JPH07330494A - Production of znse single crystal - Google Patents

Abstract

PURPOSE:To obtain a process for producing ZnSe single crystal capable of easily producing the high-quality single crystal free from crystal defects, such as twins and dislocation, with good productivity. CONSTITUTION:This process production of the ZnSe single crystal comprises growing the single crystal under high-temp. isotropic pressurization in the state of arranging a ZnSe polycrystalline substance into sealing materials. In this invention, these sealing materials 2 are melted by heating and the ZnSe polycrystalline substance 3 having a relative density >=95% is embedded into the melt 2A of the sealing materials and is subjected in this state to the high- temp. isotropic pressurization. B2O3 is adequate as the sealing materials 2, 2A. Execution of the high-temp. isotropic pressurization in a high-temp. and high-pressure atmosphere of >=100kgf/cm<2> and 1000 to 1400 deg.C is better as the treating conditions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-quality ZnSe single crystal used as a substrate material or a seed crystal for growing a single crystal such as a blue semiconductor laser device and a blue light emitting diode device.

[0002]

2. Description of the Related Art So-called wide-gap semiconductor materials having a bandgap corresponding to the energy of blue light are used for manufacturing light emitting devices such as blue semiconductor lasers and blue semiconductor diodes. Among wide-gap semiconductor materials, II-VI group compound semiconductors of ZnSe are most promising.

A ZnSe single crystal substrate is required as a substrate for epitaxial growth in manufacturing a blue light emitting device device, and the single crystal substrate is usually processed from a bulk single crystal. As a method for industrially growing the bulk single crystal,
Although a melt growth method of growing crystals from a melt is advantageous from the viewpoint of productivity, ZnSe has a melting point at 1526 ° C.,
When a crystal is grown by a melt growth method such as Bridgman method, a phase transition from a hexagonal crystal of a high temperature phase to a cubic crystal of a low temperature phase occurs at around 1420 ° C. Therefore, a twin crystal defect caused by this occurs. However, there is a drawback that a high quality single crystal cannot be obtained (Journal of Crystal Growth, vol.86, 1988,132
See page 137).

In order to avoid twin defects due to the phase transition, it is theoretically possible to grow the crystal at a temperature of 1420 ° C. or lower to grow the cubic crystal phase. As a method therefor, there is a low temperature growth method such as a chemical vapor deposition method or a physical vapor deposition method as disclosed in JP-A-1-264990, but the growth rate is slow and the productivity is very poor. There's a problem.

On the other hand, as a method for producing a single crystal having a high crystal growth rate, as disclosed in Japanese Patent Application Laid-Open No. 60-11293, a large amount of ZnSe synthesized by a chemical vapor deposition method (CVD method) is used. After vacuum encapsulating the crystal in a capsule made of Pyrex glass or quartz glass, this capsule is isostatically pressed (HIP) at a high temperature of 1000 ° C.
A method of doing so is disclosed.

[0006]

However, in the conventional method for producing a single crystal by HIP, the work of vacuum-encapsulating the raw material ZnSe polycrystal in a capsule is complicated and the productivity is poor. Further, although the capsule softens during the HIP treatment, it is difficult for the capsule to come into close contact with the surroundings of the raw material.
Shear stress is easily generated in e, and defects such as twins and dislocations are likely to occur. Furthermore, since the encapsulant adhered around the crystal after the HIP treatment must be removed mechanically, unnecessary stress acts on the single crystal during the removal.
Crystal defects such as twins and dislocations may occur.

The present invention has been made in view of the above problems, has good productivity, can suppress generation of crystal defects such as twins and dislocations, and can easily obtain a high-quality single crystal. , A method for producing a ZnSe single crystal using HIP is provided.

[0008]

Zn according to claim 1 of the present invention
The Se single crystal manufacturing method is a method of manufacturing a ZnSe single crystal in which a ZnSe polycrystal is placed in a sealing material, isotropically pressurized at high temperature to grow a single crystal, and the sealing material is heated. The ZnSe polycrystal having a relative density of 95% or more melted and embedded in the melt of the sealing material is subjected to high-temperature isotropic pressing.

Further, the manufacturing method according to claim 2 is such that the ZnSe content is high.
Encapsulate a crystalline body and Zn with a heat resistant soft material
The sealing material is placed in a sealing material, and the sealing material is heated and melted.
High temperature isotropic pressurization with the above-mentioned encapsulant embedded in the melt.
To do. The sealing material is B₂O₃Is preferred and processing
The condition is 100 kgf / cm ² More than 1000-14
It is best to apply high temperature isotropic pressure in a high temperature and high pressure atmosphere of 00 ℃.
Yes.

