Influence of the shallow impurity environment on the luminescence of single-quantum dots

The evolution of low-temperature photoluminescence (PL) spectra of single GaAs/AlGaAs quantum dots (QD) is studied as a function of laser excitation power. At very low powers, where multi-exciton occupation of the QD can be excluded, an unexpected and pronounced spectral evolution is observed. In this weak excitation regime, a significant difference in the fine structure of single-QD spectra is observed not only among different, structurally identical QDs of the same sample, but also among spectra taken from the same single QD excited above and below the AlGaAs barrier. A time-resolved, two-color pump and probe PL experiment on a single QD indicates relaxation times between the different spectral shapes in the ms-range. A model, taking into account the influence of the shallow impurities in the environment of each QD, explains the experimental results.