CN1313652C - Preparation method of compound semiconductor single crystal - Google Patents

Abstract

A method for producing a compound semiconductor single crystal according to the liquid-sealed Czochralski method: in a method for growing a crystal by holding a semiconductor raw material and a sealant in a raw material melt holding portion comprising a 1 st crucible having a cylindrical shape with a bottom and a 2 nd crucible provided inside the 1 st crucible and having a communicating hole at the bottom thereof with the 1 st crucible, heating the raw material holding portion to melt the raw material, bringing a seed crystal into contact with the surface of the raw material melt in a state covered with the sealant, and pulling up the seed crystal, a temperature of a heater is controlled so that the diameter of the grown crystal is substantially the same as the inner diameter of the 2 nd crucible, and the crystal is grown until the crystal growth is completed while maintaining the surface of the grown crystal covered with the sealant.

Description

Preparation method of compound semiconductor single crystal

technical field

The present invention relates to a method for producing a compound semiconductor single crystal, and particularly relates to a technique effectively applicable to a method for producing, for example, a ZnTe-based compound semiconductor single crystal by a liquid-encapsulated Czochralski (LEC) method.

Background technique

At present, ZnTe-based compound semiconductor single crystal is expected to be applied in pure green light-emitting devices.

Usually, ZnTe-based compound semiconductor single crystals are mostly prepared by the following vapor phase growth method: a raw material ZnTe polycrystal is placed at one end of a quartz ampoule, the polycrystal is heated to sublimate at a temperature near the melting point, and the ZnTe single crystal Precipitates on the substrate on the other side of the quartz ampoule. By this method, a rectangular ZnTe single crystal substrate with a maximum size of about 20mm×20mm can be obtained. Recently, in order to further improve the light-emitting characteristics of light-emitting elements, efforts are being made to increase the conductivity of crystals, and the methods include adding impurities such as phosphorus and arsenic to the crystals.

In addition, the ZnTe-based compound semiconductor single crystal can also be grown by vertical Bridgman (VB) method or vertical temperature gradient cooling (VGF) method. The VB method or the VGF method can add impurities during crystal growth, and thus has the advantage of easily controlling the conductivity of the crystal by adding impurities. In addition, the liquid surface of the raw material melt is covered with a sealant, which can prevent the problem of hindering the formation of single crystal due to impurities mixed in from the upper part of the melt, and can also slightly suppress the temperature fluctuation in the melt.

However, in ZnTe-based compound semiconductor crystal growth by the vapor phase growth method, it is difficult to add desired impurities during growth, and thus it is difficult to control the resistivity of ZnTe-based compound semiconductor single crystal. In addition, in the vapor phase growth method, since the growth rate of the ZnTe crystal is remarkably slow, it is difficult to obtain a sufficiently large single crystal, which has a disadvantage of low productivity.

And, even if the ZnTe compound semiconductor single crystal is grown by the vapor phase growth method, a large substrate of about 20 mm × 20 mm can be manufactured, but the substrate itself becomes very expensive due to low productivity, and it is possible to use a ZnTe compound semiconductor single crystal. The problem of obstacles to component development.

For the above reasons, ZnTe-based compound semiconductor single crystals are produced by the vapor phase growth method, which is not practical as an industrial production method.

On the other hand, ZnTe-based compound semiconductor single crystals can be grown into large crystals by the VB method or VGF method. However, since the crystals are grown by cooling in a state covered with a sealant, the sealant and the growth of the crystals are different. The difference in thermal expansion often leads to crystal cracking.

In addition, like the VB method or VGF method, the LEC method can also add impurities, so it has the advantage of easily controlling the conductivity of the crystal by adding impurities. Crystal example.

An object of the present invention is to provide a method for producing a compound semiconductor single crystal capable of growing a large ZnTe-based compound semiconductor single crystal or other compound semiconductor single crystals with excellent crystal quality.

Contents of the invention

The present invention is a method for preparing a compound semiconductor single crystal by a liquid-sealed Czochralski method invented in order to achieve the above object: a cylindrical first crucible with a bottom and an inner side of the first crucible are arranged on the bottom, and the above-mentioned The semiconductor raw material and the sealant are contained in the raw material molten solution containing part of the second crucible formed by the communication hole of the first crucible, and the above-mentioned raw material containing part is heated to melt the raw material, and the seed crystal and the raw material are melted in a state covered with the above-mentioned sealant. The surface of the liquid is contacted, and the seed crystal is grown while pulling the seed crystal. In this method, the temperature of the heater is controlled so that the diameter of the growing crystal is approximately the same as the inner diameter of the second crucible, while the surface of the growing crystal is kept covered by the above-mentioned While the sealant is covered, the crystal is grown until the crystal growth is completed.

This prevents constituent components from evaporating from the surface of the crystal, so that the temperature gradient in the sealant can be made very small, and crystals of excellent quality can be grown. In addition, by reducing the temperature gradient in the sealant, the temperature fluctuation in the raw material melt can be suppressed, so materials such as ZnTe, which are currently difficult to obtain single crystals, can also be grown from seed crystals.

By controlling the temperature of the heater, the diameter of the growing crystal can be made approximately the same as the inner diameter of the second crucible, so that a single crystal of a desired diameter can be easily obtained, and relatively complicated temperature control procedures for controlling the diameter of the growing crystal are basically unnecessary.

The amount of the sealing agent added is set to an amount capable of filling the space generated between the growing crystal and the second crucible as the crystal grows, and covering the entire surface of the growing crystal. That is, the amount of addition is adjusted so that the sealing agent remains on the upper surface of the growing crystal even if it fills the space created between the growing crystal and the second crucible. As a result, the grown crystal is reliably kept covered with the sealant, so the constituent elements of the grown crystal do not evaporate.

As the second crucible, a crucible having a tapered structure in which the inner diameter of the bottom of the crucible is smaller than the inner diameter of the upper part of the crucible is used. Thus, since the diameter of the grown crystal to be pulled up is smaller than the inner diameter of the corresponding position of the second crucible, the grown crystal will not contact the crucible wall outside the growth interface, so high-quality crystals can be obtained.

Preferably, the side surface of the second crucible is inclined in a range of 0.2° to 10° with respect to the vertical direction, and is formed into a tapered shape. As a result, the volume of the space generated between the growing crystal and the second crucible is relatively small, so that the entire surface of the growing crystal can be covered with the sealing agent without requiring an extremely large amount of sealing agent.

The above-mentioned second crucible is immersed in the raw material melt contained in the above-mentioned first crucible at a distance of 10 mm to 40 mm, so that the diameter of the above-mentioned communication hole is 1/5 or less of the inner diameter of the above-mentioned second crucible. This can effectively suppress temperature fluctuations in the raw material melt in the second crucible, so that an excellent single crystal can be grown. In addition, since the connection path with the first crucible is limited, even if impurities and the like are mixed into the raw material melt in the second crucible, by pulling the second crucible, the impurities can be discharged from the second crucible into the first crucible, which can Prevent impurities from mixing into the growing crystal.

When adding impurities such as dopants, the impurity concentration in the raw material melt in the first crucible is different from the impurity concentration in the second crucible. /5 or less, the impurity concentration difference in the molten liquid can be controlled, so that the impurity concentration in the raw material molten liquid in the second crucible can be kept constant.

By making the temperature gradient in the above-mentioned raw material melt be at least 20° C./cm or less, generation of polycrystals or twin crystals can be prevented. Also, the growing crystal is always covered by the encapsulant, so there is no fear of decomposition even if the temperature gradient is reduced.

Brief description of the drawings

Fig. 1 is a schematic configuration diagram of a crystal growth apparatus used in an embodiment of the present invention.

Fig. 2 is an enlarged view of the raw material containing part in the crystal growth device of Fig. 1 .

The best way to practice the invention

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic structural view of a crystal growth apparatus used in an embodiment of the present invention, and FIG. 2 is an enlarged view of a raw material container.

