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  • Articles  (106)
  • 2000-2004  (34)
  • 1990-1994  (72)
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  • 1
    Electronic Resource
    Electronic Resource
    Coupled surface and channel transport in semiconductor heterostructures (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6135-6139 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron transport in a channel separated from the surface by a thin insulating barrier layer is shown to be profoundly affected by electrical conditions on the surface. Nonuniformities in the coupled surface and channel systems lead to depletion and accumulation regions in the channel and the depletion regions can cause the current to saturate at unusually low voltages. Even when there are no nonuniformities it is shown that the coupled system exhibits a density instability that leads to similar phenomena. These effects are described in terms of an analytical model that takes into account diffusion and hot-electron transport applied to the AlGaN/GaN system. It is noted that the effect of any extension of the channel under the cathode (source) can produce depletion and current saturation that can be mistaken for the result of a nonohmic contact resistance. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1412569
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  • 2
    Electronic Resource
    Electronic Resource
    Hot carriers and the frequency response of quantum well lasers (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2579-2588 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple analytical model is obtained to describe the effect of carrier heating on the frequency response of a quantum well laser. The principal factors are taken to be injection heating, recombination heating, and hot phonons. The model is applied to the GaAs/GaInAs strained layer system and is shown to qualitatively account for many of the nonideal features observed. The nonlinear effects cannot be described satisfactorily by a single phenomenological "gain suppression'' factor. However, at low drives the conventional gain suppression factor can be expressed in terms of the phonon lifetime and the temperature-relaxation time. The response is mediated by several time constants which, in our example, combine to give an effective time constant of about 10 ps. The modulation frequency response becomes seriously impaired when the differential gain is lowered by a factor of 2 and the time constants describing scattering and phonon lifetime are increased by a factor of 2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351557
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  • 3
    Electronic Resource
    Electronic Resource
    Phonon scattering suppression in short periodic AlAs/GaAs multiple-quantum-well structures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3491-3499 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The suppression of longitudinally polarized optical-phonon (LOP) electron scattering in multiple quantum wells (MQWs) was sought in short periodic AlAs/GaAs with well widths of 12, 15, and 20 monolayers and AlAs barrier widths of 2 and 4 monolayers, based on a study of electron mobility in the plane of the MQW. Two-dimensional electron-gas structures with MQWs of up to eight wells in their channel were grown. Their mobilities at room temperature were slightly reduced, as compared to samples without MQW channel, due to interaction with interface polaritons from AlAs barriers, while mobility at temperatures 〈50 K improved due to reduction of remote ionized impurity scattering. The theoretical analysis of the results based on the model of hybridon-electron interaction in an infinite superlattice is presented. The reduction of room-temperature mobility in the MQWs is believed to be caused by the interaction of electrons with both barrier interface-polariton (IP) -like modes and the well LOP-IP hybrids. An alternative explanation of the results of a similar experiment done elsewhere is offered denying the evidence of strong suppression of LOP scattering there.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356111
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  • 4
    Electronic Resource
    Electronic Resource
    Hole-phonon scattering in strained SiGe quantum wells (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 5546-5550 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction between holes confined in a strained Si1−xGex quantum well and acoustic and optical phonons is investigated in an effort to elucidate in-plane carrier transport. This treatment utilizes conventional deformation potential theory within the context of the momentum conservation approximation in the confinement direction to obtain analytical expressions for both acoustic and optical phonon scattering rates as functions of carrier energy. The optical phonon interaction explicitly accounts for the three vibrational modes: Si-Si, Si-Ge, and Ge-Ge by incorporating experimentally determined longitudinal optical (LO) phonon frequency shifts in the calculation of the matrix elements. The oscillator strengths for each of these LO (short wavelength) modes are approximated using a binomial distribution to describe the local atomic arrangement of a unit cell. The two-dimensional scattering rates are evaluated and compared with bulk scattering calculations for a well of fixed width and varying Ge content. It is found that the overall hole-phonon scattering rate in a SiGe well is higher than that of holes in strained SiGe layers due to the combined effects of similar two- and three-dimensional density of states and large inter-sub-band scattering. A qualitative description of high field transport within the well is obtained by calculating the relative contributions of particular optical phonon modes to the overall scattering rate at high carrier energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354213
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  • 5
    Electronic Resource
    Electronic Resource
    Electron transport across a wide AlGaAs barrier (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 5606-5621 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experimental and theoretical study has been made of electron transport over a wide AlGaAs barrier with graded interfaces sandwiched between GaAs contact layers. The width of the central barrier region was varied between 700 and 2100 A(ring). Two series of samples with nominally identical structures but from different sources were investigated. Extensive measurements of both the voltage and temperature dependence of the current were made, as well as measurements of capacitance and magnetoresistance. Drift-diffusion thermionic emission theory has been used to interpret the data. Both numerical and analytical solutions of the model have been developed and were found to be in good agreement with each other. The presence of space charge in the barrier region, which has the effect of increasing the barrier height, was seen to be crucial to an understanding of the data. When the effect of space charge was included in the model good agreement was obtained between theory and experiment for electric fields up to 10 kV cm−1. The numerical solution required only one adjustable parameter, namely the value of the space-charge density. The parameters used in the analytical model were all derived from the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354222
