JP4822232B2 - Hexagonal boron nitride single crystal and ultraviolet light emitting device using the same - Google Patents
Hexagonal boron nitride single crystal and ultraviolet light emitting device using the same Download PDFInfo
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- 239000013078 crystal Substances 0.000 title claims abstract description 74
- 229910052582 BN Inorganic materials 0.000 title claims abstract description 25
- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 title claims abstract description 25
- 230000031700 light absorption Effects 0.000 claims description 9
- 239000000463 material Substances 0.000 claims description 9
- 239000012535 impurity Substances 0.000 abstract description 9
- 239000002904 solvent Substances 0.000 description 23
- 230000015572 biosynthetic process Effects 0.000 description 13
- 238000003786 synthesis reaction Methods 0.000 description 13
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 10
- 238000005136 cathodoluminescence Methods 0.000 description 10
- 239000002994 raw material Substances 0.000 description 10
- 238000001953 recrystallisation Methods 0.000 description 10
- 239000002775 capsule Substances 0.000 description 9
- 238000006243 chemical reaction Methods 0.000 description 9
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 8
- 229910052750 molybdenum Inorganic materials 0.000 description 8
- 239000011733 molybdenum Substances 0.000 description 8
- 230000003287 optical effect Effects 0.000 description 8
- 238000000034 method Methods 0.000 description 7
- 239000000126 substance Substances 0.000 description 7
- 238000002474 experimental method Methods 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 6
- 229910052788 barium Inorganic materials 0.000 description 5
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 5
- 238000011161 development Methods 0.000 description 5
- 230000001747 exhibiting effect Effects 0.000 description 5
- 229910052757 nitrogen Inorganic materials 0.000 description 5
- 230000002194 synthesizing effect Effects 0.000 description 5
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 4
- 229910052783 alkali metal Inorganic materials 0.000 description 4
- 150000001340 alkali metals Chemical class 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 229910003460 diamond Inorganic materials 0.000 description 4
- 239000010432 diamond Substances 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 239000012299 nitrogen atmosphere Substances 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- 238000011160 research Methods 0.000 description 4
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 3
- 150000001342 alkaline earth metals Chemical class 0.000 description 3
- 238000000354 decomposition reaction Methods 0.000 description 3
- 238000010574 gas phase reaction Methods 0.000 description 3
- 239000004065 semiconductor Substances 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- 238000001308 synthesis method Methods 0.000 description 3
- 230000007704 transition Effects 0.000 description 3
- 238000002834 transmittance Methods 0.000 description 3
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 2
- 238000000862 absorption spectrum Methods 0.000 description 2
- 229910021529 ammonia Inorganic materials 0.000 description 2
- QZPSXPBJTPJTSZ-UHFFFAOYSA-N aqua regia Chemical compound Cl.O[N+]([O-])=O QZPSXPBJTPJTSZ-UHFFFAOYSA-N 0.000 description 2
- 239000012298 atmosphere Substances 0.000 description 2
- 229910052810 boron oxide Inorganic materials 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- JKWMSGQKBLHBQQ-UHFFFAOYSA-N diboron trioxide Chemical compound O=BOB=O JKWMSGQKBLHBQQ-UHFFFAOYSA-N 0.000 description 2
- 238000011049 filling Methods 0.000 description 2
- 229910052744 lithium Inorganic materials 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000004904 shortening Methods 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 230000001954 sterilising effect Effects 0.000 description 2
- 238000004659 sterilization and disinfection Methods 0.000 description 2
- 229910002601 GaN Inorganic materials 0.000 description 1
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 1
- 238000010306 acid treatment Methods 0.000 description 1
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 1
- 238000006392 deoxygenation reaction Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 238000000295 emission spectrum Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 239000011810 insulating material Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
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Abstract
Description
本発明は、波長２３５ｎｍ以下、特に波長２１５ｎｍ〜２１０ｎｍの領域において発光する高輝度固体発光物質と該物質からなる短波長発光素子に関する。 The present invention relates to a high-intensity solid-state light-emitting substance that emits light in a wavelength region of 235 nm or less, particularly in a wavelength range of 215 nm to 210 nm, and a short-wavelength light-emitting element comprising the substance.
高輝度紫外線発光素子の開発は、近年窒化ガリウムおよびその固溶体を始め、種々の材料によって、発光波長３００ｎｍ台の発光素子が提案され、実用化に向けて開発が進められている。これら固体発光素子の発光波長の短波長化は、記録媒体への書き込みの高密度化等を始めとして、多くの需要があり、現在までのところ２００ｎｍ台の発光素子としてダイヤモンド、立方晶窒化ホウ素（以下、ｃＢＮと記載する）ならびに窒化アルミニウムが候補として挙げられ、応用に向けた研究が進められている。短波長領域の高輝度発光素子を探索する上では、広いバンドギャップを有すること、化学的に安定であること、望ましくは直接遷移型の半導体であることなどが重要な要因として挙げられる。 In recent years, the development of high-intensity ultraviolet light-emitting elements has been proposed with various materials such as gallium nitride and its solid solution, and light-emitting elements with an emission wavelength of about 300 nm have been proposed and are being developed for practical use. There has been a great demand for shortening the emission wavelength of these solid-state light emitting devices, such as increasing the density of writing to a recording medium. To date, diamond, cubic boron nitride ( Hereinafter, cBN) and aluminum nitride are listed as candidates, and research for application is underway. In searching for a high-intensity light-emitting element in a short wavelength region, important factors include a wide band gap, chemical stability, and preferably a direct transition type semiconductor.
