Method for preparing hexagonal boron nitride monocrystal
Technical Field
The invention relates to the technical field of ultra-wide band gap semiconductor single crystal growth, in particular to Ni-Li + A method for preparing hexagonal boron nitride monocrystal by using cosolvent.
Background
Hexagonal boron nitride (h-BN) is a novel wide bandgap semiconductor, is similar to a graphene structure, has a bandgap reaching more than 6.0eV, and has a large bandgap, high mechanical strength, good thermal stability, high thermal conductivity, low dielectric constant, high breakdown field strength and other excellent physical and chemical properties. The method is widely applied to the fields of deep ultraviolet light emitting devices, laser devices and deep ultraviolet detectors, and can be used for preparing high-temperature and high-frequency electronic power devices. The light-emitting material can also form a full-band light-emitting material with a mature wide-band semiconductor, and is a wide-band semiconductor material with higher exploration value.
At present, a method for preparing hexagonal boron nitride (h-BN), such as a chemical vapor deposition method or a physical vapor deposition method, has a plurality of influencing factors (such as a substrate, temperature, pressure, atmosphere and the like), a growth mechanism is not clear, and h-BN with larger size is difficult to grow. The fluxing agent method is that after solute is completely dissolved in metal flux at high temperature, the temperature is reduced at extremely low speedThe method has the advantages that the size of the method is controlled by the cooling rate, and the method takes a long time and is not thick. In 2007 Japanese National Institute for Materials Science, high purity cubic boron nitride (cBN) and hBN single crystals were synthesized as a Ba-BN solution at high temperature and high pressure for 20 to 40 hours. Because the high-temperature high-pressure method has harsh growth conditions and the growth size is difficult to further expand, the method is converted into a high-temperature normal-pressure method for preparing the h-BN monocrystal. Tetsuya Yamada et al, 2019, melted Li in BN crucible at normal pressure by controlling the flux and heating temperature 2 CO 3 The grown h-BN crystal has a novel polyhedral structure, the size is more than 3 microns, and a research thought is provided for subsequent experimental exploration. The existing metal fluxing agent system for growing h-BN under normal pressure comprises the following components: nickel tungsten, cobalt chromium, nickel chromium, copper chromium, iron chromium, pure iron, stainless steel alloys, etc., with growth dimensions on the order of microns to centimeters and thicknesses on the order of microns only.
In general, the h-BN single crystal material is still in the basic research stage of material preparation, and application research is just started, and mainly focused on the research of single crystal films. The preparation of h-BN single crystal materials with large size and high quality becomes a great difficulty.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method for preparing hexagonal boron nitride monocrystal, which can be used for preparing Ni-Li monocrystal + High-quality and large-size h-BN monocrystal is prepared in a fluxing agent system.
In order to solve the technical problems, the invention adopts the following technical scheme:
a method of hexagonal boron nitride single crystal comprising the steps of:
step one, fusing agent Ni-Li 2 Placing a mixture of an O system, a source material and carbon powder in a crucible, and adding the source material B or BN; placing the crucible containing the mixture in a heater with a furnace chamber, sealing the furnace chamber, and purifying the atmosphere in the furnace chamber;
step two, argon is filled into the furnace chamber, and when the furnace chamber is heated to 1400-1600 ℃ of melting temperature, the furnace chamber is kept at constant temperature for 5-13 hours, so that the metal is fully melted and the source material is dissolved to form a solution;
step three, after the solution reaches saturation, heating from the melting temperature to the growing temperature of 1500-1650 ℃;
step four, after the solution is stabilized for 0.5 to 2 hours, starting a vacuum pump to pump the pressure in the furnace chamber to 1 multiplied by 10 -4 Filling high-purity nitrogen or nitrogen-argon mixed gas into the furnace chamber under Pa, keeping the growth temperature constant for 5-24h, dissolving nitrogen into the flux, and cooling to the lowest temperature which can be detected by a temperature detector in the furnace chamber at a cooling rate of 10-300 ℃/h;
and fifthly, naturally cooling to room temperature, and taking out the product from the crucible after deflating.
