[1] Sun Yat Sen Univ, State Key Lab Optoelect Mat & Technol, Guangzhou 510275, Peoples R China
[2] Natl Univ Singapore, Dept Elect & Comp Engn, Ctr Optoelect, Singapore 119260, Singapore
[3] Inst Mat Res & Engn, Singapore 117602, Singapore
[4] MIT, Dept Mat Sci & Engn, Cambridge, MA 02139 USA
[5] Int Inst Informat Technol, Pune 411027, Maharashtra, India