STM-cathodoluminescence of self-assembled InGaAs quantum dots

Low temperature STM-cathodoluminescence spectroscopy has been performed on single self-assembled InGaAs quantum dots. Specially designed samples with an electron injector have been grown by MBE on a GaAs substrate, which allow for controlled state filling in the self-assembled dots. Our samples have been analyzed by both spatially resolved photoluminescence and STM-cathodoluminescence. In contrast to the inhomogeneously broadened photoluminescence the STM-cathodoluminescence shows sharp excitonic lines corresponding to discrete levels of a single dot. The occupancy of the dot can be increased in a controlled way 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 a single dot is observed.