Charge origin and localization at the n-type SrTiO3/LaAlO3 interface

We report a first-principles study of (LaAlO3)(m)/(SrTiO3)(n) heterostructures using density-functional theory at the 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 LaAlO3 layer is calculated to be 0.24 V/A. 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 SrTiO3 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 2x10(13) cm(-2) can be easily achieved.