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  • 1990-1994  (34)
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  • 1
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353897
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351708
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Voltage tunable acoustoelectric interaction in GaAs/AlGaAs heterojunctions (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2422-2424 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction between surface acoustic waves and high mobility quasi-two-dimensional electron systems (2DES) in GaAs/AlGaAs heterojunctions with variable carrier density is investigated experimentally. In specially designed samples the strength of this acoustoelectric interaction can be controlled via the field-effect induced variation of the carrier density of the 2DES. Since the sensitivity of surface acoustic wave experiments is particularly high at very low conductivities, the proposed technique will be an especially valuable tool for the investigation of 2DES with extremely low sheet carrier densities. We demonstrate that the proper use of a metallic gate electrode does not conflict with the piezoelectric interaction between the mobile carriers confined in the heterostructure and the surface acoustic wave propagating on the piezoelectric substrate. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112694
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  • 4
    Electronic Resource
    Electronic Resource
    Logarithmically graded quantum well far-infrared modulator (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 348-350 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have designed and fabricated a remotely doped "logarithmic'' potential well intended to have a tunable, narrow band absorption at far-infrared frequencies. A surface gate, epitaxially grown backgate, and contact to the electron gas in the quantum well allow independent control of the absorption frequency and the integrated absorption strength. The resonance frequency is dominated by the well curvature at the potential minimum and can be Stark shifted from ω/2πc=35 cm−1 to a frequency of 125 cm−1 by moving the electron gas through the asymmetric well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111144
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  • 5
    Electronic Resource
    Electronic Resource
    Infrared absorption of holes in a parabolic quantum well (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2226-2228 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We observe the infrared absorption of holes in a wide graded AlxGa1−xAs parabolic quantum well to be at a single frequency, independent of the number of holes in the well. The resonant absorption frequency appears to be determined by the light hole mass, not the heavy hole mass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112771
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  • 6
    Electronic Resource
    Electronic Resource
    High-efficiency and low-threshold InGaAs/AlGaAs quantum-well lasers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 3932-3934 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-efficiency and low-threshold InGaAs/AlGaAs quantum-well laser structures have been grown by molecular beam epitaxy. Material characterization was performed on polyimide-planarized ridge-waveguide lasers. The measured material gain data are compared to theoretical calculations that include the valence-band mixing effects. Total injection current densities of 84 and 60 A/cm2 have been measured from 50-μm-wide laser diodes with cavity lengths of 2850 μm (from a double-quantum-well sample) and 1770 μm (from a single-well sample), respectively. Moreover, we have also obtained a cw threshold current as low as 2.1 mA from a 1.7-μm-wide and 140-μm-long as-cleaved ridge-waveguide device. In addition, the lateral current leakage for the double-quantum-well sample is found to be twice that of the single-well one.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357408
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  • 7
    Electronic Resource
    Electronic Resource
    Low-temperature carrier distributions in wide quantum wells of different shapes from capacitance-voltage measurements (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1003-1007 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The carrier distributions in modulation-doped wide graded quantum wells that a measurement of the capacitance C between a surface gate and an ohmic contact to the carriers as a function of the applied bias V would yield are calculated. These capacitance-voltage (C-V) distributions are found to agree inexactly, but closely, with the calculated true carrier distributions. Density modulation features, induced by superlattices or by abrupt changes in the curvature of band-gap grading, are strikingly reproduced. Electron distributions extracted from actual measurements on a wide parabolic well and on a parabolic well with superimposed superlattice are in good agreement with theory. For the case of the parabolic well, the occupancy of a finite number of subbands is manifested as structure in the C-V distributions. This technique is relevant to the measurement of carrier distributions in any wide carrier system with more than one electric subband occupied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357886
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  • 8
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354026
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  • 9
    Electronic Resource
    Electronic Resource
    Lateral carrier diffusion and surface recombination in InGaAs/AlGaAs quantum-well ridge-waveguide lasers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4479-4487 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We measured the increase in threshold currents due to lateral carrier diffusion in InGaAs/AlGaAs quantum-well ridge-waveguide laser diodes. The ridge stripes were fabricated by using both in situ monitored pure Cl2 reactive ion etching and selective wet etching to completely eliminate the spreading current in the conductive upper cladding layer while keeping the ridge sidewalls straight. After comparing the threshold data with a theoretical model, the ambipolar diffusion coefficient is found to be 22 cm2/s in the population-inverted InGaAs layer. This model is based on the calculated optical gain curve and the ambipolar carrier transport in the quantum-well and waveguiding layers. The dependence of carrier lifetime on the local carrier concentration is included in the calculation. Moreover, from another set of devices with the portions of the active layer outside the ridge stripes etched away, the surface recombination velocity is found to be around 1–2×105 cm/s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357279
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  • 10
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352975
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