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

We explore the Bi-surfactant-directed self-assembly and structure of InAs quantum dots (QDs) 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 (SK), 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 QDs with high-resolution transmission electron microscopy reveals that larger islands grown by the SK mode are plastically relaxed, while small islands grown by the on-demand approach are coherent. Strain relaxation along the [] direction is achieved by 90° pure-edge dislocations with dislocation lines running along [001]. In contrast, strain relief along [001] is by 60° misfit dislocations. This behavior is consistent with observations of planar (In, Ga)As/GaAs(110) layers. These results illustrate how surfactant Bi can provoke and control QD formation where it normally does not occur.