Ferroelectric metal and method of making and using same

Abstract

The application provides a ferroelectric metal and a preparation method and application thereof. The ferroelectric metal of the application is composed of cubic silicon carbide crystals and doping elements doped therein, wherein the concentration of the doping elements is greater than or equal to 1*10 18 cm ‑3 The material of the application can be prepared by a chemical vapor deposition method, a high-temperature solution growth method, a solid-phase sintering method, a pulse laser deposition method and the like. Since the conductivity of metal, the switching characteristics of ferroelectric and the force-electric coupling characteristics of piezoelectric are integrated, the ferroelectric metal of the application has great application value in the fields of high-performance transducers, high-sensitivity sensors, low-power micro-electro-mechanical system (MEMS), next-generation multifunctional electronic devices and the like.

Description

Technical Field

[0001] This invention belongs to the field of novel electronic functional materials, specifically relating to a ferroelectric metal, its preparation method, and its application. Background Technology

[0002] Ferroelectric materials are functional materials that exhibit spontaneous polarization when an external electric field is zero, and the direction of this spontaneous polarization can be reversed by an external electric field. They play a crucial role in numerous electronic devices such as non-volatile memories, sensors, and piezoelectric actuators. However, traditionally, ferroelectricity is considered to be mutually exclusive with metallic conductivity because the high concentration of free electrons in metals can annihilate the polarized electric dipoles within the material through electrostatic shielding, thereby disrupting the macroscopic polarization field, i.e., the long-range ferroelectric order. Therefore, the vast majority of ferroelectric materials discovered to date are either insulators or semiconductors.

[0003] This traditional understanding was challenged theoretically in 1965. Anderson and Blount (PW Anderson, EI Blount, Symmetry considerations on martensitic transformations: “Ferroelectric” metals? Physical Review Letters. (1965) 14, 217–219.) first proposed the concept of “ferroelectric metals,” theoretically predicting that certain metallic materials could lose their inversion symmetry center through structural phase transitions, thereby generating reversible spontaneous polarization, i.e., simultaneously possessing metallic conductivity and ferroelectricity. However, for nearly half a century afterward, this prediction lacked solid experimental evidence.

[0004] Until 2013, researchers experimentally confirmed the existence of polar metals for the first time. They discovered that LiOsO3 undergoes a structural phase transition from the centrosymmetric space group (R-3c) to the non-centrosymmetric space group (R3c) below 140 K, and the material retains its metallic properties before and after this phase transition (Nature Materials, 2013, 12, 1024). While this work confirmed the existence of "polar metals" with polar structures, there was still no direct experimental data to confirm the characteristics of "ferroelectric metals" (macroscopic spontaneous polarization that can be reversed by an electric field). Therefore, for a long time, there has been a consensus in the fields of condensed matter physics and materials research that ferroelectricity and metallicity cannot coexist.

[0005] However, the polar metallic materials discovered so far, such as LiOsO3, still have significant limitations that severely restrict their practical applications:

[0006] Element toxicity issue: The Os (osmium) element in LiOsO3 is toxic, which does not conform to the trend of green and environmentally friendly material development.

[0007] Performance bottleneck: Its room temperature resistivity (about 1.5 mΩ·cm) is much higher than that of conventional metals (such as silver, which has a room temperature resistivity of 0.00168 mΩ·cm), resulting in low efficiency in conductive applications.

[0008] Fabrication and size limitations: The reported material sizes are so small (e.g., on the order of 200 µm) that they are insufficient to meet the requirements for fabricating macroscopic devices.

[0009] Therefore, there is an urgent need in this field to develop a novel ferroelectric metal material that is truly non-toxic, has lower resistivity, and is easy to prepare on a large scale, in order to promote its practical application in transducers, sensors and microelectromechanical systems, information storage, energy storage and electro-optical control.

[0010] Cubic silicon carbide (3C-SiC), as an important third-generation wide-bandgap semiconductor material, has attracted much attention due to its high thermal conductivity, high critical breakdown electric field, excellent chemical stability, and outstanding mechanical properties, and also exhibits good compatibility with existing semiconductor manufacturing processes. Currently, research on doping of cubic silicon carbide mainly focuses on controlling its conductivity type (n-type or p-type) for use in power electronic devices, or on introducing transition metals (such as Mn, Fe, etc.) to prepare dilute magnetic semiconductors. No published literature or technical data has yet demonstrated that doping of cubic silicon carbide can induce its intrinsic ferroelectricity, let alone reveal how to achieve efficient coexistence of ferroelectricity and metallicity. In existing technologies, doped cubic silicon carbide is only considered as a conductor, semiconductor, or magnetic material; its application potential as a ferroelectric metal is completely unknown. Summary of the Invention

[0011] In view of the problems and shortcomings of the existing technology, the present invention aims to overcome the lack of ferroelectric metal materials and direct experimental data to prove the existence of ferroelectric metals, as well as the inherent defects of existing polar metal materials (such as LiOsO3), and provide a new type of ferroelectric metal material with excellent comprehensive performance, environmental friendliness and easy industrialization and its preparation method.