The crystal growth apparatus 100 of the present embodiment is composed of a high-pressure container 1; a heat insulating material 2 and a heater 3 arranged concentrically with the high-pressure container inside the high-pressure container; and a rotation shaft provided perpendicular to the central part of the high-pressure container 1. 4; a base 13 arranged on the upper end of the rotating shaft 4; a bottomed cylindrical pBN outer crucible (first crucible) 5 fitted on the base; an inner crucible made of pBN arranged inside the outer crucible 5 (Second crucible) 6; vertically arranged on the top of the inner crucible 6, the lower end has a rotating pulling shaft 7 with a seed crystal holder 8 for fixing the seed crystal 9.

The inner crucible 6 has a communication hole 6a on the bottom surface that communicates with the outer crucible 5 , and the raw material melt 12 can move from the outer crucible 5 to the inner crucible 6 through the communication hole. The inner crucible 6 is fixed on the outer crucible 5 or other fixtures by appropriate holders (not shown).

The inner crucible 6 has a tapered structure with a smaller inner diameter at the bottom than the inner diameter of the upper part, so the diameter of the grown crystal to be pulled is smaller than the inner diameter at the corresponding position of the second crucible, and the grown crystal will not contact the crucible wall outside the growth interface. In addition, the volume of the space generated between the growing crystal and the second crucible during crystal growth is relatively small, which reduces the amount of sealant flowing into the space. Therefore, it is preferable that the side surface of the inner crucible is within the range of 0.2°-10° relative to the vertical direction. Tilted to form a cone.

The rotating pulling shaft 7 is connected with a driving part (not shown) arranged outside the high-pressure container to form a rotating pulling mechanism. The rotating shaft 4 is connected with a driving part (not shown) arranged outside the high-pressure container, and constitutes a crucible rotating mechanism, and simultaneously constitutes a base lifting mechanism. The rotation and lifting movements of the rotating pulling shaft 7 and the crucible rotating shaft 4 are independently set and controlled.

Using the crystal growth apparatus described above, a single crystal rod grown from a seed crystal can be pulled while being rotated by the liquid-enclosed Czochralski (LEC) method, and a high-purity single crystal can be grown at the lower end thereof.

Next, as an example of a compound semiconductor, a method for producing a ZnTe compound semiconductor single crystal using the crystal growth apparatus 100 will be specifically described.

In this embodiment, a pBN crucible with an inner diameter of 100mmφ×height of 100mm×a wall thickness of 1mm is used as the outer crucible 5, and a pBN with a tapered structure of an inner diameter of 54mmφ (bottom d2) to 56mmφ (upper part d3)×height of 100mm×wall thickness of 1mm is used. Make crucible as inner crucible 6. At this time, the inclination angle θ of the side surface of the inner crucible 6 is about 0.57° with respect to the vertical direction.

A communication hole 6 a having a diameter ( d1 ) of 10 mm is formed in the center portion of the bottom surface of the inner crucible 6 . The size of the communication hole 6 a is not limited to 10 mm, but only needs to be 1/5 or less of the inner diameter of the inner crucible 6 .

First, a total of 1.5 kg of zinc with a purity of 6N and tellurium with a purity of 6N are put into the outer crucible 5 and the inner crucible as raw materials, so that the zinc and tellurium are in an equimolar ratio, and 400 g of sealant (B ₂ O ₃ ) 11 is covered thereon, The thickness of the sealant layer was 35mm. The inner crucible 6 was fixed with a holder so that after the raw material was melted by the heater 2, it was immersed at a depth of 20 mm from the liquid surface of the raw material melt. As the crystal grows, the raw material melt gradually decreases, and the pedestal 13 (outer crucible 5 ) is raised by the up-and-down driving of the rotating shaft 4 , thereby controlling the immersion state of the inner crucible 6 . For example, the inner crucible 6 is maintained in a state of being immersed at a depth of 10 mm to 40 mm from the liquid surface of the raw material melt.

Next, the above-mentioned crucibles 5 and 6 are set on the base 13, and the inside of the high-pressure vessel 1 is filled with an inert gas (for example, argon) to adjust to a predetermined pressure. Then, while sealing the raw material surface with a sealant, it is heated at a predetermined temperature with the heater 2 to melt zinc and tellurium and directly synthesize it.

