Strain-free, symmetrical, InGaAs quantum dots as single photon emitters in the telecomC-band

Non-classical photon sources made of semiconductor quantum dots (QDs) emitting in the telecommunication C-band are crucial components for low-loss, long-distance photonic quantum communication networks. Here we designed and fabricated strain–free In${}_{0.7}$Ga${}_{0.3}$As/In${}_{0.7}$Al${}_{0.3}$As QDs grown on GaAs(111)A substrates working as single-photon emitters in the 1550 nm window. The QDs were grown via local droplet etching method in a molecular beam epitaxy environment, employing a thin In${}_{0.7}$Al${}_{0.3}$As metamorphic buffer layer with the same lattice constant of the QD material, thus allowing for a completely strain–free self-assembly of the QDs. The QDs exhibit a C${}_{3v}$ symmetry with a ground state emission in the 1400–1600 nm range. The exciton lifetimes of $\approx$ 1.3–1.9 ns and linewidths as low as $\approx$ 300 $\mu$eV show the good quality of the fabricated QDs. Second-order autocorrelation measurements under pulsed excitation confirmed the single-photon purity of the emitters, yielding a $g^{(2)}(0)$ value of $0.141\pm 0.027$