IGZO thin films deposited by ultrasonic spray pyrolysis: effect of Zn precursor milling and In and Ga concentration

Abstract

Codoped zinc oxide thin films with indium and gallium (IGZO) were deposited on soda-lime glass substrates by the ultrasonic chemical spray (USP) technique. The influence of the mechanical grinding process of Zn precursor (zinc acetate, AcZn) and the In and Ga concentrations was analyzed. The grinding process was carried out in a planetary ball mill, with a ball:/precursor ratio of 4:1, and a constant rotation speed of 300 RPM. The starting solutions were prepared at a molar concentration of 0.2 and variable In and Ga atomic concentration (1, 1.5, 2, 2.5 and 3 at%). The deposition conditions were kept constant, substrate temperature of 450 °C and deposition time of 7 min. Structural, morphological, optical, and electrical properties were analyzed. From the structural analysis a preferential orientation along the (101) plane for dominant In concentrated IGZO films was observed, whereas for dominant Ga concentrated was the (002) plane. The average optical transmission was in the range of 83–90%, confirming the high transparency of all the deposited films. The bandgap values, Eg, showed slight variations, from 3.43 to 3.53 eV. The best electrical properties were obtained in the IGZO films with an In:Ga ratio of 1.5:1 [IGZO(1.5:1)], evaluated by the figure of merit, 3.50 × 10–3 (Ω/□)−1, calculated for an optical transmission of 86% and a sheet resistance of 63 Ω/□. According to the obtained results, the IGZO thin films deposited by the USP technique, are potentially applicable in the field of optoelectronics, mainly as transparent electrode.