Improvement of optical properties of Mg doped ZnO by nanostructuring for applications in optoelectronics

Abstract

We have studied the structural, optical, electronic and electrical properties of pure and Mg doped ZnO nanosheets compared to bulk ZnO, using the Density Functional Theory (DFT) within the Full Potential Linearized Augmented Plane Wave (FP-LAPW) formalism. The calculated band structure, total and partial densities of states show that the ZnO nanosheet have a large band gap than the other found in the bulk ZnO, which increases with increasing concentration of Mg. The absorption coefficient and optical transmittance show a red-shift after doping ZnO, whereas, the reflectivity and electrical conductivity are reduced. These good optical properties of ZnO nanosheets make it promising in optoelectronic devices, especially in solar cell application. IntroductionDue to their applications in various optoelectronic devices, zinc oxide crystallized in three-dimensional (3D) structures is one of the most transparent oxides studied experimentally and theoretically in recent years. Actually, the successful development of two-dimensional (2D) nanostructures, such as MoS 2 /MoSe 2 is crucially important for their applications in multifunctional integrated photonics and optoelectronics devices [1-3]. Also, ZnO nanosheet [4, 5] as well as BN boron nitride and graphene [6], has a great importance for the construction of devices at the nanoscale. These nanomaterial's can be used in energy storage or conversion [7], photocatalysis [8,9], data storage, and optoelectronics [10] due to the effects of their small thickness and their high surface area/volume ratio. Various methods, such as the carbothermic reduction process [11], magnetron sputtering [12], physical vapor transport (PVT) [13], electrodeposition [4] and pulsed laser ablation [14], have been used to elaborate a few layers nanostructured of ZnO like graphene.Recently, ZnO nanosheets have been developed on a substrate of Pd (111) confirming the possibility of obtaining honeycomb structure like grapheme. However, the synthesis of a monolayer having atoms in the same plane like graphene, has not been performed experimentally. The study of such structure will facilitate the study of other structures, for instance: ZnO nanotubes (1D) by winding, ZnO fullerene (0D) by enveloping, and bulk ZnO (3D) by stacking [15].The optical, magnetic, mechanical and electrical properties of the bulk ZnO are very different from 2D, 1D and 0D ZnO due to the quantum confinement resulting from the reduction of their dimensions. In the following, we will cite some theoretical work around ZnO-2D. For example Thanayut et al [16], showed that pure ZnO-2D gap energy decreases by applying tensile or pressure stresses, using ab-initio methods. This later is employed by Haneen Ali Rashed to the stability and electronic properties of Si-doped ZnO nanosheet, their results demonstrate that the gap decreases with the increase in number of Si dopant atoms in ZnO nanosheet and the substitutional silicon atoms on oxygen sites lightly prefer to occupy nearest neighbor sites of zinc [17]. While, Chang-Wen et al [18],...

Investigation of structural, morphological, optical and electronic properties of Cu-doped PbS thin films: a comparative experimental and theoretical study

“…The investigation of the electronic behavior of materials is important to understand different atomic orbital contributions in their respective conduction band (CB) and valence band (VB) formation along with the material's bandgap nature [40]. The experimentally determined energy band gap (E g ) values for pure and Cudoped PbS thin films are presented in figure 4, which is obtained by Tauc-plot [41].…”