JPH03218997A - Production of thin film of lithium niobate single crystal - Google Patents

Abstract

PURPOSE:To obtain the thin film of a lithium niobate single crystal having the film thickness adequate for a thin-film waveguide type SHG element, etc., by bringing a lithium tantalate substrate into contact with a melt of a specific compsn. and epitaxially growing the lithium niobate. CONSTITUTION:The lithium tantalate substrate is brought into contact with the melt which consists mainly of Li2O, V2O5, Nb2O5, Na2O, and MgO, has the compsn. range of the Li2O, V2O5 and Nb2O5 within the region enclosed by the 4 compsn. points of A (88.90, 2.22, 8.88), B(55.0, 43.0, 2.00), C(46.5, 51.5, 2.00), D(37.50, 5.00, 57.50) in a triangular diagram and contains the Na2O at Na2O/LiO2=2.0/98.0 to 93.5/6.5 by molar ratio and the MgO at MgO/lithium niobate=0.1/99.9 to 25.0/75.0 by molar ratio. The thin film of the lithium niobate single crystal is then epitaxially grown on the (0001) face of the lithium tantalate by matching the lattice constants of the a-axis at 600 to 1,250 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing lithium niobate having a film thickness suitable for various optical materials including thin film waveguide type SHG elements.

(Prior Art) With the recent progress in optical application technology, there is a demand for shorter wavelength laser light sources.

This is because recording density and photosensitivity can be improved by shortening the wavelength, and application to the field of optical equipment such as optical disks and laser printers can be considered.

For this reason, research has been conducted on second harmonic generation (SHG) elements that can convert the wavelength of incident laser light to 1/2.

As such a second harmonic generation (SHG) element, a bulk single crystal of a nonlinear optical crystal has conventionally been used using a high-output gas laser as a light source. However, there is a strong demand for miniaturization of devices such as optical disk devices and laser printers, and while gas lasers require an external modulator for optical modulation, semiconductor lasers do not require a modulator. Also, semiconductor lasers have come to be mainly used instead of gas lasers due to their low cost.

Therefore, since it is necessary to obtain high conversion efficiency with a low light source output of several mW to several tens of mW, a thin film waveguide type SHG element has become necessary.

Conventional nonlinear optical materials for such thin-film waveguide type SHG devices include waveguides made of a layer in which the refractive index is changed by diffusing Ti or the like into a lithium niobate bulk single crystal, and tantalum acid. Waveguides using a lithium niobate thin film formed by high-frequency sputtering on a lithium substrate are known, but in both cases it is difficult to obtain a lithium niobate thin film with excellent crystallinity, resulting in high conversion efficiency. I couldn't get it.

Incidentally, a liquid phase epitaxial method is considered to be suitable as a method for producing a single crystal thin film with excellent crystallinity.

Examples of the liquid phase epitaxial method for obtaining a lithium niobate thin film include: 1) Applied Physics Let. ter
s, Vol. 26, No. l, January 1
975 uses lithium tantalate as a substrate, L1,
0, V20. An example is described in which a lithium niobate thin film for an optical waveguide is formed by a liquid phase epitaxial growth method using as a flux to guide light.

2) Japanese Patent Publication No. 51-9720 discloses that lithium tantalate is used as a substrate, and Li2O, ■, 0. A method of forming a lithium niobate thin film for an optical waveguide by a liquid phase epitaxial growth method using as a flux is described.

Furthermore, 3) Japanese Patent Publication No. 56-47160 states that Li2
O, V30. As a flux, lithium niobate containing Mg was grown on the substrate by epitaxial growth.
A method for forming lithium tantalate solid solution thin film single crystals is described.

In addition, 4) Japanese Patent Publication No. 11650/1983 states that Li2
O, ■, 0. A method is described in which a thin film single crystal of a lithium niobate/lithium tantalate solid solution is formed on a substrate by an epitaxial growth method using as a flux.

However, in the conventionally known liquid phase epitaxial method, not only is it not possible to obtain a lithium niobate single crystal with excellent crystallinity on a lithium tantalate substrate, but also
It is difficult to obtain a lithium niobate single crystal with a film thickness necessary for manufacturing a G element, and there are no known examples of a thin film waveguide type SHG element being put into practical use.

