Pairing of cation vacancies and gap-state creation in TiO2 and HfO2

Abstract

Based on the first-principles calculations, the authors study defect-defect interactions between cation vacancies in rutile TiO2 and monoclinic HfO2. It is found that vacancies are greatly stabilized at small separations because of a large reconstruction of nearby oxygen atoms that have two broken bonds. As a result, O-O bonds resembling O2 or O 3 molecules are formed near the divacancy site. The defect levels originated from antibonding states of O p orbitals are identified within the energy gap, which can affect leakage currents and the density of trapped charges of oxides substantially. © 2007 American Institute of Physics