1. Department of Physics of Semiconductors and Nanoelectronics, Peter the Great St. Petersburg Polytechnic University, 29 Polytechnicheskaya Str., St. Petersburg 195251, Russia
2. Institute for Physics of Microstructures of RAS, Nizhny Novgorod 603950, Russia
3. Department of Theoretical Physics, Institute of Semiconductor Physics NASU, Kyiv 03028, Ukraine
4. Ioffe Institute, 26 Polytechnicheskaya Str., St. Petersburg 194021, Russia
5. Submicron Heterostructures for Microelectronics Research and Engineering Center of RAS, 26 Polytechnicheskaya Str., St. Petersburg 194021, Russia
6. Department of Electronics and Nanoengineering, Aalto University, P.O. Box 13500, Aalto FI-00076, Finland