Dielectric function of polycrystalline SiC from 190 nm to 15 μm

We have studied polycrystalline SiC using spectroscopic ellipsometry (from the mid-IR to the quartz-UV), X-ray diffraction, and Raman scattering. In the UV, the pseudodielectric function is affected by surface roughness, and the E₁ peak is broadened due to the finite grain size. X-ray rocking curves indicate a preferred orientation with the hexagonal axis along the surface normal and a mosaic spread of 3.5°. FTIR ellipsometry shows a reststrahlen band due to phonon absorption and a strong anistropy peak near the zero crossing of the extraordinary dielectric function at its LO energy. The Raman phonon energies agree with the FTIR results. The Raman data also show the effects of finite grain size and stacking disorder. We conclude that the poly-SiC wafer is anisotropic, but does not have a well-defined polytype (such as 6H or 4H).