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Sample records for 311b gaas substrates

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

    SciTech Connect

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

    2007-12-17

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  3. Blue vertical-cavity surface-emitting lasers based on second-harmonic generation grown on (311)B and (411)A GaAs substrates

    NASA Astrophysics Data System (ADS)

    Kaneko, Yasuhisa; Nakagawa, Shigeru; Ichimura, Yoshikatsu; Yamada, Norihide; Mars, Dan E.; Takeuchi, Tetsuya

    2000-02-01

    We have studied blue vertical-cavity surface-emitting lasers (VCSELs) based on second-harmonic generation (SHG) grown on (411)A and (311)B GaAs substrates in order to investigate suitable substrate orientations for SHG-VCSELs. The comparison among substrate orientations has been made on three parameters, SHG conversion efficiency, transparency current density and gain coefficient. The transparency current density and the gain coefficient are characterized by edge emitting lasers grown on the above substrates. We also discuss the transparency current density and the gain coefficient for (311)A reported previously by Takahashi et al. [M. Takahashi, M. Hirai, K. Fujita, N. Egami, and K. Iga, J. Appl. Phys. 82, 4551 (1997)]. SHG conversion efficiency is 38 and 30% W for SHG-VCSELs grown on (311)B and (411)A substrates, respectively, which is consistent with theory, assuming identical nonlinear coefficients for the A face and B face. Transparency current density for (311)A, (311)B and (411)A is 80, 105 and 60 A/cm2, and gain coefficients for (311)A, (311)B and (411)A are 20, 13 and 18 cm-1, respectively. There are no significant differences between (311)A and (411)A, while those for (311)B are less than those for (311)A. In conclusion, SHG efficiency is dependent on crystal orientation consistent with theory and thus the (311) orientation is preferable. Optical gain is independent of substrate orientation, while it is dependent on substrate face and A face is preferable.

  4. Deep-level Transient Spectroscopy of GaAs/AlGaAs Multi-Quantum Wells Grown on (100) and (311)B GaAs Substrates

    PubMed Central

    2010-01-01

    Si-doped GaAs/AlGaAs multi-quantum wells structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates have been studied by using conventional deep-level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques. One dominant electron-emitting level is observed in the quantum wells structure grown on (100) plane whose activation energy varies from 0.47 to 1.3 eV as junction electric field varies from zero field (edge of the depletion region) to 4.7 × 106 V/m. Two defect states with activation energies of 0.24 and 0.80 eV are detected in the structures grown on (311)B plane. The Ec-0.24 eV trap shows that its capture cross-section is strongly temperature dependent, whilst the other two traps show no such dependence. The value of the capture barrier energy of the trap at Ec-0.24 eV is 0.39 eV. PMID:21170404

  5. Complex laterally ordered InGaAs and InAs quantum dots by guided self-organized anisotropic strain engineering on shallow- and deep-patterned GaAs (311)B substrates

    SciTech Connect

    Selcuk, E.; Hamhuis, G. J.; Noetzel, R.

    2007-11-01

    Self-organized anisotropic strain engineering guided on shallow- and deep-patterned GaAs (311)B substrates is exploited for formation of complex laterally ordered architectures of connected InGaAs quantum dot (QD) arrays and isolated InAs QD groups by molecular beam epitaxy. The combination of strain and step engineerings on shallow stripe-patterned substrates transforms the periodic spotlike arrangement of the InGaAs QD arrays and InAs QD groups (on planar substrates) into a zigzag arrangement of periodic stripes which are well ordered over macroscopic areas on zigzag mesa-patterned substrates. In contrast, the formation of slow-growing facets on deep-patterned substrates produces QD-free mesa sidewalls, while InGaAs QD arrays and InAs QD groups form on the GaAs (311)B top and bottom planes with arrangements modified only close to the sidewalls depending on the sidewall orientation. The QDs on the shallow- and deep-patterned substrates exhibit excellent optical properties up to room temperature. Therefore, the concept of guided self-organization demonstrated on shallow-patterned (due to steps) and deep-patterned (due to facets) substrates is highlighted for creation of complex architectures of laterally ordered QDs for future quantum functional devices.

  6. Raman scattering of InAs/AlAs quantum dot superlattices grown on (001) and (311)B GaAs surfaces

    PubMed Central

    2012-01-01

    We present a comparative analysis of Raman scattering by acoustic and optical phonons in InAs/AlAs quantum dot superlattices grown on (001) and (311)B GaAs surfaces. Doublets of folded longitudinal acoustic phonons up to the fifth order were observed in the Raman spectra of (001)- and (311)B-oriented quantum dot superlattices measured in polarized scattering geometries. The energy positions of the folded acoustic phonons are well described by the elastic continuum model. Besides the acoustic phonons, the spectra display features related to confined transverse and longitudinal optical as well as interface phonons in quantum dots and spacer layers. Their frequency positions are discussed in terms of phonon confinement, elastic stress, and atomic intermixing. PMID:22916827

  7. Fabrication of InAs quantum dot stacked structure on InP(311)B substrate by digital embedding method

    NASA Astrophysics Data System (ADS)

    Akahane, Kouichi; Yamamoto, Naokatsu; Kawanishi, Tetsuya

    2015-12-01

    Self-assembled InAs quantum dots (QDs) grown on an InP(311)B substrate were embedded using lattice-matched InAlAs/InGaAs superlattice with the digital embedding method. The thickness of quantum wells and barriers of the superlattice varied from 2 to 16 monolayers. The six layer stacking structures were successfully grown without any degradation of the QD and superlattice structure. The cross-sections of QDs embedded within the superlattice were visualized by scanning transmission microscope. The emission wavelength of the QDs was measured by photoluminescence and could be changed by changing the thickness of the superlattice.

  8. Analysis of defects in GaAsN grown by chemical beam epitaxy on high index GaAs substrates

    SciTech Connect

    Bouzazi, Boussairi; Kojima, Nobuaki; Ohshita, Yoshio; Yamaguchi, Masafumi

    2013-09-27

    The lattice defects in GaAsN grown by chemical beam epitaxy on GaAs 311B and GaAs 10A toward [110] were characterized and discussed by using deep level transient spectroscopy (DLTS) and on the basis of temperature dependence of the junction capacitances (C{sub J}). In one hand, GaAsN films grown on GaAs 311B and GaAs 10A showed n-type and p-type conductivities, respectively although the similar and simultaneous growth conditions. This result is indeed in contrast to the common known effect of N concentration on the type of conductivity, since the surface 311B showed a significant improvement in the incorporation of N. Furthermore, the temperature dependence of C{sub J} has shown that GaAs 311B limits the formation of N-H defects. In the other hand, the energy states in the forbidden gap of GaAsN were obtained. Six electron traps, E1 to E6, were observed in the DLTS spectrum of GaAsN grown on GaAs 311B, with apparent activation energies of 0.02, 0.14, 0.16, 0.33, 0.48, and 0.74 eV below the bottom edge of the conduction band, respectively. In addition, four hole traps, H1 to H4, were observed in the DLTS spectrum of GaAsN grown on GaAs 10A, with energy depths of 0.13, 0.20, 0.39, and 0.52 eV above the valence band maximum of the alloy, respectively. Hence, the surface morphology of the GaAs substrate was found to play a key factor role in clarifying the electrical properties of GaAsN grown by CBE.

  9. Influence of substrate orientation on the structural properties of GaAs nanowires in MOCVD

    NASA Astrophysics Data System (ADS)

    Muhammad, R.; Othaman, Z.; Wahab, Y.; Ibrahim, Z.; Sakrani, S.

    2016-04-01

    In this study, the effect of substrate orientation on the structural properties of GaAs nanowires grown by a metal organic chemical vapor deposition has been investigated. Gold colloids were used as catalyst to initiate the growth of nanowiresby the vapour-liquid-solid (VLS) mechanism. From the field-emission scanning electron microscopy (FE-SEM), the growth of the nanowires were at an elevation angle of 90°, 60°, 65° and 35° with respect to the GaAs substrate for (111)B, (311)B, (110) and (100) orientations respectively. The preferential NW growth direction is always <111>B. High-resolution transmission electron microscope (HRTEM) micrograph showed the NWs that grew on the GaAs(111)B has more structural defects when compared to others. Energy dispersive X-ray analysis (EDX) indicated the presence of Au, Ga and As. The bigger diameter NWs dominates the (111)B substrate surface.

  10. Microwave GaAs Integrated Circuits On Quartz Substrates

    NASA Technical Reports Server (NTRS)

    Siegel, Peter H.; Mehdi, Imran; Wilson, Barbara

    1994-01-01

    Integrated circuits for use in detecting electromagnetic radiation at millimeter and submillimeter wavelengths constructed by bonding GaAs-based integrated circuits onto quartz-substrate-based stripline circuits. Approach offers combined advantages of high-speed semiconductor active devices made only on epitaxially deposited GaAs substrates with low-dielectric-loss, mechanically rugged quartz substrates. Other potential applications include integration of antenna elements with active devices, using carrier substrates other than quartz to meet particular requirements using lifted-off GaAs layer in membrane configuration with quartz substrate supporting edges only, and using lift-off technique to fabricate ultrathin discrete devices diced separately and inserted into predefined larger circuits. In different device concept, quartz substrate utilized as transparent support for GaAs devices excited from back side by optical radiation.

  11. Raman scattering studies of strain effects in (100) and (311)B GaAs{sub 1−x}Bi{sub x} epitaxial layers

    SciTech Connect

    Steele, J. A. Lewis, R. A.; Henini, M.; Lemine, O. M.; Alkaoud, A.

    2013-11-21

    We report room-temperature Raman studies of strained (100) and (311)B GaAs{sub 1−x}Bi{sub x} epitaxial layers for x ≤ 0.039. The Raman spectra exhibit a two-mode behavior, as well as disorder-activated GaAs-like phonons. The experimental results show that the GaAs-like LO(Γ) mode experiences a strong composition-dependent redshift as a result of alloying. The peak frequency decreases linearly from the value for pure GaAs (∼293 cm{sup −1}) with the alloyed Bi fraction x and the introduced in-plane lattice strain ε{sub ∥}, by Δω{sub LO}=Δω{sub alloy}−Δω{sub strain}. X-ray diffraction measurements are used to determine x and ε{sub ∥} allowing Δω{sub alloy} to be decoupled and is estimated to be −12(±4) cm{sup −1}/x for (100) GaAs{sub 1−x}Bi{sub x}. Δω{sub LO} is measured to be roughly double for samples grown on (311)B-oriented substrates to that of (100) GaAs. This large difference in redshift is accounted for by examining the Bi induced strain, effects from alloying, and defects formed during high-index (311)B crystal growth.

  12. 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.

  13. GaAs Photovoltaics on Polycrystalline Ge Substrates

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Pal, AnnaMaria T.; McNatt, Jeremiah S.; Wolford, David S.; Landis, Geoffrey A.; Smith, Mark A.; Scheiman, David; Jenkins, Phillip P.; McElroy Bruce

    2007-01-01

    High efficiency III-V multijunction solar cells deposited on metal foil or even polymer substrates can provide tremendous advantages in mass and stowage, particularly for planetary missions. As a first step towards that goal, poly-crystalline p/i/n GaAs solar cells are under development on polycrystalline Ge substrates. Organo Metallic Vapor Phase Epitaxy (OMVPE) parameters for pre-growth bake, nucleation and deposition have been examined. Single junction p/i/n GaAs photovoltaic devices, incorporating InGaP front and back window layers, have been grown and processed. Device performance has shown a dependence upon the thickness of a GaAs buffer layer deposited between the Ge substrate and the active device structure. A thick (2 m) GaAs buffer provides for both increased average device performance as well as reduced sensitivity to variations in grain size and orientation. Illumination under IR light (lambda > 1 micron), the cells showed a Voc, demonstrating the presence of an unintended photoactive junction at the GaAs/Ge interface. The presence of this junction limited the efficiency to approx.13% (estimated with an anti-refection coating) due to the current mismatch and lack of tunnel junction interconnect.

  14. Au impact on GaAs epitaxial growth on GaAs (111){sub B} substrates in molecular beam epitaxy

    SciTech Connect

    Liao, Zhi-Ming; Chen, Zhi-Gang; Xu, Hong-Yi; Guo, Ya-Nan; Sun, Wen; Zhang, Zhi; Yang, Lei; Lu, Zhen-Yu; Chen, Ping-Ping; Lu, Wei; Zou, Jin; Centre for Microscopy and Microanalysis, The University of Queensland, St. Lucia, Queensland 4072

    2013-02-11

    GaAs growth behaviour under the presence of Au nanoparticles on GaAs {l_brace}111{r_brace}{sub B} substrate is investigated using electron microscopy. It has been found that, during annealing, enhanced Ga surface diffusion towards Au nanoparticles leads to the GaAs epitaxial growth into {l_brace}113{r_brace}{sub B} faceted triangular pyramids under Au nanoparticles, governed by the thermodynamic growth, while during conventional GaAs growth, growth kinetics dominates, resulting in the flatted triangular pyramids at high temperature and the epitaxial nanowires growth at relatively low temperature. This study provides an insight of Au nanoparticle impact on GaAs growth, which is critical for understanding the formation mechanisms of semiconductor nanowires.

  15. GaAs Substrates for High-Power Diode Lasers

    NASA Astrophysics Data System (ADS)

    Mueller, Georg; Berwian, Patrick; Buhrig, Eberhard; Weinert, Berndt

    GaAs substrate crystals with low dislocation density (Etch-Pit Density (EPD) < 500,^-2) and Si-doping ( ~10^18,^-3) are required for the epitaxial production of high-power diode-lasers. Large-size wafers (= 3 mathrm{in} -> >=3,) are needed for reducing the manufacturing costs. These requirements can be fulfilled by the Vertical Bridgman (VB) and Vertical Gradient Freeze (VGF) techniques. For that purpose we have developed proper VB/VGF furnaces and optimized the thermal as well as the physico-chemical process conditions. This was strongly supported by extensive numerical process simulation. The modeling of the VGF furnaces and processes was made by using a new computer code called CrysVUN++, which was recently developed in the Crystal Growth Laboratory in Erlangen.GaAs crystals with diameters of 2 and 3in were grown in pyrolytic Boron Nitride (pBN) crucibles having a small-diameter seed section and a conical part. Boric oxide was used to fully encapsulate the crystal and the melt. An initial silicon content in the GaAs melt of c (melt) = 3 x10^19,^-3 has to be used in order to achieve a carrier concentration of n = (0.8- 2) x10^18,^-3, which is the substrate specification of the device manufacturer of the diode-laser. The EPD could be reduced to values between 500,^-2 and 50,^-2 with a Si-doping level of 8 x10^17 to 1 x10^18,^-3. Even the 3in wafers have rather large dislocation-free areas. The lowest EPDs ( <100,^-2) are achieved for long seed wells of the crucible.

  16. Inversion-mode GaAs wave-shaped field-effect transistor on GaAs (100) substrate

    NASA Astrophysics Data System (ADS)

    Zhang, Jingyun; Lou, Xiabing; Si, Mengwei; Wu, Heng; Shao, Jiayi; Manfra, Michael J.; Gordon, Roy G.; Ye, Peide D.

    2015-02-01

    Inversion-mode GaAs wave-shaped metal-oxide-semiconductor field-effect transistors (WaveFETs) are demonstrated using atomic-layer epitaxy of La2O3 as gate dielectric on (111)A nano-facets formed on a GaAs (100) substrate. The wave-shaped nano-facets, which are desirable for the device on-state and off-state performance, are realized by lithographic patterning and anisotropic wet etching with optimized geometry. A well-behaved 1 μm gate length GaAs WaveFET shows a maximum drain current of 64 mA/mm, a subthreshold swing of 135 mV/dec, and an ION/IOFF ratio of greater than 107.

  17. Inversion-mode GaAs wave-shaped field-effect transistor on GaAs (100) substrate

    SciTech Connect

    Zhang, Jingyun; Si, Mengwei; Wu, Heng; Ye, Peide D.; Lou, Xiabing; Gordon, Roy G.; Shao, Jiayi; Manfra, Michael J.

    2015-02-16

    Inversion-mode GaAs wave-shaped metal-oxide-semiconductor field-effect transistors (WaveFETs) are demonstrated using atomic-layer epitaxy of La{sub 2}O{sub 3} as gate dielectric on (111)A nano-facets formed on a GaAs (100) substrate. The wave-shaped nano-facets, which are desirable for the device on-state and off-state performance, are realized by lithographic patterning and anisotropic wet etching with optimized geometry. A well-behaved 1 μm gate length GaAs WaveFET shows a maximum drain current of 64 mA/mm, a subthreshold swing of 135 mV/dec, and an I{sub ON}/I{sub OFF} ratio of greater than 10{sup 7}.

  18. Relationship between planar GaAs nanowire growth direction and substrate orientation

    NASA Astrophysics Data System (ADS)

    Dowdy, Ryan S.; Walko, Donald A.; Li, Xiuling

    2013-01-01

    Planar GaAs nanowires are epitaxially grown on GaAs substrates of various orientations, via the Au-catalyzed vapor-liquid-solid mechanism using metal organic chemical vapor deposition. The nanowire geometry and growth direction are examined using scanning electron microscopy and x-ray microdiffraction. A hypothesis relating the planar nanowire growth direction to the surface projections of <111> B crystal directions is proposed. GaAs planar nanowire growth on vicinal substrates is performed to test this hypothesis. Good agreement between the experimental results and the projection model is found.

  19. Structural and optical characterization of Mg-doped GaAs nanowires grown on GaAs and Si substrates

    SciTech Connect

    Falcão, B. P. Leitão, J. P.; Correia, M. R.; Soares, M. R.; Morales, F. M.; Mánuel, J. M.; Garcia, R.; Gustafsson, A.; Moreira, M. V. B.; Oliveira, A. G. de; González, J. C.

    2013-11-14

    We report an investigation on the morphological, structural, and optical properties of large size wurtzite GaAs nanowires, low doped with Mg, grown on GaAs(111)B and Si(111) substrates. A higher density of vertical nanowires was observed when grown upon GaAs(111)B. Very thin zinc-blende segments are observed along the axis of the nanowires with a slightly higher linear density being found on the nanowires grown on Si(111). Low temperature cathodoluminescence and photoluminescence measurements reveal an emission in the range 1.40–1.52 eV related with the spatial localization of the charge carriers at the interfaces of the two crystalline phases. Mg related emission is evidenced by cathodoluminescence performed on the GaAs epilayer. However, no direct evidence for a Mg related emission is found for the nanowires. The excitation power dependency on both peak energy and intensity of the photoluminescence gives a clear evidence for the type II nature of the radiative transitions. From the temperature dependence on the photoluminescence intensity, non-radiative de-excitation channels with different activation energies were found. The fact that the estimated energies for the escape of the electron are higher in the nanowires grown on Si(111) suggests the presence of wider zinc-blende segments.

  20. Surface analysis of different oriented GaAs substrates annealed under bismuth flow

    NASA Astrophysics Data System (ADS)

    Fitouri, H.; Moussa, I.; Rebey, A.; El Jani, B.

    2007-03-01

    Several orientations of GaAs substrates, including (1 0 0), (4 1 1), (1 1 1) and (5 1 1) have been annealed in a metalorganic vapour phase epitaxy (MOVPE) horizontal reactor at different annealing temperatures and under different trimethyl-bismuth (TMBi) flux. Surface morphology of the annealed GaAs substrates was investigated by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show islands formation on all the studied samples. The density and size of Bi islands vary greatly with annealing temperature and TMBi flow. For different substrate orientations, the activation energies were deduced from Arrhenius plot of island density. Except for (5 1 1) oriented GaAs, all the studied orientations show the same activation energy of 1.8 eV. For low annealing temperature 420 °C, and under different Bi flux, each oriented substrate shows a specific behaviour. For higher temperatures 700 °C and above Bi islands are totally removed and the substrates are smooth. Surface change of (1 0 0) oriented GaAs substrate was in situ monitored by laser reflectometry.

  1. Highly efficient single-junction GaAs thin-film solar cell on flexible substrate.

    PubMed

    Moon, Sunghyun; Kim, Kangho; Kim, Youngjo; Heo, Junseok; Lee, Jaejin

    2016-01-01

    There has been much interest in developing a thin-film solar cell because it is lightweight and flexible. The GaAs thin-film solar cell is a top contender in the thin-film solar cell market in that it has a high power conversion efficiency (PCE) compared to that of other thin-film solar cells. There are two common structures for the GaAs solar cell: n (emitter)-on-p (base) and p-on-n. The former performs better due to its high collection efficiency because the electron diffusion length of the p-type base region is much longer than the hole diffusion length of the n-type base region. However, it has been limited to fabricate highly efficient n-on-p single-junction GaAs thin film solar cell on a flexible substrate due to technical obstacles. We investigated a simple and fast epitaxial lift-off (ELO) method that uses a stress originating from a Cr/Au bilayer on a 125-μm-thick flexible substrate. A metal combination of AuBe/Pt/Au is employed as a new p-type ohmic contact with which an n-on-p single-junction GaAs thin-film solar cell on flexible substrate was successfully fabricated. The PCE of the fabricated single-junction GaAs thin-film solar cells reached 22.08% under air mass 1.5 global illumination. PMID:27435899

  2. Highly efficient single-junction GaAs thin-film solar cell on flexible substrate

    PubMed Central

    Moon, Sunghyun; Kim, Kangho; Kim, Youngjo; Heo, Junseok; Lee, Jaejin

    2016-01-01

    There has been much interest in developing a thin-film solar cell because it is lightweight and flexible. The GaAs thin-film solar cell is a top contender in the thin-film solar cell market in that it has a high power conversion efficiency (PCE) compared to that of other thin-film solar cells. There are two common structures for the GaAs solar cell: n (emitter)-on-p (base) and p-on-n. The former performs better due to its high collection efficiency because the electron diffusion length of the p-type base region is much longer than the hole diffusion length of the n-type base region. However, it has been limited to fabricate highly efficient n-on-p single-junction GaAs thin film solar cell on a flexible substrate due to technical obstacles. We investigated a simple and fast epitaxial lift-off (ELO) method that uses a stress originating from a Cr/Au bilayer on a 125-μm-thick flexible substrate. A metal combination of AuBe/Pt/Au is employed as a new p-type ohmic contact with which an n-on-p single-junction GaAs thin-film solar cell on flexible substrate was successfully fabricated. The PCE of the fabricated single-junction GaAs thin-film solar cells reached 22.08% under air mass 1.5 global illumination. PMID:27435899

  3. Highly efficient single-junction GaAs thin-film solar cell on flexible substrate

    NASA Astrophysics Data System (ADS)

    Moon, Sunghyun; Kim, Kangho; Kim, Youngjo; Heo, Junseok; Lee, Jaejin

    2016-07-01

    There has been much interest in developing a thin-film solar cell because it is lightweight and flexible. The GaAs thin-film solar cell is a top contender in the thin-film solar cell market in that it has a high power conversion efficiency (PCE) compared to that of other thin-film solar cells. There are two common structures for the GaAs solar cell: n (emitter)-on-p (base) and p-on-n. The former performs better due to its high collection efficiency because the electron diffusion length of the p-type base region is much longer than the hole diffusion length of the n-type base region. However, it has been limited to fabricate highly efficient n-on-p single-junction GaAs thin film solar cell on a flexible substrate due to technical obstacles. We investigated a simple and fast epitaxial lift-off (ELO) method that uses a stress originating from a Cr/Au bilayer on a 125-μm-thick flexible substrate. A metal combination of AuBe/Pt/Au is employed as a new p-type ohmic contact with which an n-on-p single-junction GaAs thin-film solar cell on flexible substrate was successfully fabricated. The PCE of the fabricated single-junction GaAs thin-film solar cells reached 22.08% under air mass 1.5 global illumination.

  4. Growth of Epitaxial Co Layers on Sb-Passivated GaAs(110) Substrates

    NASA Astrophysics Data System (ADS)

    Teodorescu, C. M.; Chrost, J.; Ascolani, H.; Avila, J.; Soria, F.; Asensio, M. C.

    The role of Sb in the formation of the Co/GaAs(110) interfaces has been investigated by angular photoelectron diffraction (PD), synchrotron-radiation (SR) core-level photoemission and low-energy electron diffraction. We find that Co forms a metastable bcc phase on GaAs(110), with its principal crystallographic axes parallel to the substrate. From polar-angle-scanned PD, we determine an outward expansion of up to 14% of the lattice constant perpendicular to the surface, for epitaxial Co films grown on nontreated substrates. By Sb passivation of the GaAs(110) surface prior to the Co deposition, the epitaxial quality of the metallic overlayer is improved. The resulting Co phase is found to grow in a perfect bcc (110) orientation with a minor disruption of the substrate underneath and a reduced intralayer spacing outward expansion of less than 1%.

  5. Measurement of Young's modulus of GaAs nanowires growing obliquely on a substrate

    SciTech Connect

    Alekseev, P. A. Dunaevskii, M. S.; Stovpyaga, A. V.; Lepsa, M.; Titkov, A. N.

    2012-05-15

    A convenient and fast method for measuring Young's modulus of semiconductor nanowires obliquely standing on the growth substrate is presented. In this method, the nanowire is elastically bent under the force exerted by the probe of an atomic-force microscope, and the load-unload dependences for the bending of the probe cantilever are recorded. Next, these curves are used to find the bending stiffness of the tilted nanowires, after which, taking into account the nanowire dimensions, Young's modulus is obtained. The implementation of this method is demonstrated for tilted GaAs nanowires growing on a GaAs (111) substrate. Young's modulus is determined by applying finite-element analysis to the problem of the stationary elastic bending of a nanowire taking into account the actual nanowire shape and faceting. It proves that a fairly accurate estimate of Young's modulus can be obtained even if the nanowire shape is approximated by a circular cylinder with a single cross-sectional area. The values of Young's modulus obtained for GaAs nanowires of cubic lattice symmetry are 2 to 3 times smaller than its value for bulk GaAs. This difference is attributed to the presence of stacking faults in the central part of the nanowires.

  6. 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.

  7. High quality GaAs single photon emitters on Si substrate

    SciTech Connect

    Bietti, S.; Sanguinetti, S.; Cavigli, L.; Accanto, N.; Vinattieri, A.; Minari, S.; Abbarchi, M.; Isella, G.; Frigeri, C.

    2013-12-04

    We describe a method for the direct epitaxial growth of a single photon emitter, based on GaAs quantum dots fabricated by droplet epitaxy, working at liquid nitrogen temperatures on Si substrates. The achievement of quantum photon statistics up to T=80 K is directly proved by antibunching in the second order correlation function as measured with a H anbury Brown and Twiss interferometer.

  8. Monolithic integration of optical grade GaAs on Si (001) substrates deeply patterned at a micron scale

    SciTech Connect

    Bietti, Sergio; Scaccabarozzi, Andrea; Bonera, Emiliano; Miglio, Leo; Sanguinetti, Stefano; Frigeri, Cesare; Falub, Claudiu V.; Känel, Hans von

    2013-12-23

    Dense arrays of micrometric crystals, with areal filling up to 93%, are obtained by depositing GaAs in a mask-less molecular beam epitaxy process onto Si substrates. The substrates are patterned into tall, micron sized pillars. Faceted high aspect ratio GaAs crystals are achieved by tuning the Ga adatom for short surface diffusion lengths. The crystals exhibit bulk-like optical quality due to defect termination at the sidewalls. Simultaneously, the thermal strain induced by different thermal expansion parameters of GaAs and Si is fully relieved. This opens the route to thick film applications without crack formation and wafer bowing.

  9. P-type Ge epitaxy on GaAs (100) substrate grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Jin, Y. J.; Chia, C. K.; Liu, H. F.; Wong, L. M.; Chai, J. W.; Chi, D. Z.; Wang, S. J.

    2016-07-01

    In this work, Ga-doped Geranium (Ge) films have been grown on GaAs (100) substrates by metal-organic chemical vapor deposition (MOCVD). Undesired pillar structures have been observed on the epilayers prepared at relatively lower temperatures. Energy dispersive X-ray spectroscopy (EDX) indicated that the pillars are mainly consisted of Ga atoms, which is totally different from that of the Ge film. It was demonstrated that the pillar structures could be reduced by simply raising the growth temperature while keeping the other growth conditions unchanged. In this regard, the growth mechanism of the pillars was related to the Ge-Ga dimers formed during the growth of p-Ge films. By further studying the influence of a GaAs or Ge buffer layer on the growth of p-Ge layers, we found that the GaAs substrate with lower density of Ga or Ge dangling bonds was helpful in suppressing the formation of the undesired pillar structures.

  10. Reflection Properties of Metallic Gratings on ZnO Films over GaAs Substrates

    NASA Technical Reports Server (NTRS)

    Hickernell, Fred S.; Kim, Yoonkee; Hunt, William D.

    1994-01-01

    A potential application for piezoelectric film deposited on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Metallic gratings are basic elements required for the construction of such devices, and analyzing the reflectivity and the velocity change due to metallic gratings is often a critical design parameter. In this article, Datta and Hunsinger technique is extended to the case of a multilayered structure, and the developed technique is applied to analyze shorted and open gratings on ZnO films sputtered over (001)-cut (110)-propagating GaAs substrates. The analysis shows that zero reflectivity of shorted gratings can be obtained by a combination of the ZnO film and the metal thickness and the metalization ratio of the grating. Experiments are performed on shorted and an open gratings (with the center frequency of about 180 MHz) for three different metal thicknesses over ZnO films which are 0.8 and 2.6 micrometers thick. From the experiments, zero reflectivity at the resonant frequency of the grating is observed for a reasonable thickness (h/Alpha = 0.5%) of aluminum metalization. The velocity shift between the shorted and the open grating is also measured to be 0.18 MHz and 0.25 MHz for 0.8 and 1.6 micrometers respectively. The measured data show relatively good agreement with theoretical predictions.

  11. Origin and reduction of impurities at GaAs epitaxial layer-substrate interfaces

    NASA Astrophysics Data System (ADS)

    Kanber, H.; Yang, H. T.; Zielinski, T.; Whelan, J. M.

    1988-09-01

    Surface cleaning techniques used for semi-insulating GaAs substrates prior to epitaxial growth can have an important and sometimes detrimental effect on the quality and characteristics of epitaxial layers that are grown on them. We observe that a HF rinse followed by a 5:1:1 H 2SO 4:H 2O 2:H 2O etch and H 2O rinse drastically reduced the maximum concentrations and total amount of both SIMS detected S and Si for MOCVD grown GaAs undoped epitaxial layers. Subsequent final HCl and H 2O reduced the S interfacial residues to the SIMS detection limit. Total amounts of residual Si are estimated to be equivalent to 10 -2 to 10 -3 monolayers. Residual S is less. Alternately the S residue can be comparable reduced by a HF rinse followed by a NH 4OH:H 2O 2:H 2O etch and H 2O rinse. Hot aqueous HCl removes S but not Si residues. The Si residue is not electrically active and most likely exists as islands of SiO 2. The relative significance of the impurity residues is most pronounced for halide VPE, smaller for MBE and least for MOCVD grown GaAs epitaxial layers.

  12. Tailoring broadband light trapping of GaAs and Si substrates by self-organised nanopatterning

    NASA Astrophysics Data System (ADS)

    Martella, C.; Chiappe, D.; Mennucci, C.; de Mongeot, F. Buatier

    2014-05-01

    We report on the formation of high aspect ratio anisotropic nanopatterns on crystalline GaAs (100) and Si (100) substrates exploiting defocused Ion Beam Sputtering assisted by a sacrificial self-organised Au stencil mask. The tailored optical properties of the substrates are characterised in terms of total reflectivity and haze by means of integrating sphere measurements as a function of the morphological modification at increasing ion fluence. Refractive index grading from sub-wavelength surface features induces polarisation dependent anti-reflection behaviour in the visible-near infrared (VIS-NIR) range, while light scattering at off-specular angles from larger structures leads to very high values of the haze functions in reflection. The results, obtained for an important class of technologically relevant materials, are appealing in view of photovoltaic and photonic applications aiming at photon harvesting in ultrathin crystalline solar cells.

  13. Tailoring broadband light trapping of GaAs and Si substrates by self-organised nanopatterning

    SciTech Connect

    Martella, C.; Chiappe, D.; Mennucci, C.; Buatier de Mongeot, F.

    2014-05-21

    We report on the formation of high aspect ratio anisotropic nanopatterns on crystalline GaAs (100) and Si (100) substrates exploiting defocused Ion Beam Sputtering assisted by a sacrificial self-organised Au stencil mask. The tailored optical properties of the substrates are characterised in terms of total reflectivity and haze by means of integrating sphere measurements as a function of the morphological modification at increasing ion fluence. Refractive index grading from sub-wavelength surface features induces polarisation dependent anti-reflection behaviour in the visible-near infrared (VIS-NIR) range, while light scattering at off-specular angles from larger structures leads to very high values of the haze functions in reflection. The results, obtained for an important class of technologically relevant materials, are appealing in view of photovoltaic and photonic applications aiming at photon harvesting in ultrathin crystalline solar cells.

  14. Molecular beam epitaxial growth and characterization of GaSb layers on GaAs (0 0 1) substrates

    NASA Astrophysics Data System (ADS)

    Li, Yanbo; Zhang, Yang; Zhang, Yuwei; Wang, Baoqiang; Zhu, Zhanping; Zeng, Yiping

    2012-06-01

    We report on the growth of GaSb layers on GaAs (0 0 1) substrates by molecular beam epitaxy (MBE). We investigate the influence of the GaAs substrate surface treatment, growth temperature, and V/III flux ratios on the crystal quality and the surface morphology of GaSb epilayers. Comparing to Ga-rich GaAs surface preparation, the Sb-rich GaAs surface preparation can promote the growth of higher-quality GaSb material. It is found that the crystal quality, electrical properties, and surface morphology of the GaSb epilayers are highly dependent on the growth temperature, and Sb/Ga flux ratios. Under the optimized growth conditions, we demonstrate the epitaxial growth of high quality GaSb layers on GaAs substrates. The p-type nature of the unintentionally doped GaSb is studied and from the growth conditions dependence of the hole concentrations of the GaSb, we deduce that the main native acceptor in the GaSb is the Ga antisite (GaSb) defect.

  15. TEM based analysis of III-Sb VECSELs on GaAs substrates for improved laser performance.

    NASA Astrophysics Data System (ADS)

    Ahirwar, P.; Shima, D.; Rotter, T. J.; Clark, S. P. R...; Addamane, S. J.; Hains, C. P.; Dawson, L. R.; Balakrishnan, G.; Bedford, R.; Lai, Y. Y.; Laurain, A.; Hader, J.; Moloney, J. V.

    2013-02-01

    The antimonide based vertical external cavity surface emitting lasers (VECSELs) operating in the 1.8 to 2.8 Tm wavelength range are typically based on InGaAsSb/AlGaAsSb quantum wells on AlAsSb/GaSb distributed Bragg reflectors (DBRs) grown lattice-matched on GaSb substrates. The ability to grow such antimonide VECSEL structures on GaAs substrates can take advantage of the superior AlAs based etch-stop layers and mature DBR technology based on GaAs substrates. The growth of such III-Sb VECSELs on GaAs substrates is non-trivial due to the 7.78% lattice mismatch between the antimonide based active region and the GaAs/AlGaAs DBR. The challenge is therefore to reduce the threading dislocation density in the active region without a very thick metamorphic buffer and this is achieved by inducing 90 ° interfacial mist dislocation arrays between the GaSb and GaAs layers. In this presentation we make use of cross section transmission electron microscopy to analyze a variety of approaches to designing and growing III-Sb VECSELs on GaAs substrates to achieve a low threading dislocation density. We shall demonstrate the failure mechanisms in such growths and we analyze the extent to which the threading dislocations are able to permeate a thick active region. Finally, we present growth strategies and supporting results showing low-defect density III-Sb VECSEL active regions on GaAs.

  16. GaAs buffer layer technique for vertical nanowire growth on Si substrate

    SciTech Connect

    Xu, Xiaoqing Parizi, Kokab B.; Huo, Yijie; Kang, Yangsen; Philip Wong, H.-S.; Li, Yang

    2014-02-24

    Gold catalyzed vapor-liquid-solid method is widely applied to III–V nanowire (NW) growth on Si substrate. However, the easy oxidation of Si, possible Si contamination in the NWs, high defect density in the NWs, and high sensitivity of the NW morphology to growth conditions largely limit its controllability. In this work, we developed a buffer layer technique by introducing a GaAs thin film with predefined polarity as a template. It is found that samples grown on these buffer layers all have high vertical NW yields in general, due to the single-orientation of the buffer layers. Low temperature buffer with smoother surface leads to highest yield of vertical NWs, while high temperature (HT) buffer with better crystallinity results in perfect NW quality. The defect-free property we observed here is very promising for optoelectronic device applications based on GaAs NW. Moreover, the buffer layers can eliminate Si contamination by preventing Si-Au alloy formation and by increasing the thickness of the Si diffusion barrier, thus providing more flexibility to vertical NW growth. The buffer layer technique we demonstrated here could be easily extended to other III-V on Si system for electronic and photonic applications.

  17. Growth of single-crystal Al layers on GaAs and Si substrates for microwave superconducting resonators

    NASA Astrophysics Data System (ADS)

    Tournet, J.; Gosselink, D.; Jaikissoon, M.; Miao, G.-X.; Langenberg, D.; Mariantoni, M.; Wasilewski, Zr

    Thin Al layers on dielectrics are essential building blocks of circuits used in the quest for scalable quantum computing systems. While molecular beam epitaxy (MBE) has been shown to produce the highest quality Al layers, further reduction of losses in superconducting resonators fabricated from them is highly desirable. Defects at the Al-substrate interface are likely the key source of losses. Here we report on the optimization of MBE growth of Al layers on GaAs and Si substrates. Si surfaces were prepared by in-situ high temperature substrate annealing. For GaAs, defects typically remaining on the substrate surfaces after oxide desorption were overgrown with GaAs or GaAs/AlAs superlattice buffer layers. Such surface preparation steps were followed by cooling process to below 0°C, precisely controlled to obtain targeted surface reconstructions. Deposition of 110 nm Al layers was done at subzero temperatures and monitored with RHEED at several azimuths simultaneously. The resulting layers were characterized by HRXRD, AFM and Nomarski. Single crystal, near-atomically smooth layers of Al(110) were demonstrated on GaAs(001)-2x4 surface whereas Al(111) of comparable quality was formed on Si(111)-1x1 and 7x7 surfaces.

  18. Removal of GaAs growth substrates from II-VI semiconductor heterostructures

    NASA Astrophysics Data System (ADS)

    Bieker, S.; Hartmann, P. R.; Kießling, T.; Rüth, M.; Schumacher, C.; Gould, C.; Ossau, W.; Molenkamp, L. W.

    2014-04-01

    We report on a process that enables the removal of II-VI semiconductor epilayers from their GaAs growth substrate and their subsequent transfer to arbitrary host environments. The technique combines mechanical lapping and layer selective chemical wet etching and is generally applicable to any II-VI layer stack. We demonstrate the non-invasiveness of the method by transferring an all-II-VI magnetic resonant tunneling diode. High resolution x-ray diffraction proves that the crystal integrity of the heterostructure is preserved. Transport characterization confirms that the functionality of the device is maintained and even improved, which is ascribed to completely elastic strain relaxation of the tunnel barrier layer.

  19. Thin film GaAs solar cells on glass substrates by epitaxial liftoff

    SciTech Connect

    Lee, X.Y.; Goertemiller, M.; Boroditsky, M.; Ragan, R.; Yablonovitch, E.

    1997-02-01

    In this work, we describe the fabrication and operating characteristics of GaAs/AlGaAs thin film solar cells processed by the epitaxial liftoff (ELO) technique. This technique allows the transfer of these cells onto glass substrates. The performance of the lifted-off solar cell is demonstrated by means of electrical measurements under both dark and illuminated conditions. We have also optimized the light trapping conditions in this direct-gap material. The results show that good solar absorption is possible in active layers as thin as 0.32 {mu}m. In such a thin solar cell, the open circuit voltage would be enhanced. We believe that the combination of an epitaxial liftoff thin GaAs film, and nano-texturing can lead to record breaking performance. {copyright} {ital 1997 American Institute of Physics.}

  20. Growth and characterization of Czochralski-grown n and p-type GaAs for space solar cell substrates

    NASA Technical Reports Server (NTRS)

    Chen, R. T.

    1983-01-01

    Progress in LEC (liquid encapsulated Czochralski) crystal growth techniques for producing high-quality, 3-inch-diameter, n- and p-type GaAs crystals suitable for solar cell applications is described. The LEC crystals with low dislocation densities and background impurities, high electrical mobilities, good dopant uniformity, and long diffusion lengths were reproducibly grown through control of the material synthesis, growth and doping conditions. The capability for producing these large-area, high-quality substrates should positively impact the manufacturability of highly efficiency, low cost, radiation-hard GaAs solar cells.

  1. Effect of GaAs substrate orientation on the growth kinetic of GaN layer grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Laifi, J.; Chaaben, N.; Bouazizi, H.; Fourati, N.; Zerrouki, C.; El Gmili, Y.; Bchetnia, A.; Salvestrini, J. P.; El Jani, B.

    2016-06-01

    We have investigated the kinetic growth of low temperature GaN nucleation layers (LT-GaN) grown on GaAs substrates with different crystalline orientations. GaN nucleation layers were grown by metal organic vapor phase epitaxy (MOVPE) in a temperature range of 500-600 °C on oriented (001), (113), (112) and (111) GaAs substrates. The growth was in-situ monitored by laser reflectometry (LR). Using an optical model, including time-dependent surface roughness and growth rate profiles, simulations were performed to best approach the experimental reflectivity curves. Results are discussed and correlated with ex-situ analyses, such as atomic force microscopy (AFM) and UV-visible reflectance (SR). We show that the GaN nucleation layers growth results the formation of GaN islands whose density and size vary greatly with both growth temperature and substrate orientation. Arrhenius plots of the growth rate for each substrate give values of activation energy varying from 0.20 eV for the (001) orientation to 0.35 eV for the (113) orientation. Using cathodoluminescence (CL), we also show that high temperature (800-900 °C) GaN layers grown on top of the low temperature (550 °C) GaN nucleation layers, grown themselves on the GaAs substrates with different orientations, exhibit cubic or hexagonal phase depending on both growth temperature and substrate orientation.

  2. Formation of oxides and their role in the growth of Ag nanoplates on GaAs substrates.

    SciTech Connect

    Sun, Y.; Gosztola, D.; Lei, C.; Haasch, R.; Center for Nanoscale Materials; Univ. of Illinois

    2008-10-21

    Simple galvanic reactions between highly doped n-type GaAs wafers and a pure aqueous solution of AgNO3 at room temperature provide an easy and efficient protocol to directly deposit uniform Ag nanoplates with tunable dimensions on the GaAs substrates. The anisotropic growth of the Ag nanoplates in the absence of surfactant molecules might be partially ascribed to the codeposition of oxides of gallium and arsenic, which are revealed by extensive data from electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, during the growth of the Ag nanoplates. The electron microscopic characterization shows that each Ag nanoplate has a 'necked' geometry, that is, it pins on the GaAs lattices through only a tiny neck (with sizes of <10 nm). In addition, the as-grown Ag nanoplates exhibit strong enhancement toward Raman scattering of materials on (or around) their surfaces.

  3. Lithography-free shell-substrate isolation for core-shell GaAs nanowires.

    PubMed

    Haggren, Tuomas; Perros, Alexander Pyymaki; Jiang, Hua; Huhtio, Teppo; Kakko, Joona-Pekko; Dhaka, Veer; Kauppinen, Esko; Lipsanen, Harri

    2016-07-01

    A facile and scalable lithography-free technique(5) for the rapid construction of GaAs core-shell nanowires incorporating shell isolation from the substrate is reported. The process is based on interrupting NW growth and applying a thin spin-on-glass (SOG) layer to the base of the NWs and resuming core-shell NW growth. NW growth occurred in an atmospheric pressure metalorganic vapour phase epitaxy (MOVPE) system with gold nanoparticles used as catalysts for the vapour-liquid-solid growth. It is shown that NW axial core growth and radial shell growth can be resumed after interruption and even exposure to air. The SOG residues and native oxide layer that forms on the NW surface are shown to prevent or perturb resumption of epitaxial NW growth if not removed. Both HF etching and in situ annealing of the air-exposed NWs in the MOVPE were shown to remove the SOG residues and native oxide layer. While both procedures are shown capable of removing the native oxide and enabling resumption of epitaxial NW growth, in situ annealing produced the best results and allowed construction of pristine core-shell NWs. No growth occurred on SOG and it was observed that axial NW growth was more rapid when a SOG layer covered the substrate. The fabricated p-core/n-shell NWs exhibited diode behaviour upon electrical testing. The isolation of the NW shells from the substrate was confirmed by scanning electron microscopy and electrical measurements. The crystal quality of the regrown core-shell NWs was verified with a high resolution transmission electron microscope. The reported technique potentially provides a pathway using MOVPE for scalable and high-throughput production of shell-substrate isolated core-shell NWs on an industrial scale. PMID:27242347

  4. Lithography-free shell-substrate isolation for core–shell GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Haggren, Tuomas; Pyymaki Perros, Alexander; Jiang, Hua; Huhtio, Teppo; Kakko, Joona-Pekko; Dhaka, Veer; Kauppinen, Esko; Lipsanen, Harri

    2016-07-01

    A facile and scalable lithography-free technique5 for the rapid construction of GaAs core–shell nanowires incorporating shell isolation from the substrate is reported. The process is based on interrupting NW growth and applying a thin spin-on-glass (SOG) layer to the base of the NWs and resuming core–shell NW growth. NW growth occurred in an atmospheric pressure metalorganic vapour phase epitaxy (MOVPE) system with gold nanoparticles used as catalysts for the vapour‑liquid‑solid growth. It is shown that NW axial core growth and radial shell growth can be resumed after interruption and even exposure to air. The SOG residues and native oxide layer that forms on the NW surface are shown to prevent or perturb resumption of epitaxial NW growth if not removed. Both HF etching and in situ annealing of the air-exposed NWs in the MOVPE were shown to remove the SOG residues and native oxide layer. While both procedures are shown capable of removing the native oxide and enabling resumption of epitaxial NW growth, in situ annealing produced the best results and allowed construction of pristine core–shell NWs. No growth occurred on SOG and it was observed that axial NW growth was more rapid when a SOG layer covered the substrate. The fabricated p-core/n-shell NWs exhibited diode behaviour upon electrical testing. The isolation of the NW shells from the substrate was confirmed by scanning electron microscopy and electrical measurements. The crystal quality of the regrown core–shell NWs was verified with a high resolution transmission electron microscope. The reported technique potentially provides a pathway using MOVPE for scalable and high-throughput production of shell-substrate isolated core–shell NWs on an industrial scale.

  5. ZnO Films on {001}-Cut <110>-Propagating GaAs Substrates for Surface Acoustic Wave Device Applications

    NASA Technical Reports Server (NTRS)

    Kim, Yoonkee; Hunt, William D.; Hickernell, Frederick S.; Higgins, Robert J.; Jen, Cheng-Kuei

    1995-01-01

    A potential application for piezoelectric films on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on {001}-cut <110> -propagating GaAs substrates are investigated in this article, including SAW Velocity effective piezoelectric coupling constant, propagation loss. diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films or different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(exp 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2, or Si3N4 on {001}-cut GaAs samples are reported using two different techniques: 1) knife-edge laser probe, 2) line-focus-beam scanning acoustic microscope. It was found that near the <110> propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the <100> direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.

  6. Croissance epitaxiale de GaAs sur substrats de Ge par epitaxie par faisceaux chimiques

    NASA Astrophysics Data System (ADS)

    Belanger, Simon

    La situation energetique et les enjeux environnementaux auxquels la societe est confrontee entrainent un interet grandissant pour la production d'electricite a partir de l'energie solaire. Parmi les technologies actuellement disponibles, la filiere du photovoltaique a concentrateur solaire (CPV pour concentrator photovoltaics) possede un rendement superieur et mi potentiel interessant a condition que ses couts de production soient competitifs. La methode d'epitaxie par faisceaux chimiques (CBE pour chemical beam epitaxy) possede plusieurs caracteristiques qui la rendent interessante pour la production a grande echelle de cellules photovoltaiques a jonctions multiples a base de semi-conducteurs III-V. Ce type de cellule possede la meilleure efficacite atteinte a ce jour et est utilise sur les satellites et les systemes photovoltaiques a concentrateur solaire (CPV) les plus efficaces. Une des principales forces de la technique CBE se trouve dans son potentiel d'efficacite d'utilisation des materiaux source qui est superieur a celui de la technique d'epitaxie qui est couramment utilisee pour la production a grande echelle de ces cellules. Ce memoire de maitrise presente les travaux effectues dans le but d'evaluer le potentiel de la technique CBE pour realiser la croissance de couches de GaAs sur des substrats de Ge. Cette croissance constitue la premiere etape de fabrication de nombreux modeles de cellules solaires a haute performance decrites plus haut. La realisation de ce projet a necessite le developpement d'un procede de preparation de surface pour les substrats de germanium, la realisation de nombreuses sceances de croissance epitaxiale et la caracterisation des materiaux obtenus par microscopie optique, microscopie a force atomique (AFM), diffraction des rayons-X a haute resolution (HRXRD), microscopie electronique a transmission (TEM), photoluminescence a basse temperature (LTPL) et spectrometrie de masse des ions secondaires (SIMS). Les experiences ont permis

  7. The growth of low band-gap InAs on (111)B GaAs substrates

    NASA Technical Reports Server (NTRS)

    Welser, Roger E.; Guido, L. J.

    1996-01-01

    Growth on the (111)B orientation exhibits a number of advantageous properties as compared to the (100) during the early stages of strained-layer epitaxy. In accordance with a developing model of nucleation and growth, we have deposited thin (60 A - 2500 A), fully relaxed InAs films on (111)B GaAs substrates. Although thicker InAs films are subject to the formation of twin defects common to epitaxy on the (111)B orientation, appropriate control of the growth parameters can greatly minimize their density. Using this knowledge base, InAs films up to 2 microns in thickness with improved morphology and structural quality have been grown on (111)B GaAs substrates.

  8. The Growth of Low Band-Gap InAs on (111)B GaAs Substrates

    NASA Technical Reports Server (NTRS)

    Weiser, R. E.; Guido, L. J.

    1995-01-01

    Growth on the (111)B orientation exhibits a number of advantageous properties as compared to the (100) during the early stages of strained-layer epitaxy. In accordance with a developing model of nucleation and growth, we have deposited thin (60 A - 2500 A), fully relaxed InAs films on (111)B GaAs substrates. Although thicker InAs films are subject to the formation of twin defects common to epitaxy on the (111)B orientation, appropriate control of the growth parameters can greatly minimize their density. Using this knowledge base, InAs films up to 2 microns in thickness with improved morphology and structural quality have been grown on (111)B GaAs substrates.

  9. Effect of InGaAs interlayer on the properties of GaAs grown on Si (111) substrate by molecular beam epitaxy

    SciTech Connect

    Wen, Lei; Gao, Fangliang; Li, Jingling; Guan, Yunfang; Wang, Wenliang; Zhou, Shizhong; Lin, Zhiting; Zhang, Xiaona; Zhang, Shuguang E-mail: mssgzhang@scut.edu.cn; Li, Guoqiang E-mail: mssgzhang@scut.edu.cn

    2014-11-21

    High-quality GaAs films have been epitaxially grown on Si (111) substrates by inserting an In{sub x}Ga{sub 1−x}As interlayer with proper In composition by molecular beam epitaxy (MBE). The effect of In{sub x}Ga{sub 1−x}As (0 < x < 0.2) interlayers on the properties of GaAs films grown on Si (111) substrates by MBE has been studied in detailed. Due to the high compressive strain between InGaAs and Si, InGaAs undergoes partial strain relaxation. Unstrained InGaAs has a larger lattice constant than GaAs. Therefore, a thin InGaAs layer with proper In composition may adopt a close lattice constant with that of GaAs, which is beneficial to the growth of high-quality GaAs epilayer on top. It is found that the proper In composition in In{sub x}Ga{sub 1−x}As interlayer of 10% is beneficial to obtaining high-quality GaAs films, which, on the one hand, greatly compensates the misfit stress between GaAs film and Si substrate, and on the other hand, suppresses the formation of multiple twin during the heteroepitaxial growth of GaAs film. However, when the In composition does not reach the proper value (∼10%), the In{sub x}Ga{sub 1−x}As adopts a lower strain relaxation and undergoes a lattice constant smaller than unstrained GaAs, and therefore introduces compressive stress to GaAs grown on top. When In composition exceeds the proper value, the In{sub x}Ga{sub 1−x}As will adopt a higher strain relaxation and undergoes a lattice constant larger than unstrained GaAs, and therefore introduces tensile stress to GaAs grown on top. As a result, In{sub x}Ga{sub 1−x}As interlayers with improper In composition introduces enlarged misfit stress to GaAs epilayers grown on top, and deteriorates the quality of GaAs epilayers. This work demonstrates a simple but effective method to grow high-quality GaAs epilayers and brings up a broad prospect for the application of GaAs-based optoelectronic devices on Si substrates.

  10. Silver as Seed-Particle Material for GaAs Nanowires—Dictating Crystal Phase and Growth Direction by Substrate Orientation

    PubMed Central

    2016-01-01

    Here we investigate the feasibility of silver as seed-particle material to synthesize GaAs nanowires and show that both crystal phase and growth direction can be controlled by choice of substrate orientation. A (111)B substrate orientation can be used to form vertically aligned wurtzite GaAs nanowires and a (100) substrate orientation to form vertically aligned zinc blende GaAs nanowires. A 45–50% yield of vertical nanowire growth is achieved on the (100) substrate orientation without employing any type of surface modification or nucleation strategy to promote a vertical growth direction. In addition, photoluminescence measurements reveal that the photon emission from the silver seeded wurtzite GaAs nanowires is characterized by a single and narrow emission peak at 1.52 eV. PMID:26998550

  11. Silver as Seed-Particle Material for GaAs Nanowires--Dictating Crystal Phase and Growth Direction by Substrate Orientation.

    PubMed

    Lindberg, Caroline; Whiticar, Alexander; Dick, Kimberly A; Sköld, Niklas; Nygård, Jesper; Bolinsson, Jessica

    2016-04-13

    Here we investigate the feasibility of silver as seed-particle material to synthesize GaAs nanowires and show that both crystal phase and growth direction can be controlled by choice of substrate orientation. A (111)B substrate orientation can be used to form vertically aligned wurtzite GaAs nanowires and a (100) substrate orientation to form vertically aligned zinc blende GaAs nanowires. A 45-50% yield of vertical nanowire growth is achieved on the (100) substrate orientation without employing any type of surface modification or nucleation strategy to promote a vertical growth direction. In addition, photoluminescence measurements reveal that the photon emission from the silver seeded wurtzite GaAs nanowires is characterized by a single and narrow emission peak at 1.52 eV. PMID:26998550

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

    NASA Technical Reports Server (NTRS)

    Oh, J. E.; Bhattacharya, P. K.; Chen, Y. C.; Tsukamoto, S.

    1989-01-01

    Epitaxial layers of InSb were grown on InP and GaAs substrates by molecular beam epitaxy. The dependence of the epilayer quality on flux ratio, J sub Sb4/J sub In, was studied. Deviation from an optimum value of J sub Sb4/J sub In (approx. 2) during growth led to deterioration in the surface morphology and the electrical and crystalline qualities of the films. Room temperature electron mobilities as high as 70,000 and 53,000 sq cm /V-s were measured in InSb layers grown on InP and GaAs substrates, respectively. Unlike the previous results, the conductivity in these films is n-type even at T = 13 K, and no degradation of the electron mobility due to the high density of dislocations was observed. The measured electron mobilities (and carrier concentrations) at 77 K in InSb layers grown on InP and GaAs substrates are 110,000 sq cm/V-s (3 x 10(15) cm(-3)) and 55,000 sq cm/V-s (4.95 x 10(15) cm(-3)), respectively, suggesting their application to electronic devices at cryogenic temperatures.

  13. ZnO films on /001/-cut (110)-propagating GaAs substrates for surface acoustic wave device applications

    NASA Technical Reports Server (NTRS)

    Hickernell, Frederick S.; Higgins, Robert J.; Jen, Cheng-Kuei; Kim, Yoonkee; Hunt, William D.

    1995-01-01

    A potential application for piezoelectric films substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on /001/-cut group of (110) zone axes-propagating GaAs substrates are investigated in this article, including SAW velocity, effective piezoelectric coupling constant, propagation loss, diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films of different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(sup 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2 or Si3N4 on /001/-cut GaAs samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. It was found that near the group of (110) zone axes propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the (100) direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.

  14. Acoustic resonator with Al electrodes on an AlN layer and using a GaAs substrate

    DOEpatents

    Kline, Gerald R.; Lakin, Kenneth M.

    1985-12-03

    A method of fabricating an acoustic wave resonator wherein all processing steps are accomplished from a single side of said substrate. The method involves deposition of a multi-layered Al/AlN structure on a GaAs substrate followed by a series of fabrication steps to define a resonator from said composite. The resulting resonator comprises an AlN layer between two Al layers and another layer of AlN on an exterior of one of said Al layers.

  15. Heteroepitaxial InP solar cells on Si and GaAs substrates

    NASA Technical Reports Server (NTRS)

    Weinberg, Irving; Swartz, Clifford K.; Brinker, David J.

    1990-01-01

    The characteristics of InP cells processed from thin layers of InP heteroepitaxially grown on GaAs, on silicon with an intervening GaAs layer, and on GaAs with intervening Ga(x)In(1-x)As layers are described, and the factors affecting cell efficiency are discussed. Under 10 MeV proton irradiations, the radiation resistances of the heteroepitaxial cells were superior to that of homoepitaxial InP cells. The superior radiation resistance is attributed to the high dislocation densities present in the heteroepitaxial cells.

  16. MBE growth of Sb-based nBn photodetectors on large diameter GaAs substrates

    NASA Astrophysics Data System (ADS)

    Lubyshev, Dmitri; Fastenau, Joel M.; Qiu, Yueming; Liu, Amy W. K.; Koerperick, Edwin J.; Olesberg, Jonathon T.; Norton, Dennis; Faleev, Nikolai N.; Honsberg, Christiana B.

    2013-06-01

    The GaSb-based family of materials and heterostructures provides rich bandgap engineering possibilities for a variety of infrared (IR) applications. Mid-wave and long-wave IR photodetectors are progressing toward commercial manufacturing applications, but to succeed they must move from research laboratory settings to general semiconductor production and they require larger diameter substrates than the current standard 2-inch and 3-inch GaSb. Substrate vendors are beginning production of 4-inch GaSb, but another alternative is growth on 6-inch GaAs substrates with appropriate metamorphic buffer layers. We have grown generic MWIR nBn photodetectors on large diameter, 6-inch GaAs substrates by molecular beam epitaxy. Multiple metamorphic buffer architectures, including bulk GaSb nucleation, AlAsSb superlattices, and graded GaAsSb and InAlSb ternary alloys, were employed to bridge the 7.8% mismatch gap from the GaAs substrates to the GaSb-based epilayers at 6.1 Å lattice-constant and beyond. Reaching ~6.2 Å extends the nBn cutoff wavelength from 4.2 to <5 µm, thus broadening the application space. The metamorphic nBn epiwafers demonstrated unique surface morphologies and crystal properties, as revealed by AFM, high-resolution XRD, and cross-section TEM. GaSb nucleation resulted in island-like surface morphology while graded ternary buffers resulted in cross-hatched surface morphology, with low root-mean-square roughness values of ~10 Å obtained. XRD determined dislocation densities as low as 2 × 107 cm-2. Device mesas were fabricated and dark currents of 1 × 10-6 A/cm2 at 150K were measured. This work demonstrates a promising path to satisfy the increasing demand for even larger area focal plane array detectors in a commercial production environment.

  17. High-performance organic/inorganic hybrid heterojunction based on Gallium Arsenide (GaAs) substrates and a conjugated polymer

    NASA Astrophysics Data System (ADS)

    Jameel, D. A.; Felix, J. F.; Aziz, M.; Al Saqri, N.; Taylor, D.; de Azevedo, W. M.; da Silva, E. F.; Albalawi, H.; Alghamdi, H.; Al Mashary, F.; Henini, M.

    2015-12-01

    In this paper, we present an extensive study of the electrical properties of organic-inorganic hybrid heterojunctions. Polyaniline (PANI) thin films were deposited by a very simple technique on (1 0 0) and (3 1 1)B n-type Gallium Arsenide (GaAs) substrates to fabricate hybrid devices with excellent electrical properties. The hybrid devices were electrically characterized using current-voltage (I-V), capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements in the temperature range 20-440 K. The analysis of I-V characteristics based on the thermionic emission mechanism has shown a decrease of the barrier height and an increase of the ideality factor at lower temperatures for both hybrid devices. The interface states were analyzed by series resistance obtained using the C-G-V methods. The interface state density (Dit) of PANI/(1 0 0) GaAs devices is approximately one order of magnitude higher than that of PANI/(3 1 1)B GaAs devices. This behaviour is attributed to the effect of crystallographic orientation of the substrates, and was confirmed by DLTS results as well. Additionally, the devices show excellent air stability, with rectification ratio values almost unaltered after two years of storage under ambient conditions, making the polyaniline an interesting conductor polymer for future devices applications.

  18. Growth of In xGa 1- xAs layers with pyramidal morphology on (1 0 0)GaAs patterned substrates by liquid-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Iida, S.; Balakrishnan, K.; Koyama, T.; Hayakawa, Y.; Kumagawa, M.

    2000-05-01

    Liquid-phase epitaxial growth of In xGa 1- xAs ( x=0.6) layers on various types of patterned (1 0 0)GaAs substrates was investigated. Non-planar InGaAs layer having filled tent-like structure was grown on non-patterned substrate. When the InGaAs was grown on circular-patterned substrate, a non-hollow pyramid structure was obtained. Perfect hollow pyramid structured InGaAs was found to be grown on trench substrates of (1 0 0)GaAs.

  19. Etching Technique to Reveal Dislocations in Thin GaAs Films Grown on Si Substrates

    NASA Astrophysics Data System (ADS)

    Nishikawa, Hironobu; Soga, Tetsuo; Mikuriya, Nobuo; Jimbo, Takashi; Umeno, Masayoshi

    1988-02-01

    Dislocations in GaAs and GaAs/Si are revealed by the etching technique at room temperature. The etchant is composed of H2O, K2Cr2O7, HNO3, HCl and H2SO4. The dislocation density of GaAs grown on Si by MOCVD using GaP and strained layer superlattices is about 1× 106 cm-2.

  20. Interfacial study and band alignment of ultrathin La2Hf2O7 films on GaAs substrates

    NASA Astrophysics Data System (ADS)

    Wei, F.; Xiong, Y.-H.; Zhang, X.-Q.; Du, J.; Tu, H.-L.