Thereafter, the molten raw material is maintained for a certain period of time, and then the seed crystal 9 is brought into contact with the surface of the molten raw material. Here, a seed crystal of crystal orientation (100) was used as the seed crystal. In addition, in order to prevent the decomposition of the seed crystal 9, the seed crystal is covered with a shell (not shown) made of molybdenum.

Then, while rotating the pulling rotating shaft 7 at a rotation speed of 1 to 2 rpm, and pulling at a speed of 2.5 mm/h, the shoulder of the crystal was formed. After the shoulder is formed, continue to rotate the crucible rotating shaft at 1-5rpm, and pull at a speed of 2.5mm/h to form the main body. At this time, as shown in FIG. 2, the diameter of the main body of the growing crystal 10 is approximately the same as the inner diameter of the inner crucible 6, so it is not necessary to perform fine diameter control by the pulling speed and the rotation speed of the crucible or the pulling shaft, and can easily obtain Crystals of desired diameter.

In addition, since the inner crucible 6 has a tapered structure, when the crystal 10 is pulled as the crystal grows, the growing crystal 10 will not contact the crucible wall outside the growth interface. That is, as shown in FIG. 2 , a gap is formed between the growing crystal 10 and the inner crucible 6 , and the sealant enters the gap to cover the surface of the growing crystal. This can prevent the quality of the crystal from deteriorating due to the growing crystal contacting the wall surface of the inner crucible 6 .

In addition, since the gap between the growing crystal 11 and the inner crucible 6 is small, the amount of the sealant 11 on the top of the crystal entering the gap is small, and the surface of the crystal can always be kept covered by the sealant 11 . This prevents the evaporation of the constituent elements of the grown crystal 10, makes the temperature gradient in the sealing agent very small, and obtains a grown crystal of excellent quality.

Although the inclination angle θ of the side surface of the inner crucible relative to the vertical direction is 0.57° in this embodiment, the inclination angle of the side surface relative to the vertical direction is 0.2°-10°.

The temperature fluctuation in the raw material melt in the inner crucible 6 is about 0.5°C, and the temperature fluctuation in the raw material melt between the inner crucible 6 and the outer crucible 5 is 1-2°C. It can be known that by making a double crucible structure, Temperature fluctuations in the inner crucible 6 can be suppressed.

Also, the temperature gradient in the raw material melt during crystal growth is 10°C/cm or less, but since the surface of the growing crystal 10 is always covered with the sealant 11, decomposition of the crystal does not occur.

As described above, the crystal growth is carried out by the liquid sealing Czochralski method, and after the crystal growth, the growing crystal 10 is separated from the sealing agent 11 to obtain a ZnTe compound semiconductor crystal without cracks. The obtained ZnTe compound semiconductor crystal is an extremely good single crystal that does not generate polycrystals or twin crystals. The size of the grown crystal is 54mmφ in diameter x 60mm in length, and it is possible to enlarge the ZnTe-based compound semiconductor single crystal, which was considered difficult in the past.

The inventor's invention has been specifically described above based on the examples, but the present invention is not limited to the above examples.

For example, in the above-mentioned embodiment, one communicating hole with a diameter of 10 mmφ is formed on the bottom surface of the inner crucible 6, but the number of communicating holes is not limited to one, and it is believed that even if a plurality of communicating holes are provided, effects of suppressing temperature fluctuations, etc. can be obtained. Effect.

In addition, the conductivity of the crystal can be easily controlled by adding an impurity as a dopant to the raw material melt. At this time, although there is a difference between the impurity concentration in the raw material melt in the outer crucible 5 and the impurity concentration in the inner crucible 6, by setting the size of the connecting hole of the second crucible at 1/1 of the inner diameter of the second crucible 5 or less, the difference in impurity concentration in the raw material melt can be controlled, and the impurity concentration in the raw material melt in the inner crucible 6 can be kept constant.

