Gas phase annealing method of tellurium-zinc-cadmium crystal

Abstract

The invention relates to a gas phase annealing method of a cadmium zinc telluride crystal. The gas phase annealing method comprises the following steps: S1, detecting the type and the defect concentration of point defects in the cadmium zinc telluride crystal; s2, determining a corresponding gas phase source for annealing regulation and control according to a point defect detection result; s3, preparing a gas phase source film on the quartz plate through physical vapor deposition; s4, confirming the gas phase source gas pressure of annealing; and S5, respectively packaging the tellurium-zinc-cadmium wafer and the quartz plate deposited with the gas-phase source film at two ends of an annealing quartz tube, then placing the annealing quartz tube in an annealing furnace, respectively heating the two ends of the annealing quartz tube, and finally obtaining the CdZnTe crystal modified by gas-phase annealing. Compared with the prior art, the method has the advantages that the variety and content of the gas phase source can be regulated and controlled, and finally the tellurium-zinc-cadmium crystal of which the internal defects are remarkably reduced and the electrical property of the crystal is remarkably improved is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of cadmium zinc telluride crystals, and in particular relates to a vapor phase annealing method of cadmium zinc telluride crystals. Background Art

[0002] Radiation detectors operating at room temperature need to have excellent energy resolution, and the compound semiconductor materials used to make the detectors need to have high purity and crystal structure integrity to ensure that the detectors have high charge collection efficiency, and the detectors need to have good energy resolution. CdTe-based II-VI compound semiconductors are semiconductor materials used in many important scenarios, among which cadmium zinc telluride crystals (CdZnTe crystals, CZT) perform well in detecting gamma rays and other forms of radiation, especially in improving the accuracy of radiation detection. It has a wide range of applications in nuclear medical imaging, X-ray detectors, space telescopes, nuclear science and technology, space astronomical observations, security inspections and other fields.

[0003] However, point defects may be introduced into CdZnTe crystals during their growth, resulting in missing or excess atoms or ions in the crystal structure, forming point defects such as Cd vacancies and impurities. Failure to eliminate these defects will reduce the quality of the crystal, thereby reducing the crystal resistivity, increasing the dark current of the detector, and ultimately affecting the electrical and optical properties of the detector. Therefore, in order to meet the preparation requirements of room temperature radiation detectors, the grown crystals need to be subsequently processed to remove harmful defects and adjust the concentration of various defects in the crystals to improve the performance of the crystals.

[0004] Annealing modification of semiconductor materials is considered to be an effective method to improve crystal quality and detector performance. In recent years, there have been many studies on methods to improve the performance of cadmium zinc telluride annealing. Vapor phase annealing is the main method to improve crystal quality and device performance. However, the vapor phase annealing method needs to be carried out in a specific atmosphere (such as Cd or Te atmosphere). The selection and control of the atmosphere are crucial to the annealing effect. However, in actual operation, precise control of the atmosphere is difficult and may cause new defects, which will have a significant impact on the electrical and optical properties of the material. By precisely controlling the amount of vapor phase source and annealing conditions, the type and concentration of point defects can be effectively adjusted, which not only helps to optimize the electrical properties of the material, but also improves its optical properties and mechanical strength, and reduces electrical properties such as crystal resistivity.

[0005] Therefore, in order to address the problem that the gas source is difficult to accurately control during the CdZnTe vapor phase annealing process, which leads to internal defects in the crystal, a new vapor phase annealing modification method for CdZnTe crystals needs to be developed to further improve the reliability and accuracy of CdZnTe crystal annealing. Summary of the invention

[0006] The purpose of the present invention is to provide a vapor phase annealing method for CdZnTe crystals in order to overcome the problem that the vapor source is difficult to accurately control during the existing vapor phase annealing process of CdZnTe crystals, which leads to internal defects in the crystals, so as to obtain CdZnTe crystals with significantly reduced internal defects and significantly improved crystal electrical properties.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A vapor phase annealing method for cadmium zinc telluride crystals comprises the following steps:

[0009] S1: Detect the type and concentration of point defects inside the CdZnTe wafer;

[0010] S2: Determine the corresponding gas phase source for annealing control according to the point defect detection results;

[0011] S3: Preparation of vapor source thin film on quartz wafer by physical vapor deposition;

[0012] S4: confirming the gas source pressure of annealing;

[0013] S5: The cadmium zinc telluride wafer and the quartz sheet deposited with the vapor source film are respectively packaged at the two ends of the annealing quartz tube, and then placed in an annealing furnace to heat the two ends of the annealing quartz tube respectively, and finally a CdZnTe crystal modified by vapor phase annealing is obtained.

[0014] Furthermore, in step S1, the point defects include Cd vacancies, Zn vacancies, Te vacancies and Te antisite defects.

[0015] Furthermore, in step S2, when the point defect is a Cd vacancy, a Zn vacancy or a Te vacancy, a corresponding gas is selected as a gas phase source, and the vacancy is filled through a high temperature annealing process to reduce the defect concentration.

[0016] Furthermore, in step S2, when the point defect is a Te antisite defect, an excess of Te is selected as a gas phase source. For a Te antisite defect, a gas phase source containing an excess of Te can be selected to promote Te atoms to occupy the correct lattice position through annealing.

[0017] Furthermore, in step S3, the specific steps of the physical vapor deposition are: placing the vapor source material on the heater of the vacuum coating machine, photolithography a desired pattern size on the quartz wafer, heating the vapor source material to the evaporation point in a vacuum environment and condensing it into a vapor source film on the cooled quartz wafer, and stopping the coating after the thickness reaches a predetermined film thickness as detected by a film thickness meter of the vacuum coating machine.

[0018] Furthermore, in step S3, the purity of the quartz sheet and the gas-phase source material is not less than 99.999%, preferably 99.9999%.

[0019] Furthermore, in step S4, the annealing pressure is determined based on the relationship between the vapor equilibrium pressure of the gas phase source and the CdZnTe wafer.

[0020] Furthermore, in step S5, a gas phase source cavity and a cadmium zinc telluride wafer cavity are provided in the annealing quartz tube, and a diffusion pipe for diffusion of the gas phase source is connected between the two cavities.

[0021] Furthermore, the gas phase source cavity and the cadmium zinc telluride wafer cavity are both provided with clamping grooves, which are used to support and fix the quartz plate and the cadmium zinc telluride wafer on which the gas phase source film is deposited, respectively.

[0022] Furthermore, in step S5, the annealing furnace includes at least two annealing zones along the axial direction, the temperatures of which can be independently controlled.

[0023] Furthermore, the gas source cavity and the cadmium zinc telluride wafer cavity in the annealing quartz tube are respectively located in annealing zones at two ends of the annealing furnace.

[0024] Furthermore, in step S5, the temperature of the CdZnTe wafer end is lower than the temperature of the gas phase source end, so that the gas phase source material can diffuse into the CdZnTe wafer cavity by independently controlling the heating temperatures in the two cavities.

[0025] Furthermore, in step S5, the heating rate of the CdZnTe wafer end is 15-20°C / min, and the final temperature is 400-600°C.

[0026] Furthermore, in step S5, the heating rate of the gas phase source end is 20-30°C / min, and the final temperature is 600-800°C.

[0027] Furthermore, in step S5, the heat preservation and cooling process of the vapor phase annealing is specifically as follows: after the cadmium zinc telluride wafer end and the vapor phase source end are heated to the final temperature, they are kept warm for 30-60 minutes, then cooled to 200-400°C at a cooling rate of 40-60°C / h and kept warm for 4-6 hours, and finally cooled to room temperature at a cooling rate of 40-60°C / h.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The present invention first detects the type and defect concentration of point defects inside the CdZnTe wafer, and determines the type and content of the gas phase source that needs to be regulated by annealing according to the detection results. Then, a corresponding gas phase source film required for annealing is prepared on a quartz wafer, and the quartz wafer and the CdZnTe wafer are placed at two ends of an annealing furnace, respectively, and heated and regulated to perform gas phase annealing, and finally a CdZnTe crystal with significantly reduced internal defects and significantly improved crystal electrical properties is obtained.

[0030] (2) The present invention adopts physical vapor deposition (PVD) technology to heat the gas source material to the evaporation point so that it condenses on the quartz substrate to form a uniform film, and combines with a film thickness meter to detect the film thickness in real time to ensure that the required nanometer-level precision is achieved. Photolithography assists in controlling the size of the deposition pattern on the quartz wafer to further accurately control the film thickness and surface area. In addition, the present invention also calculates the gas pressure of the Te gas source at this temperature through the Knudsen formula and the ideal gas formula to ensure the stability of the gas source vapor pressure. At the same time, the annealing furnace of the present invention is designed as a multi-temperature section structure, and the temperature of the two ends of the quartz tube is controlled by independent heating in different zones to maintain the temperature of the gas source end higher than the chip end. The diffusion pipeline designed by the quartz tube is used to adjust the diffusion of the gas source from the high temperature zone to the low temperature zone to ensure uniform airflow.

[0031] (3) The present invention achieves fine control of the internal defects of the crystal by precisely controlling the gas pressure and diffusion rate of the gas phase source. By adjusting the gas pressure inside the quartz tube and the diffusion rate of the gas phase source, the concentration and distribution of point defects in the crystal can be more accurately managed, thereby optimizing the electrical and optical properties of the crystal. The present invention greatly improves the utilization efficiency of the gas phase source during the annealing process by precisely controlling the gas pressure and diffusion rate of the gas phase source, ensuring the uniform diffusion of the gas phase source. This precise control not only reduces the non-uniformity caused by uncontrolled gas phase diffusion, but also significantly improves the overall quality and performance of the crystal.

[0032] (4) The annealing quartz tube of the present invention is ingeniously designed with a CdZnTe wafer cavity and a gas source cavity, which are connected by a diffusion pipe, and the diffusion of the gas source material into the CdZnTe wafer cavity can be achieved by independently controlling the heating temperature in the two cavities. In addition, the gas pressure in the annealing quartz tube remains constant throughout the annealing process, and the constant pressure helps prevent excessive aggregation or uneven diffusion of the gas source, which is crucial for maintaining uniformity and reducing defects in crystal annealing.

