Abstract
Wurtzite ferroelectrics have transformative potential for next-generation microelectronics. A comprehensive understanding of their ferroelectric properties and domain energetics is crucial for tailoring their ferroelectric characteristics and exploiting their functional properties in practical devices. Despite burgeoning interest, the exact configurations and electronic structures of domain walls in wurtzite ferroelectrics remain elusive. Here we explain the atomic configurations and electronic properties of electric-field-induced domain walls in ferroelectric ScGaN. By combining transmission electron microscopy and theoretical calculations, a charged domain wall with a buckled two-dimensional hexagonal phase is revealed. Density functional theory calculations confirm that such domain-wall structures further give rise to unprecedented mid-gap states within the forbidden band. Quantitative analysis unveils a universal charge-compensation mechanism stabilizing antipolar domain walls in ferroelectric materials, in which the polarization discontinuity at the 180° domain wall is compensated by the unbonded valence electrons. Furthermore, the reconfigurable conductivity of these domain walls is experimentally demonstrated, showcasing their potential for ultrascaled device applications.
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Data availability
The datasets generated and/or analysed during the current study in the main text are available at the University of Michigan (https://doi.org/10.7302/1awc-qa67). The datasets generated and/or analysed during the current study in the Extended Data items are available from the corresponding authors.
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Acknowledgements
This experiment work is supported by the National Science Foundation under grant no. 2235377, Army Research Office grant nos. W911NF2420210 and W911NF2220176, and College of Engineering at the University of Michigan. The theoretical calculations work at the University of Michigan was supported by the National Science Foundation under grant no. 2328701 and is supported in part by funds from federal agency and industry partners as specified in the Future of Semiconductors (FuSe) programme. S. Yuan and H.G. gratefully acknowledge financial support from the Natural Science and Engineering Research Council (NSERC) of Canada and support from the Digital Research Alliance of Canada and the High-Performance Computing Center of McGill University for the computing facilities. We also acknowledge the technical support from the Lurie Nanofabrication Facility (LNF) and the Michigan Center for Materials Characterization [(MC)2] at the University of Michigan. Computational resources are provided by the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the US Department of Energy under contract no. DE-AC02-05CH11231.
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Z.M. conceived the idea. Ding Wang and Danhao Wang performed the molecular beam epitaxy growth, device fabrication and ferroelectric measurements. Ding Wang, Danhao Wang, S. Yang, J.L., M.H. and Y.W. collected data and performed the material characterization. Ding Wang, Danhao Wang, S. Yang, K.S. and T.M. carried out the transmission electron microscopy characterization and analysis. M.M., Y.L., S. Yuan, H.G. and E.K. conducted and discussed the theoretical calculations. Ding Wang, Danhao Wang, S. Yang, K.S., M.M., Y.L., S. Yuan, H.G., E.K. and Z.M. discussed the data analysis. Ding Wang, Danhao Wang and Z.M. wrote the initial draft of the manuscript, which was then revised by the other co-authors. All authors have given approval for the final version of the manuscript.
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Extended data figures and tables
Extended Data Fig. 1 Microstructure of as-grown ScGaN on GaN template.
a, Schematic of the sample structure. b, Cross-sectional STEM image and corresponding elemental map, indicating uniform elemental distribution. Scale bar, 50 nm. c, The wurtzite lattice group of the ScGaN layer is further evidenced by the nanobeam electron diffraction patterns. d, High-resolution STEM images of as-grown ScGaN on GaN. Magnified images with HAADF and iDPC contrast (scale bar, 1 nm) are taken from different regions in the heterostructure as indicated in the low-magnification STEM image on the left (scale bar, 20 nm), showing uniform metal polarity in the ScGaN film before ferroelectric switching. This further supports that the N-polar regions in switched capacitors result from electric-field-induced polarity switching rather than being attributable to localized defects inherent to the material.
Extended Data Fig. 2 Ferroelectric switching in metal/ScGaN/n-GaN capacitors.
a, Schematic of the device structure. b, Optical microscope image of the fabricated capacitors. Scale bar, 50 μm. Highly doped n-GaN serves as the bottom electrode, with a metal stack functioning as the top electrode. I–V (c) and P–V (d) loops of the capacitor using triangular voltage profiles at 10 Hz and 2.5 kHz, respectively, at room temperature. Displacement current peaks can be observed in both directions. Non-switching currents have been subtracted to better show the hysteresis loop in d. e, PUND measurement results using triangular voltage pulses with a pulse width of 80 μs, suggesting a remanent polarization of about 129 μC cm−2 (ascertained by averaging the Pr value at 39 V). Arrows in the figures highlight the polarization direction of the ScGaN layer before and after electrical switching. f, Exemplary pulse transients using trapezoidal voltage pulses to better show the displacement current. g, PFM amplitude and phase hysteresis loops of ScGaN. A clear butterfly-shaped amplitude diagram and a box-shaped phase diagram with approximately 180° separations can be observed, showing clear ferroelectric polarization switching under external biasing. h, PFM phase and amplitude maps after poling the capacitor (circular regions) with different voltages. The electrodes are removed using HF before PFM measurements. Scale bars, 10 μm. During measurements, the tip frequency is 15 kHz and VAC is 10 V applied to the tip.
