Controlling Ag diffusion in ZnO by donor doping: A first principles study

Silver interdiffusion is often detrimental to the performance of thin-film coatings and devices that contain Ag/ZnO interfaces. Using a first principles computational analysis, a strategy is proposed which limits this diffusion by incorporating substitutional donor dopants into ZnO. First principles nudged elastic band calculations indicate that interstitial silver is likely to diffuse towards its nearby interstitial positions along [0001] in ZnO, with a relatively small energy barrier of 0.75 eV. Doping ZnO with Al slightly increases this energy barrier to 0.89 eV. In Sn-doped ZnO and Sc-doped ZnO, interstitial silver may bind to Sn or Sc and a neighbouring oxygen atom to form a Ag-O-Sn/Sc trimer in the ground state which increases the Ag migration barrier to 1.01 eV and 1.34 eV, respectively. An analysis of the Bader charges and bond strengths shows that electrostatic interactions and ionic radii have a more significant impact on Ag migration than charge transfer between the interstitial and its neighbours. In particular, the binding between Ag, O and Sn/Sc is found to be the main effect responsible for inhibiting Ag diffusion in doped ZnO.