1. Department of Physics, OSED, Semiconductor Photonics Research Center, Xiamen University, Xiamen, Fujian 361005, People's Republic of China
2. School of Opto-electronic and Communication Engineering, Xiamen University of Technology, Fujian Provincial Key Laboratory of Optoelectronic Technology and Devices, Xiamen, Fujian 361024, People's Republic of China
3. School of Materials Science and Engineering, Nankai University, Tianjin, Tianjin 300071, People's Republic of China