It was recalled that so-called anomalous fast diffusion in metallic alloys and semiconductors was often analyzed within an interstitial-substitutional model. The equations used for modeling these mechanisms were of reaction-diffusion type, whose analytical solutions were available only after drastic simplification. The dissociative variety of this model was simulated using both finite difference and Monte Carlo methods. In Monte Carlo simulation, diffusion of different species (interstitial impurities Bi, substitutional Bs, and vacancies V) and reaction jumps occurred according to the suitable probabilities which were jump frequency dependent. In the finite difference method, an implicit scheme was used to solve the system of non-linear partial differential equations. In both cases, the finite source conditions were considered. Good agreement between results obtained using the two methods was found. On the other hand, the double-stages of simulated profiles were found to have similar shapes to those obtained experimentally in Nb(Co) and in GaAs(Zn). The first stage was well analyzed by a Gaussian function, whereas the second one was well represented by an erfc-type function. A detailed study of the two stages led to qualitative agreement with Stolwijk's analysis in two limited cases where the diffusion was vacancy- or foreign interstitial-controlled. However, the effective diffusion coefficients presented a quantitative departure from those obtained using Stolwijk's expressions.

Numerical Studies of Anomalous Fast Diffusion in Metallic Alloys and Semiconductors. A.Hasnaoui, A.Benmakhlouf, A.Hoummada, J.K.Naciri, A.Menai: Applied Surface Science, 2000, 162, 100-10