High-electron-mobility AlGaN/GaN transistors (HEMTs) for fluid monitoring applications

High-electron-mobility transistors (HEMTs) based on AlGaN/GaN heterostructures were success fully 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.