[0033] (5) The present invention optimizes the annealing environment of the CdZnTe crystal and reduces the corresponding defects in the crystal by precisely controlling the mass and pressure of the gas source and controlling the mass, position and temperature of the gas source to achieve a more uniform and directional gas source distribution.

[0034] (6) The present invention realizes nanometer-level controllable thickness of the vapor source through physical vapor deposition technology and real-time detection of the film thickness meter.

[0035] (7) The vapor phase annealing method of the present invention is not only applicable to common vapor phase sources such as Cd, Zn and Te, but also can adjust the type and quantity of vapor phase sources according to the requirements of different crystal materials. It has wide applicability and can meet different requirements for cadmium zinc telluride crystals.

[0036] (8) The resistivity of the CdZnTe crystal obtained by the vapor phase annealing method of the present invention is significantly improved compared with that before annealing; and the resistivity of the CdZnTe crystal finally obtained by the present invention is compared with the excessive vapor source annealing method without controlling the amount of vapor source, and the resistivity difference is as high as 6 orders of magnitude, which can fully meet the detector-level CdZnTe quality standard and can better meet the application requirements of high-performance CdZnTe crystals in electronic and optical devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic structural diagram of the annealed quartz tube of the present invention.

[0038] Figure 2 4-5 before and after annealing point defect concentration diagram; wherein, (a) is the point defect concentration diagram before and after Cd annealing in Example 4, and (b) is the point defect concentration diagram before and after Te annealing in Example 5.

[0039] Figure 3 These are infrared microscopic comparison images of tellurium inclusions before and after annealing in Examples 4-5; wherein (a) is an infrared image of tellurium inclusions before and after Cd annealing in Example 4, and (b) is an infrared image of tellurium inclusions before and after Te annealing in Example 5.

[0040] Figure 4 4-5 before and after annealing IV curve diagram; wherein, (a) is the IV curve diagram before and after Cd annealing in Example 4, and (b) is the IV curve diagram before and after Te annealing in Example 5.

[0041] Description of the markings in the figure:

[0042] 1- Annealed quartz tube;

[0043] 2-gas source cavity;

[0044] 3-CdZnTe wafer cavity;

[0045] 4-Diffusion pipe;

[0046] 5-Card slot;

[0047] 6- Quartz plate;

[0048] 7- Cadmium zinc telluride wafer. DETAILED DESCRIPTION

[0049] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0050] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0051] Among them, the PICTS deep energy level defect test is used to characterize the type and concentration of point defects inside the CdZnTe wafer; an infrared microscope is used to characterize the inclusion phase inside the CdZnTe wafer; the Keithley2400iv test is used to characterize the current and voltage of the CdZnTe crystal, and then the resistivity of the CdZnTe crystal is obtained.

[0052] Embodiment 1:

[0053] This embodiment provides a vapor phase annealing method for a CdZnTe crystal, which mainly includes the following steps:

[0054] S1: Detect the type and concentration of point defects inside the CdZnTe wafer;

[0055] S2: Determine the corresponding gas phase source for annealing control according to the point defect detection results;

[0056] S3: Preparation of vapor source thin film on quartz wafer by physical vapor deposition;

[0057] S4: confirm annealing pressure;

[0058] S5: The cadmium zinc telluride wafer and the quartz sheet deposited with the vapor source film are respectively packaged at the two ends of the annealing quartz tube, and then placed in an annealing furnace to heat the two ends of the annealing quartz tube respectively, and finally a CdZnTe crystal modified by vapor phase annealing is obtained.

[0059] In this embodiment, the point defect types and defect concentrations inside the CdZnTe wafer are first detected by a point defect tester and other devices, and the type and content of the gas phase source that needs to be regulated by annealing are determined according to the detection results. Then, the corresponding gas phase source film required for annealing is prepared on the quartz wafer by physical vapor deposition, and the quartz wafer and the CdZnTe wafer are placed at the two ends of the annealing furnace, respectively, and heated and vapor-phase annealed to finally obtain a CdZnTe crystal with significantly reduced internal defects and significantly improved crystal electrical properties.

[0060] Embodiment 2:

[0061] This embodiment provides a vapor phase annealing method for a CdZnTe crystal, which mainly includes the following steps:

[0062] S1: Detect the type and concentration of point defects inside the CdZnTe wafer.

[0063] S2: Determine the corresponding gas phase source for annealing control according to the point defect detection results.

[0064] In step S1, the point defects include Cd vacancies, Zn vacancies, Te vacancies and Te antisite defects. In step S2, when the point defect is a Cd vacancy, a Zn vacancy or a Te vacancy, the corresponding Cd, Zn or Te is selected as a gas phase source; when the point defect is a Te antisite defect, an excess of Te is selected as a gas phase source.

[0065] S3: Prepare a vapor source thin film on a quartz wafer by physical vapor deposition.

[0066] In step S3, the specific steps of the physical vapor deposition are as follows: the mask pattern is accurately exposed on a quartz wafer by a photolithography machine. The high resolution of the photolithography machine allows the pattern size to reach the micron level, further improving the control accuracy of the gas source amount. On the exposed pattern area, the gas source material is deposited by the PVD process. Since the pattern size has been limited by photolithography, the gas source material is only deposited at a specific position, controlling the distribution and coverage area of ​​the gas source. The film thickness meter monitors the film thickness in real time to ensure that the deposited gas source film reaches the predetermined nanometer-level thickness. This step accurately controls the gas source amount.

