JP2861166B2 - Strained quantum well semiconductor laser - Google Patents

Description

【発明の詳細な説明】 〔産業上の利用分野〕 Er⁺ドープファイバーアンプ及びNd:YAG固体レーザ等
の励起光源として最適な半導体レーザに関するものであ
る。The present invention relates to a semiconductor laser which is most suitable as an excitation light source such as an Er ⁺ -doped fiber amplifier and an Nd: YAG solid-state laser.

〔従来の技術〕[Conventional technology]

Er⁺ドープファイバーアンプは、光信号−電気信号の
変換を必要とせずに長距離の伝送が可能となるため、近
年、光通信システムの分野で注目を集めている。Er⁺ド
ープファイバーアンプ用の光源としては0.67μｍ帯,0.9
8μｍ帯,1.48μｍ帯等の波長域が考えられるが、中でも
0.98μｍ帯は他の波長帯に比べて増幅効率が高いために
最も有望視されている。Er ⁺ -doped fiber amplifiers have attracted attention in the field of optical communication systems in recent years, because they enable long-distance transmission without the need for optical signal-electrical signal conversion. 0.67μm band, 0.9 as a light source for Er ⁺ doped fiber amplifier
Wavelength ranges such as the 8 μm band and the 1.48 μm band are conceivable.
The 0.98 μm band is considered most promising because of its higher amplification efficiency than other wavelength bands.

0.98μｍ帯で発振する半導体レーザとしては、例え
ば、図４に示すようなInGaAs/GaAs歪量子井戸型半導体
レーザが報告されている（アイオーオーシイ1989ポスト
デエッドライン,IOOC1989Post deadline20PDB−11）。
この構造では、活性層15を構成するInGaAs量子井戸層は
ｎ−GaAs基板１と格子整合はとれていないが、井戸幅が
110Åと薄いためヘテロ界面からミスフィット転位が発
生することはなく、0.98μｍの良好な発振特性が得られ
る。水平横モードは、発光領域以外のｐ−Al_0.6Ga_0.4As
クラッド層16と活性層直上までエッチングで除去したリ
ッジ導波構造により制御される。ｐ−クラッド層16の屈
折率は空気よりも高いため、実効的に発光領域の屈折率
が高くなり、横モード制御が達成される。この構造にお
いて発振しきい値15mA,最大出力85mWと高出力発振特性
が得られている。As a semiconductor laser which oscillates in the 0.98 μm band, for example, an InGaAs / GaAs strained quantum well semiconductor laser as shown in FIG.
In this structure, the InGaAs quantum well layer constituting the active layer 15 is not lattice-matched with the n-GaAs substrate 1, but has a well width.
Since it is as thin as 110 °, misfit dislocation does not occur from the hetero interface, and good oscillation characteristics of 0.98 μm can be obtained. In the horizontal and lateral modes, p-Al _0.6 Ga _0.4 As
It is controlled by a ridge waveguide structure which is removed by etching just above the cladding layer 16 and the active layer. Since the refractive index of the p-cladding layer 16 is higher than that of air, the refractive index of the light emitting region is effectively increased, and the transverse mode control is achieved. In this structure, a high output oscillation characteristic with an oscillation threshold of 15 mA and a maximum output of 85 mW is obtained.

〔発明が解決しようとする課題〕[Problems to be solved by the invention]

しかしながら従来の技術ではリッジ導波構造であるた
めｐサイドアップでヒートシンクに融着しなければなら
ない。このため熱放射が低下し、高出力動作が熱飽和に
よって制限されてしまう。また発光領域の活性層にひず
みが導入されやすい構造となっているため、良好な信頼
性を確保しにくい。こうした高出力動作の制限，信頼性
の低下を解決することが本発明の課題である。However, in the prior art, the ridge waveguide structure has to be fused to the heat sink by p-side up. This reduces heat radiation and limits high power operation by thermal saturation. Further, since the active layer in the light emitting region has a structure in which strain is easily introduced, it is difficult to secure good reliability. It is an object of the present invention to solve such a limitation of high-output operation and a decrease in reliability.

