1. School of Physics School of Microelectronics State Key Laboratory of Crystal Materials Shandong University Jinan 250100 P. R. China
2. State Key Laboratory of Infrared Physics Shanghai Institute of Technical Physics Chinese Academy of Sciences Shanghai 200083 P. R. China
3. State Key Laboratory of High Power Semiconductor Lasers Changchun University of Science and Technology Changchun 130022 P. R. China
4. Institute of Optoelectronics and Nanomaterials MIIT Key Laboratory of Advanced Display Materials and Devices College of Materials Science and Engineering Nanjing University of Science and Technology Nanjing 210094 China
5. Key Laboratory for Micro‐Nano Optoelectronic Devices of Ministry of Education School of Physics and Electronics Hunan University Changsha 410082 P. R. China
6. Department of Materials Science and Engineering City University of Hong Kong Hong Kong 999077 P. R. China