JP4501194B2

JP4501194B2 - Nitride semiconductor light emitting device

Info

Publication number: JP4501194B2
Application number: JP34917499A
Authority: JP
Inventors: 元量山田
Original assignee: Nichia Corp
Current assignee: Nichia Corp
Priority date: 1999-12-08
Filing date: 1999-12-08
Publication date: 2010-07-14
Anticipated expiration: 2019-12-08
Also published as: JP2001168384A

Description

【０００１】
【産業上の利用分野】
本発明は、Ａｌ_XＩｎ_YＧａ_1-X-YＮ（０≦Ｘ、０≦Ｙ、Ｘ＋Ｙ≦１）からなる窒化物半導体を用いた発光素子に関し、特に、異なる色を発する井戸層を積層し、それらの発光を混色して、所望の演色性を有する光を発する発光素子に関する。
【０００２】
【従来の技術】
近年窒化物半導体を用いた発光素子の開発によって、青色、緑色の発光が可能となり、これにより赤色、緑色、青色（いわゆるＲＧＢ）の高輝度タイプの発光素子が量産されるようになった。特に窒化物半導体を用いた発光素子は、その混晶比を変化させることにより紫外域から赤色領域まで発光色を調整することが可能である。
【０００３】
一方、発光素子の高輝度、低消費電力、小型化可能や高信頼性などの優れた特性を生かして、例えば、車載メータの光源、液晶バックライト光源や各種照明などの技術分野で、その利用が急速に広がりつつある。
【０００４】
このような発光素子の利用分野において、特に白色が人間の目には快適で好感を与える色であり、特に需要が高い。これまで白色光を実現するためには、赤色、緑色、青色、あるいは青色および黄色などの異なる発光色を有する複数の発光素子を同一ステム上に配置して、それら発光色の混色により希望の白色光を得るか、あるいは、青色発光する発光素子とその補色関係にある黄色で蛍光発光する蛍光物質とを用いて白色光を得ていた。
【０００５】
さらに特開平１１−２８９１０８では少なくともＩｎとＧａとを含む窒化ガリウム系化合物半導体からなる発光層を含んだ積層構造を持つ窒化ガリウム系化合物半導体発光素子において、前記発光層は、面内でＩｎ比率の比較的小さい領域とＩｎ比率の比較的大きい領域とを有し、それぞれの領域からの発光の混合により、前記発光層からの発光が白色となる単一の素子構造の窒化物半導体発光素子を開示している。また特開平１０−２２５２５では多重量子井戸構造の各井戸層の混晶比を変化させることで禁制帯幅を変化させることができ、発光のピーク波長を混晶比により変化させている。これにより、活性層は混晶比の違うＡｌＧａＩｎＮからなる２つまたは３つの発光領域を有し、白色発光する窒化物半導体発光素子を開示している。
【０００６】
【発明が解決しようとする課題】
しかしながら複数の発光素子を同一のステム上に配置して白色光を得る場合、混色性（光を混合したときに１つの色として一様に見える見え方）を向上させるために複数の発光素子同士を近づける必要はあるが、これには限界がある。同様に蛍光体を利用して白色光を得る場合、発光素子に蛍光体を付着させる必要があり、工程が複雑となる。
【０００７】
また、特開平１１−２８９１０８ではほぼ青色の短波長側の発光とほぼ黄緑色の長波長側の発光との２色により白色発光を実現しているが、２色による発光では高い演色性Ｒａを得ることができず、せいぜいＲａ≦５５である。特開平１０−２２５２５では２つまたは３つの発光領域を光取り出し面に近い側から禁制帯幅が広くなるように設定されている。しかし単一の素子構造内に複数の異なる混晶比を有する発光層がある場合、すべての発光層に同一の電流がかかってしまうので、所望の色の発光色を得るためにはそれぞれの混晶比、膜厚等を制御しなければならず、特に同一膜厚では発光効率が低いという問題があった。
【０００８】
【課題を解決するための手段】
本発明は演色性の高い、また発光効率の高い所望の演色性を有する光を発する発光素子を得るものであり、基板上に、ｎ型窒化物半導体層、活性層、ｐ型窒化物半導体層を順に有し、前記活性層は、Ｉｎを含む窒化物半導体からなる少なくとも１つの第１の井戸層を有する第１の発光領域と、該第１の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体から成る少なくとも１つの第２の井戸層を有する第２の発光領域と、該第２の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体からなる少なくとも１つの第３の井戸層を有する第３の発光領域と、を備えた多重量子井戸構造から成る窒化物半導体発光素子において、前記第２の井戸層が発する光の主ピーク波長が４８０乃至５７０ｎｍであり、前記ｎ型半導体層は超格子層を有しており、前記活性層は前記ｐ型窒化物半導体層側から見て、前記第１の発光領域、前記第３の発光領域、前記第２の発光領域の順で積層された構成を少なくとも１つ含んでなることを特徴とする窒化物半導体発光素子。
この構成により所望の演色性を有する光を発する発光効率の高い窒化物半導体発光素子を得ることができる。
【０００９】
また、本発明は基板上に、ｎ型窒化物半導体層、活性層、ｐ型窒化物半導体層を順に有し、前記活性層は、Ｉｎを含む窒化物半導体からなる少なくとも１つの第１の井戸層を有する第１の発光領域と、該第１の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体から成る少なくとも１つの第２の井戸層を有する第２の発光領域と、該第２の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体からなる少なくとも１つの第３の井戸層を有する第３の発光領域と、を備えた多重量子井戸構造から成る窒化物半導体発光素子において、前記第２の井戸層が発する光の主ピーク波長が４８０乃至５７０ｎｍであり、前記ｎ型半導体層は超格子層を有しており、前記活性層は前記ｐ型窒化物半導体層側から見て、前記第１の発光領域、前記第３の発光領域、前記第２の発光領域の順で積層された構成のみから成ることを特徴とする窒化物半導体発光素子。
この構成により比較的簡単に所望の演色性を有する光を発する発光効率の高い窒化物半導体発光素子を得ることができる。
【００１０】
また、本発明は基板上に、ｎ型窒化物半導体層、活性層、ｐ型窒化物半導体層を順に有し、前記活性層は、Ｉｎを含む窒化物半導体からなる少なくとも１つの第１の井戸層と、該第１の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体から成る少なくとも１つの第２の井戸層と、該第２の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体からなる少なくとも１つの第３の井戸層と、を備えた多重量子井戸構造から成る窒化物半導体発光素子において、前記第２の井戸層が発する光の主ピーク波長が４８０乃至５７０ｎｍであり、前記ｎ型半導体層は超格子層を有しており、前記活性層は前記ｐ型窒化物半導体層側から見て、障壁層、前記第１の井戸層、障壁層、前記第３の井戸層、障壁層、前記第２の井戸層、障壁層の順で積層された構成を少なくとも１つ含むことを特徴とする窒化物半導体発光素子。
この構成により比較的簡単に所望の演色性を有する光を発する発光効率の高い窒化物半導体発光素子を得ることができる。
【００１１】
また、本発明は基板上に、ｎ型窒化物半導体層、活性層、ｐ型窒化物半導体層を順に有し、前記活性層は、Ｉｎを含む窒化物半導体からなる少なくとも１つの第１の井戸層と、該第１の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体から成る少なくとも１つの第２の井戸層と、該第２の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体からなる少なくとも１つの第３の井戸層と、を備えた多重量子井戸構造から成る窒化物半導体発光素子において、前記第２の井戸層が発する光の主ピーク波長が４８０乃至５７０ｎｍであり、前記ｎ型半導体層は超格子層を有しており、前記活性層は前記ｐ型窒化物半導体層側から見て、障壁層、前記第１の井戸層、障壁層、前記第３の井戸層、障壁層、前記第２の井戸層、障壁層の順で積層された構成のみからなることを特徴とする窒化物半導体発光素子。
この構成により最も簡単に所望の演色性を有する光を発する発光効率の高い窒化物半導体発光素子を得ることができる。
【００１２】
また、本発明は前記第１の井戸層が発する光の主ピーク波長が４００乃至４８０ｎｍで、前記第３の井戸層が発する光の主ピーク波長が５７０乃至８００ｎｍであることを特徴とする請求項１乃至請求項４のいずれかに記載の窒化物半導体発光素子。
この構成により所望の演色性を有する白色光の発光効率の高い窒化物半導体発光素子を得ることができる。
【００１３】
また、本発明は第１の井戸層が発する光の主ピーク波長が４２０乃至４６０ｎｍ、上記第２の井戸層が発する光の主ピーク波長が４８０乃至５２０ｎｍ、上記第３の主ピーク波長が５７０乃至６００ｎｍであることを特徴とする。この構成により赤色領域程度の長波長で発光する井戸層を設けることなく所望の演色性を有する白色光の発光効率の高い窒化物半導体発光素子を得ることができる。
また、本発明の窒化物半導体発光素子は、基板上に、ｎ型窒化物半導体層、活性層、ｐ型窒化物半導体層を順に有し、前記活性層は、Ｉｎを含む窒化物半導体からなるｎ個（ｎ≧４）の井戸層を備えた多重量子井戸構造からなり、第１の井戸層、第２の井戸層、・・・、第ｎの井戸層の順に主ピーク波長が短い窒化物半導体発光素子において、前記第２の井戸層が発する光の主ピーク波長が４８０乃至５７０ｎｍであり、前記ｎ型半導体層は超格子層を有しており、主ピーク波長が最も短い前記第１の井戸層を前記ｐ型窒化物半導体層の最も近くに有し、その次に前記ｐ型窒化物半導体層に近い位置に、主ピーク波長が最も長い前記第ｎの井戸層を有することを特徴とする窒化物半導体発光素子。
また、本発明の窒化物半導体発光素子は、ｎ型半導体層に超格子層を有することを特徴とする。また、超格子層は、アンドープＧａＮとＳｉドープＧａＮからなることを特徴とする。
【００１４】
【発明の実施の形態】
以下に図を用いて本発明を詳細に説明するが、これらは単に例示的なものであって、本発明を限定するものではない。
単一の素子構造内に複数の異なる混晶比を有する発光層を有する活性層を形成することで、白色発光の窒化物半導体発光素子が得られる。これは同一ステム上にＲＧＢ等の異なる発光色を有する複数の発光素子を配置して、それらの発光色の混色により希望の白色光を得る場合と比べて小型化でき、消費電力も抑えることができるので多岐にわたる応用が考えられる。しかしながら単一の素子構造内に複数の異なる混晶比を有する発光層がある場合、すべての発光層に同一の電流がかかってしまうので、所望の色の発光色を得るためにはそれぞれの混晶比、膜厚等を制御しなければならず、特に同一膜厚では発光効率が低いという問題があった。
【００１５】
そこで我々は鋭意研究を重ね、窒化物半導体発光素子における以下の特徴を踏まえ、発光効率の高い窒化物半導体発光素子を開発するに至った。窒化物半導体発光素子の特徴の１つとしては、ｎ型窒化物半導体層とｐ型窒化物半導体層に挟まれた活性層はその活性層中ではｐ型窒化物半導体層に近い方が良く光るという点が挙げられる。これは一般の発光ダイオードの特徴でもあり、ｎ型窒化物半導体層から活性層に供給される電子とｐ型窒化物半導体層から供給されるホールとを比較した場合、ホールの方が質量が大きいため、活性層中のｎ型窒化物半導体層側まで達するホールは少なく、活性層中でもｐ型窒化物半導体層側にホールが多く存在してしまう。逆に電子はホールより質量が小さいため、ｐ型窒化物半導体層側にも多く存在する。このことから電子とホールとの再結合は、活性層中でもｐ型窒化物半導体層側で起こりやすい。これが大きな要因となって、ｐ型窒化物半導体層に近い方が良く光ると考えられている。
【００１６】
窒化物半導体発光素子のもう１つの特徴としては、発光層はバンドギャップの小さい層から光り始める点である。これに関しては具体的な要因はわかっていないが、バンドギャップの小さい方から伝導体に電子がたまっていくので、小さい方から光り始めるのではないかと推測できる。
【００１７】