The film thickness required to manufacture the thin film waveguide type SHG element is, in other words, in order to phase match the incident laser light and the second harmonic, the fundamental wavelength light of wavelength λ and the wavelength λ/
This refers to the film thickness that can match the effective refractive index with the second harmonic of When creating a lithium niobate thin film, in order to match the effective refractive index, a lithium niobate thin film with a thickness of 5 μm or more is required, considering the amount removed by polishing.

(Problems to be Solved by the Invention) As described above, until now it has not been possible to practically produce a lithium niobate single crystal thin film having the thickness necessary to create an SHG element optical device on a lithium tantalate substrate. There was no way.

As a result of various studies, the inventors of the present invention have found that this problem occurs because the lattice constant of the lithium niobate single crystal thin film is smaller than the lattice constant of the lithium tantalate substrate.
We believe that this is because distortion occurs in the crystal lattice of the obtained lithium niobate single crystal thin film as a result of liquid phase epitaxial growth.To solve this problem, we investigated the lattice constant of the lithium tantalate substrate and the lithium niobate single crystal thin film. It was concluded that it would be better to make the lattice constants of

The present inventors have discovered that by incorporating sodium and magnesium into a lithium niobate single crystal, the lithium niobate single crystal can be prevented from being photodamaged (the refractive index of the crystal changes when irradiated with strong light), and In addition, the lattice constant of the lithium niobate substrate is adjusted to match (lattice match) the lattice constant of the lithium tantalate substrate, and the lithium niobate monolayer is made with a film thickness necessary to create an optical device such as an S}IG element. The inventors have made a completely new discovery that crystals can be practically produced, and have completed the present invention.

However, Journal of Crystal Gro
wth 54 (1981) 572-576, a sodium-containing lithium niobate thin film single crystal with a film thickness of 2 μm was formed on a Y-cut lithium niobate substrate by liquid phase epitaxial growth by adding sodium to lithium niobate. Examples are given.

Also, Journal of Crystal Gro
Wth 84 (1987) 402-412 describes an example of adding sodium to lithium niobate and forming a sodium-containing lithium niobate thin film single crystal on a Y-cut lithium tantalate substrate by liquid phase epitaxial growth. There is.

However, although these documents describe that the lattice constant of lithium niobate single crystal changes due to sodium content, SAW (Surface Acoust
ic Wave) device, and there is no mention of optical properties or the fact that a film with excellent optical properties can be obtained by lattice matching with a lithium tantalate substrate. Furthermore, the lithium niobate single crystal thin films shown in these documents are for SAiil devices; the thin films described in the former document use lithium niobate as a substrate, and the thin films described in the latter document use tantalum. Although the thin film is formed on a lithium oxide substrate, there is no lattice matching between the thin film and the substrate, so none of them can be used as the optical material aimed at in the present application.

Furthermore, US Pat. No. 4,093,781 discloses a method in which when forming a lithium ferrite film on a substrate by liquid phase epitaxial growth, lithium is replaced with sodium to bring the lattice constant closer to that of the substrate, thereby forming a strain-free lithium ferrite film. Are listed.

However, this is a technology related to lithium ferrite, and cannot be used for optical materials, which is the object of the present application.

(Means for Solving the Problems) The present invention is a method of bringing a lithium tantalate substrate into contact with a melt and growing a lithium niobate single crystal thin film by epitaxial growth.
,TeLi,0,■,0. , Nb,0, , Na,0, Mg
The above Li,0 consisting of O and excluding Na,0 and MgO,
v20,, Nb,0, (7) composition range is Li2O-V
2O, -Nb2O. (7) 3? In the trigonometric diagram of the fractional system,
A (88.90, 2.22, 8.88), B (55
．． 00, 43.00; 2.00), C (46,50
, 51.50, 2.00), D(37.50, 5
．． 00, 57.50), the a-axis lattice constant of the lithium niobate single crystal thin film and the a-axis lattice constant of the lithium tantalate substrate were matched. A method for producing a lithium niobate single crystal thin film characterized by:

(Function) According to the present invention, when depositing a lithium niobate single crystal thin film on a lithium tantalate substrate, the melts used in the epitaxial growth method are mainly Cite, L110, and V2.
O■Nb. O,, Na2O, MgO, Na2
The above Li, Q, V, O,, Nb2 excluding O and MgO
O. The composition range of Li, O-V, O, -Nb
, O, in the triangular diagram of the three-component system, ite, A (88.90
, '2.22, 8.88), B (55.00, 4
3.00, 2.00), C(46.50, 5].50
, 2.00), D(37.50, 5,00,57.
Matching the a-axis lattice constant of the lithium niobate single crystal thin film and the a-axis lattice constant of the lithium tantalate substrate by using a composition having the composition ratio shown in the region surrounded by the four composition points in 50). is necessary.

