Optimal As/Ga flux ratio for low-temperature overgrowth of InAs quantum dots dependent on the GaAs overgrowth rate

We reveal a strong dependence of optical properties of InAs quantum dots (QDs) on the As/Ga flux ratio used during the overgrowth with a low-temperature GaAs layer. Evaluating various characteristics of the photoluminescence spectra, we determine an optimal As/Ga flux ratio which allows formation of QDs emitting at the longest wavelengths, with the highest intensity and the largest energy separation of quantum states. The optimal As/Ga flux ratio depends on the overgrowth rate, with a value of ∼4 for slow overgrowth, decreasing to ∼2 for rapid overgrowth. This trend suggests that at higher overgrowth rates, high arsenic flux increases the probability of non-radiative defects, presumably due to the capture of excess arsenic atoms that violate the stoichiometry of the structure and create additional centers for non-radiative recombination of charge carriers. For each overgrowth rate, the optical properties of QDs deteriorate under non-optimal As/Ga flux ratios because of their enhanced decomposition during the overgrowth. Additionally, we observed that increasing the overgrowth rate leads to a saturation of the QD emission wavelength at ∼1220 nm (300 K), which cannot be further extended by adjusting the As/Ga flux ratio.