Electrical and optical properties of indium tin oxide thin films prepared on low-temperature substrates by rf magnetron sputtering under an applied external magnetic field

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Abstract
Indium tin oxide (ITO) films were prepared with relatively high deposition rate by rf magnetron sputtering under an applied external dc magnetic field. The films with resistivity as low as 2×10−4 Ω cm and average transmittance above 85% at wavelengths between 400 and 800 nm were able to form on the substrates at temperatures below 140 °C by using a target composition of 95 wt. % In2O3–5 wt. % SnO2. The characteristic features of the ITO films deposited on low-temperature substrates were their high carrier concentration and relatively low mobility. It was found that the use of a 95 wt. % In2O3–5 wt. % SnO2 target is better than that of a 90 wt. % In2O3–10 wt. % SnO2 target for deposition on low-temperature substrates, while the use of a 90 wt. % In2O3–10 wt. % SnO2 is desirable for deposition on substrates of high temperatures, about 350 °C. It was also found that the resistivity of the ITO films deposited on low-temperature substrates can be lowered by heat treatment at 400 °C in either a vacuum or nitrogen gas. After heat treatment at 400 °C in air, the magnitude of the resistivity of the ITO films increased several times. The resistivity after heat treatment in air was easily regained to the as-deposited state by sequential heat treatment at 300–400 °C in hydrogen gas.