1. Institute of Integrated Photonics, RWTH Aachen University and JARA-Fundamentals of Future Information Technologies, 52074 Aachen, Germany
2. Institut für Halbleitertechnik, University of Stuttgart, 70569 Stuttgart, Germany
3. Peter Grünberg Institute 9, Forschungszentrum Jülich and JARA-Fundamentals of Future Information Technologies, 52428 Jülich, Germany
4. IHP-Leibniz Institut für innovative Mikroelektronik, 15236 Frankfurt (Oder), Germany
5. School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
6. Department of Science, Roma Tre University, Viale G. Marconi 446, 00146 Rome, Italy