Transparent Conductive Indium Zinc Oxide Films: Temperature and Oxygen Dependences of the Electrical and Optical Properties

Abstract

Achieving high-efficiency optoelectronic devices often requires the development of high transparency in the extended range and high-conductivity materials, which can be ensured by the high mobility of charge carriers being used as the electrode. Among the candidate materials, transparent conductive indium zinc oxide (IZO) has attracted significant interest because of its superior electron mobility (5−60 cm2/V·s) and the thermal stability of its structure. In this study, the IZO films were deposited by the radio frequency magnetron sputtering of the IZO ceramic target (containing 10 wt.% ZnO) by varying the two variables of the substrate temperature and the oxygen content in the working gas. Here, the importance of the deposition of the IZO films at a low substrate temperature, not exceeding 100 °C, in order to get the minimum values of the film resistivity is revealed. At a substrate temperature of 100 °C, the film deposited in pure argon demonstrated a minimum resistance of 3.4 × 10−4 Ω·cm. Despite the fact that, with the addition of O2 in the working gas, an increase in resistivity was observed, the IZO film that deposited under 0.4% O2 content demonstrated the highest mobility (μ = 35 cm2/V·s at ρ = 6.0 × 10−4 Ω·cm) and enhanced transparency in the visible (VIS, 400−800 nm) and near-infrared (NIR, 800−1250 nm) ranges (TVIS ≥ 77% and TNIR ≥ 76%). At an oxygen content above 0.4%, a significant deterioration in electrical properties and a decrease in optical characteristics were observed. SEM and XRD studies of the microstructure of the IZO films allowed the clarification of the effect of both the substrate temperature and the oxygen content on the functional characteristics of the transparent conducting IZO films.