JP3816176B2 - Semiconductor light emitting device and optical semiconductor device - Google Patents

Description

【００９６】
（その他の例）
記の第１〜第３の例においては、基板の主面として（１−１００）面、或いは、（１１−２１）面等のジャスト面を用いているが、双晶等を抑制するために、（１−１００）面、或いは、（１１−２１）面をオフ角θ（０°≦θ≦１０°）の範囲内でオフした基板を用いても良い。
【００９７】
さらに、上記の例においては、活性層としてGa_0.9In_0.1N を用いているが、必要とする波長に応じて混晶比をAl_x Ga_1-x-y In_y N （０≦ｘ≦１、０≦ｙ≦１）の範囲内で変えても良いものであり、且つ、それに伴って、光ガイド層及びクラッド層の混晶比をAl_a Ga_1-a-b In_b N （０≦ａ≦１、０≦b ≦１）の範囲内で変えても良い。
【００９８】
上記の例においては光ガイド層を用いているが、必ずしも必要なものでなく、クラッド層と活性層とによって直接へテロ接合を形成しても良く、さらに、光ガイド層及びクラッド層は必ずしも上下対称的にする必要はなく、互いに混晶比の異なるAl_a Ga_1-a-b In_b N を用いても良いものである。
また、上記した例に用いた原料も上記の原料に限られるものではなく、有機金属原料はメチル系に代えてエチル系、即ち、ＴＥGa（トリエチルガリウム）、ＴＥAl（トリエチルアルミニウム）、及び、ＴＥIn（トリエチルインジウム）を用いても良く、さらに、窒素（Ｎ）源としてもアンモニアの代わりに、N₂H₄、( ＣＨ₃)₃CNH₂ 、C₂H₅N₃、或いは、ＣＨ₃NH ・NH₂ を用いても良い。
【００９９】
さらに、不純物原料も、ｎ型用としてはSi₂H₆ の代わりに、SiH₄或いはＣＨ₃SiH₃ を用いても良く、また、ｐ型用としてはビスシクロペンタジエニルマグネシウム〔(C₅H₅)₂Mg 〕の代わりに、(CＨ₃C₅H₄)₂ Mg、(C₅H₅C₅H₄)₂Mg 、（i-C₃H₇C₅H₄)₂Mg、或いは、（n-C₃H₇C₅H₄)₂を用いても良い。
（第２実施形態）
図１０は本実施形態の面発光半導体レーザの基本構造を示す斜視図である。図１１は本発明の活性層の結晶方位を表す図であり、図１０に表された半導体レーザの活性層の結晶方位と座標軸との関係を表している。
【０１００】
本発明の第一の構成では、図１０を参照して、基板４１の上方に形成された活性層４２は、その面内にｃ軸を有する六方晶の半導体層から構成される。即ち、図１０及び図１１に示すように、活性層４２の主面内にｘｚ平面を活性層４２の垂直方向にｙ軸をとるとき、活性層４２を構成する六方晶半導体結晶のｃ軸の方向、即ち＜０００１＞方向を、活性層４２面内にあるｚ軸に向けて配置する。
【０１０１】
このように活性層４２の面内にｃ軸を含むようにすることにより、以下に説明するように発振光の偏光面が規定される。なお、ｘ及びｙ軸方位の結晶方位はとくに制限されないが、例えば、＜１１−２０＞方向を活性層４２の面内にあるｘ軸に、かつ＜１−１００＞方位を活性層２の膜厚方向にあるｙ軸とすることができる。
【０１０２】
以下、本実施形態において発振光の偏光面が規定される理由を説明する。
初めに活性層内に歪がない場合について説明する。図１２はGaN のエネルギバンド構造図であり、六方晶半導体のバンド構造を表している。図１２に示すように、GaN の価電子帯ＶＢは、電子の波動ベクトルｋ＝０の近傍で、ＨＨ、ＣＨ及びＬＨの３つのバンドが禁止帯の底の近くに存在する。
【０１０３】
ここで、GaN 中に歪が無い場合、波動ベクトルｋ＝０において、最もエネルギが高い価電子帯のバンドをＨＨバンドと、次にエネルギが高いものをＬＨバンドと、最低のエネルギのものをＣＨバンドとしている。なお、これらのＨＨ、ＬＨ、ＣＨバンドは結晶のｃ軸方向をＸＹＺ３軸直交座標のＺ軸にとるとき、ｃ軸に垂直な方向に分極を有する２つのｐ軌道関数ｐ_x 及びｐ_y と、ｃ軸方向に分極を有する軌道関数ｐ_z とを用いて次のように表される。
【０１０４】
ＨＨバンド； （ｐ_x ＋ｐ_y ）／√２
ＬＨバンド； （ｐ_x −ｐ_y ）／√２
ＣＨバンド； ｐ_z
このうちＨＨバンドが最も禁止帯の底に近いため、伝導帯ＣＢから価電子帯ＶＢへの自然放出はＨＨバンドへの発光遷移が優先する。このＨＨバンドはｐ軌道の結合状態からなり、ｃ軸廻りに対称である。このため、GaN の自然放出に伴う発光は、ｃ軸に垂直に電場が振動する偏光状態を有する。また、かかる偏光を生ずる遷移確率は、振動方位のｃ軸廻りの回転に対して等価である。なお、上述の説明はGaN についてしたが、六方晶半導体結晶についても同ようである。なお、閃亜鉛鉱型半導体結晶では、三軸等方であるため光学特性は等方的である。
【０１０５】
従来の垂直共振器を有する面発光半導体レーザでは、図２６に示すように、活性層１０２はｃ軸１０４に垂直に形成されるから、発振光はｃ軸１０４に沿って進行する。このため発振光の偏光面はｃ面となり、電場はｃ軸１０４に垂直に振動する。その結果、上述した自然放出光の偏光のｃ軸廻りの対称性から、ＸＹ面内の何れの方向に振動する発振光も同等に生ずる。従って、発振光の偏光面は固定されず、発振が不安定となる。
【０１０６】
他方、本実施形態では、図１０に示すように、活性層４２は面内にｃ軸を有するから、発振光の進行方向はｃ軸に垂直である。既述のようにＨＨがバンド端の場合に自然放出光の電場の振動方向はｃ軸に垂直であるから、発振光の電場の振動方向は、ｃ軸と発振光の進行方向との両方位に垂直な方向、即ち、活性層面内に含まれかつｃ軸に垂直な方向に一義的に定まる。
【０１０７】
従って、本構成の面発光半導体レーザでは、活性層に垂直に進行する発振光の電場方向はｃ軸に垂直な方向に固定される。なお、面発光半導体レーザでは、共振器が膜厚方向にあるので、トップバンドによって決定される偏光方向（発光の電場ベクトルの方向）は、必ず活性層面内である必要がある。即ち、発光の電場ベクトルの向きを決定するトップバンドの分極は、活性層面内にある必要がある。
【０１０８】
次に、活性層のＰＬ( フォトルミネッセンス) 発光波長とその偏光面方位について説明する。図１３は、ＨＨがバンド端の場合の本発明の活性層のＰＬ発光特性を表す図であり、第一の構成の半導体レーザに用いられるｃ軸を面内に有するGaN 薄膜からなる活性層のＰＬ発光強度の計算値を表している。図１３中のパラメータは、ＰＬ光の偏光面の方位、即ち、活性層表面内での電場の振動方向とｃ軸とのなす角度θである。なお、以下の説明はGaN に限らず、六方晶半導体結晶についても同ように適用できる。
【０１０９】
図１３に示すように、活性層のＰＬ発光を偏光面、即ち電場の偏光面と波長とについて分光したとき、ＰＬ光の偏光面がｃ軸に直交する場合（図中の９０°で示す) に、活性層のＰＬ発光スペクトル強度は最大となる。この最大強度に対応する波長は約３６６nmであり、この波長は、図１２に示すように、伝導帯ＣＢから価電子帯ＶＢのＨＨバンドへの推移による発光に対応している。他方、ＰＬ光の偏光面がｃ軸に平行な場合( 図中の０°で示す）、発光強度は小さく、そのスペクトルの極大の波長は略３６０nmと短くなる。これは、ＰＬ発光の偏光面をｃ軸に垂直な偏光面からｃ軸に平行な偏光面に変化することで、ＰＬ発光が、ＨＨバンドへの遷移による発光からＣＨバンドへの遷移による発光に移行したことを示している。
【０１１０】
即ち、ｘ軸方向へ分極するｐ軌道からなるＨＨバンドへの遷移は偏光面がｃ軸に垂直な光のみを放出するのに対し、ＣＨバンドはｚ軸方向へ分極するｐ軌道からなるため、ｃ軸に平行な偏光面を有する光の放出はＣＨバンドへの遷移により初めて可能となるからである。
また、本実施形態では、半導体層２のフォトルミネッセンス光の偏光面及び波長をフォトルミネッセンス光強度が最大となるように選択した場合に、フォトルミネッセンス光の波長と、光共振器の共振波長とを合わせる。この波長の光の工ネルギは、電子のＨＨバンドへの遷移に伴う発光のフォトェネルギに等しい。従って、かかる波長で発振させることにより、発振光をＨＨバンドへの電子の遷移による発光のみに制限することができる。この場合、ｃ軸に平行な偏光面を有するＣＨバンドへの遷移に伴う発光は混在できないから、発振光の偏光面の変動をー層確実に防止することができる。
【０１１１】
なお、その共振波長は、厳密に最大強度が得られる波長である必要はない。例えば、主としてＨＨバンドへの電子の遷移に伴う発光が起こり且つＣＨバンドへの遷移に伴う発光が少なく、しかもその結果、ＨＨバンドへの電子の遷移による発振からＣＨバンドへの電子の遷移による発振へ発振モードが変動することを抑制できる程度に、最大強度に近い波長であればよい。
【０１１２】
次に活性層内に歪がある場合について説明する。
図１４(a) 〜(e) は、GaN のエネルギバンドの歪依存性を表す図であり、歪みを有するGaN の価電子帯のエネルギーの計算値を表している。なお、図１１を参照して、＜０００１＞方向の歪をε_z 、＜１１−２０＞方向の歪をε_x 、及び＜１−１００＞方位の歪をε_y とし、それぞれの歪みの値は、圧縮歪の状態を負に、引張歪の状態を正として示されている。
【０１１３】
図１４(a) は、ε_z ＝０とし、ε_x を変えた場合である。なお、ε_y は、ｙが成長方向のため拘束の無い状態である。即ち、結晶の＜１１−２０＞方向に一軸歪を加えたときの価電子帯のエネルギの変化を計算した結果である。同ように、図１４(b) は、ε_z に０. ５％の引張歪を付加し、さらにε_x を加えた場合である。また、図１４(c) 、(d) はそれぞれε_z に０. ５％及び１. ０％の圧縮歪を付加し、さらにε_x を加えた場合である。なお、ε_y の拘束は無い状態である。
【０１１４】
図１４(a) 〜(c) を参照して、歪ε_x が圧縮でε_z が１．０％以上の圧縮の場合は、ｐ軌道からなるＸ又はＺブランチがエネルギーバンド構造の禁止帯の底（即ち、価電子帯の最上）に位置する価電子帯のバンドとなる。従って、伝導帯からの発光遷移はＸ又はＺブランチへの遷移が優先的に起こり、その結果、Ｘが上の場合は上述した歪が無い場合の発光と同ように、ｃ軸に垂直な偏光面を有する光のみが発振する。また、Ｚがバンド端の場合はｃ軸に平行な光が発振する。
【０１１５】
一方、図１４(d) を参照して、歪ε_z が１％以上の圧縮歪を有し、かつε_x が引張歪の場合は、Ｘ及びＹブランチよりもＺブランチの方がエネルギが高くなる。このため、伝導帯からの電子の遷移については、Ｚブランチへの推移が優先してｃ軸に平行な偏光面で発振する光が生じる。なお、前述したように面発光半導体レーザは、活性層に垂直に共振器があるため、電場ベクトルは活性層面内である必要がある。従って、電場ベクトルを決定するトップバンドの波動関数の分極が活性層面内にあることが必要となる。即ち、図１１のような構造を作製するきには、Ｙ方向が共振器となるため、Ｙがトップバンドでは発振しない。
【０１１６】
図１４(e) は、ε_y を拘束の無い状態としたとき、ε_z ＝ε_x とした場合、言い換えれば＜０００１＞と＜１１−２０＞を含む面内に面内二軸性歪を与えた場合の価電子帯のエネルギバンドの計算値である。面内圧縮歪に対して、Ｘが最もエネルギが高く、この場合はａ軸方向に電場方向のある発振光が生ずる。なお、光の進行方向がＹブランチの分極方向を向く場合は、ＣＨバンドへの遷移に基づく発振が生ずる。
【０１１７】
上述のように、活性層に歪を有する場合は、発振光はｃ軸に垂直な偏光面を有する場合と、ｃ軸に平行な偏光面を有する場合とが生ずる。しかし、いずれの場合も発振光の偏光面は光共振器の光軸と結晶軸方向により一義に定まるから、面発光半導体レーザの偏光面は予め規定されかつ偏光面は変動しない。
ところで、図１０に示す構成において、活性層４２としては、GaN 、lnGaN 若しくはAIGalnN を含む多重量子井戸層（ＭＱＷ）、又は、GaN 、lnGaN 若しくはAIGalnN からなる単層のいずれかを選択する。
【０１１８】
また、図１０に示した基板４１として、（１１−２０）面を主面とするSiC 基板を用いてもよい。また、（１−１００）面を主面とするSiC 基板、又は、（１−１０２）面を主面とするサファイア基板を用いてもよい。
さらに、その基板４１の主面の上には、第一導電型の第一の障壁層４７、活性層４２、第二導電型の第二の障壁層４８が順次成長され、それらによってダブルヘテロ接合構造が構成される。また、そのダブルヘテロ接合構造の上又は下に反射面を形成すると、第一の障壁層４７、活性層４２、第二の障壁層４８を光共振器として構成することができる。第一及び第二の障壁層４７、４８の構成材料をAIGaN とし、さらに、活性層４２をAIGaN 又はGaN 又はInGaN の単層、又は、そのような材料を含む多重量子井戸層から構成することにより、ｃ軸が面内に存在するGaN 系半導体からなる活性層４２を有する面発光半導体レーザが実現される。
【０１１９】
次に、本実施形態を図面に基づいてさらに説明する。
本出願の発明者は、活性層４２のＰＬ発光のスペクトルを測定することにより、ＰＬ発光の波長と偏光面との関係が、伝導帯からＨＨバンドへの遷移による発光と、伝導帯からＣＨバンドへの遷移による発光により説明できることを以下の実験により明らかにした。
【０１２０】
先ず、（１−１００）面を主面とするSiC 基坂の上に、周知のＭＯＶＰＥ（有機金属気相エピタキシャル成長) 法を用いて、アンドープのGaN 薄膜を堆積し、そのフォトルミネッセンス光の偏光面方位及び波長に対するフォトルミネッセンス光強度を測定した。
図１５及び図１６にその結果を示す。図１５は本実施形態の活性層４２のＰＬ発光スペクトルであり、図１５中のＡは電場ベクトルがｃ軸に垂直なフォトルミネッセンス光を、Ｂは電場ベクトルがｃ軸に平行なフォトルミネッセンス光を表している。図１６は本発明の活性層のＰＬ発光強度の偏光面依存性を表す図であり、偏光面を固定したときのＰＬ発光の最大強度( 以下「ピーク強度」という。) が偏光面により変化するよう子を表している。なお、図１６中のＣは実験値を、Ｄは計算値を表している。
【０１２１】
図１５を参照して、ｃ軸に垂直な偏光面を有するフォトルミネッセンス光の強度Ａは、３６６nm近傍に強い極大を有する。これに対して、ｃ軸に平行な偏光面を有するフォトルミネッセンス光の強度Ｂは、より短波長の３６２nm近傍に弱い極大値を有する。これらの極大値が現れる波長及び極大の大きさは、図１３に示す計算値と良く一致する。
【０１２２】
次に、図１６に示すように、ＰＬ発光のピーク強度は、偏光面がｃ軸に垂直なとき最大となり、偏光面がｃ軸に平行なとき最少となる。この実験値Ｃは、計算値Ｄと良く一致する。このことは、図１３の計算結果が実験をよく再現することを意味している。
図１７は、本実施形態をさらに具体化した素子の断面図であり、その素子は、垂直共振器を有する面発光半導体レーザである。
【０１２３】
基板４１, 例えば（１１−２０）面を主面とするSiC 基坂４１の上に、ＭＯＶＰＥ法を用いて、低温で成長する厚さ５０nmのGaN バッファ層５２、厚さ０. ５μｍのｎ型GaN コンタクト層４９、厚さ１μｍのSiドープn 型Al_0.1Ga_0.9N 障壁層４７, 厚さ０. １μｍのアンドープGaN 活性層４２, 厚さ１μｍのＭｇドープｐ型Al_0.1Ga_0.9N 障壁層４８, 及びｐ型GaN コンタクト層５１を下から順に成長する。
【０１２４】
続いて、厚さ３０nmのSiO₂膜と厚さ３０nmのAl₂O₃ 膜を交互に各２０層ずつ贋層した多層膜を堆積し、この多層膜をフォトレジストリソグラフィーによりパターニングして平面形状が円又は方形のＤＢＲ鏡４３を形成する。このＤＢＲ鏡４３は、ｎ型コンタクト層４９と基板４１との界面を反射面として波長３６６nmの垂直光共振器を構成する。
【０１２５】
次いで、ＤＢＲ鏡４３の一側方の領域にある各層を反応性イオンエッチング（ＲＩＥ）法によりエッチングし、これによりｎ型コンタクト層４９の一部を露出させる。その後に、ｎ型コンタクト層４９の表出面に厚さ１００nmのTiよりなる電極５０ａを形成し、ｐ型のコンタクト層５１の上に膜厚１００nmのNiよりなる電極５０ｂを形成する。さらに、基板４１の裏面を研磨して光が出射する光学的窓を形成して面発光半導体レーザを完成する。
【０１２６】
そのような面発光半導体レーザでは、基板４１のｃ軸の垂直方向が電場の振動方向となる光を発振し偏光面が固定されるから、予め偏光方向が規定されたレーザ光を安定に発振させることができる。
本実施形態例の面発光半導体レーザの他の例は、活性層を多重量子井戸層構造としたものである。（１１−２０) 面を主面とするSiＣ基板４１上に、ＭＯＶＰＥ法を用いて、低温で成長する厚さ０. ５nmのAIN バッファ層４２, 厚さ０. ５μｍのｎ型GaN コンタクト層４９、厚さ１μｍのSiドープｎ型Al_0.1Ga_0.9N 障壁層４７、In_0.15Ga_0.85N 井戸層とln_0.05Ga_0.95N バリア層とを交互に各１０層づつ重層した多重量子井戸層からなる活性層４２, 厚さ１μｍのMgドープｐ型Al_0.1Ga_0.9N 障壁層４８、及びｐ型GaN コンタクト層５１をこの順序で堆積する。そして、既述の実施形態と同様の工程を経て面発光半導体レーザが製造される。
【０１２７】
上述した面発光半導体レーザでは、（１−１００）面又は（１１−２０）面を主面とする基板を用いることにより、光の偏向を揃わせている。そのような面発光半導体レーザを構成する基板には、受光素子を併せて搭載した構造を採用することが可能である。
図１８(a) は、面発光半導体レーザ（発光素子）とフォトダイオード（受光素子）を搭載した光装置を示す断面図、図１８(b) は、その光装置を示す平面図である。
【０１２８】
図１８(a) 及び(b) において、SiC 基板５３の主面である（１−１００）面又は（１１−２０）面の上には、膜厚５０nmのAlN 高温バッファ層５４、多層構造のミラー層５５、膜厚１μｍのｎ型の障壁層５６、膜厚５００nmのアンドープの下側光閉じ込め層５７、アンドープのＭＱＷ活性層５８、ｐ型の障壁層５９、膜厚５００nmのアンドープの上側光閉じ込め層６０、膜厚５０nmのGaN コンタクト層６０ａがＭＯＶＰＥ法によって順に積層されている。
【０１２９】
ミラー層５５は、膜厚４０nmのAl_0.4Ga_0.6 N層と膜厚４０nmのAl_0.1Ga_0.9N 層を交互に３０周期積層して構成されたものである。また、ＭＱＷ活性層５８は、膜厚４nmのIn_0.2Ga_0.8N 井戸層を膜厚４nmのIn_0.05Ga_0.95N 障壁層で挟んだ構造を有している。また、下側及び上側の光閉じ込め層５７，６０はそれぞれGaN より形成されている。
【０１３０】
さらに、ｎ型及びｐ型の障壁層５６，５９はそれぞれAl_0.1Ga_0.9N から構成され、そのうちのｎ型の障壁層５６は、不純物濃度２×１０¹⁸ atoms/cm³でSiがドープされ、また、ｐ型の障壁層５９は、不純物濃度１×１０¹⁷ atoms/cm³でMgがドープされている。ｐ型の障壁層の上のコンタクト層６０ａには１×１０¹⁸atoms/cm³ でMgがドープされている。
【０１３１】
ｎ型の障壁層５６からｐ型の障壁層５９までの複数の層は、ＳＣＨ(separate confinement heterostructure)構造を構成している。
このように積層した化合物半導体層は、複数回のパターニングを経て図１８(a),(b) に示すような断面構造及び平面構造の形状に加工されている。
すなわち、面発光半導体レーザ６６と受光素子６７は同じ形状を有しており、コンタクト層６０ａからｎ型の障壁層５６の上部までは直径２０μｍの円柱部６２となり、さらにｎ型の障壁層５６の下部からミラー層５５の上部までは円柱部の外方に広がったフランジ部６３となっている。ミラー層５５はアンドープであり、高抵抗となっているので、円柱部６２とフランジ部６３は他の領域の化合物半導体層から略筒状の溝６１を介して電気的に分離されている。
【０１３２】
そして、円柱部６２のコンタクト層６０ａの上面には、中央に直径１０μｍ程度の光放出窓６４ａを有する環状のTiよりなるｐ側電極６４が接続され、また、フランジ部６３のｎ型障壁層５６には、円柱部６２に接触しないNiよりなるｎ側電極６５が接続されている。
以上のような円柱部６２とその下のｎ型の障壁層５６によって膜厚方向の共振器が形成される。
【０１３３】
フォトダイオード６７は、図１８(b) に示すように、面発光半導体レーザ６６の周囲に離れて複数個、例えば４個形成されている。
それらのような面発光半導体レーザ６６とフォトダイオード６７を有する光装置は、例えば光磁気ディスク装置に取付けられる。そして、面発光半導体レーザ６６ではｐ側電極６４とｎ側電極６５に正バイアスの電圧６８が印加されて小さくても閾値電流が供給される。また、フォトダイオード６７ではｐ側電極６４とｎ側電極６５に逆バイアスの電圧が印加され、これによりフォトダイオード６７への入射光量によって検出回路６９に流れる電流値が大きくなる。
【０１３４】
この場合、面発光半導体レーザ６６が発振して窓６４ａを通して光が照射され、図示しない回折格子、レンズなどを通して光磁気ディスクに照射される。光磁気ディスクで反射したその光は、レンズ、偏向プリズムを通して４つの受光素子６７に入力する。その面発光半導体レーザ６６では、既に説明したように、基板４１のｃ軸の垂直方向が電場の振動方向となる光を発振し偏光面が固定されるから、レーザ光の偏光面が揃うことになる。しかも、光磁気ディスクで反射したレーザ光は、同じ偏光面のフォトダイオード６７に入射する。
【０１３５】
このように、同じ基板上に形成された面発光半導体レーザ６６とフォトダイオード６７が偏光面を有することになったので、光磁気ディスク装置の書込み用光素子と読み出し用光素子を集積化することができ、それらの装置の小型化と製造効率が良くなる。
以上のように、本実施形態によれば、活性層に垂直な共振軸を有する垂直共振型の面発光半導体レーザにおいて、発振光の偏光面が活性層の結晶方位により一義に規定されるため、発振光の偏光方位を予め定めることができ、かつ偏光方位の変動が少ない安定した動作特性を有する垂直共振型の面発光半導体レーザを提供することができるので、情報処理装置の性能向上に寄与するところが大きい。
【０１３６】
なお、活性層５８は、GaN 、InGaN 、AlGaN 又はAlGaInN のいずれから形成してもよいし、また、半導体よりなる障壁層５７，５９は、GaN 、InGaN 、AlGaN 又はAlGaInN から構成してもよい。ただし、活性層５８と障壁層５７，５９が同じ材料系より構成する場合には、障壁層５７，５９よりも活性層５８の方がエネルギーバンドギャップが小さくなる組成比を選択する必要がある。
【０１３７】
なお、基板の材料として炭化シリコン（SiＣ）の他にサファイアを使用してもよい。
（第３実施形態）
従来の発光ダイオードは、光の出射方向に対して円偏光であるので、直線偏光を得たい場合には、ポラロイド等の偏光子を通すことによって直線偏光した偏光光を得ていた。
【０１３８】
また、直線偏光した偏光光を利用して立体画像を表示する場合、右目用画像と左目用画像を互いに偏光方向の異なる光で表示し、それを互いに偏光方向の異なる右目用偏光子と左目用偏光子を介して見ることによって立体画像として認識しており、特に、大型立体画像表示装置の場合には、投影方式を採用している。
しかし、従来の発光ダイオードを用いて直線偏光を得ようとする場合には、偏光子を必要とするため部品点数が多くなるという問題があり、且つ、発光ダイオードと偏光子とを組み合わせる工程が必要になるため、生産コストが高くつくという問題がある。
【０１３９】
また、偏光子を介して円偏光を特定の方向に偏光した直線偏光にしているので、偏光子の偏光方向と偏光方向の異なる光は取り出せず無駄になるので、発光効率が悪いという問題がある。
さらに、大型立体表示装置の場合には、投影方式であるため、従来の投影方式の表示装置と同ように、明るいところでは表示画像が非常に見ずらくなり、実質的に利用できないという問題もある。
【０１４０】
図１９は本実施形態の原理的構成の説明図であり、この図１９を参照して本発明における課題を解決するための手段を説明する。
本実施形態は、図１９(a) 及び(b) に例示するように、発光ダイオード７０において、発光ダイオード７０を構成するウルツ鉱型化合物半導体結晶のｃ軸方向が光の放出方向とほぼ直交していることを特徴とする。
【０１４１】
このようにGaN のようなウルツ鉱型化合物半導体を用いた場合、ウルツ鉱型化合物半導体は、GaAs等の他のIII-V 族化合物半導体と異なり六方晶系であり、このようなウルツ鉱型化合物半導体における発光は伝導帯から価電子帯のＨＨ（Heavy Hole）あるいはＬＨ（Light Hole）への遷移によって起こるが、これらはａ軸方向に関するバンドであるため、ｃ軸方向、即ち、＜０００１＞方向に垂直な方向に偏光した光が強く現れ、逆にｃ軸方向に平行に偏光した光はほとんど現れないので、偏光子を用いなくとも直線偏光した光が得られることになる。
【０１４２】
なお、本発明において、ｃ軸方向が光の放出方向とほぼ直交するとは、ｃ軸と最も強度の大きな光の放出方向とが純粋に直交するもの以外に、±５°の範囲の角度を含むものである。
また、本実施形態は、ウルツ鉱型化合物半導体結晶のｃ軸方向と結晶成長方向とがー致していることを特徴とする。
【０１４３】
成長基板として、サファイアの｛０００１｝面、｛１１−２０｝面、６Ｈ−ＳｉＣの｛０００１｝面、或いは、スピネルの｛１１１｝面を用いた場合、ウルツ鉱型化合物半導体結晶の結晶成長方向はｃ軸方向となるので、図１(a) に示すように活性層に平行に光を取り出すことによって、直線偏光した光が得られる。 なお、本明細書においては、“１バー" 或いは“２バー" 等の結晶方位を便宜的に、“−１" 或いは“−２" 等として表す。
【０１４４】
また、本実施形態は、ウルツ鉱型化合物半導体結晶のｃ軸方向と結晶成長方向とがほぼ直交していることを特徴とする。
成長基板の主面として、サファイア基板のｒ面、即ち、｛１−１０２｝面、又は、６Ｈ−ＳｉＣの｛１−１００｝面若しくは｛１１−２０｝面を用いた場合、ウルツ鉱型化合物半導体結晶の結晶成長方向はｃ軸方向とほぼ平行になるので、図１(b) に示すように活性層に垂直に光を取り出すことによって、直線偏光した光が得られ、且つ、広い面からの光が偏光光となるので、発光領域を大きく取ることができる。
【０１４５】
また、本実施形態は、上記したウルツ鉱型化合物半導体が、III 族の窒化物からなるIII-V 族化合物半導体であることを特徴とする。
このように、ウルツ鉱型化合物半導体として、安定な結晶構造を有するGaN 系化合物半導体等のIII 族の窒化物からなるIII-V 族化合物半導体を用いることによって、１. ９eV〜６. ２eVの広い範囲に渡り高効率の短波長発光が得られ、混晶比を調整することによって、所望の発光波長を得ることができる。
【０１４６】
さらに、本実施形態は、表示装置において、光の放出方向がｃ軸方向とほぼ直交するウルツ鉱型化合物半導体結晶からなる複数の発光ダイオード７０を用い、この複数の発光ダイオード７０を、偏光方向がある方向ｕに偏光した右目用発光ダイオードと、右目用発光ダイオードの偏光方向ｕに垂直な方向ｖに偏光した左目用発光ダイオードとになるように配置し、立体表示を得るようにしたことを特徴とする。
【０１４７】
光の放出方向がｃ軸方向とほぼ直交するウルツ鉱型化合物半導体結晶からなる発光ダイオード７０は、ｃ軸方向に垂直に、即ち、a 軸方向に偏光しており、このａ軸方向に偏光した発光ダイオード７０を光の放出方向を軸として９０°回転させた場合には、ｃ軸方向に垂直で、且つ、回転させる前の偏光方向に対して垂直に偏光した直線偏光光となるため、一方を右目用とし、他方を左目用とすることによって、立体画像の表示が可能になる。
