Physical properties of gallium and aluminium co-doped zinc oxide thin films deposited at different radio frequency magnetron sputtering power

Gallium and aluminium co-doped zinc oxide (GAZO) thin films were deposited by radio frequency (rf) magnetron sputtering onto glass substrates and the effect of rf power on their structural, optical and electrical properties was respectively investigated by X-ray Diffraction (XRD), Spectrophotometry and Four–Point Probe Resistivity measurements. All films had a hexagonal wurtzite crystal structure with a preferred (002) grain orientation. The films’ crystallinity deteriorated with increasing rf power from 150 W to 250 W as revealed by the increase in full width at half maximum (FWHM), decrease in mean crystallite size and increase in dislocation density. A further increase in rf power to 300 W caused slight improvements in crystallinity due to enhanced surface diffusion of the ad-atoms. High optical transmittances, around 80–90% were observed for all films in the visible region and their optical band gap red shifted from 3.32 eV to 3.20 eV with increasing rf power. The electrical resistivity firstly increased as the rf power changed from 150 W to 250 W and then decreased at 300 W. The lowest electrical resistivity of 5.0×10⁻¹Ωcm and maximum figure of merit of 4.8×10⁻⁴Ω⁻¹ were obtained for films deposited at 150 W, indicating their better performance in optoelectronic applications.