Ferroelectric metal and preparation method and application thereof

Abstract

The invention provides ferroelectric metal and a preparation method and application thereof. The ferroelectric metal is composed of cubic silicon carbide crystals and doping elements doped in the cubic silicon carbide crystals, and the concentration of the doping elements is larger than or equal to 1 * 10 < 18 > cm <-3 >. The material can be prepared by a chemical vapor deposition method, a high-temperature solution growth method, a solid-phase sintering method, a pulsed laser deposition method and the like. Due to the fact that the conductivity of metal, the switching characteristic of ferroelectricity and the force-electricity coupling characteristic of piezoelectricity are integrated at the same time, the ferroelectric metal has huge application value in the fields of high-performance transducers, high-sensitivity sensors, low-power-consumption micro-electro-mechanical systems (MEMS), next-generation multifunctional electronic devices and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of novel electronic functional materials, and particularly relates to a ferroelectric metal and a preparation method and application thereof. BACKGROUND

[0002] Ferroelectric materials are a kind of functional materials that can produce spontaneous polarization when an external electric field is zero, and the direction of the spontaneous polarization can be reversed by an external electric field. Ferroelectric materials play an important role in many electronic devices such as non-volatile memories, sensors, piezoelectric drivers, etc. However, traditional ferroelectricity is considered to be mutually exclusive with metal conductivity, because the high concentration of free electrons in metals will annihilate the internal polarization electric dipoles through the electrostatic shielding effect, thereby destroying the macroscopic polarization field, i.e. long-range ferroelectric order. Therefore, to date, most of the discovered ferroelectric materials are insulators or semiconductors.

[0003] This traditional understanding was challenged in 1965. Anderson and Blount (P. W. Anderson, E. I. Blount, Symmetry considerations on martensitic transformations: “Ferroelectric” metals? Physical Review Letters. (1965) 14, 217-219.) first proposed the concept of “ferroelectric metal”, and theoretically predicted that certain metallic substances might lose inversion symmetry centers through structural phase transition, thereby generating a reversible spontaneous polarization, i.e. simultaneously possessing metallic conductivity and ferroelectricity. However, in the subsequent nearly half a century, this prediction has always lacked solid experimental evidence.

[0004] Until 2013, researchers first confirmed the existence of a polar metal experimentally. They found that LiOsO3 undergoes a structural phase transition from a centrosymmetric space group (R-3c) to a non-centrosymmetric space group (R3c) below 140 K, and the material remains metallic before and after the phase transition (Nature Materials, 2013, 12, 1024). Although this work confirmed the existence of a “polar metal” with a polar structure, it still lacked direct experimental data confirming the characteristics of “ferroelectric metal” (reversible macroscopic spontaneous polarization by electric field). Therefore, for a long time, it has been a consensus in the fields of condensed matter physics and materials research that ferroelectricity and metallic conductivity cannot coexist.

[0005] However, the currently discovered polar metal materials, such as LiOsO3, still have obvious limitations, which seriously restrict their practical applications:

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

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

[0008] Preparation and size limitation: The reported material size is small (such as 200 µm order of magnitude), which is difficult to meet the needs of macro device manufacturing.

[0009] Therefore, there is an urgent need in the art to develop a truly, non-toxic, low resistivity, and easy to scale new ferroelectric metal material to promote its practical application in transducers, sensors and micro-electro-mechanical systems, information storage, energy storage and electro-optical control, etc.

[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 field, excellent chemical stability and outstanding mechanical properties, and has good compatibility with existing semiconductor manufacturing processes. Currently, the doping research of cubic silicon carbide mainly focuses on adjusting its conductivity type (n-type or p-type) for power electronic devices, or introducing transition metals (such as Mn, Fe, etc.) to prepare diluted magnetic semiconductors. There is no public literature or technical material indicating that the intrinsic ferroelectricity of cubic silicon carbide can be induced by doping treatment, and the efficient coexistence of ferroelectricity and metallicity in it has never been disclosed. In the prior art, doped cubic silicon carbide is only considered as a conductor, semiconductor or magnetic material, and its application potential as a ferroelectric metal is completely unknown. SUMMARY

[0011] In view of the problems and deficiencies of the prior art, the present application aims to overcome the lack of ferroelectric metal materials and direct experimental data confirming the existence of ferroelectric metals, and the inherent defects of existing polar metal materials (such as LiOsO3), and provides a new type of ferroelectric metal material with excellent comprehensive performance, environmental friendliness and easy industrialization, and a preparation method thereof.

