Optical determination of free-carrier concentration in epitaxial layers of n-type silicon grown on N+ or N− substrates

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Abstract
In this paper it is shown that the optical determination of free‐carrier concentration N0 in 5–10 μm thick epitaxial layers of n‐type silicon grown on N+ or N− substrates is possible for concentrations ≥2×1016 cm−3 by measuring p‐polarized reflected light Rp near the Brewster angle at a wavelength ≂10 μm. Good crystallinity, constant concentration profiles normal to the surface, as well as relatively small differences in the index of refraction with respect to the substrate are essential requirements in order to get high resolution. Good agreement with the angular derivative of Rp is obtained.