Bismuth-surfactant-induced growth and structure of InAs/GaAs(110) quantum dots

TL;DR

This study demonstrates how bismuth surfactant influences the growth mode, structure, and strain relaxation of InAs quantum dots on GaAs(110), enabling controlled quantum dot formation through molecular beam epitaxy.

Contribution

It reveals the role of Bi surfactant in inducing and controlling 3D InAs quantum dot growth on GaAs(110), which normally does not support such formation.

Findings

Bi flux changes InAs growth from 2D to 3D islands.

Larger islands are plastically relaxed, small ones are coherent.

Strain relaxation occurs via specific dislocation types along different directions.

Abstract

We explore the Bi-surfactant-directed self-assembly and structure of InAs quantum dots grown on GaAs(110) by molecular beam epitaxy. The addition of a Bi flux during InAs deposition changes the InAs growth mode from two-dimensional (2D) Frank-van der Merwe to Stranski-Krastanov, resulting in the formation of three-dimensional (3D) InAs islands on the surface. Furthermore, exposing static InAs 2D layers to Bi induces a rearrangement of the strained layer into 3D islands. We explore the effect of varying the InAs thickness and Bi flux for these two growth approaches, observing a critical thickness for 3D island formation in both cases. Characterization of (110) InAs quantum dots with high-resolution transmission electron microscopy reveals that larger islands grown by the Stranski-Krastanov mode are plastically relaxed, while small islands grown by the on-demand approach are coherent. Strain relaxation along the [1-10] direction is achieved by 90 degree pure-edge dislocations with dislocation lines running along [001]. In contrast, strain relief along [001] is by 60 degree misfit dislocations. This behaviour is consistent with observations of planar (In,Ga)As/GaAs(110) layers. These results illustrate how surfactant Bi can provoke and control quantum dot formation where it normally does not occur.