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  • 1
    Electronic Resource
    Electronic Resource
    Growth modes and microstructures of ZnO layers deposited by plasma-assisted molecular-beam epitaxy on (0001) sapphire (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 5115-5119 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transmission electron microscopy and high resolution x-ray diffraction are used to characterize defects in ZnO layers grown by plasma-assisted molecular-beam epitaxy on (0001) sapphire. Two- and three-dimensional types of growth modes are described and the observed mosaic structure is analyzed in each case. It is found that two-dimensional layers exhibit a roughness as low as 6 nm. Their subdomains have small lateral coherence lengths and a mean in-plane misorientation of ±0.4°, leading to an important dislocation density of 1–4×1010 cm−2. On the contrary, it is demonstrated that, through numerous interactions between dislocations, the three-dimensional growth mode leads to a better structural quality with a larger lateral coherence length and a smaller in-plane mosaic spread of ±0.07°. The total dislocation density is consequently reduced by 1 order of magnitude down to 3–5×109 cm−2 and the radical modification of the structure results in a change of the dislocation distribution. Our results thus demonstrate that two-dimensional growth mode and low full width at half maximum for symmetric x-ray diffraction are a not reliable indicator of a good structural quality. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1412572
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  • 2
    Electronic Resource
    Electronic Resource
    Built-in electric-field effects in wurtzite AlGaN/GaN quantum wells (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3714-3720 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: AlGaN/GaN quantum well (QW) structures are grown on c-plane sapphire substrates by molecular beam epitaxy. Control at the monolayer scale of the well thickness is achieved and sharp QW interfaces are demonstrated by the low photoluminescence linewidth. The QW transition energy as a function of the well width evidences a quantum-confined Stark effect due to the presence of a strong built-in electric field. Its origin is discussed in terms of piezoelectricity and spontaneous polarization. Its magnitude versus the Al mole fraction is determined. The role of the sample structure geometry on the electric field is exemplified by changing the thickness of the AlGaN barriers in multiple-QW structures. Straightforward electrostatic arguments well account for the overall trends of the electric-field variations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371241
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  • 3
    Electronic Resource
    Electronic Resource
    Buffer free direct growth of GaN on 6H–SiC by metalorganic vapor phase epitaxy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 577-583 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth of GaN on 6H–SiC is three dimensional (3D) and results in the formation of large islands presenting hexagonal truncated shape with {1–101} lateral facets and a top {0001} facet. In this work, we present a three steps growth process that enables us to grow high quality mirrorlike GaN layers without using AlN buffer layers. During a first step, a thin 3D GaN layer is deposited at high temperature. This layer is smoothed under ammonia flow for several minutes when the growth is interrupted. The subsequent growth of GaN is two dimensional. 600 nm thick GaN films were grown. They were analyzed by high resolution x-ray diffraction, reflectivity, and photoluminescence. All the layers are under strong tensile biaxial strain. The correlation between residual tensile strain in GaN layers and their optical properties is reported for biaxial deformations cursive-epsilonxx ranging up to 0.37%. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371902
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  • 4
    Electronic Resource
    Electronic Resource
    Structural and optical characterization of ZnSe single crystals grown by solid-phase recrystallization (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2983-2989 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate by high-resolution x-ray diffraction (HRXRD), temperature-dependent photoluminescence (PL) and reflectivity spectroscopies, and low-temperature selective-photoluminescence spectroscopy ZnSe single crystals grown by solid-phase recrystallization. HRXRD reveals the high structural perfection of the samples which exhibit rocking-curve linewidths in the 15–20 arcsec range. The low-temperature PL spectra are dominated by the so-called Ideep1 excitonic line, a neutral-acceptor bound-exciton line I1, the free-exciton emission FX, and the n=2 excited state of FX. We identify the main residual impurities to be Li acceptors. Donor–acceptor pair bands are very hardly detected at low temperature which indicates a low donor content. A major characteristics of these samples is the quasi-absence of any Cu-related deep emission which generally plagues the PL spectra of bulk ZnSe. Consequently, Ideep1 is ascribed to Zn-vacancy–donor complexes. Finally, from the temperature dependence of the PL emission and reflectivity, the band-gap energy of bulk ZnSe is found to linearly shrink with the temperature above 80 K at a rate of −4.3×10−4 eV K−1. The room-temperature gap is estimated to 2720±2 meV. Our results indicate that solid-phase recrystallization produces ZnSe samples with the highest structural quality and purity achievable at present time. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363155
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  • 5
    Electronic Resource
    Electronic Resource
