Stability and photoelectric nature of polar surfaces of ZnO: Effects of surface reconstruction

The photoelectric properties and structural stability of polar ZnO (0001) and ZnO (000-1) surfaces are studied by ab-initiocalculations with the aid of the global optimization method and GGA+U. The interlayer distance contraction of ZnO (0001) is smaller than that of ZnO (000-1), which is related to the bonding flexibility of zinc atoms. In addition, the absorption spectra are derived from the real and imaginary parts of the dielectric function, which are calculated by first principles using the Kramer-Kronig relation. It is not surprising that the absorption peak of the polar surface is located in the ultraviolet region and extends to the visible region after reconstruction. And the electronic effective mass of the ZnO(0001) surface is smaller than that of the ZnO(000-1) surface. In addition, in the case of ZnO (0001), the surface acts as an n-type conductor, while ZnO (000-1) has a p-type conduction behavior. (C) 2021 Elsevier B.V. All rights reserved.