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The rapidly developing quantum communication technology requiresdeterministic quantum emitters that can generate single photons and entangledphoton pairs in the third telecom window, in order to be compatible withexisting optical fiber networks and on-chip silicon photonic processors.InAs/InP quantum dots (QDs) are among the leading candidates for this purpose,due to their high emission efficiency in the required spectral range. However,fabricating versatile InAs/InP QD-based quantum emitters is challenging,especially as these QDs typically have asymmetric profiles in the growth plane,resulting in a substantial bright-exciton fine structure splitting (FSS). Thishinders the generation of entangled photon pairs and thus, compromises theversatility of InAs/InP QDs. We overcome this by implementing droplet epitaxy(DE) synthesis of low surface density (2.8$\times$10$^8$ cm$^{-2}$) InAs QDs onan (001)-oriented InP substrate. The resulting QDs are located in etched pits,have concave bases, and most importantly, have symmetric in-plane profiles. Weprovide an analytical model to explain the kinetics of pit formation and QDbase shape modification. Our theoretical calculations of electronic statesreveal the properties of neutral and charged excitons and biexcitons confinedin such QDs, which agree with the optical investigations of individual QDs. Theoptical response of QD ensembles suggests that FSS may indeed be negligible, asreflected in the vanishing degree of linear polarization. However, single QDspectrum gathered from an etched mesa shows moderate FSS of (50$\pm$5) $\mu$eVthat we link to destructive changes made in the QD environment during thepost-growth processing. Finally, we show that the studied DE QDs provide aclose-to-ideal single-photon emission purity of (92.5$\pm$7.5) $\%$ in thethird telecom window.

Droplet epitaxy symmetric InAs/InP quantum dots for quantum emission in the third telecom window: morphology, optical and electronic properties