the wire, from pure GaN to higher In concentration demonstrate the successful growth of a complex InGaN/GaN NW heterostructure. Photoluminescence (PL) spectra of these heterostructure NW ensembles show rather broad and intense emission peak at 2.1 eV. However, μ-PL spectra measured on single NWs reveal a reduced broadening of the visible luminescence. The analysis of the longitudinal optical phonon Raman peak position and its shape reveal a variation in the In content between 20% and 30%, in agreement with the values estimated by PL and HRTEM investigations. The reported studies are important for understanding of the growth and properties of NW heterostructures suitable for applications in optoelectronics and photovoltaics.

  17. Structural and optical properties of InGaN--GaN nanowire heterostructures grown by molecular beam epitaxy

    DOE PAGESBeta

    Limbach, F.; Gotschke, T.; Stoica, T.; Calarco, R.; Sutter, E.; Ciston, J.; Cusco, R.; Artus, L.; Kremling, S.; Hofling, S.; et al

    2011-01-01

    InGaN/GaN nanowire (NW) heterostructures grown by plasma assisted molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multifaceted InGaN cap wrapping the top part of the GaN NW. High-resolution transmission electron microscopy (HRTEM) images taken from different parts of a InGaN/GaN NW show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it, while additional crystallographic domains are observed whithin the InGaN cap region. Large changes in the lattice parameter along the wire, from pure GaNmore » to higher In concentration demonstrate the successful growth of a complex InGaN/GaN NW heterostructure. Photoluminescence (PL) spectra of these heterostructure NW ensembles show rather broad and intense emission peak at 2.1 eV. However, μ-PL spectra measured on single NWs reveal a reduced broadening of the visible luminescence. The analysis of the longitudinal optical phonon Raman peak position and its shape reveal a variation in the In content between 20% and 30%, in agreement with the values estimated by PL and HRTEM investigations. The reported studies are important for understanding of the growth and properties of NW heterostructures suitable for applications in optoelectronics and photovoltaics.« less

  18. Strain relaxation in semipolar (20 2 ¯ 1 ) InGaN grown by plasma assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sawicka, M.; Kryśko, M.; Muziol, G.; Turski, H.; Siekacz, M.; Wolny, P.; Smalc-Koziorowska, J.; Skierbiszewski, C.

    2016-05-01

    Strain relaxation in semipolar (20 2 ¯ 1 ) InGaN layers grown by plasma assisted molecular beam epitaxy (PAMBE) was investigated with high-resolution X-ray diffraction (XRD) reciprocal space mapping, cathodoluminescence (CL), fluorescent light microscopy (FLM), and atomic force microscopy. We find that XRD detects lattice relaxation much later than its actual onset occurs. Other techniques used in this study allowed to detect local footprints of plastic relaxation before it was evidenced by XRD: at the initial stages of strain relaxation, we observed changes in layer morphology, i.e., formation of short trench line segments on the surface along the ⟨ 11 2 ¯ 0 ⟩ direction as well as dark lines in CL and FLM. The misfit dislocations formation and glide were observed in two slip systems: initially in basal slip system ⟨ 11 2 ¯ 0 ⟩{0001 } and for larger amount of strain in non-basal, prismatic slip system ⟨11 2 ¯ 0 ⟩{1 1 ¯ 00 } . Experimentally determined critical thickness for InGaN layers grown by PAMBE on semipolar (20 2 ¯ 1 ) bulk GaN substrates agrees well with literature data obtained with metalorganic vapor phase epitaxy and follows the Matthews-Blakeslee model prediction. We discuss the impact of substrate structural properties on the strain relaxation onset and mechanisms. We also describe the layer morphology and surface roughness evolution related to the increasing In content and strain relaxation of the semipolar (20 2 ¯ 1 ) InGaN layers.

  19. Two-step fabrication of self-catalyzed Ga-based semiconductor nanowires on Si by molecular-beam epitaxy.

    PubMed

    Yu, Xuezhe; Li, Lixia; Wang, Hailong; Xiao, Jiaxing; Shen, Chao; Pan, Dong; Zhao, Jianhua

    2016-05-19

    For the epitaxial growth of Ga-based III-V semiconductor nanowires (NWs) on Si, Ga droplets could provide a clean and compatible solution in contrast to the common Au catalyst. However, the use of Ga droplets is rather limited except for that in Ga-catalyzed GaAs NW studies in a relatively narrow growth temperature (Ts) window around 620 °C on Si. In this paper, we have investigated the two-step growth of Ga-catalyzed III-V NWs on Si (111) substrates by molecular-beam epitaxy. First, by optimizing the surface oxide, vertically aligned GaAs NWs with a high yield are obtained at Ts = 620 °C. Then a two-temperature procedure is adopted to preserve Ga droplets at lower Ts, which leads to an extension of Ts down to 500 °C for GaAs NWs. Based on this procedure, systematic morphological and structural studies for Ga-catalyzed GaAs NWs in the largest Ts range could be presented. Then within the same growth scheme, for the first time, we demonstrate Ga-catalyzed GaAs/GaSb heterostructure NWs. These GaSb NWs are axially grown on the GaAs NW sections and are pure zinc-blende single crystals. Compositional measurements confirm that the catalyst particles indeed mainly consist of Ga and GaSb sections are of high purity but with a minor composition of As. In the end, we present GaAsSb NW growth with a tunable Sb composition. Our results provide useful information for the controllable synthesis of multi-compositional Ga-catalyzed III-V semiconductor NWs on Si for heterogeneous integration. PMID:27194599

  20. Characterization of high quality InN grown on production-style plasma assisted molecular beam epitaxy system

    SciTech Connect

    Gherasoiu, I.; O'Steen, M.; Bird, T.; Gotthold, D.; Chandolu, A.; Song, D. Y.; Xu, S. X.; Holtz, M.; Nikishin, S. A.; Schaff, W. J.

    2008-05-15

    In this work, the authors report step-flow growth mode of InN on [0001] oriented GaN templates, using a production-style molecular beam epitaxy system, Veeco GEN200 registered , equipped with a plasma source. Using adaptive growth conditions, they have obtained a surface morphology that exhibits the step-flow features. The root mean squared roughness over an area of 5x5 {mu}m{sup 2} is 1.4 nm with monolayer height terrace steps (0.281 nm), based on atomic force microscopy. It has been found that the presence of In droplets leads to defective surface morphology. From x-ray diffraction, they estimate edge and screw dislocation densities. The former is dominant over the latter. Micro-Raman spectra reveal narrow E{sub 2}{sup 2} phonon lines consistent with excellent crystalline quality of the epitaxial layers. The Hall mobility of 1 {mu}m thick InN layers, grown in step-flow mode, is slightly higher than 1400 cm{sup 2}/V s, while for other growth conditions yielding a smooth surface with no well-defined steps, mobility as high as 1904 cm{sup 2}/V s at room temperature has been measured. The samples exhibit high intensity photoluminescence (PL) with a corresponding band edge that shifts with free carrier concentration. For the lowest carrier concentration of 5.6x10{sup 17} cm{sup -3}, they observe PL emission at {approx}0.64 eV.

  1. Structural and magnetic characterization of Sm-doped GaN grown by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Dehara, Kentaro; Miyazaki, Yuta; Hasegawa, Shigehiko

    2016-05-01

    We have investigated structural, optical and magnetic properties of Sm-doped GaN thin films grown by plasma-assisted molecular beam epitaxy. Reflection high-energy electron diffraction and X-ray diffraction reveal that Ga1- x Sm x N films with a SmN mole fraction of ˜8% or below are grown on GaN templates without segregation of any secondary phases. With increasing SmN mole fraction, the c-axis lattice parameter of the GaSmN films linearly increases. GaSmN films with low Sm concentrations exhibit inner-4f transitions of Sm3+ in photoluminescence spectra. The present findings show that Sm atoms are substituted for some Ga atoms as trivalent ions (Sm3+). The Ga1- x Sm x N films display hysteresis loops in magnetization versus external magnetic field (M-H) curves even at 300 K. We will discuss the origin of these features together with the corresponding temperature dependences of magnetization.

  2. Deep traps in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Hurni, C. A.; Arehart, A. R.; Yang, J.; Myers, R. C.; Speck, J. S.; Ringel, S. A.

    2012-01-01

    Deep level defects in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy were characterized using deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) and compared with polar c-plane GaN that was grown simultaneously in the same growth run. Significant differences in both the levels present and their concentrations were observed upon comparison of both growth orientations. DLTS revealed electron traps with activation energies of 0.14 eV, 0.20 eV, and 0.66 eV in the m-plane material, with concentrations that were ˜10-50 × higher than traps of similar activation energies in the c-plane material. Likewise, DLOS measurements showed ˜20 × higher concentrations of both a CN acceptor-like state at EC - 3.26 eV, which correlates with a high background carbon concentration observed by secondary ion mass spectroscopy for the m-plane material [A. Armstrong, A. R. Arehart, B. Moran, S. P. DenBaars, U. K. Mishra, J. S. Speck, and S. A. Ringel, Appl. Phys. Lett. 84, 374 (2004)], and the VGa-related state level at EC - 2.49 eV, which is consistent with an enhanced yellow luminescence observed by photoluminescence. The findings suggest a strong impact of growth dynamics on the incorporation of impurities and electrically active native point defects as a function of GaN growth plane polarity.

  3. Photoconductivity of ultra-thin Ge(GeSn) layers grown in Si by low-temperature molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Talochkin, A. B.; Chistokhin, I. B.; Mashanov, V. I.

    2016-04-01

    Photoconductivity (PC) spectra of Si/Ge(GeSn)/Si structures with the ultra-thin (1.0-2.3 nm) Ge and GeSn alloy layers grown by the low-temperature (T = 100 °C) molecular beam epitaxy are studied. Photoresponse in the range of 1.2-0.4 eV related to light absorption in the buried Ge(GeSn) layer is observed. It is shown that in case of lateral PC, a simple diffusion model can be used to determine the absorption coefficient of this layer α ˜ 105 cm-1. This value is 100 times larger than that of a single Ge quantum dot layer and is reached significantly above the band gap of most bulk semiconductors. The observed absorption is caused by optical transitions between electron and hole states localized at the interfaces. The anomalous high value of α can be explained by the unusual state of Ge(GeSn) layer with high concentration of dangling bonds, the optical properties of which have been predicted theoretically by Knief and von Niessen (Phys. Rev. B 59, 12940 (1999)).

  4. Large anomalous Hall resistance of pair {delta}-doped GaAs structures grown by molecular-beam epitaxy

    SciTech Connect

    Jung, D. W.; Noh, J. P.; Touhidul Islam, A. Z. M.; Otsuka, N.

    2008-02-15

    Beryllium/silicon pair {delta}-doped GaAs structures grown by molecular-beam epitaxy exhibit a Hall resistance which has a nonlinear dependence on the applied magnetic field and which is strongly correlated to the negative magnetoresistance observed under the applied magnetic field parallel to the {delta}-doped layers. Dependence of the occurrence of the nonlinear Hall resistance on the growth condition is investigated. A significantly large increase in both the magnitude and the nonlinearity of the Hall resistance is observed from samples whose GaAs buffer layers are grown under the condition of a low As/Ga flux ratio. Reflection high energy electron diffraction and electron microscope observations show that a faceted surface develops with the growth and postgrowth annealing of a GaAs buffer layer under the condition of a low As flux. From samples which have only Si {delta}-doped layers and exhibit the n-type conduction, such nonlinear Hall resistance is not observed. The nonlinearity of the Hall resistance of Be/Si pair {delta}-doped structures depends on the single parameter B/T, where B and T are the applied magnetic field and the temperature, respectively. Based on these results, it is suggested that the nonlinear Hall resistance of Be/Si pair {delta}-doped structures is the anomalous Hall effect caused by localized spins in {delta}-doped layers.

  5. Optical properties and structural characteristics of ZnMgO grown by plasma assisted molecular beam epitaxy

    SciTech Connect

    Wassner, Thomas A.; Laumer, Bernhard; Maier, Stefan; Stutzmann, Martin; Laufer, Andreas; Meyer, Bruno K.; Eickhoff, Martin

    2009-01-15

    Wurtzite Zn{sub 1-x}Mg{sub x}O thin films with Mg contents between x=0 and x=0.37 were grown on c-plane sapphire substrates by plasma assisted molecular beam epitaxy using a MgO/ZnMgO buffer layer. The a-lattice parameter is independent from the Mg concentration, whereas the c-lattice parameter decreases from 5.20 A for x=0 to 5.17 A for x=0.37, indicating pseudomorphic growth. The near band edge photoluminescence shows a blueshift with increasing Mg concentration to an emission energy of 4.11 eV for x=0.37. Simultaneously, the energetic position of the deep defect luminescence shows a linear shift from 2.2 to 2.8 eV. Low temperature transmission measurements reveal strong excitonic features for the investigated composition range and alloy broadening effects for higher Mg contents. The Stokes shift as well as the Urbach energy is increased to values of up to 125 and 54 meV for x=0.37, respectively, indicating exciton localization due to alloy fluctuations.

  6. InN nanorods prepared with CrN nanoislands by plasma-assisted molecular beam epitaxy

    PubMed Central

    2011-01-01

    The authors report the influence of CrN nanoisland inserted on growth of baseball-bat InN nanorods by plasma-assisted molecular beam epitaxy under In-rich conditions. By inserting CrN nanoislands between AlN nucleation layer and the Si (111) substrate, it was found that we could reduce strain form Si by inserting CrN nanoisland, FWHM of the x-ray rocking curve measured from InN nanorods from 3,299 reduced to 2,115 arcsec. It is due to the larger strain from lattice miss-match of the film-like InN structure; however, the strain from lattice miss-match was obvious reduced owing to CrN nanoisland inserted. The TEM images confirmed the CrN structures and In droplets dissociation from InN, by these results, we can speculate the growth mechanism of baseball-bat-like InN nanorods. PMID:21736722

  7. Kinetic limitation of chemical ordering in Bi2Te3-x Se x layers grown by molecular beam epitaxy.

    PubMed

    Schreyeck, S; Brunner, K; Kirchner, A; Bass, U; Grauer, S; Schumacher, C; Gould, C; Karczewski, G; Geurts, J; Molenkamp, L W

    2016-04-13

    We study the chemical ordering in Bi2Te3-x Se x grown by molecular beam epitaxy on Si substrates. We produce films in the full composition range from x  =  0 to 3, and determine their material properties using energy dispersive x-ray spectroscopy, x-ray diffraction and Raman spectroscopy. By fitting the parameters of a kinetic growth model to these results, we obtain a consistent description of growth at a microscopic level. Our main finding is that despite the incorporation of Se in the central layer being much more probable than that of Te, the formation of a fully ordered Te-Bi-Se-Bi-Te layer is prevented by kinetic of the growth process. Indeed, the Se concentration in the central layer of Bi2Te2Se1 reaches a maximum of only  ≈75% even under ideal growth conditions. A second finding of our work is that the intensity ratio of the 0 0 12 and 0 0 6 x-ray reflections serves as an experimentally accessible quantitative measure of the degree of ordering in these films. PMID:26962934

  8. Plasma assisted molecular beam epitaxy of GaN with growth rates >2.6 μm/h

    NASA Astrophysics Data System (ADS)

    McSkimming, Brian M.; Wu, F.; Huault, Thomas; Chaix, Catherine; Speck, James S.

    2014-01-01

    Plasma-assisted molecular beam epitaxial (PAMBE) growth of gallium nitride (GaN) was explored with a novel modification of a commercially available nitrogen plasma source. The modified nitrogen plasma source enabled a dramatic increase in the flux of active nitrogen and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N2 gas flow rates between 1 and 8 sccm while varying the plasma source's RF forward power from 200 to 600 W. The highest growth rate, and therefore the highest active nitrogen flux achieved was ~2.65 μm/h. For optimized growth conditions the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 μm×3 μm) on the order of 1 nm. Secondary ion mass spectroscopy (SIMS) impurity analysis demonstrates oxygen and hydrogen incorporation of 1×1016 and 5×1016 respectively, comparable to the metal organic chemical vapor deposition (MOCVD) grown template layer. Initial un-optimized electron mobility measurements of 1 μm thick GaN layers have shown a peak mobility of ~705 cm2/V s for an electron concentration of ~3.5×1016 cm-3. A revised universal growth diagram is proposed allowing the rapid determination of the metal flux needed to grow in a specific growth regime for any and all active nitrogen fluxes available.

  9. InN nanorods prepared with CrN nanoislands by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Liu, Kuang-Wei; Chang, Shoou-Jinn; Young, Sheng-Joue; Hsueh, Tao-Hung; Hung, Hung; Mai, Yu-Chun; Wang, Shih-Ming; Chen, Kuan-Jen; Wu, Ya-Ling; Chen, Yue-Zhang

    2011-07-01

    The authors report the influence of CrN nanoisland inserted on growth of baseball-bat InN nanorods by plasma-assisted molecular beam epitaxy under In-rich conditions. By inserting CrN nanoislands between AlN nucleation layer and the Si (111) substrate, it was found that we could reduce strain form Si by inserting CrN nanoisland, FWHM of the x-ray rocking curve measured from InN nanorods from 3,299 reduced to 2,115 arcsec. It is due to the larger strain from lattice miss-match of the film-like InN structure; however, the strain from lattice miss-match was obvious reduced owing to CrN nanoisland inserted. The TEM images confirmed the CrN structures and In droplets dissociation from InN, by these results, we can speculate the growth mechanism of baseball-bat-like InN nanorods.

  10. Growth of p-type and n-type m-plane GaN by molecular beam epitaxy

    SciTech Connect

    McLaurin, M.; Mates, T. E.; Wu, F.; Speck, J. S.

    2006-09-15

    Plasma-assisted molecular beam epitaxial growth of Mg-doped, p-type and Si-doped, n-type m-plane GaN on 6H m-plane SiC is demonstrated. Phase-pure, m-plane GaN films exhibiting a large anisotropy in film mosaic ({approx}0.2 deg. full width at half maximum, x-ray rocking curve scan taken parallel to [1120] versus {approx}2 deg. parallel to [0001]) were grown on m-plane SiC substrates. Maximum hole concentrations of {approx}7x10{sup 18} cm{sup -3} were achieved with p-type conductivities as high as {approx}5 {omega}{sup -1} cm{sup -1} without the presence of Mg-rich inclusions or inversion domains as viewed by cross-section transmission electron microscopy. Temperature dependent Hall effect measurements indicate that the Mg-related acceptor state in m-plane GaN is the same as that exhibited in c-plane GaN. Free electron concentrations as high as {approx}4x10{sup 18} cm{sup -3} were measured in the Si-doped m-plane GaN with corresponding mobilities of {approx}500 cm{sup 2}/V s measured parallel to the [1120] direction.

  11. Molecular beam epitaxy of CdTe and HgCdTe on large-area Si(100)

    NASA Astrophysics Data System (ADS)

    Sporken, R.; Lange, M. D.; Faurie, Jean-Pierre

    1991-09-01

    The current status of molecular beam epitaxy (MBE) of CdTe and HgCdTe on Si(100) is reviewed. CdTe and HgCdTe grow in the (111)B orientation on Si(100); monocrystalline films with two domains are obtained on most nominal Si(100) substrates, single domain films are grown on misoriented substrates and on nominal Si(100) preheated to 900-950 degree(s)C. Double-crystal x-ray rocking curves (DCRCs) with full-width at half-maximum (FWHM) as low as 110 arcsec are reported for HgCdTe on silicon; these layers are n-type, and electron mobilities higher than 5 X 104 cm2V-2s-1 are measured at 23 K for x equals 0.26. Excellent thickness and composition uniformity is obtained: standard deviation of the CdTe thickness 0.4% of the average thickness on 2-in. and 2.3% on 5-in., standard deviation of the Cd concentration in the HgCdTe layers 0.6% of the average concentration on 3-in. and 2.4% on 5-in. First results regarding growth of CdTe on patterned Si substrates are also reported.

  12. Nucleation and stochiometry dependence of rutile-TiO2 thin films grown by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Constantin, Costel; Sun, Kai; Feenstra, R. M.

    2008-03-01

    Considerable interest has been shown of late in transition-metal oxides. One case is the titanium dioxide system, which can have applications as a high-k dielectric gate insulator for Si-based devicesootnotetextZ. J. Luo et al., Appl. Phys. Lett. 79, 2803. In this study, rutile-TiO2 thin films were grown on GaN(0001) substrates by oxygen plasma-assisted molecular beam epitaxy. Two sets of films were grown, one in which the initial GaN surface is prepared WITH the pseudo 1x1 Ga-rich surface reconstruction, and the other set, WITHOUT the pseudo 1x1. On top of these two type of surfaces, the rutile-TiO2 thin films were grown at Ts˜ 600 ^oC, and with a thickness ˜ 40 - 50 nm. During growth, reflection high-energy electron diffraction indicated a reversible stoichiometry transition from O-rich to Ti-rich growth. Post-growth x-ray diffraction measurements performed on the samples WITHOUT the GaN pseudo 1x1, show the presence of additional peaks at 2θ = 52.9^o, which implies the existence of additional phases. In addition, the high-resolution transmission electron microscopy performed on these samples show a high degree of disorder, as compared to the samples prepared WITH the pseudo 1x1. Work supported by ONR.

  13. Antimony segregation in Ge and formation of n-type selectively doped Ge films in molecular beam epitaxy

    SciTech Connect

    Yurasov, D. V. Antonov, A. V.; Drozdov, M. N.; Schmagin, V. B.; Novikov, A. V.; Spirin, K. E.

    2015-10-14

    Antimony segregation in Ge(001) films grown by molecular beam epitaxy was studied. A quantitative dependence of the Sb segregation ratio in Ge on growth temperature was revealed experimentally and modeled theoretically taking into account both the terrace-mediated and step-edge-mediated segregation mechanisms. A nearly 5-orders-of-magnitude increase in the Sb segregation ratio in a relatively small temperature range of 180–350 °C was obtained, which allowed to form Ge:Sb doped layers with abrupt boundaries and high crystalline quality using the temperature switching method that was proposed earlier for Si-based structures. This technique was employed for fabrication of different kinds of n-type Ge structures which can be useful for practical applications like heavily doped n{sup +}-Ge films or δ-doped layers. Estimation of the doping profiles sharpness yielded the values of 2–5 nm per decade for the concentration gradient at the leading edge and 2–3 nm for the full-width-half-maximum of the Ge:Sb δ-layers. Electrical characterization of grown Ge:Sb structures revealed nearly full electrical activation of Sb atoms and the two-dimensional nature of charge carrier transport in δ-layers.

