JPH0826895A - Method for producing yttrium vanadate single crystal - Google Patents

Abstract

PURPOSE:To obtain an yttrium vanadate single crystal in a higher yield and suppress the developing of crystal defects causing losses to laser beams while maintaining the simplicity of making a {100}-plane wafer. CONSTITUTION:This yttrium vanadate single crystal is obtained by pull method. In this case, the azimuth of the seed crystal is set at <110>.

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 yttrium vanadate single crystal by a pulling method, which is used as a material for optical applications, mainly as a small solid-state laser.

[0002]

2. Description of the Related Art Yttrium vanadate single crystals are YV
It is a material that can be represented by the chemical formula of O ₄ , and is used as a laser crystal to which a rare earth element such as Nd is added. Yttrium vanadate single crystal is usually doped with 2 to 3 atomic% of Nd. Yttrium vanadate single crystal containing 2 atomic% of Nd is the most common laser crystal containing 1 atomic% of Nd. Compared with aluminum garnet, the absorption coefficient for semiconductor laser light with a wavelength of 0.8 μm is about 6 times larger. Therefore, when laser oscillation is performed by exciting a crystal from the end face with a semiconductor laser, the length of the laser crystal in the optical axis direction may be about 1 mm, and it is particularly used as a small-sized solid-state laser material.

This crystal belongs to a tetragonal system and is optically anisotropic. The absorption coefficient for so-called π-polarized light whose electric field vector is parallel to the c-axis is σ-polarized light perpendicular to the c-axis. Larger than light. Therefore, a small piece of a few mm square is cut out from a {100} plane wafer having a thickness of about 1 mm and used as a laser crystal in a laser oscillator so that the optical axis of the crystal is perpendicular to the c-axis.

The yttrium vanadate single crystal is produced by the pulling method. To produce the above {100} plane wafer, the single crystal produced by setting the seed crystal orientation to <100> or <001>. Is easy to use. In the case of a single crystal manufactured with a seed crystal orientation of <100>, the {100} plane wafer can be manufactured simply by cutting in the direction perpendicular to the pulling axis direction. When the seed crystal orientation is <001>, in the manufactured crystal, the {100} plane always appears on the crystal surface of the grown portion where the crystal diameter is controlled to be constant, that is, on the surface of the straight body portion. Therefore, the wafer can be manufactured by cutting the crystal parallel to the {100} plane.

As described above, when the above two seed crystal orientations are used, there is a reference direction or plane when the {100} plane wafer is cut, so that {1} can be easily and accurately obtained.
A 00} plane wafer can be manufactured. Therefore, <100> or <001> is exclusively used as the seed crystal orientation when producing the yttrium vanadate single crystal used as the laser material.

[0006]

One of the conditions that the laser crystal should have is that it does not have a crystal defect.
This is because when a wafer with crystal defects is used as a laser crystal for laser oscillation, the crystal defects act as a loss factor of the laser light for the scatterer for the laser light, that is, the laser resonator, so that high-intensity laser light output cannot be obtained. Is.

However, a single crystal manufactured with a seed crystal orientation of <100> or <001> has a drawback that it has many crystal defects. In the crystal growth by the pulling method, the temperature in the crystal growth furnace is controlled to form a straight body with a constant crystal diameter.However, in the production of yttrium vanadate single crystal, the crystal is projected and suddenly increases in the diameter direction. A phenomenon called rapid growth frequently occurred. here,
The direction in which the crystal grows in a protruding manner is fixed, and always <1
00> direction. It is considered that the reason is that the growth rate of the {100} plane is higher than that of other planes.
Generally, rapidly grown crystals have many defects, but in the case of yttrium vanadate single crystal, the parts where rapid growth occurs have more crystal defects such as voids than other parts, which causes seed crystal orientation The quality of the single crystal manufactured as 100> or <001> was deteriorated.

The object of the present invention is to suppress the occurrence of crystal defects that act as a loss for laser light and maintain the yield of single crystals in the production of yttrium vanadate single crystals while maintaining the simplicity of producing {100} plane wafers. To improve.

[0009]

In order to achieve the above-mentioned object, the present invention provides a seed crystal having an orientation of <110> in a method for producing a yttrium vanadate single crystal by a pulling method.
It is characterized by being manufactured as.

[0010]

When the orientation of the seed crystal is <110>, it is possible to prevent the appearance of the {100} plane during the production of the straight body portion, so that it is possible to prevent sudden growth. If the {100} plane appears during the production of the straight body, the angle between the pulling axis and the plane of the crystal bottom that is in contact with the melt in the crucible, the so-called crystal bottom angle, becomes 45 degrees. Only {1
This is because the {00} plane appears. Since the crystal bottom angle can be easily changed by adjusting the temperature environment in the furnace, the appearance of the {100} plane can be easily prevented.

