Abstract
Devising the two-dimensional (2D) structures of low-cost and non-toxic semiconductors for nanoscale technological applications has attracted substantial interest since the past decade. In this work, we design two types of ZnO monolayers derived from polar 0001-plane and nonpolar 11 (2) over bar0-plane of the wurtzite structure, and explore their physical properties using the first-principles approach. Both ZnO(11 (2) over bar0) and Zn0(0001) monolayers exhibited cohesive and formation energies comparable to that of the stable wurtzite-structured ZnO. However, both monolayers exhibited substantially different electronic structures of band gaps 1.56 eV for single-layered ZnO(11 (2) over bar0) and 0.71 eV for ZnO(0001) monolayer. The edges of the valence and conduction bands of ZnO(11 (2) over bar0) monolayer are formed by parabolic bands, whereas almost flat band gap edges have been seen for Zn0(0001) surface. As a result, charge carriers associated with ZnO(11 (2) over bar0) monolayer exhibited relatively lighter effective mass than ZnO(0001) monolayer. The ZnO(0001) monolayer exhibited symmetrical bond lengths and subsequently isotropic optical spectra, whereas asymmetrical bond lengths and anisotropic subsequent optical spectra have been recorded for ZnO(11 (2) over bar0) monolayer. The optical absorption recorded for the designed monolayers has been found higher than their bulk counterpart. The refraction spectra indicated these monolayers of transparent behavior over a significant range of the electromagnetic spectrum. These fascinating features of ZnO (11 (2) over bar0) and ZnO(0001) monolayers suggest them suitable for applications in electronic and optoelectronic devices.