JP2004341092A - Electic field absorption type optical modulator, semiconductor integrated element with electic field absorption type optical modulator, module using them, and method for manufacturing semiconductor integrated element with electic field absorption type optical modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress holes and holing up of electrons and to provide a light source for transmission signal which has excellent chirping characteristics. <P>SOLUTION: An n-side GRIN-SCH (Grated Index-Separate Confinement Heterostructure) layer 4 is constructed with three layers, that is, a 1.0Q layer 4a with 20 nm thickness, a 1.1Q layer 4b with 20 nm thickness and a 1.2Q layer 4c with 20 nm thickness from the n-type InP substrate side. An MQW (Multiple Quantum Well) absorption layer 5 is constructed with eight layers of well layers 5A respectively with 10 nm thickness and barrier layers 5B respectively with 5 nm thickness. The first to fourth layers from the n-type InP substrate side of the barrier layers 5B are respectively constructed with 1.2Q layers with 5 nm thickness and the fifth to seventh layers are respectively constructed with InGaAlAs with 5 nm thickness corresponding to 1.15 μm bands. A p-side GRIN-SH layer 6 is constructed so as to make the composition continuously vary from a 1.15 μm band to InGaAlAs corresponding to a 1.0 μm band starting from the MQW absorption layer 5 to a p-type InP upper cladding layer 7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２２】
前記αパラメータは、光ファイバで光信号を伝送した後の波形の劣化（チャーピング）を引き起こす度合いを示し、αパラメータの劣化は伝送距離を妨げる原因になる。また、パイルアップは、高周波特性（Ｒａｄｉｏ ｆｒｅｑｕｅｎｃｙ特性；以下ＲＦ特性という）も劣化させる原因になる。
【００２３】
また、半導体レーザ素子とＥＡ変調器と集積させた半導体集積素子においては、該半導体レーザ素子の発振波長と該ＥＡ変調器の吸収端波長との波長差Δλ_Ｅ−Ｄ（ＥＡ変調器の吸収端波長−半導体レーザ素子の発振波長）を消光比や光出力といった静特性及びチャーピング特性の制御という理由から一定に保つ必要がある。しかしながら、実際にはＥＡ変調器の吸収層を形成する際に、その吸収端波長がねらいとずれてしまうことがあり、Δλ_Ｅ−Ｄを一定に保つことが難しかった。
【００２４】
本発明は上記に鑑みてなされたものであって、チャーピング特性が良好な送信用信号光源を提供することを目的とする。
【００２５】
【課題を解決するための手段】
上記目的を達成するために、請求項１にかかる電界吸収型光変調器は、第１の導電型の半導体基板上に、少なくとも下側分離光閉込め層（ＳＣＨ層）、吸収層、上側分離光閉込め層（ＳＣＨ層）及び前記第１の導電型とは逆の導電型である第２の導電型のクラッド層を含む積層体を有し、前記積層体の上方には第２の導電型の電極、前記半導体基板の前記積層体を形成した面と反対側の面には第１の導電型の電極を有する電界吸収型光変調器において、前記第１または第２の導電型はｐ型またはｎ型であって、ｐ側の分離光閉込め層（ＳＣＨ層）の一部をＩｎＧａＡｌＡｓ層で形成し、ｎ側の分離光閉込め層（ＳＣＨ層）の一部をＩｎＧａＡｓＰ層で形成することを特徴としている。
【００２６】
この電界吸収型光変調器によれば、少なくともｐ側のＳＣＨ層の一部をΔＥｖが小さくかつＩｎＰ半導体基板に格子整合するＩｎＧａＡｌＡｓ系材料で形成し、かつ少なくともｎ側のＳＣＨ層の一部をΔＥｃが小さくかつ半導体基板に格子整合するＩｎＧａＡｓＰ系材料で形成することによって、ホール及び電子の蓄積が起こりにくい、すなわちホールのパイルアップ及び電子のパイルアップが起こりにくい電界吸収型光変調器を提供することができる。
【００２７】
なお、上記効果は、ｐ側及びｎ側のＳＣＨ層の一部を上述した材料で構成することにより得ることができるが、好ましくはその全てを上述した材料で、すなわちｐ側のＳＣＨ層の全体をＩｎＧａＡｌＡｓ系材料で形成し、ｎ側のＳＣＨ層の全体をＩｎＧａＡｓＰ系材料で形成することが好ましい。
【００２８】
また、前記ｐ側及びｎ側ＳＣＨ層は、一種類の組成でも、組成が徐々に変化するＧＲＩＮ−ＳＣＨ（Ｇｒａｔｅｄ Ｉｎｄｅｘ Ｓｅｐａｒａｔｅ Ｃｏｎｆｉｎｅｍｅｎｔ Ｈｅｔｅｒｏｓｔｒｕｃｔｕｒｅ）層とすることもできる。ＧＲＩＮ−ＳＣＨ層において、組成は連続的に変化しても良いし、階段状に変化しても良い。ＧＲＩＮ−ＳＣＨ層を用いた場合には、上記効果に加え、高光入力時にホールのパイルアップが起こりにくいという効果を得ることができる。
【００２９】
また、請求項２にかかる電界吸収型光変調器は、第１の導電型の半導体基板上に、少なくとも吸収層及び前記第１の導電型とは逆の導電型である第２の導電型のクラッド層を含む積層体を有し、前記積層体の上方には第２の導電型の電極、前記半導体基板の前記積層体を形成した面と反対側の面には第１の導電型の電極を有する電界吸収型光変調器において、前記第１または第２の導電型はｐ型またはｎ型であって、かつ前記吸収層は２以上の障壁層を有し、少なくとも最もｐ側の障壁層をＩｎＧａＡｌＡｓ層で形成し、少なくとも最もｎ側の障壁層をＩｎＧａＡｓＰ層で形成することを特徴としている。
【００３０】
この電界吸収型光変調器によれば、少なくとも最もｐ側の障壁層をΔＥｖが小さくかつＩｎＰ半導体基板に格子整合またはＩｎＰと比較的近い格子定数を持つＩｎＧａＡｌＡｓ系材料で形成し、かつ少なくとも最もｎ側の障壁層をΔＥ_ｃが小さくかつ半導体基板に格子整合かつＩｎＰ半導体基板に格子整合またはＩｎＰと比較的近い格子定数を持つＩｎＧａＡｓＰ系材料で形成することによって、ホール及び電子の蓄積が起こりにくい、すなわちホールのパイルアップ及び電子のパイルアップが起こりにくい電界吸収型光変調器を提供することができる。
【００３１】
上記効果は、それぞれ最もｐ側もしくはｎ側の障壁層を上述した材料で構成することにより得ることができるが、好ましくは活性層中心からｐ側もしくはｎ側の全ての障壁層を上述した材料で、すなわち活性層中心からｐ側の全ての障壁層をＩｎＧａＡｌＡｓ系材料で形成し、活性層中心からｎ側の全ての障壁層をＩｎＧａＡｓＰ系材料で形成することが好ましい。なお、障壁層が奇数である場合には、中央の障壁層はＩｎＧａＡｌＡｓ層、ＩｎＧａＡｓＰ層のいずれでも良い。
【００３２】
また、請求項３にかかる電界吸収型光変調器は、上記発明において、前記吸収層は、量子井戸型吸収層であることを特徴としている。このようにすると電界吸収型光変調器は効果的に量子閉込め効果を利用することができる。
【００３３】
また、請求項４にかかる電界吸収型光変調器は、上記発明において、前記量子井戸型吸収層は多重量子井戸型吸収層であることを特徴としている。このようにすると、より大きな消光比を低電圧で得られるという効果を得ることができる。また、前記多重量子井戸吸収層最外層が障壁層となっていることが好ましく、また井戸数は６〜１０層程度とすることが好ましい。
【００３４】
また、請求項５にかかる電界吸収型光変調器モジュールは、上記発明にかかる電界吸収型光変調器と、光を入力端から前記電界吸収型光変調器に伝搬する入力側光ファイバと、変調後の光を前記電界吸収型光変調器から出力端に伝搬する出力側光ファイバと、前記電界吸収型光変調器の入力端面と前記入力側光ファイバ及び前記電界吸収型光変調器の出力端面と前記出力側光ファイバとを光結合するレンズとを備えたことを特徴としている。
【００３５】
この電界吸収型光変調器モジュールによれば、少なくともｐ側のＳＣＨ層の一部またはｐ側の障壁層をΔＥｖが小さくかつＩｎＰ半導体基板に格子整合またはＩｎＰと比較的近い格子定数を持つＩｎＧａＡｌＡｓ系材料で形成し、かつ少なくともｎ側のＳＣＨ層の一部またはｎ側の障壁層をΔＥｃが小さくかつ半導体基板に格子整合またはＩｎＰと比較的近い格子定数を持つＩｎＧａＡｓＰ系材料で形成することによって、ホール及び電子の蓄積が起こりにくい、すなわちホールのパイルアップ及び電子のパイルアップが起こりにくい電界吸収型光変調器を提供することができる。
【００３６】
また、請求項６にかかる電界吸収型光変調器モジュールは、上記発明において、電気信号の入力用高周波コネクタ有し、かつ該入力用高周波コネクタと前記電界吸収型光変調器とを電気的に接続する信号ラインをマイクロストリップラインで構成することを特徴としている。このようにすると、高周波信号を損失を少なくかつより効果的に伝播させることが可能になるという効果を得ることができる。
【００３７】
この電界吸収型光変調器モジュールによれば、少なくともｐ側のＳＣＨ層の一部またはｐ側の障壁層をΔＥｖが小さくかつＩｎＰ半導体基板に格子整合またはＩｎＰと比較的近い格子定数を持つＩｎＧａＡｌＡｓ系材料で形成し、かつ少なくともｎ側のＳＣＨ層の一部またはｎ側の障壁層をΔＥｃが小さくかつ半導体基板に格子整合またはＩｎＰと比較的近い格子定数を持つＩｎＧａＡｓＰ系材料で形成することによって、ホール及び電子の蓄積が起こりにくい、すなわちホールのパイルアップ及び電子のパイルアップが起こりにくい電界吸収型光変調器モジュールを提供することができる。
【００３８】
上記目的を達成するために、請求項７にかかる電界吸収型光変調器付き半導体集積素子は、請求項１乃至４に記載の電界吸収型光変調器と共通の基板を有するように少なくとも第１の導電型のクラッド層、活性層、前記第１の導電型とは逆の導電型である第２の導電型のクラッド層を含む積層体を有し、基板の前記積層体を形成したのと反対側の面には第１の導電型の電極、前記積層体の基板と反対側の面には第２の導電型の電極を有する半導体レーザ素子が形成されていることを特徴としている。
【００３９】
この電界吸収型光変調器付き半導体集積素子によれば、上記発明の電界吸収型光変調器を半導体レーザ素子と集積させることによって、ホール及び電子の蓄積が起こりにくい、すなわちホールのパイルアップ及び電子のパイルアップが起こりにくい電界吸収型光変調器付き半導体集積素子を提供することができる。
【００４０】
また、請求項８にかかる電界吸収型光変調器付き半導体集積素子は、上記発明において、前記半導体レーザ素子は、分布帰還型半導体レーザ素子または分布ブラッグ反射型半導体レーザ素子であることを特徴としている。このようにすると半導体レーザ素子からの発振波長を単一波長とすることができるので、送信用信号光源として好ましい。特に前記半導体レーザ素子を分布帰還型半導体レーザとすると、回折格子の設計により所望通りの発振波長を得ることができるのでより好ましい。
【００４１】
また、請求項９にかかる電界吸収型光変調器付き半導体集積素子モジュールは、請求項７または請求項８に記載の電界吸収型光変調器付き半導体集積素子と、前記電界吸収型光変調器付き半導体集積素子の電界吸収型光変調器の出力端面からの変調後の光を出力端に伝搬する出力側光ファイバと、前記出力端面と前記出力側光ファイバとを光結合するレンズとを備えたことを特徴としている。
【００４２】
この電界吸収型光変調器付き半導体集積素子モジュールによれば、少なくともｐ側のＳＣＨ層の一部またはｐ側の障壁層をΔＥｖが小さくかつＩｎＰ半導体基板に格子整合またはＩｎＰと比較的近い格子定数を持つＩｎＧａＡｌＡｓ系材料で形成し、かつ少なくともｎ側のＳＣＨ層の一部またはｎ側の障壁層をΔＥｃが小さくかつ半導体基板に格子整合またはＩｎＰと比較的近い格子定数を持つＩｎＧａＡｓＰ系材料で形成することによって、ホール及び電子の蓄積が起こりにくい、すなわちホールのパイルアップ及び電子のパイルアップが起こりにくい電界吸収型光変調器を提供することができる。
【００４３】
また、請求項１０にかかる電界吸収型光変調器付き半導体集積素子モジュールは、上記発明において、電気信号の入力用高周波コネクタ有し、かつ該入力用高周波コネクタと前記電界吸収型光変調器付き半導体集積素子とを電気的に接続する信号ラインをマイクロストリップラインで構成することを特徴としている。このようにすると、高周波信号を損失を少なく、かつより効果的に伝播できるという効果を得ることができる。