【０１４８】
なお、図１９において、６９ａ，６９ｂは、発光ダイオード７０に接続される１対の端子を示している。
第１例
ここで、図２０(a),(b) 及び図２１(a),(b) を参照して、本実施形態の第１例を説明する。図２０(a) は発光ダイオードの断面図であり、図２０(b) は発光ダイオードを素子化した場合の断面図である。また、図２１(a) はGaN 系化合物半導体のΓ点近傍のバンドダイヤグラムであり、さらに、図２１(b) は、発光強度の偏光角分布を示す図である。
【０１４９】
まず、図２０(a) に示すように、（０００１）面、即ち、ｃ面を主面とするサファイア基板７１上に、ＭＯＶＰＥ法（有機金属気相成長法）を用いて、厚さ５〜５０nm、例えば２０nmのGaN バッファ層７２、厚さ０. ５〜５. ０μｍ、例えば、３. ０μｍのｎ型Al_0.05 Ga_0.95N層７３、厚さ１０〜１００nm、例えば５０nmのIn_0.1Ga_0.9N 活性層７４、及び、厚さ０. １〜１. ０μｍ、例えば０. ５μｍのｐ型Al_0.05Ga_0.95N 層７５を順次エピタキシャル成長させる。
【０１５０】
次いで、ｎ型Al_0.05Ga_0.95N 層７３の一部が露出するように反応性イオンエッチング法によってエッチングしたのち、ｐ型Al_0.05Ga_0.95N 層７５の表面にｐ側電極としてNi電極７６を設けるとともに、ｎ型Al_0.05Ga_0.95N 層７３の露出表面にｎ側電極としてTi電極７７を設ける。
なお、この場合、GaN バッファ層７２からｐ型Al_0.05Ga_0.95N 層７５までの各層は、サファイア基板７１のｃ軸方向に成長するので、そのｃ軸はサファイア基板１７の主面と垂直になる。そのｃ軸方向は＜０００１＞方向と等価である。
【０１５１】
上記のようにして形成した発光ダイオード７８を、図２０(b) に示すように、その光の放出方向が、ｃ軸方向とほぼ垂直になるようにステム７９にマウントする。
この場合、ステム７９に対しては短絡を防止するために絶縁体スペーサ８０を介してマウントするとともに、ｎ側電極であるTi電極７７をマイナス端子８１にワイヤボンディングし、また、ｐ側電極であるNi電極７６をプラス端子８２にワイヤボンディングし、最後に、エポキシ樹脂等で樹脂モールドする。
【０１５２】
図２１(a) は、GaN 系化合物半導体のΓ点近傍のバンドダイヤグラムであり、図から明らかなように、価電子帯におけるホールからみてエネルギー的に一番低いバンド、即ち、ＨＨ（Heavy Hole）とＬＨ（Light Hole）が２重に縮退し、スピン軌道相互作用による分だけエネルギー的に分離しており、また、それ以外に、GaN 系化合物半導体に特有なCHというバンドが現れる。
【０１５３】
そして、このようなGaN 系化合物半導体においては、Γ点、即ちＫz ＝０における伝導帯とＨＨバンド及びＬＨバンドとの間の遷移によって発光が生ずることになるが、Γ点におけるＨＨバンド及びＬＨバンドはａ軸方向に関するバンドであるのでｃ軸に垂直な方向に偏光した光が得られることになる。
図２１(b) は、本発明の本実施形態の発光ダイオードの光の放出方向からみた発光強度の偏光角分布を示す図であり、ａ軸に平行な、即ち、ａ軸方向に偏光した光が得られるが、ａ軸に対して９０°偏光した、即ち、ａ軸に垂直に偏光した光は殆ど得られない。
【０１５４】
したがって、本発明においては、偏光子等を用いることなく特定の方向に偏光した直線偏光光を得ることができるので、部品点数が増加することなく、且つ、発光ダイオードと偏光子の組み合わせ工程が不要になるので、生産コストを低コストにすることができる。
なお、この第１例においては、基板として、（０００１）面を主面とするサファイア基板を用いているが、（０００１）面を主面とするサファイア基板に限られるものではなく、（１１−２０）面を主面とするサファイア基板（０００１）面を主面とする６Ｈ−ＳｉＣ基板、或いは、（１１１）面を主面とするスピネル基板を用いても良いものである。
【０１５５】
第２例
次に、図２２を参照して本発明の第２の例を説明する。まず、図２２(a) に示すように、（１−１０２）面、即ち、ｒ面を主面とするサファイア基板９１上に、ＭＯＶＰＥ法を用いて、厚さ５〜５０nm、例えば２０nmのGaN バッファ層９２、厚さ０. ５〜５. ０μｍ、例えば３. ０μｍのｎ型Al_0.05Ga_0.95N 層９３、厚さ１０〜１００nm、例えば５０nmのln_0.1Ga_0.9N 活性層９４、及び、厚さ０. １〜１. ０μｍ 、例えば０. ５μｍのｐ型Al_0.05Ga_0.95N 層９５を順次エピタキシャル成長させる。
【０１５６】
次いで、反応性イオンエッチング法によってｎ型Al_0.05Ga_0.95N 層９３の一部を露出させたのち、ｐ型Al_0.05Ga_0.95N 層９５の表面にｐ側電極として非常に薄いNiからなる半透明電極９６を設けるとともに、ｎ型Al_0.05Ga_0.95N 層９３の露出表面にｎ側電極としてTi電極９７を設ける。
なお、この場合、GaN バッファ層９２からｐ型Al_0.05Ga_0.95N 層９５の各層のｃ軸の方向は、サファイア基板９１の基板面内の方向に向いて成長するので、ｃ軸は基板面と平行になる。
【０１５７】
そのようにして形成された発光ダイオード８４は、図２２(b) に示すように、その光の放出方向をｃ軸方向とほぼ垂直になるように導電性ペーストを用いてステム８５にマウントする。
そして、ｎ側電極であるTi電極９７をマイナス端子８６にワイヤボンディングすると共に、ｐ側電極である半透明電極９６をプラス端子８７にワイヤボンディングし、最後に、エポキシ樹脂等のモールド樹脂８８によって封止する。
【０１５８】
この場合にも、第１例と同ように、光の放出方向はｃ軸に垂直であるので、ａ軸方向に偏光した光が得られ、ａ軸に対して９０°偏光した、即ち、ａ軸に垂直に偏光した光は殆ど得られない。
したがって、本発明においては、偏光子等を用いることなく特定の方向に偏光した直線偏光光を得ることができるので、部品点数が増加することなく、且つ、発光ダイオードと偏光子の組み合わせ工程が不要になる。この結果、発光ダイオードの生産コストは低コストになる。
【０１５９】
また、この第２例の場合は、面発光型であるので、上記の第１例に比べて発光領域を大きくすることができ、第１例と比べて１０倍程度の発光強度が期待できる。
なお、第２例においては、基板として、ｒ面を主面とするサファイア基板を用いているが、ｒ面を主面とするサファイア基板に限られるものではなく、（１−１００）面を主面とするＳｉＣ基板、或いは、（１１−２０）面を主面とするＳｉＣ基板を用いても良いものである。
【０１６０】
また、第２例においては、ｐ側電極として薄いNi膜からなる半透明電極９６を用いているが、半透明電極９６に限られるものではなく、通常の厚さのNi電極をメッシュ状に設けて、メッシュの間から光を取り出すようにしても良い。
第３例
次に、図２３を参照して本発明の第３例を説明する。
【０１６１】
図２３は、上記の第１例、第２例の発光ダイオードを用いた立体画像表示用の表示パネル９０を表すものである。例えば、第１例の発光ダイオードを用いて、その偏光方向がＸ方向になるように配置した発光ダイオード９８と、この発光ダイオード９８の光軸を中心として偏向方向を９０°回転させて配置したＹ方向に偏光する発光ダイオード９９とを組み合わせて構成したものである。なお、Ｘ方向とＹ方向は、ともに表示パネル９０の面に対して平行であり、かつ、Ｘ方向とＹ方向は互いに直交する関係にある。
【０１６２】
この場合、一方の発光ダイオード９８を右目用とし、他方の発光ダイオード９９を左目用とし、両者に互いに異なった画像信号を入力し、この発光表示画像を右目用と左目用とで互いに異なった偏光子を介して見ることによって立体画像を表示することになる。
なお、この場合、ａ軸方向に純粋に平行な角度に対して±２０°程度の範囲の偏光角の光を有効に利用することができる。
【０１６３】
この第３例の表示装置は、発光表示であるので、従来の投影方式の立体表示装置より輝度を高くすることができ、したがって、大型化した場合にも明るい場所での使用が可能になる。
この場合、例えば、１００インチの表示パネル９０を構成する場合には、約２００万画素で構成することになる。そして、Ｘ方向に偏光した発光ダイオード９８とＹ方向に偏光する発光ダイオード９９との配置は、図２３に示すように１個毎交互に配置しても良いし、或いは、特に図示しないが、画素毎に纏まった個数の発光ダイオードを交互に配置しても良く、さらに、各発光ダイオードの発光波長を調整することによってカラー表示も可能になる。
【０１６４】
なお、上記の実施の形態における面方位は一例であり、記載されている面方位と結晶学的に等価な全ての面を含むものである。
また、上記の各例においては、活性層としてln組成比が０. １のln_0.1Ga_0.9N を用いているが、必要とする波長に応じて混晶比をAl_x In _yGa_1-x-y N （０≦x ≦１、０≦y ≦１）の範囲内で変えても良いものであり、それに伴って、活性層を挟むｐ型Al_0.05Ga_0.95N 層及びｎ型Al_0.05Ga_0.95N 層を活性層より禁制帯幅の大きなAI_a ln_b Ga_1-a-b N （０≦a ≦１、０≦b ≦１）で構成すれば良い。
【０１６５】
さらに、GaN 基板の代わりにサファイア基板を使用する場合には、基板の主面を（１１−２０）面とする。
以上述べたように、本実施形態によれば、GaN 系化合物半導体等のウルツ鉱型化合物半導体を用いて発光ダイオードを構成する場合、光の放出方向をウルツ鉱型化合物半導体のｃ軸と垂直にすることによって、偏光子を用いることなく直線偏光した光を得ることができ、また、このようは直線偏光した発光ダイオードを用いることによって、明るい場所でも使用が可能な発光表示による立体画像表示装置を構成することができる。
【０１６６】
【発明の効果】
以上述べたように本発明によれば、結晶基板の主面を選ぶことによって、その結晶基板の上に形成される六方晶型又はウルツ鉱型の半導体層のｃ軸がその半導体層の面に対して垂直でなくなるために、その結晶基板の上に形成される六方晶型又はウルツ鉱型の活性層に、面方向の圧縮歪又は引張歪をかけてその活性層に３軸異方性を持たせることができ、活性層の価電子帯での縮退を解くことができ、そのような活性層を有する半導体レーザの発振の閾値電流を低下することができる。
【０１６７】
また、そのような構造によれば、化合物半導体層による発光の偏光面が一義的に決定できるので、そのような結晶基板の上に障壁層、活性層などを成長して面発光半導体レーザを形成すると、活性層の面内異方性が大きくなって電場ベクトルが一方向に定められるため、偏光が決定できる。
さらに、面発光半導体レーザの発振光の偏光面が一義的に定まると、光磁気ディスク装置の光源としての使用が可能になるとともに、面発光半導体レーザと同一基板に受光素子を製造することが容易になる。これにより、従来行っていた半導体レーザと受光素子の取付け作業が不要になるとともに、受発光装置の小型化をさらに促進することができる。
【０１６８】
一方、発光ダイオードを構成するウルツ鉱型化合物半導体結晶のｃ軸方向が、光の放出方向とほぼ直交するようにすると、偏光方向が定まるので、そのような発光ダイオードを表示装置の表示面に複数個配置し、１つの発光ダイオードによって画素の一部又は全部を構成するようにするととともに、隣接する発光ダイオードの偏光方向を互いに９０度相違し、これにより、右目偏光方向用の発光ダイオードと左目偏光用の発光ダイオードを隣接することができ、立体表示装置で偏向子を省略して部品点数を減らし、製造コストを低減できる。しかも、そのような表示装置は画像が明るくなる。
【図面の簡単な説明】
【図１】 図１(a) は、本発明の第１実施形態のクラッド層と活性層の層構造図、図１(b) は、図１(a) の層構造によって得られる活性層の価電子帯エネルーバンド構造図、図１(c) は、本発明の第１実施形態で使用する基板の主面の面方位を示す図である。
【図２】図２(a) は、本発明の第１実施形態の層構造を採用した半導体レーザの第１の例を光出力端から見た層構造図、図２(b) は、図２(a) の層構造によって得られる活性層の価電子帯エネルーバンド構造図、図２(c) は、２つのクラッド層と活性層の相対的なエネルギーバンド構造図である。
【図３】図３は、本発明の第１実施形態の層構造を採用した半導体レーザの基板を高抵抗材から形成する場合の構造図である。
【図４】図４(a) は、本発明の第１実施形態の層構造を採用した半導体レーザの第２の例を光出力端から見た層構造図、図４(b) は、図４(a) の層構造によって得られる活性層の価電子帯エネルーバンド構造図である。
【図５】図５(a) は、本発明の第１実施形態の層構造を採用した半導体レーザの第３の例の斜視図、図５(b) は、図５(a) の半導体レーザにおける基板主面に対する小面の傾斜角度を示す図である。
【図６】図６(a) は、本発明の第１実施形態の層構造を採用した半導体レーザの第４の例を光出力端から見た層構造図、図６(b) は、その第４の例で基板を高抵抗材料から構成した場合の半導体レーザを光出力端から見た層構造図である。
【図７】 図７は、本発明の第１実施形態において、主面に平行なｃ軸を有する正方晶基板の主面の上に、六方晶半導体層を形成する場合の各結晶の完面像の特殊形の相対的関係を示す図である。
【図８】図８は、本発明の第１実施形態において、正方晶基板上に形成した六方晶層のＸ線回折ロッキングカーブを示す図である。
【図９】図９は、正方晶のLiAlO₂基板上に六方晶のAl_x Ga_1-x-y In_y N 層を成長する場合に、組成比ｘと組成比ｙの関係を示すｘｙ座標図である。
【図１０】図１０は、本発明の第２実施形態を示す面発光レーザの電極を除いた層構造示す斜視図である。
【図１１】図１１は、本発明の第２実施形態を示す面発光レーザの活性層の結晶の完面像の特殊形を示す斜視図である。
【図１２】図１２は、本発明の第２実施懈怠の面発光レーザの活性層のエネルギーバンド構造図である。
【図１３】 図１３は、本発明の第２実施形態の面発光レーザにおいて、活性層の偏光面の方位とｃ軸のなす角度をパラーメータにした場合の波長とＰＬ発光強度の関係を計算で求めた図である。
【図１４】図１４(a) 〜(e) は、本発明の第２実施形態の面発光レーザにおいて、活性層を構成するGaN のエネルギーバンドの結晶歪依存性を示す図である。
【図１５】図１５は、本発明の第２実施形態の面発光レーザにおいて、活性層の偏光面の方位とｃ軸のなす角度をパラーメータにした場合の波長とＰＬ発光強度の関係の実験により求めた図である。
【図１６】図１６は、本発明の第２実施形態の面発光レーザにおいて、活性層の偏光面の方位とｃ軸のなす角度とＰＬ発光強度の関係を示す曲線を計算と実験で求めた図である。
【図１７】図１７は、本発明の第２実施形態の面発光レーザを示す断面図である。
【図１８】図１８(a) は、面発光レーザと受光素子を有する本発明の第２実施形態の光装置を示す断面図、図１８(b) は、その光装置の平面図である。
【図１９】 図１９(a) は、本発明の第３実施形態の端部発光型の発光ダイオードの原理的構成図、図１９(b) は、本発明の第３実施形態の面発光型の発光ダイオードの原理的構成図である。
【図２０】図２０(a) は、本発明の第３実施形態の端部発光型の発光ダイオードの層構造図、図２０(b) は、その発光ダイオードをパッケージ化した構成を示す断面図である。
【図２１】図２１(a) は、図２０(a) で示した発光ダイーオドにおけるGaN 系化合物半導体のバンドダイヤグラム、図２１(b) は、その発光ダイオードの光の放出方向からみた発光強度の偏光角分布を示す図である。
【図２２】図２２(a) は、本発明の第３実施形態の面発光型の発光ダイオードの層構造図、図２２(b) は、その発光ダイオードをパッケージ化した構成を示す断面図である。
【図２３】図２３は、本発明の第３実施形態の表示装置に使用する発光ダイオードの偏向関係を示す平面構成図である。
【図２４】図２４(a) は、従来の半導体ダイオードの第１例を示す断面図、図２４(b) は、従来の半導体ダイオードの第２例を示す断面図である。
【図２５】 図２５(a) 、(b) は、従来の半導体ダイオードの価電子帯のエネルギーバンド図である。
【図２６】図２６は、従来の面発光型半導体レーザを示す斜視図である。
【符号の説明】
１ 第一の半導体
２ 第二の半導体
３ 第三の半導体
１ l ｎ型GaN （１−１００）基板
１２ ｎ型Al_0.1Ga_0.9N クラッド層
１３ ｎ型GaN 光ガイド層
１４ Ga_0.9In_0.1N 活性層
１５ ｐ型GaN 光ガイド層
１６ ｐ型Al_0.1Ga_0.9N クラッド層
１７ Ti／Au電極
１８ Ni／Au電極
２１ ｎ型GaN （１−１００）基板
２２ ｎ型Al_0.4Ga_0.3In_0.3Nクラッド層
２３ ｎ型Al_0.15Ga_0.65In_0.2N光ガイド層
２４ Ga_0.9In_0.1N 活性層
２５ ｐ型Al_0.15Ga_0.65In_0.2N光ガイド層
２６ ｐ型Al_0.4Ga_0.3In_0.3Nクラッド層
２７ Ti／Au電極
２８ Ni／Au電極
３１ ｎ型GaN （０００１）基板
３２ （１１−２１）小面
３３ 絶縁膜
３４ （１−１００）劈開面
４１ 基板
４２ 活性層
４３ ＤＢＲ鏡
４４ ｃ軸
４４a ｚ偏光
４５ ｘ偏光
４６ ｙ偏光
４７, ４８ 障壁層
４９, ５１ コンタクト層
５０ａ、５０ｂ 電極
５２ バッファ層
５３ SiC 基板
５４ AlN 高温バッファ層
５５ ミラー層
５６ ｎ型の障壁層
５７ 下側光閉じ込め層
５８ 活性層
５９ ｐ型の障壁層
６０ 上側光閉じ込め層
６１ 溝
６２ 円柱部
６３ フランジ部
６４ 光放出窓
６５ ｎ側電極
６６ 面発光半導体レーザ（発光素子）
６７ フォトダイオード（受光素子）
６８ 電源
６９ 光量検出回路
７０ 発光ダイオード
７１ サファイア基板
７２ GaN バッファ層
７３ ｎ型Al_0.05Ga_0.95N 層
７４ Al_0.1Ga_0.9N 活性層
７５ ｐ型Al_0.05Ga_0.95N 層
７６ Ni電極
７７ Ti電極
７８ 発光ダイオード
７９ ステム
８０ 絶縁体スベーサ
８１ マイナス端子
８２ プラス端子
８３ モールド樹脂
８４ 発光ダイオード
８５ ステム
８６ マイナス端子
８７ プラス端子
８８ モールド樹脂
９０ 表示パネル
９１ サファイア基板
９２ GaN バッファ層
９３ ｎ型Alo.o ５Gao.９ ５N 層
９４ Al_0.1Ga_0.9N 活性層
９５ ｐ型Al_0.05Ga_0.95N 層
９６ 半透明電極
９７ Ti電極
９８ 水平方向に偏光する発光ダイオード
９９ 垂直方向に偏光する発光ダイオード[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light-emitting element, an optical semiconductor element, a light-emitting diode, and a display device. More specifically, the light-emitting part includes a wurtzite compound semiconductor such as GaN that emits light in a wavelength band from blue to ultraviolet. The present invention relates to a semiconductor light emitting element, an optical semiconductor element, a light emitting diode, and a display device.
[0002]
[Prior art]
In recent years, a short wavelength laser having a wavelength in a region from blue to ultraviolet has been actively developed as a light source for optical disks. As a blue laser light source, there are an optical element using a II-VI group ZnSe-based material and an optical element using a group III-V GaN-based material. Among them, there is a report that ZnSe-based materials are ahead in research on semiconductor lasers, and continuous oscillation at room temperature has already been obtained. However, ZnSe-based materials are inherently prone to deterioration and thus have a problem in reliability, and have not yet been put into practical use.
[0003]
On the other hand, with the announcement of high-brightness LEDs using GaN several years ago, GaN with excellent environmental resistance has been reviewed, and a large increase in researchers has been observed all over the world. In 1996, Nichia announced a semiconductor laser that oscillates using InGaN.
Since GaN-based semiconductors used as light-emitting elements are wurtzite compound semiconductors, MOVPE (organometallic vapor phase epitaxy) is performed on a hexagonal sapphire substrate or 6H-SiC substrate having a similar crystal structure. It was used for epitaxial growth. Here, “H” in 6H—SiC indicates a crystal having a sixth-order rotational symmetry, and “6” indicates that the crystal is periodically formed in an array of six-phase atoms or molecules. It shows that the crystal has a six-phase synchronized structure.
[0004]
A semiconductor laser using a hexagonal sapphire substrate or a 6H-SiC substrate is formed by the following procedure.
When a sapphire substrate is used, for example, as shown in FIG. 24A, an n-type Al layer is formed on a sapphire (0001) substrate 141 having a (0001) plane as a main surface through a GaN buffer layer 142._0.1Ga_0.9N clad layer 143, n-type GaN light guide layer 144, Ga_0.9ln_0.1N active layer 145, p-type GaN light guide layer 146, and p-type Al_0.1Ga_0.9After N-cladding layer 147 is epitaxially grown by MOVPE, n-type Al is etched._0.1Ga_0.9N A part of the cladding layer 143 is exposed, and an n-side electrode composed of a Ti / Au electrode 148 is provided on the exposed surface, and a p-type Al_0.1Ga_0.9A p-side electrode made of Ni / Au electrode 14 9 is provided on the N clad layer 147, and a semiconductor laser is formed by such a process.
[0005]
On the other hand, when a 6H—SiC substrate is used, as shown in FIG._SiN-type Al layer on the Si surface of the 6H-SiC (0001) substrate 151 via the n-type AIN buffer layer 15 2._0.1Ga_0.9N clad layer 153, n-type GaN light guide layer 154, Ga_0.9ln_0.1N active layer 155, p-type GaN light guide layer 156, and p-type Al_0.1Ga_0.9After the N clad layer 157 is epitaxially grown by the MOVPE method, an n-side electrode made of a Ti / Au electrode 158 is further provided on the back surface of the 6H-SiC (0001) substrate 151, and p-type Al_0.1Ga_0.9A semiconductor laser is formed through a process of providing a p-side electrode made of a Ni / Au electrode 159 on the N clad layer 157.
[0006]
In such a conventional light emitting device, the GaN-based epitaxial layers 142 to 147 and 152 to 157 have the (0001) plane in the <0001> direction of the sapphire (0001) substrate 141 or 6H-SiC (0001) substrate 151. As it grows, the in-plane strain becomes isotropic and Ga_0.9ln_0.1N active layers 145 and 155 remained uniaxially anisotropic. The <0001> direction is the c-axis direction.
[0007]
