Low-density arrays of ultra-small InAs nanostructures obtained by two-stage arsenic exposure during droplet epitaxy

Abstract

In order to consider quantum dots as single objects and to use them in modern electronic and photonic devices, they must be well-isolated from each other and have an appropriate size and structural quality. This is a big challenge that is difficult to achieve with traditional technological methods, such as the Stranski-Krastanov growth mechanism. In this paper, we present a novel droplet epitaxial technique for the fabrication of small-sized (∼25 nm) InAs/GaAs nanostructures with a low surface density (<1∙108cm−2). To achieve this result, we develop a growth method based on two-stage crystallization in the arsenic flux. At the first stage, the droplet size is reduced by spreading the droplet material over the surface due to the diffusion decay of droplets in an ultra-low arsenic flux. At the second stage, crystallization is carried out in a large arsenic flux while heating the substrate in order to fix the size and shape of nanodroplets and prevent them from further decaying. We demonstrate that the size dispersion of nanostructures is small and the process is well-reproducible. Thus, the presented approach makes it possible to obtain low-density quantum dots with an ultra-small size required for advanced optical applications.