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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4677-4682 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electronic transport mechanism in polypyrrole is discussed in terms of Mott variable range hopping (VRH) in samples with a wide range of conductivities and which have been formed using different doping techniques. Samples were synthesized in both aqueous and organic media and samples were either doped during polymerization or dedoped afterwards giving a three order of magnitude range of conductivities at 300 K and a range of sample morphologies. No difference in behavior is observed for materials with different morphologies, suggesting that transport predominantly involves monomer units and occurs independent of structure. The various transport parameters obtained appear reasonable with the exception of the apparent "hopping attempt frequency,'' related to the phonon frequency in VRH, some values of which are anomalously high. The density of states at the Fermi level was found to be between 5×1018 and 1×1022 eV−1 cm−3 for a range of samples and the mean hopping distances ranged between 2 and 34 monomer units. The minimum hopping distance of 2 monomer units is consistent with electron delocalization on individual monomer units. An upper limit of conductivity in polypyrrole of no more than 400 S cm−1 is suggested in the limit of the VRH regime in which hopping occurs between adjacent monomer units.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3571-3577 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The significance of alloy scattering on the electron mobility of InAs1−xSbx is studied in detail. Since little experimental data are available for the InAs1−xSbx compound, calculations of the electron mobility of the binary InAs and InSb semiconductors are first evaluated from the average momentum relaxation times, 〈τm〉 of the individual mechanisms (comprising ionized and neutral impurities, acoustic phonon deformation potential and piezoelectric, optical phonon deformation potential and polar) so that they can be compared to available experimental results. Having ensured that the calculated data are in good agreement with the experimental results in these binary compounds, the electron mobility of the ternary, InAs1−xSbx as a function of x at 77 K and 300 K is calculated by introducing an alloy scattering term. At 77 K, for a total doping concentration of (approximately-equal-to)1017 cm−3, the electron mobility of InAs1−xSbx is limited by ionized impurity scattering and alloy scattering is insignificant. However, for doping concentration of (approximately-equal-to)1015 cm−3, alloy scattering is found to be the most significant process from about x=0.1 to 0.8. At 300 K the alloy scattering reduces the total electron mobility from between a few percent at x=0.15 to a maximum of about 11% for x=0.60. It is observed that alloy scattering is greatest at x=0.15 but it still is about 11% of the total electron mobility at this composition. The alloy mobilities at 77 K for x=0.6 and x=0.15 are 1.28×106 cm2 V−1s−1 and 7.96×105 cm2 V−1s−1, respectively. The mobilities at x=0.60 are further evaluated as a function of the doping carrier concentration at 77 and 300 K. It is found that alloy scattering becomes increasingly significant for lightly doped semiconductors at low temperatures.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 7711-7713 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conductivity of doped polypyrrole, as high as 100 Scm−1 in freshly prepared samples, falls slowly with time on exposure to atmospheric oxygen. Typically, the fall in conductivity is fairly slow at room temperature, but the process can be accelerated by heating samples and measuring the decrease in conductivity as a function of time. Analysis of the kinetics of this process shows a preliminary, 120 min regime in which a surface adsorption-diffusion mechanism with an activation energy of 0.41 eV appears to mediate. Once a degree of adsorbate saturation is attained subsequent behavior is well described by standard bulk diffusion considerations and is activated at 0.48 eV. We propose a mechanism whereby oxygen adsorption onto the surfaces of the polymer fibrils and diffusion into the interior are respective rate limiting steps in the incorporation of oxygen into the closely cross-linked mesh, blocking conducting pathways.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4125-4129 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The correlation deep level transient spectroscopy (DLTS) method is developed for insulator/semiconductor interface studies. Trap transient modeling indicates that the energy range in which the trap transients can contribute to the DLTS signals of the correlation method is about 12 kT, and is much wider than that of the boxcar method (several kT). Moreover, large voltage pulse for saturation will cause the capacitance transient to shift away from the ideal exponential due to the sum of the various emission rates. Hence, the equations for determination of interface trap density suitable for the boxcar method is invalid for the correlation method. For this reason, an equation for determining the interface trap density suitable for the correlation method is derived. The interface trap density determined by this method agrees well with other methods.