JP7258293B2 - Gallium oxide crystal growth crucible - Google Patents

Description

The present invention relates to a crucible for growing gallium oxide crystals.

Patent Document 1 (Japanese Patent Application Laid-Open No. 2017-193466) describes a method for producing a single crystal of gallium oxide (especially a β-Ga ₂ O ₃ single crystal, which will be described below as a β-Ga ₂ O ₃ single crystal). It is The method described in Patent Document 1 uses a platinum-rhodium (PtRh) alloy fine seed crucible in a crystal growth apparatus under an air atmosphere, using the vertical Bridgman method (VB method) or a vertical temperature gradient. A β-Ga ₂ O ₃ single crystal is grown by a solidification method. PtRh alloys (particularly those with an Rh content of 10 to 30 wt %) have a high melting point of 1800° C. or higher and are suitable for growing β-Ga ₂ O ₃ single crystals at high temperatures.

The thin seed crucible has a lower part and an upper part that are joined by welding, and as shown in Patent Document 2 (Japanese Patent Application Laid-Open No. 2001-58896), etc., the lower part has a bottom in which the seed crystal can be stored stably. It consists of a cylindrical small-diameter portion and an enlarged-diameter portion extending upward from the upper end of the small-diameter portion, and the upper portion is a large-diameter portion (desired crystal) extending cylindrically upward from the upper portion of the enlarged-diameter portion. diameter).
Since the fine seed crucible has an irregular shape, it is formed by joining the enlarged diameter portion to the upper end of the small diameter portion by welding, and by joining the large diameter portion to the upper portion of the enlarged diameter portion by welding.

JP 2017-193466 A JP-A-2001-58896

PtRh alloy fine seed crucibles are used by mixing Pt and Rh into an alloy so that they can be used at high temperatures in the atmosphere.
However, since Rh easily dissolves into the crystal, it is desired to use the Rh ratio as low as possible. However, if it is lowered too much, the melting point will be lowered and the crucible may melt. Increasing the Rh ratio raises the melting point of the crucible, but the hardness of the material itself increases, making it difficult to weld.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a gallium oxide crystal-growing crucible that allows easy and good welding and prevents melt leakage.

A crucible for growing gallium oxide crystals according to the present invention is made of an alloy of platinum and rhodium containing platinum as a main composition, and is a crucible for growing gallium oxide crystals, wherein the upper portion and the lower portion of the crucible are joined by welding. A composition ratio of rhodium in the upper portion of the crucible is higher than a composition ratio of rhodium in the lower portion of the crucible.

The lower portion of the crucible is composed of a bottomed tubular small diameter portion in which the seed crystal is accommodated, and an enlarged diameter portion that is welded to the upper end of the small diameter portion and extends upward in diameter, and the upper portion of the crucible comprises the enlarged diameter portion. It can be applied to a crucible consisting of a large-diameter portion that is welded to the upper portion of the portion and extends upward in a cylindrical shape.

If the upper portion of the enlarged diameter portion is formed into a cylindrical portion with a constant diameter, and the cylindrical large diameter portion is welded to the cylindrical portion, welding can be performed easily and reliably.
The composition ratio of rhodium in the upper portion of the crucible may be 15 to 30 wt%, and the composition ratio of rhodium in the lower portion of the crucible may be 10 to 25 wt%.

The thickness of the upper portion of the crucible may be thinner than the thickness of the lower portion of the crucible.
In this case, the upper portion of the crucible may have a thickness of 0.1 to 0.2 mm, and the lower portion of the crucible may have a thickness of 0.15 to 0.3 mm.

According to the crucible for growing gallium oxide crystals according to the present invention, by using a material having a lower Rh content than the material of the upper portion of the crucible as the material of the lower portion of the crucible, the hardness and melting point are lowered. By using a welding rod having a low hardness and a low melting point, the crucible upper part and the crucible lower part can be welded easily and satisfactorily, cracks and holes can be prevented, and melt leakage can be prevented.
In addition, if the thickness of the crucible upper part is thinner than that of the crucible lower part, the grown crystal can be easily taken out, and since the crucible lower part is thick, workability during welding is improved. can be easily and reliably performed, cracks and holes can be prevented, and melt leakage can be reduced.

