Magnetotunneling spectroscopy of ring-shaped (InGa)As quantum dots: Evidence of excited states with 2pz character

We study the effect of a high magnetic field (B) on the current-voltage characteristics, I(V), of a GaAs/(AlGa)As resonant tunneling diode incorporating a layer of ring-shaped quantum dots (QDs) in the quantum well (QW). The dots give rise to a series of four unusual resonances in I(V) which show a high degree of reproducibility across the epitaxial wafer. By combining data for B parallel and perpendicular to the growth axis z, we identify that the unusual resonances arise from resonant tunneling into QD excited states with 2pz-like symmetry. The two series of magneto-oscillations in I for B∥z allow us to determine the resonant charging and discharging of the QW with varying bias.