A ZnO:Al target was sputtered concurrently with additional Zn or Al, by co-sputtering it with either a Zn or an Al target. The influence of the deposition of these additional atoms on the ZnO:Al film properties was investigated. When co-sputtering the Zn target, the film resistivity shows a minimum for an adequate supply of Zn. With this supply of Zn, both the carrier concentration and the Hall mobility show maxima, and the optical transmittance and absorption edge are improved. When co-sputtering with the Al target, the carrier concentration alone is increased. These results indicate that there is a considerable Zn deficiency in the ZnO:Al films prepared in pure Ar gas, and additional Zn or Al atoms during film deposition can compensate for these Zn defects, in addition to the increased donor concentration in the film.