H-related defect complexes in HfO2: A model for positive fixed charge defects

Based on first-principles theoretical calculations, we investigate the hydrogenation effect on the defect properties of oxygen vacancies (VO) in HfO2. A defect complex of VO and H behaves as a shallow donor for a wide range of Fermi levels, with a positive charge state, and this complex is energetically stable against its dissociation into VO and H. We suggest that the VO–H complex is responsible for the formation of positive fixed charges, which neutralize negative fixed charges during the postannealing process of SiOx/HfO2 stack.