Patent ID: 7442585

Claim:
A method for forming a semiconductor device, comprising: providing a semiconductor substrate that has a substrate surface; selectively etching the substrate surface to form a recessed substrate region adjacent to an elevated substrate structure; epitaxially growing a first semiconductor structure over a sidewall of the elevated substrate structure along a growth direction that is substantially parallel to the substrate surface to fill a portion of the recessed substrate region, wherein said first semiconductor structure comprises a semiconductor alloy comprising a first material and a second, material which is different than the first material, and wherein concentration of the second material is graded in said first semiconductor structure along its growth direction; and epitaxially growing a second semiconductor structure over the first semiconductor structure to fill an additional portion of the recessed substrate region, wherein the first semiconductor structure is used to form a channel region for the semiconductor device, wherein the elevated substrate structure and the second semiconductor structure are used to form a source region and a drain region for the semiconductor device, and wherein a gate structure comprising a gate dielectric layer and a gate electrode is formed over the channel region.