The optical constants of p-type tin telluride at room temperature have been determined as functions of carrier concentration over the spectral range from 0.1 to 3.8 eV. The indices of refraction and absorption coefficients were obtained from analysis of normal reflectance and transmittance measurements on epitaxial films ranging in carrier concentration from 3.6×1019 to 6.8×1020 cm-3. At energies greater than approximately 1.0 eV the optical dispersion is found to arise primarily from bound carriers. In contrast, the dispersion at energies less than about 0.4 eV is in excellent agreement with that calculated on the basis of classical free-carrier dispersion. The fundamental absorption edge is characterized by a large, Burstein-type shift produced by changes of carrier concentration. Bound-carrier indices of refraction nBC are found to be unusually large and carrier-concentration dependent. A Kramers-Kronig analysis gives values of nBC in good agreement with experiment for energies less than 2 eV. Extrapolation of our experimental values of nBC to zero energy using the Kramers-Kronig relation yielded values of the optical dielectric constant ε∞. This quantity is found to be carrier-concentration dependent, ranging in value from 38 to 46 for the carrier concentrations studied here. It is shown that this variation in ε∞, is primarily due to the Burstein shift of the fundamental absorption edge.
R. B. SCHOOLAR and J. R. DIXON, "Optical Properties of Tin Telluride in the Visible and Infrared Regions," J. Opt. Soc. Am. 58, 119-124 (1968)