Hydrogen Sensing Characteristics of a Metal–Oxide–Semiconductor Diode With Bimetallic Catalysts and a GaO x Dielectric

Abstract

A new metal–oxide–semiconductor (MOS) diode with bimetallic catalysts and a GaOx dielectric is employed herein to fabricate a hydrogen sensor. Bimetallic catalysts, including Pt nanoparticles (NPs) and a Pd thin film, are formed by the proper vacuum thermal evaporation (VTE) approach, and a GaOx dielectric is produced by H2O2 treatment on the GaN surface. The presence of this bimetallic structure can effectively increase the surface area-to-volume ratio and provide a “spill-over” effect. This can substantially enhance the dissociation and adsorption of hydrogen molecules and atoms. The use of a GaOx dielectric effectively suppresses the surface leakage current and increases the adsorption sites for hydrogen atoms. Experimentally, excellent hydrogen sensing properties, including a very high sensing response of $1.1 \times 10^{7}$ under 1% H2/air gas at 300 K, an extremely low detection level (≤100 ppb H2/air), a widespread hydrogen concentration sensing range, and a relatively fast sensing speed, were obtained. From a thermodynamic analysis, it is clear that the hydrogen adsorption of the studied device is an exothermic reaction. Therefore, based on the above-mentioned advantages, the studied Pt NP/Pd thin film/GaOx/GaN-based MOS diode shows promise for high-performance hydrogen sensing applications.