Next, the energy band structure of the GaN-based semiconductor will be described.
FIG. 25 (a) is a diagram showing the band structure of the valence band of a GaN-based semiconductor in an undistorted state, and the bands of HH (Heavy Hole) and LH (Light Hole) are almost degenerate. In GaN-based semiconductors, the CH band is close.
In the conventional light emitting device shown in FIG. 24 (a), n-type Al_0.1Ga_0.9N clad layer 143 to p-type Al_0.1Ga_0.9The in-plane lattice constant of the N cladding layer 147 is n-type Al immediately above the GaN buffer layer 142._0.1Ga_0.9Since it is defined by the lattice constant of the N cladding layer 143, the coherently grown n-type GaN light guide layer 144 to p-type GaN light guide layer 146 are subjected to compressive stress due to lattice mismatch and thermal expansion coefficient difference.
[0008]
The same applies to the element shown in FIG. 24 (b)._0.9ln_0.1The N active layer 155 is strongly influenced by the strain due to the lattice constant, and compressive stress is acting.
In addition to the above semiconductor lasers, the present inventors have found that the optical gain of GaN is much higher than that of conventional materials, and have confirmed that this material is suitable for surface emitting lasers.
[0009]
Next, the surface emitting laser will be described.
An optical resonator (vertical resonator) having a resonance axis in the vertical direction of the active layer formed on the substrate has a structure for emitting light in the vertical direction of the surface of the active layer. Such a surface emitting semiconductor laser has a short cavity length and a low threshold current, can easily realize a two-dimensional array of semiconductor laser elements, has a large number of elements per unit wafer area, or is an element as a wafer. Development of surface-emitting lasers that oscillate short-wavelength light, particularly for optical disks or short-distance optical communication, has been promoted.
[0010]
However, since the direction of the polarization plane of the oscillation light is not fixed in the surface emitting laser of the conventional material, the polarization plane may change during use, or the light output characteristics may be kinked with the change of the polarization plane. This makes it impossible to read the optical disk using polarized light, and to stably perform writing and reading with light, and further stable communication cannot be realized.
[0011]
Therefore, it is necessary to fix and stabilize the polarization plane orientation of the oscillation light of the surface emitting semiconductor laser.
The active layer of a conventional surface emitting semiconductor laser has been deposited on a substrate whose principal surface is the (001) plane of a zinc blende crystal. On the other hand, when a surface-emitting semiconductor laser having a hexagonal semiconductor represented by GaN as an active layer is configured in the same structure, on a substrate having a (0001) plane perpendicular to the c-axis of the hexagonal crystal as the main surface. It is expected to deposit an active layer. Hereinafter, a conventional surface emitting semiconductor laser having such a structure will be described.
[0012]
FIG. 26 is a perspective view of a conventional surface emitting semiconductor laser, showing the basic structure of a surface emitting semiconductor laser having a vertical resonator.
As shown in FIG. 26, the substrate 101 is made of a hexagonal crystal, for example, sapphire, and has a main surface perpendicular to the c-axis 104. Alternatively, the substrate 1 has a (001) plane of zinc blende type crystal as a main surface. On the substrate 101, a first conductivity type barrier layer 107, an active layer 102, and a second conductivity type barrier layer 108 are sequentially deposited in a processive manner. Further, the reflecting mirror 103 made of a disk-shaped multilayer film is formed on the second conductivity type barrier layer 108. The reflecting mirror 103 is used as one reflecting surface, and the lower surface of the barrier layer 107, that is, the interface between the barrier layer 107 and the substrate 101 is used as another reflecting surface, and the reflecting surface parallel to the active layer 102 and the resonance perpendicular to the active layer 102 are used. An optical resonator having an axis is configured.
[0013]
By the way, in a surface emitting semiconductor laser using an active layer of zinc blende type crystal currently realized, the reflecting mirror 103 has a semiconductor multilayer structure and is provided on both reflecting surfaces of the optical resonator.
On the other hand, a surface emitting semiconductor laser using GaN having a large optical gain as an active layer can be oscillated by providing the reflecting mirror 103 on one side. The oscillation light is emitted from an optical window formed on the lower surface (opposite surface of the main surface) of the substrate 101.
[0014]
The active layer 102 of the surface emitting semiconductor laser described above is epitaxially deposited on the substrate 101. Therefore, the active layer 102 made of hexagonal crystal or zinc blende type crystal is formed as a thin layer whose hexagonal c-axis or zinc oxide type crystal <001> axis is perpendicular to the plane.
On the other hand, since the resonator has a resonance axis perpendicular to the active layer 102, the oscillation light travels perpendicular to the active layer 102, and the surface of the active layer 102 becomes the polarization defining surface. That is, when the polarization defining plane is the xy plane and the traveling direction of the light is on the z axis, the oscillation light is composed of the x polarization 105 whose polarization plane includes the x axis and the y polarization 106 whose polarization plane includes the y axis. This z-axis is perpendicular to the active layer 2, that is, parallel to the hexagonal c-axis or the <001> axis of the zinc blende type crystal and forms a rotationally symmetric axis of optical anisotropy. The optical coupling with the y-polarized light 106 is equal to the crystal. For this reason, crystallographically, both the x-polarized light 105 and the y-polarized light 106 can oscillate with the same intensity, so the polarization plane of the oscillation light is not fixed and the polarization plane becomes unstable.
[0015]
In order to stabilize the polarization plane of the oscillation light, a semiconductor laser that oscillates only one of the x-polarized light 105 and the y-polarized light 106 by developing an elliptical or rectangular reflecting mirror has been developed. However, this semiconductor laser has a problem that the emitted light does not become a circular beam, and it is difficult to precisely manufacture the shape of the reflecting mirror.
Furthermore, in order to eliminate such inconvenience, an in-plane refractive index distribution is formed in the active layer 102 or the barrier layers 107 and 108 to degrade the symmetry of the refractive index around the z axis, thereby defining the polarization plane of the oscillation light. A semiconductor laser has been proposed. However, a process for forming the refractive index distribution is necessary, and it is inevitable that the manufacturing process becomes complicated.
[0016]
[Problems to be solved by the invention]
In the case of a conventional GaN-based semiconductor, the highest energy bands HH and LH in the valence band are double degenerate, and in such a GaN-based semiconductor, holes are present in both the HH and LH bands. Therefore, there is a problem that the threshold current density for causing laser oscillation increases.
[0017]
In addition, when a GaN-based semiconductor is grown on a 6H—SiC substrate, cracking is likely to occur due to stress generated by thermal expansion on the (0001) plane of the GaN-based semiconductor layer, and it is difficult to obtain a crystal with good crystallinity. .
The above Ga constituting the light emitting part_0.9ln_0.1N When the active layers 145 and 155 are subjected to compressive stress due to a difference in thermal expansion coefficient and lattice mismatch in the (0001) plane, as shown in FIG. Only has a relatively low band structure with respect to HH and LH, and the bands HH and LH having the highest valence band energy remain double degenerate.
[0018]
Furthermore, another reason for the high threshold current density is that the sapphire substrate is not cleaved.
In addition to these problems, in the surface emitting semiconductor laser having a conventional vertical cavity, the polarization plane of the oscillation light is not fixed because the in-plane anisotropy of the active layer is small, and the polarization plane of the emitted light can be fixed. It is not possible or the oscillation is not stable.
[0019]
  In addition, in the structure where the reflecting mirror is rectangular and the plane of polarization is defined, the emitted light is converted into a circular beam.NotFurther, there is a problem that it is difficult to form a rectangular pattern as the size is reduced. Furthermore, the method of forming an in-plane refractive index in the active layer or the barrier layer has a limit in simplifying the manufacturing process. By the way, the fact that the plane of polarization of the oscillation light is not fixed causes another problem when the surface emitting semiconductor laser is used as the light source of the magneto-optical disk apparatus.
[0020]
That is, in the magneto-optical disk apparatus, it is necessary that the polarization planes of the laser beams are aligned in order to read data by detecting the rotation of the polarization plane of the light. However, conventional surface emitting lasers are not used as data reading elements because their polarization planes are not uniform.
The present invention reduces the threshold current density necessary for light oscillation, has a GaN-based semiconductor layer in which cracking does not easily occur, and can fix the polarization plane of light and suppress fluctuations in the polarization plane in a surface emitting semiconductor laser. An object is to provide a semiconductor light emitting element, an optical semiconductor element, a light emitting diode, and a display device.
[0021]
[Means for Solving the Problems]
  As illustrated in FIG. 2 or FIG. 10, the above problem is that the second semiconductor layer 13 (47) formed directly on the main surface of the substrate 11 (41) or via the first semiconductor layer 12 (52). ), And an active layer 14 made of a semiconductor having a uniaxial anisotropy that is formed on the second semiconductor layer 13 (47) and has an energy band gap smaller than that of the second semiconductor layer 13 (47). (42), a third semiconductor layer 15 (48) formed on the active layer 14 (42) and having an energy band gap larger than that of the active layer 14 (42), and the second semiconductor layer 13 ( 47), and a pair of electrodes 17 and 18 for flowing a current in the film thickness direction through the active layer 14 (42) and the third semiconductor layer 15 (48), and at least the active layer 14 (42). The film thickness direction is different from the uniaxial anisotropy axis. Direction der thatThe active layer 14 (42) is a single layer having a thickness of 1 to 20 nm. Al _x Ga _1-xy In _y N (However, it has a single layer structure consisting of 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) or a multilayer having a thickness of 1 to 20 nm. Al _x Ga _1-xy In _y N (However, it has a multi-quantum well structure of 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and strain is added in a plane that is not perpendicular to the c-axis indicating anisotropy, resulting in anisotropic c-plane strain. Have sexSolved by a semiconductor light emitting device characterized by(Hereinafter, this semiconductor light emitting element is referred to as “semiconductor light emitting element. I ”).
Semiconductor light emitting device I The substrate is SiC (Hereinafter, this semiconductor light-emitting element is referred to as “semiconductor light-emitting element.” II ”).
[0022]
As illustrated in FIG. 2 or FIG. GaN Or AlN A second semiconductor layer 13 (47) formed directly or via a first semiconductor layer 12 (52) on a main surface of a substrate 11 (41) comprising the second semiconductor layer 13 (47) An active layer 14 (42) made of a semiconductor having an energy band gap smaller than that of the second semiconductor layer 13 (47) and having uniaxial anisotropy; and on the active layer 14 (42) A third semiconductor layer 15 (48) having an energy band gap larger than that of the active layer 14 (42), the second semiconductor layer 13 (47), the active layer 14 (42), and the first semiconductor layer 15 (48). The semiconductor layer 15 (48) has a pair of electrodes 17 and 18 for flowing current in the film thickness direction, and at least the film thickness direction of the active layer 14 (42) is the axis of the uniaxial anisotropy. Are in different directions and the active layer 14 (42 There Al _x Ga _1-xy In _y N (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and the light emitting portion of the active layer 14 (42) is distorted in a plane that is not perpendicular to the c-axis indicating anisotropy. This is solved by a semiconductor light emitting device characterized by having c-plane strain anisotropy (hereinafter referred to as “semiconductor light emitting device”). III ”).
[0023]
The above semiconductor element II Or III The main surface of the substrate 11 (41) is -5 degrees to +5 degrees from the {11-20} plane, the {1-100} plane, the {11-20} plane, or the {1-100} plane. The surface is inclined within the range.
Also, the semiconductor element II Or III The main surface of the substrate 11 (41) has an off-angle θ relative to any one of the {11-20} plane and the {1-100} plane (where 0 ° ≦ θ ≦ Ten The feature is that the surface is only off.
[0024]
Also, the semiconductor element II Or III The main surface of the substrate 11 (41) is a {11-20} plane, a plane tilted within a range of −5 to +5 degrees from the {11-20} plane, or a {11-20} plane Off angle θ (however, 0 ° ≦ θ ≦ Ten The substrate 11 (41), the second semiconductor layer 13 (47), the third semiconductor layer 15 (48), and the active layer 14 (42) are {0001}. It is characterized by being cleaved by a plane or {1-100} plane.
[0025]
Also, the semiconductor element II Or III The main surface of the substrate 11 (41) is a {1-100} plane, a plane tilted within a range of −5 to +5 degrees from the {1-100} plane, or a {1-100} plane Off angle θ (however, 0 ° ≦ θ ≦ Ten The substrate 11 (41), the second semiconductor layer 13 (47), the third semiconductor layer 15 (48), and the active layer 14 (42) are {0001}. It is characterized by being cleaved at a plane or {11-20} plane.
Also, the semiconductor element II Or III The main surface of the substrate 41 is a {0001} plane, and a small surface having a plane orientation intersecting the main surface is provided on the surface of the substrate 41, and the substrate 41 is formed above the small surface. The active layer is a light emitting portion. In this case, the facet is formed in a plane orientation perpendicular to the {1-100} plane or the {11-20} plane, and the {1-100} plane or the {11-20} plane is at both ends of the resonator. It is a cleavage plane.
[0026]
Further, as illustrated in FIG. 2 or FIG. 10, the above-described problem is a second problem that is formed directly on the main surface of the substrate 11 (41) made of sapphire or via the first semiconductor layer 12 (52). Semiconductor formed on the semiconductor layer 13 (47) and the second semiconductor layer 13 (47) and having an energy band gap smaller than that of the second semiconductor layer 13 (47) and having uniaxial anisotropy An active layer 14 (42), a third semiconductor layer 15 (48) formed on the active layer 14 (42) and having an energy band gap larger than that of the active layer 14 (42), and the second semiconductor layer 15 (48). A pair of electrodes 17 and 18 for flowing a current in the film thickness direction through the semiconductor layer 13 (47), the active layer 14 (42) and the third semiconductor layer 15 (48), and the substrate 11 The main surface of (41) is the {1-102} surface There is a direction different from the thickness direction of the uniaxial anisotropy axis of at least the active layer 14 (42), the active layer 14 (42) Al _x Ga _1-xy In _y N (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and the light emitting portion of the active layer 14 (42) is distorted in a plane that is not perpendicular to the c-axis indicating anisotropy. This is solved by a semiconductor light emitting device characterized by having c-plane strain anisotropy (hereinafter referred to as “semiconductor light emitting device”). IV ”).
[0027]
As illustrated in FIG. 2 or FIG. LiAlO ₂ A second semiconductor layer 13 (47) formed directly or via a first semiconductor layer 12 (52) on a main surface of a substrate 11 (41) comprising the second semiconductor layer 13 (47) An active layer 14 (42) made of a semiconductor having an energy band gap smaller than that of the second semiconductor layer 13 (47) and having uniaxial anisotropy; and on the active layer 14 (42) A third semiconductor layer 15 (48) having an energy band gap larger than that of the active layer 14 (42), the second semiconductor layer 13 (47), the active layer 14 (42), and the first semiconductor layer 15 (48). The semiconductor layer 15 (48) has a pair of electrodes 17 and 18 for flowing current in the film thickness direction, and at least the film thickness direction of the active layer 14 (42) is the axis of the uniaxial anisotropy. Are in different directions and the active layer 14 (42 There Al _x Ga _1-xy In _y N (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and the light emitting portion of the active layer 14 (42) is distorted in a plane that is not perpendicular to the c-axis indicating anisotropy. This is solved by a semiconductor light emitting device characterized by having c-plane strain anisotropy (hereinafter referred to as “semiconductor light emitting device”). V ”).
Semiconductor light emitting device V The main surface of the substrate 11 (41) is a {100} plane or a plane off from the {100} plane at an angle of −5 degrees to +5 degrees (hereinafter, this semiconductor light emitting device is referred to as “ Semiconductor light emitting device VI ”).
Also, the semiconductor light emitting device V Or VI Said Al _x Ga _1-xy In _y N The composition ratio x and the composition ratio y are in the range between a straight line indicating y = 0.214x−0.328 and a straight line indicating y = 0.353x−0.209 in the xy coordinates. And
[0028]
Semiconductor light emitting device I Etc., the second semiconductor layer 13 (47) is Al _u Ga _1-uv ln _v N (However, 0 ≦ u ≦ 1 , 0 ≦ v ≦ 1 ) And the third semiconductor layer 15 (48) Al _w Ga _1-wz In _z N (However, 0 ≦ w ≦ 1, 0 ≦ z ≦ 1).
[0029]
Also, the semiconductor light emitting device I Etc., the a-axis lattice constant a of the active layer 14 (42) ₁ And the a-axis lattice constant a of the second semiconductor layer 13 (47) and the third semiconductor layer 15 (48). ₂ , A _Three And a ₁ <A ₂ , A ₁ <A _Three And the c-axis lattice constant c of the active layer 14 (42). ₁ And the c-axis lattice constant c of the second semiconductor layer 13 (47) and the third semiconductor layer 15 (48). ₂ , C _Three And c ₁ <C ₂ And c ₁ <C _Three It is characterized by satisfying the relationship.
Also, the semiconductor light emitting device I Etc., the a-axis lattice constant a of the active layer 14 (42) ₁ And the a-axis lattice constant a of the second semiconductor layer 13 (47) and the third semiconductor layer 15 (48). ₂ , A _Three And a ₁ > A ₂ , A ₁ > A _Three And the c-axis lattice constant c of the active layer 14 (42). ₁ And the c-axis lattice constant c of the second semiconductor layer 13 (47) and the third semiconductor layer 15 (48). ₂ , C _Three And c ₁ > C ₂ And c ₁ > C _Three It is characterized by satisfying the relationship.
[0030]
Also, the semiconductor light emitting device I 17, a mirror layer is formed below the second semiconductor layer 47 or above the third semiconductor layer 48 as illustrated in FIG. 17. The active layer 42, with the mirror layer as one end, A resonator is formed in the film thickness direction of the second and third semiconductor layers 47 and 48. In this case, the resonance wavelength of the resonator is a wavelength that maximizes the photoluminescence light intensity.
[0031]
Also, the semiconductor light emitting device I Etc., the active layer 42 comprises: GaN Or InGaN A first layer of AlGaInN , GaN Or InGaN A multiple quantum well layer having a multilayer structure composed of the second layer of GaN Single layer, InGaN Single layer, and AlGaInN It consists of one of the single layers. In this case, the second semiconductor layer 47 is of the first conductivity type. AlGaN And the third semiconductor layer 48 is of the second conductivity type. AlGaN It is characterized by comprising.
[0032]
As shown in FIG. GaN Or AlN A first active layer 58 made of a wurtzite structure crystal formed above the substrate 53, and a first conductivity type impurity formed under the first active layer 58. The barrier layer 56, the second barrier layer 60 including a second conductivity type impurity formed on the first active layer 58, and the first active layer 58 and the first and second barrier layers 56 , 60, a surface emitting semiconductor laser 66 having electrodes 64, 65 for flowing current in the film thickness direction, a second active layer 58 made of a wurtzite structure crystal formed above the substrate 53, the second The first semiconductor layer 56 including a first conductivity type impurity formed under the active layer 58 and the second semiconductor layer 60 including a second conductivity type impurity formed over the second active layer 58. And in the film thickness direction of the second active layer 58 and the first and second semiconductor layers 56, 60. An optical semiconductor device having electrodes 64 and 65 for taking out current to the outside and a light receiving element 67 electrically isolated from the surface emitting semiconductor laser 66, wherein the first active layer 58 is uniaxial. The active layer 58 is made of a semiconductor having anisotropy, and at least the film thickness direction of the active layer 58 is different from the axis of the uniaxial anisotropy. Al _x Ga _1-xy In _y N (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and the light emitting portion of the active layer 58 is strained in a plane that is not perpendicular to the c-axis indicating anisotropy. This is solved by an optical semiconductor device having in-plane strain anisotropy (hereinafter, this optical semiconductor device is referred to as “optical semiconductor device I”).
In the optical semiconductor device I, the main surface of the substrate 53 is a {1-100} plane or a {11-20} plane.
[0033]
As shown in FIG. 18, the above-mentioned problem is that a substrate made of sapphire whose principal surface is a {1-102} plane, a first active layer made of a wurtzite structure crystal formed above the substrate, the first A first barrier layer including a first conductivity type impurity formed under the first active layer, a second barrier layer including a second conductivity type impurity formed over the first active layer, and A surface-emitting semiconductor laser having an electrode for flowing current in the film thickness direction of the first active layer and the first and second barrier layers, and a second composed of a wurtzite structure crystal formed above the substrate An active layer; a first semiconductor layer including a first conductivity type impurity formed under the second active layer; and a second semiconductor layer including a second conductivity type impurity formed over the second active layer. The semiconductor layer and the current flowing in the film thickness direction of the second active layer and the first and second semiconductor layers are extracted to the outside. An optical semiconductor device having a pole and a light receiving element electrically separated from the surface emitting semiconductor laser, wherein the first active layer is made of a semiconductor having uniaxial anisotropy, and at least the active The thickness direction of the layer is different from the axis of uniaxial anisotropy, and the active layer is Al _x Ga _1-xy In _y N (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and the light emitting portion of the active layer is strained in a plane that is not perpendicular to the c-axis indicating anisotropy and is c-plane This is solved by an optical semiconductor device having an internal strain anisotropy (hereinafter referred to as “optical semiconductor device”). II ”).
Optical semiconductor device I Etc., the first active layer 58 and the second active layer 58 are: GaN , InGaN , AlGaN Or AlGaInN It is characterized by comprising.
In the optical semiconductor device or the like, the first barrier layer 56, the second barrier layer 60, the first semiconductor layer 56, and the second semiconductor layer 60 are: GaN , InGaN , AlGaN Or AlGaInN It is characterized by comprising.
[0034]
  Next, the operation of the above-described invention will be described. In the present invention, the main surface of the substrate is selected to be formed on the substrate.Al _x Ga _1-xy In _y N Active layer consisting ofThe c-axis is not perpendicular to the surface of the semiconductor layer. Therefore, formed on the substrateAl _x Ga _1-xy In _y N Active layer consisting ofFurther, when a compressive strain or tensile strain in the plane direction is applied, the active layer has triaxial anisotropy. As a result, the degeneration in the valence band of the active layer is solved, and the oscillation threshold current of the semiconductor laser having such an active layer is reduced.
[0035]
According to such a structure, the polarization plane (optical anisotropy) of light emission by the compound semiconductor layer can be uniquely determined.
When a surface emitting semiconductor laser is formed by growing such an active layer on a substrate, the in-plane anisotropy of the active layer is increased and the electric field vector is determined in one direction, so that polarization can be determined. .
[0036]
Thus, when the plane of polarization of the oscillation light of the surface emitting semiconductor laser is uniquely determined, it can be used as a light source for the magneto-optical disk device, and a light receiving element is manufactured on the same substrate as the surface emitting semiconductor laser. Becomes easier. As a result, the conventional mounting operation of the semiconductor laser and the light receiving element becomes unnecessary, and the size of the light receiving and emitting device is further reduced.
[0037]
  As the substrate, wurtzite structure such as GaN, LiAlO₂A tetragonal crystal such as sapphire and a hexagonal crystal such as 6H—SiC are used. By the way, when the c-axis direction of the wurtzite compound semiconductor crystal constituting the light emitting diode is set to be substantially orthogonal to the light emission direction, the polarization direction is determined. Therefore, a plurality of such light emitting diodes are arranged on the display surface of the display device so that one light emitting diode forms part or all of a pixel, and the polarization directions of adjacent light emitting diodes differ from each other by 90 degrees. Let Thereby, the light-emitting diode for the right-eye polarization direction and the light-emitting diode for the left-eye polarization can be adjacent to each other, and the number of components can be reduced by omitting the deflector in the stereoscopic display device, thereby reducing the manufacturing cost. Moreover, such a display device brightens the image.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
FIGS. 1A and 1B are configuration diagrams of the first embodiment of the present invention.
In the semiconductor laser shown in FIGS. 1A and 1B, the first semiconductor layer 1 having a uniaxial anisotropic crystal structure is used as a light emitting portion, and the axis perpendicular to the axis indicating the anisotropy of the first semiconductor layer 1 is used. In this plane, distortion is applied to give triaxial anisotropy.
[0039]
As described above, when strain is applied in a plane that is not perpendicular to the axis indicating anisotropy (that is, the c-axis), the applied strain is isotropic in each direction and exhibits triaxial anisotropy. . As a result, the degeneracy of HH and LH in the valence band is solved, and the threshold current density for laser oscillation is reduced.
That is, as shown in FIG. 1 (b), the degeneracy of the HH and LH bands, which was the highest in terms of energy, is solved, and the energy difference between the LH, HH, and CH (crystalline field split hole) bands. Therefore, for laser oscillation, carriers need only be shifted to HH, and the threshold current density increases. At this time, a resonator is manufactured perpendicular to the direction of the electric field vector determined by the polarization of the top band.
[0040]
On the other hand, as described in the prior art, in a semiconductor laser having an active layer subjected to compressive stress in the (0001) plane of the GaInN layer perpendicular to the c-axis, HH and LH Both of the two bands need to be filled with carriers, which increases the threshold current density.
In FIG. 1 (a), the first semiconductor layer 1 is sandwiched between the second and third semiconductors 2 and 3 having a lattice constant different from that of the first semiconductor layer 1, and the interface between these layers is the first. The semiconductor layer 1 is not perpendicular to the axis indicating the anisotropy.
[0041]
In this way, the main surface of the light emitting portion made of the first semiconductor layer 1 is configured by a surface that is not perpendicular to the c-axis, and the second semiconductor 2 and the third semiconductor layer having a lattice constant different from that of the first semiconductor layer 1. When the first semiconductor layer 1 is sandwiched between the semiconductor layers 3, strain is added in a plane that is not perpendicular to the c-axis based on the difference between the lattice constants, so that the light emitting portion can have triaxial anisotropy.
Next, materials and crystal lattice constants for the first to third semiconductor layers 1, 2, and 3 will be described.
[0042]
As a material constituting the first semiconductor layer 1 described above, for example, AI_xGa_1-xyIn_yN (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is used. Such a wurtzite type nitride semiconductor is most typical and useful as a semiconductor material for a light emitting device having uniaxial anisotropy.
In addition, as a material constituting the second semiconductor layer 2, Al_uGa_1-uvIn_vN (however, 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) is adopted, and Al is used as a material constituting the third semiconductor layer 3._wGa_1-wzIn_zN (where 0 ≦ w ≦ 1, 0 ≦ z ≦ 1) is adopted. As the second semiconductor layer 2 and the third semiconductor layer 3, by using a GaN-based semiconductor having a mixed crystal ratio different from that of the first semiconductor layer 1 made of the same GaN-based material, the first semiconductor layer 2 and the third semiconductor layer 3 are not affected by the loss of crystallinity. Stress can be applied to the semiconductor layer 1. The mixed crystal ratio of the second semiconductor layer 2 and the third semiconductor layer 3 may be the same.
[0043]
Further, the a-axis lattice constant a of the first semiconductor layer 1₁And the a-axis lattice constant a of the second semiconductor layer 2 and the third semiconductor layer 3₂, A_ThreeAnd a₁<A₂, A₁<A_ThreeTo satisfy the relationship. In addition, the c-axis lattice constant c of the first semiconductor layer 1₁And the c-axis lattice constant c of the second semiconductor layer 2 and the third semiconductor layer 3₂, C_ThreeAnd c₁<C₂, C₁<C_ThreeTo satisfy the relationship.
[0044]
With such a lattice constant relationship, in-plane biaxial tensile stress can be applied to the first semiconductor layer 1, whereby the degeneration of the band can be solved and the threshold current density can be reduced. In this case, the energy difference between the highest band and the second band in terms of energy in the valence band is larger than the compressive stress (see FIG. 14), and the top band is LH. The density is further reduced.
[0045]
On the other hand, the a-axis lattice constant a of the first semiconductor layer 1₁And the a-axis lattice constant a of the second semiconductor layer 2 and the third semiconductor layer 3₂, A_ThreeAnd a₁> A₂, A₁> A_ThreeTo satisfy the relationship. And the c-axis lattice constant c of the first semiconductor layer 1₁And the c-axis lattice constant c of the second semiconductor layer 2 and the third semiconductor layer 3₂, C_ThreeAnd c₁> C₂, C₁> C_ThreeTo satisfy the relationship.
[0046]
With such a lattice constant relationship, compressive stress (strain) can be applied in the plane of the first semiconductor layer 1, thereby degenerating the HH and LH bands and reducing the threshold current density. At the same time, since there is no concern about the occurrence of cracks compared to the case of tensile stress, the reliability is further improved.
Further, a material and a film thickness are selected such that the energy band gap of the second semiconductor layer 2 and the third semiconductor layer 3 is larger than the energy gap of the first semiconductor layer 1. By setting such an energy band gap relationship, light and carriers are confined in the first semiconductor layer 1, and efficient light emission is obtained.
[0047]
In addition, a material made of GaN, AIN, or SiC is selected as the constituent material of the substrate constituting the semiconductor laser. When a substrate made of GaN, AIN, or SiC having a uniaxial anisotropic crystal structure is used as a semiconductor substrate constituting a semiconductor laser, it is grown on the substrate by appropriately selecting its main surface. When strain is applied to the first semiconductor layer 1, the first semiconductor layer 1 can be given triaxial anisotropy.
[0048]
The semiconductor layer first provided on the substrate constituting the semiconductor laser has the same composition as the substrate. For example, a GaN mixed crystal substrate is used, and a clad layer having the same composition is directly provided on the base slope. Thereby, distortion can be effectively applied to the first semiconductor layer 1 constituting the light emitting portion on the cladding layer.
Next, the plane orientation of the above substrate will be described.
[0049]
The main surface of the semiconductor substrate constituting the semiconductor laser is formed on a surface that is turned off from either the {1-100} plane or the {11-20} plane by an off angle θ (where 0 ° ≦ θ ≦ 10 °). To do. In the present specification, an index normally represented by “1 bar” or “2 bar” is represented by “−1”, “−2” or the like for convenience.
When a semiconductor having a uniaxial anisotropic crystal structure is used as the substrate constituting the semiconductor laser, the first semiconductor above the substrate is formed by setting its main surface to the {1-100} plane or {11-20} plane. The layer 1 can be strained to have triaxial anisotropy. In this case, as shown in FIG. 1C, the main surface may be turned off by an off angle θ (where 0 ° ≦ θ ≦ 10 °) in order to suppress the generation of twins and the like.
[0050]
Further, the cleavage plane constituting the resonator of the semiconductor laser is any one of {0001} plane, {1-100) plane, and {11-20} plane.
When the {1-100} plane is used as the main surface of the substrate, either the {0001} plane or the {11-20} plane is a cleavage plane perpendicular to the main surface of the substrate. Further, when the {11-20} plane is used as the main surface of the substrate, either the {0001} plane or the {1-100} plane is a cleavage plane perpendicular to the main surface of the substrate. In this case, a resonator is constituted by two cleaved surfaces of the first semiconductor layer 1.
[0051]
Further, the main surface of the semiconductor substrate constituting the semiconductor laser is a {0001} plane, and a small surface other than the {0001} surface is provided on the surface of the substrate, and the first semiconductor layer 1 provided on this small surface is provided. Was the light emitting part (active layer). The small surface is a concept including a surface inclined with respect to the {0001} plane of the semiconductor substrate.
In this way, a small surface other than the {0001} surface for giving triaxial anisotropy may be provided on a part of the substrate, and the small surface allows, for example, a TS (Terraced Substrate) type semiconductor. A part of a laser or the like can be configured.
[0052]
The facet may be a plane perpendicular to either the {1-100} plane or the {11-20} plane, and this perpendicular plane may be a cleavage plane constituting the resonator.
