Electrical conductivity enhancement of indium tin oxide (ITO) thin films reactively sputtered in a hydrogen plasma

Transparent conducting oxides are materials characterized by the simultaneous occurrence of high optical transparency and electrical conductivity. Among them, tin-doped indium oxide (ITO) has been established as the best material with these criteria. This work focused on the enhancement of the electrical conductivity of ITO thin films through reactive DC sputtering under a hydrogen plasma. The films were deposited on heated substrates (350 °C) with the hydrogen concentration varying from 0 to 20% of the flow rate of argon. The structural properties (crystalline orientation and surface roughness) varied as functions of the hydrogen concentration. The electrical resistivity reached a minimum value of 2.0 × 10⁻⁴ Ω cm for a hydrogen concentration of 15%, corresponding to a reduction by a factor of 4 compared to the films deposited without hydrogen. The optical band gap of the films was 4 eV, and was not affected by the hydrogen concentration. The average visible transmittance decreased as the hydrogen concentration increased but maintained a value above 80%. The infrared reflectance increased upon hydrogenation, shifting the plasmon frequency into the near-infrared spectral range.