1. Department of Applied Physics, School of Physics and Electronics, Hunan University, Changsha 410082, China
2. Guangdong Provincial Key Laboratory of Information Photonics Technology, School of Materials and Energy, Guangdong University of Technology, Guangzhou, Guangdong 510006, P. R. China
3. School of Semiconductor Science and Technology, Guangdong Provincial Key Laboratory of Chip and Integration Technology, South China Normal University, Foshan 528225, P. R. China
4. Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang 330063, China
5. College of Optical Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, P. R. China