Reconstruction of electrostatic field at the interface leads to formation of two-dimensional electron gas at multivalent (110) LaAl O3/SrTi O3 interfaces

The interfacial atomic arrangement, which is different from that in the bulk form of the heterojunction, can induce a reconstruction of electrostatic field at the interface. For conventional semiconductor heterointerfaces, it is known that such reconstruction results in band bending, creating a quantum well in which the two-dimensional electron gas (2DEG) is formed. In this article, we show that this mechanism still works in a multivalent oxide heterojunction: for (110)LaAlO3/SrTiO3 (LAO/STO) heterojunctions, the coexistence of La and Ti in ABO3 perovskite unit cells at the interface reduces the valence of Ti, generating a local field leading to band bending in the interfacial STO layers. The extra free electrons are trapped in this bent conduction band forming a 2DEG. It unifies two independent mechanisms for 2DEG at LAO/STO interfaces, the "polar catastrophe" model and the "La1-xSrxTiO3" layers model, and is expected to end the decade-old controversy. This study opens insight into atomic-scale band engineering to control the behavior of complex oxide heterojunctions.