[1] Wuhan Univ Sci & Technol, Sch Informat Sci & Engn, Wuhan 430081, Peoples R China
[2] Wuhan Univ, Sch Phys & Technol, Wuhan 430072, Peoples R China
[3] Qingdao Univ, Coll Microtechnol & Nanotechnol, Qingdao 266071, Peoples R China
[4] Hunan Univ, Sch Phys & Elect, Key Lab Micro Nano Optoelect Devices, Minist Educ, Changsha 410082, Peoples R China