JP5388068B2 - COMPOSITE SUBSTRATE FOR LIGHT EMITTING ELEMENT FORMATION AND MANUFACTURING METHOD THEREOF - Google Patents
COMPOSITE SUBSTRATE FOR LIGHT EMITTING ELEMENT FORMATION AND MANUFACTURING METHOD THEREOF Download PDFInfo
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- C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
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- C04B2235/30—Constituents and secondary phases not being of a fibrous nature
- C04B2235/38—Non-oxide ceramic constituents or additives
- C04B2235/3852—Nitrides, e.g. oxynitrides, carbonitrides, oxycarbonitrides, lithium nitride, magnesium nitride
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- C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
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- C04B2235/38—Non-oxide ceramic constituents or additives
- C04B2235/3852—Nitrides, e.g. oxynitrides, carbonitrides, oxycarbonitrides, lithium nitride, magnesium nitride
- C04B2235/3873—Silicon nitrides, e.g. silicon carbonitride, silicon oxynitride
Description
関連出願
本件出願は、２００７年９月４日付けで日本国特許庁に出願した特願２００７−２２９２６３号に基づく優先権を主張する出願であり、その出願の内容はここに参照して含める。
技術分野
本発明は、ディスプレイ、照明、バックライト光源等に利用できる発光素子形成用複合基板及びその製造方法に関し、特に蛍光を発する光変換材料を用いた発光ダイオード素子用の形成用複合基板及びその製造方法に関する。Related Application This application is an application claiming priority based on Japanese Patent Application No. 2007-229263 filed with the Japan Patent Office on September 4, 2007, the contents of which are incorporated herein by reference.
TECHNICAL FIELD The present invention relates to a composite substrate for forming a light emitting element that can be used for a display, illumination, a backlight light source, and the like, and a method for manufacturing the same, and particularly to a composite substrate for forming a light emitting diode element using a light conversion material that emits fluorescence. It relates to a manufacturing method.
近年、窒化物系化合物半導体（ＩｎｘＡｌｙＧａ１−ｘ−ｙＮ、０≦ｘ≦１、０≦ｙ≦１、０≦ｘ＋ｙ≦１）を用いた青色発光素子を発光源とする白色発光ダイオードの開発研究が盛んに行われている。白色発光ダイオードは軽量で、水銀を使用せず、長寿命であることから、今後、需要が急速に拡大することが予測されている。青色発光素子の青色光を白色光へ変換する方法として最も一般的に行なわれている方法は、例えば特開２０００−２０８８１５号公報に記載されているように、青色光を発光する発光素子の前面に、青色光の一部を吸収して黄色光を発する蛍光体を含有するコーティング層と、光源の青色光とコーティング層からの黄色光を混色するためのモールド層とを設け、補色関係にある青色と黄色を混色することにより擬似的に白色を得るものである。従来、コーティング層としては、セリウムで付活されたＹＡＧ（Ｙ３Ａｌ５Ｏ１２：Ｃｅ）粉末とエポキシ樹脂の混合物が採用されている。しかし本方法ではコーティング層を塗布する際に、含まれる蛍光体粉末の分布のむら、発光ダイオード個体毎の蛍光体粉末の量のバラツキ等が生じやすく、それに起因する発光ダイオードの色むらが指摘されている。
それを回避するため、本発明者らは、ＰＣＴ／ＪＰ２００５／０１９７３９（ＷＯ２００６／０４３７１９）において、セラミック複合酸化物からなる光変換材料基板上にＩｎｘＡｌｙＧａ１−ｘ−ｙＮ（０≦ｘ≦１、０≦ｙ≦１、０≦ｘ＋ｙ≦１）からなる窒化物半導体層を形成し、発光層から発光される青色光を直接基板に入射し基板自身から均質な黄色蛍光を発光させることで、蛍光体粉末を含むコーティング層を用いずに発光チップのみで色むらのない均質な白色を得る方法を提案している。In recent years, a blue light emitting element using a nitride compound semiconductor (In x Al y Ga 1-xy N, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) is used as a white light source. Research and development of light-emitting diodes has been actively conducted. White light-emitting diodes are lightweight, do not use mercury, and have a long life, so that demand is expected to increase rapidly in the future. The most commonly used method for converting blue light of a blue light emitting element into white light is the front surface of a light emitting element that emits blue light, as described in, for example, Japanese Patent Application Laid-Open No. 2000-208815. In addition, a coating layer containing a phosphor that absorbs a part of blue light and emits yellow light and a mold layer for mixing the blue light of the light source and the yellow light from the coating layer are provided and have a complementary color relationship A pseudo white color is obtained by mixing blue and yellow. Conventionally, a mixture of YAG (Y 3 Al 5 O 12 : Ce) powder activated with cerium and an epoxy resin is employed as the coating layer. However, in this method, when the coating layer is applied, uneven distribution of the phosphor powder contained therein, variation in the amount of the phosphor powder among the individual light emitting diodes, etc. are likely to occur, and the resulting color unevenness of the light emitting diodes is pointed out. Yes.
In order to avoid this, the present inventors have disclosed In x Al y Ga 1-xy N (0 ≦ 0) on a light conversion material substrate made of a ceramic composite oxide in PCT / JP2005 / 019739 (WO 2006/043719). a nitride semiconductor layer of x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) is formed, and blue light emitted from the light emitting layer is directly incident on the substrate to emit homogeneous yellow fluorescence from the substrate itself. Therefore, a method for obtaining a uniform white color with no color unevenness using only a light emitting chip without using a coating layer containing phosphor powder has been proposed.
しかしながら、特許文献２の実施例に示すバッファー層としてＧａＮを用いる方法では、Ａｌ２Ｏ３相に優先的に窒化物半導体層が形成されやすいという問題があった。このため、Ａｌ２Ｏ３相に優先的に形成された窒化物半導体は、Ａｌ２Ｏ３相以外の領域で互いに孤立するため、良好な素子形成が困難となる。これを回避し、基板表面全面を窒化物半導体層で覆うためには、厚膜化が必要になる。しかし、厚膜化を行うと、その膜厚の増大にともない、基板と窒化物半導体層の格子定数と熱膨張係数の違いから、最終的に歪みが生じ、素子特性に悪影響を与える傾向が強くなる。良好な特性の素子を得るためには、窒化物半導体層が形成の初期から、基板全面に均一な層が形成していくことが重要である。これを実現するためには、Ａｌ２Ｏ３相とガーネット型構造を有する蛍光を発する酸化物相の両相から互いに同様な窒化物半導体層を形成する工程が必要とされ、同工程を経て発光素子を作製することにより、得られる素子の特性向上が期待される。
本発明者らは、光変換材料基板に窒化物半導体層を形成する際に、窒化物半導体層成長温度と同様か、または、それ以上の高温にて、すくなくともＡｌを含む窒化物層を形成し、バッファー層として用いることにより、基板における蛍光体を発する酸化物相からもＡｌ２Ｏ３相と同様に窒化物半導体層の結晶成長を行うことが可能であることを見出し、本発明に至った。
すなわち、本発明は、光変換材料基板に、少なくともＡｌを含む窒化物バッファー層が形成されており、該バッファー層が光変換材料基板を全面に覆うことを特徴とする発光素子形成用複合基板に関する。
さらに、本発明において好ましい形態として、蛍光体相が少なくともＹ元素、Ａｌ元素、Ｃｅ元素を含むガーネット型構造であることを特徴とする発光素子形成用複合基板に関する。
さらに、本発明において好ましい形態として、前記バッファー層が、Ａｌ２Ｏ３相のＣ面と蛍光体相の（１１２）面を同時に主面とする光変換材料基板に形成されていることを特徴とする発光素子形成用複合基板に関する。
また、光変換材料基板に、少なくともＡｌを含む窒化物バッファー層を形成し、該バッファー層により光変換材料基板が全面に覆われていることを特徴する発光素子形成用複合基板の製造方法に関する。
さらに好ましい形態として、前記窒化物半導体層の形成を有機金属気相反応法で行うことを特徴とする発光素子形成用複合基板の製造方法に関する。
さらに好ましい形態として、前記Ａｌを含む窒化物バッファー層を９００℃以上１４００℃未満の温度で形成することを特徴とする発光素子形成用複合基板の製造方法に関する。
このように作製された発光素子形成用複合基板においては、Ａｌ２Ｏ３相とガーネット型構造を有する蛍光体を発する酸化物相の両相から互いに同様に窒化物半導体層を形成することが可能であり、同工程を経ることにより高特性の白色発光素子を作製することができる。
このような発光層を形成する窒化物半導体層としては、ＩｎｘＡｌｙＧａ１−ｘ−ｙＮ（０≦ｘ≦１、０≦ｙ≦１、０≦ｘ＋ｙ≦１）からなる窒化物半導体層が好適である。However, the method using GaN as the buffer layer shown in the example of Patent Document 2 has a problem that a nitride semiconductor layer is likely to be preferentially formed in the Al 2 O 3 phase. Thus, preferentially formed nitride semiconductor Al 2 O 3 phase to isolated each other in regions other than Al 2 O 3 phase, excellent device formation becomes difficult. In order to avoid this and to cover the entire surface of the substrate with the nitride semiconductor layer, it is necessary to increase the film thickness. However, when the film thickness is increased, the difference between the lattice constant and the thermal expansion coefficient of the substrate and the nitride semiconductor layer will eventually cause distortion as the film thickness increases, and the device characteristics tend to be adversely affected. Become. In order to obtain a device with good characteristics, it is important to form a uniform layer over the entire surface of the substrate from the initial stage of the formation of the nitride semiconductor layer. In order to realize this, it is necessary to form a similar nitride semiconductor layer from both the Al 2 O 3 phase and the fluorescence emitting oxide phase having a garnet structure, and light emission is performed through the same step. By producing the element, improvement in characteristics of the obtained element is expected.
