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  • 11
    Electronic Resource
    Electronic Resource
    Diffusion and drift of Si dopants in δ-doped n-type AlxGa1−xAs (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2592-2594 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The study of diffusion and drift of Si in AlxGa1−xAs by means of capacitance-voltage measurements reveals that low substrate temperatures during growth by molecular beam epitaxy are required to achieve δ-function-like doping profiles. The diffusion coefficient of Si in Al0.3Ga0.7As is determined. We further show theoretically that the random Poisson distribution (usually assumed for dopant distributions in semiconductors) should be modified at high dopant concentrations due to repulsive interactions of impurities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101059
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  • 12
    Electronic Resource
    Electronic Resource
    Novel photovoltaic δ-doped GaAs superlattice structure (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2247-2249 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An asymmetric δ-doped GaAs structure is described which exhibits novel photovoltaic effects and low-intensity nonlinear optics. Of particular interest in this kind of structure is the ability to design the electro-optical and nonlinear optical properties and the material response time over a wide range by appropriate design of the doping profile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101138
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  • 13
    Electronic Resource
    Electronic Resource
    Diffusion of atomic silicon in gallium arsenide (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 293-295 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Silicon impurities with an initial Dirac-delta-function-like distribution profile are diffused into GaAs using rapid thermal annealing. The diffusion of atomic Si is determined by a novel method of comparing experimental capacitance-voltage profiles with a corresponding self-consistent profile calculation. Capacitance-voltage profiles broaden from 30 to 137 A(ring) upon rapid thermal annealing at 1000 °C for 5 s. The diffusion coefficient and the activation energy of atomic Si diffusion in GaAs are determined to be D0=4×10−4 cm2/s and Ea=2.45 eV, respectively. The diffusion coefficient is two orders of magnitude smaller as compared to Si-pair diffusion in GaAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99917
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  • 14
    Electronic Resource
    Electronic Resource
    Tunable stimulated emission of radiation in GaAs doping superlattices (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 757-759 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tunable stimualted emission of radiation is achieved in AlxGa1−xAs/GaAs double heterostructures, in which the waveguiding GaAs region consists of a delta-doped doping superlattice. The low-temperature emission energy is 45 meV below the bulk band gap of GaAs for homogeneous optical excitation of the Fabry–Perot cavity. The emission energy is continuously tunable over 35 A(ring) by inhomogeneous excitation of the cavity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101797
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  • 15
    Electronic Resource
    Electronic Resource
    Spatial imaging of the critical current density in epitaxial Y1Ba2Cu3O7 films (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2132-2134 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the first spatially resolved measurement of the critical transport current density of c-axis oriented epitaxial Y1Ba2Cu3O7 films on 〈100〉 SrTiO3 using low-temperature scanning electron microscopy (LTSEM). The local critical current density, imaged with a spatial resolution of ∼1 μm, has been found to vary considerably in these films. Possible reasons for the observed spatial inhomogeneities are surface imperfections of the substrate and precipitates in the film. The spatial inhomogeneity of the critical current density in epitaxial films might be a reason for differences in the temperature dependences of the critical current density obtained by magnetic and transport measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102346
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  • 16
    Electronic Resource
    Electronic Resource
    Dopant distribution for maximum carrier mobility in selectively doped Al0.30Ga0.70As/GaAs heterostructures (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1350-1352 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnitude of potential fluctuations due to remote ionized dopants is calculated for selectively doped heterostructures using unscreened and screened Coulomb potentials. Potential fluctuations are found to be minimized (corresponding to maximum carrier mobility) if the dopant distribution is δ-function-like. Our experimental study of electron mobilities in selectively doped heterostructures grown by molecular beam epitaxy reveals that carrier mobility indeed increases as the thickness of the doped layer is reduced, in agreement with the calculation. A peak electron mobility of 5.5×106 cm2 /V s is obtained at low temperatures in a selectively δ-doped heterostructure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100712
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  • 17
    Electronic Resource
    Electronic Resource
    Carbon doping in molecular beam epitaxy of GaAs from a heated graphite filament (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2661-2663 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carbon doping of GaAs grown by molecular beam epitaxy has been obtained for the first time by use of a heated graphite filament. Controlled carbon acceptor concentrations over the range of 1017–1020 cm−3 were achieved by resistively heating a graphite filament with a direct current power supply. Capacitance-voltage, p/n junction, and secondary-ion mass spectrometry measurements indicate that there is negligible diffusion of carbon during growth and with post-growth rapid thermal annealing. Carbon was used for p-type doping in the base of Npn AlGaAs/GaAs heterojunction bipolar transistors. Current gains greater than 100 and near-ideal emitter heterojunctions were obtained in transistors with a carbon base doping of 1×1019 cm−3. These preliminary results indicate that carbon doping from a solid graphite source may be an attractive substitute for beryllium which is known to have a relatively high diffusion coefficient in GaAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100187
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  • 18
    Electronic Resource
    Electronic Resource
    Spatial localization of impurities in δ-doped GaAs (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 1508-1510 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Capacitance-voltage profiles on δ-doped GaAs grown by molecular beam epitaxy reveal extremely narrow widths of (approximately-less-than)40 A(ring) at room temperature. Subband structure and capacitance-voltage (C-V) profiles of δ-doped GaAs are calculated self-consistently. Experimental C-V profiles agree with self-consistent results, only if we assume that Si impurities are localized on the length scale of the lattice constant in the host GaAs zinc-blende lattice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99114
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  • 19
    Electronic Resource
    Electronic Resource
    Selectively δ-doped AlxGa1−xAs/GaAs heterostructures with high two-dimensional electron-gas concentrations n2DEG≥1.5×1012 cm−2 for field-effect transistors (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1170-1172 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The δ-doping concept is applied to selectively doped heterostructures in the AlxGa1−xAs/GaAs material system. High two-dimensional electron-gas concentrations ≥1.5×1012 cm−2 are obtained at T=300 K in such selectively δ-doped heterostructures due to (i) size quantization in the AlxGa1−xAs and (ii) localization of donor impurities within one atomic monolayer. Shubnikov–de Haas measurements yield n2DEG =1.1×1012 cm−2 at 300 mK and at a spacer thickness of 25 A(ring). Selectively δ-doped heterostructure transistors (SΔDHT's) are fabricated and have excellent characteristics due to the enhanced electron-gas concentrations achieved. A very high transconductance of gm (approximately-equal-to)360 mS/mm at a gate length of 1.2 μm is obtained in depletion-mode SΔDHT's at T=300 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98722
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  • 20
    Electronic Resource
    Electronic Resource
    Heat treatment of wires on the basis of the high Tc superconductor YBa2Cu3Ox (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 917-918 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ag-sheathed powder-in-tube wires on the basis of the high Tc superconductor YBa2Cu3Ox are produced by a drawing process. After cold working, the wires are not superconducting. By heat treatment at temperatures 〉900 °C, lattice defects are healed and the contact between the grains is improved. After this heat treatment the wires are slowly cooled in an O2 atmosphere in order to adjust the optimum O2 stoichiometry. The annealing temperature has a strong influence on the attainable critical current density. By annealing a wire with 420 ppm carbon content at 950 °C, jc values of 5020 A/cm2 at 4.2 K and 1130 A/cm2 at 77 K were achieved. Drastically reduced critical current densities in wires with high carbon content demonstrate the importance of a low carbon content for achieving high critical current densities in YBa2Cu3Ox .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102451
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