Masami Onuki

Drift Mobilities of Photocarriers in Amorphous Hydrogenated GaP Made by Reactive Evaporation

The drift mobilities of photoelectrons and photoholes in a film of a-GaP:H at 300 K were estimated to be 2.3×10-3 cm2/Vs and 1.3×10-3 cm2/Vs, respectively, from a time-of-flight measurement in which the mole ratio of Ga to P, r, in the film was nearly equal to unity. Spectra of the ac photoconductivity for different hydrogenated films with different values of r were measured at 90 K and the results at low photon energies suggest an excitation of electrons and holes at the gap states to the mobility edges of the conduction and valence bands, respectively, owing to the transport of mobile holes as well as mobile electrons deduced from time-of-flight measurements.

Anisotropic thermal diffusivity in crystalline YBCO superconductors

Abstract The thermal diffusivity of crystalline YBCO for the vertical and parallel directions to c-axis has been measured to clarify the electron-phonon interaction below T c , by using the transient method. From the diffusivity vs temperature, the scaled BCS gap and electron-phonon coupling strength are anisotropic.

Photoconductivity of hydrogenated amorphous GaP / chrystalline GaP junction

Abstract Possibility of applications of a-GaP:H films to electronic devices has been checked by investigating photovoltaic and electro-luminescent effects in a junction of a-GaP:H film deposited by reactive evaporation on GaP single crystals. Green luminescence has been observed on the a-GaP:H side of the junction, and the origin is suggested to be an electronic transition between free electrons and vacant localized states related to P vacancies and/or Ga-Ga wrong bonds.

AC photoconductivity of amorphous GaP diodes made by reactive evaporation under implantation of hydrogen ions

Abstract The gap states and mobility gap in a GaP:H films have been determined by measuring the optical absorption spectrum, and the amplitude and phase lag of the ac photocurrent, under periodically chopped illumination and a dc voltage, vs. the wavelength. Two kinds of the gap states due to defects other than dangling bonds are proposed, which are concerned with P-vacancies and/or Ga-Ga wrong bonds and Ga-vacancies and/or P-P wrong bonds. The mobility gap is estimated to be 2.6 eV at 90 K and 2.2 eV at 300 K.

Amorphous gallium phosphide (a-GaP) pn-diode by ion beam assisted deposition

Abstract Amorphous gallium phosphide (a-Ga x P) has been formed as pn-diode by using electron beam deposition under hydrogen and/or nitrogen ion beam assistance. The rectification performance limited due to localized states, is improved to an optical device application grade through a higher current source of hydrogen and/or nitrogen ions. It is suggested, that a selective usage of the two ions can optimize the carrier type and junction states. In the case of an optimized ion-assisted amorphous film on crystal GaP, blue light luminescence has been observed.

Time-of-flight measurement of hydrogenated amorphous GaP

Abstract Measurements on the time-of-flight for hydrogenated amorphous gallium phosphide, a-GarP:H with different values of r and different doses of hydrogen atoms, have been carried out in an attempt to evaluate the drift mobilities of electrons and holes in the materials, where r is the mole ratio of Ga to P. The mobilities are increased, when the amount of dosed hydrogen atoms is increased and the value of r approached to unity. The value of the electron drift mobility in a-GaP:H at 300 K is as high as about 2.5 × 10−2 cm2/Vs, which is comparable with that of electrons in a-Si:H measured by Shirafuji ea. The drift mobility of holes in a-GarP:H is comparable with that in a-Si:H obtained by Krag et al.

Dielectric losses of TTF-TCNQ and K0.30MoO3 at low temperatures

Abstract Measurements on the temperature dependences of the dielectric loss for TTF-TCNQ and K 0.30 MoO 3 have been carried out at various frequencies at temperatures much lower than the Peierls transition temperature by using the blocking electrode method. The observed results are discussed by CDWs domain model under an analogy of the ion-transport in solids, then the values of pinning frequency of CDWs and energy barrier height between domains are obtained. Further, depinning CDWs /or exciting solitons stimulated under electric fields enough high to reduce energy barrier height of inter-domains are suggested from experimental data.

Storage current in amorphous silicon solar cells

Abstract Measurements of the storage current in amorphous silicon P + IN + diodes used for solar cells are carried out in an attempt to make clear the transient response of charging and recovery of the current and to evaluate the life time of excess carriers in the device. Charging and recovery of the current are interpreted in terms of device parameters. According to our analysis on experimental results, the life time of excess carriers is very small.

Electron-phonon interaction and thermal diffusivity of high Tc superconductors

Abstract The thermal diffusivity of YBa 2 Cu 3 O z , typical one of high T c superconductors, has been measured by a transient method, in order to make clear the electron-phonon interaction around T c in the material. The diffusivity shows an abrupt increase with decreasing temperature below T c . The BCS energy gap in the material has been estimated from the results, by using the Bardeen-Rickayzen-Tewordt (BRT) theory on the phonon transport.

Doping for making n- and p-type a-GaP:H films during reactive evaporation and sputtering

Techniques of doping with zinc and sulfur to a-GaP:H films during hydrogen-reactive evaporation (RE) and sputtering (SP), and properties of p-n junction diodes made of different a-GaP:H films are described. The conductivity of a-GaP:H films, made by RE and SP method, increases drastically by doping. Junction diodes composed of p-type RE /or SP a-GaP:H films doped with Zn on n-type crystalline GaP substrates, show a comparatively good rectification property, while that of a diode of (p-type SP film doped with Zn) /(n-type RE film doped with S) is in bad shape at present. On the other hand, the latter diode shows the photo-voltaic effect, the spectrum of which is compared with the photoconductivity one of RE a-GaP:H films reported by us previously.