CN110699752B

CN110699752B - Method for growing weak magnetic Fe-V co-doped SiC crystal step by step

Info

Publication number: CN110699752B
Application number: CN201911043221.6A
Authority: CN
Inventors: 卓世异; 刘学超; 严成锋; 施尔畏
Original assignee: Anhui Microchip Changjiang Semiconductor Materials Co ltd
Current assignee: Anhui microchip Changjiang semiconductor materials Co.,Ltd.
Priority date: 2019-10-30
Filing date: 2019-10-30
Publication date: 2022-03-22
Anticipated expiration: 2039-10-30
Also published as: CN110699752A

Abstract

The invention relates to a method for growing weak magnetic Fe-V co-doped SiC crystals step by step, which comprises the following steps: (1) mixing a high-purity SiC crystal block, Fe powder and V powder, placing the mixture at the bottom of a crucible as a crystal material, spreading a layer of silicon carbide powder on the surface of the crystal material, taking a 6H-SiC wafer as a seed crystal, and starting crystal growth by adopting a physical vapor transport method to obtain an excessive Fe-V co-doped SiC crystal, wherein the addition amount of the Fe powder and the V powder is more than the solid solubility of Fe and V in the SiC crystal at room temperature; (2) and (3) cutting the obtained excessive Fe-V co-doped SiC crystal into blocks, placing the blocks at the bottom of a crucible, taking a 6H-SiC wafer as a seed crystal, and starting secondary growth by adopting a physical vapor transport method to obtain the weak magnetic Fe-V co-doped silicon carbide crystal.

Description

Method for growing weak magnetic Fe-V co-doped SiC crystal step by step

Technical Field

The invention relates to a method for growing a Fe-V co-doped silicon carbide crystal with weak magnetism, belonging to the technical field of growth of novel weak magnetic semiconductor crystal materials.

Background

Magnetic silicon carbide (SiC) is one of magnetic semiconductor materials in which carriers have both the spin and charge properties of electrons (or holes), and is widely used in emerging spintronics devices. The preparation of magnetic SiC materials is usually achieved by doping with transition group metal elements (or rare earth elements) by the principle of partial replacement of Si lattice site atoms (or C lattice site atoms) in the silicon carbide lattice with magnetic ions, which typically have unpaired d-orbital electrons (or f-orbital electrons). The magnetic coupling between the partially substituted doped magnetic ions makes the doped SiC material weakly magnetic.

Currently, researchers report methods for preparing magnetic SiC materials having various morphologies. For example, patent 1 (chinese application publication No. CN101404198A) discloses a diluted magnetic semiconductor material with a high curie temperature and a method for preparing the same. In the special sectionThe method comprises the following main steps of firstly performing surface cleaning pretreatment on the selected 4H-SiC substrate material, then injecting iron (Fe) ions with certain concentration into the substrate material, and finally sequentially placing the substrate material after injection in hydrogen (H)₂) Nitrogen (N)₂) And annealing in hydrogen (H). Through these steps, a magnetic semiconductor material having ferromagnetism at room temperature is obtained. Patent 2 (chinese application publication No. CN106542826A) discloses a magnetic SiC material and a method for preparing the same. The method is mainly characterized in that the magnetic SiC ceramic material is obtained by calcining R element doped silicon carbide powder in argon (Ar) atmosphere, wherein the R element is at least one of aluminum (Al), boron (B), Fe, manganese (Mn), zinc (Zn), cobalt (Co), vanadium (V) and nickel (Ni). By preferably selecting different R elements and doping amounts, the magnetic properties of the magnetic SiC material can be adjusted. Patent 3 (chinese application publication No. CN107527949A) discloses a heterojunction spin field effect transistor based on Cr-doped 4H-SiC substrate and a method for manufacturing the same. The method is implemented by the following main steps of firstly selecting 4H-SiC as a substrate, and secondly extending a layer of Ca on the substrate₂O₃And then injecting chromium (Cr) ions into the previous step material to form a source region and a drain region, and finally forming a Schottky contact gate electrode on the surface of the epitaxial layer by utilizing a magnetron sputtering process to finally form the Cr-doped 4H-SiC substrate heterojunction spin field effect transistor. Patent 4 (chinese application publication No. CN105551794A) discloses a SiC-based diluted magnetic semiconductor film and a method for preparing the same. The main implementation mode of the method is a certain dosage of carbon particles (A)¹²C) The SiC film is irradiated, and the ferromagnetism of the material is adjusted by changing the radiation dose.