Also in this case, the resonator can be configured by two cleavage planes by using the {1-100} plane or the {11-20} plane perpendicular to the facet as a cleavage plane.
Next, the structure of the above-described optical semiconductor device and the manufacturing method thereof will be specifically described.
[0053]
First example
First, as shown in FIG. 2 (a), TMGa (trimethylgallium) is added at 10 to 100 μmol / min, for example, on an n-type GaN (1-100) substrate 11 having a (1-100) plane as a main surface. 45 μmol / min, 10 to 100 μmol / min of TMA1 (trimethylaluminum), for example, 45 μmol / min, ammonia (NH_Three) Between 0.02 and 0.2 mol / min, for example, 0.1 mol / min, Si₂H₆Of 0.0001 to 0.002 μmol / min, for example, 0.0007 μmol / min, and 300 to 3000 sccm of hydrogen as a carrier gas, for example, 1000 sccm, a growth pressure of 70 to 760 Torr, for example, 100 Torr, and a growth temperature N-type Al of 100 to 5000 nm, preferably 2000 nm in a state of 850 to 1100 ° C., for example, 950 ° C._0.1Ga_0.9N Clad layer 12 is grown.
[0054]
Subsequently, TMGa is 10 to 100 μmol / min, for example, 45 μmol / min, ammonia is 0.02 to 0.2 mol / min, for example, 0.1 mol / min, Si₂H₆Of 0.0001 to 0.002 μmol / min, for example, 0.007 μmol / min, and 300 to 3000 sccm of hydrogen as a carrier gas, for example, 1000 sccm, and a growth pressure of 70 to 760 Torr, for example, 100 Torr. The n-type GaN light guide layer 13 having a thickness of 50 to 500 nm, preferably 100 nm is grown in a state where the temperature is 800 to 1050 ° C., for example, 930 ° C.
[0055]
Subsequently, TMGa is 2.5 to 25 μmol / min, for example, 10 μmol / min, TMIn (trimethylindium) is 25 to 250 μmol / min, for example, 100 μmol / min, ammonia is 0.02 to 0.2 mol / min, For example, 0.1 mol / min and nitrogen as a carrier gas are flowed through 300 to 3000 sccm, for example, 1000 sccm, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 550 to 800 ° C., for example, 650 Ga at a thickness of 1 to 20 nm, preferably 3 nm, at a temperature of_0.9In_0.1N The active layer 14 is grown.
[0056]
Subsequently, TMGa is 10 to 100 μmol / min, such as 45 μmol / min, ammonia is 0.02 to 0.2 mol / min, such as 0.1 mol / min, and biscyclopentadienylmagnesium is 0.01 to 0.00. 5 μmol / min, for example, 0.05 μmol / min, and 300 to 3000 sccm, for example, 1000 sccm of hydrogen as a carrier gas are allowed to flow, the growth pressure is 70 to 760 Torr, for example, 100 Torr, and the growth temperature is 800 to 1050 ° C. For example, the p-type GaN light guide layer 15 having a thickness of 50 to 500 nm, preferably 100 nm is grown in a state of 930 ° C.
[0057]
Subsequently, TMGa is 10 to 100 μmol / min, such as 45 μmol / min, TMAl is 10 to 100 μmol / min, such as 45 μmol / min, ammonia is 0.02 to 0.2 mol / min, such as 01 mol / min, Biscyclopentadienylmagnesium is supplied in an amount of 0.01 to 0.5 μmol / min, for example, 0.05 μmol / min, and hydrogen as a carrier gas is supplied in an amount of 300 to 3000 sccm, for example, 1000 sccm, and a growth pressure is set to 70 to 760 Torr, for example, 100 Torr and a growth temperature of 850 to 1100 ° C., for example, 950 ° C., 100 to 2000 nm, preferably 500 nm p-type Al._0.1Ga_0.9N Clad layer 16 is grown.
[0058]
In this case, Al_0.1Ga_0.9The growth rate of the N cladding layers 12 and 16 is 0.6 to 5.5 μm / hour, typically 2.6 μm / hour, and the growth rate of the GaN light guide layers 13 and 15 is 0.5 to 5 2 μm / hour, typically 2.4 μm / hour, and Ga_0.9In_0.1The growth rate of the N active layer 14 is 0.1 to 1.5 μm / hour, typically 0.6 μm / hour.
[0059]
Next, a Ti / Au electrode 17 as an n-side electrode is provided on the back surface of the n-type GaN (1-100) substrate 11, while p-type Al_0.1Ga_0.9A Ni / Au electrode 18 is provided on the N clad layer 16 as a p-side electrode, and after appropriate element separation, cleavage is performed on the (0001) plane to form a resonator, thereby completing a semiconductor laser.
In this case, since the (0001) plane is perpendicular to the (1-100) plane which is the main surface of the substrate, the pair of cleavage planes act as a resonator.
[0060]
In this first example, since the (1-100) plane is used as the substrate, the n-type Al grown thereon is used._0.1Ga_0.9N clad layer 12 to p-type Al_0.1Ga_0.9The growth surface of the N cladding layer 16 is also a (1-100) plane, and Ga_0.9In_0.1The N active layer 14 has a triaxial anisotropy because it receives a compressive stress in the (1-100) plane due to a difference in lattice constant with the n-type GaN light guide layer 13.
[0061]
That is, the in-plane atomic spacing in the first example is n-type Al._0.1Ga_0.9N Since the lattice constants of the a-axis and c-axis of the clad layer 12 are defined by 3.189 and 5.185Å, the lattice constants of the a-axis and c-axis are 3.225Å and 5.243Å, respectively._0.9In_0.1A compressive stress is applied to the N active layer 14 to provide triaxial anisotropy.
Ga_0.9In_0.1N, GaN, and Al_0.1Ga_0.9The energy band gaps of N are 3.15 eV, 3.4 eV, and 3.7 eV, respectively.
[0062]
When in-plane compressive stress is applied to such a GaN-based semiconductor, as shown in FIG. 2 (b), the degenerate HH and LH bands that are degenerate at the top of energy are separated. , LH becomes the highest level, and laser oscillation is performed by the transition between the LH and the conduction band, and the threshold current density is greatly reduced.
In this first example, the GaN (1-100) substrate 11 having the (1-100) plane as the main surface is used as the substrate, but a GaN substrate having the (11-20) plane as the main surface is used. Further, an AlN substrate or SiC substrate having a (1-100) plane or a (11-20) plane as a main surface may be used, and the (1-100) plane or the main surface may be used. This includes all planes that are crystallographically equivalent to the (11-20) plane, and the same applies to the following examples of this embodiment.
[0063]
As the substrate on which the active layer and cladding layer of the semiconductor laser are formed, in addition to GaN, AlN, SiC or other substrates may be used. For example, the GaN substrate in the element structure shown in FIG. 2 (a) may be replaced with an AlN substrate, and the same structure as in FIG. 2 (a) may be provided thereon. The same structure as that shown in FIG. 2 (a) may be provided on the SiC base slope through an n-type AlN buffer layer having a thickness of 5 to 100 nm, for example, 20 nm.
[0064]
As shown in FIG. 3, when the resistance of the AlN substrate 11a is considered to be high, a structure in which the electrode 17a is connected to a part of the AlGaN cladding layer 12 is adopted. The same applies when using an AlN buffer layer. These may be similarly adopted in the following examples.
In this embodiment and the following embodiments, as shown in FIG. 2C, the energy band gap of the active layer is smaller than the energy band gap of the cladding layer, the guide layer described later, and the optical confinement layer described later. .
[0065]
Second example
Next, a second example of this embodiment will be described with reference to FIG.
First, as shown in FIG. 4 (a), TMGa is added on the n-type GaN (1-100) substrate 21 having the (1-100) plane as a main surface, and the thickness is 2.5 to 25 μmol / min, for example, 10 μmol / min. Min, TMAl 30-300 μmol / min, eg 150 μmol / min, TMIn 250-2500 μmol / min, eg 1000 μmol / min, ammonia 0.02-0.2 mol / min, eg 01 mol / min, Si₂H₆Of 0.0001 to 0.002 μmol / min, for example, 0.007 μmol / min, and nitrogen as a carrier gas is allowed to flow at 300 to 3000 sccm, for example, 1000 sccm, the growth pressure is set at 70 to 760 Torr, for example, 100 Torr, and the growth temperature N-type Al of 100 to 5000 nm, preferably 2000 nm in a state of 550 to 900 ° C., for example 700 ° C._0.4Ga_0.3 In_0.3An N clad layer 22 is grown.
[0066]
Subsequently, TMGa is 5 to 50 μmol / min, for example, 20 μmol / min, TMAl is 10 to 100 μmol / min, for example, 50 μmol / min, TMIn is 150 to 1500 μmol / min, for example, 660 μmol / min, and ammonia is 0.5%. 02 to 0.2 mol / min, for example, 0.1 mol / min, Si₂H₆Of 0.0001 to 0.002 μmol / min, for example, 0.007 μmol / min, and 300 to 3000 sccm, for example, 1000 sccm of nitrogen as a carrier gas, and a growth pressure of 70 to 760 Torr, for example, 100 Torr. N-type Al having a thickness of 50 to 500 nm, preferably 100 nm, at a temperature of 550 to 900 ° C., for example 700 ° C._0.15Ga_0.65In_0.2N light guide layer 23 is grown.
[0067]
Subsequently, TMGa is 2.5 to 25 μmol / min, for example 10 μmmol / min, TMIn is 25 to 250 μmol / min, for example 100 μmol / min, Ammonia is 0.02 to 0.2 mol / min, for example 01 mol / min. The thickness of the carrier gas is 300 to 3000 sccm, for example 1000 sccm, the growth pressure is 70 to 760 Torr, for example 100 Torr, and the growth temperature is 550 to 900 ° C., for example 700 ° C. 1-20 nm, preferably 3 nm Ga_0.9In_0.1N The active layer 24 is grown.
[0068]
Subsequently, TMGa is 5 to 50 μmol / min, such as 20 μmol / min, TMAl is 10 to 100 μmol / min, such as 50 μmol / min, TMIn is 150 to 1500 μmol / min, such as 660 μmol / min, and ammonia is 0.02. 0.2 mol / min, for example 0.1 mol / min, biscyclopentadienyl magnesium 0.01-0.5 μmol / min, for example 0.05 μmol / min, and nitrogen as the carrier gas 300- A p-type film having a thickness of 50 to 500 nm, preferably 100 nm in a state where a flow rate of 3000 sccm, for example, 1000 sccm, a growth pressure of 70 to 760 Torr, for example, 100 Torr, and a growth temperature of 550 to 900 ° C., for example, 700 ° C. Al_0.15Ga_0.65In_0.2N light guide layer 25 is grown.
[0069]
Subsequently, TMGa is 2.5 to 25 μmol / min, for example 10 μmol / min, TMAl is 30 to 300 μmol / min, for example 150 μmol / min, TMIn is 250 to 2500 μmol / min, for example 1000 μmol / min, and ammonia is 0 02 to 0.2 mol / min, for example, 0.1 mol / min, biscyclopentadienylmagnesium to 0.01 to 0.5 μmol / min, for example, 0.05 mol / min, and as a carrier gas A nitrogen flow of 300 to 3000 sccm, for example, 1000 sccm, a growth pressure of 70 to 760 Torr, for example, 100 Torr, a growth temperature of 550 to 900 ° C., for example, 700 ° C., and a p of 100 to 2000 nm, preferably 500 nm. Type Al_0.4Ga_0.3In_0.3An N clad layer 26 is grown.
[0070]
In this case, Al_0.4Ga_0.3In_0.3The growth rate of the N clad layers 22 and 26 is 0.2 to 3.0 μm / hour, typically 1.2 μm / hour._0.15Ga_0.65In_{0, .2}The growth rate of the N light guide layers 23 and 25 is 0.3 to 5.0 μm / hour, typically 1.8 μm / hour._0.9In_0.1The growth rate of the N active layer 14 is 0.1 to 1.5 μm / hour, typically 0.6 μm / hour.
[0071]
Next, a Ti / Au electrode 27 is provided as an n-side electrode on the back surface of the n-type GaN substrate 21 having a (1-100) surface, while p-type Al_0.4Ga_0.3In_0.3A Ni / Au electrode 28 is provided as a p-side electrode on the N clad layer 26, and after appropriate element separation, cleavage is performed on the (0001) plane to form a resonator, thereby completing a semiconductor laser.
In this second example, since the (1-100) plane is used as the substrate, n-type Al grown on it is used._0.4Ga_0.3In_0.3N clad layer 22 to p-type Al_0.4Ga_0.3In_0.3The growth surface of the N cladding layer 26 is also a (1-100) plane, and Ga_0.9In_0.1Since the N active layer 24 receives tensile stress, it becomes triaxial anisotropy.
[0072]
That is, the in-plane atomic spacing in the second example is n-type Al._0.4Ga_0.3In_0.3N Since the clad layer 22 is defined by the a-axis and c-axis lattice constants of 3.266、３ and 5.276Å, the a-axis and c-axis lattice constants are 3.225Å and 5.243Å._0.9In_0.1A tensile stress is applied to the N active layer 24, resulting in triaxial anisotropy.
Ga_0.9In_0.1N, Al_0.15Ga_0.65In_0.2N and Al_0.4Ga_0.3In_0.3The energy band gaps of N are 3.15 eV, 3.4 eV and 3.6 eV, respectively.
[0073]
In this way, when in-plane tensile stress is applied to the GaN-based semiconductor, as shown in FIG. 4 (b), the degeneracy of the HH and LH bands that are degenerate at the highest energy level is resolved and separated. In addition, since HH becomes the highest level and the energy difference between LH and HH can be increased, the threshold current density can be further reduced.
As described above, regarding the reduction of the threshold current density, the band structure of the valence band in FIG. 2 (b) due to the biaxial compressive stress in the growth plane is different from that in FIG. 4 (b) due to the in-plane biaxial tensile stress. The band structure of the valence band is preferable because the energy difference between the first and second bands can be increased, but in the case of tensile stress, the active layer is more likely to crack. Therefore, compressive stress is more desirable from the viewpoint of device lifetime.
[0074]
Also in this second example, when an AlN substrate is used, the GaN substrate in the element structure shown in FIG. 4 (a) is replaced with an AlN substrate, and the same structure as in FIG. 4 (a) is provided thereon. If a SiC substrate is used, the same structure as that shown in FIG. 4A can be provided on an n-type SiC substrate through an AlN buffer layer having a thickness of 5 to 100 nm, for example, 20 nm. It ’s fine.
[0075]
Third example
Next, a third example of the present embodiment will be described with reference to FIG. 5. Since the manufacturing conditions are exactly the same as those in the first example, the structure will be described.
The element shown in the perspective view in FIG. 5 is a so-called TS type semiconductor laser, and has a (11-21) facet formed of a (11-21) face at a step portion of a GaN substrate having a (0001) face as a main face. The n-type GaN (0001) substrate 31 provided with is used. On this n-type GaN (0001) substrate 31, n-type Al is exactly the same as in the first example._0.1Ga_0.9N clad layer 12, n-type GaN light guide layer 13, Ga_0.9In_0.1N active layer 14, p-type GaN light guide layer 15, and p-type Al_0.1Ga_0.9The N clad layer 16 is grown sequentially.
[0076]
Next, Ti / Au electrode 17 and SiO₂The Ni / Au electrode 18 is provided through an opening provided in the insulating film 33 and the like to appropriately separate the elements, and then the (1-100) plane is cleaved to form a pair of (1-100) cleavage planes 34. A TS type semiconductor laser as a resonator is completed.
In this case, the main surface of the substrate is a (0001) plane that is perpendicular to the c-axis, but the light emitting section, that is, the laser oscillation section is actually a plane parallel to the (11-21) plane. In this (11-21) plane, a compressive stress is applied to form triaxial anisotropy, and the degeneration can be solved as shown in FIG. 2B, so that the threshold current density is lowered, but the stress is applied (11-21). ) Since the face is 32, the influence of stress is smaller than that of the first example, and the effect of reducing the threshold current density is inferior.
[0077]
In this case, the facet is not limited to (11-21) facet 32.
Also in this third example, the substrate is GaN, LiAlO._ThreeHowever, AlN or SiC may be used, and the configuration change accompanying the change of the material of the substrate is the same as the replacement in the first example, and the same as in the second example. When a semiconductor having such a composition is used, a tensile stress is applied to the active layer as in the second example.
[0078]
Fourth example
In the above first to third examples, a binary compound substrate is used as the substrate._0.1Ga_0.9N or Al_0.4Ga_0.3In_0.3A mixed crystal substrate such as N may be used. In that case, Al formed on it_0.1Ga_0.9N clad layer or Al_0.4Ga_0.3In_0.3Since the lattice matching with the N cladding layer can be perfectly taken, the crystallinity of the growth layer is not impaired.
[0079]
As a substrate used for forming other semiconductor lasers, as shown in FIG. 6 (a), LiAlO having tetragonal crystals is used.₂A substrate 35 may be used, an example of which will be described below. LiAlO₂Is called lithium aluminate.
So next, LiAlO₂A process of forming a semiconductor laser using the substrate 35 will be described.
[0080]
LiAlO₂As the main surface of the substrate 35, a {100} plane or a surface that is turned off within a predetermined angle, for example, ± 5 degrees from the {100} plane is used.
First, LiAlO using an organic cleaning agent such as isopropyl alcohol and ethyl alcohol₂The surface of the substrate 35 is cleaned.
Next, on the susceptor in the growth furnace of the metalorganic vapor phase epitaxy apparatus (not shown), LiAlO₂A substrate 35 is placed. After that, LiAlO₂While replacing the atmosphere around the substrate 35 with nitrogen, the pressure in the atmosphere is reduced to 100 Torr.
[0081]
Subsequently, LiAlO at a temperature 50 degrees higher than the growth temperature described later.₂Substrate 35 is heated and thereby LiAlO₂Thermal cleaning is performed by sublimating elements on the surface of the substrate 35.
After that, LiAlO₂The substrate 35 is lowered to a growth temperature of, for example, 800 to 1050 ° C., and then TMGa gas, ammonia gas, Si₂H₆Introduce gas. TMGa is gasified by bubbling with nitrogen gas in a thermostatic chamber, and the nitrogen gas is used as a carrier gas. Si₂H₆Of these, the Si element functions as an n-type dopant.
[0082]
The flow rate of TMGa gas is set within a range of 10 to 100 μmol / min. The flow rate of ammonia gas is 2 × 10^Four~ 2x10^FiveWithin the range of μmol / min. Furthermore, the nitrogen gas is set within a range of 0.3 to 3.0 μmol / min.
In this case, the flow rate of TMGa gas is 45 μmol / min and the flow rate of ammonia gas is 1 × 10.^FiveWhen the flow rate of nitrogen gas is set to 1.0 μmol / min and the growth temperature is set to 930 ° C., LiAlO₂The growth rate of GaN on the substrate is 2.4 μm / h. Note that, according to the above conditions within the range of gas flow rate and growth temperature, the growth rate of GaN is 0.5 to 5.2 μm / h.
[0083]
LiAlO depending on such conditions₂On the substrate 35, an n-type GaN buffer layer 36 having a thickness of, for example, 5 to 100 nm is grown.
Subsequently, n-type Al under the same conditions as in the first example_0.1Ga_0.9N cladding layer 12, GaN light guide layer 13, Ga_0.9In_0.1N active layer 14, p-type GaN light guide layer 15, p-type Al_0.1Ga_0.9N clad layer 16 is formed in order. Note that magnesium (Mg) is used as the p-type dopant.
[0084]
The formation conditions, film thickness, and source gas of these layers are the same as those in the first example.
Next, LiAlO₂After removing the substrate 35 from the growth furnace, n-type Al_0.1Ga_0.9N A part of the cladding layer 12 is exposed and its n-type Al_0.1Ga_0.9N Ti / Au electrode 37 is formed as an n-side electrode on a part of clad layer 12, and p-type Al_0.1Ga_0.9A Ti / Au electrode 18 is formed on the N clad layer 16 as a p-side electrode. And LiAlO₂The substrate 35, the layers 36, 12 to 16 and the electrodes thereon and the electrodes are appropriately separated to complete the semiconductor laser.
[0085]
By the way, as shown in FIG.₂When hexagonal GaN is grown on the {100} face of the substrate 35, LiAlO₂The a-axis of GaN and c-axis of GaN are parallel, and LiAlO₂The c-axis of GaN and the a-axis of GaN are parallel.
As a result, LiAlO₂On the {100} face of the substrate 35, GaN grows with the (1-100) face up._0.1Ga_0.9The ground below the N cladding layer 12 is the (1-100) plane of the GaN layer 36.
[0086]
Therefore, as in the first example, Al_0.1Ga_0.9N cladding layer 12, GaN light guide layer 13, Ga_0.9In_0.1N active layer 14, p-type GaN light guide layer 15, p-type Al_0.1Ga_0.9The growth surface of the N cladding layer 16 is also a (1-100) plane, and Ga_0.9In_0.1Since the N active layer 14 receives compressive stress in the (1-100) plane due to the difference in lattice constant from the n-type GaN optical guide layer 13, it has triaxial anisotropy as in the first example. It will be.
