1. Department of Materials Science and Engineering Henry Samueli School of Engineering and Applied Science University of California Los Angeles Los Angeles CA 90095 USA
2. State Key Laboratory of Integrated Optoelectronics College of Electronic Science and Engineering Jilin University 2699 Qianjin Street Changchun 130012 China
3. Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems School of Materials Science & Engineering Micro Nano Technology Center School of Physics Beijing Institute of Technology 5 Zhongguancun South Street, Haidian District Beijing 100081 China
4. State Key Lab of Precision Measurement Technology and Instruments Department of Precision Instrument Tsinghua University Haidian Beijing 100084 China