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  • 11
    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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  • 12
    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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  • 13
    Electronic Resource
    Electronic Resource
    Superconducting Mg–B films by pulsed-laser deposition in an in situ two-step process using multicomponent targets (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 394-396 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting thin films have been prepared in an in situ two-step process, using the Mg–B plasma generated by pulsed-laser ablation. The target was composed of a mixture of Mg and MgB2 powders to compensate for the volatility of Mg and, therefore, to ensure a high Mg content in the film. The films were deposited at temperatures ranging from room temperature to 300 °C followed by a low-pressure in situ annealing procedure. Various substrates have been used and diverse ways to increase the Mg content into the film were applied. The films show a sharp transition in the resistance and have a zero resistance transition temperature of 22–24 K. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1385345
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  • 14
    Electronic Resource
    Electronic Resource
    Magnesium-diboride ramp-type Josephson junctions (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 2141-2143 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Josephson junctions have been realized in which two superconducting magnesium-diboride (MgB2) layers are separated by a thin MgO barrier layer, using the ramp-type configuration. Their current–voltage characteristics follow the behavior described by the resistively shunted junction model, with an excess current of about 30% of the critical current Ic. A suppression of 70% of Ic was achieved in applied magnetic fields. Shapiro steps were observed by irradiating the junctions with 10.0 GHz microwaves, and the dependence of the step height on applied rf current is well described by a current–source model. Reference samples prepared without the MgO layer showed strong-link behavior with large Ic values. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1462869
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  • 15
    Electronic Resource
    Electronic Resource
    Superconducting quantum interference device based on MgB2 nanobridges (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 2420-2422 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The superconductor MgB2, with a transition temperature of 39 K, has significant potential for future electronics. An essential step is the achievement of Josephson circuits, of which the superconducting quantum interference device (SQUID) is the most important. Here, we report Josephson quantum interference in superconducting MgB2 thin films. Modulation voltages of up to 30 μV are observed in an all-MgB2 SQUID, based on focused-ion-beam patterned nanobridges. These bridges, with a length scale 〈100 nm, have outstanding critical current densities of 7×106 A/cm2 at 4.2 K. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1407864
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  • 16
    Electronic Resource
    Electronic Resource
    Electron densities and temperatures in a diamond-depositing direct-current arcjet plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 1093-1098 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Langmuir probe measurements of electron density and temperature are made in the plume of a dc arcjet reactor. A dc arc is struck in an argon or argon/hydrogen mixture at 6 atm pressure and expands through a converging/diverging nozzle into the reactor with a pressure of 25 Torr. Methane and methane/nitric oxide are added in the diverging nozzle, and diamond film grows on a substrate in the gas plume. Electron temperatures of 1–2 eV are significantly hotter than the neutral gas temperature in the plume. Electron densities range from 1010 to 1013 cm−3, well above the Saha equilibrium for the gas temperature and pressure and well below the equilibrium for the electron temperature. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363852
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  • 17
    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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  • 18
    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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  • 19
    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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  • 20
    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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