1. Faculty of Engineering, IMTEK, Albert-Ludwigs-University Freiburg, Georges-Köhler-Allee 103, Freiburg 79110, Germany
2. V. Lashkarev Institute of Semiconductor Physics NAS Ukraine, 45 Nauki Avenue, Kiev 03028, Ukraine
3. Faculty of Physics, M.V. Lomonosov Moscow State University, Leninskie Gory 1, Moscow 119991, Russia
4. Fraunhofer-Institut für Solare Energiesysteme ISE, Heidenhofstr. 2, Freiburg 79110, Germany
5. Max-Planck-Institute of Microstructure Physics, Weinberg 2, Halle 06120, Germany
6. MIND-IN2UB, Departament d'Electrònica, Universitat de Barcelona, C/Martí i Franquès, 1, Barcelona 08028, Spain
7. CCiT, Scientific and Technical Centers, Universitat de Barcelona, C/Lluís Solé i Sabaris 1, Barcelona 08028, Spain
8. Optics and Photonics, School of Information and Communication Technology, Royal Institute of Technology (KTH), Electrum 229, Kista SE-16440, Sweden