A microscopic picture for the GaAs overgrowth of self-organized $\mathrm{InAs}/\mathrm{GaAs}(001)$ quantum dots is developed. Scanning tunneling microscopy measurements reveal two capping regimes: the first being characterized by a dot shrinking and a backward pyramid-to-dome shape transition. This regime is governed by fast dynamics resulting in island morphologies close to thermodynamic equilibrium. The second regime is marked by a true overgrowth and is controlled by kinetically limited surface diffusion processes. A simple model is developed to describe the observed structural changes which are rationalized in terms of energetic minimization driven by lattice mismatch and alloying.

• Received 30 March 2006

DOI:https://doi.org/10.1103/PhysRevLett.96.226106