Influence of Sc, Y, and B dopants on structural distortions and polarization switching in AlN-based ferroelectrics

Abstract

Doped aluminum nitride (AlN) ferroelectrics exhibit a unique combination of high coercive fields and large remanent polarization, offering strong potential for enabling high-performance ferroelectric memory devices. Common dopants such as Sc, Y, and B have been widely used, but how they affect structural distortion, spontaneous polarization, and the polarization switching process remains insufficiently studied. This motivates our comparative first-principles study of Sc-, Y-, and B-doped AlN. Structural stability analyses reveal that, as the doping level increases, Sc- and Y-doped systems tend to undergo a phase transition from the polar wurtzite phase to the non-polar hexagonal phase, accompanied by a reduction in spontaneous polarization. In contrast, B-doped systems maintain an increasing polarization across the doping range. Nudged Elastic Band (NEB) calculations uncover an individual polarization switching model mediated by a β-BeO-like intermediate phase, distinct from conventional collective switching models, and enable lower polarization switching barriers. Specifically, YxAl1−xN alloys exhibit lower polarization switching barriers than their Sc-doped counterparts at low doping concentrations (x), whereas Sc-doped systems become more favorable in terms of switching barrier at higher x. BxAl1−xN displays a significant change in switching barrier across doping concentrations. These results indicate that Sc and B doping enable tunable coercive fields through precise control of doping concentrations, whereas Y doping leads to more stable coercive fields across different concentration levels. The discovery of β-BeO-mediated switching deepens the understanding of wurtzite ferroelectric polarization mechanisms and provides strategic guidelines for designing III-nitride-based nonvolatile memory devices through targeted doping engineering.