1. Department of Energy and Materials Engineering, Dongguk University, 26 Pil-dong, 3 ga, Jung-gu, Seoul 100-715, South Korea
2. Advanced
Materials Research Institute, Samsung Fine Chemicals Co., Ltd., Suwon, Gyeongi 443-803, South Korea
3. Division of Physics and Semiconductor Science, Dongguk University, 26 Pil-dong, 3 ga, Jung-gu, Seoul 100-715, South Korea