Preparation method of cadmium telluride polycrystal

Abstract

The invention provides a preparation method of cadmium telluride polycrystals. The preparation method comprises the following steps: A) filling tellurium powder at the bottom of a quartz tube; b) filling the mixed powder of tellurium powder and cadmium powder into the quartz tube, and enabling the mixed powder to be in contact with the tellurium powder but not to be mixed with the tellurium powder, so that the mixed powder of the tellurium powder and cadmium powder is above the tellurium powder when the quartz tube is vertically placed; c) welding and sealing a quartz tube in vacuum, and vertically placing the quartz tube above a heating device capable of moving up and down; and D) moving the heater upwards from the bottom of the quartz tube for heating, stopping heating and moving when the material in the quartz tube is separated from the heating area, and cooling to obtain the cadmium telluride polycrystal. According to the method, the compact ingot of the cadmium telluride polycrystal can be directly prepared at the temperature lower than the melting point of the cadmium telluride, and the temperature does not need to be increased to exceed the melting point of the cadmium telluride for melting into the ingot. According to the method, the reaction intensity is effectively controlled, the material loss caused by material splashing during synthesis is reduced, and the product yield is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor materials, and in particular relates to a method for preparing cadmium telluride polycrystal. Background Art

[0002] Cadmium telluride is a compound semiconductor material with a bandgap value of 1.45eV, and it is a direct bandgap, which is in the ideal solar cell bandgap range and has a good photoelectric conversion efficiency. Cadmium telluride thin-film solar cells have low manufacturing costs and high efficiency, and are suitable for large-scale industrialization. They are also used to make infrared modulators, HgCdTe substrates, infrared window field-induced light-emitting devices, photovoltaic cells, infrared detection, X-ray detection, etc.

[0003] At present, there are various methods for synthesizing cadmium telluride, mainly using tellurium powder and cadmium powder mixed for synthesis. For example, patent CN103818886B discloses a method for preparing cadmium telluride, which is to mix tellurium powder and cadmium powder in a molar ratio of 1:1, place them in a graphite boat, put them in a synthesis furnace, exhaust the air, and heat them in three stages for one synthesis; similarly, patent CN103420346B discloses a method for preparing cadmium telluride, which is to mix tellurium powder and cadmium powder in a molar ratio of 1:1, place them in a graphite boat, put them in a quartz tube in a synthesis furnace, exhaust the air, and heat them in three stages for one synthesis. However, in the synthesis of cadmium telluride in the prior art, tellurium powder and cadmium powder react violently, which may even cause splashing, causing waste of cadmium telluride and low product yield. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing cadmium telluride polycrystals. The method of the present invention can effectively control the intensity of the reaction, reduce the material loss caused by material splashing during synthesis, and improve the product yield.

[0005] The present invention provides a method for preparing cadmium telluride polycrystal, comprising the following steps:

[0006] A) Tellurium powder is loaded at the bottom of the quartz tube;

[0007] B) filling a mixed powder of tellurium powder and cadmium powder into a quartz tube, contacting the tellurium powder but not mixing it, so that when the quartz tube is placed vertically, the mixed powder of tellurium powder and cadmium powder is above the tellurium powder;

[0008] C) A vacuum-sealed quartz tube is placed vertically above a heating device that can move up and down;

[0009] D) The heater is moved upward from the bottom of the quartz tube to heat. When the material in the quartz tube leaves the heating area, the heating and movement are stopped, and cadmium telluride polycrystals are obtained after cooling.

[0010] Preferably, the tellurium powder in step A) has a purity of 5N and a particle size of 100-150 mesh.

[0011] Preferably, the tellurium powder in step B) has a purity of 5N and a particle size of 100-150 mesh.

[0012] Preferably, the purity of the cadmium powder in step B) is 5N, and the particle size is 100-150 mesh.

[0013] Preferably, in step B), the molar ratio of tellurium powder to cadmium powder is 1:(0.9-1.1).

[0014] Preferably, in step B), the molar ratio of tellurium powder to cadmium powder is 1:1.

[0015] Preferably, the mass of the tellurium powder in step A) is 15-25% of the mass of the mixed powder of tellurium powder and cadmium powder in step B).

