Effects of oxygen concentration on the properties of Al-doped ZnO transparent conductive films deposited by pulsed DC magnetron sputtering

The effect of oxygen concentration on the properties of Al-doped ZnO (AZO) transparent conductive films has been investigated on the films deposited by pulsed DC magnetron sputtering using a cylindrical ZnO target containing 2 wt% Al. AZO films were deposited at 230 °C to the thickness of about 1000 nm and the oxygen concentration was controlled by varying the O2/Ar supply ratio from 0 to 0.167. With the increasing O2/Ar ratio, crystallinity of the AZO films deteriorated while the film surface became smooth. Accompanying this, electrical properties also deteriorated significantly. When the O2/Ar ratios were 0 and 0.033, the AZO films showed metallic conduction behavior with the electrical resistivity in the mid 10−4 Ω cm range. However, when the ratios were 0.100 and 0.167, the films showed poor electrical conduction behavior similar to semiconductors as deduced from the transmittance behavior. Spectroscopic analysis showed that such deteriorating properties are due to the formation of condensed oxide group through the reaction between excess oxygen and dopant aluminum.