Although the above representative patents disclose methods, the preparation of current magnetic SiC materials in particular practice requires further optimization and development due to the nucleation characteristics of SiC which make the crystal lattice susceptible to breakage, the single crystal crystals difficult to grow and difficult to dope. Such as: (1) the magnetic SiC materials obtained generally exhibit the morphology of ceramics, particles, thin films, in which a large number of SiC intrinsic point defects are inevitably present, thus reducing the magnetic and electrical properties of the material; (2) the transition metal elements or rare earth elements introduced by doping are not uniformly dispersed and easily form clusters, so that the magnetic coupling effect in the prepared material is weakened; (3) the preparation process is complex, and various special devices are often needed to realize the growth of the matrix, the introduction of magnetic ions and the subsequent annealing treatment, which brings the problems of process control and preparation cost.

Disclosure of Invention

In view of the new technical requirements appearing in the preparation process of the magnetic semiconductor material at the present stage, the invention aims to provide a method for growing weak magnetic Fe-V co-doped SiC crystals step by step, which comprises the following steps:

(1) mixing a high-purity SiC crystal block, Fe powder and V powder, placing the mixture at the bottom of a crucible as a crystal material, spreading a layer of silicon carbide powder on the surface of the crystal material, taking a 6H-SiC wafer as a seed crystal, and starting crystal growth by adopting a physical vapor transport method to obtain an excessive Fe-V co-doped SiC crystal, wherein the addition amount of the Fe powder and the V powder is more than the solid solubility of the Fe and the V at room temperature (27 ℃) in the SiC crystal;

(2) and (3) cutting the obtained excessive Fe-V co-doped SiC crystal into blocks, placing the blocks at the bottom of a crucible, taking a 6H-SiC wafer as a seed crystal, and starting secondary growth by adopting a physical vapor transport method to obtain the weak magnetic Fe-V co-doped silicon carbide crystal.

In the method, the growth of the weak-magnetism Fe-V co-doped SiC crystal is realized by using a method of replacing the step-by-step doping of the magnetic elements. Specifically, the growth of the magnetic Fe-V co-doped SiC crystal with high crystal quality and weak magnetism is realized by a multi-step growth method of doping magnetic elements (Fe and V) in a high-purity SiC crystal (the purity is more than 99.99%) in an excessive way and subsequent secondary growth (secondary decomposition doping).

Preferably, the preparation method of the high-purity SiC crystal block comprises the following steps: putting the silicon carbide powder in a crucible, taking a 6H-SiC wafer as a seed crystal, growing for more than or equal to 60 hours at 2200-2400 ℃ in an inert atmosphere to obtain a high-purity SiC crystal, removing the edge part, and cutting to obtain a high-purity SiC crystal block; preferably, the inert atmosphere is Ar gas, the purity is more than or equal to 99.999%, and the gas pressure is 1000-3000 Pa. In this step, in the growth of high purity SiC crystal, keeping the temperature of the charge region in the crucible high (2200 to 2400 ℃) can increase the sublimation rate of SiC, whereas the high Ar atmosphere pressure (1000 to 3000Pa) can suppress the distribution of sublimation gas, so that the recrystallization of sublimation atmosphere particles of SiC at the SiC seed crystal is preferable.

Preferably, the preparation process of the silicon carbide powder comprises the following steps: placing a silicon carbide raw material in a crucible, and pretreating at 1000-1300 ℃ for more than or equal to 3 hours in an inert atmosphere to obtain the silicon carbide powder; preferably, the inert atmosphere is Ar gas, the purity is more than or equal to 99.999%, and the gas pressure is 1000-1300 Pa. The pretreatment in the temperature range can ensure that common light elements in SiC raw materials (SiC powder) are doped, gasified and overflowed on one hand, and ensure that the treatment temperature is lower than the sublimation temperature of SiC on the other hand, thereby reducing the loss of Si and C in the powder.

