Strain-dependent intersubband absorption in the valence band of SiGe quantum wells

We present intersubband absorption measurements performed on p-type Si1-xGex/Si(0 0 1) quantum wells (x = 0.35) in the presence of an external strain. We find that the in-plane polarized absorption band is rather insensitive to the strain. For the incident light polarized along the growth direction, the absorption strength increases under the tensile strain. The latter observation is well accounted for by a six-band k . p model and is explained by redistribution of hole population between the heavy-and the light-hole subbands caused by the strain-induced energy shifts of the bands.