Photonic Characterisation of Indium Tin Oxide as a Function of Deposition Conditions

Indium tin oxide (ITO) has recently gained prominence as a photonic nanomaterial, for example, in modulators, tuneable metasurfaces and for epsilon-near-zero (ENZ) photonics. The optical properties of ITO are typically described by the Drude model and are strongly dependent on the deposition conditions. In the current literature, studies often make several assumptions to connect the optically measured material parameters to the electrical properties of ITO, which are not always clear, nor do they necessarily apply. Here, we present a comprehensive study of the structural, electrical, and optical properties of ITO and showed how they relate to the deposition conditions. We use guided mode resonances to determine the dispersion curves of the deposited material and relate these to structural and electrical measurements to extract all relevant material parameters. We demonstrate how the carrier density, mobility, plasma frequency, electron effective mass, and collision frequency vary as a function of deposition conditions, and that the high-frequency permittivity (e(8)) can vary significantly from the value of e???????(8) = 3.9 that many papers simply assume to be a constant. The depth of analysis we demonstrate allows the findings to be easily extrapolated to the photonic characterisation of other transparent conducting oxides (TCOs), whilst providing a much-needed reference for the research area.

Automated summary

In this study, the structural, electrical, and optical properties of ITO were comprehensively investigated and their relationship with deposition conditions was demonstrated. Guided mode resonances were used to determine the dispersion curves of the deposited material, and these were correlated with structural and electrical measurements to extract relevant material parameters. The findings showed that the carrier density, mobility, plasma frequency, electron effective mass, and collision frequency varied with deposition conditions, and the high-frequency permittivity (e(8)) could significantly differ from the assumed constant value of e???????(8) = 3.9 in many papers. This analysis provides a valuable reference for the characterization of other transparent conducting oxides (TCOs) in photonics research.