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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 306-310 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By separating a 2-μm-thick molecular-beam-epitaxial GaAs layer grown at 200 °C from its 650-μm-thick substrate, we have been able to obtain accurate Hall-effect and conductivity data as functions of annealing temperature from 300 to 600 °C. At a measurement temperature of 300 K, analysis confirms that hopping conduction is much stronger than band conduction for all annealing temperatures. However, at higher measurement temperatures (up to 500 K), the band conduction becomes comparable, and a detailed analysis yields the donor and acceptor concentrations and the donor activation energy. Also, an independent absorption study yields the total and charged AsGa concentrations. Comparisons of all of these quantities as a function of annealing temperature TA show a new feature of the annealing dynamics, namely, that the dominant acceptor (probably VGa related) strongly decreases and then increases as TA is increased from 350 to 450 °C. Above 450 °C, ND, NA, and [AsGa] all decrease, as is known from previous studies.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5981-5984 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A thin, undoped, molecular beam epitaxial (MBE) GaAs cap layer grown on top of an n-type conductive layer significantly reduces the free-electron depletion from the latter. By analyzing electron transfer to surface, interface, and bulk acceptor states in the cap, as a function of cap thickness, we show that either (1) the usual EC−0.7 eV surface states are absent, (2) a dense donor near EC−0.4 eV exists or (3) a high donor interface charge (∼5×1012 cm−2) is present. Any of these conclusions constitutes an important new aspect of low-temperature MBE GaAs.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 3864-3867 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence measurements at 2 and 2–40 K were made to study effects due to In alloying for InxGa1−xAs semi-insulating substrate materials grown by the liquid-encapsulated Czochralski method. The neutral CAs bound exciton is a good photoluminescence transition to determine a small variation of In composition in the range of 0≤x≤0.014. The band-gap reduction ΔEg (eV) can be expressed by −1.59x. The radial nonuniformity of In concentration and photoluminescence intensity were determined. The axial segregation of In was also analyzed with the help of the neutron activation analysis and spark-source mass spectrometry.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1375-1377 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The pits formed on an etched GaAs surface, due to the anisotropic etching around dislocations, are efficient light scatterers, and thus reduce transmission. We have derived a quantitative relationship between the fractional transmission and the etch-pit density (EPD) and have shown that the same absorption apparatus which is commonly used to obtain a whole-wafer [EL2] map can also be used to generate an EPD map. The technique is verified by comparing the fractional transmission with the actual EPD count at 166 points on a three-inch, low-pressure, liquid-encapsulated Czochralski wafer. Also, [EL2] and EPD maps, with more than 3500 points each, are compared.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2188-2190 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transmission mappings (500 μm×500 μm resolution) at wavelengths of 0.9–1.5 μm on 3 in., n+-GaAs wafers (n(approximately-equal-to)1–2×1018 cm−3) correlate well with carrier concentration n, measured by the Hall effect, and dislocation density, as confirmed by KOH etch-pit patterns. The absorption for λ(approximately-greater-than)1.0 μm (below band edge) varies directly with n via free-carrier interconduction-band transitions, while the absorption for λ(approximately-less-than)0.95 μm (near band edge) varies inversely with n because of band-filling effects. Both phenomena are highly useful for n+-GaAs wafer characterization. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2900-2902 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Absorption measurements at 1.1 and 1.2 μm were used along with the known electron and hole photoionization cross sections for EL2 to determine deep donor (EL2-like) and acceptor concentrations ND=9.9×1019 and NA=7.9×1018 cm−3, respectively, in a 2-μm-thick molecular-beam epitaxial GaAs layer grown at 200 °C on a 2-in.-diam semi-insulating wafer. Both lateral and depth uniformities of ND over the wafer were excellent as was also the case for the conductivity. Band conduction was negligible compared to hopping conduction at 296 K as evidenced by the lack of a measurable Hall coefficient.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 1000-1002 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have evaluated the uniformity in [EL2], dislocation (or etch-pit) density (EPD), resistivity, mobility, and carrier concentration for 3-in., semi-insulating GaAs wafers grown by the vertical-gradient-freeze (VGF) technique. Although slight W or U patterns were observed in [EL2] and EPD along the 〈110〉 directions, for the first time, nevertheless the overall uniformity was excellent, and comparable to that in the best In-doped and whole-boule-annealed ingots grown by the liquid-encapsulated Czochralski (LEC) technique. Based on results from implant-activation studies on LEC wafers, it is estimated that the measured nonuniformities in EPD and [EL2] for the VGF wafers would contribute only about 1% to implant-activation-efficiency nonuniformities in Si-implanted wafers designed for field-effect transistor applications.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    International urology and nephrology 18 (1986), S. 271-275 
    ISSN: 1573-2584
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Epidemiological information on calcium oxalate urolithiasis is reviewed and interpreted according to a proposed stress-related mechanism. This mechanism involves hypothalamo-hypophyseal secretion firstly of vasopressin which acts directly to produce hypertonic urine and secondly of adrenocorticotropin which acts via a secondary hyperparathyroid mechanism to raise serum calcium levels.
    Type of Medium: Electronic Resource
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