[0010]

Since the ZnSe polycrystal is hot and isotropically pressurized while being embedded in the melt of the encapsulant, the melt encapsulant completely adheres to the periphery of the polycrystal. Therefore, the pressure with excellent isotropy acts on the polycrystalline body. For this reason, it becomes difficult for shear stress due to the unevenness of the applied pressure to act on the inside of the single crystal during the growth process of the single crystal, and crystal defects are less likely to occur. Further, since the polycrystal is embedded in the encapsulating material only by melting the encapsulating material, the work is very easy.

Further, since the relative density of the ZnSe polycrystal is 95% or more, the pores in the polycrystal are independent of each other, and the sealing material melted at the isotropic pressure is polycrystal. There is no danger of penetrating into the inner pores and the growth of crystal grains is not hindered. The raw material is preferably a polycrystalline body having a relative density of 99% or more. The pores in the polycrystal are removed outside the crystal due to the growth of the crystal during HIP and the diffusion at high temperature. The more pores, the longer the removal takes. Further, the pores may contain an atmospheric gas at the time of synthesizing the polycrystal, and this gas component tends to hinder the densification at the time of HIP, which in turn hinders the growth of the single crystal. Therefore, it is preferable that the number of pores in the polycrystal is as small as possible, and the relative density is 99% or more.

An encapsulation body in which a ZnSe polycrystal and Zn are encapsulated with a heat resistant soft material is embedded in a melt of the encapsulant, and H
By IP, Zn vapor is filled in the heat resistant soft material at the time of HIP, and Zn-rich ZnSe single crystal, that is, n
A crystal with low electrical resistance can be easily obtained. B ₂ O ₃ is suitable as the sealing material. B ₂ O ₃ has a melting point of about 5
Since the temperature is as low as 50 ° C., even in the cooling process after the treatment, a complete isotropic pressure can be maintained until the temperature drops to this melting point, and stress is unlikely to occur inside the crystal. The softening point of Pyrex glass is 820 ° C., and stress due to uneven pressure is likely to occur inside the crystal even during the cooling process. Further, B ₂ O ₃ is soluble in an organic solvent such as methyl alcohol, and the removal work of B ₂ O ₃ after the HIP treatment can be easily performed by a non-mechanical means such as boiling in an organic solvent. Therefore, it is possible to prevent unnecessary stress from being generated in the crystal when the sealing material is removed, and it is possible to easily obtain a high-quality single crystal.

The conditions for HIP treatment during single crystal growth are as follows:
It is preferable that the pressure is 100 kgf / cm ² (preferably 500 kgf / cm ² ) or more and the temperature is 1000 to 1400 ° C. (preferably 1200 to 1400 ° C.). Pressure is 10kg
If it is f / cm ² or more, the dissociation of Zn from the ZnSe polycrystal can be suppressed and the fluctuation of the components can be prevented, but by setting it to 100 kgf / cm ² or more, preferably 500 kgf / cm ² or more , The pores in the polycrystal can be crushed, and even if a raw material having a low relative density (however, 95% or more) is used, the true density can be almost achieved during the HIP treatment, and the crystal grain growth Since it is possible to remove the pores that hinder the growth of crystal grains, the growth of crystal grains is promoted and large crystal grains are easily generated. If the treatment temperature is lower than 1000 ° C., the crystal growth rate is slow, and if the pressure is about 100 kgf / cm ² , it becomes difficult to collapse the pores. Processing temperature 1200
By increasing the temperature above ℃, the growth rate increases rapidly, and a cm-order single crystal is grown in less than half a day.
It is possible to manufacture in an industrial manufacturing cycle such as cooling at night. On the other hand, if the temperature exceeds 1400 ° C, there is a possibility that the temperature may reach the phase transformation temperature (1420 ° C) range due to variations in temperature control or the like.

[0014]

EXAMPLES To carry out the present invention, as shown in FIG. 1 (A), first, a ZnSe polycrystalline body 3 as a raw material is placed in a container 1 formed of a heat-resistant material having airtightness, and further, ZnS having a melting point below the HIP processing temperature during crystal growth and ZnS
The sealing material 2 made of a material that does not react with e is filled.

