JP4087152B2 - Surface emitting semiconductor laser device and laser array - Google Patents

Description

【００１８】
実験例２の結果から、Ａｌ_0.9Ｇａ_0.1Ａｓ／Ａｌ_0.2Ｇａ_0.8Ａｓのペア数ｎが、ＡｌＡｓ／Ａｌ_0.2Ｇａ_0.8Ａｓのペア数ｍとＡｌ_0.9Ｇａ_0.1Ａｓ／Ａｌ_0.2Ｇａ_0.8Ａｓのペア数ｎとの和（ｍ＋ｎ）に対して２０／３５以下であれば、活性層部分の温度上昇をほぼ２０℃以下に抑えることができることが判った。
【００１９】
上記目的を達成するために、上述の実験例１で得た知見に基づいて、本発明に係る面発光半導体レーザ素子は、基板と、該基板上に設けられ夫々が低屈折率層及び高屈折率層から成るペア層を複数形成した上部及び下部半導体多層膜反射鏡と、該半導体多層膜反射鏡の間に配設された活性層と、前記上部半導体多層膜反射鏡中に設けられた、特定半導体層の一部領域を選択的に酸化してなる電流狭窄層とを有し、電流注入により前記基板と垂直にレーザ光を放射する面発光半導体レーザ素子において、
前記下部半導体多層膜反射鏡が、第１の領域と、該第１の領域と前記活性層との間に配設される第２の領域とを備え、前記第１の領域中の前記低屈折率層がＡｌＡｓ層からなり、前記第２の領域中の前記低屈折率層がＡｌＧａＡｓ層からなることを特徴としている。
【００２０】
低屈折率層にＡｌＡｓ層を採用することにより、下部半導体多層膜反射鏡の熱伝導率が向上し、活性層部分の温度上昇を抑制し、レーザ光出力の熱飽和特性が良好で、高温の動作環境でも高出力で安定して動作する面発光半導体レーザ素子を実現することができる。
ＡｌＡｓ層よりも酸化速度の遅い材料からなる低屈折率層を有する第２の領域が、前述のように介在することにより、特定半導体層の酸化工程の際に、前述のＡｌＡｓ層の酸化が防止され、製造工程でのレーザ素子の劣化を効果的に防止することができる。
本発明で、特定半導体層とはＡｌを含む被酸化層であって、例えばＡｌ_yＧａ_1-yＡｓ（０．９５≦ｙ≦１．０）層を使用する。
【００２１】
前述の第２の領域の構成には制約はないが、好適には、相互にＡｌ組成が異なるＡｌ_x1Ｇａ_1-x1Ａｓ（０．５≦ｘ１≦０．９２）／Ａｌ_x2Ｇａ_1-x2Ａｓ（０．１５≦ｘ２≦０．５、ｘ１＞ｘ２）ペア層として設けられ、下部半導体多層膜反射鏡の一部を構成するようにする。
つまり、前記特定半導体層がＡｌ_yＧａ_1-yＡｓ（０．９５≦ｙ≦１．０）層であり、前記下部半導体多層膜反射鏡を、ＡｌＡｓ層を低屈折率層として有するペアからなる第１の領域と、前記第１の領域と前記活性層との間に形成され、相互にＡｌ組成が異なるＡｌ_x1Ｇａ_1-x1Ａｓ（０．５≦ｘ１≦０．９２）／Ａｌ_x2Ｇａ_1-x2Ａｓ（０．１５≦ｘ２≦０．５、ｘ１＞ｘ２）ペア層からなる第２の領域とで構成する。
第２の領域を設けることにより、第１の領域のＡｌＡｓ層が前記エッチングの際に露出して前記ＡｌＡｓ層が酸化してしまうことを防止する酸化防止層として機能する。第２の領域を構成するＡｌＧａＡｓ／ＡｌＧａＡｓのペアは、下部半導体多層膜反射鏡、活性層、クラッド層等をエッチングしてメサポスト構造を形成する際のエッチング深さのマージン層として機能する。
【００２２】
更には、上述の実験例２で得た知見に基づいて、ｍ、ｎを整数とし、前記第１の領域のペア数をｍ、前記第２の領域のペア数をｎとするとき、ｎ／（ｍ＋ｎ）≦４／７の関係が成立するようにする。
前述の関係を有することにより、一層確実に、活性層部分の温度上昇を抑制して、レーザ光出力の熱飽和特性を改善することができる。
本発明は特にＧａＡｓ基板上に成長する面発光半導体レーザ素子に適用することによって、良好な結果が得られている。
【００２３】
本発明は特に前記基板がｎ型半導体であり、前記下部半導体多層膜反射鏡がｎ型半導体であり、前記上部半導体多層膜反射鏡がｐ型半導体である面発光半導体レーザ素子に適用することによって、良好な結果が得られている。
本発明は前記基板がｎ型半導体であり、前記下部半導体多層膜反射鏡及び前記上部半導体多層膜反射鏡が真性半導体である面発光半導体レーザ素子に適用することによって、特に１３００ｎｍ帯で高出力な面発光半導体レーザ素子を実現することができる。
【００２４】
本発明は前記基板が半絶縁性基板であり、前記下部半導体多層膜反射鏡がｎ型半導体であり、前記上部半導体多層膜反射鏡がｐ型半導体である面発光半導体レーザ素子に適用することによって、電極を同一面上に形成し、フリップチップボンディング等に対応する装置として製造することができる。
本発明は前記基板が半絶縁性基板であり、前記下部半導体多層膜反射鏡及び前記上部半導体多層膜反射鏡が真性半導体である面発光半導体レーザ素子に適用することによって、特に１３００ｎｍ帯で高出力な面発光半導体レーザ素子で、且つ、電極を同一面上に形成し、フリップチップボンディング等に対応する装置として製造することができる。
【００２５】
また、本発明は、発振波長の長短にかかわらず、半導体多層膜反射鏡の材料にＡｌを含む材料系の面発光半導体レーザ素子に適用できるが、特に発振波長が６００〜１６００ｎｍの面発光半導体レーザ素子に適用することによって、良好な結果が得られている。
【００２６】
また、本発明に係るレーザアレイは、本発明に係る面発光半導体レーザ素子を同一基板上に複数備え、該面発光半導体レーザ素子を１次元又は２次元のアレイ状に集積したことを特徴としている。前述と同様の効果が得られ、これにより用途が拡大する。
【００２７】
【発明の実施の形態】
以下に、添付図面を参照し、実施形態例を挙げて本発明の実施の形態を具体的かつ詳細に説明する。
実施形態例
本実施形態例は、本発明に係る面発光半導体レーザ素子の実施形態の一例であって、図１は本実施形態例の面発光半導体レーザ素子の構成を示す斜視断面図で、図２は本実施形態例の面発光半導体レーザ素子の層構造を模式的に示す断面図である。図１及び図２に示すもののうち、図５及び図６に示したものと同じものには、同じ符号を付して説明を省略する。
面発光半導体レーザ素子４０は、発光波長８５０ｎｍの面発光型の半導体レーザ素子であって、図１及び図２に示すように、下部反射鏡４２の構成が従来の面発光半導体レーザ素子１０の下部反射鏡１４の構成と異なることを除いて、面発光半導体レーザ素子１０と同じ構成を備えている。
【００２８】
本実施形態例の下部反射鏡４２は、図２に示すように、低屈折率膜として設けられたｎ−ＡｌＡｓ膜４４と、高屈折率膜として設けられたｎ−Ａｌ_0.2Ｇａ_0.8Ａｓ膜４６の２５．５ペアからなる下部多層膜４８と、下部多層膜４８上に形成され、ｎ−Ａｌ_0.2Ｇａ_0.8Ａｓ膜４６とｎ−Ａｌ_0.9Ｇａ_0.1Ａｓ膜５０の１０ペアからなる上部多層膜５２とから構成されている。