[0012] Through long-term experimental research, the inventors of this invention unexpectedly discovered that when the doping concentration in cubic silicon carbide (3C-SiC) crystal is greater than or equal to 1×10⁻⁶, 18 cm -3When certain elements are used, stable and reversible spontaneous polarization can be induced in semiconductor materials that are not normally ferroelectric, thus giving them significant ferroelectricity. Simultaneously, this high concentration of doping provides a large number of free charge carriers, enabling the material to exhibit good metallic conductivity. Ultimately, this achieves efficient and stable coexistence of ferroelectricity and metallicity in a single material. This discovery breaks through the traditional theoretical understanding that ferroelectricity and metallicity are mutually exclusive, opening up a completely new material system for the ferroelectric metal materials family that is highly compatible with existing semiconductor processes.

[0013] Based on the above findings, in a first aspect, the present invention provides a ferroelectric metal, which is composed of cubic silicon carbide crystal and doping elements therein, wherein the concentration of the doping elements is greater than or equal to 1 × 10⁻⁶. 18 cm -3 .

[0014] The inventors of this application unexpectedly discovered that when cubic silicon carbide is doped with a high concentration (greater than or equal to 1 × 10⁻⁶), 18 cm -3 When certain elements (such as N, P, As, Sb, Al, Ti, B, Ti, V, Cr, Mn, Fe, Co, Ni, or Cu) are used, efficient coexistence of ferroelectricity and metallicity can be achieved.

[0015] Preferably, in the ferroelectric metal of the present invention, the resistivity of the ferroelectric metal exhibits metallic behavior in relation to temperature, and the room temperature resistivity is 0.0001-1 mΩ·cm.

[0016] In the context of this invention, the term "room temperature" refers to 20-25 °C, which is commonly used in the art.

[0017] In the context of this invention, the concentration refers to the number of doped atoms per unit volume, in cm³. -3 .

[0018] Preferably, in the ferroelectric metal of the present invention, the doping element is selected from one or more of the elements N, P, As, Sb, Al, Ti, B, Ti, V, Cr, Mn, Fe, Co, Ni and Cu.

[0019] Preferably, in the ferroelectric metal of the present invention, the ferroelectric metal is in the form of a single crystal, polycrystalline powder, thin film, or two-dimensional material.

[0020] Preferably, in the ferroelectric metal of the present invention, the ferroelectric metal has room temperature ferroelectricity.

[0021] Preferably, in the ferroelectric metal of the present invention, the ferroelectric metal has a piezoelectric effect.

[0022] Preferably, in the ferroelectric metal of the present invention, the ferroelectric metal has an inverse piezoelectric effect.

[0023] Preferably, in the ferroelectric metal of the present invention, the ferroelectric metal is prepared by liquid phase method, solid phase method, chemical vapor deposition method or physical vapor transport method.

[0024] In a second aspect, the present invention provides a method for preparing ferroelectric metals of the present invention, wherein the preparation method is a liquid phase method, a solid phase method, a chemical vapor deposition method or a physical vapor transport method, and includes: in an atmosphere containing dopant elements or in the presence of raw materials, applying energy to cause a silicon source, a carbon source and the dopant elements to react on a substrate, or to combine cubic silicon carbide raw materials with the dopant elements to form the doped cubic silicon carbide crystals;

[0025] The amount of the dopant element added is such that its doping concentration in the cubic silicon carbide crystal is greater than or equal to 1 × 10⁻⁶. 18 cm -3 .

[0026] Thirdly, the present invention provides a method for preparing the ferroelectric metal of the present invention, wherein the preparation method is a liquid-phase method, comprising the following steps:

[0027] (1) Place the flux in a graphite crucible and evacuate the growth furnace. Then introduce a mixed atmosphere or a pure inert gas (such as argon, helium or hydrogen) to control the gas pressure inside the growth furnace.

[0028] (2) Heat the graphite crucible until the flux is completely melted to form a melt and reach the growth temperature of SiC;

[0029] (3) Pushing down the graphite pull rod in the growth furnace makes the seed crystal come into contact with the melt, thereby growing N, P, Al or B doped cubic silicon carbide single crystal.

[0030] In the liquid-phase method of the present invention, when the mixed atmosphere is composed of nitrogen and one or more selected from hydrogen, helium and argon, N-doped cubic silicon carbide single crystals can be obtained; when the mixed atmosphere is composed of one or more selected from hydrogen, helium and argon, nitrogen-containing compounds (such as magnesium nitride or lithium nitride) with melting points below 1850 °C can be added to the flux to obtain N-doped cubic silicon carbide single crystals; when the mixed atmosphere is composed of a B-containing gas (such as B2H6), a P-containing gas (such as PH3) or an Al-containing gas (such as (CH3)3Al) and one or more selected from hydrogen, helium and argon, P, Al or B-doped cubic silicon carbide single crystals can be obtained accordingly.

