1. State Key Laboratory for Superlattices and MicrostructuresInstitute of SemiconductorsChinese Academy of Sciences Beijing 100083 China
2. State Key Laboratory on Integrated OptoelectronicsCollege of Electronic Science and EngineeringJilin University Changchun 130012 P. R. China
3. College of Materials Science and Opto‐Electronic TechnologyUniversity of Chinese Academy of Sciences Beijing 100029 China