ｎ−ＡｌＡｓ膜４４の膜厚は、約５０ｎｍであり、ｎ−Ａｌ_0.2Ｇａ_0.8Ａｓ膜４６及びｎ−Ａｌ_0.9Ｇａ_0.1Ａｓ膜５０の膜厚は、それぞれ、約４０ｎｍ及び約５０ｎｍである。
また、上部反射鏡２４の最下層は、ｐ−Ａｌ_0.9Ｇａ_0.1Ａｓ膜５４に代えて膜厚５０ｎｍのｐ−ＡｌＡｓ膜１７が成膜され、かつＡｌＡｓ層１７中のＡｌを選択的に酸化することにより、円筒状溝２８の側壁に沿ってＡｌ酸化層１６が形成されている。Ａｌ酸化層１６は電流ブロッキング層となり、ＡｌＡｓ層１７の中央領域は、酸化されることなくそのままＡｌＡｓ層として存在し、電流注入経路を構成している。
【００２９】
次に、図１及び図２を参照して、本実施形態例の面発光半導体レーザ素子４０の作製方法を説明する。
先ず、有機金属気相成長法（ＭＯＣＶＤ法）により、図２に示すように、ｎ−ＧａＡｓ基板１２上に、２５．５ペアのｎ−ＡｌＡｓ膜４４／ｎ−Ａｌ_0.2Ｇａ_0.8Ａｓ膜４６からなる下部多層膜４８、続いて１０ペアのｎ−Ａｌ_0.2Ｇａ_0.8Ａｓ膜４６／ｎ−Ａｌ_0.9Ｇａ_0.1Ａｓ膜５０からなる上部多層膜５２を成長させ、下部反射鏡４２を形成する。
【００３０】
次いで、上部多層膜５２上に、膜厚９３ｎｍのノンドープＡｌ_0.3Ｇａ_0.7Ａｓ下部クラッド層１８、ＧａＡｓ／Ａｌ_0.2Ｇａ0.8Ａｓ多重量子井戸構造２０、及び膜厚９３ｎｍのノンドープＡｌ_0.3Ｇａ_0.7Ａｓ上部クラッド層２２を成長させる。
ＧａＡｓ量子井戸発光層３層を含む、ＧａＡｓ／Ａｌ_0.2Ｇａ_0.8Ａｓ多重量子井戸構造２０は、３層の膜厚７ｎｍのＧａＡｓ量子井戸層と、膜厚１０ｎｍのＡｌ_0.2Ｇａ_0.8Ａｓ障壁層とから構成されている。
【００３１】
更に、上部クラッド層２２上に、ｐ型ドーピングしたｐ−Ａｌ_0.9Ｇａ_0.1Ａｓ膜５４とｐ−Ａｌ_0.2Ｇａ_0.8Ａｓ膜５６の３０ペアからなる多層膜を成長させて上部反射鏡２４を形成する。上部反射鏡２４の形成の際、上部反射鏡２４の最下層は、ｐ−Ａｌ_0.9Ｇａ_0.1Ａｓ膜５４に代えて、膜厚５０ｎｍのｐ−ＡｌＡｓ層１７を成膜する。
続いて、上部反射鏡２４の最上層のｐ−Ａｌ_0.2Ｇａ_0.8Ａｓ膜５６上に膜厚１０ｎｍのｐ−ＧａＡｓキャップ層２６を成長させる。
【００３２】
尚、下部反射鏡４２及び上部反射鏡２４をそれぞれ構成するｎ型及びｐ型多層膜の成膜に際し、各層の界面には、厚さ２０ｎｍの組成傾斜層を形成するように成膜する。
また、Ａｌ_0.2Ｇａ_0.8Ａｓ膜４６（５６）及びＡｌ_0.9Ｇａ_0.1Ａｓ膜５０（５４）の膜厚は、それぞれ、４０ｎｍ及び５０ｎｍとする。
以上の工程により、図２に示す化合物半導体積層構造体５８を形成することができる。
【００３３】
次に、化合物半導体積層構造体５８のｐ−ＧａＡｓキャップ層２６上にプラズマＣＶＤ法によりシリコン窒化膜薄膜（図示せず）を成膜し、更にその上にフォトレジスト膜（図示せず）を成膜する。
次いで、直径約４０〜４５μｍの円形パターンをフォトリソグラフィ技術でフォトレジスト膜に転写し、円形レジスト・エッチングマスク（図示せず）を形成する。
【００３４】
続いて、円形レジスト・エッチングマスクを用い、ＣＦ₄ガスをエッチングガスとする反応性イオンエッチング（ＲＩＥ）法によりシリコン窒化膜薄膜をエッチングする。
更に、塩素ガスを用いた反応性イオンビームエッチング（ＲＩＢＥ）法を用いて下部反射鏡４２の多層膜に到達するまで、上部反射鏡２４、上部クラッド層２２、ＧａＡｓ／Ａｌ_0.2Ｇａ_0.8Ａｓ多重量子井戸構造２０、及び下部クラッド層１８、ｐ−ＡｌＡｓ層１７をエッチングして、円筒状溝２８を形成する。これにより、柱状のメサポスト構造３０ができる。
尚、エッチングの際には、選択酸化層であるｐ−ＡｌＡｓ膜１７と、下部反射鏡４２のＡｌＡｓ／Ａｌ_0.2Ｇａ_0.8Ａｓペアからなる下部多層膜４８の間、つまり上部多層膜５２で、エッチングの進行を停止させる。つまり、１０ペアのｎ−Ａｌ_0.2Ｇａ_0.8Ａｓ膜４６／ｎ−Ａｌ_0.9Ｇａ_0.1Ａｓ膜５０からなる上部多層膜５２をエッチング深さの制御層として機能させる。
【００３５】
次に、メサポスト構造３０を有する化合物半導体積層構造体５８を水蒸気雰囲気中で４００℃に加熱し、約２５分放置する。
これにより、ｐ−ＡｌＡｓ膜１７を選択的に酸化して、図１に示すように、円筒状溝２８の溝壁からＡｌ酸化層１６を生成すると共にメサポスト構造３０の中央領域を元のｐ−ＡｌＡｓ層１７のままとする。
この酸化工程で酸化されなかったメサポスト構造３０の中央領域のｐ−ＡｌＡｓ層１７は、直径約１５〜２０μｍの円形領域であって、電流注入経路を構成する。
尚、選択酸化の際、１０ペアのｎ−Ａｌ_0.2Ｇａ_0.8Ａｓ膜４６／ｎ−Ａｌ_0.9Ｇａ_0.1Ａｓ膜５０からなる上部多層膜５２の途中でエッチングが停止するため、下部多層膜４８中のｎ−ＡｌＡｓ膜４４が酸化してＡｌ酸化層に転化するのを防止することができる。また、これにより製造上の歩留まりを向上させることができる。
【００３６】
次いで、シリコン窒化膜薄膜（図示せず）をＲＩＥ法により完全に除去した後に、改めて、プラズマＣＶＤ法によってシリコン窒化膜薄膜３２を全面に成膜する。
メサポスト構造３０の上面のシリコン窒化膜３２を直径３０μｍの円形に除去し、そこにｐ側電極３４として内径２０μｍ、外径３０μｍのリング状のＡｕＺｎ電極を形成する。更に、ｐ側電極引き出し用電極３６としてＴｉ／Ｐｔ／Ａｕパッドを形成する。
また、ｎ−ＧａＡｓ基板１２の裏面を研磨して基板厚さを１００μｍ程度に調整した後、裏面にＡｕＧｅＮｉ／Ａｕ電極を蒸着してｎ側電極３８とする。
最後に、窒素雰囲気中で約４００℃でアニール処理を施すと、図１に示す発振波長が約８５０ｎｍの面発光半導体レーザ素子４０を完成することができる。
【００３７】
試験例１
本実施形態例の構成を備え、電流経路面積が様々に異なる面発光半導体レーザ素子試料を同一ウェハ上に形成して、実施形態例試料の面発光半導体レーザ素子とした。
次いで、実施形態例試料の電流経路面積と熱抵抗との関係を調べたところ、図３の○に示すような結果を得た。熱抵抗は、発光面積（電流経路面積）が広くなるにつれて小さくなっている。
下部反射鏡にＡｌＡｓ層を低屈折率膜とする下部多層膜を備えていないことを除いて実施形態例試料と同じ構成を備えた面発光半導体レーザ素子、つまり前述した従来の面発光半導体レーザ素子１０と同じ構成の従来例試料を実施形態例試料と同様に作製し、本実施形態例の面発光半導体レーザ素子に対する比較試料とした。
上述の実施形態例試料と同様にして、比較例試料の電流経路面積と熱抵抗との関係を調べたところ、図３の●に示すような結果を得た。
【００３８】
実施形態例試料及び従来例試料の面発光半導体レーザ素子の試験結果の比較から、本実施形態例の面発光半導体レーザ素子の熱抵抗（Ｋ／Ｗ）は、従来例の面発光半導体レーザ素子に比べて、電流経路面積約２００μｍ² から約４００μｍ² にわたって３００Ｋ／Ｗ程度低い値を示した。