The reason why lithium tantalate is used as a substrate in the present invention is that the crystal system of the lithium tantalate substrate is similar to a lithium niobate single crystal and easy to grow epitaxially, and furthermore, the lithium tantalate substrate is commercially available. This is because products of good quality can be stably obtained.

Further, as the lithium tantalate substrate, one containing various elements or one whose surface has been chemically etched can be used.

As the melt, Li2O, v30. ,Nb2O,,
The reason why Na, O, and MgO are necessary will be explained below.

The Li2O and V2O act as a flux to realize liquid phase epitaxial growth of a lithium niobate single crystal.

Furthermore, by using the aforementioned Na, 0, and MgO as melt components, sodium and magnesium can be contained in the lithium niobate single crystal thin film.

By incorporating sodium and magnesium into the lithium niobate single crystal thin film, the a-axis lattice constant of the lithium niobate single crystal thin film can be increased. The a-axis lattice constant of the lithium single crystal thin film is
It is possible to obtain a lithium niobate single crystal thin film that can be matched to the a-axis lattice constant of the lithium tantalate substrate, has a large film thickness, and has excellent optical properties.

Generally, the a-axis lattice constant of lithium niobate is smaller than that of lithium tantalate, so in order to match the a-axis lattice constants of the lithium tantalate substrate and the lithium niobate single crystal thin film, it is necessary to lithium oxide a
It is desirable to increase the lattice constant of the axis.

The reason for containing sodium and magnesium at the same time is
Magnesium alone cannot lattice match the lithium tantalate substrate and the lithium niobate single crystal thin film.
Moreover, although lattice matching is possible with sodium alone, optical damage cannot be prevented.

Since magnesium has the effect of preventing optical damage, it is suitable for optical materials.

When the sodium and magnesium are contained in the lithium niobate single crystal thin film, the a-axis lattice constant increases, but this is because sodium and magnesium ions or atoms are doped into the lithium niobate crystal lattice. Or, it is caused by substitution with ions or atoms constituting the lithium niobate crystal lattice.

Moreover, Li2O excluding Na2O and MgO in the present invention
, ■． 0. , Nb2O, (7) Composition range
O-V2O. -Nb2O, (7) In the triangular diagram of the three-component system, A(88.90, 2.22, 8.88),
B (55.00, 43.00, 2.00), C (4
6.50, 51.50, 2.00), D(37,5
The reason why the composition ratio shown in the region surrounded by the four composition points (0, 5.00, 57.50) is required is that the optical properties of the lithium niobate thin film obtained in this range are excellent, and However, the optical propagation loss is low and it is possible to obtain a high quality lithium niobate single crystal thin film.

Said, L120, V10. , the composition range of Nb,0, is
Furthermore, Li,0-V,0,-Nb,0, (7) Triangular diagram of the three-component system, E(69.85, 21.33,
8.82), F (49.95, 45.02, 5.
03), G (44.13, 16.76, 39.11
), H (54.72, 11, 12, 34.16), and the composition ratio is preferably expressed by a region surrounded by four composition points: LiO, O-Vo, -Nb, 0, In the triangular diagram of the component system, I(57.43, 35,05,
7.52), J (49.95, 42.53, 7.
52), K (47.36, 26.32, 26.32
), L(56.38, 17.91, 25.71).

As the composition ratio of Na2O in the present invention, the molar ratio is N
a2O/Li2O is 2.0798. 0 to 93.
The reason why it is necessary that the range satisfies 576.5 is that if the proportion of Na2O deviates from the above molar ratio range,
Lithium niobate single crystal thin. This is because the film and the lithium tantalate substrate cannot be lattice matched.

As mentioned above, as the composition ratio of Na2O, the molar ratio is Na2O/
It is preferable that Li2O is in a range satisfying 7.4792.6 to 80.0/20.0, and 16.7783.3
It is preferable that the range satisfies 48.4751.6 to 48.4751.6.

Further, as the composition ratio of MgO, the molar ratio of MgO/lithium niobate is 0. 1/99,9 ~25,0/75
, O is desirable. The above-mentioned lithium niobate means the theoretical amount of lithium niobate that can be precipitated from the composition of the melt.