[0031] Preferably, when the mixed atmosphere is formed by mixing nitrogen, a gas containing B, a gas containing P, or a gas containing Al with one or more selected from hydrogen, helium, and argon, the volume of nitrogen, the gas containing B, the gas containing P, or the gas containing Al in the mixed atmosphere accounts for 10%-100%, preferably 40%-100%.

[0032] Preferably, in the liquid phase method of the present invention, the control of the gas pressure in the growth furnace in step (1) is carried out under the condition that the gas pressure in the growth furnace is controlled to be 0.2-1.2 atm.

[0033] Preferably, in the liquid phase method of the present invention, the co-solvent comprises Si, Cr, and metal M; the metal M is selected from one or more of Co, Ce, Ti, Fe, and Al.

[0034] Preferably, in the liquid phase method of the present invention, the molar ratio of Si, Cr and metal M in the co-solvent is (35-60):(35-60):(0.1-10).

[0035] Fourthly, the present invention provides a method for preparing the ferroelectric metal of the present invention, wherein the preparation method is a solid-state method, comprising the following steps:

[0036] (1) Mix silicon powder and carbon powder in a molar ratio of 1:1 and add dopant;

[0037] (2) The mixed raw material obtained in step (1) is ball-milled; then the ball-milled mixed raw material is sintered to obtain doped cubic silicon carbide;

[0038] The dopant may be an element selected from one or more of the elements P, As, Sb, Al, Ti, B, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu; or the dopant may be a compound selected from one or more compounds containing the above-mentioned elemental elements.

[0039] Preferably, in the solid-state method of the present invention, the amount of the dopant is 0.1-5.0 mol%; wherein the amount of the dopant is calculated based on the molar amount of the elemental substance contained in the dopant. For example, when the dopant is As₂O₃, it is calculated based on the molar amount of As element contained in the dopant.

[0040] Preferably, in the solid-state method of the present invention, the sintering is carried out under the following conditions: sintering temperature of 1800-2200℃ and sintering time of 10-30 h.

[0041] Fifthly, the present invention provides a method for preparing the ferroelectric metal of the present invention, wherein the preparation method is a chemical vapor deposition method, comprising the following steps:

[0042] (1) Place the cubic silicon carbide substrate in the chemical vapor deposition chamber;

[0043] (2) During crystal growth, a mixed gas containing SiH4, C3H8 and N2 is introduced to obtain N-doped cubic silicon carbide single crystal; a mixed gas containing SiH4, C3H8 and B2H6 is introduced to obtain B-doped cubic silicon carbide single crystal; a mixed gas containing SiH4, C3H8 and (CH3)3Al is introduced to obtain Al-doped cubic silicon carbide single crystal; or a mixed gas containing SiH4, C3H8 and PH3 is introduced to obtain P-doped cubic silicon carbide single crystal.

[0044] The volume ratio of SiH4, C3H8 and N2 is (1-3): (5-7): (1-2);

[0045] The volume ratio of SiH4, C3H8 and B2H6 is (1-3): (5-7): (1-2);

[0046] The volume ratio of SiH4, C3H8 and (CH3)3Al is (1-3): (5-7): (1-2);

[0047] The volume ratio of SiH4, C3H8 and PH3 is (1-3): (5-7): (1-2).

[0048] Preferably, in the chemical vapor deposition method of the present invention, the gas pressure during crystal growth is 7500-8500 Pa.

[0049] Preferably, in the chemical vapor deposition method of the present invention, the growth temperature during crystal growth is 1500-1650℃.

[0050] Sixthly, the present invention provides a method for preparing the ferroelectric metal of the present invention, wherein the preparation method is a physical vapor transport method, comprising the following steps:

[0051] (1) Place the cubic silicon carbide substrate on the sample stage of the pulsed laser deposition vacuum chamber and install the cubic silicon carbide target.

[0052] (2) The substrate is heated and a mixed gas is introduced to control the gas pressure, and then a laser is used to bombard the target to deposit N, B, Al or P doped cubic silicon carbide single crystals; wherein, when the mixed gas contains nitrogen, N doped cubic silicon carbide single crystals can be obtained; when the mixed gas contains B2H6, B doped cubic silicon carbide single crystals can be obtained; when the mixed gas contains (CH3)3Al, Al doped cubic silicon carbide single crystals can be obtained; when the mixed gas contains PH3, P doped cubic silicon carbide single crystals can be obtained.

[0053] Preferably, the volume of nitrogen, B2H6, (CH3)3Al or PH3 in the mixed gas is 10%-100%, more preferably 40%-100%.

