1. Institute for Physics of Microstructures RAS, GSP-105, 603950 Nizhny Novgorod, Russia
2. Lobachevsky State University of Nizhny Novgorod, Gagarin Avenue 23, 603022 Nizhny Novgorod, Russia
3. HSE University, Myasnitskaya str. 20, 101000 Moscow, Russia
4. Semiconductor Physics Section, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium