JP4084575B2 - Manufacturing method of surface emitting semiconductor laser element, surface emitting semiconductor laser element formed using the manufacturing method of surface emitting semiconductor laser element, optical transmission module, optical transmitting / receiving module using the surface emitting semiconductor laser element, Optical communication system - Google Patents

Description

【００４２】
図１２において、ＧａＩｎＮＡｓ／ＧａＡｓ２重量子井戸構造に対応して、活性層２０４中に２つの窒素（Ｎ）ピークが見られる。そして、活性層２０４において、酸素（Ｏ）のピークが検出されている。しかし、ＮとＡｌを含まない中間層２０３における酸素濃度は活性層２０４の酸素濃度よりも約１桁低い濃度となっている。
【００４３】
一方、クラッド層２０２，２０５をＧａＩｎＰとし、中間層２０３をＧａＡｓとし、活性層２０４をＧａＩｎＮＡｓ／ＧａＡｓ２重量子井戸構造として構成した素子について、酸素（Ｏ）濃度の深さ方向分布を測定した場合には、活性層２０４中の酸素（Ｏ）濃度はバックグラウンドレベルであった。
【００４４】
すなわち、窒素化合物原料と有機金属Ａｌ原料を用いて、エピタキシャル成長装置により、基板２０１と窒素を含む活性層２０４との間にＡｌを含む半導体層を設けた半導体発光素子を連続的に結晶成長すると、窒素を含む活性層２０４中に酸素が取り込まれることが本願の発明者の実験により明らかとなった。活性層２０４に取り込まれた酸素は非発光再結合準位を形成するため、活性層２０４の発光効率を低下させてしまう。この活性層２０４に取り込まれた酸素が、基板２０１と窒素を含む活性層２０４との間にＡｌを含む半導体層を設けた半導体発光素子における発光効率を低下させる原因であることが新たに判明した。この酸素の起源は、装置内に残留している酸素を含んだ物質、または、窒素化合物原料中に不純物として含まれる酸素を含んだ物質と考えられる。
【００４５】
次に、酸素の取り込まれる原因について検討した。図１３は、図１２と同じ試料のＡｌ濃度の深さ方向分布を示す図である。測定はＳＩＭＳによって行った。次表（表２）に測定条件を示す。
【００４６】
【表２】

【００４７】
図１３から、本来Ａｌ原料を導入していない活性層２０４において、Ａｌが検出されている。しかし、Ａｌを含む半導体層（クラッド層２０２，２０５）に隣接した中間層（ＧａＡｓ層）２０３においては、Ａｌ濃度は活性層よりも約１桁低い濃度となっている。これは、活性層２０４中のＡｌがＡｌを含む半導体層（クラッド層２０２，２０５）から拡散，置換して混入したものではないことを示している。
【００４８】
一方、ＧａＩｎＰのようにＡｌを含まない半導体層上に窒素を含む活性層を成長した場合には、活性層中にＡｌは検出されなかった。
【００４９】
従って、活性層２０４中に検出されたＡｌは、成長室内またはガス供給ラインに残留したＡｌ原料、または、Ａｌ反応物、または、Ａｌ化合物、または、Ａｌが、窒素化合物原料または窒素化合物原料中の不純物（水分，アルコール等）と結合して活性層２０４中に取りこまれたものである。すなわち、窒素化合物原料と有機金属Ａｌ原料を用いて、１台のエピタキシャル成長装置により、基板２０１と窒素を含む活性層２０４との間にＡｌを含む半導体層を設けた半導体発光素子を連続的に結晶成長すると、窒素を含む活性層２０４中に自然にＡｌが取り込まれてしまうことが新たにわかった。
【００５０】
図１２に示した同じ素子における、窒素（Ｎ）濃度と酸素（Ｏ）濃度の深さ方向分布と比較すると、２重量子井戸活性層中の２つの酸素ピークプロファイルは、窒素濃度のピークプロファイルと対応しておらず、図１３のＡｌ濃度プロファイルと対応している。このことから、ＧａＩｎＮＡｓ井戸層中の酸素不純物は、窒素原料と共に取り込まれるというよりも、むしろ井戸層中に取り込まれたＡｌと結合して一緒に取り込まれることがわかった。すなわち、成長室内に残留したＡｌ原料、または、Ａｌ反応物、または、Ａｌ化合物、または、Ａｌが窒素化合物原料と接触すると、Ａｌと窒素化合物原料中に含まれる水分またはガスラインや反応室中に残留する水分などの酸素を含んだ物質とが結合して、活性層２０４中にＡｌと酸素が取り込まれる。この活性層２０４に取り込まれた酸素が活性層２０４の発光効率を低下させることが本願の発明者の実験により初めて明らかとなった。
【００５１】
よって、これを改善するためには、少なくとも成長室内の窒素化合物原料または窒素化合物原料中に含まれる不純物が触れる場所に、Ａｌ原料、または、Ａｌ反応物、または、Ａｌ化合物、またはＡｌが存在しない状態で、窒素を含む活性層を成長することが好ましいことがわかった。
【００５２】
この方法として、Ａｌを含んだ半導体層を成長後、別の反応室に基板を移動させて窒素を含む活性層を成長させることが好ましい。つまり、Ａｌを含んだ半導体層を別のＭＯＣＶＤ成長室またはＭＢＥ成長室等の他の成長室で成長してから窒素を含む活性層をＭＯＣＶＤ成長することが好ましい。この方法によれば、窒素を含む活性層を成長するため成長室に窒素化合物原料を供給したときに、反応室に残留したＡｌ原料、または、Ａｌ反応物、または、Ａｌ化合物、または、Ａｌと、窒素化合物原料または窒素化合物原料中に含まれる不純物及び装置内に残留する酸素を含んだ物質とが反応して、活性層に取り込まれるＡｌ及び酸素不純物の濃度を低減することができる。
【００５３】
例えば、窒素を含む活性層中のＡｌ濃度を１×１０¹⁹ｃｍ^-3以下に低減することにより、室温連続発振が可能となった。さらに、窒素を含む活性層中のＡｌ濃度を２×１０¹⁸ｃｍ^-3以下に低減することにより、Ａｌを含まない半導体層上に形成した場合と同等の発光特性が得られた。
【００５４】
次表（表３）には、ＡｌＧａＡｓをクラッド層（Ａｌを含む層）とし、ＧａＩｎＮＡｓ２重量子井戸構造（窒素を含む層）を活性層としたブロードストライプレーザを試作して閾電流密度を評価した結果が示されている。
【００５５】
【表３】

【００５６】
Ａｌを構成元素として含む半導体層に、窒素を含む活性層を連続的に形成した構造においては、活性層中に２×１０¹⁹ｃｍ^-3以上のＡｌ及び１×１０¹⁸ｃｍ^-3以上の酸素が取り込まれており、閾電流密度は１０ｋＡ／ｃｍ²以上と著しく高い値となった。しかし、活性層中のＡｌ濃度を１×１０¹⁹ｃｍ^-3以下に低減することにより、活性層中の酸素濃度が１×１０¹⁸ｃｍ^-3以下に低減され、閾電流密度２〜３ｋＡ／ｃｍ²でブロードストライプレーザが発振した。ブロードストライプレーザの閾電流密度が数ｋＡ／ｃｍ²以下の活性層品質であれば、室温連続発振が可能である。従って、窒素を含む活性層中のＡｌ濃度を１×１０¹⁹ｃｍ^-3以下に抑制することにより、室温連続発振可能な半導体レーザを提供することが可能となる。
【００５７】
通常のＭＢＥ法のように、有機金属Ａｌ原料と窒素化合物原料を用いない結晶成長方法で作製した場合には、基板と窒素を含む活性層との間にＡｌを含む半導体層を設けた半導体発光素子における著しい発光効率低下については特に報告されていない。
【００５８】
ＭＢＥ法は超減圧（高真空中）で結晶成長が行われるのに対して、ＭＯＣＶＤ法は、通常数１０Ｔｏｒｒから大気圧程度と、ＭＢＥ法に比べて反応室の圧力が高いため、平均自由行程が圧倒的に短く、供給された原料やキャリアガスがガスラインや反応室等で他と接触，反応するためと考えられる。よって、ＭＯＣＶＤ法のように、反応室やガスラインの圧力が高い成長方法の場合、Ａｌを含んだ半導体層を成長後、窒素を含んだ活性層を同じ反応室で成長するのではなく、別の反応室に基板を移動させて成長させることが好ましい。
【００５９】
上記のように本発明は、ＧａＮＡｓ，ＧａＰＮ， ＧａＮＰＡｓ，ＧａＩｎＮＡｓ，ＧａＩｎＮＰ，ＧａＮＡｓＳｂ，ＧａＩｎＮＡｓＳｂ等の窒素を含む活性層の場合に効果があることがわかった。
【００６０】
これにより量産化に有利なＭＯＣＶＤ法で良好な品質のＧａＩｎＮＡｓ面発光型半導体レーザ素子の多層膜構造体を結晶成長できる。
【００６９】
（２）請求項２記載の面発光型半導体レーザ素子の製造方法は、請求項１記載の面発光型半導体レーザ素子の製造方法において、活性層を成長する成長室において、活性層を成長する前にＧａ_ｘＩｎ_{1- ｘ}Ｐ_ｙＡｓ_１−ｙ（０＜ｘ≦１，０＜ｙ≦１）層を成長することを特徴としている。
【００７０】
キャリアが注入される活性領域中を再成長界面とすると、酸化等により非発光再結合が生じ発光効率を落とす恐れがあるが、成長室移動後、活性層を成長する前にＧａ_ｘＩｎ_{1- ｘ}Ｐ_ｙＡｓ_１−ｙ（０＜ｘ≦１，０＜ｙ≦１）層を成長すると、Ｇａ_ｘＩｎ_{1- ｘ}Ｐ_ｙＡｓ_１−ｙ（０＜ｘ≦１，０＜ｙ≦１）よりナローギャップの材料（例えばＧａＡｓ）で活性領域を形成することが可能となるので、上記発光効率低下の心配がなくなり、再成長界面による素子性能への影響をなくすことができる。なお、Ｇａ_ｘＩｎ_{1- ｘ}Ｐ_ｙＡｓ_１−ｙ（０＜ｘ≦１，０＜ｙ≦１）層にはＡｌが含まれておらず、キャリアが主に注入される領域よりワイドギャップであれば良く、ＢＮ、Ｓｂ、等、他のIII-Ｖ族元素が含まれていても良い。
【００７１】
（３）請求項３記載の面発光型半導体レーザ素子の製造方法は、請求項１記載の面発光型半導体レーザ素子の製造方法において、各成長間の界面である再成長界面を半導体分布ブラッグ反射鏡部分とすることを特徴としている。
【００７２】
キャリアが注入される活性領域中を再成長界面とすると、酸化等により非発光再結合が生じ発光効率を落とす恐れがあるが、請求項３のように再成長界面を反射鏡部分に設けると、成長界面と活性領域との間にワイドギャップである低屈折率層が存在するので、上記恐れがなくなり、再成長界面による素子性能への影響をなくすことができる。
【００７３】
（４）請求項４記載の面発光型半導体レーザ素子の製造方法は、請求項１記載の面発光半導体レーザ素子の製造方法において、複数の結晶成長室が真空搬送路等で連結されており、大気中にさらすことなく被成長基板を搬送して結晶成長することを特徴としている。
【００７４】
請求項４の構成によれば、大気にさらすことがないので、大気にさらしたとき生じる再成長界面での酸化膜などの形成を抑制でき、良好な多層膜構造体を成長できる。
【００７９】
（５）請求項５記載の面発光型半導体レーザ素子は、請求項１から４のいずれか一項に記載の製造方法を用いて形成されたことを特徴としている。
【００８０】
すなわち、ＧａＡｓよりも格子定数が大きいＧａＩｎＡｓにＮを添加することで、ＧａＩｎＮＡｓはＧａＡｓに格子整合させることが可能となるとともに、そのバンドギャップが小さくなり、１．３μｍ，１．５５μｍ帯での発光が可能となる。ＧａＡｓ基板格子整合系なので、ワイドギャップのＡｌＧａＡｓやＧａＩｎＰをクラッド層に用いることができる。
【００８１】
さらに、Ｎの添加により上記のようにバンドギャップが小さくなるとともに、伝導帯，価電子帯のエネルギーレベルがともに下がり、ヘテロ接合における伝導帯のバンド不連続が極めて大きくなる結果、レーザの動作電流の温度依存性を極めて小さくできる。
【００８２】
さらに、面発光型半導体レーザ素子は、小型，低消費電力及び２次元集積化による並列伝送に有利である。面発光型半導体レーザ素子は、従来のＧａＩｎＰＡｓ／ＩｎＰ系では実用化に絶え得る性能を得るのは困難であるが、ＧａＩｎＮＡｓ系材料によるとＧａＡｓ基板を用いた０．８５μｍ帯面発光型半導体レーザ素子などで実績のあるＡｌ（Ｇａ）Ａｓ／（Ａｌ）ＧａＡｓ系半導体多層膜分布ブラッグ反射鏡や、ＡｌＡｓの選択酸化による電流狭さく構造が適用できるので、実用化が期待できる。
【００８３】
これを実現するためには、ＧａＩｎＮＡｓ活性層の結晶品質の向上や、多層膜反射鏡の低抵抗化、面発光型半導体レーザ素子としての多層膜構造体の結晶品質や制御性の向上が重要であったが、本発明の請求項１から４による製造方法のいずれかまたは複数を用いることで、低抵抗で駆動電圧が低く、低しきい値電流動作し、温度特性が良い面発光型半導体レーザ素子を容易に実現できる。
【００８４】
（６）請求項６記載の光送信モジュールは、請求項５記載の面発光型半導体レーザ素子を光源として用いたことを特徴としている。上記の如き低抵抗で駆動電圧が低く、低しきい値電流動作し、温度特性が良い面発光型半導体レーザ素子を用いることによって、冷却素子が不要な低コストな光送信モジュールを実現することができる。
【００８５】
（７）請求項７記載の光送受信モジュールは、請求項５記載の面発光型半導体レーザ素子を光源として用いたことを特徴としている。上記の如き低抵抗で駆動電圧が低く、低しきい値電流動作し、温度特性が良い面発光型半導体レーザ素子を用いることによって、冷却素子が不要な低コストな光送受信モジュールを実現することができる。
【００８６】
（８）請求項８記載の光通信システムは、請求項５記載の面発光型半導体レーザ素子を光源として用いたことを特徴としている。上記の如き低抵抗で駆動電圧が低く、低しきい値電流動作し、温度特性が良い面発光型半導体レーザ素子を用いることによって、冷却素子不要な低コストな光ファイバー通信システム，光インターコネクションシステムなどの光通信システムを実現することができる。
【００８７】
【発明の実施の形態】
以下、本発明の実施例を、図面を用いて詳細に説明する。
【００８８】
（第１の実施例）
本発明の第１の実施例に係るＧａＩｎＮＡｓ面発光型半導体レーザ素子について説明する。
【００８９】
図４は、本発明の第１の実施例に係る面発光型半導体レーザ素子の構造を示す図である。図４に示すように、本実施例における面発光型半導体レーザ素子は、２インチの大きさの面方位（１００）のｎ−ＧａＡｓ基板２０上に，それぞれの媒質内における発振波長の１／４倍の厚さでｎ−Ａｌ_xＧａ_1-xＡｓ（ｘ＝０．９）とｎ−ＧａＡｓを交互に３５周期積層した周期構造からなるｎ−半導体分布ブラッグ反射鏡（下部半導体分布ブラッグ反射鏡：単に下部反射鏡ともいう）２１が形成（図４では詳細は省略）されている。その上にアンドープ下部ＧａＡｓスペーサ層２２，３層のＧａ_xＩｎ_1-xＮ_yＡｓ_1-y（ｘ、ｙ）井戸層とＧａＡｓバリア層１５ｎｍからなる多重量子井戸活性層２３，アンドープ上部ＧａＡｓスペーサ層２４が形成されている。
