Strong terahertz emission from copper oxides/silver micro thin film deposited on nanoparticles aggregation substrate

Abstract Terahertz emission properties of oxidized silver/copper micro thin film were investigated. Enhanced terahertz emission was observed from the oxidized micro thin film deposited on nanoparticles aggregation substrate due to the various directions of transient current surge. The amplitude of terahertz emission from the film was comparable to that from traditional non-external gallium arsenide. The sample, firstly, was synthesized by hydrothermal method to fabricate nanoparticles aggregation substrate. Next, the etched sample was treated by physical vapor deposition to grow silver/copper micro thin film and oxidized at 200 °C atmosphere environment. The space charge region was the dominant area for terahertz emission, built-in field at depletion layer played a key role in terahertz emission, and the contribution arising from optical rectification and photogalvanic was negligible due to the centrosymmetry structure; high band gap, low carriers concentration and mobility leads to the photon drag effect was not obvious; Because the differences of mobility and mass between hole and electron were not distinct, the Dember effect was also ineffective. The intensity of the terahertz emission was related to the thickness of the silver film because the silver film has a close relationship with the oxidation rate of the copper layer, leading to a dramatic influence on band gap structure, which produced a direct response on optical absorption at red zone. Compared with the planar substrate, the radiation of the nanoparticles substrate is 1.2 times that of the planar substrate, and the enhancement of the terahertz emission was ascribed to the various vibrated directions of photo-generated carriers. Our results could provide a potential portable terahertz emitter, which is economical, simple processing and operatable at room temperature.