Delayed plastic relaxation on patterned Si substrates:: Coherent SiGe pyramids with dominant {111} facets

Unimodal SiGe islands with dominant {111} facets were grown coherently on pit-patterned Si (001) substrates by molecular beam epitaxy. With increasing Ge deposition, the {111} pyramids evolve from dome-shaped islands, reaching significantly larger volumes than are coherently possible on flat substrates. Finite element calculations and molecular dynamics simulations show that SiGe islands in pits can have less misfit strain with respect to islands of the same shape on flat substrates. The injection of dislocations is thus delayed, allowing for the observed development of coherent islands with a very high aspect ratio.