1. School of Microelectronics, South China University of Technology, Guangzhou, China
2. Engineering Research Center for Optoelectronics, School of Physics and Optoelectronics, South China University of Technology, Guangzhou, China
3. School of Microelectronics and the Engineering Research Center for Optoelectronics, School of Physics and Optoelectronics, South China University of Technology, Guangzhou, China