We discuss the properties of the nonlinear diffusion equation which was presented for the approximation of high-concentration arsenic and boron profiles. Typical features of the profile are a flat region near the surface, a decreasing intermediate region and a tail region dropping sharply down compared with an error function complement. Earlier the nonlinear equation of the diffusion where the diffusion coefficient is directly proportional to the concentration of the impurities has been proposed. This proposal has been made on the theoretical assumption that diffusion is the result of Brownian movement and must occur with a finite velocity.