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  • 1
    Electronic Resource
    Electronic Resource
    Optical generation of high-frequency acoustic waves in GaAs/AlxGa1−xAs periodic multilayer structures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2761-2768 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A picosecond study of ultrahigh-frequency acoustic phonons in specifically engineered GaAs/AlxGa1−xAs periodic multilayer structures is presented. The lattice-matched boundary conditions for photothermal acoustic generation and optical properties of these materials make these structures ideal for sound-wave generation in the 100 GHz to THz range. The acoustics are generated using ultrashort-laser-pulse excitation and detected in real time by measuring the strain-induced change in reflectivity with the pump-probe technique. By using 12 nJ, 90 fs pulses from a Ti:sapphire laser source, the generation and detection of ∼50 GHz acoustics in a 6-bilayer, [001]-oriented GaAs/Al0.4Ga0.6As structure, 500 A(ring) thickness per layer, on a GaAs substrate, are successfully demonstrated. The structure was specifically designed to give the maximum sensitivity to the acoustics through étalon-induced modulations in the reflectivity spectrum. With similarly designed multilayer structures, the upper frequency limit can be achieved for the thermoelastic generation of coherent acoustic phonons, that is, ∼300 GHz in GaAs for ∼1 eV above band-gap-energy photons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356214
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  • 2
    Electronic Resource
    Electronic Resource
    Use of Raman spectroscopy to examine the effects of growth stops on the interfaces of superlattices grown by molecular beam epitaxy (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 570-572 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman spectroscopy of confined longitudinal optical phonons is used to examine the abruptness of the interfaces in a sequence of (GaAs)7(AlAs)7 superlattice samples grown by molecular beam epitaxy. The duration and stoichiometry of growth stops at each heterointerface was varied throughout the sequence. Arsenic rich, group III rich, and approximately stoichiometric growth stops were investigated. It was found that, when the arsenic beam remains on during the growth stops, the surfaces continuously become smoother, resulting in more abrupt interfaces. However, when growth is stopped under group III rich or stoichiometric conditions, an initial roughening of the surface occurs, followed by gradual smoothing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99396
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  • 3
    Electronic Resource
    Electronic Resource
    Phosphorus-vacancy-related deep levels in GaInP layers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1587-1590 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Deep levels in lattice-matched Ga0.51In0.49P/GaAs heterostructure have been investigated by thermal-electric effect spectroscopy (TEES) and temperature-dependent conductivity measurements. Four samples were grown by molecular-beam epitaxy with various phosphorus (P2) beam-equivalent pressures (BEP) of 0.125, 0.5, 2, and 4×10−4 Torr. A phosphorus vacancy (VP) -related deep level, an electron trap, was observed located at EC−0.28±0.02 eV. This trap dominated the conduction-band conduction at T(approximately-greater-than)220 K and was responsible for the variable-range hopping conduction when T〈220 K. Its concentration decreased with the increasing phosphorous BEP. Successive rapid thermal annealing showed that its concentration increased with the increasing annealing temperature. Another electron trap at EC−0.51 eV was also observed only in samples with P2 BEP less than 2×10−4 Torr. Its capture cross section was 4.5×10−15 cm2. This trap is attributed to VP-related complexes. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358911
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  • 4
    Electronic Resource
    Electronic Resource
    Growth of Al nitride layers on GaAs(100) by reaction with condensed ammonia (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2623-2627 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An Al nitride-GaAs(100) bilayer formed by deposition of Al into a solid ammonia overlayer on GaAs(100) at T=100 K is studied using synchrotron radiation photoemission. Al does not react with NH3 to an appreciable amount at 100 K, but stable AlN layers are formed as the temperature of the substrate is raised to room temperature. The Al1−xNx layer formed is stable upon annealing up to 600 K, and detectable amounts of AlAs are not observed during deposition of 20 A(ring) of Al into NH3 or after heating the sample to 300 K and higher.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349374
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of substrate misorientation and background impurities on electron transport in molecular-beam-epitaxial-grown GaAs/AlGaAs modulation-doped quantum-well structures (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 954-960 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single GaAs quantum wells, clad with Al0.3Ga0.7As, and modulation doped with silicon introduced in the Al0.3Ga0.7As after the quantum wells are grown have been grown by molecular-beam epitaxy on GaAs substrates tilted a few degrees from the nominal (001) plane towards either of the (111) planes. The low-field two-dimensional electron gas mobility is observed to be a function of the tilt angle (0°, 2°, 4°, 6.5°) and of the direction of tilt [towards (111)A or (111)B]. The two-dimensional electron gas mobilities in quantum-well structures grown on substrates tilted towards (111)A are larger than those in structures grown on nominally flat (001) substrates. The improvement in two-dimensional electron gas transport is attributed to an improvement in the quality of the inverted interface (i.e., GaAs grown on AlGaAs). Quantum wells grown on substrates tilted toward (111)A also exhibit larger two-dimensional electron gas mobilities than quantum wells grown on substrates tilted toward (111)B for a given angle of tilt. For quantum-well structures where interface scattering from the inverted interface is significant, the two-dimensional electron gas mobility is observed to be anisotropic and larger in the [110] direction in comparison to the [1¯10] direction. The anisotropy in electron transport in the GaAs quantum well is observed to be larger for structures where the substrate tilt is towards (111)B in comparison to (111)A. For quantum wells grown on substrates tilted toward (111)A the anisotropy in two-dimensional electron gas mobility gets progressively larger as the tilt angle gets smaller. Larger molecular-beam epitaxy machine background impurity concentrations are observed to significantly increase the magnitude of the anisotropy in two-dimensional electron gas mobility suggesting that impurities and/or defects introduced during MBE growth are the origin of the anisotropic transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339707
