Papers by Author: Yoshiyuki Yonezawa

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Authors: Takashi Tsuji, T. Tawara, Ryohei Tanuma, Yoshiyuki Yonezawa, Noriyuki Iwamuro, K. Kosaka, H. Yurimoto, S. Kobayashi, Hirofumi Matsuhata, Kenji Fukuda, Hajime Okumura, Kazuo Arai
Abstract: The authors fabricated pn diodes with Al+ implantation in p-type epitaxial layers, and investigated the influence of the implantation dose on reverse leakage currents. Only in the highest dose with the Al concentration of 2x1020cm-3, more than 90% of the devices showed high leakage currents above 10-4A at the maximum electric field of 3MV/cm. In such devices, almost all of the emissive spots corresponded to threading screw dislocations (TSDs) by the analysis of emission microscopy and X-ray topography. These TSDs were defined as killer defects with the estimated density of 500cm-2 in the case of the highest dose. The emissions were supposed to be due to microplasmas, since the spectra of the emissions were different from those of heat radiation. Condensation of Al atoms, nitrogen atoms and DI defects were excluded as the origin of the emissions by secondary ion mass spectrometry and low temperature photoluminescence analyses.
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Authors: Ryohei Tanuma, Tae Tamori, Yoshiyuki Yonezawa, Hirotaka Yamaguchi, Hirofumi Matsuhata, Kenji Fukuda, Kazuo Arai
Abstract: This paper describes the study of non-hollow-core elementary screw dislocations (SDs) in silicon carbide (SiC) diodes using X-ray microbeam three-dimensional topography. Strain analysis shows that typical screw dislocations having a symmetric strain field tend to cause microplasma breakdown, whereas deformed SDs do not. The symmetry break in SDs will relax the focussing of strain and lessen the formation of defects, thereby leading to the desirable non-leak property.
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Authors: Shuji Katakami, Manabu Arai, Kensuke Takenaka, Yoshiyuki Yonezawa, Hitoshi Ishimori, Mitsuo Okamoto, Kazutoshi Kojima, Kenji Fukuda
Abstract: We investigated the effect of post-oxidation annealing in wet O2 and N2O ambient, following dry O2 oxidation on the SiC MOS interfacial properties by using p-type MOS capacitors. The interfacial properties were dramatically improved by the introduction of hydrogen or nitrogen atoms into the SiO2/SiC interface, in each POA process. Notably, the N2O-POA process at 1200 °C or higher reduced the interface state density more effectively than the wet-O2-POA process, and offers a promising method to further improve the inversion channel mobility of p-channel SiC MOS devices.
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