阅读说明：本技术 一种铁磁性碳化硅晶体及其制备方法 (Ferromagnetic silicon carbide crystal and preparation method thereof ) 是由 张宁 石志强 姜彦鹏 高超 杨晓俐 李博 刘鹏飞 于 2021-07-26 设计创作，主要内容包括：本申请公开了一种铁磁性碳化硅晶体及其制备方法,属于半导体材料领域。该铁磁性的碳化硅晶体中具有P型掺杂离子和空穴,所述P型掺杂离子与空穴的浓度比为1：3-10,以使得所述碳化硅晶体为具有铁磁性的P型碳化硅晶体。该碳化硅晶体在经过磁场后能够在室温下达到较高的饱和磁化强度,以满足常温对半导体碳化硅晶体中的铁磁性强度需求。(The application discloses a ferromagnetic silicon carbide crystal and a preparation method thereof, belonging to the field of semiconductor materials. The ferromagnetic silicon carbide crystal contains P-type doped ions and holes, and the concentration ratio of the P-type doped ions to the holes is 1: 3-10, so that the silicon carbide crystal is a P-type silicon carbide crystal with ferromagnetism. The silicon carbide crystal can reach higher saturation magnetization intensity at room temperature after passing through a magnetic field so as to meet the requirement of ferromagnetism intensity in the semiconductor silicon carbide crystal at room temperature.)

1. A ferromagnetic silicon carbide crystal having P-type dopant ions and holes therein, wherein the concentration ratio of P-type dopant ions to holes is 1: 3-10, so that the silicon carbide crystal is a P-type silicon carbide crystal with ferromagnetism.

2. The ferromagnetic silicon carbide crystal according to claim 1, wherein the silicon carbide crystal has a saturation magnetization at room temperature of not less than 0.05 emu/g;

preferably, the saturation magnetization of the silicon carbide crystal at room temperature is greater than 0.07 emu/g;

more preferably, the saturation magnetization of the silicon carbide crystal at room temperature is greater than 0.08 emu/g;

preferably, the remanent polarization is not greater than 0.01 emu/g.

3. The ferromagnetic silicon carbide crystal according to claim 1, wherein the P-type dopant ions are selected from at least one of valence and atomic radius adaptations of group iii elements or transition elements.

4. The ferromagnetic silicon carbide crystal according to claim 1, wherein the concentration of P-type dopant ions is 2.03 x 10²⁰cm^-3-5.6×10²³cm^-3。

5. The ferromagnetic silicon carbide crystal according to any one of claims 1-4, wherein the resistivity of the silicon carbide crystal is 0.0183 Ω -cm^-1-0.2238Ω·cm^-1The concentration of the P-type doped ions is 2.03 multiplied by 10²⁰cm^-3～1.68×10²²cm^-3The concentration of holes was 6.09X 10²⁰cm^-3～1.78×10²³cm^-3。

6. The ferromagnetic silicon carbide crystal according to claim 1, wherein the P-type dopant ions are aluminum ions, and the concentration ratio of the aluminum ions to the holes is 1: 3-6;

preferably, the P-type doped ions are aluminum ions, and the saturation magnetization of the silicon carbide crystal at room temperature is more than 0.07 emu/g;

more preferably, the P-type doped ions are aluminum ions, and the saturation magnetization of the silicon carbide crystal at room temperature is more than 0.08 emu/g;

preferably, the P-type doped ions are aluminum ions, and the remanent polarization is less than 0.008 emu/g.

7. The ferromagnetic silicon carbide crystal according to claim 6, wherein the silicon carbide crystal has a resistivity of 0.0113 Ω -cm^-1-0.0328Ω·cm^-1The doping concentration of the aluminum ions is 5 multiplied by 10¹⁹cm^-3～6.5×10²⁰cm^-3The concentration of holes was 9.26X 10¹⁹cm^-3；

Preferably, the resistivity of the silicon carbide crystal is 0.02 Ω · cm^-1-0.0215Ω·cm^-1The doping concentration of Al atoms is 5.8X 10²⁰cm^-3The concentration of holes was 2.32X 10²¹cm^-3。

8. The ferromagnetic silicon carbide crystal according to claim 1 or 6, wherein the threading dislocation density in the silicon carbide crystal is less than 100cm^-2Basal plane dislocation density of less than 50cm^-2Total dislocation density less than 1000cm^-2。

9. The ferromagnetic silicon carbide crystal according to claim 1 or 6, wherein the thickness of the silicon carbide crystal is 10-40mm, the intra-crystal shear stress is 2-6 Mpa; and/or

The stress from the edge of the crystal to the center of the crystal varies linearly from 6Mpa to 2 Mpa.

