Effects of aluminum and indium incorporation on the structural and optical properties of ZnO thin films synthesized by spray pyrolysis technique

This paper reports the effects of Al and In content on the structural and optical properties of ZnO thin films synthesized by the spray pyrolysis technique. The concentration ratio of [Al]/[Zn] or [In]/[Zn] was kept at 1 at.%. Thickness of the films was in the range 315–320 nm. X-ray diffraction analysis indicates that the film doped with Al using aluminum chloride (AlCl3·2H2O) has a textured structure with (0 0 2) preferred orientation, but no texturisation is observed when doped with Al using aluminum nitrate (Al(NO3)3·9H2O) and also with In using indium nitrate (In(NO3)3·9H2O). The surface morphology and grain size for the film doped with Al using aluminum chloride is slightly different from those of the films doped with Al and In using aluminum nitrate and indium nitrate, respectively. The grains of the film doped with Al using aluminum chloride were found to be well defined but those appeared to form clusters in the case of the other two films. From the optical study a slight shrinkage of band gap has been observed in the case of the film doped with In. Also, in the case of this film, width of the localized state in the band gap region was found to be higher compared to the other two films doped with Al. Thus, from all these studies it is evident that in the films prepared by spray pyrolysis the nature of dopant salt influences the grain structure, surface morphology and nucleation process which ultimately govern the structural and optical properties of the samples.