Stability of nitrogen incorporated Al2O3 surfaces: Formation of AlN layers by oxygen desorption

The incorporation of nitrogen on Al2O3(0001) and (1 1 ̅ 02) surfaces is theoretically investigated on the basis of total-energy electronic-structure calculations within the density functional theory. The calculated surface energies as functions of oxygen and nitrogen chemical potentials reveal that under pregrowth conditions the O atoms of Al2O3 surfaces can be replaced by N atoms. Moreover, we find that the outermost O atoms tend to desorb from the surface and AlN layers are consequently formed on Al2O3 surfaces. This implies that the desorption of oxygen is crucial for the nitridation process. The structures of nitrogen incorporated Al2O3 surfaces obtained in the present study are consistent with those observed in the experiments.