1. Key Laboratory of Polar Materials and Devices (MOE), Department of Electronics, East China Normal University, Shanghai 200241, China
2. Shanghai Institute of Ceramics, Key Laboratory of Inorganic Functional Materials and Devices, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, People's Republic of China
3. National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, Shanghai 200083, China