Preferably, the total mass of the crystal material and the silicon carbide powder is 100wt%, and the total content of the Fe powder and the V powder is more than or equal to 0.1%, preferably 0.5-5 wt%; more preferably, the mass ratio of the Fe powder to the V powder is 1: (1-1.5).

Preferably, the total mass of the crystal material and the silicon carbide powder is 100wt%, and the content of the silicon carbide powder is less than or equal to 5%.

Preferably, in step (1), the parameters of crystal growth include: the growth temperature is 2000-2200 ℃; the growth time is more than or equal to 30 hours; the growing atmosphere is inert atmosphere, the purity is more than or equal to 99.999 percent, and the air pressure is 100-1000 Pa. In the step, in the growth of the excessive Fe-V co-doped SiC crystal, the lower Ar atmosphere pressure (100 Pa-1000 Pa) can promote the dispersion of sublimed particles of SiC, so that the excessive Fe-V co-doped SiC crystal can grow at a higher speed.

Preferably, in step (2), the parameters of the secondary growth include: the growth temperature is 2000-2200 ℃; the growth time is more than or equal to 60 hours; the growth atmosphere is inert atmosphere, and the air pressure is 1000-3000 Pa. The crystal blocks obtained by excessive Fe-V doping are used as raw materials, so that Fe and V doping can effectively enter SiC crystal lattices in the secondary growth process of the crystal, the formation of Fe/V metal clusters is avoided, and the magnetic strength of the Fe-V co-doped SiC crystal is improved. Moreover, the higher Ar ambient pressure described above may promote the crystal quality of SiC recrystallization at the seed crystal.

Preferably, the inert atmosphere is Ar gas, and the purity is more than or equal to 99.999 percent.

Preferably, the crucible is a graphite crucible; preferably, the material purity of the graphite crucible is more than or equal to 99.999 percent; more preferably, the graphite crucible is pretreated at a high temperature of 2000 to 2500 ℃. Wherein, the high-temperature pretreatment of the crucible refers to the high-temperature pretreatment of the graphite crucible with the material purity superior to 99.999 percent in a vacuum annealing device at 2000-2500 ℃. The further annealing treatment can reduce the possibility of vaporization or exudation of impurities in the graphite crucible, particularly in the inner wall of the graphite crucible, during the subsequent crystal growth.

In another aspect, the invention provides a weakly magnetic Fe-V co-doped silicon carbide crystal prepared according to the method.

According to the invention, the prepared weak-magnetism Fe-V co-doped SiC crystal can further meet the application requirement of a spintronics device on a novel material.

Has the advantages that:

the doping content in the graphite crucible and the SiC raw material is reduced by adopting a multi-step pretreatment front stage, and the crystal secondary growth process under unique conditions is adopted, so that the weak magnetic Fe-V co-doped SiC crystal has higher crystal quality, magnetic property and optical transmission property, and an alternative material is provided for the preparation of a spintronics device. Meanwhile, in the implementation process of the invention, on one hand, the conventional Fe and V metal doping is adopted, so that the method has the characteristic of environmental friendliness; on the other hand, the crystal growth is completed by conventional equipment in a centralized manner, so that the production cost is reduced, and the method has the technical advantage of mass production.

Drawings

FIG. 1 is a schematic sectional view of a crucible used in a high purity SiC crystal growth step;

FIG. 2 is a schematic cross-sectional view of a crucible used in the step of excess Fe-V co-doping a silicon carbide crystal;

FIG. 3 is a slice of a weakly magnetic Fe-V co-doped silicon carbide crystal: (i) low concentration Fe-V doped SiC wafers prepared in example 1; (ii) the high concentration Fe-V doped SiC wafer prepared in example 2;

FIG. 4 shows the results of M-H curve characterization of the weakly magnetic Fe-V co-doped silicon carbide crystal prepared in example 1-2;

FIG. 5 shows the results of the X-ray diffraction rocking curve characterization of the weakly magnetic Fe-V co-doped silicon carbide crystal prepared in example 1-2;

FIG. 6 is a transmission spectrum of a weakly magnetic Fe-V co-doped silicon carbide crystal prepared in example 1-2.

