1. Key Laboratory of Inorganic Function Materials and Devices; Shanghai Institute of Ceramics; Chinese Academy of Sciences; University of Chinese Academy of Sciences; 1295 Dingxi Rd. Shanghai 200050 China
2. Key Laboratory of Polar Materials and Devices; Ministry of Education; Department of Electronic Engineering; East China Normal University; 500 Dongchuan Rd. Shanghai 200241 China
3. Institute of Electronics, Microelectronics and Nanotechnology (IEMN)-DOAE; UMR CNRS 8520; Université des Sciences et Technologies de Lille; Villeneuve d'Ascq Cedex 59652 France