上述した以外に発光波長が２００ｎｍ台の発光特性を示す固体発光材料としては、バンドギャップが５．８ｅＶ付近で、直接遷移型の半導体である六方晶窒化ホウ素（以下、ｈＢＮと記載する）が挙げることができるが、これについては実現を阻む要因があった。ｈＢＮは化学的に安定な絶縁材料として古くから利用され、酸化ホウ素とアンモニアとの気相反応によって合成され、今日では多くの形態（粉末、焼結体、膜状の形態など）で利用されている。しかしながら、前示した気相反応によって得られるｈＢＮは、後述するように不純物に起因し、その固有のバンドギャップに相当する発光特性を有するものを得ることは困難であった。今後、この材料を短波長領域の高輝度発光素子として利用しようとすると、高純度単結晶の合成手段を確立することが先決である。現段階では、発光波長２００ｎｍ台の固体発光素子としての可能性に着目し、ｈＢＮの合成方法によって、高純度のものを得、期待される発光特性を持ったｈＢＮ単結晶を得るのに成功したとの報告はなされていない（例えば、非特許文献３）。 In addition to the above, a solid light-emitting material exhibiting light emission characteristics with an emission wavelength in the 200 nm range includes hexagonal boron nitride (hereinafter referred to as hBN) which is a direct transition type semiconductor with a band gap of about 5.8 eV. However, there were factors that hindered its realization. hBN has long been used as a chemically stable insulating material, synthesized by a gas phase reaction between boron oxide and ammonia, and is now used in many forms (powder, sintered body, film-like form, etc.). Yes. However, hBN obtained by the gas phase reaction shown above is caused by impurities as described later, and it has been difficult to obtain one having light emission characteristics corresponding to its inherent band gap. In the future, if this material is to be used as a high-intensity light-emitting element in the short wavelength region, it is the first decision to establish a means for synthesizing a high-purity single crystal. At this stage, paying attention to the possibility as a solid-state light emitting device with an emission wavelength of 200 nm, we succeeded in obtaining a high-purity hBN single crystal with expected emission characteristics by the hBN synthesis method. No report has been made (for example, Non-Patent Document 3).
ｈＢＮは、その合成手法としては、酸化ホウ素とアンモニアとの熱分解反応（例えば、非特許文献６）や気相反応（例えば、特許文献１、非特許文献４および５）によって合成されていることが知られているが、この反応によって高純度単結晶を得ることは困難であり、単結晶製造手段としては、確立された合成手段とは言えなかった。一方、ｈＢＮの高圧相である立方晶窒化ホウ素（以下、ｃＢＮという）は、ｈＢＮ等を原料とし、これにアルカリ金属あるいはアルカリ土類金属のホウ窒化物を溶媒として使用し、該原料を溶媒中で５．５万気圧、１６００℃、高温高圧下で再結晶化することにより合成されることが知られているが、得られるｃＢＮ単結晶はダイヤモンドに次ぐ硬度を有し、超硬質材料として広く用いられるなど、このｃＢＮの合成手法はすでに工業的に確立されている。 hBN is synthesized by a thermal decomposition reaction between boron oxide and ammonia (for example, Non-Patent Document 6) or a gas phase reaction (for example, Patent Document 1, Non-Patent Documents 4 and 5). However, it is difficult to obtain a high-purity single crystal by this reaction, and it cannot be said that the single crystal production means is an established synthesis means. On the other hand, cubic boron nitride (hereinafter referred to as cBN), which is a high-pressure phase of hBN, uses hBN or the like as a raw material, and alkali metal or alkaline earth metal boronitride as a solvent. It is known that it is synthesized by recrystallization at 55,000 atm, 1600 ° C. under high temperature and pressure, but the obtained cBN single crystal has hardness next to diamond and is widely used as an ultra-hard material. The method for synthesizing this cBN has already been established industrially.
