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  • 1
    Electronic Resource
    Electronic Resource
    Resonant polaron effects on impurity metastable states in n-GaAs (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3698-3700 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Resonant polaron effects on donor metastable states in n-GaAs have been studied using far infrared Fourier transform magneto-spectroscopy in the 100 –350 cm−1 region. From the observed splitting and pinning effects, absolute values for the matrix elements of the electron-phonon interaction between the ||3,1,0〉||0〉 and ||4,1,0〉||0〉 states on the one hand, and the ||1s0〉||1〉 and ||2p−1〉||1〉 states on the other hand are deduced. The energy splitting at resonance appear to be about a factor of two smaller than those for the corresponding Landau levels, and to depend less strongly on the quantum number N.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356040
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  • 2
    Electronic Resource
    Electronic Resource
    Band gap of GaN films grown by molecular-beam epitaxy on GaAs and GaP substrates (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1838-1842 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: There has been controversy concerning the energy gap of the cubic (zinc-blende) form of the wide-gap semiconductor GaN. Measurements are reported of the band gaps of both hexagonal (wurtzite) and cubic thin films deposited by a modified molecular-beam-epitaxy process on (001) GaAs and GaP substrates. The important difference from conventional MBE lies in the method of supplying nitrogen to the growing film. Here a rf nitrogen plasma source operating at 13 MHz is used. The structure of the films was monitored by x-ray diffraction and controlled by the addition of an As beam which results in growth of the cubic form—otherwise films grow with the hexagonal structure. The band gaps were measured at room temperature by optical reflectivity, as evidenced by the sharp reduction in interference oscillations as the photon energy approached the band edge, and confirmed by the observation of band-edge photoluminescence. The results can be summarized as Eg=3.42±0.02 eV for the hexagonal and 3.22±0.02 eV for the cubic form. The observation of films containing mixed hexagonal and cubic phases, which may have led to earlier errors in band-gap measurements, is also reported. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360217
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  • 3
    Electronic Resource
    Electronic Resource
    Identification and ionization energies of the shallow donor metastable states in GaAs:Si (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6323-6328 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transitions from the 1s0 ground state to the shallow donor metastable states in n-GaAs have been investigated at a temperature of T=4.2 K, magnetic fields up to 6 T, and for far-infrared transition energies between 50 and 300 cm−1. The final states of these transitions have been identified and characterized by high-field quantum numbers. The magnetic-field dependence of the ionization energies of some of these metastable states have been determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345151
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  • 4
    Electronic Resource
    Electronic Resource
    Selection criteria for AlGaAs-GaAs heterostructures in view of their use as a quantum Hall resistance standard (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3487-3497 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of several practical properties of GaAs-AlGaAs heterostructures on the accuracy of a quantum-Hall resistance standard at a level of 1:108 are discussed. Conduction through a parallel layer, metallic current contacts, homogeneity of the electron density, sample size, and mobility are addressed. Measurements are presented concerning the influences of sample size and mobility. As regards mobility, the slope of the Hall plateau, longitudinal resistance, and critical current have been investigated. Recommendations are given on sample geometry and mobility. Feasible measurement methods are presented to check the absence of a parallel conducting layer and the quality of the contacts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342619
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  • 5
    Electronic Resource
    Electronic Resource
    Photoluminescence decay time studies of type II GaAs/AlAs quantum-well structures (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3606-3609 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the temperature dependence of the photoluminescence (PL) decay kinetics of a series of GaAs/AlAs quantum-well structures where the GaAs thickness was kept constant at 25 A(ring) and the AlAs was varied between 41 and 19 A(ring). In these structures the band alignment is type II and the dominant photoluminescence process at 4 K is due to recombination of excitons involving electrons confined at the AlAs X point and holes in the GaAs. At 4 K on the low-energy side of the zero-phonon type II transition the PL decay is a single exponential over at least two decades. The time constant of this decay is a strong function of the AlAs layer thickness. The variation of this decay time is described by a change in the oscillator strength of the type II process due to the change in the mixing between the Xz (AlAs) electron states and the Γ (GaAs) electron states. At higher temperatures (T〉15 K) the photoluminescence intensity and the decay time decrease very rapidly with increasing temperature. This is due to the increased influence of nonradiative processes as the type II excitons become delocalized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342640
