1. A method of growing a GaN crystal by recrystallization, comprising the steps of:

(1) adding a fluxing agent into a crucible, vertically placing a partition plate with a through hole on the surface in the crucible, and respectively recording areas on two sides of the partition plate in the crucible as a crystal growth area and a raw material decomposition area;

(2) placing GaN crystal powder into the raw material decomposition area, and placing GaN seed crystals into the crystal growth area;

(3) placing the crucible in a reaction kettle, sealing the reaction kettle, and placing the reaction kettle in crystal growth equipment for heat preservation growth to obtain a GaN crystal; the temperature for heat preservation growth is 600-950 ℃, and the nitrogen pressure is 0.2-10 MPa.

2. The method of claim 1, wherein step (1) further comprises adding gallium metal to the crucible, mixing with the flux, and placing a baffle plate in the crucible after mixing.

3. The method of claim 1, wherein the crucible is a molybdenum crucible, an alumina crucible, or a boron nitride crucible, and wherein the crucible is cylindrical in shape.

4. The method of claim 1, wherein the fluxing agent is an alkali metal and/or an alkaline earth metal; the alkali metal is sodium and/or lithium, and the alkaline earth metal is one or more of barium, strontium, calcium and magnesium.

5. The method of claim 2 or 4, wherein the molar ratio of the flux to the metallic gallium is (1-10): (0-9).

6. The method according to claim 1, wherein the steps (1) to (2) are performed under an inert gas atmosphere.

7. The method of claim 1, wherein the rotation rate of the reaction kettle is 0-85 circles/minute during the heat preservation growth process.

8. The method according to claim 1 or 7, characterized in that after the incubation growth is finished, the method further comprises the step of carrying out post-treatment on the obtained growth product, wherein the post-treatment comprises the following steps:

and soaking the growth product in the crucible in ethanol, cold water and hydrochloric acid in sequence, taking out the GaN crystal, and cleaning and drying the GaN crystal in sequence.

9. The method of claim 1, wherein the crystal growth apparatus comprises a high temperature furnace and a rotary lifting device disposed within a chamber of the high temperature furnace; a heater is arranged on the inner wall of the high-temperature furnace; the rotary lifting device comprises a rotary lifting controller, a rotary lifting shaft connected with the rotary lifting controller, and a rotary platform arranged at the top end of the rotary lifting shaft.

10. A crystal growth device comprises a high-temperature furnace and a rotary lifting device arranged in a cavity of the high-temperature furnace; a heater is arranged on the inner wall of the high-temperature furnace; the rotary lifting device comprises a rotary lifting controller, a rotary lifting shaft connected with the rotary lifting controller, and a rotary platform arranged at the top end of the rotary lifting shaft.

Background

With the continuous development of modern science and technology, the requirements of various working systems on the performance of microelectronic devices and optoelectronic devices are continuously increased. However, the improvement of performance of conventional Si-based devices and GaAs-based devices through structural optimization has been very limited due to the limitation of intrinsic physical properties of the materials. Therefore, it is very urgent to find new semiconductor materials for manufacturing devices. GaN is a representative of novel wide bandgap nitride semiconductor materials, has become an ideal material for manufacturing new-generation microelectronic devices and optoelectronic devices by virtue of excellent properties such as high breakdown voltage, wide bandgap, large thermal conductivity, high electron saturation drift velocity, strong radiation resistance, good chemical stability and the like, and has a very wide application prospect in the fields of weaponry, aerospace, 5G network communication, illumination, new energy automobiles, automatic driving and the like. In addition, nitride-based microelectronic devices and photoelectronic devices have very high energy conversion efficiency, the use of the devices can improve the use efficiency of electric energy, reduce the combustion of fossil fuels and the emission of related pollutants, are favorable for relieving and solving the energy problem faced by the current society, can improve the living environment on which people live, and have very important significance for building an environment-friendly society.

