Saichi Katayama

Relationship between etch pit densities and oxygen concentrations on CdTe

The density of etch pits and the concentration of O in melt‐grown CdTe increased as the residual gas pressure in ampoules during preparation increased. The etch pit density increased proportionally to the integral strength of an infrared TeO2 absorption band, which presents the oxygen concentration.

Thermal Conductivities of (Bi1-xSbx)2Te3 and Bi2(Te1-ySey)3 Compounds

Thermal conductivity of the semiconducting compounds (Bi1-xSbx)2Te3 and Bi2(Te1-ySey)3 is measured in the cleavage planes in the temperature range of 90?300K. It is found that the heat conduction by charge carriers is smaller than that by phonons and the heat conduction due to the simultaneous thermal diffusion of electron and hole is as important as the lattice thermal conduction at temperatures near 300K. The anharmonicity and disorder parameter are obtained from the lattice thermal conductivity with the aid of the Klemens-Callaway theory. Consideration of the relations between the anharmonicity and the disorder parameter leads to the following conclusion: the three-phonon processes are modified by point defects, and the phonon-phonon interaction of the type a+a\rightleftarrows0 participates in the lattice thermal conduction, where a and 0 refer to the acoustic and optical phonon, respectively.

Segregation coefficients and activation of indium in cadmium telluride grown from tellurium-rich melt by the Bridgman technique

Abstract In-doped CdTe was grown from Te excess CdTe melts by the Bridgman technique. The segregation coefficient of the In atoms in the CdTe crystals was almost independent of the concentration of the In atoms and the Te atom excess with respect to the stoichiometric CdTe ratio for high In atom concentrations. The segregation coefficient was obviously dependent on the concentration of In atoms and excess Te atom concentration for low In atom concentrations. The electrical activity of the In atoms in the CdTe crystals decreased with increasing excess Te atom concentration. Degradation of the activity was caused by the solid solubility limit of the In atoms, the formation of acceptor-like complexes such as V 2− Cd −In + Cd , and the formation of undesirable compounds such as InTe, In 2 Te 3 and CdIn 2 Te 4 .

Behavior of Excess Te Atoms in Undoped p-type CdTe Annealed under Te Vapor Pressures

The number of Te atoms and hole concentrations in undoped p-type CdTe quenched into water after annealing were investigated as functions of annealing temperature and Te2 vapor pressure. The number of Te atoms diffused from the annealing atmosphere into CdTe increased with increasing annealing temperature and Te2 vapor pressure, but decreased with additional increasing Cd vapor pressure. Te precipitates were observed by a scanning electron microscope in CdTe with diffused Te atoms more than approximately 1×1019 cm-3. The number of Te precipitates was increased with increasing Te vapor pressure, but was decreased by adding Cd vapor pressure. It was found that the precipitates resulted in a decrease in the concentration of the holes in p-type CdTe.

Degradation of High-Temperature Superconductor YBa2Cu3O7-x in Water

The degradation of YBa1Cu3O7-x(YBCO) sintered disks was examined by soaking the disks in water at 25°C. By magnetic susceptibility measurements, the degree of the degradation was found to depend on the pressure aplied when forming the disk from YBCO powders. From the analysis of our results, we derived an optimum pressure of 16.5 kbar to minimize degradation.

Dependence of Resistivites of Cadmium Telluride on Residual Gas Pressure in Ampoules during Preparation

Resistivities of cadmium telluride (CdTe) grown by the Bridgman method varied largely with residual gas pressure in ampoules used for preparation. Spectroscopy of residual gas in the ampoules and measurements of photoluminescences and infrared absorptions for grown CdTe crystals revealed that the resistivity increased as the concentration of oxygen incorporated from the atmosphere into CdTe during preparation decreased.

Thermally-Stimulated Current in p-Type CdTe Annealed in Various Atmospheres

The thermally-stimulated currents were measured in the space-charge region of a Schottky diode formed on as-grown or annealed p-type CdTe. The as-grown samples were annealed at temperatures from 200–600°C for 300 min in Cd or Te vapor. Four traps, all of which have been previously reported in the literature, were found in as-grown CdTe at 0.24, 0.40, 0.48 and 0.53 eV above the valence band. Four new traps at 0.053, 0.11, 0.15 and 0.18 eV above the valence band were found in p-type CdTe annealed in Te vapor, and two traps with energies of Ev+0.098 and Ev+0.28 eV were found in p-type CdTe annealed in Cd vapor. It was evident from TSC measurements combined with the removal of a very thin film that the traps found in the annealed samples are localized near the surface.

Deposition of hydrogenated amorphous silicon by an inductively coupled glow discharge reactor with shield electrodes

A plasma was produced using an inductively coupled glow discharge method in which electrodes connected to earth were located in the neighborhood of both sides of the rf working coil. The plasma did not vary according to the position of the substrates. The deposition rate and the electrical property of grown hydrogenated amorphous silicon (a‐Si:H) films, however, depended on the position of the substrate. This was due to the fact that the concentration of H varied much more with position than the concentration of a‐Si:H film precursors as the large H flux removes Si atoms from the a‐Si:H film surface [F. J. Kampas, J. Appl. Phys. 53, 6408 (1982)].

GaAs Films Heteroepitaxially Grown on Si Substrates by Mixture Beams of Ions and Molecules

Thin GaAs films were heteroepitaxially grown on Si substrates by mixture beams of 60 eV ions and neutral molecules without prebaking at a high temperature or intermediate layers. Surfaces of the Si substrates were amorphized by collision of the low-energy ions. The amorphous Si surface layers were automatically inserted between Si substrates and GaAs films and they served as a buffer layer to relieve strain due to large lattice mismatch and difference in coefficients of linear expansion between GaAs films and Si substrates.

Oxidation and stress relief in air at room temperature of amorphous silicon hydrogenated in a glow discharge

Abstract Glow-discharge-hydrogenated amorphous silicon ( a -Si : H) was found to be oxidized in the following two ways after exposing to air at room temperature; first, thin oxide films grew uniformly on the a -Si : H, slowly with increase of exposure time; secondly, oxide with a columnar morphology grew rapidly with the increase of exposure time and the cross section of the columnar oxide was small. Mechanical stress caused by the differences of the thermal expansion coefficient and the crystallographical structure between the a -Si : H and substrates was relieved with the increase in the amount of the columnar oxide.