Proximity Ferroelectricity Driven by Mobile High-Miller-Index Domain Walls

TL;DR

This paper uncovers a new mechanism for ferroelectric switching in multilayered materials, driven by high-Miller-index domain walls that can migrate through undoped layers, explaining proximity ferroelectricity.

Contribution

It reveals that high-Miller-index domain walls facilitate low-field switching in multilayers, a process previously misunderstood, using first-principles and machine-learning simulations.

Findings

High-index domain walls can migrate with low barriers.

Dopants stabilize high-index walls and promote nucleation.

Mobile walls enable switching in thick undoped layers.

Abstract

Wurtzite ferroelectrics such as scandium-doped aluminum nitride (AlScN) are promising for next-generation memory because of their compatibility with semiconductor processes and strong spontaneous polarization. Ferroelectric switching in these materials is typically attributed to doping-induced softening of the bulk switching barrier. However, recent reports of proximity ferroelectricity, in which undoped AlN layers up to 500 nm thick fully switch in AlN/AlScN multilayers, challenge this view. Here, we reveal an alternative switching mechanism mediated by high-Miller-index domain walls, long overlooked due to their complex geometry and presumed instability. Using first-principles calculations and machine-learning molecular dynamics simulations, we show that these walls, once nucleated, migrate with exceptionally low barriers. The Sc dopants play a dual role: they stabilize high-index walls and thereby promote nucleation, while also introducing pinning that hinders wall motion. In multilayers, our simulations demonstrate that mobile domain walls nucleated in AlScN can propagate deep into adjacent AlN, where they move easily without dopant pinning, enabling low-field switching across thick undoped layers. This microscopic divide-and-conquer mechanism resolves the puzzle of proximity ferroelectricity and highlights high-index interfaces as an underexplored lever for controlling ferroelectric switching.