Structural, optical, and electrical properties of heteroepitaxial ITO/YSZ thin films

Control over the structure and oxygen vacancy of the thin film provide powerful means to engineer the structural, electronic, and optical response of transparent conducting oxides. Here, we demonstrate tunability in heteroepitaxial indium tin oxide (ITO) films grown on (100) yttria-stabilized zirconia (YSZ). Post-deposition annealing in vacuum, argon, and oxygen atmospheres induces distinct modifications in morphology, crystallinity, and oxygen vacancies, as quantitatively and qualitatively revealed by comprehensive structural (XRD, SEM/AFM), chemical (XPS), and vibrational (Raman) characterization techniques. These modifications correlate directly with electrical transport and optical properties, including carrier densities ranging from 10 ²⁰ –10 ²¹ cm ⁻³ , mobilities up to 65 cm ² /Vs, resistivities as low as 2.2 × 10 ⁻⁴ Ωcm, and epsilon-near-zero (ENZ) wavelength tunability across 1.2–2.1 μ m with low-loss permittivity values ( ε ₂ =0.33 –0.45). An application-oriented figure of merit analysis ( σ / α ) identifies oxygen as the key post-growth parameter where vacuum annealing yields high-conductivity ENZ-active films, argon annealing balances transparency with low-loss ENZ behavior near 2 μ m, and oxygen annealing maximizes near-infrared (NIR) transparency. These findings establish heteroepitaxial ITO/YSZ as a versatile platform for transparent optoelectronics and ENZ photonic applications.