JP2858598B2 - Method for producing CdTe single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-resistance CdTe single crystal useful for a radiation detecting element or the like.

[0002]

2. Description of the Related Art A CdTe single crystal is useful for a radiation detecting element capable of operating at room temperature, and its production method has been studied for the purpose of improving the energy resolution of the element.

In order to achieve high energy resolution,
It is important that the resistivity is high. Signal noise of low resistivity and the radiation detector is increased undesirably, 1 × 10 ⁸
Ωcm or more is required.

However, in the case of a CdTe single crystal with no impurity added, vacancies of Cd serve as acceptors, resulting in 100 Ω p-type.
A resistivity of only about cm can be obtained.

There is also known a method of improving the resistivity by adding a donor impurity such as Cl or In to compensate for acceptors due to Cd vacancies.
In the case where is added, there is a problem that the count rate of the manufactured radiation detecting element changes greatly with the time after the application of the bias voltage. In the case of adding In, there is no such a problem, but there is a problem that a CdTe single crystal having a high resistivity cannot be produced with good reproducibility.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems and provides a method for producing a high resistivity CdTe single crystal doped with In with good reproducibility.

[0007]

[Means and Actions for Solving the Problems]
In 0.001 wt ppm or more, 0.5 wt ppm or less
It was added to a concentration below were grown in THM method C
dTe single crystal is placed in a vacuum or in an inert gas for 17 hours.
A method for producing a CdTe single crystal characterized by performing a heat treatment at a temperature of 0 ° C. or more and 230 ° C. or less . According to the present invention, a high-resistance In-doped CdTe suitable for a radiation detecting element is provided.
A single crystal can be obtained with good reproducibility.

The present inventor considered that the thermal history of the crystal greatly affected the resistivity, and conducted an experiment in which CdTe single crystals having different In concentration levels were heat-treated while changing the heat treatment temperature, and the resistivity was measured. FIG. 1 shows the experimental results.

[0009] Experiments have shown that the In concentration in the CdTe single crystal is 0.05 wt ppm, 0.5 wt ppm, 1.9 wt p
Four types of CdTe single crystals, one with pm and one without In, were cut into wafers, and were cut from 110 ° C. to 375 in vacuum.
After heat treatment for 15 hours in a temperature range of ° C., the resistivity was measured.

From FIG. 1, it can be seen that the resistivity without addition of In is almost unchanged at 1 × 10 ² Ωcm regardless of the heat treatment temperature. When the In concentration was 1.9 wt ppm, the resistivity decreased as the heat treatment temperature increased. On the other hand, the In concentration was 0.05 wt ppm and 0.5 wt ppm.
In the case of those with the weight ppm, the resistivity shows the highest value near the heat treatment temperature of 200 ° C. and reaches 1 × 10 ⁹ Ωcm.

The heat treatment temperature in the present invention is 170 ° C. or more and 230 ° C. or less in order to make the resistivity 5 × 10 ⁸ Ωcm or more necessary for the radiation detecting element.

In the present invention, the concentration of In added to the CdTe single crystal is at least 0.001 ppm by weight , and 0.5 ppm by weight.
m or less . When the content is less than 0.001 ppm by weight, only the same result as that when no additive is obtained is obtained, and when the content exceeds 0.5 ppm by weight , the resistivity becomes less than 5 × 10 ⁸ Ωcm.

The heat treatment atmosphere in the present invention is a vacuum or an inert gas atmosphere such as Ar or nitrogen for preventing the oxidation of the crystal.

[0014] The heat treatment time of the present invention is 1 hour or more,
Preferably, it is 15 hours or more. It should be noted that the same effect can be obtained whether the CdTe single crystal is heat-treated in a wafer or in an ingot.

[0015]

EXAMPLE CdTe single crystals were grown by the THM method by adding In such that the In concentration in the crystals was 0.5 ppm by weight.

The CdTe single crystal is cut into wafers,
After heat-treating at 220 ° C. for 15 hours in a vacuum, the resistivity was measured after cooling in a heat-treating furnace to room temperature at a cooling rate of 10 to 50 ° C./Hr. The resistivity is all (1-2) x 1
0 ⁹ [Omega] cm and a uniform, it was of sufficient resistivity to the radiation detecting element.

[0017]

[Comparative Example 1] was measured while resistivity without performing a heat treatment of single crystal grown in Example 1, 1 × 10 ⁵ ~
It showed a large variation of 3 × 10 ⁷ Ωcm, and the resistivity was insufficient for a radiation detecting element.

[0018]

According to the present invention, the content of In is 0.001 wt ppm or more .
THM is added so as to have a concentration of 5 ppm by weight or less.
By heating the CdTe single crystal grown by the method at a temperature of 170 ° C. or higher and 230 ° C. or lower in a vacuum or an inert gas, a high resistivity In-doped CdTe single crystal suitable for a radiation detecting element is obtained. It can be obtained with good reproducibility.

[Brief description of the drawings]

FIG. 1 is a diagram showing the results of measuring the resistivity of CdTe single crystals having different In concentration levels by performing a heat treatment while changing a heat treatment temperature.

Claims (1)

(57) [Claims] 1. A In the 0.001 ppm or greater, 0.5
THM method by adding so that the concentration becomes less than ppm by weight
A method for producing a CdTe single crystal, characterized by subjecting the CdTe single crystal grown in 1) to a heat treatment at a temperature of 170 ° C. or more and 230 ° C. or less in a vacuum or an inert gas.