Flux recovery device and method for growing gallium nitride single crystal by flux method

Abstract

The invention discloses a fluxing agent recovery device and method for growing gallium nitride single crystals through a fluxing agent method, and belongs to the technical field of crystal material preparation. The device comprises a high-pressure cavity which internally comprises a flow choking cover, a backflow cavity and a single crystal growth cavity from top to bottom in sequence; wherein the backflow cavity is of a double-cone flow guide structure; the top of the backflow cavity is covered with the flow choking cover. The pressure regulation and control system comprises a pressure oscillation gas circuit, a crystal growth gas circuit and a pressure controller; the pressure oscillation gas circuit is used for introducing inert gas into the high-pressure cavity; the crystal growth gas circuit is directly communicated to the single crystal growth cavity from the outside of the high-pressure cavity, the crystal growth gas circuit and the pressure oscillation gas circuit are both connected with the pressure controller, and the pressure controller is used for periodically adjusting the internal pressure of the high-pressure cavity and controlling gas introduction of the crystal growth gas circuit. The heating element is used for heating the backflow cavity and the single crystal growth cavity respectively; according to the invention, the grown crystal can be effectively separated from the fluxing agent, and recovery of the fluxing agent is realized.

Description

Technical Field

[0001] This invention relates to the field of crystal material preparation technology, and specifically to a flux recovery device and method for growing gallium nitride single crystals using a flux method. Background Technology

[0002] Gallium nitride (GaN) possesses advantages such as a large bandgap and high electron mobility, making it one of the key materials for high-frequency, high-power microwave RF devices. Currently, flux-based GaN crystal growth is one of the effective techniques for growing high-quality GaN crystals. However, in traditional flux-based GaN single crystal growth equipment, the crystal is encapsulated in a flux alloy. To separate the crystal from the flux alloy, alcohol-water stepwise cleaning is typically used to remove residual flux, resulting in the inability to recycle and reuse the flux. Summary of the Invention

[0003] The purpose of this invention is to overcome the problems in the prior art and provide a flux recovery device for growing gallium nitride single crystals using the flux method. This solves the problem in the prior art where residual flux is removed by gradual cleaning with alcohol and water, resulting in the flux being unable to be recovered and reused.

[0004] The flux recovery device for growing gallium nitride single crystals using the flux method of the present invention includes a high-pressure chamber, which internally includes, from top to bottom, a flow-blocking shroud, a reflux chamber, and a single crystal growth chamber; wherein, the reflux chamber has a double-cone flow-guiding structure; and the flow-blocking shroud covers the top of the reflux chamber. A pressure control system includes a pressure oscillation gas path, a crystal growth gas path, and a pressure controller. The pressure oscillation gas path is used to introduce inert gas into the high-pressure chamber. The crystal growth gas path extends directly from the outside of the high-pressure chamber to the single crystal growth chamber to provide single crystal growth gas. Both the crystal growth gas path and the pressure oscillation gas path are connected to the pressure controller. The pressure controller is used to periodically adjust the internal pressure of the high-pressure chamber and control the gas flow rate of the crystal growth gas path. The heating element includes an upper heating section and a lower heating section, wherein the upper heating section covers the outside of the reflux cavity and the lower heating section covers the outside of the single crystal growth cavity.

[0005] Preferably, the reflux chamber includes an outer wall of the reflux chamber, a first horizontal annular segment fixedly connected to the outer wall of the reflux chamber and extending towards the center, a first conical side surface circumferentially surrounding to form a first conical structure, a second conical side surface circumferentially surrounding to form a second conical structure, and a second horizontal annular segment. The bottom of the first conical side surface is connected to the inner wall of the first horizontal annular segment, and the top of the first conical side surface is connected to the top of the second conical side surface to form an annular platform. Multiple flux pores are provided circumferentially on the annular platform. The top diameter of the first conical side surface is smaller than its bottom diameter; the top diameter of the second conical side surface is larger than its bottom diameter, so that the first... A conical channel is formed below the annular platform between the conical side surface and the second conical side surface, communicating with each flux pore; the second horizontal ring segment is located at the bottom of the second conical side surface, and the center of the second conical side surface is also provided with a longitudinal channel identical to the center hole of the second horizontal ring segment. The first conical structure, the second conical structure, and the longitudinal channel are all coaxially arranged. The flow hood is provided with a first through hole corresponding to the vertical longitudinal channel. The crystal growth gas path is located in the first through hole and the longitudinal channel. The crystal growth gas path passes through the flow hood and the return cavity and extends directly to the single crystal growth cavity. The upper heating section covers the outside of the outer wall of the return cavity.

