Physicochemical conditions for ZnO films deposited by microwave chemical bath deposition

Physicochemical analysis was carried out to obtain the species distribution diagrams (SDDs) for the deposition of ZnO films as a function of OH- ion concentration ([OH-]) in the reaction solution. The study of SDDs predicts nucleation and ZnO film growth by means of the dominant species at a given pH value. To confirm this, a series of experiments were made varying the [OH-] in the reaction solution and keeping the others parameters constant. Structured zinc oxide (ZnO) films were obtained on glass substrates by microwave chemical bath deposition (MWCBD). Structural, optical and morphological ZnO film properties were investigated as a function of [OH-]. X-Ray diffraction technique (XRD) measurements show multiple diffraction peaks, indicating the polycrystalline nature of ZnO films. Scanning Electron Microscopy (SEM) images of ZnO structures showed morphological changes with the variation of [OH-]. The stoichiometry of the structures changed as the [OH-] was varied in solution. From Raman spectra, it was observed that the [OH-] of the reaction mixture strongly affects the crystal quality of ZnO structures. A reaction pathway for the synthesis of ZnO structures based on our results is proposed. Experimental results are consistent with the physical-chemical analysis.