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  • 1
    Electronic Resource
    Electronic Resource
    Saturation current and excess carrier distribution in exponentially graded p-n junctions (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5033-5040 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Excess carrier distribution and saturation current generated by a graded p-n junction are investigated, approximating the dopant profile by an exponential function. Analytical solutions of the steady-state continuity equation are presented for lifetime dominated by Auger, radiative, or Shockley–Read recombination mechanisms, for both ohmic and electrically reflecting boundary conditions. The saturation current generated by the graded region is derived for each of the dominant mechanisms and boundary conditions. Unlike previous published works the result of this analysis is a set of concise analytical expressions that make them a useful tool for simulation and investigation of graded structures such as silicon solar cells. The results are calculated for HgCdTe diodes, demonstrating the effect of the profile slope as determined by surface and bulk concentrations and junction depth. It is shown that the contribution of the graded region to the saturation current, as compared to that of the substrate, is significant, and that by proper selection of the diode parameters it is possible to substantially reduce this contribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350604
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  • 2
    Electronic Resource
    Electronic Resource
    Reflecting boundary conditions for graded p-n junctions (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 865-867 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a graded junction, the formalism for handling reflecting boundary conditions must be modified. Since a significant drift term is present, zero recombination velocity at the surface does not imply a zero excess carrier gradient but rather zero overall flux. A model for analyzing p-n junctions fabricated by implantation or diffusion is presented, assuming the dominant recombination mechanism in the graded region is Auger. The model enables optimization of diode design. By proper selection of parameters, mainly by reducing surface concentration or by increasing the steepness of the dopant profile, it is possible to drastically reduce the saturation current generated by the graded region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346771
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  • 3
    Electronic Resource
    Electronic Resource
    Subband quantum scattering times for AlGaAs/GaAs obtained using digital filtering (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3940-3944 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this study we investigate both the transport and quantum scattering times as a function of the carrier concentration for a modulation doped Al0.3Ga0.7As/GaAs structure. Carriers in the well are generated as a result of the persistent photoconductivity effect. When more than one subband becomes populated, digital filtering is used to separate the components for each of the excited subbands. We find that the quantum scattering time for the ground subband increases initially as the carrier concentration is increased. However, once the second subband becomes populated, the ground subband scattering time begins to decrease. The quantum scattering time for the excited subband is also observed to decrease as the concentration is increased. Our results are consistent with the theoretical results by A. Isihara and L. Smrcka [J. Phys. C 19, 6777 (1986)]. Finally, from the ratio of the transport and quantum scattering times, it is seen that the transport in the well becomes more isotropic as the concentration is increased. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359913
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  • 4
    Electronic Resource
    Electronic Resource
    Two carrier analysis of persistent photoconductivity in modulation-doped structures (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 321-329 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simultaneous fit of Hall and conductivity data gives quantitative results on the carrier concentration and mobility in both the quantum well and the parallel conduction channel. In this study this method was applied to reveal several new findings on the effect of persistent photoconductivity (PPC) on free-carrier concentrations and mobilities. The increase in the two-dimensional electron-gas (2DEG) concentration is significantly smaller than the apparent one derived from single carrier analysis of the Hall coefficient. In the two types of structures investigated, delta doped and continuously doped barrier, the apparent concentration almost doubles following illumination, while analysis reveals an increase of about 20% in the 2DEG. The effect of PPC on mobility depends on the structure. For the sample with a continuously doped barrier the mobility in the quantum well more than doubles. This increase is attributed to the effective screening of the ionized donors by the large electron concentration in the barrier. In the delta doped barrier sample the mobility is reduced by almost a factor of 2. This decrease is probably caused by strong coupling between the two wells, as is demonstrated by self-consistent analysis. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360679
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  • 5
    Electronic Resource
    Electronic Resource
    Photoresponse of semiconductor on semi-insulator structure (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5321-5325 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new type of photoconductivity is demonstrated in a p-type GaAs epitaxial layer grown on a semi-insulating substrate. Rather than increasing the hole concentration in the epilayer, the photons absorbed in the substrate reduce the junction depletion region, thus increasing the thickness of the conducting path in the epilayer. Small photon fluxes increase drastically the conductance of the structure. A flux of 3×1013 cm−2 s−1 is sufficient to double the conductance at room temperature. Voltage responsivities of the order of 5×106 V/W were obtained at a wavelength of 0.84 μm at room temperature. Hall measurements indicate that the total hole concentration increases slowly at low fluxes (below 1015 cm−2 s−1) and steeply at higher ones. These two regions correspond to two processes contributing to the increased population. Photons absorbed in the substrate, originally n type, turn it into p type in the vicinity of the junction, since the lifetime of holes, dominated by recombination with EL2 traps, is four orders of magnitude larger than that of electrons. Thus, the configuration changes from a p/n junction to p/p−. Hence, the depletion region is reduced significantly and the conductance increases accordingly. At higher intensities the hole concentration in the substrate becomes the dominant component in the integral hole concentration thus increasing linearly with photon flux. This process saturates as the injection starts affecting trap occupancy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355734
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  • 6
    Electronic Resource
    Electronic Resource
    Polarization dependence of spectral transmission and photoconductive response of a p-doped multiple quantum well structure (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1998-2000 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comparison between the optical transmission and the photoconductive response of p-type quantum well infrared photodetectors is demonstrated. The dependence on polarization was found to be different for these two processes. Light polarized perpendicular to the growth layers was more efficiently absorbed by the quantum wells, while the photoconductive response was stronger for the parallel polarized light. The difference is attributed to the different vertical transport behavior of light and heavy holes and the mixed nature of hole subbands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357667
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of the transport properties of channel delta-doped structures by light-modulated Shubnikov–de Haas measurements (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6626-6632 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transport properties of channel delta-doped quantum-well structures were characterized by conventional Hall effect and light-modulated Shubnikov–de Haas (SdH) effect measurements. The large number of carriers that become available due to the delta doping of the channel, leads to an apparent degeneracy in the well. As a result of this degeneracy, the carrier mobility remains constant as a function of temperature from 300 down to 1.4 K. The large amount of impurity scattering, associated with the overlap of the charge carriers and the dopants, resulted in low carrier mobilities and restricted the observation of the oscillatory magnetoresistance used to characterize the two-dimensional electron gas by conventional SdH measurements. By light modulating the carriers, we were able to observe the SdH oscillation at low magnetic fields, below 1.4 T, and derive a value for the quantum scattering time. Our results for the ratio of the transport and quantum scattering times are lower than those previously measured for similar structures using much higher magnetic fields. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360484
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  • 8
    Electronic Resource
    Electronic Resource
    Calculation of semiconductor intrinsic properties using a nonparabolic three-band model (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 411-413 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The intrinsic carrier concentration and the Fermi level are calculated using an approximation of the three-band k⋅p model. The approach is suitable for temperatures from 0 to 400 K and includes the contribution of electrons in the lowest conduction band, heavy holes, and light holes. An approximation for the nonparabolic Fermi–Dirac integral is used in the calculation of carrier concentrations. The resulting expressions are simple and depend explicitly on temperature, semiconductor band gap, carrier effective masses, and nonparabolicity factors. Consequently, the present approach seems suitable for the calculation of intrinsic properties of any semiconductor material for which the three-band k⋅p model is applicable. The model is compared with a numerical integration of the k⋅p model for Hg1−xCdxTe (0.17〈x〈1) and with experimental measurements (0.2〈x〈0.29). We also present a comparison between the model and a numerical evaluation of the three-band model for InGaAs. Because of their simplicity the new expressions seem suitable for both numerical and analytical modeling of semiconductor devices and materials. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359341
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  • 9
    Electronic Resource
    Electronic Resource
    Analysis of transients in semiconductor/semi-insulator junctions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2035-2041 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A junction between an epitaxial semiconductor and a semi-insulating substrate serves as a tool for analyzing transient behavior in semi-insulators (SI). At equilibrium a narrow region which is fully depleted from electrons exists in the SI. The application of a reverse bias results in an additional partially depleted region, initially depleted just from free carriers, adjacent to the fully depleted one. As the transient progresses electrons are released from the deep traps in the SI. The partially depleted region collapses into a wider fully depleted region. This process is manifested by a substantial current transient through the SI. The charges emitted recombine in the epitaxial layer leading to a decrease in its conductance due to a narrowing conducting path. Thus it is possible to characterize this process by measuring the (large) current through the epilayer rather than the (small) current through the SI. These transients are a function of the emission coefficient. Their analysis provides data also on the energy gap of the traps, their capture coefficient, and the electron lifetime. The long decays can be accelerated by illuminating with photons of energy below the band gap but larger than the energy spacing between the deep traps and the conduction band.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356305
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  • 10
    Electronic Resource
    Electronic Resource
    Laser beam interference effects on the photovoltage of a p-n junction diode (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5459-5463 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photovoltage developed by a p-n junction diode illuminated by an interference pattern through a slit depends both on the distance between fringes and the phase of the interference pattern relative to the position of the slit. For a slit width which accommodates an integer number N of fringes, the voltage is independent of the phase of the pattern but this is no longer the case for a noninteger number of fringes. The maximum dependence is observed for N+1/2 fringes within the slit but the effect decreases as N increases. When the fringe distance is no longer negligible compared to the minority carrier diffusion length the dependence of the photovoltage on the number of fringes becomes more pronounced. A theory is presented which shows how the diffusion length can be obtained from the experimental data. Experiments on GaAs and Si diodes are reported. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362735
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