Broadening of single quantum dot exciton luminescence spectra due to interaction with randomly fluctuating environmental charges

We studied line broadening of single-dot exciton emissions in terms of fluctuating interaction between the quantum dot (QD) exciton and environmental charges. We examined two types of QD excitons: one accompanied by trapped charge whereby the exciton line redshifts under the trapped charge population and the other nearly free from trapped charges. To avoid population decay of exciton\char22{}which results from multiple-carrier capture into the QDs, thereby leading to line broadening\char22{}and to highlight the effect of the fluctuating charges, we selected QDs that reject the capture of carriers in the barrier material. Interferometric correlation measurements of the single-dot emissions uncover the importance of the trapped charges near the QDs: The fluctuation of the Coulomb field caused by the trapping or detrapping of charges in point defects changes the autocorrelation function into Gaussian decay. A model dealing with the dynamics of the charge occupation driven by the thermally activated carrier capture and photoinduced carrier emissions is constructed consistent with the experiment. Upon temperature rise, the rate of the phase decoherence prevails over that of the charge fluctuation, and the autocorrelation function thereby turns to exponential. In contrast, in the QD nearly free from the trapped nearby charges, the autocorrelation decay obeys a simple exponential function, which is consistent with the absence of the fluctuating charge perturbation. Under an intense excitation, another decoherence due to the exciton or biexciton transition opens. We finally discuss the autocorrelation function in terms of the zero-phonon line and the phonon sideband.