Injection of point defects into GaAs/AlxGa1-xAs heterostructures by oxidation of AlxGa1-xAs is investigated. The blueshift of the PL emission from GaAs quantum wells is measured as a function of rapid thermal annealing conditions in as-grown and thermally oxidized samples. Contrary to published data for point defect injection by oxidation of GaAs, oxidation of AlxGa1-xAs appears to reduce the interdiffusion of the quantum wells. The PL peak shifts after annealing have been fit assuming Al diffusion in the quantum wells and solving the singleparticle Schrödinger equation. These fits show a reduction in group-III diffusivity of over an order of magnitude with an oxidized layer of AlxGa1-xAs on the surface.