[0067] The purity of the quartz sheet and the gas source material is not less than 99.999%. The content of the gas source required for annealing is very low, and the content entering the cadmium zinc telluride crystal is at the ppm level, so that point defects can be effectively controlled.

[0068] S4: confirming the annealing pressure; the annealing pressure is confirmed based on the relationship between the vapor equilibrium pressure of the gas phase source and the CdZnTe wafer.

[0069] S5: The cadmium zinc telluride wafer and the quartz sheet deposited with the vapor source film are respectively packaged at the two ends of the annealing quartz tube, and then placed in an annealing furnace to heat the two ends of the annealing quartz tube respectively, and finally a CdZnTe crystal modified by vapor phase annealing is obtained.

[0070] In step S5, a gas phase source cavity and a CdZnTe wafer cavity are provided in the annealing quartz tube, a diffusion pipe for gas phase source diffusion is connected between the two cavities, and a card slot is provided in the gas phase source cavity and the CdZnTe wafer cavity, respectively used to support and fix the quartz sheet and the CdZnTe wafer on which the gas phase source film is deposited. The annealing furnace is a multi-temperature section annealing furnace, which includes at least two annealing zones with independently adjustable temperatures along the axial direction, and the gas phase source cavity and the CdZnTe wafer cavity in the annealing quartz tube are respectively located in the annealing zones at both ends of the multi-temperature section annealing furnace.

[0071] The relevant parameters of the vapor phase annealing in this embodiment are as follows:

[0072] The temperature of the CdZnTe wafer is lower than that of the gas phase source to promote the migration of gas molecules from the high temperature area to the low temperature area through the diffusion pipe. The heating rate of the CdZnTe wafer is 15-20℃ / min, and the final temperature is 400-600℃; the heating rate of the gas phase source is 20-30℃ / min, and the final temperature is 600-800℃.

[0073] The specific heat preservation and cooling process of vapor phase annealing is as follows: after the CdZnTe wafer end and the vapor source end are heated to the final temperature, they are kept warm for 30-60 minutes to allow the vapor phase material to fully contact and react with the wafer to form a high-quality crystal structure; then the temperature is reduced to 200-400°C at a cooling rate of 40-60°C / h and kept for 4-6 hours, and the cooling rate is slowed down to avoid stress inside the crystal due to rapid cooling, which may lead to crystal cracks or other defects; finally, the temperature is slowly reduced to room temperature at a cooling rate of 40-60°C / h.

[0074] Embodiment 3:

[0075] This embodiment provides a vapor phase annealing method for cadmium zinc telluride crystals, which evaporates the material by heating it in a vacuum environment through a physical vapor deposition method, and then condenses it on a high-purity quartz sheet of standard size on a cooled substrate to form a thin film. The film thickness is detected in real time by a film thickness meter to achieve a controllable thickness at the nanometer level, thereby controlling the gas source to achieve a controllable quality at the atomic level. Subsequently, the coated quartz sheet and the cadmium zinc telluride wafer are placed together in a quartz crucible, and the volume and annealing temperature in the quartz tube are controlled by the vapor equilibrium pressure relationship between the gas source and the wafer to achieve the control of the gas pressure of the gas source. By accurately controlling the gas pressure and distribution of the gas source during the annealing process, the point defects inside the CdZnTe crystal are reduced, and the electrical properties of the crystal are significantly improved. This method provides a new idea for the preparation and optimization of CdZnTe crystals, and has broad application prospects.

[0076] To achieve the above purpose, this embodiment specifically adopts the following steps:

[0077] (1) Point defect detection and analysis:

[0078] First, a point defect tester (such as PICTS) is used to detect the type and defect concentration of point defects inside the CdZnTe wafer. According to the test results, the type and content of the gas phase source that needs to be regulated by annealing are determined. This step ensures the pertinence and effectiveness of the subsequent gas phase annealing process. Among them, the point defect tester has the accuracy of the type and concentration of point defects, and can effectively detect deep energy level traps in CdZnTe crystals. This can fully understand the types and distribution of point defects in CdZnTe crystals.

[0079] For example, it can be identified that the main point defect types in the crystal are Cd vacancies (V_Cd), Zn vacancies (V_Zn), Te vacancies (V_Te) or antisite defects (such as Te antisites at Cd sites), as well as the concentration distribution of these defects, thereby providing the necessary basic data for the subsequent vapor phase annealing process. The concentration of the gas source and the annealing time need to be precisely controlled according to the test results. If the concentration is too high or the annealing time is too long, new defects may be generated; if the concentration is too low or the annealing time is insufficient, the existing defects may not be effectively repaired. Therefore, selecting the appropriate type and concentration of the gas source based on the point defect detection results is the basis for ensuring the effectiveness of the vapor phase annealing process.

