Domain walls in wurtzite ferroelectrics

Abstract

A device includes a substrate, a ferroelectric structure supported by the substrate, the ferroelectric structure having a wurtzite crystal structure, a switchable conduction path in the ferroelectric structure, the switchable conduction path being disposed along a lateral domain all in the ferroelectric structure, the lateral domain wall defining a first portion of the ferroelectric structure and a second portion of the ferroelectric structure having a first polarity and a second polarity, respectively, and an electrode disposed relative to the ferroelectric structure such that a voltage applied to the electrode establishes or removes the lateral domain wall and the switchable conduction path in the ferroelectric structure.

Description

DOMAIN WALLS IN WURTZITE FERROELECTRICSCROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisional application entitled “Domain Walls in Wurtzite Ferroelectrics,” filed December 11 , 2023, and assigned Serial No. 63 / 608,812, and the benefit of U.S. provisional application entitled “Domain Walls in Wurtzite Ferroelectrics,” filed February 19, 2024, and assigned Serial No. 63 / 555,305, the entire disclosures of which are hereby expressly incorporated by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under Contracts Nos. 2235377 and 2329109 awarded by the National Science Foundation. The government has certain rights in the invention.BACKGROUND OF THE DISCLOSUREField of the Disclosure

[0003] The disclosure relates generally to ferroelectric wurtzite materials.Brief Description of Related Technology

[0004] The recent discovery of ferroelectricity in wurtzite nitride semiconductors has sparked renewed interest in the electronics and photonics community. This new class of ferroelectrics, including ScAIN, BAIN, ScGaN, and YAIN, yields superior properties, including low dielectric constants, thickness scaling to nanometer dimensions, tunable coercive fields (Ec), high remnant polarizations (Pr), and superior thermal stability. These characteristics position the new class of ferroelectrics as useful in modern microelectronics, from high-frequency resonators to advanced memory and computing architectures, while seamlessly integrating with mainstream semiconductor platforms.

[0005] Fully harnessing the capabilities of the new ferroelectrics and meeting the rigorous demands of modern electronics calls for refining critical parameters such as coercivity, endurance, stability, and leakage. This demands foundational understanding beyond indirect macroscopic methods to unravel the underlying physics of ferroelectric interfaces at the unit cell level. Recently, researchers have explored the transient polarity reversal process in ferroelectric AI0.94B0.06N triggered by prolonged electron beam exposure in transmission electron microscopy (TEM). However, the polarity switching mechanism under the influence of an external electric field, which is involved in the operation of ferroelectric devices and occurs on a much shorter time scale, may be entirely different. To date, the intrinsic switching dynamics and domain energetics under realistic device operating conditions have remained elusive for the emerging class of wurtzite ferroelectric nitrides.SUMMARY OF THE DISCLOSURE

[0006] In accordance with one aspect of the disclosure, a device includes a substrate, a ferroelectric structure supported by the substrate, the ferroelectric structure having a wurtzite crystal structure, a switchable conduction path in the ferroelectric structure, the switchable conduction path being disposed along a lateral domain wall in the ferroelectric structure, the lateral domain wall defining a first portion of the ferroelectric structure and a second portion of the ferroelectric structure having a first polarity and a second polarity, respectively, and an electrode disposed relative to the ferroelectric structure such that a voltage applied to the electrode establishes or removes the lateral domain wall and the switchable conduction path in the ferroelectric structure.

[0007] In accordance with another aspect of the disclosure, a method of fabricating a device includes forming a ferroelectric structure supported by a substrate, the ferroelectric structure including a wurtzite crystal structure, forming a temporary electrode supported by the ferroelectric structure, applying a poling voltage to the temporary electrode to establish a lateral domain wall in the ferroelectric structure, the lateral domain wall defining a first portion of the ferroelectric structure and a second portion of the ferroelectric structure having a first polarity and a second polarity, respectively, removing the temporary electrode after applying the voltage, and forming first and second terminals of the device, the first and second terminals being electrically coupled to one another via the lateral domain wall.

[0008] In accordance with yet another aspect of the disclosure, a device includes a substrate, first and second electrode layers supported by the substrate, a ferroelectric structure disposed between the first and second electrode layers, the ferroelectric structure having a wurtzite crystal structure, and a switchable conduction path in the ferroelectric structure, the switchable conduction path being disposed along a domain wall in the ferroelectric structure, the domain wall defining a first portion of the ferroelectric structure and a second portion of the ferroelectric structure having a first polarity and a second polarity, respectively. The ferroelectric structure and the first electrode extend laterally beyond the second electrode such that a voltage applied between the first and second electrodes establishes a position of the domain wall.

[0009] In connection with any one of the aforementioned aspects, the devices and / or methods described herein may alternatively or additionally include or involve any combination of one or more of the following aspects or features, the lateral domain wall has a triangular atomic configuration. The ferroelectric structure includes a wurtzite semiconductor. The lateral domain wall includes a buckled hexagonal phase of the wurtzite semiconductor. The lateral domain wall has an atomic-scale thickness. The lateral domain wall has a single-digit number of monolayers. The device further includes a pair of terminals supported by the substrate, the pair of terminals being electrically coupled via the switchable conduction path. The device further includes a first terminal supported by the substrate. The electrode is configured as a second terminal. The first and second terminals are electrically coupled via the switchable conduction path. The first and second terminals are disposed in different layers such that the switchable conduction path extends both laterally and non-laterally. The device further includes a source electrode and a drain electrode, the source and drain electrodes being supported by the substrate and electrically coupled via the switchable conduction path. The switchable conduction path is configured as a transistor channel. The lateral domain wall includes a transition region between the first polarity and the second polarity. The ferroelectric structure includes a Ill-nitride alloy. The lateral domain wall has partial nitrogen site occupancy. The lateral domain wall has partial metal site occupancy. The lateral domain wall exhibits six-fold rotational symmetry. The first polarity and the second polarity are metal polarity and nitrogen polarity, respectively, and the first portion of the ferroelectric structure is adjacent the electrode. The first polarity and the second polarity are nitrogen polarity and metal polarity, respectively, and the first portion of the ferroelectric structure is adjacent the electrode. The device further includes a base layer supported by the substrate, the voltage being applied between the electrode and the base layer. The base layer includes a Ill-nitride semiconductor. The baselayer includes silicon, silicon carbide, aluminum, or molybdenum. Layouts of the electrode and the base layer do not match such that the lateral domain wall has a vertical component extending from the electrode to the base layer and an electric field controllable inclination based on a level of the voltage. A method of operating a device as described herein includes applying a first voltage to modulate a characteristic of the switchable conduction path, and applying a second voltage to remove the lateral domain wall. The characteristic is a charge distribution at the lateral domain wall. The method further includes forming a base layer supported by the substrate, the base layer being disposed between the substrate and the ferroelectric structure. The ferroelectric structure includes a Ill-nitride alloy. The Ill-nitride alloy in the lateral domain wall has a buckled hexagonal phase. The first electrode includes a doped Ill-nitride semiconductor. The ferroelectric structure includes ScGaN.BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0010] For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawing figures, in which like reference numerals identify like elements in the figures.