[0012] The inventors of the present application have unexpectedly found that when the doping concentration of cubic silicon carbide (3C-SiC) crystal is greater than or equal to 1×10 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, expressed 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 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 according to the present application, the ferroelectric metal has a converse piezoelectric effect.

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

[0024] In a second aspect, the present application provides a method for preparing the ferroelectric metal according to the present application, wherein the method is a liquid phase method, a solid phase method, a chemical vapor deposition method or a physical vapor transport method, and comprises: reacting a silicon source, a carbon source and a dopant element in the presence of an atmosphere or a raw material containing the dopant element, or combining a cubic silicon carbide raw material with the dopant element, by applying energy to form the doped cubic silicon carbide crystal.

[0025] Preferably, in the method for preparing the ferroelectric metal according to the present application, the amount of the dopant element added is such that the doping concentration of the dopant element in the cubic silicon carbide crystal is greater than or equal to 1 x 10 18 cm -3 .

[0026] In a third aspect, the present application provides a method for preparing the ferroelectric metal according to the present application, wherein the method is a liquid phase method, and comprises the following steps:

[0027] (1) placing a cosolvent in a graphite crucible, evacuating the growth furnace, and then introducing a mixed atmosphere or pure inert gas (such as argon, helium or hydrogen) to control the gas pressure in the growth furnace;

[0028] (2) heating the graphite crucible to completely melt the cosolvent to form a melt, and reaching the growth temperature of SiC;

[0029] (3) pushing down the graphite pulling rod in the growth furnace to make the seed crystal contact with the melt, and then growing the N, P, Al or B doped cubic silicon carbide single crystal.

[0030] In the liquid phase method according to the present application, when the mixed atmosphere is formed by mixing nitrogen with one or more selected from hydrogen, helium and argon, an N doped cubic silicon carbide single crystal can be prepared; when the mixed atmosphere is formed by mixing one or more selected from hydrogen, helium and argon, a nitrogen-containing compound (such as magnesium nitride or lithium nitride) with a melting point lower than 1850 ℃ can be added to the cosolvent, and then an N doped cubic silicon carbide single crystal can be prepared; when a B-containing gas (such as B2H6), a P-containing gas (such as PH3) or an Al-containing gas (such as (CH3)3Al) is mixed with one or more selected from hydrogen, helium and argon, a P, Al or B doped cubic silicon carbide single crystal can be prepared 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) placing a cubic silicon carbide substrate in a chemical vapor deposition chamber;

[0043] (2) during crystal growth, introducing a mixed gas containing SiH4, C3H8 and N2 to prepare a N-doped cubic silicon carbide single crystal; introducing a mixed gas containing SiH4, C3H8 and B2H6 to prepare a B-doped cubic silicon carbide single crystal; introducing a mixed gas containing SiH4, C3H8 and (CH3)3Al to prepare an Al-doped cubic silicon carbide single crystal; or introducing a mixed gas containing SiH4, C3H8 and PH3 to prepare a P-doped cubic silicon carbide single crystal;

[0044] wherein 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 application, the gas pressure during crystal growth is 7500-8500 Pa.

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

[0050] In a sixth aspect, the present application provides a method for preparing the ferroelectric metal of the present application, which is a physical vapor transport method, comprising the following steps:

[0051] (1) placing a cubic silicon carbide substrate on a sample table of a pulsed laser deposition vacuum chamber, and installing a cubic silicon carbide target;

[0052] (2) heating the substrate and introducing a mixed gas to control the gas pressure, and then bombarding the target with a laser to deposit a N-, B-, Al- or P-doped cubic silicon carbide single crystal; wherein when the mixed gas contains nitrogen, a N-doped cubic silicon carbide single crystal can be prepared; when the mixed gas contains B2H6, a B-doped cubic silicon carbide single crystal can be prepared; when the mixed gas contains (CH3)3Al, an Al-doped cubic silicon carbide single crystal can be prepared; and when the mixed gas contains PH3, a P-doped cubic silicon carbide single crystal can be prepared.