さらに窒化物半導体発光素子のもう１つの特徴としては、長波長での発光ほど出力が小さくなる点である。これに関しても具体的な要因はわかっていないが、窒化物半導体発光素子は発光層の混晶比を変えることで紫外域から赤色領域までの発光が可能であり、窒化物半導体発光素子として代表的な青色発光（４２０ｎｍ程度）は発光層としてはＩｎＧａＮが使われる。さらにこのＩｎＧａＮのＩｎの混晶比を高くすることで、長波長の領域での発光が可能となる。しかしながら基本的に窒化物半導体発光素子はＧａＮで形成されているため、長波長の発光を得るために発光層のＩｎの混晶比を大きくすると、該発光層とその他の層との間の格子歪が大きくなってしまい、該発光層の結晶性が悪くなってしまう。結晶性が悪くなると当然のことながら発光出力も下がってしまう。これが長波長での発光ほど出力が小さくなる要因ではないかと推測できる。
【００１８】
以上をまとめると窒化物半導体発光素子の特徴として、１）活性層中ではｐ型窒化物半導体層に近い方が良く光る、２）発光層はバンドギャップの小さい層から光り始める、３）長波長の発光ほど出力が小さくなる、ことが挙げられる。これらの特徴から、活性層をｐ型窒化物半導体層側から見て、第１の発光領域、第３の発光領域、第２の発光領域の順で積層することで、発光効率の高い窒化物半導体発光素子が得られる。これは、３）の長波長の発光ほど出力が小さくなることから第３の井戸層を有する第３の発光領域は出力が他と比べて小さくなるという特徴を、第３の発光領域を、良く光るｐ型窒化物半導体層側に形成することで補い、出力を高めている。しかしながらｐ型窒化物半導体層に最も近い発光層を第３の井戸層を有する第３の発光領域としてしまうと、２）のバンドギャップが小さい方から光り始めるので、結果的に他の層より出力が高くなってしまう。そこで、最後に光り始める短波長の第１の井戸層を有する第１の発光領域をｐ型窒化物半導体層に最も近い層とすることで、どの発光領域での発光も強く成りすぎないようにしている。すなわち、活性層中で最も短い波長を有する発光領域をｐ型窒化物半導体側に最も近い層とし、活性層中で最も長い波長を有する発光領域をその次にｐ型窒化物半導体側に近い層とすることで、所望の演色性を有する、発光効率の高い窒化物半導体発光素子を実現した。また、その他の波長を有する発光領域の位置はこだわらないが、その他の中間の波長を有する発光領域は２）、３）それぞれの特徴を少なからず有しているので、１）の良く光るｐ型窒化物半導体層側とは反対のｎ型窒化物半導体側に形成するのが好ましい。
【００１９】
本発明において、ここでは少なくとも１つの第１の井戸層を有する第１の発光領域と、該第１の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、少なくとも１つの第２の井戸層を有する第２の発光領域と、該第２の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、少なくとも１つの第３の井戸層を有する第３の発光領域と、を備えた多重量子井戸構造から成る活性層を有する窒化物半導体発光素子について説明したが、例えば上記３つの発光領域にとどまらず、少なくとも１つの第（ｎ−１）の井戸層を有する光の主ピーク波長よりも長い主ピーク波長の光を発する、少なくとも第ｎの井戸層を有する第ｎの発光領域を有するような、ｎ種の異なる波長をもつｎ個の発光領域を備えた多重量子井戸構造から成る活性層（４≦ｎ）からなる窒化物半導体発光素子の場合でも、主ピーク波長が最も短い第１の井戸層を有する第１の発光領域をｐ型窒化物半導体側の最も近くに、その次にｐ型不純物半導体に近い層として、主ピーク波長が最も長い第ｎの井戸層を有する第ｎの発光領域を形成することで、４種以上の主ピーク波長の異なる井戸層を有する活性層でも、所望の演色性を有する、発光効率の高い窒化物半導体発光素子を得ることができる。
【００２０】
【実施例】
図１は本発明の一実施例にかかる窒化物半導体発光素子の構造を示す模式的な断面図である。以下この図を元に実施例１について説明する。なお、本発明の発光素子は図１の構造に限定されるものではない。
（実施例１）
図１は、本発明の発光素子１００を示す模式的断面図である。発光素子１００は、サファイア基板１０１上に、ＧａＮバッファ層１０２、アンドープＧａＮ層１０３、ＳｉドープのＧａＮからなるｎ型コンタクト層兼クラッド層１０４、超格子層１０５、多重量子井戸構造からなる活性層１０６、ＭｇドープのＡｌＧａＮからなるｐ型クラッド層１１１、ＭｇドープのＧａＮからなるｐ型コンタクト層１１２が順に形成されている。また活性層１０６は、障壁層１０７とＩｎＧａＮからなる第２の井戸層１０８、第３の井戸層１０９および第１の井戸層１１０とから構成されている。またすべての井戸層のうち、第１の井戸層のＩｎ含有量が最も少なく、第３の井戸層のＩｎ含有量が最も多い。さらに活性層１０６はｎ型コンタクト層側から順に第２の井戸層１０８、第３の井戸層１０９、第１の井戸層１１０が障壁層１０７に挟まれて形成されている。
【００２１】
またｐ型コンタクト層１１２上にｐ側透明電極１１３、ｐ側パッド電極１１４が、ｎ型コンタクト層１０４上にｎ電極１１５が形成されていることで、混色光が発光可能な発光素子１００を形成することができる。次に、本発明にかかる発光素子の形成方法について説明する。
【００２２】
ＭＯＣＶＤ法により窒化物半導体を成膜して発光素子を形成する。まず、洗浄した２インチのサファイア（Ｃ面）よりなる基板１０１をＭＯＣＶＤ装置の反応容器内にセットする。反応容器を真空化しつつ、Ｈ₂を流して容器内をＨ₂で十分置換した後、基板温度を１０５０℃まで上昇させて、基板１０１をクリーニングする。尚、半導体基板１０１としては、Ｃ面サファイアの他、Ｒ面、Ａ面を主面とするサファイア、スピネル（ＭｇＡｌ₂Ｏ₄）のような絶縁性基板、ＳｉＣ（６Ｈ、４Ｈ、３Ｃを含む）、Ｓｉ、ＺｎＯ、ＧａＡｓ、およびＧａＮなどの材料を用いることができる。
【００２３】
次に、成膜温度を５１０℃まで下げＴＭＧ（トリメチルガリウム）、ＮＨ₃を原料ガス、Ｈ₂をキャリアガスとして供給し、厚さ約１５０ÅのＧａＮ層をサファイア基板１０１上に成膜して、バッファ層１０２を形成する。なお、バッファ層１０２はＧａＮの他、ＡｌＮやＡｌＧａＮなどの材料を利用することができる。
【００２４】
続いて、原料ガスの流入を一旦止め、キャリアガスを流しながら、基板温度を１０５０℃に上げる。成膜温度が安定した後、ＴＭＧおよびＮＨ₃を原料ガスＨ２をキャリアガスとして流し、厚さ１．５μｍのアンドープＧａＮ層をバッファ層１０２上に積層する。
【００２５】
そして、成膜温度を１０５０℃に維持したまま、原料ガスとしてＴＭＧおよびＮＨ₃、キャリアガスとしてＨ₂、不純物ガスとしてＳｉＨ₄を流し、５×１０¹⁸／ｃｍ³のＳｉ不純物濃度を有するＧａＮ層であるｎ型コンタクト層１０４を厚さ２．２５μｍでアンドープＧａＮ層１０３上に形成する。
【００２６】
さらに、活性層１０６の結晶性を向上させ、均一に全面発光させるために、ｎ型コンタクト層１０４上に超格子層１０５を形成することが好ましい。成膜温度を１０５０℃に維持した状態で、不純物ガスであるＳｉＨ₄の供給を制御することにより、厚さ約７５ÅのアンドープＧａＮ層と、厚さ約２５ÅのＳｉドープＧａＮ層とを成膜する。これを１周期として、２５周期繰り返して総膜厚２５００Åの超格子層１０５をｎ型コンタクト層１０４上に成膜する。なお、超格子層１０５を構成するＳｉドープＧａＮ層は、互いに異なる不純物濃度（Ｓｉ）を有し、いわゆる変調ドープされている。
【００２７】
次に、多重量子井戸構造の活性層１０６の構成を詳細に説明する。多重量子井戸構造の活性層１０６は、厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎＧａＮからなる第２の井戸層１０８、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎＧａＮからなる第３の井戸層１０９、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎＧａＮからなる第１の井戸層１１０、最後に厚さ約２５０ÅのＧａＮからなる障壁層１０７を積層する。
【００２８】
さらに、多重量子井戸構造の活性層１０６の具体的な形成方法について説明する。ＭＯＣＶＤ法を用いて成膜温度１０５０℃で、原料ガスとしてＴＭＧおよびＮＨ₃、キャリアガスとしてＨ₂を流すことにより、約２５０Åの厚さの障壁層１０７を超格子層１０５上に成膜する。
【００２９】
続いて原料ガスの流入を一旦止め、成膜温度を８００℃に調整した後、再び原料ガスとしてＴＭＧ、ＴＭＩ（トリメチルインジウム）およびＮＨ₃、キャリアガスとしてＮ₂を流すことにより、約３０Åの厚さのＩｎ_0.63Ｇａ_0.37Ｎを成膜して第２の井戸層を形成する。
【００３０】
その後、成膜温度を１０５０℃とし原料ガスとしてＴＭＧおよびＮＨ₃、キャリアガスとしてＨ₂を流すことにより、約２５０Åの厚さのＧａＮ障壁層１０７を第２の井戸層１０８上に成膜する。
【００３１】
続いて原料ガスの流入を一旦止め、成膜温度を８００℃に調整した後、再び原料ガスとしてＴＭＧ、ＴＭＩおよびＮＨ₃、キャリアガスとしてＮ₂を流すことにより、約３０Åの厚さのＩｎ_0.84Ｇａ_0.16Ｎを成膜して第３の井戸層１０９を形成する。
【００３２】
その後、成膜温度を１０５０℃とし原料ガスとしてＴＭＧおよびＮＨ₃、キャリアガスとしてＨ₂を流すことにより、約２５０Åの厚さのＧａＮ障壁層１０７を第３の井戸層１０９上に成膜する。
【００３３】
さらに続いて原料ガスの流入を一旦止め、成膜温度を８００℃に調整した後、再び原料ガスとしてＴＭＧ、ＴＭＩおよびＮＨ₃、キャリアガスとしてＮ₂を流すことにより、約３０Åの厚さのＩｎ_0.44Ｇａ_0.56Ｎを成膜して第１の井戸層１１０を形成する。
【００３４】
さらに続いて成膜温度を１０５０℃とし原料ガスとしてＴＭＧおよびＮＨ₃、キャリアガスとしてＨ₂を流すことにより、約２５０Åの厚さのＧａＮ障壁層１０７を第１の井戸層１１０上に成膜する。
【００３５】
活性層１０６を成膜後、超格子構造を有するｐ型クラッド層１１１を形成する。厚さ約４０ÅのＭｇドープのＡｌＧａＮ層と厚さ約２５ÅのＭｇドープＩｎＧａＮとを成膜する。これを１周期として繰り返し５周期成膜することにより、ｐ型クラッド層１１１を形成する。具体的には、ＭＯＣＶＤ法により成膜温度を１０５０℃とし、原料ガスとしてＴＭＧ、ＴＭＡ（トリメチルアルミニウム）およびＮＨ₃、不純物ガスとしてＣｐ₂Ｍｇ（シクロペンタジエニルマグネシウム）、そしてキャリアガスとしてＨ₂を流すことにより、厚さが約４０ÅのＡｌＧａＮ層を成膜する。次に、原料ガスの流入を一旦止め、成膜温度を８５０℃に調整した後に、再び原料ガスとしてＴＭＧ、ＴＭＩ、およびＮＨ₃、不純物ガスとしてＣｐ₂Ｍｇ、そしてキャリアガスとしてＮ₂を流すことにより、厚さ約２５ÅのＩｎＧａＮ層を成膜する。これを５周期繰り返し、約３２５Åの厚さを有する超格子構造のｐ型クラッド層１１１を成膜する。なお、ｐ型クラッド層１１１はこのように超格子構造を有していてもよいが、ＡｌＧａＮやＡｌＢＧａＮ等の単層構造を有していてもよい。
【００３６】
そして、成膜温度を１０５０℃とし、原料ガスとしてＴＭＧおよびＮＨ₃、キャリアガスとしてＨ₂、そして不純物ガスとしてＣｐ₂Ｍｇを流し、１×１０²⁰／ｃｍ³のＭｇ不純物濃度を有するＧａＮ層であるｐ型コンタクト層１１２を、０．２μｍの膜厚でｐ型クラッド層１１１上に形成する。ｐ型クラッド層１１１形成後、温度を室温まで下げ、窒素雰囲気中でウエハーを７００℃でアニーリング処理し、ｐ型層をさらに低抵抗化する。
【００３７】
アニーリング処理後、ウエハーを反応容器から取り出し、所望の形状のマスクを最上層のｐ型コンタクト層１１２の表面に形成し、ＲＩＥ（反応性イオンエッチング）装置でｐ型コンタクト層１１２側からエッチング処理を行い、ｐ型およびｎ型半導体表面を露出させる。
【００３８】
エッチング処理後、スパッタリング装置によりｐ型コンタクト層１１２のほぼ全面に膜厚２００ÅのＮｉとＡｕを含むｐ側透明電極１１３と、ｐ側透明電極１１３の上にボンディング用のＡｕよりなる０．５μｍの膜厚のｐ側パッド電極１１４と、を形成する。他方、エッチング処理により露出したｎ型コンタクト層１０４上に、ＷとＡｌとを含むｎ電極１１５を形成する。最後に、ｐ側透明電極１１３の表面を保護するためにＳｉＯ₂よりなる絶縁層（図示せず）を保護膜として形成する。こうして形成された窒化物半導体ウエハーをスクライブラインを引いた後、外力により分割し、発光素子として３５０μｍ角のＬＥＤチップを完成する。
【００３９】
