Doped GexSilx/ Si multiple quantum well structures have been grown by UHV/ CVD and characterized by various techniques. SIMS and X-ray confirm the intended modulation of germanium and boron concentrations, and photoluminescence has been used to assess material quality. Strong free-carrier absorption has been observed at normal incidence in some samples. The results suggest that doping intermediate between 4 x 1018 cm" 3 and 4 x 1019 cm-3 is necessary for useful detectors.