Amorphous WO3 thin films designed as gigahertz/terahertz dielectric lenses

Abstract

Herein, tungsten oxide thin films comprising excess oxygen are treated as optical resonator suitable for gigahertz/terahertz applications. WO3 thin films which are prepared by the thermal evaporation technique under a vacuum pressure of 10− 5 mbar are structurally, compositionally and optically evaluated. The amorphous WO3 films which showed high transparency permit electronic transitions within an indirect allowed energy band gap of 3.05 eV. The band gap comprised energy band tails of width of 190 meV. Four dominant dielectric resonators centered in the infrared (IR), visible (VIS) and ultraviolet (UV) ranges of light are detected. Analysis of the optical conductivity in accordance with the Drude-Lorentz approaches have shown that the drift mobility of free holes in this amorphous layer can be as large as 5.61 cm2/Vs an as low as 1.59 cm2/Vs when exposed to IR and UV light signals, respectively. In addition, the gigahertz/terahertz cutoff frequency (\({f}_{co}\)) spectra demonstrated \({f}_{co}\) values in the gigahertz frequency domain when exposed to IR light. Excitations with light signals in the VIS and UV spectral ranges allow \({f}_{co}\) values that extends from 0.7 to 40.0 THz. The wide range of tunability of the WO3 dielectric resonators nominates them as dielectric lenses suitable for optical communications.