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  • 1
    Digitale Medien
    Digitale Medien
    Logarithmically graded quantum well far-infrared modulator (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 348-350 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have designed and fabricated a remotely doped "logarithmic'' potential well intended to have a tunable, narrow band absorption at far-infrared frequencies. A surface gate, epitaxially grown backgate, and contact to the electron gas in the quantum well allow independent control of the absorption frequency and the integrated absorption strength. The resonance frequency is dominated by the well curvature at the potential minimum and can be Stark shifted from ω/2πc=35 cm−1 to a frequency of 125 cm−1 by moving the electron gas through the asymmetric well.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.111144
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  • 2
    Digitale Medien
    Digitale Medien
    Midinfrared studies of the contact region at superconductor–semiconductor interfaces (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 215-217 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: InAs quantum wells (QWs) have been used as weak links in many recent studies of novel superconductor-normal metal–superconductor junctions. The degree of coupling between the superconducting electrodes depends sensitively on both the superconductor/InAs interface and the QW material in the weak link, factors that are difficult to separate in dc transport studies. Here we used midinfrared spectroscopy to investigate the superconductor/semiconductor contact region. The remnant intersubband absorption we observe in Nb-clad InAs shows that the superconductor/InAs interface produced some confinement of electrons in the InAs. This confinement is, however, consistent with phase coherent transport in the InAs. We find no evidence for charge transfer from the superconductor to the InAs on cooling below the critical temperature of Nb. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.125706
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  • 3
    Digitale Medien
    Digitale Medien
    Relaxation times in InAs/AlSb quantum wells (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2439-2441 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have measured energy relaxation and longitudinal-optical (LO) phonon emission times in modulation-doped InAs quantum wells driven by high dc fields, and by intense ac fields at frequencies from 0.49 to 0.66 terahertz. We find that for electron temperatures between 50 and 200 K, LO phonon emission dominates energy relaxation. We determine a large net LO phonon emission time, indicating a strong LO phonon bottleneck both in high dc and in intense terahertz fields. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.121377
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  • 4
    Digitale Medien
    Digitale Medien
    Nonlinear response of quantum-confined electrons in nonparabolic subbands (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2533-2535 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We show that quantum confinement can dramatically alter the density-dependence of the third-order susceptibility, χ(3)NP, that arises from band nonparabolicity. Our results predict an oscillatory dependence of the efficiencies for third-harmonic generation and four-wave mixing on the subband occupation of quantum wells, and for narrow wells with high charge densities predict an enhancement over the bulk susceptibility. We also make a simple estimate of the fields required to saturate this nonparabolicity contribution to χ(3). We discuss these results in light of recent experiments on third-harmonic generation from narrow-gap quantum wells at frequencies of ∼1 THz, and show that nonparabolicity may not be the only nonlinearity contributing to the large χ(3) observed. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363040
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  • 5
    Digitale Medien
    Digitale Medien
    Interband impact ionization by terahertz illumination of InAs heterostructures (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3975-3977 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Experimental studies of InAs heterostructures illuminated by far-infrared (FIR) radiation reveal an abrupt increase in the charge density for FIR intensities above a threshold value that rises with increasing frequency. We attribute this charge density rise to interband impact ionization in a regime in which ωτm∼1, where τm is the momentum relaxation time, and f=ω/2π is the FIR frequency. The dependence of the density rise on the FIR field strength supports this interpretation, and gives threshold fields of 3.7–8.9 kV/cm for the frequency range 0.3–0.66 THz. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.117842
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  • 6
    Digitale Medien
    Digitale Medien
    Temperature of quasi-two-dimensional electron gases under steady-state terahertz drive (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 829-831 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We use photoluminescence to study the time-average energy distribution of electrons in the presence of strong steady-state drive at terahertz (THz) frequencies, in a modulation-doped 125 A(ring) AlGaAs/GaAs square well that is held at low lattice temperature TL. We find that the energy distribution can be characterized by an effective electron temperature, Te((approximately-greater-than)TL), that agrees well with values estimated from the THz-illuminated, dc conductivity. This agreement indicates that under strong THz drive, LO phonon scattering dominates both energy and momentum relaxation; that the carrier distribution maintains a heated, thermal form; and that phonon drift effects are negligible. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.116547
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  • 7
    Digitale Medien
    Digitale Medien
    Low-density high-mobility electron gas in wide parabolic GaAs/AlxGa1−xAs wells (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2823-2825 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Remotely doped wide parabolic GaAs/AlxGa1−xAs wells are used to create thick ((approximately-greater-than) 1000 A(ring)) layers of high-mobility ((approximately-greater-than) 2×105 cm2/V s) electron gas with three-dimensional densities below (by a factor ∼3) the metal-insulator transition for doped GaAs. The temperature dependences of the Hall mobility and sheet density show no qualitative changes in a series of three samples spanning the metal-insulator transition. Shubnikov–de Haas oscillation measurements are used to determine the width of the electron gas layers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.103753
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