Papers by Author: Hirohumi Seki

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Authors: Masanobu Yoshikawa, Hirohumi Seki, Keiko Inoue, Takuma Kobayashi, Tsunenobu Kimoto
Abstract: We measured Fourier transform infrared (FT-IR) and cathodoluminescence (CL) spectra of SiO2 films with various thicknesses, grown on 4H-SiC substrates. The appearance of broad phonon modes at ~1150–1250 cm-1 in p-polarized light and their disappearance in s-polarized light confirmed that the phonon modes at ~1150–1250 cm-1 originated from surface polaritons (SPPs). For the thin SiO2 film (8-nm thick), the peak frequency of the transverse optical (TO) phonon in the SiO2 film on the 4H-SiC substrate was observed at ~1080 cm-1 and was higher than that in SiO2 films on the Si substrate (1074 cm-1). This suggested that the thin SiO2 film (8-nm thick) is under compressive stresses at the interface between the SiO2 film and SiC substrate. On the other hand, for the thick SiO2 films (85 and 130-nm thick), the TO phonon peak frequency tended to shift toward lower frequencies with increasing oxide layer thickness. The CL measurement indicated that the CL peak intensity at ~640 nm, attributed to non-bridging oxidation hole centers (NBOHCs), became stronger with increasing oxide layer thickness, relative to that of the CL peaks at ~460 and 490 nm due to oxygen vacancy centers (OVCs). By comparing the FT-IR and CL measurements, we concluded that the TO phonon red-shift with increasing oxide layer thickness can mainly be attributed to an increase in inhomogeneity with increasing oxide layer thickness for the thick SiO2 films.
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Authors: Masanobu Yoshikawa, Keiko Inoue, Junichiro Sameshima, Hirohumi Seki
Abstract: We measured Fourier transform infrared (FT-IR) and cathodoluminescence (CL) spectra of SiO2 films with a various thickness, grown on 4H-SiC substrates. The peak frequency of the transverse optical (TO) phonon mode was blue-shifted by about 5 cm−1 as the oxide-layer thickness decreased from 50-60 nm to 10 nm. The blue shift of the TO mode is considerd to be caused by interfacial compressive stresses in the oxide-layer. On the other hand, the TO phonon mode was found to dramatically decrease as the oxide-layer thickness decreased from 10 nm to 1.7 nm. The CL measurement indicates that the intensity of the CL peaks at about 460 and 490 nm attributed to oxygen vacancy centers (OVCs) for No.2 become stronger than that for No.1. From a comparison between FT-IR and CL measurements, we concluded that the red-shift of the TO phonon with decreasing the oxide-layer thickness can mainly be attributed to an increase in inhomogeneity at the SiO2/SiC interface with decreasing oxide-layer thickness.
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