A method for growing P-type 4H-SiC single crystal by PVT method

Abstract

The present invention discloses a method for growing P-type 4H-SiC single crystals by the PVT method, belonging to the field of semiconductor technology. Before the growth of SiC single crystals, the Si surface of the SiC substrate is pretreated by electrochemical etching, specifically: the Si surface of the SiC substrate is exposed and the C surface is covered; the covered surface of the substrate is connected to a graphite electrode as the anode, and the cathode is selected from a graphite electrode or a platinum electrode; the anode and the cathode are symmetrically placed, the SiC substrate is placed in the electrolyte, and the power supply is connected to perform electrochemical etching on the growth surface of the substrate; the electrochemically etched substrate is continuously immersed in the electrolyte, then immersed in deionized water and ultrasonically treated, and finally dried with an inert gas. The method for growing P-type 4H-SiC single crystals by the PVT method provided by the present invention can provide more nucleation sites, reduce the nucleation energy of 4H on the Si surface, provide a window for the nucleation and growth of 4H-SiC, increase the doping of aluminum elements, and stabilize the growth of P-type 4H-SiC single crystals by performing electrochemical etching pretreatment on the Si surface of the SiC substrate before the growth of SiC single crystals by the PVT method.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly relates to a method for growing P-type 4H-SiC single crystal by the PVT method. Background Art

[0002] SiC materials not only have high high-temperature strength and creep resistance, excellent corrosion resistance, and good thermal conductivity, but also have unique characteristics such as a large bandgap, high breakdown field strength, high electron saturation drift velocity, small dielectric constant, and strong radiation resistance. They are more suitable for manufacturing high-temperature, high-power, high-frequency devices, and substrates for other thin film materials (such as AlN, GaN, diamond) and X-ray masks. SiC has a wide range of applications in white light illumination, optical storage, screen display, aerospace, high-temperature radiation environment, oil exploration, automation, radar and communication, automotive electronics, etc. It is an ideal semiconductor material for manufacturing optoelectronic devices, high-frequency high-power devices, and high-temperature electronic devices.

[0003] Currently, the most important quality problems in SiC crystal growth are the generation of defects and the control of doping, which will directly affect the yield of wafers. For defects, microtubes can currently be reduced to extremely low levels, but there are still defects such as threading edge dislocations (TED), threading screw dislocations (TSD), and basal plane dislocations (BPD) that need to be further controlled and reduced. For doping, more rigorous requirements are needed for controlling the doping concentration and elements.

[0004] For the application of SiC in power electronic devices, SiC needs to have relatively high P-type and N-type doping concentrations, which can only be achieved through doping. Currently, the physical vapor transport method (abbreviated as PVT) is the mainstream growth method for SiC single crystals. If P-type or N-type SiC is to be grown, adjustments need to be made to the growth raw materials and growth processes. At present, the growth process of N-type 4H-SiC single crystals is relatively perfect. Generally, the C plane is used as the growth surface for growing N-type 4H-SiC single crystals. The surface energy of the C plane is relatively low, which can provide a suitable growth window for the nucleation and growth of 4H-SiC. Nitrogen is also more likely to be incorporated on the C plane and the nitrogen source can be continuously supplied, which enables good control of the doping concentration and doping uniformity of nitrogen, and the doping concentration can even reach 1.0E18 cm -3 (or even higher). Therefore, the supply and application ratio of N-type 4H-SiC in the market is relatively large. However, when P-type 4H-SiC single crystals are doped and grown on the C plane, although the single crystal form of 4H-SiC can be guaranteed, the doping of aluminum on the C plane is much lower than that of nitrogen. Coupled with the fact that the aluminum source is difficult to continuously supply, there are still problems of difficult doping and uneven doping in the growth of P-type 4H-SiC single crystals, which seriously affect the growth quality and application of P-type 4H-SiC single crystals.

