1. Department of Electrical and Electronic Engineering; Southern University of Science and Technology; Shenzhen 518055 P. R. China
2. The Institute of Applied Physics and Materials Engineering; University of Macau; Avenida da Universidade Taipa Macau
3. College of Physics and Energy; Shenzhen University; Shenzhen 518060 P. R. China
4. School of Science and Engineering; The Chinese University of Hong Kong; Shenzhen P. R. China