Anion selective potentiometric sensor based on gallium nitride crystalline membrane

Gallium nitride (GaN) (0001) grown on sapphire has been used as a sensor element for the development of a potentiometric sensor. The GaN-based ion-selective electrode has pH sensitivity which originates from the direct interaction of the gallium with the hydroxide ions. At the same time the sensor shows very good selectivity towards the very hydrophilic anion of orthophosphate, over the very lipophilic ClO4_. Potentiometry and impedance spectroscopy suggest that the observed potentiometric sensitivity originates from the direct interaction of anions in solution with the acidic gallium(III) on the surface of the GaN (0001) crystal. This is also supported by the fact that the gallium atoms are electron deficient due to the induced polarity of the Ga to the N bond, enhancing the electrostatic interaction between the Lewis basic anions. The semiconductor properties of the GaN allow for its application as an all solid-state semiconductor-based anion potentiometric sensor, or alternatively as the transducer in composite cation sensitive potentiometric sensors. The latter has been demonstrated with the deposition of a potassium selective liquid polymeric membrane on top of the GaN surface.