Highly mismatched heteroepitaxy: 2D platelets assisted nucleation of self-assembled 3D quantum dots

In the early stages of highly mismatched heteroepitaxy (e.g. for InAs deposited on GaAs) self assembled dots (SAD) with a sharp distribution in sizes appear as soon as the coverage exceeds a critical value. We show that this phenomenon is determined by the preliminary growth of 2D platelets which act as precursors for the formation of 3D coherent islands. The argumentation is based on a total energy calculation using a valence force field approach for the elastic part (including dimers), the residual surface contribution (dangling bonds) being added separately. It is demonstrated that the existence of a critical coverage is related to the interaction between platelets. The proposed mechanism provides an appealing explanation for the fairly good calibration of the observed 3D islands. Moreover, our description appears to give the right order of magnitude for the 2D platelets size, the early quantum dots size, the width of the Gaussian distribution, the magnitude of the critical coverage, and finally the fact that such a phenomenon is not observed at lower values of the mismatch.