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_0.7Ga_0.3As/In_0.7Al_0.3As 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_0.7Al_0.3As 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 μeV 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