[0054] Preferably, in the physical gas phase transport method of the present invention, the mixed gas is composed of nitrogen, B2H6, (CH3)3Al or PH3 and one or more selected from hydrogen, helium and argon.

[0055] Preferably, in the physical gas phase transport method of the present invention, the control pressure in step (2) is carried out under the condition that the pressure of the vacuum chamber is controlled to 1-5 Pa.

[0056] In a seventh aspect, the present invention provides an application of the ferroelectric metal of the present invention in transducers, sensors, microelectromechanical systems, information storage devices, energy storage devices, or electro-optical controllers.

[0057] The present invention has the following beneficial effects:

[0058] (1) For the first time, the efficient coexistence of ferroelectricity and metallicity was successfully achieved: by performing high-concentration doping (greater than or equal to 1×10⁻⁶) on cubic silicon carbide. 18 cm -3 This invention breaks with the traditional notion that the two cannot coexist, and provides a novel material system that simultaneously possesses room temperature ferroelectricity / piezoelectricity and excellent metallic conductivity (room temperature resistivity as low as 0.0001-1 mΩ·cm). Unlike previous polarized metals such as LiOsO3, in addition to being proven to be a polar metal, it also achieves the reversal of ferroelectricity and ferroelectric polarization direction under an electric field.

[0059] (2) Non-toxic and environmentally friendly, with high safety: The present invention uses cubic silicon carbide as the matrix, and the selected doping elements (such as N, P, Al, B, etc.) are all non-toxic or low-toxic, which fundamentally solves the toxicity and environmental risks brought about by elements such as osmium in LiOsO3, and conforms to the development trend of green materials.

[0060] (3) Excellent overall electrical performance: The room temperature resistivity of the provided ferroelectric metal is significantly lower than that of the previously reported LiOsO3 (1.5 mΩ·cm), reaching a level comparable to that of traditional metals, which is beneficial to reduce energy loss during device operation and improve signal response speed.

[0061] (4) The materials have diverse forms, and the preparation process is mature and easy to scale up:

[0062] The material can be made into various forms such as single crystal, polycrystalline powder, thin film, and two-dimensional material to meet the needs of different application scenarios.

[0063] The chemical vapor deposition, solution growth, solid-state sintering, and pulsed laser deposition methods used are all mature and controllable conventional processes in the industry, overcoming the bottleneck of existing ferroelectric metals being unable to prepare large-size samples, and have great potential for industrial application.

[0064] (5) Broad application prospects: Due to the simultaneous integration of the conductivity of metal, the switching characteristics of ferroelectricity and the electromechanical coupling characteristics of piezoelectricity, this material has great application value in the fields of high-performance transducers, high-sensitivity sensors, low-power microelectromechanical systems (MEMS), and next-generation multifunctional electronic devices. Attached Figure Description

[0065] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0066] Figure 1 A photograph of a 6-inch nitrogen-doped cubic silicon carbide ferroelectric metal grown using Example 1;

[0067] Figure 2 Raman image of a 6-inch nitrogen-doped cubic silicon carbide crystal grown using Example 1;

[0068] Figure 3 The resistivity versus temperature of a 6-inch nitrogen-doped cubic silicon carbide crystal grown using Example 1.

[0069] Figure 4 The piezoelectric test pattern of the 6-inch nitrogen-doped cubic silicon carbide crystal obtained by Example 1;

[0070] Figure 5 The image shows the SHG plot of the 6-inch nitrogen-doped cubic silicon carbide crystal grown using Example 1; where the power of the lines increases sequentially from bottom to top.

[0071] Figure 6 The graph shows the relationship between SHG intensity and laser intensity for a 6-inch nitrogen-doped cubic silicon carbide crystal grown using Example 1.

[0072] Figure 7 The phase and amplitude diagrams of the PFM of the 6-inch nitrogen-doped cubic silicon carbide crystal obtained by Example 1 are shown.

[0073] Figure 8 The resistivity of the nitrogen-doped cubic silicon carbide ferroelectric single crystal grown in Example 2 is shown as a temperature-dependent curve.

[0074] Figure 9 The SHG test results are obtained by randomly selecting three locations to measure the nitrogen-doped cubic silicon carbide ferroelectric metal single crystal grown in Example 2.

[0075] Figure 10The results are angle-dependent SHG measurements of the nitrogen-doped cubic silicon carbide ferroelectric single crystal grown using Example 2.

[0076] Figure 11 The results of PFM testing are for the nitrogen-doped cubic silicon carbide ferroelectric metal single crystal grown using Example 2.

[0077] Figure 12 A photograph of the nitrogen-doped cubic silicon carbide ferroelectric metal single crystal grown in Example 3;

[0078] Figure 13 The resistivity of nitrogen-doped cubic silicon carbide ferroelectric metal grown in Example 3 is shown as a temperature-dependent curve.

