SiGe/Si quantum well layers are selectively grown by low pressure chemical vapor deposition on patterned Si substrates. Transmission electron microscopy (TEM) shows that the growth rate of SiGe in convex corners between different surface planes is at least ten times higher than the growth rate observed on (001) planes. This high growth rate leads to the formation of quantum wires and dots between such facets. Photoluminescence (PL) spectra of square and rectangular patterns, bounded by quantum wires, ranging in size from 300&mgr;m down to 500nm are taken. The observed energy shifts of the (001) quantum well PL–peaks are explained by surface diffusion of Ge adatoms into the quantum wires. A surface diffusion model is used to obtain a Ge diffusion length of &lgr;=2.5±0.6 &mgr;m at 700°C. Thus, a method for the determination of surface diffusion lengths in strained layer epitaxy is introduced. For SiGe layers grown above the Stranski–Krastanow critical thickness for three dimensional (3D) growth, a competition between the SiGe wires in the interfacet corners and the SK islands on the (001) planes is observed. In squares as large as 2×2 &mgr;m2the SiGe wires lead to a suppression of 3D growth on the (001) plane altogether, as observed by TEM and PL. ©1995 American Institute of Physics.