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Sample records for gas-source molecular-beam epitaxy

  1. 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.

  2. 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.

  3. 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.

  4. Buried-heterostructure quantum-cascade laser overgrown by gas-source molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chashnikova, M.; Monastyrskyi, G.; Aleksandrova, A.; Klinkmüller, M.; Semtsiv, M. P.; Masselink, W. T.

    2012-05-01

    We describe the realization of buried-heterostructure quantum-cascade lasers (QCLs) using gas-source molecular beam epitaxy both for the growth of the active region as well as for the regrowth of InP:Fe. The regrowth of the semi-insulating InP:Fe layer was carried out at 470 °C, which is more than 100 °C below the standard growth temperature during metal-organic vapor-phase epitaxy, the standard method for laser overgrowth. The electrical resistivity of the InP:Fe insulation layer, measured in test samples grown on (001) InP, is as large as 2×108Ωcm. High-resistivity InP:Fe is overgrown non-selectively over the etched laser ridge, followed by the top contact alloyed through it to the active region. The processed quantum-cascade lasers show no evidence of parallel leakage current and exhibit lower threshold current density than lasers using SiO2 as an insulator. The ability to fabricate buried heterostructure lasers without exceeding 600 °C is important for strain-compensated AlAs-InGaAs quantum cascade lasers with large internal strain because these devices do not typically withstand temperatures used to grow InP:Fe using vapor-phase epitaxy.

  5. InAsPSb quaternary alloy grown by gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tsai, Gene; Wang, De-Lun; Wu, Chia-En; Wu, Chen-Jun; Lin, Yan-Ting; Lin, Hao-Hsiung

    2007-04-01

    Quaternary InAs xP ySb 1-x-y alloys nearly lattice-matched to InAs substrates have been successfully grown by gas source molecular beam epitaxy (GSMBE) with the composition covering the immiscibility region. Through high resolution X-ray diffractometry, we observed the compositional inhomogeneity in these alloys. Enhancement in the As incorporation in the growth can not only narrow the inhomogeneous broadening but also improve the surface morphology. Carrier recombination in band-tail states caused by the compositional inhomogeneity is attributed to the low-temperature PL emission in these samples. The PL peak energy is thus lower than the predicted band-gap energy. The energy discrepancy can be as large as 0.26 eV, and decreases dramatically to 36 meV as the As mole fraction increases to 0.681. For the high As mole fraction sample, band-to-band recombination is observed as the temperature is higher than 100 K.

  6. Si(011)16x2 gas-source molecular beam epitaxy: Growth kinetics

    SciTech Connect

    Taylor, N.; Kim, H.; Desjardins, P.; Foo, Y. L.; Greene, J. E.

    2000-05-15

    The growth rates R{sub Si} of Si layers deposited on Si(011)''16x2'' by gas-source molecular beam epitaxy from Si{sub 2}H{sub 6} were determined as a function of temperature T{sub s} (400-975 degree sign C) and Si{sub 2}H{sub 6} flux J{sub Si{sub 2}}{sub H{sub 6}}(5.0x10{sup 15}-9.0x10{sup 16} cm{sup -2} s{sup -1}). R{sub Si} ranges from 0.0015 {mu}m h-1 at T{sub s}=400 degree sign C to 0.415 {mu}m h-1 at T{sub s}=975 degree sign C with J{sub Si{sub 2}}{sub H{sub 6}}=2.2x10{sup 16} cm{sup -2} s{sup -1}. In the surface-reaction-limited regime at T{sub s}<725 degree sign C, R{sub Si} initially exhibits an exponential decrease with 1/T{sub s}, then decreases at a slower rate at T{sub s}{<=}550 degree sign C as an additional deposition pathway becomes operative. In the impingement-flux-limited regime, 725{<=}T{sub s}{<=}900 degree sign C, R{sub Si} is independent of T{sub s} but increases linearly with J{sub Si{sub 2}}{sub H{sub 6}}. At T{sub s}>900 degree sign C, R{sub Si}(T{sub s}) increases with T{sub s} due to surface roughening. Overall, R{sub Si}(J{sub Si{sub 2}}{sub H{sub 6}},T{sub s}) is well described at T{sub s}{<=}900 degree sign C by a kinetic model incorporating two competing film growth mechanisms: (1) dissociative chemisorption of Si{sub 2}H{sub 6} onto dangling bonds followed by fast surface dissociation steps and second-order H{sub 2} desorption from the surface monohydride phase; and (2) Si{sub 2}H{sub 6} insertion into Si-H surface bonds followed by second-order desorption of SiH{sub 4}. (c) 2000 American Institute of Physics.

  7. 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

  8. 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.

  9. Growth initiation for buried-heterostructure quantum-cascade laser regrowth by gas-source molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Flores, Y. V.; Elagin, M.; Kurlov, S. S.; Aleksandrova, A.; Monastyrskyi, G.; Kischkat, J.; Semtsiv, M. P.; Masselink, W. T.

    2014-07-01

    We describe an optimized growth sequence for the overgrowth of quantum cascade laser ridge sidewalls with semi-insulating InP:Fe. A thin In0.52Al0.48As spacer layer grown on the laser ridge sidewalls before InP:Fe prevents the formation of void defects at this interface, which appear otherwise. Elimination of these voids at the sidewalls has led to more than a two-fold improvement of the thermal conductivity in a 7 μm wide buried-heterostructure quantum-cascade laser overgrown with InP:Fe by gas-source molecular-beam epitaxy, and has allowed the continuous-wave operation of the laser up to 210 K. The measured thermal conductance is Gth=500 W/K cm2 at 210 K and Gth=1020 W/K cm2 at 127 K, comparable to the state of the art literature values obtained with regrowth by metal-organic vapor-phase epitaxy.

  10. Gas-source molecular beam epitaxy of SiGe virtual substrates: I. Growth kinetics and doping

    NASA Astrophysics Data System (ADS)

    Hartmann, J. M.; Gallas, B.; Ferguson, R.; Fernàndez, J.; Zhang, J.; Harris, J. J.

    2000-04-01

    We have studied the growth by gas-source molecular beam epitaxy (GS-MBE) of SiGe virtual substrates. We have first determined the relationship existing between the Ge concentration in SiGe thick films and the gas phase ratio of disilane and germane, and its behaviour versus growth temperature. We find that Si atoms are 4.6 times more likely to be incorporated than Ge atoms at 550 °C. This incorporation probability decreases as the growth temperature increases, following a thermally activated law with a 0.082-0.126 eV characteristic energy. The dependence of SiGe growth rate on substrate temperatures has a cross-over point at approximately 8% of Ge, above which the growth rate decreases significantly as the temperature increases . Otherwise, we show what p-type or n-type doping levels are typically achievable in SiGe virtual substrates, and the influence diluted diborane and arsine have on the growth kinetics of SiGe. Additionally, we demonstrate that the `pre-build-up/flash-off' technique originally proposed by Iyer et al for solid-source MBE (1981 J. Appl. Phys. 52 5608) yields abrupt arsenic doping profiles in GS-MBE.

  11. Arsenic-doped Si(001) gas-source molecular-beam epitaxy: Growth kinetics and transport properties

    SciTech Connect

    Soares, J.A.; Kim, H.; Glass, G.; Desjardins, P.; Greene, J.E.

    1999-03-01

    Arsenic-doped Si(001) layers with concentrations C{sub As} up to 5{times}10{sup 18} cm{sup {minus}3} were grown on Si(001)2{times}1 at temperatures T{sub s}=575{endash}900{degree}C by gas-source molecular-beam epitaxy (GS-MBE) using Si{sub 2}H{sub 6} and AsH{sub 3}. This is almost an order of magnitude higher than the initially reported {open_quotes}maximum attainable{close_quotes} saturated C{sub As} value for GS-MBE from hydride precursors. At constant J{sub AsH{sub 3}}/J{sub Si{sub 2}H{sub 6}}, C{sub As} decreases, while the film growth rate R{sub Si} increases, with T{sub s}. Temperature programmed desorption measurements show that As segregates strongly to the growth surface and that the observed decrease in C{sub As} at high film growth temperatures is primarily due to increasingly rapid arsenic desorption from the segregated layer. Decreasing T{sub s} enhances As incorporation. However, it also results in lower film growth rates due to higher steady-state As surface coverages which, because of the lone-pair electrons associated with each As adatom, decrease the total dangling bond coverage and, hence, the Si{sub 2}H{sub 6} adsorption rate. At constant T{sub s}, C{sub As} increases, while R{sub Si} decreases, with increasing J{sub AsH{sub 3}}/J{sub Si{sub 2}H{sub 6}}. All incorporated As resides at substitutional electrically active sites for concentrations up to 3.8{times}10{sup 18} cm{sup {minus}3}, the highest value yet reported for Si(001):As growth from hydride source gases, and temperature-dependent electron mobilities are equal to those of the best bulk Si:As. {copyright} {ital 1999 American Institute of Physics.}

  12. Thermally detected optical absorption, reflectance and photo-reflectance of In(As,P)/InP quantum wells grown by gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Disseix, P.; Payen, C.; Leymarie, J.; Vasson, A.; Mollot, F.

    2001-06-01

    This work reports a consistent optical study of a series of In(As,P)/InP strained quantum wells (QWs) grown by gas source molecular beam epitaxy (GSMBE). Thermally detected optical absorption (TDOA), reflectance (R) and photo-reflectance (PR) measurements have been performed in order to determine all the exciton energies. Envelope function calculations are used to interpret the experimental data. The fit of the optical transition energies leads to an accurate determination of the structural and optical material parameters. The arsenic concentration inside the wells is evaluated and the conduction band offset ratio ( Qc=0.70) as well as the bowing parameter of In(As,P) ( b=0.14 eV) are determined. This study provides also useful information about the nanometer-scale P-As interface mixing.

  13. Thermally detected optical absorption, reflectance, and photoreflectance of In(As,P)/InP quantum wells grown by gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Disseix, P.; Payen, C.; Leymarie, J.; Vasson, A.; Mollot, F.

    2000-10-01

    This work reports an extensive optical study of a series of In(As,P)/InP strained quantum wells grown by gas source molecular beam epitaxy with various thicknesses and compositions. Thermally detected optical absorption, reflectance, and photoreflectance measurements have been performed in order to determine all the exciton energies. An envelope function model including band nonparabolicity, intervalence band coupling, and also possible group V element exchange at the interfaces, is used to interpret the experimental data. The fit of the optical transition energies leads to an accurate determination of the crucial structural and optical parameters. The arsenic concentration inside the wells is evaluated and the conduction band offset ratio (Qc=0.70) as well as the bowing parameter of In(As,P) (C=0.14 eV) are determined. These studies also provide useful information about the nanometer-scale P-As interface mixing.

  14. 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.

  15. 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.

  16. Semi-insulating InP:Fe for buried-heterostructure strain-compensated quantum-cascade lasers grown by gas-source molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Semtsiv, M. P.; Aleksandrova, A.; Elagin, M.; Monastyrskyi, G.; Kischkat, J.-F.; Flores, Y. V.; Masselink, W. T.

    2013-09-01

    We describe the realization of buried-heterostructure strain-compensated quantum-cascade lasers that incorporate a very high degree of internal strain and are grown on InP substrates using gas-source molecular-beam epitaxy (GSMBE). The active region of the lasers contains AlAs layers up to 1.6 nm thick with 3.7% tensile strain; restricting any post-growth processing to temperatures below 600 °C to avoid relaxation. We demonstrate that buried-heterostructure devices can be realized by using GSMBE to over-grow the etched laser ridge with insulating InP:Fe at temperatures low enough to preserve the crystal quality of the strain-compensated active region. Two distinct growth techniques are described, both leading to successful device realization: selective regrowth at 550 °C and non-selective regrowth at 470 °C. The resulting buried-heterostructure lasers are compared to a reference laser from the same wafer, but with SiO2 insulation; all three have very similar threshold current densities, operational thermal stability, and waveguide losses.

  17. Optical properties and band bending of InGaAs/GaAsBi/InGaAs type-II quantum well grown by gas source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Pan, Wenwu; Zhang, Liyao; Zhu, Liang; Li, Yaoyao; Chen, Xiren; Wu, Xiaoyan; Zhang, Fan; Shao, Jun; Wang, Shumin

    2016-09-01

    Photoluminescence (PL) properties of In0.2Ga0.8As/GaAs0.96Bi0.04/In0.2Ga0.8As quantum well (QW) grown on GaAs substrates by gas source molecular beam epitaxy were studied by varying excitation power and temperature, respectively. The type-II transition energy shifts from 1.149 eV to 1.192 eV when increasing the excitation power from 10 mW to 150 mW at 4.5 K, which was ascribed to the band-bending effect. On the other hand, the type-II PL quenches quickly along with fast redshift with the increasing temperature due to the relaxation of the band bending caused by the thermal excitation process. An 8 band k.p model was used to analyze the electronic properties and the band-bending effect in the type-II QW. The calculated subband levels and transition energy fit well with the experiment results, and two thermal activation energies of 8.7 meV and 50 meV, respectively, are deduced.

  18. 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.

  19. 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

  20. 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

  1. Molecular-Beam-Epitaxy Program

    NASA Technical Reports Server (NTRS)

    Sparks, Patricia D.

    1988-01-01

    Molecular Beam Epitaxy (MBE) computer program developed to aid in design of single- and double-junction cascade cells made of silicon. Cascade cell has efficiency 1 or 2 percent higher than single cell, with twice the open-circuit voltage. Input parameters include doping density, diffusion lengths, thicknesses of regions, solar spectrum, absorption coefficients of silicon (data included for 101 wavelengths), and surface recombination velocities. Results include maximum power, short-circuit current, and open-circuit voltage. Program written in FORTRAN IV.

  2. 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.

  3. 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.

  4. 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.

  5. Ultra-highly doped Si{sub 1-x}Ge{sub x}(001):B gas-source molecular-beam epitaxy: Boron surface segregation and its effect on film growth kinetics

    SciTech Connect

    Kim, H.; Glass, G.; Desjardins, P.; Greene, J. E.

    2001-01-01

    Si{sub 1-x}Ge{sub x}(001) layers doped with B concentrations C{sub B} between 2x10{sup 16} and 2x10{sup 21}cm{sup -3} were grown on Si(001)2x1 at T{sub s}=500--700{sup o}C by gas-source molecular-beam epitaxy (GS-MBE) from Si{sub 2}H{sub 6}, Ge{sub 2}H{sub 6}, and B{sub 2}H{sub 6}. Secondary-ion mass spectrometry measurements of modulation-doped structures demonstrate that B doping has no effect on the Ge incorporation probability. Steady-state B and Ge surface coverages ({theta}{sub B} and {theta}{sub Ge}) were determined as a function of C{sub B} using in situ isotopically tagged temperature-programmed desorption. Results for Si{sub 0.82}Ge{sub 0.18} layers grown at T{sub s}=500{sup o}C show that {theta}{sub Ge} remains constant at 0.63 ML while the bulk B concentration increases linearly up to 4.6x10{sup 20}cm{sup -3}, corresponding to saturation coverage at {theta}{sub B,sat}=0.5ML, with the incident precursor flux ratio {xi}=J{sub B{sub 2}H{sub 6}}/(J{sub Si{sub 2}H{sub 6}}+J{sub Ge{sub 2}H{sub 6}}). B is incorporated into substitutional electrically active sites over this entire concentration range. At higher B concentrations, C{sub B} increases faster than {xi} and there is a large decrease in the activated fraction of incorporated B. The B segregation enthalpy during Si{sub 0.82}Ge{sub 0.18}(001) growth is -0.42 eV, compared to -0.53 and -0.64 eV during Si(001):B and Ge(001):B GS-MBE, respectively. Measured segregation ratios r{sub B}={theta}{sub B}/x{sub B}, where x{sub B} is the bulk B fraction, range from 15 to 500 with a temperature dependence which is consistent with equilibrium segregation. Film deposition rates R{sub SiGe}(C{sub B}) decrease by up to a factor of 2 with increasing C{sub B}{>=}5x10{sup 19}cm{sup -3}, due primarily to a B-segregation-induced decrease in the dangling bond density. The above results were used to develop a robust model for predicting the steady-state H coverage {theta}{sub H}, {theta}{sub B}, {theta}{sub Ge}, and R{sub Si

  6. Arsenic incorporation during Si(001):As gas-source molecular-beam epitaxy from Si{sub 2}H{sub 6} and AsH{sub 3}: Effects on film-growth kinetics

    SciTech Connect

    Kim, H.; Glass, G.; Soares, J. A. N. T.; Desjardins, P.; Greene, J. E.

    2000-12-15

    The effects of As doping, at concentrations C{sub As}{<=}4.8x10{sup 18}cm{sup -3}, on the growth kinetics of Si(001):As layers deposited at temperatures T{sub s}=575--900{sup o}C by gas-source molecular-beam epitaxy from Si{sub 2}H{sub 6} and AsH{sub 3} have been investigated. With constant AsH{sub 3} and Si{sub 2}H{sub 6} fluxes, film deposition rates R{sub Si} increase while C{sub As} decreases with increasing T{sub s}. All incorporated As resides at substitutional electrically active sites for C{sub As} up to 3.8x10{sup 18}cm{sup -3} (T{sub s}=800{sup o}C), the highest value yet reported for Si(001):As growth from hydride source gases. Immediately following film growth or partial-monolayer As adsorption on clean Si(001), the samples were quenched to 300{sup o}C and exposed to atomic deuterium (D) until saturation coverage. In situ D{sub 2} temperature-programmed desorption (TPD) spectra from both as-deposited Si(001):As and As-adsorbed Si(001) layers are composed of {beta}{sub 1} and {beta}{sub 2} peaks, due to D{sub 2} desorption from Si monodeuteride and dideuteride surface phases, together with a new peak {beta}{sub 3} which we attribute to desorption from Si--As mixed dimers. Analyses of the TPD spectra show that, because of the lone-pair electrons associated with each As surface atom, the total dangling-bond coverage, and hence R{sub Si}, decreases with increasing incoming flux J{sub AsH{sub 3}} at constant T{sub s}. From measurements of the steady-state As surface coverage {theta}{sub As} vs C{sub As} and T{sub s}, we obtain an As surface segregation enthalpy {Delta}H{sub s}=-0.92eV. Dissociative AsH{sub 3} adsorption on Si(001) was found to follow second-order kinetics with a relatively T{sub s}-independent reactive sticking probability of 0.3. Associative As{sub 2} desorption is also second order with a rate constant k{sub d,As{sub 2}}=1x10{sup 13}exp(-3.0eV/kT{sub s}). From the combined set of results, we develop a predictive model with no fitting

  7. Infrared Rugates by Molecular Beam Epitaxy

    NASA Technical Reports Server (NTRS)

    Rona, M.

    1993-01-01

    Rugates are optical structures that have a sinusoidal index of refraction (harmonic gradient-index field). As their discrete high/ low index filter counterparts, they can be used as narrow rejection band filters. However, since rugates do not have abrupt interfaces, they tend to have a smaller absorption, hence deliver a higher in band reflectivity. The absence of sharp interfaces makes rugates even more desirable for high-energy narrow band reflectors. In this application, the lack of a sharp interface at the maximum internal standing wave electric field results in higher breakdown strengths. Our method involves fabricating rugates, with molecular beam epitaxy, on GaAs wafers as an Al(x)Ga(1-x)As single-crystal film.

  8. InPBi Single Crystals Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    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.

    2014-06-01

    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.

  9. 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

  10. In-situ microscopic observation of GaAs surfaces during molecular beam epitaxy and metalorganic molecular beam epitaxy by scanning microprobe reflection high energy electron diffraction

    NASA Astrophysics Data System (ADS)

    Isu, Toshiro; Watanabe, Akiyoshi; Hata, Masayuki; Katayama, Yoshifumi

    1990-03-01

    Microscopic observations of epitaxial growth layers of GaAs were made with a scanning microprobe reflection high energy electron diffraction (RHEED). A scanning microprobe electron gun has been combined with a specially designed molecular beam epitaxy (MBE) system with both solid sources and gas sources. Scanning reflection electron microscope (SREM) images using the specular beam spot revealed granular features over the entire surfaces of MBE-grown GaAs layers, which were thought to come from undulation of the surface. Similar features of the surface were observed on the layers grown by gas-source MBE using trimethylgallium and arsine. A microscopic surface morphology was found to be fairly rough and the features depended on the species of the sources and growth conditions.

  11. 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.

  12. 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.

  13. A molecular beam epitaxy facility for in situ neutron scattering

    SciTech Connect

    Dura, J. A.; LaRock, J.

    2009-07-15

    A molecular beam epitaxy (MBE) facility has been built to enable in situ neutron scattering measurements during growth of epitaxial layers. While retaining the full capabilities of a research MBE chamber, this facility has been optimized for polarized neutron reflectometry measurements. Optimization includes a compact lightweight portable design, a neutron window, controllable magnetic field, deposition across a large 76 mm diameter sample with exceptional flux uniformity, and sample temperatures continuously controllable from 38 to 1375 K. A load lock chamber allows for sample insertion, storage of up to 4 samples, and docking with other facilities. The design and performance of this chamber are described here.

  14. Molecular beam epitaxial growth of GaP on Si

    NASA Astrophysics Data System (ADS)

    Wright, S. L.; Kroemer, H.; Inada, M.

    1984-04-01

    The molecular beam epitaxial growth of GaP on Si was investigated, with the aim of at least approaching device-quality interfaces. Gallium-primed growth on (211)-oriented substrates yielded layers which were free of antiphase domains, and which were of much higher quality than growths on other orientations. A tentative energy-band lineup is proposed, which is consistent with the electrical data. Heterojunction bipolar transistors were fabricated with emitter injection efficiencies up to 90 percent, in spite of indications that the epitaxial emitter layer was far less heavily doped than the base.

  15. 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.

  16. Molecular beam epitaxy growth of monolayer niobium diselenide flakes

    NASA Astrophysics Data System (ADS)

    Hotta, Takato; Tokuda, Takuto; Zhao, Sihan; Watanabe, Kenji; Taniguchi, Takashi; Shinohara, Hisanori; Kitaura, Ryo

    2016-09-01

    Monolayer niobium diselenide (NbSe2) is prepared through molecular beam epitaxy with hexagonal boron nitride (hBN) as substrates. Atomic force microscopy and the Raman spectroscopy have shown that the monolayer NbSe2 grown on the hBN possesses triangular or truncated triangular shape whose lateral size amounts up to several hundreds of nanometers. We have found that the precisely controlled supply rate and ultraflat surface of hBN plays an important role in the growth of the monolayer NbSe2.

  17. Molecular beam epitaxy grown indium self-assembled plasmonic nanostructures

    NASA Astrophysics Data System (ADS)

    Gibson, Ricky; Gehl, Michael; Sears, Jasmine; Zandbergen, Sander; Nader, Nima; Keiffer, Patrick; Hendrickson, Joshua; Arnoult, Alexandre; Khitrova, Galina

    2015-09-01

    We describe molecular beam epitaxy (MBE) growth conditions for self-assembled indium nanostructures, or islands, which allow for the tuning of the density and size of the indium nanostructures. How the plasmonic resonance of indium nanostructures is affected by the island density, size, distribution in sizes, and indium purity of the nanostructures is explored. These self-assembled nanostructures provide a platform for integration of resonant and non-resonant plasmonic structures within a few nm of quantum wells (QWs) or quantum dots (QDs) in a single process. A 4× increase in peak photoluminescence intensity is demonstrated for near-surface QDs resonantly coupled to indium nanostructures.

  18. Molecular-Beam Epitaxy Of IrSi3

    NASA Technical Reports Server (NTRS)

    Lin, True-Lon

    1991-01-01

    Molecular-beam epitaxy grows layers of iridium silicide (IrSi3) on silicon at temperatures of 630 to 800 degrees C. Particularly useful as photodetector material because it forms Schottky diodes having potential barriers of only 0.12 to 0.15 eV - lowest of any metal on silicon. Photodiodes sensitive to infrared radiation at wavelengths as large as 8 to 10 micrometers. New, lower formation temperature expected to enable growth of arrays of IrSi3/Si infrared detectors on Si wafers without thermally damaging image-processing circuitry integrated on wafers.

  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. GaN quantum dots by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Daudin, B.; Adelmann, C.; Gogneau, N.; Sarigiannidou, E.; Monroy, E.; Fossard, F.; Rouvière, J. L.

    2004-03-01

    The conditions to grow GaN quantum dots (QDs) by plasma-assisted molecular beam epitaxy will be examined. It will be shown that, depending on the Ga/N ratio value, the growth mode of GaN deposited on AlN can be either of the Stranski-Krastanow (SK) or of the Frank-Van der Merwe type. Accordingly, quantum wells or QDs can be grown, depending on the desired application. In the particular case of modified SK growth mode, it will be shown that both plastic and elastic strain relaxation can coexist. Growth of GaN QDs with N-polarity will also be discussed and compared to their counterpart with Ga polarity.

  1. Surface Properties of SiC Layer Grown by Molecular Beam Epitaxy (MBE) with Helicon Sputtering Molecular Beam Source

    NASA Astrophysics Data System (ADS)

    Kakuta, Akira; Moronuki, Nobuyuki; Furukawa, Yuji

    Although there have been some attempts to produce a monocrystalline silicon carbide (SiC) flat surface, the surface properties, such as surface roughness, have not satisfied the required specifications. In this study, we apply a helicon sputtering device to molecular beam epitaxy (MBE) to improve those properties. The helicon sputtering device was used as a molecular beam source for generating a Si molecular beam, where the electric field caused by the helicon coil supplied energy to the sputtered Si molecules. The amount of energy was controlled by the electric power applied to the coil. High-purity acetylene gas was used as the carbon (C) molecular beam source. The substrate was a monocrystalline (111) Si wafer. With the increase of the electric power, that is, the supply of high energy to molecules, the roughness of the surface was improved. A uniform mirror surface of monocrystalline SiC was produced over the entire substrate with a roughness of 1nm (Ra) order.

  2. 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.

  3. 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.

  4. Photo-metalorganic molecular-beam epitaxy: A new epitaxial growth technique

    SciTech Connect

    Tokumitsu, E.; Yamada, T.; Konagai, M.; Takahashi, K.

    1989-05-01

    Metalorganic molecular-beam epitaxy (MOMBE) combines many important advantages of molecular-beam epitaxy and metalorganic chemical vapor deposition. One of the most important features of MOMBE is that photochemical reaction can be used and we can call this new technique ''photo-MOMBE.'' Triisobutylaluminum (TIBA) has been used in photo-MOMBE instead of triethylaluminum (TEA) as a new aluminum source in order to enhance the photodecomposition. The optical absorption coefficient of TIBA for 193 nm was found to be three times greater than that of TEA. Selective deposition of Al, AlAs, and GaAlAs was carried out by using an ArF excimer laser. The Al mole fraction of GaAlAs ternary alloy grown with the excimer laser irradiation was greater than that of the film grown without the laser irradiation.

  5. 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.

  6. 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.

  7. 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.

  8. Growth of (111) GaAs on (111) Si using molecular-beam epitaxy

    NASA Technical Reports Server (NTRS)

    Radhakrishnan, G.; Liu, J.; Grunthaner, F.; Katz, J.; Morkoc, H.

    1988-01-01

    (111) GaAs layers have been grown epitaxially on (111) Si wafers, both on-axis as well as 3-deg off-axis towards the 1 -1 0 direction, using molecular-beam epitaxy. The grown layers have been characterized by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy.

  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. Molecular Beam Epitaxial Growth of Cuprate Superconductors and Related Phases

    NASA Astrophysics Data System (ADS)

    Schlom, Darrell Galen

    The discovery of a class of new layered crystalline materials which exhibit superconductivity at unprecedented temperatures has opened new possibilities for the future of electronic devices and for molecular beam epitaxy (MBE) as a potential method to grow device structures containing these materials. The low growth temperature and atomic layering capability that MBE has demonstrated for the growth of semiconductors suggests that the MBE growth of non-equilibrium layered structures and metastable phases within oxide systems encompassing the high transition temperature (T _{rm c}) superconductors might be possible. If available, such a growth technique would be useful not only for device fabrication, but would offer an unparalleled technique to fabricate metastable superlattice mixtures to test high T_{ rm c} theories, which might then allow the growth of even higher temperature superconducting compounds. In contrast to the simplicity of the materials systems to which MBE has been successfully applied, the growth of fully oxidized, multi-element compounds by MBE involves significant challenges. This thesis describes research to develop in situ growth techniques allowing the growth of layered superconducting cuprates and related phases by MBE, and characterization of grown films. The conditions necessary to achieve this in situ ability, including the use of highly oxidizing species in order to maintain a long mean free path necessary for MBE, appropriate substrate temperature, precise composition control, and suitable substrates are discussed. The MBE apparatus used and design improvements made during the course of this research are described. The experimental results of films grown in the Dy-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems demonstrate the ability of this shuttered, layer-by-layer MBE technique to grow smooth, layered, metastable compounds, including ordered superlattices, in situ using ozone. Both cross -sectional TEM images and a comparison of the observed x -ray

  12. 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

  13. Molecular-beam epitaxially grown InP/InGaAsP heterostructure for inversion-channel devices

    SciTech Connect

    Kovacic, S.J.; Robinson, B.J.; Swoger, J.H.