[0005] Related research shows that when growing P-type SiC single crystals, the aluminum content in the 6H-SiC single crystals grown on the Si face is much higher than that in the 4H-SiC single crystals grown on the C face. On the Si face of the SiC seed crystal, aluminum is more easily incorporated. However, in the traditional PVT process, it is impossible to grow 4H-SiC single crystals on the Si face, and generally only 6H-SiC single crystals can be grown on the Si face of the seed crystal. However, the bandgap width of 6H-SiC single crystals is smaller than that of 4H-SiC, and the performance is slightly worse than that of 4H. To address this problem, the present invention proposes a method for growing P-type 4H-SiC single crystals on the Si face of SiC seeds by the PVT method. Summary of the Invention

[0006] The object of the present invention is to provide a method for growing P-type 4H-SiC single crystals by the PVT method, which solves the problems of unstable growth of 4H-SiC single crystals on the Si face and difficult doping of aluminum sources. It can ensure the growth of P-type 4H-SiC single crystal form on the Si face while increasing the absorption of aluminum, achieving the purpose of cost reduction and efficiency improvement.

[0007] To achieve the above object, the present invention provides a method for growing P-type 4H-SiC single crystals by the PVT method. Before the growth of SiC crystals by the PVT method, the Si face of the SiC substrate is pretreated by electrochemical etching, which can provide more nucleation sites, reduce the nucleation energy of 4H on the Si face, provide a window for the nucleation and growth of 4H-SiC, increase the doping of aluminum elements, and stabilize the growth of P-type 4H-SiC single crystals.

[0008] Preferably, the specific steps of the electrochemical etching pretreatment of the Si face of the SiC substrate are as follows:

[0009] (1) Expose the Si face of the SiC substrate to be pretreated and cover the C face.

[0010] (2) Connect the C face of the substrate to a graphite electrode as the anode, and select a graphite electrode or a platinum electrode as the cathode.

[0011] (3) Place the anode and cathode symmetrically, place the SiC substrate in the electrolyte, connect the power supply and energize to perform electrochemical etching on the Si face of the substrate.

[0012] (4) Immerse the electrochemically etched substrate in the electrolyte, then immerse it in deionized water and ultrasonicate, and finally dry it with an inert gas.

[0013] Preferably, in step (2), the C face of the substrate is adhesively connected or vacuum-adsorbed to the graphite electrode through a conductive adhesive.

[0014] Preferably, in step (3), the distance between the cathode and the anode is 1-20 cm, the power supply voltage is 0-50 V, and the current is 0-500 mA.

[0015] Preferably, in the step (3), the electrolyte is an HF solution with a concentration of 0 - 60 wt% and a temperature of 0 - 50 °C, and the electrochemically etching time is 0 - 5 h.

[0016] Preferably, in the step (4), it is soaked in the electrolyte for 0 - 12 hours and soaked and ultrasonically treated in deionized water for 0 - 10 hours.

[0017] Preferably, in the step (4), the inert gas is Ar or He.

[0018] The process of electrochemically etching basically includes two parts: In the first part, holes are generated during the etching process, a current is formed at the SiC - electrolyte interface, and SiC is oxidized into SiO x film. In the second part, the SiO x film is dissolved in the electrolyte. The type / concentration of the electrolyte, the electrochemically etching time / temperature, the external auxiliary conditions (such as ultraviolet light irradiation, ultrasonic vibration, etc.), the load voltage / current, and the electrode spacing will all affect the electrochemically etching effect.

[0019] The main method of the present invention is to perform electrochemically etching pretreatment on the Si surface of the SiC substrate before growing the SiC crystal by the PVT method. After the electrochemically etching pretreatment, SiC powder doped with an aluminum source is used as the raw material, and P - type 4H - SiC single crystal is grown on the Si surface by the PVT method. The basic principle of the electrochemically etching pretreatment is that electrochemically etching can provide more nucleation sites on the substrate, reduce the nucleation energy of 4H on the Si surface, provide a suitable window for the nucleation and growth of 4H - SiC, break the current situation that only 6H - SiC can grow on the Si surface and 4H - SiC can only grow on the C surface, make full use of the characteristic that it is easier for aluminum elements to be incorporated on the Si surface, increase the absorption of aluminum elements, improve the quality of single crystal growth, avoid the generation of grain boundaries and polytypes, thereby stabilizing the single crystal form of 4H - SiC on the Si surface and making the doping and growth of P - type 4H - SiC single crystal easier.

