An Al-doped 4H-SiC nanowire field emission cathode and its preparation method

Abstract

This invention relates to the field of field emission cathode technology, and more particularly to an Al-doped 4H-SiC nanowire field emission cathode and its preparation method. The method includes the following steps: electrochemically etching a 4H-SiC wafer to fabricate a bamboo-like 4H-SiC nanowire array on the wafer surface; peeling off the bamboo-like 4H-SiC nanowire array and immersing it in an aluminum source solution containing Al, followed by drying; sintering the obtained 4H-SiC nanowire array in an inert environment at 800–900°C to obtain an Al-doped 4H-SiC nanowire array, which serves as the Al-doped 4H-SiC nanowire field emission cathode. This invention retains the unique structure of the bamboo-like 4H-SiC nanowires while achieving Al doping at a relatively low temperature, resulting in a field emission cathode with a low turn-on field strength and high electron emission stability.

Description

Technical Field

[0001] This invention relates to the field of field emission cathode technology, and in particular to an Al-doped 4H-SiC nanowire field emission cathode and its preparation method. Background Technology

[0002] As a core component of vacuum electronic devices, the two most important requirements for cathodes are low turn-on electric field and high electron emission stability. Compared with carbon nanotube cathodes, SiC nanomaterial cathodes have attracted much attention due to their excellent mechanical properties, low coefficient of thermal expansion, and stable chemical properties. Field emission cathodes developed based on SiC nanomaterials maintain a low turn-on electric field while exhibiting higher electron emission stability, with low attenuation of electron emission over long-term operation.

[0003] Al doping in existing technologies is often achieved through in-situ methods, which makes it difficult to accurately control the morphology of nanowires and requires very high temperatures for preparation. For example, Chinese patent CN106298398B discloses the preparation and application of in-situ Al-doped SiC nanowires with a network surface. The surface of the Al-doped SiC nanowires is a network nanostructure composed of SiO2 nanospheres connecting the Al-doped SiC nanowires. Polycarbosilane, silicon powder, and aluminum nitrate are used as reactants, and nickel nitrate is used as a catalyst. The mixed and ground reactants and a graphite substrate with the catalyst are placed in a graphite reaction chamber and then placed in a vacuum atmosphere furnace. Ar gas is introduced, and the vacuum is evacuated to 50–80 Pa. The temperature is increased to 1350–1450 °C at a heating rate of 15 °C / min and held for 60–90 min. The obtained in-situ Al-doped SiC nanowires with a network surface, used as a field emission cathode material, have an on-state electric field of 0.5 V / μm and a current density fluctuation rate of 5.8%, which is relatively high. For example, Chinese patent application CN118026731A discloses a multifunctional Al-doped core-shell structure SiC nanowire, its preparation method, and its application. A mixed powder of SiO powder and Al powder is used as a precursor. A matrix loaded with a catalyst is suspended above the precursor powder, then sealed, and then subjected to negative pressure heat treatment at 1250-1400℃ to prepare multifunctional Al-doped core-shell structure SiC nanowires. These nanowires are then applied in the field of optoelectronic materials. Summary of the Invention

[0004] The purpose of this invention is to propose an Al-doped 4H-SiC nanowire field emission cathode and its preparation method. While retaining the unique structure of bamboo-like 4H-SiC nanowires, Al doping is achieved at a lower temperature. The resulting field emission cathode has a low turn-on field strength and high electron emission stability.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] A method for preparing an Al-doped 4H-SiC nanowire field emission cathode includes the following steps:

[0007] (1) Electrochemical etching is performed on the 4H-SiC wafer to process a bamboo-shaped 4H-SiC nanowire array on the surface of the 4H-SiC wafer, and the 4H-SiC nanowire array is peeled off from the 4H-SiC wafer.

[0008] (2) The 4H-SiC nanowire array obtained in step (1) is immersed in an aluminum source solution containing Al, and then taken out and dried;

[0009] (3) The 4H-SiC nanowire array obtained in step (2) is sintered in an inert environment at 800-900℃ to obtain an Al-doped 4H-SiC nanowire array, which is the Al-doped 4H-SiC nanowire field emission cathode.