    1993-05-01

    A heterostructure, based on InP/InGaAsP alloys grown by gas source molecular-beam epitaxy, is presented which can be used to implement the inversion-channel family of devices. The double-heterostructure optoelectronic switch (DOES) is demonstrated for the first time in the InP/InGaAsP materials system and the current density versus voltage characteristics are presented. Numerical simulations are used to demonstrate the tolerances required in materials growth, doping, and layer thickness in order to successfully realize the heterostructure and the associated I-V characteristics of the DOES. In addition, material and interface quality are shown by simulations to affect the I-V characteristics of the InP/InGaAsP-based DOES. 13 refs., 4 figs.

  14. 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.

  15. HgTe-CdTe-InSb heterostructures by molecular beam epitaxy

    SciTech Connect

    Ballingall, J.M.; Leopold, D.J.; Peterman, D.J.

    1985-08-01

    HgTe-CdTe heterostructures have been grown by molecular beam epitaxy on (100) InSb substrates. Separate elemental Hg and Te beams were used for the HgTe growth at a substrate temperature of 160 C. X-ray diffraction measurements indicate that thin epitaxial layers are of high crystalline quality. Secondary-ion mass spectroscopy measurements show substantial In and Sb diffusion into the epitaxial layers with a concentration enhancement at the HgTe-CdTe interface. 9 references.

  16. Origin and reduction of interfacial boron spikes in silicon molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Iyer, S. S.; Delage, S. L.; Scilla, G. J.

    1988-02-01

    An interfacial boron spike is formed during the molecular beam epitaxial growth of Si. We show two possible sources for this unintentional spike. We have found that some boron contamination invariably occurs when silicon surfaces are exposed to air. A greater degree of contamination results when the sample is heated to temperatures greater than 800 °C, as required for creating an atomically clean surface prior to molecular beam epitaxial growth. A source of boron suboxides, internal to the ultrahigh-vacuum system, was detected by residual gas analysis. While anneals at 1000 °C or greater result in almost complete activation of the B, we observe that for a cleaning regimen at 850 °C, less than 10% of the boron is active. Our results are consistent with the oxidation of the suboxides on oxygen-contaminated surfaces and their subsequent reduction at higher temperatures by silicon, with the volatization of SiO. Subsequent incorporation is by indiffusion.

  17. Molecular beam epitaxial growth and structural characterization of ZnS on (001) GaAs

    NASA Technical Reports Server (NTRS)

    Benz, R. G., II; Huang, P. C.; Stock, S. R.; Summers, C. J.

    1988-01-01

    The effect of surface nucleation processes on the quality of ZnS layers grown on (001) GaAs substrates by molecular beam epitaxy is reported. Reflection high energy electron diffraction indicated that nucleation at high temperatures produced more planar surfaces than nucleation at low temperatures, but the crystalline quality as assessed by X-ray double crystal diffractometry is relatively independent of nucleation temperature. A critical factor in layer quality was the initial roughness of the GaAs surfaces.

  18. ZnSe/CdSe Superlattice Nanowires by Catalyst-assisted Molecular Beam Epitaxy

    SciTech Connect

    Karczewski, G.; Dluzewski, P.; Kret, S.; Klopotowski, L.; Wojtowicz, T.

    2007-04-10

    We report on Au catalyst-assisted molecular beam epitaxy growth and properties of pure ZnSe and ZnSe/CdSe superlattice nanowires. In particular, we concentrate our attention on the morphological characterization by transmission and scanning electron microscopy of pure ZnSe NWs and we compare their optical properties with those of ZnSe/CdSe superlattice NWs fabricated at the same technological conditions.

  19. 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.

  20. 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.

  1. 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.

  2. (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.

  3. 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.

  4. Molecular-Beam Epitaxy Of CrSi2 on Si(111)

    NASA Technical Reports Server (NTRS)

    Fathauer, Robert W.; Grunthaner, Paula J.; Lin, True-Lon; Jamieson, David N.; Mazur, Jurek H.

    1989-01-01

    Crystalline layers grown in commercial apparatus. Experiments show CrSi2 grown on (111) face of single-crystal Si substrate by molecular-beam epitaxy. Epitaxial CrSi2 produced thus far not in desired single-crystal form. Because CrSi2 semiconductor with band gap of 0.3 eV, experimental process potential for monolitic integration of microelectronic devices based on CrSi2 (e.g., infrared detectors) with signal-processing circuitry based on Si.

  5. Zinc-blende CrAs/GaAs multilayers grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Akinaga, H.; Mizuguchi, M.

    2004-12-01

    The epitaxial growth of zinc-blende CrAs/GaAs multilayers has been achieved by using the molecular-beam epitaxy method. The crystallographic quality was evaluated by reflection high-energy electron diffraction (RHEED) and cross-sectional transmission electron microscopy (TEM). The increase of the substrate temperature during growth up to 300 °C brings the RHEED pattern to a streak, in contrast to the case at 200 °C. TEM images show the atomically flat surface and interface of the multilayer.

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

    PubMed

    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°.

  8. Development of molecular beam epitaxy technology for III–V compound semiconductor heterostructure devices

    SciTech Connect

    Cheng, K. Y.

    2013-09-15

    Molecular beam epitaxy (MBE) is a versatile ultrahigh vacuum technique for growing multiple epitaxial layers of semiconductor crystals with high precision. The extreme control of the MBE technique over composition variation, interface sharpness, impurity doping profiles, and epitaxial layer thickness to the atomic level makes it possible to demonstrate a wide variety of novel semiconductor structures. Since its invention nearly 40 years ago, the MBE technique has evolved from a laboratory apparatus for exploring new materials and novel devices to a favored tool for the mass production of III–V high-speed devices. This paper will review some of the past developments in this technology and propose an outlook of future developments.

  9. Electrical properties of Si:Er/Si layers grown by sublimation molecular-beam epitaxy

    SciTech Connect

    Belova, O. V.; Shabanov, V. N.; Kasatkin, A. P.; Kuznetsov, O. A.; Yablonskii, A. N.; Kuznetsov, M. V.; Kuznetsov, V. P. Kornaukhov, A. V.; Andreev, B. A.; Krasil'nik, Z. F.

    2008-02-15

    Temperature dependences of the concentration and electron Hall mobility in Si:Er/Sr epitaxial layers grown at T = 600 Degree-Sign C and annealed at 700 or 900 Degree-Sign C have been investigated. The layers were grown by sublimation molecular-beam epitaxy in vacuum ({approx}10{sup -5} Pa). The energy levels of Er-related donor centers are located 0.21-0.27 eV below the bottom of the conduction band of Si. In the range 80-300 K, the electron Hall mobility in unannealed Si:Er epitaxial layers was lower than that in Czochralski-grown single crystals by a factor of 3-10. After annealing the layers, the fraction of electron scattering from Er donor centers significantly decreases.

  10. Electrical properties of Si:Er/Si layers grown by sublimation molecular-beam epitaxy

    SciTech Connect

    Belova, O. V.; Shabanov, V. N.; Kasatkin, A. P.; Kuznetsov, O. A.; Yablonskii, A. N.; Kuznetsov, M. V.; Kuznetsov, V. P. Kornaukhov, A. V.; Andreev, B. A.; Krasil'nik, Z. F.

    2008-02-15

    Temperature dependences of the concentration and electron Hall mobility in Si:Er/Sr epitaxial layers grown at T = 600 deg. C and annealed at 700 or 900 deg. C have been investigated. The layers were grown by sublimation molecular-beam epitaxy in vacuum ({approx}10{sup -5} Pa). The energy levels of Er-related donor centers are located 0.21-0.27 eV below the bottom of the conduction band of Si. In the range 80-300 K, the electron Hall mobility in unannealed Si:Er epitaxial layers was lower than that in Czochralski-grown single crystals by a factor of 3-10. After annealing the layers, the fraction of electron scattering from Er donor centers significantly decreases.

  11. 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.

  12. 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.

  13. Crystallographic dependence of photocatalytic activity of WO3 thin films prepared by molecular beam epitaxy.

    PubMed

    Li, Guoqiang; Varga, Tamas; Yan, Pengfei; Wang, Zhiguo; Wang, Chongmin; Chambers, Scott A; Du, Yingge

    2015-06-21

    We investigated the impact of crystallographic orientation on the photocatalytic activity of single crystalline WO3 thin films prepared by molecular beam epitaxy on the photodegradation of rhodamine B (RhB). A clear effect is observed, with (111) being the most reactive surface, followed by (110) and (001). Photoreactivity is directly correlated with the surface free energy determined by density functional theory calculations. The RhB photodegradation mechanism is found to involve hydroxyl radicals in solution formed from photo-generated holes and differs from previous studies performed on nanoparticles and composites.

  14. 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.

  15. 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).

  16. 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.

  17. Graphitic carbon growth on crystalline and amorphous oxide substrates using molecular beam epitaxy

    PubMed Central

    2011-01-01

    We report graphitic carbon growth on crystalline and amorphous oxide substrates by using carbon molecular beam epitaxy. The films are characterized by Raman spectroscopy and X-ray photoelectron spectroscopy. The formations of nanocrystalline graphite are observed on silicon dioxide and glass, while mainly sp2 amorphous carbons are formed on strontium titanate and yttria-stabilized zirconia. Interestingly, flat carbon layers with high degree of graphitization are formed even on amorphous oxides. Our results provide a progress toward direct graphene growth on oxide materials. PACS: 81.05.uf; 81.15.Hi; 78.30.Ly. PMID:22029707

  18. 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.

  19. 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.

  20. Growth behaviors of ultrathin ZnSe nanowires by Au-catalyzed molecular-beam epitaxy

    SciTech Connect

    Cai, Y.; Wong, T. L.; Chan, S. K.; Sou, I. K.; Wang, N.; Su, D. S.

    2008-12-08

    Ultrathin ZnSe nanowires grown by Au-catalyzed molecular-beam epitaxy show an interesting growth behavior of diameter dependence of growth rates. The smaller the nanowire diameter, the faster is its growth rate. This growth behavior is totally different from that of the nanowires with diameters greater than 60 nm and cannot be interpreted by the classical theories of the vapor-liquid-solid mechanism. For the Au-catalyzed nanowire growth at low temperatures, we found that the surface and interface incorporation and diffusion of the source atoms at the nanowire tips controlled the growth of ultrathin ZnSe nanowires.

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Molecular beam epitaxy growth and optical properties of single crystal Zn3N2 films

    NASA Astrophysics Data System (ADS)

    Wu, Peng; Tiedje, T.; Alimohammadi, H.; Bahrami-Yekta, V.; Masnadi-Shirazi, M.; Wang, Cong

    2016-10-01

    Single crystal Zn3N2 films with (100) orientation have been grown by plasma-assisted molecular beam epitaxy on MgO and A-plane sapphire substrates with in situ optical reflectance monitoring of the growth. The optical bandgap was found to be 1.25-1.28 eV and an electron Hall mobility as high as 395 cm2 V-1 s-1 was measured. The films were n-type with carrier concentrations in the 1018-1019 cm-3 range.

  3. 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.

  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. Photoluminescence from CdTe/sapphire films prepared by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Edwards, S. T.; Schreiner, A. F.; Myers, T. M.; Schetzina, J. F.

    1983-11-01

    Photoluminescence studies at 77 K are reported for CdTe/sapphire films prepared by molecular beam epitaxy. The CdTe/sapphire epilayers exhibited very bright photoluminescence spectra that were dominated by the near-edge emission band at 1.58 eV. The best CdTe/sapphire film proved to be the brightest source of luminescence of any CdTe specimen studied in our laboratories, including homoepitaxial films and bulk hydroplane polished samples. The CdTe/sapphire films also exhibited the best lateral uniformity as manifested by a nearly constant luminescence intensity over their surfaces. These results provide new evidence that high quality CdTe epitaxy on sapphire has been achieved.

  6. 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

  7. 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.

  8. Cleaning chemistry of InSb(100) molecular beam epitaxy substrates

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Lewis, B. F.; Grunthaner, F. J.

    1983-01-01

    InSb has been used as a substrate for molecular beam epitaxy. For good epitaxial growth, a substrate surface which is smooth and clean on an atomic scale is required. Chemical cleaning procedures provide an oxide film to passivate the surface. This film is then desorbed by in situ heating. The material forming the film should, therefore, have a high vapor pressure at some temperature less than the substrate melting temperature. A chloride film appears to satisfy the latter requirement. The present investigation is, therefore, concerned with the formation of a chloride film rather than an oxide film. Carbon contamination has been found to cause problems in chemical cleaning procedures. The level of carbon contamination found in the case of chloride film formation, is therefore compared with the corresponding level observed in procedures using oxide films. It appears that a chloride film grown in connection with a short exposure time to a Cl2 plasma is preferable to other passivation films studied.

  9. Hexagonal Boron Nitride Tunnel Barriers Grown on Graphite by High Temperature Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Cho, Yong-Jin; Summerfield, Alex; Davies, Andrew; Cheng, Tin S.; Smith, Emily F.; Mellor, Christopher J.; Khlobystov, Andrei N.; Foxon, C. Thomas; Eaves, Laurence; Beton, Peter H.; Novikov, Sergei V.

    2016-09-01

    We demonstrate direct epitaxial growth of high-quality hexagonal boron nitride (hBN) layers on graphite using high-temperature plasma-assisted molecular beam epitaxy. Atomic force microscopy reveals mono- and few-layer island growth, while conducting atomic force microscopy shows that the grown hBN has a resistance which increases exponentially with the number of layers, and has electrical properties comparable to exfoliated hBN. X-ray photoelectron spectroscopy, Raman microscopy and spectroscopic ellipsometry measurements on hBN confirm the formation of sp2-bonded hBN and a band gap of 5.9 ± 0.1 eV with no chemical intermixing with graphite. We also observe hexagonal moiré patterns with a period of 15 nm, consistent with the alignment of the hBN lattice and the graphite substrate.

  10. 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.

  11. 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.

  12. 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.

  13. Hexagonal Boron Nitride Tunnel Barriers Grown on Graphite by High Temperature Molecular Beam Epitaxy

    PubMed Central

    Cho, Yong-Jin; Summerfield, Alex; Davies, Andrew; Cheng, Tin S.; Smith, Emily F.; Mellor, Christopher J.; Khlobystov, Andrei N.; Foxon, C. Thomas; Eaves, Laurence; Beton, Peter H.; Novikov, Sergei V.

    2016-01-01

    We demonstrate direct epitaxial growth of high-quality hexagonal boron nitride (hBN) layers on graphite using high-temperature plasma-assisted molecular beam epitaxy. Atomic force microscopy reveals mono- and few-layer island growth, while conducting atomic force microscopy shows that the grown hBN has a resistance which increases exponentially with the number of layers, and has electrical properties comparable to exfoliated hBN. X-ray photoelectron spectroscopy, Raman microscopy and spectroscopic ellipsometry measurements on hBN confirm the formation of sp2-bonded hBN and a band gap of 5.9 ± 0.1 eV with no chemical intermixing with graphite. We also observe hexagonal moiré patterns with a period of 15 nm, consistent with the alignment of the hBN lattice and the graphite substrate. PMID:27681943

  14. 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.

  15. Studies of molecular-beam epitaxy growth of GaAs on porous Si substrates

    NASA Technical Reports Server (NTRS)

    Mii, Y. J.; Kao, Y. C.; Wu, B. J.; Wang, K. L.; Lin, T. L.; Liu, J. K.

    1988-01-01

    GaAs has been grown on porous Si directly and on Si buffer layer-porous Si substrates by molecular-beam epitaxy. In the case of GaAs growth on porous Si, transmission electron microscopy (TEM) reveals that the dominant defects in GaAs layers grown on porous Si are microtwins and stacking faults, which originate from the GaAs/porous Si interface. GaAs is found to penetrate into the porous Si layers. By using a thin Si buffer layer (50 nm), GaAs penetration diminishes and the density of microtwins and stacking faults is largely reduced and localized at the GaAs/Si buffer interface. However, there is a high density of threading dislocations remaining. Both Si (100) aligned and four degree tilted substrates have been examined in this study. TEM results show no observable effect of the tilted substrates on the quality of the GaAs epitaxial layer.

  16. Continuum model of surface roughening and epitaxial breakdown during low-temperature Ge(001) molecular beam epitaxy

    SciTech Connect

    Bratland, K. A.; Spila, T.; Cahill, D. G.; Greene, J. E.; Desjardins, P.

    2011-03-15

    Numerical simulations based on a discrete model describing step edge motion are used to compute the surface morphological evolution of Ge(001) layers deposited by low-temperature (T{sub s} = 45-230 deg. C) molecular beam epitaxy and to probe the relationship between surface roughening and the onset of epitaxial breakdown - the abrupt growth mode transition from epitaxial to amorphous - at temperature-dependent critical film thicknesses h{sub 1}(T{sub s}). Computed surface widths w and in-plane coherence lengths d as a function of layer thickness h exhibit good agreement with experimental values. Inspired by experimental results indicating that epitaxial breakdown is initiated at facetted interisland trenches as the surface roughness reaches a T{sub s}-independent overall aspect ratio, we show that simulated data for w/d = 0.03 correspond to thicknesses h{sub 1{proportional_to}} exp (-E{sub 1}/kT{sub s}) with E{sub 1} = 0.63 eV, a value equal to the Ge adatom diffusion activation energy on Ge(001). Simulated h{sub 1} values agree well with experimental data. Above a critical growth temperature of 170 deg. C, computed w/d values saturate at large film thicknesses, never reaching the critical aspect ratio w/d = 0.03. Thus, the model also predicts that epitaxial breakdown does not occur for T{sub s} > 170 deg. C as observed experimentally.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. InP/InGaAs/InP double heterojunction bipolar transistors with improved dc and microwave performance grown by solid source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, Hong; Ng, Geok I.; Zheng, Hai Qun; Radhakrishnan, Kaladhar; Yoon, Soon Fatt; Xiong, Yongzhong; Chua, Lye H.; Yang, Hongru; Halder, Subrata; Tan, Chee L.

    2000-10-01

    This paper describes the fabrication and characterization of the InP/InAs/InP double heterojunction bipolar transistors grown by solid-source molecular beam epitaxy (SSMBE). An improvement in current gain and microwave noise has been observed for the SSMBE-grown InP/InGaAs DHBTs. The HBT with a 50 nm, 2 X 19 cm-3 Be-doped base exhibits dc current gain as high as 350, which is about two times of that measured on the referenced devices grown by gas-source molecular beam epitaxy. The HBT with 5 X 5 micrometers 2 emitter shows a minimum noise figure of 1.04 dB and associated gain of 16 dB measured at 2 GHz with Ic equals 1 mA. In comparison, the HBT grown by GSMBE gives an Fmin of 1.9 dB under same measurement condition. A slight increase in fT and fmax for the SSMBE-grown HBT has also been observed. The drastic increase of current gain for the SSMBE-grown HBT could be explained by reducing base recombination due to the ful elimination of hydrogen contamination during the material growth.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Synthesis of long group IV semiconductor nanowires by molecular beam epitaxy

    PubMed Central

    2011-01-01

    We report the growth of Si and Ge nanowires (NWs) on a Si(111) surface by molecular beam epitaxy. While Si NWs grow perpendicular to the surface, two types of growth axes are found for the Ge NWs. Structural studies of both types of NWs performed with electron microscopies reveal a marked difference between the roughnesses of their respective sidewalls. As the investigation of their length dependence on their diameter indicates that the growth of the NWs predominantly proceeds through the diffusion of adatoms from the substrate up along the sidewalls, difference in the sidewall roughness qualitatively explains the length variation measured between both types of NWs. The formation of atomically flat {111} sidewalls on the <110>-oriented Ge NWs accounts for a larger diffusion length. PMID:21711645

  9. Mechanisms of droplet formation and Bi incorporation during molecular beam epitaxy of GaAsBi

    SciTech Connect

    Vardar, G.; Warren, M. V.; Kang, M.; Jeon, S.; Goldman, R. S.; Paleg, S. W.

    2013-01-28

    We have examined the mechanisms of droplet formation and Bi incorporation during molecular beam epitaxy of GaAsBi. We consider the role of the transition from group-V-rich to group-III-rich conditions, i.e., the stoichiometry threshold, in the presence of Bi. For As-rich GaAsBi growth, Bi acts as a surfactant, leading to the formation of droplet-free GaAsBi films. For films within 10% of the stoichiometric GaAsBi growth regime, surface Ga droplets are observed. However, for Ga-rich GaAsBi growth, Bi acts as an anti-surfactant, inducing Ga-Bi droplet formation. We propose a growth mechanism based upon the growth-rate-dependence of the stoichiometry threshold for GaAsBi.

  10. Deep levels in Ga-doped ZnSe grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Venkatesan, S.; Pierret, R. F.; Qiu, J.; Kobayashi, M.; Gunshor, R. L.; Kolodziejski, L. A.

    1989-10-01

    Results of a deep-level transient spectroscopy study of Ga-doped ZnSe thin films grown by molecular-beam epitaxy are presented. Two prominent deep levels were observed in all the samples investigated. The concentration of the trap detected at 0.34 eV below the conduction-band edge was essentially independent of the doping concentration and is attributed to native defects arising from Se vacancies in the ZnSe films. The second level with an activation energy of 0.26 eV shows a very strong doping dependence and is tentatively identified as arising from dopant-site (gallium-on-zinc-site) defects complexed with selenium vacancies. Preliminary results also indicate that planar doping of ZnSe significantly reduces the concentration of the Ga-vacancy complex.

  11. 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.

  12. Nickel enhanced graphene growth directly on dielectric substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wofford, Joseph M.; Speck, Florian; Seyller, Thomas; Lopes, Joao Marcelo J.; Riechert, Henning

    2016-07-01

    The efficacy of Ni as a surfactant to improve the crystalline quality of graphene grown directly on dielectric Al2O3(0001) substrates by molecular beam epitaxy is examined. Simultaneously exposing the substrate to a Ni flux throughout C deposition at 950 °C led to improved charge carrier mobility and a Raman spectrum indicating less structural disorder in the resulting nanocrystalline graphene film. X-ray photoelectron spectroscopy confirmed that no residual Ni could be detected in the film and showed a decrease in the intensity of the defect-related component of the C1s level. Similar improvements were not observed when a lower substrate temperature (850 °C) was used. A close examination of the Raman spectra suggests that Ni reduces the concentration of lattice vacancies in the film, possibly by catalytically assisting adatom incorporation.

  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. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Molecular beam epitaxy of single crystalline GaN nanowires on a flexible Ti foil

    NASA Astrophysics Data System (ADS)

    Calabrese, Gabriele; Corfdir, Pierre; Gao, Guanhui; Pfüller, Carsten; Trampert, Achim; Brandt, Oliver; Geelhaar, Lutz; Fernández-Garrido, Sergio

    2016-05-01

    We demonstrate the self-assembled growth of vertically aligned GaN nanowire ensembles on a flexible Ti foil by plasma-assisted molecular beam epitaxy. The analysis of single nanowires by transmission electron microscopy reveals that they are single crystalline. Low-temperature photoluminescence spectroscopy demonstrates that in comparison to standard GaN nanowires grown on Si, the nanowires prepared on the Ti foil exhibit an equivalent crystalline perfection, a higher density of basal-plane stacking faults, but a reduced density of inversion domain boundaries. The room-temperature photoluminescence spectrum of the nanowire ensemble is not influenced or degraded by the bending of the substrate. The present results pave the way for the fabrication of flexible optoelectronic devices based on GaN nanowires on metal foils.

  1. 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%.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Molecular beam epitaxy grown GaN p-n vertical diodes are demonstrated on single-crystal GaN substrates. A low leakage current <3 nA/cm2 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 cm2 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.

  3. 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.

  4. 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.

  5. 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

  6. Controllable growth of layered selenide and telluride heterostructures and superlattices using molecular beam epitaxy

    DOE PAGESBeta

    Vishwanath, Suresh; Liu, Xinyu; Rouvimov, Sergei; Basile, Leonardo; Lu, Ning; Azcatl, Angelica; Magno, Katrina; Wallace, Robert M.; Kim, Moon; Idrobo, Juan -Carlos; et al

    2016-01-06

    Layered materials are an actively pursued area of research for realizing highly scaled technologies involving both traditional device structures as well as new physics. Lately, non-equilibrium growth of 2D materials using molecular beam epitaxy (MBE) is gathering traction in the scientific community and here we aim to highlight one of its strengths, growth of abrupt heterostructures, and superlattices (SLs). In this work we present several of the firsts: first growth of MoTe2 by MBE, MoSe2 on Bi2Se3 SLs, transition metal dichalcogenide (TMD) SLs, and lateral junction between a quintuple atomic layer of Bi2Te3 and a triple atomic layer of MoTe2.more » In conclusion, reflected high electron energy diffraction oscillations presented during the growth of TMD SLs strengthen our claim that ultrathin heterostructures with monolayer layer control is within reach.« less

  7. 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.

  8. 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

  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. 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.

  11. 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.

  12. 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.

  13. Molecular beam epitaxy grown (Ga,Mn)(As,P) with perpendicular to plane magnetic easy axis

    SciTech Connect

    Rushforth, A. W.; Wang, M.; Farley, N. R. S.; Campion, R. P.; Edmonds, K. W.; Staddon, C. R.; Foxon, C. T.; Gallagher, B. L.

    2008-10-01

    We present an experimental investigation of the magnetic, electrical, and structural properties of Ga{sub 0.94}Mn{sub 0.06}As{sub 1-y}P{sub y} layers grown by molecular beam epitaxy on GaAs substrates for y{<=}0.3. X-ray diffraction measurements reveal that the layers are under tensile strain, which gives rise to a magnetic easy axis perpendicular to the plane of the layers. The strength of the magnetic anisotropy and the coercive field increases as the phosphorous concentration is increased. The resistivity of all samples shows metallic behavior with the resistivity increasing as y increases. These materials will be useful for studies of micromagnetic phenomena requiring metallic ferromagnetic material with perpendicular magnetic anisotropy.

  14. 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.

  15. 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

  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. 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.

  18. 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.

  19. 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)

  20. 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.

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

    PubMed

    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).

  2. 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.

  3. 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}.

  4. 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).

  5. NO-assisted molecular-beam epitaxial growth of nitrogen substituted EuO

    NASA Astrophysics Data System (ADS)

    Wicks, R.; Altendorf, S. G.; Caspers, C.; Kierspel, H.; Sutarto, R.; Tjeng, L. H.; Damascelli, A.

    2012-04-01

    We have investigated a method for substituting oxygen with nitrogen in EuO thin films, which is based on molecular beam epitaxy distillation with NO gas as the oxidizer. By varying the NO gas pressure, we produce crystalline, epitaxial EuO1 -xNx films with good control over the films' nitrogen concentration. In situ x-ray photoemission spectroscopy reveals that nitrogen substitution is connected to the formation Eu3+4f6 and a corresponding decrease in the number of Eu2+4f7, indicating that nitrogen is being incorporated in its 3- oxidation state. While small amounts of Eu3+ in over-oxidized Eu1-δO thin films lead to a drastic suppression of the ferromagnetism, the formation of Eu3+ in EuO1-xNx still allows the ferromagnetic phase to exist with an unaffected Tc, thus providing an ideal model system to study the interplay between the magnetic f7 (J = 7/2) and the non-magnetic f6 (J = 0) states close to the Fermi level.

  6. 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

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

    PubMed

    Zhong, Aihua; Hane, Kazuhiro

    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

  8. Single orientation graphene synthesized on iridium thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Dangwal Pandey, A.; Krausert, K.; Franz, D.; Grânäs, E.; Shayduk, R.; Müller, P.; Keller, T. F.; Noei, H.; Vonk, V.; Stierle, A.

    2016-08-01

    Heteroepitaxial iridium thin films were deposited on (0001) sapphire substrates by means of molecular beam epitaxy, and subsequently, one monolayer of graphene was synthesized by chemical vapor deposition. The influence of the growth parameters on the quality of the Ir films, as well as of graphene, was investigated systematically by means of low energy electron diffraction, x-ray reflectivity, x-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, and atomic force microscopy. Our study reveals (111) oriented iridium films with high crystalline quality and extremely low surface roughness, on which the formation of large-area epitaxial graphene is achieved. The presence of defects, like dislocations, twins, and 30° rotated domains in the iridium films is also discussed. The coverage of graphene was found to be influenced by the presence of 30° rotated domains in the Ir films. Low iridium deposition rates suppress these rotated domains and an almost complete coverage of graphene was obtained. This synthesis route yields inexpensive, air-stable, and large-area graphene with a well-defined orientation, making it accessible to a wider community of researchers for numerous experiments or applications, including those which use destructive analysis techniques or irreversible processes. Moreover, this approach can be used to tune the structural quality of graphene, allowing a systematic study of the influence of defects in various processes like intercalation below graphene.

