Two-dimensional O-phase group III monochalcogenides for photocatalytic water splitting

The atomically thin group III monochalcogenides have emerged as potential candidates for nanoscale optoelectronic applications due to their tunable bandgaps and high carrier mobility. In this work, by means of ab initio calculations, we have systematically investigated the geometrical structures, electronic structures, and optical properties of the orthogonal phase (O-phase) group III monochalcogenides MX (M = Ga and In, X = S, Se and Te) monolayers, nanoribbons, heterostructures and their potential applications as photocatalysts for water splitting. It is highlighted that the two-dimensional (2D) O-phase MX monolayers not only are dynamically and thermally stable, but also exhibit distinguished optical properties (∼10⁵ cm^-1) with broad absorption spectrum in the visible and ultraviolet light regions. Furthermore, it is noted that nano-structure designing can further modulate their electronic structures in desirable ways. For instance, the bandgap of O-phase GaTe is relevant to the width of 1D nanoribbon. On the other hand, the type-II InSe/GaTe and InTe/GaTe heterostructures confine the photo-generated electrons and holes at the opposite parts, which is beneficial for the separation of hydrogen and oxygen during the photocatalysis water splitting process.