JP4093709B2 - Semiconductor laser element - Google Patents

Description

【００５３】
【表２】

次に、この上にマスク層としてＡｌ₂Ｏ₃膜１９を蒸著し、フォトリソグラフィーによりストライプ状にパターン加工する。その後、Ａｌ₂Ｏ₃膜１９をマスクとして湿式エッチングを行ってコンタクト層１８、中間バンドギャップ層１７およびｐ型第３クラッド層１６のうち、Ａｌ₂Ｏ₃膜１９の両側に相当する部分を除去してＡｌ₂Ｏ₃膜１９直下の部分にメサ部３１を形成する。なお、ｐ−ＡｌＧａＩｎＰ第３クラッド層１６を除去する際には、ｐ−ＧａＩｎＰエッチングストップ層１５との選択エッチングによりエッチングを確実に停止させる。
【００５４】
その後、第２回目のＭＢＥ成長を行って、メサ部３１の両側にｎ−ＧａＡｓ電流ブロック層２０を断面凸状に成長させる。このとき、Ａｌ₂Ｏ₃膜１９上にはｎ−ＧａＡｓ多結晶層２１が断面凸状に形成される。
【００５５】
この上に、図１（ｂ）に示すようにフォトレジスト３２を塗布する。そして、フォトリソグラフィーによりｎ−ＧａＡｓ多結晶層２１の部分に開口２３を設けて、ｎ−ＧａＡｓ多結晶層２１の頂部３３を露出させる。
【００５６】
次に、図１（ｃ）に示すように、硫酸系エッチング液を用いて、Ａｌ₂Ｏ₃膜１９に対してｎ−ＧａＡｓ多結晶層２１を選択エッチングして除去し、続いて、フォトレジスト３２を除去する。
【００５７】
そして、図１（ｄ）に示すように、フッ酸系エッチング液を用いて、Ａｌ₂Ｏ₃膜１９をエッチングして除去する。その後、コンタクト層１８の表面、基板１１の裏面に各々電極（図示せず）を形成して本実施形態の半導体レーザ素子が得られる。
【００５８】
次に、高温で高い信頼性を有する半導体レーザ素子を得るために、本願の発明者が量子井戸幅およびθ⊥について、特定の関係を見い出した経緯について説明する。
【００５９】
まず、上述したＵ．Ｓ．ＤＶＤ Ｃｏｎｆｅｒｅｎｃｅ Ｍａｙ２８ａｎｄ２９、１９９７予稿集に記載されている活性層の構造を図８に示す。
【００６０】
この図８において、横軸は積層方向の距離を示し、縦軸は（Ａｌ_yＧａ_1-y）_xＩｎ_1-xＰのＡｌ混晶比ｙを示す。活性層を構成する量子井戸層１４６はＧａ_xＩｎ_1-xＰであり、その井戸幅は８５オングストローム、光ガイド層１４２、１４３の厚さは５００オングストローム、光ガイド層１４２、１４３のＡｌ混晶比は０．５、クラッド層１１２、１１４のＡｌ混晶比は０．７である。この構造では、出射光の、活性層の積層面に対して垂直な方向の半値幅θ⊥が２５．５°になる。
【００６１】
図９に、この半導体レーザ素子における信頼性試験結果を示す。この構造によれば、温度３０℃、光出力３０ｍＷの条件でＭＴＴＦ５４００時間が得られている。しかし、装置の環境温度を保証するために必要な５０℃では、光出力３０ｍＷが得られずに半導体レーザ素子が劣化するという問題が生じる。
【００６２】
従って、高温での動作を行うためには、動作電流、すなわち、発振閾値電流をさらに下げる必要がある。
【００６３】
このため、本願の発明者は、量子井戸層の組成をＧａ_xＩｎ_1-xＰとしたまま量子井戸層厚（量子井戸幅）と光ガイド構造を変化させて以下のように実験を行った。ここで、光ガイド構造とは、具体的には（１）光ガイド層Ａｌ混晶比、（２）クラッド層Ａｌ混晶比および（３）光ガイド層厚である。また、光ガイド層のＡｌ混晶比と障壁層のＡｌ混晶比は同じとした。
【００６４】
本実施形態では、表３に示すように量子井戸幅、光ガイド層厚、光ガイド層Ａｌ混晶比およびクラッド層Ａｌ混晶比を変化させた半導体レーザ素子を作製した。また、比較のために表４に示すような半導体レーザ素子を作製した。この表４中、ロット名Ｘ０３が図８に示した従来の半導体レーザ素子を示す。
【００６５】
【表３】

【００６６】
【表４】

このとき、半導体レーザ素子の発振波長は、活性層の歪み量、具体的にはＧａ_xＩｎ_1-xＰ層の混晶比ｘを調整して、ＤＶＤ−Ｒ用に最適な６３５ｎｍから６４２ｎｍの範囲になるように設定した。なお、混晶比ｘと格子歪み量の関係は以下の通りである。
【００６７】
混晶比Ｘ＝０．５１−格子歪み量（％）×０．１３５
さらに、この半導体レーザ素子のθ⊥は、量子井戸幅と光ガイド層の厚さとガイド層Ａｌ混晶比およびクラッド層Ａｌ混晶比によって決定される。図３に計算と実験から求めたθ⊥と光ガイド層およびクラッド層の混晶比の関係を示す。なお、計算は、マックスウェルの方程式を数値解法により解いて求めている。ここでは、光ガイド層厚を５００オングストロームとしているが、光ガイド層厚が大きくなると光が活性層付近に集まるためにθ⊥が小さくなり、光ガイド層厚が小さくなるとθ⊥は大きくなる。
【００６８】
この図３から、例えば、量子井戸層厚が１１０オングストロームで光ガイド層のＡｌ混晶比が０．５６およびクラッド層のＡｌ混晶比が０．６８では、θ⊥２３．７°が得られる。
【００６９】
図４に、このようにして作製した半導体レーザ素子の量子井戸幅とθ⊥と閾値電流との関係を示す。この図中、数値は２５℃における閾値電流を示している。
【００７０】
この図４によれば、井戸幅が大きい方がＩｔｈが低くなり、θ⊥が小さい方がＩｔｈが大きくなっている。
【００７１】
井戸幅が大きい方がＩｔｈが低くなる理由は以下の通りである。
【００７２】
図５に、発振波長と量子井戸幅と活性層歪量との関係を示す。
【００７３】
発振波長の中心値を６３８ｎｍにするために、井戸幅が決まると、図５の実線上に活性層歪量の値をｘを調整して設定する。井戸幅が大きいと、ｘを大きくしなければ同じ波長を得ることができないため量子井戸層の引っ張り歪量が増大する。
【００７４】
図５の上に、Γ点付近の電子準位、ライトホール準位、ヘビィホール準位の運動量空間におけるエネルギー依存性を示す。引張り歪量が増大することにより、Γ点ではライトホール準位のエネルギーがヘビィホール準位のエネルギーより十分高くなるので注入されたキャリア（ホール）はライトホールとして分布する。
【００７５】
ヘビィホールと電子の再結合によるレーザ光とライトホールと電子の再結合によるレーザ光とでは偏光方向や利得が異なる。ライトホール準位とヘビィホール準位のエネルギーが等しく、同じ量のキャリアが存在している場合には、利得の低い偏光方向で発振が生じ、もう一方の偏光方向に寄与するキャリアは自然放出光となってレーザ発振には寄与しないので発振閾値が高くなってしまう。ライトホール準位のエネルギーがヘビィホール準位のエネルギーより十分高い本実施形態の半導体レーザ素子ではヘビィホール準位にしかキャリアが無いため、注入されたキャリアは全て一方の偏光方向のレーザ光にのみ寄与するので発振閾値が低くなり、効率も高くなるので動作電流が低くなる。即ち、温度特性が良くなるのである。
【００７６】
量子井戸層厚７０オングストローム以上の各半導体レーザ素子について、信頼性を評価した結果を示す。信頼性試験は、５０℃、３０ｍＷの条件で光出力一定とした駆動方法により測定した。
【００７７】
この図６から、Ｘ８４、Ｘ８６およびＸ８９の半導体レーザ素子は全て、５０℃、３０ｍＷにおいて高い信頼性を有し、十分に実用化が可能であることがわかる。
【００７８】
しかし、Ｘ１０８の半導体レーザ素子に関しては、θ⊥を大きくして活性層の光閉じ込め係数を上げることにより動作電流（Ｉｏｐ）は低下したが、信頼性試験では突然に停止する故障モードとなった。劣化した素子の光出射端面の発光パターン測定したところ、活性層中央部に暗部があり、明らかに端面部の光密度が大きいために劣化したと考えられる。この理由は、半導体レーザ素子内部での光密度が高いため、レーザ端面部分での酸化等により劣化が進み、突然に劣化する故障モードが現れていると考えられる。
【００７９】
レーザ端面部分での光密度を下げるためには、活性層付近での光ビームサイズを広げることが必要であり、これは、半導体レーザ素子から出射される光の活性層の積層面に対して垂直な方向の半値幅（θ⊥）が狭くなることにつながる。従って、この実験よりθ⊥を２７°以下にする必要がある。
【００８０】
θ⊥が２７°以下ではレーザ端面部分での劣化が生じないため、図６に示した半導体レーザ素子の信頼性はほぼ発振閾値電流の値によって決まる。すなわち、発振閾値電流の低いロットは高い信頼性を有している。同じロット内の個々の素子においても、初期Ｉｏｐの高い素子は電流の増加率も高く、初期Ｉｏｐの低い素子は電流の増加率も低いことから、初期Ｉｏｐ、すなわち発振閾値電流を下げることが高い信頼性を得るために必要であることがわかる。
【００８１】
上記表３および表４に各半導体レーザ素子の発振閾値電流、発振波長、θ⊥、θ／／（出射光の、活性層の積層面に対して平行な方向の半値幅）、および信頼性を示す推定平均故障時間ＭＴＴＦも同時に示した。
【００８２】
以上の結果から、波長６３０ｎｍ以上６４２ｎｍで発振する半導体レーザ素子において、５０℃および３０ｍＷでＭＴＴＦ３０００時間以上を得るためには、量子井戸層厚９０オングストローム以上１２０オングストローム未満でθ⊥を２２°以上２７°以下にすればよい。
【００８３】
さらに、量子井戸層厚１００オングストローム以上１２０オングストローム未満でθ⊥を２２°以上２７°以下にすれば、より閾値電流を低くすることができるので好ましい。
【００８４】
（実施形態２）
本実施形態では、ｐ型第２クラッド層１４およびｐ型第３クラッド層１６のドーピング量について検討を行った。
【００８５】
ｐ−ＡｌＧａＩｎＰ第３クラッド層１６のＢｅドーピング量を５×１０¹⁷ｃｍ^-3とした以外は、実施形態１において表３に示したＸ８９と同様の構造の半導体レーザ素子を作製した。
【００８６】
図７（ａ）はｐ型第３クラッド層１６のＢｅドーピング量を５×１０¹⁷ｃｍ^-3とした半導体レーザ素子のＩ−Ｌ（電流一光出力）特性を示す図であり、図７（ｂ）はｐ型第３クラッド層１６のＢｅドーピング量を１×１０¹⁸ｃｍ^-3とした半導体レーザ素子（Ｘ８９）のＩ−Ｌ（電流−光出力）特性を示す図である。
【００８７】
