JP2003031902A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser that can be lowered in threshold current and improved in efficiency, by improving the uniformity of carrier density distribution. SOLUTION: This semiconductor laser has a GaAs substrate, an n-type clad layer 3, and a p-type clad layer 7. The laser also has a multiplex quantum well active layer 5 having two or more wells. The clad layers 3 and 5 and active layer 5 are constituted of AlGaAs-based materials and thicknesses t1, t2, t3, and t4 of barrier layers 14 which constitute the active layer 5 become gradually thicker (t1<t2<t3<t4), going farther away from the clad layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser used as a semiconductor laser for distance measurement or laser welding or the like which constitutes an eye of a robot or a laser radar system. .

[0002]

2. Description of the Related Art As a means for reducing the oscillation threshold current of a semiconductor laser and improving the luminous efficiency, a multiple quantum well structure (Multiple quantum well structure) in which an active layer is composed of a plurality of quantum wells is used.
Quantum Well: MQW) is used. In this structure, well layers having a small energy band gap and barrier layers having a large energy band gap are alternately stacked. Here, when the thickness of the well layer is reduced to about 20 nm or less, the quantum effect appears. The MQW structure laser is a laser utilizing this quantum effect.

Usually, in these MQW structures, the film thicknesses and energy band gaps of a plurality of well layers and barrier layers are different between well layers and barrier layers, as disclosed in, for example, Japanese Patent Application Laid-Open No. 7-221395. They are formed in the same way.

[0004]

FIG. 17 generally shows an SC.
H-MQW (SCH: Separate Confinement Heteros
An example of the energy band diagram of a structure called tructure) is shown. Electrons and holes that are carriers are M from the n-type cladding layer side and holes are from the p-type cladding layer side by M
It is injected into the QW active layer. The injected electrons and holes are recombined in the well layer in the MQW active layer to emit light and become laser light. Therefore, in order to obtain efficient laser characteristics, it is necessary to efficiently recombine electrons and holes. However, since the semiconductor laser usually has a pn junction diode structure, the injection directions of electrons and holes are opposite to each other. That is, electrons are injected from the n-type cladding layer side, while holes are injected from the p-type cladding layer side. Therefore, when the active layer has an MQW structure, in FIG. 17, the carrier density from the position x = 0 in the MQW active layer in contact with the n-light guide layer to the position x = 1 in contact with the p-light guide layer is as shown in FIG.
It becomes like 8. As shown in FIG. 18, electrons have a distribution that is biased toward the n-type layer side, and holes have a distribution that is biased toward the p-type layer side. Therefore, the recombination rate between electrons and holes is shown in FIG. As described above, the distribution is not uniform in the active layer, and is non-uniform with the maximum at a certain position. Such non-uniformity of distribution causes deterioration of laser characteristics. The shape of the distribution is band offset (conduction band side: ΔEc, valence band side Δ.
Since it depends on the magnitude relationship of Ev), it is necessary to design appropriately according to the material.

Therefore, an object of the present invention is to provide a semiconductor laser capable of improving the uniformity of carrier density distribution and obtaining a highly efficient laser having a low threshold current.

[0006]

According to the invention of claim 1, n
In a semiconductor laser including a p-type cladding layer, a p-type cladding layer, and a multiple quantum well active layer having two or more wells, the band offset on the conduction band side is larger than the band offset on the valence band side (ΔEc> ΔEv). ). In such a material system, since the potential barrier on the conduction band side is high, carriers on the conduction band side, that is, electrons are less likely to be injected into the multiple quantum well active layer. Therefore, in order to efficiently inject electrons, the thickness of the barrier layer on the n-type cladding layer side is reduced and gradually increased to facilitate injection of electrons to the p-type cladding layer side. As a result, the uniformity of the electron carrier density distribution is further improved, and as a result, the threshold current can be lowered more effectively and a highly efficient laser can be obtained.

According to the second aspect of the invention, an n-type cladding layer,
In a semiconductor laser including a p-type cladding layer and a multiple quantum well active layer having two or more wells, a band gap on the valence band side is made larger than a band offset on the conduction band side (ΔEc <ΔEv). There is. In such a material system, since the potential barrier on the valence band side is high,
Carriers on the valence band side, that is, holes, are less likely to be injected into the multiple quantum well active layer. Therefore, in order to efficiently inject holes, the thickness of the barrier layer on the p-type clad layer side is reduced and gradually increased to facilitate the injection of holes into the n-type clad layer side. There is. As a result, the uniformity of carrier density distribution of holes is further improved, and as a result, the threshold current can be lowered more effectively and a highly efficient laser can be obtained.

According to the third aspect of the invention, the multiple quantum well active layer is made of an AlGaAs type material on the GaAs substrate. In this material, the band offset on the conduction band side is larger than the band offset on the valence band side, so that the electron has a structure that is more difficult to be injected into the multiple quantum well active layer. Therefore, by forming the barrier layers forming the multi-quantum well active layer in order of increasing thickness with increasing distance from the n-type cladding layer,
Since the barrier layer close to the n-type clad layer is thin, tunneling is easy (passing is easy). As a result, the uniformity of the electron carrier density distribution mainly in the active layer is improved, the uniformity of the electron-hole recombination velocity distribution is improved, and a highly efficient laser with a low threshold current is obtained. be able to.

According to a fourth aspect of the invention, the multiple quantum well active layer is made of an AlInGaAs-based material on the InP substrate. In this material system, the band offset on the conduction band side is larger than the band offset on the valence band side. Therefore, the same action and effect as those of the third aspect can be obtained by forming the barrier layer constituting the multiple quantum well active layer in order of increasing thickness as it goes away from the n-type cladding layer.

In the fifth aspect of the invention, the multiple quantum well active layer is made of an InGaAsP-based material on the InP substrate. In this material system, the band offset on the valence band side is larger than the band offset on the conduction band side, so that holes are more difficult to be injected into the multiple quantum well active layer. Therefore, holes are formed by forming the barrier layers constituting the multi-quantum well active layer in order of increasing thickness with increasing distance from the p-type cladding layer.
Since the barrier layer close to the p-type clad layer is thin, tunneling is easy (passing through is easy). As a result, the uniformity of the carrier density distribution of holes mainly in the active layer is improved, the uniformity of the recombination velocity distribution between electrons and holes is improved, and a highly efficient laser having a low threshold current is obtained. Obtainable.

According to a sixth aspect of the invention, an n-type clad layer,
In a semiconductor laser including a p-type cladding layer and a multiple quantum well active layer having two or more wells, the barrier layers constituting the multiple quantum well active layer have different energy band gaps. Therefore, since it is possible to appropriately design the conduction band side and the valence band side so that the distributions of the carrier densities of electrons and holes become uniform depending on the constituent materials, the threshold current is low and the efficiency is high. A laser can be obtained.

According to a seventh aspect of the invention, an n-type cladding layer,
In a semiconductor laser including a p-type cladding layer and a multi-quantum well active layer having two or more wells, the energy band gap of the barrier layer forming the multi-quantum well active layer gradually increases as the distance from the n-type cladding layer increases. It is characterized by being. Since electrons have a small energy band gap in the barrier layer close to the n-type cladding layer, electrons are easily injected into the adjacent well layer. Therefore, the uniformity of the electron carrier density distribution is improved mainly in the active layer, so that the uniformity of the electron-hole recombination velocity distribution is improved, and a highly efficient laser with a low threshold current is obtained. You can

According to an eighth aspect of the invention, an n-type cladding layer,
In a semiconductor laser including a p-type clad layer and a multi-quantum well active layer having two or more wells, the energy band gap of the barrier layer forming the multi-quantum well active layer increases in order with increasing distance from the p-type clad layer. It is characterized by being. Since holes have a small energy band gap in the barrier layer close to the p-type cladding layer, holes are likely to be injected into the adjacent well layer. Therefore, the uniformity of the carrier density distribution of holes mainly in the active layer is improved to improve the uniformity of the electron-hole recombination velocity distribution, and a highly efficient laser with a low threshold current is obtained. be able to.

According to a ninth aspect of the present invention, in the seventh aspect of the present invention, the band offset on the conduction band side is larger than the band offset on the valence band side. In such a material system, since the potential barrier on the conduction band side is high, carriers on the conduction band side, that is, electrons are less likely to be injected into the multiple quantum well active layer. Therefore, in order to efficiently inject electrons, the energy band gap of the barrier layer on the side closer to the n-type cladding layer is made smaller and gradually increased to facilitate injection of electrons to the p-type cladding layer side. ing. As a result, the uniformity of the electron carrier density distribution mainly in the active layer is improved to improve the uniformity of the electron-hole recombination velocity distribution, and a highly efficient laser with a low threshold current is obtained. be able to.

According to a tenth aspect of the present invention, in the eighth aspect of the present invention, the band offset on the valence band side is larger than the band offset on the conduction band side. In such a material system, since the potential barrier on the valence band side is high, carriers on the valence band side, that is, holes are more difficult to be injected into the multiple quantum well active layer. Therefore, in order to inject holes efficiently, the energy band gap of the barrier layer on the side close to the p-type cladding layer is reduced and gradually increased to inject holes into the n-type cladding layer side. Making it easier.
As a result, the uniformity of the carrier density distribution of holes mainly in the active layer is improved, the uniformity of the recombination velocity distribution between electrons and holes is improved, and a highly efficient laser with a low threshold current is obtained. Obtainable.

According to an eleventh aspect of the invention, in the semiconductor laser of the sixth to ninth aspects, since GaAs is used as the substrate and the multiple quantum well active layer is made of an AlGaAs type material, the band offset on the conduction band side is obtained. Is larger than the band offset on the valence band side. This material structure has a structure in which electrons are less likely to be injected into the multiple quantum well active layer. Therefore, by changing the energy band gap of each barrier layer of the multi-quantum well active layer, the carrier density distribution of electrons can be made more nearly uniform, and as a result, the threshold current is low and the efficiency is high. A laser can be obtained.

According to a twelfth aspect of the invention, in the semiconductor laser according to the sixth to ninth aspects, InP is used as the substrate,
Since the multiple quantum well active layer is made of an AlInGaAs-based material, the band offset on the conduction band side is larger than the band offset on the valence band side. This material structure has a structure in which electrons are less likely to be injected into the multiple quantum well active layer. Therefore, by changing the energy band gap of each barrier layer of the multi-quantum well active layer, the carrier density distribution of electrons can be made more nearly uniform, and as a result, the threshold current is low and the efficiency is high. A laser can be obtained.

According to the invention of claim 13, claims 6, 7 and
In the semiconductor lasers described in 8 and 10, I is used as a substrate.
Since nP is used and the multiple quantum well active layer is made of an InGaAsP-based material, the band offset on the valence band side is larger than the band offset on the conduction band side. This material structure has a structure in which holes are less likely to be injected into the multiple quantum well active layer. Therefore, by changing the energy band gap of each barrier layer of the multiple quantum well active layer, the carrier density distribution of mainly holes can be made more uniform, and as a result, high efficiency with low threshold current can be obtained. Laser can be obtained.

According to the fourteenth aspect of the present invention, the multiple quantum well active layer is made of an AlGaAs type material on the GaAs substrate. In this material system, the band offset on the conduction band side is larger than the band offset on the valence band side, so that the electron has a structure that is more difficult to be injected into the multiple quantum well active layer. Therefore, by increasing the energy band gap of the barrier layer forming the multiple quantum well active layer in order as the distance from the n-type clad layer increases, the energy band gap of the barrier layer near the n-type clad layer is increased for electrons. Since it is small, it is easily injected into the adjacent well layer. As a result, the uniformity of the electron carrier density distribution mainly in the active layer is improved, the uniformity of the electron-hole recombination velocity distribution is improved, and a highly efficient laser with a low threshold current is obtained. be able to.

In the fifteenth aspect of the present invention, the multiple quantum well active layer is made of an AlInGaAs-based material on the InP substrate. In this material system, the band offset on the conduction band side is larger than the band offset on the valence band side, so that the electron has a structure that is more difficult to be injected into the multiple quantum well active layer. Therefore, by making the energy band gap of the barrier layer constituting the multi-quantum well active layer gradually increase with increasing distance from the n-type cladding layer, it is possible to obtain the same action and effect as in the fourteenth aspect.

In the sixteenth aspect of the present invention, the multiple quantum well active layer is made of an InGaAsP-based material on the InP substrate. In this material system, the band offset on the valence band side is larger than the band offset on the conduction band side, so that holes are more difficult to be injected into the multiple quantum well active layer. Therefore, by increasing the energy band gap of the barrier layer forming the multiple quantum well active layer in order with increasing distance from the p-type clad layer, holes can have an energy band gap close to the p-type clad layer. Is small, it is easy to be injected into the adjacent well layer. As a result, the uniformity of the carrier density distribution of holes mainly in the active layer is improved, the uniformity of the recombination velocity distribution between electrons and holes is improved, and a highly efficient laser having a low threshold current is obtained. Obtainable.

The invention of claim 17 aims at the effects of both the invention of claim 1 and the invention of claim 7. That is, in a semiconductor laser including an n-type clad layer, a p-type clad layer, and a multiple quantum well active layer having two or more wells, the material system in which the band offset on the conduction band side is larger than the band offset on the valence band side. And the thickness of the barrier layer constituting the multiple quantum well active layer is gradually increased with increasing distance from the n-type cladding layer, and the energy band gap of the barrier layer is increased with increasing distance from the n-type cladding layer. Making it big. In this material structure, the potential barrier on the conduction band side is high, and therefore carriers on the conduction band side, that is, electrons are less likely to be injected into the multiple quantum well active layer. Therefore, by changing both the thickness of the barrier layer and the energy band gap of the multiple quantum well active layer as described above, electrons are more effectively injected into the adjacent well layer. As a result, the uniformity of the electron carrier density distribution mainly in the active layer is improved, the uniformity of the electron-hole recombination velocity distribution is improved, and a highly efficient laser with a low threshold current is obtained. be able to.

