JP5697209B2 - Paramagnetic garnet single crystal and method for producing the same - Google Patents

Description

本発明は、常磁性ガーネット単結晶及びその製造方法に関し、更に詳しく述べると、ＬＰＥ法（液相エピタキシャル法）により育成したＴＧＧ（テルビウム・ガリウム・ガーネット）を主成分とする常磁性ガーネット単結晶及びその製造方法に関するものである。この技術は、特にファラデー回転子などに用いる光学用単結晶材料の製造に有用である。   The present invention relates to a paramagnetic garnet single crystal and a method for producing the same, and more specifically, a paramagnetic garnet single crystal mainly composed of TGG (terbium gallium garnet) grown by an LPE method (liquid phase epitaxial method) and It relates to the manufacturing method. This technique is particularly useful for the production of optical single crystal materials used for Faraday rotators and the like.

ＴＧＧ結晶は、低光損失、高熱伝導率、高ダメージ閾値、高ベルデ定数の光学用結晶として知られており、主に４００ｎｍ〜１１００ｎｍ用光アイソレータなどのファラデー素子として利用されている。   The TGG crystal is known as an optical crystal having a low optical loss, a high thermal conductivity, a high damage threshold, and a high Verde constant, and is mainly used as a Faraday element such as an optical isolator for 400 nm to 1100 nm.

ＴＧＧ結晶の一般的な製造方法としては、坩堝中で溶融した原料に種結晶をつけて回転させながら引き上げるチョクラルスキー法（ＣＺ法）が知られている。しかし、溶融液からの育成では、育成温度が１１００℃以上の高温になり、主成分であるガリウムの蒸散が激しく、育成方向の組成変動が大きくなり、そのため結晶の捩れ、割れなどが発生する。このような理由で、従来技術では直径１インチ程度の結晶を得るのが限度であった。しかも、得られた結晶にはコアと呼ばれる不均一な部分が生じており、それらを除いた部分からファラデー素子を切り出すために、結晶中の利用可能領域が制限され、ファラデー素子材の収量が少なくなる欠点があった。そのため市販のＴＧＧ結晶は高価なものになっており、そのＴＧＧ結晶を用いた光アイソレータも高価なものになり、それが普及を妨げる要因となっている。   As a general method for producing a TGG crystal, a Czochralski method (CZ method) in which a seed crystal is attached to a raw material melted in a crucible and pulled while rotating is known. However, in the growth from the melt, the growth temperature becomes a high temperature of 1100 ° C. or higher, the gallium as the main component is transpirationed, the composition variation in the growth direction becomes large, and thus the crystal is twisted and cracked. For this reason, the limit of obtaining crystals with a diameter of about 1 inch is the limit in the prior art. In addition, the obtained crystal has a non-uniform portion called a core, and since the Faraday element is cut out from the portion other than the core, the usable area in the crystal is limited, and the yield of the Faraday element material is small. There was a drawback. Therefore, a commercially available TGG crystal is expensive, and an optical isolator using the TGG crystal is also expensive, which is a factor that hinders its spread.

最近、ＴＧＧ結晶で２価、４価の陽イオンを置換することにより、結晶性を改善することが試みられている（特許文献１参照）。それによれば、従来技術に比べて大型のＴＧＧ結晶が製造できるとされているが、それでも直径６０ｍｍ程度に止まっている。   Recently, attempts have been made to improve crystallinity by substituting divalent and tetravalent cations with TGG crystals (see Patent Document 1). According to this, it is said that a large TGG crystal can be manufactured as compared with the prior art, but it is still only about 60 mm in diameter.

このような改良にも関わらず、上記のようなＣＺ法によるＴＧＧ結晶の製造では、直径６０ｍｍ程度よりも大型の単結晶の育成は困難である。また、育成温度が高く、育成方向の組成変動が生じ易いなどの問題がある。   In spite of such improvements, it is difficult to grow single crystals larger than about 60 mm in diameter in the production of TGG crystals by the CZ method as described above. In addition, there is a problem that the growth temperature is high and composition variation in the growth direction is likely to occur.

なお、単結晶の他の育成方法としてＬＰＥ法があるが、現状では光学用として良好な特性を持つＴＧＧ結晶の製造手法は報告されていない。   As another method for growing a single crystal, there is an LPE method. However, at present, no method for producing a TGG crystal having good characteristics for optical use has been reported.

特開２００９−２２１０３５号公報JP 2009-221035 A

本発明が解決しようとする課題は、高品質で大型のＴＧＧ結晶を、安価に且つ容易に製造できるようにすることである。   The problem to be solved by the present invention is to enable high-quality and large-sized TGG crystals to be manufactured inexpensively and easily.

本発明は、ＧＧＧ結晶からなる基板上に、ＬＰＥ法で育成したＴＧＧ結晶であって、前記ＴＧＧ結晶は、組成Ｔｂ₃ Ｍ_x Ｇａ_5-x Ｏ₁₂で表され、前記ＭがＳｃ、Ｉｎから選ばれる少なくとも１種の３価元素であって０．１≦ｘ≦０．５を満たしており、且つ前記基板のＧＧＧ結晶と育成したＴＧＧ結晶の垂直方向の格子定数差が±０．０２Å以下となっていることを特徴とする常磁性ガーネット単結晶である。 The present invention is a TGG crystal grown by an LPE method on a substrate made of a GGG crystal, wherein the TGG crystal is represented by a composition Tb ₃ M _x Ga _5-x O ₁₂ , and the M is composed of Sc and In. At least one selected trivalent element that satisfies 0.1 ≦ x ≦ 0.5, and the difference in lattice constant between the GGG crystal of the substrate and the grown TGG crystal is ± 0.02０．０ or less It is a paramagnetic garnet single crystal characterized by

また本発明は、ＳＧＧＧ結晶からなる基板上に、ＬＰＥ法で育成したＴＧＧ結晶であって、前記ＴＧＧ結晶は、組成Ｔｂ₃ Ｍ_x Ｇａ_5-x Ｏ₁₂で表され、前記ＭがＳｃ、Ｉｎから選ばれる少なくとも１種の３価元素であって０．９≦ｘ≦１．６５を満たしており、且つ前記基板のＳＧＧＧ結晶と育成したＴＧＧ結晶の垂直方向の格子定数差が±０．０２Å以下となっていることを特徴とする常磁性ガーネット単結晶である。 The present invention is also a TGG crystal grown by an LPE method on a substrate made of SGGG crystal, wherein the TGG crystal is represented by a composition Tb ₃ M _x Ga _{5 -x} O ₁₂ , and the M is Sc, In The lattice constant difference in the vertical direction between the SGGG crystal of the substrate and the grown TGG crystal is ± 0.02Å, which is at least one trivalent element selected from It is a paramagnetic garnet single crystal characterized by:

更に本発明は、上記の常磁性ガーネット単結晶を製造する方法であって、Ｔｂ₄ Ｏ₇ 、Ｇａ₂ Ｏ₃ 、及びＭ₂ Ｏ₃ （但し、ＭはＳｃ、Ｉｎから選ばれる少なくとも１種）をガーネット原料、ＰｂＯ及びＢ₂ Ｏ₃ をフラックスとした融液の表面に、前記基板の片面を接触させ、８５０〜９８０℃でＴＧＧ結晶をＬＰＥ成長させる常磁性ガーネット単結晶の製造方法である。ここで前記融液中に、ＳｉＯ₂ 、ＧｅＯ₂ 、ＴｉＯ₂ から選ばれる１種以上の酸化物が含まれており、その重量濃度の合計が０．５ｗｔ％以下であるように調整されていてもよい。あるいは前記融液中にＣｅＯ₂ が含まれており、その重量濃度が０．２ｗｔ％以下であるように調整されていてもよい。 Furthermore, the present invention is a method for producing the above-mentioned paramagnetic garnet single crystal, wherein Tb ₄ O ₇ , Ga ₂ O ₃ , and M ₂ O ₃ (where M is at least one selected from Sc and In). Is a method for producing a paramagnetic garnet single crystal, in which one side of the substrate is brought into contact with the surface of a melt using garnet raw material, PbO and B ₂ O ₃ as a flux, and TGG crystal is grown by LPE at 850 to 980 ° C. Here, the melt contains one or more oxides selected from SiO ₂ , GeO ₂ and TiO _2, and the total weight concentration is adjusted to 0.5 wt% or less. Also good. Alternatively, CeO ₂ may be contained in the melt, and the weight concentration may be adjusted to be 0.2 wt% or less.

また本発明は、これらの常磁性ガーネット単結晶の製造方法によりＬＰＥ成長させたＴＧＧ結晶を、水素０．５〜６ｖｏｌ％を含む窒素との混合雰囲気下、４５０〜８００℃で還元処理する常磁性ガーネット単結晶の製造方法である。   In addition, the present invention is a paramagnetic method in which a TGG crystal grown by LPE by the method for producing a paramagnetic garnet single crystal is reduced at 450 to 800 ° C. in a mixed atmosphere with nitrogen containing 0.5 to 6 vol% of hydrogen. This is a method for producing a garnet single crystal.