【００４４】
さらに、前述した目的を達成するために、請求項１１にかかる電界吸収型光変調器付き半導体集積素子の製造方法は、第１の導電型の半導体基板上に、少なくとも電界吸収型光変調器の吸収層を有する第１の積層体を形成した後、半導体レーザ素子の発振波長を決定する構造を有する第２の積層体を形成し、その後前記半導体基板の前記第１の積層体及び前記第２の積層体上方には第２の導電型の電極、前記半導体基板の前記第１の積層体及び第２の積層体形成面とは反対側の面には第１の導電型の電極、前記第３の積層体の上面には第２の導電型の電極を形成することを特徴としている。
【００４５】
この電界吸収型光変調器付き半導体集積素子の製造方法によれば、電界吸収型光変調器の吸収層を有する積層体を形成した後、半導体レーザ素子の発振波長を決定する構造を有する第２の積層体を形成するので、電界吸収型光変調器の吸収短波長と半導体レーザ素子の発振波長との差を容易に設定することができる。
【００４６】
また、請求項１２にかかる電界吸収型光変調器付き半導体集積素子の製造方法は、上記発明において、前記第２の積層体は少なくとも前記第１の積層体の吸収層を除去した部分に形成されることを特徴としている。
【００４７】
また、請求項１３にかかる電界吸収型光変調器付き半導体集積素子の製造方法は、上記発明において、前記除去は、前記第１の積層体の成長方向と略平行方向のエッチングと前記成長方向と略垂直方向のエッチングを組み合わせて行うことを特徴とする２段階エッチングであることを特徴としている。このようにすると成長方向と略垂直方向の深さ制御を独立にすることができる。また、成長方向のエッチングはドライエッチングを用いて行うことが好ましい。
【００４８】
また、請求項１４にかかる電界吸収型光変調器付き半導体集積素子の製造方法は、上記発明において、記前記第１の積層体の成長方向と略垂直方向のエッチングの後、前記吸収層は前記第１の積層体の成長方向と略平行方向のエッチングにより形成された側面から１５０〜５００ｎｍの深さの空隙を有することを特徴としている。なお、前記空隙は２００〜３００ｎｍであることがより好ましい。このようにすると再成長層の積層欠陥を低減、またはボイドの発生を抑制することができる。また、略平行方向のエッチングを用いて行うことが好ましい。
【００４９】
また、請求項１５にかかる電界吸収型光変調器付き半導体集積素子の製造方法は、上記発明において、前記半導体レーザ素子の発振波長を決定する構造は、活性層とは独立に設けられていることを特徴としている。
【００５０】
また、請求項１６にかかる電界吸収型光変調器付き半導体集積素子の製造方法は、上記発明において、前記半導体レーザ素子の発振波長を決定する構造は、回折格子であることを特徴としている。このようにすると半導体レーザ素子の塾方向の光分布を制御することができる。また、回折格子は屈折率型であることが好ましい。
【００５１】
また、請求項１７にかかる電界吸収型光変調器付き半導体集積素子の製造方法は、第１の導電型の半導体基板上に、少なくとも半導体レーザ素子の発振波長を決定する構造を形成するための層を形成し、次いで少なくとも電界吸収型光変調器の吸収層を形成した後、前記半導体素子の発振波長を決定する構造を形成するための層に半導体素子の発振波長を形成する構造を形成し、その後、第２の導電型の電極、前記半導体基板の前記第１の積層体及び第２の積層体形成面とは反対側の面には第１の導電型の電極、前記第３の積層体の上面には第２の導電型の電極を形成することを特徴としている。
【００５２】
また、請求項１８にかかる電界吸収型光変調器付き半導体集積素子の製造方法は、上記発明において、前記半導体レーザ素子の発振波長を決定する構造は、回折格子であることを特徴としている。。
【００５３】
また、請求項１９にかかる電界吸収型光変調器付き半導体集積素子の製造方法は、上記発明において、前記電界吸収型光変調器の吸収端波長を測定した後、前記半導体レーザ素子の発振波長を決定する構造を形成することを特徴としている。このようにするとＥＡ変調器の構造を形成した後にレーザの発振波長との差を容易に制御することができる。
【００５４】
また、請求項２０にかかる電界吸収型光変調器付き半導体集積素子の製造方法は、上記発明において、前記吸収端波長は１枚のウエハの中で所定の分布を持つように形成されていることを特徴としている。このようにすると一枚のウエハの中でそれぞれの半導体集積素子の発振波長域を広範囲とすることができる。また、前記吸収端波長のウエハ面内の分布はレーザ素子とＥＡ変調器の波長差を一定とするような分布とすることが好ましい。
【００５５】
【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１
図１は本実施形態例１の電界吸収型光変調器（ＥＡ変調器）１の構造を示す部分破断斜視図、図２は該ＥＡ変調器１の吸収層近傍の構造を示す模式図である。ＥＡ変調器１は、ｎ型ＩｎＰ基板２上に、ｎ型ＩｎＰ下部クラッド層３、ｎ側ＧＲＩＮ−ＳＣＨ層４、ＭＱＷ吸収層５、ｐ側ＧＲＩＮ−ＳＣＨ層６、ｐ型ＩｎＰ上部クラッド層７、及びｐ型ＩｎＧａＡｓコンタクト層８からなる積層構造を備えている。
【００５６】
ＥＡ変調器１の積層構造のうち、図１に示すように、ｐ型ＩｎＰ上部クラッド層７、ｐ側ＧＲＩＮ−ＳＣＨ層６、ＭＱＷ吸収層５、ｎ側ＧＲＩＮ−ＳＣＨ層４、ｎ型ＩｎＰ下部クラッド層３、及びｎ型ＩｎＰ基板２の上部は、メサとして形成されている。メサの両脇は、順次、成長させた、半絶縁性のＦｅドープＩｎＰ層１２、及びｎ型ＩｎＰ層１３で埋め込まれ、横方向の電流閉じ込め構造が形成されている。半絶縁性のＦｅドープＩｎＰ層１２を設けるのは、電子トラップ層として働かせると同時に、寄生容量を低減するためである。更に、容量低減のために、メサに沿って積層構造をエッチングして、トレンチ１４が形成されている。なお、図示の関係上、トレンチ１４はメサの片側だけに記載しているが、実際には両側に形成されている。メサ上及びｎ型ＩｎＰ層１３上には、ｐ型ＩｎＰ再成長クラッド層１５、及びｐ型ＩｎＧａＡｓコンタクト層８が順次積層され、更にｐ側電極９が設けてある。なお、ｎ型ＩｎＰ半導体基板２の前記積層構造形成面とは他方の面にはｎ側電極１０が設けてある。
【００５７】
次いで、図２を用いて本実施形態例１のＥＡ変調器１の吸収層近傍の構造について説明する。図２は、ｎ側ＧＲＩＮ−ＳＣＨ層４、ＭＱＷ吸収層５、ｐ側ＧＲＩＮ−ＳＣＨ層６についてのエネルギーバンドギャップ構造を模式的に示した図である。本実施形態例１において、ｎ側ＧＲＩＮ−ＳＣＨ層４は、図１に示したｎ型ＩｎＰ基板２側から順に厚さ２０ｎｍの１．０Ｑ層４ａ（１．０Ｑとは１．０μｍ相当のエネルギーバンドギャップ波長を有するＩｎＧａＡｓＰを示す。以下同様）、厚さ２０ｎｍの１．１Ｑ層４ｂ、厚さ２０ｎｍの１．２Ｑ層４ｃの３層で構成される。
【００５８】
また、ＭＱＷ吸収層５は、各々の厚さが１０ｎｍである８層の井戸層５Ａの各層の間に各々の厚さが５ｎｍである障壁層５Ｂで構成される。ここで、井戸層５Ａは、ＩｎＰに対して歪が０．５％程度の１．４９Ｑで構成される。また障壁層５Ｂは以下の構成を有する。すなわち、図１に示したｎ型ＩｎＰ基板２側から１〜４層は、厚さ５ｎｍの１．２Ｑ（屈折率３．３４、ＩｎＰに対する歪−０．１％）で構成され、５〜７層は、厚さ５ｎｍの１．１５μｍ帯相当のエネルギーバンドギャップ波長を有するＩｎＧａＡｌＡｓ（屈折率３．３４、ＩｎＰに対する歪−０．１％）で構成される。
【００５９】
また、ｐ側ＧＲＩＮ−ＳＣＨ層６は、前記ＭＱＷ吸収層５から図１に示したｐ型ＩｎＰ上部クラッド層７へ向かって、組成が１．１５μｍ帯から１．０μｍ帯相当のエネルギーバンドギャップ波長を有するＩｎＧａＡｌＡｓへと連続的に変化するように構成される。ｐ側ＧＲＩＮ−ＳＣＨ層６の膜厚は４５ｎｍである。ここで、ｐ側ＧＲＩＮ−ＳＣＨ層６の膜厚がｎ側ＧＲＩＮ−ＳＣＨ層４の総厚（６０ｎｍ）と異なるのは、ＦＦＰ（Ｆａｒ Ｆｉｅｌｄ Ｐａｔｔｅｒｎ）が前記ＭＱＷ吸収層５を中心に対称となるようにするためである。
【００６０】
本実施形態例１に記載したＥＡ変調器１に、別途作製したＤＦＢレーザ素子から波長１．５５μｍの光を入力して、特性の評価を行った。その結果を表１に示す。
【００６１】
【表１】

【００６２】
ここで、評価項目１はＥＡ変調器に加える電圧（Ｖ_ＥＡ）が０Ｖの時の光−電気の高周波特性（ＲＦ特性）であり、評価項目２は、ＥＡ変調器に加える電圧（Ｖ_ＥＡ）を０Ｖから０３Ｖまで変化させた場合のαパラメータ（α_ｐ）、評価項目３はαパラメータ（α_ｐ）が０の時のＥＡ変調器に加える電圧（Ｖ_ＥＡ）、評価項目４は分散特性が２０ｐｓ／ｎｍ／ｋｍであるシングルモードファイバ（ＳＭＦ；Ｓｉｎｇｌｅ Ｍｏｄｅ Ｆｉｂｅｒ）内を９．９５Ｇｂｐｓで８０ｋｍ伝送させた後のパワーペナルティである。
【００６３】
比較例１
実施形態例１に対する比較例１として、実施形態例１のｎ側ＧＲＩＮ−ＳＣＨ層４、障壁層５Ｂ及びｐ側ＧＲＩＮ−ＳＣＨ層６の組成をエネルギーバンドギャップ波長を変えずに全てＩｎＧａＡｓＰで形成した以外は実施形態例１と同様のＥＡ変調器を作製した。
【００６４】
比較例２
実施形態例１に対する比較例２として、実施形態例１のｎ側ＧＲＩＮ−ＳＣＨ層４、障壁層５Ｂ及びｐ側ＧＲＩＮ−ＳＣＨ層６の組成をエネルギーバンドギャップ波長を変えずに全てＩｎＧａＡｌＡｓで形成した以外は実施形態例１と同様のＥＡ変調器を作製した。
【００６５】
比較例１及び２について、実施形態例１と同様の項目について評価したところ、表２のようになった。表２に示した結果から比較例１及び比較例２に対する実施形態例１の優位性を確認することができた。
【００６６】
【表２】

【００６７】
なお、実施形態例１においては、全てのｎ側ＧＲＩＮ−ＳＣＨ層４及びｎ側の障壁層５Ｂ（１〜４層）をＩｎＧａＡｓＰで形成し、また全てのｐ型ＧＲＩＮ−ＳＣＨ層６とｐ側の障壁層５Ｂ（５〜７層）をＩｎＧａＡｌＡｓで形成したが、この実施形態例は本願発明の範囲を限定するものではない。したがって、ｎ側ＧＲＩＮ−ＳＣＨ層４の少なくとも一部をＩｎＧａＡｓＰで形成し、ｐ側ＧＲＩＮ−ＳＣＨ層６の少なくとも一部をＩｎＧａＡｌＡｓしたＥＡ変調器や最もｎ側の障壁層５Ｂ（１層）をＩｎＧａＡｓＰで形成し、また最もｐ側の障壁層５Ｂ（７層）をＩｎＧａＡｌＡｓで形成したＥＡ変調器も先に述べた効果を得ることができる。しかしながら、最も好ましいのは本実施形態例１のように全てのｎ側ＧＲＩＮ−ＳＣＨ層４及びｎ側の障壁層５Ｂ（１〜４層）をＩｎＧａＡｓＰで形成し、また全てのｐ型ＧＲＩＮ−ＳＣＨ層６とｐ側の障壁層５Ｂ（５〜７層）をＩｎＧａＡｌＡｓで形成したＥＡ変調器１である。
【００６８】
また、本実施形態例１ではｎ側ＧＲＩＮ−ＳＣＨ層４を階段構造、ｐ側ＧＲＩＮ−ＳＣＨ層６を連続変化構造としたが、両者は共に階段構造であっても良いし、連続変化構造であっても良い。さらに、ｎ型ＩｎＰ下部クラッド層３は必須ではなく、ｎ型ＩｎＰ基板２の厚さを厚くして実施的にｎ型ＩｎＰ基板２にｎ型ＩｎＰ下部クラッド層３の機能を持たせることによって省略することができる。
さらに、本実施形態例１においては、ｎ型ＩｎＰ基板にほぼ格子整合するＥＡ変調器を例にとって説明したが、各半導体層の導電型は逆であっても良い。また、ＧａＡｓ基板にほぼ格子整合するＥＡ変調器にも適用することができる。
【００６９】
実施形態例２
図３は本実施形態例２のＥＡ変調器モジュール１００の構造を示す模式図である。ＥＡ変調器モジュール１００はＥＡ変調器１０１と、光をＥＡ変調器モジュール１００の入力端から前記ＥＡ変調器１０１に伝搬する入力側光ファイバ１０２と、変調後の光を前記ＥＡ変調器１０１からＥＡ変調器モジュール１００の出力端に伝搬する出力側光ファイバ１０３と、前記ＥＡ変調器１０１の入力端面と前記入力側光ファイバ１０２とを光学的に結合するレンズ１０４ａ、１０４ｂ及び前記ＥＡ変調器１０１の出力端面と前記出力側光ファイバ１０３とを光学的に結合するレンズ１０５ａ、１０５ｂとを備えている。
【００７０】
また、本実施形態例２にかかるＥＡ変調器モジュール１００は１０ＧＨｚ以上という高周波用ＥＡ変調器モジュールであるため、電気信号の入力用高周波コネクタ１０６を有し、かつ該入力用高周波コネクタ１０６と前記ＥＡ変調器１０１とを電気的に接続する信号ラインは図示しないマイクロストリップラインで構成されている。なお、本実施形態例２で用いたＥＡ変調器モジュール１００の周波数は１０ＧＨｚである。また、ＥＡ変調器１０１は実施形態例１で用いたＥＡ変調器１と同じであるため、詳細な説明は省略する。
【００７１】
なお、ここでレンズ系としては、ＥＡ変調器１０１の入力端面と前記入力側光ファイバ１０２とを光学的に結合するレンズ１０４ａ、１０４ｂ及びＥＡ変調器１０１の出力端面と前記出力側光ファイバ１０３とを光学的に結合するレンズ１０５ａ、１０５ｂとも２レンズ系を用いたが、本願発明はこの実施形態には限定されず、例えば、光ファイバ１０２及び光ファイバ１０３のＥＡ変調器１０１側の端面をレンズ上に加工することによって、レンズドファイバとし、１レンズ系とすることもできる。なお、本実施形態例２を周波が２．５ＧＨｚ以下のような比較的低周波数用ＥＡ変調器モジュールに適用することもできる。低周波数用ＥＡ変調器モジュールの場合には、高周波コネクタ１０６に代えて通常のリード線を用いることができる。
【００７２】
実施形態例３
図４は本実施形態例３のＥＡ変調器付き半導体集積素子２０の構造を示す部分破断斜視図、図５は該ＥＡ変調器付き半導体集積素子２０の半導体レーザ素子、具体的にはＤＦＢレーザ２１の活性層近傍の構造を示す模式図である。なお、本実施形態例３のＥＡ変調器１’の構造は実施形態例１のＥＡ変調器１と同じであるため、対応する箇所に同じ符号を付し、詳細な説明は省略する。
【００７３】
