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  • 1
    Electronic Resource
    Electronic Resource
    A study of the effects of post-deposition treatments on CdS/CdTe thin film solar cells using high resolution optical beam induced current (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3725-3727 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical beam induced current (OBIC) technique was applied using a scanning optical microscope (SOM) to study n-Cds/p-CdTe thin film solar cells which had been subjected to different post-deposition treatments. High spatial resolution maps were obtained of the current collection with and without an applied reverse bias. The quantum efficiency of the devices was also measured with high spatial resolution. The results both quantify and illustrate vividly the manner in which the well known CdCl2 treatment increases collection efficiency. The high uniformity in the best cells indicates that grain boundaries do not play a substantial role in limiting collection efficiency. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115986
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  • 2
    Electronic Resource
    Electronic Resource
    The effect of Mn on the positive temperature coefficient of resistance characteristics of donor doped BaTiO3 ceramics (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 4530-4535 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: BaTiO3 positive temperature coefficient of resistance (PTCR) specimens were made from commercial BaTiO3 which was mixed with 0.35 mol. % of Ho2O3 to make it semiconducting and 0.07 mol. % of MnCO3. After sintering at 1320 °C the samples were annealed in batches at 1220 °C for various periods between 0 and 5 h. The effect of Mn was studied by making direct comparison with previous results obtained from Mn free but otherwise identical specimens. Room-temperature dielectric measurements in the audio and radio frequency ranges revealed that Mn had a negligible effect on the grain bulk resistance. Mn was found to result in an increase in the minimum and maximum values of the resistivity, the temperature at which the resistivity is a maximum and the slope of the resistivity-temperature characteristic in the transition region, all of which were attributed to an enhancement of the potential barrier at the grain boundaries. The acceptor state energy of the Mn-doped samples was found to be ∼1.4 eV, while a lower value was obtained for Mn-free material (∼1.12 eV). The effective concentration of Mn acceptors was observed to increase with the annealing time. To explain this behavior a thin Mn-rich boundary layer was assumed to exist, within which there was partial compensation of the Mn ions due to the formation of ionized oxygen vacancies. During annealing in air at 1220 °C, oxidation takes place and more of these vacancies are filled resulting in an increase in the effective Mn concentration. This model is also capable of explaining other phenomena such as the disappearance of the PTCR effect in reduced samples and the effects of cooling rate and quenching on the PTCR behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340150
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  • 3
    Electronic Resource
    Electronic Resource
    Twin nucleation in layers of CdTe on {lll} CdTe grown by metalorganic vapor-phase epitaxy (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 2624-2625 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Homoepitaxial layers of CdTe ranging from 0.5 to 5 μm in thickness have been grown on twin free, single-crystal {111}A oriented CdTe substrates by metalorganic vapor phase epitaxy over the temperature range 360–440 °C. The as-grown surfaces were invariably very smooth resulting in reflection high energy electron diffraction (RHEED) patterns characterized by streaks of diffracted intensity lying perpendicular to the shadow edge of the sample. After a light chemical etch, the 〈110〉 zone axis RHEED patterns exhibited an arrangement of double spots which corresponds to a twinned fcc structure. Furthermore, this twinned structure was observed in all layers grown on substrates of this specific orientation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337134
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  • 4
    Electronic Resource
    Electronic Resource
    Copper centers in CdSe (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 1670-1675 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Deep levels in single crystals of CdSe intentionally doped with copper have been investigated by photoconductivity and space-charge region capacitance techniques. The only center which can be conclusively associated with the copper impurity was found to have an activation energy of ∼1 eV with respect to the valence band. Estimates of 10−13 and 10−18 cm2 were made for the hole and electron capture cross sections for this center. The capture cross-section ratio of ∼105 indicates that this center is behaving as a photoconductivity sensitizing center. However, another center with an activation energy of ∼0.65 eV with respect to the valence band, and which is commonly observed in undoped material, would appear to be the dominant sensitizing center for all but the highest levels of copper doping. Two further centers, with activation energies of ∼0.5 and ∼0.9 eV, relative to the conduction band, were also found. In addition, there is evidence for the existence of at least two distinct centers with the same activation energy of ∼0.2 eV with respect to the valence band, one of which appears to be copper related.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337256
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  • 5
    Electronic Resource
    Electronic Resource
    The effects of donor dopant concentration on the grain boundary layer characteristics in n-doped BaTiO3 ceramics (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 6477-6482 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Positive temperature coefficient of resistance BaTiO3 specimens containing different donor dopant concentrations of Ho ranging from 0.05 to 1.8 at. % were investigated. The intergranular barrier layer capacitance per unit area, C'L, measured at a constant frequency of 30 kHz at both 40 and 160 °C was found to be proportional to the donor concentration up to 0.55 at. %, but then began to decrease as the donor concentration was increased beyond this. This indicated that both the density of acceptor states at the grain surfaces, Ns, and the relative permittivity εL of the material within the barrier layer were not affected by donor impurity concentrations below 0.55 at. % Ho. However, above this level of Ho concentration, the decrease in C'L appears to be related mainly to an increase in the value of Ns although it is possible that there were changes in εL. Initially both the maximum resistance and the room-temperature resistance (normalized per grain boundary per unit area), ρ'max and ρcold, respectively, were found to decrease sharply with donor concentration towards a broad minimum between ∼0.5 and ∼1.5 at. %, followed thereafter by a gradual increase. The temperature Tmax at which ρ'max occurred was also affected by the donor concentration; initially Tmax was found to increase with donor concentration followed by a reduction forming a broad maximum between about the same donor concentration limits corresponding to the minima in ρcold and ρ'max. These results are interpreted in terms of the well-established Heywang model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342064
