Factors limiting doping efficiency of Iridium in pulsed laser deposited TiO₂ transparent conducting oxide

High transmittance and low resistivity make doped TiO₂ films outstanding electrodes for use in optoelectronic devices operating in the infra-red region. In this work, we studied the impact of Ir doping in TiO₂ thin films on the optoelectrical properties. High-quality nanocrystalline Ti_1−x Ir _x O₂ thin films ~60 nm thick were grown by pulsed laser deposition from an Ir-doped target (x = 0–0.15 wt%). Films were deposited on quartz glass at a base pressure of 2 × 10⁻³ Pa and a substrate temperature of 780 K. The resistivity of the films decreased by 3 orders of magnitude when x increased from 0 to 0.10. The carrier mobility and concentrations increased by a factor of 2.55 from 18 to 46 cm² V⁻¹ s⁻¹ at 5 %, and rose by ~2 orders of magnitude from 10¹⁹ to 10²¹ cm⁻³ at 15 % Ir, respectively. Optimal film properties were measured to be at x = 0.10, where resistivity, mobility, and carrier concentrations were 5 × 10⁻⁴ Ω cm, 32 cm² V⁻¹ s⁻¹, and 10²⁰ cm⁻³, respectively. The highest observed doping efficiency was ~1.1 which is similar to common dopants. At the same time, film transmittance was measured to be above 80 % in the visible and infrared regions, suitable for use in both spectral regimes. The films were characterized by X-ray diffraction, Hall transport, optical transmission, and Raman spectroscopy.