【００３９】
試験例２
本実施形態例の面発光半導体レーザ素子を評価するために、本実施形態例の面発光半導体レーザ素子と同じ構成を備え、発光面積が３００μｍ² の面発光半導体レーザ素子を上述の実施形態例の方法に従って作製し、実施形態例試料とした。
続いて、動作温度、つまり環境温度をパラメータにして実施形態例試料の電流−光出力特性を測定し、電流−光出力特性の温度依存性を調べたところ、図４（ａ）に示すような結果を得た。
【００４０】
また、下部反射鏡にＡｌＡｓ層を低屈折率膜とする下部多層膜を備えていないことを除いて実施形態例試料と同じ構成を備えた面発光半導体レーザ素子、つまり前述した従来の面発光半導体レーザ素子１０と同じ構成の従来例試料を実施形態例試料と同様に作製し、本実施形態例の面発光半導体レーザ素子に対する比較試料とした。
続いて、実施形態例試料と同様にして、動作温度、つまり環境温度をパラメータにして従来例試料の電流−光出力特性を測定し、電流−光出力特性の温度依存性を調べたところ、図４（ｂ）に示すような結果を得た。
【００４１】
図４（ａ）と図４（ｂ）との比較から判る通り、本実施形態例の面発光半導体レーザ素子は、従来例試料に対して、２０℃から３０℃の室温では光出力特性に顕著な差はないものの、７０℃の温度では、本実施形態例の面発光半導体レーザ素子は、室温での光出力の９０％程度の光出力を得ることができ、しかも注入電流を増加させることによって光出力を更に増大させることができる。
一方、従来例の面発光半導体レーザ素子の光出力は、約８．５ｍＷで飽和し、注入電流を増加してもそれ以上の光出力を出すことはできない。
【００４２】
以上の試験例１及び２の結果から、本実施形態例の面発光半導体レーザ素子４０は、従来の面発光半導体レーザ素子１０に比べて、光出力の熱飽和特性が著しく良好であって、高温の動作環境でも高出力で安定して動作することが実証された。
【００４３】
本実施形態例では、活性層２０とＡｌＡｓ／Ａｌ_0.2Ｇａ_0.8Ａｓからなる下部多層膜４８との間に１０ペアのＡｌ_0.9Ｇａ_0.1Ａｓ／Ａｌ_0.2Ｇａ_0.8Ａｓからなる上部多層膜５２を介在させている。
上部多層膜５２は、下部多層膜４８の酸化防止層として、またメサポスト形成時のエッチング深さの制御性を良好にするためのエッチング制御層として設けたものであり、ＡｌＡｓ被酸化層１７の直下の層でエッチングを停止させることができれば、Ａｌ_0.9Ｇａ_0.1Ａｓ／Ａｌ_0.2Ｇａ_0.8Ａｓのペア数を減らす、もしくはなくすことにより、下部反射鏡の熱抵抗を更に一層低減することができる。
【００４４】
本実施形態例では、発振波長８５０ｎｍの面発光半導体レーザ素子を例にして説明したが、本発明は、発振波長の長短にかかわらず、半導体多層膜反射鏡の材料としてＡｌを含む材料系であれば適用可能である。
例えば、ＧａＡｓ基板上に形成した波長９００ｎｍ以上で発振するＧａＩｎＡｓ歪量子井戸活性層を有する面発光半導体レーザ素子や、更にはＧａＩｎＮＡｓ系量子井戸活性層を有する面発光半導体レーザ素子、量子ドット活性層を有する面発光半導体レーザ素子やＧａＡｓ（Ｓｂ）系量子井戸活性層を有する面発光半導体レーザ素子などにも適用可能である。
また、本発明は、本実施形態例のような面発光半導体レーザ素子を同一基板上に１次元的又は２次元的に集積したレーザアレイにも適用可能である。
その他、上記実施形態例の構成から種々の修正及び変更を施した面発光半導体レーザ素子も、本発明の範囲に含まれる。
【００４５】
【発明の効果】
本発明によれば、下部半導体多層膜反射鏡を構成する低屈折率ＡｌＡｓ層と活性層との間に酸化防止層を設けることにより、レーザ光出力の熱飽和特性が良好で、高温の動作環境でも高出力で安定して動作する面発光半導体レーザ素子及びレーザアレイを歩留まり良く実現している。
本発明により、ペルチェフリー動作が可能な面発光半導体レーザ素子及びレーザアレイが実現でき、データ通信分野で使用する光通信装置の光源などへの応用が期待される。
【図面の簡単な説明】
【図１】実施形態例の面発光半導体レーザ素子の構成を示す斜視断面図である。
【図２】実施形態例の面発光半導体レーザ素子の層構造を模式的に示す断面図である。
【図３】電流経路面積と熱抵抗との関係を示すグラフである。
【図４】図４（ａ）及び（ｂ）は、それぞれ、動作環境温度をパラメータとした実施形態例試料及び従来例試料の注入電流と光出力との関係を示すグラフである。
【図５】従来の面発光半導体レーザ素子の構成を示す斜視断面図である。
【図６】従来の面発光半導体レーザ素子の層構造を模式的に示す断面図である。
【図７】下部反射鏡の熱伝導率と熱抵抗との関係を示すグラフである。
【図８】下部反射鏡の熱伝導率と活性層部分の温度上昇との関係を示すグラフである。
【図９】ＡｌＧａＡｓ混晶の混晶比と熱伝導率との関係を示すグラフである。
【図１０】熱抵抗値と面発光半導体レーザ素子の最大光出力との関係を示すグラフである。
【符号の説明】
１０ 従来の発光波長８５０ｎｍの面発光半導体レーザ素子
１２ ｎ−ＧａＡｓ基板
１４ ｎ型多層膜からなる下部反射鏡
１６ Ａｌ酸化層
１７ ｐ−ＡｌＡｓ層
１８ ノンドープＡｌＧａＡｓ下部クラッド層
２０ ＧａＡｓ量子井戸発光構造
２２ ノンドープＡｌＧａＡｓ上部クラッド層
２４ ｐ型多層膜からなる上部反射鏡
２６ ｐ−ＧａＡｓキャップ層
２８ 円筒状溝
３０ メサポスト構造
３２ シリコン窒化膜
３４ ｐ側電極
３６ ｐ側電極の引き出し用電極
３８ ｎ側電極
４０ 実施形態例の発光波長８５０ｎｍの面発光半導体レーザ素子
４２ ｎ型多層膜からなる下部反射鏡
４４ ｎ−ＡｌＡｓ膜
４６ ｎ−Ａｌ_0.2Ｇａ_0.8Ａｓ膜
４８ 下部多層膜
５０ ｎ−Ａｌ_0.9Ｇａ_0.1Ａｓ膜
５２ 上部多層膜
５４ ｐ−Ａｌ_0.9Ｇａ_0.1Ａｓ膜
５６ ｐ−Ａｌ_0.2Ｇａ_0.8Ａｓ膜
５８ 化合物半導体積層構造体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface emitting semiconductor laser device and a laser array. More specifically, the present invention has good temperature characteristics, that is, good thermal saturation characteristics of laser light output, and operates stably at high output even in a high temperature operating environment. The present invention relates to a surface emitting semiconductor laser element and a laser array.
