JP3037829B2 - Single crystal growing method and single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a growth method for growing a single crystal under the surface of a melt by lowering the temperature of the melt, such as a chiroporous method or a TSSG method, and more particularly to a flux method. KTiOPO grown from
₄ (KTP), KTiOAsO ₄ , RbTiOPO ₄ , R
bTiOAsO ₄ , TlTiOPO ₄ , TlTiOAsO
_{(4) The present} invention relates to a method for producing a single crystal and a high-quality single crystal grown by the method.

[0002]

2. Description of the Related Art In recent years, KTP single crystals and their analogous compounds have been used as materials for various wavelength conversion elements because of their excellent nonlinear optical characteristics. Conventionally, KTP single crystals and their analogous compounds have been grown by hydrothermal synthesis at a pressure of 500 to 700 ° C. and a pressure of at least 1000 atm (for example, US Pat. No. 3,949,323). In addition, KTP
The single crystal is a single crystal represented by KTiOPO ₄ ,
Analogous compounds of KTP include KTiOAsO ₄ , RbTi
OPO ₄ , RbTiOAsO ₄ , TlTiOPO ₄ , Tl
TiOAsO ₄ or the like. However, since the apparatus of the hydrothermal synthesis method is special and the crystal is expensive, a method of growing the crystal supply that is cheaper and easier is studied.
A growth method based on the flux method as described in US Pat. No. 9598 has been developed. In crystal growth by the flux method, potassium phosphate or a mixture of potassium phosphate and tungsten oxide is used as the flux. Conventionally, the following four methods have been mainly used as crystal growing methods by the flux method. The first method is to slowly cool the entire melt to precipitate crystals of several mm square at the bottom of the crucible, and the second method is to sink a seed crystal of the same quality as the crystal to be grown near the center of the melt. The so-called Holden method is a method of growing a crystal on a seed crystal in this melt, and the third method is to attach a seed crystal of the same quality as the crystal to be grown on the surface of the melt and gradually cool the melt temperature. A method for growing crystals below the surface of the melt, which is referred to as the so-called chiroporous method. In the fourth method, a seed crystal of the same quality as the crystal to be grown is attached to the surface of the melt, and the temperature of the melt is gradually reduced. A method of growing crystals below the surface of the melt while cooling and slowly pulling the crystals, which is called the TSSG method. In the Czochralski method, which is often used as a method for growing single crystals, the crystallization of the melt is performed at the interface between the crystal and the melt in the vicinity of the melt surface, whereas in the flux method such as the chiroporous method or the TSSG method, the melt is crystallized. Crystallization of the liquid takes place at the interface in the melt as precipitation of crystalline components from the flux. For this reason, there is a great difference in the shape of the crystal. In the Czochralski method, a crystal having a cylindrical shape is formed. The crystal grows in a shape having a characteristic. For example, the appearance of a KTP crystal grown in the b-axis direction using potassium phosphate as a flux is as shown in FIG. FIG. 2 shows a crystal grown in the b-axis direction using a flux containing potassium phosphate containing tungsten oxide.
It has been reported that the appearance of the crystal differs depending on the flux even in the crystal grown in the same coaxial orientation of the same crystal (Preprints of the Japan Society of Artificial Minerals 1990, p9). In general, if the axial orientation is different, the crystal shape is also different.
FIG. 3 shows a schematic diagram of the crystal shape as viewed from the Y and Z axis directions.
(J. Crys. Growth110 (1991) P6)
97) When growing a crystal by the chiroporous method or the TSSG method, when the temperature is decreased very slowly, the crystal grows while gradually depositing around the rotating seed crystal. 1 and 2 regardless of the crystal diameter.
This is a characteristic growth having shape anisotropy as shown in FIG. However, conventionally, seed crystals used for crystal growth are:
An elongated rectangular parallelepiped, whose cross-sectional shape is almost a square, and different from the cross-sectional shape of the grown crystal was used. In addition, Chiroporous method and TSS
In the G method, the seed crystal placed on the seed holder was slowly lowered to attach the seed crystal near the melt surface. However, depending on the operator, it is considered that the length of the crystal may be about 1 mm, but the length of the crystal submerged in the melt has not been specified.