【００９０】
その上にｐ−半導体分布ブラッグ反射鏡（上部半導体分布ブラッグ反射鏡：単に上部反射鏡ともいう）２５が形成されている。上部反射鏡２５は、被選択酸化層となるＡｌＡｓをＡｌＧａＡｓで挟んだ３λ／４厚さの低屈折率層（λ／４−１５ｎｍのＣドープｐ−Ａｌ_xＧａ_1-xＡｓ（ｘ＝０．９）、３０ｎｍのＣドープｐ−ＡｌＡｓ被選択酸化層２５１、２λ／４−１５ｎｍのＣドープのｐ−Ａｌ_xＧａ_1-xＡｓ（ｘ＝０．９））と厚さλ／４のＧａＡｓ（１周期）、及びＣドープのｐ−Ａｌ_xＧａ_1-xＡｓ（ｘ＝０．９）とｐ−ＧａＡｓをそれぞれの媒質内における発振波長の１／４倍の厚さで交互に積層した周期構造 例えば、２５周期から構成されている（図では詳細は省略）。
【００９１】
上部反射鏡２５の最上部のＧａＡｓ層２５２は電極とコンタクトを取るコンタクト層を兼ねている。活性層２３内の井戸層のＩｎ組成ｘは３７％，窒素組成は０．５％とした。井戸層の厚さは７ｎｍとした。ＧａＡｓ基板２０に対して約２．５％の圧縮歪（高歪）を有していた。
【００９２】
本実施例における図４の面発光型半導体レーザ素子の各層の結晶成長は、図５に示すような結晶成長装置で行われる。図５に示すように、本実施例に係る結晶成長装置においては、ＭＯＣＶＤ成長室３１とＭＢＥ成長室３２とが真空搬送路を通して結合されており、反射鏡をＭＯＣＶＤ成長室３１で成長させ、ＧａＩｎＮＡｓ活性層をＭＢＥ成長室３２で成長させるように、ＧａＡｓスペーサ層の途中でＧａＡｓ基板２０を移動した。結晶成長装置におけるＭＯＣＶＤ装置とＭＢＥ装置とをそれぞれ別々とし、ＧａＡｓ基板２０を一度大気中に取り出すようにしてもよいが、望ましくは図５のように一体化して大気にさらさないようにした方がよい。再成長界面に取り込まれてしまう酸素の濃度を低減できるからである。
【００９３】
本実施例において、ＭＢＥ法でのＧａＩｎＮＡｓ成長には固体ソースのＧａ，Ｉｎ，Ａｓ，そしてＮ₂ガスをＲＦラジカルセルで分解した窒素を用いた。またＭＯＣＶＤ装置によるＡｌＧａＡｓ系成長にはＴＭＧ（トリメチルガリウム），ＴＭＩ（トリメチルインジウム），ＡｓＨ₃（アルシン）を用い、キャリアガスにはＨ₂（水素）を用いた。本実施例の素子の活性層のように歪が大きい場合は、非平衡となる低温成長が好ましい。本実施例ではＧａＩｎＮＡｓ層は４３０℃で成長させた。
【００９４】
所定の大きさのメサを少なくともｐ−ＡｌＡｓ被選択酸化層２５１の側面を露出させて形成し、側面の現れたＡｌＡｓを水蒸気で側面から酸化してＡｌ_xＯ_y電流狭さく層２６を形成した。そして次にポリイミド２７でエッチング部を埋め込んで平坦化し、ｐコンタクト層２５２と光出射部２８のある上部反射鏡上のポリイミドを除去し、ｐコンタクト層２５２上の光出射部２８以外にｐ側電極２９を形成し、基板２０の裏面にｎ側電極３０を形成した。
【００９５】
作製した面発光型半導体レーザ素子の発振波長は約１．３μｍであった。ＧａＩｎＮＡｓを活性層に用いたので、ＧａＡｓ基板上に長波長帯の面発光型半導体レーザ素子を形成できた。また、ＡｌとＡｓを主成分とした被選択酸化層の選択酸化により電流狭さくを行ったので、しきい値電流は低かった。被選択酸化層を選択酸化したＡｌ酸化膜からなる電流狭さく層を用いた電流狭さく構造によると、電流狭さく層を活性層に近づけて形成することで電流の広がりを抑えられ、大気に触れない微小領域に効率良くキャリアを閉じ込めることができる。
【００９６】
さらに酸化してＡｌ酸化膜となることで屈折率が小さくなり凸レンズの効果でキャリアの閉じ込められた微小領域に効率良く光を閉じ込めることができ、極めて効率が良くなり、しきい値電流は低減される。また、容易に電流狭さく構造を形成できることから製造コストを低減できる。このように本実施例によれば、低消費電力で低コストの１．３μｍ帯の面発光型半導体レーザ素子を実現できる。なお、移動回数を低減し製造時間を短縮するために、ｎ側多層膜反射鏡２１と活性層２３をＭＢＥ成長室で成長し、ｐ側多層膜反射鏡２５のみをＭＯＣＶＤ成長室で成長することもできる。
【００９７】
（第２の実施例）
本発明の第２の実施例に係るＧａＩｎＮＡｓ面発光型半導体レーザ素子について説明する。本実施例におけるＧａＩｎＮＡｓ面発光型半導体レーザ素子の構造は、第１の実施例と同様に図４の通りであり、第１の実施例と異なる点は結晶成長方法である。本実施例での結晶成長は、２つのＭＯＣＶＤ成長室を有するＭＯＣＶＤ装置で行った。
【００９８】
図６は、本実施例でＧａＩｎＮＡｓ面発光型半導体レーザ素子の結晶成長を行う２つのＭＯＣＶＤ成長室４１，４２を有するＭＯＣＶＤ装置の概要図である。
【００９９】
本実施例では、Ａｌを含んだ層を用いた反射鏡（図４の下部反射鏡２１と上部反射鏡２５）は第１のＭＯＣＶＤ成長室４１で成長させ、窒素を含んだ層を用いたＧａＩｎＮＡｓ活性層（図４のＧａＩｎＮＡｓ活性層２３）は第２のＭＯＣＶＤ成長室４２で成長させた。なお、本実施例では第１のＭＯＣＶＤ成長室４１は縦型反応管を用い、第２のＭＯＣＶＤ成長室４２は横型反応管を用いた。ＧａＡｓスペーサ層２２の成長途中で基板を真空搬送路４３を通して移動して成長させた。
【０１００】
ＭＯＣＶＤ法によるＧａＩｎＮＡｓ活性層２３の原料にはＴＭＧ（トリメチルガリウム），ＴＭＩ（トリメチルインジウム），ＡｓＨ₃（アルシン），そして窒素の原料にはＤＭＨｙ（ジメチルヒドラジン）を用いた。キャリアガスにはＨ₂を用いた。ＤＭＨｙは、低温で分解するので６００℃以下のような低温成長に適しており、特に低温成長の必要な歪みの大きい量子井戸層を成長する場合好ましい原料である。本実施例のＧａＩｎＮＡｓ面発光型半導体レーザ素子の活性層２３のように歪が大きい場合は、非平衡となる低温成長が好ましい。本実施例ではＧａＩｎＮＡｓ層２３は５４０℃で成長させた。また、窒素の原料とＡｌ原料はガスライン中で出会わないようにした。具体的には、図６に示すＯＮ，ＯＦＦバルブの開け閉めで出会わないようにしている。
【０１０１】
第１のＭＯＣＶＤ成長室４１に用いた縦型反応管は均一性に優れており多層膜反射鏡の成長に適している。また、第２のＭＯＣＶＤ成長室４２に用いた横型反応管は層流を作りやすいという特徴がある。また上流と下流が存在するので原料ガスの事前分解などもでき、低温成長化に有利であり、ＧａＩｎＮＡｓの成長に適している。図６のような縦型反応管と横型反応管の組み合わせに限らず、例えば複数の形態の違った縦型反応管の組み合わせ等、複数の成長室を有すると、それぞれの成長層に適した成長室形態にすることができ、様々な多層膜構造体を容易に最適化して成長できるメリットがある。
【０１０２】
本実施例では、全てＭＯＣＶＤ装置を用い、しかも真空搬送路４３で結合しているので、再成長界面の悪影響も無く、スループット良くＧａＩｎＮＡｓ面発光型半導体レーザ素子を製造できた。
【０１０３】
また、再成長界面をＧａＡｓスペーサ層の途中としたが、これに限るものではない（第１の実施例でも同様である）。キャリアが注入される活性領域中を再成長界面とすると酸化等により非発光再結合が生じ発光効率を落とす可能性があるので、反射鏡部分に設けるとよい。例えば反射鏡を構成する高屈折率層と低屈折率層を１ペア２ｎｄ成長（活性領域を成長するステップ）で成長するとよい。
【０１０４】
この場合、Ａｌを含まない層を再成長界面とするのが好ましいので（Ａｌを含む層を再成長界面とすると真空搬送を行っても酸化による悪影響が問題になる場合がある）、高屈折率層をＧａＡｓとし、低屈折率層をＡｌ（Ｇａ）Ａｓとし、ＧａＡｓ層中を再成長界面とするとよい。特にＭＯＣＶＤ法では、ＧａＩｎＮＡｓを成長する反応室でＡｌを含んだ層を成長すると問題が生じる場合（特に、基板と窒素を含む活性層との間にＡｌを含んだ層を成長する場合）があるので、低屈折率層にはＧａ_xＩｎ_1-xＰ_yＡｓ_1-y（０＜ｘ≦１，０＜ｙ≦１）などＡｌを含まない材料を用いることが好ましい。
【０１０５】
この例を図１４に示す。図１４では、活性領域を成長するステップ（２ｎｄ成長）においてＧａＩｎＮＡｓ活性層を成長する前にＧａ_xＩｎ_1-xＰ_yＡｓ_1-y（０＜ｘ≦１，０＜ｙ≦１）層を成長している。また、このＧａ_xＩｎ_1-xＰ_yＡｓ_1-y（０＜ｘ≦１，０＜ｙ≦１）層は、下部反射鏡を構成する低屈折率層のうちの１層となっている。なお、上部反射鏡は図４と同じ構成とし、下部反射鏡の低屈折率層のみがＧａ_xＩｎ_1-xＰ_yＡｓ_1-y（０＜ｘ≦１，０＜ｙ≦１）となっている。活性領域を成長するステップ（２ｎｄ成長）で上部反射鏡を構成する低屈折率層部分（被選択酸化層となるＡｌＡｓをＡｌＧａＡｓで挟んだ３λ／４厚さの低屈折率層）をＡｌＧａＡｓ系材料で構成したが、次回の窒素を含む活性層成長までに充分時間があるので、その間に装置を真空引き等でクリーニングすることでＡｌ及び酸素の活性層への混入を防ぐことができる。なお、このクリーニングは通常でも行うので特に製造工程は増加しない。また、クリーニング方法としては、キャリアガスである水素ガスを供給しながら成長室内の加熱体を加熱すると効率が良い。加熱体を加熱する場合、成長温度より高い温度で行なうのが好ましい。望ましくは、活性層を成長させる成長室は、Ａｌを含んだ材料を成長しない、つまりＡｌ原料を供給しない成長室であると良い。確実にＡｌとともに酸素が窒素を含む活性層に取りこまれるのを防止できるからである。
【０１０６】
（第３の実施例）
図７は、本発明の第３の実施例を示す図で、第１の実施例に係る面発光型半導体レーザ素子と光ファイバーとを組み合わせた光送信モジュールの概要図である。本実施例では１．３μｍ帯ＧａＩｎＮＡｓの面発光型半導体レーザ素子５１からのレーザ光５３が石英系光ファイバー５２に入力され、伝送される。発振波長の異なる複数の面発光型半導体レーザ素子を１次元または２次元にアレイ状に配置して、波長多重送信することにより伝送速度を増大することが可能となる。また、面発光型半導体レーザ素子を１次元または２次元にアレイ状に配置し、それぞれに対応する複数の光ファイバー５２からなる光ファイバー束とを結合させて伝送速度を増大することもできる。
【０１０７】
さらに、本発明による面発光型半導体レーザ素子を光通信システムに用いると、低コストで信頼性が高い光送信モジュールを実現できる他、これを用いた低コスト，高信頼の光通信システムを実現できる。また、ＧａＩｎＮＡｓを用いた面発光型半導体レーザ素子は温度特性が良いこと、及び低しきい値であることにより、発熱が少なく、高温まで冷却なしで使えるシステムを実現できる。
【０１０８】
（第４の実施例）
図８は、本発明の第４の実施例を示す図で、第２の実施例の面発光型半導体レーザ素子と、受信用フォトダイオードと、光ファイバーとを組み合わせた光送受信モジュールの概要図である。
【０１０９】
本発明による面発光型半導体レーザ素子を光通信システムに用いる場合、面発光型半導体レーザ素子は低コストであるので、図８に示すように送信用の面発光型半導体レーザ素子（１．３μｍ帯ＧａＩｎＮＡｓ面発光型半導体レーザ素子）６１と、受信用フォトダイオード６２と、光ファイバー６３とを組み合わせた光送信モジュールを用いた低コスト高信頼性の光通信システムを実現できる。また、本発明に係るＧａＩｎＮＡｓを用いた面発光型半導体レーザ素子の場合，温度特性が良いこと、動作電圧が低いこと、及び、低しきい値であることにより、発熱が少なく、高温まで冷却なしで使えるより低コストのシステムを実現できる。
【０１１０】
さらに、１．３μｍ等の長波長帯で低損失となるフッ素添加ＰＯＦ（プラスチックファイバ）とＧａＩｎＮＡｓを活性層に用いた面発光型レーザとを組み合わせるとファイバが低コストであること、ファイバの径が大きくてファイバとのカップリングが容易で実装コストを低減できることから、極めて低コストのモジュールを実現できる。
【０１１１】
本発明に係る面発光型半導体レーザ素子を用いた光通信システムとしては光ファイバーを用いた長距離通信に用いることができるのみならず、ＬＡＮ（Local Area Network）などのコンピュータ等の機器間伝送、さらにはボード間のデータ伝送、ボード内のＬＳＩ間、ＬＳＩ内の素子間等、光インターコネクションとして短距離通信に用いることができる。
【０１１２】
近年ＬＳＩ等の処理性能は向上しているが、これらを接続する部分の伝送速度が今後ボトルネックとなる。システム内の信号接続を従来の電気接続から光インターコネクトに変えると、例えばコンピュータシステムのボード間、ボード内のＬＳＩ間、ＬＳＩ内の素子間等を本発明に係る光送信モジュールや光送受信モジュールを用いて接続すると、超高速コンピュータシステムが可能となる。
【０１１３】
また、複数のコンピュータシステム等を本発明に係る光送信モジュールや光送受信モジュールを用いて接続した場合、超高速ネットワークシステムが構築できる。特に面発光型半導体レーザ素子は端面発光型レーザに比べて桁違いに低消費電力化でき２次元アレイ化が容易なので並列伝送型の光通信システムに適している。
【０１１４】
以上説明したように、ＧａＩｎＮＡｓ系材料によるとＧａＡｓ基板を用いた０．８５μｍ帯面発光型半導体レーザ素子などで実績のあるＡｌ（Ｇａ）Ａｓ／（Ａｌ）ＧａＡｓ系半導体多層膜分布ブラッグ反射鏡や、ＡｌＡｓの選択酸化による電流狭さく構造が適用でき、第１の実施例や第２の実施例または後述の第５の実施例のように面発光型半導体レーザ素子を製造することにより、ＧａＩｎＮＡｓ活性層の結晶品質の向上や、多層膜反射鏡の低抵抗化、面発光型半導体レーザ素子としての多層膜構造体の結晶品質や制御性の向上ができるので、実用レベルの高性能の１．３μｍ帯等の長波長帯面発光型半導体レーザ素子を実現でき、さらにこれらの素子を用いると、冷却素子不要で低コストの光ファイバー通信システム、光インターコネクションシステムなどの光通信システムを実現することができる。
【０１１５】
（第５の実施例）
図１５は第５の実施例の面発光型半導体レーザ素子の構成例を示す図である。なお、活性領域付近の拡大図も示されている。第２の実施例の素子（図１４）との違いはＧａ_ｘＩｎ_{1- ｘ}Ｐ_ｙＡｓ_１−ｙ（０＜ｘ≦１，０＜ｙ≦１）層（第二スペーサ層）が共振器の中にあることである。本実施例では共振器部の厚さは１波長分の厚さとなっている。共振器部は３層からなるＧａＩｎＮＡｓ量子井戸層とＧａＡｓ障壁層とからなる活性層と、ＧａＡｓを第一スペーサ層、Ｇａ_ｘＩｎ_{1- ｘ}Ｐ_ｙＡｓ_１−ｙ（０＜ｘ≦１，０＜ｙ１）層を第二スペーサ層とした構造となっている。Ｇａ_ｘＩｎ_{1- ｘ}Ｐ_ｙＡｓ_１−ｙ（０＜ｘ≦１，０＜ｙ≦１）層は、ＧａＡｓ層よりバンドギャップが大きいので、キャリアが注入される活性領域は実質ＧａＡｓ第一スペーサ層までとなり、実施例２の素子と同様な効果が得られる。
【０１１６】
なお、成長室を移すための成長中断界面はＧａ_xＩｎ_1-xＰ_yＡｓ_1-y（０＜ｘ≦１，０＜ｙ≦１）層の途中に設けたが、Ｇａ_xＩｎ_1-xＰ_yＡｓ_1-y（０＜ｘ≦１，０＜ｙ≦１）層とＡｌを含んだ層との間にＧａＡｓ層を設けてその層の途中などで行うこともできる。
【０１１７】
また成長装置としてはＭＯＣＶＤ反応室とＭＢＥ反応室が真空搬送路で結合された装置を用いることもできる。この場合、ｎ側の下部反射鏡をＭＢＥ反応室で成長し、窒素を含んだ活性層とｐ側反射鏡は連続してＭＯＣＶＤ成長室で成長することができる。このときには、基板の成長室間の移動は１回で済むので短時間で成長できる。この場合でもＭＯＣＶＤ成長による窒素を含んだ活性層中の酸素の取り込まれを低減できる。またｐ側反射鏡の抵抗を低減できる。
【０１１８】
【発明の効果】
本発明によれば、高品質で実用レベルのＧａＩｎＮＡｓ面発光型半導体レーザ素子の製造方法（請求項１〜４）、該面発光型半導体レーザ素子の製造方法を用いて形成した面発光型半導体レーザ素子（請求項５）、該面発光型半導体レーザ素子を用いた光送信モジュール（請求項６）、光送受信モジュール（請求項７）、光通信システム（請求項８）を実現できる。
【０１１９】
さらに詳しくは、
（１）請求項１記載の面発光型半導体レーザ素子の製造方法によれば、半導体多層膜反射鏡をＭＯＣＶＤ法で、ＧａＩｎＮＡｓ活性層を含む活性領域をＭＢＥ法で成長することにより、容易に低抵抗の多層膜反射鏡を形成でき、また容易に高品質のＧａＩｎＮＡｓ活性層を形成できる。
【０１２４】
（２）請求項２記載の面発光型半導体レーザ素子の製造方法によれば、活性層を成長するステップにおいて、活性層を成長する前にＧａ_ｘＩｎ_{1- ｘ}Ｐ_ｙＡｓ_１−ｙ（０＜ｘ≦１，０＜ｙ≦１）層を成長することにより、再成長界面による素子性能への影響をなくすことができる。
【０１２５】
（３）請求項３記載の面発光型半導体レーザ素子の製造方法によれば、各成長間の界面である再成長界面を半導体分布ブラッグ反射鏡部分とすることにより、再成長界面による素子性能への影響をなくすことができる。
【０１２６】
（４）請求項４記載の面発光型半導体レーザ素子の製造方法によれば、複数の結晶成長室が真空搬送路等で連結されており、大気中にさらすことなく被成長基板を搬送して結晶成長するようにしたことにより、大気にさらしたときに生じる再成長界面での酸化膜などの形成を抑制でき、良好な多層膜構造体を成長できる。
【０１２９】
（５）請求項５記載の面発光半導体レーザ素子は、請求項１から４のいずれか一項に記載の製造方法を用いて形成されたものであり、低抵抗で駆動電圧が低く、低しきい値電流で動作し、温度特性が良い面発光型半導体レーザ素子を容易に実現できる。
【０１３０】
（６）請求項６記載の光送信モジュールは、請求項５記載の面発光型半導体レーザ素子を光源として用いたものであり、冷却素子が不要な低コストな光送信モジュールを実現することができる。
【０１３１】
（７）請求項７記載の光送受信モジュールは、請求項５記載の面発光型半導体レーザ素子を光源として用いたものであり、冷却素子が不要な低コストな光送受信モジュールを実現することができる。
【０１３２】
（８）請求項８記載の光通信システムは、請求項５記載の面発光型半導体レーザ素子を光源として用いたものであり、冷却素子不要な低コストな光ファイバー通信システム，光インターコネクションシステムなどの光通信システムを実現することができる。
【図面の簡単な説明】
【図１】ＭＯＣＶＤ装置の概略図である。
【図２】ＭＢＥ装置の概略図である。
【図３】Ａｌ組成２０％のＡｌＧａＩｎＮＰとＧａＩｎＮＰを成長したときのＶ族原料に対する窒素原料である[DMHy]/([PH3]+[DMHy])と窒素取りこまれ量の関係を示す図である。
【図４】本発明の第１の実施例に係る面発光型半導体レーザ素子の構造を示す図である。
【図５】本発明の第１の実施例に係る結晶成長装置の概念図である。
【図６】本発明の第２の実施例に係る２つのＭＯＣＶＤ成長室を有するＭＯＣＶＤ装置の概要図である。
【図７】本発明の第３の実施例に係る、面発光型半導体レーザ素子とファイバーとを組み合わせた光送信モジュールの概要図である。
【図８】本発明の第４の実施例に係る、面発光型半導体レーザ素子と受信用フォトダイオードと光ファイバーとを組み合わせた光送受信モジュールの概要図である。
【図９】しきい値電流密度の窒素組成依存性を示す図である。
【図１０】本願の発明者のＭＯＣＶＤ装置で作製したＧａＩｎＮＡｓ量子井戸層とＧａＡｓバリア層とからなるＧａＩｎＮＡｓ／ＧａＡｓ ２重量子井戸構造からなる活性層からの室温フォトルミネッセンススペクトルを示す図である。
【図１１】半導体発光素子の試料構造を示す図である。
【図１２】図１１に示した半導体発光素子の一例として、クラッド層をＡｌＧａＡｓとし、中間層をＧａＡｓとし、活性層をＧａＩｎＮＡｓ／ＧａＡｓ２重量子井戸構造として構成した素子を１台のエピタキシャル成長装置（ＭＯＣＶＤ装置）を用いて形成したときの、窒素（Ｎ）濃度と酸素（Ｏ）濃度の深さ方向分布を示す図である。
【図１３】図１２と同じ試料のＡｌ濃度の深さ方向分布を示す図である。
【図１４】第２の実施例の面発光型半導体レーザの構造を示す図である。
【図１５】第５の実施例の面発光型半導体レーザの構造を示す図である。
【符号の説明】
１１ 基板出し入れ口
１２ 成長室（反応室）
１３ 水素精製機
１４ 液体、固体バブラー
１５ ガスシリンダー
１６ バルブ
Ａ 原料ガス供給部
Ｂ 加熱部
Ｃ 排気部
２０ ｎ−ＧａＡｓ基板
２１ ｎ−半導体分布ブラッグ反射鏡（下部半導体分布ブラッグ反射鏡）
２２ 下部ＧａＡｓスペーサ層
２３ 多重量子井戸活性層
２４ 上部ＧａＡｓスペーサ層
２５ ｐ−半導体分布ブラッグ反射鏡（上部半導体分布ブラッグ反射鏡）
２５１ 被選択酸化層
２５２ ｐ−ＧａＡｓ層（コンタクト層）
２６ Ａｌ_xＯ_y電流狭さく部
２７ ポリイミド
２８ 光出射部
２９ ｐ側電極
３０ ｎ側電極
３１ ＭＯＣＶＤ成長室
３２ ＭＢＥ成長室
４１ 第１のＭＯＣＶＤ成長室
４２ 第２のＭＯＣＶＤ成長室
４３ 真空搬送路
４４ 基板出し入れ室
４５ ガス供給部
５１ １．３μｍ帯ＧａＩｎＮＡｓの面発光型半導体レーザ素子
５２ 石英系光光ファイバー
５３，６４ レーザ光
６１ １．３μｍ帯ＧａＩｎＮＡｓ面発光型半導体レーザ素子
６２ 受信用フォトダイオード
６３ 光ファイバー
２０１ ＧａＡｓ基板
２０２ 下部クラッド層
２０３ 中間層
２０４ 活性層
２０５ 上部クラッド層[0001]
BACKGROUND OF THE INVENTION
  The present invention mainly relates to a semiconductor laser technology for optical communication, and in particular, a method for manufacturing a surface emitting semiconductor laser element.And method for manufacturing the surface emitting semiconductor laser elementThe present invention relates to a surface-emitting type semiconductor laser device formed by using the above, an optical transmission module, an optical transmission / reception module, and an optical communication system using the surface-emitting type semiconductor laser device.
[0002]
[Prior art]
In recent years, the amount of information handled as seen in the explosive spread of the Internet has increased dramatically, and is expected to accelerate further in the future. For this reason, optical fiber is introduced not only in trunk lines but also in subscriber lines such as homes and offices and transmission lines close to users such as LAN (Local Area Network), as well as between each equipment and within the equipment. Large-capacity information transmission technology is extremely important.
[0003]
In order to increase the capacity of the optical network and the optical wiring without being concerned about the distance at low cost, the transmission loss of the silica fiber as the light source is small and the matching is good in the 1.3 μm band and the 1.55 μm band. A surface emitting semiconductor laser element (VCSEL: Vertical Cavity Surface Emitting Laser) is very promising. Surface-emitting semiconductor laser devices are suitable for low cost, low power consumption, miniaturization, and two-dimensional integration compared to edge-emitting lasers. The 0.85 μm band that can actually be formed on a GaAs substrate is already a high-speed LAN. It has been put to practical use in some 1 Gbit / s Ethernet.
[0004]
In the 1.3 μm band, the material system on the InP substrate is common, and the edge emitting laser has a track record. However, this conventional long-wavelength semiconductor laser has a major drawback that the operating current increases three times as the environmental temperature is changed from room temperature to 80 ° C. In addition, since there is no material suitable for a reflecting mirror in a surface-emitting type semiconductor laser element, it is difficult to achieve high performance, and a practical level of characteristics has not been obtained.
[0005]
For this reason, the current highest performance is obtained by the structure in which the active layer on the InP substrate and the AlGaAs / GaAs reflector on the GaAs substrate are directly bonded (V. Jayaraman, JC Geske, MH MacDougal FH Peters, TD Lowes, and TT Char, Electron. Lett., 34, (14), pp. 1405-1406, 1998.).
[0006]
However, this method is unavoidable in terms of mass productivity because of the inevitable increase in cost. Therefore, recently, a material system capable of forming a 1.3 μm band on a GaAs substrate has attracted attention, and (Ga) InAs quantum dots, GaAsSb and GaInNAs (for example, see JP-A-6-37355) have been studied. GaInNAs, which is a new material, has attracted attention as a material that can make the temperature dependence of laser characteristics extremely small.
