1. Center of Opto-Electronic Materials and Devices, Post-Silicon Semiconductor Institute, Korea Institute of Science and Technology (KIST), Seoul 136-791, Korea
2. Institute of Physics and Applied Physics, Yonsei University, Seoul 120-749, Korea
3. Materials and Life Science Research Division, Korea Institute of Science and Technology (KIST), Seoul 136-791, Korea
4. Department of Nanomaterials and Nano Science, Korea University of Science and Technology (KUST), Daejun 305-350, Korea