実施形態例３では、前記ＥＡ変調器１’と集積させる半導体レーザ素子としてはＤＦＢレーザ２１を用いた。ＤＦＢレーザ２１は、前記ＥＡ変調器１’と共通のｎ型ＩｎＰ基板２２（２）上に、ｎ型ＩｎＰ下部クラッド層２３、ｎ側ＧＲＩＮ−ＳＣＨ層２４、ＭＱＷ活性層２５、ｐ側ＧＲＩＮ−ＳＣＨ層２６、ｐ型ＩｎＰ上部クラッド層２７、及びｐ型ＩｎＧａＡｓコンタクト層２８からなる積層構造を備えている。そして上部クラッド層２７中には、ＤＦＢレーザ２１の発振波長を決定する回折格子２７ａが形成されている。
【００７４】
ＤＦＢレーザ２１の積層構造のうち、図４に示すように、前記ｐ型ＩｎＰ上部クラッド層２７、ｐ側ＧＲＩＮ−ＳＣＨ層２６、ＭＱＷ活性層２５、ｎ側ＧＲＩＮ−ＳＣＨ層２４、ｎ型ＩｎＰ下部クラッド層２３、及びｎ型ＩｎＰ基板２２（２）の上部は、メサ３１として形成されている。メサ３１は半絶縁性のＦｅドープＩｎＰ層３２、及びｎ型ＩｎＰ層３３で埋め込まれ、横方向の電流閉じ込め構造が形成されている。また、容量低減のために、メサ３１に沿って積層構造をエッチングして、トレンチ３４が形成されている。なお、図示の関係上、トレンチ３４はメサ３１の片側だけに記載しているが、実際には両側に形成されている。
【００７５】
前記メサ３１上及びｎ型ＩｎＰ層３３上には、ＥＡ変調器１’と共通のｐ型ＩｎＰ再成長クラッド層３５（１５）、及びコンタクト層２８が順次積層され、更にｐ側電極２９を設けている。また、ｐ側電極２９とＥＡ変調器１’のｐ側電極９との間には、ＥＡ変調器１’とＤＦＢレーザ２１の電流制御を独立に行うために、再成長クラッド層３５（１５）の一部にまで達する分離溝３６が形成されている。そしてｎ型ＩｎＰ半導体基板２２（２）の前記積層構造形成面とは他方の面にはｎ側電極１０が設けてある。
【００７６】
なお、メサ３１はＤＦＢレーザ２１のメサ３１を構成する積層構造とＥＡ変調器１’のメサを構成する積層構造を形成した後、エッチングによりＥＡ変調器１’のメサと同時に形成することができる。また、トレンチ３４もＥＡ変調器１’のトレンチ１４と同時に形成することができる。
【００７７】
次いで、図５を用いて本実施形態例３のＤＦＢレーザ２１の活性層近傍の構造について説明する。図５は、図４におけるｎ側ＧＲＩＮ−ＳＣＨ層２４、ＭＱＷ活性層２５、ｐ側ＧＲＩＮ−ＳＣＨ層２６、回折格子２７ａを含むｐ型ＩｎＰ上部クラッド層２７についてのエネルギーバンドギャップ構造を模式的に示した図である（図５においては図示の関係上、符号２５は省略している）。本実施形態例３において、ｎ側ＧＲＩＮ−ＳＣＨ層２４は、図４に示したｎ型ＩｎＰ基板２２側から順に厚さ３０ｎｍの１．１０Ｑ層２４ａ、厚さ３０ｎｍの１．１５Ｑ層２４ｂ、厚さ１２ｎｍの１．２０Ｑ層２４ｃの３層で構成される。
【００７８】
また、ＭＱＷ活性層２５は、各々の厚さが４．５ｎｍである６層の井戸層２５Ａの各層の間に各々の厚さが１２ｎｍである障壁層２５Ｂで構成される。ここで、井戸層５Ａは１．５５Ｑで構成され、障壁層５Ｂは１．２０Ｑで構成される。また、ｐ側ＧＲＩＮ−ＳＣＨ層２６は、ｎ側ＧＲＩＮ−ＳＣＨ層２４とＭＱＷ活性層２５を挟んで対称に構成される。すなわち、前記ＭＱＷ活性層２５から図４に示したｐ型ＩｎＰ上部クラッド層２７へ向かって、順に厚さ１２ｎｍの１．２０Ｑ層２６ａ、厚さ３０ｎｍの１．１５Ｑ層２６ｂ、厚さ３０ｎｍの１．１０Ｑ層２６ｃの３層で構成されている。
【００７９】
また、回折格子２７ａは厚さ２０ｎｍの１．５Ｑで構成され、その回折格子パターンは、所望の発振波長λ_ｇと回折格子２７ａ部分の実効的屈折率ｎ_ｅｆｆ及び回折格子ピッチΛとの関係式λ_ｇ＝２ｎ_ｅｆｆΛを満足するように決定される。例えば、本実施形態例３においては、回折格子ピッチΛが２４２ｎｍ、そのデューティー比は３０％とした。また、回折格子２７ａと前記障壁層２６ｃとの距離は１８０ｎｍとした。
【００８０】
以上のように作製したＥＡ変調器付き半導体集積素子２０について、実施形態例１と同項目について評価をしたところ、実施形態例１と同様な値を得ることができた。また、実施形態例３では、ＥＡ変調器１’とＤＦＢレーザ２１を集積させたＥＡ変調器付き半導体集積素子２０としたので、実施形態例１に示すようにＥＡ変調器１とＤＦＢレーザ素子とを独立に設けた場合に比べて、同等の動特性を持ちながら変調時の平均光出力を大きく取るという効果を得ることができた。
【００８１】
なお、実施形態例３においても、実施形態例１と同様に全てのｎ側ＧＲＩＮ−ＳＣＨ層２４及びｎ側の障壁層２５Ｂ（１〜４層）をＩｎＧａＡｓＰで形成し、また全てのｐ型ＧＲＩＮ−ＳＣＨ層２６とｐ側の障壁層２５Ｂ（５〜７層）をＩｎＧａＡｌＡｓで形成する必要はない。しかしながら、最も好ましいのは本実施形態例３のように全てのｎ側ＧＲＩＮ−ＳＣＨ層２４及びｎ側の障壁層２５Ｂ（１〜４層）をＩｎＧａＡｓＰで形成し、また全てのｐ型ＧＲＩＮ−ＳＣＨ層２６とｐ側の障壁層２５Ｂ（５〜７層）をＩｎＧａＡｌＡｓで形成したＥＡ変調器１’である。
【００８２】
また、ｎ側ＧＲＩＮ−ＳＣＨ層２４及び側ＧＲＩＮ−ＳＣＨ層２６についても、実施形態例１と同様、両者は共に階段構造であっても良いし、連続変化構造であっても良い。また、ｎ型ＩｎＰ下部クラッド層２３は必須ではなく、ｎ型ＩｎＰ基板２２（２）の厚さを厚くして実施的にｎ型ＩｎＰ基板２２（２）にｎ型ＩｎＰ下部クラッド層２３の機能を持たせることによって省略することができる点も同様である。
さらに、本実施形態例３においては、ｎ型ＩｎＰ基板にほぼ格子整合するＥＡ変調器付き半導体集積素子２０を例にとって説明したが、各半導体層の導電型は逆であっても良い。また、ＧａＡｓ基板にほぼ格子整合するＥＡ変調器付き半導体集積素子にも適用することができる。
【００８３】
また、ＤＦＢレーザ２１の構造も実施形態例３の構造に限定されず、例えば、回折格子２７ａがＭＱＷ活性層２５よりもｎ型ＩｎＰ基板２２側にあっても良い。
さらに、ＤＦＢレーザ２１に代えて分布ブラッグ反射型半導体レーザ（Ｄｉｓｔｒｉｂｕｔｅｄ Ｂｒａｇｇ Ｒｅｆｌｅｃｔｏｒ Ｌａｓｅｒ；以下ＤＢＲレーザという）を用いることができる。ＤＢＲレーザを用いると波長可変性に優れたＥＡ変調器付き半導体集積素子を得ることができるが、高出力化という観点からすればＤＦＢレーザを用いることが好ましい。
【００８４】
なお、本実施形態例３のＥＡ変調器付き半導体集積素子２０は以下のように作製された。まず、ｎ型ＩｎＰ基板２２（２）の全面にＤＦＢレーザ２１の上部ＩｎＰクラッド層２７までの積層構造を通常行われている製造方法で形成した後、ＳｉＮ等の誘電体膜をマスクとして、ＤＦＢレーザ２１のＭＱＷ活性層２５を含むように前記積層構造を通常行われているエッチング方法により除去する。次いで、ＥＡ変調器１’ＩｎＰクラッド層７まで形成した後、ＤＦＢレーザ２１上のマスクを除去する。次いで、新たなＳｉＮ膜などの誘電体膜をマスクとして通常行われているエッチング方法により、１．５μｍ程度の幅のメサ１１（３１）を形成する。次いでメサ１１（３１）の側面を半絶縁性のＦｅドープＩｎＰ層１２（３２）及びｎ型ＩｎＰ層１３（３３）で埋め込み、横方向の電流閉じ込め構造が形成された。
【００８５】
また、容量低減のために、メサ１１（３１）に沿って積層構造をエッチングして、トレンチ１４（３４）を形成する。次いで前記メサ１１（３１）上及びｎ型ＩｎＰ層１３（３３）上には、ｐ型ＩｎＰ再成長クラッド層１５（３５）及びコンタクト層８（２８）が順次積層されたのち、ＥＡ変調器１’とＤＦＢレーザ２１への電流注入を独立に行うために、再成長クラッド１５（３５）の一部にまで達する分離溝３６が形成される。更にコンタクト層８上にｐ側電極９、コンタクト層２８上にｐ側電極２９を形成する。その後、ｎ型ＩｎＰ基板２（２２）の裏面を研磨した後、ｎ側電極１０を形成した。
【００８６】
なお、本願発明に係るＥＡ変調器付き半導体集積素子は実施形態例３に記載された製造方法に限定されず、例えば、選択成長 （ＳＡＧ；Ｓｅｌｅｃｔｉｖｅ Ａｒｅａ Ｇｒｏｗｔｈ） 方法によりＭＱＷ吸収層５及びＭＱＷ活性層２５を含む層を一工程で形成することもできる。
【００８７】
実施形態例４
図６は本実施形態例４のＥＡ変調器付き半導体集積素子モジュール１１０の構造を示す模式図である。ＥＡ変調器付き半導体集積素子モジュール１１０はＥＡ変調器付き半導体集積素子１１１と、変調後の光を前記ＥＡ変調器付き半導体集積素子１１１の出力端面（ＥＡ変調器側）からＥＡ変調器付き半導体集積素子モジュール１１０の出力端に伝搬する出力側光ファイバ１１３と、前記ＥＡ変調器付き半導体集積素子１１１の出力端面と前記出力側光ファイバ１１３とを光学的に結合するレンズ１１５ａ、１１５ｂとを備えている。
【００８８】
また、本実施形態例４にかかるＥＡ変調器付き半導体集積素子モジュール１１０は１０ＧＨｚ以上という高周波用ＥＡ変調器付き半導体集積素子モジュールであるため、電気信号の入力用高周波コネクタ１１６を有し、かつ該入力用高周波コネクタ１１６と前記ＥＡ変調器付き半導体集積素子１１１とを電気的に接続する信号ラインは図示しないマイクロストリップラインで構成されている。なお、本実施形態例４で用いたＥＡ変調器モジュール１１０の周波数は１０ＧＨｚである。また、ＥＡ変調器付き半導体集積素子１１１は実施形態例３で用いたＥＡ変調器付き半導体集積素子２０と同じであるため、詳細な説明は省略する。
【００８９】
なお、ここでレンズ系としては、ＥＡ変調器付き半導体集積素子１１１の出力端面と前記出力側光ファイバ１１３とを光学的に結合するレンズ１１５ａ、１１５ｂとして２レンズ系を用いたが、本願発明はこの実施形態には限定されず、例えば、光ファイバ１１３のＥＡ変調器付き半導体集積素子１１１側の端面をレンズ上に加工することによって、レンズドファイバとし、１レンズ系とすることもできる。また、高周波用ＥＡ変調器付き半導体集積素子モジュールとしない場合には、高周波コネクタ１１６は必要ない。なお、本実施形態例４を周波が２．５ＧＨｚ以下のような比較的低周波数用ＥＡ変調器モジュールに適用することもできる。低周波数要ＥＡ変調器モジュールの場合には、高周波コネクタ１１６に代えて通常のリード線を用いることができる。
【００９０】
実施形態例５
図７（ａ）〜（ｄ）、図８（ｅ）〜（ｈ）、図９（ｉ）〜（ｌ）は本実施形態例５のＥＡ変調器付き半導体集積素子の製造方法についての概略説明図である。なお、実施形態例５において製造するＥＡ変調器付き半導体集積素子２０’の構造は、ＥＡ変調器１’’のｐ側ＧＲＩＮ−ＳＣＨ層２６、障壁層及びｎ側ＧＲＩＮ−ＳＣＨ層２４をそれぞれＩｎＧａＡｓＰで形成したこと以外は実施形態例３のＥＡ変調器付き半導体集積素子２０と同じであるため、対応する箇所に同じ符号を付し、詳細な説明は省略する。
【００９１】
実施形態例５においては、まず図７（ａ）に示すように、ｎ型ＩｎＰ基板２の全面にＤＦＢレーザ２１を上部ＩｎＰクラッド層２７の一部までの積層構造を通常行われている製造方法で形成した後、図示しないＳｉＮ等の誘電体膜をマスクとして、ＥＡ変調器の形成領域Ａに形成されている前記積層構造のうち、ｎ型ＧＲＩＮ−ＳＣＨ２４迄を通常のエッチング法により除去した（図７（ｂ））。
【００９２】
次いで、ＥＡ変調器１’’を前記積層構造と同じ高さになるように上部ＩｎＰクラッド層７まで形成した（図７（ｃ））。ここで、ＥＡ変調器１’’の吸収端波長を測定した。
さらにＤＦＢレーザ２１上のマスクを除去し、回折格子形成層２７ａ’（厚さ２０ｎｍの１．５Ｑ層）をＤＦＢレーザ２１形成領域Ｂ及びＥＡ変調器１’’形成領域Ａに積層した（図７（ｄ））。ここで、ＤＦＢレーザ２１上に先に測定した吸収端波長と所望の波長差（実施形態例５においては６０ｎｍ）になるよう決定した回折格子パターンを電子描画装置で描画させ、次いで回折格子形成層２７ａ’にドライエッチングを施し回折格子２７ａを形成させた。なお、この際にＥＡ変調器１’’上に形成されていた回折格子形成層２７ａ’は除去され、回折格子２７ａを埋め込むように所定の高さまでｐ型ＩｎＰ再成長クラッド層３５（１５）を積層させて回折格子領域２７Ａを形成した（図８（ｅ））。なお、前記図８（ｅ）、及び以下に説明で用いる図８（ｆ）は概略図なので図示された回折格子２７ａのピッチとデューティー比は実際に形成されたものとは異なる。
【００９３】
その後、ｐ型ＩｎＰ再成長クラッド層３５（１５）上に図示しないＳｉＮ膜などの誘電体膜を施し、該誘電体膜をマスクとして通常行われているエッチング方法により、１．５μｍ程度の幅のメサ３１（１１）を形成した（図８（ｆ）。次いでメサ３１（１１）の側面を半絶縁性のＦｅドープＩｎＰ層３２（１２）及びｎ型ＩｎＰ層３３（１３）で埋め込み、横方向の電流閉じ込め構造を形成した（図８（ｇ））。
【００９４】
次いで、残りのｐ型ＩｎＰ再成長クラッド層３５（１５）及びコンタクト層２８（８）を順次積層した（図８（ｈ））のち、容量を低減させるためにメサに沿って積層構造をエッチングして、トレンチ３４（１４）を形成した（図９（ｉ））。また、ＥＡ変調器１’’とＤＦＢレーザ２１への電流注入を独立に行うために、再成長クラッド３５（１５）の一部にまで達する分離溝３６を形成した（図９（ｊ））。更にコンタクト層８上にｐ側電極９、コンタクト層２８上にｐ側電極２９を形成した後、ｎ型ＩｎＰ基板２（２２）の裏面を研磨した後、ｎ側電極１０を形成した（図９（ｋ））。また、トレンチ３４（１４）の表面にＳｉＮからなる誘電体膜３７を施した。
【００９５】
以上のように作製したＥＡ変調器付き半導体集積素子２０’について、実施形態例１及び２と同項目について評価をしたところ、実施形態例１及び２と同様な値を得ることができた。
【００９６】
なお、本実施形態例５では、回折格子形成層２７ａ’をＤＦＢレーザ２１形成領域及びＥＡ変調器１’’形成領域に積層したが、回折格子２７ａはＤＦＢレーザ２１上に形成されれば良いので、ＤＦＢレーザ２１形成領域のみに形成しても良い。
【００９７】
