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  • 1
    Digitale Medien
    Digitale Medien
    Implosion-driven hypervelocity accelerator (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5254-5256 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A hypervelocity accelerator has been developed utilizing the extreme condition produced by the collapse of the cylindrical imploding shock wave. The cylindrical shell of the explosive is detonated by the explosion of rows of copper wires bound around it. The wire explosion is caused by the application of an impulsive electric current. The energy concentrated at the implosion center is imparted to the projectile accelerating it. The launch velocity of 1.2 km/s has been attained for a 2 g launched weight with a 60 g explosive (PETN: pentaerythritoltetranitrate). A further increase of the launch velocity is expected by increasing either the explosive thickness or the height of the cylindrical shell within practical limit.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.350585
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  • 2
    Digitale Medien
    Digitale Medien
    Numerical simulation of cylindrical converging shocks in solids (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2605-2611 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Cylindrically converging shock waves in solids have been analyzed by the random choice method (RCM). A Riemann solver for fluidlike solids with the Grüneisen-type equation of state is constructed and incorporated into the RCM. It is then applied to the cylindrical shock tube problems for solid copper with driving pressures of 20 and 200 GPa. The numerical results are compared with those of the finite difference method (FDM). The shock speed is smaller and the discontinuity at the shock front is smeared out due to the artificial viscosity in the FDM calculation. Spatial distributions of pressure, density, and particle velocity calculated by the RCM show that the steepness at the shock front is maintained both in the converging and reflecting stages. It is shown that the pressure on the shock front and the total energy contained in the central circular area are much larger in the reflecting stage than in the focusing stage. The dimensional analysis has shown that the similarity solution exists; however the numerical result shows that the flow does not fall within the similarity regime in the region of calculation. It suggests that the self-similar flow is only limited in extreme proximity to the axis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.351560
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  • 3
    Digitale Medien
    Digitale Medien
    Rapid collapse of Wannier–Stark localization caused by space charge electric field screening in short-period superlattices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5094-5105 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A rapid optical absorption change is observed in a GaAs/AlAs short-period superlattice having Wannier–Stark localization. This phenomenon is clearly explained by a rapid collapse of Wannier–Stark localization due to electric field screening by photogenerated space charges. The screening causes a positive feedback loop between restoration of the blue-shifted wavelength of the absorption band-edge towards the red and an increase in optical absorption, which causes an additional field screening. The experimental bias voltage dependence of the intensity of photoluminescence and photocurrent under high optical excitation, agree well with a model applying Fowler–Nordheim tunneling at the heterointerface cladding layer. It is concluded that the space charges are stopped near the cladding layer and that the superlattice region is almost fully screened to near the flat-band bias condition. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363489
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  • 4
    Digitale Medien
    Digitale Medien
    Influence of exciton diffusion and localization on cathodoluminescence imaging of quantum well structures (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1211-1216 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effect of exciton diffusion and localization on the cathodoluminescence (CL) intensity distribution using a scanning electron microscope has been investigated in a single quantum well and a multiple quantum well structure prepared by growth interrupted molecular beam epitaxy. Although of different origin, lateral variations of the exciton confinement energy occur in both samples on a length scale much larger than the exciton Bohr radius. The spectral and spatial CL intensity distribution is substantially influenced by diffusion of excitons to quantum well regions with low exciton confinement energy. The CL micrographs from both quantum well structures exhibit a similar bright/dark pattern with a typical length scale, which is determined by the exciton diffusion length in this material. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.358988
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  • 5
    Digitale Medien
    Digitale Medien
    Pseudo-negative photocurrent spectroscopy in GaAs-AlAs superlattices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4197-4202 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Pseudo-negative photocurrent spectra, i.e., the appearance of a minimum in photocurrent at an absorption maximum, are experimentally studied at different temperatures and excitation intensities in GaAs-AlAs superlattices on GaAs substrates. Superlattice and substrate are isolated by a thick Al0.3Ga0.7As barrier, but electrically connected through penetrating contacts. A simple model is proposed for the analysis of the conditions which can lead to pseudo-negative photocurrent in this sample configuration. The radiative recombination of the carriers in the superlattice was found to be the main process determining the sign of the photocurrent at an absorption maximum. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.361877
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  • 6
    Digitale Medien
    Digitale Medien