At present, nitride-based semiconductor devices are still under initial research stage, and besides GaN-based light emitting diode devices, the commercial performance of the rest of the devices is far lower than that of contemporary laboratories. The device also has many scientific problems and technical problems in the fields of reliability, preparation process, device performance and the like. Among them, the lack of a high crystalline quality GaN substrate is the most major technical bottleneck hindering the development of devices. At present, GaN devices mainly use sapphire single crystals and silicon single crystals as substrates. However, the lattice constant and the thermal expansion coefficient of the material have very large difference, which can cause a large amount of dislocation defects inside the device, and seriously affect the performance and the service life of the device. In addition, some high-performance GaN devices adopt SiC as a substrate, so that the performance of the device can be relatively improved, but the SiC substrate has the defect of high price.

The most ideal substrate for manufacturing the nitride-based semiconductor device is the corresponding nitride single crystal, so that the problem of crystal defects caused by lattice mismatch and thermal conductivity mismatch can be solved, the complicated process in the manufacturing process of the device can be reduced, and the yield of the device is improved. However, the GaN substrate has poor crystal quality, and the dislocation density of the crystal can reach 10⁶cm^-2As described above, it is difficult to meet the demand for further improvement in the performance of GaN devices. In addition, GaN single crystal substrates have problems of high cost and lack of high quality nonpolar plane substrates, which also seriously hinders the commercial application of their devices.

At present, a fluxing agent method mainly adopts a liquid phase epitaxy technology to grow gallium nitride crystals, but the technology has the defects of poor stability and limited growth time, and the gallium nitride crystals with large size and high crystallization quality are difficult to obtain. Since the N source for growing the GaN crystal by the liquid phase epitaxy technology comes from external nitrogen dissolution, the growth environment needs to be connected with the outside through a gas guide tube, which can cause the metal Na in the solution to be continuously volatilized due to high temperature, and the Ga element in the solution can be consumed by the crystal during the growth process, which can cause the composition and proportion of the fluxing agent solution to be changed, and finally, the sustainability and stability of the growth of the GaN crystal are affected.

Disclosure of Invention

In view of the above, the present invention provides a method of growing a GaN crystal by recrystallization and a crystal growing apparatus. According to the invention, the decomposition of the GaN crystal powder provides an N source and a Ga source for crystal growth, so that the problems of poor sustainability and stability in the growth of the GaN crystal can be overcome, and the large-size high-crystallization-quality gallium nitride crystal can be obtained.

In order to achieve the above object, the present invention provides the following technical solutions:

a method of growing a GaN crystal by recrystallization, comprising the steps of:

(1) adding a fluxing agent into a crucible, vertically placing a partition plate with a through hole on the surface in the crucible, and respectively recording areas on two sides of the partition plate in the crucible as a crystal growth area and a raw material decomposition area;

(2) placing GaN crystal powder into the raw material decomposition area, and placing GaN seed crystals into the crystal growth area;

(3) placing the crucible in a reaction kettle, sealing the reaction kettle, and placing the reaction kettle in crystal growth equipment for heat preservation growth to obtain a GaN crystal; the temperature for heat preservation growth is 600-950 ℃, and the nitrogen pressure is 0.2-10 MPa.

Preferably, the step (1) further comprises adding gallium metal into the crucible, mixing with the flux, and placing the partition plate in the crucible after mixing.

Preferably, the crucible is a molybdenum crucible, an alumina crucible or a boron nitride crucible, and the crucible is cylindrical in shape.

Preferably, the fluxing agent is an alkali metal and/or an alkaline earth metal; the alkali metal is sodium and/or lithium, and the alkaline earth metal is one or more of barium, strontium, calcium and magnesium.

Preferably, the molar ratio of the fluxing agent to the metal gallium is (1-10): (0-9).

Preferably, the steps (1) to (2) are carried out under the protection of inert gas.

Preferably, in the heat preservation growth process, the rotation rate of the reaction kettle is 0-85 circles per minute.

Preferably, after the incubation growth is finished, the method further comprises the step of carrying out post-treatment on the obtained growth product, wherein the post-treatment comprises the following steps:

and soaking the growth product in the crucible in ethanol, cold water and hydrochloric acid in sequence, taking out the GaN crystal, and cleaning and drying the GaN crystal in sequence.