[0079] Figure 14 The phase test results are for the PFM of the nitrogen-doped cubic silicon carbide ferroelectric metal grown in Example 3.

[0080] Figure 15 The amplitude test results are for the PFM of the nitrogen-doped cubic silicon carbide ferroelectric metal grown in Example 3.

[0081] Figure 16 Raman spectra of a cubic silicon carbide single crystal obtained in Example 3 were obtained by randomly selecting multiple points for testing. The Raman test results showed that the entire ingot was 3C-SiC, with no other crystalline phases.

[0082] Figure 17 The piezoelectric test results are shown for cubic silicon carbide single crystals grown using Example 3.

[0083] Figure 18 The image shows the piezoelectric test results of cubic silicon carbide single crystals obtained by growing in Example 3 after being flipped 180 degrees.

[0084] Figure 19 The curve showing the relationship between silicon carbide resistivity and temperature obtained using Comparative Example 1 is shown. Detailed Implementation

[0085] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0086] Example 1

[0087] The crucible used in this embodiment is a graphite crucible with an inner diameter of 200 mm and a height of 150 mm. The seed crystal is a 6-inch (0001) positive orientation semi-insulating 4H-SiC single crystal with a silicon facet. The raw materials are high-purity Si, Cr, and Ce blocks. The fluxing solution ratio is Si:Cr:Ce = 46:53:1, and the height of the melt after melting in the crucible is 30 mm.

[0088] A SiC seed crystal is fixed onto a graphite seed crystal rod, and a flux is placed in a graphite crucible. The graphite seed crystal rod and graphite crucible are placed in a crystal growth furnace, and then the growth furnace is evacuated. The vacuum level in the growth chamber is evacuated to 10... -5 The furnace chamber was then filled with 20 kPa of high-purity nitrogen and 30 kPa of high-purity argon. The crucible was heated to 1900℃ at the surface of the flux solution, maintaining the bottom temperature of the melt higher than the surface temperature, with a temperature gradient of 10℃ / cm within the melt. The mixture was held at this temperature for 2 hours. During growth, the seed crystal was rotated clockwise at 180 r / min, and the pulling speed was 30 μm / h. After 24 hours of growth, the crystal was pulled upwards for in-situ annealing, with a slow cooling time of 24 hours. After cooling to room temperature, the grown nitrogen-doped cubic silicon carbide single crystal was obtained.

[0089] The SIMS test results of the nitrogen-doped cubic silicon carbide single crystal grown in this embodiment show that the nitrogen doping concentration is 1.9 × 10⁻⁶. 20 cm -3 .

[0090] Implementation Results and Analysis:

[0091] Figure 1 This is a photograph of a 6-inch nitrogen-doped cubic silicon carbide crystal grown using this embodiment.

[0092] Figure 2 Raman spectroscopy for a 6-inch nitrogen-doped cubic silicon carbide crystal grown using this embodiment.

[0093] Figure 3 The resistivity versus temperature relationship of a 6-inch nitrogen-doped cubic silicon carbide crystal grown using Example 1. Figure 3 The material is shown to be metallic, with a room temperature resistivity of 0.58 mΩ·cm.

[0094] Figure 4 The piezoelectric test pattern of the 6-inch nitrogen-doped cubic silicon carbide crystal obtained by this embodiment shows that the material has an inverse piezoelectric effect.

[0095] Figure 5The SHG pattern of the 6-inch nitrogen-doped cubic silicon carbide crystal grown using this example is shown, with a laser wavelength of 800 nm.

[0096] Figure 6 The graph shows the relationship between SHG intensity and laser intensity for a 6-inch nitrogen-doped cubic silicon carbide crystal grown using this example. The slope of the straight line showing the correspondence between SHG signal intensity and laser wavelength is 2.01, indicating that the SHG signal is the signal of the sample itself.

[0097] Figure 7 The phase and amplitude diagrams of the PFM for the 6-inch nitrogen-doped cubic silicon carbide crystal grown using this example show that the sample exhibits room-temperature ferroelectricity.

[0098] Example 2

[0099] The crucible used in this embodiment is a graphite crucible with an inner diameter of 150 mm and a height of 100 mm. The seed crystal is a 4-inch (0001) positive orientation semi-insulating 4H-SiC single crystal with a silicon facet. The raw materials are high-purity Si, Cr, and Co blocks. The fluxing solution ratio is Si:Cr:Co = 46:53:1, and the height of the melt after melting in the crucible is 40 mm.

