1. College of Electronic Science and Technology; 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
4. Department of Materials Science and Engineering; City University of Hong Kong; Kowloon 999077 Hong Kong SAR