Spatially resolved spectroscopy on single self-assembled quantum dots

We report about spatially resolved experiments on self-assembled InGaAs quantum dots. Single quantum dots can be investigated by using STM-induced luminescence spectroscopy. The quantum dot occupancy can be increased via the STM tip current, which results in state filling and therefore in the onset of discrete excited state luminescence. In the limit of low injection currents, a single emission line from the ground state of the dot is observed. Using near-field spectroscopy through shadow masks, we have investigated the optical properties of single self-assembled InGaAs quantum dots as a function of occupancy and magnetic field. This allows us to fully resolve diamagnetic/orbital effects, Zeeman splitting, and to determine many body-corrections. Photoluminescence excitation spectra further reveal a strong contribution of phonon assisted processes in quantum dot absorption.