1. State Key Laboratory of Electronic Thin Films and Integrated Devices School of Optoelectronic Science and Engineering University of Electronic Science and Technology of China Chengdu 610054 P. R. China
2. Laboratory of Micro‐Nano Optoelectronic Materials and Devices Key Laboratory of Materials for High‐Power Laser Shanghai Institute of Optics and Fine Mechanics Chinese Academy of Sciences Shanghai 201800 P. R. China
3. School of Physics and Electronics Henan University Kaifeng 475004 P. R. China
4. School of Physics and Optoelectronic Engineering Shenzhen University Shenzhen 518060 P. R. China
5. Department of Physics and School of Engineering Brown University Providence RI 02912 USA