Concentration contours in regions with both normal and enhanced diffusion coefficients

Formulas are obtained for impurity concentration where diffusion is from a surface, and the diffusion coefficient is a step function across a plane boundary normal to the surface. Asymptotic expressions are obtained for the case in which the ratio of the diffusion coefficients is large. The results are applicable to diffusion in materials having regions of enhanced diffusion coefficient, such as irradiated semiconductors.