JPH08217590A - Method for growing single crystal - Google Patents

Abstract

PURPOSE: To obtain a large-diameter single crystal by THM with good reproducibility. CONSTITUTION: A growth vessel 1 having a positioning means for placing the lower end of a raw material 4 on a step 1a between the part where the inner diameter of the vessel 1 is smaller than the outer diameter of the lower end of the raw material and the upper part having a larger diameter is used, the lower end of the raw material is positioned by the positioning means at the start of crystal growth, then the vessel is relatively moved to a heater 5, and the crystal growth is started. Consequently, a large-sized single crystal with the grain boundaries and twin crystals reduced is obtained with good reproducibility.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a single crystal and a method for growing a crystal by a traveling heater method (THM), and more particularly to a technique useful for producing a compound semiconductor single crystal such as CdTe.

[0002]

2. Description of the Related Art As a method for growing a single crystal of a compound semiconductor such as CdTe, a columnar raw material having the same composition as the crystal to be grown and a solvate serving as a solvent for dissolving the raw material at the time of crystal growth are used. Placed in a growth vessel so that it contacts the upper end of the raw material, the solvate is locally heated by a heater to melt and the lower end of the raw material is also dissolved to form a dissolution zone, and then the heater is moved upward, or Is a THM in which a single crystal is continuously deposited and grown from the lower end of the melting zone by moving the growth container downward. The crystal growth by THM is superior to the crystal obtained by other growth methods in Cd for semiconductor radiation detection elements.
There is an advantage that a Te single crystal can be obtained.

Generally, in the case of growing a CdTe single crystal by THM, a growth container such as a quartz ampoule is provided with
Put Te as a solvent or an alloy block in which Te is dissolved into Te with an appropriate amount of CdTe, and put a columnar polycrystalline raw material of CdTe on it, and further seal the quartz ampoule in a vacuum atmosphere or inert gas atmosphere. Perform crystal growth. This is to prevent the evaporation of the Te solvent and the oxidation of the polycrystalline raw material of CdTe. When a seed crystal is used, the seed crystal is put in advance at the bottom of the quartz ampoule, and a simple substance of Te or the like serving as a solvent and a polycrystalline raw material are sequentially put into the quartz ampoule to start crystal growth.

[0004]

[Problems to be Solved by the Invention] However, CdT
e has a feature that the difference in growth energy between different crystal orientation planes is small and twinning is likely to occur. Further, in the above-mentioned THM, Cd- which is largely deviated from the stoichiometric composition to the Te excess side. Since a crystal is precipitated from the Te solution, it is difficult to obtain a CdTe single crystal having a large grain size and a desired crystal orientation with good reproducibility regardless of the presence or absence of a seed crystal.

The present invention has been made to solve the above problems, and an object thereof is to obtain a single crystal having a large grain size, particularly a CdTe single crystal with good reproducibility by THM.

[0006]

In order to achieve the above object, the present inventor conducted a growth experiment of a CdTe crystal by THM, and carried out the amount of the dissolution zone during the crystal growth, the shape of the crystal precipitation interface and the growth. Detailed studies were conducted on crystals.
As a result, it is preferable that the lower surface of the melting zone has a convex shape in order to grow a single crystal, but it is not possible to obtain a single crystal with good reproducibility. It turned out that the cause was poor. A more detailed study showed that the solvate to be the Te solvent and the polycrystalline raw material were simply put in a quartz ampoule and locally heated to form a dissolution zone. The conclusion is that the (immersion amount) cannot be controlled, that is, the amount of the dissolution zone existing below the raw material at the start of crystal growth cannot be set to an appropriate amount each time crystal growth is performed. Came to.

