GaN has shown to be a very unique material for the development of chemical sensors and biosensors, mainly due to its semiconductor properties and its increased chemical stability.

We have shown previously that GaN (0001) grown on sapphire can be used as sensor element, or transducer, for the development of electrochemical sensors.  In particular, we developed an all solid-state GaN-based sensor that shows anion sensitivity.  Potentiometric and impedance spectroscopy proved that the observed electrochemical sensitivity originates from the direct interaction of the anions in the 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.  It has thus been concluded that the mode of response originate from the direct interaction of the reactive Lewis acidic gallium atoms with the Lewis bases in solution (OH^‑ , Cl^‑ etc) and not with Lewis acis (H⁺, K⁺ etc). 

Moving one step forward, in this work we will present our recent study in which we investigate how crystal orientation and/or induced polarity of the outer surface atom influence the potentiometric response of these III-N surfaces.  More particular, in this work two differently crystal oriented GaN surfaces (c-plane, Ga-face and a-plane) as well as InN (In-face) surface are examined and compared.  According to the observed results it is shown that crystal orientation has little or any effect on the potentiometric response of these materials, while the bond polarity and thus the electron deficiency of the outer atom of these surfaces has a greater influence on their potentiometric response.

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