Barium Oxide Thin Films Designed as Electro-OpticalGigahertz/Terahertz Filters

Abstract

Herein barium oxide thin films are studied as a promising electro-opticalsystem. The deposited films exhibited a polycrystalline tetragonalstructure and are composed of a mixture of BaO and BaO2 . The p-type filmsare highly transparent (80%) with an energy band gap of 3.55 eV containingexponential band tails of widths of 1.22 eV. Analyses using the Drude-Lorentzmodel demonstrated the films suitability for nonlinear optical applications,with optical conductivity parameters revealing a scattering time constantin the range of 0.4–1.8 fs, a free hole concentration of 10 18−10 19 cm−3 anddrift mobility values of 0.70–3.16 cm 2 Vs−1 . Terahertz cutoff frequency spectracalculations indicated the films capability as efficient terahertz band filterswith a cutoff frequency range of 3.2–193.0 THz. Additionally, the nonlinearthird-order optical susceptibility increased with decreasing incident photonenergy. Applying an AC signal with a driving frequency of 0.01–1.40 GHz acrossthe terminals of Yb/BaO/Ag devices revealed a high cutoff frequency (≈9 GHz)in the microwave frequency domain. These properties highlight the potential ofBaO films as nonlinear optical filters and microwave waveguides, positioningthem as candidates for gigahertz/terahertz technology applications