  14. GaN nanowires with pentagon shape cross-section by ammonia-source molecular beam epitaxy

    DOE PAGESBeta

    Lin, Yong; Leung, Benjamin; Li, Qiming; Figiel, Jeffrey J.; Wang, George T.

    2015-07-14

    In this study, ammonia-based molecular beam epitaxy (NH3-MBE) was used to grow catalyst-assisted GaN nanowires on (11¯02) r-plane sapphire substrates. Dislocation free [112¯0] oriented nanowires are formed with pentagon shape cross-section, instead of the usual triangular shape facet configuration. Specifically, the cross-section is the result of the additional two nonpolar {101¯0} side facets, which appear due to a decrease in relative growth rate of the {101¯0} facets to the {101¯1} and {101¯1} facets under the growth regime in NH3-MBE. Compared to GaN nanowires grown by Ni-catalyzed metal–organic chemical vapor deposition, the NH3-MBE grown GaN nanowires show more than an ordermore » of magnitude increase in band-edge to yellow luminescence intensity ratio, as measured by cathodoluminescence, indicating improved microstructural and optical properties.« less

  15. GaN nanowires with pentagon shape cross-section by ammonia-source molecular beam epitaxy

    SciTech Connect

    Lin, Yong; Leung, Benjamin; Li, Qiming; Figiel, Jeffrey J.; Wang, George T.

    2015-07-14

    In this study, ammonia-based molecular beam epitaxy (NH3-MBE) was used to grow catalyst-assisted GaN nanowires on (11¯02) r-plane sapphire substrates. Dislocation free [112¯0] oriented nanowires are formed with pentagon shape cross-section, instead of the usual triangular shape facet configuration. Specifically, the cross-section is the result of the additional two nonpolar {101¯0} side facets, which appear due to a decrease in relative growth rate of the {101¯0} facets to the {101¯1} and {101¯1} facets under the growth regime in NH3-MBE. Compared to GaN nanowires grown by Ni-catalyzed metal–organic chemical vapor deposition, the NH3-MBE grown GaN nanowires show more than an order of magnitude increase in band-edge to yellow luminescence intensity ratio, as measured by cathodoluminescence, indicating improved microstructural and optical properties.

  16. Metal–organic molecular beam epitaxy of GaAsNSe films using Ga droplets on GaP(001)

    NASA Astrophysics Data System (ADS)

    Shimomura, Yuki; Igarashi, Yosuke; Kimura, Shinji; Suzuki, Yuhei; Tada, Yoshihiro; Fukuda, Hisashi; Uesugi, Katsuhiro

    2016-08-01

    GaAsNSe films were grown by metal–organic molecular beam epitaxy using Ga droplets prepared on GaP(001) substrates. Ga droplets were formed on Sb-terminated GaP surfaces at a low density of 5.3 × 108 cm‑2 at a substrate temperature of 520 °C. The Ga droplets were ∼63 nm in height and ∼164 nm in diameter. At the initial growth of GaAsNSe on GaP, step-flow growth was promoted by the atomic diffusion from the Ga droplets and flat terraces spread over the surface. Although there was a large lattice mismatch of 3.5% between GaAsNSe and GaP, three-dimensional island growth and pit formation were reduced considerably by the surface diffusion of Ga. In this paper, we report the contribution of Ga droplets to the heterogrowth process of GaAsNSe/GaP.

  17. Structural, electrical, and optical characterization of coalescent p-n GaN nanowires grown by molecular beam epitaxy

    SciTech Connect

    Kolkovsky, Vl.; Zytkiewicz, Z. R.; Sobanska, M.; Klosek, K.; Korona, K. P.

    2015-12-14

    The electrical, structural, and optical properties of coalescent p-n GaN nanowires (NWs) grown by molecular beam epitaxy on Si (111) substrate are investigated. From photoluminescence measurements the full width at half maximum of bound exciton peaks AX and DA is found as 1.3 and 1.2 meV, respectively. These values are lower than those reported previously in the literature. The current-voltage characteristics show the rectification ratio of about 10{sup 2} and the leakage current of about 10{sup −4} A/cm{sup 2} at room temperature. We demonstrate that the thermionic mechanism is not dominant in these samples and spatial inhomogeneties and tunneling processes through a ∼2 nm thick SiN{sub x} layer between GaN and Si could be responsible for deviation from the ideal diode behavior. The free carrier concentration in GaN NWs determined by capacitance-voltage measurements is about 4 × 10{sup 15 }cm{sup −3}. Two deep levels (H190 and E250) are found in the structures. We attribute H190 to an extended defect located at the interface between the substrate and the SiN{sub x} interlayer or near the sidewalls at the bottom of the NWs, whereas E250 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect.

  18. Defects, strain relaxation, and compositional grading in high indium content InGaN epilayers grown by molecular beam epitaxy

    SciTech Connect

    Bazioti, C.; Kehagias, Th.; Pavlidou, E.; Komninou, Ph.; Karakostas, Th.; Dimitrakopulos, G. P.; Papadomanolaki, E.; Iliopoulos, E.; Walther, T.; Smalc-Koziorowska, J.

    2015-10-21

    We investigate the structural properties of a series of high alloy content InGaN epilayers grown by plasma-assisted molecular beam epitaxy, employing the deposition temperature as variable under invariant element fluxes. Using transmission electron microscopy methods, distinct strain relaxation modes were observed, depending on the indium content attained through temperature adjustment. At lower indium contents, strain relaxation by V-pit formation dominated, with concurrent formation of an indium-rich interfacial zone. With increasing indium content, this mechanism was gradually substituted by the introduction of a self-formed strained interfacial InGaN layer of lower indium content, as well as multiple intrinsic basal stacking faults and threading dislocations in the rest of the film. We show that this interfacial layer is not chemically abrupt and that major plastic strain relaxation through defect introduction commences upon reaching a critical indium concentration as a result of compositional pulling. Upon further increase of the indium content, this relaxation mode was again gradually succeeded by the increase in the density of misfit dislocations at the InGaN/GaN interface, leading eventually to the suppression of the strained InGaN layer and basal stacking faults.

  19. Piezoelectric InAs (211)B quantum dots grown by molecular beam epitaxy: Structural and optical properties

    SciTech Connect

    Dialynas, G. E.; Kalliakos, S.; Xenogianni, C.; Androulidaki, M.; Kehagias, T.; Komninou, P.; Savvidis, P. G.; Pelekanos, N. T.; Hatzopoulos, Z.

    2010-11-15

    The structural and optical properties of piezoelectric (211)B InAs nanostructures grown by molecular beam epitaxy are systematically investigated as a function of the various growth parameters. Depending on the specific growth conditions, we show that the InAs nanostructures take the form of a quantum dot (QD) or a quantum dash, their height ranges between 2 and 20 nm, and their density varies from a few times 10{sup 8} cm{sup -2} all the way up to a few times 10{sup 10} cm{sup -2}. The (211)B QDs are characterized by large aspect ratios, which are compatible with a truncated pyramid morphology. By analyzing the QD emission spectrum, we conclude that only small size QDs, with heights less than 3 nm, are optically active. This is consistent with high resolution transmission electron microscopy observations showing that large QDs contain misfit dislocations, whereas small QDs are dislocation-free. The formation of a two-dimensional wetting layer is observed optically, and its thickness is determined to be between 0.30 and 0.39 nm. Finally, the large blueshift in the QD emission observed with increasing excitation power represents a clear evidence of the strong built-in piezoelectric field present in these dots.

  20. Molecular beam epitaxy growth of high electron mobility InAs/AlSb deep quantum well structure

    SciTech Connect

    Wang Juan; Wang Guowei; Xu Yingqiang; Xing Junliang; Xiang Wei; Tang Bao; Zhu Yan; Ren Zhengwei; He Zhenhong; Niu Zhichuan

    2013-07-07

    InAs/AlSb deep quantum well (QW) structures with high electron mobility were grown by molecular beam epitaxy (MBE) on semi-insulating GaAs substrates. AlSb and Al{sub 0.75}Ga{sub 0.25}Sb buffer layers were grown to accommodate the lattice mismatch (7%) between the InAs/AlSb QW active region and GaAs substrate. Transmission electron microscopy shows abrupt interface and atomic force microscopy measurements display smooth surface morphology. Growth conditions of AlSb and Al{sub 0.75}Ga{sub 0.25}Sb buffer were optimized. Al{sub 0.75}Ga{sub 0.25}Sb is better than AlSb as a buffer layer as indicated. The sample with optimal Al{sub 0.75}Ga{sub 0.25}Sb buffer layer shows a smooth surface morphology with root-mean-square roughness of 6.67 A. The electron mobility has reached as high as 27 000 cm{sup 2}/Vs with a sheet density of 4.54 Multiplication-Sign 10{sup 11}/cm{sup 2} at room temperature.

  1. Kinetic limitation of chemical ordering in Bi2Te3-x Se x layers grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Schreyeck, S.; Brunner, K.; Kirchner, A.; Bass, U.; Grauer, S.; Schumacher, C.; Gould, C.; Karczewski, G.; Geurts, J.; Molenkamp, L. W.

    2016-04-01

    We study the chemical ordering in Bi2Te3-x Se x grown by molecular beam epitaxy on Si substrates. We produce films in the full composition range from x  =  0 to 3, and determine their material properties using energy dispersive x-ray spectroscopy, x-ray diffraction and Raman spectroscopy. By fitting the parameters of a kinetic growth model to these results, we obtain a consistent description of growth at a microscopic level. Our main finding is that despite the incorporation of Se in the central layer being much more probable than that of Te, the formation of a fully ordered Te-Bi-Se-Bi-Te layer is prevented by kinetic of the growth process. Indeed, the Se concentration in the central layer of Bi2Te2Se1 reaches a maximum of only  ≈75% even under ideal growth conditions. A second finding of our work is that the intensity ratio of the 0 0 12 and 0 0 6 x-ray reflections serves as an experimentally accessible quantitative measure of the degree of ordering in these films.

  2. Growth and characterization of molecular beam epitaxy-grown Bi2Te3-xSex topological insulator alloys

    NASA Astrophysics Data System (ADS)

    Tung, Y.; Chiang, Y. F.; Chong, C. W.; Deng, Z. X.; Chen, Y. C.; Huang, J. C. A.; Cheng, C.-M.; Pi, T.-W.; Tsuei, K.-D.; Li, Z.; Qiu, H.

    2016-02-01

    We report a systematic study on the structural and electronic properties of Bi2Te3-xSex topological insulator alloy grown by molecular beam epitaxy (MBE). A mixing ratio of Bi2Se3 to Bi2Te3 was controlled by varying the Bi:Te:Se flux ratio. X-ray diffraction and Raman spectroscopy measurements indicate the high crystalline quality for the as-grown Bi2Te3-xSex films. Substitution of Te by Se is also revealed from both analyses. The surfaces of the films exhibit terrace-like quintuple layers and their size of the characteristic triangular terraces decreases monotonically with increasing Se content. However, the triangular terrace structure gradually recovers as the Se content further increases. Most importantly, the angle-resolved photoemission spectroscopy results provide evidence of single-Dirac-cone like surface states in which Bi2Te3-xSex with Se/Te-substitution leads to tunable surface states. Our results demonstrate that by fine-tuned MBE growth conditions, Bi2Te3-xSex thin film alloys with tunable topological surface states can be obtained, providing an excellent platform for exploring the novel device applications based on this compound.

  3. A growth diagram for plasma-assisted molecular beam epitaxy of In-face InN

    SciTech Connect

    Gallinat, C. S.; Koblmueller, G.; Brown, J. S.; Speck, J. S.

    2007-09-15

    We investigated the role of temperature and In/N flux ratios to determine suitable growth windows for the plasma-assisted molecular beam epitaxy of In-face (0001) InN. Under vacuum, InN starts decomposing at 435 deg. C as defined by the release of N{sub 2} from the InN crystal and a buildup of an In adlayer and liquid In droplets on the sample surface. At temperatures greater than 470 deg. C, InN decomposition was characterized by a release of both In vapor and N{sub 2} in the absence of a significant accumulation of an In adlayer. No growth was observed at substrate temperatures above 500 deg. C or at temperatures in which the decomposition rates were higher than the growth rates. A growth diagram was then constructed consisting of two growth regimes: the 'In-droplet regime' characterized by step-flow growth and relatively flat surfaces and the ''N-rich regime'' characterized by rough, three-dimensional surfaces. The growth diagram can then be used to predict the surface structure of films grown at varying substrate temperatures and In fluxes. A 2.5 monolayer In adlayer was observed during In-droplet growth, suggesting that an In wetting layer was necessary for step-flow growth.

  4. O thin films with different Mg contents on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chen, W.; Pan, X. H.; Ding, P.; Zhang, H. H.; Chen, S. S.; Dai, W.; Huang, J. Y.; Lu, B.; Ye, Z. Z.

    2014-09-01

    We report the growth and characterization of a series of non-polar Zn1- x Mg x O thin films with different Mg contents, which have been prepared on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy. Structural properties are anisotropic and surfaces of films show stripes running along the c-axis direction. The films exhibit atomically smooth surface with the minimal root mean square surface roughness of 0.36 nm. Non-polar Zn1- x Mg x O thin film is much easier to obtain pure a-plane single crystal orientation when Mg content is high. The quality of the non-polar Zn1- x Mg x O thin films is evidenced by X-ray diffraction (XRD) rocking curves full-width at half-maximum of 1,350 arcsec for the () reflection and 1,760 arcsec for the () reflection, respectively. Room temperature photoluminescence peak shifts monotonously from 3.29 to 3.56 eV as Mg content increases from 0 to 0.13. Alloying with Mg is found to widen the bandgap energy of the ZnO.

  5. Structural and Magnetotransport Study of SrTiO3-δ/Si Films Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Currie, Alex; Cottier, Ryan; Villarreal, Oscar; Cantu, Jesus; Ponce, Arturo; Theodoropoulou, Nikoleta; Texas State University, San Marcos Collaboration; University of Texas, San Antonio Collaboration

    2014-03-01

    SrTiO3 (STO) films were grown on p-Si (001) substrates using molecular beam epitaxy (MBE). Oxygen vacancies were introduced by controlling the Oxygen resulting in SrTiO3-δ with δ ~ 0.02% for the lowest pressure. The single phase STO/Si films were of high crystalline quality as verified by x-ray diffraction, transmission electron microscopy, and had an rms roughness of less than 0.5nm measured by atomic force microscopy. Transport measurements were performed on the STO/Si structures in a Van der Pauw configuration. We measured resistance as a function of temperature, T = 3K-300K and as a function of an applied magnetic field , H =0 to +/- 9T. The resistivity decreased from 1 Ohm cm to 3x10-2 Ohm cm as the film thickness increased (3nm-60nm) for all temperatures. The magnetoresistance (MR) shows a reproducible trend for all films, the MR is positive at 300K, becomes negative between 200K and 100K and at low temperatures T =3-20K the MR is positive at low H =0 to +/- 2T but at high fields, it starts decreasing again. The MR behavior combined with the Hall effect data indicates the presence of localized electrons that delocalize with H and T. This research was supported by NSF Carrer Award DMR-1255629.

  6. Molecular-beam epitaxy growth and in situ arsenic doping of p-on-n HgCdTe heterojunctions

    NASA Astrophysics Data System (ADS)

    Arias, Jose; Zandian, M.; Pasko, J. G.; Shin, S. H.; Bubulac, L. O.; DeWames, R. E.; Tennant, W. E.

    1991-02-01

    In this paper we present, results on the growth of in situ doped p-on-n heterojunctions on HgCdTe epilayers grown on (211)B GaAs substrates by molecular-beam epitaxy (MBE). Long wavelength infrared (LWIR) photodiodes made with these grown junctions are of high performance. The n-type MBE HgCdTe/GaAs alloy epilayer in these structures was grown at Ts=185 °C and it was doped with indium (high 1014 cm-3 range) atoms. This epilayer was directly followed by the growth, at Ts=165 °C, of an arsenic-doped (1017-1018 cm-3 ) HgTe/CdTe superlattice structure which was necessary to incorporate the arsenic atoms as acceptors. After the structure was grown, a Hg annealing step was needed to interdiffuse the superlattice and obtain the arsenic-doped p-type HgCdTe layer above the indium-doped layer. LWIR mesa diodes made with this material have 77 K R0A values of 5×103, 81, 8.5, and 1.1 Ω cm2 for cutoff wavelengths of 8.0, 10.2, 10.8, and 13.5 μm, respectively; the 77 K quantum efficiency values for these diodes were greater than 55%. These recent results represent a significant step toward the demonstration of MBE as a viable growth technique for the in situ fabrication of large area LWIR focal plane arrays.

  7. Demonstration of isotype GaN/AlN/GaN heterobarrier diodes by NH{sub 3}-molecular beam epitaxy

    SciTech Connect

    Fireman, Micha N.; Browne, David A.; Mazumder, Baishakhi; Speck, James S.; Mishra, Umesh K.

    2015-05-18

    The results of vertical transport through nitride heterobarrier structures grown by ammonia molecular beam epitaxy are presented. Structures are designed with binary layers to avoid the effects of random alloy fluctuations in ternary nitride barriers. The unintentional incorporation of Ga in the AlN growth is investigated by atom probe tomography and is shown to be strongly dependent on both the NH{sub 3} flowrate and substrate temperature growth parameters. Once nominally pure AlN layer growth conditions are achieved, structures consisting of unintentionally doped (UID) GaN spacer layers adjacent to a nominally pure AlN are grown between two layers of n+ GaN, from which isotype diodes are fabricated. Varying the design parameters of AlN layer thickness, UID spacer layer thickness, and threading dislocation density show marked effects on the vertical transport characteristics of these structures. The lack of significant temperature dependence, coupled with Fowler-Nordheim and/or Milliken-Lauritsen analysis, point to a prevalently tunneling field emission mechanism through the AlN barrier. Once flatband conditions in the UID layer are achieved, electrons leave the barrier with significant energy. This transport mechanism is of great interest for applications in hot electron structures.

  8. Characteristics of AlN/GaN nanowire Bragg mirror grown on (001) silicon by molecular beam epitaxy

    SciTech Connect

    Heo, Junseok; Bhattacharya, Pallab; Zhou, Zifan; Guo, Wei; Ooi, Boon S.

    2013-10-28

    GaN nanowires containing AlN/GaN distributed Bragg reflector (DBR) heterostructures have been grown on (001) silicon substrate by molecular beam epitaxy. A peak reflectance of 70% with normal incidence at 560 nm is derived from angle resolved reflectance measurements on the as-grown nanowire DBR array. The measured peak reflectance wavelength is significantly blue-shifted from the ideal calculated value. The discrepancy is explained by investigating the reflectance of the nanoscale DBRs with a finite difference time domain technique. Ensemble nanowire microcavities with In{sub 0.3}Ga{sub 0.7}N nanowires clad by AlN/GaN DBRs have also been characterized. Room temperature emission from the microcavity exhibits considerable linewidth narrowing compared to that measured for unclad In{sub 0.3}Ga{sub 0.7}N nanowires. The resonant emission is characterized by a peak wavelength and linewidth of 575 nm and 39 nm, respectively.

  9. High-mobility Sb-doped p-type ZnO by molecular-beam epitaxy

    SciTech Connect

    Xiu, F.X.; Yang, Z.; Mandalapu, L.J.; Zhao, D.T.; Liu, J.L.; Beyermann, W.P.

    2005-10-10

    Reproducible Sb-doped p-type ZnO films were grown on n-Si (100) by electron-cyclotron-resonance-assisted molecular-beam epitaxy. The existence of Sb in ZnO:Sb films was confirmed by low-temperature photoluminescence measurements. An acceptor-bound exciton (A deg. X) emission was observed at 3.358 eV at 8 K. The acceptor energy level of the Sb dopant is estimated to be 0.2 eV above the valence band. Temperature-dependent Hall measurements were performed on Sb-doped ZnO films. At room temperature, one Sb-doped ZnO sample exhibited a low resistivity of 0.2 {omega} cm, high hole concentration of 1.7x10{sup 18} cm{sup -3} and high mobility of 20.0 cm{sup 2}/V s. This study suggests that Sb is an excellent dopant for reliable and reproducible p-type ZnO fabrication.

  10. Photoluminescence study on heavily donor and acceptor impurity doped GaAs layers grown by molecular-beam epitaxy

    SciTech Connect

    Islam, A. Z. M. Touhidul; Jung, D. W.; Noh, J. P.; Otsuka, N.

    2009-05-01

    Gallium arsenide layers doped with high concentrations of Be and Si by molecular-beam epitaxy are studied by photoluminescence (PL) spectroscopy. PL peaks from doped layers are observed at energies significantly lower than the band-gap of GaAs. The growth and doping conditions suggest that the origin of these peaks is different from that of low energy PL peaks, which were observed in earlier studies and attributed to impurity-vacancy complexes. The dependence of the peak energy on the temperature and the annealing is found to differ from that of the peaks attributed to impurity-vacancy complexes. On the basis of these observations, it is suggested that the low energy peaks are attributed to short range ordered arrangements of impurity ions. This possibility is examined by calculations of the PL spectra with models of pairs of acceptor and donor delta-doped layers and PL experiments of a superlattice of pairs of Be and Si delta-doped layers.

  11. Super-dense array of Ge quantum dots grown on Si(100) by low-temperature molecular beam epitaxy

    SciTech Connect

    Talochkin, A. B. Shklyaev, A. A.; Mashanov, V. I.

    2014-04-14

    Ge layer grown on Si(100) at the low temperature of ∼100 °C by molecular beam epitaxy is studied using scanning tunneling microscopy and Raman spectroscopy. It is found that crystalline and pseudomorphic to the Si substrate Ge islands are formed at the initial growth stage. The islands acquire the base size of 1.2–2.6 nm and they form arrays with the super-high density of (5–8) × 10{sup 12} cm{sup −2} at 1–2 nm Ge coverages. Such a density is at least 10 times higher than that of Ge “hut” clusters grown via the Stranski-Krastanov growth mode. It is shown that areas between the crystalline Ge islands are filled with amorphous Ge, which is suggested to create potential barrier for holes localized within the islands. As a result, crystalline Ge quantum dots appear being isolated from each other.

