Semi-insulating compound single crystal and preparation method thereof
By using diamond polishing and a network carbon layer to treat the seed crystal, the problem of crystal cracking caused by thermal stress in the production of semi-insulating silicon carbide single crystals was solved, and the growth of high-purity and high-insulation-performance semi-insulating compound single crystals was achieved.
Patent Information
- Application Number
- CN202610000190.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-04
- Publication Date
- 2026-03-20
AI Technical Summary
In the production process of semi-insulating silicon carbide single crystals, thermal stress caused by local overheating or undercooling between the seed crystal and the graphite crucible can easily lead to crystal cracking. In addition, the growth of silicon and carbon elements generated by the vaporization of silicon carbide mixed powder is uneven, which affects the performance of single crystals.
The surface of the seed crystal is polished with diamond polishing fluid to form a network carbon layer, which is then mixed with phenolic resin to prepare a pretreated seed crystal. By growing compound single crystals at high temperature, the network carbon layer is used as an adsorption site and a soft intermediate layer to grow single crystals uniformly and buffer thermal stress.
It effectively reduces lattice distortion and internal stress in single crystals, improves insulation performance, prevents crystal cracking, and ensures the continuity and high purity of single crystals.
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Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention relates to the field of single crystal growth technology, specifically to a semi-insulating compound single crystal and its preparation method. Background Technology
[0002] Compound single crystals are single crystals characterized by the long-range ordered and periodic arrangement of the structural units such as atoms, ions, or molecules of compounds in three-dimensional space. They are characterized by their material or shape, with a continuous and unbroken overall crystal lattice and internal structural units arranged according to the same spatial rules. They have characteristics such as anisotropy and specific optical or electrical properties, and are widely used in microwave communications, airborne radar, shipborne radar and other fields. Among them, semi-insulating silicon carbide single crystals have many excellent properties such as a large bandgap, high thermal conductivity, and high critical breakdown field strength, making them ideal semiconductor materials for the fabrication of high-power devices.
[0003] Semi-insulating silicon carbide single crystals can be doped with vanadium to form deep energy levels, thereby compensating for shallow energy level impurities and obtaining semi-insulating properties. However, during the current production process of single crystals, the thermal stress caused by local overheating or undercooling between the seed crystal and the graphite crucible can easily lead to crystal cracking. In addition, the silicon and carbon elements generated by the vaporization of silicon carbide mixed powder grow unevenly on the carbon surface of the silicon carbide seed crystal, affecting the performance of semi-insulating silicon carbide single crystals. Summary of the Invention
[0004] This invention provides a semi-insulating compound single crystal and its preparation method, which solves the problem that thermal stress caused by local overheating or undercooling between the seed crystal and the graphite crucible can easily lead to crystal cracking.
[0005] The technical solution of this invention:
[0006] A method for preparing a single crystal of a semi-insulating compound includes the following steps:
[0007] S1. Mix silicon carbide powder and vanadium carbide powder to obtain silicon carbide mixed powder;
[0008] S2. Place the silicon carbide mixed powder at the bottom of the graphite crucible, place the pretreated seed crystal on the graphite crucible cover, and then place it on the top of the graphite crucible. After assembly, place it in the single crystal growth furnace and seal it to form the assembled single crystal growth furnace.
[0009] S3. The assembled single crystal growth furnace is evacuated, inert gas is introduced, and after heating and reaction, the pressure is reduced and increased, and then cooled to room temperature to obtain a semi-insulating compound single crystal.
[0010] The pretreated seed crystal is obtained by polishing the seed crystal with diamond polishing liquid, mixing it with phenolic resin, and then calcining it.
[0011] Further, in step S1, the mass ratio of silicon carbide powder to vanadium carbide powder is 1:(0.01-0.1).
[0012] Further, in step S3, the inert gas is argon or nitrogen; the pressure of introducing the inert gas into the furnace is 40-60 kPa.
[0013] Further, in step S3, the heating reaction conditions are specifically as follows: the temperature at the silicon carbide mixed powder is 2200-2300℃, the temperature at the pretreated seed crystal is 2000-2200℃, and the heating reaction time is 2-5h.
