1. Guangdong Provincial Key Laboratory of Information Photonics Technology School of Materials and Energy Guangdong University of Technology Guangzhou Guangdong 510006 P. R. China
2. Institute of Semiconductors South China Normal University Guangzhou Guangdong 510631 P. R. China
3. Guangdong Provincial Key Laboratory of Chip and Integration Technology Guangzhou Guangdong 510631 P. R. China