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  • 1
    Electronic Resource
    Electronic Resource
    Neutron diffraction and Mössbauer effect study of several Nd2Fe17−xAlx solid solutions : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6029-6031 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Aluminum-substituted Nd2Fe17−xAlx solid solutions with x=2.30, 4.44, 6.13, 8.00, and 9.40 have been studied by neutron diffraction and Mössbauer spectroscopy. A Rietveld analysis of the neutron scattering indicates that the aluminum atoms have a high initial affinity for the 18h site, show a high affinity for the 6c site at high aluminum concentrations, and are absent from the 9d site at all aluminum concentrations. The Mössbauer spectra show a maximum in both the maximum and weighted average hyperfine field for x≈2. This indicates that the lattice expansion which occurs with aluminum substitution is sufficient, at least for small values of x, where magnetic dilution is small, to enhance the intrasublattice coupling between the iron moments, and to increase the magnetic hyperfine fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353459
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  • 2
    Electronic Resource
    Electronic Resource
    Normal-incidence electroabsorption in Ga1−xAlxSb/AlSb L-valley quantum wells for 3–5 μm optical modulation (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2810-2812 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Theoretical investigations are presented of the electric-field dependence of normal-incidence interconduction subband absorption in Ga1−xAlxSb/AlSb L-valley quantum wells. Under an applied electric field of 50 kV/cm, a blue shift of the absorption peak from 4.94 to 4.82 μm was found in a Ga0.7Al0.3Sb/AlSb structure with well width of 25 A(ring). The ability to absorb normally incident light and to achieve significant Stark shifts with bias makes the Ga1−xAlxSb/AlSb L-valley system an attractive choice for the 3–5 μm vertical optical modulators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354630
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  • 3
    Electronic Resource
    Electronic Resource
    Orientation dependence of intersubband absorption in AlAs/Ga1−xAlxAs X valley superlattices (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 3681-3685 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present the first systematic studies of infrared absorption from interconduction subband transitions for AlAs/Ga1−xAlxAs X-valley superlattices grown in the [001], [115], [113], [112], [111], and [110] directions. In the AlAs quantum well material, electrons occupy X valleys with ellipsoidal constant energy surfaces. Due to the effective mass anisotropy of electrons in the ellipsoidal valleys, these structures can absorb normally incident radiation when the superlattice growth direction is not collinear with the principal axes of at least one of the ellipsoids (i.e., not grown along the 〈001(approximately-greater-than) directions). For both parallel and normal incidence radiation at wavelengths of 12–20 μm, peak absorption coefficients of 3000–6000 cm−1 were obtained for the [113] and [112] superlattices with well widths in the range of 30–50 A(ring) and sheet doping concentrations of 1012 cm−2. Their ability to detect normally incident light and to obtain absorption comparable to that in the GaAs/Ga1−xAlxAs superlattice detectors makes these novel structures promising for use as normal incidence infrared photodetectors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352312
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  • 4
    Electronic Resource
    Electronic Resource
    Growth rates of current-excited plasma waves in semiconductor layered systems (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4767-4772 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the growth rates of current-driven plasma waves in semiconductor layered systems. We compare amplification performance of different layered systems, as well as investigate in detail the effects of various material parameters on the growth rates. This analysis provides guidelines for selecting the best systems for possible device applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352088
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  • 5
    Electronic Resource
    Electronic Resource
    Intersubband absorption in Ga1−xAlxSb/AlSb superlattices for infrared detection (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 3152-3156 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The infrared absorption from intersubband transitions between the lowest two superlattice conduction minibands is investigated for n-type Ga1−xAlxSb/AlSb superlattices. In such an indirect semiconductor superlattice, intersubband transitions can be induced by normally incident light because of the effective-mass anisotropy and the tilted orientation of conduction-band valleys with respect to the growth direction. The absorption coefficients and peak transition wavelengths are calculated for superlattices grown in the [001], [110], and [111] directions for both normal and parallel incidence. In the [110] Ga1−xAlxSb/AlSb superlattice, peak absorption coefficients of 5000–7000 cm−1 are obtained for both normally and parallel incident radiation in the wavelength range of 8–14 μm with moderate sheet doping concentrations of 1012 cm−2. The ability to detect normally incident radiation and to achieve absorption comparable to that in the GaAs/Ga1−xAlxAs detectors makes the Ga1−xAlxSb/AlSb devices promising for future applications in long-wavelength infrared detection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349296