Preferably, the crystal growth equipment comprises a high-temperature furnace and a rotary lifting device arranged in a cavity of the high-temperature furnace; a heater is arranged on the inner wall of the high-temperature furnace; the rotary lifting device comprises a rotary lifting controller, a rotary lifting shaft connected with the rotary lifting controller, and a rotary platform arranged at the top end of the rotary lifting shaft.

The invention also provides crystal growth equipment, which comprises a high-temperature furnace and a rotary lifting device arranged in the cavity of the high-temperature furnace; a heater is arranged on the inner wall of the high-temperature furnace; the rotary lifting device comprises a rotary lifting controller, a rotary lifting shaft connected with the rotary lifting controller, and a rotary platform arranged at the top end of the rotary lifting shaft.

The invention provides a method for growing GaN crystal by recrystallization, which comprises the steps of adding a fluxing agent into a crucible, and dividing a partition board in the crucible into a crystal growth area and a raw material decomposition area by using a partition board with through holes on the surface; placing GaN crystal powder into a raw material decomposition area, placing GaN seed crystals into a crystal growth area, then placing a crucible into a reaction kettle, sealing the reaction kettle, and placing the reaction kettle into crystal growth equipment for heat preservation growth to obtain GaN crystals; the temperature for heat preservation growth is 600-950 ℃, and the nitrogen pressure is 0.2-10 MPa. According to the invention, GaN crystal powder is used as a raw material, a gallium source and a nitrogen source are provided for crystal growth by utilizing the decomposition of the GaN crystal powder, the GaN crystal powder firstly reacts with a fluxing agent to generate Ga ions and release nitrogen, the nitrogen enters the gas and is ionized, and then is dissolved in the solution again, the nitrogen pressure in the heat preservation growth process is higher, the N ion concentration in the solution is higher, the supersaturation degree of the solution is higher, and the GaN seed crystal can be inoculated for growth after the supersaturation degree of the solution exceeds a certain value; according to the invention, the nitrogen pressure in the heat preservation growth process is controlled to be 0.2-10 MPa, and the supersaturation degree of the solution can be indirectly controlled, so that the growth of GaN polycrystal is inhibited, and the high-quality crystal with smooth and flat crystal surface is obtained.

In addition, the nitrogen source comes from the decomposition of the GaN crystal powder, an external nitrogen source is not required to be connected, the fluxing agent is not volatilized, the GaN crystal powder and the GaN seed crystal are separated by the partition plate with the through hole, Ga ions generated by the decomposition of the GaN crystal powder can pass through the through hole, the gallium source is continuously provided for the growth of the GaN seed crystal, meanwhile, the partition plate can prevent the GaN crystal powder from moving to the vicinity of the GaN seed crystal, and the components and the proportion of the fluxing agent around the GaN seed crystal cannot be changed, so that the sustainability and the stability of the growth of the GaN crystal are ensured.

The invention introduces the recrystallization technology into the fluxing agent method to form a closed GaN crystal growth system, thereby improving the stability of the GaN crystal growth, enhancing the continuity of the crystal growth and prolonging the crystal growth time.

Furthermore, the invention also adds metal gallium into the fluxing agent, and the metal gallium is also used as a gallium source for the growth of the GaN crystal, thereby further improving the stability of the growth of the GaN crystal.

The invention also provides crystal growth equipment, and the GaN crystal can be grown by using the crystal growth equipment, so that the growth temperature and the rotation rate of the crystal can be conveniently controlled, and the high-quality GaN crystal can be obtained.

Drawings

FIG. 1 is a schematic structural view of a crystal growth apparatus, wherein 1-a high temperature furnace, 2-an upper heater, 3-a lower heater, 4-a rotary elevating controller, 5-a rotary elevating shaft, 6-a rotary platform, and 7-a reaction vessel;

FIG. 2 is a schematic view of a growth process of a re-crystallized grown GaN crystal;

FIG. 3 is a schematic view showing a process for growing a GaN crystal by recrystallization;

FIG. 4 is an X-ray diffraction pattern of a GaN crystal prepared in example 1;

FIG. 5 is an optical photograph of a GaN crystal prepared in example 1.