  9. Molecular Beam Epitaxy Growth of High Crystalline Quality LiNbO3

    NASA Astrophysics Data System (ADS)

    Tellekamp, M. Brooks; Shank, Joshua C.; Goorsky, Mark S.; Doolittle, W. Alan

    2016-10-01

    Lithium niobate is a multi-functional material with wide reaching applications in acoustics, optics, and electronics. Commercial applications for lithium niobate require high crystalline quality currently limited to bulk and ion sliced material. Thin film lithium niobate is an attractive option for a variety of integrated devices, but the research effort has been stagnant due to poor material quality. Both lattice matched and mismatched lithium niobate are grown by molecular beam epitaxy and studied to understand the role of substrate and temperature on nucleation conditions and material quality. Growth on sapphire produces partially coalesced columnar grains with atomically flat plateaus and no twin planes. A symmetric rocking curve shows a narrow linewidth with a full width at half-maximum (FWHM) of 8.6 arcsec (0.0024°), which is comparable to the 5.8 arcsec rocking curve FWHM of the substrate, while the film asymmetric rocking curve is 510 arcsec FWHM. These values indicate that the individual grains are relatively free of long-range disorder detectable by x-ray diffraction with minimal measurable tilt and twist and represents the highest structural quality epitaxial material grown on lattice mismatched sapphire without twin planes. Lithium niobate is also grown on lithium tantalate producing high quality coalesced material without twin planes and with a symmetric rocking curve of 193 arcsec, which is nearly equal to the substrate rocking curve of 194 arcsec. The surface morphology of lithium niobate on lithium tantalate is shown to be atomically flat by atomic force microscopy.

  10. 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.

  11. Red vertical-cavity surface-emitting lasers grown by solid-source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Saarinen, M.; Xiang, N.; Vilokkinen, V.; Melanen, P.; Orsila, S.; Uusimaa, P.; Savolainen, P.; Toivonen, M.; Pessa, M.

    2001-07-01

    Plastic optical fibres, which have a local attenuation minimum at 650 nm, have attracted much interest for low-cost short-haul communication systems. Red vertical-cavity surface-emitting lasers (VCSELs) provide a potential solution as light sources for these systems. The operation of vertical cavity emitters is based on a Fabry-Perot microcavity, which is formed by placing an optically active region inside of two parallel mirrors. These mirrors are usually formed epitaxially. So far, metal organic chemical vapour deposition (MOCVD) has been the major technology used for growing visible VCSELs. Recently, an alternative growth method—solid-source molecular beam epitaxy (SSMBE)—has been introduced to be a viable solution to the fabrication of these structures. The authors present the first MBE-grown visible AlGaInP vertical-cavity surface-emitting lasers. A laser with a 10 μm emitting window has an external quantum efficiency of 6.65% under continuous wave operation and it is still lasing at 45°C. Furthermore, a threshold current less than 1.0 mA is obtained for a device, which has an 8 μm emitting window.

  12. 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

  13. Dependence of the concentration of ionized donors on epitaxy temperature for Si:Er/Si layers grown by sublimation molecular-beam epitaxy

    SciTech Connect

    Kuznetsov, V. P.; Shmagin, V. B.; Drozdov, M. N.; Marychev, M. O.; Kudryavtsev, K. E.; Kuznetsov, M. V.; Andreev, B. A.; Kornaukhov, A. V.; Krasilnik, Z. F.

    2011-01-15

    The dependence of the concentrations of the Er impurity and ionized donors on the epitaxy temperature has been studied before and after annealing of Si:Er/Si layers grown by sublimation molecular-beam epitaxy. n-Si:Er layers have been grown in the temperature range 400-800 Degree-Sign C and annealed in hydrogen atmosphere at a temperature of 800 Degree-Sign C for 30 min. The possible nature of the donor centers is discussed.

  14. Electron molecular beam epitaxy: Layer-by-layer growth of complex oxides via pulsed electron-beam deposition

    NASA Astrophysics Data System (ADS)

    Comes, Ryan; Gu, Man; Khokhlov, Mikhail; Liu, Hongxue; Lu, Jiwei; Wolf, Stuart A.

    2013-01-01

    Complex oxide epitaxial film growth is a rich and exciting field, owing to the wide variety of physical properties present in oxides. These properties include ferroelectricity, ferromagnetism, spin-polarization, and a variety of other correlated phenomena. Traditionally, high quality epitaxial oxide films have been grown via oxide molecular beam epitaxy or pulsed laser deposition. Here, we present the growth of high quality epitaxial films using an alternative approach, the pulsed electron-beam deposition technique. We demonstrate all three epitaxial growth modes in different oxide systems: Frank-van der Merwe (layer-by-layer); Stranski-Krastanov (layer-then-island); and Volmer-Weber (island). Analysis of film quality and morphology is presented and techniques to optimize the morphology of films are discussed.

  15. Selective-area epitaxial growth of GaAs in deep dielectric windows using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Loke, W. K.; Yoon, S. F.; Zheng, H. Q.

    2001-01-01

    An improved selective-area epitaxial growth process for GaAs in deep dielectric windows (DDWs) is reported. The growth was carried out on (100)-oriented semi-insulating (SI) GaAs substrate at ˜520°C by solid source molecular beam epitaxy (SSMBE) using a valved arsenic cracker source. Dielectric stacks with 10 periods of alternating silicon nitride (2000 Å) and silicon dioxide (1000 Å) layers were deposited using plasma-enhanced chemical vapor deposition (PECVD) for the formation of deep (3 μm) dielectric windows. The alternating dielectric layer stack has been shown to be of greater stability than a single dielectric layer for the purpose of forming the DDW. A process of fabricating the DDW structures, which eliminates the possible contamination at the growth area during photoresist patterning and removing, and subsequent etching of the DDW, has resulted in improved epitaxial layer quality. Micro-Raman spectroscopy measurements showed a significant increase in the longitudinal-optic (LO) to transverse-optic (TO) signal intensity ratio ( ILO/TO) from ˜4.0 to ˜16.0 of the first-order Raman line of GaAs. Supporting evidence from low-temperature (4 K) photoluminescence (PL) showed a reduction in intensity of the conduction band to neutral carbon acceptor (e-C°) emission by a factor of 4.5. This suggests lower levels of carbon contamination originating from the improved fabrication process of the DDW. Scanning electron microscopy (SEM) images showed smoother surface morphology of the GaAs inside the DDW area. These results have important implications on the process of MBE regrowth for optoelectronics integration.

  16. 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.

  17. 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.

  18. Impact of extended defects on recombination in CdTe heterostructures grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zaunbrecher, Katherine N.; Kuciauskas, Darius; Swartz, Craig H.; Dippo, Pat; Edirisooriya, Madhavie; Ogedengbe, Olanrewaju S.; Sohal, Sandeep; Hancock, Bobby L.; LeBlanc, Elizabeth G.; Jayathilaka, Pathiraja A. R. D.; Barnes, Teresa M.; Myers, Thomas H.

    2016-08-01

    Heterostructures with CdTe and CdTe1-xSex (x ˜ 0.01) absorbers between two wider-band-gap Cd1-xMgxTe barriers (x ˜ 0.25-0.3) were grown by molecular beam epitaxy to study carrier generation and recombination in bulk materials with passivated interfaces. Using a combination of confocal photoluminescence (PL), time-resolved PL, and low-temperature PL emission spectroscopy, two extended defect types were identified and the impact of these defects on charge-carrier recombination was analyzed. The dominant defects identified by confocal PL were dislocations in samples grown on (211)B CdTe substrates and crystallographic twinning-related defects in samples on (100)-oriented InSb substrates. Low-temperature PL shows that twin-related defects have a zero-phonon energy of 1.460 eV and a Huang-Rhys factor of 1.50, while dislocation-dominated samples have a 1.473-eV zero-phonon energy and a Huang-Rhys factor of 1.22. The charge carrier diffusion length near both types of defects is ˜6 μm, suggesting that recombination is limited by diffusion dynamics. For heterostructures with a low concentration of extended defects, the bulk lifetime was determined to be 2.2 μs with an interface recombination velocity of 160 cm/s and an estimated radiative lifetime of 91 μs.

  19. 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.

  20. 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.

  1. Impurity doping of HgTe--CdTe superlattices during growth by molecular-beam epitaxy

    SciTech Connect

    Wroge, M.L.; Peterman, D.J.; Feldman, B.J.; Morris, B.J.; Leopold, D.J.; Broerman, J.G.

    1989-03-01

    We demonstrate the use of In and Ag as n- and p-type dopants, respectively, to controllably dope (100)-oriented HgTe--CdTe superlattices during molecular-beam epitaxial (MBE) growth. When normalized by the superlattice growth rate, the low-temperature Hall-carrier concentrations of both In- and Ag-doped superlattices are shown to have an exponential dependence on the respective effusion-cell temperatures in the electron and hole concentration ranges of approx.10/sup 16/ to 10/sup 18/ cm/sup -3/ . The upper limit on the diffusion coefficient for In at the low MBE growth temperature of approx.160 /sup 0/C is determined to be 5 x 10/sup -15/ cm/sup 2/ /s by use of secondary-ion mass spectrometry. Hall-effect and current--voltage measurements verify that the combination of In and Ag doping allows the formation of p--n electrical junctions. These results provide the first evidence of p--n junction formation in a HgTe--CdTe superlattice.

  2. 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.

  3. 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.

  4. 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.

  5. HgCdTe Research at FFI: Molecular Beam Epitaxy Growth and Characterization

    NASA Astrophysics Data System (ADS)

    Haakenaasen, R.; Selvig, E.; Tonheim, C. R.; Kongshaug, K. O.; Lorentzen, T.; Trosdahl-Iversen, L.; Andersen, J. B.; Gundersen, P.

    2010-07-01

    This paper presents results from recent work on molecular beam epitaxy growth of HgCdTe at the Norwegian Defence Research Establishment (FFI), including studies of material properties and fabrication of photodiodes and nanostructures. Systematic studies of defect morphology in HgTe and Hg1- x Cd x Te have revealed that there is a minimum in the area covered by defects just below the onset of Te precipitation. The shape and density of microvoids in HgTe can be used to determine the deviation from the optimal growth temperature. This can be further related to the optimal growth temperature of Hg1- x Cd x Te with any Cd mole fraction by thermodynamic calculations. A mechanism for the formation of microvoids and needles has been presented. Photoluminescence (PL) has been used to study layers without doping and with Hg vacancy, Ag, and In doping. Planar photodiodes with high dynamic resistance and good quantum efficiency were fabricated by ion-milling vacancy-doped mid-wave and long-wave infrared layers. Quantum wells (QWs) with good crystallinity and high PL light output have been grown. Surface patterning has been found to enhance light emission from HgCdTe thin-film and QW samples by ˜30%. Single-crystal HgTe and segmented HgTe/Te nanowires have been grown, and the resistivity of the nanowires has been measured by conductive atomic force microscopy (AFM), where the AFM tip has been used as a mobile electrode.

  6. Mapping growth windows in quaternary perovskite oxide systems by hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Brahlek, Matthew; Zhang, Lei; Zhang, Hai-Tian; Lapano, Jason; Dedon, Liv R.; Martin, Lane W.; Engel-Herbert, Roman

    2016-09-01

    Requisite to growing stoichiometric perovskite thin films of the solid-solution A'1-xAxBO3 by hybrid molecular beam epitaxy is understanding how the growth conditions interpolate between the end members A'BO3 and ABO3, which can be grown in a self-regulated fashion, but under different conditions. Using the example of La1-xSrxVO3, the two-dimensional growth parameter space that is spanned by the flux of the metal-organic precursor vanadium oxytriisopropoxide and composition, x, was mapped out. The evolution of the adsorption-controlled growth window was obtained using a combination of X-ray diffraction, atomic force microscopy, reflection high-energy electron-diffraction (RHEED), and Rutherford backscattering spectroscopy. It is found that the stoichiometric growth conditions can be mapped out quickly with a single calibration sample using RHEED. Once stoichiometric conditions have been identified, the out-of-plane lattice parameter can be utilized to precisely determine the composition x. This strategy enables the identification of growth conditions that allow the deposition of stoichiometric perovskite oxide films with random A-site cation mixing, which is relevant to a large number of perovskite materials with interesting properties, e.g., high-temperature superconductivity and colossal magnetoresistance, that emerge in solid solution A'1-xAxBO3.

  7. 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.

  8. 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.

  9. Graphitic platform for self-catalysed InAs nanowires growth by molecular beam epitaxy

    PubMed Central

    2014-01-01

    We report the self-catalysed growth of InAs nanowires (NWs) on graphite thin films using molecular beam epitaxy via a droplet-assisted technique. Through optimising metal droplets, we obtained vertically aligned InAs NWs with highly uniform diameter along their entire length. In comparison with conventional InAs NWs grown on Si (111), the graphite surface led to significant effects on the NWs geometry grown on it, i.e. larger diameter, shorter length with lower number density, which were ascribed to the absence of dangling bonds on the graphite surface. The axial growth rate of the NWs has a strong dependence on growth time, which increases quickly in the beginning then slows down after the NWs reach a length of approximately 0.8 μm. This is attributed to the combined axial growth contributions from the surface impingement and sidewall impingement together with the desorption of adatoms during the diffusion. The growth of InAs NWs on graphite was proposed following a vapour-solid mechanism. High-resolution transmission electron microscopy reveals that the NW has a mixture of pure zinc-blende and wurtzite insertions. PMID:25024683

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Plasma-assisted molecular beam epitaxy growth of ZnSnN2

    NASA Astrophysics Data System (ADS)

    Feldberg, Nathaniel; Aldous, James; Yao, Yuan; Tanveer, Imtiaz; Keen, Benjamin; Linhart, Wojciech; Veal, Tim; Song, Young-Wook; Reeves, Roger; Durbin, Steve

    2012-02-01

    The Zn-IV-nitrides are a promising series of ``earth abundant element'' semiconductors with a predicted band gap range of 0.6 eV to 5.4 eV, which, like the (Al,Ga,In)N family, spans the entire visible solar spectrum. Considering this alternative family has a number of advantages, including the avoidance of indium, the price of which has varied almost an order of magnitude over the past decade, and surface electron accumulation which is present in the In-rich alloys. Not all members of this family have yet been synthesized, in particular ZnSnN2, the most important member for PV with its predicted band gap of approximately 2 eV. We have successfully grown a series of these films using plasma-assisted molecular beam epitaxy using elemental Zn and Sn sources. In this report, we discuss the relationship between process parameters and microstructure, as well as stoichiometry as determined by Rutherford backscattering spectrometry. Additionally, we provide preliminary estimates for its bandgap energy based on photoluminescence and optical absorption.

  15. 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.

  16. 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.

  17. 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.

  18. Evolution of Surface Morphology of Patterned GaAs(100) during Molecular Beam Epitaxial Growth

    NASA Astrophysics Data System (ADS)

    Kan, Hung-Chih; Shah, Sonam; Tadayyon-Eslami, Tabassom; Phaneuf, Raymond

    2003-03-01

    We report the results of an investigation of the evolution of the surface morphology during molecular beam epitaxial growth on a patterned GaAs(100) surface. The initial GaAs(100) surfaces were patterned lithographically with arrays of cylindrical pits whose diameters and center-to-center distances are varied in a combinatorial manner. Using atomic force microscopy (AFM), we characterized the evolution of the corrugation throughout the growth. We compare the measured height profiles with simulations from various continuum models[1]. This comparison allows us to discriminate between various continuum modes of growth. * Work supported by the Minta-Martin Foundation, the Laboratory for Physical Sciences, and an NSF-MRSEC, DMR 00-8008. Reference 1 Mehran Kardar, Giorgio Parisi, and Yi-Cheng Zhang, Physical Review Letters 56 (9), 889 (1986); Tao Sun, Hong Guo, and Martin Grant, Physical Review A 40 (11), 6763 (1989); Z.-W. Lai and S. Das Sarma, Physical Review Letters 66 (18), 2348 (1991); M. D. Johnson, C. Orme, A. W. Hunt et al., Physical Review Letters 72 (1), 116 (1994).

  19. 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.

  20. 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.

  1. 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.

  2. Molecular beam epitaxy and characterization of thin Bi2Se3 films on Al2O3 (110)

    NASA Astrophysics Data System (ADS)

    Tabor, Phillip; Keenan, Cameron; Urazhdin, Sergei; Lederman, David

    2011-07-01

    The structural and electronic properties of thin Bi2Se3 films grown on Al2O3 (110) by molecular beam epitaxy are investigated. The epitaxial films grow in the Frank-van der Merwe mode and are c-axis oriented. They exhibit the highest crystallinity, the lowest carrier concentration, and optimal stoichiometry at a substrate temperature of 200 °C determined by the balance between surface kinetics and desorption of Se. The crystallinity of the films improves with increasing Se/Bi flux ratio. Our results enable studies of thin topological insulator films on inert, non-conducting substrates that allow optical access to both film surfaces.

  3. Growth and characterization of GaAs layers on Si substrates by migration-enhanced molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Kim, Jae-Hoon; Liu, John K.; Radhakrishnan, Gouri; Katz, Joseph; Sakai, Shiro

    1988-01-01

    Migration-enhanced molecular beam epitaxial (MEMBE) growth and characterization of the GaAs layer on Si substrates (GaAs/Si) are reported. The MEMBE growth method is described, and material properties are compared with those of normal two-step MBE-grown or in situ annealed layers. Micrographs of cross-section view transmission electron microscopy and scanning surface electron microscopy of MEMBE-grown GaAs/Si showed dislocation densities of 10 to the 7th/sq cm. AlGaAs/GaAs double heterostructures have been successfully grown on MEMBE GaAs/Si by both metalorganic chemical vapor deposition and liquid phase epitaxy.

  4. Single-crystal cubic boron nitride thin films grown by ion-beam-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hirama, Kazuyuki; Taniyasu, Yoshitaka; Karimoto, Shin-ichi; Krockenberger, Yoshiharu; Yamamoto, Hideki

    2014-03-01

    We investigated the formation of cubic boron nitride (c-BN) thin films on diamond (001) and (111) substrates by ion-beam-assisted molecular beam epitaxy (MBE). The metastable c-BN (sp3-bonded BN) phase can be epitaxially grown as a result of the interplay between competitive phase formation and selective etching. We show that a proper adjustment of acceleration voltage for N2+ and Ar+ ions is a key to selectively discriminate non-sp3 BN phases. At low acceleration voltage values, the sp2-bonded BN is dominantly formed, while at high acceleration voltages, etching dominates irrespective of the bonding characteristics of BN.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Selective molecular beam epitaxy of germanium on oxide-covered silicon

    NASA Astrophysics Data System (ADS)

    Li, Qiming

    This study demonstrates that Ge can be selectively grown on Si through openings in SiO2 nanotemplates by molecular beam epitaxy without applying selectivity-control agents. The SiO2 nanotemplates are created either by interferometric lithography or by "touchdown" process. The "touchdown" process takes advantage of the unique interaction between Ge and an ultra-thin layer of chemical SiO2. Due to the high concentration of OH groups in the chemical oxide layer, Ge readily diffuses through the oxide, segregates at the SiO2/Si interface, and creates dense nanoscale windows in the chemical oxide. Ge then selectively grows in the windows and coalesces into a high-quality relaxed Ge epilayer over the remaining SiO2. The high-quality and relaxation are attributed to three mechanisms: (1) the strain at the junction pad decays below the critical limit within 2 nm due to the nanoscale heterojunction; (2) the remaining SiO2 serves as artificially introduced 60° dislocations; and (3) the intermixing between Ge and Si at the heterojunction reduces the effective lattice mismatch. To understand the surface phenomena governing the selectivity, we further experimentally measure the desorption activation energy (Edes = 42 +/- 3 kJ/mol) of Ge on SiO2 surface. The low Edes gives rise to a high Ge desorption flux from the SiO2 surface and a low diffusion barrier ( Edif ˜ 13 kJ/mol), which in turn leads to a long characteristic diffusion length. Based on these findings, we further demonstrate that hexagonally packed, single-crystal Ge rings can be grown at the contact region between self-assembled SiO2 spheres and chemical oxide covered Si substrates. These SiO2 spheres provide a surface diffusion path, which guides the Ge adspecies to the substrate. The Ge adspecies on SiO2 spheres undergo surface diffusion as well as desorption, and a fraction of Ge adspecies aggregate at the sphere/substrate contact region to form epitaxial rings by "touchdown" through the chemical SiO2.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. Electrical properties of solid-solution SrZrxTi1-xO3 grown epitaxially on Ge by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Moghadam, Reza; Ahmadi, Kamyar; Xiao, Z.-Y.; Hong, Xia; Ngai, Joseph

    The epitaxial growth of crystalline oxides on semiconductors enables new functionalities to be introduced to semiconductor devices. In particular, dielectric and ferroelectric oxides grown epitaxially on semiconductors provide a pathway to realize ultra-low power logic and memory devices. Here we present electrical characterization of solid-solution SrZrxTi1-xO3 grown epitaxially on Ge through oxide molecular beam epitaxy. SrZrxTi1-xO3 is of particular interest since the band offset with respect to the semiconductor can be tuned through Zr content x. We will present current-voltage, capacitance-voltage and piezoforce microscopy characterization of SrZrxTi1-xO3 -Ge heterojunctions. In particular, we will discuss how the electrical characteristics of SrZrxTi1-xO3 -Ge heterojunctions evolve with respect to composition, annealing and film thickness.

  15. 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.

  16. Characteristics and device applications of erbium doped III-V semiconductors grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sethi, S.; Bhattacharya, P. K.

    1996-03-01

    We have studied the properties of molecular beam epitaxially (MBE)-grown Erdoped III-V semiconductors for optoelectronic applications. Optically excited Er3+ in insulating materials exhibits optical emission chiefly around 1.54 μm, in the range of minimum loss in silica fiber. It was thought, therefore, that an electrically pumped Er-doped semiconductor laser would find great applicability in fiber-optic communication systems. Exhaustive photoluminescence (PL) characterization was conducted on several of As-based III-V semiconductors doped with Er, on bulk as well as quantum-well structures. We did not observe any Errelated PL emission at 1.54 μm for any of the materials/structures studied, a phenomenon which renders impractical the realization of an Er-doped III-V semiconductor laser. Deep level transient spectroscopy studies were performed on GaAs and AlGaAs co-doped with Er and Si to investigate the presence of any Er-related deep levels. The lack of band-edge luminescence in the GaAs:Er films led us to perform carrier-lifetime measurements by electro-optic sampling of photoconductive transients generated in these films. We discovered lifetimes in the picosecond regime, tunable by varying the Er concentration in the films. We also found the films to be highly resistive, the resistivity increasing with increasing Er-concentration. Intensive structural characterization (double-crys-tal x-ray and transmission electron microscopy) performed by us on GaAs:Er epilayers indicates the presence of high-density nanometer-sized ErAs precipitates in MBE-grown GaAs:Er. These metallic nanoprecipitates probably form internal Schottky barriers within the GaAs matrix, which give rise to Shockley-Read-Hall recombination centers, thus accounting for both the high resistivities and the ultrashort carrier lifetimes. Optoelectronic devices fabricated included novel tunable (in terms of speed and responsivity) high-speed metal-semiconductor-metal (MSM) photodiodes made with Ga

  17. Electrical Characterization of Molecular Beam Epitaxy Grown Mercury-Cadmium Alloy Under Low Magnetic Field Strength

    NASA Astrophysics Data System (ADS)

    Wijewarnasuriya, P. S.

    HgCdTe alloy is currently the most important semiconductor material for IR detection technology. Different growth techniques are used to produce HgCdTe, but achieving a high-quality material is still a major objective in the field. Among the growth techniques for HgCdTe, molecular beam epitaxy (MBE) is one of the most promising, mainly because of its versatility. Furthermore, the growth by MBE is carried out at a low temperature which limits interdiffusion processes. The focus of this research is the understanding of the electrical properties of HgCdTe layers grown by MBE technique. Using a model based on a single discrete acceptor level near the valence band and a corresponding fully ionized donor level, a good fit to the observed Hall data on p-type epilayers was obtained. In some samples, another acceptor level was needed. Also, analysis of R _{h} data and low temperature mobilities indicated that the p-type MBE growth layers were highly compensated. This was also confirmed by mercury saturated annealing experiments. Annealing of (111)B epilayers with Hg pressure leads us to believe that Hg vacancies are responsible for the p-type character. The findings reveal that the electrical properties differ drastically between different growth orientations, with (111)B having the highest residual doping levels for a particular Cd composition. It is concluded that MBE growth for HgCdTe is essentially a Te rich growth and our understanding is that this extra Te is responsible for the n-type character in the epilayers. A comparison between HgCdTe twinned layers and twin-free layers has shown that electrically active acceptors and high hole mobilities are associated with the presence of twins. Incorporation of several foreign elements also tried and all were found to substitute the metal sites during growth. With magnetic field studies on R_ {h}, resistivity and conductivity tensor analysis, the band structure of the HgCdTe alloy is also investigated. Junction depth and the

  18. Molecular beam epitaxy growth of Al-rich AlGaN nanowires for deep ultraviolet optoelectronics

    NASA Astrophysics Data System (ADS)

    Zhao, S.; Woo, S. Y.; Sadaf, S. M.; Wu, Y.; Pofelski, A.; Laleyan, D. A.; Rashid, R. T.; Wang, Y.; Botton, G. A.; Mi, Z.

    2016-08-01

    Self-organized AlGaN nanowires by molecular beam epitaxy have attracted significant attention for deep ultraviolet optoelectronics. However, due to the strong compositional modulations under conventional nitrogen rich growth conditions, emission wavelengths less than 250 nm have remained inaccessible. Here we show that Al-rich AlGaN nanowires with much improved compositional uniformity can be achieved in a new growth paradigm, wherein a precise control on the optical bandgap of ternary AlGaN nanowires can be achieved by varying the substrate temperature. AlGaN nanowire LEDs, with emission wavelengths spanning from 236 to 280 nm, are also demonstrated.

  19. Physical properties and band structure of reactive molecular beam epitaxy grown oxygen engineered HfO{sub 2{+-}x}

    SciTech Connect

    Hildebrandt, Erwin; Kurian, Jose; Alff, Lambert

    2012-12-01

    We have conducted a detailed thin film growth structure of oxygen engineered monoclinic HfO{sub 2{+-}x} grown by reactive molecular beam epitaxy. The oxidation conditions induce a switching between (111) and (002) texture of hafnium oxide. The band gap of oxygen deficient hafnia decreases with increasing amount of oxygen vacancies by more than 1 eV. For high oxygen vacancy concentrations, defect bands form inside the band gap that induce optical transitions and p-type conductivity. The resistivity changes by several orders of magnitude as a function of oxidation conditions. Oxygen vacancies do not give rise to ferromagnetic behavior.

  20. 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.

  1. Fabrication of IrSi(3)/p-Si Schottky diodes by a molecular beam epitaxy technique

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Iannelli, J. M.

    1990-01-01

    IrSi(3)/p-Si Schottky diodes have been fabricated by a molecular beam epitaxy technique at 630 C. Good surface morphology was observed for IrSi(3) layers grown at temperatures below 680 C, and an increasing tendency to form islands is observed in samples grown at higher temperatures. Good diode current-voltage characteristics were observed and Schottky barrier heights of 0.14-0.18 eV were determined by activation energy analysis and spectral response measurement.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. Peculiarly strong room-temperature ferromagnetism from low Mn-doping in ZnO grown by molecular beam epitaxy

    SciTech Connect

    Zuo Zheng; Morshed, Muhammad; Liu Jianlin; Beyermann, W. P.; Zheng Jianguo; Xin Yan

    2013-03-15

    Strong room-temperature ferromagnetism is demonstrated in single crystalline Mn-doped ZnO thin films grown by molecular beam epitaxy. Very low Mn doping concentration is investigated, and the measured magnetic moment is much larger than what is expected for an isolated ion based on Hund's rules. The ferromagnetic behavior evolves with Mn concentration. Both magnetic anisotropy and anomalous Hall effect confirm the intrinsic nature of ferromagnetism. While the Mn dopant plays a crucial role, another entity in the system is needed to explain the observed large magnetic moments.

  7. 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.

  8. 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.

  9. A growth diagram for plasma-assisted molecular beam epitaxy of GaN nanocolumns on Si(111)

    SciTech Connect

    Fernandez-Garrido, S.; Grandal, J.; Calleja, E.; Sanchez-Garcia, M. A.; Lopez-Romero, D.

