JPH0948699A - Production of znse bulk single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a ZnSe bulk single crystal having high purity and quality in a clean environment of h furnace by suppressing the scattering of raw material from a crucible to prevent the loss of the raw material and the variation of the molten liquid composition and preventing the contamination of the crystal with the raw material in the furnace and a material generated from the crucible. SOLUTION: A ZnSe bulk single crystal is produced from a molten liquid by a high-pressure melting method using a vertical Bridgman furnace or a vertical annealing furnace. In the above process, a crucible charged with a seed crystal, a ZnSe raw material and an encapsulant (selected from B2 O3 and fluorine compounds such as CaF2 or AIF3 ) in the order is heated in a high- pressure furnace. The obtained single crystal has extremely low impurity content and high crystallinity.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a high-purity ZnSe bulk single crystal used as a substrate for constructing a blue light-emitting device such as a semiconductor laser or a light-emitting diode by epitaxially growing a thin film of a ZnSe-based compound portion. Regarding

[0002]

2. Description of the Related Art Usually, in a growth method for growing a melt using a substance having a high vapor pressure of the melt, a method of encapsulating a raw material in a quartz ampoule and growing it in the ampoule is adopted. However, quartz glass begins to soften at about 1200 ° C. and is deformed or devitrified at a temperature higher than that, and therefore cannot be used for crystal growth of a substance having a high melting point of 1520 ° C. such as ZnSe.

Therefore, as a conventional melt growth method of ZnSe, the raw material is put into a crucible made of graphite or sintered BN, and the crucible is put into a high-pressure container and pressurized with an inert gas such as Ar to melt. A high-pressure melting method has been used in which crystals are grown while suppressing the evaporation of the liquid.

[0004]

The above-mentioned high-pressure melting method is a method of growing a crystal while reducing the evaporation amount of the melt with a high-pressure inert gas. The high-pressure inert gas belongs only to reduce the loss of the raw material from the crucible, and cannot completely prevent the evaporation of the melt.

Further, in order to obtain a good quality single crystal, it is necessary to raise the furnace pressure in order to grow for a long time at a sufficiently low growth rate. Therefore, it is usually performed under a very large pressure of 90 to 100 atm. Although it was being trained, it had the following problems.

In the above method, since part of the raw material is scattered during the growth, the weight of the crystal becomes smaller than the weight of the charged raw material, and the components scattered from the crucible are deposited in the low temperature part of the furnace. It has a drawback that it significantly contaminates the inside of the furnace.

Further, in ZnSe used as a raw material, since the partial pressures and diffusion coefficients of Zn and Se, which are component vapors, are different, the composition of the melt tends to shift toward the excess of Se. This causes compositional supercooling therein, which makes it difficult to form a single crystal, and also many point defects occur in the obtained crystal, which is a factor of deteriorating electrical characteristics.

Further, structurally, since it is an open tube system from the viewpoint of the crucible, the crystals are contaminated by the material constituting the furnace, or the crucible itself is unavoidable.

Therefore, an object of the present invention is to suppress the scattering of the raw material from the crucible to eliminate the loss of the raw material and the fluctuation of the melt composition, and further to prevent the contamination from the raw material in the furnace and the crucible, thereby achieving high purity. It is an object of the present invention to provide a method for producing a ZnSe bulk single crystal that is made into a good quality single crystal and is performed under a clean furnace environment.

[0010]

Means for Solving the Problems As a result of intensive studies aimed at achieving the above object, the present inventors have found that in a method for growing a single crystal from a ZnSe melt by a vertical Bridgman method or a vertical annealing method, an inorganic fluorine compound or B _{When 2} O ₃ is used as a sealant, these sealants have no compatibility or reactivity with the ZnSe melt, and therefore, they have found that the above-mentioned problems can be solved and reached the present invention.

That is, first, the present invention relates to a method of producing a ZnSe bulk single crystal from a melt by a high pressure melting method using a vertical Bridgman furnace or a vertical annealing furnace, in which a ZnSe raw material and a sealant are placed on a seed crystal. A method for producing a ZnSe bulk single crystal, which comprises growing a single crystal on the seed crystal by heat-treating the crucibles sequentially filled in a high-pressure furnace; secondly, the sealing agent is B ₂ O ₃ , CaF
The present invention provides the method according to the second aspect, which is selected from the group consisting of ₂ , AlF ₃ , LiF, NaF and KF, or a eutectic mixture thereof.

[0012]

The apparatus used in the embodiments of the present invention is a pressurized single crystal pulling apparatus (manufactured by Kokusai Electric Co., Ltd.) partially modified to enable growth by the vertical Bridgman method or the vertical annealing method.

As the raw material ZnSe, a polycrystalline body having a purity of 6N or more is used, but it may be one synthesized by a vapor phase transport method or one used as a material for optics obtained by a chemical vapor deposition (CVD) method.

In the growing method in the method of the present invention, first, a pyrolytic boron nitride (P
The BN) crucible is filled with seed crystals, raw materials, and a sealant in this order from the bottom, and then the crucible is inserted into a graphite container and attached to a crucible moving shaft in the furnace so that the crucible moves to a predetermined position in the furnace. Install. After installation, the inside of the furnace is replaced with an inert gas such as Ar or N _2, and the gas is introduced to a predetermined pressure. Next, the temperature inside the furnace was raised to the melting point of the sealant, and only this sealant was melted to cover the surface of the raw material.

Next, the temperature inside the furnace is heated to near the melting point of ZnSe to melt the raw material. However, since the above-mentioned sealing agent exhibits stable properties at the interface with ZnSe, it is compatible and reactive with the ZnSe melt. And has a specific gravity lower than that of the ZnSe melt, it floats on the ZnSe melt and covers the surface of the melt.

