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  • Elsevier  (16)
  • American Institute of Physics (AIP)  (11)
  • Institute of Physics  (3)
  • Wiley-Blackwell
  • 1985-1989  (30)
  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 7259-7267 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Optical bistability has been observed in highly concentrated substituted fluorescein dye solution and in thin (∼1 μm) doped polymeric films. For fluorescein, at concentrations larger than 10−5 mol/l dye dimers are formed. The dimer–monomer equilibrium constant is 105 l/mol so that most of the dye species are in the dimer form. At 480 nm the dimer absorption cross section is 10−18 cm2/molecule, while that for the dye monomer molecule is 7.6×10−17 cm2/molecule. Upon laser excitation dimers dissociate to form monomers thus providing a highly nonlinear laser induced absorption. The high nonlinear absorption coefficient can be utilized for optically bistable response of the dye system. Optical bistability was observed by placing dye solutions or dye thin films inside a Fabry–Perot resonator and exciting it with 480 nm dye laser pulses of 10 ns duration. The effect is more pronounced in 10−4 mol/ l fluorescein than in 10−6 mol/l fluorescein in which dimer formation is not that efficient. In disodium fluorescein, eosin Y and erythrosin B no significant dimer formation is observed even at 10−3 mol/l dye concentration. The observed bistability both in solution and in thin films can be explained in terms of recent models for optical bistability in nonlinearly absorbing molecular system.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 6373-6378 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We use a highly accurate numerical computer model to solve the problem of equilibrium barrier formation in graded Hg1−xCdxTe heterojunctions including valence-band offsets. The present calculation is an extension of our previous work [J. Appl. Phys. 62, 3267 (1987)], which incorporated physical features designed to improve upon previous calculations, but employed the common anion rule. First, we analyze and compare our results to the recent work of Oda [Infrared Phys. 27, 49 (1987)] and find significant differences. Then, we make a comparison with the results of our previous work. We observe clear trends between our results with and without the valence-band offset. Unlike Oda, we do not make general predictions with regard to the conditions needed to support the formation and growth of a barrier in the conduction band, but instead find the band profiles to be a complex function of all the junction design parameters. For the present study involving narrow gap p on wide gap n heterojunctions, and the assumed: HgTe:CdTe 300-meV valence-band offset, the band profiles do not differ significantly from the profiles assuming the common anion rule.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 4300-4307 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It is shown that when account is taken of the attenuation of incident radiation into the bulk of a photoconductor, as a result of the absorption, the expressions for the responsivity and detectivity are modified. An earlier derivation [Infrared Phys. 20, 385 (1980)] attributed the difference in the operation of the detectors in the transverse and longitudinal geometries to carefully defined "effective'' quantum efficiencies. Here we show that a more physically motivated view attributes the difference to the different photoconductive gains for the two geometries. It is shown that the appropriate gains for the responsivity and detectivity are not the same.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 2770-2772 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The intrinsic carrier concentrations in Hg1−xCdxTe are calculated with the use of the Fermi–Dirac statistics thus expanding on our previous calculation which employed the Boltzmann statistics. The use of Boltzmann statistics for Hg1−xCdxTe is limited to x≥0.20 and is not appropriate for the narrow band gap x〈0.20 compositions. Our present treatment improves on existing calculations by using composition and temperature dependent momentum matrix element squared, which is the input to the Kane's k ⋅ p theory, and by making no approximations to the band structure beyond those inherent to Kane's theory. We find that our results for x≥0.20 using both statistics are in excellent agreement. We also compare our results with those of Hansen and Schmit. Good agreement is found for the range of 0.15≤x≤0.40.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 2533-2540 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We are presenting an analytic model for the figures of merit of a novel extrinsic infrared quantum detector—the blocked impurity band (BIB) detector. The detector consists of top and bottom contacts, a heavily doped active layer, and a nearly intrinsic layer, called the blocking layer, to stop the motion of hopping carriers in the impurity band. The responsivity, gain, excess noise factor, and detectivity of the BIB detector are calculated as functions of the device dimensions, doping concentrations, and the applied reverse bias, which controls the electric field in the depletion region, devoid of hopping carriers, of the device underneath the blocking layer. Central to our model is the inclusion of impact ionization of carriers in the calculation of the detector response and of the associated noise. For practical detector dimensions and doping concentrations, and at 2-V reverse bias, we calculate the responsivity to be on the order of 2 A/W, and detectivities, with 1012 photons/cm2 s background photon flux, on the order of 1013 cm Hz1/2/W. We provide analytic expressions for the figures of merit which should prove useful to other researchers in the field who want to optimize the detector design.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 5583-5588 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In a recent paper [F. Szmulowicz and F. L. Madarasz, J. Appl. Phys. 62, 2533 (1987)] we introduced details of an analytical model for a top side illuminated blocked impurity band infrared detector operating under background limited conditions (BLIP). In the present paper we extend that model to a bottom side illuminated detector operating in the presence of thermally generated carriers (non-BLIP case) as well as the optically generated background carriers. We display results of a parametric study including gain, quantum efficiency, the excess noise factor, and hence the detector figures of merit responsivity and detectivity, as functions of the detector temperature. Our study of the thermal noise includes the Poole–Frenkel effect. The results of the present calculation determine optimal operating temperatures as well as bias voltages. We show that Si:As blocked impurity band detectors, doped to 5×1017 cm−3, will be background limited below 13.5 K at low background, 1010 photons cm−2 s−1 operation, with responsivities and detectivities on the order of 5 A/W and 1014 cm Hz1/2/W, respectively.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 3267-3277 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The problem of equilibrium barrier formation in graded Hg1−xCdxTe heterojunctions is solved with the use of a highly accurate computer model. The present calculation incorporates several features designed to improve on past efforts. The Poisson equation is solved as a nonlinear integro-differential equation. Fermi–Dirac statistics are used to allow for the degeneracy associated with inversion for narrowly graded junctions and the degeneracy of the native defect donors. The band structure is obtained from the numerical solution of the secular equation. Fermi–Dirac statistics are taken to govern the degree of ionization of the acceptors and acceptorlike traps. Acceptors are treated as divalent flaws and their ionization energies as linear functions of the cadmium composition. The results are compared to the recent work of Bratt and Casselman [J. Vac. Sci. Technol. A 3, 238 (1985)], and the earlier work of Migliorato and White [Solid-State Electron. 26, 65 (1983)]. Significant differences are found. The results and differences are analyzed. Further computations are made in order to investigate the impact of elevated temperatures and the interdiffusion of doping concentrations along with compensation effects. It is shown that even a smeared p-n junction can have an advantageous effect.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 310-311 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It is shown that the photoconductive gain of a longitudinal detector is given by the ratio of the average carrier lifetime to the interelectrode transit time regardless of the absorption profile of the detector. Both corpuscular and macroscopic points of view are considered.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 361-365 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Intrinsic carrier concentrations are calculated for the semiconductor alloy Hg1−xCdxTe. Unlike previous calculations we make no approximations to the band structure, and hence to the density of states, beyond those inherent in the Kane k ⋅ p theory. Our results are compared with the recent calculation of Hansen and Schmit. Close agreement is found in the low compositional x range. However, significant differences, up to 50%, were found for higher alloy compositions. The reasons for the disagreement between the two calculations are discussed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 252-255 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The room-temperature lattice thermal conductivity of GaAs-InAs alloys is calculated and compared to recently measured thermal conductivity of GaAs dilutely alloyed with InAs [M. C. Ohmer, W. C. Mitchel, G. A. Graves, D. E. Holmes, H. Kuwamoto, and P. W. Yu, J. Appl. Phys. 64, 2775 (1988)] and with older data at higher concentrations. Our calculation considers both the normal and Umklapp anharmonic interaction, as well as mass differences and size distortions for the scattering by point defects. The results indicate that it is the size-distortion scattering which leads to a very abrupt decrease in the thermal conductivity for dilute alloys. The theory of Klemens and Callaway used in the present work is in semiquantitative agreement with experiments, consistent with both the experimental and theoretical uncertainties. Unlike previous calculations, we were able to reproduce a very sharp decline in the thermal conductivity upon alloying for very dilute alloys.
    Materialart: Digitale Medien
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