[0011] Figure 1 depicts atomic evidence of polarity switching in a metal / wurtzite ferroelectric / semiconductor (metal / ScGaN / GaN) capacitor in accordance with one example, including (A) a schematic view of polarity switching in the example capacitor, (B) a cross- sectional TEM overview of the example capacitor, and (C) a schematic illustration of the example metal / ScGaN / GaN capacitor, (D) a high resolution HAADF-STEM and iDPC images captured near the ScGaN / GaN interface, in which the atomic arrangement is indicated by blue (nitrogen atoms) and red (metal atoms) spheres, and (E-G) magnified images captured in different regions of ferroelectric layer of the example capacitor, in which N-polar regions are clearly observed from above the transition region to the top surface of ScGaN, confirming homogenous switching (scale bars: (B) 20 nm; (D) 2 nm; (E-G) 1 nm).

[0012] Figure 2 depicts an electric-field-induced vertical domain wall in a ferroelectric (ScGaN) structure, including (A) a schematic view of the ferroelectric structure, (B) an atomic model of the vertical domain wall, with atoms represented by spheres (red for metal, blue for nitrogen), (C) a high magnification HAADF-STEM image of the ferroelectric structure, (D) corresponding in-plane distance mapping of the vertical domain wall, (E) high magnification iDPC-STEM images of the ferroelectric structure, (F) corresponding dumbbell angle mapping for the sameregion shown in parts (C) and (D) (scale bar for parts (C-F): 1 nm), (G) a high-resolution dDPC image of the vertical domain wall structure, (H) a graphical plot of the intensity profile of the selected region in the dDPC-STEM image shown in part (G), (I) average atomic distances in the dimer pattern in the vertical domain wall structure, and (J) a DFT model of the vertical domain wall structure viewed along different projections, in which the average atomic distances are labeled in comparison with part (I).

[0013] Figure 3 depicts an electric-field-induced horizontal (or lateral) domain wall in a ferroelectric (ScGaN) structure, including (A) a schematic view of the ferroelectric structure, (B) an atomic model of the horizontal domain wall, with atoms represented by spheres (red for metal, blue for nitrogen), (C) a high magnification HAADF-STEM image of the ferroelectric structure, (D) corresponding out-of-plane distance mapping of horizontal domain wall in the of the ferroelectric structure, (E) a high magnification iDPC image of the ferroelectric structure, (F) corresponding dumbbell angle mapping for the same region shown in parts (C) and D) (scale bar for parts (C-F): 1 nm), (G) a high resolution dDPC image of the horizontal domain wall structure, (H) a graphical plot of the intensity profile of the selected area in the dDPC-STEM image in part (G), (I) average atomic distances in the triangular configurations in the horizontal domain wall structure, (J) a DFT model of the horizontal domain wall structure viewed along

[1120] , in which the average atomic distances are labeled in comparison with part (I), and (K) a graphical plot comparing the electronic density of states of the horizontal domain wall structure with bulk ScGaN, demonstrating the appearance of partially occupied dangling bond states within the bandgap, with the inset showing the charge density of the mid-gap dangling bond states.

[0014] Figure 4 depicts schematic views of a device having a ferroelectric structure with a lateral domain wall-based switchable conduction path before and after poling voltage application in accordance with one example.

[0015] Figure 5 depicts schematic views of a transistor device having a ferroelectric structure with a lateral domain wall-based switchable conduction path before and after large gate voltage application in accordance with one example.

[0016] Figure 6 depicts a method of fabricating a device having a ferroelectric structure with a lateral domain wall-based switchable conduction path in accordance with one example.

[0017] Figure 7 depicts a method of operating a device having a ferroelectric structure with a lateral domain wall-based switchable conduction path in accordance with one example.

[0018] Figure 8 depicts a schematic view of a device having a ferroelectric structure with a lateral domain wall-based switchable conduction path in accordance with one example.

[0019] Figure 9 depicts example devices having an electric field controllable conductive domain wall, including (A) a schematic view of inclined domain walls generated near a top electrode edge, (B, C) schematic views of simulations of vertical electric field distributions under different voltages, (D-G) representations of AFM, PFM and CAFM measurements over four regions with different poling conditions, and (H-K) graphical plots of current line profiles across the electrode regions, extracted from CAFM maps by averaging 20 horizontal pixels, along with schematic views of the corresponding device configurations.

[0020] The embodiments of the disclosed devices and methods may assume various forms. Specific embodiments are illustrated in the drawing and hereafter described with the understanding that the disclosure is intended to be illustrative. The disclosure is not intended to limit the invention to the specific embodiments described and illustrated herein.DETAILED DESCRIPTION OF THE DISCLOSURE

[0021] Devices having a wurtzite ferroelectric structure with a switchable conduction path are described. The switchable conduction paths of the disclosed devices are based on atomic- scale polarity switching in the wurtzite ferroelectric structure. Examples of the polarity switching involve an electric-field-induced domain wall (e.g., lateral domain wall) in a monocrystalline wurtzite ferroelectric structure. In some cases, the domain wall and corresponding switchable conduction path are configured as a channel of a transistor device. Methods for fabricating and operating such devices are also described.

[0022] The disclosed devices and methods are based upon a fundamental understanding of the intricate microstructures within the ferroelectric structures thereof at the atomic scale. Such understanding is useful for addressing the contemporary challenges in wurtzite ferroelectrics, but also for use and application of wurtzite ferroelectrics in domain wall-based electronics. The quasi-two-dimensional nature of domain walls, coupled with their distinct symmetry and local chemical composition, enable a wide variety of unconventional electric, magnetic, and optical properties, offering a useful path for next-generation nanoelectronics such as domain-wallmemory and ferroelectric field-effect transistors. Accordingly, set forth herein are details regarding domain walls in wurtzite ferroelectrics, and the application thereof in the disclosed devices and methods.

