1. Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus−Senftenberg, K.-Zuse-Str. 1, Cottbus 03046, Germany
2. SENTECH Instruments GmbH, Schwarzschildstraße 2, Berlin 12489, Germany
3. Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, Prague 8 18000, Czech Republic
4. IHP─Leibniz-Institut für innovative Mikroelektronik, Im Technologiepark 25, Frankfurt (Oder) 15236, Germany