JP2556288B2 - Semiconductor laser - Google Patents
Semiconductor laserInfo
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- JP2556288B2 JP2556288B2 JP9981594A JP9981594A JP2556288B2 JP 2556288 B2 JP2556288 B2 JP 2556288B2 JP 9981594 A JP9981594 A JP 9981594A JP 9981594 A JP9981594 A JP 9981594A JP 2556288 B2 JP2556288 B2 JP 2556288B2
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- Japan
- Prior art keywords
- layer
- quantum well
- electrons
- semiconductor
- energy
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Description
【0001】[0001]
【産業上の利用分野】本発明は光通信および光情報処理
用の光源として用いられる半導体レーザに関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used as a light source for optical communication and optical information processing.
【0002】[0002]
【従来の技術】近年、光通信を加入者にまで広げるため
に光源となる半導体レーザには従来よりも低閾値、かつ
温度特性の良いものが求められている。さらに、低価格
化のため外部変調器を用いないとすると変調特性も1G
b/s程度あることが望まれる。半導体レーザの閾値電
流を低減し、量子効率を向上させ、高温動作を可能にす
るため、また、高速変調を可能にするために活性層に多
重量子井戸構造を導入することが広く行われてきた。こ
のとき、量子井戸層と障壁層の伝導帯の不連続が小さい
と電子が量子井戸層だけでなく障壁層にも熱的に分布す
るため多重量子井戸構造を導入しても諸特性が向上しな
くなる。このため、量子井戸層と障壁層の禁制帯の差は
大きいことが望ましいとされてきた。また、最近量子井
戸層に基板より格子定数の大きい半導体を用いる、いわ
ゆる歪量子井戸の利用が盛んに検討されているが、これ
は歪みによって価電子帯のバンド構造を変化させ最低準
位の正孔の有効質量が小さくできるためである。この歪
量子井戸の効果を得るには価電子帯の不連続を大きくし
て正孔の最低準位と励起準位とのエネルギー差を大きく
する必要がある。2. Description of the Related Art In recent years, in order to extend optical communication to subscribers, semiconductor lasers serving as light sources are required to have lower thresholds and better temperature characteristics than ever before. Furthermore, if an external modulator is not used for cost reduction, the modulation characteristic will also be 1G.
It is desired that it is about b / s. It has been widely practiced to introduce a multiple quantum well structure into an active layer in order to reduce the threshold current of a semiconductor laser, improve quantum efficiency, enable high temperature operation, and enable high speed modulation. . At this time, when the discontinuity of the conduction band between the quantum well layer and the barrier layer is small, electrons are thermally distributed not only in the quantum well layer but also in the barrier layer, so that various characteristics are improved even if the multiple quantum well structure is introduced. Disappear. Therefore, it has been considered desirable that the difference in the forbidden band between the quantum well layer and the barrier layer is large. Recently, the use of so-called strained quantum wells, which use a semiconductor with a lattice constant larger than that of the substrate for the quantum well layer, has been actively studied. This is because the band structure of the valence band is changed by strain and the positive level of the lowest level is changed. This is because the effective mass of the holes can be reduced. In order to obtain the effect of the strained quantum well, it is necessary to increase the discontinuity of the valence band and increase the energy difference between the lowest level of holes and the excited level.
【0003】ところが量子井戸層と障壁層の禁制帯の差
が大きく、価電子帯の不連続が大きいと正孔は量子井戸
に強く閉じ込められるため、多重量子井戸にしたときp
クラッド層に近い井戸に正孔がたまり、離れた井戸には
正孔がわずかしか注入されなくなる正孔の局在化が起き
る。正孔が注入されない井戸は利得に寄与できないため
レーザの特性は向上しない。つまり、量子井戸の効果と
正孔の局在化の効果はトレードオフの関係にある。従来
は量子井戸層と障壁層の禁制帯の差を最適化することが
試みられてきた。例えば、高岡と櫛部は第54回応用物
理学会学術講演会講演番号28p−H−3(1993
年)において、1.3μm 帯InGaAsP量子井戸レ
ーザで、InGaAsP障壁層組成が禁制帯波長1.1
3μm のとき量子効率の特性温度が最適となることを報
告している。荻田らは同講演会講演番号28p−H−5
で1.3μm 帯歪InGaAsP量子井戸レーザで、I
nGaAsP障壁層組成が禁制帯波長1.1μm のとき
特性温度が最大になることを、鬼頭らは同講演会講演番
号28p−H−6で1.3μm 帯歪InGaAsP量子
井戸レーザで、InGaAsP障壁層組成が禁制帯波長
1.05μm のとき緩和振動周波数が最適化されること
を報告している。However, if the forbidden band of the quantum well layer and the barrier layer is large and the discontinuity of the valence band is large, holes are strongly confined in the quantum well.
Holes are localized in wells close to the clad layer, and holes are only slightly injected into wells apart from the cladding layer. Since the well in which holes are not injected cannot contribute to the gain, the characteristics of the laser are not improved. That is, the effect of quantum well and the effect of localization of holes are in a trade-off relationship. In the past, attempts have been made to optimize the forbidden band difference between the quantum well layer and the barrier layer. For example, Takaoka and Kushibe have a lecture number 28p-H-3 (1993) of the 54th Academic Meeting of Applied Physics.
, A 1.3 μm band InGaAsP quantum well laser with an InGaAsP barrier layer composition of 1.1 forbidden band wavelength.
It is reported that the characteristic temperature of the quantum efficiency becomes optimal when the thickness is 3 μm. Ogita et al., Lecture number 28p-H-5
At 1.3 μm band strained InGaAsP quantum well laser
The characteristic temperature is maximized when the composition of the nGaAsP barrier layer is 1.1 μm in the forbidden band, and Kito et al. gave a lecture in the lecture number 28p-H-6 of 1.3 μm band strained InGaAsP quantum well laser. It is reported that the relaxation oscillation frequency is optimized when the composition has a forbidden band wavelength of 1.05 μm.
【0004】また、正孔の局在化を抑えるために障壁層
を薄膜化し、正孔が隣の井戸へトンネリングにより移動
する確率を高めることも試みられている。例えば、魚見
らは第51回応用物理学会学術講演会講演番号28p−
H−3(1991年)において、InGaAs/InG
aAsP量子井戸レーザで障壁層厚を10nmから5nmに
することで緩和振動周波数が約2倍になることを報告し
ている。また、山田らは第54回応用物理学会学術講演
会講演番号28p−H−10(1993年)において、
1.3μm 帯InGaAsP量子井戸レーザで障壁層厚
を3nmから10nmまで変化させ障壁層が薄いほど微分利
得が大きくなることを報告している。It has also been attempted to reduce the thickness of the barrier layer in order to suppress the localization of holes, thereby increasing the probability that holes will move to an adjacent well by tunneling. For example, Uomi et al., Lecture number 28p-
H-3 (1991), InGaAs / InG
It has been reported that the relaxation oscillation frequency is approximately doubled by changing the barrier layer thickness from 10 nm to 5 nm in the aAsP quantum well laser. In addition, Yamada et al., At the 54th Annual Meeting of the Applied Physics Academic Lecture No. 28p-H-10 (1993),
It has been reported that in a 1.3 μm band InGaAsP quantum well laser, the barrier layer thickness is changed from 3 nm to 10 nm and the thinner the barrier layer, the larger the differential gain.
【0005】別の面でレーザの特性を改善する試みとし
て、クラッド層にII−VI族半導体を用いて活性層か
らクラッド層へのキャリアのもれを低減することが、西
田により特開昭59−86282号公報(特願昭57−
195254号)で、柊元によって特開平1−1757
89号公報(特願昭62−335868号)で、提案さ
れている。また、クラッド層にII−VI族半導体を用
いると活性層からクラッド層へのキャリアのもれを低減
すると同時に光の活性層への閉じ込めも増大し閾値キャ
リア密度を下げることができレーザ特性の向上が期待で
きる。In another aspect, as an attempt to improve the characteristics of a laser, a II-VI semiconductor is used for the cladding layer to reduce carrier leakage from the active layer to the cladding layer. -86282 publication (Japanese Patent Application No. 57-
195254) by Hiiragimoto.
89 (Japanese Patent Application No. 62-335868). Further, if a II-VI group semiconductor is used for the clad layer, leakage of carriers from the active layer to the clad layer can be reduced, and at the same time, confinement of light in the active layer can be increased and threshold carrier density can be lowered to improve laser characteristics. Can be expected.
【0006】[0006]
【発明が解決しようとする課題】しかし、上述のような
最適化では量子井戸層と障壁層の禁制帯の差が小さくな
ることにより量子井戸の効果が犠牲になる。障壁層を薄
膜化した場合でも電子が3次元化するため、バンド端で
の状態密度が小さくなって利得が低下する他、正孔のバ
ンド構造も変わるため特に歪量子井戸にした時の効果が
小さくなってここでも量子井戸の効果と正孔の局在化の
効果はトレードオフの関係が現れる。このため、さらに
レーザ特性を向上させるには量子井戸の効果と正孔の局
在化の効果のトレードオフの関係を解消する必要があ
る。However, the above-mentioned optimization sacrifices the effect of the quantum well because the difference in the forbidden band between the quantum well layer and the barrier layer becomes small. Even when the barrier layer is thinned, the electrons become three-dimensional, so that the density of states at the band edge becomes small and the gain decreases, and the band structure of holes also changes, so that the effect particularly when the strained quantum well is formed is obtained. As the size of the quantum well becomes smaller, a trade-off relationship appears between the quantum well effect and the hole localization effect. Therefore, in order to further improve the laser characteristics, it is necessary to eliminate the trade-off relationship between the quantum well effect and the hole localization effect.
【0007】また、クラッド層にII−VI族半導体を
用いることには、II−VI族半導体でIII−V族半
導体並みの十分低抵抗なp型半導体を得るのは現在でも
困難であり素子抵抗の増大による温度上昇を招き特性の
向上を妨げるという問題がある。さらにキャリア閉じ込
めと光閉じ込めの向上をめざしてクラッド層にI−VI
I族半導体や絶縁体を用いるとキャリアの電流注入自体
が困難となる。量子効果の増大を目的として活性層をな
す量子井戸の障壁層をバンドギャップの大きい材料であ
るII−VI族半導体、I−VII族半導体や絶縁体を
用いたときにも同様の問題が生じる。Further, when a II-VI group semiconductor is used for the cladding layer, it is still difficult to obtain a p-type semiconductor of II-VI group semiconductor having a resistance sufficiently low as that of a III-V group semiconductor, and the element resistance is still present. However, there is a problem in that the temperature rise due to the increase of the temperature rise and the improvement of the characteristics is prevented. Furthermore, in order to improve carrier confinement and optical confinement, I-VI is used for the cladding layer.
When a group I semiconductor or an insulator is used, it becomes difficult to inject current into carriers. The same problem occurs when using a II-VI group semiconductor, a I-VII group semiconductor, or an insulator, which is a material having a large bandgap, for the barrier layer of the quantum well forming the active layer for the purpose of increasing the quantum effect.
【0008】従って、本発明の目的は高いキャリアと光
閉じ込めおよび量子効果による低閾値キャリア密度動作
を可能とするバンドギャップの大きな材料を活性層をな
す量子井戸の障壁層やクラッド層に用いてしかもキャリ
アの電流注入を効率的に行うことのできる構造を持つこ
とにより、閾値電流、量子効率、温度特性、高速変調と
いった諸特性の優れた半導体レーザを提供することにあ
る。Therefore, an object of the present invention is to use a material having a large bandgap, which enables high carrier and optical confinement and low threshold carrier density operation by the quantum effect, for the barrier layer and the cladding layer of the quantum well forming the active layer. An object of the present invention is to provide a semiconductor laser having various characteristics such as threshold current, quantum efficiency, temperature characteristics, and high-speed modulation by having a structure capable of efficiently injecting carrier current.
【0009】[0009]
【課題を解決するための手段】本発明の半導体レーザは
以下のような特徴を持つ。The semiconductor laser of the present invention has the following features.
【0010】1)III−V族半導体を活性層とし、活
性層を挟むクラッド層を活性層より誘電率が小さいI−
VII族またはII−VI族半導体、または絶縁体から
なり、レーザ発振に必要なキャリアを積層方向に平行に
注入する。1) A group III-V semiconductor is used as an active layer, and a clad layer sandwiching the active layer is I- having a dielectric constant smaller than that of the active layer.
Carriers made of a VII group or a II-VI group semiconductor or an insulator and required for laser oscillation are injected parallel to the stacking direction.
【0011】2)レーザ発振をおこなう活性層がIII
−V族半導体を井戸層とし、I−VII族またはII−
VI族半導体、または絶縁体を障壁層とする量子井戸を
含む。2) The active layer for laser oscillation is III
-V group semiconductor is used as a well layer, and group I-VII or II-
It includes a quantum well having a Group VI semiconductor or an insulator as a barrier layer.
【0012】3)レーザ発振をおこなう活性層がIII
−V族半導体を井戸層としI−VII族またはII−V
I族半導体、あるいは絶縁体を障壁層とする量子井戸か
らなり、量子井戸のバンド間遷移のエネルギーが所要の
光子エネルギーより大きく、電子のサブバンド間遷移の
エネルギーが所要の光子エネルギーにほぼ等しくなるよ
うに設定され、量子井戸の電子の高次サブレベルに選択
的に電子を注入する機構により電子のサブバンド間遷移
によりレーザ発振する。3) The active layer for laser oscillation is III
-V group semiconductor is used as a well layer and group I-VII or II-V
It consists of a quantum well with a group I semiconductor or an insulator as a barrier layer, and the energy of the interband transition of the quantum well is larger than the required photon energy, and the energy of the electron intersubband transition is almost equal to the required photon energy. The laser is oscillated by the intersubband transition of electrons by the mechanism of selectively injecting electrons into the higher order sublevels of the electrons in the quantum well.
【0013】4)3)の半導体レーザで、活性層を構成
する量子井戸の電子のレーザ発振にかかわる高次サブレ
ベル以上のエネルギーに伝導帯端をもつn型半導体から
なる電子注入層を持つ。4) The semiconductor laser of 3) has an electron injection layer made of an n-type semiconductor having a conduction band edge at an energy higher than a higher sub-level related to laser oscillation of electrons in a quantum well constituting an active layer.
【0014】5)3)の半導体レーザで、n型半導体か
らなる電子注入層が活性層を構成する量子井戸の電子の
レーザ発振にかかわる高次サブレベル以上のエネルギー
に量子準位がある量子井戸を持つ。5) In the semiconductor laser of 3), a quantum well having a quantum level at an energy higher than a higher sub-level related to laser oscillation of electrons in a quantum well in which an electron injection layer made of an n-type semiconductor constitutes an active layer. have.
【0015】6)3)の半導体レーザで、活性層に電流
によりキャリアを注入し、同時に活性層を構成する量子
井戸の電子のサブバンド間遷移のエネルギーより大きな
エネルギーを持つ光を注入して高次サブバンドに電子を
生成する。6) In the semiconductor laser of 3), carriers are injected into the active layer by a current, and at the same time, light having an energy larger than the energy of intersubband transition of electrons in the quantum well forming the active layer is injected to increase the intensity. Generates electrons in the next subband.
【0016】7)3)の半導体レーザで、光子エネルギ
ーが活性層を構成する量子井戸の電子と正孔の最低サブ
バンドの間の遷移のエネルギーより小さく電子の高次サ
ブバンドと正孔との間の遷移エネルギーの1/2より大
きな光を用いて2光子吸収により高次サブバンドに電子
を生成する。7) In the semiconductor laser of 3), the photon energy is smaller than the energy of the transition between the lowest subbands of electrons and holes in the quantum well constituting the active layer, and the higher subbands of electrons and holes are separated. Electrons are generated in higher subbands by two-photon absorption using light larger than 1/2 of the transition energy between.
【0017】[0017]
【実施例】図1は本発明の第1の実施例の構造を示す断
面図である。InPの基板11の上に、ノンドープのZ
nSe0.54Te0.46を1μm 積層したクラッド層12、
ノンドープでバンドギャップ波長が1.1μm の基板に
格子整合したInGaAsPからなる厚さ40nmのバッ
ファー層13、バンドギャップ波長が1.35μmで格
子定数が基板より0.5%短いInGaAsPの井戸層
とZnSe0.54Te0.46の障壁層をそれぞれ5nmと7nm
交互に20層ずつ積層した厚さ0.24μmの量子井戸
活性層14、ノンドープでバンドギャップ波長が1.1
μm の基板に格子整合したInGaAsPからなる厚さ
40nmのバッファー層15、ZnSe0.54Te0.46を1
μm 積層したクラッド層16の各層をMBE装置により
成長した後、クラッド層16、バッファー層15、量子
井戸活性層14およびバッファー層13を幅0.5μm
の導波路を残してRIBEで除去する。導波路の一側面
にBe濃度5×1017cm-3のp型InPのpクラッド層
17とBe濃度2×1018cm-3のp型InGaAsPの
コンタクト層18を、他方の側面にSi濃度5×1017
cm-3のn型InPのnクラッド層19とSi濃度1×1
018cm-3のn型InPのコンタクト層20を選択成長に
より積層し、それぞれの上に電極を形成する。1 is a sectional view showing the structure of a first embodiment of the present invention. On the InP substrate 11, non-doped Z
nSe 0.54 Te 0.46 1 μm laminated clad layer 12,
A buffer layer 13 of InGaAsP having a thickness of 40 nm, which is lattice-matched to an undoped substrate having a bandgap wavelength of 1.1 μm, an InGaAsP well layer having a bandgap wavelength of 1.35 μm and a lattice constant 0.5% shorter than that of the substrate, and ZnSe. 0.54 Te 0.46 barrier layers 5 nm and 7 nm respectively
The quantum well active layer 14 having a thickness of 0.24 μm, which is formed by alternately stacking 20 layers each, has an undoped bandgap wavelength of 1.1.
A 40 nm-thick buffer layer 15 made of InGaAsP lattice-matched to the substrate of μm, and ZnSe 0.54 Te 0.46 are used as 1
After each layer of the clad layer 16 laminated by μm is grown by the MBE apparatus, the clad layer 16, the buffer layer 15, the quantum well active layer 14 and the buffer layer 13 are formed with a width of 0.5 μm.
The remaining waveguide is removed by RIBE. A p-type InP p-cladding layer 17 having a Be concentration of 5 × 10 17 cm -3 and a p-type InGaAsP contact layer 18 having a Be concentration of 2 × 10 18 cm -3 are provided on one side surface of the waveguide, and a Si concentration is provided on the other side surface. 5 x 10 17
cm −3 n-type InP n-clad layer 19 and Si concentration 1 × 1
An n-type InP contact layer 20 of 0 18 cm −3 is laminated by selective growth, and an electrode is formed on each.
【0018】このような構造のレーザにおいて量子井戸
活性層14とバッファー層13、15からなる導波層の
屈折率は約3でありZnSe0.54Te0.46のクラッド層
12、16の屈折率は2.4である。このとき光の閉じ
込め係数は導波層の厚さが0.3μm 程度のとき図2に
示すように0.7程度となり、通常のInPをクラッド
層とし、10層程度の量子井戸層を活性層とした構造の
閉じ込め係数が0.1程度であるのに比べると7倍大き
くなる。このことは本実施例の半導体レーザの量子井戸
一層あたりの閾値利得が通常の10層量子井戸レーザの
14分の1であることを示しており閾値キャリア密度が
大幅に減少する。このため、活性層の微分利得が増大し
効率や高速性が向上する。さらにオージェ電流が減少す
るため温度特性が向上する。導波層とクラッド層の屈折
率差が大きくなると高次モードが立ちやすくなるが図3
に示すように厚さが0.34μm 以下では基本モードだ
けが存在しうる。In the laser having such a structure, the refractive index of the waveguiding layer comprising the quantum well active layer 14 and the buffer layers 13 and 15 is about 3, and the refractive index of the cladding layers 12 and 16 of ZnSe 0.54 Te 0.46 is 2. It is 4. At this time, the optical confinement coefficient is about 0.7 as shown in FIG. 2 when the thickness of the waveguide layer is about 0.3 μm, and ordinary InP is used as the cladding layer and about 10 quantum well layers are used as the active layers. The structure has a confinement coefficient of about 0.1, which is 7 times larger. This means that the threshold gain per quantum well layer of the semiconductor laser of this embodiment is 1/14 of that of a normal 10-layer quantum well laser, and the threshold carrier density is greatly reduced. Therefore, the differential gain of the active layer is increased, and the efficiency and speed are improved. Further, since the Auger current is reduced, the temperature characteristic is improved. When the difference in the refractive index between the waveguiding layer and the cladding layer becomes large, higher-order modes tend to stand up.
As shown in (3), only the fundamental mode can exist when the thickness is 0.34 μm or less.
【0019】この構造ではキャリアは量子井戸活性層の
側面のクラッド層から注入されるため、上下のクラッド
層の電気的特性の影響を受けない。また、高い量子障壁
にもかかわらずキャリアはすべての量子井戸に一様に注
入される。In this structure, carriers are injected from the clad layers on the side surfaces of the quantum well active layer, so that they are not affected by the electrical characteristics of the upper and lower clad layers. Also, despite the high quantum barrier, carriers are uniformly injected into all quantum wells.
【0020】また、量子井戸活性層14の障壁層にバン
ドギャップエネルギーの大きなII−VI族半導体を用
いることにより、電子の障壁の高さは0.9eV、正孔
の障壁の高さは0.7eVとなりキャリアの井戸層への
閉じ込めが増大するため量子効果によって量子井戸での
光学利得が増大する。さらに、障壁層と井戸層の屈折率
差が大きくなるため励起子の束縛エネルギーが大きくな
り利得にたいする励起子による増強が顕著になり微分利
得が増大する。By using a II-VI semiconductor having a large bandgap energy for the barrier layer of the quantum well active layer 14, the electron barrier height is 0.9 eV and the hole barrier height is 0. Since it becomes 7 eV and confinement of carriers in the well layer increases, the optical gain in the quantum well increases due to the quantum effect. Furthermore, since the difference in refractive index between the barrier layer and the well layer becomes large, the binding energy of excitons becomes large, and the enhancement by excitons with respect to the gain becomes remarkable, and the differential gain increases.
【0021】本実施例ではクラッド層と量子井戸の障壁
層にII−VI族半導体を用いたが、さらにバンドギャ
ップエネルギーの大きいI−VII像半導体のCuCl
0.27I0.73、CuBr0.5 I0.5 や絶縁体であるCaS
rF2 などを用いることもできる。これらをクラッド層
に用いたときにも基本モードだけが存在しうる導波層厚
での閉じ込め係数は0.7−0.8であまり変化しない
が同じ閉じ込め係数を得るための導波層厚を小さくでき
るので閾値電流が小さくなる。また、量子井戸の障壁層
に用いることによりさらに量子効果が強まって量子井戸
での光学利得が増大し、同時に障壁層と井戸層の間の誘
電率の差が大きいため鏡像電荷により励起子の束縛エネ
ルギーが増大し励起子増強による微分利得も増大する。In the present embodiment, II-VI group semiconductors are used for the cladding layer and the barrier layer of the quantum well, but CuCl which is an I-VII image semiconductor having a larger band gap energy.
0.27 I 0.73 , CuBr 0.5 I 0.5 and insulator CaS
It is also possible to use rF 2 or the like. When these are used for the cladding layer, only the fundamental mode can exist. The confinement coefficient at the waveguide layer thickness is 0.7-0.8, which does not change much, but the waveguide layer thickness for obtaining the same confinement coefficient is set. Since it can be made smaller, the threshold current becomes smaller. Moreover, the quantum effect is further enhanced by using it in the barrier layer of the quantum well, and the optical gain in the quantum well is increased. At the same time, since the difference in the dielectric constant between the barrier layer and the well layer is large, the exciton is bound by the image charge. Energy increases and differential gain due to exciton enhancement also increases.
【0022】本実施例では活性層に量子井戸を用いたが
活性層とクラッド層の大きな屈折率差による光の閉じ込
めの増大には必ずしもこの必要はなくバルク半導体を用
いても閾値キャリア密度の減少による閾値電流の低減、
量子効率、高速性、温度特性などの向上が実現される。In this embodiment, the quantum well is used for the active layer, but this is not always necessary for increasing the light confinement due to the large difference in the refractive index between the active layer and the cladding layer, and the threshold carrier density is reduced even if the bulk semiconductor is used. Reduction of the threshold current,
Improvements in quantum efficiency, high speed, temperature characteristics, etc. are realized.
【0023】また、基板にInPを用い、これにほぼ格
子整合する材料を用いたがGaAs、GaSbなどの他
のIII−V族半導体やII−VI族半導体、Siなど
のその他の半導体、サファイアなどの絶縁体を基板とし
この上に良好な結晶の得られる半導体を活性層の材料と
して用いることもできる。Although InP is used for the substrate and a material that is substantially lattice-matched to InP is used, other III-V group semiconductors such as GaAs and GaSb, II-VI group semiconductors, other semiconductors such as Si, sapphire, etc. It is also possible to use the above insulator as a substrate and a semiconductor on which a good crystal can be obtained as a material for the active layer.
【0024】図4は本発明の第2の実施例の構造を示す
断面図である。InPの基板11の上にCaSrF2 を
1μm 積層したクラッド層12、ノンドープInPから
なる厚さ40nmのバッファー層13、InPに格子整合
したInGaAsの井戸層とCaSrF2 の障壁層をそ
れぞれ6nmと4nm交互に20層ずつ積層した厚さ0.2
μm の量子井戸活性層14、ノンドープInPからなる
厚さ40nmのバッファー層15、CaSrF2 を1μm
積層したクラッド層16の各層をMBE装置により成長
した後、クラッド層16、バッファー層15、量子井戸
活性層14およびバッファー層13を幅0.3μm の導
波路を残してRIBEで除去する。導波路の側面にn型
ZnSe0.54Te0.46のnクラッド層19、23とn型
InPのコンタクト層18、20を選択成長により積層
し、それぞれの上に電極を形成した。FIG. 4 is a sectional view showing the structure of the second embodiment of the present invention. A clad layer 12 having 1 μm of CaSrF 2 laminated on an InP substrate 11, a buffer layer 13 made of non-doped InP having a thickness of 40 nm, an InGaAs well layer lattice-matched with InP, and a CaSrF 2 barrier layer are alternately 6 nm and 4 nm, respectively. 20 layers each with a thickness of 0.2
A quantum well active layer 14 of μm, a buffer layer 15 of non-doped InP having a thickness of 40 nm, and CaSrF 2 of 1 μm
After growing each of the laminated clad layers 16 by the MBE apparatus, the clad layer 16, the buffer layer 15, the quantum well active layer 14, and the buffer layer 13 are removed by RIBE while leaving a waveguide having a width of 0.3 μm. On the side surfaces of the waveguide, n-type ZnSe 0.54 Te 0.46 n-clad layers 19 and 23 and n-type InP contact layers 18 and 20 were laminated by selective growth, and electrodes were formed on the respective layers.