[0080] (2) Gas source selection and preparation:

[0081] Different gas sources can be selected for different types of point defects. For example, for Cd vacancies and Zn vacancies, Cd gas or Zn gas can be selected as the gas source, and the vacancies can be filled through a high-temperature annealing process to reduce the defect concentration. For Te antisite defects, a gas source containing excess Te can be selected, and annealing can be used to promote Te atoms to occupy the correct lattice position. The gas source must be made of high-purity materials. Gas sources containing impurities will introduce new defects and affect crystal performance. In order to ensure the purity and stability of the gas source, the present invention uses high-purity (purity of 99.9999%) Cd, Zn and Te materials.

[0082] (3) Physical vapor deposition (PVD) process:

[0083] Place the above-mentioned vapor source materials on the heater of the vacuum coating machine, photoetch the quartz plate into a standard pattern, and place it on the substrate of the coating machine to prepare for physical vapor deposition. In the vacuum coating machine, evacuate the environment to 8×10 -4 Pa. The material is heated to its evaporation point, evaporated in a vacuum environment, and condensed on a cooled high-purity quartz substrate to form a thin film. During this process, the film thickness meter of the vacuum coating machine is used to detect the film thickness in real time to ensure that the film thickness reaches the required nanometer-level accuracy. When the predetermined film thickness is reached, the coating is stopped.

[0084] (4) Control of vapor balance pressure between gas source and wafer:

[0085] The required gas pressure and volume are obtained by combining the vapor equilibrium pressure relationship between the gas source and the cadmium zinc telluride wafer and the principle of ideal equilibrium gas pressure.

[0086] (5) Vapor phase annealing treatment:

[0087] Gas phase annealing is a key technology used to improve the crystal structure and optimize its electrical and physical properties. The annealing quartz tube of this embodiment is provided with a gas phase source cavity and a CdZnTe wafer cavity, and a diffusion pipe for gas phase source diffusion is connected between the two cavities. Both the gas phase source cavity and the CdZnTe wafer cavity are provided with a card slot, which is used to support and fix the quartz sheet and CdZnTe wafer deposited with the gas phase source film, respectively. The card slot can ensure that the quartz sheet and the CdZnTe wafer maintain the correct position relationship during the entire annealing process. The annealing quartz tube of this embodiment is a kind of annealing crucible, which needs to be able to withstand high temperature and can be used in vacuum or a specific atmosphere. The gas phase source cavity, the CdZnTe wafer cavity and the diffusion pipe form a bracket installed in the annealing quartz tube as a whole, which is used to fix the quartz sheet and the CdZnTe wafer to ensure that they maintain a suitable position and stability during the annealing process.

[0088] The specific operation is as follows: place the coated quartz plate at one end of the quartz tube, and place the CdZnTe wafer at the other end of the quartz tube. Both the quartz plate and the CdZnTe wafer are fixed in place by means of a slot. Evacuate the quartz tube to a vacuum of 8×10 -4 Pa, and then weld the quartz tube to ensure the purity and stability of the internal environment. The welded quartz tube is placed in a multi-temperature section annealing furnace. The quartz tube needs to be placed horizontally to ensure that the CdZnTe wafer is located at one end of the annealing furnace, and the gas phase source is located at the other end of the annealing furnace. The temperature of both ends can be controlled independently. This layout helps to achieve effective delivery of the gas phase source to the CdZnTe wafer through the temperature gradient in the annealing furnace.

[0089] Before the formal heating annealing, the temperature of the gas source end and the CdZnTe wafer end needs to be set. Usually, the temperature of the gas source end is slightly higher than that of the wafer end to promote the migration and diffusion of gas molecules from the high temperature area to the low temperature area through the diffusion pipe. When the temperature of the gas source and the wafer end reaches the preset value, this temperature state is maintained for a period of time to allow the gas phase substance to fully contact and react with the wafer. This step is the key to forming a high-quality crystal structure, because the adsorption, diffusion and reaction of gas molecules on the wafer surface directly affect the final quality of the wafer. After the heat preservation is completed, the temperature is gradually reduced according to the predetermined cooling rate. This process needs to be carried out slowly to avoid stress inside the crystal due to rapid cooling, which leads to crystal cracks or other defects. By controlling the cooling rate, the microstructure of the crystal can be further optimized and its uniformity and performance can be improved. Finally, when the temperature drops to room temperature, the quartz tube can be removed from the annealing furnace, and the quartz tube can be opened in a dust-free environment to take out the CdZnTe crystal modified by gas phase annealing.

[0090] The CdZnTe crystal prepared by the above-mentioned vapor phase annealing method has significantly reduced internal defects and significantly improved electrical properties of the crystal compared to the crystal prepared by the conventional vapor phase annealing method. In multiple experiments in the following examples, the CdZnTe crystal annealed by this method exhibited lower dark current and higher detection efficiency, proving the superiority of this method in controlling the concentration and distribution of the vapor phase source.

[0091] Based on the above-mentioned vapor phase annealing method of CdZnTe crystal, different CdZnTe wafer sample materials are subjected to vapor phase annealing modification, and the specific steps are shown in Examples 4-5. Among them, the point defect type and concentration inside the CdZnTe wafer are characterized by PICTS deep level defect test; the inclusion phase inside the CdZnTe wafer is characterized by infrared microscope; the current and voltage of the CdZnTe crystal are characterized by Keithley2400iv test, and the resistivity of the CdZnTe crystal is obtained.

