Morphological, optical and X-ray photoelectron chemical state shift investigations of ZnO thin films

The ZnO thin films of different (51.72 nm, 73.93 nm, 108.20 nm) thickness have been grown on glass substrate through atomic layer deposition (ALD). The effect of thickness on the morphology, optical and chemical state shift was investigated by X-ray diffractometer (XRD), UV–vis spectrometer, X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). The transmittance found to decrease with the increase in the ZnO thin film thickness. The morphological parameter such as grain size, strain, dislocation density and texture coefficient were calculated. The XPS chemical state analysis of O1s peak of the ZnO thin film at different thickness revealed that dissociation of oxygen vacancies increased with the films thickness. The XPS high resolution spectra of Zn 2p3/2indicate the increase in the Zn concentration associated with the films thickness. The XRD data confirm the improved crystallinty with films thickness. The FESEM images also validate the results of XPS and XRD at different thickness. The XPS investigation reveals that the chemical state shift in the binding energy of the surface elements is associated with thickness of the deposited ZnO thin films.