When forming the nitride semiconductor layer on the light conversion material substrate, the present inventors formed a nitride layer containing at least Al at a temperature similar to or higher than the growth temperature of the nitride semiconductor layer. , It was found that by using it as a buffer layer, it is possible to perform crystal growth of the nitride semiconductor layer from the oxide phase emitting phosphors in the substrate in the same manner as the Al 2 O 3 phase, and the present invention has been achieved. .
That is, the present invention relates to a composite substrate for forming a light emitting element, wherein a nitride buffer layer containing at least Al is formed on a light conversion material substrate, and the buffer layer covers the entire surface of the light conversion material substrate. .
Furthermore, as a preferable form in the present invention, the present invention relates to a composite substrate for forming a light emitting element, characterized in that the phosphor phase has a garnet structure including at least a Y element, an Al element, and a Ce element.
Further, as a preferred embodiment in the present invention, the buffer layer is formed on a light conversion material substrate having a C 2 surface of Al 2 O 3 phase and a (112) surface of a phosphor phase as main surfaces at the same time. The present invention relates to a composite substrate for forming a light emitting element.
The present invention also relates to a method for manufacturing a composite substrate for forming a light emitting element, wherein a nitride buffer layer containing at least Al is formed on a light conversion material substrate, and the light conversion material substrate is entirely covered with the buffer layer.
As a more preferred embodiment, the present invention relates to a method for manufacturing a composite substrate for forming a light emitting element, wherein the nitride semiconductor layer is formed by a metal organic vapor phase reaction method.
As a more preferred embodiment, the present invention relates to a method for manufacturing a composite substrate for forming a light emitting element, wherein the Al-containing nitride buffer layer is formed at a temperature of 900 ° C. or higher and lower than 1400 ° C.
In the composite substrate for forming a light emitting element thus fabricated, a nitride semiconductor layer can be formed in the same manner from both the Al 2 O 3 phase and the oxide phase emitting a phosphor having a garnet structure. Thus, a high-performance white light-emitting element can be manufactured through the same process.
As a nitride semiconductor layer forming such a light emitting layer, a nitride semiconductor made of In x Al y Ga 1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) is used. A layer is preferred.
図１Ａ及び１Ｂは本発明の発光素子形成用複合基板の一実施形態を示す模式的断面図である。
図２は光変換材料の組織構造の一例を示す電子顕微鏡写真である。
図３は実施例１により得られたＧａＮ層の顕微鏡断面写真である。
図４は比較例１により得られたＧａＮ層の顕微鏡断面写真である。1A and 1B are schematic cross-sectional views showing an embodiment of a composite substrate for forming a light emitting device of the present invention.
FIG. 2 is an electron micrograph showing an example of the structure of the light conversion material.
FIG. 3 is a microscopic cross-sectional photograph of the GaN layer obtained in Example 1.
FIG. 4 is a microscopic cross-sectional photograph of the GaN layer obtained in Comparative Example 1.
図中の符号の説明
１ 光変換材料基板
１ａ 光変換材料基板のＡｌ２Ｏ３結晶相
１ｂ 光変換材料基板のＹ３Ａｌ５Ｏ１２：Ｃｅ結晶相
２ バッファー層