このように、本発明の発光素子は、一般に、多重量子井戸構造の活性層を有し、この活性層はＩｎを含む窒化物半導体からなる第１の井戸層１１０と第２の井戸層１０８と第３の井戸層１０９を有する。本発明による井戸層は、Ｉｎを含む窒化物半導体として、例えばＡｌ_XＩｎ_YＧａ_1-X-YＮ（０≦Ｘ、０≦Ｙ、Ｘ＋Ｙ≦１）で形成され、好ましくは三元混晶のＩｎ_YＧａ_1-YＮ（０≦Ｙ≦１）で形成される。本発明の多重量子井戸構造の活性層はさらに、第１の井戸層１１０、第２の井戸層１０８、第３の井戸層１０９、もしくはその他の井戸層の計ｎ種（ｎ≧３）からなる井戸層よりバンドギャップの大きな窒化物半導体より成る障壁層１０７を有し、これら井戸層１１０、１０８、１０９とその間に挟まれる障壁層１０７とを積層して形成される。障壁層１０７は特に限定されないが、ＧａＮ、ＩｎＧａＮ、ＡｌＧａＮ等の材料により、ｎ種の井戸層より厚く、例えば数百Å程度の膜厚を有するように形成される。また、第１の井戸層１１０、第２の井戸層１０８、第３の井戸層１０９、さらにはｎ種のすべての井戸層の膜厚としては特に限定されないが、例えば１００Å以下の膜厚を有することが好ましく、さらに好ましくは７０Å以下、最も好ましくは５０Å以下の膜厚に調整する。１００Åよりも厚いと、井戸層が弾性歪み限界以上の膜厚となり、井戸層中の微少なクラック、あるいは結晶欠陥が入りやすい。
【００４０】
また、ｐ型半導体およびｎ型半導体としては、特に限定されないが、例えば窒化物半導体から成るｐ導電型およびｎ導電型の半導体を用いることができる。本発明の窒化物半導体の材料組成は、Ａｌ_XＩｎ_YＧａ_1-X-YＮ（０≦Ｘ、０≦Ｙ、Ｘ＋Ｙ≦１）と表され、上述の通り、ｐ型導電性またはｎ型導電性を有するように、ｐ型またはｎ型不純物をドープする。
【００４１】
また、本発明で用いている窒化物半導体素子であるＩｎ_YＧａ_1-YＮ（０≦Ｙ≦１）のＩｎの混晶比はバンドギャップエネルギーＥｇとの関係式、Ｅｇ＝３．４＊（１−Ｙ）＋１．９５＊Ｙ−Ａ＊Ｙ＊（１−Ｙ）において、Ａ＝１としたときに概算された値であり、またＡｌ_XＧａ_1-XＮ（０≦Ｘ≦１）のＡｌ混晶比Ｘはバンドギャップエネルギーとの関係式、Ｅｇ＝３．４＊（１−Ｘ）＋６．２＊Ｘ−Ａ＊Ｘ＊（１−Ｘ）において、Ａ＝１としたときに概算された値である。上記２つの関係式の第１項と第２項の係数はそれぞれ、３．４はＧａＮのバンドギャップエネルギー（ｅＶ）を、１．９５はＩｎＮのバンドギャップエネルギー（ｅＶ）を、６．２はＡｌＮのバンドギャップエネルギー（ｅＶ）を示している。
【００４２】
発光ダイオードランプのリードフレームは、銀メッキした鉄入り銅で形成される。リードフレームの一方は、ＬＥＤチップを配置するためのカップを有するマウント・リードで、他方は、ＬＥＤチップの一方の電極とワイヤを介して電気的に接続するインナー・リードを有する。エポキシ樹脂を用いて、ＬＥＤチップをマウントリード上にダイボンディングした後、ＬＥＤチップのｐ電極およびｎ電極に直径３５μｍの金線ワイヤの一方をボールボンディングし、他方をリードフレームの先端にステッチボンディングする。これにより、ＬＥＤチップの各電極とインナー・リードおよびマウント・リードとをそれぞれ電気的に接続する。
【００４３】
こうして得られた発光ダイオードランプに２０ｍＡ（Ｖ_f＝３．５Ｖ）の順方向電流を流したところ、図２に示すように、ＣＩＥの色度図上の座標が（Ｘ、Ｙ）＝（０．２７６、０．３０２）で表される発光スペクトルを有する白色光が得られ、演色性はＲａ＝６９であった。このとき、第１、第２および第３井戸層１１０、１０８、１０９から、各々約４４８ｎｍ、５００ｎｍおよび５７０ｎｍの波長を有する発光が確認される。また、図３に示すように第３の井戸層１０９が発する発光スペクトルは、第２の井戸層１０８が発する発光スペクトルに比べて半値幅が広く、演色性に優れており、第２の井戸層１０８が発する発光スペクトルは、第１の井戸層１１０が発する発光スペクトルに比べて半値幅が広く、演色性に優れている。また本発明に係る発光素子は、異なる発光スペクトルを発する井戸層が３つに限定されるものではなく、ｎ種（ｎ≧４）の井戸層を設けることができる。これにより、発光素子としてのスペクトル幅を広げることができる。
【００４４】
（比較例１）
実施例１と比較するために、比較例１として活性層の第１の井戸層、第２の井戸層および第３の井戸層の積層順序を入れ替えて形成した。具体的には、ｎ型窒化物半導体層側から見て、障壁層、第３の井戸層、障壁層、第２の井戸層、障壁層、第１の井戸層、障壁層の順で積層し、光取り出し面（ｐ型窒化物半導体層側）に近い側から禁制帯幅が広く（すなわち波長が短く）なるように形成した。
【００４５】
この発光ダイオードは図２に示すように、ＣＩＥの色度図上の座標が（Ｘ、Ｙ）＝（０．２０５、０．４１７）で表される発光スペクトルを有し、輝度は実施例１の発光ダイオードランプと比べて低く、その発光色は緑がかって見えた。これは、５００ｎｍの波長を有する第２の井戸層の発光スペクトル強度が実施例１と比べて、相対的に他の波長の発光スペクトルより高くなったためである。
【００４６】
（実施例２）
実施例１において、活性層１０６を次のように形成した他は同様にして発光ダイオードランプを得た。
多重量子井戸構造の活性層１０６は、まず厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.63Ｇａ_0.37Ｎからなる第２の井戸層１０８、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.84Ｇａ_0.16Ｎからなる第３の井戸層１０９、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.44Ｇａ_0.56Ｎからなる第１の井戸層１１０、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７を積層する。
【００４７】
さらに続けて、厚さ約３０ÅのＩｎ_0.63Ｇａ_0.37Ｎからなる第２の井戸層１０８、厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ０．８４Ｇａ０．１６Ｎからなる第３の井戸層１０９、厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.44Ｇａ_0.56Ｎからなる第１の井戸層１１０、最後に厚さ約２５０ÅのＧａＮからなる障壁層１０７を積層する。
【００４８】
このようにして得られた発光ダイオードランプに２０ｍＡ（Ｖ_f＝３．８Ｖ）の順方向電流を流したところ白色光が得られ、演色性はＲａ＝６９であった。また、第１、第２および第３井戸層１１０、１０８、１０９から、各々約４４８ｎｍ、５００ｎｍおよび５７０ｎｍの波長を有する発光が確認された。このように実施例１の活性層の構成を１ペアとし、このペア数を増やす（一部障壁層を除く）ことで発光ダイオードランプの出力を上げることができる。また、異なる発光スペクトルを発する井戸層が３つに限定されるものではなく、ｎ種（ｎ≧４）の井戸層を設けることもできる。
【００４９】
（実施例３）
実施例１において、活性層１０６を次のように形成した他は同様にして発光ダイオードランプを得た。
多重量子井戸構造の活性層１０６は、まず厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.44Ｇａ_0.56Ｎからなる第１の井戸層１１０、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.63Ｇａ_0.37Ｎからなる第２の井戸層１０８、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.84Ｇａ_0.16Ｎからなる第３の井戸層１０９、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.44Ｇａ_0.56Ｎからなる第１の井戸層１１０、最後に厚さ約２５０ÅのＧａＮからなる障壁層１０７を積層する。
【００５０】
このようにして得られた発光ダイオードランプに２０ｍＡ（Ｖ_f＝３．６Ｖ）の順方向電流を流したところ白色光が得られた。また、第１、第２および第３井戸層１１０、１０８、１０９から、各々約４４８ｎｍ、５００ｎｍおよび５７０ｎｍの波長を有する発光が確認された。このように実施例１の活性層の構成を含み、ｎ型窒化物半導体側にさらに第１の井戸層１１０を１層追加したことで、実施例１より色温度の高い発光ダイオードランプを得ることができる。また、異なる発光スペクトルを発する井戸層が３つに限定されるものではなく、ｎ種（ｎ≧４）の井戸層を設けることもできる。
【００５１】
（実施例４）
実施例１において、活性層１０６を次のように形成した他は同様にして発光ダイオードランプを得た。
多重量子井戸構造の活性層１０６は、まず厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.63Ｇａ_0.37Ｎからなる第２の井戸層１０８、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.84Ｇａ_0.16Ｎからなる第３の井戸層１０９、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.44Ｇａ_0.56Ｎからなる第１の井戸層１１０、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.44Ｇａ_0.56Ｎからなる第１の井戸層１１０、最後に厚さ約２５０ÅのＧａＮからなる障壁層１０７を積層する。
【００５２】
このようにして得られた発光ダイオードランプに２０ｍＡ（Ｖ_f＝３．６Ｖ）の順方向電流を流したところ白色光が得られた。また、第１、第２および第３井戸層１１０、１０８、１０９から、各々約４４８ｎｍ、５００ｎｍおよび５７０ｎｍの波長を有する発光が確認された。このように実施例１の活性層の構成を含み、ｐ型窒化物半導体側にさらに第１の井戸層１１０を１層追加したことで、実施例１より色温度の高い発光ダイオードランプを得ることができる。また、異なる発光スペクトルを発する井戸層が３つに限定されるものではなく、ｎ種（ｎ≧４）の井戸層を設けることもできる。
【００５３】
（実施例５）
実施例１において、活性層１０６を次のように形成した他は同様にして発光ダイオードランプを得た。
多重量子井戸構造の活性層１０６は、まず厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.70Ｇａ_0.30Ｎからなる第２の井戸層１０８、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.96Ｇａ_0.04Ｎからなる第３の井戸層１０９、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.52Ｇａ_0.48Ｎからなる第１の井戸層１１０、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７を積層する。
【００５４】
このようにして得られた発光ダイオードランプに順方向電流を流したところ白色光が得られた。また、第１、第２および第３井戸層１１０、１０８、１０９から、各々約４７０ｎｍ、５２０ｎｍおよび６２０ｎｍの波長を有する発光が確認された。
【００５５】
（実施例６）
実施例１において、活性層１０６を次のように形成した他は同様にして発光ダイオードランプを得た。
多重量子井戸構造の活性層１０６は、まず厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.70Ｇａ_0.30Ｎからなる第２の井戸層１０８、さらに厚さ約５０ÅのＡｌ_0.3Ｇａ_0.7Ｎからなる中間層、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.96Ｇａ_0.04Ｎからなる第３の井戸層１０９、さらに厚さ約５０ÅのＡｌ_0.3Ｇａ_0.7Ｎからなる中間層、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.52Ｇａ_0.48Ｎからなる第１の井戸層１１０、さらに厚さ約５０ÅのＡｌ_0.3Ｇａ_0.7Ｎからなる中間層、さらに厚さ約２５０ÅのＧａＮからなる障壁層１０７を積層する。
【００５６】
このようにして得られた発光ダイオードランプに順方向電流を流したところ白色光が得られた。また、第１、第２および第３井戸層１１０、１０８、１０９から、各々約４７０ｎｍ、５２０ｎｍおよび６２０ｎｍの波長を有する発光が確認された。このように、活性層の井戸層と障壁層との間の井戸層上にＡｌ_0.3Ｇａ_0.7Ｎのような中間層を形成すると、Ｖ_fが下がる傾向にある。
