1. Department of Applied Physics and Centre for New Materials, Aalto University, P.O. Box 15100, FI-00076 Aalto, Espoo, Finland
2. CIDETEC-IK4, Po Miramón 196, E-20009 Donostia-San Sebastián, Spain
3. Optoelectronics Research Centre, Tampere University of Technology, P.O. Box 692, 33101 Tampere, Finland
4. Microelectronics and Materials Physics Laboratories, EMPART Group, Infotech Oulu, University of Oulu, P.O. Box 4500, 90014 Oulu, Finland
5. Canatu Ltd., Konalankuja 5, 00390 Helsinki, Finland