Hexagonal group IV-V (IV=C, Si, Ge, V=N, P, As) binary monolayers: First-principles study

A series of hexagonal group IV-V (IV=C, Si, Ge, V=N, P, As) phase-α and -β monolayers are studied using the first-principle calculation. The 18 monolayers are all optical transparent semiconductors with band gaps in the range of 1.91–6.06 eV and have good light adsorption in UV range. And each monolayer has its own unique properties. The CN phase-α and -β monolayers have good mechanical properties (large 2D Young's moduli, 555.3 N m⁻¹ and 585.5 N m⁻¹) comparable to that of two layer graphene. The CP-β monolayer is the only one with direct band gap and can translate into indirect semiconductor when applied biaxial tensile strain greater than 4 %, while the CP-α, CAs-α and CAs-β monolayers can realize the transition from the indirect semiconductor to direct one with 6–10 % biaxial tensile strain. The SiN and GeN monolayers are ductile with large Poisson's ratio (∼0.30). And the GeN monolayers can maintain indirect band gaps under 10 % strain and have linear relationships between the band gaps and strains. The GeAs monolayers have partial light adsorption in visible range (several 10⁴ cm⁻¹ in 390–450 nm) and possess water-splitting photocatalytic properties under suitable conditions (neutral and alkaline for the GeAS-α and alkaline for GeAS-β). The different properties of each hexagonal group IV-V (IV=C, Si, Ge, V=N, P, As) binary monolayers can be potential applied in different two dimensional electronic devices.