1. Semiconductor Electronics Department of Lviv Polytechnic National University, 12 Bandera Str., 79013 Lviv, Ukraine
2. Department of Chemical Technology of Silicates of Lviv Polytechnic National University, 12 Bandera Str., 79013 Lviv, Ukraine
3. Department of Applied Physics and Nanomaterials Science of Lviv Polytechnic National University, 12 Bandera Str., 79013 Lviv, Ukraine
4. Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland