1. College of Applied Physics and Materials Wuyi University 22 Dongcheng Village Jiangmen 529020 P. R. China
2. Department of Materials Science Fudan University Shanghai 200433 P. R. China
3. Guangdong Engineering Research Center of Optoelectronic Functional Materials and Devices Institute of Semiconductors South China Normal University Guangzhou 510631 P. R. China
4. Guangdong Institute of Semiconductor Industrial Technology Guangdong Academy of Sciences Guangzhou 510650 P. R. China