[0014] Further, in step S3, the pressure reduction specifically involves reducing the pressure to 2-3 kPa and maintaining it for 100-150 hours; the pressure increase specifically involves increasing the pressure to 40-60 kPa and maintaining it for 50-100 hours.
[0015] Furthermore, the pretreated seed crystal is specifically prepared by the following steps:
[0016] A1. After the seed crystal is polished with diamond polishing solution, it is taken out, washed with water, and dried to obtain the polished seed crystal. The polishing pressure is 1-2MPa, the polishing time is 60-80min, and the flow rate of polishing solution is 10-15mL / min.
[0017] A2. Add phenolic resin to ethanol, stir evenly, add polished seed crystals, stir at 90℃ until the ethanol solvent evaporates, remove, place in a carbonization furnace, carbonize at 900-1000℃ for 2-4 hours, cool to room temperature, and obtain pretreated seed crystals.
[0018] Furthermore, during the A1 reaction process described above, hydrogen peroxide in the diamond polishing slurry decomposes in an alkaline environment to generate hydroxyl radicals, which have strong oxidizing properties. These radicals can react with metallic impurities and oxide layers on the seed crystal surface, transforming hard impurities that are difficult to grind into easily soluble or easily detachable compounds. This reduces residual impurities on the seed crystal surface, ensuring that the seed crystal surface is free of scratches and subsurface damage layers, and also reduces the impurity concentration in the seed crystal, which is beneficial for preparing high-purity semi-insulating compound single crystals.
[0019] Furthermore, in the above A2 reaction process, the polished seed crystal is mixed with phenolic resin, and the phenolic resin is dissolved in ethanol, which can then coat the surface of the polished seed crystal. After high-temperature carbonization, the phenolic resin is thermally decomposed to form a network carbon layer, thereby achieving the synthesis of a network carbon layer on the surface of the polished seed crystal and obtaining a pretreated seed crystal.
[0020] Further, in step A1, the diamond polishing solution is composed of diamond micro powder, sodium dodecyl sulfate, hydrogen peroxide and deionized water mixed in a mass ratio of (10-15):(0.5-1):(1-2):(60-80).
[0021] Furthermore, in step A1, the pH of the diamond polishing solution is 9-13.
[0022] Furthermore, in step A1, the seed crystal is a 4H type silicon carbide seed crystal with a deflection angle of 4-8 degrees.
[0023] Furthermore, in step A1, the surface roughness of the polished seed crystal is 0.1-0.5 nm.
[0024] Further, in step A2, the mass ratio of the phenolic resin, ethanol and the polished seed crystal is (2-3):(20-30):(3-4).
[0025] The present invention has the following beneficial effects:
[0026] (1) In the technical solution of the present invention, the seed crystal is polished with diamond polishing liquid. Diamond micro powder has high hardness and can accurately grind the micro protrusions, oxide layer and impurities on the surface of the seed crystal. In addition, hydrogen peroxide in diamond polishing liquid can remove micro impurities that are difficult to reach by mechanical grinding, reduce surface residue, avoid micro protrusions, oxide layer and impurities from affecting the continuity of subsequent single crystal growth, and is conducive to the preparation of high-purity semi-insulating compound single crystal.
[0027] (2) In the technical solution of the present invention, a network carbon layer is synthesized on the surface of the polished seed crystal. On the one hand, the network carbon layer can serve as an adsorption site for silicon, carbon and vanadium elements generated by the gasification of silicon carbide mixed powder on the carbon surface of the silicon carbide seed crystal, so that silicon, carbon and vanadium elements are uniformly adsorbed on the surface of the polished seed crystal, thereby achieving uniform growth of single crystal on the carbon surface of the silicon carbide seed crystal. This can effectively reduce the lattice distortion of the single crystal and reduce the internal stress, thereby forming a semi-insulating compound single crystal. On the other hand, when the network carbon layer is filled between the seed crystal and the graphite crucible, the network carbon layer has good porosity and thermal conductivity during the high-temperature production of single crystal, which can improve thermal contact, make the heat flow distribution more uniform, and avoid the thermal stress caused by local overheating or overcooling between the seed crystal and the graphite crucible, which can lead to crystal cracking. In addition, the network carbon layer has good toughness and compressibility. As a soft intermediate layer, it absorbs and buffers part of the stress caused by thermal expansion mismatch, protecting the brittle seed crystal.
