1. Institute of Microscale Optoelectronics Shenzhen University Shenzhen 518060 P. R. China
2. Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province College of Optoelectronic Engineering Shenzhen University Shenzhen 518060 P. R. China
3. Institute for Advanced Study Shenzhen University Shenzhen 518060 P. R. China