The synchrotron x-ray absorption near edge structures (XANES) technique was used in conjunction with first-principles calculations to characterize Al-doped ZnO films. Standard characterizations revealed that the amount of carrier concentration and mobility depend on the growth conditions, i.e. ${\mathrm{H}}_2$ $(\mathrm{or}{\mathrm{O}}_2)/\mathrm{Ar}$ gas ratio and Al concentration. First-principles calculations showed that Al energetically prefers to substitute on the Zn site, forming a donor ${\mathrm{Al}}_{\mathrm{Zn}}$, over being an interstitial (${\mathrm{Al}}_i$). The measured Al $K$-edge XANES spectra are in good agreement with the simulated spectra of ${\mathrm{Al}}_{\mathrm{Zn}}$, indicating that the majority of Al atoms are substituting for Zn. The reduction in carrier concentration or mobility in some samples can be attributed to the ${\mathrm{Al}}_{\mathrm{Zn}}\mathrm{\text{−}}{V}_{\mathrm{Zn}}$ and $2{\mathrm{Al}}_{\mathrm{Zn}}\mathrm{\text{−}}{V}_{\mathrm{Zn}}$ complex formations that have similar XANES features. In addition, XANES of some samples showed additional features that are the indication of some $\alpha \mathrm{\text{−}}{\mathrm{Al}}_2{\mathrm{O}}_3$ or $n{\mathrm{Al}}_{\mathrm{Zn}}\mathrm{\text{−}}{\mathrm{O}}_i$ formation, explaining their poorer conductivity.

• Received 29 August 2012

DOI:https://doi.org/10.1103/PhysRevLett.110.055502