Shuichi Okano
Kanazawa University
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Featured researches published by Shuichi Okano.
Japanese Journal of Applied Physics | 1989
Dharam Pal Gosain; Minoru Nakamura; Tomoyasu Shimizu; Masakuni Suzuki; Shuichi Okano
The phase transitions from amorphous to crystalline states, and vice versa, by applying electrical pulses were studied for sandwich structures of metal/GexTe100-x thin film/metal. A systematic study of the crystallization temperature in GexT100-x(5\leqslant x \leqslant 30) thin films has been carried out. In some compositions, more than 104 repetitions of amorphous to crystalline states, and vice versa, were attained by the application of electric pulses. A model is proposed to explain the results observed.
Journal of Non-crystalline Solids | 1983
Shuichi Okano; Masakuni Suzuki; Ken Imura; Noboru Fukada; Akio Hiraki
Amorphous As2Se1Te2 (a-As2Se1Te2) films, into which Cu or Cd ions were doped by thermal diffusion below the glass transition temperature exhibited the increase of conductivity by several orders of magnitude. In addition, these samples exhibited enhanced photoconductivity and the activation type conduction. From the measurements of the thermoelectric power, it was found that Cu doped samples were p-type and Cd doped samples were n-type. The impurities was also studied by SIMS.
Japanese Journal of Applied Physics | 1985
Shuichi Okano; Masakuni Suzuki; Takeshi Imura; Akio Hiraki
Thin film diodes with Al/a-As2Se2Te/Sb structures were fabricated by vacuum deposition. Al ions were found to diffuse into a-As2Se2Te films below the glass transition temperature. Measurements of ac conductance and capacitance of the diodes revealed that they consist of two layers of different resistivity which correspond to undoped and Al-doped layers. The upward shift of the Fermi level due to Al doping was inferred from the variation of the forward and backward current with time. Accordingly, the p-n junction formed between the undoped p-type layer and the Al doped n--layer is responsible for the rectification.
Japanese Journal of Applied Physics | 1981
Shuichi Okano; Makoto Suzuki; Masakuni Suzuki
Several metals were found to form rectifying contact with chalcogenide amorphous films. Photovoltaic effects were also found for samples exhibiting rectifying phenomena. Measurements of the frequency dependence of parallel resistance and capacitance revealed that a high resistivity layer with large thickness existed in the contact region between the amorphous films and metals with a strong inoization tendency, which should be referred to as the rectifying layer. This layer is though to be the alloy layer which was formed by a chemical reaction at the interface. The alloying processes due to the chemical reaction were inferred from the observation of a small short circuit current.
Solid State Communications | 1978
Shuichi Okano; H. Nagaoka; Masakuni Suzuki; Tomonobu Hata
Abstract The acoustic flux injection method was applied to amorphous As 2 S 3 . The velocity and the attenuation constant for shear wave at ∼ 100MHz were measured through the observation of the Brillouin scattering of the light beam from a He-Ne laser. The optical transmission around absorption edge was found to change after the injection of acoustic fluxes. It was also found that the sound velocity decreased with increasing injection time of acoustic fluxes and the amount of the change of the sound velocity reached ∼ 20% after 10 5 injections. The changes in the optical transmission and the sound velocity tended to be erased by annealing below the glass transition temperature. These phenomena are considered to be due to structural changes caused by the injection of strong acoustic fluxes.
Japanese Journal of Applied Physics | 1984
Shuichi Okano; Masakuni Suzuki; Noboru Fukada; Takeshi Imura; Akio Hiraki
Diffusion profile of Cu and Cd ions in amorphous As2Se1Te2 films has been studied by secondary ion mass spectroscopy (SIMS). Drive-in processes of the metal ions were carried out at 100°C which is below the glass transition temperature of a-As2Se1Te2. Cd was found to exhibit a familiar diffusion profile of Gaussian type while Cu was found to exhibit an anomalous diffusion profile. Extremely high diffusivity of interstitial Cu ions and electro-chemical reaction at the interface are considered to be responsible for anomalous diffusion profile.
Japanese Journal of Applied Physics | 1984
Shuichi Okano; Akio Suzuki; Noboru Fukada; Takeshi Imura; Akio Hiraki
Cu and Cd ions were found to diffuse into a-As2Se1Te2 films below the glass transition temperature. Cu-doped samples exhibited p-type conduction, while Cd-doped samples exhibited n-type conduction, and the conductivity of the sample films doped with these metal ions increased with the impurity content. Activation-type conduction was dominant over a wide temperature range even in heavily-doped samples, and the band-gap shrinkage due to doping with impurities was small compared with the decrease in the activation energy for conduction. The strong impurity effects are thus considered to be caused not by an increase in the portion of hopping conduction through defect states but by a shift in the Fermi level. A model explaining the formation of donor and acceptor centers in Cu-doped and Cd-doped samples is presented.
Thin Solid Films | 1991
Tsutomu Bando; Dharam Pal Gosain; Shuichi Okano; Masakuni Suzuki
Abstract The composition of evaporated films of the AsSe system depends strongly on the preparation conditions of the bulk and the evaporation conditions. The best conditions for obtaining stoichiometric As 2 Se 3 films are reported. The results are explained on the basis of chemical order and polymerization in AsSe bulk glasses.
Japanese Journal of Applied Physics | 1987
Shuichi Okano; Hiroshi Yamakawa; Masakuni Suzuki; Akio Hiraki
Chalcogenide amorphous semiconductor diodes were fabricated using low-temperature thermal diffusion techniques. Anomalous diffusion profiles of Cd ions were observed by secondary ion mass spectroscopy. Two opposite potential barriers were formed owing to a peculiar diffusion profile of Cd; thus, the rectifying effects became poor. A high density of vacancies and dislocation-like defects, especially in the surface region, is considered to cause anomalous diffusion profiles of Cd ions.
Japanese Journal of Applied Physics | 1981
Masakuni Suzuki; Toshikazu Maekawa; Shuichi Okano; Tsutomu Bandow
Amorphous silicon films were prepared by rf-bias sputtering with a magnetron target and the effects of substrate bias on the electrical and optical properties of sputtered films were studied. Moderate substrate bias was found to improve film quality: photoconductivity increased to ~2×10-4 \mho/cm and the spin density decreased to ~4×1017 cm-3 for the biased samples. The results are interpreted in terms of the removal of loosely bound materials from the surface by ion-bombardment. Low voltage sputtering due to the magnetron target in high argon pressure would also play some roles in the improvement of film quality.