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  • 1
    Electronic Resource
    Electronic Resource
    Modeling of a low-intensity electro-optical semiconductor switching device due to intrinsic photoconductivity (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2522-2528 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An electro-optical device consisting of a stack of undoped alternating layers of narrow- and wide-gap materials (e.g., GaAs/AlGaAs) together with a series resistor under constant voltage bias is analyzed theoretically. The GaAs heterolayers with a width in the order of a carrier mean free-path are a photo-active region of this vertical device. The device operates only in the presence of a low-intensity light beam due to the intrinsic photoconductivity of the active region. The Franz–Keldysh effect, the strong accumulation of the photocarriers in the photo-active layers due to the charge separation in the presence of the static electric field, and the ballistic component of the total current are responsible for the unusually large electro-optical nonlinearity of the device. Kirchhoff's law for the electrical circuit of the device provides a sensitive feedback between the voltage drop over the layer and the photocurrent. In a Fabry–Perot cavity a room temperature electro-optical bistabitity is obtained at light intensities less than 10 mW/cm2 with a switching time of about 100 ns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357613
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  • 2
    Electronic Resource
    Electronic Resource
    Carrier-induced reduction of the index of refraction of GaInP measured with distributed feedback lasers (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 3414-3416 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present new results on the effective refractive index of GaInP/AlGaInP distributed feedback (DFB) lasers with grating periods around 100 nm, operated at 77 K and at room temperature. Double heterostructure (DH) lasers as well as multiple quantum well lasers show DFB-laser emission at 300 K over a range of 15 nm. For the DH lasers a clear difference of absolute value and dispersion of the effective refractive index was observed between 77 and 300 K, which is explained by high carrier density effects. For a carrier density of N=2.5×1018 cm−3 the refractive index of GaInP decreases by 0.05, which is compared with an ab initio calculation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110157
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of the finite lateral potential barriers on the optical spectra of quantum well wires (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 2824-2826 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We calculate the plasma-density dependent optical absorption spectra of quantum well wires with finite lateral confinement with respect to the quantum well. The excitonic absorption spectrum consists of a series of resonances due to quantum wire as well as higher lying quantum well states. The calculations include phase-space filling, band-gap renormalization, and excitonic enhancement within the Hartree–Fock approximation. For a well depth of (approximately-equal-to)40 meV, which is a typical value for intermixed GaAs/AlGaAs quantum well wires, the line shape of the quantum wire absorption spectrum is shown to be strongly influenced by the presence of lateral barrier states for all plasma densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111437
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  • 4
    Electronic Resource
    Electronic Resource
    Study of the Coulomb Boltzmann kinetics in a quasi-twodimensional electron gas by eigenfunction expansions and Monte Carlo simulations (1992)
    Springer
    The European physical journal 86 (1992), S. 345-357 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract For carrier-carrier scattering the relaxation kinetics of a quasi-twodimensional degenerate electron gas is studied in the framework of the Boltzmann equation using a static RPA screening. The time development of an initial nonequilibrium distribution is calculated both by ensemble Monte Carlo simulations and by expansions in terms of eigenfunctions of the linearized collision operator. A systematic comparison of the results of both methods yields a rather detailed understanding of the Coulomb relaxation kinetics and of the strengths and limitations of both methods. The dependence of the relaxation rate on the position and width of the initial population deviation is investigated and conditions for nonexponential decay are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01323727
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  • 5
    Electronic Resource
    Electronic Resource
    Coulomb quantum kinetics in pulse-excited semiconductors (1993)
    Springer
    The European physical journal 92 (1993), S. 532-532 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320517
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  • 6
    Electronic Resource
    Electronic Resource
    Prominent cortical atrophy with neuronal loss as correlate of human immunodeficiency virus encephalopathy (1991)
    Springer
    Acta neuropathologica 82 (1991), S. 229-233 
    Details
    ISSN: 1432-0533
