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X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and spectrophotometry were used to study the effect of RF power on the properties of gallium and aluminium co-doped zinc oxide (GAZO) thin films for optoelectronic device fabrication. Two peaks appeared in the XPS spectra of the Zn 2p core-level at 1045 and 1022 eV, and these were assigned to Zn2p1/2 and Zn2p3/2, respectively. The O 1s core-level revealed peaks at 530 and 531 eV which indicated the presence of two different forms of oxygen. Raman spectroscopy confirmed the films' hexagonal wurtzite crystal structure and revealed the presence of few defects and negligible residual tensile stress. Spectral dependence of the refractive index was analyzed on the basis of the Cauchy's dispersion model and the Wemple and DiDomenico (WDD) single oscillator model. Low refractive indices (1.6-2.0) and nearly zero extinction coefficients were obtained in the visible region (400-700 nm), indicating the high transparency nature of the GAZO thin films. The optical band gap decreased with increasing RF power, in accordance with the Burstein-Moss effect. Low Urbach energy values were obtained at low RF power, indicating less structural disorder. The free carrier concentration to effective mass ratio (Nc/m∗), plasma frequency (ωP) and zero frequency dielectric constant (ε∞) were determined. Films deposited at 150 W exhibited the optimum optical properties, desirable for optoelectronic application. [ABSTRACT FROM AUTHOR]

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 − 1 Ω c m and maximum figure of merit of 4.8 × 10 − 4 Ω − 1 were obtained for films deposited at 150 W, indicating their better performance in optoelectronic applications. [ABSTRACT FROM AUTHOR]

Gallium-doped zinc oxide (GZO) thin films were deposited onto glass substrates by the spray pyrolysis technique and the effect of gallium (Ga) doping on their structural, optical and electrical properties was investigated by X-ray Diffraction (XRD), Spectrophotometry and Current–Voltage ( I – V ) measurements, respectively. XRD studies revealed that all films were polycrystalline in nature, with a hexagonal wurtzite crystal structure and a predominant (002) c -axis orientation. Ga doping resulted in deterioration of the film's crystallinity, increase in full width at half maximum (FWHM) and reduction in the mean crystallite sizes. All GZO thin films had relatively higher average transmittances, approximately 70–85% in the visible region as compared to the undoped ZnO thin films. Introduction of Ga led to a blue shift in the optical band gap from 3.26 eV to 3.30 eV and an increase in the Urbach energy from around 67 meV to 100 meV. Ga doping induced a decrease in sheet resistance leading to a minimum electrical resistivity of 1.2 Ω cm and a maximum figure of merit of 1.02 × 10 − 4 Ω − 1 for the 1 at% GZO thin film, indicating its suitability for optoelectronic applications, especially transparent electrode fabrication. [ABSTRACT FROM AUTHOR]