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  • 6
    Electronic Resource
    Electronic Resource
    The in-plane effective mass in strained-layer quantum wells (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4667-4673 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The problem of calculating the valence-band structure of strained-layer quantum wells in the effective-mass approximation is reviewed. Using the spherical approximation and exploiting the simplicity of the infinitely deep well model we show that the in-plane effective mass is determined by two factors—a splitting contribution which is dominant at large strains, and a quantum confinement contribution. A model for finite-depth wells is presented which gives analytic expressions for the zone-center in-plane mass and associated nonparabolicity factor, and it is applied to the system InxGa1−xAs/GaAs. The model allows the computation of valence-band structure using no more than a pocket calculator. It is shown to give results in reasonable agreement with experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346178
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  • 7
    Electronic Resource
    Electronic Resource
    Polarization-induced electron populations (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 990-992 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron populations induced by spontaneous and piezoelectric polarization in semiconductor heterostructures can be estimated simply by using elementary electrostatic theory. The method is illustrated for the AlGaN/GaN system in which the AlGaN barrier is either undoped, or doped n type, and the effect of a GaN overlayer is described. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288817
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  • 8
    Electronic Resource
    Electronic Resource
    Comparative analysis of zinc-blende and wurtzite GaN for full-band polar optical phonon scattering and negative differential conductivity (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2707-2709 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For high-power electronics applications, GaN is a promising semiconductor. Under high electric fields, electrons can reach very high energies where polar optical phonon (POP) emission is the dominant scattering mechanism. So, we undertake a full-band analysis of POP scattering of conduction-band electrons based on an empirical pseudopotential band structure. To uncover the directional variations, we compute POP emission rates along high-symmetry directions for the zinc-blende (ZB) crystal phase of GaN. We also compare the results with those of the wurtzite phase. In general, the POP scattering rates in the zinc-blende phase are lower than the wurtzite phase. Our analysis also reveals appreciable directional dependence, with the Γ–L direction of ZB GaN being least vulnerable to POP scattering, characterized by a scattering time of 11 fs. For both crystal phases, we consider the negative differential conductivity possibilities driven by the negative effective mass part of the band structure. According to our estimation, for the ZB phase the onset of this effect requires fields above ∼1 MV/cm. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1320020
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  • 9
    Electronic Resource
    Electronic Resource
    Comparison of the theoretical and experimental differential gain in strained layer InGaAs/GaAs quantum well lasers (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 1162-1164 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical model that uses simple, analytic valence band equations to calculate the differential gain in strained layer InGaAs/GaAs quantum wells shows good agreement with experimental differential gain values obtained from multiple quantum well strained layer lasers. The differential gain in these devices is 7 times greater than in bulk, p-type doped InGaAsP lasers. Calculations including nonlinear damping effects indicate that modulation bandwidths exceeding 60 GHz should be achievable in strained layer quantum well lasers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105543
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  • 10
    Electronic Resource
    Electronic Resource
    Is the Arctic Surface Layer a Source and Sink of NOx in Winter/Spring? (2000)
    Springer
    Journal of atmospheric chemistry 36 (2000), S. 1-22 
    Details
    ISSN: 1573-0662
    Keywords: active nitrogen ; ozone ; radicals ; snow chemistry ; Arctic ; surface layer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Measurements of NOx (NO +NO2) and the sum of reactive nitrogenconstituents, NOy, were made near the surface atAlert (82.5°N), Canada during March and April1998. In early March when solar insolation was absentor very low, NOx mixing ratios were frequentlynear zero. After polar sunrise when the sun was abovethe horizon for much or all of the day a diurnalvariation in NOx and NOy was observed withamplitudes as large as 30–40 pptv. The source ofactive nitrogen is attributed to release from the snowsurface by a process that is apparently sensitized bysunlight. If the source from the snowpack is a largescale feature of the Arctic then the diurnal trendsalso require a competing process for removal to thesurface. From the diurnal change in the NO/NO2ratio, mid-April mixing ratios for the sum of peroxyand halogen oxide radicals of ≤10 pptv werederived for periods when ozone mixing ratios were inthe normal range of 30–50 ppbv. Mid-day ozoneproduction and loss rates with the active nitrogensource were estimated to be ∼1–2 ppbv/day and in nearbalance. NOy mixing ratios which averaged only295±66 pptv do not support a large accumulation inthe high Arctic surface layer in the winter and springof 1998. The small abundance of NOy relative tothe elevated mixing ratios of other long-livedanthropogenic constituents requires that reactivenitrogen be removed to the surface during transport toor during residence within the high Arctic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006301029874
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