1. Department of Physics, Pukyong National University, Busan 48513, Republic of Korea
2. Division of Physics and Semiconductor Science, Dongguk University, Seoul 04620, Republic of Korea
3. Quantum-Functional Semiconductor Research Center, Dongguk University, Seoul 04620, Republic of Korea
4. Department of Chemical Engineering, Program in Biomedical Science & Engineering, Inha University, Incheon 22212, Republic of Korea