JPH0791156B2 - Method for producing CdTe single crystal - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing a CdTe single crystal useful as a radiation detecting element and the like.

Conventional technology CdTe single crystals are useful for radiation detectors, etc.
A method for producing a Te single crystal is being studied.

A large carrier lifetime is important as a crystal characteristic for achieving high energy resolution.
It is known that the carrier lifetime is significantly affected by the crystal purity, and therefore, crystals for radiation detection elements have been produced by the traveling heater method or the like, which is said to have a high purification effect.

Problems to be Solved by the Present Invention However, there is a problem that even a crystal grown by a traveling heater method or the like does not necessarily have a sufficient carrier lifetime for a radiation detection element.

Structure of the Invention The present invention is to solve the above problems, in the method for producing a CdTe single crystal for a radiation detection element, Te and Cd
The composition ratio (Te / Cd) of 1.1 is an atomic ratio of 1.1 to 9 and the melt is cooled from one side to precipitate CdTe, and then the precipitated CdTe is separated from the remaining Te excess portion to obtain high-purity CdTe. First to get
Step and Te with a trace amount of chlorine source added as a solvent, and the CdTe obtained in the first step is brought into contact with this to heat the Te solvent, and this heating part is gradually moved to the CdTe side. The present invention relates to a method for producing a CdTe single crystal, which comprises a second step of depositing a CdTe single crystal on the side opposite to the moving direction by moving the CdTe single crystal.

Means and Actions for Solving Problems The present inventors have found that the raw material CdTe mass used has a composition of CdTe.
By using crystals precipitated from the melt in a Te-excessive state, the carrier lifetime of the grown crystals is significantly increased, and the radiation detection element using the crystals thus produced has a good energy resolution. The present invention has been newly found out to have the following, and has led to the present invention.

The first step of the present invention is the high purity used in the second step.
This is the process of obtaining CdTe lumps. Cd and T with a purity of 99.9999% or more
e is sealed in a container such as a quartz ampoule in a vacuum or an inert gas atmosphere so that the composition ratio (Te / Cd) is 1.1 or more and 9 or less in atomic ratio. Already Cd and Te with a purity of 99.9999% or more
The CdTe crystal synthesized from and Te may be mixed in the above composition ratio.

This is set so that the entire ampoule enters the soaking section of the electric furnace having the temperature distribution as shown in FIG. 1, and the inside of the ampoule is made into a melted solution. The temperature of the soaking part at this time depends on the composition ratio of Te and Cd, and can be lowered as the degree of excess Te increases. For example, (Te / Cd)
= 1.1, it is possible to melt at 1050 ℃,
When (Te / Cd) = 9, it is possible to melt at 700 ° C.

The composition ratio of Te and Cd (Te / Cd) must be 1.1 or more in atomic ratio. If it is less than 1.1, the melting point of the melt exceeds 1050 ° C., the precipitation temperature of CdTe is high, and the purification effect is reduced due to contamination from the ampoule, which is not effective. Further, the composition ratio of Te and Cd (Te / Cd) needs to be 9 or less in atomic ratio.
If it exceeds 9, the concentration of Cd in the melt is too low and not only CdTe but also Te is simultaneously precipitated in CdTe, which is not preferable.

In this way, the whole of the ampoule is melted, and the melted solution is moved to the low temperature side to deposit CdTe on the low temperature side. The temperature distribution may be moved with respect to the ampoule. A good ampoule moving speed is 0.1-5 mm / hr. When the moving speed of the ampoule is 0.1 mm / hr or less, the first step takes 1 month or more, which is not preferable because the productivity is not good industrially. At a speed of 5 mm / hr or more, Te remains in CdTe, which is not preferable because the purification effect is not improved.

High-purity CdTe can be deposited by the above method. This is because the crystals can be precipitated at a temperature lower than 1092 ° C., which is the melting point of CdTe, and the contamination from the ampoule is reduced. This is also because the melt having a composition in excess of Te has a higher effect of gettering impurities than the melt of CdTe. This gives the desired high purity CdTe for use in the next second step. For example, the carrier concentration of the CdTe lump obtained in this first step is 2 × 10 ¹⁴ /
Very low with cm ³ or less and high purity.

In this way, after a high-purity CdTe mass is deposited, the deposited CdTe is separated from a portion having a composition excess of Te. This includes
After the deposition of CdTe is completed, it is preferable to cool the ampoule, take out the contents, and split the CdTe deposited near the boundary between the deposited CdTe portion and the Te-excess portion to separate it, because mixing is small.

The second step of the present invention is a step of performing crystal growth by using the CdTe mass obtained in the first step as a raw material.

By using Te to which a trace amount of chlorine source is added as a solvent, and contacting it with the CdTe obtained in the first step, heating the Te solvent, and gradually moving this heating part to the CdTe side. , CdTe crystals are deposited on the opposite side of the moving direction.

