Study of the aluminum doping of zinc oxide films prepared by atomic layer deposition at low temperature

This study presents the effect of purge pulses conditions on the electrical and optical properties of zinc oxide films doped with aluminum and grown by ALD at low temperature (160 °C). Undoped ZnO films showed a clear improvement of the carrier concentration when purges were lengthened, which suggests that this purge lengthening causes a higher defect related doping. It was also showed that this purge lengthening leads to a further increase of the carrier concentration in the case of ZnO:Al films attributed to a better spatial repartition of the Al dopants in the film. The evolution of optical properties was also studied and compared to the electrical properties highlighting free carrier absorption and a Burstein–Moss shift. An abnormal modification of the optical properties was observed when the aluminum content in the film was increased.