    2013-09-01

    We report ultrathin amorphous La2Hf2O7 (LHO) films grown on p-GaAs (0 0 1) substrates as high-k gate dielectric using the pulsed laser deposition method. Interfacial characterization of the LHO/GaAs has been carried out. It shows that the interfacial layer with a thickness of less than 0.5 nm is composed of Ga2O3. Experimental results show that the 5.7 ± 0.1 eV bandgap of LHO is aligned to the bandgap of GaAs with a valence band offset of 3.15 ± 0.05 eV and a conduction band offset of 1.1 ± 0.1 eV. Capacitance-voltage and current-voltage measurements indicate that LHO could be a promising gate dielectric for GaAs metal-oxide-semiconductor devices.

  1. Single-Crystalline Aluminum Nanostructures on a Semiconducting GaAs Substrate for Ultraviolet to Near-Infrared Plasmonics.

    PubMed

    Liu, Hsuan-Wei; Lin, Fan-Cheng; Lin, Shi-Wei; Wu, Jau-Yang; Chou, Bo-Tsun; Lai, Kuang-Jen; Lin, Sheng-Di; Huang, Jer-Shing

    2015-04-28

    Aluminum, as a metallic material for plasmonics, is of great interest because it extends the applications of surface plasmon resonance into the ultraviolet (UV) region and is superior to noble metals in natural abundance, cost, and compatibility with modern semiconductor fabrication processes. Ultrasmooth single-crystalline metallic films are beneficial for the fabrication of high-definition plasmonic nanostructures, especially complex integrated nanocircuits. The absence of surface corrugation and crystal boundaries also guarantees superior optical properties and applications in nanolasers. Here, we present UV to near-infrared plasmonic resonance of single-crystalline aluminum nanoslits and nanoholes. The high-definition nanostructures are fabricated with focused ion-beam milling into an ultrasmooth single-crystalline aluminum film grown on a semiconducting GaAs substrate with a molecular beam epitaxy method. The single-crystalline aluminum film shows improved reflectivity and reduced two-photon photoluminescence (TPPL) due to the ultrasmooth surface. Both linear scattering and nonlinear TPPL are studied in detail. The nanoslit arrays show clear Fano-like resonance, and the nanoholes are found to support both photonic modes and localized surface plasmon resonance. We also found that TPPL generation is more efficient when the excitation polarization is parallel rather than perpendicular to the edge of the aluminum film. Such a counterintuitive phenomenon is attributed to the high refractive index of the GaAs substrate. We show that the polarization of TPPL from aluminum preserves the excitation polarization and is independent of the crystal orientation of the film or substrate. Our study gains insight into the optical property of aluminum nanostructures on a high-index semiconducting GaAs substrate and illustrates a practical route to implement plasmonic devices onto semiconductors for future hybrid nanodevices. PMID:25848830

  2. 17 CFR 260.11b-6 - Definition of “self-liquidating paper” in section 311(b)(6).

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... Rules Under Section 311 § 260.11b-6 Definition of “self-liquidating paper” in section 311(b)(6). The term self-liquidating paper, as used in section 311(b)(6) of the Act, means any draft, bill of exchange... simultaneously with the creation of the creditor relationship with the obligor arising from the making,...

  3. 17 CFR 260.11b-6 - Definition of “self-liquidating paper” in section 311(b)(6).

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... Rules Under Section 311 § 260.11b-6 Definition of “self-liquidating paper” in section 311(b)(6). The term self-liquidating paper, as used in section 311(b)(6) of the Act, means any draft, bill of exchange... simultaneously with the creation of the creditor relationship with the obligor arising from the making,...

  4. The growth of low band-gap InAs on (111)B GaAs substrates

    SciTech Connect

    Welser, R.E.; Guido, L.J.

    1995-10-01

    The use of low band-gap materials is of interest for a number of photovoltaic and optoelectronic applications, such as bottom cells of optimized multijunction solar cell designs, long wavelength light sources, detectors, and thermophotovoltaics. However, low band-gap materials are generally mismatched with respect to lattice constant, thermal expansion coefficient, and chemical bonding to the most appropriate commercially available substrates (Si, Ge, and GaAs). For the specific case of III-V semiconductor heteroepitaxy, one must contend with the strain induced by both lattice constant mismatch at the growth temperature and differences in the rates of mechanical deformation during the cool down cycle. Several experimental techniques have been developed to minimize the impact of these phenomena (i.e., compositional grading, strained layer superlattices, and high-temperature annealing). However, in highly strained systems such as InAs-on-GaAs, three-dimensional island formation and large defect densities (greater than or equal to 10(exp 8)/ cm(exp {minus}2)) tend to limit their applicability. In these particular cases, the surface morphology and defect density must be controlled during the initial stages of nucleation and growth. At the last SPRAT conference, the authors reported on a study of the evolution of InAs islands on (100) and (111)B GaAs substrates. Growth on the (111)B orientation exhibits a number of advantageous properties as compared to the (100) during these early stages of strained-layer epitaxy. In accordance with a developing model of nucleation and growth, the authors have deposited thin (60 A - 2500 A), fully relaxed InAs films on (111)B GaAs substrates. Although thicker InAs films are subject to the formation of twin defects common to epitaxy on the (111)B orientation, appropriate control of the growth parameters can greatly minimize their density.

  5. High Ms Fe16N2 thin film with Ag under layer on GaAs substrate

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaowei; Jiang, Yanfeng; Yang, Meiyin; Allard, Lawrence F.; Wang, Jian-Ping

    2016-05-01

    (001) textured Fe16N2 thin film with Ag under layer is successfully grown on GaAs substrate using a facing target sputtering (FTS) system. After post annealing, chemically ordered Fe16N2 phase is formed and detected by X-ray diffraction (XRD). High saturation magnetization (Ms) is measured by a vibrating sample magnetometer (VSM). In comparison with Fe16N2 with Ag under layer on MgO substrate and Fe16N2 with Fe under layer on GaAs substrate, the current layer structure shows a higher Ms value, with a magnetically softer feature in contrast to the above cases. In addition, X-ray photoelectron spectroscopy (XPS) is performed to characterize the binding energy of N atoms. To verify the role of strain that the FeN layer experiences in the above three structures, Grazing Incidence X-ray Diffraction (GIXRD) is conducted to reveal a large in-plane lattice constant due to the in-plane biaxial tensile strain.

  6. Magnetic anisotropy in ultrathin Fe films on GaAs, ZnSe, and Ge (001) substrates

    SciTech Connect

    Tivakornsasithorn, K.; Liu, X.; Li, X.; Dobrowolska, M.; Furdyna, J. K.

    2014-07-28

    We discuss magnetic anisotropy parameters of ferromagnetic body-centered cubic (bcc) Fe films grown by molecular beam epitaxy (MBE) on (001) substrates of face-centered cubic (fcc) GaAs, ZnSe, and Ge. High-quality MBE growth of these metal/semiconductor combinations is made possible by the fortuitous atomic relationship between the bcc Fe and the underlying fcc semiconductor surfaces, resulting in excellent lattice match. Magnetization measurements by superconducting quantum interference device (SQUID) indicate that the Fe films grown on (001) GaAs surfaces are characterized by a very strong uniaxial in-plane anisotropy; those grown on (001) Ge surfaces have a fully cubic anisotropy; and Fe films grown on ZnSe represent an intermediate case between the preceding two combinations. Ferromagnetic resonance measurements carried out on these three systems provide a strikingly clear quantitative picture of the anisotropy parameters, in excellent agreement with the SQUID results. Based on these results, we propose that the observed anisotropy of cubic Fe films grown in this way results from the surface reconstruction of the specific semiconductor substrate on which the Fe film is deposited. These results suggest that, by controlling surface reconstruction of the substrate during the MBE growth, one may be able to engineer the magnetic anisotropy in Fe, and possibly also in other MBE-grown ferromagnetic films.

  7. Nucleation, transition, and maturing of the self-assembled Au droplets on various type-A GaAs substrates

    SciTech Connect

    Li, Ming-Yu Sui, Mao; Kim, Eun-Soo; Lee, Jihoon

    2014-08-28

    In this study, the fabrication of self-assembled Au droplets is successfully demonstrated on various type-A GaAs substrates: (711)A, (511)A, (411)A, and (311)A. The nucleation of the self-assembled tiny Au clusters is observed at 300 °C. As an intermediate stage, corrugated Au nanostructures are clearly observed at 350 °C on various type-A GaAs surfaces, rarely witnessed on other substrates. Based on the Volmer-Weber growth mode, the dome-shaped Au droplets with excellent uniformities are successfully fabricated between 500 and 550 °C. As a function of annealing temperature, the self-assembled Au droplets show the increased dimensions including average height and diameter, compensated by the decreased average density. Depending on the substrate indices utilized, the size and density of Au droplets show clear differences throughout the whole temperature range. The results are symmetrically analyzed by using atomic force microscope images, cross-sectional line-profiles, size and density plots, height distribution histograms, and Fourier filter transform power spectra.

  8. The growth of low band-gap InAs on (111)B GaAs substrates

    NASA Technical Reports Server (NTRS)

    Welser, R. E.; Guido, L. J.

    1995-01-01

    The use of low band-gap materials is of interest for a number of photovoltaic and optoelectronic applications, such as bottom cells of optimized multijunction solar cell designs, long wavelength light sources, detectors, and thermophotovoltaics. However, low band-gap materials are generally mismatched with respect to lattice constant, thermal expansion coefficient, and chemical bonding to the most appropriate commercially available substrates (Si, Ge, and GaAs). For the specific case of III-V semiconductor heteroepitaxy, one must contend with the strain induced by both lattice constant mismatch at the growth temperature and differences in the rates of mechanical deformation during the cool down cycle. Several experimental techniques have been developed to minimize the impact of these phenomena (i.e., compositional grading, strained layer superlattices, and high-temperature annealing). However, in highly strained systems such as InAs-on-GaAs, three-dimensional island formation and large defect densities (greater than or equal to 10(exp 8)/ cm(exp -2)) tend to limit their applicability. In these particular cases, the surface morphology and defect density must be controlled during the initial stages of nucleation and growth. At the last SPRAT conference, we reported on a study of the evolution of InAs islands on (100) and (111)B GaAs substrates. Growth on the (111)B orientation exhibits a number of advantageous properties as compared to the (100) during these early stages of strained-layer epitaxy. In accordance with a developing model of nucleation and growth, we have deposited thin (60 A - 2500 A), fully relaxed InAs films on (111)B GaAs substrates. Although thicker InAs films are subject to the formation of twin defects common to epitaxy on the (111)B orientation, appropriate control of the growth parameters can greatly minimize their density. Using this knowledge base, InAs films up to 2 microns in thickness with improved morphology and structural quality have

  9. Multilayers of InGaAs Nanostructures Grown on GaAs(210) Substrates

    PubMed Central

    2010-01-01

    Multilayers of InGaAs nanostructures are grown on GaAs(210) by molecular beam epitaxy. With reducing the thickness of GaAs interlayer spacer, a transition from InGaAs quantum dashes to arrow-like nanostructures is observed by atomic force microscopy. Photoluminescence measurements reveal all the samples of different spacers with good optical properties. By adjusting the InGaAs coverage, both one-dimensional and two-dimensional lateral ordering of InGaAs/GaAs(210) nanostructures are achieved. PMID:20676193

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

    NASA Astrophysics Data System (ADS)

    Bastiman, Faebian; Küpers, Hanno; Somaschini, Claudio; Geelhaar, Lutz

    2016-03-01

    For the Ga-assisted growth of GaAs nanowires on Si(111) substrates by molecular beam epitaxy, growth temperature, As flux, and Ga flux have been systematically varied across the entire window of growth conditions that result in the formation of nanowires. A range of GaAs structures was observed, progressing from pure Ga droplets under negligible As flux through horizontal nanowires, tilted nanowires, vertical nanowires, and nanowires without droplets to crystallites as the As flux was increased. Quantitative analysis of the resulting sample morphology was performed in terms of nanowire number and volume density, number yield and volume yield of vertical nanowires, diameter, length, as well as the number and volume density of parasitic growth. The result is a growth map that comprehensively describes all nanowire and parasitic growth morphologies and hence enables growth of nanowire samples in a predictive manner. Further analysis indicates the combination of global Ga flux and growth temperature determines the total density of all objects, whereas the global As/Ga flux ratio independently determines the resultant sample morphology. Several dependencies observed here imply that all objects present on the substrate surface, i.e. both nanowires and parasitic structures, originate from Ga droplets.

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

    NASA Astrophysics Data System (ADS)

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

    2002-04-01

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

  12. The role of AsH3 partial pressure on anti-phase boundary in GaAs-on-Ge grown by MOCVD - Application to a 200 mm GaAs virtual substrate

    NASA Astrophysics Data System (ADS)

    Kohen, David; Bao, Shuyu; Lee, Kwang Hong; Lee, Kenneth Eng Kian; Tan, Chuan Seng; Yoon, Soon Fatt; Fitzgerald, Eugene A.

    2015-07-01

    We demonstrate the influence of the arsine partial pressure (p(AsH3)) on the quality of a GaAs layer grown on Ge substrate by metal organic chemical vapor deposition. The GaAs quality improves with p(AsH3) used during the 100 nm thick GaAs buffer layer. By growing a GaAs buffer layer at 630 °C with p(AsH3) of 5 mbar, we obtain a smooth GaAs layer with a root mean square roughness of 4.7 Å. This GaAs layer does not contain anti-phase boundaries. With these optimized growth parameters, we fabricate a virtual GaAs substrate on a 200 mm silicon wafer as a first step towards the integration of III-V devices on silicon.

  13. Characterization and Effect of Thermal Annealing on InAs Quantum Dots Grown by Droplet Epitaxy on GaAs(111)A Substrates.

    PubMed

    Bietti, Sergio; Esposito, Luca; Fedorov, Alexey; Ballabio, Andrea; Martinelli, Andrea; Sanguinetti, Stefano

    2015-12-01

    We report the study on formation and thermal annealing of InAs quantum dots grown by droplet epitaxy on GaAs (111)A surface. By following the changes in RHEED pattern, we found that InAs quantum dots arsenized at low temperature are lattice matched with GaAs substrate, becoming almost fully relaxed when substrate temperature is increased. Morphological characterizations performed by atomic force microscopy show that annealing process is able to change density and aspect ratio of InAs quantum dots and also to narrow size distribution. PMID:26058506

  14. Growth and properties of crystalline barium oxide on the GaAs(100) substrate

    SciTech Connect

    Yasir, M.; Dahl, J.; Lång, J.; Tuominen, M.; Punkkinen, M. P. J.; Laukkanen, P. Kokko, K.; Kuzmin, M.; Korpijärvi, V.-M.; Polojärvi, V.; Guina, M.

    2013-11-04

    Growing a crystalline oxide film on III-V semiconductor renders possible approaches to improve operation of electronics and optoelectronics heterostructures such as oxide/semiconductor junctions for transistors and window layers for solar cells. We demonstrate the growth of crystalline barium oxide (BaO) on GaAs(100) at low temperatures, even down to room temperature. Photoluminescence (PL) measurements reveal that the amount of interface defects is reduced for BaO/GaAs, compared to Al{sub 2}O{sub 3}/GaAs, suggesting that BaO is a useful buffer layer to passivate the surface of the III-V device material. PL and photoemission data show that the produced junction tolerates the post heating around 600 °C.

  15. Laser-driven growth of silver nanoplates on p-Type GaAs substrates and their surface-enhanced raman scattering activity.

    SciTech Connect

    Sun, Y.; Pelton, M.

    2009-03-20

    Contact between aqueous solutions of silver nitrate (AgNO{sub 3}) and pristine surfaces of p-type gallium arsenide (GaAs) wafers results in essentially no reaction at room temperature and in the dark. The galvanic reactions between the GaAs wafers and AgNO{sub 3} can be triggered under illumination of laser beams with power densities higher than a critical value ({approx}15 mW/cm{sup 2} for a 630 nm laser), resulting in the growth of silver (Ag) nanoplates on the GaAs surface. The density and dimensions (including both thickness and edge length) of the resulting nanoplates can be readily tuned by controlling the growth time and laser power density. The as-grown Ag nanoplates on the substrates significantly enhance Raman signals of interesting molecules and serve as a new class of promising surface-enhanced Raman scattering substrates for sensitive chemical detection.

  16. Progress toward thin-film GaAs solar cells using a single-crystal Si substrate with a Ge interlayer

    NASA Technical Reports Server (NTRS)

    Yeh, Y. C. M.; Wang, K. L.; Zwerdling, S.

    1982-01-01

    Development of a technology for fabricating light-weight, high-efficiency, radiation-resistant solar cells for space applications is reported. The approaches currently adopted are to fabricate shallow homojunction n(+)/p as well as p/n AlGaAs-heteroface GaAs solar cells by organometallic chemical vapor deposition (OM-CVD) on single-crystal Si substrates using in each case, a thin Ge epi-interlayer first grown by CVD. This approach maintains the advantages of the low specific gravity of Si as well as the high efficiency and radiation-resistant properties of the GaAs solar cell which can lead to greatly improved specific power for a solar array. The growth of single-crystal GaAs epilayers on Ge epi-interlayers on Si substrates is investigated. Related solar cell fabrication is reviewed.

  17. First principle calculation in FeCo overlayer on GaAs substrate

    SciTech Connect

    Jain, Vishal Lakshmi, N.; Jain, Vivek Kumar; K, Sijo A.; Venugopalan, K.

    2015-06-24

    In this work the first principle electronic structure calculation is reported for FeCo/GaAs thin film system to investigate the effect of orientation on the electronic structural properties. A unit cell describing FeCo layers and GaAs layers is constructed for (100), (110), (111) orientation with vacuum of 30Å to reduce dimensions. It is found that although the (110) orientation is energetically more favorable than others, the magnetic moment is quite large in (100) and (111) system compared to the (110) and is due to the total DOS variation with orientation.

  18. First principle calculation in FeCo overlayer on GaAs substrate

    NASA Astrophysics Data System (ADS)

    Jain, Vishal; Lakshmi, N.; Jain, Vivek Kumar; K, Sijo A.; Venugopalan, K.

    2015-06-01

    In this work the first principle electronic structure calculation is reported for FeCo/GaAs thin film system to investigate the effect of orientation on the electronic structural properties. A unit cell describing FeCo layers and GaAs layers is constructed for (100), (110), (111) orientation with vacuum of 30Å to reduce dimensions. It is found that although the (110) orientation is energetically more favorable than others, the magnetic moment is quite large in (100) and (111) system compared to the (110) and is due to the total DOS variation with orientation

  19. Measured and computed performance of a microstrip filter composed of semi-insulating GaAs on a fused quartz substrate

    NASA Technical Reports Server (NTRS)

    Siegel, Peter H.; Dengler, Robert J.; Oswald, John E.; Sheen, David M.; Ali, Sami M.

    1991-01-01

    The performance of a microstrip hammerhead filter that has been fabricated on an electrically thin layer of semiinsulating GaAs backed by a fused quartz substrate was measured and compared to results of a three-dimensional finite-difference time-domain (FD-TD) program used to calculate the response of the filter both with and without the GaAs layer. The program, presented by Sheen et al. (1990), discretizes the entire structure and then simulates the propagation of a Gaussian pulse through the filter. The microstrip filter is intended for applications involving ultrathin lifted-off or etched-back GaAs containing both active devices and passive microstrip circuitry backed by a much thicker mechanically rigid low-loss, low-dielectric-constant substrate. The low-pass characteristics of the hammerhead filter with the intermediate GaAs layer are compared with those of the same filter on quartz alone. Both the measured and computed data show a significant shift in cutoff frequency (about 10 percent at the 3 dB points) for a GaAs layer that is 0.007 wavelengths thick at 4 GHz.

  20. High mobility single-crystalline-like GaAs thin films on inexpensive flexible metal substrates by metal-organic chemical vapor deposition

    SciTech Connect

    Dutta, P. Rathi, M.; Gao, Y.; Yao, Y.; Selvamanickam, V.; Zheng, N.; Ahrenkiel, P.; Martinez, J.

    2014-09-01

    We demonstrate heteroepitaxial growth of single-crystalline-like n and p-type doped GaAs thin films on inexpensive, flexible, and light-weight metal foils by metal-organic chemical vapor deposition. Single-crystalline-like Ge thin film on biaxially textured templates made by ion beam assisted deposition on metal foil served as the epitaxy enabling substrate for GaAs growth. The GaAs films exhibited strong (004) preferred orientation, sharp in-plane texture, low grain misorientation, strong photoluminescence, and a defect density of ∼10{sup 7 }cm{sup −2}. Furthermore, the GaAs films exhibited hole and electron mobilities as high as 66 and 300 cm{sup 2}/V-s, respectively. High mobility single-crystalline-like GaAs thin films on inexpensive metal substrates can pave the path for roll-to-roll manufacturing of flexible III-V solar cells for the mainstream photovoltaics market.

  1. Recent Progress in MBE Growth of CdTe and HgCdTe on (211)B GaAs Substrates

    NASA Astrophysics Data System (ADS)

    Carmody, M.; Yulius, A.; Edwall, D.; Lee, D.; Piquette, E.; Jacobs, R.; Benson, D.; Stoltz, A.; Markunas, J.; Almeida, A.; Arias, J.

    2012-10-01

    Alternate substrates for molecular beam epitaxy growth of HgCdTe including Si, Ge, and GaAs have been under development for more than a decade. MBE growth of HgCdTe on GaAs substrates was pioneered by Teledyne Imaging Sensors (TIS) in the 1980s. However, recent improvements in the layer crystal quality including improvements in both the CdTe buffer layer and the HgCdTe layer growth have resulted in GaAs emerging as a strong candidate for replacement of bulk CdZnTe substrates for certain infrared imaging applications. In this paper the current state of the art in CdTe and HgCdTe MBE growth on (211)B GaAs and (211) Si at TIS is reviewed. Recent improvements in the CdTe buffer layer quality (double crystal rocking curve full-width at half-maximum ≈ 30 arcsec) with HgCdTe dislocation densities of ≤106 cm-2 are discussed and comparisons are made with historical HgCdTe on bulk CdZnTe and alternate substrate data at TIS. Material properties including the HgCdTe majority carrier mobility and dislocation density are presented as a function of the CdTe buffer layer quality.

  2. Control of threading dislocations by Al(Ga)InAs reverse-graded buffers grown on GaAs substrates

    NASA Astrophysics Data System (ADS)

    He, Yang; Sun, Yurun; Song, Yan; Zhao, Yongming; Yu, Shuzhen; Dong, Jianrong

    2016-06-01

    High-quality strain-relaxed InP layers with undulating step-graded Al(Ga)InAs buffers were grown on GaAs substrates by metal–organic chemical vapor deposition. Transmission electron microscopy, high-resolution electron microscopy (HREM), atom force microscopy, and photoluminescence were carried out to characterize the metamorphic buffers. V-shaped dislocations in [001] Al(Ga)InAs reverse-graded layers were observed by HREM and the behavior of reverse-graded layers was simulated theoretically using analytical models. Both the experimental and theoretical results indicated that the insertion of reverse-graded layers with appropriately designed thicknesses and In grading coefficients promotes the annihilation and coalescence reactions between threading dislocations and reduces threading dislocations density.

  3. Antimony incorporation in InAs quantum dots grown on GaAs substrate by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Rihani, J.; Sallet, V.; Christophe, H. J.; Oueslati, M.; Chtourou, R.

    2008-01-01

    We have grown InAs(Sb) quantum dots (QDs) on GaAs (0 0 1) substrates by molecular beam epitaxy (MBE) using two different antimony exposures ( ΦSb). Atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy were carried out to investigate the dot size evolution as function of the incorporated antimony content in InAs/GaAs QDs material. Anomalous asymmetric-band feature was observed in room temperature photoluminescence (RTPL) spectra of the investigated QD samples grown at relatively high temperature (490 °C). From the temperature-dependent PL measurements, it was found that the asymmetric-band feature is associated with the ground-states transitions from QDs with bimodal size distribution. The analysis of the pump power dependent PL spectra allows us to suggest a type II band lineup for the InAsSb/GaAs QDs materials system.

  4. Comparison of different pathways in metamorphic graded buffers on GaAs substrate: Indium incorporation with surface roughness

    NASA Astrophysics Data System (ADS)

    Kumar, Rahul; Mukhopadhyay, P.; Bag, A.; Jana, S. Kr.; Chakraborty, A.; Das, S.; Mahata, M. Kr.; Biswas, D.

    2015-01-01

    In this work, compositionally graded In(Al,Ga)As metamorphic buffers (MBs) on GaAs substrate have been grown by MBE through three different paths. A comparative study has been done to comprehend the effect of underlying MB on the constant composition InAlAs healing layer by analyzing the relaxation behaviour, composition and surface morphology of the grown structures. The compositional variation between the constant composition healing layers on top of graded MB has been observed in all three samples although the growth conditions have been kept same. Indium incorporation rate has been found to be dependent on underlying MB. By combining the result of atomic force microscopy, photo-luminescence and X-ray reciprocal space mapping, varying surface roughness has been proposed as the probable driving force behind different Indium incorporation rate.

  5. Metamorphic approach to single quantum dot emission at 1.55 {mu}m on GaAs substrate

    SciTech Connect

    Semenova, E. S.; Hostein, R.; Patriarche, G.; Mauguin, O.; Largeau, L.; Robert-Philip, I.; Beveratos, A.; Lemaitre, A.

    2008-05-15

    We report on the fabrication and the characterization of InAs quantum dots (QDs) embedded in an indium rich In{sub 0.42}Ga{sub 0.58}As metamorphic matrix grown on a GaAs substrate. Growth conditions were chosen so as to minimize the number of threading dislocations and other defects produced during the plastic relaxation. Sharp and bright lines, originating from the emission of a few isolated single quantum dots, were observed in microphotoluminescence around 1.55 {mu}m at 5 K. They exhibit, in particular, a characteristic exciton/biexciton behavior. These QDs could offer an interesting alternative to other approaches as InAs/InP QDs for the realization of single photon emitters at telecom wavelengths.

  6. Improved GaSb-based quantum well laser performance through metamorphic growth on GaAs substrates

    SciTech Connect

    Richardson, Christopher J. K. He, Lei; Apiratikul, Paveen; Siwak, Nathan P.; Leavitt, Richard P.

    2015-03-09

    The promise of the metamorphic growth paradigm is to enable design freedom of the substrate selection criteria beyond current choices that are limited by lattice matching requirements. A demonstration of this emerging degree of freedom is reported here by directly comparing identical laser structures grown both pseudomorphically on a GaSb substrate and metamorphically on a GaAs substrate. Improved thermal performance of the metamorphic laser material enables a higher output power before thermal roll-over begins. These performance gains are demonstrated in minimally processed gain-guided broad-area type-I lasers emitting close to 2-μm wavelengths and mounted p-side up. Continuous wave measurements at room temperature yield a T{sub 0} of 145 K and peak output power of 192 mW from metamorphic lasers, compared to a T{sub 0} of 96 K and peak output power of 164 mW from identical lasers grown pseudomorphically on GaSb.

  7. Characterization of reclaimed GaAs substrates and investigation of reuse for thin film InGaAlP LED epitaxial growth

    NASA Astrophysics Data System (ADS)

    Englhard, M.; Klemp, C.; Behringer, M.; Rudolph, A.; Skibitzki, O.; Zaumseil, P.; Schroeder, T.

    2016-07-01

    This study reports a method to reuse GaAs substrates with a batch process for thin film light emitting diode (TF-LED) production. The method is based on an epitaxial lift-off technique. With the developed reclaim process, it is possible to get an epi-ready GaAs surface without additional time-consuming and expensive grinding/polishing processes. The reclaim and regrowth process was investigated with a one layer epitaxial test structure. The GaAs surface was characterized by an atomic force microscope directly after the reclaim process. The crystal structure of the regrown In0.5(Ga0.45Al0.55)0.5P (Q55) layer was investigated by high resolution x-ray diffraction and scanning transmission electron microscopy. In addition, a complete TF-LED grown on reclaimed GaAs substrates was electro-optically characterized on wafer level. The crystal structure of the epitaxial layers and the performance of the TF-LED grown on reclaimed substrates are not influenced by the developed reclaim process. This process would result in reducing costs for LEDs and reducing much arsenic waste for the benefit of a green semiconductor production.

  8. Comparison of luminescent efficiency of InGaAs quantum well structures grown on Si, GaAs, Ge, and SiGe virtual substrate

    NASA Astrophysics Data System (ADS)

    Yang, V. K.; Ting, S. M.; Groenert, M. E.; Bulsara, M. T.; Currie, M. T.; Leitz, C. W.; Fitzgerald, E. A.

    2003-05-01

    In order to study the luminescent efficiency of InGaAs quantum wells on Si via SiGe interlayers, identical In0.2Ga0.8As quantum well structures with GaAs and Al0.25Ga0.75As cladding layers were grown on several substrates by an atmospheric metalorganic vapor deposition system. The substrates used include GaAs, Si, Ge, and SiGe virtual substrates. The SiGe virtual substrates were graded from Si substrates to 100% Ge content. Because of the small lattice mismatch between GaAs and Ge (0.07%), high-quality GaAs-based thin films with threading dislocation densities <3×106 cm-2 were realized on these SiGe substrates. Quantitative cathodoluminescence was used to compare the luminescent efficiency of the quantum well structure on the different substrates and cross-sectional transmission electron microscopy was used to characterize dislocation densities. Our results show that the InGaAs quantum wells grown on the GaAs substrates have the highest luminescent efficiencies due to the lowest dislocation densities. Interestingly, InGaAs quantum wells grown on the SiGe virtual substrates outperform those on Ge substrates, both in terms of luminescent efficiency and dislocation density. This difference is attributed to the variation in thermal expansion coefficient (α) and its impact on defect structure during the process cycle. The SiGe virtual substrate has a smaller α compared to a Ge substrate because of the smaller α of the Si substrate, which helps minimize compressive strain in the quantum well layer during the temperature decrease from the growth temperature. Consequently, fewer misfit dislocations are created between the quantum well and cladding interfaces. These misfits can greatly affect the luminescent efficiency since they can act as recombination sites. In general, the efficiencies of the quantum wells on the SiGe and Ge substrates were affected only by higher misfit dislocation densities, whereas the quantum wells on the Si substrate had low efficiency due to

  9. Domains of molecular beam epitaxial growth of Ga(In)AsBi on GaAs and InP substrates

    NASA Astrophysics Data System (ADS)

    Bennarndt, Wolfgang; Boehm, Gerhard; Amann, Markus-Christian

    2016-02-01

    We investigate the molecular beam epitaxial growth of GaAsBi and GaInAsBi layers on GaAs and InP-substrates as the materials are intended to serve as an active region in optoelectronic devices. The layers were grown at substrate temperatures between 250-400 °C and for all layers the growth rate was kept at a value of 1 ML/s. We show that bismuth incorporation into Ga(In)As is independent of the applied arsenic (As4) overpressure and can be allocated to different growth domains depending solely on the parameters bismuth flux and substrate temperature, respectively. The maximum bismuth content that could be incorporated was as high as 20.0% in GaAs.

  10. Droplet-Confined Alternate Pulsed Epitaxy of GaAs Nanowires on Si Substrates down to CMOS-Compatible Temperatures.

    PubMed

    Balaghi, Leila; Tauchnitz, Tina; Hübner, René; Bischoff, Lothar; Schneider, Harald; Helm, Manfred; Dimakis, Emmanouil

    2016-07-13

    We introduce droplet-confined alternate pulsed epitaxy for the self-catalyzed growth of GaAs nanowires on Si(111) substrates in the temperature range from 550 °C down to 450 °C. This unconventional growth mode is a modification of the migration-enhanced epitaxy, where alternating pulses of Ga and As4 are employed instead of a continuous supply. The enhancement of the diffusion length of Ga adatoms on the {11̅0} nanowire sidewalls allows for their targeted delivery to the Ga droplets at the top of the nanowires and, thus, for a highly directional growth along the nanowire axis even at temperatures as low as 450 °C. We demonstrate that the axial growth can be simply and abruptly interrupted at any time without the formation of any defects, whereas the growth rate can be controlled with high accuracy down to the monolayer scale, being limited only by the stochastic nature of nucleation. Taking advantage of these unique possibilities, we were able to probe and describe quantitatively the population dynamics of As inside the Ga droplets in specially designed experiments. After all, our growth method combines all necessary elements for precise growth control, in-depth investigation of the growth mechanisms and compatibility with fully processed Si-CMOS substrates. PMID:27351336

  11. Influence of phosphorus vapor ambient for InGaAsP growth on GaAs substrate

    NASA Astrophysics Data System (ADS)

    Ishikawa, Joji; Ito, Toshio; Shin-ichi Takahashi, N.; Kurita, Shoichi

    1986-12-01

    For visible-light-emitting laser diodes, InGaAsP double heterostructures have been grown on GaAs substrates using liquid-phase epitaxy. As the growth temperature is as high as about 780 °C, a large amount of phosphorus evaporates from the solutions for the cladding layers during the growth process. The phosphorus vapor disturbs the solution composition for the active layer, so that very thin and uniform active layers cannot be obtained. By using In-P-Sn solution and supplying the phosphorus partial pressure around the graphite boat, the influence of phosphorus vapor ambient for InGaAsP (λPL=805 nm) growth is confirmed. When the phosphorus partial pressure increases, the surface of epitaxial layer becomes rough and the substrate is partly etched back. From x-ray diffraction and photoluminescence spectral measurements, the composition of the grown layer is also found to be changed. As a result of increasing the flow rate of H2 gas in order to protect the solution for the active layer from phosphorus contamination, the double heterostructure wafers with the high-quality active layer can be obtained reproducibly. Thus, pulsed lasing operation at room temperature has been achieved. The lasing wavelength is 816 nm and the threshold current density is ˜4.6 kA/cm2.

  12. Large-scale and uniform preparation of pure-phase wurtzite GaAs NWs on non-crystalline substrates

    PubMed Central

    2012-01-01

    One of the challenges to prepare high-performance and uniform III-V semiconductor nanowires (NWs) is to control the crystal structure in large-scale. A mixed crystal phase is usually observed due to the small surface energy difference between the cubic zincblende (ZB) and hexagonal wurtzite (WZ) structures, especially on non-crystalline substrates. Here, utilizing Au film as thin as 0.1 nm as the catalyst, we successfully demonstrate the large-scale synthesis of pure-phase WZ GaAs NWs on amorphous SiO2/Si substrates. The obtained NWs are smooth, uniform with a high aspect ratio, and have a narrow diameter distribution of 9.5 ± 1.4 nm. The WZ structure is verified by crystallographic investigations, and the corresponding electronic bandgap is also determined to be approximately 1.62 eV by the reflectance measurement. The formation mechanism of WZ NWs is mainly attributed to the ultra-small NW diameter and the very narrow diameter distribution associated, where the WZ phase is more thermodynamically stable compared to the ZB structure. After configured as NW field-effect-transistors, a high ION/IOFF ratio of 104 − 105 is obtained, operating in the enhancement device mode. The preparation technology and good uniform performance here have illustrated a great promise for the large-scale synthesis of pure phase NWs for electronic and optical applications. PMID:23171521

  13. Study of the microstructure information of GaAs epilayers grown on silicon substrate using synchrotron radiation.

    PubMed

    Kumar, Ravi; Dixit, V K; Sinha, A K; Ganguli, Tapas; Mukherjee, C; Oak, S M; Sharma, T K

    2016-01-01

    Williamson-Hall (WH) analysis is a well established method for studying the microstructural properties of epilayers grown on foreign substrates. However, the method becomes inapplicable in specific cases where the structure factor considerations and the presence of anti-phase domains forbid the data acquisition for certain reflections in conventional high-resolution X-ray diffraction (HRXRD) measurements. Here, this limitation is overcome by exploiting the large intensity (25 µW mm(-2)) and high photon energy (15.5 keV) of the X-ray beam obtained from a synchrotron radiation source. The lateral coherence length, vertical coherence length, tilt and micro-strain of GaAs epilayers grown on Si substrate have been successfully measured using the conventional WH analysis. The microstructure information obtained from the conventional WH analysis based on the data acquired at the synchrotron radiation source is in reasonable agreement with the results obtained from atomic force microscope and surface profiler measurements. Such information cannot be obtained on a laboratory-based HRXRD system where modification of the WH method by involving a set of parallel asymmetric crystallographic planes is found to be essential. However, the information obtained from the modified WH method is along a different crystallographic orientation. PMID:26698069

  14. Distinctions of the growth and structural-spectroscopic investigations of thin AlN films grown on the GaAs substrates

    NASA Astrophysics Data System (ADS)

    Seredin, P. V.; Kashkarov, V. M.; Arsentyev, I. N.; Bondarev, A. D.; Tarasov, I. S.

    2016-08-01

    Using X-ray diffraction analysis, atomic force microscopy, IR and UV spectroscopy, the properties of thin aluminium nitride films (<200 nm) that were obtained by ion-plasma reactive sputtering on GaAs substrates with different orientations were studied. The films of aluminium nitride can have a refractive index within the range of 1.6-4.0 for the wavelength band around ~250 nm and an optical band-gap of ~5 eV. It was shown that the morphology, surface composition and optical functional characteristics of AlN/GaAs heterophase systems can be controlled owing to the use of misoriented GaAs substrates as well choice of the technological parameters used for the film growth.

  15. Formation of GaAs and Ga1-xAlxAs (0 ≤ x ≤ 0.3) layers on GaAs (111)A substrate by organometallic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Larkin, S.; Avksentyev, A.; Vakiv, M.; Krukovsky, R.; Kost, Y.; Mykhashchuk, Y.; Krukovsky, S.; Saldan, I.

    2015-09-01

    The GaAs and Ga1-xAlxAs (0 ≤ x ≤ 0.3) epitaxial growth on GaAs (111)A substrate was carried out by organometallic vapor phase epitaxy at total pressure ˜70 Torr. The regime of quantitative modulation of trimethyl gallium, Ga(CH3)3, gas flow was applied to optimize the atomic ratio between AIII and BV, while the tangential and normal parameters of the growth rate were comparable. Deposited GaAs and Ga1-xAlxAs (0 ≤ x ≤ 0.3) layers with crystallographic orientation of (111)A were obtained at ˜0.1-0.2 Torr of arsine, AsH3, pressure and low crystallization temperature ˜570-620 °C. Proposed optimization of the BV/AIII relationship and reaction conditions resulted in a smooth surface of the deposited layers. Using the technological approach, a si-GaAs/n-GaAs:Si/p-GaAlAs:Zn/p+-GaAs:Zn hetero-structure was successfully synthesized. Structural and electrical properties of the prepared epitaxial structure were studied by high-resolution x-ray diffraction and electrochemical capacitance-voltage profiling. Obtained experimental results confirmed excellent crystal and interfacial quality as well as steep transitions in charge carrier concentration through the deposited layers.

  16. Preliminary design of betavoltaic battery using Co-60 and Pm-147 with GaAs substrate

    NASA Astrophysics Data System (ADS)

    Waris, A.; Kusumawati, Y.; Alfarobi, A. S.; Aji, I. K.; Basar, K.

    2016-03-01

    Battery is very important for the present daily life, especially for portable devices. The longer utilization time the better performance of battery. Betavoltaic battery is a device that converts energy from beta decays of radioactive nuclide into electric current. One of merits of the later battery is the life time that can be more than ten years without recharging. To develop the betavoltaic battery for energy source of portable devices we have performed a preliminary simulation design of betavoltaic battery using Pm-147 and Co-60 a beta emitter radionuclides with n-GaAs substrate. From the results we found that the combination of Pm-147 with n-GaAs substrate results in 9.0% of efficiency and higher output current compared to references.

  17. Integration of GaAs, GaN, and Si-CMOS on a common 200 mm Si substrate through multilayer transfer process

    NASA Astrophysics Data System (ADS)

    Lee, Kwang Hong; Bao, Shuyu; Zhang, Li; Kohen, David; Fitzgerald, Eugene; Tan, Chuan Seng

    2016-08-01

    The integration of III–V semiconductors (e.g., GaAs and GaN) and silicon-on-insulator (SOI)-CMOS on a 200 mm Si substrate is demonstrated. The SOI-CMOS donor wafer is temporarily bonded on a Si handle wafer and thinned down. A second GaAs/Ge/Si substrate is then bonded to the SOI-CMOS-containing handle wafer. After that, the Si from the GaAs/Ge/Si substrate is removed. The GaN/Si substrate is then bonded to the SOI–GaAs/Ge-containing handle wafer. Finally, the handle wafer is released to realize the SOI–GaAs/Ge/GaN/Si hybrid structure on a Si substrate. By this method, the functionalities of the materials used can be combined on a single Si platform.

  18. Metastable bcc phase formation in 3d ferromagnetic transition metal thin films sputter-deposited on GaAs(100) substrates

    SciTech Connect

    Minakawa, Shigeyuki Ohtake, Mitsuru; Futamoto, Masaaki; Kirino, Fumiyoshi; Inaba, Nobuyuki

    2015-05-07

    Co{sub 100−x}Fe{sub x} and Ni{sub 100−y}Fe{sub y} (at. %, x = 0–30, y = 0–60) films of 10 nm thickness are prepared on GaAs(100) substrates at room temperature by using a radio-frequency magnetron sputtering system. The detailed growth behavior is investigated by in-situ reflection high-energy electron diffraction. (100)-oriented Co and Ni single-crystals with metastable bcc structure are formed in the early stage of film growth, where the metastable structure is stabilized through hetero-epitaxial growth. With increasing the thickness up to 2 nm, the Co and the Ni films start to transform into more stable hcp and fcc structures through atomic displacements parallel to bcc(110) slide planes, respectively. The stability of bcc phase is improved by adding a small volume of Fe atoms into a Co film. The critical thickness of bcc phase formation is thicker than 10 nm for Co{sub 100−x}Fe{sub x} films with x ≥ 10. On the contrary, the stability of bcc phase for Ni-Fe system is less than that for Co-Fe system. The critical thicknesses for Ni{sub 100−y}Fe{sub y} films with y = 20, 40, and 60 are 1, 3, and 5 nm, respectively. The Co{sub 100−x}Fe{sub x} single-crystal films with metastable bcc structure formed on GaAs(100) substrates show in-plane uniaxial magnetic anisotropies with the easy direction along GaAs[011], similar to the case of Fe film epitaxially grown on GaAs(100) substrate. A Co{sub 100−x}Fe{sub x} film with higher Fe content shows a higher saturation magnetization and a lower coercivity.

  19. Impact of vicinal GaAs(001) substrates on Bi incorporation and photoluminescence in molecular beam epitaxy-grown GaAs1-xBix

    NASA Astrophysics Data System (ADS)

    Li, Jincheng; Collar, Kristen; Jiao, Wenyuan; Kong, Wei; Kuech, Thomas F.; Babcock, Susan E.; Brown, April

    2016-06-01

    The controlled incorporation of Bi into GaAs is a key challenge to synthesizing dilute Bi materials. This work reveals the importance of the surface step density and direction on Bi incorporation. Steps in the [110 ] direction are demonstrated to enhance Bi incorporation, but at the cost of reduced photoluminescence intensity at a red-shifted peak position, while steps in the [1 ¯ 10 ] direction yield the opposite behavior. A qualitative model based on the competitive incorporation of As and Bi at different step edges is used to rationalize the observed differences in Bi incorporation.

  20. Growth of InSb on GaAs Substrates Using InAlSb Buffers for Magnetic Field Sensor Applications

    SciTech Connect

    BIEFELD,ROBERT M.; PHILLIPS,J.D.

    1999-12-08

    We report the growth of InSb on GaAs using InAlSb buffers of high interest for magnetic field sensors. We have grown samples by metal-organic chemical vapor deposition consisting of {approx}0.55{micro}m thick InSb layers with resistive InAlSb buffers on GaAs substrates with measured electron mobilities of {approx}40,000 cm{sup 2}/V.s. We have investigated the In{sub 1-x}Al{sub x}Sb buffers for compositions x {le} 0.22 and have found that the best results are obtained near x = 0.12 due to the tradeoff of buffer layer bandgap and lattice mismatch.

  1. High-resolution transmission electron microscopy study on the growth modes of GaSb islands grown on a semi-insulating GaAs (001) substrate

    NASA Astrophysics Data System (ADS)

    Kim, Y. H.; Lee, J. Y.; Noh, Y. G.; Kim, M. D.; Oh, J. E.

    2007-06-01

    The initial growth behaviors of GaSb on a GaAs substrate were studied using a high-resolution electron microscope (HRTEM). Four types of GaSb islands were observed by HRTEM. HRTEM micrographs showed that strain relaxation mechanisms were different in the four types of islands. Although 90° misfit dislocations relieve misfit strain in the islands, additional mechanisms are required to relax the remaining strain. The existence of elastic deformation near the surface related to dislocations and intermediate layers between GaSb and GaAs were demonstrated in island growths. Finally, the generation of planar defects to relieve strain was observed in a specific GaSb growth.

  2. Monitoring of ZnCdSe layer properties by in situ x-ray diffraction during heteroepitaxy on (001)GaAs substrates

    SciTech Connect

    Benkert, A.; Schumacher, C.; Brunner, K.; Neder, R. B.

    2007-04-16

    The authors demonstrate in situ high-resolution x-ray diffraction applied during heteroepitaxy on (001)GaAs for instant layer characterization. The current thickness, composition, strain, and relaxation dynamics of pseudomorphic layers are precisely determined from q{sub z} scans at the (113) reflection measured at a molecular beam epitaxy chamber with a conventional x-ray tube in static geometry. A simple fitting routine enables real-time in situ x-ray diffraction analysis of layers as thin as 20 nm. Critical thicknesses for dislocation formation and plastic relaxation of ZnCdSe layers versus Cd content are determined. The strong influence of substrate temperature on heteroepitaxial nucleation process, deposition rate, composition, and strain relaxation dynamics of ZnCdSe on GaAs is also studied.

  3. Spin-Resolved Electronic Structure of Ultrathin Epitaxial Fe Films on Vicinal and Singular GaAs(100) Substrates

    SciTech Connect

    Morton, S A; Waddill, G D; Spangenberg, M; Seddon, E A; Neal, J; Shen, T; Tobin, J G

    2003-03-10

    Recently there has been considerable interest in the study of spin injection at ferromagnetic semiconductor heterojunctions and ferromagnetic metal--semiconductor contacts. Studies of ntype semiconductors have demonstrated spin-coherent transport over large distances5 and the persistence of spin coherence over a sizeable time scale. Clearly such investigations have been stimulated by the potential of the development of ''spintronics'', electronic devices utilizing the information of the electron spin states. To understand and improve the magnetic properties of ultrathin Fe films on GaAs has been the aim of many research groups over recent years. The interest in this system has both technological and fundamental scientific motivations. Technologically, Fe on GaAs may serve to realize spin electronic devices. From a fundamental science point of view, Fe on GaAs serves as a prototype for studies of the interplay between the crystalline structure and morphology of an ultrathin film, its electronic structure and the long range magnetic order it exhibits. Furthermore, it is well known that an oxidized Cs layer on GaAs substantially alters the work-function of the GaAs surface, which plays a very important role in the application of GaAs as a spin polarized electron source.

  4. Study of the formation mechanism of InGaAs pyramidal layers on GaAs(100) patterned substrates by LPE

    NASA Astrophysics Data System (ADS)

    Balakrishnan, K.; Iida, S.; Kumagawa, M.; Hayakawa, Y.

    2002-07-01

    A study of the liquid phase epitaxial growth of InxGa1-xAs (x = 0.06) layers on different types of patterned GaAs(100) substrates has been carried out. The dependence of growth morphology on the stripe orientation of the star patterned trench substrate has been observed. Pyramid layers were grown in the stripes oriented along the <001> direction. Broken tent structures formed along the <012> direction. Pyramidal structured layers looked to grow faster than the tent-like and broken tent-like structures. In order to analyse the hollow pyramid structure growth in detail, they were grown on circular trench substrates for different periods of time. Hollow pyramidal structures of InGaAs have been grown on circular patterned trench substrates. Effective defect filtration can be realized in this kind of growth of hollow pyramidal structures. The formation mechanism of the hollow pyramid structured layers has been studied in detail.

  5. Substrate temperature dependence of GaAs, GaInAs, and GaAlAs growth rates in metalorganic molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kobayashi, N.; Benchimol, J. L.; Alexandre, F.; Gao, Y.

    1987-12-01

    The substrate temperature (Ts) dependence (350-700 °C) of GaAs and Ga1-y InyAs growth rates was investigated in metalorganic molecular beam epitaxy (MOMBE), using triethylgallium (TEG), trimethylindium (TMI), and solid arsenic (As4) sources. For GaAs growth, four distinct Ts dependent regions are observed, including a weak desorption process (500-650 °C) characteristic of MOMBE, preceding atomic Ga desorption (Ts >650 °C). When adding a TMI flux to grow Ga1-yInyAs, this desorption process was much enhanced up to 550 °C, and then decreased above 550 °C when the In desorption phenomenon takes place. Correlatively, the In alloy composition peaks at 550 °C. The same dependence was observed in Ga1-yInyAs growth using solid In and TEG sources. However, in Ga1-xAlxAs growth using solid Al or triethylaluminum (TEA) and TEG sources, the weak desorption observed in GaAs MOMBE was strongly minimized. From these results, possible growth mechanisms are discussed.

  6. Structural and band alignment properties of Al2O3 on epitaxial Ge grown on (100), (110), and (111)A GaAs substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hudait, M. K.; Zhu, Y.; Maurya, D.; Priya, S.; Patra, P. K.; Ma, A. W. K.; Aphale, A.; Macwan, I.

    2013-04-01

    Structural and band alignment properties of atomic layer Al2O3 oxide film deposited on crystallographically oriented epitaxial Ge grown in-situ on (100), (110), and (111)A GaAs substrates using two separate molecular beam epitaxy chambers were investigated using cross-sectional transmission microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). High-resolution triple axis x-ray measurement demonstrated pseudomorphic and high-quality Ge epitaxial layer on crystallographically oriented GaAs substrates. The cross-sectional TEM exhibited a sharp interface between the Ge epilayer and each orientation of the GaAs substrate as well as the Al2O3 film and the Ge epilayer. The extracted valence band offset, ΔEv, values of Al2O3 relative to (100), (110), and (111) Ge orientations using XPS measurement were 3.17 eV, 3.34 eV, and 3.10 eV, respectively. Using XPS data, variations in ΔEv related to the crystallographic orientation were ΔEV(110)Ge>ΔEV(100)Ge≥ΔEV(111)Ge and the conduction band offset, ΔEc, related to the crystallographic orientation was ΔEc(111)Ge>ΔEc(110)Ge>ΔEc(100)Ge using the measured ΔEv, bandgap of Al2O3 in each orientation, and well-known Ge bandgap of 0.67 eV. These band offset parameters are important for future application of Ge-based p- and n-channel metal-oxide field-effect transistor design.

  7. Long-wavelength light emission from InAs quantum dots covered by GaAsSb grown on GaAs substrates

    NASA Astrophysics Data System (ADS)

    Akahane, Kouichi; Yamamoto, Naokatsu; Ohtani, Naoki

    2004-03-01

    We fabricated InAs quantum dots (QDs) with a GaAsSb strain-reducing layer (SRL) on a GaAs(0 0 1) substrate. The wavelength of emission from InAs QD is shown to be controllable by changing the composition and thickness of the SRL. An increase in photoluminescence intensity with increasing compositions of Sb and thickness of the GaAsSb SRL is also seen. The efficiency of radiative recombination was improved under both conditions because the InAs/GaAsSb/GaAs hetero-interface band structure more effectively suppressed carrier escape from the InAs QDs.

  8. 2 {mu}m laterally coupled distributed-feedback GaSb-based metamorphic laser grown on a GaAs substrate

    SciTech Connect

    Apiratikul, P.; He, L.; Richardson, C. J. K.

    2013-06-10

    We report a type-I GaSb-based laterally coupled distributed-feedback (DFB) laser grown on a GaAs substrate operating continuous wave at room temperature. The laser structure was designed to operate near a wavelength of 2 {mu}m and was grown metamorphically with solid-source molecular beam epitaxy. The device was fabricated using a 6th-order deep etch grating structure as part of the sidewalls of the narrow ridge waveguide. The DFB laser emits total output power of up to 40 mW in a single longitudinal mode operation at a heat-sink temperature of 20 Degree-Sign C.

  9. Kinetic and interface studies for MOCVD CdTe and HgCdTe epilayers grown on GaAs substrates

    NASA Astrophysics Data System (ADS)

    Rui-wu, Peng; Fei, Xu; Yong-qing, Ding

    1991-12-01

    The growth rates of CdTe and CMT on GaAs and on CdTe/GaAs substrates were studied as a function of temperature and gas composition. A Langmuir-Hinshelwood model for surface reaction control region is proposed. The CdTe/GaAs interface was examined by X-ray double crystal diffraction, laser Raman spectroscopy and transmission electron microscopy (TEM). A defect layer was observed at CdTe/GaAs interface. The relationship between the interface qualities and electrical properties of the CMT overlayers was discussed.

  10. Direct growth of AlGaAs/GaAs single quantum wells on GaAs substrates cleaned by Electron Cyclotron Resonance (ECR) hydrogen plasma

    NASA Astrophysics Data System (ADS)

    Kondo, Naoto; Nanishi, Yasushi; Fujimoto, Masatomo

    1994-01-01

    Direct growth of AlGaAs/GaAs single quantum wells (SQWs) on GaAs substrates without growing buffer layers is carried out by using electron cyclotron resonance (ECR) hydrogen plasma cleaning. SQW structures are successively grown by molecular beam epitaxy (MBE) after the cleaning process without breaking the vacuum. Photoluminescence shows intense and narrow spectra, in clear contrast to that of conventional thermal cleaning. Atomic force microscopy (AFM) and secondary ion mass spectroscopy (SIMS) analyses show that surface roughness and interface impurity accumulations are significantly reduced as well. A flat and clean surface obtained by plasma cleaning improves the quality of grown layers.

  11. Direct Growth of AlGaAs/GaAs Single Quantum Wells on GaAs Substrates Cleaned by Electron Cyclotron Resonance (ECR) Hydrogen Plasma

    NASA Astrophysics Data System (ADS)

    Kondo, Naoto; Nanishi, Yasushi; Fujimoto, Masatomo

    1994-01-01

    Direct growth of AlGaAs/GaAs single quantum wells (SQWs) on GaAs substrates without growing buffer layers is carried out by using electron cyclotron resonance (ECR) hydrogen plasma cleaning. SQW structures are successively grown by molecular beam expitaxy (MBE) after the cleaning process without breaking the vacuum. Photoluminescence shows intense and narrow spectra, in clear contrast to that of conventional thermal cleaning. Atomic force microscopy (AFM) and secondary ion mass spectroscopy (SIMS) analyses show that surface roughness and interface impurity accumulations are significantly reduced as well. A flat and clean surface obtained by plasma cleaning improves the quality of grown layers.

  12. 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.

  13. Effect of hydrostatic pressure on degradation of CdTe/CdMgTeheterostructures grown by molecular beam epitaxy on GaAs substrates

    SciTech Connect

    Wasik, D.; Baj, M.; Siwiec-Matuszyk, J.; Gronkowski, J.; Jasinski, J.; Karczewski, G.

    2001-04-18

    We have shown that external hydrostatic pressure leads to the creation of structural defects, mainly in the vicinity of the II-VI/GaAs interface in the CdTe/Cd{sub 1-x}Mg{sub x}Te heterostructures grown by the molecular beam epitaxy method on GaAs substrates. These defects propagating across the epilayer cause permanent damage to the samples from the point of view of their electrical properties. In contrast, photoluminescence spectra are only weakly influenced by pressure. Our results shed light on the degradation process observed even without pressure in II-VI-based heterostructures.

  14. Quantum Dots: Growth of InAs Quantum Dots on GaAs (511)A Substrates: The Competition between Thermal Dynamics and Kinetics (Small 31/2016).

    PubMed

    Wen, Lei; Gao, Fangliang; Zhang, Shuguang; Li, Guoqiang

    2016-08-01

    On page 4277, G. Li and co-workers aim to promote III-V compound semiconductors and devices for a broad range of applications with various technologies. The growth process of InAs quantum dots on GaAs (511)A substrates is systematically studied. By carefully controlling the competition between growth thermal-dynamics and kinetics, InAs quantum dots with high size uniformity are prepared, which are highly desirable for the fabrication of high-efficiency solar cells. PMID:27510365

  15. Two orders of magnitude reduction in the temperature dependent resistivity of Ga1-xMnxAs grown on (6 3 1) GaAs insulating substrates

    NASA Astrophysics Data System (ADS)

    Rangel-Kuopp, Victor-Tapio; Martinez-Velis, Isaac; Gallardo-Hernandez, Salvador; Lopez-Lopez, Maximo

    2013-12-01

    The temperature dependent van der Pauw (T-Pauw) technique was used to investigate the resistivity of three Ga1-xMnxAs layers grown on (6 3 1) GaAs semi-insulating substrates. The samples had Mn concentration of 3.52×l020 cm-3, 5.05×1020 cm-3 and 1.12×l021 cm-3, corresponding to Mn cell effusion temperature TMn of 700 °C, 715 °C and 745 °C, respectively. They were compared to samples grown under the same conditions but on (0 0 1) GaAs semi-insulating substrates. For the sample grown at TMn=700 °C on a (6 3 1) substrate, a two orders of magnitude decrease in the resistivity is observed, when compared with the sample grown on a (0 0 1) substrate. For the sample grown at TMn=715 °C the decrease is approximately four times, while for the sample grown at TMn=745 °C the decrease is approximately forty times. We plotted the resistivities as a function of temperature in Arrhenius plots, where we extracted two activation energies, the smallest one between 6 and 11 meV, and the largest one between 25 and 183 meV. Both activation energies increased as TMn increased. These results are in agreement with SIMS analysis where we observed that manganese concentration in the (6 3 1) orientation growth is around two order of magnitude larger than in the samples grown in the (0 0 1) orientation substrate.

  16. Growth of InAs Quantum Dots on GaAs (511)A Substrates: The Competition between Thermal Dynamics and Kinetics.

    PubMed

    Wen, Lei; Gao, Fangliang; Zhang, Shuguang; Li, Guoqiang

    2016-08-01

    The growth process of InAs quantum dots grown on GaAs (511)A substrates has been studied by atomic force microscopy. According to the atomic force microscopy studies for quantum dots grown with varying InAs coverage, a noncoherent nucleation of quantum dots is observed. Moreover, due to the long migration length of In atoms, the Ostwald ripening process is aggravated, resulting in the bad uniformity of InAs quantum dots on GaAs (511)A. In order to improve the uniformity of nucleation, the growth rate is increased. By studying the effects of increased growth rates on the growth of InAs quantum dots, it is found that the uniformity of InAs quantum dots is greatly improved as the growth rates increase to 0.14 ML s(-1) . However, as the growth rates increase further, the uniformity of InAs quantum dots becomes dual-mode, which can be attributed to the competition between Ostwald ripening and strain relaxation processes. The results in this work provide insights regarding the competition between thermal dynamical barriers and the growth kinetics in the growth of InAs quantum dots, and give guidance to improve the size uniformity of InAs quantum dots on (N11)A substrates. PMID:27348495

  17. Effect of growth temperature and GaAs substrate misorientation on the morphology of InAsBi nanoislands grown by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Boussaha, R.; Fitouri, H.; Rebey, A.; Jani, B. El

    2014-02-01

    The structural properties of InAsBi nanoislands grown on semi insulating GaAs by atmospheric pressure metalorganic vapor phase epitaxy, using trimethyl indium, trimethyl bismuth, and arsine as precursor sources have been studied. The influence of growth temperature and substrate misorientation on the surface morphologies of these nanostructures have been controlled by means of atomic force microscopy. The results show InAsBi islands formation on the studied samples. The density, shape, size and the size dispersion of these islands vary greatly with growth temperature. So, below 400 °C island density increases with increasing growth temperature and accompanied by appearance of ridges. Increasing temperature over 400 °C induces a decrease in the island density and enlargement of sizes. In addition, samples grown on 10° misoriented substrates exhibit a clearly ridge on the surface.

  18. Molecular beam epitaxy and characterizations of PbTe grown on GaAs(211) substrates using CdTe/ZnTe buffers

    NASA Astrophysics Data System (ADS)

    Shu, Tianyu; Lu, Pengqi; Zhang, Bingpo; Wang, Miao; Chen, Lu; Fu, Xiangliang; Xu, Gangyi; Wu, Huizhen

    2015-06-01

    Narrow-gap semiconductor PbTe has exhibited versatility in both mid-infrared optoelelctronics and thermoelectrics. However, the absence of commercially obtainable PbTe crystal substrates limits its wide applications. In this paper, heteroepitaxy of high-quality PbTe crystal on GaAs(211) using CdTe/ZnTe buffers by molecular beam epitaxy is presented for the first time. Optimal growth parameters have been obtained by both in-situ and ex-situ characterizations. In-situ reflection high-energy electron diffraction observed a transition of growth mode from 2D to 3D, which is in agreement with the results of atomic force microscope and scanning electron microscope characterizations. High resolution X-ray diffraction revealed that the growth of PbTe crystal is along [531] direction which is different from the [211] substrate orientation. Multiple phonon modes related to PbTe were observed by Raman scattering while mid-infrared light emission from epitaxial PbTe is observed at a peak of 3.5 μm by photoluminescence. Different from PbTe grown on BaF2(111), n-type conductivity with electron densities of ~5×1017 cm-3 and mobilities of 675 cm2/V s at room temperature and 4300 cm2/V s at 2 K is observed. The high quality PbTe grown on GaAs(211) substrates using CdTe/ZnTe buffers renders promising applications in both optoelectronics and thermoelectrics.

  19. Six-fold hexagonal symmetric nanostructures with various periodic shapes on GaAs substrates for efficient antireflection and hydrophobic properties.