[0087]
Also, as shown in FIG. 7, tetragonal LiAlO₂Interatomic distance L in the a-axis direction₁Is 5.1687Å, tetragonal LiAlO₂Inter-atomic distance L in the c-axis direction₂Is a tetragonal crystal of 6.2679Å, and the interatomic distance L in the a-axis direction of hexagonal GaN_ThreeIs 3.189Å, and the interatomic distance L in the c-axis direction of hexagonal GaN_FourIs 5.185cm.
Therefore, considering the interatomic distance, the a-axis direction, and the c-axis direction, the GaN buffer layer and LiAlO₂The mutual lattice mismatch of the substrates is as follows.
[0088]
In the c-axis direction of the GaN buffer layer 36, the GaN buffer layer 36 and LiAlO₂The lattice mismatch of the substrate 35 is small as in the following formula (1).
(C_GaN-A_LiAlO2/ A_LiAlO2  = 3.2 × 10^-3    ... (1)
Where c_GaNIs the distance between atoms in the c-axis direction of GaN, a_LiAlO2LiAlO₂The interatomic distance in the a-axis direction.
[0089]
In addition, in the a-axis direction of the GaN buffer layer, the GaN buffer layer and LiAlO₂The lattice mismatch of the substrate is small as in the following equation (2).
(2xa_GaN-C_LiAlO2) / C_LiAlO2  = 1.8 × 10^-3  ... (2)
However, a_GaNIs the interatomic distance in the a-axis direction of GaN, c_LiAlO2LiAlO₂The distance between atoms in the c-axis direction.
[0090]
LiAlO like this₂When the lattice mismatch between the substrate 35 and the GaN layer 36 is small, either the {100} plane or the plane off by 0 to 5 degrees from the plane is LiAlO.₂If the GaN layer 36 is formed on the main surface of the substrate 35, the GaN layer 36 is unlikely to crack due to thermal expansion.
In this case, the c-axis of the GaN layer 36 is LiAlO.₂The inclination is 0 to 5 degrees from the main surface of the substrate 35, and the GaN layer 36 is distorted in a plane that is not perpendicular to the c-axis. As a result, the strain applied to the GaN layer 36 exhibits triaxial anisotropy, which solves the double degeneration of HH and LH in the valence band of the energy band structure, thereby increasing the threshold current density of the semiconductor laser. descend.
[0091]
Further, when a rocking curve showing the intensity distribution of diffraction of X-ray irradiation of such a (1-100) plane-grown single-crystal GaN layer was measured, as shown in FIG. A film having good crystallinity (") can be obtained.
In the above description, LiAlO₂Although the formation of the GaN film on the substrate has been described, as shown in FIG.₂Al on the substrate 35_xGa_1-xyIn_yThe same crystal structure is obtained when the N layer is formed directly. That is, a surface which is 0 or 0 to 5 degrees off from the {100} face or {100} face is LiAlO.₂The main surface of the substrate 35 is formed, and the n-type Al is formed on the main surface in the same manner as in the second example._0.4Ga_0.3In_0.3N clad layer 12, n-type Al_0.15Ga_0.65In_0.2N light guide layer 13, Ga_0.9In_0.1N active layer 14, p-type Al_0.15Ga_0.65In_0.2N light guide layer 115, n-type Al_0.4Ga_0.3In_0.3The N clad layer 16 may be formed in order, and a semiconductor laser may be configured from these layers. The growth conditions, film thickness, etc. in this case are the same as those in the second example.
[0092]
By the way, Al_xGa_1-xyIn_yN (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) interatomic distance La in the a-axis direction₁LiAlO represented by the formula (11)₂C-axis interatomic distance La₂Is represented by equation (12) and Al_xGa_1-xyIn_yA axis direction of N and LiAlO₂The c-axis directions are parallel. Also, Al_xGa_1-xyIn_yInter-atomic distance Lc in the c-axis direction of N₁The interatomic distance Lc in the a-axis direction of GaN₂Is represented by formula (14) and Al_xGa_1-xyIn_yC axis direction of N and LiAlO₂The a-axis direction is parallel.
[0093]
La₁= Xa_AlN+ A_GaN-Xa_GaN-Ya_GaN+ Ya_InN    (11)
La₂= C_LiAlO2            (12)
Lc₁= Xc_AlN+ C_GaN-Xc_GaN-Yc_GaN+ Yc_InN    ... (13)
Lc₂= A_LiAlO2            ... (14)
In those equations, a_AlNIs the distance between atoms in the a-axis direction of AlN, a_GaNIs the interatomic distance in the a-axis direction of GaN, a_InNIs the interatomic distance in the a-axis direction of InN, c_LiAlO2LiAlO₂Is the distance between atoms in the c-axis direction, and c_AlNIs the distance between atoms in the c-axis direction of AlN, c_GaNIs the distance between atoms in the c-axis direction of GaN, c_InNIs the distance between atoms in the c-axis direction of InN, a_LiAlO2LiAlO₂The interatomic distance in the a-axis direction.
[0094]
Also, Al_xGa_1-xyIn_yFor the composition ratio x, y of N, the lattice mismatch is 2 × 10^-2When the expressions (15) to (18) for the condition of% are obtained and drawn in the x and y coordinates, x and y satisfying the conditions of the expressions (15) to (18) are indicated by hatched lines in FIG. When the composition ratio of x and y indicated by the oblique lines is selected, the crystallinity is good and cracks due to thermal expansion or the like are less likely to occur in the crystal. Equation (15) is not represented in FIG. 9 because y is negative when x ≦ 1.
[0095]
[Expression 1]

[0096]
(Other examples)
In the first to third examples, a just surface such as the (1-100) surface or the (11-21) surface is used as the main surface of the substrate. Alternatively, a substrate in which the (1-100) plane or the (11-21) plane is turned off within the range of the off angle θ (0 ° ≦ θ ≦ 10 °) may be used.
[0097]
Furthermore, in the above example, Ga is used as the active layer._0.9In_0.1N is used, but the mixed crystal ratio is Al depending on the required wavelength._xGa_1-xyIn_yN (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) may be changed, and accordingly, the mixed crystal ratio of the light guide layer and the cladding layer is changed to Al._aGa_1-abIn_bYou may change within the range of N (0 <= a <= 1, 0 <= b <= 1).
[0098]
In the above example, the light guide layer is used. However, this is not always necessary, and the heterojunction may be formed directly by the clad layer and the active layer. There is no need to make it symmetrical, Al with different mixed crystal ratios_aGa_1-abIn_bN may be used.
In addition, the raw materials used in the above examples are not limited to the above raw materials, and the organic metal raw materials are ethyl based instead of methyl based, that is, TEGa (triethylgallium), TEAl (triethylaluminum), and TEIn ( Triethylindium) may be used, and nitrogen (N) source may be replaced with ammonia instead of ammonia.₂H_Four, (CH_Three)_ThreeCNH₂ , C₂H_FiveN_ThreeOr CH_ThreeNH ・ NH₂May be used.
[0099]
Furthermore, the impurity material is Si for n-type.₂H₆Instead of SiH_FourOr CH_ThreeSiH_ThreeIn addition, biscyclopentadienyl magnesium [(C_FiveH_Five)₂Instead of (Mg), (CH_ThreeC_FiveH_Four)₂Mg, (C_FiveH_FiveC_FiveH_Four)₂Mg, (i-C_ThreeH₇C_FiveH_Four)₂Mg or (n-C_ThreeH₇C_FiveH_Four)₂May be used.
(Second Embodiment)
FIG. 10 is a perspective view showing the basic structure of the surface emitting semiconductor laser of this embodiment. FIG. 11 is a diagram showing the crystal orientation of the active layer of the present invention, and shows the relationship between the crystal orientation of the active layer of the semiconductor laser shown in FIG. 10 and the coordinate axis.
[0100]
In the first configuration of the present invention, referring to FIG. 10, active layer 42 formed above substrate 41 is formed of a hexagonal semiconductor layer having a c-axis in its plane. That is, as shown in FIGS. 10 and 11, when the xz plane is taken in the main surface of the active layer 42 and the y-axis is taken in the direction perpendicular to the active layer 42, the c-axis of the hexagonal semiconductor crystal constituting the active layer 42 is shown. The direction, that is, the <0001> direction is arranged toward the z axis in the active layer 42 plane.
[0101]
Thus, by including the c-axis in the plane of the active layer 42, the plane of polarization of the oscillation light is defined as described below. The crystal orientation of the x and y axis orientations is not particularly limited. For example, the <11-20> direction is the x axis in the plane of the active layer 42 and the <1-100> orientation is the film of the active layer 2. The y axis in the thickness direction can be used.
[0102]
Hereinafter, the reason why the plane of polarization of oscillation light is defined in this embodiment will be described.
First, a case where there is no strain in the active layer will be described. FIG. 12 is a diagram showing the energy band structure of GaN, which shows the band structure of a hexagonal semiconductor. As shown in FIG. 12, the valence band VB of GaN has three bands of HH, CH, and LH near the bottom of the forbidden band in the vicinity of the electron wave vector k = 0.
[0103]
Here, when there is no distortion in GaN, in wave vector k = 0, the highest energy valence band is the HH band, the next highest energy is the LH band, and the lowest energy is CH. A band. These HH, LH, and CH bands have two p-orbital functions p having polarization in the direction perpendicular to the c-axis when the c-axis direction of the crystal is taken as the Z-axis of the XYZ 3-axis orthogonal coordinates._xAnd p_yAnd orbital function p having polarization in the c-axis direction_zAnd is expressed as follows.
[0104]
HH band; (p_x+ P_y) / √2
LH band; (p_x-P_y) / √2
CH band; p_z
Among these, since the HH band is closest to the bottom of the forbidden band, the emission transition to the HH band is prioritized for spontaneous emission from the conduction band CB to the valence band VB. This HH band consists of a p-orbital coupling state and is symmetric about the c-axis. For this reason, light emission accompanying spontaneous emission of GaN has a polarization state in which the electric field vibrates perpendicularly to the c-axis. Further, the transition probability that causes such polarization is equivalent to the rotation of the vibration direction around the c-axis. Although the above description has been given for GaN, the same applies to hexagonal semiconductor crystals. In addition, since the zinc blende type semiconductor crystal is triaxial isotropic, its optical characteristics are isotropic.
[0105]
In the conventional surface emitting semiconductor laser having a vertical cavity, the active layer 102 is formed perpendicular to the c-axis 104 as shown in FIG. For this reason, the plane of polarization of the oscillation light is the c-plane, and the electric field vibrates perpendicularly to the c-axis 104. As a result, oscillating light that vibrates in any direction in the XY plane is equally generated due to the symmetry of the polarization of spontaneous emission light around the c-axis. Therefore, the polarization plane of the oscillation light is not fixed, and the oscillation becomes unstable.
[0106]
On the other hand, in the present embodiment, as shown in FIG. 10, the active layer 42 has a c-axis in the plane, and thus the traveling direction of the oscillation light is perpendicular to the c-axis. As described above, since the vibration direction of the electric field of spontaneous emission light is perpendicular to the c-axis when HH is at the band edge, the vibration direction of the electric field of the oscillation light is both the c-axis and the traveling direction of the oscillation light. It is uniquely determined in the direction perpendicular to the direction, that is, the direction included in the active layer plane and perpendicular to the c-axis.
[0107]
Therefore, in the surface emitting semiconductor laser of this configuration, the electric field direction of the oscillation light traveling perpendicular to the active layer is fixed in the direction perpendicular to the c-axis. In the surface emitting semiconductor laser, since the resonator is in the film thickness direction, the polarization direction (direction of the electric field vector of light emission) determined by the top band must be in the active layer plane. That is, the polarization of the top band that determines the direction of the electric field vector of light emission needs to be in the active layer plane.
[0108]
Next, the PL (photoluminescence) emission wavelength of the active layer and its polarization plane orientation will be described. FIG. 13 is a diagram showing the PL emission characteristics of the active layer of the present invention when HH is at the band edge. The active layer made of a GaN thin film having a c-axis in the plane used in the semiconductor laser having the first configuration is shown in FIG. The calculated value of PL emission intensity is shown. The parameter in FIG. 13 is the orientation of the polarization plane of the PL light, that is, the angle θ formed by the oscillation direction of the electric field in the active layer surface and the c-axis. The following description is applicable not only to GaN but also to hexagonal semiconductor crystals.
[0109]
As shown in FIG. 13, when the PL emission of the active layer is dispersed with respect to the plane of polarization, that is, the plane of polarization of the electric field and the wavelength, the plane of polarization of the PL light is perpendicular to the c-axis (shown at 90 ° in the figure). In addition, the PL emission spectrum intensity of the active layer is maximized. The wavelength corresponding to the maximum intensity is about 366 nm, and this wavelength corresponds to light emission due to the transition from the conduction band CB to the HH band of the valence band VB as shown in FIG. On the other hand, when the polarization plane of PL light is parallel to the c-axis (indicated by 0 ° in the figure), the emission intensity is small and the maximum wavelength of the spectrum is as short as about 360 nm. This is because by changing the polarization plane of PL emission from a polarization plane perpendicular to the c-axis to a polarization plane parallel to the c-axis, the PL emission changes from emission due to transition to the HH band to emission due to transition to the CH band. Indicates that it has migrated.
[0110]
That is, the transition to the HH band consisting of the p orbital polarized in the x axis direction emits only light whose polarization plane is perpendicular to the c axis, whereas the CH band consists of the p orbital polarized in the z axis direction. This is because light having a polarization plane parallel to the c-axis can be emitted only by transition to the CH band.
In this embodiment, when the polarization plane and wavelength of the photoluminescence light of the semiconductor layer 2 are selected so that the photoluminescence light intensity is maximized, the wavelength of the photoluminescence light and the resonance wavelength of the optical resonator are Match. The energy of light of this wavelength is equal to the photoenergy of light emission accompanying the transition of electrons to the HH band. Therefore, by oscillating at such a wavelength, the oscillation light can be limited only to light emission due to the transition of electrons to the HH band. In this case, since light emission accompanying the transition to the CH band having a polarization plane parallel to the c-axis cannot be mixed, fluctuation of the polarization plane of the oscillation light can be surely prevented.
[0111]
Note that the resonance wavelength does not have to be a wavelength that can strictly obtain the maximum intensity. For example, light emission mainly occurs due to the transition of electrons to the HH band and light emission associated with the transition to the CH band is small, and as a result, oscillation due to the transition of electrons to the HH band to transition to the CH band. It is sufficient that the wavelength is close to the maximum intensity to the extent that fluctuations in the oscillation mode can be suppressed.
[0112]
Next, a case where there is a strain in the active layer will be described.
FIGS. 14A to 14E are diagrams showing the strain dependence of the energy band of GaN, and represent calculated values of the energy of the valence band of GaN having strain. Referring to FIG. 11, the strain in the <0001> direction is ε_z, Strain in the <11-20> direction is ε_x, And <1-100> orientation strain ε_yThe respective strain values are shown with the compression strain state being negative and the tensile strain state being positive.
[0113]
FIG. 14 (a) shows ε_z= 0 and ε_xThis is the case where Ε_yIs an unconstrained state because y is the growth direction. That is, it is the result of calculating the change in energy of the valence band when uniaxial strain is applied in the <11-20> direction of the crystal. Similarly, FIG. 14 (b) shows ε_z0.5% tensile strain is added to the_xIs added. 14 (c) and 14 (d) are respectively ε_z0.5% and 1.0% compression strains are added to the_xIs added. Ε_yThere is no restraint.
[0114]
Referring to FIGS. 14 (a) to 14 (c), the strain ε_xIs compressed and ε_zWhen the compression is 1.0% or more, the X or Z branch consisting of the p orbital becomes a band of the valence band located at the bottom of the forbidden band of the energy band structure (that is, the top of the valence band). Therefore, the emission transition from the conduction band preferentially occurs to the X or Z branch. As a result, when X is above, the polarization perpendicular to the c-axis is the same as the emission without the distortion described above. Only light with a surface oscillates. When Z is the band edge, light oscillating parallel to the c-axis oscillates.
[0115]
On the other hand, referring to FIG._zHas a compression strain of 1% or more and ε_xIs tensile strain, the Z branch has higher energy than the X and Y branches. For this reason, with respect to the transition of electrons from the conduction band, the transition to the Z branch is prioritized, and light is generated that oscillates on a polarization plane parallel to the c axis. As described above, since the surface emitting semiconductor laser has a resonator perpendicular to the active layer, the electric field vector needs to be in the active layer plane. Therefore, the polarization of the top band wave function that determines the electric field vector needs to be in the active layer plane. That is, when the structure as shown in FIG. 11 is manufactured, since the Y direction becomes a resonator, Y does not oscillate in the top band.
[0116]
FIG. 14 (e) shows ε_yIs in an unconstrained state, ε_z= Ε_xIn other words, it is a calculated value of the energy band of the valence band when in-plane biaxial strain is applied in the plane including <0001> and <11-20>. X has the highest energy with respect to the in-plane compressive strain. In this case, oscillation light having an electric field direction in the a-axis direction is generated. When the traveling direction of light faces the polarization direction of the Y branch, oscillation based on transition to the CH band occurs.
[0117]
As described above, when the active layer is strained, the oscillation light has a polarization plane perpendicular to the c-axis and a polarization plane parallel to the c-axis. However, in any case, the plane of polarization of the oscillation light is uniquely determined by the optical axis and the crystal axis direction of the optical resonator, so that the plane of polarization of the surface emitting semiconductor laser is defined in advance and the plane of polarization does not vary.
In the configuration shown in FIG. 10, as the active layer 42, either a multiple quantum well layer (MQW) containing GaN, lnGaN or AIGalnN or a single layer made of GaN, lnGaN or AIGalnN is selected.
[0118]
Further, as the substrate 41 shown in FIG. 10, a SiC substrate having the (11-20) plane as the main surface may be used. Moreover, you may use the SiC substrate which makes a (1-100) plane a main surface, or the sapphire substrate which makes a (1-102) surface a main surface.
Further, a first conductivity type first barrier layer 47, an active layer 42, and a second conductivity type second barrier layer 48 are sequentially grown on the main surface of the substrate 41, thereby forming a double heterojunction. Structure is constructed. Further, when a reflective surface is formed above or below the double heterojunction structure, the first barrier layer 47, the active layer 42, and the second barrier layer 48 can be configured as an optical resonator. By configuring the first and second barrier layers 47 and 48 as AIGaN, and further forming the active layer 42 from a single layer of AIGaN or GaN or InGaN, or a multiple quantum well layer containing such a material. Thus, a surface emitting semiconductor laser having an active layer 42 made of a GaN-based semiconductor having a c-axis in-plane is realized.
[0119]
Next, this embodiment is further demonstrated based on drawing.
The inventor of the present application measures the PL emission spectrum of the active layer 42, so that the relationship between the PL emission wavelength and the polarization plane is such that the emission from the transition from the conduction band to the HH band and the CH band from the conduction band. It was clarified by the following experiment that it can be explained by light emission due to transition to.
[0120]
First, an undoped GaN thin film is deposited on a SiC base slope having a (1-100) plane as a main surface by using a well-known MOVPE (metal organic vapor phase epitaxy) method, and the polarization plane of the photoluminescence light. Photoluminescence light intensity with respect to azimuth and wavelength was measured.
The results are shown in FIGS. FIG. 15 shows a PL emission spectrum of the active layer 42 of the present embodiment. A in FIG. 15 represents photoluminescence light whose electric field vector is perpendicular to the c axis, and B represents photoluminescence light whose electric field vector is parallel to the c axis. Represents. FIG. 16 is a diagram showing the polarization plane dependency of the PL emission intensity of the active layer of the present invention. The maximum intensity of PL emission (hereinafter referred to as “peak intensity”) when the polarization plane is fixed varies depending on the polarization plane. Represents Yoko. In FIG. 16, C represents an experimental value, and D represents a calculated value.
[0121]
Referring to FIG. 15, the intensity A of photoluminescence light having a polarization plane perpendicular to the c-axis has a strong maximum in the vicinity of 366 nm. On the other hand, the intensity B of photoluminescence light having a polarization plane parallel to the c-axis has a weak maximum value near 362 nm, which is a shorter wavelength. The wavelength at which these maximum values appear and the size of the maximum are in good agreement with the calculated values shown in FIG.
[0122]
Next, as shown in FIG. 16, the peak intensity of PL emission is maximum when the polarization plane is perpendicular to the c-axis, and is minimum when the polarization plane is parallel to the c-axis. This experimental value C agrees well with the calculated value D. This means that the calculation result of FIG. 13 reproduces the experiment well.
FIG. 17 is a cross-sectional view of an element that further embodies this embodiment, and the element is a surface emitting semiconductor laser having a vertical resonator.
[0123]
A GaN buffer layer 52 having a thickness of 50 nm and an n-type layer having a thickness of 0.5 μm is grown on the substrate 41, for example, a SiC base slope 41 having a (11-20) plane as a main surface by using the MOVPE method. GaN contact layer 49, Si-doped n-type Al with a thickness of 1 μm_0.1Ga_0.9N barrier layer 47, 0.1 μm thick undoped GaN active layer 42, 1 μm thick Mg doped p-type Al_0.1Ga_0.9An N barrier layer 48 and a p-type GaN contact layer 51 are grown in order from the bottom.
[0124]
Subsequently, 30 nm thick SiO₂Film and 30nm thick Al₂O_ThreeA multilayer film in which 20 films are alternately laminated is deposited, and this multilayer film is patterned by photoresist lithography to form a DBR mirror 43 having a circular or square planar shape. The DBR mirror 43 constitutes a vertical optical resonator having a wavelength of 366 nm with the interface between the n-type contact layer 49 and the substrate 41 as a reflection surface.
[0125]
Next, each layer in a region on one side of the DBR mirror 43 is etched by a reactive ion etching (RIE) method, thereby exposing a part of the n-type contact layer 49. Thereafter, an electrode 50 a made of Ti having a thickness of 100 nm is formed on the exposed surface of the n-type contact layer 49, and an electrode 50 b made of Ni having a thickness of 100 nm is formed on the p-type contact layer 51. Further, the rear surface of the substrate 41 is polished to form an optical window through which light is emitted, thereby completing the surface emitting semiconductor laser.
[0126]
In such a surface emitting semiconductor laser, since the polarization direction is fixed by oscillating light whose vertical direction of the c-axis of the substrate 41 is the electric field oscillation direction, the laser light whose polarization direction is defined in advance is stably oscillated. be able to.
Another example of the surface emitting semiconductor laser according to the present embodiment is an active layer having a multiple quantum well layer structure. On the SiC substrate 41 having the (11-20) plane as the main surface, the MOVPE method is used to grow the AIN buffer layer 42 having a thickness of 0.5 nm and the n-type GaN contact layer 49 having a thickness of 0.5 μm. Si-doped n-type Al with a thickness of 1 μm_0.1Ga_0.9N barrier layer 47, In_0.15Ga_0.85N well layer and ln_0.05Ga_0.95N active layer 42 consisting of multiple quantum well layers with 10 barrier layers alternately stacked, 1 μm thick Mg-doped p-type Al_0.1Ga_0.9An N barrier layer 48 and a p-type GaN contact layer 51 are deposited in this order. Then, a surface emitting semiconductor laser is manufactured through the same process as that of the above-described embodiment.
[0127]
In the surface emitting semiconductor laser described above, the deflection of light is aligned by using a substrate having a (1-100) plane or a (11-20) plane as a main surface. It is possible to employ a structure in which a light receiving element is also mounted on the substrate constituting such a surface emitting semiconductor laser.
18A is a cross-sectional view showing an optical device on which a surface emitting semiconductor laser (light emitting element) and a photodiode (light receiving element) are mounted, and FIG. 18B is a plan view showing the optical device.
[0128]
18 (a) and 18 (b), a 50 nm thick AlN high-temperature buffer layer 54 and a multilayer structure are formed on the (1-100) plane or (11-20) plane, which is the main surface of the SiC substrate 53. Mirror layer 55, 1 μm thick n-type barrier layer 56, 500 nm thick undoped lower light confinement layer 57, undoped MQW active layer 58, p-type barrier layer 59, 500 nm thick undoped upper light A confinement layer 60 and a GaN contact layer 60a having a thickness of 50 nm are sequentially stacked by the MOVPE method.
[0129]
The mirror layer 55 is made of Al with a film thickness of 40 nm._0.4Ga_0.6 N layer and 40nm thick Al_0.1Ga_0.9N layers are alternately stacked for 30 periods. In addition, the MQW active layer 58 has a thickness of 4 nm._0.2Ga_0.8N well layer 4nm thick In_0.05Ga_0.95N It has a structure sandwiched between barrier layers. The lower and upper optical confinement layers 57 and 60 are each formed of GaN.
[0130]
Further, the n-type and p-type barrier layers 56 and 59 are made of Al, respectively._0.1Ga_0.9N type of which the n-type barrier layer 56 has an impurity concentration of 2 × 10¹⁸ atoms / cm^ThreeAnd the p-type barrier layer 59 has an impurity concentration of 1 × 10¹⁷ atoms / cm^ThreeMg is doped. The contact layer 60a on the p-type barrier layer has 1 × 10¹⁸atoms / cm^Three Mg is doped.
[0131]
A plurality of layers from the n-type barrier layer 56 to the p-type barrier layer 59 form an SCH (separate confinement heterostructure) structure.
The compound semiconductor layers stacked in this way are processed into a cross-sectional structure and a planar structure as shown in FIGS. 18A and 18B through multiple times of patterning.
That is, the surface emitting semiconductor laser 66 and the light receiving element 67 have the same shape, and the cylindrical portion 62 having a diameter of 20 μm is formed from the contact layer 60 a to the upper portion of the n-type barrier layer 56. From the lower part to the upper part of the mirror layer 55 is a flange part 63 that spreads outward from the cylindrical part. Since the mirror layer 55 is undoped and has a high resistance, the cylindrical portion 62 and the flange portion 63 are electrically separated from the compound semiconductor layer in other regions via the substantially cylindrical groove 61.
[0132]
A p-side electrode 64 made of annular Ti having a light emission window 64a having a diameter of about 10 μm is connected to the upper surface of the contact layer 60a of the cylindrical portion 62, and the n-type barrier layer 56 of the flange portion 63. An n-side electrode 65 made of Ni that does not contact the cylindrical portion 62 is connected to the cylindrical portion 62.
A resonator in the film thickness direction is formed by the cylindrical portion 62 and the n-type barrier layer 56 therebelow.
[0133]
As shown in FIG. 18B, a plurality of, for example, four photodiodes 67 are formed around the surface emitting semiconductor laser 66 as shown in FIG.
An optical device having such a surface emitting semiconductor laser 66 and a photodiode 67 is attached to, for example, a magneto-optical disk device. In the surface emitting semiconductor laser 66, a positive bias voltage 68 is applied to the p-side electrode 64 and the n-side electrode 65, and a threshold current is supplied even if it is small. In the photodiode 67, a reverse bias voltage is applied to the p-side electrode 64 and the n-side electrode 65, whereby the value of the current flowing through the detection circuit 69 is increased by the amount of light incident on the photodiode 67.
[0134]
In this case, the surface emitting semiconductor laser 66 oscillates and emits light through the window 64a, and irradiates the magneto-optical disk through a diffraction grating and a lens (not shown). The light reflected by the magneto-optical disk is input to the four light receiving elements 67 through the lens and the deflection prism. In the surface emitting semiconductor laser 66, as already described, since the polarization plane is fixed by oscillating light whose vertical direction of the c-axis of the substrate 41 is the vibration direction of the electric field, the polarization plane of the laser light is aligned. Become. Moreover, the laser light reflected by the magneto-optical disk is incident on the photodiode 67 having the same polarization plane.
[0135]
Thus, since the surface emitting semiconductor laser 66 and the photodiode 67 formed on the same substrate have the polarization plane, the writing optical element and the reading optical element of the magneto-optical disk apparatus can be integrated. Therefore, downsizing and manufacturing efficiency of those devices are improved.
As described above, according to the present embodiment, in the vertical cavity surface emitting semiconductor laser having the resonance axis perpendicular to the active layer, the polarization plane of the oscillation light is uniquely defined by the crystal orientation of the active layer. It is possible to provide a vertical cavity surface emitting semiconductor laser having a stable operating characteristic in which the polarization direction of the oscillation light can be determined in advance and with little fluctuation in the polarization direction, which contributes to the improvement of the performance of the information processing apparatus. However, it is big.
[0136]
The active layer 58 may be formed of any one of GaN, InGaN, AlGaN, or AlGaInN, and the barrier layers 57 and 59 made of a semiconductor may be formed of GaN, InGaN, AlGaN, or AlGaInN. However, when the active layer 58 and the barrier layers 57 and 59 are made of the same material system, it is necessary to select a composition ratio in which the active layer 58 has a smaller energy band gap than the barrier layers 57 and 59.
[0137]
In addition, you may use sapphire other than a silicon carbide (SiC) as a material of a board | substrate.
(Third embodiment)
Since the conventional light emitting diode is circularly polarized with respect to the light emitting direction, when it is desired to obtain linearly polarized light, linearly polarized polarized light is obtained by passing a polarizer such as Polaroid.
[0138]
In addition, when displaying a stereoscopic image using linearly polarized polarized light, the right-eye image and the left-eye image are displayed with lights having different polarization directions, and the right-eye polarizer and left-eye images having different polarization directions are displayed. It is recognized as a stereoscopic image when viewed through a polarizer, and in particular, in the case of a large stereoscopic image display device, a projection method is adopted.
However, when obtaining linearly polarized light using a conventional light emitting diode, there is a problem that the number of parts is increased because a polarizer is required, and a process of combining the light emitting diode and the polarizer is necessary. Therefore, there is a problem that the production cost is high.
[0139]
In addition, since circularly polarized light is converted into linearly polarized light that is polarized in a specific direction via a polarizer, light having a polarization direction different from that of the polarizer cannot be extracted and is wasted, resulting in a problem of poor luminous efficiency. .
Furthermore, in the case of a large-sized stereoscopic display device, since it is a projection method, the display image becomes very difficult to see in a bright place as in the case of a conventional projection method display device, and there is a problem that it cannot be used substantially. is there.
[0140]
FIG. 19 is an explanatory diagram of the principle configuration of the present embodiment, and means for solving the problems in the present invention will be described with reference to FIG.
In this embodiment, as illustrated in FIGS. 19A and 19B, in the light emitting diode 70, the c-axis direction of the wurtzite compound semiconductor crystal constituting the light emitting diode 70 is substantially orthogonal to the light emission direction. It is characterized by.
[0141]
Thus, when a wurtzite compound semiconductor such as GaN is used, the wurtzite compound semiconductor is a hexagonal system unlike other III-V compound semiconductors such as GaAs. Light emission in a semiconductor is caused by a transition from a conduction band to an HH (Heavy Hole) or LH (Light Hole) in the valence band. Since these are bands in the a-axis direction, the c-axis direction, that is, the <0001> direction. Since light polarized in the direction perpendicular to the light appears strongly, and light polarized parallel to the c-axis direction hardly appears, linearly polarized light can be obtained without using a polarizer.
[0142]
In the present invention, the c-axis direction being substantially orthogonal to the light emission direction includes an angle in the range of ± 5 °, in addition to the case where the c-axis and the light emission direction with the highest intensity are orthogonal to each other. It is a waste.
Further, the present embodiment is characterized in that the c-axis direction of the wurtzite type compound semiconductor crystal and the crystal growth direction coincide.
[0143]
Crystal growth direction of wurtzite compound semiconductor crystal when {0001} face, {11-20} face, {0001} face of 6H-SiC, or {111} face of spinel is used as the growth substrate Since it is in the c-axis direction, linearly polarized light can be obtained by extracting light parallel to the active layer as shown in FIG. In the present specification, crystal orientations such as “1 bar” or “2 bar” are represented as “−1” or “−2” for convenience.
[0144]
In addition, this embodiment is characterized in that the c-axis direction of the wurtzite compound semiconductor crystal and the crystal growth direction are substantially orthogonal.
When the r-plane of the sapphire substrate, that is, the {1-102} plane, or the 6H-SiC {1-100} plane or {11-20} plane is used as the main surface of the growth substrate, the wurtzite compound Since the crystal growth direction of the semiconductor crystal is substantially parallel to the c-axis direction, linearly polarized light can be obtained by extracting light perpendicular to the active layer as shown in FIG. Since this light becomes polarized light, a large light emitting region can be taken.
[0145]
In addition, the present embodiment is characterized in that the wurtzite type compound semiconductor is a III-V group compound semiconductor made of a group III nitride.
Thus, by using a III-V group compound semiconductor made of a group III nitride such as a GaN-based compound semiconductor having a stable crystal structure as the wurtzite type compound semiconductor, a wide range of 1.9 eV to 6.2 eV is obtained. High-efficiency short wavelength light emission can be obtained over a range, and a desired light emission wavelength can be obtained by adjusting the mixed crystal ratio.
[0146]
Furthermore, in the present embodiment, in the display device, a plurality of light emitting diodes 70 made of a wurtzite compound semiconductor crystal whose light emission direction is substantially orthogonal to the c-axis direction are used. The right-eye light-emitting diode polarized in a certain direction u and the left-eye light-emitting diode polarized in a direction v perpendicular to the polarization direction u of the right-eye light-emitting diode are arranged to obtain a stereoscopic display. And
[0147]
The light emitting diode 70 made of a wurtzite compound semiconductor crystal whose light emission direction is substantially orthogonal to the c-axis direction is polarized perpendicular to the c-axis direction, that is, the a-axis direction, and polarized in the a-axis direction. When the light emitting diode 70 is rotated 90 ° about the light emission direction as an axis, linearly polarized light is polarized perpendicular to the c-axis direction and perpendicular to the polarization direction before being rotated. For the right eye and the other for the left eye, a stereoscopic image can be displayed.
[0148]
In FIG. 19, 69 a and 69 b indicate a pair of terminals connected to the light emitting diode 70.
First example
Here, a first example of the present embodiment will be described with reference to FIGS. 20 (a) and 20 (b) and FIGS. 21 (a) and 21 (b). 20A is a cross-sectional view of the light emitting diode, and FIG. 20B is a cross-sectional view of the light emitting diode as an element. FIG. 21 (a) is a band diagram in the vicinity of the Γ point of a GaN-based compound semiconductor, and FIG. 21 (b) is a diagram showing a polarization angle distribution of emission intensity.
[0149]
First, as shown in FIG. 20A, a thickness of 5 to 5 is formed on a sapphire substrate 71 having a (0001) plane, that is, a c-plane as a main surface by using the MOVPE method (metal organic chemical vapor deposition method). GaN buffer layer 72 of 50 nm, for example 20 nm, n-type Al of thickness 0.5 to 5.0 μm, for example 3.0 μm_0.05 Ga_0.95N layer 73, 10-100 nm thick, for example 50 nm In_0.1Ga_0.9N active layer 74 and p-type Al with a thickness of 0.1 to 1.0 μm, for example 0.5 μm_0.05Ga_0.95N layer 75 is epitaxially grown sequentially.
[0150]
N-type Al_0.05Ga_0.95After etching by reactive ion etching so that part of the N layer 73 is exposed, p-type Al_0.05Ga_0.95An Ni electrode 76 is provided as a p-side electrode on the surface of the N layer 75, and n-type Al_0.05Ga_0.95A Ti electrode 77 is provided as an n-side electrode on the exposed surface of the N layer 73.
In this case, the GaN buffer layer 72 to the p-type Al_0.05Ga_0.95Each layer up to the N layer 75 grows in the c-axis direction of the sapphire substrate 71, so that the c-axis is perpendicular to the main surface of the sapphire substrate 17. The c-axis direction is equivalent to the <0001> direction.
[0151]
The light emitting diode 78 formed as described above is mounted on the stem 79 so that the light emission direction is substantially perpendicular to the c-axis direction, as shown in FIG.
In this case, the stem 79 is mounted via an insulator spacer 80 to prevent a short circuit, and the Ti electrode 77 which is an n-side electrode is wire-bonded to the negative terminal 81 and is also a p-side electrode. The Ni electrode 76 is wire-bonded to the plus terminal 82, and finally resin-molded with an epoxy resin or the like.
[0152]
FIG. 21 (a) is a band diagram in the vicinity of the Γ point of a GaN-based compound semiconductor. As is clear from the figure, the lowest band in terms of energy in view of the holes in the valence band, that is, HH (Heavy Hole). And LH (Light Hole) double degenerate and are separated energetically by the amount of spin-orbit interaction. In addition, a band called CH that is peculiar to GaN compound semiconductors appears.
[0153]
In such a GaN-based compound semiconductor, light emission occurs due to the transition between the Γ point, that is, the conduction band at Kz = 0, the HH band, and the LH band, but the HH band and the LH band at the Γ point. Since this is a band in the a-axis direction, light polarized in a direction perpendicular to the c-axis can be obtained.
FIG. 21 (b) is a diagram showing the polarization angle distribution of the light emission intensity as seen from the light emission direction of the light emitting diode according to the present embodiment of the present invention. The light is parallel to the a axis, that is, light polarized in the a axis direction. However, almost no light polarized by 90 ° with respect to the a-axis, ie, polarized perpendicular to the a-axis can be obtained.
[0154]
Therefore, in the present invention, linearly polarized light polarized in a specific direction can be obtained without using a polarizer or the like, so that the number of parts does not increase and the process of combining a light emitting diode and a polarizer is unnecessary. Therefore, the production cost can be reduced.
In the first example, a sapphire substrate having a (0001) plane as a main surface is used as the substrate, but the substrate is not limited to a sapphire substrate having a (0001) plane as a main surface. 20) A 6H-SiC substrate having a (0001) surface as a main surface or a spinel substrate having a (111) surface as a main surface may be used.
[0155]
  Second example
  Next, a second example of the present invention will be described with reference to FIG. First, as shown in FIG. 22 (a), the (1-102) plane, that is,rA GaN buffer layer 92 having a thickness of 5 to 50 nm, for example, 20 nm, and a n-type Al having a thickness of 0.5 to 5.0 μm, for example, 3.0 μm are formed on a sapphire substrate 91 having a main surface as a surface._0.05Ga_0.95N layer 93, ln with a thickness of 10 to 100 nm, for example 50 nm_0.1Ga_0.9N active layer 94 and p-type Al with a thickness of 0.1 to 1.0 μm, for example 0.5 μm_0.05Ga_0.95N layer 95 is epitaxially grown sequentially.
[0156]
Next, n-type Al is formed by reactive ion etching._0.05Ga_0.95After exposing part of the N layer 93, p-type Al_0.05Ga_0.95A semi-transparent electrode 96 made of very thin Ni is provided on the surface of the N layer 95 as a p-side electrode, and n-type Al_0.05Ga_0.95A Ti electrode 97 is provided on the exposed surface of the N layer 93 as an n-side electrode.
In this case, the GaN buffer layer 92 to the p-type Al_0.05Ga_0.95Since the c-axis direction of each layer of the N layer 95 grows in the direction in the substrate surface of the sapphire substrate 91, the c-axis becomes parallel to the substrate surface.
[0157]
The light emitting diode 84 thus formed is mounted on the stem 85 using a conductive paste so that the light emission direction is substantially perpendicular to the c-axis direction, as shown in FIG.
Then, the Ti electrode 97 that is an n-side electrode is wire-bonded to the minus terminal 86, and the translucent electrode 96 that is the p-side electrode is wire-bonded to the plus terminal 87, and finally sealed with a mold resin 88 such as an epoxy resin. Stop.
[0158]
Also in this case, as in the first example, since the light emission direction is perpendicular to the c-axis, light polarized in the a-axis direction is obtained, and 90 ° polarized with respect to the a-axis, that is, a Almost no light polarized perpendicular to the axis is obtained.
Therefore, in the present invention, linearly polarized light polarized in a specific direction can be obtained without using a polarizer or the like, so that the number of parts does not increase and the process of combining a light emitting diode and a polarizer is unnecessary. become. As a result, the production cost of the light emitting diode is low.
[0159]
In the case of the second example, since it is a surface-emitting type, the light emitting region can be made larger than that in the first example, and a light emission intensity about 10 times that in the first example can be expected.
In the second example, a sapphire substrate having an r-plane as a main surface is used as the substrate, but is not limited to a sapphire substrate having an r-plane as a main surface, and a (1-100) plane is mainly used. A SiC substrate having a plane or a SiC substrate having a (11-20) plane as a main surface may be used.
[0160]
In the second example, a semi-transparent electrode 96 made of a thin Ni film is used as the p-side electrode. However, the semi-transparent electrode 96 is not limited to this, and a Ni electrode having a normal thickness is provided in a mesh shape. Then, light may be extracted from between the meshes.
Third example
Next, a third example of the present invention will be described with reference to FIG.
[0161]
FIG. 23 shows a display panel 90 for stereoscopic image display using the light emitting diodes of the first and second examples. For example, using the light emitting diode of the first example, the light emitting diode 98 arranged so that the polarization direction thereof is in the X direction, and the Y direction arranged by rotating the deflection direction by 90 ° around the optical axis of the light emitting diode 98. A light emitting diode 99 that is polarized in the direction is combined. The X direction and the Y direction are both parallel to the surface of the display panel 90, and the X direction and the Y direction are orthogonal to each other.
[0162]
In this case, one light-emitting diode 98 is used for the right eye, the other light-emitting diode 99 is used for the left eye, and different image signals are input to both, and this light-emitting display image is polarized differently for the right eye and the left eye. A stereoscopic image is displayed by viewing through the child.
In this case, light having a polarization angle in a range of about ± 20 ° with respect to an angle purely parallel to the a-axis direction can be effectively used.
[0163]
Since the display device of the third example is a light-emitting display, it can have higher luminance than a conventional projection-type stereoscopic display device, and therefore can be used in a bright place even when it is enlarged.
In this case, for example, when a 100-inch display panel 90 is configured, the display panel 90 is configured with about 2 million pixels. Then, the arrangement of the light emitting diodes 98 polarized in the X direction and the light emitting diodes 99 polarized in the Y direction may be alternately arranged as shown in FIG. The number of light emitting diodes collected every time may be alternately arranged, and color display is also possible by adjusting the light emission wavelength of each light emitting diode.
[0164]
The plane orientation in the above embodiment is an example, and includes all planes crystallographically equivalent to the plane orientation described.
