Optical and electrical properties of Ta-doped ZnSnO3 transparent conducting films by sol-gel

Undoped and Ta-doped ZnSnO3 thin films with different Ta concentrations were deposited on glass substrates by using sol-gel spin coating method. Effects of Ta concentration (0-4 at.%) on structure, surface morphology, electrical and optical properties were investigated. Single phase and crystallinity deterioration were observed in the XRD spectrum. The porosity rate was calculated by processed SEM figures with different dopant content. XPS spectrum and results of Hall measurement indicated that there might be substitution of Ta5+ for Sn4+ dominantly when doping content is lower than 2 at.% and main substitution of Ta5+ for Zn2+ when doping content is up to 2 at.%. A minimum resistivity of 1.716 Omega cm were obtained for films with 2 at.% Ta. The optical transmittances clearly exhibited absorption edges shift to longer wavelength, and those in the visible range increased up to over 91 % with increasing Ta concentration. The work function of undoped and 2 at.% ZnSnO3 are 5.17 and 5.06 eV respectively, which are higher than ITO, FTO.