Devising square- and hexagonal-shaped monolayers of ZnO for nanoscale electronic and optoelectronic applications. (15th November 2020)

• Record Type: Journal Article
• Authors: Ul Haq, Bakhtiar; AlFaify, S.; Alshahrani, Thamraa; Ahmed, R.; Butt, Faheem K.; Ur Rehman, Sajid; Tariq, Zeeshan
• Is Part Of: Solar energy. Volume 211(2020)
• Page Start: 920
• Page End: 927
• Publication Date: 2020-11-15
• Subjects: First-principles calculations -- ZnO monolayers -- Electronic band structures -- Optical spectra -- Optoelectronic applications; Solar energy -- Periodicals; Solar engines -- Periodicals; 621.47
• DOI: 10.1016/j.solener.2020.09.075
• Languages: English
• ISSNs: 0038-092X

Abstract

Highlights: Devising of novel 2D polymorphs of ZnO (110- and 011-monolayers) from β-BeO type structure. Demonstration of indirect bandgap by 110-monolayer and direct bandgap by 011-monolayers. Demonstration of isotropic optical spectra by 110-monolayer and anisotropic spectra by 011-monolayer. Abstract: The atomically thin two-dimensional (2D) materials have received remarkable attention for their promising applications in cutting-edge technological applications. In this article, we devised square and hexagonal shaped monolayers from the 110-facet and 011-facet of β-BeO type structured ZnO by separating them from the adjacent layers by a distance of 20 Å. The energetic stability, lattice parameters, electronic and optical properties of these monolayers have been examined comprehensively using the density functional theory. In pursuit of this study, the wurtzite structured ZnO ( w -ZnO) is first transformed into the β-BeO structure by applying a negative pressure of −5.4 GPa. The obtained monolayers exhibited comparable cohesive and formation energy to that of w -ZnO. The electronic structure calculations performed with the Tran-Blaha modified Becke Johnson exchange potential, demonstrated the 110-monolayer as indirect bandgap and 011-monolayer as direct bandgap semiconductors having bandgaps 1.59 eV and 1.72 eV respectively. The 110-monolayer exhibited isotropic optical coefficients whereas considerable anisotropy has been recorded in the dispersion of optical spectra of 011-monolayer. Also, these monolayers exhibited thermally stable excitons of binding energies estimated as 3.32 eV for 110-monolayer and 1.53 eV along the x- axis and 1.19 eV along the y- axis for 011-monolayer. Investigations of the refractive indices indicated both monolayers as of transparent nature. Our study provides the pathways to serve as a useful reference for designing low-cost and nontoxic 2D polymorphs of ZnO for optoelectronic applications in miniaturized portable devices.