1. College of Optical and Electronical Information Changchun University of Science and Technology, Changchun, China
2. National Institute of LED on Silicon Substrate, Nanchang University, Nanchang, P. R. China
3. School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong, P.R. China
4. Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education, School of Physics and Electronic Engineering, Harbin Normal University, Harbin, P.R. China