Enhanced Performance of Titanium-Coated Barium Oxide Thin Films Designed as Light Absorbers and Millimeter-Wave Waveguides

Abstract

Thermally deposited thin films of barium oxide (BaO) coated with titanium (Ti) were fabricated under a vacuum pressure of 10−5 mbar. Ti coating significantly influenced the structural parameters of polycrystalline tetragonal BaO films, enhancing light absorption in the spectral range of 1.38–4.10 eV, with a maximum increase of 256% at 3.20 eV. It also suppressed free carrier absorption in the infrared range and reduced the energy band gap and Urbach tails in BaO films. Planar waveguides with 1.0 mm channel widths, using BaO/Ti as substrates, demonstrated strong agreement between theoretical and experimental cutoff limits. Ti coating altered scattering time constants and localized state densities near the Fermi level, reducing electrical conductivity and capacitance while enhancing the cutoff frequency of BaO waveguides from 32 to 126 GHz. The linear variation of cutoff frequencies with quad frequencies highlights the suitability of BaO/Ti planar waveguides for millimeter-wave technology applications.