JP2004214289A - Semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an improvement in output power and stabilization in the characteristics of a red color semiconductor laser. <P>SOLUTION: An n-type cladding layer, an active layer, a p-type cladding layer, and a p-type contact layer are sequentially stacked on the main surface of an n-type GaAs substrate. The p-type cladding layer is formed of a thin flat layer (thickness: h) formed on the active layer, and a projected ridge stripe part (ridge lower width: Ws) formed on this flat layer. The red color semiconductor laser is constituted of the above structure. The flat layer is also provided with an n-type current block layer covering the side surface of the ridge stripe. Ws is ≥1.0 μm in the relationship of h≥0.17(Ws-1), 0.1 μm≤h≤0.35 μm. Moreover, a coating film formed to the forward emitting surface is formed of a first layer (SiN film) and a second layer (SiO<SB>2</SB>film) formed on the first layer, and the coating film has the thickness equal to 0.5 times the wavelength of the laser beam and the reflectivity of 6 to 9%. The cladding layer or the like is formed of AlGaInP and GaInP. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

（ＴＥモードの場合）
【数２】
Ｈ_ｙ （ｘ，ｙ）＝Ｘ（ｘ）・Ｙ（ｙ）
【００４７】
【数３】

【００４８】
【数４】

【００４９】
図４は半導体レーザ素子１において、シングルモード発振するためのｐ−クラッド層の寸法条件を示すグラフであり、ｐ−クラッド層を構成する平坦層（ｐクラッド層膜厚ｈ）と、リッジストライプ部幅（ストライプ幅Ｗｓ）との相関を示すグラフである。図４ではｐ−クラッド層５のリッジストライプ部５ｂの幅Ｗｓの上限及び下限を規定するとともに、ｐ−クラッド層５の平坦層５ａの厚さｈの上限及び下限を設定して半導体レーザ素子１がシングルモード発振するようになっている。
【００５０】
ｐ−クラッド層５の平坦層５ａの膜厚ｈに対するリッジストライプ部５ｂの下部の幅Ｗｓの上限は、図４の解析結果となる。但し、活性層４の膜厚・組成によってはこの境界が若干変化するため、図４の境界線以下のリッジストライプ幅Ｗｓで範囲を規定した。
【００５１】
リッジストライプ部５ｂの下部の幅Ｗｓの下限は、素子抵抗の増大を防ぐため、即ち、シリーズ抵抗を１０Ω以下にするため１μｍ以上が必要である。換言するならば、前記リッジストライプ部（リッジ）の最も幅が狭い部分の幅は１．０μｍ以上にする必要がある。リッジストライプ部５ｂの形成時、リッジ側面を略垂直形成することも可能であり、この場合、リッジの厚さ方向のいずれの幅も同じ寸法になる。
【００５２】
発光部への光の閉じ込めは、図６（ｃ）に示すように、発光部と非発光部の屈折率差（Ｎｅ１とＮｅ２の差）により行い、導波路構造を形成している。半導体レーザ素子の駆動は活性層４へのキャリア注入によりレーザ発振を行わせるため、レーザ動作時に活性層４のキャリア濃度が増加すると屈折率が低下する。キャリア注入による屈折率変化はせいぜい、１０^−３程度であり、このような状況においても、安定な光閉じ込めを実現するためには、１．５×１０^−３以上が望ましく、２．０×１０^−３以上の屈折率差を設けておく必要がある。これにより、平坦層５ａの膜厚ｈの上限としては、０．３５μｍ以下、望ましくは０．３μｍ以下となる。
【００５３】
また、半導体レーザ素子は、ｐｎ接合を用いて形成されており、逆方向電流に対してはある程度の耐圧がある。素子の実使用上は、逆方向耐圧は、数ボルト程度あれば問題なく使用できるが、膜厚ｈを薄くしていくと、ｎ−電流ブロック層６の部分がブレークダウンし易くなるため、逆方向耐圧が低下してしまう。実用上問題ないレベルを確保するためにはｈ≧０．１μｍが必要になる。
【００５４】
これらのことから、リッジストライプ部５ｂにおける下部の幅Ｗｓと平坦層５ａの膜厚ｈの範囲は、図４の斜線部とする必要がある。下部の幅Ｗｓの上限は、平坦層５ａの厚さをｈとし、前記リッジストライプ部のリッジ底部の幅をＷｓとした場合、ｈ＝０．１７（Ｗｓ−１）の関係になっている。境界線ｈ＝０．１７（Ｗｓ−１）は、図４に示すように、本発明者がシュミレーションによる解析結果によって得た曲線を直線と見なした数式（関数）である。
【００５５】
本実施形態１では、例えば、リッジストライプ部５ｂの幅は、上部の幅Ｗ１を１．３μｍ、下部の幅Ｗｓを２．４μｍとし、ｐ−クラッド層５の平坦層５ａの厚みｈ（活性層４とｎ−電流ブロック層６との間隔）を０．２７μｍとして、導波路構造がシングルモード発振するように設計した。
【００５６】
ところで、前述のように、光ディスク等に用いる高出力半導体レーザ素子は、７０℃程度の高温域で使用される。本発明者は低温域（室温：２５℃）及び高温域における前方出射面に設ける端面反射膜の反射率Ｒf と動作電流Ｉopとの相関について検討した結果、図９は半導体レーザ素子の高温時と低温時における光出力Ｉopと反射率Ｒf との相関を示すグラフである。同グラフから分かるように、７．５％前後（６〜９％）程度が高温域で最も動作電流Ｉopが低下する。即ち、動作電流Ｉopを低減することは、レーザ素子の発熱・温度上昇を抑制し、逆に高温域において光出力の増大を図ることになる。
【００５７】
本実施形態１の半導体レーザ素子１は、図２に示すように、前方出射面１２に設けるコーティング膜３１を共振器１０の端面に形成される第１層３１ａと、この第１層３１ａ上に形成される第２層３１ｂとで形成し、かつ第１層３１ａの厚さｄ1 と第２層３１ｂの厚さｄ2 の和はレーザ光の波長の０．４５倍から０．５５倍の厚さにし、屈折率を７．５％前後（６〜９％）程度としたものである。
【００５８】
本実施形態１では、例えば、第１層３１ａとして屈折率が１．９５のＳｉＮ_Ｘ膜を用い、第２層３１ｂとして屈折率が１．４５のＳｉＯ_２膜を用いた。そして、ＳｉＮ_Ｘ膜の膜厚を０．２２λ、ＳｉＯ_２膜の膜厚を０．２３λとして、コーティング膜３１の膜厚をλ／２（０．５λ）とした。
【００５９】
また、後方出射面１３にもコーティング膜３３を設ける。このコーティング膜３３は、λ／４の厚さのＳｉＯ_２膜とＳｉＮ膜を１０層程度交互に形成して屈折率を９３％程度とした層である。
【００６０】
端面反射膜（コーティング膜）の形成においては、１バッチ処理における面内の膜厚ばらつきや製造レートのばらつきにより、各半導体レーザ素子の端面反射膜の膜厚にばらつきが生じる。ばらつきの大きさや、変動の仕方は個々の製造装置により異なるが、±１０％程度の膜厚ばらつきが生じた場合、本発明による２層膜構造では反射率のばらつき幅は１％程度に留まるのに対し、従来の方法では４％程度のばらつきが生じてしまう。
【００６１】
ここで、本実施形態１のような高出力半導体レーザにおいて、前方出射面での反射率Ｒf が７．５％程度必要である理由について説明する。
半導体レーザの閾値（閾値電流）Ｉ_ｔｈは次式で与えられる。
【００６２】
【数５】

【００６３】
半導体レーザのスロープ効率η_ｓは次式で与えられる。
【数６】

【００６４】
ここで、Ｊ_０：利得発生に必要な電流、ｄ：活性層の膜厚、α_ｉ：内部損失、Ｌ：共振器長さ、Ｒ_ｆ：前方出射面の反射率、Ｒ_ｒ：後方出射面の反射率である。
高出力時の動作電流Ｉopは次式で与えられる。
【００６５】
【数７】

