Improved electrical properties of ZnO:Al transparent conducting oxide films using a substrate bias

Aluminium doped zinc oxide (ZnO:Al) films were deposited on glass substrate by DC magnetron sputtering from a ZnO target mixed with a various wt% Al2O3. The lowest resistivity of 8.54×10−4 Ω cm as well as over 90% of optical transmission of the ZnO:Al film was obtained with a 2 wt% Al2O3 doped ZnO target for the following processing conditions: substrate temperature of 400 ∘C; discharge power of 40 W; Ar pressure of 1 mtorr. In order to reduce the electrical resistivity, positive and negative biases (−60 V to +40 V) were applied to the substrate. We report the effects of substrate bias on the structure, deposition rate, electrical properties, and optical transmission of ZnO:Al thin films. Films deposited with either positive or negative bias have strong (002) preferred orientation. The electrical resistivity of the film decreases significantly as either the positive or negative bias increases. However, as the positive and the negative bias increases over 30 V and −40 V, the resistivity decreases. Films with electrical resistivity as low as 4.3×10−4 Ω cm and optical transmittance of 91.5% were obtained with a substrate bias of +30 V.