The invention of claim 18 aims at the effects of both the invention of claim 2 and the invention of claim 8. That is, in a semiconductor laser including an n-type cladding layer, a p-type cladding layer, and a multiple quantum well active layer having two or more wells, the material system in which the band offset on the valence band side is larger than the band offset on the conduction band side. The thickness of the barrier layer constituting the multi-quantum well active layer is gradually increased as the distance from the p-type cladding layer increases, and the energy band gap of the barrier layer is increased as the distance from the p-type cladding layer increases. Making it big. In this material structure, the potential barrier on the valence band side is high, so that carriers on the valence band side, that is, holes, are less likely to be injected into the multiple quantum well active layer. Therefore, by changing both the thickness of the barrier layer and the energy band gap of the multiple quantum well active layer as described above, holes can be more effectively injected into the adjacent well layer. As a result, the uniformity of the carrier density distribution of holes mainly in the active layer is improved, the uniformity of the recombination velocity distribution between electrons and holes is improved, and a highly efficient laser having a low threshold current is obtained. Obtainable.

The invention of claim 19 aims at the effects of both the invention of claim 3 and the invention of claim 14. That is, in a semiconductor laser including a GaAs substrate, an n-type cladding layer, a p-type cladding layer, and a multiple quantum well active layer having two or more wells, an n-type cladding layer, a p-type cladding layer, and a multiple quantum well active layer Is made of an AlGaAs-based material, the thickness of the barrier layer forming the multi-quantum well active layer is gradually increased with increasing distance from the n-type cladding layer, and the energy band gap of the barrier layer is increased from the n-type cladding layer. It becomes larger in order as it gets away. Since the potential barrier on the conduction band side is high in this material configuration, carriers on the conduction band side, that is,
The structure is such that electrons are less likely to be injected into the multiple quantum well active layer. Therefore, by changing both the thickness of the barrier layer and the energy band gap of the multiple quantum well active layer as described above, electrons are more effectively injected into the adjacent well layer. As a result, the uniformity of the electron carrier density distribution mainly in the active layer is improved, the uniformity of the electron-hole recombination velocity distribution is improved, and a highly efficient laser with a low threshold current is obtained. be able to.

The invention of claim 20 aims at the effects of both the invention of claim 4 and the invention of claim 15. That is, in a semiconductor laser including an InP substrate, an n-type clad layer, a p-type clad layer, and a multiple quantum well active layer having two or more wells, the n-type clad layer and the p-type clad layer are made of InP or AlInGaAs-based material. In addition, the multiple quantum well active layer is made of an AlInGaAs-based material, and the thickness of the barrier layer forming the multiple quantum well active layer is formed in order as the distance from the n-type cladding layer increases, and The energy band gap is increased in order with increasing distance from the n-type cladding layer. In this material structure, the potential barrier on the conduction band side is high, and therefore carriers on the conduction band side, that is, electrons are less likely to be injected into the multiple quantum well active layer. Therefore, by changing both the thickness of the barrier layer and the energy band gap of the multiple quantum well active layer as described above, electrons are more effectively injected into the adjacent well layer. As a result, the uniformity of the electron carrier density distribution mainly in the active layer is improved, the uniformity of the electron-hole recombination velocity distribution is improved, and a highly efficient laser with a low threshold current is obtained. be able to.

The invention of claim 21 aims at the effects of both the invention of claim 5 and the invention of claim 16. That is, in a semiconductor laser including an InP substrate, an n-type cladding layer, a p-type cladding layer, and a multiple quantum well active layer having two or more wells, an n-type cladding layer, a p-type cladding layer, and a multiple quantum well active layer Is InGaAsP
The barrier layer is made of a system material, and the thickness of the barrier layer constituting the multi-quantum well active layer is gradually increased as the distance from the p-type clad layer increases, and the energy band gap of the barrier layer increases from the p-type clad layer. Therefore, they are increased in order. In this material structure, the potential barrier on the valence band side is high, so that carriers on the valence band side, that is, holes, are less likely to be injected into the multiple quantum well active layer. Therefore, by changing both the thickness of the barrier layer and the energy band gap of the multiple quantum well active layer as described above, holes can be more effectively injected into the adjacent well layer. As a result, the uniformity of the carrier density distribution of holes mainly in the active layer is improved to improve the uniformity of the recombination velocity distribution between electrons and holes,
A laser with a low threshold current and high efficiency can be obtained.

According to the invention of claim 22, in the semiconductor laser according to any one of claims 1 to 21, the number of wells in the multiple quantum well active layer is 5 or more. Therefore, it is possible to obtain a high-power semiconductor laser without overflowing the carriers injected into the multiple quantum well active layer even at the time of driving a large current.

According to a twenty-third aspect of the invention, in the semiconductor laser according to any one of the first to twenty-second aspects, the stripe width of the light emitting region of the semiconductor active layer is 100 μm or more. A high power semiconductor laser of 10 W class can be obtained.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a cross-sectional structure of the high power semiconductor laser according to this embodiment. Further, FIG. 2 shows an energy band diagram in the vicinity of the active layer of the high power semiconductor laser of this embodiment.

In FIG. 1, an n-type GaAs substrate 1 has n
-GaAs buffer layer 2, n-Al _0.4Ga_0.6Askura
Pad layer 3, n-Al_0.2Ga_0.8As light guide layer 4, Al
_0.2Ga_0.8As / GaAs multiple quantum well structure
Layer 5, p-Al_0.2Ga_{0. 8}As light guide layer 6, p-A
l_0.4Ga_0.6As clad layer 7, p-GaAs cap
Layers 8 are stacked in order. The active layer 5 is shown in FIG.
Sea urchin Al_0.2Ga_0.8As and GaAs are stacked alternately
Al_0.2Ga_0.84 layers of As and 5 layers of GaAs are formed.
Has been. In this case, the energy band gap is small
GaAs becomes the well layer 13 and the energy band gap
Large Al_0.2Ga_0.8As becomes the barrier layer 14.
Further, in FIG. 1, n-Al_0.4Ga_0.6As clad
Layer 3 and n-Al_0.2Ga_0.8As light guide layer 4 and MQW activity
Layer 5 and p-Al_0.2Ga_0.8As light guide layer 6 and p-A
l_0.4Ga_0.6As clad layer 7 and p-GaAs cap
Layer 8 has a mesa shape. This mesa and n-GaA
The insulating film 9 is formed on the upper surface of the s buffer layer 2.
On the upper surface of the mesa portion of the insulating film 9 (p-GaAs
A window 9a is formed on the upper surface of the top layer 8). this
On the insulating film 9 including the window 9a, Cr / Pt / Au is formed.
A p-type electrode 10 made of is formed.

The thickness of the n-GaAs buffer layer 2 is 500.
nm, n-Al _0.4 Ga _0.6 As clad layer 3 has a thickness of 1
μm, n-Al _0.2 Ga _0.8 As Optical guide layer 4 has a thickness of 1
μm.

Further, in the active layer 5, as shown in FIG. 2, the thickness t of Al _0.2 Ga _0.8 As which is the barrier layer 14 is set.
1, t2, t3, and t4 are t1 = 3 nm and t2 in order with increasing distance from the n-Al _0.4 Ga _0.6 As cladding layer 3.
= 4 nm, t3 = 5 nm, and t4 = 6 nm, which are thicker by 1 nm. The thickness of each GaAs well layer 13 in the active layer 5 is 12 nm, and the thickness of each layer is constant. Therefore, the total thickness of the active layer 5 is 78 nm.

Further, in FIG. 1, the p-Al _0.2 Ga _0.8 As optical guide layer 6 has a thickness of 1 μm, the p-Al _0.4 Ga _0.6 As clad layer 7 has a thickness of 1 μm, and the p-GaAs cap layer 8 has a thickness of 1 μm.
Has a thickness of 0.8 μm.

On the other hand, Au is formed on the back surface of the n-GaAs substrate 1.
An n-type electrode 11 made of Ge / Ni / Au is formed, and n
-Ohmic contact is made with the GaAs substrate 1. On the surface of the n-type electrode 11, Au /
The Sn layer 12 is formed, so that the semiconductor laser element and the pedestal made of Cu or Fe (not shown) are bonded to each other.

Next, a method of manufacturing the high power semiconductor laser will be described. First, M on the n-GaAs substrate 1 in FIG.
BE (Molecular Beam Epitaxy) method and MOCVD (Me
n-GaAs buffer layer 2, n-Al _0.4 Ga _0.6 A by the tal organic chemical vapor deposition method or the like.
s clad layer _{3, n-Al 0. 2 Ga} 0.8 As optical guide layer _{4, Al 0.2 Ga 0.8 As /} GaAs multi-quantum well active layer 5 consisting of structure, p-Al _0.2 Ga _0.8 As optical guide layer 6, p- Al _0.4 Ga _0.6 As clad layer 7, p-GaA
The s cap layer 8 is sequentially laminated. Then, the mesa portion is formed by etching.

Subsequently, an insulating film 9 made of SiO _{2 is} formed on the upper surfaces of the n-GaAs buffer layer 2 and the mesa portion by plasma C.
A film is formed by the VD method, and a window 9a is formed by opening a window by etching. The width of this window 9a becomes the stripe width (the stripe width of the light emitting region in the active layer). After that, Cr / Pt / Au (film thickness 15 nm /
A p-type electrode 10 composed of (300 nm / 600 nm) is formed by an electron beam evaporation method, and heat treatment is performed at about 360 ° C. to make ohmic contact. As the material of the p-type electrode 10, Ti / Pt / Au or the like may be used instead.

Further, Au is formed on the back surface of the n-GaAs substrate 1.
An n-type electrode 11 made of Ge / Ni / Au is formed by an electron beam evaporation method, and heat treatment is performed to obtain an ohmic electrode. Then, the Au / Sn layer 12 is formed by the electron beam evaporation method. Finally, the end face is cleaved to form a semiconductor laser chip.

The horizontal and vertical dimensions of this high-power semiconductor laser (semiconductor laser chip) are 500 μm × 800 μm,
The stripe width is 400 μm. In the case of a high power semiconductor laser of several tens of W class, in order to obtain a high output, the stripe width of the electrode for passing a current through the device is at least 10
0 μm or more is required.

In this embodiment, the multi-quantum well active layer 5 is A
It is composed of a 1GaAs-based material. That is, Al _x G
In a _1-x As, the well layer 13 is GaAs with x = 0, and the barrier layer 14 is Al _0.2 Ga _0.8 As with x = 0.2. Therefore, as shown in FIG. 2, the band offset ΔEc on the conduction band side is larger than the band offset ΔEv on the valence band side. Therefore, since the potential barrier on the conduction band side is high and electrons are less likely to be injected into the MQW, the thicknesses t1 and t of the barrier layers 14 in the MQW are increased.
2, t3, and t4 are formed thicker in order as the distance from the n-AlGaAs cladding layer 3 increases (t1
<T2 <t3 <t4), electrons can be efficiently injected (electrons are easily injected into the p-type cladding layer 7 side), and the distribution can be made more uniform. That is, for the electrons, since the barrier layer near the n-type cladding layer 3 is thin, tunneling is easy (passing through), and the uniformity of the carrier density distribution of electrons mainly in the active layer is improved. as a result,
The recombination rate of electrons and holes has a nearly uniform distribution, and a highly efficient laser can be obtained with a low threshold current.

FIG. 3 shows the simulation result of the carrier density distribution of electrons and holes, and FIG. 4 shows the simulation result of the recombination velocity distribution. The horizontal axis in FIGS. 3 and 4 is the position x in the active layer (see FIG. 2), the position in contact with the n-light guide layer 4 is x = 0, and the position in contact with the p-light guide layer 6 is x = 1. I am trying.

In the simulation, electron and hole carrier densities were calculated as D _e (x) and D _h (x), respectively, using a simplified model as shown in the following equation. D _e (x) = 1 / α _e · [1-exp (−α _e )] * exp [−α _e x] (1) D _h (x) = 1 / α _h · [1-exp (−α _h )] * exp [−α _h (1-x)] (2) where α _e is the attenuation coefficient of the electron density and α _h is the attenuation coefficient of the hole density.

The recombination rate between electrons and holes was calculated as being limited by the smaller one of the electron and hole densities calculated by the above equations (1) and (2). Here, the ease with which electrons and holes are injected can be quantitatively expressed by changing the calculation parameters α _e and α _h (in this calculation, α _e = α _h = 0.2, It is assumed that electron carrier injection is the same as hole carrier injection).

From the simulation results shown in FIGS. 3 and 4, it was confirmed that the following effects can be obtained by forming the barrier layer in the MQW active layer by changing the thickness in order.

First, FIG. 3 and FIG. 18 will be compared. FIG. 18 shows a simulation result when the thickness of the barrier layer is constant as shown in FIG. Compared with FIG. 18, in FIG. 3, the carrier density distribution of electrons and holes becomes closer to uniform. next,
FIG. 4 and FIG. 19 are compared. FIG. 19 shows a simulation result when the thickness of the barrier layer is constant as shown in FIG. Compared with FIG. 19, in FIG. 4, the recombination velocity distribution between electrons and holes is made uniform. As a result, when the structure of the present embodiment is applied as a laser element, it is possible to obtain a laser with a low threshold current and high efficiency.

