Optoelectronic properties of Al:ZnO: critical dosage for an optimal transparent conductive oxide

We study the effects of aluminum doping on the electronic and optical properties of ZnO, via density functional simulations. We discuss the bandstructure and absorption properties of Al:ZnO as a function of the dopant concentration, and compare with recent experimental data. Our results support the formation of a transparent conductive oxide compound up to an incorporation of Al of about 3% in substitutional Zn sites. We propose an explanation to the observed degradation of conductivity in terms of interstitial defects expected to occur at high doping concentrations, beyond the Al solubility limit.