Density-controlled Stranski–Krastanow GaN quantum dots grown on in-plane ordered AlN nanowires

GaN quantum dots (QDs) emitting in the ultraviolet (UV) range have been studied both as ensembles and single emitters, but achieving precise tunability over their density and spatial location remains a challenge. In this work, we demonstrate the possibility of using a novel approach to overcome these limitations by utilizing dislocation-free AlN nanowires (NWs) grown by plasma-assisted molecular beam epitaxy. We show that the density of GaN QDs grown on top of AlN NWs can be tuned over two orders of magnitude solely by adjusting the Ga flux. In particular, for Ga flux as low as 0.01 ML/s, we demonstrate that AlN NWs containing from one to a few GaN QDs each can be grown. The optical properties of such QDs are studied by cathodoluminescence, revealing an emission energy range spanning from 3.3 to 4.7 eV. Our results provide a scalable platform for the realization of low-density single-photon emitters in the UV range by taking advantage of the intrinsic size limitation of the AlN NW top surface. Thus, they open the path to the controlled realization of arrays of single GaN QD emitters for a variety of basic and applied studies.