Self-assembling of Ge dots on nanopatterns: Experimental investigation of their formation, evolution and control

Abstract

Understanding and predicting quantum dots ordering is a central problem for many physical processes. Here, we investigate the mechanisms which govern the self-assembling of Ge dots on nanopatterned vicinal Si substrate. In a first part, we investigate the formation of nanopatterns by self-organization of growth instabilities which develop during epitaxial growth of Si and ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ layers on Si substrates. Evolution laws of kinetic and thermodynamic growth instabilities as a function of temperature, deposited thickness, and strain are determined on vicinal (111) and (001). In a second part, we analyze the Ge dots ordering on full scale wafer patterns formed by self-organization of the growth instabilities. Depending on the nature of the latter ones, we show that Ge dots can align either in the valley of the instability undulations or on their top. We explain these results by the predominant effect of surface diffusion, surface free energy anisotropy, and strain energy relaxation, respectively.