Improving unbiased terahertz photoconductive antenna based on dissimilar Schottky barriers using plasmonic mode excitation

A new design for an unbiased antennaless terahertz (THz) photoconductive antenna (PCA) using an array of bimetallic nanostructures located underneath the low temperature gallium arsenide (LT-GaAs) layer is designed and proposed which is highly under focus for THz imaging applications. Each element of array consists an asymmetric metal-semiconductor-metal (MSM) structure with dissimilar Schottky barriers. Simulation results demonstrated that by irradiating this structure using 800 nm femtosecond laser, THz field as high as a conventional biased PCA can be generated. Finite element method was used to optimize the PCA's geometrical parameters through solving the Maxwell's equation in combination with drift-diffusion/Poisson's equations. According to the simulation results, by optimizing the array's periodicity, width and height of the proposed bimetallic nanostructures, plasmonic resonant cavity mode between two adjacent nanostructures enhances the optical absorption and so, the transient photocurrent. Transient photocurrent of 45 mu A was obtained that is 29% higher than the one from the conventional biased PCA.