    PubMed

    Leem, Jung Woo; Song, Young Min; Yu, Jae Su

    2011-12-01

    We fabricated various periodic nanostructures with a six-fold hexagonal symmetry on gallium arsenide (GaAs) substrates using simple process steps, together with a theoretical analysis of their antireflective properties. Elliptical photoresist (PR) nanopillars, which are inevitably generated by the asymmetric intensity distribution of the laser interference, were converted to rounded lens-like patterns by a thermal reflow process without any additional complex optic systems, thus leading to an exact six-fold hexagonal symmetry. Various shaped periodic nanostructures including nanorods, cones, truncated cones, and even parabolic patterns were obtained under different etching conditions using the rounded lens-like PR patterns formed by the reflow process. For the parabolic structure, the calculated lowest average reflectance of ∼ 2.3% was obtained. To achieve better antireflection characteristics, an aluminum-doped zinc oxide (AZO) film was deposited on the GaAs parabolas, which forms an AZO/GaAs parabolic nanostructure. The structure exhibited a low average reflectance of ∼ 1.2% over a wide wavelength region of 350-1800 nm and a hydrophobic surface with a water contact angle of θ(c) ∼ 115°. The calculated reflectances were reasonably consistent with the measured results. PMID:22071365

  20. Implanted Si atoms shifting between Ga sites and As sites by thermal stress in conductive-layer GaAs crystals on semi-insulating substrates

    NASA Astrophysics Data System (ADS)

    Saito, Yasuyuki

    1992-04-01

    Large (0.8 V order) discrepancies of threshold voltage Vth between the predicted Vth values by the Lindhard-Scharff-Schio/tt Gaussian approximate calculation and the Vth of the tungsten nitride (WNx) self-alignment (SA) gate GaAs metal-semiconductor field-effect transistors (MESFETs) were observed. These discrepancies were confirmed by the comparison of the Vth of the WNx-SA-gate MESFETs and the Vth of the (N+: high carrier concentration layers self-aligned of source-drain electrodes)-less conventional MESFETs on 2-in.-diam semi-insulating substrates from liquid-encapsulated-Czochralski-technique-grown <100> boules. The discrepancy was also analyzed by the capacitance-voltage (C-V) measurement of large-diameter (440 μm) Schottky diodes which were built into the MESFET arrays. It was found that for obtained SA-process carrier depth profiles (Si, 150 keV, 3×1012 cm-2) the carrier concentration at a depth of 0.25 μm decreased from 5.3×1016 to 2.0×1016 cm-3, but, on the other hand, the peak carrier concentration slightly decreased from 12.8×1016 to 12.4×1016 cm-3. By the calculation for Vth on the basis of the actual C-V carrier depth profiles, it was found that the carrier concentration decrease was comparable to the Vth variation (0.8 V). Furthermore, the Vth variation of the shallow channel implantation (50 keV) was comparable to that of the deep channel implantation (150 keV). As a result of the experiment and analysis, it was found that the large Vth variation for the SA N+ process was caused by reoccupation (Ga sites to As sites) of implanted Si atoms in the channel active-layer crystal by tensile stress formed by the thermal-expansion coefficient difference between chemical-vapor deposition (CVD) phosphosilicate glass (or CVD SiO2) film and (100) GaAs substrate crystal. The Si atom reoccupation quantity was, for the first time, explained by the Si atom compensation ratio equation as a function of the bond length (Si-As and Si-Ga) variation, an equation

  1. Growth and magnetic properties of zb-type MnAs films on GaAs substrates by high-temperature MBE

    NASA Astrophysics Data System (ADS)

    Kubo, K.; Kato, Y.; Kanai, K.; Ohta, J.; Fujioka, H.; Oshima, M.

    2008-10-01

    We have grown MnAs films on GaAs(1 1 1)B substrates by high-temperature molecular beam epitaxy (MBE) and have investigated their crystal structures and magnetic properties. X-ray diffraction (XRD) and grazing incidence X-ray diffraction (GIXD) results showed that two kinds of zb-type MnAs films with lattice constants of 5.73 and 5.96 Å were grown. The zb-type MnAs films show higher Curie temperature than 350 K and larger magnetization than the reported zb-type MnAs. At the initial stage of MnAs growth, Ga 1-xMn xAs was grown and this Ga 1-xMn xAs layer might play an important role of a buffer layer to enable the zb-MnAs growth.

  2. Catalyst-free growth of InP nanowires on patterned Si (001) substrate by using GaAs buffer layer

    NASA Astrophysics Data System (ADS)

    Li, Shiyan; Zhou, Xuliang; Kong, Xiangting; Li, Mengke; Mi, Junping; Pan, Jiaoqing

    2016-04-01

    The catalyst-free metal organic vapor phase epitaxial growth of InP nanowires on silicon (001) substrate is investigated using selectively grown GaAs buffer layers in V-shaped trenches. A yield up to 70% of nanowires is self-aligned in uncommon <112> directions under the optimized growth conditions. The evolution mechanism of self-aligned <112> directions for nanowires is discussed and demonstrated. Using this growth method, we can achieve branched and direction switched InP nanowires by varying the V/III ratio in situ. The structure of the nanowires is characterized by scanning electron microscope and transmission electron microscopy measurements. The crystal structure of the InP nanowires is stacking-faults-free wurtzite with its c axis perpendicular to the nanowire axis.

  3. On the optimization of asymmetric barrier layers in InAlGaAs/AlGaAs laser heterostructures on GaAs substrates

    SciTech Connect

    Zhukov, A. E.; Asryan, L. V.; Semenova, E. S.; Zubov, F. I.; Kryzhanovskaya, N. V.; Maximov, M. V.

    2015-07-15

    Band offsets at the heterointerface are calculated for various combinations of InAlGaAs/AlGaAs heteropairs that can be synthesized on GaAs substrates in the layer-by-layer pseudomorphic growth mode. Patterns which make it possible to obtain an asymmetric barrier layer providing the almost obstruction-free transport of holes and the highest possible barrier height for electrons are found. The optimal compositions of both compounds (In{sup 0.232}Al{sup 0.594}Ga{sup 0.174}As/Al{sup 0.355}Ga{sup 0.645}As) at which the flux of electrons across the barrier is at a minimum are determined with consideration for the critical thickness of the indium-containing quaternary solid solution.

  4. Longer than 1.9 μm photoluminescence emission from InAs quantum structure on GaAs (001) substrate

    SciTech Connect

    Liu, Ke; Ma, Wenquan Huang, Jianliang; Zhang, Yanhua; Cao, Yulian; Huang, Wenjun; Luo, Shuai; Yang, Tao

    2015-07-27

    We report on photoluminescence (PL) emission with long wavelength for quantum structure by the sub-monolayer (SML) growth technique on GaAs (001) substrate. It is found that the PL emission wavelength can be controlled by controlling the SML InAs deposition amount. At 12 K, the PL peak position of the grown samples changes from about 1.66 to 1.78 μm. At 120 K, the PL emission of a sample reaches 1.91 μm. The physical mechanism responsible for the measured long wavelength PL emission may be related to strong In segregation and intermixing effects occurred in the structure grown by SML growth technique.

  5. Polarity driven simultaneous growth of free-standing and lateral GaAsP epitaxial nanowires on GaAs (001) substrate

    NASA Astrophysics Data System (ADS)

    Sun, Wen; Guo, Yanan; Xu, Hongyi; Gao, Qiang; Hoe Tan, Hark; Jagadish, Chennupati; Zou, Jin

    2013-11-01

    Simultaneous growth of ⟨111⟩B free-standing and ±[110] lateral GaAsP epitaxial nanowires on GaAs (001) substrates were observed and investigated by electron microscopy and crystallographic analysis. It was found that the growth of both free-standing and lateral ternary nanowires via Au catalysts was driven by the fact that Au catalysts prefer to maintain low-energy {111}B interfaces with surrounding GaAs(P) materials: in the case of free-standing nanowires, Au catalysts maintain {111}B interfaces with their underlying GaAsP nanowires; while in the case of lateral nanowires, each Au catalyst remain their side {111}B interfaces with the surrounding GaAs(P) material during the lateral nanowire growth.

  6. Photoluminescence characteristics of ZnTe bulk crystal and ZnTe epilayer grown on GaAs substrate by MOVPE

    NASA Astrophysics Data System (ADS)

    Lü, Hai-Yan; Mu, Qi; Zhang, Lei; Lü, Yuan-Jie; Ji, Zi-Wu; Feng, Zhi-Hong; Xu, Xian-Gang; Guo, Qi-Xin

    2015-12-01

    Excitation power and temperature-dependent photoluminescence (PL) spectra of the ZnTe epilayer grown on (100) GaAs substrate and ZnTe bulk crystal are investigated. The measurement results show that both the structures are of good structural quality due to their sharp bound excitonic emissions and absence of the deep level structural defect-related emissions. Furthermore, in contrast to the ZnTe bulk crystal, although excitonic emissions for the ZnTe epilayer are somewhat weak, perhaps due to As atoms diffusing from the GaAs substrate into the ZnTe epilayer and/or because of the strain-induced degradation of the crystalline quality of the ZnTe epilayer, neither the donor-acceptor pair (DAP) nor conduction band-acceptor (e-A) emissions are observed in the ZnTe epilayer. This indicates that by further optimizing the growth process it is possible to obtain a high-crystalline quality ZnTe heteroepitaxial layer that is comparable to the ZnTe bulk crystal. Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20120131110006), the Key Science and Technology Program of Shandong Province, China (Grant No. 2013GGX10221), the Key Laboratory of Functional Crystal Materials and Device (Shandong University, Ministry of Education), China (Grant No. JG1401), the National Natural Science Foundation of China (Grant No. 61306113), the Major Research Plan of the National Natural Science Foundation of China (Grant No. 91433112), and the Partnership Project for Fundamental Technology Researches of the Ministry of Education, Culture, Sports, Science and Technology, Japan.

  7. A bow-tie photoconductive antenna using a low-temperature-grown GaAs thin-film on a silicon substrate for terahertz wave generation and detection

    NASA Astrophysics Data System (ADS)

    Darío Velásquez Ríos, Rubén; Bikorimana, Siméon; Ummy, Muhammad Ali; Dorsinville, Roger; Seo, Sang-Woo

    2015-12-01

    This paper presents heterogeneously integrated bow-tie emitter-detector photoconductive antennas (PCAs) based on low-temperature grown-gallium arsenide (LTG-GaAs) thin-film devices on silicon-dioxide/silicon (SiO2/Si) host substrates for integrated terahertz (THz) systems. The LTG-GaAs thin-film devices are fabricated with standard photolithography and thermal evaporation of metal-contact layers of chromium (Cr), nickel (Ni) and gold (Au). They are etched selectively and separated from their growth GaAs substrate. The LTG-GaAs thin-film devices are then heterogeneously integrated on bow-tie antenna electrodes patterned on the surface of a SiO2/Si host substrate for THz emitters and THz detectors. Cost-effective and selective integration of LTG-GaAs thin-film devices on a Si platform is demonstrated. THz radiation from the fabricated THz PCAs is successfully measured using a pump-probe THz time-domain configuration. The THz temporal duration was measured at full width half maximum of 0.36 ps. Its frequency spectrum exhibits a broadband response with a peak resonant frequency of about 0.31 THz. The demonstration illustrates the feasibility of creating heterogeneously integrated THz systems using separately optimized LTG-GaAs devices and Si based electronics.

  8. Feasibility of the LPE Growth of AlxGayIn1-x-yP on GaAs Substrates

    NASA Astrophysics Data System (ADS)

    Kazumura, Masaru; Ohta, Issey; Teramoto, Iwao

    1983-04-01

    The maximum direct bandgap energy of AlxGayIn1-x-yP lattice-matched to GaAs is found to be 2.17 eV at x{=}0.21 and y{=}0.34. This is the largest value among the III-V compounds with the zinc-blende structure. The phase diagram is calculated of the quaternary system Al-Ga-In-P. It is predicted that the LPE growth of AlxGayIn1-x-yP will encounter serious difficulties resulting from the extremely large segregation coefficient of aluminum. In fact, experiments have shown that aluminum is not incorporated into the crystals grown from the quaternary solutions because of the instant depletion of aluminum at the very early stage of the cooling process.

  9. Optical and morphological study of misoriented GaAs substrates exposed to bismuth flow using in situ spectral reflectance and atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Massoudi, I.; Habchi, M. M.; Rebey, A.; El Jani, B.

    2012-08-01

    (100) GaAs substrates with different misorientations were exposed to trimethyl-bismuth (TMBi) flow. The wafers were examined after exposure times of 9 and 43 min. The wafers growth was carried out at atmospheric pressure, in a metalorganic vapor phase epitaxy (MOVPE) reactor, at a temperature of 375 °C. The in situ spectral reflectance (SR) in the spectral range 400-1000 nm was used to monitor the deposition. The reflectivity is marked by two temporal phases, an increase followed by a slow decrease. The atomic force microscopy (AFM) measurements show two different growth modes of bismuth, big isolated islands for early exposure time and a high density of small islands for long exposure times. We also note that the islands' density and size change greatly with the misorientation of the substrate. The correlation between the results given by ex situ AFM and in situ SR is performed via theoretical simulations. We show that roughness, as well as optical and thermal effects are mainly responsible for the reflectivity behavior. We have successfully quantified the spectral evolution of the sensitivity σSR of the incident beam wavelength to the surface undulations.

  10. Structural and electrical properties of metamorphic nanoheterostructures with a high InAs content (37-100%) grown on GaAs and InP substrates

    SciTech Connect

    Galiev, G. B.; Vasil'evskii, I. S.; Imamov, R. M.; Klimov, E. A.; Pushkarev, S. S.; Subbotin, I. A.

    2011-09-15

    A complex study of the structural and electrical properties of nanoheterostructures containing a metamorphic barrier with a high InAs content (37-100%) in the active region have been performed by the Van der Pauw and X-ray diffraction methods. All peaks observed in the rocking curves for the samples studied (throughout the entire structure) have been revealed and identified. It is shown that, having properly chosen the design of the metamorphic buffer and the compositional gradient in it, one can obtain mobilities and concentrations of the 2D electron gas in the In{sub x}Ga{sub 1-x}As quantum well in the heterostructures formed on GaAs substrates that are comparable with the corresponding values for the nanoheterostructures grown on InP substrates. It is established that the mobility and concentration of 2D electron gas depend both on the metamorphic barrier design and on the structural quality of heterostructure as a whole.

  11. 1.3-μm edge- and surface-emitting quantum dot lasers grown on GaAs substrates

    NASA Astrophysics Data System (ADS)

    Ustinov, Victor M.; Zhukov, Alexey E.; Maleev, Nikolay A.; Egorov, Anton Y.; Kovsh, Alexey R.; Mikhrin, Sergei S.; Cherkashin, Nikolai A.; Shernyakov, Yuri M.; Maximov, Mikhail V.; Tsatsul'nikov, Anrei; Ledentsov, Nikolai N.; Alferov, Zhores I.; Lott, James A.; Bimberg, Dieter

    2002-06-01

    The development of 1.3 micron VCSELs is currently considered to give a strong impulse for a wide use of ultra-fast local area networks. In the present work we discuss MBE growth and characteristics of InAs/GaAs quantum dot (QD) lasers, we also give characteristics of 1.3 micron QD VCSELs grown on GaAs and compare them with those of 1.3 micron InGaAsN/GaAs QW VCSELs. Overgrowing the InAs quantum dot array with thin InGaAs layer allows us to achieve 1.3 micron emission. Long stripe lasers showed low threshold current density (<100 A/cm2), high differential efficiency (>50%), and low internal loss (1-2 cm-1). Maximum continuous wave (CW) output power for wide stripe lasers was as high as 2.7 W and 110 mW for single mode devices. Uncoated broad area lasers showed no visible degradation of characteristics during 450 hours (60C, ambient environment). 1.3 micron InGaAsN/GaAs QW VCSELs are characterized by higher optical loss and lower differential efficiency than QD VCSELs. Due to high gain in the active region QW VCSELS demonstrate high output power (1 mW). QW VCSELs show extremely low internal round-trip optical loss (<0.05%), low threshold currents (<2 mA), high differential efficiency (40%) and output power (600 microW).

  12. Facile Five-Step Heteroepitaxial Growth of GaAs Nanowires on Silicon Substrates and the Twin Formation Mechanism.

    PubMed

    Yao, Maoqing; Sheng, Chunyang; Ge, Mingyuan; Chi, Chun-Yung; Cong, Sen; Nakano, Aiichiro; Dapkus, P Daniel; Zhou, Chongwu

    2016-02-23

    Monolithic integration of III-V semiconductors with Si has been pursued for some time in the semiconductor industry. However, the mismatch of lattice constants and thermal expansion coefficients represents a large technological challenge for the heteroepitaxial growth. Nanowires, due to their small lateral dimension, can relieve strain and mitigate dislocation formation to allow single-crystal III-V materials to be grown on Si. Here, we report a facile five-step heteroepitaxial growth of GaAs nanowires on Si using selective area growth (SAG) in metalorganic chemical vapor deposition, and we further report an in-depth study on the twin formation mechanism. Rotational twin defects were observed in the nanowire structures and showed strong dependence on the growth condition and nanowire size. We adopt a model of faceted growth to demonstrate the formation of twins during growth, which is well supported by both a transmission electron microscopy study and simulation based on nucleation energetics. Our study has led to twin-free segments in the length up to 80 nm, a significant improvement compared to previous work using SAG. The achievements may open up opportunities for future functional III-V-on-Si heterostructure devices. PMID:26831573

  13. Structural properties of Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} topological insulators grown by molecular beam epitaxy on GaAs(001) substrates

    SciTech Connect

    Liu, X.; Leiner, J.; Dobrowolska, M.; Furdyna, J. K.; Smith, D. J.; Fan, J.; Zhang, Y.-H.; Cao, H.; Chen, Y. P.; Kirby, B. J.

    2011-10-24

    Thin films of Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} have been grown on deoxidized GaAs(001) substrates using molecular beam epitaxy. Cross-sectional transmission electron microscopy established the highly parallel nature of the Te(Se)-Bi-Te(Se)-Bi-Te(Se) quintuple layers deposited on the slightly wavy GaAs substrate surface and the different crystal symmetries of the two materials. Raman mapping confirmed the presence of the strong characteristic peaks reported previously for these materials in bulk form. The overall quality of these films reveals the potential of combining topological insulators with ferromagnetic semiconductors for future applications.

  14. Photoluminescence spectroscopy and the effective mass theory of strained (In,Ga)As/GaAs heterostructures grown on (112)B GaAs substrates

    NASA Technical Reports Server (NTRS)

    Henderson, R. H.; Sun, D.; Towe, E.

    1995-01-01

    The photoluminescence characteristics of pseudomorphic In(0.19)Ga(0.81)As/GaAs quantum well structures grown on both the conventional (001) and the unconventional (112)B GaAs substrate are investigated. It is found that the emission spectra of the structures grown on the (112)B surface exhibit some spectral characteristics not observed on similar structures grown on the (001) surface. A spectral blue shift of the e yields hh1 transition with increasing optical pump intensity is observed for the quantum wells on the (112) surface. This shift is interpreted to be evidence of a strain-induced piezoelectric field. A second spectral feature located within the band gap of the In(0.19)Ga(0.81)As layer is also observed for the (112) structure; this feature is thought to be an impurity-related emission. The expected transition energies of the quantum well structures are calculated using the effective mass theory based on the 4 x 4 Luttinger valence band Hamiltonian, and related strain Hamiltonian.

  15. Fabrication of 160-nm T-gate metamorphic AlInAs/GaInAs HEMTs on GaAs substrates by metal organic chemical vapour deposition

    NASA Astrophysics Data System (ADS)

    Li, Hai-Ou; Huang, Wei; Tang Chak, Wah; Deng, Xiao-Fang; Lau Kei, May

    2011-06-01

    The fabrication and performance of 160-nm gate-length metamorphic AlInAs/GaInAs high electron mobility transistors (mHEMTs) grown on GaAs substrate by metal organic chemical vapour deposition (MOCVD) are reported. By using a novel combined optical and e-beam photolithography technology, submicron mHEMTs devices have been achieved. The devices exhibit good DC and RF performance. The maximum current density was 817 mA/mm and the maximum transconductance was 828 mS/mm. The non-alloyed Ohmic contact resistance Rc was as low as 0.02 Ω-mm. The unity current gain cut-off frequency (fT) and the maximum oscillation frequency (fmax) were 146 GHz and 189 GHz, respectively. This device has the highest fT yet reported for a 160-nm gate-length HEMTs grown by MOCVD. The output conductance is 28.9 mS/mm, which results in a large voltage gain of 28.6. Also, an input capacitance to gate-drain feedback capacitance ratio, Cgs/Cgd, of 4.3 is obtained in the device.

  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. Comparison of different grading schemes in InGaAs metamorphic buffers on GaAs substrate: Tilt dependence on cross-hatch irregularities

    NASA Astrophysics Data System (ADS)

    Kumar, Rahul; Bag, Ankush; Mukhopadhyay, Partha; Das, Subhashis; Biswas, Dhrubes

    2015-12-01

    InGaAs graded metamorphic buffers (MBs) with different grading strategies have been grown by molecular beam epitaxy (MBE) on GaAs (0 0 1) substrate. A detailed comparative analysis of surface using atomic force microscopy (AFM), and bulk properties using high resolution X-ray diffraction (HRXRD) and room temperature photoluminescence (RTPL) of grown MBs have been presented to comprehend the effectiveness of different grading scheme on InGaAs MBs. Conventional, statistical and fractal analysis on measured AFM data has been performed for in-depth investigation of these surfaces. The grading scheme has been found to have little impact on residual strain while it affects the epitaxial tilt significantly. Moreover, the tilt has been found to depend on growth front irregularities. Tilt magnitude in a graded MB has been found to vary with composition while tilt azimuth has been found to be almost same in the graded layers. PL Intensity and a shift in the PL peaks have been used to study the quality of the MB and residual strain comparatively.

  18. High-crystalline GaSb epitaxial films grown on GaAs(001) substrates by low-pressure metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wang, Lian-Kai; Liu, Ren-Jun; Lü, You; Yang, Hao-Yu; Li, Guo-Xing; Zhang, Yuan-Tao; Zhang, Bao-Lin

    2015-01-01

    Orthogonal experiments of GaSb films growth on GaAs(001) substrates have been designed and performed by using a low-pressure metal-organic chemical vapor deposition (LP-MOCVD) system. The crystallinities and microstructures of the produced films were comparatively analyzed to achieve the optimum growth parameters. It was demonstrated that the optimized GaSb thin film has a narrow full width at half maximum (358 arc sec) of the (004) ω-rocking curve, and a smooth surface with a low root-mean-square roughness of about 6 nm, which is typical in the case of the heteroepitaxial single-crystal films. In addition, we studied the effects of layer thickness of GaSb thin film on the density of dislocations by Raman spectra. It is believed that our research can provide valuable information for the fabrication of high-crystalline GaSb films and can promote the integration probability of mid-infrared devices fabricated on mainstream performance electronic devices. Project supported by the National Natural Science Foundation of China (Grant No. 61076010) and the International Science and Technology Cooperation Program of Science and Technology Bureau of Changchun, China (Grant No. 12ZX68).

  19. GaAsSb/InGaAs type-II quantum wells for long-wavelength lasers on GaAs substrates

    SciTech Connect

    KLEM,JOHN F.; SPAHN,OLGA B.; KURTZ,STEVEN R.; FRITZ,IAN J.; CHOQUETTE,KENT D.

    2000-03-15

    The authors have investigated the properties of GaAsSb/InGaAs type-II bilayer quantum well structures grown by molecule beam epitaxy for use in long-wavelength lasers on GaAs substrates. Structures with layer, strains and thicknesses designed to be thermodynamically stable against dislocation formation exhibit room-temperature photoluminescence at wavelengths as long as 1.43 {mu}m. The photoluminescence emission wavelength is significantly affected by growth temperature and the sequence of layer growth (InGaAs/GaAsSb vs GaAsSb/InGaAs), suggesting that Sb and/or In segregation results in non-ideal interfaces under certain growth conditions. At low injection currents, double heterostructure lasers with GaAsSb/InGaAs bilayer quantum well active regions display electroluminescence at wavelengths comparable to those obtained in photoluminescence, but at higher currents the electroluminescence shifts to shorter wavelengths. Lasers have been obtained with threshold current densities as low as 120 A/cm{sup 2} at 1.17 {mu}m, and 2.1 kA/cm{sup 2} at 1.21 {mu}m.

  20. 10Gbps operation of a metamorphic InGaP buffered In 0.53Ga 0.47As p-i-n photodetector grown on GaAs substrate

    NASA Astrophysics Data System (ADS)

    Liao, Yu-Sheng; Lin, Gong-Ru; Lin, Chi-Kuan; Chu, Yi-Shiang; Kuo, Hao-Chung; Feng, Milton

    2005-11-01

    A novel top-illuminated In 0.53Ga 0.47As p-i-n photodiodes (MM-PINPD) grown on GaAs substrate by using a linearly graded metamorphic In xGa 1-xP (x graded from 0.49 to 1) buffer layer has been demonstrated on the SONET OC-192 receiving performance. With a cost-efficient TO-46 package, the MM-PINPD at data rate of 10 Gbit/s can be obtained at minimum optical power of -19.5 dBm. At wavelength of 1550nm, the dark current, optical responsivities, noise equivalent power, and operational bandwidth of the MM-PINPD with aperture diameter of 60 μm are 13 pA, 0.6 A/W, 3.4×10 -15 W/Hz 1/2, and 8 GHz, respectively. All the parameters are comparable to those of similar devices made on InP substrate or other InGaAs products epitaxially grown on an InGaAlAs buffered GaAs substrate. The performances of the MM-PINPD on GaAs are analyzed by impulse injecting of 1.2-ps pulse-train, eye pattern at 10Gbps, and frequency response from VNA.

  1. Epitaxial growth of antiphase boundary free GaAs layer on 300 mm Si(001) substrate by metalorganic chemical vapour deposition with high mobility

    NASA Astrophysics Data System (ADS)

    Alcotte, R.; Martin, M.; Moeyaert, J.; Cipro, R.; David, S.; Bassani, F.; Ducroquet, F.; Bogumilowicz, Y.; Sanchez, E.; Ye, Z.; Bao, X. Y.; Pin, J. B.; Baron, T.

    2016-04-01

    Metal organic chemical vapor deposition of GaAs on standard nominal 300 mm Si(001) wafers was studied. Antiphase boundary (APB) free epitaxial GaAs films as thin as 150 nm were obtained. The APB-free films exhibit an improvement of the room temperature photoluminescence signal with an increase of the intensity of almost a factor 2.5. Hall effect measurements show an electron mobility enhancement from 200 to 2000 cm2/V s. The GaAs layers directly grown on industrial platform with no APBs are perfect candidates for being integrated as active layers for nanoelectronic as well as optoelectronic devices in a CMOS environment.

  2. Integration of GaAs epitaxial layer to Si-based substrate using Ge condensation and low-temperature migration enhanced epitaxy techniques

    SciTech Connect

    Oh, Hoon Jung; Choi, Kyu Jin; Loh, Wei Yip; Htoo, Thwin; Chua, Soo Jin; Cho, Byung Jin

    2007-09-01

    A GaAs defect-free epitaxial layer has been grown on Si via a Ge concentration graded SiGe on insulator (SGOI) for application in high channel-mobility metal-oxide-semiconductor field effect transistor. The SGOI layer, 42 nm thick, serves as the compliant and intermediate buffer to reduce the lattice and thermal expansion mismatches between Si and GaAs. A modified two-step Ge condensation technique achieves the surface Ge concentration in SGOI as high as 71%. It is also found that low-temperature migration enhanced epitaxy during the initial GaAs nucleation on the SGOI surface is critical to obtain a device quality GaAs layer by epitaxial growth.

  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. Metamorphic Ga0.76In0.24As/GaAs0.75Sb0.25 tunnel junctions grown on GaAs substrates

    NASA Astrophysics Data System (ADS)

    García, I.; Geisz, J. F.; France, R. M.; Kang, J.; Wei, S.-H.; Ochoa, M.; Friedman, D. J.

    2014-08-01

    Lattice-matched and pseudomorphic tunnel junctions have been developed in the past for application in a variety of semiconductor devices, including heterojunction bipolar transistors, vertical cavity surface-emitting lasers, and multijunction solar cells. However, metamorphic tunnel junctions have received little attention. In 4-junction Ga0.51In0.49P/GaAs/Ga0.76In0.24As/Ga0.47In0.53As inverted-metamorphic solar cells (4J-IMM), a metamorphic tunnel junction is required to series connect the 3rd and 4th junctions. We present a tunnel junction based on a metamorphic Ga0.76In0.24As/GaAs0.75Sb0.25 structure for this purpose. This tunnel junction is grown on a metamorphic Ga0.76In0.24As template on a GaAs substrate. The band offsets in the resulting type-II heterojunction are calculated using the first-principles density functional method to estimate the tunneling barrier height and assess the performance of this tunnel junction against other material systems and compositions. The effect of the metamorphic growth on the performance of the tunnel junctions is analyzed using a set of metamorphic templates with varied surface roughness and threading dislocation density. Although the metamorphic template does influence the tunnel junction performance, all tunnel junctions measured have a peak current density over 200 A/cm2. The tunnel junction on the best template has a peak current density over 1500 A/cm2 and a voltage drop at 15 A/cm2 (corresponding to operation at 1000 suns) lower than 10 mV, which results in a nearly lossless series connection of the 4th junction in the 4J-IMM structure.

  5. Ultra-Thin-Film GaAs Solar Cells

    NASA Technical Reports Server (NTRS)

    Wang, K. L.; Shin, B. K.; Yeh, Y. C. M.; Stirn, R. J.

    1982-01-01

    Process based on organo-metallic chemical vapor deposition (OM/CVD) of trimethyl gallium with arsine forms economical ultrathin GaAs epitaxial films. Process has higher potential for low manufacturing cost and large-scale production compared with more-conventional halide CVD and liquid-phase epitaxy processes. By reducing thickness of GaAs and substituting low-cost substrate for single-crystal GaAs wafer, process would make GaAs solar cells commercially more attractive.

  6. Structural and band alignment properties of Al{sub 2}O{sub 3} on epitaxial Ge grown on (100), (110), and (111)A GaAs substrates by molecular beam epitaxy

    SciTech Connect

    Hudait, M. K.; Zhu, Y.; Maurya, D.; Priya, S.; Patra, P. K.; Ma, A. W. K.; Aphale, A.; Macwan, I.

    2013-04-07

    Structural and band alignment properties of atomic layer Al{sub 2}O{sub 3} oxide film deposited on crystallographically oriented epitaxial Ge grown in-situ on (100), (110), and (111)A GaAs substrates using two separate molecular beam epitaxy chambers were investigated using cross-sectional transmission microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). High-resolution triple axis x-ray measurement demonstrated pseudomorphic and high-quality Ge epitaxial layer on crystallographically oriented GaAs substrates. The cross-sectional TEM exhibited a sharp interface between the Ge epilayer and each orientation of the GaAs substrate as well as the Al{sub 2}O{sub 3} film and the Ge epilayer. The extracted valence band offset, {Delta}E{sub v}, values of Al{sub 2}O{sub 3} relative to (100), (110), and (111) Ge orientations using XPS measurement were 3.17 eV, 3.34 eV, and 3.10 eV, respectively. Using XPS data, variations in {Delta}E{sub v} related to the crystallographic orientation were {Delta}E{sub V}(110)Ge>{Delta}E{sub V}(100)Ge{>=}{Delta}E{sub V}(111)Ge and the conduction band offset, {Delta}E{sub c}, related to the crystallographic orientation was {Delta}E{sub c}(111)Ge>{Delta}E{sub c}(110)Ge>{Delta}E{sub c}(100)Ge using the measured {Delta}E{sub v}, bandgap of Al{sub 2}O{sub 3} in each orientation, and well-known Ge bandgap of 0.67 eV. These band offset parameters are important for future application of Ge-based p- and n-channel metal-oxide field-effect transistor design.

  7. Thickness modulation and strain relaxation in strain-compensated InGaP/InGaP multiple-quantum-well structure grown by metalorganic molecular beam epitaxy on GaAs (100) substrate

    NASA Astrophysics Data System (ADS)

    Mitsuhara, M.; Watanabe, N.; Yokoyama, H.; Iga, R.; Shigekawa, N.

    2016-09-01

    We have investigated the structural features of a strain-compensated InGaP/InGaP multiple-quantum-well (MQW) structure on GaAs (100) substrate with a band-gap energy of around 1.7 eV for solar cell applications. In transmission electron microscopy images, noticeable thickness modulation was observed in the barrier layers for a sample grown at the substrate temperature of 530 °C. Meanwhile, the X-ray diffraction patterns indicated that strain relaxation predominantly occurred in the well layers. Decreasing the substrate temperature from 530 to 510 °C was effective in suppressing both the thickness modulation and strain relaxation. Additionally, increasing the growth rate of the well layer further suppressed the thickness modulation. In room-temperature photoluminescence (PL) emission spectra, the sample grown at 510 °C showed approximately 50 times higher PL peak intensity than the one grown at 530 °C.

  8. Surface morphologies and electrical properties of molecular beam epitaxial InSb and InAs(x)Sb(1-x) grown on GaAs and InP substrates

    NASA Technical Reports Server (NTRS)

    Oh, J. E.; Chen, Y. C.; Bhattacharya, P. K.; Tsukamoto, S.

    1989-01-01

    Surface morphologies and electrical properties of molecular beam epitaxial InSb and InAs(x)Sb(1-x) grown on GaAs and InP substrates are discussed. The crystals are all n-type at 300 K and lower temperatures. The surface morphology and electrical characteristics are strongly dependent on Sb(4)/In flux ratio and substrate temperature. The highest mobilities in InSb on InP are 70,000 at 300 K and 110,000 cm(2)/V.s (n=3x10(15) cm(-3)) at 77 K. The mobilities in the alloys also increase monotonically with lowering of temperature. Good quality InAs(x)Sb(1-x) was grown directly on InP substrates by molecular beam epitaxy.

  9. Transparent self-electro-optic effect device based on Wannier-Stark localization in unstrained {InxGa1-xAs}/{InxAl1-xAs} superlattices on GaAs substrate

    NASA Astrophysics Data System (ADS)

    Tominaga, K.; Hosoda, M.; Watanabe, T.; Fujiwara, K.

    The first transparent-type Wannier-Stark localization self-electro-optic effect device made without substrate removal is reported. Unstrained 100-period {InxGa1-xAs}/{InxAl1-xAs} superlattice layers were successfully grown by molecular beam epitaxy on GaAs substrate by introducing specially designed buffer layers that consist of two sections. The first section is an In-composition-graded In yGa 1- yAs, whose In content Y changes linearly from 0 to X, and the second is a strain-relaxed In xGa 1- xAs layer. The introduction of the strain relaxation layer allows us to choose a wide range of In content X and an ample number of superlattice periods avoiding the critical layer thickness problem. When X = 0.17, the operating wavelength is 933 nm, which can penetrate through the GaAs substrate. The operating wavelength of 1064 nm is accomplished when X = 0.3, and clear bistability is demonstrated using a Nd:YAG laser as a light source.

  10. IR spectroscopy of lattice vibrations and comparative analysis of the ZnTe/CdTe quantum-dot superlattices on the GaAs substrate and with the ZnTe and CdTe buffer layers

    SciTech Connect

    Kozyrev, S. P.

    2009-07-15

    A comparative analysis of multiperiod ZnTe/CdTe superlattices with the CdTe quantum dots grown by molecular beam epitaxy on the GaAs substrate with the ZnTe and CdTe buffer layers is carried out. The elastic-stress-induced shifts of eigenfrequencies of the modes of the CdTe- and ZnTe-like vibrations of materials forming similar superlattices but grown on different buffer ZnTe and CdTe layers are compared. The conditions of formation of quantum dots in the ZnTe/CdTe superlattices on the ZnTe and CdTe buffer layers differ radically.

  11. Tilt generation in step-graded InxGa1-xAs metamorphic pseudosubstrate on a singular GaAs substrate using a low-temperature grown InGaP interlayer

    NASA Astrophysics Data System (ADS)

    Ghanad Tavakoli, Shahram; Hulko, Oksana; Thompson, David A.

    2008-05-01

    Metamorphic pseudosubstrates of In0.42Ga0.58As were grown by molecular beam epitaxy using step-graded InxGa1-xAs buffer layers grown either directly on a (001) GaAs substrate or on a GaAs substrate overgrown with a layer of low-temperature grown In0.51Ga0.49P (LT-InGaP). The structures were examined using x-ray reciprocal space mapping to determine the characteristics of the pseudosubstrates and buffer layers. For the sample grown on the LT-InGaP layer, the pseudosubstrate exhibited an asymmetric tilt around [11¯0] toward the [110] direction. Weak-beam dark-field electron imaging shows an imbalance of misfit dislocations with opposite sign Burgers vector. An explanation for this tilt is given and it is suggested that it may be responsible for the improved quality of epitaxial layers grown on such pseudosubstrates.

  12. Tilt generation in step-graded In{sub x}Ga{sub 1-x}As metamorphic pseudosubstrate on a singular GaAs substrate using a low-temperature grown InGaP interlayer

    SciTech Connect

    Ghanad Tavakoli, Shahram; Hulko, Oksana; Thompson, David A.

    2008-05-15

    Metamorphic pseudosubstrates of In{sub 0.42}Ga{sub 0.58}As were grown by molecular beam epitaxy using step-graded In{sub x}Ga{sub 1-x}As buffer layers grown either directly on a (001) GaAs substrate or on a GaAs substrate overgrown with a layer of low-temperature grown In{sub 0.51}Ga{sub 0.49}P (LT-InGaP). The structures were examined using x-ray reciprocal space mapping to determine the characteristics of the pseudosubstrates and buffer layers. For the sample grown on the LT-InGaP layer, the pseudosubstrate exhibited an asymmetric tilt around [110] toward the [110] direction. Weak-beam dark-field electron imaging shows an imbalance of misfit dislocations with opposite sign Burgers vector. An explanation for this tilt is given and it is suggested that it may be responsible for the improved quality of epitaxial layers grown on such pseudosubstrates.

  13. GaAs solar cell development

    NASA Technical Reports Server (NTRS)

    Knechtli, R. C.; Kamath, S.; Loo, R.

    1977-01-01

    The motivation for developing GaAs solar cells is based on their superior efficiency when compared to silicon cells, their lower degradation with increasing temperature, and the expectation for better resistance to space radiation damage. The AMO efficiency of GaAs solar cells was calculated. A key consideration in the HRL technology is the production of GaAs cells of large area (greater than 4 sg cm) at a reasonable cost without sacrificing efficiency. An essential requirement for the successful fabrication of such cells is the ability to grow epitaxially a uniform layer of high quality GaAs (buffer layer) on state-of-the-art GaAs substrates, and to grow on this buffer layer the required than layer of (AlGa)As. A modified infinite melt liquid phase epitaxy (LPE) growth technique is detailed.

  14. LEC GaAs for integrated circuit applications

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, C. G.; Chen, R. T.; Homes, D. E.; Asbeck, P. M.; Elliott, K. R.; Fairman, R. D.; Oliver, J. D.

    1984-01-01

    Recent developments in liquid encapsulated Czochralski techniques for the growth of semiinsulating GaAs for integrated circuit applications have resulted in significant improvements in the quality and quantity of GaAs material suitable for device processing. The emergence of high performance GaAs integrated circuit technologies has accelerated the demand for high quality, large diameter semiinsulating GaAs substrates. The new device technologies, including digital integrated circuits, monolithic microwave integrated circuits and charge coupled devices have largely adopted direct ion implantation for the formation of doped layers. Ion implantation lends itself to good uniformity and reproducibility, high yield and low cost; however, this technique also places stringent demands on the quality of the semiinsulating GaAs substrates. Although significant progress was made in developing a viable planar ion implantation technology, the variability and poor quality of GaAs substrates have hindered progress in process development.

  15. Molecular beam epitaxial growth of Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} topological insulators on GaAs (111) substrates: a potential route to fabricate topological insulator p-n junction

    SciTech Connect

    Zeng, Zhaoquan; Morgan, Timothy A.; Li, Chen; Hirono, Yusuke; Hu, Xian; Hawkridge, Michael E.; Benamara, Mourad; Salamo, Gregory J.; Fan, Dongsheng; Yu, Shuiqing; Zhao, Yanfei; Lee, Joon Sue; Wang, Jian; Wang, Zhiming M.

    2013-07-15

    High quality Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} topological insulators films were epitaxially grown on GaAs (111) substrate using solid source molecular beam epitaxy. Their growth and behavior on both vicinal and non-vicinal GaAs (111) substrates were investigated by reflection high-energy electron diffraction, atomic force microscopy, X-ray diffraction, and high resolution transmission electron microscopy. It is found that non-vicinal GaAs (111) substrate is better than a vicinal substrate to provide high quality Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} films. Hall and magnetoresistance measurements indicate that p type Sb{sub 2}Te{sub 3} and n type Bi{sub 2}Te{sub 3} topological insulator films can be directly grown on a GaAs (111) substrate, which may pave a way to fabricate topological insulator p-n junction on the same substrate, compatible with the fabrication process of present semiconductor optoelectronic devices.

  16. Acoustic Wave Chemical Microsensors in GaAs

    SciTech Connect

    Albert G. Baca; Edwin J. Heller; Gregory C. Frye-Mason; John L. Reno; Richard Kottenstette; Stephen A. Casalnuovo; Susan L. Hietala; Vincent M. Hietala

    1998-09-20

    High sensitivity acoustic wave chemical microsensors are being developed on GaAs substrates. These devices take advantage of the piezoelectric properties of GaAs as well as its mature microelectronics fabrication technology and nascent micromachining technology. The design, fabrication, and response of GaAs SAW chemical microsensors are reported. Functional integrated GaAs SAW oscillators, suitable for chemical sensing, have been produced. The integrated oscillator requires 20 mA at 3 VK, operates at frequencies up to 500 MHz, and occupies approximately 2 mmz. Discrete GaAs sensor components, including IC amplifiers, SAW delay lines, and IC phase comparators have been fabricated and tested. A temperature compensation scheme has been developed that overcomes the large temperature dependence of GaAs acoustic wave devices. Packaging issues related to bonding miniature flow channels directly to the GaAs substrates have been resolved. Micromachining techniques for fabricating FPW and TSM microsensors on thin GaAs membranes are presented and GaAs FPW delay line performance is described. These devices have potentially higher sensitivity than existing GaAs and quartz SAW sensors.

  17. GaAs shallow-homojunction solar cells

    NASA Technical Reports Server (NTRS)

    Fan, J. C. C.

    1981-01-01

    The feasibility of fabricating space resistant, high efficiency, light weight, low cost GaAs shallow homojunction solar cells for space application is investigated. The material preparation of ultrathin GaAs single crystal layers, and the fabrication of efficient GaAs solar cells on bulk GaAs substrates are discussed. Considerable progress was made in both areas, and conversion efficiency about 16% AMO was obtained using anodic oxide as a single layer antireflection coating. A computer design shows that even better cells can be obtained with double layer antireflection coating. Ultrathin, high efficiency solar cells were obtained from GaAs films prepared by the CLEFT process, with conversion efficiency as high as 17% at AMI from a 10 micrometers thick GaAs film. A organometallic CVD was designed and constructed.

  18. Study of a MHEMT heterostructure with an In{sub 0.4}Ga{sub 0.6}As channel MBE-grown on a GaAs substrate using reciprocal space mapping

    SciTech Connect

    Aleshin, A. N. Bugaev, A. S.; Ermakova, M. A.; Ruban, O. A.

    2015-08-15

    The crystallographic characteristics of the design elements of a metamorphic high-electron-mobility (MHEMT) heterostructure with an In{sub 0.4}Ga{sub 0.6}As channel are determined based on reciprocal space mapping. The heterostructure is grown by molecular beam epitaxy on the vicinal surface of a GaAs substrate with a deviation angle from the (001) plane of 2° and consists of a stepped metamorphic buffer containing six layers including an inverse step, a high-temperature buffer layer with constant composition, and active HEMT layers. The InAs content in the layers of the metamorphic buffer is varied from 0.1 to 0.48. Reciprocal space maps are constructed for the (004) symmetric reflection and (224)+ asymmetric reflection. It is found that the heterostructure layers are characterized both by a tilt angle relative to the plane of the (001) substrate and a rotation angle around the [001] axis. The tilt angle of the layer increases as the InAs concentration in the layer increases. It is shown that a high-temperature buffer layer of constant composition has the largest degree of relaxation compared with all other layers of the heterostructure.

  19. High mobility two-dimensional hole system in GaAs/AlGaAs quantum wells grown on (100) GaAs substrates

    SciTech Connect

    Manfra, M.J.; Pfeiffer, L.N.; West, K.W.; Picciotto, R. de; Baldwin, K.W.

    2005-04-18

    We report on the transport properties of a high mobility two-dimensional hole system (2DHS) confined in GaAs/AlGaAs quantum wells grown by molecular-beam epitaxy on the (100) surface of GaAs. The quantum wells are modulation doped with carbon utilizing a resistive filament source. At T=0.3 K and carrier density p=1x10{sup 11} cm{sup -2}, a mobility of 10{sup 6} cm{sup 2}/Vs is achieved. At fixed carrier density p=10{sup 11} cm{sup -2}, the mobility is found to be a nonmonotonic function of the quantum well width. The mobility peaks at 10{sup 6} cm{sup 2}/Vs for a 15-nm well and is reduced for both smaller and larger well widths for these (100) samples. The mobility anisotropy is found to be small. Mobility along [011] is approximately 20% higher than along the [011] direction. In addition, the low-temperature carrier density is found to have low sensitivity to light. The hole density increases by only {approx}10% after exposure to red light at T=4.2 K. In structures designed for a lower carrier density of 3.6x10{sup 10} cm{sup -2}, a mobility of 800 000 cm{sup 2}/Vs is achieved at T=15 mK.

  20. Quality-enhanced In{sub 0.3}Ga{sub 0.7}As film grown on GaAs substrate with an ultrathin amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer

    SciTech Connect

    Gao, Fangliang; Li, Guoqiang

    2014-01-27

    Using low-temperature molecular beam epitaxy, amorphous In{sub 0.6}Ga{sub 0.4}As layers have been grown on GaAs substrates to act as buffer layers for the subsequent epitaxial growth of In{sub 0.3}Ga{sub 0.7}As films. It is revealed that the crystallinity of as-grown In{sub 0.3}Ga{sub 0.7}As films is strongly affected by the thickness of the large-mismatched amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer. Given an optimized thickness of 2 nm, this amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer can efficiently release the misfit strain between the In{sub 0.3}Ga{sub 0.7}As epi-layer and the GaAs substrate, trap the threading and misfit dislocations from propagating to the following In{sub 0.3}Ga{sub 0.7}As epi-layer, and reduce the surface fluctuation of the as-grown In{sub 0.3}Ga{sub 0.7}As, leading to a high-quality In{sub 0.3}Ga{sub 0.7}As film with competitive crystallinity to that grown on GaAs substrate using compositionally graded In{sub x}Ga{sub 1-x}As metamorphic buffer layers. Considering the complexity of the application of the conventional In{sub x}Ga{sub 1-x}As graded buffer layers, this work demonstrates a much simpler approach to achieve high-quality In{sub 0.3}Ga{sub 0.7}As film on GaAs substrate and, therefore, is of huge potential for the InGaAs-based high-efficiency photovoltaic industry.

  1. Use of ZnSe as an interlayer for GaAs growth on Si

    NASA Astrophysics Data System (ADS)

    Bringans, R. D.; Biegelsen, D. K.; Swartz, L.-E.; Ponce, F. A.; Tramontana, J. C.

    1992-07-01

    ZnSe has been used as an interlayer between Si substrates and GaAs layers in molecular beam epitaxial growth of GaAs on Si. It is found that thin GaAs layers are much more uniform and have fewer defects when grown on ZnSe interlayers than when they are grown directly on Si. The growth of GaAs on ZnSe is much more difficult than the more usual reverse sequence, and different growth modes for the epitaxy of GaAs on ZnSe are compared. Deposition of GaAs on ZnSe at room temperature followed by solid phase regrowth led to an epitaxial layer plus a polycrystalline layer. A slow ramping of the substrate temperature during the GaAs epitaxial growth was found to give the best crystal quality.

  2. Structure characterization of MHEMT heterostructure elements with In0.4Ga0.6As quantum well grown by molecular beam epitaxy on GaAs substrate using reciprocal space mapping

    NASA Astrophysics Data System (ADS)

    Aleshin, A. N.; Bugaev, A. S.; Ermakova, M. A.; Ruban, O. A.

    2016-03-01

    The crystallographic parameters of elements of a metamorphic high-electron-mobility transistor (MHEMT) heterostructure with In0.4Ga0.6As quantum well are determined using reciprocal space mapping. The heterostructure has been grown by molecular-beam epitaxy (MBE) on the vicinal surface of a GaAs substrate with a deviation angle of 2° from the (001) plane. The structure consists of a metamorphic step-graded buffer (composed of six layers, including an inverse step), a high-temperature buffer of constant composition, and active high-electron-mobility transistor (HEMT) layers. The InAs content in the metamorphic buffer layers varies from 0.1 to 0.48. Reciprocal space mapping has been performed for the 004 and 224 reflections (the latter in glancing exit geometry). Based on map processing, the lateral and vertical lattice parameters of In x Ga1- x As ternary solid solutions of variable composition have been determined. The degree of layer lattice relaxation and the compressive stress are found within the linear elasticity theory. The high-temperature buffer layer of constant composition (on which active MHEMT layers are directly formed) is shown to have the highest (close to 100%) degree of relaxation in comparison with all other heterostructure layers and a minimum compressive stress.

  3. GaAs photoconductive semiconductor switch

    DOEpatents

    Loubriel, G.M.; Baca, A.G.; Zutavern, F.J.

    1998-09-08

    A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device is disclosed. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices. 5 figs.

  4. GaAs photoconductive semiconductor switch

    DOEpatents

    Loubriel, Guillermo M.; Baca, Albert G.; Zutavern, Fred J.

    1998-01-01

    A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices.

  5. Effects of confinements on morphology of In{sub x}Ga{sub 1–x}As thin film grown on sub-micron patterned GaAs substrate: Elastoplastic phase field model

    SciTech Connect

    Arjmand, M.; Deng, J.; Swaminathan, N.; Morgan, D.; Szlufarska, I.

    2014-09-21

    An elastoplastic phase field model is developed to investigate the role of lateral confinement on morphology of thin films grown heteroepitaxially on patterned substrates. Parameters of the model are chosen to represent In{sub x}Ga{sub 1-x}As thin films growing on GaAs patterned with SiO₂. We determined the effect of misfit strain on morphology of thin films grown in 0.5 μm patterns with non-uniform deposition flux. Growth of islands inside patterns can be controlled by non-uniformity of deposition flux, misfit strain between film and the substrate, and also strain energy relaxation due to plastic deformation. Our results show that the evolution of island morphology depends non-monotonically on indium content and associated misfit strain due to coupling between the plastic relaxation and the confinements effects. Low indium concentration (0%–40%) causes formation of instabilities with relatively long wavelengths across the width of the pattern. Low surface diffusion (due to low indium concentration) and fewer islands across the pattern (due to small misfit strain) lead to formation and growth of islands near the walls driven by overflow flux. Further increase in indium concentration (40%–75%) increases the lattice mismatch and surface diffusivity of the film, and also activates plastic deformation mechanism, which leads to coalescence of islands usually away from the edges. By further increasing the indium concentration (up to 100%), plastic deformation relaxes most of the strain energy density of the film, which prevents formation of instabilities in the film. Hence, in this case, islands are only formed near the walls.

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

    NASA Astrophysics Data System (ADS)

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

    2006-01-01

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

  7. Structural and magnetic properties of GaMnAs layers with high Mn-content grown by migration-enhanced epitaxy on GaAs(100) substrates

    NASA Astrophysics Data System (ADS)

    Sadowski, J.; Mathieu, R.; Svedlindh, P.; Domagała, J. Z.; Bak-Misiuk, J.; Światek, K.; Karlsteen, M.; Kanski, J.; Ilver, L.; Åsklund, H.; Södervall, U.

    2001-05-01

    Ferromagnetic GaMnAs containing up to 10% Mn has been grown by migration-enhanced epitaxy at a substrate temperature of 150 °C. The lattice constant of hypothetical zinc-blende structure MnAs is determined to be 5.90 Å, which deviates somewhat from previously reported values. This deviation is ascribed to growth-condition-dependent density of point defects. Magnetization measurements showed an onset of ferromagnetic ordering around 75 K for the GaMnAs layer with 10% Mn. This means that the trend of falling Curie temperatures with increasing Mn concentrations above 5.3% is broken.

  8. Peeled film GaAs solar cell development

    NASA Technical Reports Server (NTRS)

    Wilt, D. M.; Thomas, R. D.; Bailey, S. G.; Brinker, D. J.; Deangelo, F. L.

    1990-01-01

    Thin-film, single-crystal gallium arsenide (GaAs) solar cells could exhibit a specific power approaching 700 W/kg including coverglass. A simple process has been described whereby epitaxial GaAs layers are peeled from a reusable substrate. This process takes advantage of the extreme selectivity of the etching rate of aluminum arsenide (AlAs) over GaAs in dilute hydrofluoric acid. The feasibility of using the peeled film technique to fabricate high-efficiency, low-mass GaAs solar cells is presently demonstrated. A peeled film GaAs solar cell was successfully produced. The device, although fractured and missing the aluminum gallium arsenide window and antireflective coating, had a Voc of 874 mV and a fill factor of 68 percent under AM0 illumination.

  9. Lateral epitaxial overgowth of GaAs by organometallic chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Gale, R. P.; Mcclelland, R. W.; Fan, J. C. C.; Bozler, C. O.

    1982-01-01

    Lateral epitaxial overgrowth of GaAs by organometallic chemical vapor deposition has been demonstrated. Pyrolytic decomposition of trimethylgallium and arsine, without the use of HCl, was used to deposit GaAs on substrates prepared by coating (110) GaAs wafers with SiO2, then using photolithography to open narrow stripes in the oxide. Lateral overgrowth was seeded by epitaxial deposits formed on the GaAs surfaces exposed by the stripe openings. The extent of lateral overgrowth was investigated as a function of stripe orientation and growth temperature. Ratios of lateral to vertical growth rates greater than five have been obtained. The lateral growth is due to surface-kinetic control for the two-dimensional growth geometry studied. A continuous epitaxial GaAs layer 3 microns thick has been grown over a patterned mask on a GaAs substrate and then cleaved from the substrate.

  10. Growth, microstructure, and luminescent properties of direct-bandgap InAlP on relaxed InGaAs on GaAs substrates

    NASA Astrophysics Data System (ADS)

    Mukherjee, K.; Beaton, D. A.; Christian, T.; Jones, E. J.; Alberi, K.; Mascarenhas, A.; Bulsara, M. T.; Fitzgerald, E. A.

    2013-05-01

    Direct-bandgap InAlP alloy has the potential to be an active material in nitride-free yellow-green and amber optoelectronics with applications in solid-state lighting, display devices, and multi-junction solar cells. We report on the growth of high-quality direct-bandgap InAlP on relaxed InGaAs graded buffers with low threading dislocation densities. Structural characterization reveals phase-separated microstructures in these films which have an impact on the luminescence spectrum. While similar to InGaP in many ways, the greater tendency for phase separation in InAlP leads to the simultaneous occurrence of compositional inhomogeneity and CuPt-B ordering. Mechanisms connecting these two structural parameters are presented as well as results on the effect of silicon and zinc dopants on homogenizing the microstructure. Spontaneous formation of tilted planes of phase-separated material, with alternating degrees of ordering, is observed when InAlP is grown on vicinal substrates. The photoluminescence peak-widths of these films are actually narrower than those grown on exact (001) substrates. We find that, despite phase-separation, ordered direct-bandgap InAlP is a suitable material for optoelectronics.

  11. Influence of buffer-layer construction and substrate orientation on the electron mobilities in metamorphic In{sup 0.70}Al{sup 0.30}As/In{sup 0.76}Ga{sup 0.24}As/In{sup 0.70}Al{sup 0.30}As structures on GaAs substrates

    SciTech Connect

    Kulbachinskii, V. A.; Oveshnikov, L. N.; Lunin, R. A.; Yuzeeva, N. A.; Galiev, G. B.; Klimov, E. A.; Pushkarev, S. S.; Maltsev, P. P.

    2015-07-15

    The influence of construction of the buffer layer and misorientation of the substrate on the electrical properties of In{sup 0.70}Al{sup 0.30}As/In{sup 0.76}Ga{sup 0.24}As/In{sup 0.70}Al{sup 0.30}As quantum wells on a GaAs substrate is studied. The temperature dependences (in the temperature range of 4.2 K < T < 300 K) and field dependences (in magnetic fields as high as 6 T) of the sample resistances are measured. Anisotropy of the resistances in different crystallographic directions is detected; this anisotropy depends on the substrate orientation and construction of the metamorphic buffer layer. In addition, the Hall effect and the Shubnikov–de Haas effect are studied. The Shubnikov–de Haas effect is used to determine the mobilities of electrons separately in several occupied dimensionally quantized subbands in different crystallographic directions. The calculated anisotropy of mobilities is in agreement with experimental data on the anisotropy of the resistances.

  12. The development of integrated chemical microsensors in GaAs

    SciTech Connect

    CASALNUOVO,STEPHEN A.; ASON,GREGORY CHARLES; HELLER,EDWIN J.; HIETALA,VINCENT M.; BACA,ALBERT G.; HIETALA,S.L.

    1999-11-01

    Monolithic, integrated acoustic wave chemical microsensors are being developed on gallium arsenide (GaAs) substrates. With this approach, arrays of microsensors and the high frequency electronic components needed to operate them reside on a single substrate, increasing the range of detectable analytes, reducing overall system size, minimizing systematic errors, and simplifying assembly and packaging. GaAs is employed because it is both piezoelectric, a property required to produce the acoustic wave devices, and a semiconductor with a mature microelectronics fabrication technology. Many aspects of integrated GaAs chemical sensors have been investigated, including: surface acoustic wave (SAW) sensors; monolithic SAW delay line oscillators; GaAs application specific integrated circuits (ASIC) for sensor operation; a hybrid sensor array utilizing these ASICS; and the fully monolithic, integrated SAW array. Details of the design, fabrication, and performance of these devices are discussed. In addition, the ability to produce heteroepitaxial layers of GaAs and aluminum gallium arsenide (AlGaAs) makes possible micromachined membrane sensors with improved sensitivity compared to conventional SAW sensors. Micromachining techniques for fabricating flexural plate wave (FPW) and thickness shear mode (TSM) microsensors on thin GaAs membranes are presented and GaAs FPW delay line and TSM resonator performance is described.

  13. Anomalous diffusion of Ga and As from semi-insulating GaAs substrate into MOCVD grown ZnO films as a function of annealing temperature and its effect on charge compensation

    SciTech Connect

    Biswas, Pranab; Banerji, P.; Halder, Nripendra N.; Kundu, Souvik; Shripathi, T.; Gupta, M.

    2014-05-15

    The diffusion behavior of arsenic (As) and gallium (Ga) atoms from semi-insulating GaAs (SI-GaAs) into ZnO films upon post-growth annealing vis-à-vis the resulting charge compensation was investigated with the help of x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy. The films, annealed at 600 ºC and 700 ºC showed p-type conductivity with a hole concentration of 1.1 × 10{sup 18} cm{sup −3} and 2.8 × 10{sup 19} cm{sup −3} respectively, whereas those annealed at 800 ºC showed n-type conductivity with a carrier concentration of 6.5 × 10{sup 16} cm{sup −3}. It is observed that at lower temperatures, large fraction of As atoms diffused from the SI-GaAs substrates into ZnO and formed acceptor related complex, (As{sub Zn}–2V{sub Zn}), by substituting Zn atoms (As{sub Zn}) and thereby creating two zinc vacancies (V{sub Zn}). Thus as-grown ZnO which was supposed to be n-type due to nonstoichiometric nature showed p-type behavior. On further increasing the annealing temperature to 800 ºC, Ga atoms diffused more than As atoms and substitute Zn atoms thereby forming shallow donor complex, Ga{sub Zn}. Electrons from donor levels then compensate the p-type carriers and the material reverts back to n-type. Thus the conversion of carrier type took place due to charge compensation between the donors and acceptors in ZnO and this compensation is the possible origin of anomalous conduction in wide band gap materials.

  14. GaSb thermophotovoltaic cells grown on GaAs by molecular beam epitaxy using interfacial misfit arrays

    NASA Astrophysics Data System (ADS)

    Juang, Bor-Chau; Laghumavarapu, Ramesh B.; Foggo, Brandon J.; Simmonds, Paul J.; Lin, Andrew; Liang, Baolai; Huffaker, Diana L.

    2015-03-01

    There exists a long-term need for foreign substrates on which to grow GaSb-based optoelectronic devices. We address this need by using interfacial misfit arrays to grow GaSb-based thermophotovoltaic cells directly on GaAs (001) substrates and demonstrate promising performance. We compare these cells to control devices grown on GaSb substrates to assess device properties and material quality. The room temperature dark current densities show similar characteristics for both cells on GaAs and on GaSb. Under solar simulation the cells on GaAs exhibit an open-circuit voltage of 0.121 V and a short-circuit current density of 15.5 mA/cm2. In addition, the cells on GaAs substrates maintain 10% difference in spectral response to those of the control cells over a large range of wavelengths. While the cells on GaSb substrates in general offer better performance than the cells on GaAs substrates, the cost-savings and scalability offered by GaAs substrates could potentially outweigh the reduction in performance. By further optimizing GaSb buffer growth on GaAs substrates, Sb-based compound semiconductors grown on GaAs substrates with similar performance to devices grown directly on GaSb substrates could be realized.

  15. GaSb thermophotovoltaic cells grown on GaAs by molecular beam epitaxy using interfacial misfit arrays

    SciTech Connect

    Juang, Bor-Chau Laghumavarapu, Ramesh B.; Foggo, Brandon J.; Lin, Andrew; Simmonds, Paul J.; Liang, Baolai; Huffaker, Diana L.

    2015-03-16

    There exists a long-term need for foreign substrates on which to grow GaSb-based optoelectronic devices. We address this need by using interfacial misfit arrays to grow GaSb-based thermophotovoltaic cells directly on GaAs (001) substrates and demonstrate promising performance. We compare these cells to control devices grown on GaSb substrates to assess device properties and material quality. The room temperature dark current densities show similar characteristics for both cells on GaAs and on GaSb. Under solar simulation the cells on GaAs exhibit an open-circuit voltage of 0.121 V and a short-circuit current density of 15.5 mA/cm{sup 2}. In addition, the cells on GaAs substrates maintain 10% difference in spectral response to those of the control cells over a large range of wavelengths. While the cells on GaSb substrates in general offer better performance than the cells on GaAs substrates, the cost-savings and scalability offered by GaAs substrates could potentially outweigh the reduction in performance. By further optimizing GaSb buffer growth on GaAs substrates, Sb-based compound semiconductors grown on GaAs substrates with similar performance to devices grown directly on GaSb substrates could be realized.

  16. 8-band and 14-band kp modeling of electronic band structure and material gain in Ga(In)AsBi quantum wells grown on GaAs and InP substrates

    SciTech Connect

    Gladysiewicz, M.; Wartak, M. S.; Kudrawiec, R.

