SUBSTRATE MODIFICATION FOR SUPERLATTICE CRITICAL THICKNESS IMPROVEMENT

A method and apparatus for forming strain relaxed buffers that may be used in semiconductor devices incorporating superlattice structures are provided. The method includes epitaxially depositing a first silicon germanium layer over the substrate. The first silicon germanium layer has a first surface that contacts a frontside surface of the substrate and a second surface opposite the first surface. The first silicon germanium layer has a first thickness and a germanium concentration gradient that increases from the first surface to the second surface. The method further includes epitaxially depositing a silicon germanium capping layer on the first silicon germanium layer. The silicon germanium capping layer has a second thickness and a substantially uniform germanium concentration that is equal to, substantially equal to, or greater than a maximum germanium concentration of the germanium concentration gradient.