このｃＢＮも広いバンドギャップ（Ｅｇ：６．３ｅＶ）を有するため、古くから固体の短波長発光素子としての研究も進められてきた。しかしながら、これまでに報告されているｃＢＮ単結晶は、いずれも琥珀色からオレンジ色等に着色しており、その発光特性にはｃＢＮ固有のバンドギャップに対応する発光挙動を観測しうる状況にはいたっていなかった。その理由、原因としては、ｃＢＮ結晶内部に含まれる不純物の影響が大きいことが挙げられる。したがって、今後、ｃＢＮ単結晶を、該結晶のバンドギャップに相応する固有の発光特性を有するものとして利用しようとすると、ｃＢＮ固有の発光特性を十分に把握しておく必要があることは勿論、ｃＢＮ単結晶の高純度化を達成する合成反応を確立することが重要な研究課題となっていた。このような背景の下に、ｃＢＮ合成条件を、敢えて、ｈＢＮが安定に生成する温度、圧力条件に設定し、ｈＢＮ単結晶の合成を試みたとの報告がされている（非特許文献１）。しかしながら、この合成実験で用いた育成溶媒からは着色したｃＢＮ結晶が得られ、付随的に生成したｈＢＮ結晶の発光挙動については、高輝度の短波長発光は、全く示されていない。 Since this cBN also has a wide band gap (Eg: 6.3 eV), research on solid-state short-wavelength light emitting devices has been advanced for a long time. However, all the cBN single crystals reported so far are colored from amber to orange, etc., and the emission characteristics corresponding to the band gap unique to cBN can be observed in the emission characteristics. It was n’t there. The reason and cause is that the influence of impurities contained in the cBN crystal is large. Therefore, in the future, if the cBN single crystal is to be used as having a specific light emission characteristic corresponding to the band gap of the crystal, it is necessary to sufficiently understand the light emission characteristic specific to cBN. Establishing synthetic reactions to achieve high purity of single crystals has been an important research topic. Against this background, it has been reported that the synthesis of hBN single crystals was attempted by setting the cBN synthesis conditions to the temperature and pressure conditions at which hBN is stably generated (Non-patent Document 1). However, a colored cBN crystal is obtained from the growth solvent used in this synthesis experiment, and the light emission behavior of the incidentally generated hBN crystal does not show any high-intensity short wavelength light emission.
かかる状況下で、本発明者らにおいては、高純度ｃＢＮ単結晶を得るべく合成条件を鋭意研究した。その結果、高純度のｃＢＮ結晶を得るために必要な要因を見出し、これによって、ｃＢＮ結晶固有の光学的特性を有する高純度ｃＢＮ単結晶の合成に成功し、これを学術文献に発表した（非特許文献２）。この合成方法は、要約すると、清浄な乾燥窒素雰囲気を確立した上で、吟味して精製した溶媒（ホウ窒化バリウムなど）を用いて結晶の育成を行なうものであり、この手法によって、高純度ｃＢＮ単結晶を得るのに成功したものである（非特許文献２）。 Under such circumstances, the present inventors have intensively studied synthesis conditions in order to obtain a high-purity cBN single crystal. As a result, a factor necessary for obtaining a high-purity cBN crystal was discovered, and as a result, a high-purity cBN single crystal having optical characteristics unique to the cBN crystal was successfully synthesized and published in the academic literature (non- Patent Document 2). In summary, this synthesis method establishes a clean dry nitrogen atmosphere and grows crystals using a solvent (such as barium boronitride) that has been examined and refined. By this method, high-purity cBN is obtained. It has succeeded in obtaining a single crystal (nonpatent literature 2).
以上が、短波長領域の発光特性を有するものとして期待されるｈＢＮ材料あるいはその高圧相ｃＢＮの現状である。特に、ワイドバンドギャップ半導体であるｈＢＮは直接遷移型であり、高輝度で短波長の固体発光素子として期待されているにもかかわらず、現状は前述したとおりであり、この期待に応えるためには物質本来の特性を引き出すこと、すなわち、不純物の影響を受けない高純度単結晶の合成方法を確立することが急務であり、その実現が要請されている。 The above is the current state of the hBN material or its high-pressure phase cBN that is expected to have light emission characteristics in the short wavelength region. In particular, hBN, which is a wide bandgap semiconductor, is a direct transition type and is expected to be a solid state light emitting device with high brightness and short wavelength. There is an urgent need to extract the original characteristics of a substance, that is, to establish a method for synthesizing a high-purity single crystal that is not affected by impurities.
本発明は、これに応えようというものである。すなわち、本発明が解決しようとする課題は、従来のｈＢＮの合成手法ではなし得なかった高純度ｈＢＮ単結晶を合成し、ｈＢＮ固有の特性を反映した高輝度短波長紫外線発光を実現しようというものである。 The present invention is intended to respond to this. That is, the problem to be solved by the present invention is to synthesize a high-purity hBN single crystal that cannot be achieved by the conventional synthesis method of hBN, and to realize high-luminance short-wavelength ultraviolet light emission that reflects the unique characteristics of hBN. It is.
そのため本発明者らは、前述非特許文献２において報告した、ｈＢＮ原料から出発し、これを清浄な乾燥窒素雰囲気と精製溶媒とによって高純度ｃＢＮ単結晶を得る合成実験につき、これをさらに進め、高純度ｃＢＮ単結晶を合成する臨界条件を精査、把握する実験を試みた結果、温度圧力条件を適宜調整することによって、高純度ｈＢＮ単結晶が得られることを見出したものである。 Therefore, the present inventors further proceeded with the synthesis experiment reported in the above-mentioned Non-Patent Document 2, starting from the hBN raw material and obtaining a high-purity cBN single crystal using a clean dry nitrogen atmosphere and a purification solvent, As a result of an experiment to scrutinize and grasp the critical conditions for synthesizing a high-purity cBN single crystal, the inventors have found that a high-purity hBN single crystal can be obtained by appropriately adjusting the temperature and pressure conditions.
そして、得られた該高純度ｈＢＮ単結晶の光学特性等を精査した結果、以下の光学特性を示すことを知見し、明らかにしたものである。すなわち、得られた結晶は、無色透明、高い電気抵抗を有する高純度の結晶であった。その光学的特性を観察、評価したところ、カソードルミネッセンスにより電子線を用いた励起により、室温において波長２１５ｎｍに著しく高輝度の発光があることが観察された。また温度８３Ｋにおいては波長２１０ｎｍから２３５ｎｍに発光が観測された。光吸収実験によれば、波長２０８ｎｍと２１３ｎｍに光吸収構造を示すことを特徴とする吸収スペクトルが得られた。これを、同じ条件で測定した高純度ダイヤモンド単結晶からの紫外線発光と比較すると、ｈＢＮ単結晶からの室温における波長２１５ｎｍの発光強度はダイヤモンドの場合のおよそ１０００倍以上の値を示すことを見いだしたものである。 As a result of examining the optical characteristics and the like of the obtained high-purity hBN single crystal, it has been found and revealed that the following optical characteristics are exhibited. That is, the obtained crystal was colorless and transparent, and a high-purity crystal having high electrical resistance. As a result of observation and evaluation of the optical characteristics, it was observed that light emission with extremely high luminance was observed at a wavelength of 215 nm at room temperature by excitation using an electron beam by cathodoluminescence. At a temperature of 83K, light emission was observed from a wavelength of 210 nm to 235 nm. According to the light absorption experiment, an absorption spectrum characterized by showing a light absorption structure at wavelengths of 208 nm and 213 nm was obtained. When this was compared with ultraviolet emission from a high-purity diamond single crystal measured under the same conditions, it was found that the emission intensity at a wavelength of 215 nm at room temperature from the hBN single crystal was about 1000 times or more that of diamond. Is.
すなわち、本発明は、前述文献（非特許文献１、２）に記載された先行技術を前提技術とし、高純度ｈＢＮ単結晶を得るべき鋭意研究した結果、非特許文献２記載の高純度ｃＢＮ単結晶を得る合成条件を、ｈＢＮ単結晶の生成条件に設定して実験したところ、波長２１５ｎｍ近傍の短波長領域の発光特性を有してなる高純度ｈＢＮ単結晶を合成しうることを新たに知見したものである。本発明はこの新たな知見に基づいてなされたものであり、その構成は以下に記載の通りである。
（１）少なくとも室温において波長２１５ｎｍに最大発光強度を有する紫外線発光を有してなることを特徴とする、六方晶窒化ホウ素単結晶。
（２）温度８３Ｋにおいて波長２１１ｎｍに紫外線発光をさらに有してなることを特徴とする、前記（１）項に記載の六方晶窒化ホウ素単結晶。
（３）温度８Ｋにおいて波長２１３ｎｍに光吸収構造を示すことを特徴とする、前記（１）または（２）項に記載の六方晶窒化ホウ素単結晶。
（４）温度８Ｋにおいて波長２０８ｎｍに光吸収構造を示すことを特徴とする、前記（１）ないし（３）の何れか１項に記載の六方晶窒化ホウ素単結晶。
（５）前記（１）ないし（４）の何れか１項に記載の六方晶窒化ホウ素単結晶を発光材料として使用することを特徴とする、紫外線発光素子。
That is, the present invention is based on the prior art described in the above-mentioned documents (Non-Patent Documents 1 and 2), and as a result of earnest research to obtain a high-purity hBN single crystal, the high-purity cBN single-crystal described in Non-Patent Document 2 was obtained. Experiments were conducted by setting the synthesis conditions for obtaining crystals to the production conditions for hBN single crystals, and it was newly found that high-purity hBN single crystals having emission characteristics in the short wavelength region near 215 nm wavelength can be synthesized. It is a thing. The present invention has been made on the basis of this new finding, and the configuration thereof is as described below.
(1) A hexagonal boron nitride single crystal having ultraviolet emission having a maximum emission intensity at a wavelength of 215 nm at least at room temperature.
(2) The hexagonal boron nitride single crystal as described in (1) above, further having ultraviolet light emission at a wavelength of 211 nm at a temperature of 83K.
(3) The hexagonal boron nitride single crystal as described in (1) or (2) above, which exhibits a light absorption structure at a wavelength of 213 nm at a temperature of 8K.