【００５７】
（実施例７）
実施例１において、活性層１０６を次のように形成した他は同様にして発光ダイオードランプを得た。
多重量子井戸構造の活性層１０６は、まず厚さ約２５０ÅのＧａＮからなる障壁層１０７と厚さ約３０ÅのＩｎ_0.79Ｇａ_0.21Ｎからなる第３の井戸層、さらに厚さ約２５０ÅのＧａＮからなる障壁層と厚さ約３０ÅのＩｎ_0.70Ｇａ_0.30Ｎからなる第２の井戸層、さらに厚さ約２５０ÅのＧａＮからなる障壁層と厚さ約３０ÅのＩｎ_0.96Ｇａ_0.04Ｎからなる第４の井戸層、さらに厚さ約２５０ÅのＧａＮからなる障壁層と厚さ約３０ÅのＩｎ_0.52Ｇａ_0.48Ｎからなる第１の井戸層、さらに厚さ約２５０ÅのＧａＮからなる障壁層を積層する。
【００５８】
このようにして得られた発光ダイオードランプに順方向電流を流したところ白色光が得られた。また、第１、第２、第３および第４井戸層は、各々約４７０ｎｍ、５２０ｎｍ、５５０ｎｍおよび６２０ｎｍの波長を有する発光が確認された。また、実施例５と比較して４７０ｎｍ、５２０ｎｍ、６２０ｎｍの３種の波長に５５０ｎｍの波長を加えて形成することで、実施例５より演色性を上げることができた。
【００５９】
【発明の効果】
本発明は、以上説明したような形態で実施され、以下に記載されるような効果を奏する。
本発明に係る窒化物半導体発光素子の活性層は、ｐ型窒化物半導体層側から見て、第１の発光領域、第３の発光領域、第２の発光領域の順で積層された構成を少なくとも１つ含むことで、所望の演色性を有する白色光の発光効率の高い窒化物半導体発光素子を得ることができる。
【図面の簡単な説明】
【図１】本発明の一実施に係る窒化物半導体発光素子の構造を示す模式的な断面図。
【図２】実施例１および比較例１により形成された発光素子が発する光の色度図上の座標を示した図。
【図３】実施例１に係る窒化物半導体発光素子の発光スペクトル図。
【符号の説明】
１０１・・・サファイア基板
１０２・・・バッファ層
１０３・・・アンドープＧａＮ層
１０４・・・ｎコンタクト兼ｎクラッド層
１０５・・・超格子層
１０６・・・活性層
１０７・・・障壁層
１０８・・・第２の井戸層
１０９・・・第３の井戸層
１１０・・・第１の井戸層
１１１・・・ｐクラッド層
１１２・・・ｐコンタクト層
１１３・・・ｐ側透明電極
１１４・・・ｐ側パッド電極
１１５・・・ｎ電極[0001]
[Industrial application fields]
The present invention provides Al _X In _Y Ga _1-XY In particular, the present invention relates to a light-emitting element using a nitride semiconductor composed of N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1). In particular, a well layer emitting different colors is stacked, and the emitted light is mixed to obtain a desired color rendering property. The present invention relates to a light emitting element that emits light having the following.
[0002]
[Prior art]
In recent years, the development of light-emitting elements using nitride semiconductors has made it possible to emit blue and green light, and high-luminance light-emitting elements of red, green, and blue (so-called RGB) have been mass-produced. In particular, a light-emitting element using a nitride semiconductor can adjust the emission color from the ultraviolet region to the red region by changing the mixed crystal ratio.
[0003]
On the other hand, taking advantage of the excellent characteristics of light-emitting elements such as high brightness, low power consumption, miniaturization, and high reliability, it can be used in technical fields such as in-vehicle meter light sources, liquid crystal backlight light sources, and various illuminations. Is spreading rapidly.
[0004]
In the field of use of such light emitting elements, white is particularly a color that is comfortable and pleasing to the human eye, and is particularly in high demand. In order to realize white light up to now, a plurality of light emitting elements having different emission colors such as red, green, blue, or blue and yellow are arranged on the same stem, and a desired white color can be obtained by mixing these emission colors. Light is obtained, or white light is obtained by using a light emitting element that emits blue light and a fluorescent substance that emits yellow fluorescence that is complementary to the light emitting element.
[0005]
Further, in JP-A-11-289108, in a gallium nitride compound semiconductor light emitting device having a laminated structure including a light emitting layer made of a gallium nitride compound semiconductor containing at least In and Ga, the light emitting layer has an In ratio in the plane. Disclosed is a nitride semiconductor light emitting device having a single element structure having a relatively small region and a region having a relatively large In ratio, and light emission from the light emitting layer becomes white by mixing light emission from each region. is doing. In Japanese Patent Laid-Open No. 10-22525, the forbidden band width can be changed by changing the mixed crystal ratio of each well layer of the multiple quantum well structure, and the peak wavelength of light emission is changed by the mixed crystal ratio. Thus, a nitride semiconductor light emitting device that emits white light is disclosed, in which the active layer has two or three light emitting regions made of AlGaInN having different mixed crystal ratios.
[0006]
[Problems to be solved by the invention]
However, when white light is obtained by arranging a plurality of light emitting elements on the same stem, the plurality of light emitting elements are mutually improved in order to improve color mixing properties (appearance that looks uniform as one color when light is mixed). However, there is a limit to this. Similarly, when white light is obtained using a phosphor, it is necessary to attach the phosphor to the light emitting element, which complicates the process.
[0007]
In Japanese Patent Laid-Open No. 11-289108, white light emission is realized by two colors of light emission of substantially blue short wavelength side and light emission of substantially yellowish green long wavelength side, but high color rendering property Ra is obtained by light emission by two colors. Ra ≦ 55 at most. In Japanese Patent Laid-Open No. 10-22525, two or three light emitting regions are set so that the forbidden band width is widened from the side close to the light extraction surface. However, when there are a plurality of light emitting layers having different mixed crystal ratios in a single element structure, the same current is applied to all the light emitting layers. The crystal ratio, film thickness, and the like must be controlled, and there is a problem that the light emission efficiency is low particularly at the same film thickness.