２ａ Ａｌを含む窒化物層
２ｂ ＧａＮ層DESCRIPTION OF REFERENCE NUMERALS 1 Light conversion material substrate 1a Al 2 O 3 crystal phase of light conversion material substrate 1b Y 3 Al 5 O 12 : Ce crystal phase 2 of light conversion material substrate 2 Buffer layer 2a Nitride layer 2b containing Al GaN layer
本発明の発光素子形成用複合基板の形態として、例えば、図１Ａに示されるような光変換材料基板１の表面に、その複雑に絡み合うＡｌ２Ｏ３相１ａと蛍光体を発する酸化物相１ｂの結晶の違いによらず、全面にバッファー層２が形成されている。該バッファー層は少なくともＡｌを含む窒化物層２ａを含む。また、図１Ｂに示されるような複合基板表面の均質性を向上させるために、Ａｌを含む窒化物層上にＧａＮ層２ｂを形成してもよい。
本発明の発光素子形成用複合基板を構成する光変換材料基板は、単一金属酸化物および複合金属酸化物から選ばれる少なくとも２つ以上の酸化物相が連続的にかつ三次元的に相互に絡み合って形成されている凝固体からなり、該凝固体中の酸化物相のうち少なくとも１つはＡｌ２Ｏ３結晶相であり、また、前記凝固体中の酸化物相のうち少なくとも１つは蛍光を発する金属元素酸化物を含有している。単一金属酸化物とは、１種類の金属の酸化物であり、複合金属酸化物は、２種以上の金属の酸化物である。それぞれの酸化物は、単結晶状態となって三次元的に相互に絡み合った構造をしている。このような単一金属酸化物としては、酸化アルミニウム（Ａｌ２Ｏ３）、酸化ジルコニウム（ＺｒＯ２）、酸化マグネシウム（ＭｇＯ）、酸化シリコン（ＳｉＯ２）、酸化チタン（ＴｉＯ２）酸化バリウム（ＢａＯ）、酸化ベリリウム（ＢｅＯ）、酸化カルシウム（ＣａＯ）、酸化クロミウム（Ｃｒ２Ｏ３）等の他、希土類元素酸化物（Ｌａ２Ｏ３、Ｙ２Ｏ３、ＣｅＯ２、Ｐｒ６Ｏ１１、Ｎｄ２Ｏ３、Ｓｍ２Ｏ３、Ｇｄ２Ｏ３、Ｅｕ２Ｏ３、Ｔｂ４Ｏ７、Ｄｙ２０３、Ｈｏ２Ｏ３、Ｅｒ２Ｏ３、Ｔｍ２Ｏ３、Ｙｂ２Ｏ３、Ｌｕ２Ｏ３）が挙げられる。また、複合金属酸化物としては、ＬａＡｌＯ３、ＣｅＡｌＯ３、ＰｒＡｌＯ３、ＮｄＡｌＯ３、ＳｍＡｌＯ３、ＥｕＡｌＯ３、ＧｄＡｌＯ３、ＤｙＡｌＯ３、ＥｒＡｌＯ３、Ｙｂ４Ａｌ２Ｏ９、Ｙ３Ａｌ５Ｏ１２、Ｅｒ３Ａｌ５Ｏ１２、Ｔｂ３Ａｌ５Ｏ１２、１１Ａｌ２Ｏ３・Ｌａ２Ｏ３、１１Ａｌ２Ｏ３・Ｎｄ２Ｏ３、３Ｄｙ２Ｏ３・５Ａｌ２Ｏ３、２Ｄｙ２Ｏ３・Ａｌ２Ｏ３、１１Ａｌ２Ｏ３・Ｐｒ２Ｏ３、ＥｕＡｌ１１Ｏ１８、２Ｇｄ２Ｏ３・Ａｌ２Ｏ３、１１Ａｌ２Ｏ３・Ｓｍ２Ｏ３、Ｙｂ３Ａｌ５Ｏ１２、ＣｅＡｌ１１Ｏ１８、Ｅｒ４Ａｌ２Ｏ９等が挙げられる。
光変換材料基板は、２種以上の酸化物相からなっているため、その組み合わせにより、様々な結晶格子間隔を選択することができる。このため、発光ダイオードの種々の半導体の格子間隔に合わせることが可能であり、結晶構造上の整合性が良く、欠陥の少ない良好な半導体層を成膜でき、半導体層内に形成された発光層から効率の良い発光を得ることができる。さらに、光変換材料基板は、蛍光体でもあるため、半導体層中の発光層からの光により均一な蛍光も発することができる。
発光ダイオード用半導体層が窒化物半導体層である場合は、光変換材料基板を構成する前記凝固体の中で、単一金属酸化物であるＡｌ２Ｏ３結晶を含む組み合わせが好ましい凝固体として挙げられる。上述のようにＡｌ２Ｏ３結晶は可視光を発する窒化物半導体層を構成する代表的なＩｎＧａＮと結晶構造上整合性が良く、窒化物半導体の良好な発光層を形成することができるためである。そして、Ａｌ２Ｏ３結晶と少なくともセリウムで付活された複合金属酸化物であるガーネット型結晶単結晶との組み合わせがさらに好ましい凝固体として挙げられる。ガーネット型結晶はＡ３Ｘ５Ｏ１２の構造式で表され、構造式中ＡにはＹ，Ｔｂ，Ｓｍ，Ｇｄ，Ｌａ，Ｅｒの群から選ばれる１種以上の元素、同じく構造式中ＸにはＡｌ，Ｇａから選ばれる１種以上の元素が、含まれる場合が特に好ましい。この特に好ましい組み合わせからなる光変換材料は、紫から青色の光を透過しながら、その一部を吸収し、黄色の蛍光を発するためである。なかでもセリウムで付活されたＹ３Ａｌ５Ｏ１２との組み合わせは強い蛍光を発するため好適である。
図１Ａ及び１Ｂに示した一実施形態であるＡｌ２Ｏ３／Ｙ３Ａｌ５Ｏ１２：Ｃｅの光変換材料基板は、Ａｌ２Ｏ３単結晶とＹ３Ａｌ５Ｏ１２：Ｃｅ単結晶から構成され、各酸化物相が連続的にかつ３次元的に相互に絡み合って形成されており、全体として２個の単結晶の相から構成されている。各相が単結晶であることは非常に重要である。単結晶でないと良質の窒化物半導体層を形成することはできない。光変換材料基板は、例えば、上記Ａｌ２Ｏ３／Ｙ３Ａｌ５Ｏ１２：Ｃｅの凝固体を所定厚みに切断し、表面を必要な状態に研磨し、洗浄することにより得られる。光変換材料基板の切出し方位はＡｌ２Ｏ３の（０００１）面を主面とすることが特に好ましい。Ａｌ２Ｏ３は窒化物系化合物半導体であるＩｎｘＡｌｙＧａ１−ｘ−ｙＮと類似の結晶構造を有し、Ａｌ２Ｏ３（０００１）面とＩｎｘＡｌｙＧａ１‐ｘ‐ｙＮの格子間隔は差が小さく整合性が良い。このため、Ａｌ２Ｏ３の（０００１）面を利用することで、良質な窒化物半導体層が得られ良好な発光層を形成することができる。
本発明に用いる光変換材料を構成する凝固体は、原料金属酸化物を融解後、凝固させることで作製される。例えば、所定温度に保持したルツボに仕込んだ溶融物を、冷却温度を制御しながら冷却凝結させる簡単な方法で凝固体を得ることができるが、最も好ましいのは一方向凝固法により作製されたものである。一方向凝固をおこなうことにより含まれる結晶相が単結晶状態で連続的に成長し、各相が単一の結晶方位となるためである。
本発明に用いる光変換材料は、少なくとも１つの相が蛍光を発する金属元素酸化物を含有していることを除き、本願出願人が先に特開平７−１４９５９７号公報、特開平７−１８７８９３号公報、特開平８−８１２５７号公報、特開平８−２５３３８９号公報、特開平８−２５３３９０号公報および特開平９−６７１９４号公報並びにこれらに対応する米国出願（米国特許第５，５６９，５４７号、同第５，４８４，７５２号、同第５，９０２，９６３号）等に開示したセラミック複合材料と同様のものであることができ、これらの出願（特許）に開示した製造方法で製造できるものである。これらの出願あるいは特許の開示内容はここに参照して含めるものである。
発光素子形成用複合基板上に形成する窒化物半導体層は、複数の窒化物系化合物半導体の層からなる。複数の窒化物系化合物半導体の層は、それぞれ、一般式、ＩｎｘＡｌｙＧａ１−ｘ−ｙＮ（０≦ｘ≦１、０≦ｙ≦１、０≦ｘ＋ｙ≦１）で表わされる窒化物系化合物により構成されることが好ましい。そして、窒化物半導体層は、少なくとも可視光を発する発光層を有する。良好な発光層を形成するためには、それぞれの層で、各機能に最適な組成に調整した複数の窒化物系化合物半導体の層を積層することが好ましい。複数の窒化物系化合物半導体の層およびこれらの層の形成方法は、例えば、Ｊｐｎ．Ｊ．Ａｐｐｌ．Ｐｈｙｓ．Ｖｏｌ．３４（１９９５），Ｌ７９７等に開示されているように公知の技術である。具体的には、基板上に、ＧａＮのバッファー層（厚さ３０ｎｍ）、ｎ電極が形成されるｎ型−ＧａＮ：Ｓｉコンタクト層（厚さ５μｍ）、ｎ型−Ａｌ０．１Ｇａ０．９Ｎ：Ｓｉ層、ｎ型−Ｉｎ０．０５Ｇａ０．９５Ｎ：Ｓｉ層、単一量子井戸構造型発光層を形成するＩｎＧａＮ層、ｐ型‐Ａｌ０．１Ｇａ０．９Ｎ：Ｍｇ障壁層、ｐ電極が形成されるｐ型‐ＧａＮ：Ｍｇ層をＭＯＣＶＤなどの方法により、順に積層することにより得ることができる。発光層の構造は他に、多重量子井戸構造や、ホモ構造、ヘテロ構造あるいはダブルヘテロ構造としても良い。ただし、本発明では、上記基板として本発明の発光素子形成用複合基板を用いるので、発光素子形成用複合基板上に形成する窒化物半導体層は、発光素子形成用複合基板が表面にＡｌを含む窒化物層を有しているので、ＧａＮのバッファー層（厚さ３０ｎｍ）は省略できる。
