EN
We use the eight-band k·p model to describe the infrared inter-subband absorption in Si-Si_{1-x}Ge_{x}-Si quantum wells, which takes explicitly into account the Γ'_{25}(Γ_{8}^{+}+Γ_{7}^{+} in the double group) valence band and the second conduction band Γ'_{2}(Γ_{7}ˉ). We then obtain an accurate description of mixing of the S wave function with the valence band functions.