1. School of
Semiconductor and Chemical Engineering, Semiconductor Physics Research
Center, Chonbuk National University, Jeonju
561-756, South Korea
2. Korea Basic Science Institute (KBSI), Jeonju Center,
664-14 Dukjin dong 1-ga, Dukjin-gu, Jeonju 561-756, South Korea
3. Department of Electrical Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 305 701,
South Korea