[0002]
[Prior art]
A surface-emitting semiconductor laser element is a semiconductor laser element that emits laser light in a direction orthogonal to the substrate surface, and has the feature that a large number of laser elements can be integrated two-dimensionally on the same substrate. It is suitable for parallel optical information processing that makes use of parallelism of light such as connections and optical computing, or for large-capacity parallel optical transmission. Recently, a laser array in which a large number of two-dimensional surface emitting semiconductor laser elements are integrated on the same substrate has been attracting attention recently.
As a surface emitting semiconductor laser element, a pair of semiconductor multilayer mirrors made of a pair of AlGaAs / AlGaAs having different Al compositions formed on a GaAs substrate and a pair of semiconductor multilayer mirrors in recent years are used. An 850-nm band surface emitting semiconductor laser element, which is provided and has a GaAs active layer serving as a light emitting region, is particularly attracting attention as a light source of an optical communication device used in the data communication field.
[0003]
The surface-emitting semiconductor laser element includes, for example, an n-type semiconductor multilayer mirror (hereinafter referred to as DBR) formed on the upper surface of an n-type GaAs substrate, and a mesa post structure on the n-type DBR. The formed active layer and the p-type DBR are provided.
As a surface emitting semiconductor laser device having a DBR, one or a plurality of AlGaAs layers having a higher Al composition than any other compound semiconductor layer are formed in a part of the DBR in the mesa post, and the layer having the higher Al composition is formed. By selectively oxidizing only a part of the region to form an Al oxide layer with high electrical resistance and providing a current confinement structure that limits the current path, the luminous efficiency is increased and the threshold current is lowered. Thus, a surface emitting semiconductor laser element having good laser characteristics has been realized.
[0004]
Here, referring to FIGS. 5 and 6, an n-type DBR formed on an n-type GaAs substrate, an active layer formed as a mesa post structure on the n-type DBR, and a p-type DBR are provided, and Al The structure of a conventional surface emitting semiconductor laser element having an emission wavelength of 850 nm and having a current confinement structure by an oxide layer will be described. FIG. 5 is a perspective sectional view showing a configuration of a conventional surface emitting semiconductor laser element, and FIG. 6 is a sectional view schematically showing a layer structure of the conventional surface emitting semiconductor laser element.
As shown in FIGS. 5 and 6, the conventional surface emitting semiconductor laser device 10 having an emission wavelength of 850 nm is formed of an n-type semiconductor multilayer film sequentially formed on an n-GaAs substrate 12 having a substrate thickness of about 100 μm. From the lower reflecting mirror 14, the Al oxide layer 16 formed as a current confinement structure in a predetermined region of the AlAs layer 17, the undoped AlGaAs lower cladding layer 18, the GaAs quantum well light emitting structure 20, the undoped AlGaAs upper cladding layer 22, and the p-type multilayer film A laminated structure including an upper reflecting mirror 24 and a p-GaAs cap layer 26 is provided.
[0005]
Of the laminated structure, the p-GaAs cap layer 26, the upper reflector 24, the undoped AlGaAs upper cladding layer 22, the GaAs quantum well light emitting structure 20, the undoped AlGaAs lower cladding layer 18, and the Al oxide layer 16 / AlAs layer 17 are cylindrical. By providing the groove 28, a mesa post structure 30 having a diameter of 40 to 45 μm is formed.
The Al oxide layer 16 is formed by selectively oxidizing Al in the AlAs layer 17 along the side wall of the mesa post structure 30. The central region of the AlAs layer 17 exists as an AlAs layer without being oxidized and constitutes a current injection path.
[0006]
As shown in FIG. 6, the lower reflecting mirror 14 is n-Al._0.9Ga_0.1As film 50 and n-Al_0.2Ga_0.8The As film 46 is composed of 35.5 pairs of multilayer films laminated via a composition gradient layer.
The upper reflector 24 is p-Al_0.9Ga_0.1As film 54 and p-Al_0.2Ga_0.8The As film 56 is composed of 30 pairs of multilayer films laminated via a composition gradient layer.
Al_0.2Ga_0.8As film 46 (56) and Al_0.9Ga_0.1The film thickness of the As film 50 (54) is 40 nm and 50 nm, respectively.
[0007]
Further, the uppermost layer of the upper reflecting mirror 24 is made of n-Al as shown in FIG._0.9Ga_0.1Instead of the As film 54, an n-AlAs film 17 having a film thickness of 50 nm formed by forming the Al oxide layer 16 along the groove wall of the cylindrical groove 28 is formed.
That is, the Al oxide layer 16 is a layer in which Al in the outer region facing the cylindrical groove 28 of the p-AlAs layer 17 is selectively oxidized, and functions as a current confinement region having high electrical resistance. On the other hand, the p-AlAs layer 17 inside the mesa post structure 30 and not oxidized is a circular region having a diameter of 15 μm to 20 μm and constitutes a current injection path.
[0008]
A silicon nitride film 32 is formed on the entire surface including the groove wall of the cylindrical groove 28 and the mesa post structure 30.
Then, the silicon nitride film 32 on the upper surface of the mesa post structure 30 is removed in a circular shape with a diameter of 30 μm to expose the p-GaAs cap layer 26. A ring-shaped AuZn metal laminated film having an inner diameter of 20 μm and an outer diameter of 30 μm is formed as a p-side electrode 34 there. Further, a Ti / Pt / Au laminated metal pad connected so as to cover the p-side electrode 34 so as to have a circular opening at the center is formed as an extraction electrode 36 of the p-side electrode 34.