[0007]
Since the band gap of the GaInNAs semiconductor laser on the GaAs substrate is reduced by adding nitrogen, a long wavelength band such as a 1.3 μm band can be formed on the GaAs substrate. When the In composition is 10%, the nitrogen composition is about 3% and a 1.3 μm band can be formed. However, there is a problem that the threshold current density rapidly increases as the nitrogen composition increases. FIG. 9 is a graph showing the nitrogen composition dependency of the threshold current density. The horizontal axis represents the nitrogen composition ratio (%), and the vertical axis represents the threshold current density. The reason why the threshold current density rapidly increases as the nitrogen composition increases is that the crystallinity of the GaInNAs layer deteriorates as the nitrogen composition increases.
[0008]
For this reason, the issue is how to grow GaInNAs with high quality. As such GaInNAs crystal growth methods, MOCVD (Metal Organic Chemical Vapor Deposition) and MBE (Molecular Beam Epitaxy) have been tried.
[0009]
The MOCVD method does not require a high vacuum like the MBE method. In the MBE method, the material supply is controlled by changing the cell temperature, whereas the MOCVD method only needs to control the material gas flow rate. Since the speed can be increased and the throughput can be easily increased, the growth method is extremely suitable for mass production. The MOCVD method is used in all production of 0.85 μm band surface emitting semiconductor laser devices that are actually put into practical use (in most cases).
[0010]
Recently, many reports of semiconductor lasers using this new GaInNAs-based material have been reported. However, most of these cases were based on the MBE method. Very recently, surface emitting semiconductor laser elements have also been reported. First report by Hitachi (1.18μm) in 1998 (MC Larson, M. Kondow, T. Kitatani, K. Nakahara, K. Tamura, H. Inoue, and K. Uomi, IEEE Photonics Technol. Lett., 10, pp. 188-190, 1998.), reported in 2000 by Stanford (1.215 μm), Sandia + Cielo (1.294 μm), Tokyo Tech + Ricoh (1.262 μm), and Infineon (1.285 μm).
[0011]
[Problems to be solved by the invention]
However, this new GaInNAs surface emitting semiconductor laser device has only one report of MOCVD method suitable for mass production, and all others have been grown by MBE method and have sufficient characteristics. It is not a thing. In particular, those grown by the MBE method have a very high resistance of the p-side multilayer reflector, so a method that does not use the p-side multilayer reflector as a current path is used, but eventually the operating voltage increases. It had problems such as. A manufacturing method and manufacturing apparatus for a novel GaInNAs-based surface-emitting type semiconductor laser device that has solved such a problem has not yet been established.
[0012]
  The present invention improves a manufacturing technology of a surface emitting semiconductor laser device, and a method for manufacturing a GaInNAs surface emitting semiconductor laser device having a high quality and a practical level.4)And method for manufacturing the surface emitting semiconductor laser elementSurface emitting semiconductor laser element formed usingClaim 5), An optical transmission module using the surface emitting semiconductor laser element (Claim 6), Optical transceiver module (Claim 7), Optical communication system (Claim 8).
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is characterized by adopting the following configuration. Hereinafter, each claim will be described in detail.
[0014]
(1) A method of manufacturing a surface-emitting type semiconductor laser device according to claim 1 is for obtaining an active region including at least one active layer (23) for generating laser light on a semiconductor substrate, and laser light. Has a resonator structure including reflectors (21, 25) provided on the upper and lower portions of the active layer (23), and reflectors (21, 25) provided on the upper and lower portions of the active layer (23). ) Is a p-side semiconductor reflecting mirror, the active layer (23) contains Ga, In, N, As as main components, and at least the p-side semiconductor of the reflecting mirrors. The reflector includes a semiconductor distributed Bragg reflector that periodically changes the refractive index and reflects incident light by light wave interference, and the active layer (23) is grown by the MBE method, and at least the p-side of the reflector Semiconductor reflector is MOCVD It is characterized in that in grown.
[0015]
First, two growth methods of MOCVD method and MBE method described in claim 1 will be described with reference to FIG. 1 and FIG. The MOCVD method (Metal Organic Chemical Vapor Deposition) is a vapor phase growth method that uses at least a part of an organic metal raw material to grow crystals by thermal decomposition of the raw material gas and surface reaction with the substrate to be grown. is there.
[0016]
FIG. 1 is a schematic view of an MOCVD apparatus. As shown in the figure, the MOCVD apparatus includes a source gas supply unit A to which source gas is supplied, a heating means (not shown) for heating the growth substrate, a heating unit (heating body) B, a reaction This is a configuration having an exhaust part C (exhaust pump or the like) for exhausting the exhausted gas. Usually, the substrate is introduced from the substrate loading / unloading port 11 so that air does not enter the growth chamber (reaction chamber) 12 and is transferred to the growth chamber (reaction chamber) 12 after being evacuated by the exhaust part C.
[0017]
As the pressure in the growth chamber 12, a reduced pressure of about 50 Torr to 100 Torr is often used. As the raw material, an organic metal such as Ga: TMG (trimethylgallium), TEG (triethylgallium), Al: TMA (trimethylaluminum), or In: TMI (trimethylindium) is used as a group III raw material. In addition, group V raw materials include AsH_Three(Arsine), TBA (tertiary butyl arsine), PH_ThreeHydride gas and organic compounds such as (phosphine) and TBP (tertiarybutylarsine) are generally used.