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1410-1415 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron mobility in InAs1−xSbx is calculated for an ionized impurity density between 5× 1014 cm−3 and 1 × 1017 cm−3 at 77 K. The various methods of calculating electron mobility are discussed and their respective merits and limitations summarized. In general, alloy scattering is the mobility limiting process at low carrier density (n ≤ 1015 cm−3) while ionized impurity scattering is important at higher carrier density. The effect of compensation (NA/ND) on low field drift mobility is also calculated for a range of carrier concentrations at x=0.1, 0.6, 0.9, and 1.0 compositions of particular technological significance. Compensation is found to degrade electron mobility quite significantly in all cases. The calculations at x=1.0 (InSb) are also found to be in good agreement with available experimental data.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3486-3491 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experimental investigation is reported of optical transitions in narrow, symmetric, triangular well structures. Quantum wells as narrow as 2.5 nm have been grown in AlGaAs using an analog grading strategy in a conventional, solid source molecular beam epitaxy (MBE) system. Linearly graded heterostructures are analyzed in terms of Airy function solutions of the one-dimensional wave equation and energy levels more evenly spaced than in the equivalent square well are predicted. Transition energies obtained from photoluminescence, photoreflectance, and differential photoreflectance measurements agree well with calculated values. The differing spatial extents of wave functions in the triangular well case also modify the relative intensities of the lines identified, in particular the normally faint transition from n=3 heavy hole state to conduction-band ground state (hh3-e1) appears enhanced.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5369-5371 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: AlN intended for metal-insulator-semiconductor applications has been prepared by laser activated chemical vapor deposition from ammonia and trimethylaluminum precursors. The films are high-density polycrystalline with 〈100〉 preferential orientation, and there is no evidence of the presence of Al2O3. A consistent band gap of 6.00±0.03 eV is obtained for film thickness in the range 0.3–1.2 μm. Conductivity is below 5×10−14 Ω−1 cm−1 at room temperature and is thermally activated with a range of excitation energies between 0.6 and 0.8 eV. The breakdown electric field is about 3×106 V/cm, while the relative permittivity varies between 7.8 and 8.2 in the frequency range 100 Hz–13 MHz.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3370-3380 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Symmetric, triangular barriers with alloy induced heights of about 250 meV and between 40 and 150 nm thick have been grown in AlGaAs by linear ramping of composition in a conventional solid-source molecular beam epitaxy system and their current–voltage characteristics measured between 55 to 300 K. Characteristics are also calculated, with electron tunneling contributions included by a finite-element Wentzel–Kramers–Brillouin approach which allows an arbitrary composition and/or doping profile to be modeled. Theory and experiment generally coincide, increased tunneling contributions are detected at lower temperatures and in narrower barriers, principally through a reduction in barrier height and an increase in ideality factor. The incorporation of dopants in the barrier produces an ionized-donor space charge with a consequent reduction in real barrier height and width, while anomalous behavior in some samples seems to be associated with trapping within the barrier.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1831-1837 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pressure dependence of the electrical conductivity of a range of polypyrrole samples doped to various levels is interpreted in terms of variable-range hopping theory. All samples are well described by a model that treats the density of localized states around the Fermi level as the pressure-dependent commodity. The presumption of invariance of wave-function inverse localization length is vindicated by samples with a range of mean hopping lengths all being described by a single state-compressibility term. This term is defined by the elastic constants of polypyrrole and measurements of macroscopic elasticity confirm the value deduced from the pressure dependence of conductivity versus temperature curves.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6217-6221 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Aluminum nitride insulating layers have been grown at room temperature with a film resistivity of 3.3×1016 Ω cm on mercury cadmium telluride substrates. Insulator breakdown fields of 640 MV/m were reached. Capacitance–voltage measurements with Al/AlN/Hg0.76Cd0.24Te metalinsulator-semiconductor devices demonstrate band bending at the semiconductor surface indicating that damage to the substrate was minimized during film growth. A fixed interface charge density (given here as total charge per unit area divided by the electron charge=Qss/q) of +2×1011 cm−2 and a slow interface state density of 4×1010 cm−2 were measured. The procedures for achieving these high quality insulating layers are reported. Frequency dependent dielectric constant and dielectric loss tangent measurements, carried out at room temperature and 100 K, are also presented. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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