Further, an AuGeNi / Au film is formed as an n-side electrode 38 on the back surface of the n-GaAs substrate 12.
[0009]
[Problems to be solved by the invention]
However, the above-described conventional surface emitting semiconductor laser element having an emission wavelength of 850 nm has a problem that the thermal saturation characteristic of the optical output is not good.
That is, in a high-temperature operating environment, the maximum light output of the surface emitting semiconductor laser element reaches a saturated state and cannot output any more light output, so the maximum light output is low. For example, as shown in FIG. 4B, the optical output-current characteristic approaches saturation in an operating environment of 50 ° C., and the optical output-current characteristic is saturated at about 8.5 mW in an operating environment of 70 ° C. Even if the injection current is increased, the light output does not increase.
Taking the surface emitting semiconductor laser device having an emission wavelength of 850 nm as an example, the problem of thermal saturation characteristics of the optical output has been described. This problem is a universal problem of surface emitting semiconductor laser devices regardless of the emission wavelength. is there.
[0010]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a surface emitting semiconductor laser element and a laser array which have good thermal saturation characteristics of laser light output and can stably operate at high output even in a high temperature operating environment.
[0011]
[Means for Solving the Problems]
The present inventor has recognized that it is important to suppress the temperature rise of the active layer part in order to improve the thermal saturation characteristic of the light output of the conventional surface emitting semiconductor laser element, As a result of conducting the above experiments, the facts summarized as Experimental Examples 1 and 2 were found.
Experimental example 1
In this experiment, the thermal resistance R of the surface emitting semiconductor laser element_thWe focused on (K / W).
Thermal resistance R_thIn simple terms, the thermal conductivity of each material σ_thAnd the structural dimensions (length l, area S).
R_th= L / (σ_thS) = ρ_thl / S
If the power consumption in the active layer is Q, the temperature rise ΔT of the active layer is
ΔT = R_th・ Q
And the thermal resistance R_thThe larger the is, the greater the temperature rise of the active layer.
[0012]
Therefore, the thermal resistance R of the surface emitting semiconductor laser element_thThe thermal resistance R is intended to reduce (K / W) and suppress the temperature rise of the active layer portion._thThe following factors were found by studying the factors that decrease
(1) When the thermal conductivity of the lower reflecting mirror is increased, the thermal resistance R as shown in FIGS._thDecreases, and the effect of suppressing the temperature rise ΔT of the active layer portion is large.
(2) Even if the thermal conductivity of the upper reflecting mirror is increased, the effect of suppressing the temperature rise of the active layer portion is small.
(3) Also, according to the experiment, Al_XGa_1-XAs shown in FIG. 9, the thermal conductivity of the As mixed crystal shows non-linearity with respect to the Al composition (X), and X is relatively large near 0, takes a minimum value near 0.5, and increases again. It becomes maximum at 1.0.
Furthermore, when the above results are arranged, as shown in FIG. 10, the maximum light output of the surface emitting semiconductor laser element increases as the thermal resistance value decreases.
[0013]
From the above results, it was found that the thermal saturation characteristics of the light output of the surface emitting semiconductor laser element can be improved by increasing the thermal conductivity of the lower reflecting mirror.
[0014]
For example, a pair of AlGaAs that constitutes a semiconductor multilayer film of a lower reflector is conventionally Al_0.9Ga_0.1As and Al_0.2Ga_0.8A combination such as As is used. And the composition of the Al oxidized layer is changed to Al_0.98Ga_0.02Al is selectively oxidized to form an Al oxide layer by using an Al or higher Al composition, for example, an AlAs layer.
However, Al_0.9Ga_0.1As and Al_0.2Ga_0.8As has a thermal conductivity of 25.8 W / Km and 15 W / Km, respectively, which is significantly lower than 91.0 W / Km of AlAs.
[0015]
Therefore, AlAs and Al having high thermal conductivity as the low refractive index layer._0.2Ga_0.8It was conceived to improve the thermal saturation characteristics of the optical output of the semiconductor laser device by forming a lower reflecting mirror made of a pair with As, and the present invention was invented after confirming by experiments. The thermal conductivity of the GaAs substrate is 54.0 W / Km, and Al_0.9Ga_0.1As and Al_0.2Ga_0.8It is sufficiently higher than the thermal conductivity of As.
[0016]
Experimental example 2
In this experimental example, in order to reduce the thermal resistance in configuring the lower reflector, the total number of pairs of lower reflectors and AlAs / Al_0.2Ga_0.8An experiment was conducted to examine the relationship between the number of pairs of As.
AlAs / Al_0.2Ga_0.8A pair of m pairs of As and Al_0.9Ga_0.1As / Al_0.2Ga_0.8A semiconductor laser device sample including various lower reflectors made of a semiconductor multilayer film (m + n = 35) having As pairs of n and m changed from 0 to 35 was fabricated, and AlAs / Al_0.2Ga_0.8The relationship between the number of pairs with As, the magnitude of the thermal resistance, and the temperature rise of the active layer was investigated. The following results were obtained.
[0017]

[0018]
From the results of Experimental Example 2, Al_0.9Ga_0.1As / Al_0.2Ga_0.8The number n of As is AlAs / Al_0.2Ga_0.8As pairs m and Al_0.9Ga_0.1As / Al_0.2Ga_0.8It was found that when the sum (m + n) of the number of As pairs with n is 20/35 or less, the temperature rise of the active layer portion can be suppressed to approximately 20 ° C. or less.
[0019]
  In order to achieve the above object, based on the knowledge obtained in Experimental Example 1, the surface emitting semiconductor laser device according to the present invention is provided with a substrate, a low refractive index layer and a high refractive index provided on the substrate, respectively. An upper and lower semiconductor multilayer film reflecting mirror formed with a plurality of pair layers composed of an index layer, an active layer disposed between the semiconductor multilayer film mirrors, and provided in the upper semiconductor multilayer film mirror, In a surface emitting semiconductor laser element having a current confinement layer formed by selectively oxidizing a partial region of a specific semiconductor layer and emitting laser light perpendicular to the substrate by current injection,
  The lower semiconductor multilayer mirror includes a first region and a second region disposed between the first region and the active layer, and the low refraction in the first region The refractive index layer is an AlAs layer, and the low refractive index layer in the second region isAlGaAs layerIt is characterized by consisting of.
[0020]
By adopting the AlAs layer as the low refractive index layer, the thermal conductivity of the lower semiconductor multilayer film reflector is improved, the temperature rise of the active layer portion is suppressed, the thermal saturation characteristics of the laser light output are good, and the high temperature It is possible to realize a surface emitting semiconductor laser element that operates stably at a high output even in an operating environment.
Since the second region having the low refractive index layer made of a material having a slower oxidation rate than the AlAs layer is interposed as described above, the oxidation of the AlAs layer is prevented during the oxidation process of the specific semiconductor layer. In addition, it is possible to effectively prevent the deterioration of the laser element in the manufacturing process.
In the present invention, the specific semiconductor layer is an oxidized layer containing Al, for example, Al_yGa_1-yAs (0.95 ≦ y ≦ 1.0) layer is used.
