1. Research Center for Advanced Information Materials (CAIM), Huangpu Research & Graduate School of Guangzhou University, Guangzhou 510555, China
2. Solid State Physics & Material Research Laboratory, School of Physics and Material Science, Guangzhou University, Guangzhou 510006, China
3. Department of Education of Guangdong Province, Key Lab of Si-based Information Materials & Devices and Integrated Circuits Design, Guangzhou 510006, China