[0006] Preferably, the bottom surface of the flow barrier is provided with a conical groove along the circumference, and the top of the conical groove is connected to the flux vent on the annular platform and corresponds vertically.

[0007] Preferably, a gap is reserved between the top of the flow barrier and the top of the high-pressure cavity, and a vent hole is provided on the edge of the flow barrier; the outlet of the pressure oscillation gas path is located above the flow barrier near the center position, so that the outlet of the pressure oscillation gas path is misaligned with the vent hole on the edge of the flow barrier, and the gas injected into the outlet of the pressure oscillation gas path enters the vent hole through the reserved gap and then enters the return cavity.

[0008] Preferably, the pressure controller includes a PID control board; electric valves and pressure transmitters are provided in both the crystal growth gas path and the pressure oscillation gas path; the pressure transmitters are used to measure the pressure in each gas path and transmit the pressure values ​​to the PID control board; the PID control board compares the measured pressure values ​​with the set pressure values ​​and adjusts the opening degree of the corresponding electric valves.

[0009] The present invention also provides a method for recovering pressure oscillation flux used in the flux-driven growth of gallium nitride single crystals using the above-described apparatus, including... Gallium nitride single crystal growth is completed within a single crystal growth cavity; Heating the reflux chamber and the single crystal growth chamber creates a negative temperature gradient between them. The pressure control system periodically injects inert gas into the high-pressure chamber and periodically controls the pressure of the inert gas to generate pressure oscillations, thereby enabling the flux to flow back into the return chamber.

[0010] Preferably, when heating the reflux cavity and the single crystal growth cavity, the reflux cavity is heated to 400°C~500°C through the upper heating section, and the single crystal growth cavity is heated to 450°C~600°C through the lower heating section, so as to form a negative temperature gradient between the reflux cavity and the single crystal growth cavity.

[0011] Preferably, during the pressure oscillation, the internal pressure of the high-pressure cavity oscillates at a frequency of 0.01Hz to 0.1Hz between 0.1MPa and 4MPa.

[0012] Compared with existing technologies, the beneficial effects of this invention are as follows: The flux recovery device for gallium nitride single crystal growth using the flux method designed in this invention changes the boiling point of the flux by applying periodically varying gas pressure to a high-pressure chamber at a certain temperature gradient, causing the flux to transition between gaseous and liquid states. The effective recovery of the flux is achieved through the double-cone flow guiding structure and flow-blocking shroud of the reflux chamber. Based on this device, the grown crystal and flux can be effectively separated, and the flux can be recovered, solving the problem in existing technologies where residual flux is removed through gradual cleaning with alcohol and water, resulting in the inability to recycle and reuse the flux. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the flux recovery process in the flux recovery device for the flux-driven growth of gallium nitride single crystals according to the present invention. Figure 2 This is a schematic diagram of the flux recovery device for growing gallium nitride single crystals using the flux method of the present invention after the flux recovery is completed; Figure 3 This is a schematic diagram of the assembly of the single crystal growth cavity, the reflow cavity, and the flow choke of the flux recovery device for the flux method of gallium nitride single crystal growth of the present invention. Figure 4 This is a schematic diagram of the high-pressure chamber assembly of the flux recovery device for the flux method of gallium nitride single crystal growth of the present invention; Figure 5 This is a pressure oscillation curve used in an embodiment of the flux recovery apparatus for the flux-driven growth of gallium nitride single crystals according to the present invention.

[0014] Explanation of reference numerals in the attached figures: 1. High-pressure chamber; 2. Single crystal growth chamber; 3. Recirculation chamber; 4. Flow hood; 5. Gallium nitride single crystal; 6. Growth flux; 7. Crystal growth gas path; 8. Pressure oscillation gas path; 9. Pressure controller; 10. Heating element; 11. Flux recovery; 12. Flux convection diagram; 13. Flux volatilization diagram. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0016] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms “first,” “second,” and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as “comprising” or “including” indicate that the elements or objects preceding “comprising” or “including” encompass the elements or objects listed following “comprising” or “including” and their equivalents, and do not exclude other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships; when the absolute position of the described objects changes, the relative positional relationship may also change accordingly.

