Method and device for growing cadmium zinc telluride single crystal

Abstract

The invention discloses a method and a device for growing a cadmium zinc telluride single crystal, and is characterized in that the method comprises the following steps: (1) putting a cadmium zinc telluride polycrystal ingot into a pyrolytic boron nitride crucible, the cadmium zinc telluride polycrystal ingot is obtained by a preset temperature gradient synthesis method, and has [111] crystal orientation cluster crystal grains in the growth direction; (2) putting the pyrolytic boron nitride crucible into a vacuum closed quartz container, controlling a six-temperature-zone growth furnace through a computer to complete the melting process of a polycrystalline material, and before formal growth, forming a solid-liquid interface distribution structure in which polycrystals are not melted and the rest parts are completely melted at the center of the bottom, wherein the diameter of the solid-liquid interface distribution structure is not less than 30mm; (3) after heat preservation is conducted for a preset time, two-step cooling is achieved in a VGF mode; in the first cooling stage, an initial temperature gradient is formed, and after heat preservation is conducted for a preset time, elimination, merging and growth of [111] crystal nuclei are completed; in the second cooling stage, stable and continuous propulsion of a solid-liquid interface is completed, and continuous growth of single crystals is achieved; and finally, cooling to room temperature to obtain the cadmium zinc telluride single crystal. According to the method, the effect of growing the cadmium zinc telluride crystal with high single crystal rate under the seed crystal-free condition is realized.

Description

Technical Field

[0001] The invention relates to a method and a device for growing cadmium zinc telluride crystals. Technical Background

[0002] Cadmium zinc telluride material is an important semiconductor material. It can be used as a substrate for mercury cadmium telluride epitaxial materials to prepare and produce high-performance infrared focal plane detectors, and can also be directly used to prepare and produce high-energy ray detectors that sense gamma rays. Currently, these two types of detectors have been widely used in aerospace remote sensing, medical equipment, security inspection and military equipment. Compared with widely used Si materials and GaAs materials, the defect formation energy of CdZnTe materials is very low, and the thermal conductivity is very low. The grown CdZnTe ingots are very easy to produce polycrystalline and twinned.

[0003] In the existing technology, there are three mainstream methods for growing CdZnTe single crystals, namely vertical Bridgman method (VB), vertical gradient solidification method (VGF) and moving heater method (THM). However, these methods are highly dependent on seed crystals and have the following problems:

[0004] 1. In the actual process of using seed crystal technology to grow crystals, due to the extremely low thermal conductivity of CdZnTe, latent heat of crystallization will be released when CdZnTe crystals are generated. If there is no heat dissipation channel for the latent heat, the interface will become unstable, thereby disrupting the directional growth of the crystal. Moreover, in the process of CdZnTe growth, fine

[111] crystal-oriented seed crystals are difficult to play a seeding role, while equal-diameter coarse

[111] oriented seed crystals are difficult to obtain and are costly.

[0005] 2. The cutting surface of the CdZnTe crystal used as the substrate must be (111) or (211). Due to the existence of twins, the cutting surface and the growth plane are also likely to be at a certain angle, resulting in spatial distribution differences due to the sequential condensation of Zn in the cut wafer, making it difficult to meet the uniformity requirements of large-array HgCdTe infrared detectors.

[0006] 3. Oriented seed crystals are used to provide nucleation in the initial stage. However, due to the large difference between the Zn component of the seed crystal and the component of the melt to be grown, it cannot always be guaranteed that the crystal will grow smoothly from the seed crystal. At the same time, the processing of the seed crystal will also introduce impurities and then introduce defects in the crystal.

[0007] The inventors have found that by optimizing the polycrystalline synthesis technology to generate more

[111] grains in the polycrystalline, combined with a specific growth temperature field distribution, it is possible to achieve directional growth of CdZnTe single crystals along the

[111] direction during the crystal growth process. Therefore, the present invention provides a method and device for growing CdZnTe single crystals to solve the problems of difficult welding of seed crystals and difficult control of crystal orientation in CdZnTe crystals during traditional crystal growth, thereby directional growth of large-sized CdZnTe crystals. Summary of the invention

[0008] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a method and device for growing a cadmium zinc telluride single crystal, aiming to solve the problem that the seed crystal is difficult to weld and the crystal orientation of the large-sized cadmium zinc telluride crystal grown is difficult to control. The purpose of the present invention is achieved by the following technical solution:

[0009] A method for growing a cadmium zinc telluride single crystal, characterized in that the method comprises the following steps:

[0010] (1) placing a cadmium zinc telluride polycrystalline ingot into a pyrolytic boron nitride crucible, wherein the cadmium zinc telluride polycrystalline ingot is obtained by a preset temperature gradient synthesis method and has clustered grains with a

[111] crystal orientation in the growth direction;

