Apparatus and method for growing cadmium zinc telluride crystals based on thm

Abstract

The application relates to the technical field of photoelectric material preparation, in particular to a device for growing cadmium zinc telluride crystals based on THM, which comprises: a one-piece quartz crucible, the quartz crucible has a first cavity, a second cavity and a third cavity; the inner surface of the first cavity is a conical surface, and the half-cone angle of the conical surface is between 10 DEG and 20 DEG; the inner surface of the third cavity is a conical surface, and the half-cone angle of the conical surface is between 50 DEG and 70 DEG; and the second cavity is connected with the first cavity and the third cavity. In the application, the conical angle structure is introduced to guide the polycrystalline raw material particles to be more closely and uniformly stacked above the seed crystal, so that the axial temperature gradient at the growth interface is improved, and the crystal can be stably grown under the optimal thermal field condition from the initial stage.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic material preparation technology, specifically to an apparatus and method for growing zinc cadmium telluride crystals based on THM. Background Technology

[0002] In the actual THM growth process, temperature field control and the geometry of the quartz crucible are important factors affecting crystal quality, yield, and production cost.

[0003] Chinese Patent Application No. 202310259350.9 discloses a seed crystal fusion method and apparatus for growing cadmium zinc telluride (CZT) crystals based on THM. The apparatus includes a growth quartz crucible, an insulating support for placing the growth quartz crucible, a SiC heat-conducting rod placed at the bottom of the growth quartz crucible, and a thermocouple for monitoring the temperature of the CZT single crystal seed. The seed crystal fusion method includes the following steps: S1, pre-treating the CZT single crystal seed and the first CZT polycrystalline ("dummy seed"), placing the first CZT polycrystalline, the CZT single crystal seed, the tellurium-rich solvent region material, and the third CZT polycrystalline sequentially from bottom to top, and then evacuating, heating, and holding at the temperature; S2, moving the heater downwards to heat and dissolve part of the components of the CZT single crystal seed; S3, moving the heater upwards to allow the CZT crystal to begin continuous growth. Compared with the prior art, the present invention reduces the size requirements of cadmium zinc telluride single crystal seed crystals, enhances the release of latent heat of crystallization during fusion growth, and improves the quality of cadmium zinc telluride crystals.

[0004] However, the quartz crucible in the Chinese patent application number 202310259350.9 is cylindrical, which cannot suppress the growth of impurity crystals and has a low single crystal ratio.

[0005] Therefore, it is necessary to provide a new technical solution to overcome the above-mentioned defects. Summary of the Invention

[0006] The purpose of this invention is to provide an apparatus and method for growing zinc cadmium telluride crystals based on THM, which effectively suppresses the growth of side impurities, increases the single crystal rate, reduces the cost of seed crystals, improves the economic efficiency of the process, optimizes heat conduction, and enhances the axial temperature gradient in the initial growth stage.

[0007] To achieve the objectives of this invention, the following technical solution is adopted: An apparatus for growing cadmium zinc telluride crystals based on THM includes: an integrally formed quartz crucible having a first cavity, a second cavity, and a third cavity; the inner surface of the first cavity is a conical surface with a half-cone angle between 10° and 20°, and the inner surface of the third cavity is a conical surface with a half-cone angle between 50° and 70°; the second cavity connects the first cavity and the third cavity.

[0008] Furthermore: the conical surface of the first cavity is an upright conical surface, the conical surface of the third cavity is an inverted conical surface, the small end of the first cavity is directly opposite the small end of the third cavity, and the inner surface of the second cavity is a cylindrical surface.

[0009] Furthermore, the length of the third cavity is 3 to 5 mm.

[0010] Furthermore: the end of the third cavity extends to form a fourth cavity. The method for growing zinc cadmium telluride crystals based on THM includes the following steps: Step S1: Cleaning; Soak the quartz crucible in acetone for 24 hours, then rinse it with deionized water; Soak it in aqua regia at a 1:3 (volume ratio) solution for 24 hours, then rinse it with deionized water again; Soak it in a 10% hydrofluoric acid solution for 1 hour, then rinse it with deionized water.

[0011] Step S2: Loading; Load the materials into the cleaned quartz crucible in a top-to-bottom order. First, put the single crystal seed crystal into the first or second cavity, then fill the first cavity with cadmium zinc telluride polycrystalline material powder, then fill the tellurium-rich block, and at least fill the third cavity, and finally fill the blocky CZT polycrystalline material. Step S3: Vacuuming; use a bottle stopper to initially seal the quartz crucible, then evacuate the vacuum, and finally fuse the bottle stopper to the quartz crucible to form a completely sealed quartz ampoule.

[0012] Step S4: Heat preservation; place the sealed quartz ampoule in the corresponding position of the THM crystal growth furnace at 890 to 910°C, and after heat preservation for 20 hours, the heating area starts to move upward from the bottom of the quartz ampoule.

[0013] Further: In step S2: The material is filled from top to bottom. The single crystal seed is filled into the first cavity and partially enters the second region. Then, the first cavity is filled with cadmium zinc telluride polycrystalline powder. The quartz crucible is vibrated so that the cadmium zinc telluride polycrystalline powder fills the single crystal seed and the inner surface area of ​​the quartz crucible and is compacted.

[0014] Furthermore: In step S2, the molar ratio of tellurium-rich block to cadmium zinc telluride polycrystalline material is 1:1, and the ratio of the height of the tellurium-rich block to the diameter of the grown crystal is 1:1.

[0015] Furthermore: the tellurium-rich particles have a diameter of 1 cm to 2 cm and are located in the middle of the second region to the fourth region.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention is based on a device for growing zinc cadmium telluride crystals using THM. By designing a conical angle structure for the seed crystal fusion zone, a good seed crystal fusion effect can still be achieved even after reducing the seed crystal size, thereby reducing the preparation cost of the seed crystal.

[0017] 2. This invention relates to a device for growing cadmium zinc telluride (CZN) crystals using THM (Thawed Metal Membrane). It suppresses the growth of impurities on the seed crystal's sidewalls through a small-angle reverse cone design and eliminates the unavoidable annular voids between the seed crystal sidewalls and the crucible walls in traditional cylindrical crucibles by filling with polycrystalline powder. These voids are the root cause of heterogeneous nucleation and lateral impurity growth. This ensures stable crystal growth in a single crystal orientation from the seed crystal stage, significantly improving the single crystal yield.

[0018] 3. The device for growing zinc cadmium telluride crystals based on THM in this invention introduces a conical structure to guide polycrystalline raw material particles to be stacked more compactly and uniformly on top of the seed crystal, thereby increasing the axial temperature gradient at the growth interface and ensuring that the crystal can grow stably under optimal thermal field conditions from the initial stage. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0020] Figure 1 This is a schematic diagram of a quartz crucible.

[0021] Figure 2 This is a schematic diagram of the material being filled.

[0022] In the diagram: 100, first cavity; 200, second cavity; 300, third cavity; 400, fourth cavity. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0024] Cadmium zinc telluride (Cd1-xZnxTe, CZT) crystal is a high-performance ternary semiconductor material. Due to its high atomic number, excellent resistivity, and tunable bandgap, it has become a key substrate material for room-temperature nuclear radiation detectors and infrared focal plane array detectors. Among various crystal growth methods, the Vertical Bridgman (VB) method and the Traveling Heater Method (THM) are the mainstream technologies for growing large-size, high-quality CZT crystals. The THM method, in particular, exhibits unique advantages in preparing low-defect, highly uniform CZT crystals due to its low growth temperature, flat solid-liquid interface, and minimal component segregation effect, and is considered an important pathway to the industrialization of high-performance detector-grade CZT crystals.

[0025] The core process of the THM method involves sealing a pre-synthesized polycrystalline CZT ingot, tellurium-rich material, and a single-crystal seed crystal within a quartz crucible. A narrow heater (or temperature zone) is moved along the axial direction of the crucible, causing localized melting of the raw material. The material then recrystallizes onto the seed crystal behind the moving heater, thus achieving directional crystal growth. The entire growth process occurs in a solid-liquid-solid coexistence state, requiring extremely high stability at the growth interface. In practical THM growth processes, temperature field control and the geometric design of the quartz crucible are crucial factors affecting crystal quality, yield, and production costs. Currently, the traditional THM growth quartz crucible commonly used in the industry consists primarily of a cylindrical cavity of uniform diameter. This design reveals several significant drawbacks in process implementation, severely restricting the reliable and economical preparation of high-performance CZT crystals: (1) Problem of lateral impurity crystal growth: Traditional cylindrical quartz crucibles require the seed crystal to also be processed into a matching cylindrical shape. However, in actual assembly, it is difficult to achieve a perfect fit between the outer wall of the cylindrical seed crystal and the inner wall of the cylindrical quartz crucible, and there is usually a small annular gap (or "thermal gap"). In the early stage of crystal growth, when the heater moves through this area, the raw material or vapor in the gap is very likely to undergo non-uniform nucleation, thereby inducing additional crystal nuclei on the side of the seed crystal. These laterally grown impurities (polycrystalline) will compete with the main crystal for growth in the subsequent growth process, quickly destroying the integrity of the single crystal structure, resulting in crystal growth failure or a significant reduction in the volume of the single crystal region and a low single crystal ratio.

[0026] (2) High cost of seed crystals: In order to grow crystals with the target diameter (e.g., φ60mm or more), traditional methods must use cylindrical single crystal seed crystals with the same diameter and size as the target crystal. Large-sized CZT single crystal seed crystals with high structural integrity are difficult to prepare and extremely expensive, which directly increases the raw material cost of each crystal growth and becomes an important economic bottleneck for industrialization.

[0027] (3) Insufficient temperature gradient due to filler gaps: Traditional cylindrical flat-bottom structures have inherent defects in the raw material filling area directly below the seed crystal. Furthermore, the cylindrical constant-diameter design requires the heater's heat to reach the seed crystal end through a raw material body with a large cross-sectional area and a relatively diffuse heat conduction path. This weakens the axial temperature gradient necessary for the growth interface, thus inducing non-uniform nucleation in the melt, resulting in polycrystalline or high-defect-density regions at the crystal initiation, affecting crystal quality. like Figure 1 As shown, the apparatus for growing zinc cadmium telluride crystals based on THM according to the present invention includes: an integrally formed quartz crucible having a first cavity 100, a second cavity 200 and a third cavity 300; the inner surface of the first cavity 100 is a conical surface with a half-cone angle between 10° and 20°, and the inner surface of the third cavity 300 is a conical surface with a half-cone angle between 50° and 70°; the second cavity 200 connects the first cavity 100 and the third cavity 300.

[0028] The cone surface of the first cavity 100 is an upright cone surface, and the cone surface of the third cavity 300 is an inverted cone surface. That is to say, the small end of the first cavity 100 is directly opposite the small end of the third cavity 300, and the inner surface of the second cavity 200 is a cylindrical surface.

[0029] As a further improvement to the invention: the end of the third cavity 300 continues to extend to form a fourth cavity 400, the inner surface of the fourth cavity 400 is a cylindrical surface, and the length of the third cavity 300 is 3 to 5 mm.

[0030] The purpose of the first cavity 100 in this application is to facilitate the placement of the seed crystal into the quartz crucible. The diameter of the seed crystal is processed to be approximately 1 mm smaller than the diameter of the fusion surface, and it is inserted into the first cavity 100 from the upper end of the quartz crucible. A curved spatial gap with a triangular cross-section is formed between the quartz crucible and the seed crystal. The gap is filled with cadmium zinc telluride polycrystalline powder with a particle size of less than 0.1 mm, allowing the inner conical surface of the quartz crucible to achieve a large-area, gapless, and tight fit with the polycrystalline material. This fit eliminates the annular harmful voids in traditional cylindrical structures, preventing the raw material melt or vapor from lingering in this area and thus avoiding uniform nucleation. This physically eliminates the spatial conditions for the generation of impurities on the sides. Furthermore, the small gaps between the polycrystalline powder and the quartz wall that induce impurities are reduced in size by the tight-fitting design at a small angle, putting them at a disadvantage in grain competition.

[0031] The purpose of the third cavity 300 in this application is to present a relatively open, upward-opening conical funnel-shaped structure. After the seed crystal is installed, one end will be at the center of a cylindrical surface of equal diameter. Subsequently, tellurium-rich material is filled until it covers the conical region. At this point, the contact between the tellurium-rich material and the inner wall of the crucible is not a plane, but a gradually expanding annular region guided by the conical wall. This significantly increases the initial thermal contact and mass exchange area, facilitating uniform heat transfer and forming a more stable and complete initial solid-liquid interface, improving weld quality and crystal head integrity. Due to the presence of this conical angle, a conical seed crystal with a lower diameter much smaller than the target crystal diameter can be used. During growth, the crystal starts from the small size at the lower end of the seed crystal, and as the growth interface rises within the 60° conical region, the crystal diameter will naturally and smoothly expand to the designed diameter of the upper seed crystal growth region. This means that the volume and weight of the seed crystal itself can be significantly reduced, directly lowering the cost of expensive single-crystal seed crystal materials.

[0032] The method for calculating the semi-cone angle of the inner surface of the first cavity 100 is as follows: According to the interface stability criterion (Mullins-Sekerka theory), the stability of the solid-liquid interface is related to the temperature gradient G and the growth rate v as follows:

[0033] Where ΔT is the supercooling, DL is the solute diffusion coefficient, mL is the liquidus slope, C0 is the initial melt concentration, and k is the solute partition coefficient. To improve interfacial stability, a high G needs to be maintained in the early stages of growth. According to Fick's law of heat conduction and the focusing effect principle, the conical structure has a converging effect on heat flux. The relationship between heat flux density q and cross-sectional area A is:

[0034] Where λ is the thermal conductivity and A(x) is the cross-sectional area along the axial direction x. The small cone angle structure gradually reduces the cross-sectional area, thereby forming heat flow convergence at the end of the seed crystal and enhancing the axial temperature gradient. According to heat conduction simulation calculations, when α=10°, the heat flow convergence coefficient (defined as the ratio of the end heat flow density to the inlet heat flow density) reaches a peak of 1.8. This angle ensures that heat is preferentially transferred to the end of the seed crystal along the axial direction, while maintaining radial temperature uniformity.

[0035] Based on the aforementioned quartz crucible, the present invention also provides a method for growing zinc cadmium telluride crystals based on THM, the method comprising the following steps: Step S1: Cleaning; Soak the quartz crucible in acetone for 24 hours, then rinse it with deionized water; Soak it in aqua regia at a 1:3 (volume ratio) solution for 24 hours, then rinse it with deionized water again; Soak it in a 10% hydrofluoric acid solution for 1 hour, then rinse it with deionized water.

[0036] Step S2: Loading; Load the materials into the cleaned quartz crucible in a top-to-bottom order. First, put the single crystal seed crystal into the first cavity 100 or the second cavity 200. Then fill the first cavity 100 with cadmium zinc telluride polycrystalline material powder. Then fill the tellurium-rich block and at least fill the third cavity 300. Finally, fill the blocky CZT polycrystalline material. Please see Figure 2 The material is filled from top to bottom. The single crystal seed is filled into the first cavity 100 and part of it enters the second region. Then, the first cavity 100 is filled with cadmium zinc telluride polycrystalline powder. The quartz crucible is vibrated so that the cadmium zinc telluride polycrystalline powder fills the single crystal seed and the inner surface area of ​​the quartz crucible and is compacted. Step S3: Vacuuming; use a bottle stopper to initially seal the quartz crucible, then evacuate the vacuum, and finally fuse the bottle stopper to the quartz crucible to form a completely sealed quartz ampoule.

