Normally off AlGaN/GaN ion-sensitive field effect transistors realized by photoelectrochemical method for pH sensor application

Abstract

We fabricate an AlGaN/GaN ion-sensitive field-effect transistor through the photoelectrochemical method for pH sensor application. The photoelectrochemical reaction transforms the AlGaN barrier into oxide, which can deplete the two demensional electron gas to achieve the normally-off operation. Besides, the oxide on the surface enhances the sensitivity to approximately 56.3 mV/pH, a value close to the room temperature Nernstian limit. Based on surface characterization results, the needle-like native oxide (a mixture of Al2O3 and Ga2O3) is transformed into a smooth Al2O3-dominated film. The enhanced surface status and transconductance of the normally-off device is regarded as the possible reason to effective improve the pH sensitivity.