1. Chongqing Key Laboratory of Micro & Nano Structure Optoelectronics, School of Physical Science and Technology, Southwest University 1 , Chongqing 400715, China
2. School of Primary Education, Chongqing Normal University 2 , Chongqing 400700, China
3. Department of Electrical and Computer Engineering, University of California 3 , Riverside, California 92521, USA
4. Department of Physics and Electronic Engineering, Tongren University 4 , Tongren 554300, China