[0028] (3) In the technical solution of the present invention, silicon carbide powder and vanadium carbide powder form a silicon carbide mixed powder. At high temperature, nitrogen gas is introduced, and the silicon carbide mixed powder sublimates. The elements generated by vaporization grow crystals on the carbon surface of the silicon carbide seed crystal to obtain a semi-insulating compound single crystal. Among them, by introducing a specific deep-level impurity vanadium element, the unavoidable impurities in the silicon carbide single crystal are precisely compensated, thereby "freezing" the charge carriers, achieving high resistivity, improving the insulation performance of the compound single crystal, and compensating for the lattice distortion caused by nitrogen element, thereby reducing the stress in the compound single crystal and reducing the dislocation density inside the compound single crystal. Detailed Implementation
[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0030] The raw materials used in the embodiments of this invention are shown below, and all reagents used are analytical grade.
[0031] Among them, the particle size of silicon carbide powder is 3μm, the particle size of vanadium carbide powder is 2.5μm, and the particle size of diamond micro powder is 1μm.
[0032] The inert gas is nitrogen.
[0033] The seed crystal is a 4H type silicon carbide seed crystal with a deflection angle of 4-8 degrees.
[0034] The phenolic resin, product number P875865, was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.
[0035] Example 1
[0036] A method for preparing a single crystal of a semi-insulating compound includes the following steps:
[0037] S1. Mix silicon carbide powder and vanadium carbide powder to obtain silicon carbide mixed powder; the mass ratio of silicon carbide powder to vanadium carbide powder is 1:0.01;
[0038] S2. Place the silicon carbide mixed powder at the bottom of the graphite crucible, place the pretreated seed crystal on the graphite crucible cover, and then place it on the top of the graphite crucible. After assembly, place it in the single crystal growth furnace and seal it to form the assembled single crystal growth furnace.
[0039] S3. The assembled single crystal growth furnace is evacuated, and inert gas is introduced to bring the furnace pressure to 40 kPa. After heating and reacting, the pressure is reduced and increased, and then cooled to room temperature to obtain a semi-insulating compound single crystal. The specific heating and reaction conditions are as follows: the temperature at the silicon carbide mixed powder is 2200℃, the temperature at the pretreated seed crystal is 2000℃, and the heating and reaction time is 2h. The specific pressure reduction is as follows: the pressure is reduced to 2 kPa and held for 100h. The specific pressure increase is as follows: the pressure is increased to 40 kPa and held for 50h.
[0040] The pretreated seed crystals are prepared by the following steps:
[0041] After polishing the A1.4H type silicon carbide seed crystal with diamond polishing slurry, it was removed, washed with water, and dried in an oven at 80℃ for 10 min to obtain the polished seed crystal. The polishing pressure was 1 MPa, the polishing time was 60 min, and the flow rate of the polishing slurry was 10 mL / min. The surface roughness of the polished seed crystal was 0.1 nm.
[0042] The diamond polishing solution is composed of diamond micro powder, sodium dodecyl sulfate, hydrogen peroxide, and deionized water in a mass ratio of 10:0.5:1:60; the pH of the diamond polishing solution is 9.
[0043] A2. Add phenolic resin to ethanol, stir evenly, add polished seed crystal, stir at 90℃ until the ethanol solvent evaporates, take it out, place it in a carbonization furnace, carbonize at 900℃ for 2 hours, cool to room temperature, and obtain pretreated seed crystal.
[0044] The mass ratio of phenolic resin, ethanol, and polished seed crystal is 2:20:3.
