FIG. 8 illustrates a cross-sectional view of another embodiment of the silicon germanium layer 53 in the fin 58 of the FinFET device 100 of FIG. 5. The silicon germanium layer 53 in FIG. 8 is similar to that in FIG. 6, except without the segment B and without the segment D of FIG. 6. In particular, the silicon germanium layer 53 in FIG. 8 has a segment A, which serves as a buffer layer and may have a thickness between about 0 nm and 5 nm and a germanium concentration between about 0 at % and about 5 at %. The segment C is a gradient sublayer with the germanium concentration decreasing continuously as the segment C extends away from the epitaxial material 52. The germanium concentration at the bottom of the segment C (e.g., proximate the interface 111 between the segments A and C) is between about 25 at % and about 28 at %, and the germanium concentration at the top of the segment C (e.g., proximate the upper surface 53U) is between about 10 at % and about 20 at %. A thickness of the segment C is between about 50 nm and about 60 nm.
