1. State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, P. R. China
2. Department of Bioengineering, University of California, Los Angeles, Los Angeles, California 90095, United States
3. Institute of Optoelectronic Technology, Chinese Academy of Sciences, Chengdu 610209, P. R. China