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  • 1
    Electronic Resource
    Electronic Resource
    Optical and electronic properties of vanadium in gallium arsenide (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 163-170 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of vanadium doping on the electrical and optical properties of GaAs were systematically studied in melt-grown crystals prepared by the liquid-encapsulated Czochralski and horizontal Bridgman techniques and in epitaxial crystals prepared by liquid-phase electroepitaxy. By employing deep-level transient spectroscopy, Hall-effect measurements and the V2+(3d3) and V3+(3d2) intracenter optical-absorption spectra, one vanadium-related level was identified in all crystals, i.e., the substitutional-vanadium acceptor level (V3+/V2+) at 0.15±0.01 eV below the bottom of the conduction band. From the absorption measurements we conclude that the vanadium (V4+/V3+) donor level must be located within the valence band. Because of its energy position, the above level cannot account for the reported semi-insulating properties of V-doped GaAs. We observed no midgap levels resulting from vanadium-impurity (defect) complexes. The high resistivity reported for certain V-doped GaAs crystals must result from indirect effects of vanadium, such as the gettering of shallow-level impurities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339174
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  • 2
    Electronic Resource
    Electronic Resource
    Erratum: "Electronic and optical properties of Ti-doped GaAs and InP; semi-insulating InP'' [J. Appl. Phys. 65, 3459 (1989)] (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 2768-2768 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344502
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  • 3
    Electronic Resource
    Electronic Resource
    Gettering of donor impurities by V in GaAs and the growth of semi-insulating crystals (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 3309-3316 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vanadium added to the GaAs melt getters shallow donor impurities (Si and S) and decreases their concentration in the grown crystals. This gettering is driven by chemical reactions in the melt rather than in the solid. Employing V gettering, we were able to grow reproducibly semi-insulating GaAs by horizontal Bridgman and liquid-encapsulated Czochralski techniques, although V did not introduce any midgap energy levels. The compensation mechanism in these crystals was controlled by the balance between the native midgap donor EL2 and residual shallow acceptors. Vanadium gettering contributed to the reduction of the concentration of shallow donors below the concentration of acceptors. The present findings clarify the long-standing controversy on the role of V in achieving semi-insulating GaAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344126
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  • 4
    Electronic Resource
    Electronic Resource
    Electronic and optical properties of Ti-doped GaAs and InP; semi-insulating InP (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3459-3469 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A systematic study of the effects of Ti doping on the electrical and optical properties of GaAs and InP has been carried out employing both melt and solution-grown crystals. Utilizing deep level transient spectroscopy, Hall effect measurements, photoconductivity, and optical absorption measurements, it was found that Ti introduces two deep levels in GaAs at Ec −0.23 eV and Ec −1.00 eV which were identified as the Ti3+/Ti2+ acceptor level and the Ti4+/Ti3+ donor level, respectively. In InP the Ti4+/Ti3+ donor level was found near midgap at Ec −0.63 eV, while the Ti3+/Ti2+ acceptor level was found to lie within the conduction band. As a consequence of the midgap position of this donor level, we developed a formulation for producing semi-insulating InP based on doping with Ti to compensate shallow acceptors. Resistivities in excess of 107 Ω cm can easily be obtained using this technique. This is the first semi-insulating III-V compound having a compensation mechanism based on a deep donor impurity. In view of the fact that Ti is expected to have a very low diffusivity in InP, Ti-doped semi-insulating InP should exhibit far greater thermal stability than Fe-doped InP and thus it should prove technologically significant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342614
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  • 5
    Electronic Resource
    Electronic Resource
    Native acceptor levels in Ga-rich GaAs (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 596-599 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A photoluminescence, photocapacitance, and thermal annealing study of Ga-rich GaAs has revealed the complex behavior of acceptor levels at 68–77 and 200 meV above the valence band. The concentration of all levels is enhanced by Ga-rich growth conditions, however, only the 77- and 200-meV levels formed preferably in n-type GaAs are consistent with a double-acceptor model of the gallium antisite defect. In p-type GaAs the 68-meV level associated with a different single-acceptor defect is dominant. It is argued that the inhibited formation of double-acceptor GaAs defects in p-type crystals is caused by the Fermi-energy control of the defect formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343114
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  • 6
    Electronic Resource
    Electronic Resource
    A model for the evolution of the Vicia faba chloroplast genome (1987)
    Springer
    Theoretical and applied genetics 74 (1987), S. 125-139 
    Details
    ISSN: 1432-2242
    Keywords: Vicia faba ; Chloroplast genomic evolution ; Rearrangements ; Recombination sites ; Deletions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The Vicia faba chloroplast genome lacks inverted repeat sequences and contains only one set of ribosomal RNA genes. The genetic organization has been altered by inversions, relative to the typical arrangement of most higher plant chloroplast genomes. The Vicia faba plastid genome thus represents one of the more interesting results of chloroplast genomic evolution. The present study employs small DNA probes and Southern blot hybridizations to investigate the steps involved in the evolution of the Vicia faba chloroplast genome. The data from heterologous hybridizations between chloroplast DNA of Brassica napus (a conserved genome) and of Vicia faba led to three observations: 1) The inverted repeat segment closest to the psbA gene was deleted prior to the rearrangements. 2) A quarter of the ancestral small single copy region was lost during the deletion. 3) The genetic organization observed in Vicia faba resulted from three inversions after the deletion event. Our findings, combined with previous observations, helped devise a stepwise model for the evolution of the Vicia faba chloroplast genome. The area of the small single copy region absent from the Vicia faba chloroplast chromosome lacks in vivo transcription activity in Brassica napus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00290095
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