Detailed Description

The invention provides a method for growing a GaN crystal through recrystallization, which comprises the following steps:

(1) adding a fluxing agent into a crucible, vertically placing a partition plate with a through hole on the surface in the crucible, and respectively recording areas on two sides of the partition plate in the crucible as a crystal growth area and a raw material decomposition area;

(2) placing GaN crystal powder into a raw material decomposition area, and placing GaN seed crystals into a crystal growth area;

(3) placing the crucible in a reaction kettle, sealing the reaction kettle, and placing the reaction kettle in crystal growth equipment for heat preservation growth to obtain a GaN crystal; the temperature for heat preservation growth is 600-950 ℃, and the nitrogen pressure is 0.2-10 MPa.

The invention adds fluxing agent into the crucible, vertically places the clapboard with through holes on the surface in the crucible, and respectively marks the areas on two sides of the clapboard in the crucible as a crystal growth area and a raw material decomposition area. In the present invention, the flux is preferably an alkali metal and/or an alkaline earth metal; the alkali metal is sodium and/or lithium, the alkaline earth metal is one or more of barium, strontium, calcium and magnesium, in a specific embodiment of the present invention, the fluxing agent is preferably a mixture of sodium, calcium and lithium, the mass fraction of sodium in the mixture is preferably 94-95%, more preferably 94.7%, the mass fraction of lithium is preferably 3-4%, more preferably 3.2%, and the mass fraction of calcium is preferably 2-2.5%, more preferably 2.1%; the crucible is preferably a molybdenum crucible, an alumina crucible or a boron nitride crucible, and the crucible is preferably cylindrical in shape; the size of the partition plate is preferably consistent with the inner diameter of the crucible, and the height of the partition plate is preferably consistent with the height of the crucible; vertically inserting a partition plate into the crucible, thereby dividing the crucible into two regions; in the invention, the size of the through hole on the partition plate is preferably 2-3 mm.

In the present invention, the step (1) preferably further comprises adding gallium metal into the crucible, mixing with the flux, and placing a partition plate in the crucible after mixing; the mol ratio of the fluxing agent to the metal gallium is preferably (1-10): 0-9, more preferably (2-8): 8-2, and further preferably (3-7): 7-3; when the fluxing agent is a mixture, the molar amount of the fluxing agent is based on the total molar amount of each substance.

According to the invention, GaN crystal powder is placed in the raw material decomposition area, and GaN seed crystals are placed in the crystal growth area. The invention has no special requirement on the dosage ratio of the GaN crystal and the GaN crystal powder, and the dosage ratio can be any ratio. In the specific embodiment of the invention, a GaN crystal with a better form is preferably selected as the seed crystal, a seed rod is designed and manufactured according to the selected GaN crystal, the seed crystal is fixed on the seed rod, then the seed crystal is vertically placed in the crystal growth region of the crucible by using the seed rod, the seed crystal is preferably placed at the upper part of the crucible, the specific position is preferably controlled according to the liquid level of the fluxing agent, and the seed crystal is suspended and immersed in the fluxing agent during the thermal growth. In the invention, the GaN crystal powder is directly placed at the bottom of the raw material decomposition area.

In the present invention, the steps (1) and (2) are preferably performed under the protection of an inert gas, in particular, in a glove box filled with an inert gas, preferably argon.

After the GaN crystal powder and the GaN seed crystal are placed, the crucible is placed in a reaction kettle, the reaction kettle is sealed and then placed in crystal growth equipment for heat preservation growth, and the GaN crystal is obtained. In the invention, the top of the reaction kettle is provided with a barometer for displaying the pressure in the reaction kettle, and a valve for adjusting the pressure in the reaction kettle is arranged on a pipeline connected with the barometer and the reaction kettle.

In the invention, the crystal growth equipment structure preferably comprises a high-temperature furnace and a rotary lifting device arranged in a cavity of the high-temperature furnace; the inner wall of the high-temperature furnace is provided with heaters, and the heaters preferably comprise two groups, namely an upper heater and a lower heater arranged at the lower end of the upper heater; the rotary lifting device comprises a rotary lifting controller, a rotary lifting shaft connected with the rotary lifting controller, and a rotary platform arranged at the top end of the rotary lifting shaft. In the invention, the structure schematic diagram of the crystal growth device is shown in fig. 1, wherein in fig. 1: 1-high temperature furnace, 2-upper heater, 3-lower heater, 4-rotary lifting controller, 5-rotary lifting shaft, 6-rotary platform and 7-reaction kettle.

