The effect of strain‐induced band‐gap narrowing on high concentration phosphorus diffusion in silicon

A strain effect has been found to explain the anomalous reduction in P diffusivity at surface concentrations greater than ∼4×10²⁰ cm⁻³. It is shown that at diffusion temperatures, misfit‐induced strain causes a reduction in the effective Si band gap up to ∼−130 meV at the solubility limit of P. This band‐gap narrowing results in reduced P diffusivity through a relative reduction of P⁺V⁼ pairs in the surface region. This complex is the dominant species for P transport at high P concentrations. The diffusion of P in the tail region is dominated by V⁻ vacancies liberated during P⁺V⁼ pair dissociation events. Thus, the tail diffusivity will likewise be reduced by band‐gap narrowing in the surface region. These reductions in diffusivity can be by as much as a factor of 6 depending upon temperature and P doping.