  12. Precipitation control and activation enhancement in boron-doped p+-BaSi2 films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Khan, M. Ajmal; Nakamura, K.; Du, W.; Toko, K.; Usami, N.; Suemasu, T.

    2014-06-01

    Precipitation free boron (B)-doped as-grown p+-BaSi2 layer is essential for the BaSi2 p-n junction solar cells. In this article, B-doped p-BaSi2 layers were grown by molecular beam epitaxy on Si(111) substrates, and the influence of substrate growth temperature (TS) and B temperature (TB) in the Knudsen cell crucible were investigated on the formation of B precipitates and the activation efficiency. The hole concentration, p, reached 1.0 × 1019 cm-3 at room temperature for TS = 600 and TB = 1550 °C. However, the activation rate of B was only 0.1%. Furthermore, the B precipitates were observed by transmission electron microscopy (TEM). When the TS was raised to 650 °C and the TB was decreased to 1350 °C, the p reached 6.8 × 1019 cm-3, and the activation rate increased to more than 20%. No precipitation of B was also confirmed by TEM.

  13. Effects of growth temperature on Mg-doped GaN grown by ammonia molecular beam epitaxy

    SciTech Connect

    Hurni, Christophe A.; Lang, Jordan R.; Burke, Peter G.; Speck, James S.

    2012-09-03

    The hole concentration p in Mg-doped GaN films grown by ammonia molecular beam epitaxy depends strongly on the growth temperature T{sub GR}. At T{sub GR}=760 Degree-Sign C, GaN:Mg films showed a hole concentration of p=1.2 Multiplication-Sign 10{sup 18} cm{sup -3} for [Mg]=4.5 Multiplication-Sign 10{sup 19} cm{sup -3}, while at T{sub GR}=840 Degree-Sign C, p=4.4 Multiplication-Sign 10{sup 16} cm{sup -3} for [Mg]=7 Multiplication-Sign 10{sup 19} cm{sup -3}. Post-growth annealing did not increase p. The sample grown at 760 Degree-Sign C exhibited a low resistivity of 0.7 {Omega}cm. The mobility for all the samples was around 3-7 cm{sup 2}/V s. Temperature-dependent Hall measurements and secondary ion mass spectroscopy suggest that the samples grown at T{sub GR}>760 Degree-Sign C are compensated by an intrinsic donor rather than hydrogen.

  14. Oxygen plasma power dependence on ZnO grown on porous silicon substrates by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Nam, Giwoong; Kim, Min Su; Kim, Do Yeob; Yim, Kwang Gug; Kim, Soaram; Kim, Sung-O.; Lee, Dong-Yul; Leem, Jae-Young; Department of Nano Systems Engineering, Center for Nano Manufacturing, Inje University, Gimhae, Gyungnam 621-749

    2012-10-15

    ZnO thin films were deposited on porous silicon by plasma-assisted molecular beam epitaxy using different radio frequency power settings. Optical emission spectrometry was applied to study the characteristics of the oxygen plasma, and the effects of the radio frequency power on the properties of the ZnO thin films were evaluated by X-ray diffraction, scanning electron microscopy, and photoluminescence. The grain sizes for radio frequency powers of 100, 200, and 300 W were 46, 48, and 62 nm, respectively. In addition, the photoluminescence intensities of the ultraviolet and the visible range increased at 300 W, because the density of the atomic oxygen transitions increased. The quality of the ZnO thin films was enhanced, but the deep-level emission peaks increased with increasing radio frequency power. The structural and optical properties of the ZnO thin films were improved at the radio frequency power of 300 W. Moreover, the optical properties of the ZnO thin films were improved with porous silicon, instead of Si.

  15. Arsenic p-Doping of HgCdTe Grown by Molecular Beam Epitaxy (MBE): A Solved Problem?

    NASA Astrophysics Data System (ADS)

    Garland, James W.; Grein, Christoph; Sivananthan, Sivalingam

    2013-11-01

    The goal of achieving well-controlled, reproducibly p-doped mercury cadmium telluride (HgCdTe) with sharp p- n junctions and low Shockley-Read-Hall contribution τ SRH to the minority carrier lifetime τ has been pursued for the past 30 years by the HgCdTe molecular beam epitaxial (MBE) growth community, but remains elusive. On the other hand, n-doping with In avoids the short τ SRH characteristic of arsenic-doped MBE-grown HgCdTe and is well controlled, stable, and reproducibly 100% activated as-grown. However, as discussed herein, because of inherent limitations of n-doped absorber layers, overcoming the challenges of successfully p-doping HgCdTe remains an important problem, especially for long-wavelength infrared detectors. We briefly review the achievements that have been made in p-doping HgCdTe, point out the reasons why achieving well-controlled, reproducibly p-doped MBE-grown HgCdTe with a lifetime τ not limited by τ SRH remains a very important task, discuss the probable origin of the short τ SRH in MBE-grown HgCdTe, and discuss possible ways to achieve much longer values of τ SRH in MBE-grown p-doped HgCdTe.

  16. Tailoring of polar and nonpolar ZnO planes on MgO (001) substrates through molecular beam epitaxy

    PubMed Central

    2012-01-01

    Polar and nonpolar ZnO thin films were deposited on MgO (001) substrates under different deposition parameters using oxygen plasma-assisted molecular beam epitaxy (MBE). The orientations of ZnO thin films were investigated by in situ reflection high-energy electron diffraction and ex situ X-ray diffraction (XRD). The film roughness measured by atomic force microscopy evolved as a function of substrate temperature and was correlated with the grain sizes determined by XRD. Synchrotron-based X-ray absorption spectroscopy (XAS) was performed to study the conduction band structures of the ZnO films. The fine structures of the XAS spectra, which were consistent with the results of density functional theory calculation, indicated that the polar and nonpolar ZnO films had different electronic structures. Our work suggests that it is possible to vary ZnO film structures from polar to nonpolar using the MBE growth technique and hence tailoring the electronic structures of the ZnO films. PACS: 81; 81.05.Dz; 81.15.Hi. PMID:22405056

  17. Semipolar and nonpolar GaN epi-films grown on m-sapphire by plasma assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Mukundan, Shruti; Mohan, Lokesh; Chandan, Greeshma; Roul, Basanta; Krupanidhi, S. B.

    2014-11-01

    We hereby report the development of non-polar epi-GaN films of usable quality, on an m-plane sapphire. Generally, it is difficult to obtain high-quality nonpolar material due to the planar anisotropic nature of the growth mode. However, we could achieve good quality epi-GaN films by involving controlled steps of nitridation. GaN epilayers were grown on m-plane (10-10) sapphire substrates using plasma assisted molecular beam epitaxy. The films grown on the nitridated surface resulted in a nonpolar (10-10) orientation while without nitridation caused a semipolar (11-22) orientation. Room temperature photoluminescence study showed that nonpolar GaN films have higher value of compressive strain as compared to semipolar GaN films, which was further confirmed by room temperature Raman spectroscopy. The room temperature UV photodetection of both films was investigated by measuring the I-V characteristics under UV light illumination. UV photodetectors fabricated on nonpolar GaN showed better characteristics, including higher external quantum efficiency, compared to photodetectors fabricated on semipolar GaN. X-ray rocking curves confirmed better crystallinity of semipolar as compared to nonpolar GaN which resulted in faster transit response of the device.

  18. High purity GaAs and Al xGa 1-xAs grown by metalorganic molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Furuhata, Naoki; Okamoto, Akihiko; Hoshino, Hitoshi

    1990-06-01

    High purity GaAs and Al xGa 1- xAs were grown by metalorganic molecular beam epitaxy (MOMBE) using metalorganic sources and arsenic (As 4). In GaAs growth using triethylgallium (TEG) and As 4, carrier concentrations depended on As 4 pressure and substrate temperatures. Below 1.5 x 10 -4 Torr As 4 pressure, the p-type carrier concentrations decreased with an increase in As 4 pressure. Above 1.5 x 10 -4 Torr As 4 pressure, the epilayer converted from p-type to n-type conductivity. Carrier concentrations decreased with a decrease in substrate temperatures. At 500°C and 1.5 x 10 -4 Torr As 4 pressure, the carrier concentration in the p-type GaAs epilayer exhibited 1.5 x 10 14 cm -3 with a room temperature mobility of 400 cm 2/V.s. Al xGa 1-xAs ( x=0.1-0. .2) was also grown using TEG, three different Al sources (triethylaluminum (TEA), trimethylaluminum (TMA) and dimethylaluminum hydride (DMAH) and As 4. Using TEG, TEA and As 4, the Al 0.15Ga 0.85As epilayer showed p-type conduction with carrier concentration of 1.2x10 15 cm -3 and mobility of 117 cm 2/V.s. This carrier concentration is the lowest value ever reported for Al xGa 1- xAs grown by MOMBE.

  19. First-principles studies on molecular beam epitaxy growth of GaAs1-xBix

    DOE PAGESBeta

    Luo, Guangfu; Yang, Shujiang; Li, Jincheng; Arjmand, Mehrdad; Szlufarska, Izabela; Brown, April S.; Kuech, Thomas F.; Morgan, Dane

    2015-07-14

    We investigate the molecular beam epitaxy (MBE) growth of GaAs1-xBix film using density functional theory with spin-orbit coupling to understand the growth of this film, especially the mechanisms of Bi incorporation. We study the stable adsorption structures and kinetics of the incident molecules (As₂ molecule, Ga atom, Bi atom, and Bi₂ molecule) on the (2 x 1)-Gasub||Bi surface and a proposed q(1 x 1)-Gasub||AsAs surface has a quasi-(1 x 1) As layer above the Ga-terminated GaAs substrate and a randomly oriented As dimer layer on top. We obtain the desorption and diffusion barriers of the adsorbed molecules and also themore » reaction barriers of three key processes related to Bi evolution, namely, Bi incorporation, As/Bi exchange, and Bi clustering. The results help explain the experimentally observed dependence of Bi incorporation on the As/Ga ratio and growth temperature. Furthermore, we find that As₂ exchange with Bi of the (2 x 1)-Gasub||Bi surface is a key step controlling the kinetics of the Bi incorporation. Finally, we explore two possible methods to enhance the Bi incorporation, namely, replacing the MBE growth mode from codeposition of all fluxes with a sequential deposition of fluxes and applying asymmetric in-plane strain to the substrate.« less

  20. Growth and optical properties of ZnTe quantum dots on ZnMgSe by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Fan, W. C.; Huang, S. H.; Chou, W. C.; Tsou, M. H.; Yang, C. S.; Chia, C. H.; Phu, Nguyen Dang; Hoang, Luc Huy

    2015-09-01

    Self-assembled type-II ZnTe quantum dots (QDs) were grown on GaAs (0 0 1) substrates with Zn1-xMgxSe (x=0.24 and 0.52) buffer layers by molecular beam epitaxy. The optical properties of ZnTe QDs were investigated by low-temperature photoluminescence (PL) and time-resolved PL. An abrupt variation of the PL peak energy with coverage implies the existence of wetting layer of 3.2 MLs and 4.0 MLs for the Mg concentration x=0.24 and 0.52, respectively. The thickness of wetting layer is larger than that of ZnTe QDs grown on ZnSe buffer layers because the strain between ZnTe and Zn1-xMgxSe is smaller. The non-mono-exponential decay profiles reflect the processes of carrier transfer and recapture. The Kohlrausch's stretching exponential well fits the decay profiles of ZnTe/Zn1-xMgxSe QDs.

  1. Growth map for Ga-assisted growth of GaAs nanowires on Si(111) substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bastiman, Faebian; Küpers, Hanno; Somaschini, Claudio; Geelhaar, Lutz

    2016-03-01

    For the Ga-assisted growth of GaAs nanowires on Si(111) substrates by molecular beam epitaxy, growth temperature, As flux, and Ga flux have been systematically varied across the entire window of growth conditions that result in the formation of nanowires. A range of GaAs structures was observed, progressing from pure Ga droplets under negligible As flux through horizontal nanowires, tilted nanowires, vertical nanowires, and nanowires without droplets to crystallites as the As flux was increased. Quantitative analysis of the resulting sample morphology was performed in terms of nanowire number and volume density, number yield and volume yield of vertical nanowires, diameter, length, as well as the number and volume density of parasitic growth. The result is a growth map that comprehensively describes all nanowire and parasitic growth morphologies and hence enables growth of nanowire samples in a predictive manner. Further analysis indicates the combination of global Ga flux and growth temperature determines the total density of all objects, whereas the global As/Ga flux ratio independently determines the resultant sample morphology. Several dependencies observed here imply that all objects present on the substrate surface, i.e. both nanowires and parasitic structures, originate from Ga droplets.

  2. Comparison of morphology evolution of Ge(001) homoepitaxial films grown by pulsed laser deposition and molecular-beam epitaxy

    SciTech Connect

    Shin Byungha; Leonard, John P.; McCamy, James W.; Aziz, Michael J.

    2005-10-31

    Using a dual molecular-beam epitaxy (MBE)-pulsed laser deposition (PLD) ultrahigh vacuum chamber, we have conducted the first experiments under identical thermal, background, and surface preparation conditions to compare Ge(001) homoepitaxial growth morphology in PLD and MBE. We find that in PLD with low kinetic energy and in MBE the film morphology evolves in a similar fashion: initially irregularly shaped mounds form, followed by pyramidal mounds with edges of the square-base along the <100> directions; the film roughness and mound separation increase with film thickness. In PLD with high kinetic energy, well-defined pyramidal mounds are not observed and the morphology rather resembles that of an ion-etched Ge(001) surface. The areal feature density is higher for PLD films than for MBE films grown at the same average growth rate and temperature. Furthermore, the dependence upon film thickness of roughness and feature separation differ for PLD and MBE. We attribute these differences to the higher yield of defect generation by energetic species in PLD.

  3. Semipolar and nonpolar GaN epi-films grown on m-sapphire by plasma assisted molecular beam epitaxy

    SciTech Connect

    Mukundan, Shruti; Mohan, Lokesh; Chandan, Greeshma; Krupanidhi, S. B.; Roul, Basanta

    2014-11-28

    We hereby report the development of non-polar epi-GaN films of usable quality, on an m-plane sapphire. Generally, it is difficult to obtain high-quality nonpolar material due to the planar anisotropic nature of the growth mode. However, we could achieve good quality epi-GaN films by involving controlled steps of nitridation. GaN epilayers were grown on m-plane (10-10) sapphire substrates using plasma assisted molecular beam epitaxy. The films grown on the nitridated surface resulted in a nonpolar (10-10) orientation while without nitridation caused a semipolar (11-22) orientation. Room temperature photoluminescence study showed that nonpolar GaN films have higher value of compressive strain as compared to semipolar GaN films, which was further confirmed by room temperature Raman spectroscopy. The room temperature UV photodetection of both films was investigated by measuring the I-V characteristics under UV light illumination. UV photodetectors fabricated on nonpolar GaN showed better characteristics, including higher external quantum efficiency, compared to photodetectors fabricated on semipolar GaN. X-ray rocking curves confirmed better crystallinity of semipolar as compared to nonpolar GaN which resulted in faster transit response of the device.

  4. Structural, electrical, and optical characterization of coalescent p-n GaN nanowires grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kolkovsky, Vl.; Zytkiewicz, Z. R.; Korona, K. P.; Sobanska, M.; Klosek, K.

    2015-12-01

    The electrical, structural, and optical properties of coalescent p-n GaN nanowires (NWs) grown by molecular beam epitaxy on Si (111) substrate are investigated. From photoluminescence measurements the full width at half maximum of bound exciton peaks AX and DA is found as 1.3 and 1.2 meV, respectively. These values are lower than those reported previously in the literature. The current-voltage characteristics show the rectification ratio of about 102 and the leakage current of about 10-4 A/cm2 at room temperature. We demonstrate that the thermionic mechanism is not dominant in these samples and spatial inhomogeneties and tunneling processes through a ˜2 nm thick SiNx layer between GaN and Si could be responsible for deviation from the ideal diode behavior. The free carrier concentration in GaN NWs determined by capacitance-voltage measurements is about 4 × 1015 cm-3. Two deep levels (H190 and E250) are found in the structures. We attribute H190 to an extended defect located at the interface between the substrate and the SiNx interlayer or near the sidewalls at the bottom of the NWs, whereas E250 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect.

  5. High-Resistivity Semi-insulating AlSb on GaAs Substrates Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Vaughan, E. I.; Addamane, S.; Shima, D. M.; Balakrishnan, G.; Hecht, A. A.

    2016-04-01

    Thin-film structures containing AlSb were grown using solid-source molecular beam epitaxy and characterized for material quality, carrier transport optimization, and room-temperature radiation detection response. Few surface defects were observed, including screw dislocations resulting from shear strain between lattice-mismatched layers. Strain was also indicated by broadening of the AlSb peak in x-ray diffraction measurements. Threading dislocations and interfacial misfit dislocations were seen with transmission electron microscopy imaging. Doping of the AlSb layer was introduced during growth using GaTe and Be to determine the effect on Hall transport properties. Hall mobility and resistivity were largest for undoped AlSb samples, at 3000 cm2/V s and 106 Ω cm, respectively, and increased doping levels progressively degraded these values. To test for radiation response, p-type/intrinsic/ n-type (PIN) diode structures were grown using undoped AlSb on n-GaAs substrates, with p-GaSb cap layers to protect the AlSb from oxidation. Alpha-particle radiation detection was achieved and spectra were produced for 241Am, 252Cf, and 239Pu sources. Reducing the detector surface area increased the pulse height observed, as expected based on voltage-capacitance relationships for diodes.

  6. Formation of long single quantum dots in high quality InSb nanowires grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Fan, Dingxun; Li, Sen; Kang, N.; Caroff, Philippe; Wang, L. B.; Huang, Y. Q.; Deng, M. T.; Yu, C. L.; Xu, H. Q.

    2015-09-01

    We report on realization and transport spectroscopy study of single quantum dots (QDs) made from InSb nanowires grown by molecular beam epitaxy (MBE). The nanowires employed are 50-80 nm in diameter and the QDs are defined in the nanowires between the source and drain contacts on a Si/SiO2 substrate. We show that highly tunable QD devices can be realized with the MBE-grown InSb nanowires and the gate-to-dot capacitance extracted in the many-electron regimes is scaled linearly with the longitudinal dot size, demonstrating that the devices are of single InSb nanowire QDs even with a longitudinal size of ~700 nm. In the few-electron regime, the quantum levels in the QDs are resolved and the Landé g-factors extracted for the quantum levels from the magnetotransport measurements are found to be strongly level-dependent and fluctuated in a range of 18-48. A spin-orbit coupling strength is extracted from the magnetic field evolutions of a ground state and its neighboring excited state in an InSb nanowire QD and is on the order of ~300 μeV. Our results establish that the MBE-grown InSb nanowires are of high crystal quality and are promising for the use in constructing novel quantum devices, such as entangled spin qubits, one-dimensional Wigner crystals and topological quantum computing devices.

  7. SiGe/Si heterojunction internal photoemission long-wavelength infrared detectors fabricated by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Lin, True-Lon; Ksendzov, A.; Dejewski, Suzan M.; Jones, Eric W.; Fathauer, Robert W.; Krabach, Timothy N.; Maserjian, Joseph

    1991-01-01

    A new SiGe/Si heterojunction internal photoemission (HIP) long-wavelength infrared (LWIR) detector has been fabricated by molecular beam epitaxy (MBE). The detection mechanism of the SiGe/Si HIP detector is infrared absorption in the degenerately doped p+-SiGe layer followed by internal photoemission of photoexcited holes over a heterojunction barrier. By adjusting the Ge concentration in the SiGe layer, and, consequently, the valence band offset between SiGe and Si, the cutoff wavelength of SiGe HIP detectors can be extended into the LWIR (8-17-micron) regime. Detectors were fabricated by growing p+-SiGe layers using MBE on patterned p-type Si substrates. The SiGe layers were boron-doped, with concentrations ranging from 10 to the 19th/cu cm to 4 x 10 to the 20th/cu cm. Infrared absorption of 5-25 percent in a 30-nm-thick p+-SiGe layer was measured in the 3-20-micron range using a Fourier transform infrared spectrometer. Quantum efficiencies of 3-5 percent have been obtained from test devices in the 8-12-micron range.

  8. An Effective Approach to Improving Cadmium Telluride (111)A Surface by Molecular-Beam-Epitaxy Growth of Tellurium Monolayer.

