Doping effect on concentration dependence of the diffusion coefficient in semiconductors

New expression for the concentration dependence of diffusion coefficient of ionized impurity in semiconductors which is valid the whole range of carrier degeneracy is derived. It is shown that due to reduction of the impurity field screening by mobile carriers at degenerate conditions the diffusion coefficient is a monotonously increasing function of the impurity concentration. Taking the band gap narrowing into account is found to result in a reduction of the diffusion coefficient in comparison with that corresponding to the case of unperturbed band structure, and a decreasing concentration dependence of the diffusion coefficient can be realized at relatively low impurity concentrations.