Effect of heat treatment on microstructure and transparent conducting properties of sol-gel ZnO/Al thin films

Transparent and conducting Al doped ZnO (AZO) thin films with c axis preferred orientation were prepared on glass substrates via the sol-gel route. The physical and chemical changes of the precursors during thermal treatment were systematically investigated by differential scanning calorimeter and thermogravimetric analysis and the crystallinity of AZO films was characterised by X-ray diffraction. The surface morphology evolution of the films post-heated at 420, 450, 530 and 550 degrees C respectively was observed by SEM. Results reveal that the crystallising process of ZnO/Al comprises two stages: the primary nucleation and growth occurs at 318 degrees C and the continuous crystallisation at 488 degrees C. The optimised preheating and post-heating temperatures are determined at 420 and 530 degrees C respectively. The annealing treatment in vacuum can contribute considerably to the electrical conductivity. The film post-heated at 530 degrees C shows a homogenous dense microstructure and exhibits the minimum sheet resistance of 140 Omega/sq. The visible optical transmittance of all films is more than 90%.