Optical and electrical characterizations of cerium oxide thin films

The optical dielectric function of cerium oxide (CeO 2 ) was characterized by the spectroscopic ellipsometry (SE) technique using the Kramers–Kronig relation and the Tauc–Lorentz (TL) dispersion model. Experimental results showed that the bandgap energy and refractive index at 632.8 nm of CeO 2 are about 3.23 ± 0.05 eV and 2.33 ± 0.08, respectively. Based on the optical properties, the electrical conduction mechanisms in CeO 2 thin films are determined to be Schottky emission in a medium electric field (0.5–1.6 MV cm −1 ) from 350 to 500 K and Poole–Frenkel emission in a high electric field (>2.36 MV cm −1 ) from 450 to 500 K. Accordingly, the conduction band offsets between Al and CeO 2 and the trap energy level are about 0.62 ± 0.01 eV and 1.53 ± 0.01 eV, respectively.