10. A method of preparing a ferromagnetic silicon carbide crystal according to any one of claims 1 to 9, comprising the steps of:

1) assembling a crystal growth chamber: placing one or more silicon carbide wafers in a raw material cavity, wherein the silicon carbide wafers divide the raw material cavity into a plurality of sub raw material cavities which are arranged along the direction close to seed crystals, raw materials containing P-type dopants are filled in the sub raw material cavities, and the amount of the P-type dopants in the sub raw material cavities is increased along the direction close to the seed crystals;

2) crystal growth: carrying out crystal growth by using the device in the step 1) to prepare a coarse silicon carbide crystal;

3) regulation of the cavity: and (3) rapidly cooling the coarse silicon carbide crystal or doping a small amount of nitrogen during crystal growth to prepare a target number of holes, namely the ferromagnetic silicon carbide crystal is prepared.

Technical Field

The application relates to a ferromagnetic silicon carbide crystal and a preparation method thereof, belonging to the field of semiconductor materials.

Background

The semiconductor device mainly uses the charge property of electrons to process and transmit information, and the information storage function is realized by using ferromagnetism, i.e. the spin property of electrons. With the continuous development of information technology and the rapid increase of processing and transmission speed, the existing semiconductor integrated circuit is difficult to meet the requirements of people. It would certainly create a tremendous technological breakthrough if the charge of electrons could be combined with the spin properties. Spintronics has been produced in response to this ideal becoming a reality.

SiC has good application prospect in the fields of high-frequency and high-power devices and the like as a third-generation semiconductor with excellent performance. If the ferromagnetic transformation can be realized in the SiC crystal, the obtained SiC-based diluted magnetic semiconductor has important scientific research value.

d⁰Ferromagnetic refers to a property of a material (e.g., graphite, CaB6, Hf02, etc.) that has ferromagnetism and a curie temperature greater than room temperature without unpaired electrons in the d-and f-orbitals. In the past, ferromagnetism is a property peculiar to unpaired d electronic elements such as Fe, Co and Ni and unpaired f electronic elements such as rare earth. The presence of lattice or bond defects causes hetero-bands to appear and spin polarization to occur. Electrons enter the "hetero-band" spontaneously or by defect, creating spin asymmetry, and thus d⁰Ferromagnetic properties.

Compared with silicon carbide powder, silicon carbide crystals are difficult to have high ferromagnetism, and in recent years, a plurality of researchers inject a plurality of ferromagnetic atoms into the silicon carbide crystals in an ion injection mode to obtain the silicon carbide crystals with ferromagnetic characteristics at low temperature or high temperature, and the ferromagnetism of the obtained silicon carbide crystals is weak and unobvious. How to regulate the ferromagnetic property of the silicon carbide crystal through doping and improve the ferromagnetic property of the silicon carbide at room temperature become important propositions.

Disclosure of Invention

In order to solve the above problems, a ferromagnetic silicon carbide crystal having a high saturation magnetization and further having a high saturation magnetization at room temperature, and a method for producing the same are provided. The silicon carbide crystal can keep high saturation magnetization intensity at room temperature after passing through a magnetic field so as to meet the requirement of ferromagnetism intensity in the semiconductor silicon carbide crystal at room temperature.

According to one aspect of the present application, there is provided a ferromagnetic silicon carbide crystal having P-type dopant ions and holes therein, the concentration ratio of P-type dopant ions to holes being 1: 3-10, so that the silicon carbide crystal is a P-type silicon carbide crystal with ferromagnetism. The concentration ratio therein is a quantitative ratio such as an amount per unit weight or an amount per unit volume.

Optionally, the saturation magnetization of the silicon carbide crystal at room temperature is not lower than 0.05 emu/g. Preferably, the saturation magnetization of the silicon carbide crystal at room temperature is greater than 0.07 emu/g. More preferably, the saturation magnetization of the silicon carbide crystal is greater than 0.08emu/g at room temperature. More preferably, the saturation magnetization of the silicon carbide crystal is greater than 0.085emu/g at room temperature.