【００６６】
一般にはある反射率Ｒf において動作電流Ｉopが最小になり、反射率Ｒf には最適値が存在する。換言するならば、素子寿命を高める、低電流で使いやすい素子を提供する等の理由から、動作電流Ｉopを低減する必要がある。
【００６７】
反射率Ｒf が小の時、スロープ効率η_ｓは大きくなるが、ｌｎ（１／Ｒ_ｆＲ_ｒ）の項が増大して閾値電流Ｉ_ｔｈ及び動作電流Ｉopが増加する。また、反射率Ｒf が大の時、スロープ効率η_ｓが低下して動作電流Ｉopが増加する。
【００６８】
特に高温域においては、η_ｉ及びβの低下、Ｊ_０，α_ｉの増加により閾値Ｉ_ｔｈの増大が顕著になるため、Ｉopを最小とするＲf の値が高反射率側にシフトする。半導体レーザ素子を構成する材料、構造等により異なるが、経験的に前方出射面の反射率は数％が最適となる。
【００６９】
本実施形態１のように、前方出射面の反射率を６〜９％程度とし、後方出射面の反射率を９３％とする非対称コーティングを施した半導体レーザ素子１では、Ｒｕｎ−ｔｏ−Ｒｕｎの反射率ばらつきは、±５％の範囲にあり、スロープ効率や閾値電流等の半導体レーザ素子の特性ばらつきも抑えられた。
【００７０】
図７は半導体レーザ素子の前方出射面を被うコーティング膜の膜構成の違いによる反射率とコーティング膜の膜厚との相関を示すグラフ、図８は半導体レーザ素子の前方出射面を被うコーティング膜の膜構成の違いによる反射率とコーティング膜の膜厚ずれとの相関を示すグラフである。
【００７１】
図７のグラフには、前方出射面における端面反射膜を、従来仕様であるＳｉＯ_２膜単層（反射率７．５％）のものと、本発明仕様であるＳｉＮ膜とＳｉＯ_２膜による２層コートの例を示してある。２層コートの場合では反射率が７．５％，１０％，２０％のものを示す。２層コートでは、全体の厚さを変えずに、各層の膜厚比を変えることで反射率が調整できる。ＳｉＯ_２膜単層の場合、７．５％で設計するならば□印の膜厚になる。また、２層コートの場合は、各々の曲線における○印の箇所が設計値となる。図７では、単純に膜厚を変化させた場合に反射率がどのように変化するかを計算した例を表示したものである。
【００７２】
実際には、面内ばらつきが成膜レートの変動、素子の波長変化により膜厚がずれる等により、２層の膜厚が略比例してずれる。図８は製造ばらつきによる反射率の変動を示すもので、ＳｉＯ_２膜単層７．５％と、２層コートにおける７．５％，１０％，３０％のものを示すグラフである。コーティング膜の膜厚ずれによる反射率の変動は小さくなる。即ち、±１０％の膜厚ばらつきが発生しても、図８から分かるように、本発明の場合には反射率のばらつきは１％に留まる。
【００７３】
コーティング膜３１の反射率を、例えば、６〜９％程度とした場合、第１層３１ａの膜厚ｄ1 と、第２層３１ｂの膜厚ｄ2 との比率、ｄ1 ／ｄ2 は、０．５４≦ｄ1 ／ｄ2 ≦０．９５、または１．０５≦ｄ1 ／ｄ2 ≦１．８６の関係にある。これにより、コーティング膜の反射率を所望の設計値に設定し、尚かつコーティング膜の膜厚の製造ばらつきによる反射率の変動を抑制した反射率の安定なコーティング膜が形成できる。膜厚比が高い第１層３１ａが厚くてもまたは薄くてもよい。膜厚比は第１層３１ａまたは第２層３１ｂを形成する材質の屈折率によって決まる。
【００７４】
例えば、第１層３１ａの屈折率が２．４となる誘電体膜であり、第２層３１ｂの屈折率が１．４３となる誘電体膜である場合、両膜の厚さ比率を選択することによって、コーティング膜３１の反射率を１〜３０％のうちのいずれかの数値の反射率にすることができる。これにより、設計可能な反射率の範囲を広げた反射率のばらつきの小さいコーティング膜を構成することができる。
【００７５】
また、第１層３１ａの屈折率が２．０となるＳｉＮ_Ｘ膜であり、第２層３１ｂの屈折率が１．４３となるＳｉＯ_２膜である場合、両膜の厚さ比率を選択することによって、コーティング膜３１の反射率を５〜３０％のうちのいずれかの数値の反射率にすることができる。
【００７６】
コーティング膜３１ａおよび３１ｂには、ＳｉＯ_２、ＴｉＯ_２等の酸化膜や、ＳｉＮ_Ｘ等の窒化膜等の誘電体膜を用い、第１層３１ａの屈折率ｎｄ1 を１．６≦ｎｄ1 ≦２．４、第２層３１ｂの屈折率ｎｄ2 を１．２≦ｎｄ2 ≦２．０の関係となるようにコーティング膜の材料を選択し、第１層３１ａの屈折率が第２層３１ｂの屈折率よりも大きく、即ち、ｎｄ1 ≧ｎｄ2 となるように材料を選択すれば良い。
【００７７】
図１０は本実施形態１の半導体レーザ素子（本発明素子）及び従来素子における前方出射面反射率Ｒf と波長λp との相関を示すグラフである。従来素子の場合は、波長が６００〜７００ｎｍの間で膜厚変化により反射率が大きく変動し、かつ高温域で反射率が低下するが、本発明素子の場合は波長が６００〜７００ｎｍの間で反射率は７．５〜８．８％程度の間の少しの変動である。
【００７８】
図１１は本実施形態１の半導体レーザ素子（本発明素子）及び従来素子における、光出力と電流との相関を示すグラフである。従来素子の場合では７０℃と高い温度下での使用では光出力が５０ｍＷ程度が最大であるのに対して、本発明素子の場合は７０℃と高い温度下での使用でも光出力は９０ｍＷ以上と極めて高い数値が得られる。本発明によれば、閾値電流が低下し、スロープ効率が向上し、動作電流を大きく低減することができる。また、動作電流の低減によって、特に高温域での半導体レーザ素子の発熱を抑えられるため、従来の半導体レーザ素子よりも高い温度で動作させることができるようになった。
【００７９】
また、ｐ−クラッド層５のリッジストライプ部５ｂの幅は、従来の半導体レーザ素子の場合における５μｍ程度に対して、本発明では２．４μｍと半分程度になっているにもかかわらず、両者の素子抵抗（シリーズ抵抗）はどちらも約５Ωであり、１ＧＨｚ以上の周波数帯域幅が得られた。
【００８０】
本実施形態１によれば以下の効果を有する。
（１）電流狭窄層（ｎ−電流ブロック層６）に禁制帯幅が大きく、レーザ光に対して透明な材料を用いることにより、レーザ内部の光の損失を低減できるリアルガイド構造となるため、従来のＧａＡｓ電流ブロック層に代表されるロスガイドの導波路構造の素子に比べて低閾値化、高効率化の特性改善が図れる。この結果、光出力の増大を図ることができる。
【００８１】
（２）本発明による半導体レーザ素子１ではキンクレベルが向上し、高い光出力が得られる。即ち、キンクレベルを向上させて高い光出力を得るためには、ｐ−クラッド層５におけるリッジストライプ部５ｂの幅Ｗｓ及び平坦層５ａの厚さｈを調整し、レーザ内で高次のモードが存在し得ないシングルモード導波路（共振器）となるように設計すればよい。ｈ＝０．１７（Ｗｓ−１）となる相関線よりＷｓが狭いか、またはｈを大きくすることにより、導波路構造がシングルモードとなり、この範囲に設計することによりキンクが発生せず、直線性の良い光出力−電流特性を持った半導体レーザ素子１を製造することができる。
【００８２】
（３）前方出射面に設けるコーティング膜（端面反射膜）３１は、２層の誘電体膜構造になっているとともに、コーティング膜３１の膜厚は〜λ／２となっていることから、反射率Ｒf は波長依存性のｄＲf ／ｄλが略零となる安定点に設定できる。即ち、前方出射面の反射率Ｒf は、２層の誘電体膜の膜厚比を調整することにより、１〜３０％の範囲で任意の値に調整が可能であり（ＳｉＮ_Ｘ膜の膜厚がＳｉＯ_２の膜厚より大の場合は、ＳｉＮ_Ｘ膜を厚くすると共に反射率Ｒf は大きくなり、逆の場合はＳｉＮ_Ｘ膜を厚くすると共に反射率Ｒf が低下する。）、反射率の設計値によらず安定点に設定できるため、プロセスばらつきが生じても、反射率の設計値からのずれを略零に抑えることができる。
【００８３】
（４）本発明においては、高温域での発振波長に対して端面反射膜の膜厚が約λ／２に設定することにより、室温あるいは半導体レーザ素子１の動作温度範囲下限よりも高温域において端面反射膜の反射率が大きくなるように設計することができ、高温域での動作電流の増加を抑制でき、光出力の向上を図ることができる。即ち、一般的にレーザ素子特性は端面の反射率に依存して変動する。前方出射面の反射率が低下すると、効率は増加するものの閾値電流が増加し、特に高温域での閾値電流の増加が顕著になる。このため、半導体レーザ素子の高温特性が低下し、高温域でスロープ効率が低下し、動作電流が急増する可能性がある。しかし、本発明によりこのような問題点も解消できることになる。
【００８４】
（実施形態２）
図１２は本発明の他の実施形態（実施形態２）である半導体レーザ素子の製造方法を示す工程断面図である。本実施形態２では実施形態１の半導体レーザ素子１において、リッジストライプ部５ｂとｐ−コンタクト層７との間にｐ−ＧａＩｎＰバッファ層４０を設けて、ｐ−コンタクト層７とリッジストライプ部５ｂとの間の階段状のバンドギャップの差を小さくしてヘテロ接合界面のポテンシャル障壁を低減し、シリーズ抵抗を低減する構造に本発明を適用した例である。
【００８５】
本実施形態２の半導体レーザ素子１は、図１２（ｄ）に示すように、ｐ−クラッド層５のリッジストライプ部５ｂの両側に設けるｎ−電流ブロック層を、ｎ−ＡｌＧａＩｎＰ層６ａと、この上に形成されるｎ−ＧａＡｓ層６ｂとで形成すること、リッジストライプ部５ｂの上面にｐ−ＧａＩｎＰバッファ層４０を形成すること、ｐ−コンタクト層７はｐ−ＧａＩｎＰバッファ層４０とｎ−ＧａＡｓ層６ｂの上面を被うことで実施形態１の半導体レーザ素子１と異なるが、他の各部の構造は実施形態１の半導体レーザ素子１と同じである。ｎ−電流ブロック層６を２層構造とすることによって、コンタクト層７の埋込成長を行なう際に結晶表面にＡｌを含む層が露出せず、結晶の酸化による結晶欠陥の発生を抑えるとともに、電流ブロック効果が安定する。
【００８６】
つぎに、本実施形態２の半導体レーザ素子１の製造について図１２（ａ）〜（ｄ）を参照しながら説明する。図１２（ａ）〜（ｄ）は、実施形態１の半導体レーザ素子の製造方法を示す図３（ａ）〜（ｄ）に対応する図であり、符号の同じものは実施形態１の半導体レーザ素子の製造と同じ材料になっている。また、図１２においても単一の半導体レーザ素子部分のみを示すことにする。
【００８７】
実施形態１の場合と同様に、図１２（ａ）に示すように、厚さ３５０〜４５０μｍ程度のｎ−ＧａＡｓ母基板（ウエハ）２ａを用意する。
つぎに、ＭＯＣＶＤ法によって、前記ウエハ２ａの主面上にそれぞれ所定組成からなる半導体結晶を順次成長させ、ｎ−クラッド層３，活性層４，ｐ−クラッド層５，ｐ−ＧａＩｎＰバッファ層４０及びｎ−ＧａＡｓキャップ層２２を順次重ねるように形成する。実施形態１の場合と異なる点はｐ−クラッド層５とｎ−ＧａＡｓキャップ層２２との間にｐ−ＧａＩｎＰバッファ層４０を設けることである。ｐ−ＧａＩｎＰバッファ層４０は、厚さが０．５μｍのＧａ_０．５Ｉｎ_０．５Ｐからなっている。
【００８８】
つぎに、図１２（ｂ）に示すように、実施形態１の場合と同様に、リッジストライプ部を形成するため、前記ｎ−ＧａＡｓキャップ層２２の上面に選択的にストライプ状のマスク２３を形成し、このマスク２３をエッチング用マスクとして使用して常用のドライエッチングによってｐ−クラッド層５を所定深さまでエッチングして、平坦層５ａ及びリッジストライプ部５ｂを形成する。
【００８９】
つぎに、塩素系のエッチャント（Ｈｃｌ水溶液）によってｐ−クラッド層５の表面をライトエッチングして表面層を除去し、ついで、図１２（ｃ）に示すように、ｐ−クラッド層５のエッチングで除去した部分にｎ−ＡｌＧａＩｎＰ層６ａ及びｎ−ＧａＡｓ層６ｂを順次形成してｎ−電流ブロック層６を形成する。
【００９０】
つぎに、図１２（ｄ）に示すように、マスク２３及びｎ−ＧａＡｓキャップ層２２を常用のエッチングによって除去する。この際、リッジストライプ部５ｂの上面のｐ−ＧａＩｎＰバッファ層４０はそのまま残留している。つぎに、図１２（ｄ）に示すように、ｎ−電流ブロック層６及びリッジストライプ部５ｂの上面を被うように厚さ３μｍ程度のｐ−ＧａＡｓからなるコンタクト層７を形成する。
【００９１】
つぎに、実施形態１と同様にウエハ２ａの表裏面にｎ電極８及びｐ電極９を形成し、ついでウエハ２ａを短冊状に劈開させた後、劈開面にＡＲ膜やＨＲ膜を形成し、その後、短冊体を所定寸法で切断して図１２（ｄ）に示すような半導体レーザ素子１を多数製造する。
【００９２】
本実施形態２の半導体レーザ素子１は、ＡｌＧａＩｎＰからなるリッジストライプ部５ｂと、ＧａＡｓからなるｐ−コンタクト層７との間にバンドギャップがその中間になるＧａＩｎＰからなるｐ−ＧａＩｎＰバッファ層４０を介在させる結果、ヘテロ接合部分のポテンシャル障壁を分散されて大きなギャップが生じなくなる為、シリーズ抵抗を低減することができる。
【００９３】
（実施形態３）
図１３は本発明の他の実施形態（実施形態３）である半導体レーザ素子の共振器に直交する面の模式的断面図、図１４は半導体レーザ素子の共振器方向に沿う面の一部の模式的断面図である。
【００９４】
本実施形態３の半導体レーザ素子１は、リッジストライプ部５ｂの両側のｎ−電流ブロック層６をｎ−ＧａＡｓ層６ｄとした以外は、他の部分は実施形態１の半導体レーザ素子１と同じである。即ち、ｎ−電流ブロック層６をｎ−ＧａＡｓ層６ｄとし、前方出射面１２に実施形態１と同様に、第１層３１ａ（ＳｉＮ_Ｘ膜）及び第２層３１ｂ（ＳｉＯ_２ 膜）からなるコーティング膜３１を形成した場合でも、従来素子に比べて、７０℃の動作電流は約１３ｍＡ低減でき、飽和光出力は約１０ｍＷ向上させることができた。また、本実施形態３の半導体レーザ素子１も、前方出射面に設けたコーティング膜３１の反射率ばらつきが、従来素子の±１０％から±５％に半減できる。この結果、閾値電流及びスロープ効率の特性ばらつきも略半減することができた。
【００９５】
以上本発明者によってなされた発明を実施形態に基づき具体的に説明したが、本発明は上記実施形態に限定されるものではなく、その要旨を逸脱しない範囲で種々変更可能であることはいうまでもない。
【００９６】
【発明の効果】
本願において開示される発明のうち代表的なものによって得られる効果を簡単に説明すれば、下記のとおりである。
（１）光出力の増大が可能になるシングルモード発振する赤色半導体レーザ素子を提供することができる。
（２）赤色半導体レーザ素子において、コーティング膜（端面反射膜）の製造ばらつきに起因する反射率の変動を改善することができる。
（３）高温域でも安定して高出力のレーザ光を出射できる赤色半導体レーザ素子を提供することができる。
（４）スロープ効率の向上や動作電流の低減を図ることができる赤色半導体レーザ素子を提供することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態（実施形態１）である半導体レーザ素子の共振器に直交する面の模式的断面図である。
【図２】前記半導体レーザ素子の共振器方向に沿う面の模式的断面図である。
【図３】前記半導体レーザ素子の製造方法を示す工程断面図である。
【図４】前記半導体レーザ素子において、シングルモード発振するためのｐ型クラッド層の寸法条件を示すグラフであり、ｐ型クラッド層を構成する平坦層（ｐクラッド層膜厚ｈ）と、リッジストライプ部幅（ストライプ幅Ｗｓ）との相関を示すグラフである。
【図５】前記寸法条件を計算するために使用するｐ型クラッド層の各部に寸法記号を付した半導体レーザ素子の模式図である。
【図６】前記寸法条件を計算するための各部が現れるように示す半導体レーザ素子の各断面の模式図である。
【図７】前記半導体レーザ素子の前方出射面を被うコーティング膜の膜構成の違いによる反射率とコーティング膜の膜厚との相関を示すグラフである。
【図８】前記半導体レーザ素子の前方出射面を被うコーティング膜の膜構成の違いによる反射率とコーティング膜の膜厚ずれとの相関を示すグラフである。
【図９】前記半導体レーザ素子の高温時と低温時における光出力Ｉopと反射率Ｒf との相関を示すグラフである。
【図１０】本実施形態１の半導体レーザ素子（本発明素子）及び従来素子における前方出射面反射率Ｒf と波長λp との相関を示すグラフである。
【図１１】本実施形態１の半導体レーザ素子（本発明素子）及び従来素子における、光出力と電流との相関を示すグラフである。
【図１２】本発明の他の実施形態（実施形態２）である半導体レーザ素子の製造方法を示す工程断面図である。
【図１３】本発明の他の実施形態（実施形態３）である半導体レーザ素子の共振器に直交する面の模式的断面図である。
【図１４】前記半導体レーザ素子の共振器方向に沿う面の一部の模式的断面図である。
【符号の説明】
１…半導体レーザ素子、２…ｎ−ＧａＡｓ基板、２ａ…ウエハ（ＧａＡｓ母基板）、３…クラッド層（ｎ−クラッド層）、４…活性層、５…クラッド層（ｐ−クラッド層）、５ａ…平坦層、５ｂ…リッジストライプ部、６…ｎ−電流ブロック層、６ａ…ｎ−ＡｌＧａＩｎＰ層、６ｂ…ｎ−ＧａＡｓ層、７…ｐ−コンタクト層、８…ｎ電極、９…ｐ電極、１０…共振器、１１…レーザ光、１２…前方出射面、１３…後方出射面、２２…ｎ−ＧａＡｓキャップ層、２３…マスク、３１…コーティング膜、３１ａ…第１層、３１ｂ…第２層、３３…コーティング膜、４０…ｐ−ＧａＩｎＰバッファ層。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor laser device, and more particularly to a technology effective when applied to a manufacturing technology of a red semiconductor laser device having a wavelength (oscillation wavelength) of 620 to 700 nm.
[0002]
[Prior art]
A 0.6 μm red semiconductor laser (semiconductor laser element) is expected as a light source for various information processing devices. For example, a semiconductor laser in the 650 nm band is used as a light emitting source for a DVD (Digital Versatile Disc), and a semiconductor laser in the 630 nm band is used as a light source for a measuring device or the like.
2. Description of the Related Art As a high-output semiconductor laser that oscillates in a single transverse mode and is used for an optical disc, a semiconductor laser having a double heterostructure having a GaInP / AlGaInP quantum well structure as an active region formed on a GaAs substrate is known. (For example, see Patent Document 1).
