JPH0694400B2 - Method for producing GaAs single crystal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a GaAs single crystal, and more particularly to a method for producing a GaAs single crystal by a direct synthesis pulling method of GaAs.

[Prior Art] FIG. 2 shows an example of a direct synthesis pulling method (LEC method) of a GaAs (gallium arsenide) single crystal. As shown in the drawing, a crucible 4 is installed in the pressure vessel 2 via a susceptor 5 and a crucible shaft 11. Ga (gallium) 9 and As (arsenic) 8 are stored in the crucible 4 as raw materials, and B ₂ O ₃ (boron oxide) 7 is stored as a liquid sealant. Then, the crucible 4 is heated by the heater 6 to cause Ga9 and As8 to react with each other so that Ga
As to synthesize melt. After that, the seed crystal 3 fixed to the pulling shaft 1 located right above the crucible 4 is lowered, one end of the seed crystal 3 is brought into contact with the GaAs melt, and then the seed crystal 3 is pulled up to bring a new GaAs to the tip of the seed crystal. Growing crystals.

[Problems to be Solved by the Invention] By the way, the above As8 has a high vapor pressure of 50 to 60 kg / cm ^{2 at} a temperature for synthesizing a GaAs melt, and has a property of being very easily volatilized. Therefore, conventionally, in order to prevent the volatilization of As8, B ₂ O ₃ was used as the liquid sealant to cover the GaAs liquid surface.
7 is used, but a sufficient effect is not obtained. This is because the molten B ₂ O ₃ 7 and As8 are not completely in contact with each other, or even if they are in contact with each other, As8 becomes bubbles and penetrates into B ₂ O ₃ 7.

Therefore, considering the volatilization of As8, the As8
However, the amount of volatilization is not always constant, and there is a large variation in the composition of the melt obtained.

In addition, since the volatilized As8 aggregates in the low temperature portion of the furnace, it contaminates the inside of the furnace and cleaning the inside of the furnace is very difficult.

The present invention was created in view of the conventional problems as described above, and an object thereof is to provide a method for producing a GaAs crystal capable of preventing the volatilization of As during the synthesis of a GaAs melt by the direct synthesis pulling method. Especially.

[Means for Solving the Problems] In order to achieve the above object, the present invention uses Ga and As as raw materials in a crucible having a tapered side wall surface as a liquid sealant.
After accommodating B ₂ O ₃ and closing the upper opening of the crucible by contacting and supporting the lid body made in advance with Ga and As as the raw material in contact with the side wall surface of the crucible, the bottom of the crucible was made of GaAs. The upper part of the crucible is heated to a temperature above the sublimation temperature of As and below the melting temperature of the lid to melt Ga and As.
Are reacted to synthesize a GaAs melt, and after the synthesis reaction is completed,
After lowering the seed crystal from above the crucible, the lid was pressed to be broken into the crucible and dissolved in the melt, and one end of the seed crystal was attached to the melt to pull up the GaAs single crystal. This is a method of manufacturing a GaAs single crystal characterized by the above.

[Operation] According to the above configuration, by using the lid made of GaAs as a raw material to block the upper opening of the crucible during the GaAs melt synthesis, the volatilization of As from the inside of the crucible is suppressed and the vaporization of As is caused. It is possible to largely prevent the fluctuation of the melt composition and the contamination in the furnace. Further, since the lid body is dropped into the crucible after the above synthesis and melted, the crystal pulling operation thereafter is not hindered at all.

Here, the material of the lid that closes the upper opening of the crucible needs to be GaAs, but when a doped crystal having a high vapor pressure is prepared, a dopant is added to the material of the lid. Is preferred. This is because after the above synthesis, the lid melts into the synthesized melt.

Further, the lid body is required to be supported on the crucible or inside the crucible without coming into contact with the melt being synthesized. This is because if the raw material Ga before synthesis and the GaAs melt during synthesis are brought into contact with each other like a dropping lid, the following four defects will occur.

As the temperature of the GaAs lid rises, As vaporizes from the surface.

If the raw material Ga and the lid are in contact with each other, GaAs will dissolve in Ga even at a temperature below the melting point of GaAs.

When As and B ₂ O ₃ do not come into contact with each other because of being blocked by the lid, As bubbles easily form in B ₂ O ₃ .

If the raw material is not placed flat, the lid will also tilt and a gap will be created between the crucible side wall and the desired effect cannot be obtained.

Then, when the bottom of the crucible is heated to the GaAs synthesis temperature, it is necessary that the lid supported above the raw material is cold enough not to be thermally damaged. For that purpose, a certain distance is required from the bottom of the crucible to the lid, but this distance cannot be uniformly defined because it varies depending on the hot zone structure, synthesis conditions and the like.

