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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5110-5113 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The band gap and microstructure of Ga0.5In0.5P have been shown to vary with deposition conditions. However, growth on (511)B GaAs substrates has been reported to give Ga0.5In0.5P with band gaps close to that of disordered material. It is shown here, that with appropriate selection of the growth parameters, Ga0.5In0.5P can be grown with low band gap and significant ordering on even the (511)B substrates, implying that surface steps play an important role in the ordering process. For the lattice-matched composition, a band gap of 1.83 eV was obtained using low growth temperature (575 °C), low growth rate (0.55 μm/h), and high phosphine pressure (5 Torr).
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6378-6384 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: YBa2Cu3O7−δ superconductor–normal–superconductor junctions in step-edge geometry are fabricated by an in situ process using off-axis sputter deposition. Gold is used as the normal metal interlayer. A special inhibiting layer is introduced to ensure proper separation of the superconducting electrodes. The temperature dependence of the critical current Ic is nearly linear. The junctions show high normal resistances up to RN=10 Ω and high IcRN products up to 8.8 mV at 4.2 K. I–V characteristics exhibit a large excess current Iex over the whole temperature range, even for electrically narrow junctions. The power dependence of Shapiro step heights shows characteristic deviations from the resistively and capacitively shunted junction model. Calculations using the time-dependent Ginzburg–Landau equations are carried out to model the measured I–V characteristics with and without microwave irradiation. A point-contact-like superconductor–constriction–superconductor model is suggested to explain the excess current and the measured temperature dependence of Ic and Iex. Time-dependent Ginzburg–Landau equations are used to account for the observed dynamic characteristics. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The formation chemistry and growth dynamics of thin-film CuInSe2 grown by physical vapor deposition have been considered along the reaction path leading from the CuxSe:CuInSe2 two-phase region to single-phase CuInSe2. The (Cu2Se)β(CuInSe2)1−β (0〈β≤1) mixed-phase precursor is created in a manner consistent with a liquid-phase assisted growth process. At substrate temperatures above 500 °C and in the presence of excess Se, the film structure is columnar through the film thickness with column diameters in the range of 2.0–5.0 μm. Films deposited on glass are described as highly oriented with nearly exclusive (112) crystalline orientation. CuInSe2:CuxSe phase separation is identified and occurs primarily normal to the substrate plane at free surfaces. Single-phase CuInSe2 is created by the conversion of the CuxSe into CuInSe2 upon exposure to In and Se activity. Noninterrupted columnar growth continues at substrate temperatures above 500 °C. The addition of In in excess of that required for conversion produces an In-rich near-surface region with a CuIn3Se5 surface chemistry. A model is developed that describes the growth process. The model provides a vision for the production of thin-film CuInSe2 in industrial scale systems. Photovoltaic devices incorporating Ga with total-area efficiencies of 14.4%–16.4% have been produced by this process and variations on this process. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We present the design of a new ultrahigh vacuum scanning tunneling microscope (STM) which operates at T〈20 K inside the bore of a 2.5 T superconducting split-coil magnet. The tip/sample region can easily be controlled visually, thus allowing safe and fast exchange of samples and tips while the microscope stays at low temperatures. A newly developed rotary motion stepper motor is presented which allows rotation of the sample by 〉270° about an axis perpendicular to the tip axis. This feature allows metal or molecular beam evaporation normal to the sample surface. Even more important, by means of this device tip and sample can be brought into a parallel or antiparallel magnetic configuration thus opening a novel approach to the study of magnetic phenomena on an atomic length scale. In addition, measurements of the magneto-optical Kerr effect can be carried out without removing the sample from the STM. Also a new tip exchange mechanism is described. The microscopic and spectroscopic performance of the new instrument is illustrated on Au(111)/mica, on Tb(0001)/W(110), and on Gd(0001)/W(110). © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1455-1457 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A new ultrahigh vacuum (UHV) scanning tunneling microscope design has been developed and optimized for in situ investigations of thin-film growth. The basic concept of the microscope is to retract the sample by means of the coarse positioning motor under an angle of 30° with respect to the piezotube scanner. This geometric arrangement allows normal film deposition and excludes any interaction between the evaporation beam and the tip. The instrument has the capability of regaining a particular microscopic location on the sample surface with an accuracy of less than 100 nm posterior to a sample displacement of more than 20 mm. Sequences of images of a spot during homoepitaxial growth of Cr on a Cr(100) single-crystal substrate have been obtained. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3300-3306 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: GaInAs/InP single quantum well structures with thicknesses below 5 nm were grown by metalorganic vapor phase epitaxy at reduced pressure. The sharpness of the heterojunctions in this III/V system is found to be strongly dependent on the applied gas switching sequence between the growth of the two materials caused by As carry over after GaInAs and by group V atom exchange at the surface during a hydride stabilized growth interruption. The photoluminescence properties can be improved by adding intermediate monolayers of InAsP between InP and GaInAs and GaInAsP between GaInAs and InP. The photoluminescence of very thin quantum wells is split into multiplets due to the formation of growth islands at the interface. Size and lateral distribution of these islands have been observed directly by cathodoluminescence analysis. On the other hand, transmission electron microscopy measurements show that the interfaces within the growth island regions are not atomically smooth but of a certain roughness. Small microislands with diameters of a few lattice constants form the "internal'' interface structure.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2659-2661 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Using simultaneous measurements of electron beam induced current and cathodoluminescence intensity it is possible to distinguish between different contributions to signal magnitude and contrast at defects. In this letter we report on the application of this technique to investigate the role of impurity aggregation and defect decoration on the recombination behavior of dislocations in GaAs. In the experiment described here we diffused copper into the crystal. We observed an increase of signal contrasts and changes in the contrast profiles. With the help of computer simulations these experimental results can be interpreted as a homogeneous decoration of dislocations, the formation of precipitates at the dislocations, and a reduced minority-carrier diffusion length in the bulk.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 458-460 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We demonstrate a compact ultraviolet light source based on frequency-converted diode-pumped passively Q-switched miniature Nd:yttrium–aluminum–garnet (YAG) ring lasers. A unique pulse-to-pulse stability in single-frequency operation is obtained by diffusion-bonding the Nd:YAG crystal with the Cr4+:YAG saturable absorber crystal to form an all-solid-state quasimonolithic ring laser cavity. Amplified in a longitudinally pumped Nd:vanadate (YVO4) crystal and single-pass frequency quadrupled in periodically poled potassium titanyl phosphate and barium borate crystals, an average output power of 485 mW at 266 nm with 25 μJ pulse energy is achieved with an overall efficiency of 3.3% with respect to the diode pump power. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 714-716 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We demonstrate a compact source of ultraviolet single-frequency pulses with high average output power realized by subsequent single-pass frequency doubling and quadrupling of a diode-pumped passively Q-switched miniature Nd:YAG ring laser. Pulse widths of 2 ns (full width at half maximum), 20 μJ single pulse energy, and 10 kW peak power are achieved at a wavelength of 266 nm with kilohertz repetition rates. A single-pass energy conversion efficiency of 22% with respect to the fundamental light at 1064 nm and an overall efficiency of 2.8% with respect to the diode pump power are obtained. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 696-698 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Current transport across each of the two YBa2Cu3O7–Au interfaces in a step-edge superconductor–normal metal–superconductor (SNS) Josephson junction could be investigated independently, due to contacts to the Au interlayer. The I–V characteristics of each superconductor–normal metal (SN) interface showed dc and ac Josephson-like effects fitting well to a model, which takes into account the influence of proximity effect in the normal metal layer on the transport across the SN interface, and Andreev reflection at the interface. In the investigated junctions, both SN interfaces of the step SNS junctions had similar transparencies. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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