[0021]
  AboveAlthough there is no restriction on the configuration of the second region, it is preferable that the Al compositions differ from each other._x1Ga_1-x1As (0.5 ≦ x1 ≦ 0.92) / Al_x2Ga_1-x2It is provided as an As (0.15 ≦ x2 ≦ 0.5, x1> x2) pair layer, and constitutes a part of the lower semiconductor multilayer film reflecting mirror.
  That is, the specific semiconductor layer is made of Al._yGa_1-yAn As (0.95 ≦ y ≦ 1.0) layer, wherein the lower semiconductor multilayer reflector is formed of a pair of first regions having an AlAs layer as a low refractive index layer; the first region; Al formed between the active layers and having different Al compositions from each other_x1Ga_1-x1As (0.5 ≦ x1 ≦ 0.92) / Al_x2Ga_1-x2The second region is composed of an As (0.15 ≦ x2 ≦ 0.5, x1> x2) pair layer.
  Providing the second region functions as an antioxidant layer that prevents the AlAs layer in the first region from being exposed during the etching and oxidizing the AlAs layer. The AlGaAs / AlGaAs pair constituting the second region functions as a margin layer having an etching depth when the mesa post structure is formed by etching the lower semiconductor multilayer reflector, the active layer, the cladding layer, and the like.
[0022]
Furthermore, on the basis of the knowledge obtained in Experimental Example 2 described above, when m and n are integers, the number of pairs in the first region is m, and the number of pairs in the second region is n, n / The relationship (m + n) ≦ 4/7 is established.
By having the above-mentioned relationship, it is possible to more reliably suppress the temperature increase of the active layer portion and improve the thermal saturation characteristics of the laser light output.
Good results have been obtained by applying the present invention to a surface emitting semiconductor laser device grown on a GaAs substrate.
[0023]
The present invention is particularly applicable to a surface emitting semiconductor laser device in which the substrate is an n-type semiconductor, the lower semiconductor multilayer reflector is an n-type semiconductor, and the upper semiconductor multilayer reflector is a p-type semiconductor. Good results have been obtained.
The present invention is applied to a surface emitting semiconductor laser device in which the substrate is an n-type semiconductor, and the lower semiconductor multilayer reflector and the upper semiconductor multilayer reflector are intrinsic semiconductors. A surface emitting semiconductor laser element can be realized.
[0024]
The present invention is applied to a surface emitting semiconductor laser device in which the substrate is a semi-insulating substrate, the lower semiconductor multilayer reflector is an n-type semiconductor, and the upper semiconductor multilayer reflector is a p-type semiconductor. The electrodes can be formed on the same surface and manufactured as a device corresponding to flip chip bonding or the like.
The present invention is applied to a surface emitting semiconductor laser device in which the substrate is a semi-insulating substrate, and the lower semiconductor multilayer reflector and the upper semiconductor multilayer reflector are intrinsic semiconductors. The surface emitting semiconductor laser device can be manufactured as a device corresponding to flip chip bonding or the like by forming electrodes on the same surface.
[0025]
In addition, the present invention can be applied to a surface emitting semiconductor laser element of a material system containing Al as a material for a semiconductor multilayer mirror regardless of the length of the oscillation wavelength, and in particular, a surface emitting semiconductor laser having an oscillation wavelength of 600 to 1600 nm. Good results have been obtained by applying the device.
[0026]
A laser array according to the present invention is characterized in that a plurality of surface emitting semiconductor laser elements according to the present invention are provided on the same substrate, and the surface emitting semiconductor laser elements are integrated in a one-dimensional or two-dimensional array. . The same effect as described above can be obtained, thereby expanding the application.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below specifically and in detail with reference to the accompanying drawings.
Example embodiment
This embodiment is an example of an embodiment of a surface emitting semiconductor laser device according to the present invention. FIG. 1 is a perspective sectional view showing the configuration of the surface emitting semiconductor laser device of this embodiment, and FIG. It is sectional drawing which shows typically the layer structure of the surface emitting semiconductor laser element of the example of an embodiment. 1 and FIG. 2 that are the same as those shown in FIG. 5 and FIG.
The surface emitting semiconductor laser element 40 is a surface emitting semiconductor laser element having an emission wavelength of 850 nm. As shown in FIGS. 1 and 2, the configuration of the lower reflecting mirror 42 is a lower part of the conventional surface emitting semiconductor laser element 10. The configuration is the same as that of the surface emitting semiconductor laser element 10 except that the configuration of the reflecting mirror 14 is different.
[0028]
As shown in FIG. 2, the lower reflecting mirror 42 of the present embodiment includes an n-AlAs film 44 provided as a low refractive index film and an n-Al film provided as a high refractive index film._0.2Ga_0.8A lower multilayer film 48 composed of 25.5 pairs of As films 46, and formed on the lower multilayer film 48, n-Al_0.2Ga_0.8As film 46 and n-Al_0.9Ga_0.1The upper multilayer film 52 is composed of 10 pairs of As films 50.
The film thickness of the n-AlAs film 44 is about 50 nm, and n-AlAs_0.2Ga_0.8As film 46 and n-Al_0.9Ga_0.1The thickness of the As film 50 is about 40 nm and about 50 nm, respectively.
The lowermost layer of the upper reflector 24 is p-Al._0.9Ga_0.1A p-AlAs film 17 having a thickness of 50 nm is formed in place of the As film 54, and Al in the AlAs layer 17 is selectively oxidized to form the Al oxide layer 16 along the side wall of the cylindrical groove 28. Is formed. The Al oxide layer 16 becomes a current blocking layer, and the central region of the AlAs layer 17 exists as an AlAs layer as it is without being oxidized, and constitutes a current injection path.
[0029]
Next, with reference to FIG. 1 and FIG. 2, a method for manufacturing the surface emitting semiconductor laser element 40 of the present embodiment will be described.
First, as shown in FIG. 2, 25.5 pairs of n-AlAs films 44 / n-Al are formed on the n-GaAs substrate 12 by metal organic chemical vapor deposition (MOCVD)._0.2Ga_0.8Lower multilayer film 48 made of As film 46, followed by 10 pairs of n-Al_0.2Ga_0.8As film 46 / n-Al_0.9Ga_0.1The upper multilayer film 52 made of the As film 50 is grown, and the lower reflecting mirror 42 is formed.
[0030]
Next, a non-doped Al film having a thickness of 93 nm is formed on the upper multilayer film 52._0.3Ga_0.7As lower cladding layer 18, GaAs / Al_0.2Ga0.8As multiple quantum well structure 20 and 93 nm thick non-doped Al_0.3Ga_0.7An As upper cladding layer 22 is grown.
GaAs / Al containing three GaAs quantum well light-emitting layers_0.2Ga_0.8The As multiple quantum well structure 20 includes three GaAs quantum well layers with a thickness of 7 nm and Al with a thickness of 10 nm._0.2Ga_0.8And an As barrier layer.
[0031]
Further, p-type doped p-Al on the upper cladding layer 22._0.9Ga_0.1As film 54 and p-Al_0.2Ga_0.8A multilayer film composed of 30 pairs of As films 56 is grown to form the upper reflecting mirror 24. When forming the upper reflecting mirror 24, the lowermost layer of the upper reflecting mirror 24 is p-Al._0.9Ga_0.1Instead of the As film 54, a p-AlAs layer 17 having a thickness of 50 nm is formed.
Subsequently, p-Al on the uppermost layer of the upper reflector 24_0.2Ga_0.8A p-GaAs cap layer 26 having a thickness of 10 nm is grown on the As film 56.
