Influence of discharge power and annealing temperature on the properties of indium tin oxide thin films prepared by pulsed-DC magnetron sputtering

Indium tin oxide (ITO) films, prepared by a pulsed direct current magnetron sputtering system, are investigated at powers from 0.4 to 2.0 kW (power density in the range 0.8-4.1 W/cm2). It is found that the carrier concentration and crystallinity of the ITO films increase with increasing discharge power, while the electron mobility decreases from 49.2 cm2/Vs at 0.4 kW to 30.3 cm2/Vs at 2.0 kW. X-ray photoelectron spectroscopy measurements demonstrate that the ITO films prepared at high powers have more oxygen deficient and Sn4+ bonding states. These two types of bonding states are most relevant to the oxygen vacancies and substitutional tin atoms, which are the dominant electron donors in ITO. This observation explains why highly conductive ITO films are achieved at high deposition powers. Besides the investigation of the as-deposited ITO properties, annealing induced changes are explored in air ambient. The ITO properties are maintained for most of the samples when annealed at 150 °C, while degraded ITO properties are observed when annealed at 200 °C, especially for films grown at low powers. The annealing induced changes are most probably related to changes of the film crystallinity. A clear improvement of the crystallinity is observed for low power deposited ITO films after annealing at 200 °C for 240 min.