本発明に係る常磁性ガーネット単結晶の製造方法は、ＧＧＧ基板またはＳＧＧＧ基板を用いてＬＰＥ法により育成する方法であるから、直径３インチ（７６ｍｍ程度）の大型で平板状のＴＧＧ結晶が得られる。本発明方法では、フラックスを用いた融液からＴＧＧ結晶を育成するので、育成温度を１０００℃未満に下げることができるため結晶成分のガリウム蒸散を抑えることができ、高品位の均質なＴＧＧ結晶が得られる。   Since the method for producing a paramagnetic garnet single crystal according to the present invention is a method for growing by a LPE method using a GGG substrate or an SGGG substrate, a large and flat TGG crystal having a diameter of 3 inches (about 76 mm) is obtained. . In the method of the present invention, since the TGG crystal is grown from the melt using the flux, the growth temperature can be lowered to less than 1000 ° C., so that gallium transpiration of the crystal component can be suppressed, and a high-quality homogeneous TGG crystal is obtained. can get.

本発明で基板として用いるＧＧＧ結晶はＹＩＧ育成用基板として、またＳＧＧＧ結晶はビスマス置換ガーネット結晶育成基板として使われており、入手が容易で安価であり、且つ３インチの大型基板が市販されている。それらの上にＴＧＧ結晶をＬＰＥ法によって育成するので、直径３インチの大型結晶が得られ、且つ結晶形状が板状であるため、切断や研磨が容易である。そのため、加工費まで含めたトータルコストを低く抑えることができる。これによって、光アイソレータ用ファラデー回転子に有用な安価なＴＧＧ結晶チップが得られる。   The GGG crystal used as a substrate in the present invention is used as a YIG growth substrate, and the SGGG crystal is used as a bismuth-substituted garnet crystal growth substrate. It is easy to obtain and inexpensive, and a 3-inch large substrate is commercially available. . Since the TGG crystal is grown on them by the LPE method, a large crystal having a diameter of 3 inches is obtained, and the crystal shape is plate-like, so that cutting and polishing are easy. Therefore, the total cost including the processing cost can be kept low. Thereby, an inexpensive TGG crystal chip useful for a Faraday rotator for an optical isolator can be obtained.

透過率スペクトルの還元温度依存性を示すグラフ。The graph which shows the reduction temperature dependence of the transmittance | permeability spectrum. 波長５３２ｎｍの透過率と還元温度との関係を示すグラフ。The graph which shows the relationship between the transmittance | permeability of wavelength 532nm, and reduction temperature. 波長５３２ｎｍの透過率と還元処理時の水素濃度との関係を示すグラフ。The graph which shows the relationship between the transmittance | permeability of wavelength 532nm, and the hydrogen concentration at the time of a reduction process. ＣｅＯ２添加融液から育成したＴＧＧ結晶の透過スペクトル。Transmission spectrum of TGG crystal grown from CeO2 added melt.

本発明は、ＧＧＧ結晶またはＳＧＧＧ結晶からなる基板上に、ＬＰＥ法で育成したＴＧＧ結晶であって、前記ＴＧＧ結晶は、組成Ｔｂ₃ Ｍ_x Ｇａ_5-x Ｏ₁₂で表され、前記ＭがＳｃ、Ｉｎから選ばれる少なくとも１種の３価元素である。基板がＧＧＧ結晶の場合には、前記ｘが０．１≦ｘ≦０．５を満たし、且つ前記基板のＧＧＧ結晶と育成したＴＧＧ結晶の垂直方向の格子定数差が±０．０２Å以下となるようにする。そこで、ＭがＳｃ単独の場合は前記ｘ量を０．１５≦ｘ≦０．５とし、ＭがＩｎ単独の場合は前記ｘ量を０．１≦ｘ≦０．４とする。また基板がＳＧＧＧ結晶の場合には、前記ｘが０．９≦ｘ≦１．６５を満たし、且つ前記基板のＳＧＧＧ結晶と育成したＴＧＧ結晶の垂直方向の格子定数差が±０．０２Å以下となるようにする。そこで、ＭがＳｃ単独の場合は前記ｘ量を１．２５≦ｘ≦１．６５とし、ＭがＩｎ単独の場合は前記ｘ量を０．９≦ｘ≦１．２５とする。 The present invention is a TGG crystal grown by an LPE method on a substrate made of GGG crystal or SGGG crystal, wherein the TGG crystal is represented by the composition Tb ₃ M _x Ga _5-x O ₁₂ , and the M is Sc. And at least one trivalent element selected from In. When the substrate is a GGG crystal, x satisfies 0.1 ≦ x ≦ 0.5, and the vertical lattice constant difference between the GGG crystal of the substrate and the grown TGG crystal is ± 0.02 ± or less. Like that. Therefore, when M is Sc alone, the x amount is 0.15 ≦ x ≦ 0.5, and when M is In alone, the x amount is 0.1 ≦ x ≦ 0.4. When the substrate is an SGGG crystal, x satisfies 0.9 ≦ x ≦ 1.65, and the vertical lattice constant difference between the SGGG crystal of the substrate and the grown TGG crystal is ± 0.02Å or less. To be. Therefore, when M is Sc alone, the x amount is 1.25 ≦ x ≦ 1.65, and when M is In alone, the x amount is 0.9 ≦ x ≦ 1.25.

ＧＧＧ結晶はＹＩＧ育成用基板として、ＳＧＧＧ結晶はビスマス置換ガーネット結晶育成基板として使われており、入手が容易で安価であり、しかも３インチの大型基板が市販されている。そのため、それらの上にＬＰＥ法によりＴＧＧ結晶を育成することで３インチの大型結晶が得られることになる。また、育成した結晶形状は平板状であるため、切断や研磨が容易であり、加工費まで含めたトータルコストを抑えることができる。   The GGG crystal is used as a YIG growth substrate, and the SGGG crystal is used as a bismuth-substituted garnet crystal growth substrate. It is easily available and inexpensive, and a large 3 inch substrate is commercially available. Therefore, a 3-inch large crystal can be obtained by growing a TGG crystal on them by the LPE method. Further, since the grown crystal shape is flat, cutting and polishing are easy, and the total cost including the processing cost can be suppressed.

ここで問題となるのは、それらＧＧＧ結晶あるいはＳＧＧＧ結晶からなる基板とＴＧＧ結晶とは格子定数が異なるということである。ＴＧＧ（Ｔｂ₃ Ｇａ₅ Ｏ₁₂）結晶の格子定数は１２．３４Åであり、ＧＧＧ結晶の格子定数は１２．３８Å、ＳＧＧＧ結晶の格子定数は１２．４９６±０．００３Åである。このように、ＴＧＧ結晶の格子定数は基板に比べて小さく、そのままではクラックや欠陥が生じて、膜厚数百ミクロン以上の良質な結晶は育成できない。そのため本発明では、イオン半径の大きな元素を置換して格子をマッチングさせる。 The problem here is that the lattice constant is different between the GGG crystal or the substrate made of SGGG crystal and the TGG crystal. The lattice constant of TGG (Tb ₃ Ga ₅ O ₁₂ ) crystal is 12.34Å, the lattice constant of GGG crystal is 12.38Å, and the lattice constant of SGGG crystal is 12.496 ± 0.003Å. Thus, the lattice constant of the TGG crystal is smaller than that of the substrate, and cracks and defects are generated as it is, and a high-quality crystal having a film thickness of several hundred microns or more cannot be grown. Therefore, in the present invention, the lattice is matched by replacing an element having a large ion radius.

ＴＧＧ結晶が属するガーネット構造には、酸素配位数が８｛Ｃ｝、６［ａ］、４（ｄ）の三つのサイトがある。ファラデー効果を有するＴｂ³⁺はＣサイトに配置されている。そのため、イオン半径の大きな元素をＣサイトのＴｂ³⁺と置換して格子定数を合わせることは好ましくない。これに対しＧａ³⁺は、ａ，ｄサイトに配置されている。ａサイト（６配位）に配置しているＧａ³⁺のイオン半径は０．６２Åである。そこで、Ｓｃ³⁺及び／又はＩｎ³⁺を置換して格子定数を大きくし、基板とマッチングさせることを試みた。因みに、Ｓｃ³⁺のイオン半径は０．７４５Å、Ｉｎ³⁺のイオン半径は０．８０Åである。 The garnet structure to which the TGG crystal belongs has three sites with oxygen coordination numbers of 8 {C}, 6 [a], and 4 (d). Tb ³⁺ having the Faraday effect is arranged at the C site. Therefore, it is not preferable to match the lattice constant by replacing an element having a large ionic radius with Tb ³⁺ at the C site. On the other hand, Ga ³⁺ is arranged at the a and d sites. The ionic radius of Ga ³⁺ arranged at the a site (6-coordinate) is 0.62Å. Therefore, an attempt was made to increase the lattice constant by substituting Sc ³⁺ and / or In ³⁺ and to match the substrate. Incidentally, the ion radius of Sc ³⁺ is 0.745Å, and the ion radius of In ³⁺ is 0.80Å.