    PubMed

    Ren, Jie; Fu, Li; Bian, Guang; Su, Jie; Zhang, Hao; Velury, Saavanth; Yukawa, Ryu; Zhang, Longxiang; Wang, Tao; Zha, Gangqiang; Guo, Rongrong; Miller, Tom; Hasan, M Zahid; Chiang, Tai-Chang

    2016-01-13

    The surface cleansing treatment of non-natural cleavage planes of semiconductors is usually performed in vacuum using ion sputtering and subsequent annealing. In this Research Article, we report on the evolution of surface atomic structure caused by different ways of surface treatment as monitored by in situ core-level photoemission measurements of Cd-4d and Te-4d atomic levels and reflection high-energy electron diffraction (RHEED). Sputtering of surface increases the density of the dangling bonds by 50%. This feature and the less than ideal ordering can be detrimental to device applications. An effective approach is employed to improve the quality of this surface. One monolayer (ML) of Te grown by the method of molecular beam epitaxy (MBE) on the target surface with heating at 300 °C effectively improves the surface quality as evidenced by the improved sharpness of RHEED pattern and a reduced diffuse background in the spectra measured by high-resolution ultraviolet photoemission spectroscopy (HRUPS). Calculations have been performed for various atomic geometries by employing first-principles geometry optimization. In conjunction with an analysis of the core level component intensities in terms the layer-attenuation model, we propose a "vacancy site" model of the modified 1 ML-Te/CdTe(111)A (2 × 2) surface. PMID:26672795

  9. Formation of long single quantum dots in high quality InSb nanowires grown by molecular beam epitaxy.

    PubMed

    Fan, Dingxun; Li, Sen; Kang, N; Caroff, Philippe; Wang, L B; Huang, Y Q; Deng, M T; Yu, C L; Xu, H Q

    2015-09-28

    We report on realization and transport spectroscopy study of single quantum dots (QDs) made from InSb nanowires grown by molecular beam epitaxy (MBE). The nanowires employed are 50-80 nm in diameter and the QDs are defined in the nanowires between the source and drain contacts on a Si/SiO2 substrate. We show that highly tunable QD devices can be realized with the MBE-grown InSb nanowires and the gate-to-dot capacitance extracted in the many-electron regimes is scaled linearly with the longitudinal dot size, demonstrating that the devices are of single InSb nanowire QDs even with a longitudinal size of ∼700 nm. In the few-electron regime, the quantum levels in the QDs are resolved and the Landég-factors extracted for the quantum levels from the magnetotransport measurements are found to be strongly level-dependent and fluctuated in a range of 18-48. A spin-orbit coupling strength is extracted from the magnetic field evolutions of a ground state and its neighboring excited state in an InSb nanowire QD and is on the order of ∼300 μeV. Our results establish that the MBE-grown InSb nanowires are of high crystal quality and are promising for the use in constructing novel quantum devices, such as entangled spin qubits, one-dimensional Wigner crystals and topological quantum computing devices. PMID:26308470

  10. Controllable Growth of Vertical Heterostructure GaTe(x)Se(1-x)/Si by Molecular Beam Epitaxy.

    PubMed

    Liu, Shanshan; Yuan, Xiang; Wang, Peng; Chen, Zhi-Gang; Tang, Lei; Zhang, Enze; Zhang, Cheng; Liu, Yanwen; Wang, Weiyi; Liu, Cong; Chen, Chen; Zou, Jin; Hu, Weida; Xiu, Faxian

    2015-08-25

    Two dimensional (2D) alloys, especially transition metal dichalcogenides, have attracted intense attention owing to their band-gap tunability and potential optoelectrical applications. Here, we report the controllable synthesis of wafer-scale, few-layer GaTexSe1-x alloys (0 ≤ x ≤ 1) by molecular beam epitaxy (MBE). We achieve a layer-by-layer growth mode with uniform distribution of Ga, Te, and Se elements across 2 in. wafers. Raman spectroscopy was carried out to explore the composition-dependent vibration frequency of phonons, which matches well with the modified random-element-isodisplacement model. Highly efficient photodiode arrays were also built by depositing few-layer GaTe0.64Se0.36 on n-type Si substrates. These p-n junctions have steady rectification characteristics with a rectifying ratio exceeding 300 and a high external quantum efficiency around 50%. We further measured more devices on MBE-grown GaTexSe1-x/Si heterostructures across the full range to explore the composition-dependent external quantum efficiency. Our study opens a new avenue for the controllable growth of 2D alloys with wafer-scale homogeneity, which is a prominent challenge in 2D material research. PMID:26234804

  11. Effect of interaction in the Ga-As-O system on the morphology of a GaAs surface during molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ageev, O. A.; Balakirev, S. V.; Solodovnik, M. S.; Eremenko, M. M.

    2016-05-01

    A thermodynamic analysis of processes of interphase interaction in the Ga-As-O system has been performed and their theoretical laws have been determined, taking into account nonlinear thermal physical properties of the compounds, the oxide film compositions, and modes of molecular-beam epitaxy of GaAs. The processes of interaction of the native oxide of GaAs with the substrate material and also with Ga and As4 from a vapor gaseous phase have been studied experimentally. The experimental results correlate with the results of the thermodynamic analysis. The laws of influence of the removal of the proper oxide on the evolution of the GaAs surface morphology under conditions of the molecular-beam epitaxy have been proposed.

  12. On the use of a O 2:SF 6 plasma treatment on GaAs processed surfaces for molecular beam epitaxial regrowth

    NASA Astrophysics Data System (ADS)

    Desplats, O.; Gallo, P.; Doucet, J. B.; Monier, G.; Bideux, L.; Jalabert, L.; Arnoult, A.; Lacoste, G.; Armand, C.; Voillot, F.; Fontaine, C.

    2009-01-01

    Preparation of processed GaAs surface cleaning in view of molecular beam epitaxy regrowth by means of a O 2SF 6 microwave plasma has been investigated. Photoemission, Auger electron spectroscopy, atomic force microscopy and secondary ion mass spectrometry have been used for characterization. The O 2SF 6 plasma treatment was found to be very efficient for decontaminating the GaAs surface and leads to the formation of an oxide layer that can be taken off by a thermal or low-temperature H-plasma-assisted deoxidation. The levels of oxygen and carbon contaminants at the regrowth interface were measured to be in the range of a standard homoepitaxial layer-epiready substrate interface. Fluorine was observed to be eliminated upon deoxidation while sulphur is present, particularly in the case of low temperature grown layers. This plasma treatment was found to be efficient for preparation of processed GaAs surfaces for molecular beam epitaxial regrowth.

  13. Control over the morphology of AlN during molecular beam epitaxy with the plasma activation of nitrogen on Si (111) substrates

    SciTech Connect

    Mizerov, A. M. Kladko, P. N.; Nikitina, E. V.; Egorov, A. Yu.

    2015-02-15

    The results of studies of the growth kinetics of AlN layers during molecular beam epitaxy with the plasma activation of nitrogen using Si (111) substrates are presented. The possibility of the growth of individual AlN/Si (111) nanocolumns using growth conditions with enrichment of the surface with metal near the formation mode of Al drops, at a substrate temperature close to maximal, during molecular beam epitaxy with the plasma activation of nitrogen (T{sub s} ≈ 850°C) is shown. The possibility of growing smooth AlN layers on a nanocolumnar AlN/Si (111) buffer with the use of T{sub s} ≈ 750°C and growth conditions providing enrichment with metal is shown.

  14. Magnetic and transport properties of epitaxial thin film MgFe2O4 grown on MgO (100) by molecular beam epitaxy

    PubMed Central

    Wu, Han-Chun; Mauit, Ozhet; Coileáin, Cormac Ó; Syrlybekov, Askar; Khalid, Abbas; Mouti, Anas; Abid, Mourad; Zhang, Hong-Zhou; Abid, Mohamed; Shvets, Igor V.

    2014-01-01

    Magnesium ferrite is a very important magnetic material due to its interesting magnetic and electrical properties and its chemical and thermal stability. Here we report on the magnetic and transport properties of epitaxial MgFe2O4 thin films grown on MgO (001) by molecular beam epitaxy. The structural properties and chemical composition of the MgFe2O4 films were characterized by X-Ray diffraction and X-Ray photoelectron spectroscopy, respectively. The nonsaturation of the magnetization in high magnetic fields observed for M (H) measurements and the linear negative magnetoresistance (MR) curves indicate the presence of anti-phase boundaries (APBs) in MgFe2O4. The presence of APBs was confirmed by transmission electron microscopy. Moreover, post annealing decreases the resistance and enhances the MR of the film, suggesting migration of the APBs. Our results may be valuable for the application of MgFe2O4 in spintronics. PMID:25388355

  15. High-efficiency broad-area single-quantum-well lasers with narrow single-lobed far-field patterns prepared by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Larsson, A.; Muttelstein, M.; Arakawa, Y.; Yariv, A.

    1986-01-01

    Broad-area single-quantum-well graded-index waveguide separate-confinement heterostructure lasers were fabricated by molecular beam epitaxy. A high external quantum efficiency of 79 percent and stable, single-lobed far-field patterns with a beam divergence as narrow as 0.8 deg (1.9 times diffraction limit) for a 100 micron-wide laser were obtained under pulsed conditions.

  16. Structural and optical properties of Cd 0.7Hg 0.3Te-CdTe heterostructures grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lentz, G.; Magnea, N.; Mariette, H.; Tuffigo, H.; Feuillet, G.; Fontenille, J.; Ligeon, E.; Saminadayar, K.

    1990-04-01

    Layers and single quantum wells of Cd xHg 1- xTe with x ⋍ 0.7 have been grown by molecular beam epitaxy. Structural analysis shows that growth free of defects (twins, dislocations) can be achieved on (111)Te Cd 0.96Zn 0.04Te substrates. The Photoluminescence analysis of the layers and the wells reveal that they are efficient light emittors in the 1.3-1.5 μm range.

  17. Effect of the annealing temperature on the low-temperature photoluminescence in Si:Er light-emitting structures grown by molecular-beam epitaxy

    SciTech Connect

    Andreev, B. A.; Sobolev, N. A. Denisov, D. V.; Shek, E. I.

    2013-10-15

    The photoluminescence spectra of light-emitting structures based on silicon doped with erbium during the course of molecular-beam epitaxy at a temperature of 500 Degree-Sign C are studied at 4.2 K on being annealed at 800-900 Degree-Sign C. Three sets of lines belonging to the emitting centers of erbium in silicon with a low oxygen-impurity concentration are revealed.

  18. Interfacial stability of CoSi2/Si structures grown by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    George, T.; Fathauer, R. W.

    1992-01-01

    The stability of CoSi2/Si interfaces was examined in this study using columnar silicide structures grown on (111) Si substrates. In the first set of experiments, Co and Si were codeposited using MBE at 800 C and the resulting columnar silicide layer was capped by epitaxial Si. Deposition of Co on the surface of the Si capping layer at 800 C results in the growth of the buried silicide columns. The buried columns grow by subsurface diffusion of the deposited Co, suppressing the formation of surface islands of CoSi2. The column sidewalls appear to be less stable than the top and bottom interfaces, resulting in preferential lateral growth and ultimately in the coalescence of the columns to form a continuous buried CoSi2 layer. In the second set of experiments, annealing of a 250 nm-thick buried columnar layer at 1000 C under a 100 nm-thick Si capping layer results in the formation of a surface layer of CoSi2 with a reduction in the sizes of the CoSi2 columns. For a sample having a thicker Si capping layer the annealing leads to Ostwald ripening producing buried equiaxed columns. The high CoSi2/Si interfacial strain could provide the driving force for the observed behavior of the buried columns under high-temperature annealing.

  19. The study of in situ scanning tunnelling microscope characterization on GaN thin film grown by plasma assisted molecular beam epitaxy

    SciTech Connect

    Yang, R.; Krzyzewski, T.; Jones, T.

    2013-03-18

    The epitaxial growth of GaN by Plasma Assisted Molecular Beam Epitaxy was investigated by Scanning Tunnelling Microscope (STM). The GaN film was grown on initial GaN (0001) and monitored by in situ Reflection High Energy Electron Diffraction and STM during the growth. The STM characterization was carried out on different sub-films with increased thickness. The growth of GaN was achieved in 3D mode, and the hexagonal edge of GaN layers and growth gradient were observed. The final GaN was of Ga polarity and kept as (0001) orientation, without excess Ga adlayers or droplets formed on the surface.

  20. Molecular beam epitaxial growth and characterization of single crystal ferromagnetic shape memory nickel-manganese-gallium films

    NASA Astrophysics Data System (ADS)

    Dong, Jianwei

    In this thesis, single-crystal ferromagnetic shape memory Ni2MnGa thin films have been grown by molecular beam epitaxy (MBE) on GaAs substrates. The properties of the as-grown and free-standing Ni2MnGa films have been thoroughly investigated. It is demonstrated for the first time that the free-standing Ni2MnGa films can be deformed macroscopically by an external magnetic field, which strongly supports the idea of developing Ni2MnGa-based ferromagnetic micro-electro-mechanical-system (MEMS) actuators to realize both large strain and fast response. The MBE growth of Ni2MnGa thin films was carried out using GaAs (001) substrates. The effects of NiGa and ScErAs interlayers, alternate layer epitaxy, and growth temperatures on the structural and magnetic properties of the epitaxial Ni2MnGa films have been studied to optimize the growth. Three MBE-stabilized tetragonal phases as well as two martensite structures have been confirmed. The films are ferromagnetic at room temperature and have Curie temperatures ˜340 K. Free-standing patterned Ni2MnGa films were processed using bulk micro-machining techniques in both bridge and cantilever forms with dimensions ranging from 100 to 400 mum. Tent-like configurations have been observed in released bridges at room temperature (RT) in a film with a composition of ˜Ni50Mn30Ga20. Magnetic measurements confirmed that the film was in the martensitic phase at RT with enhanced magnetic anisotropy. In a free-standing cantilever, repeatable martensitic phase transformation and a unique two-way shape memory effect have been observed by polarized light microscopy. Magnetic field induced strain in a free-standing stoichiometric Ni 2MnGa film was studied at low temperatures. When a magnetic field was applied perpendicularly to the film surface at 135--150 K, dramatic shape change has been observed in free-standing bridges. The shape change saturated at ˜1.2 Tesla. Heating the film up to ˜200 K reverted the sample to the austenite phase and

  1. Structural and band alignment properties of Al2O3 on epitaxial Ge grown on (100), (110), and (111)A GaAs substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hudait, M. K.; Zhu, Y.; Maurya, D.; Priya, S.; Patra, P. K.; Ma, A. W. K.; Aphale, A.; Macwan, I.

    2013-04-01

    Structural and band alignment properties of atomic layer Al2O3 oxide film deposited on crystallographically oriented epitaxial Ge grown in-situ on (100), (110), and (111)A GaAs substrates using two separate molecular beam epitaxy chambers were investigated using cross-sectional transmission microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). High-resolution triple axis x-ray measurement demonstrated pseudomorphic and high-quality Ge epitaxial layer on crystallographically oriented GaAs substrates. The cross-sectional TEM exhibited a sharp interface between the Ge epilayer and each orientation of the GaAs substrate as well as the Al2O3 film and the Ge epilayer. The extracted valence band offset, ΔEv, values of Al2O3 relative to (100), (110), and (111) Ge orientations using XPS measurement were 3.17 eV, 3.34 eV, and 3.10 eV, respectively. Using XPS data, variations in ΔEv related to the crystallographic orientation were ΔEV(110)Ge>ΔEV(100)Ge≥ΔEV(111)Ge and the conduction band offset, ΔEc, related to the crystallographic orientation was ΔEc(111)Ge>ΔEc(110)Ge>ΔEc(100)Ge using the measured ΔEv, bandgap of Al2O3 in each orientation, and well-known Ge bandgap of 0.67 eV. These band offset parameters are important for future application of Ge-based p- and n-channel metal-oxide field-effect transistor design.

  2. The effects of vacuum conditions on epitaxial Al/GaAs contacts formed by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Missous, M.; Rhoderick, E. H.; Singer, K. E.

    1986-10-01

    The effects of the quality of the vacuum on the epitaxy of aluminum on (100) gallium arsenide have been investigated. It was found that leaving the ion gauge running during the cooling down of the GaAs prior to the deposition of the Al and the presence of a helium cryopump both affected the nature of the epitaxy and the height of the resulting Schottky barrier. Reproducible results were only obtained with the ion gauge off and the cryopump on. The Al film was found to take up the (100) orientation irrespective of the reconstruction of the GaAs surface [c(2×8), c(4×4), or (4×6)]. The height of the Schottky barrier on n-type GaAs was 0.77±0.01 eV, and was independent of the GaAs reconstruction. The I-V characteristics were the most nearly ideal that have been reported, a plot of log{I/[1-exp(-qV/kT)]} vs V being linear over the whole voltage range from +0.5 to -1.0 V, with an ideality factor of 1.01 which can be explained solely in terms of image-force lowering. The barrier height on p-type GaAs was 0.64±0.01 eV, also irrespective of the GaAs reconstruction, so that φbn+φbp is equal to the band gap within the experimental error.

  3. Molecular beam epitaxy of gallium arsenide antimonide-based ultra-high-speed double heterojunction bipolar transistors and light emitting transistors

    NASA Astrophysics Data System (ADS)

    Wu, Bing-Ruey

    In this work, GaAsSb-based double heterojunction bipolar transistors (DHBTs) and light emitting transistors (LETs) are grown using gas source molecular beam epitaxy (GSMBE). High-speed GaAs0.5Sb0.5/InP DHBTs are developed through the exercise of GSMBE growth optimization, device fabrication, and characterization. By adjusting the growth temperature and V/III flux ratio, the optimal conditions for growing GaAs0.5Sb0.5 base are found to be at high growth temperature and low V/III ratio. The switching sequence is also optimized so that the Sb segregation effect is minimized. By using GaAs0.5Sb0.5-In0.2Ga0.8As 0.7Sb0.3 compositional grading in the base of the GaAsSb/InP DHBT, a significant improvement of fT from 380 GHz to 500 GHz was achieved compared to a uniform GaAs0.5Sb 0.5 DHBT, while maintaining a high breakdown voltage BVCEO ˜ 4V. The cutoff frequency---breakdown voltage product, fT·BVCEO, of over 2000 GHz-V, is the record value for DHBTs of any material system. Incorporating graded InAs-InGaAs emitter contact layer is also shown to effectively reduce the total emitter resistance, further improving the DHBT high speed performance. LET characteristics with quantum wells (QWs) inserted into the base region of GaAsSb/InP DHBTs are also investigated and the preliminary results are presented. An LET with a tensile strained InGaAsSb/GaAs0.65Sb 0.35 DQW in the base was designed and achieved the emission wavelength of ˜1.6 mum, despite of its low light output intensity. The potential and limitation of realizing a transistor laser with an emission wavelength of 1.55 mum using GaAsSb/InP material system will be discussed.

  4. Deep traps in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy

    SciTech Connect

    Zhang, Z.; Arehart, A. R.; Hurni, C. A.; Speck, J. S.; Yang, J.; Myers, R. C.; Ringel, S. A.

    2012-01-30

    Deep level defects in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy were characterized using deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) and compared with polar c-plane GaN that was grown simultaneously in the same growth run. Significant differences in both the levels present and their concentrations were observed upon comparison of both growth orientations. DLTS revealed electron traps with activation energies of 0.14 eV, 0.20 eV, and 0.66 eV in the m-plane material, with concentrations that were {approx}10-50 x higher than traps of similar activation energies in the c-plane material. Likewise, DLOS measurements showed {approx}20 x higher concentrations of both a C{sub N} acceptor-like state at E{sub C} - 3.26 eV, which correlates with a high background carbon concentration observed by secondary ion mass spectroscopy for the m-plane material [A. Armstrong, A. R. Arehart, B. Moran, S. P. DenBaars, U. K. Mishra, J. S. Speck, and S. A. Ringel, Appl. Phys. Lett. 84, 374 (2004)], and the V{sub Ga}-related state level at E{sub C} - 2.49 eV, which is consistent with an enhanced yellow luminescence observed by photoluminescence. The findings suggest a strong impact of growth dynamics on the incorporation of impurities and electrically active native point defects as a function of GaN growth plane polarity.

  5. Molecular beam epitaxy of GaNAs alloys with high As content for potential photoanode applications in hydrogen production

    SciTech Connect

    Novikov, S. V.; Staddon, C. R.; Foxon, C. T.; Yu, K. M.; Broesler, R.; Hawkridge, M.; Liliental-Weber, Z.; Walukiewicz, W.; Denlinger, J.; Demchenko, I.

    2009-10-06

    The authors have succeeded in growing GaN1?xAsx alloys over a large composition range (0 < x < 0.8) by plasma-assisted molecular beam epitaxy. The enhanced incorporation of As was achieved by growing the films with high As{sub 2} flux at low (as low as 100 C) growth temperatures, which is much below the normal GaN growth temperature range. Using x-ray and transmission electron microscopy, they found that the GaNAs alloys with high As content x > 0.17 are amorphous. Optical absorption measurements together with x-ray absorption and emission spectroscopy results reveal a continuous gradual decrease in band gap from -3.4 to < 1 eV with increasing As content. The energy gap reaches its minimum of -0.8 eV at x - 0.8. The composition dependence of the band gap of the crystalline GaN{sub 1?x}As{sub x} alloys follows the prediction of the band anticrossing model (BAC). However, our measured band gap of amorphous GaN{sub 1?x}As{sub x} with 0.3 < x < 0.8 are larger than that predicted by BAC. The results seem to indicate that for this composition range the amorphous GaN{sub 1?x}As{sub x} alloys have short-range ordering that resembles random crystalline GaN{sub 1?x}As{sub x} alloys. They have demonstrated the possibility of the growth of amorphous GaN{sub 1?x}As{sub x} layers with variable As content on glass substrates

  6. Scanning Tunneling Microscopy and Spectroscopy of Air Exposure Effects on Molecular Beam Epitaxy Grown WSe2 Monolayers and Bilayers.

    PubMed

    Park, Jun Hong; Vishwanath, Suresh; Liu, Xinyu; Zhou, Huawei; Eichfeld, Sarah M; Fullerton-Shirey, Susan K; Robinson, Joshua A; Feenstra, Randall M; Furdyna, Jacek; Jena, Debdeep; Xing, Huili Grace; Kummel, Andrew C

    2016-04-26

    The effect of air exposure on 2H-WSe2/HOPG is determined via scanning tunneling microscopy (STM). WSe2 was grown by molecular beam epitaxy on highly oriented pyrolytic graphite (HOPG), and afterward, a Se adlayer was deposited in situ on WSe2/HOPG to prevent unintentional oxidation during transferring from the growth chamber to the STM chamber. After annealing at 773 K to remove the Se adlayer, STM images show that WSe2 layers nucleate at both step edges and terraces of the HOPG. Exposure to air for 1 week and 9 weeks caused air-induced adsorbates to be deposited on the WSe2 surface; however, the band gap of the terraces remained unaffected and nearly identical to those on decapped WSe2. The air-induced adsorbates can be removed by annealing at 523 K. In contrast to WSe2 terraces, air exposure caused the edges of the WSe2 to oxidize and form protrusions, resulting in a larger band gap in the scanning tunneling spectra compared to the terraces of air-exposed WSe2 monolayers. The preferential oxidation at the WSe2 edges compared to the terraces is likely the result of dangling edge bonds. In the absence of air exposure, the dangling edge bonds had a smaller band gap compared to the terraces and a shift of about 0.73 eV in the Fermi level toward the valence band. However, after air exposure, the band gap of the oxidized WSe2 edges became about 1.08 eV larger than that of the WSe2 terraces, resulting in the electronic passivation of the WSe2. PMID:26991824

  7. Enhancement of minority carrier lifetime of GaInP with lateral composition modulation structure grown by molecular beam epitaxy

    SciTech Connect

    Park, K. W.; Ravindran, Sooraj; Kang, S. J.; Hwang, H. Y.; Jho, Y. D.; Park, C. Y.; Jo, Y. R.; Kim, B. J.; Lee, Y. T.

