1. State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, P. R. China
2. School of Physics and Electronics, Henan University, No. 1, Jinming Street, Kaifeng 475004, P. R. China
3. School of Physics and Microelectronics, Zhengzhou University, 100 Kexue Avenue, Zhengzhou 450015, P. R. China