Local droplet etching-assisted quantum dot epitaxy for telecom C-band quantum light emitters

Original Abstract

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 using the local droplet etching (LDE) approach. The resulting well-defined, low-density ($10^9$/cm$^2$) QDs based on In$_{x}$Ga$_{1-x}$As are formed in symmetric LDE nanoholes (in-plane aspect ratio of 1.14) in In$_{0.52}$Al$_{0.48}$As. Detailed transmission electron microscopy provides comprehensive insight into the structural integrity, interface quality, and compositional profiles of the QDs, which underpin their promising optical properties. Photoluminescence spectroscopy reveals narrow emission lines (0.2 meV) and high optical quality, while second-order autocorrelation measurements confirm clear single-photon emission, with $g^{(2)}(0)=0.07\pm0.02$ under above-band continuous-wave excitation and $g^{(2)}(0)=0.16 \pm 0.18$ under pulsed excitation. Precise numerical modeling, combining multiband $\boldsymbol{k} \cdot \boldsymbol{p}$ and configuration-interaction methods, supports the optical characterization and 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 pave the way toward scalable fabrication of quantum light sources with tailored emission properties.