1. Wuhan National High Magnetic Field Center, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Luoyu Road 1037, Hongshan District, Wuhan 430074, China
2. Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742-3511, USA
3. Institute of Solid State Physics, University of Latvia, Kengaraga Street 8, Riga LV-1063, Latvia
4. School of Electrical and Electronics Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
5. Anhui East China Photoelectric Technology Research Institute Co., Ltd., Wuhu 241002, China