1. Department of Materials Science and Engineering, National Tsing-Hua University, 30013, Taiwan
2. College of Semiconductor Research, National Tsing-Hua University, Hsinchu, 30013, Taiwan
3. Department of Physics, National Sun Yat-Sen University, Kaohsiung, 80424, Taiwan
4. Department of Materials Science and Engineering, Korea University, Seoul 02841, Republic of Korea