Prepyramid-to-pyramid transition of SiGe islands on Si(001)

The morphology of the first three-dimensional islands appearing during strained growth of SiGe alloys on Si(001) was investigated by scanning tunneling microscopy. High resolution images of individual islands and a statistical analysis of island shapes were used to reconstruct the evolution of the island shape as a function of size. As they grow, islands undergo a transition from completely unfacetted rough mounds (prepyramids) to partially (105) facetted islands and then they gradually evolve to (105) facetted pyramids. The results are in good agreement with the predictions of a recently proposed theoretical model. © 2003 The American Physical Society.