1. Institute for Solar Energy Research Hamelin (ISFH), Am Ohrberg 1, D-31860 Emmerthal, Germany
2. Laboratory of Nano and Quantum Engineering (LNQE), Leibniz Universität Hannover, Schneiderberg 32, D-30167 Hannover, Germany
3. Institute for Electronic Materials and Devices, Leibniz Universität Hannover, Schneiderberg 32, D-30167 Hannover, Germany
4. Institute of Solid-State Physics, Leibniz Universität Hannover, Appelstrasse 2, D-30167 Hannover, Germany