Plasmonic photoconductive antennas with rectangular and stepped rods: a theoretical analysis

Abstract

Photoconductive antennas (PCAs) have extensive industrial applications as terahertz (THz) emitters. It is an established belief that the existence of periodic metallic structures at the edges of the antenna electrodes, as is the case in plasmonic PCAs, can remarkably improve the antenna performance. In this paper, we start with introducing a theoretical model for the analysis of plasmonic PCAs, considering the effect of the screening electric field as well. The results of the model, applied to a plasmonic PCA with periodic rectangular rods, agree well with the experimental measurements. Finally, guided by the theoretical model, a plasmonic PCA with buried stepped rods is proposed for improved performance in THz radiation power and in generated current. The enhancements turn out to be the consequence of two welcoming phenomena: First, according to the theoretical model (as well as independent finite element simulations), for the PCA with buried stepped rods, the power transmitted into the low-temperature-grown GaAs (LT-GaAs) substrate is 70% in the THz wavelength range and complete at an optical wavelength of 0.8 μm and 40% enhancement in the optical power transmission as compared to the rectangular rods. Second, in comparison with the rectangular rods, a larger portion of the carriers are generated in the vicinity of the rod corners, which favorably contributes to the current generation but does not contribute much to the unwanted screening electric field.