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

: Wolff, Niklas; Fichter, Simon; Haas, Benedikt; Islam, Md Redwanul; Niekiel, Florian; Kessel, Maximilian; Ambacher, Oliver; Koch, Christoph; Wagner, Bernhard; Lofink, Fabian; Kienle, Lorenz


Journal of applied physics 129 (2021), No.3, Art. 034103, 10 pp.
ISSN: 0021-8979
ISSN: 1089-7550
Journal Article
Fraunhofer IAF ()
Fraunhofer ISIT ()

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).An isotropic 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 XRDpole figures reveal a Pitsch-Schrader type orientation relation between the Mo electrode and the AlScN film.