High-resistance cadmium telluride crystal doping method

Abstract

The invention provides a high-resistance cadmium telluride crystal doping method which comprises the following steps: preparing materials including 7N Te and Cd simple substances and 5N CdBr2, and purifying the 7N Te and Cd simple substances once again; feeding the purified Te and Cd simple substances and cadmium bromide according to a ratio, and sealing a tube for synthesis to obtain a bromine-containing cadmium telluride polycrystal I; smashing the cadmium telluride polycrystal I into powder for sealing; feeding purified Te and Cd elementary substances according to a ratio, and sealing a tube for synthesis to obtain cadmium telluride polycrystals II; feeding the polycrystal I and the polycrystal II according to a ratio, sealing a tube and growing crystals to obtain cadmium telluride single crystals; cutting, grinding and polishing the cadmium telluride single crystal to obtain a 10 * 10 * 1mm < 3 > wafer; making an electrode on the wafer; testing by Hall equipment to obtain resistivity and carrier concentration; and processing data. According to the invention, Br is doped into cadmium telluride, so that the resistivity of cadmium telluride is improved, the carrier concentration is reduced, the conductivity of the material is changed, and semi-insulating cadmium telluride can be grown.

Description

Technical Field

[0001] The present invention relates to the technical field of high-end medical equipment, and in particular to a high-resistance cadmium telluride crystal doping method. Background Art

[0002] Cadmium telluride has good crystal structure and electrical properties, and can detect and count single X-ray photons, so that image information can be obtained more accurately. Cadmium telluride, as a material for photon counting CT detectors, can multiply the X-ray dose efficiency and significantly reduce the radiation dose while ensuring excellent image quality. This is of great significance for patients who need multiple CT examinations and people who are sensitive to radiation, such as children and pregnant women, and greatly expands the scope of application of CT examinations, allowing more patients to benefit from CT examinations.

[0003] Good detector materials must have high resistivity (>10 9 Ω·cm) to reduce dark current and device noise; and a large μτ product (mobility-lifetime product) to ensure that the carriers generated by radiation can pass through the detector material and be collected by the electrode. The free carrier concentration in cadmium telluride should be controlled at 10 6 cm -3 The following is the best way to achieve the best effect.

[0004] In the prior art, cadmium telluride is usually grown from a melt under Te-rich conditions. The vapor pressure of cadmium is lower than that of tellurium, resulting in the loss of cadmium during crystal growth. The resulting undoped cadmium telluride is usually p-type with low resistivity, which is mainly caused by the presence of a large number of cadmium vacancies in the crystal. Therefore, it is difficult to prepare semi-insulating cadmium telluride as an excellent detector material in the existing scheme, which in turn leads to poor subsequent use results. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a high-resistance cadmium telluride crystal doping method to solve the problems raised in the above background technology. The present invention dopes Br into cadmium telluride to increase the resistivity of cadmium telluride and reduce the carrier concentration, thereby changing the conductive properties of the material and growing semi-insulating cadmium telluride.

[0006] In order to achieve the above object, the present invention is implemented by the following technical solution: a high-resistance cadmium telluride crystal doping method, comprising the following steps:

[0007] Step 1: Prepare materials, including 7N Te and Cd elements and 5N CdBr 2 , and 7N Te and Cd were purified again;

[0008] Step 2, preparing bromine-containing cadmium telluride polycrystal I;

[0009] Step 3, crushing the cadmium telluride polycrystal I into powder and sealing it;

[0010] Step 4: preparing cadmium telluride polycrystal II;

[0011] Step 5, preparing cadmium telluride single crystal;

[0012] Step 6: Processing the cadmium telluride single crystal to obtain a wafer of fixed size;

[0013] Step 7: Make electrodes on the wafer;

[0014] Step 8: Test the Hall device and process the data.

[0015] Furthermore, in the step 1, the number of times 7N Te and Cd single substances are purified again is 1 time.

