A method for growing a cadmium zinc telluride crystal

Abstract

The application provides a growth method of a cadmium zinc telluride crystal, which comprises the following steps: placing a quartz crucible filled with materials in a pulling furnace, melting the materials to obtain a mixed melt of tellurium, zinc and cadmium, contacting a cadmium zinc telluride seed crystal with the mixed melt, and pulling up to grow a cadmium zinc telluride single crystal. The method can obtain a cadmium zinc telluride single crystal with low dislocation, high single crystal ratio, small double crystal diffraction half-peak width, few micro-precipitation phases, high resistivity, small dislocation etching pit density and small leakage current.

Description

Technical Field

[0001] This invention belongs to the field of crystal growth technology, and particularly relates to a method for growing cadmium zinc telluride crystals. Background Technology

[0002] With the advancement and development of science and technology, more and more semiconductor crystals are receiving increasing attention due to their prominent role in optoelectronic systems.

[0003] Among these semiconductor materials, high-resistivity cadmium zinc telluride (Cd) 0.9 Zn 0.1 Te (Te) crystal materials have attracted considerable attention. X-ray and gamma-ray detectors made from cadmium zinc telluride (CdT) crystals can operate at room temperature and maintain low leakage current even under high bias voltages, thereby reducing detector noise and improving energy resolution. They are widely used in X-ray fluorescence analysis, medical imaging, security detection, and industrial online monitoring. Obtaining crystals with good crystal quality and high resistivity is crucial for manufacturing high-performance detectors. However, CdT has a melting point of around 1100℃. During the traditional VB or VGF melt growth method, the vapor pressure of cadmium is very high, causing some cadmium to volatilize from the melt, resulting in a large number of cadmium vacancies and Te precipitation in the crystal, disrupting the crystal's stoichiometry. Simultaneously, high-temperature crystal growth inevitably leads to crucible contamination, introducing many impurities. Furthermore, high-temperature CdT crystal growth introduces numerous defects such as dislocations, which severely affect the detection performance of CdT crystals. When preparing cadmium zinc telluride crystals using the Czochralski method, similar problems exist as with traditional VB and VGF methods. Therefore, it is necessary to design a new crystal growth method. Summary of the Invention

[0004] To address the above problems, this invention provides a novel method for growing zinc cadmium telluride crystals.

[0005] To address the problems existing in the prior art, the present invention provides the following technical solution:

[0006] A method for growing cadmium zinc telluride crystals, comprising:

[0007] The quartz crucible containing the raw materials is placed in a Czochralski furnace. The raw materials are melted to obtain a mixed melt of tellurium, zinc and cadmium. The molar ratio of tellurium, zinc and cadmium in the mixed melt is 25-90:1:9. Tellurium zinc cadmium seed crystals are brought into contact with the melt and pulled upwards to grow tellurium zinc cadmium single crystals.

[0008] The chemical formula of the cadmium zinc telluride crystal is Cd. 0.9 Zn 0.1 Te.

[0009] The applicant discovered in the research that when preparing cadmium zinc telluride crystals by the pull method, using a quartz crucible as a container and not following the stoichiometric ratio of the crystals, but instead significantly increasing the amount of tellurium as a solvent, can lower the crystal growth temperature, thereby reducing the volatilization of cadmium, which in turn reduces the generation of defects such as stress and vacancies, and also reduces the erosion and contamination of the crucible by the melt.

[0010] As a further improvement of the present invention, the quartz crucible is a carbon-plated quartz crucible. The carbon-plated quartz crucible can prevent direct contact between the tellurium, zinc, and cadmium melts and the quartz, thus preventing contamination of the raw materials by the quartz crucible.

[0011] As a further improvement of the present invention, the zinc cadmium telluride seed crystal is a single crystal of zinc cadmium telluride with a

[111] orientation. Research has shown that a

[111] oriented seed crystal can effectively reduce the generation of twins, which is beneficial to improving the crystal yield.

[0012] As a further improvement of the present invention, the molar ratio of tellurium, zinc, and cadmium in the mixed melt is 60-90:1:9. During crystal growth, the temperature needs to be lowered to the crystallization temperature of the melt. After the tellurium-zinc-cadmium melt in the melt reaches saturation, it begins to precipitate at the seed crystal and grows into a tellurium-zinc-cadmium single crystal. Excessive tellurium content will lead to waste of high-purity raw materials, while excessively low tellurium content will cause the crystal growth temperature to rise, increasing the number of dislocations in the crystal.

