Water Vapor Interaction with Well-Ordered GaInP(100) Surfaces

Multiabsorber structures for photoelectrochemical devices based on III-V semiconductor compounds enable direct solar-to-fuel conversion with the highest efficiencies to date as their tunable band gaps allow optimal exploitation of the solar spectrum. In monolithic tandem record devices, GaInP is frequently utilized to tune suitable band gap energies for use as a top photoabsorber or as a charge-selective contact. Therefore, a detailed understanding of the reactions at the GaInP-electrolyte heterointerface is of particular interest to tailor the semiconductor surface to avoid losses of photogenerated carriers and to reduce photocorrosion. Here, we study the interaction of water vapor with GaInP(100) surfaces prepared with atomically well-defined, either group III-rich or phosphorus-rich surface reconstructions. We combine surface-sensitive optical in situ spectroscopy with in system X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS). We support the experimental results with ab initio molecular dynamics simulations. Our results show that the surface reconstruction of GaInP(100) significantly affects its interaction with water vapor. The P-rich GaInP(100) surface shows a much higher stability compared to the group III-rich surface. While no corrosion or oxidation is observed on the P-rich surface, we observed the rapid formation of In(OH) x with a subsequent transition to InO x on the group III-rich surface due to water exposure.