Reference numerals:

a is a graphite crucible;

b is seed crystal;

c is SiC raw material;

d is Fe/V mixed powder;

e is a SiC crystal block.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

In the present disclosure, a weak magnetic Fe-V co-doped SiC crystal (SiC single crystal material having weak ferromagnetism at low and near room temperature) is grown stepwise by means of Physical Vapor Transport (PVT). In addition, the weak-magnetism Fe-V co-doped SiC crystal grown by the method has the characteristics of high crystallization quality, obvious ferromagnetic signal, excellent light transmission performance and the like, and has great application potential in spinning electronic devices.

In one embodiment of the invention, the method for step-by-step growth of the weak magnetic Fe-V co-doped SiC crystal comprises the following steps: pretreatment of SiC raw materials, growth of high-purity SiC crystals, growth of excessive iron-vanadium (Fe-V) codoped SiC crystals, and secondary growth of excessive iron-vanadium (Fe-V) codoped SiC crystals. The growing step of the high-purity SiC crystal refers to primary growth of the high-purity SiC crystal under the conditions of high Ar gas pressure and high material zone temperature. The growing step of the excessive Fe-V co-doped silicon carbide crystal refers to the step of repeatedly utilizing the crystal obtained in the growing step of the high-purity SiC crystal, cutting the crystal into small blocks, uniformly mixing the small blocks with high-purity Fe powder and V powder with the purity of more than 99.999 percent to serve as raw materials, and growing the crystal under the conditions of lower gas pressure and lower temperature. The secondary growth of the excessive iron-vanadium (Fe-V) codoped SiC crystal refers to that the excessive iron-vanadium (Fe-V) codoped SiC crystal in the previous step is subjected to edge removal and is cut into small pieces to be used as raw materials, and the secondary growth of the crystal is carried out under the conditions of high gas pressure and low temperature. The method improves the problem that the doped crystal lattice of the SiC crystal is easy to damage, and can obtain the Fe-V co-doped silicon carbide single crystal with weak magnetism. The method has the characteristics of strong operability, small environmental pollution, high crystal quality of prepared crystals and the like, and provides an effective technical approach for the development of the spintronic material in the future. The following exemplarily illustrates the preparation process of a weakly magnetic Fe-V co-doped SiC crystal.

And (4) pretreating the crucible. The crucible used in the growth process is a high-purity graphite crucible, the material purity of the high-purity graphite crucible is better than 99.999 percent, and the high-temperature pretreatment is carried out in a vacuum annealing device at 2000-2500 ℃.

And (4) preprocessing the SiC raw material. As an example, silicon carbide powder with the purity of more than 99.999 percent is put into a crucible (preferably the crucible obtained after pretreatment is adopted), the temperature of a material area in the crucible is within the range of 1000-1300 ℃, the atmosphere in the crucible is Ar with the purity of more than 99.999 percent, the treatment time is more than or equal to 3 hours, and the treated silicon carbide raw material is divided into 3 parts for standby according to the mass ratio of 8:1: 1.

As shown in fig. 1 and 2, the two steps involved in the method for step-growth of a weakly magnetic Fe-V co-doped SiC crystal respectively are: growing high-purity SiC crystal and growing excessive Fe-V doped SiC crystal. Of course, the schematic cross-sectional view of the crucible for secondary growth of an excess Fe-V co-doped silicon carbide crystal is also highly similar to that shown in FIGS. 1 and 2. As is conventional, these may be readily understood and inferred by persons skilled in the art or based on the teachings of this patent. In the schematic views of FIGS. 1 and 2, the seed crystal (b) was adhered to the top of the graphite crucible (a), and the SiC raw material (silicon carbide powder) (c), Fe/V mixed powder (d), and SiC boule (e) were placed at the bottom of the graphite crucible.