[0018]
Carrier gas includes hydrogen gas (H₂) Is usually used, and is usually supplied after removing impurities through a hydrogen purifier. An organic compound such as DMHy (dimethylhydrazine) or MMHy (monomethylhydrazine) can be used as a raw material for nitrogen. The raw material is not limited to this. Liquid or solid raw materials such as organic metals and organic nitrogen compounds are supplied by bubbling through a carrier gas in a bubbler 14. The hydride is supplied in a gas cylinder 15. FIG. 1 shows an example in which there are two types of bubblers 14 (liquid and solid raw material bubblers # 1, # 2) and gas cylinders 15 (gas cylinders # 1, # 2).
[0019]
The path of the source gas is switched by the valve 16, and necessary materials and compositions are grown by controlling the supply amount with an MFC (mass flow controller) or the like. In general, dummy lines (see dummy lines # 1 and # 2 in the figure) are provided so that the gas flow is not disturbed as much as possible. The growth thickness is controlled by the supply time of the source gas. As a result, the necessary structure can be grown, so the throughput is good and the method is suitable for mass production.
[0020]
Next, the MBE method will be described. MBE (Molecular Beam Epitaxy) is a type of vacuum deposition method, in which source molecules and atoms released from a source cell reach a heated substrate in a high-vacuum chamber and adsorb to the crystal lattice. It is a method of growing by being embedded.
[0021]
The MBE method has various names due to differences in raw material supply methods. Solid source (SS) -MBE using a solid source, organometallic (MO) -MBE using an organic metal as a group III material, gas source (GS) -MBE using a hydride as a group V material, an organic metal and a hydride There is CBE (Chemical Beam Epitaxy) used. As a raw material for nitrogen, a radical cell is generally used, and N₂Is decomposed and activated.
[0022]
FIG. 2 is a schematic diagram of the MBE apparatus. FIG. 2 shows an example in which two types of solid sources (in the figure, raw material molecular beam cell 1, raw material molecular beam cell 2) and nitrogen raw material (in the figure, nitrogen radical cell) are used. In particular, since solid source MBE does not contain carbon and hydrogen as raw materials, it can be grown with a low impurity concentration. Since the vacuum is high in principle, the raw material supply cannot be increased. Increasing it has the disadvantage of placing a burden on the exhaust system. Although a high vacuum exhaust system exhaust pump is required, the throughput is poor because the exhaust system is burdened and easily broken to remove residual raw materials in the MBE chamber.
[0023]
Here, it has been found that the MBE method is easier to improve the quality of GaInNAs than the MOCVD method. GaInNAs is a material with extremely strong immiscibility, and requires non-equilibrium growth such as low-temperature growth. In the MOCVD method, a compound gas is used for each raw material, and the substrate to be grown is heated and grown by utilizing the thermal decomposition of the raw material gas and the substrate surface reaction. Therefore, growth at the decomposition temperature or higher is necessary. Actually, the MBE method can grow at a low temperature of about 100 ° C. as compared with the MOCVD method. In addition, the raw material in the MOCVD method includes carbon (C) and hydrogen (H), and it is considered that impurities are incorporated into the film as impurities and the crystallinity is easily lowered.
[0024]
On the other hand, a surface emitting semiconductor laser element is configured by sandwiching an active region including at least one active layer that generates laser light between semiconductor multilayer reflectors. Whereas the thickness of the crystal growth layer of the edge-emitting laser is about 3 μm, for example, a 1.3 μm wavelength band-emitting semiconductor laser element requires a thickness exceeding 10 μm.
[0025]
The thickness of the active region is usually very small compared to the whole (10% or less), and most of them are layers constituting the multilayer mirror. The semiconductor multilayer mirror is formed by alternately laminating a low refractive index layer and a high refractive index layer (for example, 20 to 40) with a thickness (1/4) of the oscillation wavelength in each medium (λ / 4 thickness). Pair) is formed.
[0026]
In a surface emitting semiconductor laser device on a GaAs substrate, an AlGaAs-based material is used, and an Al composition is changed to form a low refractive index layer (Al composition large) and a high refractive index layer (Al composition small). In practice, however, the resistance is increased particularly on the p side due to the hetero-barrier of each layer. Therefore, an interlayer having an Al composition between the low refractive index layer and the high refractive index layer is inserted to reflect the multilayer film. The resistance of the mirror is reduced.
[0027]
As described above, the surface emitting semiconductor laser element has to grow semiconductor layers having different compositions as many as 100 layers, and in addition, between the low refractive index layer and the high refractive index layer of the multilayer reflector. It is an element that needs to control the amount of raw material supply instantaneously, such as providing a layer. However, in the MBE method, the supply amount is controlled by changing the temperature of the raw material cell, and the composition cannot be controlled flexibly. Therefore, it is difficult to reduce the resistance of the semiconductor multilayer mirror grown by the MBE method, and the operating voltage is high.
[0028]
In addition, since the MBE method requires a high vacuum, the raw material supply amount cannot be increased, the growth rate is about 1 μm / h, and growth for changing the raw material supply amount to grow a thickness of 10 μm. Even if there is no interruption time, it takes at least 10 hours.
[0029]
On the other hand, the MOCVD method only needs to control the raw material gas flow rate, can control the composition instantaneously, does not require a high vacuum like the MBE method, and can easily increase the growth rate to 3 μm / h or more, for example. Since the throughput can be increased, it has been found that this is a growth method extremely suitable for mass production, and that it is easier to grow the semiconductor multilayer mirror by the MOCVD method.
[0030]
Therefore, in the present invention, the lower semiconductor multilayer mirror is grown by the MOCVD method in the first first step, the active region including the GaInNAs active layer is grown by the MBE method in the second step, and the upper multilayer reflector is grown in the third step. The film reflector was grown by the MOCVD method. As a result, a low-resistance multilayer mirror can be easily formed, and a high-quality GaInNAs active layer can be easily formed.
[0031]
In addition, since the growth by the MBE method is very small (about 1 μm or less), the burden on the apparatus is small and the failure is difficult, and the time required for the growth can be shortened as compared with the conventional method in which everything is grown by the MBE method. effective. However, the n-side (n-side semiconductor) multilayer reflector has a carrier concentration of 1 × 10 even by alternately laminating low refractive index layers and high refractive index layers.¹⁸cm^-3Since the resistance can be easily lowered by simply increasing the concentration to a certain level without special measures, only the multilayer mirror on the p side (p side semiconductor) may be grown by the MOCVD method. According to this, the growth process can be simplified.
[0033]
  Also,The inventor of the present application stated that one of the reasons why high quality of GaInNAs is easier in the MBE method than in the MOCVD method is that the reaction between the nitrogen source and the Al source is very strong in the MOCVD method. It has been found that the following problems may occur when forming a structure including a layer containing nitrogen and a layer containing nitrogen.
[0034]
First, its high reactivity. FIG. 3 shows a molar ratio [DMHy] / ([PH3] of DMHy, which is a nitrogen source, with respect to a group V source when AlGaInNP and GaInNP having an Al composition of 20% are grown (shown here are experimental results of a p-based material). + [DMHy]) and the amount of nitrogen uptake, with the horizontal axis representing the molar ratio [DMHy] / ([PH3] + [DMHy]) and the vertical axis representing the amount of nitrogen uptake. Yes. Here, AlGaInNP was grown at 700 ° C. (experiment points are indicated by white circles), and GaInNP was grown at 650 ° C. (experiment points are indicated by black circles).
[0035]
In general, the amount of nitrogen uptake is higher when the growth temperature is lower and higher when [DMHy] / ([PH3] + [DMHy]) is larger. The experimental results shown in FIG. According to the results, AlGaInNP containing Al (see white circle) captures nitrogen overwhelmingly even though the growth temperature is high and [DMHy] / ([PH3] + [DMHy]) is negligible. It turns out that it is easy to be rare. Also, organic nitrogen compounds such as DMHy, which are nitrogen raw materials, are difficult to exclude water during the purification process, and some amount of water (H₂O). Al is very reactive and reacts particularly well with water.
[0036]
The GaInNAs surface emitting semiconductor laser element is a structure including a multilayer reflector made of an AlGaAs-based material containing Al and an active layer made of GaInNAs containing nitrogen. When a lower multilayer mirror including a layer containing Al is grown, if an Al source remains in the reaction tube, it reacts with the nitrogen source when growing the active layer, and the active layer contains Al or oxygen (O) is incorporated into the material, affecting the quality, or reacting with the nitrogen raw material in advance, reducing the amount of nitrogen incorporated into the growth layer, and causing extremely serious problems. In particular, the incorporation of oxygen creates deep impurity levels in the active layer and adversely affects the optical characteristics. That is, the luminous efficiency is lowered and the threshold current is increased in the case of a laser.
[0037]
Specific experimental results are shown below.
[0038]
FIG. 10 is a diagram showing a room temperature photoluminescence spectrum from an active layer having a GaInNAs / GaAs double quantum well structure composed of a GaInNAs quantum well layer and a GaAs barrier layer, which was produced by the MOCVD apparatus of the inventors of the present application. FIG. 11 is a diagram showing a sample structure of the semiconductor light emitting device. Referring to FIG. 11, the sample structure is such that a lower cladding layer 202, an intermediate layer 203, an active layer 204 containing nitrogen, an intermediate layer 203, and an upper cladding layer 205 are sequentially stacked on a GaAs substrate 201. . In FIG. 10, symbol A is a room temperature photoluminescence spectrum from an active layer 204 of a sample in which a double quantum well structure is formed on an AlGaAs cladding layer 202 with a GaAs intermediate layer 203 interposed therebetween, and symbol B is a GaInP cladding layer 202. It is a room temperature photoluminescence spectrum from an active layer 204 of a sample in which a double quantum well structure is continuously formed with a GaAs intermediate layer 203 interposed therebetween.
[0039]
As shown in FIG. 10, the photoluminescence intensity of sample A is reduced to half or less than that of sample B. Therefore, if an active layer containing nitrogen such as GaInNAs is continuously formed on a semiconductor layer containing Al as a constituent element using a single MOCVD apparatus, the light emission intensity of the active layer will deteriorate. There was a problem. Therefore, the threshold current density of the GaInNAs laser formed on the AlGaAs cladding layer is more than twice as high as that formed on the GaInP cladding layer.
[0040]
The inventor of the present application further examined the cause elucidation. FIG. 12 shows, as an example of the semiconductor light emitting device shown in FIG. 11, one device in which the cladding layers 202 and 205 are made of AlGaAs, the intermediate layer 203 is made of GaAs, and the active layer 204 is made of a GaInNAs / GaAs double quantum well structure. It is a figure which shows the depth direction distribution of nitrogen (N) density | concentration and oxygen (O) density | concentration when it forms using this epitaxial growth apparatus (MOCVD apparatus). The measurement was performed by SIMS. The measurement conditions are shown in the following table (Table 1).
[0041]
[Table 1]

[0042]
In FIG. 12, two nitrogen (N) peaks are seen in the active layer 204 corresponding to the GaInNAs / GaAs double quantum well structure. In the active layer 204, an oxygen (O) peak is detected. However, the oxygen concentration in the intermediate layer 203 not containing N and Al is about one digit lower than the oxygen concentration in the active layer 204.
[0043]
On the other hand, when the depth direction distribution of oxygen (O) concentration is measured for an element in which the cladding layers 202 and 205 are made of GaInP, the intermediate layer 203 is made of GaAs, and the active layer 204 is made of a GaInNAs / GaAs double quantum well structure. The oxygen (O) concentration in the active layer 204 was at the background level.
[0044]
That is, when a semiconductor light emitting device in which a semiconductor layer containing Al is provided between a substrate 201 and an active layer 204 containing nitrogen is continuously grown by an epitaxial growth apparatus using a nitrogen compound raw material and an organometallic Al raw material, It has become clear from experiments by the inventors of the present application that oxygen is taken into the active layer 204 containing nitrogen. Oxygen incorporated into the active layer 204 forms a non-radiative recombination level, which reduces the light emission efficiency of the active layer 204. It has been newly found that the oxygen taken into the active layer 204 is a cause of lowering the light emission efficiency in the semiconductor light emitting device in which the semiconductor layer containing Al is provided between the substrate 201 and the active layer 204 containing nitrogen. . The origin of oxygen is considered to be a substance containing oxygen remaining in the apparatus or a substance containing oxygen contained as an impurity in the nitrogen compound raw material.
[0045]
Next, the cause of oxygen uptake was examined. FIG. 13 is a diagram showing a depth direction distribution of Al concentration of the same sample as FIG. The measurement was performed by SIMS. The measurement conditions are shown in the following table (Table 2).