    2014-07-28

    We report the enhancement of the minority carrier lifetime of GaInP with a lateral composition modulated (LCM) structure grown using molecular beam epitaxy (MBE). The structural and optical properties of the grown samples are studied by transmission electron microscopy and photoluminescence, which reveal the formation of vertically aligned bright and dark slabs corresponding to Ga-rich and In-rich GaInP regions, respectively, with good crystal quality. With the decrease of V/III ratio during LCM GaInP growth, it is seen that the band gap of LCM GaInP is reduced, while the PL intensity remains high and is comparable to that of bulk GaInP. We also investigate the minority carrier lifetime of LCM structures made with different flux ratios. It is found that the minority carrier lifetime of LCM GaInP is ∼37 times larger than that of bulk GaInP material, due to the spatial separation of electrons and holes by In-rich and Ga-rich regions of the LCM GaInP, respectively. We further demonstrate that the minority carrier lifetime of the grown LCM GaInP structures can easily be tuned by simply adjusting the V/III flux ratio during MBE growth, providing a simple yet powerful technique to tailor the electrical and optical properties at will. The exceptionally high carrier lifetime and the reduced band gap of LCM GaInP make them a highly attractive candidate for forming the top cell of multi-junction solar cells and can enhance their efficiency, and also make them suitable for other optoelectronics devices, such as photodetectors, where longer carrier lifetime is beneficial.

  8. Electrical and photovoltaic properties of CdTe/ZnTe n-i-p junctions grown by molecular beam epitaxy

    SciTech Connect

    Zielony, E. Płaczek-Popko, E.; Racino, A.; Gumienny, Z.; Olender, K.; Wosiński, T.; Karczewski, G.; Chusnutdinow, S.

    2014-06-28

    Preliminary studies have been performed on photoelectrical properties of CdTe/ZnTe n-i-p junctions grown using the molecular beam epitaxy technique. Photovoltaic properties of the cells have been investigated by the measurements of current-voltage (I-V) characteristics under 1-sun illumination. I-V characteristics yield efficiencies of the cells varying from 3.4% to 4.9%. The low efficiency can be due to the presence of electrically active defects. In order to study the origin of defects in CdTe/ZnTe photovoltaic junctions, space charge techniques (C-V and deep level transient spectroscopy (DLTS)) have been applied. From the C-V measurements, a doping profile was calculated confirming charge accumulation in the i-CdTe layer. The results of the DLTS studies revealed the presence of four traps within a temperature range from 77–420 K. Three of them with activation energies equal to 0.22 eV, 0.45 eV, and 0.78 eV have been ascribed to the hole traps present in the i-CdTe material and their possible origin has been discussed. The fourth, high-temperature DLTS peak observed at ∼350 K has been attributed to extended defects as its amplitude and temperature position depends on the value of the filling pulse width. It is assumed that the defects related to the trap are either located in the i-CdTe layer or at the i-CdTe/ZnTe interface. However, it was found that the trap exhibits twofold nature: it behaves as a majority or as a minority trap, depending on the filling pulse height, which is a characteristic feature of recombination centers. This trap is presumably responsible for the low efficiency of the cells.

  9. Internal quantum efficiency of III-nitride quantum dot superlattices grown by plasma-assisted molecular-beam epitaxy

    SciTech Connect

    Gacevic, Z.; Kehagias, Th.; Koukoula, T.; Komninou, Ph.

    2011-05-15

    We present a study of the optical properties of GaN/AlN and InGaN/GaN quantum dot (QD) superlattices grown via plasma-assisted molecular-beam epitaxy, as compared to their quantum well (QW) counterparts. The three-dimensional/two-dimensional nature of the structures has been verified using atomic force microscopy and transmission electron microscopy. The QD superlattices present higher internal quantum efficiency as compared to the respective QWs as a result of the three-dimensional carrier localization in the islands. In the QW samples, photoluminescence (PL) measurements point out a certain degree of carrier localization due to structural defects or thickness fluctuations, which is more pronounced in InGaN/GaN QWs due to alloy inhomogeneity. In the case of the QD stacks, carrier localization on potential fluctuations with a spatial extension smaller than the QD size is observed only for the InGaN QD-sample with the highest In content (peak emission around 2.76 eV). These results confirm the efficiency of the QD three-dimensional confinement in circumventing the potential fluctuations related to structural defects or alloy inhomogeneity. PL excitation measurements demonstrate efficient carrier transfer from the wetting layer to the QDs in the GaN/AlN system, even for low QD densities ({approx}10{sup 10} cm{sup -3}). In the case of InGaN/GaN QDs, transport losses in the GaN barriers cannot be discarded, but an upper limit to these losses of 15% is deduced from PL measurements as a function of the excitation wavelength.

  10. Growth and characterization of metamorphic InAs/GaSb tunnel heterojunction on GaAs by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Liu, Jheng-Sin; Clavel, Michael B.; Pandey, Rahul; Datta, Suman; Meeker, Michael; Khodaparast, Giti A.; Hudait, Mantu K.

    2016-06-01

    The structural, morphological, optical, and electrical transport characteristics of a metamorphic, broken-gap InAs/GaSb p-i-n tunnel diode structure, grown by molecular beam epitaxy on GaAs, were demonstrated. Precise shutter sequences were implemented for the strain-balanced InAs/GaSb active layer growth on GaAs, as corroborated by high-resolution X-ray analysis. Cross-sectional transmission electron microscopy and detailed micrograph analysis demonstrated strain relaxation primarily via the formation of 90° Lomer misfit dislocations (MDs) exhibiting a 5.6 nm spacing and intermittent 60° MDs at the GaSb/GaAs heterointerface, which was further supported by a minimal lattice tilt of 180 arc sec observed during X-ray analysis. Selective area diffraction and Fast Fourier Transform patterns confirmed the full relaxation of the GaSb buffer layer and quasi-ideal, strain-balanced InAs/GaSb heteroepitaxy. Temperature-dependent photoluminescence measurements demonstrated the optical band gap of the GaSb layer. Strong optical signal at room temperature from this structure supports a high-quality material synthesis. Current-voltage characteristics of fabricated InAs/GaSb p-i-n tunnel diodes measured at 77 K and 290 K demonstrated two bias-dependent transport mechanisms. The Shockley-Read-Hall generation-recombination mechanism at low bias and band-to-band tunneling transport at high bias confirmed the p-i-n tunnel diode operation. This elucidated the importance of defect control in metamorphic InAs/GaSb tunnel diodes for the implementation of low-voltage and high-performance tunnel field effect transistor applications.

  11. Realization of Cu-Doped p-Type ZnO Thin Films by Molecular Beam Epitaxy.

    PubMed

    Suja, Mohammad; Bashar, Sunayna B; Morshed, Muhammad M; Liu, Jianlin

    2015-04-29

    Cu-doped p-type ZnO films are grown on c-sapphire substrates by plasma-assisted molecular beam epitaxy. Photoluminescence (PL) experiments reveal a shallow acceptor state at 0.15 eV above the valence band edge. Hall effect results indicate that a growth condition window is found for the formation of p-type ZnO thin films, and the best conductivity is achieved with a high hole concentration of 1.54 × 10(18) cm(-3), a low resistivity of 0.6 Ω cm, and a moderate mobility of 6.65 cm(2) V(-1) s(-1) at room temperature. Metal oxide semiconductor capacitor devices have been fabricated on the Cu-doped ZnO films, and the characteristics of capacitance-voltage measurements demonstrate that the Cu-doped ZnO thin films under proper growth conditions are p-type. Seebeck measurements on these Cu-doped ZnO samples lead to positive Seebeck coefficients and further confirm the p-type conductivity. Other measurements such as X-ray diffraction, X-ray photoelectron, Raman, and absorption spectroscopies are also performed to elucidate the structural and optical characteristics of the Cu-doped p-type ZnO films. The p-type conductivity is explained to originate from Cu substitution of Zn with a valency of +1 state. However, all p-type samples are converted to n-type over time, which is mostly due to the carrier compensation from extrinsic defects of ZnO. PMID:25835032

  12. Localized Si enrichment in coherent self-assembled Ge islands grown by molecular beam epitaxy on (001)Si single crystal

    SciTech Connect

    Valvo, M.; Bongiorno, C.; Giannazzo, F.; Terrasi, A.

    2013-01-21

    Transmission electron microscopy (TEM), atomic force microscopy, and Rutherford backscattering spectrometry (RBS) have been used to investigate the morphology, structure, and composition of self-assembled Ge islands grown on Si (001) substrates by molecular beam epitaxy (MBE) at different temperatures. Increasing the temperature from 550 Degree-Sign C to 700 Degree-Sign C causes progressive size and shape uniformity, accompanied by enhanced Si-Ge intermixing within the islands and their wetting layer. Elemental maps obtained by energy filtered-TEM (EF-TEM) clearly show pronounced Si concentration not only in correspondence of island base perimeters, but also along their curved surface boundaries. This phenomenon is strengthened by an increase of the growth temperature, being practically negligible at 550 Degree-Sign C, while very remarkable already at 650 Degree-Sign C. The resulting island shape is affected, since this localized Si enrichment not only provides strain relief near their highly stressed base perimeters but it also influences the cluster surface energy by effective alloying, so as to form Si-enriched SiGe interfaces. Further increase to 700 Degree-Sign C causes a shape transition where more homogenous Si-Ge concentration profiles are observed. The crucial role played by local 'flattened' alloyed clusters, similar to truncated pyramids with larger bases and enhanced Si enrichment at coherently stressed interfaces, has been further clarified by EF-TEM analysis of a multi-layered Ge/Si structure containing stacked Ge islands grown at 650 Degree-Sign C. Sharp accumulation of Si has been here observed not only in proximity of the uncapped island surface in the topmost layer but also at the buried Ge/Si interfaces and even in the core of such capped Ge islands.

  13. Deep traps in n-type GaN epilayers grown by plasma assisted molecular beam epitaxy

    SciTech Connect

    Kamyczek, P.; Placzek-Popko, E.; Zielony, E.; Gumienny, Z.; Zytkiewicz, Z. R.

    2014-01-14

    In this study, we present the results of investigations on Schottky Au-GaN diodes by means of conventional DLTS and Laplace DLTS methods within the temperature range of 77 K–350 K. Undoped GaN layers were grown using the plasma-assisted molecular beam epitaxy technique on commercial GaN/sapphire templates. The quality of the epilayers was studied by micro-Raman spectroscopy (μ-RS) which proved the hexagonal phase and good crystallinity of GaN epilayers as well as a slight strain. The photoluminescence spectrum confirmed a high crystal quality by intense excitonic emission but it also exhibited a blue emission band of low intensity. DLTS signal spectra revealed the presence of four majority traps: two high-temperature and two low-temperature peaks. Using the Laplace DLTS method and Arrhenius plots, the apparent activation energy and capture cross sections were obtained. For two high-temperature majority traps, they were equal to E{sub 1} = 0.65 eV, σ{sub 1} = 8.2 × 10{sup −16} cm{sup 2} and E{sub 2} = 0.58 eV, σ{sub 2} = 2.6 × 10{sup −15} cm{sup 2} whereas for the two low-temperature majority traps they were equal to E{sub 3} = 0.18 eV, σ{sub 3} = 9.7 × 10{sup −18} cm{sup 2} and E{sub 4} = 0.13 eV, σ{sub 4} = 9.2 × 10{sup −18} cm{sup 2}. The possible origin of the traps is discussed and the results are compared with data reported elsewhere.

  14. Growth of 1.5-1.55 micron gallium indium nitrogen arsenic antimonide lasers by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bae, Hopil

    With the advent of new Internet services for exchaging not only texts and pictures but also home-made videos and high-definition movies, the appetite for more internet bandwidth is still growing at a fast pace. Satisfying these demands require extending the high-speed fiber optical networks all the way to the end users. This approach will require high-performance lasers, detectors, and modulators that are also very inexpensive and power-efficient. VCSELs are ideal light sources for this application due to their low power consumption, easier fiber coupling, ease of fabrication, and the possibility of dense 2-D integration. A new GaAs-based gain material, GaInNAsSb, can be an enabling technology for VCSELs in the 1.3-1.6mum wavelength range appropriate for optical communications. It can also enable high-power lasers for pumping Raman amplifiers, which can significantly increase the usable bandwidth of optical fibers. Growth of GaInNAsSb by molecular beam epitaxy has been very challenging, but various improvements in growth and annealing conditions lead to very low-threshold 1.55mum edge-emitting lasers and the first GaAs-based pulsed-mode 1.534mum VCSELs. Improving their temperature stability and achieving room-temperature continuous-wave(CW) VCSELs was the main objective of this thesis work. This thesis first discusses additional improvements in annealing and growth conditions, which led to a factor of 4 increase in the peak pholuminescence intensity. Edge-emitting lasers employing different numbers and structures of GaInNasSb QWs were compared, and the carrier leakage to the GaNAs barriers has been identified to be the dominant source of carrier recombination, by measurements using segmented contacts. Using the same triple QW structures and carefully designed AlGaAs/GaAs DBR mirrors, the first-ever all-epitaxial near-room-temperature CW VCSELs at 1528nm are realized on GaAs substrates.

  15. Angle-resolved photoemission spectroscopy of strontium lanthanum copper oxide thin films grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Harter, John Wallace

    Among the multitude of known cuprate material families and associated structures, the archetype is "infinite-layer" ACuO2, where perfectly square and flat CuO2 planes are separated by layers of alkaline earth atoms. The infinite-layer structure is free of magnetic rare earth ions, oxygen chains, orthorhombic distortions, incommensurate superstructures, ordered vacancies, and other complications that abound among the other material families. Furthermore, it is the only cuprate that can be made superconducting by both electron and hole doping, making it a potential platform for decoding the complex many-body interactions responsible for high-temperature superconductivity. Research on the infinite-layer compound has been severely hindered by the inability to synthesize bulk single crystals, but recent progress has led to high-quality superconducting thin film samples. Here we report in situ angle-resolved photoemission spectroscopy measurements of epitaxially-stabilized Sr1-chiLa chiCuO2 thin films grown by molecular-beam epitaxy. At low doping, the material exhibits a dispersive lower Hubbard band typical of other cuprate parent compounds. As carriers are added to the system, a continuous evolution from Mott insulator to superconducting metal is observed as a coherent low-energy band develops on top of a concomitant remnant lower Hubbard band, gradually filling in the Mott gap. For chi = 0.10, our results reveal a strong coupling between electrons and (pi,pi) anti-ferromagnetism, inducing a Fermi surface reconstruction that pushes the nodal states below the Fermi level and realizing nodeless superconductivity. Electron diffraction measurements indicate the presence of a surface reconstruction that is consistent with the polar nature of Sr1-chiLachiCuO2. Most knowledge about the electron-doped side of the cuprate phase diagram has been deduced by generalizing from a single material family, Re2-chi CechiCuO4, where robust antiferromagnetism has been observed past chi

  16. Self-assembly of InAs quantum dots on GaAs(001) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wu, Ju; Jin, Peng

    2015-02-01

    Currently, the nature of self-assembly of three-dimensional epitaxial islands or quantum dots (QDs) in a lattice-mismatched heteroepitaxial growth system, such as InAs/GaAs(001) and Ge/Si(001) as fabricated by molecular beam epitaxy (MBE), is still puzzling. The purpose of this article is to discuss how the self-assembly of InAs QDs in MBE InAs/GaAs(001) should be properly understood in atomic scale. First, the conventional kinetic theories that have traditionally been used to interpret QD self-assembly in heteroepitaxial growth with a significant lattice mismatch are reviewed briefly by examining the literature of the past two decades. Second, based on their own experimental data, the authors point out that InAs QD self-assembly can proceed in distinctly different kinetic ways depending on the growth conditions and so cannot be framed within a universal kinetic theory, and, furthermore, that the process may be transient, or the time required for a QD to grow to maturity may be significantly short, which is obviously inconsistent with conventional kinetic theories. Third, the authors point out that, in all of these conventional theories, two well-established experimental observations have been overlooked: i) A large number of "floating" indium atoms are present on the growing surface in MBE InAs/GaAs(001); ii) an elastically strained InAs film on the GaAs(001) substrate should be mechanically unstable. These two well-established experimental facts may be highly relevant and should be taken into account in interpreting InAs QD formation. Finally, the authors speculate that the formation of an InAs QD is more likely to be a collective event involving a large number of both indium and arsenic atoms simultaneously or, alternatively, a morphological/structural transformation in which a single atomic InAs sheet is transformed into a three-dimensional InAs island, accompanied by the rehybridization from the sp 2-bonded to sp 3-bonded atomic configuration of both indium

  17. Molecular beam epitaxy growth and characterization of dysprosium phosphide and dysprosium arsenide in gallium arsenide and gallium phosphide

    NASA Astrophysics Data System (ADS)

    Lee, Paul Piyawong

    The ability to grow thermally stable Schottky/ohmic contacts and buried, epitaxial metallic or semimetallic layers on semiconductors has many potential applications in novel device structures. Many rare earth group-V compounds with the sodium chloride structure possess the properties that make them potential candidates for stable contacts, buried layers, and other applications. In this work, two novel rare earth compounds, namely dysprosium phosphide (DyP) and dysprosium arsenide (DyAs) have been studied for high temperature ohmic/Schottky contacts to III-V semiconductors as well as for buried metal layers in semiconductor/metal/semiconductor structures. DyP and DyAs have been grown by molecular beam epitaxy on GaAs and GaP substrates. Both DyP and DyAs display metallic behavior and have room temperature resistivities of 8 x 10--5 and 1 x 10--4 Ocm, respectively. The electron concentrations for DyP and DyAs are about 4 x 1020 and 1 x 1021 cm--3, respectively. High quality DyP films as determined by XRD, AFM, and TEM can be achieved at a wide range of substrate temperatures (500°C to 600°C) with excess phosphorus pressure. Unlike most rare earth-group V compounds, DyP films are stable in air with no sign of oxidation. DyP films deposited on n-type GaAs and GaP exhibit Schottky behavior with room temperature barrier heights of 0.83 and 0.90 eV, respectively, with ideality factors close to unity and low reverse bias leakage current densities. These contacts are stable up to 250°C and 350°C for GaAs and GaP, respectively. DyAs films on the other hand, oxidize in air and display weak Schottky behavior on n-type GaAs. DyP has been grown as buried layers in both GaAs/DyP/GaAs and GaAs/DyP/GaP structures. Although high quality DyP layers have been achieved, the GaAs overlayers contain defects such as twins. The poor wetting of GaAs on DyP and the crystal symmetry between the two materials are responsible for the three-dimensional growth and the defects found in the Ga

  18. Improved crystalline properties of laser molecular beam epitaxy grown SrTiO{sub 3} by rutile TiO{sub 2} layer on hexagonal GaN

    SciTech Connect

    Luo, W. B.; Zhu, J.; Chen, H.; Wang, X. P.; Zhang, Y.; Li, Y. R.

    2009-11-15

    Epitaxial SrTiO{sub 3} films were fabricated by laser molecular beam epitaxy on bare and TiO{sub 2} buffered GaN(0002), respectively. The whole deposition processes were in situ monitored by reflection high energy electron diffraction (RHEED). X-ray diffraction (XRD) was carried out to study the growth orientation and crystalline quality of STO films. The interfacial characters and epitaxial relationships were also investigated by high revolution transition electron microscope and selected area electron diffraction (SAED). According to the RHEED observation, the lowest epitaxy temperature of STO on TiO{sub 2} buffered GaN was decreased compared with the direct deposited one. The epitaxial relationship was (111)[110]STO//(0002)[1120]GaN in both cases as confirmed by RHEED, XRD, and SAED. The full width at half maximum of omega-scan and PHI-scan of STO on TiO{sub 2} buffered GaN was reduced compared with that deposited on bare GaN, indicating that epitaxial quality of STO film is improved by inserting TiO{sub 2} layer. In summary, the lattice mismatch was reduced by inserting rutile TiO{sub 2}. As a result, the crystalline temperature was reduced and enhanced epitaxial quality of STO thin film was obtained.

  19. Atomic Layer Epitaxy of h-BN(0001) Multilayers on Co(0001) and Molecular Beam Epitaxy Growth of Graphene on h-BN(0001)/Co(0001).

    PubMed

    Driver, M Sky; Beatty, John D; Olanipekun, Opeyemi; Reid, Kimberly; Rath, Ashutosh; Voyles, Paul M; Kelber, Jeffry A

    2016-03-22

    The direct growth of hexagonal boron nitride (h-BN) by industrially scalable methods is of broad interest for spintronic and nanoelectronic device applications. Such applications often require atomically precise control of film thickness and azimuthal registry between layers and substrate. We report the formation, by atomic layer epitaxy (ALE), of multilayer h-BN(0001) films (up to 7 monolayers) on Co(0001). The ALE process employs BCl3/NH3 cycles at 600 K substrate temperature. X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) data show that this process yields an increase in h-BN average film thickness linearly proportional to the number of BCl3/NH3 cycles, with BN layers in azimuthal registry with each other and with the Co(0001) substrate. LEED diffraction spot profile data indicate an average BN domain size of at least 1900 Å. Optical microscopy data indicate the presence of some domains as large as ∼20 μm. Transmission electron microscopy (TEM) and ambient exposure studies demonstrate macroscopic and microscopic continuity of the h-BN film, with the h-BN film highly conformal to the Co substrate. Photoemission data show that the h-BN(0001) film is p-type, with band bending near the Co/h-BN interface. Growth of graphene by molecular beam epitaxy (MBE) is observed on the surface of multilayer h-BN(0001) at temperatures of 800 K. LEED data indicate azimuthal graphene alignment with the h-BN and Co(0001) lattices, with domain size similar to BN. The evidence of multilayer BN and graphene azimuthal alignment with the lattice of the Co(0001) substrate demonstrates that this procedure is suitable for scalable production of heterojunctions for spintronic applications. PMID:26940024

  20. Mössbauer study on epitaxial Co{sub x}Fe{sub 4−x}N films grown by molecular beam epitaxy

    SciTech Connect

    Ito, Keita; Sanai, Tatsunori; Yasutomi, Yoko; Gushi, Toshiki; Toko, Kaoru; Yanagihara, Hideto; Kita, Eiji; Suemasu, Takashi; Tsunoda, Masakiyo

    2015-05-07

    We prepared Co{sub x}Fe{sub 4−x}N (x = 0, 1, 3) films on SrTiO{sub 3}(STO)(001) substrates by molecular beam epitaxy. The epitaxial relationship with Co{sub x}Fe{sub 4−x}N[100](001) || STO[100](001) was confirmed by ω-2θ (out-of-plane) and ϕ-2θ{sub χ} (in-plane) x-ray diffraction (XRD) measurements. The degree of order of atoms (S) in the Co{sub x}Fe{sub 4−x}N films was estimated to be ∼0.5 by the peak intensity ratio of Co{sub x}Fe{sub 4−x}N(100) (superlattice diffraction line) to (400) (fundamental diffraction line) in the ϕ-2θ{sub χ} XRD patterns. Conversion electron Mössbauer spectroscopy studies for the Co{sub x}Fe{sub 4−x}N films revealed that some N atoms are located at interstitial sites between the two nearest corner sites in the Co{sub x}Fe{sub 4−x}N films, and/or Fe atoms are located at both the corner and face-centered sites in the CoFe{sub 3}N and Co{sub 3}FeN films. In order to realize high spin-polarized Co{sub x}Fe{sub 4−x}N films having large S, further optimization of growth condition is required to prevent the site-disorders.

