Optical properties of GaAs/AlGaAs quantum dots grown by droplet epitaxy with post-growth annealing

We have studied the post-annealing effects on the optical properties and the spectral homogeneous broadening of GaAs/AlGaAs quantum dots (QDs) fabricated by modified droplet epitaxy. The photoluminescence (PL) intensity of the QDs increased drastically and the peak energy shifted toward high energy, by about 69 meV, after annealing. These effects may be caused by the improved crystallinity of the QD systems, the size reduction of the QDs, and/or composition changes in the QDs by post-annealing. From precise examination of the micro-PL spectra under weak excitation conditions, the minimal homogeneous linewidth of the QDs was estimated to be 1.45 - 1.6 meV at 77 K.