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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2615-2617 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the direct formation of self-assembled GaAs/AlGaAs quantum dots by low-temperature molecular beam epitaxy. To drive a three dimensional growth mode, the (1×1) AlGaAs surface was exposed alternately to the Ga and As sources. The resulting GaAs nanocrystals having {111} facets were clearly identified by high-resolution transmission electron microscopy. The emission spectra also confirmed the formation of dots. The transition to a three-dimensional growth mode is attributed to the limited surface migration of Ga adatoms on the AlGaAs surface, which has excess As at low substrate temperature. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermally stable, low-resistance PdGe-based ohmic contacts to high–low doped n-GaAs have been developed. The lowest contact resistance obtained is two times lower than that of previously reported PdGe ohmic contacts. The contacts are thermally stable even after isothermal annealing for 5 h at 400 °C under atmosphere ambient. X-ray diffraction results and Auger depth profiles show that the good PdGe-based ohmic contact is due to the formation of both AuGa and TiO compounds. The AuGa compound enhances the creation of more Ga vacancies, followed by the incorporation of Ge into Ga vacancies, and the TiO compound suppresses As outdiffusion from the GaAs substrate, respectively. © 1995 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. 3642-3644 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the intrinsic Schottky barrier height of Au/n-GaN metal–semiconductor diodes by performing current–voltage measurement on a series of diodes with varying in the range 1017–1019 cm−3 in the GaN layer. The effective barrier height (ΦB) monotonically decreases with increasing doping level. Taking account of the image-charge lowering (ΔΦ), the intrinsic barrier height ΦB0=ΦB+ΔΦ, is almost constant at (0.934±0.015) V up to ∼5×1018 cm−3, which is close to the Schottky limit of 0.94 V. © 2001 American Institute of Physics.
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  • 4
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the ZnSe/GaAs heterostructure, the problems of interdiffusion and thermal stability are very crucial. We have investigated the effects of annealing on ZnSe grown on GaAs by photoluminescence and double-crystal x-ray measurement. In order to investigate annealing effects of the ZnSe/GaAs heterostructure, we used 1.0-μm-thick and 0.2-μm-thick samples. Samples were annealed in the temperature range of 200–500 °C in an N2 ambient for 3 min using a face-to-face configuration with ZnSe epitaxial layer as a cap layer. In the annealing temperature above 450 °C, new emission peaks appeared in the range of 2.62–2.72 eV. The biaxial compressive strain due to lattice mismatch at the growth temperature is mostly relaxed at 400 °C, and the epilayer annealed at 500 °C has a biaxial tensile strain. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The quantum Hall effect measurements have been applied on modulation-doped GaAs/AlGaAs heterostructures with various spacer-layer thicknesses (0–100 A(ring)) for investigating the effects of an undoped layer on localization. The fraction of localized states (α) of Landau levels has been evaluated from the plateau widths in the quantized Hall resistance, and its functional dependences are proposed in terms of electron mobility and magnetic field. The mobility dependence gives an exponential profile, α∼exp(−μ/μ0), which results from a change in the long-range interaction by the variation of spacer-layer thickness. The characteristic mobility, μ0, is within (2.55±0.20)×105 cm2/V s for all step indices from i=4 to i=10, but the localized fraction has an additional dependence on step index. The fraction of localized states as a function of magnetic field shows B3/4 dependence which may be attributed to short-range contribution by interface states or interface roughness between the AlGaAs undoped layer and the GaAs buffer layer.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-acryloyl pyrrolidone (NAP) was synthesized by reaction of pyrrolidone with acryloyl chloride. First, the polymerization of NAP and copolymerization of NAP with styrene (St) were carried out at 60°C, using 2,2′-azobisisobutyronitrile (AIBN) as an initiator. Kinetic studies showed that the rate of polymerization (Rp) could be expressed by Rp = K [AIBN]0.5 [NAP]1.0. The reactivity of NAP was found to be larger than that of N-methacryloyl pyrrolidone. The overall activation energy was calculated to be 24.3 kcal mole-1. The following monomer reactivity ratio and Q and e values were obtained. NAP(M1) - St(M2): r1 = 1.50, r2 = 0.35, Q1 = 0.42, and e1 = 1.60. Second, graft copolymers were synthesized by reacting pyrrolidone, in the presence of a catalytic amount of its potassium salt, with poly(NAP-co-St).
    Additional Material: 10 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5325-5328 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method of evaluating interface states for coupled superlattices has been developed. Explicit solutions for these states have been obtained within the framework of the Kronig–Penney model for the case of two semiconductor superlattices coupled by a tunnel barrier. The interface states are shown to be largely dependent on the coupling strength if the constituent superlattices have identical structure parameters, while insensitive to the tunnel barrier thickness if their structure parameters differ. In the latter case, electrons behave as if the system were composed of two decoupled semi-infinite superlattices.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Ar-electron-cyclotron-resonance (ECR) microwave (MW) plasma has been applied on GaAs surfaces for investigating the effects of radio-frequency bias on etching reaction and radiation damage. The etch depths as a function of the etching time gave a linear profile with etch rates of 75 and 100 A(ring)/min for 150- and 300-W MW powers under a 4-W rf bias, respectively, but for the etch rates an exponential profile is obtained as a function of the square root of the rf bias power. The electrical characteristics of Schottky barriers fabricated on the etched surface show strong rf bias dependence. Increasing the rf bias power, the donor concentration near surface and the barrier height decrease but the ideality factor and the depletion layer width increase monotonically. The changes are attributed to the radiation damage induced by the Ar ECR plasma which becomes gradually deeper in the damage layer and higher in concentration with increasing rf bias power. The rf biasing in the ECR plasma (which has the exceptional characteristic of being applicable to semi-insulating specimens) is very similar in effect to dc biasing.
    Type of Medium: Electronic Resource
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