1 is an end view of a crucible in the first embodiment; FIG. FIG. 11 is an end view of the crucible in the second embodiment; 1 is a graph showing the relationship between the composition (wt%) and the melting point of a Pt/Rh alloy created based on existing literature data and experimental data. 1 is a photograph of the crucible of Example 1, showing the state of the crucible before use on the left and the state of the crucible after crystal growth and before removal of the crystal on the right. 10 is a photograph of the crucible of Example 2, showing the state of the crucible after crystal growth and before crystal removal. FIG. 6A is a photograph of a crucible of a comparative example showing a state of a crucible in which melt leakage occurs, and FIG. 6B is a photograph of a crucible of a comparative example showing a state where leaked melt adheres to a crucible receiver. .

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
FIG. 1 is an end view of a crucible (thin seed crucible) 10 in the first embodiment.
The crucible 10 is a crucible for growing a single crystal of gallium oxide (β-Ga ₂ O ₃ ) in an air atmosphere by the vertical Bridgman method (VB method) or the vertical temperature gradient solidification method, and is mainly composed of platinum. It is made of platinum-rhodium alloy.
As the crystal growth apparatus itself, for example, a crystal growth apparatus under an air atmosphere disclosed in JP-A-2017-193466 can be used.

As described above, the crucible 10 has a lower portion 12 composed of a bottomed cylindrical small diameter portion 14 in which the seed crystal is stably accommodated and an enlarged diameter portion extending upward from the upper end of the small diameter portion 14. 16, and an upper portion 18 consists of a large diameter portion (having a diameter that provides the desired crystal diameter) 20 that extends cylindrically upward from the upper portion of the enlarged diameter portion 16 . The small diameter portion 14 and the large diameter portion 20 are cylindrical.

Since the fine seed crucible 10 has an irregular shape, the enlarged diameter part 16 is welded to the upper end (part A) of the small diameter part 14, and the large diameter part 20 is welded to the upper part (part B) of the enlarged diameter part 16. It is formed by joining. The bottom portion and the tubular portion of the small diameter portion 14 are also joined by welding. Since it is difficult to weld the large-diameter portion 20 to the upper end surface of the funnel-shaped enlarged diameter portion 16, the upper portion of the enlarged diameter portion 16 is formed into a low-height, constant-diameter cylindrical portion. A cylindrical large diameter portion 20 is preferably welded to the upper end (portion B) of the portion.
The crucible 10 in the first embodiment has a uniform thickness throughout. The thickness can be about 0.11-0.5 mm.

FIG. 2 is an end view of a second embodiment of crucible 10. As shown in FIG.
This embodiment is the same as the first embodiment except that the thickness of the crucible upper portion 18 is made thinner than the thickness of the crucible lower portion 12 .
The thickness of the crucible upper portion 18 can be, for example, 0.1-0.2 mm, and the thickness of the crucible lower portion 12 can be, for example, 0.15-0.3 mm.

The present embodiment (first and second embodiments) is characterized in that the composition ratio of rhodium in the crucible upper portion 18 is higher than that in the crucible lower portion 12 .
It is preferable to set the composition ratio of rhodium in the crucible upper portion 18 to about 15 to 30 wt% and the rhodium composition ratio in the crucible lower portion 12 to about 10 to 25 wt%.

FIG. 3 shows the relationship between the composition (wt%) and the melting point of the PtRh alloy created based on existing literature data and experimental data. PtRh alloys have different melting points depending on the content of Rh contained in Pt.
From melting experiments of β-Ga ₂ O ₃ , β-Ga ₂ O ₃ completely melts at about 1795°C. Therefore, it is clear that Pt, which has a melting point of 1768° C., cannot be applied as a crucible material for melting and holding β-Ga ₂ O ₃ . However, as shown in _Fig . 3, _the melting point of the PtRh alloy containing ₂ wt% or more of Rh exceeds the melting point of β- _Ga2O3 . can be used as

In the actual crystal growth of β-Ga ₂ O ₃ , the melting point of the PtRh alloy crucible required to stably hold the β-Ga ₂ O ₃ melt with a melting point of about 1795°C for crystal growth is as follows. It varies depending on the crystal growth principle, the size of the crystal to be grown, and the crystal growth conditions.

