[1] Advanced Semiconductor Research Center, Division of Electronics and Computer Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea, Republic of
[2] Department of Physics, Research Institute of Basic Sciences, Kyung Hee University, Seoul 137-701, Korea, Republic of
[3] Department of Information and Communications, Gwangju Institute of Science and Technology, 1 Oryong-dong, Puk-gu, Gwangju 500-712, Korea, Republic of