1. Department of Electrical and Computer Engineering, Baylor University, Waco, Texas 76798, USA
2. Department of Electrical and Computer Engineering, University of Houston, Houston, Texas 77204, USA
3. Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054, China
4. State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054, China
5. Materials Science and Engineering, University of Houston, Houston, Texas 77204, USA