JP3617703B2 - Method for producing ZnSe bulk single crystal - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for producing a high-purity ZnSe bulk single crystal used for a substrate for epitaxially growing a thin film of a ZnSe-based compound part and constructing a blue light emitting element such as a semiconductor laser or a light emitting diode.
[0002]
[Prior art]
Usually, in a growth method in which a melt is grown using a substance having a high vapor pressure of the melt, a method in which a raw material is enclosed in a quartz ampule and grown therein is employed. However, quartz glass begins to soften at about 1200 ° C., and deforms or devitrifies at higher temperatures, so it cannot be used for crystal growth of a substance having a melting point as high as 1520 ° C. like ZnSe.
[0003]
For this reason, as a conventional ZnSe melt growth method, raw materials are put into a crucible made of graphite or sintered BN, this crucible is put into a high-pressure vessel, and pressurized with an inert gas such as Ar to evaporate the melt. A high-pressure melting method has been used in which crystals are grown while holding down.
[0004]
[Problems to be solved by the invention]
The high-pressure melting method is a method of growing crystals while reducing the amount of evaporation of the melt with a high-pressure inert gas, but it belongs to an open tube system when viewed from a normal crucible form, and the high-pressure inert gas is a crucible. The loss of the raw material from was only reduced, and the evaporation of the melt could not be completely prevented.
[0005]
Also, in order to obtain a high quality single crystal, it is necessary to increase the furnace pressure in order to perform growth for a long time at a sufficiently low growth rate. Therefore, the growth is usually performed under a very large pressure of 90 to 100 atm. However, it had the following problems.
[0006]
In the above method, since a 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, There was a drawback of significant contamination.
[0007]
Furthermore, in ZnSe used as a raw material, since the partial pressure and diffusion coefficient of Zn and Se, which are component vapors, are different, the composition of the melt tends to shift toward Se excess. In addition to causing excessive supercooling, it is difficult to obtain a single crystal, and a large number of point defects are generated in the obtained crystal, resulting in deterioration of electrical characteristics.
[0008]
Furthermore, structurally, since it is an open tube system as seen from the crucible, the crystal is contaminated by the material substance constituting the furnace, or contamination from the crucible material itself cannot be avoided.
[0009]
Therefore, the 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 to prevent the contamination from the material substance and the crucible in the furnace, thereby achieving a high-purity and high-quality unit. Another object of the present invention is to provide a method for producing a ZnSe bulk single crystal which is made into a crystal and is performed in a clean furnace environment.
[0010]
[Means for Solving the Problems]
As a result of diligent research to achieve the above object, the present inventors have used an inorganic fluorine compound or B ₂ O ₃ as a sealing agent in a method for growing a single crystal from a ZnSe melt by a vertical Bridgman method or a vertical slow cooling method. For example, since these sealing agents have no compatibility or reactivity with the ZnSe melt, the inventors have found that the above-mentioned problems can be solved and have reached the present invention.
[0011]
That is, according to the present invention, first, in 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 slow cooling furnace, a ZnSe raw material and a sealing agent are placed on the seed crystal from the bottom. The crucibles sequentially filled in the inert gas high-pressure furnace having a vapor pressure higher than that of the ZnSe melt are first stopped at a temperature at which the sealant melts, and only the sealant is melted to be positioned below. A method for producing a ZnSe bulk single crystal, comprising: covering a surface of a raw material, and then growing the single crystal on the seed crystal by starting the temperature rise again and melting the raw material; The ZnSe bulk single crystal as described in the above item 1, wherein the sealant is selected from one of B ₂ O ₃ , CaF ₂ , AlF ₃ , LiF, NaF, and KF or a eutectic mixture thereof. Providing manufacturing method It is.
[0012]
[Action]
The apparatus used in the examples of the present invention is a part of a pressurized single crystal pulling apparatus (manufactured by Kokusai Denki Co., Ltd.), which can be grown by the vertical Bridgman method or the vertical slow cooling method.
[0013]
As the raw material ZnSe, a polycrystalline body having a purity of 6N or more is used, but it may be synthesized by a vapor transport method or may be a material for optics obtained by a chemical vapor deposition (CVD) method.
[0014]
In the growth method in the method of the present invention, first, seed crystals, raw materials, and sealant are filled in order from the bottom of a pyrolytic boron nitride (PBN) crucible for crystal growth, and then the crucible is filled in a graphite container. In the state inserted into the crucible, it is attached to the crucible moving shaft in the furnace and installed at a predetermined position in the furnace. After the 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 furnace temperature was raised to the melting point of the sealant, and only this sealant was melted to cover the surface of the raw material.
[0015]
Next, the temperature in the furnace is heated to near the melting point of ZnSe to melt the raw material. However, since the sealing agent exhibits a stable property at the interface with ZnSe, it does not have compatibility or reactivity with the ZnSe melt. Moreover, since the specific gravity is lower than that of the ZnSe melt, it floats on the ZnSe melt and covers the surface of the melt.
