Barium Oxide Thin Films Designed as Electro‐Optical Gigahertz/Terahertz Filters

Abstract Herein barium oxide thin films are studied as a promising electro‐optical system. The deposited films exhibited a polycrystalline tetragonal structure and are composed of a mixture of BaO and BaO 2 . The p ‐type films are highly transparent (80%) with an energy band gap of 3.55 eV containing exponential band tails of widths of 1.22 eV. Analyses using the Drude‐Lorentz model demonstrated the films suitability for nonlinear optical applications, with optical conductivity parameters revealing a scattering time constant in the range of 0.4–1.8 fs, a free hole concentration of 10 18 −10 19 cm −3 and drift mobility values of 0.70–3.16 cm 2 Vs −1 . Terahertz cutoff frequency spectra calculations indicated the films capability as efficient terahertz band filters with a cutoff frequency range of 3.2–193.0 THz. Additionally, the nonlinear third‐order optical susceptibility increased with decreasing incident photon energy. Applying an AC signal with a driving frequency of 0.01–1.40 GHz across the terminals of Yb/BaO/Ag devices revealed a high cutoff frequency (≈9 GHz) in the microwave frequency domain. These properties highlight the potential of BaO films as nonlinear optical filters and microwave waveguides, positioning them as candidates for gigahertz/terahertz technology applications.