1. Key Laboratory for Physical Electronics and Devices of the Ministry of Education & School of Science & Shaanxi Key Lab of Information Photonic Technique & Institute of Wide Bandgap Semiconductors; Xi'an Jiaotong University; Xi'an 710049 P.R. China
2. Department of Electrical and Computer Engineering; National University of Singapore; 4 Engineering Drive 3 117583 Singapore
3. Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute of Electronic Paper Displays; South China Academy of Advanced Optoelectronics; South China Normal University; Guangzhou 510006 China
4. National Center for International Research on Green Optoelectronics; South China Normal University; Guangzhou 510006 China
5. College of Physics and Electronic Engineering; Hengyang Normal University; Hengyang 421002 China