  1. High in-plane anisotropy of epitaxial CoPt(110) alloy films prepared by cosputtering or molecular beam epitaxy on MgO

    SciTech Connect

    Abes, M.; Ersen, O.; Meny, C.; Schmerber, G.; Acosta, M.; Arabski, J.; Ulhaq-Bouillet, C.; Dinia, A.; Panissod, P.; Pierron-Bohnes, V.

    2007-03-15

    We present structural and magnetic properties of three sets of structures: as-deposited CoPt films cosputtered at 900 K on MgO(110) substrates with a Pt(110) buffer layer and CoPt films deposited by molecular beam epitaxy directly on MgO(110) substrates at 900 K, as prepared and annealed at 900 K. All layers have the L1{sub 0} tetragonal structure. The chemical long-range ordering for the as-deposited CoPt films is incomplete in contrast with the annealed CoPt films, where long-range order is the highest. The structural study of these CoPt films grown on MgO(110) has pointed out that three variants of the L1{sub 0} phase coexist. The proportion of x and y variants, with the concentration modulation along a vector oriented at 45 degree sign with respect to the growth direction, is higher than the proportion of the z variant with the concentration modulation within the plane. The magnetic study shows an in-plane easy magnetization axis with a large magnetic anisotropy. This is interesting for the magnetic recording media with classical longitudinal writing and reading heads. The simulation of the magnetization loops confirms that the easy magnetization axis is within the plane and along the [110] direction, favored by the dominant x and y variants.

  2. Single domain Bi{sub 2}Se{sub 3} films grown on InP(111)A by molecular-beam epitaxy

    SciTech Connect

    Guo, X.; Xu, Z. J.; Liu, H. J.; Ho, W. K.; Xie, M. H.; Liu, H. C.; Wang, J. N.; Zhao, B.; Dai, X. Q.; He, H. T.

    2013-04-15

    We report the growth of single-domain epitaxial Bi{sub 2}Se{sub 3} films on InP(111)A substrate by molecular-beam epitaxy. Nucleation of Bi{sub 2}Se{sub 3} proceeds at steps, so the lattices of the substrate play the guiding role for a unidirectional crystalline film in the step-flow growth mode. There exists a strong chemical interaction between atoms at the heterointerface, so the growth does not follow the van der Waals epitaxy process. A mounded morphology of thick Bi{sub 2}Se{sub 3} epilayers suggests a growth kinetics dictated by the Ehrlich-Schwoebel barrier. The Schubnikov de Haas oscillations observed in magnetoresistance measurements are attributed to Landau quantization of the bulk states of electrons.

  3. Characterization of molecular beam epitaxy grown β-Nb2N films and AlN/β-Nb2N heterojunctions on 6H-SiC substrates

    NASA Astrophysics Data System (ADS)

    Nepal, Neeraj; Katzer, D. Scott; Meyer, David J.; Downey, Brian P.; Wheeler, Virginia D.; Storm, David F.; Hardy, Matthew T.

    2016-02-01

    β-Nb2N films and AlN/β-Nb2N heterojunctions were grown by molecular beam epitaxy (MBE) on 6H-SiC. The epitaxial nature and β-Nb2N phase were determined by symmetric and asymmetric high-resolution X-ray diffraction (HRXRD) measurements, and were confirmed by grazing incidence diffraction measurements using synchrotron photons. Measured lattice parameters and the in-plane stress of β-Nb2N on 6H-SiC were c = 5.0194 Å, a = 3.0558 Å, and 0.2 GPa, respectively. The HRXRD, transmission electron microscopy, and Raman spectroscopy revealing epitaxial growth of AlN/β-Nb2N heterojunctions have identical orientations with the substrate, abrupt interfaces, and bi-axial stress of 0.88 GPa, respectively. The current finding opens up possibilities for the next generation of high-power devices that cannot be fabricated at present.

  4. Electron scattering mechanisms in GZO films grown on a-sapphire substrates by plasma-enhanced molecular beam epitaxy

    SciTech Connect

    Liu, H. Y.; Avrutin, V.; Izyumskaya, N.; Oezguer, Ue.; Morkoc, H.; Yankovich, A. B.; Kvit, A. V.; Voyles, P. M.

    2012-05-15

    We report on the mechanisms governing electron transport using a comprehensive set of ZnO layers heavily doped with Ga (GZO) grown by plasma-enhanced molecular-beam epitaxy on a-plane sapphire substrates with varying oxygen-to-metal ratios and Ga fluxes. The analyses were conducted by temperature dependent Hall measurements which were supported by microstructural investigations as well. Highly degenerate GZO layers with n > 5 x 10{sup 20} cm{sup -3} grown under metal-rich conditions (reactive oxygen-to-metal ratio <1) show relatively larger grains ({approx}20-25 nm by x-ray diffraction) with low-angle boundaries parallel to the polar c-direction. For highly conductive GZO layers, ionized-impurity scattering with almost no compensation is the dominant mechanism limiting the mobility in the temperature range from 15 to 330 K and the grain-boundary scattering governed by quantum-mechanical tunnelling is negligible. However, due to the polar nature of ZnO having high crystalline quality, polar optical phonon scattering cannot be neglected for temperatures above 150 K, because it further reduces mobility although its effect is still substantially weaker than the ionized impurity scattering even at room temperature (RT). Analysis of transport measurements and sample microstructures by x-ray diffraction and transmission electron microscopy led to a correlation between the grain sizes in these layers and mobility even for samples with a carrier concentration in the upper 10{sup 20} cm{sup -3} range. In contrast, electron transport in GZO layers grown under oxygen-rich conditions (reactive oxygen-to-metal ratio >1), which have inclined grain boundaries and relatively smaller grain sizes of 10-20 nm by x-ray diffraction, is mainly limited by compensation caused by acceptor-type point-defect complexes, presumably (Ga{sub Zn}-V{sub Zn}), and scattering on grain boundaries. The GZO layers with n <10{sup 20} cm{sup -3} grown under metal-rich conditions with reduced Ga fluxes

  5. Bandgap tuning of GaAs/GaAsSb core-shell nanowires grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kasanaboina, Pavan Kumar; Krishna Ojha, Sai; Sami, Shifat Us; Reynolds, C. Lewis, Jr.; Liu, Yang; Iyer, Shanthi

    2015-10-01

    Semiconductor nanowires have been identified as a viable technology for next-generation infrared (IR) photodetectors with improved detectivity and detection across a range of energies as well as for novel single-photon detection in quantum networking. The GaAsSb materials system is especially promising in the 1.3-1.55 μm spectral range. In this work we present band-gap tuning up to 1.3 μm in GaAs/GaAsSb core-shell nanowires, by varying the Sb content using Ga-assisted molecular beam epitaxy. An increase in Sb content leads to strain accumulation in shell manifesting in rough surface morphology, multifaceted growths, curved nanowires, and deterioration in the microstructural and optical quality of the nanowires. The presence of multiple PL peaks for Sb compositions ≥12 at.% and degradation in the nanowire quality as attested by broadening of Raman and x-ray diffraction peaks reveal compositional instability in the nanowires. Transmission electron microscope (TEM) images show the presence of stacking faults and twins. Based on photoluminescence (PL) peak energies and their excitation power dependence behavior, an energy-band diagram for GaAs/GaAsSb core-shell nanowires is proposed. Optical transitions are dominated by type II transitions at lower Sb compositions and a combination of type I and type II transitions for compositions ≥12 at.%. Type I optical transitions as low as 0.93 eV (1.3 μm) from the GaAsSb for Sb composition of 26 at.% have been observed. The PL spectrum of a single nanowire is replicated in the ensemble nanowires, demonstrating good compositional homogeneity of the latter. A double-shell configuration for passivation of deleterious surface states leads to significant enhancement in the PL intensity resulting in the observation of room temperature emission, which provides significant potential for further improvement with important implications for nanostructured optoelectronic devices operating in the near-infrared regime.

  6. Effects of hydrogen on the optical properties of ZnCdO/ZnO quantum wells grown by molecular beam epitaxy

    SciTech Connect

    Buyanova, I. A.; Wang, X. J.; Chen, W. M.; Pozina, G.; Lim, W.; Norton, D. P.; Pearton, S. J.; Osinsky, A.; Dong, J. W.; Hertog, B.

    2008-06-30

    Temperature-dependent cw- and time-resolved photoluminescence (PL), as well as optically detected magnetic resonance (ODMR) measurements are employed to evaluate effects of deuterium (2H) doping on optical properties of ZnCdO/ZnO quantum well structures grown by molecular beam epitaxy. It is shown that incorporation of {sup 2}H from a remote plasma causes a substantial improvement in radiative efficiency of the investigated structures. Based on transient PL measurements, the observed improvements are attributed to efficient passivation by hydrogen of competing nonradiative recombination centers via defects. This conclusion is confirmed from the ODMR studies.

  7. Band gap properties of Zn{sub 1-x}Cd{sub x}O alloys grown by molecular-beam epitaxy

    SciTech Connect

    Wang, X. J.; Buyanova, I. A.; Chen, W. M.; Izadifard, M.; Rawal, S.; Norton, D. P.; Pearton, S. J.; Osinsky, A.; Dong, J. W.; Dabiran, Amir

    2006-10-09

    Optical absorption and reflectance measurements are performed to evaluate compositional and temperature dependences of band gap energies of Zn{sub 1-x}Cd{sub x}O alloys grown by molecular-beam epitaxy. The compositional dependence of the band gap energy, determined by taking into account excitonic contributions, is shown to follow the trend E{sub g}(x)=3.37-2.82x+0.95x{sup 2}. Incorporation of Cd was also shown to somewhat slow down thermal variation of the band gap energies, beneficial for future device applications.

  8. Band gap tunability of molecular beam epitaxy grown lateral composition modulated GaInP structures by controlling V/III flux ratio

    SciTech Connect

    Park, K. W.; Park, C. Y.; Lee, Y. T.

    2012-07-30

    Lateral composition modulated (LCM) GaInP structures were grown on (001) GaAs substrate by molecular beam epitaxy with different V/III flux ratios. Band gap of LCM structures could be tuned from 1.93 eV to 1.83 eV by decreasing flux ratio while maintaining the same photoluminescence intensity, enhanced light absorption, and widened absorption spectrum. It is shown that for band gap tuning of LCM structures, flux ratio adjustment is a more viable method compared to growth temperature adjustment.

  9. Optimized growth of lattice-matched In{sub x}Al{sub 1-x}N/GaN heterostructures by molecular beam epitaxy

    SciTech Connect

    Schmult, S.; Siegrist, T.; Sergent, A. M.; Manfra, M. J.; Molnar, R. J.

    2007-01-08

    The authors present a systematic study on the growth of the ternary compound In{sub x}Al{sub 1-x}N by molecular beam epitaxy. This work concentrates on In mole fractions x around 0.17, as this composition is in-plane lattice matched to GaN. At a growth temperature of 540 degree sign C, high quality material was obtained using a total metal to nitrogen flux ratio of {approx}1. Using these growth parameters, high quality GaN/InAlN superlattices were obtained without growth interruptions.

  10. Magneto-transport properties of InAs nanowires laterally-grown by selective area molecular beam epitaxy on GaAs (110) masked substrates

    SciTech Connect

    Akabori, M.; Yamada, S.

    2013-12-04

    We prepared InAs nanowires (NWs) by lateral growth on GaAs (110) masked substrates in molecular beam epitaxy. We measured magneto-transport properties of the InAs NWs. In spite of parallel-NW multi-channels, we observed fluctuating magneto-conductance. From the fluctuation, we evaluated phase coherence length as a function of measurement temperature, and found decrease in the length with increase in the temperature. We also evaluate phase coherence length as a function of gate voltage.

  11. Effect of hydrostatic pressure on degradation of CdTe/CdMgTeheterostructures grown by molecular beam epitaxy on GaAs substrates

    SciTech Connect

    Wasik, D.; Baj, M.; Siwiec-Matuszyk, J.; Gronkowski, J.; Jasinski, J.; Karczewski, G.

    2001-04-18

    We have shown that external hydrostatic pressure leads to the creation of structural defects, mainly in the vicinity of the II-VI/GaAs interface in the CdTe/Cd{sub 1-x}Mg{sub x}Te heterostructures grown by the molecular beam epitaxy method on GaAs substrates. These defects propagating across the epilayer cause permanent damage to the samples from the point of view of their electrical properties. In contrast, photoluminescence spectra are only weakly influenced by pressure. Our results shed light on the degradation process observed even without pressure in II-VI-based heterostructures.

  12. New structure of three-terminal GaAs p(+)-n(-)-delta(p+)-n(-)-n(+) switching device prepared by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, Y. H.; Yarn, K. F.; Chang, C. Y.; Jame, M. S.

    1987-08-01

    A new three-terminal GaAs p(+)-n(-)-delta(p+)-n(-)-n(+), voltage-controlled switching device grown by molecular beam epitaxy is presented. A simple method to contact the third terminal is employed by applying the Au-Zn to the delta(p+) barrier using the B-groove etching technique, in which the delta(p+) barrier height can be directly modulated by the external voltage. The device may be more effective than other voltage-controlled devices due to the direct barrier modulation.

  13. Surface photo-voltage characterization of GaAs/AlGaAs single quantum well laser structures grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Muralidharan, R.; Ramesh, V.; Mishra, Puspashree; Srinivasan, T.

    2014-03-01

    We present surface photo-voltage (SPV) measurements on molecular beam epitaxy (MBE) grown single quantum well (SQW) laser structures. Each layer in the hetero-structure has been identified by measurement of the SPV signal after a controlled sequential chemical etching process. These results have been correlated with high resolution x-ray diffraction and photoluminescence (PL) measurements. Quantum confined Stark effect and the carrier screening of electric field have been taken into consideration both theoretically and experimentally to account for the differences observed in SPV and PL results. It is shown that SPV can be used as a very effective tool for evaluation of hetero-structures involving multiple layers.

  14. Investigation of the optical properties of GaAs with δ-Si doping grown by molecular-beam epitaxy at low temperatures

    SciTech Connect

    Lavrukhin, D. V. Yachmenev, A. E.; Bugaev, A. S.; Galiev, G. B.; Klimov, E. A.; Khabibullin, R. A.; Ponomarev, D. S.; Maltsev, P. P.

    2015-07-15

    Molecular-beam epitaxy is used for the preparation of structures based on “low-temperature” grown GaAs with introduced d-Si doping. Specific features in the photon-energy range of 1.28–1.48 eV are observed in the photoluminescence spectrum after structures annealing at temperatures of 520 and 580°C; these features are related to the formation of point defects and their complexes. The “pump–probe” light transmission measurements reveal that the characteristic lifetimes of nonequilibrium carriers in the fabricated structures amount to T{sup c} ≈ 1.2–1.5 ps.

  15. Incorporation model of N into GaInNAs alloys grown by radio-frequency plasma-assisted molecular beam epitaxy

    SciTech Connect

    Aho, A.; Korpijärvi, V.-M.; Tukiainen, A.; Puustinen, J.; Guina, M.

    2014-12-07

    We present a Maxwell-Boltzmann electron energy distribution based model for the incorporation rate of nitrogen into GaInNAs grown by molecular beam epitaxy (MBE) using a radio frequency plasma source. Nitrogen concentration is predicted as a function of radio-frequency system primary resistance, N flow, and RF power, and group III growth rate. The semi-empirical model is shown to be repeatable with a maximum error of 6%. The model was validated for two different MBE systems by growing GaInNAs on GaAs(100) with variable nitrogen composition of 0%–6%.

  16. Effects of using As2 and As4 on the optical properties of InGaAs quantum rods grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Li, L. H.; Patriarche, G.; Linfield, E. H.; Khanna, S. P.; Davies, A. G.

    2010-11-01

    We investigate the effect of the arsenic source (As2 and As4) on the optical properties of InGaAs quantum rods (QRs) grown by molecular beam epitaxy. Owing to differences in the In and Ga diffusion lengths under As2 and As4 fluxes, photoluminescence (PL) peak energies of the QR samples depend strongly on the As source when similar growth conditions are used. A marked improvement in the PL intensities from QR samples grown using As4 is achieved. However, for both As2 and As4, an increase of the As overpressure results in a PL intensity degradation, probably due to the formation of nonradiative recombination centers.

  17. Low-temperature GaN growth on silicon substrates by single gas-source epitaxy and photo-excitation

    SciTech Connect

    Trivedi, R.A.; Tolle, J.; Chizmeshya, A.V.G.; Roucka, R.; Ritter, Cole; Kouvetakis, J.; Tsong, I.S.T.

    2005-08-15

    We report a unique low-temperature growth method for epitaxial GaN on Si(111) substrates via a ZrB{sub 2}(0001) buffer layer. The method utilizes the decomposition of a single gas-source precursor (D{sub 2}GaN{sub 3}){sub 3} on the substrate surface to form GaN. The film growth process is further promoted by irradiation of ultraviolet light to enhance the growth rate and ordering of the film. The best epitaxial film quality is achieved at a growth temperature of 550 deg. C with a growth rate of 3 nm/min. The films exhibit intense photoluminescence emission at 10 K with a single peak at 3.48 eV, indicative of band-edge emission for a single-phase hexagonal GaN film. The growth process achieved in this study is compatible with low Si processing temperatures and also enables direct epitaxy of GaN on ZrB{sub 2} in contrast to conventional metalorganic chemical vapor deposition based approaches.

  18. Molecular beam epitaxy growth of high quality p-doped SnS van der Waals epitaxy on a graphene buffer layer

    SciTech Connect

    Wang, W.; Leung, K. K.; Fong, W. K.; Wang, S. F.; Surya, C.; Hui, Y. Y.; Lau, S. P.; Chen, Z.; Shi, L. J.; Cao, C. B.

    2012-05-01

    We report on the systematic investigation of optoelectronic properties of tin (IV) sulfide (SnS) van der Waals epitaxies (vdWEs) grown by molecular beam epitaxy (MBE) technique. Energy band simulation using commercial CASTEP code indicates that SnS has an indirect bandgap of size 0.982 eV. Furthermore, our simulation shows that elemental Cu can be used as a p-type dopant for the material. Growth of high quality SnS thin films is accomplished by MBE technique using graphene as the buffer layer. We observed significant reduction in the rocking curve FWHM over the existing published values. Crystallite size in the range of 2-3 {mu}m is observed which is also significantly better than the existing results. Measurement of the absorption coefficient, {alpha}, is performed using a Hitachi U-4100 Spectrophotometer system which demonstrate large values of {alpha} of the order of 10{sup 4} cm{sup -1}. Sharp cutoff in the values of {alpha}, as a function of energy, is observed for the films grown using a graphene buffer layer indicating low concentration of localized states in the bandgap. Cu-doping is achieved by co-evaporation technique. It is demonstrated that the hole concentration of the films can be controlled between 10{sup 16} cm{sup -3} and 5 x 10{sup 17}cm{sup -3} by varying the temperature of the Cu K-cell. Hole mobility as high as 81 cm{sup 2}V{sup -1}s{sup -1} is observed for SnS films on graphene/GaAs(100) substrates. The improvements in the physical properties of the films are attributed to the unique layered structure and chemically saturated bonds at the surface for both SnS and the graphene buffer layer. Consequently, the interaction between the SnS thin films and the graphene buffer layer is dominated by van der Waals force and structural defects at the interface, such as dangling bonds or dislocations, are substantially reduced.

  19. Electron spin resonance of Zn{sub 1-x}Mg{sub x}O thin films grown by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Wassner, T. A.; Stutzmann, M.; Brandt, M. S.; Laumer, B.; Althammer, M.; Goennenwein, S. T. B.; Eickhoff, M.

    2010-08-30

    Zn{sub 1-x}Mg{sub x}O thin films with a Mg content x between 0 and 0.42 grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates were investigated by electron spin resonance at 5 K. Above band gap illumination induces a persistent resonance signal, which is attributed to free conduction band electrons. The g-factors of the Zn{sub 1-x}Mg{sub x}O epitaxial layers and their anisotropy were determined experimentally and an increase from g{sub ||}=1.957 for x=0 to g{sub ||}=1.970 for x=0.42 was found, accompanied by a decrease in anisotropy. A comparison with g-factors of the Al{sub x}Ga{sub 1-x}N system is also given.

  20. Near-infrared intersubband absorption in molecular-beam epitaxy-grown lattice-matched InAlN/GaN superlattices

    SciTech Connect

    Malis, O.; Edmunds, C.; Manfra, M. J.; Sivco, D. L.

    2009-04-20

    Strong near-infrared intersubband absorption is observed directly at room temperature in silicon-doped lattice-matched InAlN/GaN superlattices grown by molecular-beam epitaxy on GaN templates grown by hydride vapor-phase epitaxy. X-ray diffraction characterization of the heterostructures indicates excellent layer thickness uniformity and low interface roughness. For 2-4.5 nm quantum wells, the intersubband transition energies span the technologically relevant range between 2.3 and 2.9 {mu}m. The experimental results are in good agreement with calculations of the transition energies using a conduction band offset of 1 eV and spontaneous polarization of 3 MV/cm.

  1. Observation of reflection high-energy electron diffraction oscillation during metalorganic-molecular-beam epitaxy of AlAs and control of carbon incorporation

    NASA Astrophysics Data System (ADS)

    Ganapathy, Sasikala; Kurimoto, Makoto; Thilakan, Periyasamy; Uesugi, Kasturi; Suemune, Ikuo; Machida, Hideaki; Shimoyama, Norio

    2003-10-01

    The in situ observation of reflection high-energy electron diffraction (RHEED) oscillations during the metalorganic-molecular-beam epitaxy deposition of AlAs and AlGaAs epitaxial layers is reported. In situ RHEED oscillations as well as atomic force microscopy measurements confirmed the layer-by-layer growth of the AlAs as well as the AlGaAs layers on GaAs substrates. RHEED oscillation was successfully applied to the precise control of the AlAs/GaAs superlattices and of the alloy compositions in the AlGaAs alloys. High-resolution x-ray diffraction and Hall effect measurements revealed the unintentional doping of carbon into the AlGaAs layers, but it was found that the increase in the V/III ratio is able to reduce the carbon incorporation.

