Plasmon-Induced Graphene/Silicon Schottky Junctions for Ultrasensitive Gas Sensing

Modulating metal oxide-based gas sensors with light is emerging as an alternative to enhance their sensitivity and selectivity. Plasmonic gas sensors based on excitation of the localized surface plasmon resonance (LSPR) in noble metals have recently shown promising properties. The classic approach of incorporating LSPR in sensors is to measure changes in the optical properties of the plasmonic material that depend on the surrounding local environment, i.e., an optical sensor device. The less common approach is to utilize chemiresistive sensors that consist of a gas-sensitive material (like graphene) decorated with plasmonic nanoparticles and employ solely electrical measurements for sensing data acquisition. This work demonstrates a chemiresistive gas sensor graphene/silicon Schottky junction decorated with palladium nanoparticles (PdNPs) that exhibit LSPR in the UV light range. We demonstrate a method of recording responses of plasmonic gas sensors based only on their DC characteristic measurements, which is simplified compared to optical and spectroscopic methods. Supported by the DC characteristics recorded under different UV wavelengths (255 nm, 275 nm, 355 nm), we show that the highest sensitivity to NO₂ and NH₃ is obtained for plasmonic resonant wavelength excitation of the PdNPs occurring at about 275 nm. The LSPR-modulated sensor response is nearly 14 times greater for NO₂ gas compared to NH₃ and exhibits a sensitivity toward NO₂ gas with an ultralow detection limit of 4 ppb, thus showing that both the selectivity and sensitivity of plasmonic chemiresistive gas sensors can be significantly enhanced by LSPR-tuned light modulation.