JP3013206B2 - Method for producing lithium niobate 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 method for producing a lithium niobate single crystal, and more particularly to a method for producing a lithium niobate single crystal by a liquid phase epitaxial method.

[0002]

2. Description of the Related Art Lithium niobate (LiNbO ₃ ) single crystals are expected to be applied as substrate materials for waveguide type optical switches. The Czochralski method is generally used as a method for producing this type of single crystal. However, the crystal composition obtained by this method is a congruent (harmonic melting) composition, with Li / Nb = 0.94, and lithium is insufficient. This is considered to be a cause of DC drift (fluctuation of drive voltage) in the waveguide type optical switch and lowering of an optical damage threshold when an optical harmonic is generated. Therefore, Li / Nb =
There is a demand for improved properties using crystals having a 1.0 or stoichiometric (stoichiometric) composition. The liquid phase epitaxial method is used for manufacturing semiconductor crystals, magnetic ganates, and the like, and has advantages such as low cost and easy composition control as a single crystal manufacturing method. In the production of a single crystal film by the liquid phase epitaxial method, it is required that the substrate crystal and the crystal film have the same crystal structure, and that there is no large difference between the two lattice constants. Stoichiometric composition lithium niobate single crystal film (lattice constant a = 5.150, c =
13.857) At the time of production, a single crystal of lithium niobate having a congruent composition and a composition of niobium (a lattice constant a = 5.149, c = 13.865) or a single crystal of lithium tantalate (a lattice constant a = 5.153, c =
13.785) is used.

[0003]

However, the lattice constant of the former is large for this crystal film, and the lattice constant of the latter is conversely small. This difference in lattice constant causes stress strain between the substrate crystal and the crystal film, and thus causes the crystal film to crack. In view of the above, the technical problem of the present invention is to solve the above problems and obtain a high quality single crystal film by reducing the mismatch between the lattice constant of the substrate crystal and the crystal film.
An object of the present invention is to provide a method for manufacturing a single crystal that reduces stress strain.

[0004]

SUMMARY OF THE INVENTION The present invention is the manufacturing method by the liquid phase epitaxial process of stoichiometric composition of lithium niobate single crystal film, LiNb _1-x Ta _x O
₃ (0 <x <0.9).

[0005]

In the present invention, a single crystal of lithium niobate-lithium tantalate mixed crystal is used as a substrate crystal.
In this substrate crystal, the a-axis lattice constant monotonically increases and the c-axis lattice constant monotonically decreases as x increases. Therefore, mismatch between the lattice constant of the substrate crystal and the crystal film to be grown can be reduced.

[0006]

Examples of the present invention will be described below with reference to comparative examples. (Embodiment) FIG. 1 is a sectional view showing the inside of a single crystal growing furnace by a liquid phase epitaxial method. As shown in FIG. 1, the single crystal growing furnace comprises a platinum crucible 1, a melt 2, a single crystal substrate of a mixed crystal of lithium niobate-lithium tantalate 3, a crystal holder 4, a crystal holder support rod 5, a resistance heater 6, And a crystal rotation mechanism 7. Using this single crystal growing furnace, x = 0.02, 0.7 in a lithium carbonate-niobium pentoxide-vanadium pentoxide-based melt 2 held at 850 ° C. in a platinum crucible 1.
0,0.90 the LiNb _1-x Ta x O ₃ crystal substrate 3 having the composition formed by dipping for 60 minutes, was grown stoichiometric composition of lithium niobate single crystal film on the c-plane of the crystal substrate 3. When the substrate of the same composition was grown five times, a high quality single crystal film without cracks was obtained.

COMPARATIVE EXAMPLE A lithium tantalate crystal substrate 3 was placed on a lithium carbonate-niobium pentoxide-vanadium pentoxide-based melt 2 at 850 ° C. held in a platinum crucible 1 by a device similar to that shown in FIG. Is immersed for 60 minutes to form a stoichiometric composition lithium niobate single crystal film at x = 0,
0.95,1.0 composed composition LiNb _1-x Ta x O ₃ was grown on the c-plane of the crystal substrate 3. 5 for substrates of the same composition
After multiple growth, the single crystal film was cracked, and it was impossible to obtain a good quality single crystal film. Table 1 shows the growth results of Examples and Comparative Examples of the present invention (for the values of lattice constants, see J. Crystal Groth, vol. 33, (1976) p199.). The circles in Table 1 indicate that the crystal did not crack,
The marks indicate those having cracks.

[0008]

[Table 1]

[0009] Incidentally, not only the embodiments described above, the present invention _{is, LiNb 1-x Ta x O} 3 (0 <x <0.9) composed of lithium niobate having a composition - lithium tantalate mixed single crystal If it is used, it can be applied to all methods for producing a lithium niobate single crystal film having a desired composition.

[0010]

As described above, by using the present invention, it is possible to prevent cracking of a grown single crystal film during production of a lithium niobate single crystal film having a desired composition by a liquid phase epitaxial method. The industrial use value is great because it becomes possible.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a growth furnace in which a melt and a substrate crystal held in a platinum crucible are inserted into a growth furnace.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Platinum crucible 2 Crystal raw material 3 Crystal substrate 4 Crystal holder 5 Crystal holter support rod 6 Resistance heating element

Claims (1)

(57) [Claims] 1. A method for producing a lithium niobate single crystal by liquid phase epitaxial _{method, LiNb 1-x Ta x O} 3 lithium niobate having a (0 <x <0.9) having a composition as the substrate crystal - Tantalum A method for producing a lithium niobate single crystal, comprising using a lithium oxide mixed crystal single crystal.