[0003]

In the conventional method, crystal defects such as dislocations, small-angle grain boundaries, bubbles, and microcracks are likely to be introduced in the initial stage of crystal growth, which is important for high-quality crystal growth. As a result, there is a problem that it is difficult to improve the quality of the single crystal. Therefore, the seed crystal portion of the crystal grown by such a defect has extremely poor crystallinity, and the area around the seed crystal is optically opaque and cloudy. When the crystal shape becomes large to some extent, the quality gradually improves and becomes transparent, but since many of the crystal defects introduced into the crystal near the seed crystal are inherited, it goes without saying that this is a problem in crystal quality. . It is well known that crystal defects generated in a single crystal near the seed crystal of a single crystal tend to propagate to the grown crystal. Also, when growing a crystal below the melt surface by lowering the temperature of the melt by a method such as the TSSG method, it is more important to perform seeding and initial crystal growth without generation of these defects. . In view of the above problems, the present invention, when growing a single crystal under the surface of the melt by lowering the temperature as in the chiroporous method,
It is an object of the present invention to provide a method of growing a single crystal of KTP and its analogous compound single crystal from a flux with high yield and high quality, and to provide a good quality crystal by the method.

[0004]

Means for Solving the Problems A first aspect of the present invention is a single crystal growing method for growing a single crystal under a melt by lowering the temperature of the melt to use a crystal attached to the melt surface as a seed crystal. The seed crystal is grown or grown in such a manner that at least a part of the side surface of the seed crystal submerged in the melt is processed to have a plane orientation substantially parallel to the crystal easy-to-grow surface so that at least a part of the seed crystal becomes substantially similar to the grown crystal. A single crystal growing method characterized by using a small piece of crystal. Since only the side surfaces are substantially parallel to the easy growth surface, processing of the grown crystal is very easy. The second invention is a single crystal growing method in which a crystal attached to the surface of the melt is grown as a seed crystal by lowering the temperature of the melt to grow a single crystal under the melt. The formed surface or cut and polished surface of the seed crystal in the submerged portion is processed into a plane orientation almost parallel to the crystal growth easy surface so that at least a part of the seed crystal becomes almost similar to the grown crystal, and is immersed in an etching solution in advance and surface processing distortion A single crystal growing method characterized by using a crystal or a small piece of a grown crystal from which a layer has been removed. It is possible to obtain a better single crystal by performing etching. In addition, the present invention relates to a method for growing a MTiOXO ₄ (where M
Is one or more of K and Rb, and X is one or more of As and P). In the present application, it is preferable that the seed crystal be immersed in the melt at least 2 mm from the surface of the melt.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. (Example 1) K ₂ HPO ₄ , TiO ₂ and W as starting materials
Using O ₃ , the flux (K ₂ WO ₄
· P ₂ O ₅₎ and created the crystalline component (KTiOPO _4). 4K ₂ HPO ₄ + 2TiO ₂ + 3WO ₃ = 2KTiOP
_{O 4 + 3K 2 WO 4 ·} P 2 O 5 + 2H 2 O The above raw materials diameter 70
It was placed in a platinum crucible having a height of 70 mm and a height of 70 mm, and was heated and melted at 1000 ° C. in a normal vertical electric furnace using a Kanthal heater. A seed crystal is attached to the surface of the melt, and while rotating the crystal at about 100 rpm, the crystal is grown while lowering the melt temperature at about 3 ° C./day, and a size of about 15 * 15 * 7 mm is obtained in about one week. A crystal was grown. The seed crystal used for the growth had the axial orientation and shape shown in FIG. FIG.
(A) to (c) are used for growing a crystal by rotating the crystal around the Y-axis orientation of the crystal. (A) is a comparative seed crystal formed on a plane parallel to each of the X, Y, and Z planes. (B) is a side view of the KTP grown crystal shown in FIG. 3 in which the XZ cross section and the XY cross section are substantially similar in shape, and the XZ cross section of the seed crystal is formed. (C) is a seed crystal formed to include a portion similar to the XZ cross section of the KTP crystal shown in FIG. 3 and also similar to the Y-axis orientation. 4D to 4F are used for growing the crystal by rotating the crystal about the Z-axis direction. (D) is X,
This is a comparative seed crystal formed on a plane parallel to each of the Y and Z planes. (E) shows a side view of the KTP grown crystal shown in FIG. 3 having a shape similar to that of the XY section, and the XZ and XY sections of the seed crystal formed. (F) is a seed crystal formed to include a portion similar to the XZ cross section of the KTP crystal shown in FIG. 3 and also similar to the Y-axis orientation. When the KTP crystal was grown in the Y-axis and Z-axis directions using the respective seeds, when (a) and (d) were used, an opaque portion was formed around the seed crystal to a size of about 8 mm. I was On the other hand, when (b) and (e) were used, the cloudiness around the seed crystal was reduced to about 6 mm.
The area was about a corner. In the case of using (c) and (f), no white turbidity around the seed crystal is observed, or it is reduced to at most about 4 mm square, and crystal defects around the seed crystal are greatly reduced. I understand. Therefore, the production yield of the high quality part has been improved, and the quality of the grown part has also been improved by improving the quality near the seed crystal.

