Enhanced Solubility of Impurities and Enhanced Diffusion near Crystal Surfaces

Any defect or impurity has some inherent stress, so near a free surface its energy is reduced by relief of this stress. The defect stress also couples to the intrinsic surface stress. In general, the result is to enhance impurity solubility and diffusion near the surface. With certain assumptions regarding the kinetics, the high impurity density near the surface can be frozen in as the crystal grows, permitting the growth of highly supersaturated solid solutions, e.g., high dopant concentrations in semiconductors. Calculations for carbon near the Si(001) surface illustrate the solubility enhancement.