1. Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland
2. Paul Drude Institute for Solid State Electronics, Hausvogteiplatz 5-7, 10117 Berlin,
Germany
3. Leibniz Institute for Crystal Growth, Max-Born
Strasse 2, 12489 Berlin, Germany
4. TopGaN Sp. z o.o., Sokolowska 29/37, 01-142
Warsaw, Poland