Escape probability of Auger electrons from noncrystalline solids: Exact solution in the transport approximation

The probability that an Auger electron, generated at a certain depth in a semi-infinite target, escapes from the surface under a certain emission angle is described by the so-called depth distribution function. The exact solution for this depth distribution function has been found in the transport approximation, employing transport theory. The results are in good agreement with data found in the literature and emphasize that strong deviations from exponential behavior occur. These deviations are most pronounced for oblique emission. To assess the validity of the transport approximation two kinds of Monte Carlo calculations have been performed. In one case the realistic Mott cross section for elastic scattering has been used while in the other the corresponding momentum transfer cross section was used. The latter procedure exactly fits the transport approximation. A very good agreement between the two approaches has been obtained. This indicates that the transport approximation is an effective tool in transport problems provided the angular distribution of the particle flux density varies slowly with the angle.