Semi-insulating GaAs surface modifications and their influence in the response of THz devices

Abstract In this work, we use the Metal-Assisted Chemical Etching (MACE) technique together with an NH3 plasma treatment using a Remote Plasma-Enhanced Chemical Vapor Deposition (RPECVD) equipment to modify the surface of semi-insulating GaAs (SI-GaAs) substrates. Using our modified SI-GaAs, we fabricate photoconductive antennas for THz emission to study the modification's influence on the optical and electrical antenna response. We found substantial gaps in the frequency-domain spectra of the devices, whose origin could reside in a change of the substrate's optical absorption due to: (a) a surficial chemical change or (b) a substrate topographic modification or a combination of both. We showed experimentally that slight and reproducible substrate surface modifications could lead to significant variations in the electrical behavior and THz response of SI-GaAs devices.