[0046]
[Table 2]

[0047]
From FIG. 13, Al is detected in the active layer 204 which is not originally introduced with the Al raw material. However, in the intermediate layer (GaAs layer) 203 adjacent to the Al-containing semiconductor layer (cladding layers 202 and 205), the Al concentration is about one digit lower than that of the active layer. This indicates that Al in the active layer 204 is not mixed by diffusion and substitution from a semiconductor layer containing Al (clad layers 202 and 205).
[0048]
On the other hand, when an active layer containing nitrogen was grown on a semiconductor layer not containing Al, such as GaInP, Al was not detected in the active layer.
[0049]
Therefore, the Al detected in the active layer 204 is the Al raw material remaining in the growth chamber or the gas supply line, or the Al reactant, Al compound, or Al is contained in the nitrogen compound raw material or the nitrogen compound raw material. It is incorporated into the active layer 204 by combining with impurities (water, alcohol, etc.). That is, using a nitrogen compound raw material and an organometallic Al raw material, a semiconductor light-emitting element in which a semiconductor layer containing Al is provided between a substrate 201 and an active layer 204 containing nitrogen is continuously crystallized by a single epitaxial growth apparatus. It has been newly found that, when grown, Al is naturally taken into the active layer 204 containing nitrogen.
[0050]
Compared with the depth distribution of the nitrogen (N) concentration and the oxygen (O) concentration in the same element shown in FIG. 12, the two oxygen peak profiles in the double quantum well active layer are: It does not correspond, and corresponds to the Al concentration profile of FIG. From this, it was found that the oxygen impurities in the GaInNAs well layer were taken together with Al taken in the well layer rather than taken together with the nitrogen source. That is, when the Al raw material, Al reactant, Al compound, or Al remaining in the growth chamber comes into contact with the nitrogen compound raw material, the moisture contained in the Al and nitrogen compound raw material or in the gas line or reaction chamber Residual substances containing oxygen such as moisture are combined, and Al and oxygen are taken into the active layer 204. It has become clear for the first time through experiments by the inventors of the present application that oxygen taken into the active layer 204 reduces the luminous efficiency of the active layer 204.
[0051]
Therefore, in order to improve this, there is no Al raw material, Al reactant, Al compound, or Al at least in a place where the nitrogen compound raw material or impurities contained in the nitrogen compound raw material are in contact with the growth chamber. It has been found that it is preferable to grow an active layer containing nitrogen in the state.
[0052]
As this method, it is preferable to grow an active layer containing nitrogen by growing the semiconductor layer containing Al and then moving the substrate to another reaction chamber. That is, it is preferable to grow an active layer containing nitrogen after growing a semiconductor layer containing Al in another growth chamber such as another MOCVD growth chamber or MBE growth chamber. According to this method, when a nitrogen compound raw material is supplied to the growth chamber to grow an active layer containing nitrogen, the Al raw material remaining in the reaction chamber, the Al reactant, the Al compound, or Al and The concentration of Al and oxygen impurities taken into the active layer can be reduced by the reaction between the nitrogen compound raw material or the impurities contained in the nitrogen compound raw material and the substance containing oxygen remaining in the apparatus.
[0053]
For example, the Al concentration in the active layer containing nitrogen is set to 1 × 10¹⁹cm^-3By reducing to the following, continuous oscillation at room temperature became possible. Furthermore, the Al concentration in the active layer containing nitrogen is set to 2 × 10.¹⁸cm^-3By reducing to the following, light emission characteristics equivalent to those formed on a semiconductor layer not containing Al were obtained.
[0054]
In the following table (Table 3), a broad stripe laser using AlGaAs as a cladding layer (a layer containing Al) and a GaInNAs double quantum well structure (a layer containing nitrogen) as an active layer was prototyped and the threshold current density was evaluated. Results are shown.
[0055]
[Table 3]

[0056]
In a structure in which an active layer containing nitrogen is continuously formed on a semiconductor layer containing Al as a constituent element, 2 × 10 6 in the active layer.¹⁹cm^-3Above Al and 1 × 10¹⁸cm^-3More oxygen is taken in, and the threshold current density is 10 kA / cm²This was a remarkably high value. However, the Al concentration in the active layer is 1 × 10¹⁹cm^-3By reducing to the following, the oxygen concentration in the active layer becomes 1 × 10¹⁸cm^-3Reduced to a threshold current density of 2-3 kA / cm²The broad stripe laser oscillated. Broad stripe laser threshold current density is several kA / cm²Continuous oscillation at room temperature is possible with the following active layer quality. Therefore, the Al concentration in the active layer containing nitrogen is 1 × 10 5.¹⁹cm^-3By suppressing to the following, a semiconductor laser capable of continuous oscillation at room temperature can be provided.
[0057]
Semiconductor light emission in which a semiconductor layer containing Al is provided between a substrate and an active layer containing nitrogen when the crystal growth method does not use an organometallic Al raw material and a nitrogen compound raw material, as in a normal MBE method There is no particular report on a significant decrease in luminous efficiency in the device.
[0058]
The MBE method grows crystals under ultra-low pressure (in a high vacuum), whereas the MOCVD method usually has a pressure of several tens of Torr to atmospheric pressure, and the pressure in the reaction chamber is higher than the MBE method. This is presumably because the material and carrier gas supplied are in contact with and react with each other in the gas line and reaction chamber. Therefore, in the case of a growth method in which the pressure in the reaction chamber or gas line is high, such as the MOCVD method, after growing the semiconductor layer containing Al, the active layer containing nitrogen is not grown in the same reaction chamber. It is preferable to grow the substrate by moving it to the reaction chamber.
[0059]
As described above, it has been found that the present invention is effective in the case of an active layer containing nitrogen, such as GaNAs, GaPN, GaNPAs, GaInNAs, GaInNP, GaNASSb, GaInNAsSb.
[0060]
As a result, a multilayer structure of a GaInNAs surface-emitting type semiconductor laser device of good quality can be crystal-grown by the MOCVD method advantageous for mass production.
[0069]
  (2) Claim 2The method of manufacturing the surface-emitting type semiconductor laser device according to claim1In the surface emitting semiconductor laser device manufacturing method described above, in the growth chamber in which the active layer is grown, the Ga layer is grown before the active layer is grown._xIn_{1- x}P_yAs_1-y(0 <x ≦ 1, 0 <y ≦ 1) layers are grown.
[0070]
  If the regrowth interface is in the active region where carriers are injected, non-radiative recombination may occur due to oxidation or the like, which may reduce luminous efficiency., MatureAfter moving the long chamber, before growing the active layer, Ga_xIn_{1- x}P_yAs_1-yWhen the (0 <x ≦ 1, 0 <y ≦ 1) layer is grown, Ga_xIn_{1- x}P_yAs_1-ySince the active region can be formed with a narrow gap material (for example, GaAs) from (0 <x ≦ 1, 0 <y ≦ 1), there is no need to worry about the decrease in the light emission efficiency, and the device performance due to the regrowth interface. The influence on can be eliminated. Ga_xIn_{1- x}P_yAs_1-yThe (0 <x ≦ 1, 0 <y ≦ 1) layer does not contain Al and may have a wider gap than the region where carriers are mainly injected, and other III-, such as BN, Sb, etc. V group element may be contained.
[0071]
  (3) Claim 3The method of manufacturing the surface-emitting type semiconductor laser device according to claim1The above-described surface emitting semiconductor laser device manufacturing method is characterized in that a regrowth interface which is an interface between each growth is a semiconductor distributed Bragg reflector portion.
[0072]
  If the regrowth interface is in the active region where carriers are injected, non-radiative recombination may occur due to oxidation or the like, which may reduce luminous efficiency.Claim 3If a regrowth interface is provided in the reflector part as shown in the above, a low refractive index layer with a wide gap exists between the growth interface and the active region. Can be eliminated.
[0073]
  (4) Claim 4The method of manufacturing the surface-emitting type semiconductor laser device according to claim1In the surface-emitting semiconductor laser device manufacturing method described above, a plurality of crystal growth chambers are connected by a vacuum transfer path or the like, and a crystal is grown by transferring the substrate to be grown without being exposed to the atmosphere.
[0074]
  Claim 4According to the configuration, since it is not exposed to the atmosphere, the formation of an oxide film or the like at the regrowth interface that occurs when exposed to the atmosphere can be suppressed, and a good multilayer structure can be grown.
[0079]
  (5) Claim 5The surface-emitting type semiconductor laser device according to claim 1 is from4The manufacturing method according to any one ofThe lawIt is characterized by being formed using.
[0080]
That is, by adding N to GaInAs, which has a larger lattice constant than GaAs, GaInNAs can be lattice-matched to GaAs and its band gap becomes smaller, and light emission in the 1.3 μm and 1.55 μm bands is achieved. Is possible. Since it is a GaAs substrate lattice matching system, wide gap AlGaAs or GaInP can be used for the cladding layer.
[0081]
In addition, the addition of N reduces the band gap as described above, lowers the energy levels of both the conduction band and the valence band, and extremely increases the band discontinuity of the conduction band at the heterojunction. Temperature dependence can be made extremely small.
[0082]
Furthermore, the surface emitting semiconductor laser device is advantageous for parallel transmission by small size, low power consumption and two-dimensional integration. Although it is difficult to obtain performance that can be put to practical use in the conventional GaInPAs / InP system, the surface emitting semiconductor laser element is a 0.85 μm band surface emitting semiconductor laser element using a GaAs substrate according to a GaInNAs material. Al (Ga) As / (Al) GaAs-based semiconductor multilayer distributed Bragg reflectors and the current narrowing structure by selective oxidation of AlAs can be applied, so that practical application can be expected.
[0083]
  To achieve this, it is important to improve the crystal quality of the GaInNAs active layer, to reduce the resistance of the multilayer reflector, and to improve the crystal quality and controllability of the multilayer structure as a surface emitting semiconductor laser device. From claim 1 of the present invention,4Manufacturing method byLegalBy using one or more, it is possible to easily realize a surface emitting semiconductor laser element having low resistance, low driving voltage, low threshold current operation, and good temperature characteristics.
[0084]
  (6) Claim 6The optical transmission module described isClaim 5The surface-emitting type semiconductor laser device described is used as a light source. By using a surface emitting semiconductor laser element having a low resistance, a low driving voltage, a low threshold current operation, and good temperature characteristics, a low-cost optical transmission module that does not require a cooling element can be realized. it can.
[0085]
  (7) Claim 7The optical transceiver module described isClaim 5The surface-emitting type semiconductor laser device described is used as a light source. By using a surface emitting semiconductor laser element having a low resistance, a low driving voltage, a low threshold current operation, and good temperature characteristics, a low-cost optical transceiver module that does not require a cooling element can be realized. it can.
[0086]
  (8) Claim 8The optical communication system described isClaim 5The surface-emitting type semiconductor laser device described is used as a light source. Low cost optical fiber communication system, optical interconnection system, etc. that do not require a cooling element by using a surface emitting semiconductor laser device with low resistance, low driving voltage, low threshold current operation, and good temperature characteristics as described above An optical communication system can be realized.
[0087]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0088]
(First implementationExample)
  A GaInNAs surface-emitting type semiconductor laser device according to the first embodiment of the present invention will be described.
[0089]
FIG. 4 is a diagram showing the structure of a surface emitting semiconductor laser device according to the first embodiment of the present invention. As shown in FIG. 4, the surface-emitting type semiconductor laser device in this example is formed on an n-GaAs substrate 20 having a surface orientation (100) of 2 inches in size and ¼ of the oscillation wavelength in each medium. N-Al with double thickness_xGa_1-xAn n-semiconductor distributed Bragg reflector (lower semiconductor distributed Bragg reflector: also simply referred to as a lower reflector) 21 having a periodic structure in which 35 cycles of As (x = 0.9) and n-GaAs are alternately stacked is formed (see FIG. The details are omitted in FIG. On top of this, undoped lower GaAs spacer layers 22, 3 layers of Ga_xIn_1-xN_yAs_1-yA multiple quantum well active layer 23 comprising an (x, y) well layer and a GaAs barrier layer 15 nm, and an undoped upper GaAs spacer layer 24 are formed.
