ERA NanoSci - Optical interface for gate-controlled quantum dots
Theoretische Chemie: Elektronenstruktur, Dynamik, Simulation
Zusammenfassung der Projektergebnisse
For the implementation of a quantum optical interface a 2DEG hybrid heterostructure was proposed consisting of an inverted 2DEG and of self assembled In(Ga)As QDs positioned close to the 2DEG in tunneling distance. We have shown that it is possible to grow such 2DEG hybrid samples with QD-2DEG distances in the range between 15 and 60 nm without degrading the electrical properties of the 2DEG too much. For appropriate QD densities the 2DEG still meets the electrical specifications required for gate defined QDs. We could show that the 2DEG hybrid samples are reproducibly gateable within a certain topgate voltage range. In an AC transport measurement we observed a QD signature in the voltage along the hallbar during a topgate upsweep. The distinct peaks in the imaginary part of the longitudinal voltage are associated with different charge states of the QDs. This technique might be a new characterization method for hybrid samples complementary to established techniques like capacitance-voltage measurements where the 2DEG has to be in the conductive regime. In contrast, our measurements were performed at topgate voltages for which the 2DEG was (partially) depleted. We showed that it is possible to optically address a single QD on a gated hallbar structure. The charge state of the QD could be controlled by a semitransparent topgate. It is thus possible to tune the energy levels of the QD in resonance to the 2DEG for the specific 2DEG hybrid samples applying appropriate topgate voltages. Electron tunneling between the 2DEG and the QD can be switched on and off by the means of the topgate, a major requirement for the proposed optical interface. No nanowire hybrid samples were fabricated as the MBE machine used for nanowire growth was not suitable for generating heterostructures with high optical quality. We concentrated on fundamental studies of the growth process. We could show that it is possible to generated WZ as well as ZB nanowires with very high crystal quality (no crystal structure mixing) by adjusting the growth parameters accordingly. The pure WZ GaAs nanowires were used to study the optical properties of the WZ crystal phase. We investigated the position controlled nanowire growth by nano-pattering the substrate in order to obtain the same local growth condition for each nanowire. Our findings can be used to generate crystal optimized nanowire hybrid samples reducing or eliminating e.g. scattering effects at crystal boundaries.
Projektbezogene Publikationen (Auswahl)
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Position controlled self-catalyzed growth of GaAs nanowires by molecular beam epitaxy, Nanotechnology 21 (2010)
B. Bauer, A. Rudolph, M. Soda, A. Fontcuberta i Morral, J. Zweck, D. Schuh, E. Reiger
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Determination of the band gap and the split-off band in wurtzite GaAs using Raman and photoluminescence excitation spectroscopy, Phys. Rev. B 83, 125307 (2011)
Bernt Ketterer, Martin Heiss, Marie J. Livrozet, Andreas Rudolph, Elisabeth Reiger, and Anna Fontcuberta i Morral
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Direct correlation of crystal structure and optical properties in wurtzite/zinc-blende GaAs nanowire heterostructures, Phys. Rev. B 83, 045303 (2011)
M. Heiss, S. Conesa-Boj, J. Ren, H. Tseng, A. Gali, A. Rudolph, E. Uccelli, F. Peiro, J. Morante, D. Schuh, E. Reiger, E. Kaxiras, J. Arbiol, and A. Fontcuberta i Morral
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Transition from Au to pseudo-Ga catalyzed growth mode observed in GaAs nanowires grown by molecular beam epitaxy, Phys. Rev. B. 85, 245450 (2012)
Soda, M., Rudolph, A., Schuh, D., Zweck, J., Bougeard, D., Reiger, E.
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Wechselwirkung zwischen zweidimensionalen Elektronengasen und selbstorganisierten Quantenpunkten, PhD Thesis, 2012, University of Regensburg
Dominik Scholz
