Influence of Al, In, Cu, Fe and Sn dopants in the microstructure of zinc oxide thin films obtained by spray pyrolysis

A spray pyrolytic system was used to obtain ZnO:X films doped with different elements, X = Al, In, Cu, Fe and Sn. A 0.1 M solution of zinc acetate in a mixture of ethanol and deionised water, in a volume proportion of 3:1, was employed. Dopant sources were aluminium chloride, indium acetate, copper acetate, iron chloride and tin tetrachloride. The atomic percentage of dopant in solution were X/Zn = 1, 3, 5, 7, 10 and 15 at.%. The proportion between dopant atoms and Zn atoms are not the same in the film as in solution, only indium-doped films maintain almost the same proportion. In the other cases, the dopant proportion in the film is less than that in the solution. X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to study the microstructure and surface morphology of the films. We can conclude that the amount as well as the type of dopant modifies the film growth process and by consequence the microstructure and surface morphology. Since it goes from non-oriented growth, for undoped films, Co strongly (002) oriented, at intermediate (similar to 1 at.%) doping level; and finally again to non-oriented and poor crystallinity, at high (>3 at.%) doping level. This behaviour is the same for all the dopants treated in this work and the highest (002) orientation seems to be happening at about the same concentration (similar to 1 at.%). Cross section micrographs show that the microstructure of the films consists of densely packed grains, which can be interpreted as a transition structure between a porous arrangement of tapered crystallites and dense columnar grains. (C) 2000 published by Elsevier Science S.A. All rights reserved.