?
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 varies with the overgrowth rate, ranging from ~4 for slow overgrowth to ~2 for rapid overgrowth.
This trend suggests that at higher overgrowth rates, high arsenic flux increases the probability of nonradiative
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.