    Wannier–Stark localization in strained barrier GaAs/InXAl1−XAs superlattices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2285-2290 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the observation of the Wannier–Stark localization effect in short period GaAs/ InXAl1−XAs superlattices with strained barriers. The superlattices, each of which is contained in the intrinsic region of a p-i-n diode structure, consist of GaAs (3.0 nm) wells and strained shallow InXAl1−XAs (0.9 nm) barriers (X=0, 0.1, 0.2, and 0.3) grown on GaAs by molecular beam epitaxy. In spite of the use of strained barriers, the Wannier–Stark localization effect is clearly observed for all samples at room temperature. Even the superlattice sample with the highest In content of X=0.3 exhibits distinct photocurrent spectra showing several peaks associated with Wannier–Stark ladder transitions as well as Franz–Keldysh oscillations. It is found that the transition intensities are consistent with theoretically calculated oscillator strengths based on the simplified tight-binding model. By increasing the In content X, the miniband width increases and the absorption peak energy due to the zeroth order ladder (e1-hh1 and e1-lh1) transitions decreases because of the reduced barrier height. The transition energies are consistently explained by taking modulation effects into account on the valence subbands due to the compressively strained barriers. The above results show that the use of a large strain effect on the barriers is possible in Wannier–Stark localization effect type devices. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363057
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  • 7
    Digitale Medien
    Digitale Medien
    Structural and optical investigations of high quality InGaAs/InAlAs short period superlattices grown on an InGaAs quasisubstrate (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5915-5920 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Unstrained InGaAs (4.5 nm)/InAlAs (1.0 nm) short-period superlattices grown on a (100) GaAs substrate were studied. To achieve this growth, an In-composition-graded buffer layer and a thick InGaAs buffer layer were adopted. Structural properties were investigated by x-ray diffraction, atomic force microscopy, and a compositional analysis by the thickness fringe method. X-ray diffraction patterns showed clear periodicity in the superlattices and atomic force spectroscopy images showed cross-hatch morphology for the main ridge along the (011¯) direction. Clear thickness fringes in the bright-field electron microscope images for the superlattice region and ambiguous fringes for the graded buffer layer indicate that misfit dislocation due to lattice mismatch concentrates in the graded buffer and a high-quality superlattice is successfully grown in spite of the large lattice mismatch between the superlattice and the substrate. Optical characteristics measured by photocurrent spectroscopy reveal a clear Wannier–Stark localization effect at room temperature. The experimental absorption energies agree well with calculated values by a transfer matrix method using parameters for bulk InGaAs and InAlAs. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363587
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  • 8
    Digitale Medien
    Digitale Medien
    Cathodoluminescence studies of exciton localization in GaAs-AlGaAs single quantum wells (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 396-398 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The temperature dependence of the spectrally resolved cathodoluminescence intensity from a 3.5- nm-thick GaAs-AlGaAs single quantum well prepared by growth interrupted molecular beam epitaxy has been investigated between 5 and 120 K. As the temperature increases, we observe thermally activated carrier transfer from wider quantum well regions to narrower ones. This observation indicates that there is exciton localization within the wider quantum well regions, one or two monolayers larger in width, at low temperatures. The contrast in spectrally resolved cathodoluminescence images of the quantum well is significantly influenced by this exciton localization and therefore does not necessarily reflect the lateral island distribution. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359336
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  • 9
    Digitale Medien
    Digitale Medien
    Radiative properties of a highly excited quantum well (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1485-1487 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We study by time-resolved luminescence, the radiative recombination from a single quantum well placed inside a graded confinement structure. We are able to produce a cold (T〈50 K), high-density (5×1011〈N〈5×1012 cm−2) plasma. We compare our spectra with usual lineshape fitting procedures and give evidence for the shortcomings of such an analysis. We detail the consequences of the present work for the determination of band-gap renormalization, the conservation of k-selection rule, and the measurement of the radiative recombination rate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.105204
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  • 10
    Digitale Medien
    Digitale Medien
    Observation of free excitons in room-temperature photoluminescence of GaAs/AlGaAs single quantum wells (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 675-677 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Observation of free excitons is reported in room-temperature photoluminescence of nominally undoped GaAs/AlGaAs single quantum wells grown by molecular beam epitaxy. A comparative study with parallel-conduction photocurrent spectroscopy shows that a sharp luminescence peak with a linewidth of 14 meV observed for the 6.1-nm-wide well coincides within 2 meV with the n=1 heavy-hole free-exciton resonance line at excess carrier densities less than 1017 cm−3. Excitonic decay channels dominate the luminescence spectrum even at room temperature as a result of quantum confinement effects, although photogenerated carriers are also provided for photocurrents by exciton dissociations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.99847
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