[0037] Step S4: Heat preservation; Place the sealed quartz ampoule in the corresponding position of the THM crystal growth furnace at 890 to 910°C and keep it at that temperature for 20 hours. Then, the heating zone starts to move upward from the bottom of the quartz ampoule. The tellurium-rich material area melts first and forms an initial fusion interface with the end of the seed crystal. As the heater continues to move upward, the main polycrystalline material is gradually melted and continuously transported to the end of the seed crystal through the melting zone, allowing the crystal to grow upward continuously.

[0038] In step S2, the theoretical basis for loading the material into the cleaned quartz crucible is: For a crystal to precipitate from a melt, it must overcome the Gibbs free energy barrier. The critical free energy change for homogeneous nucleation is:

[0039] In the formula, γsl is the solid-liquid interface energy, and ΔGv is the driving force for phase transition per unit volume (proportional to the supercooling ΔT). In practical systems, the presence of a heterogeneous substrate (such as the wall of a quartz crucible) can significantly reduce the nucleation barrier. The critical free energy change for heterogeneous nucleation is:

[0040] Where θ is the contact angle (wetting angle) between the nucleus and the substrate, and the expression for the nucleation barrier reduction factor f(θ) is:

[0041] When θ = 180°, f(θ) = 1, and the nucleation difficulty is comparable to that of uniform nucleation; when θ = 0°, f(θ) = 0, the nucleation barrier disappears, and the substrate completely induces nucleation. In the annular gap between the seed crystal and the quartz crucible wall, there exists a heterogeneous nucleation interface on the surface of the quartz crucible wall (quartz). The contact angle between the CZT melt and the quartz is θquartz ≈ 120°. From 140°, we can obtain f(θ)≈0.20 0.30, meaning the nucleation barrier is reduced to 1 / 5 of that for uniform nucleation. The probability of nucleation is significantly increased by 1 / 3. In addition, the millimeter-scale size of the voids is much larger than the critical nucleus radius of the CZT system. Therefore, the void space does not pose a geometric restriction on the growth of the nucleus. On the contrary, it provides sufficient space for the nucleus to grow into a macroscopic heterocrystal.

[0042] After polycrystalline powder fills the millimeter-scale voids, it covers the quartz crucible wall, and the powder particles are densely packed, isolating the quartz surface from the melt and preventing the melt from directly contacting the quartz crucible wall. The previously exposed heterogeneous substrate (quartz) is replaced by a CZT powder surface. Since the CZT powder and melt are homogeneous materials, their contact angle θCZT≈0° (complete wetting), at which point the nucleation barrier approaches zero. This means that on the powder surface, the melt can directly epitaxially grow without overcoming the energy barrier, which is precisely the seed crystal continuation growth we expect. It is evident that after powder filling, the quartz crucible wall, which could potentially induce heterogeneous crystals, is covered, while the powder surface provides an epitaxial growth channel with an extremely low barrier. In competitive nucleation, the growth rate of the main crystal (seed crystal and powder layer) will far exceed the nucleation rate of any potential heterogeneous crystals, thus ensuring stable crystal growth along a single crystal orientation.

[0043] In step S2, the molar ratio of tellurium-rich blocks to cadmium zinc telluride polycrystalline material is 1:1, and the ratio of the height of the tellurium-rich blocks to the diameter of the grown crystal is 1:1. The tellurium-rich blocks have a particle size of 1-2 cm and are located in the middle of the second region to the fourth region.

[0044] This embodiment uses the seed crystal moving heater method to grow 40mm diameter cadmium zinc telluride (CZN) crystals as an example. The seed crystal is a cylinder with a thickness of 5mm and a diameter of 29mm. The tellurium-rich region is formed by high-temperature mixing of 20g pure tellurium material and 30g CZN polycrystalline material, and then crushed into 1cm particle size fragments. The CZN polycrystalline material is a cylinder with a diameter of 39mm and a height of 100mm. The small-angle cone angle of the seed crystal fusion zone is determined to be 15°, and the cone angle of the initial crystal growth zone is 60°.

[0045] The quartz crucible must be placed vertically and stably on the growth furnace support rod. The growth furnace is heated to 900℃, and the support rod is continuously rotated at a speed of 2.5 r / min. The resulting cadmium zinc telluride crystal seed crystal has good fusion, a single crystal rate of >90%, and no cracks. It can be cut and reused.

[0046] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. An apparatus for growing zinc cadmium telluride crystals based on THM, characterized in that: include: An integrally formed quartz crucible having a first cavity, a second cavity, and a third cavity; the inner surface of the first cavity is a conical surface with a half-cone angle between 10° and 20°, and the inner surface of the third cavity is a conical surface with a half-cone angle between 50° and 70°; the second cavity connects the first cavity and the third cavity.

2. The apparatus for growing cadmium zinc telluride crystals based on THM as described in claim 1, characterized in that: The first cavity has an upright conical surface, the third cavity has an inverted conical surface, the small end of the first cavity is directly opposite the small end of the third cavity, and the inner surface of the second cavity is a cylindrical surface.

3. The apparatus for growing cadmium zinc telluride crystals based on THM as described in claim 2, characterized in that: The length of the third cavity is 3 to 5 mm.

4. The apparatus for growing zinc cadmium telluride crystals based on THM as described in claim 3, characterized in that: The end of the third cavity continues to extend to form a fourth cavity.

5. The method for growing zinc cadmium telluride crystals based on THM as described in claim 4, characterized in that: Includes the following steps: Step S1: Cleaning; Soak the quartz crucible in acetone for 24 hours, then rinse it with deionized water; Soak it in aqua regia at a 1:3 (volume ratio) solution for 24 hours, then rinse it with deionized water again; Soak it in a 10% hydrofluoric acid solution for 1 hour, then rinse it with deionized water. Step S2: Loading; Load the materials into the cleaned quartz crucible in a top-to-bottom order. First, put the single crystal seed crystal into the first or second cavity, then fill the first cavity with cadmium zinc telluride polycrystalline material powder, then fill the tellurium-rich block, and at least fill the third cavity, and finally fill the blocky CZT polycrystalline material. Step S3: Vacuuming; use a bottle stopper to initially seal the quartz crucible, then perform vacuuming, and finally fuse the bottle stopper to the quartz crucible to form a completely sealed quartz ampoule. Step S4: Heat preservation; place the sealed quartz ampoule in the corresponding position of the THM crystal growth furnace at 890 to 910°C, and after heat preservation for 20 hours, the heating area starts to move upward from the bottom of the quartz ampoule.

6. The apparatus for growing cadmium zinc telluride crystals based on THM as described in claim 5, characterized in that: In step S2: The material is filled from top to bottom. The single crystal seed is filled into the first cavity and partially enters the second region. Then, the first cavity is filled with cadmium zinc telluride polycrystalline powder. The quartz crucible is vibrated so that the cadmium zinc telluride polycrystalline powder fills the single crystal seed and the inner surface area of ​​the quartz crucible and is compacted.

7. The apparatus and method for growing zinc cadmium telluride crystals based on THM as described in claim 6, characterized in that: In step S2, the molar ratio of tellurium-rich blocks to cadmium zinc telluride polycrystalline material is 1:1, and the ratio of the height of the tellurium-rich blocks to the diameter of the grown crystal is 1:

1.

8. The apparatus and method for growing zinc cadmium telluride crystals based on THM as described in claim 7, characterized in that: The tellurium-rich particles range in size from 1 cm to 2 cm and are located in the middle of the second region to the fourth region.

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