    2009-12-15

    The morphology of GaN samples grown by plasma-assisted molecular beam epitaxy on Si(111) was systematically studied as a function of impinging Ga/N flux ratio and growth temperature (730-850 deg. C). Two different growth regimes were identified: compact and nanocolumnar. A growth diagram was established as a function of growth parameters, exhibiting the transition between growth regimes, and showing under which growth conditions GaN cannot be grown due to thermal decomposition and Ga desorption. Present results indicate that adatoms diffusion length and the actual Ga/N ratio on the growing surface are key factors to achieve nanocolumnar growth.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. Single-crystal cubic boron nitride thin films grown by ion-beam-assisted molecular beam epitaxy

    SciTech Connect

    Hirama, Kazuyuki Taniyasu, Yoshitaka; Karimoto, Shin-ichi; Krockenberger, Yoshiharu; Yamamoto, Hideki

    2014-03-03

    We investigated the formation of cubic boron nitride (c-BN) thin films on diamond (001) and (111) substrates by ion-beam-assisted molecular beam epitaxy (MBE). The metastable c-BN (sp{sup 3}-bonded BN) phase can be epitaxially grown as a result of the interplay between competitive phase formation and selective etching. We show that a proper adjustment of acceleration voltage for N{sub 2}{sup +} and Ar{sup +} ions is a key to selectively discriminate non-sp{sup 3} BN phases. At low acceleration voltage values, the sp{sup 2}-bonded BN is dominantly formed, while at high acceleration voltages, etching dominates irrespective of the bonding characteristics of BN.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Ultra-high frequency photoconductivity decay in GaAs/Ge/GaAs double heterostructure grown by molecular beam epitaxy

    SciTech Connect

    Hudait, M. K.; Zhu, Y.; Johnston, S. W.; Maurya, D.; Priya, S.; Umbel, R.

    2013-03-04

    GaAs/Ge/GaAs double heterostructures (DHs) were grown in-situ using two separate molecular beam epitaxy chambers. High-resolution x-ray rocking curve demonstrates a high-quality GaAs/Ge/GaAs heterostructure by observing Pendelloesung oscillations. The kinetics of the carrier recombination in Ge/GaAs DHs were investigated using photoconductivity decay measurements by the incidence excitation from the front and back side of 15 nm GaAs/100 nm Ge/0.5 {mu}m GaAs/(100)GaAs substrate structure. High-minority carrier lifetimes of 1.06-1.17 {mu}s were measured when excited from the front or from the back of the Ge epitaxial layer, suggests equivalent interface quality of GaAs/Ge and Ge/GaAs. Wavelength-dependent minority carrier recombination properties are explained by the wavelength-dependent absorption coefficient of Ge.

  20. GaN Schottky diodes with single-crystal aluminum barriers grown by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tseng, H. Y.; Yang, W. C.; Lee, P. Y.; Lin, C. W.; Cheng, Kai-Yuan; Hsieh, K. C.; Cheng, K. Y.; Hsu, C.-H.

    2016-08-01

    GaN-based Schottky barrier diodes (SBDs) with single-crystal Al barriers grown by plasma-assisted molecular beam epitaxy are fabricated. Examined using in-situ reflection high-energy electron diffractions, ex-situ high-resolution x-ray diffractions, and high-resolution transmission electron microscopy, it is determined that epitaxial Al grows with its [111] axis coincident with the [0001] axis of the GaN substrate without rotation. In fabricated SBDs, a 0.2 V barrier height enhancement and 2 orders of magnitude reduction in leakage current are observed in single crystal Al/GaN SBDs compared to conventional thermal deposited Al/GaN SBDs. The strain induced piezoelectric field is determined to be the major source of the observed device performance enhancements.

  1. Structural properties of SrO thin films grown by molecular beam epitaxy on LaAlO3 substrates

    NASA Astrophysics Data System (ADS)

    Maksimov, O.; Heydemann, V. D.; Fisher, P.; Skowronski, M.; Salvador, P. A.

    2006-12-01

    SrO films were grown on LaAlO3 substrates by molecular beam epitaxy and characterized using reflection high-energy electron diffraction (RHEED) and x-ray diffraction (XRD). The evolution of the RHEED pattern is discussed as a function of film thickness. 500Å thick SrO films were relaxed and exhibited RHEED patterns indicative of an atomically smooth surface having uniform terrace heights. Films had the epitaxial relationship (001)SrO‖(001)LaAlO3; [010]SrO‖[110]LaAlO3. This 45° in-plane rotation minimizes mismatch and leads to films of high crystalline quality, as verified by Kikuchi lines in the RHEED patterns and narrow rocking curves of the (002) XRD peak.

  2. 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.

  3. 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.

  4. Influence of substrate misorientation on defect and impurity incorporation in GaAs/AlGaAs heterostructures grown by molecular-beam epitaxy

    NASA Technical Reports Server (NTRS)

    Radulescu, D. C.; Wicks, G. W.; Schaff, W. J.; Calawa, A. R.; Eastman, L. F.

    1988-01-01

    GaAS/AlGaAs heterostructures have been grown by molecular-beam epitaxy on GaAs substrates intentionally oriented (tilted) a few degrees (0-6.5) off the (001) plane towards either (111)A, (111)B, or (011). It was observed that the 4-K photoluminescence and low-field electron transport properties of these structures may be functions of the substrate tilt angle and tilt direction, depending on the concentration of impurities incorporated during growth. A substrate tilt during molecular-beam epitaxy is observed to have the largest effect on these properties when the background impurity concentration in the molecular-beam epitaxial machine is high. This supports the contention that the observed changes in material characteristics are due to differences in the incorporation of defects and impurities. The incorporation of defects and impurities are reduced by using substrates tilted toward (111)A, in comparison to nominally flat (001) substrates or substrates tilted toward (111)B.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Materials Design and Molecular-Beam Epitaxy of Half-Metallic Zinc-Blende CrAs and the Heterostructures

    NASA Astrophysics Data System (ADS)

    Akinaga, Hiro; Mizuguchi, Masaki; Nagao, Kazutaka; Miura, Yoshio; Shirai, Masafumi

    Zinc-blende half-metallic ferromagnets are promising materials in order to open up a new world of semiconductor spintronics. We design a new class of half-metallic ferromagnets, the zinc-blende transition-metal mono-pnictides, using ab-initio calculations based on the density-functional theory. The calculations show that the total-energy difference between the ferromagnetic and the antiferromagnetic states for the zinc-blende CrAs is the largest among all the studied compounds and the highly spin-polarized electronic band structure is almost unaffected from the spin-orbit interaction.We further study the properties of zinc-blende CrAs/GaAs multilayers theoretically and show that they keep a high spin polarization. Experimental realization of the previously nonexistent zinc-blende CrAs thin film has been achieved by molecular-beam epitaxy. The crystallographic analysis is presented together with the magnetic properties of the epitaxial film. The morphological structure and the magnetic properties change sensitively depending on the substrate temperature during the growth. The room-temperature saturation magnetization of the film grown under optimum conditions reaches about 3 μB per formula unit, which agrees with the theoretically predicted value and reflects the half-metallic behavior. The epitaxial growth of multilayers consisting of 2-4 monolayers of CrAs and 2-4 monolayers GaAs with atomically flat surfaces and interfacess is demonstrated.

  10. 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

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. Comparison of Island Formation Between Pulsed Laser Deposition and Molecular Beam Epitaxy:. a Kinetic Monte Carlo Simulation

    NASA Astrophysics Data System (ADS)

    Tan, X.; Zhou, Y. C.; Zheng, X. J.

    Based on a hexagonal lattice which includes deposition, dissociation, and diffusion, we performed a kinetic Monte Carlo model to explore thin film growth via pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) within the submonolayer regime. First and second nearest-neighbor interactions calculated by the Morse potential are taken into account in this case. These simulations show that thin film deposition by PLD is markedly different from that by MBE. With PLD, as pulse duration decreases, the island density increases and the island size decreases. Similarly, at temperature T = 550 K, the scaling function for MBE is rather similar to that of the analytical prediction for a critical island size of i = 2, while the scaling function for PLD changes from an i = 1 behavior to an i = 0 behavior with the decrease in pulse duration.

  16. Structural and Electrical Properties of MoTe2 and MoSe2 Grown by Molecular Beam Epitaxy.

    PubMed

    Roy, Anupam; Movva, Hema C P; Satpati, Biswarup; Kim, Kyounghwan; Dey, Rik; Rai, Amritesh; Pramanik, Tanmoy; Guchhait, Samaresh; Tutuc, Emanuel; Banerjee, Sanjay K

    2016-03-23

    We demonstrate the growth of thin films of molybdenum ditelluride and molybdenum diselenide on sapphire substrates by molecular beam epitaxy. In situ structural and chemical analyses reveal stoichiometric layered film growth with atomically smooth surface morphologies. Film growth along the (001) direction is confirmed by X-ray diffraction, and the crystalline nature of growth in the 2H phase is evident from Raman spectroscopy. Transmission electron microscopy is used to confirm the layered film structure and hexagonal arrangement of surface atoms. Temperature-dependent electrical measurements show an insulating behavior that agrees well with a two-dimensional variable-range hopping model, suggesting that transport in these films is dominated by localized charge-carrier states. PMID:26939890

  17. Electron beam source molecular beam epitaxial growth of analog graded Al(x)Ga(1-x)As ballistic transistors

    NASA Technical Reports Server (NTRS)

    Malik, Roger J.; Levi, Anthony F. J.

    1988-01-01

    A new method has been developed for the growth of graded band-gap Al(x)Ga(1-x)As alloys by molecular beam epitaxy which is based upon electron beam evaporation of the group III elements. The metal fluxes are measured and feedback controlled using a modulated ion gauge sensor. The system is computer controlled which allows precise programming of the Ga and Al evaporation rates. The large dynamic response of the metal sources enables growth of variable band-gap III-V alloys with arbitrary composition profiles. This new technique is demonstrated by synthesis of analog graded Al(x)Ga(1-x)As unipolar ballistic electron transistors.

  18. Structural and Electrical Properties of MoTe2 and MoSe2 Grown by Molecular Beam Epitaxy.

    PubMed

    Roy, Anupam; Movva, Hema C P; Satpati, Biswarup; Kim, Kyounghwan; Dey, Rik; Rai, Amritesh; Pramanik, Tanmoy; Guchhait, Samaresh; Tutuc, Emanuel; Banerjee, Sanjay K

    2016-03-23

    We demonstrate the growth of thin films of molybdenum ditelluride and molybdenum diselenide on sapphire substrates by molecular beam epitaxy. In situ structural and chemical analyses reveal stoichiometric layered film growth with atomically smooth surface morphologies. Film growth along the (001) direction is confirmed by X-ray diffraction, and the crystalline nature of growth in the 2H phase is evident from Raman spectroscopy. Transmission electron microscopy is used to confirm the layered film structure and hexagonal arrangement of surface atoms. Temperature-dependent electrical measurements show an insulating behavior that agrees well with a two-dimensional variable-range hopping model, suggesting that transport in these films is dominated by localized charge-carrier states.

  19. Perpendicular Magnetic Anisotropy and Spin Glass-like Behavior in Molecular Beam Epitaxy Grown Chromium Telluride Thin Films.

    PubMed

    Roy, Anupam; Guchhait, Samaresh; Dey, Rik; Pramanik, Tanmoy; Hsieh, Cheng-Chih; Rai, Amritesh; Banerjee, Sanjay K

    2015-04-28

    Reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), vibrating sample magnetometry, and other physical property measurements are used to investigate the structure, morphology, magnetic, and magnetotransport properties of (001)-oriented Cr2Te3 thin films grown on Al2O3(0001) and Si(111)-(7×7) surfaces by molecular beam epitaxy. Streaky RHEED patterns indicate flat smooth film growth on both substrates. STM studies show the hexagonal arrangements of surface atoms. Determination of the lattice parameter from the atomically resolved STM image is consistent with the bulk crystal structures. Magnetic measurements show the film is ferromagnetic, having a Curie temperature of about 180 K, and a spin glass-like behavior was observed below 35 K. Magnetotransport measurements show the metallic nature of the film with a perpendicular magnetic anisotropy along the c-axis.

  20. Improved control over spontaneously formed GaN nanowires in molecular beam epitaxy using a two-step growth process.

    PubMed

    Zettler, J K; Corfdir, P; Geelhaar, L; Riechert, H; Brandt, O; Fernández-Garrido, S

    2015-11-01

    We investigate the influence of modified growth conditions during the spontaneous formation of GaN nanowires (NWs) on Si(111) in plasma-assisted molecular beam epitaxy. We find that a two-step growth approach, where the substrate temperature is increased during the nucleation stage, is an efficient method to gain control over the area coverage, average diameter, and coalescence degree of GaN NW ensembles. Furthermore, we also demonstrate that the growth conditions employed during the incubation time that precedes nanowire nucleation do not influence the properties of the final nanowire ensemble. Therefore, when growing GaN NWs at elevated temperatures or with low Ga/N ratios, the total growth time can be reduced significantly by using more favorable growth conditions for nanowire nucleation during the incubation time.

  1. 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.

  2. High-performance K-band GaAs power field-effect transistors prepared by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Saunier, P.; Shih, H. D.

    1983-01-01

    The maturity of the molecular beam epitaxy (MBE) technique for preparing device quality GaAs material for microwave applications is demonstrated by the excellent performance characteristics of K-band GaAs power field-effect transistors (FETs) fabricated on the MBE wafers. An output power of 710 mW with 4.5-dB gain and 17.7 percent power-added efficiency was achieved at 21 GHz with a 1.26-mm gate width pi-gate device. A similar device with a 0.56-mm gate width produced an output power of 320 mW with 5.0-dB gain and 26.6 percent power-added efficiency at 21 GHz. These are the best results yet reported to date for GaAs power FETs operated in the K-band frequency range.

  3. Cleaning chemistry of GaAs(100) and InSb(100) substrates for molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Lewis, B. F.; Grunthaner, F. J.

    1983-01-01

    Ploog (1980) and Bachrach and Krusor (1981) have pointed out the importance of substrate preparation and surface cleaning for obtaining high quality films with the aid of molecular beam epitaxial growth techniques. In the present investigation, high resolution X-ray photoemission (XPS) is used to determine the oxide removal mechanism for GaAs(100) substrates which have undergone a standardized cleaning procedure. Other objectives of the investigation are related to a comparison of different cleaning procedures in order to minimize carbon contamination, the extension of these cleaning techniques to other III-V compound semiconductors such as InSb, and the evaluation of the sensitivity of the compositional results to electron-induced damage effects.

  4. 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.

  5. Surface morphology of molecular-beam epitaxially grown Si(1-x)Ge(x) layers on (100) and (110) Si

    NASA Technical Reports Server (NTRS)

    Pike, W. T.; Fathauer, R. W.; Anderson, M. S.

    1992-01-01

    The surface morphology and dislocation structure of Si(1-x)Ge(x) layers grown on (100) and (110) Si substrates have been investigated using atomic force microscopy, and scanning and transmission electron microscopy. The layers, which have up to a 1.2 percent lattice mismatch with the substrates, were grown by molecular-beam epitaxy at 550 C at thicknesses above those required for the introduction of dislocations. Si(1-x)Ge(x) layers grown on (100) show a crosshatch morphology which is correlated to the underlying misfit dislocation network. Annealing greatly enhances the surface roughness producing a partial islanding growing on the preexisting crosshatch morphology. On the (110) substrates no annealing is necessary to produce a roughened surface. The roughened surface morphology is analyzed as a strain-reducing growth mode which enables partial relaxation of the near-surface atomic planes.

  6. 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.

  7. 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.

  8. Molecular beam epitaxial growth and characterization of Al(Ga)N nanowire deep ultraviolet light emitting diodes and lasers

    NASA Astrophysics Data System (ADS)

    Mi, Z.; Zhao, S.; Woo, S. Y.; Bugnet, M.; Djavid, M.; Liu, X.; Kang, J.; Kong, X.; Ji, W.; Guo, H.; Liu, Z.; Botton, G. A.

    2016-09-01

    We report on the detailed molecular beam epitaxial growth and characterization of Al(Ga)N nanowire heterostructures on Si and their applications for deep ultraviolet light emitting diodes and lasers. The nanowires are formed under nitrogen-rich conditions without using any metal catalyst. Compared to conventional epilayers, Mg-dopant incorporation is significantly enhanced in nearly strain- and defect-free Al(Ga)N nanowire structures, leading to efficient p-type conduction. The resulting Al(Ga)N nanowire LEDs exhibit excellent performance, including a turn-on voltage of ∼5.5 V for an AlN nanowire LED operating at 207 nm. The design, fabrication, and performance of an electrically injected AlGaN nanowire laser operating in the UV-B band is also presented.

  9. 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.

  10. Molecular beam epitaxy-grown wurtzite MgS thin films for solar-blind ultra-violet detection

    NASA Astrophysics Data System (ADS)

    Lai, Y. H.; He, Q. L.; Cheung, W. Y.; Lok, S. K.; Wong, K. S.; Ho, S. K.; Tam, K. W.; Sou, I. K.

    2013-04-01

    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.

  11. Evolution of strain and composition of Ge islands on Si (001) grown by molecular beam epitaxy during postgrowth annealing

    SciTech Connect

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

    2008-06-01

    Self-assembled Ge islands have been grown using a Stranski-Krastanov growth mechanism on Si (001) substrates by solid source molecular beam epitaxy. We performed time varying annealing experiments at a representative temperature of 650 deg. C to study the shape and size evolution of islands for a relatively high Ge coverage. Islands are found to coarsen due to heat treatment via structural and compositional changes through continuous strain relaxation. Different island morphologies, namely, 'pyramids', 'transitional domes', and 'domes' are found during the annealing sequence. The dominant coarsening mechanisms for the temporal evolution of islands of as-grown and annealed samples are explained by the comprehensive analysis of Rutherford back scattering, Raman spectroscopy, high-resolution x-ray diffraction, and atomic force microscopy. A correlation of the morphological evolution with the composition and strain relaxation of grown islands is presented.

  12. Catalyst-free highly vertically aligned ZnO nanoneedle arrays grown by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, J. S.; Yang, C. S.; Chen, P. I.; Su, C. F.; Chen, W. J.; Chiu, K. C.; Chou, W. C.

    2009-11-01

    This work describes the growth of highly vertically aligned ZnO nanoneedle arrays on wafer-scale catalyst-free c-plane sapphire substrates by plasma-assisted molecular beam epitaxy under high Zn flux conditions. The photoluminescence spectrum of the as-grown samples reveals strong free exciton emissions and donor-bound exciton emissions with an excellent full width at half maximum (FWHM) of 1.4 meV. The field emission of highly vertically aligned ZnO nanoneedle arrays closely follows the Fowler-Nordheim theory. The turn-on electric field was about 5.9 V/µm with a field enhancement factor β of around 793.

  13. Nucleation of single GaN nanorods with diameters smaller than 35 nm by molecular beam epitaxy

    SciTech Connect

    Chen, Yen-Ting; Araki, Tsutomu; Palisaitis, Justinas; Persson, Per O. Å.; Olof Holtz, Per; Birch, Jens; Chen, Li-Chyong; Chen, Kuei-Hsien; Nanishi, Yasushi

    2013-11-11

    Nucleation mechanism of catalyst-free GaN nanorod grown on Si(111) is investigated by the fabrication of uniform and narrow (<35 nm) nanorods without a pre-defined mask by molecular beam epitaxy. Direct evidences show that the nucleation of GaN nanorods stems from the sidewall of the underlying islands down to the Si(111) substrate, different from commonly reported ones on top of the island directly. Accordingly, the growth and density control of the nanorods is exploited by a “narrow-pass” approach that only narrow nanorod can be grown. The optimal size of surrounding non-nucleation area around single nanorod is estimated as 88 nm.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Influence of substrate quality on structural properties of AlGaN/GaN superlattices grown by molecular beam epitaxy

    SciTech Connect

    Schubert, F.; Merkel, U.; Schmult, S.; Mikolajick, T.

    2014-02-28

    Short-period AlGaN/GaN superlattices were established as versatile test structures to investigate the structural properties of molecular beam epitaxy (MBE)-grown GaN and AlGaN layers and their dependence on the GaN substrate quality. X-ray diffractometry data of the investigated superlattices allow access to relevant structural parameters such as aluminum mole fraction and layer thicknesses. The occurrence of theoretically predicted intense high-order satellite peaks and pronounced interface fringes in the diffraction pattern reflects abrupt interfaces and perfect 2-dimensional growth resulting in smooth surfaces. The data unambiguously demonstrate that the structural quality of the MBE grown layers is limited by the structural properties of the GaN substrate.

  3. Molecular beam epitaxy of n-Zn(Mg)O as a low-damping plasmonic material at telecommunication wavelengths

    SciTech Connect

    Sadofev, Sergey; Kalusniak, Sascha; Schaefer, Peter; Henneberger, Fritz

    2013-05-06

    We demonstrate that Zn(Mg)O:Ga layers can be grown by molecular beam epitaxy in a two-dimensional mode with high structural perfection up to Ga mole fractions of about 6.5%. The doping efficiency is practically 100% so that free-carrier concentrations of almost 10{sup 21} cm{sup -3} can be realized providing a zero-crossover wavelength of the real part of the dielectric function as short as 1.36 {mu}m, while the plasmonic damping does not exceed 50 meV. Structural, electrical, and optical data consistently demonstrate a profound change of the Ga incorporation mode beyond concentrations of 10{sup 21} cm{sup -3} attended by deterioration of the plasmonic features.

  4. 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.

  5. 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.

  6. Spontaneous formation of highly regular superlattice structure in InGaN epilayers grown by molecular beam epitaxy

    SciTech Connect

    Wu, Z. H.; Kawai, Y.; Honda, Y.; Yamaguchi, M.; Amano, H.; Fang, Y.-Y.; Chen, C. Q.; Kondo, H.; Hori, M.

    2011-04-04

    In this letter, we have investigated the structural properties of thick InGaN layers grown on GaN by plasma-assisted molecular beam epitaxy, using two growth rates of 1.0 and 3.6 A/s. A highly regular superlattice (SL) structure is found to be spontaneously formed in the film grown at 3.6 A/s but not in the film grown at 1.0 A/s. The faster grown film also exhibits superior structural quality, which could be due to the surface roughness suppression caused by kinetic limitation, and the inhibition of the Frank-Read dislocation generation mechanism within the spontaneously formed SL structure.

  7. 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}.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. In situ investigation of growth modes during plasma-assisted molecular beam epitaxy of (0001) GaN

    SciTech Connect

    Koblmueller, G.; Fernandez-Garrido, S.; Calleja, E.; Speck, J. S.

    2007-10-15

    Real-time analysis of the growth modes during homoepitaxial (0001) GaN growth by plasma-assisted molecular beam epitaxy was performed using reflection high energy electron diffraction. A growth mode map was established as a function of Ga/N flux ratio and growth temperature, exhibiting distinct transitions between three-dimensional (3D), layer-by-layer, and step-flow growth modes. The layer-by-layer to step-flow growth transition under Ga-rich growth was surfactant mediated and related to a Ga adlayer coverage of one monolayer. Under N-rich conditions the transition from 3D to layer-by-layer growth was predominantly thermally activated, facilitating two-dimensional growth at temperatures of thermal decomposition.

  17. 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.

  18. A comprehensive diagram to grow InAlN alloys by plasma-assisted molecular beam epitaxy

    SciTech Connect

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

    2008-11-10

    Indium incorporation and surface morphology of InAlN layers grown on (0001) GaN by plasma-assisted molecular beam epitaxy were investigated as a function of the impinging In flux and the substrate temperature in the 450-610 deg. C range. In incorporation was found to decrease with substrate temperature due to thermal decomposition of the growing layer, while for a given temperature it increased with the impinging In flux until stoichiometry was reached at the growth front. The InN losses during growth followed an Arrhenius behavior characterized by an activation energy of 2.0 eV. A growth diagram highly instrumental to identify optimum growth conditions was established.

  19. 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.

  20. Molecular-beam-epitaxy growth of ferromagnetic Ni2MnGe on GaAs(001)

    NASA Astrophysics Data System (ADS)

    Lu, J.; Dong, J. W.; Xie, J. Q.; McKernan, S.; Palmstrøm, C. J.; Xin, Y.

    2003-09-01

    Single-crystal Heusler alloy Ni2MnGe thin films have been grown on GaAs(001) by molecular-beam epitaxy. X-ray diffraction and transmission electron microscopy were used for postgrowth structural characterization. The Ni2MnGe grew in a tetragonally distorted L21-like structure (a=5.65 Å, c=5.96 Å) with the c axis perpendicular to the film surface. An in-plane ordering with 2× periodicity and an out-of-plane ordering with 3× periodicity was observed for the as-grown films. Magnetometry measurements performed at 50 K indicate that the films are ferromagnetic and have a weak in-plane anisotropy with a coercivity ˜5.5 Oe and saturation magnetization of ˜450 emu/cm3. The Curie temperature was measured to be ˜320 K.

  1. Correlation of nanochemistry and electrical properties in HfO2 films grown by metalorganic molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Moon, Tae-Hyoung; Ham, Moon-Ho; Myoung, Jae-Min

    2005-03-01

    We present the annealing effects on nanochemistry and electrical properties in HfO2 dielectrics grown by metalorganic molecular-beam epitaxy. After the postannealing treatment of HfO2 films in the temperature range of 600-800°C, the thicknesses and chemical states of the films were examined by high-resolution transmission electron microscopy and angle-resolved x-ray photoelectron spectroscopy. By comparing the line shapes of core-level spectra for the samples with different annealing temperatures, the concentrations of SiO and Hf-silicate with high dielectric constant are found to be highest for HfO2 film annealed at 700°C. This result supports that the accumulation capacitance of the sample annealed at 700°C is not deteriorated in spite of a steep increase in interfacial layer thickness compared with that of the sample annealed at 600°C.

  2. 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.

  3. 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.

  4. 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%.

  5. 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.

  6. Oxygen vacancy induced photoluminescence and ferromagnetism in SrTiO{sub 3} thin films by molecular beam epitaxy

    SciTech Connect

    Xu, Wenfei; Yang, Jing; Bai, Wei; Tang, Kai; Zhang, Yuanyuan; Tang, Xiaodong

    2013-10-21

    SrTiO{sub 3} thin films were epitaxially grown on (100) SrTiO{sub 3} substrates using molecular beam epitaxy. The temperature for growth of the films was optimized, which was indicated by x-ray diffraction and further confirmed by microstructural characterization. Photoluminescence spectra show that oxygen-vacancy contributes to red and blue luminescence of oxygen-deficient post-annealed films, and a red shift was observed in blue region. On the other hand, ferromagnetism in film form SrTiO{sub 3} was observed from 5 K to 400 K and could be further enhanced with decreasing oxygen plasma partial pressure in annealing processes, which might be explained by the theory involving d{sup 0} magnetism related to oxygen-vacancy. From the cooperative investigations of optical and magnetic properties, we conclude that intrinsic defects, especially oxygen-vacancy, can induce and enhance luminescence and magnetism in SrTiO{sub 3} films.

  7. Surfactant effect of gallium during molecular-beam epitaxy of GaN on AlN (0001)

    NASA Astrophysics Data System (ADS)

    Mula, Guido; Adelmann, C.; Moehl, S.; Oullier, J.; Daudin, B.

    2001-11-01

    We study the adsorption of Ga on (0001) GaN surfaces by reflection high-energy electron diffraction. It is shown that a dynamically stable Ga bilayer can be formed on the GaN surface for appropriate Ga fluxes and substrate temperatures. The influence of the presence of this Ga film on the growth mode of GaN on AlN(0001) by plasma-assisted molecular-beam epitaxy is studied. It is demonstrated that under nearly stoichiometric and N-rich conditions, the GaN layer relaxes elastically during the first stages of epitaxy. At high temperatures the growth follows a Stranski-Krastanov mode, whereas at lower temperatures kinetically formed flat platelets are observed. Under Ga-rich conditions-where a Ga bilayer is rapidly formed due to excess Ga accumulating on the surface-the growth follows a Frank-van der Merwe layer-by-layer mode at any growth temperature and no initial elastic relaxation occurs. Hence, it is concluded that excess Ga acts as a surfactant, effectively suppressing both Stranski-Krastanov islanding and platelet formation. It is further demonstrated that the Stranski-Krastanov transition is in competition with elastic relaxation by platelets, and it is only observed when relaxation by platelets is inefficient. As a result, a growth mode phase diagram is outlined for the growth of GaN on AlN(0001).