[0023] The examples described below provide a detailed investigation of the intricate interface microstructures and ferroelectric domain walls in Sc-I I l-nitride heterostructures by combining sub-angstrom resolution scanning transmission electron microscopy (STEM) and density functional theory (DFT) calculations. The fully epitaxial and monocrystalline nature of ScGaN grown by molecular beam epitaxy (MBE) enables direct atomic-scale observations of localized polar order within the wurtzite lattice. Harnessing the robust ferroelectric properties of ScGaN, sub-nanometer “side-by-side” vertical domain walls with antiparallel polarization were successfully created via an external electric field. Electric-field-induced “head-to-head” horizontal domain walls (HDWs or "lateral domain walls") were also created. As described below, the lateral domain walls, being only a few monolayers in thickness and featuring a large number of metal dangling bonds, reveal a unique a buckled 2D hexagonal nitride phase with unprecedented metallic mid-gap states. A quantitative comparison of the charges carried by the dangling bonds to the bound polarization charge further reveals a universal chargecompensation mechanism in wurtzite ferroelectrics. Building on these features, example devices having reconfigurable conductive domain walls in nitride ferroelectrics are described and experimentally demonstrated through conductive atomic force microscopy (CAFM). These and other examples described herein provide further details regarding useful applications of the ferroelectric switching process and domain wall energetics in wurtzite ferroelectrics. Such applications include a wide variety of nitride domain-wall-based nanodevices.

[0024] As described herein, the domain walls of the disclosed devices may be charged (e.g., charged horizontal or other lateral domain walls) and exhibiting a distinctive buckled 2D hexagonal phase. The high density of dangling bonds in this charged domain wall give rise to unprecedented and unexpected metallic-like mid-gap states within the forbidden band. The quantitative analysis presented herein reveals that the geometry of the charged domain wall enables near-complete compensation of the 180° polarization discontinuity by the charge of the dangling-bond electrons. This aspect of the disclosed devices involves a universal chargecompensation mechanism that may be applied in a wide variety of wurtzite ferroelectric devices. Furthermore, the reconfigurability of these domain walls provides yet additional utility in various device applications.

[0025] Described herein are examples of devices with ferroelectric structures configured and utilized in accordance with an atomic-level understanding of the switching mechanisms and domain energetics of wurtzite ferroelectrics. By combining scanning transmission electron microscopy and density functional theory, sub-nanometer electric-field-induced domain walls were revealed in an example wurtzite ferroelectric (ScGaN) structure. Vertical domain walls with side-by-side antiparallel polarization and horizontal (or lateral) domain walls featuring a “2H MoS2-like” configuration or buckled 2D hexagonal phase are shown and described. As described below, the lateral domain walls may have a sub-nanometer dimension or size. The configuration of the lateral domain walls exhibits a buckled hexagonal phase with large polarization discontinuity and rich dangling bonds, offering a useful platform for domain wallbased electronic devices. The detailed understanding of ferroelectric domain switching in wurtzite ferroelectric materials supports a wide variety of device applications.

[0026] While both 2H M0S2 and the lateral domain walls described herein (e.g., in ScGaN) exhibit a trigonal prism atomic configuration, a distinctive feature of the lateral domain walls described herein is that only half of the vertices are occupied, coupled with the presence of one dangling bond at each metal site. Furthermore, the lateral domain wall structures described herein maintain the six-fold rotational symmetry of the host wurtzite material and satisfy the symmetry requirement on the manifestation of alternate domain and domain wall projections at regular 60-degree intervals when observed from a consistent viewing angle.

[0027] Although described in connection with capacitor and transistor devices, the disclosed methods and devices may be applied to a wide variety of devices, including, for instance, tunnel junctions, ferroelectric diodes, non-volatile memory devices, phase change memory devices, etc.

[0028] Although described in connection with examples of epitaxially grown ScGaN ferroelectric structures, the disclosed methods and devices may be applied to a wide variety of Ill-nitride alloys and other wurtzite materials. The disclosed methods and devices may thus include or involve the incorporation of scandium into other Ill-nitride wurtzite structures. For instance, the disclosed methods and devices may include or involve one or more epitaxially grown ScxAli-xN structures, ScxAlyGai-x-yN structures, or Scxlni.xN structures. Still other wurtzite ferroelectric materials may be used, including, for instance, YAIN, AIBN, YGaN, ZnMgO, etc.

[0029] The configuration, construction, fabrication, and other characteristics of the heterostructures (and ferroelectric structures thereof) may also vary from the examplesdescribed. For instance, the heterostructures may include any number of epitaxially grown segments of ferroelectric and non-ferroelectric nature.

[0030] The disclosed methods and devices are not limited to Ill-nitride alloys including scandium. For instance, the Ill-nitride alloys may include additional or alternative group II IB elements, such as yttrium (Y) and lanthanum (La).

[0031] Although described in connection with examples having a base or template segment composed of GaN, the heterostructures of the disclosed devices may include alternative or additional Ill-nitride semiconductor segments as a template, base, intermediate, or other structure or layer. Additional or alternative types of materials may also be used in the heterostructures, including, for instance, other semiconductor materials. For instance, other nitride semiconductors, such as Ill-nitrides without incorporating a II IB element. Still other materials may be used, including, for instance, silicon, silicon carbide, and metals such as aluminum and molybdenum.

[0032] Although the disclosed methods are described in connection with MBE growth procedures, additional or alternative non-sputtered epitaxial growth procedures may be used. For instance, metal-organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), atomic layer deposition (ALD), and atomic layer epitaxy (ALE) growth procedures may be used. Still other procedures may be used, including, for instance, pulsed laser deposition procedures.

[0033] In the examples described below, ScGaN / GaN heterostructures were grown on 2-inch n-GaN / sapphire templates using a Veeco GENxplor molecular beam epitaxy (MBE) system equipped with a radio frequency (RF) plasma-assisted nitrogen source for supplying active nitrogen (N*, 99.9999%), dual filaments SUMO cells for providing gallium (Ga, 99.99999%), and a high-temperature Knudsen effusion cell for providing scandium (Sc, 99.999%). The GaN layer was highly Si-doped with a carrier concentration of about 2x1019 cm3, and serves as a bottom electrode. The ScGaN layer was grown under N-rich conditions with a thickness of about 100 nm. The growth conditions and other parameters may vary in other cases, e.g., in cases involving other wurtzite materials. In these examples, Ti / Au (20 nm / 120 nm) top electrodes were deposited in an electron-beam evaporator and defined via photolithography and lift-off process.