[0016] Preferably, in the step D), the heater is first heated to 700-900° C., and then the heater is moved upward from the bottom of the quartz tube.

[0017] Preferably, the heating rate of the heater is 40-60° C. / hour.

[0018] Preferably, the heater moves at a speed of 30-50 mm / day.

[0019] The present invention provides a method for preparing cadmium telluride polycrystals, comprising the following steps: A) filling tellurium powder at the bottom of a quartz tube; B) filling a mixed powder of tellurium powder and cadmium powder into the quartz tube, contacting with the tellurium powder but not mixing, so that when the quartz tube is placed vertically, the mixed powder of tellurium powder and cadmium powder is above the tellurium powder; C) vacuum welding the quartz tube and vertically placing it above a heating device that can move up and down; D) moving the heater upward from the bottom of the quartz tube for heating, and when the material in the quartz tube leaves the heating area, stopping heating and moving, and cooling to obtain cadmium telluride polycrystals. The present invention adopts a traveling heater method (THM), the material is fixed, and the heater is moved for heating. The method of the present invention can not only prepare cadmium telluride polycrystals at a temperature lower than the melting point of cadmium telluride, but also can directly prepare dense ingots of cadmium telluride polycrystals at this low temperature, without further heating to exceed the melting point of cadmium telluride to melt into ingots. The method of the present invention effectively controls the intensity of the reaction, reduces material loss caused by material splashing during synthesis, and improves product yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0021] Figure 1 Schematic diagram of a quartz tube filled with materials in Examples 1 to 3 of the present invention;

[0022] Figure 1 In the figure, 1 is a quartz tube, 2 is a sealing welding area, 3 is a quartz sealing bubble, 4 is a tellurium / cadmium mixed powder, and 5 is tellurium powder;

[0023] Figure 2 Schematic diagram of the positions of the quartz tube and the heater filled with materials in Examples 1 to 3 of the present invention;

[0024] Figure 2 In the figure, 6 is a heat insulating layer, 7 is a heat preservation material, 8 is a heating wire, and 6, 7 and 8 together constitute a heater;

[0025] Figure 3 Schematic diagram of the changes of materials in the quartz tube during the heating process in Examples 1 to 3 of the present invention;

[0026] Figure 3 In the figure, 4 is a tellurium / cadmium mixed powder, 9 is a loose cadmium telluride layer, 10 is a melting zone, and 11 is a cadmium telluride polycrystal;

[0027] Figure 4 The product taken out after the preparation in Examples 1 to 3 of the present invention;

[0028] Figure 4 In the figure, 11 is cadmium telluride polycrystal, and 12 is tellurium block;

[0029] Figure 5 Schematic diagram of the heating process in Comparative Examples 1 to 3 of the present invention;

[0030] Figure 5 In the figure, 4 is a tellurium / cadmium mixed powder;

[0031] Figure 6 Schematic diagram of a quartz tube filled with materials in Comparative Examples 4 to 6 of the present invention;

[0032] Figure 6 In the figure, 1 is a quartz tube, 2 is a sealing welding area, 3 is a quartz sealing bubble, and 4 is a tellurium / cadmium mixed powder;

[0033] Figure 7 Schematic diagram of the positions of the quartz tube and the heater filled with materials in Comparative Examples 4 to 6 of the present invention;

[0034] Figure 8 This is a schematic diagram of stopping heating in Comparative Examples 4 to 6 of the present invention;

[0035] Figure 7-8 In the figure, 6 is a heat insulating layer, 7 is a heat preservation material, 8 is a heating wire, and 6, 7 and 8 together constitute a heater. DETAILED DESCRIPTION

[0036] The present invention provides a method for preparing cadmium telluride polycrystal, comprising the following steps:

[0037] A) Tellurium powder is loaded at the bottom of the quartz tube;

[0038] B) loading the mixed powder of tellurium powder and cadmium powder into a quartz tube, contacting with the tellurium powder but not mixing, so that when the quartz tube is placed vertically, the mixed powder of tellurium powder and cadmium powder is above the tellurium powder;

[0039] C) A vacuum-sealed quartz tube is placed vertically above a heating device that can move up and down;

[0040] D) The heater is moved upward from the bottom of the quartz tube to heat. When the material in the quartz tube leaves the heating area, the heating and movement are stopped, and cadmium telluride polycrystals are obtained after cooling.

[0041] In the present invention, during the material filling process, the quartz tube is preferably placed vertically, and tellurium powder is first filled at the bottom of the quartz tube. The purity of the tellurium powder is preferably 5N, and the particle size of the tellurium powder is preferably 100-150 mesh, more preferably 120-140 mesh.

[0042] Then take tellurium powder and cadmium powder, mix them in a certain proportion, and fill the mixed powder into the above-mentioned quartz tube, so that it contacts the tellurium powder at the bottom of the quartz tube but does not mix. It is preferred to maintain a clear or relatively clear horizontal interface between the mixed powder and the tellurium powder, so that when the quartz tube is placed vertically, the mixed powder of tellurium powder and cadmium powder is above the tellurium powder.

[0043] In the present invention, in the mixed powder, the purity of tellurium powder is 5N, and the particle size is preferably 100-150 mesh, more preferably 120-140 mesh; the purity of cadmium powder is 5N, and the particle size is preferably 100-150 mesh, more preferably 120-140 mesh; the molar ratio of tellurium powder to cadmium powder in the mixed powder is preferably 1: (0.9-1.1), more preferably 1:1.

[0044] In the present invention, the mass of the tellurium powder at the bottom of the quartz tube is 15-25% of the mass of the mixed powder, and more preferably 18-22%, such as 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, preferably a range value with any of the above values ​​as the upper or lower limit.

[0045] After the quartz tube is filled with the above materials, the present invention places the quartz tube vertically above the heater, and after the heater is heated to a certain temperature, the quartz tube remains stationary, and the heater moves uniformly upward from the bottom of the quartz tube at a certain speed to heat.

[0046] During the movement of the heater, the tellurium powder at the bottom of the quartz tube first enters the high-temperature zone and is melted into liquid. Then the mixed powder gradually enters the high-temperature zone, reaches the reaction temperature, and reacts from bottom to top as the heater moves, generating loose and porous cadmium telluride and dissolving it into the tellurium solution below until it is saturated. As the heater moves, the saturated molten zone gradually exits the high-temperature zone, and cadmium telluride crystals will precipitate below the molten zone. Therefore, during the movement of the heater, the cadmium telluride that has reacted above the molten zone continues to dissolve into the molten zone, and cadmium telluride polycrystals continue to precipitate below the molten zone. The molten zone will continue to move upward with the heater, and eventually all cadmium telluride will precipitate to the bottom of the quartz tube, and the resulting product is a dense ingot with dense cadmium telluride polycrystals on the bottom and tellurium blocks on the top.

[0047] In the present invention, the heating rate of the heater is preferably 40~60℃ / hour, more preferably 45~55℃ / hour, and most preferably 50~55℃ / hour. The heating temperature is preferably 700~900℃, more preferably 700~800℃, such as 700℃, 750℃, 800℃, 850℃, 900℃, preferably a range value with any of the above values ​​as the upper or lower limit.

[0048] In the present invention, the movement rate of the heater is preferably 30~50 mm / day, more preferably 35~45 mm / day, such as 30 mm / day, 35 mm / day, 40 mm / day, 45 mm / day, 50 mm / day, preferably a range value with any of the above values ​​as the upper or lower limit; the movement time of the heater is not particularly limited, and is determined within the above-mentioned movement speed range according to the loading amount of tellurium powder and mixed powder.

[0049] After the material in the quartz tube leaves the heating area, the heating and movement are stopped, and the material in the quartz tube is cooled to room temperature and the product is taken out, which is a dense ingot with cadmium telluride polycrystal at the bottom and tellurium block at the top.

[0050] The present invention provides a method for preparing cadmium telluride polycrystals, comprising the following steps: A) filling tellurium powder at the bottom of a quartz tube; B) filling a mixed powder of tellurium powder and cadmium powder into the quartz tube, contacting with the tellurium powder but not mixing, so that when the quartz tube is placed vertically, the mixed powder of tellurium powder and cadmium powder is above the tellurium powder; C) vacuum welding the quartz tube and vertically placing it above a heating device that can move up and down; D) moving the heater upward from the bottom of the quartz tube for heating, and when the material in the quartz tube leaves the heating area, stopping heating and moving, and cooling to obtain cadmium telluride polycrystals. The present invention adopts the THM method, the material is fixed, and the heater is moved for heating. The method of the present invention can not only prepare cadmium telluride polycrystals at a temperature lower than the melting point of cadmium telluride, but also can directly prepare dense ingots of cadmium telluride polycrystals at this low temperature, without further heating to exceed the melting point of cadmium telluride to melt into ingots. The method of the present invention effectively controls the intensity of the reaction, reduces the material loss caused by material splashing during synthesis, and improves the product yield.

[0051] In order to further illustrate the present invention, a method for preparing cadmium telluride polycrystal provided by the present invention is described in detail below in conjunction with examples, but it should not be understood as limiting the protection scope of the present invention.

[0052] Embodiment 1~3

[0053] 1. Take Z (g) 5N tellurium powder and put it at the bottom of the furnace quartz tube.

[0054] 2. Take X (g) 5N tellurium powder and Y (g) 5N cadmium powder respectively, mix them in a molar ratio of 1:1, and put them into a quartz tube (to the top of the tellurium powder).

[0055] 3. Vacuum seal the quartz tube. Figure 1 .

[0056] 4. Install the quartz tube on the heating furnace that can move up and down, so that the bottom of the quartz tube is S (mm) above the furnace mouth. Figure 2 .

[0057] 5. Raise the temperature of the heater to T (°C) at a rate of 50°C / h.

[0058] 6. The heater moves upward at a speed of V (mm / d), and the quartz tube remains stationary, e.g. Figure 3 . The total moving time is t(d).

[0059] 7. Stop moving, turn off heating, and take out the product after it drops to room temperature. Figure 4 As shown. Remove the top tellurium block to obtain a cadmium telluride polycrystalline rod, weighing the mass Q (g) and the yield P (%). Here, the yield P (%) = Q / M × 100%, where M is the mass of the mixed powder of tellurium and cadmium.

[0060] The process parameters and yields in Examples 1 to 3 are shown in Table 1.

[0061] Table 1 Process parameters and yields in Examples 1 to 3

[0062]

[0063] Comparative Examples 1-3 (directly synthesized at high temperature and then melted into ingots)

[0064] 1. Take X (g) 5N tellurium powder and Y (g) 5N cadmium powder respectively, mix them in a molar ratio of 1:1, and put them into a quartz tube.

[0065] 2. Vacuum seal the quartz tube.

[0066] 3. Install the quartz tube into the heating furnace so that the material can completely enter the heating zone. Figure 5 .

[0067] 4. Heat the heater to 300°C at a rate of 50°C / h and keep it warm for 2 hours; then heat to 500°C at 20°C / h and keep it warm for 6 hours; heat to 1130°C at 50°C / h and keep it warm for 6 hours.

[0068] 5. Turn off the heating and take out the product after it cools down to room temperature. The weighed mass is Q (g) and the yield is P (%). Here, the yield P (%) = Q / M × 100%, where M is the mass of the mixed powder of tellurium and cadmium.

[0069] The process parameters and yields in Comparative Examples 1 to 3 are shown in Table 2.

[0070] Table 2 Process parameters and yields in Comparative Examples 1 to 3

[0071]

[0072] In Examples 1 to 3, the temperature throughout the process was only 700 to 900°C, and the material reactions were orderly and controllable, without causing material splashing, and no tube cracking or explosion, and the product yield was greater than 98%. In Comparative Examples 1 to 3, direct high-temperature synthesis was used, and then the temperature was increased to melt the synthetic material into an ingot, and the highest temperature needed to be above the melting point of cadmium telluride. In Comparative Example 1, due to excessive material, a cracked tube was found after the temperature was raised to the highest temperature and maintained for 32 minutes, and the material was scrapped. In Comparative Examples 2 and 3, during the material reaction, there was varying degrees of material splashing and sticking to the quartz tube wall, reducing the product yield. Therefore, the cadmium telluride polycrystalline preparation method provided by the present invention can effectively improve product yield and production safety.

[0073] Comparative Examples 4 to 6 (without pure tellurium powder)

[0074] 1. Take X (g) 5N tellurium powder and Y (g) 5N cadmium powder respectively, mix them in a molar ratio of 1:1, and put them into a quartz tube.

[0075] 2. Vacuum seal the quartz tube. Figure 6 .

[0076] 3. Install the quartz tube on a heating furnace that can move up and down, so that the bottom of the quartz tube is 100 (mm) above the furnace mouth. Figure 7 .

[0077] 4. Raise the temperature of the heater to T (°C) at a rate of 50°C / h.

[0078] 5. The heater moves upward at a speed of 30 (mm / d), and the quartz tube remains stationary until all the materials exit from the bottom of the heater, then the heater stops moving. Figure 8 .

[0079] 6. Stop moving, turn off heating, and take out the product after it drops to room temperature. Remove the top tellurium block to obtain a cadmium telluride polycrystalline rod, weighing the mass Q (g) and the yield P (%). Here, the yield P (%) = Q / M × 100%, where M is the mass of the mixed powder of tellurium and cadmium.

[0080] The process parameters and yields in Comparative Examples 4 to 6 are shown in Table 3.

[0081] Table 3 Process parameters and yields in Comparative Examples 4 to 6

[0082]

[0083] In Comparative Example 4, although the mixed powder can be synthesized at 700°C, the cadmium telluride formed is in a loose state, not a dense ingot, and part of the material adheres to the quartz tube wall, resulting in a low yield. In Comparative Examples 5 and 6, the temperature is increased to 1130 to ensure that the mixed powder can be melted into a liquid after the reaction and finally solidified into a dense ingot. However, during the process, due to the high temperature, the tube cracked in Comparative Example 6, resulting in the outflow of materials and scrapping, with a yield of 0%. The experimental results of Comparative Examples 4 to 6 and Examples 1 to 3 show that the method of using a tellurium melting zone to achieve mass transfer can achieve low-temperature production of cadmium telluride ingots, effectively improving production safety.

[0084] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing cadmium telluride polycrystal, comprising the following steps: A) Tellurium powder is loaded at the bottom of the quartz tube; B) filling a mixed powder of tellurium powder and cadmium powder into a quartz tube, contacting the tellurium powder but not mixing it, so that when the quartz tube is placed vertically, the mixed powder of tellurium powder and cadmium powder is above the tellurium powder; C) A vacuum-sealed quartz tube is placed vertically above a heating device that can move up and down; D) The heater is moved upward from the bottom of the quartz tube to heat. When the material in the quartz tube leaves the heating area, the heating and movement are stopped, and cadmium telluride polycrystals are obtained after cooling.

2. The preparation method according to claim 1, characterized in that: The tellurium powder in step A) has a purity of 5N and a particle size of 100-150 meshes.

3. The preparation method according to claim 1, characterized in that: The purity of the tellurium powder in step B) is 5N, and the particle size is 100-150 mesh.

4. The preparation method according to claim 1, characterized in that: The purity of the cadmium powder in step B) is 5N, and the particle size is 100-150 meshes.

5. The preparation method according to claim 1, characterized in that: In the step B), the molar ratio of tellurium powder to cadmium powder is 1:(0.9-1.1).

6. The preparation method according to claim 4, characterized in that: In the step B), the molar ratio of tellurium powder to cadmium powder is 1:

1.

7. The preparation method according to claim 1, characterized in that: The mass of the tellurium powder in step A) is 15-25% of the mass of the mixed powder of tellurium powder and cadmium powder in step B).

8. The preparation method according to claim 1, characterized in that: In the step D), the heater is first heated to 700-900° C., and then the heater is moved upward from the bottom of the quartz tube.

9. The preparation method according to claim 8, characterized in that: The heating rate of the heater is 40-60°C / hour.

10. The preparation method according to claim 8, characterized in that: The speed at which the heater moves is 30-50 mm / day.

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