The electronic and optical properties of monovalent atom-doped ZnO monolayers: the density functional theory

Abstract

The current study deals with the structural, electronic and optical properties of monovalent element-doped ZnO monolayers using density functional theory. Specifically, we have considered structural and optical properties of monovalent ($\mathrm {M}=\mathrm {Li}$, Na and K) atom-doped ZnO monolayers. Among these monovalent elements, the substitution of Li with Zn atom maintains the hexagonal planar geometry of the ZnO monolayer, but Na and K elements protrude out from the plane of the ZnO monolayer. The Li atom binds more strongly with the ZnO sheet compared with Na and K atoms. A Li-doped ZnO monolayer shows metallic behaviour whereas Na- and K-doped ZnO monolayers show half metallic magnetic behaviour. The magnetic moment is of the order of $1\upmu _{\mathrm{B}}$. The magnetic moment mainly originates from nonbonding O$_{\mathrm{p}}$ states. The substitution of an alkali metal element-doped ZnO monolayer leads to a red-shift in optical spectra. The dielectric constant of a monovalent element-doped ZnO sheet increases compared with that of a pristine ZnO sheet. This study provides the basis to develop opto-electronic devices using doped ZnO monolayers.