Optical properties of LaFeO₃ films studied using spectroscopic ellipsometry

LaFeO₃ film is an intermediate charge transfer/Mott–Hubbard insulator. LaFeO₃ thin films were grown on SrTiO₃ substrates using radio frequency magnetron sputtering deposition method at 500 °C. After growth, the LaFeO₃ thin films were annealed in air at 800 °C for 2 h. The LaFeO₃ films grown on SrTiO₃ substrates showed atomically sharp interfaces even though they were grown using a sputtering deposition. LaFeO₃ films show orthorhombic structures according to X-ray diffraction measurements. We obtained the dielectric functions (ε = ε₁ + ε₂) of the thin films using spectroscope ellipsometry and obtained the optical gap energies from the absorption coefficients (α = 4πk/λ). The optical gap energy of LaFeO₃ thin films was determined to be an indirect gap energy of 2.21 eV, and a direct gap energy of 2.73 eV. Forbidden direct gap energy was estimated to be 1.94 eV for LaFeO₃ thin films. The critical point (CP) energies were determined using the second-order energy derivative spectra of the dielectric functions. The optical gap energies and the CP energies were compared to band structure calculations in the literature.