1. State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors; Chinese Academy of Sciences; No. A35, Qinghua East Road, Haidian District Beijing 100083 P.R. China
2. Key Laboratory of Nanodevices and Applications of CAS, Suzhou Institute of Nano-Tech and Nano-Bionics; Chinese Academy of Sciences; No. 398, Ruoshui Road, Suzhou Industrial Park Suzhou 215123 P.R. China