[1] Nanyang Technol Univ, Sch Mat Sci & Engn, Singapore 639798, Singapore
[2] Xidian Univ, Sch Adv Mat & Nanotechnol, Key Lab Wide Band Gap, Semicond Technol, Xian 710071, Peoples R China
[3] King Abdullah Univ Sci & Technol, Solar & Photovolta Engn Res Ctr, Thuwal 239556900, Saudi Arabia
[4] Lanzhou Univ, Sch Phys Sci & Technol, Lanzhou 730000, Peoples R China
[5] Inst Mat Res & Engn, Mat Ctr Innovat, Singapore 117602, Singapore