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 Ti1−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.