Theoretical calculations of the broadening of dilute Si, Al and Be doped δ layers in GaAs during SIMS depth profiling

The ability to grow very thin δ doped layers is an important feauture of molecular beam epitaxial growth and in principle sub-monolayer deposition of dopant during interruption of the flux of matrix atoms allows the subsequently buried doped layer to be confined to only one or two layers. SIMS analysis of such layers to confirm the growth characteristics requires detailed modelling of the mixing processes to interpret the data in terms of the initial dopant distributions. The IMPETUS code, based on the solution of a set of coupled non-linear Fokker-Planck type equations, has been used to explain the form of experimentally measured depth profiles of Si, Al and Be δ layers in GaAs. It is shown that the different profile widths can be explained in terms of the specific diffusion behaviour of the dopant species in the matrix.