Patent ID: 7436006

Claim:
A semiconductor structure, comprising: (a) a substrate; (b) a first semiconductor region on the substrate, wherein the first semiconductor region comprises a first semiconductor material and a second semiconductor material, which is different from the first semiconductor material, and wherein the first semiconductor region has a first crystallographic orientation; (c) a second semiconductor region on the first semiconductor region, wherein the second semiconductor region comprises the first and second semiconductor materials, and wherein the second semiconductor region has the first crystallographic orientation; (d) a third semiconductor region on the substrate, wherein the third semiconductor region comprises the first and second semiconductor materials, and wherein the third semiconductor region has a second crystallographic orientation different than the first crystallographic orientation; and (e) a fourth semiconductor region on the third semiconductor region, wherein the fourth semiconductor region comprises the first and the second semiconductor materials, wherein the fourth semiconductor region has the second crystallographic orientation, wherein a first ratio in number of atoms of the first semiconductor material to the second semiconductor material in the fist semiconductor region is smaller than a second ratio in number of atoms of the first semiconductor material to the second semiconductor material in the second semiconductor region, wherein a third ratio in number of atoms of the first semiconductor material to the second semiconductor material in the third semiconductor region is greater than a fourth ratio in number of atoms of the first semiconductor material to the second semiconductor material in the fourth semiconductor region, wherein the first semiconductor material comprises silicon, and wherein the second semiconductor material comprises carbon.