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  • 6
    Electronic Resource
    Electronic Resource
    Enhancement of intersubband Stark effects in L-valley step quantum wells for infrared modulation and voltage tunable detection (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1195-1198 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We propose a new type of optical modulator employing two-step Ga1−xAlxSb/Ga1−yAlySb/Ga1−zAlzSb L-valley quantum wells to enhance the Stark shifts of the intersubband transition energy and therefore to achieve large absorption spectral changes with applied bias. Due to the effective-mass anisotropy of electrons in the L-valleys and the tilted growth direction with respect to the valleys, this novel structure can intrinsically absorb normal incidence light. Under an electric field of 50 kV/cm, a blue shift of the absorption peak from 10.9 to 9.8 μm was found from our calculations in a Ga0.7Al0.3Sb/Ga0.5Al0.5Sb/Ga0.4Al0.6Sb structure with a Ga0.7Al0.3Sb well width of 25 A(ring) and a Ga0.5Al0.5Sb step width of 25 A(ring). The ability to absorb normally incident light and to achieve significant Stark effects with bias makes this structure an attractive choice for such high-speed optoelectronic devices as vertical infrared light modulators and voltage tunable photodetectors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354920
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  • 7
    Electronic Resource
    Electronic Resource
    Normal incidence infrared photoabsorption in p-type GaSb/GaxAl1−xSb quantum wells (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2844-2847 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Absorption of infrared radiation at normal incidence from intervalence-subband transitions is investigated in p-type GaSb/Ga1−xAlxSb quantum wells. Normal incidence absorption is allowed in conventional p-type quantum wells due to the favorable properties of the p-like valence-band Bloch states and the heavy- and light-hole mixing. By using GaSb as the quantum-well material, which has the smallest heavy-hole effective mass of the commonly used III-V semiconductors, absorption can be further enhanced. We find that normal incidence absorption of 3000–6000 cm−1 can be easily achieved in these proposed quantum wells with well widths of 55–90 A(ring) for the wavelength range of 8–12 μm and typical sheet doping concentrations of 1012 cm−2. This absorption strength is comparable to that in the intrinsic Hg1−xCdxTe detector. Strong absorption of normally incident radiation makes this structure a good candidate for infrared photodetection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351015
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  • 8
    Electronic Resource
    Electronic Resource
    Induction response of plasma in nonadiabatic magnetic compression heating (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 633-641 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fast magnetic compression, where the compression time is shorter than the ion gyroperiod, is illustrated by a simple model. In this model the Vlasov–Ampère equation gives a Bernstein–Greene–Kruskal (BGK) stationary state at the so-called zero-β limit. It is possible to achieve hundreds of keV ion energy by the fast compression heating, because there is very little shielding from the plasma currents in the heating phase. Strong shielding appears when the compression has generated strongly phase-correlated oscillations of the ion orbits. Thresholds of plasma β for the appearance of ion stochasticity and ion trapping are estimated. Parameters in a 500 keV ion energy case are presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871415
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  • 9
    Electronic Resource
    Electronic Resource
    Toroidal stability boundaries for tearing modes in tokamaks (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2423-2426 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear stability boundaries for resistive and ideal external modes in circular cross section tokamaks are studied by means of toroidal magnetohydrodynamical (MHD) computations. The resistive MHD prediction at zero pressure is clearly more unstable than experimental results. For Lundquist numbers S=τr/τA of the order 107 or larger, the resistive stability boundaries for moderate beta are rather close to the ideal ones. These boundaries are in reasonable agreement with experimental results. The stabilizing effect of a conducting wall is studied. At high S, the lower limit to the inductance tends to be set by resistive wall modes rather than by tearing modes. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871926
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  • 10
    Electronic Resource
    Electronic Resource
    Influence of parallel viscosity on tearing mode stability (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3335-3340 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of parallel viscosity on the linear stability of tearing modes is analyzed. The parallel viscosity is introduced as a fluid approximation of ion Landau damping. Solution of the resistive layer equations shows that the toroidal stabilization resulting from favorable averaged curvature is rather robust and is only weakly reduced by the parallel viscosity. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871167
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