1. Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Onogawa 1-16, Tsukuba, Ibaraki 305-8568, Japan
2. Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Umezono 1-1-1, Tsukuba, Ibaraki 305-8568, Japan
3. NTT Device Technology Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa, 243-0198, Japan
4. NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa, 243-0198, Japan