Theoretical Study On Optical And Adsorption Properties Of ZnO Monolayer

The discovery of two-dimensinal(2D)graphene has led to the intense interest in other potential 2D materials with novel properties.With the development of the 2D materials,they have attracted extensive interest recently due to their unique structure and properties different from corresponding bulk materials.Recently,with the development of the transparent conducting oxide(TCO),it is necessary to achieve the high transparency and conductivity in the visible region.ZnO monolayer has attracted many research interests because of its optoelectronic characteristic,such as the high transparency and the wide optical band gap.Such properties make it well suited for the transparent electronic and touch screen.All of the calculations were performed with the ultrasoft pesudopotentials method,which were based on the density functional theory.In this work,we systematically investigated the electrical and optical characterization of pristine and Al,Ga and In doped ZnO monolayer.We found that the band gap of pristine and Al-doped ZnO monolayer is larger than that of pristine ZnO monolayer.Meanwhile,the transparency in visible light region is significantly enhanced compared to bulk counterpart.Furthermore,our calculations show that the electrical conductivity of ZnO monolayer is enhanced by Al doping and exhibits relatively high value.These results show that Al-doped ZnO monolayer is a promising transparent conducting electrode for optoelectronic device applications.The structures and properties of Al,Ga and In are compared with ZnO monolayer.It is found that when the doping concentration of Al,Ga and In is less than 12.5 at.%,the average transmittance reaches up to 99 % in the visible and UV regions.Moreover,the electrical conductivity is enhanced for the Al,Ga and In doped systems.In particular,a good electrical conductivity with a significant improvement for the In doped ZnO monolayer is achieved in the lower doping concentration.In addition,we have investigated the adsorption properties of ZnO monolayer.We have found that the CO molecules can adsorbed in the surface of Al,Ga and In doped ZnO monolayer.The band gap of CO molecules adsorbed in Al,Ga and In doped ZnO monolayer decreases and the shallow donor states are created around the bottom of the conduction band,leading to the increase of carrier concentration.The interaction between the ZnO monolayer and the adsorbed gas is enhanced by introducing the energy level of the impurity.Furthermore,the optical properties of ZnO monolayer have changed.