The gallium nitride (GaN) semiconductor is used as the sensing element for the development of a potentiometric anion sensor. The anion recognition mechanism is based on the selective interaction of anions in solution with the epitaxial Ga-face polarity GaN (0001) wurtzite crystal film grown on sapphire. The native GaN crystal is used for the development of an ion blocked sensor. The potential is based on the Volta potential, generated at the semiconductor/solution interface and within the Helmholtz layer, due to specifically adsorbed anions. The selectivity of the sensor is based on the direct interaction of the anionic ligand with the outer electron-defective gallium atoms; thus, it is not dependent on the lipophilicity of the adsorbed charged species. The chemical resistivity of the GaN crystal provides sensors with excellent lifetime, signal stability, and reproducibility.
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.
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