1. Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea
2. Department of Physics, UNIST, Ulsan 44919, Republic of Korea
3. Department of Physics, Inha University, Incheon 22212, Republic of Korea
4. Department of Physics, Korea University, Seoul 02841, Republic of Korea
5. Graduate School of Semiconductor Materials and Devices Engineering, UNIST, Ulsan 44919, Republic of Korea