(4) The hexagonal boron nitride single crystal according to any one of (1) to (3) above, which exhibits a light absorption structure at a wavelength of 208 nm at a temperature of 8K.
(5) An ultraviolet light-emitting device using the hexagonal boron nitride single crystal according to any one of (1) to (4) as a light-emitting material.
本発明は、従来の技術では得られなかった波長２３５ｎｍ以下、特に２１５ｎｍ近辺に強い高輝度発光挙動を示す六方晶窒化ホウ素単結晶の供給が可能となった。これによって、高輝度紫外線固体発光素子を設計することが可能となり、高密度記録媒体の開発、紫外線による殺菌など多くの分野でその発光波長の短波長化に向けた需要に応え得ることが可能となった。 The present invention has made it possible to supply a hexagonal boron nitride single crystal exhibiting a strong high-luminance emission behavior at a wavelength of 235 nm or less, particularly in the vicinity of 215 nm, which has not been obtained by the prior art. This makes it possible to design a high-intensity ultraviolet solid-state light-emitting device, which can meet the demand for shortening the emission wavelength in many fields such as development of high-density recording media and sterilization by ultraviolet rays. became.
本発明は、短波長領域で紫外発光する高純度ｈＢＮ単結晶とその合成プロセスであり、短波長領域で紫外発光する高純度ｈＢＮ単結晶は、原料ｈＢＮを高純度のアルカリ金属、あるいはアルカリ土類金属ホウ窒化物溶媒の存在下で高温高圧処理し、これによって再結晶化するプロセスによるものであり、再結晶によって、不純物のない、２３５ｎｍ以下、特に２１５ｎｍ近辺において高輝度紫外線発光を有するｈＢＮ単結晶を得ることが出来るものである。そのための温度、圧力条件は、高温、高圧を必要とする。一応の目安として２万気圧、１５００℃以上が好ましい。 The present invention relates to a high-purity hBN single crystal that emits ultraviolet light in a short wavelength region and a synthesis process thereof. The high-purity hBN single crystal that emits ultraviolet light in a short wavelength region is obtained by using a high-purity alkali metal or alkaline earth as a raw material hBN. HBN single crystal having a high-intensity ultraviolet light emission at 235 nm or less, particularly in the vicinity of 215 nm, free from impurities, by a process of high-temperature and high-pressure treatment in the presence of a metal boronitride solvent and thereby recrystallization. Can be obtained. The temperature and pressure conditions for that purpose require high temperature and high pressure. As a temporary guide, 20,000 atmospheres and 1500 ° C. or higher are preferable.
この条件は、原料である窒化ホウ素が溶媒の共存下でｈＢＮに再結晶する温度、圧力条件であり、その間に溶媒として用いたアルカリ金属ないしアルカリ土類金属のホウ窒化物が酸化したり、分解したりせず安定に存在することが必要となる。高圧力下で反応を進めることは有効であり、これによって溶媒の分解が抑制され、大型高純度結晶合成のための長時間の結晶育成が可能となり、好ましい。 These conditions are the temperature and pressure conditions at which the raw material boron nitride recrystallizes to hBN in the presence of a solvent, during which the alkali metal or alkaline earth metal boronitride used as the solvent is oxidized or decomposed. It is necessary to exist stably. It is effective to proceed the reaction under high pressure, which is preferable because it prevents the decomposition of the solvent and enables crystal growth for a long time for synthesizing a large high-purity crystal.
しかしながら、過度に圧力を高くすると、原料として用いたｈＢＮは、高圧相であるｃＢＮへの相転換が起きるので注意を要する。すなわち、目的とする高純度ｈＢＮ単結晶を得るためには、ｃＢＮ単結晶が生じない領域の温度圧力条件を必要とする。図１は、ｈＢＮの再結晶条件とする温度圧力条件を示すものである。この図によるとｃＢＮの熱力学的安定条件下であってもｈＢＮへの再結晶は可能であるが、圧力の増加とともにｃＢＮへの転換が容易に進行し、ｈＢＮの再結晶化を進めるにはｈＢＮの安定条件となる高い反応温度が必要となる。 However, if the pressure is excessively increased, the hBN used as a raw material will undergo phase conversion to cBN, which is a high-pressure phase, so care must be taken. That is, in order to obtain a target high-purity hBN single crystal, a temperature and pressure condition in a region where no cBN single crystal is generated is required. FIG. 1 shows the temperature and pressure conditions for the hBN recrystallization conditions. According to this figure, cBN can be recrystallized to hBN even under the thermodynamically stable condition. However, conversion to cBN easily proceeds with increasing pressure, and to promote recrystallization of hBN. A high reaction temperature, which is a stable condition for hBN, is required.