この図７からわかるように、ｐ型第２クラッド層１４およびｐ型第３クラッド層１６のＢｅドーピング量を５×１０¹⁷ｃｍ^-3とした半導体レーザ素子では、２５℃での閾値電流はＸ８９とほぼ同じ値であちが、高温５０℃での閾値電流および動作電流はＸ８９よりも高くなっている。
【００８８】
これは、ｐ型クラッド層のドーピング濃度が低いと、キャリアである電子が活性層からｐ型クラッド層ヘオーバーフローするのを防ぐ実効的なバリア効果が下がるためである。つまり、ｐ型クラッド層のドーピング濃度が低いと、電子がオーバーフローし易く、その結果、温度特性が悪くなって５０℃で３０ｍＷの光出力を得ることができない。特に、波長が６４２ｎｍ以下と短いため、活性層のバンドギャップが大きくなり、相対的に活性層とクラッド層によるバリア効果が小さくなるので、ｐ型クラッド層のドーピング量を増やしてバリア効果を得ることは重要である。
【００８９】
ここで、５０℃で３０ｍＷの光出力を得るためには、ｐ型クラッド層のドーピング量を１×１０¹⁸ｃｍ^-3とするのが好ましい。また、他の半導体レーザ素子の実験から、ドーピング量がある程度以上になるとＩｔｈが上昇するという結果が得られているので、本発明においても適宜ドーピング量を調整するのが好ましい。
【００９０】
なお、上記実施形態では半導体層の成長のためにＭＢＥ装置を用いている。その他の成長装置として、ＡｌＧａＩｎＰ系の半導体レーザ素子の製造においては一般に、ＭＯＣＶＤ装置が用いられている。このＭＯＣＶＤ装置では、ｐ型ドーパントとしてＺｎまたはＭｇが使用されるが、ＺｎまたはＭｇは結晶内での拡散係数が大きいので、成長中または熱処理時の拡散が起こり、ｐ型クラッド層のドーピング濃度を高くすることができない。これは、ドーピング濃度を高くすると、活性層へのドーパントの拡散が生じ、閾値電流が増加するからである。
【００９１】
一方、Ｂｅではこのようなドーパントの拡散の問題が生じないが、有機原料が一般的でなく、また、除外装置の関係からもドーパントとしてＢｅを用いる成長はＭＢＥ法に限られる。従って、上記実施形態のように、製造装置としてＭＢＥ装置を用い、ｐ型クラッド層のドーパントとしてＢｅを用いれば、５０℃、３０ｍＷ以上の条件で実用上十分に高い信頼性を有する半導体レーザ素子を得ることができる。
【００９２】
（実施の形態３）
本実施例では、波長６５０ｎｍから６６０ｎｍにおける最適構造の例を示す。波長６５０ｎｍはDVD-video、DVD-ROM、DVD-audioなどの再生用として、光出力５ｍＷから１０ｍＷが必要とされている。再生用の半導体レーザは記録用の半導体レーザと違い、10000時間以上の高い信頼性を必要とされる。高い信頼性を得るためには、低い閾値電流と良好な温度特性と、高い温度での動作電流を低減し、高い信頼性を得る必要がある。
【００９３】
本実施例は、DVD-video、DVD-ROM、DVD-audioなどのDVDファミリーディスクの再生専用ドライブに用いられる、半導体レーザ素子の例を示す。図10は本半導体レーザ素子の概略構造を示す図である。
【００９４】
本実施例の構造は実施の形態１の構造と多重量子井戸活性層４１の構造が異なる以外は同一である。
【００９５】
図11に本実施の形態の多重量子井戸の構造図を示す。量子井戸の数及び量子井戸幅は図１３のように変化させた。ここで、光ガイド層４３及び４２のＡｌ混晶比は０．５０、ｎ型クラッド層１２及びｐ型クラッド層１４のＡｌ混晶比は０．７２である。光ガイド層４３及び４２の混晶比、ｎ型クラッド層１２及びｐ型クラッド層１４のＡｌ混晶比は量子井戸数、量子井戸幅を変えても、すべて同一としている。
【００９６】
本実施例の作成方法は、実施の形態１と活性層構造を除き、同一のため省略する。
【００９７】
次に高温で高い信頼性を有する半導体レーザ素子を得るために本願の発明者が量子井戸幅及び量子井戸の数について、特定の関係を見出した経緯について説明する。
【００９８】
発振波長６５０ｎｍから６６０ｎｍにおける最適構造は以下のように決定する。
【００９９】
図１２に、発振波長と量子井戸幅と活性層歪量の関係を示す。図中には６５０ｎｍ及び６６０ｎｍの波長を得るための関係を示している。
【０１００】
発振波長として６５０ｎｍまたは６６０ｎｍを得るためには、図１２の６５０ｎｍまたは６６０ｎｍと記したライン上の任意の井戸幅を選ぶことができるが、発振閾値をできるだけ下げ、高温度での動作電流を低減し、信頼性を上げるためには、実施の形態１で記述したように、ヘビィホール準位とライトホール準位のエネルギーがなるべく離れ、ヘビィホールまたはライトホールにキャリアを集中させる方がよい。
【０１０１】
図１２の中で２点鎖線で示したラインは、ヘビィホール準位とライトホール準位が一致するラインである。このラインより上では、ヘビィホール準位のエネルギーがライトホール準位のエネルギーよりも高いため、活性層に注入されたホールは、ヘビィホール準位に集中し、レーザ発振はヘビィホールと電子の性結合により発生する。逆にこのラインより下では、ライトホール準位のエネルギーがヘビィホール準位のエネルギーより高いため、活性層に注入されたホールは、ライトホール準位に集中し、レーザ発振はヘビィホールと電子の再結合により発生する。図の２点鎖線の上でも下でも、このラインより離れれば、閾値は下がるが、図１２よりわかるように発振波長が、６５０ｎｍまたは６６０ｎｍでは、井戸幅が、略１００Åより大きいところでは量子井戸の井戸幅を変化させても歪量を変化させることはできず、その結果、ライトホールとヘビィホール準位の一致するラインに近い構成になってしまうことが分かる。
【０１０２】
したがって、準位の一致するラインから離すことが可能な、井戸幅７０Å以下が有利である。
【０１０３】
図１３に、井戸幅４０Åから１１５Åに、井戸数を９層から２層に変化させたときの、動作電流Ｉop（７０℃）、閾値電流Ith（２５℃）、特性温度TOの結果を示す。図１３では、７０Åより右方向になると、閾値が上昇し、特性温度TOが低くなる。これは、井戸幅が大きくなると、ヘビィホール準位とライトホール準位のエネルギが接近して、発振に必要とされる価電子帯を充填するためのキャリアが増えるためである。また左方向（４０Å以下）では、再び閾値電流が増加する。これは、量子井戸界面の効果と考えられる。即ち、井戸層とバリア層の界面では、素子成長時に構成材料の量を切り替えるが、この切り替えが完全に行われないために、理想の結晶状態よりずれ、非発光再結合中心が存在する。活性層が厚い場合は、この非発光再結合の効果は少ないが、井戸幅が小さくなると効果は増大し、閾値が上昇することになる。
【０１０４】
一方、波長６３０ｎｍから６４０ｎｍでは、ヘビィホール準位とライトホール準位のエネルギーが一致するラインより上の領域は、井戸幅７０Åより薄い領域となり、ラインより離れるためには、さらに小さい領域は非発光再結合の領域に入るため、十分な、ヘビィホール準位とライトホール準位のエネルギーの分離が得られない。したがって、６３０ｎｍから６４０ｎｍでは、実施の形態１で述べたようなライトホール準位とヘビィホール準位が一致するラインより下の領域で、且つ歪の大きいことから起因する結晶破壊のない領域を選ぶ必要がある。
【０１０５】
したがって、必要とする発振波長により、自動的に活性層の量子井戸層の厚さに最適点が存在する。尚、ヘビィホール準位とライトホール準位のエネルギーが一致するラインより上の領域は、ヘビィホールと電子による再結合のため、レーザ発振は、ｐ-ｎ接合面に電界が平行なＴＥモードとなり、ヘビィホール準位とライトホール準位のエネルギーが一致するラインより下の領域はライトホールと電子による再結合のため、レーザ発振はｐ-ｎ接合面に電界が垂直なＴＭモードとなる。
【０１０６】
図１３の上下方向は井戸幅×井戸数を示す。この井戸幅×井戸数は活性層の利得を持つトータルな厚さを示す。また、井戸幅×井戸数が大きくなると、光閉じ込め係数が増大するため、特性温度がよくなるが、活性層内部の体積が増えるために、同じ閾値キャリア密度を得るために閾値電流が増える。また、井戸幅×井戸数が小さくなると、光閉じ込め係数が減少し、レーザ発振を得るために必要とされる利得が増大し、閾値電流が増える。したがって、井戸幅×井戸数にも最適点が存在する。
【０１０７】
ここで、Ｉthの一番小さい井戸幅は約７５Åであるが、井戸幅５０Åの方が特性温度TOが高いため、Iop（７０℃）が一番近い５０Å×４層が一番良い特性になる。
【０１０８】
図１４に井戸幅×井戸数に対する温度特性の依存性を示す。井戸幅×井戸数はほぼ活性層の光閉じ込め係数に関係する。同じ井戸幅では、特性温度TOは井戸幅×井戸数が大きくなると大きくなる傾向がある。しかし、図１４ではその関係が井戸幅によって変わることを示しており、井戸幅５０Åにおいて、同じ井戸幅×井戸数でも高い特性温度が得られ、したがって高い温度でも低い動作電流が得られることを示す。
【０１０９】
本実施例の半導体レーザ素子（量子井戸幅５０Å、量子井戸数４）の発振閾値Ith（２５℃）が４９ｍＡ、θ⊥は３０°、θ／／は８．５°であった。
【０１１０】
図１５に、本実施形態の半導体レーザ素子の信頼性を示す。Ｉopが初期の１．２倍になる時間を寿命として平均故障時間（MTTF）を推定すると、７０℃５ｍＷで推定ＭＴＴＦは１０万時間以上と十分な信頼性を有し、ＤＶＤファミリーの再生用ディスクの再生用ドライブの半導体レーザ素子として十分使用できる。
【０１１１】
ここで、本実施例では、ｐ型第２クラッド層１４及びｐ型第３クラッド層１６のドーピング量について検討を行った。ｐ型ＡｌＧａＩｎＰ第３クラッド層及び第２クラッド層のＢｅドーピング量を５×１０¹⁷ｃｍ^-3とし、量子井戸幅５０Å、量子井戸数４とした。
【０１１２】
この比較用の素子の７０℃５ｍＷでの動作電流が高い。したがって推定ＭＴＴＦは１５００時間と再生用ドライブに要求される値（約１００００時間）より低くなる。
【０１１３】
（実施の形態４）
本実施例では、書き換えを行うＤＶＤ−ＲＡＭ及びＤＶＤ−ＲＷドライブに用いられる６５０ｎｍ６６０ｎｍを出射する高出力半導体レーザ素子について記述する。
【０１１４】