In the invention, the reaction kettle is placed on a rotary platform of crystal growth equipment, and a barometer of the reaction kettle extends out of the top of the crystal growth equipment; the invention can control the position of the reaction kettle in the furnace through the rotary lifting device, and the heating power of the upper heater and the lower heater can conveniently control the heating temperature in the reaction kettle.

In the invention, the temperature of the heat preservation growth is 600-950 ℃, preferably 700-900 ℃, further preferably 750-850 ℃, the nitrogen pressure is 0.2-10 MPa, preferably 1-8 MPa, further preferably 3-5 MPa, and the time of the heat preservation growth is preferably 100-500 h, and more preferably 100-300 h. Preferably, a certain amount of nitrogen is filled in a reaction kettle in advance, then the reaction kettle is sealed and placed in a crystal growth device, then the temperature is raised to the heat preservation growth temperature, when the growth temperature reaches the preset temperature, a valve is connected with an air pipe to adjust the pressure in the reaction kettle to the preset pressure, and finally the air pipe is removed and the heat preservation and pressure maintaining are carried out to grow crystals; the invention has no special requirement on the amount of the nitrogen gas which is pre-filled, and the nitrogen gas can be regulated and controlled according to the preset pressure intensity; according to the invention, a certain amount of nitrogen is filled in, so that the environment in the reactor is ensured to be a nitrogen environment when the reaction starts, and the stable growth of the GaN crystal is ensured. In the invention, the heating rate of heating to the temperature for heat preservation growth is preferably 2.5 ℃/min; in the heat preservation growth process, the rotation rate of the reaction kettle is preferably 0-80 circles/minute, more preferably 5-60 circles/minute, and the rotation rate of the reaction kettle is preferably controlled by a rotary lifting device.

In the heat preservation growth process, GaN crystal powder is decomposed to provide Ga source and N source for GaN crystal, and nitrogen generated by GaN decomposition can maintain the nitrogen pressure in the reaction kettle in the range under the heat preservation growth temperature condition of the invention, and external nitrogen is not required to be accessed in the heat preservation growth process. In the invention, a schematic diagram of the growth process of the recrystallization growth GaN crystal is shown in FIG. 2, wherein a crucible is arranged in a reaction kettle, a melt is arranged in the crucible, the melt is melted to form a growth solution, the inside of the crucible is divided into a raw material decomposition area and a crystal growth area by a partition plate with a through hole, GaN crystal powder is arranged at the bottom of the raw material decomposition area, GaN seed crystals are vertically suspended at the top of the crystal growth area, the GaN crystal powder is decomposed to provide Ga ions and release nitrogen, the nitrogen is re-dissolved in the solution to form a supersaturated state, and the seed crystals are inoculated and grown in the supersaturated state.

After the heat preservation growth is finished, the crystal growth device is preferably naturally cooled to the room temperature, then the reaction kettle is opened, the crucible is taken out, and the product in the crucible is subjected to post-treatment. In the present invention, the post-treatment preferably comprises the steps of: soaking the growth product in the crucible in ethanol, cold water and hydrochloric acid in sequence, taking out the GaN crystal, and cleaning and drying the GaN crystal in sequence; the present invention has no particular requirement for specific conditions of soaking in ethanol, cold water and hydrochloric acid, and cleaning and drying of the GaN crystal, and may employ conditions well known to those skilled in the art.

The invention also provides crystal growth equipment, the structure of which is consistent with the scheme and is not described herein any more, and the crystal growth equipment can conveniently control the growth temperature and the rotation rate of the crystal to obtain the high-quality GaN crystal.

The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.

FIG. 3 is a schematic view showing a process for growing a GaN crystal by recrystallization in an embodiment of the present invention; the crystal growth apparatus used in the examples is shown in FIG. 1.