Example 2 A seed crystal similar to that of Example 1 was prepared, and the relationship between the degree of precipitation of the seed crystal into the melt and the crystallinity was examined. In the crystal growth, the crystal diameter expands on the melt surface and the crystal grows in the melt, and the size of the crystal grows. Therefore, when the seed crystal is not settled in the melt, the crystal growth on the surface is a large part of the crystal growth in the initial stage of crystal growth, which is different from the ideal natural KTP crystal growth shown in FIG. The growth rate was extremely slow. On the other hand, when the seed crystal is submerged in the melt, crystal growth occurs simultaneously on the surface and inside of the melt, and in the initial stage of crystal growth, growth occurs in a shape similar to the ideal shape of the crystal. It has been confirmed that the crystal growth is as quick as possible when the seed crystal is not submerged in the melt and that the crystal grows easily even if the temperature drop rate is reduced, so that the crystal growth occurs without difficulty and without difficulty.

Example 3 A seed crystal was formed into an arbitrary shape shown in b, c, e, and f of FIG. 4 and processed, and then the crystal surface was etched to remove a processed strain layer on the surface. . In the crystal grown using this crystal, the number of dislocations contained in the crystal was reduced to about half or less of the conventional one.

(Embodiment 4) KTP crystal and KTiOAsO ₄ , RbTiOPO ₄ , RbTiOAs by the same method as in Embodiments 1 to 3 above.
O ₄ , TlTiOPO ₄ , and TlTiOAsO ₄ single crystals were grown. High quality is achieved by applying both crystals,
Significant contributions to stabilization of characteristics and high efficiency of optical devices using this were confirmed.

[0009]

According to the present invention, in a method of growing a single crystal below the surface of a melt by lowering the temperature of the melt, the cross-sectional shape of the grown crystal in the liquid surface direction is substantially similar to that of the single crystal. Since a seed crystal having a sectional shape is used, a high-quality single crystal having no crystal defects is grown with a high yield. In addition, since the KTP single crystal and its analogous compound grown by the present invention are of high quality with very few crystal defects, they are extremely effective in increasing the efficiency and stabilizing the operation of SHG devices using these crystals as nonlinear optical devices. It is.

[Brief description of the drawings]

FIG. 1. KT grown using potassium phosphate flux
It is an external view of a P crystal.

FIG. 2 is an external view of a KTP crystal grown using a flux in which tungsten oxide and potassium phosphate are mixed.

FIG. 3 is a schematic external view of a KTP crystal as viewed from the X, Y, and Z axis directions.

FIG. 4 is an external view of seed crystals of various shapes used for growing a crystal according to the present invention.

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C30B 1/00-35/00

Claims (3)

(57) [Claims] 1. A method for growing a single crystal under a melt by using a crystal attached to the surface of the melt as a seed crystal by lowering the temperature of the melt, wherein a portion to be submerged in the melt as a seed crystal is provided. A single crystal growing method, characterized by using a seed crystal processed so that at least a side surface of the seed crystal has a shape substantially similar to that of the grown crystal so as to have a plane orientation substantially parallel to the crystal easy-to-grow surface. 2. A method for growing a single crystal under a melt by using a crystal attached to the surface of the melt as a seed crystal by lowering the temperature of the melt.
Growing the shaped or cut and polished surface of the seed crystal
And crystal growth so that at least part of it is almost similar
Use a seed crystal that has been processed to a plane orientation almost parallel to the easy plane and that has been previously immersed in an etchant to remove the surface processing strain layer
A method for growing a single crystal, comprising: 3. A method of growing a single crystal according to claim 1 or 2, wherein MTiOXO ₄ (where M is K, R
b is a single crystal, and X is one or more of As and P).