1. School of Semiconductor Science and Technology South China Normal University Foshan 528225 P. R. China
2. State Key Laboratory for Mechanical Behavior of Materials Xi′an Jiaotong University Xi'an 710049 P. R. China
3. State Key Laboratory of Superlattices and Microstructures Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 P. R. China
4. Guangdong Provincial Key Laboratory of Information Photonics Technology School of Materials and Energy Guangdong University of Technology Guangzhou 510006 P. R. China
5. College of Optical Science and Engineering Zhejiang University Hangzhou 310027 P. R. China
6. Guangdong Provincial Key Laboratory of Chip and Integration Technology Guangzhou 510631 P. R. China