Highly conducting transparent undoped indium oxide films deposited below 100°C by activated reactive evaporation

Abstract

Highly transparent and conducting undoped indium oxide films have been obtained with a resistivity of ≈;4 × 10−1 Ωcm, a carrier density of ≈; × 1020 cm−3 and a mobility of ≈;18 cm2 V−1−1 at a substrate temperature <70° C and a deposition rate of ≈;8 A/s by an activated reactive evaporation process. The stability of electrical and optical properties at room temperature in the open air is reasonable for a film optimized for conductivity. The optical bandgap of these films is ≈;3.3 eV, lower than that of a high temperature deposited tin doped indium oxide film. It is found that undoped indium oxide films with the best conductivity cannot be obtained if a threshold temperature of ≈;200° C is exceeded either during deposition or during post deposition vacuum anneals. However, highly conductive tin doped indium oxide can be easily obtained at high temperature (T ≈; 400° C) by activated reactive evaporation. It is also noted that highly conductive tin doped indium oxide films are more difficult to make at the lower end of the temperature range unless certain precautions are taken.