A model of Si diffusion in GaAs based on the effect of the Fermi level

We propose a quantitative model for Si diffusion in GaAs. In this model we incorporate the experimental result that Si is an amphoteric impurity which constitutes a shallow donor when occupying the Ga site, Si+Ga, and a shallow acceptor when occupying the As site, Si−As. At high concentrations Si+Ga and Si−As coexist. The amphoteric behavior of Si may be viewed as an effect of the Fermi level. We assume that Si+Ga and Si−As diffuse respectively on the Ga and As sublattices. That is, the diffusion of Si+Ga and Si−As is governed by the variously charged Ga vacancies and As vacancies (or self-interstitials), respectively. The experimentally observed Si diffusivity is concentration dependent which results from the Si amphoteric nature as well as from another effect of the Fermi level, which is its influence on the concentrations of the charged point-defect species. Satisfactory quantitative descriptions of available experimental results are obtained. An analysis of the data on Si diffusion into a Sn-doped GaAs substrate has led us to believe that the previously proposed Si-pair diffusion model may no longer be favored.