[Example] Before showing an example of the present invention, a comparative example according to a conventional technique will be described. Direct synthesis and pulling of a GaAs single crystal was carried out using the apparatus shown in FIG. First of all, as a raw material, a pyrolysis boron nitride (PBN) crucible 4 with a diameter of 6 inches was used as a raw material
600 g of 000 g of Ga9 and 3235 g of As8 as a liquid sealant
B ₂ O ₃ 7 of the. Then use heater 6 to move crucible 4 90
Heated to 0 ° C. The pressure in the pressure vessel 2 at this time is
The pressure was 70 kg / cm ² in an argon gas atmosphere. The seed crystal 3 fixed to the pulling shaft 1 located right above the crucible 4 was lowered into the GaAs melt synthesized under these conditions, and one end of the seed crystal 3 was brought into contact with the GaAs single crystal to pull it up. The volatilization amount of As8 determined from the difference between the weight of the contents and crystals of the crucible 4 after taking out the crystals and the weight of the raw material contained in the crucible 4 was 126 g.

Next, FIG. 1 shows an embodiment of the present invention. As shown in the drawing, a PBN crucible 4 having an upper diameter of 6 inches, whose side wall surface is tapered so that the diameter is gradually increased upward, is used. 3000 g of Ga9 and 3130 g of As8 are used as raw materials in the crucible 4. ,
600 g of B ₂ O ₃ 7 was contained as a liquid sealant. After that, a lid made of a GaAs polycrystalline disk 12 having a diameter of 148 mm and a thickness of 1 mm was installed so as to close the upper opening of the crucible 4. Since the side wall surface of the crucible 4 has a taper, the circular plate 12 is supported by the side wall of the crucible 4 within about 80 mm from the bottom surface of the crucible 4. Also this disk 12
After the synthesis is completed, split it into the crucible 4 so that it can be easily dropped.
A cross-shaped scratch was previously formed on the back surface.

In this state, the crucible 4 was heated using the heater 6 to synthesize the GaAs melt. The atmosphere for synthesizing the GaAs melt was 70 kg / cm ^{2 of} argon gas as in the comparative example. The end point of the GaAs melt synthesis can be determined by detecting the temperature with the thermocouple 10 installed under the crucible 4. That is, when the synthesis of the GaAs melt is started, the temperature rises sharply, and when it ends, the temperature drops and becomes stable. Therefore, even if the inside of the crucible 4 could not be directly observed by the GaAs polycrystalline disk 12, there was no problem in the work of GaAs melt synthesis. After the melt synthesis of GaAs is completed, the crucible 4 is further heated to 1240 ° C. to prepare a GaAs melt, and then the pull-up shaft 1 located directly above the crucible 4 is lowered and fixed to this. The GaAs polycrystalline disk 12 was dropped into the crucible 4 at the tip of the seed crystal 3.
The GaAs polycrystal pieces (broken pieces of the GaAs polycrystal disk 12) dropped in the crucible 4 were completely dissolved by dissolving in the synthesized GaAs melt. Then, a GaAs single crystal was pulled from this GaAs melt. The volatilization amount of As8 obtained under the same conditions as in the comparative example was only 11 g. After that, when the experiment was performed 10 times under the same conditions, the volatilization amount of As8 was always in the range of 8 to 12 g, and it was confirmed that there was very little variation and good reproducibility.

[Advantages of the Invention] In short, according to the present invention, since the atmosphere in the crucible is the As atmosphere, the volatilization of As before and during the GaAs melt synthesis can be greatly reduced.

As a result, the composition of the GaAs melt can be accurately controlled, and the characteristic variation of the pulled single crystal can be greatly reduced.

Also, since the lid is made of the same GaAs as the raw material, the lid can be dropped into the crucible and melted after the GaAs melt has been synthesized. Can be done consistently.

In addition, since the lid is made of GaAs, the inside of the furnace is not contaminated.

Furthermore, since the amount of As volatilized can be greatly reduced, cleaning inside the furnace after completion of crystal growth can be greatly reduced.

Furthermore, since the volatilization amount of As is greatly reduced, the observation window for observing crystals is not fogged and observation inside the furnace is facilitated.

Further, due to the large reduction in the amount of As vaporized, the amount of extra As that must be accommodated in the crucible can be reduced, and the economical efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view for explaining an embodiment of the present invention, and FIG. 2 is a schematic vertical sectional view for explaining a conventional example. In the figure, 3 is a seed crystal, 4 is a crucible, 7 is B ₂ O ₃ , 8 is As, 9
Is Ga and 12 is a lid.

Claims (1)

[Claims] 1. Ga and As as a raw material and B ₂ O ₃ as a liquid sealant are contained in a crucible having a tapered side wall surface, and the upper opening of the crucible is made of the Ga and As as a raw material in advance. After closing the lid by contacting and supporting the side wall of the crucible to close it, the bottom of the crucible is at a temperature at which GaAs melts, and the top of the crucible is at a temperature above the sublimation temperature of As and below the melting temperature of the lid. After heating, Ga and As are reacted to synthesize a GaAs melt, and after the completion of the synthesis reaction, the seed crystal is lowered from above the crucible to press the lid and crack it into the crucible to form a melt. A method for producing a GaAs single crystal, characterized in that, after melting, one end of a seed crystal is attached to the melt to pull up the GaAs single crystal.