1. Guangdong Provincial Key Laboratory of Chip and Integration Technology, School of Electronic Science and Engineering, South China Normal University, Foshan 528225, P. R. China
2. RWTH International Academy gGmbH, RWTH Aachen University, Aachen 52074, Germany
3. School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006, China