Patent ID: 7138650

Claim:
A semiconductor substrate comprising: an Si substrate; a first SiGe layer on the Si substrate; and a second SiGe layer on the first SiGe layer either directly or with an Si layer arranged between the second SiGe layer and the first SiGe layer; wherein the first SiGe layer has a film thickness that is thinner than twice a critical thickness at which dislocation occurs resulting in lattice relaxation due to increased film thickness, a Ge composition ratio of the second SiGe layer is at least lower than an intralayer maximum value of a Ge composition ratio in the first SiGe layer or in the first SiGe layer at a contact surface with the Si layer, and the second SiGe layer has an incremental composition region in which the Ge composition ratio gradually increases towards a surface of the second SiGe layer at least in a portion thereof.