1. Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education and Hunan Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics, Hunan University, Changsha 410082, China
2. Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Universite Catholique de Louvain, Louvain-la-Neuve B-1348, Belgium
3. Changsha Semiconductor Technology and Application Research Institute, Engineering Research Center of Advanced Semiconductor Technology, College of Semiconductor (College of Integrated Circuit), Hunan University, Changsha 410082, China
4. Zhangzhou Heqi Target Technology Company, Ltd., Jiulong Industrial Park, Hua’an Economic Development Zone, Zhangzhou, Fujian 363000, P. R. China