1. Department of Semiconductor Materials Engineering, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370Wrocław, Poland
2. Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, Warszawa02-668, Poland
3. Łukasiewicz Research Network − PORT Polish Center for Technology Development, Stabłowicka 147, Wrocław54-066, Poland
4. Faculty of Physics, University of Wrocław, Plac Maxa Borna 9, 50-204Wrocław, Poland