1. Fujian Provincial Key Laboratory of Quantum Manipulation and New Energy Materials; College of Physics and Energy; Fujian Normal University; Fuzhou 350117 China
2. Fujian Provincial Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices; Xiamen 361005 China
3. Tsinghua-Foxconn Nanotechnology Research Center and Department of Physics; Tsinghua University; Beijing 100084 China