Understanding W Doping in Wurtzite ZnO

Abstract

In the context of band gap engineering of the ZnO photoactive material for solar harvesting applications via W doping, a number of a priori discrepant experimental observations in the literature concerning ZnO c axis expansion/contraction, band gap red-or blue-shifting, the Zn-substitutional or interstitial nature of W atoms, or the W 6+ charge compensation view with ZnO native defects are addressed by thorough density functional theory calculations on a series of bulk supercell models encompassing a large range of W contents. The present results reconcile the observations, which are dissimilar at first sight, by showing that interstitial W (W i ) is only energetically preferred over substitutional (W Zn ) at large W doping concentrations; the W Zn c lattice expansion can be compensated by a W-triggered Zn-vacancy (V Zn ) c lattice contraction. The presence of W Zn energetically fosters nearby V Zn defects, and vice versa, up to a double V Zn situation. The quantity of mono-or divacancies explains the lattice contraction/ expansion, and both limiting situations imply gap states which reduce the band gaps, but increase the energy gaps. On the basis of the present results, the ZnO band gap redshifting necessary for solar light-triggered processes is achievable by W doping in Zn-rich conditions.

First-principles study on surface stability of tantalum carbides

“…The result is much smaller than 2.99 J/m 2 reported in ref. 20, since the ignorance of surface relaxation in that reference results in a large error for severely rumpled TaC (0 0 1) surface [21,30]. To estimate the strength of QSE in TaC films, we have calculated the band structure and density of states of bulk TaC, as shown in Fig.…”

“…In this paper, first-principles study has been made on the surface energies of the three stoichiometric phases, γ-TaC, α-Ta2C, and ζ-Ta4C3, and the high-fracture-toughness nonstoichiometric ζ-Ta4C3-x phase. Especially, QSEs are carefully considered in determining accurate surface energies of these metallic films, which have been neglected in previous studies [20][21]. The Ta terminated surface formed by the basal planes of ζ-Ta4C3-x phase is found to be more stable than that of ζ-Ta4C3, due to weaker metallic bonds between Ta atoms introduced by the structural vacancies at C sites.…”

Environmental Remediation of Real Textile Dyeing Wastewater Under Visible Light and Inactivation of Pathogenic Bacteria Using ZnO/CuO Nano‐Needles

“…[ 6 ] Among them zinc oxide (ZnO), II–VI transition metal oxide is considered to be the heart of technological applications which includes UV‐light and blue‐light emitting and laser diodes, transparent electrodes, field‐effect transistors, photodetectors, solar cells, and piezoelectric generators. [ 7 ] Only a small portion of the solar spectrum in the UV region can be absorbed by ZnO to improve its efficiency further, and some metals are loaded on the semiconductor surface. [ 8 ] Due to its inimitable catalytic, UV‐filtering, antibacterial, anti‐inflammatory, and anti‐fungicidal properties owing to its smaller size, ZnO has gained immense attention.…”

Strong Volta potential change in doped zinc oxide as a photoresponse to UV irradiation

“…The chosen doping concentration of W is based on the ndings from DFT calculations in ref. 12. The aim was to achieve a doping of around 2 at% W, which was shown by the authors to form a stable state due to the presence of W Zn .…”