High-Electron-Mobility AlGaN/GaN Transistors (HEMTs) for Fluid Monitoring Applications

High-electron-mobility transistors (HEMTs) based on AlGaN/GaN heterostructures were successfully tested as chemically sensing devices. Exposing the unprotected polar GaN surface in the gate area of a HEMT to liquids of different polarity, milliampere changes in the source–drain current could be detected. These sensing effects are likely to arise from chemical interactions with a sheet of ionic charge on the free GaN surface which compensates the electronic charge of a two-dimensional electron gas at a subsurface AlGaN/GaN interface.