    2015-08-07

    The electronic band structure and material gain have been calculated for GaAsBi/GaAs quantum wells (QWs) with various bismuth concentrations (Bi ≤ 15%) within the 8-band and 14-band kp models. The 14-band kp model was obtained by extending the standard 8-band kp Hamiltonian by the valence band anticrossing (VBAC) Hamiltonian, which is widely used to describe Bi-related changes in the electronic band structure of dilute bismides. It has been shown that in the range of low carrier concentrations n < 5 × 10{sup 18 }cm{sup −3}, material gain spectra calculated within 8- and 14-band kp Hamiltonians are similar. It means that the 8-band kp model can be used to calculate material gain in dilute bismides QWs. Therefore, it can be applied to analyze QWs containing new dilute bismides for which the VBAC parameters are unknown. Thus, the energy gap and electron effective mass for Bi-containing materials are used instead of VBAC parameters. The electronic band structure and material gain have been calculated for 8 nm wide GaInAsBi QWs on GaAs and InP substrates with various compositions. In these QWs, Bi concentration was varied from 0% to 5% and indium concentration was tuned in order to keep the same compressive strain (ε = 2%) in QW region. For GaInAsBi/GaAs QW with 5% Bi, gain peak was determined to be at about 1.5 μm. It means that it can be possible to achieve emission at telecommunication windows (i.e., 1.3 μm and 1.55 μm) for GaAs-based lasers containing GaInAsBi/GaAs QWs. For GaInAsBi/Ga{sub 0.47}In{sub 0.53}As/InP QWs with 5% Bi, gain peak is predicted to be at about 4.0 μm, i.e., at the wavelengths that are not available in current InP-based lasers.

  17. Liquid encapsulated Czochralski growth of low dislocation GaAs

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, C. G.; Chen, R. T.; Holmes, D. E.

    1982-01-01

    The availability of high-quality, large-diameter GaAs substrates is key to the successful development and production of high-speed GaAs devices and high-efficiency GaAs solar cells. The liquid encapsulated Czochralski (LEC) technique has provided a means for producing large-diameter GaAs. Progress in improving the LEC growth process which has resulted in 3-inch GaAs crystals with exceptionally low dislocation densities and reduced propensity for twinning is reported. Undoped, semi-insulating GaAs ingots were grown in a Melbourn high-pressure LEC system. The effects of seed perfection, seed necking, cone angle, melt stoichiometry, ambient pressure, thickness of the B2O3 encapsulating layer, and diameter control on the dislocation density were investigated. The material was characterized by preferential etching and X-ray topography. It is shown that 3-inch diameter substrates can be produced with dislocation densities as low as 6000 per sq cm through proper selection and control of growth parameters. Also, the incidence of twinning can be reduced significantly by growing from slightly As-rich melts.

  18. Simulation of silicon diffusion in GaAs

    NASA Astrophysics Data System (ADS)

    Saad, A. M.; Velichko, O. I.

    2011-03-01

    The simulation of coupled diffusion of silicon atoms and point defects in GaAs has been carried out for diffusion at the temperatures of 1000 and 850 °C. The amphoteric behavior of silicon atoms in GaAs has been taken into account in the investigation of high concentration diffusion from silicon layer deposited on GaAs substrate. The calculated dopant profiles agree well with the experimental ones and they confirm the adequacy of the model of silicon diffusion used for simulation. A comparison with the experimental data has enabled this work to obtain the parameters of silicon effective diffusivity and other values describing high concentration silicon diffusion in GaAs.

  19. Advances in large-diameter liquid encapsulated Czochralski GaAs

    NASA Technical Reports Server (NTRS)

    Chen, R. T.; Holmes, D. E.; Kirkpatrick, C. G.

    1982-01-01

    The purity, crystalline perfection, and electrical properties of n- and p-type GaAs crystals grown by the liquid encapsulated Czochralski (LEC) technique are evaluated. The determination of the dislocation density, incidence of twinning, microstructure, background purity, mobility, and minority carrier diffusion length is included. The properties of the LEC GaAs crystals are generally comparable to, if not superior to those of small-diameter GaAs material grown by conventional bulk growth techniques. As a result, LEC GaAs is suitable for application to minority carrier devices requiring high-quality and large-area substrates.

  20. High efficiency thin-film GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Zwerdling, S.; Wang, K. L.; Yeh, Y. C. M.

    1981-01-01

    The paper demonstrates the feasibility of producing high-efficiency GaAs solar cells with high power-to-weight ratios by organic metallic chemical vapor deposition (OM-CVD) growth of thin epi-layers on suitable substrates. An AM1 conversion efficiency of 18% (14% AM0), or 17% (13% AM0) with a 5% grid coverage is achieved for a single-crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer. Thin GaAs epi-layers OM-CVD grown can be fabricated with good crystallographic quality using a Si-substrate on which a thin Ge epi-interlayer is first deposited by CVD from GeH4 and processed for improved surface morphology

  1. Enhancing optical absorption in InP and GaAs utilizing profile etching

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Fatemi, Navid S.; Landis, Geoffrey A.

    1991-01-01

    The current state of profile etching in GaAs and InP is summarized, including data on novel geometries attainable as a function of etchant temperature, composition, and rate; substrate orientation; carrier concentration; and oxide thickness between substrate and photoresist. V-grooved solar cells were manufactured with both GaAs and InP, and the improved optical absorption was demonstrated. Preferred parameters for various applications are listed and discussed.

  2. Enhancing optical absorption in InP and GaAs utilizing profile etching

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Fatemi, Navid S.; Landis, Geoffrey A.

    1991-01-01

    The current state of profile etching in GaAs and InP is summarized, including data on novel geometries attainable as a function of etchant temperature, composition, and rate; substrate orientation; carrier concentration; and oxide thickness between substrate and photoresist. V-grooved solar cells have been manufactured with both GaAs and InP, and the improved optical absorption demonstrated. Preferred parameters for various applications are listed and discussed.

  3. GaAs transistors formed by Be or Mg ion implantation

    NASA Technical Reports Server (NTRS)

    Hunsperger, R. G.; Marsh, O. J.

    1974-01-01

    N-p-n transistor structures have been formed in GaAs by implanting n-type substrates with Be ions to form base regions and then implanting them with 20-keV Si ions to form emitters. P-type layers have been produced in GaAs by implantation of either Mg or Be ions, with substrate at room temperature, followed by annealing at higher temperatures.

  4. Epitaxial and polycrystalline GaAs solar cells using OM-CVD techniques

    NASA Technical Reports Server (NTRS)

    Yeh, Y. C. M.; Wang, K. L.; Shin, B. K.; Stirn, R. J.

    1980-01-01

    GaAs epitaxial films were grown by chemical vapor deposition using organo-metallic sources (OM-CVD) on single crystal and polycrystalline bulk GaAs, as well as on bulk polycrystalline and recrystallized thin-film Ge substrates. Details of Antireflecting Metal-Oxide-Semiconductor (AMOS) solar cells fabricated on GaAs films grown on bulk polycrystalline Ge and recrystallized Ge thin-film substrates will be discussed, as well as preliminary photovoltaic results obtained for n(+)/p homojunction structures.

  5. ZnSe Films in GaAs Solar Cells

    NASA Technical Reports Server (NTRS)

    Kachare, Ram H.

    1987-01-01

    ZnSe increases efficiency and conserves material. Two proposed uses of zinc selenide films promise to boost performance and reduce cost of gallium arsenide solar cells. Accordingly ZnSe serves as surface-passivation layer and as sacrificial layer enabling repeated use of costly GaAs substrate in fabrication.

  6. Study of strain boundary conditions and GaAs buffer sizes in InGaAs quantum dots

    NASA Technical Reports Server (NTRS)

    Oyafuso, F.; Klimeck, G.; Boykin, T. B.; Bowen, R. C.; Allmen, P. von

    2003-01-01

    NEMO 3-D has been developed for the simulation of electronic structure in self-assembled InGaAs quantum dots on GaAs substrates. Typical self-assembled quantum dots in that material system contain about 0.5 to 1 million atoms. Effects of strain by the surrounding GaAs buffer modify the electronic structure inside the quantum dot significantly and a large GaAs buffer must be included in the strain and electronic structure.

  7. Free-standing GaAs nanowires growth on ITO glass by MOCVD

    NASA Astrophysics Data System (ADS)

    Wu, D.; Tang, X. H.; Olivier, A.; Li, X. Q.

    2015-04-01

    GaAs nanowires (NWs) are directly grown on indium tin oxide (ITO) glass substrate by metalorganic chemical vapour deposition (MOCVD), using Au nanoparticles (NPs) as catalyst. By functionalization of the ITO glass and optimization of the Au NPs deposition time, the Au NPs area density deposited on the ITO glass reaches 92 NP μm-2. Uniform and free-standing GaAs NWs without kinking or worm-shape defects have been grown at 430 °C. More than 96% of the NWs have tilt angles larger than 45° with respect of the substrate. The effects of the growth temperature and the Au NPs size on the GaAs NWs growth rate, the NW diameter, and tapering effect are investigated. These results of GaAs NWs growth are the essential step for understanding III-V NWs integration on transparent conductive oxide coated low cost substrate and developing high efficiencyhybrid solar cells.

  8. Cubic GaS: A Surface Passivator For GaAs

    NASA Technical Reports Server (NTRS)

    Hepp, Aloysius F.; Barron, Andrew R.; Power, Michael B.; Jenkins, Phillip P.; Macinnes, Andrew N.

    1994-01-01

    Thin films of cubic form of gallium sulfide (GaS) formed on surfaces of gallium arsenide (GaAs) substrates via metal/organic chemical vapor deposition (MOCVD). Deposited cubic GaS, crystalline lattice matched to substrate GaAs, neutralizes electrically active defects on surfaces of both n-doped and p-doped GaAs. Enabling important GaAs-based semiconducting materials to serve as substrates for metal/insulator/semiconductor (MIS) capacitors. Cubic GaS enables fabrication of ZnSe-based blue lasers and light-emitting diodes. Because GaS is optically transparent, deposited to form window layers for such optoelectronic devices as light-emitting diodes, solar optical cells, and semiconductor lasers. Its transparency makes it useful as interconnection material in optoelectronic integrated circuits. Also useful in peeled-film technology because selectively etched from GaAs.

  9. Peeled film GaAs solar cells for space power

    SciTech Connect

    Wilt, D.M.; Deangelo, F.L.; Thomas, R.D.; Bailey, S.G.; Landis, G.A.; Brinker, D.J.; Fatemi, N.S.

    1990-05-01

    Gallium arsenide (GaAs) peeled film solar cells were fabricated, by Organo-Metallic Vapor Phase Epitaxy (OMVPE), incorporating an aluminum arsenide (AlAs) parting layer between the device structure and the GaAs substrate. This layer was selectively removed by etching in dilute hydrofloric (HF) acid to release the epitaxial film. Test devices exhibit high series resistance due to insufficient back contact area. A new design is presented which uses a coverglass superstrate for structural support and incorporates a coplanar back contact design. Devices based on this design should have a specific power approaching 700 W/Kg.

  10. Peeled film GaAs solar cells for space power

    NASA Technical Reports Server (NTRS)

    Wilt, D. M.; Deangelo, F. L.; Thomas, R. D.; Bailey, S. G.; Landis, G. A.; Brinker, D. J.; Fatemi, N. S.

    1990-01-01

    Gallium arsenide (GaAs) peeled film solar cells were fabricated, by Organo-Metallic Vapor Phase Epitaxy (OMVPE), incorporating an aluminum arsenide (AlAs) parting layer between the device structure and the GaAs substrate. This layer was selectively removed by etching in dilute hydrofloric (HF) acid to release the epitaxial film. Test devices exhibit high series resistance due to insufficient back contact area. A new design is presented which uses a coverglass superstrate for structural support and incorporates a coplanar back contact design. Devices based on this design should have a specific power approaching 700 W/Kg.

  11. Electronic contribution to friction on GaAs

    SciTech Connect

    Applied Science and Technology Graduate Group, UC Berkeley; Dept. of Materials Sciences and Engineering, UC Berkeley; Salmeron, Miquel; Qi, Yabing; Park, J.Y.; Hendriksen, B.L.M.; Ogletree, D.F.; Salmeron, Miquel

    2008-04-15

    The electronic contribution to friction at semiconductor surfaces was investigated by using a Pt-coated tip with 50nm radius in an atomic force microscope sliding against an n-type GaAs(100) substrate. The GaAs surface was covered by an approximately 1 nm thick oxide layer. Charge accumulation or depletion was induced by the application of forward or reverse bias voltages. We observed a substantial increase in friction force in accumulation (forward bias) with respect to depletion (reverse bias). We propose a model based on the force exerted by the trapped charges that quantitatively explains the experimental observations of excess friction.

  12. Heterogeneous integration of GaAs pHEMT and Si CMOS on the same chip

    NASA Astrophysics Data System (ADS)

    Li-Shu, Wu; Yan, Zhao; Hong-Chang, Shen; You-Tao, Zhang; Tang-Sheng, Chen

    2016-06-01

    In this work, we demonstrate the technology of wafer-scale transistor-level heterogeneous integration of GaAs pseudomorphic high electron mobility transistors (pHEMTs) and Si complementary metal–oxide semiconductor (CMOS) on the same Silicon substrate. GaAs pHEMTs are vertical stacked at the top of the Si CMOS wafer using a wafer bonding technique, and the best alignment accuracy of 5 μm is obtained. As a circuit example, a wide band GaAs digital controlled switch is fabricated, which features the technologies of a digital control circuit in Si CMOS and a switch circuit in GaAs pHEMT, 15% smaller than the area of normal GaAs and Si CMOS circuits.

  13. Vapor phase epitaxy of CdTe on sapphire and GaAs

    NASA Astrophysics Data System (ADS)

    Kasuga, Masanobu; Futami, Hiroyuki; Iba, Yoshihiro

    1991-12-01

    CdTe films were deposited on three kinds of sapphire substrate and two kinds of GaAs substrate by open tube vapor transport. X-ray Laue diffraction study showed that CdTe(111) film grew on every kind of sapphire substrate used, i.e. on the (0001) basal plane, the (11 overline20)A plane and the (1 overline102)R plane, and that there exist a few degrees of tilt angel between CdTe(111) and the lattice plane of each substrate. The process of making the tilt angle may be explained by the atomistic mismatch model of the Cd and Al arrangement which is projected on the film-substrate interface. On GaAs(100), either CdTe(111) or CdTe(100) was obtained, whereas only a twin crystalline film was obtained on GaAs(111). These results are also consistent with the mismatch model of Cd and Ga atoms.

  14. Structural Evolution During Formation and Filling of Self-patterned Nanoholes on GaAs (100) Surfaces

    PubMed Central

    2008-01-01

    Nanohole formation on an AlAs/GaAs superlattice gives insight to both the “drilling” effect of Ga droplets on AlAs as compared to GaAs and the hole-filling process. The shape and depth of the nanoholes formed on GaAs (100) substrates has been studied by the cross-section transmission electron microscopy. The Ga droplets “drill” through the AlAs layer at a much slower rate than through GaAs due to differences in activation energy. Refill of the nanohole results in elongated GaAs mounds along the [01−1] direction. As a result of capillarity-induced diffusion, GaAs favors growth inside the nanoholes, which provides the possibility to fabricate GaAs and AlAs nanostructures. PMID:20596345

  15. High-voltage picosecond photoconductor switch based on low-temperature-grown GaAs

    NASA Technical Reports Server (NTRS)

    Frankel, Michael Y.; Whitaker, John F.; Mourou, Gerard A.; Smith, Frank W.; Calawa, Arthur R.

    1990-01-01

    A GaAs material grown by molecular beam epitaxy at a low substrate temperature was used to fabricate a photoconductor switch that produces 6-V picosecond electrical pulses. The pulses were produced on a microwave coplanar-strip transmission line lithographically patterned on the low-temperature (LT) GaAs. A 150-fs laser pulse was used to generate carriers in the LT GaAs gap between the metal strips, partially shorting a high DC voltage placed across the lines. The 6-V magnitude of the electrical pulses obtained is believed to be limited by the laser pulse power and not by the properties of the LT GaAs. Experiments were also performed on a picosecond photoconductor switch fabricated on a conventional ion-damaged silicon-on-sapphire substrate. Although comparable pulse durations were obtained, the highest pulse voltage achieved with the latter device was 0.6 V.

  16. 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.

  17. Photonic crystal thin films of GaAs prepared by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Povey, I. M.; Whitehead, D.; Thomas, K.; Pemble, M. E.; Bardosova, M.; Renard, J.

    2006-09-01

    Photonic crystal thin films were fabricated via the self-assembly of a lattice of silica spheres on silicon (100) substrates. Progressive infilling of the air spaces within the structure with GaAs was achieved using trimethylgallium and arsine under atomic-layer-deposition conditions. Samples with the highest levels of GaAs infill were subsequently inverted using selective etching. Reflectance spectra are interpreted via the Bragg expression and calculated photonic band structure diagrams. For GaAs infilled and inverted samples, the relative positions of the first and second order Bragg reflections are strongly influenced by the wavelength dependent refractive index.

  18. Electron transfer and capture dynamics in ZnSe quantum wells grown on GaAs

    SciTech Connect

    Dongol, A.; Wagner, H. P.

    2013-12-04

    We investigate the transfer and capture dynamics of electrons in phase coherent photorefractive ZnSe quantum wells grown on GaAs using degenerate three-beam four-wave-mixing. The measurements reveal electron capture times by the quantum well in the order of several tens of picoseconds and a transit time of approximately 5 picoseconds from the GaAs substrate through the ZnMgSe barrier.

  19. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Lagowski, J.

    1981-01-01

    Experimental and theoretical efforts in the development of crystal growth approaches, effective techniques for electronic characterization on a macro and microscale, and in the discovery of phenomena and processes relevant to GaAs device applications are reported. The growth of electron trap-free bulk GaAS with extremely low density of dislocations is described. In electroepitaxy, growth configuration which eliminates the substrate back-contact was developed. This configuration can be extended to the simultaneous growth on many substrates with a thin solution layer sandwiched between any two of them. The significant reduction of Joule heating effects in the configuration made it possible to realize the in situ measurement of the layer thickness and the growth velocity. Utilizing the advantages of electroepitaxy in achieving abrupt acceleration (or deceleration) of the growth it was shown that recombination centers are formed as a result of growth acceleration.

  20. Experimental examination of gaas dissolution in in-p melt

    NASA Astrophysics Data System (ADS)

    Bolkhovityanov, Yu. B.; Bolkhovityanova, R. I.; Chikichev, S. I.

    1983-05-01

    The “solubility” of GaAs crystals in quaternary In-Ga-As-P liquids (X{Ga/I} = X{As/I}) has been studied experi-mentally at 770°C using seed-dissolution technique. The location of the true liquidus isotherm has been established independently by means of the direct vi-sual observation technique. Comparison between the two data sets indicates that the first method can be successfully used only for those In-Ga-As-P melt compositions which have the corresponding solid InxGa1-xAsyP1-y alloys nearly lattice-matched to the GaAs substrate. In other cases the results obtained by this method are totally misleading although in-teresting as they are. The phenomenon of “catastro-phic” substrate erosion is investigated. The results of the present study are interpreted within the conceptual framework developed previously.

  1. GaAs VLSI for aerospace electronics

    NASA Technical Reports Server (NTRS)

    Larue, G.; Chan, P.

    1990-01-01

    Advanced aerospace electronics systems require high-speed, low-power, radiation-hard, digital components for signal processing, control, and communication applications. GaAs VLSI devices provide a number of advantages over silicon devices including higher carrier velocities, ability to integrate with high performance optical devices, and high-resistivity substrates that provide very short gate delays, good isolation, and tolerance to many forms of radiation. However, III-V technologies also have disadvantages, such as lower yield compared to silicon MOS technology. Achieving very large scale integration (VLSI) is particularly important for fast complex systems. At very short gate delays (less than 100 ps), chip-to-chip interconnects severely degrade circuit clock rates. Complex systems, therefore, benefit greatly when as many gates as possible are placed on a single chip. To fully exploit the advantages of GaAs circuits, attention must be focused on achieving high integration levels by reducing power dissipation, reducing the number of devices per logic function, and providing circuit designs that are more tolerant to process and environmental variations. In addition, adequate noise margin must be maintained to ensure a practical yield.

  2. Implantation of carbon in GaAs

    SciTech Connect

    Moll, A.J.

    1992-03-01

    Carbon implanted into GaAs and thermally annealed typically exhibits very low (<3%) electrical activity. It has been demonstrated that the electrical activity of C can be significantly enhanced by co-implantation with Ga. Improved activation may result from either additional damage of the crystal lattice or from stoichiometric changes, forcing the C atoms onto As sites. To determine the relative importance of each of these effects, I have undertaken a systematic study of carbon activation in GaAs. A range of co-implants have been used: group III (B, Ga), group V (N, P, As) and noble gases (Ar, Kr). The damage introduced to the substrate will depend on the mass of the ion implanted. The group III and group V co-implants will affect the crystal stoichiometry. The results indicate that both lattice damage and crystal stoichiometry are important for high electrical activity of C. Increasing the damage will increase the activation due to the increased number of As vacancies but maximum activation can be obtained only by a co-implant which not only damages the lattice but also forces the C to occupy an As site.

  3. Epitaxial Fe on free-standing GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Yang, Mingze; Darbandi, Ali; Majumder, Sarmita; Watkins, Simon; Kavanagh, Karen

    2016-07-01

    Epitaxial Fe contacts have been fabricated onto the top half of free-standing, Te-doped GaAs nanowires (NWs) via electrodeposition. Electrical isolation from the substrate via a polymeric layer enabled the measurement of electrical transport through individual wires. Using a fixed probe within a scanning electron microscope, an average metal-semiconductor diode barrier height of 0.69 ± 0.03 eV (ideality factor 1.48 ± 0.02) was found.

  4. Wafer-fused orientation-patterned GaAs

    NASA Astrophysics Data System (ADS)

    Li, Jin; Fenner, David B.; Termkoa, Krongtip; Allen, Mark G.; Moulton, Peter F.; Lynch, Candace; Bliss, David F.; Goodhue, William D.

    2008-02-01

    The fabrication of thick orientation-patterned GaAs (OP-GaAs) films is reported using a two-step process where an OP-GaAs template with the desired crystal domain pattern was prepared by wafer fusion bonding and then a thick film was grown over the template by low pressure hydride vapor phase epitaxy (HVPE). The OP template was fabricated using molecular beam epitaxy (MBE) followed by thermocompression wafer fusion, substrate removal, and lithographic patterning. On-axis (100) GaAs substrates were utilized for fabricating the template. An approximately 350 μm thick OP-GaAs film was grown on the template at an average rate of ~70 μm/hr by HVPE. The antiphase domain boundaries were observed to propagate vertically and with no defects visible by Nomarski microscopy in stain-etched cross sections. The optical loss at ~2 μm wavelength over an 8 mm long OP-GaAs grating was measured to be no more than that of the semi-insulating GaAs substrate. This template fabrication process can provide more flexibility in arranging the orientation of the crystal domains compared to the Ge growth process and is scalable to quasi-phase-matching (QPM) devices operating from the IR to terahertz frequencies utilizing existing industrial foundries.

  5. Droplet-mediated formation of embedded GaAs nanowires in MBE GaAs1-x Bi x films

    NASA Astrophysics Data System (ADS)

    Wood, Adam W.; Collar, Kristen; Li, Jincheng; Brown, April S.; Babcock, Susan E.

    2016-03-01

    We have examined the morphology and composition of embedded nanowires that can be formed during molecular beam epitaxy of GaAs1-x Bi x using high angle annular dark field (‘Z-contrast’) imaging in an aberration-corrected scanning transmission electron microscope. Samples were grown in Ga-rich growth conditions on a stationary GaAs substrate. Ga-rich droplets are observed on the surface with lateral trails extending from the droplet in the [110] direction. Cross-sectional scanning transmission electron microscopy of the film reveals epitaxial nanowire structures of composition ˜GaAs embedded in the GaAs1-x Bi x epitaxial layers. These nanowires extend from a surface droplet to the substrate at a shallow angle of inclination (˜4°). They typically are 4 μm long and have a lens-shaped cross section with major and minor axes dimensions of 800 and 120 nm. The top surface of the nanowires exhibits a linear trace in longitudinal cross-section, across which the composition change from ˜GaAs to GaAs1-x Bi x appears abrupt. The bottom surfaces of the nanowires appear wavy and the composition change appears to be graded over ˜25 nm. The droplets have phase separated into Ga- and Bi-rich components. A qualitative model is proposed in which Bi is gettered into Ga droplets, leaving Bi depleted nanowires in the wakes of the droplets as they migrate in one direction across the surface during GaAs1-x Bi x film growth.

  6. High power cascaded mid-infrared InAs/GaSb light emitting diodes on mismatched GaAs

    SciTech Connect

    Provence, S. R. Ricker, R.; Aytac, Y.; Boggess, T. F.; Prineas, J. P.

    2015-09-28

    InAs/GaSb mid-wave, cascaded superlattice light emitting diodes are found to give higher radiance when epitaxially grown on mismatched GaAs substrates compared to lattice-matched GaSb substrates. Peak radiances of 0.69 W/cm{sup 2}-sr and 1.06 W/cm{sup 2}-sr for the 100 × 100 μm{sup 2} GaSb and GaAs-based devices, respectively, were measured at 77 K. Measurement of the recombination coefficients shows the shorter Shockley-Read-Hall recombination lifetime as misfit dislocations for growth on GaAs degrade the quantum efficiency only at low current injection. The improved performance on GaAs was found to be due to the higher transparency and improved thermal properties of the GaAs substrate.

  7. Processing and characterization of epitaxial GaAs radiation detectors

    NASA Astrophysics Data System (ADS)

    Wu, X.; Peltola, T.; Arsenovich, T.; Gädda, A.; Härkönen, J.; Junkes, A.; Karadzhinova, A.; Kostamo, P.; Lipsanen, H.; Luukka, P.; Mattila, M.; Nenonen, S.; Riekkinen, T.; Tuominen, E.; Winkler, A.

    2015-10-01

    GaAs devices have relatively high atomic numbers (Z=31, 33) and thus extend the X-ray absorption edge beyond that of Si (Z=14) devices. In this study, radiation detectors were processed on GaAs substrates with 110 - 130 μm thick epitaxial absorption volume. Thick undoped and heavily doped p+ epitaxial layers were grown using a custom-made horizontal Chloride Vapor Phase Epitaxy (CVPE) reactor, the growth rate of which was about 10 μm / h. The GaAs p+/i/n+ detectors were characterized by Capacitance Voltage (CV), Current Voltage (IV), Transient Current Technique (TCT) and Deep Level Transient Spectroscopy (DLTS) measurements. The full depletion voltage (Vfd) of the detectors with 110 μm epi-layer thickness is in the range of 8-15 V and the leakage current density is about 10 nA/cm2. The signal transit time determined by TCT is about 5 ns when the bias voltage is well above the value that produces the peak saturation drift velocity of electrons in GaAs at a given thickness. Numerical simulations with an appropriate defect model agree with the experimental results.

  8. Fracture mechanics evaluation of GaAs

    NASA Technical Reports Server (NTRS)

    Chen, C. P.

    1984-01-01

    A data base of mechanical and fracture properties for GaAs was generated. The data for single crystal GaAs will be used to design reusable GaAs solar modules. Database information includes; (1) physical property characterizations; (2) fracture behavior evaluations; and (3) strength of cells determined as a function of cell processing and material parameters.

  9. Enhanced light absorption in GaAs solar cells with internal Bragg reflectors

    NASA Astrophysics Data System (ADS)

    Tobin, S. P.; Vernon, S. M.; Sanfacon, M. M.; Mastrovito, A.

    The use of epitaxial multilayer dielectric mirrors (Bragg reflectors) as back-surface reflectors in thin-film GaAs solar cells on GaAs and silicon substrates is investigated. Al0.3Ga0.9As/Al0.85Ga0.15As Bragg reflectors were grown by low-pressure MOCVD on GaAs substrates and shown to exhibit near-ideal optical reflectance and structural perfection. Thin GaAs solar cells grown on Bragg reflectors showed increases in short-circuit current (0.5 to 1.0 mA/sq cm) and efficiency (0.7 percentage points) relative to cells without back reflectors. Efficiencies of 24.7 percent at one sun AM1.5 were measured for GaAs cells only 2 microns thick on Bragg reflectors. In addition to the optical enhancements, Bragg reflectors also appear to improve the defect structure of GaAs-on-Si solar cells. This approach should lead to improved efficiency for GaAs-on-Si solar cells and improved radiation resistance on GaAs cells.

  10. High purity liquid phase epitaxial GaAs for radiation detectors

    SciTech Connect

    Wynne, D.I.; Haller, E.E.; Rossington Tull, C.S.

    1998-12-31

    The authors report on the growth of high purity n-GaAs using Liquid Phase Epitaxy (LPE) and the fabrication of room temperature p-i-n radiation detectors. The epilayers are grown from a Ga solvent in a graphite boat in a pure hydrogen atmosphere. Growth is started at a temperature of approximately 800 C. The best epilayers show a net-residual-donor concentration of 2 {times} 10{sup 13} cm{sup {minus}3}, confirmed by Hall effect measurements. The residual donors have been analyzed by far infrared spectroscopy and found to be sulfur and silicon. Epilayers with thicknesses of up to 120 {micro}m have been deposited on 650 {micro}m thick semi-insulating GaAs substrates and on 500 {micro}m thick n{sup +}-type GaAs substrates. The authors report the results obtained with Schottky barrier diodes fabricated from these high purity n-type GaAs epilayers and operated as X-ray detectors. The Schottky barrier contacts consisted of evaporated circular gold contacts on epilayers on n{sup +} substrates. The ohmic contacts were formed by evaporated and alloyed Ni-Ge-Au films on the back of the substrate. Several of the diodes exhibit currents of the order of 1 to 10 nA at reverse biases depleting approximately 50 {micro}m of the epilayer. This very encouraging result, demonstrating the possibility for fabricating GaAs p-i-n diodes with depletion layers in high purity GaAs instead of semi-insulating GaAs, is supported by similar results obtained by several other groups. The consequences of using high purity instead of semi-insulating GaAs will be much reduced charge carrier trapping. Diode electrical characteristics and detector performance results using {sup 55}Fe and {sup 241}Am radiation will be discussed.

  11. Evolution Of Surface Topography On GaAs(100) And GaAs(111) At Normal And Oblique Incidence Of Ar{sup +}-Ions

    SciTech Connect

    Venugopal, V.; Basu, T.; Garg, S.; Majumder, S.; Sarangi, S. N.; Som, T.; Das, P.; Bhattacharyya, S. R.; Chini, T. K.

    2010-10-04

    Nanoscale surface structures emerging from medium energy (50-60 keV)Ar{sup +}-ion sputtering of p-type GaAs(100) and semi-insulating GaAs(111) substrates have been investigated. For normally incident 50 keV Ar{sup +}-ions of fluence 1x10{sup 17} ions/cm{sup 2} on GaAs(100) and GaAs(111) features in the form of nanoscale pits/holes without short range ordering are observed with densities 5.2x10{sup 9} /cm{sup 2} and 5.9x10{sup 9} /cm{sup 2}, respectively along with irregularly shaped patches of islands. For GaAs(111) on increasing the influence to 5x10{sup 17} /cm{sup 2} the pit density increases marginally to 6.2x10{sup 9} /cm{sup 2}. For 60 deg. off-normal incidence of 60 keV Ar.{sup +}-ions of fluence 2x10{sup 17} ions/cm{sup 2} on GaAs(100) microscale wavelike surface topography is observed. In all cases well-defined nanodots are absent on the surface.

  12. Fracture strength of GaAs solar cells as a function of manufacturing process steps

    NASA Technical Reports Server (NTRS)

    Chen, C. P.; Leipold, M. H.

    1985-01-01

    Fracture of single crystal GaAs substrate during the solar cell processing is an important factor in solar cell yield and cost. Fracture mechanics technique was utilized to evaluate cell cracking characteristics and changes in fracture strength of GaAs solar cells in a present state-of-the-art of manufacturing process for GaAs solar cells from wafer to complete cell of a typical production line. Considerable change in the fracture strength of GaAs solar cells as a function of cell processing was found. The strength data were described by Weibull statistical analysis and can be interpreted with the change of flaw distribution of each of the manufacturing process steps.

  13. Epitaxial thin film GaAs solar cells using OM-CVD techniques. [Organometallics

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.; Wang, K. L.; Yeh, Y. C. M.

    1981-01-01

    A new approach has been initiated at JPL to fabricate thin-film, high efficiency GaAs solar cells on low-cost, single-crystal Si substrates having a thin CVD interlayer of Ge to minimize the lattice and thermal expansion mismatch. For initial experiments, n(+)/p GaAs cells were grown by OM-CVD on single-crystal GaAs and Ge wafers. Details of the growths and performance results will be presented. Subsequently, a combined epitaxial structure of OM-CVD GaAs on a strongly adherent Ge interlayer on (100) Si was grown. This is the first report of the successful growth of this composite structure. Low module costs projected by JPL SAMICS methodology calculations and the potential for 400-600W/kg space solar arrays will be discussed.

  14. Quantitative study of GaAs nanowires catalyzed by Au film of different thicknesses

    PubMed Central

    2012-01-01

    In this letter, we quantitatively investigated epitaxial GaAs nanowires catalyzed by thin Au films of different thicknesses on GaAs (111)B substrates in a metal-organic chemical vapor deposition reactor. Prior to nanowire growth, the de-wetting of Au thin films to form Au nanoparticles on GaAs (111)B in AsH3 ambient at different temperatures is investigated. It is found that with increasing film thickness, the size of the Au nanoparticles increases while the density of the nanoparticles reduces. Furthermore, higher annealing temperature produces larger Au nanoparticles for a fixed film thickness. As expected, the diameters and densities of the as-grown GaAs nanowires catalyzed by these thin Au films reflect these trends. PMID:23095345

  15. Basic properties of GaAs oxide generated by scanning probe microscope tip-induced nano-oxidation process

    NASA Astrophysics Data System (ADS)

    Okada, Yoshitaka; Iuchi, Yoshimasa; Kawabe, Mitsuo; Harris, James S.

    2000-07-01

    The basic properties of GaAs oxide generated by atomic force microscope (AFM) tip-induced nano-oxidation process have been investigated. The chemical analysis of the AFM tip-generated GaAs oxide was performed by using scanning microprobe x-ray photoelectron spectroscopy, and the main constituents of GaAs anodic oxide were determined to be Ga2O3 and As2O3. The electrical characterization showed that the electron transport across a GaAs oxide nanodot of ˜5.7 nm thickness, from a doped n+-Si tip into the n+-GaAs substrate follows the Fowler-Nordheim tunneling mechanism over a range of applied bias. Further, the tip-generated GaAs oxide nanodots were found to withstand moderate thermal treatments, but some volume reduction was observed.

  16. Some Aspects of the RHEED Behavior of Low-Temperature GaAs Growth

    SciTech Connect

    Nemcsics, A.

    2005-11-15

    The reflection high-energy electron diffraction (RHEED) behavior manifested during MBE growth on a GaAs(001) surface under low-temperature (LT) growth conditions is examined in this study. RHEED and its intensity oscillations during LT GaAs growth exhibit some particular behavior. The intensity, phase, and decay of the oscillations depend on the beam equivalent pressure (BEP) ratio and substrate temperature, etc. Here, the intensity dependence of RHEED behavior on the BEP ratio, substrate temperature, and excess of As content in the layer are examined. The change in the decay constant of the RHEED oscillations is also discussed.

  17. High-efficiency thin-film GaAs solar cells, phase2

    NASA Technical Reports Server (NTRS)

    Yeh, Y. C. M.

    1981-01-01

    Thin GaAs epi-layers with good crystallographic quality were grown using a (100) Si-substrate on which a thin Ge epi-interlayer was grown by CVD from germane. Both antireflection-coated metal oxide semiconductor (AMOS) and n(+)/p homojunction structures were studied. The AMOS cells were fabricated on undoped-GaAs epi-layers deposited on bulk poly-Ge substrates using organo-metallic CVD film-growth, with the best achieved AM1 conversion efficiency being 9.1%. Both p-type and n(+)-type GaAs growth were optimized using 50 ppm dimethyl zinc and 1% hydrogen sulfide, respectively. A direct GaAs deposition method in fabricating ultra-thin top layer, epitaxial n(+)/p shallow homojunction solar cells on (100) GaAs substrates (without anodic thinning) was developed to produce large area (1 sq/cm) cells, with 19.4% AM1 conversion efficiency achieved. Additionally, an AM1 conversion efficiency of 18.4% (17.5% with 5% grid coverage) was achieved for a single crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer.

  18. A V-grooved GaAs solar cell

    NASA Technical Reports Server (NTRS)

    Bailey, S. G.; Fatemi, N. S.; Landis, G. A.; Wilt, D. M.; Thomas, R. D.; Arrison, A.

    1988-01-01

    V-grooved GaAs solar cells promise the benefits of improved optical coupling, higher short-circuit current, and increased tolerance to particle radiation compared to planar cells. A GaAs homojunction cell was fabricated by etching a V-groove pattern into an n epilayer (2.1 x 10 to the 17th power per cu cm) grown by metalorganic chemical vapor deposition (MOCVD) on an n+ substrate (2.8 x 10 to the 18th power per cu cm) and then depositing and MOCVD p epilayer (4.2 x 10 to the 18th power per cu cm). Reflectivity measurements on cells with and without an antireflective coating confirm the expected decrease in reluctance of the microgrooved cell compared to the planar structure. The short circuit current of the V-grooved solar cell was 13 percent higher than that of the planar control.

  19. Investigation of interfacial roughness of In sub x Ga sub 1 minus x As epitaxial layers on GaAs and InP substrates by soft x-ray reflectivity

    SciTech Connect

    Krol, A.; Resat, H.; Sher, C.J.; Woronick, S.C.; Ng, W.; Kao, Y.H. ); Cole, T.L.; Green, A.K.; Lowe-Ma, C.K.; Nee, T.; Rehn, V. )

    1991-01-15

    The grazing incidence x-ray reflectivity is a nondestructive and sensitive technique for probing the depth profile of electron density in layered structures. This method has been utilized in the soft x-ray regime to determine the roughness of interfaces, and the epilayer thickness in In{sub {ital x}}Ga{sub 1{minus}{ital x}}As/InP and In{sub {ital x}}Ga{sub 1{minus}{ital x}}As/GaAs heterostructures, for {ital x}=0.57 and {ital x}=0.60, grown by molecular beam epitaxy. By fitting the experimental results to our model, assuming uncorrelated interfacial roughness, we conclude that the top surface roughness does not depend on the type of the substrate or presence of stress in the epilayer, and is always smaller than interfacial roughness. The main factors which control the interfacial roughness are the quality of substrate and/or growth conditions rather than strain or lattice mismatch.

  20. 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.

  1. Gallium loading of gold seed for high yield of patterned GaAs nanowires

    SciTech Connect

    Boulanger, J. P.; Chia, A. C. E.; LaPierre, R. R.

    2014-08-25

    A method is presented for maximizing the yield and crystal phase purity of vertically aligned Au-assisted GaAs nanowires grown with an SiO{sub x} selective area epitaxy mask on GaAs (111)B substrates. The nanowires were grown by the vapor-liquid-solid (VLS) method in a gas source molecular beam epitaxy system. During annealing, Au VLS seeds will alloy with the underlying GaAs substrate and collect beneath the SiO{sub x} mask layer. This behavior is detrimental to obtaining vertically aligned, epitaxial nanowire growth. To circumvent this issue, Au droplets were pre-filled with Ga assuring vertical yields in excess of 99%.

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

    PubMed Central

    2010-01-01

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

  3. X-ray photoelectron spectroscopy studies of initial growth mechanism of CdTe layers grown on (100)GaAs by organometallic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Sone, Syuji; Ekawa, Mitsuru; Yasuda, Kazuhito; Sugiura, Yoshiyuki; Saji, Manabu; Tanaka, Akikazu

    1990-02-01

    Variations of the GaAs surface conditions and the adsorption of the precursor elements of Cd and Te on the (100)GaAs substrate were studied by x-ray photoelectron spectroscopy at the initial stage of CdTe growth by organometallic vapor phase epitaxy. The stoichiometry of GaAs substrates was found to recover by annealing in the H2 environment (500 °C, 5 min), while the surface was initially in an As-rich condition after etching with H2SO4:H2O2:H2O (5:1:1). The preferential adsorption of Te on the GaAs surface was also observed. <100> oriented growth was obtained routinely when the GaAs surface was fully stabilized with Te after the H2 anneal under the above conditions. <111> oriented growth resulted when dimethylcadmium was first introduced after the anneal.

  4. Investigation of the optical and electrical properties of p-type porous GaAs structure

    NASA Astrophysics Data System (ADS)

    Saghrouni, H.; Missaoui, A.; Hannachi, R.; Beji, L.

    2013-12-01

    Porous GaAs layers have been formed by electrochemical anodic etching of (1 0 0) heavily doped p-type GaAs substrate in a HF:C2H5OH solution. The surface morphology of porous GaAs has been studied using atomic force microscopy (AFM). Nano-structural nature of the porous layer has been demonstrated by X-ray diffraction analysis (XRD) and confirmed by AFM. An estimation of the main size of the GaAs crystallites obtained from effective mass theory and based on PL data was close to the lowest value obtained from the AFM results. The porous p-GaAs samples are characterised by spectroscopic ellipsometry and modulation spectroscopy techniques. The objective of this study is to determine the porosity, refractive index, and thickness. The porosity of GaAs determined by atomic force microscopy confirmed by the value obtained from the spectroscopic ellipsometry. In fact the current-voltage I(V) characteristics of metal-semiconductor Au/p-GaAs are investigated and compared with Au/p-porous GaAs structures. From the forward bias I(V) characteristics of these devices, the main electrical parameters such as ideality factor, barrier height, and series resistance have been determined.

  5. 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.

  6. Fabrication of 80-nm T-gate high indium In0.7Ga0.3As/In0.6Ga0.4As composite channels mHEMT on GaAs substrate with simple technological process

    NASA Astrophysics Data System (ADS)

    Xian, Ji; Xiaodong, Zhang; Weihua, Kang; Zhili, Zhang; Jiahui, Zhou; Wenjun, Xu; Qi, Li; Gongli, Xiao; Zhijun, Yin; Yong, Cai; Baoshun, Zhang; Haiou, Li

    2016-02-01

    An 80-nm gate length metamorphic high electron mobility transistor (mHEMT) on a GaAs substrate with high indium composite compound-channels In0.7Ga0.3 As/In0.6Ga0.4 As and an optimized grade buffer scheme is presented. High 2-DEG Hall mobility values of 10200 cm2/(V·s) and a sheet density of 3.5 × 1012 cm-2 at 300 K have been achieved. The device's T-shaped gate was made by utilizing a simple three layers electron beam resist, instead of employing a passivation layer for the T-share gate, which is beneficial to decreasing parasitic capacitance and parasitic resistance of the gate and simplifying the device manufacturing process. The ohmic contact resistance Rc is 0.2 ω·mm when using the same metal system with the gate (Pt/Ti/Pt/Au), which reduces the manufacturing cycle of the device. The mHEMT device demonstrates excellent DC and RF characteristics. The peak extrinsic transconductance of 1.1 S/mm and the maximum drain current density of 0.86 A/mm are obtained. The unity current gain cut-off frequency (fT) and the maximum oscillation frequency (fmax) are 246 and 301 GHz, respectively. Project supported by the Key Laboratory of Nano-Devices and Applications, Nano-Fabrication Facility of SINANO, Chinese Academy of Sciences, the National Natural Science Foundation of China (Nos. 61274077, 61474031, 61464003), the Guangxi Natural Science Foundation (Nos. 2013GXNSFGA019003, 2013GXNSFAA019335), the National Basic Research Program of China (Nos. 2011CBA00605, 2010CB327501), the Project (No. 9140C140101140C14069), and the Innovation Project of GUET Graduate Education (Nos. GDYCSZ201448, GDYCSZ201449, YJCXS201529).

  7. Substrate structures for InP-based devices

    DOEpatents

    Wanlass, Mark W.; Sheldon, Peter

    1990-01-01

    A substrate structure for an InP-based semiconductor device having an InP based film is disclosed. The substrate structure includes a substrate region having a lightweight bulk substrate and an upper GaAs layer. An interconnecting region is disposed between the substrate region and the InP-based device. The interconnecting region includes a compositionally graded intermediate layer substantially lattice-matched at one end to the GaAs layer and substantially lattice-matched at the opposite end to the InP-based film. The interconnecting region further includes a dislocation mechanism disposed between the GaAs layer and the InP-based film in cooperation with the graded intermediate layer, the buffer mechanism blocking and inhibiting propagation of threading dislocations between the substrate region, and the InP-based device.

  8. Preparation and characterization of pulse electrodeposited GaAs films

    NASA Astrophysics Data System (ADS)

    Murali, K. R.; Trivedi, D. C.

    2006-04-01

    GaAs is a III-V compound possessing high mobility and a direct band gap of 1.43 eV, making it a very suitable candidate for photovoltaic applications. Thin GaAs films were prepared by plating an aqueous solution containing GaCl3 and As2O3 at a pH of 2 and at room temperature. The current density was kept at 50 mA cm-2 and the duty cycle was varied in the range 10-50%. The films were deposited on titanium, nickel and tin oxide coated glass substrates. Films exhibited polycrystalline nature with peaks corresponding to single-phase GaAs. Optical absorption measurements indicated a direct band gap of 1.40 eV. Atomic force microscope measurements indicated uniform coverage with large crystallites for the films deposited at higher duty cycles. Photoelectrochemical cells were made using the films as photoelectrodes and graphite as counter electrode in 1 M polysulphide electrolyte. At 60 mW cm-2 illumination, an open-circuit voltage of 0.5 V and a short-circuit current density of 5.0 mA cm-2 were observed for the films deposited at a duty cycle of 50%.

  9. Integration of colossal magnetoresistors with GaAs

    NASA Astrophysics Data System (ADS)

    Khartsev, S. I.; Kim, J.-H.; Grishin, A. M.

    2005-10-01

    Colossal magnetoresistive (CMR) La 0.67Ca 0.33MnO 3 (LCMO) and La 0.67Sr 0.33MnO 3 (LSMO) films have been grown by pulsed laser deposition technique on GaAs(0 0 1) substrates buffered with epitaxial MgO layer. X-ray diffraction revealed strong c-axis out-of-plane orientation and strong in-plane texture of CMR/MgO bilayers on GaAs single crystal. The maximum temperature coefficient of resistivity TCR=9.0% K -1 at 223 K and 2.0% K -1 at 327 K, and the magnetoresistance Δ ρ/ ρ˜-7.95% kOe -1 and -1.47% kOe -1 have been achieved for LCMO/MgO/GaAs and LSMO/MgO/GaAs heteroepitaxial structures, respectively. Comparison with the test LCMO and LSMO films grown directly onto the bulk MgO(0 0 1) single crystal demonstrates the identity of LSMO/MgO/GaAs and LSMO/MgO films properties whereas the LCMO films grown on MgO buffered GaAs show lower transition temperature T=242 K compared to 253 K in LCMO/MgO.

  10. Phononic Crystal Waveguiding in GaAs

    NASA Astrophysics Data System (ADS)

    Azodi Aval, Golnaz

    Compared to the much more common photonic crystals that are used to manipulate light, phononic crystals (PnCs) with inclusions in a lattice can be used to manipulate sound. While trying to propagate in a periodically structured media, acoustic waves may experience geometries in which propagation forward is totally forbidden. Furthermore, defects in the periodicity can be used to confine acoustic waves to follow complicated routes on a wavelength scale. Using advanced fabrication methods, we aim to implement these structures to control surface acoustic wave (SAW) propagation on the piezoelectric surface and eventually interact SAWs with quantum structures. To investigate the interaction of SAWs with periodic elastic structures, SAW interdigital transducers (IDTs) and PnC fabrication procedures were developed. GaAs is chosen as a piezoelectric substrate for SAWs propagation. Lift-off photolithography processes were used to fabricate IDTs with finger widths as low as 1.5 microns. PnCs are periodic structures of shallow air holes created in GaAs substrate by means of a wet-etching process. The PnCs are square lattices with lattice constants of 8 and 4 microns. To predict the behavior of a SAW when interacting with the PnC structures, an FDTD simulator was used to calculate the band structures and SAW wave displacement on the crystal surface. The bandgap (BG) predicted for the 8 micron crystal ranges from 180 MHz to 220 MHz. Simulations show a shift in the BG position for 4 microns crystals ranging from 391 to 439 MHz. Two main waveguide geometries were considered in this work: a simple line waveguide and a funneling entrance line waveguide. Simulations indicated an increase in acoustic power density for the funneling waveguides. Fabricated device evaluated with electrical measurements. In addition, a scanning Sagnac interferometer is used to map the energy density of the SAWs. The Sagnac interferometer is designed to measure the outward displacement of a surface due to

  11. Weak interaction between germanene and GaAs(0001) by H intercalation: A route to exfoliation

    SciTech Connect

    Kaloni, T. P.; Schwingenschlögl, U.

    2013-11-14

    Epitaxial germanene on a semiconducting GaAs(0001) substrate is studied by ab initio calculations. The germanene-substrate interaction is found to be strong for direct contact but can be substantially reduced by H intercalation at the interface. Our results indicate that it is energetically possible to take the germanene off the GaAs(0001) substrate. While mounted on the substrate, the electronic structure shows a distinct Dirac cone shift above the Fermi energy with a splitting of 175 meV. On the other hand, we find for a free standing sheet a band gap of 24 meV, which is due to the intrinsic spin orbit coupling.

  12. Oxidation of GaAs Using Helicon-Wave Excited Nitrogen-Oxygen-Argon Plasma

    NASA Astrophysics Data System (ADS)

    Wada, Satoshi; Kasahara, Fumio; Hara, Akio; Ikoma, Hideaki

    1998-04-01

    GaAs (100) substrates were exposed to the helicon-wave excited N2 O2 Ar plasma without and with substrate heating at 200°C. The oxide dominantly composed of Ga2O3 and As2O3, was grown on the GaAs substrate using this technique. The chemical composition of this oxide was highly uniform along the thickness of the oxide film. Relatively good capacitance-voltage (C V) characteristics were obtained. X-ray photoelectron spectroscopic data indicated that gallium nitride (GaN) bonds were formed at the oxide/GaAs interface only with both substrate heating and post-thermal annealing at 200°C for 30 min in a nitrogen ambient. The formation of the GaN/GaAs interface improved the C V characteristics to some extent.

  13. Nano-structure fabrication of GaAs using AFM tip-induced local oxidation method: different doping types and plane orientations

    PubMed Central

    2011-01-01

    In this study, we have fabricated nano-scaled oxide structures on GaAs substrates that are doped in different conductivity types of p- and n-types and plane orientations of GaAs(100) and GaAs(711), respectively, using an atomic force microscopy (AFM) tip-induced local oxidation method. The AFM-induced GaAs oxide patterns were obtained by varying applied bias from approximately 5 V to approximately 15 V and the tip loading forces from 60 to 180 nN. During the local oxidation, the humidity and the tip scan speed are fixed to approximately 45% and approximately 6.3 μm/s, respectively. The local oxidation rate is further improved in p-type GaAs compared to n-type GaAs substrates whereas the rate is enhanced in GaAs(100) compared to and GaAs(711), respectively, under the identical conditions. In addition, the oxide formation mechanisms in different doping types and plane orientations were investigated and compared with two-dimensional simulation results. PMID:21978373

  14. Sol-gel derived ? thin films on GaAs

    NASA Astrophysics Data System (ADS)

    Arscott, S.; Smith, N.; Kurchania, R.; Milne, S. J.; Miles, R. E.

    1998-02-01

    Sol-gel derived thin films of lead zirconate titanate (PZT) have been fabricated on a platinized GaAs substrate using a propane-1,3-diol based sol-gel route. PZT can be used as the piezoelectric component in bulk acoustic wave devices for monolithic microwave integrated circuit applications. A 100 nm silicon nitride buffer layer was deposited onto the GaAs by plasma-enhanced chemical vapour deposition in order to prevent gallium and arsenic outdiffusion during film fabrication. Rapid thermal processing (RTP) techniques were employed to decompose thermally the sol-gel layer to PZT in a further effort to minimize problems of gallium and arsenic outdiffusion. Adhesion between the bottom electrode and substrate was found to improve when an intermediate titanium layer deposited between the platinum and silicon nitride was oxidized prior to deposition of the platinum electrode. A crystalline PZT film was produced on the 0268-1242/13/2/016/img9 substrate configuration by firing the sol-gel coating at 0268-1242/13/2/016/img10C for 10 s using RTP. A single deposition of sol resulted in a film having a thickness of 0268-1242/13/2/016/img11. Ferroelectric hysteresis measurements yielded average values of remanant polarization and coercive field of 0268-1242/13/2/016/img12 and 0268-1242/13/2/016/img13 respectively.

  15. Micromechanical Switches on GaAs for Microwave Applications

    NASA Technical Reports Server (NTRS)

    Randall, John N.; Goldsmith, Chuck; Denniston, David; Lin, Tsen-Hwang

    1995-01-01

    In this presentation, we describe the fabrication of micro-electro-mechanical system (MEMS) devices, in particular, of low-frequency multi-element electrical switches using SiO2 cantilevers. The switches discussed are related to micromechanical membrane structures used to perform switching of optical signals on silicon substrates. These switches use a thin metal membrane which is actuated by an electrostatic potential, causing the switch to make or break contact. The advantages include: superior isolation, high power handling capabilities, high radiation hardening, very low power operations, and the ability to integrate onto GaAs monolithic microwave integrated circuit (MMIC) chips.

  16. Bandgap and optical absorption edge of GaAs1-xBix alloys with 0 < x < 17.8%

    NASA Astrophysics Data System (ADS)

    Masnadi-Shirazi, M.; Lewis, R. B.; Bahrami-Yekta, V.; Tiedje, T.; Chicoine, M.; Servati, P.

    2014-12-01

    The compositional dependence of the fundamental bandgap of pseudomorphic GaAs1-xBix layers on GaAs substrates is studied at room temperature by optical transmission and photoluminescence spectroscopies. All GaAs1-xBix films (0 ≤ x ≤ 17.8%) show direct optical bandgaps, which decrease with increasing Bi content, closely following density functional theory predictions. The smallest measured bandgap is 0.52 eV (˜2.4 μm) at 17.8% Bi. Extrapolating a fit to the data, the GaAs1-xBix bandgap is predicted to reach 0 eV at 35% Bi. Below the GaAs1-xBix bandgap, exponential absorption band tails are observed with Urbach energies 3-6 times larger than that of bulk GaAs. The Urbach parameter increases with Bi content up to 5.5% Bi, and remains constant at higher concentrations. The lattice constant and Bi content of GaAs1-xBix layers (0 < x ≤ 19.4%) are studied using high resolution x-ray diffraction and Rutherford backscattering spectroscopy. The relaxed lattice constant of hypothetical zincblende GaBi is estimated to be 6.33 ± 0.05 Å, from extrapolation of the Rutherford backscattering spectrometry and x-ray diffraction data.

  17. High Quality GaAs Growth by MBE on Si Using GeSi Buffers and Prospects for Space Photovoltaics

    NASA Technical Reports Server (NTRS)

    Carlin, J. A.; Ringel, S. A.; Fitzgerald, E. A.; Bulsara, M.

    2005-01-01

    III-V solar cells on Si substrates are of interest for space photovoltaics since this would combine high performance space cells with a strong, lightweight and inexpensive substrate. However, the primary obstacles blocking III-V/Si cells from achieving high performance to date have been fundamental materials incompatabilities, namely the 4% lattice mismatch between GaAs and Si, and the large mismatch in thermal expansion coefficient. In this paper, we report on the molecular beam epitaxial (MBE) growth and properties of GaAs layers and single junction GaAs cells on Si wafers which utilize compositionally graded GeSi Intermediate buffers grown by ultra-high vacuum chemical vapor deposition (UHVCVD) to mitigate the large lattice mismatch between GaAs and Si. Ga As cell structures were found to incorporate a threading dislocation density of 0.9-1.5 x 10 (exp 6) per square centimeter, identical to the underlying relaxed Ge cap of the graded buffer, via a combination of transmission electron microscopy, electron beam induced current, and etch pit density measurements. AlGaAs/GaAs double heterostructures wre grown on the GeSi/Si substrates for time-resolved photoluminescence measurements, which revealed a bulk GaAs minority carrier lifetime in excess of 10 ns, the highest lifetime ever reported for GaAs on Si. A series of growth were performed to ass3ss the impact of a GaAs buffer to a thickness of only 0.1 micrometer. Secondary ion mass spectroscopy studies revealed that there is negligible cross diffusion of Ga, As and Ge at he III-V/Ge interface, identical to our earlier findings for GaAs grown on Ge wafers using MBE. This indicates that there is no need for a buffer to "bury" regions of high autodopjing,a nd that either pn or np configuration cells are easily accomodated by these substrates. Preliminary diodes and single junction Al Ga As heteroface cells were grown and fabricated on the Ge/GeSi/Si substrates for the first time. Diodes fabricated on GaAs, Ge and Ge

  18. Pseudo-Rhombus-Shaped Subwavelength Crossed Gratings of GaAs for Broadband Antireflection

    NASA Astrophysics Data System (ADS)

    Chen, Xi; Fan, Zhong-Chao; Zhang, Jing; Song, Guo-Feng; Chen, Liang-Hui

    2010-12-01

    Holographic lithography coupled with the nonlinear response of photoresist to the exposure is adopted to fabricate porous photoresist (PR) mask. Conventional dot PR mask is also generated, and both patterns are transferred into a underlying GaAs substrate by the optimal dry etching process to obtain tapered subwavelength crossed gratings (SWCGs) to mimic the moth-eye structure. In comparison of the experiment and simulation, the closely-packed pseudo-rhombus-shaped GaAs SWCGs resulting from the porous mask outperforms the conical counterpart which comes from the dot mask, and achieves a reported lowest mean spectral reflectance of 1.1%.

  19. Fabrication of ordered GaAs nanowhiskers using electron-beam lithography

    SciTech Connect

    Soshnikov, I. P.; Afanas'ev, D. E.; Cirlin, G. E.; Petrov, V. A.; Tanklevskaya, E. M.; Samsonenko, Yu. B.; Bouravlev, A. D.; Khrebtov, A. I.; Ustinov, V. M.

    2011-06-15

    The formation of ordered GaAs nanowhiskers obtained on GaAs (111)As substrates using electron-beam lithography and catalytic molecular-beam epitaxy (MBE) growth is studied experimentally. The main parameters of the e-beam lithographic process necessary for obtaining Au catalyst droplets 10-150 nm in size are determined. It is established that subsequent MBE growth proceeds predominantly by the diffusion mechanism. In the regions subjected to a repeated e-beam exposure after the lift-off process, suppression of nanowhisker growth can take place.

  20. Single crystal and polycrystalline GaAs solar cells using AMOS technology

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.; Yeh, Y. C. M.

    1976-01-01

    A description is given of current technology for fabricating single AMOS (antireflection-coated metal oxide semiconductor) solar cells, with attention given to thermal, plasma, and anodic oxidation, native oxide stripping, and X-ray photoelectron spectroscopy results. Some preliminary results are presented on the chemistry and electrical characterization of such cells, and the characteristics of cells fabricated on sliced polycrystalline GaAs wafers are examined. Consideration is also given to the recrystallization of evaporated Ge films for use as low-cost substrates for polycrystalline GaAs solar cells.

  1. Electron Beam Excited GaAs Maskless Etching Using C12 Nozzle Installed FIB/EB Combined System

    NASA Astrophysics Data System (ADS)

    Takado, Norikazu; Ide, Yuichi; Asakawa, Kiyoshi

    1990-02-01

    We have developed a new fine-beam assisted GaAs maskless etching system capable of nanofabrication; a focused ion beam (FIB) and electron beam (EB) combined etching system with a reactive gas nozzle. In this FIB/EB combined system, EB excited GaAs etching was successfully performed by irradiating Cl2 gas on a temperature-controlled substrate. 5KeV EB was raster-scanned in a 100pm X 20pm rectangular pattern on a GaAs surface. With special care to remove the native oxide layer, spatially selective etching was also confirmed on a cleaned GaAs surface by controlling the Cl2 pressure.

  2. Frequency-tunable continuous-wave terahertz sources based on GaAs plasmonic photomixers

    NASA Astrophysics Data System (ADS)

    Yang, Shang-Hua; Jarrahi, Mona

    2015-09-01

    We present frequency-tunable, continuous-wave terahertz sources based on GaAs plasmonic photomixers, which offer high terahertz radiation power levels at 50% radiation duty cycle. The use of plasmonic contact electrodes enhances photomixer quantum efficiency while maintaining its ultrafast operation by concentrating a large number of photocarriers in close proximity to the device contact electrodes. Additionally, the relatively high thermal conductivity and high resistivity of GaAs allow operation under high optical pump power levels and long duty cycles without reaching the thermal breakdown limit of the photomixer. We experimentally demonstrate continuous-wave terahertz radiation with a radiation frequency tuning range of more than 2 THz and a record-high radiation power of 17 μW at 1 THz through plasmonic photomixers fabricated on a low temperature grown GaAs substrate at 50% radiation duty cycle.

  3. 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

  4. Monolithic optical integrated control circuitry for GaAs MMIC-based phased arrays

    NASA Technical Reports Server (NTRS)

    Bhasin, K. B.; Ponchak, G. E.; Kascak, T. J.

    1985-01-01

    Gallium arsenide (GaAs) monolithic microwave integrated circuits (MMIC's) show promise in phased-array antenna applications for future space communications systems. Their efficient usage will depend on the control of amplitude and phase signals for each MMIC element in the phased array and in the low-loss radiofrequency feed. For a phased array contining several MMIC elements a complex system is required to control and feed each element. The characteristics of GaAs MMIC's for 20/30-GHz phased-array systems are discussed. The optical/MMIC interface and the desired characteristics of optical integrated circuits (OIC's) for such an interface are described. Anticipated fabrication considerations for eventual full monolithic integration of optical integrated circuits with MMIC's on a GaAs substrate are presented.

  5. Frequency-tunable continuous-wave terahertz sources based on GaAs plasmonic photomixers

    SciTech Connect

    Yang, Shang-Hua; Jarrahi, Mona

    2015-09-28

    We present frequency-tunable, continuous-wave terahertz sources based on GaAs plasmonic photomixers, which offer high terahertz radiation power levels at 50% radiation duty cycle. The use of plasmonic contact electrodes enhances photomixer quantum efficiency while maintaining its ultrafast operation by concentrating a large number of photocarriers in close proximity to the device contact electrodes. Additionally, the relatively high thermal conductivity and high resistivity of GaAs allow operation under high optical pump power levels and long duty cycles without reaching the thermal breakdown limit of the photomixer. We experimentally demonstrate continuous-wave terahertz radiation with a radiation frequency tuning range of more than 2 THz and a record-high radiation power of 17 μW at 1 THz through plasmonic photomixers fabricated on a low temperature grown GaAs substrate at 50% radiation duty cycle.