Before the SiC crystal grows, on one hand, high-temperature pretreatment is carried out on a high-purity graphite crucible; on the other hand, the SiC raw material is pretreated, volatile impurities in the graphite crucible (particularly the inner wall of the graphite crucible) and the SiC raw material are discharged, and pollution caused by unintentional doping in the crystal growth process is avoided. It should be noted that the annealing treatment of the SiC raw material and the subsequent crystal growth all adopt the high-purity graphite crucible after the high-temperature pretreatment in this step.

And growing high-purity SiC crystals. Specifically, FIG. 1 is a schematic sectional view of a crucible used in a high purity SiC crystal growth step. The crucible adopted in the growth process is a high-purity graphite crucible, and the seed crystal is a high-purity 6H silicon carbide wafer. Detailed steps of high purity SiC crystal growth, as shown in fig. 1: adhering a high-purity 6H-SiC wafer serving as a seed crystal (b) to the top of a high-purity graphite crucible (a), placing pretreated SiC powder (c) at the bottom of the high-purity graphite crucible (a), and growing the crystal under the conditions that the temperature of a material region in the crucible is 2200-2400 ℃, the atmosphere is Ar with the purity of better than 99.999%, the gas pressure is 1000-3000 Pa, and the growth time is more than or equal to 60 hours. And cutting the edge removing part of the obtained high-purity SiC crystal into small blocks and cleaning the small blocks for later use. In the step, the material area in the crucible is kept at a higher temperature (2200-2400 ℃) to increase the sublimation speed of SiC, and the higher Ar atmosphere pressure (1000-3000 Pa) can inhibit the dredging of sublimation gas, so that the recrystallization of SiC sublimation atmosphere particles at SiC seed crystals is optimized, and high-purity SiC crystals are obtained to be used as the doped background material in the subsequent step.

And (4) growing excessive Fe-V co-doped silicon carbide crystals. FIG. 2 is a schematic cross-sectional view of a crucible used in the excess Fe-V co-doped silicon carbide crystal growth step. The crucible used in the growth process is a high-purity graphite crucible (preferably a high-purity graphite crucible obtained by adopting high-temperature pretreatment), and the seed crystal is a high-purity 6H silicon carbide wafer. As shown in FIG. 2, in the excess Fe-V co-doped SiC crystal growth step, a high purity 6H-SiC wafer seed crystal (b) is adhered to the top of a high purity graphite crucible (a), and a high purity SiC crystal (e) subjected to dicing treatment, a mixture of Fe powder and V powder having a purity of better than 99.999% are placed at the bottom of the high purity graphite crucible (a). Considering the solid solubility limit of dopants in SiC crystals, the total mass of the mixture of the high-purity silicon carbide crystal cutting blocks, the high-purity Fe powder, the high-purity V powder and the pretreated silicon carbide powder is 100wt%, wherein the mass percentage of the high-purity Fe powder and the high-purity V powder is more than or equal to 0.1%. Considering the difference of sublimation rate between the doped powder and the SiC crystal, a layer of silicon carbide powder covers the upper part of the mixture, and the mass percentage of the silicon carbide powder in the mixed powder is less than or equal to 5 percent (c) so as to prevent the Fe and V from volatilizing too fast to reach the SiC seed crystal position. And the pretreated silicon carbide powder covered on the upper part of the mixture can prevent the Fe powder and the V powder from being doped too fast and volatilizing to reach the seed crystal position. In the crystal growth, the temperature of a material area in the crucible is controlled within the range of 2000-2200 ℃, the atmosphere in the crucible is Ar with the purity of better than 99.999 percent, the gas pressure in the crucible is controlled within the range of 100-1000 Pa, and the growth time is more than or equal to 30 hours. Under the condition, SiC crystal can grow rapidly and obtain excessive Fe-V doping. And finally, cutting the edge removing part of the obtained excess doped SiC crystal into small blocks and cleaning the small blocks for later use.