[0045] Example 2
[0046] A method for preparing a single crystal of a semi-insulating compound includes the following steps:
[0047] S1. Mix silicon carbide powder and vanadium carbide powder to obtain silicon carbide mixed powder; the mass ratio of silicon carbide powder to vanadium carbide powder is 1:0.05;
[0048] S2. Place the silicon carbide mixed powder at the bottom of the graphite crucible, place the pretreated seed crystal on the graphite crucible cover, and then place it on the top of the graphite crucible. After assembly, place it in the single crystal growth furnace and seal it to form the assembled single crystal growth furnace.
[0049] S3. The assembled single crystal growth furnace is evacuated, and inert gas is introduced to bring the furnace pressure to 50 kPa. After heating and reacting, the pressure is reduced and increased, and then cooled to room temperature to obtain a semi-insulating compound single crystal. The specific heating and reaction conditions are as follows: the temperature at the silicon carbide mixed powder is 2250℃, the temperature at the pretreated seed crystal is 2100℃, and the heating and reaction time is 3 hours. The specific pressure reduction is as follows: the pressure is reduced to 2.5 kPa and held for 130 hours. The specific pressure increase is as follows: the pressure is increased to 50 kPa and held for 80 hours.
[0050] The pretreated seed crystals are prepared by the following steps:
[0051] After polishing the A1.4H type silicon carbide seed crystal with diamond polishing slurry, it was removed, washed with water, and dried in an oven at 80℃ for 10 min to obtain the polished seed crystal. The polishing pressure was 1.5 MPa, the polishing time was 70 min, and the flow rate of the polishing slurry was 13 mL / min. The surface roughness of the polished seed crystal was 0.3 nm.
[0052] The diamond polishing solution is composed of diamond micro powder, sodium dodecyl sulfate, hydrogen peroxide, and deionized water in a mass ratio of 13:0.8:1.5:70; the pH of the diamond polishing solution is 10.
[0053] A2. Add phenolic resin to ethanol, stir evenly, add polished seed crystal, stir at 90℃ until ethanol solvent evaporates, take out, place in carbonization furnace, carbonize at 950℃ for 3h, cool to room temperature to obtain pretreated seed crystal.
[0054] The mass ratio of phenolic resin, ethanol, and polished seed crystal is 2.5:25:3.5.
[0055] Example 3
[0056] A method for preparing a single crystal of a semi-insulating compound includes the following steps:
[0057] S1. Mix silicon carbide powder and vanadium carbide powder to obtain silicon carbide mixed powder; the mass ratio of silicon carbide powder to vanadium carbide powder is 1:0.1;
[0058] S2. Place the silicon carbide mixed powder at the bottom of the graphite crucible, place the pretreated seed crystal on the graphite crucible cover, and then place it on the top of the graphite crucible. After assembly, place it in the single crystal growth furnace and seal it to form the assembled single crystal growth furnace.
[0059] S3. The assembled single crystal growth furnace is evacuated, and inert gas is introduced to bring the furnace pressure to 60 kPa. After heating and reacting, the pressure is reduced and increased, and then cooled to room temperature to obtain a semi-insulating compound single crystal. The specific heating and reaction conditions are as follows: the temperature at the silicon carbide mixed powder is 2300℃, the temperature at the pretreated seed crystal is 2200℃, and the heating and reaction time is 5h. The specific pressure reduction is as follows: the pressure is reduced to 3 kPa and held for 150h. The specific pressure increase is as follows: the pressure is increased to 60 kPa and held for 100h.
[0060] The pretreated seed crystals are prepared by the following steps:
[0061] After polishing the A1.4H type silicon carbide seed crystal with diamond polishing slurry, it was removed, washed with water, and dried in an oven at 80℃ for 10 min to obtain the polished seed crystal. The polishing pressure was 2 MPa, the polishing time was 80 min, and the flow rate of the polishing slurry was 15 mL / min. The surface roughness of the polished seed crystal was 0.5 nm.
[0062] The diamond polishing solution is composed of diamond micro powder, sodium dodecyl sulfate, hydrogen peroxide, and deionized water in a mass ratio of 15:1:2:80; the pH of the diamond polishing solution is 13.