ＤＶＤ−ＲＡＭ及びＤＶＤ−ＲＷドライブでは、例えばメディアの結晶状態を変えて（相変化）情報を記録する。その結晶の相を変化させるために高い出力の半導体レーザ素子が必要である。その出力パワーはパルス駆動条件で光出力５０ｍＷ（ＣＷ駆動条件で３５ｍＷに相当）または光出力７０ｍＷ（ＣＷ駆動条件で５０ｍＷ）が必要とされる。
【０１１５】
図１７は本実施例の半導体レーザ素子の概略構成を示す断面図である。本実施例の構造は実施の形態１の構造と多重量子井戸活性層４１の構造が異なる以外は同一である。
【０１１６】
図１８に多重量子井戸活性層の構造図を示す。ここで光ガイド層４３および４２のＡｌ混晶比は０．５９、ｎ型クラッド層１２、ｐ型クラッド層１４のＡｌ混晶比は０．６９である。
【０１１７】
実施の形態３と同じく、波長が６５０ｎｍから６６０ｎｍであるため、同様の理由により、活性層の厚さは５０Åが最適である。
【０１１８】
高出力を得るためには、端面の光密度を低減するために、活性層部分での光を拡げる必要がある。
【０１１９】
図１９に活性層の量子井戸の数に対するθ⊥（出射光の、活性層の積層面に対して垂直な方向の半値幅）および活性層での光密度の値を示す。井戸数が増えるほど、一定出力での光密度が上がっていく。
【０１２０】
したがって、井戸幅はそのままで、井戸の数を４層から３層に減らし、活性層部分での光密度を低減した構造とした。ここで光ガイド層４３、４２、ｎ型クラッド層１２、及びｐ型クラッド層１４のＡｌ混晶比を変えることにより屈折率が変化し、端面での光密度、及びθ⊥を変えることができる。（クラッド層のＡｌ混晶比）−（ガイド層のＡｌ混晶比）を０．１とすることで、井戸数２でθ⊥２２°を得ることができる。
【０１２１】
その他の部分は、実施の形態３と同様である。実施の形態３と同様の方法で半導体レーザ素子を作成し、特性を測定した。室温での閾値電流は５１ｍＷであり、θ⊥２２°を得られた。図２０に７０°３５ｍＷ（ＣＷ）での信頼性試験の結果を示す。１０００時間以上安定に動作し、推定寿命ＭＴＴＦは７万時間であり、十分な信頼性を有する。
【０１２２】
（実施の形態５）
次に、パルス７０ｍＷの光出力を得るためには、光出力が上昇する分、さらに端面の光分布を広げ、活性層部分での光密度を下げる必要がある。したがって、井戸の層数を３層からさらに数を減少させ、井戸幅５０Å、井戸数２層とした。その他の部分は、実施の形態４と同じ構造である。
【０１２３】
実施の形態４と同様の方法で、半導体レーザ素子を作成し、特性を測定した。室温での閾値電流は５４ｍＡであり、θ⊥２１．５°が得られた。活性層のトータルの厚さを小さくしたために、活性層での光分布が広がり、したがって高い光出力を出した場合でも、活性層の光密度はあまりあがらない。図２１に７０℃、パルス７０ｍＷにおける信頼性試験結果を示す。７０℃７０ｍＷでも安定に動作し、推定ＭＴＴＦは３０００時間と、書き込み用の半導体レーザ素子として十分な信頼性を得ることができた。
【０１２４】
また、比較のために、本実施の形態５と同じ構造で、ｐ型第２クラッド層１４及びｐ型第３クラッド層１６のドーピング量について検討を行った。ｐ型ＡｌＧａＩｎＰ第３クラッド層及び第２クラッド層のＢｅドーピング量を７×１０¹⁷ｃｍ^-3とし、量子井戸幅５０Å、量子井戸数２とした。図２２に、この比較用の素子の７０℃７０ｍＷパルスの信頼性走行経過を示す。Ｂｅドーピング濃度が低いと、温度特性が悪く、７０℃５ｍＷでの動作電流が高い。したがって、７０℃７０ｍＷのパルスでの信頼性試験では、初期より劣化の程度が大きく、初期Ｉopの１．２倍となる点を寿命として推定すると、ＭＴＴＦは５００時間となる。端面での光密度を下げるために、量子井戸層の厚さの総和を小さくすることにより、活性層での光閉じ込め係数が減少する。したがって、温度特性が比較的悪くなるため、ｐ型クラッド層でのＢｅ濃度が１×１０¹⁸ｃｍ^-3以上であることが重要である。
【０１２５】
以上の説明は基板面の向きに依存しない。しかし、より高い信頼性を得るために基板の主面を（１００）面から［０１１］方向に１０〜１５度傾けても良いことは言うまでもない。
【０１２６】
【発明の効果】
以上詳述したように、本発明によれば、波長６３０ｎｍ以上６４２ｎｍで光出力３０ｍＷの半導体レーザ素子において、５０℃の高温条件で書き込み用の半導体レーザ素子として十分なＭＴＴＦ３０００時間以上という高い信頼性を有する半導体レーザ素子を得ることができる。従って、本発明の半導体レーザ素子は、ＤＶＤ−Ｒ用の半導体レーザ素子として好適に使用することができ、光磁気ディスクや光ディスク等の光情報処理システム等において、記録コストを低廉化し、記録容量を大きくするために非常に有効である。
【０１２７】
また、波長６５０ｎｍ以上６６０ｎｍ以下で、光出力５ｍＷ、３５ｍＷ（ＣＷ）、７０ｍＷ（パルス）のいずれかの半導体レーザ素子において、７０℃の高温条件で、再生用、書き換え用、書き込み用のいずれかの半導体レーザ素子として十分な、それぞれ、ＭＴＴＦ１０万時間以上、７万時間以上、３０００時間以上という高い信頼性を有する半導体レーザ素子を得ることができる。従って、本発明の半導体レーザ素子は、DVD-video、DVD-ROM、DVD-audioなどのDVDファミリーディスクの再生専用ドライブ、或いは、DVD-RAM、DVD-RWドライブに用いる半導体レーザ素子として好適に使用することができ、光磁気ディスクや光ディスク等の光情報処理システム等において、記録コストを低廉化し、記録容量を大きくするために非常に有効である。
【０１２８】
さらに、ＧａＡｓまたはＧａＰ基板上のＧａＩｎＰやＧａＮまたはＳｉ基板上のＧａＩｎＮ、ＧａＡｓまたはＧａＰ基板上のＧａＩｎＡｓ、ＧａＳｂ基板上のＧａＩｎＳｂにおけるＩｎ量といった組成比によって歪量が変化する化合物半導体材料を用いて、発振波長を変えても、容易に最適な量子井戸活性層の構成を導くことができ、狙った波長で、狙った特性を持つ半導体レーザ素子およびその製造方法を提供することが可能になる。
【図面の簡単な説明】
【図１】実施形態の半導体レーザ素子の製造工程を説明するための断面図である。
【図２】実施形態の半導体レーザ素子における量子井戸活性層の概略構造を示す図である。
【図３】実施形態の半導体レーザ素子におけるθ⊥と光ガイド層のＡｌ混晶比とクラッド層のＡｌ混晶比の関係を示す図である。
【図４】実施形態の半導体レーザ素子における量子井戸幅とθ⊥と閾値電流の関係を示す図である。
【図５】実施形態の半導体レーザ素子における波長と量子井戸幅と活性層歪量の関係を示す図である。
【図６】実施形態の半導体レーザ素子における信頼性評価結果を示す図である。
【図７】実施形態の半導体レーザ素子におけるＩ−Ｌ特性を示す図である。
【図８】従来の半導体レーザ素子における量子井戸活性層の概略構造を示す図である。
【図９】従来の半導体レーザ素子における信頼性評価結果を示す図である。
【図１０】実施形態の半導体レーザ素子の概略構造を示す図である。
【図１１】実施形態の半導体レーザ素子における量子井戸活性層の概略構造を示す図である。
【図１２】実施形態の半導体レーザ素子における波長と量子井戸幅と活性層歪量の関係を示す図である。
【図１３】実施形態の半導体レーザ素子における（井戸幅×井戸数）と、井戸幅とを変化させたときの、動作電流Ｉop、閾値電流Ith、特性温度TOの値を示す図である。
【図１４】実施形態の半導体レーザ素子における（井戸幅×井戸数）と、温度特性TOとの関係を示す図である。
【図１５】実施形態の半導体レーザ素子における信頼性評価結果を示す図である。
【図１６】比較用の素子における信頼性評価結果を示す図である。
【図１７】実施形態の半導体レーザ素子の概略構造を示す図である。
【図１８】実施形態の半導体レーザ素子における量子井戸活性層の概略構造を示す図である。
【図１９】実施形態の半導体レーザ素子における、井戸層の数と活性層での光密度、及びθ⊥との関係を示す図である。
【図２０】実施形態の半導体レーザ素子における信頼性評価結果を示す図である。
【図２１】実施形態の半導体レーザ素子における信頼性評価結果を示す図である。
【図２２】比較用の素子における信頼性評価結果を示す図である。
【符号の説明】
１１ ｎ−ＧａＡｓ基板
１２ ｎ−ＡｌＧａＩｎＰ第１クラッド層
１４ ｐ−ＡｌＧａＩｎＰ第２クラッド層
１５ ｐ−ＧａＩｎＰエッチングストップ層
１６ ｐ−ＡｌＧａＩｎＰ第３クラッド層
１７ ｐ−ＡｌＧａＩｎＰ中間バンドギャップ層
１８ ｐ−ＧａＡｓコンタクト層
１９ マスク層
２０ ＧａＡｓ電流ブロック層
２１ ＧａＡｓ多結晶層
２３ 開口
３１ メサ部
４１ 量子井戸活性層
４２ ＡｌＧａＩｎＰ第２光ガイド層
４３ ＡｌＧａＩｎＰ第１光ガイド層
４６ ＧａＩｎＰ井戸層
４７ ＡｌＧａＩｎＰ障壁層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an AlGaInP-based semiconductor laser element suitably used as a light source for recording and reading in an optical information system such as a magneto-optical disk and an optical disk, and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, AlGaInP semiconductor laser elements have begun to be used as light sources for recording and reading in optical information systems such as magneto-optical disks and optical disks. In particular, a semiconductor laser element having an oscillation wavelength of 635 nm to 650 nm is used as a key device for realizing a high-density optical disk such as a DVD.
