1. Institute of Semiconductor Science and Technology, South China Normal University, Foshan, 528225, P. R. China
2. Guangdong Provincial Key Laboratory of Chip and Integration Technology, Guangzhou 510631, P. R. China
3. Department of Electronic Engineering, The Chinese University of Hong Kong, Hong Kong, 999077, P. R. China
4. Guangdong Engineering Research Center of Optoelectronic Functional Materials and Devices, Guangzhou 510631, P. R. China