On the other hand, there has been proposed a semiconductor laser device for optical communication having an antireflection film made of first and second dielectric thin films on an end face of a resonator. (For example, see Patent Document 2).
[0003]
[Patent Document 1]
JP-A-10-209553 (page 2-3, FIG. 2)
[Patent Document 2]
JP-A-10-51072 (page 2-3, FIG. 1)
[0004]
[Problems to be solved by the invention]
2. Description of the Related Art With the spread of audio-visual (AV) devices using optical disks such as personal computers (PCs), CDs (compact disks), and DVDs, demands for semiconductor laser devices for information terminal devices are rapidly increasing. In particular, a recordable optical disk device such as a DVD-R / RW (writable / rewritable) or a CD-R / RW is generally mounted on a PC as a standard, and a high-power semiconductor laser serving as a light source of the optical disk device. This is a major factor in increasing demand for devices. In addition, a recording type DVD device capable of recording video for a long time can be applied to a high-performance recording device utilizing the characteristics of an optical disk device, so that a further increase in demand is expected in the future. In order to meet such market demands, it has become an important issue to stably supply a semiconductor laser device having small variations in characteristics and excellent characteristics.
[0005]
One of the causes of the variation in the characteristics of the semiconductor laser device is a change in the reflectance due to the variation in the film thickness production of the coating film (end reflection film) provided on the end surface (the emission surface for emitting the laser light) of the device. . In particular, an AR (Anti-Reflection) film having a low reflectance is coated on a front emission surface (an emission surface for emitting a laser beam having a large output used) of the element, and a rear emission surface (a small output used for a monitor or the like) is coated. In a high-power semiconductor laser device in which an HR (High-Reflection) film having a large reflectivity is coated on a laser light emitting surface (emission surface), a variation in reflectivity of a front emission surface has a large effect on device characteristics, and a slope efficiency and an operation. Not only does the current, monitor current, etc. fluctuate, lowering the device sorting yield, but also causes problems such as the need to adjust the control circuit of the device incorporating the semiconductor laser device.
[0006]
In addition, rewritable optical disk devices such as DVD-RW and CD-RW are often used as built-in storage devices of personal computers, and are used in a state where the ambient temperature is extremely high due to heat generation in the devices. In order to ensure normal operation even in such a state, an operating current of the semiconductor laser element is reduced, and an element having excellent temperature characteristics is provided so that deterioration in characteristics due to heat generation of the element itself can be suppressed as much as possible. There is a need.
[0007]
In a semiconductor laser element (hereinafter also referred to as an element) used for an optical disk described in Patent Document 1, an AlGaInP-based semiconductor laser element using a GaInP or AlGaInP crystal transparent to a laser beam for a part of a current block layer Is used. In addition, by setting the width of the current confinement structure, that is, the width of the stripe structure to 2.5 to 5 μm, the kink level is improved and the output of the semiconductor laser device is increased.
[0008]
However, in such a semiconductor laser device, no consideration is given to the series resistance of the device for achieving high output. That is, when an AlGaInP-based semiconductor laser device is manufactured by a general method and the above-described stripe structure is formed, the width of the upper portion of the current confinement portion (stripe structure) becomes very narrow, and the series resistance increases, thereby increasing the device resistance. A problem is supposed that the frequency response is reduced or the light output in a high temperature range is reduced due to an increase in heat generation.
[0009]
In addition, the kink level of the semiconductor laser device changes depending on the distance between the current confinement structure and the active layer and other structures. Therefore, it is difficult to sufficiently increase the kink level only by defining the width of the current confinement portion. is there.
[0010]
On the other hand, a coating film (end face reflection film) is provided on each of the front emission surface and the rear emission surface of the semiconductor laser device that emits laser light as described above. As the end face reflection film, it is general that a single dielectric thin film has a film thickness corresponding to λ / 4 or λ / 2 with respect to the wavelength (oscillation wavelength) λ of the semiconductor laser device. A semiconductor laser device having a relatively high optical output often uses a low reflection film of λ / 4 (reflectance of about 5%), and a semiconductor laser device of low output often uses an end reflection film of λ / 2.
[0011]
Assuming that a single dielectric thin film has a thickness corresponding to λ / 4 (0.25λ) or λ / 2 (0.5λ), the variation in the oscillation wavelength of the semiconductor laser device and the variation in the reflectance with respect to the variation in the film thickness are as follows. Although it can be reduced, the reflectivity that can be produced is determined by the refractive index of the material used for forming the end face reflection film. In addition, if an end face reflection film having a thickness deviating from an integral multiple of λ / 4 is used to realize a reflectance different from such a value, the dependency of the reflectance on the film thickness and wavelength becomes large, and manufacturing variability is increased. Causes fluctuations in device characteristics.
[0012]
In order to obtain a desired reflectance, a method of overlapping a plurality of layers is employed. Patent Document 2 discloses that a first layer of silicon nitride having a refractive index of 1.82 to 2.00 and an optical thickness of 0.17 to 0.23 times the oscillation wavelength, and an optical thickness of 0 to the oscillation wavelength of 0. There is disclosed a semiconductor laser device in which an antireflection film having a two-layer structure composed of a silicon oxide of a second layer of 0.03 times to 0.15 times is formed. That is, the thickness of the antireflection film (end face reflection film) is 0.2λ to 0.38λ.
[0013]
On the other hand, a high-output semiconductor laser device used for an optical disk or the like is used in a high temperature range of about 70 ° C., for example. The present inventor has studied the correlation between the reflectance Rf of the end face reflection film provided on the front emission surface and the operating current Iop in the low temperature region (room temperature: 25 ° C.) and the high temperature region. 9%), it was found that the operating current Iop decreased most in the high temperature range.
[0014]
SUMMARY OF THE INVENTION An object of the present invention is to provide a single-mode oscillating red semiconductor which is capable of improving fluctuations in reflectivity due to manufacturing variations of a coating film (edge reflection film), and having excellent temperature characteristics and stably obtaining a high optical output. It is to provide a laser element.
The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.
[0015]
[Means for Solving the Problems]
The outline of a typical invention among the inventions disclosed in the present application will be briefly described as follows.
(1) The semiconductor laser device of the present invention
A first conductivity type cladding layer, a single or multiple quantum well structure active layer, and a second conductivity type cladding layer sequentially stacked on a first conductivity type semiconductor substrate;