[0017] This invention provides a flux recovery device for the flux-driven growth of gallium nitride single crystals, comprising a high-pressure chamber 1. The high-pressure chamber 1 internally includes, from top to bottom, a flow-blocking shroud 4, a reflux chamber 3, and a single crystal growth chamber 2. The reflux chamber 3 has a double-cone flow-guiding structure. The flow-blocking shroud 4 covers the top of the reflux chamber 3. The high-pressure chamber 1, as the pressure-bearing main body of the entire system, is made of a high-temperature and high-pressure resistant nickel-based alloy material, possessing good sealing performance and thermal stability. The internal space of the chamber is arranged axially from top to bottom with the flow-blocking shroud 4, the reflux chamber 3, and the single crystal growth chamber 2 arranged in a vertically interconnected multi-level functional area structure. The flow hood 4 is located at the top and is mainly used to restrict the gas flow path and prevent flux vapor from directly impacting the top of the cavity; the return cavity 3 is located in the middle and undertakes the functions of guiding, condensing and temporarily storing flux vapor; the single crystal growth cavity 2 is located at the bottom and is used to contain the gallium nitride single crystal 5 that has been grown and the residual flux. It should be noted that the flow hood 4, the return cavity 3 and the single crystal growth cavity 2 are made of boron nitride.

[0018] The pressure control system includes a pressure oscillation gas path 8, a crystal growth gas path 7, and a pressure controller 9. The pressure oscillation gas path 8 is used to introduce inert gas into the high-pressure chamber 1. The crystal growth gas path 7 extends directly from the outside of the high-pressure chamber 1 to the single crystal growth chamber 2 and is used to provide single crystal growth gas. Both the crystal growth gas path 7 and the pressure oscillation gas path 8 are connected to the pressure controller 9. The pressure controller 9 is used to periodically adjust the internal pressure of the high-pressure chamber 1 and control the gas flow into the crystal growth gas path 7.

[0019] In this embodiment, the pressure oscillation gas path 8 is connected to an inert gas source, such as argon or nitrogen, and its outlet extends into the upper region of the high-pressure chamber 1 for periodically injecting gas to increase the pressure inside the chamber. The crystal growth gas path 7 is independently set up, penetrating from the outside into the single crystal growth chamber 2, and is used to transport ammonia or other nitrogen-containing precursor gases during the early growth stage. Both gas paths are controlled by the same pressure controller 9, which is programmable to set the pressure change waveform, such as a sine wave or square wave; frequency range and amplitude range, thereby precisely controlling the periodic fluctuations of the pressure inside the chamber. Through this active pressure intervention mechanism, repeated evaporation-condensation cycles of the flux can be induced without introducing additional chemical reagents. More specifically, the pressure controller 9 includes a PID control board; electric valves and pressure transmitters are installed on both the crystal growth gas path 7 and the pressure oscillation gas path 8; the pressure transmitters are used to measure the pressure in each gas path and transmit the pressure value to the PID control board; the PID control board compares the measured pressure value with the set pressure value and adjusts the opening degree of the corresponding electric valve.

[0020] In this embodiment, the heating element 10 can employ resistance heating, consisting of an upper heating section and a lower heating section, which respectively cover the outer walls of the reflux chamber 3 and the single crystal growth chamber 2. The two heating sections can be independently temperature-controlled to establish a stable longitudinal temperature gradient between the reflux chamber 3 and the single crystal growth chamber 2. For example, during the recycling process, the single crystal growth chamber 2 can be maintained at a higher temperature to facilitate flux vaporization, while the reflux chamber 3 can be kept at a relatively lower temperature to promote vapor condensation. This creates a thermodynamic driving force that assists pressure oscillations in propelling the flux upwards and ultimately achieving liquefaction and collection. An insulation layer can also be added to the exterior of the heating element 10 to reduce heat loss and improve energy efficiency.

[0021] This invention achieves in-situ, efficient, and reusable recovery of residual flux after growth without disassembling the equipment or using chemical cleaning agents. Specifically, in recovery mode, the target temperature difference between the reflux chamber 3 and the single crystal growth chamber 2 is first set by the heating element 10. Then, the pressure controller 9 is activated to control the intermittent gas supply of the pressure oscillating gas path 8 according to a preset frequency (e.g., 0.01Hz~0.1Hz) and pressure amplitude (e.g., 0.1MPa~4MPa). As the pressure inside the chamber rises and falls periodically, the flux alternately undergoes vaporization and partial reflux states in the single crystal growth chamber 2. Its gaseous products move upward along the axial direction and enter the reflux chamber 3 under the guidance of the double-cone flow guide structure, where they condense into liquid in the low-temperature zone and accumulate at the bottom. Due to the presence of the flow baffle 4, steam backflow or splashing is effectively suppressed, improving condensation efficiency. After several pressure cycles, most of the flux is transferred to the reflux chamber 3, achieving effective separation from the gallium nitride single crystal 5.

