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-alpha and -beta 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-alpha and -beta 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-beta 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-alpha, CAs-alpha and CAs-beta 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 (similar to 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 10(4) cm(-1) in 390-450 nm) and possess water-splitting photocatalytic properties under suitable conditions (neutral and alkaline for the GeAS-alpha and alkaline for GeAS-beta). 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.