Native point defects in LaAlO3: A hybrid functional study

We investigate the electronic structure of defects in LaAlO3 (LAO) and their effects on electronic properties of bulk and heterostructures. Our calculations indicate that vacancies have lower formation energies than interstitials and antisites. The La vacancy (V-La) and the Al vacancy (V-Al) are deep acceptors, while the oxygen vacancy (VO) is a deep donor. The impact of these defects on the performance of metal-oxide-semiconductor devices is analyzed by placing the LAO band edges and defect levels with respect to the band edges of GaN, InGaAs, and Si. V-O introduces levels in the gap or in the vicinity of the semiconductor conduction band, resulting in carrier traps and/or leakage current through the gate oxide, while V-La and V-Al are sources of negative fixed charges. We also discuss how oxygen vacancies in LAO can influence the observed two-dimensional electron gas (2DEG) in LaAlO3/SrTiO3 heterostructures. We conclude that V-O in the LAO layer may provide electrons that fill compensating surface states, resulting in higher 2DEG densities, at least for modest LAO layer thicknesses.