As a material of the container 1, specifically, P
Refractory metals such as BN, pyrolytic graphite, glassy carbon and molybdenum are used. On the other hand, as the sealing material 2, specifically, a mixture of B ₂ O ₃ (boric anhydride: melting point of about 550 ° C.), AlF ₃ and CaF _{2 in} a ratio of 4: 6 (Japanese Journal of A).
pplied Physics, Vol. 31, L383, published in 1992) and the like can be used. As the form of the encapsulant, the powder has good handling and filling workability,
Since the powder has a large apparent volume reduction at the time of melting, it is preferable to use a block-shaped powder having a low bulk density together. In addition, B ₂ O ₃ is described in a document (Journal of Electrochemistry Society, Vol. 10) that reacts with ZnSe.
6, page 830, issued 1959), but no remarkable reaction is observed in the temperature range of the embodiment of the present invention described later, and it can be used as a sealing material.

Next, the container filled with the ZnSe polycrystal 3 and the encapsulant 2 is housed in a pressure furnace capable of high temperature treatment under a high pressure atmosphere of an inert gas such as Ar or nitrogen as in a HIP device. Then, the inside of the furnace is evacuated to remove the air remaining in the furnace. At this time, it is preferable to heat to a temperature of about 400 ° C. in order to remove water and gas adsorbed in the furnace, the container, and the sealing material.

Next, after injecting an inert gas for a pressurizing medium into the furnace, it is heated to a temperature higher than the melting point of the sealing material under a low pressure of less than about 10 kgf / cm ² to melt the sealing material. As shown in FIG. 1 (B), the ZnSe polycrystalline body 3 as the processed material is embedded in the melt 2A of the sealing material. Then, the furnace pressure and temperature are increased. When the pressure reaches 1000 ° C, 1
00kgf / cm ² or more (preferably 500 kgf / cm ² or higher) is desirably. Under the treatment conditions or higher, the pore-like defects contained in the polycrystal are crushed and the treated product is densified. Therefore, the pores that hinder the growth of crystal grains are removed, so that the crystal grains grow rapidly in the subsequent crystal growth process, and large crystal grains are generated.

When the temperature inside the furnace is raised, if the temperature is raised in a state where the temperature distribution in the entire raw material is not so large, crystal grains grow from various parts of the raw material polycrystalline body, and finally some large crystal grains are generated. Will be a collection of. In order to prevent such growth, it is necessary to raise the temperature with a temperature gradient such that the upper side is higher than the lower side so that the crystal grains grow in one direction from the upper side to the lower side. preferable. In addition, it is also possible to use a material in which a large single crystal (seed crystal) is deposited at one end of the raw material polycrystal by performing such treatment in advance.

Next, the temperature and pressure are maintained under crystal growth conditions. The pressure in the growth step may be at least the dissociation pressure of ZnSe at the holding temperature (about ² kgf / cm ² at 1400 ° C.). Also, as will be described later, when Zn is sealed together with a heat resistant soft material, the vapor pressure of Zn (30 kg at 1400 ° C)
f / cm ² ) or higher). However, when using a raw material polycrystal having a relative density of about 95 to 98%, in order to crush the pores in the crystal to promote the growth of the crystal, as described above, 100 kgf / cm ² or more. It is better to The treatment time is preferably long, but if the temperature is considerably close to 1400 ° C., it can be easily grown into crystal grains having a size of about 10 mm by holding for about 3 hours.

The temperature and pressure during cooling after the crystal growth is ZnS.
In order to suppress decomposition of e, cooling is always performed while applying a pressure equal to or higher than the dissociation pressure of ZnSe corresponding to the temperature of the processed material. In addition, when cooled rapidly, a temperature gradient occurs inside the crystal,
Since twin crystals may be generated due to the thermal stress resulting from this, the cooling rate is preferably slow (preferably 1000 ° C./hr or less), although it depends on the size of the single crystal. .

In order to grow a Zn-rich ZnSe single crystal having a low n-type electrical resistance, the raw material may be in a Zn vapor atmosphere during the crystal growth. In order to form such an atmosphere, ZnSe polycrystal as a processing raw material and Zn (melting point 420
℃) is wrapped in a heat-resistant soft material such as a graphite sheet, which is then sealed in a polyethylene bag and subjected to cold isostatic pressing, and the bag is removed, and the polycrystalline body and Zn are almost airtightly encapsulated in the graphite sheet. The encapsulated body thus obtained is obtained, and the encapsulated body is embedded in the melt of the sealing material, and the HIP treatment is performed.