[0020] Therefore, the present invention provides a method for growing P - type 4H - SiC single crystal by the PVT method. By selecting a suitable substrate pretreatment scheme, using electrochemically etching to reduce the surface nucleation energy of the Si surface, while ensuring the growth of the single crystal form of P - type 4H - SiC on the Si surface, the absorption of aluminum elements is increased, achieving the purpose of reducing costs and increasing efficiency.

[0021] The technical solution of the present invention will be further described in detail below through the drawings and embodiments. Brief Description of the Drawings

[0022] Figure 1 It is a device diagram for the electrochemically etching used in the present invention;

[0023] Figure 2It is the thermal field structure diagram used for growing P-type 4H-SiC single crystal by the PVT method of the present invention;

[0024] Figure 3 It is the Raman mapping diagram of the SiC single crystal grown by the direct PVT method on the Si surface of the SiC substrate without treatment;

[0025] Figure 4 It is the Raman mapping diagram of the SiC single crystal grown by the PVT method after the Si surface of the SiC substrate is pretreated by electrochemical etching;

[0026] Reference numerals in the drawings

[0027] 1 - Anode electrode; 2 - Cathode electrode; 3 - Tetrafluoroethylene cover plate; 4 - Power supply; 5 - Electrolyte; 6 - SiC substrate; 7 - Graphite screw rod; 8 - Wire; 9 - Upper temperature measurement hole; 10 - Lower temperature measurement hole; 11 - Upper thermal insulation; 12 - Lower thermal insulation; 13 - Side thermal insulation; 14 - Seed crystal holder; 15 - Seed crystal; 16 - Crystal growth crucible; 17 - P-type SiC powder. Specific embodiments

[0028] The present invention provides a method for growing P-type 4H-SiC single crystal by the PVT method. Before the growth of the SiC crystal by the PVT method, the Si surface of the SiC substrate is pretreated by electrochemical etching, which can provide more nucleation sites, reduce the nucleation energy of 4H on the Si surface, provide a window for the nucleation and growth of 4H-SiC, increase the doping of aluminum element, and stabilize the growth of P-type 4H-SiC single crystal.

[0029] In the present invention, the specific steps for pretreating the Si surface of the SiC substrate by electrochemical etching are as follows:

[0030] (1) Expose the Si surface of the SiC substrate to be pretreated and cover the C surface;

[0031] (2) Connect the C surface of the substrate to a graphite electrode as the anode, and select a graphite electrode or a platinum electrode as the cathode;

[0032] (3) Place the anode and the cathode symmetrically, place the SiC substrate in the electrolyte, connect the power supply and energize it to perform electrochemical etching on the Si surface of the substrate;

[0033] (4) Immerse the substrate after electrochemical etching in the electrolyte continuously, then immerse it in deionized water and soak and ultrasonicate, and finally dry it with an inert gas.

[0034] In the present invention, the device used for electrochemical etching is as Figure 1As shown in the figure, it consists of an anode electrode 1, a cathode electrode 2, a tetrafluoroethylene cover plate 3, a power supply 4, an electrolyte 5, a SiC substrate 6, a graphite screw rod 7, and a wire 8. Among them, the anode and cathode are symmetrically placed up and down. The distance between the two electrodes is fixed and adjusted by a thread between the graphite screw rod 7 and the tetrafluoroethylene cover plate 3. The distance between the cathode and the anode is 1 - 20 cm. The masked surface of the SiC substrate 6 is adhered to the anode electrode 1 by conductive adhesive or connected by vacuum adsorption. The pre-etched surface is in contact with the electrolyte 5. The distance between the anode electrode 1 (graphite electrode) and the cathode electrode 2 (graphite electrode) is fixed and adjusted by a thread between the graphite screw rod 7 and the tetrafluoroethylene cover plate 3. The graphite screw rod 7 is screwed tightly with the graphite electrodes 1 and 2 to conduct electricity, and the wire 8 is connected to the graphite screw rod 7 by a conductive clip to conduct electricity.

