1. Laboratory of Advanced Nano Materials and Devices, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, P. R. China
2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
3. School of Microelectronics, Shandong University, Jinan 250100, P. R. China
4. Ningbo Wakan Electronic Science Technology Co. LTD, Ningbo 315475, P. R. China