1. College of Science, Hunan University of Science and Engineering 1 , Yongzhou 425199, China
2. College of Materials Science and Engineering, Hunan University 2 , Changsha 410082, China
3. Fujian Provincial Key Laboratory of Semiconductors and Applications, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Physics, Xiamen University 3 , Xiamen 361005, China