Microstructural characterization and physical properties of transparent conducting magnesium-titanium co-doped zinc oxide thin films

The transparent conductive oxide (TCO) thin films of magnesium-titanium co-doped zinc oxide (MT-ZnO) were deposited on quartz substrates by magnetron sputtering. The growth temperature dependence of microstructural and physical properties of the deposited films was investigated by XRD, SEM, four-point probe, ultraviolet-visible spectrophotometer and optical characterization methods. Experimental results show that all the deposited films have a hexagonal wurtzite-type crystal structure and a [002]-preferred orientation. The MT-ZnO sample deposited at the growth temperature of 550 K exhibits the best crystal quality and optoelectronic properties, with the minimum lattice strain of 1.281 x 10(-3), dislocation density of 4.857 x 10(10) cm(-2) and resistivity of 2.531 x 10(-3) omega center dot cm, the highest average visible transmittance of 90.7% and the maximum figure of merit of 4.052 x 10(3) omega(-1)center dot cm(-1). The optical constants of the deposited films were determined by the method of optical spectrum fitting. Meanwhile, the refractive index dispersion behavior was studied by means of the Wemple-DiDomenico (WDD) single-oscillator theory. The oscillator parameters and direct optical bandgaps were achieved. The results demonstrate that the microstructure and optoelectronic properties of the MT-ZnO TCO films are subjected to the growth temperature.