An atomically resolved study of droplet epitaxy InAs quantum dots grown on InGa(As,P)/InP by MOVPE for quantum photonic applications

We investigated droplet epitaxy InAs/InP quantum dots (QDs) grown by MOVPE on two different substrate interlayers of InGaAs and InGaAsP, both lattice-matched to InP, by cross-sectional scanning tunneling microscopy (X-STM) and AFM (atomic force microscopy). We compared, at the atomic scale, the structural and compositional properties of the QDs grown on the two different surfaces. On both interlayers, the QDs present a truncated pyramid shape with a rhomboid base, flat top and bottom facets, and side planes corresponding to {136} planes. Finite element simulations (FESs) are performed to fit the experimental outward relaxation of the QDs and the lattice constant profiles. The X-STM results and FES confirm that the QDs grown on InGaAsP present a composition with less than 5% P intermixing, whereas the QDs on InGaAs have a slightly higher P incorporation but still less than 10% of P intermixing. This study confirms that both interlayers suppress the etching mechanisms, previously identified as etch pits and trenches, when growing InAs QDs directly on InP. The InGaAs and InGaAsP interlayers both show lateral composition modulation, with much stronger fluctuations and filamentation displayed in the InGaAsP interlayer. We demonstrate that the growth on InGaAsP produces InAs QDs with a high crystal quality comparable to those grown on InP and control over the etching mechanisms. The detailed study performed in this work shows the successful integration of high-quality InAs/InP QDs with the InGaAsP surface, which is used in many applications in a wide range of photonic devices and quantum technologies.