Aluminium nitride-based solid solutions, e.g., wurtzite-type (wz-) Al1-xScxN exhibit considerable potential for introducing ferroelectric functionality into novel transistor structures for high-frequency power conversion or integrated memory.[1,2] Although most of the challenges targeting the materials integration, e.g., temperature stability[3], thickness scaling[4] and epitaxy with GaN,[5] have been overcome over the past years, fundamental understanding of the ferroelectric switching mechanisms based on intrinsic domain structure examinations and their influence by the film’s microstructure properties, e.g., defects and interfaces is subject of thriving investigations. Our investigations by transmission electron microscopy showed the analog switching capabilities achieved in sub-5 nm thin films and demonstrated for the first time the realization of a multiple domain state within a single grain of AlScN linked to the presence of horizontal polarization discontinuities. [4] The control of these stable domain boundaries and its coupling with the film’s resistivity promise a potential approach to memristive memory. With this contribution we compare the identified nanoscale domain structures in epitaxial systems of Al1-xScxN/GaN produced by metal organic chemical vapor deposition, sputter deposition and molecular beam epitaxy and discuss possible atomic structures of the electric field induced domain walls driving ferroelectric switching. For example, we could evidence the stabilization of persistent M-polar domains after polarization switching to N-polarity (see Figure 1). Ferroelectric switching is dominantly driven by these initial domains since vertical domain wall movement requires less energy than forming new nucleation sites.

References
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[2] T. Mikolajick, S. Slesazeck, H. Mulaosmanovic, M. Park, S. Fichtner, P. Lomenzo, M. Hoffmann,
U. Schroeder, Journal of Applied Physics 2021, 129, 10.
[3] M. R. Islam, N. Wolff, M. Yassine, G. Sch¨onweger, B. Christian, H. Kohlstedt, O. Ambacher,
F. Lofink, L. Kienle, S. Fichtner, Applied Physics Letters 2021, 118, 23.
[4] G. Schönweger, N. Wolff, M. R. Islam, M. Gremmel, A. Petraru, L. Kienle, H. Kohlstedt, S. Ficht-
ner, Advanced Science 2023, 10, 25 2302296.
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H. Kohlstedt, S. Fichtner, Advanced Functional Materials 2022, 32, 21 2109632.