[0010] Furthermore, the Al doping amount in the Al-doped 4H-SiC nanowire array is 0.16 at% to 1.63 at%.

[0011] Furthermore, in step (2), the 4H-SiC nanowire array is immersed in an aluminum source solution containing Al for 3 to 10 minutes, and then air-dried or dried at a temperature below 60°C.

[0012] Furthermore, the aluminum source solution is an aqueous solution of aluminum chloride, aluminum nitrate, or aluminum sulfate; or the aluminum source solution is an acidic solution of aluminum chloride, aluminum nitrate, or aluminum sulfate.

[0013] Furthermore, in step (3), the 4H-SiC nanowire array obtained in step (2) is placed in a tube furnace, the tube furnace is evacuated to -0.1 MPa, and then an inert gas is introduced to atmospheric pressure, and the process is repeated multiple times.

[0014] The temperature is increased to 800-900℃ at a heating rate of 5℃ / min, held for 20-40 min, then decreased to 400-500℃ at a cooling rate of 5℃ / min, and finally cooled to room temperature with the furnace.

[0015] Furthermore, in step (1), the 4H-SiC wafer is used as the anode and the Pt wafer is used as the cathode. The C-side of the 4H-SiC wafer is used as the etching surface and is placed directly opposite the Pt electrode in the etching solution for etching. The etching voltage is 20V and the etching time is 27-30min.

[0016] The etching solution contains 99 vol% ethylene glycol, 45 wt% hydrofluoric acid, and 30 wt% hydrogen peroxide in a volume ratio of 6:3:1.

[0017] Furthermore, the etched 4H-SiC nanowire array is peeled off from the wafer, then immersed in an ethanol solution, cleaned, and air-dried.

[0018] Before etching, the 4H-SiC wafer was ultrasonically cleaned in acetone, ethanol and deionized water in sequence, and then air-dried.

[0019] Furthermore, the 4H-SiC wafer is an N-doped 4H-SiC wafer, and the length and width of the 4H-SiC wafer are 1cm × 0.5cm.

[0020] Furthermore, the nanowires of the bamboo-like 4H-SiC nanowire array have a length of 110–150 μm and a width of 15–38 nm.

[0021] An Al-doped 4H-SiC nanowire field emission cathode is prepared by the above-described method for preparing an Al-doped 4H-SiC nanowire field emission cathode.

[0022] The technical solution provided by this invention may include the following beneficial effects:

[0023] 1. Bamboo-like 4H-SiC nanowires were fabricated on a wafer by electrochemical etching, making the growth process and morphology of the nanowires controllable. Al doping was then performed on this basis, perfectly preserving the unique structure of the nanowires. The prepared Al-doped 4H-SiC nanowires have excellent field emission performance, with a turn-on field strength as low as 0.42V / μm and an electron emission fluctuation as low as 1.0% after 3 hours of continuous operation.

[0024] 2. In the sintering step of this invention, Al-doped 4H-SiC nanowires can be obtained by using a relatively low temperature of 800-900°C;

[0025] 3. The method for preparing Al-doped 4H-SiC nanowire field emission cathode of the present invention is simple, and the resulting field emission cathode exhibits a low turn-on electric field and extremely high electron emission stability. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope (SEM) image of a 4H-SiC nanowire array;

[0027] Figure 2 This is the energy dispersive X-ray spectroscopy (EDX) spectrum of Al-doped 4H-SiC nanowires.

[0028] Figure 3 This is a surface scan of Al elements in Al-doped 4H-SiC nanowires;

[0029] Figure 4These are the electron emission stability test results of an Al-doped 4H-SiC nanowire field emission cathode that has been running continuously for 3 hours.

[0030] Figure 5 These are the test results of the turn-on electric field of the emitting cathode obtained in Examples 1, 2, 1, and 2. Detailed Implementation

[0031] This invention discloses a method for preparing an Al-doped 4H-SiC nanowire field emission cathode. The Al doping temperature is low and the nanowire array morphology is complete, resulting in a field emission cathode with low turn-on field strength and high electron emission stability.

[0032] The preparation method of the present invention includes the following steps:

[0033] (1) Electrochemical etching is performed on the 4H-SiC wafer to process a bamboo-shaped 4H-SiC nanowire array on the surface of the 4H-SiC wafer, and then the 4H-SiC nanowire array is peeled off from the 4H-SiC wafer.

[0034] (2) The 4H-SiC nanowire array obtained in step (1) is immersed in an aluminum source solution containing Al, and then taken out and dried;

[0035] (3) The 4H-SiC nanowire array obtained in step (2) is sintered in an inert environment at 800-900℃ to obtain an Al-doped 4H-SiC nanowire array, which is the Al-doped 4H-SiC nanowire field emission cathode.

[0036] In this invention, bamboo-like 4H-SiC nanowires are first fabricated on a wafer using electrochemical etching technology, making the growth process and morphology of the nanowires controllable. Then, Al doping is performed on this basis, perfectly preserving the unique structure of the nanowires. The prepared Al-doped 4H-SiC nanowires exhibit excellent field emission performance, with a turn-on field strength as low as 0.42 V / μm and electron emission fluctuation as low as 1.0% after 3 hours of continuous operation. The method for preparing the Al-doped 4H-SiC nanowire field emission cathode of this invention is simple, and the resulting field emission cathode exhibits a low turn-on electric field and extremely high electron emission stability.

[0037] This invention further investigates the Al doping amount, wherein the Al doping amount in the Al-doped 4H-SiC nanowire array is 0.16 at% to 1.63 at%. Al doping can alter the band structure of SiC, reducing the band gap. When the Al doping amount is within this range, it exhibits a low turn-on electric field and high electron emission stability. Preferably, the Al doping amount in the Al-doped 4H-SiC nanowire array is 0.36 at%.

[0038] To achieve the desired Al doping level, further in step (2), the 4H-SiC nanowire array is immersed in an aluminum source solution containing Al for 3–10 minutes, then removed and air-dried or dried at a temperature below 60°C. After immersing the 4H-SiC nanowire array in the aluminum source solution for a period of time, Al elements can penetrate into and adhere to the nanowire array. After removal, it is air-dried or dried at a temperature below 60°C to prevent oxidation of the nanowires.

[0039] Specifically, the aluminum source solution is an aqueous solution of aluminum chloride, aluminum nitrate, or aluminum sulfate; or the aluminum source solution is an acidic solution of aluminum chloride, aluminum nitrate, or aluminum sulfate. When aluminum chloride, aluminum nitrate, or aluminum sulfate dissolves in an acidic solution or water, no interfering elements are introduced. For example, the acidic solution is hydrochloric acid or sulfuric acid.

[0040] In order to ensure the doping effect and prevent the nanowires from oxidizing, in step (3), the 4H-SiC nanowire array obtained in step (2) is placed in a tube furnace, the tube furnace is evacuated to -0.1 MPa, and then an inert gas is introduced to atmospheric pressure, and the process is repeated several times.

[0041] The temperature is increased to 800-900℃ at a heating rate of 5℃ / min, held for 20-40 min, then decreased to 400-500℃ at a cooling rate of 5℃ / min, and finally cooled to room temperature with the furnace.

[0042] In this technical solution, by controlling the heating rate, maximum temperature, and cooling rate, the thermal kinetic energy of the dopant atoms is increased, promoting the diffusion of dopant elements in the SiC lattice and ensuring the doping amount. Preferably, the temperature is raised to 900℃ at a heating rate of 5℃ / min, held for 30min, then cooled to 500℃ at a cooling rate of 5℃ / min, and finally cooled to room temperature in the furnace, thus achieving an Al doping amount of 0.16at% to 1.63at%.

[0043] For example, the 4H-SiC wafer obtained in step (2) is placed in a tube furnace, the tube furnace is evacuated to -0.1 MPa, and then an inert gas is introduced to atmospheric pressure. This process is repeated three times to reduce the oxygen content in the furnace tube as much as possible, so that the internal environment of the tube furnace tube remains an inert environment and prevents the bamboo-shaped 4H-SiC nanowire array from being oxidized by oxygen in the subsequent high-temperature annealing process.

[0044] In order to obtain a bamboo-shaped 4H-SiC nanowire array with excellent morphology, in step (1), the 4H-SiC wafer is used as the anode and the Pt wafer is used as the cathode. The C-side of the 4H-SiC wafer is used as the etching surface and is placed directly opposite the Pt electrode in the etching solution for etching. The etching voltage is 20V and the etching time is 27-30min.

[0045] The etching solution contains 99 vol% ethylene glycol, 45 wt% hydrofluoric acid, and 30 wt% hydrogen peroxide in a volume ratio of 6:3:1.

[0046] In this invention, a bamboo-like 4H-SiC nanowire array is obtained by using a specific etching solution and limiting the etching voltage and time. During the etching process, a mesoporous structure is first formed on the surface of the 4H-SiC wafer. Subsequently, the pore size increases and the pore length and depth increase within the mesoporous layer. Then, the pore walls between adjacent pores are etched away, and the pores connect with each other. The continuous connection of pores leads to the unetched parts being etched and divided into nanowires, thus forming a bamboo-like nanowire structure. The bamboo-like nanowires obtained by this method are independent, neatly arranged, and straight, without forming a strip. Their surface is periodically arranged with concave and convex junctions. These sharp, protruding junctions can act as electron emission sites during field emission testing, emitting a large number of electrons under the same electric field strength, thus ensuring a sufficiently low turn-on electric field.

[0047] It should be noted that after etching, a nanowire array layer and a porous layer are formed on the surface of the 4H-SiC wafer. The nanowire array layer is located between the porous layer and the unetched area of ​​the 4H-SiC wafer, so that the adhesive tape adheres tightly to the porous layer. Tearing off the adhesive tape allows the porous layer to carry the nanowire array layer away from the 4H-SiC wafer, thus achieving the peeling of the 4H-SiC nanowire array from the 4H-SiC wafer.

[0048] Preferably, the 4H-SiC nanowire array obtained after etching is immersed in an ethanol solution, cleaned, and then air-dried to prevent oxidation. Before etching, the 4H-SiC wafer is ultrasonically cleaned in acetone, ethanol, and deionized water in sequence, and then air-dried to obtain a clean wafer, thereby etching to obtain bamboo-like nanowires with good morphology.

[0049] The 4H-SiC wafer in this embodiment of the invention is an N-doped 4H-SiC wafer, and the length and width of the 4H-SiC wafer are 1cm × 0.5cm.

[0050] Furthermore, the nanowires in the bamboo-like 4H-SiC nanowire array have a length of 110–150 μm and a width of 15–38 nm. The diameter, width, and overall length of the nanowires have a significant impact on field emission performance: the thinner and longer the nanowires, the lower the field emission turn-on electric field, but the lower the stability. In this design, the length and width of the nanowires are reasonable, enabling the field emission cathode to simultaneously possess a low turn-on electric field and high stability.

[0051] Accordingly, the present invention also provides an Al-doped 4H-SiC nanowire field emission cathode, which is prepared by the above-described method for preparing an Al-doped 4H-SiC nanowire field emission cathode.

[0052] The present invention will be further illustrated below through examples and comparative examples.

[0053] Example 1

[0054] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment includes the following steps:

[0055] S1. Take an N-doped 4H-SiC wafer with a length and width of 1cm × 0.5cm, and clean it with ultrasonic waves in acetone, ethanol and deionized water in sequence, and then let it air dry.

[0056] Using S2 and 4H-SiC wafers as the anode and a Pt wafer as the cathode, the C-side of the 4H-SiC wafer was placed directly opposite the Pt electrode in an etching solution for etching. The etching voltage was 20V, and the etching time was 30min. The etching solution contained 99 vol% ethylene glycol, 45 wt% hydrofluoric acid, and 30 wt% hydrogen peroxide in a volume ratio of 6:3:1. The resulting bamboo-like 4H-SiC nanowire array had nanowires ranging from 110 to 150 μm in length and 15 to 38 nm in width. Figure 1 The resulting 4H-SiC nanowire array was peeled off from the 4H-SiC wafer.

[0057] S3. Immerse the obtained 4H-SiC nanowire array in an ethanol solution for 5 minutes, clean it, and then air dry it naturally.

[0058] S4. Immerse the 4H-SiC nanowire array in a 0.01 g / ml AlCl3 aqueous solution for 5 min, then remove and air dry or dry at a temperature below 60°C.

[0059] S5. The obtained 4H-SiC nanowire array is placed in a tube furnace, and the tube furnace is evacuated to -0.1 MPa. Then, an inert gas is introduced to atmospheric pressure and the cycle is repeated three times. The temperature is increased to 900℃ at a heating rate of 5℃ / min and held for 30 min. Then, the temperature is decreased to 500℃ at a cooling rate of 5℃ / min and finally cooled to room temperature with the furnace.

[0060] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.36 at% to 0.44 at% ( Figure 2 and Figure 3 The turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.42 V / μm. Figure 5 The electron emission fluctuation after 3 hours of continuous operation was 1.3%. Figure 4 ).

[0061] Example 2

[0062] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Example 1, except that the 4H-SiC nanowire array in step S4 is immersed in 0.03 g / ml AlCl3 aqueous solution for 5 min.

[0063] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 1.46 at% to 1.63 at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.73 V / μm. Figure 5 The electron emission fluctuation was 1.6% after 3 hours of continuous operation.

[0064] Example 3

[0065] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Example 1, except that the 4H-SiC nanowire array in step S4 is immersed in 0.005 g / ml AlCl3 aqueous solution for 5 min.

[0066] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.16 at% to 0.23 at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.55 V / μm, and the electron emission fluctuation is 2.1% after 3 hours of continuous operation.

[0067] Example 4

[0068] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Example 1, except that in step S4, the 4H-SiC nanowire array is immersed in a 0.01 g / ml aluminum nitrate aqueous solution for 5 min.

[0069] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.34 at% to 0.48 at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.44 V / μm, and the electron emission fluctuation is 1.5% after 3 hours of continuous operation.

[0070] Example 5

[0071] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Example 1, except that the 4H-SiC nanowire array in step S4 is immersed in 0.01 g / ml AlCl3 aqueous solution for 3 min.

[0072] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.28 at% to 0.32 at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.51 V / μm, and the electron emission fluctuation is 1.5% after 3 hours of continuous operation.

[0073] Example 6

[0074] The preparation method of the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Example 1, except that:

[0075] In step S4, the 4H-SiC nanowire array was immersed in a 0.01 g / ml AlCl3 aqueous solution for 10 min.

[0076] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.52 at% to 0.63 at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.64 V / μm, and the electron emission fluctuation is 1.8% after 3 hours of continuous operation.

[0077] Example 7

[0078] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Example 1, except that the etching time in step S2 is 27 min.

[0079] The turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.70 V / μm, and the electron emission fluctuation is 1.0% after 3 hours of continuous operation.

[0080] Example 8

[0081] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Example 1, except that: in step S5, the temperature is increased to 800°C at a heating rate of 5°C / min, held for 30 min, then cooled to 500°C at a cooling rate of 5°C / min, and finally cooled to room temperature with the furnace.

[0082] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.26 at% to 0.32 at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.48 V / μm, and the electron emission fluctuation is 2.3% after 3 hours of continuous operation.

[0083] Example 9

[0084] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Example 1, except that: in step S5, the temperature is increased to 900°C at a heating rate of 5°C / min, held for 20 min, then cooled to 500°C at a cooling rate of 5°C / min, and finally cooled to room temperature with the furnace.

[0085] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.32at% to 0.38at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.46V / μm, and the electron emission fluctuation is 1.5% after 3 hours of continuous operation.

[0086] Comparative Example 1

[0087] In this comparative example, the 4H-SiC nanowire array obtained in step S3 of Example 1 was used as the field emission cathode, with an on-state electric field of 0.81 V / μm. Figure 5 ).

[0088] Comparative Example 2

[0089] The preparation method of the Al-doped 4H-SiC nanowire field emission cathode in this comparative example is basically the same as that in Example 1, except that the 4H-SiC wafer in step S4 is immersed in 0.05 g / ml AlCl3 aqueous solution for 5 min.

[0090] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 5.27 at% to 8.93 at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 1.50 V / μm. Figure 5 ).

[0091] Comparative Example 3

[0092] The preparation method of the Al-doped 4H-SiC nanowire field emission cathode in this comparative example is basically the same as that in Example 1, except that: in step S5, the temperature is raised to 600°C at a heating rate of 5°C / min, held for 30 min, then cooled to 500°C at a cooling rate of 5°C / min, and finally cooled to room temperature with the furnace.

[0093] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this comparative example is 0.18 at% to 0.24 at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.58 V / μm.

[0094] Comparative Example 4

[0095] The preparation method of the Al-doped 4H-SiC nanowire field emission cathode in this comparative example is basically the same as that in Example 1, except that the etching time in step S2 is 32 min.

[0096] The Al-doped 4H-SiC nanowire field emission cathode obtained in this embodiment has an on-state electric field of 0.36 V / μm and an electron emission fluctuation of 3.4% after 3 hours of continuous operation.

[0097] Other components and operations of the Al-doped 4H-SiC nanowire field emission cathode and its preparation method according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here.

[0098] In the description of this specification, references to terms such as "embodiment," "example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0099] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing an Al-doped 4H-SiC nanowire field emission cathode, characterized in that, Includes the following steps: (1) Electrochemical etching is performed on the 4H-SiC wafer to process a bamboo-shaped 4H-SiC nanowire array on the surface of the 4H-SiC wafer, and the 4H-SiC nanowire array is peeled off from the 4H-SiC wafer. (2) The 4H-SiC nanowire array obtained in step (1) is immersed in an aluminum source solution containing Al, and then taken out and dried; (3) The 4H-SiC nanowire array obtained in step (2) is sintered in an inert environment at 800~900℃ to obtain an Al-doped 4H-SiC nanowire array, which is the Al-doped 4H-SiC nanowire field emission cathode. The length of the bamboo-shaped 4H-SiC nanowire array obtained in step (2) is 110~150μm and the width is 15~38nm; the Al doping amount in the Al-doped 4H-SiC nanowire array obtained in step (3) is 0.16at%~1.63at.

2. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 1, characterized in that, In step (2), the 4H-SiC nanowire array is immersed in an aluminum source solution containing Al for 3 to 10 minutes, and then air-dried or dried at a temperature below 60°C.

3. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 2, characterized in that, The aluminum source solution is an aqueous solution of aluminum chloride, aluminum nitrate, or aluminum sulfate; or the aluminum source solution is an acidic solution of aluminum chloride, aluminum nitrate, or aluminum sulfate.

4. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 1, characterized in that, In step (3), the 4H-SiC nanowire array obtained in step (2) is placed in a tube furnace, the tube furnace is evacuated to -0.1 MPa, and then an inert gas is introduced to atmospheric pressure, and the process is repeated multiple times. The temperature is increased to 800~900℃ at a heating rate of 5℃ / min, held for 20~40min, then decreased to 400~500℃ at a cooling rate of 5℃ / min, and finally cooled to room temperature with the furnace.

5. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 1, characterized in that, In step (1), the 4H-SiC wafer is used as the anode and the Pt wafer is used as the cathode. The C-side of the 4H-SiC wafer is used as the etching surface and is placed directly opposite the Pt electrode in the etching solution for etching. The etching voltage is 20V and the etching time is 27~30min. The etching solution contains 99 vol% ethylene glycol, 45 wt% hydrofluoric acid, and 30 wt% hydrogen peroxide in a volume ratio of 6:3:

1.

6. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 5, characterized in that, The 4H-SiC nanowire array on the etched 4H-SiC wafer is peeled off, then soaked in an ethanol solution, cleaned, and air-dried. Before etching, the 4H-SiC wafer was ultrasonically cleaned in acetone, ethanol and deionized water in sequence, and then air-dried.

7. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 5, characterized in that, The 4H-SiC wafer is an N-doped 4H-SiC wafer, and the length and width of the 4H-SiC wafer are 1cm × 0.5cm.

8. An Al-doped 4H-SiC nanowire field emission cathode, characterized in that, It was prepared by the method for preparing Al-doped 4H-SiC nanowire field emission cathode according to any one of claims 1 to 7.

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