The second conductivity type clad layer is processed, and includes a flat layer formed on the active layer, and a ridge stripe portion formed in a stripe shape on the flat layer,
A current blocking layer of a first conductivity type covering a side surface of the ridge stripe portion on the flat layer;
A second conductivity type contact layer is provided on the upper surface side of the ridge stripe portion and the current block layer,
A first electrode is formed on a lower surface of the semiconductor substrate, and a second electrode is formed on an upper surface of the contact layer;
A coating film (edge reflection film) covering the semiconductor substrate, the first conductivity type cladding layer, the active layer, the second conductivity type cladding layer, and the contact layer is provided on both end surfaces of the ridge stripe portion. And
A semiconductor laser device that emits laser light from an end face of a resonator formed by the active layer portion corresponding to the ridge stripe portion,
When the thickness of the flat layer is h and the width of the ridge bottom of the ridge stripe portion is Ws, Ws is 1.0 μm or more and h ≧ 0.17 (Ws−1). .1 μm ≦ h ≦ 0.35 μm,
The coating film is formed of a first layer formed on the resonator end face, and a second layer formed on the first layer,
The sum of the thickness d1 of the first layer and the thickness d2 of the second layer is 0.45 to 0.55 times the wavelength of the laser light,
The reflectance of the coating film becomes 6 to 9%,
The semiconductor substrate is n-type GaAs, and each semiconductor layer formed on the upper surface side of the semiconductor substrate is AlGaInP or GaInP, and is a semiconductor laser device that emits laser light having a wavelength of 620 to 700 nm.
[0016]
According to the above means (1),
(A) Since Ws is 1.0 μm or more, h ≧ 0.17 (Ws−1), and 0.1 μm ≦ h ≦ 0.35 μm, single-mode oscillation occurs, causing kink. Since the generation of higher-order guided modes can be suppressed, an optical output-current characteristic excellent in linearity can be obtained, and a laser element that operates stably even at a high optical output can be provided.
(B) The thickness of the coating film is 0.45 to 0.55 times the wavelength of the laser beam, and the reflectance of the coating film is 6 to 9%, and the operating current value can be minimized. The operation becomes possible, and reduction in power consumption and improvement in light output can be achieved.
(C) Since the light output is high and the light emission characteristics at high temperatures are good, the semiconductor laser device is suitable for a light emission source of CD, DVD, AV equipment and the like.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for describing the embodiments of the present invention, components having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.
[0018]
(Embodiment 1)
1 to 11 are diagrams related to a semiconductor laser device according to an embodiment (Embodiment 1) of the present invention. In the first embodiment, an example in which the present invention is applied to a red semiconductor laser device having a first conductivity type of n-type and a second conductivity type of p-type and a wavelength (oscillation wavelength) of 620 to 700 nm band will be described.
[0019]
The semiconductor laser device 1 according to the first embodiment has a structure shown in FIGS. FIG. 1 is a schematic sectional view of a surface of the semiconductor laser device orthogonal to the resonator, and FIG. 2 is a schematic sectional view of a surface of the semiconductor laser device along the resonator direction.
[0020]
As shown in FIGS. 1 and 2, the semiconductor laser device 1 is manufactured based on a semiconductor substrate 2 of a first conductivity type (n-type), specifically, an n-GaAs substrate 2. On the upper surface (main surface) of the n-GaAs substrate 2, a cladding layer 3 made of n-AlGaInP is formed, and on this n-cladding layer 3, an active layer 4 is formed. Is formed with a cladding layer 5 made of AlGaInP of the second conductivity type (p-type).
[0021]
The p-cladding layer 5 includes a thin flat portion (flat layer 5 a) having a thickness h formed on the upper surface of the active layer 4 and a ridge stripe portion 5 b formed in a stripe shape on the flat layer 5 a. Has become. The ridge stripe portion 5b is formed by selectively etching the p-clad layer formed to have the thickness of the ridge stripe portion 5b. That is, the ridge stripe portion 5b is formed by etching both sides of the p-cladding layer by a predetermined thickness except for the center. In this etching, the width Ws of the lower portion of the ridge is wider than the width W1 of the upper surface by, for example, about 0.2 to 0.8 [mu] m.
[0022]
For the n-cladding layer 3, the mixed crystal ratio of the elements is selected, for example, n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 Consists of P. The thickness is about 1.8 μm. The p-cladding layer 5 is, for example, n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 The thickness of the ridge stripe portion 5b is about 1.6 μm.
[0023]
The active layer 4 has a multiple quantum well (MQW) structure, a barrier layer is located between the well layers, and this structure is repeatedly formed. An undoped (u) -GaInP layer is selected for the well layer, and a u-AlGaInP layer is selected for the barrier layer. The active layer 4 has a three-period well layer and has a strained multiple quantum well structure depending on the selection of the material.
[0024]
On the flat layer 5a of the p-cladding layer 5, a current block layer 6 made of n-AlInP covering the side surface of the ridge stripe portion 5b is provided. This n-current block layer 6 is made of n-Al _0.5 In _0.5 It is made of P and is formed to a thickness that covers the p-cladding layer portion removed by etching, for example, a thickness of about 0.5 to 0.8 μm.
Further, a contact layer 7 made of p-GaAs having a thickness of about 3 μm is provided so as to cover the upper surfaces of the n-current block layer 6 and the ridge stripe portion 5b.
[0025]
On the lower surface of the n-GaAs substrate 2, an n-electrode 8 is formed as a first electrode, and on the upper surface of the p-contact layer 7, a p-electrode 9 is formed as a second electrode. Each of the electrodes is formed of a material containing gold.
[0026]
In such a semiconductor laser device 1, by applying a predetermined voltage between the n-electrode 8 and the p-electrode 9, the portion of the active layer 4 corresponding to the ridge stripe portion 5 b forms a resonator 10, and FIG. As shown in FIG. 5, laser light 11 is emitted from both ends (emission surface) of the resonator 10. In general, a high-output semiconductor laser is used for use with one of its emission surfaces being increased in output, and the light intensity of the laser light emitted from the other emission surface is monitored by reducing the light output in many cases. The former emission surface is called a front emission surface, and the latter emission surface on the monitor side is called a rear emission surface. In FIG. 2, the left emission surface is the front emission surface 12, and the right emission surface is the rear emission surface 13.
The semiconductor laser device 1 can select the oscillation wavelength from about 620 to 700 nm by selecting the mixed crystal ratio of the elements of each layer and the like.
[0027]
Next, a method of manufacturing such a semiconductor laser device 1 will be described with reference to FIGS. As shown in FIG. 3A, an n-GaAs mother substrate (wafer) 2a having a thickness of about 350 to 450 μm is prepared.
[0028]
Next, semiconductor crystals having a predetermined composition are sequentially grown on the main surface of the wafer 2a by MOCVD (Metalorganic Chemical Vapor Deposition), and the n-cladding layer 3, active layer 4, p -The clad layer 5 and the n-GaAs cap layer 22 are formed so as to be sequentially stacked. The wafer 2a is formed of a GaAs substrate having a diameter of several inches, and a large number of semiconductor laser devices are manufactured by finally dividing the wafer. FIG. 3 shows only a single semiconductor laser element portion.
[0029]
