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Keiichi YAMAGUCHI Shuichi YOSHIKAWA Tsuyoshi TAKENAKA Syuichi FUJINO Kunihiko HAYASHI Tsutomu MITSUZUKA Katsumi SUZUKI Youichi ENOMOTO
Step-edge Josephson junctions (SEJJs), which are made by YBa2Cu3O7 (YBCO) thin films on MgO (100) substrates with gentle step angle (below 40 degrees) have been successfully fabricated. The step-edge, with several angles on the MgO substrate, were made using photolithography and Ar ion beam etching, and then YBCO films were deposited on the step-edges by pulsed laser deposition method. The relationships between step-angles and I-V characteristics, microwave properties and structure of SEJJs were systematically investigated. Shapiro steps were clearly observed only in step-angle range between 10 and 30 degrees. Intermittence and hysteresis on the I-V characteristics were observed above 30 mA without effect from step-angles.
Shinichiro KOBA Moriaki UCHIYA Akio NAKAO Satoru HIGO Iwazo KAWANO Tetsuya OGUSHI
The barrier-layer was successfully fabricated for a preparation of tunneling junction using high Tc oxidesuperconductor such as Bi-Sr-Ca-Cu-O system. Bi2Sr2Ca2Cu3Ox films were used for both superconducting electrodes and the barrier was mainly Bi2Sr2CaCu2O and the rest that was formed by effects of de-calcium from the first sputtered (2223) film. The reaction of de-calcium occurred immersing it in carbonated water. The change of (2223) phase of BSCCO was confirmed with a comparison of the intensity of X-ray diffraction. The superconductive transition temperature of the junction is different from that of the single film (2223) which had no treatment with carbonated water. Zero-bias-currents through fabricated barrier are observed and the critical currents depend on temperature so far as measured temperature region of 79 K-72 K.
Akitaka MURATA Morio NAKAMURA Akira ASAI Ichiro TANIGUCHI
Surface damage to n-type silicon wafers induced by Reactive Ion Etching (RIE) with CF4 gas was evaluated using X-ray photoelectron spectroscopy (XPS) and the current-voltage (I-V) characteristics of Au/n-Si Schottky diodes fabricated on the damaged surface. The reaction products (SiF, SiF2, and SiF3) in the damaged layer were detected by XPS. Assuming the surface damage on a silicon wafer induced by RIE acts as a donor, the donor density was found to be about 21019 cm-3. The distribution of SiF3 and the donor density in the depth direction were almost equal. The thickness of the damaged layer was about 15 nm. These findings suggest that the donor in the damaged layer on a silicon surface induced by RIE may be SiF3.