It was recalled that N was known to reduce leakage currents and charge trapping in high-dielectric-constant gate oxides such as HfO2. It was shown that this occurred because N, substituting for O atoms next to O vacancy sites, repelled the occupied gap states due to the neutral and positively charged O vacancies out of the band gap into its conduction band. The state of the negatively charge vacancy was also repelled upwards but remained as a shallow gap state. This occurred because the vacancy became effectively positively charged; the adjacent Hf ions relaxed outwards from the vacancy and shifted its states upwards. This was shown using ab initio calculation methods which did not require an empirical correction to the band gap.

Passivation of Oxygen Vacancy States in HfO2 by Nitrogen. K.Xiong, J.Robertson, S.J.Clark: Journal of Applied Physics, 2006, 99[4], 044105 (4pp)