  2. Structural, Optical and Electrical Properties of n-type GaN on Si (111) Grown by RF-plasma assisted Molecular Beam Epitaxy

    SciTech Connect

    Chin, C. W.; Hassan, Z.; Yam, F. K.

    2008-05-20

    In this paper, we present the study of the structural, optical and electrical of n-type GaN grown on silicon (111) by RF plasma-assisted molecular beam epitaxy (RF-MBE). X-ray diffraction (XRD) measurement reveals that the GaN was epitaxially grown on silicon. For the photoluminescence (PL) measurement, a sharp and intense peak at 364.5 nm indicates that the sample is of high optical quality. Hall effect measurement shows that the film has a carrier concentration of 3.28x10{sup 19} cm{sup -3}. The surface of the n-type GaN was smooth and no any cracks and pits.

  3. Growth of InP on GaAs (001) by hydrogen-assisted low-temperature solid-source molecular beam epitaxy

    SciTech Connect

    Postigo, P. A.; Suarez, F.; Sanz-Hervas, A.; Sangrador, J.; Fonstad, C. G.

    2008-01-01

    Direct heteroepitaxial growth of InP layers on GaAs (001) wafers has been performed by solid-source molecular beam epitaxy assisted by monoatomic hydrogen (H*). The epitaxial growth has been carried out using a two-step method: for the initial stage of growth the temperature was as low as 200 deg. C and different doses of H* were used; after this, the growth proceeded without H* while the temperature was increased slowly with time. The incorporation of H* drastically increased the critical layer thickness observed by reflection high-energy electron diffraction; it also caused a slight increase in the luminescence at room temperature, while it also drastically changed the low-temperature luminescence related to the presence of stoichiometric defects. The samples were processed by rapid thermal annealing. The annealing improved the crystalline quality of the InP layers measured by high-resolution x-ray diffraction, but did not affect their luminescent behavior significantly.

  4. IV-VI diluted magnetic semiconductor Ge{sub 1-x}Mn{sub x}Te epilayer grown by molecular beam epitaxy

    SciTech Connect

    Fukuma, Y.; Goto, K.; Senba, S.; Miyawaki, S.; Asada, H.; Koyanagi, T.; Sato, H.

    2008-03-01

    Growth of the IV-VI diluted magnetic semiconductor Ge{sub 1-x}Mn{sub x}Te by molecular beam epitaxy is reported. The epitaxial growth of Ge{sub 1-x}Mn{sub x}Te (x=0.13) on BaF{sub 2} (111) with a GeTe buffer layer is confirmed by x-ray diffraction and reflection high-energy electron diffraction. The ferromagnetic order is clearly established by the magnetization and magnetotransport measurements. The Curie temperature of 100 K is obtained for the hole concentration of 7.86x10{sup 20} cm{sup -3}. The existence of the strong p-d exchange which gives rise to the ferromagnetic order is revealed by the hard x-ray photoemission measurements.

  5. Topological insulator Bi{sub 2}Se{sub 3} thin films grown on double-layer graphene by molecular beam epitaxy

    SciTech Connect

    Song Canli; Jiang Yeping; Chang Cuizu; Xue Qikun; Wang Yilin; Zhang Yi; Wang Lili; He Ke; Fang Zhong; Dai Xi; Xie Xincheng; Ma Xucun; Chen Xi; Jia Jinfeng; Wang Yayu; Qi Xiaoliang; Zhang Shoucheng

    2010-10-04

    Atomically flat thin films of topological insulator Bi{sub 2}Se{sub 3} have been grown on double-layer graphene formed on 6H-SiC(0001) substrate by molecular beam epitaxy. By a combined study of reflection high energy electron diffraction and scanning tunneling microscopy, we identified the Se-rich condition and temperature criterion for layer-by-layer growth of epitaxial Bi{sub 2}Se{sub 3} films. The as-grown films without doping exhibit a low defect density of 1.0{+-}0.2x10{sup 11}/cm{sup 2}, and become a bulk insulator at a thickness of ten quintuple layers, as revealed by in situ angle resolved photoemission spectroscopy measurement.

  6. Growth mechanisms of plasma-assisted molecular beam epitaxy of green emission InGaN/GaN single quantum wells at high growth temperatures

    SciTech Connect

    Yang, W. C.; Wu, C. H.; Tseng, Y. T.; Chiu, S. Y.; Cheng, K. Y.

    2015-01-07

    The results of the growth of thin (∼3 nm) InGaN/GaN single quantum wells (SQWs) with emission wavelengths in the green region by plasma-assisted molecular beam epitaxy are present. An improved two-step growth method using a high growth temperature up to 650 °C is developed to increase the In content of the InGaN SQW to 30% while maintaining a strong luminescence intensity near a wavelength of 506 nm. The indium composition in InGaN/GaN SQW grown under group-III-rich condition increases with increasing growth temperature following the growth model of liquid phase epitaxy. Further increase in the growth temperature to 670 °C does not improve the photoluminescence property of the material due to rapid loss of indium from the surface and, under certain growth conditions, the onset of phase separation.

  7. Two-dimensional semiconductor HfSe{sub 2} and MoSe{sub 2}/HfSe{sub 2} van der Waals heterostructures by molecular beam epitaxy

    SciTech Connect

    Aretouli, K. E.; Tsipas, P.; Tsoutsou, D.; Marquez-Velasco, J.; Xenogiannopoulou, E.; Giamini, S. A.; Vassalou, E.; Kelaidis, N.; Dimoulas, A.

    2015-04-06

    Using molecular beam epitaxy, atomically thin 2D semiconductor HfSe{sub 2} and MoSe{sub 2}/HfSe{sub 2} van der Waals heterostructures are grown on AlN(0001)/Si(111) substrates. Details of the electronic band structure of HfSe{sub 2} are imaged by in-situ angle resolved photoelectron spectroscopy indicating a high quality epitaxial layer. High-resolution surface tunneling microscopy supported by first principles calculations provides evidence of an ordered Se adlayer, which may be responsible for a reduction of the measured workfunction of HfSe{sub 2} compared to theoretical predictions. The latter reduction minimizes the workfunction difference between the HfSe{sub 2} and MoSe{sub 2} layers resulting in a small valence band offset of only 0.13 eV at the MoSe{sub 2}/HfSe{sub 2} heterointerface and a weak type II band alignment.

  8. Investigation of ZnO thin films deposited on ferromagnetic metallic buffer layer by molecular beam epitaxy toward realization of ZnO-based magnetic tunneling junctions

    SciTech Connect

    Belmoubarik, M.; Nozaki, T.; Sahashi, M.; Endo, H.

    2013-05-07

    Deposition of ZnO thin films on a ferromagnetic metallic buffer layer (Co{sub 3}Pt) by molecular beam epitaxy technique was investigated for realization of ZnO-based magnetic tunneling junctions with good quality hexagonal ZnO films as tunnel barriers. For substrate temperature of 600 Degree-Sign C, ZnO films exhibited low oxygen defects and high electrical resistivity of 130 {Omega} cm. This value exceeded that of hexagonal ZnO films grown by sputtering technique, which are used as tunnel barriers in ZnO-MTJs. Also, the effect of oxygen flow during deposition on epitaxial growth conditions and Co{sub 3}Pt surface oxidation was discussed.

  9. Layer by layer growth of BaTiO 3 thin films with extremely smooth surfaces by laser molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, H. S.; Ma, K.; Cui, D. F.; Peng, Z. Q.; Zhou, Y. L.; Lu, H. B.; Chen, Z. H.; Li, L.; Yang, G. Z.

    1997-05-01

    Using pure ozone-assisted laser molecular beam epitaxy, we have grown c-axis-oriented single crystal BaTiO 3 thin films on SrTiO 3 substrates at temperatures ( Ts) of 400-750°C and under ambient gas pressures of 5 × 10 -5 to 1 × 10 -1 Pa, respectively. Stripy reflection high-energy electron diffraction (RHEED) patterns and regular RHEED intensity oscillations reveal the smooth surface and layer-by-layer epitaxial growth of the films. Scanning electron microscopy analysis shows that the films are free of pinholes, grain boundaries and outgrowths on the surface. In addition, we found a strong dependence of the film lattice constant c on Ts, which might be related to the strain in the film.

  10. Selective-area growth of GaN nanowires on SiO2-masked Si (111) substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kruse, J. E.; Lymperakis, L.; Eftychis, S.; Adikimenakis, A.; Doundoulakis, G.; Tsagaraki, K.; Androulidaki, M.; Olziersky, A.; Dimitrakis, P.; Ioannou-Sougleridis, V.; Normand, P.; Koukoula, T.; Kehagias, Th.; Komninou, Ph.; Konstantinidis, G.; Georgakilas, A.

    2016-06-01

    We analyze a method to selectively grow straight, vertical gallium nitride nanowires by plasma-assisted molecular beam epitaxy (MBE) at sites specified by a silicon oxide mask, which is thermally grown on silicon (111) substrates and patterned by electron-beam lithography and reactive-ion etching. The investigated method requires only one single molecular beam epitaxy MBE growth process, i.e., the SiO2 mask is formed on silicon instead of on a previously grown GaN or AlN buffer layer. We present a systematic and analytical study involving various mask patterns, characterization by scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy, as well as numerical simulations, to evaluate how the dimensions (window diameter and spacing) of the mask affect the distribution of the nanowires, their morphology, and alignment, as well as their photonic properties. Capabilities and limitations for this method of selective-area growth of nanowires have been identified. A window diameter less than 50 nm and a window spacing larger than 500 nm can provide single nanowire nucleation in nearly all mask windows. The results are consistent with a Ga diffusion length on the silicon dioxide surface in the order of approximately 1 μm.

  11. Exciton localization and large Stokes shift in quaternary BeMgZnO grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Toporkov, Mykyta; Ullah, Md. Barkat; Hafiz, Shopan; Nakagawara, Tanner; Avrutin, Vitaliy; Morkoç, Hadis; Özgür, Ümit

    2016-02-01

    Owing to wide range bandgap tunability to more than 5 eV, the quaternary (Be,Mg)ZnO solid solutions are attractive for a variety of UV optoelectronic applications, inclusive of solar blind photodetectors, and intersubband transition devices. The mutual compensation effects of Be and Mg on the formation energy and strain allows a wide range of compositions and bandgaps beyond those achievable by MgZnO and BeZnO ternaries. Localization effects are well pronounced in such wide-bandgap semiconductor alloys due to large differences in metal covalent radii and the lattice constants of the binaries, resulting in strain-driven compositional variations within the film and consequently large potential fluctuations, in addition to that possibly caused by defects. However, carrier localization may suppress recombination through nonradiative channels, and thus, facilitate high-efficiency optoelectronic devices. To investigate potential fluctuations and localization in BexMgyZn(1-x-y)O films grown by plasma-assisted molecular beam epitaxy, optical absorption and steady-state and time-resolved photoluminescence (PL) measurements were performed. O-polar BexMgyZn(1-x-y)O samples grown on GaN templates with compositions up to x = 0.04 and y = 0.18 were used for timeresolved studies, and O-polar BexMgyZn(1-x-y)O samples grown on sapphire with compositions up to x = 0.19 and y = 0.52 were used for absorption measurements. From spectrally resolved PL transients, BeMgZnO samples with higher Mg/Be content ratio were found to exhibit smaller localization depth, Δ0=98 meV for Be0.04Mg0.17Zn0.79O and Δ0=173 meV for Be0.10Mg0.25Zn0.65O, compared to samples with smaller Mg/Be ratio, Δ0=268 meV for Be0.11Mg0.15Zn0.74O. Similar correlation is observed in temporal redshift of the PL peak position of 8 meV, 42 meV and 55 meV for Be0.04Mg0.17Zn0.79O, Be0.10Mg0.25Zn0.65O and Be0.11Mg0.15Zn0.74O, respectively, that originates from potential fluctuations and removal of band filling effect in the

  12. Effect of nitridation on the growth of GaN on ZrB{sub 2}(0001)/Si(111) by molecular-beam epitaxy

    SciTech Connect

    Wang, Z.-T.; Yamada-Takamura, Y.; Fujikawa, Y.; Sakurai, T.; Xue, Q. K.; Tolle, J.; Kouvetakis, J.; Tsong, I. S. T.

    2006-08-01

    The effect of nitridation on the epitaxial growth of GaN on lattice-matched ZrB{sub 2}(0001) films prepared ex situ and in situ was studied using an ultrahigh-vacuum molecular-beam epitaxy (MBE)-scanning probe microscopy system. The growth of GaN was carried out by rf-plasma-assisted MBE, and epitaxy of wurtzite GaN was observed on both ex situ and in situ prepared ZrB{sub 2} samples. The polarity was found to be consistently N-polar regardless of the samples, based on the observation of a series of N-polar Ga-rich reconstructions: (3x3) (6x6), and c(6x12). The nitridation of ZrB{sub 2} film was conducted by exposing it to active nitrogen and well-ordered hexagonal-BN (h-BN) formation was observed when the annealing temperature was above 900 deg.C. The partially formed BN layer affected neither the epitaxy nor the polarity of GaN, but when the surface was fully covered with well-ordered h-BN, GaN growth did not occur.

  13. Deep levels in a-plane, high Mg-content Mg{sub x}Zn{sub 1-x}O epitaxial layers grown by molecular beam epitaxy

    SciTech Connect

    Guer, Emre; Tabares, G.; Hierro, A.; Chauveau, J. M.

    2012-12-15

    Deep level defects in n-type unintentionally doped a-plane Mg{sub x}Zn{sub 1-x}O, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of Mg{sub x}Zn{sub 1-x}O were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of E{sub c} - 1.4 eV, 2.1 eV, 2.6 V, and E{sub v} + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at E{sub c} - 2.1 eV, E{sub v} + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at E{sub v} + 0.3 eV and E{sub c} - 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the E{sub v} + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the E{sub c} - 1.4 eV and E{sub c} - 2.6 eV levels in Mg alloyed samples.

  14. Growth of polar and non-polar nitride semiconductor quasi-substrates by hydride vapor phase epitaxy for the development of optoelectronic devices by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Moldawer, Adam Lyle

    The family of nitride semiconductors has had a profound influence on the development of optoelectronics for a large variety of applications. However, as of yet there are no native substrates commercially available that are grown by liquid phase methods as with Si and GaAs. As a result, the majority of electronic and optoelectronic devices are grown heteroepitaxially on sapphire and SiC. This PhD research addresses both the development of polar and non-polar GaN and AIN templates by Hydride Vapor Phase Epitaxy (HVPE) on sapphire and SiC substrates, as well as the growth and characterization of optoelectronic devices on these templates by molecular beam epitaxy (MBE). Polar and non-polar GaN templates have been grown in a vertical HVPE reactor on the C- and R-planes of sapphire respectively. The growth conditions have been optimized to allow the formation for thick (50um) GaN templates without cracks. These templates were characterized structurally by studying their surface morphologies by SEM and AFM, and their structure through XRD and TEM. The polar C-plane GaN templates were found to be atomically smooth. However, the surface morphology of the non-polar GaN films grown on the R-plane of sapphire were found to have a facetted surface morphology, with the facets intersecting at 120° angles. This surface morphology reflects an equilibrium growth, since the A-plane of GaN grows faster than the M-planes of GaN due to the lower atomic density of the plane. For the development of deep-UV optoelectronics, it is required to grow AIGaN quantum wells on AIN templates. However, since AIN is a high melting point material, such templates have to be grown at higher temperatures, close to half the melting point of the material (1500 °C). As these temperatures cannot be easily obtained by traditional furnace heating, an HVPE reactor has been designed to heat the substrate inductively to these temperatures. This apparatus has been used to grow high-quality, transparent AIN films

  15. Growth study of nonpolar Zn{sub 1-x}Mg{sub x}O epitaxial films on a-plane bulk ZnO by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Laumer, Bernhard; Schuster, Fabian; Stutzmann, Martin; Bergmaier, Andreas; Dollinger, Guenther; Vogel, Stephen; Gries, Katharina I.; Volz, Kerstin; Eickhoff, Martin

    2012-09-17

    Nonpolar Zn{sub 1-x}Mg{sub x}O epitaxial films were grown by plasma-assisted molecular beam epitaxy on a-plane ZnO substrates. A smooth surface morphology was accomplished under oxygen-rich growth conditions. The benefits of the use of ZnO substrates on the structural properties are reflected by a low-density of threading dislocations. Furthermore, no indications for the generation of basal plane stacking faults are found. The pseudomorphic growth on a-plane ZnO substrates efficiently locks the epitaxial Zn{sub 1-x}Mg{sub x}O films to the wurtzite structure up to x = 0.25. The Mg concentration is not constant and increases with larger thickness. The optical properties reflect the influence of alloy disorder.

  16. Accurate determination of optical bandgap and lattice parameters of Zn{sub 1-x}Mg{sub x}O epitaxial films (0{<=}x{<=}0.3) grown by plasma-assisted molecular beam epitaxy on a-plane sapphire

    SciTech Connect

    Laumer, Bernhard; Schuster, Fabian; Stutzmann, Martin; Bergmaier, Andreas; Dollinger, Guenther; Eickhoff, Martin

    2013-06-21

    Zn{sub 1-x}Mg{sub x}O epitaxial films with Mg concentrations 0{<=}x{<=}0.3 were grown by plasma-assisted molecular beam epitaxy on a-plane sapphire substrates. Precise determination of the Mg concentration x was performed by elastic recoil detection analysis. The bandgap energy was extracted from absorption measurements with high accuracy taking electron-hole interaction and exciton-phonon complexes into account. From these results a linear relationship between bandgap energy and Mg concentration is established for x{<=}0.3. Due to alloy disorder, the increase of the photoluminescence emission energy with Mg concentration is less pronounced. An analysis of the lattice parameters reveals that the epitaxial films grow biaxially strained on a-plane sapphire.

  17. Optical and structural properties of microcrystalline GaN on an amorphous substrate prepared by a combination of molecular beam epitaxy and metal–organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Min, Jung-Wook; Hwang, Hyeong-Yong; Kang, Eun-Kyu; Park, Kwangwook; Kim, Ci-Hyun; Lee, Dong-Seon; Jho, Young-Dahl; Bae, Si-Young; Lee, Yong-Tak

    2016-05-01

    Microscale platelet-shaped GaN grains were grown on amorphous substrates by a combined epitaxial growth method of molecular beam epitaxy (MBE) and metal–organic chemical vapor deposition (MOCVD). First, MBE GaN was grown on an amorphous substrate as a pre-orienting layer and its structural properties were investigated. Second, MOCVD grown GaN samples using the different growth techniques of planar and selective area growth (SAG) were comparatively investigated by transmission electron microscopy (TEM), cathodoluminescence (CL), and photoluminescence (PL). In MOCVD planar GaN, strong bound exciton peaks dominated despite the high density of the threading dislocations (TDs). In MOCVD SAG GaN, on the other hand, TDs were clearly reduced with bending, but basal stacking fault (BSF) PL peaks were observed at 3.42 eV. The combined epitaxial method not only provides a deep understanding of the growth behavior but also suggests an alternative approach for the growth of GaN on amorphous substances.

  18. Molecular-beam epitaxy of monolayer and bilayer WSe2: a scanning tunneling microscopy/spectroscopy study and deduction of exciton binding energy

    NASA Astrophysics Data System (ADS)

    Liu, H. J.; Jiao, L.; Xie, L.; Yang, F.; Chen, J. L.; Ho, W. K.; Gao, C. L.; Jia, J. F.; Cui, X. D.; Xie, M. H.

    2015-09-01

    Interest in two-dimensional (2D) transition-metal dichalcogenides (TMDs) has prompted some recent efforts to grow ultrathin layers of these materials epitaxially using molecular-beam epitaxy (MBE). However, growths of monolayer (ML) and bilayer (BL) WSe2—an important member of the TMD family—by the MBE method remain uncharted, probably because of the difficulty in generating tungsten fluxes from the elemental source. In this work, we present a scanning tunneling microscopy and spectroscopy (STM/S) study of MBE-grown WSe2 ML and BL, showing atomically flat epifilm with no domain boundary (DB) defect. This contrasts epitaxial MoSe2 films grown by the same method, where a dense network of the DB defects is present. The STS measurements of ML and BL WSe2 domains of the same sample reveal not only the bandgap narrowing upon increasing the film thickness from ML to BL, but also a band-bending effect across the boundary (step) between ML and BL domains. This band-bending appears to be dictated by the edge states at steps of the BL islands. Finally, comparison is made between the STS-measured electronic bandgaps with the exciton emission energies measured by photoluminescence, and the exciton binding energies in ML and BL WSe2 (and MoSe2) are thus estimated.

  19. Surface effects of vapour-liquid-solid driven Bi surface droplets formed during molecular-beam-epitaxy of GaAsBi

    NASA Astrophysics Data System (ADS)

    Steele, J. A.; Lewis, R. A.; Horvat, J.; Nancarrow, M. J. B.; Henini, M.; Fan, D.; Mazur, Y. I.; Schmidbauer, M.; Ware, M. E.; Yu, S.-Q.; Salamo, G. J.

    2016-07-01

    Herein we investigate a (001)-oriented GaAs1‑xBix/GaAs structure possessing Bi surface droplets capable of catalysing the formation of nanostructures during Bi-rich growth, through the vapour-liquid-solid mechanism. Specifically, self-aligned “nanotracks” are found to exist trailing the Bi droplets on the sample surface. Through cross-sectional high-resolution transmission electron microscopy the nanotracks are revealed to in fact be elevated above surface by the formation of a subsurface planar nanowire, a structure initiated mid-way through the molecular-beam-epitaxy growth and embedded into the epilayer, via epitaxial overgrowth. Electron microscopy studies also yield the morphological, structural, and chemical properties of the nanostructures. Through a combination of Bi determination methods the compositional profile of the film is shown to be graded and inhomogeneous. Furthermore, the coherent and pure zincblende phase property of the film is detailed. Optical characterisation of features on the sample surface is carried out using polarised micro-Raman and micro-photoluminescence spectroscopies. The important light producing properties of the surface nanostructures are investigated through pump intensity-dependent micro-PL measurements, whereby relatively large local inhomogeneities are revealed to exist on the epitaxial surface for important optical parameters. We conclude that such surface effects must be considered when designing and fabricating optical devices based on GaAsBi alloys.

