Two-dimensional materials have been developed as novel photovoltaic and photocatalytic devices because of their excellent properties. In this work, four δ-IV–VI monolayers, GeS, GeSe, SiS and SiSe, are investigated as semiconductors with desirable bandgaps using the first-principles method. These δ-IV–VI monolayers exhibit exceptional toughness; in particular, the yield strength of the GeSe monolayer has no obvious deterioration at 30% strain. Interestingly, the GeSe monolayer also possesses ultrahigh electron mobility along the x direction of approximately 32,507 cm²·V⁻¹·s⁻¹, which is much higher than that of the other δ-IV–VI monolayers. Moreover, the calculated capacity for hydrogen evolution reaction of these δ-IV–VI monolayers further implies their potential for applications in photovoltaic and nano-devices.

Two-dimensional materials present abundant novel properties when used in advanced applications, which develops considerable focus. In this investigation, the first-principles calculations are explored to study the structural characteristic of the monolayered SiP₂, which is stable even at 1200 K. The SiP₂ monolayer is a semiconductor with an indirect bandgap of 2.277 eV. The decent band alignment and light absorption capacity imply that the application is a suitable photocatalyst for water splitting. Furthermore, the SiP₂ monolayer possesses an ultrafast electron mobility at 33,153 cm²·V⁻¹·s⁻¹ in the transport direction. The excellent Gibbs free energy of the SiP₂ monolayer is also addressed in an examination of the hydrogen evolution reaction.

Two-dimensional materials are widely used as a new generation of functional materials for photovoltaic, photocatalyst, and nano-power devices. Strain engineering is a popular method to tune the properties of two-dimensional materials so that performances can be improved or more applications can be obtained. In this work, a two-dimensional heterostructure is constructed from SiC and GaN monolayers. Using first-principle calculations, the SiC/GaN heterostructure is stacked by a van der Waals interaction, acting as a semiconductor with an indirect bandgap of 3.331 eV. Importantly, the SiC/GaN heterostructure possesses a type-II band structure. Thus, the photogenerated electron and hole can be separated in the heterostructure as a potential photocatalyst for water splitting. Then, the external biaxial strain can decrease the bandgap of the SiC/GaN heterostructure. From pressure to tension, the SiC/GaN heterostructure realizes a transformation from a type-II to a type-I semiconductor. The strained SiC/GaN heterostructure also shows suitable band alignment to promote the redox of water splitting at pH 0 and 7. Moreover, the enhanced light-absorption properties further explain the SiC/GaN heterostructure’s potential as a photocatalyst and for nanoelectronics.