[0003]
When a semiconductor laser element is used as a light source for such an optical information processing system, a shorter wavelength is required for higher information density, and a higher output is required for faster rewriting. Furthermore, in order to guarantee the high temperature operation of the system main body, the high temperature operation of the semiconductor laser element and the high reliability in the environment are required.
[0004]
Furthermore, recently, a once-writable DVD-R has been established and commercialized, and it is considered that this DVD-R will be widely spread in the future due to its low recording cost and large recording capacity.
[0005]
The semiconductor laser element used in this DVD-R drive has an oscillation wavelength limited to 630 nm to 642 nm at room temperature (25 ° C.) (hereinafter, all oscillation wavelengths are oscillation wavelengths at room temperature). This is because a dye having a large absorption coefficient only in the vicinity of 630 nm to 642 nm is used as a recording material for DVD-R media. In addition, the DVD-R drive requires a high output of 30 mW for writing, and further, the semiconductor laser element is required to operate at a high temperature in order to guarantee the operation of the apparatus body at a high temperature. Is done.
[0006]
However, such a short-wavelength and high-power semiconductor laser device is much more difficult to manufacture than a long-wavelength semiconductor laser device. The reason is as follows.
[0007]
In order to shorten the oscillation wavelength, it is necessary to increase the band gap of the active layer. Thus, when the band gap of the active layer is increased, the band gap difference between the active layer and the cladding layer is reduced. However, in the semiconductor laser device, overflow of electrons or holes from the active layer is prevented by the band gap difference. Accordingly, when the difference in band gap between the active layer and the cladding layer is reduced, the overflow of electrons increases. As a result, in the semiconductor laser element, the threshold current and operating current at a high temperature increase in degree to the threshold current and operating current with respect to the temperature, and so-called temperature characteristics are deteriorated.
[0008]
AlGaInP material To charge In the case of a representative group III-V compound semiconductor, it is known that increasing the ratio of Al to Ga can increase the band gap with almost no change in lattice constant. For this reason, it is possible to shorten the oscillation wavelength if a layer having a large proportion of Al to Ga is used for the active layer. However, Al is an active element, and it is a well-known fact that the reliability of the semiconductor laser element is lowered. It is. For this reason, a semiconductor laser element using, for example, a GaInP quantum well active layer in which Al is not contained in the active layer has been developed.
[0009]
In order to shorten the oscillation wavelength by using the GaInP layer as the active layer, the ratio of In to Ga may be reduced. Alternatively, the quantum level may be changed by reducing the thickness of the quantum well layer. However, if the ratio of In and Ga is changed, the lattice constant of the quantum well layer and the lattice constant of the GaAs substrate are different, so that strain (lattice strain) occurs in the quantum well layer. For example, when In and Ga are 1: 1, no strain is generated, so that a so-called lattice matching state is obtained. However, when the In ratio is increased, the lattice constant of the quantum well layer increases, and the quantum well layer has a compressive strain ( On the contrary, when the In ratio is decreased, the lattice constant of the quantum well layer is reduced, and tensile strain (negative strain) is applied to the quantum well layer.
[0010]
When the absolute value of strain exceeds a certain value, so-called crystal breakage occurs, in which the crystal is hatched. It is known that the absolute value of strain at which crystal breakdown occurs is approximately proportional to the product of the thickness of the quantum well layer (the sum of the quantum well layers if there are a plurality of quantum well layers) and the absolute value of strain. When the quantum well layer undergoes crystal breakdown, it cannot be used as a semiconductor laser element.
[0011]
That is, in order to use a strained layer as the active layer, it is necessary to use a sufficiently thin layer, for example, 200 angstroms or less, as the quantum well layer.
[0012]
Further, in the case of a high-power semiconductor laser element, a thinner active layer is used than in the case of a low-power semiconductor laser element in order to reduce the light density inside the element. For this reason, since the light confinement coefficient in the active layer is lowered, the temperature characteristics are further deteriorated.
[0013]
At present, semiconductor laser devices having a relatively long oscillation wavelength of 650 nm and an optical output of 30 mW have been developed that can operate at temperatures of 60 ° C. to 70 ° C. (for example, the 44th JSAP Related Proceedings 31a -NG-6). However, a semiconductor laser element that can be used at an oscillation wavelength of 642 nm or less and an optical output of 30 mW or more, which is essential as a semiconductor laser element for a DVD-R device, cannot be used at a temperature of 40 ° C. or more in consideration of reliability ( US DVD Conference May 28 and 29, 1997).
[0014]
In this way, it is difficult to use a semiconductor laser element having a maximum operating temperature of 40 ° C. or less using a drive device in consideration of the guaranteed temperature (maximum 50 ° C.) of the drive device. Need to use. However, the use of a cooling device increases the size of the drive device and further increases the cost.
[0015]
[Problems to be solved by the invention]
As described above, a semiconductor laser element having an oscillation wavelength of 630 nm to 642 nm at room temperature and an optical output of 30 mW has not been realized so far that has sufficient reliability under a temperature condition of 50 ° C.
[0016]
For the same reason, a semiconductor laser element having an oscillation wavelength of 650 nm to 660 nm at room temperature that can operate at a temperature of 70 ° C. or higher has not been realized.
[0017]
In order to obtain a semiconductor laser device having sufficient reliability at a high temperature, it is desirable to reduce the threshold current and the end face light density. However, these parameters are generally contradictory.
[0018]
For example, the light distribution near the active layer is expanded to , Activity Layered Laminated Against the face When the half-value width θ⊥ in the vertical direction is reduced, the light density at the end face is lowered and deterioration at the end face can be prevented. Here, the half-value width of the emitted light is 1 of the maximum value of the light output on the opposite side across the direction of the maximum value from the direction of 1/2 of the maximum value of the light output in the far-field image of the emitted light. Suppose that it is represented by an angle (full width at half maximum) formed with the direction to be / 2. However, in this case, the light confinement factor is also reduced, and the threshold current for laser oscillation is increased. Accordingly, the number of carriers required for laser oscillation in the active layer increases, and electrons serving as carriers overflow into the cladding layer, resulting in poor light emission efficiency. As a result, there is a problem that the reliability of the semiconductor laser element is lowered.
[0019]
The present invention has been made to solve such problems of the prior art, and can operate at a high output (light output 30 mW) at a wavelength of 630 nm or more and 642 nm or less, and is sufficient even at a high temperature condition (50 ° C.). An object of the present invention is to provide a semiconductor laser device capable of obtaining reliability (MTTF 3000 hours) and a method for manufacturing the same.
[0020]
It is another object of the present invention to provide a semiconductor laser device capable of obtaining sufficient reliability (MTTF 10,000 hours) even at a high temperature condition (70 ° C.) at an oscillation wavelength of 650 nm or more and 660 nm or less at room temperature, and a manufacturing method thereof.
[0021]
Furthermore, using a compound semiconductor material in which the amount of strain changes depending on the composition ratio such as the amount of In in GaInP on a GaAs or GaP substrate, GaInN on a GaN or Si substrate, GaInAs on a GaAs or GaP substrate, GaInSb on a GaSb substrate, or the like. It is an object of the present invention to provide a semiconductor laser device having a target characteristic at a target wavelength and a method for manufacturing the same, which can easily lead to an optimum quantum well active layer configuration even when the oscillation wavelength is changed.
[0022]
[Hand throws to solve problems]
As a result of intensive studies, the inventors of the present application have found that a semiconductor laser element having high reliability at a targeted wavelength when the well width of the quantum well active layer and the amount of strain in the active layer have a specific relationship. Has been found, and the present invention has been completed.
[0023]
Also, the well width (well layer thickness) that determines the structure of the quantum well active layer, and the emission light of the semiconductor laser device , Active layer of Laminated Against the face It has been found that a semiconductor laser device having high reliability at a high temperature can be obtained when the half-value width θ⊥ in the vertical direction has a certain relationship, and the present invention has been completed.
[0024]
The semiconductor laser device of the present invention is
In a semiconductor laser device having a quantum well active layer made of a material system in which the amount of strain changes when the composition of atoms constituting the crystal is changed and the band gap energy is changed,
The quantum well active layer has a plurality of quantum well layers, and each well width of the quantum well layer is 40 mm or more and less than 120 mm,
The quantum well layer is set to a strain amount that maximizes the absolute value of the difference between the energy level of the heavy hole at the Γ point of the quantum well layer and the energy level of the light hole in a range where crystal breakdown does not occur. Therefore, the above object can be achieved.
