JP3010891B2 - Single crystal growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-linear optical material MTIOXO ₄ (M = K, Rb, Cs, X = P, As).
And a method for growing a single crystal.

[0002]

2. Description of the Related Art In recent years, with the advent of a laser having a strong output and good coherence, a second harmonic (SHG: Second harmonic) has been developed using a nonlinear optical material.
As a generation, light of a half wavelength of the fundamental wavelength has been obtained.

As the nonlinear optical material, MTIOXO ₄ (M = K, Rb, C
s, X = P, As) single crystal, particularly a KTiOPO ₄ single crystal (hereinafter simply referred to as KTP) is used.

Incidentally, the above-mentioned MTIOXO ₄ (M = K,
As a method for growing a single crystal of Rb, Cs, X = P, As, a TSSG method (Top Seed Solution) is used.
ongrowth) is common. The TSSG method is a type of the flux method in which a raw material is melted in a flux (flux) to create a supersaturated state and grow crystals only in a seed crystal. Actually, using the above-described TSSG method,
When growing an O ₄ (M = K, Rb, Cs, X = P, As) single crystal, the raw material is melted into a flux, and the seed crystal is gradually cooled while rotating while being kept in contact with the melt. In this case, the seed crystal may be grown in a supersaturated state. The TSSG method is characterized in that the crystal can be expected to be large and the growth direction of the grown crystal can be controlled by selecting the direction of the seed crystal.

[0005]

However, the above TSS
According to the G method, MTiOXO ₄ (M = K, Rb, Cs, X
= P, As) When growing a single crystal, the following problems occur. That is, the seed crystal is gradually cooled while rotating while being kept in contact with the melt, so that the seed crystal is made of MTiOXO ₄ (M
= K, Rb, Cs, X = P, As) When growing a single crystal, since the rotation speed of the seed crystal is constant, as the grown single crystal grows, the growth point in the single crystal (peripheral portion) ), The convection of the melt changes, and the solid-liquid interface is disturbed. As a result, a phenomenon in which a highly viscous flux is taken into the crystal (flux inclusion) occurs. When such flux inclusion occurs, defects occur in the single crystal, and the SHG characteristics as a nonlinear optical material deteriorate.

[0006] The present invention has been proposed in view of such a conventional situation, and has been proposed in which MTiOXO ₄ (M = K, Rb,
(Cs, X = P, As) A high-quality crystal with good SHG characteristics as a nonlinear optical material for the purpose of suppressing flux inclusion generated when growing a single crystal and reducing defects generated in the crystal. It is an object of the present invention to provide a single crystal growing method capable of efficiently growing a single crystal.

[0007]

According to the present invention, in order to achieve the above object, a seed crystal is brought into contact with a melt containing a flux,
The seed crystal is gradually cooled while rotating, and M
In a single crystal growing method for growing a single crystal of a composite oxide represented by TiOXO ₄ (M = K, Rb, Cs, X = P, As), the rotation speed ω _s of the seed crystal at the start of single crystal growth
Is higher than the rotation speed ω _e of the seed crystal at the end of the growth.

When the rotation speed of the seed crystal at which the maximum yield is obtained when the difference ΔT between the growth start temperature and the growth end temperature of the single crystal is constant is ω _MAX , the rotation speed of the seed crystal at the start of the single crystal growth ω _s satisfies ω _MAX > ω _s ≧ ω _MAX / 2.

That is, in the present invention, MTIOXO ₄ (M = K, R
b, Cs, X = P, As) for growing a single crystal. The TSSG method is a type of the flux method in which a raw material is melted in a flux (flux) to create a supersaturated state and grow crystals only in a seed crystal. The TSSG method is characterized in that the crystal can be expected to be large, and the growth direction of the grown crystal can be controlled by selecting the direction of the seed crystal.

MTiOXO ₄ (M = K, Rb, Cs, X
= P, As) A single crystal may be grown while gradually cooling it in a supersaturated melt in accordance with the usual TSSG method. The raw material is melted into a flux, and the seed crystal is brought into contact with the melt. What is necessary is just to gradually cool while rotating in a state, and to grow a crystal in a seed crystal in a supersaturated state.

