1. School of Semiconductor Science and Technology, South China Normal University, Foshan 528225, China
2. School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, China
3. Guangdong Zhongshan Supervision Testing Institute of Quality & Metrology, Zhongshan City, Guangdong Province, China
4. Institute of Semiconductors, Guangdong Academy of Sciences, Guangzhou 510650, China