〔課題を解決するための手段〕[Means for solving the problem]

本発明の歪量子井戸型半導体レーザは２つあり、その
１つは、第１導電型のGaAs基板上に、少なくとも第１導
電型のAlGaAsクラッド層,GaAs光ガイド層でIn_xGa_1-xAs
量子井戸層を挟んで成るSCH構造の活性層，メサ部を有
する第２導電型のAl_yGa_1-yAsクラッド層の積層構造を有
し、メサ部両脇の前記第２導電型のクラッド層上に、第
１導電型のIn_0.5Ga_0.5Pを積層した構造を有し、かつ、
ｙ＜0.38とすることで水平横モードが制御されることを
特徴とする構成になっている。Strained quantum well type semiconductor laser of the present invention there are two, one of which, on a first conductivity type GaAs substrate, at least a first conductivity type AlGaAs cladding layer, of GaAs optical guide layer an In _x Ga _1-x As
An active layer having a SCH structure having a quantum well layer interposed therebetween, a second conductive type Al _y Ga _1-y As clad layer having a mesa portion having a lamination structure having a mesa portion, and the second conductive type cladding on both sides of the mesa portion. Having a structure in which In _0.5 Ga _0.5 P of the first conductivity type is laminated on the layer, and
By setting y <0.38, the horizontal / lateral mode is controlled.

２つ目は、第１導電型のGaAs基板上に、少なくとも第
１導電型のAlGaAsクラッド層,GaAs光ガイド層で井戸幅L
₁のIn_xGa_1-xAs量子井戸層を挟んで成るSCH構造の活性
層，メサ部を有する第２導電型のAl_yGa_1-yAsクラッド層
の積層構造を有し、メサ部両脇の前記第２導電型のクラ
ッド層上に井戸幅L₂のIn_zGa_1-zAs井戸層とGaAs障壁層か
ら成る第１導電型の歪超格子埋め込み層を有し、かつ、
L₁＜L₂又はｘ＜ｚとすることで水平横モードが制御され
ることを特徴とする構成になっている。Secondly, at least a first conductivity type AlGaAs cladding layer and a GaAs light guide layer are formed on a first conductivity type GaAs substrate and have a well width L.
Active layer of the _first In _x Ga _1-x As SCH structure comprising sandwiching the quantum well layer has a laminated structure of a second conductivity type Al _y Ga _1-y As cladding layer having a mesa portion, mesa both A first conductivity type strained superlattice buried layer comprising an In _z Ga _1-z As well layer having a well width L ₂ and a GaAs barrier layer on the side of the second conductivity type cladding layer; and
The horizontal and horizontal modes are controlled by setting L ₁ <L ₂ or x <z.

〔作用〕[Action]

図１に示した本発明の第１の構造では、メサ部のｐ−
Al_0.3Ga_0.7Asクラッド層４の屈折率がメサ側部のｎ−In
_0.5Ga_0.5Asの埋め込み層６の値より大ききため、水平方
向に等価的な導波構造が形成され、水平横モードが安定
に制御される。図２に示した本発明の第２の構造では、
メサ側部のｎ−InGaAs/GaAs歪超格子埋め込み層９の量
子井戸層が発光部のIn_0.2Ga_0.8As量子井戸層12に比べて
バンドギャップが小さいか又は井戸幅が大きいため、埋
め込み層９は発振光に対して吸収損失をもつ。従ってメ
サ側部の等価的な屈折率が低下し、水平方向に導波構造
が形成され、水平横モードが安定に制御される。また、
図1,図２いずれの構造においてもｐ電極側は平坦になっ
ているためｐサイドダウンでヒートシンクに融着するこ
とが可能であり高出力時に熱飽和することがない。さら
にメサ側部が半導体層で埋め込まれているため発光部に
ひずみが加わることもなく良好な信頼性を確保すること
ができる。In the first structure of the present invention shown in FIG.
The refractive index of the Al _0.3 Ga _0.7 As cladding layer 4 is n-In on the mesa side.
_{Since it is} larger than the value of the buried layer 6 of _0.5 Ga _0.5 As, an equivalent waveguide structure is formed in the horizontal direction, and the horizontal transverse mode is stably controlled. In the second structure of the present invention shown in FIG.
Since the quantum well layer of the n-InGaAs / GaAs strained superlattice buried layer 9 on the mesa side has a smaller band gap or a larger well width than the In _0.2 Ga _0.8 As quantum well layer 12 of the light emitting section, the buried layer 9 Has an absorption loss for oscillating light. Therefore, the equivalent refractive index on the mesa side is reduced, a waveguide structure is formed in the horizontal direction, and the horizontal transverse mode is stably controlled. Also,
In each of the structures shown in FIGS. 1 and 2, since the p-electrode side is flat, it can be fused to a heat sink with the p-side down, and does not saturate at high output. Further, since the mesa side is buried in the semiconductor layer, good reliability can be ensured without strain being applied to the light emitting portion.