Further, by setting the stripe length to 100 μm or more, it is possible to obtain laser light of several tens W class at a pulse current of several tens A. As described above in detail, according to the present embodiment, the recombination rate of carriers in the MQW active layer can be obtained by making the density distribution of electrons and holes uniform according to the band offset peculiar to the material. The distribution can be made uniform. Therefore, when this structure is applied to a semiconductor laser, highly efficient laser characteristics can be obtained with a low threshold current.

Further, by setting the number of wells in the multiple quantum well active layer to 5 or more, a high power semiconductor laser can be obtained without overflow of the carriers injected into the multiple quantum well active layer even at the time of driving a large current. be able to.
Further, as described above, by setting the stripe width of the light emitting region of the semiconductor active layer to 100 μm or more, it is possible to obtain a high power semiconductor laser of tens of W class with a pulse current of tens of A. (Second Embodiment) Next, the second embodiment will be described with reference to the first embodiment.
The difference from the above embodiment will be mainly described.

FIG. 5 shows a sectional view of the high-power semiconductor laser according to this embodiment. Further, FIG. 6 shows an energy band diagram in the vicinity of the active layer of the high power semiconductor laser of this embodiment.

In FIG. 5, n is formed on the n-InP substrate 21.
-InP buffer layer 22, n-InP clad layer 23,
n-Al _0.23 In _0.53 Ga _0.24 As Optical guide layer 24, A
an active layer 25 having a multi-quantum well structure of lInGaAs,
_{p-Al 0.23 In 0.53 Ga 0.} 24 As optical guide layer 26, p
A -InP clad layer 27 and a p-InGaAs cap layer 28 are sequentially stacked. The n-type cladding layer 23
The p-type cladding layer 27 may be made of AlInGaAs material. The active layer 25 is made of AlInG as shown in FIG.
The aAs well layers 29 and the AlInGaAs barrier layers 30 are alternately arranged. The specific composition is Al _x In _y Ga.
_{In 1-xy} As, the well layer 29 has x = 0, y = 0.5
3 and the barrier layer 30 has x = 0.23 and y = 0.53.

As described above, the semiconductor laser includes the InP substrate 21, the n-type cladding layer 23, the p-type cladding layer 27, and the multiple quantum well active layer 25 having two or more wells.
The n-type cladding layer 23 and the p-type cladding layer 27 are made of InP (or AlInGaAs) -based material, and the multiple quantum well active layer 25 is made of AlInGaAs-based material (Al _x In _y Ga).
_1-xy As). Then, the thicknesses t11 and t1 of the barrier layers 30 constituting the multiple quantum well active layer 25
2, t13, and t14 become thicker in order with increasing distance from the n-type cladding layer 23 (t11 <t12 <t1.
3 <t14).

As described above, in the semiconductor laser of this embodiment using the AlInGaAs-based material as the multiple quantum well active layer 25 on the InP substrate 21, the band offset ΔEc on the conduction band side is the band offset ΔEv on the valence band side. Larger than that of the multiple quantum well active layer 2
By forming the barrier layer 30 constituting No. 5 in the order of increasing thickness from the n-type cladding layer 23, the same action and effect as those of the first embodiment can be obtained. (Third Embodiment) Next, the third embodiment will be described with reference to the first embodiment.
The difference from the above embodiment will be mainly described.

FIG. 7 shows a sectional view of the high-power semiconductor laser according to this embodiment. Further, FIG. 8 shows an energy band diagram in the vicinity of the active layer of the high power semiconductor laser of this embodiment.

On the n-InP substrate 31, an n-InP buffer layer 32, an n-InP clad layer 33, and an n-InG having a composition having an energy band gap Eg = 1.05 eV.
aAsP optical guide layer 34, InGaAsP / InGaA
The active layer 35 having an s multiple quantum well structure and p-In having a composition with an energy band gap Eg = 1.05 eV
GaAsP optical guide layer 36, p-InP clad layer 3
7 and a p-InGaAs cap layer 38 are sequentially stacked. The active layer 35 has an energy band gap Eg =
InGaAsP having a composition of 1.05 eV and In _0.53
Ga _0.47 As and alternating layers of InGaAsP
Five layers of In _0.53 Ga _0.47 As are formed. In this case, In _0.53 Ga having a small energy band gap
_0.47 As (Eg = 0.75 eV) becomes the well layer 39,
InGaAsP (E with large energy band gap
g = 1.05 eV) becomes the barrier layer 40. Also, n-I
nP clad layer 33, n-InGaAsP optical guide layer 3
4, the MQW active layer 35, the p-InGaAsP optical guide layer 36, the p-InP clad layer 37, and the p-InGaAs cap layer 38 are mesa-shaped.

The thickness of the n-InP buffer layer 32 is 500.
nm, the thickness of the n-InP clad layer 33 is 1 μm, n-
The thickness of the InGaAsP light guide layer 34 is 1 μm.
In addition, in the active layer 35, InG that is the barrier layer 40 is used.
The thickness t21, t22, t23, t24 of aAsP is p-
As the distance from the InP clad layer 37 increases, t2 increases in order.
1 = 3 nm, t22 = 4 nm, t23 = 5 nm, t24
= 6 nm and 1 nm thick. The thickness of the InGaAs well layer 39 in the active layer 35 is 12 each.
nm and the thickness of one layer is constant. Therefore, the total thickness of the active layer 35 is 78 nm.

The p-InGaAsP optical guide layer 36 has a thickness of 1 μm, and the p-InP clad layer 37 has a thickness of 1 μm.
The p-InGaAs cap layer 38 has a thickness of 0.8 μm.

On the back surface of the n-InP substrate 31, AuGe /
The n-type electrode 11 made of Ni / Au is formed, and n-In
An ohmic contact is made with the P substrate 31. An Au / Sn layer 12 as a bonding material is formed on the surface of the n-type electrode 11, and thereby a semiconductor laser element and a pedestal made of Cu or Fe (not shown) are bonded.

The vertical and horizontal dimensions of this high power semiconductor laser are 5
00μm × 800μm, stripe width is 400μ
m. In order to obtain a large output, a high power semiconductor laser of several tens of W class needs a stripe width of at least 100 μm or more for an electrode for passing a current through the device.

