JPH0687697A - Production of thin film of lithium niobate single crystal - Google Patents

Abstract

PURPOSE:To obtain a thin film of a lithium niobate single crystal ensuring reduced optical transmission loss and suitable for use as a thin film optical waveguide type element. CONSTITUTION:When a thin film of a lithium niobate single crystal is formed by liq. phase epitaxial growth, a substrate of an MgO doped lithium niobate single crystal is immersed in a melt consisting of, by mol. 40-56.3% LiO2, 6.7-13% Nb2O5, 26.3-50% B2O3 and 0-20% MoO3 as starting materials and a thin film is grown on the substrate.

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 thin film, which is suitable for a thin film optical waveguide type device and has a reduced optical propagation loss.

[0002]

2. Description of the Related Art Growth of a single crystal thin film using a liquid phase epitaxial (hereinafter abbreviated as LPE) method is widely used as a method for growing an oxide crystal or a compound crystal. Among them, the isothermal rotary dipping LPE method is excellent in crystallinity and uniformity and is known to be advantageous for growing a large area crystal. In the LPE method, a raw material in which a solute component and a solvent (flux) component are mixed is heated and melted at a liquidus temperature or higher to form a melt for growth. In principle, the flux method is used because a flux is used as the melt component Is almost the same as. The difference between the LPE method and the flux method is that LP
In the E method, a substrate to be a seed crystal is immersed in a melt kept in a supercooled state, and the crystal is deposited and grown on the substrate. Grow crystals. For this reason, the flux method has drawbacks such as long growth time and easy concentration variation due to component segregation, but the LPE method does not easily cause the above problems because the substrate is epitaxially grown on the substrate while rotating. However, as in the case of the flux method, since a flux component serving as a solvent is contained in the melt, it is a drawback of the LPE method that this flux component is easily mixed in the crystal. The necessary conditions for the flux component are to lower the liquidus temperature to a practical temperature range, to dissolve the solute component in solid solution,
It does not impede the crystal growth or does not replace the solute component, but these are also the fundamental factors of the LPE method. Therefore, depending on the quality of the flux component, LP
It is no exaggeration to say that the success or failure of the E law will be affected.

The proposed lithium niobate single crystal thin film is
The example formed by the PE method is (1) Applied P
hysics Letters, Vol. 26, No.
1,1 January 1975 (P8), or (2) J. Appl. physs, Vol. 70, No.
5,1 September 1991 (P2536) and the like, the flux components used are all Li ₂ O—V ₂ O ₅ . In addition, (3) Japanese Patent Fair 3-69
Japanese Patent No. 586 describes using K ₂ O-V ₂ O ₅ as a flux component.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention (1) to (3)
Among the flux components of the technology shown in, V ₂
Although O ₅ is commonly used, the V element and the Nb element of the solute component are located in the same VA group. Therefore, V
_{When a} lithium niobate single crystal thin film is formed from a melt containing a mixture of ₂ O ₅ components, it is highly possible that V element is mixed into the film and replaces the Nb element which is a constituent element of the thin film. When light is guided into the film in which the V element is mixed, light is absorbed in the film and the light propagation loss is several tens (d).
B / cm) has been pointed out. (For example, (1) Journal of Crystal Gr
owth, 46, (1979) P314, (2) J. A
ppl. physs, Vol. 70, No. 5,1 Sep
The present invention aims to provide a method for producing a lithium niobate single crystal thin film which solves the above problems.

[0005]

The present invention relates to a method of forming a lithium niobate single crystal thin film by a liquid phase epitaxial growth method, wherein Li ₂ O, Nb ₂ O ₅ , B ₂ O ₃ and MoO ₃ are used as raw material components. A method for producing a lithium niobate single crystal thin film, which comprises immersing a MgO-doped lithium niobate single crystal substrate in the molten solution described above to grow a thin film on the substrate. The composition of the melt is 40 mol% to 56.3 mol% of Li ₂ O, 6.7 mol% to 13 mol% of Nb ₂ O ₅ , and ₂ mol of B ₂ O _3.
6.3 mol% to 50 mol% and 0% MoO ₃
It is characterized by being in the range of ˜20 mol%.

