The interfacial trapped charge of quintuple-layers Al2O3 induced by point defect

For two-dimensional (2D) polar semiconductors with out-of-plane polarization, as the number of stacked layers increases, the electronic properties could change from single-layer semiconductor to multi-layer metal. The metallic characteristic manifests as the formation of 2D conductive electron and hole gas on the surfaces. In this study, we investigate the mechanism behind the formation of a two-dimensional electron gas (hole gas) on the surface and interlayer directional charge transfer process of polar quintuple-layers (QLs)-Al2O3 through first-principles calculations. The accumulated polarized electric field acts as the thermodynamic driving force for directional charge transfer between QL-Al2O3 layers, involving all Al and O atoms in the charge transfer process. However, the point defects in 2QLs-Al2O3, including different effective charge, significantly influence the dynamic process of directional interlayer charge transfer. The presence of unsaturated oxygen atoms at the interface contributes to the formation of interface trapped charges in 2QLs-Al2O3.