[0034] Further details on the epitaxial growth conditions, procedures, and related parameters that may be used to form the ferroelectric structures and heterostructures described herein are set forth in WO 2023 / 022768 ("Epitaxial Nitride Ferroelectronics"), International Application No. PCT / US23 / 13727 ("Epitaxial Nitride Ferroelectronic Devices" filed February 23, 2023), P. Wang, et al., "Fully epitaxial ferroelectric ScAIN grown by molecular beam epitaxy," Applied Physics Letters, vol. 118, p. 223504 (2021 ), D. Wang et aL, "An Epitaxial Ferroelectric ScAIN / GaN Heterostructure Memory," Advanced Electronic Materials, p. 2200005 (2022), D. Wang, et aL, "Fully epitaxial ferroelectric ScGaN grown on GaN by molecular beam epitaxy," Appl Phys Lett 119 (11), 1 11902 (2021 ), D. Wang et al., "Impact of dislocation density on the ferroelectric properties of ScAIN grown by molecular beam epitaxy," Appl Phys Lett 121 (4), 042108 (2022), P. Wang et aL, "Quaternary alloy ScAIGaN: A promising strategy to improve the quality of ScAIN," Appl Phys Lett 120 (1 ), 012104 (2022), and P. Wang et al. "Ferroelectric Nitride Heterostructures on CMOS Compatible Molybdenum for Synaptic Memristors," ACS Appl.Mater. Interfaces 2023, 15, 14, 18022-18031 (2023), the entire disclosures of which are hereby incorporated by reference.

[0035] Figure 1 , part A, illustrates a device having a ferroelectric structure with a switchable conduction path in accordance with one example. The device has a ferroelectric / semiconductor interface with incomplete charge compensation that underpins a transition region with rich domain wall structures. In this example, the ferroelectric structure is composed of, or otherwise includes, ScGaN, which is compatible with mainstream semiconductor platforms and has a moderate bandgap. The device also includes a lower or base electrode layer. Unlike the ferroelectric structure, the lower electrode layer is unswitchable. In this example, the lower electrode layer is composed of, or otherwise includes, a doped Ill-nitride semiconductor, such as n-GaN.

[0036] The atomic scale control of MBE ensures fully epitaxial layers with precise lattice alignment, atomically sharp interfaces, uniform element distribution, and minimal crystal defects, thereby enabling atomic-level investigations of the interface and domain wall structures. Prior to TEM studies, the ferroelectric nature of ScGaN was confirmed by a series of electrical measurements and piezo-response force microscopy (PFM) characterizations. High resolution STEM imaging with a high-angle annular dark-field (HAADF) detector and integrated differential phase contrast (iDPC) was used to visualize the metal and nitrogen atomic positions and determine the crystallographic orientation.

[0037] After electrical poling, different regions are capable of being defined by their polarization orientations, as schematically shown in Figure 1 , parts B and C. Illustrated in the right panel of Figure 1 , part D, the alignment of atoms is clearly discernible, with Sc (or Ga) and nitrogen (N) atoms positioned on opposing ends of the dumbbell-shaped atomic pairs. The polarity of the layer stack is subsequently ascertained from the stacking order of the metal (M) and nitrogen (N) atoms within these dumbbells. Figure 1 , part D, also demonstrates the coexistence of electric-field-induced nitrogen-polar (N-polar) regions, an intermediary realm marked by mixed polarity, and unswitched metal-polar (M-polar) regions close to an M-polar GaN base (Figure 1 , part G).

[0038] The as-fabricated ScGaN / GaN heterostructure, without any prior poling, exhibits exclusively metal polarity. The uniformity of N-polar domains, extending from the transition region up to the top electrode, is evident in Figure 1 , parts D to F. This uniformity, in agreement with the electrical and PFM characterizations, suggests that the N-polar domains result from a comprehensive polarity reversal, rather than from localized defects or specific domain structures generated during growth. The observation of such distinct N-polar regions after electrical poling thus provides unambiguous evidence of ferroelectric polarization switching in epitaxial Sc-lll- nitrides.

[0039] The existence of an unswitchable layer at the ferroelectric / electrode interface has also been observed in other (non-wurtzite) ferroelectric systems, representing a combined result of domain energy and incomplete charge compensation. Such non-wurtzite ferroelectric systems also exhibited fundamental differences in the domain wall structure, including, e.g., differences arising from the difference in crystal structure. In the disclosed devices and methods, this unswitched region is harnessed to promote the formation of in-plane domain walls.

[0040] Side-bv-side, vertical domain walls. Domains and domain walls underlie polarity switching dynamics and also represent energetically favorable configurations amidst significant depolarization fields. In ferroelectrics with out-of-plane polarization, vertical domain walls (VDWs) typically form to minimize the energy and area of the domain walls. Figure 2, part A, illustrates such a “side-by-side” domain arrangement, where adjacent domains with antiparallel polarizations are separated by an abrupt polarity transition. The crystal symmetry of the wurtzite material suggests a lateral polarity inversion through a unique 8- and 4-fold ring arrangement, as shown in Figure 2, part B. Such vertical domain wall structures have been referred to as IDB* in epitaxial films.

[0041] Figure 2, parts C to F, show high-resolution STEM images with differing contrast in the transition region of polarity reversed ScGaN, clearly showing the presence of distinct, atomically sharp vertical domain walls. These domain walls are characterized by a notable step in each metal plane between the M-polar and N-polar regions (Figure 2, part C). At the domain wall, metal atoms from opposing polarities overlap slightly within one or two columns, forming a dimer pattern along the

[0001] direction. Two-dimensional Gaussian fitting of the STEM images was conducted to determine the precise position of each metal atom column. Notably, the in-plane atomic spacing appears moderately expanded at the VDW, as shown in the in-plane distance mapping (Figure 2, part D). Integrated differential phase contrast (iDPC) images are examined to locate the position of N atoms. By collectively fitting the positions of N and metal atoms, the angles of the M-N dumbbells are determined (Figure 2, parts E and F), delineating a clear polarity transition across the metal dimer region. The corresponding differentiated differential phase contrast (dDPC) images of the VDW structure further unveil a unique atomic arrangement having two metal and two nitrogen atoms (Figure 2, part G). The atomic contrast measurements enable precise determination of interatomic distance within this structure (Figure 2, part H). A slightly larger separation between metal atoms (0.123c) was identified, compared to nitrogen atoms (0.11 1 c), along the

[0001] direction, where c is the lattice constant of ScGaN away from the interface (Figure 2, part I).

[0042] DFT calculations further confirm the VDW structural hypothesis, validating the experimentally observed increase of in-plane atomic spacing, as well as the corresponding M-M and N-N atomic distances along the

[0001] direction (Figure 2, part J). While the STEM imaging performed along the

[1120] direction successfully captures the in-plane lattice expansion at the domain wall, the absence of clear 8- / 4-fold rings is ascribed to a slight shift of the domain boundary within the (1120) plane. Although similar VDW structures have been previously reported in epitaxial films where two domains of different polarities meet, this investigation presents the first demonstration of electrically induced VDWs in wurtzite nitrides at atomic resolution. Such VDWs have been identified as efficient radiative recombination centers and may be used to fabricate lateral homojunctions. These electrically induced and sub-nanometer thick VDWs may be used to realize nanoscale electronic devices based on single domain walls.

