Single-layer group III-IV-VI semiconductors: potential photocatalysts for water splitting with high carrier mobilities

As a novel member of the two-dimensional (2D) family, the GaGeTe monolayer has been successfully synthesized recently, attracting extensive research attention for its unique physical and chemical properties. However, due to its narrow bandgap, it cannot be applied in photocatalysis. In this work, we have systematically investigated new 2D ternary materials with the chemical formula MSiX (M = Ga, In; X = S, Se, Te) using first-principles calculations. The results show that the stable MSiX monolayers exhibit semiconductor characteristics with band gaps ranging from 1.44 eV to 2.43 eV. GaSiS, GaSiSe, InSiS, and InSiSe can be efficient photocatalysts at pH = 0. By tuning the pH value, the GaSiTe monolayer exhibits promising photocatalytic activity in a neutral environment. The favorable pH ranges for water splitting of GaSiS, GaSiSe, GaSiTe, InSiS, and InSiSe monolayers are found to be 0-9.5, 0-12.4, 4.1-16.1, and 0-6.2, respectively. Biaxial strain tests indicate that these five structures can operate at applicable strain levels (-3% to 3%). All six MSiX monolayers exhibit strong visible-ultraviolet absorption (105 cm-1) and high carrier mobilities (similar to 103 cm2 V-1 s-1). Due to the band degeneracy of VBMs, the effective carrier mobilities of MSiX monolayers were calculated using multi-valley transport theory. These monolayers exhibit high solar-to-hydrogen (STH) efficiency, up to 16.78% at pH = 7 for GaSiS. After stacking, the STH efficiency of trilayer GaSiS increased to 12.51% at pH = 0. The electron-hole recombination rates were also examined via NAMD simulations. Our findings predict that all MSiX monolayers (except for InSiTe) can be potential candidates for photocatalytic water splitting.