Effects of titanium and niobium nanosheets on the performance of selenium gigahertz/terahertz electro-optical filters

Abstract

Selenium thin films coated onto glass and Pt substrates are designed as electro-optical filters suitable for utilization in the gigahertz and terahertz frequency domains. Depositing titanium and niobium nanosheets onto the Se films enhanced their structural, optical, dielectric, and electrical properties. Specifically, Ti and Nb nanosheets improve the crystallinity, suppressed free carrier absorption, narrowed the energy band gap of Se from 1.86 eV to 1.55 eV and 1.25 eV, respectively, and widened the tail states from 0.29 eV to 0.60 eV and 0.78 eV, respectively. Furthermore, as a dielectric layer, Nb nanosheets decreased the dielectric constant more effectively than Ti nanosheets. This reduction resulted in a remarkable enhancement in the terahertz cutoff frequency by 267% and 620% at an incident photon energy of 1.85 eV. Electrical measurements conducted in the frequency range of 0.01–1.50 GHz revealed wide tunability of capacitance and microwave cutoff frequency based on the imposed carrier frequency. Additionally, analyses aimed at determining the electro-optical parameters of the gigahertz/terahertz filters indicated free charge carrier concentrations in the range of 1017– 1019 cm− 3 and drift mobility values of 4.07–13.56 cm2/ Vs, associated with the propagation of light signals in the infrared and visible light frequency domains. The enhanced properties of Se/(Ti, Nb) band filters show promise for a variety of electro-optical applications, including terahertz and 4G technologies