Computational modeling of plasmonic thin-film terahertz photoconductive antennas

This work presents a computational approach for investigating terahertz photoconductive antennas with enhanced performance via thin-film plasmonic electrode configurations. The commercially available finite element method solver COMSOL Multiphysics is implemented to solve Maxwell’s wave equations along with the coupled drift-diffusion/Poisson’s equations. The proposed approach is compared with other computational and experimental results from the literature, showing good agreement. A nanodisk array is deposited on top of a 120 nm LT-GaAs layer with the antenna electrodes located below the photoconductive layer. A femtosecond optical pump is utilized to excite the photoconductive antenna. The obtained results demonstrated significant increase in the conversion of optical energy to photocurrents as compared with conventional antennas and other plasmonic antennas from the literature. The proposed thin-film antenna with plasmonic nanostructures showed the greatest improvement in peak photocurrent—almost 336 times higher than the conventional antenna. Additionally, the thin-film antenna demonstrates a fast device response time even at a long carrier lifetime of 48 ps. The results support the capability of the proposed design to yield high optical-to-terahertz conversion efficiency, addressing the problem of low output power in terahertz photoconductive antennas.