A Review on Gallium Nitride for Liquid Sensors: Fabrications to Applications

Gallium nitride (GaN) exhibits high internal spontaneous and piezoelectric polarizations, leading to the formation of a two-dimensional electron gas (2DEG) channel in the heterojunctions. Additionally, its chemical stability, increased electron concentration, and high mobility contribute to its outstanding performance in applications, such as liquid sensing (LS). In this article, we review the sensitivity and reactivity of the GaN surface with polar liquids and aqueous solutions. A comprehensive understanding of the interaction between the GaN surface and water molecules is presented. The results from a myriad of characterization techniques are discussed at great length to elucidate the correlation between the reduction of GaN conductivity and the dissociation of water, which plays a key role in water splitting (WS) and LS applications of GaN. Finally, we present valuable conclusions drawn from theoretical and experimental studies conducted to determine GaN–water interfacial properties.