Electrical and optical properties of ZnO:Al thin films prepared by laser ablation

Abstract

Thin films of ZnO:Al have been deposited on glass substrates by laser ablation using an ArF laser (λ = 193 nm). A minimum resistivity of 1.43 × 10-6 Ω·m (sheet resistance of 9.3 Ω/sq) was obtained for a film deposited at a substrate temperature of 300°C and a pressure of 1 × 10-5 Pa. An optical transmittance of around 88% was observed in the visible region of the spectrum for a 154-nm-thick film. In order to increase the optical transmittance, oxygen gas was introduced into the plume and onto the substrate at a rate of 1 sccm. Thus, a maximum transmittance of 95.6% was obtained in the visible region of 400∼700 nm for the same film. A resistivity of 5.62 × 10-6Ω·m (39.5 Ω/sq) was obtained for a film deposited at room temperature. An optical transmittance of around 87% was obtained in the visible region for this 142-nm-thick film. It was found from high-resolution SEM images that the surface morphologies of films grown by the laser ablation method were natter than those of films deposited by the sputter method. The spectrum of the plume generated in the laser ablation process was compared with those of the plasma induced in the sputter process. No luminescent peaks were detected in the spectrum for the plume except for that emitted from the target element. On the other hand, many, strong peaks were detected in the spectrum for the plasma. It was deduced from this result that the surface morphology was strongly affected by the chemical properties in the deposition process.