[0063] A2. Add phenolic resin to ethanol, stir evenly, add polished seed crystal, stir at 90℃ until the ethanol solvent evaporates, take it out, place it in a carbonization furnace, carbonize at 1000℃ for 4 hours, cool to room temperature, and obtain pretreated seed crystal.
[0064] The mass ratio of phenolic resin, ethanol, and polished seed crystal is 3:30:4.
[0065] Comparative Example 1
[0066] A method for preparing a single crystal of a semi-insulating compound includes the following steps:
[0067] S1. Place silicon carbide powder at the bottom of a graphite crucible, place the pretreated seed crystal on the graphite crucible lid, place it on the top of the graphite crucible, assemble it, place it in a single crystal growth furnace, seal it, and form an assembled single crystal growth furnace.
[0068] S3. The assembled single crystal growth furnace is evacuated, and inert gas is introduced to bring the furnace pressure to 60 kPa. After heating and reacting, the pressure is reduced and increased, and then cooled to room temperature to obtain a semi-insulating compound single crystal. The specific heating and reaction conditions are: the temperature at the silicon carbide powder is 2300℃, the temperature at the pretreated seed crystal is 2200℃, and the heating and reaction time is 5h. The specific pressure reduction is: reduce the pressure to 3 kPa and hold for 150h. The specific pressure increase is: increase the pressure to 60 kPa and hold for 100h.
[0069] The pretreated seed crystals are prepared by the following steps:
[0070] After polishing the A1.4H type silicon carbide seed crystal with diamond polishing slurry, it was removed, washed with water, and dried in an oven at 80℃ for 10 min to obtain the polished seed crystal. The polishing pressure was 2 MPa, the polishing time was 80 min, and the flow rate of the polishing slurry was 15 mL / min. The surface roughness of the polished seed crystal was 0.5 nm.
[0071] The diamond polishing solution is composed of diamond micro powder, sodium dodecyl sulfate, hydrogen peroxide, and deionized water in a mass ratio of 15:1:2:80; the pH of the diamond polishing solution is 13.
[0072] A2. Add phenolic resin to ethanol, stir evenly, add polished seed crystal, stir at 90℃ until the ethanol solvent evaporates, take it out, place it in a carbonization furnace, carbonize at 1000℃ for 4 hours, cool to room temperature, and obtain pretreated seed crystal.
[0073] The mass ratio of phenolic resin, ethanol, and polished seed crystal is 3:30:4.
[0074] Comparative Example 2
[0075] A method for preparing a single crystal of a semi-insulating compound includes the following steps:
[0076] S1. Mix silicon carbide powder and vanadium carbide powder to obtain silicon carbide mixed powder; the mass ratio of silicon carbide powder to vanadium carbide powder is 1:0.1;
[0077] S2. Place the silicon carbide mixed powder at the bottom of the graphite crucible, place the pretreated seed crystal on the graphite crucible cover, and then place it on the top of the graphite crucible. After assembly, place it in the single crystal growth furnace and seal it to form the assembled single crystal growth furnace.
[0078] S3. The assembled single crystal growth furnace is evacuated, and inert gas is introduced to bring the furnace pressure to 60 kPa. After heating and reacting, the pressure is reduced and increased, and then cooled to room temperature to obtain a semi-insulating compound single crystal. The specific heating and reaction conditions are as follows: the temperature at the silicon carbide mixed powder is 2300℃, the temperature at the pretreated seed crystal is 2200℃, and the heating and reaction time is 5h. The specific pressure reduction is as follows: the pressure is reduced to 3 kPa and held for 150h. The specific pressure increase is as follows: the pressure is increased to 60 kPa and held for 100h.
[0079] The pretreated seed crystals are prepared by the following steps:
[0080] Phenolic resin was added to ethanol and stirred evenly. 4H type silicon carbide seed crystals were added and stirred at 90°C until the ethanol solvent evaporated. The mixture was then removed, placed in a carbonization furnace, and carbonized at 1000°C for 4 hours. After cooling to room temperature, pretreated seed crystals were obtained.
[0081] The mass ratio of phenolic resin, ethanol and 4H-type silicon carbide seed crystals is 3:30:4.