[0032]
When forming the n-type and p-type multilayer films constituting the lower reflecting mirror 42 and the upper reflecting mirror 24, respectively, the film is formed so as to form a composition gradient layer having a thickness of 20 nm at the interface between the layers.
Al_0.2Ga_0.8As film 46 (56) and Al_0.9Ga_0.1The film thickness of the As film 50 (54) is 40 nm and 50 nm, respectively.
Through the above steps, the compound semiconductor multilayer structure 58 shown in FIG. 2 can be formed.
[0033]
Next, a silicon nitride thin film (not shown) is formed on the p-GaAs cap layer 26 of the compound semiconductor multilayer structure 58 by plasma CVD, and a photoresist film (not shown) is further formed thereon. Film.
Next, a circular pattern having a diameter of about 40 to 45 μm is transferred to the photoresist film by a photolithography technique to form a circular resist / etching mask (not shown).
[0034]
Subsequently, using a circular resist / etching mask, CF_FourThe silicon nitride thin film is etched by reactive ion etching (RIE) using a gas as an etching gas.
Further, the upper reflecting mirror 24, the upper cladding layer 22, and the GaAs / Al are used until the multilayer film of the lower reflecting mirror 42 is reached using a reactive ion beam etching (RIBE) method using chlorine gas._0.2Ga_0.8The As multiple quantum well structure 20, the lower cladding layer 18, and the p-AlAs layer 17 are etched to form a cylindrical groove 28. Thereby, the columnar mesa post structure 30 is formed.
At the time of etching, the p-AlAs film 17 as a selective oxidation layer and the AlAs / Al of the lower reflecting mirror 42 are used._0.2Ga_0.8The progress of etching is stopped between the lower multilayer films 48 made of As pairs, that is, in the upper multilayer film 52. That is, 10 pairs of n-Al_0.2Ga_0.8As film 46 / n-Al_0.9Ga_0.1The upper multilayer film 52 made of the As film 50 functions as an etching depth control layer.
[0035]
Next, the compound semiconductor multilayer structure 58 having the mesa post structure 30 is heated to 400 ° C. in a water vapor atmosphere and left for about 25 minutes.
As a result, the p-AlAs film 17 is selectively oxidized to form the Al oxide layer 16 from the groove wall of the cylindrical groove 28 as shown in FIG. 1, and the central region of the mesa post structure 30 is restored to the original p-type. The AlAs layer 17 remains as it is.
The p-AlAs layer 17 in the central region of the mesa post structure 30 that has not been oxidized in this oxidation step is a circular region having a diameter of about 15 to 20 μm, and constitutes a current injection path.
In selective oxidation, 10 pairs of n-Al_0.2Ga_0.8As film 46 / n-Al_0.9Ga_0.1Since etching stops in the middle of the upper multilayer film 52 made of the As film 50, it is possible to prevent the n-AlAs film 44 in the lower multilayer film 48 from being oxidized and converted into an Al oxide layer. This also improves the manufacturing yield.
[0036]
Next, after the silicon nitride film thin film (not shown) is completely removed by the RIE method, the silicon nitride film thin film 32 is again formed on the entire surface by the plasma CVD method.
The silicon nitride film 32 on the upper surface of the mesa post structure 30 is removed into a circle having a diameter of 30 μm, and a ring-shaped AuZn electrode having an inner diameter of 20 μm and an outer diameter of 30 μm is formed thereon as a p-side electrode. Further, a Ti / Pt / Au pad is formed as the electrode 36 for extracting the p-side electrode.
Further, after polishing the back surface of the n-GaAs substrate 12 to adjust the substrate thickness to about 100 μm, an AuGeNi / Au electrode is evaporated on the back surface to form the n-side electrode 38.
Finally, when annealing is performed at about 400 ° C. in a nitrogen atmosphere, the surface emitting semiconductor laser device 40 having an oscillation wavelength of about 850 nm shown in FIG. 1 can be completed.
[0037]
Test example 1
A surface emitting semiconductor laser element having the configuration of this embodiment example and having different current path areas was formed on the same wafer to obtain a surface emitting semiconductor laser element of the embodiment example sample.
Next, when the relationship between the current path area and the thermal resistance of the sample of the embodiment example was examined, a result as indicated by ◯ in FIG. 3 was obtained. The thermal resistance decreases as the light emitting area (current path area) increases.
A surface emitting semiconductor laser device having the same structure as the sample of the embodiment except that the lower reflecting mirror does not include a lower multilayer film having an AlAs layer as a low refractive index film, that is, the conventional surface emitting semiconductor laser device described above. A conventional sample having the same configuration as that of Example 10 was produced in the same manner as the sample of the embodiment, and used as a comparative sample for the surface emitting semiconductor laser device of this embodiment.
When the relationship between the current path area and the thermal resistance of the comparative example sample was examined in the same manner as the above-described embodiment example sample, the result shown by ● in FIG. 3 was obtained.
[0038]
From the comparison of the test results of the surface emitting semiconductor laser element of the embodiment example sample and the conventional example sample, the thermal resistance (K / W) of the surface emitting semiconductor laser element of this embodiment example is the same as that of the surface emitting semiconductor laser element of the conventional example. Compared with current path area of about 200μm²About 400μm²A value as low as about 300 K / W was exhibited.
[0039]
Test example 2
In order to evaluate the surface emitting semiconductor laser device of this embodiment, the surface emitting semiconductor laser device has the same configuration as that of the surface emitting semiconductor laser device of this embodiment and has a light emitting area of 300 μm.²The surface-emitting semiconductor laser device was manufactured according to the method of the above-described embodiment example, and used as an embodiment example sample.
Subsequently, the current-light output characteristics of the sample of the embodiment were measured using the operating temperature, that is, the environmental temperature as a parameter, and the temperature dependence of the current-light output characteristics was examined. As shown in FIG. The result was obtained.
[0040]
A surface emitting semiconductor laser device having the same configuration as the sample of the embodiment except that the lower reflecting mirror does not include a lower multilayer film having an AlAs layer as a low refractive index film, that is, the conventional surface emitting semiconductor described above. A conventional sample having the same configuration as that of the laser device 10 was produced in the same manner as the sample of the embodiment, and used as a comparative sample for the surface emitting semiconductor laser device of the present embodiment.
Subsequently, the current-light output characteristics of the conventional sample were measured using the operating temperature, that is, the environmental temperature as a parameter, in the same manner as the embodiment sample, and the temperature dependence of the current-light output characteristics was examined. The result as shown in 4 (b) was obtained.
[0041]
As can be seen from a comparison between FIG. 4A and FIG. 4B, the surface-emitting semiconductor laser device of this embodiment has a remarkable light output characteristic at room temperature of 20 ° C. to 30 ° C. compared to the conventional sample. Although there is no significant difference, at a temperature of 70 ° C., the surface emitting semiconductor laser element of this embodiment can obtain an optical output of about 90% of the optical output at room temperature, and by increasing the injection current. The light output can be further increased.
On the other hand, the optical output of the conventional surface emitting semiconductor laser element is saturated at about 8.5 mW, and even if the injection current is increased, no further optical output can be produced.
[0042]
From the results of Test Examples 1 and 2 above, the surface emitting semiconductor laser element 40 of this embodiment example has significantly better thermal saturation characteristics of light output than the conventional surface emitting semiconductor laser element 10 and has a high temperature. It has been demonstrated that it can operate stably at high output even in the operating environment.
