1. Institute of Semiconductor Electronics, RWTH Aachen University, Sommerfeldstrasse 24, 52074 Aachen, Germany
2. Department for Theoretical
Physics, Technical University Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany
3. Advanced Microelectronic Center Aachen (AMICA), AMO GmbH, Otto-Blumenthal-Strasse 25, 52074 Aachen, Germany