Equilibrium size distributions of clusters during strained epitaxial growth

Heteroepitaxial growth is the key technology that enables band-gap engineering, which is the ability to tailor the electronic and optical properties of materials. The growth of materials with different lattice parameters increases the spectrum of possibilities that one would ultimately have if all heteroepitaxial systems were perfectly matched, since strain can also affect materials properties. Films grown under stress store elastic energy by adapting their lattice parameter to the underlying substrate. Eventually, a portion of the elastic energy stored in the film is relaxed, by either introducing dislocations or by roughening of the growth front. This work focuses on the spontaneous formation of nanocrystals during heteroepitaxy, which produces ensembles of clusters with good uniformity. This observation prompts several questions regarding the mechanisms of cluster formation. More specifically, the relative importance of kinetics and energetics has been a controversial issue. We present data that sheds light onto this issue, addressing the distribution functions of island sizes and their evolution in order to separate kinetic from equilibrium processes. (C) 1999 Elsevier Science S.A. All rights reserved.