【0025】この実施例においては導波層とクラッド層
の屈折率差が大きいため、第1の実施例の説明で述べた
ように光の閉じ込め係数が大きく小さな閾値利得でレー
ザ発振する。さらに図5に示すように本実施例の量子井
戸活性層は電子の第1サブレベルと第2サブレベルとの
エネルギー差が波長1.55μm に対応する0.8eV
である。また、nクラッド層のZnSe0.54Te0.46の
伝導帯のエネルギー端は量子井戸の電子の第2サブレベ
ルより0.14eVだけ高エネルギーであるから電子は
量子井戸の第2サブレベルに選択的に注入される。第1
サブレベルと第2サブレベルとのエネルギー差が大きい
ためフォノン放出による電子の第2サブレベルから第1
サブレベルへの緩和の確率は小さく注入された電子は第
2サブレベルに溜まるため第1サブレベルと第2サブレ
ベルとの間に反転分布が実現され光学利得が生じる。こ
のように本実施例のレーザにおいては電子のサブバンド
間遷移による利得を利用しており通常の半導体レーザに
おけるような電子と正孔の発光再結合を利用していない
ためpn接合を設ける必要はなく、クラッド層の導電型
はn型のみでよい。電流は電子がnクラッド層から量子
井戸の第2サブレベルに注入され、光を出しながら第1
サブレベルに落ち、もう一方のnクラッド層から外へ流
れることによって生じる。ここで、二つのサブレベルの
電子の層面内の有効質量はほぼ等しいから利得はサブレ
ベル間の双極子能率と反転分布の積に比例し、通常のバ
ンド間遷移のような結合状態密度と分布関数の積を積分
する必要はない。このため、光学利得はキャリアの分布
すなわち温度によらなくなり、温度特性の極めてよいレ
ーザが実現される。実際上、温度特性は第2サブレベル
からnクラッド層への電子のもれだけに支配される。な
お、量子井戸活性層の量子井戸の電子と正孔の最低サブ
レベル間の遷移エネルギーは約1.1eVでレーザ発振
光はバンド間吸収による損失を受けない。In this embodiment, since the difference in the refractive index between the waveguide layer and the cladding layer is large, the laser confinement coefficient is large and the laser oscillation occurs with a small threshold gain as described in the description of the first embodiment. Further, as shown in FIG. 5, in the quantum well active layer of this embodiment, the energy difference between the first sub-level and the second sub-level of electrons is 0.8 eV corresponding to a wavelength of 1.55 μm.
Is. Further, since the energy edge of the conduction band of ZnSe 0.54 Te 0.46 of the n-clad layer is higher by 0.14 eV than the second sublevel of electrons in the quantum well, the electrons are selectively injected into the second sublevel of the quantum well. To be done. First
Since the energy difference between the sub-level and the second sub-level is large, the first to the second sub-levels of electrons due to phonon emission
The probability of relaxation to the sub-level is small, and the injected electrons are accumulated in the second sub-level, so that the population inversion is realized between the first sub-level and the second sub-level, and optical gain occurs. As described above, in the laser of this embodiment, the gain due to the intersubband transition of electrons is used, and the radiative recombination of electrons and holes is not used as in the ordinary semiconductor laser. However, the conductivity type of the cladding layer may be only n-type. In the current, electrons are injected from the n-clad layer into the second sub-level of the quantum well, and light is emitted from the first sub-level.
It is caused by falling to the sub-level and flowing out from the other n-clad layer. Here, the effective masses of two sub-level electrons in the layer plane are almost equal, so the gain is proportional to the product of the dipole efficiency and the population inversion between sub-levels, and the coupling state density and distribution like ordinary interband transitions. There is no need to integrate the product of the functions. Therefore, the optical gain does not depend on the carrier distribution, that is, the temperature, and a laser having excellent temperature characteristics is realized. In fact, the temperature characteristics are dominated by the leakage of electrons from the second sublevel to the n-clad layer. The transition energy between the lowest sub-levels of electrons and holes in the quantum well active layer is about 1.1 eV, and the laser oscillation light is not lost due to band-to-band absorption.
【0026】この実施例におけるnクラッド層は量子井
戸又は超格子で構成してもよい。例えば上で説明した第
2の実施例のnクラッド層を片側だけIn0.52Al0.48
AsとZnSe0.54Te0.46を2原子層(約1.2nm)
ずつ積層した超格子とすると超格子の電子のサブバンド
端がほぼ量子井戸の第2サブレベルに一致するため電子
が共鳴的に効率良く注入される。The n-clad layer in this embodiment may be composed of a quantum well or a superlattice. For example, the n-clad layer of the second embodiment described above may be In 0.52 Al 0.48 on one side only.
As and ZnSe 0.54 Te 0.46 in two atomic layers (about 1.2 nm)
When the superlattices are stacked one by one, the subband edges of the electrons of the superlattice almost coincide with the second sublevel of the quantum well, so that electrons are resonantly and efficiently injected.
【0027】また、基板にGaAsを用い、CaF2 を
1μm 積層したクラッド層2、ノンドープGaAsから
なる厚さ40nmのバッファー層13、GaAsの井戸層
とCaF2 の障壁層をそれぞれ4.65nmと5nm交互に
20層ずつ積層した厚さ約0.2μm の量子井戸活性層
14、ノンドープGaAsからなる厚さ40nmのバッフ
ァー層15、CaF2 を1μm 積層したクラッド層16
の各層と導波路の側面に積層するn型AlAsのnクラ
ッド層19、23とn型GaAsのコンタクト層18、
20の組み合わせでも電子の第1サブレベルと第2サブ
レベルとのエネルギー差が波長1.55μm に対応する
0.8eVとなるがnクラッド層からの電子は第1サブ
レベルに注入される。このため0.98μm の光を発振
するInGaAs/GaAs歪量子井戸レーザ構造をサ
ブレベル間遷移で発振させるレーザに結合するように集
積化する。0.98μm の光により電子は第1サブレベ
ルから第2サブレベルに励起され反転分布が実現されて
レーザ発振を起こす。このときの温度特性は主に励起用
のInGaAs/GaAs歪量子井戸レーザの温度特性
で決まり、150K程度の高い特性温度が得られる。In addition, GaAs is used as a substrate and a clad layer 2 in which CaF 2 is laminated to a thickness of 1 μm, a buffer layer 13 made of non-doped GaAs and having a thickness of 40 nm, a GaAs well layer and a CaF 2 barrier layer are 4.65 nm and 5 nm, respectively. Approximately 0.2 μm thick quantum well active layers 14 each having 20 layers alternately, a buffer layer 15 made of non-doped GaAs having a thickness of 40 nm, and a clad layer 16 having 1 μm of CaF 2 laminated.