  8. Arrayed van der Waals Vertical Heterostructures Based on 2D GaSe Grown by Molecular Beam Epitaxy.

    PubMed

    Yuan, Xiang; Tang, Lei; Liu, Shanshan; Wang, Peng; Chen, Zhigang; Zhang, Cheng; Liu, Yanwen; Wang, Weiyi; Zou, Yichao; Liu, Cong; Guo, Nan; Zou, Jin; Zhou, Peng; Hu, Weida; Xiu, Faxian

    2015-05-13

    Vertically stacking two-dimensional (2D) materials can enable the design of novel electronic and optoelectronic devices and realize complex functionality. However, the fabrication of such artificial heterostructures on a wafer scale with an atomically sharp interface poses an unprecedented challenge. Here, we demonstrate a convenient and controllable approach for the production of wafer-scale 2D GaSe thin films by molecular beam epitaxy. In situ reflection high-energy electron diffraction oscillations and Raman spectroscopy reveal a layer-by-layer van der Waals epitaxial growth mode. Highly efficient photodetector arrays were fabricated, based on few-layer GaSe on Si. These photodiodes show steady rectifying characteristics and a high external quantum efficiency of 23.6%. The resultant photoresponse is super-fast and robust, with a response time of 60 μs. Importantly, the device shows no sign of degradation after 1 million cycles of operation. We also carried out numerical simulations to understand the underlying device working principles. Our study establishes a new approach to produce controllable, robust, and large-area 2D heterostructures and presents a crucial step for further practical applications.

  9. 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.

  10. Strain relaxation in single crystal SrTiO3 grown on Si (001) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Choi, Miri; Posadas, Agham; Dargis, Rytis; Shih, Chih-Kang; Demkov, Alexander A.; Triyoso, Dina H.; David Theodore, N.; Dubourdieu, Catherine; Bruley, John; Jordan-Sweet, Jean

    2012-03-01

    An epitaxial layer of SrTiO3 grown directly on Si may be used as a pseudo-substrate for the integration of perovskite oxides onto silicon. When SrTiO3 is initially grown on Si (001), it is nominally compressively strained. However, by subsequent annealing in oxygen at elevated temperature, an SiOx interlayer can be formed which alters the strain state of SrTiO3. We report a study of strain relaxation in SrTiO3 films grown on Si by molecular beam epitaxy as a function of annealing time and oxygen partial pressure. Using a combination of x-ray diffraction, reflection high energy electron diffraction, and transmission electron microscopy, we describe the process of interfacial oxidation and strain relaxation of SrTiO3 on Si (001). Understanding the process of strain relaxation of SrTiO3 on silicon will be useful for controlling the SrTiO3 lattice constant for lattice matching with functional oxide overlayers.

  11. Molecular beam epitaxial growth of high-quality InSb on InP and GaAs substrates

    SciTech Connect

    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.

  12. 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.

  13. 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

  14. 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

  15. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    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

  16. 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.

  17. 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.

  18. 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.

  19. Columnar and subsurface silicide growth with novel molecular beam epitaxy techniques

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; George, T.; Pike, W. T.

    1992-01-01

    We have found novel growth modes for epitaxial CoSi2 at high temperatures coupled with Si-rich flux ratios or low deposition rates. In the first of these modes, codeposition of metal and Si at 600-800 C with excess Si leads to the formation of epitaxial silicide columns surrounded by single-crystal Si. During the initial stages of the deposition, the excess Si grows homoepitaxially in between the silicide, which forms islands, so that the lateral growth of the islands is confined. Once a template layer is established by this process, columns of silicide form as a result of selective epitaxy of silicide on silicide and Si on Si. This growth process allows nanometer control over silicide particles in three dimensions. In the second of these modes, a columnar silicide seed layer is used as a template to nucleate subsurface growth of CoSi2. With a 100 nm Si layer covering CoSi2 seeds, Co deposited at 800C and 0.01 nm/s diffuses down to grow on the buried seeds rather than nucleating surface silicide islands. For thicker Si caps or higher deposition rates, the surface concentration of Co exceeds the critical concentration for nucleation of islands, preventing this subsurface growth mode from occurring. Using this technique, single-crystal layers of CoSi2 buried under single-crystal Si caps have been grown.

  20. 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.

  1. Features of molecular beam epitaxy of the GaN (0001) and GaN (0001-bar) layers with the use of different methods of activation of nitrogen

    SciTech Connect

    Mizerov, A. M. Jmerik, V. N.; Kaibyshev, V. K.; Komissarova, T. A.; Masalov, S. A.; Ivanov, S. V.

    2009-08-15

    The results of comparative studies of the growth kinetics of the GaN layers of different polarity during ammonia molecular beam epitaxy and plasma-assisted molecular beam epitaxy (PA MBE) of nitrogen with the use of sapphire substrates and GaN(0001-bar)/c-Al{sub 2}O{sub 3} templates grown by gas-phase epitaxy from metalorganic compounds are presented. The possibility is shown of obtaining the GaN layers with an atomically smooth surface during molecular beam epitaxy with plasma activation of nitrogen. For this purpose, it is suggested to carry out the growth in conditions enriched with metal near the mode of formation of the Ga drops at a temperature close to the decomposition temperature of GaN (TS {approx} 760 deg. C). The conclusion is made that an increase in the growth temperature positively affects the structural, optical, and electrical properties of the GaN (0001-bar) layers. A high quality of the GaN (0001) films grown by the PA MBE method at a low temperature of {approx}700 deg. C on the GaN/c-Al{sub 2}O{sub 3} templates is shown.

  2. Molecular-beam epitaxy of CrSi2 on Si(111)

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Grunthaner, P. J.; Lin, T. L.; Chang, K. T.; Mazur, J. H.

    1988-01-01

    The growth of CrSi2 on Si(111) in a commercial MBE system with a base pressure in the low 10 to the -11th torr range is reported. CrSi2 layers grown on Si(111) exhibit a strong tendency to form islands. Two particular epitaxial relationships are identified. Thick (210 nm) layers have been grown by four different techniques, with best results obtained by codepositing Cr and Si at elevated temperature. The grain size is observed to increase with substrate temperature, reaching 1-2 microns in a layer deposited at 825 C.

  3. Sn-mediated Ge/Ge(001) growth by low-temperature molecular-beam epitaxy: Surface smoothening and enhanced epitaxial thickness

    SciTech Connect

    Bratland, K.A.; Foo, Y.L.; Spila, T.; Seo, H.-S.; Haasch, R.T.; Desjardins, P.; Greene, J.E.

    2005-02-15

    Fully strained single-crystal metastable Ge{sub 1-x}Sn{sub x} layers were grown on Ge(001) in order to probe the role of Sn dopant and alloy concentrations (C{sub Sn}=1x10{sup 18} cm{sup -3} to 6.1 at. %) on surface roughening pathways leading to epitaxial breakdown during low-temperature (155 deg. C) molecular-beam epitaxy of compressively strained films. The addition of Sn was found to mediate Ge(001) surface morphological evolution through two competing pathways. At very low Sn concentrations (x < or approx. 0.02), the dominant effect is a Sn-induced enhancement in both the Ge surface diffusivity and the probability of interlayer mass transport. This, in turn, results in more efficient filling of interisland trenches, and thus delays epitaxial breakdown. In fact, breakdown is not observed at all for Sn concentrations in the doping regime, 1x10{sup 18}{<=}C{sub Sn}<4.4x10{sup 20} cm{sup -3} (2.3x10{sup -5}{<=}x<0.010){exclamation_point} At higher concentrations, there is a change in Ge{sub 1-x}Sn{sub x}(001) growth kinetics due to a rapid increase in the amount of compressive strain. This leads to a gradual reduction in the film thickness h{sub 1}(x) corresponding to the onset of breakdown as strain-induced roughening overcomes the surface smoothening effects, and results in an increase in the overall roughening rate. We show that by varying the Sn concentration through the dopant to dilute alloy concentration range during low-temperature Ge(001) growth, we can controllably manipulate the surface roughening pathway, and hence the epitaxial thickness, over a very wide range.

  4. 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

    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.

  5. 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.

  6. 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

  7. Molecular Beam Epitaxial Growth and Characterization of Mismatched Indium Gallium Arsenide and Indium Aluminum Arsenide Layers on Indium Phosphide

    NASA Astrophysics Data System (ADS)

    Bennett, Brian R.

    Mismatched epitaxial layers of In_ {x}Ga_{1-x}As and In_{y}Al_ {1-y}As were grown on (001) InP by molecular beam epitaxy. The layers were characterized by a technique we developed known as variable azimuthal-angle ellipsometry. It reveals large optical anisotropy for many strained layers. We attribute the anisotropy to strain-induced surface roughening during growth. Samples were also characterized by high -resolution x-ray diffraction (HRXRD) to assess layer quality as well as composition and strain. HRXRD measurements reveal orthorhombic distortion of partially relaxed layers of InGaAs and InAlAs in tension or compression, with preferential strain relief in the (110) direction. We show that HRXRD epilayer peak width and interference fringes are sensitive, non-destructive criteria to judge the structural quality of strained heterostructures. For layers ranging from 300 to 10,000 A, with lattice mismatch of +/- 1% or less, the crystalline quality consistently remains high to thicknesses up to 3-9 times the Matthews -Blakeslee critical layer thickness. We investigated the thermal stability of these layers, using HRXRD to measure structural changes caused by high-temperature anneals. We also compared the electron mobility of modulation-doped heterostructures before and after annealing. Both techniques demonstrate that our high-quality strained layers are stable to temperatures of at least 800-850^circ C. We explain this result by the limited sources available for the nucleation of misfit dislocations. The findings are applied to the design and growth of high-performance pseudomorphic InAlAs/InGaAs/InP heterostructure field-effect transistors with layers exceeding the Matthews-Blakeslee limit. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. Infrared Photodiodes Made by Low Energy Ion Etching of Molecular Beam Epitaxy Grown Mercury-Cadmium Alloy

    NASA Astrophysics Data System (ADS)

    Yoo, Sung-Shik

    Ion etching was used to form junctions on the p-type (111)B Hg_{1-x}Cd_ {x}Te grown by Molecular Beam Epitaxy(MBE). When Hg_{1-x}Cd_{x}Te layers are etched by Ar ions at energies ranging between 300 and 450eV, the top Hg_{1 -x}Cd_{x}Te layer is converted to n-type. The converted region is electrically characterized as a defective n^+-region near the surface, and a low doped n^--region exist below the damaged region. The total thickness of the converted n-type layer was found to be considerable. These results suggest that the creation of the n-type layer is due to the filling of mercury vacancies by mercury atoms displaced by the Ar ion irradiation on the surface. For the performance of the resulting photodiodes on MBE grown (111)B Hg_{1-x}Cd _{x}Te using this technique, the dynamic resistances at 80K are one order of magnitude less than those of junctions made on Liquid Phase Epitaxially and Bulk grown Hg_{1 -x}Cd_{x}Te. The ion etching technique was compared with ion implantation technique by fabricating diodes on the same MBE grown (111)B Hg _{1-x}Cd_{x}Te layers. The result of the comparison illustrates that ion etching technique is as good as ion implantation technique for the fabrication of Hg_{1-x}Cd _{x}Te photodiodes. Also it is believed that the performance of the diodes is limited by a relatively large density of twin defects usually found in MBE grown (111)B Hg_{1-x}Cd _{x}Te.

  14. Transient-mode liquid phase epitaxial growth of GaAs on GaAs-coated Si substrates prepared by migration-enhanced molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Nakamura, Shuji; Sakai, Shiro; Chang, Shi S.; Ramaswamy, Ramu V.; Kim, Jae-Hoon; Radhakrishnan, Gouri; Liu, John K.; Katz, Joseph

    1989-01-01

    Planar oxide-maskless growth of GaAs was demonstrated by transient-mode liquid phase epitaxy (TMLPE) on GaAs-coated Si substrates that were prepared by migration-enhanced molecular beam epitaxy (MEMBE). In TMLPE, the cool substrate was brought into contact with hot melts for a short time. A GaAs layer as thick as 30 microns was grown in 10 sec. The etch pits observed in TMLPE-grown layers became longer in one direction and decreased in density with increasing the TMLPE epilayer thickness. The density of etch pits in a 20 micron-thick layer was approximately 5 x 10 the 6th/sq cm. Strong bandgap emission elliptically polarized with a major axis perpendicular to the surface was observed at about 910 nm, while deep-level emission from the TMLPE/MEMBE GaAs interface was detected at 980 nm. The photoluminescence intensity divided by the carrier concentration of the TMLPE-grown layer was about 270 times larger than that of the MEMBE-grown layer used as a substrate.

  15. Energy band alignment of atomic layer deposited HfO{sub 2} on epitaxial (110)Ge grown by molecular beam epitaxy

    SciTech Connect

    Hudait, M. K.; Zhu, Y.; Maurya, D.; Priya, S.

    2013-03-04

    The band alignment properties of atomic layer HfO{sub 2} film deposited on epitaxial (110)Ge, grown by molecular beam epitaxy, was investigated using x-ray photoelectron spectroscopy. The cross-sectional transmission electron microscopy exhibited a sharp interface between the (110)Ge epilayer and the HfO{sub 2} film. The measured valence band offset value of HfO{sub 2} relative to (110)Ge was 2.28 {+-} 0.05 eV. The extracted conduction band offset value was 2.66 {+-} 0.1 eV using the bandgaps of HfO{sub 2} of 5.61 eV and Ge bandgap of 0.67 eV. These band offset parameters and the interface chemical properties of HfO{sub 2}/(110)Ge system are of tremendous importance for the design of future high hole mobility and low-power Ge-based metal-oxide transistor devices.

  16. 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

  17. Control of tensile strain and interdiffusion in Ge/Si(001) epilayers grown by molecular-beam epitaxy

    SciTech Connect

    Luong, T. K. P.; Dau, M. T.; Zrir, M. A.; Le Thanh, V.; Petit, M.; Stoffel, M.; Rinnert, H.; Ghrib, A.; El Kurdi, M.; Boucaud, P.; Murota, J.

    2013-08-28

    Tensile-strained and n-doped Ge has emerged as a potential candidate for the realization of optoelectronic devices that are compatible with the mainstream silicon technology. Tensile-strained Ge/Si epilayers can be obtained by using the difference of thermal expansion coefficients between Ge and Si. We have combined various surface, structural, and compositional characterizations to investigate the growth mode and the strain state in Ge/Si epilayers grown by molecular-beam epitaxy. The Ge growth was carried out using a two-step approach: a low-temperature growth to produce relaxed and smooth buffer layers, which is followed by a high-temperature growth to get high quality Ge layers. The existence of a substrate temperature window from 260 to 300 °C is evidenced, which allows to completely suppress the Ge/Si Stranski-Krastanov growth. As a consequence of the high temperature growth, a tensile strain lying in the range of 0.22%–0.24% is obtained. Concerning the effect of thermal annealing, it is shown that cyclic annealing may allow increasing the tensile strain up to 0.30%. Finally, we propose an approach to use carbon adsorption to suppress Si/Ge interdiffusion, which represents one of the main obstacles to overcome in order to realize pure Ge-based optoelectronic devices.

  18. 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.

  19. Position-controlled growth of GaN nanowires and nanotubes on diamond by molecular beam epitaxy.

    PubMed

    Schuster, Fabian; Hetzl, Martin; Weiszer, Saskia; Garrido, Jose A; de la Mata, María; Magen, Cesar; Arbiol, Jordi; Stutzmann, Martin

    2015-03-11

    In this work the position-controlled growth of GaN nanowires (NWs) on diamond by means of molecular beam epitaxy is investigated. In terms of growth, diamond can be seen as a model substrate, providing information of systematic relevance also for other substrates. Thin Ti masks are structured by electron beam lithography which allows the fabrication of perfectly homogeneous GaN NW arrays with different diameters and distances. While the wurtzite NWs are found to be Ga-polar, N-polar nucleation leads to the formation of tripod structures with a zinc-blende core which can be efficiently suppressed above a substrate temperature of 870 °C. A variation of the III/V flux ratio reveals that both axial and radial growth rates are N-limited despite the globally N-rich growth conditions, which is explained by the different diffusion behavior of Ga and N atoms. Furthermore, it is shown that the hole arrangement has no effect on the selectivity but can be used to force a transition from nanowire to nanotube growth by employing a highly competitive growth regime.

  20. 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.

  1. Growth map for Ga-assisted growth of GaAs nanowires on Si(111) substrates by molecular beam epitaxy.

    PubMed

    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. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. Ultrafast carrier dynamics and the role of grain boundaries in polycrystalline silicon thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Titova, Lyubov V.; Cocker, Tyler L.; Xu, Sijia; Baribeau, Jean-Marc; Wu, Xiaohua; Lockwood, David J.; Hegmann, Frank A.

    2016-10-01

    We have used time-resolved terahertz spectroscopy to study microscopic photoconductivity and ultrafast photoexcited carrier dynamics in thin, pure, non-hydrogenated silicon films grown by molecular beam epitaxy on quartz substrates at temperatures ranging from 335 °C to 572 °C. By controlling the growth temperature, thin silicon films ranging from completely amorphous to polycrystalline with minimal amorphous phase can be achieved. Film morphology, in turn, determines its photoconductive properties: in the amorphous phase, carriers are trapped in bandtail states on sub-picosecond time scales, while the carriers excited in crystalline grains remain free for tens of picoseconds. We also find that in polycrystalline silicon the photoexcited carrier mobility is carrier-density-dependent, with higher carrier densities mitigating the effects of grain boundaries on inter-grain transport. In a film grown at the highest temperature of 572 °C, the morphology changes along the growth direction from polycrystalline with needles of single crystals in the bulk of the film to small crystallites interspersed with amorphous silicon at the top of the film. Depth profiling using different excitation wavelengths shows corresponding differences in the photoconductivity: the photoexcited carrier lifetime and mobility are higher in the first 100-150 nm from the substrate, suggesting that thinner, low-temperature grown polycrystalline silicon films are preferable for photovoltaic applications.

  9. Properties of MIS structures based on graded-gap HgCdTe grown by molecular beam epitaxy

    SciTech Connect

    Voitsekhovskii, A. V. Nesmelov, S. N.; Dzyadookh, S. M.; Varavin, V. S.; Dvoretskii, S. A.; Mikhailov, N. N.; Sidorov, Yu. G.; Vasiliev, V. V.

    2008-11-15

    The effect of near-surface graded-gap layers on the electrical characteristics of MIS structures fabricated based on heteroepitaxial Hg{sub 1-x} Cd{sub x}Te films grown by molecular beam epitaxy with a two-layer SiO{sub 2}/Si{sub 3}N{sub 4} insulator and anodic oxide film is studied experimentally. It is shown that a larger modulation of capacitance (depth and width of the valley) is observed compared with the structures without the graded-gap layer. The field dependences of photovoltage of MIS structures with the graded-gap layers had a classical form and were characterized by a drop only in the enrichment region. For the structures without the graded-gap layer with x = 0.22, a drop in the voltage dependence of the photocurrent is observed in the region of pronounced inversion. This drop is governed by limitation of the space charge region by processes of tunneling generation via deep levels. The properties of the HgCdTe-insulator interfaces are studied.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. Direct imaging of InSb (110)-(1x1) surface grown by molecular beam epitaxy

    SciTech Connect

    Mishima, T. D.

    2011-10-01

    High-resolution transmission electron microscopy under a profile imaging condition (HR-profile TEM) was employed to determine the structural model for the InSb(110)-(1x1) relaxation surface grown by molecular beam epitaxy (MBE). HR-profile TEM analyses indicate that the chevron model, which is widely accepted for zinc-blende-type III-V(110)-(1x1) surfaces prepared by cleavage, is also applicable to the InSb(110)-(1x1) surface prepared under an Sb-rich MBE condition. The assignment of atomic species (In or Sb) of InSb(110)-(1x1) surfaces was confirmed based on a HR-profile TEM image that captures the connected facets of InSb(110)-(1x1) and InSb(111)B-(2x2). On the basis of the well-known atomic species of InSb(111)B-(2x2), the atomic species of the InSb(110)-(1x1) surface were deduced straightforwardly: the atoms shifted upward and downward at the topmost layer of the InSb(110)-(1x1) surface are Sb and In, respectively. The atomic arrangements of the InSb(110)-(1x1)-InSb(111)B-(2x2) facet determined by HR-profile TEM may represent the atomic arrangements of zinc-blende-type III-V(331)B surfaces.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Magnetic properties of MnSb inclusions formed in GaSb matrix directly during molecular beam epitaxial growth

    SciTech Connect

    Lawniczak-Jablonska, Krystyna; Wolska, Anna; Klepka, Marcin T.; Kret, Slawomir; Kurowska, Boguslawa; Kowalski, Bogdan J.; Twardowski, Andrzej; Wasik, Dariusz; Kwiatkowski, Adam; Sadowski, Janusz

    2011-04-01

    Despite of intensive search for the proper semiconductor base materials for spintronic devices working at room temperature no appropriate material based on ferromagnetic semiconductors has been found so far. We demonstrate that the phase segregated system with MnSb hexagonal inclusions inside the GaSb matrix, formed directly during the molecular beam epitaxial growth reveals the ferromagnetic properties at room temperature and is a good candidate for exploitation in spintronics. Furthermore, the MnSb inclusions with only one crystalline structure were identified in this GaMn:MnSb granular material. The SQUID magnetometry confirmed that this material exhibits ferromagnetic like behavior starting from helium up to room temperature. Moreover, the magnetic anisotropy was found which was present also at room temperature, and it was proved that by choosing a proper substrate it is possible to control the direction of easy axis of inclusions' magnetization moment between in-plane and out-of-plane; the latter is important in view of potential applications in spintronic devices.

  3. Incorporation and Activation of Arsenic Dopant in Single-Crystal CdTe Grown on Si by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Park, J. H.; Farrell, S.; Kodama, R.; Blissett, C.; Wang, X.; Colegrove, E.; Metzger, W. K.; Gessert, T. A.; Sivananthan, S.

    2014-08-01

    We report the use of molecular beam epitaxy to achieve p-type doping of CdTe grown on Si(211) substrates, by use of an arsenic cracker and post-growth annealing. A high hole density in CdTe is crucial for high efficiency II-VI-based solar cells. We measured the density of As in single-crystal CdTe by secondary ion mass spectroscopy; this showed that high As incorporation is achieved at low growth temperatures. Progressively higher incorporation was observed during low-temperature growth, presumably because of degradation of crystal quality with incorporation of As at such defect sites as dislocations and defect complexes. After As activation annealing under Hg overpressure, hole concentrations were obtained from Hall measurements. The highest doping level was ˜2.3 × 1016 cm-3, and near-1016 cm-3 doping was readily reproduced. The activation efficiency was ˜50%, but further optimization of the growth and annealing conditions is likely to improve this value.

  4. 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.

  5. Avoiding polar catastrophe in the growth of polarly orientated nickel perovskite thin films by reactive oxide molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Yang, H. F.; Liu, Z. T.; Fan, C. C.; Yao, Q.; Xiang, P.; Zhang, K. L.; Li, M. Y.; Liu, J. S.; Shen, D. W.

    2016-08-01

    By means of the state-of-the-art reactive oxide molecular beam epitaxy, we synthesized (001)- and (111)-orientated polar LaNiO3 thin films. In order to avoid the interfacial reconstructions induced by polar catastrophe, screening metallic Nb-doped SrTiO3 and iso-polarity LaAlO3 substrates were chosen to achieve high-quality (001)-orientated films in a layer-by-layer growth mode. For largely polar (111)-orientated films, we showed that iso-polarity LaAlO3 (111) substrate was more suitable than Nb-doped SrTiO3. In situ reflection high-energy electron diffraction, ex situ high-resolution X-ray diffraction, and atomic force microscopy were used to characterize these films. Our results show that special attentions need to be paid to grow high-quality oxide films with polar orientations, which can prompt the explorations of all-oxide electronics and artificial interfacial engineering to pursue intriguing emergent physics like proposed interfacial superconductivity and topological phases in LaNiO3 based superlattices.

  6. InN nanorods prepared with CrN nanoislands by plasma-assisted molecular beam epitaxy.

    PubMed

    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

    2011-01-01

    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. 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

  8. Defects in Ga(In)NAs thin films grown by atomic H-assisted molecular beam epitaxy

    SciTech Connect

    Shimizu, Yukiko; Mura, Yusuke; Uedono, Akira; Okada, Yoshitaka

    2006-09-15

    The vacancy-type defects in Ga{sub 1-y}In{sub y}N{sub x}As{sub 1-x} dilute nitride films grown by atomic H-assisted molecular beam epitaxy (H-MBE) were investigated. The positron annihilation measurements showed that the densities of vacancy-type defects in GaN{sub x}As{sub 1-x} (x=0%-1.3%) films grown under an optimized atomic H flux were as low as that for a liquid encapsulated Czochralski (LEC) GaAs substrate. Further, the influence of vacancy-type defects on the crystal quality and optical properties were studied by x-ray diffraction and photoluminescence (PL) measurements. The integrated PL intensity at 77 K drastically decreased as N composition was increased, but we found no clear correlation between the density or volume of vacancy defects and optical properties, and the S parameters were nearly constant at a value of {approx}0.516 in all Ga{sub 1-y}In{sub y}N{sub x}As{sub 1-x} films grown by our H-MBE technique.

  9. 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

  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 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Composition and luminescence of AlInGaN layers grown by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Bejtka, K.; Edwards, P. R.; Martin, R. W.; Fernandez-Garrido, S.; Calleja, E.

    2008-10-01

    A study of AlInGaN epilayers, grown by plasma-assisted molecular beam epitaxy, was performed using spatially resolved x-ray microanalysis and luminescence spectroscopy in order to investigate competition between the incorporation of In, Al, and Ga as a function of the growth temperature in the 565-660 deg. C range and the nominal AlN mole fraction. The samples studied have AlN and InN mole fractions in the ranges of 4%-30% and 0%-16%, respectively. Composition measurements show the effect of decreasing temperature to be an increase in the incorporation of InN, accompanied by a small but discernible decrease in the ratio of GaN to AlN mole fractions. The incorporation of In is also shown to be significantly increased by decreasing the Al mole fraction. Optical emission peaks, observed by cathodoluminescence mapping and by photoluminescence, provide further information on the epilayer compositions as a function of substrate temperature, and the dependencies of peak energy and linewidth are plotted.

  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. 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.

  19. InN nanorods prepared with CrN nanoislands by plasma-assisted molecular beam epitaxy.

    PubMed

    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

    2011-01-01

    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.

  20. 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.

  1. 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.

  2. 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

    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.

  3. 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.

  4. Structural properties of Bi2-xMnxSe3 thin films grown via molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Babakiray, Sercan; Johnson, Trent A.; Borisov, Pavel; Holcomb, Mikel B.; Lederman, David; Marcus, Matthew A.; Tarafder, Kartick

    2015-07-01

    The effects of Mn doping on the structural properties of the topological insulator Bi2Se3 in thin film form were studied in samples grown via molecular beam epitaxy. Extended x-ray absorption fine structure measurements, supported by density functional theory calculations, indicate that preferential incorporation occurs substitutionally in Bi sites across the entire film volume. This finding is consistent with x-ray diffraction measurements which show that the out of plane lattice constant expands while the in plane lattice constant contracts as the Mn concentration is increased. X-ray photoelectron spectroscopy indicates that the Mn valency is 2+ and that the Mn bonding is similar to that in MnSe. The expansion along the out of plane direction is most likely due to weakening of the Van der Waals interactions between adjacent Se planes. Transport measurements are consistent with this Mn2+ substitution of Bi sites if additional structural defects induced by this substitution are taken into account.

  5. 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.

  6. Atomic layer-by-layer growth of superconducting Bi Sr Ca Cu O thin films by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bove, P.; Rogers, D. J.; Hosseini Teherani, F.

    2000-11-01

    In situ reflection high-energy electron diffraction (RHEED) is employed to investigate the growth kinetics, and monitor the crystal surface evolution, during plasma-assisted molecular beam epitaxy growth of Bi 2Sr 2Ca n-1 Cu nO (BSCCO) compounds. By varying the growth parameters such as operating pressure, substrate temperature, cation flux and shutter opening pulse duration, it is found that the crystal growth front exhibits surface reconstructions with (1×1), (2×2), c(2×2) and (3×1) symmetries for the Sr, Ca and Cu species, and a RHEED pattern characteristic of twinning for Bi. Through manipulation of these surface reconstructions, and use of an adapted growth mode, it was possible to achieve a monolayer coverage for each species supplied. For the n=1, 2 and 3 compounds the resulting films exhibit a crystal quality characterised by an X-ray diffraction rocking curve width of 0.03° and an atomic force microscope mean surface roughness of 0.9 nm [over 10×10 μm] for 40 nm thick films.

  7. 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.

  8. 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.

