We present results on the analysis of the interdiffusion process of a discrete GaAs layer into an Al0.5In0.5P half space using Si doping as an agent for enhanced layer interdiffusion. We have observed enhanced interdiffusion on both column III and column V sites, with the column III interdiffusion coefficient exceeding the column V interdiffusion coefficient by two orders of magnitude. Due to the disparity between these diffusion coefficients, substantial defect producing strain is introduced by the interdiffusion process. We have shown that by modeling the resulting strain profiles and applying a generalization of a critical thickness analysis, the instability of such interdiffused structures can be understood.