Microstructural and nonlinear optical properties of quaternary gallium-titanium-zinc-oxide transparent conductive semiconductor thin films

Transparent and conductive quaternary gallium-titanium-zinc-oxide films were grown on glass substrates by radio-frequency magnetron sputtering. The effects of growth temperature on structure, morphology, electrical, and nonlinear optical properties of the films were investigated systematically. All the deposited films possess hexagonal wurtzite structure with (002) preferred crystallographic orientation. The obtained optical bandgaps of the deposited films are larger than that of pure zinc oxide, which is ascribed to the reduction in band tail width. The film deposited at growth temperature of 375 & LCIRC;C exhibits the optimum crystalline quality with the lowest dislocation density of 1.4 x 10-4 nm-2, the highest visible light transparency of 82.06%, the minimum sheet resistance of 11.2 & omega;/sq, and the maximum figure-of-merit of 1.24 x 10-2 & omega;-1. The present findings indicate that the gallium-titanium-zinc-oxide films are promisingly utilized as transparent conductive layer. The refractive index and extinction coefficient of the deposited films were estimated by using spectrum fitting approach. A normal optical dispersion behavior was observed in visible region, while an anomalous dispersion behavior appeared in ultraviolet region. In addition, the nonlinear optical parameters were obtained. This first-hand information is useful for future rational design of multicomponent zinc oxide semiconductor materials for optoelectronic applications.