Effect of the plasmonic enhanced absorption and bias field enhancement in nano-electrode THz photo-conductive antennas

Metallic nano-electrodes improve the emission efficiency of THz photo-conductive antennas. But the main enhancement mechanism has not been systematically studied. In this study, we experimentally compared the effect of plasmonic enhanced absorption and bias field enhancement at the apex of nano-fingers. We concluded that the bias field enhancement dominates over the plasmon effect at low optical excitation densities. Both effects significantly saturated as the optical excitation power increases. Thus, we fabricated a large-aperture emitter for higher output power, obtained more than 1500 nA of peak-to-peak detector current with 2.5 THz of emission bandwidth.