本発明者が鋭意検討した結果、基板であるＧＧＧ結晶あるいはＳＧＧＧ結晶とＴＧＧ結晶膜の垂直方向の格子定数差が±０．０２Å以内であれば、膜厚２００μｍ以上の良質な結晶が得られることが判明した。そこで、上記のように、基板がＧＧＧ結晶の場合には、前記ｘが０．１≦ｘ≦０．５を満たすようにし、基板がＳＧＧＧ結晶の場合には、前記ｘが０．９≦ｘ≦１．６５を満たすようにして、上記格子定数差が±０．０２Å以内となるように基板とＴＧＧ結晶の格子をマッチングさせている。より好ましくは、上記格子定数差が±０．０１Å以内となるように基板とＴＧＧ結晶の格子をマッチングさせることである。そのためには、例えば基板がＧＧＧ結晶の場合は、前記ｘが０．２５≦ｘ≦０．４２を満たすようにする。これらの数値範囲は、後述する実施例についての実験結果から導き出されたものである。   As a result of intensive studies by the present inventors, if the difference in the lattice constant in the vertical direction between the GGG crystal or SGGG crystal as the substrate and the TGG crystal film is within ± 0.02 mm, a high-quality crystal having a thickness of 200 μm or more can be obtained. There was found. Therefore, as described above, when the substrate is a GGG crystal, x satisfies 0.1 ≦ x ≦ 0.5, and when the substrate is an SGGG crystal, x satisfies 0.9 ≦ x. In order to satisfy ≦ 1.65, the lattice of the substrate and the TGG crystal are matched so that the lattice constant difference is within ± 0.02Å. More preferably, the lattice of the substrate and the TGG crystal are matched so that the lattice constant difference is within ± 0.01 mm. For this purpose, for example, when the substrate is a GGG crystal, x satisfies 0.25 ≦ x ≦ 0.42. These numerical ranges are derived from the experimental results of the examples described later.

このような常磁性ガーネット単結晶の製造は、Ｔｂ₄ Ｏ₇ 、Ｇａ₂ Ｏ₃ 、及びＭ₂ Ｏ₃ （但し、ＭはＳｃ、Ｉｎから選ばれる少なくとも１種）をガーネット原料とし、ＰｂＯ及びＢ₂ Ｏ₃ をフラックスとした融液（メルト）の表面に、前記基板の片面を接触させ、８５０〜９８０℃でＴＧＧ結晶をＬＰＥ成長させる。これによって、ＧＧＧ結晶またはＳＧＧＧ結晶からなる基板上に、ＬＰＥ法により大型（例えば直径３インチ）の平板状のＴＧＧ結晶を容易に育成できる。この方法は、フラックスを用いた融液からＴＧＧ結晶を育成するので、育成温度を１０００℃未満に下げることができるため結晶成分のガリウム蒸散を抑えることができ、高品位の均質な単結晶が得られる。しかも大型の平板状ＴＧＧ結晶が得られるので、それを切断、研磨することにより、容易に安価なチップに加工することができる。 Such a paramagnetic garnet single crystal is produced by using Tb ₄ O ₇ , Ga ₂ O ₃ , and M ₂ O ₃ (wherein M is at least one selected from Sc and In) as a garnet raw material, and PbO and B One surface of the substrate is brought into contact with the surface of a melt (melt) using ₂ O ₃ as a flux, and TGG crystals are grown by LPE at 850 to 980 ° C. This makes it possible to easily grow a large-sized (eg, 3 inch diameter) flat TGG crystal on the substrate made of GGG crystal or SGGG crystal by the LPE method. Since this method grows TGG crystals from a melt using flux, the growth temperature can be lowered to less than 1000 ° C., so that gallium transpiration of crystal components can be suppressed, and a high-quality homogeneous single crystal can be obtained. It is done. Moreover, since a large flat TGG crystal is obtained, it can be easily processed into an inexpensive chip by cutting and polishing it.

ところが、このようにして育成したＴＧＧ結晶には着色が見られた。吸収スペクトルを測定したところ、波長１０００ｎｍ未満において吸収が生じていた。この場合でも、波長１０００ｎｍ以上で使用する用途では問題はなく、例えば、ＴＧＧ結晶の応用製品である光アイソレータの用途を想定した場合、発振波長が１０６４ｎｍであるＮｄ：ＹＡＧレーザー光源の反射戻り光対策用などには使用できる。しかし、波長１０００ｎｍ以下の吸収を低減して使用可能な波長範囲を広げることができれば、更に用途が広がる。   However, the TGG crystal grown in this manner was colored. When the absorption spectrum was measured, absorption occurred at a wavelength of less than 1000 nm. Even in this case, there is no problem in the application used at a wavelength of 1000 nm or more. For example, when an application of an optical isolator which is an application product of TGG crystal is assumed, a countermeasure against reflected return light of an Nd: YAG laser light source having an oscillation wavelength of 1064 nm Can be used for such purposes. However, if the usable wavelength range can be expanded by reducing the absorption at a wavelength of 1000 nm or less, the applications are further expanded.

まず、着色除去対策について種々試みた結果、ＴＧＧ結晶を育成した後、還元処理を実施することによって吸収を低減できることが判明した。因みに酸化処理では更に吸収が大きくなった。   First, as a result of various attempts at color removal measures, it was found that absorption can be reduced by carrying out a reduction treatment after growing a TGG crystal. Incidentally, the absorption was further increased by the oxidation treatment.

そこで、適切な条件を見出すため、還元処理について詳細に検討した。還元雰囲気を窒素ベースの水素２．７ｖｏｌ％含有雰囲気、還元時間を６時間に固定し、温度を変えてＴＧＧ結晶を還元処理した。還元処理前、還元温度４５０℃、７００℃での各吸収スペクトルを図１に示す。また、波長５３２ｎｍにおける透過率の還元温度依存性を図２に示す。なお、試料はＬＰＥ法により、３インチサイズのＧＧＧ基板上に育成したＴＧＧ結晶である。このＴＧＧ結晶は、基板との格子定数を合わせるためにガリウムの一部をスカンジウムに置換したＴｂ₃ （ＳｃＧａ）₅ Ｏ₁₂で表される結晶であり、育成膜厚は２．４ｍｍである。それを３ｍｍ角に切断し、基板を除去して３ｍｍ角の両面を鏡面に仕上げた。仕上げ膜厚は２．３２ｍｍである。そして、３ｍｍ角の面に垂直に光を入射して、透過スペクトルを測定している。 Therefore, in order to find appropriate conditions, the reduction process was examined in detail. The reducing atmosphere was a nitrogen-based atmosphere containing 2.7 vol% hydrogen, the reduction time was fixed at 6 hours, and the TGG crystals were reduced by changing the temperature. Each absorption spectrum at a reduction temperature of 450 ° C. and 700 ° C. before the reduction treatment is shown in FIG. Further, FIG. 2 shows the reduction temperature dependence of the transmittance at a wavelength of 532 nm. The sample is a TGG crystal grown on a 3-inch size GGG substrate by the LPE method. This TGG crystal is a crystal represented by Tb ₃ (ScGa) ₅ O _{12 in} which a part of gallium is substituted with scandium in order to match the lattice constant with the substrate, and the grown film thickness is 2.4 mm. It was cut into 3 mm square, the substrate was removed, and both sides of 3 mm square were finished as mirror surfaces. The finished film thickness is 2.32 mm. Then, light is incident perpendicularly to a 3 mm square surface, and a transmission spectrum is measured.

還元温度が４００℃以下では透過率は殆ど変わらなかった。しかし、４５０℃以上では顕著な透過率の向上が見られた。また、８００℃では僅かに膜表面の荒れが見られ、透過率が少し低下した。この程度であれば問題ないが、８００℃を超える温度では、更に荒れが進行するため好ましくない。これにより、還元温度は４５０℃以上８００℃以下が適当である。   When the reduction temperature was 400 ° C. or lower, the transmittance was hardly changed. However, a remarkable improvement in transmittance was observed at 450 ° C. or higher. Further, at 800 ° C., the film surface was slightly roughened, and the transmittance slightly decreased. If it is about this level, there is no problem, but a temperature exceeding 800 ° C. is not preferable because the roughness further proceeds. Thereby, the reduction temperature is suitably 450 ° C. or higher and 800 ° C. or lower.

更に、還元雰囲気依存性を検討した結果を図３に示す。今度は還元温度を７００℃、還元時間を６時間に固定し、窒素中の水素濃度と５３２ｎｍにおける透過率の関係を調査した。その結果、水素濃度が０．５ｖｏｌ％未満では透過率の向上が小さく、また、６ｖｏｌ％を超えると透過率の低下が見られた。このことから、水素濃度は０．５ｖｏｌ％以上６ｖｏｌ％以下が好ましい。   Further, FIG. 3 shows the result of studying the dependency on the reducing atmosphere. This time, the reduction temperature was fixed at 700 ° C. and the reduction time was fixed at 6 hours, and the relationship between the hydrogen concentration in nitrogen and the transmittance at 532 nm was investigated. As a result, when the hydrogen concentration was less than 0.5 vol%, the improvement in transmittance was small, and when it exceeded 6 vol%, the transmittance was decreased. Therefore, the hydrogen concentration is preferably 0.5 vol% or more and 6 vol% or less.

還元処理によって吸収が低減した原因は、３価と４価が安定なテルビウムのＴｂ⁴⁺がＴｂ³⁺に還元されたためと考えられ、吸収要因はＴｂ⁴⁺であると推察された。だとすれば、Ｔｂ⁴⁺が結晶中に取り込まれることを妨げることによっても、吸収を低減することが可能と考えられる。そもそもＴｂ⁴⁺は、電荷補償効果によりＰｂ²⁺とセットで結晶中に取り込まれるものと推測される。何故なら、ガーネット結晶の陽イオンは３価において、酸素の陰イオンと静電的バランスが採れるからである。ここで、Ｐｂ²⁺はフラックスとして必須の元素であり、その一部が結晶中に取り込まれることは不可避である。ならば、Ｐｂ²⁺とセットで取り込まれる４価の陽イオンを故意にメルト（融液）中に仕込めば、そのイオンとＰｂ²⁺がセットで結晶中に取り込まれ、Ｔｂ⁴⁺の混入を抑制できると考えられた。 The reason why the absorption was reduced by the reduction treatment was thought to be that the trivalent and tetravalent stable terbium Tb ⁴⁺ was reduced to Tb ³⁺ , and the absorption factor was assumed to be Tb ⁴⁺ . If so, it is considered that absorption can be reduced also by preventing Tb ⁴⁺ from being taken into the crystal. In the first place, Tb ⁴⁺ is presumed to be taken into the crystal as a set together with Pb ²⁺ due to the charge compensation effect. This is because the cation of the garnet crystal is trivalent and can be electrostatically balanced with the anion of oxygen. Here, Pb ²⁺ is an essential element as a flux, and it is inevitable that a part of it is taken into the crystal. Then, if a tetravalent cation taken in the set with Pb ²⁺ is intentionally charged into the melt (melt), the ions and Pb ²⁺ are taken into the crystal as a set, and the mixing of Tb ⁴⁺ It was thought that it could be suppressed.

そこで着色防止対策として、融液中に４価の陽イオンとしてＣｅ⁴⁺、Ｓｉ⁴⁺、Ｇｅ⁴⁺、Ｔｉ⁴⁺を添加してＴＧＧ結晶を育成したところ着色が低減した。例えば、上記Ｔｂ₃ （ＳｃＧａ）₅ Ｏ₁₂を作製した原料にＣｅＯ₂ を０．２ｗｔ％添加し、ＧＧＧ基板上にＴｂ₃ （ＳｃＧａ）₅ Ｏ₁₂結晶を育成して、透過率スペクトルを測定した結果を図３に示す。なお、試料は厚さ２．３２ｍｍであり、光入出射面に反射防止膜は施されていない。図３より、透過率が向上したことが分かる。ここでＣｅＯ₂ 添加量を０．６ｗｔ％に増加したところ、メルトに溶け込まない不溶物が浮遊した（後述する比較例１３参照）。浮遊物は欠陥原因となる可能性があり、多すぎる添加は好ましくない。 Therefore, as a measure for preventing coloring, when a TGG crystal was grown by adding Ce ⁴⁺ , Si ⁴⁺ , Ge ⁴⁺ , Ti ⁴⁺ as tetravalent cations in the melt, coloring was reduced. For example, 0.2 wt% of CeO ₂ was added to the raw material from which the Tb ₃ (ScGa) ₅ O ₁₂ was produced, and a Tb ₃ (ScGa) ₅ O ₁₂ crystal was grown on the GGG substrate, and the transmittance spectrum was measured. The results are shown in FIG. The sample has a thickness of 2.32 mm, and no antireflection film is applied to the light incident / exit surface. FIG. 3 shows that the transmittance is improved. Here, when the amount of CeO ₂ added was increased to 0.6 wt%, insoluble matter that did not dissolve in the melt floated (see Comparative Example 13 described later). Floating substances can cause defects, and adding too much is not preferable.

ＳｉＯ₂ を添加した場合も、ＣｅＯ₂ と同様に、添加することにより波長５３２ｎｍにおける透過率が向上した。しかし、添加ＳｉＯ₂ 濃度が０．５ｗｔ％で成長速度の低下が見られ、３ｗｔ％では膜が育成されなかった。これより、ＳｉＯ₂ の添加量は０．５ｗｔ％以下が好ましい。ＧｅＯ₂ とＴｉＯ₂ においても、ＳｉＯ₂ と同様の効果が見られた。このような手法は、還元処理が不要となるため、波長１０００ｎｍ以下で用いるファラデー素子のコストダウンを図るのに有効である。 Also when SiO ₂ was added, the transmittance at a wavelength of 532 nm was improved by adding it as in CeO ₂ . However, the growth rate decreased when the added SiO ₂ concentration was 0.5 wt%, and the film was not grown at 3 wt%. Accordingly, the addition amount of SiO ₂ is preferably 0.5 wt% or less. In GeO ₂ and TiO ₂ , the same effect as in SiO ₂ was observed. Such a method is effective for reducing the cost of a Faraday element used at a wavelength of 1000 nm or less because no reduction treatment is required.

以上のように、Ｔｂ₃ Ｇａ₅ Ｏ₁₂をベース組成とし、それに格子定数の大きなＳｃやＩｎを置換し、ＧＧＧ基板やＳＧＧＧ基板との垂直方向の格子定数差を±０．０２Å以下にすることにより、ＬＰＥ法により高品質なＴＧＧ結晶を作製できた。また、作製されたＴＧＧ結晶を水素濃度０．５〜６ｖｏｌ％を含む窒素雰囲気下、４５０〜８００℃で還元することにより、ほぼ無色にすることができた。更に、予め４価の陽イオンとなる化合物をメルト中に加えておくことにより、As-grownのＴＧＧ結晶の可視光域吸収を低減できた。 As described above, Tb ₃ Ga ₅ O ₁₂ is used as the base composition, and Sc and In having a large lattice constant are substituted for it, so that the difference in the lattice constant in the vertical direction with respect to the GGG substrate and the SGGG substrate is ± 0.02Å or less. Thus, a high quality TGG crystal could be produced by the LPE method. Further, the produced TGG crystal could be made almost colorless by reducing it at 450 to 800 ° C. in a nitrogen atmosphere containing a hydrogen concentration of 0.5 to 6 vol%. Further, by adding a compound that becomes a tetravalent cation in advance to the melt, the absorption of visible light in the As-grown TGG crystal can be reduced.

＜実施例１〜５＞
Ｔｂ₄ Ｏ₇ 、Ｓｃ₂ Ｏ₃ 、及びＧａ₂ Ｏ₃ をガーネット原料とし、ＰｂＯとＢ₂ Ｏ₃ をフラックスとする出発原料を白金坩堝に入れ、縦型の抵抗加熱炉中で、１１００℃で５時間加熱溶融し、その後、同じ１１００℃で１時間攪拌した。次いで８８０℃に降温し、格子定数が１２．３８ÅのＧＧＧ基板（Ｇｄ₃ Ｇａ₅ Ｏ₁₂）の小片を４０ｒｐｍで回転させながら２分間浸して引き上げ、炉から取り出した。続いて、直径３インチ、厚み５００μｍのＧＧＧ基板を炉に入れ、片面を白金坩堝内メルト液面に浸し、４０ｒｐｍで回転させた。所定時間経過後、メルト液面より１０ｍｍ引き上げて切り離し、そのまま炉の中で室温まで冷却した。その後、ＧＧＧ基板を炉から取り出し酸洗浄した。 <Examples 1-5>
Starting materials using Tb ₄ O ₇ , Sc ₂ O ₃ , and Ga ₂ O ₃ as garnet raw materials and PbO and B ₂ O ₃ as fluxes are put in a platinum crucible and placed in a vertical resistance heating furnace at 1100 ° C. The mixture was melted by heating for 5 hours and then stirred at the same 1100 ° C. for 1 hour. Next, the temperature was lowered to 880 ° C., a small piece of a GGG substrate (Gd ₃ Ga ₅ O ₁₂ ) having a lattice constant of 12.38 Å was immersed for 2 minutes while rotating at 40 rpm, and taken out from the furnace. Subsequently, a GGG substrate having a diameter of 3 inches and a thickness of 500 μm was placed in a furnace, and one surface was immersed in the melt liquid surface in the platinum crucible and rotated at 40 rpm. After a lapse of a predetermined time, the melt was pulled up 10 mm from the surface of the melt and separated, and then cooled as it was to room temperature in a furnace. Thereafter, the GGG substrate was taken out of the furnace and acid cleaned.

ＧＧＧ小片、及び３インチＧＧＧ基板には、その（１１１）面上に組成がＴｂ₃ Ｓｃ_x Ｇａ_5-x Ｏ₁₂で表されるガーネット結晶が成長していた。この作業を、主に出発原料のＳｃ₂ Ｏ₃ 濃度を変えて繰り返し行った。実施例１から５に向かって、Ｓｃ₂ Ｏ₃ 濃度を高くしている。 In the GGG piece and the 3-inch GGG substrate, a garnet crystal having a composition represented by Tb ₃ Sc _x Ga _5-x O ₁₂ was grown on the (111) plane. This operation was repeated mainly by changing the Sc ₂ O ₃ concentration of the starting material. From Example 1 to Example 5, the Sc ₂ O ₃ concentration is increased.

