2D–3D growth transition in metamorphic InAs/InGaAs quantum dots

Abstract

We study the growth by Molecular Beam Epitaxy of InAs quantum dots (QDs) on InGaAs metamorphic buffers (MBs), allowing independent control of the mismatch f between QDs and MBs (7.2% > f > 4.5%) and the In content x of the surface underlying QDs (0 ≤ x ≤ 0.35), taking advantage of the dependence of MB strain relaxation on MB thickness. AFM characterization indicated an enlargement of QD diameters for x ≥ 0.35, while changing f had negligible effects. The two-dimensional (2D) to three-dimensional (3D) critical thickness θ_c was measured by RHEED: for fixed x, θ_c increases with reducing f due to the reduction of the elastic energy of the 2D InAs wetting layer (WL), in agreement with literature model predictions. For fixed f, θ_c reduces with increasing x, an effect not reported so far that we discuss in terms of: (i) enhanced surface diffusion of In atoms on In-richer surfaces and (ii) In-richer WLs in the picture of 2D–3D transition due to In segregation in WLs. These results indicate that metamorphic QDs provide interesting possibilities to control structure properties and can be a model system to investigate the physical mechanisms of the 2D–3D transition.