Further, in the first step, the fluxing agent Ni-Li 2 In the O system, ni accounts for 90 to 97 percent of the total mass of the system and Li is calculated by mass ratio 2 O accounts for 3-10% of the total mass of the system.
Further, in the first step, the crucible is baked in an oven at 105 ℃ for 120 minutes before use.
Further, in the first step, after the furnace chamber is sealed, a vacuum pump connected with the furnace chamber is started to pump the pressure in the furnace chamber to 1 multiplied by 10 -4 Under Pa, high-purity argon is filled into the furnace chamber until the pressure is 50000Pa-150000Pa; starting the vacuum pump to pump the pressure in the furnace chamber to 1×10 -4 Pa or less; repeating the above operation for 2-3 times, purifying the atmosphere in the furnace chamber, washing off the residual background gas in the furnace chamber, and reducing the content of carbon and oxygen impurities.
Further, in the second step, 101.325KPa of high purity argon gas is filled into the furnace chamber. The high purity argon is filled to prevent the generation of aluminum nitride under inert gas.
Further, in the second step, the heating rate is 233-300 ℃/h when the material is heated to the melting temperature.
Further, in the third step, the heating rate when heating to the growth temperature is 200 ℃/h.
Further, in the fourth step, the partial pressure ratio of the nitrogen-argon mixed gas is 50% -99% of nitrogen and 1% -50% of argon.
The invention uses metal Ni and lithium oxide (Li 2 O) as a cosolvent, nitrogen and boron (B) or Boron Nitride (BN) as source materials, by means of a cosolventThe method grows a large-size high-quality h-BN monocrystal, the temperature is kept for a certain time at a certain material temperature, so that the solvent reaches a saturated state, B or BN is fully dissolved in the flux, the temperature is raised to the growth temperature, the temperature is kept for a certain time at a constant temperature in nitrogen or nitrogen-argon mixed gas, and the temperature is lowered at a certain cooling rate, so that spontaneous nucleation and growth are realized.
Ni and Li 2 O is used as a cosolvent, the capacity of dissolving B or BN of Ni is larger than that of other transition metals, and Li 2 O increases the N-dissolving capacity of the flux and has a certain BN-dissolving capacity, and B and N are combined in the flux. At present, cr which is taken as a main cosolvent for dissolving N reacts with B to generate chromium-boron compound, and Li is explored + Instead of Cr-dissolved N, it is of exploratory value that the flux system can grow large-size h-BN single crystals with fewer defects, thermal strains and impurities.
The prepared h-BN has the characteristic of high anisotropy of optical properties, and has larger performance advantages in the aspects of ultraviolet light emission, detection devices and the like.
The invention is firstly in Ni-Li + The high-quality large-size h-BN single crystal is prepared in the system, a new research thought and a new method for exploring and preparing the h-BN single crystal are provided, and Ni-Li is adopted + The flux system grows to a maximum size of 500 micrometers at 1366cm under the conditions of high temperature and normal pressure by controlling parameters such as flux proportion, nitrogen-argon proportion, soaking time, cooling rate and the like -1 The half height width of the Raman is 7.78cm -1 High quality h-BN single crystals.
In addition, the method does not need ultrahigh pressure and is carried out under normal pressure, the source materials are easy to obtain, the manufacturing cost is low, and the operation is safe and simple.
Drawings
FIG. 1 is example 1Ni-Li 2 Optical microscopy images of h-BN single crystals grown by O fluxing agent;
FIG. 2 is example 1Ni-Li 2 O fluxing agent grows a Raman spectrum of the h-BN monocrystal;
FIG. 3 is example 1Ni-Li 2 h-BN monocrystal stuck on the surface of the O system;
FIG. 4 is an optical microscope photograph of comparative example 1;
FIG. 5 is an optical microscope photograph of comparative example 2;
FIG. 6 is a photograph of the inside of a crucible of comparative example 3.
Detailed Description
The following examples are provided to further illustrate the claimed invention. However, examples and comparative examples are provided for the purpose of illustrating embodiments of the present invention and do not exceed the scope of the inventive subject matter, which is not limited by the examples. Unless specifically indicated otherwise, materials and reagents used in the present invention are available from commercial products in the art.
Example 1
The corundum crucible is put into a baking oven at 105 ℃ to bake for 120 minutes and then dried.
