1. AMO GmbH, Advanced Microelectronic Center Aachen, Otto-Blumenthal-Strasse 25, Aachen, Germany
2. Chair of Electronic Devices, RWTH Aachen University, Otto-Blumenthal-Strasse 2, Aachen, Germany
3. II. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, Köln, Germany
4. Department of Chemistry, University of California Berkeley, Berkeley, California 94720, United States