  6. Optical Response in Amorphous GaAs Thin Films Prepared by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Kiwa, Toshihiko; Kawashima, Ichiro; Nashima, Shigeki; Hangyo, Masanori; Tonouchi, Masayoshi

    2000-11-01

    Femtosecond optical response in GaAs thin films has been studied. We prepared GaAs thin films on MgO substrates and on YBa2Cu3O7-δ (YBCO) thin films using pulsed laser deposition (PLD) at temperatures below 250^\\circC@. A photocarrier lifetime of less than 1 ps is measured for the prepared GaAs thin films using femtosecond time-domain reflectivity change measurements. Pulsed electromagnetic wave [terahertz (THz) radiaiton] containing a frequency component of up to 1 THz is emitted from fabricated photoconductive switches using the prepared thin films. We also evaluated the THz radiation properties emitted from the photoswitches on the YBCO thin films.

  7. GaAs Refractive Index Dependence On Carrier Density and Optimizing Terahertz Devices

    NASA Astrophysics Data System (ADS)

    Kim, Christopher; Wu, Dong Ho; Graber, Benjamin

    GaAs is used for various applications, including high speed transistors, high-efficiency photovoltaic cells, electro-optics and terahertz (THz) emitters and detectors. To date, information on the refractive index of GaAs is available only over a limited wave spectrum of 0.2-17um, where the refractive index varies from 1.3 to 5.0. As detailed information on the refractive index of GaAs at THz frequencies is not available or inadequate for our effort to develop an improved GaAs-based THz emitter, we experimentally investigated the behavior of the refractive index of GaAs for different charge carrier densities, especially with or without the presence of surface plasma. Using a Time Domain THz Spectrometer, which is capable of measuring THz pulses containing a wave spectrum over 100-3000um with a time accuracy better than 6 femtoseconds, we measured the delay of THz pulses traversing through a GaAs substrate of known thickness while modulating the charge carrier concentration. From the experimental data we estimated the refractive index for THz frequencies to vary from 3.5 to 3.8 for different charge carrier concentrations. We will discuss details of our experiments and implications of our experimental results, especially for our GaAs-based THz devices.

  8. Technological steps reduction in the fabrication of high efficiency GaAs solar cells

    NASA Astrophysics Data System (ADS)

    Gavand, M.; Mayet, L.; Montegu, B.; Laugier, A.

    A simplified method to make high-efficiency GaAs solar cells by isothermal liquid-phase epitaxy has been investigated. A graded GaAlAs window layer was grown by isothermal contact between a Be-doped GaAlAs melt and a n-type GaAs substrate. With the aim of further reducing the fabrication cost, attempts were made to grow the junction and the window on the as-cut side of the wafers; with small modifications in the cleaning process, efficiencies up to 20 percent were obtained. The following substrates were considered: polycrystalline, chemically/mechanically polished monocrystalline, and buffer layer. The best efficiency of 22.7 percent (under 24 suns AM1.5, 25 deg C) was obtained when buffer-layer substrates were used.

  9. Droplet-mediated formation of embedded GaAs nanowires in MBE GaAs(1-x)Bi(x) films.

    PubMed

    Wood, Adam W; Collar, Kristen; Li, Jincheng; Brown, April S; Babcock, Susan E

    2016-03-18

    We have examined the morphology and composition of embedded nanowires that can be formed during molecular beam epitaxy of GaAs(1-x)Bi(x) using high angle annular dark field ('Z-contrast') imaging in an aberration-corrected scanning transmission electron microscope. Samples were grown in Ga-rich growth conditions on a stationary GaAs substrate. Ga-rich droplets are observed on the surface with lateral trails extending from the droplet in the [110] direction. Cross-sectional scanning transmission electron microscopy of the film reveals epitaxial nanowire structures of composition ∼GaAs embedded in the GaAs(1-x)Bi(x) epitaxial layers. These nanowires extend from a surface droplet to the substrate at a shallow angle of inclination (∼4°). They typically are 4 μm long and have a lens-shaped cross section with major and minor axes dimensions of 800 and 120 nm. The top surface of the nanowires exhibits a linear trace in longitudinal cross-section, across which the composition change from ∼GaAs to GaAs(1-x)Bi(x) appears abrupt. The bottom surfaces of the nanowires appear wavy and the composition change appears to be graded over ∼25 nm. The droplets have phase separated into Ga- and Bi-rich components. A qualitative model is proposed in which Bi is gettered into Ga droplets, leaving Bi depleted nanowires in the wakes of the droplets as they migrate in one direction across the surface during GaAs(1-x)Bi(x) film growth. PMID:26876494

  10. High antimony content GaAs1-zNz-GaAs1-ySby type-II ``W'' structure for long wavelength emission

    NASA Astrophysics Data System (ADS)

    Rathi, M. K.; Khandekar, A. A.; Song, Xueyan; Babcock, S. E.; Mawst, L. J.; Kuech, T. F.

    2009-09-01

    GaAs1-zNz-GaAs1-ySby type-II "W" structures were studied for long wavelength (1300-1600 nm) applications. These structures were grown on a GaAs substrate using metal-organic vapor phase epitaxy. The antimony and nitrogen compositions in the pseudomorphic GaAs1-ySby and GaAs1-zNz were estimated by separately growing GaAs1-ySby-GaAs and GaAs1-zNz-GaAs strained superlattices. X-ray studies indicate that a maximum of y =0.37 antimony can be incorporated in the pseudomorphic GaAs1-ySby film grown using triethyl gallium (TEGa), trimethyl antimony (TMSb) and arsine (AsH3) at the growth temperatures employed. A postgrowth anneal was used to improve the emission intensity but leads to shifts in the emission wavelength. An emission wavelength as long as 1.47 μm was realized using a GaAs1-zNz-GaAs1-ySby-GaAs1-zNz structure.

  11. Characterization of GaAs solar cells made by ion implantation and rapid thermal annealing using selective photoetching

    SciTech Connect

    van Sark, W.G.J.H.M.; Weyher, J.L.; Giling, L.J. ); de Potter, M.; van Rossum, M. )

    1990-05-01

    Shallow {ital n}-{ital p} GaAs solar cells have been made by implantation of Si into Zn-doped ({ital p}-type) GaAs substrates followed by rapid thermal annealing. The structure of the GaAs crystal has been determined by the DSL photoetching method (Diluted Sirtl-like etchants used with Light). It was found that implantation-induced-damage (revealed by DSL as microroughness and craters) was not removed after annealing for energies exceeding 60 keV. This leads to substrates that contain many precipitates, which appears to be disastrous for the fabrication of good solar cells. In addition, good cell performance is hampered by compensation effects in the {ital n}-{ital p} transition region and in the {ital n}-type layer itself.

  12. Pulse transformer for GaAs laser

    NASA Technical Reports Server (NTRS)

    Rutz, E. M.

    1976-01-01

    High-radiance gallium arsenide (GaAs) laser operating at room temperature is utilized in optical navigation system. For efficient transformer-to-laser impedance match, laser should be connected directly to pulse transformer secondary winding.

  13. Development of MBE II-VI Epilayers on GaAs(211)B

    NASA Astrophysics Data System (ADS)

    Jacobs, R. N.; Nozaki, C.; Almeida, L. A.; Jaime-Vasquez, M.; Lennon, C.; Markunas, J. K.; Benson, D.; Smith, P.; Zhao, W. F.; Smith, D. J.; Billman, C.; Arias, J.; Pellegrino, J.

    2012-10-01

    Large-area, low-cost substrates are envisioned for next-generation HgCdTe infrared focal-plane arrays (IRFPA). Si, GaAs, Ge, and InSb have been previously examined as potential candidates. Fabrication of IRFPAs based on these substrates is limited by fundamental materials properties that potentially lead to lower detector performance and operability. Lattice and thermal mismatch between the substrate and epilayer are just two of several material factors that must be considered. We have reviewed these factors in the context of more recent data, and determined it worthwhile to revisit the use of GaAs substrates for epitaxial growth of HgCdTe. Our study starts with an evaluation of the surface quality (epireadiness) of commercially available (211) B-oriented GaAs substrates. Molecular beam epitaxial growth of CdTe buffer layers and subsequent HgCdTe absorber layers are performed in separate vacuum-interconnected chambers. The importance of optimization of the CdTe buffer layer growth for high-quality HgCdTe is detailed through surface morphology and x-ray studies. x-Ray diffraction rocking-curve full-width at half-maximum values as low as 52 arcsec have been obtained. Long-wave infrared Hg1- x Cd x Te ( x = 0.23) has been grown on these buffer layers, producing cross-hatch-dominated surface morphologies, with dislocation densities as low as ˜3 × 106 cm-2. We have also obtained (for optimized layers), 80-K Hall-effect n-type carrier concentration and electron mobility of approximately ~1.5 × 1015 cm-3 and 1 × 105 cm2 V-1 s-1, respectively. Finally, we briefly compare GaAs and Si in light of our preliminary investigation.

  14. 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.

  15. Multi-spectral optical absorption in substrate-free nanowire arrays

    SciTech Connect

    Zhang, Junpeng; Chia, Andrew; Boulanger, Jonathan; LaPierre, Ray; Dhindsa, Navneet; Khodadad, Iman; Saini, Simarjeet

    2014-09-22

    A method is presented of fabricating gallium arsenide (GaAs) nanowire arrays of controlled diameter and period by reactive ion etching of a GaAs substrate containing an indium gallium arsenide (InGaP) etch stop layer, allowing the precise nanowire length to be controlled. The substrate is subsequently removed by selective etching, using the same InGaP etch stop layer, to create a substrate-free GaAs nanowire array. The optical absorptance of the nanowire array was then directly measured without absorption from a substrate. We directly observe absorptance spectra that can be tuned by the nanowire diameter, as explained with rigorous coupled wave analysis. These results illustrate strong optical absorption suitable for nanowire-based solar cells and multi-spectral absorption for wavelength discriminating photodetectors. The solar-weighted absorptance above the bandgap of GaAs was 94% for a nanowire surface coverage of only 15%.

  16. Analysis of twin defects in GaAs nanowires and tetrahedra and their correlation to GaAs(1 1 1)B surface reconstructions in selective-area metal organic vapour-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Yoshida, Hiroatsu; Ikejiri, Keitaro; Sato, Takuya; Hara, Shinjiroh; Hiruma, Kenji; Motohisa, Junichi; Fukui, Takashi

    2009-12-01

    We analyzed twin defects in GaAs nanowires as thin as 100-400 nm and tetrahedral structures as small as 1.0 μm, which were selectively grown by metal organic vapour-phase epitaxy (MOVPE) within a SiO 2 mask window fabricated on GaAs(1 1 1)B substrates. In particular, we focused on the correlation between the twins and GaAs(1 1 1)B surface reconstructions. We confirmed that the shape of GaAs crystals selectively grown on GaAs(1 1 1)B substrates changed from hexagonal nanowires to truncated tetrahedra when the size of the mask opening was increased from 100 to 1000 nm under the same growth conditions. The shape also changed from tetrahedral to hexagonal with decreasing growth temperature ( Tg: 600-800 °C) and with increasing arsine (AsH 3) partial pressure (1.0×10 -4 to 5.0×10 -4 atm). Rotational twins around the <1 1 1> axis were found in the tetrahedra by transmission electron microscopy (TEM) and scanning electron microscopy observations. In addition, the probability of twins developing in the tetrahedra increased with decreasing mask opening size, with decreasing Tg, and with increasing AsH 3 partial pressure. The TEM study also revealed the existence of a high density of rotational twins in the nanowires, and their density increased with decreasing nanowire diameter, suggesting a correlation between the twins and the shape/size of GaAs crystals. These findings were semi-quantitatively compared with a reported phase diagram for GaAs(1 1 1)B surface reconstruction. By analyzing the relationship between twin development and MOVPE conditions, we found that the shape change of GaAs crystals on GaAs(1 1 1)B and the formation of twins coincided well with the transition of GaAs surface reconstruction between the (2×2) and (√19×√19) structures.

  17. GaAs Semi-Insulating Layer for a GaAs Device

    NASA Technical Reports Server (NTRS)

    Sherrill, G.; Mattauch, R. J.

    1986-01-01

    Improved design for GaAs electronic device or integrated circuit designed to operate at cryogenic temperatures, customary SiO2 insulating layer replaced by semi-insulating layer of GaAs. Thermal expansions of device and covering layer therefore match closely, and thermal stresses caused by immersion in cryogenic chamber nearly eliminated.

  18. Preparation of pulse plated GaAs films

    NASA Astrophysics Data System (ADS)

    Murali, K. R.; Trivedi, D. C.

    2006-07-01

    Thin GaAs films were prepared by pulse plating from an aqueous solution containing 0.20 M GaCl3 and 0.15 M As2O3 at a pH of 2 and at room temperature. The current density was kept as 50 mA cm-2 the duty cycle was varied in the range 10 50%. The films were deposited on titanium, nickel and tin oxide coated glass substrates. Films exhibited polycrystalline nature with peaks corresponding to single phase GaAs. Optical absorption measurements indicated a direct band gap of 1.40 eV. Photoelectrochemical cells were made using the films as photoelectrodes and graphite as counter electrode in 1 M polysulphide electrolyte. At 60 mW cm-2 illumination, an open circuit voltage of 0.5 V and a short circuit current density of 5.0 mA cm-2 were observed for the films deposited at a duty cycle of 50%.

  19. Coupling reactions of trifluoroethyl iodide on GaAs(100)

    NASA Astrophysics Data System (ADS)

    Singh, N. K.; Kemp, N. T.; Paris, N.; Balan, V.

    2004-07-01

    We report on the reactions of 2-iodo-1,1,1-trifluoroethane (CF3CH2I) on gallium-rich GaAs(100)-(4×1), studied using the techniques of temperature programmed desorption and x-ray photoelectron spectroscopy. The study is to provide evidence for the formation of a higher fluorinated alkene, 1,1,4,4,4-pentafluoro-1-butene (CF2=CHCH2CF3) and alkane, 1,1,1,4,4,4-hexafluorobutane (CF3CH2CH2CF3) from the coupling reactions of covalently bonded surface alkyl (CF3CH2•) moieties. CF3CH2I adsorbs nondissociatively at 150 K. Thermal dissociation of this weakly chemisorbed state occurs below room temperature to form adsorbed CF3CH2• and I• species. The surface CF3CH2• species undergoes β-fluoride elimination to form gaseous CF2=CH2 and this represents the major pathway for the removal of CF3CH2• species from the surface. In competition with the β-fluoride elimination process the adsorbed CF3CH2• species also undergoes, recombination with surface iodine atoms to form recombinative molecular CF3CH2I, olefin insertion reaction with CF2=CH2 to form gaseous CF2=CHCH2CF3, and last self-coupling reaction to form CF3CH2CH2CF3. The adsorbed surface iodine atoms, formed by the dissociation of the molecularly chemisorbed CF3CH2I, and fluorine atoms formed during the β-fluoride elimination reaction, both form etch products (GaI, GaF, AsI, AsF, and As2) by their reactions with the surface layer Ga atoms, subsurface As atoms, and GaAs substrate. In this article we discuss the mechanisms by which these products form from the adsorbed CF3CH2• and I• species, and the role that the GaAs surface plays in the proposed reaction pathways. We compare the reactivity of the GaAs surface with transition metals in its ability to facilitate dehydrogenation and coupling reactions in adsorbed alkyl species. .

  20. Mechanism of catalyst-free growth of GaAs nanowires by selective area MOVPE

    NASA Astrophysics Data System (ADS)

    Ikejiri, Keitaro; Noborisaka, Jinichiro; Hara, Shinjiroh; Motohisa, Junichi; Fukui, Takashi

    2007-01-01

    We studied the growth mechanism of GaAs nanowires in selective-area metalorganic vapor phase epitaxy (MOVPE) by investigating the dependences on substrate orientations and growth conditions. The nanowire structures were formed only on GaAs (1 1 1)B substrate under high temperature (750 °C) and low arsine partial pressure conditions. Structures selectively grown on substrates with various orientations always exhibited specific low-index facets such as {1 1 0}, {1 1 1}A, and {1 1 1}B. It was also found that the appearance of these facets depended strongly on the growth conditions. Furthermore, we have observed a considerable lateral growth on the sidewalls of the nanowires when the growth temperature was lowered and arsine partial pressure was increased, indicating that the growth mode could be changed by the growth conditions. These results demonstrate that the growth mechanism of GaAs nanowires by SA-MOVPE is neither catalyst nor oxide assisted but by the formation of facets during growth.

  1. Growing antiphase-domain-free GaAs thin films out of highly ordered planar nanowire arrays on exact (001) silicon

    SciTech Connect

    Li, Qiang; Ng, Kar Wei; Lau, Kei May

    2015-02-16

    We report the use of highly ordered, dense, and regular arrays of in-plane GaAs nanowires as building blocks to produce antiphase-domain-free GaAs thin films on exact (001) silicon. High quality GaAs nanowires were grown on V-grooved Si (001) substrates using the selective aspect ratio trapping concept. The 4.1% lattice mismatch has been accommodated by the initial GaAs, a few nanometer-thick with high density stacking faults. The bulk of the GaAs wires exhibited smooth facets and a low defect density. An unusual defect trapping mechanism by a “tiara”-like structure formed by Si undercuts was discovered. As a result, we were able to grow large-area antiphase-domain-free GaAs thin films out of the nanowires without using SiO{sub 2} sidewalls for defect termination. Analysis from XRD ω-rocking curves yielded full-width-at-half-maximum values of 238 and 154 arc sec from 900 to 2000 nm GaAs thin films, respectively, indicating high crystalline quality. The growth scheme in this work offers a promising path towards integrated III-V electronic, photonic, or photovoltaic devices on large scale silicon platform.

  2. Femtosecond probe-probe transmission studies of LT-grown GaAs near the band edge

    SciTech Connect

    Radousky, H.B.; Bello, A.F.; Erskine, D.J.; Dinh, L.N.; Bennahmias, M.J.; Perry, M.D.; Ditmire, T.R.; Mariella, R.P. Jr.

    1993-12-01

    We have studied the near-edge optical response of a LT-grown GaAs sample which was deposited at 300{degrees}C on a Si substrate, and then annealed at 600{degrees}C. The Si was etched away to leave a 1 micron free standing GaAs film. Femtosecond transmission measurements were made using an equal pulse technique at four wavelengths between 825 and 870 nm. For each wavelength we observe both a multipicosecond relaxation time, as well as a shorter relaxation time which is less than 100 femtoseconds.

  3. High-Performance GaAs Nanowire Solar Cells for Flexible and Transparent Photovoltaics.

    PubMed

    Han, Ning; Yang, Zai-xing; Wang, Fengyun; Dong, Guofa; Yip, SenPo; Liang, Xiaoguang; Hung, Tak Fu; Chen, Yunfa; Ho, Johnny C

    2015-09-16

    Among many available photovoltaic technologies at present, gallium arsenide (GaAs) is one of the recognized leaders for performance and reliability; however, it is still a great challenge to achieve cost-effective GaAs solar cells for smart systems such as transparent and flexible photovoltaics. In this study, highly crystalline long GaAs nanowires (NWs) with minimal crystal defects are synthesized economically by chemical vapor deposition and configured into novel Schottky photovoltaic structures by simply using asymmetric Au-Al contacts. Without any doping profiles such as p-n junction and complicated coaxial junction structures, the single NW Schottky device shows a record high apparent energy conversion efficiency of 16% under air mass 1.5 global illumination by normalizing to the projection area of the NW. The corresponding photovoltaic output can be further enhanced by connecting individual cells in series and in parallel as well as by fabricating NW array solar cells via contact printing showing an overall efficiency of 1.6%. Importantly, these Schottky cells can be easily integrated on the glass and plastic substrates for transparent and flexible photovoltaics, which explicitly demonstrate the outstanding versatility and promising perspective of these GaAs NW Schottky photovoltaics for next-generation smart solar energy harvesting devices. PMID:26284305

  4. The role of proximity caps during the annealing of UV-ozone oxidized GaAs

    SciTech Connect

    Ghosh, S. C.; Biesinger, M. C.; LaPierre, R. R.; Kruse, P.

    2007-06-01

    This study provides a deeper insight into the chemistry and physics of the common engineering practice of using a proximity cap, while annealing compound semiconductors such as GaAs. We have studied the cases of a GaAs proximity cap, a Si proximity cap, and no proximity cap. Using x-ray photoelectron spectroscopy, it has been found that annealing increases the gallium to arsenic ratio in the oxide layer in all cases. During the annealing of UV-ozone oxidized GaAs, it has been observed that GaAs proximity caps also serve as a sacrificial layer to accelerate the desorption of oxide species. In all cases surface deterioration due to pit formation has been observed, and the depth of pits is found to depend on the effective role played by the capping material. Energy dispersive x-ray analysis provides additional evidence that pits mainly consist of elemental As and gallium oxide, with most of the elemental As situated at the pit-substrate interface. Deposition of a thin layer of gold and subsequent annealing to 500 deg. C for 300 s under different capping conditions shows the use of a proximate cap to be practically insignificant in annealing Au deposited films.

  5. Effects of surface passivation on twin-free GaAs nanosheets.

    PubMed

    Arab, Shermin; Chi, Chun-Yung; Shi, Teng; Wang, Yuda; Dapkus, Daniel P; Jackson, Howard E; Smith, Leigh M; Cronin, Stephen B

    2015-02-24

    Unlike nanowires, GaAs nanosheets exhibit no twin defects, stacking faults, or dislocations even when grown on lattice mismatched substrates. As such, they are excellent candidates for optoelectronic applications, including LEDs and solar cells. We report substantial enhancements in the photoluminescence efficiency and the lifetime of passivated GaAs nanosheets produced using the selected area growth (SAG) method with metal organic chemical vapor deposition (MOCVD). Measurements are performed on individual GaAs nanosheets with and without an AlGaAs passivation layer. Both steady-state photoluminescence and time-resolved photoluminescence spectroscopy are performed to study the optoelectronic performance of these nanostructures. Our results show that AlGaAs passivation of GaAs nanosheets leads to a 30- to 40-fold enhancement in the photoluminescence intensity. The photoluminescence lifetime increases from less than 30 to 300 ps with passivation, indicating an order of magnitude improvement in the minority carrier lifetime. We attribute these enhancements to the reduction of nonradiative recombination due to the compensation of surface states after passivation. The surface recombination velocity decreases from an initial value of 2.5 × 10(5) to 2.7 × 10(4) cm/s with passivation. PMID:25565000

  6. Low Temperature Photoluminescence Kinetics of Double-Ring Structured GaAs Quantum Dots.

    PubMed

    Myoung, Soung; Mun, Ok Mi; Yim, Sang-Youp; Kim, Jong Su

    2015-11-01

    This work is focused on spectroscopically characterizing kinetic properties of concentric quantum-ring complexes of GaAs quantum dots. Quantum-ring (or double-ring) GaAs quantum dots, embedded in an Al0.3Ga0.7As barrier layer, were grown by a droplet epitaxy method during molecular beam epitaxy on a GaAs (001) substrate. Emission peaks of photoluminescence spectra with different excitation power, were measured as 702 nm at 0.17 mW and 690 nm at 400 mW, were blue-shifted as the excitation power increased. In addition, excitation laser power dependence of time-resolved photoluminescence of double-ring GaAs quantum dots at 10 K under 400 nm excitation wavelength was performed, revealing that photoluminescence lifetime slowly decreased in comparison to that of single disc-like quantum dots as excitation power increased, implying that carrier transfer between inner ring and outer ring could slow down the decay process. The luminescence lifetime at 10 K increased from 245 to 409 ps in the range from 0.17 to 400 mW of excitation power. PMID:26726575

  7. Morphology of thermal oxide layers on GaAs

    NASA Astrophysics Data System (ADS)

    Beserman, R.; Schwarz, S. A.; Hwang, D. M.; Chen, C. Y.

    1991-08-01

    The oxidation process of pure GaAs has been studied with use of several complementary experimental techniques: Raman scattering, electrical conductivity, transmission electron microscopy, and secondary-ion mass spectrometry. The morphology of the oxide layer and the oxide-GaAs interface evolve as a function of oxidation time. A high density of well-oriented As microcrystallites penetrates into the substrate, forming a conductive interfacial layer in the early stages of the oxidation process. After longer oxidation times, when the Raman As intensity and the interfacial conductivity are reduced, As is distributed into the oxide layer, forming crystallites that are no longer well oriented. Simultaneously, the crystalline gallium oxide breaks up to into microcrystallites that could provide channels for the outdiffusion of As. From the experimental evidence, we deduce that the interfacial density of crystalline As is reduced for long oxidation times.

  8. Mid-wave T2SLs InAs/GaSb single pixel PIN detector with GaAs immersion lens for HOT condition

    NASA Astrophysics Data System (ADS)

    Martyniuk, Piotr; Benyahia, Djalal; Kowalewski, Andrzej; Kubiszyn, Łukasz; Stępień, Dawid; Gawron, Waldemar; Rogalski, Antoni

    2016-05-01

    In this paper we report on high operating temperature mid-wave infrared detector based on type-II superlattice InAs/GaSb mesa PIN architecture with 50% cut-off wavelength ∼5.2 μm at 230 K. The 1.1 mm thick GaAs substrate was converted into immersion lens to limit an influence of the defects occurring during growth on GaAs substrate and to increase detectivity, ∼2 × 1010 cm Hz1/2/W at 230 K, under reverse bias 100 mV and ∼4 × 109 cm Hz1/2/W at 300 K, under 500 mV. Presented results are better than PIN architectures with the same and lower cut-off wavelength grown on GaAs without immersion lens and grown on GaSb substrates.

  9. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1979-01-01

    The optimization of space processing of GaAs is described. The detailed compositional, structural, and electronic characterization of GaAs on a macro- and microscale and the relationships between growth parameters and the properties of GaAs are among the factors discussed. The key parameters limiting device performance are assessed.

  10. Photoluminescence of Mn+ doped GaAs

    NASA Astrophysics Data System (ADS)

    Zhou, Huiying; Qu, Shengchun; Liao, Shuzhi; Zhang, Fasheng; Liu, Junpeng; Wang, Zhanguo

    2010-10-01

    Photoluminescence is one of the most useful techniques to obtain information about optoelectronic properties and defect structures of materials. In this work, the room-temperature and low temperature photoluminescence of Mn-doped GaAs were investigated, respectively. Mn-doped GaAs structure materials were prepared by Mn+ ion implantation at room temperature into GaAs. The implanted samples were subsequently annealed at various temperatures under N2 atmosphere to recrystallize the samples and remove implant damage. A strong peak was found for the sample annealed at 950 °C for 5 s. Transitions near 0.989 eV (1254 nm), 1.155 eV (1074 nm) and 1.329 eV (933 nm) were identified and formation of these emissions was analyzed for all prepared samples. This structure material could have myriad applications, including information storage, magnet-optical properties and energy level engineering.

  11. GaAs Solar Cell Radiation Handbook

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.

    1996-01-01

    The handbook discusses the history of GaAs solar cell development, presents equations useful for working with GaAs solar cells, describes commonly used instrumentation techniques for assessing radiation effects in solar cells and fundamental processes occurring in solar cells exposed to ionizing radiation, and explains why radiation decreases the electrical performance of solar cells. Three basic elements required to perform solar array degradation calculations: degradation data for GaAs solar cells after irradiation with 1 MeV electrons at normal incidence; relative damage coefficients for omnidirectional electron and proton exposure; and the definition of the space radiation environment for the orbit of interest, are developed and used to perform a solar array degradation calculation.

  12. Study of processes of self-catalyzed growth of gaas crystal nanowires by molecular-beam epitaxy on modified Si (111) surfaces

    SciTech Connect

    Samsonenko, Yu. B. Cirlin, G. E.; Khrebtov, A. I.; Bouravleuv, A. D.; Polyakov, N. K.; Ulin, V. P.; Dubrovskii, V. G.; Werner, P.

    2011-04-15

    The processes of growth of self-catalyzed GaAs crystal nanowires on Si (111) surfaces modified by three different methods are studied. For the technology of production of the GaAs nanowires, molecular-beam epitaxy is used. It is found that, in the range of substrate temperatures between 610 and 630 Degree-Sign C, the surface density of nanowires and their diameter sharply increases, whereas the temperature dependence of the nanowire length exhibits a maximum at 610 Degree-Sign C. An increase in the temperature to 640 Degree-Sign C suppresses the formation of nanowires. The method that provides a means for the fabrication of purely cubic GaAs nanowires is described. A theoretical justification of the formation of the cubic phase in self-catalyzed GaAs nanowires is presented.

  13. Strain redistribution at the phase transition of MnAs /GaAs(001) films

    NASA Astrophysics Data System (ADS)

    Adriano, C.; Giles, C.; Couto, O. D. D.; Brasil, M. J. S. P.; Iikawa, F.; Däweritz, L.

    2006-04-01

    We investigated the thermal evolution of the lattice parameters of a MnAs film epitaxially grown on GaAs(001) around its magnetostructural first-order phase transition using x-ray diffraction. Despite the substrate constraint, large variation of one of the in-plane lattice parameters is preserved, typical of bulk MnAs phase transition, during a large temperature range where two phases coexist. We demonstrated that the condition of the constant film length along this direction, in accord to the substrate length, is always fulfilled during the process. The effect is attributed to the gliding of misfit dislocations present on the film.

  14. Strain-induced high ferromagnetic transition temperature of MnAs epilayer grown on GaAs (110)

    PubMed Central

    2011-01-01

    MnAs films are grown on GaAs surfaces by molecular beam epitaxy. Specular and grazing incidence X-ray diffractions are used to study the influence of different strain states of MnAs/GaAs (110) and MnAs/GaAs (001) on the first-order magnetostructural phase transition. It comes out that the first-order magnetostructural phase transition temperature Tt, at which the remnant magnetization becomes zero, is strongly affected by the strain constraint from different oriented GaAs substrates. Our results show an elevated Tt of 350 K for MnAs films grown on GaAs (110) surface, which is attributed to the effect of strain constraint from different directions. PACS: 68.35.Rh, 61.50.Ks, 81.15.Hi, 07.85.Qe PMID:21711651

  15. Coherent heteroepitaxy of Bi{sub 2}Se{sub 3} on GaAs (111)B

    SciTech Connect

    Richardella, A.; Zhang, D. M.; Lee, J. S.; Koser, A.; Rench, D. W.; Samarth, N.; Yeats, A. L.; Buckley, B. B.; Awschalom, D. D.

    2010-12-27

    We report the heteroepitaxy of single crystal thin films of Bi{sub 2}Se{sub 3} on the (111)B surface of GaAs by molecular beam epitaxy. We find that Bi{sub 2}Se{sub 3} grows highly c-axis oriented, with an atomically sharp interface with the GaAs substrate. By optimizing the growth of a very thin GaAs buffer layer before growing the Bi{sub 2}Se{sub 3}, we demonstrate the growth of thin films with atomically flat terraces over hundreds of nanometers. Initial time-resolved Kerr rotation measurements herald opportunities for probing coherent spin dynamics at the interface between a candidate topological insulator and a large class of GaAs-based heterostructures.

  16. Zero-strain GaAs quantum dot molecules as investigated by x-ray diffuse scattering

    SciTech Connect

    Hanke, M.; Schmidbauer, M.; Grigoriev, D.; Schaefer, P.; Koehler, R.; Metzger, T. H.; Wang, Zh. M.; Mazur, Yu. I.; Salamo, G. J.

    2006-07-31

    The authors report on x-ray diffuse scattering at nominally strain-free GaAs(001) quantum dot molecules (QDMs). Al{sub 0.3}Ga{sub 0.7}As deposited by molecular beam epitaxy on GaAs(001) acts as barrier layer between the GaAs(001) substrate and subsequently grown QDMs; the adjusted thickness of 50 nm preserves the in-plane lattice parameter. Pairs of lenselike quantum dots are created with preferential orientation along [110] placed on shallow hills. Grazing incidence diffraction along with kinematical scattering simulations indicate completely strain-free QDs which prove a strongly suppressed intermixing between QDMs and the underlying AlGaAs barrier layer.

  17. Stress-modified structural and electronic properties of epitaxial MnAs layers on GaAs

    NASA Astrophysics Data System (ADS)

    Takagaki, Y.; Herrmann, C.; Herfort, J.; Hucho, C.; Friedland, K.-J.

    2008-12-01

    We compare the transport properties in MnAs layers epitaxially grown on GaAs substrates with various orientation relationships, including MnAs(11¯00)/GaAs(001) , MnAs(0001)/GaAs(111), and MnAs(11¯00)/GaAs(111) . Due to the anisotropic abrupt change in the lattice constants at the phase transition between α - and β-MnAs , the phase-transition stress varies over a wide range depending on the c -axis orientation of MnAs. We employ the temperature range of the phase coexistence to evaluate the strength of the stress. The complex Fermi surface of MnAs is found to alter the Hall coefficient remarkably between holelike and electronlike behaviors in spite of rather subtle changes in the band structure by the strain. We also show that enormously strong pinning of domain walls arises in MnAs layers on GaAs(111)B when in-plane and out-of-plane c -axis orientations are simultaneously present.

  18. ZnSe Window Layers for GaAs and GaInP2 Solar Cells

    NASA Technical Reports Server (NTRS)

    Olsen, Larry C.

    1997-01-01

    This report concerns studies of the use of n-type ZnSe as a window layer for n/p GaAs and GaInP2 solar cells. Emphasis was placed in this phase of the project on characterizing the interface between n-type ZnSe films grown on epi-GaAs films grown onto single crystal GaAs. Epi-GaAs and heteroepitaxial ZnSe films were grown by MOCVD with a Spire 50OXT Reactor. After growing epitaxial GaAs films on single crystal GaAs wafers, well-oriented crystalline ZnSe films were grown by MOCVD. ZnSe films were grown with substrate temperatures ranging from 250 C to 450 C. Photoluminescence studies carried out by researchers at NASA Lewis determined that the surface recombination velocity at a GaAs surface was significantly reduced after the deposition of a heteroepitaxial layer of ZnSe. The optimum temperature for ZnSe deposition appears to be on the order of 350 C.

  19. Continuous wave terahertz radiation from antennas fabricated on C¹²-irradiated semi-insulating GaAs.

    PubMed

    Deshmukh, Prathmesh; Mendez-Aller, M; Singh, Abhishek; Pal, Sanjoy; Prabhu, S S; Nanal, Vandana; Pillay, R G; Döhler, G H; Preu, S

    2015-10-01

    We demonstrate continuous wave (CW) terahertz generation from antennas fabricated on C12-irradiated semi-insulating (SI) GaAs substrates. The dark current drawn by the antennas fabricated on irradiated substrates is ∼3 to 4 orders of magnitude lower compared to antennas fabricated on un-irradiated substrates, while the photocurrents decrease by only ∼1.5 orders of magnitude. This can be attributed to the strong reduction of the carrier lifetime that is 2.5 orders of magnitude, with values around τ(rec)=0.2  ps. Reduced thermal heating allows for higher bias voltages to the irradiated antenna devices resulting in higher CW terahertz power, just slightly lower than that of low-temperature grown GaAs (LT GaAs)at similar excitation conditions. PMID:26421576

  20. Grazing-incidence X-ray diffraction of single GaAs nanowires at locations defined by focused ion beams

    PubMed Central

    Bussone, Genziana; Schott, Rüdiger; Biermanns, Andreas; Davydok, Anton; Reuter, Dirk; Carbone, Gerardina; Schülli, Tobias U.; Wieck, Andreas D.; Pietsch, Ullrich

    2013-01-01

    Grazing-incidence X-ray diffraction measurements on single GaAs nanowires (NWs) grown on a (111)-oriented GaAs substrate by molecular beam epitaxy are reported. The positions of the NWs are intentionally determined by a direct implantation of Au with focused ion beams. This controlled arrangement in combination with a nanofocused X-ray beam allows the in-plane lattice parameter of single NWs to be probed, which is not possible for randomly grown NWs. Reciprocal space maps were collected at different heights along the NW to investigate the crystal structure. Simultaneously, substrate areas with different distances from the Au-implantation spots below the NWs were probed. Around the NWs, the data revealed a 0.4% decrease in the lattice spacing in the substrate compared with the expected unstrained value. This suggests the presence of a compressed region due to Au implantation. PMID:24046493

  1. Elastic and magnetic properties of epitaxial MnAs layers on GaAs

    NASA Astrophysics Data System (ADS)

    Iikawa, F.; Santos, P. V.; Kästner, M.; Schippan, F.; Däweritz, L.

    2002-05-01

    We have investigated the elasto- and magneto-optical properties of MnAs layers epitaxially grown on (001) GaAs for temperatures around the structural (hexagonal/orthorhombic) and magnetic (ferromagnetic/paramagnetic) phase transition of MnAs at Tc~40 °C. The phase transition is accompanied by a large variation of the MnAs lattice parameter a of ~1%, which induces a strong and anisotropic strain field in the MnAs/GaAs heterostructures. The latter was measured by detecting the optical anisotropy induced on the GaAs substrate by means of polarization-sensitive light transmission measurements. The experimental results show clear evidence for the quasi-uniaxial strain induced on the GaAs substrate during the phase transition, which extends over a temperature range of ~30 °C in the MnAs/GaAs heterostructures. The strain levels are well reproduced by an elastic model for the heterostructures which assumes that the strain is transferred across the MnAs/GaAs interface without relaxation. The elastic properties during the phase transition were compared to the average magnetization probed using a SQUID magnetometer and to the magnetization near the front and the back surfaces of the MnAs films detected using the magneto-optical Kerr effect. The smaller temperature range of the phase transition observed in the magneto-optical Kerr effect measurements indicates a lower stability of the ferromagnetic phase near the surface of the MnAs layers.

  2. ECR plasma synthesis of silicon nitride films on GaAs and InSb

    SciTech Connect

    Barbour, J.C.; Lovejoy, M.L.; Ashby, C.I.H.; Howard, A.J.; Custer, J.S.; Shul, R.J.

    1993-12-31

    Growth of high-quality dielectric films from Electron Cyclotron Resonance (ECR) plasmas provides for low-temperature surface passivation of compound semiconductors. Silicon nitride (SiN{sub x}) films were grown at temperatures from 30 to 250 C on GaAs substrates. Stress in films was measured as a function of bias applied during growth (varied from 0 to 200 V), and of sample annealing treatments. Composition profiles of the samples were measured using ion beam analysis. The GaAs photoluminescence (PL) signal after SiN{sub x} growth without an applied bias (ion energy {congruent}30 eV) was twice as large as the PL signal from the cleaned GaAs substrate. The PL signal from samples biased at -50 and -100 V indicated that damage degraded the passivation quality, while atomic force microscopy of these samples showed a three fold increase in rms surface roughness relative to unbiased samples. The sample grown with a bias of -200 V showed the largest reduction in film stress but also the smallest PL signal.

  3. AP-MOVPE of thin GaAs 1-xBi x alloys

    NASA Astrophysics Data System (ADS)

    Fitouri, H.; Moussa, I.; Rebey, A.; Fouzri, A.; El Jani, B.

    2006-10-01

    GaAs 1-xBi x alloy was grown by atmospheric-pressure metalorganic vapour-phase epitaxy using a horizontal reactor. GaAs 1-xBi x epilayers were elaborated on exactly (1 0 0)-oriented p-GaAs substrates. Trimethyl-gallium, trimethyl bismuth (TMBi), and arsine were used as precursor sources at a growth temperature of 420 °C within a very narrow range of V/III ratios and molar flow rates of TMBi. The lattice mismatch between the layer and the substrate was examined by using high-resolution X-ray diffraction technique. The measurements were performed on (0 0 4) and (1 1 5) planes. The solid composition of GaBi content in the GaAs 1-xBi x alloy reaches a maximum value of about 3.7%. In analyzing the surface morphology, scanning electron microscopy (SEM) and SEM-energy dispersive X-ray spectrometer were used to qualify films properties.

  4. DIRECT DETERMINATION OF THE STACKING ORDER IN GD2O3 EPI LAYERS ON GAAS.

    SciTech Connect

    YACOBY,Y.; SOWWAN,M.; PINDAK,R.; CROSS,J.; WALKO,D.; STERN,E.; PITNEY,J.; MACHARRIE,R.; HONG,M.; CLARKE,R.

    2002-12-06

    We have used Coherent Bragg Rod Analysis (COBRA) to investigate the atomic structure of a 5.6 nm thick Gd{sub 2}O{sub 3} film epitaxially grown on a (100) GaAs substrate. COBRA is a method to directly obtain the structure of systems periodic in two-dimensions by determining the complex scattering factors along the substrate Bragg rods. The system electron density and atomic structure are obtained by Fourier transforming the complex scattering factors into real space. The results show that the stacking order of the first seven Gd{sub 2}O{sub 3} film layers resembles the stacking order of Ga and As layers in GaAs then changes to the stacking order of cubic bulk Gd{sub 2}O{sub 3}. This behavior is distinctly different from the measured stacking order in a 2.7 nm thick Gd{sub 2}O{sub 3} in which the GaAs stacking order persists throughout the entire film.

  5. Ab initio study of the strain dependent thermodynamics of Bi doping in GaAs

    NASA Astrophysics Data System (ADS)

    Jacobsen, Heather; Puchala, Brian; Kuech, Thomas F.; Morgan, Dane

    2012-08-01

    The thermodynamics of Bi incorporation into bulk and epitaxial GaAs was studied using density functional theory (DFT) and anharmonic elasticity calculations. The equilibrium concentration of Bi was determined as a function of epitaxial strain state, temperature, and growth conditions. For a bulk, unstrained system, Bi in GaAs under typical growth conditions (Ga-rich and Bi-metal-rich at 400 °C) has a dilute heat of solution of 572 meV/Bi and a solubility of x=5.2×10-5 in GaAs1-xBix. However, epitaxial strain can greatly enhance this solubility, and under the same conditions an epitaxial film of GaAs1-xBix with 5% in-plane tensile strain is predicted to have a Bi solubility of x=7.3×10-3, representing approximately a hundred times increase in solubility over the unstrained bulk case. Despite these potentially large increases in solubility, the equilibrium solubility is still very low compared to values that have been achieved experimentally through nonequilibrium growth. These values of solubility are also sensitive to the choice of the Bi reference state. If the primary route for phase separation is the formation of GaBi within the same structure, rather than Bi metal, GaBi would serve as the source/sink for Bi. If GaBi is used as the Bi reference state, the epitaxial formation energy on a bulk unstrained GaAs substrate is reduced dramatically to 144 meV/Bi, yielding a Bi solubility of x=0.083 in GaAs1-xBix. These calculations suggest that Bi solubility could be greatly enhanced if Bi metal formation is inhibited and the system is forced to remain constrained to the GaAs1-xBix structure. Although GaBi is not a naturally stable compound, it could potentially be stabilized through a combination of kinetic limitations and alloying.

  6. GaAs optoelectronic neuron arrays

    NASA Technical Reports Server (NTRS)

    Lin, Steven; Grot, Annette; Luo, Jiafu; Psaltis, Demetri

    1993-01-01

    A simple optoelectronic circuit integrated monolithically in GaAs to implement sigmoidal neuron responses is presented. The circuit integrates a light-emitting diode with one or two transistors and one or two photodetectors. The design considerations for building arrays with densities of up to 10,000/sq cm are discussed.

  7. GaAs Solar Cell Radiation Handbook

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.

    1996-01-01

    History of GaAs solar cell development is provided. Photovoltaic equations are described along with instrumentation techniques for measuring solar cells. Radiation effects in solar cells, electrical performance, and spacecraft flight data for solar cells are discussed. The space radiation environment and solar array degradation calculations are addressed.

  8. Growth of InSb on GaAs Using InAlSb Buffer Layers

    SciTech Connect

    BIEFELD, ROBERT M.; PHILLIPS, JAMIE D.

    1999-09-20

    We report the growth of InSb on GaAs using InAlSb buffers of high interest for magnetic field sensors. We have grown samples by metal-organic chemical vapor deposition consisting of {approximately} 0.55 {micro}m thick InSb layers with resistive InAlSb buffers on GaAs substrates with measured electron nobilities of {approximately}40,000 cm{sup 2}/V.s. We have investigated the In{sub 1{minus}x}Al{sub x}Sb buffers for compositions x{le}0.22 and have found that the best results are obtained near x=0.12 due to the tradeoff of buffer layer bandgap and lattice mismatch.

  9. Strain-driven growth of GaAs(111) quantum dots with low fine structure splitting

    NASA Astrophysics Data System (ADS)

    Yerino, Christopher D.; Simmonds, Paul J.; Liang, Baolai; Jung, Daehwan; Schneider, Christian; Unsleber, Sebastian; Vo, Minh; Huffaker, Diana L.; Höfling, Sven; Kamp, Martin; Lee, Minjoo Larry

    2014-12-01

    Symmetric quantum dots (QDs) on (111)-oriented surfaces are promising candidates for generating polarization-entangled photons due to their low excitonic fine structure splitting (FSS). However, (111) QDs are difficult to grow. The conventional use of compressive strain to drive QD self-assembly fails to form 3D nanostructures on (111) surfaces. Instead, we demonstrate that (111) QDs self-assemble under tensile strain by growing GaAs QDs on an InP(111)A substrate. Tensile GaAs self-assembly produces a low density of QDs with a symmetric triangular morphology. Coherent, tensile QDs are observed without dislocations, and the QDs luminescence at room temperature. Single QD measurements reveal low FSS with a median value of 7.6 μeV, due to the high symmetry of the (111) QDs. Tensile self-assembly thus offers a simple route to symmetric (111) QDs for entangled photon emitters.

  10. Strain-driven growth of GaAs(111) quantum dots with low fine structure splitting

    SciTech Connect

    Yerino, Christopher D.; Jung, Daehwan; Lee, Minjoo Larry; Simmonds, Paul J.; Liang, Baolai; Huffaker, Diana L.; Schneider, Christian; Unsleber, Sebastian; Vo, Minh; Kamp, Martin; Höfling, Sven

    2014-12-22

    Symmetric quantum dots (QDs) on (111)-oriented surfaces are promising candidates for generating polarization-entangled photons due to their low excitonic fine structure splitting (FSS). However, (111) QDs are difficult to grow. The conventional use of compressive strain to drive QD self-assembly fails to form 3D nanostructures on (111) surfaces. Instead, we demonstrate that (111) QDs self-assemble under tensile strain by growing GaAs QDs on an InP(111)A substrate. Tensile GaAs self-assembly produces a low density of QDs with a symmetric triangular morphology. Coherent, tensile QDs are observed without dislocations, and the QDs luminescence at room temperature. Single QD measurements reveal low FSS with a median value of 7.6 μeV, due to the high symmetry of the (111) QDs. Tensile self-assembly thus offers a simple route to symmetric (111) QDs for entangled photon emitters.

  11. Tilt and dislocations in epitaxial laterally overgrown GaAs layers

    NASA Astrophysics Data System (ADS)

    Zytkiewicz, Z. R.; Domagala, J. Z.; Dobosz, D.; Dobaczewski, L.; Rocher, A.; Clement, C.; Crestou, J.

    2007-01-01

    Transmission electron microscopy (TEM) and high-resolution x-ray diffraction were used to study the crystalline quality of GaAs layers grown by liquid phase epitaxial lateral overgrowth (ELO) on SiO2-masked (001) GaAs substrates. A low-angle grain boundary with a well-organized set of dislocations accommodating the misorientation of tilted ELO wings was found at the coalescence front of ELO layers. Similar behavior is often reported for GaN on sapphire ELO structures. Unlike the GaN case, however, no dislocations were found above edges of the mask, which is explained by the much smaller wing tilt angle in our case. The geometry of the dislocation network and analysis of thickness fringes on TEM images were used to measure misorientation of merging ELO wings. The values obtained are in good agreement with those determined by x-ray diffraction.

  12. Direct Measurement of Surface Defect Level Distribution Associated with GaAs Antiphase Boundaries

    SciTech Connect

    Xu, Q.; Hsu, J.W.

    1999-01-01

    Using an electrostatic force microscope, we measure surface contact potential (SCP) variations across antiphase boundaries (APBs) on GaAs films grown on Ge substrates. The SCP at the APBs is consistently and reproducibly measured to be 30 mV higher than that at GaAs domains. This is due to Fermi levels being pinned at different surface states. The identical electrical behavior observed for all APBs indicates that they are the lowest energy {l_brace}110{r_brace} orientation. The sign of observed Fermi level shift is consistent with a prevalence of Ga-Ga bonds at real {l_brace}110{r_brace} APBs. {copyright} {ital 1999} {ital The American Physical Society}

  13. High-efficiency thin-film GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.

    1979-01-01

    GaAs chemical vapor deposition (CVD) growth on single-crystal GaAs substrates was investigated over a temperature range of 600 to 750 C, As/GA mole-ratio range of 3 to 11, and gas molefraction range 5 x 10 to the minus 9th power to 7x 10 to the minus 7th power for H2S doping. GasAs CVD growth on recrystallized Ge films was investigated for a temperature range of 550 to 700 C, an As/GA mole ratio of 5, and for various H2S mole fraction. The highest efficiency cell observed on these films with 2 mm dots was 4.8% (8% when AR-coated). Improvements in fill factor and opencircuit voltage by about 40% each are required in order to obtain efficiencies of 15% or greater.

  14. Relaxation dynamics and residual strain in metamorphic AlSb on GaAs

    SciTech Connect

    Ripalda, J. M.; Rivera, A.; Alen, B.; Gonzalez, Y.; Gonzalez, L.; Briones, F.; Sanchez, A. M.; Taboada, A. G.; Rotter, T. J.; Balakrishnan, G.

    2012-01-02

    We have observed the evolution of the accumulated stress during heteroepitaxial growth of highly lattice mismatched AlSb on GaAs by measuring the deformation of the substrate as a function of time. High resolution transmission electron microscopy images show almost all of the plastic relaxation is accommodated by an array of 90 deg. misfit dislocations at the interface. The in-plane lattice parameter of the resulting metamorphic AlSb is slightly smaller (0.3%) than the bulk value and perfectly matches the lattice parameter of bulk GaSb. It is, therefore, possible to grow nearly stress-free GaSb on GaAs using a metamorphic AlSb buffer layer.

  15. Gallium surface diffusion on GaAs (001) surfaces measured by crystallization dynamics of Ga droplets

    SciTech Connect

    Bietti, Sergio Somaschini, Claudio; Esposito, Luca; Sanguinetti, Stefano; Fedorov, Alexey

    2014-09-21

    We present accurate measurements of Ga cation surface diffusion on GaAs surfaces. The measurement method relies on atomic force microscopy measurement of the morphology of nano–disks that evolve, under group V supply, from nanoscale group III droplets, earlier deposited on the substrate surface. The dependence of the radius of such nano-droplets on crystallization conditions gives direct access to Ga diffusion length. We found an activation energy for Ga on GaAs(001) diffusion E{sub A}=1.31±0.15 eV, a diffusivity prefactor of D₀=0.53(×2.1±1) cm² s⁻¹ that we compare with the values present in literature. The obtained results permit to better understand the fundamental physics governing the motion of group III ad–atoms on III–V crystal surfaces and the fabrication of designable nanostructures.

  16. Formation of columnar (In,Ga)As quantum dots on GaAs(100)

    SciTech Connect

    He, J.; Noetzel, R.; Offermans, P.; Koenraad, P.M.; Gong, Q.; Hamhuis, G.J.; Eijkemans, T.J.; Wolter, J.H.

    2004-10-04

    Columnar (In,Ga)As quantum dots (QDs) with homogeneous composition and shape in the growth direction are realized by molecular-beam epitaxy on GaAs(100) substrates. The columnar (In,Ga)As QDs are formed on InAs seed QDs by alternating deposition of thin GaAs intermediate layers and monolayers of InAs with extended growth interruptions after each layer. The height of the columnar (In,Ga)As QDs is controlled by varying the number of stacked GaAs/InAs layers. The structural and optical properties are studied by cross-sectional scanning tunneling microscopy, atomic force microscopy, and photoluminescence spectroscopy. With increase of the aspect ratio of the columnar QDs, the emission wavelength is redshifted and the linewidth is reduced.

  17. ZnSe Window Layers for GaAs and GaInP2 Solar Cells

    NASA Technical Reports Server (NTRS)

    Olsen, Larry C.

    1995-01-01

    This report concerns studies of the use of ZnSe as a window layer for GaAs solar cells. Well-oriented crystalline ZnSe films on (100) single crystal GaAs substrates were grown by MOCVD. In particular, ZnSe films were grown by reacting a zinc adduct with hydrogen selenide at temperatures in the range of 200 C to 400 C. X-ray diffraction studies and images obtained with an atomic force microscope determined that the films were highly oriented but were polycrystalline. Particular emphasis was placed on the use of a substrate temperature of 350 C. Using iodine as a dopant, n-type ZnSe films with resistivities in the range of .01 to .05 ohm-cm were grown on semi-insulating GaAs. Thus procedures have been developed for investigating the utility of n-type ZnSe window layers on n/p GaAs structures. Studies of recombination at n-ZnSe/n-GaAs interfaces in n-ZnSe/n-GaAs/p-GaAs cell structures are planned for future work.

  18. MBE-Grown CdTe Layers on GaAs with In-assisted Thermal Deoxidation

    NASA Astrophysics Data System (ADS)

    Arı, Ozan; Bilgilisoy, Elif; Ozceri, Elif; Selamet, Yusuf

    2016-03-01

    Molecular beam epitaxy (MBE) growth of thin (˜2 μm) CdTe layers characterized by high crystal quality and low defect density on lattice mismatched substrates, such as GaAs and Si, has thus far been difficult to achieve. In this work, we report the effects of in situ thermal deoxidation under In and As4 overpressure prior to the CdTe growth on epiready GaAs(211)B wafers, aiming to enhance CdTe crystal quality. Thermally deoxidized GaAs samples were analyzed using in situ reflection high energy electron diffraction, along with ex situ x-ray photo-electron spectroscopy (XPS) and atomic force microscopy. MBE-grown CdTe layers were characterized using x-ray diffraction (XRD) and Everson-type wet chemical defect decoration etching. We found that In-assisted desorption allowed for easier surface preparation and resulted in a smoother surface compared to As-assisted surface preparation. By applying In-assisted thermal deoxidation to GaAs substrates prior to the CdTe growth, we have obtained single crystal CdTe films with a CdTe(422) XRD rocking curve with a full-width half-maximum value of 130.8 arc-s and etch pit density of 4 × 106 cm-2 for 2.54 μm thickness. We confirmed, by XPS analysis, no In contamination on the thermally deoxidized surface.

  19. Assembly of Submicron Ferromagnets in GaAs Semiconductors*

    NASA Astrophysics Data System (ADS)

    Shi, Jing

    1996-03-01

    Spin-dependent electronic phenomena discovered in nanoscale metallic systems have raised interesting scientific questions regarding spin interactions and are currently finding technological applications. In particular, incorporating microscopic magnets within semiconducting compounds offers the exciting possibility of combining local magnetism with the flexibility of semiconductor-based quantum electronic structures. This work demonstrates that submicron room-temperature ferromagnets have been successfully formed in GaAs semiconductors through a simple process of ion implantation and subsequent heat treatment (J. Shi et al), Nature 377, 707 (1995); J. Shi et al, J. Appl. Phys. (accepted for publication, 1996).. A combination of transmission electron, atomic force, and magnetic force microscopies have been used in conjunction with magnetization measurements to directly examine the structural and magnetic properties of this new system. After Mn^+-implantation at various doses, rapid thermal annealing crystallizes in situ submicron GaMn ferromagnetic particles ( ~ 200 nm) at the GaAs surface. These GaMn particles are crystalline, some with quasicrystalline-like order. Bulk magnetization measurements show that the GaMn particles are room temperature ferromagnets with a Curie temperature far exceeding room temperature. Both the particle size and coercivity can be varied by controlling the implantation and annealing conditions. High resolution magnetic force microscopy images on single GaMn ferromagnets reveal that unmagnetized samples contain both magnetic single- and multi-domain particles, but after initial magnetization, the single-domain state predominates, with magnetic moments aligned preferentially along the [001] directions of the GaAs substrate. In particular, magnetic force imaging has been performed in a changing magnetic field (up to 8 kOe) to directly study and image magnetization reversal of single-domain particles. *Work done in collaboration with D

  20. Nitride chemical passivation of a GaAs (100) Surface: Effect on the electrical characteristics of Au/GaAs surface-barrier structures

    SciTech Connect

    Berkovits, V. L. L'vova, T. V.; Ulin, V. P.

    2011-12-15

    The effect of chemical nitridation of GaAs substrates in a hydrazine-sulfide solution on the electrical characteristics of Au/GaAs Schottky structures has been studied. In nitridation of this kind, a solid passivating gallium nitride film with a monolayer thickness is formed on the surface of GaAs, providing almost direct contact between the semiconductor and the metal deposited on its surface. Au/GaAs structures fabricated on nitride substrates have ideality factors close to unity and are characterized by a narrow scatter of potential barrier heights. Prolonged heating of these structures at 350 Degree-Sign C does not change these parameters. The data obtained show that the nitride monolayer formed on the GaAs surface upon treatment in hydrazidesulfide solutions effectively hinders atomic migration across the metal-semiconductor phase boundary.

  1. Correlating structure, strain, and morphology of self-assembled InAs quantum dots on GaAs

    NASA Astrophysics Data System (ADS)

    Kumah, D. P.; Wu, J. H.; Husseini, N. S.; Dasika, V. D.; Goldman, R. S.; Yacoby, Y.; Clarke, R.

    2011-01-01

    We report on the use of a direct x-ray phase retrieval method, coherent Bragg rod analysis, to characterize self-assembled InAs quantum dots (QDs) grown epitaxially on GaAs substrates. Electron density maps obtained close to the x-ray absorption edges of the constituent elements are compared to deconvolute composition and atomic spacing information. Our measurements show no evidence of a wetting layer and reveal bowing of the atomic layers throughout the QD, extending from the QD-substrate interface. This leads to a half-layer stacking shift which may act to partially decouple the QDs electronically from the substrate.

  2. Interface composition between Fe3O4 nanoparticles and GaAs for spintronic applications

    NASA Astrophysics Data System (ADS)

    Hihath, Sahar; Kiehl, Richard A.; Benthem, Klaus van

    2014-08-01

    Recent interest in spintronic applications has necessitated the study of magnetic materials in contact with semiconductor substrates; importantly, the structure and composition of these interfaces can influence both device functionality and the magnetic properties. Nanoscale ferromagnet/semiconductor structures are of particular interest. In this study, the interface structure between a monolayer of ferromagnetic magnetite (Fe3O4) nanoparticles and a GaAs substrate was studied using cross-sectional transmission electron microscopy techniques. It was found that a continuous amorphous oxide interface layer separates the nanoparticles from the GaAs substrate, and that iron diffused into the interface layer forming a compositional gradient. Electron energy-loss near-edge fine structures of the O K absorption edge revealed that the amorphous oxide is composed of γ-Fe2O3 directly underneath the Fe3O4 nanoparticles, followed by a solid solution of Ga2O3 and FeO and mostly Ga2O3 when approaching the buckled oxide/substrate interface. Real-space density functional theory calculations of the dynamical form factor confirmed the experimental observations. The implication of the findings on the optimization of these structures for spin injection is discussed.

  3. The effects of As overpressure and diffusion source on the diffusion of Mn in GaAs

    NASA Astrophysics Data System (ADS)

    Wu, C. H.; Hsieh, K. C.

    1992-12-01

    Data are presented to show the effect of As overpressure on the diffusion of Mn in GaAs using four different Mn sources. These sources include solid Mn thin film deposited directly on the GaAs substrate and Mn vapors from pure Mn, MnAs, and Mn3As solids. In the circumstance for which a solid Mn film is used as the diffusion source, a nonuniform doping distribution and poor surface morphology is obtained due to a reaction between the Mn film and the GaAs matrix. The degraded surface consists of a layer of polycrystalline cubic alloy having a lattice constant of nearly 8.4 Å and a composition close to MnGa2 with a small amount of As. Of the remaining diffusion sources (Mn, MnAs, and Mn3As), only MnAs consistently produces a uniform doping distribution and smooth surface morphology. For diffusions at 800 °C, a uniform surface hole carrier concentration as high as 1020/cm3 can be obtained using MnAs as the source. The As overpressure is found to drastically alter the Mn diffusion profile, and Mn, like Zn, may diffuse in GaAs interstitial-substitutionally. Vapor from both the Mn and Mn3As solids degrade the GaAs surface. Mn3As, however, uncharacteristically degrades the surface more rapidly although the details of such are not well understood. With the presence of a high As overpressure, however, both surfaces of the Mn and Mn3As sources are converted to (Mn,As) compounds, the compositions being close to MnAs. High enough As overpressures are shown to completely suppress the GaAs surface degradation which is evident when Mn3As alone is used as the diffusion source.

  4. Piezoelectric field in strained GaAs.

    SciTech Connect

    Chow, Weng Wah; Wieczorek, Sebastian Maciej

    2005-11-01

    This report describes an investigation of the piezoelectric field in strained bulk GaAs. The bound charge distribution is calculated and suitable electrode configurations are proposed for (1) uniaxial and (2) biaxial strain. The screening of the piezoelectric field is studied for different impurity concentrations and sample lengths. Electric current due to the piezoelectric field is calculated for the cases of (1) fixed strain and (2) strain varying in time at a constant rate.

  5. Eight-Bit-Slice GaAs General Processor Circuit

    NASA Technical Reports Server (NTRS)

    Weissman, John; Gauthier, Robert V.

    1989-01-01

    Novel GaAs 8-bit slice enables quick and efficient implementation of variety of fast GaAs digital systems ranging from central processing units of computers to special-purpose processors for communications and signal-processing applications. With GaAs 8-bit slice, designers quickly configure and test hearts of many digital systems that demand fast complex arithmetic, fast and sufficient register storage, efficient multiplexing and routing of data words, and ease of control.

  6. UV laser activated digital etching of GaAs

    SciTech Connect

    Meguro, T.; Aoyagi, Y.

    1996-12-31

    The self-limited etching characteristics of digital etching employing an UV laser/Cl{sub 2}/GaAs system are presented. The self-limiting nature is the key mechanism and plays an important role in digital etching for obtaining etch rates independent of etching parameters. Surface processes based on photodissociation of physisorbed chlorine on GaAs with diffusion of negatively charged Cl into GaAs are also discussed.

