Terahertz reflection and visible light transmission of ITO films affected by annealing temperature and applied in metamaterial absorber

The ITO film with visible light transparence, and high terahertz (THz) reflectivity is a promising material for the commercial and engineering applications in the THz field. This study investigates the terahertz optical performance and electrical properties of ITO films prepared by DC magnetron sputtering in the presence of oxygen at different annealing temperatures. By comparing the XPS spectra of ITO films before and after the annealing, the doping theory is employed to explain why and how the ratio of Sn4+/Sn2+ can be changed because of annealing, and it is concluded that Sn with low valence (Sn2+) can result in a lower visible transmission. In the THz region, the ITO film has high reflectance that observes the Hagen-Rubens (HR) relationship to some extent. According to the HR relation, the THz reflectance of the ITO film is mainly affected by the conductivity which can be controlled by adjusting the annealing temperature and the oxygen flow in the process of preparation. Applying the prepared ITO film with high THz reflectance into our proposed metamaterial absorber, the experimental result proves that the maximum absorptivity of 94.66%. can be achieved at 4.26 THz.