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

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

[0055] Preferably, in the physical vapor transport method of the present application, the pressure control in step (2) is performed by controlling the pressure of the vacuum chamber to 1-5 Pa.

[0056] In a seventh aspect, the present application provides an application of the ferroelectric metal of the present application in a transducer, a sensor, a micro-electro-mechanical system, an information storage, an energy storage or an electro-optical modulator.

[0057] The present application has the following advantages:

[0058] (1) The present application successfully realizes the efficient coexistence of ferroelectricity and metallicity for the first time: by high-concentration doping (greater than or equal to 1×10 18 cm -3 ) in cubic silicon carbide, the present application breaks the traditional concept that the two cannot coexist, and provides a brand-new material system that has room-temperature ferroelectricity / piezoelectric effect and excellent metal conductivity (room-temperature resistivity as low as 0.0001-1 mΩ·cm) at the same time, which is different from the previous polarized metals such as LiOsO3, and realizes the ferroelectricity and the reversal of the ferroelectric polarization direction under an electric field in addition to confirming the polarized metal.

[0059] (2) Non-toxic, environmentally friendly and high safety: the present application uses cubic silicon carbide as the substrate, and the selected doping elements (such as N, P, Al, B, etc.) are non-toxic or low-toxic, which fundamentally solves the toxicity and environmental risk brought by the osmium element in LiOsO3, and meets the development trend of green materials.

[0060] (3) Excellent comprehensive electrical performance: the room-temperature resistivity of the ferroelectric metal provided by the present application is significantly lower than that of the reported LiOsO3 (1.5 mΩ·cm), reaching the level of traditional metals, which is conducive to reducing the energy loss in device operation and improving the signal response speed.

[0061] (4) Multiple material forms, mature preparation process and easy to scale:

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

[0063] The adopted chemical vapor deposition, solution growth method, solid phase sintering, pulse laser deposition and the like are mature, controllable and conventional processes in the industry, which overcomes the bottleneck that the existing ferroelectric metal is difficult to prepare large-size samples, and has great industrialization application potential.

[0064] (5) Wide application prospect: since the material simultaneously integrates the conductivity of metal, the switching characteristics of ferroelectric and the force-electric coupling characteristics of piezoelectric, the material has great application value in high-performance transducers, high-sensitivity sensors, low-power micro-electro-mechanical systems (MEMS), next-generation multifunctional electronic devices and the like. BRIEF DESCRIPTION OF DRAWINGS

[0065] Hereinafter, the embodiments of the present application will be described in detail with reference to the accompanying drawings, in which:

[0066] Figure 1 It is a photo of 6-inch nitrogen-doped cubic silicon carbide ferroelectric metal grown by using Example 1;

[0067] Figure 2 It is a Raman chart of 6-inch nitrogen-doped cubic silicon carbide crystal obtained by using Example 1;

[0068] Figure 3 It is a relationship chart of resistivity and temperature of 6-inch nitrogen-doped cubic silicon carbide crystal obtained by using Example 1;

[0069] Figure 4 It is a piezoelectric test chart of 6-inch nitrogen-doped cubic silicon carbide crystal obtained by using Example 1;

[0070] Figure 5 It is a SHG chart of 6-inch nitrogen-doped cubic silicon carbide crystal obtained by using Example 1; wherein the lines increase in power from bottom to top;

[0071] Figure 6 It is a chart of SHG intensity and laser intensity of 6-inch nitrogen-doped cubic silicon carbide crystal obtained by using Example 1;

[0072] Figure 7 It is a phase chart and amplitude chart of PFM of 6-inch nitrogen-doped cubic silicon carbide crystal obtained by using Example 1;

[0073] Figure 8 It is a curve of resistivity of nitrogen-doped cubic silicon carbide ferroelectric metal single crystal grown by using Example 2 and temperature;

[0074] Figure 9 It is a SHG test result of nitrogen-doped cubic silicon carbide ferroelectric metal single crystal grown by using Example 2 and randomly selected three positions;

[0075] Figure 10Angle dependent SHG test results for a nitrogen doped cubic silicon carbide ferroelectric metal single crystal grown using Example 2;

[0076] Figure 11 PFM test results for a nitrogen doped cubic silicon carbide ferroelectric metal single crystal grown using Example 2;

