1. Nordic Hysitron Laboratory, Department of Materials Science and Engineering, Aalto University, 00076 Aalto, Finland
2. Optoelectronics Research Centre, Tampere University of Technology, 33101 Tampere, Finland
3. Institute of Materials Science, University of Silesia, 75 Pułku Piechoty 1, 45-500 Chorzów, Poland
4. Institute of Physics, University of Silesia, 75 Pułku Piechoty 1, 45-500 Chorzów, Poland
5. Department of Physics, University of Helsinki, P.O. Box 43, FI-00014, Helsinki, Finland