FIG. 9 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. 9 is similar to that in FIG. 6, except without the segments A, B and D of FIG. 6. In other words, the silicon germanium layer 53 in FIG. 9 only has the segment C, which 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 lower surface 53L) 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.
