Investigations on the Growth Mechanism of Nanostructured ZnO: Shedding Light on the Effect of Al 3+ Doping

Herein the growth mechanism of an un-doped zinc oxide (i-ZnO) and an Al-doped zinc oxide (AZO) was investigated using electrochemical techniques. Zinc and aluminum nitrates precursors were used in an aqueous bath solution, under a fixed potential of about –1.0 V, at 80°C. The variations of the morphological, structural, and optical properties of AZO were investigated in terms of Al 3+ concentrations ranging from 0 to 4 atomic percentage in the starting solution. The X-ray diffraction patterns showed the hexagonal wurtzite structure for all samples. The effect of the lateral growth mechanism of AZO instead of the longitudinal growth process of ZnO was confirmed by calculating the texture coefficient and by studying the surface morphology under high magnification via scanning electron microscopy. It was found that the morphology evolved from hexagonal flat nanorods into a mixture of tapered hexagonal nanorods and nanosheets, to larger nanosheets by adding aluminum ions dopants. All films demonstrated a transmittance of about 80% in the visible range and exhibited a slight red shift in the absorption edge with Al 3+ doping. The optical band gap of AZO nanosheets was found to be lower than that of i-ZnO nanorods. These findings provide fundamental understanding of the growth mechanism and shape control of a nanostructured zinc oxide.