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.
Atomic scale confirmation of ferroelectric polarization inversion in wurtzite-type AlScN
Niklas Wolff, Simon Fichtner, Benedikt Haas, Md Redwanul Islam, Florian Niekiel, Maximilian Kessel, Oliver Ambacher, Christoph Koch, Bernhard Wagner, Fabian Lofink, Lorenz Kienle; Atomic scale confirmation of ferroelectric polarization inversion in wurtzite-type AlScN. J. Appl. Phys. 21 January 2021; 129 (3): 034103. https://doi.org/10.1063/5.0033205
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