Improving conductivity and texture in ZnO:Al sputtered thin films by sequential chemical and thermal treatments

Smooth, transparent and conductive ZnO:Al (AZO) thin films have been deposited by sputtering at room temperature on glass substrates. The conductivity and texture of the as-grown layers have been enhanced by the application of thermal heating at 350 °C and chemical etching in HCl or HF solutions. The structure, morphology, optical and electrical properties of the layers have been analysed before and after the successive thermal and chemical treatments, which were performed in different sequences. The surface texture has been characterized optically by the haze parameter for transmittance, which has been related to the root mean square roughness and the autocorrelation length coefficients for each sample. The highest optical scattering has been achieved with the HF etching and subsequent heating sequence, which gave also the highest root mean square roughness. In this way, an average haze of 36%, together with total visible transmittance about 80% and sheet resistance of 8 Ω/sq have been obtained. Otherwise, the application of heating before HCl or HF etching resulted in AZO films with average haze of 11%, visible transmittance about 85% and sheet resistance near 6 Ω/sq.