ＧＧＧ小片を用いて、Ｘ線回折法により育成したＴＧＧ結晶とＧＧＧ結晶の育成面垂直方向の格子定数差Δａ（ＴＧＧ結晶格子定数−ＧＧＧ結晶格子定数）を測定した。また、３インチＧＧＧ基板付ＴＧＧ結晶は、３ｍｍ角に切断し、研磨によりＧＧＧ基板を削除して両面を鏡面加工し、３ｍｍ角チップとした。この３ｍｍ角チップの面に垂直方向に光を通し、透過率（波長５３２ｎｍと１０６４ｎｍ）、ベルデ定数（１０６４ｎｍ）と消光比（１０６４ｎｍ）を測定した。また、３ｍｍ角チップを用いて、ＥＰＭＡ（電子線マイクロアナライザ）により、組成分析した。   Using a GGG piece, the difference in lattice constant Δa between the TGG crystal grown by the X-ray diffraction method and the GGG crystal in the vertical direction of the growth plane (TGG crystal lattice constant−GGG crystal lattice constant) was measured. Further, the TGG crystal with a 3-inch GGG substrate was cut into 3 mm squares, the GGG substrate was removed by polishing, and both surfaces were mirror-finished to obtain 3 mm square chips. Light was passed in the direction perpendicular to the surface of the 3 mm square chip, and the transmittance (wavelengths 532 nm and 1064 nm), the Verde constant (1064 nm) and the extinction ratio (1064 nm) were measured. The composition was analyzed by EPMA (electron beam microanalyzer) using a 3 mm square chip.

表１に、育成時間、育成膜厚、育成面垂直方向の格子定数差、育成されたガーネット結晶の欠陥、亀裂の検査結果を示す。また表２に、３ｍｍ角チップの加工後の膜厚、光透過率、ベルデ定数、消光比の測定結果を示す。   Table 1 shows the inspection results of growth time, growth film thickness, lattice constant difference in the vertical direction of the growth surface, defects of the grown garnet crystal, and cracks. Table 2 shows the measurement results of film thickness, light transmittance, Verde constant, and extinction ratio after processing of a 3 mm square chip.

これらの結果から、育成したＴＧＧ結晶は、いずれも格子定数差が±０．０２Å以内に収まっており、欠陥及び亀裂が少なく、良好であった。また、波長１０６４ｎｍにおける透過率は８０％を超えており、ベルデ定数は０．１２ｍｉｎ／（Ｏｅ・ｃｍ）、消光比４０ｄＢであり、いずれも良好であった。   From these results, all the grown TGG crystals had good lattice constant differences within ± 0.02 mm, few defects and cracks. Further, the transmittance at a wavelength of 1064 nm exceeded 80%, the Verde constant was 0.12 min / (Oe · cm), and the extinction ratio was 40 dB.

＜比較例１〜３＞
実施例１〜５と同様に、ＬＰＥ法によりＴＧＧ結晶の育成を行った。比較例１は出発原料にＳｃ₂ Ｏ₃ を含まないものである。また、比較例２は実施例１よりもＳｃ₂ Ｏ₃ 濃度が低く、比較例３は実施例５よりもＳｃ₂ Ｏ₃ 濃度が高い。検査結果を前記表１に実施例１〜５と併せて示す。比較例１〜３では、育成されたＴＧＧ結晶とＧＧＧ基板の格子定数差はいずれも、±０．０２Åを超えており、育成した結晶には欠陥や亀裂が多数認められた。 <Comparative Examples 1-3>
As in Examples 1 to 5, TGG crystals were grown by the LPE method. In Comparative Example 1, the starting material does not contain Sc ₂ O ₃ . Comparative Example 2 has a lower Sc ₂ O ₃ concentration than Example 1, and Comparative Example 3 has a higher Sc ₂ O ₃ concentration than Example 5. The test results are shown in Table 1 together with Examples 1-5. In Comparative Examples 1 to 3, the difference in lattice constant between the grown TGG crystal and the GGG substrate exceeded ± 0.02%, and many defects and cracks were observed in the grown crystal.

＜実施例６〜８＞
出発原料がＴｂ₄ Ｏ₇ 、Ｉｎ₂ Ｏ₃ 、Ｇａ₂ Ｏ₃ 、ＰｂＯ、Ｂ₂ Ｏ₃ である以外は実施例１〜５と同様の手法でＴＧＧ結晶を育成した。育成したＴＧＧ結晶の検査結果を表３に示す。 <Examples 6 to 8>
TGG crystals were grown in the same manner as in Examples 1 to 5 except that the starting materials were Tb ₄ O ₇ , In ₂ O ₃ , Ga ₂ O ₃ , PbO, and B ₂ O ₃ . Table 3 shows the inspection results of the grown TGG crystal.

いずれも格子定数差は±０．０２Å以内であり、欠陥あるいは亀裂の少ない良好なＴＧＧ結晶が得られた。また、波長１０６４ｎｍにおける光学特性も、透過率は８０％を超えており、ベルデ定数は０．１２ｍｉｎ／（Ｏｅ・ｃｍ）、消光比４０ｄＢであって、いずれも良好であった。   In either case, the difference in lattice constant was within ± 0.02%, and a good TGG crystal with few defects or cracks was obtained. Also, the optical characteristics at a wavelength of 1064 nm were good, with the transmittance exceeding 80%, the Verde constant being 0.12 min / (Oe · cm), and the extinction ratio of 40 dB.

＜比較例４〜５＞
実施例６〜８と同様に、ＬＰＥ法によるＴＧＧ結晶の育成を行った。比較例４は実施例６よりもＩｎ₂ Ｏ₃ 濃度が低く、比較例５は実施例８よりもＩｎ₂ Ｏ₃ 濃度が高い。検査結果を前記表３に実施例６〜８と併せて示す。いずれも、育成されたＴＧＧ結晶とＧＧＧ基板の格子定数差は±０．０２Åを超えており、育成された結晶には欠陥や亀裂が多数認められた。 <Comparative Examples 4-5>
Similarly to Examples 6-8, TGG crystals were grown by the LPE method. Comparative Example 4 has a lower In ₂ O ₃ concentration than Example 6, and Comparative Example 5 has a higher In ₂ O ₃ concentration than Example 8. The test results are shown in Table 3 together with Examples 6-8. In both cases, the difference in lattice constant between the grown TGG crystal and the GGG substrate exceeded ± 0.02%, and many defects and cracks were observed in the grown crystal.

＜実施例９〜１１＞
出発原料がＴｂ₄ Ｏ₇ 、Ｓｃ₂ Ｏ₃ 、Ｉｎ₂ Ｏ₃ 、Ｇａ₂ Ｏ₃ 、ＰｂＯ、Ｂ₂ Ｏ₃ である以外は実施例１〜５と同様の手法によってＴＧＧ結晶を育成した。つまり、Ｓｃ₂ Ｏ₃ とＩｎ₂ Ｏ₃ の同時添加の例である。育成したＴＧＧ結晶の検査結果を表４に示す。いずれも格子定数差が±０．０２Å以内であり、欠陥、亀裂の少ない良好なＴＧＧ結晶が得られた。また、波長１０６４ｎｍにおける光学特性も、透過率は８０％を超えており、ベルデ定数は０．１２ｍｉｎ／（Ｏｅ・ｃｍ）、消光比４０ｄＢであって、いずれも良好であった。 <Examples 9 to 11>
A TGG crystal was grown by the same method as in Examples 1 to 5 except that the starting materials were Tb ₄ O ₇ , Sc ₂ O ₃ , In ₂ O ₃ , Ga ₂ O ₃ , PbO, and B ₂ O ₃ . That is, this is an example of simultaneous addition of Sc ₂ O ₃ and In ₂ O ₃ . Table 4 shows the inspection results of the grown TGG crystal. In all cases, the difference in lattice constant was within ± 0.02%, and a good TGG crystal with few defects and cracks was obtained. Also, the optical characteristics at a wavelength of 1064 nm were good, with the transmittance exceeding 80%, the Verde constant being 0.12 min / (Oe · cm), and the extinction ratio of 40 dB.

これらの結果より、ＳｃとＩｎが同時に置換されていても、格子定数差が±０．０２Å以内であれば良好な結晶が得られることが分かる。基板との格子定数差を±０．０２Å以内にする場合、Ｓｃ（置換量ｙ）とＩｎ（置換量ｚ）の合計置換量ｘの下限は、イオン半径の大きなＩｎが主に置換される場合である。Ｉｎだけが置換される場合はＩｎが０．１atoms/f.u.で格子定数差が−０．０２Åとなることから、ＩｎとＳｃの同時置換ではＩｎが主に置換され、そこに僅かにＳｃが置換された場合が、格子定数差の下限となり、両者の合計置換量ｘは０．１を僅かに上回るものになる。これとは反対に、ＳｃとＩｎの合計置換量ｘの上限は、イオン半径の小さいＳｃが主に置換され、そこにＩｎが僅かに置換された場合なので、両者の合計置換量は０．５を僅かに下回るものになる。   From these results, it can be seen that even if Sc and In are simultaneously substituted, a good crystal can be obtained as long as the difference in lattice constant is within ± 0.02%. When the difference in lattice constant from the substrate is within ± 0.02 mm, the lower limit of the total substitution amount x of Sc (substitution amount y) and In (substitution amount z) is when In having a large ionic radius is mainly substituted. It is. When only In is substituted, In is 0.1 atoms / fu and the lattice constant difference is −0.02Å. In the simultaneous substitution of In and Sc, In is mainly substituted, and there is a slight substitution of Sc. When this is done, it becomes the lower limit of the difference in lattice constant, and the total substitution amount x of both slightly exceeds 0.1. On the contrary, since the upper limit of the total substitution amount x of Sc and In is the case where Sc having a small ionic radius is mainly substituted and In is slightly substituted there, the total substitution amount of both is 0.5. Will be slightly below.