In this embodiment, the multiple quantum well active layer is In
It is composed of a GaAsP-based material. In other words, In _x G
a _1-x As _y P _1-y , the well layer 39 has x = 0.53,
In _0.53 Ga _0.47 As with y = 1, and the barrier layer 40 is x.
= 0.79, y = 0.45, InGaAsP. Therefore, the band offset ΔEv on the valence band side is larger than the band offset ΔEc on the conduction band side (ΔEc <ΔEv). Therefore, since carriers having a valence band side, that is, holes, are less likely to be injected into the MQW, the thicknesses t21 and t of the barrier layer 40 in the MQW are increased.
22, t23, and t24 are formed thicker in order as the distance from the p-InP cladding layer 37 increases (t
21 <t22 <t23 <t24), holes can be efficiently injected (holes are easily injected to the n-type cladding layer 33 side),
The carrier density distribution of holes can be made more uniform. That is, for holes, the p-type cladding layer 37
Since the barrier layer close to is thin, tunneling is facilitated (passage is facilitated), and uniformity of carrier density distribution of holes mainly in the active layer is improved. As a result, the recombination rate of electrons and holes has an almost uniform distribution, and a high-efficiency laser can be obtained with a low threshold current.

That is, also in this embodiment, when the carrier density distribution and the recombination velocity are simulated as in the first embodiment, the results shown in FIGS. 3 and 4 are obtained, and it is understood that the recombination velocity becomes a distribution that is almost uniform. . As a result, a highly efficient laser with a low threshold current can be obtained.

Further, by setting the stripe length to 100 μm or more, it is possible to obtain laser light of several tens W class at a pulse current of several tens of A. (Fourth Embodiment) Next, a fourth embodiment will be described.
The difference from the above embodiment will be mainly described.

FIG. 9 shows an energy band diagram in the vicinity of the active layer of the high power semiconductor laser according to this embodiment. In the present embodiment, in the multiple quantum well active layer 5, the barrier layer 5
The Al composition ratio x of Al _x Ga _1-x As, which is 0, is n-Al.
As the distance from the _0.4 Ga _0.6 As cladding layer 3 increases, x = 0.04, 0.08, 0.12, 0.16 and 0.
It is formed so as to increase by 04. At this time, the thickness of the barrier layer 50 is constant at 4 nm. Like this
The energy band gaps Eg1, Eg2, Eg3, Eg4 of the barrier layer 50 are sequentially changed as shown in FIG. 9 by changing the l composition ratio. That is, the energy band gaps Eg1, Eg2, Eg of the barrier layer 50
3, Eg4 increases in order with increasing distance from the n-type cladding layer 3 (Eg1 <Eg2 <Eg3 <Eg
4). Other configurations and film thickness are the same as those in the first embodiment.

Even with such a configuration, the same effect as that of the first embodiment can be obtained. That is, also in this configuration, since the band offset ΔEc on the side of the conduction band is larger than the band offset ΔEv on the side of the valence band, the potential barrier on the side of the conduction band is high, and the electrons are in the MQW active layer. It has a material composition that is difficult to inject. Therefore, in the present embodiment, the energy band gap of the barrier layer 50 on the side closer to the n-type cladding layer 3 is reduced and gradually increased to facilitate injection of electrons into the p-type cladding layer 7 side. That is, in order to efficiently inject electrons, the energy band gap of the barrier layer on the side close to the n-type cladding layer 3 is reduced and gradually increased to inject electrons into the p-type cladding layer 7 side. Making it easier. As a result, as in the first embodiment, the uniformity of the electron carrier density distribution mainly in the active layer 5 is improved, and thus the uniformity of the electron-hole recombination velocity distribution is improved and the threshold current is increased. And a laser with high efficiency can be obtained. (Fifth Embodiment) Next, a fifth embodiment will be described.
The difference from the above embodiment will be mainly described.

FIG. 10 shows an energy band diagram in the vicinity of the active layer of the high power semiconductor laser of this embodiment. n
The type cladding layer 23 and the p-type cladding layer 27 are made of InP (or AlInGaAs) -based material, and the multiple quantum well active layer 25 is made of AlInGaAs-based material.
Energy band gaps Eg11, Eg12, Eg13, E of the barrier layer 60 constituting the multiple quantum well active layer 25
g14 increases in order with increasing distance from the n-type cladding layer 23 (Eg11 <Eg12 <Eg13 <.
Eg 14).

As described above, also in the present embodiment, the band offset ΔEc on the conduction band side is larger than the band offset ΔEv on the valence band side, and electrons are less likely to be injected into the multiple quantum well active layer 25. It has a structure. Therefore, by changing the energy band gap of each barrier layer 60 of the multiple quantum well active layer 25 (Eg11 <Eg12 <Eg13 <Eg14), the carrier density distribution of mainly electrons can be made closer to a uniform distribution. As a result, a highly efficient laser with a low threshold current can be obtained. (Sixth Embodiment) Next, a sixth embodiment will be described.
The difference from the above embodiment will be mainly described.

FIG. 11 shows an energy band diagram in the vicinity of the active layer of the high power semiconductor laser of this embodiment. In the present embodiment, in the multiple quantum well active layer 35, the energy band gaps Eg21, Eg22, Eg23, and Eg24 of InGaAsP that is the barrier layer 70 are p-In.
As the distance from the P clad layer 37 increases, Eg21
= 0.81 eV, Eg22 = 0.87 eV, Eg23 =
0.93eV, Eg24 = 0.99eV and 0.06eV
It is formed so that it becomes larger each time. At this time, the barrier layer 7
The thickness of 0 is constant at 4 nm. InG like this
The energy band gap of the barrier layer 70 is sequentially changed as shown in FIG. 11 by changing the composition of aAsP (Eg21 <Eg22 <Eg23 <Eg2.
4). Other configurations and film thickness are the same as those in the third embodiment.

Even with such a configuration, the same effect as that of the third embodiment can be obtained. That is, also in this configuration, since the band offset ΔEv on the valence band side is made of a material larger than the band offset ΔEc on the conduction band side, the potential barrier on the valence band side is high, and the holes are the MQW active layer. It is made of a material that is hard to be injected inside. Therefore, in this embodiment, the p-type cladding layer 3
7 is reduced by gradually increasing the energy band gap of the barrier layer 70 on the side closer to 7.
It is made easy to inject into the mold cladding layer 33 side. That is, the energy band gap of the barrier layer on the side closer to the p-type cladding layer 37 is reduced so that holes are efficiently injected,
By gradually increasing the size, holes are easily injected into the n-type cladding layer 33 side. As a result, similarly to the third embodiment, the uniformity of the carrier density distribution of holes mainly in the active layer is improved, the uniformity of the recombination velocity distribution between electrons and holes is improved, and the threshold value is increased. A laser with low current and high efficiency can be obtained. (Seventh Embodiment) Next, the seventh embodiment will be described with reference to the first embodiment.
Also, description will be made centering on differences from the fourth embodiment.

