Comparison of Methods and Results for Determining Optical Characteristics of Bismuth Ferrite Thin Films Grown by Reactive Magnetron Co-Sputtering

Bismuth ferrite (BFO) thin films were deposited by reactive magnetron co-sputtering in a pure oxygen environment at varying substrate temperatures in the range of 475 °C–550 °C in increments of 25 °C. As-deposited films were characterized for their structural, morphological and optical properties using X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical absorption measurements. SEM and XRD analysis showed increase grain growth and crystallinity with increase of substrate temperature. Highest phase purity was observed in the sample grown at 500 °C and higher temperatures showed degraded phase purity with highest content of Bi 2 Fe 4 O 9 and β -Bi 2 O 3 . The optical band gap of BFO films varied in the range of 2.32–2.36 eV. The refractive index n( λ ) was evaluated using Kramers-Kronig relations and the Swanepoel envelope method. Kramers-Kronig relations calculation showed a monotonic increase in n( λ ) as opposed to Swanepoel envelope methods non-monotonic results. Transfer matric models confirmed that the values of n( λ ) obtained by the Swanepoel envelope method align more closely to experimental transmittance spectra despite the samples weakly modulated spectra.