Local Droplet Etching-Assisted Quantum Dot Epitaxy for Telecom C-Band Quantum Light Emitters

Significant progress in quantum light sources for quantum communication applications requires reproducible and symmetric quantum emitters acting as single-photon sources capable of generating entangled photons on demand at specific telecom wavelengths. Here, we propose telecom-emitting epitaxial quantum dots (QDs) fabricated by metal-organic vapor phase epitaxy (MOVPE) using the local droplet etching (LDE) approach. The resulting well-defined, low-density ( $10^9$ / ${cm}^2$ ) QDs based on ${\text{In}}_x{\text{Ga}}_{1-x}\text{As}$ are formed in symmetric LDE nanoholes in ${\text{In}}_{0.52}{\text{Al}}_{0.48}\text{As}$ . Detailed transmission electron microscopy provides comprehensive insight into the structural properties of the QDs. Photoluminescence spectroscopy reveals single QD emission lines (linewidth $\sim 0.2$  meV, fine structure splitting $\sim 60$  μeV) with negligible impact of nonradiative processes, with decay $\sim 1-2$  ns comparable to theoretical simulations, whereas second-order autocorrelation measurements confirm clear single-photon emission with $g^{\left(2\right)}\left(0\right)=0.07\pm 0.02$ under above-band continuous-wave excitation and $g^{\left(2\right)}\left(0\right)=0.16\pm 0.18$ under pulsed excitation. Precise numerical modeling, combining multiband $k\cdot p$ and configuration interaction methods, identifies thermal excitation pathways that explain the persistence of emission up to liquid-nitrogen temperatures. These results highlight the versatility of the LDE approach for integrating new material systems and provide a promising foundation for future studies aimed at scalable fabrication of quantum light sources with tailored emission properties.