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  • 6
    Electronic Resource
    Electronic Resource
    Epitaxial growth of (Hg,Mn)Te by the interdiffused multilayer process (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2983-2985 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial films of (Hg,Mn)Te have been grown by metalorganic vapor phase epitaxy using the interdiffused multilayer process (IMP), on GaAs (100) substrates with a ∼1 μm buffer layer of CdTe. In order to grow the MnTe component, it was found necessary to grow at 380 °C with a precursor partial pressure ratio (Mn:Te) of 5–8. The IMP layers were found to be more uniform in composition and thickness than comparable layers of (Hg,Mn)Te grown by the more conventional direct alloy growth method. X-ray rocking curve widths for IMP layers were typically ∼200‘ with a variation across the layer of ∼10%. Variations in composition were 〈10%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109164
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  • 7
    Electronic Resource
    Electronic Resource
    Positron trapping at divacancies in thin polycrystalline CdTe films deposited on glass (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1380-1382 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed positron annihilation experiments on CdTe films grown by vacuum evaporation at 220 °C on both plain glass and indium-tin-oxide-coated glass substrates. By checking the linearity of the valence annihilation parameter S versus the core annihilation parameter W we introduce a method to analyze the data which directly shows that the same vacancy defect can be present in all the films. By comparing the core annihilation parameter at the defect to that at the VCd vacancy we can identify this defect as the divacancy VCd-VTe. Its concentration in the films decreases from about 1018 to less than 1016 cm−3 after annealing in air at 400 °C for about 30 min. Chlorine doping seems to stabilize the divacancies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111994
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  • 8
    Electronic Resource
    Electronic Resource
    Humidity-dependent impedance in porous spinel nickel germanate ceramic (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 3077-3079 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spinel ceramic material nickel germanate, Ni2GeO4, has been found to exhibit a humidity-dependent impedance. A change in the magnitude of the impedance at 100 Hz, from 108 Ω at 20% RH to 104 Ω at 98% RH, at 298 K, is typical. The effect of frequency on the complex impedance has been investigated over the frequency range 10 mHz–10 MHz, using the technique of impedance spectroscopy. The observed impedance spectra show two regions, indicative of an ionic-charge transport process and a charge transfer to the electrodes, suggesting that at high levels of humidity conduction is essentially electrochemical. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121546
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  • 9
    Electronic Resource
    Electronic Resource
    The influence of Mn on the grain-boundary potential barrier characteristics of donor-doped BaTiO3 ceramics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 2088-2092 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two compositions of BaTiO3 positive temperature coefficient of resistance ceramics, prepared identically except for the fact that a small addition of Mn (0.04 at. %) was made to one of them, were studied. The samples were sintered simultaneously in air at 1400 °C for 1 h and then annealed at 1200 ° for 5 h, using a muffle furnace. Room-temperature dielectric measurements in the audio- and radio-frequency ranges confirmed that Mn has a negligible effect on the bulk resistance. Arrhenius plots of resistivity vs 1/[Tε'm(T)] were found to give straight lines for Tc〈T〈Tmax (where ε'm is the relative permittivity of the specimen measured at a constant frequency of 30 kHz, Tc is the ferroelectric transition temperature, Tmax is the temperature corresponding to the maximum in resistivity, and T is the absolute temperature), in accordance with the well-known Heywang model. The height of the potential barriers at different temperatures, as calculated from the slopes of these plots, were found to increase by about 40% (from ∼0.34 to ∼0.50 eV) by the addition of Mn. A small increase in the acceptor-state density at the grain surfaces, which was again obtained from these plots, was observed in Mn-doped specimens (3.9×1013 cm−2 as compared to 2.7×1013 for Mn-free specimens). It was also found that the inclusion of Mn had a negligible effect on ε'm above Tc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345567
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  • 10
    Electronic Resource
    Electronic Resource
    High temperature optical properties of cadmium telluride (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 6374-6379 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The high temperature optical properties of cadmium telluride have been studied at temperatures up to 1104 K by measurement of the incandescence spectra from a wafer of that material. These measurements provided information equivalent to that of a transmission experiment and allowed the optical absorption spectra of the material to be determined using a theoretical expression for the refractive index and its dispersion with wavelength modified to account for the effect of temperature. This analysis required only a knowledge of the temperature dependence of the fundamental gap of cadmium telluride. Absorption by intrinsic carriers was not found to be significant at photon energies in the region of the fundamental gap even at such elevated temperatures and accordingly the near band-edge absorption was clearly discernable. As is typical in II-VI compound semiconductors, a disorder related exponential absorption (Urbach) tail was observed below the fundamental (mobility) gap and it was to such values of the absorption coefficient that this experiment was sensitive for the relatively thick sample used here. The absorption data were well fitted by assuming the energy gap to have a linear temperature coefficient of −0.34±0.02 meV K−1 and determining the absorption spectra self-consistently with that temperature dependence. At very low values of absorption, however, the condition of the sample surface dominated the spectra. Such measurements may have application in the in situ monitoring of the bulk growth of CdTe by vapour phase techniques, providing information regarding temperature, structural disorder, and surface stoichiometry. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364371
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