At this time, in the present invention, the rotation speed ω _s of the seed crystal at the start of single crystal growth is set to be higher than the rotation speed ω _e at the end of single crystal growth. In other words, as the single crystal grows, the rotation speed of the seed crystal is reduced, the peripheral speed at the single crystal growth point (peripheral portion) is always kept constant, the convection of the melt changes, and the solid-liquid interface is disturbed. Is to suppress the occurrence of flux inclusion and the occurrence of defects in the crystal due to the flux inclusion. Furthermore, the rotation speed ω _e of the seed crystal at the end of the growth of the single crystal is 1/5 ω _s ≦ ω _e ≦ 4.
It is preferred that / 5ω _s. The rotational speed ω _e of the single crystal growth end, 1 / is less than 5ω _s, the difference between the rotational speed ω _s at the start of the single crystal growth is too large, if it is greater than 4 / 5ω _s, single Since the difference from the rotation speed ω _s at the start of crystal growth is too small, it is difficult to keep the peripheral speed at the growth point (outer peripheral portion) of the single crystal constant, and the convection of the melt changes and the solid-liquid interface changes. Can not suppress the occurrence of disturbances, etc.
It is not possible to reduce the flux inclusion and the occurrence of defects in the crystal due to the flux inclusion.

When the rotation speed of the seed crystal at which the maximum yield is obtained when the difference ΔT between the growth start temperature and the growth end temperature of the single crystal is constant is ω _MAX , the rotation speed of the seed crystal at the start of the growth of the single crystal is ω _s is assumed to be a _{ω MAX> ω s ≧ ω MAX} / 2. The rotation speed ω _s of the seed crystal at the start of single crystal growth is ω
_If it is more than _MAX , defects are easily generated in the crystal, and the yield is reduced. When the rotation speed ω _s of the seed crystal at the start of single crystal growth is less than ω _MAX / 2, the yield is small and sub-grains are likely to occur.

As the raw material and the flux, any ordinary ones can be used. For example, the flux may be 3K ₂ W
O ₄ · P ₂ O ₅ , K ₆ P ₄ O ₁₃ , WO ₃ + K ₆ P ₄ O
₁₃ mag is used.

The seed crystal at this time is a square rod-shaped seed crystal of several mm square, for example, 2 mm on a side and 10 to 10 mm in length.
A C-axis crystal having a rectangular rod shape of about 15 mm and having a C axis coincident with the longitudinal direction is used.

[0015]

[Function] MTIOXO used as a nonlinear optical material
₄ (M = K, Rb, Cs, X = P, As) A single crystal is generally cooled slowly while rotating the seed crystal in contact with a melt containing a flux, so as to be in a supersaturated state. The crystal is grown by growing the crystal from the tip.

However, since the rotation speed of the seed crystal is always constant, the peripheral speed at the growth point (outer peripheral portion) in the single crystal increases as the grown single crystal increases, and the convection of the melt changes. Or disturbance of the solid-liquid interface. Therefore, a phenomenon in which a highly viscous flux is taken into the crystal (flux inclusion) occurs, a defect occurs in the single crystal, and the SHG characteristic as a nonlinear optical material deteriorates.

In the present invention, in the method for growing a single crystal as described above, the rotation speed ω _s of the seed crystal at the start of single crystal growth is higher than the rotation speed ω _e of the seed crystal at the end of growth. The peripheral velocity at the growth point (peripheral portion) of the single crystal can always be kept constant, suppressing the change of the convection of the melt and the disorder of the solid-liquid interface, and the flux inclusion and the defects in the crystal due to this. Occurrence can be reduced.

When the rotation speed of the seed crystal at which the maximum yield is obtained when the difference ΔT between the growth start temperature and the growth end temperature of the single crystal is ω _MAX , the rotation speed ω _s of the seed crystal at the start of single crystal growth However, since ω _MAX > ω _s ≧ ω _MAX / 2, a single crystal having no defect in the single crystal can be efficiently grown.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments to which the present invention is applied will be described based on experimental results with reference to the drawings. The schematic configuration of the single crystal growing apparatus used in the present embodiment is as shown in FIG. 1. This apparatus includes a platinum crucible 2 containing a raw material melt 1 containing a flux and a rotation for rotating a seed crystal 3. And a shaft 4. Seed crystal 3 to be used
Has a rectangular cross section (2 mm x 2 mm) and a length of 10 to 15 m
m, and the single crystal growing direction is defined as a length direction (Z direction in the figure). The single crystal 5 is grown in the melt 1 as shown in the figure.

Experimental Example 1 A KTP single crystal was grown under the following conditions using the single crystal growing apparatus described above and a KTP single crystal as the seed crystal 3. First, the flux used was K ₆ P
₄ O ₁₃ , and the composition ratio of the raw materials is as follows. <Raw material composition> KH ₂ PO ₄ 0.500 (molar ratio) K ₂ HPO ₄ 0.242 (molar ratio) TiO ₂ 0.258 (molar ratio) .680:
0.320 (molar ratio), and mixed with platinum crucible 2
The temperature was kept at 1150 ° C. in the furnace to heat and melt.

Next, as a seed crystal 3, a KTP single crystal is
Attached to the tip of the rotating shaft 4 so that the axis is in the direction of growing a single crystal (Z direction in the figure), this is put into a melt 1 (melt temperature 1010 ° C.) obtained by melting the mixture, and a single crystal 5 ( KTP
(Single crystal) was deposited and grown. The growth conditions are shown below. <Growth conditions> Seed crystal rotation speed 200 rpm Seed crystal pulling speed 0 mm / h Seed crystal orientation <001> Slow cooling rate 0.24 ° C / h Grow time 140 h

FIG. 2 shows the grown single crystal. In this single crystal, generation of flux inclusion shown in black was observed in the growth boundary region. FIG. 3 shows the state of the growth of the single crystal as the relationship between the growth time of the single crystal and the size of the crystal at this time. As shown in FIG. 3, the growth of the crystal is slow for about 50 hours after the start of the growth of the single crystal, and then reaches the growth boundary region of the single crystal.
It was found that crystals were growing rapidly. Therefore, in the KTP single crystal grown in this experimental example shown in FIG. 2, the growth boundary region of the single crystal was reached about 50 hours after the start of single crystal growth, and the crystal rapidly grew. It is considered that the peripheral velocity at the point (outer peripheral portion) rapidly increased, the convection of the melt changed, and the solid-liquid interface was disturbed, so that flux inclusion occurred in the growth boundary region.

Experimental Example 2 In this experimental example, a KTP single crystal was grown in the same manner as in Experimental Example 1, except that the number of revolutions of the seed crystal during the growth of the single crystal was changed during the growth. As described in Experimental Example 1, when a KTP single crystal was grown under the growth conditions of Experimental Example 1, the crystal growth was gradual for 50 hours after the start of single crystal growth, and thereafter, the growth boundary region of the single crystal. , And the crystal grows rapidly, so that the peripheral velocity at the growth point (outer periphery) in the single crystal rapidly increases, and flux inclusion occurs in the growth boundary region. Therefore, the present inventors have found that the rotation speed of the seed crystal is gradually reduced before the single crystal grows and reaches the growth boundary region, so that the peripheral speed at the growth point of the single crystal becomes constant, and other growth is performed. The conditions were the same as in Experimental Example 1, and KT
A single crystal of P was grown. That is, the rotation speed of the seed crystal at the start of the KTP single crystal growth was set to 200
rpm, the seed crystal rotation speed was maintained at 200 rpm for 42 hours after the start of single crystal growth before reaching the growth boundary region, and thereafter, the rotation speed was reduced at a rate of 0.714 rpm / h (seed at the end of growth). Crystal rotation speed, 130 rpm
m) KTP single crystal was grown in the same manner as in Experimental Example 1 under other growing conditions. The rotation speed of the seed crystal was controlled using a personal computer.

FIG. 4 shows the grown single crystal. In the single crystal of this experimental example, the generation of flux inclusion indicated by black in the growth boundary region was well suppressed, and a uniform single crystal could be grown.

EXPERIMENTAL EXAMPLE 3 In this experimental example, a KTP single crystal was grown in the same manner as in Experimental Example 1, except that the number of revolutions of the seed crystal during the growth of the single crystal was changed during the growth. However, contrary to the experimental example 2, the rotation speed of the seed crystal was gradually accelerated before the single crystal grew and reached the growth boundary region, and other growth conditions were the same as in the experimental example 1.
A single crystal of P was grown.

That is, the rotation speed of the seed crystal at the start of the growth of the KTP single crystal was set to 200 rpm as in Experimental Example 1, and 42 hours after the start of the growth of the single crystal before reaching the growth boundary region,
The seed crystal rotation speed was maintained at 200 rpm, and
The rotation speed was increased at a rate of 714 rpm / h (the rotation speed of the seed crystal at the end of the growth, 270 rpm), and KTP single crystals were grown in the same manner as in Experimental Example 1 under the other growth conditions. The rotation speed of the seed crystal was controlled using a personal computer.

FIG. 5 shows the grown single crystal. In the single crystal of the present experimental example, the flux inclusions shown in black also occurred in the growth boundary region, and more flux inclusions occurred than in the single crystal of the experimental example 1 shown in FIG.

