Chemistry and electronic structure of AlInP (001) surfaces upon exposure to water and oxygen

Abstract

For solar water splitting, semiconducting surfaces must be stable and able to efficiently transfer charge carriers across the semiconductor/aqueous electrolyte interface. Despite its ubiquitous use as the topmost layer in various record-breaking photoelectrochemical (PEC) devices, the initial interaction of the AlInP (001) with water remains unexplored. This study examines the interactions between atomically ordered AlInP (001) surfaces prepared with either phosphorus (P-rich) or indium (In-rich) terminations and reactive electrolyte species such as water and oxygen are examined. Using photoemission and reflection anisotropy spectroscopy combined with computational calculations, changes to surface states, chemistry, and near-surface band structure under representative adsorbate environments are investigated. Water dissociates on both terminations: on the P-rich surface, the Al and In sites are active, whereas on the In-rich surface, the In-In bonds dissociate promptly, increasing surface reactivity. Prolonged oxygen exposure causes surface reordering, resulting in a decrease in band bending from 1.00 to 0.85 eV on the P-rich and from 1.80 to 0.85 eV on the In-rich surface. Time-resolved two-photon photoemission measurements show that the near-surface band edges remain stable within 0.15 eV upon exposure to water and heat despite the work function increasing by 0.32 eV in UPS. Meanwhile, hydroxylation reduces surface dipoles. Initial O2 exposure has little effect on the P-rich surface, but prolonged exposure leads to the dehydrogenation of hydroxyls on the In-rich surface. DFT calculations indicate that the reactivity is dependent on reconstruction, showing that molecular water adsorption on the In-rich surface (-0.40 eV) is more favorable than on the P-rich AlInP (-0.23 eV). These findings provide a comprehensive understanding of AlInP (001) surfaces under conditions representative of PEC and other applications of III-V heterostructures.