Size Dependence of the Photoluminescence Decay Time in Unstrained GaAs Quantum Dots

We report the size dependence of the photoluminescence (PL) decay time of unstrained GaAs quantum dot (QD) ensembles grown on an Al0.3Ga0.7As/GaAs (100) surface by using droplet epitaxy. The density of GaAs QDs is 3 x 10(9)/cm(2), which indicates that each QD is isolated from neighboring QDs. The low-temperature PL spectrum of the GaAs QD ensembles shows a Gausian profile with a linewidth broadening of 30 nm. The PL decay time of the GaAs QDs increases monotonically with increasing emission wavelength, which corresponds to the dot size. This result can be explained by a reduction in the exciton oscillator strength in larger dots. In addition, the PL decay time decreases with increasing excitation power. This can be explained by the state filling effect, which leads to an increase in electron-hole wave-function overlapping.