Structural, electrical and optical properties of transparent conductive titanium–gallium–zinc oxide films by magnetron sputtering

The transparent semiconductors of titanium–gallium–zinc oxide (TiGa–ZnO) thin films were prepared on glass substrates by radio frequency (rf) magnetron sputtering. The dependence of the grain-growth orientation, structure, electrical and optical properties of thin films on rf power was investigated by X-ray diffractometer, UV–visible spectrophotometer and Hall effect measurement system. Experimental results show that all nanocrystalline TiGa–ZnO thin films possess preferential orientation along the (002) plane. The rf power strongly affects the crystal structure, electrical and optical properties of thin films. When the rf power is at 190 W, the thin film deposited on the glass substrates has the optimal crystal quality and optoelectronic properties, with the largest mean grain size (83.1 nm), the minimum lattice strain (6.287 × 10⁻⁴), the highest average transmittance in the visible range (84.62 %), the lowest electrical resistivity (9.68 × 10⁻⁴ Ω cm) and the maximum figure of merit (6.173 × 10³ Ω⁻¹ cm⁻¹). The optical bandgaps of thin films were evaluated by extrapolation method and observed to increase firstly and then decrease with the increment of rf power. Furthermore, the optical parameters including refractive index, extinction coefficient, dielectric constant and dissipation factor of the thin films were determined by the pointwise unconstrained optimization method. The dispersion behaviour of refractive index was also analyzed using the Wemple–DiDomenico single-oscillator theory.