How ferroelectric BaTiO$_3$ can tune a two-dimensional electron gas at the interface of LaInO3 and BaSnO$_3$: a first-principles study

The emerging interest in two-dimensional electron gases (2DEGs), formed at interfaces between two insulating oxide perovskites poses crucial fundamental question in view of future electronic devices. In the framework of density-functional theory, we investigate the possibility to control the characteristics of the 2DEG formed at the LaInO$_3$/BaSnO$_3$ interface by including a ferroelectric BaTiO$_3$ layer. To do so, we examine how the orientation of the ferroelectric polarization impacts density and confinement of the 2DEG. We find that aligning the ferroelectric polarization toward (outward) the LaInO$_3$/BaSnO$_3$ interface leads to an accumulation (depletion) of the interfacial 2DEG. Varying its magnitude, we find a linear effect on the 2DEG charge density that is confined within the BaSnO$_3$ side. Analysis of the optimized geometries revels that inclusion of the BaTiO$_3$ block makes structural distortions at the LaInO$_3$/BaSnO$_3$ less pronounced, which, in turn, enhances the 2DEG density. Thicker ferroelectric layers allow for reaching higher polarization magnitudes. We discuss the mechanisms behind all these findings and rationalize how the characteristics of both 2DEG and 2D hole gases can be controlled in the considered heterostructures. Overall, our results can be generalized to other combinations of ferroelectric, polar, and nonpolar materials.