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of undoped GaAs spacers on the characteristics of GaAs-(Al,Ga)As-GaAs single barrier structures (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1183-1188 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of undoped spacer layers on the electrical properties of single barrier heterostructures (both alloy and superlattice) have been investigated by measuring incremental slope resistance over the bias range −400 to +400 mV and at convenient temperature intervals between 70 and 290 K. The zero bias slope resistance, Rs(0), and the effective barrier heights increase with spacer thickness. Also, the low-temperature slope resistances, Rs(V), decrease exponentially with the magnitude of the bias, V, while the effective barrier heights, deduced from high-temperature measurements, decrease approximately linearly. This suggests that the decrease in Rs(V) with bias is due simply to the voltage-induced decrease in effective barrier height. Rs(0) varies exponentially with zero bias effective barrier height for both alloy and superlattice barriers and this is consistent with the Γ electrons dominating the current transport through the barriers. All of our Rs(V) curves are asymmetric and, using Airy function calculations, we have modeled curves similar to the experimental ones by assuming different doping levels for the two doped GaAs layers on either side of the barriers. This is possibly due to Si migration into the "undoped'' barrier or the spacer layer closest to the substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343061
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  • 7
    Electronic Resource
    Electronic Resource
    Energy relaxation by hot electrons in n-GaN epilayers (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 973-979 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The energy relaxation rate for hot electrons in n-type GaN epilayers has been measured over the temperature range 1.5–300 K. Several samples grown by molecular-beam epitaxy and having different electron concentrations have been studied. At low electron temperatures (Te〈20 K), the energy relaxation is via acoustic phonon emission. The magnitude and temperature dependence of the energy relaxation are found to be in good agreement with theoretical calculations using appropriate values of the deformation potential and piezoelectric coupling constants and ignoring screening. For Te≥70 K, the dominant mechanism of energy loss is optic phonon emission. For the several samples studied, consistent values of the optic phonon energy and electron-optic phonon relaxation time, 90±4 meV and 5–10 fs, respectively, are measured. The energy agrees well with values obtained by other methods and the relaxation time is consistent with theoretical calculations of the Fröhlich interaction and indicate that hot phonon effects are absent up to 10−8 W/electron dissipation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1334642
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  • 8
    Electronic Resource
    Electronic Resource
    Two-dimensional electron gas structures with mobilities in excess of 3×106 cm2 V−1 s−1 (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 1219-1221 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have demonstrated that the mobility of two-dimensional electron gas (2DEG) structures shows a gradual improvement with the number of uninterrupted growth runs in the molecular-beam-epitaxy system. Some, but not all, of this improvement can be attributed to the cleanup of the GaAs layers in the structure, and we suggest that there is a corresponding cleanup of the (Al,Ga)As which is also influencing the mobility. Once the system has passed the cleanup phase, a systematic trend of carrier density and mobility with undoped spacer thickness was observed, with a peak mobility at 4 K of 2.12×106 cm2 V−1 s−1 for a sheet carrier density of 2×10−11 cm−2 occurring at a spacer thickness of 800 A(ring). A further increase in mobility was achieved by using a thicker region of doped (Al,Ga)As, thereby moving the ionized centers in the surface depletion layer further away from the 2DEG. This has enabled us to produce a sample with mobility at 4 K of 3.1×106 cm2 V−1 s−1 (at a sheet charge of 3.1×1011 cm−2)—the first time such a value, to our knowledge, has been reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338174
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  • 9
    Electronic Resource
    Electronic Resource
    Modeling the spectral response of the quantum well solar cell (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 614-621 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The quantum well solar cell is an alternative to more conventional multiband gap approaches to higher cell efficiency. Preliminary studies have shown that the insertion of a series of quantum wells into the depletion region of a GaAs/AlxGa1−xAs p-i-n solar cell can significantly enhance the cell's short-circuit current. We present here a model for the spectral response of GaAs and AlxGa1−xAs p-n and p-i-n solar cells, with and without quantum wells, based on a standard solution of the minority-carrier equations. Particular emphasis is placed on modeling the absorption coefficient of the AlxGa1−xAs and of the quantum wells. We find that our model can accurately predict the spectral response of a wide variety of cells: both conventional p-n junctions in GaAs and AlxGa1−xAs, and various geometries of quantum well solar cell in AlxGa1−xAs/GaAs (x∼0.3). We discuss the strengths and weaknesses of the model and its underlying assumptions, and conclude by using the model to design p-i-n quantum well solar cells with higher short-circuit current outputs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355275
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  • 10
    Electronic Resource
    Electronic Resource
    Low-power, all-optical nonlinear absorption in asymmetric double quantum wells (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2889-2891 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate all-optical nonlinearities at low cw pump powers (50 W/cm2) using a novel heterostructure design which spatially separates photoexcited electron-hole pairs. Theoretical calculations based on many-body interactions are in good agreement with the measured spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104738
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