[0043]
In the present embodiment example, the active layer 20 and AlAs / Al_0.2Ga_0.810 pairs of Al between the lower multilayer film 48 made of As_0.9Ga_0.1As / Al_0.2Ga_0.8An upper multilayer film 52 made of As is interposed.
The upper multilayer film 52 is provided as an antioxidant layer for the lower multilayer film 48 and as an etching control layer for improving the controllability of the etching depth when forming the mesa post, and is directly below the AlAs oxidized layer 17. If the etching can be stopped at this layer, Al_0.9Ga_0.1As / Al_0.2Ga_0.8By reducing or eliminating the number of As pairs, the thermal resistance of the lower reflecting mirror can be further reduced.
[0044]
In the present embodiment example, the surface emitting semiconductor laser element having an oscillation wavelength of 850 nm has been described as an example. However, the present invention may be a material system including Al as the material of the semiconductor multilayer reflector regardless of the length of the oscillation wavelength. If applicable.
For example, a surface emitting semiconductor laser element having a GaInAs strained quantum well active layer that oscillates at a wavelength of 900 nm or more formed on a GaAs substrate, a surface emitting semiconductor laser element having a GaInNAs quantum well active layer, and a quantum dot active layer The present invention is also applicable to a surface emitting semiconductor laser device having a surface emitting semiconductor laser device having a GaAs (Sb) -based quantum well active layer.
The present invention can also be applied to a laser array in which surface-emitting semiconductor laser elements as in this embodiment are integrated one-dimensionally or two-dimensionally on the same substrate.
In addition, a surface emitting semiconductor laser element in which various modifications and changes are made from the configuration of the above embodiment is also included in the scope of the present invention.
[0045]
【The invention's effect】
According to the present invention, by providing an antioxidant layer between the low refractive index AlAs layer constituting the lower semiconductor multilayer reflector and the active layer, the thermal saturation characteristic of the laser light output is good and the operating environment is high. However, a surface emitting semiconductor laser element and a laser array that operate stably at a high output are realized with a high yield.
According to the present invention, a surface emitting semiconductor laser element and a laser array capable of Peltier-free operation can be realized, and application to a light source of an optical communication device used in the data communication field is expected.
[Brief description of the drawings]
FIG. 1 is a perspective sectional view showing a configuration of a surface emitting semiconductor laser element according to an embodiment.
FIG. 2 is a cross-sectional view schematically showing a layer structure of a surface emitting semiconductor laser element according to an embodiment.
FIG. 3 is a graph showing the relationship between current path area and thermal resistance.
FIGS. 4A and 4B are graphs showing the relationship between the injection current and light output of the example embodiment sample and the conventional example sample, respectively, using the operating environment temperature as a parameter.
FIG. 5 is a perspective sectional view showing a configuration of a conventional surface emitting semiconductor laser element.
FIG. 6 is a cross-sectional view schematically showing a layer structure of a conventional surface emitting semiconductor laser element.
FIG. 7 is a graph showing the relationship between thermal conductivity and thermal resistance of the lower reflecting mirror.
FIG. 8 is a graph showing the relationship between the thermal conductivity of the lower reflecting mirror and the temperature rise of the active layer portion.
FIG. 9 is a graph showing the relationship between the mixed crystal ratio of AlGaAs mixed crystal and thermal conductivity.
FIG. 10 is a graph showing the relationship between the thermal resistance value and the maximum light output of the surface emitting semiconductor laser element.
[Explanation of symbols]
10 Conventional surface emitting semiconductor laser device having an emission wavelength of 850 nm
12 n-GaAs substrate
14 Lower reflector made of n-type multilayer film
16 Al oxide layer
17 p-AlAs layer
18 Non-doped AlGaAs lower cladding layer
20 GaAs quantum well light emitting structure
22 Non-doped AlGaAs upper cladding layer
24 Upper reflector made of p-type multilayer film
26 p-GaAs cap layer
28 Cylindrical groove
30 Mesa post structure
32 Silicon nitride film
34 p-side electrode
36 Lead electrode for p-side electrode
38 n-side electrode
40 Surface-emitting semiconductor laser device having an emission wavelength of 850 nm according to the embodiment
42 Lower reflector made of n-type multilayer film
44 n-AlAs film
46 n-Al_0.2Ga_0.8As film
48 Lower multilayer film
50 n-Al_0.9Ga_0.1As film
52 Upper multilayer film
54 p-Al_0.9Ga_0.1As film
56 p-Al_0.2Ga_0.8As film
58 Compound Semiconductor Multilayer Structure

Claims (10)

A substrate, and upper and lower semiconductor multilayer reflectors formed on the substrate, each of which is formed with a plurality of pair layers composed of a low refractive index layer and a high refractive index layer, are disposed between the semiconductor multilayer reflectors. An active layer, and a current confinement layer provided in the upper semiconductor multilayer film reflector by selectively oxidizing a partial region of the specific semiconductor layer, and a laser perpendicular to the substrate by current injection. In a surface emitting semiconductor laser device that emits light,
The lower semiconductor multilayer mirror includes a first region and a second region disposed between the first region and the active layer, and the low refraction in the first region 2. A surface emitting semiconductor laser device comprising: a refractive index layer made of an AlAs layer; and the low refractive index layer in the second region made of an AlGaAs layer . The specific semiconductor layer is an Al _y Ga _1-y As (0.95 ≦ y ≦ 1.0) layer, and the second region has Al _x1 Ga _1-x1 As (0. 5. The surface emitting semiconductor according to claim 1, comprising a pair layer of 5 ≦ x1 ≦ 0.92) / Al _x2 Ga _1-x2 As (0.15 ≦ x2 ≦ 0.5, x1> x2). Laser element. When m and n are integers, the number of pairs in the first region is m, and the number of pairs in the second region is n, the relationship n / (m + n) ≦ 4/7 holds. The surface-emitting semiconductor laser device according to claim 2 . The surface-emitting semiconductor laser device according to claim 1, wherein the substrate is a GaAs substrate. The surface emitting according to any one of claims 1 to 4 , wherein the substrate is an n-type semiconductor, the lower semiconductor multilayer reflector is an n-type semiconductor, and the upper semiconductor multilayer reflector is a p-type semiconductor. Semiconductor laser element. Wherein the substrate is an n-type semiconductor, the lower semiconductor multilayer reflection mirror and the upper semiconductor multilayer reflection mirror is an intrinsic semiconductor, the surface emitting semiconductor laser device according to any one of claims 1 to 4. Wherein the substrate is a semi-insulating substrate, the lower semiconductor multilayer reflection mirror is n-type semiconductor, the upper semiconductor multilayer reflection mirror is a p-type semiconductor, the surface of any one of claims 1 to 4 Light emitting semiconductor laser element. Wherein the substrate is a semi-insulating substrate, the lower semiconductor multilayer reflection mirror and the upper semiconductor multilayer reflection mirror is an intrinsic semiconductor, the surface emitting semiconductor laser device according to any one of claims 1 to 4. Oscillation wavelength is characterized in that in 600 to 1600 nm, a surface emitting semiconductor laser device according to any one of claims 1 to 8. Laser arrays, wherein a surface-emitting semiconductor laser device according to any one of claims 1 to 9 comprising a plurality on the same substrate, with integrated said surface emitting semiconductor laser device in a one-dimensional or two-dimensional array.

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