In each of the above examples, the active layer has an ln composition ratio of 0.1._0.1Ga_0.9N is used, but the mixed crystal ratio is Al depending on the required wavelength._xIn_yGa_1-xyN (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) may be changed, and accordingly, p-type Al sandwiching the active layer_0.05Ga_0.95N layer and n-type Al_0.05Ga_0.95N layer has a larger forbidden bandwidth than active layer_aln_bGa_1-abWhat is necessary is just to comprise by N (0 <= a <= 1, 0 <= b <= 1).
[0165]
Furthermore, when using a sapphire substrate instead of a GaN substrate, the main surface of the substrate is the (11-20) plane.
As described above, according to the present embodiment, when a light-emitting diode is configured using a wurtzite compound semiconductor such as a GaN-based compound semiconductor, the light emission direction is perpendicular to the c-axis of the wurtzite compound semiconductor. By doing so, it is possible to obtain linearly polarized light without using a polarizer, and by using a linearly polarized light emitting diode in this way, a stereoscopic image display device by light emitting display that can be used even in a bright place is provided. Can be configured.
[0166]
【The invention's effect】
As described above, according to the present invention, by selecting the main surface of the crystal substrate, the c-axis of the hexagonal or wurtzite type semiconductor layer formed on the crystal substrate becomes the surface of the semiconductor layer. In order to become non-perpendicular to the crystal substrate, a hexagonal or wurtzite active layer formed on the crystal substrate is subjected to a compressive strain or a tensile strain in the plane direction to give triaxial anisotropy to the active layer. Therefore, the degeneration of the active layer in the valence band can be solved, and the oscillation threshold current of the semiconductor laser having such an active layer can be reduced.
[0167]
In addition, according to such a structure, the plane of polarization of light emitted by the compound semiconductor layer can be uniquely determined, so that a surface emitting semiconductor laser is formed by growing a barrier layer, an active layer, etc. on such a crystal substrate. Then, since the in-plane anisotropy of the active layer is increased and the electric field vector is determined in one direction, polarization can be determined.
Further, when the plane of polarization of the oscillation light of the surface emitting semiconductor laser is uniquely determined, it can be used as a light source for a magneto-optical disk device, and a light receiving element can be easily manufactured on the same substrate as the surface emitting semiconductor laser. become. As a result, the conventional mounting operation of the semiconductor laser and the light receiving element becomes unnecessary, and the downsizing of the light receiving and emitting device can be further promoted.
[0168]
On the other hand, since the polarization direction is determined when the c-axis direction of the wurtzite compound semiconductor crystal constituting the light emitting diode is substantially orthogonal to the light emission direction, a plurality of such light emitting diodes are provided on the display surface of the display device. Each of the pixels is arranged so that a part or all of the pixel is constituted by one light emitting diode, and the polarization directions of adjacent light emitting diodes are different from each other by 90 degrees. The light emitting diodes can be adjacent to each other, and the number of parts can be reduced by omitting the deflector in the stereoscopic display device, thereby reducing the manufacturing cost. Moreover, such a display device brightens the image.
[Brief description of the drawings]
FIG. 1 (a) is a layer structure diagram of a cladding layer and an active layer according to a first embodiment of the present invention, and FIG. 1 (b) is an active layer obtained by the layer structure of FIG. 1 (a). FIG. 1 (c) is a diagram showing the plane orientation of the principal surface of the substrate used in the first embodiment of the present invention.
FIG. 2A is a layer structure view of a first example of a semiconductor laser adopting the layer structure of the first embodiment of the present invention as viewed from the light output end, and FIG. The valence band energy band structure diagram of the active layer obtained by the layer structure of 2 (a), FIG. 2 (c) is the relative energy band structure diagram of the two clad layers and the active layer.
FIG. 3 is a structural diagram when a substrate of a semiconductor laser employing the layer structure of the first embodiment of the present invention is formed from a high resistance material.
FIG. 4 (a) is a layer structure view of a second example of a semiconductor laser employing the layer structure of the first embodiment of the present invention as viewed from the light output end, and FIG. 4 (b) is a diagram of FIG. It is a valence band energy band structure diagram of an active layer obtained by the layer structure of 4 (a).
FIG. 5 (a) is a perspective view of a third example of a semiconductor laser employing the layer structure of the first embodiment of the present invention, and FIG. 5 (b) is a semiconductor laser of FIG. 5 (a). It is a figure which shows the inclination-angle of the small surface with respect to the board | substrate main surface in.
FIG. 6 (a) is a layer structure view of a fourth example of the semiconductor laser employing the layer structure of the first embodiment of the present invention as seen from the light output end, and FIG. It is the layer structure figure which looked at the semiconductor laser at the time of comprising a substrate from a high resistance material in the 4th example from the optical output end.
FIG. 7 is a view showing the completed state of each crystal when a hexagonal semiconductor layer is formed on the main surface of a tetragonal substrate having a c-axis parallel to the main surface in the first embodiment of the present invention. It is a figure which shows the relative relationship of the special form of an image.
FIG. 8 is a diagram showing an X-ray diffraction rocking curve of a hexagonal crystal layer formed on a tetragonal substrate in the first embodiment of the present invention.
FIG. 9 shows tetragonal LiAlO.₂Hexagonal Al on the substrate_xGa_1-xyIn_yIt is an xy coordinate diagram showing the relationship between the composition ratio x and the composition ratio y when growing an N layer.
FIG. 10 is a perspective view showing a layer structure excluding an electrode of a surface emitting laser showing a second embodiment of the present invention.
FIG. 11 is a perspective view showing a special form of a complete image of a crystal of an active layer of a surface emitting laser according to a second embodiment of the present invention.
FIG. 12 is an energy band structure diagram of an active layer of a surface emitting laser according to a second embodiment of the present invention.
FIG. 13 is a graph showing the relationship between the wavelength and PL emission intensity when the angle between the orientation of the polarization plane of the active layer and the c-axis is a parameter in the surface emitting laser according to the second embodiment of the present invention. FIG.
FIGS. 14A to 14E are diagrams showing the crystal strain dependence of the energy band of GaN constituting the active layer in the surface emitting laser according to the second embodiment of the present invention.
FIG. 15 is a graph showing the relationship between the wavelength and PL emission intensity when the angle between the orientation of the polarization plane of the active layer and the c-axis is a parameter in the surface emitting laser according to the second embodiment of the present invention. FIG.
FIG. 16 is a graph showing the relationship between the orientation of the polarization plane of the active layer, the angle formed by the c-axis, and the PL emission intensity in the surface emitting laser according to the second embodiment of the present invention. FIG.
FIG. 17 is a sectional view showing a surface emitting laser according to a second embodiment of the present invention.
FIG. 18 (a) is a cross-sectional view showing an optical device according to a second embodiment of the present invention having a surface emitting laser and a light receiving element, and FIG. 18 (b) is a plan view of the optical device.
FIG. 19 (a) is a diagram showing the basic configuration of an edge-emitting light emitting diode according to a third embodiment of the present invention, and FIG. 19 (b) is a surface emitting type according to the third embodiment of the present invention. It is a fundamental block diagram of the light emitting diode.
FIG. 20 (a) is a layer structure diagram of an edge-emitting light emitting diode according to a third embodiment of the present invention, and FIG. 20 (b) is a cross-sectional view showing a packaged configuration of the light emitting diode. It is.
FIG. 21 (a) is a band diagram of a GaN-based compound semiconductor in the light emitting diode shown in FIG. 20 (a), and FIG. 21 (b) is a graph showing the emission intensity as seen from the light emission direction of the light emitting diode. It is a figure which shows polarization angle distribution.
FIG. 22 (a) is a layer structure diagram of a surface light emitting type light emitting diode according to a third embodiment of the present invention, and FIG. 22 (b) is a sectional view showing a configuration in which the light emitting diode is packaged. is there.
FIG. 23 is a plan view showing a deflection relationship of light emitting diodes used in a display device according to a third embodiment of the present invention.
24 (a) is a cross-sectional view showing a first example of a conventional semiconductor diode, and FIG. 24 (b) is a cross-sectional view showing a second example of a conventional semiconductor diode.
FIGS. 25A and 25B are energy band diagrams of a valence band of a conventional semiconductor diode. FIGS.
FIG. 26 is a perspective view showing a conventional surface emitting semiconductor laser.
[Explanation of symbols]
1 First semiconductor
2 Second semiconductor
3 Third semiconductor
1 l n-type GaN (1-100) substrate
12 n-type Al_0.1Ga_0.9N clad layer
13 n-type GaN light guide layer
14 Ga_0.9In_0.1N active layer
15 p-type GaN light guide layer
16 p-type Al_0.1Ga_0.9N clad layer
17 Ti / Au electrode
18 Ni / Au electrode
21 n-type GaN (1-100) substrate
22 n-type Al_0.4Ga_0.3In_0.3N clad layer
23 n-type Al_0.15Ga_0.65In_0.2N light guide layer
24 Ga_0.9In_0.1N active layer
25 p-type Al_0.15Ga_0.65In_0.2N light guide layer
26 p-type Al_0.4Ga_0.3In_0.3N clad layer
27 Ti / Au electrode
28 Ni / Au electrode
31 n-type GaN (0001) substrate
32 (11-21) Facets
33 Insulating film
34 (1-100) cleavage plane
41 Substrate
42 Active layer
43 DBR mirror
44 c-axis
44a z-polarized light
45 x polarization
46 y polarization
47, 48 barrier layers
49, 51 Contact layer
50a, 50b electrode
52 Buffer layer
53 SiC substrate
54 AlN high temperature buffer layer
55 Mirror layer
56 n-type barrier layer
57 Lower optical confinement layer
58 Active layer
59 p-type barrier layer
60 Upper optical confinement layer
61 groove
62 Cylinder
63 Flange
64 Light emission window
65 n-side electrode
66 Surface emitting semiconductor laser (light emitting device)
67 Photodiode (light receiving element)
68 Power supply
69 Light intensity detection circuit
70 Light emitting diode
71 Sapphire substrate
72 GaN buffer layer
73 n-type Al_0.05Ga_0.95N layers
74 Al_0.1Ga_0.9N active layer
75 p-type Al_0.05Ga_0.95N layers
76 Ni electrode
77 Ti electrode
78 Light Emitting Diode
79 stem
80 Insulator Subaser
81 Negative terminal
82 Positive terminal
83 Mold resin
84 Light-emitting diode
85 stem
86 Negative terminal
87 Positive terminal
88 Mold resin
90 Display panel
91 Sapphire substrate
92 GaN buffer layer
93 n-type Alo.o 5Gao.9 5N layer
94 Al_0.1Ga_0.9N active layer
95 p-type Al_0.05Ga_0.95N layers
96 translucent electrode
97 Ti electrode
98 Light Emitting Diode Polarized in Horizontal Direction
99 Light Emitting Diode Polarized in the Vertical Direction

Claims (25)

A second semiconductor layer formed directly or via the first semiconductor layer on the main surface of the substrate;
An active layer formed on the second semiconductor layer and made of a semiconductor having an energy band gap smaller than that of the second semiconductor layer and having uniaxial anisotropy;
A third semiconductor layer formed on the active layer and having an energy band gap larger than that of the active layer;
A pair of electrodes for passing a current in the film thickness direction through the second semiconductor layer, the active layer, and the third semiconductor layer;
The thickness direction of at least the active layer is up direction der different from the axis of the uniaxial anisotropy,
Does the active layer have a single layer structure composed of one layer of Al _x Ga _{1 -xy} In _y N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) having a thickness of 1 to 20 nm? Or having a multiple quantum well structure composed of multiple layers of Al _x Ga _{1 -xy} In _y N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) each having a thickness of 1 to 20 nm, and the active layer The light emitting portion of the semiconductor light emitting element has a c in-plane strain anisotropy by adding strain in a plane that is not perpendicular to the c-axis indicating anisotropy .   The substrate is SiC The semiconductor light-emitting device according to claim 1, wherein GaN Or AlN A second semiconductor layer formed directly or via the first semiconductor layer on the main surface of the substrate comprising:
  An active layer formed on the second semiconductor layer and made of a semiconductor having an energy band gap smaller than that of the second semiconductor layer and having uniaxial anisotropy;
  A third semiconductor layer formed on the active layer and having an energy band gap larger than that of the active layer;
  A pair of electrodes for passing a current in the film thickness direction through the second semiconductor layer, the active layer, and the third semiconductor layer;
  At least the film thickness direction of the active layer is a direction different from the axis of uniaxial anisotropy,
  The active layer is Al _x Ga _1-x-y In _y N (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and the light emitting portion of the active layer is strained in a plane that is not perpendicular to the c-axis indicating anisotropy and is c-plane A semiconductor light emitting device having internal strain anisotropy.   The main surface of the substrate is a {11-20} plane, a {1-100} plane, or a plane tilted within a range of −5 to +5 degrees from the {11-20} plane or the {1-100} plane The semiconductor light-emitting device according to claim 2, wherein   The main surface of the substrate has an off-angle θ (where 0 ° ≦ θ ≦ with respect to any of the {11-20} plane and the {1-100} plane) Ten The semiconductor light emitting device according to claim 2, wherein the semiconductor light emitting device is a surface that is turned off only by (°).   The main surface of the substrate is a {11-20} plane, a plane tilted within a range of −5 to +5 degrees from the {11-20} plane, or an off angle θ (provided that 0 ° ≦ θ ≦ Ten And the substrate, the second semiconductor layer, the third semiconductor layer, and the active layer are cleaved at a {0001} plane or a {1-100} plane. The semiconductor light emitting device according to claim 2 or 3.   The main surface of the substrate is a {1-100} plane, a plane tilted within a range of −5 to +5 degrees from the {1-100} plane, or an off-angle θ (provided that 0 ° ≦ θ ≦ Ten And the substrate, the second semiconductor layer, the third semiconductor layer, and the active layer are cleaved at a {0001} plane or a {11-20} plane. The semiconductor light emitting device according to claim 2 or 3.   The main surface of the substrate is a {0001} plane, a small surface having a plane orientation intersecting the main surface is provided on the surface of the substrate, and the active layer formed above the small surface emits light The semiconductor light emitting element according to claim 2, wherein the semiconductor light emitting element is a part.   The facet is formed in a plane orientation perpendicular to the {1-100} plane or the {11-20} plane, and the {1-100} plane or the {11-20} plane is a cleavage plane at both ends of the resonator. 9. The semiconductor light emitting device according to claim 8, wherein the semiconductor light emitting device is provided. A second semiconductor layer formed directly on the main surface of the substrate made of sapphire or via the first semiconductor layer;
  An active layer formed on the second semiconductor layer and made of a semiconductor having an energy band gap smaller than that of the second semiconductor layer and having uniaxial anisotropy;
  A third semiconductor layer formed on the active layer and having an energy band gap larger than that of the active layer;
  A pair of electrodes for passing a current in the film thickness direction through the second semiconductor layer, the active layer, and the third semiconductor layer;
  The main surface of the substrate is a {1-102} surface,
  At least the film thickness direction of the active layer is a direction different from the axis of uniaxial anisotropy,
  The active layer is Al _x Ga _1-x-y In _y N (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and the light emitting portion of the active layer is strained in a plane that is not perpendicular to the c-axis indicating anisotropy and is c-plane A semiconductor light emitting device having internal strain anisotropy. LiAlO ₂ A second semiconductor layer formed directly or via the first semiconductor layer on the main surface of the substrate comprising:
  An active layer formed on the second semiconductor layer and made of a semiconductor having an energy band gap smaller than that of the second semiconductor layer and having uniaxial anisotropy;
  A third semiconductor layer formed on the active layer and having an energy band gap larger than that of the active layer;
  A pair of electrodes for passing a current in the film thickness direction through the second semiconductor layer, the active layer, and the third semiconductor layer;
  At least the film thickness direction of the active layer is a direction different from the axis of uniaxial anisotropy,
  The active layer is Al _x Ga _1-x-y In _y N (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and the light emitting portion of the active layer is strained in a plane that is not perpendicular to the c-axis indicating anisotropy and is c-plane A semiconductor light emitting device having internal strain anisotropy.   12. The semiconductor light emitting device according to claim 11, wherein the main surface of the substrate is a {100} plane or a plane off at an angle of -5 degrees to +5 degrees from the {100} plane.   Said Al _x Ga _1-x-y In _y N The composition ratio x and the composition ratio y are in a range between a straight line showing y = 0.214x−0.328 and a straight line showing y = 0.353x−0.209 in the xy coordinates. The semiconductor light-emitting device according to claim 11 or 12.   The second semiconductor layer is Al _u Ga _1-u-v ln _v N (However, 0 ≦ u ≦ 1 , 0 ≦ v ≦ 1 And the third semiconductor layer is composed of Al _w Ga _1-w-z In _z N (However, 0 ≦ w ≦ 1, 0 The semiconductor light-emitting element according to claim 1, wherein ≦ z ≦ 1).   A-axis lattice constant a of the active layer ₁ And the a-axis lattice constant a of the second semiconductor layer and the third semiconductor layer ₂ , A _Three And a ₁ <A ₂ , A ₁ <A _Three And the c-axis lattice constant c of the active layer ₁ And c-axis lattice constant c of the second semiconductor layer and the third semiconductor layer ₂ , C _Three And c ₁ <C ₂ And c ₁ <C _Three The semiconductor light emitting device according to claim 1, wherein the relationship is satisfied.   A-axis lattice constant a of the active layer ₁ And the a-axis lattice constant a of the second semiconductor layer and the third semiconductor layer ₂ , A _Three And a ₁ > A ₂ , A ₁ > A _Three And the c-axis lattice constant c of the active layer ₁ And c-axis lattice constant c of the second semiconductor layer and the third semiconductor layer ₂ , C _Three And c ₁ > C ₂ And c ₁ > C _Three The semiconductor light emitting device according to claim 1, wherein the relationship is satisfied.   A mirror layer is formed below the second semiconductor layer or above the third semiconductor layer, and the mirror layer serves as one end in the film thickness direction of the active layer and the second and third semiconductor layers. The semiconductor light-emitting device according to claim 1, wherein a resonator is formed.   The semiconductor light emitting element according to claim 17, wherein a resonance wavelength of the resonator is a wavelength at which a photoluminescence light intensity is maximum.   The active layer is GaN Or InGaN A first layer of AlGalnN , GaN Or InGaN A multiple quantum well layer having a multilayer structure composed of the second layer of GaN Single layer, InGaN Single layer, and AlGalnN The semiconductor light-emitting element according to claim 1, comprising any one of a single layer.   The second semiconductor layer is of a first conductivity type AlGaN And the third semiconductor layer is of the second conductivity type. AlGaN The semiconductor light-emitting device according to claim 19, comprising: GaN Or AlN A first active layer made of a wurtzite structure crystal formed above the substrate, a first barrier layer containing a first conductivity type impurity formed under the first active layer, A second barrier layer containing a second conductivity type impurity formed on the first active layer, and a current to flow in the film thickness direction of the first active layer and the first and second barrier layers. A surface emitting semiconductor laser having a plurality of electrodes;
  A second active layer made of a wurtzite structure crystal formed above the substrate; a first semiconductor layer containing a first conductivity type impurity formed under the second active layer; and the second active layer A second semiconductor layer containing a second conductivity type impurity formed on the layer, and an electrode for taking out current flowing in the film thickness direction of the second active layer and the first and second semiconductor layers to the outside An optical semiconductor device having a light receiving element electrically isolated from the surface emitting semiconductor laser,
  The first active layer is made of a semiconductor having uniaxial anisotropy, and at least the film thickness direction of the active layer is different from the axis of uniaxial anisotropy, and the active layer has Al _x Ga _1-x-y In _y N (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and the light emitting portion of the active layer is strained in a plane that is not perpendicular to the c-axis indicating anisotropy and is c-plane An optical semiconductor device having internal strain anisotropy.   The optical semiconductor device according to claim 21, wherein the main surface of the substrate is a {1-100} plane or a {11-20} plane.   A substrate made of sapphire whose principal surface is a {1-102} plane, a first active layer made of a wurtzite structure crystal formed above the substrate, and a first active layer formed under the first active layer A first barrier layer including a conductivity type impurity; a second barrier layer including a second conductivity type impurity formed on the first active layer; and the first active layer and the first and second layers A surface emitting semiconductor laser having an electrode for flowing current in the thickness direction of the barrier layer;
  A second active layer made of a wurtzite structure crystal formed above the substrate; a first semiconductor layer containing a first conductivity type impurity formed under the second active layer; and the second active layer Formed on the layer A second semiconductor layer containing the second conductivity type impurity, and an electrode for taking out current flowing in the thickness direction of the second active layer and the first and second semiconductor layers to the outside, An optical semiconductor device having a light receiving element electrically separated from the light emitting semiconductor laser,
  The first active layer is made of a semiconductor having uniaxial anisotropy, and at least the film thickness direction of the active layer is different from the axis of uniaxial anisotropy, and the active layer has Al _x Ga _1-x-y In _y N (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and the light emitting portion of the active layer is strained in a plane that is not perpendicular to the c-axis indicating anisotropy and is c-plane An optical semiconductor device having internal strain anisotropy.   The first active layer and the second active layer are: GaN , InGaN , AlGaN Or AlGaInN The optical semiconductor device according to any one of claims 21 to 23, wherein the optical semiconductor device comprises:   The first barrier layer, the second barrier layer, the first semiconductor layer, and the second semiconductor layer are: GaN , InGaN , AlGaN Or AlGaInN 25. The optical semiconductor device according to any one of claims 21 to 24, comprising:

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