1. School of Electronics
and Information Technology, Sun Yat-sen University, Guangzhou 510275, People’s Republic of China
2. State Key Laboratory for Optoelectronics Materials and
Technology, Sun Yat-sen University, Guangzhou 510275, People’s Republic of China
3. School of
Materials Science and Engineering, Sun Yat-sen University, Guangzhou 510275, People’s Republic of China