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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]

ZnO nanowires were grown by hydrothermal synthesis and the effect of annealing on their physical properties was investigated by field-emission scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Raman spectroscopy, spectrophotometry and Hall effect measurements. The nanowires adopted the c-axis [0 0 1] growth orientation of the underlying gallium and aluminium co-doped ZnO seed layer and their vertical alignment improved with annealing temperature up to 250 °C, above which it became random at 350 °C. This was attributed to the improvement in crystallinity up to 250 °C and its deterioration at 350 °C. Energy dispersive spectroscopy confirmed that the Zn:O atomic ratios for all samples were nearly stoichiometric. Average optical transmittances around 50–70% were observed in the visible region. The optimum electrical properties for transparent electrode fabrication were achieved at 250 °C, where the carrier concentration was maximum (5.5 × 10 20  cm −3 ) and electrical resistivity was minimum (1.1 × 10 −2  Ω cm). [ABSTRACT FROM AUTHOR]

Ga and Al co-doped ZnO thin films were prepared on glass substrates by radio frequency magnetron sputtering and the effect of O 2 /Ar flow ratio on their physical properties was investigated. The films exhibited a hexagonal wurtzite structure with a predominant (002) peak intensity and their crystallinity improved with O 2 /Ar flow ratio. Raman spectroscopy confirmed the films’ wurtzite structure and revealed a decrease in residual tensile stress and charge carrier concentration with increasing O 2 /Ar flow ratio. Low surface roughness resulted in high optical transmittances around 85–90% in the visible region. The Urbach energy decreased with increasing O 2 /Ar flow ratio indicating a reduction in structural disorders. This was consistent with Raman spectroscopy and X-ray diffraction analysis. The least electrical resistivity ( 2.6 × 10 1      Ω cm ) and highest figure of merit (8.8 × 10 −6 Ω −1 ) for films prepared with oxygen admittance were obtained at 0.667 O 2 /Ar flow ratio, indicating their suitability in optoelectronic device fabrication. [ABSTRACT FROM AUTHOR]

We report the hydrothermal synthesis of ZnO nanowires on rf sputtered gallium and aluminium co-doped ZnO (GAZO) thin films as seed layers. Their morphological, structural, optical and electrical properties were systematically tuned by optimizing the growth temperature, time and solution concentration for application as transparent electrodes in solar cells. The GAZO seed layer had a mean particle size of 77.82 nm, root mean square surface roughness of 6.07 nm and predominant (002) grain orientation. Energy dispersive spectroscopy confirmed the presence of only Zn and O in the ZnO nanowires. Growth temperature and time had pronounced effects on the nanowires' axial growth rate while solution concentration affected their lateral growth. The nanowires adopted a (002) preferred growth orientation of the GAZO seed layer and their crystallinity improved with growth temperature, time and solution concentration. Average optical transmittances around 50–80% were observed in the visible region. Raman spectroscopy confirmed the presence of few defects and negligible residual stress in the nanowires. Well-aligned, hexagonal column shaped nanowires with low electrical resistivity ( 1.4 × 10 − 2 Ωcm ) and high figure of merit ( 8.3 × 10 − 3 Ω − 1 ) were obtained with optimized growth parameters (2 h, 90 °C and 25 mM), demonstrating their suitability for transparent electrode fabrication. [ABSTRACT FROM AUTHOR]