A quantitative model was proposed for the behavior of Si. The model took account of the fact that Si was an amphoteric impurity which acted as a shallow donor when it occupied the Ga site (SiGa+) and as a shallow acceptor when it occupied the As site (SiAs-). Both SiGa+ and SiAs- existed at high concentrations. The amphoteric behavior of Si could be viewed as being an effect of the Fermi level. It was assumed that SiGa+ and SiAs- diffused on the Ga and As sub-lattices, respectively. Thus, the diffusion of SiGa+ and SiAs- was governed by the variously charged Ga vacancies and As vacancies (or self-interstitials) respectively. The experimentally observed Si diffusivity was concentration dependent, and this was attributed to the amphoteric nature of Si as well as to another effect of the Fermi level. The latter involved its influence upon the concentrations of charged point-defect species. Satisfactory quantitative descriptions of available experimental data were obtained. An analysis of results on the diffusion of Si into a Sn-doped GaAs substrate suggested that a previously proposed Si-pair diffusion model was unfavorable.

S.Yu, U.M.Gösele, T.Y.Tan: Journal of Applied Physics, 1989, 66[7], 2952-61