Plasmonic grating assisted photo-absorption enhancement in terahertz photoconductive antenna

Abstract

A large aperture photoconductive antenna (PCA) with a plasmonic grating structure was fabricated and characterized. The intensity of the terahertz radiation from the plasmonic PCA was enhanced two-fold compared with that from the conventional PCA without the plasmonic grating structure. By using an electrically isolated nano-grating structure, the performance enhancement was found to be due to the plasmonic effect other than bias field enhancement. The photo-absorption enhancement near the GaAs surface and the plasmonic grating interface was investigated to elucidate the terahertz radiation enhancement mechanism in the plasmonic PCA. The highly localized electric field near the nanoscale grating shows optical absorption at the GaAs surface was enhanced. The enhanced optical absorption increased the photo-generated carrier density at the device surface, leading to enhanced intensity and bandwidth of the terahertz radiation from the plasmonic PCA.