Two epitaxial growth mechanisms and the resulting defect generation have been examined. The first involves standard growth by molecular beam epitaxy (MBE), while the second employs wet oxidation to form a Ge-rich epilayer from an initially amorphous film. The MBE-grown high Ge content layers evolve by island coalescence, while the oxidationproduced high Ge content layers form by a Ge exchange mechanism below a contamination layer, which results in a more uniform epitaxial layer. Thus, the resulting threading dislocation, stacking fault and twin densities, along with the surface roughness can be quite different. Results also indicate a high misfit dislocation density limited to the Si/SiGe interface and a strain redistribution into the Si substrate for the oxidation-produced epilayers.