Using SIMS profiling, temperature-dependent Hall measurements, electronic Raman scattering, and infra-red absorption, a detailed study is presented examining the effects of Si dopant behaviour on intersubband absorption in GaAs/Al .32Ga .68As MQW’s. The samples were grown by molecular beam epitaxy at substrate temperatures ranging from 520 to 680°C with Si doping in the GaAs quantum wells only. SIMS profiling reveals that, with increasing substrate temperature, substantial Si migration into the Al .32Ga.68 As barrier layers occurs during epitaxial growth. Hall measurements indicate that both at elevated growth temperatures and under reduced incident As4 beam fluxes, the electron sheet concentration is reduced in the QW’s. In both cases, loss of free carriers is attributed to enhanced Si compensation. Shifts in the absolute frequency of the infra-red absorption resonance, determined by electronic Raman scattering, as well as variations in the integrated absorption intensity, are both shown to directly reflect the growth-induced variations in the free-carrier concentration in the quantum wells.