Optical spectroscopy of charged excitons in single quantum dot photodiodes

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. The strength of the tunneling coupling between the quantum dots and the diode's n region is 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 tunneling interaction.