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  • 1
    Electronic Resource
    Electronic Resource
    Optimization of modulation-doped Ga1−xInxAs/InP heterostructures towards extremely high mobilities (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4489-4493 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper presents a study of the electrical and structural properties of inverted modulation-doped GaInAs/InP heterostructures grown by low-pressure metalorganic vapor phase epitaxy. First, the thickness of the GaInAs layer was optimized in lattice-matched samples to find the smallest thickness in which high Hall mobility is observed. Next, in a section closest to the InP the In content was varied. A steady increase of mobility with indium composition was observed. A maximum of 450 000 and 15 500 cm2/V s was obtained for a 10-nm-thick Ga1−xInxAs layer with x=0.77 at 6 and 300 K, respectively. Channels with higher indium content exceed the critical thickness and mobility drops off sharply. The decreasing mobility correlates with the formation of misfit dislocations at the interface indicating increasing scattering processes of the GaInAs layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352789
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  • 2
    Electronic Resource
    Electronic Resource
    Interdiffusion and short-range order in amorphous Ta-Si multilayer structures (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2694-2701 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Sequential sputter deposition of amorphous 4-nm-thick Ta and 7-nm-thick Si layers leads to the formation of a periodic multilayer that can be regarded as a synthetic one-dimensional crystal. A simple kinematical diffraction model is presented to discuss x-ray diffraction patterns obtained from the multilayer structure during annealing. Post-deposition annealing up to temperatures above 530 °C, where the lattice structure disappears, leads to Si diffusion into the Ta layers forming a nonstoichiometric Ta-Si phase. The high diffusion rate of Si in Ta leads to a homogeneous distribution of Si in the Ta (silicide) regimes. As shown by cross-sectional transmission electron microscopy, the interfaces remain sharp during the interdiffusion process. This makes the observation of low-angle Bragg reflections up to the 12th order possible. The local atomic structure around the Ta atoms was analyzed by measuring the extended x-ray-absorption fine structure above the Ta LIII edge at different probing depth conditions. During annealing the local Ta environment was found to be TaSi2 like, even if only a small portion of the Si has diffused into the Ta layers, and the silicide formation is far from stoichiometry. The formation of a Ta suboxide was detected in the surface region of the top Ta layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346469
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  • 3
    Electronic Resource
    Electronic Resource
    Preparation of highly transparent superconductor-semiconductor contacts (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 3522-3526 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this report we present a procedure to fabricate highly transmissive superconducting Nb-In0.77Ga0.23As contacts. A combination of a sulphur passivation of the etched semiconductor prior to the deposition of Nb and an annealing step is used. To quantitatively classify the transparency of the contacts, transport measurements of the differential conductance are carried out at 300 mK and compared with a model given by Blonder, Tinkham, and Klapwijk [Phys. Rev. B 25, 4515 (1981)]. The procedure yields almost ideal superconductor-semiconductor contacts. Additionally, a high reproducibility of the contact transparency is achieved. The results are interpreted in terms of diffusion of In in both the niobium and the In0.77Ga0.23As. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288504
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  • 4
    Electronic Resource
    Electronic Resource
    Quantized conductance in a split-gate point contact based on a pseudomorphic InGaAs/InP heterostructure (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 871-875 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper the fabrication and characterization of split-gate point contacts based on a pseudomorphic InGaAs/InP heterostructure with an indium content of 77% in the strained channel layer is described. Steps in the conductance were observed, which are due to quantized conductance through the quasi one-dimensional constriction formed by the split-gates. Deviations from the ideal quantization are studied by applying differing bias voltages on the two fingers forming the point contact. Since the channel layer of our structure consists of a ternary material it is argued that, beside impurity and interface roughness scattering, alloy scattering processes contribute significantly to the observed deviations of the ideal quantized conductance. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360907
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  • 5
    Electronic Resource
    Electronic Resource
    Low- and high-field transport properties of pseudomorphic InxGa1−xAs/InP (0.73≤x≤0.82) p-type modulation-doped single-quantum-well structures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3507-3515 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transport properties of three p-type modulation-doped InxGa1−xAs/InP (0.73≤x≤0.82) single-quantum-well structures grown by metalorganic chemical-vapor deposition are reported. High carrier mobilities of μH=7800 cm2/V s coupled with total carrier concentrations of pS=2.1×1012 cm−2 were reached, for example, for x=0.73 at 5 K. Shubnikov–de Haas and quantum Hall-effect measurements at 50 mK showed the population of two spin-split V3/2 subbands. Using p-modulation-doped field-effect transistors with a gate length of LG=1 μm, fabricated on the same samples, the carrier transport at moderate and high fields was investigated at 77 K. Thereby, the population of the heavy-hole subband and, above a critical field, also the occupation of the light-hole subband were verified. With the help of dc transconductance (gmext-VGS) and magnetotransconductance measurements a decoupling between both subbands at cryogenic conditions and moderate fields was observed, resulting in two clearly defined conducting channels. Further analysis of the measured mobility-voltage (μ-VGS) and velocity-field (vavg-Eavg) profiles revealed that carrier transport in compressively strained two-dimensional hole gas (2DHG) systems is strongly affected by intersubband scattering and shows a nonlinear behavior at low fields, caused by the zone-center degeneracy of their E-k(parallel) distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356113
