The normal incidence absorption between 2 and 14 &mgr;m in a pseudomorphicp‐Si0.81Ge0.19/Si multiple quantum well sample with doping 5×1012cm−2per well is described by a Drude conductivity characteristic of free carriers, with an in‐plane mobility of 32 cm2/V s and a relaxation time of 5.5 fs at 77 K. When the absorption is scaled with dopant concentration these parameters predict quantum efficiencies for quantum well infrared photodetectors in reasonable agreement with experiment.