[0035] The power supply is energized, the power supply voltage is 0 - 50 V, and the current is 0 - 500 mA. Hydroxide ions (OH - ) accumulate at the anode. The hydroxide ions (OH - ) and holes (h + ) form free radicals ( . OH). The free radicals are unstable and easily diffuse between the SiC at the anode and the electrolyte interface, oxidizing SiC into SiO x and CO x . Then, the oxidation products SiO x and CO x dissolve in the HF electrolyte. The process can be expressed as:

[0036] 4OH - -4e - →2H2O + O2;

[0037] OH - + h + → . OH;

[0038] SiC + 4 . OH + O2 → SiO2 + CO2 + 2H2O;

[0039] SiO2 + 6HF → 2H + + SiF6 2- + 2H2O.

[0040] In the present invention, the specific steps of electrochemical etching + P-type 4H-SiC single crystal growth are as follows:

[0041] Step 1: Expose the Si surface of the SiC substrate to be pretreated and cover the C surface;

[0042] Step 2: The C surface of the substrate is connected to a graphite electrode as the anode, and the cathode is selected from a graphite electrode or a platinum electrode (the C surface of the substrate is preferably attached to the graphite electrode by conductive adhesive or vacuum adsorption).

[0043] Step 3: The anode and the cathode are placed symmetrically in an electrolyte with a concentration of 0 - 60 wt%, connected to a power supply to conduct electricity, and the growth surface of the substrate is electrochemically etched for 0 - 5 h.

[0044] The temperature of the electrolyte is controlled at 0 - 50 °C. Auxiliary conditions can be selected, such as ultraviolet light irradiation, ultrasonic vibration, etc. The types of electrolytes can be neutral (such as: NaCl solution), alkaline (such as: KOH solution), acidic (such as: HF solution). In the present invention, HF solution is preferably selected as the electrolyte.

[0045] Step 4: The electrochemically etched substrate is first immersed in the electrolyte for 0 - 12 hours, then immersed in deionized water multiple times with ultrasonic vibration, and the time is controlled within 0 - 10 hours. Finally, it is dried with an inert gas such as Ar gas or He gas for standby.

[0046] Step 5: The Si surface of the pre-treated seed crystal 15 is used as the growth surface and fixed on the seed crystal holder 14 (the fixing method is not limited, and can be: adhesive bonding, mechanical fixing, chemical fixing, etc.). The P-type SiC powder 17 is placed at the bottom of the crystal growth crucible 16, and the crucible is tightened and placed in the corresponding heat preservation thermal field (the material of the crystal growth crucible can be selected from isostatic graphite, tantalum carbide, tantalum carbide coating, or tungsten metal, etc.).

[0047] Step 6: After the furnace loading is completed, the single crystal growth furnace is evacuated to make the pressure in the furnace reach 10^ -6 mbar, and then the corresponding temperature control and pressure control programs are set.

[0048] Step 7: Under vacuum conditions, a heating program is set. After heating to 1100 - 1450 °C in 2 - 6 hours, the argon gas inlet is opened (the gas flow rate is controlled at 0 - 5 L / min). After pressurizing to 200 - 900 mbar in 0.5 - 3 hours, under the condition of constant pressure with flowing argon, after heating to 2000 - 2300 °C in 2 - 6 hours, then under the condition of constant temperature with flowing argon, the pressure is reduced to 0.1 - 50 mbar within 0.5 - 50 hours. Under the growth conditions of a temperature of 2000 - 2300 °C and a pressure of 0.1 - 50 mbar, crystal growth is carried out for 3 - 15 days.

[0049] Step 8: Before pressurizing and cooling, keep the argon gas inlet open (the gas flow rate is controlled at 0 - 5 L / min). After pressurizing to 200 - 900 mbar in 0.5 - 3 hours, cool down to 700 - 1400 °C in 10 - 20 hours, and then cool down naturally to end the entire crystal growth.

[0050] In the present invention, the thermal field device used for crystal growth is as follows Figure 2 As shown, it includes an upper temperature measurement hole 9, a lower temperature measurement hole 10, an upper thermal insulation 11, a lower thermal insulation 12, a side thermal insulation 13, a seed crystal holder 14, a pre-treated seed crystal 15, a crystal growth crucible 16, and P-type SiC powder 17. From top to bottom, there are an upper thermal insulation 11, a side thermal insulation 13, and a lower thermal insulation 12. Among them, the upper and lower temperature measurement holes 9 and 10 are respectively located in the middle of the upper and lower thermal insulations. The crystal growth crucible 16 is placed in the middle of the lower thermal insulation 12. The P-type SiC powder 17 is placed at the bottom of the crystal growth crucible 16. The pre-treated seed crystal 15 is fixed on the seed crystal holder 14, and the seed crystal holder 14 is connected to the crystal growth crucible by a threaded knob.