[0090]
A p-semiconductor distributed Bragg reflector (upper semiconductor distributed Bragg reflector: also simply referred to as an upper reflector) 25 is formed thereon. The upper reflecting mirror 25 is a 3λ / 4-thick low-refractive-index layer (λ / 4-15 nm C-doped p-Al layer) in which AlAs serving as a selective oxidation layer is sandwiched between AlGaAs._xGa_1-xAs (x = 0.9), 30 nm C-doped p-AlAs selectively oxidized layer 251, 2λ / 4-15 nm C-doped p-Al_xGa_1-xAs (x = 0.9)) and GaAs / 4 thickness (1 period), and C-doped p-Al_xGa_1-xPeriodic structure in which As (x = 0.9) and p-GaAs are alternately stacked at a thickness that is ¼ times the oscillation wavelength in each medium. For example, it is composed of 25 periods (details omitted in the figure). ).
[0091]
The uppermost GaAs layer 252 of the upper reflecting mirror 25 also serves as a contact layer that contacts the electrode. The In composition x of the well layer in the active layer 23 was 37%, and the nitrogen composition was 0.5%. The thickness of the well layer was 7 nm. The GaAs substrate 20 had a compressive strain (high strain) of about 2.5%.
[0092]
Crystal growth of each layer of the surface-emitting type semiconductor laser device of FIG. 4 in this embodiment is performed by a crystal growth apparatus as shown in FIG. As shown in FIG. 5, in the crystal growth apparatus according to the present embodiment, the MOCVD growth chamber 31 and the MBE growth chamber 32 are coupled through a vacuum transfer path, and a reflecting mirror is grown in the MOCVD growth chamber 31 to obtain GaInNAs. The GaAs substrate 20 was moved in the middle of the GaAs spacer layer so that the active layer was grown in the MBE growth chamber 32. The MOCVD apparatus and the MBE apparatus in the crystal growth apparatus may be separated from each other, and the GaAs substrate 20 may be once taken out into the atmosphere. However, it is preferable that the GaAs substrate 20 is integrated and not exposed to the atmosphere as shown in FIG. Good. This is because the concentration of oxygen taken into the regrowth interface can be reduced.
[0093]
In the present embodiment, solid-state Ga, In, As, and N are used for GaInNAs growth by MBE.₂Nitrogen obtained by decomposing the gas with an RF radical cell was used. Also, for AlGaAs growth by MOCVD equipment, TMG (trimethylgallium), TMI (trimethylindium), AsH_Three(Arsine) and H as the carrier gas₂(Hydrogen) was used. When the strain is large as in the active layer of the device of this example, low temperature growth that is non-equilibrium is preferable. In this example, the GaInNAs layer was grown at 430 ° C.
[0094]
A mesa having a predetermined size is formed by exposing at least the side surface of the p-AlAs selective oxidation layer 251, and AlAs appearing on the side surface is oxidized from the side surface with water vapor to form Al._xO_yA current narrowing layer 26 was formed. Then, the etched portion is buried and planarized with polyimide 27 to remove the polyimide on the upper reflecting mirror having the p contact layer 252 and the light emitting portion 28, and the p-side electrode other than the light emitting portion 28 on the p contact layer 252. 29 and the n-side electrode 30 was formed on the back surface of the substrate 20.
[0095]
The oscillation wavelength of the manufactured surface emitting semiconductor laser element was about 1.3 μm. Since GaInNAs was used for the active layer, a long wavelength surface emitting semiconductor laser element could be formed on the GaAs substrate. In addition, the threshold current was low because the current was narrowed by selective oxidation of the selective oxidation layer mainly composed of Al and As. According to the current narrowing structure using the current narrowing layer made of the Al oxide film that selectively oxidizes the selective oxidation layer, the current spreading can be suppressed by forming the current narrowing layer close to the active layer, so that it does not touch the atmosphere. Carriers can be confined efficiently in the region.
[0096]
Furthermore, the refractive index is reduced by oxidizing to an Al oxide film, and light can be efficiently confined in a minute region in which carriers are confined by the effect of the convex lens, which is extremely efficient and the threshold current is reduced. The In addition, the manufacturing cost can be reduced because the current narrowing structure can be easily formed. As described above, according to the present embodiment, a 1.3 μm band surface emitting semiconductor laser device with low power consumption and low cost can be realized. In order to reduce the number of movements and shorten the manufacturing time, the n-side multilayer reflector 21 and the active layer 23 are grown in the MBE growth chamber, and only the p-side multilayer reflector 25 is grown in the MOCVD growth chamber. You can also.
[0097]
(Second implementationExample)
  A GaInNAs surface-emitting type semiconductor laser device according to a second embodiment of the present invention will be described. The structure of the GaInNAs surface emitting semiconductor laser device in this example is as shown in FIG. 4 as in the first example, and the difference from the first example is the crystal growth method. Crystal growth in this example was performed by an MOCVD apparatus having two MOCVD growth chambers.
[0098]
FIG. 6 is a schematic diagram of an MOCVD apparatus having two MOCVD growth chambers 41 and 42 for crystal growth of a GaInNAs surface emitting semiconductor laser element in this embodiment.
[0099]
In this embodiment, the reflecting mirrors using the Al-containing layer (the lower reflecting mirror 21 and the upper reflecting mirror 25 in FIG. 4) are grown in the first MOCVD growth chamber 41, and the GaInNAs using the nitrogen-containing layer is used. The active layer (GaInNAs active layer 23 in FIG. 4) was grown in the second MOCVD growth chamber 42. In the present embodiment, the first MOCVD growth chamber 41 uses a vertical reaction tube, and the second MOCVD growth chamber 42 uses a horizontal reaction tube. During the growth of the GaAs spacer layer 22, the substrate was moved through the vacuum transfer path 43 and grown.
[0100]
The raw material for the GaInNAs active layer 23 by MOCVD is TMG (trimethylgallium), TMI (trimethylindium), AsH._Three(Arsine), and DMHy (dimethylhydrazine) was used as a raw material for nitrogen. Carrier gas is H₂Was used. DMHy is suitable for low-temperature growth at 600 ° C. or lower because it decomposes at low temperatures, and is a preferable raw material for growing a quantum well layer having a large strain required for low-temperature growth. When the strain is large as in the active layer 23 of the GaInNAs surface-emitting type semiconductor laser device of this example, low temperature growth that is non-equilibrium is preferable. In this example, the GaInNAs layer 23 was grown at 540 ° C. Nitrogen and Al materials were not allowed to meet in the gas line. Specifically, the ON / OFF valve shown in FIG. 6 is not opened or closed.
[0101]
The vertical reaction tube used in the first MOCVD growth chamber 41 has excellent uniformity and is suitable for the growth of a multilayer mirror. In addition, the horizontal reaction tube used in the second MOCVD growth chamber 42 has a feature that a laminar flow is easily generated. Further, since there are upstream and downstream, the raw material gas can be decomposed in advance, which is advantageous for low temperature growth and suitable for the growth of GaInNAs. It is not limited to the combination of the vertical reaction tube and the horizontal reaction tube as shown in FIG. 6, but has a plurality of growth chambers such as a combination of vertical reaction tubes having different forms, for example, a growth suitable for each growth layer. There is an advantage that it can be made into a chamber shape and various multilayer film structures can be easily optimized and grown.
[0102]
In this example, all of the MOCVD apparatus was used, and the bonding was performed by the vacuum transfer path 43. Therefore, the GaInNAs surface emitting semiconductor laser device could be manufactured with good throughput without the adverse effect of the regrowth interface.
[0103]
Further, although the regrowth interface is in the middle of the GaAs spacer layer, it is not limited to this (the same applies to the first embodiment). If the active region into which carriers are injected is used as a regrowth interface, non-radiative recombination may occur due to oxidation or the like, which may reduce luminous efficiency. For example, the high-refractive index layer and the low-refractive index layer constituting the reflecting mirror may be grown by one pair 2nd growth (step of growing the active region).
[0104]
In this case, it is preferable to use a layer that does not contain Al as the regrowth interface (if the layer containing Al is used as the regrowth interface, the negative effect of oxidation may be a problem even if vacuum transfer is performed), so a high refractive index. The layer may be GaAs, the low refractive index layer may be Al (Ga) As, and the GaAs layer may be a regrowth interface. In particular, in the MOCVD method, a problem may occur when an Al-containing layer is grown in a reaction chamber for growing GaInNAs (particularly, when an Al-containing layer is grown between a substrate and an active layer containing nitrogen). Therefore, the low refractive index layer has Ga_xIn_1-xP_yAs_1-yIt is preferable to use a material that does not contain Al, such as (0 <x ≦ 1, 0 <y ≦ 1).
[0105]
An example of this is shown in FIG. In FIG. 14, before the GaInNAs active layer is grown in the step of growing the active region (2nd growth)._xIn_1-xP_yAs_1-y(0 <x ≦ 1, 0 <y ≦ 1) layers are grown. This Ga_xIn_1-xP_yAs_1-yThe (0 <x ≦ 1, 0 <y ≦ 1) layer is one of the low refractive index layers constituting the lower reflecting mirror. The upper reflector has the same configuration as that shown in FIG. 4, and only the low refractive index layer of the lower reflector is Ga._xIn_1-xP_yAs_1-y(0 <x ≦ 1, 0 <y ≦ 1). Low-refractive-index layer portion (3λ / 4-thickness low-refractive-index layer in which AlAs to be a selective oxidation layer is sandwiched between AlGaAs) constituting the upper reflector in the step of growing the active region (2nd growth) is an AlGaAs-based material However, since there is sufficient time until the next active layer growth including nitrogen, mixing of the Al and oxygen into the active layer can be prevented by cleaning the apparatus during that time by vacuuming or the like. In addition, since this cleaning is usually performed, the manufacturing process is not particularly increased. As a cleaning method, it is efficient to heat the heating body in the growth chamber while supplying hydrogen gas as a carrier gas. When heating a heating body, it is preferable to carry out at a temperature higher than the growth temperature. Desirably, the growth chamber for growing the active layer is a growth chamber that does not grow a material containing Al, that is, does not supply an Al raw material. This is because it is possible to reliably prevent oxygen from being taken into the active layer containing nitrogen together with Al.
[0106]
(Third implementationExample)
  FIG. 7 is a diagram showing a third embodiment of the present invention, and is a schematic diagram of an optical transmission module combining a surface-emitting type semiconductor laser device and an optical fiber according to the first embodiment. In this embodiment, a laser beam 53 from a 1.3 μm band GaInNAs surface emitting semiconductor laser element 51 is input to a silica-based optical fiber 52 and transmitted. It is possible to increase the transmission speed by arranging a plurality of surface emitting semiconductor laser elements having different oscillation wavelengths in an array in one or two dimensions and performing wavelength multiplexing transmission. It is also possible to increase the transmission speed by arranging the surface-emitting type semiconductor laser elements in a one-dimensional or two-dimensional array and combining them with optical fiber bundles composed of a plurality of optical fibers 52 corresponding thereto.
[0107]
Furthermore, when the surface emitting semiconductor laser device according to the present invention is used in an optical communication system, a low-cost and highly reliable optical transmission module can be realized, and a low-cost and high-reliability optical communication system using the same can be realized. . In addition, since the surface emitting semiconductor laser element using GaInNAs has a good temperature characteristic and a low threshold value, a system that generates less heat and can be used without cooling to a high temperature can be realized.
[0108]
(Fourth implementationExample)
  FIG. 8 is a diagram showing a fourth embodiment of the present invention, and is a schematic diagram of an optical transceiver module in which a surface emitting semiconductor laser element, a receiving photodiode, and an optical fiber according to the second embodiment are combined. .
[0109]
When the surface-emitting type semiconductor laser device according to the present invention is used in an optical communication system, the surface-emitting type semiconductor laser device is low in cost, and therefore, as shown in FIG. A low-cost and high-reliability optical communication system using an optical transmission module in which a GaInNAs surface emitting semiconductor laser element) 61, a receiving photodiode 62, and an optical fiber 63 are combined can be realized. Further, in the case of the surface emitting semiconductor laser device using GaInNAs according to the present invention, the temperature characteristics are good, the operating voltage is low, and the threshold value is low, so there is little heat generation and no cooling to high temperature. A lower cost system can be realized.
[0110]
Furthermore, when a fluorine-doped POF (plastic fiber) that has a low loss in a long wavelength band such as 1.3 μm and a surface emitting laser using GaInNAs as an active layer are combined, the cost of the fiber is reduced and the diameter of the fiber is reduced. Since it is large and can be easily coupled with a fiber and the mounting cost can be reduced, a very low-cost module can be realized.
