JPH0769798A - Production of cdte crystal - Google Patents

Abstract

PURPOSE:To improve productivity and to reduce production cost by bringing a-Cd-Te melt containing excessive Te into contact with a CdTe raw material in a crystal growth container, cooling and solidifying crystal under a specific condition. CONSTITUTION:A holding fixture 3 which is supported by a quartz ampule l made of quartz having a large number of venting holes is prepared and a coating film of graphite is formed on the inside of the quartz ampule 1 and the surface of the holding fixture 3. A Cd-Te alloy containing excessive Te, having the molar ratio of Cd:Te of 40:60 having dissolved CdCl2 so as to contain about 300ppm chlorine in weight concentration based on melt, the holding fixture 3, the Cd-Te alloy containing excessive Te and a CdTe ingot are inserted in this order into the quartz ampule l from the bottom, the container is evacuated in vacuum, an Ar gas is introduced up to 100Torr pressure and the ampule 1 is sealed. The ampule is firstly heated by an electric furnace under a temperature distribution shown by the right figure to form a Cd-Te melt 4 containing excessive Te. The temperature distribution is maintained and the melt is cooled and solidified from a direction opposite to the direction wherein the Cd-Te melt 4 is in contact with CdTe raw materials 2 in terms of a stoichimetric composition.

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 CdTe crystal, and particularly to a chlorine doped C useful as a radiation detecting element.
The present invention relates to a method for producing dTe crystals with high productivity.

[0002]

2. Description of the Related Art CdTe is a semiconductor having a higher radiation absorption coefficient than Si and Ge and a large energy gap at room temperature. Therefore, when it is used as a radiation detecting element, an element having excellent characteristics can be obtained. You can

A CdTe radiation detecting element generally has a structure in which electrodes for applying a bias voltage are formed on two opposite surfaces of a crystal, and positive and negative carriers generated when the CdTe crystal is irradiated with radiation. (Electron-hole pair)
Is to detect the electric current generated by being attracted to the electrode. Therefore, the CdTe crystal used has an electrically high resistance so that a current does not flow when it is not irradiated with radiation, and the positive / negative generated by radiation irradiation in order to increase the radiation-current conversion efficiency. It is important that the carrier has a long life.

The high-resistance CdTe crystal satisfying the above requirements is grown from high-purity Cd and Te as raw materials while doping several ppm of chlorine under the condition that inclusions called "inclusion" are not generated. Is obtained by
The most common one is THM (Traveling Heater Method)
Is.

In this method, first, a cylindrical C that is a raw material is used.
Te containing a trace amount of chlorine at the lower end of the dTe polycrystalline ingot
A quartz ampoule in which is used as a solvent is prepared, and the lower end of the ampoule is heated by using a heater with a narrow heating width to melt Te, and at the same time, CdTe immediately above is melted by the solubility at that temperature. Form a Cd-Te zone. When the ampoule is lowered at a low speed while maintaining the heating temperature, the Cd-Te melt zone has CdT above it.
The e-polycrystal is melted and moves upward while maintaining its composition, and a chlorine-doped CdTe crystal grows downward. When a CdTe crystal is precipitated from a Te-excess Cd-Te melt, the segregation coefficient of chlorine from the melt to the CdTe crystal is small at 0.003 to 0.006, and the amount of the melt is almost constant during crystal growth. Therefore, a CdTe crystal in which chlorine is uniformly doped in the growth direction can be obtained.

Furthermore, the chlorine doped Cd obtained by THM
Te crystal is C having stoichiometric composition such as Bridgman method.
Compared with the chlorine-doped CdTe crystal obtained from the dTe melt, it has a higher energy when used as a radiation detection element.
It is also excellent in that the deterioration of the detection performance is small when the above radiation is irradiated.

[0007]

However, according to the conventional THM, the chlorine doping CdTe for a radiation detecting element is used.
In the case of producing a crystal, in addition to the step of separately preparing a columnar raw material CdTe polycrystal that can be inserted into an ampoule without a gap, in addition to a narrow melting band width when the diameter of the crystal is increased to about 30 mm. In order to grow, the growth rate must be as low as about 3 to 4 mm / day (0.12 to 0.17 mm / Hr), and there is a problem that productivity is low and manufacturing cost is high.