[0051] The following will further elaborate on the present invention in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention. In addition, it should be understood that after reading the content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application and all belong to the protection scope of the present invention.

[0052] Unless otherwise defined, the meanings of the technical terms used herein are the same as those generally understood by those skilled in the technical field to which this application belongs; the use of relevant terms herein is only for describing specific embodiments and is not intended to limit this application.

[0053] In the present invention, unless otherwise specified, the reagents, instruments, equipment, etc. used are all the reagents, instruments, and equipment commonly used by those skilled in the art in this field.

[0054] Embodiment

[0055] This embodiment provides a method for growing P-type 4H-SiC single crystals by the PVT method on the Si surface after electrochemically etching and pre-treating the Si surface of a SiC substrate. The specific steps are as follows:

[0056] Step 1: Expose the Si surface of the SiC substrate 6, and use conductive glue to connect the C surface to the graphite electrode 1 so that there is full contact between the SiC substrate 6 and the graphite electrode 1.

[0057] Step 2: The SiC substrate 6 and the graphite electrode 1 are used as anodes and connected to the positive pole of the power supply, and a graphite electrode 2 of the same size and thickness is used as a cathode and connected to the negative pole of the power supply. The distance between the two electrodes is 6 cm, the output voltage of the power supply 4 is 15 V, and the current is 50 mA.

[0058] Step 3: Electrochemically etch the SiC substrate with the exposed Si surface in HF electrolyte 5 with a concentration of 10 wt% for 10 minutes, and control the temperature of electrolyte 5 at 30°C.

[0059] Step 4: Immerse the electrochemically etched substrate in electrolyte 5 for 12 hours first, then ultrasonically immerse it in deionized water for 2 hours, and finally dry it with Ar gas for standby.

[0060] Step 5: Use the Si surface of the pre-treated seed crystal 15 as the growth surface and fix it on the seed crystal holder 14 (the fixing method is not limited and can be: adhesive bonding, mechanical fixing, chemical fixing, etc.). Place the P-type SiC powder 17 at the bottom of the crystal growth crucible 16, tighten the crucible, and place it in the corresponding heat preservation thermal field.

[0061] Step 6: After the furnace loading is completed, evacuate the single crystal growth furnace to make the pressure in the furnace reach 10 -6 mbar, and then set the corresponding temperature control and pressure control programs.

[0062] Step 7: Under vacuum conditions, set the heating program. Heat up to 1350°C in 3 hours. At this time, open the argon gas inlet (gas flow rate is 1 L / min). Increase the pressure to 300 mbar in 1 hour. Under the condition of constant pressure with flowing argon, heat up to 2100°C in 3 hours. Then, under the condition of constant temperature with flowing argon, reduce the pressure to 5 mbar within 1 hour. Under the growth conditions of a temperature of 2100°C and a pressure of 5 mbar, grow the crystal for 5 days.

[0063] Step 8: Before increasing and decreasing the pressure and temperature, keep the Ar gas inlet open (gas flow rate is 1 L / min). Increase the pressure to 800 mbar in 1 hour, cool down to 1100°C in 15 hours, and then cool down naturally to end the entire crystal growth.

[0064] Perform SIMS tests on the P-type 4H-SiC single crystals grown with N-type 4H-SiC substrates with two different crystal planes after electrochemical etching pretreatment as seed crystals. The results are shown in Table 1.

[0065] Table 1

[0066] Growth conditions <![CDATA[Aluminum concentration (cm -3 )]]> Growth of P-type 4H-SiC on the Si face of N-type 4H seed crystal 4.0E15 - 6.0E15 Growth of P-type 4H-SiC on the C face of N-type 4H seed crystal 1.0E15 - 2.0E15

[0067] From the data in Table 1, it can be seen that the absorption of aluminum elements by the P-type 4H-SiC single crystal grown on the Si surface is much higher than that of the P-type 4H-SiC single crystal grown on the C surface (2 - 6 times), indicating that: if the growth of the 4H-SiC single crystal is stabilized on the Si surface, it can increase the absorption of aluminum, which is beneficial to the doped growth of the P-type 4H-SiC single crystal.

[0068] Raman mapping scanning tests were carried out on SiC single crystals grown by the PVT method directly on the Si surface of the SiC substrate without treatment and on SiC single crystals grown by the PVT method after electrochemical etching pretreatment of the Si surface of the SiC substrate for characterization.

[0069] Raman mapping scanning tests can determine the SiC crystal form distribution. The same color represents the same characteristic peaks and the same crystal form. Among them, the blue characteristic peaks are: 204, 776 representing 4H-SiC; the green characteristic peaks are: 150, 789 representing 6H-SiC; the red characteristic peaks are: 173, 785 representing 15R-SiC. Figure 3 In the case where single crystal growth is directly carried out on the Si surface of the SiC substrate without treatment, the color of the Raman mapping diagram is not single, indicating the presence of 6H, 4H, and 15R crystal forms, and there is a phenomenon of polytype inclusion. And Figure 4 This is the Raman mapping diagram of the SiC single crystal grown by the PVT method after electrochemical etching pretreatment of the Si surface of the SiC substrate. After electrochemical etching pretreatment, the color of the Raman mapping diagram is single, all blue, indicating that the grown crystals are all 4H-SiC single crystals. This shows that electrochemical etching pretreatment can promote and stabilize the growth of the single crystal form of 4H-SiC on the Si surface.

[0070] In summary, before growing SiC crystals by the PVT method, electrochemical etching pretreatment of the Si surface of the SiC substrate can provide more nucleation sites, reduce the nucleation energy of 4H on the Si surface, provide a window for the nucleation and growth of 4H-SiC, stabilize the growth of the single crystal form of 4H-SiC on the Si surface, and at the same time increase the doping of aluminum elements, which is beneficial to solving the problem of difficult doping of aluminum elements in the growth of P-type SiC single crystals, breaking the technical barrier of growing 4H on the C surface and 6H on the Si surface, and providing a new idea for the growth of P-type SiC crystals.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for growing a P-type 4H-SiC single crystal by a PVT method, characterized in that: Before the PVT growth of SiC single crystal, the Si surface of the SiC substrate is pretreated by electrochemical etching to provide more nucleation sites, reduce the nucleation energy of 4H on the Si surface, provide a window for the nucleation growth of 4H-SiC, increase the doping of aluminum elements, and stabilize the growth of P-type 4H-SiC single crystal. The specific steps of electrochemical etching pretreatment of the Si surface of the SiC substrate are: (1) Exposing the Si surface of the SiC substrate to be pretreated and covering the C surface; (2) The C-side of the substrate is connected to a graphite electrode as the anode, and a graphite electrode or a platinum electrode is selected as the cathode; (3) The anode and cathode are placed symmetrically, the SiC substrate is placed in the electrolyte, the power supply is connected and the Si surface of the substrate is electrochemically etched; (4) The electrochemically etched substrate is further immersed in the electrolyte, then immersed in deionized water for ultrasonic treatment, and finally dried with an inert gas; The electrolyte is HF solution, the concentration is 0-60wt%, the temperature is 0-50°C, and the electrochemical etching time is 0-5h.

2. The method for growing a P-type 4H-SiC single crystal by a PVT method according to claim 1, characterized in that: In the step (2), the C surface of the substrate and the graphite electrode are connected by conductive adhesive bonding or vacuum adsorption.

3. The method for growing a P-type 4H-SiC single crystal by a PVT method according to claim 1, characterized in that: In the step (3), the distance between the cathode and the anode is 1-20 cm, the power supply voltage is 0-50 V, and the current is 0-500 mA.

4. The method for growing a P-type 4H-SiC single crystal by a PVT method according to claim 1, characterized in that: In the step (4), the electrolyte is immersed for 0-12 hours, and the ultrasonic soaking is performed in deionized water for 0-10 hours.

5. The method for growing a P-type 4H-SiC single crystal by a PVT method according to claim 1, characterized in that: In the step (4), the inert gas is Ar or He.

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