Self-assembly of Ga droplets attached to GaAs quantum dots

We report the site-selective formation of Ga droplets on a surface where self-assembled GaAs quantum dots (QDs) were formed by droplet epitaxy. On the surface with the GaAs QDs, all the Ga droplets form adjacent to the QDs and are attached to the (1 1 1)B side facets of the QDs, which was confirmed by selective etching. While some of the QDs have two small droplets on both sides, most of the QDs have one large droplet on one side. We attribute the mechanism of the site-selectivity of the droplets to the morphology of the QDs and the high surface energies of the (1 1 1)B side facet.

► Preferential nucleation sites of Ga droplets exist on the (1 1 1)B facets of QDs.
► A multi-step droplet epitaxy process is proposed.
► High probability site-control was achieved and the growth mechanism is discussed.
► This technique will help to achieve position control of Ga droplets and GaAs QDs.