1. School of Science, Minzu University of China, Beijing 100081, China
2. Optoelectronic Research Laboratory (OERL), Department of Physics, COMSATS University Islamabad, Park Road, Chak Shahzad, Islamabad 45550, Pakistan
3. Electric Material and Nanotechnology Lab, North Dakota State University, Fargo, North Dakota 58102, United States
4. Optoelectronics Research Center, Minzu University of China, Beijing 100081, China