[0008]

SUMMARY OF THE INVENTION The present invention has solved the above-mentioned problems, and is characterized in that Te is contained in a crystal growth container.
After maintaining the excess Cd-Te melt and the stoichiometric CdTe raw material in contact with each other, the Te excess Cd
A method for producing a CdTe crystal, which comprises cooling and solidifying a Te melt from a direction opposite to a direction in which the CdTe raw material having the stoichiometric composition is in contact.

Further, the present invention provides a method for producing a CdTe crystal, characterized in that chlorine is dissolved in the above Te-excessive Cd-Te melt. First, the inventor of the present invention, as described above, when the chlorine-doped CdTe crystal produced by THM is used as a radiation detection element, its performance is superior to that obtained by the Bridgman method or the like.
In the production of CdTe crystals for a radiation detection element, a Cd-Te melt having a composition in which Te is in excess of the stoichiometric composition, that is, a solution in which Cd is dissolved using Te as a solvent is Cd
We thought that the mechanism of Te crystal precipitation was important.

However, unlike the THM, it is possible to easily supply Cd with excess Te without supplying CdTe as a raw material continuously.
As a method of obtaining crystals from a Te solution, for example, 3
When a CdTe crystal having a stoichiometric composition is to be precipitated by cooling a melt of 5 mol% Cd-65 mol% Te from one end, a phase diagram (T-x diagram) of a Cd-Te binary system is obtained. According to the liquidus line shown, the first crystal precipitates from the melt at 1000 ° C., but as the concentration of Cd in the melt gradually decreases, the crystal precipitation temperature decreases. That is, since the melt near the crystal growth boundary surface is likely to be in a structurally supercooled state as the crystal grows, it is necessary to gradually slow the descending speed of the ampoule or change the heating temperature distribution of the ampoule with time. Only the crystal of extremely poor quality can be obtained because the melt is taken into the crystal and the ink is generated.

Further, in the above method, when chlorine-doped CdTe crystals for a radiation detecting element are to be obtained by dissolving chlorine in the melt, the crystals are deposited in the crystals as the precipitation of the crystals progresses. The increase in chlorine doping reduces the yield of crystals that can be used for high performance radiation detection elements. By the way, 35 mol% Cd-65 mol%
The amount of chlorine doping in the crystal obtained by cooling the melt in which Te has a chlorine concentration of about 600 ppm with respect to Te at a constant rate from one end is about 2 ppm at the beginning, but 10 ppm in the latter half. As a result of making a radiation detecting element using this crystal and examining its performance, only about 30% of the first grown portion showed satisfactory characteristics.

From the above consideration, the present inventor found that Te-excessive C
By growing a CdTe crystal from a state in which a CdTe raw material having a stoichiometric composition is immersed in a d-Te melt, an increase in the amount of chlorine doping in the crystal is suppressed, and a structure caused by a change in the melt composition The present invention has been made on the idea that it is possible to suppress overcooling.

In the method of the present invention, the Te-excessive Cd-Te melt is prevented from increasing the Te concentration due to the growth of CdTe crystals by melting the CdTe raw material having a stoichiometric composition into the melt. The melt composition is maintained at the composition on the liquidus line at the heating temperature until all the CdTe raw materials are melted. Moreover, since it is not necessary to narrow the zone width as in THM, the crystal can be upsized and the growth rate can be increased. The stoichiometric composition of the CdTe raw material is not strict, and there is no particular problem as long as it is within a range of about ± 1 at%.

[0014]

EXAMPLE A shape as shown in FIG. 1 (lower inner diameter 30 mm
A quartz ampoule having a length of 170 mm, an upper inner diameter of 35 mm and a length of 160 mm) and a quartz holder having a large number of liquid passage holes with a diameter of 3 mm supported by a portion where the inner diameter of the ampoule is narrowed are prepared. A graphite film was formed on the surface of the quartz holder.

From the bottom of the quartz ampoule, cadmium chloride was dissolved so as to contain chlorine of about 300 ppm by weight with respect to the melt, and the molar ratio of Cd: Te was 40:60 Te.
Excess Cd-Te alloy ingot 500 g, quartz holder, Te excess Cd-Te alloy ingot 250
g and 280 g of CdTe ingots were inserted in that order, and after evacuation, an ampoule was sealed while Ar gas was introduced up to a pressure of 100 Torr.

