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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Short-circuit current and energy efficiency enhancement in a low-dimensional structure photovoltaic device (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 135-137 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the forward bias behavior of AlGaAs/GaAs p-i-n multiquantum well (MQW) photodiodes. In samples with low background impurity levels in the intrinsic region the high quantum efficiency observed in reverse bias is maintained into forward bias even for carriers photoexcited in the wells. We compare our MQW devices with structures which are identical apart from having AlGaAs intrinsic regions without quantum wells. The short-circuit currents in the MQW structures are much higher than in the control samples though the open-circuit voltages are somewhat smaller. In one case the energy conversion efficiency of the MQW device in white light is 110% higher than the control. We discuss the implications of our results for the development of low-dimensional structure solar cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105553
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  • 7
    Electronic Resource
    Electronic Resource
    Gallium desorption from GaAs and (Al,Ga)As during molecular beam epitaxy growth at high temperatures (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 1203-1205 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct measurements of the desorption rate of gallium from GaAs and (Al,Ga)As during growth by molecular beam epitaxy at high temperatures have been made by modulated beam mass spectrometry. The activation energy for desorption is dependent upon the nature of the site from which the gallium is lost. From free gallium atoms not incorporated into the lattice, behavior similar to that encountered under equilibrium conditions for gallium over gallium or gallium over GaAs is observed. For gallium lost from the GaAs lattice the apparent activation energy is higher and is influenced by the arsenic flux reaching the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103485
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  • 8
    Electronic Resource
    Electronic Resource
    Recombination processes in quantum well lasers with superlattice barriers (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2380-2382 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spontaneous emission spectra from GaAs quantum well lasers grown by molecular beam epitaxy show that the radiative recombination rate in (AlAs)(GaAs) superlattice barriers is greater than in alloy barriers of the same average composition (x=0.25) due to reduction in effective gap by superlattice effects. Measurements of emission spectra as functions of temperature show that these radiative processes account for a significant part of the temperature variation of the threshold current and we estimate that the nonradiative lifetime in the superlattice barriers is an order of magnitude longer than in alloy barriers grown under similar conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102023
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  • 9
    Electronic Resource
    Electronic Resource
    Temperature dependence of spontaneous emission in GaAs-AlGaAs quantum well lasers (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1167-1169 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using quantum well laser devices with a window in the p-type contact, we have measured the relative change of spontaneous emission intensity at threshold with temperature for 58-A(ring)-wide GaAs wells. Over the range 250–340 K the data are in good agreement with the linear relation obtained from a gain-current calculation which includes transition broadening. This linear behavior contrasts with the stronger temperature dependence of the total measured threshold current of the same devices which includes nonradiative barrier recombination processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101686
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  • 10
    Electronic Resource
    Electronic Resource
    Slope resistance characteristics of GaAs-(Al,Ga)As-GaAs single barrier structures (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 305-307 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of the incremental slope resistance of a GaAs-(Al,Ga)As-GaAs single barrier structure have been made at temperatures between 70 and 230 K. In contrast with other work we deliberately concentrate on the region close to zero applied bias. The deficiencies in the often-used Wentzel–Kramers–Brillouin analysis of the electrical characteristics are exposed in this regime, and an exact, Airy function approach is found to be essential to describe our observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99501
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