1. Fraunhofer Institute for Integrated Systems and Device Technology (IISB), Erlangen 91058, Germany
2. Erlangen Graduate School in Advanced Optical Technologies (SAOT), Erlangen 91052, Germany
3. Chair of Electron Devices (LEB), University of Erlangen-Nuremberg, Erlangen 91058, Germany
4. CEMES, Université de Toulouse, CNRS, 29 Rue Jeanne Marvig, Toulouse 31055, France