JPH04139094A - Method for growing magneto-optical garnet crystal - Google Patents

Abstract

PURPOSE:To reduce film defects with Pt as nuclei by introducing an inert gas such as Ar, He, N2 or CO2 into a furnace for growing a Bi substd. garnet film. CONSTITUTION:An inert gas such as Ar, He, Ne or CO2 is allowed to flow in a growth furnace at a prescribed flow rate and a Pt crucible filled with a prescribed amt. of molten starting material is set in the furnace. A Bi substd. garnet film is grown on a substrate of Ga-Mg-Zr substd. Gd3Ga5O12, etc., by a liq. phase epitaxial growth method at a prescribed growth temp. and a magneto-optical garnet crystal having a low Pt content is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical isolator using the Faraday effect;
The present invention relates to a method for manufacturing a bismuth (Bi) substituted magnetic garnet crystal used in magneto-optical elements such as optical circulators and optical switches.

[Prior Art] In an optical transmission circuit that uses a semiconductor laser (LD) as a light source, if reflected return light from optical components such as connectors and switches, or light receiving elements enters the LD, laser oscillation becomes unstable and transmission quality deteriorates. known to deteriorate. As a countermeasure to this problem, an optical isolator that blocks reflected light returning to the LD has been proposed, and is currently being put into practical use.

Optical isolators make good use of the non-reciprocity of the Faraday effect, which is a magneto-optical effect that rotates the plane of linear polarization of transmitted light.

A Faraday rotator material that exhibits the Faraday effect and is used in the near-infrared region with a wavelength of 1.3 to 1.55 μm is a magneto-optic garnet crystal. Among these, yttrium-iron-garnet (YIG) crystals were first used as Faraday rotators in optical isolators.

In recent years, the miniaturization and cost reduction of optical isolators have rapidly progressed, and along with this, there has been a strong desire for miniaturization of elements and reduction in manufacturing costs.

In order to downsize optical isolators, it is essential to downsize the Faraday rotator, which is the main component.

By the way, when used as a Faraday rotator, it needs to be long enough to rotate the incident polarization plane by 45 degrees.
This length is proportional to the magnitude of the Faraday rotation coefficient. Therefore, in order to further downsize the Faraday rotator, it is necessary to select a material with a large Faraday rotation coefficient.

Garnet containing Bi as a solid solution is generally known as a material with a large Faraday rotation coefficient.

This material can be manufactured by a CVD method, a sputtering method, a flux method, a liquid phase epitaxial (LPE) method, or the like. However, the CVD method and the sputtering method mainly have problems with crystallinity, and it is still difficult to put them into practical use.

The flux method uses yttrium oxide (
Along with iron oxide (Fe203) and iron oxide (Y2O2), lead oxide (p b o) and boron oxide (B20
3) is melted, the melt is maintained at a temperature higher than the liquidus temperature to make it uniform, and then the melt is slowly cooled to grow garnet crystals by natural nucleation. Washing with water had some disadvantages, such as concentration variations due to the segregation of garnet components, and cracks in the crystals as the flux solidified, but these problems were resolved by the improved flux method.

However, since natural nuclei are grown, crystal growth requires a long time, precision processing is required to form devices, and mass productivity is poor.

Under these circumstances, the LPE method, which was developed as a method for growing garnet thin films for magnetic bubble devices, has attracted attention, and various studies have been made to develop Bi-substituted magnetic garnet thick films using water washing.

Well, Th1n 5olid Films, 114 (1
As shown in 984)69, the Faraday rotation coefficient increases in proportion to the amount of Bi substitution. However, since the solid solubility of Bi in garnet crystals is extremely small,
It is also known that replacement is very difficult.

In order to replace a large amount of Bi, (a) searching for an optimal component system, (b) optimizing the LPE conditions, and (c) optimizing the melt composition, etc. have been proposed;
Crystal Growth 71 (1985) 4
09 and Phys, 5tat, Sol, (a) 1
00 (1987) 213, etc.
The methods (b) and (c) above are particularly effective.

In (b), it is mainly known that the degree of supercooling (ΔT: saturation temperature - film growth temperature) increases and the film growth temperature (TG) decreases, while in (c), the It is important to increase the amount of Bi and O in order to increase the concentration of Bi ions.

By the way, the starting materials for the melt for garnet film growth are all oxides, a large amount of Bi2O3 and Pb0 are filled, and the raw material mixed with these is 1100%
Due to reasons such as heating to a high temperature of ~1300℃, LP
The material of the crucible for growing E-garnet crystals is pure platinum (Pt), which has excellent oxidation resistance and corrosion resistance, or a Pt-based alloy.

However, even if the above-mentioned Pt material is used, oxidation or corrosion gradually progresses, and Pt is dissolved into the melt, which is a major problem, and this is one of the weaknesses of the LPE method.

[Problems to be solved by the invention] The Pt dissolved in the melt is (a) Pt2+ or P
It becomes t4+ ion and mixes into the membrane, disrupting the valence balance in the membrane. The deviation in valence balance is described in the Journal of the Japanese Society of Applied Magnetics Vol. 1.10. No.

2 (1986) As also shown in P2S5,
It is known to lead to increased light absorption.

(b) Some of the Pt floating in the melt without being incorporated into the film is J, Magn, Soc, Jpn, V
As is known from ol, ll, 5I (1987) P347, this contributes to film defects, and this defective portion is
7, the optical characteristics deteriorate.

Therefore, melting of Pt crucibles is a very serious problem.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an inert gas of Ar, He5N, and C
The present invention provides a method for growing magneto-optic garnet crystals, which is characterized by introducing O, gas, etc.

That is, the present invention is a method for growing a magneto-optic garnet crystal, which is characterized by introducing an inert gas into a growth furnace when growing a bismuth-substituted garnet film by the liquid phase epitaxial (LPE) method.

In the present invention, the inert gas is particularly Ar.

He, N, CO2 gas, etc. are used.

As a result of intensive research into the cause of crucible melting, the present inventor found that it strongly depends on the valence balance in the melt, leading to the present invention.

As mentioned above, it is known that Pt2+ ions or Pt4+ ions (or both) exist in Pt.

In order to confirm which of Pt2+ and Pt4+ is predominant in the film, the present inventors first added Ca2+, a divalent element, and Si4+, a tetravalent element, and the Pt content in the film at that time. The behavior of the amount was observed.

Table 1 shows the results.

Table 1 Relationship between Pt content in the film and added elements EPMA analysis value (wt%) The Pt content in the film without additives is 0.76 (wt%), but when Ca2+ is added, it increases to 1 .88
(wt%). On the other hand, it was found that when Si4+ was added, it decreased to 0.43 (wt%). In each case, LPE was performed in the air, and the grown film thickness was 4 to 6 μm. From this result, Pt in the film
It was suggested that the valence of Pt4+ is dominant. If a large amount of Pt4+ is incorporated into the film, it can be easily inferred that Pt4+ is dominant in the melt as well.

Now, since the raw materials constituting the melt are all oxides like the raw materials for the flux method described above, it is said that the type of atomic bonds in the raw materials are mostly ionic bonds. Therefore, Pt
In order for the 4+ ion to dissolve into the melt, an ion that forms an ionic bond with Pt4+ is required, but that ion is most likely to be 02-, and its bond state is p to
,it is conceivable that.

This 02 also exists in the melt, but the 0. is Fe
As can be seen from the bonding states of 2O3, Bi, O, etc., all of them are ionically bonded to various ions, and it is thought that there is no extra 02 bonded to Pt. therefore.

There is a high probability that the above 02 is supplied from the atmosphere outside the melt.

From the above, it can be seen that in order to prevent the dissolution of Pt4+ ions, it is sufficient to remove the 02- ions outside the melt.

The present invention is characterized in that inert gases such as Ar, He, N2, and CO2 gases are introduced into the growth furnace to remove 0□-ions.

The present invention will be explained in detail below using Examples.

[Example] <Example 1> Ar gas was flowed into the growth furnace at a rate of about 300 CC/min, and Ca
- Grow an LPE garnet film of about 5 μm on a Mg-Zr substituted Ga3Ga5012 substrate at a growth temperature of 745°C,
The pt content in the film was analyzed using EPMA, and as shown in Example 1 in Table 2, it was 0.16 (wt%).

Note that the Pt content in the film grown in the same manner in the weather was 0.81 (wt%) as shown in the comparative example in Table 2.

(Leaving space below) Table 2 <Example 2> Approximately 500 CC/min of He gas was flowed into the growth furnace, and Ca
An LPE garnet film of approximately 6 μm was grown on a -Mg-Zr substituted G d3G a5012 substrate at a growth temperature of 746°C, and the Pt content in the film was analyzed using EPMA, as shown in Example 2 in Table 2. It was 0.20 (wt%).

<Example 3> Approximately 300 CC/min of N2 gas was flowed into the growth furnace, and Ca
An LPE garnet film of about 4 μm was grown on a -M g -Z r-substituted Gd3Ga5O12 substrate at a growth temperature of 750°C, and the Pt content in the film was analyzed using EPMA, as shown in Example 3 in Table 2. It was 0.41 (wt%).

<Example 4> About 300 CC of CO2 gas was introduced into the growth furnace for 7 minutes, and the CO2 gas was
An LPE garnet film of about 7 μm was grown on a -M g -Z r-substituted Gd3Ga5O12 substrate at a growth temperature of 747°C, and the Pt content in the film was analyzed using EPMA. The results are shown in Example 4 in Table 2. 0.31 (wt%
)Met.

<Example 5> As a result of examining the correlation between film defects generated with Pt particles floating in the melt as nuclei and the oxygen concentration in the furnace, as shown in Figure 1, as the oxygen concentration increases, The membrane defects increased almost logarithmically.

<Example 6> Approximately 50 cc/min of Ar gas was introduced into the furnace.
A 100cc Pt crucible filled with 0g of melt was installed, and after LPEL at a growth temperature of 740°C for about 30 hours, LPE
As a result of measuring the weight difference between the front and rear crucibles, it was found that there was a decrease of about 0.9 g.

In addition, as a result of measuring the weight difference between the LPEL and the crucible under similar conditions in the atmosphere, it was found that the weight was reduced by about 3.1 g.

<Example 7> A Pt crucible filled with about 5000 g of melt was heated to about 10K.
After LPE was performed for about 50 hours at a growth temperature of 743° C. in a furnace sealed with Ar gas of g/cm 2 , the weight difference of the crucible before and after LPE was measured, and the result was a decrease of about 0.5 g.

In addition, as a result of performing LPE in the air under similar conditions and measuring the difference in weight of the crucible, it was found that the weight decreased by about 10.3 g.

[Effects of the Invention] According to the present invention, since the melting of the Pt crucible is significantly suppressed, the amount of Pt mixed into the film is reduced, and light absorption is reduced. Since floating Pt in the melt decreases, film defects centered on Pt are reduced. Furthermore, it has extremely great practical value because it greatly contributes to improving magneto-optical properties such as extending the life of the crucible, improving device yield, and further reducing cost.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in film defects when the oxygen concentration is changed.゛・-ノ

Claims (5)

[Claims] (1) A method for growing a magneto-optic garnet crystal in which a bismuth-substituted garnet film is grown in a growth furnace by a liquid phase epitaxial method, characterized in that an inert gas is introduced into the growth furnace. Method. (2) The method for growing a magneto-optic garnet crystal according to claim 1, wherein the inert gas is Ar. (3) The method for growing a magneto-optic garnet crystal according to claim 1, wherein the inert gas is He. (4) The method for growing a magneto-optic garnet crystal according to claim 1, wherein the inert gas is N_2. (5) The method for growing a magneto-optic garnet crystal according to claim 1, wherein the inert gas is CO_2.