  9. Band lineup in GaAs(1-x)Sbx/GaAs strained-layer multiple quantum wells grown by molecular-beam epitaxy

    NASA Technical Reports Server (NTRS)

    Ji, G.; Agarwala, S.; Huang, D.; Chyi, J.; Morkoc, H.

    1988-01-01

    GaAs(1-x)Sbx/GaAs strained-layer multiple quantum wells have been grown by molecular-beam epitaxy and characterized by room-temperature photoreflectance (PR). The PR spectra denote that high-quality layers can be grown in the GaAs(1-x)Sbx/GaAs system. The method for determining the band offset Q(vh) is discussed in this strained-layer system.

  10. Recombination-current suppression in GaAs p-n junctions grown on AlGaAs buffer layers by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Rancour, D. P.; Melloch, M. R.; Pierret, R. F.; Lundstrom, M. S.; Klausmeier-Brown, M. E.; Kyono, C. S.

    1987-08-01

    n+pp+GaAs and n+pP+ GaAs/GaAs/Al0.3Ga0.7As mesa diodes have been fabricated from films grown by molecular-beam epitaxy. The diodes made from films employing an AlGaAs buffer layer show marked improvements (a factor of 5 reduction) in recombination current densities. Deep level transient spectroscopy measurements moreover indicate that deep level concentrations are reduced by the AlGaAs buffer.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Growth and characteristics of self-assembly defect-free GaN surface islands by molecular beam epitaxy.

    PubMed

    Hsu, Kuang-Yuan; Wang, Cheng-Yu; Liu, Chuan-Pu

    2011-04-01

    GaN surface nano-islands of high crystal quality, without any dislocations or other extended defects, are grown on a c-plane sapphire substrate by plasma-assisted molecular beam epitaxy. Nano-island growth requires special conditions in terms of V/III ratio and substrate temperature, distinct from either film or nanocolumn growth. The insertion of a nitrided Ga layer can effectively improve the uniformity of the nano-islands in both shape and size. The islands are well faced truncated pyramids with island size ranged from 30 to 110 nm, and height ranged from 30 to 55 nm. On, the other hand, the density and facet of the GaN surface islands would be affected by the growth conditions. An increase of the V/III ratio from 30 to 40 led to an increase in density from 1.4 x 10(9) to 4.3 x 10(9) cm(-2) and an evolution from {1-21-1} facets to {1-21-2} facets. The GaN layers containing the surface islands can moderate the compressive strain due to the lattice and thermal mismatch between GaN and c-sapphire. Conductive atomic force microscopy shows that the off-axis sidewall facets are more electrically active than those at the island center. The formation of the GaN surface islands is strongly induced by the Ehrlich-Schwoebel barrier effect of preexisting islands grown in the early growth stage. GaN surface islands are ideal templates for growing nano-devices.

  19. 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.

  20. Localized Si enrichment in coherent self-assembled Ge islands grown by molecular beam epitaxy on (001)Si single crystal

    NASA Astrophysics Data System (ADS)

    Valvo, M.; Bongiorno, C.; Giannazzo, F.; Terrasi, A.

    2013-01-01

    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 °C to 700 °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 °C, while very remarkable already at 650 °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 °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 °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.

  1. Kinetics versus thermodynamics of the metal incorporation in molecular beam epitaxy of (InxGa1-x)2O3

    NASA Astrophysics Data System (ADS)

    Vogt, Patrick; Bierwagen, Oliver

    2016-08-01

    We present a detailed study of the reaction kinetics and thermodynamics of the plasma-assisted oxide molecular beam epitaxy of the ternary compound (InxGa1-x)2O3 for 0 ≤ x ≤ 1. We measured the growth rate of the alloy in situ by laser reflectrometry as a function of growth temperature TG for different metal-to-oxygen flux ratios rMe, and nominal In concentrations xnom in the metal flux. We determined ex situ the In and Ga concentrations in the grown film by energy dispersive X-ray spectroscopy. The measured In concentration x shows a strong dependence on the growth parameters TG, rMe, and xnom whereas growth on different co-loaded substrates shows that in the macroscopic regime of ˜μm3 x does neither depend on the detailed layer crystallinity nor on crystal orientation. The data unveil that, in presence of In, Ga incorporation is kinetically limited by Ga2O desorption the same way as during Ga2O 3 growth. In contrast, In incorporation during ternary growth is thermodynamically suppressed by the presence of Ga due to stronger Ga-O bonds. Our experiments revealed that Ga adatoms decompose/etch the In-O bonds whereas In adatoms do not decompose/etch the Ga-O bonds. This result is supported by our thermochemical calculations. In addition we found that a low TG and/or excessively low rMe kinetically enables In incorporation into (InxGa1-x)2O3. This study may help growing high-quality ternary compounds (InxGa1-x)2O3 allowing band gap engineering over the range of 2.7-4.7 eV.

  2. 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.

  3. 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.

  4. 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

  5. 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

  6. 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.

  7. Electron beam pumped III-V nitride vertical cavity surface emitting lasers grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ng, Hock Min

    The design and fabrication by molecular beam epitaxy of a prototype vertical cavity laser based on the III-V nitrides were investigated in this work. The bottom mirror of the laser consists of distributed Bragg reflectors (DBRs) based on quarterwave AlN (or AlxGa1-xN) and GaN layers. Such DBRs were designed for maximum reflectivity in the spectral region from 390--600 nm. The epitaxial growth of these two binaries on each other revealed that while AlN grows on GaN in a two-dimensional mode (Frank-van der Merwe mode), GaN grows on AlN in a three-dimensional mode (Stranski-Krastanov mode). In spite of that, DBRs with peak reflectance up to 99% and bandwidths of 45nm were fabricated. The measured reflectance spectra were compared with simulations using the transmission matrix method. The mechanical stability of these DBR structures due to non-uniform distribution of strain arising from lattice or thermal mismatch of the various components were also addressed. The active region of the laser consists of InGaN/GaN multiple quantum wells (MQWs). The existence of up to the third order diffraction peaks in the x-ray diffraction spectra suggests that the interfaces between InGaN and GaN are sharp with little interdiffusion at the growth temperature. The photoluminescence and cathodoluminescence spectra were analyzed to determine the optical quality of the MQWs. The best MQWs were shown to have a single emission peak at 397nm with full width half maximum (FWHM) of 11nm. Cathodoluminescence studies showed that there are spatially localized areas of intense light emission. The complete device was formed on (0001) sapphire substrates using the previously described DBRs as bottom mirrors and the MQWs as the active region. The top mirror of the device consists of metallic silver. The device was pumped by an electron beam from the top mirror side and the light output was collected from the sapphire side. Measurements at 100K showed narrowing of the linewidth with increasing pump

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. Molecular-beam epitaxy of Co2MnSi Heusler alloy thin films epitaxially grown on Si(0 0 1)

    NASA Astrophysics Data System (ADS)

    Stephan, R.; Dulot, F.; Mehdaoui, A.; Berling, D.; Wetzel, P.

    We report on the investigation of structural and magnetic properties of the ternary Heusler alloy Co2MnSi grown on Si(0 0 1) by molecular-beam epitaxy. Low-energy electron diffraction (LEED), inelastic medium-energy electron diffraction (IMEED) and X-ray photoelectron diffraction (XPD) measurements clearly show the growth of crystalline Co2MnSi. The best crystallographic and magnetic quality of the Co2MnSi films have been achieved after codeposition of the three Co, Mn and Si elements on the Si(0 0 1) substrate held at 587 K. Quantitative determinations of magnetic anisotropies were performed using transverse bias initial inverse susceptibility and torque measurements (TBIIST). Co2MnSi reveals to have an in-plane fourfold magnetocrystalline anisotropy with easy axis along <0 1 0> directions for evaporation fluxes perpendicular to the substrate surface. On the other hand, grazing-incidence fluxes invariably generate a dominant uniaxial in-plane magnetic anisotropy contribution with easy axis perpendicular to the incidence plane.

  14. 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.

  15. Increased effective barrier heights in Schottky diodes by molecular-beam epitaxy of CoSi2 and Ga-doped Si on Si(111)

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Lin, T. L.; Grunthaner, P. J.; Andersson, P. O.; Iannelli, J. M.

    1988-01-01

    Increasing the effective Schottky-barrier height of epitaxial CoSi2/Si(111) diodes by the use of thin, highly doped Si layers in close proximity to the metal-semiconductor interface has been studied. Intrinsic Si, Si doped by coevaporation of Ga, and epitaxial CoSi2 layers have all been grown in the same molecular-beam epitaxy system. Current-voltage and photoresponse characterization yield barrier heights ranging from 0.61 eV for a sample with no p(+) layer to 0.89 eV for a sample with a 20-nm-thick p(+) layer. These results are compared to theoretical values based on a one-dimensional solution of Poisson's equation under the depletion approximation.

  16. 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.

  17. Study of Nitrogen Incorporation in Indium Antimonide on Gallium Arsenide by Molecular Beam Epitaxy for Long Wavelength Infrared Devices

    NASA Astrophysics Data System (ADS)

    Patra, Nimai Chand

    The distinguishing features of dilute nitride III-V semiconductors lie in the large simultaneous reduction in the band gap and lattice parameter when N is incorporated in small amounts in an otherwise wide band gap III-V material. In particular, N incorporation in InSb is attracting great attention due to its potential applications in the long wavelength infrared (LWIR) applications. However, the relatively small atomic size of N with respect to Sb makes the growth of good quality InSbN layers challenging with effective N incorporation. In this dissertation we present a correlation of the molecular beam epitaxial growth parameters on the type of N-bonding in the InSbN epilayers. Lower growth temperatures of ~290 °C were observed to favor formation of more substitutional N (In-N) and less interstitial N (Sb-N, N-N and In-N-Sb) in the InSbN epilayers. The types of N-bonding were observed to have dominant effect on the structural, vibrational, electrical and optical properties of these dilute nitride epilayers grown on GaAs substrates. As-grown epilayers with high N incorporation of 2.6 % were observed to exhibit a blue shift in the absorption edge to 0.132 eV due to Moss-Burstein effect. Both ex-situ and in-situ annealing at 430 °C improved the quality of the layers as attested to by the micro-Raman spectra, reduced the carrier concentration to ~10 16 cm-3, increased the mobility (micro) to ~13,000 cm2/V-s and red shift the absorption edge to ~10 microm at room temperature (RT). Amongst the heterostructures examined, consisting of different combination of thickness of InSb and InSbN layers, the growth of a relatively thick (~1.4 microm) InSb buffer layer was found to prevent the propagation of rotational and threading dislocations into the subsequent InSbN epilayers. Thus, high RT micro exceeding 40,000 cm2/Vs and an optical absorption edge at ~12 microm in the LWIR range have been achieved for 450 °C ex-situ annealed 0.4 microm InSbN/ 1.4 microm InSb/ Ga

  18. 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

  19. High-quality GaNAs/GaAs quantum wells with light emission up to 1.44 {mu}m grown by molecular-beam epitaxy

    SciTech Connect

    Wang, S.M.; Gu, Q.F.; Wei, Y.Q.; Sadeghi, M.; Larsson, A.; Zhao, Q.X.; Wang, X.D.; Ma, C.H.; Xing, Z.G.

    2005-10-03

    High-quality GaNAs/GaAs quantum wells with high substitutional N concentrations, grown by molecular-beam epitaxy, are demonstrated using a reduced growth rate in a range of 0.125-1 {mu}m/h. No phase separation is observed and the GaNAs well thickness is limited by the critical thickness. Strong room-temperature photoluminescence with a record long wavelength of 1.44 {mu}m is obtained from an 18-nm-thick GaN{sub 0.06}As{sub 0.94}/GaAs quantum well.

  20. Molecular beam epitaxy of SrTiO{sub 3} on Si (001): Early stages of the growth and strain relaxation

    SciTech Connect

    Niu, G.; Saint-Girons, G.; Vilquin, B.; Delhaye, G.; Botella, C.; Robach, Y.; Hollinger, G.

    2009-08-10

    The molecular beam epitaxy of SrTiO{sub 3} (STO) layers on Si (001) is studied, focusing on the early stages of the growth and on the strain relaxation process. Evidence is given that even for optimized growth conditions, STO grows initially amorphous on silicon and recrystallizes, leading to the formation of an atomically abrupt heterointerface with silicon. Just after recrystallization, STO is partially strained. Further increase in its thickness leads to the onset of a progressive plastic relaxation mechanism. STO recovers its bulk lattice parameter for thicknesses of the order of 30 ML.

  1. Surfactant effect of gallium during the growth of GaN on AlN(0001xAF) by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Gogneau, N.; Sarigiannidou, E.; Monroy, E.; Monnoye, S.; Mank, H.; Daudin, B.

    2004-08-01

    The growth mode of N-face GaN deposited on AlN(0001¯) by plasma-assisted molecular beam epitaxy has been investigated. Based on reflection high-energy electron diffraction experiments, we demonstrate that for appropriate Ga fluxes and substrate temperature, a self-regulated 1-ML-thick Ga excess film can be formed on the growing surface. Depending on the presence of this Ga monolayer, the growth can proceed following either the Stranski-Krastanow or the Frank Van der Merwe growth modes, hence enabling the synthesis of either quantum dots or quantum wells.

  2. 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%.

  3. 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.

  4. Strain-induced In incorporation coefficient variation in the growth of Al1 - xInxAs alloys by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Turco, F.; Massies, J.

    1987-12-01

    The reported experimental results demonstrate the influence of the substrate-induced strain on the In incorporation coefficient in the growth of AlInAs by molecular beam epitaxy. AlInAs has either been grown lattice matched to InP or with a 2.3% lattice mismatch with GaAs. The In incorporation coefficient has been determined through reflection high-energy electron diffraction intensity oscillations. The strain effect on the In incorporation coefficient is supported by a thermodynamic analysis applied to the more simple but similar case of strained InAs growth.

  5. Photoluminescence of GeSi/Si nanoclusters formed by sublimation molecular-beam epitaxy in GeH{sub 4} medium

    SciTech Connect

    Filatov, D. O. Kruglova, M. V.; Isakov, M. A.; Siprova, S. V.; Marychev, M. O.; Shengurov, V. G.; Chalkov, V. Yu.; Denisov, S. A.

    2008-09-15

    The morphology and photoluminescence spectra of GeSi/Si(001) heterostructures with nanoclusters formed by sublimation molecular-beam epitaxy in GeH{sub 4} medium are investigated as functions of growth conditions. It is established that the clusters nucleate by the Stranski-Krastanow mechanism; however, the coalescence processes substantially affect their morphology during further growth. Doubling of photoluminescence lines in nanoclusters associated with the radiative recombination inside the clusters and the blue shift of lines with increasing growth time associated with the Si diffusion from substrate into the clusters are observed. The conditions of forming uniform nanocluster arrays emitting at room temperature are determined.

  6. 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.

  7. 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.

  8. Fabrication and characterization of molecular beam epitaxy grown thin-film GaAs waveguides for mid-infrared evanescent field chemical sensing.

    PubMed

    Charlton, Christy; Giovannini, Marcella; Faist, Jérôme; Mizaikoff, Boris

    2006-06-15

    Thin-film GaAs waveguides were designed and fabricated by molecular beam epitaxy for use in mid-infrared (MIR) evanescent field liquid sensing. Waveguides were designed to facilitate the propagation of a single mode at a wavelength of 10.3 microm emitted from a distributed feedback quantum cascade laser, which overlaps with molecular selective absorption features of acetic anhydride. The characterization of the waveguides shows transmission across a broad MIR band. Evanescent field absorption measurements indicate a significant sensitivity enhancement in contrast to multimode planar silver halide waveguides.

  9. Development of gallium nitride-based ultraviolet and visible light-emitting diodes using hydride vapor-phase epitaxy and molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Cabalu, Jasper Sicat

    Much of the work done on ultraviolet (UV) and visible III-Nitrides-based light emitting diodes (LEDs) involves growth by metal-organic chemical vapor deposition (MOCVD). In this dissertation, the growth, development, and fabrication of III-Nitrides-based UV and visible LEDs with very high photon conversion and extraction efficiencies using hydride vapor-phase epitaxy (HVPE) and radio frequency (rf) plasma-assisted molecular beam epitaxy (PAMBE) is presented. High-power electrically-pumped UV-LEDs based on GaN/AlGaN multiple quantum wells (MQWs) emitting at 340 nm and 350 nm have been fabricated in a flip-chip configuration and evaluated. Under pulsed operation, UV-LEDs emitting at 340 nm have output powers that saturate, due to device heating, at approximately 3 mW. Devices emitting at 350 nm show DC operation output powers as high as 4.5 mW under 200 mA drive current. These results were found to be equivalent with those of UV-LEDs produced by the MOCVD and HVPE methods. The concept of using textured MQWs on UV-LED structures was tested by optical pumping of GaN/AlGaN MQWs grown on textured GaN templates. Results show highly enhanced (>700 times) blue-shifted photoluminescence (PL) at 360 nm compared to similarly produced MQWs on smooth GaN templates whose PL emission is red-shifted. These results are attributed partly to enhancement in light extraction efficiency (LEE) and partly to enhancement in internal quantum efficiency (IQE). The origin of the increase in IQE is partly due to reduction of the quantum-confined Stark effect (QCSE) on QW-planes not perpendicular to the polarization direction and partly due to charge redistribution in the QWs caused by the polarization component parallel to the planes of the QWs. Similar studies have been done for visible LEDs using InGaN/GaN MQWs. Growth of LED structures on textured GaN templates employing textured MQW-active regions resulted in the production of dichromatic (430 nm and 530 nm) phosphorless white LEDs with

  10. Patterned growth of InGaN/GaN quantum wells on freestanding GaN grating by molecular beam epitaxy

    PubMed Central

    2011-01-01

    We report here the epitaxial growth of InGaN/GaN quantum wells on freestanding GaN gratings by molecular beam epitaxy (MBE). Various GaN gratings are defined by electron beam lithography and realized on GaN-on-silicon substrate by fast atom beam etching. Silicon substrate beneath GaN grating region is removed from the backside to form freestanding GaN gratings, and the patterned growth is subsequently performed on the prepared GaN template by MBE. The selective growth takes place with the assistance of nanoscale GaN gratings and depends on the grating period P and the grating width W. Importantly, coalescences between two side facets are realized to generate epitaxial gratings with triangular section. Thin epitaxial gratings produce the promising photoluminescence performance. This work provides a feasible way for further GaN-based integrated optics devices by a combination of GaN micromachining and epitaxial growth on a GaN-on-silicon substrate. PACS 81.05.Ea; 81.65.Cf; 81.15.Hi. PMID:21711618

  11. Molecular beam epitaxial growth and electronic transport properties of high quality topological insulator Bi2Se3 thin films on hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Park, Joon Young; Lee, Gil-Ho; Jo, Janghyun; Cheng, Austin K.; Yoon, Hosang; Watanabe, Kenji; Taniguchi, Takashi; Kim, Miyoung; Kim, Philip; Yi, Gyu-Chul

    2016-09-01

    We report the molecular beam epitaxial growth and characterization of high quality topological insulator Bi2Se3 thin films on hexagonal boron nitride (h-BN). A two-step growth was developed, enhancing both the surface coverage and crystallinity of the films on h-BN. High-resolution transmission electron microscopy study showed an atomically abrupt and epitaxial interface formation between the h-BN substrate and Bi2Se3. We performed gate tuned magnetotransport characterizations of the device fabricated on the thin film and confirmed a high mobility surface state at the Bi2Se3/h-BN interface. The Berry phase obtained from Shubnikov-de Haas oscillations suggested this interfacial electronic state is a topologically protected Dirac state.

  12. 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.

  13. 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.

  14. Molecular beam epitaxy of high structural quality Bi{sub 2}Se{sub 3} on lattice matched InP(111) substrates

    SciTech Connect

    Schreyeck, S.; Tarakina, N. V.; Schumacher, C.; Borzenko, T.; Bruene, C.; Buhmann, H.; Gould, C.; Brunner, K.; Molenkamp, L. W.; Karczewski, G.

    2013-01-28

    Epitaxial layers of the topological insulator Bi{sub 2}Se{sub 3} have been grown by molecular beam epitaxy on laterally lattice-matched InP(111)B substrates. High resolution X-ray diffraction shows a significant improvement of Bi{sub 2}Se{sub 3} crystal quality compared to layers deposited on other substrates. The measured full width at half maximum of the rocking curve is {Delta}{omega}=13 arc sec, and the ({omega}-2{theta}) scans exhibit clear layer thickness fringes. Atomic force microscope images show triangular twin domains with sizes increasing with layer thickness. The structural quality of the domains is confirmed on the microscopic level by transmission electron microscopy.

  15. 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.

  16. 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.

  17. Surface composition of BaTiO{sub 3}/SrTiO{sub 3}(001) films grown by atomic oxygen plasma assisted molecular beam epitaxy

    SciTech Connect

    Barbier, A.; Stanescu, D.; Jegou, P.; Magnan, H.; Mocuta, C.; Jedrecy, N.

    2012-12-01

    We have investigated the growth of BaTiO{sub 3} thin films deposited on pure and 1% Nb-doped SrTiO{sub 3}(001) single crystals using atomic oxygen assisted molecular beam epitaxy and dedicated Ba and Ti Knudsen cells. Thicknesses up to 30 nm were investigated for various layer compositions. We demonstrate 2D growth and epitaxial single crystalline BaTiO{sub 3} layers up to 10 nm before additional 3D features appear; lattice parameter relaxation occurs during the first few nanometers and is completed at {approx}10 nm. The presence of a Ba oxide rich top layer that probably favors 2D growth is evidenced for well crystallized layers. We show that the Ba oxide rich top layer can be removed by chemical etching. The present work stresses the importance of stoichiometry and surface composition of BaTiO{sub 3} layers, especially in view of their integration in devices.

  18. The structure and properties of phthalocyanine films grown by the molecular beam epitaxy technique. III. Preparation and characterization of lutetium diphthalocyanine films

    NASA Astrophysics Data System (ADS)

    Hoshi, Hajime; Dann, Anthony J.; Maruyama, Yusei

    1990-06-01

    Two types of epitaxial films of lutetium diphthalocyanine, LuPc2, have been obtained on KBr, LuPc2 /KBr, and on the film of fluoro-bridged aluminum phthalocyanine polymer, (AlPcF)n, on KBr, LuPc2 /(AlPcF)n /KBr, by the molecular beam epitaxy technique. Their structures have been studied by transmission electron microscopy as well as scanning electron microscopy. The phase of LuPc2 /KBr is bidirectionally oriented tetragonal, KBr(100)((10)1/2×(10)1/2) R±27°-LuPc2. The phase of LuPc2 /(AlPcF)n /KBr is predominantly unidirectionally oriented tetragonal, KBr(100)(3×3)R45°-LuPc2 /(AlPcF)n, but some bidirectional orthorhombic phase, KBr(100)C(6×3)R45°-LuPc2 /(AlPcF)n, is also present.

  19. 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.

  20. 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.

  1. Mössbauer comparison of Fe(100)/Ni and Fe(110)/Ni heterostructures grown by molecular beam epitaxy (abstract)

    NASA Astrophysics Data System (ADS)

    Gutierrez, C. J.; Wieczorek, M. D.; Qiu, Z. Q.; Tang, H.; Walker, J. C.

    1990-05-01

    Epitaxial Fe(100)/Ni and Fe(110)/Ni heterostructures were grown using a Perkin-Elmer PHI 430B molecular-beam-epitaxy system equipped with (RHEED) and quadrupole mass analysis. The growth system typically achieved a base pressure of less than 5×10-10 Torr, and a growth pressure of less than 3×10-9 Torr. Typical growth rates were 3 Å/min for Fe and 2 Å/min for Ni. For all the heterostructures, the Ni thickness was held at 14 Å, the number of repetitions varied between 8 and 15 cycles, and growth always began with the Fe bilayer. Protective Ag covers were grown on all films. Three Fe (100)/Ni heterostructures were grown on 5-kÅ single-crystal Ag(100) bases grown on NaCl(001).1 The single-crystal Fe(100) bilayer thicknesses were 3, 8, or 12 monolayers (ML). The substrate growth temperature for this series was ramped from 40 to 80 °C due to radiant heating from the effusion cells. Four Fe(110)/Ni heterostructures were grown with Fe bilayer thicknesses of 2, 4, 8, and 12 ML. These heterostructures were grown on 5-kÅ Ag(111) single-crystal bases grown on single-crystal natural muscovite mica. An intervening epilayer of NaCl (150 Å) deposited between the mica and Ag base facilitated film removal from the Fe-contaminated mica for ex situ transmission 57Fe Mössbauer analysis. The substrate growth temperature for this series was held at 180 °C, since this appears to be optimal for Fe(110) growth on Ag(111).2 Note that the resultant Fe(110) growth is mosaic with Fe[001] parallel to Ag<110> (threefold symmetry). The RHEED observation of the growth of Ni on Fe(100) always resulted in the Ni RHEED pattern closely following that of the Fe (100) pattern, with broader Ni RHEED lines apparent. The characteristic behavior of our Ni RHEED patterns mimicked that observed by Heinrich et al. for bcc Ni(100),3 and did not match that of fcc Ni. The Ni-on-Fe(110) growth was analogous in RHEED characteristics to that of the (100) case. The Ni RHEED patterns again closely matched

  2. Azimuthal reflection high-energy electron diffraction study of MnAs growth on GaAs(001) by molecular beam epitaxy

    SciTech Connect

    Satapathy, Dillip K.; Jenichen, Bernd; Ploog, Klaus H.; Braun, Wolfgang

    2011-07-15

    Azimuthal reflection high-energy electron diffraction (ARHEED) and in situ grazing incidence synchrotron x-ray diffraction techniques are employed to investigate the growth, epitaxial orientation, and interfacial structure of MnAs layers grown on GaAs(001) by molecular beam epitaxy (MBE). We demonstrate the power and reliability of ARHEED scans as a routine tool in characterizing the formation of epitaxial films. The ARHEED scans clearly reveal the formation of the rectangular MnAs unit cell during growth on GaAs(001) for a MnAs layer thickness of 2.1 {+-} 0.2 monolayers with a tensile strain along the MnAs[1120] direction. A periodic coincidence site lattice, which is known to form along the MnAs [0001] direction to release the strain due to the huge lattice mismatch ({approx}30%) also produces periodic satellites of the diffraction spots in the ARHEED scan. The formation of different epitaxial orientations of MnAs during MBE growth can be directly observed using ARHEED scans. ARHEED is demonstrated to have a resolution similar to synchrotron x-ray diffraction with a double crystal monochromator, yielding full width at half maximum values of reflections as small as 0.005 reciprocal lattice units.

  3. Phase transformation of molecular beam epitaxy-grown nanometer-thick Gd₂O₃ and Y₂O₃ on GaN.

    PubMed

    Chang, Wen-Hsin; Wu, Shao-Yun; Lee, Chih-Hsun; Lai, Te-Yang; Lee, Yi-Jun; Chang, Pen; Hsu, Chia-Hung; Huang, Tsung-Shiew; Kwo, J Raynien; Hong, Minghwei

    2013-02-01

    High quality nanometer-thick Gd₂O₃ and Y₂O₃ (rare-earth oxide, R₂O₃) films have been epitaxially grown on GaN (0001) substrate by molecular beam epitaxy (MBE). The R₂O₃ epi-layers exhibit remarkable thermal stability at 1100 °C, uniformity, and highly structural perfection. Structural investigation was carried out by in situ reflection high energy electron diffraction (RHEED) and ex-situ X-ray diffraction (XRD) with synchrotron radiation. In the initial stage of epitaxial growth, the R₂O₃ layers have a hexagonal phase with the epitaxial relationship of R₂O₃ (0001)(H)<1120>(H)//GaN(0001)(H)<1120>(H). With the increase in R₂O₃ film thickness, the structure of the R₂O₃ films changes from single domain hexagonal phase to monoclinic phase with six different rotational domains, following the R₂O₃ (201)(M)[020](M)//GaN(0001)(H)<1120>(H) orientational relationship. The structural details and fingerprints of hexagonal and monoclinic phase Gd₂O₃ films have also been examined by using electron energy loss spectroscopy (EELS). Approximate 3-4 nm is the critical thickness for the structural phase transition depending on the composing rare earth element.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. Characterization of structural defects in SnSe2 thin films grown by molecular beam epitaxy on GaAs (111)B substrates

    NASA Astrophysics Data System (ADS)

    Tracy, Brian D.; Li, Xiang; Liu, Xinyu; Furdyna, Jacek; Dobrowolska, Margaret; Smith, David J.