In the case of β-Ga ₂ O ₃ crystal growth by the VB method (vertical Bridgman method), the lower limit of the Rh content in the applicable PtRh alloy crucible must be 10 wt% or more. When the Rh content is 10 wt %, the melting point of the crucible is about 1850° C., as clearly shown in FIG.
Moreover, the Rh content is about 20 wt %, and the melting point of the crucible is about 1900° C., which is a high melting point, so that crystals with a diameter of about 100 mm can be grown.
In the PtRh alloy crucible, if the Rh content is too high, the problem of Rh leaching occurs, so the Rh content is preferably 30 wt % or less.

In the case of β-Ga ₂ O ₃ crystal growth by the VB method (vertical Bridgman method), the upper part of the crucible 10 is heated to a high temperature in order to melt the gallium oxide material in the growth furnace, and the lower part of the crucible 10 is heated to a high temperature. The temperature is set lower than the upper part for growth.
When a PtRh alloy with a Rh content of 30 wt %, which has a high melting point, is used as the crucible material, β-Ga ₂ O ₃ crystal growth can be performed satisfactorily as described above.

However, when a PtRh alloy with a Rh content of 30 wt%, which has a high melting point, is used as the crucible material for both the crucible upper portion 18 and the crucible lower portion 12, the hardness of the crucible increases, and the crucible upper portion 18 and the crucible lower portion 12 It was found that the welding of the lower portion 12 could not be performed satisfactorily, and as a result, cracks or holes were formed in the vicinity of the welded portion, causing melt leakage. If the melt leaks, it not only makes crystal growth impossible, but also damages the crystal growth apparatus by cracking a crucible support (susceptor) made of zirconia or the like that accommodates the crucible 10 .

Therefore, in the present embodiment, a material having a lower Rh content than the material of the crucible upper part 18 is used as the material of the lower crucible part 12 . The lower the Rh content, the lower the hardness. For example, by using the same low-hardness welding rod as the lower material, welding between the crucible upper part 18 and the crucible lower part 12 can be easily and well performed, and cracks can occur. It was possible to prevent occurrence and perforation, and prevent melt leakage. Welding between the expanded diameter portion 16 and the small diameter portion 14 having a low hardness and welding between the cylindrical portion and the bottom portion of the small diameter portion 14 can also be performed easily and satisfactorily.

The composition of the crucible material varies depending on the principle of crystal growth, the size of the crystal to be grown, and the crystal growth conditions. , the composition ratio of rhodium in the crucible upper portion 18 is preferably 15 to 30 wt%, and the rhodium composition ratio in the crucible lower portion 12 is preferably 10 to 25 wt%.

Even if the composition ratio of rhodium in the lower portion 12 of the crucible is 10 wt %, the melting point is about 1850° C. as described above, which is sufficient for growing β-Ga ₂ O ₃ crystals.
On the other hand, in order to suppress the elution of Rh into the melt, it is desirable to reduce the Rh content in the crucible upper part 18, but this lowers the melting point. Furthermore, the composition of the crucible upper part 18 is determined according to the crystal growth conditions.

By the way, in the case of β-Ga ₂ O ₃ crystal growth by the VB method (vertical Bridgman method), the upper part of the crucible may be broken (peeled off) to take out the produced crystal.
In this case, if the thickness of the crucible is large, it is difficult to break the upper part of the crucible, which has a high hardness.
Therefore, in the second embodiment, the crucible upper portion 18 is made thinner than the crucible lower portion 12, thereby facilitating extraction of the crystal.

Further, in the second embodiment, the crucible lower portion 12 is thicker than the crucible upper portion 18 .
By increasing the thickness of the crucible lower portion 12, workability and handling during welding are facilitated.
As described above, the reduction in the Rh content in the crucible lower part 12 facilitates welding, and by increasing the thickness of the crucible lower part 12, welding between the crucible upper part 18 and the crucible lower part 12 can be made easier, the reliability of welding can be improved, cracks and perforations can be prevented, and melt leakage can be reduced.

Although the fine seed crucible has been described in the above embodiment, the present invention can be applied to all crucibles in which the crucible upper portion and the crucible lower portion are joined by welding, even if the crucible does not necessarily have a fine seed crucible shape.

(Example of β-Ga ₂ O ₃ crystal growth)
Directionally solidified β-Ga ₂ O ₃ crystals were grown in a VB furnace.
The crucibles are the crucibles shown in FIGS. 1 and 2, and two crucibles each having an inner diameter of 53 mm and a height of 50 mm were prepared. The composition ratio (wt) was 70/30 for Pt/Rh in the upper portion 18 of the crucible and 80/20 for Pt/Rh in the lower portion 12 of the crucible. The two crucibles of FIG. The two crucibles in FIG. 2 are referred to as Example 2.

