THE DIFFUSION-APPROXIMATION IN ATOMIC MIXING

A brief review is given of the diffusion approximation for atomic mixing by ion beams in the dilute implant case. The case of an initially thin implant is treated, and the shift and broadening of the subsequent sputtering erosion profile are calculated. The results are shown to be in reasonable agreement with those from transport theory. Saturation effects at high implant densities are considered. The concept of a 'collective current' is introduced and used to modify the diffusion theory to give a nonlinear equation applicable to saturation conditions. Some qualitative features of this equation are discussed.