Modulation of photoelectric properties of indium tin oxide thin films via oxygen control, and its application to epsilon-near-zero properties for an infrared absorber

Indium tin oxide (ITO) films with tunable epsilon-near-zero (ENZ) properties have attracted great interest among researchers. In this study, ITO films with tunable photoelectric properties were prepared by a magnetron sputtering technique under different oxygen flow rates, and their structures and optical properties are studied. The ENZ wavelength shift and electron accumulation layer were observed from their permittivity and carrier concentrations, which were calculated by a graded model combined with an oscillator model. This demonstrated that the variable carrier concentrations induced the tunable ENZ property of the ITO films. Meanwhile, the interface of the film and the substrate was found to have a significant influence on the loose lower layer by researching the profile of permittivity and carrier concentrations. Furthermore, the simulation of the transfer matrix method indicated that using ENZ materials as substrates can achieve zero reflection at an ENZ wavelength. ITO films serve as absorbers based on this characteristic. An absorption device was fabricated; its largest absorption rate was 97.41% at 1576 nm, and it maintained high absorption over a wide range of incident angles. The absorption mechanism in the ENZ film is illustrated by absorption maps and electric field distribution.