Low-density InGaAs/AlGaAs Quantum Dots in Droplet-Etched Nanoholes

Over the past two decades, epitaxial semiconductor quantum dots (QDs) have demonstrated very promising properties as sources of single photons and entangled photons on-demand. Among different growth methods, droplet etching epitaxy has allowed the growth of almost strain-free QDs, with low and controllable surface densities, small excitonic fine structure splitting (FSS), and fast radiative decays. Here, we extend the local droplet etching technique to In(Ga)As QDs in AlGaAs, thereby increasing the achievable emission wavelength range beyond that accessible to GaAs/AlGaAs QDs, while benefiting from the aforementioned advantages of this growth method. We observe QD densities of $\sim 0.2\ \mu\mathrm{m}^{-2}$, FSS values as small as $3\ \mu\mathrm{eV}$, and short radiative lifetimes of $\sim 300\ \mathrm{ps}$, while extending the achievable emission range to $\sim 920\ \mathrm{nm}$ at cryogenic temperatures. We envision these QDs to be particularly suitable for integrated quantum photonics applications.