It was noted that the density of grown-in voids was controlled by the diffusion-limited flow of vacancies to the voids. This flow was calculated here for both single- and double-octahedral voids. It was found that, if a void was initially formed as a double octahedron, it would evolve into a stable shape which was different to that which was observed experimentally. It was concluded that the voids were initially of single-octahedral shape, but could become double-octahedral in the later stages of evolution. This morphological change was thought to be caused by an O monolayer at the void facets. This monolayer initially covered only a fraction of the void surface, but gradually spread over the entire surface. The remaining area of non-covered surface was a source of growth steps which were produced by 2-dimensional nucleation. When the non-covered spot became small, the steps could pile up at the boundary between the non-covered and covered parts of a facet; thus giving rise to a new void. The factors which affected the single-to-double transition included the O concentration, cooling rate and vacancy concentration.

Diffusion-Limited Growth of Single- and Double-Octahedral Voids in Silicon and the Effect of a Surface Oxygen Monolayer. V.V.Voronkov, R.Falster: Journal of Crystal Growth, 2001, 226[2-3], 192-202