Evolution of strain and composition of Ge islands on Si (001) grown by molecular beam epitaxy during postgrowth annealing

Self-assembled Ge islands have been grown using a Stranski-Krastanov growth mechanism on Si (001) substrates by solid source molecular beam epitaxy. We performed time varying annealing experiments at a representative temperature of 650 degrees C to study the shape and size evolution of islands for a relatively high Ge coverage. Islands are found to coarsen due to heat treatment via structural and compositional changes through continuous strain relaxation. Different island morphologies, namely, "pyramids," "transitional domes," and "domes" are found during the annealing sequence. The dominant coarsening mechanisms for the temporal evolution of islands of as-grown and annealed samples are explained by the comprehensive analysis of Rutherford back scattering, Raman spectroscopy, high-resolution x-ray diffraction, and atomic force microscopy. A correlation of the morphological evolution with the composition and strain relaxation of grown islands is presented. (C) 2008 American Institute of Physics.