Infrared Properties of Hexagonal Silicon Carbide

Abstract

Infrared transmission and reflectivity measurements from 1 to 25 \ensuremath{\mu} (microns) have been made on several samples of green alpha (hexagonal) SiC. The residual ray bands have been observed for the ordinary and extraordinary rays. The resonance frequencies are 2.380\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ (12.60 \ensuremath{\mu}) and 2.356\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ (12.73 \ensuremath{\mu}), respectively. From the reflectivity the high-frequency dielectric constant is found to be 6.7. A careful analysis shows that the residual ray bands can be fitted within experimental error by the classical dispersion theory within the correct choice of the dispersion parameters. From the parameters the value 10.0 is obtained for the low-frequency dielectric constant. The effective charge is $0.94e$. Complete description of the residual ray band for the extraordinary ray required, in addition to the main resonance, a weak resonance at 2.647\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ (11.33 \ensuremath{\mu}). A study on the effects of several different surface treatments shows the reflectivities reported here are an intrinsic property of the crystal. The room-temperature absorption coefficient as a function of wavelength in the range 1 to 10 \ensuremath{\mu} has been determined from transmission measurements. A number of weak lattice bands are observed between 5 and 10 \ensuremath{\mu}.