[0008]
[Means for Solving the Problems]
The present invention provides a light-emitting element that emits light having a desired color rendering property with high color rendering properties and high luminous efficiency, On the substrate, an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially provided. A first light emitting region having at least one first well layer made of a nitride semiconductor containing In, and emitting light having a main peak wavelength longer than a main peak wavelength of light emitted by the first well layer. A second light emitting region having at least one second well layer made of a nitride semiconductor containing, and emitting light having a main peak wavelength longer than a main peak wavelength of light emitted by the second well layer. And a third light-emitting region having at least one third well layer made of a nitride semiconductor. Ru In a compound semiconductor light emitting device, The main peak wavelength of light emitted from the second well layer is 480 to 570 nm, the n-type semiconductor layer has a superlattice layer, Active layer Said Seen from the p-type nitride semiconductor layer side, Said A first light emitting region, Said A third light emitting region, Said A nitride semiconductor light-emitting element comprising at least one structure laminated in the order of the second light-emitting region.
With this configuration, it is possible to obtain a nitride semiconductor light emitting element with high luminous efficiency that emits light having a desired color rendering property.
[0009]
The present invention also provides On the substrate, an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially provided. A first light emitting region having at least one first well layer made of a nitride semiconductor containing In, and emitting light having a main peak wavelength longer than a main peak wavelength of light emitted by the first well layer. A second light emitting region having at least one second well layer made of a nitride semiconductor containing, and emitting light having a main peak wavelength longer than a main peak wavelength of light emitted by the second well layer. And a third light-emitting region having at least one third well layer made of a nitride semiconductor. Ru In a compound semiconductor light emitting device, The main peak wavelength of light emitted from the second well layer is 480 to 570 nm, the n-type semiconductor layer has a superlattice layer, Active layer Said Seen from the p-type nitride semiconductor layer side, Said A first light emitting region, Said A third light emitting region, Said A nitride semiconductor light emitting device comprising only a structure in which the second light emitting regions are stacked in this order.
With this configuration, it is possible to obtain a nitride semiconductor light emitting device with high luminous efficiency that emits light having a desired color rendering property relatively easily.
[0010]
The present invention also provides On the substrate, an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially provided. At least one first well layer made of a nitride semiconductor containing In, and a nitride semiconductor containing In that emits light having a main peak wavelength longer than the main peak wavelength of light emitted by the first well layer At least one second well layer and at least one third well layer made of a nitride semiconductor containing In that emits light having a main peak wavelength longer than the main peak wavelength of light emitted by the second well layer And a multi-quantum well structure with Ru In a compound semiconductor light emitting device, The main peak wavelength of light emitted from the second well layer is 480 to 570 nm, the n-type semiconductor layer has a superlattice layer, Active layer Said As viewed from the p-type nitride semiconductor layer side, the barrier layer, Said A first well layer, a barrier layer, Said A third well layer, a barrier layer, Said A nitride semiconductor light emitting device comprising at least one structure in which a second well layer and a barrier layer are stacked in this order.
With this configuration, it is possible to obtain a nitride semiconductor light emitting device with high luminous efficiency that emits light having a desired color rendering property relatively easily.
[0011]
The present invention also provides On the substrate, an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially provided. At least one first well layer made of a nitride semiconductor containing In, and a nitride semiconductor containing In that emits light having a main peak wavelength longer than the main peak wavelength of light emitted by the first well layer At least one second well layer and at least one third well layer made of a nitride semiconductor containing In that emits light having a main peak wavelength longer than the main peak wavelength of light emitted by the second well layer And a multi-quantum well structure with Ru In a compound semiconductor light emitting device, The main peak wavelength of light emitted from the second well layer is 480 to 570 nm, the n-type semiconductor layer has a superlattice layer, Active layer Said As viewed from the p-type nitride semiconductor layer side, the barrier layer, Said A first well layer, a barrier layer, Said A third well layer, a barrier layer, Said A nitride semiconductor light emitting device comprising only a structure in which a second well layer and a barrier layer are stacked in this order.
With this configuration, it is possible to obtain a nitride semiconductor light emitting device with high luminous efficiency that emits light having a desired color rendering property in the simplest manner.
[0012]
In the present invention, the main peak wavelength of light emitted from the first well layer is 400 to 480 nm. ,in front 5. The nitride semiconductor light emitting device according to claim 1, wherein a main peak wavelength of light emitted from the third well layer is 570 to 800 nm.
With this configuration, it is possible to obtain a nitride semiconductor light emitting device having desired color rendering properties and high white light emission efficiency.
[0013]
In the present invention, the main peak wavelength of light emitted from the first well layer is 420 to 460 nm, the main peak wavelength of light emitted from the second well layer is 480 to 520 nm, and the third main peak wavelength is 570 to 570 nm. It is 600 nm. With this configuration, it is possible to obtain a nitride semiconductor light emitting device having high light emission efficiency of white light having a desired color rendering property without providing a well layer that emits light with a long wavelength of about the red region.
The nitride semiconductor light emitting device of the present invention has an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer in this order on a substrate, and the active layer is made of a nitride semiconductor containing In. Nitride having a multiple quantum well structure with n (n ≧ 4) well layers and having a short main peak wavelength in the order of the first well layer, the second well layer,..., the nth well layer In a semiconductor light emitting device, A main peak wavelength of light emitted from the second well layer is 480 to 570 nm, the n-type semiconductor layer has a superlattice layer; The shortest main peak wavelength Said The first well layer Said next to the p-type nitride semiconductor layer, then Said The main peak wavelength is the longest at a position close to the p-type nitride semiconductor layer. Said A nitride semiconductor light emitting device having an nth well layer.
The nitride semiconductor light emitting device of the present invention has a superlattice layer in the n-type semiconductor layer. The superlattice layer is characterized by comprising undoped GaN and Si-doped GaN.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In the following, the present invention will be described in detail with reference to the drawings, which are merely illustrative and do not limit the present invention.
By forming an active layer having a plurality of light emitting layers having different mixed crystal ratios in a single element structure, a nitride semiconductor light emitting element emitting white light can be obtained. Compared to the case where a plurality of light emitting elements having different emission colors such as RGB are arranged on the same stem and the desired white light is obtained by mixing these emission colors, the size can be reduced and the power consumption can be suppressed. A wide range of applications can be considered. However, when there are a plurality of light-emitting layers having different mixed crystal ratios in a single element structure, the same current is applied to all the light-emitting layers. The crystal ratio, film thickness, and the like must be controlled, and there is a problem that the light emission efficiency is low particularly at the same film thickness.
[0015]
In view of the following characteristics of the nitride semiconductor light emitting device, we have developed a nitride semiconductor light emitting device with high luminous efficiency. One of the characteristics of the nitride semiconductor light emitting device is that the active layer sandwiched between the n-type nitride semiconductor layer and the p-type nitride semiconductor layer emits light better when the active layer is closer to the p-type nitride semiconductor layer. The point is mentioned. This is also a feature of a general light-emitting diode, and when electrons supplied from the n-type nitride semiconductor layer to the active layer are compared with holes supplied from the p-type nitride semiconductor layer, the holes have a larger mass. Therefore, there are few holes reaching the n-type nitride semiconductor layer side in the active layer, and many holes exist on the p-type nitride semiconductor layer side in the active layer. Conversely, since electrons have a smaller mass than holes, there are many electrons on the p-type nitride semiconductor layer side. Therefore, recombination of electrons and holes is likely to occur on the p-type nitride semiconductor layer side even in the active layer. This is a major factor, and it is considered that light closer to the p-type nitride semiconductor layer emits light better.
[0016]
Another feature of the nitride semiconductor light emitting device is that the light emitting layer starts to shine from a layer having a small band gap. Although no specific factor is known in this regard, it can be inferred that since the electrons accumulate in the conductor from the smaller band gap, it will begin to shine from the smaller one.
[0017]
Furthermore, another feature of the nitride semiconductor light emitting device is that the output becomes smaller as the light is emitted at a longer wavelength. Although no specific factor is known in this regard, nitride semiconductor light emitting devices can emit light from the ultraviolet region to the red region by changing the mixed crystal ratio of the light emitting layer, and are typical as nitride semiconductor light emitting devices. For blue light emission (about 420 nm), InGaN is used as the light emitting layer. Furthermore, by increasing the In mixed crystal ratio of InGaN, light emission in a long wavelength region is possible. However, since the nitride semiconductor light emitting device is basically made of GaN, the lattice between the light emitting layer and other layers is increased when the In mixed crystal ratio of the light emitting layer is increased in order to obtain long wavelength light emission. The strain becomes large and the crystallinity of the light emitting layer is deteriorated. When the crystallinity is deteriorated, the light emission output is naturally reduced. It can be inferred that this is a factor that the output becomes smaller as the light emitted at a longer wavelength.
[0018]
In summary, the characteristics of the nitride semiconductor light emitting device are as follows: 1) the active layer emits light closer to the p-type nitride semiconductor layer, 2) the light emitting layer starts to shine from a layer having a small band gap, and 3) a long wavelength. It is mentioned that the output decreases as the light emission increases. From these features, the active layer is seen from the p-type nitride semiconductor layer side, and the first light emitting region, the third light emitting region, and the second light emitting region are stacked in this order, thereby providing a nitride with high light emission efficiency. A semiconductor light emitting device is obtained. This is because the third light emitting region having the third well layer has a smaller output than the other, since the output becomes smaller as the light having a longer wavelength of 3) is emitted. The output is increased by making up on the shining p-type nitride semiconductor layer side. However, if the light emitting layer closest to the p-type nitride semiconductor layer is used as the third light emitting region having the third well layer, the light emission starts from the side having the smaller band gap of 2), and as a result, the output is higher than the other layers. Will become high. Therefore, by making the first light emitting region having the first well layer having a short wavelength that starts to shine last, the layer closest to the p-type nitride semiconductor layer, the light emission in any light emitting region does not become too strong. ing. That is, the light emitting region having the shortest wavelength in the active layer is the layer closest to the p-type nitride semiconductor side, and the light emitting region having the longest wavelength in the active layer is the layer closest to the p-type nitride semiconductor side. As a result, a nitride semiconductor light emitting device having desired color rendering properties and high luminous efficiency was realized. Further, the position of the light emitting region having other wavelengths is not particular, but the light emitting regions having other intermediate wavelengths have 2) and 3) various characteristics, so that the p-type that shines well in 1). It is preferable to form it on the n-type nitride semiconductor side opposite to the nitride semiconductor layer side.
[0019]
In the present invention, here, a first light emitting region having at least one first well layer and at least one light emitting a main peak wavelength longer than a main peak wavelength of light emitted by the first well layer A second light emitting region having a second well layer and a third light emitting region having at least one third well layer that emits light having a main peak wavelength longer than a main peak wavelength of light emitted from the second well layer. A nitride semiconductor light emitting device having an active layer having a multiple quantum well structure provided with a plurality of light emitting regions has been described. However, for example, at least one (n-1) well layer is not limited to the above three light emitting regions. N light emitting regions having n different wavelengths, such as having an nth light emitting region having at least an nth well layer, emitting light having a main peak wavelength longer than the main peak wavelength of light having Multiquantum Even in the case of a nitride semiconductor light emitting device comprising an active layer (4 ≦ n) having a door structure, the first light emitting region having the first well layer having the shortest main peak wavelength is closest to the p-type nitride semiconductor side. Next, by forming an nth light emitting region having an nth well layer having the longest main peak wavelength as a layer closest to the p-type impurity semiconductor, four or more types of well layers having different main peak wavelengths are formed. Even with the active layer, a nitride semiconductor light emitting device having desired color rendering properties and high light emission efficiency can be obtained.
[0020]
【Example】
FIG. 1 is a schematic cross-sectional view showing the structure of a nitride semiconductor light emitting device according to an embodiment of the present invention. Hereinafter, Example 1 will be described with reference to FIG. Note that the light-emitting element of the present invention is not limited to the structure shown in FIG.
Example 1
FIG. 1 is a schematic cross-sectional view showing a light emitting device 100 of the present invention. The light emitting device 100 includes a GaN buffer layer 102, an undoped GaN layer 103, an n-type contact / cladding layer 104 made of Si-doped GaN, a superlattice layer 105, and an active layer 106 made of a multiple quantum well structure on a sapphire substrate 101. A p-type cladding layer 111 made of Mg-doped AlGaN and a p-type contact layer 112 made of Mg-doped GaN are sequentially formed. The active layer 106 includes a barrier layer 107, a second well layer 108 made of InGaN, a third well layer 109, and a first well layer 110. Of all the well layers, the first well layer has the lowest In content and the third well layer has the highest In content. Further, the active layer 106 is formed by sandwiching a second well layer 108, a third well layer 109, and a first well layer 110 between the barrier layers 107 in order from the n-type contact layer side.
[0021]
Further, the p-side transparent electrode 113 and the p-side pad electrode 114 are formed on the p-type contact layer 112, and the n-electrode 115 is formed on the n-type contact layer 104, thereby forming the light emitting element 100 capable of emitting mixed color light. can do. Next, a method for forming a light emitting device according to the present invention will be described.
[0022]
A light emitting element is formed by forming a nitride semiconductor by MOCVD. First, the cleaned substrate 101 made of 2-inch sapphire (C surface) is set in a reaction vessel of an MOCVD apparatus. While evacuating the reaction vessel, ₂ And H inside the container ₂ Then, the substrate temperature is raised to 1050 ° C., and the substrate 101 is cleaned. As the semiconductor substrate 101, in addition to C-plane sapphire, sapphire or spinel (MgAl ₂ O _Four ), And materials such as SiC (including 6H, 4H, and 3C), Si, ZnO, GaAs, and GaN can be used.
[0023]
Next, the film formation temperature is lowered to 510 ° C., TMG (trimethylgallium), NH _Three Raw material gas, H ₂ As a carrier gas, a buffer layer 102 is formed by forming a GaN layer having a thickness of about 150 mm on the sapphire substrate 101. The buffer layer 102 may be made of a material such as AlN or AlGaN in addition to GaN.
[0024]
Subsequently, the inflow of the raw material gas is temporarily stopped, and the substrate temperature is raised to 1050 ° C. while flowing the carrier gas. After the deposition temperature stabilizes, TMG and NH _Three Then, an undoped GaN layer having a thickness of 1.5 μm is stacked on the buffer layer 102.
[0025]
Then, while maintaining the film formation temperature at 1050 ° C., TMG and NH as source gases _Three , H as carrier gas ₂ SiH as impurity gas _Four 5 × 10 ¹⁸ / Cm ^Three An n-type contact layer 104, which is a GaN layer having a Si impurity concentration, is formed on the undoped GaN layer 103 with a thickness of 2.25 μm.
[0026]
Furthermore, it is preferable to form the superlattice layer 105 on the n-type contact layer 104 in order to improve the crystallinity of the active layer 106 and uniformly emit light over the entire surface. SiH, which is an impurity gas, with the deposition temperature maintained at 1050 ° C. _Four Is controlled to form an undoped GaN layer having a thickness of about 75 mm and a Si-doped GaN layer having a thickness of about 25 mm. With this as one cycle, the superlattice layer 105 having a total thickness of 2500 mm is formed on the n-type contact layer 104 by repeating 25 cycles. Note that the Si-doped GaN layers constituting the superlattice layer 105 have different impurity concentrations (Si) and are so-called modulation-doped.
[0027]
Next, the configuration of the active layer 106 having a multiple quantum well structure will be described in detail. The multi-quantum well structure active layer 106 includes a barrier layer 107 made of GaN having a thickness of about 250 mm, a second well layer 108 made of InGaN having a thickness of about 30 mm, and a barrier layer 107 made of GaN having a thickness of about 250 mm. A third well layer 109 made of InGaN having a thickness of about 30 mm, a barrier layer 107 made of GaN having a thickness of about 250 mm and a first well layer 110 made of InGaN having a thickness of about 30 mm, and finally having a thickness of about 250 mm. A barrier layer 107 made of GaN is stacked.
[0028]
Further, a specific method for forming the active layer 106 having a multiple quantum well structure will be described. TMG and NH as source gases at a film forming temperature of 1050 ° C. using MOCVD _Three , H as carrier gas ₂ To form a barrier layer 107 having a thickness of about 250 mm on the superlattice layer 105.
[0029]
Subsequently, the inflow of the source gas is temporarily stopped and the film forming temperature is adjusted to 800 ° C., and then again TMG, TMI (trimethylindium) and NH as source gases. _Three N as carrier gas ₂ About 30 mm thick In _0.63 Ga _0.37 N is deposited to form a second well layer.
[0030]
Thereafter, the film forming temperature is set to 1050 ° C., and TMG and NH are used as source gases. _Three , H as carrier gas ₂ As a result, a GaN barrier layer 107 having a thickness of about 250 mm is formed on the second well layer 108.
[0031]
Subsequently, the inflow of the source gas is temporarily stopped, the film forming temperature is adjusted to 800 ° C., and then TMG, TMI and NH are again used as source gases. _Three N as carrier gas ₂ About 30 mm thick In _0.84 Ga _0.16 A third well layer 109 is formed by depositing N.
[0032]
Thereafter, the film forming temperature is set to 1050 ° C., and TMG and NH are used as source gases. _Three , H as carrier gas ₂ As a result, a GaN barrier layer 107 having a thickness of about 250 mm is formed on the third well layer 109.
[0033]
Further, after the flow of the raw material gas is temporarily stopped and the film forming temperature is adjusted to 800 ° C., TMG, TMI and NH are again used as the raw material gases. _Three N as carrier gas ₂ About 30 mm thick In _0.44 Ga _0.56 N is deposited to form the first well layer 110.
[0034]
Subsequently, the film forming temperature is set to 1050 ° C., and TMG and NH are used as source gases. _Three , H as carrier gas ₂ As a result, a GaN barrier layer 107 having a thickness of about 250 mm is formed on the first well layer 110.
[0035]
After forming the active layer 106, a p-type cladding layer 111 having a superlattice structure is formed. A Mg-doped AlGaN layer having a thickness of about 40 mm and an Mg-doped InGaN film having a thickness of about 25 mm are formed. The p-type cladding layer 111 is formed by repeating this as one cycle and forming a film for five cycles. Specifically, the film forming temperature is set to 1050 ° C. by MOCVD, and TMG, TMA (trimethylaluminum) and NH are used as source gases. _Three Cp as impurity gas ₂ Mg (cyclopentadienyl magnesium) and H as the carrier gas ₂ To form an AlGaN layer having a thickness of about 40 mm. Next, after stopping the inflow of the source gas and adjusting the film forming temperature to 850 ° C., TMG, TMI, and NH are again used as source gases. _Three Cp as impurity gas ₂ Mg and N as carrier gas ₂ To form an InGaN layer having a thickness of about 25 mm. This is repeated for five cycles to form a superlattice p-type cladding layer 111 having a thickness of about 325 mm. The p-type cladding layer 111 may have a superlattice structure as described above, but may have a single layer structure such as AlGaN or AlBGaN.
[0036]
And the film-forming temperature shall be 1050 degreeC and TMG and NH as source gas _Three , H as carrier gas ₂ Cp as impurity gas ₂ 1 × 10 with Mg flow ²⁰ / Cm ^Three A p-type contact layer 112 which is a GaN layer having a Mg impurity concentration of 0.2 μm is formed on the p-type cladding layer 111. After forming the p-type cladding layer 111, the temperature is lowered to room temperature, and the wafer is annealed at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.
[0037]
After the annealing process, the wafer is taken out of the reaction vessel, a mask having a desired shape is formed on the surface of the uppermost p-type contact layer 112, and an etching process is performed from the p-type contact layer 112 side with an RIE (reactive ion etching) apparatus. To expose the p-type and n-type semiconductor surfaces.
[0038]
After the etching process, a sputtering apparatus is used to form a p-side transparent electrode 113 containing Ni and Au with a thickness of 200 mm on almost the entire surface of the p-type contact layer 112, and 0.5 μm made of bonding Au on the p-side transparent electrode 113. A p-side pad electrode 114 having a film thickness is formed. On the other hand, an n-electrode 115 containing W and Al is formed on the n-type contact layer 104 exposed by the etching process. Finally, in order to protect the surface of the p-side transparent electrode 113, SiO ₂ An insulating layer (not shown) made of is formed as a protective film. The nitride semiconductor wafer thus formed is drawn with a scribe line and then divided by external force to complete a 350 μm square LED chip as a light emitting element.
[0039]
As described above, the light emitting device of the present invention generally has an active layer having a multiple quantum well structure, and the active layer includes a first well layer 110 and a second well layer 108 made of a nitride semiconductor containing In. A third well layer 109 is provided. The well layer according to the present invention is, for example, Al as a nitride semiconductor containing In. _X In _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), preferably ternary mixed crystal In _Y Ga _1-Y N (0 ≦ Y ≦ 1). The active layer of the multiple quantum well structure of the present invention further comprises a total of n types (n ≧ 3) of the first well layer 110, the second well layer 108, the third well layer 109, or other well layers. The barrier layer 107 is made of a nitride semiconductor having a band gap larger than that of the well layer, and the well layers 110, 108, and 109 and the barrier layer 107 sandwiched therebetween are stacked. Although the barrier layer 107 is not particularly limited, the barrier layer 107 is made of a material such as GaN, InGaN, or AlGaN so as to be thicker than the n-type well layer, for example, to have a thickness of about several hundreds of liters. The thicknesses of the first well layer 110, the second well layer 108, the third well layer 109, and all the n-type well layers are not particularly limited, but have a thickness of, for example, 100 mm or less. Preferably, the film thickness is adjusted to 70 mm or less, most preferably 50 mm or less. If it is thicker than 100 mm, the well layer has a thickness exceeding the elastic strain limit, and minute cracks or crystal defects in the well layer are likely to enter.
[0040]
The p-type semiconductor and the n-type semiconductor are not particularly limited. For example, p-conductivity type and n-conductivity type semiconductors made of a nitride semiconductor can be used. The material composition of the nitride semiconductor of the present invention is Al _X In _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and as described above, p-type or n-type impurities are doped so as to have p-type conductivity or n-type conductivity.
