JPH0429638B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to the field of growing crystals using the floating zone melting method in which infrared rays are focused using a spheroidal internal mirror, and in particular, to the field of growing LeB ₆ single crystals. Sometimes it relates to a method suitable for growing a large single crystal with few dislocations.

[Background of the invention]

Borides, represented by lanthanum hexaboride (LaB ₆ ), have characteristics such as a low work function, high melting point, and low vapor pressure at high temperatures, and are used as high-brightness electron beam source materials. .

Conventionally, known methods for growing LaB ₆ single crystals include the metal flux method, vapor phase growth method, and floating zone melting method, but the floating zone melting method is generally appropriate for growing high-quality, large-sized crystals. be. High frequency heating (Japanese Patent Publication No. 58-52958) is usually used as the heating source. However, in high-frequency induction heating, the buoyancy force due to eddy current acts strongly on the molten floating zone.
As a result, the molten zone blows up, causing a phenomenon in which the shape of the molten zone changes significantly. Therefore, it is extremely difficult to maintain the molten zone stably, and the shape of the molten zone changes with heating time, causing problems such as the tendency for defects to occur in the crystal due to thermal stress.

[Purpose of the invention]

The purpose of the present invention is to solve these drawbacks, and to use a device that condenses infrared rays with a spheroidal internal mirror when growing LaB ₆ single crystals by the floating zone melting method. This provides a large, high-quality single crystal with low dislocation density.

[Summary of the invention]

The present invention is characterized by the ability to maintain a molten zone stably despite LaB ₆ having a high melting point of 2,600°C, since it is melted using a device that condenses infrared rays with a spheroidal inner mirror. This is because the crystal can be grown stably without being affected by the buoyancy force seen in high-frequency heating equipment, and the ratio of diameter to length of the molten part during crystal growth can be set to a desirable value of 0.8 to 2.0. be.

A device that focuses infrared light using a spheroidal internal mirror.
In order to grow LaB ₆ single crystals, it is necessary to consider the following matters.

A quartz tube is usually provided to maintain the growth atmosphere, but since LaB ₆ has a high melting point of 2600°C, there is a problem that the quartz tube is deformed by radiant heat during growth. If the inner diameter of the quartz tube is increased in order to prevent this deformation, the quartz tube wall becomes colder, and evaporated matter of LaB ₆ adheres to the inner wall of the quartz tube, changing the transmittance of infrared rays. As a result, the problem arises that the diameter of the crystal varies during growth. We have found that the above-mentioned drawbacks can be overcome by using a sapphire tube with excellent heat resistance instead of the quartz tube, and by widening the quartz tube near the floating zone into a spherical shape. When the diameter of the spherical part of the quartz tube was less than 35 mm, deformation occurred, and when it was more than 55 mm, evaporated matter adhered to the inner wall.

Next, materials for fixing the raw material rod and the seed crystal will be explained. Since LaB ₆ has a high melting point and high thermal conductivity, the material for fixing the raw material rod and seed crystal must have excellent heat resistance and be a material that does not react with LaB ₆ . In the present invention, Re, Ta, W, Mo,
It was clarified that by using C, melting and reactions due to temperature rise can be prevented.

In addition, when using platinum group wire rods, it was revealed that the raw material rod could be fixed without melting if the raw material rod was fixed at a distance of 40 mm or more from the molten part.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 The raw material rod of LaB ₆ used for crystal growth is made of LaB ₆ powder.
It was molded into a round bar with a diameter of 10 mm and a length of 100 mm using a press pressure of 1 ton/cm ² and heated at a temperature of 2200℃ in an argon atmosphere for 3 days.
It was made by baking for hours.

Figure 1 shows the structure of a growth furnace using infrared rays.
The raw material rod 6 was suspended from a raw material rod moving shaft 7 provided at the top by a Re wire 4 having a diameter of 0.2 mm. A seed crystal 5 was fixed to a ceramic holder on the lower shaft with Re wire.

As for the growth conditions, the raw material rod and seed crystal are grown at 5mm/h.
The raw material rod and seed crystal were rotated in the same direction at 10 rpm while moving downward. The atmosphere during the marriage was argon. A sapphire tube 3 with an inner diameter of 35 mm was used as the cylindrical container for atmospheric gas control. A single crystal with a diameter of 8 mm was grown under these conditions. During growth, no buoyancy force observed during high-frequency heating was observed in the melted zone.

