1. State Key Laboratory of Superlattices and Microstructures Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China
2. Center of Materials Science and Optoelectronics Engineering & CAS Center of Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing 100049 China
3. Optoelectronics Research Line Istituto Italiano di Tecnologia (IIT) Via Morego 30 Genoa 16163 Italy
4. Nanochemistry Istituto Italiano di Tecnologia (IIT) Via Morego 30 Genoa 16163 Italy