1. Materials Department, University of California, Santa Barbara, California 93106, United States
2. Institute of Nano Optoelectronics Research and Technology, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
3. CNRS−CRHEA, Rue Bernard Grégory, 06560 Valbonne, France
4. Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93117, United States