    Keywords: Human immunodeficiency virus ; Acquired immune deficiency syndrome (AIDS) ; Encephalopathy ; Cortical atrophy ; Morphometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A 25-year-old homosexual AIDS patient presented with progressive cognitive, motor and behavioral disturbances consistent with HIV encephalopathy. CT scans demonstrated progressive diffuse brain atrophy. Neuropathology showed predominant cortical changes including severe neuronal loss corroborated by morphometry. Only minimal changes were found in the white matter and basal ganglia. Immunocytochemistry for HIV stained occasional microglial cells more markedly in the cerebral cortex. This suggests that HIV infection of the brain may cause predominant cortical nerve cell loss, and that HIV encephalopathy is not necessarily due to white matter lesions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00294450
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  • 7
    Electronic Resource
    Electronic Resource
    Loss of neurons in the frontal cortex in AIDS brains (1990)
    Springer
    Acta neuropathologica 80 (1990), S. 92-94 
    Details
    ISSN: 1432-0533
    Keywords: Acquired immune deficiency syndrome (AIDS) ; Cerebral cortex ; Dementia ; Morphometry ; Neuronalloss
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Neurons of Area 11 in the fronto-orbital cortex of 18 unselected AIDS brains are analyzed by means of stereology. Neurological abnormalities including dementing symptoms were described in eight patients. Neuropathology diagnosed human immunodeficiency virus (HIV)-specific changes in four, and diffuse poliodystrophy in eight brains. The majority (71.4%) of these brains was immunoreactive for HIV antigens when tested by immunocytochemistry. A significant loss of neurons is found as compared to normal controls. Neuronal density in AIDS brains is reduced by 18%, and the perikaryon volume fractions is reduced by 31%. Although only speculation on pathogenesis of this neuronal loss is possible at present, it may represent a part of the pathomorphological substrate of AIDS-related dementia. Moreover, it confirms by quantitative means damage to the cerebral cortex in AIDS which has been described only qualitatively as diffuse poliodystrophy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00294228
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  • 8
    Electronic Resource
    Electronic Resource
    Neuronal damage in the cerebral cortex of AIDS brains: a morphometric study (1993)
    Springer
    Acta neuropathologica 85 (1993), S. 185-189 
    Details
    ISSN: 1432-0533
    Keywords: Morphometry ; Stereology ; Cerebral cortex ; HIV-encephalitis ; HIV-leukoencephalopathy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Using stereological methods, two cerebral cortical areas from AIDS brains were investigated. Neuronal density, profile area of neurons, and perikaryon volume fraction were measured and compared to age-matched control brains. In the fronto-orbital cortex (area 11) of AIDS brains, a significant loss of neurons was seen. The perikaryon volume fraction was likewise decreased. The size of neurons did not differ between control and AIDS brains. In patients with clinical signs of progressive dementia and in brains with human immunodeficiency virus (HIV)-specific neuropathology (HIV-leukoencephalopathy and/or HIV-encephalitis) as compared to patients lacking these features, a small decrease in neuronal density was noted but this difference did not reach the level of statistical significance (P=0.16). In the superior parietal lobule (are 7) of AIDS brains, no loss of nerve cells was noted. AIDS patients with progressive dementia and brains with HIV-specific neuropathology showed no difference in neuronal densities as compared to those without such features. We conclude that the fronto-orbital cortex, in contrast to the parietal cortex, is mainly damaged in AIDS brains. Neuronal loss was not significantly correlated with development of dementing symptoms and of HIV-specific neuropathology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00227766
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  • 9
    Electronic Resource
    Electronic Resource
    Coulomb effects in an optically excited electron-hole plasma of a disordered semiconductor (1990)
    Springer
    The European physical journal 81 (1990), S. 199-208 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we extend the work of Altshuler and Aronov [1] on the effect of Coulomb interaction in disordered metals to the case of an optically generated quasi-equilibrium electron-hole plasma in a disordered semiconductor in view of its possible implications for nonlinear optics. The nonlinearity considered here arises through the optically excited plasma density. The plasma is bipolar and not necessarily degenerate as in the metallic case. The density of states and the optical spectra due to freecarrier interband transitions are numerically computed in the presence and in the absence of the Altshuler-Aronov Coulomb-disorder singularity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01309349
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  • 10
    Electronic Resource
    Electronic Resource
    The kinetics of hole-burning in semiconductor lasers (1991)
    Springer
    The European physical journal 83 (1991), S. 447-451 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is shown that the nonequilibrium electron distributions of a lasing semiconductor can be calculated from a linearized Boltzmann equation for the intraband Coulombcollision rate. A successive expansion for small momentum transfer yields an integro-differential equation, whose differential part is the usual Fokker-Planck equation. The additional integral part assures the conservation of the total momentum and energy of the electron gas. A formal solution of the resulting kinetic equation is given from which one can calculate the hole burned into the electron distribution by the laser field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313416
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