1. Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany
2. Energy and Semiconductor Research Laboratory, Carl von Ossietzky University of Oldenburg, 26129 Oldenburg, Germany
3. NEXT ENERGY-EWE Research Centre for Energy Technology at Carl von Ossietzky University of Oldenburg, 26129 Oldenburg, Germany
4. MAPEX Center of Materials and Processes, University of Bremen, 28359 Bremen, Germany
5. Institute of Semiconductor Technology, Braunschweig University of Technology, 38092 Braunschweig, Germany
6. Laboratory for Emerging Nanometrology (LENA), Braunschweig University of Technology, 38092 Braunschweig, Germany