1. College of Physics The State Key Laboratory of Inorganic Synthesis and Preparative Chemistry International Center of Future Science Jilin University Changchun 130012 P. R. China
2. State Key Laboratory for Superlattices and Microstructures Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 P. R. China
3. MOE Key Laboratory for UV Light‐Emitting Materials and Technology Northeast Normal University Changchun Jilin 130024 P. R. China
4. Center of Materials Science and Optoelectronic Engineering University of Chinese Academy of Sciences Beijing 100029 P. R. China