BORON-DIFFUSION ACROSS SILICON-SILICON GERMANIUM BOUNDARIES

Most baron diffusion studies in Si-Ge have been made in regions of uni form germanium content. In this paper diffusion is observed from a bar on-doped epitaxial silicon layer across surrounding Si-Ge layers. Pile up of baron in the Si-Ge layers shows that the activity coefficient fo r baron in Si-Ge is lower than that for pure silicon. A simple pairing model for Si-B interaction fitted the pileup quite well, with the sam e equilibrium constant applying to both Si0.9Ge0.1 and Si0.97Ge0.03 la yers. The effect of this was simply to immobilize a significant fracti on of the boron while retaining its acceptor qualities, the ratio of i mmobile baron to normal substitutional baron being proportional to the germanium content. Quasielectric field effects at the Si-SiGe interfa ce have a strong effect on the results obtained. (C) 1998 American Ins titute of Physics.