Interface\nEnergetics and Charge Carrier Density Amplification by Sn-Doping in\nLaAlO₃/SrTiO₃ Heterostructure

Abstract

Tailoring\nthe two-dimensional electron gas (2DEG) at the <i>n</i>-type\n(TiO₂)⁰/(LaO)⁺¹ interface between\nthe polar LaAlO₃ (LAO) and nonpolar SrTiO₃ (STO)\ninsulators can potentially provide desired functionalities for next-generation\nlow-dimensional nanoelectronic devices. Here, we propose a new approach\nto tune the electronic and magnetic properties in the <i>n</i>-type LAO/STO heterostructure (HS) system via electron doping. In\nthis work, we modeled four types of layer doped LAO/STO HS systems\nwith Sn dopants at different cation sites and studied their electronic\nstructures and interface energetics by using first-principles electronic\nstructure calculations. We identified the thermodynamic stability\nconditions for each of the four proposed doped configurations with\nrespect to the undoped LAO/STO interface. We further found that the\nSn-doped LAO/STO HS system with Sn at Al site (Sn@Al) is energetically\nmost favorable with respect to decohesion, thereby strengthening the\ninterface, while the doped HS system with Sn at La site (Sn@La) exhibits\nthe lowest interfacial cohesion. Moreover, our results indicate that\nall the Sn-doped LAO/STO HS systems exhibit the <i>n</i>-type conductivity with the typical 2DEG characteristics except the\nSn@La doped HS system, which shows <i>p</i>-type conductivity.\nIn the Sn@Al doped HS model, the Sn dopant exists as a Sn⁴⁺ ion and introduces one additional electron into the HS system, leading\nto a higher charge carrier density and larger magnetic moment than\nthat of all the other doped HS systems. An enhanced charge confinement\nof the 2DEG along the <i>c</i>-axis is also found in the\nSn@Al doped HS system. We hence suggest that Sn@Al doping can be an\neffective way to enhance the electrical conduction and magnetic moment\nof the 2DEG in LAO/STO HS systems in an energetically favorable manner.