Data are presented showing that Zn diffusion into an AlAs‐GaAs superlattice (41Lz∼45‐A˚ GaAs layers, 40LB∼150‐A˚ AlAs layers), or into AlxGa1−xAs‐GaAs quantum‐well heterostructures, increases the Al‐Ga interdiffusion at the heterointerfaces and creates, even at low temperature (<600 °C), uniform compositionally disordered AlxGa1−xAs. For the case of the superlattice, the diffusion‐induced disordering causes a change from direct‐gap AlAs‐GaAs (Eg∼1.61 eV) to indirect‐gap AlxGa1−xAs (x∼0.77,EgX∼2.08 eV).