Next, specific examples will be given. Example 1 A small lump (20 × 10 × 7 mm, about 4 g) of a ZnSe polycrystal (relative density 99.9% or more, average particle size 5 to 10 μm, manufactured by Raytheon Co.) manufactured by the CVD method was manufactured by PBN. After being placed in the container of No. _2, it was filled with sufficiently dried B ₂ O ₃ powder. After this the ZnSe polycrystalline body and B ₂ O ₃ powder was container placed in a HIP apparatus, the inside of the furnace was evacuated and replaced twice with argon (Ar) gas pressure of about 5 kgf / cm ² It was filled with 10 kgf / cm ² of Ar gas. Subsequently, the temperature rise and pressurization with Ar gas were started, and 1400
The temperature was maintained at 1000 kgf / cm ² for 3 hours. After holding 50
The temperature was lowered at a cooling rate of 0 ° C./hr, and after cooling, the container was taken out.

The entire container was immersed in methyl alcohol and heated, and B ₂ O ₃ was dissolved while boiling the methyl alcohol to take out ZnSe crystals from the container. The crystal color was yellow with a slight orange tinge. When the weight was measured, no weight change was observed before and after the treatment. In addition, as a result of observing the surface of the crystal by etching with a calcium hydroxide aqueous solution, it was confirmed that the whole was composed of almost three large crystal grains.

No twin defects were found inside these three crystal grains. On the other hand, the dislocation density was measured to be about 2000 / cm ² , and high quality crystals were obtained despite the simple treatment. This is because B ₂ O ₃ has a low melting point, so that isotropic property can be maintained even at a low temperature during cooling, and stress is unlikely to be generated in the crystal when B ₂ O ₃ is removed after the treatment. Was estimated.

Note that nitrogen gas is used instead of Ar gas.
When HIP processing was performed under the same conditions, the color turned yellow.
Except for the thickening, it is almost the same as when Ar gas is used.
It was the same. Example 2 The same raw material as in Example 1 was used, and the length direction was made vertical.
Put it in a glassy carbon container and let it dry thoroughly
B₂O₃Filled with powder. Put this container in the HIP device
Then, vacuuming and Ar gas replacement operation are performed in the same manner as in Example 1.
Yes, 10 kgf / cm ² After charging Ar gas of
Start and the pressure is 300kgf / cm² When the temperature exceeds
From 600 ℃), the temperature of the upper part of the HIP device will rise.
Adjust the heating power so that the internal temperature distribution is approximately 20 ° C / cm
The temperature was controlled as described above. Finally raw polycrystal
Control the temperature at the upper part of the body to about 1350 ° C, and press
1000kgf / cm² It was held for 5 hours. Then about 900
A container containing crystals by lowering the temperature at a cooling rate of ° C / hr.
Took out.

According to the same method as in Example 1, the crystals were taken out from the container, subjected to etching treatment and observed. As a result, there was almost no change in weight and the color was almost the same as in Example 1. Moreover, it was confirmed that the whole crystal consisted of one single crystal. Example 3 The same polycrystalline material as in Example 1 and about 0.4 mg of Zn particles (average particle size of about 1 mm) were used as a flexible graphite sheet (trade name: Grafoil, 0.4 mm thickness was fired at about 700 ° C.).
The whole was vacuum-sealed in a polyethylene bag and subjected to cold isostatic pressurization at a pressure of 1000 kgf / cm ² , after which the bag was removed and sealed with a graphite sheet almost airtightly. I got a package. The envelope was placed in a glassy carbon container, filled with sufficiently dried B ₂ O ₃ powder, and subjected to HIP treatment under the same conditions as in Example 1.

As a result of observing the crystal after the treatment, there was a characteristic that the color was close to yellow, but twin crystals did not occur and the whole crystal was two large crystal grains of about 7 mm and two crystal grains of about 2 to 3 mm. It was composed of two relatively small grains. Comparative Example 1 High-purity ZnSe powder was cooled to 100% by cold isostatic pressing.
A molded body (about 3 g) having a relative density of about 55% was prepared by molding at a pressure of 0 kgf / cm ² . Using this compact, crystals were grown under the same processing conditions as in Example 1.

After the treatment, the sample was yellow and the decomposition of ZnSe seemed to be suppressed, but it was found that the molten B ₂ O ₃ penetrated into the pores of the molded body. Comparative Example 2 The HIP treatment was performed under the same conditions as in Example 1 except that the same raw material as in Example 1 was used and the treatment temperature in the crystal growth process was 1420 ° C.