[0043] Head-to-head, horizontal (or other lateral) domain walls. Horizontal domain walls (HDWs), characterized by a head-to-head configuration, are rarer than their vertical counterparts due to the substantial electrostatic energy from significant polarizationdiscontinuity. In epitaxial films, the formation of HDWs often necessitates the introduction of foreign atoms, such as silicon and oxygen, to compensate the dangling bonds and maintain lattice symmetry. These foreign atoms substantially neutralize the polarization charges, obscuring the intrinsic electrical characteristics of the HDWs.

[0044] In contrast, in ferroelectric nitrides and other wurtzite materials, controllable HDWs are capable of being created via an applied electric field. Figure 3, part A, shows a schematic of an example “head-to-head” HDW in a ferroelectric Ill-nitride structure of a device. In this example, the device is configured as, or otherwise includes, a capacitor. An example atomic configuration within the HDW in the ferroelectric structure is depicted in Figure 3, part B. Figure 3, parts C and D, showcase high-magnification HAADF-STEM images and corresponding out-of-plane distance mapping of the HDWs observed in the polarity-reversed ScGaN capacitor. The M atom arrangement maintains the zigzag pattern seen in wurtzite materials, highlighting the continuity of the metal sublattice in the presence of HDWs. Within the central region of the HAADF image, metal-metal dimer patterns are again observed, but exhibit contracted interatomic spacing compared to those in VDWs. Coinciding with the metal-metal dimer pattern formation, an out-of- plane lattice expansion at the respective HDW region is also observed (Figure 3, part D), indicated by a sub-nanometer transition region in the M-N dumbbell angle mapping (Figure 3, parts E and F). Alongside the M-N dumbbells within each domain, a distinctive triangular configuration is identified in the domain wall region, with every metal occupying a central position and symmetrically bordered by a pair of N atoms, as highlighted by the overlaid blue (N atom) and red (M atom) spheres. Compared to the N atoms in the M-N dumbbells away from the HDW, the intensities of the N atoms in the HDW exhibit a noticeable reduction, which indicates decreased N atom occupation in these atomic layers. The metal atom column sites are more distinct in the dDPC image, shown in Figure 3, part G. Subsequent atomic distance measurements based on the dDPC image are presented in Figure 3, part H. The average N-N distance in the triangular configuration is measured to be 0.321 c, while the average M-M distance between two different atomic layers is determined as 0.56c (Figure 3, part I).

[0045] In some cases, decreased metal occupation may be exhibited at or along the lateral domain wall. For instance, the above-described ScGaN example may have decreased metal occupation at or along the lateral domain wall.

[0046] DFT calculations were conducted to further confirm the HDW structural details. Remarkably, as depicted in the DFT model (Figure 3, part J), despite the disorder at the metalsites, the atoms within the HDW a unique buckled 2D hexagonal phase. The trigonal prismatic atomic arrangements from DFT align with TEM observations and quantitatively match the experimentally observed N-N spacings and out-of-plane atomic distance expansion. Along the

[0001] axis, the configuration retains its inherent hexagonal symmetry, aligning seamlessly with conventional wurtzite nitrides. Notably, within the domain wall, each metal atom bonds with only three nitrogen atoms, creating a high density of dangling bonds, indicating that the HDWs are highly electrically active and are charged domain walls. In Figure 3, part K, the total electronic density of states of the HDWs are compared to that of bulk ScGaN. While the density of states of the VDWs and bulk ScGaN are nearly identical, the HDWs exhibit rich mid-gap states due to the unpassivated dangling bonds of metal atoms in the domain wall and neighboring planes. The dangling bond nature of these metallic mid-gap states is further confirmed by the plot of their charge density (inset of Figure 3, part K). These results indicate that the HDWs are highly electrically active and are charged domain walls.

[0047] Given the large spontaneous polarization of ScGaN, the net polarization charge is estimated to be approximately 200 pC / cm2, which is among the highest values achievable in all ferroelectric materials. These results reveal the “2H MoS2-like” or buckled 2D hexagonal phase of the HDW as a useful atomically thin functional interface, enabling rich physics and a variety of device configurations and applications.

[0048] Quantitative comparison of the charge density further reveals an intriguing interplay between the dangling bond and bound polarization discontinuity charges at the HDWs. Inspection of the structure reveals that the interface exhibits two cation dangling bonds per two- dimensional unit cell, with each bond carrying an excess charge of -3e / 4 at the HDW, reflecting the trivalent cation donating 3 / 4 of an electron to each of its four nitrogen neighbors. This generates an excess of electrons at the interface with a density of -1 .59 x 1015e / cm2, among the highest reported for any interface. For a spontaneous polarization of about 1 .29 C / m2for Sco.31Gao69N, a bound charge of 2Psp= +1 .61 x 1015e / cm2at the HDW interface is estimated. This bound positive charge is nearly perfectly compensated by the negative charge arising from the dangling bonds and thus usefully contributes to the stability of the interface, potentially suppressing the formation of columnar domain patterns running through the entire film. Conversely, the exceptionally high polarization discontinuity at such a domain wall helps sustain this remarkably high charge density, usefully for device applications. The reciprocal relationship between the dangling bonds and bound polarization charges, where each stabilizes the other,reveals a powerful mechanism for promoting interface stability in ScGaN (and other ferroelectric structures) and may be applied to a wide variety of high-performance electronics based on this unique interfacial feature. While more accurate calculations would involve taking into consideration the lattice distortion near the interface, the conclusions remain valid. The nearly complete compensation of the bound charge by the dangling bond electrons is not a coincidence, but a geometrical feature of tetrahedral ferroelectrics for any amount of charge transfer between cations and anions. Moreover, the feature applies both for head-to-head and tail-to-tail antipolar domain walls.

[0049] As noted and shown herein, the electric field induced domain walls may be removed by switching the lattice polarity back to M-polar, which is in stark contrast to the inherently irreversible domain walls obtained during epitaxial growth.

[0050] Both the VDW and HDW maintain six-fold rotational symmetry, in line with the host wurtzite material. Such symmetry is notable, as it involves the manifestation of alternate domain and domain wall projections at regular 60-degree intervals when observed from a consistent viewing angle. Visually, the atomic configuration of the HDWs suggests a vertical displacement of nitrogen atoms during polarization reversal, resulting in a 50% occupancy of the N sites in the original M-polar lattice. Conversely, the VDWs indicate a simultaneous displacement of both M and N atoms following polarity inversion. Compared to the previously postulated planar hexagonal phase during polarity switching in Sc-lll-N alloys, the unveiled HDW structure adopts a buckled hexagonal form that is overall non-polar along the

[0001] axis. This implies that tetrahedral inversion within the HDW may occur at a lower energy threshold compared to the bulk, offering a pathway to mitigate the high coercive field in wurtzite ferroelectrics.