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  • 6
    Electronic Resource
    Electronic Resource
    Transmission and gain of singly and doubly focusing refractive x-ray lenses (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5855-5861 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Multiple refractive lenses with a focal length of 1 to 2 m are a new tool for focusing hard x rays to a spot size in the micrometer range. They may be used for microdiffraction, microfluorescence, and coherent imaging. The lenses may be focusing in one or two dimensions. In this article, we have calculated the transmission and the gain for linear lens arrays, for crossed linear arrays and for doubly focusing lenses with parabolic profile. It is essential to minimize the mass absorption coefficient μ/ρ by choosing low Z materials in order to optimize the transmission. The gain of the lenses can be as high as 5000 and more, i.e., the intensity in the focal spot can be 5000 times higher than that behind a pinhole of size equal to the spot size. In real lenses the gain is smaller and the focal spot is blurred by lens imperfections, by Compton scattering, and by small angle x-ray scattering (SAS). In the present investigation different low Z materials have been tested for SAS. Different linear and crossed linear lenses made of beryllium, boron nitride, pyrographite, plexiglass, polycarbonate, polyoxymethylene, Vespel, and aluminium have been tested for focal spot size, gain, and background. The maximum gain obtained up to now was 13. The focal spot size is slightly larger than the value expected from demagnification of the source size. Possibilities for improving the lens performance are discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368899
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  • 7
    Electronic Resource
    Electronic Resource
    High resolution imaging and lithography with hard x rays using parabolic compound refractive lenses : Papers from the 12th National Synchrotron Radiation Instrumentation Conference (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1640-1642 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Parabolic compound refractive lenses are high quality optical components for hard x rays. They are particularly suited for full field imaging, with applications in microscopy and x-ray lithography. Taking advantage of the large penetration depth of hard x rays, the interior of opaque samples can be imaged with submicrometer resolution. To obtain the three-dimensional structure of a sample, microscopy is combined with tomographic techniques. In a first hard x-ray lithography experiment, parabolic compound refractive lenses have been used to project the reduced image of a lithography mask onto a resist. Future developments are discussed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1445827
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  • 8
    Electronic Resource
    Electronic Resource
    Gas source molecular beam epitaxy of FeSi2/Si(111) heterostructures (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2271-2273 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial iron disilicide thin layers have been grown on silicon by gas source molecular beam epitaxy (GSMBE) in the temperature range 450–550 °C. Fe(CO)5 and SiH4 are used as sources for the silicide growth on a heated Si(111) surface. The growth phases are characterized in situ by means of high-resolution electron energy loss spectroscopy, ultraviolet and x-ray photoelectron spectroscopies. The formation of an epitaxial metallic γ-FeSi2 layer at the interface with the silicon substrate is revealed and no complete relaxation of this strained metastable interface layer is observed, as the growth proceeds with the semiconducting equilibrium β-FeSi2 phase. The coexistence in the GSMBE grown heterostructures of the metallic (CaF2) and semiconducting (orthorhombic) FeSi2 structures is confirmed by cross-section transmission electron microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109411
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of electron-electron interaction on hot ballistic electron beams (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 3603-3605 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron-electron scattering of ballistic electrons in a two-dimensional electron gas was studied as a function of the electron excess energy above the Fermi energy and of temperature. At low temperatures of 1.4 K it is found that for excess energies of approximately 30% of the Fermi energy the electrons in a ballistic electron beam are already scattered significantly due to electron-electron interaction. A very good agreement between our experimental data and theory was found, when the measured data were compared with numerical calculations based on a theory of Giuliani and Quinn [Phys. Rev. B 26, 4421 (1982)], while the agreement was only poor for the analytical approximation of the electron-electron scattering rate. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113801
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  • 10
    Electronic Resource
    Electronic Resource
    A microscope for hard x rays based on parabolic compound refractive lenses (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3924-3926 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe refractive x-ray lenses with a parabolic profile that are genuine imaging devices, similar to glass lenses for visible light. They open considerable possibilities in x-ray microscopy, tomography, microanalysis, and coherent scattering. Based on these lenses a microscope for hard x rays is described, that can operate in the range from 2 to 50 keV, allowing for magnifications up to 50. At present, it is possible to image an area of about 300 μm in diameter with a resolving power of 0.3 μm that can be increased to 0.1 μm. This microscope is especially suited for opaque samples, up to 1 cm in thickness, which do not tolerate sample preparation, like many biological and soil specimens. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124225
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