[0013] As a further improvement of the present invention, the growth of the single crystal is completed in a hydrogen atmosphere. The hydrogen atmosphere can react with the oxygen introduced by the raw materials, avoiding excessive oxygen content in the melt, which would prevent crystal growth from proceeding.

[0014] As a further improvement of the present invention, the pulling rate of the single crystal is 0.1-2 mm / h, more preferably 0.2-1 mm / h. A pulling rate that is too slow will severely affect the yield, while a pulling rate that is too fast will lead to an increase in crystal dislocations.

[0015] As a further improvement of the present invention, the pulling method employs rotation, wherein the rotation is both forward and reverse, with a rotation speed of 5-20 rpm and a plateau time of 10-30 s. When the crystal is not rotated, it grows freely, making it impossible to obtain a wafer-like crystal, thus reducing crystal utilization. When the crystal rotates in a single direction or at high speed, concave interfaces are prone to appear, leading to an increase in tellurium inclusions in the crystal. If the crystal rotation speed is too low, the crystal interface becomes too convex, causing serious defects. If the plateau time is too short, melt convection becomes chaotic; if the plateau time is too long, the forward and reverse scouring effect is reduced, both of which will affect crystal performance.

[0016] As a further improvement of the present invention, the shoulder angle of the crystal is 30-60°. An excessively large shoulder angle causes the crystal to develop shoulders too quickly, increasing the number of dislocations in the crystal, while an excessively small shoulder angle results in material waste.

[0017] Furthermore, the crystal-driving temperature is 680-920℃.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This method can obtain low-dislocation zinc-cadmium telluride single crystals with a high single crystal ratio, small half-width of bicrystalline diffraction peaks, fewer micro-precipitates, higher resistivity, lower dislocation corrosion pit density, and lower leakage current. Detailed Implementation

[0020] A method for growing cadmium zinc telluride crystals, comprising:

[0021] The quartz crucible containing the raw materials is placed in a Czochralski furnace. The raw materials are melted to obtain a mixed melt of tellurium, zinc and cadmium. The molar ratio of tellurium, zinc and cadmium in the mixed melt is 25-90:1:9. Tellurium zinc cadmium seed crystals are brought into contact with the melt and pulled upwards to grow tellurium zinc cadmium single crystals.

[0022] In some preferred examples, the quartz crucible is a carbon-coated quartz crucible.

[0023] In some preferred examples, the cadmium zinc telluride seed crystal is a single crystal of cadmium zinc telluride with the orientation

[111] .

[0024] In some preferred examples, the molar ratio of tellurium, zinc, and cadmium in the mixed melt is 60-90:1:9.

[0025] In some preferred examples, crystal growth is carried out in a hydrogen atmosphere.

[0026] In some preferred examples, the crystal pulling rate is 0.1-2 mm / h.

[0027] In some preferred examples, the crystal is rotated in both forward and reverse directions, with a rotation speed of 5-20 rpm, more preferably 5-10 rpm, and a plateau time of 10-30 s, more preferably 15-30 s.

[0028] In some preferred examples, the crystal shoulder angle is 30-60°.

[0029] In some preferred examples, the seeding temperature is 680-920°C.

[0030] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0031] Example 1

[0032] The quartz crucible containing the raw materials was placed in a Czochralski furnace. In a hydrogen atmosphere, the raw materials were melted to obtain a mixed melt of tellurium, zinc, and cadmium in a molar ratio of 90:1:9. The seeding temperature was controlled at 680°C according to conventional methods. A tellurium-zinc-cadmium seed crystal with a seed crystal orientation of

[111] was brought into contact with the melt, and the crystal was rotated upwards and pulled to grow tellurium-zinc-cadmium (Cd).0.9 Zn 0.1 Te single crystal, rotating in both forward and reverse directions at a speed of 5 rpm, with a plateau time of 30 s, a pulling rate of 0.2 mm / h, and a shoulder angle of 30°. The seeding temperature T can be obtained from the following formula:

[0033] T = 500 + 2000x - 2000x 2 (1),

[0034] Where x is the molar ratio of Te in the ingredients.

[0035] The cooling rate v during crystal growth is conventionally controlled, and its calculation formula is as follows:

[0036]

[0037] Where x1 is the initial molar ratio of Te, w is the real-time weight of the crystal, and a is the initial total number of moles of the raw materials, derived from the following formula:

[0038]

[0039] Where w1 is the initial total weight of the ingredients.

[0040] The growth method of zinc cadmium telluride crystals in Examples 2-27 is similar to that in Example 1, except that the process parameters are different. See Table 1 for details. The cooling rate is controlled according to formulas (2) and (3). In addition, since the mixed melt composition is different in some examples, the suitable crystal-initiating temperature is different. The crystal-initiating temperature in Examples 5-7 is 920°C, the crystal-initiating temperature in Example 8 is 745°C, the crystal-initiating temperature in Example 9 is 665°C, and the crystal-initiating temperature in Example 10 is 945°C.

[0041] The single-crystal ratio and other performance parameters of the cadmium zinc telluride crystals prepared in each embodiment were measured, specifically including:

[0042] Measurement of single crystal ratio: The weight of single crystals that can be used after crystal growth is completed is divided by the amount of charge.

[0043] Measurements of double-crystal diffraction half-width, microprecipitate phase, resistivity, dislocation corrosion pit density, and leakage current: Refer to "GBT39123-2020 Specification for Cadmium Zinc Telluride Single Crystal Materials for X-ray and Gamma Ray Detectors".

[0044] The process parameters and measured characterization parameters of Examples 1-27 are shown in Table 1.

[0045] Table 1. Process parameters and crystal material characterization data for Examples 1-27

[0046]

[0047]

[0048]

[0049] Examples 1-4 show that, compared to quartz crucibles, carbon-plated quartz crucibles, graphite crucibles, and pBN crucibles, carbon-plated quartz crucibles exhibit the highest single-crystal ratio, the smallest half-width at half-maximum (WHM) of twin-crystal diffraction, the fewest micro-precipitates, the highest resistivity, the lowest dislocation pit density, and the lowest leakage current. This demonstrates that carbon-plated quartz crucibles are the preferred crucible type and play a positive role in improving the quality of cadmium zinc telluride crystals.

[0050] As can be seen from Examples 2 and 5-7, when growing crystals in

[111] ,

[100] , arbitrary seed crystal direction and polycrystalline seed crystal, the crystal grown by

[111] seed crystal has better performance in terms of single crystal ratio, double crystal diffraction half-peak width, micro precipitate phase, resistivity, dislocation corrosion pit density and leakage current than other methods.

[0051] As can be seen from Examples 2 and 8-10, when the molar ratio of tellurium, zinc and cadmium in the melt is 90:1:9-25:1:9, the crystal has better quality.

[0052] As can be seen from Examples 2 and 11-12, when crystals are grown in a hydrogen atmosphere, the crystals exhibit superior performance in terms of single-crystal ratio, double-crystal diffraction half-width, micro-precipitate phase, resistivity, dislocation corrosion pit density, and leakage current compared to other methods.

[0053] As can be seen from Examples 2 and 13-16, when the crystal pulling rate is 0.1-2 mm / h, the crystal has good quality.

[0054] As can be seen from Examples 2 and 17-23, when the crystal is rotated in both forward and reverse directions, with a rotation speed of 5-20 rpm and a plateau time of 10-30 s, the crystal has good quality.

[0055] As can be seen from Examples 2 and 24-27, when the shoulder angle of the crystal is 30-60°, the crystal has better quality.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for growing cadmium zinc telluride crystals, characterized in that, include: The quartz crucible containing the charge is placed in a Czochralski furnace. The raw materials are melted to obtain a mixed melt of tellurium, zinc, and cadmium. The molar ratio of tellurium, zinc, and cadmium in the mixed melt is 25-90:1:

9. A tellurium-zinc-cadmium seed crystal is brought into contact with the mixed melt, and a tellurium-zinc-cadmium single crystal is grown by pulling upwards. The tellurium-zinc-cadmium seed crystal is a tellurium-zinc-cadmium single crystal with an orientation of [111]. The quartz crucible is a carbon-plated quartz crucible. The pulling is carried out by a rotational pulling method, and the rotation is both forward and reverse, with a rotation speed of 5-20 rpm and a plateau time of 10-30 s. The crystal-guiding temperature is 680-920℃, and the shoulder angle of the crystal is 30-60°.

2. The method for growing cadmium zinc telluride crystals as described in claim 1, characterized in that, The molar ratio of tellurium, zinc, and cadmium in the mixed melt is 60-90:1:

9.

3. The method for growing cadmium zinc telluride crystals as described in claim 1, characterized in that, The growth of the single crystal was completed in a hydrogen atmosphere.

4. The method for growing cadmium zinc telluride crystals as described in claim 1, characterized in that, The pulling rate of the single crystal is 0.1-2 mm / h.

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