Rapid diffusion of V elements during the conversion of GaAs to GaAsP on a GaP substrate

A computational model for mass transport occurring during the conversion of GaAs to GaAsP on a GaP substrate is presented. The mass transport equations in the liquid and solid phases, and the phase diagram together with appropriate interface and boundary conditions were solved numerically by the finite element method. Numerical solutions agree with experimental results and explain well the conversion phenomenon. The conversion process is initiated by the non-equilibrium condition between the GaAsP solution and the GaAs layer and promoted by the rapid diffusion of V elements into the GaAs (GaAsP conversion) layer. Further analysis shows that the period required for the conversion increases parabolically with increasing thickness of the GaAs layer.