The reasons for limiting the melt composition of the present invention will be described below. Li ₂ O and Nb ₂ O ₅ are each 40 mol% to
56.3 mole%, and can not be used as an optical single crystal thin film from that mixed with LiNb ₃ O _6, or Li ₃ NbO ₄ crystal or the like is deposited LiNbO ₃ crystals other than 6.7 mole% to 13 mole% . Li ₂ O and Nb ₂ O ₅
The range of 44 mol% to 52 mol% and 7.3 mol% to 12 mol% are preferable. In addition,
The Li ₂ O / Nb ₂ O ₅ ratio is preferably 4.0 to 6.5. B ₂ O ₃ has a liquidus temperature of 10 at 26.3 mol% or less.
Since the substrate temperature is higher than 00 ° C., the substrate is easily cracked, and the growth rate is increased to several μm / min or more, so that the crystallinity of the thin film is deteriorated. On the other hand, when it is 50 mol% or more, the viscosity of the melt increases and the composition in the melt does not become uniform. Desirably, 30 mol% to 45 mol% is suitable.

When MoO ₃ is 20 mol% or more, MoO ₃ remains on the film surface after the substrate is pulled up. Desirably 0
Mol% to 15 mol% are preferred. The substrate used in the present invention is preferably an optical lithium niobate single crystal doped with MgO. This is because the thin film to be formed has the same crystal system, which facilitates the epitaxial growth. The main component of the substrate is the same as that of the thin film, so that the lattice matching can be easily achieved. Since it becomes smaller than that, it becomes possible to confine guided light in a thin film, and so on. The growth surface of the substrate is preferably the (0001) plane and needs to be optically polished.

By the way, in the formation of a lithium niobate single crystal thin film by the LPE method, as an example in which B ₂ O ₃ and MoO ₃ were used as flux, (1) Jour
nal of Crystal Growth, 46,
(1979) P314, and (2) Applied
Physics Letters, Vol. 26, N
o. Although 9,1May 1975 discloses a description of the extent also that tasted cases, flux system has proceeded in detail was Li ₂ O-V ₂ O ₅ system. Also,
(3) Journal of Crystal Gro
wth, 43, (1978) P197 contains LiB
Although there are reports of studies on O ₂ and Li ₂ MoO ₄ systems, they have ended up being a tasting as in (1) and (2) above.

Further, (4) Journal of Cr
ystal Growth, 29, (1975) P28
9 reports a study of the Li ₂ B ₂ O ₄ system, the content of which mainly describes the results of making a phase diagram of a pseudo binary system with LiNbO ₃ and the intention of the present invention. It is fundamentally different from the technology used.

[0010]

EXAMPLES The present invention will be described below with reference to examples. _{(Example) Li 2 CO 3, Nb 2} O 5, B 2 O 3 and / or MoO _3, were mixed in compositions shown in Table 1, after filling the mixture in a platinum crucible at about 1100 to 1200 ° C. Heat to homogenize. Then, the melt is kept in a supercooled state, and a MgO-doped lithium niobate single crystal substrate is dipped in the solution to stand still or about 30 to 100.
LPE was performed for about 1-10 minutes while rotating at rpm. During rotation, the rotation direction was reversed at intervals of about 5 to 10 seconds. After the LPE, the surface of the film was washed, and the optical propagation loss for a semiconductor laser beam having a wavelength of 0.83 μm was measured by a prism moving method (see Nishihara, et al .: Optical integrated circuit (Ohm) P251). The results are shown in Table 1. A schematic diagram of the prism moving method is shown in FIG.

[Table 1]

[0011]

INDUSTRIAL APPLICABILITY According to the present invention, a lithium niobate single crystal thin film having a very small light propagation loss can be produced, and thus it is suitable as an optical device material such as an optical waveguide device.

[Brief description of drawings]

FIG. 1 is a view showing a measuring apparatus of a prism moving method used for evaluation of a lithium niobate single crystal thin film according to the present invention.

Claims (2)

[Claims] 1. A method for producing a lithium niobate single crystal thin film by forming a lithium niobate single crystal thin film by a liquid phase epitaxial growth method, comprising: Li ₂ O, Nb ₂ O ₅ , B ₂
Manufacture of a lithium niobate single crystal thin film characterized by immersing a MgO-doped lithium niobate single crystal substrate in a melt containing O ₃ and MoO ₃ as raw material components to grow a thin film on the substrate. Method 2. The composition of the melt is 40 mol% to 56.3 mol% of Li ₂ O and 6.7 mol% to 13 of Nb ₂ O _5.
The lithium niobate single crystal thin film according to claim 1, wherein the mole%, B ₂ O ₃ are in the range of 26.3 mole% to 50 mole%, and MoO ₃ is in the range of 0 mole% to 20 mole%. Manufacturing method.