Interdiffusion can be either increased or decreased when annealing epitaxial layers covered by an oxide of GaAs. AlGaAs/GaAs quantum wells (QWs) of different widths were grown by organometallic vapor phase epitaxy. A top layer of GaAs was thermally oxidized at 450 °C, and rapid thermal annealing (RTA) was performed at 950 °C under Ar. Photoluminescence showed that an order of magnitude increase in interdiffusion occurred in the oxide-covered QWs compared to uncovered QWs. However, when a thin layer of Al was evaporated over the oxide layer prior to RTA, the rate of interdiffusion was reduced by more than order of magnitude compared to that of uncovered QWs. Interdiffusion slows because the oxide, composed primarily ofGa2O3,is quickly reduced by Al metal during RTA to form atomic Ga andAl2O3.TheAl2O3layer formed over the QWs traps the free Ga as interstitials in the GaAs. The excess Ga interstitial concentration reduces the group III vacancy concentration, and it is this reduction in group III vacancy concentration which slows the interdiffusion rate. The results show that metallurgical reactions may be used as a tool for engineering native defect concentrations and associated diffusivities. ©1998 American Institute of Physics.