1. State Key Laboratory of Artificial Microstructure and Mesoscopic Physics School of Physics Nano-Optoelectronics Frontier Center of Ministry of Education (NFC-MOE) Peking University Beijing 100871 China
2. MOCVD Department Advanced Micro-Fabrication Equipment Inc. Shanghai 201201 China
3. Electron Microscopy Laboratory School of Physics Peking University Beijing 100871 China
4. Songshan Lake Materials Laboratory Dongguan Guangdong 523808 China
5. Dongguan Institute of Optoelectronics Peking University Dongguan Guangdong 523808 China