1. Department of Physics of Semiconductors and Nanoelectronics, Peter the Great St. Petersburg Polytechnic University, St. Petersburg 195251, Russia
2. School of Electrical Engineering, Aalto University, Espoo 02150, Finland
3. Department of Theoretical Physics, Institute of Semiconductor Physics NASU, Kyiv 03028, Ukraine
4. Department of Solid State Electronics, Institute of Physics NASU, Kyiv 03028, Ukraine