[0111]
The optical communication system using the surface emitting semiconductor laser device according to the present invention can be used not only for long-distance communication using an optical fiber, but also for transmission between devices such as a LAN (Local Area Network) and the like, and Can be used for short-distance communication as an optical interconnection such as data transmission between boards, between LSIs in a board, between elements in an LSI, and the like.
[0112]
In recent years, the processing performance of LSIs and the like has improved, but the transmission speed of the portion connecting them will become a bottleneck in the future. When the signal connection in the system is changed from the conventional electrical connection to the optical interconnect, for example, the optical transmission module or the optical transmission / reception module according to the present invention is used between the boards of the computer system, between the LSIs in the board, between the elements in the LSI, etc. Connection, an ultra-high-speed computer system becomes possible.
[0113]
In addition, when a plurality of computer systems are connected using the optical transmission module or the optical transmission / reception module according to the present invention, an ultra-high speed network system can be constructed. In particular, the surface-emitting type semiconductor laser element is suitable for a parallel transmission type optical communication system because the power consumption can be reduced by orders of magnitude compared to the edge-emitting type laser and the two-dimensional array can be easily formed.
[0114]
As described above, according to the GaInNAs material, an Al (Ga) As / (Al) GaAs semiconductor multilayer distributed Bragg reflector having a proven record in a 0.85 μm band-emitting semiconductor laser device using a GaAs substrate, etc. A current narrowing structure by selective oxidation of AlAs can be applied, and a GaInNAs active layer is manufactured by manufacturing a surface emitting semiconductor laser device as in the first embodiment, the second embodiment, or the fifth embodiment described later. Can improve crystal quality, reduce the resistance of multilayer reflectors, and improve the crystal quality and controllability of multilayer structures as surface-emitting semiconductor laser elements. Long-wavelength surface emitting semiconductor laser elements such as optical fiber communication systems and optical interconnects that do not require cooling elements and that can be used with these elements. An optical communication system such as a communication system can be realized.
[0115]
(Fifth implementationExample)
  FIG. 15 is a diagram showing a configuration example of the surface emitting semiconductor laser element of the fifth embodiment. An enlarged view near the active region is also shown. The difference from the device of the second embodiment (FIG. 14) is Ga_xIn_{1- x}P_yAs_1-y(0 <x ≦ 1, 0 <y ≦ 1) layer (second spacer layer) is in the resonator. In this embodiment, the thickness of the resonator portion is one wavelength. The resonator section includes an active layer composed of a GaInNAs quantum well layer composed of three layers and a GaAs barrier layer, GaAs as a first spacer layer, Ga_xIn_{1- x}P_yAs_1-yThe (0 <x ≦ 1, 0 <y1) layer is a second spacer layer. Ga_xIn_{1- x}P_yAs_1-ySince the (0 <x ≦ 1, 0 <y ≦ 1) layer has a larger band gap than the GaAs layer, the active region into which carriers are injected is substantially up to the GaAs first spacer layer, which is the same as the device of the second embodiment. An effect is obtained.
[0116]
Note that the growth interruption interface for transferring the growth chamber is Ga._xIn_1-xP_yAs_1-y(0 <x ≦ 1, 0 <y ≦ 1) provided in the middle of the layer, but Ga_xIn_1-xP_yAs_1-yA GaAs layer may be provided between the (0 <x ≦ 1, 0 <y ≦ 1) layer and the Al-containing layer, and the process may be performed in the middle of the layer.
[0117]
Further, as the growth apparatus, an apparatus in which the MOCVD reaction chamber and the MBE reaction chamber are coupled by a vacuum transfer path can be used. In this case, the n-side lower reflecting mirror can be grown in the MBE reaction chamber, and the active layer containing nitrogen and the p-side reflecting mirror can be continuously grown in the MOCVD growth chamber. In this case, since the substrate can be moved between the growth chambers only once, it can be grown in a short time. Even in this case, the incorporation of oxygen in the active layer containing nitrogen by MOCVD growth can be reduced. Moreover, the resistance of the p-side reflecting mirror can be reduced.
[0118]
【The invention's effect】
  According to the present invention, a high-quality and practical-use GaInNAs surface-emitting type semiconductor laser device manufacturing method (claims 1 to 5).4)And method for manufacturing the surface emitting semiconductor laser elementSurface emitting semiconductor laser element formed usingClaim 5), An optical transmission module using the surface emitting semiconductor laser element (Claim 6), Optical transceiver module (Claim 7), Optical communication system (Claim 8) Can be realized.
[0119]
For more details,
(1) According to the method for manufacturing a surface-emitting type semiconductor laser device according to the first aspect, the semiconductor multilayer mirror is easily grown by the MOCVD method and the active region including the GaInNAs active layer is grown by the MBE method. A resistive multilayer mirror can be formed, and a high-quality GaInNAs active layer can be easily formed.
[0124]
  (2) Claim 2According to the surface-emitting type semiconductor laser device manufacturing method described above, in the step of growing the active layer, the Ga layer is grown before the active layer is grown._xIn_{1- x}P_yAs_1-yBy growing the layer (0 <x ≦ 1, 0 <y ≦ 1), the influence of the regrowth interface on the device performance can be eliminated.
[0125]
  (3) Claim 3According to the surface emitting semiconductor laser device manufacturing method described above, the regrowth interface, which is an interface between each growth, is a semiconductor distributed Bragg reflector portion, thereby eliminating the influence of the regrowth interface on the device performance. it can.
[0126]
  (4) Claim 4According to the manufacturing method of the surface-emitting type semiconductor laser device described above, a plurality of crystal growth chambers are connected by a vacuum transfer path or the like, and the substrate to be grown is transferred and crystal grown without being exposed to the atmosphere. Thus, formation of an oxide film or the like at the regrowth interface that occurs when exposed to the atmosphere can be suppressed, and a good multilayer structure can be grown.
[0129]
  (5) Claim 5The surface-emitting semiconductor laser device according to claim 1 from4The manufacturing method according to any one ofThe lawA surface-emitting type semiconductor laser device that is formed by using, has a low resistance, a low driving voltage, operates at a low threshold current, and has good temperature characteristics can be easily realized.
[0130]
  (6) Claim 6The optical transmission module described isClaim 5The surface-emitting type semiconductor laser element described is used as a light source, and a low-cost optical transmission module that does not require a cooling element can be realized.
[0131]
  (7) Claim 7The optical transceiver module described isClaim 5The surface-emitting semiconductor laser element described is used as a light source, and a low-cost optical transceiver module that does not require a cooling element can be realized.
[0132]
  (8) Claim 8The optical communication system described isClaim 5The surface-emitting type semiconductor laser device described is used as a light source, and an optical communication system such as a low-cost optical fiber communication system or an optical interconnection system that does not require a cooling element can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic view of an MOCVD apparatus.
FIG. 2 is a schematic diagram of an MBE apparatus.
FIG. 3 is a diagram showing a relationship between [DMHy] / ([PH3] + [DMHy]), which is a nitrogen source relative to a group V source, and the amount of nitrogen taken in when AlGaInNP and GaInNP having an Al composition of 20% are grown. is there.
FIG. 4 is a diagram showing a structure of a surface emitting semiconductor laser device according to a first example of the present invention.
FIG. 5 is a conceptual diagram of a crystal growth apparatus according to a first embodiment of the present invention.
FIG. 6 is a schematic view of an MOCVD apparatus having two MOCVD growth chambers according to a second embodiment of the present invention.
FIG. 7 is a schematic diagram of an optical transmission module combining a surface-emitting type semiconductor laser device and a fiber according to a third embodiment of the present invention.
FIG. 8 is a schematic diagram of an optical transceiver module according to a fourth embodiment of the present invention, in which a surface emitting semiconductor laser element, a receiving photodiode, and an optical fiber are combined.
FIG. 9 is a graph showing the nitrogen composition dependence of threshold current density.
FIG. 10 is a diagram showing a room temperature photoluminescence spectrum from an active layer having a GaInNAs / GaAs double quantum well structure composed of a GaInNAs quantum well layer and a GaAs barrier layer, produced by the MOCVD apparatus of the inventors of the present application.
FIG. 11 is a diagram showing a sample structure of a semiconductor light emitting device.
FIG. 12 shows an example of the semiconductor light emitting device shown in FIG. 11 in which a device having a cladding layer made of AlGaAs, an intermediate layer made of GaAs, and an active layer made up of a GaInNAs / GaAs double quantum well structure is formed by a single epitaxial growth apparatus (MOCVD). It is a figure which shows the depth direction distribution of nitrogen (N) density | concentration and oxygen (O) density | concentration when forming using an apparatus.
13 is a diagram showing a depth direction distribution of Al concentration of the same sample as FIG. 12; FIG.
FIG. 14 is a view showing a structure of a surface emitting semiconductor laser according to a second embodiment.
FIG. 15 is a view showing a structure of a surface emitting semiconductor laser according to a fifth embodiment.
[Explanation of symbols]
11 Substrate entrance / exit
12 Growth chamber (reaction chamber)
13 Hydrogen purification machine
14 Liquid, solid bubbler
15 Gas cylinder
16 Valve
A Raw material gas supply section
B Heating part
C Exhaust section
20 n-GaAs substrate
21 n-semiconductor distributed Bragg reflector (lower semiconductor distributed Bragg reflector)
22 Lower GaAs spacer layer
23 Multiple quantum well active layer
24 Upper GaAs spacer layer
25 p-semiconductor distributed Bragg reflector (upper semiconductor distributed Bragg reflector)
251 Selective oxidation layer
252 p-GaAs layer (contact layer)
26 Al_xO_yCurrent narrowing part
27 Polyimide
28 Light emitting part
29 p-side electrode
30 n-side electrode
31 MOCVD growth chamber
32 MBE Growth Office
41 First MOCVD growth chamber
42 Second MOCVD growth chamber
43 Vacuum transfer path
44 Substrate loading / unloading chamber
45 Gas supply section
51 1.3 μm Band GaInNAs Surface Emitting Semiconductor Laser Device
52 Silica-based optical fiber
53, 64 Laser light
61 1.3 μm Band GaInNAs Surface Emitting Semiconductor Laser Element
62 Photodiode for reception
63 Optical fiber
201 GaAs substrate
202 Lower cladding layer
203 Middle layer
204 Active layer
205 Upper cladding layer

Claims (8)

  An active region including at least one active layer for generating laser light on a semiconductor substrate, and a resonator structure including reflectors provided above and below the active layer for obtaining laser light. A method of manufacturing a surface-emitting type semiconductor laser device in which one of the reflecting mirrors provided above and below the active layer is a p-side semiconductor reflecting mirror, wherein the active layer includes Ga, In, N, As as a main component, and at least the p-side semiconductor reflector among the reflectors includes a semiconductor distributed Bragg reflector that periodically changes the refractive index and reflects incident light by light wave interference, and the active layer Is a method of manufacturing a surface-emitting type semiconductor laser device, which is grown by an MBE method and at least a p-side semiconductor reflector among the reflectors is grown by an MOCVD method. In the growth chamber for growing the active layer, a Ga _x In _{1- x} P _y As _1-y (0 <x ≦ 1, 0 <y ≦ 1) layer is grown before growing the active layer. method for manufacturing a surface-emitting type semiconductor laser device according to claim 1 Symbol placement. Method for manufacturing a surface-emitting type semiconductor laser device according to claim 1 Symbol placement regrowth interface is an interface, characterized in that a semiconductor distributed Bragg reflector mirror portion between the growth. A plurality of crystal growing chamber is coupled with the vacuum transfer path, etc., according to claim 1 Symbol mounting of the surface-emitting type semiconductor laser device characterized by crystal growth by conveying the growth substrate without exposing to the atmosphere Production method. The surface-emitting type semiconductor laser element characterized in that it is formed by using a manufacturing how the surface-emitting type semiconductor laser device according to any one of claims 1 to 4. An optical transmission module comprising the surface-emitting type semiconductor laser device according to claim 5 as a light source. 6. An optical transceiver module using the surface-emitting type semiconductor laser device according to claim 5 as a light source. 6. An optical communication system using the surface-emitting type semiconductor laser device according to claim 5 as a light source.

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