A method to obtain thin (less than 300 nm) strain-relaxed Si.sub.1-x
Ge.sub.x buffer layers on Si or silicon-on-insulator (SOI) substrates.
These buffer layers have a homogeneous distribution of misfit dislocations
that relieve the strain, remarkably smooth surfaces, and a low threading
dislocation (TD) density, i.e. less than 10.sup.6 cm.sup.2. The approach
begins with the growth of a pseudomorphic or nearly pseudomorphic
Si.sub.1-x Ge.sub.x layer, i.e., a layer that is free of misfit
dislocations, which is then implanted with He or other light elements and
subsequently annealed to achieve the substantial strain relaxation. The
very effective strain relaxation mechanism operating with this method is
dislocation nucleation at He-induced platelets (not bubbles) that lie
below the Si/Si.sub.1-x Ge.sub.x interface, parallel to the Si(001)
surface.
