1. Department of Microelectronic Science and Engineering, School of Physical Science and Technology, Ningbo University, Ningbo 315211, Zhejiang, P. R. China
2. Institute of Solid State Physics, Shanxi Datong University, Datong 037009, Shanxi, P. R. China
3. XLIM Research Institute, UMR 7252 CNRS/University of Limoges, Avenue Albert Thomas, 87060 Limoges, France