First-principles study on intrinsic point defects in rhombohedral LaAlO ₃ and their effects on electrical properties

Formation energies and energy levels of various neutral and charged defects in bulk rhombohedral LaAlO ₃ 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 LaAlO ₃ are also discussed. The results obtained by calculations show that the formation energy becomes low for oxygen interstitial if LaAlO ₃ 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 LaAlO ₃ under different treatment atmospheres. Furthermore, the calculations can interpret a large tunnelling current that is often observed in a metal-oxide-silicon structure using LaAlO ₃ as the oxide layer, since the O vacancy has an energy level near the valence band maximum of Si.