Engineering Nanohole-Etched Quantum Dots for Telecom-Band Single-Photon Generation

Bright and high-purity single-photon sources at telecom wavelengths are essential for scalable quantum networks. Nanohole-etched GaSb/AlGaSb quantum dots (QDs) are an emerging platform for telecom-band emitters, offering freedom from strain-induced decoherence and indium-related nuclear spin noise of conventional InGaAs QDs. Here, we present a comprehensive optical spectroscopy study that reveals correlations between nanohole morphology, exciton recombination dynamics, and single-photon performance in GaSb QDs. Shallow nanoholes lead to ultrafast charge transfer that limits optical coherence, whereas deeper nanoholes yield clean neutral-exciton emission with a high bright-to-dark state branching ratio (98 ± 1%), indicating favorable conditions for efficient photon generation. Under pulsed quasi-resonant excitation, these QDs exhibit significantly enhanced single-photon purity with <i>g</i>⁽²⁾(0) = 0.029 ± 0.011, compared to above-band excitation (<i>g</i>⁽²⁾(0) = 0.18 ± 0.05). Polarization-resolved measurements across tens of QDs further reveal ultrasmall fine-structure splitting of the neutral exciton (11 ± 5 μeV), relevant for entangled-photon generation at telecom wavelengths. These results highlight the potential of GaSb QDs for high-performance quantum emitters and scalable spin-photon interfaces in the telecom band.