The present invention has been made on the basis of the above findings and the like, and a columnar raw material and a solvate serving as a solvent for dissolving the raw material at the time of crystal growth are brought into contact with the upper end of the solvate. By putting it in a growth container, melting the solvate by local heating with a heater and melting the lower end of the raw material to form a dissolution zone, and moving the heater upward relative to the growth container. When a single crystal is continuously deposited and grown from the lower end of the melting zone, it is positioned by the positioning means provided in the growth container so that the lower end of the raw material comes to a predetermined height in contact with the melting zone. After that, the relative movement of the heater is started.

A seed crystal may be arranged in the growth vessel so as to come into contact with the lower end of the solvate and after the formation of the dissolution zone, contact with the lower end of the dissolution zone.

Further, the solute concentration in the sorbent body placed in the growth container is preferably 50% or more and 100% or less of the saturated concentration of the solute in the solvent at the crystal growth temperature.

Further, after the raw material and the solvate are put in the growth container, first, the entire growth container is first heated and held by a heater in a temperature range above the melting temperature of the solvate but below the crystal growth temperature. To melt the solvate into a solvent, and then locally heat the solvent to a crystal growth temperature with a heater to form the dissolution zone, and then start relative movement of the locally heated heater. You may do it.

Then, for example, the solvate is Te-excess C
It is a d-Te alloy, the raw material is a polycrystal of CdTe, and the crystal to be grown is a single crystal of CdTe.

Further, in the positioning means, the inner diameter of a part or all of the lower half portion of the bottomed cylindrical growth container is smaller than the outer diameter of the lower end of the raw material, By holding and supporting the lower end of the raw material on the stepped portion between the portion having a small inner diameter and the upper half portion of the growth container for containing the raw material, the lower end of the raw material is held at a predetermined height. In addition, a convex portion projects inward from the inner peripheral wall of the bottomed cylindrical growth container, and the lower end of the raw material is placed on and supported by the convex portion. May be.

[0013]

According to the above-mentioned means, when a single crystal is grown by THM, the lower end of the solvate and the raw material placed in the growth container are locally heated and melted by the heater to form a dissolution zone at that time. Since the lower end of the raw material was positioned by the positioning means of the growth container so that the lower end of the raw material was in contact with the melting zone at a predetermined height, relative movement of the heater was started to start crystal growth. Every time I do,
At the start of crystal growth, the amount of the dissolution zone existing below the raw material becomes appropriate, so that the lower surface of the dissolution zone has a smooth convex shape, and a single crystal having a large grain size grows reproducibly.

At this time, if a seed crystal is arranged in the growth container so as to contact the lower end of the dissolution zone, a single crystal having a desired crystal orientation can be obtained.

The solute concentration in the solvate is preferably 50% or more and 100% or less of the saturated concentration of the solute in the solvent at the crystal growth temperature. The reason is that if the solute concentration is lower than the lower limit value, the lower end of the raw material is remarkably melted when the dissolution zone is formed and the lower end shape of the raw material changes, and the lower end of the raw material is fixed by the positioning means of the growth container. This is because it is difficult to position it at a position, and when the seed crystal is used, the seed crystal is melted so much that it becomes difficult to set the holding position at the lower end of the raw material. On the other hand, at a solute concentration exceeding the upper limit value, the solvate does not completely melt, the amount of the dissolution zone does not reach the desired amount, and when the seed crystal is used, the contact between the seed crystal and the dissolution zone is This is because you cannot get it completely.

Further, the entire growth container containing the raw material and the solvate is once heated and held in a temperature range above the melting temperature of the solvate and below the crystal growth temperature to melt the solvate, and then the melted solvent is locally added. By starting the crystal growth after heating to the crystal growth temperature to form the dissolution zone, the gap between the raw material and the growth vessel is filled with the solvent in advance before the crystal growth starts, so that the evaporation of the solvent is prevented. , The amount of dissolution zone during crystal growth is kept constant.

Here, for example, the solvate is Te excess Cd-.
When a Te alloy is used and the raw material is a polycrystal of CdTe and a CdTe single crystal is grown, a high-quality CdTe single crystal suitable for a semiconductor radiation detection element can be obtained with a high yield.