On the main surface of the wafer 2a, n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P is formed to a thickness of about 1.8 μm. On the n-cladding layer 3, a three-period strained multiple quantum well structure is formed as the active layer 4 using u-GaInP as a well layer and u-AlGaInP as a barrier layer. On the active layer 4, n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P is formed to a thickness of about 1.6 μm. An n-GaAs cap layer 22 having a thickness of about 0.5 μm is formed on the p-cladding layer 5.
[0030]
Next, as shown in FIG. 3B, a stripe-shaped mask 23 is selectively formed on the upper surface of the n-GaAs cap layer 22 to form a ridge stripe portion. The mask 23 is made of, for example, SiO 2 on the n-GaAs cap layer 22. ₂ After the film is formed by the sputtering method, a stripe-shaped mask 23 having a width of about 2 μm is formed by a conventional photoresist technique and etching technique. Thereafter, using the mask 23 as an etching mask, the p-clad layer 5 is etched to a depth of about 1.4 μm by ordinary dry etching to form the flat layer 5a and the ridge stripe portion 5b. The thickness of the flat layer 5a and the dimensions of the ridge stripe portion 5b will be described later in detail.
[0031]
Next, the surface of the p-cladding layer 5 is light-etched with a chlorine-based etchant (HCl aqueous solution) to remove the surface layer damaged by dry etching, and then the portion of the p-cladding layer 5 removed by etching. N-Al _0.5 In _0.5 P is formed to a thickness of about 0.5 to 0.8 μm to form the n-current blocking layer 6 (see FIG. 3C).
[0032]
Next, after removing the mask 23 and the n-GaAs cap layer 22 by ordinary etching, a contact made of p-GaAs having a thickness of about 3 μm is formed so as to cover the upper surfaces of the n-current block layer 6 and the ridge stripe portion 5b. The layer 7 is formed.
[0033]
Next, when the wafer is divided and formed into chips, isolation grooves are formed vertically and horizontally on the main surface side of the wafer 2a (not shown) to facilitate chip separation. That is, the p-electrode 9 is selectively formed on the p-contact layer 7 (see FIG. 3D). Thereafter, the lower surface of the wafer 2a is polished to a predetermined thickness, and the crystal strain layer generated by the polishing is removed by chemical etching to obtain a wafer 2a having a thickness of about 100 μm, and then the n-electrode 8 is formed on the lower surface of the wafer 2a. .
[0034]
Next, although not shown, the wafer 2a is divided by performing cleavage of the crystal in a direction orthogonal to the stripes of the ridge stripe portion 5b to form an elongated strip having a width of about 900 μm. Since both side surfaces of the strip serve as laser light emission surfaces, a coating film serving as a protective film and a reflection film is formed on each emission surface by a sputtering method. The configuration of this coating film will be described later in further detail.
[0035]
Next, a large number of semiconductor laser devices 1 as shown in FIG. 3D are manufactured by cutting the strip into predetermined dimensions. Thereby, a semiconductor laser device 1 having a cavity length of 900 μm, a width of 250 μm, and a thickness of about 100 μm can be obtained.
[0036]
In the first embodiment, the width W1 of the upper surface of the ridge stripe portion 5b, the width Ws of the lower portion thereof, and the thickness h of the flat layer 5a are selected as described below in order to cause the laser light to oscillate in a single mode.
[0037]
The dimensional condition of the ridge stripe portion 5b is determined as follows. FIG. 5 is a schematic cross-sectional view of the semiconductor laser device 1 in which each part of the p-type cladding layer used for calculating the dimensional conditions is given a dimensional symbol. FIGS. 6A to 6C are schematic views of respective cross sections of the semiconductor laser device 1 in which respective portions for calculating dimensional conditions appear.
[0038]
FIG. 5 is a cross-sectional view showing a surface of the ridge stripe portion 5b that is perpendicular to the direction in which the resonator 10 extends. For convenience of explanation, the vertical axis is the y-axis, and the horizontal axis is the x-axis. In FIG. 5, the portion of the active layer 4 corresponding to the width Ws below the stripe portion 5b becomes a light emitting portion, and the active layer 4 corresponding to the flat layer 5a deviating from the ridge stripe portion 5b becomes a non-light emitting portion. The width below the ridge stripe portion 5b is Ws, and the thickness (height) of the flat layer 5a is h.
[0039]
FIG. 6A is a graph showing the correlation between the refractive index distribution in the y direction crossing the ridge stripe portion 5b serving as the light emitting portion and the refractive index. Although the refractive index in the active layer 4 portion is as large as na, the cladding layers located above and below the active layer 4 have different conductivity types but the same composition, so that the refractive indices are both nc. The effective refractive index ne (x) is Ne1.
[0040]
FIG. 6B is a graph showing a correlation between the refractive index distribution in the y direction crossing the flat layer 5a and the n-current blocking layer 6 which are non-light emitting portions outside the ridge stripe portion 5b and the refractive index. The refractive index of the active layer 4 is increased to na, and the cladding layers located above and below the active layer 4 are different in conductivity type but have the same composition. In the case of 6, the refractive index is further reduced to nb. The effective refractive index ne (x) is Ne2.
[0041]
FIG. 6C is a graph showing the correlation between the refractive index distribution in the x direction and the effective refractive index ne (x), and shows Ne1 and Ne2. The effective refractive index of the portion of the width Ws below the ridge stripe portion 5b becomes Ne1, and the effective refractive index of the portion of the flat layer 5a becomes Ne2.
[0042]
Here, a method of analyzing the resonator (waveguide) will be described. The structure of the semiconductor laser and the distribution of the refractive index are as shown in FIGS. 5 and 6A to 6C. In these figures, the refractive indices of the cladding layers above and below the refractive index of the active layer 4 are equal, but the refractive indices of both the p and n cladding layers may be different. In addition, the active layer 4 is generally configured to have a single or multiple quantum well structure, but the whole quantum well structure is simplified and described as a single layer. In the case of a quantum well structure, analysis can be performed by a similar method.
[0043]
Although it is difficult to obtain a strict light intensity distribution in the semiconductor laser device 1 as shown in these figures, it is possible to easily analyze the waveguide structure by using the equivalent refractive index method in the device design. is there.
[0044]
(1) First, with respect to the longitudinal direction of the light emitting portion (current injection portion) and the non-light emitting portion (lower of the block layer), the following wave equation and Equation 1 are respectively expressed by using the refractive index distributions of FIGS. 6 (a) and 6 (b). , And the effective refractive index in the vertical direction (y direction) was determined. In the equivalent refractive index method, it is assumed that the distribution function of the electromagnetic field is represented by variable separation and can be described as in the following Expression 2. From Equations 1 and 2, Equations 3 and 4 can be derived for X and Y. Therefore, a solution can be obtained by solving the equations in the y direction and the x direction in order. Here, ne (x) is the effective refractive index in the vertical direction (y direction) at the position x.
[0045]
(2) The effective refractive index obtained in the above (1) is defined as the refractive index distribution in the horizontal direction (FIG. 6C), and the effective refractive index of the entire waveguide is calculated by applying the equivalent refractive index method again in the horizontal direction. The waveguide mode was analyzed.
[0046]
(Equation 1)