[0025]
The semiconductor laser device of the present invention has a quantum well active layer made of a GaInP-based material, and in a semiconductor laser device having an oscillation wavelength of 630 nm or more and 642 nm or less at room temperature, the layer thickness of the quantum well layer constituting the active layer Is 90 angstroms or more and less than 120 angstroms. , Active layer of Laminated Against the face The full width at half maximum θ の in the vertical direction is not less than 22 ° and not more than 27 °, whereby the above object is achieved.
[0026]
The quantum well layer preferably has a thickness of 100 angstroms or more and less than 120 angstroms, and the θ 前 記 is 23 ° or more and 27 ° or less.
[0027]
The semiconductor laser device of the present invention is
When the quantum well layer is made of a GaInP-based material and the oscillation at room temperature is not less than 650 nm and not more than 660 nm,
The well width of the quantum well layer is not less than 40 and not more than 70, thereby achieving the above object.
[0028]
The semiconductor laser device of the present invention is
The number of the quantum well layers is 2 or more and 4 or less, whereby the above object is achieved.
[0029]
The semiconductor laser device of the present invention has a Active layer Laminated Against the face The full width at half maximum θ の in the vertical direction is 19 ° or more and 31 ° or less, whereby the above object is achieved.
[0030]
In the semiconductor laser device of the present invention, the number of the quantum well layers is 2 or 3, and the θ⊥ is 20 ° or more and 24 ° or less, whereby the above object is achieved.
[0031]
Of the pair of cladding layers sandwiching the quantum well active layer, the impurity concentration of the p-type cladding layer is 1 × 10 ¹⁸ cm ^-3 The above is preferable.
[0032]
The dopant of the p-type cladding layer is preferably Be.
[0033]
In the method for manufacturing a semiconductor laser device of the present invention, it is preferable that the semiconductor layer is grown by a molecular beam epitaxial apparatus.
[0034]
The operation of the present invention will be described below.
[0035]
In the present invention,
In a semiconductor laser device having a quantum well active layer made of a material system in which the amount of strain changes when the composition of atoms constituting the crystal is changed and the band gap energy is changed,
The quantum well active layer has a plurality of quantum well layers, and each well width of the quantum well layer is 40 mm or more and less than 120 mm,
The quantum well layer is set to a strain amount that maximizes the absolute value of the difference between the energy level of the heavy hole at the Γ point of the quantum well layer and the energy level of the light hole in a range in which crystal breakdown does not occur. thing
And
[0036]
As a result, as shown in an embodiment described later, the strain amount of the quantum well is as far as possible from the line where the energy levels of the heavy hole and the light hole of the quantum well coincide with each other, and the critical film thickness does not cause crystal defects. Therefore, even if the oscillation wavelength of the laser is changed, carriers can be concentrated in heavy holes or light holes, and efficient laser oscillation can be induced.
[0037]
In the present invention, in a semiconductor laser element made of an AlGaInP-based material and having an oscillation wavelength of 630 nm or more and 642 nm or less, the thickness of the GaInP quantum well layer is 90 angstroms or more and less than 120 angstroms, , Active layer of Laminated Against the face The full width at half maximum θ⊥ in the vertical direction is set to 22 ° to 27 °. Thereby, as shown in the embodiment to be described later, the end face light density is sufficiently lowered to prevent deterioration due to light at the end face portion, and crystal breakage (hatching) due to exceeding the limit of lattice distortion does not occur, Since the optical confinement factor is sufficient, the operating current is reduced. Further, since the oscillation threshold current is sufficiently low, the operating current is low, and the rate of increase in current is low, so that the reliability is improved. As a result, MTTF of 3000 hours or more sufficient reliability as a semiconductor laser device for rewriting can be obtained under the conditions of an optical output of 30 mW and a temperature of 50 ° C.
[0038]
When the layer thickness of the quantum well layer is 100 angstroms or more and less than 120 angstroms and θ 、 is 23 ° or more and 27 ° or less, the threshold current is further reduced.
[0039]
In the present invention, in a semiconductor laser element made of an AlGaInP-based material and having an oscillation wavelength of 650 nm or more and 660 nm or less, the thickness of the GaInP quantum well layer is set to 40 angstroms or more and less than 70 angstroms, and the quantum well layer thickness is set to 2 or more and 4 The output light , Active layer of Laminated Against the face The half-value width θ⊥ in the vertical direction is set to 19 ° or more and 24 ° or less.
[0040]
Thereby, as shown in the embodiment to be described later, the end face light density is sufficiently lowered to prevent deterioration due to light at the end face portion, and crystal breakage (hatching) due to exceeding the limit of lattice distortion does not occur, Since the optical confinement factor is sufficient, the operating current is reduced. Further, since the oscillation threshold current is sufficiently low, the operating current is low, and the rate of increase in current is low, so that the reliability is improved. As a result, a reliability of MTTF of 100,000 hours or more sufficient for a semiconductor laser device for reproduction can be obtained under the conditions of an optical output of 5 mW and a temperature of 70 ° C.
[0041]
If the number of quantum well layers is 2 or 3, and θ 、 is 20 ° or more and 24 ° or less, the light density at the end face can be further reduced, and the light in the active layer portion can be spread. As a result, a reliability of MTTF of 70,000 hours or more sufficient for a rewrite semiconductor laser device can be obtained under the conditions of an optical output of 35 mW (CW) and a temperature of 70 ° C.
[0042]
If the number of quantum well layers is 2 and θ 、 is 21.5 °, the light distribution at the end face can be further expanded and the light density at the active layer portion can be reduced. As a result, MTTF of 3000 hours or more sufficient reliability as a semiconductor laser device for writing can be obtained under the conditions of an optical output of 70 mW (pulse) and a temperature of 70 ° C.
[0043]
Further, the impurity concentration of the p-type cladding layer is 1 × 10. ¹⁸ cm ^-3 In this way, the barrier effect for preventing electrons as carriers from overflowing from the active layer to the p-type cladding layer is increased.
[0044]
When Zn or Mg is used as the dopant for the p-type cladding layer, the diffusion coefficient in the crystal is large, so that diffusion occurs during the growth of the semiconductor layer or during heat treatment, and the impurity concentration of the p-type cladding layer cannot be increased. Therefore, Be is preferably used as the dopant of the p-type cladding layer.
[0045]
For the growth of the AlGaInP-based semiconductor layer, MOCVD (metal organic vapor phase epitaxy) or MBE (molecular beam epitaxy) can be used. However, organic materials are not generally used for Be, and it is preferable to use an MBE apparatus from the viewpoint of an exclusion apparatus.
[0046]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0047]
(Embodiment 1)
FIG. 1D is a cross-sectional view showing a schematic structure of the semiconductor laser device of this embodiment.
[0048]
This semiconductor laser device is an AlGaInP-based refractive index guided semiconductor laser device, and includes an n-AlGaInP first cladding layer 12, an AlGaInP first light guide layer 43, a multiple quantum well active layer 41, on an n-GaAs substrate 11. An AlGaInP second light guide layer 42, a p-AlGaInP second cladding layer 14, and a p-GaInP etching stop layer 15 are provided. A striped mesa portion 31 comprising a p-AlGaInP third cladding layer 16, a p-GaInP intermediate band gap layer 17, and a p-GaAs contact layer 18 is provided thereon. An n-GaAs current blocking layer 20 is provided on both sides of the mesa portion 31. Further, electrodes (not shown) are provided on the contact layer 18 and the back surface of the substrate 11.
[0049]
This semiconductor laser element can be manufactured, for example, as follows.
[0050]
First, as shown in FIG. 1A, an n-AlGaInP first cladding layer 12, an AlGaInP first light guide layer 43, a multiple quantum well active layer 41, an AlGaInP second light are formed on an n-GaAs substrate 11 by MBE. The guide layer 42, the p-AlGaInP second clad layer 14, the p-GaInP etching stop layer 15, the p-AlGaInP third clad layer 16, the p-GaInP intermediate band gap layer 17, and the p-GaAs contact layer 18 are sequentially grown.
[0051]
At this time, as the active layer 41, a multiple quantum well active layer composed of two GaInP quantum well layers 46 and one AlGaInP barrier layer 47 as shown in FIG. 2 was formed. Further, the quantum well layer thickness (quantum well width), the light guide layer thickness, the light guide layer Al mixed crystal ratio, and the cladding layer Al mixed crystal ratio were changed as shown in Table 3 described later. Where (Al _y Ga _1-y ) _x In _1-x The y of P is referred to as Al mixed crystal ratio. The n-AlGaInP first cladding layer 12, the p-AlGaInP second cladding layer 14, the p-AlGaInP third cladding layer 16, the quantum well layer 46 and the barrier layer 47 of the multiple quantum well active layer 41, the etching stop layer 15, The layer thickness and mixed crystal ratio (x, y) of the intermediate band gap layer 17 and the contact layer 18 were set as shown in Table 1 below. Further, the doping amount in each layer is such that the n-type first cladding layer 12 is made of 1 × 10 6 Si. ¹⁸ cm ^-3 The light guide layer 43, the quantum well active layer 41, and the light guide layer 43 are non-doped, and the p-type third cladding layer 16 is 1 × 10 1 Be. ¹⁸ cm ^-3 It was. Further, impurities and concentrations of the p-type second cladding layer 14, the etching stop layer 15, the intermediate band gap layer 17 and the contact layer 18 were set as shown in Table 2 below.
[0052]
[Table 1]

[0053]
[Table 2]

Next, as a mask layer on this, Al ₂ O _Three The film 19 is evaporated and patterned into a stripe shape by photolithography. Then Al ₂ O _Three Of the contact layer 18, the intermediate band gap layer 17, and the p-type third cladding layer 16, wet etching is performed using the film 19 as a mask. ₂ O _Three Al corresponding to both sides of the film 19 is removed to remove Al ₂ O _Three A mesa portion 31 is formed immediately below the film 19. Note that when removing the p-AlGaInP third cladding layer 16, the etching is surely stopped by selective etching with the p-GaInP etching stop layer 15.
[0054]
Thereafter, the second MBE growth is performed to grow the n-GaAs current blocking layer 20 on both sides of the mesa portion 31 in a convex cross section. At this time, Al ₂ O _Three On the film 19, an n-GaAs polycrystalline layer 21 is formed in a convex cross section.