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

[0078] Figure 13 A plot of resistivity versus temperature for a nitrogen doped cubic silicon carbide ferroelectric metal grown using Example 3;

[0079] Figure 14 PFM phase test results for a nitrogen doped cubic silicon carbide ferroelectric metal grown using Example 3;

[0080] Figure 15 PFM amplitude test results for a nitrogen doped cubic silicon carbide ferroelectric metal grown using Example 3;

[0081] Figure 16 A Raman plot for a crystal tested at random points on a cubic silicon carbide single crystal grown using Example 3. The Raman test results show that the entire crystal ingot is 3C-SiC, with no other crystalline phases;

[0082] Figure 17 A piezoelectric test results plot for a cubic silicon carbide single crystal grown using Example 3;

[0083] Figure 18 A piezoelectric test results plot for a cubic silicon carbide single crystal grown using Example 3, flipped 180 degrees;

[0084] Figure 19 A plot of resistivity versus temperature for a silicon carbide obtained using Comparative Example 1. DETAILED DESCRIPTION

[0085] The application will be further described in details with reference to specific embodiments, which are given by way of illustration only and are not intended to limit the scope of the application.

[0086] Example 1

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

[0088] The SiC seed crystal is fixed on a graphite seed crystal rod, and the fluxing agent is placed in a graphite crucible. The graphite seed crystal rod and the graphite crucible are placed in a crystal growth furnace, and then the growth furnace is evacuated. When the vacuum degree of the growth chamber is extracted to 10 -5 Pa, 20 kPa of high-purity nitrogen gas and 30 kPa of high-purity argon gas are filled into the furnace chamber. The crucible is heated to make the temperature at the liquid level of the fluxing solution reach 1900°C, the temperature at the bottom of the melt is kept higher than the temperature at the liquid level, the temperature gradient in the melt is controlled to be 10°C / cm, and the temperature is kept constant for 2 h. During the growth process, the seed crystal is rotated clockwise at a speed of 180 r / min, and the pulling speed of the seed crystal is 30 μm / h. After 24 h of growth, the crystal is pulled upward for in-situ annealing, and the slow cooling time is 24 h. After cooling to room temperature, the grown nitrogen-doped cubic silicon carbide single crystal is obtained.

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

[0090] Implementation results and analysis:

[0091] Figure 1 The photo of the 6-inch nitrogen-doped cubic silicon carbide crystal obtained by using the growth method of this example is shown.

[0092] Figure 2 The Raman spectrum of the 6-inch nitrogen-doped cubic silicon carbide crystal obtained by using the growth method of this example is shown.

[0093] Figure 3 The relationship between the resistivity and the temperature of the 6-inch nitrogen-doped cubic silicon carbide crystal obtained by using the growth method of Example 1 is shown. Figure 3 It is shown that the material has metallic properties, and the room temperature resistivity is 0.58 mΩ·cm.

[0094] Figure 4 The piezoelectric test graph of the 6-inch nitrogen-doped cubic silicon carbide crystal obtained by using the growth method of this example is shown, which shows that the material has an inverse piezoelectric effect.

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

[0096] Figure 6 The SHG intensity versus laser intensity graph of the 6-inch nitrogen-doped cubic silicon carbide crystal grown in this example is shown in Figure 7. The slope of the straight line showing the correspondence between the SHG signal intensity and the laser wavelength is 2.01, which indicates that the SHG signal is the signal of the sample itself.

[0097] Figure 7 The phase and amplitude graphs of the PFM of the 6-inch nitrogen-doped cubic silicon carbide crystal grown in this example are shown in Figure 8, which shows that the sample has room-temperature ferroelectricity.

[0098] Example 2

[0099] The crucible used in this example 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 crystal direction semi-insulating 4H-SiC single crystal, and the growth surface is the silicon surface. The raw materials are high-purity Si blocks, Cr blocks, and Co blocks. The ratio of the complexing solution used is Si:Cr:Co = 46:53:1, and the height of the melt after the solution is melted in the crucible is 40 mm.

