1. Key Laboratory for UV Light-Emitting Materials and Technology (Northeast Normal University), Ministry of Education 1 , 5268 Renmin Street, Changchun 130024, China
2. National Demonstration Center for Experimental Physics Education, Northeast Normal University 2 , Changchun 130024, China
3. Institute of Microelectronics, Chinese Academy of Sciences 3 , Beijing 100029, China
4. University of Chinese Academy of Sciences 4 , Beijing 100049, China