FIG. 12 shows an energy band diagram in the vicinity of the active layer of the high power semiconductor laser according to this embodiment. The present embodiment has a configuration in which the first embodiment and the fourth embodiment are combined. That is, in the MQW active layer 5, the thickness t31 of the Al _x Ga _{1 -x} As that is the barrier layer 80,
t32, t33, t34 is sequentially t31 = 3 nm as the distance from the n-Al _0.4 Ga _0.6 As cladding layer 3,
t32 = 4 nm, t33 = 5 nm, t34 = 6 nm and 1
It is formed thicker by nm. At the same time, the Al composition ratio x is n
-X = 0.04, 0.08, 0.12, 0.16 and 0.
The energy band gaps Eg31, Eg32, Eg3 of the barrier layer 80 are formed so as to increase by 04.
3, Eg34 increases in order with increasing distance from the n-type cladding layer 3 (Eg31 <Eg32 <Eg3
3 <Eg34). Thus, by changing the thickness of the barrier layer 80 and the Al composition ratio at the same time, the thickness t31 to t34 of the barrier layer 80 and the energy band gap Eg3 as shown in FIG.
The configuration is such that 1 to Eg34 change in order. Other configurations and film thickness are the same as those in the first embodiment.

In such a structure, the effects of the first and fourth embodiments can be obtained at the same time,
The effect can be increased. That is, also in this configuration, since the band offset ΔEc on the side of the conduction band is larger than the band offset ΔEv on the side of the valence band, the potential barrier on the side of the conduction band is high, and the electrons are in the MQW active layer. It has a material composition that is difficult to inject.

Therefore, in the present embodiment, the barrier layer 80 on the side closer to the n-type cladding layer 3 is made thinner and the energy band gap is made smaller.
It is made easy to inject into the mold clad layer 7 side. That is, electrons are injected into the adjacent well layer more effectively. As a result, the uniformity of the carrier density distribution in the active layer can be further improved, as shown in FIG. 13, as compared with the case where the first and fourth embodiments are individually carried out. . As a result, FIG.
As shown in FIG. 4, as compared with FIG. 4, the uniformity of the recombination velocity distribution between electrons and holes is further improved, the threshold current is further lower, and a more efficient laser can be obtained. (Eighth Embodiment) Next, the eighth embodiment will be described with reference to the second embodiment.
Also, the description will focus on the differences from the fifth embodiment.

FIG. 15 shows an energy band diagram in the vicinity of the active layer of the high power semiconductor laser of this embodiment. In this embodiment, the second embodiment and the fifth embodiment are combined. That is, the n-type clad layer 23 and the p-type clad layer 27 are made of InP (or AlInGaA).
s) -based material, and the multiple quantum well active layer 25 is AlI
The barrier layer 90, which is made of an nGaAs-based material and constitutes the multiple quantum well active layer 25, has thicknesses t41, t42, and t.
43 and t44 become thicker in order with increasing distance from the n-type cladding layer 23 (t41 <t42 <t43 <
t44), the energy band gap Eg of the barrier layer 90
41, Eg42, Eg43, and Eg44 increase in order with increasing distance from the n-type cladding layer 23 (E
g41 <Eg42 <Eg43 <Eg44).

As described above, in this embodiment, since the potential barrier on the conduction band side is high, carriers on the conduction band side, that is, electrons are less likely to be injected into the multi-quantum well active layer, and the multiple quantum well active layer is formed. By changing both the thickness of the barrier layer of the quantum well active layer and the energy bandgap, electrons are more effectively injected into the adjacent well layer. As a result, the uniformity of the electron carrier density distribution mainly in the active layer is improved, the uniformity of the electron-hole recombination velocity distribution is improved, and a highly efficient laser with a low threshold current is obtained. be able to. (Ninth Embodiment) Next, the ninth embodiment will be described with reference to the third embodiment.
Also, the differences from the sixth embodiment will be mainly described.

FIG. 16 shows an energy band diagram in the vicinity of the active layer of the high power semiconductor laser according to this embodiment. The present embodiment has a configuration in which the third embodiment and the sixth embodiment are combined. That is, in the MQW active layer 35, the thickness t51, t5 of the InGaAsP barrier layer 100.
2, t53, t54 are separated from the p-InP clad layer 37 by t51 = 3 nm and t52 = 4n.
m, t53 = 5 nm, t54 = 6 nm, 1 nm thick, and the energy band gaps Eg51, Eg52, Eg53, of the InGaAsP barrier layer 100 are formed.
As Eg54 is separated from the p-InP cladding layer 37, Eg51 = 0.81 eV and Eg52 = 0.8 in order.
7 eV, Eg53 = 0.93 eV, Eg54 = 0.99
It is formed so as to increase by eV and 0.06 eV, respectively. Thus, the thickness and energy band gap of the barrier layer 100 are simultaneously changed as shown in FIG. Other configurations and film thickness are the same as those in the third embodiment.

In such a structure, the effects of the third and sixth embodiments can be obtained at the same time,
The effect can be increased. That is, in this configuration, since the band offset ΔEv on the valence band side is made larger than the band offset ΔEc on the conduction band side, the potential barrier on the valence band side is high,
Holes have a material configuration in which holes are less likely to be injected into the MQW active layer. Therefore, in this embodiment, since the thickness of the barrier layer 100 on the side closer to the p-type cladding layer 37 is reduced and the energy band gap is reduced, holes are more easily injected into the n-type cladding layer 33 side. ing. That is,
The holes are more effectively injected into the adjacent well layer. As a result, it is possible to further improve the uniformity of the carrier density distribution of holes mainly in the active layer, as compared with the case where the third embodiment and the sixth embodiment are independently performed. As a result, the uniformity of the electron-hole recombination velocity distribution is further improved, and a highly efficient laser with a low threshold current can be obtained.

In each of the above embodiments, the laser structure is formed by laminating it on the n-type substrate, but the same effect can be obtained by forming the laser structure on the p-type substrate. In each of the above embodiments, the thickness of each of the n-clad layer (3), the n-light guide layer (4), the p-light guide layer (6), and the p-clad layer (7) is 1 μm. However, it is not limited to this, and even if it is formed to have a thickness of more than 1 μm,
It may be formed thin, and the thickness of each layer may be the same or different. Further, the thickness of one well layer in the MQW active layer is set to 12 nm, but the thickness is not limited to this, and normally 30 nm or less where the quantum effect appears is used. .5
nm to 20 nm is suitable.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of a semiconductor laser according to a first embodiment.

FIG. 2 is an energy band diagram near the active layer of the semiconductor laser according to the first embodiment.

FIG. 3 is a carrier density distribution diagram in the active layer of the first embodiment.

FIG. 4 is a carrier recombination velocity distribution map in the active layer according to the first embodiment.

FIG. 5 is a sectional view showing the structure of a semiconductor laser according to a second embodiment.

FIG. 6 is an energy band diagram near the active layer of the semiconductor laser according to the second embodiment.

FIG. 7 is a sectional view showing the structure of a semiconductor laser according to a third embodiment.