The entire ampoule was first heated in an electric furnace under the temperature distribution as shown in FIG.
Forming a Te melt, 0.5m while maintaining its temperature distribution
The ampoule was lowered by 200 mm at a speed of m / Hr, and then the whole was cooled to room temperature at a speed of 20 ° C./Hr. The taken out ampoule was cut together with the contents at a position 130 mm from the tip, and the lower crystal was extracted. 1 from the tip of the crystal
A small amount of ink was observed in the area of 10 mm or more, so that area was cut and 100 mm from the tip,
When the distribution of chlorine doping amount was examined for about 450 g of CdTe crystal, it was 2.5 ± 0.5 p over the entire cavity.
It was within the range of pm and was uniform.

A radiation detecting element was produced from this chlorine-doped CdTe crystal, and its radiation detecting performance was compared with that of the crystal obtained by THM. As a result, any crystal cut from any position with a total length of 100 mm was equivalent to a THM crystal. Showed the performance of. In the examples, a Cd-Te alloy having a Te-rich composition was used to prepare a Te-rich Cd-Te melt, but the present invention is not limited to this, and Cd and Te should be added in such a proportion that Te becomes excessive. You can

Further, an example in which the molar concentration of Cd is 35% as the Te-excess Cd-Te melt composition is shown, but it should be 20% or more and 45% or less, that is, the crystal precipitation temperature should be 800 ° C or more and 1050 ° C or less. Needless to say, the present invention can be applied. In addition, it is difficult to grow CdTe containing no inclusions at a practical rate from a melt having a Cd molar concentration of 20% or less, that is, a melt having a crystal precipitation temperature of less than 800 ° C., and a Cd molar concentration of 50%. That is, a high-performance CdTe radiation detecting element cannot be obtained from a crystal grown from a melt having a stoichiometric composition with a crystal precipitation temperature of 1092 ° C.

Further, the crystal precipitation rate is set to 0.5 mm / H.
Although r is used, it can be selected within a range of 1 mm / Hr or less. It should be noted that, if it exceeds 1 mm / Hr, the ink droplets will be generated. Further, as the method for contact-holding the CdTe raw material in the melt, the quartz holder having the liquid passage hole is shown, but it is obvious that a material having a proper material or shape can be used.

Further, although the ampoule is moved in the embodiment, the heater may be moved and the temperature distribution may be changed by temperature control. Further, in the embodiment, the CdTe raw material is contacted from the upper surface of the melt and cooled and solidified from the lower surface of the melt, but conversely, the CdTe raw material is contacted from the lower surface of the melt and cooled and solidified from the upper surface of the melt.

[0021]

As described above, according to the present invention, after the Te-excessive Cd-Te melt and the stoichiometric CdTe raw material are kept in contact with each other in the crystal growth container,
The Te-rich Cd-Te melt was added to the stoichiometric composition of CdT.
Since the melt of Te-rich Cd-Te is cooled from one side in an ampoule that is cooled and solidified from the direction opposite to the direction in which the e raw material is in contact with the CdTe crystal to grow, it is more productive than THM. The effect is that crystals of equivalent quality can be manufactured.

[Brief description of drawings]

FIG. 1 is a schematic view showing a method for producing a CdTe crystal according to the present invention.

[Explanation of symbols]

 1 Quartz Ampoule 2 Stoichiometric CdTe Raw Material 3 Holder 4 Te Excess Cd-Te Melt 5 CdTe Crystal

Claims (2)

[Claims] 1. An excess of Cd—Te in a crystal growth container in a Te growth chamber.
After maintaining the melt and the stoichiometric CdTe raw material in contact with each other, the Te-excessive Cd-Te melt is in a direction opposite to the direction in which the stoichiometric CdTe raw material is in contact. A method for producing a CdTe crystal, which comprises cooling and solidifying from. 2. The CdT according to claim 1, wherein chlorine is dissolved in the Te-excessive Cd-Te melt.
e Crystal manufacturing method.