Dependence of the properties of sputter deposited Al-doped ZnO thin films on base pressure

Al-doped ZnO (AZO) thin films were prepared on glass substrates by RF magnetron sputtering at room temperature. The dependence of electrical, structural, and optical properties on the base pressure was investigated. The lower base pressures for AZO thin film deposition resulted in improved electrical conductivity owing to an increase in the carrier concentration and mobility, giving a resistivity as low as 7.3 × 10−4 Ω cm. The improved conductivity is attributed to increased ZnO bond formation and a subsequent increase in oxygen vacancies as the base pressure is reduced. The average transmittance of all the thin films deposited was above 84% in the visible spectrum. With decreasing base pressure, the figure of merit for the AZO thin film improved linearly. The control of base pressure plays a major role in the subsequent properties of AZO thin films deposited at room temperature.

► The formation of the OZn bonds was initially enhanced at the first decrease of the base pressure and then an oxygen deficiency was promoted at the second decrease.
► At the first decrease of the base pressure, the mobility increases owing to an improvement in crystallinity.
► At the second decrease, the carrier concentration is enhanced by an increase in oxygen vacancies.
► Both these mechanisms cause a reduction of the resistivity with a reduction in base pressure.