    (001) GaAs substrate preparation for direct ZnSe heteroepitaxy (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 7012-7017 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the influence of the (001) GaAs substrate preparation on the first stages of ZnSe heteroepitaxial growth by molecular beam epitaxy. We show that three different GaAs reconstructions occur depending on the ex situ substrate preparation, the Se residual pressure in the growth chamber and the temperature of heating. After deoxidation, an epiready substrate leads to a (2×1)-reconstructed surface at high temperature (∼600 °C) which turns into an unreconstructed surface when cooling down to the growth temperature (280 °C). An etched substrate, on the other hand, exhibits a (2×3) or a (4×3) reconstruction depending on the temperature reached during deoxidation. Both reconstructions are stable upon cooling down to the growth temperature. Direct nucleation of ZnSe on such deoxidized substrates leads to three-dimensional (3D), quasi two-dimensional (2D) and purely 2D growth modes on the unreconstructed, (2×3) and (4×3) reconstructed surfaces, respectively. Very pronounced oscillations of the reflection high-energy electron diffraction intensity are observed during nucleation on the (4×3) surface. Excellent agreement is obtained between simulated and experimental x-ray rocking curves for pseudomorphic layers grown on a (4×3) starting surface. In addition, their low-temperature photoluminescence spectra are dominated by free exciton recombinations without any defect-related line. Our results thus demonstrate that we have achieved a substantial improvement of ZnSe heteroepitaxy on bare GaAs substrates. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365266
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  • 6
    Electronic Resource
    Electronic Resource
    Gas source molecular beam epitaxy of wurtzite GaN on sapphire substrates using GaN buffer layers (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 240-242 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Wurtzite GaN was grown by gas source molecular beam epitaxy on (0001) sapphire substrates. Taking advantage of the catalytic decomposition of ammonia on the growing surface, high growth rates (〉1 μm/h) were achieved for substrate temperatures ranging between 800 and 850 °C. Surface morphology, structural, and optical properties of thick (2–4 μm) GaN films were investigated versus the growth temperature of the GaN buffer layer. It is shown that this parameter has a drastic influence on the GaN properties. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119526
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  • 7
    Electronic Resource
    Electronic Resource
    Epitaxial relationships between GaN and Al2O3(0001) substrates (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 643-645 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaN thin layers (200 Å) were grown by gas-source molecular beam epitaxy on c-plane Al2O3 substrates. Transmission electron microscopy reveals that two different epitaxial relationships may occur. The well-known GaN orientation with the c axis perpendicular to the Al2O3 surface and [11¯00]GaN||[112¯0]Al2O3 is observed when the substrate is nitridated prior to the growth. On the other hand, GaN layers deposited on bare Al2O3 surfaces exhibit a different crystallographic orientation: [112¯0]GaN||[11¯00]Al2O3 and [11¯03]GaN||[112¯0]Al2O3. This corresponds to a tilt of about 19° of the c axis with respect to the substrate surface. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118205
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  • 8
    Electronic Resource
    Electronic Resource
    Structural and optical properties of lattice-matched ZnBeSe layers grown by molecular-beam epitaxy onto GaAs substrates (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 3564-3566 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the molecular-beam epitaxy of ZnBeSe ternary alloys lattice matched onto GaAs substrates. We demonstrate that these alloys can be grown with a high structural perfection. X-ray linewidths down to 27 arcsec are obtained even though the growth is carried out on bare substrates. Transmission electron microscopy reveals the high quality of the interface. Photoluminescence spectra of undoped layers are dominated by free-exciton recombinations. The excitonic gap is determined to be 2.863 eV at 9 K. Finally, high carrier concentrations are obtained for both n-type and p-type doping. These results are promising in view of fabricating laser diodes with this material system. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119234
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  • 9
    Electronic Resource
    Electronic Resource
    Critical thickness of Zn1−xCdxSe/ZnSe heterostructures grown on relaxed ZnSe buffer layers on bare GaAs substrates (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 217-219 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study through high-resolution x-ray diffraction (HRXRD) and photoluminescence spectroscopy a series of Zn1−xCdxSe/ZnSe multi-quantum-well heterostructures grown by molecular-beam epitaxy on relaxed ZnSe buffer layers, themselves grown on bare GaAs substrates. We show that HRXRD experiments combined with simulations allow one to accurately assess the strain state of the heterostructures which appear to follow closely the Matthews and Blakeslee model [J. Cryst. Growth 27, 118 (1974)]. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120690
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  • 10
    Electronic Resource
    Electronic Resource
    Indium incorporation above 800 °C during metalorganic vapor phase epitaxy of InGaN (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2587-2589 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the indium incorporation into InGaN ternary alloys during low-pressure metalorganic vapor-phase epitaxy as a function of the trimethylindium flow and the growth temperature in the 800–860 °C range. Partially relaxed InxGa1−xN bulk films with indium compositions 0.02(approximately-less-than)x(approximately-less-than)0.14 have been grown. In relation to the band-gap energy at room temperature, determined by photothermal deflection spectroscopy, we find a downward band-gap bowing of 2.65±0.15 eV. The required change of the trimethylindium flow as a function of the growth temperature, necessary to obtain isocomposition InGaN films, can be described by an Arrhenius law. We find an indium desorption energy of 0.8±0.3 eV. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125086
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