All-GaAs Broadband Terahertz Absorber Based on Deep Etched High-Aspect-Ratio Metamaterials

This paper reports an all-GaAs broadband terahertz absorber (BTA) consisting of an array of unit-cells featuring circle and cross channels. The BTA was designed to reach a peak absorption at 1.15 THz and to sustain absorption levels over 80% across a broad bandwidth exceeding 500 GHz. Utilizing a deep etching process, the GaAs structure was with etching depth of approximately $70\ \mu\mathrm{m}$ and an aspect ratio of ∼4:1. The fabrication process is compatible with standard micro-electro-mechanical system (MEMS) process. The demonstration of high-aspect-ratio all-GaAs metamaterial potentiates the integration of III-V photonic circuits with MEMS towards microsystem.