The thickness of the crucible of Example 1 is 0.2 mm for both the crucible upper portion 18 and the crucible lower portion 12 . In Example 2, the crucible upper portion 18 was 0.15 mm thick, and the crucible lower portion 12 was 0.2 mm thick.
As comparative crucibles, two crucibles were prepared in which the composition ratio of both the crucible upper portion 18 and the crucible lower portion 12 was 70/30, and the crucible upper portion 18 and the crucible lower portion 12 had a thickness of 0.2 mm.

Seed crystals and β-Ga ₂ O ₃ sintered raw materials were filled in a Pt-Rh alloy crucible, and the temperature gradient near the melting point of β-Ga ₂ O ₃ (approximately 1795°C) was 5-10°C/cm. It was completely melted in a high-temperature furnace in air at 1800°C or higher with a temperature distribution set so that After that, unidirectional solidification was performed by moving the crucible and lowering the temperature in the furnace. After cooling, the crucible was peeled off and the grown crystal was taken out.

When the crucibles of Examples 1 and 2 were used, crack-free single crystals of β-Ga ₂ O ₃ were obtained in each of the two crucibles.
On the other hand, one of the comparative examples produced a crack-free β-Ga ₂ O ₃ single crystal, while the other crucible had a welded portion between the crucible upper portion 18 and the crucible lower portion 12 (part B). ), melt leakage occurred, and good crystals could not be obtained.

FIG. 4 is a photograph of one of the two crucibles of Example 1, showing the state of the crucible before use on the left side and after growing the crystal and before taking out the crystal on the right side. It can be seen that no melt leakage occurred in the crystal after crystal growth.
FIG. 5 is a photograph showing the state of one of the two crucibles in Example 2, which is after crystal growth and before crystal removal. It can be seen that no melt leakage occurs.
In the crucible of Example 2, the thickness of the crucible upper portion 18 was thinner than that of Example 1, so that the crucible was easily peeled off and the crystal was easily taken out.

6A and 6B are photographs showing the state of the crucible in which melt leakage occurred in one of the two crucibles of the comparative example. As shown in FIG. 6A, cracks were generated at the welded portion between the crucible upper portion 18 and the crucible lower portion 16, and it was found that the melt leaked. FIG. 6B shows a state in which the leaked melt solidifies and adheres to the top of the crucible receiver.

10 crucible 12 crucible lower part 14 small diameter part 16 enlarged diameter part 18 crucible upper part 20 large diameter part

Claims (6)

A crucible for growing gallium oxide crystals, which is made of an alloy of platinum and rhodium with platinum as the main composition,
The top and bottom of the crucible are joined by welding,
A crucible for growing a gallium oxide crystal, wherein the composition ratio of rhodium in the upper part of the crucible is higher than the composition ratio of rhodium in the lower part of the crucible. The lower portion of the crucible is composed of a bottomed tubular small diameter portion in which the seed crystal is accommodated, and an enlarged diameter portion that is welded to the upper end of the small diameter portion and extends upward in diameter, and the upper portion of the crucible comprises the enlarged diameter portion. 2. A crucible for growing gallium oxide crystals according to claim 1, characterized in that it comprises a large-diameter portion which is welded to the upper portion of the portion and extends upward in a cylindrical shape. 3. The crucible for growing gallium oxide crystals according to claim 2, wherein the upper portion of said enlarged diameter portion is formed into a tubular portion having a constant diameter, and said tubular large diameter portion is welded to said tubular portion. The oxidation according to any one of claims 1 to 3, wherein the composition ratio of rhodium in the upper part of the crucible is 15 to 30 wt%, and the composition ratio of rhodium in the lower part of the crucible is 10 to 25 wt%. A crucible for growing gallium crystals. A crucible for growing a gallium oxide crystal according to any one of claims 1 to 4, wherein the crucible upper portion is thinner than the crucible lower portion. 6. The crucible for growing gallium oxide crystals according to claim 5, wherein the crucible upper portion has a thickness of 0.1 to 0.2 mm and the crucible lower portion has a thickness of 0.15 to 0.3 mm.

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