Density Functional Theory simulations of water adsorption and activation on the (-201) β-Ga₂O₃ surface

Density functional theory (DFT) calculations are used to study the molecular and dissociative adsorption of water on the (-201)β-Ga₂O₃ surface. The effect of adsorption of different water-like species on geometry, binding energies, vibrational spectra and the electronic structure of the surface are discussed. The study shows that while the hydrogen evolution reaction requires a small amount of energy to become energetically favourable, the over-potential for activating the oxygen evolution reaction is quite high. The results of our calculations provide insight as to why a high voltage is required in experiments to activate the water-splitting reaction, while previous studies of gallium oxide predicted very low activation energies for other energetically more favourable facets. Application of this work to studies of GaN-based chemical sensors with gallium oxide surface shows it is possible to select the gate bias so that the sensors are not influenced by water splitting reactions. It was also found that in the region where water-splitting does not occur, the surface can exist in two states: water or hydroxyl terminated.