1. Key Laboratory of Optoelectronics Technology Ministry of Education Beijing University of Technology Beijing 100124 China
2. Université Côte d'Azur Centre de Recherche sur l'Hétéro‐Epitaxie et ses Applications (CRHEA) CNRS Valbonne 06560 France
3. Department of Physics Baylor University Waco TX 76798 USA
4. Institute of Semiconductor Chinese Academy of Sciences Beijing 100083 China
5. National Centre for Nanoscience and Technology Beijing 100190 China
6. Department of Physics and Astronomy University of California Irvine CA 92697 USA