Optical properties of tantalum carbide from the infrared to the near ultraviolet

Optical properties of a nearly stoichiometric single crystal of tantalum carbide are reported. Specular reflectance was measured between 0.03 and 6.0 eV and ellipsometry measurements were made between 1.2 and 4.6 eV. The ellipsometry results were used to fix the value of the phase obtained from a Kramers--Kronig analysis of the reflectance over a finite energy interval and optical functions were computed between 0 and 6 eV. The optical conductivity at zero photon energy agrees well with the electrical conductivity obtained from resistivity measurements made by the van der Pauw method. Intraband contributions to the optical properties are assessed in terms of both one-carrier and two-carrier models. Broad structure near 5 eV is interpreted as due to interband transitions between states near the square face of the Brillouin zone. 19 ref.--AA