According to the present invention, a compound semiconductor single crystal is produced by a liquid-sealed Czochralski method: a bottomed cylindrical first crucible is provided inside the first crucible, and a communication hole with the first crucible is provided at the bottom. The raw material molten liquid containing part constituted by the second crucible contains semiconductor raw material and sealing agent, the raw material containing part is heated to melt the raw materials, and the seed crystal is brought into contact with the surface of the raw material molten liquid while covering the sealing agent, and the material is pulled up. The seed crystal is grown while the crystal is grown. In the above-mentioned production method, the temperature of the heater is controlled so that the diameter of the grown crystal is approximately the same as the inner diameter of the second crucible, and the surface of the grown crystal is kept covered with the above-mentioned sealant. The crystal grows until the end of the crystal growth, thereby eliminating the need for complicated diameter control, and the desired diameter can be easily obtained. At the same time, the constituent components can be prevented from evaporating from the crystal surface during the crystal growth, resulting in the effect that crystals with excellent quality can be grown.

In addition, due to the double crucible structure, the temperature fluctuation in the raw material melt contained in the crucible can be suppressed, so the generation of twin crystals or polycrystals can be prevented, resulting in the effect of obtaining extremely excellent crystals.

Industrial applicability

The present invention is not limited to ZnTe compound semiconductor single crystals, and may be used in the preparation of ternary or higher ZnTe compound semiconductor single crystals containing ZnTe or other compound semiconductor single crystals.

Claims (8)

1. A method for preparing a compound semiconductor single crystal, which is a method for preparing a compound semiconductor single crystal by a liquid-sealed Czochralski method: a cylindrical first crucible with a bottom and an inner side of the first crucible, at the bottom The semiconductor raw material and the sealing agent are contained in the raw material molten liquid containing part of the second crucible having a communication hole with the first crucible, and the raw material molten liquid containing part is heated to melt the raw material, and the raw material is covered with the sealing agent. The seed crystal is brought into contact with the surface of the raw material melt, and the seed crystal is pulled to grow the crystal, It is characterized in that: the inner diameter of the bottom of the crucible is smaller than the inner diameter of the upper part of the crucible, the side surface is inclined in the range of 0.2° to 10° relative to the vertical direction, and the diameter of the communication hole is 1/5 or less of the inner diameter of the crucible. The crucible serves as the above-mentioned second crucible, When the main body of the crystal is grown, the temperature of the heater is controlled so that crystallization proceeds until it reaches the inner wall of the second crucible at the interface between the growing crystal and the raw material melt, so that the diameter of the main body of the growing crystal is at the interface. Crystallization is carried out so that the inner diameter of the second crucible is uniform, and the diameter of the main body of the growing crystal is restricted by the inner wall of the second crucible, and at the same time, the crystal is grown while the surface of the growing crystal is covered with the sealing agent, until the crystal Growth ends. 2. The method for preparing a compound semiconductor single crystal according to claim 1, wherein the amount of the sealing agent added is set to fill the space between the growing crystal and the second crucible and cover the entire surface of the growing crystal as the crystal grows. amount. 3. The method for producing a compound semiconductor single crystal according to claim 1, wherein the crystal growth is carried out in a state where the second crucible is immersed in the raw material melt contained in the first crucible at a depth of 10 mm to 40 mm. 4. The method for producing a compound semiconductor single crystal according to claim 2, wherein the crystal growth is performed in a state where the second crucible is immersed in the raw material melt contained in the first crucible at a depth of 10 mm to 40 mm. 5. The method for preparing a compound semiconductor single crystal according to claim 1, characterized in that the temperature gradient in the raw material melt is not more than 20°C/cm. 6. The method for preparing a compound semiconductor single crystal according to claim 2, characterized in that the temperature gradient in the raw material melt is not more than 20°C/cm. 7. The method for preparing a compound semiconductor single crystal according to claim 3, characterized in that the temperature gradient in the raw material melt is not more than 20°C/cm. 8. The method for preparing a compound semiconductor single crystal according to claim 4, characterized in that the temperature gradient in the raw material melt is not more than 20°C/cm.

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