1. Department of Physics, International Christian University, 3-10-2 Osawa, Mitaka, Tokyo 181-8585, Japan
2. Semiconductor Physics, Chemnitz University of Technology, D-09107 Chemnitz, Germany
3. Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8011, Japan
4. Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba 305-8565, Japan
5. Department of Material Science and Engineering, National University of Singapore, 9 Engineering Drive, Singapore 119077
6. Eiwa Bussan Company Limited, 2-9-14 Uchikanda, Chiyoda-ku, Tokyo, Japan