1. Department of Semiconductor Materials Engineering, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
2. Department of Materials Science and Engineering, University of Wisconsin-Madison, 1509 University Ave., Madison, Wisconsin 53706, USA
3. Department of Experimental Physics, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland