JPH085756B2 - Oxide garnet single crystal and method for producing the same - Google Patents

Description

The present invention relates to an oxide garnet single crystal, and particularly to a strain crystal which is useful as a substrate crystal for crystal growth which is useful as an optical isolator or a magnetic sensor. The present invention relates to an oxide garnet single crystal with little remaining and a method for producing the same.

(Prior Art) As a Faraday rotator used for an optical isolator, a garnet single crystal film grown on a substrate crystal is used.

(Problems to be Solved by the Invention) However, this has a problem that the extinction ratio of the Faraday rotator using this is lowered due to the strain existing inside the substrate crystal. There is also a disadvantage that the garnet crystal film is likely to be cracked, which increases the insertion loss of light.

The oxide garnet single crystal as the substrate crystal is generally manufactured by the Czochralski method, but the single crystal obtained by this method is liable to crack in the cone portion and cuts the cone portion and the straight body portion. When this occurs, this crack also extends to the straight body portion, so that there is also a drawback that the productivity of the substrate crystal obtained thereby becomes extremely low.

(Means for Solving the Problem) The present invention relates to an oxide garnet single crystal capable of solving such disadvantages and drawbacks, and a method for producing the same, which is characterized by an extinction ratio of F35 dB or more. In a method for producing an oxide garnet single crystal and an oxide garnet single crystal by the Czochralski method by high frequency induction heating, an oxidation characterized by gradually lowering a crucible with respect to a work coil when pulling up a cone portion of the crystal Garnet single crystal manufacturing method.

That is, as a result of various studies on the substrate crystal that does not reduce the extinction ratio of the Faraday rotator, the present inventors have found that if the substrate crystal has an extinction ratio of 35 dB or more, a magnetic garnet film grown on the substrate crystal is formed. It was found that cracks disappeared and that when this is used as a Faraday rotator, it does not lower the extinction ratio or increase the insertion loss of light, and this extinction ratio is 35 dB or more. As for the production of garnet single crystal, when this is produced by the Czochralski method, the top of the crucible is placed higher than the top of the work coil when forming the neck of the growing crystal to prevent crystal twist. , When pulling up the crystal cone, gradually lower the crucible with respect to the work coil to reduce the temperature gradient directly above the melt. Since the distortion of the crystal due to the thermal strain of the part is suppressed, the distortion of the crystal straight body part is almost eliminated in the result, and the occurrence of cracks from the cone part when cutting the straight body part from the cone part is also eliminated, and The present invention has been completed by confirming that an extinction ratio of 35 dB or more can be obtained since link-like dislocations are also eliminated.

 This will be described in more detail below.

(Operation) The present invention relates to an oxide garnet single crystal having an extinction ratio of 35 dB or more and a method for producing the oxide garnet single crystal.

First, as described above, with respect to an Araday rotator made from a garnet film grown on a substrate crystal made of an oxide garnet single crystal, the extinction ratio is deteriorated by the strain existing in the substrate crystal, and The insertion loss of light also increases due to the cracks in the garnet single crystal film generated by the cracks present in 1. However, this is solved by using a substrate crystal having an extinction ratio of 35 dB or more.

That is, a substrate crystal having an extinction ratio of 35 dB or more can be obtained by the improved Czochralski method described later, but the oxide garnet single crystal used as the substrate crystal produced by this method has almost no strain. It will be a dead thing,
Since there is no crack, and the extinction ratio is 35 dB or more, the garnet crystal film formed on this substrate crystal by the liquid phase epitaxial method does not generate cracks, and the Faraday rotator using this does not The advantage is provided that the ratio is not degraded and the optical insertion loss is not increased.

It should be noted that this garnet crystal film may be a known one, and therefore it is represented by the general formula A ₃ B ₅ O _12, where A is Si, G
a, a rare earth element, for example, an element selected from Y, Gd, Nd, Sm, Lu, Eu, B is a transition metal element, for example, Fe, Co, etc., a non-magnetic metal, for example, Ge, Ga, Al, Sc, Si, etc. It may have an oxide garnet structure consisting of an element selected from
A in A ₃ B ₅ O ₁₂ produced as described above for the magnetic garnet material, platinum predetermined amount of the oxide of the metal component is selected as B PbO as flux component, as weighed with a predetermined amount of B ₂ O ₃ The crucible was placed in a crucible and heated to a temperature above its melting point to form a melt, which was kept in a supercooled state, and then a substrate crystal such as GGG described later was inserted into this crucible, and this substrate was formed by a liquid phase epitaxial method. A magnetic garnet film may be grown on the crystal with a predetermined thickness.

Next, the substrate crystal is manufactured by the Czochralski method using high frequency induction heating, which is carried out by the method shown in FIGS. 1 and 3 are longitudinal sectional views of a crystal pulling group by the Czochralski method, and FIG.
5 and 5 are diagrams showing the relationship between the crucible position and the cone length, and FIG. 2 is a schematic vertical sectional view of the pulled oxide garnet single crystal. The oxide garnet single crystal obtained by the Czochralski method is shown in FIG. Is manufactured by the method shown in FIGS.

The oxide garnet single crystal pulling apparatus shown in FIGS. 1 and 3 stores a crucible 1 in a heating furnace 3 having a work coil 2, and the target oxide garnet is placed in the crucible 1. After charging the metal oxide that constitutes the single crystal and heating it from the work coil to form the melt 4,
The single crystal is pulled up by immersing the seed crystal in this and pulling it up. At the beginning of pulling up the single crystal, the upper end 5 (cp) of the crucible is the upper end of the work coil 2 as shown in FIG. Although it is positioned above (0), when the cone portion 6 is pulled up as shown in FIG. 3, the crucible 1 is gradually lowered to finally move to the third position.
It is necessary that the upper end 5 (cp) of the crucible be located below the upper end (0) of the work coil 2 as shown in the figure.

However, the position of the crucible at the start of pulling the oxide garnet single crystal by the Czochralski method requires that the upper end (cp) of the crucible be higher than the upper end of the work coil 2, which is shown in FIG. If it is above the AC line, cracks are likely to occur in the obtained single crystal cone portion, and if it is below this BD line, the obtained single crystal is easily twisted. mm), which is the range surrounded by A, B, C, and D shown in FIG. 4, which is 0.25d to 0.745d [d is the diameter (mm) of the straight body of the single crystal,
[See FIG. 2]. Specifically, it may be set within the range shown in FIG. 5, and after the single crystal pulling is started, the crucible is gradually lowered as the growth of the cone portion progresses. Then, as shown in FIG. 3, the upper end 5 (cp) of the crucible may be located at a position of 0 to -0.75d from the upper end of the work coil 2.

With this treatment, since the upper end 5 of the crucible is located higher than the upper end of the work coil 2 when forming the neck of the desired oxide garnet single crystal, twisting of the desired single crystal is prevented, and the single crystal is prevented. When the cone is pulled up, the upper end 5 of the crucible is gradually lowered with respect to the work coil 2, the temperature gradient inside the cone is reduced, and the distortion of the crystal due to the thermal strain inside the cone is suppressed. Almost no distortion of the crystal straight body part is recognized, cracks do not occur from the cone part even when cutting the straight body part from the cone part, and further, ring-shaped dislocations are suppressed,
It has the advantage that an extinction ratio of 35 dB or more can be easily obtained, and the surface of the wafer obtained by cutting the oxide garnet single crystal thus obtained is observed with a polarization microscope (× 10). As a result, it was confirmed that this product had no distortion as shown in FIG. 6 and had an extinction ratio of 35 dB or more.

The oxide garnet single crystal as a substrate crystal for the purpose of the present invention is cadolinium gallium garnet (hereinafter abbreviated as GGG), samarium gallium garnet (hereinafter abbreviated as SGG), neodymium gallium.
Garnet (hereinafter abbreviated as NGG) may be (Gd Ga Ca Mg Zr) ₈ O ₁₂ in which a part of the above GGG is replaced with Ca, Mg, and Zr, and these are Gd ₂ O ₃ , Sm ₂ O ₃ , Nd ₂ O ₃ or C as required
AO, MgO, ZrO _{2 and the} like are charged into the crucible with a predetermined amount of Ga ₂ O ₃ , respectively, and heated to a temperature higher than the melting point of each by high-frequency induction to melt, and then a single crystal is prepared from this melt by the method described above. It can be pulled up, but this is represented by the formula Y ₃ Fe ₅ O ₁₂ especially when it is used as a substrate crystal of an optical isolator.
From the matching property of the lattice constant between the YIG bismuth-containing garnet single crystal and the epitaxial magnetic film, the formula (Gd Ga
An oxide garnet represented by Ca Mg Zr) ₈ O ₁₂ is suitable.

(Example) Next, the Example of this invention is given.

Example In a 100 mm diameter, 100 mm high crucible made of iridium,
A total of 3,700 g of a predetermined amount of a mixture of Gd ₂ O ₃ , GeO ₂ , CaCO ₃ , MgO, and ZrO ₂ was charged, and the mixture was heated to 1,700 ° C. or higher in a high-frequency induction heating furnace and melted to obtain a melt.

Then, set the upper end (cp) of this crucible at a position 25 mm higher than the upper end of the work coil, seed at this position, and pull up a single crystal with a neck diameter of 10 mmφ at a crystal pulling speed of 2 to 5 mm / hour to create a neck without twisting. After forming the part, the cone part is pulled up at the same speed and the diameter of the cone part is 16 mmφ.
The crucible was gradually lowered from the point when it became, and when the single crystal reached a straight body part diameter with a cone length of 55 mm and a diameter of 56 mmφ, the crucible lowering was stopped. Position is 2-3mm with respect to the upper end of the work coil
The change in the crucible position with respect to the cone length at this time was as shown in FIG.

After that, when the straight body part was pulled up from this stopped crucible, the formula (Gd Ga Ca Mg Zr) _{8 with} a straight body length of 100 mm was obtained.
Oxide garnet single crystal represented by O ₁₂ was obtained, and the upper and lower parts of the single crystal straight body were cut with an inner cutting machine and etched with a hot phosphoric acid solution at 180 ° C. When the pits were observed, ring-shaped dislocations were not observed in the pits, and cracks were not observed during the cutting.

Next, the straight body part of this single crystal was cylindrically ground, and this was slice-lapped and polished to make a double-sided polished wafer with a diameter of 51 mm and a thickness of 0.5 mm. The apparatus shown in FIG. When the extinction ratio was measured using, all of these showed values of 35 to 38 dB, and when this wafer was examined for distortion at 10 times under a polarizing microscope,
As shown in FIG. 6, no strain was observed in this.

However, for the purpose of comparison, the crucible position was fixed at the initial position, and the same procedure as above was used to obtain a diameter of 56 mmφ.
When a single crystal was made and cut out with an inner cutting machine, cracks were generated at this time, and when the extinction ratio of the wafer obtained by processing in the same manner as above was measured, these were all below 30 dB. When the wafer was examined with a polarization microscope, an image corresponding to strain was observed as shown in FIG. 7. To measure the extinction ratio, use the device shown in Fig. 8 and insert the sample between the polarizer and the analyzer, and place a laser beam with a wavelength of 1,317 nm from the LD light source on it with a light beam diameter of 1.5 mmφ and an output of 1,200 mW. The light quantity is measured with a photodetector by setting the polarizer and the analyzer in the positional relationship of parallel Nicols and orthogonal Nicols, and the minimum light transmission quantity at the parallel Nicols position.
T ₁ and the minimum light transmission amount T ₂ at the orthogonal Nicols position were obtained and calculated by the equation (1).

Extinction ratio = ₁₀ log ₁₀ (T ₁ / T ₂ ) ... (1) (Effect of the invention) The present invention is for growing an oxide garnet single crystal, particularly a garnet crystal film used for optical isolators, magnetic sensors and the like. An oxide garnet single crystal that is useful as a substrate crystal of
This is because, as described above, in an oxide garnet single crystal having an extinction ratio of 35 dB or more, and in a method for producing an oxide garnet single crystal by the Czochralski method, a crucible is gradually added to a work coil when pulling a cone portion of the crystal. The present invention relates to a method for producing an oxide garnet single crystal, which is characterized in that

This oxide garnet single crystal has an extinction ratio of 35 dB or more, but since it is manufactured by the above-mentioned manufacturing method, there is no crack and no crystal distortion or ring-shaped dislocation is observed. Therefore, if this is used as a substrate crystal, cracks will not occur in the magnetic garnet crystal film used for optical isolators and magnetic sensors grown on this, and this will be the extinction ratio for the Faraday rotator element made using it. Is provided, and the advantage that the insertion loss of light does not increase is given.

Further, when this oxide garnet single crystal is manufactured by the above-described manufacturing method, the strain in the crystal straight body part is almost eliminated,
Cracks and ring-shaped dislocations disappear even when cutting the straight body part, and the extinction ratio is 35 dB or more, so this is a substrate for growing a magnetic garnet crystal film used for isolators and magnetic sensors. It is said to be useful as a crystal.

[Brief description of drawings]

1 and 3 are longitudinal sectional views of an apparatus for producing an oxide garnet single crystal by the method of the present invention, FIG. 2 is a schematic longitudinal sectional view of an oxide garnet single crystal obtained by this method, and FIG. The relationship graph between the cone length and the crucible position when pulling the oxide garnet single crystal by the method of the invention, FIG. 5 is the relationship graph between the cone length and the crucible position in the example, and FIG. 6 is obtained by the present invention. Surface diagram of the oxide garnet single crystal wafer observed by a polarization microscope, FIG. 7 is a surface state diagram of the oxide garnet single crystal wafer obtained in a comparative example by a polarization microscope, and FIG. 8 measures the extinction ratio. It is a longitudinal cross-sectional view of the device.

Claims (5)

[Claims] 1. An oxide garnet single crystal having an extinction ratio of 35 dB or more. 2. The oxide garnet single crystal according to claim 1, which has a composition formula represented by (GdGaCaMgZr) ₈ O ₁₂ . 3. A method for producing an oxide garnet single crystal by the Czochralski method by high frequency induction heating, characterized in that a crucible is gradually lowered with respect to a work coil when a cone portion of the crystal is pulled up. Method for producing garnet single crystal. 4. The relationship between the cone length and the crucible position when the crucible descends is A (0,0.75d), B (0,0.25d), C in FIG.
4. A range surrounded by (L, 0), D (L, -0.75d) [where L is the total length of the cone portion (mm) and d is the diameter of the straight body portion of the crystal (mm)]. The method for producing an oxide garnet single crystal according to 1. 5. The oxide garnet single crystal has a composition formula (GdGaCa
The method for producing an oxide garnet single crystal according to claim 3 or 4, which is represented by MgZr) ₈ O ₁₂ .