(For TE mode)
(Equation 2)
H _y (X, y) = X (x) · Y (y)
[0047]
[Equation 3]

[0048]
(Equation 4)

[0049]
FIG. 4 is a graph showing the dimensional conditions of the p-cladding layer for performing single mode oscillation in the semiconductor laser device 1, and includes a flat layer (p-cladding layer thickness h) constituting the p-cladding layer and a ridge stripe portion. It is a graph which shows the correlation with width (stripe width Ws). In FIG. 4, the upper and lower limits of the width Ws of the ridge stripe portion 5b of the p-clad layer 5 are defined, and the upper and lower limits of the thickness h of the flat layer 5a of the p-clad layer 5 are set. Are designed to oscillate in single mode.
[0050]
The upper limit of the width Ws below the ridge stripe portion 5b with respect to the thickness h of the flat layer 5a of the p-clad layer 5 is the analysis result of FIG. However, since this boundary slightly changes depending on the thickness and composition of the active layer 4, the range is defined by the ridge stripe width Ws below the boundary line in FIG.
[0051]
The lower limit of the width Ws of the lower portion of the ridge stripe portion 5b needs to be 1 μm or more to prevent an increase in element resistance, that is, to reduce the series resistance to 10Ω or less. In other words, the width of the narrowest portion of the ridge stripe (ridge) needs to be 1.0 μm or more. When forming the ridge stripe portion 5b, it is also possible to form the ridge side surface substantially vertically, and in this case, the width of each of the ridges in the thickness direction has the same size.
[0052]
As shown in FIG. 6 (c), the light is confined in the light emitting portion by the refractive index difference between the light emitting portion and the non-light emitting portion (difference between Ne1 and Ne2) to form a waveguide structure. Since the semiconductor laser device is driven to perform laser oscillation by injecting carriers into the active layer 4, the refractive index decreases when the carrier concentration of the active layer 4 increases during laser operation. The refractive index change due to carrier injection is at most 10 ^-3 Even in such a situation, 1.5 × 10 ^-3 More preferably, 2.0 × 10 ^-3 It is necessary to provide the above refractive index difference. Thus, the upper limit of the thickness h of the flat layer 5a is 0.35 μm or less, preferably 0.3 μm or less.
[0053]
The semiconductor laser device is formed using a pn junction, and has a certain withstand voltage against a reverse current. In practical use of the element, the reverse breakdown voltage can be used without any problem if it is about several volts. However, as the film thickness h is reduced, the portion of the n-current blocking layer 6 is easily broken down. The directional breakdown voltage is reduced. In order to secure a practically acceptable level, h ≧ 0.1 μm is required.
[0054]
For these reasons, the range between the lower width Ws of the ridge stripe portion 5b and the thickness h of the flat layer 5a needs to be shaded in FIG. The upper limit of the lower width Ws is h = 0.17 (Ws−1), where h is the thickness of the flat layer 5a and Ws is the width of the ridge bottom of the ridge stripe portion. The boundary line h = 0.17 (Ws-1) is a mathematical expression (function) in which the inventor regards a curve obtained based on the analysis result by the simulation as a straight line, as shown in FIG.
[0055]
In the first embodiment, for example, the width of the ridge stripe portion 5b is such that the upper width W1 is 1.3 μm, the lower width Ws is 2.4 μm, and the thickness h (active layer) of the flat layer 5a of the p-cladding layer 5 is set. The distance between the first and fourth n-current blocking layers 6 was set to 0.27 μm, and the waveguide structure was designed to perform single mode oscillation.
[0056]
By the way, as described above, a high-output semiconductor laser device used for an optical disk or the like is used in a high temperature range of about 70 ° C. The present inventor examined the correlation between the operating current Iop and the reflectance Rf of the end face reflection film provided on the front emission surface in the low temperature range (room temperature: 25 ° C.) and the high temperature range. 6 is a graph showing a correlation between the light output Iop and the reflectance Rf at a low temperature. As can be seen from the graph, the operating current Iop is the lowest at around 7.5% (6 to 9%) in the high temperature range. That is, reducing the operating current Iop suppresses heat generation and temperature rise of the laser element, and conversely increases light output in a high temperature range.
[0057]
As shown in FIG. 2, in the semiconductor laser device 1 of the first embodiment, a coating film 31 provided on the front emission surface 12 has a first layer 31a formed on an end face of the resonator 10 and a first layer 31a formed on the first layer 31a. And the sum of the thickness d1 of the first layer 31a and the thickness d2 of the second layer 31b is 0.45 to 0.55 times the wavelength of the laser light. And the refractive index is about 7.5% (6 to 9%).
[0058]
In the first embodiment, for example, SiN having a refractive index of 1.95 is used as the first layer 31a. _X Using a film, SiO 2 having a refractive index of 1.45 as the second layer 31 b ₂ A membrane was used. And SiN _X The film thickness is 0.22λ, SiO ₂ The thickness of the film was set to 0.23λ, and the thickness of the coating film 31 was set to λ / 2 (0.5λ).
[0059]
Also, a coating film 33 is provided on the rear emission surface 13. This coating film 33 is made of SiO having a thickness of λ / 4. ₂ This is a layer having a refractive index of about 93% by alternately forming about 10 films and SiN films.
[0060]
In the formation of the end face reflection film (coating film), the thickness of the end face reflection film of each semiconductor laser device varies due to in-plane film thickness variation and manufacturing rate variation in one batch process. Although the magnitude of the variation and the manner of the variation vary depending on the individual manufacturing apparatus, when the thickness variation of about ± 10% occurs, the variation width of the reflectance in the two-layer film structure according to the present invention is only about 1%. On the other hand, the conventional method has a variation of about 4%.
[0061]
Here, the reason why the reflectance Rf at the front emission surface needs to be about 7.5% in the high-power semiconductor laser as in the first embodiment will be described.
Semiconductor laser threshold (threshold current) I _th Is given by the following equation.
[0062]
(Equation 5)