The reason for this is that when the proportion of MgO is lower than the above range,
The effect of preventing Mg from optical damage is insufficient, and MgO
This is because if the ratio is high, crystals of magnesium niobate will precipitate and a lithium niobate single crystal thin film cannot be obtained.

Further, as for the composition ratio of MgO, it is preferable that the molar ratio of MgO/lithium niobate is in a range of 0.77100 to 9.07100, and 3.57100 to 9.07100.
It is preferable that the range satisfies 6.07100.

The raw material composition in the present invention is selected so that the composition ratio of its oxide is within the above composition range, but the raw material component is preferably an oxide or a compound that changes into an oxide upon heating, such as Na , CO,, Nbl
lO,, Li, Co,, ■. 0. , MgO%NaVO,
, NaNbO, , LiVO. , LiNbO, and the like.

It is desirable that the raw material components are heated and melted at 600 to 1300°C. Further, it is preferable that the heating and melting is performed in an air atmosphere or an oxidizing atmosphere.

According to the present invention, it is desirable that after the melt is brought into a supercooled state, a lithium tantalate substrate is contacted and grown.

The cooling rate for bringing the melt into a supercooled state is 0.
It is desirable that the temperature is 5 to 300°C.

The temperature for the growth is preferably 600 to 1250°C. The reason for this is that the melting point of lithium niobate is 1
The temperature is 250°C, and at temperatures higher than this, crystals will not precipitate, and since 600°C is the melting point of the melting agent (Li2O-V2O.), at temperatures lower than this, the raw material cannot be made into a melt. This is because it is not possible.

In the present invention, it is desirable to use the (0001) plane of the lithium tantalate substrate as the growth plane of the lithium niobate single crystal thin film.

The (0001) plane of the lithium tantalate substrate refers to a plane perpendicular to the C axis of lithium tantalate. The reason why it is desirable to use the (0001) plane of the lithium tantalate substrate as the growth plane of the lithium niobate single crystal thin film is that the crystal structure of the lithium tantalate is hexagonal (first
(see figure), and since the (0001) plane consists of only the a-axis, by using the (0001) plane as the growth plane, it is possible to simply change the lattice constant of the a-axis of the lithium niobate single crystal thin film. This is because lattice matching can be achieved.

Further, in the present invention, the lattice constant (a-axis) of the lithium niobate single crystal thin film is 99.81 to 100. It is desirable to set it to 0.7%.

When the lattice constant is outside the above range, the difference in the a-axis lattice between the lithium tantalate substrate and the lithium niobate single crystal thin film becomes large, making it difficult to produce a lithium niobate single crystal thin film with excellent optical properties that can be used as an optical material. This is because it cannot be formed sufficiently thick.

Furthermore, the lattice constant (a
axis) is 99.92 to 1 of the lithium tantalate substrate.
It is preferable to set it to 00.03%.

The a-axis lattice constant of the lithium tantalate substrate is 5.
In the case of 1538 people, the a-axis lattice constant of the lithium niobate single crystal is preferably in the range of 5.150 to 5,155A.

During the growth, it is desirable to rotate the lithium tantalate substrate. This is because by rotating the lithium tantalate substrate, crystals with uniform properties and film thickness can be formed.

Further, it is desirable that at least one side of the lithium tantalate substrate is optically polished.

In the present invention, by appropriately selecting the contact time between the lithium tantalate substrate and the melt and the temperature of the melt,
The thickness of the lithium niobate single crystal thin film deposited on the lithium niobate substrate that is deposited on the lithium tantalate substrate can be controlled.

In the present invention, the melt composition includes Li2O, .
0. ,Nb2O,,Na,O and MgO, as well as Nd%
Rh, Zn%Ni, Co. Oxides of elements selected from Ti, Cr, etc. can be used.

Said Nd, Rh, Zn, Ni, Co, Ti,
By adding elements such as Cr, the refractive index and lattice constant of the lithium niobate single crystal thin film can be changed.

In particular, the Ti can reduce the lattice constant of the lithium niobate single crystal.

As described above, the lithium niobate single crystal thin film obtained by the production method of the present invention is integrated with the lithium tantalate substrate, has extremely few lattice distortions and crystal defects, and is of high quality without cracks. It is a thin film waveguide type S because it has properties suitable for an optical waveguide, especially low optical propagation loss, and can obtain a thicker film than conventional ones.
}Not only is it optimal as a constituent material for IG elements, but it can also be used for optical deflectors, optical modulators, and multimode optical devices.

Next, examples of the present invention will be described.

Example 1 (1) Na, C 44.4 mol%, Li, CO 344.
4 mol%, V, O, 5.6 mol%, Nb, 0.5.6
Mol%, LiN that can precipitate MgO from the raw material composition
5 mol 2 added to the theoretical amount of bO (MgO/LiN
bO,・5/95) L, the mixture was placed in a platinum lupus and heated in an epitaxial growth apparatus under an air atmosphere for 11 minutes.
The contents of the Luppo were dissolved by heating to 00°C.

(2) Cool the melt at a cooling rate of 60°C per hour to 840°C.
After slowly cooling to ℃, lithium tantalate single crystal (00
01) After optically polishing the surface, the chemically etched material was used as a substrate material and immersed in the melt for 15 minutes while rotating at loOrpm.

(3) Pull up the substrate material from the solution and rotate at 100 O.
After shaking the melt over the melt at rpm for 30 seconds, the melt was slowly cooled to room temperature to obtain a lithium niobate single crystal thin film containing sodium and magnesium with a thickness of about 19 μm on the substrate material.

(4) The amounts of sodium and magnesium contained in the obtained single crystal thin film of lithium niobate were 1 mol% and 6 mol%, respectively. In addition, the lattice constant (a
axis) is 5. ] 53A, the refractive index measured at an incident light wavelength of 1.15 μm was 2.230±0.001.

Example 2 (1) Li, Co, 69%, V, 0.16MoJL,%
%Nb, 0.15 mol%, Na, Co. is 6 for the theoretical amount of LiNbOs that can be precipitated from the raw material composition.
0 mol% addition (Na2O/Li2O=45/69), M
LiNbO.gO can be precipitated from the raw material composition. 6 moAt% addition (MgO/LiNbO,
・6/94) A mixture in which 2 mol% of Cr2O was added to the theoretical amount of LiNbO that can be precipitated from the raw material composition was placed in a platinum crucible, and the mixture was heated to 1100°C in an air atmosphere in an epitaxial growth growth apparatus. Heat was applied to dissolve the contents of the Luppo.

(2) Cool the melt to 954°C at a cooling rate of 60°C per hour.
After slowly cooling the lithium tantalate single crystal to (000
1) After the surface was optically polished, the chemically etched material was immersed as a substrate material in a melt for IO minutes while rotating at IOO rpm.

(3) Pull up the substrate material from the melt and rotate at 100O.
After shaking the melt over the melt at rpm for 30 seconds, it was slowly cooled to room temperature, and the substrate material was coated with chromium with a thickness of about 11 μm.
A lithium niobate single crystal thin film containing sodium and magnesium was obtained.

(4) The amounts of chromium, sodium, and magnesium contained in the single crystal thin film of lithium niobate obtained were:
They were 2 mol%, 2 mol%, and 7 mol%, respectively. The lattice constant (a-axis) of the thin film is 5,155, and the refractive index measured at an incident light wavelength of 1.15 μm is 2.236±0.
It was 001.

Example 3 (1) Na, Cos 44.4 mol%, Li, Co,
37.8 mol%, ■10.15 mol%, Nb,0,
2.8 mol%, Li that can precipitate MgO from the raw material composition
NbO. Addition of 3 mol% (MgO/
LiNbO, 3/97), Tie, is 1 for the theoretical amount of LiNbO that can be precipitated from the raw material composition.
The mixture to which 5 mol% was added was placed in a platinum crucible and heated to 1100° C. in an air atmosphere in an epitaxial growth and growth apparatus to melt the contents of the crucible.

(2) Cool the melt to 780°C at a cooling rate of 60°C per hour.
After slowly cooling the lithium tantalate single crystal to (000
l) After optically polishing the surface, the chemically etched material was used as a substrate material and immersed in the melt for 8 minutes while rotating at 100 rpm.

(3) Pull up the substrate material from the melt and rotate at 1000 rotations.
The melt was shaken off on the melt for 30 seconds while rotating at rpm, and then slowly cooled to room temperature to obtain a single crystal thin film of lithium niobate containing sodium, magnesium, and titanium with a thickness of about 7 μm on the substrate.

(4) The amounts of sodium, magnesium, and titanium in the obtained single crystal thin film of lithium niobate were 1.2 mol%, 4 mol%, and 8 mol%, respectively. The lattice constant (a-axis) was 5.154, and the refractive index measured at an incident light wavelength of 1.15 μm was 2.239±0.001.

Example 4 (1) Li, C0, 52 mol%, V, 0. 44 mol%, Nb, 0. 4 mol%, Na, CO, with respect to the theoretical amount of LiNbO, which can be precipitated from the raw material composition,
Addition of 48 mol% (Na, 0/Li, 0=7, 4/52)
, ljNbo, which can precipitate MgO from the raw material composition,
Addition of 5 mol% (MgO/LiNbO
, =5/95) Put the mixed mixture into a platinum crucible and boil it. 1100°C under air atmosphere in a growth system
to dissolve the contents of the crucible.

(2) Cool the melt to 835°C at a cooling rate of 60°C per hour.
After slowly cooling the lithium tantalate single crystal to (000
l) A material whose surface had been optically polished was used as a substrate material and immersed in the melt for 12 minutes while rotating at IOO rpm.

(3) Pull up the substrate material from the melt and rotate at 100o.
After shaking off the melt on the melt for 30 seconds at rpm,
The mixture was slowly cooled to room temperature, and a lithium niobate single crystal thin film containing sodium and magnesium with a thickness of about 8 μm was obtained on the substrate material.

(4) The amounts of sodium and magnesium contained in the obtained single crystal thin film of lithium niobate were 1 mol% and 6 mol%, respectively. The lattice constant (a-axis) of the thin film was 5,153, and the refractive index measured at an incident light wavelength of 1.15 μm was 2.232±0.001.

Example 5 (1) Li, C0, 50 mol%, V, 0. LiNbO.30 mol%, Nb, 0.20 mol%, Na, Co, can be precipitated from the raw material composition. 5 for the theoretical quantity of
0 mol% addition (Na, 0/Li, 0 40/50), M
LiNbO.go can be precipitated from the raw material composition. Addition of 4 mol% to the theoretical amount of (MgO/LiNbO, =
4/96) The mixture was placed in a platinum crucible and heated to 1150°C in an air atmosphere in an epitaxial growth and growth apparatus to melt the contents of the crucible.

(2) Cool the melt to 995°C at a cooling rate of 60°C per hour.
After slowly cooling the lithium tantalate single crystal to (000
l) After optically polishing the surface, the chemically etched material was used as a substrate material and immersed in the melt for 12 minutes while rotating at loorpm.

(3) Pull up the substrate material from the melt and rotate at 100O.
After shaking off the melt on the melt for 30 seconds at rpm,
The mixture was slowly cooled to room temperature, and a lithium niobate single crystal thin film containing sodium and magnesium with a thickness of about 9 μm was obtained on the substrate material.

(4) The amounts of sodium and magnesium contained in the obtained single crystal thin film of lithium niobate were 2 mol% and 5 mol%, respectively. The lattice constant (a-axis) of the thin film was 5.155, and the refractive index measured at an incident light wavelength of 1.15 μm was 2,233±0.001.

Example 6 (1) Na, Co, 47.4 mol%, Li, CO,
23.7 mol%, V, O. 4.2 mol%, Nb,0,
24.7 mol%, MgO added to the theoretical amount of LiNbO that can be precipitated from the raw material composition (MgO
gO/LiNbO.・2/90) The mixture was placed in a platinum crucible and heated to 1150° C. in an air atmosphere in an epitaxial growth growth apparatus to melt the contents of the crucible.

(2) The melt was cooled at a cooling rate of 60°C per hour to 1023°C.
After slowly cooling to ℃, lithium tantalate single crystal (00
After optically polishing the surface, the chemically etched material was immersed in the melt for 13 minutes as a substrate material while rotating at 10 rpm.

(3) Pull up the substrate material from the melt and rotate at 100O.
After shaking off the melt on the melt for 30 seconds at rpm,
The mixture was slowly cooled to room temperature, and a lithium niobate single crystal thin film containing sodium and magnesium with a thickness of about It μm was obtained on the substrate material.

(4) The amounts of sodium and magnesium contained in the obtained single crystal thin film of lithium niobate were 2.5 mol2 and 3 mol2, respectively. The lattice constant (a-axis) of the thin film is 5,156A, and the wavelength of the incident light is 1. 15μ
The refractive index measured in m was 2,235±0.001.

Example 7 (1) Na, Co, 45.9 mol%, Li, CO,
36.8 mol%, V, O, 2.7 mol%, Nb, 0,
14.6 mol%, 4 mol% added (MgO) to the theoretical amount of LiNbO that can be precipitated from the raw material composition
gO/LiNbO, = 4/96), Nd2O, was added in an amount of 1 mol % based on the theoretical amount of LiNbO that can be precipitated from the raw material composition, and the mixture was placed in a platinum lupo and grown in an epitaxial growth apparatus under an air atmosphere. The contents of Luppo were dissolved by heating to 1150°C.

(2) Cool the melt to 970°C at a cooling rate of 60°C per hour.
After slowly cooling the lithium tantalate single crystal to (000
l) After optically polishing the surface, the chemically etched material was used as a substrate material and immersed in the melt for 18 minutes while rotating at loorpm.

(3) Pull up the substrate material from the melt and rotate at 100O.
After shaking off the melt on the melt for 30 seconds at rpm,
The mixture was slowly cooled to room temperature, and a lithium niobate single crystal thin film containing sodium, magnesium, and neodymium with a thickness of about 9 μm was obtained on the substrate material.

(4) The amounts of sodium, magnesium, and neodymium contained in the obtained single crystal thin film of lithium niobate were 1.2 mol%, 5 mol%, and 0.3 mol%, respectively. The lattice constant (a-axis) of the thin film is 5,154.
The refractive index measured at an incident light wavelength of 1.15 μm is 2.233
It was ±0.001.

Example 8 (1) Li, Co, 60 mol%, v20.20 mol%
, Nb,0. 20-El%, Na, Co, were added at 50 mol% (Na2O/Li, 0.40/
60), MgO can be precipitated from the raw material composition and iN
4 mol% addition (MgO/Li
NbO, 4/96) The mixture was placed in a platinum crucible and heated for 11 hours in an air atmosphere in an epitaxial growth apparatus.
It was heated to 50° C. to dissolve the contents of the Lutuho.

(2) Cool the melt to 995°C at a cooling rate of 60°C per hour.
After slowly cooling the lithium tantalate single crystal to (000
l) After optically polishing the surface, the chemically etched material was immersed in a melt for 12 minutes as a substrate material while rotating at IOO rpm.

(3) Pull up the substrate material from the melt and rotate at 100O.
After shaking off the melt on the melt for 30 seconds at rpm,
The mixture was slowly cooled to room temperature, and a thin lithium niobate single crystal containing sodium and magnesium having a thickness of about 8 μm was obtained on the substrate material.

(4) The amounts of sodium and magnesium contained in the obtained single crystal thin film of lithium niobate were 1.8 mol% and 5 mol%, respectively. Also, the lattice constant of the thin film (
a-axis) is 5.155 people, and the refractive index measured at an incident light wavelength of 1.15 μm is 2. It was 233±0.001.

Example 9 (1) Li, Co, 52 mol%, V, 0, 44 mol%)
Ii%, Nb, 0.4 mol%, Na, Co, LiN
93 mol% addition to bO, MgO to LiNbO
, 0. The mixture to which mol % of Ol was added was placed in a platinum crucible and heated to 1150° C. in an air atmosphere in an epitaxial growth and growth apparatus to melt the contents of the crucible.

(2) Cool the melt at a cooling rate of 60°C per hour to 835°C.
After slowly cooling to ℃, lithium tantalate single crystal (00
01) After optically polishing the surface, the chemically etched material was used as a substrate material and immersed in the melt for 12 minutes while rotating at 10 rpm.

(3) Pull up the substrate material from the melt and rotate at 100o.
After shaking off the melt on the melt for 30 seconds at rpm,
The mixture was slowly cooled to room temperature, and a lithium niobate single crystal thin film containing sodium and magnesium with a thickness of about 8 μm was obtained on the substrate material.

(4) The amounts of sodium and magnesium in the obtained single crystal thin film of lithium niobate were 2 mol% and 0.0 mol%, respectively.
It was 2 mol%. Also, the lattice constant (a-axis) of the thin film is s,
153 A, the refractive index measured at an incident light wavelength of 1.15 μm is 2. It was 232±0.001.

Example 10 (1) Li, C0, 50 mol χ, V2OS 30 mol%
, Nb,0. 20 mol% Na, Co, liNbo
, 86 mol% of MgO was added to LiNbO. 0.2 mol% of the mixture was put into a platinum crucible,
115 in an air atmosphere in an epitaxial growth growth apparatus.
The contents of the crucible were dissolved by heating to 0°C.

