Combined effect of the target composition and deposition temperature on the properties of ZnO:Ga transparent conductive oxide films in pulsed dc magnetron sputtering

Abstract

Composition-dependent changes in the properties of Ga-doped ZnO (GZO) transparent conductive oxide (TCO) films were investigated by preparing a series of GZO films on glass substrates via pulsed dc magnetron sputtering with ZnO ceramic targets having various Ga2O3 concentrations at various temperatures. As the Ga2O3 content in the target increased, crystalline quality was improved as revealed in the intense ZnO (0 0 2) diffraction peaks, which accompanied increased carrier concentrations. When the Ga2O3 content was low, it was deduced from the crystallinity and carrier concentration that Ga or its oxide species functioned primarily as a crystal growth promoter, which was more distinctive at lower deposition temperatures. Meanwhile, formation of the secondary oxide phases, detrimental to the carrier mobility, was rather enhanced up to intermediate temperature and then suppressed by further increasing the deposition temperature. Consequently, improved crystallinity and enhanced doping efficiency and therefore the lowest electrical resistivity could be achieved with the combination of higher Ga2O3 content in the target and higher deposition temperature. Electrical resistivity and optical transmittance of the GZO films prepared by the pulsed dc magnetron sputtering in this study fulfilled requirements for TCO films.