Further, the positioning means is adapted to place the lower end of the raw material on the stepped portion between the portion where the inner diameter of the growth container is smaller than the outer diameter of the lower end of the raw material and the portion above the lower end of the raw material to support it. Or, by supporting the lower end of the raw material by placing it on the convex portion projecting inward from the inner peripheral wall of the growth container, the lower end of the raw material can be placed at a predetermined position with the growth container having a simple structure. Can be held.

[0019]

EXAMPLES The features of the present invention will be clarified below with reference to examples in which the present invention is applied to the growth of CdTe single crystals. Needless to say, the present invention is not limited to the following examples.

(First Embodiment) First, as shown in FIG.
A seed crystal 2 made of a CdTe single crystal ingot, a solvate 3 made of a Te-excessive Cd-Te alloy ingot, and a columnar raw material 4 made of a CdTe polycrystal ingot are sequentially placed in a growth container 1 such as a quartz ampoule. Further, Ar gas was introduced so that the internal pressure became 0.3 atm, and the growth vessel 1
Was sealed.

Here, the growth container 1 used has an inner diameter d1 of 30 mm from the lower end to, for example, 30 mm above, and an inner diameter d2 of the part further up to the upper end through the stepped portion 1a serving as the positioning means is 32 mm. It was the one. The position of the stepped portion 1a is determined by the required amount of the dissolution zone composed of the solvent body 3 or the like melted at the start of crystal growth. The difference between the inner diameter d2 of the upper half and the inner diameter d1 of the lower half (d2-d1
) Is suitably 3 mm or less. The reason is that if the difference (d2-d1) exceeds 3 mm, polycrystals may be generated from the step portion 1a during crystal growth. The lower limit of the difference in inner diameter (d2 -d1) is determined by the outer diameter of the raw material 4, and as shown in FIG. 2, it is sufficient to support the lower end peripheral edge of the raw material 4 sinking in the solvent 3A. .

The seed crystal 2 has an outer diameter of 29 mm and a length of 1
It was 0 mm. Solvent body 3 is Te50g and CdTe57g
And are alloyed at 920 ° C and have a melting point of 910
° C. The alloy ingot had an outer diameter of 28 mm and a length of 34 mm. The raw material 4 had an outer diameter of 31.5 mm and a length of 110 mm.

The entire growth container 1 sealed by the above procedure is set at 91
The mixture was heated to 0 ° C. and kept for 10 minutes to once melt the solvate 3 and then cooled. After that, the growth container 1 is placed in a THM furnace, and the heater 5 is used to move the growth container 1 20 mm from the bottom surface.
The solvate 3 is melted by heating locally so that the internal temperature becomes 920 ° C. around the upper position and the raw material 4
The lower end of was dissolved to form a dissolution zone. After holding the growth container 1 in that state for 3 hours, the growth container 1 was lowered 100 mm at a speed of 5 mm per day to perform crystal growth. After the crystal growth was completed, the ingot was taken out from the growth container 1 and examined, and it was found that a single crystal had grown from the seed crystal 2.

Next, a sample was prepared in which the seed crystal 2, the solvent body 3, and the raw material 4 were enclosed together with Ar gas in the growth container 1 by the above procedure. The entire growth vessel 1 was heated to 910 ° C., held for 10 minutes and then cooled, followed by THM.
It was placed in a furnace, and was locally heated so that the internal temperature was 920 ° C. around a position 20 mm above the bottom surface of the growth vessel 1, held for 3 hours, and then rapidly cooled. When the obtained ingot 6 was examined, as shown in the longitudinal section in FIG. 3, a region 22 mm in length (solvent) sandwiched between the seed crystal 2B having a length 8 mm and the raw material 4B held by the step portion 1a. It was confirmed that (corresponding part) 3B corresponds to solvent 3A.
Then, it was found that the surplus solvent of the solvent 3A completely filled the gap between the raw material 4 and the inner peripheral wall of the growth container 1.