また、本実施形態例５ではＥＡ変調器１’’の吸収層を含む積層構造の除去を通常のエッチング法で行ったが、このエッチングは前記積層構造の成長方向と略平行方向に進むドライエッチングを施した後、前記成長方向と略垂直方向に進むウエットエッチングを施す２段階エッチング法を用いることもできる。このようにすると、前記ウエットエッチングによってそのエッチング側面から１５０〜５００ｎｍの深さの空隙を形成することができる。このような空隙を設けると、ドライエッチングの際にマストランスポート現象が発生し、ＩｎＰ溶け出すことが前記空隙に流入させることができるため、突き合わせ接合面を所望の形状に形成することができる。
【００９８】
【発明の効果】
以上に説明したように、本発明にかかる電界吸収型光変調器、電界吸収型光変調器付き半導体集積素子及び電界吸収型光変調器付き半導体集積素子によれば、チャーピング特性が良好でメトロ系に適した送信用信号光源を提供することができる。
【図面の簡単な説明】
【図１】図１は、本実施形態例１の電界吸収型光変調器（ＥＡ変調器）１の構造を示す部分破断斜視図である。
【図２】図２は、該ＥＡ変調器１の吸収層近傍の構造を示す模式図である。
【図３】図３は、本実施形態例２のＥＡ変調器モジュール１００の構造を示す模式図である。
【図４】図４は、本実施形態例３のＥＡ変調器付き半導体集積素子２０の構造を示す部分破断斜視図である。
【図５】図５は、実施形態例３のＥＡ変調器付き半導体集積素子２０のＤＦＢレーザ２１の活性層近傍の構造を示す模式図である。
【図６】図６は、本実施形態例４のＥＡ変調器付き半導体集積素子モジュール１１０の構造を示す模式図である。
【図７】図７（ａ）〜（ｄ）は、ＥＡ変調器付き半導体集積素子の製造方法についての第１の概略説明図である。
【図８】図８（ｅ）〜（ｈ）は、ＥＡ変調器付き半導体集積素子の製造方法についての第２の概略説明図である。
【図９】図９（ｉ）〜（ｍ）は、ＥＡ変調器付き半導体集積素子の製造方法についての第３の概略説明図である。
【図１０】図１０は、従来の光集積デバイスの構成を示す部分破断斜視図である。
【図１１】図１１は、図１０の線ＩＩ−ＩＩの断面図である。
【符号の説明】
１、１’、１’’ 電界吸収型光変調器（ＥＡ変調器）
２ ｎ型ＩｎＰ基板
３ ｎ型ＩｎＰ下部クラッド層
４ ｎ側ＧＲＩＮ−ＳＣＨ層
４ａ １．０Ｑ層
４ｂ １．１Ｑ層
４ｃ １．２Ｑ層
５ ＭＱＷ吸収層
５Ａ 井戸層
５Ｂ 障壁層
６ ｐ側ＧＲＩＮ−ＳＣＨ層
７ ｐ型ＩｎＰ上部クラッド層
８ ｐ型ＩｎＧａＡｓコンタクト層
９ ｐ側電極
１０ ｎ側電極１０
１１、３１ メサ
１２、３２ ＦｅドープＩｎＰ層
１３、３３ ｎ型ＩｎＰ層
１４、３４ トレンチ
１５、３５ ｐ型ＩｎＰ再成長クラッド層
２０、２０’ ＥＡ変調器付き半導体集積素子
２１ ＤＦＢレーザ
２２ ｎ型ＩｎＰ基板
２３ ｎ型ＩｎＰ下部クラッド層
２４ ｎ側ＧＲＩＮ−ＳＣＨ層
２４ａ １．１０Ｑ層
２４ｂ １．１５Ｑ層
２４ｃ １．２０Ｑ層
２５ ＭＱＷ活性層
２５Ａ 井戸層
２５Ｂ 障壁層
２６ ｐ側ＧＲＩＮ−ＳＣＨ層
２６ａ １．２０Ｑ層
２６ｂ １．１５Ｑ層
２６ｃ １．１０Ｑ層
２７ ｐ型ＩｎＰ上部クラッド層
２７ａ 回折格子
２７ａ’ 回折格子形成層
２７Ａ 回折格子領域
２８ ｐ型ＩｎＧａＡｓコンタクト層
２９ ｐ側電極
３６ 分離溝
３７ 誘電体膜
１００ 電界吸収型光変調器（ＥＡ変調器）モジュール
１０１ ＥＡ変調器
１０２ 入力側光ファイバ
１０３ 出力側光ファイバ
１０４ａ、１０４ｂ レンズ
１０５ａ、１０５ｂ レンズ
１０６ 高周波コネクタ
１１０ 電界吸収型光変調器（ＥＡ変調器）付き半導体集積素子モジュール
１１１ ＥＡ変調器付き半導体集積素子
１１３ 出力側光ファイバ
１１５ａ、１１５ｂ レンズ
１１６ 高周波コネクタ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electro-absorption modulator, a semiconductor integrated device with an electro-absorption optical modulator in which an electro-absorption optical modulator and a semiconductor laser are integrated.
[0002]
[Prior art]
With the demand for larger transmission capacity, a wavelength division multiplex (WDM) system in an optical fiber communication network has been introduced. A signal light source for transmission in a wavelength division multiplexing system includes a semiconductor laser device and a modulating unit that modulates light emitted from the semiconductor laser device. As the semiconductor laser element, it is preferable to be able to oscillate at a single wavelength from the application, and a distributed feedback semiconductor laser (hereinafter, referred to as a DFB laser) or the like is used. Further, as the modulating means, LiNbO₃There are an external modulator such as an LN modulator using a crystal and an electroabsorption modulator (hereinafter, referred to as an EA modulator) using a quantum confined Stark effect.
[0003]
The EA modulator is an optical modulator to which an electroabsorption effect generated by a change in an absorption coefficient due to an electric field is applied. An EA modulator having a quantum well layer in an absorption layer applies a reverse bias voltage to exciton (excitation). (Exciton) is an optical element capable of moving the absorption edge of the semiconductor laser element to a longer wavelength side (lower energy side) to absorb and extinguish light emitted from the semiconductor laser element. The extinction ratio varies depending on the configuration of the quantum well structure of the EA modulator, such as the thickness of the well layer and the number of well layers. Since the quantum well structure of the EA modulator and the quantum well structure of the semiconductor laser device are not necessarily the same, in order to maximize the characteristics of the optical integrated device, the quantum well structure of the semiconductor laser device and the EA modulator must be It is important that each of the well layers is formed with an optimum number of layers and film thickness.
[0004]
In recent years, the laying of the trunk line system has been completed, and a line system called a metro system having a transmission distance of several tens km to several hundred km has been developed. The transmission signal light source used in the metro system is not required to have such low chirp characteristics as used in the backbone system, but is required to be more inexpensive.
[0005]
In addition, a conventional laser device with an EA modulator (Electro Absorption Modulated Laser; hereinafter, referred to as EML) in which the EA modulator and the semiconductor laser device are integrated has an average output of 1 mW or less in an operating state. For example, an EML with an average output of 0.8 mW corresponds to -1 dBm. When transmission is performed using a normal single mode fiber of 40 km, the fiber loss is expected to be about 9 dB, so that the output at the receiving end is -10 dBm. Therefore, reception can be performed using a relatively inexpensive pin-PD having a minimum reception sensitivity of -14 dBm as a receiver.
[0006]
However, when an EML having the same average output as the above-mentioned EML is used as a light source and the transmission distance is 80 km, the fiber loss is 18 dB, which is twice as large as that when the transmission distance is 40 km. Is -19 dBm, and there is insufficient power to receive without using an amplifier in a pin-PD having a minimum receiving sensitivity of -14 dBm. If a high-performance light receiving element called an avalanche photodiode (hereinafter, referred to as APD) is used, it is possible to receive even with a power of about -19 dBm, but since the APD is effective, the system cost increases. Invite.
[0007]
Therefore, in order to reduce the system cost, it is also important to increase the output of the signal light source.
For example, when an EML having an average output of 2.5 mW (corresponding to 4 dBm) is used as a light source, the output at the receiving end becomes -14 dBm even if the fiber loss is 18 dB, and a relatively inexpensive pin-PD is used. Can be received. That is, it is not necessary to use an expensive light receiving element such as an APD. In other words,
If a high-output EML can be realized, the transmission distance can be extended while suppressing the cost, which can lead to a high added value.
