1. Institute for Solar Energy Research Hamelin (ISFH); Am Ohrberg 1 31860 Emmerthal Germany
2. Institute of Electronic Materials and Devices (MBE); Leibniz Universität Hannover; Schneiderberg 32 30167 Hanover Germany
3. Institute for Solid State Physics; Leibniz Universität Hannover; Appelstraße 2 30167 Hanover Germany