Comparative study by DFT method of structural, electronic and optical properties of monolayer, bilayer and bulk CdS

In this work, we studied structural, electronic and optical properties of binary compound CdS in bulk, bilayer and monolayer forms using density functional theory method with full potential integrated in Wien2k code. In our calculations, we have used the PBEsol approximation for the structural properties and the TB-mBJ approximation for the electronic and the optical properties. The equilibrium lattice constants and the band gap energy obtained with monolayer and bilayer are higher than those of bulk wurtzite, while the bond length between Cd and S atoms is reduced. The bond length contraction is due to the effect of sp2 hybridization in 2D graphene-like structure, which is stronger than the effect of sp3 hybridization in bulk wurtzite. The increase in band gap energy can be explained by quantum confinement effects associated with the size reduction of CdS structure. For optical properties, we found that CdS monolayer and bilayer have low absorption and high transparency than the bulk in visible range, which is also explained by quantum confinement effects. According to these obtained properties, CdS graphene-like can be one of the promising nanomaterials for optoelectronic applications.