And (4) secondary growth of excessive Fe-V co-doped silicon carbide crystals. The crucible used in the growth process is a high-purity graphite crucible (preferably a high-purity graphite crucible obtained by adopting high-temperature pretreatment), and the seed crystal is a high-purity 6H silicon carbide wafer.

Furthermore, in the secondary growth step, a high-purity graphite crucible (a) obtained by high-temperature pretreatment is adopted, a high-purity 6H silicon carbide wafer is adopted as a seed crystal (b), the excessive Fe-V co-doped silicon carbide crystal small blocks subjected to cutting treatment are placed into the crucible, the temperature of a material area in the crucible is in the range of 2000-2200 ℃, the atmosphere in the crucible is Ar with the purity of better than 99.999 percent, the gas pressure in the crucible is in the range of 1000-3000 Pa, and the growth time is not less than 60 hours. In this step, the higher Ar atmosphere pressure may promote the crystal quality of the SiC recrystallized at the seed crystal. In addition, the crystal blocks obtained by excessive Fe-V doping are used as raw materials, so that Fe and V doping can effectively enter SiC crystal lattices in the secondary growth process of the crystal, the formation of Fe/V metal clusters is avoided, and the magnetic strength of the Fe-V co-doped SiC crystal is improved.

Further, it is shown in fig. 3 (i) and (ii) that the weakly magnetic Fe-V co-doped SiC crystal slab obtained by the secondary growth is light white when the Fe-V doping content is low, and light yellow when the Fe-V doping content is high. The obtained wafers were subjected to magnetic property test at low temperature or near room temperature using a superconducting quantum interference magnetometer, as shown by a curve Q1 and a curve Q2 in fig. 4. The obtained wafers were subjected to rocking curve test at room temperature using X-ray diffraction to characterize the crystalline quality of the crystals, as shown by curves Q3 and Q4 in fig. 5. The obtained wafers were subjected to transmission spectrum testing at room temperature to characterize the optical transmittance of the crystals, as shown by curves Q5 and Q6 in fig. 6.

In general, a method for producing a magnetic SiC crystal is necessary. The novel method should achieve the following implementation convenience: (1) the form of the material is SiC crystal, so that the material is ensured to have a relatively complete lattice structure; (2) the doping element has the advantages of easy doping, environmental protection and low cost, and is convenient for controlling the cost in the later-stage large-scale production; (3) the implementation process is completed in conventional equipment, so that the preparation procedures are reduced, and the reliability of the implementation method is improved as much as possible. The method for growing the SiC crystal doped with the magnetic elements has the characteristics of strong operability, low cost and high crystal crystallization quality. Particularly preferably applied to the spintronics device.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.

Example 1: the growth of the SiC crystal with low Fe-V doping concentration is implemented according to the following steps in sequence:

step (1): a high-purity graphite crucible (a). Carrying out high-temperature pretreatment on the graphite crucible in a 2300 ℃ vacuum annealing device;

step (2): and SiC raw material (c) pretreatment. The SiC raw material is treated for 3 hours at the temperature of 1000 ℃ under the atmosphere of Ar with the purity of more than 99.999 percent. Dividing the processed silicon carbide raw material into 3 parts according to the mass ratio of 8:1:1 for later use;

and (3): and growing high-purity SiC crystals. Respectively bonding 6H-SiC seed crystals and a large-weight SiC raw material obtained by pretreatment at the top and the bottom of a high-purity graphite crucible (a), controlling the temperature of a material area in the crucible to 2200 ℃, controlling the atmosphere in the crucible to be Ar with the purity of more than 99.999 percent, controlling the gas pressure in the crucible to be in the range of 2000Pa, and controlling the growth time to be 60 hours. Cutting the edge-removed part of the obtained high-purity SiC crystal into small blocks and cleaning the small blocks for later use;

