1. Division of Physics and Semiconductor Science, Dongguk University-Seoul, Seoul 04620, Republic of Korea
2. School of Electronic and Electrical Engineering, Hongik University, Seoul 04066, Republic of Korea
3. Department of Energy Systems Engineering, Soonchunhyang University, Asan-si 31538, Republic of Korea
4. Department of Physics, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea
5. School of Materials Science and Engineering, Kookmin University, Seoul 02707, Republic of Korea