US Patent 7863653 Method of enhancing hole mobility

A semiconductor device is provided comprising an oxide layer over a first silicon layer and a second silicon layer over the oxide layer, wherein the oxide layer is between the first silicon layer and the second silicon layer. The first silicon layer and the second silicon layer comprise the same crystalline orientation. The device further includes a graded germanium layer on the first silicon layer, wherein the graded germanium layer contacts a spacer and the first silicon layer and does not contact the oxide layer. A lower portion of the graded germanium layer comprises a higher concentration of germanium than an upper portion of the graded germanium layer, wherein a top surface of the graded germanium layer lacks germanium.