A comprehensive review of gallium nitride (GaN)-based gas sensors and their dynamic responses

Gas-sensing technology that is ubiquitous has progressively gained significance in our daily lives. There is a growing requirement for real-time, dependable and low-concentration gas detection to monitor toxic and flammable gases in industrial facilities, guarantee environmental air quality, identify automotive exhaust emissions, perform breath analysis for the early detection of diseases and so on. The appeal for gallium nitride (GaN)-based gas sensors has surged due to their chemical and temperature stability, making them suitable for deployment under harsh demanding conditions. The dynamic characteristics of GaN-based gas sensors reflect the absorption/desorption kinetics of molecules, and play a crucial role in determining their sensing performance, efficiency, and subsequent signal processing. This paper provides a comprehensive review of recent advancements in GaN-based gas sensors, with a focus on their dynamic response-related behaviors. The following key aspects are covered: First, we present an overview of the representative device structures of GaN-based gas sensors and highlight their figures of merits. Second, we examine the various techniques employed in the fabrication of these sensors. Third, we delve into the dipole-based sensing mechanism, the thermodynamic model governing gas absorption and desorption processes, and explore the relationship between response and recovery times with temperature and concentration. Fourth, we explore the practical applications of the gas sensors' dynamic responses. Finally, we analyze the impact of device structure design on the dynamic responses of GaN-based gas sensors, along with post-signal processing methods.