Charge origin and localization at then-typeSrTiO3/LaAlO3interface

We report a first-principles study of ${\left({\text{LaAlO}}_3\right)}_m/{\left({\text{SrTiO}}_3\right)}_n$ heterostructures using density-functional theory at the $\text{LDA}+U$ level. Our results support the original explanation of Ohtomo and Hwang [Nature (London) 427, 423 (2004)] that the charge at the $n$-type interface may be due to electrostatic doping. The internal electric field in the ${\text{LaAlO}}_3$ layer is calculated to be $0.24\text{V}/\text{Å}$. Though it is not sufficient to cause the dielectric breakdown in a wide band-gap La aluminate, it causes charge transfer into the adjacent narrower gap ${\text{SrTiO}}_3$ layer. The quasi-two-dimensional nature of the charge distribution is caused by a combination of the crystal-field effect, pseudo-Jahn-Teller distortion, and interface chemistry. Our theoretical estimate suggests that the interfacial carrier density of about $2\times {10}^{13}{\text{cm}}^{-2}$ can be easily achieved.