[0063]
Slope efficiency η of semiconductor laser _s Is given by the following equation.
(Equation 6)

[0064]
Where J ₀ : Current required for generating gain, d: film thickness of active layer, α _i : Internal loss, L: resonator length, R _f : Reflectivity of front emission surface, R _r : Reflectance of the rear emission surface.
The operating current Iop at the time of high output is given by the following equation.
[0065]
(Equation 7)

[0066]
Generally, the operating current Iop is minimized at a certain reflectance Rf, and there is an optimum value for the reflectance Rf. In other words, the operating current Iop needs to be reduced for reasons such as extending the life of the element and providing an element that is easy to use with a low current.
[0067]
When the reflectance Rf is small, the slope efficiency η _s Becomes larger, but ln (1 / R _f R _r ) Is increased and the threshold current I _th And the operating current Iop increases. When the reflectance Rf is large, the slope efficiency η _s And the operating current Iop increases.
[0068]
Especially in the high temperature range, η _i And decrease of β, J ₀ , Α _i Threshold I _th Is remarkable, the value of Rf that minimizes Iop shifts to the higher reflectance side. The reflectivity of the front emission surface is optimally a few% empirically, though it differs depending on the material, structure, etc. constituting the semiconductor laser element.
[0069]
As in the first embodiment, in the semiconductor laser device 1 having an asymmetric coating in which the reflectance of the front emission surface is about 6 to 9% and the reflectance of the rear emission surface is 93%, Run-to-Run The variation in the reflectance was in the range of ± 5%, and the variation in the characteristics of the semiconductor laser device such as the slope efficiency and the threshold current was also suppressed.
[0070]
FIG. 7 is a graph showing the correlation between the reflectance and the thickness of the coating film due to the difference in the film configuration of the coating film covering the front emission surface of the semiconductor laser device. FIG. 8 is a graph showing the coating covering the front emission surface of the semiconductor laser device. 4 is a graph showing a correlation between a reflectance and a film thickness shift of a coating film due to a difference in a film configuration of the film.
[0071]
The graph of FIG. 7 shows that the end face reflection film on the front emission surface is made of SiO. ₂ A single-layer film (with a reflectivity of 7.5%), and a SiN film and SiO ₂ An example of a two-layer coating with a film is shown. In the case of a two-layer coating, the reflectance is 7.5%, 10%, and 20%. In the two-layer coating, the reflectance can be adjusted by changing the thickness ratio of each layer without changing the overall thickness. SiO ₂ In the case of a single-layer film, if the design is performed at 7.5%, the film thickness is indicated by □. In the case of a two-layer coat, the positions indicated by a circle in each curve are design values. FIG. 7 shows an example of how the reflectance changes when the film thickness is simply changed.
[0072]
Actually, the thicknesses of the two layers are displaced almost in proportion due to the in-plane variation, the film thickness being shifted due to the variation of the film forming rate, the change of the wavelength of the element, and the like. FIG. 8 shows a change in reflectance due to manufacturing variations. ₂ It is a graph which shows the thing of 7.5%, 10%, and 30% in a film single layer 7.5% and a two-layer coat. The change in the reflectance due to the deviation in the thickness of the coating film is reduced. That is, even if a film thickness variation of ± 10% occurs, as can be seen from FIG. 8, in the case of the present invention, the reflectance variation is only 1%.
[0073]
When the reflectance of the coating film 31 is, for example, about 6 to 9%, the ratio of the thickness d1 of the first layer 31a to the thickness d2 of the second layer 31b, d1 / d2, is 0.54 ≦ d1 / d2≤0.95 or 1.05≤d1 / d2≤1.86. As a result, it is possible to form a coating film having a stable reflectance by setting the reflectance of the coating film to a desired design value and suppressing a change in the reflectance due to manufacturing variations in the film thickness of the coating film. The first layer 31a having a high film thickness ratio may be thick or thin. The thickness ratio is determined by the refractive index of the material forming the first layer 31a or the second layer 31b.
[0074]
For example, when the first layer 31a is a dielectric film having a refractive index of 2.4 and the second layer 31b is a dielectric film having a refractive index of 1.43, the thickness ratio of both films is selected. Thereby, the reflectance of the coating film 31 can be set to any one of numerical values of 1 to 30%. This makes it possible to form a coating film in which the range of reflectance that can be designed is widened and the variation in reflectance is small.
[0075]
Further, SiN in which the refractive index of the first layer 31a is 2.0 _X SiO 2, which is a film and has a refractive index of the second layer 31 b of 1.43. ₂ In the case of a film, the reflectance of the coating film 31 can be set to any one of numerical values of 5 to 30% by selecting the thickness ratio of the two films.
[0076]
The coating films 31a and 31b include SiO ₂ , TiO ₂ Oxide film such as SiN _X The first layer 31a has a refractive index nd1 of 1.6 ≦ nd1 ≦ 2.4, and the second layer 31b has a refractive index nd2 of 1.2 ≦ nd2 ≦ 2.0. The material of the coating film may be selected so as to have a relationship, and the material may be selected such that the refractive index of the first layer 31a is larger than the refractive index of the second layer 31b, that is, nd1 ≧ nd2.
[0077]
FIG. 10 is a graph showing the correlation between the front emission surface reflectance Rf and the wavelength λp of the semiconductor laser device of the first embodiment (the device of the present invention) and the conventional device. In the case of the conventional device, the reflectance greatly fluctuates due to a change in the film thickness in the wavelength range of 600 to 700 nm, and the reflectance decreases in a high-temperature region. However, in the case of the device of the present invention, the wavelength ranges from 600 to 700 nm. The reflectivity is a small variation between around 7.5 and 8.8%.
[0078]
FIG. 11 is a graph showing the correlation between the light output and the current in the semiconductor laser device of the first embodiment (the device of the present invention) and the conventional device. In the case of the conventional element, the light output is about 50 mW at the maximum when used at a high temperature of 70 ° C., whereas in the case of the element of the present invention, the light output is 90 mW or more even when used at a high temperature of 70 ° C. And an extremely high value can be obtained. According to the present invention, the threshold current is reduced, the slope efficiency is improved, and the operating current can be greatly reduced. In addition, since the heat generation of the semiconductor laser element particularly in a high temperature range can be suppressed by reducing the operating current, the semiconductor laser element can be operated at a higher temperature than the conventional semiconductor laser element.
[0079]
Also, the width of the ridge stripe portion 5b of the p-cladding layer 5 is about 2.4 μm in the present invention, which is about half of the conventional semiconductor laser element of about 5 μm. The element resistance (series resistance) was about 5Ω in both cases, and a frequency bandwidth of 1 GHz or more was obtained.
[0080]
According to the first embodiment, the following effects can be obtained.
(1) Since a material having a large forbidden band width and a material transparent to laser light is used for the current confinement layer (n-current block layer 6), a real guide structure capable of reducing light loss inside the laser is obtained. As compared with a conventional device having a waveguide structure of a loss guide typified by a GaAs current block layer, characteristics can be improved such as lower threshold and higher efficiency. As a result, the light output can be increased.
[0081]
(2) In the semiconductor laser device 1 according to the present invention, the kink level is improved and a high light output is obtained. That is, in order to improve the kink level and obtain a high optical output, the width Ws of the ridge stripe portion 5b and the thickness h of the flat layer 5a in the p-cladding layer 5 are adjusted, and a higher-order mode in the laser is generated. What is necessary is just to design so that it may become a single mode waveguide (resonator) which cannot exist. When Ws is narrower than h or 0.17 (Ws-1), or when h is increased, the waveguide structure becomes a single mode. The semiconductor laser device 1 having good light output-current characteristics can be manufactured.
[0082]
(3) Since the coating film (end face reflection film) 31 provided on the front emission surface has a two-layer dielectric film structure and the thickness of the coating film 31 is ~ λ / 2, The rate Rf can be set to a stable point where the wavelength-dependent dRf / dλ becomes substantially zero. That is, the reflectance Rf of the front emission surface can be adjusted to an arbitrary value in the range of 1 to 30% by adjusting the thickness ratio of the two dielectric films (SiN _X When the film thickness is SiO ₂ If the film thickness is larger than _X As the thickness of the film increases, the reflectivity Rf increases. _X As the film becomes thicker, the reflectance Rf decreases. ) Since the stable point can be set irrespective of the design value of the reflectance, even if a process variation occurs, the deviation from the design value of the reflectance can be suppressed to substantially zero.
[0083]
(4) In the present invention, the thickness of the end face reflection film is set to about λ / 2 with respect to the oscillation wavelength in the high temperature range, so that the temperature is higher at room temperature or higher than the lower limit of the operating temperature range of the semiconductor laser device 1. The reflectivity of the end face reflection film can be designed to be large, the increase in operating current in a high temperature range can be suppressed, and the light output can be improved. That is, generally, the characteristics of the laser element fluctuate depending on the reflectance of the end face. When the reflectance of the front emission surface decreases, the threshold current increases although the efficiency increases, and the increase in the threshold current particularly in a high-temperature region becomes remarkable. For this reason, there is a possibility that the high-temperature characteristics of the semiconductor laser device are reduced, the slope efficiency is reduced in a high-temperature region, and the operating current is rapidly increased. However, the present invention can solve such a problem.
[0084]
(Embodiment 2)
FIG. 12 is a process sectional view showing a method for manufacturing a semiconductor laser device according to another embodiment (Embodiment 2) of the present invention. In the second embodiment, in the semiconductor laser device 1 of the first embodiment, a p-GaInP buffer layer 40 is provided between the ridge stripe portion 5b and the p-contact layer 7, and the p-contact layer 7 and the ridge stripe portion 5b are formed. This is an example in which the present invention is applied to a structure in which a stepwise band gap difference is reduced to reduce a potential barrier at a heterojunction interface and reduce series resistance.
[0085]
As shown in FIG. 12D, the semiconductor laser device 1 according to the second embodiment includes an n-AlGaInP layer 6a and an n-AlGaInP layer 6a provided on both sides of the ridge stripe portion 5b of the p-cladding layer 5. The p-GaInP buffer layer 40 is formed on the upper surface of the ridge stripe portion 5b. The p-contact layer 7 is formed of the p-GaInP buffer layer 40 and the n-GaAs. Although it differs from the semiconductor laser device 1 of the first embodiment by covering the upper surface of the layer 6b, the structure of each of the other parts is the same as that of the semiconductor laser device 1 of the first embodiment. By forming the n-current block layer 6 into a two-layer structure, a layer containing Al is not exposed on the crystal surface when the contact layer 7 is buried and grown, thereby suppressing the generation of crystal defects due to crystal oxidation. The current blocking effect is stabilized.
[0086]
Next, the manufacture of the semiconductor laser device 1 according to the second embodiment will be described with reference to FIGS. FIGS. 12A to 12D are views corresponding to FIGS. 3A to 3D illustrating the method for manufacturing the semiconductor laser device of the first embodiment. It is made of the same material as the device. FIG. 12 also shows only a single semiconductor laser element portion.
[0087]
As in the case of the first embodiment, as shown in FIG. 12A, an n-GaAs mother substrate (wafer) 2a having a thickness of about 350 to 450 μm is prepared.
Next, semiconductor crystals each having a predetermined composition are sequentially grown on the main surface of the wafer 2a by MOCVD, and the n-cladding layer 3, the active layer 4, the p-cladding layer 5, the p-GaInP buffer layer 40 and The n-GaAs cap layers 22 are formed so as to be sequentially stacked. The difference from the first embodiment is that a p-GaInP buffer layer 40 is provided between the p-cladding layer 5 and the n-GaAs cap layer 22. The p-GaInP buffer layer 40 has a thickness of 0.5 μm _0.5 In _0.5 Consists of P.
[0088]
Next, as shown in FIG. 12B, a stripe-shaped mask 23 is selectively formed on the upper surface of the n-GaAs cap layer 22 in order to form a ridge stripe portion as in the case of the first embodiment. Then, using the mask 23 as an etching mask, the p-cladding layer 5 is etched to a predetermined depth by ordinary dry etching to form the flat layer 5a and the ridge stripe portion 5b.
[0089]
Next, the surface of the p-cladding layer 5 is lightly etched with a chlorine-based etchant (Hcl aqueous solution) to remove the surface layer, and then the p-cladding layer 5 is etched as shown in FIG. An n-AlGaInP layer 6a and an n-GaAs layer 6b are sequentially formed on the removed portion to form an n-current block layer 6.
[0090]
Next, as shown in FIG. 12D, the mask 23 and the n-GaAs cap layer 22 are removed by ordinary etching. At this time, the p-GaInP buffer layer 40 on the upper surface of the ridge stripe portion 5b remains as it is. Next, as shown in FIG. 12D, a contact layer 7 made of p-GaAs with a thickness of about 3 μm is formed so as to cover the upper surfaces of the n-current block layer 6 and the ridge stripe portion 5b.
[0091]
Next, the n-electrode 8 and the p-electrode 9 are formed on the front and back surfaces of the wafer 2a in the same manner as in the first embodiment, and then the wafer 2a is cleaved in a strip shape. Then, an AR film or an HR film is formed on the cleaved surface. Thereafter, the strip is cut to a predetermined size to manufacture a large number of semiconductor laser devices 1 as shown in FIG.
[0092]
In the semiconductor laser device 1 of the second embodiment, a p-GaInP buffer layer 40 made of GaInP having a band gap between the ridge stripe portion 5b made of AlGaInP and a p-contact layer 7 made of GaAs is interposed. As a result, the potential barrier at the heterojunction portion is dispersed and a large gap is not generated, so that the series resistance can be reduced.
[0093]
(Embodiment 3)
FIG. 13 is a schematic cross-sectional view of a surface of a semiconductor laser device according to another embodiment (Embodiment 3) of the present invention orthogonal to the resonator. FIG. 14 is a partial view of a surface of the semiconductor laser device along the resonator direction. It is a typical sectional view.
[0094]
The semiconductor laser device 1 according to the third embodiment is the same as the semiconductor laser device 1 according to the first embodiment except that the n-current blocking layers 6 on both sides of the ridge stripe portion 5b are replaced with an n-GaAs layer 6d. is there. That is, the n-current blocking layer 6 is an n-GaAs layer 6d, and the first layer 31a (SiN _X Film) and the second layer 31b (SiO ₂ Even when the coating film 31 made of the film was formed, the operating current at 70 ° C. could be reduced by about 13 mA and the saturation light output could be improved by about 10 mW as compared with the conventional device. Also, in the semiconductor laser device 1 of the third embodiment, the variation in the reflectivity of the coating film 31 provided on the front emission surface can be reduced by half from ± 10% of the conventional device to ± 5%. As a result, the variation in the characteristics of the threshold current and the slope efficiency was able to be substantially reduced by half.
[0095]
Although the invention made by the inventor has been specifically described based on the embodiment, the present invention is not limited to the above embodiment, and various changes can be made without departing from the gist of the invention. Nor.
[0096]
【The invention's effect】
The effects obtained by the typical inventions among the inventions disclosed in the present application will be briefly described as follows.
(1) It is possible to provide a single-mode oscillating red semiconductor laser device capable of increasing light output.
(2) In the red semiconductor laser device, it is possible to improve the fluctuation of the reflectance caused by the manufacturing variation of the coating film (the end face reflection film).
(3) It is possible to provide a red semiconductor laser device capable of stably emitting a high-power laser beam even at a high temperature range.
(4) A red semiconductor laser device capable of improving slope efficiency and reducing operating current can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a plane orthogonal to a resonator of a semiconductor laser device according to an embodiment (Embodiment 1) of the present invention.
FIG. 2 is a schematic cross-sectional view of a surface of the semiconductor laser device along a cavity direction.
FIG. 3 is a process sectional view illustrating a method for manufacturing the semiconductor laser device.
FIG. 4 is a graph showing a dimensional condition of a p-type cladding layer for performing single mode oscillation in the semiconductor laser device, wherein a flat layer (p-cladding layer thickness h) constituting the p-type cladding layer and a ridge stripe; It is a graph which shows a correlation with a part width (stripe width Ws).
FIG. 5 is a schematic diagram of a semiconductor laser device in which each part of a p-type cladding layer used for calculating the dimensional conditions is given a dimensional symbol.
FIG. 6 is a schematic diagram of each cross section of the semiconductor laser device in which each part for calculating the dimensional condition appears so as to appear.
FIG. 7 is a graph showing the correlation between the reflectance and the thickness of the coating film depending on the difference in the film configuration of the coating film covering the front emission surface of the semiconductor laser device.
FIG. 8 is a graph showing a correlation between a reflectance and a film thickness deviation of the coating film due to a difference in a film configuration of a coating film covering a front emission surface of the semiconductor laser device.
FIG. 9 is a graph showing the correlation between the optical output Iop and the reflectance Rf of the semiconductor laser device at high and low temperatures.
FIG. 10 is a graph showing the correlation between the front emission surface reflectance Rf and the wavelength λp in the semiconductor laser device of the first embodiment (the device of the present invention) and the conventional device.
FIG. 11 is a graph showing the correlation between light output and current in the semiconductor laser device of the first embodiment (device of the present invention) and a conventional device.
FIG. 12 is a process sectional view illustrating a method for manufacturing a semiconductor laser device according to another embodiment (Embodiment 2) of the present invention.
FIG. 13 is a schematic sectional view of a plane orthogonal to a resonator of a semiconductor laser device according to another embodiment (Embodiment 3) of the present invention.
FIG. 14 is a schematic cross-sectional view of a part of a surface of the semiconductor laser device along a cavity direction.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser element, 2 ... n-GaAs substrate, 2a ... Wafer (GaAs mother substrate), 3 ... Cladding layer (n-cladding layer), 4 ... Active layer, 5 ... Cladding layer (p-cladding layer), 5a ... flat layer, 5b ... ridge stripe portion, 6 ... n-current block layer, 6a ... n-AlGaInP layer, 6b ... n-GaAs layer, 7 ... p-contact layer, 8 ... n electrode, 9 ... p electrode, 10 ... Resonator, 11 laser light, 12 front emission surface, 13 rear emission surface, 22 n-GaAs cap layer, 23 mask, 31 coating film, 31 a first layer, 31 b second layer, 33: Coating film, 40: p-GaInP buffer layer.