[0092] Embodiment 4:

[0093] This embodiment provides a cadmium zinc telluride crystal modified by vapor phase annealing of a limited Cd source, and the preparation method is as follows:

[0094] (1) Detect the type and concentration of point defects inside the CdZnTe crystal using the PICTS test instrument. The point defect test instrument PICTS collects information about the effect of sub-bandgap light on crystal defects by continuously irradiating the CdZnTe wafer with a 730nm laser source. Collect the relevant point defect types and defect concentrations through Labview. According to the defect type and defect concentration, the results are as follows: Figure 2 (a).

[0095] (2) Based on Figure 2 (a) It can be seen that there are too many Cd vacancies in the tellurium-rich CdZnTe wafer. Therefore, the type of gas source required for annealing control is Cd gas source, and the concentration of Cd atoms to be supplemented is 1.5×10 14 cm -3 Through the relationship between the vapor equilibrium pressure of the gas source and the wafer, and according to the principle of ideal gas pressure, the mass of the Cd gas source and the gas pressure of the gas source are obtained. The derivation process is as follows:

[0096] Known m Cd =1.86×10 -22 g, so M Cd =N Cd ×m Cd =1.5×10 14 ×V×1.86×10 -22 g, V is the sample volume, generally 1 cm 3 , so the mass of Cd gas source required is M Cd About 2.79×10 -8g, and then calculate the air pressure using the ideal gas formula:

[0097]

[0098] n cd =2.79×10 -8 / 112.41=2.48×10 -10 mol

[0099] T = 873k, after substituting it into P Cd =3.2×10 -8 Pa.

[0100] (3) Preparation for physical vapor deposition: According to the quality of the vapor source, select the corresponding high-purity Cd vapor source material as the vapor source, place the material on the heater of the vacuum coating machine, and carve an area of ​​1 cm on the quartz sheet by photolithography. 2 The pattern is placed on the substrate of the vacuum coating machine and then evacuated to 8×10 -4 Pa, and then the material is heated to the evaporation point, so that it evaporates in a vacuum environment onto the cooled quartz substrate and condenses into a thin film. The film thickness is detected in real time by the film thickness meter of the vacuum coating machine, and the coating is stopped after the expected film thickness of 50mm is reached. The coated quartz sheet is rinsed to leave multiple squares of the same area coated with gas phase sources.

[0101] (4) Place the coated quartz wafer in the gas source chamber at one end of the annealing quartz tube, and place the CdZnTe wafer in the CdZnTe wafer chamber at the other end, and then package it. Evacuate the quartz tube to 8×10 -4 Pa, and then weld the quartz tube. The welded quartz tube is placed in a three-stage annealing furnace and placed horizontally, with the wafer at one end of the annealing furnace and the gas phase source quartz sheet at the other end of the annealing furnace, so that each zone can be heated independently.

[0102] (5) Within 30 minutes, the temperature of the wafer end is raised to 400°C, the temperature of the gas phase source end is raised to 600°C, and kept at this temperature for 30 minutes, then cooled to 400°C at a rate of 50°C per hour and kept at this temperature for another 2 hours, then cooled to room temperature at a rate of 50°C per hour, and then the CdZnTe wafer is taken out to obtain a CdZnTe crystal modified by gas phase annealing with a limited Cd source.

[0103] Tellurium inclusions before and after annealing are shown in the attached Figure 3 As shown in (a), it can be seen that the tellurium inclusions are much reduced after Cd vapor source annealing compared to before annealing. Figure 2 (a) shows the different point defects before and after annealing. Before annealing, there are Cd vacancies, tellurium antisites, and tellurium inclusions. After annealing, the concentration of Cd vacancies is greatly reduced, indicating that the compensation of Cd during annealing fills the peak of Cd vacancies. Figure 3(a) shows that there is no Cd gap, indicating that the diffused Cd concentration is very low. Figure 4 The IV diagram in (a) shows that the resistivity does not change significantly before and after annealing, indicating that the finite source annealing eliminates tellurium inclusions without introducing excessive Cd to cause Cd gaps and reduce the resistivity, indicating that the finite source annealing method of this embodiment is feasible.

[0104] Embodiment 5:

[0105] This embodiment provides a cadmium zinc telluride crystal modified by gas phase annealing of a limited Te source, and the preparation method is as follows:

[0106] (1) Detect the type and concentration of point defects inside the CdZnTe crystal using the PICTS test instrument. The point defect test instrument PICTS collects information about the effect of sub-bandgap light on crystal defects by continuously irradiating the CdZnTe wafer with a 730nm laser source. Collect the relevant point defect types and defect concentrations through Labview. According to the defect type and defect concentration, the results are as follows: Figure 2 (b).

