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  • Articles: DFG German National Licenses  (26)
  • 1985-1989  (26)
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  • Articles: DFG German National Licenses  (26)
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  • 1
    Electronic Resource
    Electronic Resource
    Transmission electron microscopy studies of superconducting Y-Ba-Cu-O films prepared by laser deposition (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 1834-1836 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The polycrystalline structure of pulsed-laser deposited Y-Ba-Cu-O thin films was studied using transmission electron microscopy. Many grains of the superconducting films on (001) SrTiO3 substrates had the c axis normal to the surface, while grains on (110) facets had their c axis oriented preferentially along the interface. Observation of an amorphous layer of thickness ∼6 nm at some oriented grain-substrate interfaces suggests that the amorphous layer is formed subsequent to the formation of the crystalline structures. Surface ridges were found to facilitate the formation of triple points where the grain boundaries between nonepitaxial grains were pinned.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99730
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Microstructure of in situ epitaxially grown superconducting Y-Ba-Cu-O thin films (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1702-1704 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure of in situ epitaxially grown Y-Ba-Cu-O thin films on (001) SrTiO3 substrates was studied using cross-sectional transmission electron microscopy. The films, prepared by pulsed laser deposition at substrate holder temperature of 650 °C without post-annealing, exhibit zero resistivity above 90 K and critical currents exceeding 106 A/cm2 at 77 K. The films are of heavily faulted single crystalline structure with the c axis approximately perpendicular to the substrate (001) surface. We suggest that, due to the fast quenching and low substrate temperature, crystalline defects and chemical fluctuations are locked into a faulted structure after each laser pulse. Despite their rather imperfect microstructure, the films are free from macroscopic grain boundaries and secondary phases and possess superb superconducting properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101562
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Optical investigation of atomic steps in ultrathin InGaAs/InP quantum wells grown by vapor levitation epitaxy (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 442-444 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrathin InGaAs/InP single quantum well structures, grown by chloride transport vapor levitation epitaxy, have been investigated by low-temperature photoluminescence (PL). Well-resolved multiple peaks are observed in the PL spectra, instead of an expected single peak. We attribute this to monolayer (a0/2=2.93 A(ring)) variations in quantum well (QW) thickness. Separate peak positions for QW thicknesses corresponding to 2–6 monolayers have been determined, providing an unambiguous thickness calibration for spectral shifts due to quantum confinement. The PL peak corresponding to two monolayers occurs at 1.314 eV, corresponding to an energy shift of 524 meV. Experimental data agree very well with a simple effective mass theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100946
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  • 4
    Electronic Resource
    Electronic Resource
    Smooth high Tc Y1Ba2Cu3Ox films by laser deposition at 650 °C (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 517-519 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting Y1Ba2Cu3Ox films 300 nm thick with local surface roughness 〈5 nm have been prepared by laser deposition at 650 °C and subsequent heat treatments at 450 °C; highest zero resistance temperature was above 85 K. Smooth topography and low-temperature processing are crucial for device fabrication. These films are crack-free and density of particles with 〉1 μm diameter was 〈10/cm2. We suggest that an effective increase in surface temperature and deposition directly in the orthorhombic phase contributes to film quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100622
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  • 5
    Electronic Resource
    Electronic Resource
    GaAs-on-InP heteroepitaxial waveguides grown by molecular beam epitaxy (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 1242-1244 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The GaAs-on-InP heteroepitaxial waveguides are demonstrated for the first time using molecular beam epitaxy. A propagation loss of 9.3 dB/cm was obtained for waveguides grown on a 3° off (100) InP substrate. Compared to the 16 dB/cm loss for waveguides on (100) InP substrates, the waveguides on misoriented InP substrates exhibited a significantly lower loss. Based on photoluminescence studies, we attribute the propagation loss in both samples mainly to optical absorption by crystal defects. Defect densities of 4×1017 cm−3 and 2×1017 cm−3 are estimated for material on (100) and 3° off (100) substrates, respectively. Such heteroepitaxial waveguides may have applications in long-wavelength photonic integrated circuits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100026
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  • 6
    Electronic Resource
    Electronic Resource
    InAs strained-layer quantum wells with band gaps in the 1.2–1.6 μm wavelength range (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 892-894 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Strained In0.52Al0.48As/InAs single quantum wells have been grown by molecular beam epitaxy on InP substrates and their structural quality and commensurability demonstrated by transmission electron microscopy. Intense photoluminescence in the wavelength range of 1.2–1.6 μm for well widths between 10 and 30 A(ring) was obtained, indicating a very efficient carrier collection into the highly (3.4%) biaxially compressed InAs wells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99264
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    X-ray interference measurement of ultrathin semiconductor layers (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1774-1776 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have characterized, using the interference structure in x-ray rocking curves, a single or double strained GaInP layer grown on an InP substrate. The measured GaInP layer thicknesses are 9±3 A(ring) and 107±3 A(ring) for the single strained layer samples and 7 A(ring)/50 A(ring) and 32 A(ring)/32 A(ring) for the double strained layer samples. The rocking curve results for the 107 A(ring) single-barrier sample and the 7 A(ring)/50 A(ring) double-barrier sample agreed well with the cross-section transmission electron microscopy data and the secondary-ion mass spectrometry data. The x-ray interference structure for the single strained barrier samples indicates the existence of many half-monolayer steps within the 1×1 mm2 x-ray beam spot at each GaInP/InP interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102189
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  • 8
    Electronic Resource
    Electronic Resource
    Single quantum wire semiconductor lasers (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2715-2717 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single quantum wire GaAs/AlGaAs injection lasers were fabricated using organometallic chemical vapor deposition on V-grooved GaAs substrates. The quantum wire active region has a crescent-shaped cross section ∼100 A(ring) thick and less than 1000 A(ring) wide. Amplified spontaneous emission and lasing spectra of the quantum wire lasers exhibit effects due to transitions between quasi-one-dimensional subbands separated by ∼10 meV. Single quantum wire laser structures with tight optical confinement exhibited threshold currents as low as 3.5 mA for uncoated devices at room temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101934
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    High critical currents in epitaxial YBa2Cu3O7−x thin films on silicon with buffer layers (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 754-756 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: As-deposited superconducting thin films (∼0.1 μm) of YBa2Cu3O7−x have been prepared by pulsed laser deposition on (100) Si with buffer layers of BaTiO3/MgAl2O4. X-ray diffraction studies reveal that the films grow epitaxially with the c axis preferentially oriented normal to the substrate surface. This is confirmed by ion channeling measurements along the (100) (normal to the surface) and (110) directions of the Si substrate showing a minimum yield of 54% along the (100), and 78% along the (110) axes using 2.8 MeV He++. Preliminary transmission electron microscopy study also supports these results. The as-deposited films have zero resistance temperatures of 86–87 K, and critical current densities of 6×104 A/cm2 at 77 K and 1.2×105 A/cm2 at 73 K. Our results indicate that the superconducting properties of the films are limited primarily by the quality and degree of epitaxal growth of the buffer layers on the silicon substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101471
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    High-temperature superconductivity in ultrathin films of Y1Ba2Cu3O7−x (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 581-583 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have grown ultrathin films of Y1Ba2Cu3O7−x in situ on (001) SrTiO3 by pulsed laser deposition. The zero resistance transition temperature (Tc0) is 〉90 K for films 〉300 A(ring) thick. The critical current density (Jc at 77 K) is 0.8×106 A/cm2 for a 300 A(ring) film and 4–5×106 A/cm2 for a 1000 A(ring) film. The Tc0 and Jc deteriorate rapidly below 300 A(ring), reaching values of 82 K and 300 A/cm2 at 77 K, respectively, for a 100 A(ring) film. Films only 50 A(ring) thick exhibit metallic behavior and possible evidence of superconductivity without showing zero resistance to 10 K. These results are understood on the basis of the defects formed at the film-substrate interface, the density of which rapidly decreases over a thickness of 100 A(ring). We have studied these defects by ion channeling measurements and cross-section transmission electron microscopy. Our results suggest that the superconducting transport in these films is likely to be two dimensional in nature, consistent with the short coherence length along the c axis of the crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101463
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    Paper (German National Licenses)
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