[0051] Turning to Figure 9, the disclosed devices may include various reconfigurable conductive domain walls in wurtzite ferroelectric structures. The HDWs and other domain walls described herein may act as conductive pathways. For ferroelectric materials with polarization directions along the out-of-plane direction, it is challenging to measure the conductivity of the horizontal domain walls directly. Here, inclined domain walls with controllable horizontal components are realized and used to explore the electrical properties of the electric field induced domain walls using conductive atomic force microscopy (CAFM).

[0052] Figure 9, part A, illustrates an example capacitor device 900 in which the formation of inclined domain walls 902 in a ferroelectric ScGaN structure 904 at an edge of an electrode 906. Due to the asymmetric electrode configuration (non-matching layouts of the ferroelectricstructure 904 and the electrode 906), the distribution of the vertical electric field near the electrode edge is not uniform. By varying the applied voltage, the inclination angle of the region reaching the coercive field can then be manipulated to create inclined domain walls with different horizontal components, as illustrated in Figure 9, parts B and C.

[0053] To enhance the contrast in conductivity, the thickness of the ScGaN layer 904 was reduced to 50 nm, yielding a positive switching voltage of about 20 V. The top electrodes are removed using dry exfoliation after poling to prevent chemical contamination and surface damage. Figure 9, parts D to G, present the surface morphology, phase contrast, and conductivity maps of the electrode regions given different poling conditions. Figure 9, parts H to K, further show the current profiles across the electrode regions extracted from the CAFM map. The appearance of conductive channels between the switched and unswitched regions is evident (Figure 9, parts E, I). Increasing the poling voltage to 28 V leads to an increase of the domain wall inclination angle (Figure 9, part C), reducing the horizontal component and resulting in lower conductivity compared to 21 V (Figure 9, parts F, J). Applying a large negative bias can both switch back the polarity and remove the conductive channels at the electrode edge (Figure 9, parts G, K). These results identify the horizontal components of the inclined domain walls as contributors to enhanced conductivity at the electrode edge. The slight increase in the overall contrast within the poled region of Figure 9, parts E, I, is attributed to the formation of domain walls due to fluctuations in the coercive field, which vanish when the poling voltage is increased to 28 V (Figure 9, parts F, J). These results yield the first direct observation and electrical manipulation of conductive domain walls in wurtzite semiconductors and devices based thereon.

[0054] The investigation of the examples described herein provides exceptional atomic-scale insights into the electric-field-induced domain walls in ScGaN and other wurtzite ferroelectric materials. The agreement between STEM observations and DFT calculations validates the atomic configuration of the domain walls. With their atomic-scale thickness and readily tunable properties via external electric fields, these domain walls useful in the configuration of a wide variety of nanoscale devices. Moreover, the observation of the “2H MoS2-like” configuration or buckled 2D hexagonal phase of the Ill-nitride material will also support a wide variety of applications.

[0055] Further examples of devices utilizing a lateral domain wall are described below in connection with Figures 4, 5, and 8. The structures shown may constitute a portion of a devicehaving a number of other structures and / or components not shown. The devices may accordingly include alternative or additional layers, structures, or other components or elements.

[0056] Figure 4 depicts an example device 400 having a metal-polar (or N-polar) ferroelectric layer (or other structure) 402 in which a lateral domain wall 404 is established or removed via application of a poling voltage. The device 400 is depicted both before and after poling voltage application. Upon creation, the lateral domain wall 404 defines a top portion 406 of the ferroelectric structure 402 having a first polarity (e.g., nitrogen polarity) and a bottom portion 408 of the ferroelectric structure 402 having a second polarity (e.g., metal polarity). In this example, the poling voltage is applied between a top electrode 410 and a bottom electrode 412. The polarities of the top and bottom portions 406, 408 may be reversed in connection with examples having an opposite polarity (e.g., nitrogen polarity) before poling voltage application.

[0057] The example devices depict how domain walls, the intrinsic atomic-scale structures delineating regions with divergent electric polarizations, may be useful as novel functional interfaces. The unique reduced dimensionality of the domain walls, combined with distinct symmetrical and compositional characteristics, lead to physical properties absent in the bulk material. Nitride ferroelectrics, with their impressive suite of properties outshining oxide counterparts, are useful in connection with the properties of domain walls. The presence of a non-switchable region in nitride ferroelectrics (referred to as the 'dead layer') may nonetheless be strategically utilized to facilitate the formation of in-plane domain walls and, in so doing, realize devices characterized by ultra-compact dimensions and useful configurations suited for nanoscale applications.

[0058] Nitride ferroelectric domain walls may exhibit either enhanced or diminished electronic conductivity relative to adjacent domains, potentially functioning as ultra-compact conductive channels. As described herein, these domain walls can dynamically appear, change size or vanish in response to applied electric fields, implying that the domain walls can be created, moved and erased (or otherwise removed) on demand. This adaptability facilitates real-time manipulation of domain-wall positions, densities, and orientations. These features may be utilized in a variety of reconfigurable domain-wall-based electronic circuits.

[0059] Figure 5 depicts a reconfigurable non-volatile nitride ferroelectric domain wall fieldeffect transistor device 500 in accordance with one example. The device 500 is depicted both before and after gate voltage application. The device 500 includes a ferroelectric layer or structure 502 supported by a substrate 504. By applying a large gate voltage pulse to a gateelectrode 506, the polarity of an upper layer or portion 508 of the ferroelectric layer or other structure 502 under the gate electrode 506 is switched, leading to the formation or vanishment of a lateral domain wall 510 in the ferroelectric structure 502. When the domain wall 510 is present, the conductive properties of the domain wall 510 allow the domain wall 510 to act as a conducting channel or other conduction path, making the domain wall 510 suitable for fieldeffect transistor applications. Conversely, when (and / or where) the domain wall 510 is eliminated, the conducting channel is erased. As shown in the example of Figure 5, the conduction channel may couple source and drain regions 512, 514. The reconfigurable, nonvolatile conductive characteristics of the ferroelectric domain wall field-effect transistor are useful in a wide variety of applications, including, for instance, artificial synaptic networks and neuromorphic computing systems.

[0060] Figure 6 shows a method 600 of fabricating a device having a ferroelectric structure in accordance with one example. The method 600 may be used to fabricate any one of the devices described herein, or other devices.