  7. Properties of CsI, CsBr and GaAs thin films grown by pulsed laser deposition

    SciTech Connect

    Brendel, V M; Garnov, S V; Yagafarov, T F; Iskhakova, L D; Ermakov, R P

    2014-09-30

    CsI, CsBr and GaAs thin films have been grown by pulsed laser deposition on glass substrates. The morphology and structure of the films have been studied using X-ray diffraction and scanning electron microscopy. The CsI and CsBr films were identical in stoichiometry to the respective targets and had a polycrystalline structure. Increasing the substrate temperature led to an increase in the density of the films. All the GaAs films differed in stoichiometry from the target. An explanation was proposed for this fact. The present results demonstrate that, when the congruent transport condition is not fulfilled, films identical in stoichiometry to targets can be grown by pulsed laser deposition in the case of materials with a low melting point and thermal conductivity. (interaction of laser radiation with matter)

  8. Observation of linear I-V curves on vertical GaAs nanowires with atomic force microscope

    NASA Astrophysics Data System (ADS)

    Geydt, P.; Alekseev, P. A.; Dunaevskiy, M.; Lähderanta, E.; Haggrén, T.; Kakko, J.-P.; Lipsanen, H.

    2015-12-01

    In this work we demonstrate the possibility of studying the current-voltage characteristics for single vertically standing semiconductor nanowires on standard AFM equipped by current measuring module in PeakForce Tapping mode. On the basis of research of eight different samples of p-doped GaAs nanowires grown on different GaAs substrates, peculiar electrical effects were revealed. It was found how covering of substrate surface by SiOx layer increases the current, as well as phosphorous passivation of the grown nanowires. Elimination of the Schottky barrier between golden cap and the top parts of nanowires was observed. It was additionally studied that charge accumulation on the shell of single nanowires affects its resistivity and causes the hysteresis loops on I-V curves.

  9. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1984-01-01

    The crystal growth, device processing and device related properties and phenomena of GaAs are investigated. Our GaAs research evolves about these key thrust areas. The overall program combines: (1) studies of crystal growth on novel approaches to engineering of semiconductor materials (i.e., GaAs and related compounds); (2) investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; (3) investigation of electronic properties and phenomena controlling device applications and device performance. The ground based program is developed which would insure successful experimentation with and eventually processing of GaAs in a near zero gravity environment.

  10. High efficiency, low cost thin GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Fan, J. C. C.

    1982-01-01

    The feasibility of fabricating space-resistant, high efficiency, light-weight, low-cost GaAs shallow-homojunction solar cells for space application is demonstrated. This program addressed the optimal preparation of ultrathin GaAs single-crystal layers by AsCl3-GaAs-H2 and OMCVD process. Considerable progress has been made in both areas. Detailed studies on the AsCl3 process showed high-quality GaAs thin layers can be routinely grown. Later overgrowth of GaAs by OMCVD has been also observed and thin FaAs films were obtained from this process.

  11. LEO Flight Testing of GaAs on Si Solar Cells Aboard MISSES

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Clark, Eric B.; Ringel, Steven A.; Andre, Carrie L.; Smith, Mark A.; Scheiman, David A.; Jenkins, Phillip P.; Maurer, William F.; Fitzgerald, Eugene A.; Walters, R. J.

    2004-01-01

    Previous research efforts have demonstrated small area (0.04 cm) GaAs on Si (GaAs/Si) solar cells with AM0 efficiencies in excess of 17%. These results were achieved on Si substrates coated with a step graded buffer of Si(x),Ge(1-x) alloys graded to 100% Ge. Recently, a 100-fold increase in device area was accomplished for these devices in preparation for on-orbit testing of this technology aboard Materials International Space Station Experiment number 5 (MISSE5). The GaAs/Si MISSE5 experiment contains five (5) GaAs/Si test devices with areas of lcm(exp 2) and 4cm(exp 4) as well as two (2) GaAs on GaAs control devices. Electrical performance data, measured on-orbit for three (3) of the test devices and one (1) of the control devices, will be telemetered to ground stations daily. After approximately one year on orbit, the MISSE5 payload will be returned to Earth for post flight evaluation. This paper will discuss the development of the GaAs/Si devices for the MISSE5 flight experiment and will present recent ground and on-orbit performance data.

  12. Engineering Controlled Spalling in (100)-Oriented GaAs for Wafer Reuse

    SciTech Connect

    Sweet, Cassi A.; McNeely, Joshua E.; Gorman, Brian; Young, David L.; Ptak, Aaron J.; Packard, Corinne E.

    2015-06-14

    Controlled spalling offers a way to cleave thin, single-crystal films or devices from wafers, particularly if the fracture planes in the material are oriented parallel to the wafer surface. Unfortunately, misalignment between the favored fracture planes and the wafer surface preferred for photovoltaic growth in (100)-oriented GaAs produces a highly faceted surface when subject to controlled spalling. This highly faceted cleavage surface is problematic in several ways: (1) it can result in large variations of spall depth due to unstable crack propagation; (2) it may introduce defects into the device zone or underlying substrate; and (3) it consumes many microns of material outside of the device zone. We present the ways in which we have engineered controlled spalling for (100)-oriented GaAs to minimize these effects. We expand the operational window for controlled spalling to avoid spontaneous spalling, find no evidence of dislocation activity in the spalled film or the parent wafer, and reduce facet height and facet height irregularity. Resolving these issues provides a viable path forward for reducing III-V device cost through the controlled spalling of (100)-oriented GaAs devices and subsequent wafer reuse when these processes are combined with a high-throughput growth method such as Hydride Vapor Phase Epitaxy.

  13. GaAs CLEFT solar cells for space applications. [CVD thin film growth technology

    NASA Technical Reports Server (NTRS)

    Fan, J. C. C.; Mcclelland, R. W.; King, B. D.

    1984-01-01

    Although GaAs solar cells are radiation-resistant and have high conversion efficiencies, there are two major obstacles that such cells must overcome before they can be widely adopted for space applications: GaAs wafers are too expensive and cells made from these wafers are too heavy. The CLEFT process permits the growth of thin single-crystal films on reusable substrates, resulting in a drastic reduction in both cell cost and cell weight. Recent advances in CLEFT technology have made it possible to achieve efficiencies of about 14 percent AM0 for 0.51-sq cm GaAs solar cells 5 microns thick with a 41-mil-thick coverglass. In preliminary experiments efficiencies close to 19 percent AM1 have been obtained for 10-micron-thick cells. It is suggested that the CLEFT technology should yield inexpensive, highly efficient modules with a beginning-of-life specific power close to 1 kW/kg (for a coverglass thickness of 4 mils).

  14. Magnetic properties of ultra thin epitaxial Fe films on GaAs(001)

    SciTech Connect

    Morton, S A; Tobin, J G; Spangenberg, M; Neal, J R; Shen, T H; Waddill, G D; Matthew, J D; Greig, D; Malins, A R; Seddon, E A; Hopkinson, M

    2003-10-02

    The magnetic properties of epitaxial Fe films on GaAs in the range of the first few monolayers have been the subject of a considerable number of investigations in recent years. The absence of magnetic signatures at room temperature has been attributed to the existence of a magnetic ''dead'' layer as well as superparamagnetism. By examining the temperature dependence of the magnetic linear dichroism of the Fe core level photoelectrons, we found that these ''non-ferromagnetic'' layers had in fact a Curie temperature, T{sub c}, substantially lower than room temperature, e.g., a T{sub c} of about 240K for thin films of a nominal thickness of 0.9 nm. The values of Curie temperature were sensitive to the initial GaAs substrate conditions and the thickness of the Fe over-layer with a layer of thickness of 1.25 nm showing a T{sub c} above room temperature. The data suggest that the ultrathin Fe films on GaAs(001) are ferromagnetic, although a weaker exchange interaction in the films lead to a substantial reduction in Curie temperature.

  15. A technique for large-area position-controlled growth of GaAs nanowire arrays.

    PubMed

    Kauppinen, Christoffer; Haggren, Tuomas; Kravchenko, Aleksandr; Jiang, Hua; Huhtio, Teppo; Kauppinen, Esko; Dhaka, Veer; Suihkonen, Sami; Kaivola, Matti; Lipsanen, Harri; Sopanen, Markku

    2016-04-01

    We demonstrate a technique for fabricating position-controlled, large-area arrays of vertical semiconductor nanowires (NWs) with adjustable periods and NW diameters. In our approach, a Au-covered GaAs substrate is first coated with a thin film of photoresponsive azopolymer, which is exposed twice to a laser interference pattern forming a 2D surface relief grating. After dry etching, an array of polymer islands is formed, which is used as a mask to fabricate a matrix of gold particles. The Au particles are then used as seeds in vapour-liquid-solid growth to create arrays of vertical GaAs NWs using metalorganic vapour phase epitaxy. The presented technique enables producing NWs of uniform size distribution with high throughput and potentially on large wafer sizes without relying on expensive lithography techniques. The feasibility of the technique is demonstrated by arrays of vertical NWs with periods of 255-1000 nm and diameters of 50-80 nm on a 2 × 2 cm area. The grown NWs exhibit high long range order and good crystalline quality. Although only GaAs NWs were grown in this study, in principle, the presented technique is suitable for any material available for Au seeded NW growth. PMID:26895144

  16. A technique for large-area position-controlled growth of GaAs nanowire arrays

    NASA Astrophysics Data System (ADS)

    Kauppinen, Christoffer; Haggren, Tuomas; Kravchenko, Aleksandr; Jiang, Hua; Huhtio, Teppo; Kauppinen, Esko; Dhaka, Veer; Suihkonen, Sami; Kaivola, Matti; Lipsanen, Harri; Sopanen, Markku

    2016-04-01

    We demonstrate a technique for fabricating position-controlled, large-area arrays of vertical semiconductor nanowires (NWs) with adjustable periods and NW diameters. In our approach, a Au-covered GaAs substrate is first coated with a thin film of photoresponsive azopolymer, which is exposed twice to a laser interference pattern forming a 2D surface relief grating. After dry etching, an array of polymer islands is formed, which is used as a mask to fabricate a matrix of gold particles. The Au particles are then used as seeds in vapour-liquid-solid growth to create arrays of vertical GaAs NWs using metalorganic vapour phase epitaxy. The presented technique enables producing NWs of uniform size distribution with high throughput and potentially on large wafer sizes without relying on expensive lithography techniques. The feasibility of the technique is demonstrated by arrays of vertical NWs with periods of 255-1000 nm and diameters of 50-80 nm on a 2 × 2 cm area. The grown NWs exhibit high long range order and good crystalline quality. Although only GaAs NWs were grown in this study, in principle, the presented technique is suitable for any material available for Au seeded NW growth.

  17. High resolution scanning photoluminescence characterization of semi-insulating GaAs using a laser scanning microscope

    NASA Astrophysics Data System (ADS)

    Marek, J.; Elliot, A. G.; Wilke, V.; Geiss, R.

    1986-12-01

    Spatially resolved photoluminescence properties of semi-insulating, liquid encapsulated Czochralski-grown GaAs substrates are analyzed with a laser scanning microscope. The improved resolution of the laser scanning microscope results in the observation of single dislocations within the subgrain boundaries of the polyganized dislocation cell network for the first time by photoluminescence. Both the cell structure and the Cottrell cloud are clearly resolved.

  18. Growth of CdTe films on GaAs by ionized cluster beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tang, H. P.; Feng, J. Y.; Fan, Y. D.; Li, H. D.

    1991-06-01

    Stoichiometric epitaxial films of CdTe were grown on (100)GaAs substrates by ionized cluster beam (ICB) epitaxy. Streaky RHEED patterns indicated good crystallinity and surface flatness of the epitaxial CdTe films. CdTe(100) orientation was obtained when the substrate preheating temperature was 480°C, while CdTe growth inboth (100) and (111) orientations occured when the substrate preheating temperature was above 550°C. The characteristics of the ICB growth process were investigated and the cluster-involving growth behavior has been evidenced. When sufficient clusters were generated in the deposition beam under adequate source vapor pressures, the crystalline quality of the resulting CdTe epilayers improved significantly with the increase of kinetic energy of the CdTe clusters. The best CdTe epilayer obtained exhibited a CdTe(400) double crystal rocking curve (DCRC) having a FWHM of 630 arc sec.

  19. Velocity surface measurements for ZnO films over /001/-cut GaAs

    NASA Technical Reports Server (NTRS)

    Kim, Yoonkee; Hunt, William D.; Liu, Yongsheng; Jen, Cheng-Kuei

    1994-01-01

    A potential application for a piezoelectic film deposited on a GaAs substrate is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the filmed structure is critical for the optimum design of such devices. In this article, the measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metallized ZnO/SiO2 or Si3N4/GaAs /001/-cut samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. Comparisons, such as measurement accuracy and tradeoffs, between the former (dry) and the latter (wet) method are given. It is found that near the group of zone axes (110) propagation direction the autocollimating SAW property of the bare GaAs changes into a noncollimating one for the layered structure, but a reversed phenomenon exists near the group of zone axes (100) direction. The passivation layer of SiO2 or Si3N4 (less than 0.2 micrometer thick) and the metallization layer change the relative velocity but do not significantly affect the velocity surface. On the other hand, the passivation layer reduces the propagation loss by 0.5-1.3 dB/microseconds at 240 MHz depending upon the ZnO film thickness. Our SAW propagation measurements agree well with theorectical calculations. We have also obtained the anisotropy factors for samples with ZnO films of 1.6, 2.8, and 4.0 micrometer thickness. Comparisons concerning the piezoelectric coupling and acoustic loss between dc triode and rf magnetron sputtered ZnO films are provided.

  20. Generation of THz transients by photoexcited single-crystal GaAs meso-structures

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Mikulics, Martin; Adam, Roman; Grützmacher, Detlev; Sobolewski, Roman

    2013-12-01

    We report a sub-picosecond photoresponse and THz transient generation of GaAs single-crystal mesoscopic platelets excited by femtosecond optical pulses. Our structures were fabricated by a top-down technique, by patterning an epitaxial, 500-nm-thick GaAs film grown on top of an AlAs sacrificial layer and then transferring the resulting etched away 10 × 20-μm2 platelets onto an MgO substrate using a micropipette. The freestanding GaAs devices, incorporated into an Au coplanar strip line, exhibited extremely low dark currents and ~0.4 % detection efficiency at 10 V bias. The all-optical, pump-probe carrier dynamics analysis showed that, for 800-nm-wavelength excitation, the intrinsic relaxation of photocarriers featured a 310-fs-wide transient with a 290 fs fall time. We have also carried out a femtosecond, time-resolved electro-optic characterization of our devices and recorded along the transmission line the electrical transients as short as ~600 fs, when the platelet was excited by a train of 100-fs-wide, 800-nm-wavelength optical laser pulses. The platelets have been also demonstrated to be very efficient generators of free-space propagating THz transients with the spectral bandwidth exceeding 2 THz. The presented performance of the epitaxial, freestanding GaAs meso-structured photodevices makes them uniquely suitable for THz-frequency optoelectronic applications, ranging from ultrafast photodetectors to THz-bandwidth optical-to-electrical transducers and photomixers.

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

    SciTech Connect

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

    1988-02-01

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

  2. Micro-inhomogeneity effects and radiation damage in semi-insulating GaAs radiation detectors

    SciTech Connect

    Bates, R.; O`Shea, V.; Raine, C.; Smith, K.M.; Didziulis, R.; Kazukauskas, V.; Rinkevicius, V.; Storasta, J.; Vaitkus, J.

    1998-06-01

    Thermally-stimulated current (TSC) measurements and a detailed analysis of current-voltage (I-V) characteristics have been made on semi-insulating GaAs (SI-GaAs) Schottky diode particle detectors, fabricated on substrates from several supplies, before and after irradiation with 24 GeV protons and 300 MeV pions. The analysis of I-V characteristics allows the determination of the barrier height and bulk resistance in detectors. Changes observed in I-V characteristics and TSC spectra after irradiation are described and a dislocation-net model of radiation-damaged devices is proposed.

  3. Pulsed Molecular Beams For Growth Of InAs On GaAs

    NASA Technical Reports Server (NTRS)

    Grunthaner, Frank J.

    1989-01-01

    Pauses for annealing reduce number of defects. Deposition process that includes pulsed molecular beams produces high-quality epitaxial layers of indium arsenide on gallium arsenide substrates. Layers made as much as 30 atoms thick without introducing excessive numbers of dislocations, despite 7.4-percent mismatch between InAs and GaAs crystal lattices. Layers offer superior electrical properties in such devices as optically addressed light modulators, infrared sensors, semiconductor lasers, and high-electron-mobility transistors. Technique applicable to other epitaxial systems in which lattices highly mismatched.

  4. GaAs interfacial self-cleaning by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Hinkle, C. L.; Sonnet, A. M.; Vogel, E. M.; McDonnell, S.; Hughes, G. J.; Milojevic, M.; Lee, B.; Aguirre-Tostado, F. S.; Choi, K. J.; Kim, H. C.; Kim, J.; Wallace, R. M.

    2008-02-01

    The reduction and removal of surface oxides from GaAs substrates by atomic layer deposition (ALD) of Al2O3 and HfO2 are studied using in situ monochromatic x-ray photoelectron spectroscopy. Using the combination of in situ deposition and analysis techniques, the interfacial "self-cleaning" is shown to be oxidation state dependent as well as metal organic precursor dependent. Thermodynamics, charge balance, and oxygen coordination drive the removal of certain species of surface oxides while allowing others to remain. These factors suggest proper selection of surface treatments and ALD precursors can result in selective interfacial bonding arrangements.

  5. Efficient thermophotovoltaic solar cells on bent substrates

    NASA Astrophysics Data System (ADS)

    Shmavonyan, Gagik; Zadoyan, Ovsanna

    2013-04-01

    Thermophotovoltaic devices show promise as a method of reclaiming waste industrial heat and may provide a competitive and quiet low output heat conversion power supply for remote rural areas. GaSb based devices are well matched to a 1500-2000^oC blackbody emission temperature as well as to the solar spectrum when paired with GaAs. The growth of GaSb on GaAs proceeds via the Stranski-Krastanow mechanism, resulting in rectangular islands of GaSb with their edges orientated along the 110directions. The size of the islands is dependent on the growth temperature with smaller islands being produced for lower temperatures. The rectification behavior of p-GaSb/n-GaAs heterojunctions is also strongly dependent on the growth temperature. Possible mechanisms for the rectification at low temperature include more rapid turnover of interface dislocations and a corresponding reduction in carrier generation/recombination processes or passivation of defect centres by greater incorporation of impurities such as hydrogen. By optimizing the growth conditions, efficient p-GaSb/n-GaAs thermophotovoltaic devices have been produced. A series of GaSb and GaAs epilayers grown onto substrates has been used to investigate the effect of bent substrate on external quantum efficiency and spectral response.

  6. Efficient thermophotovoltaic solar cells on bent substrates

    NASA Astrophysics Data System (ADS)

    Shmavonyan, Gagik; Zadoyan, Ovsanna

    2013-04-01

    Thermophotovoltaic devices show promise as a method of reclaiming waste industrial heat and may provide a competitive and quiet low output heat conversion power supply for remote rural areas. GaSb based devices are well matched to a 1500-2000°C blackbody emission temperature as well as to the solar spectrum when paired with GaAs. The growth of GaSb on GaAs proceeds via the Stranski-Krastanow mechanism, resulting in rectangular islands of GaSb with their edges orientated along the <110> directions. The size of the islands is dependent on the growth temperature with smaller islands being produced for lower temperatures. The rectification behavior of p-GaSb/n-GaAs heterojunctions is also strongly dependent on the growth temperature. Possible mechanisms for the rectification at low temperature include more rapid turnover of interface dislocations and a corresponding reduction in carrier generation/recombination processes or passivation of defect centres by greater incorporation of impurities such as hydrogen. By optimizing the growth conditions, efficient p-GaSb/n-GaAs thermophotovoltaic devices have been produced. A series of GaSb and GaAs epilayers grown onto substrates has been used to investigate the effect of bent substrate on external quantum efficiency and spectral response. Department of Microelectronics and Biomedical Devices, Yerevan, 0002, Armenia

  7. Interface magnetization profiling by x-ray magnetometry of marker impurities on Fe /GaAs(001)-(4×6)

    NASA Astrophysics Data System (ADS)

    Giovanelli, L.; Panaccione, G.; Rossi, G.; Fabrizioli, M.; Tian, C. S.; Gastelois, P. L.; Fujii, J.; Back, C. H.

    2005-07-01

    We use Co atoms dispersed in a ferromagnetic Fe film as a magnetic marker material to probe the magnetic properties of the Fe film grown epitaxially on GaAs(001)-(4×6). X-ray magnetic circular dichroism on CoL2,3 edges has been used to perform, in a Mössbauer-like experiment, a layer-dependent analysis. We find an enhancement of the Co orbital magnetic moment near the interface with the GaAs substrate, as well as a decrease of the spin magnetic moment when approaching the interface and at the surface of the Fe film.

  8. Multiwafer growth of CdTe on GaAs by metalorganic chemical vapor deposition in a vertical, high-speed, rotating disk reactor

    NASA Astrophysics Data System (ADS)

    Tompa, G. S.; Nelson, C. R.; Saracino, M. A.; Colter, P. C.; Anderson, P. L.

    1989-07-01

    Growth by the MOCVD (at temperatures between 308 and 402 C) of CdTe (111) layers on GaAs (100) and GaAs (111) substrates in a commercial vertical high-speed rotating disk reactor was investigated, using dimethylcadmium (DMCd) and diisopropyltelluride as the growth precursors. For growth temperatures greater than 368 C, DMCd molar growth efficiencies greater than 50 percent were obtained. Results of SEM, IR spectroscopy, and FIR reflectivity examinations indicate that the CdTe films obtained in the vertical reactor were more uniform and of higher quality than the best films produced in a horizontal reactor using similar growth procedures.

  9. Epitaxial ferromagnetic thin films and heterostructures of Mn-based metallic and semiconducting compounds on GaAs

    NASA Astrophysics Data System (ADS)

    Tanaka, Masaaki

    1998-07-01

    We present two approaches to integrate magnetic materials with III-V semiconductors. One is epitaxial ferromagnetic metallic films and heterostructures on GaAs (0 0 1) substrates. Although crystal structure, lattice constant, chemical bonding and other properties are dissimilar, ferromagnetic hexagonal MnAs thin films and MnAs/NiAs ferromagnet/nonmagnet heterostructures (HSs) are grown on GaAs by molecular beam epitaxy (MBE). Multi-stepped magnetic hysteresis are controllably realized in MnAs/NiAs HSs, making this material promising for the application to multi-level nonvolatile recording on semiconductors. The other approach is to prepare a new class of GaAs based magnetic semiconductor, GaMnAs, by low-temperature molecular beam epitaxy (LT-MBE) on GaAs (0 0 1). New III-V based superlattices consisting of ferromagnetic semiconductor GaMnAs and nonmagnetic semiconductor AlAs are also successfully grown. Structural and magnetic properties of these new heterostructures are presented.

  10. Growth of GaAs “nano ice cream cones” by dual wavelength pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Schamp, C. T.; Jesser, W. A.; Shivaram, B. S.

    2007-05-01

    Harmonic generation crystals inherently offer the possibility of using multiple wavelengths of light in a single laser pulse. In the present experiment, the fundamental (1064 nm) and second harmonic (532 nm) wavelengths from an Nd:YAG laser are focused together on GaAs and GaSb targets for ablation. Incident energy densities up to about 45 J/cm 2 at 10 Hz with substrate temperatures between 25 and 600 °C for durations of about 60 s have been used in an ambient gas pressure of about 10 -6 Torr. The ablated material was collected on electron-transparent amorphous carbon films for TEM analysis. Apart from a high density of isolated nanocrystals, the most common morphology observed consists of a crystalline GaAs cone-like structure in contact with a sphere of liquid Ga, resembling an "ice cream cone", typically 50-100 nm in length. For all of the heterostuctures of this type, the liquid/solid/vacuum triple junction is found to correspond to the widest point on the cone. These heterostructures likely form by preferential evaporation of As from molten GaAs drops ablated from the target. The resulting morphology minimizes the interfacial and surface energies of the liquid Ga and solid GaAs.

  11. GaAs nanowires with oxidation-proof arsenic capping for the growth of an epitaxial shell.

    PubMed

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

    2016-08-25

    We propose an arsenic-capping/decapping method, allowing the growth of an epitaxial shell around the GaAs nanowire (NW) core which is exposed to an ambient atmosphere, and without the introduction of impurities. Self-catalyzed GaAs NW arrays were firstly grown on Si(111) substrates by solid-source molecular beam epitaxy. Aiming for protecting the active surface of the GaAs NW core, the arsenic-capping/decapping method has been applied. To validate the effect of this method, different core/shell NWs have been fabricated. Analyses highlight the benefit of the As capping-decapping method for further epitaxial shell growth: an epitaxial shell with a smooth surface is achieved in the case of As-capped-decapped GaAs NWs, comparable to the in situ grown GaAs/AlGaAs NWs. This As capping method opens a way for the epitaxial growth of heterogeneous material shells such as functional oxides using different reactors. PMID:27513669

  12. Vertically aligned GaAs nanowires on graphite and few-layer graphene: generic model and epitaxial growth.

    PubMed

    Munshi, A Mazid; Dheeraj, Dasa L; Fauske, Vidar T; Kim, Dong-Chul; van Helvoort, Antonius T J; Fimland, Bjørn-Ove; Weman, Helge

    2012-09-12

    By utilizing the reduced contact area of nanowires, we show that epitaxial growth of a broad range of semiconductors on graphene can in principle be achieved. A generic atomic model is presented which describes the epitaxial growth configurations applicable to all conventional semiconductor materials. The model is experimentally verified by demonstrating the growth of vertically aligned GaAs nanowires on graphite and few-layer graphene by the self-catalyzed vapor-liquid-solid technique using molecular beam epitaxy. A two-temperature growth strategy was used to increase the nanowire density. Due to the self-catalyzed growth technique used, the nanowires were found to have a regular hexagonal cross-sectional shape, and are uniform in length and diameter. Electron microscopy studies reveal an epitaxial relationship of the grown nanowires with the underlying graphitic substrates. Two relative orientations of the nanowire side-facets were observed, which is well explained by the proposed atomic model. A prototype of a single GaAs nanowire photodetector demonstrates a high-quality material. With GaAs being a model system, as well as a very useful material for various optoelectronic applications, we anticipate this particular GaAs nanowire/graphene hybrid to be promising for flexible and low-cost solar cells. PMID:22889019

  13. Panel fabrication utilizing GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Mardesich, N.

    1984-01-01

    The development of the GaAs solar cells for space applications is described. The activities in the fabrication of GaAs solar panels are outlined. Panels were fabricated while introducing improved quality control, soldering laydown and testing procedures. These panels include LIPS II, San Marco Satellite, and a low concentration panel for Rockwells' evaluation. The panels and their present status are discussed.

  14. Linearity of photoconductive GaAs detectors to pulsed electrons

    SciTech Connect

    Ziegler, L.H.

    1995-12-31

    The response of neutron damaged GaAs photoconductor detectors to intense, fast (50 psec fwhm) pulses of 16 MeV electrons has been measured. Detectors made from neutron damaged GaAs are known to have reduced gain, but significantly improved bandwidth. An empirical relationship between the observed signal and the incident electron fluence has been determined.

  15. Impacts of crystal orientation of GaAs on the interfacial structures and electrical properties of Hf{sub 0.6}La{sub 0.4}O{sub x} films

    SciTech Connect

    Jia, Tingting; Kimura, Hideo; Zhao, Hongyang; Yao, Qiwen; Cheng, Zhenxiang; Cheng, Xinghong; Yu, Yuehui

    2014-04-07

    One of the major challenges in realizing the GaAs channel in the metal oxide semiconductor field effect transistor is the degrading in electron transport properties at the interface between GaAs and the gate oxide. In this study, Hf{sub 0.6}La{sub 0.4}O{sub x} gate oxide films were deposited at a low temperature (200 °C) on GaAs(111)A and GaAs(100) substrates by plasma enhanced atomic layer deposition. Microstructure analysis indicates that residuals of gallium oxide, arsenic oxide, and As element remained at the interface of Hf{sub 0.6}La{sub 0.4}O{sub x}/GaAs(100). On contrast, a smoother interface is observed between Hf{sub 0.6}La{sub 0.4}O{sub x} thin film and GaAs(111)A substrate. Furthermore, a reduction of interfacial layer is observed in Hf{sub 0.6}La{sub 0.4}O{sub x}/GaAs(111)A. Electrical characterization of the metal-insulator-semiconductor Pt/Hf{sub 0.6}La{sub 0.4}O{sub x}/n-GaAs(111)A capacitor indicated a reduction of D{sub it} and leakage current compared with the capacitor fabricated on GaAs(100)

  16. Parameters study on the growth of GaAs nanowires on indium tin oxide by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wu, Dan; Tang, Xiaohong; Wang, Kai; Olivier, Aurelien; Li, Xianqiang

    2016-03-01

    After successful demonstration of GaAs nanowire (NW) epitaxial growth on indium tin oxide (ITO) by metal organic chemical vapor deposition, we systematically investigate the effect of growth parameters' effect on the GaAs NW, including temperature, precursor molar flow rates, growth time, and Au catalyst size. 40 nm induced GaAs NWs are observed with zinc-blende structure. Based on vapor-liquid-solid mechanism, a kinetic model is used to deepen our understanding of the incorporation of growth species and the role of various growth parameters in tuning the GaAs NW growth rate. Thermally activated behavior has been investigated by variation of growth temperature. Activation energies of 40 nm Au catalyst induced NWs are calculated at different trimethylgallium (TMGa) molar flow rates about 65 kJ/mol. The GaAs NWs growth rates increase with TMGa molar flow rates whereas the growth rates are almost independent of growth time. Due to Gibbs-Thomson effect, the GaAs NW growth rates increase with Au nanoparticle size at different temperatures. Critical radius is calculated as 2.14 nm at the growth condition of 430 °C and 1.36 μmol/s TMGa flow rate. It is also proved experimentally that Au nanoparticle below the critical radius such as 2 nm cannot initiate the growth of NWs on ITO. This theoretical and experimental growth parameters investigation enables great controllability over GaAs NWs grown on transparent conductive substrate where the methodology can be expanded to other III-V material NWs and is critical for potential hybrid solar cell application.

  17. Effect of interaction in the Ga-As-O system on the morphology of a GaAs surface during molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ageev, O. A.; Balakirev, S. V.; Solodovnik, M. S.; Eremenko, M. M.

    2016-05-01

    A thermodynamic analysis of processes of interphase interaction in the Ga-As-O system has been performed and their theoretical laws have been determined, taking into account nonlinear thermal physical properties of the compounds, the oxide film compositions, and modes of molecular-beam epitaxy of GaAs. The processes of interaction of the native oxide of GaAs with the substrate material and also with Ga and As4 from a vapor gaseous phase have been studied experimentally. The experimental results correlate with the results of the thermodynamic analysis. The laws of influence of the removal of the proper oxide on the evolution of the GaAs surface morphology under conditions of the molecular-beam epitaxy have been proposed.

  18. Heteroepitaxy of single-crystal LaLuO{sub 3} on GaAs(111)A by atomic layer deposition

    SciTech Connect

    Liu Yiqun; Heo, Jaeyeong; Gordon, Roy G.; Xu Min; Ye, Peide D.

    2010-10-18

    We demonstrate that LaLuO{sub 3} films can be grown epitaxially on sulfur-passivated GaAs(111)A substrates by atomic layer deposition (ALD). Transmission electron microscopy and x-ray diffraction analyses reveal that the oxide film exhibits a cubic structure with a lattice mismatch of -3.8% relative to GaAs. The epitaxial layer has a high degree of crystalline perfection and is relaxed. Electrical characterizations performed on this structure show interfaces with a low interface state density of {approx}7x10{sup 11} cm{sup -2} eV{sup -1}. The measured dielectric constant is around 30, which is close to its bulk crystalline value. In contrast, ALD LaLuO{sub 3} is polycrystalline on GaAs(100) and amorphous on Si(111).

  19. On the use of a O 2:SF 6 plasma treatment on GaAs processed surfaces for molecular beam epitaxial regrowth

    NASA Astrophysics Data System (ADS)

    Desplats, O.; Gallo, P.; Doucet, J. B.; Monier, G.; Bideux, L.; Jalabert, L.; Arnoult, A.; Lacoste, G.; Armand, C.; Voillot, F.; Fontaine, C.

    2009-01-01

    Preparation of processed GaAs surface cleaning in view of molecular beam epitaxy regrowth by means of a O 2SF 6 microwave plasma has been investigated. Photoemission, Auger electron spectroscopy, atomic force microscopy and secondary ion mass spectrometry have been used for characterization. The O 2SF 6 plasma treatment was found to be very efficient for decontaminating the GaAs surface and leads to the formation of an oxide layer that can be taken off by a thermal or low-temperature H-plasma-assisted deoxidation. The levels of oxygen and carbon contaminants at the regrowth interface were measured to be in the range of a standard homoepitaxial layer-epiready substrate interface. Fluorine was observed to be eliminated upon deoxidation while sulphur is present, particularly in the case of low temperature grown layers. This plasma treatment was found to be efficient for preparation of processed GaAs surfaces for molecular beam epitaxial regrowth.

  20. Some optical and electron microscope comparative studies of excimer laser-assisted and nonassisted molecular-beam epitaxically grown thin GaAs films on Si

    NASA Technical Reports Server (NTRS)

    Lao, Pudong; Tang, Wade C.; Rajkumar, K. C.; Guha, S.; Madhukar, A.; Liu, J. K.; Grunthaner, F. J.

    1990-01-01

    The quality of GaAs thin films grown via MBE under pulsed excimer laser irradiation on Si substrates is examined in both laser-irradiated and nonirradiated areas using Raman scattering, Rayleigh scattering, and by photoluminescence (PL), as a function of temperature, and by TEM. The temperature dependence of the PL and Raman peak positions indicates the presence of compressive stress in the thin GaAs films in both laser-irradiated and nonirradiated areas. This indicates incomplete homogeneous strain relaxation by dislocations at the growth temperature. The residual compressive strain at the growth temperature is large enough such that even with the introduction of tensile strain arising from the difference in thermal expansion coefficients of GaAs and Si, a compressive strain is still present at room temperature for these thin GaAs/Si films.

  1. 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.

  2. Strain modified/enhanced ferromagnetism in Mn{sub 3}Ge{sub 2} thin films on GaAs(001) and GaSb(001)

    SciTech Connect

    Dang Duc Dung; Duong Van Thiet; Feng Wuwei; Cho, Sunglae; Park, In-Sung; Bo Lee, Sung

    2013-04-21

    Ferromagnetic Mn{sub 3}Ge{sub 2} thin films were successfully grown on GaAs(001) and GaSb(001) substrates using molecular beam epitaxy. The results of our work revealed that the substrate facilitates to modify magnetic and electrical properties of Mn{sub 3}Ge{sub 2} films due to tensile/compressive strain effect between films and substrates. The characteristic spin-flopping transition at around 150 K for the bulk Mn{sub 3}Ge{sub 2} disappeared completely for both samples. The antiferromagnetism below 150 K changed to ferromagnetism and retained above room temperature. The saturation magnetization was found to be 0.23 and 1.32 {mu}{sub B}/Mn atom at 10 K for the samples grown on GaSb(001) and GaAs(001), respectively.

  3. Ga-assisted MBE growth of GaAs nanowires using thin HSQ layer

    NASA Astrophysics Data System (ADS)

    Rieger, Torsten; Heiderich, Sonja; Lenk, Steffi; Lepsa, Mihail Ion; Grützmacher, Detlev

    2012-08-01

    We present detailed results about the molecular beam epitaxy (MBE) growth of GaAs nanowires (NWs) on GaAs (111)B substrates prepared for the growth by a new method using hydrogen silsesquioxane (HSQ). Before the growth, HSQ is converted to SiOx by thermal treatment. The NWs are grown via the vapor-liquid-solid (VLS) mechanism. The influence of five growth parameters are described: SiOx thickness, growth time, substrate temperature and Ga and As4 beam fluxes. It is shown that the nanowire density can be tuned by two orders of magnitude by adjusting the SiOx thickness. Additionally, the results demonstrate that the axial growth is controlled by the As4 beam flux whereas the lateral growth is controlled by the Ga beam flux. The observed NW tapering is mainly determined by the V/III beam flux ratio. Our study gives important information about the VLS growth mechanism, which is extended by considering the secondary adsorption process of Ga adatoms. The nanowires have predominantly zinc blende crystal structure with rotational twins. A wurtzite segment is always found at the top of the NWs being associated with the growth after the Ga shutter has been closed.

  4. Heteroepitaxial InP, and ultrathin, directly glassed, GaAs 3-5 solar cells

    NASA Technical Reports Server (NTRS)

    Hardingham, C. M.; Cross, T. A.

    1993-01-01

    The commercial application of Indium Phosphide solar cells in practical space missions is crucially dependent upon achieving a major cost reduction which could be offered by heteroepitaxy on cheaper, more rugged substrates. Furthermore, significant mass reduction, compatibility with mechanically stacked multijunction cells, and elimination of the current loss through glue discoloration, is possible in III-V solar cells by the development of ultrathin, directly glassed cells. The progress of a UK collaborative program to develop high efficiency, homojunction InP solar cells, grown by MOCVD on Si substrates, is described. Results of homoepitaxial cells (is greater than 17 percent 1 Sun AM0) are presented, together with progress in achieving low dislocation density heteroepitaxy. Also, progress in a UK program to develop ultrathin directly-glassed GaAs cells is described. Ultrathin (5 micron) GaAs cells, with 1 Sun AM0 efficiencies up to 19.1 percent, are presented, together with progress in achieving a direct (adhesive-less) bond between the cell and coverglass. Consequential development to, for example, cell grids, are also discussed.

  5. Modified dislocation filter method: toward growth of GaAs on Si by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Hu, Haiyang; Wang, Jun; He, Yunrui; Liu, Kai; Liu, Yuanyuan; Wang, Qi; Duan, Xiaofeng; Huang, Yongqing; Ren, Xiaomin

    2016-06-01

    In this paper, metamorphic growth of GaAs on (001) oriented Si substrate, with a combination method of applying dislocation filter layer (DFL) and three-step growth process, was conducted by metal organic chemical vapor deposition. The effectiveness of the multiple InAs/GaAs self-organized quantum dot (QD) layers acting as a dislocation filter was researched in detail. And the growth conditions of the InAs QDs were optimized by theoretical calculations and experiments. A 2-μm-thick buffer layer was grown on the Si substrate with the three-step growth method according to the optimized growth conditions. Then, a 114-nm-thick DFL and a 1-μm-thick GaAs epilayer were grown. The results we obtained demonstrated that the DFL can effectively bend dislocation direction via the strain field around the QDs. The optimal structure of the DFL is composed of three-layer InAs QDs with a growth time of 55 s. The method could reduce the etch pit density from about 3 × 106 cm-2 to 9 × 105 cm-2 and improve the crystalline quality of the GaAs epilayers on Si.

  6. High purity GaAs and Al xGa 1-xAs grown by metalorganic molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Furuhata, Naoki; Okamoto, Akihiko; Hoshino, Hitoshi

    1990-06-01

    High purity GaAs and Al xGa 1- xAs were grown by metalorganic molecular beam epitaxy (MOMBE) using metalorganic sources and arsenic (As 4). In GaAs growth using triethylgallium (TEG) and As 4, carrier concentrations depended on As 4 pressure and substrate temperatures. Below 1.5 x 10 -4 Torr As 4 pressure, the p-type carrier concentrations decreased with an increase in As 4 pressure. Above 1.5 x 10 -4 Torr As 4 pressure, the epilayer converted from p-type to n-type conductivity. Carrier concentrations decreased with a decrease in substrate temperatures. At 500°C and 1.5 x 10 -4 Torr As 4 pressure, the carrier concentration in the p-type GaAs epilayer exhibited 1.5 x 10 14 cm -3 with a room temperature mobility of 400 cm 2/V.s. Al xGa 1-xAs ( x=0.1-0. .2) was also grown using TEG, three different Al sources (triethylaluminum (TEA), trimethylaluminum (TMA) and dimethylaluminum hydride (DMAH) and As 4. Using TEG, TEA and As 4, the Al 0.15Ga 0.85As epilayer showed p-type conduction with carrier concentration of 1.2x10 15 cm -3 and mobility of 117 cm 2/V.s. This carrier concentration is the lowest value ever reported for Al xGa 1- xAs grown by MOMBE.

  7. Homojunction GaAs solar cells grown by close space vapor transport

    SciTech Connect

    Boucher, Jason W.; Ritenour, Andrew J.; Greenaway, Ann L.; Aloni, Shaul; Boettcher, Shannon W.

    2014-06-08

    We report on the first pn junction solar cells grown by homoepitaxy of GaAs using close space vapor transport (CSVT). Cells were grown both on commercial wafer substrates and on a CSVT absorber film, and had efficiencies reaching 8.1%, open circuit voltages reaching 909 mV, and internal quantum efficiency of 90%. The performance of these cells is partly limited by the electron diffusion lengths in the wafer substrates, as evidenced by the improved peak internal quantum efficiency in devices fabricated on a CSVT absorber film. Unoptimized highly-doped n-type emitters also limit the photocurrent, indicating that thinner emitters with reduced doping, and ultimately wider band gap window or surface passivation layers, are required to increase the efficiency.

  8. Void-free Au-Sn eutectic bonding of GaAs dice and its characterization using scanning acoustic microscopy

    NASA Astrophysics Data System (ADS)

    Matljasevic, Goran; Lee, Chin C.

    1989-03-01

    A new technique to produce perfect bonding between GaAs dice and alumina substrates is reported. Utilizing this technique, void-free bondings have been achieved consistently. The quality of the bonded devices is confirmed by a Scanning Acoustic Microscope (SAM) having a spatial resolution of 25 µm. Thermal cycling between -25° C and 125° C, and thermal shock between -196° C and 135° C, have been used to assess the reliability of the specimens. The SAM was used to study the variation of the bonds in the tests. After the tests, the bonds show no sign of degradation and the GaAs dice did not crack. Shear test has also been performed. All the well bonded specimens passed the shear test. The shear strength correlated very well with the SAM images of the specimens taken before the test.

  9. Surface-morphology evolution during growth-interrupt in situ annealing on GaAs(110) epitaxial layers

    SciTech Connect

    Yoshita, Masahiro; Akiyama, Hidefumi; Pfeiffer, Loren N.; West, Ken W.

    2007-05-15

    Temperature and surface-coverage dependence of the evolution of surface morphology during growth-interrupt in situ annealing on GaAs epitaxial layers grown on the singular (110) cleaved edges by the cleaved-edge overgrowth method with molecular-beam epitaxy has been studied by means of atomic force microscopy. Annealing at substrate temperatures below 630 degree sign C produced atomically flat surfaces with characteristic islands or pits, depending on the surface coverage. The atomic flatness of the surfaces is enhanced with increasing annealing temperature owing to the enhanced adatom migration. At a higher annealing temperature of about 650 degree sign C, however, 2-monolayer-deep triangular pits with well-defined step edges due to Ga-atom desorption from the crystal appeared in the atomically flat surface. The growth-interrupt annealing temperature optimal for the formation of atomically flat GaAs(110) surfaces is therefore about 630 degree sign C.

  10. Vapor-liquid-solid growth of GaN nanowires by reactive sputtering of GaAs

    NASA Astrophysics Data System (ADS)

    Mohanta, P.; Chaturvedi, P.; Major, S. S.; Srinivasa, R. S.

    2013-02-01

    Uniformly distributed nanosized Au-Ga alloy particles were formed on ultrathin Au coated quartz substrate by sputtering of GaAs with argon at 700 °C. Subsequent deposition of GaN by reactive sputtering of GaAs in 100 % nitrogen results in the growth of GaN nanowires. X-ray diffraction analysis confirmed the formation of hexagonal GaN. Field emission gun scanning electron microscopy studies show that the nanowires are of average length 400±50 nm and average diameter 40±5 nm. The presence of spherical Au-Ga nanoparticles of diameter ˜ 50 nm at the top of the nanowires suggests that the growth takes place by vapor-liquid-solid mechanism.

  11. Analysis of aluminum nano-gratings assisted light reflection reduction in GaAs metal-semiconductor-metal photodetectors

    NASA Astrophysics Data System (ADS)

    Fan, Zhenzhu; Su, Yahui; Zhang, Huayong; Han, Xiaohu; Ren, Feifei

    2015-09-01

    Plasmonics-based GaAs metal-semiconductor-metal photodetector (MSM-PD) with aluminum nano-gratings was proposed. A detailed numerical study of subwavelength nanogratings behavior to reduce the light reflection is performed by finite-difference time domain (FDTD) algorithm. The geometric parameters of nano-gratings, such as aperture width, the nano-gratings height, the duty cycles are optimized for subwavelength metal nanogratings on GaAs substrate and their impact on light reflection below the conventional MSM-PD is confirmed. Simulation results show that a light reflection factor around 15% can be obtained near the wavelength of 900 nm with optimized MSM-PDs, and in visible light spectrum, the Al nano-gratings show better performance than Au nano-gratings.

  12. Polarized Raman spectroscopy of corrugated MBE grown GaAs (6¯3¯1¯) homoepitaxial films

    NASA Astrophysics Data System (ADS)

    Espinosa-Vega, L. I.; Rodriguez, A. G.; Cruz-Hernandez, E.; Martinez-Veliz, I.; Rojas-Ramirez, J.; Ramirez-Lopez, M.; Nieto-Navarro, J.; Lopez-Lopez, M.; Mendez-Garcia, V. H.

    2013-09-01

    In this work, we present a Raman scattering study of GaAs layers grown on (6¯3¯1¯)-oriented substrates by molecular beam epitaxy. A set of samples whose morphology sustained different corrugation order were grown by MBE by varying the growth parameters such as temperature and As/Ga flux ratio. We employed polarized Raman spectroscopy using the backscattering configurations Z(XX) Z¯, Z(XY) Z¯ and Z(YY)Z¯. According to the calculated dipole selection rules both TO and LO phonons are allowed for backscattering from a perfect GaAs (6¯3¯1¯) crystal, but with the intensity of the TO phonon much larger than that of the LO phonon. However, it is found that the selection rules differ for corrugated samples. Besides, the TO/LO phonon resonances intensity ratio and the LO peak asymmetry depend on the corrugation order of the samples.

  13. Modeling atomic hydrogen diffusion in GaAs

    NASA Astrophysics Data System (ADS)

    Kagadei, Valerii A.; Nefyodtsev, E.

    2004-05-01

    The hydrogen diffusion model in GaAs in conditions of an intense flow of penetrating atoms has been developed. It is shown that the formation undersurface diffusion barrier layer from immobile interstitial molecules of hydrogen reduce probability of atoms penetration into crystal and rate of their diffusion in GaAs, and influence on the process of shallow- and/or deep-centers passivation. It is exhibited that the influence of diffusion barrier should be taken into account at optimum mode selection of GaAs structure hydrogenation.

  14. Photocurrent Spectroscopy of Single Wurtzite GaAs Nanowires

    SciTech Connect

    Kim, D. C.; Ahtapodov, L.; Boe, A. B.; Moses, A. F.; Dheeraj, D. L.; Fimland, B. O.; Weman, H.; Choi, J. W.; Ji, H.; Kim, G. T.

    2011-12-23

    Photocurrent of single wurtzite GaAs nanowires grown by Au-assisted molecular beam epitaxy is measured at room and low temperature (10 K). At room temperature a high photo-response with more than two orders of magnitude increase of current is observed. The wavelength dependence of the photocurrent shows a sharp change near the zinc blende GaAs band gap. The absence of the free exciton peak in the low temperature photocurrent spectrum, and problems related to determining the exact position of the energy bandgap of wurtzite GaAs from the observed data are discussed.

  15. GaAs VLSI technology and circuit elements for DSP

    NASA Astrophysics Data System (ADS)

    Mikkelson, James M.

    1990-10-01

    Recent progress in digital GaAs circuit performance and complexity is presented to demonstrate the current capabilities of GaAs components. High density GaAs process technology and circuit design techniques are described and critical issues for achieving favorable complexity speed power and cost tradeoffs are reviewed. Some DSP building blocks are described to provide examples of what types of DSP systems could be implemented with present GaAs technology. DIGITAL GaAs CIRCUIT CAPABILITIES In the past few years the capabilities of digital GaAs circuits have dramatically increased to the VLSI level. Major gains in circuit complexity and power-delay products have been achieved by the use of silicon-like process technologies and simple circuit topologies. The very high speed and low power consumption of digital GaAs VLSI circuits have made GaAs a desirable alternative to high performance silicon in hardware intensive high speed system applications. An example of the performance and integration complexity available with GaAs VLSI circuits is the 64x64 crosspoint switch shown in figure 1. This switch which is the most complex GaAs circuit currently available is designed on a 30 gate GaAs gate array. It operates at 200 MHz and dissipates only 8 watts of power. The reasons for increasing the level of integration of GaAs circuits are similar to the reasons for the continued increase of silicon circuit complexity. The market factors driving GaAs VLSI are system design methodology system cost power and reliability. System designers are hesitant or unwilling to go backwards to previous design techniques and lower levels of integration. A more highly integrated system in a lower performance technology can often approach the performance of a system in a higher performance technology at a lower level of integration. Higher levels of integration also lower the system component count which reduces the system cost size and power consumption while improving the system reliability

  16. Localized corrosion of GaAs surfaces and formation of porous GaAs

    SciTech Connect

    Schmuki, P.; Vitus, C.M.; Isaacs, H.S.; Fraser, J.; Graham, M.J.

    1995-12-01

    The present work deals with pitting corrosion of p- and n-type GaAs (100). Pit growth can be electrochemically initiated on both conduction types in chloride-containing solutions and leads after extended periods of time to the formation of a porous GaAs structure. In the case of p-type material, localized corrosion is only observed if a passivating film is present on the surface, otherwise -- e.g. in acidic solutions -- the material suffers from a uniform attack (electropolishing) which is independent of the anion present. In contrast, pitting corrosion of n-type material can be triggered independent of the presence of an oxide film. This is explained in terms of the different current limiting factor for the differently doped materials (oxide film in the case of the p- and a space charge layer in the case of the n-GaAs). The porous structure was characterized by SEM, EDX and AES, and consists mainly of GaAs. From scratch experiments it is clear that the pit initiation process is strongly influenced by surface defects. For n-type material, AFM investigations show that light induced roughening of the order of several hundred nm occurs under non-passivating conditions. This nm- scale roughening however does not affect the pitting process.

  17. Growth and characterization of epitaxial aluminum layers on gallium-arsenide substrates for superconducting quantum bits

    NASA Astrophysics Data System (ADS)

    Tournet, J.; Gosselink, D.; Miao, G.-X.; Jaikissoon, M.; Langenberg, D.; McConkey, T. G.; Mariantoni, M.; Wasilewski, Z. R.

    2016-06-01

    The quest for a universal quantum computer has renewed interest in the growth of superconducting materials on semiconductor substrates. High-quality superconducting thin films will make it possible to improve the coherence time of superconducting quantum bits (qubits), i.e., to extend the time a qubit can store the amplitude and phase of a quantum state. The electrical losses in superconducting qubits highly depend on the quality of the metal layers the qubits are made from. Here, we report on the epitaxy of single-crystal Al (011) layers on GaAs (001) substrates. Layers with 110 nm thickness were deposited by means of molecular beam epitaxy at low temperature and monitored by in situ reflection high-energy electron diffraction performed simultaneously at four azimuths. The single-crystal nature of the layers was confirmed by ex situ high-resolution x-ray diffraction. Differential interference contrast and atomic force microscopy analysis of the sample’s surface revealed a featureless surface with root mean square roughness of 0.55 nm. A detailed in situ study allowed us to gain insight into the nucleation mechanisms of Al layers on GaAs, highlighting the importance of GaAs surface reconstruction in determining the final Al layer crystallographic orientation and quality. A highly uniform and stable GaAs (001)-(2× 4) reconstruction reproducibly led to a pure Al (011) phase, while an arsenic-rich GaAs (001)-(4× 4) reconstruction yielded polycrystalline films with an Al (111) dominant orientation. The near-atomic smoothness and single-crystal character of Al films on GaAs, in combination with the ability to trench GaAs substrates, could set a new standard for the fabrication of superconducting qubits.

  18. Adding GaAs Monolayers to InAs Quantum-Dot Lasers on (001) InP

    NASA Technical Reports Server (NTRS)

    Qiu, Yueming; Chacon, Rebecca; Uhl, David; Yang, Rui

    2005-01-01

    In a modification of the basic configuration of InAs quantum-dot semiconductor lasers on (001)lnP substrate, a thin layer (typically 1 to 2 monolayer thick) of GaAs is incorporated into the active region. This modification enhances laser performance: In particular, whereas it has been necessary to cool the unmodified devices to temperatures of about 80 K in order to obtain lasing at long wavelengths, the modified devices can lase at wavelengths of about 1.7 microns or more near room temperature. InAs quantum dots self-assemble, as a consequence of the lattice mismatch, during epitaxial deposition of InAs on ln0.53Ga0.47As/lnP. In the unmodified devices, the quantum dots as thus formed are typically nonuniform in size. Strainenergy relaxation in very large quantum dots can lead to poor laser performance, especially at wavelengths near 2 microns, for which large quantum dots are needed. In the modified devices, the thin layers of GaAs added to the active regions constitute potential-energy barriers that electrons can only penetrate by quantum tunneling and thus reduce the hot carrier effects. Also, the insertion of thin GaAs layer is shown to reduce the degree of nonuniformity of sizes of the quantum dots. In the fabrication of a batch of modified InAs quantum-dot lasers, the thin additional layer of GaAs is deposited as an interfacial layer in an InGaAs quantum well on (001) InP substrate. The device as described thus far is sandwiched between InGaAsPy waveguide layers, then further sandwiched between InP cladding layers, then further sandwiched between heavily Zn-doped (p-type) InGaAs contact layer.

  19. Development of GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Mcnally, P. J.

    1972-01-01

    Calculations of GaAs solar cell output parameters were refined and a computer model was developed for parameter optimization. The results were analyzed to determine the material characteristics required for a high efficiency solar cell. Calculated efficiencies for a P/N cell polarity are higher than an N/P cell. Both cell polarities show efficiency to have a larger dependence on short circuit current than an open circuit voltage under nearly all conditions considered. The tolerances and requirements of a cell fabrication process are more critical for an N/P type than for a P/N type cell. Several solar cell fabrication considerations relative to junction formation using ion implantation are also discussed.

  20. Interface composition between Fe{sub 3}O{sub 4} nanoparticles and GaAs for spintronic applications

    SciTech Connect

    Hihath, Sahar; Kiehl, Richard A.; Benthem, Klaus van

    2014-08-28

    Recent interest in spintronic applications has necessitated the study of magnetic materials in contact with semiconductor substrates; importantly, the structure and composition of these interfaces can influence both device functionality and the magnetic properties. Nanoscale ferromagnet/semiconductor structures are of particular interest. In this study, the interface structure between a monolayer of ferromagnetic magnetite (Fe{sub 3}O{sub 4}) nanoparticles and a GaAs substrate was studied using cross-sectional transmission electron microscopy techniques. It was found that a continuous amorphous oxide interface layer separates the nanoparticles from the GaAs substrate, and that iron diffused into the interface layer forming a compositional gradient. Electron energy-loss near-edge fine structures of the O K absorption edge revealed that the amorphous oxide is composed of γ-Fe{sub 2}O{sub 3} directly underneath the Fe{sub 3}O{sub 4} nanoparticles, followed by a solid solution of Ga{sub 2}O{sub 3} and FeO and mostly Ga{sub 2}O{sub 3} when approaching the buckled oxide/substrate interface. Real-space density functional theory calculations of the dynamical form factor confirmed the experimental observations. The implication of the findings on the optimization of these structures for spin injection is discussed.

  1. Enhanced annealing of GaAs solar cell radiation damage

    NASA Technical Reports Server (NTRS)

    Loo, R.; Knechtli, R. C.; Kamath, G. S.

    1981-01-01

    Solar cells are degraded by radiation damage in space. Investigations have been conducted concerning possibilities for annealing this radiation damage in GaAs solar cells, taking into account the conditions favoring such annealing. It has been found that continuous annealing as well as the combination of injection annealing with thermal annealing can lead to recovery from radiation damage under particularly favorable conditions in GaAs solar cells. The damage caused by both electrons and protons in GaAs solar cells can be substantially reduced by annealing at temperatures as low as 150 C, under appropriate conditions. This possibility makes the GaAs solar cells especially attractive for long space missions, or for missions in severe radiation environments. Attention is given to results concerning periodic thermal annealing, continuous annealing, and injection annealing combined with thermal annealing.

  2. GaAs Films Prepared by RF-Magnetron Sputtering

    SciTech Connect

    L.H. Ouyang; D.L. Rode; T. Zulkifli; B. Abraham-Shrauner; N. Lewis; M.R. Freeman

    2001-08-01

    The authors reported on the optical absorption, adhesion, and microstructure of RF-magnetron sputtered films of hydrogenated amorphous and microcrystalline GaAs films for the 1 to 25 {micro}m infrared wavelength rate. Sputtering parameters which were varied include sputtering power, temperature and pressure, and hydrogen sputtering-gas concentration. TEM results show a sharp transition from purely amorphous GaAs to a mixture of microcrystalline GaAs in an amorphous matrix at 34 {+-} 2 C. By optimizing the sputtering parameters, the optical absorption coefficient can be decreased below 100 cm{sup -1} for wavelengths greater than about 1.25 {micro}m. These results represent the lowest reported values of optical absorption for sputtered films of GaAs directly measured by spectrophotometry for the near-infrared wavelength region.

  3. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1983-01-01

    GaAs device technology has recently reached a new phase of rapid advancement, made possible by the improvement of the quality of GaAs bulk crystals. At the same time, the transition to the next generation of GaAs integrated circuits and optoelectronic systems for commercial and government applications hinges on new quantum steps in three interrelated areas: crystal growth, device processing and device-related properties and phenomena. Special emphasis is placed on the establishment of quantitative relationships among crystal growth parameters-material properties-electronic properties and device applications. The overall program combines studies of crystal growth on novel approaches to engineering of semiconductor material (i.e., GaAs and related compounds); investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; and investigation of electronic properties and phenomena controlling device applications and device performance.

  4. GaAs monolithic RF modules for SARSAT distress beacons

    NASA Technical Reports Server (NTRS)

    Cauley, Michael A.

    1991-01-01

    Monolithic GaAs UHF components for use in SARSAT Emergency Distress beacons are under development by Microwave Monolithics, Inc., Simi Valley, CA. The components include a bi-phase modulator, driver amplifier, and a 5 watt power amplifier.

  5. XPS investigation of ion beam induced conversion of GaAs(0 0 1) surface into GaN overlayer

    NASA Astrophysics Data System (ADS)

    Kumar, Praveen; Kumar, Mahesh; Govind; Mehta, B. R.; Shivaprasad, S. M.

    2009-10-01

    For the advance of GaN based optoelectronic devices, one of the major barriers has been the high defect density in GaN thin films, due to lattice parameter and thermal expansion incompatibility with conventional substrates. Of late, efforts are focused in fine tuning epitaxial growth and in search for a low temperature method of forming low defect GaN with zincblende structure, by a method compatible to the molecular beam epitaxy process. In principle, to grow zincblende GaN the substrate should have four-fold symmetry and thus zincblende GaN has been prepared on several substrates including Si, 3C-SiC, GaP, MgO, and on GaAs(0 0 1). The iso-structure and a common shared element make the epitaxial growth of GaN on GaAs(0 0 1) feasible and useful. In this study ion-induced conversion of GaAs(0 0 1) surface into GaN at room temperature is optimized. At the outset a Ga-rich surface is formed by Ar + ion bombardment. Nitrogen ion bombardment of the Ga-rich GaAs surface is performed by using 2-4 keV energy and fluence ranging from 3 × 10 13 ions/cm 2 to 1 × 10 18 ions/cm 2. Formation of surface GaN is manifested as chemical shift. In situ core level and true secondary electron emission spectra by X-ray photoelectron spectroscopy are monitored to observe the chemical and electronic property changes. Using XPS line shape analysis by deconvolution into chemical state, we report that 3 keV N 2+ ions and 7.2 × 10 17 ions/cm 2 are the optimal energy and fluence, respectively, for the nitridation of GaAs(0 0 1) surface at room temperature. The measurement of electron emission of the interface shows the dependence of work function to the chemical composition of the interface. Depth profile study by using Ar + ion sputtering, shows that a stoichiometric GaN of 1 nm thickness forms on the surface. This, room temperature and molecular beam epitaxy compatible, method of forming GaN temperature can serve as an excellent template for growing low defect GaN epitaxial overlayers.

  6. Design and fabrication of GaAs OMIST photodetector

    NASA Astrophysics Data System (ADS)

    Kang, Xuejun; Lin, ShiMing; Liao, Qiwei; Gao, Junhua; Liu, Shi'an; Cheng, Peng; Wang, Hongjie; Zhang, Chunhui; Wang, Qiming

    1998-08-01

    We designed and fabricated GaAs OMIST (Optical-controlled Metal-Insulator-Semiconductor Thyristor) device. Using oxidation of AlAs layer that is grown by MBE forms the Ultra- Thin semi-Insulating layer (UTI) of the GAAS OMIST. The accurate control and formation of high quality semi-insulating layer (AlxOy) are the key processes for fabricating GaAs OMIST. The device exhibits a current-controlled negative resistance region in its I-V characteristics. When illuminated, the major effect of optical excitation is the reduction of the switching voltage. If the GaAs OMIST device is biased at a voltage below its dark switching voltage Vs, sufficient incident light can switch OMIST from high impedance low current 'off' state to low impedance high current 'on' state. The absorbing material of OMIST is GaAS, so if the wavelength of incident light within 600 to approximately 850 nm can be detected effectively. It is suitable to be used as photodetector for digital optical data process. The other attractive features of GaAs OMIST device include suitable conducted current, switching voltage and power levels for OEIC, high switch speed and high sensitivity to light or current injection.

  7. Carbon and group II acceptor coimplantation in GaAs

    SciTech Connect

    Morton, R.; Lau, S.S.; Poker, D.B.; Chu, P.K.; Fung, K.K.; Wang, N.

