JPH0515677B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a high-resistance cadmium telluride crystal used in radiation detectors, medical radiation diagnostic equipment, industrial X-ray nondestructive inspection equipment, etc., and a method for manufacturing the same. . (Prior technology) Radiation detectors using cadmium telluride crystals are based on Si and Ge crystals, which have traditionally been used in this field.
Compared to semiconductor radiation detectors using semiconductors, its forbidden band width and average atomic number are larger, so it can operate at room temperature and has a large radiation absorption coefficient.
Because it is possible to obtain high sensitivity even with a thin layer, it has become widely used in practical applications. In this case, in order to obtain the desired cadmium telluride crystals, it is necessary to
After dissolving CdTe polycrystals in a Te melt in a quartz ampoule, CdTe was precipitated again.
The moving heater method (THM method) is used to obtain a product by growing crystals at a growth rate of 1 to 5 mm/day in the range of ~700°C, but Cd and Te are grown in a molar ratio of 3:7. After that, 1×10 ¹⁸ ~ 1×
A Te solvent in which the product is obtained by precipitating CdTe crystals from a solution containing 10 ^{to 20} atoms/cm ³ of cadmium chloride, and growing the crystals at a growth rate of 1 to 5 mm/day in the range of 950 to 1000°C. It was according to the law. (Problem to be solved by the invention) However, when using the THM method, not only is CdTe polycrystal required in advance before obtaining the crystal, but also a molding process is required to adjust the shape when inserting the polycrystal into the ampoule. However, the process is complicated, and the growth rate of the crystal is slow, making it unsuitable for increasing the size of the crystal. When using the Te solvent method, the purity of the cadmium chloride added must be carefully selected in order to ensure the purity of the product, and the growth rate of the crystals is slow and many Te precipitates are present in the crystals. The product's performance has been questioned. The present invention aims to solve the above-mentioned problems and to obtain a cadmium telluride crystal that is large in size, highly pure, has a high specific resistance value, and can be used in a small and lightweight radiation detector with high sensitivity. This is what I did. (Means for Solving the Problems) As a result of various studies as a means for solving the above problems, the present inventors found that Ga is present in a quartz ampoule containing Cd and Te raw materials at a concentration of 5×10 ¹⁴ to 5× 10 ¹⁸ atoms/
After adding metallic Ga to a concentration of 5×10 14 to 5×10 atoms/cm ³ , the quartz ampoule is vacuum sealed, and then Ga is added to a concentration of 5×10 ¹⁴ to 5×10 atoms/cm ³ by the Bridgeman method or gradient freeze method. It has been discovered that the synthesis and growth of cadmium telluride crystals can contribute to solving the problem. (Function) In the present invention, polycrystals of CdTe are synthesized by doping a raw material mixture of Cd and Te with Ga in a quartz ampoule and heating it under vacuum sealing, and then seeding the synthesized polycrystals. A single crystal is grown as a nucleus by the Bridgeman method or gradient freeze method, and in this case, the Ga concentration in the grown polycrystal and the grown single crystal is set to 5×10 ¹⁴ to 5×10 ¹⁸ atoms/
cm ³ exhibits a high specific resistance value as described below. Furthermore, these CdTe single crystals are characterized by being relatively large and highly pure. All results were obtained when the Ga concentration was outside the above range.
The specific resistance value of the CdTe crystal did not reach the required value, which was 1×10 ⁶ to 1×10 ¹⁰ Ω・
It has become difficult to obtain cadmium telluride crystals with a high resistance of cm, making it impossible to achieve the intended purpose. In addition, in carrying out the present invention, in order to obtain a high-resistance crystal, the molar ratio of Cd and Te is 0.9 to 0.9.
It is preferable to set it to 0.9999. (Example) Cd, Te, and Ga with a purity of 99.9999% were used as raw materials, and the molar ratio of Cd and Te was 0.9995.
As shown, Cd is 178g, Te is 202g, Ga is 0.35g.
After weighing mg and inserting each of the above raw materials into a quartz ampoule with an inner diameter ^of 30 mm,
The quartz ampoule was sealed in a vacuum of 10 ^-6 Torr, and the quartz ampoule was further heated to 1150°C in a synthesis furnace to synthesize Ga-doped CdTe, and then the quartz ampoule was transferred to a crystal growth furnace, and further, 0.4℃ from 1100℃/
After crystal growth treatment of cooling at a cooling rate of hr for 100 hours, the quartz ampoule was heated at 50℃/hr.
The above quartz ampoule was cooled by the gradient freezing method, in which it was sequentially cooled down to room temperature at a cooling rate of
The fabrication was obtained by growing Ga-doped CdTe single crystals. The limited range concentration of the present invention obtained in this way
Single crystal of Ga-doped CdTe (example) and Ga concentration outside the limited range and also Cd and Te without Ga-doping
Table 1 shows the results of measuring the specific resistance value of the crystal (Example) prepared using only the combination of 1 and 2 with varying Ga concentrations.

[Table] From Table 1, in the case of the present invention, the maximum is 1.2 × 10 ⁹
(Ω・cm), and even a low resistivity value of 1×10 ⁶ (Ω・cm) is required for general radiation detectors.
It can be seen that it exhibits a resistivity value higher than cm). On the other hand, those that are adjacent to but deviate from the upper and lower limits of the Ga doping concentration of the present invention are ×10 ³ order (Ω cm)
Only a relatively low specific resistance value was obtained, and the one without Ga doping showed a low value of the order of ×10 ² (Ω·cm), making it impractical. In addition, when using the conventional method of adding cadmium chloride, the yield of the final product was only 70% due to the accidental breakage of the quartz ampoule, but compared to that, the yield of the final product was only 70%. In some cases, there were no incidents of damage to the quartz ampoules, and the yield of the product was significantly increased. In addition, according to the results of measurements of synthesized quartz ampoules obtained by the same synthesis process as above and subjected to crystal growth treatment using the Bridgeman method, the resistivity values with respect to the amount of Ga added were all the same as those obtained by the gradient-freeze method. The value was almost the same as that for the case of drying. (Effects of the Invention) As described above, according to the present invention, a cadmium telluride single crystal, which is in high demand for radiation detectors, etc., can be made relatively large and have a high specific resistance value, and can be made with high purity and a high product yield. Since it can be easily obtained, it makes a great contribution to this industry.

Claims (1)

[Claims] A cadmium telluride crystal containing 5×10 ¹⁴ to 5×10 ¹⁸ atoms/cm ³ of 1 Ga. 2 Ga in a quartz ampoule containing Cd and Te raw materials.
After adding metal Ga to a concentration of 5×10 ¹⁴ to 5×10 ¹⁸ atoms/cm ³ , the quartz ampoule is vacuum sealed, and then synthesized by the Bridgeman method or gradient freeze method, A method for producing a cadmium telluride crystal, which is characterized by growing a cadmium telluride crystal.