Mechanical and dynamic stability of ZnX chalcogenide (X=O, S, Se, Te) monolayers and their electronic, optical, and thermoelectric properties

Abstract

Graphene-like ZnX (X=O, S, Se, Te) structures are studied using the DFT+U method to address in detail the questions regarding the dynamical stability and also their utility in optoelectronic devices. The layer modulus, the Young's modulus, the shear modulus, and the Poisson coefficient demonstrate the stability of all ZnX in the presence of the Hubbard parameter U. Cohesion energy calculations show ZnO to be the most stable one and ZnSe to be the least stable one among the four systems. The presence of a direct bandgap in all the systems makes them suitable for use in optoelectronic devices. The gap values range between 2.13 eV in ZnTe and 3.50 eV in ZnO. U values tend to increase the bandgap in all the systems. This increase is seen to be as high as 100% in ZnO. A detailed study of the band structure and partial density of states is carried out. The electronic, optical, and thermoelectric properties of the ZnX monolayers are exhibited. The superior limit of the figure of merit increases with temperature and the highest value is found to be of the order of 0.6 in ZnO at 900 °C. Overall, the inclusion of the Hubbard parameter demonstrates better stability and also its importance in technological applications.