JPS5912637B2 - Single crystal manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing lithium niobate, lithium tantalate, or lithium niobium tantalate single crystal by the Czochralski method.

Usually, these single crystals are pulled up by melting raw materials in a crucible and then bringing a rotating seed crystal into contact with the crucible.

The single crystal obtained in this way can be used for piezoelectric elements, light modulation elements,
It is known to be an excellent material for surface wave devices.

Single crystals used as materials for these devices are required to have low strain and few lattice defects.

Therefore, when pulling the single crystal using the Czochralski method, the temperature of the solution is controlled extremely accurately.

However, even with such a method, a single crystal of good quality cannot be obtained in terms of strain and lattice defects.

As a result of various research and observations of the above-mentioned conventional single crystals, the present inventors found that in the case of Z-axis pulling, a triangular prism single crystal whose ridge direction is the Y-axis force direction and whose elongation direction is the Z-axis direction is used as a seed crystal. As a result, we succeeded in obtaining a high-quality single crystal.

The circumstances that led to the completion of the present invention will be described below.

Conventionally, in the case of Z-axis growth, a square prism whose extension direction is in the Z-axis direction is used as a seed crystal, as shown in FIG. 1, from the viewpoint of work efficiency.

A growth experiment was conducted using this seed crystal 1, and when the space between the seed crystal and the subsequently grown crystal was observed with the naked eye, a polarizing microscope, and X-ray topography, three lines were observed on the surface of the grown crystal, which is unique to Z-axis growth. The ridge lines do not follow the symmetry inherent in the crystal, but as shown in Figure 1, they always arise from the ridge at the end of the seed crystal, grow several times while twisting, and then three ridge lines 2 with 3-fold symmetry are formed. be done.

When a cross section was taken between this area and observed using a polarizing microscope and X-ray topography, it was found that the seed crystal part had few strains and lattice defects, but large strains and lattice defects had occurred in the growing part after the twisted part of the ridge line.

This shows that distortion and lattice defects in the crystal are caused by twisting of the edges.

For this reason, the present inventors created seed crystals with various external shapes and conducted experiments, and found that in Z-axis growth, when a triangular prism seed crystal with the ridge direction in the Y direction was used, the crystals observed in conventionally grown crystals were It was discovered that there was no twisting of the ridge lines, and that there were few strains and lattice defects in the grown crystal.

Embodiments of the present invention will be described below with reference to FIG.

That is, as shown in FIG. 2, a seed crystal 11 of a single crystal with few strains and lattice defects, whose edge direction is the Y-axis direction and whose elongation direction is the Z-axis direction, is used, and the Z-axis is pulled at a pulling speed of 5 rrun/hour. Lithium niobate, lithium tantalate, and lithium niobium tantalate were grown in the following directions.

These crystal-specific ridgelines 12 were generated from the ridgelines of the seed crystal and grew without twisting.

The grown crystal was cut parallel to the Z-axis direction and the cross section was examined using a polarizing microscope.
The strain and lattice defects were on the same level as the new seed crystal observed by X-ray topography.

It can be seen that the single crystal of the present invention is excellent as a piezoelectric element, a light modulation element, and a surface wave element by the growth method as described in the above examples.

[Brief explanation of the drawing]

FIG. 1 is a projected view in the Z-axis direction of a crystal pulled by the conventional method of pulling in the Z-axis direction, and FIG. 2 is a projected view in the Z-axis direction of the pulled crystal by the method of the present invention, which is pulled in the Z-axis direction. .

Claims (1)

[Claims] 1. In a method for producing a single crystal in which a single crystal is grown by the Czochralski method, lithium niobate, lithium tantalate, or niobium Z lithium tantalate crystal
A method for producing a single crystal characterized by growing it in the axial direction.