1. Division of Solid State Electronics, Department of Electrical Engineering, Uppsala University, 75121 Uppsala, Sweden
2. The Ångström Microstructure Laboratory, Uppsala University, 75121 Uppsala, Sweden
3. Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
4. Key Laboratory of Microelectronic Devices and Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, 100029 Beijing, China
5. Institute of Microelectronics, Chinese Academy of Sciences, 100029 Beijing, China