Papers by Author: Seiichiro Higashi

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Authors: Ryousuke Nishihara, Katsunori Makihara, Yoshihiro Kawaguchi, Mitsuhisa Ikeda, Hideki Murakami, Seiichiro Higashi, Seiichi Miyazaki
Abstract: We have formed high density nanodots of nickel silicide (NiSi) on ultrathin SiO2 and characterized their electronic charged states by using an AFM/Kelvin probe technique. Si quantum dots (Si-QDs) with an areal dot density of ~2.5x1011cm-2 were self-assembled on ~3.6nm-thick thermally-grown SiO2 by controlling the early stages of LPCVD using pure SiH4 gas. Subsequently, electron beam evaporation of Ni was carried out as thin as ~1.7nm in equivalent thickness at room temperature and followed by 300°C anneal for 5min in vacuum. XPS and AFM measurements confirm the formation of NiSi dots with an average dot height of ~8nm. After removal of Ni residue on SiO2 by a dilute HCl solution, bias conditions required for electron charging to NiSi dots were compared with those to pure Si-QDs dots and Ni dots. The surface potential changes stepwise with respect to the tip bias due to multistep electron injection and extraction of NiSi nanodots. In addition, it is confirmed that charge retention characteristics of NiSi dots are superior to those of Si-QDs with the almost same size.
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Authors: A. Yamashita, Seiichiro Higashi, S.T. Komatsu, A. Takahara, T. Kajiyama
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Authors: Tsutomu Sakata, Katsunori Makihara, Hidenori Deki, Seiichiro Higashi, Seiichi Miyazaki
Abstract: We have studied uniform growth of crystalline Ge films on quartz plate from VHF (60MHz)-ICP of 10% GeH4 diluted with H2 in the temperature range from 150 to 350°C. By optimizing total gas flow rate, gas pressure, VHF power and antenna-substrate distance, the growth rate as high as 7.4nm/s was obtained at 150°C and increased gradually up to ~7.9nm/s at 350°C. The crystallinity, which was evaluated by Raman scattering measurements as an integrated intensity ratio of TO phonons in crystalline phase to those in disordered phase, reached a value as high as ~93 % at 350°C, but degraded down to 64% at 150°C as a result of the formation of a 60~70nm-thick amorphous incubation (A. I.) layer on quartz. By applying a two-step deposition method at 150°C, in which the GeH4 concentration was selected to be 0.6% for the crystalline nucleation in the first 10s deposition, being as thin as 10nm in thickness, and then changed to 10% GeH4 for the high rate growth, the crystallinity was improved to 78% with keeping an effective growth rate as high as 7.5nm/s, because of a significant increase in the growth rate after the crystalline nucleation.
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Authors: J. Xu, Katsunori Makihara, Hidenori Deki, Yoshihiro Kawaguchi, Hideki Murakami, Seiichiro Higashi, Seiichi Miyazaki
Abstract: Light emitting diode with MOS structures containing multiple-stacked Si quantum dots (QDs)/SiO2 was fabricated and the visible-infrared light emission was observed a room temperature when the negative gate bias exceeded the threshold voltage. The luminescence intensity was increased linearly with increasing the injected current density. The possible luminescence mechanism was briefly discussed and the delta P doping was performed to obtain the doped Si QDs and the improvement of EL intensity was demonstrated.
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