[0008]
As a light source that satisfies such demands, there has been proposed a semiconductor integrated device with an electroabsorption type optical modulator (EML: Electro Absorbent Modulated Integrated Laser) in which an EA modulator and a semiconductor laser device are integrated (for example, Patent Document 1). 1).
[0009]
[Patent Document 1]
JP 2003-60285 A
[0010]
Here, with reference to FIG. 10 and FIG. 11, the configuration of the semiconductor integrated device 140 with the EA modulator in which the EA modulator and the semiconductor laser device, in particular, the DFB laser is combined and integrated by the butt joint method here will be described. FIG. 10 is a partially cutaway perspective view showing the configuration of the optical integrated device, and FIG. 11 is a sectional view taken along line II-II of FIG. 10, that is, a sectional view of the DFB laser. The optical integrated device 210 is an optical integrated device in which a DFB laser 214 and an EA modulator 216 are combined and integrated on a common n-type semiconductor substrate 212 as shown in FIG.
[0011]
The DFB laser 214 includes a lower cladding layer 218, a lower separation light confinement layer (hereinafter, referred to as an SCH layer) 220, a multiple quantum well (MQW) active layer 222, a diffraction grating 224, and an upper cladding. It has a laminated structure composed of a layer 226, a regrown cladding layer 227, and a contact layer 228. The EA modulator 216 has a laminated structure including a lower cladding layer 230, a lower SCH layer 232, an MQW absorption layer 234, an upper cladding layer 226 common to the DFB laser 214, and a contact layer 228. The DFB laser 214 and the EA modulator 216 include the p-side electrodes 235A and 235B on the contact layer 228 and the common n-side electrode 236 on the back surface of the n-type substrate 212, respectively.
[0012]
As shown in FIG. 11, of the stacked structure of the DFB laser 214, the upper clad layer 226, the diffraction grating 224, the upper SCH layer 222, the MQW active layer 220, the lower SCH layer 218, and the upper part of the n-type substrate 212 237. Both sides of the mesa 237 are sequentially buried with a semi-insulating Fe-doped InP layer 238 and an n-type InP layer 239 which are grown to form a lateral current confinement structure. The semi-insulating Fe-doped InP layer 238 is provided to function as an electron trapping layer and reduce parasitic capacitance. Further, the trench 240 is formed by etching the stacked structure along the mesa 237 to reduce the capacitance.
[0013]
In addition, as a method of manufacturing a semiconductor integrated device with an EA modulator, a part of a stacked structure of a DFB laser 214 including an MQW active layer 222 is formed on the entirety of an n-type semiconductor substrate 212, and then an EA other than the region of the DFB laser 214 is formed. Part of the stacked structure of the half-DFB laser 214 formed on the modulator 216 region is removed at least from the MQW active layer 222 to the n-type semiconductor substrate 212 side. Thereafter, a part of the stacked structure of the EA modulator 216 including the MQW absorption layer 234 is formed on the EA modulator 216 area, and then a common layer is formed on the DFB laser 214 area and the upper surface of the EA modulator 216 area. Has been proposed (for example, Patent Document 2).
[0014]
[Patent Document 2]
JP 2003-60284 A
[0015]
This manufacturing method is called a Butt-joint method, and has an advantage that the MQW absorption layer 234 of the EA modulator 216 and the MQW active layer 222 of the DFB laser 214 can be independently designed.
[0016]
As described above, the semiconductor integrated device with an EA modulator is obtained by monolithically integrating the EA modulator and a semiconductor laser device such as a DFB laser on the same substrate. The semiconductor laser device is driven by DC operation and oscillates laser light. The laser light enters the EA modulator and is absorbed by a change in the absorption coefficient due to the electric field effect of the quantum well of the EA modulator. Then, a high-frequency signal is superimposed on the EA modulator by voltage driving, and the laser light is modulated to obtain a high-speed signal.
[0017]
A WDM system includes a conventional wavelength band (1.53 to 1.56 μm) called a C band (C-band) and a wavelength band (1.57 to 1.57 μm) called a currently developed L band (L-band). 1.60 μm), but each of them is often constituted by a semiconductor laser device made of an InP-based material. The EA modulator integrated with the semiconductor laser device is formed on a common InP substrate with the semiconductor laser device. In this case, it is preferable that the EA modulator is a lattice matching system made of a semiconductor material lattice-matched to InP from the viewpoint of forming a semiconductor layer. Note that the absorption layer of the EA modulator includes a well layer and a barrier layer.
[0018]
As a material for forming the barrier layer of the EA modulator, there is an InGaAsP-based material. When the barrier layer is formed of an InGaAsP-based material, the EA modulator has an advantage that it can be easily selectively regrown by a butt junction method, but ΔEc (difference in conduction band lower energy) from the well layer is small, and ΔEc is small._v(Difference in valence band upper end energy) is large, so that there is a problem that holes easily accumulate, and as a result, pile-up of holes easily occurs.
[0019]
[Problems to be solved by the invention]
As a material for forming the barrier layer that solves the above problem, there is an InGaAlAs-based material. However, when the barrier layer is formed of an InGaAlAs-based material, ΔE_cIs large and ΔE_vHas the advantage that the accumulation of holes is less likely to occur, and as a result, the pile-up of the holes is less likely to occur. Further, since electrons with a small effective mass are strongly confined, there is an advantage that a large extinction ratio can be obtained. However, since Al is contained in the material, there is a problem that it is difficult to selectively regrow the electroabsorption optical modulator by butt-joining.
[0020]
Further, when the barrier layer is formed of InGaAlAs, the barrier against electrons increases depending on the composition, and the discharge time for electrons may increase. In this case, pile-up for holes does not occur, but pile-up for electrons sometimes occurs.
[0021]
Since these pile-ups cause a change in the refractive index, the α parameter (α) expressed by the following equation (1)_p) Gets worse. Here, λ is the wavelength of the light incident on the optical fiber, Δn is the change in the refractive index of the absorption layer of the electro-absorption optical modulator when a voltage is applied, Δα_absIs the change in the refractive index of the absorption layer of the electro-absorption optical modulator.
(Equation 1)

[0022]
The α parameter indicates the degree of causing waveform deterioration (chirping) after transmitting an optical signal through an optical fiber, and the deterioration of the α parameter may hinder the transmission distance. In addition, pile-up causes deterioration of high-frequency characteristics (Radio frequency characteristics; hereinafter, referred to as RF characteristics).
[0023]
In a semiconductor integrated device in which a semiconductor laser device and an EA modulator are integrated, a wavelength difference Δλ between the oscillation wavelength of the semiconductor laser device and the absorption edge wavelength of the EA modulator._ED(Absorption edge wavelength of the EA modulator-oscillation wavelength of the semiconductor laser element) needs to be kept constant for controlling static characteristics such as an extinction ratio and optical output and chirping characteristics. However, in practice, when the absorption layer of the EA modulator is formed, the absorption edge wavelength may be shifted if it is aimed._EDWas difficult to keep constant.
[0024]
The present invention has been made in view of the above, and an object of the present invention is to provide a transmission signal light source having good chirping characteristics.
[0025]
[Means for Solving the Problems]
In order to achieve the above object, an electro-absorption optical modulator according to claim 1 includes at least a lower separation light confinement layer (SCH layer), an absorption layer, and an upper separation light on a first conductivity type semiconductor substrate. A stacked body including a light confinement layer (SCH layer) and a cladding layer of a second conductivity type opposite to the first conductivity type, and a second conductive layer above the stacked body; An electro-absorption optical modulator having an electrode of a first conductivity type and an electrode of a first conductivity type on a surface of the semiconductor substrate opposite to the surface on which the laminate is formed, wherein the first or second conductivity type is p Type or n-type, a part of the p-side separated light confinement layer (SCH layer) is formed of an InGaAlAs layer, and a part of the n-side separated light confinement layer (SCH layer) is formed of an InGaAsP layer It is characterized by doing.
[0026]
According to this electroabsorption type optical modulator, at least a part of the p-side SCH layer is formed of an InGaAlAs-based material having a small ΔEv and lattice-matched to the InP semiconductor substrate, and at least a part of the n-side SCH layer is formed. Provided is an electroabsorption type optical modulator in which accumulation of holes and electrons hardly occurs, that is, hole pile-up and electron pile-up hardly occur by being formed of an InGaAsP-based material having a small ΔEc and lattice-matching to a semiconductor substrate. be able to.
[0027]
Note that the above effects can be obtained by configuring a part of the p-side and n-side SCH layers with the above-described materials. Is preferably formed from an InGaAlAs-based material, and the entire n-side SCH layer is formed from an InGaAsP-based material.
[0028]
Further, the p-side and n-side SCH layers may be a GRIN-SCH (Grated Index Separate Composition Heterostructure) layer whose composition gradually changes, even with one kind of composition. In the GRIN-SCH layer, the composition may change continuously or may change stepwise. In the case where the GRIN-SCH layer is used, in addition to the above-described effects, it is possible to obtain an effect that a pile-up of a hole hardly occurs at a high light input.
[0029]
Further, the electroabsorption type optical modulator according to claim 2 has at least an absorption layer and a second conductivity type which is a conductivity type opposite to the first conductivity type on the first conductivity type semiconductor substrate. A second conductive type electrode above the stacked body, and a first conductive type electrode on the surface of the semiconductor substrate opposite to the surface on which the stacked body is formed. Wherein the first or second conductivity type is p-type or n-type, and the absorption layer has two or more barrier layers, and at least the most p-side barrier layer. Is formed of an InGaAlAs layer, and at least the most n-side barrier layer is formed of an InGaAsP layer.
[0030]
According to this electro-absorption optical modulator, at least the p-side barrier layer is formed of an InGaAlAs-based material having a small ΔEv and a lattice constant to an InP semiconductor substrate or a lattice constant relatively close to InP, and at least the most n ΔE_cIs small, and lattice-matched to a semiconductor substrate and made of an InGaAsP-based material having a lattice match to an InP semiconductor substrate or a lattice constant relatively close to InP, so that holes and electrons hardly accumulate, that is, pile-up of holes and electrons It is possible to provide an electro-absorption optical modulator in which pile-up hardly occurs.
[0031]
The above effects can be obtained by configuring the most p-side or n-side barrier layers with the above-described materials, respectively. Preferably, all the p-side or n-side barrier layers from the center of the active layer are formed of the above-described materials. That is, it is preferable that all barrier layers on the p side from the center of the active layer be formed of InGaAlAs-based material, and all barrier layers on the n side from the center of the active layer be formed of InGaAsP-based material. If the number of barrier layers is odd, the central barrier layer may be either an InGaAlAs layer or an InGaAsP layer.
[0032]
The electroabsorption optical modulator according to claim 3 is characterized in that, in the above invention, the absorption layer is a quantum well absorption layer. By doing so, the electroabsorption optical modulator can effectively use the quantum confinement effect.
[0033]
The electroabsorption optical modulator according to claim 4 is characterized in that, in the above invention, the quantum well absorption layer is a multiple quantum well absorption layer. In this case, an effect that a larger extinction ratio can be obtained at a low voltage can be obtained. The outermost layer of the multiple quantum well absorption layer is preferably a barrier layer, and the number of wells is preferably about 6 to 10 layers.
[0034]
According to a fifth aspect of the present invention, there is provided an electro-absorption type optical modulator module comprising: an electro-absorption type optical modulator according to the present invention; an input side optical fiber for transmitting light from an input end to the electro-absorption type optical modulator; An output optical fiber that propagates the subsequent light from the electroabsorption optical modulator to an output end; an input end face of the electroabsorption optical modulator; an output end face of the input optical fiber and the electroabsorption optical modulator; And a lens for optically coupling the optical fiber with the output side optical fiber.
[0035]
According to this electroabsorption type optical modulator module, at least a part of the p-side SCH layer or the p-side barrier layer is made of an InGaAlAs-based material having a small ΔEv and a lattice constant to an InP semiconductor substrate or a lattice constant relatively close to InP. By forming at least a part of the n-side SCH layer or the n-side barrier layer from an InGaAsP-based material having a small ΔEc and a lattice constant to a semiconductor substrate or a lattice constant relatively close to InP, It is possible to provide an electro-absorption optical modulator in which accumulation of holes and electrons does not easily occur, that is, pile-up of holes and pile-up of electrons do not easily occur.
[0036]
According to a sixth aspect of the present invention, in the electroabsorption type optical modulator module according to the above invention, the high frequency connector for inputting an electric signal is provided, and the input high frequency connector is electrically connected to the electroabsorption type optical modulator. This is characterized in that the signal line to be formed is constituted by a microstrip line. By doing so, it is possible to obtain an effect that the high-frequency signal can be transmitted with less loss and more effectively.
[0037]
According to this electroabsorption type optical modulator module, at least a part of the p-side SCH layer or the p-side barrier layer is made of an InGaAlAs-based material having a small ΔEv and a lattice constant to an InP semiconductor substrate or a lattice constant relatively close to InP. By forming at least a part of the n-side SCH layer or the n-side barrier layer from an InGaAsP-based material having a small ΔEc and a lattice constant to a semiconductor substrate or a lattice constant relatively close to InP, It is possible to provide an electro-absorption optical modulator module in which accumulation of holes and electrons hardly occurs, that is, pile-up of holes and pile-up of electrons hardly occur.
[0038]
To achieve the above object, a semiconductor integrated device with an electroabsorption optical modulator according to claim 7 has at least a first substrate having a common substrate with the electroabsorption optical modulator according to claims 1 to 4. A cladding layer of the conductivity type, an active layer, a laminate including a cladding layer of the second conductivity type opposite to the first conductivity type, and the laminate of the substrate was formed. A semiconductor laser device having an electrode of the first conductivity type on an opposite surface and an electrode of a second conductivity type on an opposite surface to the substrate of the laminate is formed.
