1. Center for III-Nitride Technology, C3NiT-Janzén, Department of Physics, Chemistry and Biology (IFM), Linköping University 1 , SE-58183 Linköping, Sweden
2. Thin Film Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University 2 , Linköping SE-58183, Sweden
3. Terahertz Materials Analysis Center, THeMAC, Linköping University 3 , SE-58183 Linköping, Sweden
4. Solid State Physics and NanoLund, Lund University 4 , 221 00 Lund, Sweden
5. Department of Microtechnology and Nanoscience, Chalmers University of Technology 5 , SE-41296 Göteborg, Sweden
6. Saab AB 6 , SE-11122 Stockholm, Sweden