Regensburg 2013 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 74: Quantum dots: Optical properties
HL 74.3: Talk
Thursday, March 14, 2013, 10:00–10:15, H16
GaAs Quantum Dot Molecules of ultra-low density — •Achim Küster, David Sonnenberg, Andreas Graf, Christian Heyn, and Wolfgang Hansen — Institut für Angewandte Physik, Universität Hamburg, 20355 Hamburg, Germany
We present the fabrication and optical properties of GaAs quantum dot molecules (QDM). The QDM are fabricated by filling nanoholes in an AlGaAs surface with a GaAs/AlGaAs/GaAs layer sequence. The nanoholes are formed using local droplet etching with Al droplets on AlGaAs substrates. By optimizing the arsenic flux during droplet deposition an ultra-low density of some ·106 cm−2 can be achieved [1], allowing the study of single QDM. With our fabrication method we have good and independent control on the dot size and the tunnel barrier in the QDM. The AlGaAs layer between the GaAs layers forms the tunnel barrier with thickness that is tuned from 1 nm to 20 nm in our experiments. Also, the dot size can be tuned separately in these structures. In samples with tunnel barrier thickness below 5 nm we observe non-resonant tunnelling [2] in these QDMs as a clear sign of coupling, while at a barrier thickness of 15 nm the optical spectra show no signature of tunnelling any more. Furthermore, we have integrated the QDMs into Schottky-diode structures and observed strong Stark-shifts up to 25 meV at typical fields of 2 · 107 V/m. [1] D. Sonnenberg et al., APL 101, 143106 (2012); [2] M. Reischle et al., PRB 76, 085338 (2007)