[0039]
According to the semiconductor integrated device with the electroabsorption type optical modulator, the accumulation of holes and electrons hardly occurs by integrating the electroabsorption type optical modulator of the present invention with the semiconductor laser device. It is possible to provide a semiconductor integrated device with an electro-absorption type optical modulator in which pile-up hardly occurs.
[0040]
The semiconductor integrated device with an electroabsorption optical modulator according to claim 8 is characterized in that, in the above invention, the semiconductor laser device is a distributed feedback semiconductor laser device or a distributed Bragg reflection semiconductor laser device. . In this case, the oscillation wavelength from the semiconductor laser device can be made a single wavelength, which is preferable as a signal light source for transmission. In particular, it is more preferable that the semiconductor laser element is a distributed feedback semiconductor laser because a desired oscillation wavelength can be obtained by designing a diffraction grating.
[0041]
According to a ninth aspect of the present invention, there is provided a semiconductor integrated device module with an electro-absorption type optical modulator according to claim 7 or 8, and the semiconductor integrated device with an electro-absorption type optical modulator according to the seventh or eighth aspect. An output-side optical fiber that propagates light after modulation from an output end face of the electro-absorption optical modulator of the semiconductor integrated device to an output end, and a lens that optically couples the output end face and the output-side optical fiber. It is characterized by:
[0042]
According to this semiconductor integrated device module with an electroabsorption type optical modulator, at least a part of the p-side SCH layer or the p-side barrier layer has a small ΔEv and a lattice constant to the InP semiconductor substrate or a lattice constant relatively close to InP. And at least a part of the n-side SCH layer or the n-side barrier layer is formed of an InGaAsP-based material having a small ΔEc and a lattice constant to a semiconductor substrate or a lattice constant relatively close to InP. By doing so, it is possible to provide an electro-absorption optical modulator in which the accumulation of holes and electrons does not easily occur, that is, the pile-up of holes and the pile-up of electrons do not easily occur.
[0043]
A semiconductor integrated device module with an electro-absorption type optical modulator according to claim 10, further comprising a high-frequency connector for inputting an electric signal, and the input high-frequency connector and the semiconductor with the electro-absorption type optical modulator. It is characterized in that a signal line for electrically connecting to an integrated element is constituted by a microstrip line. In this way, it is possible to obtain an effect that a high-frequency signal can be transmitted with less loss and more effectively.
[0044]
Furthermore, in order to achieve the above-mentioned object, a method of manufacturing a semiconductor integrated device with an electro-absorption type optical modulator according to claim 11 is a method for manufacturing a semiconductor integrated device with an electro-absorption type optical modulator on a first conductivity type semiconductor substrate. After forming the first laminate having the absorption layer, a second laminate having a structure for determining the oscillation wavelength of the semiconductor laser element is formed, and then the first laminate and the second laminate of the semiconductor substrate are formed. A second conductive type electrode above the stacked body, a first conductive type electrode on the surface of the semiconductor substrate opposite to the first stacked body and the second stacked body forming surface, The third stacked body is characterized in that an electrode of the second conductivity type is formed on the upper surface.
[0045]
According to the method of manufacturing a semiconductor integrated device with an electroabsorption optical modulator, a second structure having a structure for determining an oscillation wavelength of a semiconductor laser device after forming a laminate having an absorption layer of the electroabsorption optical modulator. Is formed, the difference between the short absorption wavelength of the electroabsorption optical modulator and the oscillation wavelength of the semiconductor laser device can be easily set.
[0046]
In the method for manufacturing a semiconductor integrated device with an electroabsorption type optical modulator according to claim 12, in the above invention, the second laminate is formed at least in a portion of the first laminate from which an absorption layer has been removed. It is characterized by that.
[0047]
Further, in the method of manufacturing a semiconductor integrated device with an electroabsorption type optical modulator according to claim 13, in the above invention, the removing is performed by etching in a direction substantially parallel to a growth direction of the first stacked body, and The two-stage etching is characterized by performing a combination of substantially vertical etching. In this way, the depth control in the growth direction and the direction substantially perpendicular to each other can be made independent. Further, the etching in the growth direction is preferably performed using dry etching.
[0048]
Further, in the method of manufacturing a semiconductor integrated device with an electroabsorption type optical modulator according to claim 14, in the above invention, after the etching in the direction substantially perpendicular to the growth direction of the first stacked body, the absorption layer is It is characterized by having a void having a depth of 150 to 500 nm from a side surface formed by etching in a direction substantially parallel to the growth direction of the first stacked body. The gap is more preferably 200 to 300 nm. This can reduce stacking faults in the regrown layer or suppress generation of voids. Further, it is preferable that the etching be performed using etching in a substantially parallel direction.
[0049]
In the method for manufacturing a semiconductor integrated device with an electro-absorption type optical modulator according to claim 15, in the above invention, the structure for determining the oscillation wavelength of the semiconductor laser device is provided independently of the active layer. It is characterized by.
[0050]
According to a sixteenth aspect of the present invention, in the method for manufacturing a semiconductor integrated device with an electro-absorption type optical modulator, the structure for determining the oscillation wavelength of the semiconductor laser device is a diffraction grating. This makes it possible to control the light distribution of the semiconductor laser element in the direction of the jig. Further, the diffraction grating is preferably of a refractive index type.
[0051]
A method of manufacturing a semiconductor integrated device with an electro-absorption type optical modulator according to claim 17, wherein a layer for forming at least a structure for determining an oscillation wavelength of the semiconductor laser device is formed on a semiconductor substrate of the first conductivity type. Is formed, and then at least after forming the absorption layer of the electroabsorption optical modulator, forming a structure for forming the oscillation wavelength of the semiconductor element in a layer for forming a structure for determining the oscillation wavelength of the semiconductor element, Then, a second conductive type electrode, a first conductive type electrode on the surface of the semiconductor substrate opposite to the first laminate and the second laminate formation surface, and the third laminate Is characterized in that an electrode of the second conductivity type is formed on the upper surface.
[0052]
Further, a method of manufacturing a semiconductor integrated device with an electroabsorption optical modulator according to claim 18 is characterized in that, in the above invention, the structure for determining the oscillation wavelength of the semiconductor laser device is a diffraction grating. .
[0053]
In the method for manufacturing a semiconductor integrated device with an electro-absorption optical modulator according to claim 19, the oscillation wavelength of the semiconductor laser device is changed after measuring the absorption edge wavelength of the electro-absorption optical modulator. It is characterized by forming a structure to be determined. This makes it possible to easily control the difference from the oscillation wavelength of the laser after the structure of the EA modulator is formed.
[0054]
According to a twentieth aspect of the present invention, in the method for manufacturing a semiconductor integrated device with an electro-absorption type optical modulator according to the above invention, the absorption edge wavelength is formed to have a predetermined distribution in one wafer. It is characterized by. This makes it possible to widen the oscillation wavelength range of each semiconductor integrated device in one wafer. Further, it is preferable that the distribution of the absorption edge wavelength in the wafer surface is such that the wavelength difference between the laser element and the EA modulator is constant.
[0055]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described specifically and in detail with reference to the accompanying drawings by way of example embodiments.
Embodiment 1
FIG. 1 is a partially cutaway perspective view showing the structure of an electro-absorption optical modulator (EA modulator) 1 according to a first embodiment of the present invention, and FIG. 2 is a schematic view showing the structure near the absorption layer of the EA modulator 1. . The EA modulator 1 includes an n-type InP lower cladding layer 3, an n-side GRIN-SCH layer 4, an MQW absorption layer 5, a p-side GRIN-SCH layer 6, and a p-type InP upper cladding layer 7 on an n-type InP substrate 2. , And a p-type InGaAs contact layer 8.
[0056]
1, the p-type InP upper cladding layer 7, the p-side GRIN-SCH layer 6, the MQW absorption layer 5, the n-side GRIN-SCH layer 4, and the n-type InP lower part of the stacked structure of the EA modulator 1. The upper portions of the cladding layer 3 and the n-type InP substrate 2 are formed as mesas. Both sides of the mesa are buried with a semi-insulating Fe-doped InP layer 12 and an n-type InP layer 13 which are successively grown to form a lateral current confinement structure. The semi-insulating Fe-doped InP layer 12 is provided to serve as an electron trapping layer and to reduce parasitic capacitance. Further, the trench 14 is formed by etching the laminated structure along the mesa to reduce the capacitance. Although the trench 14 is shown on only one side of the mesa for the sake of illustration, it is actually formed on both sides. On the mesa and the n-type InP layer 13, a p-type InP regrowth cladding layer 15 and a p-type InGaAs contact layer 8 are sequentially laminated, and a p-side electrode 9 is further provided. An n-side electrode 10 is provided on the other surface of the n-type InP semiconductor substrate 2 from the surface on which the laminated structure is formed.
[0057]
Next, the structure near the absorption layer of the EA modulator 1 of the first embodiment will be described with reference to FIG. FIG. 2 is a diagram schematically illustrating an energy band gap structure of the n-side GRIN-SCH layer 4, the MQW absorption layer 5, and the p-side GRIN-SCH layer 6. In the first embodiment, the n-side GRIN-SCH layer 4 is a 20 nm-thick 1.0Q layer 4a (1.0Q corresponds to an energy equivalent to 1.0 μm) from the n-type InP substrate 2 side shown in FIG. InGaAsP having a bandgap wavelength is shown. The same applies to the following.) A three-layered structure includes a 1.1Q layer 4b having a thickness of 20 nm and a 1.2Q layer 4c having a thickness of 20 nm.
[0058]
The MQW absorption layer 5 is composed of barrier layers 5B each having a thickness of 5 nm between each of eight well layers 5A each having a thickness of 10 nm. Here, the well layer 5A is made of 1.49Q having a strain of about 0.5% with respect to InP. The barrier layer 5B has the following configuration. That is, the first to fourth layers from the side of the n-type InP substrate 2 shown in FIG. 1 are made of 1.2 nm (refractive index 3.34, strain -0.1% with respect to InP) having a thickness of 5 nm, and The layer is made of InGaAlAs (refractive index 3.34, strain -0.1% with respect to InP) having a thickness of 5 nm and an energy band gap wavelength corresponding to the 1.15 μm band.
[0059]
Further, the p-side GRIN-SCH layer 6 has an energy band gap wavelength corresponding to the composition from 1.15 μm band to 1.0 μm band from the MQW absorption layer 5 to the p-type InP upper cladding layer 7 shown in FIG. It is configured to continuously change to InGaAlAs having The thickness of the p-side GRIN-SCH layer 6 is 45 nm. Here, the reason why the thickness of the p-side GRIN-SCH layer 6 is different from the total thickness (60 nm) of the n-side GRIN-SCH layer 4 is that the FFP (Far Field Pattern) is symmetric about the MQW absorption layer 5. That is to ensure.
[0060]
Light having a wavelength of 1.55 μm was input to the EA modulator 1 described in the first embodiment from a separately manufactured DFB laser element, and the characteristics were evaluated. Table 1 shows the results.
[0061]
[Table 1]

[0062]
Here, the evaluation item 1 is a voltage (V) applied to the EA modulator._EA) Is a high-frequency characteristic of light-electricity (RF characteristic) when 0 V is applied, and the evaluation item 2 is a voltage (V_EA) Is changed from 0 V to 03 V._p), Evaluation item 3 is an α parameter (α_p) Is 0, the voltage applied to the EA modulator (V_EAEvaluation item 4) is a power penalty after transmitting 80 km at 9.95 Gbps in a single mode fiber (SMF: Single Mode Fiber) having a dispersion characteristic of 20 ps / nm / km.
[0063]
Comparative Example 1
As Comparative Example 1 with respect to Embodiment 1, the compositions of n-side GRIN-SCH layer 4, barrier layer 5B and p-side GRIN-SCH layer 6 of Embodiment 1 were all formed of InGaAsP without changing the energy band gap wavelength. Except for this, an EA modulator similar to that of the first embodiment was manufactured.
[0064]
Comparative Example 2
As Comparative Example 2 with respect to Embodiment 1, the compositions of the n-side GRIN-SCH layer 4, the barrier layer 5B, and the p-side GRIN-SCH layer 6 of Embodiment 1 were all formed of InGaAlAs without changing the energy band gap wavelength. Except for this, an EA modulator similar to that of the first embodiment was manufactured.
[0065]
For Comparative Examples 1 and 2, the same items as in Embodiment 1 were evaluated, and the results are as shown in Table 2. From the results shown in Table 2, the superiority of the first embodiment over the first and second comparative examples could be confirmed.
[0066]
[Table 2]

[0067]
In the first embodiment, all the n-side GRIN-SCH layers 4 and the n-side barrier layers 5B (1 to 4 layers) are formed of InGaAsP, and all the p-type GRIN-SCH layers 6 and the p-side The barrier layer 5B (5 to 7 layers) is formed of InGaAlAs, but this embodiment does not limit the scope of the present invention. Therefore, an EA modulator in which at least a part of the n-side GRIN-SCH layer 4 is formed of InGaAsP and at least a part of the p-side GRIN-SCH layer 6 is InGaAlAs, or an n-side barrier layer 5B (one layer) is formed of InGaAsP. The EA modulator in which the barrier layer 5B (seven layers) closest to the p-side is formed of InGaAlAs can also obtain the effects described above. However, it is most preferable that all the n-side GRIN-SCH layers 4 and the n-side barrier layers 5B (1 to 4 layers) are formed of InGaAsP as in the first embodiment, and that all the p-type GRIN-SCHs are formed. This is an EA modulator 1 in which the layer 6 and the p-side barrier layer 5B (5 to 7 layers) are formed of InGaAlAs.