すなわち、ｈＢＮ再結晶のための上限の圧力としては６ＧＰａ程度が適当であり、これ以上の圧力ではｈＢＮの熱力学的安定条件に合成条件を設定せねばならず、その際の温度は３０００℃付近となり、充分な大きさの結晶を得るための条件として適当ではない。このため、工業生産としての経済性を考慮すれば、当該単結晶の合成条件の上限としては、６万気圧程度でよい。下限については、溶媒の分解や酸化を抑制することができれば、１気圧以下でも再結晶化による高輝度発光高純度ｈＢＮ結晶の合成は可能である。本発明では、図１の網掛けで示したｈＢＮ再結晶領域において、高輝度発光高純度ｈＢＮ結晶が合成された。 That is, the upper limit pressure for recrystallization of hBN is suitably about 6 GPa, and at higher pressures, the synthesis conditions must be set in the thermodynamic stability condition of hBN, and the temperature at that time is around 3000 ° C. Therefore, it is not suitable as a condition for obtaining a sufficiently large crystal. For this reason, considering the economical efficiency as industrial production, the upper limit of the synthesis condition of the single crystal may be about 60,000 atmospheres. Regarding the lower limit, if the decomposition and oxidation of the solvent can be suppressed, the synthesis of high-brightness luminescent high-purity hBN crystals by recrystallization is possible even at 1 atmosphere or less. In the present invention, a high-brightness light-emitting high-purity hBN crystal was synthesized in the hBN recrystallization region shown by shading in FIG.
一方、アルカリ金属、及びアルカリ土類金属のホウ窒化物等は水分や酸素と容易に反応し、これら酸化物等を不純物として含む反応系で再結晶したｈＢＮは酸素等の不純物の影響を受け、３００ｎｍ以下の短波長領域において発光する現象を示してなるｈＢＮ単結晶を得ることが出来なかった。これに対して、本発明は、通常市販に供されているいわゆる低圧相による窒化ホウ素を原料とし、該原料を高純度溶媒を用いて溶解し、再結晶化することにより、従来技術、先行技術では得ることのできなかった、波長２３５ｎｍ以下といった短波長領域での発光、特に波長２１５ｎｍ近傍において高輝度紫外線発光を示す高純度ｈＢＮ単結晶を提供することができるものである。 On the other hand, boronitrides of alkali metals and alkaline earth metals easily react with moisture and oxygen, and hBN recrystallized in a reaction system containing these oxides as impurities is affected by impurities such as oxygen, An hBN single crystal showing a phenomenon of light emission in a short wavelength region of 300 nm or less could not be obtained. On the other hand, the present invention uses as a raw material boron nitride in a so-called low-pressure phase that is usually commercially available, dissolves the raw material using a high-purity solvent, and recrystallizes the conventional technology and the prior art. Thus, it is possible to provide a high-purity hBN single crystal exhibiting light emission in a short wavelength region such as a wavelength of 235 nm or less, particularly high-luminance ultraviolet light emission in the vicinity of a wavelength of 215 nm, which could not be obtained.
以下、本発明を実施例及び図面に基づいて説明する。但し、この実施例等は発明を容易に理解するための一助として開示するものであり、本発明はこの実施例等によって限定されるものではない。 Hereinafter, the present invention will be described based on examples and drawings. However, these examples and the like are disclosed as an aid for easily understanding the invention, and the present invention is not limited to these examples and the like.
実施例１；
真空中で１５００℃、窒素気流中で２０００℃の熱処理による脱酸素処理を施した六方晶窒化ホウ素焼結体（粒径約０．５μｍ）をホウ窒化バリウム溶媒とともに高圧容器内のモリブデンカプセルに充填した。これらの溶媒の調整並びに試料のカプセルへの充填は、すべて乾燥窒素雰囲気中で行った。高圧反応容器をベルト型超高圧力発生装置により２．５万気圧、１７００℃、の圧力、温度条件で２０時間処理した。昇温速度は５０℃／分程度であった。５００℃／分程度で冷却後、除圧し試料を圧力容器内のモリブデンカプセルと共に回収した。
機械的又は化学処理（塩酸−硝酸混液）によりモリブデンカプセルを除去し試料を回収した。無色、透明で六角柱状の結晶（１〜３ｍｍ程度）が得られ、その評価は光学顕微鏡観察、ＳＥＭ観察、Ｘ線回折による相の同定、ならびに光学的特性の評価（透過率、カソードルミネッセンス）を行った。結晶粒子のＸ線回折図形より、結晶はｈＢＮ単相であることが確かめられた。カソードルミネッセンス観察では図２に示すように室温において波長２１５ｎｍ近傍に単峰性の高輝度の紫外線発光が、また、図３に示すように温度８３Ｋにおいて２１０ｎｍから２３５ｎｍにおいて紫外線発光スペクトル（図中上向き矢印↑で示す）が観測された。
光吸収測定では、波長２５００ｎｍから２００ｎｍ近傍にかけて高い透過率を示し、図３に示すように温度８Ｋにおいて波長２０８ｎｍと２１３ｎｍに光吸収構造（図中下向き矢印↓で示す）が観測された。
Example 1;
Filled molybdenum capsules in a high-pressure vessel with hexagonal boron nitride sintered body (particle size: about 0.5μm) that has been deoxygenated by heat treatment at 1500 ° C in a vacuum and 2000 ° C in a nitrogen stream together with a barium boronitride solvent did. The preparation of these solvents and the filling of the sample capsules were all performed in a dry nitrogen atmosphere. The high-pressure reaction vessel was treated with a belt-type ultrahigh pressure generator at a pressure and temperature of 25,000 atm and 1700 ° C. for 20 hours. The heating rate was about 50 ° C./min. After cooling at about 500 ° C./min, the pressure was released and the sample was collected together with the molybdenum capsule in the pressure vessel.
