TIME-DEPENDENCE OF DOPANT DIFFUSION IN DELTA-DOPED SI FILMS AND PROPERTIES OF SI POINT-DEFECTS

The diffusion of Sb and B in thin Si films grown by low temperature mo lecular beam epitaxy is investigated in the temperature range 750-900- degrees-C for times of 0.25-60 h. The small spatial extent of the init ial 5-function-like dopant profiles allows the detection of very small diffusional displacements. The dopant atoms are used as tracers of Si point defects (vacancies and self-interstitials). Diffusion of Sb is found to be enhanced relative to equilibrium values, while that of B i s retarded. We propose a model based on an initial supersaturation of vacancies. Matching this model to the experimental data allows the ext raction of the vacancy diffusivity, the activation energy of vacancy f ormation, and the recombination lifetime of interstitials. The results show that interstitial and vacancy populations cannot be considered i ndependent at low temperature, as has been previously suggested.