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

Abstract

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 150W to 250W 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 300W 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 3.32eV to 3.20eV with increasing rf power. The electrical resistivity firstly increased as the rf power changed from 150W to 250W and then decreased at 300W. 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 150W, indicating their better performance in optoelectronic applications.