Further, by applying a pressure not lower than the vapor pressure of the ZnSe melt from above the sealant melt, this state is maintained while the evaporation of ZnSe is prevented, and a part of the seed crystal is melted and seeded. Then, the crucible itself is lowered to the low temperature region (vertical Bridgman method) or lowered while controlling the heater temperature precisely (vertical gradual cooling method) to grow a single crystal.

When all of the raw material ZnSe is sufficiently solidified, the growth is finished, the inside of the furnace is slowly cooled to room temperature, and then the crystal is taken out from the crucible.

The raising conditions in the present invention are as follows. Crucible: Made of Pyrolytic Boron Nitride (PBN) with a diameter of 1 inch Raw material melting temperature: 1650 ° C (maximum furnace temperature) Melting time: 3 hours Growth rate: 3 mm / hour Temperature gradient near melting point: 30 ° C / cm Atmosphere in the furnace: Ar gas, 3 to 50 kgf / cm ² Raw material weight: 60 to 90 g Sealant weight: 30 to 40 g As a sealant, in addition to B ₂ O ₃ , CaF ₂ and AlF.
_It has been confirmed that a eutectic mixture composed of a combination of ₃ , LiF, NaF, and KF may be used.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

[0020]

EXAMPLES FIG. 1 and FIG. 2 are both photoluminescence of ZnSe single crystals grown in this example and a comparative example.
In the spectrum, the 365 nm line of an ultra-high pressure mercury lamp was used to excite the sample, FIG. 1 shows a measurement temperature of 15 K, and FIG. 2 shows a 77 K line, which will be described below with reference to these.

(1) Pyrolytic with a diameter of 1 inch
Seed crystals (4) in a crucible made of boron nitride (PBN)
mmφ × 30L), ZnSe raw material (material for optics)
After 87 g and 34 g of B ₂ O ₃ as a sealant were sequentially charged and placed in a high-pressure furnace, the inside of the furnace was replaced with Ar gas and the furnace pressure was increased to 9.5 kgf / cm ² .

(2) Next, while heating the inside of the furnace, first, heating is interrupted at a temperature (B ₂ O ₃ 420 ° C.) at which the sealant melts to melt the sealant. Covers the surface of the raw material ZnSe.

(3) Next, the temperature is restarted to sufficiently melt the raw material (the maximum temperature in the furnace is controlled to 1650 ° C., the melting time is 3 hours), and the upper end of the seed crystal is melted to perform seeding. Then, a single crystal was grown while lowering the crucible at a rate of 3 mm / hour.

(4) As a result, crystals were obtained in a high yield of 99.9%, and the inside of the furnace was almost uncontaminated.
It was confirmed that the scattering of the raw material was suppressed by ₂ O ₃ .

The photoluminescence spectrum (exciton emission region) of the obtained crystal at a measurement temperature of 15 K is as shown in FIG. 1, and emission of I ₂ , I ₁ ^d, etc. by the bound excitons is observed and 2.801 eV Light emission by free excitons (FE) was also clearly observed in the vicinity. From this, it was found that the crystals obtained in this example had a very low impurity concentration and good crystallinity.

Further, according to FIG. 2 showing the photoluminescence spectrum at the measurement temperature of 77 K, it is clear that light emission from a deep level due to impurities and defects is not seen, and that it has good quality.

[0027]

[Comparative example]

(1) For comparison, crystals were grown by a conventional high pressure melting method without using a sealant. That is, sintered BN with a diameter of 1 inch
After filling the seed crucible with 81 g of ZnSe raw material (raw material for optics) and setting it in the high-pressure furnace,
Pressurized to 0 kgf / cm ² .

(2) After sufficiently melting the raw materials, the upper end of the seed crystal was melted to perform seeding, and then the single crystal was grown while lowering the crucible at 3 mm / hour. The crystal yield was 95%. In the high pressure furnace, Zn scattered from the crucible
Se was attached and deposited.

(3) The photoluminescence spectrum (exciton emission region) of the obtained crystal was determined and shown in FIG. 1. As a result, I ₂ (or I) due to bound excitons was obtained.
₃ ) and I ₁ ^d were observed, but the emission intensity was weaker than that shown in the examples, and no emission due to free excitons (FE) was observed.

(4) Further, as shown in FIG. 2, the light emission from the deep level observed near 2 eV is dominant, and it was found from this that the crystal purity is low.

[0031]

As described above, according to the method of the present invention, the use of a sealant having no compatibility or reactivity with the ZnSe melt as the raw material prevents the raw material from scattering from the crucible. In addition to improving the crystal yield, it is possible to prevent the crystals from being contaminated by the respective raw materials in the furnace, so that a high-purity single crystal can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a photoluminescence spectrum of ZnSe single crystals grown in Examples and Comparative Examples at a measurement temperature of 15K.

FIG. 2 is a diagram showing a photoluminescence spectrum of ZnSe single crystals grown in Examples and Comparative Examples at a measurement temperature of 77K.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location H01S 3/18 H01S 3/08 (72) Inventor Nagatoshi Nagata 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Within Dowa Mining Co., Ltd.

Claims (2)

[Claims] 1. A method for producing a ZnSe bulk single crystal from a melt by a high-pressure melting method using a vertical Bridgman furnace or a vertical annealing furnace, wherein a crucible in which a ZnSe raw material and a sealant are sequentially filled on a seed crystal is used. A method for producing a ZnSe bulk single crystal, which comprises growing a single crystal on the seed crystal by heat treatment in a high-pressure furnace. 2. The sealant is B ₂ O ₃ , CaF ₂ , Al
The method for producing a ZnSe bulk single crystal according to claim 2, wherein the ZnSe bulk single crystal is selected from one of F ₃ , LiF, NaF, and KF, or a eutectic mixture thereof.