[0041]
Further, In is a nitride semiconductor element used in the present invention. _Y Ga _1-Y The mixed crystal ratio of In of N (0 ≦ Y ≦ 1) is a relational expression with the band gap energy Eg, Eg = 3.4 * (1-Y) + 1.95 * Y-A * Y * (1-Y) , The estimated value when A = 1, and Al _X Ga _1-X The Al mixed crystal ratio X of N (0 ≦ X ≦ 1) is a relational expression with band gap energy, Eg = 3.4 * (1-X) + 6.2 * X-A * X * (1-X) , A = 1. The coefficients of the first and second terms in the above two relational expressions are as follows: 3.4 is the band gap energy (eV) of GaN, 1.95 is the band gap energy (eV) of InN, and 6.2 is The band gap energy (eV) of AlN is shown.
[0042]
The lead frame of the light emitting diode lamp is made of silver-plated iron-containing copper. One of the lead frames is a mount lead having a cup for placing the LED chip, and the other has an inner lead that is electrically connected to one electrode of the LED chip through a wire. After the LED chip is die-bonded on the mount lead using epoxy resin, one of the 35 μm diameter gold wire wires is ball bonded to the p-electrode and n-electrode of the LED chip, and the other is stitch-bonded to the tip of the lead frame. . As a result, each electrode of the LED chip is electrically connected to the inner lead and the mount lead.
[0043]
The light emitting diode lamp thus obtained was 20 mA (V _f = 3.5V), when the forward current is passed, as shown in FIG. 2, the coordinates on the CIE chromaticity diagram are expressed as (X, Y) = (0.276, 0.302). White light having a spectrum was obtained, and the color rendering property was Ra = 69. At this time, light emission having wavelengths of about 448 nm, 500 nm, and 570 nm is confirmed from the first, second, and third well layers 110, 108, and 109, respectively. In addition, as shown in FIG. 3, the emission spectrum emitted from the third well layer 109 has a wide half-value width and excellent color rendering as compared with the emission spectrum emitted from the second well layer 108. The emission spectrum emitted by 108 has a wide half-value width and is excellent in color rendering as compared with the emission spectrum emitted by the first well layer 110. Further, the light-emitting element according to the present invention is not limited to three well layers emitting different emission spectra, and can provide n types (n ≧ 4) of well layers. Thereby, the spectrum width as a light emitting element can be expanded.
[0044]
(Comparative Example 1)
In order to compare with Example 1, as Comparative Example 1, the first well layer, the second well layer, and the third well layer of the active layer were formed in a different order. Specifically, as viewed from the n-type nitride semiconductor layer side, the barrier layer, the third well layer, the barrier layer, the second well layer, the barrier layer, the first well layer, and the barrier layer are stacked in this order. The forbidden band width is wide (that is, the wavelength is short) from the side close to the light extraction surface (p-type nitride semiconductor layer side).
[0045]
As shown in FIG. 2, this light-emitting diode has an emission spectrum in which coordinates on the CIE chromaticity diagram are represented by (X, Y) = (0.205, 0.417), and the luminance is as in Example 1. Compared with the light-emitting diode lamp, the emission color appeared greenish. This is because the emission spectrum intensity of the second well layer having a wavelength of 500 nm is relatively higher than the emission spectra of other wavelengths as compared with Example 1.
[0046]
(Example 2)
A light emitting diode lamp was obtained in the same manner as in Example 1 except that the active layer 106 was formed as follows.
The active layer 106 having a multiple quantum well structure is composed of a barrier layer 107 made of GaN having a thickness of about 250 mm and an In layer having a thickness of about 30 mm. _0.63 Ga _0.37 A second well layer 108 made of N, a barrier layer 107 made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm. _0.84 Ga _0.16 A third well layer 109 made of N, a barrier layer 107 made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm. _0.44 Ga _0.56 A first well layer 110 made of N and a barrier layer 107 made of GaN having a thickness of about 250 mm are stacked.
[0047]
Continuing, In about 30mm thick _0.63 Ga _0.37 Second well layer 108 made of N, barrier layer 107 made of GaN having a thickness of about 250 mm, third well layer 109 made of In0.84Ga0.16N having a thickness of about 30 mm, and barrier made of GaN having a thickness of about 250 mm Layer 107 and about 30 mm thick In _0.44 Ga _0.56 A first well layer 110 made of N and finally a barrier layer 107 made of GaN having a thickness of about 250 mm are stacked.
[0048]
The light-emitting diode lamp thus obtained is 20 mA (V _f When a forward current of = 3.8 V) was passed, white light was obtained and the color rendering property was Ra = 69. Further, light emission having wavelengths of about 448 nm, 500 nm, and 570 nm was confirmed from the first, second, and third well layers 110, 108, and 109, respectively. Thus, the output of the light-emitting diode lamp can be increased by setting the active layer structure of Example 1 as one pair and increasing the number of pairs (excluding some barrier layers). Further, the number of well layers that emit different emission spectra is not limited to three, and n types (n ≧ 4) of well layers can be provided.
[0049]
(Example 3)
A light emitting diode lamp was obtained in the same manner as in Example 1 except that the active layer 106 was formed as follows.
The active layer 106 having a multiple quantum well structure is composed of a barrier layer 107 made of GaN having a thickness of about 250 mm and an In layer having a thickness of about 30 mm. _0.44 Ga _0.56 First well layer 110 made of N, barrier layer 107 made of GaN having a thickness of about 250 mm, and In layer having a thickness of about 30 mm _0.63 Ga _0.37 A second well layer 108 made of N, a barrier layer 107 made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm. _0.84 Ga _0.16 A third well layer 109 made of N, a barrier layer 107 made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm. _0.44 Ga _0.56 A first well layer 110 made of N and finally a barrier layer 107 made of GaN having a thickness of about 250 mm are stacked.
[0050]
The light-emitting diode lamp thus obtained is 20 mA (V _f = 3.6V), a white light was obtained when a forward current was passed. Further, light emission having wavelengths of about 448 nm, 500 nm, and 570 nm was confirmed from the first, second, and third well layers 110, 108, and 109, respectively. Thus, including the structure of the active layer of Example 1 and adding one first well layer 110 on the n-type nitride semiconductor side, a light emitting diode lamp having a higher color temperature than that of Example 1 is obtained. Can do. Further, the number of well layers that emit different emission spectra is not limited to three, and n types (n ≧ 4) of well layers can be provided.
[0051]
Example 4
A light emitting diode lamp was obtained in the same manner as in Example 1 except that the active layer 106 was formed as follows.
The active layer 106 having a multiple quantum well structure is composed of a barrier layer 107 made of GaN having a thickness of about 250 mm and an In layer having a thickness of about 30 mm. _0.63 Ga _0.37 A second well layer 108 made of N, a barrier layer 107 made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm. _0.84 Ga _0.16 A third well layer 109 made of N, a barrier layer 107 made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm. _0.44 Ga _0.56 First well layer 110 made of N, barrier layer 107 made of GaN having a thickness of about 250 mm, and In layer having a thickness of about 30 mm _0.44 Ga _0.56 A first well layer 110 made of N and finally a barrier layer 107 made of GaN having a thickness of about 250 mm are stacked.
[0052]
The light-emitting diode lamp thus obtained is 20 mA (V _f = 3.6V), a white light was obtained when a forward current was passed. Further, light emission having wavelengths of about 448 nm, 500 nm, and 570 nm was confirmed from the first, second, and third well layers 110, 108, and 109, respectively. As described above, the structure of the active layer of Example 1 is included, and the first well layer 110 is further added to the p-type nitride semiconductor side to obtain a light emitting diode lamp having a higher color temperature than that of Example 1. Can do. Further, the number of well layers that emit different emission spectra is not limited to three, and n types (n ≧ 4) of well layers can be provided.
[0053]
(Example 5)
A light emitting diode lamp was obtained in the same manner as in Example 1 except that the active layer 106 was formed as follows.
The active layer 106 having a multiple quantum well structure is composed of a barrier layer 107 made of GaN having a thickness of about 250 mm and an In layer having a thickness of about 30 mm. _0.70 Ga _0.30 A second well layer 108 made of N, a barrier layer 107 made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm. _0.96 Ga _0.04 A third well layer 109 made of N, a barrier layer 107 made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm. _0.52 Ga _0.48 A first well layer 110 made of N and a barrier layer 107 made of GaN having a thickness of about 250 mm are stacked.
[0054]
When a forward current was passed through the light-emitting diode lamp thus obtained, white light was obtained. Further, light emission having wavelengths of about 470 nm, 520 nm, and 620 nm was confirmed from the first, second, and third well layers 110, 108, and 109, respectively.
[0055]
(Example 6)
A light emitting diode lamp was obtained in the same manner as in Example 1 except that the active layer 106 was formed as follows.
The active layer 106 having a multiple quantum well structure is composed of a barrier layer 107 made of GaN having a thickness of about 250 mm and an In layer having a thickness of about 30 mm. _0.70 Ga _0.30 Second well layer 108 made of N, and about 50 mm thick Al _0.3 Ga _0.7 An intermediate layer made of N, a barrier layer 107 made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm _0.96 Ga _0.04 A third well layer 109 made of N, and about 50 mm thick Al _0.3 Ga _0.7 An intermediate layer made of N, a barrier layer 107 made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm _0.52 Ga _0.48 First well layer 110 made of N, and about 50 mm thick Al _0.3 Ga _0.7 An intermediate layer made of N and a barrier layer 107 made of GaN having a thickness of about 250 mm are stacked.
[0056]
When a forward current was passed through the light-emitting diode lamp thus obtained, white light was obtained. Further, light emission having wavelengths of about 470 nm, 520 nm, and 620 nm was confirmed from the first, second, and third well layers 110, 108, and 109, respectively. Thus, Al on the well layer between the well layer and the barrier layer of the active layer _0.3 Ga _0.7 When an intermediate layer such as N is formed, V _f Tend to go down.
[0057]
(Example 7)
A light emitting diode lamp was obtained in the same manner as in Example 1 except that the active layer 106 was formed as follows.
The active layer 106 having a multiple quantum well structure is composed of a barrier layer 107 made of GaN having a thickness of about 250 mm and an In layer having a thickness of about 30 mm. _0.79 Ga _0.21 A third well layer made of N, a barrier layer made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm _0.70 Ga _0.30 A second well layer made of N, a barrier layer made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm _0.96 Ga _0.04 A fourth well layer made of N, a barrier layer made of GaN having a thickness of about 250 mm, and an In layer having a thickness of about 30 mm _0.52 Ga _0.48 A first well layer made of N and a barrier layer made of GaN having a thickness of about 250 mm are stacked.
[0058]
When a forward current was passed through the light-emitting diode lamp thus obtained, white light was obtained. In addition, the first, second, third, and fourth well layers were confirmed to emit light having wavelengths of about 470 nm, 520 nm, 550 nm, and 620 nm, respectively. Further, compared with Example 5, the color rendering property was improved from that of Example 5 by forming by adding the wavelength of 550 nm to the three wavelengths of 470 nm, 520 nm, and 620 nm.
