1. Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warsaw, Poland
2. Faculty of Physics, University of Warsaw, Hoza 69, 00-681 Warsaw, Poland
3. Department of Electrical and Computer Engineering, McGill University, 3480 University Street, Montreal, H3A-2A7, Canada
4. IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany
5. University of Vienna, Strudlhofgasse 4, 1090 Wien, Austria
6. Institute of Microelectronics and Optoelectronics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland