Papers by Author: Satoru Kaneko

Abstract: The hetero p-n junctions of LBMO/ZnO were fabricated by ion beam sputtering. The sample shows clear temperature-dependent rectifying current (I)-voltage (V) characteristics, and junction resistance vs temperature curve is reflected by the CMR nature based on DEC model. The sample shows two-step switching, then the I-V is composed of very-low-resistance (VLR), low-resistance (LR) and high-resistance (HR) regions. The whole I-V behavior is changed by measurement running current. The switching is caused by the spot current, and the original VLR is restored when the current is reduced. The mechanism of switching is proposed in terms of the percolation paths composed of metallic FM-grains. Photo illumination effect on the I-V was investigated. The currents are increased in VLR and HR regions by the illumination. Two origins are possible, electronic process due to hole injection, and phase process. The percolation path might be reinforced by the light.

Abstract: For the purpose of the improving the efficiency of the 4H-SiC photodiode, we reported the spectral reflectance of the antireflection structure of the 140nm period like Moth Eye structure on the 4H-SiC pn epi-wafer. Measured reflectivity of the antireflection structured surface is below 2% at 310nm. The peak responsivity of SWS photodiode is 170mA/W (QE=75%) at 280nm. The response cut-off wavelength is 380nm. Sensitivity of the sensor with SWS structure has increased by compared with that without SWS structure over 260nm of wavelength. At 310 nm, the sensitivity of the photodiode with SWS has increased by 1.3 times than that without SWS. Total amount of short circuit currents was 22% of increase.

Abstract: The photo-response of 3C-SiC pn homojunction photodiodes was measured at high temperature up to 673K. At 473K, the response is hardly different from that at the room temperature. At 573K and 673K, the peak is red shift and lowering comparing that of 298K. The response increases on the long-wavelength region of the profile because of an increase in optical absorption coefficient on increase in temperature. Responsivities at various temperatures were calculated using one-dimensional diffusion model. The calculated profiles of response are qualitatively in agreement with the experimental results except for that of 473K.

Abstract: The carbonization conditions (acetylene pressure and heating rate) to obtain close carbonized layer covered on Si(001) substrate without thermal pits is studied. Subsequent hetero-epitaxial 3C-SiC with smooth surface have been grown by low-pressure CVD. Single-crystalline carbonized layers could be grown at 1050°C by using suitable carbonization processes. The surfaces of Si were covered with single-crystalline 3C-SiC layers at an early stage of carbonization, preventing out-diffusion of Si atoms from Si substrates. 3C-SiC epi-film have RMS = 0.4nm but no single domain. The protrusion density of the film was an order of 1000 cm-2.

Abstract: Bismuth cuprate superconductor has a unique structure called a structural modulation (supercell, SC) consisting of modulated several unit cells. Strain induced by multilayered structure increases the intensity of SC modulation, while an oxygen deficient sample shows expansion of SC size. In this study, as opposed to the multilayer strain, by preparing samples with thick film thicknesses the effect of strain on crystal structure was investigated including SC structure. Epitaxial growth was verified by x-ray diffraction, and the thicker film showed other epitaxial phase rotated 32° around the surface normal with respect to the initial epitaxial phase. The SC size estimated by x-ray reciprocal space mapping was double the size of the initial epitaxial phase. Interestingly, the initial epitaxial phase became a dominant structure after further deposition. In order to evaluate the different SC size and SC modulation, a new index related with an incline of the modulation vector was proposed.