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  • 6
    Electronic Resource
    Electronic Resource
    Anisotropic transport in modulation-doped quantum-well structures (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 2301-2306 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Anisotropic electron transport has been observed in GaAs modulation-doped quantum wells grown by molecular-beam epitaxy on a thick (001) Al0.3Ga0.7As buffer grown at 620 °C. The low-field electron mobility at 77 K in the [110] direction is a factor of 2 larger than the mobility in the [1¯10] direction for a 90-A(ring) quantum well. Thicker quantum wells (150, 200, and 300 A(ring)) show progressively less anisotropy, which vanishes for a 300-A(ring) quantum well. The degree of anisotropy is also reduced or eliminated by suspending growth of the Al0.3Ga0.7As for a period of 300 s prior to growing the GaAs quantum well. Growing the Al0.3Ga0.7As buffer at higher temperatures (680 °C) also reduces the degree of anisotropy. Higher two-dimensional electron gas sheet densities result in less anisotropy. The anisotropy is eliminated by replacing the thick Al0.3Ga0.7As buffer with a periodic multilayer structure comprising 15 A(ring) of GaAs and 200 A(ring) of Al0.3Ga0.7As. The degree of anisotropy is related to the thickness and growth parameters of the Al0.3Ga0.7As layer grown just prior to the growth of the GaAs quantum well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337940
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  • 7
    Electronic Resource
    Electronic Resource
    Influence of substrate misorientation on defect and impurity incorporation in GaAs/AlGaAs heterostructures grown by molecular-beam epitaxy (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 5115-5120 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaAs/AlGaAs heterostructures have been grown by molecular-beam epitaxy on GaAs substrates intentionally oriented (tilted) a few degrees (0–6.5) off the (001) plane towards either (111)A, (111)B, or (011). We observe that the 4-K photoluminescence and low-field electron transport properties of these structures may be functions of the substrate tilt angle and tilt direction depending on the concentration of impurities incorporated during growth. A substrate tilt during molecular-beam epitaxy is observed to have the largest effect on these properties when the background impurity concentration in the molecular-beam epitaxial machine is high. This supports our contention that the observed changes in material characteristics are due to differences in the incorporation of defects and impurities. The incorporation of defects and impurities are reduced by using substrates tilted toward (111)A in comparison to nominally flat (001) substrates or substrates tilted toward (111)B.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340412
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  • 8
    Electronic Resource
    Electronic Resource
    Anomalous redistribution of beryllium in GaAs grown by molecular beam epitaxy (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 4130-4134 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The purpose of this study is to investigate anomalous redistribution of beryllium (Be) in GaAs grown by molecular beam epitaxy (MBE). A concentration-dependent diffusion coefficient for Be is found from the substitutional-interstitial diffusion model. The importance of the generation of BeI from Ga point defects (vacancies or interstitials) in the diffusion process is also presented. Extremely rapid interstitial diffusion during growth, on the order of 30 μm in 1 h at 680 °C, has also been observed. This effect begins to occur for hole concentrations above 1019/cm3. Unintentional incorporation of Be into GaAs grown after closing the Be shutter is also presented. Consideration of the surface concentration of Be during MBE growth facilitates the explanation of this memory effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335543
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  • 9
    Electronic Resource
    Electronic Resource
    Properties of AlxGa1−xAs (xAl(approximately-equal-to)0.3) grown by molecular-beam epitaxy on misoriented substrates (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 1508-1512 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of substrate misorientation on the morphological and optical properties of AlxGa1−xAs (xAl(approximately-equal-to)0.3) grown by molecular-beam epitaxy (MBE) have been studied. The substrate temperatures and V/III beam-flux ratios used were such that layers grown on nominally (100) substrates typically exhibited rough morphologies and poor 4.2 K PL characteristics. By intentionally misorienting the substrate slightly from (100), smooth layers can be grown at 620 and 650 °C at typical MBE growth rates ((approximately-equal-to)1 μm/h). These smooth layers also exhibited sharp, exciton-related emission peaks at 4.2 K with half-widths as narrow as 5 meV. Since rough surfaces may lead to poor interfaces between GaAs and (Al,Ga)As and in turn to degraded performance in heterojunction devices, the present results may have significant implications for the performance of such structures grown by MBE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336456
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  • 10
    Electronic Resource
    Electronic Resource
    Defect structure and intermixing of ion-implanted AlxGa1−xAs/GaAs superlattices (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 120-123 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cross-sectional transmission electron microscopy and Raman spectroscopy have been used to study the defect structure and intermixing of annealed ion-implanted Al0.3Ga0.7As/GaAs superlattices. The results show clearly that the amount and depth of superlattice layer intermixing depends on the ion mass. In superlattices that retain their structure after implantation and annealing, the distribution of defect clusters (primarily interstitial loops) is inhomogeneous; most defect clusters are nucleated in the GaAs layers. Examination of unannealed superlattice samples reveals that ion beam damage occurs preferentially in the GaAs layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336852
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