1. School of Physics and Optoelectronic Engineering, Guangdong University of Technology, WaiHuan Xi Road, No. 100, Guangzhou 510006, China
2. School of Electronics and Communications, Guangdong Mechanical & Electrical Polytechnic, Guangzhou 510515, China
3. School of Applied Physics and Materials, Wuyi University, Jiangmen 529020, China
4. Department of Materials Science and Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon 999077, Hong Kong SAR, China