Electronic and chemical structure of the H₂O/GaN(0001) interface under ambient conditions

We employed ambient pressure X-ray photoelectron spectroscopy to investigate the electronic and chemical properties of the H₂O/GaN(0001) interface under elevated pressures and/or temperatures. A pristine GaN(0001) surface exhibited upward band bending, which was partially flattened when exposed to H₂O at room temperature. However, the GaN surface work function was slightly reduced due to the adsorption of molecular H₂O and its dissociation products. At elevated temperatures, a negative charge generated on the surface by a vigorous H₂O/GaN interfacial chemistry induced an increase in both the surface work function and upward band bending. We tracked the dissociative adsorption of H₂O onto the GaN(0001) surface by recording the core-level photoemission spectra and obtained the electronic and chemical properties at the H₂O/GaN interface under operando conditions. Our results suggest a strong correlation between the electronic and chemical properties of the material surface, and we expect that their evolutions lead to significantly different properties at the electrolyte/electrode interface in a photoelectrochemical solar cell.