1. Department of Electrical & Computer Engineering; McGill University; Montreal QC H3A0E9 Canada
2. Advanced Light Source; Lawrence Berkeley National Laboratory; Berkeley CA 94720 USA
3. Department of Physics; University of Wisconsin Madison; Madison WI 53706 USA
4. Department of Physics; McGill University; Montreal QC H3A2T8 Canada
5. Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials and Micro-Nano Devices; Renmin University of China; Beijing 100872 P. R. China
6. Science des Matériaux; IREQ; Hydro-Québec; Varennes QC J3×1S1 Canada
7. International Research Center for Renewable Energy; School of Energy & Power Engineering; Xi'an Jiaotong University; Xi'an 710049 P. R. China