and (4): and (4) growing the excessive Fe-V co-doped silicon carbide crystal. Bonding a 6H-SiC seed crystal (b) on the top of a high-purity graphite crucible (a), placing a high-purity SiC crystal (e) subjected to cutting treatment and Fe-V mixed powder (d) with the purity better than 99.999% into the crucible, covering a layer of silicon carbide powder (c) obtained by pretreatment on the upper part of the mixed material, wherein the mass percentage of the high-purity Fe powder and the high-purity V powder is 0.5% (the mass ratio of the Fe powder to the V powder is 1: 1), the mass percentage of the silicon carbide powder subjected to pretreatment is 5%, the temperature of a material area in the crucible is 2100 ℃, the atmosphere in the crucible is Ar with the purity better than 99.999%, the gas pressure in the crucible is 200Pa, the growth time is 30H, and removing edge parts of the obtained excessive Fe-V co-doped silicon carbide crystal, cutting the crystal into small blocks and cleaning the crystal for later use;

and (5): and (4) secondary growth of excessive Fe-V co-doped silicon carbide crystals. Bonding 6H-SiC seed crystal (b) on the top of the high-purity graphite crucible (a), and placing the excess Fe-V co-doped silicon carbide crystal (e) subjected to the cutting treatment into the bottom of the crucible. The temperature of the material area in the crucible is in the range of 2100 ℃, the atmosphere in the crucible is Ar with the purity of better than 99.999 percent, the gas pressure in the crucible is in the range of 2000Pa, and the growth time is 60 hours. The grown Fe-V co-doped SiC crystal was subjected to a slicing process as shown in (i) wafer of fig. 3.

The obtained crystal was subjected to magnetic property analysis using a superconducting quantum interference magnetometer system, as shown by a curve Q1 in fig. 4. From the test results, it can be seen that SiC crystals with low Fe-V doping concentration show a weaker, but distinguishable hysteresis loop. The obtained crystal was subjected to rocking curve test at room temperature using X-ray diffraction, as shown by a curve Q3 in fig. 5. As can be seen from the test results, the low Fe-V doping concentration SiC crystal showed higher diffraction peak intensity and smaller half-peak width (compared with Q4 of example 2). This shows that the lattice structure of the crystal is relatively intact at low doping concentrations. The obtained wafer was subjected to a transmission spectrum test at room temperature as shown by a curve Q5 in fig. 6. As can be seen from the test results, the SiC crystal with low Fe-V doping concentration shows higher visible light transmittance. This is because the visible light absorption of the doping level in the SiC bandgap is less with a lower Fe-V doping concentration.

Example 2: SiC crystal growth with high Fe-V doping concentration

The method is implemented according to the following steps:

and (4): and (4) growing excessive Fe-V co-doped silicon carbide crystals. Bonding a 6H-SiC seed crystal (b) on the top of a high-purity graphite crucible (a), placing a high-purity SiC crystal (e) subjected to cutting treatment and Fe-V mixed powder (d) with the purity better than 99.999% into the crucible, covering a layer of silicon carbide powder (c) obtained by pretreatment on the upper part of the mixed material, wherein the mass percentage of the high-purity Fe powder and the high-purity V powder is 3% (the mass ratio of the Fe powder to the V powder is 1: 1.5), the mass percentage of the silicon carbide powder subjected to pretreatment is 2%, the temperature of a material area in the crucible is 2100 ℃, the atmosphere in the crucible is Ar with the purity better than 99.999%, the gas pressure in the crucible is 200Pa, the growth time is 30H, and removing edge parts of the obtained excessive Fe-V co-doped silicon carbide crystal, cutting the crystal into small blocks and cleaning the crystal for later use;

The obtained crystal was subjected to magnetic property analysis using a superconducting quantum interference magnetometer system, as shown by a curve Q2 in fig. 4. As can be seen from the test results, the SiC crystal with high Fe-V doping concentration shows stronger and shows a clearly distinguishable hysteresis loop. The obtained crystal was subjected to rocking curve test at room temperature using X-ray diffraction, as shown by a curve Q4 in fig. 5. As can be seen from the test results, the high Fe-V doping concentration SiC crystal showed lower diffraction peak intensity and larger half-peak width (compared with Q3 of example 1). This shows that as the doping concentration of Fe-V increases, the crystal structure distortion increases. The obtained wafer was subjected to a transmission spectrum test at room temperature as shown by a curve Q6 in fig. 6. As can be seen from the test results, the SiC crystal with high Fe-V doping concentration shows lower visible light transmittance and oscillation peaks. This is because as the doping concentration of Fe-V increases, the doping levels in the SiC bandgap begin to manifest visible light absorption effects.

