1. Laboratory for Compound Semiconductor Microsystems, IMTEK-Department of Microsystems Engineering, University of Freiburg; Georges-Koehler-Allee 103 79110 Freiburg Germany
2. Fraunhofer Institute for Applied Solid State Physics; Tullastrasse 72 79108 Freiburg Germany
3. Laboratory for Power Electronics, INATECH-Department of Sustainable Systems Engineering; Emmy-Noether-Straße 2 79110 Freiburg Germany