Silicon carbide micro-powder applied to precise photoelectric device and preparation method of silicon carbide micro-powder

Abstract

The invention discloses silicon carbide micro powder applied to a precise photoelectric device and a preparation method of the silicon carbide micro powder. The micro powder is sub-200nm high-purity nitrogen-doped silicon carbide, the nitrogen atom doping concentration of the micro powder can be regulated and controlled in the range of 0.1-5.0 at.% as required, so that the refractive index (at 1550nm) of the micro powder is precisely adjustable in the range of 2.55-2.70, meanwhile, the total amount of metal impurities is lower than 15ppm, and the specific surface area is larger than 45m / g. The preparation method adopts a plasma-sol-gel synergistic technology and comprises the following steps: accurately controlling the ratio of trichloromethyl silicon to precursors such as methane and the like, and quickly generating a SiC nano core through plasma high-temperature cracking; then, uniformly coating the nano core by using a sol-gel method, and introducing a cross-linked network, so as to effectively control the particle size and agglomeration; and finally, carrying out thermal cracking in a nitrogen-containing atmosphere with a specific ratio to realize in-situ nitrogen doping and remove organic matters.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide materials, in particular to silicon carbide micropowder used in precision optoelectronic devices and a preparation method thereof. Background Art

[0002] Precision optoelectronic devices such as optical waveguides, microelectromechanical system (MEMS) micromirrors, tunable filters, and on-chip lasers play a vital role in optical communications, sensing, display, and information processing. The performance of these devices is highly dependent on the physical and chemical properties of their core functional materials, placing particularly stringent requirements on material purity, thermal stability, mechanical properties, and the consistency and tunability of optical constants.

[0003] The materials commonly used in precision optoelectronic devices currently include oxide systems and nitride systems. )、Hafnium oxide( ) have a high refractive index, which is beneficial for device miniaturization and light field confinement, but their thermal conductivity is usually low (e.g., The thermal conductivity is only about 8-12W When operating at higher power densities, these materials are prone to significant temperature rise due to heat accumulation, leading to problems such as thermally induced caustics and refractive index drift, which seriously affect the stability and life of the device.

[0004] Silicon nitride ( ) and other nitride materials have good thermal and chemical stability and are compatible with CMOS processes. However, The refractive index of is relatively low (usually around 2.0), which is insufficient in applications that pursue high integration and strong optical field limitation. In addition, the preparation of low defect density and high optical quality Thin films also face certain process challenges.

[0005] Silicon carbide (SiC), as a third-generation wide-bandgap semiconductor material, has shown great application potential in the field of precision optoelectronic devices due to its unique physical and chemical properties. SiC has a wide bandgap (depending on the crystal form, for example, 3C-SiC is about 2.36eV, 4H-SiC is about 3.26eV), which makes it have low intrinsic absorption in the visible to near-infrared band. At the same time, SiC has a high refractive index (usually 2.6-2.7) and excellent thermal conductivity (high-quality single-crystal SiC can exceed 350W). , far exceeding those of traditional oxide and nitride materials), as well as excellent mechanical properties (high hardness and high Young's modulus). These characteristics make SiC an ideal "photo-thermal-mechanical" material, particularly suitable for high-power, wide-temperature precision optoelectronic devices.

[0006] However, bulk SiC is extremely difficult to process. Its high hardness and chemical inertness make traditional grinding, polishing, and etching processes costly and inefficient, making it difficult to fabricate submicron precision optical structures. Therefore, developing a directly dispersible, easily moldable, and patternable SiC micro- or nanopowder and integrating it as a functional unit into devices is a key approach to overcoming this bottleneck.

[0007] Existing methods for preparing SiC powder primarily include solid-phase reaction methods (such as the Acheson method), liquid-phase methods (such as the sol-gel method, hydrothermal / solvothermal methods), and gas-phase methods (such as chemical vapor deposition and plasma methods). SiC powders prepared by the Acheson method exhibit low purity, large, and uneven particle size, making them difficult to meet the demands of precision optoelectronic applications. While the traditional sol-gel method can produce finer powders, it is prone to particle agglomeration and grain growth during subsequent heat treatment, and poses challenges in controlling purity and ensuring doping uniformity. Gas-phase methods, particularly plasma methods, can provide a high-temperature, high-energy environment that facilitates rapid decomposition of the precursor and nucleation of SiC. However, when used alone, the product may exhibit problems such as carbon segregation, a wide particle size distribution, or subsequent agglomeration.

[0008] Furthermore, to meet the precise control requirements of optical properties (such as low loss and a specific refractive index) for precision optoelectronic devices, higher requirements are placed on SiC micropowder purity (especially metal impurity content), crystal form, particle size distribution, specific surface area, and doping (such as nitrogen doping to control carrier concentration and optical properties). Existing SiC micropowder preparation technology that can simultaneously meet the requirements of sub-200 nanometer particle size, high purity (total impurity level in the ppm range), high specific surface area, controllable nitrogen doping, and excellent dispersibility is still immature, limiting the widespread application of SiC materials in high-end precision optoelectronic devices.

[0009] Therefore, there is an urgent need to develop a new method that can stably and controllably prepare silicon carbide micropowder with a specific particle size, high purity, high specific surface area and adjustable optical properties (especially by precisely controlling the amount of nitrogen doping to fine-tune the refractive index and carrier properties), and explore its efficient integration path in precision optoelectronic devices to fully utilize the excellent performance of SiC materials. Summary of the Invention

[0010] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a silicon carbide micropowder for use in precision optoelectronic devices, which has high purity, an average particle size of sub-200 nanometers, a narrow particle size distribution, a high specific surface area, and an adjustable refractive index achieved by nitrogen doping.

[0011] Another object of the present invention is to provide a method for preparing the above-mentioned silicon carbide micropowder, which uses "plasma-sol-gel synergy" technology and accurately controls the material ratio and process parameters in each step to achieve effective regulation of various performance indicators of the micropowder.

[0012] Another object of the present invention is to provide an application of the above-mentioned silicon carbide micropowder in precision optoelectronic devices, and to significantly improve the optical performance and thermal stability of the devices by integrating the micropowder into the devices.

[0013] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0014] A silicon carbide micropowder for use in precision optoelectronic devices, characterized in that the micropowder is nitrogen-doped silicon carbide micropowder and meets the following characteristics:

[0015] The atomic ratio of carbon (C) to silicon (Si) is close to the stoichiometric ratio, with the C:Si atomic ratio ranging from 0.98:1 to 1.02:1;

[0016] The nitrogen (N) atomic doping concentration is 0.1at.% to 3.0at.% relative to SiC;

[0017] Average particle size ( ) is controlled within the range of 100 nm to 200 nm, preferably 120 nm to 160 nm;

[0018] Particle size distribution index Less than 1.8, preferably less than 1.6;

[0019] The micro powder has a porous aggregate structure and the specific surface area (measured by BET method) is greater than 40 , preferably greater than 45 ;

[0020] The total content of metal impurities is less than 20ppm, preferably less than 15ppm, of which the content of single metal impurities such as Fe, Al, and Ca is less than 5ppm;

[0021] The oxygen atom content (measured by XPS method) is less than 0.5 at.%, preferably less than 0.3 at.%;

[0022] At a wavelength of 1550 nm, the refractive index can be fine-tuned within the range of 2.58 to 2.68 by adjusting the nitrogen doping concentration, preferably within the range of 2.60 to 2.66.

[0023] The method for preparing the silicon carbide micropowder comprises the following steps:

[0024] Precursor preparation and plasma pyrolysis:

[0025] Raw material selection: Organosilane and carbon source compound are used as the main precursors, and nitrogen is used as the doping source and carrier gas. The organosilane is preferably trichloromethylsilane ( , MTS), the carbon source compound is preferably methane ( Ensure the purity of raw materials, for example, the purity of trichloromethyl silicon should be no less than 99.99%, the purity of methane should be no less than 99.999%, and the purity of nitrogen should be no less than 99.999%.

[0026] Precursor Ratio: Precisely control the molar ratio of the silicon source to the carbon source to ensure a C:Si atomic ratio close to 1:1 in the final product. When using trichloromethylsilane and methane, adjust the feed flow rate ratio of the two to ensure that the total carbon to silicon molar ratio is within the range of 1:1 to 1.1:1 to compensate for possible carbon loss.

[0027] Plasma Pyrolysis: A prepared precursor gas stream (diluted with ultra-dry ethanol, with a volume ratio of ethanol to precursor of 1.5:1 to 4:1) is introduced into a microwave plasma apparatus (operating at 2.45 GHz). Pyrolysis occurs under high temperature (1650°C to 1850°C, preferably 1750°C) and moderate vacuum (50 Pa to 120 Pa, preferably 80 Pa), rapidly generating amorphous or nanocrystalline SiC cores. Plasma power is controlled between 1.5 kW and 4 kW. Nitrogen, in addition to serving as a carrier gas, also participates in the reaction or adsorbs on the nanocore surface during this stage. The volume percentage of nitrogen in the total gas flow entering the plasma zone is controlled between 60% and 85%.

[0028] Sol-gel coating and nitrogen source introduction:

[0029] Nanocore collection and dispersion: The SiC nanocores generated in the previous step are quickly transferred and dispersed in an anhydrous organic solvent, preferably anhydrous ethanol. The mass concentration of the SiC nanocores in the anhydrous ethanol is 0.2 wt % to 1.5 wt %.

[0030] Cross-linking agent introduction and gel formation: Add silane coupling agent or alkoxysilane as a cross-linking agent to the ethanol dispersion of the SiC nanocore, preferably tetramethylsilane ( , TMS) or tetraethoxysilane ( , TEOS). The molar ratio of the added amount of crosslinker to the SiC nanocore (calculated as Si) is 0.08:1 to 0.4:1. Stirring under specific pH conditions (adjusting the pH to 8.0-9.5 by adding a small amount of ammonia water) induces the crosslinker to hydrolyze and condense or react with other active groups to form crosslinkers on the surface of the SiC nanocore and between the particles. or The three-dimensional network gel structure with equal bonding wraps the SiC nanocore and restricts its excessive growth and agglomeration.

[0031] Further introduction of nitrogen source (optional): If it is necessary to further increase the nitrogen doping concentration or ensure doping uniformity, nitrogen-containing organic matter can be added as an auxiliary nitrogen source in this step, such as urea, melamine, etc. The added amount can be 0.5% to 8% by mass relative to the SiC nanocore.

[0032] Inert atmosphere thermal cracking and nitrogen doping:

[0033] Gel drying: The gel formed in the previous step is dried by spray freeze drying or supercritical drying to maintain its porous network structure and high specific surface area and prevent the nanoparticles from agglomerating during the drying process.

[0034] Thermal cracking and in-situ nitridation: The dried gel is placed in a tube furnace and heat treated under a mixed flow of inert atmosphere and nitrogen atmosphere. The mixed atmosphere is preferably argon (Ar) and nitrogen ( ) in a mixture of argon and nitrogen, wherein the volume fraction of nitrogen can be adjusted according to the desired doping concentration and controlled within the range of 8% to 35%. The heat treatment temperature is 650°C to 800°C, preferably 680°C to 750°C, and the holding time is 2 hours to 4 hours. This process is intended to remove organic components and oxygen bridges (such as Si-O bonds) in the gel network, while allowing nitrogen atoms to diffuse in situ and replace carbon sites or silicon sites in the SiC lattice (preferentially replacing carbon sites to form N-Si bonds), thereby achieving nitrogen doping and promoting the crystallization of SiC (such as conversion to 3C-SiC). The total flow rate of argon and nitrogen is related to the volume of the furnace tube. For example, for a furnace tube with an inner diameter of 50 mm, the total flow rate can be 150 sccm to 400 sccm.

[0035] Post-processing (optional):

[0036] The heat-treated powder is lightly ground or jet-milled to break up a small amount of soft agglomerates that may exist, thereby obtaining the final nitrogen-doped silicon carbide micropowder.

[0037] By adjusting the parameters in the above preparation method, the particle size, morphology, nitrogen doping concentration and optical properties of silicon carbide powder can be controlled:

[0038] Adjusting the plasma power, reaction pressure, precursor concentration and flow ratio can affect the initial size and nucleation rate of SiC nanonuclei.

[0039] By adjusting the type and amount of cross-linking agent, the concentration of SiC nanocores, the type of solvent and the pH value of the gel during the sol-gel process, the pore structure of the gel network and the degree of coating of the SiC nanocores can be controlled, thereby affecting the particle size and agglomeration state of the final micropowder.

[0040] By adjusting the concentration (partial pressure) of nitrogen in the thermal cracking step and the heat treatment temperature and time, the doping concentration and substitution position of nitrogen in SiC can be precisely controlled, thereby regulating the electrical and optical properties of the micropowder.

[0041] The beneficial effects of the present invention are:

[0042] High Purity and Precision Doping: By selecting high-purity raw materials and combining the efficiency of plasma pyrolysis with the uniform coating characteristics of the sol-gel method, the introduction of impurities and carbon enrichment are effectively suppressed, while achieving uniform and controllable nitrogen doping. The total impurity content of the resulting SiC micropowder can be less than 15ppm, and the nitrogen doping concentration can be precisely controlled within the range of 0.1-3.0at.% according to demand.

[0043] Excellent physical properties: The average particle size of the prepared SiC powder can be controlled to be sub-200nm (such as 140±20nm), and the particle size distribution is narrow ( <1.6), showing a porous aggregate structure with a high specific surface area (>45 These properties are beneficial to its dispersion in solvents and subsequent thin film and patterning processing.

[0044] Adjustable optical properties: By adjusting the nitrogen doping concentration, the refractive index of SiC powder can be fine-tuned within a range of 2.60 to 2.66 (@1550nm), meeting the optical constant requirements of various precision optoelectronic devices. Nitrogen doping also helps regulate carrier concentration, affecting the material's optical and electrical properties.

[0045] The synergistic effect is significant: plasma pyrolysis provides a high-energy activation environment, rapidly generating SiC nanonuclei and avoiding the potential for grain coarsening caused by prolonged high-temperature treatment. The sol-gel process limits the aggregation and overgrowth of the nanonuclei through network coating and provides a pathway for the uniform introduction of nitrogen. The synergistic effect enables the controllable preparation of high-quality SiC micropowders.

[0046] Improved device performance: The SiC powder prepared by the present invention is applied to precision optoelectronic devices (such as silicon-based optical waveguides, MEMS micromirrors, and tunable filters), which can significantly reduce the optical loss of the device (compared to traditional 、 The solution reduces thermal drift by 25-35% and thermal drift by 35-45%, improving the overall performance and reliability of the device. DETAILED DESCRIPTION

[0047] Below I will describe the present invention in detail with reference to specific examples. These examples are intended only to illustrate the technical key points of the present invention and are not intended to limit the scope of the present invention in any way. Unless otherwise stated, the percentages used in the examples are by mass or volume, and the temperatures are in degrees Celsius.

[0048] Selection and preparation of raw materials and equipment

[0049] Before starting the preparation process, we need to prepare high-purity raw materials and sophisticated equipment. The purity requirement of MTS is 99.999%, which is the key factor to ensure the high purity of the final product. ) as a carbon source, its purity needs to reach 99.9999%. Nitrogen ( ) plays multiple roles in this process, serving as both a carrier gas and shielding gas, as well as an important dopant source. Therefore, its purity must reach 99.9999%. Argon (Ar) is primarily used as a shielding gas, and its purity must reach 99.999%.

[0050] As for the solvent, we choose ultra-dry ethanol, whose water content must be controlled below 50ppm, which is crucial to prevent unnecessary hydrolysis and ensure product quality. , TMS) as a cross-linking agent, the purity requirement is 99.5%. Ammonia water is used to adjust the pH value, and analytical grade is selected. The content is 25-28%.

[0051] The microwave plasma device operates at a frequency of 2.45 GHz, with power precisely adjustable from 0.5 to 5 kW. Mass flow controllers are also included to ensure precise control of the flow rates of various gases. The tube furnace can reach a maximum temperature of 1200°C and features atmosphere control. A spray freeze dryer is also required to process the gel.

[0052] Characterization equipment includes X-ray diffractometer (XRD) for crystal structure analysis, high-resolution transmission electron microscope (HRTEM) for observing micromorphology, X-ray photoelectron spectrometer (XPS) for surface composition analysis, specific surface area and pore size analyzer (BET) for measuring specific surface area, inductively coupled plasma mass spectrometer (ICP-MS) for impurity element analysis, and variable angle spectroscopic ellipsometer for optical performance testing.

[0053] Example 1: Preparation of Nitrogen-Doped SiC Micropowder with a Target Nitrogen Content of About 1.2 at.%

[0054] The goal of this example is to prepare silicon carbide powder with a moderate nitrogen content, with an expected refractive index of about 2.62 at a wavelength of 1550 nm. Let's look at the preparation process step by step.

[0055] During the precursor preparation and plasma pyrolysis stages, we first stored trichloromethylsilane in a stainless steel bottle, precisely controlling its vapor flow rate at 45 sccm via a mass flow controller. Simultaneously, the methane flow rate was controlled at 50 sccm. This ratio resulted in a carbon-to-silicon atomic molar ratio of approximately 1.11:1, with MTS contributing a 1:1 carbon-to-silicon ratio and the additional methane providing approximately 0.11 carbon atoms. This slight carbon-enrichment was intended to compensate for potential carbon loss during the high-temperature plasma process.

[0056] Nitrogen was used as carrier gas and initial nitrogen source, and the flow rate was controlled at 350 sccm. and After mixing, the mixture was introduced into a 2.45 GHz microwave plasma torch. The plasma generator power was set to 2.2 kW, a level that provides sufficient energy to cleave the precursor molecules but not too high to cause excessive product agglomeration. The reaction chamber pressure was maintained at 80 Pa, a moderate vacuum conducive to maintaining a stable plasma. Under these conditions, the plasma region temperature was estimated to be approximately 1750°C. The precursor rapidly cleaved in this high-temperature environment, generating amorphous or nanocrystalline SiC cores.

[0057] During the sol-gel coating stage, we took 1.0 g of the collected SiC nanocores and dispersed them in 250 mL of ultra-dry ethanol. A 30-minute sonication treatment ensured a uniform suspension of the nanocores in the solvent. The next step was the crucial introduction of the crosslinker. We slowly added 0.15 mL of tetramethylsilane dropwise, which corresponds to approximately 0.096 g of tetramethylsilane, for a molar ratio of approximately 0.044:1 to the SiC nanocores. This ratio was carefully designed to provide sufficient coating without compromising the purity of the final product.

[0058] Adjusting the pH is also crucial. We added 0.4 mL of a 1 mol / L ammonia-ethanol solution to adjust the mixture's pH to approximately 8.5. At this pH, TMS undergoes a moderate hydrolysis reaction (utilizing the trace amount of water in the system) and reacts with the hydroxyl groups on the SiC surface, followed by a polycondensation reaction to form a Si-CO or Si-O-Si network. The entire process requires continuous stirring for 3.5 hours to ensure sufficient reaction and uniform formation of the gel network.

[0059] Following the inert atmosphere pyrolysis and nitrogen doping stages, we first used spray freeze drying to treat the gel. This drying method has the advantage of preserving the porous network structure of the gel, preventing the nanoparticles from agglomerating during the drying process, thereby maintaining a high specific surface area.

[0060] The heat treatment process uses programmed heating to raise the furnace temperature to 720°C at a rate of 8°C / min. Atmosphere control is the core of this stage. We use Ar and The mixed gas is Ar with a flow rate of 220 sccm. The flow rate is 35 sccm, The volume fraction of the nitrogen gas is 14%. This nitrogen concentration has been carefully calculated to achieve a nitrogen doping concentration of approximately 1.2 at. Heating at 720°C for 3 hours is sufficient for the organic components to completely decompose and for nitrogen atoms to diffuse and replace carbon sites in the SiC lattice, forming stable N-Si bonds.

[0061] After such a preparation process, the product we obtain has the following performance characteristics:

[0062] ;

[0063] From these data, we can see that the average particle size of the prepared SiC micropowder is 135nm, which is within the target range of 100-200nm set by us. The XRD analysis confirmed that the main crystalline phase is cubic 3C-SiC, which is the expected result. The nitrogen atomic content reached 1.3 at.%, close to our target value of 1.2 at.%. The specific surface area is 46.8 , meeting the requirement of more than 40 The total content of metal impurities is 13.5ppm, meeting the high purity requirement of less than 15ppm.

[0064] Example 2: Preparation of SiC micropowder with high nitrogen doping concentration

[0065] The goal of this example is to prepare highly doped SiC powder with a nitrogen content of about 2.2 at.%, with an expected refractive index of about 2.64. Compared with Example 1, we need to adjust several key parameters to achieve a higher nitrogen doping concentration.

[0066] During the precursor preparation stage, the MTS flow rate remains at 45 sccm, but The flow rate was slightly reduced to 48 sccm, resulting in a C / Si atomic molar ratio of approximately 1.07:1. This fine-tuning was done to maintain an appropriate carbon-silicon ratio under higher nitrogen doping conditions. The carrier gas flow rate was adjusted to 320 sccm. The increase in relative flow rate facilitated the introduction of more nitrogen atoms. The plasma power was increased to 2.5 kW. This increase in power facilitated the activation and dissociation of more nitrogen molecules.

[0067] During the sol-gel coating stage, we increased the amount of TMS to 0.20 mL (approximately 0.128 g), raising the molar ratio of TMS to SiC nanocores to approximately 0.058:1. This adjustment was made to account for the potential impact of higher nitrogen doping on the surface chemistry, necessitating slightly more crosslinker to ensure a good coating effect.

[0068] The key adjustments during the heat treatment phase are raising the temperature to 730°C and significantly increasing the nitrogen partial pressure. The volume fraction was increased to 22% (Ar flow rate 180 sccm, The higher temperature and nitrogen partial pressure work together to promote the diffusion and doping of more nitrogen atoms.

[0069] By adjusting these parameters, we get the following product performance:

[0070] ;

[0071] It is worth noting that with the increase of nitrogen doping concentration, the refractive index increases from 2.618 to 2.641, verifying the effectiveness of nitrogen doping in regulating the refractive index. At the same time, the absorption coefficient decreases from 0.12 to 0.095. , which may be related to the fact that nitrogen doping improves the electronic structure of the material.

[0072] Example 3: Preparation of SiC powder with low nitrogen doping concentration

[0073] This embodiment aims to prepare low-doped SiC powder with a nitrogen content of about 0.4 at.%, with a target refractive index of about 2.60. This low-doping concentration material is of great value in certain applications that require extremely high purity.

[0074] In terms of parameter adjustment, the MTS and The flow rate was set to 45 sccm, so that the C / Si atomic molar ratio was strictly controlled at 1:1 to avoid any excess carbon. The carrier gas flow rate was increased to 380 sccm. Although the nitrogen flow rate increased, the actual nitrogen atom activation degree was relatively low because the plasma power was reduced to 2.0 kW.

[0075] In the sol-gel stage, the amount of TMS was reduced to 0.12 mL (about 0.077 g) and the molar ratio was reduced to about 0.035:1. This lower amount of cross-linker helps to reduce the possible introduction of impurities.

[0076] During the heat treatment phase, the temperature was lowered to 690°C and the nitrogen volume fraction was significantly reduced to 8% (Ar flow rate 255 sccm, The lower temperature and nitrogen partial pressure ensure a moderate nitrogen doping level.

[0077] Product performance data are as follows:

[0078] ;

[0079] A comparison of the three examples clearly demonstrates that by precisely controlling various process parameters, we can achieve precise control of the nitrogen doping concentration within the range of 0.5-2.3 at.%, and the corresponding refractive index is also adjustable within the range of 2.598-2.641. This verifies the effectiveness and controllability of our technical solution.

[0080] The relationship between refractive index and wavelength can be described by the Sellmeier equation: , where parameters A and B will change with the change of nitrogen doping concentration. From the experimental data, it can be seen that with the increase of nitrogen doping concentration, parameter A gradually increases (from 6.02 to 6.28), while parameter B decreases (from 0.032 to 0.025 ), which reflects the effect of nitrogen doping on the optical dispersion properties of the material.

[0081] The technical solution of the present invention has good scalability and adaptability. By adjusting the precursor type, plasma type, sol-gel system, thermal treatment process parameters, etc., product performance can be further optimized or adapted to different application requirements. As long as these variations do not deviate from the core technical concept of the present invention, they should be considered extensions of the scope of protection of the present invention.

Claims

1. A silicon carbide powder for use in precision optoelectronic devices, characterized in that: The micropowder is nitrogen-doped silicon carbide micropowder and meets the following combination of characteristics: The atomic ratio of carbon (C) to silicon (Si) in the micropowder is 0.98:1 to 1.02:1; The doping concentration of nitrogen (N) atoms in the micropowder is 0.1 at.% to 3.0 at.% relative to SiC; The average particle size of the micropowder ( ) is 100nm to 200nm; The particle size distribution index of the micropowder Less than 1.8; The micropowder has a porous aggregate structure and a specific surface area greater than 40 ; The total metal impurity content of the micropowder is less than 20 ppm; The refractive index of the micropowder at a wavelength of 1550 nm can be adjusted within a range of 2.58 to 2.68 by adjusting the nitrogen doping concentration.

2. The silicon carbide micropowder according to claim 1, characterized in that The average particle size ( ) is 100nm to 150nm; the particle size distribution index Less than 1.6; the specific surface area is greater than 45 ; The total content of metal impurities is less than 15ppm; the oxygen atom content is less than 0.5at.%; and the refractive index is regulated in the range of 2.60 to 2.66 at a wavelength of 1550nm by adjusting the nitrogen doping concentration.

3. A method for preparing silicon carbide micropowder according to any one of claims 1 or 2, characterized in that: The plasma-sol-gel synergistic technology includes the following steps: (a) Precursor preparation and plasma pyrolysis: A precursor gas stream comprising an organosilicon source and a carbon source, wherein the total molar ratio of carbon atoms to silicon atoms is controlled to be between 1:1 and 1.1:1, is mixed with 60% to 85% by volume of nitrogen gas and plasma pyrolysis is performed at 1650°C to 1850°C and 50 Pa to 120 Pa to generate SiC nanocores; (b) Sol-gel coating: The SiC nanocores produced in step (a) are dispersed in an anhydrous organic solvent, and then a crosslinking agent is added, wherein the molar ratio of the crosslinking agent to the SiC nanocore is 0.08:1 to 0.4:1, and the mixture is stirred at a pH of 8.0 to 9.5 to form a three-dimensional network gel; (c) Inert atmosphere thermal cracking and nitrogen doping: After the gel formed in step (b) is dried, it is placed in an inert atmosphere containing 8% to 35% by volume of nitrogen and heat treated at 650°C to 800°C to obtain the nitrogen-doped silicon carbide micropowder.

4. The preparation method according to claim 3, characterized in that In step (a), the organosilicon source is trichloromethylsilane, and the carbon source is methane; the precursor gas flow is diluted with ultra-dry ethanol and then introduced into the plasma device, and the total volume ratio of ethanol to precursor is 1.5:1 to 4:

1.

5. The preparation method according to claim 3 or 4, characterized in that In step (b), the anhydrous organic solvent is anhydrous ethanol, and the mass concentration of SiC nanocores in the anhydrous ethanol is 0.2wt% to 1.5wt%; and the crosslinking agent is tetramethylsilane or tetraethoxysilane.

6. The preparation method according to any one of claims 3 to 5, characterized in that In step (c), the gel is dried by spray freeze drying or supercritical drying; the heat treatment temperature is 680°C to 750°C, and the holding time is 2 hours to 4 hours; and the inert atmosphere is a mixture of argon and nitrogen.

Images