[0061] The method 600 includes an act 602 in which a substrate is provided. The act 602 may include providing a substrate as described herein in an act 604. In some cases, the substrate is composed of, or otherwise includes, sapphire, but alternative substrates (e.g., silicon) may be used. An etch and / or other procedure may be implemented in an act 606 to remove an oxide layer. As described herein, the substrate may be baked in an MBE load-lock chamber in an act 608. A native oxide may also be removed in an act 610 when the substrate is moved to the growth chamber.

[0062] The method 600 includes an act 612 in which a base or template layer or structures is grown via implementation of a growth procedure. The base layer may be grown on the substrate. The act 612 may include implementation of an MBE procedure. Alternatively or additionally, the act 612 may include the deposition and patterning of a metal layer in an act 614. In cases having a metal layer, one or more surface treatment procedures may be performed to prepare the metal surface for growth of the ferroelectric structure, including, for instance, an oxide removal procedure, such as an anneal in a vacuum. Other procedures may be used as described herein. In some cases, the growth procedure of the act 612 may be configured to dope the base layer such that the base layer is configured as a bottom electrode or is otherwise conductive. For instance, a silicon-doped GaN layer is grown in an act 616.Alternative or additional segments or layers may be grown. In some cases, the template segments are grown in N-rich conditions.

[0063] The method 600 includes an act 618 in which another growth procedure is implemented to grow a ferroelectric structure (e.g., nanostructure) supported by the substrate and base layer. The ferroelectric structure may be grown on the base layer. Each ferroelectric structure may be composed of, or otherwise include, a wurtzite material such as a nitride alloy (e.g., a Ill-nitride alloy), as described herein. In some cases, the growth procedure of the act 618 is configured such that each ferroelectric structure has a Group II I B content of about 0.4 or higher The act 618 may include implementation of an MBE procedure in an act 620, but other procedures may be used as described herein. In some cases, the ferroelectric structure is grown in N-rich conditions in an act 622.

[0064] The growth procedures may be configured such that one or both of the base and ferroelectric structures have a sub-micron thickness. The base and ferroelectric structures may or may not have thicknesses on the same order of magnitude. For instance, the growth procedures may be configured such that the ferroelectric structure has a smaller thickness than the base layer.

[0065] The nanostructures may or may not be annealed in an act 624. The anneal procedure may be implemented in an act 626 in the same growth chamber in which the nanostructures are grown. The anneal procedure may be implemented under high vacuum in an act 628. Alternatively or additionally, the anneal procedure may include an act 630 in which the nanostructures are annealed with N plasma radiation or under N gas flow.

[0066] In the example of Figure 6, the method 600 includes an act 632 in which a temporary electrode supported by the ferroelectric structure is formed. The composition and other characteristics of the temporary electrode may vary. A poling voltage is then applied to the temporary electrode (e.g., between the temporary electrode and the bottom electrode) in an act 634 to establish a lateral domain wall in the ferroelectric structure. As described herein, the lateral domain wall defines an upper portion of the ferroelectric structure and a lower portion of the ferroelectric structure having a first polarity and a second polarity, respectively. In an act 636, the temporary electrode is removed after the application of the poling voltage.

[0067] One or more acts of the method 600 may be directed to forming one or more terminals or other structures or components of the device. In the example of Figure 6, a pair of terminalsof the device may be formed in an act 638. To that end, one or more metal layers may be deposited and patterned in an act 640. Alternative or additional structures may be formed, including, for instance, the epitaxial growth of one or more Ill-nitride layers in an act 642.

[0068] The method 600 may include additional, alternative, or fewer acts. For instance, the method 600 may include one or more acts directed to the formation of a further electrode, such as a gate electrode. In some cases, the gate electrode may be deposited or otherwise formed on the ferroelectric structure.

[0069] Figure 7 depicts a method 700 of operating a device having a ferroelectric structure in accordance with one example. The device may be one of the above-described devices or another device. As described herein, the device has a ferroelectric structure with a switchable conduction path disposed along a lateral domain wall in the ferroelectric structure. The device further includes an electrode disposed relative to the ferroelectric structure such that a voltage applied to the electrode establishes or removes the lateral domain wall and the switchable conduction path in the ferroelectric structure.

[0070] The method 700 may include an act 702 in which a voltage is applied to the device to modulate a characteristic of the switchable conduction path. In some cases, the voltage may be a gate voltage. For instance, the voltage may modulate (e.g., increase or decrease) the charge distribution at the lateral domain wall. The voltage may be applied to modify a state of the device. The modified state may be later accessed or otherwise used in an act 704 in which a read or other voltage is applied to the device. For instance, the voltage applied in the act 704 may be a drain-source voltage.

[0071] The method 700 may also include an act 706 in which a poling voltage is applied to the device to remove the lateral domain wall. The poling voltage may be a gate or other voltage sufficient to switch the polarization of the ferroelectric structure. The poling voltage may be used to update a state of the device (e.g., a memory device). The state of the device may later be read via application of a read voltage in an act 708.

[0072] The method 700 may include additional, alternative, or fewer acts. For instance, in binary memory device examples, the method 700 may not include the act 702.

[0073] Figure 8 depicts a reconfigurable nitride ferroelectric domain wall memory device 800 in accordance with one example. In this case, terminals 802, 804 of the device 800 are disposed in different layers, leading to an asymmetric electrode configuration. An electric field distributionresulting from application of a voltage across the asymmetric electrode configuration generates one or more conducting domain walls 806 between the terminals 802, 804. The device 800 of Figure 8 may be useful in connection with a wide variety of applications, including, for instance, reconfigurable memory systems.

[0074] Examples of devices having precise atomic configurations of wurtzite ferroelectric domain walls are described above. For the first time, the precise atomic configurations of subnanometer electric field-induced domain walls are revealed. The novel buckled 2D hexagonal phase provides a useful platform for devices that is inaccessible or not realizable in bulk materials.

[0075] Example devices having a transformative charge compensation mechanism are also described above. While wurtzite ferroelectrics exhibit both giant polarization and superior stability, the stability of the antipolar domain walls and charge compensation mechanism had previously remained unknown. The quantitative analysis presented herein reveals that the geometry of the charged domain wall enables near-complete compensation of the 180° polarization discontinuity by the charge of the dangling-bond electrons. This feature unveils a universal charge-compensation mechanism that is applicable to a wide variety of wurtzite ferroelectric structures and devices based thereon.

[0076] A number of CMOS-compatible ferroelectric domain wall devices are also described above. That the abundant dangling bonds in the horizontal domain walls give rise to metallic states within the forbidden band is used to realize and demonstrate reconfigurable conductive domain walls in support of a wide variety of CMOS-compatible ferroelectric domain wall-based devices.

