Patent ID: 7898003

Claim:
A semiconductor structure, comprising: (a) a substrate; (b) a first semiconductor region on the substrate, wherein the first semiconductor region comprises a first mixture consisting of 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 a second mixture consisting of 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 a third mixture consisting of the first and second semiconductor materials, and wherein the third semiconductor region has a second crystallographic orientation; and (e) a fourth semiconductor region on the third semiconductor region, wherein the fourth semiconductor region comprises a fourth mixture consisting of 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, and 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.