1. Experimentelle Physik 2, Technische Universität Dortmund, 44227 Dortmund, Germany
2. Ioffe Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia
3. Institute of Physics, Polish Academy of Sciences, PL-02-668 Warsaw, Poland
4. LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Materials Sciences, Nanyang Technological University, 639798 Singapore
5. Department of Electrical and Electronics Engineering, Department of Physics, UNAM − Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara, Turkey