[0016] Furthermore, the preparation process of the bromide-containing cadmium telluride polycrystal I in step 2 is: adding the purified Te and Cd single substances and cadmium bromide in proportion and then sealing the tube for synthesis.

[0017] Furthermore, the preparation process of the cadmium telluride polycrystal II includes: adding the purified Te and Cd single substances in proportion and then sealing the tube for synthesis.

[0018] Furthermore, the preparation process of the cadmium telluride single crystal includes: feeding polycrystal I and polycrystal II in proportion to obtain crystal growth by sealing a tube.

[0019] Furthermore, the processing of the cadmium telluride single crystal includes cutting, grinding and polishing.

[0020] Furthermore, the size of the prepared wafer is 10*10*1mm 3 .

[0021] Furthermore, in step eight, resistivity and carrier concentration data are obtained through Hall device testing.

[0022] Furthermore, through data processing, the data relationship diagrams between the resistivity, mobility-lifetime product and the bromine doping amount, EDP, and inclusion size can be drawn.

[0023] Beneficial effects of the present invention:

[0024] 1. The high-resistance cadmium telluride crystal doping method dopes Br into cadmium telluride, increases the resistivity of cadmium telluride and reduces the carrier concentration, changes the conductive properties of the material, and can grow semi-insulating cadmium telluride. When the cadmium telluride prepared based on this method is used as a detector material, it can effectively reduce the leakage current, so that the detector can more accurately detect the weak signals generated by X-ray photons, and improve the clarity and resolution of the image.

[0025] 2. The high-resistivity cadmium telluride prepared by the present invention can reduce the influence of polarization effect, ensure that the detector can still operate stably under long-term and high-count rate working conditions, and improve the working efficiency and reliability of photon CT.

[0026] 3. The high-resistivity cadmium telluride crystal structure prepared by the high-resistance cadmium telluride crystal doping method is more stable, can withstand higher doses of radiation without easily producing defects and performance degradation, thereby extending the service life of the detector and reducing the maintenance cost and replacement frequency of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a structural diagram of electrodes made on a wafer in a high-resistance cadmium telluride crystal doping method of the present invention;

[0028] Figure 2 is a graph showing the relationship between the bromine doping amount and the resistivity and the mobility-lifetime product in an embodiment of the present invention;

[0029] Figure 3 Graph showing the relationship between EDP, resistivity, and mobility-lifetime product in an embodiment of the present invention;

[0030] Figure 4 Graph showing the relationship between inclusion size and resistivity, mobility-lifetime product in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0032] See also Figures 1 to 4 The present invention provides the following technical solutions: a method for doping high-resistance cadmium telluride crystals. The method is directed to the prior art, in which cadmium telluride is usually grown from a melt under Te-rich conditions. Since the vapor pressure of cadmium is lower than that of tellurium, cadmium is lost during the crystal growth process. The undoped cadmium telluride thus produced is usually p-type and has a low resistivity, which is mainly caused by the presence of a large number of cadmium vacancies in the crystal. The present invention, by doping Br into cadmium telluride, increases the resistivity of cadmium telluride and reduces the carrier concentration, thereby changing the conductive properties of the material, and can grow semi-insulating cadmium telluride. When the cadmium telluride prepared based on this method is used as a detector material, the leakage current can be effectively reduced, so that the detector can more accurately detect the weak signals generated by X-ray photons, and improve the clarity and resolution of the image.

