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 molecular 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 initial 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 is retarded. We propose a model based on an initial supersaturation of vacancies. Matching this model to the experimental data allows the extraction of the vacancy diffusivity, the activation energy of vacancy formation, and the recombination lifetime of interstitials. The results show that interstitial and vacancy populations cannot be considered independent at low temperature, as has been previously suggested.