[0022] In a preferred embodiment, the reflux chamber 3 includes an outer wall of the reflux chamber 3, a first horizontal annular segment fixedly connected to the outer wall of the reflux chamber 3 and extending towards the center, a first conical side surface forming a first conical structure circumferentially around the outer wall, a second conical side surface forming a second conical structure circumferentially around the outer wall, and a second horizontal annular segment. The bottom of the first conical side surface is connected to the inner wall of the first horizontal annular segment, and the top of the first conical side surface is connected to the top of the second conical side surface to form an annular platform. Multiple flux pores are provided circumferentially on the annular platform. The top diameter of the first conical side surface is smaller than its bottom diameter; the top diameter of the second conical side surface is larger than its bottom diameter, so that the first... A conical channel is formed between the first and second conical sides below the annular platform, communicating with each flux pore; the second horizontal ring segment is located at the bottom of the second conical side, and the center of the second conical side is also provided with a longitudinal channel identical to the center hole of the second horizontal ring segment. The first conical structure, the second conical structure, and the longitudinal channel are all coaxially arranged. The flow baffle 4 is provided with a first through hole corresponding to the vertical longitudinal channel. The crystal growth gas path 7 is located in the first through hole and the longitudinal channel. The crystal growth gas path 7 passes through the flow baffle 4 and the return cavity 3 and extends directly to the single crystal growth cavity 2. The upper heating section covers the outside of the outer wall of the return cavity 3.

[0023] This embodiment optimizes the structure of the reflux chamber 3 by combining multi-level conical surfaces and annular platforms to improve the flow uniformity and transmission efficiency of flux vapor within the high-pressure chamber 1. The reflux chamber 3 is supported by its outer wall, with its inner side sequentially integrating a first horizontal annular segment, a first conical side surface, a second conical side surface, a second horizontal annular segment, and a central longitudinal channel, forming a directional and symmetrical composite flow guiding structure. The first horizontal annular segment extends from the outer wall of the reflux chamber 3 towards the center, connecting the outer wall to the internal conical structure and providing bottom support for the first conical side surface. The first conical structure has a top diameter smaller than its bottom diameter, which helps guide the rising flux vapor towards the central region, reducing flow turbulence caused by lateral diffusion. The top of the first cone side is connected to the top of the second cone side, and the two together form an annular platform. This platform not only serves as a structural connection node, but also has multiple flux pores distributed in its annular direction. These pores introduce flux vapor from the single crystal growth chamber 2 into the internal space of the return chamber 3, realizing multi-point air intake and avoiding uneven condensation or blockage caused by local airflow concentration.

[0024] The second cone structure is designed as a cone with a top diameter larger than its bottom diameter. Its bottom connects to the second horizontal ring segment, forming the lower constricted area of ​​the reflux chamber 3. The angle formed by the side surfaces of the first and second cones below the annular platform constitutes an upwardly tapering conical channel. This channel communicates with multiple flux vents on the annular platform, allowing the vapor to diffuse smoothly along the cone surface and flow downwards after entering. Because the first cone structure, the second cone structure, and the longitudinal channel are all arranged coaxially, a high degree of symmetry between the thermal and flow fields is ensured, preventing airflow deflection or temperature gradient imbalance caused by eccentric structures. This ensures stable flow and uniform condensation of the flux vapor throughout the reflux path.

[0025] In this embodiment, the longitudinal channel is located at the center of the second cone side surface, penetrating the entire reflux cavity 3 structure and aligning with the center hole of the second horizontal ring segment, forming a continuous hollow channel. This channel accommodates the crystal growth gas path 7, allowing it to enter from the top of the high-pressure chamber 1 through the first through-hole on the flow baffle 4, and continue downward through the reflux cavity 3, finally extending into the single crystal growth cavity 2, thus achieving the transport of growth gas. Since this longitudinal channel shares the same axis as the crystal growth gas path 7 and is surrounded by a double cone structure, it does not interfere with the circumferential flow path of the flux vapor. Furthermore, the upper heating section covers the outer wall of the reflux cavity 3, and by applying controllable heating to the reflux cavity 3 region, its temperature is maintained slightly lower than that of the single crystal growth cavity 2, forming a temperature gradient environment conducive to vapor condensation, further promoting the liquefaction and deposition of flux within the reflux cavity 3.

[0026] As an optional implementation, the cone angle of the first cone side can be adjusted within the range of 30° to 60° to accommodate flux systems with different evaporation rates; the cone angle of the second cone side can be set between 45° and 75° to balance airflow expansion effect and structural strength. The number of flux pores can be set to 4 to 12, evenly distributed on the annular platform, with a pore diameter ranging from 1 mm to 5 mm. The specific values ​​can be optimized according to the actual steam flow rate. In terms of material selection, the reflux chamber 3 can be made of boron nitride or molybdenum to withstand long-term high temperature and chemical corrosion environments.

