LAUSR

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 W6+ 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 (Wi) is only energetically preferred over substitutional (WZn) at large W doping concentrations; the WZn c lattice expansion can be compensated by a W-triggered Zn-vacancy (VZn) c lattice contraction. The presence of WZn energetically fosters nearby VZn defects, and vice versa, up to a double VZn situation. The quantity of mono- or divacancies explains the lattice cont...