[0068]
In the first embodiment, the n-side GRIN-SCH layer 4 has a stepped structure and the p-side GRIN-SCH layer 6 has a continuous change structure. However, both may have a step change structure, or may have a continuous change structure. There may be. Further, the n-type InP lower cladding layer 3 is not essential, and is omitted by increasing the thickness of the n-type InP substrate 2 and making the n-type InP substrate 2 have the function of the n-type InP lower cladding layer 3 effectively. can do.
Further, in the first embodiment, an EA modulator that is substantially lattice-matched to an n-type InP substrate has been described as an example, but the conductivity types of the semiconductor layers may be reversed. Further, the present invention can also be applied to an EA modulator that is substantially lattice-matched to a GaAs substrate.
[0069]
Embodiment 2
FIG. 3 is a schematic diagram illustrating the structure of the EA modulator module 100 according to the second embodiment. The EA modulator module 100 includes an EA modulator 101, an input optical fiber 102 that propagates light from the input end of the EA modulator module 100 to the EA modulator 101, and transmits the modulated light from the EA modulator 101 to the EA modulator 101. The output optical fiber 103 propagating to the output end of the modulator module 100, the lenses 104a and 104b for optically coupling the input end face of the EA modulator 101 and the input optical fiber 102, and the EA modulator 101 Lenses 105a and 105b for optically coupling the output end face and the output side optical fiber 103 are provided.
[0070]
Further, since the EA modulator module 100 according to the second embodiment is an EA modulator module for high frequency of 10 GHz or more, it has a high frequency connector 106 for inputting an electric signal, and the input high frequency connector 106 and the EA A signal line for electrically connecting the modulator 101 is constituted by a microstrip line (not shown). The frequency of the EA modulator module 100 used in the second embodiment is 10 GHz. Further, the EA modulator 101 is the same as the EA modulator 1 used in the first embodiment, and thus a detailed description is omitted.
[0071]
Here, as the lens system, lenses 104a and 104b for optically coupling the input end face of the EA modulator 101 and the input side optical fiber 102 and the output end face of the EA modulator 101 and the output side optical fiber 103 are used. Both the lenses 105a and 105b that optically couple the two lenses use a two-lens system. However, the present invention is not limited to this embodiment. For example, the end faces of the optical fibers 102 and 103 on the EA modulator 101 side are lens-shaped. By processing the above, a lensed fiber can be formed, and a one-lens system can be formed. The second embodiment can also be applied to a relatively low frequency EA modulator module having a frequency of 2.5 GHz or less. In the case of the low frequency EA modulator module, a normal lead wire can be used instead of the high frequency connector 106.
[0072]
Embodiment 3
FIG. 4 is a partially cutaway perspective view showing the structure of the semiconductor integrated device 20 with an EA modulator according to the third embodiment. FIG. 5 is a semiconductor laser device of the semiconductor integrated device 20 with an EA modulator, specifically, a DFB laser 21. FIG. 3 is a schematic view showing a structure near an active layer of FIG. Since the structure of the EA modulator 1 'of the third embodiment is the same as that of the EA modulator 1 of the first embodiment, the corresponding portions are denoted by the same reference numerals and detailed description thereof will be omitted.
[0073]
In the third embodiment, the DFB laser 21 is used as a semiconductor laser device integrated with the EA modulator 1 '. The DFB laser 21 has an n-type InP lower cladding layer 23, an n-side GRIN-SCH layer 24, an MQW active layer 25, and a p-side GRIN-type on an n-type InP substrate 22 (2) common to the EA modulator 1 '. It has a stacked structure including the SCH layer 26, the p-type InP upper cladding layer 27, and the p-type InGaAs contact layer 28. In the upper cladding layer 27, a diffraction grating 27a for determining the oscillation wavelength of the DFB laser 21 is formed.
[0074]
4, the p-type InP upper cladding layer 27, the p-side GRIN-SCH layer 26, the MQW active layer 25, the n-side GRIN-SCH layer 24, and the n-type InP lower layer in the stacked structure of the DFB laser 21. The clad layer 23 and the upper portion of the n-type InP substrate 22 (2) are formed as mesas 31. The mesa 31 is embedded with a semi-insulating Fe-doped InP layer 32 and an n-type InP layer 33 to form a lateral current confinement structure. Further, in order to reduce the capacitance, a trench 34 is formed by etching the laminated structure along the mesa 31. Although the trench 34 is shown only on one side of the mesa 31 for illustration, it is actually formed on both sides.
[0075]
On the mesa 31 and the n-type InP layer 33, a p-type InP regrowth cladding layer 35 (15) common to the EA modulator 1 'and a contact layer 28 are sequentially laminated, and a p-side electrode 29 is further provided. ing. In addition, between the p-side electrode 29 and the p-side electrode 9 of the EA modulator 1 ', the regrown cladding layer 35 (15) is used to independently control the current of the EA modulator 1' and the DFB laser 21. Is formed to reach a part of. An n-side electrode 10 is provided on the other surface of the n-type InP semiconductor substrate 22 (2) from the surface on which the laminated structure is formed.
[0076]
Note that the mesa 31 can be formed simultaneously with the mesa of the EA modulator 1 'by etching after forming the laminated structure forming the mesa 31 of the DFB laser 21 and the laminated structure forming the mesa of the EA modulator 1'. . Also, the trench 34 can be formed simultaneously with the trench 14 of the EA modulator 1 '.
[0077]
Next, the structure near the active layer of the DFB laser 21 according to the third embodiment will be described with reference to FIG. FIG. 5 schematically shows the energy band gap structure of the p-type InP upper cladding layer 27 including the n-side GRIN-SCH layer 24, the MQW active layer 25, the p-side GRIN-SCH layer 26, and the diffraction grating 27a in FIG. FIG. 5 (in FIG. 5, reference numeral 25 is omitted for the sake of illustration). In the third embodiment, the n-side GRIN-SCH layer 24 includes a 1.10Q layer 24a having a thickness of 30 nm, a 1.15Q layer 24b having a thickness of 30 nm, and a thickness in the order from the n-type InP substrate 22 shown in FIG. It is composed of three layers of 1.20Q layer 24c having a thickness of 12 nm.
[0078]
The MQW active layer 25 is composed of barrier layers 25B each having a thickness of 12 nm between each of six well layers 25A each having a thickness of 4.5 nm. Here, the well layer 5A is made of 1.55Q, and the barrier layer 5B is made of 1.20Q. Further, the p-side GRIN-SCH layer 26 is configured symmetrically with the n-side GRIN-SCH layer 24 and the MQW active layer 25 interposed therebetween. That is, from the MQW active layer 25 to the p-type InP upper cladding layer 27 shown in FIG. 4, a 1.20Q layer 26a having a thickness of 12 nm, a 1.15Q layer 26b having a thickness of 30 nm, and a 1 . 10Q layer 26c.
[0079]
The diffraction grating 27a is made of 1.5Q having a thickness of 20 nm, and its diffraction grating pattern has a desired oscillation wavelength λ._gAnd the effective refractive index n of the diffraction grating 27a_effAnd relational expression λ with diffraction grating pitch Λ_g= 2n_effΛ is determined to satisfy Λ. For example, in the third embodiment, the diffraction grating pitch ２４ is 242 nm, and the duty ratio is 30%. The distance between the diffraction grating 27a and the barrier layer 26c was 180 nm.
[0080]
When the same items as in the first embodiment were evaluated for the semiconductor integrated device 20 with an EA modulator manufactured as described above, the same values as in the first embodiment could be obtained. In the third embodiment, the EA modulator 1 'and the DFB laser 21 are integrated to form the semiconductor integrated device 20 with the EA modulator. Therefore, as shown in the first embodiment, the EA modulator 1 and the DFB laser As compared with the case where is independently provided, it is possible to obtain an effect of increasing the average optical output during modulation while having the same dynamic characteristics.
[0081]
In the third embodiment, similarly to the first embodiment, all the n-side GRIN-SCH layers 24 and the n-side barrier layers 25B (1 to 4 layers) are formed of InGaAsP, and all the p-type GRINs are formed. It is not necessary to form the SCH layer 26 and the p-side barrier layer 25B (5 to 7 layers) with InGaAlAs. However, most preferably, all the n-side GRIN-SCH layers 24 and the n-side barrier layers 25B (1 to 4 layers) are formed of InGaAsP as in the third embodiment, and all the p-type GRIN-SCHs are formed. This is an EA modulator 1 'in which the layer 26 and the p-side barrier layer 25B (5 to 7 layers) are formed of InGaAlAs.
[0082]
Also, as for the n-side GRIN-SCH layer 24 and the side GRIN-SCH layer 26, as in the first embodiment, both may have a stepped structure or a continuously changing structure. Further, the n-type InP lower cladding layer 23 is not essential, and the function of the n-type InP lower cladding layer 23 is practically increased by increasing the thickness of the n-type InP substrate 22 (2). The same can be said of the fact that it can be omitted by providing.
Further, in the third embodiment, the semiconductor integrated device 20 with an EA modulator that is substantially lattice-matched to the n-type InP substrate has been described as an example, but the conductivity types of the respective semiconductor layers may be reversed. Further, the present invention can also be applied to a semiconductor integrated device with an EA modulator that is substantially lattice-matched to a GaAs substrate.
[0083]
The structure of the DFB laser 21 is not limited to the structure of the third embodiment. For example, the diffraction grating 27a may be closer to the n-type InP substrate 22 than the MQW active layer 25.
Further, instead of the DFB laser 21, a distributed Bragg reflector laser (hereinafter, referred to as a DBR laser) can be used. When a DBR laser is used, a semiconductor integrated device with an EA modulator having excellent wavelength tunability can be obtained. However, from the viewpoint of high output, a DFB laser is preferably used.
[0084]
The semiconductor integrated device 20 with an EA modulator according to the third embodiment was manufactured as follows. First, a laminated structure up to the upper InP clad layer 27 of the DFB laser 21 is formed on the entire surface of the n-type InP substrate 22 (2) by a commonly used manufacturing method, and then the DFB is formed using a dielectric film such as SiN as a mask. The laminated structure is removed by a commonly used etching method so as to include the MQW active layer 25 of the laser 21. Next, after forming up to the EA modulator 1'InP clad layer 7, the mask on the DFB laser 21 is removed. Next, a mesa 11 (31) having a width of about 1.5 μm is formed by an ordinary etching method using a new dielectric film such as a SiN film as a mask. Next, the side surfaces of the mesas 11 (31) were buried with a semi-insulating Fe-doped InP layer 12 (32) and an n-type InP layer 13 (33) to form a lateral current confinement structure.
[0085]
Further, in order to reduce the capacity, the stacked structure is etched along the mesa 11 (31) to form the trench 14 (34). Next, on the mesa 11 (31) and the n-type InP layer 13 (33), the p-type InP regrown cladding layer 15 (35) and the contact layer 8 (28) are sequentially laminated, and then the EA modulator 1 In order to independently perform the current injection into the DFB laser 21 and the ′, a separation groove 36 reaching a part of the regrown cladding 15 (35) is formed. Further, a p-side electrode 9 is formed on the contact layer 8 and a p-side electrode 29 is formed on the contact layer 28. Then, after polishing the back surface of the n-type InP substrate 2 (22), the n-side electrode 10 was formed.
[0086]
The semiconductor integrated device with an EA modulator according to the present invention is not limited to the manufacturing method described in the third embodiment. For example, the MQW absorption layer 5 and the MQW active layer are formed by a selective growth (SAG) method. The layer containing 25 can be formed in one step.
[0087]
Embodiment 4
FIG. 6 is a schematic diagram showing the structure of the semiconductor integrated device module with EA modulator 110 according to the fourth embodiment. The semiconductor integrated device module with an EA modulator 110 includes a semiconductor integrated device with an EA modulator 111, and light after modulation is output from the output end face (EA modulator side) of the semiconductor integrated device with an EA modulator 111. An output optical fiber 113 propagating to an output end of the element module 110, and lenses 115a and 115b for optically coupling the output end face of the semiconductor integrated device 111 with an EA modulator and the output optical fiber 113 are provided. I have.
[0088]
Since the semiconductor integrated device module with an EA modulator 110 according to the fourth embodiment is a semiconductor integrated device module with an EA modulator for high frequency of 10 GHz or more, it has a high frequency connector 116 for inputting an electric signal, and A signal line for electrically connecting the input high-frequency connector 116 and the EA modulator-attached semiconductor integrated device 111 is constituted by a microstrip line (not shown). The frequency of the EA modulator module 110 used in the fourth embodiment is 10 GHz. Further, the semiconductor integrated device with EA modulator 111 is the same as the semiconductor integrated device with EA modulator 20 used in the third embodiment, and a detailed description thereof will be omitted.
[0089]
Here, as the lens system, a two-lens system is used as the lenses 115a and 115b for optically coupling the output end face of the semiconductor integrated device with EA modulator 111 and the output-side optical fiber 113. The present invention is not limited to this embodiment. For example, by processing an end surface of the optical fiber 113 on the side of the semiconductor integrated device with an EA modulator 111 on a lens, a lensed fiber can be formed as a one-lens system. If the semiconductor integrated device module with the high frequency EA modulator is not used, the high frequency connector 116 is not required. The fourth embodiment can be applied to an EA modulator module for a relatively low frequency whose frequency is 2.5 GHz or less. In the case of the EA modulator module requiring a low frequency, a normal lead wire can be used instead of the high frequency connector 116.
[0090]
Embodiment 5
7 (a) to 7 (d), 8 (e) to 9 (h), and 9 (i) to 9 (l) schematically illustrate a method for manufacturing a semiconductor integrated device with an EA modulator according to the fifth embodiment. FIG. The structure of the semiconductor integrated device with an EA modulator 20 ′ manufactured in the fifth embodiment is such that the p-side GRIN-SCH layer 26, the barrier layer and the n-side GRIN-SCH layer 24 of the EA modulator 1 ″ are formed of InGaAsP. Since it is the same as the EA modulator-attached semiconductor integrated device 20 of Embodiment 3 except that it is formed as described above, the same reference numerals are given to the corresponding portions, and detailed description is omitted.
