  Epitaxial GaAs quantum dots grown by droplet etching have recently shown
excellent properties as sources of single photons as well as entangled photon
pairs. Integration in some nanophotonic structures requires surface-to-dot
distances of less than 100 nm. This demands a surface passivation scheme, which
could be useful to lower the density of surface states. To address this issue,
sulphur passivation with dielectric overlayer as an encapsulation is used for
surface to QD distances of 40 nm, which results in the partial recovery of
emission linewidths to bulk values as well as in the increase of the
photoluminescence intensity.