  20. A low-temperature growth process of GaAs by electron-cyclotron-resonance plasma-excited molecular-beam-epitaxy (ECR-MBE)

    NASA Astrophysics Data System (ADS)

    Kondo, Naoto; Nanishi, Yasushi

    1988-09-01

    Taking advantage of plasma excitation, surface cleaning and growth process are realized at low temperatures by electron-cyclotron-resonance (ECR) plasma-excited molecular-beam-epitaxy (MBE). Prior to growth, substrates are cleaned by exposure to hydrogen plasma at temperatures ranging from 300 to 550°C. Arsine gas is introduced and cracked in an ECR plasma generation chamber. Gallium is supplied either as trimethylgallium (TMG) or as metallic Ga. Epitaxial films are successfully grown at substrate temperatures low as 430°C for the TMG-arsine system and 350°C for the metallic Ga-arsine system. The growth rate for the TMG-arsine system is found to be governed by a balance between TMG decomposition and surface atom desorption. By contrast, the metallic Ga-arsine system is only governed by the desorption process. Exposure to plasma is found to promote desorption of atoms migrating on the substrate surface. The interface between the substrate and the epitaxial layer produced by the ECR-MBE process is found to be clean without piling up of impurity.

  1. Interfacial structure and defect analysis of nonpolar ZnO films grown on R-plane sapphire by molecular beam epitaxy

    SciTech Connect

    Vennegues, P.; Korytov, M.; Deparis, C.; Zuniga-Perez, J.; Morhain, C.; Chauveau, J. M.

    2008-04-15

    The interfacial relationship and the microstructure of nonpolar (11-20) ZnO films epitaxially grown on (1-102) R-plane sapphire by molecular beam epitaxy are investigated by transmission electron microscopy. The already-reported epitaxial relationships [1-100]{sub ZnO} parallel [11-20]{sub sapphire} and <0001>{sub ZnO} parallel [-1101]{sub sapphire} are confirmed, and we have determined the orientation of the Zn-O (cation-anion) bond along [0001]{sub ZnO} in the films as being uniquely defined with respect to a reference surface Al-O bond on the sapphire substrate. The microstructure of the films is dominated by the presence of I{sub 1} basal stacking faults [density=(1-2)x10{sup 5} cm{sup -1}] and related partial dislocations [density=(4-7)x10{sup 10} cm{sup -2}]. It is shown that I{sub 1} basal stacking faults correspond to dissociated perfect dislocations, either c or a+c type.

  2. Surface effects of vapour-liquid-solid driven Bi surface droplets formed during molecular-beam-epitaxy of GaAsBi

    PubMed Central

    Steele, J. A.; Lewis, R. A.; Horvat, J.; Nancarrow, M. J. B.; Henini, M.; Fan, D.; Mazur, Y. I.; Schmidbauer, M.; Ware, M. E.; Yu, S.-Q.; Salamo, G. J.

    2016-01-01

    Herein we investigate a (001)-oriented GaAs1−xBix/GaAs structure possessing Bi surface droplets capable of catalysing the formation of nanostructures during Bi-rich growth, through the vapour-liquid-solid mechanism. Specifically, self-aligned “nanotracks” are found to exist trailing the Bi droplets on the sample surface. Through cross-sectional high-resolution transmission electron microscopy the nanotracks are revealed to in fact be elevated above surface by the formation of a subsurface planar nanowire, a structure initiated mid-way through the molecular-beam-epitaxy growth and embedded into the epilayer, via epitaxial overgrowth. Electron microscopy studies also yield the morphological, structural, and chemical properties of the nanostructures. Through a combination of Bi determination methods the compositional profile of the film is shown to be graded and inhomogeneous. Furthermore, the coherent and pure zincblende phase property of the film is detailed. Optical characterisation of features on the sample surface is carried out using polarised micro-Raman and micro-photoluminescence spectroscopies. The important light producing properties of the surface nanostructures are investigated through pump intensity-dependent micro-PL measurements, whereby relatively large local inhomogeneities are revealed to exist on the epitaxial surface for important optical parameters. We conclude that such surface effects must be considered when designing and fabricating optical devices based on GaAsBi alloys. PMID:27377213

  3. Surface effects of vapour-liquid-solid driven Bi surface droplets formed during molecular-beam-epitaxy of GaAsBi.

    PubMed

    Steele, J A; Lewis, R A; Horvat, J; Nancarrow, M J B; Henini, M; Fan, D; Mazur, Y I; Schmidbauer, M; Ware, M E; Yu, S-Q; Salamo, G J

    2016-01-01

    Herein we investigate a (001)-oriented GaAs1-xBix/GaAs structure possessing Bi surface droplets capable of catalysing the formation of nanostructures during Bi-rich growth, through the vapour-liquid-solid mechanism. Specifically, self-aligned "nanotracks" are found to exist trailing the Bi droplets on the sample surface. Through cross-sectional high-resolution transmission electron microscopy the nanotracks are revealed to in fact be elevated above surface by the formation of a subsurface planar nanowire, a structure initiated mid-way through the molecular-beam-epitaxy growth and embedded into the epilayer, via epitaxial overgrowth. Electron microscopy studies also yield the morphological, structural, and chemical properties of the nanostructures. Through a combination of Bi determination methods the compositional profile of the film is shown to be graded and inhomogeneous. Furthermore, the coherent and pure zincblende phase property of the film is detailed. Optical characterisation of features on the sample surface is carried out using polarised micro-Raman and micro-photoluminescence spectroscopies. The important light producing properties of the surface nanostructures are investigated through pump intensity-dependent micro-PL measurements, whereby relatively large local inhomogeneities are revealed to exist on the epitaxial surface for important optical parameters. We conclude that such surface effects must be considered when designing and fabricating optical devices based on GaAsBi alloys. PMID:27377213

  4. Impact of growth conditions on ZnO homoepitaxial films on ZnO substrates by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wei, Ming; Boutwell, R. Casey; Schoenfeld, Winston V.

    2013-03-01

    ZnO thin films were epitaxially grown on Zn-polar (0001) ZnO substrates by plasma-assisted molecular beam epitaxy. Surface root mean square (rms) roughness below 0.3 nm was achieved on a large range of growth temperatures by growing on ZnO substrates with 0.5 degree miscut angle toward [11¯00] axis. Surface treatment with acid etching and ozone exposure was required to remove contamination such as silica residual and carboxyl and carbonate groups on the surface. Removal of these surface impurities reduces the likelihood of extrinsic defect migration into the epitaxial films. High growth temperature (> 640°C) and oxygen rich conditions were required for films with terrace steps, but resulted in a very low growth rate (~30nm/h) and low photoluminescence (PL) lifetimes of lower than 50 ps. With moderate growth temperature (~610°C), higher growth rate and higher PL lifetime with up to 380 ps were achieved. EIT was used for the oxygen plasma to reduce reactive oxygen species etching of the surface, resulting in a higher growth rate and fewer defects in the films. Good crystalline quality was evident in Xray rocking curves with consistent narrow full width at half maximum (FWHM) of (0002), (101¯2) and (202¯1) peaks, indicating low threading dislocations. Both room-temperature and low-temperature photoluminescence indicated high optical quality of the resultant films with few non-radiative recombination centers.

  5. Suppression of planar defects in the molecular beam epitaxy of GaAs/ErAs/GaAs heterostructures

    SciTech Connect

    Crook, Adam M.; Nair, Hari P.; Ferrer, Domingo A.; Bank, Seth R.

    2011-08-15

    We present a growth method that overcomes the mismatch in rotational symmetry of ErAs and conventional III-V semiconductors, allowing for epitaxially integrated semimetal/semiconductor heterostructures. Transmission electron microscopy and reflection high-energy electron diffraction reveal defect-free overgrowth of ErAs layers, consisting of >2x the total amount of ErAs that can be embedded with conventional layer-by-layer growth methods. We utilize epitaxial ErAs nanoparticles, overgrown with GaAs, as a seed to grow full films of ErAs. Growth proceeds by diffusion of erbium atoms through the GaAs spacer, which remains registered to the underlying substrate, preventing planar defect formation during subsequent GaAs growth. This growth method is promising for metal/semiconductor heterostructures that serve as embedded Ohmic contacts to epitaxial layers and epitaxially integrated active plasmonic devices.

  6. Low density of self-assembled InAs quantum dots grown by solid-source molecular beam epitaxy on InP(001)

    SciTech Connect

    Dupuy, E.; Regreny, P.; Robach, Y.; Gendry, M.; Chauvin, N.; Tranvouez, E.; Bremond, G.; Bru-Chevallier, C.; Patriarche, G.

    2006-09-18

    The authors report on a postgrowth method to obtain low density InAs/InP(001) quantum dots by solid-source molecular beam epitaxy. They used an approach based on the ripening of the InAs sticks, which is triggered by the sample cooling under arsenic overpressure, before InP capping. Atomic force microscopy images show the evolution of InAs islands from sticks oriented along the [1-10] direction to dot-shaped islands with a density that can be reduced to about 2x10{sup 9} dots/cm{sup 2}. Macro- and microphotoluminescence reveal that these diluted InAs dots exhibit a strong spatial confinement and emit in the 1.55 {mu}m range.

  7. Strong affinity of hydrogen for the GaN(000-1) surface: Implications for molecular beam epitaxy and metalorganic chemical vapor deposition

    SciTech Connect

    Northrup, J.E.; Neugebauer, J.

    2004-10-18

    The stabilities of clean and hydrogen covered GaN(000-1) surfaces are determined using density functional theory together with a finite temperature thermodynamics approach. Hydrogen has an extremely high affinity for the N-face surface: Even under ultrahigh vacuum conditions as realized in molecular beam epitaxial growth, with a residual hydrogen pressure of 10{sup -12} atm, the hydrogen terminated surface is, for very N-rich conditions, more stable than any clean surface. A transition to a surface covered by a Ga adlayer is predicted to occur as the Ga chemical potential increases. In typical metalorganic chemical vapor deposition conditions the (000-1) surface is predicted to be covered by 0.75 monolayers of hydrogen. The slower growth rate on the (000-1) surface in comparison to the (0001) surface is attributed to low adsorption of N on the H-covered (000-1) surface.

  8. Evaluation of HgCdTe on GaAs Grown by Molecular Beam Epitaxy for High-Operating-Temperature Infrared Detector Applications

    NASA Astrophysics Data System (ADS)

    Wenisch, J.; Schirmacher, W.; Wollrab, R.; Eich, D.; Hanna, S.; Breiter, R.; Lutz, H.; Figgemeier, H.

    2015-09-01

    Molecular beam epitaxy (MBE) growth of HgCdTe (MCT) on alternative substrates enables production of both cheaper and more versatile (third-generation) infrared (IR) detectors. After rapid progress in the development of MBE-grown MCT on GaAs in recent years, the question of whether the considerable benefits of this material system are also applicable to high-operating-temperature (HOT) applications demands attention. In this paper, we present a mid-wavelength-IR 640 × 512 pixel, 15- μm-pitch focal-plane array with operability of 99.71% at operating temperature of 120 K and low dark current density. In the second part of the paper, MBE growth of short-wavelength IR material with Cd fraction of up to 0.8 is investigated as the basis for future evaluation of the material for low-light-level imaging HOT applications.

  9. Microstructural improvements of InP on GaAs (001) grown by molecular beam epitaxy by in situ hydrogenation and postgrowth annealing

    SciTech Connect

    Morales, F. M.; Garcia, R.; Molina, S. I.; Aouni, A.; Postigo, P. A.; Fonstad, C. G.

    2009-01-26

    The characterization of high quality InP on GaAs (001) fabricated by molecular beam epitaxy using a two-step growth method involving hydrogenation during growth is reported. Electron diffraction and high-resolution transmission electron microscopy confirm that {approx}2 {mu}m thick InP epilayers on GaAs are heteroepitaxial and strain relaxed. Stacking faults and threading dislocations are mostly confined near the InP/GaAs interface and their densities decrease monotonically toward the InP surface. Additionally, rapid-thermal annealing following growth is found to result in a marked reduction in the number of dislocations and the disappearance of planar defects.

  10. Impact of substrate nitridation on the growth of InN on In2O3(111) by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Cho, YongJin; Sadofev, Sergey; Fernández-Garrido, Sergio; Calarco, Raffaella; Riechert, Henning; Galazka, Zbigniew; Uecker, Reinhard; Brandt, Oliver

    2016-04-01

    We study the growth of InN films on In2O3(111) substrates by plasma-assisted molecular beam epitaxy under N excess. InN films deposited directly on In2O3(111) exhibit a strongly faceted morphology. A nitridation step prior to growth is found to convert the In2O3(111) surface to InN{0001}. The morphology of InN films deposited on such nitridated In2O3(111) substrates is characteristic for growth by instable step-flow and is thus drastically different from the three-dimensional growth obtained without nitridation. We show that this change originates from the different polarity of the films: while InN films deposited directly on In2O3(111) are In-polar, they are N-polar when grown on the nitridated substrate.

  11. High-quality molecular-beam epitaxial regrowth of (Al,Ga)As on Se-modified (100) GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Turco, F. S.; Sandroff, C. J.; Hwang, D. M.; Ravi, T. S.; Tamargo, M. C.

    1990-08-01

    It is shown that high-quality molecular-beam epitaxial (MBE) regrowth of (Al,Ga)As on GaAs can be achieved by chemically passivating the GaAs surface ex situ prior to regrowth with aqueous selenium reagents. Reflection high-energy electron diffraction intensity oscillations show the bidimensional character of the regrowth and high-resolution transmission electron microscopy reveals defect-free regrown interfaces. Photoluminescence intensity from the Se-treated GaAs surfaces on which Al0.5Ga0.5 As is regrown rivals that from an all in situ grown AlGaAs/GaAs interface. The high quality of these regrown interfaces could be attributed to the thermally and chemically stable selenium and oxygen phases that remain bound to GaAs under MBE conditions.

  12. Magnetic properties of Fe0.4Mn0.6/Co2FeAl bilayers grown on GaAs by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Meng, K. K.; Nie, S. H.; Yu, X. Z.; Wang, S. L.; Yan, W. S.; Zhao, J. H.

    2011-11-01

    Polycrystalline Fe0.4Mn0.6 layers with the different thickness are deposited on 4-nm-thick single-crystalline Co2FeAl layers, which are grown on GaAs (001) substrates at room temperature by molecular-beam epitaxy. Both the exchange bias and the in-plane magnetic anisotropies of the bilayers are strongly dependent on the thickness of the Fe0.4Mn0.6 layer. The former is described using a granular level model. A modified Stoner-Wohlfarth model is used to explain the in-plane magnetic anisotropies observed at 5 K, while one possible reason for the magnetic anisotropies measured at 300 K is the complex interfacial magnetic properties proved by x-ray magnetic circular dichroism measurements.

  13. Rubidium beam flux dependence of film properties of Ba1 - xRbxBiO3 deposited by molecular-beam epitaxy using distilled ozone

    NASA Astrophysics Data System (ADS)

    Ogihara, M.; Toda, F.; Makita, T.; Abe, H.

    1993-10-01

    We have focused our attention on the dependence of Ba1-xRbxBiO3 (BRBO) film composition ratio and film properties on rubidium-beam-flux intensity. BRBO films were deposited on MgO(100) substrates by molecular-beam epitaxy (MBE) using distilled ozone. Systematic measurements showed that the rubidium content was nearly independent of rubidium-beam-flux intensity in a wide beam-flux range. Therefore, it can be concluded that some degree of self-control of rubidium stoichiometry is actually possible in BRBO film growth by MBE. This study also revealed that the BRBO film properties had strong dependences on rubidium-beam-flux intensity even in the range for self-control of rubudium stoichiometry. Our study also clarified that rubidium-beam flux affects the barium content in the BRBO film.

  14. Domains of molecular beam epitaxial growth of Ga(In)AsBi on GaAs and InP substrates

    NASA Astrophysics Data System (ADS)

    Bennarndt, Wolfgang; Boehm, Gerhard; Amann, Markus-Christian

    2016-02-01

    We investigate the molecular beam epitaxial growth of GaAsBi and GaInAsBi layers on GaAs and InP-substrates as the materials are intended to serve as an active region in optoelectronic devices. The layers were grown at substrate temperatures between 250-400 °C and for all layers the growth rate was kept at a value of 1 ML/s. We show that bismuth incorporation into Ga(In)As is independent of the applied arsenic (As4) overpressure and can be allocated to different growth domains depending solely on the parameters bismuth flux and substrate temperature, respectively. The maximum bismuth content that could be incorporated was as high as 20.0% in GaAs.

  15. Growth of ZnMgTe/ZnTe waveguide structures on ZnTe (0 0 1) substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kumagai, Y.; Imada, S.; Baba, T.; Kobayashi, M.

    2011-05-01

    ZnMgTe/ZnTe/ZnMgTe layered structures were grown on (0 0 1) ZnTe substrates by molecular beam epitaxy. This structure was designed to apply to waveguides in various optoelectronic devices to reduce light loss. Since the lattice mismatch between ZnTe and ZnMgTe was not negligible, the critical layer thickness (CLT) was theoretically derived. Structures with varying Mg composition and layer thickness of ZnMgTe cladding layer were grown and examined for crystal quality with respect to theoretical data. The crystal quality was investigated by means of cross sectional transmission electron microscopy (TEM) and reciprocal space mapping (RSM). Optical confinements were observed by irradiating a laser beam from one end of the sample and monitoring the transmitted light from the other end.

  16. Enhanced catalyst-free nucleation of GaN nanowires on amorphous Al{sub 2}O{sub 3} by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Sobanska, Marta Klosek, Kamil; Borysiuk, Jolanta; Kret, Slawomir; Tchutchulasvili, Giorgi; Gieraltowska, Sylwia; Zytkiewicz, Zbigniew R.

    2014-01-28

    We report on plasma-assisted molecular beam epitaxial growth of GaN nanowires (NWs) on Si(111) substrates with a thin amorphous Al{sub 2}O{sub 3} buffer layer deposited by atomic layer deposition. Comparison of nucleation kinetics shows that presence of amorphous Al{sub 2}O{sub 3} buffer significantly enhances spontaneous nucleation of GaN NWs. Slower nucleation was observed on partially amorphous silicon nitride films. No growth of NWs was found on sapphire substrate under the same growth conditions which we explain by a low density of defects on monocrystalline substrate surface where NWs may nucleate. Our finding shows that tuning of substrate microstructure is an efficient tool to control rate of self-induced nucleation of GaN NWs.

  17. Structural properties of InN films grown on O-face ZnO(0001) by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Cho, Yong Jin; Brandt, Oliver; Kaganer, Vladimir M.; Ramsteiner, Manfred; Riechert, Henning; Korytov, Maxim; Albrecht, Martin

    2012-04-09

    We study the impact of substrate temperature and layer thickness on the morphological and structural properties of InN films directly grown on O-face ZnO(0001) substrates by plasma-assisted molecular beam epitaxy. With increasing substrate temperature, an interfacial reaction between InN and ZnO takes place that eventually results in the formation of cubic In{sub 2}O{sub 3} and voids. The properties of the InN films, however, are found to be unaffected by this reaction for substrate temperatures less than 550 deg. C. In fact, both the morphological and the structural quality of InN improve with increasing substrate temperature in the range from 350 to 500 deg. C. High quality films with low threading dislocation densities are demonstrated.

  18. Growth of a delta-doped silicon layer by molecular beam epitaxy on a charge-coupled device for reflection-limited ultraviolet quantum efficiency

    NASA Technical Reports Server (NTRS)

    Hoenk, Michael E.; Grunthaner, Paula J.; Grunthaner, Frank J.; Terhune, R. W.; Fattahi, Masoud; Tseng, Hsin-Fu

    1992-01-01

    Low-temperature silicon molecular beam epitaxy is used to grow a delta-doped silicon layer on a fully processed charge-coupled device (CCD). The measured quantum efficiency of the delta-doped backside-thinned CCD is in agreement with the reflection limit for light incident on the back surface in the spectral range of 260-600 nm. The 2.5 nm silicon layer, grown at 450 C, contained a boron delta-layer with surface density of about 2 x 10 exp 14/sq cm. Passivation of the surface was done by steam oxidation of a nominally undoped 1.5 nm Si cap layer. The UV quantum efficiency was found to be uniform and stable with respect to thermal cycling and illumination conditions.

  19. Hydrogen sulphide doping of GaAs and AlxGa1-xAs grown by molecular beam epitaxy (MBE)

    NASA Astrophysics Data System (ADS)

    Briones, F.; Golmayo, D.; González, L.; de Miguel, J. L.

    1985-03-01

    H2S gas has been used during molecular beam epitaxy (MBE) growth of GaAs and Al x Ga1- x As as sulphur vector for n-type doping. Doping efficiencies are less than 10-3 at usual growth temperatures, and are limited by an incorporation competitive surface process, probably 2Ga+H2S→Ga2S+H2. In AlxGa1- x As for x≧0.2 the doping efficiency is further reduced by carrier freeze-out at deep levels. Measured thermal activation energies depend on growth conditions and remain relatively low even up to the direct-indirect bandgap crossover for substrate temperatures in the 585 645 ‡C range.

  20. Photoluminescence and photocurrent from InP nanowires with InAsP quantum dots grown on Si by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kuyanov, P.; LaPierre, R. R.

    2015-08-01

    InP nanowires with InAsP quantum dots (QDs) were grown by molecular beam epitaxy on a Si (111) substrates. The structure of the InAsP QDs were studied using transmission electron microscopy, allowing the development of a model where QD growth occurs by group V desorption from the surrounding substrate surface. Micro-photoluminescence was performed at 10 K showing emission at 1.47-1.49 eV from the InP wurtzite structure, and various emission peaks between 0.93 and 1.33 eV attributed to the QDs. The emission was tuned by the QD composition. The effectiveness of an AlInP passivation shell was demonstrated via an improvement in the photoluminescence intensity. Spectrally-resolved photocurrent measurements at room temperature demonstrated infrared response due to absorption within the QDs. The absorption red-shifted with increasing As composition of the QD.