Ab initio study of oxygen-vacancy LaAlO₂(001) surface

Density functional theory is used to investigate the surface structures and the energies of two possible terminated LaAlO_3 (001) surfaces with oxygen vacancies, i.e. LaO- and AlO_2-terminated surfaces. The large displacements of ions, deviated from their crystalline sites, can lead to the formation of the surface rumpling. From thermodynamics analysis, the AlO_2-terminated surface with oxygen-vacancies is less stable than the LaO-terminated one. Some states in the gap lie under the Fermi level by about --1eV in the LaO-terminated surface with oxygen vacancies. For the AlO_2-terminated oxygen-vacancy surface, some O 2p states move into the mid-gap region and become partially unoccupied. The two types of termination surfaces exhibit conduction related to oxygen vacancies. Our results can contribute to the application of LAO films to high dielectric constant materials.