[0107] (2) Then according to Figure 2 (b) It is necessary to supplement the Te source. Therefore, the type of gas source required for annealing control is the Te gas source. Generally, the concentration of Te anti-site that needs to be supplemented cannot be too high. Therefore, according to actual experience, 1.0×10 14 cm -3 The tellurium antiposition concentration. Through the relationship between the vapor equilibrium pressure of the gas source and the wafer, and according to the principle of ideal gas pressure, the mass of the Cd gas source and the gas pressure of the gas source are obtained. The derivation process is as follows:

[0108] Known m Te =2.12×10 -22 g, so M Te =N Te ×m Te =1×10 14 ×V×2.12×10 -22 g, V is the sample volume, generally 1 cm 3 , so the mass of the required Te gas source M Te About 2.12×10 -8 g, and then calculate the air pressure using the ideal gas formula:

[0109]

[0110] n Te =2.12×10 -8 / 127.6=1.66×10 -10 mol

[0111] T = 873k, after substituting it into P Te =3.2×10 -10 Pa.

[0112] (3) Preparation for physical vapor deposition: Select the corresponding high-purity Te vapor source material as the vapor source according to the quality of the vapor source, place the material on the heater of the vacuum coating machine, and carve a 1 cm square on the quartz wafer by photolithography. 2 The pattern is placed on the substrate of the vacuum coating machine and then evacuated to 8×10 -4 Pa. Then, by heating the material to the evaporation point, the gas source material evaporates in a vacuum environment onto the cooled quartz substrate and condenses into a thin film. The film thickness is detected in real time by the film thickness meter of the vacuum coating machine. When the expected film thickness reaches 34nm, the coating is stopped. The coated quartz wafer is rinsed to remove excess tellurium, leaving only tellurium films of the same size in multiple squares.

[0113] (4) Place the coated quartz wafer in the gas source chamber at one end of the annealing quartz tube, and place the CdZnTe wafer in the CdZnTe wafer chamber at the other end, and then package it. Evacuate the quartz tube to 8×10 -4 Pa, and then weld the quartz tube. The welded quartz tube is placed in a three-stage annealing furnace and placed horizontally, with the wafer at one end of the annealing furnace and the gas phase source quartz sheet at the other end of the annealing furnace, so that each zone can be heated independently.

[0114] (5) Within 30 minutes, the temperature of the wafer end is raised to 600°C, and the temperature of the gas phase source end is raised to 800°C, and then kept at this temperature for 30 minutes. The temperature is then decreased to 300°C at a rate of 50°C per hour and kept at this temperature for another 5 hours. The temperature is then decreased to room temperature at a rate of 50°C per hour, and the CdZnTe wafer is taken out to obtain a CdZnTe crystal modified by gas phase annealing with a limited Te source.

[0115] The tellurium inclusion properties before and after annealing are shown in the attached Figure 3 As shown in (b), it can be seen that the Te gas phase source retreats, and the tellurium inclusions are greatly reduced compared to before annealing, and no new tellurium inclusions are generated due to the introduction of tellurium. Figure 2 (b) shows the different point defects before and after annealing. The tellurium anti-site concentration is low before annealing, and significantly higher after annealing, indicating that the compensation of Te during annealing is effective. Figure 4 The IV diagram in (b) shows that the resistivity after annealing is two orders of magnitude higher than that before annealing, which indicates that Te limited source annealing can eliminate tellurium inclusions while also increasing the resistivity of CdZnTe crystals.

[0116] Comparative Example 1:

[0117] This comparative example is a non-limited source vapor phase annealing modified cadmium zinc telluride crystal, and the preparation method is as follows:

[0118] (1) Place the excess Cd source in Figure 1 The left end of the container is placed in the middle, and the CdZnTe wafer is placed on the right end. Then it is placed in the quartz tube and the quartz tube is evacuated to 8×10 -4 Pa, and then weld the quartz tube. The welded quartz tube is placed in a three-stage annealing furnace and placed horizontally, with the wafer at one end and the gas source at the other end.

[0119] (2) Within 30 minutes, the temperature of the CdZnTe wafer end is raised to 400°C, and the temperature of the gas phase source end is raised to 600°C, which are kept at this temperature for 30 minutes, then cooled to 400°C at a rate of 50°C per hour and kept at this temperature for another 2 hours, then cooled to room temperature at a rate of 50°C per hour, and then the wafer is taken out to obtain a CdZnTe crystal modified by gas phase annealing of a supersaturated Cd source.

[0120] Since detector-grade CdZnTe crystals have strict requirements on their resistivity, usually not less than 10×10 9 Ω·cm, to ensure its detection accuracy and stability in detector applications. The resistivity of the CdZnTe crystal after annealing still needs to be maintained within a certain standard range, otherwise it will not be able to maintain its original high resistivity characteristics, which will directly affect its performance in detector applications. Therefore, in view of the actual use requirements of CdZnTe crystals in detectors, the present invention tests the resistivity of CdZnTe crystals after limited gas source annealing in Examples 4-5 and supersaturated Cd gas source annealing in Comparative Example 1, and the results are shown in Table 1.

[0121] Table 1 Resistivity test results

[0122]

[0123] As shown in Table 1, the resistivity of the CdZnTe crystal of Comparative Example 1 after annealing is greatly reduced, and it has dropped by 5 orders of magnitude compared with that before annealing. This significant decrease in resistivity means that the material performance after annealing no longer meets the standards required for detector-grade CdZnTe. However, the resistivity of the CdZnTe crystal prepared in Example 4 did not change significantly before and after annealing. Compared with the annealing of the supersaturated Cd source, the surface limited Cd source annealing not only does not reduce the resistivity, but also increases the resistivity by filling some Cd vacancies. This method avoids the negative effects that may occur in the supersaturated state by controlling the supply of the Cd source, so that the CdZnTe crystal after vapor phase annealing meets the resistivity requirements of the detector.