本発明における発光素子形成用複合基板に形成する窒化物半導体層中の発光層は可視光であることが好ましい。可視光が本発明の発光素子形成用複合基板を構成する光変換材料基板を透過する際に、波長変換された蛍光と変換前の可視光が混合されて、混合された光の波長に応じて、新たな擬似的な光を得ることができる。さらに、可視光は青色または紫色を発することが好ましい。発光色が青色または紫色である場合、発光層からの青色または紫色の光が、基板であるＹＡＧ：Ｃｅ単結晶に入射することにより、Ｙ３Ａｌ５Ｏ１２：Ｃｅ結晶から黄色蛍光が発生し、Ａｌ２Ｏ３結晶では青色または紫色の光がそのまま透過する。これらの光が光変換材料単結晶基板内の連続的にかつ三次元的に相互に絡み合った組織により混合され、放出されるため、色むらのない均質な白色を得ることができる。このため、窒化物半導体層中の発光層は、ＩｎｘＧａ１−ｘＮ（０≦ｘ≦１）からなることが好ましい。前記発光層を形成するＩｎＧａＮ層に含まれるＩｎのモル比を変えることにより、発光波長を変化させることができる。
本発明におけるバッファー層を設けることで、その上に前記窒化物半導体層が好ましく形成できる。本発明における窒化物バッファー層を形成した発光素子形成用複合基板を用いることで、新たにバッファー層を設けることなく、前記窒化物半導体層を形成することが可能になる。また、一般に窒化物半導体層の形成は、気相成長反応で行われるので、基板の表面は均一であることが望ましい。このため、窒化物半導体層の形成と同様に、前記バッファー層の形成についても、高品質のバッファー層を得ることができる気相反応法により行うことが好ましい。特に、品質と成長速度の観点から有機金属化学気相成長法（以下、ＭＯＣＶＤと呼ぶ）により形成することが好ましい。ＭＯＣＶＤは、原料である有機金属ガスをＨ２またはＮ２により加熱した基板上に押し流し、基板表面において結晶成長を起こす方法である。前記バッファー層に関わる原料ガスとしては、Ａｌ源としてＴＭＡ（トリメチルアルミニウム）またはＴＥＡ（トリエチルアルミニウム）等、Ｇａ源としてＴＭＧ（トリメチルガリウム）またはＴＥＧ（トリエチルガリウム）等、Ｎ源としてアンモニアまたはヒドラジン等、一般的にＭＯＣＶＤにおける窒化物半導体層の形成に用いられるものを使うことができる。
本発明における窒化物バッファー層は基板表面を全面に覆っていることを特徴とする。このことにより、窒化物半導体層の形成の際に、光変換材料基板のＡｌ２Ｏ３相と蛍光体相との境がなく、積層構造を安定的に形成することを可能にする。また、Ａｌ２Ｏ３相から優先的に成長を行い、均一な面を得ることも可能であるが、本発明の窒化物バッファー層が存在しないで、光変換材料基板（Ａｌ２Ｏ３相と蛍光体相を含む複合酸化物）だけを用いて窒化物半導体層の均一面を得るためには、厚膜化が必要であり、均一面が得られても、その歪により、クラックが生じることや、基板が歪むことがあり、素子特性に悪影響を与える。しかし、本発明におけるバッファー層が形成されている複合基板を用いることで、厚膜化が不要であり、十分な薄膜化が可能になり、素子特性への影響もほとんどない。
本発明におけるバッファー層は、少なくともＡｌを含む窒化物層を含むことを特徴とする。具体的には、ＡｌｘＧａ１−ｘＮ（０＜ｘ≦１）で表される窒化物層を含むことが好ましい。さらに好ましくはＡｌＮを含むのがよい。窒化物半導体と同程度以上の形成温度となるような、９００℃から１４００℃の温度条件で形成することが好ましい。さらに好ましくは、１１５０℃から１４００℃の温度条件で形成することがよい。９００℃から１２００℃においては、Ａｌ２Ｏ３相と蛍光体相に成長する窒化物層を均一にすることが困難であるが、蛍光体相においても窒化物層を形成することが可能である。さらに、より高温で窒化物層を形成することにより、より容易に均一面を得ることが可能になる。また、該バッファー層は、その結晶性が該バッファー層上に形成される窒化物半導体層の素子特性に大きく影響し、より結晶性がよりよい方が好適である。Ａｌを含む窒化物層としてＡｌｘＧａ１−ｘＮ（０＜ｘ≦１）の結晶性を向上させる方法は、温度条件に関わらず、窒化物半導体層の素子特性の向上へ役立てることができる。例えばＭＯＣＶＤでは、より高温にすると、得られるＡｌｘＧａ１−ｘＮ（０＜ｘ≦１）組成においてＧａが必然的に減少する。バッファー層として形成される窒化物層の品質から、Ｇａ組成の低いものの方がよりよい。
また、前記Ａｌを含む窒化物層の上に、横方向の結晶成長速度が速くなる条件でＧａＮを形成するとさらに好適である。Ａｌを含む窒化物層の形成は、光変換材料基板におけるＡｌ２Ｏ３相と蛍光体相に同様に結晶核形成を行うが、Ａｌ−ＮはＧａ−Ｎに比べ結合エネルギーが高く、表面における移動度が小さいので、Ａｌを含む窒化物層だけでは、Ａｌ２Ｏ３相と蛍光体相における窒化物層のわずかな違いが結晶性と表面形態に違いとして現れることがある。ＧａＮを成長させることで、Ａｌ２Ｏ３相と蛍光体相に成長した窒化物結晶上でマイグレーションが起こりやすくなり、それぞれの結晶相の違いを無くすることが可能になる。横方向の結晶成長速度が速くなる条件でＧａＮを形成するときにＳｉ、Ｇｅ、Ｓｅ、Ｔｅ等の不純物ドープによってｎ型化すると、上記の効果とｎ型−ＧａＮコンタクト層の形成を兼ねて行うことができ好適である。ＧａＮの横方向への結晶成長速度を上げるには、結晶成長温度、Ｖ／ＩＩＩ比等の成長条件を変えるといった公知の方法を用いることで可能であり、その方法を選ぶものではない。また、前記Ａｌを含む窒化物層に関して、原料ガスの供給法の制御によりマイグレーションを優位に行う方法を用いることによっても、同様の効果を得ることができる。
本発明による発光素子形成用複合基板を用いることで、窒化物半導体層をバッファー層なしで形成することができる。窒化物半導体層の形成には、一般的には気相成長法を用いる。窒化物半導体層を形成するために、加熱に際し窒素が欠損しやすい。Ｖ族原料ガスを流しながら加熱することで、窒素欠損が低減され、安定した窒化物半導体層の形成が可能になる。
また、本発明によれば、光変換材料基板を用いて、その基板上に本発明の発光素子形成用複合基板と同構造のバッファー層を形成し、それと連続して窒化物半導体層を形成することも可能である。窒化物半導体層の形成に際し、再加熱による窒素欠損がなく、同様の特性を有する発光素子を得ることが可能である。As a form of the composite substrate for forming a light emitting element of the present invention, for example, an intricately intertwined Al 2 O 3 phase 1a and an oxide phase 1b emitting phosphors are formed on the surface of the light conversion material substrate 1 as shown in FIG. 1A. Regardless of the crystal difference, the buffer layer 2 is formed on the entire surface. The buffer layer includes a nitride layer 2a containing at least Al. Further, in order to improve the uniformity of the composite substrate surface as shown in FIG. 1B, the GaN layer 2b may be formed on the nitride layer containing Al.
