Deterministically fabricated quantum dot single-photon source emitting indistinguishable photons in the telecom O-band

In this work we develop and study single-photon sources based on InGaAs quantum dots (QDs) emitting in the telecom O-band. The quantum devices are fabricated using in-situ electron beam lithography in combination with the thermocompression bonding to realize a backside gold mirror. Our structures are based on InGaAs/GaAs heterostructures, where the QD emission is redshifted towards the telecom O-band at 1.3 {\mu}m via a strain reducing layer. QDs pre-selected by cathodoluminescence mapping are embedded into mesa structures with a back-side gold mirror for enhanced photon-extraction efficiency. Photon-autocorrelation measurements under pulsed non-resonant wetting-layer excitation are performed at temperatures up to 40 K showing pure single-photon emission which makes the devices compatible with stand-alone operation using Stirling cryocoolers. Using pulsed p-shell excitation we realize single-photon emission with high multi-photon suppression of g(2)(0) = 0.027 +- 0.005, post-selected two-photon interference of about (96 +- 10) % and an associated coherence time of (212 +- 25) ps. Moreover, the structures show an extraction efficiency of ~5 %, which compares well with values expected from numeric simulations of this photonic structure. Further improvements on our devices will enable implementations of quantum communication via optical fibers.