Evaluations of carrier lifetime in silicon epitaxial layers grown on lightly doped substrates

The recombination lifetime of excess carriers in silicon epitaxial wafers (p/p(-) and n/n(-)) with substrates of high resistivity has been analyzed based on a continuity equation. The solutions are derived for two cases of lifetime values. Under the conditions that the wafer surfaces are chemically passivated, and that the effects of recombination velocity and built-in potential at the interface of the epitaxial/substrate layer can be neglected, an approximate expression of effective lifetime can be derived from the solutions of the continuity equation. The result indicates that the effective lifetime is not only a function of the bulk lifetimes in both the epitaxial layer and substrate, but also a function of their thicknesses. The results of analytical solutions are applied to a commercially available silicon p/p(-) epitaxial wafer. The difference between the experimental and analytical results is discussed.