    1998-11-01

    Coimplantations of carbon and one of the group II acceptors, Mg, Zn, or Cd, were performed and compared to implantations involving only a single element (Mg, Zn, or Cd) or Ga and C coimplanted into GaAs substrates. The group II and C (II/C) coimplantations act to balance the crystal stoichiometry since group II atoms prefer to reside in the Ga sublattice and C prefers to reside in the As sublattice. The electrical characteristics of the various implantations were obtained from sheet and differential Hall measurements. Rutherford backscattering spectrometry was employed to determine the amount of implantation-induced damage which was then correlated to the amount of C activation in the group II/C coimplanted samples. It was found that coimplantation of the heavier group II acceptors, Zn and Cd, resulted in layers with larger peak hole concentrations. This is a result of the large amount of lattice damage created by these elements which is thought to provide the necessary abundance of As vacancies for C activation. Secondary ion mass spectroscopy measurements of the samples after implant activation indicate that C coimplantation significantly reduces the diffusivity of the group II acceptors. Cross-sectional transmission electron microscopy indicated a unique defect structure (extrinsic dislocation loops) for the cases of group II/C coimplantation. These dislocation loops are located at the diffusion front of the group II element in the samples and therefore have a rather profound influence on the diffusion of the group II elements. A rationalization of the defect structure and the effect it has on the diffusion of group II elements is given. {copyright} {ital 1998 American Institute of Physics.}

  8. Modulating the morphology and electrical properties of GaAs nanowires via catalyst stabilization by oxygen.

    PubMed

    Han, Ning; Yang, Zaixing; Wang, Fengyun; Yip, SenPo; Dong, Guofa; Liang, Xiaoguang; Hung, TakFu; Chen, Yunfa; Ho, Johnny C

    2015-03-11

    Nowadays, III-V compound semiconductor nanowires (NWs) have attracted extensive research interest because of their high carrier mobility favorable for next-generation electronics. However, it is still a great challenge for the large-scale synthesis of III-V NWs with well-controlled and uniform morphology as well as reliable electrical properties, especially on the low-cost noncrystalline substrates for practical utilization. In this study, high-density GaAs NWs with lengths >10 μm and uniform diameter distribution (relative standard deviation σ ∼ 20%) have been successfully prepared by annealing the Au catalyst films (4-12 nm) in air right before GaAs NW growth, which is in distinct contrast to the ones of 2-3 μm length and widely distributed of σ ∼ 20-60% of the conventional NWs grown by the H2-annealed film. This air-annealing process is found to stabilize the Au nanoparticle seeds and to minimize Ostwald ripening during NW growth. Importantly, the obtained GaAs NWs exhibit uniform p-type conductivity when fabricated into NW-arrayed thin-film field-effect transistors (FETs). Moreover, they can be integrated with an n-type InP NW FET into effective complementary metal oxide semiconductor inverters, capable of working at low voltages of 0.5-1.5 V. All of these results explicitly demonstrate the promise of these NW morphology and electrical property controls through the catalyst engineering for next-generation electronics. PMID:25700210

  9. Distribution of α and β phases in the coexistence regime in MnAs(0001) layers grown on GaAs(111)B

    NASA Astrophysics Data System (ADS)

    Takagaki, Y.; Wiebicke, E.; Däweritz, L.; Ploog, K. H.

    2004-08-01

    The discontinuous change in the lattice constant that occurs at the first-order phase transition between α- and β-MnAs gives rise to a coexistence of the two phases in MnAs layers grown on GaAs substrates. When the GaAs substrates are oriented in the (111)B direction, the c axis of MnAs is aligned normal to the growth plane. We identify the domain structure of α- and β-MnAs for this crystal orientation by utilizing the different reactivities of the two phases against wet chemical etching. Submicrometer-size islands of α-MnAs are found to be interwoven in a honeycomblike network of β-MnAs. We also show that this domain structure combined with strain effects results in a formation of MnAs lumps by etching.

  10. Real-Time In Situ Monitoring of GaAs (211) Oxide Desorption and CdTe Growth by Spectroscopic Ellipsometry

    NASA Astrophysics Data System (ADS)

    Lennon, C. M.; Almeida, L. A.; Jacobs, R. N.; Markunas, J. K.; Smith, P. J.; Arias, J.; Brown, A. E.; Pellegrino, J.

    2012-10-01

    We describe the growth of CdTe (211)B by molecular beam epitaxy on large-area epiready GaAs (211)B substrates. Prior to CdTe growth, GaAs substrates were thermally cleaned under an As4 flux. Oxide desorption was verified by in situ spectroscopic ellipsometry (SE) and reflection high-energy electron diffraction. The use of in situ SE played a significant role in the study of CdTe-on-GaAs growth and annealing processes. An effective medium approximation (EMA) was used to model the overlayer thickness variation of CdTe epilayers throughout growth and in situ annealing cycles. A correlation between SE-derived EMA thickness values and surface defect formation mitigation is discussed. All annealed samples (11.5 μm to 13 μm thick) exhibited excellent crystalline quality with average double crystal rocking curve full-width at half-maximum (FWHM) values of ~60 arcsec.

  11. Thermodynamic stability and band alignment at Sr-TiO3 /GaAs(001) interface

    NASA Astrophysics Data System (ADS)

    Cott, Joelson; Droopad, Ravi; Lee, Byounghak

    2015-03-01

    The successful epitaxial growth of SrTiO3 on Si showed that it is possible to integrate the functional oxides with semiconductors incorporating unique multifunctional properties of oxides into various existing semiconductor technologies. While SrTiO3 has been also deposited on GaAs without amorphous interfacial layers, the exact interface structure has been controversial; On one hand, scanning Transmission Electron Microscopy (STEM) shows As atoms at the interface. X-ray photoelectron spectroscopy (XPS) measurements, on the other hand, do not show peaks associated with As-O bonding, indicating that the GaAs/STO interface does not involve an As/oxide layer, contradicting to STEM observations. Using ab initio calculations, we determine the interfacial structure of a SrTiO3 film on a GaAs substrate to help clarify the apparently discrepancy between the XPS and the STEM measurements. The calculations reveal that, under the condition that allows atomically abrupt interfaces, the energetically most stable interface is As/Sr/TiO2 structure, in accordance with both XPS and STEM measurements. We discuss the band offsets and the possibility of in-gap states of various interface structures. This work was supported by the Air Force Office of Scientific Research, Contract FA9950-10-1-0133.

  12. A 1.2 THz Planar Tripler Using GaAs Membrane Based Chips

    NASA Technical Reports Server (NTRS)

    Bruston, J.; Maestrini, A.; Pukala, D.; Martin, S.; Nakamura, B.; Mehdi, I.

    2001-01-01

    Fabrication technology for submillimeter-wave monolithic circuits has made tremendous progress in recent years and it is now possible to fabricate sub-micron GaAs Schottky devices on a number of substrate types, such as membranes, frame-less membranes or substrateless circuits. These new technologies allow designers to implement very high frequency circuits, either Schottky mixers or multipliers, in a radically new manner. This paper will address the design, fabrication, and preliminary results of a 1.2 THz planar tripler fabricated on a GaAs frame-less membrane, the concept of which was described previously. The tripler uses a diode pair in an antiparallel configuration similar to designs used at lower frequency. To date, this tripler has produced a peak output power of 80 microW with 0.9% efficiency at room temperature (at 1126 GHz). The measured fix-tuned 3 dB bandwidth is about 3.5%. When cooled, the output power reached a peak of 195 microW at 120 K and 250 microW at 50 K. The ease with which this circuit was implemented along with the superb achieved performance indicates that properly designed planar devices such as this tripler can now usher in a new era of practical very high frequency multipliers.

  13. MCT by MBE on GaAs at AIM: state of the art and roadmap

    NASA Astrophysics Data System (ADS)

    Figgemeier, Heinrich; Wenisch, Jan; Eich, Detlef; Hanna, Stefan; Schirmacher, Wilhelm; Lutz, Holger; Schallenberg, Timo; Breiter, Rainer

    2015-06-01

    In multiple publications over the last years, MCT MBE on GaAs has been shown to be a very versatile and promising material system and indeed may be the prime candidate among the alternative substrates for the fabrication of high-performance detectors across the whole IR composition range. In this paper we report on successful growth of MCT on GaAs over the composition range 0.2 < x(Cd) < 0.8. A single color MWIR 640 × 512, 15 μm pitch detector fabricated from this material with an operability of 99.71% at an operating temperature of 120 K is presented. In the LWIR region, an operability of 99.48% at 65 K has been achieved with a 1280 × 1024, 15 μm pitch detector. Finally we report on preliminary results of a dual-color 640 × 512, 20 μm pitch detector with cutoff wavelengths in the 3 - 4 and 4 - 5 μm range.

  14. Tandem Solar Cells Using GaAs Nanowires on Si: Design, Fabrication, and Observation of Voltage Addition.

    PubMed

    Yao, Maoqing; Cong, Sen; Arab, Shermin; Huang, Ningfeng; Povinelli, Michelle L; Cronin, Stephen B; Dapkus, P Daniel; Zhou, Chongwu

    2015-11-11

    Multijunction solar cells provide us a viable approach to achieve efficiencies higher than the Shockley-Queisser limit. Due to their unique optical, electrical, and crystallographic features, semiconductor nanowires are good candidates to achieve monolithic integration of solar cell materials that are not lattice-matched. Here, we report the first realization of nanowire-on-Si tandem cells with the observation of voltage addition of the GaAs nanowire top cell and the Si bottom cell with an open circuit voltage of 0.956 V and an efficiency of 11.4%. Our simulation showed that the current-matching condition plays an important role in the overall efficiency. Furthermore, we characterized GaAs nanowire arrays grown on lattice-mismatched Si substrates and estimated the carrier density using photoluminescence. A low-resistance connecting junction was obtained using n(+)-GaAs/p(+)-Si heterojunction. Finally, we demonstrated tandem solar cells based on top GaAs nanowire array solar cells grown on bottom planar Si solar cells. The reported nanowire-on-Si tandem cell opens up great opportunities for high-efficiency, low-cost multijunction solar cells. PMID:26502060

  15. Growth and Photovoltaic Properties of High-Quality GaAs Nanowires Prepared by the Two-Source CVD Method

    NASA Astrophysics Data System (ADS)

    Wang, Ying; Yang, Zaixing; Wu, Xiaofeng; Han, Ning; Liu, Hanyu; Wang, Shuobo; Li, Jun; Tse, WaiMan; Yip, SenPo; Chen, Yunfa; Ho, Johnny C.

    2016-04-01

    Growing high-quality and low-cost GaAs nanowires (NWs) as well as fabricating high-performance NW solar cells by facile means is an important development towards the cost-effective next-generation photovoltaics. In this work, highly crystalline, dense, and long GaAs NWs are successfully synthesized using a two-source method on non-crystalline SiO2 substrates by a simple solid-source chemical vapor deposition method. The high V/III ratio and precursor concentration enabled by this two-source configuration can significantly benefit the NW growth and suppress the crystal defect formation as compared with the conventional one-source system. Since less NW crystal defects would contribute fewer electrons being trapped by the surface oxides, the p-type conductivity is then greatly enhanced as revealed by the electrical characterization of fabricated NW devices. Furthermore, the individual single NW and high-density NW parallel arrays achieved by contact printing can be effectively fabricated into Schottky barrier solar cells simply by employing asymmetric Ni-Al contacts, along with an open circuit voltage of ~0.3 V. All these results indicate the technological promise of these high-quality two-source grown GaAs NWs, especially for the realization of facile Schottky solar cells utilizing the asymmetric Ni-Al contact.

  16. Growth and Photovoltaic Properties of High-Quality GaAs Nanowires Prepared by the Two-Source CVD Method.

    PubMed

    Wang, Ying; Yang, Zaixing; Wu, Xiaofeng; Han, Ning; Liu, Hanyu; Wang, Shuobo; Li, Jun; Tse, WaiMan; Yip, SenPo; Chen, Yunfa; Ho, Johnny C

    2016-12-01

    Growing high-quality and low-cost GaAs nanowires (NWs) as well as fabricating high-performance NW solar cells by facile means is an important development towards the cost-effective next-generation photovoltaics. In this work, highly crystalline, dense, and long GaAs NWs are successfully synthesized using a two-source method on non-crystalline SiO2 substrates by a simple solid-source chemical vapor deposition method. The high V/III ratio and precursor concentration enabled by this two-source configuration can significantly benefit the NW growth and suppress the crystal defect formation as compared with the conventional one-source system. Since less NW crystal defects would contribute fewer electrons being trapped by the surface oxides, the p-type conductivity is then greatly enhanced as revealed by the electrical characterization of fabricated NW devices. Furthermore, the individual single NW and high-density NW parallel arrays achieved by contact printing can be effectively fabricated into Schottky barrier solar cells simply by employing asymmetric Ni-Al contacts, along with an open circuit voltage of ~0.3 V. All these results indicate the technological promise of these high-quality two-source grown GaAs NWs, especially for the realization of facile Schottky solar cells utilizing the asymmetric Ni-Al contact. PMID:27071678

  17. GaAs/Ge crystals grown on Si substrates patterned down to the micron scale

    NASA Astrophysics Data System (ADS)

    Taboada, A. G.; MeduÅa, M.; Salvalaglio, M.; Isa, F.; Kreiliger, T.; Falub, C. V.; Barthazy Meier, E.; Müller, E.; Miglio, L.; Isella, G.; von Känel, H.

    2016-02-01

    Monolithic integration of III-V compounds into high density Si integrated circuits is a key technological challenge for the next generation of optoelectronic devices. In this work, we report on the metal organic vapor phase epitaxy growth of strain-free GaAs crystals on Si substrates patterned down to the micron scale. The differences in thermal expansion coefficient and lattice parameter are adapted by a 2-μm-thick intermediate Ge layer grown by low-energy plasma enhanced chemical vapor deposition. The GaAs crystals evolve during growth towards a pyramidal shape, with lateral facets composed of {111} planes and an apex formed by {137} and (001) surfaces. The influence of the anisotropic GaAs growth kinetics on the final morphology is highlighted by means of scanning and transmission electron microscopy measurements. The effect of the Si pattern geometry, substrate orientation, and crystal aspect ratio on the GaAs structural properties was investigated by means of high resolution X-ray diffraction. The thermal strain relaxation process of GaAs crystals with different aspect ratio is discussed within the framework of linear elasticity theory by Finite Element Method simulations based on realistic geometries extracted from cross-sectional scanning electron microscopy images.

  18. Recovery Act : Near-Single-Crystalline Photovoltaic Thin Films on Polycrystalline, Flexible Substrates

    SciTech Connect

    Venkat Selvamanickam; Alex Freundlich

    2010-11-29

    III-V photovoltaics have exhibited efficiencies above 40%, but have found only a limited use because of the high cost of single crystal substrates. At the other end of the spectrum, polycrystalline and amorphous thin film solar cells offer the advantage of low-cost fabrication, but have not yielded high efficiencies. Our program is based on single-crystalline-like thin film photovoltaics on polycrystalline substrates using biaxially-textured templates made by Ion Beam-Assisted Deposition (IBAD). MgO templates made by IBAD on flexible metal substrate have been successfully used for epitaxial growth of germanium films. In spite of a 4.5% lattice mismatch, heteroepitaxial growth of Ge was achieved on CeO2 that was grown on IBAD MgO template. Room temperature optical bandgap of the Ge films was identified at 0.67 eV indicating minimal residual strain. Refraction index and extinction coefficient values of the Ge films were found to match well with that measured from a reference Ge single crystal. GaAs has been successfully grown epitaxially on Ge on metal substrate by molecular beam epitaxy. RHEED patterns indicate self annihilation of antiphase boundaries and the growth of a single domain GaAs. The GaAs is found to exhibit strong photoluminescence signal and, an existence of a relatively narrow (FWHM~20 meV) band-edge excitons measured in this film indicates a good optoelectronic quality of deposited GaAs. While excellent epitaxial growth has been achieved in GaAs on flexible metal substrates, the defect density of the films as measured by High Resolution X-ray Diffraction and etch pit experiments showed a high value of 5 * 10^8 per cm^2. Cross sectional transmission electron microscopy of the multilayer architecture showed concentration of threading dislocations near the germanium-ceria interface. The defect density was found decrease as the Ge films were made thicker. The defects appear to originate from the MgO layer presumably because of large lattice mismatches

  19. GaAs nanowires and GaAs/AlGaAs core/shell nanowires synthesized by MOCVD

    NASA Astrophysics Data System (ADS)

    Peters, Brian; Minutillo, Nicholas; Carlin, John; Yang, Fengyuan

    2011-03-01

    Nanowires made by the ``bottom-up'' approach can be used in a variety of electrical and optoelectronic devices as well as in the study of low dimensional transport physics. We have grown GaAs nanowires using Au catalysts in a closed couple showerhead MOCVD system. A number of growth parameters, including the substrate temperature, growth rate, and Arsine/TMGa ratio, are explored to identify optimal conditions for growth of GaAs nanowires with large aspect ratio and minimal tapering. Higher substrate temperatures result in larger tapering and lower temperature leads to ``kinks.'' Meanwhile, large V/III source ratio gives large tapering as well. We have found that our optimal conditions are at a substrate temperature of 420°C and V/III ratio of ~ 25 , which gives a tapering of less than 1 nm increase in diameter per micron in length. In addition, GaAs/AlGaAs core/shell structured nanowires were also grown to minimize the surface states. Characterizations by SEM and photoluminescence will be presented. This work is supported by Department of Energy (DE-SC0001304).

  20. Polycrystal GaAs infrared windows

    NASA Astrophysics Data System (ADS)

    Wada, Hideo; Shibata, Ken-ichiro; Yamashita, Masashi; Nakayama, Shigeru; Fujii, Akihito

    2001-09-01

    There are difficult points such as lowering of the detection or recognition capability of some targets by aerodynamic heating with speedup of the aircraft and missile and restriction of the operation by the raindrop in rainfall time on the conventional ZnS infrared window application used for missile seeker and FLIR equipment. Therefore, in this study, the promising polycrystal GaAs which has low infrared radiations in high temperature was produced using HB method (Horizontal Boat method) and VG method (Vertical Boat method) as a new infrared window material expected the durability for rain erosion. As the result, 70mm2 windows by the HB method and 100mm diameter windows by VB method were realized. Moreover, their optical characteristics, mechanical properties and thermal shock durabilities were measured and they were confirmed to be about 56% in average transmittance in the wavelength of 10micrometers bands, 530~630kg/mm2 in their hardness and thermostable at 300 degree(s)C.

  1. Spectroscopy of GaAs quantum wells

    SciTech Connect

    West, L.C.

    1985-07-01

    A new type of optical dipole transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction band electron wavefunction, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption in three different samples with quantum well thicknesses 65, 82, and 92 A and resonant energies of 152, 121, and 108 MeV, respectively. The oscillator strength is found to have values of over 12, in good agreement with prediction. The linewidths are seen as narrow as 10 MeV at room temperature and 7 MeV at low temperature, thus proving a narrow line resonance can indeed occur between transitions of free electrons. Techniques for the proper growth of these quantum well samples to enable observation of the QWEST have also been found using (AlGa)As compounds. This QWEST is considered to be an ideal material for an all optical digital computer. The QWEST can be made frequency matched to the inexpensive Carbon Dioxide laser with an infrared wavelength of 10 microns. The nonlinearity and fast relaxation time of the QWEST indicate a logic element with a subpicosecond switch time can be built in the near future, with a power level which will eventually be limited only by the noise from a lack of quanta to above approximately 10 microwatts. 64 refs., 35 figs., 6 tabs.

  2. Magnetic properties of MnAs thin films grown on GaAs (0 0 1) by MOVPE

    NASA Astrophysics Data System (ADS)

    Sterbinsky, G. E.; May, S. J.; Chiu, P. T.; Wessels, B. W.

    2007-01-01

    The thickness dependence of the in-plane uniaxial anisotropy and coercive field of epitaxial MnAs thin films on GaAs (0 0 1) substrates has been determined from the magneto-optic Kerr effect. The metalorganic vapor phase epitaxy grown films are single α phase at room temperature with a B-type variant orientation. The coercive field of these films increases to a maximum for a film 35 nm thick and then decreases in thicker films. An increase in magnetic anisotropy field with increasing thickness is observed and is attributed to an increasing volume contribution to the anisotropy constant.

  3. OMVPE Growth and Characterization of GaInP on GaAs Using Tertiary Butylphosphine for the Phosphorous Source

    NASA Astrophysics Data System (ADS)

    Takeda, Yoshikazu; Araki, Soichiro; Takemi, Masayoshi; Noda, Susumu; Sasaki, Akio

    1990-07-01

    GaInP layers were grown on GaAs substrates by organometallic vapor-phase epitaxy (OMVPE) at atmospheric pressure using trimethylgallium (TMGa), trimethylindium (TMIn) and much less toxic tertiary butylphosphine (TBP) as source gases. Fairly smooth surfaces were obtained at the growth temperature of 65O°C and at the V/III ratio of 78. The electrical and optical characteristics are comparable to those obtained by OMVPE using phosphine as the phosphorous source and far better than the previous results obtained by OMVPE with TBP. The undoped epitaxial layers showed n-type conductivity with electron concentrations of 2--3× 1017 cm-3.

  4. Confinement in thickness-controlled GaAs polytype nanodots.

    PubMed

    Vainorius, Neimantas; Lehmann, Sebastian; Jacobsson, Daniel; Samuelson, Lars; Dick, Kimberly A; Pistol, Mats-Erik

    2015-04-01

    Polytype nanodots are arguably the simplest nanodots than can be made, but their technological control was, up to now, challenging. We have developed a technique to produce nanowires containing exactly one polytype nanodot in GaAs with thickness control. These nanodots have been investigated by photoluminescence, which has been cross-correlated with transmission electron microscopy. We find that short (4-20 nm) zincblende GaAs segments/dots in wurtzite GaAs confine electrons and that the inverse system confines holes. By varying the thickness of the nanodots we find strong quantum confinement effects which allows us to extract the effective mass of the carriers. The holes at the top of the valence band have an effective mass of approximately 0.45 m0 in wurtzite GaAs. The thinnest wurtzite nanodot corresponds to a twin plane in zincblende GaAs and gives efficient photoluminescence. It binds an exciton with a binding energy of roughly 50 meV, including central cell corrections. PMID:25761051

  5. MOCVD Growth of High-Quality and Density-Tunable GaAs Nanowires on ITO Catalyzed by Au Nanoparticles Deposited by Centrifugation.

    PubMed

    Wu, Dan; Tang, Xiaohong; Yoon, Ho Sup; Wang, Kai; Olivier, Aurelien; Li, Xianqiang

    2015-12-01

    High-quality and density-tunable GaAs nanowires (NWs) are directly grown on indium tin oxide (ITO) using Au nanoparticles (NPs) as catalysts by metal organic chemical vapor deposition (MOCVD). Au catalysts were deposited on ITO glass substrate using a centrifugal method. Compared with the droplet-only method, high-area density Au NPs were uniformly distributed on ITO. Tunable area density was realized through variation of the centrifugation time, and the highest area densities were obtained as high as 490 and 120 NP/μm(2) for 10- and 20-nm diameters of Au NPs, respectively. Based on the vapor-liquid-solid growth mechanism, the growth rates of GaAs NWs at 430 °C were 18.2 and 21.5 nm/s for the highest area density obtained of 10- and 20-nm Au NP-catalyzed NWs. The growth rate of the GaAs NWs was reduced with the increase of the NW density due to the competition of precursor materials. High crystal quality of the NWs was also obtained with no observable planar defects. 10-nm Au NP-induced NWs exhibit wurtzite structure whereas zinc-blende is observed for 20-nm NW samples. Controllable density and high crystal quality of the GaAs NWs on ITO demonstrate their potential application in hybrid a solar cell. PMID:26487507

  6. Impact of Gd2O3 passivation layer on interfacial and electrical properties of atomic-layer-deposited ZrO2 gate dielectric on GaAs

    NASA Astrophysics Data System (ADS)

    Gong, Youpin; Zhai, Haifa; Liu, Xiaojie; Kong, Jizhou; Wu, Di; Li, Aidong

    2014-02-01

    ZrO2 gate dielectric films were fabricated on n-GaAs substrates by atomic layer deposition (ALD), using metal organic chemical vapor deposition (MOCVD)-derived ultrathin Gd2O3 film as interfacial control layer between ZrO2 and n-GaAs. The interfacial structure, capacitance-voltage and current-voltage properties of ZrO2/n-GaAs and ZrO2/Gd2O3/n-GaAs metal-oxide-semiconductor (MOS) capacitors have been investigated. The introduction of an ultrathin Gd2O3 control layer can effectively suppress the formation of As oxides and high valence Ga oxide at the high k/GaAs interface which evidently improved the electrical properties of GaAs-based MOS capacitors, such as higher accumulation capacitance and lower leakage current density. It was found that the current conduction mechanism of MOS capacitors varied from Poole-Frenkel emission to Schottky-Richardson emission after introducing the thin Gd2O3 layer. The band alignments of interfaces for ZrO2/GaAs and ZrO2/Gd2O3/GaAs were established, which indicates that the conduction band offset (CBO) for ZrO2/GaAs and ZrO2/Gd2O3/GaAs stacks are ˜1.45 and ˜1.62 eV, correspondingly.

  7. High-k gate dielectric GaAs MOS device with LaON as interlayer and NH3-plasma surface pretreatment

    NASA Astrophysics Data System (ADS)

    Liu, Chao-Wen; Xu, Jing-Ping; Liu, Lu; Lu, Han-Han

    2015-12-01

    High-k gate dielectric HfTiON GaAs metal-oxide-semiconductor (MOS) capacitors with LaON as interfacial passivation layer (IPL) and NH3- or N2-plasma surface pretreatment are fabricated, and their interfacial and electrical properties are investigated and compared with their counterparts that have neither LaON IPL nor surface treatment. It is found that good interface quality and excellent electrical properties can be achieved for a NH3-plasma pretreated GaAs MOS device with a stacked gate dielectric of HfTiON/LaON. These improvements should be ascribed to the fact that the NH3-plasma can provide H atoms and NH radicals that can effectively remove defective Ga/As oxides. In addition, LaON IPL can further block oxygen atoms from being in-diffused, and Ga and As atoms from being out-diffused from the substrate to the high-k dielectric. This greatly suppresses the formation of Ga/As native oxides and gives rise to an excellent high-k/GaAs interface. Project supported by the National Natural Science Foundation of China (Grant Nos. 61176100 and 61274112).

  8. Towards low-cost high-efficiency GaAs photovoltaics and photoelectrodes grown via vapor transport from a solid source

    SciTech Connect

    Boucher, Jason; Ritenour, Andrew; Boettcher, Shannon W.

    2013-04-29

    Towards low-cost high-efficiency GaAs photovoltaics and photoelectrodes grown via vapor transport from a solid source GaAs is an attractive material for thin-film photovoltaic applications, but is not widely used for terrestrial power generation due to the high cost of metal-organic chemical vapor deposition (MOCVD) techniques typically used for growth. Close space vapor transport is an alternative that allows for rapid growth rates of III-V materials, and does not rely on the toxic and pyrophoric precursors used in MOCVD. We characterize CSVT films of GaAs using photoelectrochemical current-voltage and quantum efficiency measurements. Hole diffusion lengths which exceed 1.5 um are extracted from internal quantum efficiency measurements using the Gartner model. Device physics simulations suggest that solar cells based on these films could reach efficiencies exceeding 24 %. To reach this goal, a more complete understanding of the electrical properties and characterization of defects will be necessary, including measurements on complete solid-state devices. Doping of films is achieved by using source material containing the desired impurity (e.g., Te or Zn). We discuss strategies for growing III-V materials on inexpensive substrates that are not lattice-matched to GaAs.

  9. Preparation of GaAs and Ga1-xAlxAs Multi-Layer Structures by Metalorganic Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Tokumitsu, Eisuke; Katoh, Toshiaki; Kimura, Ryuhei; Konagai, Makoto; Takahashi, Kiyoshi

    1986-08-01

    Metalorganic molecular beam epitaxial (MOMBE) growth of GaAs and (GaAl)As using triethylgallium (TEG) and triethylaluminum (TEA) has been studied. N-GaAs/p-GaAs multi-layer structures were prepared by applying an alternating ionization voltage to hydrogen. Single-crystal Ga1-xAlxAs ternary alloy with good surface mophology was successfully grown by introducing TEA as an Al source. The epitaxial layers typically showed p-type conduction with a carrier concentration of more than 1018 cm-3, this being due to residual carbon. A (GaAl)As/GaAs multiquantum well (MQW) heterostructure was fabricated by switching TEA and it was observed that the photoluminescence peak energies from the MQW structures were shifted to the higher energy position. Furthermore, selective growth of GaAs and (GaAl)As on a partly SiO2 masked GaAs substrate was investigated. In the MOMBE growth of (GaAl)As, polycrystalline film was deposited on the SiO2 masked region, while no deposition took place in the growth of GaAs.

  10. Defect energy levels in p-type GaAsBi and GaAs grown by MBE at low temperatures

    NASA Astrophysics Data System (ADS)

    Mooney, P. M.; Tarun, M. C.; Bahrami-Yekta, V.; Tiedje, T.; Lewis, R. B.; Masnadi-Shirazi, M.

    2016-06-01

    Deep level defects in p-type GaAs1‑x Bi x (x < 1%) and GaAs grown by molecular beam epitaxy at substrate temperatures of 330 °C and 370 °C have been characterized by deep level transient spectroscopy. We find that incorporating Bi into GaAs at 330 °C does not affect the total concentration of hole traps, which is ∼4 × 1016 cm‑3, comparable to the concentration of electron traps observed in Si-doped GaAsBi having a similar alloy composition. Increasing the growth temperature of the p-type GaAsBi (x = 0.8%) layer from 330 °C to 370 °C reduces the hole trap concentration by an order of magnitude. Moreover, the defects having near mid-gap energy levels that are the most efficient non-radiative recombination centers are present only in GaAsBi layers grown at the lower temperature. These new results are discussed in the context of previous measurements of n-type GaAs and GaAsBi layers grown under similar conditions.

  11. Narrow-line self-assembled GaAs quantum dots for plasmonics

    NASA Astrophysics Data System (ADS)

    Zhang, Hongyi; Huo, Yongheng; Lindfors, Klas; Chen, Yonghai; Schmidt, Oliver G.; Rastelli, Armando; Lippitz, Markus

    2015-03-01

    We demonstrate efficient coupling of excitons in near-surface GaAs quantum dots (QDs) to surface-plasmon polaritons. We observe distinct changes in the photoluminescence of the emitters as the distance between the QDs and the gold interface decreases. Based on an electric point-dipole model, we identify the surface plasmon launching rates for different QD-surface distances. While in conventional far-field experiments only a few percent of the emitted photons can be collected due to the high refractive index semiconductor substrate, already for distances around 30 nm the plasmon launching-rate becomes comparable to the emission rate into bulk photon modes, thus much larger than the photon collection rate. For even smaller distances, the degrading optical properties of the emitter counterweight the increasing coupling efficiency to plasmonic modes.

  12. Nanoindentation response of a single micrometer-sized GaAs wall

    NASA Astrophysics Data System (ADS)

    Le Bourhis, E.; Patriarche, G.

    2005-04-01

    Wall-patterned GaAs surfaces have been elaborated by photolithography and dry etching. The mechanical response of individual μm-sized walls was tested at different positions on the wall by nanoindentation. Overall results show that contact stiffness remains constant across the wall while total penetration drastically increases at the proximity of the free sides of the wall. Transmission electron microscopy was used to get further insight into the plastic deformation of the walls and reveals that the central-plastic zone governs the mechanical response instead of the rosette arms. The application of substrate patterning with enhanced plastic compliance is suggested in order to eliminate residual dislocations appearing in mismatched structures grown for optoelectronic devices.

  13. Narrow-line self-assembled GaAs quantum dots for plasmonics

    SciTech Connect

    Zhang, Hongyi; Huo, Yongheng; Schmidt, Oliver G.; Lindfors, Klas; Chen, Yonghai; Rastelli, Armando; Lippitz, Markus

    2015-03-09

    We demonstrate efficient coupling of excitons in near-surface GaAs quantum dots (QDs) to surface-plasmon polaritons. We observe distinct changes in the photoluminescence of the emitters as the distance between the QDs and the gold interface decreases. Based on an electric point-dipole model, we identify the surface plasmon launching rates for different QD-surface distances. While in conventional far-field experiments only a few percent of the emitted photons can be collected due to the high refractive index semiconductor substrate, already for distances around 30 nm the plasmon launching-rate becomes comparable to the emission rate into bulk photon modes, thus much larger than the photon collection rate. For even smaller distances, the degrading optical properties of the emitter counterweight the increasing coupling efficiency to plasmonic modes.

  14. The GaAs solar cells with V-grooved emitters

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Fatemi, N.; Wilt, D. M.; Landis, Geoffrey A.; Thomas, R. D.

    1989-01-01

    Geometrically structured surfaces have become increasingly important to solar cell efficiency improvements and radiation tolerance. Gallium arsenide solar cells with a V-grooved front surface which demonstrate improved optical coupling and higher short-circuit current compared to planar cells were fabricated. GaAs homojunction cells were fabricated by organometallic chemical vapor deposition (OMCVD) on an n+ substrate. The V-grooves were formed on the surface with an anisotropic etch, and an n-type buffer and p-type emitter were grown by OMCVD, followed by ohmic contacts. Reflectivity measurements show significantly lower reflectance for the microgrooved cell compared to the planar structure. The short circuit current of the V-grooved solar cell is consistently higher than that of the planar controls.

  15. In-situ x-ray characterization of wurtzite formation in GaAs nanowires

    SciTech Connect

    Krogstrup, Peter; Hannibal Madsen, Morten; Nygaard, Jesper; Feidenhans'l, Robert; Hu Wen; Kozu, Miwa; Nakata, Yuka; Takahasi, Masamitu

    2012-02-27

    In-situ monitoring of the crystal structure formation during Ga-assisted GaAs nanowire growth on Si(111) substrates has been performed in a combined molecular beam epitaxy growth and x-ray characterization experiment. Under Ga rich conditions, we show that an increase in the V/III ratio increases the formation rate of the wurtzite structure. Moreover, the response time for changes in the structural phase formation to changes in the beam fluxes is observed to be much longer than predicted time scales of adatom kinetics and liquid diffusion. This suggests that the morphology of the growth interface plays the key role for the relative growth structure formation rates.

  16. A Cryogenic GaAs PHEMT/ Ferroelectric Ku-Band Tunable Oscillator

    NASA Technical Reports Server (NTRS)

    Romanofsky, Robert R.; Miranda, Felix A.; VanKeuls, Fred W.

    1998-01-01

    A Ku-band tunable oscillator operated at and below 77 K is described. The oscillator is based on two separate technologies: a 0.25 mm GaAs pseudomorphic high electron mobility transistor (PHEMT) circuit optimized for cryogenic operation, and a gold microstrip ring resonator patterned on a thin ferroelectric (SrTiO3) film which was laser ablated onto a LaAlO3 substrate. A tuning range of up to 3% of the center frequency was achieved by applying dc bias between the ring resonator and ground plane. To the best of our knowledge, this is the first tunable oscillator based on a thin film ferroelectric structure demonstrated in the microwave frequency range. The design methodology of the oscillator and the performance characteristics of the tunable resonator are described.

  17. Surface structure transitions on (0 0 1) GaAs during MBE

    NASA Astrophysics Data System (ADS)

    Preobrazhenskii, V. V.; Putyato, M. A.; Pchelyakov, O. P.; Semyagin, B. R.

    1999-05-01

    Experimental phase diagrams of GaAs (0 0 1) surface were obtained by direct measuring of the As 4 flux and the substrate temperature. The infringement of the epitaxial growth was found to occur at the ratio of As 4 to Ga fluxes less than or equal to 0.25. Hence, the As 4 incorporation coefficient is close to unity during MBE. A diffusion model was suggested to describe positions of boundaries between surface structures (SS) in the phase diagrams. Dependencies of temperatures of SS transitions on the rate of surface heating in the absence of incident fluxes were obtained. The transition temperatures were discovered to tend to constant values as the heating rate increased. A model underlying this dependence was developed.

  18. Plasma deposited hydrogenated carbon on GaAs and InP

    NASA Technical Reports Server (NTRS)

    Warner, J. D.; Pouch, J. J.; Alterovitz, S. A.; Liu, D. C.; Lanford, W. A.

    1985-01-01

    The properties of diamond like carbon films grown by RF flow discharge 30 kHz plasma using methane are reported. The Cis XPS line shape of films showed localized hybrid carbon bonds as low as 40 to as high as 95 percent. Infrared spectroscopy and N(15) nuclear reaction profiling data indicated 35 to 42 percent hydrogen, depending inversely on deposition temperature. The deposition rate of films on Si falls off exponentially with substrate temperature, and nucleation does not occur above 200 C on GaAs and InP. Optical data of the films showed bandgap values of 2.0 to 2.4 eV increasing monotonically with CH4 flow rate.

  19. Plasma deposited diamondlike carbon on GaAs and InP

    NASA Technical Reports Server (NTRS)

    Warner, J. D.; Pouch, J. J.; Alterovitz, S. A.; Liu, D. C.; Lanford, W. A.

    1984-01-01

    The properties of diamond like carbon films grown by RF flow discharge 30 kHz plasma using methane are reported. The Cls XPS line shape of films showed localized hybrid carbon bonds as low as 40 to as high as 95 percent. Infrared spectroscopy and N(15) nuclear reaction profiling data indicated 35 to 42 percent hydrogen, depending inversely on deposition temperature. The deposition rate of films on Si falls off exponentially with substrate temperature, and nucleation does not occur above 200 C on GaAs and InP. Optical data of the films showed bandgap values of 2.0 to 2.4 eV increasing monotonically with CH4 flow rate.

  20. Charge tuning in [111] grown GaAs droplet quantum dots

    SciTech Connect

    Bouet, L.; Vidal, M.; Marie, X.; Amand, T.; Wang, G.; Urbaszek, B.; Mano, T.; Ha, N.; Kuroda, T.; Sakoda, K.; Durnev, M. V.; Glazov, M. M.; Ivchenko, E. L.

    2014-08-25

    We demonstrate charge tuning in strain free GaAs/AlGaAs quantum dots (QDs) grown by droplet epitaxy on a GaAs(111)A substrate. Application of a bias voltage allows the controlled charging of the QDs from −3|e| to +2|e|. The resulting changes in QD emission energy and exciton fine-structure are recorded in micro-photoluminescence experiments at T = 4 K. We uncover the existence of excited valence and conduction states, in addition to the s-shell-like ground state. We record a second series of emission lines about 25 meV above the charged exciton emission coming from excited charged excitons. For these excited interband transitions, a negative diamagnetic shift of large amplitude is uncovered in longitudinal magnetic fields.

  1. Mechanics of precisely controlled thin film buckling on Elastomeric substrate.

    SciTech Connect

    Sun, Y.; Jiang, H.; Rogers, J.; Huang, Y.; Arizone State Univ.; Beckman Inst.; University of Illinois Urbana-Champaign

    2007-01-01

    Stretchable electronics has many important and emerging applications. Sun et al. [Nature Nanotech. 1, 201 (2006)] recently demonstrated stretchable electronics based on precisely controlled buckle geometries in GaAs and Si nanoribbons on elastomeric substrates. A nonlinear buckling model is presented in this letter to study the mechanics of this type of thin film/substrate system. An analytical solution is obtained for the buckling geometry (wavelength and amplitude) and the maximum strain in buckled thin film. This solution agrees very well with the experiments, and shows explicitly how buckling can significantly reduce the thin film strain to achieve the system stretchability.

  2. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 8 2010-10-01 2010-10-01 false Operation under current GAA/MSTS Southeast Asia Program... AUTHORITY VOYAGE DATA Sec. 7 Operation under current GAA/MSTS Southeast Asia Program. In order to adapt the provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast...

  3. Humidity effects on tribochemical removal of GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Yu, Bingjun; Gao, Jian; Jin, Chenning; Xiao, Chen; Wu, Jiang; Liu, Huiyun; Jiang, Shulan; Chen, Lei; Qian, Linmao

    2016-06-01

    Defect-free tribochemical removal of gallium arsenide (GaAs) was demonstrated in vacuum, dry air, and various humidity environments by scratching with a SiO2 tip. The removal depth increases with increasing relative humidity (1–90%), and reaches its maximum value in water. A perfect crystal matrix without defects was observed in the cross section of the scratched groove using a transmission electron microscope. A model based on reactive tip scratching-induced oxidation, water solubility of debris, and adhesion effect was proposed to interpret tribochemical removal of GaAs surface. This study provides new insights into defect-free and site-controlled nanofabrication of GaAs.

  4. Recent developments in GaAs solar cells

    SciTech Connect

    Kamath, G.S.

    1983-08-01

    The higher efficiency, radiation hardness and greater survivability at higher temperatures give GaAs cells a distinct advantage in space applications over silicon cells. Recent progress in fabrication technology has demonstrated the feasibility of high yield mass production of GaAs cells at a cost low enough to warrant their use in satellite power systems. Small panels have been assembled for several preliminary flight tests with encouraging results. Additional developments in concentrator cells as well as in all (AlGa)As cells for future systems such as cascade cells are reviewed. The (AlGa)As cells, in combination with silicon or GaAs cells, could lead to a multijunction cell with an efficiency 50% higher than any single junction cell.

  5. Unpinned GaAs MOS capacitors and transistors

    NASA Astrophysics Data System (ADS)

    Tiwari, Sandip; Wright, Steven L.; Batey, John

    1988-09-01

    Metal-oxide-semiconductor (MOS) capacitors and field-effect transistors (MOSFETs) in the GaAs semiconductor system using an unpinned interface are described. The structures utilize plasma-enhanced chemical-vapor deposition (PECVD) for the silicon-dioxide insulator on GaAs that has been terminated with a few monolayers of silicon during growth by molecular beam epitaxy. Interface densities in the structures have been reduced to about 10 to the 12th/sq cm-eV. High-frequency characteristics indicate strong inversion of both p-type and n-type GaAs. The excellent insulating quality of the oxide has allowed demonstration of quasi-static characteristics. MOSFETs operating in depletion mode with a transconductance of 60 mS/mm at 8.0-micron gate lengths have been fabricated.

  6. Atomic hydrogen cleaning of GaAS Photocathodes

    SciTech Connect

    M. Poelker; J. Price; C. Sinclair

    1997-01-01

    It is well known that surface contaminants on semiconductors can be removed when samples are exposed to atomic hydrogen. Atomic H reacts with oxides and carbides on the surface, forming compounds that are liberated and subsequently pumped away. Experiments at Jefferson lab with bulk GaAs in a low-voltage ultra-high vacuum H cleaning chamber have resulted in the production of photocathodes with high photoelectron yield (i.e., quantum efficiency) and long lifetime. A small, portable H cleaning apparatus also has been constructed to successfully clean GaAs samples that are later removed from the vacuum apparatus, transported through air and installed in a high-voltage laser-driven spin-polarized electron source. These results indicate that this method is a versatile and robust alternative to conventional wet chemical etching procedures usually employed to clean bulk GaAs.

  7. Characterization of production GaAs solar cells for space

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.

    1988-01-01

    The electrical performance of GaAs solar cells was characterized as a function of irradiation with protons and electrons with the underlying goal of producing solar cells suitable for use in space. Proton energies used varied between 50 keV and 10 MeV, and damage coefficients were derived for liquid phase epitaxy GaAs solar cells. Electron energies varied between 0.7 and 2.4 MeV. Cells from recent production runs were characterized as a function of electron and proton irradiation. These same cells were also characterized as a function of solar intensity and operating temperature, both before and after the electron irradiations. The long term stability of GaAs cells during photon exposure was examined. Some cells were found to degrade with photon exposure and some did not. Calibration standards were made for GaAs/Ge solar cells by flight on a high altitude balloon.

  8. Nonstoichiometric Low-Temperature Grown GaAs Nanowires.

    PubMed

    Díaz Álvarez, Adrian; Xu, Tao; Tütüncüoglu, Gözde; Demonchaux, Thomas; Nys, Jean-Philippe; Berthe, Maxime; Matteini, Federico; Potts, Heidi A; Troadec, David; Patriarche, Gilles; Lampin, Jean-François; Coinon, Christophe; Fontcuberta i Morral, Anna; Dunin-Borkowski, Rafal E; Ebert, Philipp; Grandidier, Bruno

    2015-10-14

    The structural and electronic properties of nonstoichiometric low-temperature grown GaAs nanowire shells have been investigated with scanning tunneling microscopy and spectroscopy, pump-probe reflectivity, and cathodoluminescence measurements. The growth of nonstoichiometric GaAs shells is achieved through the formation of As antisite defects, and to a lower extent, after annealing, As precipitates. Because of the high density of atomic steps on the nanowire sidewalls, the Fermi level is pinned midgap, causing the ionization of the subsurface antisites and the formation of depleted regions around the As precipitates. Controlling their incorporation offers a way to obtain unique electronic and optical properties that depart from the ones found in conventional GaAs nanowires. PMID:26339987

  9. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1985-01-01

    The present program has been aimed at solving the fundamental and technological problems associated with Crystal Growth of Device Quality in Space. The initial stage of the program was devoted strictly to ground-based research. The unsolved problems associated with the growth of bulk GaAs in the presence of gravitational forces were explored. Reliable chemical, structural and electronic characterization methods were developed which would permit the direct relation of the salient materials parameters (particularly those affected by zero gravity conditions) to the electronic characteristics of single crystal GaAs, in turn to device performance. These relationships are essential for the development of optimum approaches and techniques. It was concluded that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail.

  10. Characterization of production GaAs solar cells for space

    SciTech Connect

    Anspaugh, B.E.

    1988-12-01

    The electrical performance of GaAs solar cells was characterized as a function of irradiation with protons and electrons with the underlying goal of producing solar cells suitable for use in space. Proton energies used varied between 50 keV and 10 MeV, and damage coefficients were derived for liquid phase epitaxy GaAs solar cells. Electron energies varied between 0.7 and 2.4 MeV. Cells from recent production runs were characterized as a function of electron and proton irradiation. These same cells were also characterized as a function of solar intensity and operating temperature, both before and after the electron irradiations. The long term stability of GaAs cells during photon exposure was examined. Some cells were found to degrade with photon exposure and some did not. Calibration standards were made for GaAs/Ge solar cells by flight on a high altitude balloon.

  11. Interface demarcation in GaAs by current pulsing

    NASA Technical Reports Server (NTRS)

    Matthiesen, D. H.; Kafalas, J. A.; Duchene, G. A.; Bellows, A. H.

    1990-01-01

    GTE Laboratories is currently conducting a program to investigate the effect of convection in the melt on the properties of bulk grown gallium arsenide (GaAs). In addition to extensive ground based experimentation, a Get Away Special growth system has been developed to grow two GaAs crystals aboard the Space Shuttle, each with a one inch diameter. In order to perform a complete segregation analysis of the crystals grown in space, it is necessary to measure the interface shape and growth rate as well as the spatial distribution of the selenium dopant. The techniques for interface demarcation in selenium doped GaAs by current pulsing have been developed at GTE Laboratories and successful interface demarcation has been achieved for current pulses ranging from 20 to 90 amps, in both single crystal and polycrystalline regions.

  12. Temperature dependence of optical properties of GaAs

    NASA Technical Reports Server (NTRS)

    Yao, Huade; Snyder, Paul G.; Woollam, John A.

    1991-01-01

    The effect of temperature on the optical properties of GaAs was investigated using spectroscopic ellipsometry measurements, between room temperature and about 610 C in increments of 50 C, of pseudodielectric functions and related optical constants of GaAs. A quantitative analysis of the pseudodielectric function spectrum was carried out using a harmonic-oscillator approximation (HOA) to fit the measured dielectric functions. Good fits were obtained with this model, which provides a convenient means of reproducing the GaAs dielectric function at any temperature, by using the temperature-dependent oscillator parameters. The HOA analysis also provides information about band-gap variation with temperature. Using the measured optical constants at a number of fixed temperatures, an algorithm was developed for computing the dielectric function spectrum at an arbitrary temperature in the range 22-610 C.

  13. MBE Growth of GaAs Whiskers on Si Nanowires

    SciTech Connect

    Maxwell Andrews, Aaron

    2010-01-04

    We present the growth of GaAs nanowhiskers by molecular beam epitaxy on Si (111) nanowires grown by low-pressure chemical vapor deposition. The whiskers grow in the wurtzite phase, along the [0001] direction, on the {l_brace}112{r_brace} facets of the Si nanowire, forming a star-like six-fold radial symmetry. The photoluminescence shows a 30 meV blue shift with respect to bulk GaAs, additionally a GaAs/AlAs core-shell heterostructure shows increased luminescence.

  14. Ga nanoparticle-enhanced photoluminescence of GaAs

    SciTech Connect

    Kang, M.; Al-Heji, A. A.; Jeon, S.; Wu, J. H.; Lee, J.-E.; Saucer, T. W.; Zhao, L.; Sih, V.; Katzenstein, A. L.; Sofferman, D. L.; Goldman, R. S.

    2013-09-02

    We have examined the influence of surface Ga nanoparticles (NPs) on the enhancement of GaAs photoluminescence (PL) efficiency. We have utilized off-normal focused-ion-beam irradiation of GaAs surfaces to fabricate close-packed Ga NP arrays. The enhancement in PL efficiency is inversely proportional to the Ga NP diameter. The maximum PL enhancement occurs for the Ga NP diameter predicted to maximize the incident electromagnetic (EM) field enhancement. The PL enhancement is driven by the surface plasmon resonance (SPR)-induced enhancement of the incident EM field which overwhelms the SPR-induced suppression of the light emission.

  15. GaAs MMICs for EHF SATCOM ground terminals

    NASA Astrophysics Data System (ADS)

    Hampel, Daniel; Upton, Alastair

    The authors address the potential use of GaAs, and their benefits, for EHF ground terminals. This assessment of GaAs MMICs (monoltihic microwave integrated circuits), while concentrating on the analog RF front end, also includes some associated critical digital functions. Performance requirements and specific application areas, such as 20-GHz low-noise amplifiers and 44-GHz power amplifiers, are discussed and current state-of-the-art performance in low-noise high-electron-mobility transistors (HEMTs) and high-efficiency pseudomorphic HEMTs is presented, along with projected performance improvements over the next five years.

  16. Defect interactions in GaAs single crystals

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1984-01-01

    The two-sublattice structural configuration of GaAs and deviations from stoichiometry render the generation and interaction of electrically active point defects (and point defect complexes) critically important for device applications and very complex. Of the defect-induced energy levels, those lying deep into the energy band are very effective lifetime ""killers". The level 0.82 eV below the condition band, commonly referred to as EL2, is a major deep level, particularly in melt-grown GaAs. This level is associated with an antisite defect complex (AsGa - VAS). Possible mechanisms of its formation and its annihilation were further developed.

  17. GaAs laser diode pumped Nd:YAG laser

    NASA Technical Reports Server (NTRS)

    Conant, L. C.; Reno, C. W.

    1974-01-01

    A 1.5-mm by 3-cm neodymium-ion doped YAG laser rod has been side pumped using a GaAs laser diode array tuned to the 8680-A absorption line, achieving a multimode average output power of 120 mW for a total input power of 20 W to the final-stage laser diode drivers. The pumped arrangement was designed to take advantage of the high brightness of a conventional GaAs array as a linear source by introducing the pump light through a slit into a close-wrapped gold coated pump cavity. This cavity forms an integrating chamber for the pump light.

  18. GaAs solar cells with V-grooved emitters

    NASA Technical Reports Server (NTRS)

    Bailey, S. G.; Fatemi, N.; Wilt, D. M.; Landis, G. A.; Thomas, R. D.

    1989-01-01

    A GaAs solar cell with a V-grooved front surface is described. It shows improved optical coupling and higher short-circuit current compared to planar cells. The GaAs homojunction cells, manufactured by OrganoMetallic Chemical Vapor Deposition (OMCVD), are described. The V-grooves were formed by anisotropic etching. Reflectivity measurements show significantly lower reflectance for the microgrooved cell compared to the planar structure. The short circuit current of the V-grooved solar cell is consistently higher than that of the planar controls.

  19. Investigation of high efficiency GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Olsen, Larry C.; Dunham, Glen; Addis, F. W.; Huber, Dan; Linden, Kurt

    1989-01-01

    Investigations of basic mechanisms which limit the performance of high efficiency GaAs solar cells are discussed. P/N heteroface structures have been fabricated from MOCVD epiwafers. Typical AM1 efficiencies are in the 21 to 22 percent range, with a SERI measurement for one cell being 21.5 percent. The cells are nominally 1.5 x 1.5 cm in size. Studies have involved photoresponse, T-I-V analyses, and interpretation of data in terms of appropriate models to determine key cell parameters. Results of these studies are utilized to determine future approaches for increasing GaAs solar cell efficiencies.

  20. Magnetron Sputtered Gold Contacts on N-gaas

    NASA Technical Reports Server (NTRS)

    Buonaquisti, A. D.; Matson, R. J.; Russell, P. E.; Holloway, P. H.

    1984-01-01

    Direct current planar magnetron sputtering was used to deposit gold Schottky barrier electrical contacts on n-type GaAs of varying doping densities. The electrical character of the contact was determined from current voltage and electron beam induced voltage data. Without reducing the surface concentration of carbon and oxide, the contacts were found to be rectifying. There is evidence that energetic neutral particles reflected from the magnetron target strike the GaAs and cause interfacial damage similar to that observed for ion sputtering. Particle irradiation of the surface during contact deposition is discussed.

  1. Epitaxial EuO thin films on GaAs

    SciTech Connect

    Swartz, A. G.; Ciraldo, J.; Wong, J. J. I.; Li Yan; Han Wei; Lin Tao; Shi, J.; Kawakami, R. K.; Mack, S.; Awschalom, D. D.

    2010-09-13

    We demonstrate the epitaxial growth of EuO on GaAs by reactive molecular beam epitaxy. Thin films are grown in an adsorption-controlled regime with the aid of an MgO diffusion barrier. Despite the large lattice mismatch, it is shown that EuO grows well on MgO(001) with excellent magnetic properties. Epitaxy on GaAs is cube-on-cube and longitudinal magneto-optic Kerr effect measurements demonstrate a large Kerr rotation of 0.57 deg., a significant remanent magnetization, and a Curie temperature of 69 K.

  2. Simple intrinsic defects in GaAs : numerical supplement.

    SciTech Connect

    Schultz, Peter Andrew

    2012-04-01

    This Report presents numerical tables summarizing properties of intrinsic defects in gallium arsenide, GaAs, as computed by density functional theory. This Report serves as a numerical supplement to the results published in: P.A. Schultz and O.A. von Lilienfeld, 'Simple intrinsic defects in GaAs', Modelling Simul. Mater. Sci Eng., Vol. 17, 084007 (2009), and intended for use as reference tables for a defect physics package in device models. The numerical results for density functional theory calculations of properties of simple intrinsic defects in gallium arsenide are presented.

  3. Modelling of interband transitions in GaAs tunnel diode

    NASA Astrophysics Data System (ADS)

    Louarn, K.; Fontaine, C.; Arnoult, A.; Olivié, F.; Lacoste, G.; Piquemal, F.; Bounouh, A.; Almuneau, G.

    2016-06-01

    In this paper, an improved model for non-local band-to-band tunneling carrier transport is presented and compared to experimental measurement from GaAs tunnel junctions devices. By carefully taking into account the coupling between the conduction band and the light holes valence band, the model is able to predict, with realistic material parameters, the amplitude of the current density throughout the whole tunneling regime. The model suggests that elastic band-to-band tunneling instead of trap-assisted-tunneling is the predominant mechanism in GaAs tunnel junctions, which is of great interest for better understanding and improving III–V multi-junction solar cells.

  4. High efficiency thin-film GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.

    1977-01-01

    Several oxidation techniques are discussed which have been found to increase the open circuit (V sub oc) of metal-GaAs Schottky barrier solar cells, the oxide chemistry, attempts to measure surface state parameters, the evolving characteristics of the solar cell as background contamination (has been decreased, but not eliminated), results of focused Nd/YAG laser beam recrystallization of Ge films evaporated onto tungsten, and studies of AMOS solar cells fabricated on sliced polycrystalline GaAs wafers. Also discussed are projected materials availability and costs for GaAs thin-film solar cells.

  5. Development of bulk GaAs room temperature radiation detectors

    SciTech Connect

    McGregor, D.S.; Knoll, G.F. . Dept. of Nuclear Engineering); Eisen, Y. . Soreq Nuclear Research Center); Brake, R. )

    1992-10-01

    This paper reports on GaAs, a wide band gap semiconductor with potential use as a room temperature radiation detector. Various configurations of Schottky diode detectors were fabricated with bulk crystals of liquid encapsulated Czochralski (LEC) semi-insulating undoped GaAs material. Basic detector construction utilized one Ti/Au Schottky contact and one Au/Ge/Ni alloyed ohmic contact. Pulsed X-ray analysis indicated pulse decay times dependent on bias voltage. Pulse height analysis disclosed non-uniform electric field distributions across the detectors tentatively explained as a consequence of native deep level donors (EL2) in the crystal.

  6. Photoluminescence of Si-doped GaAs epitaxial layers

    SciTech Connect

    Yaremenko, N. G. Karachevtseva, M. V.; Strakhov, V. A.; Galiev, G. B.; Mokerov, V. G.

    2008-12-15

    The effect of arsenic pressure on the amphoteric behavior of Si during the growth of the Si-doped (100)-, (111)Ga-, and (111)As-oriented GaAs layers is studied by photoluminescence spectroscopy. The edge luminescence band is examined, and the concentration and the degree of compensation as functions of the arsenic pressure are determined. Nonstoichiometry defects in GaAs layers grown with a deficit and an excess of arsenic are studied. It is shown that the defects formed in the (111)Ga- and (111)As-oriented layers are different in nature.

  7. Heteroepitaxial growth and multiferroic properties of Mn-doped BiFeO3 films on SrTiO3 buffered III-V semiconductor GaAs

    NASA Astrophysics Data System (ADS)

    Gao, G. Y.; Yang, Z. B.; Huang, W.; Zeng, H. Z.; Wang, Y.; Chan, H. L. W.; Wu, W. B.; Hao, J. H.

    2013-09-01

    Epitaxial Mn-doped BiFeO3 (MBFO) thin films were grown on GaAs (001) substrate with SrTiO3 (STO) buffer layer by pulsed laser deposition. X-ray diffraction results demonstrate that the films show pure (00l) orientation, and MBFO (100)//STO(100), whereas STO (100)//GaAs (110). Piezoresponse force microscopy images and polarization versus electric field loops indicate that the MBFO films grown on GaAs have an effective ferroelectric switching. The MBFO films exhibit good ferroelectric behavior (2Pr ˜ 92 μC/cm2 and 2EC ˜ 372 kV/cm). Ferromagnetic property with saturated magnetization of 6.5 emu/cm3 and coercive field of about 123 Oe is also found in the heterostructure at room temperature.

  8. Magnetotransport Properties of Epitaxial Ge/AlAs Heterostructures Integrated on GaAs and Silicon.

    PubMed

    Hudait, Mantu K; Clavel, Michael; Goley, Patrick S; Xie, Yuantao; Heremans, Jean J

    2015-10-14

    The magnetotransport properties of epitaxial Ge/AlAs heterostructures with different growth conditions and substrate architectures have been studied under ±9 T magnetic field and at 390 mK temperature. Systematic mobility measurements of germanium (Ge) epilayers grown on GaAs substrates at growth temperatures from 350 to 450 °C allow us to extract a precise growth window for device-quality Ge, corroborated by structural and morphological properties. Our results on Si substrate using a composite metamorphic AlAs/GaAs buffer at 400 °C Ge growth temperature, show that the Ge/AlAs system can be tailored to have a single carrier transport while keeping the charge solely in the Ge layer. Single carrier transport confined to the Ge layer is demonstrated by the weak-localization quantum correction to the conductivity observed at low magnetic fields and 390 mK temperature. The weak localization effect points to a near-absence of spin-orbit interaction for carriers in the electronically active layer and is used here for the first time to pinpoint Ge as this active layer. Thus, the epitaxial Ge grown on Si using AlAs/GaAs buffer architecture is a promising candidate for next-generation energy-efficient fin field-effect transistor applications. PMID:26413844

  9. Multi-junction, monolithic solar cell using low-band-gap materials lattice matched to GaAs or Ge

    DOEpatents

    Olson, Jerry M.; Kurtz, Sarah R.; Friedman, Daniel J.

    2001-01-01

    A multi-junction, monolithic, photovoltaic solar cell device is provided for converting solar radiation to photocurrent and photovoltage with improved efficiency. The solar cell device comprises a plurality of semiconductor cells, i.e., active p/n junctions, connected in tandem and deposited on a substrate fabricated from GaAs or Ge. To increase efficiency, each semiconductor cell is fabricated from a crystalline material with a lattice constant substantially equivalent to the lattice constant of the substrate material. Additionally, the semiconductor cells are selected with appropriate band gaps to efficiently create photovoltage from a larger portion of the solar spectrum. In this regard, one semiconductor cell in each embodiment of the solar cell device has a band gap between that of Ge and GaAs. To achieve desired band gaps and lattice constants, the semiconductor cells may be fabricated from a number of materials including Ge, GaInP, GaAs, GaInAsP, GaInAsN, GaAsGe, BGaInAs, (GaAs)Ge, CuInSSe, CuAsSSe, and GaInAsNP. To further increase efficiency, the thickness of each semiconductor cell is controlled to match the photocurrent generated in each cell. To facilitate photocurrent flow, a plurality of tunnel junctions of low-resistivity material are included between each adjacent semiconductor cell. The conductivity or direction of photocurrent in the solar cell device may be selected by controlling the specific p-type or n-type characteristics for each active junction.

  10. Etching and Growth of GaAs

    NASA Technical Reports Server (NTRS)

    Seabaugh, A. C.; Mattauch, R., J.

    1983-01-01

    In-place process for etching and growth of gallium arsenide calls for presaturation of etch and growth melts by arsenic source crystal. Procedure allows precise control of thickness of etch and newly grown layer on substrate. Etching and deposition setup is expected to simplify processing and improve characteristics of gallium arsenide lasers, high-frequency amplifiers, and advanced integrated circuits.

  11. Au-Seeded Growth of Vertical and in-Plane III–V Nanowires on Graphite Substrates

    PubMed Central

    2014-01-01

    Graphene is promising as a transparent, flexible, and possibly cost-effective substrate for nanowire-based devices. We have investigated Au-seeded III–V nanowire growth with graphite as a model substrate. The highest yield of undoped vertical nanowires was found for InAs, but we also observed vertical nanowires for the InP, GaP, and GaAs materials. The yield of vertical nanowires for GaP and GaAs was strongly improved by supplying the p-dopant DEZn before nanowire growth but not by supplying H2S or HCl. In-plane GaAs and GaP nanowire growth exhibited an unexpected behavior, where the seed particles seemingly reflected on the side facets of other nanowires. These results pave the way for vertical and in-plane hybrid graphene- nanowire devices. PMID:24592968

  12. IMPATT Diodes Based on 〈111〉, 〈100〉, and 〈110〉 Oriented GaAs: A Comparative Study to Search the Best Orientation for Millimeter-Wave Atmospheric Windows

    PubMed Central

    Banerjee, Bhadrani; Tripathi, Anvita; Das, Adrija; Singh, Kumari Alka; Banerjee, J. P.

