Optical properties of δ-Bi2O3 thin films grown by reactive sputtering

The optical properties of δ-Bi2O3 thin films were investigated using spectroscopic ellipsometry and optical absorption spectrum. δ-Bi2O3 thin films were grown on Si and quartz substrates under different oxygen flow ratios (OFR) by radio frequency reactive magnetron sputtering. The Tauc-Lorentz dispersion method was adopted to model the optical dispersion functions of the thin films. The optical bandgap was obtained by three different methods. It was found that refractive index and extinction coefficient decrease, and the optical bandgap has a slight blue shift with increasing the OFR. Factors influencing the optical constants and optical bandgap are discussed.