[0100] The SiC seed crystal is fixed on a graphite seed crystal rod, and the Si, Cr, and Co complexing agents are placed in a graphite crucible. The graphite seed crystal rod and the graphite crucible are placed in a crystal growth furnace, and then the growth furnace is evacuated. After the vacuum degree of the growth chamber is extracted to 10 -5 Pa, 30 kPa of high-purity nitrogen and 20 kPa of high-purity argon are filled into the furnace chamber. The crucible is heated to make the temperature at the liquid level of the complexing solution reach 1900°C, the temperature at the bottom of the melt is kept higher than that at the liquid level, the temperature gradient in the melt is controlled to be 5°C / cm, and the temperature is kept constant for 3 h. During the growth, the seed crystal is rotated clockwise at a speed of 120 r / min, and the pulling speed of the seed crystal is 30 μm / h. After 72 h of growth, the crystal is pulled upward for in-situ annealing, the slow cooling time is 24 h, and after cooling to room temperature, a nitrogen-doped cubic silicon carbide single crystal is obtained.

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

[0102] Implementation results and analysis:

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

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

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

[0106] Figure 11 The PFM test results of the nitrogen-doped cubic silicon carbide single crystal grown in this example, which show that the nitrogen-doped cubic silicon carbide has room-temperature ferroelectricity.

[0107] Example 3

[0108] The crucible used in this example 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 crystal direction of semi-insulating 4H-SiC single crystal, and the growth surface is the silicon surface. The raw materials are high-purity Si blocks, Cr blocks, and Fe blocks. The ratio of the used cosolvent is Si:Cr:Fe = 46:49:5, and the height of the melt after the solution is melted in the crucible is 40 mm.

[0109] The SiC seed crystal is fixed on the graphite seed crystal rod, and the Si, Cr, and Fe cosolvents are placed in the graphite crucible. The graphite seed crystal rod and the graphite crucible are placed in the crystal growth furnace, and then the growth furnace is evacuated. After the vacuum degree of the growth chamber is extracted to 10 -5 Pa, 40 kPa of high-purity nitrogen and 10 kPa of high-purity argon are filled into the furnace chamber. The crucible is heated to make the temperature at the liquid level of the cosolvent reach 1900℃, the temperature at the bottom of the melt is higher than that at the liquid level, the temperature gradient in the melt is controlled to be 5℃ / cm, and the temperature is kept constant for 3 h. During the growth, the seed crystal is rotated clockwise at a speed of 150 r / min, and the pulling speed of the seed crystal is 20 μm / h. After 72 h of growth, the crystal is pulled upward for in-situ annealing, the slow cooling time is 24 h, and after cooling to room temperature, a nitrogen-doped cubic silicon carbide single crystal is obtained.

[0110] The SIMS test result of the nitrogen-doped cubic silicon carbide single crystal grown in this embodiment shows that the doping concentration of nitrogen is 3.04×10 20 cm -3 , showing metallic behavior; the room temperature resistivity is 0.33 mΩ·cm, and the sample has ferroelectricity and piezoelectric effect.

[0111] Implementation results and analysis:

[0112] Figure 12 It is a photo of the 4-inch nitrogen-doped cubic silicon carbide crystal obtained by growth in this embodiment.

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

[0114] Figure 14 It is the phase test result of PFM of the nitrogen-doped cubic silicon carbide single crystal grown in this embodiment.

[0115] Figure 15 It is the amplitude test result of PFM of the nitrogen-doped cubic silicon carbide single crystal grown in this embodiment.

[0116] Figure 16 It is the Raman spectrum of the crystal tested at random points on the cubic silicon carbide single crystal grown in this embodiment. The Raman test result shows that the entire crystal ingot is 3C-SiC, and there is no other crystal phase.

[0117] Figure 17 It is the non-inverted piezoelectric test result of the cubic silicon carbide single crystal obtained by growth in this embodiment.

[0118] Figure 18 It is the piezoelectric test result of the cubic silicon carbide single crystal obtained by growth in this embodiment after being turned over by 180 degrees. It can be seen that the d 33 value of the sample before and after turning over is equal in size and opposite in sign. Equal in size and opposite in sign indicates that the sample polarization is uniform and the performance is good.

