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  • 1
    Electronic Resource
    Electronic Resource
    Vanadium related near-band-edge absorption bands in three SiC polytypes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3160-3163 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature optical absorption experiments have been performed on a variety of n-type, p-type, and high-resistivity silicon carbide samples, including the polytypes: 4H, 6H, and 15R. These experiments reveal a set of absorption band close to the band edge with a fine structure depending upon the polytype. Each sample exhibits a spectrum with the number of lines corresponding to the number of inequivalent substitutional lattice sites contained in the polytype. A correlation of these lines with the neutral vanadium 2E→2T2 intracenter transition indicates that the initial state for the near-band-gap absorption lines is the 2E state of the 3d1 configuration of vanadium. The near-band-edge absorption lines were interpreted as due to an exciton bound to a vanadium donor with an electron occupying an atomic-like d state. The position of the vanadium acceptor level was estimated to be, at most, 250 meV from the conduction band for the cubic site in 6H SiC. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360004
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  • 2
    Electronic Resource
    Electronic Resource
    On the compensation mechanism in high-resistivity 6H–SiC doped with vanadium (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3839-3842 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model is presented which describes the compensation mechanism resulting in semi-insulating 6H silicon carbide by vanadium doping. Undoped 6H–SiC crystals grown by physical vapor transport methods frequently contain between 1×1017 and 5×1018 cm−3 uncompensated boron acceptors. Upon addition of vanadium, the 3d1 electron of the vanadium donor compensates the holes of the boron centers. It is shown that when vanadium is present in concentrations greater than that of boron, the Fermi level is pinned to the vanadium donor level. From temperature dependent Hall effect measurements, this donor level has been determined to reside 1.35 eV below the conduction band minimum. Thermally stimulated current measurements on V-doped SiC crystals show that boron is the major compensating center for the vanadium impurity. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359899
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  • 3
    Electronic Resource
    Electronic Resource
    Optical and electrical characterization of boron impurities in silicon carbide grown by physical vapor transport (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2326-2331 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Undoped SiC crystals grown by physical vapor transport have been characterized by temperature dependent Hall effect and near infrared optical absorption measurements. Crystals with reduced nitrogen content were found to exhibit p-type conductivity with carrier concentrations in the 5×1014–1×1016 cm−3 range at room temperature. The Fermi level position determined from Hall effect measurements at elevated temperatures was 0.35 eV above valence band. The primary acceptor-type impurity was identified as substitutional boron with total concentration of uncompensated acceptors in the 1×1017–5×1018 range. This interpretation was confirmed by near infrared absorption spectra, which were dominated by a broad photoionization band with a threshold at 0.7 eV and a maximum at 1.75 eV. The shape of the band was fitted, and the thermal ionization energy of the defect was found to be in the 0.3–0.4 eV range. A correlation between the photoionization band intensity, and the uncompensated boron content was used to determine the value of maximum optical cross section of boron photoionization band, which was 4.17×10−17 cm2. In addition to photoionization band, boron-containing samples exhibited set of narrow absorption lines near the fundamental absorption edge. Based on correlation with boron content and line position in different SiC polytypes, these lines were identified as due to excitons bound to neutral boron acceptors. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361158
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  • 4
    Electronic Resource
    Electronic Resource
    Concentration-dependent near and above band edge absorption in doped InP and its effect on solar cell modeling (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2666-2670 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Absorption coefficients for n- and p-type InP are reported for the first time in the energy range of 1.3–3.0 eV in this paper. In order to obtain absorption coefficients in the higher energy range of 1.8–3.0 eV, extremely thin (∼0.2 μm) InP samples were fabricated and bonded to glass substrates. For measurements in the lower energy range of 1.3–1.6 eV, samples with thickness in the range of 0.5–0.9 μm were found to be optimum. For energies below 1.6 eV, the absorption coefficients are a strong function of the doping concentration. However, in the energy range of 1.8–3.0 eV there is little doping dependence and the measured absorption coefficients follow the theoretical calculations. In the case of n-type samples, absorption coefficients decrease with increasing doping concentration and the absorption edge moves to higher energy due to the Burstein–Moss effect. For p-type samples, the absorption edge shifts to lower energies due to transitions between band tails. Model calculations show that the use of accurate doping-dependent absorption coefficients reported in this paper, as opposed to the commonly used absorption coefficients of undoped InP, can result in significant improvement in the predicted internal quantum efficiency and device parameters of InP solar cells. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360128