〔実施例〕〔Example〕

以下図面を用いて本発明に係る実施例を詳しく述べ
る。図１に本発明の第１の実施例を示す。まずMOVPE気
相成長法を用いてｎ−GaAs基板１上にｎ−Al_0.3Ga_0.7As
クラッド層2,InGaAs/GaAs−SCH構造の活性層3,p−Al_0.3
Ga_0.7Asクラッド層4,p−GaAsキャップ層５を順次積層す
る。InGaAs/GaAs−SCH構造３は、図３に示すように、井
戸幅110Åの２層のIn_0.2Ga_0.8As量子井戸層12と、層厚5
0ÅのGaAs障壁層11、及び層厚500ÅのGaAsガイド層13か
ら形成される。次に、SiO₂をマスクとしてリン酸系のウ
ェットエッチングを用いてｐ−クラッド層４中に幅５μ
ｍのメサを形成する。メサ側部のｐ−クラッド層厚は0.
3μｍとした。次にMOVPE気相成長法又はハイドライドVP
E法を用いてｎ−In_0.5Ga_0.5P埋め込み層６をメサ側部に
選択的に形成する。In_0.5Ga_0.5PはSiO₂マスクを用いて
良好な選択成長を得ることができる。さらに、ｎ−電極
7,p−電極８を形成して図１に示す本発明に係る一実施
例の構造が形成される。Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. First, n-Al _0.3 Ga _0.7 As is deposited on an n-GaAs substrate 1 by MOVPE vapor phase epitaxy.
Cladding layer 2, InGaAs / GaAs-SCH active layer 3, p-Al _0.3
A Ga _0.7 As cladding layer 4 and a p-GaAs cap layer 5 are sequentially laminated. As shown in FIG. 3, the InGaAs / GaAs-SCH structure 3 has two In _0.2 Ga _0.8 As quantum well layers 12 having a well width of 110 ° and a layer thickness of 5 mm.
A GaAs barrier layer 11 having a thickness of 0 ° and a GaAs guide layer 13 having a thickness of 500 ° are formed. Next, 5 μm width is formed in the p-cladding layer 4 using phosphoric acid-based wet etching using SiO ₂ as a mask.
m mesas are formed. The p-cladding layer thickness on the mesa side is 0.
It was 3 μm. Next, MOVPE vapor deposition or hydride VP
An n-In _0.5 Ga _0.5 P buried layer 6 is selectively formed on the mesa side by using the E method. In _0.5 Ga _0.5 P can obtain good selective growth using a SiO ₂ mask. Further, an n-electrode
The p-electrode 8 is formed to form the structure according to the embodiment of the present invention shown in FIG.

図２は本発明の別の実施例を示すレーザ構造図であ
る。MOVPE気相成長法を用いて図１と同様な積層構造と
メサを形成した後、再びMOVPE気相成長法を用いてｎ−I
nGaAs/GaAs歪超格子埋め込み層９とｎ−GaAs埋め込み層
10を順次形成する。歪超格子埋め込み層９は、層厚70Å
のIn_0.3Ga_0.7As層と層厚50ÅのGaAs層の20ペアからな
る。70ÅのIn_0.3Ga_0.7As層はミスフィット転位が発生す
る臨界層厚に比べて十分薄いため、転位のない良好な埋
め込み層を形成することができる。さらに歪超格子埋め
込み層のInGaAsのIn含有量は活性層３に比べ10％多いた
め歪超格子埋め込み層９は発振光に対して吸収損失を持
つ。最後にｎ−電極7,p−電極８を形成して本発明に係
る別の実施例の構造が形成される。FIG. 2 is a laser structure diagram showing another embodiment of the present invention. After forming the same layered structure and mesa as in FIG. 1 using MOVPE vapor phase epitaxy, n-I is again formed using MOVPE vapor phase epitaxy.
nGaAs / GaAs strained superlattice buried layer 9 and n-GaAs buried layer
10 are sequentially formed. The strained superlattice buried layer 9 has a thickness of 70 mm.
20 pairs of an In _0.3 Ga _0.7 As layer and a GaAs layer having a thickness of 50 °. Since the 70 ° In _0.3 Ga _0.7 As layer is sufficiently thinner than the critical layer thickness at which misfit dislocations occur, a good buried layer without dislocations can be formed. Further, since the In content of InGaAs in the strained superlattice buried layer is 10% higher than that of the active layer 3, the strained superlattice buried layer 9 has an absorption loss for oscillation light. Finally, an n-electrode 7 and a p-electrode 8 are formed to form the structure of another embodiment according to the present invention.

〔発明の効果〕〔The invention's effect〕

以上、本発明の構造によれば通常の気相成長技術を用
いて高出力で高信頼な0.98μｍ帯歪量子井戸型半導体レ
ーザを形成することができる。As described above, according to the structure of the present invention, a 0.98 μm-band strained quantum well semiconductor laser with high output and high reliability can be formed by using the ordinary vapor growth technique.

また本発明の実施例では、ｎ型基板を用いた場合を示
したがｐ型基板を用いても全く同様の構造を形成するこ
とができる。Further, in the embodiments of the present invention, the case where the n-type substrate is used is shown, but the same structure can be formed even when the p-type substrate is used.

【図面の簡単な説明】 図1,図２は本発明の実施例を示す構造断面図、図３は本
発明の半導体レーザの活性層近傍におけるエネルギーバ
ンド構造を示す図、図４は従来技術の構造断面図をそれ
ぞれ示す。 図において、１…ｎ−GaAs基板、２…ｎ−Al_0.3Ga_0.7As
クラッド層、３…InGaAs/GaAs−SCH構造活性層、４…ｐ
−Al_0.3Ga_0.7Asクラッド層、５…ｐ−GaAsキャップ層、
６…ｎ−In_0.5Ga_0.5P埋め込み層、７…ｎ−電極、８…
ｐ−電極、９…ｎ−InGaAs/GaAs歪超格子埋め込み層、1
0…ｎ−GaAs埋め込み層、11…GaAs障壁層、12…In_0.2Ga
_0.8As量子井戸層、13…GaAsガイド層、15…InGaAs/GaAs
−GRIN−SCH構造活性層、16…ｐ−Al_0.6Ga_0.4Asクラッ
ド層をそれぞれ示す。BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are sectional views showing a structure of an embodiment of the present invention, FIG. 3 is a diagram showing an energy band structure near an active layer of a semiconductor laser of the present invention, and FIG. The structural sectional views are shown respectively. In the figure, 1 ... n-GaAs substrate, 2 ... n-Al _0.3 Ga _0.7 As
Cladding layer, 3 ... InGaAs / GaAs-SCH structure active layer, 4 ... p
-Al _0.3 Ga _0.7 As cladding layer, 5 ... p-GaAs cap layer,
6 ... n-In _0.5 Ga _0.5 P buried layer, 7 ... n-electrode, 8 ...
p-electrode, 9 ... n-InGaAs / GaAs strained superlattice buried layer, 1
0 ... n-GaAs buried layer, 11 ... GaAs barrier layer, 12 ... In _0.2 Ga
_0.8 As quantum well layer, 13… GaAs guide layer, 15… InGaAs / GaAs
A -GRIN-SCH structure active layer and a 16... P-Al _0.6 Ga _0.4 As clad layer are shown.