The sample after the treatment had the same color and weight change as in Example 1 and was composed of four large crystal grains, and it was confirmed that the crystals were sufficiently grown. However, many parallel lines were observed in each crystal grain, and it was found that twinning occurred. Comparative Example 3 The HIP treatment was performed under the same conditions as in Example 1 except that the same raw material as in Example 1 was used and the treatment temperature in the crystal growth process was 980 ° C.

When the sample after the treatment was etched and the growth of crystal grains was observed under a microscope, the grain size was not uniform.
The average particle size was about 50 μm. From this example, 100
It is estimated that a holding time of 100 hr or more is required at a temperature lower than 0 ° C. Comparative Example 4 The same raw material as in Example 1 was used, and the raw material was housed in an ampoule of Pyrex glass and sealed while evacuating the inside. The ampoule was placed in a graphite container, placed in a HIP device, and subjected to HIP treatment under the same conditions as in Example 1. After cooling, the ampoule was mechanically removed and the crystal was taken out.

The treated sample was similar to that of Example 1 in that three large crystal grains were formed, but some lamellar band patterns due to twinning were observed. Further, when the dislocation density was measured, it was one digit higher than that in Example 1, and was 1,500.
It was more than 0 / cm ² . The very large dislocation density was caused by the thermal stress due to the difference in the coefficient of thermal expansion between the glass and the crystal during the cooling process, and the mechanical removal of the glass after the treatment. It is presumed that the stress acted on the crystal.

[0032]

As described above, according to the constitution of claim 1 of the present invention, the sealing material in a molten state is completely adhered to the periphery of the ZnSe polycrystal, and the polycrystal is excellent in isotropy. As a result of the applied pressure, it becomes difficult for stress due to the unevenness of the applied pressure to act on the inside of the single crystal, crystal defects are less likely to occur, and a high-quality single crystal can be obtained. Further, since the polycrystal is embedded in the encapsulating material only by melting the encapsulating material, the work is very easy and the productivity is excellent.

Further, according to the structure of claim 2, Zn vapor is filled in the heat resistant soft material at the time of HIP, and a Zn-rich high-quality ZnSe single crystal, that is, an n-type low electrical resistance crystal is easily obtained. And the productivity is good. By using B ₂ O ₃ as the encapsulant, it is possible to maintain a perfect isotropic pressure up to a low temperature even in the cooling process after the HIP treatment, and it is difficult to generate stress inside the crystal even in the cooling process. The removal work of ₂ O ₃ can be easily performed by non-mechanical means, unnecessary stress can be prevented from being generated in the crystal at the time of removing the sealing material, and a higher quality single crystal can be obtained. To be

The conditions for HIP treatment during single crystal growth are a pressure of 100 kgf / cm ² or more and a temperature of 10 kgf / cm ^2.
By setting the temperature to 00 to 1400 ° C., it is possible to crush the pores in the polycrystalline body while preventing the fluctuation of the components due to dissociation, promote the growth of the crystal grains, and easily generate the large crystal grains. Excellent in performance.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing a sealing procedure of a ZnSe polycrystal, in which (A) shows before melting of a sealing material and (B) shows after melting of a sealing material.

[Explanation of symbols]

 1 Container 2 Sealant (powder) 2A Sealant (melt) 3 ZnSe polycrystal

Claims (4)

[Claims] 1. A ZnSe for growing a single crystal by subjecting a ZnSe polycrystal to a high temperature isotropic pressure under the condition that the ZnSe polycrystal is placed in a sealing material.
In the method for producing a single crystal, the sealing material is heated and melted, and a ZnSe polycrystal having a relative density of 95% or more is embedded in the molten material of the sealing material, and ZnSe is isostatically pressed at a high temperature. Method for producing single crystal. 2. An encapsulant in which a ZnSe polycrystal and Zn are encased in a heat resistant soft material is placed in a sealing material, and the encapsulating material is heated and melted. A method for producing a ZnSe single crystal in which the above-mentioned encapsulated body is embedded in a high temperature and isotropically pressurized. _{3. The} use of B ₂ O ₃ as a sealing material.
Alternatively, the method for producing a ZnSe single crystal according to item 2 or 3. 4. 100 kgf / cm ² or more and 1000 to 14
The method for producing a ZnSe single crystal according to claim 1, 2 or 3, wherein isotropic high-temperature pressurization is performed in a high-temperature, high-pressure atmosphere of 00 ° C.