Claims (28)

A semiconductor substrate made of a first conductivity type semiconductor;
A first conductivity type cladding layer made of a first conductivity type semiconductor formed on an upper surface of the semiconductor substrate;
An active layer comprising a semiconductor layer formed on the cladding layer,
A second conductivity type clad layer formed of a second conductivity type semiconductor layer formed on the active layer and including a flat layer and a ridge stripe portion formed in a stripe shape on the flat layer;
A current blocking layer formed on the flat layer and including a first conductivity type semiconductor layer covering a side surface of the ridge stripe portion;
A contact layer made of a second conductivity type semiconductor layer covering an upper surface of the ridge stripe portion and the current block layer;
A semiconductor laser device that emits laser light from an end face of a resonator formed by the active layer portion corresponding to the ridge stripe portion,
When the thickness of the flat layer is h and the width of the ridge bottom of the ridge stripe portion is Ws, the relationship h ≧ 0.17 (Ws−1) is established. 2. The semiconductor laser device according to claim 1, wherein said Ws is 1.0 μm or more. 3. The semiconductor laser device according to claim 2, wherein the thickness h of the flat layer has a relationship of 0.1 μm ≦ h ≦ 0.35 μm. 4. 2. The semiconductor laser device according to claim 1, wherein when the series resistance of the ridge stripe portion is 10 Ω or less, the width of the narrowest portion of the ridge is 1.0 μm or more. 2. The semiconductor laser device according to claim 1, wherein the active layer has a multiple quantum well structure in which a plurality of quantum well structures each including a well layer and a pair of barrier layers sandwiching the well layer are stacked. The semiconductor substrate is formed of n-type GaAs;
The cladding layer and the active layer are formed of AlGaInP or GaInP,
The current block layer is formed of AlGaInP or AlInP,
2. The semiconductor laser device according to claim 1, wherein a laser beam having a wavelength of 620 to 700 nm is emitted from an end of said active layer corresponding to said ridge stripe portion. The width of the narrowest portion of the ridge is 1.0 μm or more and the width Ws is 1.0 μm or more when the series resistance of the ridge stripe portion is 10 Ω or less. Semiconductor laser device. 2. The semiconductor laser according to claim 1, wherein a buffer layer for reducing a potential barrier between the ridge stripe portion and the contact layer is provided between an upper surface of the ridge stripe portion and the contact layer. element. A semiconductor laser device comprising a coating film provided on at least one end of a cavity end face from which laser light is emitted,
The coating film is formed of a first layer formed on the resonator end face, and a second layer formed on the first layer,
A semiconductor laser device wherein the sum of the thickness d1 of the first layer and the thickness d2 of the second layer is 0.45 to 0.55 times the wavelength of laser light. 10. The semiconductor laser device according to claim 9, wherein the refractive index nd1 of the first layer is larger than the refractive index nd2 of the second layer. The first layer is a dielectric film having a refractive index of 1.6 ≦ nd1 ≦ 2.4,
The second layer is a dielectric film having a refractive index of 1.2 ≦ nd2 ≦ 2.0,
11. The semiconductor laser device according to claim 10, wherein a thickness ratio of the two films is selected, and a reflectance of the coating film is a reflectance of any one of 1 to 30%. . The first layer is a SiN _X film having a refractive index of 2.4,
The second layer is a SiO ₂ film having a refractive index of 1.43,
11. The semiconductor laser device according to claim 10, wherein the thickness ratio of the two films is selected, and the reflectance of the coating film is a reflectance of any one of 5% to 30%. . The first layer is a SiN _X film having a refractive index of 2.0,
The second layer is a SiO ₂ film having a refractive index of 1.43,
11. The semiconductor laser device according to claim 10, wherein the thickness ratio of the two films is selected, and the reflectance of the coating film is a reflectance of any one of 5% to 30%. . When the reflectance of the coating film is about 6 to 9%,
The film thickness ratio d1 / d2 is
0.54 ≦ d1 / d2 ≦ 0.95,
11. The semiconductor laser device according to claim 10, wherein a relationship of 1.05 ≦ d1 / d2 ≦ 1.86 is satisfied. A semiconductor substrate made of a first conductivity type semiconductor;
A first conductivity type cladding layer made of a first conductivity type semiconductor formed on an upper surface of the semiconductor substrate;
An active layer comprising a semiconductor layer formed on the cladding layer,
A second conductivity type clad layer formed of a second conductivity type semiconductor layer formed on the active layer and including a flat layer and a ridge stripe portion formed in a stripe shape on the flat layer;
A current blocking layer formed on the flat layer and including a first conductivity type semiconductor layer covering a side surface of the ridge stripe portion;
A contact layer made of a second conductivity type semiconductor layer covering an upper surface of the ridge stripe portion and the current block layer;
A semiconductor laser device comprising a resonator formed by the active layer portion corresponding to the ridge stripe portion, and a coating film provided on at least one end of the resonator end surface from which laser light is emitted,
When the thickness of the flat layer is h and the width of the bottom of the ridge of the ridge stripe portion is Ws, there is a relationship of h ≧ 0.17 (Ws−1).
The coating film is formed of a first layer formed on the resonator end face, and a second layer formed on the first layer,
A semiconductor laser device wherein the sum of the thickness d1 of the first layer and the thickness d2 of the second layer is 0.45 to 0.55 times the wavelength of laser light. 16. The semiconductor laser device according to claim 15, wherein said Ws is 1.0 μm or more. 17. The semiconductor laser device according to claim 16, wherein the thickness h of the flat layer has a relationship of 0.1 μm ≦ h ≦ 0.35 μm. 16. The semiconductor laser device according to claim 15, wherein when the series resistance of the ridge stripe portion is 10Ω or less, the width of the narrowest portion of the ridge is 1.0 μm or more. 16. The semiconductor laser device according to claim 15, wherein the refractive index nd1 of the first layer is larger than the refractive index nd2 of the second layer. The first layer is a dielectric film having a refractive index of 1.6 ≦ nd1 ≦ 2.4,
The second layer is a dielectric film having a refractive index of 1.2 ≦ nd2 ≦ 2.0,
20. The semiconductor laser device according to claim 19, wherein a thickness ratio of the two films is selected, and a reflectance of the coating film is a reflectance of any one of 1 to 30%. . The first layer is a dielectric film having a refractive index of 2.4,
The second layer is a dielectric film having a refractive index of 1.43,
20. The semiconductor laser device according to claim 19, wherein a thickness ratio of the two films is selected, and a reflectance of the coating film is a reflectance of any one of 1 to 30%. . The first layer is a SiN _X film having a refractive index of 2.0,
The second layer is a SiO ₂ film having a refractive index of 1.43,
20. The semiconductor laser device according to claim 19, wherein the thickness ratio of the two films is selected, and the reflectance of the coating film is a reflectance of any one of 5 to 30%. . When the reflectance of the coating film is about 6 to 9%,
The film thickness ratio d1 / d2 is
0.54 ≦ d1 / d2 ≦ 0.95,
20. The semiconductor laser device according to claim 19, wherein the relationship is 1.05≤d1 / d2≤1.86. 16. The semiconductor laser device according to claim 15, wherein the active layer has a multiple quantum well structure in which a plurality of quantum well structures each including a well layer and a pair of barrier layers sandwiching the well layer are stacked. The semiconductor substrate is formed of n-type GaAs;
The cladding layer and the active layer are formed of AlGaInP or GaInP,
The current blocking layer is formed of AlGaInP or AlInP;
16. The semiconductor laser device according to claim 15, wherein a laser beam having a wavelength of 620 to 700 nm is emitted from an end of said active layer corresponding to said ridge stripe portion. The semiconductor substrate is formed of n-type GaAs;
The cladding layer and the active layer are formed of AlGaInP or GaInP,
The current blocking layer is formed of GaAs;
16. The semiconductor laser device according to claim 15, wherein a laser beam having a wavelength of 620 to 700 nm is emitted from an end of said active layer corresponding to said ridge stripe portion. 16. The method according to claim 15, wherein when the series resistance of the ridge stripe portion is 10Ω or less, the width of the narrowest portion of the ridge is 1.0 μm or more, and the Ws is 1.0 μm or more. Semiconductor laser device. 16. The semiconductor laser according to claim 15, wherein a buffer layer for reducing a potential barrier between the ridge stripe portion and the contact layer is provided between an upper surface of the ridge stripe portion and the contact layer. element.

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