＜実施例１２〜１４＞
Ｔｂ₄ Ｏ₇ 、Ｓｃ₂ Ｏ₃ 、Ｇａ₂ Ｏ₃ 、ＰｂＯ、Ｂ₂ Ｏ₃ からなる出発原料を白金坩堝に入れ、縦型の抵抗加熱炉中で、１１００℃で５時間加熱溶融し、その後、同じ１１００℃で１時間攪拌した。次いで、９６０℃に降温し、格子定数が１２．４９６ÅのＳＧＧＧ基板［（ＣａＧｄ）₃ （ＭｇＺｒＧａ）₅ Ｏ₁₂］の小片を４０ｒｐｍで回転させながら２分間浸し引き上げ、炉から取り出した。続いて、直径３インチ、厚み５００μｍのＳＧＧＧ基板を炉に入れ、片面を白金坩堝内メルト液面に浸し、４０ｒｐｍで回転させた。所定時間経過後、メルト液面より１０ｍｍ引き上げて切り離し、そのまま炉の中で室温まで冷却した。その後、ＳＧＧＧ基板を炉から取り出し酸洗浄した。ＳＧＧＧ小片、及び３インチＳＧＧＧ基板には、その（１１１）面上に組成がＴｂ₃ Ｓｃ_x Ｇａ_5-x Ｏ₁₂で表されるＴＧＧ結晶が成長していた。この作業を、主に出発原料のＳｃ₂ Ｏ₃ 濃度を変えて繰り返し行った。実施例１２から１４に向かって、Ｓｃ₂ Ｏ₃ 濃度が高くなっている。 <Examples 12 to 14>
A starting material composed of Tb ₄ O ₇ , Sc ₂ O ₃ , Ga ₂ O ₃ , PbO, B ₂ O ₃ is placed in a platinum crucible and heated and melted at 1100 ° C. for 5 hours in a vertical resistance heating furnace. The mixture was stirred at the same 1100 ° C. for 1 hour. Next, the temperature was lowered to 960 ° C., a small piece of SGGG substrate [(CaGd) ₃ (MgZrGa) ₅ O ₁₂ ] having a lattice constant of 12.496 Å was immersed for 2 minutes while rotating at 40 rpm, and taken out from the furnace. Subsequently, an SGGG substrate having a diameter of 3 inches and a thickness of 500 μm was placed in a furnace, and one surface was immersed in the melt liquid surface in the platinum crucible and rotated at 40 rpm. After a lapse of a predetermined time, the melt was pulled up 10 mm from the surface of the melt and separated, and then cooled as it was to room temperature in a furnace. Thereafter, the SGGG substrate was taken out of the furnace and acid cleaned. In the SGGG piece and the 3-inch SGGG substrate, a TGG crystal having a composition represented by Tb ₃ Sc _x Ga _5-x O ₁₂ was grown on the (111) plane. This operation was repeated mainly by changing the Sc ₂ O ₃ concentration of the starting material. From Example 12 to 14, the Sc ₂ O ₃ concentration increases.

得られたＴＧＧ結晶について、実施例１〜５と同様に処理し、評価を行った。表５に、育成時間、育成膜厚、育成面垂直方向の格子定数差、育成されたガーネット結晶の欠陥、亀裂の検査結果を示す。育成したＴＧＧ結晶は、ＳＧＧＧ基板との格子定数差が±０．０２Å以内であり、欠陥、亀裂が少なく、良好であった。また、波長１０６４ｎｍにおける透過率は８０％を超えており、ベルデ定数は０．１２ｍｉｎ／（Ｏｅ・ｃｍ）、消光比４０ｄＢであって、いずれも良好であった。   About the obtained TGG crystal, it processed similarly to Examples 1-5, and evaluated. Table 5 shows the inspection results of the growth time, the growth film thickness, the lattice constant difference in the vertical direction of the growth surface, the defects of the grown garnet crystal, and cracks. The grown TGG crystal had a difference in lattice constant with the SGGG substrate of ± 0.02 mm or less and was good with few defects and cracks. Further, the transmittance at a wavelength of 1064 nm exceeded 80%, the Verde constant was 0.12 min / (Oe · cm), and the extinction ratio was 40 dB.

＜比較例６〜７＞
実施例１２〜１４と同様に、ＬＰＥ法によるＴＧＧ結晶の育成を行った。比較例６は実施例１２よりもＳｃ₂ Ｏ₃ 濃度が低く、比較例７は実施例１４よりもＳｃ₂ Ｏ₃ 濃度が高くなっている。これらの場合も、検査結果を前記表５に実施例１２〜１４と併せて示す。いずれも育成したＴＧＧ結晶とＳＧＧＧ基板の格子定数差は±０．０２Åを超えており、ＴＧＧ結晶には欠陥や亀裂が多数生じていた。 <Comparative Examples 6-7>
Similarly to Examples 12 to 14, TGG crystals were grown by the LPE method. Comparative Example 6 has a lower Sc ₂ O ₃ concentration than Example 12, and Comparative Example 7 has a higher Sc ₂ O ₃ concentration than Example 14. In these cases, the test results are shown in Table 5 together with Examples 12-14. In either case, the difference in lattice constant between the grown TGG crystal and the SGGG substrate exceeded ± 0.02%, and many defects and cracks were generated in the TGG crystal.

＜実施例１５〜１７＞
出発原料が、Ｔｂ₄ Ｏ₇ 、Ｉｎ₂ Ｏ₃ 、Ｇａ₂ Ｏ₃ 、ＰｂＯ、Ｂ₂ Ｏ₃ である以外は実施例１２〜１４と同様である。育成したＴＧＧ結晶の検査結果を表６に示す。いずれも格子定数差が±０．０２Å以内であり、欠陥や亀裂の少ない良好なＴＧＧ結晶が得られた。また、波長１０６４ｎｍにおける光学特性も、透過率は８０％を超えており、ベルデ定数は０．１２ｍｉｎ／（Ｏｅ・ｃｍ）、消光比４０ｄＢであって、いずれも良好であった。 <Examples 15 to 17>
The same as in Examples 12 to 14 except that the starting materials were Tb ₄ O ₇ , In ₂ O ₃ , Ga ₂ O ₃ , PbO, B ₂ O ₃ . Table 6 shows the test results of the grown TGG crystal. In either case, the lattice constant difference was within ± 0.02 mm, and a good TGG crystal with few defects and cracks was obtained. Also, the optical characteristics at a wavelength of 1064 nm were good, with the transmittance exceeding 80%, the Verde constant being 0.12 min / (Oe · cm), and the extinction ratio of 40 dB.

＜比較例８〜９＞
実施例１２〜１４と同様に、ＬＰＥ法によるＴＧＧ結晶の育成を行った。比較例８は実施例１５よりもＩｎ₂ Ｏ₃ 濃度が低く、比較例９は実施例１７よりもＩｎ₂ Ｏ₃ 濃度が高くなっている。検査結果を前記表６に実施例１５〜１７と併せて示す。いずれも、育成されたガーネット結晶とＳＧＧＧ基板の格子定数差は±０．０２Åを超えており、育成された結晶には欠陥や亀裂が多数生じていた。 <Comparative Examples 8-9>
Similarly to Examples 12 to 14, TGG crystals were grown by the LPE method. Comparative Example 8 has a lower In ₂ O ₃ concentration than Example 15, and Comparative Example 9 has a higher In ₂ O ₃ concentration than Example 17. The test results are shown in Table 6 together with Examples 15-17. In either case, the difference in lattice constant between the grown garnet crystal and the SGGG substrate exceeded ± 0.02%, and the grown crystal had many defects and cracks.

＜実施例１８〜２０＞
出発原料が、Ｔｂ₄ Ｏ₇ 、Ｓｃ₂ Ｏ₃ 、Ｉｎ₂ Ｏ₃ 、Ｇａ₂ Ｏ₃ 、ＰｂＯ、Ｂ₂ Ｏ₃ である以外は実施例１２〜１４と同様である。つまり、Ｓｃ₂ Ｏ₃ とＩｎ₂ Ｏ₃ の同時添加の例である。育成したＴＧＧ結晶の検査結果を表７に示す。いずれの例も、格子定数差は±０．０２Å以内であり、欠陥、亀裂の少ない良好なＴＧＧ結晶が得られた。また、波長１０６４ｎｍにおける光学特性も、透過率は８０％を超えており、ベルデ定数は０．１２ｍｉｎ／（Ｏｅ・ｃｍ）、消光比４０ｄＢであり、いずれも良好であった。 <Examples 18 to 20>
The same as in Examples 12 to 14 except that the starting materials were Tb ₄ O ₇ , Sc ₂ O ₃ , In ₂ O ₃ , Ga ₂ O ₃ , PbO, B ₂ O ₃ . That is, this is an example of simultaneous addition of Sc ₂ O ₃ and In ₂ O ₃ . Table 7 shows the test results of the grown TGG crystal. In each example, the difference in lattice constant was within ± 0.02 mm, and a good TGG crystal with few defects and cracks was obtained. Also, the optical characteristics at a wavelength of 1064 nm were good, with the transmittance exceeding 80%, the Verde constant being 0.12 min / (Oe · cm), and the extinction ratio of 40 dB.