Example 1

(1) 8.008g of metallic sodium, 0.309g of metallic calcium and 0.081g of metallic lithium were placed in a crucible (cylindrical molybdenum crucible) in a glove box filled with argon gas and mixed uniformly. A partition plate with holes is vertically placed in a crucible, the interior of the crucible is divided into a raw material decomposition area and a crystal growth area, GaN crystal powder is placed at the bottom of the crucible, seed crystals are fixed on a seed crystal rod, and the GaN crystal powder is vertically placed at the upper part of the crystal growth area of the crucible.

(2) Putting the crucible into a high-temperature reaction kettle, and filling partial N into the reaction kettle₂And sealing the reaction kettle. Transferring the high-temperature reaction kettle to a rotary platform in a high-temperature furnace, adjusting the rotation speed of the rotary platform to 10 circles/minute, controlling the furnace temperature to enable the crystal growth temperature to be 850 ℃, and connecting an air pipe to enable N in the reaction kettle to be in contact with the N after the temperature is raised to 850 DEG C₂Controlling the air pressure at 3.6MPa, removing the air pipe, and growing for 100h in a heat preservation way.

(3) And after the growth is finished, naturally cooling to room temperature, opening the reaction kettle, taking out the crucible, sequentially soaking a growth product in the crucible in alcohol, cold water and hydrochloric acid, removing a growth residue in the crucible, taking out the top GaN crystal, and then cleaning and drying the GaN crystal to obtain the GaN crystal with the size of 5mm x 10mm x 100 mu m.

FIG. 4 is an X-ray diffraction pattern of the obtained GaN crystal, in which the left side is a comparison of the crystal and wurtzite GaN card, and the right side is a diffraction peak of (002) plane. As can be seen from FIG. 2, the obtained GaN crystal was single-crystalline; in addition, the thickness of the grown crystal is very thin and is difficult to distinguish by naked eyes, and the existence of the peak splitting of XRD indicates that the sample has GaN crystals with two lattice parameters, which indicates that the seed crystal has the condition of seed crystal growth.

FIG. 5 is an optical photograph of the obtained GaN crystal. As can be seen from FIG. 5, the GaN crystal obtained by the present invention has a smooth and flat surface.

Example 2

(1) In a glove box filled with argon, 8.025g of metallic sodium, 0.308g of metallic calcium and 0.081g of metallic lithium were placed in a crucible (cylindrical alumina crucible) and mixed uniformly. A partition plate with holes is vertically placed in a crucible, the interior of the crucible is divided into a raw material decomposition area and a crystal growth area, GaN crystal powder is placed at the bottom of the crucible, seed crystals are fixed on a seed crystal rod, and the GaN crystal powder is vertically placed at the upper part of the crystal growth area of the crucible.

(2) Putting the crucible into a high-temperature reaction kettle, and filling partial N into the reaction kettle₂And sealing the reaction kettle. Transferring the high-temperature reaction kettle to a rotary platform in a high-temperature furnace, adjusting the rotation speed of the rotary platform to 10 circles/minute, controlling the furnace temperature to enable the crystal growth temperature to be 850 ℃, and connecting an air pipe to enable N in the reaction kettle to be in contact with the N after the temperature is raised to 850 DEG C₂Controlling the air pressure at 4.5MPa, removing the air pipe, and growing for 100h in a heat preservation way.

(3) And after the growth is finished, naturally cooling to room temperature, opening the reaction kettle, taking out the crucible, sequentially soaking a growth product in the crucible in alcohol, cold water and hydrochloric acid, removing growth residues in the crucible, taking out the top GaN crystal, cleaning and drying the GaN crystal to obtain the GaN crystal with the size of 5mm x 10mm x 20 mu m, wherein the surface of the crystal is smooth and flat.

The obtained GaN crystal was subjected to an X-ray diffraction test, and the results were similar to those of example 1, showing that the obtained GaN crystal was a single crystal and the seed crystal had a seed growth.

In addition, the results of the examination of the components of the solution in the crucible after the growth in examples 1 to 2 showed the presence of gallium metal in the solution, indicating that GaN was indeed decomposed during the crystal growth.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.