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  • 1
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    Pleistocene crees in Cyrenaica (Libya) (2011)
    Geozon Science Media
    Details
    Publication Date: 2021-03-29
    Description: Nord-Cyrenaika besteht aus einem Gebiet von Kalksteinhügeln, welche von tiefen und schmalen Tälern durchsetzt sind. Auf den Abhängen dieser Täler finden sich Schuttdecken zweierlei Alters, wovon die älteren festverkittet und mit terrassiertem Kies wechsellagern, während die jüngeren nicht verfestigt sind und keine zugeordneten Terrassen haben. Beide Schichten können archäologisch mit der Schichtfolge in der Haua Fteah-Höhle korreliert werden, wo Higgs (1961) eine klimatische Folge nachgewiesen hat. Es wurde gefunden, daß die beiden Schichten zwei sukzessiven kalten Zeiten des Spätpleistozäns entsprechen. Die Gerölle werden dem Spaltenfrost zugeschrieben, welch letzterer daher mittelbar für die terrassierten Kiese verantwortlich wäre. Es wird versucht, diese Resultate als abhängig von Temperatur und Niederschlag zu erklären.
    Description: research
    Keywords: 551.7 ; VAR 000 ; Glazialgeologie ; libya ; pleistocene ; pléistocène ; scree ; cyrenaica ; limestone hills ; valley ; terrace ; archeology ; haua fteah ; frost-shattering
    Language: English
    Type: article , publishedVersion
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    CITATION GEO-LEO
  • 2
    Electronic Resource
    Electronic Resource
    Investigation of GaAs/AlAs multilayer systems for optical Bragg reflectors using x-ray double crystal techniques (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2220-2224 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Layer systems for optical Bragg reflectors (grown by molecular beam epitaxy) were studied using double crystal topography and diffractometry. The initiation of stress relaxation was detected topographically in the substrate reflection and in different satellite reflections for undoped and slightly silicon doped layers (up to a doping level of 3×1017 cm−3). Higher silicon doping (1018 cm−3) prevented misfit dislocations. When using Czochralsky substrates it was observed that half-loops were formed by misfit dislocations between pairs of threading dislocations. Misfit dislocations were shown to be situated on different levels of the layer stack. Satellite reflection topography is suggested as a new tool for directly observing strains in multilayer systems since the signal originates in the layer stack. Even for very small layer thicknesses good defect contrasts can be expected for high-quality layers, as shown by simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353125
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  • 3
    Electronic Resource
    Electronic Resource
    On the preparation and characterization of high-quality GaAs single quantum wells (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5263-5265 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A regime for growing high-quality GaAs/AlGaAs single-quantum-well structures by molecular-beam epitaxy with interruption only at the AlGaAs-on-GaAs heterointerface is reported. For 15- and 20-nm-wide wells the luminescence linewidth is found to be 0.44 and 0.29 meV, respectively. The data are among the lowest values reported to date. Photoluminescence line splitting due to the formation of extended growth islands was not observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350588
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Deformations in (Al,Ga)As epitaxial layers wafer bonded on dissimilar substrates (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 2173-2178 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Deformations in heteroepitaxial layer stacks of AlGaAs/GaAs grown on GaAs are measured by triple crystal diffractometry before epitaxial liftoff and after subsequent wafer bonding on various substrates (GaAs, glass, Si, and LiNbO3). The tetragonal deformation present in the as-grown layer stack partially relaxes during epitaxial liftoff. The roughness of the as-grown layer stack gives rise to a bending of the atomic planes after wafer bonding. The widths of the x-ray diffraction peaks are used to estimate the misorientation of the lattice planes and compared with the atomic force microscopy measurements of the surface roughness. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1342804
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  • 5
    Electronic Resource
    Electronic Resource
    Current filament dynamics in n-GaAs (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4560-4565 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments on the controlled generation of up to 20 current filaments in n-type GaAs have been performed in the electric field region, where impurity impact-ionization avalanche breakdown takes place. This strongly nonlinear system is found to be very sensitive to small deviations of the technological parameters. In particular, we present the results of time-resolved current measurements on two filaments connected in parallel, which compete for the impressed total current due to nonlocal coupling via a common load resistor. The observed switching time constants down to 100 ns make this system very interesting as a "winner takes all'' element in synergetic computer applications. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359799
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  • 6
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358988
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  • 7
    Electronic Resource
    Electronic Resource
    Hot electron capture in highly doped GaAs (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4463-4466 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hot carrier transport processes in GaAs with δ-like high Si doping have been investigated. In the high electric field region the current density decays with time by as much as 20%, an indication of electron trapping. The electron traps are metastable and the electrons can be released by light or thermal excitation. DX− centers can explain the observations, however, other types of localized electron states cannot be unambiguously excluded. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359476
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  • 8
    Electronic Resource
    Electronic Resource
    Intrinsic origin and composition dependence of deep-level defects at the inverted GaAs/AlxGa1−xAs interface grown by molecular-beam epitaxy (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5773-5781 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electronic states in n-type GaAs/AlxGa1−xAs heterojunctions are studied by deep-level transient spectroscopy in the Al mole fraction range from 0.25 to 1.00. A series of four well-defined deep levels is characteristic of the inverted GaAs/AlxGa1−xAs interface (GaAs grown on AlxGa1−xAs) grown by conventional molecular-beam epitaxy under arsenic-stable conditions without growth interruption. It is shown that the series of four levels originates from intrinsic defects which are associated with arsenic vacancies and antisites. In particular, two charge states of the isolated arsenic vacancy VAs can be identified. Except for the sheet very close to the inverted heterointerface the n-type AlxGa1−xAs layers are found to be almost free of intrinsic deep levels in the entire composition range. For the investigated samples, the compositional dependence of the level energies shows that the arsenic vacancy is predominantly surrounded by Al atoms. From the compositional dependence of the level concentrations it follows that the arsenic vacancies at the interface are formed above a composition threshold of 0.25. The distinct distribution of intrinsic defects at the inverted GaAs/AlxGa1−xAs interface can be explained by a stable defect configuration near the AlxGa1−xAs surface during growth. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359222
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  • 9
    Electronic Resource
    Electronic Resource
    Temperature persistent bistability and threshold switching in a single barrier heterostructure hot-electron diode (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3376-3380 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bistable current–voltage characteristics caused by competition of tunneling through and field-enhanced thermionic emission across a single barrier are investigated in an n−-GaAs/Al0.34Ga0.66As/n+-GaAs structure. The S-shaped part of the characteristic persists in the whole temperature regime between 4.2 and 300 K in accordance with theoretical predictions. The delay and switching times of the transition from the low- to the high-conducting state are investigated as a function of the applied voltage and compared with simulations. The observed timescales are much longer than expected from theory, which indicates the presence of additional deep centers or interface states. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363251
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  • 10
    Electronic Resource
    Electronic Resource
    Application of liftoff low-temperature-grown GaAs on transparent substrates for THz signal generation (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2903-2905 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial liftoff (ELO) of low-temperature-grown GaAs (LT-GaAs) is employed to fabricate (sub)picosecond photoconductive switches on optically transparent substrates for THz applications. Glass is selected as a substrate for on-wafer probes while sapphire is chosen for free-space antennas. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117357
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