GaN-based anion selective sensor: Probing the origin of the induced electrochemical potential

The gallium nitride (GaN) semiconductor has been used as the sensing element in a chemical sensor for the measurement of charged species in solution. The sensor shows remarkable selectivity for anions, such as sulphate (SO42−) and hydroxide (OH−). It is shown that the GaN surface interacts selectively with Lewis bases as shown by impedance spectra. In addition, both the impedance spectra and the surface induced potential of the sensor element correlate very well with the activity of both the negatively charged hydroxide and the sulphate anions used. These results indicate that there is a direct interaction of the electron deficient gallium in the GaN surface with the Lewis base anionic ligands. A band model for the investigated GaN∕KOH-solution system has been deduced.