[0091]
In the fifth embodiment, first, as shown in FIG. 7A, a manufacturing method in which a DFB laser 21 is normally formed on the entire surface of an n-type InP substrate 2 to a part of the upper InP cladding layer 27 is usually performed. After that, using the dielectric film such as SiN (not shown) as a mask, the n-type GRIN-SCH 24 of the laminated structure formed in the formation region A of the EA modulator was removed by a normal etching method ( FIG. 7 (b)).
[0092]
Next, the EA modulator 1 '' was formed up to the upper InP cladding layer 7 so as to have the same height as the above-mentioned laminated structure (FIG. 7C). Here, the absorption edge wavelength of the EA modulator 1 '' was measured.
Further, the mask on the DFB laser 21 was removed, and the diffraction grating forming layer 27a '(1.5Q layer having a thickness of 20 nm) was laminated on the DFB laser 21 forming area B and the EA modulator 1' 'forming area A (FIG. 7). (D)). Here, a diffraction grating pattern determined so as to have a desired wavelength difference (60 nm in the fifth embodiment) with the previously measured absorption edge wavelength on the DFB laser 21 is drawn by an electronic drawing device. 27a 'was dry-etched to form a diffraction grating 27a. At this time, the diffraction grating forming layer 27a ′ formed on the EA modulator 1 ″ is removed, and the p-type InP regrown cladding layer 35 (15) is raised to a predetermined height so as to embed the diffraction grating 27a. The diffraction grating region 27A was formed by stacking (FIG. 8E). Since FIG. 8 (e) and FIG. 8 (f) used in the following description are schematic views, the pitch and duty ratio of the illustrated diffraction grating 27a are different from those actually formed.
[0093]
After that, a dielectric film such as a SiN film (not shown) is formed on the p-type InP regrown cladding layer 35 (15), and a width of about 1.5 μm is formed by an ordinary etching method using the dielectric film as a mask. A mesa 31 (11) was formed (FIG. 8 (f). Next, the side surfaces of the mesa 31 (11) were buried with a semi-insulating Fe-doped InP layer 32 (12) and an n-type InP layer 33 (13), (FIG. 8 (g)).
[0094]
Next, after the remaining p-type InP regrown cladding layer 35 (15) and contact layer 28 (8) were sequentially laminated (FIG. 8 (h)), the laminated structure was etched along the mesa to reduce the capacitance. Thus, a trench 34 (14) was formed (FIG. 9 (i)). Further, in order to independently inject current into the EA modulator 1 '' and the DFB laser 21, a separation groove 36 reaching a part of the regrown cladding 35 (15) was formed (FIG. 9 (j)). Further, after forming the p-side electrode 9 on the contact layer 8 and the p-side electrode 29 on the contact layer 28, the back surface of the n-type InP substrate 2 (22) was polished, and then the n-side electrode 10 was formed (FIG. 9). (K)). Further, a dielectric film 37 made of SiN was formed on the surface of the trench 34 (14).
[0095]
When the same items as those of the first and second embodiments were evaluated for the semiconductor integrated device with an EA modulator 20 'manufactured as described above, the same values as those of the first and second embodiments could be obtained.
[0096]
In the fifth embodiment, the diffraction grating forming layer 27 a ′ is stacked on the DFB laser 21 forming area and the EA modulator 1 ″ forming area, but the diffraction grating 27 a may be formed on the DFB laser 21. May be formed only in the region where the DFB laser 21 is formed.
[0097]
In the fifth embodiment, the removal of the laminated structure including the absorption layer of the EA modulator 1 ″ is performed by the ordinary etching method. However, this etching is dry etching that proceeds in a direction substantially parallel to the growth direction of the laminated structure. After that, a two-step etching method in which wet etching is performed in a direction substantially perpendicular to the growth direction may be used. By doing so, a gap having a depth of 150 to 500 nm can be formed from the side surface of the etching by the wet etching. When such a gap is provided, a mass transport phenomenon occurs at the time of dry etching, and the melted InP can flow into the gap, so that the butt joint surface can be formed in a desired shape.
[0098]
【The invention's effect】
As described above, according to the electro-absorption optical modulator, the semiconductor integrated device with the electro-absorption optical modulator, and the semiconductor integrated device with the electro-absorption optical modulator according to the present invention, the chirping characteristics are good and A signal light source for transmission suitable for the system can be provided.
[Brief description of the drawings]
FIG. 1 is a partially broken perspective view showing the structure of an electroabsorption optical modulator (EA modulator) 1 according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram showing a structure near an absorption layer of the EA modulator 1.
FIG. 3 is a schematic diagram illustrating a structure of an EA modulator module 100 according to Embodiment 2 of the present invention.
FIG. 4 is a partially cutaway perspective view showing the structure of a semiconductor integrated device with an EA modulator 20 according to a third embodiment;
FIG. 5 is a schematic diagram illustrating a structure near an active layer of a DFB laser of a semiconductor integrated device with an EA modulator according to a third embodiment;
FIG. 6 is a schematic diagram illustrating a structure of a semiconductor integrated device module with an EA modulator 110 according to a fourth embodiment;
FIGS. 7A to 7D are first schematic views illustrating a method for manufacturing a semiconductor integrated device with an EA modulator.
8 (e) to 8 (h) are second schematic views illustrating a method for manufacturing a semiconductor integrated device with an EA modulator.
FIGS. 9 (i) to 9 (m) are third schematic views illustrating a method for manufacturing a semiconductor integrated device with an EA modulator.
FIG. 10 is a partially broken perspective view showing a configuration of a conventional optical integrated device.
FIG. 11 is a sectional view taken along line II-II in FIG. 10;
[Explanation of symbols]
1, 1 ', 1 "Electroabsorption optical modulator (EA modulator)
2 n-type InP substrate
3 n-type InP lower cladding layer
4 n-side GRIN-SCH layer
4a 1.0Q layer
4b 1.1Q layer
4c 1.2Q layer
5 MQW absorption layer
5A well layer
5B Barrier layer
6 p-side GRIN-SCH layer
7 p-type InP upper cladding layer
8 p-type InGaAs contact layer
9 p-side electrode
10 n-side electrode 10
11, 31 Mesa
12, 32 Fe-doped InP layer
13,33 n-type InP layer
14, 34 trench
15, 35 p-type InP regrown cladding layer
20, 20 'Semiconductor integrated device with EA modulator
21 DFB laser
22 n-type InP substrate
23 n-type InP lower cladding layer
24 n-side GRIN-SCH layer
24a 1.10Q layer
24b 1.15Q layer
24c 1.20Q layer
25 MQW active layer
25A well layer
25B Barrier layer
26 p-side GRIN-SCH layer
26a 1.20Q layer
26b 1.15Q layer
26c 1.10Q layer
27 p-type InP upper cladding layer
27a Diffraction grating
27a 'Diffraction grating forming layer
27A diffraction grating area
28 p-type InGaAs contact layer
29 p-side electrode
36 Separation groove
37 Dielectric film
100 Electroabsorption type optical modulator (EA modulator) module
101 EA modulator
102 Input side optical fiber
103 Output side optical fiber
104a, 104b lens
105a, 105b lens
106 High frequency connector
110 Semiconductor integrated device module with electroabsorption optical modulator (EA modulator)
Semiconductor integrated device with 111 EA modulator
113 Output side optical fiber
115a, 115b lens
116 High frequency connector

Claims (20)

On a semiconductor substrate of a first conductivity type, at least a lower separation light confinement layer, an absorption layer, an upper separation light confinement layer, and a second conductivity type opposite to the first conductivity type. A second conductive type electrode above the stacked body, and a first conductive type electrode on the surface of the semiconductor substrate opposite to the surface on which the stacked body is formed. Wherein the first or second conductivity type is p-type or n-type, and a part of the p-side separation light confinement layer is formed of an InGaAlAs layer; An electroabsorption optical modulator, wherein a part of the separated light confinement layer is formed of an InGaAsP layer. A stack including at least an absorption layer and a second conductivity type clad layer having a conductivity type opposite to the first conductivity type on a semiconductor substrate of the first conductivity type; An electroabsorption optical modulator having a second conductivity type electrode and a first conductivity type electrode on a surface of the semiconductor substrate opposite to the surface on which the stacked body is formed; 2 is p-type or n-type, and the absorption layer has two or more barrier layers, at least the most p-side barrier layer is formed of an InGaAlAs layer, and at least the most n-side barrier layer is An electro-absorption type optical modulator formed of an InGaAsP layer. The electroabsorption optical modulator according to claim 1, wherein the absorption layer is a quantum well absorption layer. The electro-absorption optical modulator according to claim 3, wherein the quantum well type absorption layer is a multiple quantum well type absorption layer. An electro-absorption optical modulator according to claim 1, an input-side optical fiber for transmitting light from an input end to the electro-absorption optical modulator, and a light after modulation from the electro-absorption optical modulator. An output side optical fiber propagating to an output end, a lens for optically coupling the input end face of the electroabsorption type optical modulator, the input side optical fiber and the output end face of the electroabsorption type optical modulator and the output side optical fiber, An electro-absorption optical modulator module comprising: 6. The signal line according to claim 5, comprising a high-frequency connector for inputting an electric signal, and a signal line for electrically connecting the high-frequency connector for input and the electro-absorption optical modulator is constituted by a microstrip line. Electroabsorption type optical modulator module. A cladding layer and an active layer of at least a first conductivity type having a common substrate with the electroabsorption optical modulator according to claim 1, and a second conductivity type opposite to the first conductivity type. A second conductive type clad layer, a first conductive type electrode on a surface of the substrate opposite to the side on which the laminated body is formed, and a first conductive type electrode on a surface of the laminated body opposite to the substrate. Is a semiconductor integrated device with an electro-absorption type optical modulator, wherein a semiconductor laser device having a second conductivity type electrode is formed. The semiconductor integrated device with an electro-absorption optical modulator according to claim 7, wherein the semiconductor laser device is a distributed feedback semiconductor laser device or a distributed Bragg reflection semiconductor laser device. A semiconductor integrated device with an electro-absorption type optical modulator according to claim 7 or 8, and light after modulation from an output end face of the electro-absorption type optical modulator of the semiconductor integrated device with an electro-absorption type optical modulator. A semiconductor integrated device module with an electro-absorption optical modulator, comprising: an output-side optical fiber that propagates to an output end; and a lens that optically couples the output end face and the output-side optical fiber. A signal line for electrically connecting the high-frequency connector for inputting an electric signal to the semiconductor integrated device with an electro-absorption type optical modulator, wherein the signal line comprises a microstrip line. The semiconductor integrated device module with an electro-absorption type optical modulator according to claim 9. After forming a first laminate having at least an absorption layer of an electroabsorption optical modulator on a semiconductor substrate of a first conductivity type, a second laminate having a structure for determining an oscillation wavelength of a semiconductor laser device And then forming a second conductive type electrode above the first laminate and the second laminate of the semiconductor substrate, forming the first laminate and the second laminate of the semiconductor substrate. A semiconductor with an electro-absorption type optical modulator, wherein an electrode of the first conductivity type is formed on the surface opposite to the surface, and an electrode of the second conductivity type is formed on the upper surface of the third laminate. A method for manufacturing an integrated device. The method of manufacturing a semiconductor integrated device with an electro-absorption type optical modulator according to claim 11, wherein the second laminate is formed at least in a portion of the first laminate from which an absorption layer has been removed. The two-stage etching is characterized in that the removal is performed by combining etching in a direction substantially parallel to a growth direction of the first stacked body and etching in a direction substantially perpendicular to the growth direction. 13. The method for manufacturing a semiconductor integrated device with an electro-absorption optical modulator according to item 12. After etching in a direction substantially perpendicular to the growth direction of the first laminate, the absorbing layer has a depth of 150 to 500 nm from a side surface formed by etching in a direction substantially parallel to the growth direction of the first laminate. The method for manufacturing a semiconductor integrated device with an electro-absorption optical modulator according to claim 13, wherein the semiconductor integrated device has an air gap. The method of manufacturing a semiconductor integrated device with an electro-absorption optical modulator according to claim 11, wherein the structure for determining the oscillation wavelength of the semiconductor laser device is provided independently of the active layer. The method for manufacturing a semiconductor integrated device with an electro-absorption optical modulator according to claim 15, wherein the structure that determines the oscillation wavelength of the semiconductor laser device is a diffraction grating. After forming at least a layer for forming a structure for determining an oscillation wavelength of a semiconductor laser element on a semiconductor substrate of a first conductivity type, and then forming at least an absorption layer of an electroabsorption optical modulator, A structure for forming an oscillation wavelength of a semiconductor element is formed in a layer for forming a structure for determining an oscillation wavelength of the element, and then a second conductive type electrode, the first laminate of the semiconductor substrate, and a An electro-absorption type electrode, wherein an electrode of the first conductivity type is formed on the surface opposite to the surface on which the second laminate is formed, and an electrode of the second conductivity type is formed on the upper surface of the third laminate. A method for manufacturing a semiconductor integrated device with an optical modulator. 18. The method according to claim 17, wherein the structure for determining the oscillation wavelength of the semiconductor laser device is a diffraction grating. 19. The electroabsorption device according to claim 15, wherein a structure for determining an oscillation wavelength of the semiconductor laser device is formed after measuring an absorption edge wavelength of the electroabsorption optical modulator. Of manufacturing a semiconductor integrated device with a semiconductor light modulator. 20. The method according to claim 19, wherein the absorption edge wavelength is formed so as to have a predetermined distribution in one wafer.

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