    2016-11-01

    Tin selenide thin films have been grown by molecular beam epitaxy on GaAs (111)B substrates at a growth temperature of 150 °C, and a microstructural study has been carried out, primarily using the technique of transmission electron microscopy. The Se:Sn flux ratio during growth was systematically varied and found to have a strong impact on the resultant crystal structure and quality. Low flux ratios (Se:Sn=3:1) led to defective films consisting primarily of SnSe, whereas high flux ratios (Se:Sn>10:1) gave higher quality, single-phase SnSe2. The structure of the monoselenide films was found to be consistent with the Space Group Pnma with the epitaxial growth relationship of [011]SnSe// [ 1 1 bar 0 ] GaAs, while the diselenide films were consistent with the Space Group P 3 bar m1 , and had the epitaxial growth relationship [ 2 1 bar 1 bar 0 ]SnSe2// [ 1 1 bar 0 ] GaAs.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. Morphology and electronic properties of metal organic molecular beam epitaxy grown ZnO on hydrogen passivated 6H-SiC(0001)a)

    NASA Astrophysics Data System (ADS)

    Andres, Stefan; Pettenkofer, Christian; Speck, Florian; Seyller, Thomas

    2008-05-01

    Thin ZnO films were grown on hydrogen passivated 6H-SiC(0001) substrates by metal organic molecular beam epitaxy. The initial growth as well as the electronic properties of the growing interface were monitored by low electron diffraction and photoelectron spectroscopy (PES). From the PES intensities of the substrate and ZnO film a layered Frank-van-der-Merwe-like growth mode could be observed within the first 10nm. The ZnO films grow preferentially in (0001) direction and show a pronounced facetting in the {101¯2} direction. The experimentally determined band alignment reveals band offsets of ΔEVBM≈1.6eV and ΔECBM≈1.2eV between the valence and conduction bands, respectively. With growing ZnO thickness a band bending of about -0.51eV is observed in the SiC substrate.

  19. X-Ray Photoelectron Spectroscopy Study of GaAs (001) and InP (001) Cleaning Procedures Prior to Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Contour, J. P.; Massies, J.; Saletes, A.

    1985-07-01

    The effect of chemical etching by H2S04/H202/H20 (5/1/1) mixtures and of mechanopolishing by bromine-methanol diluted solution on GaAs (001) and InP (001) substrates for molecular beam epitaxy (MBE) has been studied using X-ray photoelectron spectroscopy (XPS). The final rinse in running deionized water does not produce any passivating oxide layer on the substrate surface. Oxidation observed on GaAs and InP after these cleaning procedures occurs during substrate handling in air. The H2S04/H202/H20 mixture produces arsenic rich surface layers having an atomic ratio As/Ga of 1.15, whereas the bromine-methanol mechanopolishing leads to an arsenic or phosphorus depleted surface with atomic ratios As/Ga=0.7 and P/In=0.65.

  20. High density of (pseudo) periodic twin-grain boundaries in molecular beam epitaxy-grown van der Waals heterostructure: MoTe2/MoS2

    NASA Astrophysics Data System (ADS)

    Diaz, Horacio Coy; Ma, Yujing; Chaghi, Redhouane; Batzill, Matthias

    2016-05-01

    Growth of transition metal dichalcogenide heterostructures by molecular beam epitaxy (MBE) promises synthesis of artificial van der Waals materials with controllable layer compositions and separations. Here, we show that MBE growth of 2H-MoTe2 monolayers on MoS2 substrates results in a high density of mirror-twins within the films. The grain boundaries are tellurium deficient, suggesting that Te-deficiency during growth causes their formation. Scanning tunneling microscopy and spectroscopy reveal that the grain boundaries arrange in a pseudo periodic "wagon wheel" pattern with only ˜2.6 nm repetition length. Defect states from these domain boundaries fill the band gap and thus give the monolayer an almost metallic property. The band gap states pin the Fermi-level in MoTe2 and thus determine the band-alignment in the MoTe2/MoS2 interface.

  1. High-peak-power low-threshold AlGaAs/GaAs stripe laser diodes on Si substrates grown by migration-enhanced molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Kim, Jae-Hoon; Nouhi, Akbar; Radhakrishnan, Gouri; Liu, John K.; Lang, Robert J.

    1988-01-01

    A high-peak-power low-threshold AlGaAs/GaAs double-heterostructure stripe laser diode on Si substrats, grown by hybrid migration-enhanced molecular beam epitaxy (MEMBE) and metalorganic chemical vapor deposition (MOCVD) has been demonstrated for the first time. These devices showed the highest peak powers of up to 184 mW per facet reported so far for double-heterostructure stripe laser diodes on Si substrates, room-temperature pulsed threshold currents as low as 150 mA, and differential quantum efficiencies as high as 30 percent without mirror facet coating. An intrinsic threshold current density has been estimated to be about 2 kA/sq cm when taking current spreading and lateral diffusion effects into account. Low dislocation density shows that MEMBE can be a useful method to grow high-quality GaAs and AlGaAs/GaAs layers on Si substrates by combining with MOCVD.

  2. Photoluminescence and photocurrent from InP nanowires with InAsP quantum dots grown on Si by molecular beam epitaxy.

    PubMed

    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.

  3. 1.1-μm InAs/GaAs quantum-dot light-emitting transistors grown by molecular beam epitaxy.

    PubMed

    Wu, Cheng-Han; Chen, Hsuan-An; Lin, Shih-Yen; Wu, Chao-Hsin

    2015-08-15

    In this Letter, we report the enhanced radiative recombination output from an AlGaAs/GaAs heterojunction bipolar transistor with InAs quantum dots embedded in the base region to form a quantum-dot light-emitting transistor (QDLET) grown by molecular beam epitaxy systems. For the device with a 100  μm×100  μm emitter area, we demonstrate the dual output characteristics with an electrical output and an optical output when the device is operating in the common-emitter configuration. The quantum-dot light-emitting transistor exhibits a base recombination radiation in the near-infrared spectral range with a dominant peak at λ of 1100 nm.

  4. Magnetically Hard Fe3Se4 Embedded in Bi2Se3 Topological Insulator Thin Films Grown by Molecular Beam Epitaxy.

    PubMed

    Vasconcelos, Hugo Menezes do Nascimento; Eddrief, Mahmoud; Zheng, Yunlin; Demaille, Dominique; Hidki, Sarah; Fonda, Emiliano; Novikova, Anastasiia; Fujii, Jun; Torelli, Piero; Salles, Benjamin Rache; Vobornik, Ivana; Panaccione, Giancarlo; de Oliveira, Adilson Jesus Aparecido; Marangolo, Massimiliano; Vidal, Franck

    2016-01-26

    We investigated the structural, magnetic, and electronic properties of Bi2Se3 epilayers containing Fe grown on GaAs(111) by molecular beam epitaxy. It is shown that, in the window of growth parameters leading to Bi2Se3 epilayers with optimized quality, Fe atom clustering leads to the formation of FexSey inclusions. These objects have platelet shape and are embedded within Bi2Se3. Monoclinic Fe3Se4 is identified as the main secondary phase through detailed structural measurements. Due to the presence of the hard ferrimagnetic Fe3Se4 inclusions, the system exhibits a very large coercive field at low temperature and room temperature magnetic ordering. Despite this composite structure and the proximity of a magnetic phase, the surface electronic structure of Bi2Se3 is preserved, as shown by the persistence of a gapless Dirac cone at Γ.

  5. Molecular beam epitaxial growth and transmission electron microscopy studies of thin GaAs/InAs(100) multiple quantum well structures

    NASA Technical Reports Server (NTRS)

    Grunthaner, F. J.; Fernandez, R.; Lewis, B. F.; Yen, M. Y.; Lee, T. C.; Madhukar, A.

    1985-01-01

    GaAs/InAs(100) multiple interface structures involving 7.4 percent lattice mismatch have been fabricated via molecular beam epitaxy and examined via transmission electron microscopy. It is found that high-quality, dislocation-free interfaces involving such high lattice mismatch can indeed be experimentally realized for very thin layers provided proper care is given to achieve a balance between the growth kinetics and the thermodynamics leading to the equilibrium ground state of the strained layer. The compressive strain is homogeneously accommodated and a tetragonal distortion is induced in the InAs layer with a perpendicular lattice constant in close agreement with that expected on the basis of the continuum theory and elastic constants of bulk InAs.

  6. X-ray photoelectron spectroscopic study of the oxide removal mechanism of GaAs /100/ molecular beam epitaxial substrates in in situ heating

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Lewis, B. F.; Grunthaner, F. J.

    1983-01-01

    A standard cleaning procedure for GaAs (100) molecular beam epitaxial (MBE) substrates is a chemical treatment with a solution of H2SO4/H2O2/H2O, followed by in situ heating prior to MBE growth. X-ray photoelectron spectroscopic (XPS) studies of the surface following the chemical treatment show that the oxidized As is primarily As(+ 5). Upon heating to low temperatures (less than (350 C) the As(+ 5) oxidizes the substrate to form Ga2O3 and elemental As, and the As(+ 5) is reduced to As(+ 3) in the process. At higher temperatures (500 C), the As(+ 3) and elemental As desorb, while the Ga(+ 3) begins desorbing at about 600 C.

  7. 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.

  8. Defect-free zinc-blende structured InAs nanowires realized by in situ two V/III ratio growth in molecular beam epitaxy.

    PubMed

    Zhang, Zhi; Lu, Zhen-Yu; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2015-08-01

    In this study, we devised a two-V/III-ratio procedure to control the Au-assisted growth of defect-free InAs nanowires in molecular beam epitaxy. The demonstrated two V/III ratio procedure consists of a first high V/III ratio growth step to prepare the nanowire foundation on the substrate surface, followed by a low V/III ratio step to induce the nanowire growth. By manipulating the V/III ratios in different steps, we have achieved the controlled growth of pure defect-free zinc-blende structured InAs nanowires on the GaAs {1̄1̄1̄} substrates. This study provides an approach to control not only the crystal structure of semiconductor nanowires, but also their structural qualities.

  9. Absence of vapor-liquid-solid growth during molecular beam epitaxy of self-induced InAs nanowires on Si

    NASA Astrophysics Data System (ADS)

    Hertenberger, S.; Rudolph, D.; Bolte, S.; Döblinger, M.; Bichler, M.; Spirkoska, D.; Finley, J. J.; Abstreiter, G.; Koblmüller, G.

    2011-03-01

    The growth mechanism of self-induced InAs nanowires (NWs) grown on Si (111) by molecular beam epitaxy was investigated by in situ reflection high energy electron diffraction and ex situ scanning and transmission electron microscopy. Abrupt morphology transition and in-plane strain relaxation revealed that InAs NWs nucleate without any significant delay and under the absence of indium (In) droplets. These findings are independent of the As/In-flux ratio, revealing entirely linear vertical growth rate and nontapered NWs. No evidence of In droplets nor associated change in the NW apex morphology was observed for various growth termination procedures. These results highlight the absence of vapor-liquid-solid growth, providing substantial benefits for realization of atomically abrupt doping and composition profiles in future axial InAs-based NW heterostructures on Si.

  10. Absence of vapor-liquid-solid growth during molecular beam epitaxy of self-induced InAs nanowires on Si

    SciTech Connect

    Hertenberger, S.; Rudolph, D.; Bichler, M.; Spirkoska, D.; Finley, J. J.; Koblmueller, G.; Bolte, S.; Doeblinger, M.; Abstreiter, G.

    2011-03-21

    The growth mechanism of self-induced InAs nanowires (NWs) grown on Si (111) by molecular beam epitaxy was investigated by in situ reflection high energy electron diffraction and ex situ scanning and transmission electron microscopy. Abrupt morphology transition and in-plane strain relaxation revealed that InAs NWs nucleate without any significant delay and under the absence of indium (In) droplets. These findings are independent of the As/In-flux ratio, revealing entirely linear vertical growth rate and nontapered NWs. No evidence of In droplets nor associated change in the NW apex morphology was observed for various growth termination procedures. These results highlight the absence of vapor-liquid-solid growth, providing substantial benefits for realization of atomically abrupt doping and composition profiles in future axial InAs-based NW heterostructures on Si.

  11. The thickness-dependent dynamic magnetic property of Co{sub 2}FeAl films grown by molecular beam epitaxy

    SciTech Connect

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

    2014-10-27

    Co{sub 2}FeAl 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 Co{sub 2}FeAl 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 Co{sub 2}FeAl. 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.

  12. Molecular beam epitaxy of InAs nanowires in SiO2 nanotube templates: challenges and prospects for integration of III–Vs on Si

    NASA Astrophysics Data System (ADS)

    Vukajlovic-Plestina, Jelena; Dubrovskii, Vladimir G.; Tütüncuoǧlu, Gözde; Potts, Heidi; Ricca, Ruben; Meyer, Frank; Matteini, Federico; Leran, Jean-Baptiste; Morral, Anna Fontcuberta i.

    2016-11-01

    Guided growth of semiconductor nanowires in nanotube templates has been considered as a potential platform for reproducible integration of III–Vs on silicon or other mismatched substrates. Herein, we report on the challenges and prospects of molecular beam epitaxy of InAs nanowires in SiO2/Si nanotube templates. We show how and under which conditions the nanowire growth is initiated by In-assisted vapor–liquid–solid growth enabled by the local conditions inside the nanotube template. The conditions for high yield of vertical nanowires are investigated in terms of the nanotube depth, diameter and V/III flux ratios. We present a model that further substantiates our findings. This work opens new perspectives for monolithic integration of III–Vs on the silicon platform enabling new applications in the electronics, optoelectronics and energy harvesting arena.

  13. Carbon reduction and antimony incorporation in InGaAsSb films grown by metalorganic molecular beam epitaxy using tris-dimethylaminoantimony

    NASA Astrophysics Data System (ADS)

    Mitsuhara, Manabu; Sato, Tomonari; Yamamoto, Norio; Fukano, Hideki; Kondo, Yasuhiro

    2009-07-01

    InGaAsSb layers nearly lattice-matched to InP were grown by metalorganic molecular beam epitaxy using tris-dimethylaminoantimony (TDMASb). Secondary-ion mass spectroscopy measurements revealed that TDMASb is useful not only as an Sb source but also as an additive that reduces the incorporation of C into the film from group-III metalorganic sources. In the room-temperature photoluminescence spectrum, the incorporation of Sb into InGaAs shifted the peak wavelength from 1.66 to 1.75 μm and, simultaneously, the peak intensity of InGaAsSb became more than twice that of InGaAs.

  14. Determination of CdTe bulk carrier lifetime and interface recombination velocity of CdTe/MgCdTe double heterostructures grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zhao, Xin-Hao; DiNezza, Michael J.; Liu, Shi; Campbell, Calli M.; Zhao, Yuan; Zhang, Yong-Hang

    2014-12-01

    The bulk Shockley-Read-Hall carrier lifetime of CdTe and interface recombination velocity at the CdTe/Mg0.24Cd0.76Te heterointerface are estimated to be around 0.5 μs and (4.7 ± 0.4) × 102 cm/s, respectively, using time-resolved photoluminescence (PL) measurements. Four CdTe/MgCdTe double heterostructures (DHs) with varying CdTe layer thicknesses were grown on nearly lattice-matched InSb (001) substrates using molecular beam epitaxy. The longest lifetime of 179 ns is observed in the DH with a 2 μm thick CdTe layer. It is also shown that the photon recycling effect has a strong influence on the bulk radiative lifetime, and the reabsorption process affects the measured PL spectrum shape and intensity.

  15. Structure and morphology characters of GaN grown by ECR-MBE using hydrogen-nitrogen mixed gas plasma[Electron Cyclotron Resonance-Molecular Beam Epitaxy

    SciTech Connect

    Araki, Tsutomu; Chiba, Yasuo; Nanishi, Yasushi

    2000-07-01

    GaN growth by electron-cyclotron-resonance plasma-excited molecular beam epitaxy using hydrogen-nitrogen mixed gas plasma were carried out on GaN templates with a different polar-surface. Structure and surface morphology of the GaN layers were characterized using transmission electron microscopy. The GaN layer grown with hydrogen on N-polar template showed a relatively flat morphology including hillocks. Columnar domain existed in the center of the hillock, which might be attributed to the existence of tiny inversion domain with Ga-polarity. On the other hand, columnar structure was formed in the GaN layer grown with hydrogen on Ga-polar template.

  16. 1.55 {mu}m GaAs/GaNAsSb/GaAs optical waveguides grown by radio frequency nitrogen plasma-assisted molecular beam epitaxy

    SciTech Connect

    Tan, K. H.; Yoon, S. F.; Loke, W. K.; Wicaksono, S.; Xu, Z.; Ng, T. K.; Lew, K. L.; Saadsaoud, N.; Zegaoui, M.; Decoster, D.; Chazelas, J.

    2008-03-17

    We demonstrate a 1.55 {mu}m GaAs/GaNAsSb/GaAs optical waveguide grown by molecular beam epitaxy as an alternative to the AlGaAs/GaAs system. The 0.4-{mu}m-thick GaNAsSb guiding layer contains {approx}3.5% of N and 9% of Sb, resulting in optical band gap of 0.88 eV. The refractive index of the GaNAsSb layer was measured from 800 to 1700 nm. The GaNAsSb layer has a refractive index value of 3.42 at 1.55 {mu}m wavelength. The propagation loss measured using the Fabry-Perot resonance method was found to be affected by nitrogen-related defect absorption.

  17. Thermal stability and relaxation mechanisms in compressively strained Ge0.94Sn0.06 thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Fleischmann, C.; Lieten, R. R.; Hermann, P.; Hönicke, P.; Beckhoff, B.; Seidel, F.; Richard, O.; Bender, H.; Shimura, Y.; Zaima, S.; Uchida, N.; Temst, K.; Vandervorst, W.; Vantomme, A.

    2016-08-01

    Strained Ge1-xSnx thin films have recently attracted a lot of attention as promising high mobility or light emitting materials for future micro- and optoelectronic devices. While they can be grown nowadays with high crystal quality, the mechanism by which strain energy is relieved upon thermal treatments remains speculative. To this end, we investigated the evolution (and the interplay) of composition, strain, and morphology of strained Ge0.94Sn0.06 films with temperature. We observed a diffusion-driven formation of Sn-enriched islands (and their self-organization) as well as surface depressions (pits), resulting in phase separation and (local) reduction in strain energy, respectively. Remarkably, these compositional and morphological instabilities were found to be the dominating mechanisms to relieve energy, implying that the relaxation via misfit generation and propagation is not intrinsic to compressively strained Ge0.94Sn0.06 films grown by molecular beam epitaxy.

  18. Tellurium n-type doping of highly mismatched amorphous GaN1-xAsx alloys in plasma-assisted molecular beam epitaxy

    DOE PAGESBeta

    Novikov, S. V.; Ting, M.; Yu, K. M.; Sarney, W. L.; Martin, R. W.; Svensson, S. P.; Walukiewicz, W.; Foxon, C. T.

    2014-10-01

    In this paper we report our study on n-type Te doping of amorphous GaN1-xAsx layers grown by plasma-assisted molecular beam epitaxy. We have used a low temperature PbTe source as a source of tellurium. Reproducible and uniform tellurium incorporation in amorphous GaN1-xAsx layers has been successfully achieved with a maximum Te concentration of 9×10²⁰ cm⁻³. Tellurium incorporation resulted in n-doping of GaN1-xAsx layers with Hall carrier concentrations up to 3×10¹⁹ cm⁻³ and mobilities of ~1 cm²/V s. The optimal growth temperature window for efficient Te doping of the amorphous GaN1-xAsx layers has been determined.

  19. 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.

  20. Mechanism for persistent hexagonal island formation in AlN buffer layer during growth on Si (111) by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Hsu, K.-Y.; Chung, H.-C.; Liu, C.-P.; Tu, L.-W.

    2007-05-21

    The characteristics of structure and morphology of AlN grown by a growth interruption method on Si (111) with plasma-assisted molecular beam epitaxy are investigated. It is found that the growth interruption method would improve the surface flatness of the AlN layer without the formation of Al droplets. However, AlN hexagonal islands were present and persistent throughout the entire growth owing to effective strain relaxation and Eherlich-Schowebel barrier effect of preexistent surface islands grown on higher terraces of the Si substrate. The density of threading dislocations underneath the hexagonal islands is much less than elsewhere in the film, which is presumably due to dislocation annihilation during the island growth process.

  1. Growth of single-crystalline Cu2O (111) film on ultrathin MgO modified α-Al2O3 (0001) substrate by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Li, Junqiang; Mei, Zengxia; Ye, Daqian; Liang, Huili; Liu, Yaoping; Du, Xiaolong

    2012-08-01

    We report the synthesis of Cu2O single crystalline films on the c-plane α-Al2O3 substrate by radio-frequency plasma assisted molecular beam epitaxy. An ultrathin MgO layer was adopted to modify the complex surface structure of sapphire (0001) and engineer the interfacial atomic matching between the epilayer and the substrate. The experimental results solidly proved the single crystallinity of cubic Cu2O (111) without twin crystals. A coincident match mode was proposed to explain the unusual in-plane orientation between strained MgO (111) and Cu2O (111). It was found that the crystal quality of Cu2O is very sensitive to the thickness of MgO layer, which is optimized to be ˜2 nm. The reason why MgO has a critical thickness in Cu2O single crystal growth was also tentatively discussed.

  2. The relationship between depth-resolved composition and strain relaxation in InAlN and InGaN films grown by molecular beam epitaxy

    SciTech Connect

    Jiao, Wenyuan; Kong, Wei; Li, Jincheng; Kim, Tong-Ho; Brown, April S.; Collar, Kristen

    2013-10-14

    A study of the relationship between strain and the incorporation of group III elements in ternary InGaN and InAlN grown by molecular beam epitaxy is reported. Using X-ray Photoelectron Spectroscopy compositional depth profiles with x-ray diffraction, we are able to find a clear relationship between strain and In incorporation including tensile-strained InAlN which has, to date, not been studied. The results show that fully strained films contain homogeneous indium composition while partially relaxed films have a non-homogeneous indium composition with depth. These results can be interpreted by considering the impurity formation energies of indium in host lattices.

  3. Direct formation of InAs quantum dots grown on InP (001) by solid-source molecular beam epitaxy

    SciTech Connect

    Fuster, David; Rivera, Antonio; Alen, Benito; Alonso-Gonzalez, Pablo; Gonzalez, Yolanda; Gonzalez, Luisa

    2009-03-30

    We have developed a growth process that leads to the direct formation of self-assembled InAs quantum dots on InP(001) by solid-source molecular beam epitaxy avoiding the previous formation of quantum wires usually obtained by this technique. The process consists of a periodically alternated deposition of In and As correlated with InAs(4x2){r_reversible}(2x4) surface reconstruction changes. Based on the results obtained by in situ characterization techniques, we propose that the quantum dots formation is possible due to the nucleation of In droplets over the InAs(4x2) surface during the In deposition step and their subsequent crystallization under the As step.

  4. Molecular beam epitaxy growth of niobium oxides by solid/liquid state oxygen source and lithium assisted metal-halide chemistry

    NASA Astrophysics Data System (ADS)

    Tellekamp, M. Brooks; Greenlee, Jordan D.; Shank, Joshua C.; Doolittle, W. Alan

    2015-09-01

    In order to consistently grow high quality niobium oxides and lithium niobium oxides, a novel solid/liquid state oxygen source, LiClO4, has been implemented in a molecular beam epitaxy (MBE) system. LiClO4 is shown to decompose into both molecular and atomic oxygen upon heating. This allows oxidation rates similar to that of molecular oxygen but at a reduced overall beam flux, quantified by in situ Auger analysis. LiClO4 operation is decomposition limited to less than 400 °C, and other material limitations are identified. The design of a custom near-ambient NbCl5 effusion cell is presented, which improves both short and long term stability. Films of Nb oxidation state +2, +3, and +5 are grown using these new tools, including the multi-functional sub-oxide LiNbO2.

  5. Growth, steady-state, and time-resolved photoluminescence study of CdTe/MgCdTe double heterostructures on InSb substrates using molecular beam epitaxy

    SciTech Connect

    DiNezza, Michael J.; Liu, Shi; Kirk, Alexander P.; Zhang, Yong-Hang; Zhao, Xin-Hao

    2013-11-04

    CdTe/MgCdTe double heterostructures (DHs) are grown on InSb substrates using molecular beam epitaxy and reveal strong photoluminescence with over double the intensity of a GaAs/AlGaAs DH with an identical layer structure design grown on GaAs. Time-resolved photoluminescence of the CdTe/MgCdTe DH gives a Shockley-Read-Hall recombination lifetime of 86 ns, which is more than one order of magnitude longer than that of typical polycrystalline CdTe films. These findings indicate that monocrystalline CdTe/MgCdTe DHs effectively reduce surface recombination, have limited nonradiative interface recombination, and are promising for solar cells that could reach power conversion efficiencies similar to that of GaAs.

  6. Molecular beam epitaxy of InAlN lattice-matched to GaN with homogeneous composition using ammonia as nitrogen source

    SciTech Connect

    Wong, Man Hoi; Wu Feng; Hurni, Christophe A.; Choi, Soojeong; Speck, James S.; Mishra, Umesh K.

    2012-02-13

    InAlN lattice-matched to GaN was grown by molecular beam epitaxy (MBE) using ammonia as the nitrogen source. The alloy composition, growth conditions, and strain coherence of the InAlN were verified by high resolution x-ray diffraction {omega}-2{theta} scans and reciprocal space maps. Scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy of the InAlN revealed the absence of lateral composition modulation that was observed in the films grown by plasma-assisted MBE. InAlN/AlN/GaN high electron mobility transistors with smooth surfaces were fabricated with electron mobilities exceeding 1600 cm{sup 2}/Vs and sheet resistances below 244 {Omega}/sq.

  7. Domain formation due to surface steps in topological insulator Bi{sub 2}Te{sub 3} thin films grown on Si (111) by molecular beam epitaxy

    SciTech Connect

    Borisova, S.; Kampmeier, J.; Mussler, G.; Grützmacher, D.; Luysberg, M.

    2013-08-19

    The atomic structure of topological insulators Bi{sub 2}Te{sub 3} thin films on Si (111) substrates grown in van der Waals mode by molecular beam epitaxy has been investigated by in situ scanning tunneling microscopy and scanning transmission electron microscopy. Besides single and multiple quintuple layer (QL) steps, which are typical for the step-flow mode of growth, a number of 0.4 QL steps is observed. We determine that these steps originate from single steps at the substrate surface causing domain boundaries in the Bi{sub 2}Te{sub 3} film. Due to the peculiar structure of these domain boundaries the domains are stable and penetrate throughout the entire film.

  8. 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.

  9. Impact of growth and annealing conditions on the parameters of Ge/Si(001) relaxed layers grown by molecular beam epitaxy

    SciTech Connect

    Yurasov, D. V.; Bobrov, A. I.; Daniltsev, V. M.; Novikov, A. V.; Pavlov, D. A.; Skorokhodov, E. V.; Shaleev, M. V.; Yunin, P. A.

    2015-11-15

    Influence of the Ge layer thickness and annealing conditions on the parameters of relaxed Ge/Si(001) layers grown by molecular beam epitaxy via two-stage growth is investigated. The dependences of the threading dislocation density and surface roughness on the Ge layer thickness, annealing temperature and time, and the presence of a hydrogen atmosphere are obtained. As a result of optimization of the growth and annealing conditions, relaxed Ge/Si(001) layers which are thinner than 1 μm with a low threading dislocation density on the order of 10{sup 7} cm{sup –2} and a root mean square roughness of less than 1 nm are obtained.

  10. Self-assembly of compositionally modulated Ga{sub 1−x}Mn{sub x}As multilayers during molecular beam epitaxy

    SciTech Connect

    Gallardo-Hernández, S.; Martinez-Velis, I.; Ramirez-Lopez, M.; Lopez-Lopez, M.; Kudriatsev, Y.; Escobosa-Echavarria, A.; Luiz Morelhao, S.

    2013-11-04

    GaMnAs structures were grown on GaAs(100) substrates by molecular beam epitaxy employing different growth parameters. We studied manganese incorporation employing secondary ion mass spectrometry (SIMS). At a growth temperature of 300 °C, we observed a self-assembled modulation of the manganese concentration. SIMS depth profiles were analyzed employing a depth resolution function taking into account sputtering-induced broadening of the original distribution and segregation. We found a Mn segregation length along the growth direction of ∼4 nm. The presence of GaMnAs multilayers was corroborated by high-resolution x-ray diffraction. Spinodal decomposition is a possible mechanism for the spontaneous formation of the multilayer structure.

  11. Topography and structure of ultrathin topological insulator Sb2Te3 films on Si(111) grown by means of molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lanius, M.; Kampmeier, J.; Kölling, S.; Mussler, G.; Koenraad, P. M.; Grützmacher, D.

