Description:
<jats:title>Abstract</jats:title><jats:p>The effect of heavy doping on the reflection spectra of silicon and germanium is investigated by measuring the fractional change in reflectance, Δ<jats:italic>R</jats:italic>/<jats:italic>R</jats:italic>, between pure and doped materials. This effect arises from the narrowing of the forbidden gap in heavily doped materials. The form of the Δ<jats:italic>R</jats:italic>/<jats:italic>R</jats:italic> spectrum allows to reveal the critical points of the band structure, as in electro‐, piezo‐, or thermoreflectance measurements.</jats:p>