1. Ningbo Institute of Materials Technology and EngineeringChinese Academy of Sciences Ningbo 315201 China
2. Center of Materials Science and Optoelectronics EngineeringUniversity of Chinese Academy of Sciences Beijing 100049 China
3. School of Physics and Electronics ScienceMinistry of Education Nanophotonics & Advanced Instrument Engineering Research CenterEast China Normal University Shanghai 200062 China
4. Key Laboratory of Polar Materials and DevicesMinistry of EducationEast China Normal University Shanghai 200241 China