1. Department of Physics and Key Laboratory
of Artificial Micro- and Nano-structures of Ministry of Education, Wuhan University, Wuhan 430072, China
2. Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan
3. Department of Electronic & Computer Engineering, The Hong Kong University of Science & Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China
4. Institute of Optoelectronic Display, Fuzhou University, Fuzhou 350002, China