Optionally, the remanent polarization of the silicon carbide crystal at room temperature is not more than 0.01emu/g, preferably less than 0.008emu/g, and more preferably less than 0.005 emu/g.

Optionally, the saturation magnetization and the remanent polarization of the silicon carbide crystal are the result of magnetic saturation after being treated by the magnetic field strength of not less than 4000Oe for not more than 1 s. The value of the saturation magnetization after being processed is high; the small residual magnetization proves that the smaller the energy loss is, the higher the magnetoelectric conversion efficiency of the device made of the silicon carbide crystal is.

Optionally, the P-type dopant ion is selected from at least one of valence and atomic radius adaptations of a third main group element or a transition element. Preferably, the P-type dopant is selected from at least one of B, Al, Ga, In, Tl, Fe, Co, Ni, and Ti.

Optionally, the concentration of the P-type dopant ions is 2.03 × 10²⁰cm^-3-5.6×10²³cm^-3。

Optionally, the silicon carbide crystal has a resistivity of 0.0183 Ω -cm^-1-0.2238Ω·cm^-1The P type doped ionThe concentration is 2.03X 10²⁰cm^-3～1.68×10²²cm^-3The concentration of holes was 6.09X 10²⁰cm^-3～1.78×10²³cm^-3。

Optionally, the P-type doped ions are aluminum ions, and the concentration ratio of the aluminum ions to the holes is 1: 3-6.

Optionally, the silicon carbide crystal has a resistivity of 0.4 Ω cm^-1-3Ω·cm^-1The doping concentration of the aluminum ions is 5 multiplied by 10¹⁷cm^-3～6.5×10¹⁷cm^-3The concentration of holes was 9.26X 10¹⁸cm^-3。

Preferably, the resistivity of the silicon carbide crystal is 0.485-2.306 Ω & cm^-1The doping concentration of Al atoms is 5.8X 10¹⁷cm^-3The concentration of holes was 2.32X 10²¹cm^-3。

Preferably, after the silicon carbide crystal is processed by the magnetic field intensity of not less than 4000Oe for not more than 1s, the saturation magnetization of the silicon carbide crystal at room temperature reaches 0.085emu/g, and the remanent polarization is not more than 0.01 emu/g.

Preferably, the P-type doped ions are aluminum ions, and the saturation magnetization of the silicon carbide crystal at room temperature is greater than 0.07 emu/g. More preferably, the P-type doped ions are aluminum ions, and the saturation magnetization of the silicon carbide crystal at room temperature is greater than 0.08 emu/g.

Preferably, the P-type doped ions are aluminum ions, and the remanent polarization is less than 0.008emu/g, more preferably less than 0.004 emu/g.

Optionally, after the silicon carbide crystal is processed by the magnetic field intensity of not less than 4000Oe for not more than 1s, the residual magnetization intensity of the silicon carbide crystal at room temperature is not less than 0.2 x 10^-4emu/g. Specifically, after the silicon carbide crystal is processed by the magnetic field strength of 14Oe for no more than 1s, the residual magnetization of the silicon carbide crystal at room temperature is 0.2 multiplied by 10^{- 4}emu/g; after the silicon carbide crystal is processed by the magnetic field strength of 16Oe for no more than 1s, the residual magnetization of the silicon carbide crystal at room temperature is 1.310^-4emu/g; after the silicon carbide crystal is processed by the magnetic field strength of 47Oe for no more than 1s, the residual magnetization of the silicon carbide crystal at room temperature is 3.6 multiplied by 10^-4emu/g。

Optionally, the P-type doped ions are aluminum ions, and the resistivity of the silicon carbide crystal is 0.0113 Ω · cm^-1-0.0328Ω·cm^-1The doping concentration of the aluminum ions is 5 multiplied by 10¹⁹cm^-3～6.5×10²⁰cm^-3The concentration of holes was 9.26X 10¹⁹cm^-3。

Preferably, the P-type doped ions are aluminum ions, and the resistivity of the silicon carbide crystal is 0.02 omega-cm^-1-0.0215Ω·cm^-1The doping concentration of Al atoms is 5.8X 10²⁰cm^-3The concentration of holes was 2.32X 10²¹cm^-3。

Optionally, the threading dislocation density in the silicon carbide crystal is less than 100cm^-2Basal plane dislocation density of less than 50cm^-2Total dislocation density less than 1000cm^-2. Further, the density of threading dislocations in the silicon carbide crystal is less than 50cm^-2Basal plane dislocation density of less than 20cm^-2Total dislocation density less than 100cm^-2. Further, the density of threading dislocations in the silicon carbide crystal is less than 10cm^-2Basal plane dislocation density of less than 5cm^-2Total dislocation density less than 20cm^-2。