Examples of the chlorine source include CdCl ₂ , TeCl ₂ , TeCl ₄ , Cl _{2 and the} like.
These chlorine source, Te, and CdTe obtained in the first step are put into an ampoule as shown in FIG. 2 and sealed in a vacuum or an inert gas atmosphere. As shown in FIG. 3, a single crystal serving as a seed crystal may be placed at the bottom of the ampoule. By heating the Te, the CdTe obtained in the first step is partially dissolved in Te. Here, Te is the solvent.

A heating temperature of 650 ° C to 950 ° C is suitable. More preferably
It is 700 ℃ -800 ℃. If the heating temperature is 650 ° C. or lower, the growing crystal becomes polycrystal, which is not preferable, and if the heating temperature is 950 ° C. or higher, the purity of the growing crystal is lowered, and the carrier lifetime is reduced.

By gradually moving this heating part to the CdTe side obtained in the first step, CdTe is gradually dissolved in the Te solvent, and at the same time, a single crystal is gradually precipitated on the opposite side. It suffices that the heating unit moves relative to the ampoule. Therefore, the ampoule may be fixed and the electric furnace moved, or the electric furnace may be fixed and the ampoule moved. Movement speed is 1-10
mm / day is preferred. More preferably, it is 2 to 5 mm / day.
If the moving speed is 1 mm / day or less, crystal growth takes too much time, which is not industrial. When the moving speed is 10 mm / day or more, the growing crystal becomes a polycrystal, which is not preferable.

The CdTe single crystal obtained in the second step has a high resistance because it contains a trace amount of chlorine and, at the same time, has an extremely high purity due to the first and second steps, and thus has a large carrier lifetime and radiation detection. Excellent as a crystal for devices.

[Example] 460 g of CdTe polycrystal having a purity of 99.9999% and T having a purity of 99.99999%
220 g of e was mixed and vacuum-sealed in an ampoule. (Composition (T
e / Cd) = 1.9) This is 1000 ℃ in an electric furnace as shown in Fig. 1.
After melting with, move to the low temperature side at a speed of 1 mm / hr, and
Was deposited. After cooling this, CdTe was separated from the Te excess portion to obtain a rod-shaped CdTe mass.

Next, 100 mg of CdCl ₂ , 40 g of Te, and the above CdTe lumps were put in another quartz ampoule as shown in FIG. 2 and sealed with Ar300 torr. As shown in Fig. 4, heat the Te solvent at 800 ℃ and
The ampoule was moved at mm / day to grow a CdTe single crystal.

The chlorine concentration of this crystal is 5ppm, and the carrier lifetime is
The holes were as large as 0.5 μs and the electrons were as large as 1 μs. A radiation detecting element was prepared from this crystal and the radiation of ²⁴¹ Am was measured. As a result, the half width of the spectrum was 5 keV, which was an excellent resolution.

Comparative Example 1 A CdTe polycrystal having a purity of 99.9999% was vacuum-encapsulated in an ampoule and cast at 1100 ° C. to obtain a rod-shaped CdTe lump.

Using this as a raw material, crystal growth was performed in the same manner as in the example.

The chlorine concentration of this crystal was 5 ppm and was the same as in the example,
The carrier lifetime is 0.2μs for holes and 0.5μs for electrons.
s, which was smaller than that of the example. As a result of making a radiation detector from this crystal and measuring the radiation of ²⁴¹ Am, the half width of the spectrum was 10 keV and the resolution was poor.

EFFECTS OF THE INVENTION According to the present invention, a crystal having high crystal purity and a long carrier lifetime can be obtained, and a radiation detection element produced using this crystal has an effect that energy resolution is improved as compared with the conventional one. is there.

[Brief description of drawings]

FIG. 1 shows the outline of the first step. FIG. 2 shows an outline of the ampoule in the second step. FIG. 3 shows the outline of an ampoule in the second step when a seed crystal is used. FIG. 4 shows an outline of crystal growth in the second step. 1 ... Electric furnace 2 ... Ampule 3 ... Precipitated CdTe 4 ... Te excess melt 5 ... CdTe 6 obtained in the first step ... Te solvent 7 ... Chlorine source 8 ... Seed crystal 9 ... … Electric furnace 10 …… CdTe single crystal

Claims (1)

[Claims] 1. A method for producing a CdTe single crystal for a radiation detecting element, wherein a melt having a composition ratio of Te and Cd (Te / Cd) of 1.1 to 9 in atomic ratio is cooled from one side to precipitate CdTe. After that, the precipitated CdTe is separated from the remaining Te excess to obtain a high-purity CdTe, and Te containing a trace amount of chlorine source is used as a solvent. The second step of bringing the CdTe single crystal into contact with the obtained CdTe, heating the Te solvent, and gradually moving the heating part to the CdTe side to precipitate a CdTe single crystal on the opposite side to the moving direction. A method for producing a CdTe single crystal characterized by: