First-Principles Study on Intrinsic Point Defects in Rhombohedral LaAlO3 and Their Effects on Electrical Properties

Abstract

Formation energies and energy levels of various neutral and charged defects in bulk rhombohedral LaAlO3 are calculated numerically in different equilibrium conditions under different oxygen partial pressures, using first-principles plane-wave calculations. The roles of such defects in electrical properties of LaAlO3 are also discussed. The results obtained by calculations show that the formation energy becomes low for oxygen interstitial if LaAlO3 is in an oxygen-rich condition. In contrast, an oxygen vacancy is easily formed in a condition where oxygen is deficient and metal elements are relatively rich, even if the oxygen partial pressure is high. These results explain well the concentration change of constituent elements in LaAlO3 under different treatment atmospheres. Furthermore, the calculations can interpret a large tunnelling current that is often observed in a metal–oxide–silicon structure using LaAlO3 as the oxide layer, since the O vacancy has an energy level near the valence band maximum of Si.