    2016-11-01

    We have studied the growth process of the topological insulator (TI) Sb2 Te3 on Si(111) by scanning tunneling microscopy. High quality thin films from more than 22 nm down to 1 nm in thickness have been deposited by molecular beam epitaxy. To determine the thickness and domain formation of the films, x-ray reflectivity and x-ray diffraction were utilized. In comparison to previous studies of the TI Bi2 Te3 , the growth mechanism of Sb2 Te3 shows a similar transition from nucleation and growth in Sb-Te and Te-Te bilayers, respectively, to mound formation for thicker films. Atom probe tomography measurements reveal a intermixed interface between Sb2 Te3 and Si(111) substrate. These findings can explain the high density of defects and domains.

  12. Highly repeatable room temperature negative differential resistance in AlN/GaN resonant tunneling diodes grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Growden, Tyler A.; Storm, David F.; Zhang, Weidong; Brown, Elliott R.; Meyer, David J.; Fakhimi, Parastou; Berger, Paul R.

    2016-08-01

    AlN/GaN resonant tunneling diodes grown on low dislocation density semi-insulating bulk GaN substrates via plasma-assisted molecular-beam epitaxy are reported. The devices were fabricated using a six mask level, fully isolated process. Stable room temperature negative differential resistance (NDR) was observed across the entire sample. The NDR exhibited no hysteresis, background light sensitivity, or degradation of any kind after more than 1000 continuous up-and-down voltage sweeps. The sample exhibited a ˜90% yield of operational devices which routinely displayed an average peak current density of 2.7 kA/cm2 and a peak-to-valley current ratio of ≈1.15 across different sizes.

  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. Optical quality improvement of InGaAs/AlAs/AlAsSb coupled double quantum wells grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kasai, J.; Mozume, T.; Yoshida, H.; Simoyama, T.; Gopal, A. V.; Ishikawa, H.

    2004-02-01

    We have grown InGaAs/AlAs/AlAsSb coupled double quantum wells (C-DQWs) with AlAs diffusion-stopping layers by molecular beam epitaxy. An obtained sample had many cross-hatched lines, suggesting relatively poor structural quality. Optical measurements, however, revealed that the optical quality of the C-DQWs was greatly improved compared to earlier C-DQWs without AlAs diffusion-stopping layers. The intersubband absorption saturation intensity in the present C-DQW sample was extremely low, measuring 34 fJ/m2 at the optical communication wavelength of 1.62 m, while ultrafast response times of about 600 fs were maintained.

  15. 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.

  16. Low resistance wavelength-reproducible [ital p]-type (Al,Ga)As distributed Bragg reflectors grown by molecular beam epitaxy

    SciTech Connect

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

    1993-04-05

    We report the reproducible molecular beam epitaxial growth of Be-doped piecewise linearly graded (Al,Ga)As distributed Bragg reflectors that have vertical series resistivities near bulk values. For mirrors with three linear segments per interface, the center wavelength reproducibility is 0.1% and the series resistivity is as low as 1.8[times]10[sup [minus]5] [Omega] cm[sup 2] for hole concentrations of 5[times]10[sup 18] cm[sup [minus]3]. Measured reflectivities of 6.0% per interface are comparable to conventional single-linear-grade mirrors. Vertical-cavity surface-emitting lasers incorporating these mirrors exhibit record-low voltage thresholds of less than 1.5 V.

  17. 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.

  18. Room temperature photoluminescence from In{sub x}Al{sub (1−x)}N films deposited by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Kong, W. Jiao, W. Y.; Kim, T. H.; Brown, A. S.; Mohanta, A.; Roberts, A. T.; Fournelle, J.; Losurdo, M.; Everitt, H. O.

    2014-09-29

    InAlN films deposited by plasma-assisted molecular beam epitaxy exhibited a lateral composition modulation characterized by 10–12 nm diameter, honeycomb-shaped, columnar domains with Al-rich cores and In-rich boundaries. To ascertain the effect of this microstructure on its optical properties, room temperature absorption and photoluminescence characteristics of In{sub x}Al{sub (1−x)}N were comparatively investigated for indium compositions ranging from x = 0.092 to 0.235, including x = 0.166 lattice matched to GaN. The Stokes shift of the emission was significantly greater than reported for films grown by metalorganic chemical vapor deposition, possibly due to the phase separation in these nanocolumnar domains. The room temperature photoluminescence also provided evidence of carrier transfer from the InAlN film to the GaN template.

  19. Chemical dry etching of GaAs and InP by Cl2 using a new ultrahigh-vacuum dry-etching molecular-beam-epitaxy system

    NASA Astrophysics Data System (ADS)

    Furuhata, N.; Miyamoto, H.; Okamoto, A.; Ohata, K.

    1989-01-01

    Damage and contamination-free chemical dry etching of (100)GaAs and (100)InP by Cl2 was demonstrated using a new ultrahigh-vacuum dry-etching molecular-beam-epitaxy (BME) system. This system consists of a combined etching chamber, an MBE chamber, and a sample preparation chamber, all at ultrahigh vacuum. A mirrorlike surface was obtained after etching at substrate temperatures ranging from 300 to 400 C for GaAs, and from 200 to 400 C for InP. In situ reflection high-energy electron diffraction observations were accomplished for GaAs, with a mirrorlike surface after etching, and (2 x 4) surface reconstruction was observed. Results show that a smooth surface was formed at an atomic level.

  20. Critical thickness for strain relaxation of Ge1-xSnx (x ≤ 0.17) grown by molecular beam epitaxy on Ge(001)

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Zhou, Qian; Dong, Yuan; Tok, Eng Soon; Yeo, Yee-Chia

    2015-06-01

    We investigated the critical thickness (hc) for plastic relaxation of Ge1-xSnx grown by molecular beam epitaxy. Ge1-xSnx films with various Sn mole fraction x (x ≤ 0.17) and different thicknesses were grown on Ge(001). The strain relaxation of Ge1-xSnx films and the hc were investigated by high-resolution x-ray diffraction and reciprocal space mapping. It demonstrates that the measured hc values of Ge1-xSnx layers are as much as an order of magnitude larger than that predicted by the Matthews and Blakeslee (M-B) model. The People and Bean (P-B) model was also used to predict the hc values in Ge1-xSnx/Ge system. The measured hc values for various Sn content follow the trend, but slightly larger than that predicted by the P-B model.

  1. 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.

  2. Columnar growth of CoSi2 on Si(111), Si(100) and Si(110) by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Nieh, C. W.; Xiao, Q. F.; Hashimoto, Shin

    1990-01-01

    Codeposition of silicon and cobalt on heated silicon substrates in ratios several times the silicide stoichiometry is found to result in epitaxial columns of CoSi2 surrounded by a matrix of epitaxial silicon. For (111)-oriented wafers, nearly cylindrical columns are formed, where both columns and surrounding silicon are defect free, as deduced from transmission electron microscopy. Independent control of the column diameter and separation is possible, and diameters of 27-135 nm have been demonstrated.

  3. Highly c-axis oriented growth of GaN film on sapphire (0001) by laser molecular beam epitaxy using HVPE grown GaN bulk target

    SciTech Connect

    Kushvaha, S. S.; Kumar, M. Senthil; Maurya, K. K.; Dalai, M. K.; Sharma, Nita D.

    2013-09-15

    Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500–750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for the film grown at 720 °C. The micro-Raman spectroscopy studies also exhibited the high-quality wurtzite nature of GaN film grown on sapphire at 720 °C. The SIMS measurements revealed a non-traceable amount of background oxygen impurity in the grown GaN films. The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by LMBE.

  4. Photodiodes based on self-assembled GeSi/Si(001) nanoisland arrays grown by the combined sublimation molecular-beam epitaxy of silicon and vapor-phase epitaxy of germanium

    SciTech Connect

    Filatov, D. O.; Gorshkov, A. P.; Volkova, N. S.; Guseinov, D. V.; Alyabina, N. A.; Ivanova, M. M.; Chalkov, V. Yu.; Denisov, S. A.; Shengurov, V. G.

    2015-03-15

    We investigate the photosensitivity spectra of photodiodes based on Si p-i-n structures with single-layered and multilayer self-assembled GeSi/Si(001) nanoisland arrays in the i region, which are grown using a technique combining Si molecular-beam epitaxy and Ge vapor-phase epitaxy, in dependence on the temperature, diode bias, and GeSi nanoisland parameters. We show that the temperature and field dependences of the diode photosensitivity in the spectral range of the interband optical absorption in GeSi nanoislands are determined by the ratio between the rate of emission of photoexcited holes from the nanoislands and the rate of the recombination of excess carriers in them. We demonstrate the possibility of determination of the hole recombination lifetime in GeSi nanoislands from the temperature and field dependences of the photosensitivity.

  5. Multiple Layer BeSeTe/Si Heteroepitaxial Growth on Vicinal Si (100) Surfaces by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Maldonado, Eduardo; Clark, Kevin; Basit, Nasir; Sandu, Titus; Bate, Robert; Kirk, Wiley

    2003-03-01

    The epitaxial growth of multiple layers of BeSeTe/Si films on arsenic passivated vicinal Si (100) substrates is reported. These are interesting wide bandgap heterostructures that are lattice matched to silicon. Reflection high-energy electron diffraction (RHEED) was used to investigate the entire growth regime and to optimize the initial growth conditions, which is important for reducing interface defects. Atomic layer epitaxy (ALE) was used as a growth method. Transmission electron microscopy (TEM) showed epitaxial growth with no crystal defects. Residual gas analyzer (RGA) was used for desorption studies and helped to determine that chemical interactions between VI-group and Si limit the interface quality. Rutherford backscattering spectroscopy (RBS) corroborate the lattice match between BeSe_0.41Te_0.59 and Si.

  6. Minority-carrier diffusion length, minority-carrier lifetime, and photoresponsivity of β-FeSi2 layers grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Akutsu, Keiichi; Kawakami, Hideki; Suzuno, Mitsushi; Yaguchi, Takashi; Jiptner, Karolin; Chen, Jun; Sekiguchi, Takashi; Ootsuka, Teruhisa; Suemasu, Takashi

    2011-06-01

    We have epitaxially grown undoped β-FeSi2 films on Si(111) substrates via atomic-hydrogen-assisted molecular-beam epitaxy. β-FeSi2 films grown without atomic hydrogen exhibited p-type conduction with a hole density of over 1019 cm-3 at room temperature (RT). In contrast, those prepared with atomic hydrogen showed n-type conduction and had a residual electron density that was more than two orders of magnitude lower than the hole density of films grown without atomic hydrogen (of the order of 1016 cm-3 at RT). The minority-carrier diffusion length was estimated to be approximately 16 μm using an electron-beam-induced current technique; this value is twice as large as that for β-FeSi2 prepared without atomic hydrogen. This result could be well explained in terms of the minority-carrier lifetimes measured by a microwave photoconductance decay technique. The 1/e decay time using a 904 nm laser pulse was approximately 17 μs, which is much longer than that for β-FeSi2 prepared without atomic hydrogen (3 μs). The photoresponsivity reached 13 mA/W at 1.31 μm, which is the highest value ever reported for β-FeSi2 films.

  7. Minority-carrier diffusion length, minority-carrier lifetime, and photoresponsivity of {beta}-FeSi{sub 2} layers grown by molecular-beam epitaxy

    SciTech Connect

    Akutsu, Keiichi; Kawakami, Hideki; Suzuno, Mitsushi; Yaguchi, Takashi; Jiptner, Karolin; Chen, Jun; Sekiguchi, Takashi; Ootsuka, Teruhisa; Suemasu, Takashi

    2011-06-15

    We have epitaxially grown undoped {beta}-FeSi{sub 2} films on Si(111) substrates via atomic-hydrogen-assisted molecular-beam epitaxy. {beta}-FeSi{sub 2} films grown without atomic hydrogen exhibited p-type conduction with a hole density of over 10{sup 19} cm{sup -3} at room temperature (RT). In contrast, those prepared with atomic hydrogen showed n-type conduction and had a residual electron density that was more than two orders of magnitude lower than the hole density of films grown without atomic hydrogen (of the order of 10{sup 16} cm{sup -3} at RT). The minority-carrier diffusion length was estimated to be approximately 16 {mu}m using an electron-beam-induced current technique; this value is twice as large as that for {beta}-FeSi{sub 2} prepared without atomic hydrogen. This result could be well explained in terms of the minority-carrier lifetimes measured by a microwave photoconductance decay technique. The 1/e decay time using a 904 nm laser pulse was approximately 17 {mu}s, which is much longer than that for {beta}-FeSi{sub 2} prepared without atomic hydrogen (3 {mu}s). The photoresponsivity reached 13 mA/W at 1.31 {mu}m, which is the highest value ever reported for {beta}-FeSi{sub 2} films.

  8. Growth of high-quality InN thin films on InGaN buffer layer by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Yang, Chen-Chi; Lo, Ikai; Shih, Cheng-Hung; Hu, Chia-Hsuan; Wang, Ying-Chieh; Lin, Yu-Chiao; Tasi, Cheng-Da; You, Shuo-Ting

    2015-03-01

    Four samples were grown on 2 inch c-plane (0001) sapphire substrates with 4 μm-thick GaN template. The InN thin films were grown on InGaN buffer layer by low-temperature plasma-assisted molecular beam epitaxy (PAMBE) system. These samples were grown under a varied temperature of InGaN buffer layers: 500°C, 540°C, 570°C, and 600°C. The structure properties of these samples were analyzed by X-ray diffraction (XRD). The interference fringes of InN grown on the sample 1 (the growth temperature of InGaN buffer layer at 500°C) exhibit prominent oscillations, which indicates that the sample has a high quality and layer by layer epitaxial structure. The surface morphology and microstructure of samples were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). We confirmed the smooth surface and high quality crystalline for the sample.

  9. Enhanced internal quantum efficiency and light extraction efficiency from textured GaN/AlGaN quantum wells grown by molecular beam epitaxy

    SciTech Connect

    Cabalu, J.S.; Thomidis, C.; Moustakas, T.D.; Riyopoulos, S.; Zhou Lin; Smith, David J.

    2006-03-15

    GaN/Al{sub 0.2}Ga{sub 0.8}N multiple quantum wells (MQWs) were grown by molecular beam epitaxy on randomly textured and atomically smooth (0001) GaN templates. Smooth and textured GaN templates were deposited on (0001) sapphire substrates by varying the III/V ratio and the substrate temperature during growth by the hydride vapor-phase epitaxy method. We find that the MQWs replicate the texture of the GaN template, which was found to have a Gaussian distribution. The peak photoluminescence intensity from the textured MQWs is always higher than from the smooth MQWs and for GaN (7 nm)/Al{sub 0.2}Ga{sub 0.8}N (8 nm) MQWs, it is 700 times higher than that from similarly produced MQWs on smooth GaN templates. This result is attributed partly to the enhancement in light extraction efficiency and partly to the enhancement in internal quantum efficiency. The origin of the increase in internal quantum efficiency is partly due to the reduction of the quantum-confined Stark effect, since the polarization vector intersects the quantum well (QW) planes at angles smaller than 90 deg. , and partly due to the charge redistribution in the QWs caused by the polarization component parallel to the planes of the QWs.

  10. The Study of Al0.29Ga0.71N-BASED Schottky Photodiodes Grown on Silicon by Plasma-Assisted Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Mohd Yusoff, M. Z.; Hassan, Z.; Chin, C. W.; Hassan, H. Abu; Abdullah, M. J.; Mohammad, N. N.; Ahmad, M. A.; Yusof, Y.

    2013-05-01

    In this paper, the growth and characterization of epitaxial Al0.29Ga0.71N grown on Si(111) by RF-plasma assisted molecular beam epitaxy (MBE) are described. The Al mole fraction was derived from the HR-XRD symmetric rocking curve (RC) ω/2θ scans of (0002) plane as x = 0.29. PL spectrum of sample has shown sharp and intense band edge emission of GaN without the existence of yellow emission band, showing that it is comparable in crystal quality of the sample when compared with previous reports. From the Raman measurement of as-grown Al0.29Ga0.71N layer on GaN/AlN/Si sample. We found that the dominant E2 (high) phonon mode of GaN appears at 572.7 cm-1. The E2 (high) mode of AlN appears at 656.7 cm-1 and deviates from the standard value of 655 cm-1 for unstrained AlN. Finally, AlGaN Schottky photodiode have been fabricated and analyzed by mean of electrical characterization, using current-voltage (I-V) measurement to evaluate the performance of this device.

  11. Angle-resolved photoemission study of thin molecular-beam-epitaxy-grown α-Sn1-xGex films with x~0.5

    NASA Astrophysics Data System (ADS)

    Höchst, Hartmut; Engelhardt, Michael A.; Hernández-Calderón, Isaac

    1989-11-01

    Angle-resolved synchrotron-radiation photoemission spectroscopy is used to study the electronic structure of metastable epitaxial films of α-Sn1-xGex alloys. Homogeneous crystalline alloy films were grown by molecular-beam epitaxy on Ge(100) substrates at ~400 °C up to a thickness of ~300 Å. Photoemission core-level analysis indicates a strong tendency to form a compound with a composition close to x~0.5. Angle-resolved spectra show a shift of the Γ8 valence band from ~0.6 eV in Ge(100) to ~0.16 eV below EF in the α-Sn0.48Ge0.52 alloy. The experimental information of a constant alloy Fermi level locates the top of the Γ8 valence band ~0.16 eV below EF. Assuming a linear band model, the direct band gap of Eg~0.2 eV for x~0.5 will then locate the bottom of the Γ7 conduction band ~0.04 eV above EF.

  12. Low-Temperature Growth and Doping of Mercury-Based II-Vi Multiple Quantum Well Structures by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Lansari, Yamina

    The growth of Hg-based single layers and multiple quantum well structures by conventional molecular beam epitaxy (MBE) and photoassisted MBE was studied. The use of photoassisted MBE, an epitaxial growth technique developed at NCSU, has resulted in a substantial reduction of the film growth temperature. Indeed, substrate temperatures 50 to 100^circC lower than those customarily used by others for conventional MBE growth of Hg-based layers were successfully employed. Photoassisted MBE allowed the preparation of excellent structural quality HgTe layers (FWHM for the (400) diffraction peak ~ 40 arcsec), HgCdTe layers (FWHM for the (400) diffraction peak ~ 14 arcsec), and HgTeCdTe superlattices (FWHM for the (400) diffraction peak ~ 28 arcsec). In addition, n-type and p-type modulation-doping of Hg-based multilayers was accomplished by photoassisted MBE. This technique has been shown to have a significant effect on the growth process kinetics as well as on the desorption rates of the film species, thereby affecting dopant incorporation mechanisms and allowing for the successful substitutional doping of the multilayer structures. Finally, surface morphology studies were completed using scanning electron microscopy (SEM) and Nomarsky optical microscopy to study the effects of substrate surface preparation, growth initiation, and growth parameters on the density of pyramidal hillocks, a common growth defect plaguing the Hg-based layers grown in the (100) direction. Conditions which minimize the hillock density for (100) film growth have been determined.

  13. Molecular-beam epitaxy of heterostructures of wide-gap II–VI compounds for low-threshold lasers with optical and electron pumping

    SciTech Connect

    Sorokin, S. V. Gronin, S. V.; Sedova, I. V.; Rakhlin, M. V.; Baidakova, M. V.; Kop’ev, P. S.; Vainilovich, A. G.; Lutsenko, E. V.; Yablonskii, G. P.; Gamov, N. A.; Zhdanova, E. V.; Zverev, M. M.; Ruvimov, S. S.; Ivanov, S. V.

    2015-03-15

    The paper presents basic approaches in designing and growing by molecular beam epitaxy of (Zn,Mg)(S,Se)-based laser heterostructures with multiple CdSe quantum dot (QD) sheets or ZnCdSe quantum wells (QW). The method of calculation of compensating short-period ZnSSe/ZnSe superlattices (SLs) in both active and waveguide regions of laser heterostructures possessing the different waveguide thickness and different number of active regions is presented. The method allowing reduction of the density of nonequilibrium point defects in the active region of the II–VI laser structures has been proposed. It utilizes the migration enhanced epitaxy mode in growing the ZnSe QW confining the CdSe QD sheet. The threshold power density as low as P{sub thr} ∼ 0.8 kW/cm{sup 2} at T = 300 K has been demonstrated for laser heterostructure with single CdSe QD sheet and asymmetric graded-index waveguide with strain-compensating SLs.

  14. Photoluminescence of Hg{sub 1-x}Cd{sub x}Te based heterostructures grown by molecular-beam epitaxy

    SciTech Connect

    Mynbaev, K. D. Bazhenov, N. L.; Ivanov-Omskii, V. I.; Mikhailov, N. N.; Yakushev, M. V.; Sorochkin, A. V.; Remesnik, V. G.; Dvoretsky, S. A.; Varavin, V. S.; Sidorov, Yu. G.

    2011-07-15

    Photoluminescence (PL) of Hg{sub 1-x}Cd{sub x}Te-based heterostructures grown by molecular-beam epitaxy (MBE) on GaAs and Si substrates has been studied. It is shown that a pronounced disruption of the long-range order in the crystal lattice is characteristic of structures of this kind. It is demonstrated that the observed disordering is mostly due to the nonequilibrium nature of MBE and can be partly eliminated by postgrowth thermal annealing. Low-temperature spectra of epitaxial layers and structures with wide potential wells are dominated by the recombination peak of an exciton localized in density-of-states tails; the energy of this peak is substantially lower than the energy gap. In quantum-well (QW) structures at low temperatures, the main PL peak is due to carrier recombination between QW levels and the energy of the emitted photon is strictly determined by the effective (with the QW levels taken into account) energy gap.

  15. Smoothness and cleanliness of the GaAs (100) surface after thermal desorption of the native oxide for the synthesis of high mobility structures using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lee, J. J. D.; West, K. W.; Baldwin, K. W.; Pfeiffer, L. N.

    2012-10-01

    To prepare a GaAs substrate for molecular beam epitaxial (MBE) growth, the nominal ˜3 nm native oxide is typically thermally desorbed into vacuum. To test the completeness and quality of this desorption, we describe a technique, which combines MBE, thermal desorption, atomic force microscopy (AFM), reflection high-energy electron diffraction (RHEED), and secondary ion mass spectroscopy (SIMS), for detecting roughness and trace residues of contamination on (100) GaAs surfaces before MBE growth. At all desorption temperatures in the range 600-665 °C, our RHEED measurements show that the native oxide is largely desorbed within 4 min. However, the SIMS and AFM data indicate that a residue of carbon invariably remains on the GaAs (100) surface, and tenaciously resists all further attempts at its removal by thermal desorption. Since thermal desorption of the native oxide has long been the standard technique for preparing GaAs substrates for MBE growth, we suggest that MBE growth on GaAs has in general been accomplished by epitaxially growing through a partial monolayer of carbon. We believe this is the likely reason for the generally unsatisfactory quality of GaAs MBE growth after lithographic patterning on previously MBE grown structures. Our AFM data also indicate that extended native oxide desorption times or high desorption temperatures not only are ineffective at removal of the carbon residue, but are always accompanied by additional strong roughening effects on the GaAs surface morphology. Finally, we demonstrate that smoother starting surfaces for MBE growth correlate well with higher two-dimensional carrier mobilities in the resulting AlGaAs/GaAs heterostructures.

  16. Low temperature p-type doping of (Al)GaN layers using ammonia molecular beam epitaxy for InGaN laser diodes

    SciTech Connect

    Malinverni, M. Lamy, J.-M.; Martin, D.; Grandjean, N.; Feltin, E.; Dorsaz, J.; Castiglia, A.; Rossetti, M.; Duelk, M.; Vélez, C.

    2014-12-15

    We demonstrate state-of-the-art p-type (Al)GaN layers deposited at low temperature (740 °C) by ammonia molecular beam epitaxy (NH{sub 3}-MBE) to be used as top cladding of laser diodes (LDs) with the aim of further reducing the thermal budget on the InGaN quantum well active region. Typical p-type GaN resistivities and contact resistances are 0.4 Ω cm and 5 × 10{sup −4} Ω cm{sup 2}, respectively. As a test bed, we fabricated a hybrid laser structure emitting at 400 nm combining n-type AlGaN cladding and InGaN active region grown by metal-organic vapor phase epitaxy, with the p-doped waveguide and cladding layers grown by NH{sub 3}-MBE. Single-mode ridge-waveguide LD exhibits a threshold voltage as low as 4.3 V for an 800 × 2 μm{sup 2} ridge dimension and a threshold current density of ∼5 kA cm{sup −2} in continuous wave operation. The series resistance of the device is 6 Ω and the resistivity is 1.5 Ω cm, confirming thereby the excellent electrical properties of p-type Al{sub 0.06}Ga{sub 0.94}N:Mg despite the low growth temperature.

  17. Molecular Beam Epitaxy Growth of HgCdTe on Large-Area Si and CdZnTe Substrates

    NASA Astrophysics Data System (ADS)

    Reddy, M.; Peterson, J. M.; Vang, T.; Franklin, J. A.; Vilela, M. F.; Olsson, K.; Patten, E. A.; Radford, W. A.; Bangs, J. W.; Melkonian, L.; Smith, E. P. G.; Lofgreen, D. D.; Johnson, S. M.

    2011-08-01

    This paper presents the status of HgCdTe growth on large-area Si and CdZnTe substrates at Raytheon Vision Systems (RVS). The different technological tools that were used to scale up the growth from 4 inch to 6 inch diameter on Si and from 4 cm × 4 cm to 8 cm × 8 cm on CdZnTe without sacrificing the quality of the layers are described. Extremely high compositional uniformity and low macrodefect density were achieved for single- and two-color HgCdTe layers on both Si and CdZnTe substrates. Finally, a few examples of detector and focal-plane array results are included to highlight the importance of high compositional uniformity and uniformly low macrodefect density of the epitaxial layers in obtaining high operability and low cluster outages in single- and two-color focal-plane arrays (FPAs).

  18. Electronic structures and magnetic moments of Co{sub 3}FeN thin films grown by molecular beam epitaxy

    SciTech Connect

    Ito, Keita; Sanai, Tatsunori; Yasutomi, Yoko; Toko, Kaoru; Honda, Syuta; Suemasu, Takashi; Zhu, Siyuan; Kimura, Akio; Ueda, Shigenori; Takeda, Yukiharu; Saitoh, Yuji; Imai, Yoji

    2013-12-02

    We evaluated electronic structures and magnetic moments in Co{sub 3}FeN epitaxial films on SrTiO{sub 3}(001). The experimentally obtained hard x-ray photoemission spectra of the Co{sub 3}FeN film have a good agreement with those calculated. Site averaged spin magnetic moments deduced by x-ray magnetic circular dichroism were 1.52 μ{sub B} per Co atom and 2.08 μ{sub B} per Fe atom at 100 K. They are close to those of Co{sub 4}N and Fe{sub 4}N, respectively, implying that the Co and Fe atoms randomly occupy the corner and face-centered sites in the Co{sub 3}FeN unit cell.

  19. Specific features of formation of GaAs nanowire crystals during molecular beam epitaxy on different silicon surfaces

    SciTech Connect

    Samsonenko, Yu. B. Cirlin, G. E.; Egorov, V. A.; Polyakov, N. K.; Ulin, V. P.; Dubrovskii, V. G.

    2008-12-15

    The results of experimental studies on the growth and the morphological and structural properties of GaAs nanowire crystals on different silicon surfaces are reported. It is shown that the nonplanar geometrical layout of growth allows the production of epitaxial nanowire crystals in a system with a large lattice mismatch. The growth on porous substrates, the role of the surface orientation, high-temperature annealing, and presence of an oxide layer at the surface, and some other effects typical of growth of III-V nanowire crystals on the Si surface are studied and analyzed. Intense emission from the array of GaAs nanowire crystals grown on the Si (111) surface is observed.

  20. The adsorption-controlled growth of LuFe{sub 2}O{sub 4} by molecular-beam epitaxy

    SciTech Connect

    Brooks, Charles M.; Misra, Rajiv; Schiffer, Peter; Mundy, Julia A.; Zhang Lei, A.; Liu Zikui; Holinsworth, Brian S.; O'Neal, Kenneth R.; Musfeldt, Janice L.; Heeg, Tassilo; Zander, Willi; Schubert, J.; Muller, David A.; Schlom, Darrell G.

    2012-09-24

    We report the growth of single-phase (0001)-oriented epitaxial films of the purported electronically driven multiferroic, LuFe{sub 2}O{sub 4}, on (111) MgAl{sub 2}O{sub 4}, (111) MgO, and (0001) 6H-SiC substrates. Film stoichiometry was regulated using an adsorption-controlled growth process by depositing LuFe{sub 2}O{sub 4} in an iron-rich environment at pressures and temperatures where excess iron desorbs from the film surface during growth. Scanning transmission electron microscopy reveals reaction-free film-substrate interfaces. The magnetization increases rapidly below 240 K, consistent with the paramagnetic-to-ferrimagnetic phase transition of bulk LuFe{sub 2}O{sub 4}. In addition to the {approx}0.35 eV indirect band gap, optical spectroscopy reveals a 3.4 eV direct band gap at the gamma point.