Photoinduced intersubband absorption in Si/SiGe quantum wells

We have investigated photoinduced infrared absorption in p-doped Si/SiGe quantum wells. The absorption spectra exhibit two distinct features: free-carrier absorption and intersubband absorption in the valence band. The photoinduced absorption in both p and s polarizations is found to depend on the carrier density and strongly differs from the original absorption of the doped quantum wells. Photoinduced intersubband absorption is attributed to carriers away from the Brillouin zone center. We show that photoinduced intersubband absorption spectroscopy can provide useful information on valence band mixing effects in Si/SiGe quantum wells.