[0119] Embodiment 4

[0120] High-purity silicon powder and high-purity carbon powder are mixed in a proportion of 1:1 in terms of element molar ratio, and As2O3 (calculated as As) with an atomic ratio of 1% is added as a dopant. The mixed raw materials are ball milled in a ball mill for 48 h, and the ball-milled raw materials are placed in a graphite crucible, the graphite crucible is placed in a medium-frequency induction heating furnace, and then the growth furnace is evacuated. After the vacuum degree of the growth chamber is extracted to 10 -5Pa, the high-purity argon gas was filled into the growth furnace at 90 kPa, the graphite crucible was heated to 2000 °C and kept for 20 h. The power supply of the intermediate frequency induction heating furnace was turned off, the furnace temperature was cooled to room temperature, and the graphite crucible was taken out to obtain the As-doped cubic silicon carbide polycrystal.

[0121] The SIMS test result of the As-doped cubic silicon carbide polycrystal grown in the example shows that the atomic doping concentration of As is 1.50×10 20 cm -3 .

[0122] The As-doped cubic silicon carbide polycrystal prepared in the example shows metallic behavior; the room temperature resistivity is 0.5 mΩ·cm, and the sample has ferroelectricity and piezoelectric effect.

[0123] Example 5

[0124] A 4-inch cubic silicon carbide single crystal with a growth surface of (111) silicon and a 0-degree off-angle was used as a substrate, the cubic silicon carbide substrate was placed in a mixed solution of acetone and methanol at a volume ratio of 1:1, and ultrasonic cleaning was performed for 3 minutes. The cleaned cubic silicon carbide single crystal substrate was blown dry with high-purity nitrogen. The dried cubic silicon carbide single crystal substrate was placed in a mixed solution of NaOH:H2O2:H2O=1:2:5 at 80 °C for 30 min, and then taken out and placed in deionized water for ultrasonic cleaning for 5 min. Then the single crystal substrate was placed in a solution of HF:H2O=1:10 for cleaning for 1 min, and then taken out and placed in deionized water for ultrasonic cleaning for 5 min. The cleaned cubic silicon carbide single crystal substrate was blown dry with high-purity nitrogen. The single crystal substrate was placed in a high-temperature chemical vapor deposition (CVD) chamber, the substrate temperature was heated to 700 °C, high-purity CH4 and SiH4 were introduced, C / Si=1.0, the pressure was controlled at 0.1 Pa, the growth rate was 0.2-0.5 µm / h, and a buffer layer with a thickness of 1 µm was grown. The substrate temperature was heated to 1550 °C, the cavity 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) passed through a palladium passivation device was used as a carrier gas at a flow rate of 100 ml / min, and the film was grown for 50 min to obtain the nitrogen-doped ferroelectric metal film of the application.

[0125] The SIMS test result of the nitrogen-doped ferroelectric metal film grown in the example shows that the doping concentration of nitrogen is 3.0×10 20 cm -3 .

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

[0127] Example 6

[0128] A 4-inch cubic silicon carbide substrate with (111) orientation was used as a substrate, and the single crystal substrate was sequentially cleaned in acetone, ethanol and deionized water for 15 min. The single crystal substrate was immersed in a 5% HF solution for 2 min, dried with high-purity nitrogen, and quickly placed on a sample stage in a vacuum chamber of a pulsed laser deposition (PLD). The cubic silicon carbide target was installed on a target stage. The vacuum chamber of the PLD was closed, and the vacuum degree of the deposition chamber was pumped to better than 1×10 -4 Pa using a mechanical pump and a molecular pump. The substrate was heated to 900℃, and high-purity Ar and N2 were used as the carrier gas at a volume ratio of 3:2, and the vacuum chamber pressure was 1 Pa. A KrF excimer laser with a wavelength of 248 nm was used as a laser light source to bombard the cubic silicon carbide target, the pulse energy density was 5 J / cm², the pulse frequency was 10 Hz, the target-substrate distance was 8 cm, and the nitrogen-doped ferroelectric metal single crystal thin film was deposited after growth for 30 min. After deposition, the vacuum and deposition temperature were maintained, and the substrate and the thin film were continuously annealed in situ for 30 min. After deposition and annealing, the substrate and the thin film were slowly cooled to room temperature in a vacuum at a cooling rate of less than 5℃ / min, and the nitrogen-doped ferroelectric metal thin film was obtained.

