Atomic scale confirmation of ferroelectric polarization inversion in wurtzite-type AlScN

This work presents the first atomic scale evidence for ferroelectric polarization inversion on the unit cell level in a wurtzite-type material based on epitaxial Al0.75Sc0.25N thin films. The electric field induced formation of Al-polar inversion domains in the originally N-polar film is unambiguously determined by atomic resolution imaging using aberration-corrected scanning transmission electron microscopy (STEM). Anisotropic etching supports STEM results confirming a complete and homogenous polarization inversion at the film surface for the switched regions and the virtual absence of previous inversion domains in as-deposited regions. Local evidence of residual N-polar domains at the bottom electrode interface is observed and can be explained by both stress gradients and electric field deflection. The epitaxial relationship of the sapphire/AlN/Mo/AlScN multilayer stack is discussed in detail. Selected-area electron diffraction experiments and XRD pole figures reveal a Pitsch-Schrader type orientation relation between the Mo electrode and the AlScN film.

Automated summary

This study presents atomic-scale evidence for ferroelectric polarization inversion in a wurtzite-type material using epitaxial Al0.75Sc0.25N thin films. The electric field-induced formation of Al-polar inversion domains in the originally N-polar film is confirmed by atomic resolution imaging and anisotropic etching. The epitaxial relationship of the sapphire/AlN/Mo/AlScN multilayer stack is discussed with results from electron diffraction experiments and XRD pole figures.