Extended Data Fig. 4 Metal plane displacement across VDWs and the proposed VDW structure viewed along different projections.
a, High-magnification HAADF-STEM image of the electric-field-induced VDW in ScGaN. The auxiliary lines in the figure trace the centre of each metal atom column. The position of the centre is obtained from 2D Gaussian fitting. A shift in the metal planes while crossing a VDW is evident. b, The proposed VDW structure viewed along different projections. The structure maintains the sixfold rotational symmetry of the host wurtzite material and satisfies the symmetry requirement on the manifestation of alternate domain and domain-wall projections at regular 60° intervals when observed from a consistent viewing angle. The in-plane distances of the metal atoms within the domain wall and bulk ScGaN from DFT calculations are indicated, showing the in-plane lattice expansion at the VDW.
Extended Data Fig. 5 Zigzag feature of the metal atoms across HDWs and the proposed HDW structure viewed along different projections.
a, High-resolution HAADF-STEM images of the electric-field-induced HDW in ScGaN. The auxiliary lines in the figure trace the centre of each metal atom column. The position of the centre is obtained from 2D Gaussian fitting. b, The proposed HDW structure viewed along different projections. The structure maintains the zigzag fashion and sixfold rotational symmetry of the host wurtzite material and satisfies the symmetry requirement on the manifestation of alternate domain and domain-wall projections at regular 60° intervals when observed from a consistent viewing angle. The out-of-plane distances of the metal/nitrogen atoms in the domain wall and bulk ScGaN from DFT calculations are presented, showing the out-of-plane lattice expansion at the HDW.
Extended Data Fig. 6 Atom intensity profile across the HDW.
a, dDPC-STEM image of the HDW region. b, Schematics showing the reduced intensities of N atoms in individual tetrahedrons within the HDW compared with the M-polar and N-polar regions. c, Atom intensity profiles across the HDW. In c, the N-atom intensity profiles are obtained using circular masks to isolate the N atoms in the image, whereas the M-atom intensity profiles are derived from the corresponding HAADF-STEM image. The green box in a indicates the region from which the intensity profiles were taken. We acknowledge that the STEM images only provide indirect evidence for the existence of dangling bonds, as the observed reduction of N-atom intensity may be affected by other factors.
Extended Data Fig. 7 Ab initio molecular dynamics calculations.
The proposed atomic configuration is proved to be an energetically favourable structure for head-to-head HDWs in wurtzite ferroelectrics. A canonical (NVT) ensemble with a Nosé–Hoover thermostat at 300 K was applied to simulate the atomic relaxation process. A hexagonal planar ScGaN layer was placed between the N-polar and M-polar interfaces as the initial configuration, mimicking the interface state after switching through a layered-hexagonal intermediate.
Extended Data Fig. 8 Demonstration of buckled hexagonal phase, dangling bonds in the HDW and schematic of the charge-compensation mechanism.
a, Calculated structural model of the HDW structure with dangling bonds. Note that these representations primarily showcase the presence of dangling bonds on the atoms. The specific orientations of these bonds, as depicted, are illustrative in nature and do not imply any physical meaning. b, Structural comparison of 2H MoS2 and the proposed HDW model. Both 2H MoS2 and HDWs in ScGaN exhibit a trigonal prism atomic configuration. However, a distinctive feature of ScGaN HDWs is that only half of the vertices are occupied, coupled with the presence of one dangling bond at each metal site. c, Fully relaxed DFT model of the HDW region. Considering the symmetry of the wurtzite structure, polarization reversal and the coexistence of both polarizations inevitably involve the breaking and reformation of M–N bonds along the [0001] direction. This stable structure maintains the same atomic stoichiometry as pure M-polar or N-polar phases, with no increase or decrease in atomic count. In the adjacent layers 1 and 3, M atoms retain the lattice positions of N-polar (a,e) and M-polar (b,f), respectively. However, in the domain wall layer (layer 2), the positions of M and N atoms are rearranged, with some atoms aligning with the M-polar lattice (c,h) and others with the N-polar lattice (d,g). Owing to the rearrangement of N atoms in layer 2, certain metal atoms in layers 1 and 3 (a,b) are unable to find corresponding N atoms for bonding at symmetric positions (indicated by blue dashed circles), resulting in extra unbonded valence electrons on these atoms. Furthermore, owing to the rearrangement of Ga atoms in layer 2, some metal atoms (c,d) are also unable to find corresponding N atoms for bonding in symmetric positions (blue dashed line circles), leading to unbonded valence electrons on these atoms. These unbonded electrons exist as unbonded valence electrons in the unbonded orbitals of M atoms, consistent with the formation of dangling bonds owing to symmetry break at crystal surfaces. d, Schematic of the charge-compensation mechanism in nitride ferroelectrics. In this head-to-head polarization configuration, bound charges within the domain-wall region are positive. These bound charges are effectively compensated by the unbonded valence electrons.
Extended Data Fig. 9 Polarization estimation in tetrahedral ferroelectrics.
Blue atoms are anions and the red atom represents the cation. The estimated charge transfer, atom displacement and resultant polarization, referencing the planar-hexagonal boron-nitride-like structure, are indicated.
Extended Data Fig. 10 Reconfigurable conductive domain walls in ScGaN.
a, Displacement current measurement results for 50-nm ScGaN capacitors. b–d, AFM, PFM and c-AFM measurement results, showcasing the formation and erasure of voltage-dependent conductive domain walls near the edge of electrodes. e,f, Multicycle write/erase operations of conductive domain walls near the electrode edge. The ability to continuously write and erase these conductive channels and antipolar domains confirms the reconfigurability of the domain walls. The voltage profiles for each device are shown in e.
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Wang, D., Wang, D., Molla, M. et al. Electric-field-induced domain walls in wurtzite ferroelectrics. Nature 641, 76–82 (2025). https://doi.org/10.1038/s41586-025-08812-7
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DOI: https://doi.org/10.1038/s41586-025-08812-7
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