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

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

[0131] Comparative Example 1

[0132] The preparation process of the comparative example is the same as that of Example 1, except that the volume ratio of nitrogen and argon in the furnace cavity is different. Specifically, the comparative example fills 5 kPa of high-purity nitrogen and 45 kPa of high-purity argon into the furnace cavity.

[0133] The SIMS test results of the nitrogen-doped cubic silicon carbide single crystal grown in the comparative example show that the doping concentration of nitrogen is only 9×10 17 cm -3 .

[0134] Figure 19The relationship curve between resistivity and temperature of the silicon carbide obtained by the present comparative example. It is shown by the relationship curve between resistivity and temperature that the sample does not exhibit metallic behavior, but still semiconductor behavior.

[0135] Comparative Example 2

[0136] The preparation process of the present comparative example is the same as that of Example 4, except that the amount of the dopant is different. Specifically, the atomic ratio of As2O3 of the present comparative example is 0.01% (calculated as As).

[0137] The SIMS test result of the As-doped cubic silicon carbide polycrystal grown by the present comparative example shows that the doping concentration of As is only 4x10 17 cm -3 .

[0138] It is shown by the relationship curve between resistivity and temperature that the sample does not exhibit metallic behavior, but still semiconductor behavior.

[0139] Comparative Example 3

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

[0141] The SIMS test result of the nitrogen-doped ferroelectric metal thin film grown by the present comparative example shows that the doping concentration of nitrogen is only 3x10 17 cm -3 .

[0142] It is shown by the relationship curve between resistivity and temperature that the sample does not exhibit metallic behavior, but still semiconductor behavior.

[0143] Comparative Example 4

[0144] The preparation process of the present comparative example is the same as that of Example 6, except that the volume ratio of nitrogen is different. Specifically, the present comparative example introduces high-purity Ar and N2 into the pulsed laser deposition vacuum chamber, and the volume ratio of nitrogen in the mixed gas is 5%.

[0145] The SIMS test result of the nitrogen-doped ferroelectric metal thin film grown by the present comparative example shows that the doping concentration of nitrogen is only 5x10 17 cm -3 .

[0146] It is shown by the relationship curve between resistivity and temperature that the sample does not exhibit metallic behavior, but still semiconductor behavior.

Claims

1. A ferroelectric metal, characterized by: consisting of cubic silicon carbide crystals and a dopant element doped therein, the concentration of the dopant element being greater than or equal to 1 x 10 18 cm -3 .

2. The ferroelectric metal of claim 1, wherein, The resistivity of the ferroelectric metal with respect to temperature shows metallic behavior, and the room temperature resistivity is 0.0001-1 mΩ·cm.

3. The ferroelectric metal of claim 1, wherein, The doping element is selected from one or more of N, P, As, Sb, Al, Ti, B, Ti, V, Cr, Mn, Fe, Co, Ni and Cu elements.

4. The ferroelectric metal of claim 1, wherein, The ferroelectric metal is in the form of single crystal, polycrystalline powder, thin film or two-dimensional material.

5. The ferroelectric metal of claim 1, wherein, The ferroelectric metal has room temperature ferroelectricity.

6. The ferroelectric metal of claim 1, wherein, The ferroelectric metal has piezoelectric effect.

7. The ferroelectric metal of claim 1, wherein, The ferroelectric metal has inverse piezoelectric effect.

8. The ferroelectric metal of claim 1, wherein, The ferroelectric metal is prepared by a liquid phase method, a solid phase method, a chemical vapor deposition method or a physical vapor transport method.

9. A method of producing the ferroelectric metal according to any one of claims 1 to 8, characterized by, The preparation method is a liquid phase method, a solid phase method, a chemical vapor deposition method or a physical vapor transport method, and comprises: in the presence of an atmosphere or raw material containing a doping element, reacting a silicon source, a carbon source and the doping element on a substrate by applying energy, or combining cubic silicon carbide raw material with the doping element, to form the doped cubic silicon carbide crystal; wherein the amount of the doping element added is such that the doping concentration of the doping element in the cubic silicon carbide crystal is greater than or equal to 1 x 10 18 cm -3 .

10. Use of the ferroelectric metal according to any one of claims 1 to 8 in a transducer, a sensor, a microelectromechanical system, an information storage, an energy storage or an electro-optical modulator.

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