1. Department of Semiconductor Electronics, Lviv Polytechnic National University, 12 S. Bandery Str., 79013 Lviv, Ukraine
2. Institut Jean Lamour, UMR 7198 CNRS, Université de Lorraine, Parc de Saurupt, 54011 Nancy, France
3. Fraunhofer-Institut für Physikalische Messtechnik IPM, Heidenhofstr. 8, 79110 Freiburg, Germany