[0082] Comparative Example 3
[0083] A method for preparing a single crystal of a semi-insulating compound includes the following steps:
[0084] S1. Mix silicon carbide powder and vanadium carbide powder to obtain silicon carbide mixed powder; the mass ratio of silicon carbide powder to vanadium carbide powder is 1:0.1;
[0085] S2. Place the silicon carbide mixed powder at the bottom of the graphite crucible, place the pretreated seed crystal on the graphite crucible cover, and then place it on the top of the graphite crucible. After assembly, place it in the single crystal growth furnace and seal it to form the assembled single crystal growth furnace.
[0086] S3. The assembled single crystal growth furnace is evacuated, and inert gas is introduced to bring the furnace pressure to 60 kPa. After heating and reacting, the pressure is reduced and increased, and then cooled to room temperature to obtain a semi-insulating compound single crystal. The specific heating and reaction conditions are as follows: the temperature at the silicon carbide mixed powder is 2300℃, the temperature at the pretreated seed crystal is 2200℃, and the heating and reaction time is 5h. The specific pressure reduction is as follows: the pressure is reduced to 3 kPa and held for 150h. The specific pressure increase is as follows: the pressure is increased to 60 kPa and held for 100h.
[0087] The pretreated seed crystals are prepared by the following steps:
[0088] After polishing the A1.4H type silicon carbide seed crystal with diamond polishing slurry, it was removed, washed with water, and dried in an oven at 80℃ for 10 min to obtain the polished seed crystal. The polishing pressure was 2 MPa, the polishing time was 80 min, and the flow rate of the polishing slurry was 15 mL / min. The surface roughness of the polished seed crystal was 0.5 nm.
[0089] The diamond polishing solution is composed of diamond micro powder, sodium dodecyl sulfate, and deionized water in a mass ratio of 17:1:80; the pH of the diamond polishing solution is 13.
[0090] A2. Add phenolic resin to ethanol, stir evenly, add polished seed crystal, stir at 90℃ until the ethanol solvent evaporates, take it out, place it in a carbonization furnace, carbonize at 1000℃ for 4 hours, cool to room temperature, and obtain pretreated seed crystal.
[0091] The mass ratio of phenolic resin, ethanol, and polished seed crystal is 3:30:4.
[0092] Comparative Example 4
[0093] A method for preparing a single crystal of a semi-insulating compound includes the following steps:
[0094] S1. Mix silicon carbide powder and vanadium carbide powder to obtain silicon carbide mixed powder; the mass ratio of silicon carbide powder to vanadium carbide powder is 1:0.1;
[0095] S2. Place the silicon carbide mixed powder at the bottom of the graphite crucible, place the pretreated seed crystal on the graphite crucible cover, and then place it on the top of the graphite crucible. After assembly, place it in the single crystal growth furnace and seal it to form the assembled single crystal growth furnace.
[0096] S3. The assembled single crystal growth furnace is evacuated, and inert gas is introduced to bring the furnace pressure to 60 kPa. After heating and reacting, the pressure is reduced and increased, and then cooled to room temperature to obtain a semi-insulating compound single crystal. The specific heating and reaction conditions are as follows: the temperature at the silicon carbide mixed powder is 2300℃, the temperature at the pretreated seed crystal is 2200℃, and the heating and reaction time is 5h. The specific pressure reduction is as follows: the pressure is reduced to 3 kPa and held for 150h. The specific pressure increase is as follows: the pressure is increased to 60 kPa and held for 100h.
[0097] The pretreated seed crystals are prepared by the following steps:
[0098] After polishing the A1.4H type silicon carbide seed crystal with diamond polishing slurry, it was removed, washed with water, and dried in an oven at 80℃ for 10 min to obtain the polished seed crystal. The polishing pressure was 2 MPa, the polishing time was 80 min, and the flow rate of the polishing slurry was 15 mL / min. The surface roughness of the polished seed crystal was 0.5 nm.
[0099] The diamond polishing solution is composed of diamond micro powder, sodium dodecyl sulfate, hydrogen peroxide, and deionized water in a mass ratio of 15:1:2:80; the pH of the diamond polishing solution is 13.
[0100] A2. Mix ethanol and polished seed crystals, stir at 90°C until the ethanol solvent evaporates, remove and place in a carbonization furnace, carbonize at 1000°C for 4 hours, cool to room temperature to obtain pretreated seed crystals;
[0101] The mass ratio of ethanol to polished seed crystals is 30:7.
[0102] The performance of the semi-insulating compound single crystals prepared in Examples 1-3 and Comparative Examples 1-4 was then tested.
[0103] The prepared semi-insulating compound single crystal was cut and processed into a 4-inch semi-insulating compound with a thickness of 400μm for performance testing.
[0104] The resistivity of 361 points on the substrate was measured using a non-contact resistance meter via the non-contact eddy current method. The substrate was etched with molten KOH for 30 minutes, and the distribution of screw dislocations was scanned using a fully automated dislocation scanner (LFMSi ClAuto). The screw dislocation density was then calculated.
[0105] The test results are shown in Table 1.
[0106] Table 1. Performance testing of single crystals of the semi-insulating compounds prepared in Examples 1-3 and Comparative Examples 1-4
[0107]
[0108] As can be seen from the data in Table 1, the semi-insulating compound single crystals prepared using Examples 1-3 not only have semi-insulating properties, but also have a low dislocation density.
[0109] Comparative Example 1 shows that a pretreated seed crystal prepared by replacing vanadium carbide powder with silicon carbide powder of equal mass was used to prepare a semi-insulating compound single crystal. Its insulation performance decreased and the dislocation density increased. This proves that by introducing a specific deep-level impurity vanadium element, the unavoidable impurities in silicon carbide single crystal can be precisely compensated, thereby "freezing" the charge carriers, achieving high resistivity, improving the insulation performance of the compound single crystal, and compensating for the lattice distortion caused by nitrogen element, thereby reducing the stress in the compound single crystal and reducing the dislocation density inside the compound single crystal.
[0110] Comparative Example 2 replaced the polished seed crystal with a pretreated seed crystal prepared from a 4H-type silicon carbide seed crystal to prepare a semi-insulating compound single crystal. The insulation of the seed crystal decreased and the dislocation density increased, which proves that the seed crystal was polished with diamond polishing fluid. Diamond micro powder has high hardness and can accurately grind the micro protrusions, oxide layer and impurities on the surface of the seed crystal. In addition, the hydrogen peroxide in the diamond polishing fluid can remove micro impurities that are difficult to reach by mechanical grinding, reduce surface residue, and avoid micro protrusions, oxide layer and impurities from affecting the continuity of subsequent single crystal growth. This is beneficial to the preparation of high-purity semi-insulating compound single crystals.
[0111] Comparative Example 3 used pretreated seed crystals prepared by replacing hydrogen peroxide with diamond micropowder to prepare semi-insulating compound single crystals. The insulation performance decreased and the dislocation density increased, which proves that hydrogen peroxide in diamond polishing solution can remove microscopic impurities that are difficult to reach by mechanical grinding, reduce surface residues, and avoid microscopic protrusions, oxide layers and impurities from affecting the continuity of subsequent single crystal growth, which is beneficial to the preparation of high-purity semi-insulating compound single crystals.
[0112] Comparative Example 4 used pretreated seed crystals prepared by replacing phenolic resin with polished seed crystals to prepare semi-insulating compound single crystals. The insulation properties decreased, and the dislocation density increased, demonstrating the synthesis of a network carbon layer on the surface of the polished seed crystal. On one hand, the network carbon layer on the carbon surface of the silicon carbide seed crystal can serve as adsorption sites for silicon, carbon, and vanadium elements generated by the vaporization of silicon carbide mixed powder. This allows for the uniform adsorption of silicon, carbon, and vanadium elements on the polished seed crystal surface, achieving uniform growth of single crystals on the carbon surface of the silicon carbide seed crystal and effectively reducing single crystal lattice distortion. On the one hand, the carbon network layer reduces internal stress, thereby forming a semi-insulating compound single crystal. On the other hand, when the carbon network layer is filled between the seed crystal and the graphite crucible, it has good porosity and thermal conductivity during the high-temperature single crystal production process. This can improve thermal contact, make the heat flow distribution more uniform, and avoid thermal stress caused by local overheating or undercooling between the seed crystal and the graphite crucible, which can lead to crystal cracking. In addition, the carbon network layer has good toughness and compressibility. As a soft intermediate layer, it absorbs and buffers some of the stress caused by thermal expansion mismatch, protecting the brittle seed crystal.
[0113] In the description of this specification, the references to terms such as "an embodiment," "example," "specific 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 present invention. In this specification, the 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.
[0114] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.
Claims
1. A method for preparing a single crystal of a semi-insulating compound, characterized in that, Includes the following steps: S1. Mix silicon carbide powder and vanadium carbide powder to obtain silicon carbide mixed powder; S2. Place the silicon carbide mixed powder at the bottom of the graphite crucible, place the pretreated seed crystal on the graphite crucible cover, and then place it on the top of the graphite crucible. After assembly, place it in the single crystal growth furnace and seal it to form the assembled single crystal growth furnace. S3. The assembled single crystal growth furnace is evacuated, inert gas is introduced, and after heating and reaction, the pressure is reduced and increased, and then cooled to room temperature to obtain a semi-insulating compound single crystal. The pretreated seed crystal is obtained by polishing the seed crystal with diamond polishing liquid, mixing it with phenolic resin, and then calcining it.
2. The method for preparing a semi-insulating compound single crystal according to claim 1, characterized in that, The pretreated seed crystal is obtained through the following steps: A1. After the seed crystal is polished with diamond polishing solution, it is taken out, washed with water, and dried to obtain the polished seed crystal. The polishing pressure is 1-2MPa, the polishing time is 60-80min, and the flow rate of polishing solution is 10-15mL / min. A2. Add phenolic resin to ethanol, stir evenly, add polished seed crystals, stir at 90℃ until the ethanol solvent evaporates, remove, place in a carbonization furnace, carbonize at 900-1000℃ for 2-4 hours, cool to room temperature, and obtain pretreated seed crystals.
3. The method for preparing a semi-insulating compound single crystal according to claim 2, characterized in that, In step A1, the diamond polishing fluid is composed of diamond micro powder, sodium dodecyl sulfate, hydrogen peroxide and deionized water in a mass ratio of (10-15):(0.5-1):(1-2):(60-80); In step A1, the pH of the diamond polishing solution is 9-13.
4. The method for preparing a semi-insulating compound single crystal according to claim 2, characterized in that, In step A1, the seed crystal is a 4H type silicon carbide seed crystal with a deflection angle of 4-8 degrees; In step A1, the surface roughness of the polished seed crystal is 0.1-0.5 nm.
5. The method for preparing a semi-insulating compound single crystal according to claim 2, characterized in that, In step A2, the mass ratio of the phenolic resin, ethanol and the polished seed crystal is (2-3):(20-30):(3-4).
6. The method for preparing a semi-insulating compound single crystal according to claim 1, characterized in that, In step S1, the mass ratio of silicon carbide powder to vanadium carbide powder is 1:(0.01-0.1).
7. The method for preparing a semi-insulating compound single crystal according to claim 1, characterized in that, In step S3, the inert gas is argon or nitrogen; the pressure of the inert gas introduced into the furnace is 40-60 kPa.
8. The method for preparing a semi-insulating compound single crystal according to claim 1, characterized in that, In step S3, the heating reaction conditions are as follows: the temperature at the silicon carbide mixed powder is 2200-2300℃, the temperature at the pretreated seed crystal is 2000-2200℃, and the heating reaction time is 2-5h.
9. The method for preparing a semi-insulating compound single crystal according to claim 1, characterized in that, In step S3, the pressure reduction specifically involves reducing the pressure to 2-3 kPa and maintaining it for 100-150 hours; the pressure increase specifically involves increasing the pressure to 40-60 kPa and maintaining it for 50-100 hours.
10. A semi-insulating compound single crystal prepared by the method of any one of claims 1-9.