Monte Carlo simulation of the contrast of SEM charge-collection images of dislocations in semiconductors

We describe a Monte Carlo algorithm that we have developed to simulate the electron beam induced current (EBIC) contrast of a surface perpendicular dislocation. The contrast was obtained by simulating the random diffusion and collection of the carriers that are generated at point-like sources S _i randomly distributed within the generation volume. The dislocation is described as a cylinder with a radius r_D where the minority carrier lifetime (τ_D) is lower than that in the bulk (τ_B). The dependence on the electron range R_e of the simulated EBIC contrast profiles, their full width at half maximum (FWHM) and their maximum (C_max) is analysed for a germanium sample. It is shown that with increasing R_e, the FWHM of the contrast profile increases steadily in agreement with experiment while the maximum contrast goes through a maximum and converges to zero for R_e → 0. The variation of C_max upon the diffusion length L_D within the dislocation cylinder is analysed too. The results of our simulations show that the values of the contrast obtained by the analytical approach using the first order approximation are underestimated for dislocations of strength exceeding 5.