STM-photocurrent-spectroscopy on single self-assembled InGaAs quantum dots

We report about spatially and spectrally resolved photocurrent experiments on single self-assembled In0.5Ga0.5 As quantum dots using local charge extraction, via a STM-tip. For our experiments we use special MBE-grown n–i–p structures which allow for STM-photocurrent measurements. Spectrally resolved experiments have been performed over the entire range of interest. Contributions from bulk GaAs, the InGaAs wetting layer and the quantum dots can be clearly distinguished. The photocurrent response in the energy range of the quantum dots shows characteristic sharp peaks, which are attributed to resonant single quantum dot absorption. The magnitude of the observed peaks is shown to be consistent with the photocurrent contribution expected from single dots. The position of the peaks is subjected to a Stark effect. The magnitude of the Stark shift is modelled in terms of the internal field distribution in the structure underneath the STM-tip.