[0124] In summary, the gas phase annealing method of the present invention controls the amount of gas phase source and gas flow, so that the amount diffused into the cadmium zinc telluride crystal can be controlled at the ppm level, and the internal structure and electrical properties of the CdZnTe material are optimized. The gas flow direction and flow rate of the gas phase source can be controlled by the ingenious design of the two cavities and the diffusion pipeline in the annealing quartz tube, so that the gas flow can evenly cover the surface of the cadmium zinc telluride wafer. The above structure not only ensures the elimination of the inclusion phase, but also improves the electrical properties of the cadmium zinc telluride crystal. In addition, the present invention realizes the regulation of internal point defects by the method of limited gas phase source. From the test of point defects, it can be known that the internal point defects of the cadmium zinc telluride crystal realize the adjustment of the types and concentrations of different defects after gas phase annealing. The gas phase annealing method of the present invention not only reduces the introduction of impurities by the precise control of the gas phase source, but also ensures that the impurity concentration is kept at a very low level, thereby improving the purity of the CdZnTe crystal, helping to optimize the electrical properties of the material, and has broad application prospects in the field of semiconductor devices.

[0125] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A vapor phase annealing method for cadmium zinc telluride crystals, characterized in that: The following steps are involved: S1: Detect the type and concentration of point defects inside the CdZnTe wafer; S2: Determine the corresponding gas phase source for annealing control according to the point defect detection results; S3: Preparation of vapor source thin film on quartz wafer by physical vapor deposition; S4: confirming the gas source pressure of annealing; S5: The cadmium zinc telluride wafer and the quartz sheet deposited with the vapor source film are respectively packaged at the two ends of the annealing quartz tube, and then placed in an annealing furnace to heat the two ends of the annealing quartz tube respectively, and finally a CdZnTe crystal modified by vapor phase annealing is obtained.

2. The vapor phase annealing method of CdZnTe crystal according to claim 1, characterized in that: In step S1, the point defects include Cd vacancies, Zn vacancies, Te vacancies and Te antisite defects.

3. The vapor phase annealing method of CdZnTe crystal according to claim 2, characterized in that: In step S2, when the point defect is a Cd vacancy, a Zn vacancy or a Te vacancy, a corresponding gas is selected as a gas phase source; When the point defect is a Te antisite defect, excess Te is selected as the gas phase source.

4. The vapor phase annealing method of CdZnTe crystal according to claim 1, characterized in that: In step S3, the specific steps of the physical vapor deposition are: Place the gas source material on the heater of the vacuum coating machine, use photolithography to photoetch the required pattern size on the quartz wafer, heat the gas source material to the evaporation point in a vacuum environment and condense it into a gas source film on the cooled quartz wafer, and stop coating when the thickness reaches the predetermined film thickness detected by the film thickness instrument of the vacuum coating machine.

5. The vapor phase annealing method of CdZnTe crystal according to claim 1, characterized in that: In step S3, the purity of the quartz sheet and the gas-phase source material is not less than 99.999%.

6. The vapor phase annealing method of CdZnTe crystal according to claim 1, characterized in that: In step S4, the annealing pressure is determined based on the relationship between the vapor equilibrium pressure of the gas phase source and the CdZnTe wafer.

7. The vapor phase annealing method of CdZnTe crystal according to claim 1, characterized in that: In step S5, a gas phase source cavity and a cadmium zinc telluride wafer cavity are provided in the annealing quartz tube, and a diffusion pipe for diffusion of the gas phase source is connected between the two cavities; The gas phase source cavity and the cadmium zinc telluride wafer cavity are both provided with clamping grooves, which are respectively used to support and fix the quartz plate and the cadmium zinc telluride wafer on which the gas phase source film is deposited.

8. The vapor phase annealing method of CdZnTe crystal according to claim 7, characterized in that: In step S5, the annealing furnace includes at least two annealing zones along the axial direction, the temperatures of which can be independently controlled; The gas phase source cavity and the cadmium zinc telluride wafer cavity in the annealing quartz tube are respectively located in the annealing zones at two ends of the annealing furnace.

9. The vapor phase annealing method of CdZnTe crystal according to claim 1, characterized in that: In step S5, the temperature of the CdZnTe wafer end is lower than the temperature of the gas phase source end; The heating rate of the CdZnTe wafer end is 15-20°C / min, and the final temperature is 400-600°C; The heating rate of the gas phase source end is 20-30°C / min, and the final temperature is 600-800°C.

10. The vapor phase annealing method of CdZnTe crystal according to claim 9, characterized in that: In step S5, the heat preservation and cooling process of the vapor phase annealing is specifically as follows: After the CdZnTe wafer end and the gas source end are heated to the final temperature, they are kept warm for 30-60 minutes, then cooled to 200-400°C at a cooling rate of 40-60°C / h and kept warm for 4-6 hours, and finally cooled to room temperature at a cooling rate of 40-60°C / h.

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