Spectroscopic properties of oxygen vacancies inLaAlO3

Abstract

Oxygen vacancies in LaAlO3 (LAO) play an important role in the formation of the two-dimensional electron gas observed at the LaAlO3/SrTiO3 interface and affect the performance of MOSFETs using LAO as a gate dielectric. However, their spectroscopic properties are still poorly understood, which hampers their experimental identification. Here we predict the absorption spectra and ESR parameters of oxygen vacancies in LAO using periodic and embedded cluster methods and density functional theory (DFT). The structure, charge distribution, and spectroscopic properties of the neutral and charged (1+ and 2+) oxygen vacancies in cubic and rhombohedral LaAlO3 are investigated. The highest intensity optical transitions [calculated using time-dependent DFT (TDDFT)], from the oxygen vacancy states to the conduction-band states have onsets at 3.5 and 4.2 eV for the neutral vacancy and 3.6 eV for the 1+ charged vacancy in rhombohedral LAO and 3.3 and 4.0 eV for the neutral vacancy and 3.4 eV for the 1+ charged vacancy in cubic LAO, respectively. Also reported are the isotropic g value (2.004026) and hyperfine coupling constants of the 1+ charged oxygen vacancy, which are compared to the experimental data obtained using electron spin resonance (ESR) spectroscopy, and accurately predict both the position and the width (3 mT) of its ESR signature. These results may further facilitate the experimental identification of oxygen vacancies in LAO and help to establish their role at the LAO/STO interfaces and in nanodevices using LAO.