pH response of GaN surfaces and its application for pH-sensitive field-effect transistors

Abstract

The pH-sensitivity of GaNsurfaces in electrolyte solutions has been determined. For this purpose, GaNfield-effect transistors and AlGaN/GaN high-electron-mobility transistor(HEMT) structures were used to measure the response of nonmetallized GaN gate regions to changes of the H + -concentration in an ambient electrolyte. We found a linear response to changes in the p H between p H =2 and p H =12 for both as-deposited and thermally oxidizedGaNsurfaces. Both surfaces showed an almost Nernstian behavior with sensitivities of 57.3 mV /p H for GaN:Si/GaN:Mg and 56.0 mV /p H for GaN/AlGaN/GaN HEMT structures. This suggests that the native metal oxide on the III-nitride surface is responsible for pH-sensitivity. The investigated devices showed stable operation with a resolution better than 0.05 p H over the entire p H range.