Optionally, the thickness of the silicon carbide crystal is 10-40mm, and the internal shearing stress of the crystal is 2-6 MPa. Alternatively, the stress varies linearly from the edge of the crystal to the center of the crystal, for example, the stress varies linearly from 6MPa to 2MPa from the edge of the crystal to the center of the crystal. Furthermore, the thickness of the silicon carbide crystal is 10-30mm, and the internal shear stress of the crystal is 3-5 MPa.

Optionally, the P-type dopant has a boiling point lower than the boiling point of silicon carbide.

In this application, "room temperature" means 25 ℃. + -. 2 ℃.

According to still another aspect of the present application, there is provided a method for preparing a ferromagnetic silicon carbide crystal, comprising the steps of:

1) assembling: placing one or more silicon carbide wafers in a raw material cavity, wherein the silicon carbide wafers divide the raw material cavity into a plurality of sub raw material cavities which are arranged along the direction close to seed crystals, raw materials containing P-type dopants are filled in the sub raw material cavities, and the amount of the P-type dopants in the sub raw material cavities is increased along the direction close to the seed crystals;

2) crystal growth: carrying out crystal growth by using the device in the step 1) to prepare a coarse silicon carbide crystal;

3) regulation of the cavity: and (3) rapidly cooling the coarse silicon carbide crystal or doping a small amount of nitrogen during crystal growth to prepare a target number of holes, namely the ferromagnetic silicon carbide crystal is prepared.

Preferably, the boiling point of the P-type dopant is lower than the boiling point of the silicon carbide feedstock. The silicon carbide raw material comprises silicon carbide powder and silicon carbide polycrystal.

Specifically, the P-type dopant has a relatively low sublimation temperature point, and the silicon carbide wafer is placed between the seed crystal and the raw material (including the dopant), so that on one hand, the uniformity of sublimation atmosphere is regulated and controlled by the silicon carbide wafer, and the raw material is wrapped to enable the dopant to enter the growing ferromagnetic silicon carbide crystal more uniformly and efficiently; on the other hand, the melting point of the silicon carbide wafer is higher than that of the raw material containing the dopant, and the ferromagnetic silicon carbide crystal can be flexibly obtained through slow control by placing the dopant in a layered mode and matching with the movement of the position of the high-temperature area.

Specifically, the raw material may have a silicon carbide powder and/or a silicon carbide polycrystal in addition to the dopant, and the preferred raw materials are the dopant and the silicon carbide powder.

As an embodiment, the crystal growth step of step 2) includes the following steps:

a. vacuum impurity removal: after the assembled crystal growth chamber is loaded, the furnace body is subjected to vacuum impurity removal;

b. and (3) nucleation: introducing argon and/or helium into the furnace body, rapidly boosting the pressure of the furnace body to be not less than 500mbar, raising the temperature to be 2200 +/-20 ℃ of a nucleation point after the boosting is finished, and stabilizing the temperature for not less than 1.5 h;

c. growth and defect introduction: reducing the pressure in the furnace body to be not less than 30mbar, and stably growing for not less than 50 hours at the temperature of 2300 +/-70 ℃, thus obtaining the crude silicon carbide crystal.

Optionally, a step a2 is further included between the step a and the step b, and the temperature is continuously increased: the furnace body temperature is raised to 1600 ℃ for preparation before nucleation.

The embodiment of 3 silicon carbide wafers shown in FIG. 1 is used to illustrate the method of producing a ferromagnetic silicon carbide crystal according to the present application, but is not limited to 3 silicon carbide wafers.