N-type AlAs n-clad layers 19 and 23 and n-type GaAs contact layers 18, which are laminated on the respective sides of the waveguide,
Even in the combination of 20, the energy difference between the first sublevel and the second sublevel of electrons is 0.8 eV corresponding to a wavelength of 1.55 μm, but the electrons from the n-clad layer are injected into the first sublevel. Therefore, an InGaAs / GaAs strained quantum well laser structure that oscillates 0.98 μm light is integrated so as to be coupled to a laser that oscillates at a transition between sublevels. The light of 0.98 μm excites the electrons from the first sub-level to the second sub-level to realize the population inversion and cause laser oscillation. The temperature characteristic at this time is mainly determined by the temperature characteristic of the InGaAs / GaAs strained quantum well laser for excitation, and a high characteristic temperature of about 150 K can be obtained.
【0028】上に述べたレーザでは導波路側面のクラッ
ド層にノンドープAlAsや絶縁体を用いて0.98μ
m の光を発振するInGaAs/GaAs歪量子井戸レ
ーザからの光だけによってもレーザ発振が可能である。
このとき、励起用のInGaAs/GaAs歪量子井戸
レーザの光は2光子吸収によってGaAs/CaF2量
子井戸の電子の第2サブバンドを直接励起する。GaA
s/CaF2 量子井戸の電子と正孔の最低サブレベル間
の遷移エネルギーは1.7eVで励起用レーザの光は1
光子による吸収は受けない。このときの温度特性も主に
励起用のInGaAs/GaAs歪量子井戸レーザの温
度特性で決まり、150K程度の高い特性温度が得られ
る。In the laser described above, 0.98 μm is obtained by using non-doped AlAs or an insulator in the cladding layer on the side surface of the waveguide.
Laser oscillation is also possible only with light from an InGaAs / GaAs strained quantum well laser that oscillates m 2 of light.
At this time, the light of the InGaAs / GaAs strained quantum well laser for excitation directly excites the second subband of the electrons of the GaAs / CaF 2 quantum well by two-photon absorption. GaA
The transition energy between the lowest sublevels of electrons and holes in the s / CaF 2 quantum well is 1.7 eV, and the light of the pumping laser is 1
It is not absorbed by photons. The temperature characteristic at this time is also determined mainly by the temperature characteristic of the InGaAs / GaAs strained quantum well laser for excitation, and a high characteristic temperature of about 150 K can be obtained.
【0029】[0029]
【発明の効果】以上説明したように本発明の効果を要約
すると、高いキャリアと光閉じ込めおよび量子効果によ
る低閾値キャリア密度動作を可能とするバンドギャップ
の大きな材料を活性層をなす量子井戸の障壁層やクラッ
ド層に用いてしかもキャリアの電流注入を行うことので
きる構造を持つことにより、閾値電流、量子効率、温度
特性、高速変調といった諸特性の優れた半導体レーザが
得られることである。As described above, the effects of the present invention can be summarized as follows. A material having a large bandgap that enables high carrier and optical confinement and low threshold carrier density operation by the quantum effect is used as a barrier of a quantum well forming an active layer. A semiconductor laser having excellent characteristics such as threshold current, quantum efficiency, temperature characteristics, and high-speed modulation can be obtained by having a structure capable of injecting carrier current by using it as a layer or a clad layer.
【図1】本発明の第1の実施例の構造を示す断面図。FIG. 1 is a sectional view showing a structure of a first embodiment of the present invention.
【図2】本発明のレーザ構造における導波層の厚さと閉
じ込め係数の関係を示す図。FIG. 2 is a diagram showing the relationship between the thickness of the waveguide layer and the confinement coefficient in the laser structure of the present invention.
【図3】本発明のレーザ構造において導波層とクラッド
層との屈折率差と1次横モードがカットオフになる導波
層の厚さの関係を示す図。FIG. 3 is a diagram showing the relationship between the refractive index difference between the waveguide layer and the cladding layer and the thickness of the waveguide layer at which the first-order transverse mode is cut off in the laser structure of the present invention.
【図4】本発明の第2の実施例の構造を示す断面図。FIG. 4 is a sectional view showing the structure of the second embodiment of the present invention.
【図5】本発明の第2の実施例のバンドダイアグラム。FIG. 5 is a band diagram of the second embodiment of the present invention.