[0011] (2) placing the pyrolytic boron nitride crucible into a vacuum-sealed quartz container, and completing the melting process of the polycrystalline material by controlling the six-temperature zone growth furnace through a computer, so that before the formal growth, a solid-liquid interface distribution structure is formed in which the polycrystalline with a diameter of not less than 30 mm is not melted in the center of the bottom, and the rest of the polycrystalline is completely melted;

[0012] (3) After the preset holding time, the VGF method is used to achieve two-step cooling;

[0013] Specifically, in the cooling stage 1, an initial temperature gradient is formed, and after being kept warm for a preset time, the elimination, annealing and growth of the

[111] crystal nuclei are completed; in the cooling stage 2, under the preset temperature field distribution, the solid-liquid interface is steadily and continuously advanced to achieve continuous growth of the single crystal; finally, the temperature is cooled to room temperature to obtain a cadmium zinc telluride single crystal.

[0014] Furthermore, in step (1), the preset temperature gradient range is 10°C / mm to 50°C / mm.

[0015] Furthermore, in step (2), the preset temperature field distribution is as follows: the center temperature of the bottom of the PBN crucible is 1070°C-1080°C, the side wall temperature of the bottom of the PBN crucible is 1092°C-1098°C, and the side wall temperature of the tail of the PBN crucible is 1105°C-1120°C.

[0016] Furthermore, in step (3), the holding time of the first cooling stage is 10-20 hours, and the solid-liquid interface movement speed of the second cooling stage is 0.1-1 mm / h.

[0017] In addition, a growth device using the above growth method is designed, characterized in that the device includes a six-temperature zone segmented heating furnace (1), a quartz ampoule (2), a thermocouple (3), a thermocouple (4), a thermocouple (5), a silicon carbide thermal conductive structure (6), an alumina furnace (7), and a pyrolytic boron nitride crucible (8), wherein the pyrolytic boron nitride crucible serves as a container, has a height of 70-180 mm, a diameter of 90 mm-130 mm, and an angle between the side walls of the crucible of 1-15°.

[0018] Furthermore, hot-pressed sintered silicon carbide is used as a supporting heat-conducting rod, the supporting heat-conducting rod has a diameter of 20mm-40mm and a length of 300mm-600mm, and a 3-10mm channel is provided in the middle to place a thermocouple. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the crystal growth heating furnace and quartz ampoule structure used in the present invention.

[0020] In the figure, the parts represented by the reference numerals are: six-temperature zone segmented heating furnace (1), quartz ampoule (2), thermocouple (3), thermocouple (4), thermocouple (5), silicon carbide heat conducting structure (6), alumina furnace (7), pyrolytic boron nitride crucible (8), cadmium zinc telluride melt (9)

[0021] Figure 2 It is a schematic diagram of the temperature field distribution during the crystal growth process of the present invention.

[0022] In the figure: A, B, and C are the three temperature control points of the melt.

[0023] Figure 3 Schematic diagram of a pyrolytic boron nitride crucible containing crystals used in the present invention. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0025] Embodiment 1:

[0026] 1. Place high-purity 7N cadmium rod, 7N tellurium block and 7N zinc rod into the carbon-fumed synthesis crucible according to the required stoichiometric ratio of tellurium, zinc and cadmium.

[0027] ①Put the synthetic crucible into the degassing device, heat and evacuate the vacuum to 1*10 -6 Pa, and then seal it with hydrogen-oxygen flame.

[0028] ②Put the sealed synthesis crucible into the synthesis furnace and set the process parameters as follows:

[0029] The high temperature zone was heated to above 480°C over 4 hours, the gradient was maintained at 15°C / mm, and the temperature was kept for 2 hours. The temperature was then raised to above 1120°C, shaken for 20 minutes, and kept for 20 hours, and then cooled to room temperature at a rate of 50°C / h.

[0030] ③ Place the synthesized zinc-cadmium polycrystalline material in a boron nitride crucible, ensuring that the first solidified low-temperature end containing more

[111] grains is placed at the bottom, and then place the pyrolytic boron nitride crucible into a high-purity quartz ampoule and evacuate it again to 1*10 - 6 Pa, seal with hydrogen-oxygen flame.

[0031] ④Put the sealed quartz ampoule into a six-temperature zone single crystal growth furnace and heat it to melt. Then cool down and grow in two stages. First, in the cooling stage 1, an initial temperature gradient of about 0.2℃ / mm is formed in the melt, and the temperature is kept for 10 hours to complete the elimination, annealing and growth of the crystal nucleus. Secondly, in the cooling stage 2, a specific temperature distribution is used to complete the stable and continuous advancement of the solid-liquid interface and realize the continuous growth of the single crystal. Finally, it is cooled to room temperature to obtain a cadmium zinc telluride single crystal. Among them, the temperature control of each position of the crucible is as follows:

[0032] A: 1070°C, B: 1096°C, C: 1116°C, and the growth rate is controlled to be 0.5 mm / h. The maximum diameter of the upper part of the crystal material (9) in the pyrolytic boron nitride crucible used is φ100 mm, the crystal length is 100 mm, and the angle of the crucible side wall is 10°.

