1. Key Laboratory of Optic‐Electronic Information Materials of Hebei Province Institute of Life Science and Green Development Key Laboratory of Brain‐Like Neuromorphic Devices and Systems of Hebei Province College of Physics Science and Technology Hebei University Baoding Hebei 071002 P. R. China
2. College of Electronic Information Engineering Hebei University Baoding Hebei 071002 P. R. China
3. School of Natural Sciences University of Chester Parkgate Road Chester CH1 4BJ UK
4. Department of Materials Science and Engineering National University of Singapore Singapore 117575 Singapore
5. Institute of Semiconductors Chinese Academy of Sciences P.O. Box 912, Beijing 100083 China