Effect of wetting layers on the strain and electronic structure of InAs self-assembled quantum dots

TL;DR

This study investigates how wetting layers influence the strain and electronic properties of InAs quantum dots, revealing minimal strain change but significant energy gap reduction mainly due to increased confining potential width.

Contribution

It provides a detailed atomistic analysis showing that wetting layers mainly affect electronic structure through potential width, not strain relaxation, which is a novel insight.

Findings

Wetting layers reduce the energy gap by up to 10%.

Strain inside the dot changes by less than 1%.

Electron and hole wave functions shift differently due to wetting layers.

Abstract

The effect of wetting layers on the strain and electronic structure of InAs self-assembled quantum dots grown on GaAs is investigated with an atomistic valence-force-field model and an empirical tight-binding model. By comparing a dot with and without a wetting layer, we find that the inclusion of the wetting layer weakens the strain inside the dot by only 1% relative change, while it reduces the energy gap between a confined electron and hole level by as much as 10%. The small change in the strain distribution indicates that strain relaxes only little through the thin wetting layer. The large reduction of the energy gap is attributed to the increase of the confining-potential width rather than the change of the potential height. First-order perturbation calculations or, alternatively, the addition of an InAs disk below the quantum dot confirm this conclusion. The effect of the wetting layer on the wave function is qualitatively different for the weakly confined electron state and the strongly confined hole state. The electron wave function shifts from the buffer to the wetting layer, while the hole shifts from the dot to the wetting layer.