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Highlights • Optical properties of GAZO films sputtered at various O 2 /Ar flow ratios were studied. • The films had nearly spherical grains of mean diameter around 50–100 nm. • Good microstructural and optical properties were at 0.667 O 2 /Ar flow ratio. • The prepared GAZO thin films can be used for optoelectronic device fabrication. Abstract The present study investigates the effect of oxygen admittance on the surface morphology and optical constants of gallium (Ga) and aluminium (Al) co-doped zinc oxide (GAZO) thin films deposited on glass substrates by radio frequency (RF) planar magnetron sputtering. The GAZO thin films were uniformly covered with almost spherical grains of mean diameter around 50–100 nm. In the visible region, the refractive index (n) exhibited a decreasing trend with increasing oxygen admittance and the extinction coefficient (k) was almost zero, corroborating the observed increase in transmittance with oxygen/argon (O 2 /Ar) flow ratio. Optical constants such as the Wemple and Didomenico (WDD) single oscillator dispersion energies (E o and E d), static refractive index (n 0) , dielectric constant (ε), plasma frequency (ω p) and free carrier concentration (N c) were determined. Desirable surface morphology and optical properties were observed on the GAZO thin films deposited at an O 2 /Ar flow ratio of 0.667 , indicating their suitability for optoelectronic device fabrication. [ABSTRACT FROM AUTHOR]

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 prepared on glass substrates at low temperatures by radio frequency (rf) magnetron sputtering and their physical properties were investigated. All films possessed a hexagonal wurtzite crystal structure with a strong growth orientation along the (0 0 2) c-axis. The (0 0 2) peak intensity and mean crystallite size increased with substrate temperature from room temperature (RT) to 75 °C and then decreased at 100 °C, indicating an improvement in crystallinity up to 75 °C and its deterioration at 100 °C. Scanning electron microscopy (SEM) micrographs revealed the strong dependency of surface morphology on substrate temperature and energy dispersive spectroscopy (EDS) confirmed the incorporation of Ga and Al into the ZnO films. All films exhibited excellent transmittances between 85 and 90% in the visible region and their optical band gap increased from 3.22 eV to 3.28 eV with substrate temperature. The Urbach energy decreased from 194 meV to 168 meV with increasing substrate temperature, indicating a decrease in structural disorders which was consistent with X-ray Diffraction (XRD) analysis. Films deposited at 75 °C exhibited the lowest electrical resistivity (2.4 Ωcm) and highest figure of merit (7.5 × 10 −5 Ω −1 ), proving their potential as candidates for transparent electrode fabrication. [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]