The molybdenum capsules were removed by mechanical or chemical treatment (hydrochloric acid-nitric acid mixture), and the sample was collected. Colorless, transparent, hexagonal columnar crystals (about 1 to 3 mm) are obtained. The evaluation is based on optical microscope observation, SEM observation, phase identification by X-ray diffraction, and evaluation of optical properties (transmittance, cathodoluminescence). went. From the X-ray diffraction pattern of the crystal particles, it was confirmed that the crystal was a single phase of hBN. In cathodoluminescence observation, as shown in FIG. 2, single-peaked high-intensity ultraviolet light emission is observed at room temperature near 215 nm as shown in FIG. 3, and ultraviolet light emission spectrum is observed from 210 nm to 235 nm at a temperature of 83 K as shown in FIG. ↑) was observed.
In the light absorption measurement, high transmittance was observed from a wavelength of 2500 nm to around 200 nm, and a light absorption structure (indicated by a downward arrow ↓ in the figure) was observed at a wavelength of 208 nm and 213 nm at a temperature of 8 K as shown in FIG.
実施例２；
真空中で１５００℃、窒素気流中で２０００℃の熱処理による脱酸素処理を施した六方晶窒化ホウ素焼結体（粒径約０．５μｍ）をホウ窒化バリウムとホウ窒化リチウムを重量比１：１で混合した溶媒とともにモリブデンカプセルに充填した。実施例１と同様の方法で高圧処理を行い、試料を回収した。回収した試料は実施例１同様の形態であり、ｈＢＮ結晶であることが確かめられ、カソードルミネッセンス測定により波長２１５ｎｍに高輝度の発光と共に、３００ｎｍ付近のブロードな発光が観測された。
Example 2;
A hexagonal boron nitride sintered body (particle size: about 0.5 μm) that has been deoxygenated by heat treatment at 1500 ° C. in a vacuum and 2000 ° C. in a nitrogen stream has a weight ratio of barium boronitride to lithium boronitride of 1: 1. Molybdenum capsules were filled together with the solvent mixed in. A high pressure treatment was performed in the same manner as in Example 1, and a sample was collected. The collected sample was in the same form as in Example 1 and was confirmed to be an hBN crystal, and broad emission around 300 nm was observed along with high-intensity emission at a wavelength of 215 nm by cathodoluminescence measurement.
実施例３；
真空中で１５００℃、窒素気流中で２０００℃の熱処理による脱酸素処理を施した六方晶窒化ホウ素焼結体（粒径約０．５μｍ）をホウ窒化バリウムとホウ窒化リチウムを重量比１：１で混合した溶媒とともにモリブデンカプセルに充填した。これらの溶媒の調整並びに試料のカプセルへの充填は、すべて乾燥窒素雰囲気中で行った。モリブデン反応容器を窒素気流中１気圧、１５００℃、の圧力、温度条件で２時間処理した。昇温速度は１０℃／分程度であった。２０℃／分程度で冷却後、モリブデンカプセルを回収した。
機械的又は化学処理（塩酸−硝酸混液）によりモリブデンカプセルを除去し試料を回収した。溶媒部分は一部、分解の様相を示しているが、ｈＢＮ原料との界面で一部再結晶が見られた。酸処理により溶媒成分を除去、洗浄した後ｈＢＮ結晶の評価を光学顕微鏡観察、ＳＥＭ観察、Ｘ線回折による相の同定、ならびに光学的特性の評価（透過率、カソードルミネッセンス）を行った。その結果、カソードルミネッセンス測定により波長２１５ｎｍに高輝度の発光と共に、３００ｎｍ付近のブロードな発光が観測された。
Example 3;
A hexagonal boron nitride sintered body (particle size: about 0.5 μm) that has been deoxygenated by heat treatment at 1500 ° C. in a vacuum and 2000 ° C. in a nitrogen stream has a weight ratio of barium boronitride to lithium boronitride of 1: 1. Molybdenum capsules were filled together with the solvent mixed in. The preparation of these solvents and the filling of the sample capsules were all performed in a dry nitrogen atmosphere. The molybdenum reaction vessel was treated in a nitrogen stream at 1 atm and 1500 ° C. under pressure and temperature for 2 hours. The heating rate was about 10 ° C./min. After cooling at about 20 ° C./min, the molybdenum capsules were collected.
