Water Vapor Interaction\nwith Well-Ordered GaInP(100)\nSurfaces

Multiabsorber structures for photoelectrochemical devices\nbased\non III–V semiconductor compounds enable direct solar-to-fuel\nconversion with the highest efficiencies to date as their tunable\nband gaps allow optimal exploitation of the solar spectrum. In monolithic\ntandem record devices, GaInP is frequently utilized to tune suitable\nband gap energies for use as a top photoabsorber or as a charge-selective\ncontact. Therefore, a detailed understanding of the reactions at the\nGaInP–electrolyte heterointerface is of particular interest\nto tailor the semiconductor surface to avoid losses of photogenerated\ncarriers and to reduce photocorrosion. Here, we study the interaction\nof water vapor with GaInP(100) surfaces prepared with atomically well-defined,\neither group III-rich or phosphorus-rich surface reconstructions.\nWe combine surface-sensitive optical in situ spectroscopy with in\nsystem X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS).\nWe support the experimental results with ab initio molecular dynamics\nsimulations. Our results show that the surface reconstruction of GaInP(100)\nsignificantly affects its interaction with water vapor. The P-rich\nGaInP(100) surface shows a much higher stability compared to the group\nIII-rich surface. While no corrosion or oxidation is observed on the\nP-rich surface, we observed the rapid formation of In(OH)<sub><i>x</i></sub> with a subsequent transition to InO<sub><i>x</i></sub> on the group III-rich surface due to water exposure.