1. Francisk Skorina Gomel State University, 104, Sovetskaya Str., Gomel 246019, Belarus
2. Aalto University, Aalto FI-00076, Finland
3. Rzhanov Institute of Semiconductor Physics, Siberian Branch of Russian Academy of Science, 13, Acad. Lavrent'ev Avenue, 630090 Novosibirsk, Russia
4. Stepanov Institute of Physics, National Academy of Science, Belarus, 68, Nezavisimosti Avenue, 220072 Minsk, Belarus