[0033] Embodiment 2:

[0034] 1. Place high-purity 7N cadmium rod, 7N tellurium block and 7N zinc rod into the carbon-fumed synthesis crucible according to the required stoichiometric ratio of tellurium, zinc and cadmium.

[0035] ①Put the quartz crucible in the degassing device, heat and evacuate it to 1*10 -6 Pa, and then seal it with hydrogen-oxygen flame.

[0036] ②Put the sealed synthesis crucible into the synthesis furnace and set the process parameters as follows:

[0037] The high temperature zone was heated to above 490°C over 4 hours, the gradient was maintained at 20°C / mm, and the temperature was kept for 2 hours. The temperature was then raised to above 1120°C, shaken for 20 minutes, and kept for 20 hours, and then cooled to room temperature at a rate of 50°C / h.

[0038] ③ Place the synthesized zinc-cadmium polycrystalline material in a boron nitride crucible, ensure that the first solidified low-temperature end containing more

[111] grains is placed at the bottom, then place the pyrolytic boron nitride crucible into a high-purity quartz crucible and evacuate it again by 1*10 -6 Pa, seal with hydrogen-oxygen flame.

[0039] ④Put the sealed quartz crucible into a six-temperature zone single crystal growth furnace and heat it to melt. Then cool down and grow in two stages. First, in the cooling stage 1, an initial temperature gradient of about 0.18℃ / mm is formed in the melt, and the temperature is kept for 15 hours to complete the elimination, annealing and growth of the crystal nucleus. Secondly, in the cooling stage 2, a specific temperature distribution is used to complete the stable and continuous advancement of the solid-liquid interface and realize the continuous growth of the single crystal. Finally, it is cooled to room temperature to obtain a cadmium zinc telluride single crystal. Among them, the temperature control of each position of the crucible is as follows:

[0040] A: 1080°C, B: 1098°C, C: 1120°C, and the growth rate is controlled to be 0.5 mm / h. The maximum diameter of the upper part of the crystal material (9) in the pyrolytic boron nitride crucible used is φ125 mm, the crystal length is 120 mm, and the angle of the crucible side wall is 15°.

[0041] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A method for growing a cadmium zinc telluride single crystal, characterized in that: The method comprises the following steps: (1) placing a cadmium zinc telluride polycrystalline ingot into a pyrolytic boron nitride crucible, wherein the cadmium zinc telluride polycrystalline ingot is obtained by a preset temperature gradient synthesis method and has clustered grains with a [111] crystal orientation in the growth direction; (2) placing the pyrolytic boron nitride crucible into a vacuum-sealed quartz container, and completing the melting process of the polycrystalline material by controlling the six-temperature zone growth furnace through a computer, so that before the formal growth, a solid-liquid interface distribution structure is formed in which the polycrystalline with a diameter of not less than 30 mm is not melted in the center of the bottom, and the rest of the polycrystalline is completely melted; (3) After the preset holding time, the VGF method is used to achieve two-step cooling; Specifically, in the cooling stage 1, an initial temperature gradient is formed, and after being kept warm for a preset time, the elimination, annealing and growth of the [111] crystal nuclei are completed; in the cooling stage 2, under the preset temperature field distribution, the solid-liquid interface is steadily and continuously advanced to achieve continuous growth of the single crystal; finally, the temperature is cooled to room temperature to obtain a cadmium zinc telluride single crystal.

2. The method according to claim 1, characterized in that In step (1), the preset temperature gradient range is 10°C / mm to 50°C / mm.

3. The method according to claim 1, characterized in that The preset temperature field distribution is as follows: the center of the bottom of the PBN crucible is 1070°C-1080°C, the side wall of the bottom of the PBN crucible is 1092°C-1098°C, and the side wall of the tail of the PBN crucible is 1105°C-1120°C.

4. The method according to claim 1, characterized in that: The holding time of the first cooling stage in step (3) is 10-20 hours, and the solid-liquid interface moving speed of the second cooling stage is 0.1-1 mm / h.

5. A growth device using the growth method according to claim 1, characterized in that: The device comprises a six-temperature zone segmented heating furnace (1), a quartz ampoule (2), a thermocouple (3), a thermocouple (4), a thermocouple (5), a silicon carbide heat conducting structure (6), an alumina furnace (7), and a pyrolytic boron nitride crucible (8), wherein the pyrolytic boron nitride crucible is used as a container, and has a height of 70-180 mm and a diameter of 90 mm-130 mm. The angle between the side walls of the crucible is 1-15°.

6. The growth device according to claim 4, characterized in that: Hot-pressed sintered silicon carbide is used as the supporting heat-conducting rod. The diameter of the supporting heat-conducting rod is 20mm-40mm, the length is 300mm-600mm, and a 3-10mm channel is set in the middle to place the thermocouple.

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