Abstract:In the terahertz band, high-resistivity silicon and sapphire are used as substrate materials for terahertz devices due to their low absorption, high resistivity and low spectral dispersion properties. However, their high refractive index properties result in most of the incident terahertz waves being reflected at the interface, leading reduced transmittance of the incident wave and potential Fabry-Perot resonant cavity effect, which limits the operating bandwidth of the terahertz device and also affects its sensitivity. In order to reduce the reflection of terahertz waves at the interface, this thesis proposes a broadband anti-reflection structure, which can make the interference between the reflected waves phase-canceled, and thus improves the performance of the detector. Through TMM method in MATLAB and finite-difference method in time-domain (FDTD) analysis in electromagnetic simulation, the Mylar/Al2O3/AlN three-layer structure is selected as the anti-reflection structure in the terahertz range. The simulation results show that this combination can maintain the reflectivity lower than -20 dB in the range of 275 ~ 405 GHz. Furthermore, the terahertz detector applying this anti-reflection structure exhibits a -3 dB bandwidth enhancement of more than 50 GHz and a 3.2-fold increase in responsivity at 340 GHz. The structure successfully enhances the operating bandwidth and sensitivity of the detector through a straightforward and cost-effective fabrication process, providing an economical and effective solution for broadband reflection reduction in the terahertz band.
