Interface Energetics and Charge Carrier Density Amplification by Sn-Doping in LaAlO<sub>3</sub>/SrTiO<sub>3</sub> Heterostructure

Tailoring the two-dimensional electron gas (2DEG) at the <i>n</i>-type (TiO<sub>2</sub>)<sup>0</sup>/(LaO)<sup>+1</sup> interface between the polar LaAlO<sub>3</sub> (LAO) and nonpolar SrTiO<sub>3</sub> (STO) insulators can potentially provide desired functionalities for next-generation low-dimensional nanoelectronic devices. Here, we propose a new approach to tune the electronic and magnetic properties in the <i>n</i>-type LAO/STO heterostructure (HS) system via electron doping. In this work, we modeled four types of layer doped LAO/STO HS systems with Sn dopants at different cation sites and studied their electronic structures and interface energetics by using first-principles electronic structure calculations. We identified the thermodynamic stability conditions for each of the four proposed doped configurations with respect to the undoped LAO/STO interface. We further found that the Sn-doped LAO/STO HS system with Sn at Al site (Sn@Al) is energetically most favorable with respect to decohesion, thereby strengthening the interface, while the doped HS system with Sn at La site (Sn@La) exhibits the lowest interfacial cohesion. Moreover, our results indicate that all the Sn-doped LAO/STO HS systems exhibit the <i>n</i>-type conductivity with the typical 2DEG characteristics except the Sn@La doped HS system, which shows <i>p</i>-type conductivity. In the Sn@Al doped HS model, the Sn dopant exists as a Sn<sup>4+</sup> ion and introduces one additional electron into the HS system, leading to a higher charge carrier density and larger magnetic moment than that of all the other doped HS systems. An enhanced charge confinement of the 2DEG along the <i>c</i>-axis is also found in the Sn@Al doped HS system. We hence suggest that Sn@Al doping can be an effective way to enhance the electrical conduction and magnetic moment of the 2DEG in LAO/STO HS systems in an energetically favorable manner.