[0100] A SiC seed crystal is fixed on a graphite seed crystal rod, and Si, Cr, and Co fluxing agents are placed in a graphite crucible. The graphite seed crystal rod and graphite crucible are placed in a crystal growth furnace, and then the growth furnace is evacuated. The vacuum level in the growth chamber is evacuated to 10... -5 The furnace chamber was then filled with 30 kPa of high-purity nitrogen and 20 kPa of high-purity argon. The crucible was heated to 1900℃ at the surface of the flux solution, maintaining the bottom temperature of the melt higher than the surface temperature, with a temperature gradient of 5℃ / cm within the melt. The mixture was held at this temperature for 3 hours. During growth, the seed crystal was rotated clockwise at 120 r / min, and the pulling speed was 30 μm / h. After 72 hours of growth, the crystal was pulled upwards for in-situ annealing, with a slow cooling time of 24 hours. After cooling to room temperature, nitrogen-doped cubic silicon carbide single crystals were obtained.

[0101] The SIMS test results of the nitrogen-doped cubic silicon carbide single crystal grown in this embodiment show that the nitrogen doping concentration is 2.5 × 10⁻⁶. 20 cm -3 .

[0102] Implementation Results and Analysis:

[0103] Figure 8The resistivity of the nitrogen-doped cubic silicon carbide single crystal grown in this embodiment varies with temperature. It can be seen that the nitrogen-doped cubic silicon carbide single crystal exhibits metallic behavior. The room temperature resistivity is 0.45 mΩ·cm.

[0104] Figure 9 The SHG test results are shown for the nitrogen-doped cubic silicon carbide single crystal grown using this embodiment. It can be seen that the grown nitrogen-doped cubic silicon carbide exhibits an SHG signal, indicating that the sample has a non-centrosymmetric crystal structure.

[0105] Figure 10 The results are angle-dependent SHG measurements of the nitrogen-doped cubic silicon carbide single crystal grown using this embodiment. The angle-dependent SHG measurements show that the SHG signal of nitrogen-doped cubic silicon carbide is an intrinsic signal of the material, which is consistent with the six-petaled characteristic of the angle-dependent SHG of the (111) crystal plane of the non-centrosymmetric space group F-43m.

[0106] Figure 11 The PFM test results for the nitrogen-doped cubic silicon carbide single crystal grown using this embodiment show that nitrogen-doped cubic silicon carbide exhibits room-temperature ferroelectricity.

[0107] Example 3

[0108] The crucible used in this embodiment is a graphite crucible with an inner diameter of 150 mm and a height of 100 mm. The seed crystal is a 4-inch (0001) positive orientation semi-insulating 4H-SiC single crystal with a silicon facet. The raw materials are high-purity Si, Cr, and Fe blocks. The fluxing solution ratio is Si:Cr:Fe = 46:49:5, and the height of the melt after melting in the crucible is 40 mm.

[0109] A SiC seed crystal is fixed on a graphite seed crystal rod, and Si, Cr, and Fe fluxing agents are placed in a graphite crucible. The graphite seed crystal rod and graphite crucible are placed in a crystal growth furnace, and then the growth furnace is evacuated. The vacuum level in the growth chamber is evacuated to 10... -5 The furnace chamber was then filled with 40 kPa of high-purity nitrogen and 10 kPa of high-purity argon. The crucible was heated to 1900℃ at the surface of the flux solution, maintaining the bottom temperature of the melt higher than the surface temperature, with a temperature gradient of 5℃ / cm within the melt. The mixture was held at this temperature for 3 hours. During growth, the seed crystal was rotated clockwise at 150 r / min, and the pulling speed was 20 μm / h. After 72 hours of growth, the crystal was pulled upwards for in-situ annealing, with a slow cooling time of 24 hours. After cooling to room temperature, nitrogen-doped cubic silicon carbide single crystals were obtained.

[0110] The SIMS test results of the nitrogen-doped cubic silicon carbide single crystal grown in this embodiment show that the nitrogen doping concentration is 3.04 × 10⁻⁶. 20 cm -3 It exhibits metallic behavior; the room temperature resistivity is 0.33 mΩ·cm, and the sample exhibits ferroelectricity and piezoelectricity.

[0111] Implementation Results and Analysis:

[0112] Figure 12 This is a photograph of a 4-inch nitrogen-doped cubic silicon carbide crystal grown using this embodiment.

[0113] Figure 13 The resistivity curve of the nitrogen-doped cubic silicon carbide single crystal grown in this embodiment is shown as a function of temperature. It can be seen that the nitrogen-doped cubic silicon carbide single crystal exhibits metallic behavior. The room temperature resistivity is 0.33 mΩ·cm.

[0114] Figure 14 The phase test results are for the PFM of the nitrogen-doped cubic silicon carbide single crystal grown using this embodiment.

[0115] Figure 15 The amplitude test results of the PFM of the nitrogen-doped cubic silicon carbide single crystal grown using this embodiment are shown.

[0116] Figure 16 The Raman spectra of a cubic silicon carbide single crystal obtained using this embodiment were obtained by randomly selecting multiple points for testing. The Raman test results show that the entire ingot is 3C-SiC, with no other crystalline phases.

