Effect of annealing on defect formation in aluminum doped zinc oxide

Abstract

The transparent conductive aluminum-doped zinc oxide (AZO) attracts attention as an alternative for indium tin oxide. Still, it is unclear how different point defects affect its properties. Here, we explore which defects contribute to the conductivity of AZO nanospheres and how they can be tuned by solvolysis synthesis and annealing. Using a combination of NMR, Infrared and Raman spectroscopy, the occurrence and position of the Al dopant was determined in these samples. Moreover, the microwave cavity perturbation technique (MCPT) was used to qualitatively compare the conductivity of the powders. From the results of MCPT we can conclude that, a combination of annealingand prolonged refluxing leads to an increased conductivity. Also a significant rise of an NMR Knight Shift and a broad and intense FTIR band attributed to surface plasmon resonance, both indicate free charge carriers. This is in agreement with Raman spectra showing the presence of clusters of Zn interstitials in all samples. Our first-principles calculations corroborate these findings, that annealing of Al interstitials leads to the formation of zinc interstitials in combination with substitutional Al, which results in an increased conductivity in AZO.