Electronic, Transport, and Defect Properties of Low-Dimensional Ferroelectric Systems from First-Principles
Vitaly Alexandrov (Chemical and Biomolecular Engineering)
Recent advances in nanoscale manufacturing of oxide ferroelectric devices have spawned a great deal of fundamental research aimed to further enhance device functionality. The ferroelectric oxides such as perovskites have a broad range of applications, for instance, in ferroelectric-based memory technology owing to the polarization hysteresis effect. A particularly interesting area is ferroelectric field-effect transistors (FeFETs) in which a ferroelectric substrate used as a gate dielectric is coupled with other semiconductor materials such as graphene or molybdenum disulfide (MoS2). In these devices, the switching between the high (“ON”) and low (“OFF”) conductivity states of an ad-film can be achieved by tuning the polarization of a ferroelectric substrate through the application of a necessary gate voltage.
The control over field-induced polarization switching cannot be achieved without detailed understanding of the role of atomistic effects on polarization reversal such as interfacial (electro)-chemical reactions and structural defects in the bulk and at surfaces of a ferroelectric material. The degree to which various defects can affect ferroelectric properties and their role in mediating polarization switching are still not completely understood. For example, it is recognized that the migration of oxygen vacancies may contribute considerably to the leakage current even in the OFF state and the overall resistance degradation. On the other hand, it was recently demonstrated that point defects such as oxygen vacancies might play a key role in the emergence of room-temperature ferroelectricity at the scale of a few nanometers in otherwise non-ferroelectric SrTiO3 crystal or in the emergence of ferromagnetism at nonmagnetic ferroelectric PbTiO3 surfaces. In this proposal we aim to establish a better molecular-scale understanding of the relationship between ferroelectricity and crystal defects and how the interplay between polarization and interfacial properties impacts electronic behavior of ferroelectric-based heterostructures using first-principles density-functional-theory modeling.