1. College of Electronic Science & Engineering and Microelectronic Information Functional Materials and Devices Research Center, Nanjing University of Posts and Telecommunications, Nanjing 210046, People's Republic of China
2. Department of Materials Science and Engineering and National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, People's Republic of China
3. College of Electronic and information Engineering, Hebei University, Baoding 071002, People's Republic of China