Zhenyang Zhong, W. Schwinger, F. Schaffler, G. Bauer, G. Vastola, F. Montalenti, and L. Miglio Institute for Semiconductor and Solid State Physics, Johannes Kepler University Linz, A-4040 Linz, Austria L-NESS and Department of Materials Science, University of Milano Bicocca, Via R. Cozzi 53, 20125 Milano, Italy Surface Physics Laboratory, Fudan University, Shanghai 200433, China (Received 7 August 2006; published 23 April 2007) Unimodal SiGe islands with dominant f111g facets were grown coherently on pit-patterned Si (001) substrates by molecular beam epitaxy. With increasing Ge deposition, the f111g 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.