Terahertz radiation enhancement based on LT-GaAs by optimized plasmonic nanostructure

Terahertz waves have unique penetrability, safety, spectral resolution, and many other useful properties. Therefore, terahertz waves are widely employed in medical treatment, detection, imaging, security, and spectroscopy. They also possess great development prospects in photoconductive antennas (PCAs) for telecommunication and other devices. However, terahertz PCAs are still limited by the weak photocurrents and small light absorption rates, making the development of PCAs with improved conversion efficiencies highly desirable. In this study, a new type of plasmonic PCAs with high photoelectric conversion efficiency was proposed. The interaction between the 800 nm fs laser and staggered nanorods was studied by the finite difference time domain (FDTD) method. The geometric parameters of the nanorods arrays were optimized. Compared to conventional photoconductive antennas without nanostructures, the PCAs with optimized nano-plasmonic structure I showed threefold higher electric field radiations under 800 nm fs laser irradiation. Optimized plasmonic nanostructure II increases photocurrent up to 335.553 nA that indicates 10 times enhancement in comparison with conventional structure. Hence, the developed structures greatly enhanced the light absorption of the photosensitive layer based on low-temperature-grown gallium arsenide. In sum, the proposed staggered hexagonal plasmonic structures (structure II) could effectively improve the light-terahertz conversion efficiencies of PCAs.