[0055]
On this, a photoresist 32 is applied as shown in FIG. Then, an opening 23 is provided in the portion of the n-GaAs polycrystalline layer 21 by photolithography, and the top 33 of the n-GaAs polycrystalline layer 21 is exposed.
[0056]
Next, as shown in FIG. 1C, a sulfuric acid-based etchant is used to form Al. ₂ O _Three The n-GaAs polycrystalline layer 21 is selectively etched and removed from the film 19, and then the photoresist 32 is removed.
[0057]
Then, as shown in FIG. 1 (d), using a hydrofluoric acid-based etchant, Al ₂ O _Three The film 19 is removed by etching. Thereafter, electrodes (not shown) are respectively formed on the surface of the contact layer 18 and the back surface of the substrate 11 to obtain the semiconductor laser device of this embodiment.
[0058]
Next, how the inventors of the present application have found a specific relationship between the quantum well width and θ お よ び in order to obtain a semiconductor laser device having high reliability at high temperatures will be described.
[0059]
First, U.S. S. FIG. 8 shows the structure of the active layer described in DVD Conference May 28 and 29, 1997 Proceedings.
[0060]
In FIG. 8, the horizontal axis indicates the distance in the stacking direction, and the vertical axis indicates (Al _y Ga _1-y ) _x In _1-x The Al mixed crystal ratio y of P is shown. The quantum well layer 146 constituting the active layer is made of Ga. _x In _1-x P, the well width is 85 Å, the thickness of the light guide layers 142 and 143 is 500 Å, the Al mixed crystal ratio of the light guide layers 142 and 143 is 0.5, and the Al mixed crystal ratio of the cladding layers 112 and 114 is Is 0.7. In this structure, the outgoing light , Active layer of Laminated Against the face The full width at half maximum θ⊥ in the vertical direction is 25.5 °.
[0061]
FIG. 9 shows a reliability test result in this semiconductor laser device. According to this structure, MTTF of 5400 hours is obtained under conditions of a temperature of 30 ° C. and an optical output of 30 mW. However, at 50 ° C. necessary for guaranteeing the environmental temperature of the apparatus, there arises a problem that the semiconductor laser element is deteriorated because an optical output of 30 mW cannot be obtained.
[0062]
Therefore, in order to perform an operation at a high temperature, it is necessary to further reduce the operating current, that is, the oscillation threshold current.
[0063]
For this reason, the inventors of the present application set the composition of the quantum well layer to Ga. _x In _1-x The experiment was performed as follows by changing the quantum well layer thickness (quantum well width) and the light guide structure while keeping P. Here, the light guide structure specifically means (1) light guide layer Al mixed crystal ratio, (2) cladding layer Al mixed crystal ratio, and (3) light guide layer thickness. The Al mixed crystal ratio of the light guide layer and the Al mixed crystal ratio of the barrier layer were the same.
[0064]
In the present embodiment, as shown in Table 3, a semiconductor laser device was manufactured in which the quantum well width, the light guide layer thickness, the light guide layer Al mixed crystal ratio, and the cladding layer Al mixed crystal ratio were changed. For comparison, semiconductor laser elements as shown in Table 4 were produced. In Table 4, the lot name X03 indicates the conventional semiconductor laser element shown in FIG.
[0065]
[Table 3]

[0066]
[Table 4]

At this time, the oscillation wavelength of the semiconductor laser element is the strain amount of the active layer, specifically, Ga. _x In _1-x The mixed crystal ratio x of the P layer was adjusted so as to be in the range of 635 nm to 642 nm which is optimal for DVD-R. The relationship between the mixed crystal ratio x and the amount of lattice strain is as follows.
[0067]
Mixed crystal ratio X = 0.51−Lattice strain (%) × 0.135
Further, θ⊥ of this semiconductor laser element is determined by the quantum well width, the thickness of the light guide layer, the guide layer Al mixed crystal ratio, and the cladding layer Al mixed crystal ratio. FIG. 3 shows the relationship between θ⊥ obtained from calculations and experiments and the mixed crystal ratio of the light guide layer and the cladding layer. The calculation is obtained by solving Maxwell's equations by a numerical solution. Here, the thickness of the light guide layer is set to 500 angstroms. However, as the light guide layer thickness increases, light gathers in the vicinity of the active layer, so that θ⊥ decreases, and as the light guide layer thickness decreases, θ⊥ increases.
[0068]
From FIG. 3, for example, when the quantum well layer thickness is 110 Å, the Al mixed crystal ratio of the light guide layer is 0.56, and the Al mixed crystal ratio of the cladding layer is 0.68, θ⊥23.7 ° is obtained. .
[0069]
FIG. 4 shows the relationship between the quantum well width, θ⊥, and threshold current of the semiconductor laser device fabricated as described above. In this figure, the numerical value indicates the threshold current at 25 ° C.
[0070]
According to FIG. 4, Ith is lower when the well width is larger, and Ith is larger when θ⊥ is smaller.
[0071]
The reason why Ith decreases as the well width increases is as follows.
[0072]
FIG. 5 shows the relationship between the oscillation wavelength, quantum well width, and active layer strain.
[0073]
When the well width is determined in order to set the center value of the oscillation wavelength to 638 nm, the value of the active layer strain amount is set by adjusting x on the solid line in FIG. If the well width is large, the same wavelength cannot be obtained unless x is increased, so that the amount of tensile strain in the quantum well layer increases.
[0074]
The upper part of FIG. 5 shows the energy dependence in the momentum space of the electron level, light hole level, and heavy hole level near the Γ point. As the amount of tensile strain increases, the energy of the light hole level becomes sufficiently higher than the energy of the heavy hole level at the Γ point, so that the injected carriers (holes) are distributed as light holes.
[0075]
The polarization direction and gain are different between laser light due to heavy hole and electron recombination and laser light due to light hole and electron recombination. When the energy of the light hole level and the heavy hole level are equal and the same amount of carriers are present, oscillation occurs in the polarization direction with a low gain, and the carrier that contributes to the other polarization direction is the spontaneous emission light. This does not contribute to laser oscillation, so the oscillation threshold is increased. Since the energy of the light hole level is sufficiently higher than the energy of the heavy hole level, the semiconductor laser device of this embodiment has carriers only in the heavy hole level, so all the injected carriers are only laser light in one polarization direction. This contributes to lowering the oscillation threshold and higher efficiency, resulting in lower operating current. That is, temperature characteristics are improved.
[0076]
The result of evaluating the reliability of each semiconductor laser device having a quantum well layer thickness of 70 Å or more is shown. The reliability test was measured by a driving method in which the light output was constant under the conditions of 50 ° C. and 30 mW.
[0077]
FIG. 6 shows that all of the semiconductor laser elements of X84, X86, and X89 have high reliability at 50 ° C. and 30 mW and can be sufficiently put into practical use.
[0078]
However, regarding the X108 semiconductor laser device, the operating current (Iop) was reduced by increasing the optical confinement coefficient of the active layer by increasing θ⊥, but in the reliability test, it became a failure mode that suddenly stopped. When the light emission pattern of the light emitting end face of the deteriorated element was measured, it was considered that there was a dark part in the central part of the active layer, and the light density at the end face part was clearly high, so that it deteriorated. The reason for this is considered to be a failure mode in which the light density inside the semiconductor laser element is high, and the deterioration progresses due to oxidation or the like at the laser end face portion, causing a sudden deterioration.
[0079]
In order to reduce the light density at the laser end face part, it is necessary to widen the light beam size in the vicinity of the active layer, which is the active layer of light emitted from the semiconductor laser element. of Laminated Against the face This leads to a narrow half-value width (θ⊥) in the vertical direction. Therefore, from this experiment, θ⊥ needs to be 27 ° or less.
[0080]
When θ⊥ is 27 ° or less, the laser end face portion does not deteriorate, so the reliability of the semiconductor laser device shown in FIG. 6 is almost determined by the value of the oscillation threshold current. That is, a lot with a low oscillation threshold current has high reliability. Even in the individual elements in the same lot, a device with a high initial Iop has a high current increase rate, and a device with a low initial Iop also has a low current increase rate, so that the initial Iop, that is, the oscillation threshold current is low. It turns out that it is necessary to obtain reliability.
[0081]
Tables 3 and 4 above show the oscillation threshold current, oscillation wavelength, θ⊥, θ // (emitted light of each semiconductor laser element. , Active layer of Laminated Against the face The half-width in the parallel direction) and the estimated mean failure time MTTF indicating reliability are also shown.
[0082]
From the above results, in a semiconductor laser device that oscillates at a wavelength of 630 nm or more and 642 nm, in order to obtain MTTF of 3000 hours or more at 50 ° C. and 30 mW, θ⊥ is 22 ° or more and 27 ° at a quantum well layer thickness of 90 Å or more and less than 120 Å. The following should be done.
[0083]
Furthermore, it is preferable that the quantum well layer thickness be 100 angstroms or more and less than 120 angstroms and θ⊥ be 22 ° or more and 27 ° or less because the threshold current can be further reduced.
[0084]
(Embodiment 2)
In this embodiment, the doping amount of the p-type second cladding layer 14 and the p-type third cladding layer 16 was examined.
[0085]
The Be doping amount of the p-AlGaInP third cladding layer 16 is 5 × 10 5. ¹⁷ cm ^-3 A semiconductor laser device having the same structure as that of X89 shown in Table 3 in Embodiment 1 was manufactured except that.
[0086]
FIG. 7A shows that the Be doping amount of the p-type third cladding layer 16 is 5 × 10 5. ¹⁷ cm ^-3 FIG. 7B is a diagram showing the IL (current-optical output) characteristics of the semiconductor laser device, and FIG. 7B shows the Be doping amount of the p-type third cladding layer 16 of 1 × 10. ¹⁸ cm ^-3 It is a figure which shows the IL (current-light output) characteristic of the semiconductor laser element (X89).
[0087]
As can be seen from FIG. 7, the Be doping amount of the p-type second cladding layer 14 and the p-type third cladding layer 16 is 5 × 10 5. ¹⁷ cm ^-3 In the semiconductor laser element described above, the threshold current at 25 ° C. is almost the same value as X89, but the threshold current and operating current at 50 ° C. are higher than X89.
[0088]
This is because when the doping concentration of the p-type cladding layer is low, the effective barrier effect for preventing electrons as carriers from overflowing from the active layer to the p-type cladding layer is lowered. That is, when the doping concentration of the p-type cladding layer is low, electrons easily overflow, and as a result, the temperature characteristics are deteriorated and a light output of 30 mW cannot be obtained at 50 ° C. In particular, since the wavelength is as short as 642 nm or less, the band gap of the active layer becomes large, and the barrier effect by the active layer and the clad layer becomes relatively small. Therefore, the barrier effect can be obtained by increasing the doping amount of the p-type clad layer. Is important.
[0089]
Here, in order to obtain an optical output of 30 mW at 50 ° C., the doping amount of the p-type cladding layer is 1 × 10 ¹⁸ cm ^-3 Is preferable. In addition, it is preferable to adjust the doping amount as appropriate in the present invention, since the experiment results of other semiconductor laser devices show that Ith increases when the doping amount exceeds a certain level.
[0090]
In the above embodiment, the MBE apparatus is used for the growth of the semiconductor layer. As another growth apparatus, an MOCVD apparatus is generally used in the manufacture of an AlGaInP-based semiconductor laser element. In this MOCVD apparatus, Zn or Mg is used as a p-type dopant. Since Zn or Mg has a large diffusion coefficient in the crystal, diffusion occurs during growth or during heat treatment, and the doping concentration of the p-type cladding layer is increased. Can't be high. This is because when the doping concentration is increased, the dopant diffuses into the active layer and the threshold current increases.
[0091]
On the other hand, Be does not cause such a problem of dopant diffusion, but organic raw materials are not common, and growth using Be as a dopant is limited to the MBE method because of the exclusion device. Therefore, as in the above embodiment, if an MBE apparatus is used as a manufacturing apparatus and Be is used as a dopant for a p-type cladding layer, a semiconductor laser element having sufficiently high reliability in practical use under conditions of 50 ° C. and 30 mW or more is obtained. Obtainable.
[0092]
(Embodiment 3)
In this embodiment, an example of an optimum structure at a wavelength of 650 nm to 660 nm is shown. A wavelength of 650 nm requires an optical output of 5 mW to 10 mW for reproduction of DVD-video, DVD-ROM, DVD-audio, and the like. Unlike a semiconductor laser for recording, a semiconductor laser for reproduction requires high reliability of 10,000 hours or more. In order to obtain high reliability, it is necessary to obtain high reliability by reducing a low threshold current, good temperature characteristics, and an operating current at a high temperature.
[0093]
The present embodiment shows an example of a semiconductor laser element used for a read-only drive of a DVD family disc such as DVD-video, DVD-ROM, DVD-audio or the like. FIG. 10 is a diagram showing a schematic structure of the semiconductor laser device.
[0094]
The structure of this example is the same as that of the first embodiment except that the structure of the multiple quantum well active layer 41 is different.
[0095]
FIG. 11 shows a structural diagram of the multiple quantum well of the present embodiment. The number of quantum wells and the quantum well width were changed as shown in FIG. Here, the Al mixed crystal ratio of the light guide layers 43 and 42 is 0.50, and the Al mixed crystal ratio of the n-type cladding layer 12 and the p-type cladding layer 14 is 0.72. The mixed crystal ratio of the light guide layers 43 and 42 and the Al mixed crystal ratio of the n-type cladding layer 12 and the p-type cladding layer 14 are all the same even when the number of quantum wells and the quantum well width are changed.
[0096]
Since the manufacturing method of this example is the same as that of the first embodiment except for the active layer structure, a description thereof will be omitted.
[0097]
Next, in order to obtain a semiconductor laser device having high reliability at a high temperature, the background of how the inventor of the present application has found a specific relationship with respect to the quantum well width and the number of quantum wells will be described.
[0098]
The optimum structure at an oscillation wavelength of 650 nm to 660 nm is determined as follows.
[0099]
FIG. 12 shows the relationship between the oscillation wavelength, quantum well width, and active layer strain. In the figure, the relationship for obtaining wavelengths of 650 nm and 660 nm is shown.
[0100]
In order to obtain 650 nm or 660 nm as the oscillation wavelength, an arbitrary well width on the line indicated as 650 nm or 660 nm in FIG. 12 can be selected, but the oscillation threshold is lowered as much as possible to reduce the operating current at high temperature. In order to increase the reliability, as described in the first embodiment, it is preferable that the energy of the heavy hole level and the light hole level are separated as much as possible and the carriers are concentrated in the heavy hole or the light hole.
[0101]
A line indicated by a two-dot chain line in FIG. 12 is a line in which the heavy hole level matches the light hole level. Above this line, the energy of the heavy hole level is higher than the energy of the light hole level, so the holes injected into the active layer are concentrated in the heavy hole level, and laser oscillation is a characteristic of heavy holes and electrons. Occurs by binding. Conversely, below this line, the energy of the light hole level is higher than the energy of the heavy hole level, so that the holes injected into the active layer are concentrated in the light hole level, and laser oscillation occurs between heavy holes and electrons. Generated by recombination. The threshold decreases if the distance from this line is above or below the two-dot chain line in the figure, but as can be seen from FIG. 12, when the oscillation wavelength is 650 nm or 660 nm, the well width is larger than about 100 mm. It can be seen that even if the well width is changed, the amount of strain cannot be changed, and as a result, it becomes a configuration close to a line where the light hole and heavy hole levels coincide.
[0102]
Therefore, a well width of 70 mm or less, which can be separated from the line having the same level, is advantageous.
[0103]
FIG. 13 shows the results of the operating current Iop (70 ° C.), the threshold current Ith (25 ° C.), and the characteristic temperature TO when the well width is changed from 9 to 2 with a well width of 40 to 115 mm. In FIG. 13, the threshold value increases and the characteristic temperature TO decreases as it goes to the right of 70 mm. This is because as the well width increases, the energy of the heavy hole level and the light hole level approach each other, and the number of carriers for filling the valence band required for oscillation increases. In the left direction (40 mm or less), the threshold current increases again. This is considered to be an effect of the quantum well interface. That is, at the interface between the well layer and the barrier layer, the amount of the constituent material is switched at the time of element growth. However, since this switching is not performed completely, there is a deviation from the ideal crystal state, and there is a non-radiative recombination center. When the active layer is thick, the effect of non-radiative recombination is small, but when the well width is reduced, the effect increases and the threshold value increases.
[0104]
On the other hand, in the wavelength range of 630 nm to 640 nm, the region above the line where the energy of the heavy hole level and the light hole level match is a region thinner than the well width of 70 mm. Since the recombination region is entered, sufficient energy separation between the heavy hole level and the light hole level cannot be obtained. Therefore, in the region from 630 nm to 640 nm, a region below the line where the light hole level and the heavy hole level coincide with each other as described in Embodiment 1 and a region free from crystal breakdown due to large strain are selected. There is a need.
[0105]
Therefore, the optimum point automatically exists in the thickness of the quantum well layer of the active layer depending on the required oscillation wavelength. The region above the line where the energy of the heavy hole level and the light hole level match is recombined by the heavy hole and the electron, so that the laser oscillation becomes a TE mode in which the electric field is parallel to the pn junction surface. In the region below the line where the energy of the heavy hole level and the light hole level coincide with each other, recombination by the light hole and the electron causes laser oscillation to be a TM mode in which the electric field is perpendicular to the pn junction surface.
[0106]
The vertical direction in FIG. 13 indicates well width × number of wells. The well width × the number of wells indicates the total thickness having the gain of the active layer. Further, when the well width × the number of wells is increased, the optical confinement coefficient is increased, so that the characteristic temperature is improved. However, since the volume inside the active layer is increased, the threshold current is increased in order to obtain the same threshold carrier density. Further, when the well width × the number of wells is reduced, the optical confinement factor is decreased, the gain required for obtaining laser oscillation is increased, and the threshold current is increased. Therefore, there is an optimum point in well width × number of wells.
[0107]
Here, the smallest well width of Ith is about 75 mm. However, since the characteristic temperature TO is higher at the well width of 50 mm, the 50 mm × 4 layer closest to Iop (70 ° C.) has the best characteristics. .
[0108]
FIG. 14 shows the dependence of temperature characteristics on the well width × the number of wells. The well width × the number of wells is almost related to the optical confinement coefficient of the active layer. For the same well width, the characteristic temperature TO tends to increase as the well width x the number of wells increases. However, FIG. 14 shows that the relationship changes depending on the well width. In the well width of 50 mm, a high characteristic temperature can be obtained even with the same well width × the number of wells, and thus a low operating current can be obtained even at a high temperature. .
[0109]
The oscillation threshold Ith (25 ° C.) of the semiconductor laser device of this example (quantum well width 50 Å, quantum well number 4) was 49 mA, θ⊥ was 30 °, and θ // was 8.5 °.
[0110]
FIG. 15 shows the reliability of the semiconductor laser device of this embodiment. Estimating the mean time to failure (MTTF) with the time that Iop is 1.2 times the initial value as the lifetime, the estimated MTTF at 70 ° C and 5 mW has a sufficient reliability of 100,000 hours or more, and the DVD family playback disk It can be used satisfactorily as a semiconductor laser element of a reproduction drive.
[0111]
In this example, the doping amount of the p-type second cladding layer 14 and the p-type third cladding layer 16 was examined. The Be doping amount of the p-type AlGaInP third cladding layer and the second cladding layer is set to 5 × 10. ¹⁷ cm ^-3 The quantum well width was 50 mm and the number of quantum wells was 4.
[0112]
This comparative element has a high operating current at 70 ° C. and 5 mW. Therefore, the estimated MTTF is 1500 hours, which is lower than the value required for the playback drive (approximately 10,000 hours).
[0113]
(Embodiment 4)
In this embodiment, a high-power semiconductor laser element emitting 650 nm and 660 nm used for DVD-RAM and DVD-RW drive for rewriting will be described.
[0114]
In DVD-RAM and DVD-RW drives, for example, information is recorded by changing the crystal state of the media (phase change). In order to change the crystal phase, a high-power semiconductor laser device is required. The output power is required to be 50 mW optical output under pulse driving conditions (corresponding to 35 mW under CW driving conditions) or 70 mW optical output (50 mW under CW driving conditions).