[0077] The above-described examples provide a number of novel functional interfaces for CMOS-compatible wurtzite ferroelectrics, with insights into their atomic and electronic structures, and support for a wide variety of applications. Furthermore, the long-standing debate of stability mechanisms related to antipolar domain walls in wurtzite ferroelectrics has been addressed via the identification of the underlying features and mechanisms in ferroelectric physics. These advancements are not only useful for addressing the challenges in current wurtzite ferroelectrics but also useful in various ultra-compact devices for a wide variety of multifunctional, reconfigurable electronic, photonic, and acoustic systems.

[0078] The wurtzite ferroelectric structures described herein are monocrystalline to a degree not realizable via, for instance, sputtering-based procedures for forming, e.g., Ill-nitride alloy layers. Such sputtering-based procedures are only capable of producing polycrystalline structures with x-ray diffraction rocking curve line widths on the order of a few degrees at best. As used herein, the terms "monocrystalline" and "single-crystalline" refer to structures having x- ray diffraction rocking curve line widths at least one order of magnitude lower than the order of a few degrees.

[0079] The term "about" is used herein in a manner to include deviations from a specified value that would be understood by one of ordinary skill in the art to effectively be the same as the specified value due to, for instance, the absence of appreciable, detectable, or otherwise effective difference in operation, outcome, characteristic, or other aspect of the disclosed methods and devices.

[0080] The present disclosure has been described with reference to specific examples that are intended to be illustrative only and not to be limiting of the disclosure. Changes, additions and / or deletions may be made to the examples without departing from the spirit and scope of the disclosure.

[0081] The foregoing description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom.

Claims

What is Claimed is:

1. A device comprising: a substrate; a ferroelectric structure supported by the substrate, the ferroelectric structure having a wurtzite crystal structure; a switchable conduction path in the ferroelectric structure, the switchable conduction path being disposed along a lateral domain wall in the ferroelectric structure, the lateral domain wall defining a first portion of the ferroelectric structure and a second portion of the ferroelectric structure having a first polarity and a second polarity, respectively; and an electrode disposed relative to the ferroelectric structure such that a voltage applied to the electrode establishes or removes the lateral domain wall and the switchable conduction path in the ferroelectric structure.

2. The device of claim 1 , wherein the lateral domain wall has a triangular atomic configuration.

3. The device of claim 1 , wherein: the ferroelectric structure comprises a wurtzite semiconductor; and the lateral domain wall comprises a buckled hexagonal phase of the wurtzite semiconductor.

4. The device of claim 1 , wherein the lateral domain wall has an atomic-scale thickness.

5. The device of claim 1 , wherein the lateral domain wall has a single-digit number of monolayers.

6. The device of claim 1 , further comprising a pair of terminals supported by the substrate, the pair of terminals being electrically coupled via the switchable conduction path.

7. The device of claim 1 , further comprising a first terminal supported by the substrate wherein: the electrode is configured as a second terminal; the first and second terminals are electrically coupled via the switchable conduction path; andthe first and second terminals are disposed in different layers such that the switchable conduction path extends both laterally and non-laterally.

8. The device of claim 1 , further comprising a source electrode and a drain electrode, the source and drain electrodes being supported by the substrate and electrically coupled via the switchable conduction path.

9. The device of claim 1 , wherein the switchable conduction path is configured as a transistor channel.

10. The device of claim 1 , wherein the lateral domain wall comprises a transition region between the first polarity and the second polarity.

11. The device of claim 1 , wherein the ferroelectric structure comprises a Ill-nitride alloy.

12. The device of claim 1 , wherein the lateral domain wall has partial nitrogen site occupancy.

13. The device of claim 1 , wherein the lateral domain wall has partial metal site occupancy.

14. The device of claim 1 , wherein the lateral domain wall exhibits six-fold rotational symmetry.

15. The device of claim 1 , wherein the first polarity and the second polarity are metal polarity and nitrogen polarity, respectively, and the first portion of the ferroelectric structure is adjacent the electrode.

16. The device of claim 1 , wherein the first polarity and the second polarity are nitrogen polarity and metal polarity, respectively, and the first portion of the ferroelectric structure is adjacent the electrode.

17. The device of claim 1 , further comprising a base layer supported by the substrate, the voltage being applied between the electrode and the base layer.

18. The device of claim 17, wherein the base layer comprises a Ill-nitride semiconductor.

19. The device of claim 17, wherein the base layer comprises silicon, silicon carbide, aluminum, or molybdenum.

20. The device of claim 17, wherein layouts of the electrode and the base layer do not match such that the lateral domain wall has a vertical component extending from the electrode to the base layer and an electric field controllable inclination based on a level of the voltage.

21. A method of operating the device of claim 1 , the method comprising: applying a first voltage to modulate a characteristic of the switchable conduction path; and applying a second voltage to remove the lateral domain wall.

22. The method of claim 21 , wherein the characteristic is a charge distribution at the lateral domain wall.

23. A method of fabricating a device, the method comprising: forming a ferroelectric structure supported by a substrate, the ferroelectric structure comprising a wurtzite crystal structure; forming a temporary electrode supported by the ferroelectric structure; applying a poling voltage to the temporary electrode to establish a lateral domain wall in the ferroelectric structure, the lateral domain wall defining a first portion of the ferroelectric structure and a second portion of the ferroelectric structure having a first polarity and a second polarity, respectively; removing the temporary electrode after applying the voltage; and forming first and second terminals of the device, the first and second terminals being electrically coupled to one another via the lateral domain wall.

24. The method of claim 23, further comprising forming a base layer supported by the substrate, the base layer being disposed between the substrate and the ferroelectric structure.

25. The method of claim 23, wherein: the ferroelectric structure comprises a Ill-nitride alloy; and the Ill-nitride alloy in the lateral domain wall has a buckled hexagonal phase.

26. A device comprising: a substrate; first and second electrode layers supported by the substrate; a ferroelectric structure disposed between the first and second electrode layers, the ferroelectric structure having a wurtzite crystal structure; and a switchable conduction path in the ferroelectric structure, the switchable conduction path being disposed along a domain wall in the ferroelectric structure, the domain wall defining a first portion of the ferroelectric structure and a second portion of the ferroelectric structure having a first polarity and a second polarity, respectively; wherein the ferroelectric structure and the first electrode extend laterally beyond the second electrode such that a voltage applied between the first and second electrodes establishes a position of the domain wall.

27. The device of claim 26, wherein the first electrode comprises a doped Ill-nitride semiconductor.

28. The device of claim 26, wherein the ferroelectric structure comprises ScGaN.

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