As an embodiment, the method for preparing ferromagnetic silicon carbide crystals comprises the following steps:

1) assembling: carrying out crystal growth by adopting a medium-frequency induction heating mode, assembling a crucible before heating, specifically adopting a layered charging mode, and setting Al with the boiling point (decomposition point) of 2200 DEG C₄C₃0.3g of silicon carbide wafer is placed between the upper and middle carbide wafers, and 0.6g of silicon carbide wafer is placed between the middle and lower layers; the thicknesses of the upper silicon carbide wafer, the middle silicon carbide wafer and the lower silicon carbide wafer are 500 mu m, 450 mu m and 400 mu m in sequence;

2) crystal growth:

a. vacuum impurity removal: the hearth is vacuumized to 10^-6Introducing high-purity inert gas to 300-500mbar below mbar, repeating the process for 2-3 times, and finally vacuumizing the furnace chamber to 10-^-6mbar below;

b. and (3) nucleation: the high-temperature area is in the upper sheet area: boosting the pressure to 800mbar, controlling the temperature to be 2200 +/-20 ℃, preheating and softening the growth surface of the seed crystal, and stabilizing for 2 hours;

c. growth and defect introduction:

the c1 high-temperature area is in the middle sheet area: controlling the temperature at 2250 +/-20 ℃, decomposing the upper piece and the silicon carbide raw material, wherein the growth pressure is 500mbar, and the stabilization time is 5 hours;

the c2 high temperature zone is in the following zone: controlling the temperature to be 2300 +/-20 ℃, the growth pressure to be 100mbar, stably growing for 50h, and turning off the intermediate frequency power supply after the growth is finished;

3) regulation of the cavity: the silicon carbide crystal is rapidly cooled by adopting a gas refrigeration mode, the original state just after the growth process is kept is provided with more holes, and the holes and the doped atoms act together to make a contribution to ferromagnetism of the silicon carbide crystal.

Specifically, in step c1, the small dosage of dopant reaches the surface of the seed crystal to realize uniform doping through a series of reactions along with the decomposition components. In step c2, the lower growth pressure and the higher temperature are controlled to satisfy the larger driving force of the raw material decomposition to the lower sheet position; although the pressure and temperature in step c2 are lower and higher, the silicon carbide wafer is used as the raw material at the same time, and Al₄C₃The upward driving force is low in proportion, and slow-control doping can be achieved at high temperature. Because the decomposition temperature of the doping agent is lower than that of the raw material, the content of the doping agent in the axial direction is from small to large, and the slow controlled release is carried out through a growth temperature curve. The initial position of the high-temperature area is positioned at the position of the upper silicon carbide wafer, and the high-temperature area can further improve the uniformity of the P-type dopant doped in the prepared silicon carbide crystal by moving the crucible and adjusting the position of the coil.

As an embodiment, the regulating cavitation step of step 3) includes: and after the growth is finished, reducing the temperature of the coarse silicon carbide crystal to 1200-1300 ℃, introducing low-temperature inert gas into a crystal growth chamber of the furnace body, and introducing point defects into the coarse silicon carbide crystal with higher temperature in a cold gas atmosphere to obtain the ferromagnetic silicon carbide crystal. Specifically, for example, the crude silicon carbide wafer is naturally cooled for 2h and then is cooled to the target temperature of 1200-1300 ℃; the temperature of the low temperature inert gas is less than-5 deg.C, preferably-30 deg.C.

Optionally, the regulating cavitation step of step 3) comprises: and introducing a small amount of nitrogen in the growth process, and introducing a shallow energy level energy band structure to increase the concentration of holes. In one embodiment, in the defect introducing step in the growth stage after the nucleation in step b, nitrogen is used as a gas phase component, nitrogen with the concentration of 99.999% is introduced, the flow rate is 4sccm/min, and the introduction time is 50-60 h. Nitrogen atoms enter the lattice structure to form a shallow energy level energy band structure of 0.1eV, and meanwhile, the number of holes is increased due to the difference of atom sizes, so that the ferromagnetic performance of the crystal is regulated and controlled.

The arrangement mode of the silicon carbide wafer and the raw materials in the preparation method can uniformly and efficiently dope the dopant into the ferromagnetic silicon carbide crystal. When the crystal growth temperature is raised to a range that the melting point of the P-type dopant is higher than the melting point of the silicon carbide and lower than the melting point of the silicon carbide, the P-type dopant is gasified and uniformly distributed in the sub-raw material cavity; if the raw material in the sub-raw material cavity is the mixture of silicon carbide powder and a P-type dopant, the P-type dopant is uniformly dispersed in the silicon carbide powder and uniformly permeates into the silicon carbide wafer; if only P-type dopant exists in the sub-raw material cavity, the P-type dopant is sublimated and permeates into the silicon carbide wafer above to be uniformly dispersed. And raising the crystal growth temperature to the sublimation temperature of the silicon carbide substrate, so that the raw material silicon carbide wafer and/or silicon carbide powder uniformly doped with the P-type dopant is sublimated to the surface of the seed crystal for crystal growth.