この結果から、ＳｃとＩｎが同時に置換されていても、格子定数差が±０．０２Å以内であれば良好なＴＧＧ結晶が得られることがわかる。基板との格子定数差を±０．０２Å以内にする場合、Ｓｃ（置換量ｙ）とＩｎ（置換量ｚ）の合計置換量ｘの下限はイオン半径の大きなＩｎが主に置換される場合であり、Ｉｎだけが置換される場合はＩｎが０．９atoms/f.u.で格子定数差が−０．０２Åとなることから、ＩｎとＳｃの同時置換では、Ｉｎが主に置換され、そこに僅かにＳｃが置換された場合が、格子定数差の下限となり、両者の合計置換量は０．９を僅かに上回るものになる。これとは反対に、ＳｃとＩｎの合計置換量ｘの上限は、イオン半径の小さいＳｃが主に置換され、そこにＩｎが僅かに置換された場合なので、両者の合計置換量は１．６５を僅かに下回るものになる。   From this result, it can be seen that even if Sc and In are simultaneously substituted, a good TGG crystal can be obtained if the difference in lattice constant is within ± 0.02 mm. When the difference in lattice constant from the substrate is within ± 0.02 mm, the lower limit of the total substitution amount x of Sc (substitution amount y) and In (substitution amount z) is when In having a large ionic radius is mainly substituted. Yes, when only In is substituted, In is 0.9 atoms / fu and the lattice constant difference is -0.02Å. In the simultaneous substitution of In and Sc, In is mainly substituted, When Sc is substituted, it becomes the lower limit of the difference in lattice constant, and the total substitution amount of both becomes slightly higher than 0.9. On the contrary, since the upper limit of the total substitution amount x of Sc and In is the case where Sc having a small ionic radius is mainly substituted and In is slightly substituted therefor, the total substitution amount of both is 1.65. Will be slightly below.

＜実施例２１〜２４および比較例１０＞
実施例３で作製した３ｍｍ角チップを、水素含有量が２．７ｖｏｌ％の窒素雰囲気中で温度を変えて、６時間保持し還元処理した。還元処理後、波長５３２ｎｍにおける透過率を測定した。結果を表８に示す。実施例２１〜２４では、波長５３２ｎｍの透過率が向上した。特に還元温度が５５０〜８００℃では波長５３２ｎｍの透過率が大幅に向上した。これに対し、比較例１０ではあまり変わらなかった。 <Examples 21 to 24 and Comparative Example 10>
The 3 mm square chip produced in Example 3 was reduced for 6 hours by changing the temperature in a nitrogen atmosphere with a hydrogen content of 2.7 vol%. After the reduction treatment, the transmittance at a wavelength of 532 nm was measured. The results are shown in Table 8. In Examples 21 to 24, the transmittance at a wavelength of 532 nm was improved. In particular, when the reduction temperature was 550 to 800 ° C., the transmittance at a wavelength of 532 nm was greatly improved. In contrast, Comparative Example 10 did not change much.

＜実施例２５〜２７および比較例１１〜１２＞
実施例３で作製した３ｍｍ角チップを、水素と窒素の混合ガス中で、混合ガス中の水素濃度を変えて、温度７００℃、保持時間６時間で還元処理した。還元処理後、波長５３２ｎｍにおける透過率を測定した。結果を表９に示す。実施例２５〜２７では、波長５３２ｎｍの透過率が大きく向上した。これに対し、比較例１１ではあまり変わらなかった。また、比較例１２では、膜表面が荒れていた。このことから、水素濃度は０．５ｖｏｌ％以上６ｖｏｌ％以下が適当である。 <Examples 25-27 and Comparative Examples 11-12>
The 3 mm square chip produced in Example 3 was reduced in a mixed gas of hydrogen and nitrogen while changing the hydrogen concentration in the mixed gas at a temperature of 700 ° C. and a holding time of 6 hours. After the reduction treatment, the transmittance at a wavelength of 532 nm was measured. The results are shown in Table 9. In Examples 25 to 27, the transmittance at a wavelength of 532 nm was greatly improved. In contrast, Comparative Example 11 did not change much. In Comparative Example 12, the film surface was rough. From this, the hydrogen concentration is suitably 0.5 vol% or more and 6 vol% or less.

＜実施例２８＞
実施例３を基にして、原料にＣｅＯ₂ を添加した。即ち、Ｔｂ₄ Ｏ₇ 、Ｓｃ₂ Ｏ₃ 、Ｇａ₂ Ｏ₃ 、ＰｂＯ、Ｂ₂ Ｏ₃ からなる出発原料にＣｅＯ₂ を０．２ｗｔ％添加し、白金坩堝に入れ、縦型の抵抗加熱炉中で、１１００℃で５時間加熱溶融し、その後、同じ１１００℃で１時間攪拌した。次いで、８８０℃に降温し、格子定数が１２．３８ÅのＧＧＧ基板の小片を４０ｒｐｍで回転させながら２分間浸し引き上げ炉から取り出した。続いて、直径３インチ、厚み５００μｍのＧＧＧ基板を炉に入れ、片面を白金内メルト液面に浸して４０ｒｐｍで６５時間回転させた。その後、メルト液面より１０ｍｍ引き上げて切り離し、そのまま炉の中で室温まで冷却した。その後、ＧＧＧ基板を炉から取り出し酸洗浄した。３インチＧＧＧ基板には、その（１１１）面上に組成がＴｂ₃ Ｓｃ_0.35Ｇａ_4.65Ｏ₁₂で表されるガーネット結晶が２．４ｍｍ成長しており、亀裂や欠陥が無く、殆ど着色していないＴＧＧ結晶が得られた。 <Example 28>
Based on Example 3, CeO ₂ was added to the raw material. That is, 0.2 wt% of CeO ₂ was added to a starting material composed of Tb ₄ O ₇ , Sc ₂ O ₃ , Ga ₂ O ₃ , PbO, and B ₂ O ₃ and placed in a platinum crucible. And heated and melted at 1100 ° C. for 5 hours, and then stirred at the same 1100 ° C. for 1 hour. Next, the temperature was lowered to 880 ° C., and a piece of GGG substrate having a lattice constant of 12.38 mm was immersed for 2 minutes while being rotated at 40 rpm, and taken out from the pulling furnace. Subsequently, a GGG substrate having a diameter of 3 inches and a thickness of 500 μm was placed in a furnace, and one surface was immersed in the melt surface of platinum and rotated at 40 rpm for 65 hours. Then, it pulled up 10 mm from the melt liquid level, cut off, and cooled to room temperature in the furnace as it was. Thereafter, the GGG substrate was taken out of the furnace and acid cleaned. The 3 inch GGG substrate has a garnet crystal having a composition of Tb ₃ Sc _0.35 Ga _4.65 O ₁₂ grown on its (111) surface with a thickness of 2.4 mm, has no cracks or defects, and is hardly colored. A TGG crystal was obtained.

ＧＧＧ小片を用いて、Ｘ線回折法により育成したＴＧＧ結晶とＧＧＧ基板の育成面垂直方向の格子定数差Δａを測定したところ、格子定数差はゼロであった。３インチＧＧＧ基板付ＴＧＧ結晶を３ｍｍ角に切断し、研磨によりＧＧＧ基板を削除して、３ｍｍ角面の両面を鏡面加工した。加工後の厚みは２．３２ｍｍであった。次に、３ｍｍ角面に垂直方向に光を通し、透過率を測定したところ、波長５３２ｎｍの透過率は７３％、波長１０６４ｎｍの透過率は８２％で良好であった。   Using a GGG piece, the lattice constant difference Δa in the direction perpendicular to the growth plane between the TGG crystal grown by the X-ray diffraction method and the GGG substrate was measured, and the lattice constant difference was zero. A TGG crystal with a 3-inch GGG substrate was cut into 3 mm square, the GGG substrate was removed by polishing, and both sides of the 3 mm square surface were mirror-finished. The thickness after processing was 2.32 mm. Next, when light was transmitted in the direction perpendicular to the 3 mm square and the transmittance was measured, the transmittance at a wavelength of 532 nm was 73%, and the transmittance at a wavelength of 1064 nm was good at 82%.

＜比較例１３＞
添加ＣｅＯ₂ 濃度が０．６ｗｔ％である以外は実施例２９と同様にして結晶育成を行った。ところが、１１００℃にしても不溶物があり、育成を断念した。 <Comparative Example 13>
Crystal growth was performed in the same manner as in Example 29 except that the added CeO ₂ concentration was 0.6 wt%. However, even at 1100 ° C., there was an insoluble material, and the growth was abandoned.

＜実施例２９〜３０＞
実施例３を基にして、原料にＳｉＯ₂ を添加した。即ち、Ｔｂ₄ Ｏ₇ 、Ｓｃ₂ Ｏ₃ 、Ｇａ₂ Ｏ₃ 、ＰｂＯ、Ｂ₂ Ｏ₃ からなる出発原料にＳｉＯ₂ を添加し、白金坩堝に入れ、縦型の抵抗加熱炉中、１１００℃で５時間加熱溶融し、その後、同じ１１００℃で１時間攪拌した。次に育成温度まで降温し、格子定数が１２．３８ÅのＧＧＧ基板の小片を４０ｒｐｍで回転させながら２分間浸し引き上げ、炉から取り出した。ここで育成温度とは、ＧＧＧ基板と育成したＴＧＧ結晶の格子定数が合う温度を指す。続いて、直径３インチ、厚み５００μｍのＧＧＧ基板を炉に入れ、片面を白金内メルト液面に浸し、４０ｒｐｍで所定時間回転させた。その後、メルト液面より１０ｍｍ引き上げて切り離し、そのまま炉の中で室温まで冷却した。その後、ＧＧＧ基板を炉から取り出し酸洗浄した。３インチＧＧＧ基板には、その（１１１）面上に組成がＴｂ₃ Ｓｃ_0.35Ｇａ_4.65Ｏ₁₂で表されるガーネット結晶が成長しており、亀裂や欠陥のないＴＧＧ結晶が得られた。検査結果を表１０に示す。また、３インチＧＧＧ基板付ＴＧＧ結晶を３ｍｍ角に切断し、研磨によりＧＧＧ基板を削除して３ｍｍ角面の両面を鏡面加工した。次に３ｍｍ角面に垂直方向に光を通し、透過率を測定したところ、表１１に示すように、波長５３２ｎｍの透過率が６０％以上であり良好であった。 <Examples 29 to 30>
Based on Example 3, SiO ₂ was added to the raw material. That is, SiO ₂ is added to a starting material composed of Tb ₄ O ₇ , Sc ₂ O ₃ , Ga ₂ O ₃ , PbO, B ₂ O ₃ , put in a platinum crucible, and placed in a vertical resistance heating furnace at 1100 ° C. The mixture was melted by heating for 5 hours and then stirred at the same 1100 ° C. for 1 hour. Next, the temperature was lowered to the growth temperature, and a small piece of a GGG substrate having a lattice constant of 12.38 cm was dipped for 2 minutes while rotating at 40 rpm, and taken out from the furnace. Here, the growth temperature refers to a temperature at which the lattice constants of the GGG substrate and the grown TGG crystal match. Subsequently, a GGG substrate having a diameter of 3 inches and a thickness of 500 μm was placed in a furnace, and one surface was immersed in the surface of the platinum melt and rotated at 40 rpm for a predetermined time. Then, it pulled up 10 mm from the melt liquid level, cut off, and cooled to room temperature in the furnace as it was. Thereafter, the GGG substrate was taken out of the furnace and acid cleaned. On the 3-inch GGG substrate, a garnet crystal having a composition represented by Tb ₃ Sc _0.35 Ga _4.65 O ₁₂ was grown on the (111) plane, and a TGG crystal free from cracks and defects was obtained. Table 10 shows the test results. Further, a TGG crystal with a 3-inch GGG substrate was cut into 3 mm square, the GGG substrate was deleted by polishing, and both surfaces of the 3 mm square surface were mirror-finished. Next, when light was passed through the 3 mm square surface in the vertical direction and the transmittance was measured, as shown in Table 11, the transmittance at a wavelength of 532 nm was 60% or more, which was favorable.

＜比較例１４＞
Ｔｂ₄ Ｏ₇ 、Ｓｃ₂ Ｏ₃ 、Ｇａ₂ Ｏ₃ 、ＰｂＯ、Ｂ₂ Ｏ₃ からなる出発原料にＳｉＯ₂ を３ｗｔ％添加し、白金坩堝に入れ、縦型の抵抗加熱炉中、１１００℃で５時間加熱溶融し、その後、同じ１１００℃で１時間攪拌した。次いで８５０℃まで降温し、格子定数が１２．３８ÅのＧＧＧ基板の小片を４０ｒｐｍで回転させながら２分間浸し引き上げ、炉から取り出した。ところが、結晶は成長しておらず、ＧＧＧ基板が一部溶融して薄くなっていた。このため、育成を断念した。 <Comparative example 14>
3 wt% of SiO ₂ is added to a starting material composed of Tb ₄ O ₇ , Sc ₂ O ₃ , Ga ₂ O ₃ , PbO, B ₂ O ₃ , put into a platinum crucible, and placed in a vertical resistance heating furnace at 1100 ° C. The mixture was melted by heating for 5 hours, and then stirred at the same 1100 ° C. for 1 hour. Next, the temperature was lowered to 850 ° C., a small piece of a GGG substrate having a lattice constant of 12.38 mm was dipped for 2 minutes while rotating at 40 rpm, and taken out from the furnace. However, the crystal was not grown, and the GGG substrate was partially melted and thinned. For this reason, we gave up training.

ａ 還元処理無しでの曲線。
ｂ 還元温度４５０℃での曲線。
ｃ 還元温度７００℃での曲線。 a Curve without reduction treatment.
b Curve at a reduction temperature of 450 ° C.
c Curve at a reduction temperature of 700 ° C.

Claims (6)

ＧＧＧ結晶からなる基板上に、ＬＰＥ法で育成したＴＧＧ結晶であって、前記ＴＧＧ結晶は、組成Ｔｂ₃ Ｍ_x Ｇａ_5-x Ｏ₁₂で表され、前記ＭがＳｃ、Ｉｎから選ばれる少なくとも１種の３価元素であって０．１≦ｘ≦０．５を満たしており、且つ前記基板のＧＧＧ結晶と育成したＴＧＧ結晶の垂直方向の格子定数差が±０．０２Å以下となっていることを特徴とする常磁性ガーネット単結晶。 A TGG crystal grown by an LPE method on a substrate made of a GGG crystal, wherein the TGG crystal is represented by a composition Tb ₃ M _x Ga _5-x O ₁₂ , and the M is at least one selected from Sc and In It is a kind of trivalent element and satisfies 0.1 ≦ x ≦ 0.5, and the vertical lattice constant difference between the GGG crystal of the substrate and the grown TGG crystal is ± 0.02Å or less. Paramagnetic garnet single crystal characterized by that. ＳＧＧＧ結晶からなる基板上に、ＬＰＥ法で育成したＴＧＧ結晶であって、前記ＴＧＧ結晶は、組成Ｔｂ₃ Ｍ_x Ｇａ_5-x Ｏ₁₂で表され、前記ＭがＳｃ、Ｉｎから選ばれる少なくとも１種の３価元素であって０．９≦ｘ≦１．６５を満たしており、且つ前記基板のＳＧＧＧ結晶と育成したＴＧＧ結晶の垂直方向の格子定数差が±０．０２Å以下となっていることを特徴とする常磁性ガーネット単結晶。 A TGG crystal grown by an LPE method on a substrate made of SGGG crystal, wherein the TGG crystal is represented by a composition Tb ₃ M _x Ga _5-x O ₁₂ , and the M is at least one selected from Sc and In It is a kind of trivalent element and satisfies 0.9 ≦ x ≦ 1.65, and the vertical lattice constant difference between the SGGG crystal of the substrate and the grown TGG crystal is ± 0.02 ± or less. Paramagnetic garnet single crystal characterized by that. 請求項１又は２記載の常磁性ガーネット単結晶を製造する方法であって、Ｔｂ₄ Ｏ₇ 、Ｇａ₂ Ｏ₃ 、及びＭ₂ Ｏ₃ （但し、ＭはＳｃ、Ｉｎから選ばれる少なくとも１種）をガーネット原料とし、ＰｂＯ及びＢ₂ Ｏ₃ をフラックスとする融液の表面に、前記基板の片面を接触させ、８５０〜９８０℃でＴＧＧ結晶をＬＰＥ成長させる常磁性ガーネット単結晶の製造方法。 A claim 1 or 2 method for producing a paramagnetic garnet single crystal _{according, Tb 4 O 7, Ga 2} O 3, and M ₂ O ₃ (where M is at least one Sc, selected from In) A method for producing a paramagnetic garnet single crystal, in which one side of the substrate is brought into contact with the surface of the melt using PbO and B ₂ O ₃ as a flux, and a TGG crystal is grown by LPE at 850 to 980 ° C. 前記融液中に、ＳｉＯ₂ 、ＧｅＯ₂ 、ＴｉＯ₂ から選ばれる１種以上の酸化物が含まれており、その重量濃度の合計が０．５ｗｔ％以下であるように調整されている請求項３記載の常磁性ガーネット単結晶の製造方法。 The melt contains at least one oxide selected from SiO ₂ , GeO ₂ , and TiO _2, and the total weight concentration is adjusted to 0.5 wt% or less. 3. A method for producing a paramagnetic garnet single crystal according to 3. 前記融液中に、ＣｅＯ₂ が含まれており、その重量濃度が０．２ｗｔ％以下であるように調整されている請求項３記載の常磁性ガーネット単結晶の製造方法。 The method for producing a paramagnetic garnet single crystal according to claim 3, wherein CeO ₂ is contained in the melt, and the weight concentration thereof is adjusted to 0.2 wt% or less. 請求項３記載の常磁性ガーネット単結晶の製造方法によりＬＰＥ成長させたＴＧＧ結晶を、水素０．５〜６ｖｏｌ％を含む窒素との混合雰囲気下、４５０〜８００℃で還元処理する常磁性ガーネット単結晶の製造方法。   4. A paramagnetic garnet single body, wherein a TGG crystal grown by LPE by the method for producing a paramagnetic garnet single crystal according to claim 3 is subjected to reduction treatment at 450 to 800 ° C. in a mixed atmosphere with nitrogen containing 0.5 to 6 vol% of hydrogen. Crystal production method.

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