Spatial correlation of self-assembled isotopically pure Ge/Si(001) nanoislands

By using a statistical method based on Voronoi tessellation, we investigated the nucleation of strain-driven self-assembled Ge/Si(001) nanoislands and their dynamic interaction with the local environment. The evolution of the composition and strain during the growth process was also studied by Raman scattering. The use of isotopically purified G76e source allows the observation of faint features in the three-dimensional nanoisland Raman signal at the early stage of the growth. The nucleus critical sizes are deduced from the scaling behavior of the Voronoi cell areas and the grown island volumes. The relatively small critical size suggests a stabilizing role of Si atoms and surface imperfections. Additionally, we found that the nucleation process on the metastable two-dimensional layer cannot only be described by the capture of newly deposited Ge atoms, but it is strongly governed by the diffusive interaction with the SiGe alloyed layer.