Enhancement of photocurrent in THz photoconductive antenna by a gold nanorod array

Abstract

In this article, a novel THz photoconductive antenna (THz-PCA) is proposed which is composed of a conventional THz-PCA integrated with a plasmonic nanorod array to enhance surface absorption and boost the THz wave generation. It is shown that by carefully matching the plasmon resonance wavelength of the designed plasmonic structure to the incoming laser light wavelength (λ=780 nm), it is possible to obtain a nearly perfect absorption. Specifically, light absorption inside the LT-GaAs substrate at is increased to more than 96 % which is considerably improved relative to approximately 60 % of light absorption in the conventional structure. Moreover, the designed plasmonic structure provides light absorption and photo-carrier generation mostly at the surface of the GaAs substrate which is highly beneficial due to the fact that surface charge carriers have the minimum travel distance to the antenna terminals resulting in lowest recombination probabilities. The proposed structure is numerically investigated by solving Maxwell’s equations for electromagnetic response along with the charge carrier continuity and Poisson’s equations for electrical response. For the Au nanorod array with a pitch of Λ=0.8 μm and nanorod radius of r=120 nm, photocurrent shows an improvement of nearly 250 % due to the surface absorption enhancement discussed above.