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  • 5
    Electronic Resource
    Electronic Resource
    Deep level transient spectroscopic and Hall effect investigation of the position of the vanadium acceptor level in 4H and 6H SiC (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1963-1965 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hall effect, deep level transient spectroscopy (DLTS) and optical absorption measurements were employed in concert to determine the position of the vanadium acceptor level in vanadium and nitrogen doped 6H and 4H SiC. Hall effect results indicate that the acceptor position in 4H SiC is at 0.80 eV beneath the conduction band edge, and 0.66 eV for the 6H polytype. The DLTS signature of the defect in the 4H polytype showed an ionization energy of 0.80 eV and a capture cross section of 1.8×10−16 cm−2. The optical absorption measurements proved that the levels investigated are related to isolated vanadium, and therefore the vanadium acceptor level. Based on the DLTS measurements and secondary ion mass spectroscopy data, the maximum solubility of vanadium in SiC was determined to be 3.0×1017 cm−3. At these incorporation limits and with the depth of the level, the vanadium acceptor level could be used in the creation of semi-insulating silicon carbide. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115640
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  • 6
    Electronic Resource
    Electronic Resource
    Single-crystal thin film InP: Fabrication and absorption measurements (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 1429-1431 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new process for separating high quality single-crystal InP thin films from the growth substrate is reported. These thin films were used for transmission measurements to determine InP absorption coefficients above the band edge. Photoluminescence measurements performed on these films before and after the fabrication process verified that the high quality of the separated thin film was not affected by the fabrication process. Two n-type InP thin films, one with a doping concentration of 1.4×1017 cm−3 (1 μm thick) and the other with a doping concentration of 3.2×1018 cm−3 (2.5 μm thick), were grown and subsequently separated from the substrate. Using these separated films, the first direct transmission measurements of above band edge absorption coefficients in doped InP films are reported in this letter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107560
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  • 7
    Electronic Resource
    Electronic Resource
    Semi-insulating 6H–SiC grown by physical vapor transport (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1364-1366 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Semi-insulating 6H–SiC crystals have been achieved by using controlled doping with deep-level vanadium impurities. High resistivity undoped and semi-insulating vanadium-doped single-crystals with diameters up to 50 mm were grown by physical vapor transport using an induction-heated, cold-wall system in which high purity graphite materials constituted the hot zone of the furnace. Undoped crystals were p-type due to the presence of residual acceptor impurities, mainly boron, and exhibited resistivities ranging up to 3000 Ω cm. The semi-insulating behavior of the vanadium-doped crystals is attributed to compensation of residual acceptors by the deep-level vanadium V4+(3d1) donor located near the middle of the band gap. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113202
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  • 8
    Electronic Resource
    Electronic Resource
    Calcium Action in Synaptic Transmitter Release (1987)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Neuroscience 10 (1987), S. 633-693 
    Details
    ISSN: 0147-006X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ne.10.030187.003221
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  • 9
    Electronic Resource
    Electronic Resource
    Exocytosis: Proteins and Perturbations (1996)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Pharmacology 36 (1996), S. 659-701 
    Details
    ISSN: 0362-1642
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.pa.36.040196.003303
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  • 10
    Electronic Resource
    Electronic Resource
    Presynaptic calcium signals during neurotransmitter release: Detection with fluorescent indicators and other calcium chelators
    Amsterdam : Elsevier
    Journal of Physiology-Paris 86 (1992), S. 129-134 
    Details
    ISSN: 0928-4257
    Keywords: calcium ; fluorescent indicators ; neurotransmitter release
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0928-4257(05)80017-8
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