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  • Digitale Medien  (80)
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  • Digitale Medien  (80)
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  • 1
    Digitale Medien
    Digitale Medien
    Growth and characterization of (111) and (001) oriented MgO films on (001) GaAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3276-3283 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effects of substrate preparation on the structure and orientation of MgO films grown on (001) GaAs using pulsed laser deposition has been investigated. Textured MgO films displaying a (111)MgO(parallel)(001)GaAs orientation relation with x-ray rocking curve full width at half maximum (FWHM) values as low as 1.8° were obtained in cases where the native GaAs surface oxide was only partially desorbed prior to growth. Reflection high-energy electron diffraction, transmission electron microscopy (TEM), and x-ray pole figure analysis of these films reveals a preferential orientation within the plane of the substrate: [11¯0]MgO(parallel)[11¯0]GaAs and [112¯]MgO(parallel)[110]GaAs. An interfacial layer (∼5 nm thick) was observed in high resolution TEM analysis, and was attributed to a remnant native GaAs oxide layer. Complete desorption of the native GaAs oxide at ∼600 °C in vacuum prior to MgO growth led to significant surface roughening due to Langmuir evaporation, and resulted in randomly oriented polycrystalline MgO films. Growth of MgO on Sb-passivated GaAs substrates, which provided smooth, reconstructed surfaces when heated to 350 °C in vacuum, resulted in cube-on-cube oriented films [i.e., (001)MgO(parallel)(001)GaAs,[100]MgO(parallel)[100]GaAs] with x-ray rocking curve FWHM values as low as 0.47°. TEM analysis of the cube-on-cube oriented films revealed evidence of localized strain fields at the MgO/GaAs interface, indicating the presence of misfit dislocations in the MgO layer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.352975
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  • 2
    Digitale Medien
    Digitale Medien
    Terrace width evolution during step-flow growth with multiterrace adatom migration (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7351-7357 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have developed a computer-solvable model of step-flow growth that includes both anisotropic multiterrace adatom migration and asymmetric step edge attachment. We find that terrace widths equalize not only when each adatom preferentially attaches to the ascending step edge of the terrace that it lands on, but also when adatoms preferentially migrate over ascending step edges. This latter process can equalize long-range terrace width nonuniformities much more rapidly than can the former process. We also find that a slow lateral movement of terrace width distributions occurs when each adatom adheres to the step edges of the terrace that it lands on. More significantly, we find that a rapid lateral movement of terrace width distributions occurs when adatoms cross multiple step edges. This motion is especially fast when adatoms migrate distances that are comparable to or greater than the terrace width distribution period. We simulated the evolution of an experimentally observed (Al,Ga)Sb lateral superlattice (LSL) terrace width distribution, which led to quantitative estimates of the adatom migration characteristics present during the LSLs growth. At least one type of adatom, probably Ga, migrates nearly isotropically over many terraces. This method of determining adatom migration characteristics can be extended to any material system that allows LSL layers to be grown as terrace width markers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.354026
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  • 3
    Digitale Medien
    Digitale Medien
    Capacitance-voltage profiling through graded heterojunctions: Theory and experiment (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 251-260 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Starting from the general equations for capacitance-voltage (CV) profiling through a graded heterojunction, we obtain numerical solutions to yield thermal-equilibrium energy-band diagrams, real electron profiles, and apparent electron profiles (i.e., the profile extracted from a CV measurement) for modulation-doped square, triangular, and parabolic potential wells. Room-temperature CV measurements are performed on parabolic potential wells grown by molecular beam epitaxy in the AlxGa1−xAs system, and the measured apparent electron profiles fitted to computer reconstructions whence the real electron distributions are deduced. These measurements reflect a uniform electron distribution in a parabolic well, with 3D electron density determined by well curvature. Data analysis also suggests the presence of a doping asymmetry in the modulation doping of the well. Appropriate corrections to growth conditions remove these asymmetries, as reflected in CV measurements. Besides its importance in the analysis of potential wells of different shapes, the theory presented is applicable to the determination of band offsets by the CV profiling technique where the unintentional grading of the band gap and/or doping in the neighborhood of the isotype abrupt heterojunction is known.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.353897
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  • 4
    Digitale Medien
    Digitale Medien
    Wide electron gas with periodic density modulation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1460-1463 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the growth and characterization of a high-quality wide (∼2000 A(ring)) three-dimensional electron gas (3DEG) with periodic density modulation (period ∼200 A(ring)) in a modulation-doped wide parabolic potential well with a superimposed superlattice. Computer-controlled molecular beam epitaxy is used to synthesize the potential well as a graded AlxGa1−xAs digital alloy. The density-modulated 3DEG is compared to a uniform 3DEG of the same average density and width in a parabolic well without the superlattice. The Al mole fraction profiles for the two samples are measured in calibration runs immediately prior to actual growths. The density-modulated 3DEG has a low-temperature in-plane mobility in excess of 105 cm2/V s, compared to ∼2×105 cm2/V s for the uniform 3DEG. Capacitance-voltage measurements directly reveal the modulation of the density of the electron gas in the parabolic well with superimposed superlattice, and the absence of any density modulation for the gas in the bare parabolic well.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.351708
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  • 5
    Digitale Medien
    Digitale Medien
