Compensation in Al-Doped ZnO by Al-Related Acceptor Complexes: Synchrotron X-Ray Absorption Spectroscopy and Theory

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. H2 ðor O2Þ=Ar gas ratio and Al concentration. First-principles calculations showed that Al energetically prefers to substitute on the Zn site, forming a donor AlZn, over being an interstitial (Ali). The measured Al K-edge XANES spectra are in good agreement with the simulated spectra of AlZn, 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 AlZn-VZn and 2AlZn-VZn complex formations that have similar XANES features. In addition, XANES of some samples showed additional features that are the indication of some � -Al2O3 or nAlZn-Oi formation, explaining their poorer conductivity.