[0059]
【The invention's effect】
The present invention is implemented in the form as described above, and has the effects described below.
The active layer of the nitride semiconductor light emitting device according to the present invention has a configuration in which the first light emitting region, the third light emitting region, and the second light emitting region are stacked in this order when viewed from the p-type nitride semiconductor layer side. By including at least one, it is possible to obtain a nitride semiconductor light emitting device having a desired color rendering property and high white light emission efficiency.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of a nitride semiconductor light emitting device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating coordinates on a chromaticity diagram of light emitted from light emitting elements formed according to Example 1 and Comparative Example 1;
3 is an emission spectrum diagram of the nitride semiconductor light emitting device according to Example 1. FIG.
[Explanation of symbols]
101 ... Sapphire substrate
102: Buffer layer
103 ... Undoped GaN layer
104 ... n contact and n clad layer
105 ... superlattice layer
106 ... Active layer
107 ... barrier layer
108 ... second well layer
109 ... third well layer
110: first well layer
111 ... p-clad layer
112 ... p contact layer
113 ... p-side transparent electrode
114... P-side pad electrode
115 ... n electrode

Claims

基板上に、ｎ型窒化物半導体層、活性層、ｐ型窒化物半導体層を順に有し、
前記活性層は、Ｉｎを含む窒化物半導体からなる少なくとも１つの第１の井戸層を有する第１の発光領域と、該第１の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体から成る少なくとも１つの第２の井戸層を有する第２の発光領域と、該第２の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体からなる少なくとも１つの第３の井戸層を有する第３の発光領域と、を備えた多重量子井戸構造から成る窒化物半導体発光素子において、
前記第２の井戸層が発する光の主ピーク波長が４８０乃至５７０ｎｍであり、
前記ｎ型半導体層は超格子層を有しており、
前記活性層は前記ｐ型窒化物半導体層側から見て、前記第１の発光領域、前記第３の発光領域、前記第２の発光領域の順で積層された構成を少なくとも１つ含んでなることを特徴とする窒化物半導体発光素子。 On the substrate, an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially provided.
The active layer has a first light emitting region having at least one first well layer made of a nitride semiconductor containing In, and a main peak wavelength longer than a main peak wavelength of light emitted from the first well layer. A second light-emitting region having at least one second well layer made of a nitride semiconductor containing In, which emits light, and light having a main peak wavelength longer than the main peak wavelength of the light emitted by the second well layer in the issue, at least one third of the third Ru multiple quantum well structure formed nitride compound semiconductor light-emitting device comprising a light emitting region, a having a well layer made of nitride semiconductor containing in,
A main peak wavelength of light emitted from the second well layer is 480 to 570 nm;
The n-type semiconductor layer has a superlattice layer;
The active layer when viewed from the p-type nitride semiconductor layer side, the first light emitting region, the third light-emitting region, a forward with stacked structure of the second light-emitting region at least one comprising at A nitride semiconductor light emitting device characterized by that.

基板上に、ｎ型窒化物半導体層、活性層、ｐ型窒化物半導体層を順に有し、
前記活性層は、Ｉｎを含む窒化物半導体からなる少なくとも１つの第１の井戸層を有する第１の発光領域と、該第１の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体から成る少なくとも１つの第２の井戸層を有する第２の発光領域と、該第２の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体からなる少なくとも１つの第３の井戸層を有する第３の発光領域と、を備えた多重量子井戸構造から成る窒化物半導体発光素子において、
前記第２の井戸層が発する光の主ピーク波長が４８０乃至５７０ｎｍであり、
前記ｎ型半導体層は超格子層を有しており、
前記活性層は前記ｐ型窒化物半導体層側から見て、前記第１の発光領域、前記第３の発光領域、前記第２の発光領域の順で積層された構成のみから成ることを特徴とする窒化物半導体発光素子。 On the substrate, an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially provided.
The active layer has a first light emitting region having at least one first well layer made of a nitride semiconductor containing In, and a main peak wavelength longer than a main peak wavelength of light emitted from the first well layer. A second light-emitting region having at least one second well layer made of a nitride semiconductor containing In, which emits light, and light having a main peak wavelength longer than the main peak wavelength of the light emitted by the second well layer in the issue, at least one third of the third Ru multiple quantum well structure formed nitride compound semiconductor light-emitting device comprising a light emitting region, a having a well layer made of nitride semiconductor containing in,
A main peak wavelength of light emitted from the second well layer is 480 to 570 nm;
The n-type semiconductor layer has a superlattice layer;
The active layer when viewed from the p-type nitride semiconductor layer side, and characterized in that it consists of the first light emitting region, the third light-emitting region, only the order in stacked arrangement of the second light-emitting region Nitride semiconductor light emitting device.

基板上に、ｎ型窒化物半導体層、活性層、ｐ型窒化物半導体層を順に有し、
前記活性層は、Ｉｎを含む窒化物半導体からなる少なくとも１つの第１の井戸層と、該第１の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体から成る少なくとも１つの第２の井戸層と、該第２の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体からなる少なくとも１つの第３の井戸層と、を備えた多重量子井戸構造から成る窒化物半導体発光素子において、
前記第２の井戸層が発する光の主ピーク波長が４８０乃至５７０ｎｍであり、
前記ｎ型半導体層は超格子層を有しており、
前記活性層は前記ｐ型窒化物半導体層側から見て、障壁層、前記第１の井戸層、障壁層、前記第３の井戸層、障壁層、前記第２の井戸層、障壁層の順で積層された構成を少なくとも１つ含むことを特徴とする窒化物半導体発光素子。 On the substrate, an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially provided.
The active layer includes at least one first well layer made of a nitride semiconductor containing In, and In that emits light having a main peak wavelength longer than the main peak wavelength of light emitted from the first well layer. At least one second well layer made of a nitride semiconductor and at least one nitride semiconductor containing In that emits light having a main peak wavelength longer than the main peak wavelength of light emitted by the second well layer and a third well layer, the Ru multiple quantum well structure formed nitride compound semiconductor light-emitting device comprising a,
A main peak wavelength of light emitted from the second well layer is 480 to 570 nm;
The n-type semiconductor layer has a superlattice layer;
The active layer when viewed from the p-type nitride semiconductor layer side, the barrier layer, the first well layer, barrier layer, the third well layer, a barrier layer, said second well layer, the order of the barrier layer A nitride semiconductor light-emitting device comprising at least one of the structures laminated with each other.

基板上に、ｎ型窒化物半導体層、活性層、ｐ型窒化物半導体層を順に有し、
前記活性層は、Ｉｎを含む窒化物半導体からなる少なくとも１つの第１の井戸層と、該第１の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体から成る少なくとも１つの第２の井戸層と、該第２の井戸層が発する光の主ピーク波長よりも長い主ピーク波長の光を発する、Ｉｎを含む窒化物半導体からなる少なくとも１つの第３の井戸層と、を備えた多重量子井戸構造から成る窒化物半導体発光素子において、
前記第２の井戸層が発する光の主ピーク波長が４８０乃至５７０ｎｍであり、
前記ｎ型半導体層は超格子層を有しており、
前記活性層は前記ｐ型窒化物半導体層側から見て、障壁層、前記第１の井戸層、障壁層、前記第３の井戸層、障壁層、前記第２の井戸層、障壁層の順で積層された構成のみからなることを特徴とする窒化物半導体発光素子。 On the substrate, an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially provided.
The active layer includes at least one first well layer made of a nitride semiconductor containing In, and In that emits light having a main peak wavelength longer than the main peak wavelength of light emitted from the first well layer. At least one second well layer made of a nitride semiconductor and at least one nitride semiconductor containing In that emits light having a main peak wavelength longer than the main peak wavelength of light emitted by the second well layer and a third well layer, the Ru multiple quantum well structure formed nitride compound semiconductor light-emitting device comprising a,
A main peak wavelength of light emitted from the second well layer is 480 to 570 nm;
The n-type semiconductor layer has a superlattice layer;
The active layer when viewed from the p-type nitride semiconductor layer side, the barrier layer, the first well layer, barrier layer, the third well layer, a barrier layer, said second well layer, the order of the barrier layer A nitride semiconductor light-emitting device comprising only the structure laminated with the above.

前記第１の井戸層が発する光の主ピーク波長が４００乃至４８０ｎｍで、前記第３の井戸層が発する光の主ピーク波長が５７０乃至８００ｎｍであることを特徴とする請求項１乃至請求項４のいずれかに記載の窒化物半導体発光素子。In the first main peak wavelength of 400 to 480nm of the light well layer emits, claims 1 main peak wavelength before Symbol third well layer emits light characterized in that it is a 570 to 800nm 5. The nitride semiconductor light emitting device according to claim 4.

前記第１の井戸層が発する光の主ピーク波長が４２０乃至４６０ｎｍ、前記第２の井戸層が発する光の主ピーク波長が４８０乃至５２０ｎｍ、前記第３の主ピーク波長が５７０乃至６００ｎｍであることを特徴とする請求項１乃至請求項５のいずれか１項に記載の窒化物半導体発光素子。 The main peak wavelength of light emitted from the first well layer is 420 to 460 nm, the main peak wavelength of light emitted from the second well layer is 480 to 520 nm, and the third main peak wavelength is 570 to 600 nm. The nitride semiconductor light-emitting device according to claim 1, wherein:

基板上に、ｎ型窒化物半導体層、活性層、ｐ型窒化物半導体層を順に有し、前記活性層は、Ｉｎを含む窒化物半導体からなるｎ個（ｎ≧４）の井戸層を備えた多重量子井戸構造からなり、第１の井戸層、第２の井戸層、・・・、第ｎの井戸層の順に主ピーク波長が短い窒化物半導体発光素子において、
前記第２の井戸層が発する光の主ピーク波長が４８０乃至５７０ｎｍであり、
前記ｎ型半導体層は超格子層を有しており、
主ピーク波長が最も短い前記第１の井戸層を前記ｐ型窒化物半導体層の最も近くに有し、その次に前記ｐ型窒化物半導体層に近い位置に、主ピーク波長が最も長い前記第ｎの井戸層を有することを特徴とする窒化物半導体発光素子。An n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially provided on a substrate, and the active layer includes n (n ≧ 4) well layers made of a nitride semiconductor containing In. In a nitride semiconductor light emitting device having a multi-quantum well structure and having a short main peak wavelength in the order of the first well layer, the second well layer, ..., the nth well layer,
A main peak wavelength of light emitted from the second well layer is 480 to 570 nm;
The n-type semiconductor layer has a superlattice layer;
Has a shortest first well layer main peak wavelength closest to the p-type nitride semiconductor layer, at a position closer to the p-type nitride semiconductor layer to the next, the longest the first main peak wavelength A nitride semiconductor light emitting device having n well layers.

前記超格子層は、アンドープＧａＮとＳｉドープＧａＮからなることを特徴とする請求項１乃至７のいうずれか１項に記載の窒化物半導体発光素子。The nitride semiconductor light-emitting device according to claim 1 , wherein the superlattice layer is made of undoped GaN and Si-doped GaN.