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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 127 (1988), S. 403-414 
    ISSN: 1420-9136
    Keywords: D-region ; ionospheric chemistry ; mesosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The most meaningful way to compare observations of the daytimeD-region under all ionization conditions, for the purpose of improving our understanding of this region, would appear to be through use of the effective electron recombination coefficient, Ψ=q/[e]2, whereq is the ionization production rate, and where [e] is the electron concentration. This ratio apparently increases monotonically with decreasing altitude, and is much less variable than its componentsq and [e]. This parameter appears eminently suitable as a best first order solution to [e] after determiningq. For nighttime conditions, Ψ is more sensitive toq. However, an accurate but simple formula exists for the calculation of electron concentrations.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6364-6368 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Detailed structure of the interfacial layers of Ti/Ta/Al ohmic contacts to n-type AlGaN/GaN/sapphire are investigated by means of transmission electron microscopy. High-resolution electron microscopy (HREM), optical diffractograms, and computer simulations confirmed that TiN (∼10.0 nm) and Ti3AlN (∼1.4 nm) interfacial layers form at the interface between the Ti layer and the Al0.35Ga0.65N substrate by a solid state reaction during annealing for 3 min in N2 at 950 °C. The orientation relationship between Ti3AlN and Al0.35Ga0.65N was found to be: [011]Ti3AlN(parallel)[21¯1¯0]Al0.35Ga0.65N and (11¯1)Ti3AlN(parallel)(0001)Al0.35Ga0.65N. The cubic Ti3AlN interfacial layer has a lattice parameter of 0.411±0.003 nm with the space group Pm3m matching that of Al0.35Ga0.65N. A model of the atomic configurations of the Ti3AlN/Al0.35Ga0.65N interface is proposed. This model is supported by a good match between the simulated and the experimental HREM image of the Ti3AlN/Al0.35Ga0.65N interface. The formation of TiN and Ti3AlN interfacial layers appears to be responsible for the onset of the ohmic contact behavior in Ti/Ta/Al contacts. © 2000 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2297-2299 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A free-standing GaN template grown by hydride vapor phase epitaxy has been characterized by transmission electron microscopy (TEM). The TEM investigation was augmented by x-ray diffraction, defect delineation etching process followed by imaging with atomic force microscopy and variable temperature photoluminescence. The density of dislocations near the N face was determined to be, in order, 3±1×107, 4±1×107, and about 1×107 cm−2 by cross-sectional TEM, plan-view TEM, and a defect revealing etch, respectively. The same methods on the Ga face revealed the defect concentration to be, in order, less than 1×107 cm−2 by plan-view TEM, less than 5×106 cm−2 by cross-sectional TEM, and 5×105 cm−2 by defect revealing hot H3PO4 acid, respectively. The full width at half maximum of the symmetric (0002) x-ray diffraction peak was 69 and 160 arc sec for the Ga and N faces, respectively. That for the asymmetric (101(underbar)4) peak was 103 and 140 arc sec for Ga and N faces, respectively. The donor bound exciton linewidth was about 1 meV each at 10 K, and a green band centered at about 2.44 eV was observed. © 2001 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 4159-4161 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Defects were observed in GaN:Mg grown on sapphire substrates using metal–organic chemical-vapor deposition (MOCVD) with Mg-delta doping similar to those previously observed in bulk GaN:Mg grown from Ga solution under high hydrostatic pressure of nitrogen. Pyramidal defects (pinholes) with (11¯00) hexagonal facets on the (0001) base plane and six {112¯2} side facets, and defects with a rectangular shape also delineated by planar facets on the basal (0001) planes, were observed for growth with Ga polarity for both of these very different growth methods. The Mg dopant is apparently responsible for their formation since the oxygen concentration in the MOCVD-grown samples was orders of magnitude lower than in the bulk samples. Mg segregation on these planes apparently does not allow uniform continuous growth on these planes leading to these hollow defects. Some defects in the heterolayers also develop into longer nanotubes elongated along the c axis. Change of polarity from Ga to N followed by a change back to Ga polarity also resulted in formation of planar defects previously observed in bulk samples for growth with N polarity. © 1999 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2699-2701 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Both the hexagonal and cubic GaN phases were synthesized in GaAs (001) by 50 keV N ion implantation at 380 °C and subsequent furnace annealing at 850–950 °C for 10 min–2 h. For a fluence of 1.5×1017 cm−2, transmission electron microscopy revealed that cubic GaN epitaxially crystallizes as precipitates in the GaAs matrix. A cubic-to-hexagonal GaN phase transition was observed for extended thermal anneals. By increasing the N fluence to 3×1017 cm−2, a continuous buried layer of randomly oriented hexagonal-GaN nanocrystals was produced. © 1995 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2809-2811 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evolution of defect structures and surface reconstruction of Ga0.47In0.53As epitaxial layers grown by molecular beam epitaxy on InP substrate have been investigated by TEM and RHEED over a wide growth temperature range (150 °C≤Tg≤450 °C) before and after annealing. In the growth temperature range 400 °C≤Tg≤450 °C, extensive segregation of In near the layer surface takes place. The maximum of In concentration was found to lie under the layer surface. The kinetic of surface pit formation after annealing was explained in terms of surface reconstruction and As clustering. Extensive As clustering was observed after annealing for the growth temperature range 175 °C≤Tg≤300 °C. Analysis of diffuse scattering and dark-field images made it possible to propose an atomic model of cluster structure. Precipitate formation close to the interface was observed only for the samples grown at 150 °C and annealed at 500 °C. Differences in electrical properties between LT-grown GaAs and Ga0.47In0.53As are explained in terms of the structural defects.
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  • 7
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A systematic study of the structural quality and arsenic content of as-grown In0.52Al0.48As/InP layers deposited on InP by molecular beam epitaxy at temperatures between 150 and 450 °C was performed using transmission electron microscopy and particle-induced x-ray emission. We found that the amount of As incorporated in the layers generally increases with decreasing growth temperature, with the crystalline quality of the layers being good at growth temperatures higher than 200 °C. At 150 °C, a large density of pyramidal defects is formed, the defects are related to the very large amount of excess As incorporated into the layer. The mechanisms leading to the formation of these defects are discussed. At 200 °C, however, the amount of excess As is lower than expected, and wavy streaks of diffuse scattering are seen in electron diffraction. It is shown that small ordered domains of the CuPt type on the group III atoms are responsible for these features.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2153-2155 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A systematic study of the change in structural quality of as-grown GaAs layers deposited at temperatures between 180 and 210 °C by molecular beam epitaxy was performed using transmission electron microscopy, double-crystal x-ray rocking curves, and particle-induced x-ray emission. We found that the crystal quality was correlated strongly with growth temperature near 200 °C. The lattice parameter and the amount of As incorporated in the layer were observed to increase at lower growth temperatures. After exceeding a certain growth-temperature-dependent layer thickness, large densities of pyramidal-type defects are formed, which at lowest growth temperature result in the breakdown of crystallinity and in columnar polycrystalline growth. The lattice expansion is ascribed to the excess As in the layers. The mechanisms of breakdown of crystallinity are discussed.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Advances in Space Research 2 (1982), S. 213-216 
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Advances in Space Research 2 (1982), S. 213-216 
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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