Effect of Ar:O2 ratio on reactively magnetron sputtered ZnO film’s properties

Abstract

Zinc oxide films were synthesized on silicon substrate by using direct current (DC) magnetron sputtering. The objective of this work was to explore the effects of Ar:O2 ratio on the crystal structure, surface morphology, electrical, and optical characteristics of the film. The zinc oxide (ZnO) films’ properties were studied through x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV–visible spectrometer and four probe technique. The structural characterization results revealed hexagonal ZnO films preferentially oriented along (002) plane. The ZnO (002) peak became more intense and narrow with increase of the Ar amount during the reactive sputtering process. The film’s crystallite size was changed from 8 nm to 36 nm by adjusting the Ar:O2 to 90:10. The morphological analysis also displayed smaller grains at 50:50 as compared to 90:10 Ar:O2 ratio. The improvement in the crystallinity of the films with increasing Ar amount was associated with the enhanced surface diffusion of adatoms on the substrate due to an increased sputtering of Zn from its target. The ZnO band gap was reduced from 3.53 eV to 3.41 eV by increasing the Ar:O2 ratio as 90:10. This decrease in band gap was ascribed to the reduction in oxygen vacancies due to improvement in the films’ crystallinity. The electrical resistivity was decreased due to decrease in the structural defects at the higher argon concentration than that of the oxygen.