Affiliation: | (1) Department of Physics, Chungnam National University, 220 Gung-dong, Yuseong-gu, Daejeon, 305-764, Korea;(2) Advanced Semiconductor Research Center, Division of Electrical and Computer Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul, 133-791, Korea |