The effects of zinc diffusion on the electrical and optical properties of ZnO:Al films prepared by r.f. reactive sputtering

Abstract

ZnO:Al transparent conducting films with very low resistivity were easily prepared by the following method: ZnO:Al/Zn/ZnO:Al three-layered films were deposited by r.f. reactive sputtering from a composite target consisting of zinc disc and aluminium thin wires and then zinc atoms were diffused by heat treatment in vacuum. In the case that after deposition of a ZnO:Al layer for 5 min, zinc was deposited for 3 s followed by 25 min of deposition of a ZnO:Al layer, we could obtain ZnO:Al films with a resistivity of about 4 × 10 -4 Ω cm and transparency above 90% by annealing at 350°C for 2 h. We found that the diffusion of zinc atoms was conducted through grain boundaries and caused an increase in carrier concentration and Hall mobility and hence a decrease in resistivity. Furthermore, it was also found that diffused zinc atoms were very effective in suppressing an increase in resistivity in air.