[0117] Figure 17 The piezoelectric test results of the cubic silicon carbide single crystal grown using this embodiment are shown.

[0118] Figure 18 The piezoelectric test results are shown for cubic silicon carbide single crystals grown using this embodiment after being flipped 180 degrees. It can be seen that the dpiezoelectric of the sample before and after the flipping... 33 Equal values ​​with opposite signs indicate uniform polarization and good performance of the sample.

[0119] Example 4

[0120] High-purity silicon powder and high-purity carbon powder were mixed in a 1:1 molar ratio, and 1% As₂O₃ (based on As) was added as a dopant. The mixed raw materials were ball-milled for 48 hours. The ball-milled raw materials were then placed in a graphite crucible, which was placed in a medium-frequency induction heating furnace. The growth furnace was then evacuated. The vacuum level in the growth chamber was increased to 10... -5High-purity argon gas at 90 kPa was introduced into the growth furnace to heat the graphite crucible to 2000℃, and maintained at 2000℃ for 20 h. The heating power of the medium-frequency induction heating furnace was turned off, and after the furnace temperature cooled to room temperature, the graphite crucible was removed to obtain As-doped cubic silicon carbide polycrystalline material.

[0121] The SIMS test results of the As-doped cubic silicon carbide polycrystalline silicon grown in this embodiment show that the atomic doping concentration of As is 1.50 × 10⁻⁶. 20 cm -3 .

[0122] The As-doped cubic silicon carbide polycrystalline material prepared in this embodiment exhibits metallic behavior; its room temperature resistivity is 0.5 mΩ·cm, and the sample exhibits ferroelectricity and piezoelectricity.

[0123] Example 5

[0124] Using a 4-inch cubic silicon carbide single crystal with a 0-degree offset and a (111) silicon surface as a substrate, the cubic silicon carbide substrate was placed in a 1:1 volume ratio of acetone and methanol and ultrasonically cleaned for 3 minutes. The cleaned silicon carbide single crystal substrate was then dried with high-purity nitrogen. The dried cubic silicon carbide single crystal substrate was then placed in a NaOH:H2O2:H2O = 1:2:5 volume ratio solution and boiled at 80°C for 30 minutes. The substrate was then removed and ultrasonically cleaned in deionized water for 5 minutes. Subsequently, the single crystal substrate was cleaned in a HF:H2O = 1:10 volume ratio solution for 1 minute, and then ultrasonically cleaned in deionized water for 5 minutes. The cleaned silicon carbide single crystal substrate was then dried with high-purity nitrogen. A single-crystal substrate was placed in a high-temperature chemical vapor deposition (CVD) chamber. The substrate temperature was heated to 700°C, and high-purity CH4 and SiH4 were introduced, with a C / Si ratio of 1.0. The pressure was controlled at 0.1 Pa, and the growth rate was 0.2-0.5 µm / h to grow a buffer layer with a thickness of 1 µm. The substrate temperature was then heated to 1550°C, and the chamber pressure was increased to 8000 Pa. High-purity SiH4, C3H8, and N2 were introduced at flow rates of 20 ml / min, 60 ml / min, and 10 ml / min, respectively. High-purity H2 (5N) passivated by a palladium passivator was used as the carrier gas at a flow rate of 100 ml / min. The growth was carried out for 50 min to obtain the nitrogen-doped ferroelectric metal thin film of the present invention.

[0125] The SIMS test results of the nitrogen-doped ferroelectric metal thin film grown in this embodiment show that the nitrogen doping concentration is 3.0 × 10⁻⁶. 20 cm -3 .

[0126] The nitrogen-doped ferroelectric metal film prepared in this embodiment exhibits metallic behavior; the room temperature resistivity is 0.43 mΩ·cm, and the sample has ferroelectric and piezoelectric effects.

[0127] Example 6

[0128] Using a 4-inch cubic silicon carbide substrate with an orientation of (111), the single-crystal substrate was ultrasonically cleaned for 15 min each time in acetone, ethanol, and deionized water. It was then immersed in a 5% HF solution of dilute hydrofluoric acid (HF) for 2 min, dried with high-purity nitrogen, and quickly placed into the sample stage of the vacuum chamber of pulsed laser deposition (PLD). A cubic silicon carbide target was mounted on the target stage. The vacuum chamber of the PLD was closed, and the vacuum level in the deposition chamber was evacuated to a value better than 1 × 10⁻⁶ using both mechanical and molecular pumps. -4 The substrate was heated to 900°C and subjected to a vacuum chamber pressure of 1 Pa using high-purity Ar and N₂ in a volume ratio of 3:2. A KrF excimer laser with a wavelength of 248 nm was used as the laser source to bombard the cubic silicon carbide target with a pulse energy density of 5 J / cm², a pulse frequency of 10 Hz, and a target-substrate distance of 8 cm. After 30 min of growth, a nitrogen-doped ferroelectric single-crystal thin film was deposited. After deposition, the vacuum and deposition temperature were maintained, and the substrate and film were annealed in situ for another 30 min. After deposition and annealing, the film was slowly cooled to room temperature in a vacuum at a cooling rate of less than 5°C / min to obtain the nitrogen-doped ferroelectric thin film.

