1. Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
2. Dipartimento di Fisica, Politecnico di Milano, Via Anzani 42, 22100 Como, Italy
3. L-NESS and Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy
4. Institut für Festkörpertheorie und -optik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany
5. Departement Physik, Universität Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
6. V. Lashkarev Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, 45 Nauki avenue, 03028 Kyiv, Ukraine
7. Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus UAB, 08193 Bellaterra, Spain
8. Eurofins Materials Science Netherlands BV, High Tech Campus 11, 5656 AE Eindhoven, The Netherlands