As a result of examining the dislocation density of the grown crystal using an etching method, it was found to be approximately 1.0×10 ⁴ /cm ² , which is approximately one order of magnitude higher than the value of 1.2×10 ⁵ /cm ² obtained by conventional high-frequency heating. A small number of high quality single crystals were obtained. Furthermore, since a sapphire tube was used for the cylindrical container for atmospheric gas control, no deformation of the container was observed.

When the LaB ₆ raw material rod was melted, it shrunk from 10 mm to 8 mm. When crystals were grown with the length of the molten zone being 6 mm or less, an unmelted core was present in the center of the raw material rod after solidification. Also, the length of the melt zone
It was found that if the thickness was increased to 20 mm or more, the lower part of the molten zone would sag due to gravity, making it impossible to form a stable molten zone.

From the above results, in order to achieve stable crystal growth with infrared heating, the ratio of the diameter and length of the molten zone must be adjusted.
It is preferable to set it within the range of 0.8 to 2.0.

Example 2 Using the growth conditions of Example 1, a cylindrical container for atmospheric gas control with an inner diameter of 35 mm was used instead of saphire.
When the quartz tube was grown using a transparent quartz tube, the quartz tube was deformed and devitrified during the growth, resulting in poor infrared transmission and solidification of the molten zone, making it impossible to continue the growth.

As a result of increasing the inner diameter of the quartz tube to 55 mm to prevent deformation, the temperature of the quartz tube became low.
Evaporated matter adhered to the inner wall of the quartz tube, impairing the transmission of infrared rays and making it difficult to melt the raw material rod, making it impossible to continue growing. As a result of considering the shape of the quartz tube, we found that using a spherical quartz tube 8 with an inner diameter of 35 mm and a spherical quartz tube with only the molten zone having an inner diameter of 50 mm, as shown in Figure 2, would prevent deformation and evaporation. It was possible to grow without any substances attached.

Example 3 Under the conditions of Example 1, Ta, W, Mo,
As a result of growing using C wire, there was no melting.
It turns out that it has the same effect as Re rays.

Example 4 Growth was carried out under the growth conditions of Example 1, using a platinum wire instead of the Re wire for suspending the raw material rod and fixing the seed crystal. When using platinum wire,
It was found that the position of suspending the raw material rod with a platinum wire, the position of fixing the seed crystal, and the distance of the molten zone are important. When the above distance was set to 35 mm, the platinum wire was fused during growth and the raw material rod fell. Next, when the length was increased to 42 mm, the platinum wire could be grown without melting.

This was observed not only for platinum but also for all platinum group metal wires such as Pd and Rh. In the above examples, similar results were obtained even when the crystal rotation was stopped without rotating the crystal in the same direction.

〔Effect of the invention〕

As described above, according to the present invention, the molten zone is stabilized, so it is possible to increase the size and quality of the melted zone.
LaB ₆ single crystals can be grown.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of an infrared condensing section of an apparatus showing one embodiment of the present invention, and FIG. 2 is a sectional view showing an example of a quartz container. 1...Spheroidal internal mirror, 2...Xenon lamp, 3...Saphire tube, 4...Re wire, 5...
Seed crystal, 6... Raw material rod, 7... Raw material rod moving shaft, 8... Spherical quartz container.

Claims (1)

[Claims] 1. In a method of crystallizing a lanthanum hexaboride sintered body (LaB ₆ ) by a floating zone melting method, the rotation direction of the crystal body and the raw material are the same, or the diameter of the molten part is the same as that of the raw material in a stationary state. A method for growing a lanthanum hexaboride single crystal, the length ratio being 0.8 to 2.0, and crystal growth using a device that focuses infrared light using a spheroidal internal mirror. 2. Growth of a lanthanum hexaboride single crystal according to claim 1, characterized in that a cylindrical container for atmospheric gas control is provided on the outer periphery of the LaB ₆ sample, and a material made of sapphire is used for the container. Method. 3. The method for growing a lanthanum hexaboride single crystal according to claim 1, wherein the cylindrical container for atmospheric gas control has a spherical expansion in a portion near the floating zone. 4 Raw material rods and seed crystals are Re, Ta, W, Mo,
A method for growing a lanthanum hexaboride single crystal according to claim 1, characterized in that the lanthanum hexaboride single crystal is fixed and suspended by a line C. 5. A method for growing a lanthanum hexaboride single crystal according to claim 1, characterized in that a raw material rod having a length of 40 mm or more is used.