The conversion of wettability in transparent conducting Al-doped ZnO thin film

We report on the systematic changes of surface wettability in one of the most promising transparent conducting oxide materials, AI-doped ZnO (AZO) thin films. It was revealed that the characteristic surface wettability, which would make a key role in adhesion with other layers of optoelectronic device, can be largely changed by AI concentrations and film growth temperature. Keeping the electrical conductivity constant, the water contact angle (WCA) of a 2 mol% AZO film was changed by about 50 degrees C depending on the surface roughness. In the samples grown at 300 degrees C, the roughness enhancement was large and a hydrophobic surface formed, whereas in the samples grown at 500 degrees C a hydrophilic surface formed. We attributed the variation in surface wettability with growth temperature to changes in surface morphology. This result suggests that 2 mol% AI doping concentration can be considered as a critical concentration in changing of surface morphology of AZO as well as in electrical properties. (C) 2009 Elsevier Ltd. All rights reserved.