1. State Key Laboratory for Mesoscopic Physics and Frontiers Science Center for Nano-optoelectronics, School of Physics, Peking University 1 , Beijing 100871, China
2. Enkris Semiconductor, Inc. 2 , Suzhou 215123, China
3. Dongguan Institute of Opto-electronics, Peking University 3 , Dongguan, Guangdong 523808, China
4. Songshan Lake Materials Laboratory 4 , Dongguan 523808, China