In the application, the silicon carbide wafer installed in the raw material cavity can be a silicon carbide single wafer or a silicon carbide multi-wafer, and the silicon carbide wafer is used as a part of raw material to be sublimated to the surface of the seed crystal at the top in the raw material cavity at high temperature for crystal growth.

The carrier concentration of the silicon carbide crystal in the application is equal to the hole concentration, namely the hole concentration can be known by measuring the carrier concentration.

Benefits of the present application include, but are not limited to:

1. the ferromagnetic silicon carbide crystal is a P-type semiconductor silicon carbide crystal with ferromagnetism, and the silicon carbide crystal can reach higher saturation magnetization at room temperature after passing through a magnetic field so as to meet the requirement of room temperature on the ferromagnetism strength in the semiconductor silicon carbide crystal

2. The ferromagnetic silicon carbide crystal has smaller residual magnetization, the smaller the residual magnetization proves to be the smaller the energy loss is, and the magnetoelectric conversion efficiency of a device prepared from the silicon carbide crystal is high.

3. The ferromagnetic silicon carbide crystal according to the present application has a small threading dislocation density, basal plane dislocation density, and total dislocation density.

4. The ferromagnetic silicon carbide crystal has high surface quality and uniform stress.

5. According to the preparation method of the ferromagnetic silicon carbide crystal, the doped P-type elements in the prepared silicon carbide crystal are uniform.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the application and not to limit the application. In the drawings:

fig. 1 is a schematic view of an assembled growth chamber according to an embodiment of the present application.

FIG. 2 shows the magnetization curve of a ferromagnetic silicon carbide crystal 1# prepared in example 1 of the present application.

FIG. 3 shows the surface morphology analysis of a ferromagnetic silicon carbide crystal 1# prepared in example 1 of the present application.

FIG. 4 is an XRD test chart of a ferromagnetic silicon carbide crystal 1# prepared in example 1 of the present application.

FIG. 5 is a resistivity test profile of a ferromagnetic silicon carbide crystal 1# prepared in example 1 of the present application.

Detailed Description

The present application will be described in detail with reference to examples, but the present application is not limited to these examples.

Unless otherwise specified, the raw materials and catalysts in the examples of the present application were all purchased commercially.

The analysis method in the examples of the present application is as follows:

analyzing the properties of the sample such as electricity, magnetism, specific heat and the like under the conditions of low temperature and strong field by utilizing a comprehensive measurement system (PPMS) produced by Quant mu m Design company;

secondary Ion Mass Spectrometry (SIMS) is utilized to analyze the chemical elements on the surface of the crystal, and the precision of the analysis reaches the ppm level;

the electrical properties were analyzed using a Hall measuring instrument model HL5500PC, manufactured by ACCENT corporation, uk;

the surface morphology of the samples in the sub-nanometer scale range was analyzed by testing using model number Mulr μmode 8 from Bruke corporation, usa.

Referring to fig. 1, one or more silicon carbide wafers 2 are placed in a source chamber formed in a crucible 1, the silicon carbide wafers 1 divide the source chamber into a plurality of sub-source chambers arranged in a direction close to a seed crystal, and the sub-source chambers are filled with a source material containing a P-type dopant 3. In a configuration not shown, a seed crystal is mounted on the top of the crucible, such as below the crucible lid, so that the sublimated feedstock grows on the surface of the seed crystal.

Specifically, as shown in FIG. 1, an upper, a middle and a lower 3 silicon carbide wafers 2 are placed in a crucible 1, the lower silicon carbide wafer can be directly placed on the bottom wall of the crucible, a sub-raw material cavity is not formed between the silicon carbide wafer and the bottom wall of the crucible, and the 3 silicon carbide wafers divide the raw material cavity into 2 sub-raw material cavities; or a sub-raw material cavity is formed between the lower silicon carbide wafer and the bottom of the crucible, and the 3 silicon carbide wafers divide the raw material cavity into 3 sub-raw material cavities.

Example 1

The embodiment of 3 silicon carbide wafers shown in FIG. 1 is used to illustrate the method of producing a ferromagnetic silicon carbide crystal according to the present application, but is not limited to 3 silicon carbide wafers.