In addition, it is desired to prevent this during manufacturing of the straight body part {10
The appearance of the 0} plane also increases the crystal diameter from the seed crystal to a predetermined diameter during the production of the crystal shoulder portion. Is 45 degrees, and rather, the {100} plane is positively generated on the surface of the crystal shoulder portion, whereby the reference plane for cutting the {100} plane wafer from the pulled single crystal can be produced. Crystal shoulder {100}
If the crystal is cut parallel to this plane with the plane as the reference, a {100} plane wafer can be easily and accurately manufactured.

As shown above, the seed crystal orientation <1
10> to produce a single crystal, it is possible to suppress the rapid growth of the crystal diameter, and an yttrium vanadate single crystal having no crystal defects can be produced.

[0013]

【Example】

Example 1 An example will be described. First, a mixture was prepared such that the mixing ratio of neodymium oxide to yttrium oxide was 2 atom%. The yttrium oxide had a purity of 99.999% by weight and the neodymium oxide had a purity of 99.995% by weight. Next, diameter 100m
m, depth 100 mm, iridium crucible, purity 99.9
9% by weight of vanadium pentoxide and the above mixture were mixed at a molar ratio of 1: 1 and the raw material was melted in a nitrogen atmosphere containing 2% by volume of oxygen in a high frequency heating furnace. Next, the seed crystal orientation is set to [110] of the present invention, and the yttrium vanadate seed crystal is rotated at 10 rpm and sufficiently immersed in the melt. Grows, diameter 40m
A yttrium vanadate single crystal having a length of 60 mm and a total length of 60 mm was produced. At this time, no rapid growth occurred. From this yttrium vanadate single crystal, a 5 mm thick (100)
The surface wafer was cut out and observed with an optical microscope.
No crystal defects were found in the wafer as viewed with an optical microscope.

(Comparative Example) A conventional example was also manufactured in which the seed crystal orientation was [100]. When manufacturing was performed under the same conditions except for the seed crystal orientation, rapid growth occurred at a crystal length of 20 mm. From the part where the crystal diameter became large due to the rapid growth, the thickness was 5 mm as above.
When a (100) wafer was cut out and observed with an optical microscope in the same manner, a large number of scatterers were observed only in the rapidly growing portion.

Example 2 Next, a wafer cut from a single crystal having a seed crystal orientation of [110] according to the present invention and a wafer cut from a single crystal of a conventional example having a seed crystal orientation of [100] were used. Excitation was performed with a semiconductor laser having a wavelength of 0.8 μm, and a laser oscillation experiment was performed at a wavelength of 1.06 μm. In each of the present invention and the conventional example, eight wafers were prepared, and the wafer surface was excited at 25 locations every 7 mm in length and width,
The laser output at that time was recorded. Therefore, the total number of measurement points is 400 points.

1 and 2 show the frequency distribution of the relative intensity of the laser output at each measurement point when the highest laser output intensity among the 400 measurement points is 1. FIG. 1 shows the measurement results for the seed crystal orientation of [110], and FIG. 2 for the measurement results of [100]. The yttrium vanadate single crystal wafer having a seed crystal orientation of [110] had a high laser oscillation output but a high frequency, and the average value thereof was about 30% higher than that of the seed crystal orientation of [100]. Further, the variation of the laser oscillation output depending on the position of the wafer surface was as small as 0.7 to 1.0, compared with 0.1 to 1.0 in the conventional example. The low laser output existed only in the rapid growth portion having many crystal defects.

1 and 2, the yield of the present invention was 80% and the yield of the conventional example was 27% when the product having a relative strength of 0.9 or more was regarded as a good product.

[0018]

Industrial Applicability According to the present invention, it is possible to provide a method for producing a yttrium vanadate single crystal free from crystal defects associated with rapid growth. When laser oscillation was performed using a wafer cut from a single crystal manufactured according to the present invention, there was little variation in laser output due to difference in wafer surface position, and the result was that the average value of the obtained laser output was high. Was given. The yield also improved from 27% to 80%.

[Brief description of drawings]

FIG. 1 is a diagram showing a laser oscillation power frequency distribution of a wafer having a seed crystal orientation of [110] according to the present invention.

FIG. 2 is a diagram showing a laser oscillation output frequency distribution of a wafer having a conventional seed crystal orientation of [100].

Claims (1)

[Claims] 1. A method for producing a yttrium vanadate single crystal by the pulling method, wherein the orientation of a seed crystal is <11.
0> as the yttrium vanadate single crystal.