EXPERIMENTAL EXAMPLE 4 In this experimental example, in order to efficiently grow a single crystal, an investigation was made of an optimum seed crystal rotation speed at the start of growing a single crystal. That is, in the present experimental example, the rotation speed of the seed crystal was changed for each sample (the rotation speed of the seed crystal during the growth was constant), and the other growth conditions were the same as in the first embodiment.
TP single crystal is grown, and KT for each sample at this time
The yield of P single crystal was investigated. FIG. 6 shows a case where a KTP single crystal was grown using a crucible having a diameter of 70 mm and a diameter of 40 m.
The relationship between the seed crystal rotation speed and the yield of the KTP single crystal when a KTP single crystal is grown using a m crucible is shown.
In FIG. 6, the case where a crucible having a diameter of 70 mm is used is shown by a solid line, and the case where a crucible having a diameter of 40 mm is used is shown by a dotted line. In both cases, the seed crystal rotation speed ω _MAX (the diameter of 70 mm
The case where the crucible of No. was used is shown as ω _{MAX 70} , and the case where the crucible having a diameter of 40 mm was used is shown as ω _{MAX 40} . ), The yield of KTP single crystal was reduced, and flux inclusion was observed in the KTP single crystal grown at this time. In both cases, the seed crystal rotation speed ω
However, when the seed crystal rotation speed was less than ω _MAX / 2, the yield of the KTP single crystal was reduced, and generation of subgrains was observed in the KTP single crystal grown at this time.

Therefore, when the rotation speed of the seed crystal at which the maximum yield is obtained when the difference ΔT between the single crystal growth start temperature and the growth yield temperature is constant is ω _MAX , the optimal seed crystal rotation at the start of the single crystal growth It was confirmed that the speed was defined in a range from ω _MAX / 2 to less than ω _MAX .

Although specific embodiments to which the present invention has been applied have been described based on experimental results, the present invention is not limited to these embodiments, but includes raw material compositions, types of fluxes, and growing conditions. Needless to say, these can be appropriately changed without departing from the gist of the present invention.

[0031]

As is clear from the above description, in the present invention, the seed crystal is brought into contact with the melt containing the flux, and the seed crystal is gradually cooled while being rotated.
In a single crystal growing method for growing a single crystal of a composite oxide represented by iOXO ₄ (M = K, Rb, Cs, X = P, As), the rotation speed ω _s of the seed crystal at the start of the single crystal growth is determined. It is larger than the rotation speed ω _e of the seed crystal at the end of the growth, and the difference ΔT between the single crystal growth start temperature and the growth end temperature.
When the rotational speed of the seed crystal at which the maximum yield is obtained when the constant is constant is ω _MAX , the rotational speed ω _s of the seed crystal at the start of single crystal growth is defined as ω _MAX > ω _s ≧ ω _MAX / 2. As a result, it is possible to prevent a sharp change in the peripheral velocity at the growth point (outer peripheral portion) in the single crystal, suppress a change in the convection of the melt and disturbance of the solid-liquid interface, and reduce the occurrence of flux inclusion. A large single crystal free from defects can be obtained efficiently.

Therefore, according to the present invention, it is possible to provide a high-quality nonlinear optical material, and the effect is very large.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one configuration example of a single crystal growing apparatus used when carrying out the present invention.

FIG. 2 is a plan view showing a KTP single crystal grown in Experimental Example 1.

FIG. 3 is a correlation diagram showing a relationship between a growth time and a crystal size when growing a KTP single crystal.

FIG. 4 is a plan view showing a KTP single crystal grown in Experimental Example 2.

FIG. 5 is a plan view showing a KTP single crystal grown in Experimental Example 3.

FIG. 6 is a correlation diagram showing a relationship between a seed crystal rotation speed and a KTP single crystal yield.

[Explanation of symbols]

 1 ··· Melt 2 ··· Platinum crucible 3 ··· Seed crystal 4 ··· Rotating shaft 5 ··· Single crystal

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tomichi Watanabe 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (56) References JP-A-4-69735 (JP, A) (58) ) Surveyed field (Int. Cl. ⁷ , DB name) C30B 1/00-35/00

Claims (2)

(57) [Claims] 1. A seed crystal is brought into contact with a melt containing a flux,
The seed crystal is gradually cooled while being rotated, and MTIOXO ₄ (M = K, Rb, Cs, X = P, As) is applied from the tip of the seed crystal.
In the method for growing a single crystal of a composite oxide represented by the formula, the rotation speed ω _s of the seed crystal at the start of single crystal growth is higher than the rotation speed ω _e of the seed crystal at the end of growth. A method for growing a single crystal, characterized in that: 2. The rotation speed of a seed crystal at the start of single crystal growth, where the rotation speed of the seed crystal at which the maximum yield is obtained when the difference ΔT between the single crystal growth start temperature and the growth end temperature is constant is ω _MAX. omega _{s is, ω MAX> ω s ≧ ω} MAX / 2 single crystal growth method according to claim 1, wherein the a.