1. School of Physics and Electronics; Key Laboratory for Micro-Nano Optoelectronic Devices of Ministry of Education; State Key Laboratory for Chemo/Biosensing and Chemometrics Hunan University; Changsha 410082 P. R. China
2. Key Laboratory of Polar Materials and Devices; MOE; Department of Electrical Engineering; East China Normal University; Shanghai 200241 P. R. China
3. College of Mechanical and Vehicle Engineering; State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body; Hunan University; Changsha 410082 P. R. China