[0033] This example provides 7N Te and Cd single substances and 5N CdBr 2 As a basic material for further illustrating the method, the doping method provided in this embodiment includes the following steps:

[0034] 1. 7N Te and Cd were purified once more;

[0035] 2. Add the purified Te and Cd single substances and cadmium bromide in proportion and seal the tube for synthesis to obtain bromine-containing cadmium telluride polycrystal I;

[0036] 3. Crush the cadmium telluride polycrystal I into powder and seal it;

[0037] 4. Add the purified Te and Cd single substances in proportion and seal the tube for synthesis to obtain cadmium telluride polycrystal II;

[0038] 5. Add polycrystal I and polycrystal II in proportion and seal the tube to grow crystals to obtain cadmium telluride single crystals;

[0039] 6. Cadmium telluride single crystal is cut, ground and polished to obtain 10*10*1mm 3 Wafer;

[0040] 7. Make electrodes on the wafer, such as Figure 1 As shown:

[0041] 8. Hall device test to obtain resistivity and carrier concentration;

[0042] 9. Data processing.

[0043] This embodiment also provides actual parameters of cadmium telluride prepared by the above preparation process, refer to Figure 2 , Figure 3 and Figure 4 , the specific data of the semi-insulating cadmium telluride in this embodiment are as follows:

[0044] Resistivity:

[0045] D Br ≤10ppm: R=α -3 ·D Br / (k 1· ρ 夹杂 ·k 2 ρ EPD )

[0046] 10<D Br <100ppm:R≈1.2*10 10 Ω·cm;

[0047] Mobility-lifetime product:

[0048] μτ 电子 =9.8·β 1 / 2 / D Br ·k 3 ρ 夹杂

[0049] μτ 空穴 =β1 / 2 / D Br ·k 3 ρ 夹杂

[0050] D Br : Bromine doping amount, α, k 1 , k 2、 k 3 : Fixed coefficient, ρ 夹杂 : Wafer inclusion size, ρ EPD : Corrosion pit density.

[0051] The basic principles and main features of the present invention and the advantages of the present invention are shown and described above. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention.

[0052] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A high-resistance cadmium telluride crystal doping method, characterized in that: The following steps are involved: Step 1, preparing materials, including 7N Te and Cd single substances and 5N CdBr2, and purifying 7N Te and Cd single substances again; Step 2, preparing bromine-containing cadmium telluride polycrystal I; Step 3, crushing the cadmium telluride polycrystal I into powder and sealing it; Step 4: preparing cadmium telluride polycrystal II; Step 5, preparing cadmium telluride single crystal; Step 6: Processing the cadmium telluride single crystal to obtain a wafer of fixed size; Step 7: Make electrodes on the wafer; Step 8: Test the Hall device and process the data.

2. The high-resistance cadmium telluride crystal doping method according to claim 1, characterized in that: In the step 1, the number of times of re-purifying the 7N Te and Cd single substances is 1 time.

3. The high-resistance cadmium telluride crystal doping method according to claim 1, characterized in that: The preparation process of the brominated cadmium telluride polycrystal I in step 2 is: adding the purified Te and Cd single substances and cadmium bromide in proportion and then sealing the tube for synthesis.

4. The high-resistance cadmium telluride crystal doping method according to claim 3, characterized in that: The preparation process of the cadmium telluride polycrystal II comprises: adding purified Te and Cd single substances in proportion and then sealing the tube for synthesis.

5. The high-resistance cadmium telluride crystal doping method according to claim 4, characterized in that: The preparation process of the cadmium telluride single crystal includes: feeding polycrystal I and polycrystal II in proportion to obtain the crystal by sealing the tube and growing the crystal.

6. The high-resistance cadmium telluride crystal doping method according to claim 1, characterized in that: The processing of the cadmium telluride single crystal includes cutting, grinding and polishing.

7. A high-resistance cadmium telluride crystal doping method according to claim 6, characterized in that: The size of the prepared wafer is 10*10*1mm 3 .

8. The high-resistance cadmium telluride crystal doping method according to claim 1, characterized in that: In the step eight, the resistivity and carrier concentration data are obtained by testing the Hall device.

9. A high-resistance cadmium telluride crystal doping method according to claim 8, characterized in that: Through data processing, the data relationship diagrams between resistivity, mobility-lifetime product and bromine doping amount, EDP, and inclusion size can be drawn.

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