───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 平４−80984（ＪＰ，Ａ) 特開 平４−132288（ＪＰ，Ａ) Ａｐｐｌ．Ｐｈｙｓ．Ｌｅｔｔ．55 ［14］（1989）ｐ．1378−1379 Ａｐｐｌ．Ｐｈｙｓ．Ｌｅｔｔ．49 ［24］（1986）ｐ．1659−1660 1991年（平成３年）春季第38回応物学 会予稿集 29ａ−Ｄ−５ ｐ．964 (58)調査した分野(Int.Cl.⁶，ＤＢ名) H01S 3/18──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-80984 (JP, A) JP-A-4-132288 (JP, A) Appl. Phys. Lett. 55 [14] (1989) p. 1378-1379 Appl. Phys. Lett. 49 [24] (1986) p. 1659-1660 Proceedings of the 38th Annual Meeting of the Japanese Society for Response Science, Spring 1991, 29a-D-5 p. 964 (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/18

Claims (2)

(57)【特許請求の範囲】(57) [Claims] 【請求項１】第１導電型のGaAs基板上に、少なくとも第
１導電型のAlGaAsクラッド層,GaAs光ガイド層でIn_xGa
_1-xAs量子井戸層を挟んだSCH構造の活性層，メサ部を有
する第２導電型のAl_yGa_1-yAsクラッド層の積層構造を有
し、前記メサ部両側の前記第２導電型のクラッド層上
に、第１導電型のIn_0.5Ga_0.5Pを積層した構造を有し、
かつ、ｙ＜0.38としたことを特徴とする歪量子井戸型半
導体レーザ。To 1. A first conductivity type GaAs substrate, at least a first conductivity type AlGaAs cladding layer, of GaAs optical guide layer an In _x Ga
_It has a stacked structure of an active layer of a SCH structure sandwiching a _1-x As quantum well layer and a second conductivity type Al _y Ga _1-y As clad layer having a mesa portion, and the second conductive layer on both sides of the mesa portion. Having a structure in which In _0.5 Ga _0.5 P of the first conductivity type is laminated on the cladding layer of the mold,
And a strained quantum well semiconductor laser characterized by y <0.38. 【請求項２】第１導電型のGaAs基板上に、少なくとも第
１導電型のAlGaAsクラッド層,GaAs光ガイド層で井戸幅L
₁のIn_xGa_1-xAs量子井戸層を挟んだSCH構造の活性層，メ
サ部を有する第２導電型のAl_yGa_1-yAsクラッド層の積層
構造を有し、前記メサ部両側の前記第２の導電型のクラ
ッド層上に井戸幅L₂のIn_zGa_1-zAs井戸層とGaAs障壁層か
ら成る第１導電型の歪超格子埋め込み層を少くとも有
し、かつ、L₁＜L₂又はｘ＜ｚとしたことを特徴とする歪
量子井戸型半導体レーザ。2. The method according to claim 1, wherein the first conductive type GaAs substrate has at least a first conductive type AlGaAs cladding layer and a GaAs light guide layer having a well width L.
_{1 has} a stacked structure of an active layer having a SCH structure sandwiching an In _x Ga _1-x As quantum well layer and an Al _y Ga _1-y As clad layer of a second conductivity type having a mesa portion. Having at least a first conductivity type strained superlattice buried layer comprising an In _z Ga _{1 -z} As well layer having a well width L ₂ and a GaAs barrier layer on the second conductivity type cladding layer, and A strained quantum well semiconductor laser, wherein L ₁ <L ₂ or x <z.