CdSe quantum dot in vertical ZnSe nanowire and photonic wire for efficient single-photon emission

We’ve recently demonstrated that a CdSe quantum dot (QD) in a ZnSe nanowire (NW) can emit triggered single photons up to room temperature [1]. In this contribution, we present the possibilities of enhancing the photon emission and
collection in such NW-QDs structures for a realistic application as a single photon source. We have grown vertically oriented ZnSe NWs (with typical diameter of 10 nm) by molecular beam epitaxy on a ZnSe(111)B buffer layer. The growth of a ZnMgSe passivating shell increases the (otherwise weak) ZnSe near-band-edge luminescence by two orders of magnitude. This has allowed us to observe luminescence for the first time from CdSe/ZnSe NW-QDs in the (111) direction. We managed to obtain a low NW density (~ 1 NW/4 μm2) so that single NW-QDs can be directly studied on the as-grown sample. Exciton, biexciton and charged exciton lines are clearly identified. Then we obtained conformal dielectric coating of Al2O3 on the NW-QDs using Atomic Layer Deposition so that a photonic wire is formed with the CdSe QD deterministically positioned on its axis. The collection enhancement effect is studied by measuring the emission (with pulse excitation, at saturation intensity) of single vertical NW-QDs with Al2O3 coating thickness ranging from 20 nm to 110 nm. Decay time measurements interestingly evidence an inhibition effect of the QD emission for thin Al2O3 coating, indicating that the optical dipole is orthogonal to the NW axis, in agreement with our calculations.