Fabrication and characterization of Se/WO3 heterojunctions designed as terahertz/gigahertz dielectric resonators

Abstract

In this work, Selenium (Se) thin film substrates are coated with tungsten oxide thin layers. The Se/WO3 interfaces are fabricated using a vacuum deposition technique. The substrates displayed stable polycrystalline structure of hexagonal selenium when coated with amorphous WO3. The surface morphology revealed preferred growth of Se nanowires. The coating of Se with WO3 enhanced the light absorbability in the visible and infrared ranges of light spectrum. In addition, the Se/WO3 heterojunctions exhibited conduction and valence band offsets of values of 1.31 eV and 0.0.09 eV, respectively. The band offsets are sufficiently large to force quantum confinement at the interface. It was observed that Se/WO3 behaves as good dielectric resonator revealing resonance peaks in the infrared, visible and ultraviolet ranges of light. Moreover, computing the optical conductivity parameters for these dielectric oscillators revealed drift mobility and plasmon frequency values that are suitable for optical communications. Furthermore, as a terahertz resonator, the Se/WO3 dielectric media displayed terahertz cutoff frequency values in the range of 0.6–75 THz depending on the exciting photon energy. As practical application, when photo-excited with daylight light, the carbon contacted planner Se/WO3 interfaces displayed a light power dependent photosensitivity. The photosensitivity increases 38 times upon irradiation of 0.9 W. With these features, the Se/WO3 heterojunction devices can be nominated for applications in optical communications.