    2015-01-01

    The authors have carried out the large-signal (L-S) simulation of double-drift region (DDR) impact avalanche transit time (IMPATT) diodes based on 〈111〉, 〈100〉, and 〈110〉 oriented GaAs. A nonsinusoidal voltage excited (NSVE) L-S simulation technique is used to investigate both the static and L-S performance of the above-mentioned devices designed to operate at millimeter-wave (mm-wave) atmospheric window frequencies, such as 35, 94, 140, and 220 GHz. Results show that 〈111〉 oriented GaAs diodes are capable of delivering maximum RF power with highest DC to RF conversion efficiency up to 94 GHz; however, the L-S performance of 〈110〉 oriented GaAs diodes exceeds their other counterparts while the frequency of operation increases above 94 GHz. The results presented in this paper will be helpful for the future experimentalists to choose the GaAs substrate of appropriate orientation to fabricate DDR GaAs IMPATT diodes at mm-wave frequencies.

  13. Investigation of Substrate Effects on Interface Strain and Defect Generation in MBE-Grown HgCdTe

    NASA Astrophysics Data System (ADS)

    Gu, R.; Lei, W.; Antoszewski, J.; Faraone, L.

    2016-09-01

    Si, Ge, and GaAs have been extensively investigated as alternative substrates for molecular-beam epitaxy (MBE) growth of HgCdTe and, at present, are widely used for HgCdTe-based infrared focal-plane arrays. However, the problem of high dislocation density in HgCdTe layers grown on these lattice-mismatched substrates has yet to be resolved. In this work, we investigated another alternative substrate, GaSb, which has a significantly smaller lattice mismatch with HgCdTe in comparison with Si, Ge, and GaAs, and is readily available as large-area, epiready wafers at much lower cost in comparison with lattice-matched CdZnTe substrates. The resultant stress due to lattice and thermal mismatch between the HgCdTe epilayer and various substrates has been calculated in this work using the elasticity matrix, and the corresponding stress distribution simulated using ANSYS. The simulated structures were matched by experimental samples involving MBE growth of HgCdTe on GaAs, GaSb, and CdZnTe substrates, and were characterized via reflection high-energy electron diffraction and x-ray diffraction analysis, followed by etch pit density (EPD) analysis. In comparison with other alternative substrates, GaSb is shown to have lower interface stress and lower EPD, rendering it an interesting and promising alternative substrate material for HgCdTe epitaxy.

  14. Investigation of Substrate Effects on Interface Strain and Defect Generation in MBE-Grown HgCdTe

    NASA Astrophysics Data System (ADS)

    Gu, R.; Lei, W.; Antoszewski, J.; Faraone, L.

    2016-05-01

    Si, Ge, and GaAs have been extensively investigated as alternative substrates for molecular-beam epitaxy (MBE) growth of HgCdTe and, at present, are widely used for HgCdTe-based infrared focal-plane arrays. However, the problem of high dislocation density in HgCdTe layers grown on these lattice-mismatched substrates has yet to be resolved. In this work, we investigated another alternative substrate, GaSb, which has a significantly smaller lattice mismatch with HgCdTe in comparison with Si, Ge, and GaAs, and is readily available as large-area, epiready wafers at much lower cost in comparison with lattice-matched CdZnTe substrates. The resultant stress due to lattice and thermal mismatch between the HgCdTe epilayer and various substrates has been calculated in this work using the elasticity matrix, and the corresponding stress distribution simulated using ANSYS. The simulated structures were matched by experimental samples involving MBE growth of HgCdTe on GaAs, GaSb, and CdZnTe substrates, and were characterized via reflection high-energy electron diffraction and x-ray diffraction analysis, followed by etch pit density (EPD) analysis. In comparison with other alternative substrates, GaSb is shown to have lower interface stress and lower EPD, rendering it an interesting and promising alternative substrate material for HgCdTe epitaxy.

  15. Strain relaxation of GaAs/Ge crystals on patterned Si substrates

    SciTech Connect

    Taboada, A. G. Kreiliger, T.; Falub, C. V.; Känel, H. von; Isa, F.; Isella, G.; Salvalaglio, M.; Miglio, L.; Wewior, L.; Fuster, D.; Alén, B.; Niedermann, P.; Neels, A.; Dommann, A.; Mancarella, F.

    2014-01-13

    We report on the mask-less integration of GaAs crystals several microns in size on patterned Si substrates by metal organic vapor phase epitaxy. The lattice parameter mismatch is bridged by first growing 2-μm-tall intermediate Ge mesas on 8-μm-tall Si pillars by low-energy plasma enhanced chemical vapor deposition. We investigate the morphological evolution of the GaAs crystals towards full pyramids exhibiting energetically stable (111) facets with decreasing Si pillar size. The release of the strain induced by the mismatch of thermal expansion coefficients in the GaAs crystals has been studied by X-ray diffraction and photoluminescence measurements. The strain release mechanism is discussed within the framework of linear elasticity theory by Finite Element Method simulations, based on realistic geometries extracted from scanning electron microscopy images.

  16. Effect of interwire separation on growth kinetics and properties of site-selective GaAs nanowires

    SciTech Connect

    Rudolph, D.; Schweickert, L.; Morkötter, S.; Loitsch, B.; Hertenberger, S.; Becker, J.; Bichler, M.; Finley, J. J.; Koblmüller, G.; Abstreiter, G.

    2014-07-21

    We report tuning of the growth kinetics, geometry, and properties of autocatalytic GaAs nanowires (NW) by precisely controlling their density on SiO{sub 2}-mask patterned Si (111) substrates using selective area molecular beam epitaxy. Using patterned substrates with different mask opening size (40–120 nm) and pitch (0.25–3 μm), we find that the NW geometry (length, diameter) is independent of the opening size, in contrast to non-catalytic GaAs NWs, whereas the NW geometry strongly depends on pitch, i.e., interwire separation and NW density. In particular, two distinct growth regimes are identified: a diffusion-limited regime for large pitches (low NW density) and a competitive growth regime for smaller pitches (high NW density), where axial and radial NW growth rates are reduced. The transition between these two regimes is significantly influenced by the growth conditions and shifts to smaller pitches with increasing As/Ga flux ratio. Ultimately, the pitch-dependent changes in growth kinetics lead to distinctly different photoluminescence properties, highlighting that mask template design is a very critical parameter for tuning intrinsic NW properties.

  17. Small signal model parameters analysis of GaN and GaAs based HEMTs over temperature for microwave applications

    NASA Astrophysics Data System (ADS)

    Alim, Mohammad A.; Rezazadeh, Ali A.; Gaquiere, Christophe

    2016-05-01

    Thermal and small-signal model parameters analysis have been carried out on 0.5 μm × (2 × 100 μm) AlGaAs/GaAs HEMT grown on semi-insulating GaAs substrate and 0.25 μm × (2 × 100 μm) AlGaN/GaN HEMT grown on SiC substrate. Two different technologies are investigated in order to establish a detailed understanding of their capabilities in terms of frequency and temperature using on-wafer S-parameter measurement over the temperature range from -40 to 150 °C up to 50 GHz. The equivalent circuit parameters as well as their temperature-dependent behavior of the two technologies were analyzed and discussed for the first time. The principle elevation or degradation of transistor parameters with temperature demonstrates the great potential of GaN device for high frequency and high temperature applications. The result provides some valuable insights for future design optimizations of advanced GaN and a comparison of this with the GaAs technology.

  18. Minority carrier lifetimes of metalorganic chemical vapor deposition long-wavelength infrared HgCdTe on GaAs

    NASA Astrophysics Data System (ADS)

    Zucca, R.; Edwall, D. D.; Chen, J. S.; Johnston, S. L.; Younger, C. R.

    1991-10-01

    Metalorganic chemical vapor deposition (MOCVD) growth of HgCdTe on GaAs is a promising technique that overcomes the size and crystal quality limitations of CdTe substrates. An important material parameter is the minority carrier liftetime, which determines the ultimate zero bias impedance and quantum efficiency of a photodiode. We present the first systematic study of the temperature and carrier concentration dependence of minority carrier lifetimes on n-type and p-type layers of MOCVD long-wavelength infrared HgCdTe grown on GaAs substrates. The temperature dependencies of the lifetime are compared with theoretical predictions based on Auger, radiative, and Shockley-Read recombination. Excellent fits are obtained over a broad temperature range, from 20 K to room temperature. The experimental lifetimes of n-type material reach the theoretical limit imposed by Auger+radiative recombination for carrier concentrations higher than 2×1015 cm-3. For lower carrier concentrations, the measured lifetimes are shorter than those predicted from Auguer+radiative recombination, and Shockley-Read recombination must be added to the calculations. The lifetimes of arsenic-doped and vacancy-doped p-type material are Shockley-Read limited. They are one order of magnitude longer than those previously observed on vacancy-doped liquid phase epitaxy material.

  19. First-principles studies on molecular beam epitaxy growth of GaAs1-xBix

    DOE PAGESBeta

    Luo, Guangfu; Yang, Shujiang; Li, Jincheng; Arjmand, Mehrdad; Szlufarska, Izabela; Brown, April S.; Kuech, Thomas F.; Morgan, Dane

    2015-07-14

    We investigate the molecular beam epitaxy (MBE) growth of GaAs1-xBix film using density functional theory with spin-orbit coupling to understand the growth of this film, especially the mechanisms of Bi incorporation. We study the stable adsorption structures and kinetics of the incident molecules (As₂ molecule, Ga atom, Bi atom, and Bi₂ molecule) on the (2 x 1)-Gasub||Bi surface and a proposed q(1 x 1)-Gasub||AsAs surface has a quasi-(1 x 1) As layer above the Ga-terminated GaAs substrate and a randomly oriented As dimer layer on top. We obtain the desorption and diffusion barriers of the adsorbed molecules and also themore » reaction barriers of three key processes related to Bi evolution, namely, Bi incorporation, As/Bi exchange, and Bi clustering. The results help explain the experimentally observed dependence of Bi incorporation on the As/Ga ratio and growth temperature. Furthermore, we find that As₂ exchange with Bi of the (2 x 1)-Gasub||Bi surface is a key step controlling the kinetics of the Bi incorporation. Finally, we explore two possible methods to enhance the Bi incorporation, namely, replacing the MBE growth mode from codeposition of all fluxes with a sequential deposition of fluxes and applying asymmetric in-plane strain to the substrate.« less

  20. The combination self-cleaning effect of trimethylaluminium and tetrakis (dimethyl-amino) hafnium pretreatments on GaAs

    NASA Astrophysics Data System (ADS)

    Cao, Yan-Qiang; Li, Xue-Fei; Li, Ai-Dong; Li, Hui; Wu, Di

    2012-12-01

    The self-cleaning effect of trimethylaluminium (TMA) and tetrakis (dimethyl-amino) hafnium (TDMAH) pretreatments on GaAs substrates was investigated deeply. The chemical states were carefully characterized by the X-ray photoelectron spectroscopy, which demonstrates that the pretreatment before ALD of dielectric films can suppress the formation of native oxides on GaAs substrates effectively. It is found that the combination of TMA and TDMAH pretreatments has better self-cleaning effect than single TMA pretreatment based on a ligand-exchange reaction mechanism between TMA/TDMAH and the native oxide. The transmission electron microscopy images also show a thinnest interlayer thickness of ˜0.2 nm for the TMA + TDMAH pretreated sample. TMA + TDMAH pretreated samples exhibit significantly improved interfacial and electrical properties such as the highest accumulation capacitance, the least stretch-out of capacitance-voltage curves, and the lowest interface trap density. These results indicate that the surface pretreatment by using the combination of TMA and TDMAH pulses may be a promising approach for the realization of high quality GaAs-based transistor devices.

  1. Direct determination of the stacking order in Gd{sub 2}O{sub 3} epi-layers on GaAs.

    SciTech Connect

    Yacoby, Y.; Sowwan, M.; Pindak, R.; Cross, J.; Walko, D.; Stern, E.; Pitney, J.; MacHarrie, R.; Hong, M.; Clarke, R.; Experimental Facilities Division; Hebrew Univ.; BNL; Univ. of Washington; Bell Lab Agere Stystems; Univ. of Michigan

    2003-01-01

    We have used Coherent Bragg Rod Analysis (COBRA) to investigate the atomic structure of a 5.6 nm thick Gd{sub 2}O{sub 3} film epitaxially grown on a (100) GaAs substrate. COBRA is a method to directly obtain the structure of systems periodic in two-dimensions by determining the complex scattering factors along the substrate Bragg rods. The system electron density and atomic structure are obtained by Fourier transforming the complex scattering factors into real space. The results show that the stacking order of the first seven Gd{sub 2}O{sub 3} film layers resembles the stacking order of Ga and As layers in GaAs then changes to the stacking order of cubic bulk Gd{sub 2}O{sub 3}. This behavior is distinctly different from the measured stacking order in a 2.7 nm thick Gd{sub 2}O{sub 3} in which the GaAs stacking order persists throughout the entire film.

  2. Present status of GaAs. [including space processing and solid state applications

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.; Jastrzebski, L.

    1979-01-01

    An extensive literature survey on GaAs was carried out for the period December 31, 1970, to December 31, 1977. The increasing interest in GaAs device structures increased steadily during that period. The leading research and development centers and the specific areas of interest were identified. A workshop on GaAs was held in November 1977 to assess the present status of melt-grown GaAs and the existing needs for reliable chemical, structural, and electronic characterization methods. It was concluded that the present available bulk GaAs crystals are of poor quality and that GaAs technology is lagging demonstrated or potentially feasible GaAs devices and systems.

  3. Measuring Carrier Lifetime in GaAs by Luminescence

    NASA Technical Reports Server (NTRS)

    Von Roos, O.

    1986-01-01

    Luminescence proposed as nondestructive technique for measuring Shockley-Read-Hall (SRH) recombination lifetime GaAs. Sample irradiated, and luminescence escapes through surface. Measurement requires no mechanical or electrical contact with sample. No ohmic contacts or p/n junctions needed. Sample not scrapped after tested.

  4. The 20 GHz power GaAs FET development

    NASA Technical Reports Server (NTRS)

    Crandell, M.

    1986-01-01

    The development of power Field Effect Transistors (FET) operating in the 20 GHz frequency band is described. The major efforts include GaAs FET device development (both 1 W and 2 W devices), and the development of an amplifier module using these devices.

  5. The surface chemistry of GaAs atomic layer epitaxy

    SciTech Connect

    Creighton, J.R.; Banse, B.A.

    1991-01-01

    In this paper we review three proposed mechanisms for GaAs ALE and review or present data support or contradiction of these mechanisms. Surface chemistry results clearly demonstrated that TMGa irreversibly chemisorbs on the Ga-rich GaAs(100) surface. The reactive sticking coefficient (RSC) of TMGa on the adsorbate-free Ga-rich GaAs(100) surface was measured to be {approximately}0.5, conclusively demonstrating that the selective adsorption'' mechanism of ALE is not valid. We describe kinetic evidence for methyl radical desorption in support of the adsorbate inhibition'' mechanism. The methyl radical desorption rates determined by temperature programmed desorption (TPD) demonstrate that desorption is at least a factor of {approximately}10 faster from the As-rich c(2 {times} 8)/(2 {times} 4) surface than from the Ga-rich surface. It is disparity in CH{sub 3} desorption rates between the As-rich and Ga-rich surfaces that is largely responsible for GaAs ALE behavior. A gallium alkyl radical (e.g. MMGa) is also observed during TPD and molecular beam experiments, in partial support of the flux balance'' mechanism. Stoichiometry issues of ALE are also discussed. We have discovered that arsine exposures typical of atmospheric pressure and reduced pressure ALE lead to As coverages {ge} 1 ML, which provides the likely solution to the stoichiometry question regarding the arsine cycle. 32 refs., 6 figs.

  6. GaAs MESFET with lateral non-uniform doping

    NASA Technical Reports Server (NTRS)

    Wang, Y. C.; Bahrami, M.

    1983-01-01

    An analytical model of the GaAs MESFET with arbitrary non-uniform doping is presented. Numerical results for linear lateral doping profile are given as a special case. Theoretical considerations predict that better device linearity and improved F(T) can be obtained by using linear lateral doping when doping density increases from source to drain.

  7. Gallium arsenide (GaAs) power conversion concept

    NASA Technical Reports Server (NTRS)

    Nussberger, A. A.

    1980-01-01

    A summary design analysis of a GaAs power conversion system for the solar power satellite (SPS) is presented. Eight different satellite configuration options for the solar arrays are compared. Solar cell annealing effects after proton irradiation are considered. Mass estimates for the SPS and the effect of solar cell parameters on SPS array design are discussed.

  8. V-Grooved GaAs Solar Cell

    NASA Technical Reports Server (NTRS)

    Bailey, S. G.; Landis, G. R.; Wilt, D. M.; Thomas, R. D.; Arrison, A.; Fatemi, N. S.

    1991-01-01

    V-grooved GaAs solar photovoltaic cells increase optical coupling and greater conversion of light into electricity. Increases both trapping of incident light and lengths of optical paths in cell material. Net effect increases in total absorptivity, tolerance to damage by energetic particles, and short-circuit current. These improvements expected to follow from similar improvements obtained in silicon solar cells.

  9. High purity, low dislocation GaAs single crystals

    NASA Technical Reports Server (NTRS)

    Chen, R. T.; Holmes, D. E.; Kirkpatrick, C. G.

    1983-01-01

    Liquid encapsulated Czochralski crystal growth techniques for producing undoped, high resistivity, low dislocation material suitable for device applications is described. Technique development resulted in reduction of dislocation densities in 3 inch GaAs crystals. Control over the melt stoichiometry was determined to be of critical importance for the reduction of twinning and polycrystallinity during growth.

  10. 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.

  11. 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.

  12. Conductive atomic force microscopy study of InAs growth kinetics on vicinal GaAs (110)

    SciTech Connect

    Tejedor, Paloma; Diez-Merino, Laura; Beinik, Igor; Teichert, Christian

    2009-09-21

    Conductive atomic force microscopy has been used to investigate the effect of atomic hydrogen and step orientation on the growth behavior of InAs on GaAs (110) misoriented substrates. Samples grown by conventional molecular beam epitaxy exhibit higher conductivity on [110]-multiatomic step edges, where preferential nucleation of InAs nanowires takes place by step decoration. On H-terminated substrates with triangular terraces bounded by [115]-type steps, three-dimensional InAs clusters grow selectively at the terrace apices as a result of a kinetically driven enhancement in upward mass transport via AsH{sub x} intermediate species and a reduction in the surface free energy.

  13. Growth orientation dependence of Si doping in GaAsN

    SciTech Connect

    Han, Xiuxun; Dong, Chen; Feng, Qiang; Ohshita, Yoshio; Yamaguchi, Masafumi

    2015-02-07

    The incorporation of Si in GaAsN alloys grown simultaneously on (100), (311)A, (311)B, and (211)B GaAs substrates by the chemical beam epitaxy has been investigated. The decrease in electron concentration with the increasing N composition suggests the occurrence of N and Si interaction, whereas the interaction exhibits evidently different extent depending on the growth orientation. Combined with the secondary ion mass spectrometry and photoluminescence measurements, it is revealed that (311)B and (211)B are the promising substrate orientations to reduce the N-Si passivation and improve n-type Si doping in GaAsN over a wider N composition range. A surface bonding model is utilized to explain the plane polarity dependent incorporation behaviors of Si and N.

  14. InAsSb-based nBn photodetectors: lattice mismatched growth on GaAs and low-frequency noise performance

    NASA Astrophysics Data System (ADS)

    Craig, A. P.; Thompson, M. D.; Tian, Z.-B.; Krishna, S.; Krier, A.; Marshall, A. R. J.

    2015-10-01

    An InAsSb nBn detector structure was grown on both GaAs and native GaSb substrates. Temperature dependent dark current, spectral response, specific detectivity (D*) and noise spectral density measurements were then carried out. Shot-noise-limited D*figures of 1.2× {10}10 {{Jones}} and 3.0× {10}10 {{Jones}} were calculated (based upon the sum of dark current and background photocurrent) for the sample grown on GaAs and the sample grown on GaSb, respectively, at 200 K. Noise spectral density measurements revealed knee frequencies of between 124-337 Hz and ˜8 Hz, respectively. Significantly, these devices could support focal plane arrays capable of operating under thermoelectric cooling.

  15. Formation of self-assembled InGaAs quantum dot arrays aligned along quasiperiodic multiatomic steps on vicinal (111)B GaAs

    SciTech Connect

    Akiyama, Y.; Sakaki, H.

    2006-10-30

    Dense and highly ordered arrays of self-assembled InGaAs quantum dots are formed by molecular beam epitaxy along multiatomic steps on vicinal (111)B GaAs. This unique structure has been synthesized by depositing a nominally 3-nm-thick In{sub 0.3}Ga{sub 0.7}As layer onto a periodically corrugated surface prepared on a GaAs substrate tilted 8.5 deg. from (111)B. Each dot is typically 30-50 nm in lateral size and about 4 nm in height. Accumulation and release processes of strains in InGaAs layers deposited on stepped surfaces are discussed to suggest a possible mechanism for the aligned dot formation.

  16. Interface reconstruction in the Ga2Se3/GaAs(100) and In2Se3/InAs(100) nanoheterostructures

    NASA Astrophysics Data System (ADS)

    Bezryadin, N. N.; Kotov, G. I.; Kuzubov, S. V.; Boldyreva, Ya. A.; Agapov, B. L.

    2011-05-01

    The surface of GaAs(100) and InAs(100) substrates thermally treated in selenium vapor has been investigated by transmission electron microscopy (TEM) and reflection high-energy electron diffraction. Transmission electron microscopy and high-energy electron diffraction data on these heterostructures confirms the epitaxial pseudomorphic growth of the gallium selenide Ga2Se3(100) and indium selenide In2Se3(100) phases with ordered stoichiometric cation vacancies. A model of the atomic structure of the Ga2Se3(100) and In2Se3(100) surfaces is proposed, and the 2 × 2 reconstruction of the GaAs(100) and InAs(100) surfaces after treatment in selenium vapor is discussed within this model.

  17. Nanolayer of the A {2/III} B {3/VI}(111) phase with ordered cation vacancies on GaAs(111) and InAs(111)

    NASA Astrophysics Data System (ADS)

    Bezryadin, N. N.; Kotov, G. I.; Kuzubov, S. V.; Agapov, B. L.

    2010-09-01

    The surface of GaAs(111) and InAs(111) substrates has been investigated by transmission and scanning electron microscopy after thermal treatment in selenium vapor. A pseudomorphic growth of single-crystal phases of indium selenide In2Se3(111) and gallium selenide Ga2Se3(111) is found; these compounds are crystallized into a sphalerite lattice with ordered stoichiometric cation vacancies. A model of an atomic surface is proposed for the In2Se3(111) and Ga2Se3(111) structures. The reconstruction of the (√3 × √3)- R30° surface of GaAs(111) and InAs(111) after treatment in Se vapor is considered within this model.

  18. GaP ring-like nanostructures on GaAs (100) with In{sub 0.15}Ga{sub 0.85}As compensation layers

    SciTech Connect

    Prongjit, Patchareewan Pankaow, Naraporn Boonpeng, Poonyasiri Thainoi, Supachok Panyakeow, Somsak Ratanathammaphan, Somchai

    2013-12-04

    We present the fabrication of GaP ring-like nanostructures on GaAs (100) substrates with inserted In{sub 0.15}Ga{sub 0.85}As compensation layers. The samples are grown by droplet epitaxy using solid-source molecular beam epitaxy. The dependency of nanostructural and optical properties of GaP nanostructures on In{sub 0.15}Ga{sub 0.85}As layer thickness is investigated by ex-situ atomic force microscope (AFM) and photoluminescence (PL). It is found that the characteristics of GaP ring-like structures on GaAs strongly depend on the In{sub 0.15}Ga{sub 0.85}As layer thickness.

  19. Electrical properties of GaAs metal-oxide-semiconductor structure comprising Al2O3 gate oxide and AlN passivation layer fabricated in situ using a metal-organic vapor deposition/atomic layer deposition hybrid system

    NASA Astrophysics Data System (ADS)

    Aoki, Takeshi; Fukuhara, Noboru; Osada, Takenori; Sazawa, Hiroyuki; Hata, Masahiko; Inoue, Takayuki

    2015-08-01

    This paper presents a compressive study on the fabrication and optimization of GaAs metal-oxide-semiconductor (MOS) structures comprising a Al2O3 gate oxide, deposited via atomic layer deposition (ALD), with an AlN interfacial passivation layer prepared in situ via metal-organic chemical vapor deposition (MOCVD). The established protocol afforded self-limiting growth of Al2O3 in the atmospheric MOCVD reactor. Consequently, this enabled successive growth of MOCVD-formed AlN and ALD-formed Al2O3 layers on the GaAs substrate. The effects of AlN thickness, post-deposition anneal (PDA) conditions, and crystal orientation of the GaAs substrate on the electrical properties of the resulting MOS capacitors were investigated. Thin AlN passivation layers afforded incorporation of optimum amounts of nitrogen, leading to good capacitance-voltage (C-V) characteristics with reduced frequency dispersion. In contrast, excessively thick AlN passivation layers degraded the interface, thereby increasing the interfacial density of states (Dit) near the midgap and reducing the conduction band offset. To further improve the interface with the thin AlN passivation layers, the PDA conditions were optimized. Using wet nitrogen at 600 °C was effective to reduce Dit to below 2 × 1012 cm-2 eV-1. Using a (111)A substrate was also effective in reducing the frequency dispersion of accumulation capacitance, thus suggesting the suppression of traps in GaAs located near the dielectric/GaAs interface. The current findings suggest that using an atmosphere ALD process with in situ AlN passivation using the current MOCVD system could be an efficient solution to improving GaAs MOS interfaces.

  20. Oxidation of the GaAs semiconductor at the Al2O3/GaAs junction.

    PubMed

    Tuominen, Marjukka; Yasir, Muhammad; Lång, Jouko; Dahl, Johnny; Kuzmin, Mikhail; Mäkelä, Jaakko; Punkkinen, Marko; Laukkanen, Pekka; Kokko, Kalevi; Schulte, Karina; Punkkinen, Risto; Korpijärvi, Ville-Markus; Polojärvi, Ville; Guina, Mircea

    2015-03-14

    Atomic-scale understanding and processing of the oxidation of III-V compound-semiconductor surfaces are essential for developing materials for various devices (e.g., transistors, solar cells, and light emitting diodes). The oxidation-induced defect-rich phases at the interfaces of oxide/III-V junctions significantly affect the electrical performance of devices. In this study, a method to control the GaAs oxidation and interfacial defect density at the prototypical Al2O3/GaAs junction grown via atomic layer deposition (ALD) is demonstrated. Namely, pre-oxidation of GaAs(100) with an In-induced c(8 × 2) surface reconstruction, leading to a crystalline c(4 × 2)-O interface oxide before ALD of Al2O3, decreases band-gap defect density at the Al2O3/GaAs interface. Concomitantly, X-ray photoelectron spectroscopy (XPS) from these Al2O3/GaAs interfaces shows that the high oxidation state of Ga (Ga2O3 type) decreases, and the corresponding In2O3 type phase forms when employing the c(4 × 2)-O interface layer. Detailed synchrotron-radiation XPS of the counterpart c(4 × 2)-O oxide of InAs(100) has been utilized to elucidate the atomic structure of the useful c(4 × 2)-O interface layer and its oxidation process. The spectral analysis reveals that three different oxygen sites, five oxidation-induced group-III atomic sites with core-level shifts between -0.2 eV and +1.0 eV, and hardly any oxygen-induced changes at the As sites form during the oxidation. These results, discussed within the current atomic model of the c(4 × 2)-O interface, provide insight into the atomic structures of oxide/III-V interfaces and a way to control the semiconductor oxidation. PMID:25686555

  1. alloy lattice-matched to GaAs: a first-principles study

    NASA Astrophysics Data System (ADS)

    Ma, Xiaoyang; Li, Dechun; Zhao, Shengzhi; Li, Guiqiu; Yang, Kejian

    2014-10-01

    First-principles calculations based on density functional theory have been performed for the quaternary GaAs1- x- y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1- x- y N x Bi y alloy with y/ x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1- x- y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1- x- y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1- x- y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1- x- y N x Bi y quaternary alloys in optoelectronic devices.

  2. Theoretical analysis of 1.55 μm emitting GaInNAs QD's on different substrates

    NASA Astrophysics Data System (ADS)

    Tomić, S.; Jones, T. S.

    2008-04-01

    We present a theoretical study which compares the electronic and optical properties of dilute nitrogen GaInNAs quantum dots (QD) on two different substrates, GaAs and InP. The calculations are based on a 10 band kṡp band-anti-crossing (BAC) Hamiltonian, incorporating valence, conduction and nitrogen-induced bands. We show that 1.55 μm emission can be achieved on both substrates through appropriate tailoring of the QD size. On GaAs, the dominant dipole matrix element is the e and e light polarization, whereas on InP substrate, the dominant component is the e light polarization. Our results also identifiy the different In and N QD compositions required for long-wavelength emission on both substrates.

  3. Antimonide-Based Long-Wavelength Lasers on GaAs Substrates

    SciTech Connect

    KLEM,JOHN F.; Blum, O.

    2000-08-17

    We have investigated the use of GaAsSb in edge-emitting laser active regions, in order to obtain lasing near 1.3 {micro}m. Single quantum well GaAsSb devices display electroluminescence at wavelengths as long as 1.34 {micro}m, but substantial blueshifts occur under high injection conditions. GaAsSb single quantum well edge emitters have been obtained which lase at 1.275 {micro}m with a room-temperature threshold current density as low as 535 A/cm{sup 2}. Modification of the basic GaAsSb/GaAs structure with the addition of InGaAs layers results in a strongly type-II band alignment which can be used to further extend the emission wavelength of these devices. Using GaAsSb/InGaAs active regions, lasers emitting at 1.17 {micro}m have been obtained with room-temperature threshold current densities of 120 A/cm{sup 2}, and devices operating at 1.29 {micro}m have displayed thresholds as low as 375 A/cm{sup 2}. Characteristic temperatures for devices employing various GaAsSb-based active regions have been measured to be 60-73 K.

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

    SciTech Connect

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

    1980-08-01

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

  5. Large-area, high-speed PIN detectors in GaAs

    NASA Astrophysics Data System (ADS)

    Jackson, D. J.; Persechini, D. L.

    1986-02-01

    Large-area PIN detectors have been manufactured with bandwidths exceeding 8 GHz. The devices were fabricated in concert with design rules for the manufacture of ICs and incorporate an interdigitated format which permits the large detector area with low device capacitance. The PIN detectors were deposited on GaAs substrates. First, an SiO2 layer was deposited, then etched. Next, a 50 nm layer of Zn and then a 50 nm layer of Au were sputter deposited and the interdigitated pattern was defined by photoresist techniques. The electrodes were plated to a 1 micron thickness, the photoresist was removed, and the Zn:Au film was etched away before doping the substrate with Zn and Ge. The device was then sintered at 430 C. A response level of 5 dB/div was obtained over the range 2-8 GHz, with the roll-off point at 8 GHz being 3 dB. The performance levels were achieved without packaging optimization.

  6. Femtosecond pulsed laser ablation of GaAs

    NASA Astrophysics Data System (ADS)

    Trelenberg, T. W.; Dinh, L. N.; Saw, C. K.; Stuart, B. C.; Balooch, M.

    2004-01-01

    The properties of femtosecond-pulsed laser deposited GaAs nanoclusters were investigated. Nanoclusters of GaAs were produced by laser ablating a single crystal GaAs target in vacuum or in a buffer gas using a Ti-sapphire laser with a 150 fs minimum pulse length. For in-vacuum deposition, X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) revealed that the average cluster size was approximately 7 nm for laser pulse lengths between 150 fs and 25 ps. The average cluster size dropped to approximately 1.5 nm at a pulse length of 500 ps. It was also observed that film thickness decreased with increasing laser pulse length. A reflective coating, which accumulated on the laser admission window during ablation, reduced the amount of laser energy reaching the target for subsequent laser shots and developed more rapidly at longer pulse lengths. This observation indicates that non-stoichiometric (metallic) ablatants were produced more readily at longer pulse lengths. The angular distribution of ejected material about the target normal was well fitted to a bi-cosine distribution of cos 47 θ+ cos 4 θ for ablation in vacuum using 150 fs pulses. XPS and AES revealed that the vacuum-deposited films contained excess amorphous Ga or As in addition to the stoichiometric GaAs nanocrystals seen with XRD. However, films containing only the GaAs nanocrystals were produced when ablation was carried out in the presence of a buffer gas with a pressure in excess of 6.67 Pa. At buffer gas pressure on the order of 1 Torr, it was found that the stoichiometry of the ablated target was also preserved. These experiments indicate that both laser pulse length and buffer gas pressure play important roles in the formation of multi-element nanocrystals by laser ablation. The effects of gas pressure on the target's morphology and the size of the GaAs nanocrystals formed will also be discussed.

  7. Enzyme analysis for Pompe disease in leukocytes; superior results with natural substrate compared with artificial substrates.

    PubMed

    van Diggelen, O P; Oemardien, L F; van der Beek, N A M E; Kroos, M A; Wind, H K; Voznyi, Y V; Burke, D; Jackson, M; Winchester, B G; Reuser, A J J

    2009-06-01

    Enzyme analysis for Pompe disease in leukocytes has been greatly improved by the introduction of acarbose, a powerful inhibitor of interfering alpha-glucosidases, which are present in granulocytes but not in lymphocytes. Here we show that the application of acarbose in the enzymatic assay employing the artificial substrate 4-methylumbelliferyl-alpha-D: -glucoside (MU-alphaGlc) is insufficient to clearly distinguish patients from healthy individuals in all cases. Also, the ratios of the activities without/with acarbose only marginally discriminated Pompe patients and healthy individuals. By contrast, when the natural substrate glycogen is used, the activity in leukocytes from patients (n = 82) with Pompe disease is at most 17% of the lowest control value. The use of artificial substrate in an assay with isolated lymphocytes instead of total leukocytes is a poor alternative as blood samples older than one day invariably yield lymphocyte preparations that are contaminated with granulocytes. To diagnose Pompe disease in leukocytes we recommend the use of glycogen as substrate in the presence of acarbose. This assay unequivocally excludes Pompe disease. To also exclude pseudo-deficiency of acid alpha-glucosidase caused by the sequence change c.271G>A (p.D91N or GAA2; homozygosity in approximately 1:1000 caucasians), a second assay employing MU-alphaGlc substrate plus acarbose or DNA analysis is required. PMID:19387865

  8. Ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer

    NASA Astrophysics Data System (ADS)

    Yang, Weiquan; Becker, Jacob; Liu, Shi; Kuo, Ying-Shen; Li, Jing-Jing; Landini, Barbara; Campman, Ken; Zhang, Yong-Hang

    2014-05-01

    This paper reports the proposal, design, and demonstration of ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer to optimize light management and minimize non-radiative recombination. According to our recently developed semi-analytical model, this design offers one of the highest potential achievable efficiencies for GaAs solar cells possessing typical non-radiative recombination rates found among commercially available III-V arsenide and phosphide materials. The structure of the demonstrated solar cells consists of an In0.49Ga0.51P/GaAs/In0.49Ga0.51P double-heterostructure PN junction with an ultra-thin 300 nm thick GaAs absorber, combined with a 5 μm thick Al0.52In0.48P layer with a textured as-grown surface coated with Au used as a reflective back scattering layer. The final devices were fabricated using a substrate-removal and flip-chip bonding process. Solar cells with a top metal contact coverage of 9.7%, and a MgF2/ZnS anti-reflective coating demonstrated open-circuit voltages (Voc) up to 1.00 V, short-circuit current densities (Jsc) up to 24.5 mA/cm2, and power conversion efficiencies up to 19.1%; demonstrating the feasibility of this design approach. If a commonly used 2% metal grid coverage is assumed, the anticipated Jsc and conversion efficiency of these devices are expected to reach 26.6 mA/cm2 and 20.7%, respectively.

  9. Ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer

    SciTech Connect

    Yang, Weiquan; Becker, Jacob; Liu, Shi; Kuo, Ying-Shen; Li, Jing-Jing; Zhang, Yong-Hang; Landini, Barbara; Campman, Ken

    2014-05-28

    This paper reports the proposal, design, and demonstration of ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer to optimize light management and minimize non-radiative recombination. According to our recently developed semi-analytical model, this design offers one of the highest potential achievable efficiencies for GaAs solar cells possessing typical non-radiative recombination rates found among commercially available III-V arsenide and phosphide materials. The structure of the demonstrated solar cells consists of an In{sub 0.49}Ga{sub 0.51}P/GaAs/In{sub 0.49}Ga{sub 0.51}P double-heterostructure PN junction with an ultra-thin 300 nm thick GaAs absorber, combined with a 5 μm thick Al{sub 0.52}In{sub 0.48}P layer with a textured as-grown surface coated with Au used as a reflective back scattering layer. The final devices were fabricated using a substrate-removal and flip-chip bonding process. Solar cells with a top metal contact coverage of 9.7%, and a MgF{sub 2}/ZnS anti-reflective coating demonstrated open-circuit voltages (V{sub oc}) up to 1.00 V, short-circuit current densities (J{sub sc}) up to 24.5 mA/cm{sup 2}, and power conversion efficiencies up to 19.1%; demonstrating the feasibility of this design approach. If a commonly used 2% metal grid coverage is assumed, the anticipated J{sub sc} and conversion efficiency of these devices are expected to reach 26.6 mA/cm{sup 2} and 20.7%, respectively.

  10. Cryogenic measurements of aerojet GaAs n-JFETs

    NASA Technical Reports Server (NTRS)

    Goebel, John H.; Weber, Theodore T.

    1993-01-01

    The spectral noise characteristics of Aerojet gallium arsenide (GaAs) junction field effect transistors (JFET's) have been investigated down to liquid-helium temperatures. Noise characterization was performed with the field effect transistor (FET) in the floating-gate mode, in the grounded-gate mode to determine the lowest noise readings possible, and with an extrinsic silicon photodetector at various detector bias voltages to determine optimum operating conditions. The measurements indicate that the Aerojet GaAs JFET is a quiet and stable device at liquid helium temperatures. Hence, it can be considered a readout line driver or infrared detector preamplifier as well as a host of other cryogenic applications. Its noise performance is superior to silicon (Si) metal oxide semiconductor field effect transistor (MOSFET's) operating at liquid helium temperatures, and is equal to the best Si n channel junction field effect transistor (n-JFET's) operating at 300 K.

  11. Optical detectors for GaAs MMIC integration: Technology assessment

    NASA Technical Reports Server (NTRS)

    Claspy, P. C.; Bhasin, K. B.

    1989-01-01

    Fiber optic links are being considered to transmit digital and analog signals in phased array antenna feed networks in space communications systems. The radiating elements in these arrays will be GaAs monolithic microwave integrated circuits (MMIC's) in numbers ranging from a few hundred to several thousand. If such optical interconnects are to be practical it appears essential that the associated components, including detectors, be monolithically integrated on the same chip as the microwave circuitry. The general issue of monolithic integration of microwave and optoelectronic components is addressed from the point of view of fabrication technology and compatibility. Particular attention is given to the fabrication technology of various types of GaAs optical detectors that are designed to operate at a wavelength of 830 nm.

  12. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, Harry C.; Lagowski, Jacek

    1989-01-01

    The program on Crystal Growth of Device Quality GaAs in Space was initiated in 1977. The initial stage covering 1977 to 1984 was devoted strictly to ground-based research. By 1985 the program had evolved into its next logical stage aimed at space growth experiments; however, since the Challenger disaster, the program has been maintained as a ground-based program awaiting activation of experimentation in space. The overall prgram has produced some 80 original scientific publications on GaAs crystal growth, crystal characterization, and new approaches to space processing. Publication completed in the last three years are listed. Their key results are outlined and discussed in the twelve publications included as part of the report.

  13. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1986-01-01

    It was established that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail. It was further established that in compound semiconductors with a volatile constituent, control of stoichiometry is far more critical than any other crystal growth parameter. It was also shown that, due to suppression of nonstoichiometric fluctuations, the advantages of space for growth of semiconductor compounds extend far beyond those observed in elemental semiconductors. A novel configuration was discovered for partial confinement of GaAs melt in space which overcomes the two major problems associated with growth of semiconductors in total confinement. They are volume expansion during solidification and control of pressure of the volatile constituent. These problems are discussed in detail.

  14. Formation and properties of porous GaAs

    SciTech Connect

    Schmuki, P.; Lockwood, D.J.; Fraser, J.W.; Graham, M.J.; Isaacs, H.S.

    1996-06-01

    Porous structures on n-type GaAs (100) can be grown electrochemically in chloride-containing solutions. Crystallographic etching of the sample is a precursor stage of the attack. Polarization curves reveal the existanece of a critical onset potential for por formation (PFP). PFP is strongly dependent on the doping level of the sample and presence of surface defects. Good agreement between PFP and breakdown voltage of the space charge layer is found. Surface analysis by EDX, AES, and XPS show that the porous structure consists mainly of GaAs and that anion uptake in the structure can only observed after attackhas been initiated. Photoluminescence measurements reveal (under certain conditions) visible light emission from the porous structure.

  15. GaAs arrays for X-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Owens, Alan; Andersson, Hans; Campbell, M.; Lumb, David H.; Nenonen, Seppo A. A.; Tlustos, Lukas

    2004-09-01

    We present results from our compound semiconductor laboratory program and describe the development of a large area GaAs imaging array for planetary remote sensing applications. The device is fabricated from ~150 micron thick epitaxial material, patterned into a 64 x 64 pixel array, back-thinned and contacted. It will be flip-chip bump bonded onto a custom designed, fully spectroscopic, low noise (< 20 e- rms) active pixel sensor ASIC. At present, the ASIC is still under development and so in order to validate and qualify the various technological steps, we have produced a GaAs imager based on the MEDIPIX-1 format using a MEDIPIX-1 readout chip. In X-ray tests, the device was found to work well with a bump yield of 99.9%. After flat field corrections, the spatial uniformity of the array was commensurate with Poisson noise.

  16. Single Material Band Gap Engineering in GaAs Nanowires

    SciTech Connect

    Spirkoska, D.; Abstreiter, G.; Efros, A.; Conesa-Boj, S.; Morante, J. R.; Arbiol, J.; Fontcuberta i Morral, A.

    2011-12-23

    The structural and optical properties of GaAs nanowire with mixed zinc-blende/wurtzite structure are presented. High resolution transmission electron microscopy indicates the presence of a variety of shorter and longer segments of zinc-blende or wurtzite crystal phases. Sharp photoluminescence lines are observed with emission energies tuned from 1.515 eV down to 1.43 eV. The downward shift of the emission peaks can be understood by carrier confinement at the wurtzite/zinc-blende heterojunction, in quantum wells and in random short period superlattices existent in these nanowires, assuming the theoretical staggered band-offset between wurtzite and zinc-blende GaAs.

  17. Sub-additivity in Electron Emission from GaAs

    NASA Astrophysics Data System (ADS)

    Brunkow, Evan; Clayburn, Nathan; Becker, Maria; Jones, Eric; Batelaan, Herman; Gay, Timothy

    2016-05-01

    When two spatially-overlapped laser pulses (775 nm center wavelength, 75 fs duration) are incident on an untreated <100> GaAs crystal surface, the electron emission rate depends on the temporal separation between the two pulses. We have shown that for delays between 0.2 and 1000ps, the emission rate is ``sub-additive'', i.e., is lower than when the beams have separation >> 1 ns. We believe the cause of this sub-additivity is an increase in reflectance and transmittance due to electrons occupying the excited state of the GaAs. We are now able to manipulate the magnitude of the sub-additivity by changing the number of electrons that are in the excited state. Sub-additivity is not observed with tungsten tip surfaces which have no excited state. Funded by NSF PHY-1505794, EPSCoR IIIA-1430519, and NSF 1306565 (HB).

  18. GaAs solar cells for laser power beaming

    NASA Technical Reports Server (NTRS)

    Olsen, Larry C.; Dunham, Glen; Huber, Daniel A.; Addis, F. William; Anheier, Norman; Coomes, E. P.

    1991-01-01

    Efforts to develop GaAs solar cells for coupling to laser beams in the wavelength range of 800 to 840 nm are described. This work was motivated primarily by interests in space-tp-space power beaming applications. In particular, the Battelle Pacific Northwest Laboratories is conducting studies of the utilization of power beaming for several future space missions. Modeling calculations of GaAs cell performance were carried out using PC-1D to determine an appropriate design for a p/n cell structure. Epitaxial wafers were grown by MOCVD and cells fabricated at WSU Tri-Cities. Under simulated conditions, an efficiency of 53 percent was achieved for a cell coupled to 806 nm light at 400 mW/sq cm.

  19. Oxygen-enhanced wet thermal oxidation of GaAs

    NASA Astrophysics Data System (ADS)

    Bauters, J. F.; Fenlon, R. E.; Seibert, C. S.; Yuan, W.; Plunkett, J. S. B.; Li, J.; Hall, D. C.

    2011-10-01

    An oxygen-enhanced wet thermal oxidation process is used to grow smooth, uniform, insulating native oxides of GaAs. At 420 °C, a maximum linear growth rate of 4.8 nm/min is observed for oxidation in water vapor with 2000 ppm O2 added relative to the N2 carrier gas, with growth ceasing by 7000 ppm. Films as thick as 800 nm with surface roughness as low as 0.2 nm are demonstrated. In fabricated metal-oxide-semiconductor capacitors, a 412 nm thick native oxide film exhibits a factor of ˜2700 reduction in leakage current density at 1 V relative to a direct metal (Au:Ti) to GaAs contact.

  20. Testing a GaAs cathode in SRF gun

    SciTech Connect

    Wang, E.; Kewisch, J.; Ben-Zvi, I.; Burrill, A.; Rao, T.; Wu, Q.; Holmes, D.

    2011-03-28

    RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1/2 cell SRF gun, the vacuum can be maintained at nearly 10{sup -12} Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun. Future particle accelerators, such as eRHIC and the ILC require high-brightness, high-current polarized electrons. Strained superlattice GaAs:Cs has been shown to be an efficient cathode for producing polarized electrons. Activation of GaAs with Cs,O(F) lowers the electron affinity and makes it energetically possible for all the electrons, excited into the conduction band that drift or diffuse to the emission surface, to escape into the vacuum. Presently, all operating polarized electron sources, such as the CEBAF, are DC guns. In these devices, the excellent ultra-high vacuum extends the lifetime of the cathode. However, the low field gradient on the photocathode's emission surface of the DC guns limits the beam quality. The higher accelerating gradients, possible in the RF guns, generate a far better beam. Until recently, most RF guns operated at room temperature, limiting the vacuum to {approx}10{sup -9} Torr. This destroys the GaAs's NEA surface. The SRF guns combine the excellent vacuum conditions of DC guns and the high

  1. Government systems and GaAs monolithic components

    NASA Astrophysics Data System (ADS)

    Sieger, K. J.

    1983-12-01

    The current state of monolithic GaAs technology and its current and future applications to government systems are reviewed, with attention given to the government investment strategy, commercial market impact, new technology, and challenges from silicon technology. Data obtained from a survey to determine the status of GaAs IC technology are presented. These contain the system type and acronym, a technical description of the system, the critical research and development needed to develop the particular IC, specific applications and functions of the IC in the system, the year of implementation, and the potential chip buyer. High volume applications, with chip counts of one million and more, are identified as phased arrays (radar and communication), expendable decoys, missile seekers, and satellite signal processors. Problem areas, future trends, and areas of uncertainty are discussed.

  2. High purity low dislocation GaAs single crystals

    NASA Technical Reports Server (NTRS)

    Chen, R. T.; Holmes, D. E.; Kirkpatrick, C. G.

    1982-01-01

    Recent advances in GaAs bulk crystal growth using the LEC (liquid encapsulated Czochralski) technique are described. The dependence of the background impurity concentration and the dislocation density distribution on the materials synthesis and growth conditions were investigated. Background impurity concentrations as low as 4 x 10 to the 15th power were observed in undoped LEC GaAs. The dislocation density in selected regions of individual ingots was very low, below the 3000 cm .3000/sq cm threshold. The average dislocation density over a large annular ring on the wafers fell below the 10000/sq cm level for 3 inch diameter ingots. The diameter control during the program advanced to a diameter variation along a 3 inch ingot less than 2 mm.

  3. A high-speed GaAs MESFET optical controller

    NASA Technical Reports Server (NTRS)

    Claspy, P. C.; Bhasin, K. B.; Richard, M.; Bendett, M.; Gustafson, G.

    1989-01-01

    Optical interconnects are being considered for control signal distribution in phased array antennas. A packaged hybrid GaAs optical controller with a 1:16 demultiplexed output that is suitable for this application is described. The controller, which was fabricated using enhancement/depletion mode MESFET technology, operates at demultiplexer-limited input data rates up to 305 Mb/s and requires less than 200 microW optical input power.

  4. Solar heating of GaAs nanowire solar cells.

    PubMed

    Wu, Shao-Hua; Povinelli, Michelle L

    2015-11-30

    We use a coupled thermal-optical approach to model the operating temperature rise in GaAs nanowire solar cells. We find that despite more highly concentrated light absorption and lower thermal conductivity, the overall temperature rise in a nanowire structure is no higher than in a planar structure. Moreover, coating the nanowires with a transparent polymer can increase the radiative cooling power by 2.2 times, lowering the operating temperature by nearly 7 K. PMID:26698787

  5. SEU design consideration for MESFETs on LT GaAs

    SciTech Connect

    Weatherford, T.R.; Radice, R.; Eskins, D.

    1997-12-01

    Computer simulation results are reported on transistor design and single-event charge collection modeling of metal-semiconductor field effect transistors (MESFETs) fabricated in the Vitesse H-GaAsIII{reg_sign} process on Low Temperature grown (LT) GaAs epitaxial layers. Tradeoffs in Single Event Upset (SEU) immunity and transistor design are discussed. Effects due to active loads and diffusion barriers are examined.

  6. On the dissolution properties of GaAs in Ga

    NASA Technical Reports Server (NTRS)

    Davidson, M. C.; Moynahan, A. H.

    1977-01-01

    The dissolution of GaAs in Ga was studied to determine the nature and cause of faceting effects. Ga was allowed to dissolve single crystalline faces under isothermal conditions. Of the crystalline planes with low number indices, only the (100) surface showed a direct correlation of dissolution sites to dislocations. The type of dissolution experienced depended on temperature, and there were three distinct types of behavior.

  7. GaAs Optoelectronic Integrated-Circuit Neurons

    NASA Technical Reports Server (NTRS)

    Lin, Steven H.; Kim, Jae H.; Psaltis, Demetri

    1992-01-01

    Monolithic GaAs optoelectronic integrated circuits developed for use as artificial neurons. Neural-network computer contains planar arrays of optoelectronic neurons, and variable synaptic connections between neurons effected by diffraction of light from volume hologram in photorefractive material. Basic principles of neural-network computers explained more fully in "Optoelectronic Integrated Circuits For Neural Networks" (NPO-17652). In present circuits, devices replaced by metal/semiconductor field effect transistors (MESFET's), which consume less power.

  8. Gallium arsenide (GaAs) solar cell modeling studies

    NASA Technical Reports Server (NTRS)

    Heinbockel, J. H.

    1980-01-01

    Various models were constructed which will allow for the variation of system components. Computer studies were then performed using the models constructed in order to study the effects of various system changes. In particular, GaAs and Si flat plate solar power arrays were studied and compared. Series and shunt resistance models were constructed. Models for the chemical kinetics of the annealing process were prepared. For all models constructed, various parametric studies were performed.

  9. Cathodoluminescence characterization of ion implanted GaAs

    NASA Astrophysics Data System (ADS)

    Cone, M. L.

    1980-03-01

    The unique properties of GaAs make it possible to construct integrated circuit devices that are impossible in Si. The Air Force Avionics Laboratory/AADR has been developing this technology for a number of years. The difficulty of introducing dopants by diffusion has lead ion implantation to play an increasing role in the fabrication process. The present production technique for high performance devices is to fabricate large quantities and select those few that meet the desired specifications. Having a nondestructive technique that can be used to characterize the implantation process during fabrication of the device so as to reject faulty device structures can save valuable time as well as money. Depth-resolved cathodoluminescence is a process that can be used for this purpose. This research develops and verifies a model of cathodoluminescence in ion implanted GaAs. This model can now be used as a tool for further study of ion implanted GaAs. This is the first step in developing cathodoluminescence as a tool for deducing the shape of the ion implanted depth profile in semiconductor materials.

  10. Ab initio study of hot electrons in GaAs.

    PubMed

    Bernardi, Marco; Vigil-Fowler, Derek; Ong, Chin Shen; Neaton, Jeffrey B; Louie, Steven G

    2015-04-28

    Hot carrier dynamics critically impacts the performance of electronic, optoelectronic, photovoltaic, and plasmonic devices. Hot carriers lose energy over nanometer lengths and picosecond timescales and thus are challenging to study experimentally, whereas calculations of hot carrier dynamics are cumbersome and dominated by empirical approaches. In this work, we present ab initio calculations of hot electrons in gallium arsenide (GaAs) using density functional theory and many-body perturbation theory. Our computed electron-phonon relaxation times at the onset of the Γ, L, and X valleys are in excellent agreement with ultrafast optical experiments and show that the ultrafast (tens of femtoseconds) hot electron decay times observed experimentally arise from electron-phonon scattering. This result is an important advance to resolve a controversy on hot electron cooling in GaAs. We further find that, contrary to common notions, all optical and acoustic modes contribute substantially to electron-phonon scattering, with a dominant contribution from transverse acoustic modes. This work provides definitive microscopic insight into hot electrons in GaAs and enables accurate ab initio computation of hot carriers in advanced materials. PMID:25870287

  11. Photoluminescence of Be implanted Si-doped GaAs

    SciTech Connect

    Kroon, R.E.; Botha, J.R.; Neethling, J.H.; Drummond, T.J.

    1999-11-12

    Degenerately doped n-type GaAs produces band-to-band luminescence with the peak energy dependent on the carrier concentration. In this study the photoluminescence of Si-doped GaAs is examined after implantation with high energy Be ions and annealing. The band-to-band peak energy in the unimplanted (reference) material is shown to be smaller than reported values in Te-doped GaAs of the same carrier concentration. This is attributed to compensation in the Si doped material as a result of its amphoteric nature. For the implanted samples, no luminescence was recorded for the unannealed samples or those annealed at 400 C and 500 C. Comparing the relative peak intensities from material annealed at 600 C for 15 min and 30 min indicates an increase in the number of As vacancies with anneal time. For samples annealed at 700 C and 800 C, the dominant luminescence is associated with Ga{sub As} antisite defects. It is suggested that formation of these defects occurs predominantly only at these higher temperatures. Crystal recovery as measured by the luminescence intensity increased with both anneal temperature and time. For the implanted sample annealed at 800 C for 15 min, the dominant peak height was 25% of that from the reference sample.

  12. In situ characterisation of epiready III V substrates for MOVPE

    NASA Astrophysics Data System (ADS)

    Allwood, D. A.; Grant, I. R.; Mason, N. J.; Palmer, R. A.; Walker, P. J.

    2000-12-01

    The use of the term epiready in relation to III-V substrates in MOVPE is ill defined and poorly understood. In this paper we attempt to clarify some of the issues associated with the term epiready, in particular, the thickness and distribution of native oxide on the surface of a GaAs wafer. The surface quality of a wafer is established at three stages, fresh from the packet, oxide removed, and after growth. The surface is assessed by means of atomic force microscopy on a microscopic level and laser light scattering and oxide thickness mapping on a macroscopic scale. GaAs substrates from long-term storage are also examined. It is shown that even long-term stored wafers (in excess of six years) with quite thick native oxide layers can be successfully deoxidised to give atomically flat terraces and can subsequently be used for successful homoepitaxial growth provided that atomic hydrogen (in this case, from the arsenic precursor) is used in the deoxidation stage. No difference between various manufacturers substrates has been found in respect to storage and subsequent use, nor has any difference been established between doped and undoped wafers.

  13. Selective photon-stimulated desorption of hydrogen from GaAs surfaces.

    PubMed

    Petravic, M; Deenapanray, P N; Comtet, G; Hellner, L; Dujardin, G; Usher, B F

    2000-03-01

    Photon-stimulated desorption of H(+) from hydrogenated GaAs (110) and (100) surfaces was studied as a function of photon energy. Distinct peaks, observed around As 3d core-level binding energy for desorption from the GaAs (100) surface and in the As 3d and Ga 3p region for desorption from the GaAs (110) surface, show a striking similarity with the fine structure (spin-orbit splitting) measured in the photoemission from As 3d and Ga 3p levels. These results provide clear evidence for direct desorption processes and represent a basis for selective modification of hydrogenated GaAs surfaces. PMID:11017257

  14. Recovery of gallium and arsenic from GaAs wafer manufacturing slurries

    SciTech Connect

    Jadvar, R.; McCoy, B.J. ); Ford, B.; Galt, J. )

    1991-11-01

    Lapping and polishing slurries from the gallium arsenide (GaAs) wafer manufacturing process were used to develop simple and inexpensive methods for separation and recovery of valuable gallium and toxic arsenic. The lapping slurry, containing GaAs, glycerol, alumina, iron oxide, and water, is treated by a process involving water addition, dissolution of GaAs, mixing, sedimentation, decantation, and evaporation. The polishing slurry, containing GaAs, silica, sodium bicarbonate, sodium hypochlorite and water, is treated simply by a repetitive cycle of adding water, mixing, settling, decanting, and evaporating. After treatment, the slurries contain less than 5 ppm of dissolved arsenic and are considered non-hazardous.

  15. Inverted thermal conversion - GaAs, a new alternative material for integrated circuits

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Gatos, H. C.; Kang, C. H.; Skowronski, M.; Ko, K. Y.

    1986-01-01

    A new type of GaAs is developed which exhibits inverted thermal conversion (ITC); i.e., it converts from conducting to semiinsulating upon annealing at about 850 C. In device fabrication, its low resistivity prior to high-temperature processing differentiates ITC GaAs from the standard semiinsulating GaAs. The ITC characteristics are obtained through control of the concentration of the midgap donor EL2 based on heat treatment and crystal-growth modification. Thus EL2 does not exist in the conducting state of ITC GaAs. Conversion to the semiinsulating state during 850 C annealing is caused by the formation of EL2.

  16. GaAs thin films and methods of making and using the same

    DOEpatents

    Boettcher, Shannon; Ritenour, Andrew; Boucher, Jason; Greenaway, Ann

    2016-06-14

    Disclosed herein are embodiments of methods for making GaAs thin films, such as photovoltaic GaAs thin films. The methods disclosed herein utilize sources, precursors, and reagents that do not produce (or require) toxic gas and that are readily available and relatively low in cost. In some embodiments, the methods are readily scalable for industrial applications and can provide GaAs thin films having properties that are at least comparable to or potentially superior to GaAs films obtained from conventional methods.

  17. GaAs high-speed digital IC technology: An overview

    SciTech Connect

    Larson, L.E.; Jensen, J.F.; Greiling, P.T.

    1986-10-01

    Gallium arsenide integrated circuit technology has advanced to the stage where small-scale integration (SSI) and medium-scale integration (MSI) circuits are available for implementation in high-speed digital systems. The recent availability of GaAs wafer foundries for fabrication of custom designs, along with commercially available GaAs components, allows system designers for the first time to take advantage of the inherent high speed and low power capabilities of the technology. Large-scale integration (LSI) complexity circuits are already being fabricated in the United States and abroad, and higher levels of integration are expected. This will result in improved levels of performance for large digital systems. The advantages of higher levels of integration are clearly evident, although there appears to be an optimum level of integration for each GaAs logic family beyond which system speed actually degrades. In conjunction with the development of GaAs technology, an industry-standard GaAs production process is also evolving. This generic process is available (with minor variations) from most of the GaAs wafer foundries and IC manufacturers. Here the authors review digital GaAs IC device and circuit technology and analyze the performance of GaAs circuits fabricated by this production process. They also analyze the effect of the GaAs IC integration level on computer system speed.

  18. Ordered arrays of embedded Ga nanoparticles on patterned silicon substrates.

    PubMed

    Bollani, M; Bietti, S; Frigeri, C; Chrastina, D; Reyes, K; Smereka, P; Millunchick, J M; Vanacore, G M; Burghammer, M; Tagliaferri, A; Sanguinetti, S

    2014-05-23

    We fabricate site-controlled, ordered arrays of embedded Ga nanoparticles on Si, using a combination of substrate patterning and molecular-beam epitaxial growth. The fabrication process consists of two steps. Ga droplets are initially nucleated in an ordered array of inverted pyramidal pits, and then partially crystallized by exposure to an As flux, which promotes the formation of a GaAs shell that seals the Ga nanoparticle within two semiconductor layers. The nanoparticle formation process has been investigated through a combination of extensive chemical and structural characterization and theoretical kinetic Monte Carlo simulations. PMID:24784353

  19. Photoreflectance analysis of annealed vanadium-doped GaAs thin films grown by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Fitouri, H.; Bilel, C.; Zaied, I.; Bchetnia, A.; Rebey, A.; El Jani, B.

    2015-09-01

    In this study, we investigate the optical properties of annealed vanadium-doped GaAs films grown on GaAs substrates by metalorganic vapor phase epitaxy. The temperature dependence of the photoreflectance (PR) of as-grown GaAs:V films has been studied. We used the fit with Third-Derivative Functional Form model to evaluate the physical parameters. The temperature dependence of band gap and spin-orbit energies can be described by the Bose-Einstein statistical expression. The PR spectra of the samples are measured after thermal annealing in order to check any improvement in the optical quality of the material. The PR signal amplitude of GaAs:V samples decreased after thermal annealing. Degradation of the PR signal for annealing temperature at about 850 °C is observed revealing a poor quality of the layer surface states and an important density of the recombination centers. The lock-in phase analysis of PR spectra allows to determine the time constant for GaAs:V sample before and after thermal annealing.

  20. High Quality of Liquid Phase-Deposited SiON on GaAs MOS Capacitor with Multiple Treatments

    NASA Astrophysics Data System (ADS)

    Lee, Ming-Kwei; Yen, Chih-Feng; Yeh, Min-Yen

    2016-08-01

    Silicon oxynitride (SiON) film on a p-type (100) GaAs substrate by liquid phase deposition has been characterized. Aqueous solutions of hydrofluosilicic acid, ammonia and boric acid were used as growth precursors. The electrical characteristics of SiON film are much improved on GaAs with (NH4)2S treatment. With post-metallization annealing (PMA), hydrogen ions further passivate traps in the SiON/GaAs film and interface. Both PMA and (NH4)2S treatments on a SiON/GaAs MOS capacitor produce better interface quality and lower interface state density (Dit) compared with ones without hydrogen and sulfur passivations. The leakage current densities are improved to 7.1 × 10-8 A/cm2 and 1.8 × 10-7 A/cm2 at ±2 V. The dielectric constant of 5.6 and the effective oxide charges of -5.3 × 1010 C/cm2 are obtained. The hysteresis offset of the hysteresis loop is only 0.09 V. The lowest Dit is 2.7 × 1011 cm-2/eV at an energy of about 0.66 eV from the edge of the valence band.