Telecom wavelength single quantum dots with very small excitonic fine-structure splitting

We report on molecular beam epitaxy growth of symmetric InAs/InP quantum dots (QDs) emitting at telecom C-band (1.55 $\mu$m) with ultra-small excitonic fine-structure splitting of ~2 $\mu$eV. The QDs are grown on distributed Bragg reflector and systematically characterized by micro-photoluminescence ($\mu$-PL) measurements. One order of magnitude of QD PL intensity enhancement is observed in comparison with as-grown samples. Combination of power-dependent and polarization-resolved measurements reveal background-free exciton, biexciton and dark exciton emission with resolution-limited linewidth below 35 $\mu$eV and biexciton binding energy of ~1 meV. The results are confirmed by statistical measurements of about 20 QDs.