1. Semiconductors Laboratory Toyota Technological Institute 2‐12‐1 Hisakata, Tempaku Nagoya 468‐8511 Japan
2. Institute for Materials Research Tohoku University 2‐1‐1 Katahira, Aoba‐ku Sendai 980‐8577 Japan
3. Research and Development Directorate Japan Aerospace Exploration Agency 2‐1‐1 Sengen, Tsukuba Ibaraki 305‐8505 Japan