Adding fluxing agent Ni-Li into corundum crucible 2 A mixture of O system, BN and carbon powder. Ni-Li 2 In the O system, ni accounts for 90 percent, li 2 O accounts for 10 percent, and the cosolvent Ni-Li 2 The mass ratio of the O system to the source material BN is 20:1, and the carbon powder accounts for 1.8% of the mass of the mixture. Placing corundum crucible containing the above mixture into heater, sealing the furnace chamber of the heater, starting vacuum pump, and pumping the pressure in the furnace chamber to 1×10 -4 Under Pa, high-purity argon is filled into the furnace chamber to 100000Pa, and a vacuum pump is started to pump the pressure in the furnace chamber to 1 multiplied by 10 -4 Below Pa, this operation is repeated 3 times, the atmosphere in the furnace is purged, and the residual background gas in the furnace chamber is washed off.
And filling high-purity argon with the pressure of 101.325KPa into the furnace chamber. And starting a heating system to heat the corundum crucible in the furnace chamber, wherein the heating rate is 260 ℃/h, and the melting temperature reaches 1500 ℃. After the fluxing agent melts, it is maintained at a constant temperature for 10 hours to allow the metal to sufficiently melt and dissolve the source material to form a solution.
After the solution reaches saturation, the temperature is increased from the melting temperature of 1500 ℃ to the growing temperature of 1600 ℃ with the heating rate of 200 ℃/h.
After the solution is stabilized for 1 hour, a vacuum pump is started to pump the pressure in the furnace to 1 multiplied by 10 -4 Filling high-purity nitrogen into furnace chamber under Pa, keeping constant temperature at 1600 deg.C for 18 hr to ensure that nitrogen is dissolved into flux, and cooling at 95.5 deg.C/hrThe temperature is reduced to 700 ℃, and 700 ℃ is the lowest temperature which can be detected by a temperature detector in the furnace chamber.
And after the lowest temperature measurement is reached, the power supply is turned off, and the growth is finished.
And (5) taking out the product from the corundum crucible after naturally cooling to room temperature and deflating.
Example 2
The corundum crucible is put into a baking oven at 105 ℃ to bake for 120 minutes and then dried.
Adding fluxing agent Ni-Li into corundum crucible 2 A mixture of O system, B and carbon powder. Ni-Li 2 In the O system, ni accounts for 97 percent, li 2 O accounts for 3%, and cosolvent Ni-Li 2 The mass ratio of the O system to the source material B is 20:1, and the carbon powder accounts for 1.8% of the mass of the mixture. Placing corundum crucible containing the above mixture into heater, sealing the furnace chamber of the heater, starting vacuum pump, and pumping the pressure in the furnace chamber to 1×10 -4 Under Pa, high-purity argon is filled into the furnace chamber to 50000Pa, and a vacuum pump is started to pump the pressure in the furnace chamber to 1 multiplied by 10 -4 Below Pa, this operation is repeated 2 times, the atmosphere in the furnace is purged, and the residual background gas in the furnace chamber is washed off.
And filling high-purity argon with the pressure of 101.325KPa into the furnace chamber. And starting a heating system to heat the corundum crucible in the furnace chamber, wherein the heating rate is 233 ℃/h, and the melting temperature is 1450 ℃. After the fluxing agent melts, it is held at constant temperature for 13 hours to allow the metal to sufficiently melt and dissolve the source material to form a solution.
After the solution reaches saturation, the temperature is increased from the melting temperature of 1450 ℃ to the growing temperature of 1550 ℃ at the heating rate of 200 ℃/h.
After the solution is stabilized for 0.5 hour, a vacuum pump is started to pump the pressure in the furnace to 1 multiplied by 10 -4 And filling nitrogen-argon mixed gas with the partial pressure ratio of 70% and 30% into the furnace chamber under Pa, keeping the constant temperature at 1550 ℃ for 24 hours at the growth temperature, ensuring that the nitrogen is dissolved into the flux, and then reducing the temperature to 700 ℃ at the cooling rate of 200 ℃/h, wherein the temperature is the lowest temperature which can be detected by a temperature measuring instrument in the furnace chamber.
