1. School of Physics and Electronic Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang, Jiangsu Province 212013, China
2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China and State Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050, China