(Second Embodiment) As shown in FIG. 4, a convex portion 11 serving as a positioning means is located 20 mm above the lower end of the container.
Into a growth container 11 such as a quartz ampoule in which a is projected inwardly by 2 mm, for example, a solvate 3 made of a Te-excessive Cd-Te alloy ingot and a columnar raw material 4 made of a CdTe polycrystalline ingot are sequentially placed, and the internal pressure Was prepared by introducing Ar gas so as to be 0.3 atm, and a CdTe single crystal was grown in the same manner as in the first embodiment.

Here, the position of the convex portion 11a of the growth container 11 is determined by the amount of the melting zone required at the start of crystal growth. Further, it is appropriate that the protrusion amount of the convex portion 11a is 2 mm or less. The reason is that if the protrusion amount exceeds 2 mm, polycrystals may be generated from the protrusions 11a during crystal growth. The lower limit of the protrusion amount of the convex portion 11a is determined by the outer diameter of the raw material 4, and as shown in FIG.
It is sufficient that the lower edge of the raw material 4 sinking in A can be supported.

Size of solvate 3, method of manufacture and melting point,
In addition, the size of the raw material 4 was the same as in the first embodiment. In addition, in this 2nd Example, the seed crystal was not used.

The growth vessel 11 sealed by the above procedure is placed in the THM.
It is installed in a furnace and locally heated by a heater 5 so that the internal temperature is 920 ° C. around a position 10 mm above the bottom surface of the growth container 11 to melt the solvate 3 and melt the lower end of the raw material 4. To form a dissolution zone. Growth vessel 1
After holding 1 in that state for 3 hours, the growth vessel 11 was lowered 100 mm at a speed of 5 mm per day to perform crystal growth. After the crystal growth was completed, the ingot was taken out from the growth container 11 and examined. The region up to 25 mm above the lower end of the ingot was polycrystalline, but the region above it was single crystal up to the upper end.

Next, a sample was prepared in which the solvate 3 and the raw material 4 were enclosed together with Ar gas in the growth container 11 by the above procedure. The growth vessel 11 was placed in a THM furnace, and was locally heated so that the internal temperature was 920 ° C. centered on a position 10 mm above the bottom surface of the growth vessel 11, held for 3 hours, and then rapidly cooled. When the obtained ingot 7 was examined, as shown in its longitudinal section in FIG. 6, the region 3C 20 mm directly below the raw material 4C held by the convex portion 11a (the portion corresponding to the solvent) corresponds to the solvent 3A. Was confirmed.
Then, it was found that the surplus solvent of the solvent 3A completely filled the gap between the raw material 4 and the inner peripheral wall of the growth container 11.

The seed crystal 2 may or may not be present.

Further, in each of the above-mentioned embodiments, T
Although the case of growing CdTe in an e solvent has been described as an example, the present invention is naturally applicable to the case of growing CdTe or another crystal in another solvent.

[0032]

According to the method for growing a single crystal according to the present invention, a columnar raw material and a solvate serving as a solvent for dissolving the raw material during crystal growth are brought into contact with the upper end of the solvate. In a growth container, the solvate is melted by local heating with a heater and the lower end of the raw material is melted to form a dissolution zone, and the heater is moved upward relative to the growth container. When the single crystal is continuously deposited and grown from the lower end of the melting zone by means of the positioning means provided in the growth container, the lower end of the raw material is positioned so as to have a predetermined height in contact with the melting zone. After that, since the relative movement of the heater is started, every time when the crystal growth is performed, the amount of the melting zone existing below the raw material becomes an appropriate amount at the start of the crystal growth, The Akiratsubu boundaries and twins fewer large single crystal can be obtained with good reproducibility. At that time, a single crystal having a desired crystal orientation is obtained by arranging the seed crystal in the growth container so as to come into contact with the lower end of the dissolution zone. In particular, when a CdTe single crystal is grown using a solvate of Te-rich Cd—Te alloy and a polycrystalline raw material of CdTe,
High quality C suitable as a substrate for semiconductor radiation detectors
A dTe single crystal can be obtained with a high yield.