    Raman scattering study of InAs/GaInSb strained layer superlattices (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5608-5614 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present a Raman scattering study of the InAs/GaInSb superlattice. This new superlattice is promising as a long wavelength infrared detector material. The samples were grown by molecular beam epitaxy and their structural parameters were determined by Rutherford backscattering and x-ray diffraction. Samples were grown on [001] GaAs substrates with GaSb buffers, and directly on [001] GaSb substrates. Cross-sectional transmission electron micrographs show that for the samples grown on GaAs substrates, a high density of dislocations was generated at the GaAs-GaSb interface, and many of these dislocations thread through the superlattice. The samples grown directly on GaSb had a much lower dislocation density. The Raman spectra of the InAs/GaInSb superlattice shows a single peak, which is a superposition of scattering from the LO phonons in InAs and in GaInSb. For unstrained InAs and GaInSb, the LO phonon energies are sufficiently separated that they would be well resolved in Raman scattering. However, the strain introduced into these materials by the pseudomorphic boundary conditions moves the two phonons closer together energetically so that only one peak is seen in the Raman spectrum of the superlattice. A high energy Raman scattering tail is seen in some of the samples. This tail is from Ga-As local modes. Such modes may be due to As incorporation in the GaInSb, Ga incorporation in the InAs or phase mixing at the interfaces.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.350174
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  • 6
    Digitale Medien
    Digitale Medien
    Modulation-doped graded structures: Growth and characterization (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2370-2375 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Remotely doped graded parabolic potential well structures have been grown and studied. Electrons distribute themselves uniformly in a parabolic well, the density being proportional to the curvature or quasidoping in the well. Quasidoped semiconductors are synthesized by molecular beam epitaxy in the GaAs/AlXGa1−XAs system through the digital alloy technique. The analog grading produced by the digital alloy is verified by photoluminescence excitation spectroscopy. Low temperature mobility measurements show higher mobility in these quasidoped semiconductors than in similar real-doped semiconductors. Alloy-disorder scattering is suggested to be the mobility-limiting mechanism in this digital alloy system. Capacitance–voltage profiling analysis of quasidoped semiconductors has been developed, and is used to measure carrier profiles in these structures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.348720
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  • 7
    Digitale Medien
    Digitale Medien
    Low-threshold InGaAs/GaAs strained layer single quantum well lasers with simple ridge waveguide structure (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 7892-7894 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Double heterostructure InGaAs-GaAs strained-layer single quantum well ridge waveguide lasers grown by molecular beam epitaxy were fabricated by using in situ laser monitored reactive ion etching to form the ridges. Continuous-wave threshold current as low as 3.5 mA was obtained on a ridge laser diode of 3.3 μm wide and 215 μm long having cleaved mirrors. The lasing wavelength is at 0.988 μm and the measured differential external quantum efficiency is 61%.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.347473
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  • 8
    Digitale Medien
    Digitale Medien
    Far-infrared electroluminescence from parabolic quantum well superlattices excited by resonant tunneling injection (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 172-177 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present an investigation of intersubband emission at far-infrared wavelengths from semiconductor superlattices with parabolically graded quantum wells. Light emission is produced by sequential resonant tunneling injection of electrons into higher energy levels of the quantum wells and subsequent radiative decay. The current versus voltage curves of these devices exhibit negative differential resistances characteristic of the sequential resonant tunneling injection. A single, narrow emission peak is observed from the superlattices with parabolic quantum wells demonstrating radiative decay through multiple evenly spaced energy levels. When a chirped superlattice acting as an electron energy filter replaces the barrier in each period of the structure, clearer resonances are observed in the current–voltage characteristics and more efficient injection is achieved. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.373638
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  • 9
    Digitale Medien
    Digitale Medien
    Conductance fluctuations and quantum chaotic scattering in semiconductor microstructures (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 3 (1993), S. 643-653 
    Details
    ISSN: 1089-7682
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We review recent experiments on aperiodic conductance fluctuations in ballistic GaAs/AlGaAs microstructures in the shape of a stadium billiard and a circle with point-contact leads, measured at millikelvin temperatures. Much of the observed behavior can be analyzed within a semiclassical approach to quantum chaotic scattering. After a brief review of the Landauer–Büttiker formulation of coherent transport, a variety of novel experimental phenomena and comparisons to semiclassical theory are presented. In particular, we discuss quantum-enhanced backscattering, the power spectrum of conductance fluctuations, crossover to the high-magnetic-field and tunneling regimes, and an application allowing the rate of phase-randomizing scattering to be measured in chaotic ballistic microstructures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.165927
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  • 10
    Digitale Medien
    Digitale Medien
    A two-dimensional ultrahigh vacuum positioner for scanning tunneling microscopy (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1403-1405 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A two-dimensional ultrahigh vacuum compatible positioner is presented. The positioner uses two piezoelectric inchworms which allow for motions of up to 1 cm with a precision of 4 nm mounted at right angles to each other in order to give two dimensions of motion. Images of three-dimensional In0.3Ga0.7As islands in cross section are presented to demonstrate the functionality of the positioner. It is found that motion towards the tip is smooth, while motion in the perpendicular direction is less smooth. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1148773
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