In the light conversion material substrate constituting the composite substrate for forming a light emitting element of the present invention, at least two oxide phases selected from a single metal oxide and a composite metal oxide are mutually and continuously three-dimensionally. It consists of a solidified body formed intertwined, at least one of the oxide phases in the solidified body is an Al 2 O 3 crystal phase, and at least one of the oxide phases in the solidified body is It contains a metal element oxide that emits fluorescence. The single metal oxide is an oxide of one kind of metal, and the composite metal oxide is an oxide of two or more kinds of metals. Each oxide has a single crystal state and a three-dimensionally entangled structure. Examples of such a single metal oxide include aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), magnesium oxide (MgO), silicon oxide (SiO 2 ), titanium oxide (TiO 2 ) and barium oxide (BaO). ), Beryllium oxide (BeO), calcium oxide (CaO), chromium oxide (Cr 2 O 3 ) and the like, as well as rare earth element oxides (La 2 O 3 , Y 2 O 3 , CeO 2 , Pr 6 O 11 , Nd). 2 O 3 , Sm 2 O 3 , Gd 2 O 3 , Eu 2 O 3 , Tb 4 O 7 , Dy 2 03, Ho 2 O 3 , Er 2 O 3 , Tm 2 O 3 , Yb 2 O 3 , Lu 2 O 3 ). As the composite metal oxide, LaAlO 3, CeAlO 3, PrAlO 3, NdAlO 3, SmAlO 3, EuAlO 3, GdAlO 3, DyAlO 3, ErAlO 3, Yb 4 Al 2 O 9, Y 3 Al 5 O 12, Er 3 Al 5 O 12, Tb 3 Al 5 O 12, 11Al 2 O 3 · La 2 O 3, 11Al 2 O 3 · Nd 2 O 3, 3Dy 2 O 3 · 5Al 2 O 3, 2Dy 2 O 3 · Al 2 O 3, 11Al 2 O 3 · Pr 2 O 3, EuAl 11 O 18, 2Gd 2 O 3 · Al 2 O 3, 11Al 2 O 3 · Sm 2 O 3, Yb 3 Al 5 O 12, CeAl 11 O 18 , Er 4 Al 2 O 9 and the like.
Since the light conversion material substrate is composed of two or more kinds of oxide phases, various crystal lattice spacings can be selected depending on the combination thereof. For this reason, it is possible to match the lattice spacing of various semiconductors of the light-emitting diode, it is possible to form a good semiconductor layer with good crystal structure consistency and few defects, and the light-emitting layer formed in the semiconductor layer Therefore, efficient light emission can be obtained. Furthermore, since the light conversion material substrate is also a phosphor, it can emit uniform fluorescence by light from the light emitting layer in the semiconductor layer.
When the semiconductor layer for light emitting diodes is a nitride semiconductor layer, among the solidified bodies constituting the light conversion material substrate, a combination containing an Al 2 O 3 crystal that is a single metal oxide is cited as a preferable solidified body. It is done. As described above, the Al 2 O 3 crystal has good crystal structure matching with typical InGaN constituting the nitride semiconductor layer that emits visible light, and can form a good light emitting layer of the nitride semiconductor. is there. A combination of an Al 2 O 3 crystal and a garnet-type crystal single crystal that is a composite metal oxide activated with at least cerium is further preferred as a solidified body. The garnet-type crystal is represented by a structural formula of A 3 X 5 O 12 , where A is one or more elements selected from the group of Y, Tb, Sm, Gd, La, Er, It is particularly preferable that one contains at least one element selected from Al and Ga. This is because the light conversion material composed of this particularly preferable combination absorbs part of the light conversion material while transmitting purple to blue light and emits yellow fluorescence. Among them, the combination with Y 3 Al 5 O 12 activated with cerium is suitable because it emits strong fluorescence.
The light conversion material substrate of Al 2 O 3 / Y 3 Al 5 O 12 : Ce that is one embodiment shown in FIGS. 1A and 1B is composed of an Al 2 O 3 single crystal and a Y 3 Al 5 O 12 : Ce single crystal. Each oxide phase is continuously and three-dimensionally entangled with each other, and is composed of two single crystal phases as a whole. It is very important that each phase is a single crystal. If it is not a single crystal, a good quality nitride semiconductor layer cannot be formed. The light conversion material substrate can be obtained, for example, by cutting the Al 2 O 3 / Y 3 Al 5 O 12 : Ce solidified body into a predetermined thickness, polishing the surface to a necessary state, and washing. As for the cutting direction of the light conversion material substrate, it is particularly preferable that the (0001) plane of Al 2 O 3 is the main surface. Al 2 O 3 has a crystal structure similar to In x Al y Ga 1-xy N, which is a nitride compound semiconductor, and has an Al 2 O 3 (0001) plane and In x Al y Ga 1-x-. The lattice spacing of yN has a small difference and good matching. For this reason, by using the (0001) plane of Al 2 O 3 , a good quality nitride semiconductor layer can be obtained and a good light emitting layer can be formed.
The solidified body constituting the light conversion material used in the present invention is produced by solidifying the raw metal oxide after melting. For example, it is possible to obtain a solidified body by a simple method of cooling and condensing a melt charged in a crucible held at a predetermined temperature while controlling the cooling temperature, but the most preferable one is produced by a unidirectional solidification method. It is. This is because the crystal phases contained by unidirectional solidification grow continuously in a single crystal state, and each phase has a single crystal orientation.
The light-converting material used in the present invention has previously been disclosed in Japanese Patent Application Laid-Open Nos. 7-149597 and 7-187893 by the applicant of the present application, except that at least one phase contains a metal element oxide that emits fluorescence. Publication, JP-A-8-81257, JP-A-8-253389, JP-A-8-253390, JP-A-9-67194, and corresponding US applications (US Pat. No. 5,569,547). No. 5,484,752, No. 5,902,963) and the like, and can be manufactured by the manufacturing method disclosed in these applications (patents). Is. The disclosures of these applications or patents are hereby incorporated by reference.
The nitride semiconductor layer formed on the light emitting element forming composite substrate is composed of a plurality of nitride compound semiconductor layers. The plurality of nitride compound semiconductor layers are nitrided represented by the general formula, In x Al y Ga 1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), respectively. It is preferably composed of a physical compound. The nitride semiconductor layer has at least a light emitting layer that emits visible light. In order to form a good light-emitting layer, it is preferable to stack a plurality of nitride-based compound semiconductor layers adjusted to the optimum composition for each function in each layer. A plurality of nitride compound semiconductor layers and methods for forming these layers are described in, for example, Jpn. J. et al. Appl. Phys. Vol. 34 (1995), L797 and the like. Specifically, on the substrate, a GaN buffer layer (thickness 30 nm), an n-type-GaN: Si contact layer (thickness 5 μm) on which an n-electrode is formed, and n-type-Al 0.1 Ga 0.9 N: Si layer, n-type -In 0.05 Ga 0.95 N: Si layer, InGaN layer forming a single quantum well structure type light emitting layer, p-type -Al 0.1 Ga 0.9 N: Mg barrier A p-type GaN: Mg layer on which a layer and a p-electrode are formed can be obtained by laminating sequentially by a method such as MOCVD. In addition, the structure of the light emitting layer may be a multiple quantum well structure, a homo structure, a hetero structure, or a double hetero structure. However, in the present invention, since the light emitting element forming composite substrate of the present invention is used as the substrate, the nitride semiconductor layer formed on the light emitting element forming composite substrate includes Al on the surface. Since it has a nitride layer, the GaN buffer layer (thickness 30 nm) can be omitted.
The light emitting layer in the nitride semiconductor layer formed on the light emitting element forming composite substrate in the present invention is preferably visible light. When visible light passes through the light conversion material substrate constituting the composite substrate for forming a light emitting element of the present invention, the wavelength-converted fluorescence and the visible light before conversion are mixed, and depending on the wavelength of the mixed light New pseudo light can be obtained. Furthermore, it is preferable that visible light emits blue or purple. When the emission color is blue or violet, yellow fluorescence is generated from the Y 3 Al 5 O 12 : Ce crystal when the blue or violet light from the emission layer is incident on the YAG: Ce single crystal as the substrate. In the Al 2 O 3 crystal, blue or violet light is transmitted as it is. Since these lights are mixed and emitted by the structure in which the light conversion material single crystal substrate is continuously and three-dimensionally entangled with each other, a uniform white color with no color unevenness can be obtained. For this reason, it is preferable that the light emitting layer in the nitride semiconductor layer is made of In x Ga 1-x N (0 ≦ x ≦ 1). The emission wavelength can be changed by changing the molar ratio of In contained in the InGaN layer forming the light emitting layer.
By providing the buffer layer in the present invention, the nitride semiconductor layer can be preferably formed thereon. By using the composite substrate for light emitting element formation in which the nitride buffer layer in the present invention is formed, the nitride semiconductor layer can be formed without newly providing a buffer layer. In general, since the nitride semiconductor layer is formed by vapor phase growth reaction, the surface of the substrate is preferably uniform. For this reason, as with the formation of the nitride semiconductor layer, the formation of the buffer layer is preferably performed by a gas phase reaction method capable of obtaining a high-quality buffer layer. In particular, it is preferably formed by metal organic chemical vapor deposition (hereinafter referred to as MOCVD) from the viewpoint of quality and growth rate. MOCVD is a method in which an organic metal gas as a raw material is pushed onto a substrate heated with H 2 or N 2 to cause crystal growth on the substrate surface. The source gas related to the buffer layer includes TMA (trimethylaluminum) or TEA (triethylaluminum) as an Al source, TMG (trimethylgallium) or TEG (triethylgallium) as a Ga source, ammonia or hydrazine as an N source, In general, those used for forming a nitride semiconductor layer in MOCVD can be used.
In the present invention, the nitride buffer layer covers the entire surface of the substrate. Thus, when the nitride semiconductor layer is formed, there is no boundary between the Al 2 O 3 phase and the phosphor phase of the light conversion material substrate, and it is possible to stably form a laminated structure. It is also possible to grow preferentially from the Al 2 O 3 phase and obtain a uniform surface, but without the nitride buffer layer of the present invention, the light conversion material substrate (Al 2 O 3 phase and In order to obtain a uniform surface of a nitride semiconductor layer using only a composite oxide containing a phosphor phase), it is necessary to increase the film thickness, and even if a uniform surface is obtained, cracks are generated due to the distortion. In addition, the substrate may be distorted, adversely affecting device characteristics. However, by using the composite substrate on which the buffer layer is formed in the present invention, it is not necessary to increase the film thickness, it is possible to sufficiently reduce the film thickness, and there is almost no influence on the element characteristics.
The buffer layer according to the present invention includes a nitride layer containing at least Al. Specifically, it is preferable to include a nitride layer represented by Al x Ga 1-x N (0 <x ≦ 1). More preferably, AlN is included. It is preferable to form the film under a temperature condition of 900 ° C. to 1400 ° C. so that the formation temperature is equal to or higher than that of the nitride semiconductor. More preferably, the film is formed under a temperature condition of 1150 ° C. to 1400 ° C. At 900 ° C. to 1200 ° C., it is difficult to make the nitride layer growing in the Al 2 O 3 phase and the phosphor phase uniform, but it is possible to form the nitride layer also in the phosphor phase. . Furthermore, it is possible to obtain a uniform surface more easily by forming the nitride layer at a higher temperature. Further, it is preferable that the buffer layer has better crystallinity because its crystallinity greatly affects the device characteristics of the nitride semiconductor layer formed on the buffer layer. A method for improving the crystallinity of Al x Ga 1-x N (0 <x ≦ 1) as a nitride layer containing Al can be used to improve device characteristics of the nitride semiconductor layer regardless of temperature conditions. . For example, in MOCVD, when the temperature is higher, Ga inevitably decreases in the resulting Al x Ga 1-x N (0 <x ≦ 1) composition. In view of the quality of the nitride layer formed as the buffer layer, one having a lower Ga composition is better.
Further, it is more preferable that GaN is formed on the nitride layer containing Al under the condition that the lateral crystal growth rate is increased. The formation of the nitride layer containing Al is similar to the formation of crystal nuclei in the Al 2 O 3 phase and the phosphor phase in the light conversion material substrate. Because of the low mobility, a slight difference between the Al 2 O 3 phase and the phosphor layer in the phosphor phase may appear as a difference in crystallinity and surface morphology only with the nitride layer containing Al. By growing GaN, migration is likely to occur on the nitride crystal grown in the Al 2 O 3 phase and the phosphor phase, and the difference between the crystal phases can be eliminated. When GaN is formed under the condition that the crystal growth rate in the lateral direction is increased, if n-type is formed by doping impurities such as Si, Ge, Se, Te, etc., the above effect is combined with the formation of the n-type-GaN contact layer. This is preferable. In order to increase the crystal growth rate in the lateral direction of GaN, it is possible to use known methods such as changing the growth conditions such as the crystal growth temperature and the V / III ratio, and the method is not selected. Further, the same effect can be obtained by using a method of performing migration preferentially by controlling the source gas supply method for the nitride layer containing Al.
By using the composite substrate for light emitting element formation according to the present invention, the nitride semiconductor layer can be formed without a buffer layer. In general, a vapor phase growth method is used to form the nitride semiconductor layer. In order to form the nitride semiconductor layer, nitrogen is easily lost during heating. By heating while flowing the group V source gas, nitrogen deficiency is reduced, and a stable nitride semiconductor layer can be formed.
Further, according to the present invention, a buffer layer having the same structure as the light emitting element forming composite substrate of the present invention is formed on the substrate using the light conversion material substrate, and a nitride semiconductor layer is formed continuously therewith. It is also possible. When forming the nitride semiconductor layer, it is possible to obtain a light-emitting element having no nitrogen deficiency due to reheating and having similar characteristics.
以下、具体的例を挙げ、本発明を更に詳しく説明する。
（実施例１）
α−Ａｌ２Ｏ３粉末（純度９９．９９％）をＡｌＯ３／２換算で０．８２モル、Ｙ２Ｏ３粉末（純度９９．９％）をＹＯ３／２換算で０．１７５モル、ＣｅＯ２粉末（純度９９．９％）を０．００５モルとなるよう秤量した。これらの粉末をエタノール中、ボールミルによって１６時間湿式混合した後、エバポレーターを用いてエタノールを脱媒して原料粉末を得た。原料粉末は、真空炉中で予備溶解し一方向凝固の原料とした。
次に、この原料をそのままモリブデンルツボに仕込み、一方向凝固装置にセットし、１．３３×１０−３Ｐａ（１０−５Ｔｏｒｒ）の圧力下で原料を融解した。次に同一の雰囲気においてルツボを２０ｍｍ／時間の速度で下降させ、Ａｌ２Ｏ３（サファイア）相、（Ｙ、Ｃｅ）３Ａｌ５Ｏ１２相の２つの酸化物相からなる凝固体を得た。
凝固体の凝固方向に垂直な断面組織を図２に示す。白い部分がＹ３Ａｌ５Ｏ１２：Ｃｅ結晶、黒い部分がＡｌ２Ｏ３結晶である。二つの結晶が相互に絡み合った組織を有していることが分かる。
得られた凝固体はＸ線回折により極点図の測定を行い、結晶軸の方向を調べ、Ａｌ２Ｏ３結晶相のＣ面を主面とした基板の切り出しを行った。切り出しを行った光変換材料は、研磨、洗浄を行い、これを光変換材料基板とした。得られた光変換材料基板は再度Ｘ線回折測定を行い、基板表面とＡｌ２Ｏ３のＣ面との誤差が＜±２°以内であることを確認した。
発光素子形成用複合基板のためのバッファー層の形成は一般的なＭＯＣＶＤ炉を用いて行った。原料ガスは、Ａｌ源としてＴＭＡ、Ｇａ源としてＴＭＧ、Ｓｉ源としてＴＥＳ（テトラエチルシラン）を用いた。原料ガスはＨ２により反応炉内へ導入され、加熱した光変換材料基板に結晶成長を行った。
炉内にセッティングを行った光変換材料基板は、Ｈ２雰囲気において昇温・加熱し、基板を清浄化した。目的とする温度に設定を変え、原料ガスを流し、Ａｌを含む窒化物層を形成した。引き続き横方向への成長を促進する条件において４μｍのＧａＮ：Ｓｉの成長を行うことにより、目的とする発光素子形成用複合基板を作製した。
Ａｌを含む窒化物層として、３００ｎｍのＡｌＮを１３００℃で形成し、それを用いた。電子線顕微鏡により観察した結果、図３のＧａＮ層の断面写真に示すごとく、Ａｌ２Ｏ３相と蛍光体相における境界は観測されず、均一なＧａＮ表面を形成していた。基板の黒っぽい部分がＡｌ２Ｏ３相で、白っぽい部分がＹＡＧ相である。ＧａＮ薄膜は、Ａｌ２Ｏ３相、ＹＡＧ相の両相に成長している。その結果、表面は平滑である。図３において、１ａは基板のＡｌ２Ｏ３相、１ｂはＹ３Ａｌ５Ｏ１２：Ｃｅ相であり、２ａはＡｌＮバッファー層、２ｂはＧａＮ：Ｓｉ層である。ＡｌＮバッファー層２ａは基板上で横方向に連続している。
（比較例１）
光変換材料基板として実施例１と同様に作製したものを用いて、前記掲載の論文Ｊｐｎ．Ｊ．Ａｐｐｌ．Ｐｈｙｓ．Ｖｏｌ．３４（１９９５），Ｌ７９７に従い、Ａｌを含む窒化物層の代わりに、３０ｎｍのＧａＮを５５０℃にて形成し、続けて、実施例１と同じ条件でｎ型−ＧａＮ：Ｓｉ層を形成した。バッファー層としてＧａＮを３０ｎｍの厚さに形成する理由は、上に形成するｎ型−ＧａＮ：Ｓｉ層との格子整合を良好にするためである（下記のように、バッファーＧａＮ層の厚さを増やしても結果は同じである）。
図４にＧａＮ層の断面写真を示す。Ａｌ２Ｏ３相には明らかにＧａＮの形成が確認できた。蛍光体相においては、Ａｌ２Ｏ３相からの横方向の成長によってその表面の一部はＧａＮにより覆われていたが、蛍光体相からのＧａＮの成長は確認することができず、表面の平滑性が劣っていることが分かる。図４において、Ａｌ２Ｏ３相１ａ上に成長したＧａＮ層２は、バッファーＧａＮ層（３０ｎｍ）２ｃとｎ型−ＧａＮ：Ｓｉ層（４μｍ）２ｄを合わせたＧａＮ層２の全体でも、横方向に連続していなかった（したがって、バッファーＧａＮ層２ｃの厚さを実施例１の３００ｎｍより厚く、例えば４μｍにしても、結果は同じである）。
（実施例２、比較例２）
素子特性を調べるために、実施例１、比較例１と同様に形成したＧａＮ：Ｓｉ層の形成に、続いて、ｎ型−Ａｌ０．１Ｇａ０．９Ｎ：Ｓｉ層、ｎ型−Ｉｎ０．０５Ｇａ０．９５Ｎ：Ｓｉ層、単一量子井戸構造型発光層を形成するＩｎＧａＮ層、ｐ型‐Ａｌ０．１Ｇａ０．９Ｎ：Ｍｇ障壁層、ｐ電極が形成されるｐ型‐ＧａＮ：Ｍｇ層を形成し、ｎ型コンタクト層およびｐ型コンタクト層に電極形成を行って、発光ダイオード素子を作製した。
実施例２においては、前記発光素子形成用複合基板の作製と同様に、いずれの半導体層も均一に形成することが可能であり、全面からの発光を確認することができた。
比較例２においては、その形態から電極の形成が困難であり、十分な発光を得ることができなかった。
作製した発光ダイオード素子の外部量子効率を、実施例１を基準にして比較した結果を以下にまとめる。
（実施例３）
Ａｌを含む窒化物層として、３００ｎｍのＡｌ０．１Ｇａ０．９ＮまたはＡｌ０．２５Ｇａ０．７５Ｎを１１５０℃で形成し、それを用いた以外、実施例１と同様にした。電子線顕微鏡により観察した結果、実施例１と同様に、Ａｌ２Ｏ３相と蛍光体相における境界は観測されず、複合基板上に均一なＧａＮ表面を形成していた。その様子は図３と同じである。
以上の結果により、本発明によるバッファー層を有する発光素子形成用複合基板を用いることで、光変換材料基板をより有効に活用し、良好な白色発光素子の形成が可能になることは明らかである。Hereinafter, the present invention will be described in more detail with specific examples.
Example 1
α-Al 2 O 3 powder (purity 99.99%) is 0.82 mol in terms of AlO 3/2 , Y 2 O 3 powder (purity 99.9%) is 0.175 mol in terms of YO 3/2 , CeO 2 powder (purity 99.9%) was weighed to 0.005 mol. These powders were wet mixed in ethanol by a ball mill for 16 hours, and then ethanol was removed using an evaporator to obtain a raw material powder. The raw material powder was pre-melted in a vacuum furnace and used as a raw material for unidirectional solidification.
Next, this raw material was directly charged into a molybdenum crucible and set in a unidirectional solidification apparatus, and the raw material was melted under a pressure of 1.33 × 10 −3 Pa (10 −5 Torr). Next, the crucible was lowered at a speed of 20 mm / hour in the same atmosphere to obtain a solidified body composed of two oxide phases of Al 2 O 3 (sapphire) phase and (Y, Ce) 3 Al 5 O 12 phase. .
A cross-sectional structure perpendicular to the solidification direction of the solidified body is shown in FIG. White part is Y 3 Al 5 O 12: Ce crystals are black portions are Al 2 O 3 crystal. It can be seen that the two crystals have a structure intertwined with each other.
The obtained solidified body was subjected to pole figure measurement by X-ray diffraction, the direction of the crystal axis was examined, and the substrate was cut out with the C plane of the Al 2 O 3 crystal phase as the main surface. The light conversion material cut out was polished and washed, and this was used as a light conversion material substrate. The obtained light conversion material substrate was again subjected to X-ray diffraction measurement, and it was confirmed that the error between the substrate surface and the C plane of Al 2 O 3 was within ± 2 °.
Formation of the buffer layer for the composite substrate for light emitting element formation was performed using a general MOCVD furnace. The source gas used was TMA as the Al source, TMG as the Ga source, and TES (tetraethylsilane) as the Si source. The source gas was introduced into the reactor by H 2 and crystal growth was performed on the heated light conversion material substrate.
The light conversion material substrate set in the furnace was heated and heated in an H 2 atmosphere to clean the substrate. The setting was changed to the target temperature, the raw material gas was flowed, and a nitride layer containing Al was formed. Subsequently, a GaN: Si film having a thickness of 4 μm was grown under conditions that promoted lateral growth, thereby producing a target light emitting element forming composite substrate.
As a nitride layer containing Al, AlN of 300 nm was formed at 1300 ° C. and used. As a result of observation with an electron microscope, as shown in the cross-sectional photograph of the GaN layer in FIG. 3, the boundary between the Al 2 O 3 phase and the phosphor phase was not observed, and a uniform GaN surface was formed. The dark part of the substrate is the Al 2 O 3 phase and the whitish part is the YAG phase. The GaN thin film grows in both Al 2 O 3 phase and YAG phase. As a result, the surface is smooth. In FIG. 3, 1a is an Al 2 O 3 phase of the substrate, 1b is a Y 3 Al 5 O 12 : Ce phase, 2a is an AlN buffer layer, and 2b is a GaN: Si layer. The AlN buffer layer 2a is continuous in the lateral direction on the substrate.
(Comparative Example 1)
A light conversion material substrate prepared in the same manner as in Example 1 was used, and the article Jpn. J. et al. Appl. Phys. Vol. 34 (1995), L797, 30 nm of GaN was formed at 550 ° C. in place of the Al-containing nitride layer, and then an n-type GaN: Si layer was formed under the same conditions as in Example 1. The reason why GaN is formed to a thickness of 30 nm as the buffer layer is to improve the lattice matching with the n-type GaN: Si layer formed thereon (as described below, the thickness of the buffer GaN layer is reduced). Even if you increase it, the result is the same).
FIG. 4 shows a cross-sectional photograph of the GaN layer. The formation of GaN was clearly confirmed in the Al 2 O 3 phase. In the phosphor phase, a part of the surface was covered with GaN by lateral growth from the Al 2 O 3 phase, but the growth of GaN from the phosphor phase could not be confirmed, and the surface It can be seen that the smoothness is inferior. In FIG. 4, the GaN layer 2 grown on the Al 2 O 3 phase 1a is the lateral direction of the entire GaN layer 2 including the buffer GaN layer (30 nm) 2c and the n-type GaN: Si layer (4 μm) 2d. (Thus, even if the thickness of the buffer GaN layer 2c is larger than 300 nm of Example 1, for example, 4 μm, the result is the same).
(Example 2, comparative example 2)
To investigate the device characteristics, Example 1, GaN was formed in the same manner as Comparative Example 1: formation of the Si layer, followed by, n-type -Al 0.1 Ga 0.9 N: Si layer, n-type -In 0.05 Ga 0.95 N: Si layer, InGaN layer forming a single quantum well structure type light emitting layer, p-type-Al 0.1 Ga 0.9 N: Mg barrier layer, p on which a p electrode is formed A type-GaN: Mg layer was formed, and electrodes were formed on the n-type contact layer and the p-type contact layer to produce a light-emitting diode element.
In Example 2, similar to the production of the composite substrate for forming a light emitting element, any semiconductor layer can be formed uniformly, and light emission from the entire surface was confirmed.
In Comparative Example 2, it was difficult to form an electrode due to its form, and sufficient light emission could not be obtained.
The results of comparing the external quantum efficiencies of the manufactured light-emitting diode elements with reference to Example 1 are summarized below.
(Example 3)
As the nitride layer containing Al, 300 nm Al 0.1 Ga 0.9 N or Al 0.25 Ga 0.75 N was formed at 1150 ° C., and the same procedure as in Example 1 was used except that it was used. As a result of observation with an electron microscope, the boundary between the Al 2 O 3 phase and the phosphor phase was not observed as in Example 1, and a uniform GaN surface was formed on the composite substrate. This is the same as in FIG.
From the above results, it is clear that the use of the light emitting element forming composite substrate having the buffer layer according to the present invention makes it possible to more effectively utilize the light conversion material substrate and form a good white light emitting element. .
Claims (10)
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| JP2007229263 | 2007-09-04 | ||
| JP2007229263 | 2007-09-04 | ||
| PCT/JP2008/066272 WO2009031696A1 (en) | 2007-09-04 | 2008-09-03 | Composite substrate for forming light emitting element and method for manufacturing the composite substrate |
| JP2009531310A JP5388068B2 (en) | 2007-09-04 | 2008-09-03 | COMPOSITE SUBSTRATE FOR LIGHT EMITTING ELEMENT FORMATION AND MANUFACTURING METHOD THEREOF |
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| JP2011071323A (en) | 2009-09-25 | 2011-04-07 | Koito Mfg Co Ltd | Semiconductor element, and method of manufacturing the same |
| MY160228A (en) * | 2010-12-10 | 2017-02-28 | Ube Industries | Ceramic Composite for Light Conversion and Method for Manufacture Thereof |
| EP2908330B1 (en) * | 2012-10-12 | 2021-05-19 | Sumitomo Electric Industries, Ltd. | Group iii nitride composite substrate, manufacturing method therefor, and group iii nitride semiconductor device manufacturing method |
| JP5892971B2 (en) * | 2013-04-09 | 2016-03-23 | 株式会社東芝 | Method for manufacturing nitride semiconductor layer |
| US9947110B2 (en) | 2014-02-13 | 2018-04-17 | Brainlab Ag | Method for assisting the positioning of a medical structure on the basis of two-dimensional image data |
| JP6503819B2 (en) * | 2015-03-23 | 2019-04-24 | Tdk株式会社 | Alumina substrate |
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| JPH1017396A (en) * | 1996-07-01 | 1998-01-20 | Ube Ind Ltd | Ceramic composite material |
| JP2003258299A (en) * | 2002-02-28 | 2003-09-12 | Shiro Sakai | Gallium-nitride-based compound semiconductor device and manufacturing method thereof |
| WO2004065324A1 (en) * | 2003-01-20 | 2004-08-05 | Ube Industries, Ltd. | Ceramic composite material for optical conversion and use thereof |
| JP2005303333A (en) * | 2005-07-11 | 2005-10-27 | Ngk Insulators Ltd | Method for reducing dislocation density of semiconductor light emitting device |
| WO2006043719A1 (en) * | 2004-10-21 | 2006-04-27 | Ube Industries, Ltd. | Light emitting diode element, board for light emitting diode and method for manufacturing light emitting diode element |
| JP2006324622A (en) * | 2005-04-21 | 2006-11-30 | Sharp Corp | Manufacturing method for nitride semiconductor device and light emitting device |
| WO2007018222A1 (en) * | 2005-08-10 | 2007-02-15 | Ube Industries, Ltd. | Substrate for light emitting diode and light emitting diode |
| WO2007083828A1 (en) * | 2006-01-19 | 2007-07-26 | Ube Industries, Ltd. | Ceramic composite light converting member and light emitting device using the same |
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2008
- 2008-09-03 WO PCT/JP2008/066272 patent/WO2009031696A1/en active Application Filing
- 2008-09-03 JP JP2009531310A patent/JP5388068B2/en not_active Expired - Fee Related
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Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH1017396A (en) * | 1996-07-01 | 1998-01-20 | Ube Ind Ltd | Ceramic composite material |
| JP2003258299A (en) * | 2002-02-28 | 2003-09-12 | Shiro Sakai | Gallium-nitride-based compound semiconductor device and manufacturing method thereof |
| WO2004065324A1 (en) * | 2003-01-20 | 2004-08-05 | Ube Industries, Ltd. | Ceramic composite material for optical conversion and use thereof |
| WO2006043719A1 (en) * | 2004-10-21 | 2006-04-27 | Ube Industries, Ltd. | Light emitting diode element, board for light emitting diode and method for manufacturing light emitting diode element |
| JP2006324622A (en) * | 2005-04-21 | 2006-11-30 | Sharp Corp | Manufacturing method for nitride semiconductor device and light emitting device |
| JP2005303333A (en) * | 2005-07-11 | 2005-10-27 | Ngk Insulators Ltd | Method for reducing dislocation density of semiconductor light emitting device |
| WO2007018222A1 (en) * | 2005-08-10 | 2007-02-15 | Ube Industries, Ltd. | Substrate for light emitting diode and light emitting diode |
| WO2007083828A1 (en) * | 2006-01-19 | 2007-07-26 | Ube Industries, Ltd. | Ceramic composite light converting member and light emitting device using the same |
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| JPWO2009031696A1 (en) | 2010-12-16 |
| WO2009031696A1 (en) | 2009-03-12 |
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