1. Institute of Applied Physics, TU Bergakademie Freiberg 1 , Leipziger Str. 23, 09599 Freiberg, Germany
2. Fraunhofer Institute for Integrated Systems and Device Technology 2 , Schottkystr. 10, 91058 Erlangen, Germany
3. University of Erlangen-Nürnberg 3 , Cauerstr. 6, 91058 Erlangen, Germany