(2) Cool the melt at a cooling rate of 60°C per hour to 995°C.
After slowly cooling to ℃, lithium tantalate single crystal (00
01) After optically polishing the surface, the chemically etched material was used as a substrate material and immersed in the melt for 12 minutes while rotating at 10 rpm.

(3) Pull up the substrate material from the melt and rotate at 100o.
After shaking off the melt on the melt for 30 seconds at rpm,
The mixture was slowly cooled to room temperature, and a lithium niobate single crystal thin film containing sodium and magnesium with a thickness of about 9 μm was obtained on the substrate material.

(4) The amounts of sodium and magnesium in the obtained single crystal thin film of lithium niobate were 0.3 mol% and 5 mol%, respectively.
It was mol%. Also, the lattice constant (a-axis) of the thin film is 5.1
The refractive index measured by 55 people at an incident light wavelength of 1.15 μm is
It was 2.233±0.001.

Regarding the lithium niobate single crystal thin film of the present invention obtained in Example 1-10, the wavelength was 0.83 μm by prism bonding.
The optical propagation loss for the semiconductor laser beam was measured, and the results are shown in Table 1.

Table 1 Example Optical propagation loss (dB/am) l1.3 2l. 0 31.0 41. l 5l. 3 6l. 0 71.2 8 1.0 91.0 10 1.3 (Effects of the invention) According to the present invention, lithium niobate having excellent optical properties and having a film thickness thicker than conventionally obtained is deposited on a lithium tantalate substrate. It can form a single crystal thin film, has chemical properties, and is thicker than conventionally obtained lithium niobate single crystal thin films, making it useful as a constituent material for optical devices such as SHG elements.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the (0001) plane of a lithium tantalate substrate, which is the growth plane of a lithium niobate single crystal. FIG. 2 shows Li, O-V, O, -Nb, O. It is a triangular diagram of a three-component system. Each composition point is expressed as (mol % of Li2O, mol % of V2O, mol % of Nb2OS). A(88.90 B(55.00 C(46.50 D(37.50 E(69.85 FC49.95 G(44.13 8(54,72 1(57.43 J(49.95 K() 47.36 L (56.38 2.22, 8.88) 43.00, 2.00) 5l.50, 2.00) 5.00, 57.'50) 21.33 8.82) 45. 02 5.03) 16 76 39.11) 11 12 34.16) 35 05 7.52) 42,53 7.52) 26 32 26.32) 17 91 25.71)

Claims (1)

[Claims] 1. A method for growing a lithium niobate single crystal thin film by epitaxial growth by bringing a lithium tantalate substrate into contact with a melt, the method comprising mainly Li
_2O, V_2O_5, Nb_2O_5, Na_2O,
It consists of MgO, the Li_2O, V_2O_5, Nb
The composition range of _2O_5 is Li_2O-V_2O_5-
In the triangular diagram of the three-component system of Nb_2O_5, A(88
．． 90, 2.22, 8.88), B (55.00, 43
．． 00,2.00), C(46.50,51.50,2
．． 00), D(37.50, 5.00, 57.50), and the a-axis lattice constant of the lithium niobate single crystal thin film and tantalum. A method for producing a lithium niobate single crystal thin film, the method comprising matching the a-axis lattice constant of a lithium oxide substrate. 2. The composition range of Na_2O is Na_2O in molar ratio.
/Li_2O is 2.0/98.0 to 93.5/6.5
The method for producing a lithium niobate single crystal thin film according to claim 1, which satisfies the following. 3. The composition range of the MgO is MgO/lithium niobate in a molar ratio of 0.1/99.9 to 25.0/75.0.
The method for producing a lithium niobate single crystal thin film according to claim 1, which satisfies the following. 4. The temperature for growing lithium niobate single crystal thin film is 6.
The method for producing a lithium niobate single crystal thin film according to claim 1, wherein the temperature is within the range of 00 to 1250°C. 5. The method for producing a lithium niobate single crystal thin film according to claim 1, characterized in that the lithium niobate single crystal thin film is grown on a (0001) surface of a lithium tantalate substrate. 6. The a-axis lattice constant of the lithium niobate single crystal thin film is 99.8 of the a-axis lattice constant of the lithium tantalate substrate.
The method for producing a lithium niobate single crystal thin film according to claim 1, wherein the lithium niobate single crystal thin film is in a range of 1 to 100.07%.