1. School of Materials Science and Engineering & Guangxi Key Laboratory of Information Materials Guilin University of Electronic Technology Guilin 541004 P. R. China
2. Guangxi Key Laboratory of Automatic Testing Technology and Instrument Guilin University of Electronic Technology Guilin 541004 P. R. China
3. Zhongshan Branch of State Key Laboratory of Electronic Thin Films and Integrated Devices University of Electronic Science and Technology of China Zhongshan Institute Zhongshan 528402 P. R. China