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  • 1
    Electronic Resource
    Electronic Resource
    Interfacial properties of very thin GaInAs/InP quantum well structures grown by metalorganic vapor phase epitaxy (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3300-3306 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350949
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  • 2
    Electronic Resource
    Electronic Resource
    A low-temperature ultrahigh vacuum scanning tunneling microscope with a split-coil magnet and a rotary motion stepper motor for high spatial resolution studies of surface magnetism (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 424-430 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150218
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  • 3
    Electronic Resource
    Electronic Resource
    An ultrahigh vacuum scanning tunneling microscope for in situ studies of thin-film growth (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1455-1457 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147951
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  • 4
    Electronic Resource
    Electronic Resource
    Superconductor–normal–superconductor step-edge junctions with Au barriers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6378-6384 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363715
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  • 5
    Electronic Resource
    Electronic Resource
    Low-band-gap Ga0.5In0.5P grown on (511)B GaAs substrates (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5110-5113 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355756
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  • 6
    Electronic Resource
    Electronic Resource
    Structure, chemistry, and growth mechanisms of photovoltaic quality thin-film Cu(In,Ga)Se2 grown from a mixed-phase precursor (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 153-161 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359362
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  • 7
    Electronic Resource
    Electronic Resource
    Current transport across YBa2Cu3O7–Au interfaces (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 696-698 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117810
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  • 8
    Electronic Resource
    Electronic Resource
    Impurity aggregation at individual dislocations in GaAs observed by means of a simultaneous electron beam induced current and cathodoluminescence technique (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2659-2661 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101027
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  • 9
    Electronic Resource
    Electronic Resource
    Band-gap narrowing in ordered Ga0.47In0.53As (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 1806-1808 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the first observation of band-gap energy reduction in Ga0.47In0.53As deposited on (100) InP by atmospheric pressure organometallic vapor phase epitaxy due to CuPt-type ordering. A reduction of more than 65 meV in the band-gap energy is observed for lattice-matched samples that show strong CuPt-like ordering by transmission electron microscopy. By comparison samples that show no CuPt-like ordering diffraction signatures, do not have reduced band-gap energies. Studies of the influence of growth parameters on the band-gap energy indicate a U-shaped dependence on the growth temperature with a minimum around 550 °C and decreasing band-gap energies with increasing growth rate (at a constant V/III ratio) over the range 0.5–4 μm/h.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109640
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  • 10
    Electronic Resource
    Electronic Resource
    Microwave rf SQUID integrated into a planar YBa2Cu3O7 resonator (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2303-2305 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We fabricated and characterized microwave rf SQUIDs integrated into a planar, S-shaped λ/2 microstrip resonator. This 3 GHz resonator was fabricated from a pulsed-laser-deposited YBa2Cu3O7 epitaxial film. The SQUID structures incorporated double step-edge junctions and had a loop inductance of 120 pH. Such unoptimized SQUIDs operated between 4.2 and 85 K with dV/dΦ=18–20 μV/Φ0 at 77 K. At that temperature, the energy resolution of (8±2)×10−29 J/Hz above 0.1 Hz (in the best samples) was limited by the white noise, SΦ1/2=(7±1)×10−5 Φ0/Hz1/2. Optimization may increase dV/dΦ and improve the energy resolution by up to an order of magnitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107011
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