Electronic structure of oxygen vacancy in Ta2O5

${\mathrm{Ta}}_2{\mathrm{O}}_5$ is a potential material for high dielectric constant insulators. The leakage current, however, should be reduced for application to 256 megabit dynamic random access memory. A state in the band gap induced by the oxygen vacancy is considered to lead to the leakage current. ${\mathrm{Ta}}_2{\mathrm{O}}_5$ was investigated theoretically in order to determine the effect of the oxygen vacancy. The calculated state originating from the oxygen vacancy is deeper than the experimentally obtained value. The strongly distorted local structure around the oxygen vacancy may give a shallow energy level, because the energy level of the vacancy state is shallower before structure optimization than after it.