As an embodiment, the method for preparing ferromagnetic silicon carbide crystals comprises the following steps:

1) assembling: carrying out crystal growth by adopting a medium-frequency induction heating mode, assembling a crucible before heating, specifically adopting a layered charging mode, and setting Al with the boiling point (decomposition point) of 2200 DEG C₄C₃0.3g of silicon carbide wafer is placed between the upper and middle carbide wafers, and 0.6g of silicon carbide wafer is placed between the middle and lower layers; the thicknesses of the upper silicon carbide wafer, the middle silicon carbide wafer and the lower silicon carbide wafer are 500 mu m, 450 mu m and 400 mu m in sequence;

2) crystal growth:

a. vacuum impurity removal: the hearth is vacuumized to 10^-6Introducing high-purity inert gas to 300-500mbar below mbar, repeating the process for 2-3 times, and finally vacuumizing the furnace chamber to 10-^-6mbar below;

b. and (3) nucleation: the high-temperature area is in the upper sheet area: boosting the pressure to 800mbar, controlling the temperature to be 2200 +/-20 ℃, preheating and softening the growth surface of the seed crystal, and stabilizing for 2 hours;

c. growth and defect introduction:

the c1 high-temperature area is in the middle sheet area: controlling the temperature at 2250 +/-20 ℃, decomposing the upper piece and the silicon carbide raw material, wherein the growth pressure is 500mbar, and the stabilization time is 5 hours;

the c2 high temperature zone is in the following zone: controlling the temperature to be 2300 +/-20 ℃, the growth pressure to be 100mbar, stably growing for 50h, and turning off the intermediate frequency power supply after the growth is finished to prepare a coarsened silicon crystal;

3) regulation of the cavity: naturally cooling the coarse silicon carbide crystal for 2h, introducing argon gas at-30 ℃ into a crystal growth chamber of the furnace body, and cooling to room temperature to obtain the ferromagnetic silicon carbide crystal No. 1.

And introducing a hole with target concentration by a rapid cooling mode, so that the hole and the doped atomic aluminum jointly control the ferromagnetism of the silicon carbide crystal.

Example 2

This example is different from example 1 in that Al in the raw material was adjusted₄C₃The concentrations of the doped aluminum ions and the generated holes in the prepared silicon carbide crystals are respectively tested to be different, and ferromagnetic silicon carbide crystals 2# -5# are respectively prepared, and the specific comparison result is shown in table 1 for ferromagnetic silicon carbide crystals D1# -D2 #.

The following tests are respectively carried out on the prepared ferromagnetic silicon carbide crystals 1# -5# and the comparative ferromagnetic silicon carbide crystals D1# -D2 #: magnetization curves (whether ferromagnetic or not, saturation magnetization value, etc. can be judged), SIMS test for aluminum ion concentration, Hall test for carrier concentration, resistivity and its distribution, and XRD.

Taking the test result of ferromagnetic silicon carbide crystal # 1 as an example, the performance of the ferromagnetic silicon carbide crystal of the present application is explained:

FIG. 2 shows the magnetization curve of ferromagnetic silicon carbide crystal 1#, and it can be seen from FIG. 2 that after magnetization at room temperature, the saturation magnetization can reach 0.085emu/g, and after the magnetic field is removed, the magnetic domain is rapidly reversed, and the residual magnetization is 0.005 emu/g. The magnetoelectric conversion efficiency is very high and reaches 99.6 percent, and the semiconductor and the magnetic property can be fully combined;

FIG. 3 shows a dislocation corrosion pattern obtained from a surface topography test of a ferromagnetic silicon carbide crystal 1#, wherein the total number of dislocation defects is 382, the TSD is 16, the TED is 321, and the BPD is 44, which shows ultra-high quality as shown in FIG. 3;

FIG. 4 is an XRD test chart of ferromagnetic silicon carbide crystal 1#, from FIG. 4, it can be seen that the half-peak width is 0.006, which shows good crystal quality, and proves that the doping elements completely enter the silicon carbide crystal; and

FIG. 5 is a resistivity test distribution diagram of a ferromagnetic silicon carbide crystal 1#, and it can be seen from FIG. 5 that the overall resistivity is concentrated at 0.0269-0.0428 Ω · cm, and the resistances of the rest parts except the facet parts have high consistency, showing the uniformity of the distribution of the doping elements in terms of electrical properties.