[0016]
In addition, by applying a pressure equal to or higher than the vapor pressure of the ZnSe melt from above the sealant melt, while maintaining this state while preventing the evaporation of ZnSe, the seed crystal is partly melted and seeded. Thereafter, the crucible itself is lowered to a low temperature range (vertical Bridgman method) or lowered while precisely controlling the heater temperature (vertical slow cooling method) to grow a single crystal.
[0017]
When all the raw material ZnSe is solidified, the growth is completed, and the furnace is slowly cooled down to room temperature, and then the crystal is taken out from the crucible.
[0018]
The growth conditions in the present invention are as follows.
Crucible: 1 inch Pyrolytic Boron Nitride (PBN) raw material melting temperature: 1650 ° C (maximum temperature in the furnace)
Melting time: 3 hours Growth rate: 3 mm / hour Temperature gradient near melting point: 30 ° C./cm
Furnace atmosphere: Ar gas, 3-50 kgf / cm ²
Raw material weight: 60-90g
Sealant weight: 30-40g
As the sealing agent other _B 2 _{O 3,} it was confirmed that _{CaF 2, AlF 3, LiF,} NaF, or eutectic mixture consisting of a combination of KF.
[0019]
Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.
[0020]
【Example】
FIG. 1 and FIG. 2 are photoluminescence spectra of ZnSe single crystals grown in this example and the comparative example, and a 365 nm line of an ultrahigh pressure mercury lamp is used for excitation of the sample, and FIG. 2 is 77K and will be described below with reference to these figures.
[0021]
(1) A 1 inch diameter pyrolytic boron nitride (PBN) crucible is sequentially filled with seed crystal (4 mmφ × 30 L), 87 g ZnSe raw material (material for optics), and 34 g B ₂ O ₃ as sealant. After being installed in the 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 .
[0022]
(2) Next, while heating the inside of the furnace, the heating is first interrupted at a temperature at which the sealant melts (B ₂ O ₃ 420 ° C.) to melt the sealant. The surface of the raw material ZnSe was covered.
[0023]
(3) Next, the temperature rise is started again, the raw material is sufficiently melted (the maximum temperature in the furnace is controlled to 1650 ° C., the melting time is 3 hours), and then the upper end of the seed crystal is melted and seeded. Single crystals were grown while lowering the crucible at a rate of 3 mm / hour.
[0024]
(4) As a result, it was confirmed that the crystals were obtained with a high yield of 99.9%, the furnace was hardly contaminated, and the scattering of the raw material was suppressed by the sealing agent B ₂ O ₃ . It was.
[0025]
The photoluminescence spectrum (exciton emission region) of the obtained crystal at a measurement temperature of 15 K is as shown in FIG. 1, and light emission such as I ₂ and I ₁ ^d due to bound excitons is observed, and in the vicinity of 2.801 eV Luminescence by free excitons (FE) was also clearly observed. This proved that the crystal obtained in this example had a very low impurity concentration and good crystallinity.
[0026]
Also, FIG. 2 showing the photoluminescence spectrum at a measurement temperature of 77 K clearly shows that there is no light emission from a deep level due to impurities and defects, 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, a 1-inch diameter sintered BN crucible was filled with 81 g of seed crystal and ZnSe raw material (optics raw material) and placed in a high-pressure furnace, and then the inside of the furnace was pressurized to 40 kgf / cm ² .
[0028]
(2) After sufficiently melting the raw material, the upper end of the seed crystal was melted and seeded, and then a single crystal was grown while lowering the crucible at 3 mm / hour. The yield of the crystal was 95%, ZnSe scattered from the crucible was deposited in the high pressure furnace.
[0029]
(3) The photoluminescence spectrum (exciton emission region) of the obtained crystal was obtained and shown in FIG. 1. As a result, although I ₂ (or I ₃ ) and I ₁ ^d due to bound excitons were observed, The emission intensity was weaker than that shown in the examples, and no emission due to free excitons (FE) was observed.
[0030]
(4) Further, as shown in FIG. 2, it was found that light emission from a deep level seen in the vicinity of 2 eV is dominant, which indicates that the purity of the crystal is low.
[0031]
【The invention's effect】
As described above, according to the method of the present invention, by using a sealant that is not compatible or reactive with the raw material ZnSe melt, it prevents the scattering of the raw material from the crucible and increases the crystal yield. In addition to the improvement, it is possible to prevent the crystals from being contaminated from the respective raw materials in the furnace, so that a high-purity single crystal can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a photoluminescence spectrum of a ZnSe single crystal grown in an example and a comparative example at a measurement temperature of 15K.
FIG. 2 is a diagram showing a photoluminescence spectrum of a ZnSe single crystal grown in Examples and Comparative Examples at a measurement temperature of 77K.

Claims (2)

In 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, a crucible in which a ZnSe raw material and a sealant are sequentially filled from the bottom on a seed crystal are filled with the ZnSe melt. In an inert gas high-pressure furnace having a vapor pressure higher than that, first, heating is temporarily interrupted at a temperature at which the sealant melts, and only the sealant is melted to cover the surface of the raw material located below, A method for producing a ZnSe bulk single crystal, comprising raising a temperature again and melting the raw material to grow a single crystal on the seed crystal. The ZnSe bulk unit according to claim 1, wherein the sealant is selected from one of B ₂ O ₃ , CaF ₂ , AlF ₃ , LiF, NaF, and KF or a eutectic mixture thereof. Crystal production method.

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