A Monte-Carlo simulation of positron diffusion in solids

A Monte-Carlo simulation of positron diffusion in layered structures is described. This simulation is a useful tool to extract physical properties of slow positron data. The basis of the simulation is the random-walk model of the positron diffusion (C. Hübner, T. Staab and R. Krause-Rehberg, Appl. Phys. A 61 (1995) 203) [1]. The input parameters are the temperature, the positron diffusion constants, the positron lifetimes, the positron trapping rates, and the S parameters of bulk and defect annihilation. Furthermore, assumptions on the sample layer structure, the properties of surface and interfaces, the structure of the electric field, and the positron implantation profile must be included. The results of the simulation are the S parameter, F parameter, or positron lifetimes as a function of positron implantation energy, respectively. This means that a real positron beam experiment is simulated. The resulted data can directly be compared to measured curves. A typical simulation of layered structures, such as a Schottky contact (Au-film on Si), was performed, and the data were compared with experimental data of the literature. Furthermore, we studied the effect of internal and external electric fields on defect profiling in semiconductors by slow positron beam technique.