TABLE 1

As can be seen from Table 1, the 1# crystal has the highest saturation magnetization of 0.085emu/g and the highest residual polarization of 0.005emu/g at room temperature and has good electrical properties by uniformly adjusting and controlling the doping technology to control the ratio of the doping concentration to the hole concentration to be 1: 4. The semiconductor and the spinning electron are combined together, and a foundation is laid for further developing a novel multifunctional integrated circuit.

Example 3

The method for preparing ferromagnetic silicon carbide crystals in this example is different from example 1 in that:

3) regulation of the cavity: and c, after the growth is carried out for 20 hours in the step c2, opening a nitrogen valve to control the flow to be 4sccm/min, and uniformly introducing into the growth chamber for 30 hours until the crystal growth process is finished to obtain the ferromagnetic silicon carbide crystal No. 6.

The difference between the diameter of the nitrogen doping introduced and the diameter of the silicon carbide atoms enters a cavity, and the introduced cavity and the doping atoms act together to contribute to the ferromagnetism of the silicon carbide crystal.

Example 4

The method for preparing ferromagnetic silicon carbide crystals in this example is different from example 1 in that:

replacement of the dopant aluminum carbide with a transition metal carbide: and (3) preparing the ferromagnetic silicon carbide crystal 7# by using titanium carbide with the boiling point of 1600 ℃.

Example 5

The embodiment of 3 silicon carbide wafers shown in FIG. 1 is used to illustrate the method of producing a ferromagnetic silicon carbide crystal according to the present application, but is not limited to 3 silicon carbide wafers.

The preparation method of the ferromagnetic silicon carbide crystal comprises the following steps:

1) assembling: placing three silicon carbide wafers in the raw material cavity, wherein the silicon carbide wafers divide the raw material cavity into two sub-raw material cavities, the two sub-raw material cavities are arranged along the direction close to the seed crystal, raw materials of aluminum carbide and silicon carbide powder are filled in the sub-raw material cavities, and the content of aluminum carbide in the sub-raw material cavities is increased along the direction close to the seed crystal;

2) crystal growth: carrying out crystal growth by using the device in the step 1), wherein the crystal growth step comprises the following procedures:

a. vacuum impurity removal: after the assembled crystal growth chamber is loaded, the furnace body is heated in vacuum;

a2. and (3) continuously heating: heating the furnace body to 1600 ℃ for preparation before nucleation;

b. and (3) nucleation: introducing inert gas (preferably argon gas and helium gas) into the furnace body, quickly boosting the pressure of the furnace body to 700mbar, and after the boosting is finished, raising the temperature to the nucleation point 2200 ℃, and stabilizing for 10 hours;

c. growth and defect introduction: and reducing the pressure in the furnace body to 30mbar, and stably growing for 100 hours at 2300 ℃ to obtain the crude silicon carbide crystal.

3) Regulation of the cavity: and naturally cooling the crude silicon carbide crystal for 2 hours by adopting rapid cooling, and introducing argon gas at the temperature of minus 30 ℃ into a crystal growth chamber of the furnace body to cool to room temperature to obtain the ferromagnetic silicon carbide crystal No. 8.

Comparative example 3

The method for preparing ferromagnetic silicon carbide crystals in this example is different from example 1 in that:

and (4) preparing the ferromagnetic silicon carbide crystal D3# without the step of regulating and controlling the holes in the step 3).

In the doping process, Si vacancies and C vacancies are caused in the crystal growth process due to the difference of the Al atom radius, so that the silicon carbide crystal has ferromagnetism.

Example 6

The following tests of the prepared ferromagnetic silicon carbide crystal No. 6-8 # and the comparative ferromagnetic silicon carbide crystal No. D3# respectively: the magnetization curve (which can be judged whether ferromagnetic property exists or not, saturation magnetization value), aluminum ion concentration by SIMS test, carrier concentration by Hall test, resistivity and distribution thereof, and XRD, and some of the test results are shown in table 2.

TABLE 2

As can be seen from Table 2, the ferromagnetic silicon carbide crystals 6# and 1# have different modes of introducing holes, but both can achieve ferromagnetism; the ferromagnetism of the silicon carbide crystal 7# can be realized by using other metal Ti; the temperature field in the preparation process is changed without adjusting the coil, and the prepared ferromagnetic silicon carbide crystal 8# has poor resistivity uniformity; the carbonized crystal prepared by introducing no independent hole has no ferromagnetism.

The above description is only an example of the present application, and the protection scope of the present application is not limited by these specific examples, but is defined by the claims of the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of the present application should be included in the protection scope of the present application.