It was revealed from first-principles calculations that polarization-induced asymmetric distribution of oxygen vacancies played an important role in the insulating behavior at p-type LaAlO3/SrTiO3 interface. The formation energy of the oxygen vacancy (VO) was much smaller than that at the surface of the LaAlO3 overlayer, causing all the carriers to be compensated by the spontaneously formed VO at the interface. In contrast, at an n-type interface, the formation energy of VO was much higher than that at the surface, and the VO formed at the surface enhanced the carrier density at the interface. This explained the puzzle of why the p-type interface was always insulating but the n-type interface could be conducting.

Origin of Insulating Behavior of the P-Type LaAlO3/SrTiO3 Interface: Polarization-Induced Asymmetric Distribution of Oxygen Vacancies. L.Zhang, X.F.Zhou, H.T.Wang, J.J.Xu, J.Li, E.G.Wang, S.H.Wei: Physical Review B, 82[12], 125412