[0129] The SIMS test results of the nitrogen-doped ferroelectric metal thin film grown in this embodiment show that the nitrogen doping concentration is 3.5 × 10⁻⁶. 20 cm -3 .

[0130] The nitrogen-doped ferroelectric metal film prepared in this embodiment exhibits metallic behavior; the room temperature resistivity is 0.42 mΩ·cm, and the sample has ferroelectric and piezoelectric effects.

[0131] Comparative Example 1

[0132] The preparation process for this comparative example is the same as in Example 1, except for the volume ratio of nitrogen and argon in the furnace chamber. Specifically, this comparative example involves filling the furnace chamber with 5 kPa of high-purity nitrogen and 45 kPa of high-purity argon.

[0133] SIMS testing results of the nitrogen-doped cubic silicon carbide single crystal grown in this proportion show that the nitrogen doping concentration is only 9 × 10⁻⁶. 17 cm -3 .

[0134] Figure 19This is the resistivity versus temperature curve of silicon carbide obtained using this comparative example. The resistivity versus temperature curve demonstrates that this sample does not exhibit metallic behavior, but rather semiconductor behavior.

[0135] Comparative Example 2

[0136] The preparation process for this comparative example is the same as in Example 4, except that the amount of dopant used is different. Specifically, the atomic percentage of As2O3 used in this comparative example is 0.01% (based on As).

[0137] SIMS testing results of the as-doped cubic silicon carbide polycrystalline material grown in this comparative model show that the as doping concentration is only 4 × 10⁻⁶. 17 cm -3 .

[0138] The resistivity-temperature curve shows that this sample does not exhibit metallic behavior, but rather semiconductor behavior.

[0139] Comparative Example 3

[0140] The preparation process for this comparative example is the same as in Example 5, except that the volume percentage of nitrogen is different. Specifically, high-purity SiH4, C3H8, and N2 are introduced into the chemical vapor deposition chamber in this comparative example at flow rates of 3 ml / min, 7 ml / min, and 0.5 ml / min, respectively.

[0141] SIMS tests on the nitrogen-doped ferroelectric thin film grown in this proportion showed that the nitrogen doping concentration was only 3 × 10⁻⁶. 17 cm -3 .

[0142] The resistivity-temperature curve shows that this sample does not exhibit metallic behavior, but rather semiconductor behavior.

[0143] Comparative Example 4

[0144] The preparation process for this comparative example is the same as in Example 6, except that the volume percentage of nitrogen is different. Specifically, in this comparative example, high-purity Ar and N2 are introduced into the pulsed laser deposition vacuum chamber, and the volume percentage of nitrogen in the mixture is 5%.

[0145] SIMS tests on the nitrogen-doped ferroelectric thin film grown in this proportion showed that the nitrogen doping concentration was only 5 × 10⁻⁶. 17 cm -3 .

[0146] The resistivity-temperature curve shows that this sample does not exhibit metallic behavior, but rather semiconductor behavior.

Claims

1. An application of a composite material as a ferroelectric metal, characterized in that: The composite material consists of cubic silicon carbide crystals and doping elements therein, wherein the concentration of the doping elements is greater than or equal to 1 × 10⁻⁶. 18 cm -3 ; The doping element is selected from one or more of the elements N, P, As, Sb, Al, Ti, B, Ti, V, Cr, Mn, Fe, Co, Ni and Cu.

2. The application according to claim 1, wherein, The resistivity of the composite material exhibits metallic behavior in relation to temperature, with a room temperature resistivity of 0.0001-1 mΩ·cm.

3. The application according to claim 1, wherein, The composite material is in the form of single crystal, polycrystalline powder, thin film, or two-dimensional material.

4. The application according to claim 1, wherein, The composite material exhibits room-temperature ferroelectricity.

5. The application according to claim 1, wherein, The composite material exhibits a piezoelectric effect.

6. The application according to claim 1, wherein, The composite material exhibits an inverse piezoelectric effect.

7. The application according to any one of claims 1 to 6, wherein, The composite material is used in transducers, sensors, microelectromechanical systems, information storage, energy storage, or electro-optical controllers.

8. The application according to any one of claims 1 to 6, wherein, The method for preparing the composite material is a liquid phase method, a solid phase method, a chemical vapor deposition method, or a physical vapor transport method, and includes: in an atmosphere containing dopant elements or in the presence of raw materials, applying energy to cause a reaction between a silicon source, a carbon source, and the dopant elements on a substrate, or to combine cubic silicon carbide raw materials with the dopant elements to form the doped cubic silicon carbide crystal.

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