Highly conductive air-stable ZnO thin film formation under in situ UV illumination for an indium-free transparent electrode

Abstract

Zinc oxide (ZnO) is considered as the strongest alternative to tin doped indium oxide (ITO) - a commonly used, but an expensive state-of-the-art material for transparent conducting electrodes. This work reports the low temperature atomic layer deposition (ALD) of a highly transparent, and highly conductive air-stable thin film of ZnO under in situ UV irradiation of the growing film. X-ray photoelectron spectroscopy (XPS) reveals that the UV irradiation generates oxygen vacancies, partially removes O-H bonds, and thereby improves the electrical conductivity. Thus, in contrast to 0.25 U cm resistivity of the pristine ZnO film, the in situ UV irradiated ZnO film shows an electrical resistivity of 5.5 x 10(-4) U cm, and an optical transparency of nearly 90%, which are closer to that of ITO. In addition, even on prolonged exposure of the film to air, it demonstrates high stability against the degradation of the electrical conductivity.