11 基板 12 クラッド層 13 バッファー層 14 量子井戸活性層 15 バッファー層 16 クラッド層 17 pクラッド層 18 コンタクト層 19 nクラッド層 20 コンタクト層 21 電極 22 電極 23 nクラッド層 24 導波路 141 井戸層 142 障壁層 40 InGaAsの伝導帯端 41 InGaAs/CaSrF2 量子井戸の電子の第
1サブレベル 42 InGaAs/CaSrF2 量子井戸の電子の第
2サブレベル 43 InGaAsの価電子帯端 44 InGaAs/CaSrF2 量子井戸の正孔の第
1サブレベル 45 ZnSe0.54Te0.46の伝導帯端 46 ZnSe0.54Te0.46の価電子帯端Reference Signs List 11 substrate 12 clad layer 13 buffer layer 14 quantum well active layer 15 buffer layer 16 clad layer 17 p clad layer 18 contact layer 19 n clad layer 20 contact layer 21 electrode 22 electrode 23 n clad layer 24 waveguide 141 well layer 142 barrier layer 40 InGaAs positive electrons of the first sub-level 42 InGaAs / CaSrF 2 second sublevel 43 InGaAs the valence band edge 44 InGaAs / CaSrF 2 quantum well of the quantum well of electrons in the conduction band edge 41 InGaAs / CaSrF 2 quantum well First sub-level of holes 45 ZnSe 0.54 Te 0.46 conduction band edge 46 ZnSe 0.54 Te 0.46 valence band edge
Claims (7)
を挟むクラッド層を活性層より誘電率が小さいI−VI
I族またはII−VI族半導体、または絶縁体からな
り、レーザ発振に必要なキャリアを積層方向に平行に注
入することを特徴とする半導体レーザ。1. A III-V semiconductor is used as an active layer, and a clad layer sandwiching the active layer is I-VI having a smaller dielectric constant than the active layer.
A semiconductor laser comprising a group I or group II-VI semiconductor or an insulator, and injecting carriers necessary for laser oscillation in parallel to the stacking direction.
族半導体を井戸層とし、I−VII族またはII−VI
族半導体、または絶縁体を障壁層とする量子井戸を含む
ことを特徴とする半導体レーザ。2. An active layer for performing laser oscillation is III-V.
Group I semiconductor is used as a well layer, and group I-VII or II-VI is used.
A semiconductor laser comprising a quantum well having a group semiconductor or an insulator as a barrier layer.
族半導体を井戸層としI−VII族またはII−VI族
半導体、あるいは絶縁体を障壁層とする量子井戸からな
り、量子井戸のバンド間遷移のエネルギーが所要の光子
エネルギーより大きく、電子のサブバンド間遷移のエネ
ルギーが所要の光子エネルギーにほぼ等しくなるように
設定され、量子井戸の電子の高次サブレベルに選択的に
電子を注入する機構により電子のサブバンド間遷移によ
りレーザ発振することを特徴とする半導体レーザ。3. An active layer for performing laser oscillation is III-V.
A quantum well having a group I semiconductor as a well layer and a group I-VII or II-VI semiconductor or an insulator as a barrier layer, the energy of interband transition of the quantum well is larger than a required photon energy, and an electron subband The energy of the inter-transition is set to be almost equal to the required photon energy, and laser oscillation is generated by the inter-subband transition of electrons by the mechanism of selectively injecting electrons into the higher sublevels of the electrons in the quantum well. And a semiconductor laser.
発振にかかわる高次サブレベル以上のエネルギーに伝導
帯端をもつn型半導体からなる電子注入層を持つことを
特徴とする請求項3記載の半導体レーザ。4. An electron injection layer comprising an n-type semiconductor having a conduction band edge at an energy higher than a high-order sublevel related to laser oscillation of electrons in a quantum well constituting an active layer. The semiconductor laser described.
構成する量子井戸の電子のレーザ発振にかかわる高次サ
ブレベル以上のエネルギーに量子準位がある量子井戸を
持つことを特徴とする請求項3記載の半導体レーザ。5. The electron injection layer made of an n-type semiconductor has a quantum well having a quantum level at an energy of a higher sub-level or higher relating to laser oscillation of electrons in a quantum well constituting an active layer. The semiconductor laser according to claim 3.
時に活性層を構成する量子井戸の電子のサブバンド間遷
移のエネルギーより大きなエネルギーを持つ光を注入し
て高次サブバンドに電子を生成することを特徴とする請
求項3記載の半導体レーザ。6. A carrier is injected into the active layer by a current, and at the same time, light having an energy larger than the energy of intersubband transition of electrons in the quantum well forming the active layer is injected to generate electrons in a higher subband. The semiconductor laser according to claim 3, wherein
戸の電子と正孔の最低サブバンドの間の遷移エネルギー
より小さく電子の高次サブバンドと正孔との間の遷移エ
ネルギーの1/2より大きな光を用いて2光子吸収によ
り高次サブバンドに電子を生成することを特徴とする請
求項3記載の半導体レーザ。7. The photon energy is smaller than the transition energy between the lowest subbands of electrons and holes in the quantum well constituting the active layer, and 1/2 of the transition energy between the higher order subbands of electrons and holes. 4. The semiconductor laser according to claim 3, wherein electrons are generated in a higher-order subband by two-photon absorption using larger light.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP9981594A JP2556288B2 (en) | 1994-05-13 | 1994-05-13 | Semiconductor laser |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP9981594A JP2556288B2 (en) | 1994-05-13 | 1994-05-13 | Semiconductor laser |
Publications (2)
Publication Number | Publication Date |
---|---|
JPH07307524A JPH07307524A (en) | 1995-11-21 |
JP2556288B2 true JP2556288B2 (en) | 1996-11-20 |
Family
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JP9981594A Expired - Fee Related JP2556288B2 (en) | 1994-05-13 | 1994-05-13 | Semiconductor laser |
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JP2002353569A (en) * | 2001-05-23 | 2002-12-06 | Akihiro Ishida | Semiconductor laser element and semiconductor laser |
JP4718309B2 (en) * | 2005-11-28 | 2011-07-06 | 株式会社日立製作所 | Optical semiconductor device |
JP6834626B2 (en) * | 2017-03-13 | 2021-02-24 | 住友電気工業株式会社 | Light emitting diode |
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1994
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