Crystal Phase Quantum Dots in the Ultrathin Core of GaAs-AlGaAs Core-Shell Nanowires.

Semiconductor quantum dots embedded in nanowires (NW-QDs) can be used as efficient sources of nonclassical light with ultrahigh brightness and indistinguishability, needed for photonic quantum information technologies. Although most NW-QDs studied so far focus on heterostructure-type QDs that provide an effective electronic confinement potential using chemically distinct regions with dissimilar electronic structure, homostructure NWs can localize excitons at crystal phase defects in leading to NW-QDs. Here, we optically investigate QD emitters embedded in GaAs-AlGaAs core-shell NWs, where the excitons are confined in an ultrathin-diameter NW core and localized along the axis of the NW core at wurtzite (WZ)/zincblende (ZB) crystal phase defects. Photoluminescence (PL)-excitation measurements performed on the QD-emission reveal sharp resonances arising from excited electronic states of the axial confinement potential. The QD-like nature of the emissive centers are suggested by the observation of a narrow PL line width, as low as ~300 μeV, and confirmed by the observation of clear photon antibunching in autocorrelation measurements. Most interestingly, time-resolved PL measurements reveal a very short radiative lifetime <1 ns, indicative of a transition from a type-II to type-I band alignment of the WZ/ZB crystal interface in GaAs due to the strong quantum confinement in the ultrathin NW core.