Further, since the positioning means is adapted to place and support the lower end of the raw material on the stepped portion provided on the inner peripheral wall of the growth container or on the convex portion provided on the inner peripheral wall, a simple structure is provided. The lower end of the raw material can be held at a predetermined position with the growth container described above, and a large single crystal can be easily obtained with good reproducibility.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a state before heating in which a seed crystal, a solvate, and a raw material are put in a growth container in a first embodiment of a THM method to which the present invention is applied.

FIG. 2 is a cross-sectional view schematically showing a state before starting crystal growth in which a solvate is heated to form a dissolution zone in the first embodiment.

FIG. 3 is a cross-sectional view of an ingot obtained by an experiment conducted to investigate the shape of a melting zone before the start of crystal growth by applying the first embodiment.

FIG. 4 is a cross-sectional view schematically showing a state before heating in which a solvate and a raw material are put in a growth container in a second embodiment of the THM method to which the present invention is applied.

FIG. 5 is a sectional view schematically showing a state before starting crystal growth in which a solvent body is heated to form a dissolution zone in the second embodiment.

FIG. 6 is a cross-sectional view of an ingot obtained by an experiment conducted to investigate the shape of a melting zone before the start of crystal growth by applying the second embodiment.

[Explanation of symbols]

 1, 11 Growth container 1a Stepped portion (positioning means) 2,2B Seed crystal 3 Solvent body 3A Solvent 3B, 3C Solvent equivalent portion 4, 4B, 4C Raw material 5 Heater 6, 7 Ingot 11a Convex portion (positioning means)

Claims (7)

[Claims] 1. A columnar raw material and a solvate serving as a solvent for dissolving the raw material during crystal growth are placed in a growth container so that the raw material comes into contact with the upper end of the solvate, and locally heated by a heater. By melting the solvate by melting the lower end of the raw material to form a dissolution zone, the heater is moved upward relative to the growth vessel to continuously form a single crystal from the lower end of the dissolution zone. When depositing and growing, the relative movement of the heater is started after the lower end of the raw material is positioned by the positioning means provided in the growth container so as to have a predetermined height in contact with the melting zone. A method for growing a single crystal, characterized in that 2. The seed crystal is arranged in the growth vessel so as to come into contact with the lower end of the solvate and after the formation of the dissolution zone, contact with the lower end of the dissolution zone. 1. The method for growing a single crystal according to 1. 3. The solute concentration in the solvate placed in the growth container is 50% or more and 100% or less of the saturated concentration of the solute in the solvent at the crystal growth temperature. 2. The method for growing a single crystal according to item 2. 4. After the raw material and the solvate are put into the growth container, first, the entire growth container is first heated and held by a heater in a temperature range not lower than the melting temperature of the solvate and not higher than the crystal growth temperature. To melt the solvate into a solvent, and then locally heat the solvent to a crystal growth temperature with a heater to form the dissolution zone, and then start relative movement of the locally heated heater. The method for growing a single crystal according to claim 3, characterized in that. 5. The solvate is a Te-rich Cd—Te alloy, the raw material is a polycrystal of CdTe, and the grown crystal is a single crystal of CdTe. The method for growing a single crystal according to item 3 or 4. 6. The positioning means has an inner diameter in a part or all of a lower half portion of the bottomed cylindrical growth container that is smaller than an outer diameter of a lower end of the raw material. By holding and supporting the lower end of the raw material on the stepped portion between the portion having a small inner diameter and the upper half portion of the growth container for containing the raw material, the lower end of the raw material is held at a predetermined height. The method for growing a single crystal according to claim 1, wherein 7. The positioning means has a convex portion protruding inward from an inner peripheral wall of the bottomed cylindrical growth container,
The method for growing a single crystal according to claim 1, wherein the lower end of the raw material is placed on and supported by the convex portion.