1. National Laboratory of Solid‐State MicrostructuresSchool of Electronic Science and EngineeringCollaborative Innovation Center of Advanced MicrostructuresNanjing University Nanjing 210093 P. R. China
2. College of Electronic and Optical EngineeringNanjing University of Posts and Telecommunications Nanjing Jiangsu 210023 P. R. China
3. State Key Laboratory of Optoelectronic Materials and TechnologiesGuangdong Province Key Laboratory of Display Material and TechnologySchool of Electronics and Information EngineeringSun Yat‐Sen University Guangzhou 510275 P. R. China