Claims

1. A method for growing weak ferromagnetic Fe-V co-doped silicon carbide crystals step by step is characterized by comprising the following steps:

(1) mixing a high-purity SiC crystal block, Fe powder and V powder, placing the mixture at the bottom of a crucible as a crystal material, paving a layer of silicon carbide powder on the surface of the crystal material, taking a 6H-SiC wafer as a seed crystal, and starting crystal growth by adopting a physical vapor transport method to obtain an excessive Fe-V co-doped SiC crystal, wherein the addition amount of the Fe powder and the V powder is more than the solid solubility of Fe and V in the SiC crystal at room temperature, the total mass of the crystal material and the silicon carbide powder is 100wt%, and the total content of the Fe powder and the V powder is more than or equal to 0.1%; the parameters of the crystal growth include: the growth temperature is 2000-2200 ℃; the growth time is more than or equal to 30 hours; the growth atmosphere is inert atmosphere, the purity is more than or equal to 99.999 percent, and the air pressure is 100-1000 Pa;

(2) and (3) cutting the obtained excessive Fe-V co-doped SiC crystal into blocks, placing the blocks at the bottom of a crucible, taking a 6H-SiC wafer as a seed crystal, and starting secondary growth by adopting a physical vapor transport method to obtain the weak ferromagnetic Fe-V co-doped silicon carbide crystal, wherein the secondary growth parameters comprise: the growth temperature is 2000-2200 ℃; the growth time is more than or equal to 60 hours; the growth atmosphere is inert atmosphere, and the air pressure is 1000-3000 Pa.

2. The method of claim 1, wherein the method of preparing the high purity SiC crystal mass comprises: and (3) putting the silicon carbide powder in a crucible, taking a 6H-SiC wafer as a seed crystal, growing for more than or equal to 60 hours at 2200-2400 ℃ in an inert atmosphere to obtain a high-purity SiC crystal, removing the edge part, and cutting into blocks to obtain a high-purity SiC crystal block.

3. The method according to claim 2, wherein the inert atmosphere is Ar gas, the purity is not less than 99.999%, and the gas pressure is 1000-3000 Pa.

4. The method according to claim 1, wherein the preparation process of the silicon carbide powder comprises the following steps: the silicon carbide raw material is put in a crucible and pretreated for more than or equal to 3 hours at the temperature of 1000-1300 ℃ in inert atmosphere to obtain the silicon carbide material.

5. The method according to claim 4, wherein the inert atmosphere is Ar gas, the purity is not less than 99.999%, and the gas pressure is 1000-1300 Pa.

6. The method according to claim 1, wherein the total content of the Fe powder and the V powder is 0.5-5 wt% based on 100wt% of the total mass of the crystal material and the silicon carbide powder.

7. The method according to claim 6, wherein the mass ratio of the Fe powder to the V powder is 1: (1.0-1.5).

8. The method according to claim 1, wherein the content of the silicon carbide powder is less than or equal to 5% by weight based on 100% by weight of the total mass of the crystal material and the silicon carbide powder.

9. The method according to claim 1, wherein the inert atmosphere is Ar gas, and the purity is more than or equal to 99.999%.

10. The method of any one of claims 1 to 9, wherein the crucible is a graphite crucible.

11. The method as claimed in claim 10, wherein the graphite crucible has a material purity of 99.999%.

12. The method as claimed in claim 11, wherein the graphite crucible is pretreated at a high temperature of 2000 to 2500 ℃.

13. A weakly ferromagnetic Fe-V co-doped silicon carbide crystal prepared according to the method of any one of claims 1-12.