Optical functions of KTaO3 as determined by spectroscopic ellipsometry and comparison with band structure calculations

The optical dielectric functions for single-crystal KTaO3 are determined using spectroscopic ellipsometry and optical transmission techniques. These results show that the lowest band gap is 3.64 eV (341 nm) with very low absorption up to 4.28 eV, indicating an indirect band gap. The ellipsometry results are analyzed using critical point analysis, which shows that there are three direct gaps at 4.35, 4.68, and 5.03 eV. The results are compared with band structure calculations determined using the local density approximation (LDA) and the Engel-Vosko generalized gradient approximation (GGA).