And after the lowest temperature measurement is reached, the power supply is turned off, and the growth is finished.
And (5) taking out the product from the corundum crucible after naturally cooling to room temperature and deflating.
Example 3
The corundum crucible is put into a baking oven at 105 ℃ to bake for 120 minutes and then dried.
Adding fluxing agent Ni-Li into corundum crucible 2 A mixture of O system, B and carbon powder. Ni-Li 2 In O system, ni accounts for 95 percent, li 2 O accounts for 5 percent, and the cosolvent Ni-Li 2 The mass ratio of the O system to the source material B is 20:1, and the carbon powder accounts for 1.8% of the mass of the mixture. Placing corundum crucible containing the above mixture into heater, sealing the furnace chamber of the heater, starting vacuum pump, and pumping the pressure in the furnace chamber to 1×10 -4 Under Pa, high-purity argon is filled into the furnace chamber to 150000Pa, and a vacuum pump is started to pump the pressure in the furnace chamber to 1 multiplied by 10 -4 Below Pa, this operation is repeated 2 times, the atmosphere in the furnace is purged, and the residual background gas in the furnace chamber is washed off.
And filling high-purity argon with the pressure of 101.325KPa into the furnace chamber. And starting a heating system to heat the corundum crucible in the furnace chamber, wherein the heating rate is 300 ℃/h, and the melting temperature is 1550 ℃. After the fluxing agent melts, it is held at constant temperature for 5 hours to allow the metal to fully melt and dissolve the source material to form a solution.
After the solution reaches saturation, the temperature is increased from 1550 ℃ of the melting temperature to 1650 ℃ of the growing temperature, and the heating rate is 200 ℃/h.
After the solution is stabilized for 2 hours, a vacuum pump is started to pump the pressure in the furnace to 1 multiplied by 10 -4 And filling nitrogen-argon mixed gas with the partial pressure ratio of 50% of nitrogen and 50% of argon into the furnace chamber below Pa, keeping the constant temperature at the growth temperature of 1650 ℃ for 5 hours, ensuring that the nitrogen is dissolved into the flux, and then reducing the temperature to 700 ℃ at the cooling rate of 300 ℃/h, wherein the temperature is the lowest temperature which can be detected by a temperature measuring instrument in the furnace chamber.
And after the lowest temperature measurement is reached, the power supply is turned off, and the growth is finished.
And (5) taking out the product from the corundum crucible after naturally cooling to room temperature and deflating.
Comparative example 1
The only difference from example 1 is that: adding a mixture of BN and carbon powder into a corundum crucible, wherein the carbon powder accounts for 1.8% of the mass of the mixture.
Comparative example 2
The only difference from example 1 is that: adding a mixture of fluxing agent Ni, BN and carbon powder into a corundum crucible, wherein the mass ratio of the cosolvent Ni to the source material BN is 20:1, and the carbon powder accounts for 1.8% of the mass of the mixture.
Comparative example 3
The only difference from example 1 is that: adding fluxing agent Li into corundum crucible 2 O, BN and carbon powder, fluxing agent Li 2 The mass ratio of O to the source material BN is 20:1, and the carbon powder accounts for 1.8% of the mass of the mixture.
FIG. 1 is a drawing of example 1Ni-Li 2 An optical microscopic image of an O flux grown h-BN single crystal, a size exceeding 200 μm, FIG. 2 is a view of example 1Ni-Li 2 Raman spectrum of the grown h-BN single crystal with O fluxing agent at Raman peak position 1366cm -1 Is provided with a half width of 7.78 and 7.78cm -1 Is not shown in the figure). FIG. 3 is example 1Ni-Li 2 h-BN monocrystal adhered to O system surface.
The surface of the product of comparative example 1 was observed, and as shown in FIG. 4, the optical microscope showed no significant change in BN sheet and no formation of h-BN crystals. Comparative example 2 the sample surface, as shown in fig. 5 by optical microscopy, showed no h-BN crystals were generated on the metal surface. Comparative example 3 As shown in FIG. 6, the crucible had partially undissolved BN therein, and no formation of h-BN crystals was observed, and as a result, ni-Li 2 The O system can grow h-BN monocrystal with large size and high quality.