1. Semiconductor Research Institute of Semiconductor Research Foundation, Kawauchi Aoba, Sendai 980-0862, Japan
2. Telecommunications Advancement Organization of Japan, Sendai Research Center, 19 Koeji Aza Nagamachi Aoba, Sendai 980-0868, Japan
3. Department of Materials Science and Engineering, Graduate School of Engineering, Tohoku University, 02 Aoba Aza Aramaki Aoba, Sendai 980-8579, Japan