Optically detected single-electron charging in a quantum dot

By means of photoluminescence spectroscopy we compare the bias-dependent emissions of single-quantum dots which are embedded in two differently designed photodiode structures. Controlled single-electron charging allows to identify neutral, single- and double-charged excitons in the optical spectra of both samples. At high magnetic fields, one Zeeman component of the single-charged exciton is found to be quenched, which is attributed to the competing effects of tunnelling and spin-flip processes. The strength of the tunnelling coupling between quantum dot and back-contact was found to have a strong influence on the observed spectral features—in particular, the parallel appearance of emission lines resulting from the radiative decay of differently charged quantum dot states is suppressed in case of strong tunnelling interaction.