A new hybrid metasurface design for performance improvement of thin film unbiased terahertz photoconductive source

Abstract

In this paper, a new bias free hybrid structure is proposed to improve the performance of unbiased bimetallic terahertz photoconductive antenna (PCA). Each element of unbiased bimetallic emitters consists of an asymmetric metal-semiconductor-metal (MSM) that is made of two side by side dis-similar Schottky contacts. Engineering the surface of low temperature gallium arsenide (LT-GaAs) layer by different kind of nanostructure metasurfaces in combination with bimetallic nanostructure located underneath the LT-GaAs have been used to enhance the 800 nm femtosecond laser beam absorption inside the LT-GaAs layer and so boost the terahertz wave generation. Solving the Maxwell’s equation in combination with drift-diffusion/Poisson’s using finite element method have been applied to investigate the optical and electrical response and optimize the performance of proposed structure. According to the simulation results, using optimized metasurface on LT-GaAs decreases the reflection to less than 0.8% compared to the 29% of the conventional PCA. Moreover, proposed structure shows 83% photocurrent enhancement compared to unbiased PCA without metasurface and with Si3N4 antireflection coating.