Functionalisation and optimisation of GaN/AIGaN/GaN HEMTs for use as chemical sensors in a reference-electrode-free system

This thesis focuses on the surface chemistry of GaN and AIGaN, and the development of chemical sensors based on GaN/ AIGaN/GaN-based high electron mobility transistor structures in a reference-electrode free system. The reference-electrode­-free system allows for simultaneous operation of multiple, connected sensors, minimises the stability/conditioning issue (generally associated with reference electrodes) and also leads to the possibility for miniaturisation of the sensing system. X­ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS) were undertaken for the surface chemistry studies. The development of GaN/AJGaN/GaN-based sensors was focused on the pH sensor and ion­selective sensor {nitrate and calcium ions).