First-principles investigations of optoelectronic properties of ZnO and ZnO(0001) monolayers
Advanced Functional Materials and Optoelectronics Laboratory (AFMOL), Department of Physics, Faculty of Science, King Khalid University, P.O. Box 9004, Abha, Saudi Arabia
2 Centre for High Energy Physics, University of the Punjab, Quaid-E-Azam Campus, 54590, Lahore, Pakistan
3 Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, UTM, Johor Bahru, 81310, Johor, Malaysia
Accepted: 5 February 2021
Published online: 23 February 2021
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 -plane of the wurtzite structure, and explore their physical properties using the first-principles approach. Both ZnO and ZnO(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 and 0.71 eV for ZnO(0001) monolayer. The edges of the valence and conduction bands of ZnO monolayer are formed by parabolic bands, whereas almost flat band gap edges have been seen for ZnO(0001) surface. As a result, charge carriers associated with ZnO 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 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 and ZnO(0001) monolayers suggest them suitable for applications in electronic and optoelectronic devices.
© The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2021