1. Faculty of Electronic, Photonics and Microsystems, Wrocław University of Science and Technology, Janiszewskiego 11/17, 50-372 Wrocław, Poland
2. Institute of Experimental Physics, University of Wrocław, Max Born 9, 50-204 Wrocław, Poland
3. Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Strasse 1, 03046 Cottbus, Germany