[0115]
FIG. 17 is a cross-sectional view showing a schematic configuration of the semiconductor laser device of this example. The structure of this example is the same as that of the first embodiment except that the structure of the multiple quantum well active layer 41 is different.
[0116]
FIG. 18 shows a structure diagram of the multiple quantum well active layer. Here, the Al mixed crystal ratio of the light guide layers 43 and 42 is 0.59, and the Al mixed crystal ratio of the n-type cladding layer 12 and the p-type cladding layer 14 is 0.69.
[0117]
Since the wavelength is from 650 nm to 660 nm as in the third embodiment, the thickness of the active layer is optimally 50 mm for the same reason.
[0118]
In order to obtain a high output, it is necessary to spread light in the active layer portion in order to reduce the light density at the end face.
[0119]
FIG. 19 shows the relationship between the number of quantum wells in the active layer and θ⊥ ( Half-value width of emitted light in the direction perpendicular to the active layer stacking surface ) And the light density value in the active layer. As the number of wells increases, the light density at a constant output increases.
[0120]
Therefore, the well width is kept as it is, the number of wells is reduced from four to three, and the light density in the active layer portion is reduced. Here, the refractive index is changed by changing the Al mixed crystal ratio of the light guide layers 43 and 42, the n-type cladding layer 12, and the p-type cladding layer 14, and the light density and θ 端 at the end face can be changed. . By setting (Al mixed crystal ratio of cladding layer)-(Al mixed crystal ratio of guide layer) to 0.1, θ０．１22 ° can be obtained with 2 wells.
[0121]
Other parts are the same as those in the third embodiment. A semiconductor laser device was prepared by the same method as in the third embodiment, and the characteristics were measured. The threshold current at room temperature was 51 mW, and θ⊥22 ° was obtained. FIG. 20 shows the result of the reliability test at 70 ° 35 mW (CW). It operates stably for 1000 hours or more, has an estimated lifetime MTTF of 70,000 hours, and has sufficient reliability.
[0122]
(Embodiment 5)
Next, in order to obtain a light output with a pulse of 70 mW, it is necessary to further widen the light distribution on the end face and reduce the light density in the active layer portion as the light output increases. Therefore, the number of well layers was further reduced from three to a well width of 50 mm and two wells. Other portions have the same structure as that of the fourth embodiment.
[0123]
A semiconductor laser device was prepared by the same method as in the fourth embodiment, and the characteristics were measured. The threshold current at room temperature was 54 mA, and θ⊥21.5 ° was obtained. Since the total thickness of the active layer is reduced, the light distribution in the active layer is widened. Therefore, even when a high light output is output, the light density of the active layer does not increase so much. FIG. 21 shows the reliability test results at 70 ° C. and a pulse of 70 mW. The operation was stable even at 70 ° C. and 70 mW, and the estimated MTTF was 3000 hours, and sufficient reliability as a semiconductor laser device for writing could be obtained.
[0124]
For comparison, the doping amount of the p-type second cladding layer 14 and the p-type third cladding layer 16 was examined with the same structure as in the fifth embodiment. The Be doping amount of the p-type AlGaInP third cladding layer and the second cladding layer is set to 7 × 10. ¹⁷ cm ^-3 The quantum well width is 50 mm and the number of quantum wells is 2. FIG. 22 shows the progress of reliability traveling at 70 ° C. and 70 mW pulse for this comparative element. If the Be doping concentration is low, the temperature characteristics are poor and the operating current at 70 ° C. and 5 mW is high. Therefore, in a reliability test with a pulse of 70 mW at 70 ° C., if the degree of deterioration is larger than the initial value and a point that is 1.2 times the initial Iop is estimated as the lifetime, the MTTF is 500 hours. In order to reduce the light density at the end face, the light confinement factor in the active layer is reduced by reducing the total thickness of the quantum well layers. Therefore, since the temperature characteristics are relatively poor, the Be concentration in the p-type cladding layer is 1 × 10 5. ¹⁸ cm ^-3 That is important.
[0125]
The above description does not depend on the orientation of the substrate surface. However, it goes without saying that the main surface of the substrate may be tilted by 10 to 15 degrees in the [011] direction from the (100) plane in order to obtain higher reliability.
[0126]
【The invention's effect】
As described in detail above, according to the present invention, in a semiconductor laser device having a wavelength of 630 nm or more and 642 nm and an optical output of 30 mW, high reliability of MTTF of 3000 hours or more sufficient as a semiconductor laser device for writing at a high temperature condition of 50 ° C. A semiconductor laser device having the same can be obtained. Therefore, the semiconductor laser device of the present invention can be suitably used as a semiconductor laser device for DVD-R. In optical information processing systems such as a magneto-optical disk and an optical disk, the recording cost is reduced and the recording capacity is reduced. Very effective to enlarge.
[0127]
Further, in a semiconductor laser element having a wavelength of 650 nm or more and 660 nm or less and an optical output of 5 mW, 35 mW (CW), or 70 mW (pulse), any of reproduction, rewriting, and writing is performed at a high temperature of 70 ° C. As a semiconductor laser element, a semiconductor laser element having high reliability such as MTTF of 100,000 hours or more, 70,000 hours or more and 3000 hours or more can be obtained. Therefore, the semiconductor laser device of the present invention can be suitably used as a read-only drive for DVD family discs such as DVD-video, DVD-ROM, and DVD-audio, or as a semiconductor laser device used for DVD-RAM and DVD-RW drives. Therefore, in an optical information processing system such as a magneto-optical disk or an optical disk, it is very effective for reducing the recording cost and increasing the recording capacity.
[0128]
Furthermore, using a compound semiconductor material in which the amount of strain changes depending on the composition ratio such as GaInP on a GaAs or GaP substrate, GaInN on a GaN or Si substrate, GaInAs on a GaAs or GaP substrate, or GaInSb on a GaSb substrate. Even if the oscillation wavelength is changed, the optimum configuration of the quantum well active layer can be easily derived, and it becomes possible to provide a semiconductor laser device having a target characteristic at a target wavelength and a manufacturing method thereof.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for explaining a manufacturing process of a semiconductor laser device of an embodiment.
FIG. 2 is a diagram showing a schematic structure of a quantum well active layer in the semiconductor laser device of the embodiment.
FIG. 3 is a diagram illustrating a relationship between θ⊥, an Al mixed crystal ratio of a light guide layer, and an Al mixed crystal ratio of a cladding layer in the semiconductor laser device of the embodiment.
FIG. 4 is a diagram showing the relationship between the quantum well width, θ⊥, and threshold current in the semiconductor laser device of the embodiment.
FIG. 5 is a diagram showing the relationship among the wavelength, quantum well width, and active layer strain in the semiconductor laser device of the embodiment.
FIG. 6 is a diagram showing a reliability evaluation result in the semiconductor laser device of the embodiment.
FIG. 7 is a diagram showing IL characteristics in the semiconductor laser device of the embodiment.
FIG. 8 is a diagram showing a schematic structure of a quantum well active layer in a conventional semiconductor laser device.
FIG. 9 is a diagram showing a reliability evaluation result in a conventional semiconductor laser device.
FIG. 10 is a view showing a schematic structure of a semiconductor laser device according to an embodiment.
FIG. 11 is a diagram showing a schematic structure of a quantum well active layer in the semiconductor laser device of the embodiment.
FIG. 12 is a diagram showing the relationship among the wavelength, quantum well width, and active layer strain in the semiconductor laser device of the embodiment.
FIG. 13 is a diagram showing values of an operating current Iop, a threshold current Ith, and a characteristic temperature TO when (well width × number of wells) and the well width are changed in the semiconductor laser device of the embodiment.
FIG. 14 is a diagram showing a relationship between (well width × number of wells) and temperature characteristic TO in the semiconductor laser device of the embodiment.
FIG. 15 is a diagram showing a reliability evaluation result in the semiconductor laser device of the embodiment.
FIG. 16 is a diagram showing a reliability evaluation result in a comparative element.
FIG. 17 is a view showing a schematic structure of a semiconductor laser device according to an embodiment.
FIG. 18 is a diagram showing a schematic structure of a quantum well active layer in the semiconductor laser device of the embodiment.
FIG. 19 is a diagram showing the relationship between the number of well layers, the light density in the active layer, and θ⊥ in the semiconductor laser device of the embodiment.
FIG. 20 is a diagram showing a reliability evaluation result in the semiconductor laser device of the embodiment.
FIG. 21 is a diagram showing a reliability evaluation result in the semiconductor laser device of the embodiment.
FIG. 22 is a diagram showing a reliability evaluation result in a comparative element.
[Explanation of symbols]
11 n-GaAs substrate
12 n-AlGaInP first cladding layer
14 p-AlGaInP second cladding layer
15 p-GaInP etching stop layer
16 p-AlGaInP third cladding layer
17 p-AlGaInP intermediate band gap layer
18 p-GaAs contact layer
19 Mask layer
20 GaAs current blocking layer
21 GaAs polycrystalline layer
23 Opening
31 Mesa Club
41 Quantum well active layer
42 AlGaInP second light guide layer
43 AlGaInP first optical guide layer
46 GaInP well layer
47 AlGaInP barrier layer

Claims (1)

In a semiconductor laser device having a quantum well active layer made of a material system in which the amount of strain changes when the composition of atoms constituting the crystal is changed and the band gap energy is changed,
The quantum well active layer comprises a quantum well layer having two layers sandwiched between a pair of cladding layers of p-type and n-type,
A guide layer made of an AlGaInP material is provided between the quantum well active layer and each of the pair of clad layers,
Each layer of the front Symbol quantum well layer is made of GaIn P materials, when the oscillation wavelength at room temperature is 630nm or more 642nm or less, have a well width of less than 100 Å or 120 Å, at Γ points of the quantum well layer The absolute value of the difference between the energy level of heavy hole and the energy level of light hole is set to the maximum amount of tensile strain in the range where crystal breakage does not occur,
The pair of clad layers are made of an AlGaInP material, and the p-type clad layer of the pair of clad layers contains Be having a concentration of 1 × 10 ¹⁸ cm ⁻³ or more as an impurity,
A semiconductor laser device, wherein a half-value width θ⊥ of emitted light in a direction perpendicular to the stack surface of the quantum well active layer is 23 ° or more and 27 ° or less .

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