The molybdenum capsules were removed by mechanical or chemical treatment (hydrochloric acid-nitric acid mixture), and the sample was collected. A part of the solvent portion shows a decomposition state, but a part of recrystallization was observed at the interface with the hBN raw material. After removing and washing the solvent component by acid treatment, the hBN crystal was evaluated by optical microscope observation, SEM observation, phase identification by X-ray diffraction, and evaluation of optical characteristics (transmittance, cathodoluminescence). As a result, broad light emission around 300 nm was observed along with high-intensity light emission at a wavelength of 215 nm by cathodoluminescence measurement.
比較例１；
市販のｈＢＮ焼結体及びｈＢＮ粉末を真空中で１５００℃、窒素気流中で２０００℃の熱処理による脱酸素処理を施した後、カソードルミネッセンスにより発光挙動を測定した。その結果、２１５ｎｍ近傍の単峰性の強い発光は観測されなかった。
Comparative Example 1;
The commercially available hBN sintered body and hBN powder were subjected to deoxygenation treatment by heat treatment at 1500 ° C. in a vacuum and 2000 ° C. in a nitrogen stream, and then the light emission behavior was measured by cathodoluminescence. As a result, strong unimodal light emission around 215 nm was not observed.
比較例２；
実施例１記載のプロセスにおいて、使用した溶媒が一部酸化により、酸素不純物を含んでいた場合、この溶媒を再度ｈＢＮ合成実験に再使用して、原料を仕込み高圧高温処理すると再結晶ｈＢＮ単結晶が合成される。しかし、カソードルミネッセンス測定によると、波長２１５ｎｍよりも、３００ｎｍ付近にブロードな強い発光が観測された。酸素等の不純物の影響により、高輝度の短波長発光特性が阻害されたものと考えられる。
Comparative Example 2;
In the process described in Example 1, when the solvent used contained oxygen impurities due to partial oxidation, the solvent was reused in the hBN synthesis experiment, and the raw material was charged and treated at high pressure and high temperature to recrystallize hBN single crystal. Is synthesized. However, according to the cathodoluminescence measurement, broad and strong light emission was observed near 300 nm rather than the wavelength of 215 nm. It is considered that the high-intensity short-wavelength light emission characteristic is inhibited by the influence of impurities such as oxygen.
上記比較例２の意義は、本高純度ｈＢＮ単結晶を製造し、良好な高輝度発光特性を発現させるためには、使用する溶媒は高純度の育成溶媒を用いた再結晶プロセスが重要であることを教示するものである。これら実施例並びに比較例は、本発明において高純度高輝度発光ｈＢＮ単結晶を作製する際に、合成条件における雰囲気と使用する溶媒の高純度化が重要であることを示している。低圧相窒化ホウ素を原料に用いたホウ窒化バリウム等の高純度溶媒による再結晶により、波長２１５ｎｍで単峰性の高輝度発光挙動を示す六方晶窒化ホウ素単結晶が得られた。 The significance of the above Comparative Example 2 is that a recrystallization process using a high-purity growth solvent is important as a solvent to be used in order to produce this high-purity hBN single crystal and to exhibit good high-luminance emission characteristics. It teaches that. These examples and comparative examples show that it is important to improve the atmosphere under the synthesis conditions and the solvent used when producing a high-purity, high-luminance light-emitting hBN single crystal in the present invention. Recrystallization from a high-purity solvent such as barium boronitride using low-pressure phase boron nitride as a raw material yielded a hexagonal boron nitride single crystal exhibiting a monomodal high-luminance emission behavior at a wavelength of 215 nm.
本発明は、従来の技術では得られなかった波長２３５ｎｍ以下、特に２１０ｎｍから２１５ｎｍに強い高輝度発光挙動を示す六方晶窒化ホウ素単結晶を提供するものであり、これによって、高輝度紫外線固体発光素子を容易に設計することが可能となったことに加え、近年ますます高密度記録媒体の開発が求められる中、これに応えられる基本的材料を提供できたことは大きな意義があり、産業の発展に大いに寄与するものと期待される。また、紫外線による殺菌処理を求めるニーズは、今日重要な環境対策の一つとしてクローズアップされてきた。本発明はそのための有効な材料を提供するものであることから、今後、この面でも産業の発展に寄与し、生活環境の向上に大いに寄与するものと期待される。 The present invention provides a hexagonal boron nitride single crystal exhibiting strong high-luminance emission behavior at a wavelength of 235 nm or less, particularly 210 nm to 215 nm, which was not obtained by the prior art. In addition to the fact that the development of high-density recording media has been increasingly demanded in recent years, the provision of basic materials that can meet this demand has great significance and the development of the industry. It is expected to contribute greatly to The need for sterilization treatment with ultraviolet rays has been highlighted as one of the important environmental measures today. Since the present invention provides an effective material for that purpose, it is expected that it will contribute to the development of the industry and greatly improve the living environment in this aspect.
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