1. Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstraße 20, 01069 Dresden, Germany
2. Material Systems for Nanoelectronics, Technische Universität Chemnitz, 09111 Chemnitz, Germany
3. Department of Physics, Xiamen University, Xiamen, 361005, China
4. State Key Laboratory of Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, China