Structural, optical and electrical properties of Al-doped ZnO microrods prepared by spray pyrolysis

Al-doped ZnO thin films were obtained on glass substrates by spray pyrolysis in air atmosphere. The molar ratio of Al in the spray solution was changed in the range of 0-20 at.% in steps of 5 at.%. X-ray diffraction patterns of the films showed that the undoped and Al-doped ZnO films exhibited hexagonal wurtzite crystal structure with a preferred orientation along (002) direction. Surface morphology of the films obtained by scanning electron microscopy revealed that pure ZnO film grew as quasi-aligned hexagonal shaped microrods with diameters varying between 0.7 and 1.3 μm. However, Al doping resulted in pronounced changes in the morphology of the films such as the reduction in the rod diameter and deterioration in the surface quality of the rods. Nevertheless, the morphology of Al-doped samples still remained rod-like with a hexagonal cross-section. Flower-like structures in the films were observed due to rods slanting to each other when spray solution contained 20 at.% Al. Optical studies indicated that films had a low transmittance and the band gap decreased from 3.15 to 3.10 eV with the increasing Al molar ratio in the spray solution from 0 to 20 at.%.