[0027] The outer wall of the reflux chamber 3 and the first horizontal ring segment can be fabricated using an integral molding process to improve the overall structural integrity; while the inner wall surface of the longitudinal channel can be polished to reduce gas flow friction resistance. When the crystal growth gas path 7 passes through the longitudinal channel, it can be isolated from the metal cavity by a ceramic insulating sleeve to prevent corrosion under high-temperature conditions.

[0028] In this embodiment, the design of the reflux chamber 3 improves the transmission efficiency and condensation uniformity during the flux recovery process, and optimizes the problems that easily occur in the flux during the reflux process, such as poor flow, local accumulation and incomplete recovery.

[0029] In this embodiment, the bottom surface of the flow baffle 4 is provided with a conical groove along the circumference, and the top of the conical groove is connected to the flux vent on the annular platform. In this embodiment, after the flux vapor released from the flux vent collides with the conical groove of the flow baffle 4, the conical groove structure guides the gas to diffuse to both sides, enters the bottom of the return chamber 3 and condenses.

[0030] Flux vents are located on an annular platform at the top of the reflux chamber 3, evenly distributed circumferentially. These vents guide the flux gas, which evaporates and rises from the single crystal growth chamber 2, into the main space of the reflux chamber 3. During the pressure oscillation recovery phase, the pressure in the high-pressure chamber 1 decreases periodically, causing the liquid flux in the single crystal growth chamber 2 to flash, forming high-temperature steam that flows upwards. This steam is ejected through the flux vents on the annular platform and immediately enters the conical groove at the bottom of the flow baffle 4. Because the conical groove has a tapered-diffraction composite geometry, it can initially buffer and rectify the direction of the high-speed ejected steam, reducing the impact intensity of the airflow and guiding it smoothly along the conical surface to the space above the reflux chamber 3. This prevents steam stagnation or uneven condensation caused by local vortices or turbulence.

[0031] As an optional implementation, the cone angle of the conical groove can be adjusted within the range of 30° to 90°, and can be selected as 60°±10°, so as to balance the airflow conduction efficiency and the structural mechanical strength; its depth can be designed to be 0.5mm to 3mm, depending on the actual steam flow rate and operating frequency.

[0032] In this embodiment, the conical grooves and flux vents are positioned vertically and vertically, effectively capturing and guiding the flux vapor into the predetermined flow path the moment it escapes. This reduces flow dead zones and bypass leakage risks at the interface. Simultaneously, the conical structure provides diffusion and deceleration, helping to stabilize the rising airflow pattern, suppress disturbances, and thus improve the subsequent condensation and deposition efficiency in the return chamber 3. This design is suitable for continuous recovery processes under pressure oscillation conditions of 0.01Hz to 0.1Hz, significantly improving the integrity and repeatability of flux recovery.

[0033] In this embodiment, a gap is reserved between the top of the flow-blocking hood 4 and the top of the high-pressure chamber 1, and a vent hole is provided on the edge of the flow-blocking hood 4; the outlet of the pressure oscillation gas path 8 is located above the flow-blocking hood 4 near the center, so that the outlet of the pressure oscillation gas path 8 is misaligned with the vent hole on the edge of the flow-blocking hood 4. The gas injected into the outlet of the pressure oscillation gas path 8 enters the vent hole through the reserved gap and then enters the return chamber 3. By setting a non-directly opposing gas introduction path between the flow-blocking hood 4 and the top of the high-pressure chamber 1, the introduction method of inert gas in the high-pressure chamber 1 is optimized. The flow-blocking hood 4 has a cover-like structure, and its top maintains a certain axial distance from the inner top surface of the high-pressure chamber 1; the reserved gap serves as a gas diffusion transition zone, allowing the gas output from the pressure oscillation gas path 8 to first enter the space above the flow-blocking hood 4 and expand radially. Multiple vent holes are evenly distributed on the circumferential edge of the flow-blocking hood 4. These vent holes penetrate the wall thickness direction of the flow-blocking hood 4 and are used to guide the externally input inert gas into the interior of the return chamber 3. The outlet of the pressure oscillation gas path 8 is located in the area directly above the flow baffle 4 and is positioned off-center, so that the outlet does not face any single vent hole. This achieves a spatial misalignment between the outlet and the vent hole, which increases the gas flow distance during pressure oscillation and prevents sodium vapor from entering the gas pipe.

[0034] The axial height of the reserved gap can be adjusted according to the actual cavity size and gas flow rate, generally set to 5mm~30mm. This ensures sufficient gas buffer space while avoiding pressure response delay due to excessive gap. The existence of this gap allows the high-speed ejected inert gas to first form a local pressure equalization zone above the baffle 4, slowing down the airflow speed and reducing turbulence intensity. The number of vents can be 4~12, evenly distributed around the edge of the baffle 4, ensuring that gas enters the return cavity 3 from multiple points around the circumference, improving the uniformity of air intake. The diameter of the vents is usually designed to be 2mm~8mm, and the shape can be circular, elliptical, or fan-shaped, depending on the required flow area and processing technology. The outlet end of the pressure oscillation gas path 8 can be installed on the top of the high-pressure cavity 1 through a fixed bracket, with its outlet facing downwards, located in the center of the projected area of ​​the baffle 4, slightly inside, with a horizontal offset distance of at least 10mm from the nearest vent.

[0035] In the above structure, when the pressure controller 9 initiates the pressure oscillation program, inert gas is ejected from near the center through the pressure oscillation gas path 8. It first enters the reserved gap between the flow baffle 4 and the top of the cavity. Within this area, the gas diffuses radially outward, its kinetic energy gradually decays, and the pressure tends to equalize. Subsequently, the gas flows circumferentially to the edge of the flow baffle 4 and enters the return cavity 3 through various vents. This staggered arrangement effectively avoids high-speed airflow directly impacting the internal flow field of the return cavity 3, preventing disruption of the flux vapor condensation process due to localized high pressure or severe disturbances. Simultaneously, the multi-point air intake method helps maintain the symmetry and stability of the pressure field within the return cavity 3, improving the controllability of the pressure oscillation waveform.

[0036] This embodiment also provides a method for recycling a flux recovery device for growing gallium nitride single crystal 5 using the above-mentioned flux method, including completing the growth of gallium nitride single crystal 5 in the single crystal growth chamber 2; Heating the reflux chamber 3 and the single crystal growth chamber 2 creates a negative temperature gradient between them, where the unit of the temperature gradient is ℃ / cm. The pressure control system periodically injects inert gas into the high-pressure chamber 1, and by controlling the argon pressure and adjusting the frequency, pressure oscillation is generated; thus, the flux is returned to the return chamber 3.

[0037] The process of growing gallium nitride single crystal 5 within the single crystal growth chamber 2 refers to the state after the time period for growing high-quality gallium nitride single crystal 5 in the single crystal growth chamber 2 at the bottom of the high-pressure chamber 1 using the flux method has ended. This step does not involve any change to the operational flow of the method proposed in this invention, but rather exists as a prerequisite for the subsequent flux recovery process. During this stage, the gallium nitride raw material dissolves in the flux under high temperature and high pressure, and gradually crystallizes and grows into a bulk single crystal on the surface of the seed crystal. After the growth is completed, a large amount of flux remains around the single crystal and inside the chamber.

[0038] The heating element 10 is in the form of a resistance wire and is made of a nickel-chromium alloy that is resistant to high temperature oxidation, which is suitable for long-term operation at working temperatures of 400℃~600℃.

[0039] The pressure oscillation gas path 8 consists of a gas source (such as a high-purity argon cylinder), a pressure reducing valve, an electromagnetic proportional valve, a flow meter, and pipelines. Its outlet is located above the flow baffle 4 near the center. The injected gas flows through a pre-reserved gap to the vent and then enters the return chamber 3. The pressure controller 9 receives preset program commands and controls the electromagnetic valve to open and close at a set frequency, thereby intermittently injecting inert gas, which can be argon, into the high-pressure chamber 1, causing the pressure inside the chamber to exhibit a regular rise and fall process. The pressure fluctuation amplitude is controlled between 0.1 MPa and 4 MPa, that is, it changes repeatedly from near atmospheric pressure to several megapascals; the frequency adjustment range is 0.01 Hz to 0.1 Hz (corresponding to a cycle of 10 to 100 seconds). When the pressure decreases, the flux in the single crystal growth chamber 2 experiences a drop in boiling point due to the reduced external pressure. Some of the liquid flux evaporates, transforming into a gaseous state and diffusing upwards. When the pressure increases, the boiling point of the flux gas rises again, and it rapidly condenses into droplets after entering the cooler reflux chamber 3, collecting downwards along the conical structure to the bottom storage area. This process repeats, forming a continuous cycle.

[0040] During the combined effects of pressure oscillation and temperature gradient, the flux escapes from the single crystal growth chamber 2 in gaseous form, passes through the conical channel and flux pores in the return chamber 3, and enters the upper space. Guided by the flow-blocking shroud 4, it forms local eddies to prolong the residence time, subsequently completing a phase transition and accumulating in the low-temperature region. Because the return chamber 3 employs a double-cone guiding structure, the condensate can flow smoothly to the bottom under gravity without easily flowing back, thus achieving efficient separation and centralized recovery. This achieves effective separation of the flux and gallium nitride single crystal 5 based on the principle of physical phase transition without damaging the crystal integrity.

[0041] The lower heating section is used to heat the single crystal growth chamber 2, with a target heating temperature range set between 400°C and 600°C. This temperature is higher than the operating temperature of the reflow chamber 3, thus creating a stable negative temperature gradient in the vertical direction. The saturated vapor pressure of the sodium flux increases sharply with increasing temperature between 400°C and 600°C. Pressure oscillation within this temperature range makes it easier to change the boiling point of the sodium flux through gas pressure.

[0042] In a preferred embodiment, the average temperature of the reflux chamber 3 is 50°C to 100°C lower than the average temperature of the single crystal growth chamber 2. If the temperature difference is too small (<50°C), there will be insufficient thermal driving force between the upper and lower chambers, resulting in a low flux evaporation rate, reduced condensation efficiency, and a slow recovery process. If the temperature difference is too large (>100°C), it may cause localized thermal stress concentration, especially damaging the interface between the GaN single crystal and the crucible, while also increasing the risk of material volatilization or side reactions. Therefore, this temperature gradient not only meets the requirements of thermodynamic phase transition but also takes into account equipment safety and crystal integrity protection.

[0043] In the gallium nitride single crystal growth system using sodium flux (5), the boiling point varies significantly with ambient pressure. When the cavity pressure decreases to approximately 0.1 MPa, the saturated vapor pressure of the flux relatively increases, leading to a decrease in the boiling point. This facilitates the transformation of the liquid flux into a gaseous state and its migration upwards from the single crystal growth cavity (2). Conversely, when the pressure rises to 4 MPa, the condensation temperature of the flux gas increases, causing it to rapidly condense into a liquid in the return cavity (3) region due to the slightly lower local temperature, thus achieving phase change deposition. Therefore, this pressure range can effectively drive the reversible phase change of the flux between evaporation and condensation, forming a directional transport driving force.

[0044] Furthermore, the oscillation frequency is controlled within the range of 0.01Hz to 0.1Hz, meaning that the duration of each pressure cycle is 10s to 100s. This low-frequency design fully considers the kinetic characteristics of the flux phase change process: if the frequency is too high, the flux may not be completely condensed within a cycle before being reheated or depressurized, resulting in reduced reflux efficiency and even "repeated evaporation"; while if the frequency is too low, although sufficient phase change time can be guaranteed, the overall recovery rate decreases, affecting the economics of the process. Therefore, the frequency range of 0.01Hz to 0.1Hz is an optimized choice that strikes a balance between ensuring the recovery efficiency of a single cycle and the overall processing speed.

[0045] Furthermore, this parameter combination also considers the stability of equipment operation. High-frequency or large-amplitude pressure fluctuations can easily lead to system fatigue, seal failure, or structural damage, especially under high-temperature and high-pressure environments. By limiting the pressure amplitude to 0.1MPa~4MPa and adopting a slow adjustment mode, thermal stress and mechanical shock can be reduced, extending the service life of the device and improving operational safety.

[0046] The present invention provides a flux recovery device for the flux-driven growth of gallium nitride single crystals, such as... Figure 1 As shown, a 2-inch HVPE-GaN seed crystal is placed at the bottom of the single crystal growth chamber 2, and sodium flux and gallium nitride single crystal 5 raw material are injected. The single crystal growth chamber 2 is placed at the bottom of the high-pressure chamber 1. Then, the reflow chamber 3 is placed on top of the single crystal growth chamber 2. A flow baffle 4 is installed on the top of the reflow chamber 3. The high-pressure chamber 1 is sealed, and the single crystal growth gas path and the pressure oscillation gas path 8 are connected to the top of the high-pressure chamber 1.

[0047] After the gallium nitride single crystal 5 has grown, the temperature of the single crystal growth chamber 2 is controlled within the range of 500℃~600℃ using the heating element 10, and the temperature of the reflow chamber 3 is controlled within the range of 400℃~500℃. The single crystal growth gas path is closed using the pressure controller 9. Argon gas is introduced into the pressure oscillation gas path 8, and the argon gas is controlled to oscillate at a frequency of 0.01Hz within a pressure range of 0.1MPa~2MPa. Figure 5As shown. Based on the volume of high-pressure chamber 1, after 30 cycles of pressure oscillation, the pressure inside high-pressure chamber 1 is brought to atmospheric pressure, thus achieving flux reflow into reflow chamber 3, as follows. Figure 2 As shown.

[0048] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flux recovery device for the flux-driven growth of gallium nitride single crystals, characterized in that, include: The high-pressure chamber includes, from top to bottom, a flow-blocking shroud, a reflux chamber, and a single-crystal growth chamber; wherein, the reflux chamber has a double-cone flow-guiding structure; the flow-blocking shroud covers the top of the reflux chamber; A pressure control system includes a pressure oscillation gas path, a crystal growth gas path, and a pressure controller. The pressure oscillation gas path is used to introduce inert gas into the high-pressure chamber. The crystal growth gas path extends directly from the outside of the high-pressure chamber to the single crystal growth chamber to provide single crystal growth gas. Both the crystal growth gas path and the pressure oscillation gas path are connected to the pressure controller. The pressure controller is used to periodically adjust the internal pressure of the high-pressure chamber and control the gas flow rate of the crystal growth gas path. The heating element includes an upper heating section and a lower heating section, wherein the upper heating section covers the outside of the reflux cavity and the lower heating section covers the outside of the single crystal growth cavity.

2. The flux recovery apparatus for the flux-driven growth of gallium nitride single crystals as described in claim 1, characterized in that, The reflux chamber includes an outer wall, a first horizontal annular segment fixedly connected to the outer wall and extending towards the center, a first conical side surface forming a first conical structure circumferentially, a second conical side surface forming a second conical structure circumferentially, and a second horizontal annular segment. The bottom of the first conical side surface is connected to the inner wall of the first horizontal annular segment, and the top of the first conical side surface is connected to the top of the second conical side surface to form an annular platform. Multiple flux pores are provided circumferentially on the annular platform. The top diameter of the first conical side surface is smaller than its bottom diameter; the top diameter of the second conical side surface is larger than its bottom diameter, so that the first conical side surface... A conical channel is formed below the annular platform between the first and second conical sides, communicating with each flux pore; the second horizontal ring segment is located at the bottom of the second conical side, and the center of the second conical side is also provided with a longitudinal channel identical to the center hole of the second horizontal ring segment. The first conical structure, the second conical structure, and the longitudinal channel are all coaxially arranged. The flow hood is provided with a first through hole corresponding to the vertical longitudinal channel. The crystal growth gas path is located in the first through hole and the longitudinal channel. The crystal growth gas path passes through the flow hood and the return cavity and extends directly to the single crystal growth cavity. The upper heating section covers the outside of the outer wall of the return cavity.

3. The flux recovery apparatus for the flux-driven growth of gallium nitride single crystals as described in claim 2, characterized in that, The bottom surface of the flow barrier is provided with a conical groove along the circumference, and the top of the conical groove is connected to the flux vent on the annular platform and corresponds vertically.

4. The flux recovery apparatus for the flux-driven growth of gallium nitride single crystals as described in claim 2, characterized in that, A gap is reserved between the top of the flow barrier and the top of the high-pressure chamber, and a vent hole is provided on the edge of the flow barrier; the outlet of the pressure oscillation gas path is located above the flow barrier and near the center, so that the outlet of the pressure oscillation gas path is misaligned with the vent hole on the edge of the flow barrier. The gas injected into the outlet of the pressure oscillation gas path enters the vent hole through the reserved gap and then enters the return chamber.

5. The flux recovery apparatus for the flux-driven growth of gallium nitride single crystals as described in claim 1, characterized in that, The pressure controller includes a PID control board; electric valves and pressure transmitters are installed in both the crystal growth gas path and the pressure oscillation gas path; the pressure transmitters are used to measure the pressure in each gas path and transmit the pressure value to the PID control board; the PID control board compares the measured pressure value with the set pressure value and adjusts the opening degree of the corresponding electric valve.

6. The method for recovering flux in the flux recovery apparatus for growing gallium nitride single crystals using the flux method as described in any one of claims 1-5, characterized in that, include: Gallium nitride single crystal growth is completed within a single crystal growth cavity; Heating the reflux chamber and the single crystal growth chamber creates a negative temperature gradient between them. The pressure control system periodically injects inert gas into the high-pressure chamber and controls the inert gas pressure to generate pressure oscillations, thereby enabling the flux to flow back into the return chamber.

7. The recycling method as described in claim 6, characterized in that, When heating the reflux cavity and the single crystal growth cavity, the reflux cavity is heated to 400℃~500℃ through the upper heating section, and the single crystal growth cavity is heated to 450℃~600℃ through the lower heating section, so as to form a negative temperature gradient between the reflux cavity and the single crystal growth cavity.

8. The recycling method as described in claim 6, characterized in that, During the pressure oscillation, the internal pressure of the high-pressure cavity oscillates at a frequency of 0.01Hz to 0.1Hz between 0.1MPa and 4MPa.

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