First-Principles Investigation of Interfacial Reconstruction in Epitaxial SrTiO₃/Si Photocathodes

Epitaxial SrTiO₃(STO) on Si is nowadays the benchmark initial platform for the further addition of functional oxides on Si. Starting the growth of STO on a Sr-passivated Si(001) substrate with 1/2 monolayer (ML) Sr coverage and a (1 × 2) reconstructed Si surface with rows of Si dimers, the final STO/Sr/Si stack exhibits a 1 ML Sr buffer layer and a (1 × 1) Si interface without a dimer. Using first-principles density functional theory calculations, we investigate how the interface evolves from 1/2 to 1 ML Sr coverage, concluding that the latter is indeed most stable and that the reconstruction of the interface takes place during the early stage of the layer-by-layer deposition. Going further, we argue that this (1 × 1) Si interface is non-oxidized. We determine its electronic band alignment and assess its potential interest as a photocathode for water reduction.