FIG. 8 is an energy band diagram near the active layer of the semiconductor laser according to the third embodiment.

FIG. 9 is an energy band diagram near the active layer of the semiconductor laser according to the fourth embodiment.

FIG. 10 is an energy band diagram near the active layer of the semiconductor laser according to the fifth embodiment.

FIG. 11 is an energy band diagram near the active layer of the semiconductor laser according to the sixth embodiment.

FIG. 12 is an energy band diagram near the active layer of the semiconductor laser according to the seventh embodiment.

FIG. 13 is a carrier density distribution diagram in the active layer of the seventh embodiment.

FIG. 14 is a carrier recombination velocity distribution map in the active layer of the seventh embodiment.

FIG. 15 is an energy band diagram near the active layer of the semiconductor laser according to the eighth embodiment.

FIG. 16 is an energy band diagram near the active layer of the semiconductor laser according to the ninth embodiment.

FIG. 17 is an energy band diagram near the active layer of a conventional semiconductor laser (when ΔEc> ΔEv)

FIG. 18 is a conventional carrier density distribution diagram (Δ
(When Ec> ΔEv)

FIG. 19 is a carrier recombination velocity distribution map in the conventional active layer (when ΔEc> ΔEv).

FIG. 20 is an energy band diagram near the active layer of a conventional semiconductor laser (when ΔEc <ΔEv).

FIG. 21 is a conventional carrier density distribution diagram (Δ
(When Ec <ΔEv)

FIG. 22 is a carrier recombination velocity distribution map in the conventional active layer (when ΔEc <ΔEv).

[Explanation of symbols]

1 ... n-GaAs substrate, 2 ... n-GaAs buffer layer,
3 ... n-AlGaAs cladding layer, 4 ... n-AlGaA
s optical guide layer, 5 ... MQW active layer (AlGaAs / Ga
As multiple quantum well), 6 ... p-AlGaAs optical guide layer, 7 ... p-AlGaAs cladding layer, 8 ... p-GaA
s cap layer, 9 ... Insulating film, 10 ... P-type electrode (Cr / P
t / Au), 11 ... n-type electrode (AuGe / Ni / A)
u), 12 ... Au-Sn layer, 13 ... Well layer, 14 ... Barrier layer, 21 ... n-InP substrate, 22 ... n-InP buffer layer, 23 ... n-InP clad layer, 24 ... n-Al _0.23
In _0.53 Ga _0.24 As optical guide layer, 25 ... MQW active layer (AlInGaAs / AlInGaAs multiple quantum well), 26 ... p-Al _0.23 In _0.53 Ga _0.24 As optical guide layer, 27 ... p-InP clad layer, 28 ... p- InG
aAs cap layer, 29 ... Well layer, 30 ... Barrier layer, 31
... n-InP substrate, 32 ... n-InP buffer layer, 33
... n-InP clad layer, 34 ... n-InGaAsP optical guide layer, 35 ... MQW active layer (InGaAsP / In
GaAs multiple quantum well), 36 ... p-InGaAsP optical guide layer, 37 ... p-InP clad layer, 38 ... p-I
nGaAs cap layer, 39 ... Well layer, 40 ... Barrier layer,
50 ... Barrier layer, 60 ... Barrier layer, 70 ... Barrier layer, 80 ... Barrier layer, 90 ... Barrier layer, 100 ... Barrier layer.

Claims (23)

[Claims] 1. A band offset (ΔEc) on the conduction band side, which includes an n-type cladding layer (3), a p-type cladding layer (7), and a multiple quantum well active layer (5) having two or more wells.
In a semiconductor laser having a material system having a larger band offset (ΔEv) on the valence band side, a barrier layer (1) constituting the multiple quantum well active layer (5).
A semiconductor laser characterized in that the thickness (t1, t2, t3, t4) in 4) increases in order with increasing distance from the n-type cladding layer (3). 2. An n-type cladding layer (33), a p-type cladding layer (37), and a multiple quantum well active layer (35) having two or more wells, and a band offset (ΔE) on the valence band side.
In a semiconductor laser in which v) is made of a material system larger than a band offset (ΔEc) on the conduction band side, a barrier layer (4) that constitutes the multiple quantum well active layer (35).
A semiconductor laser characterized in that the thickness (t21, t22, t23, t24) of 0) becomes thicker in order as the distance from the p-type cladding layer (37) increases. 3. A semiconductor laser including a GaAs substrate (1), an n-type cladding layer (3), a p-type cladding layer (7), and a multiple quantum well active layer (5) having two or more wells, The n-type clad layer (3) and the p-type clad layer (7)
And the multiple quantum well active layer (5) is made of an AlGaAs-based material, and the thickness (t1, t2, t3, t) of the barrier layer (14) constituting the multiple quantum well active layer (5).
4) A semiconductor laser characterized in that the thickness of 4) increases in order as the distance from the n-type cladding layer (3) increases. 4. A semiconductor laser comprising an InP substrate (21), an n-type cladding layer (23), a p-type cladding layer (27), and a multiple quantum well active layer (25) having two or more wells, The n-type clad layer (23) and the p-type clad layer (2
7) is InP or AlInGaAs type material,
The multiple quantum well active layer (25) is composed of an AlInGaAs-based material, and the multiple quantum well active layer (2)
5) The thickness (t11, t1) of the barrier layer (30) constituting
2, t13, t14) increases in order with distance from the n-type cladding layer (23). 5. A semiconductor laser including an InP substrate (31), an n-type cladding layer (33), a p-type cladding layer (37), and a multiple quantum well active layer (35) having two or more wells, The n-type clad layer (33) and the p-type clad layer (3
7) and the multiple quantum well active layer (35) is InGaAs
The barrier layer (40) made of a P-based material and constituting the multiple quantum well active layer (35) has a thickness (t21, t).
22. t23, t24) is a semiconductor laser characterized in that it becomes thicker in order with increasing distance from the p-type cladding layer (37). 6. A semiconductor laser including an n-type cladding layer (3), a p-type cladding layer (7), and a multiple quantum well active layer (5) having two or more wells, wherein the multiple quantum well active layer ( 5) Barrier layer (5)
0) energy band gap (Eg1, Eg2, E
g3 and Eg4) are different from each other. 7. A semiconductor laser including an n-type cladding layer (3), a p-type cladding layer (7), and a multiple quantum well active layer (5) having two or more wells, wherein the multiple quantum well active layer ( 5) Barrier layer (5)
0) energy band gap (Eg1, Eg2, E
A semiconductor laser characterized in that g3 and Eg4) increase in order with increasing distance from the n-type cladding layer (3). 8. A semiconductor laser including an n-type clad layer (33), a p-type clad layer (37), and a multiple quantum well active layer (35) having two or more wells. 35) constituting the barrier layer (7
0) energy band gap (Eg21, Eg2
2, Eg23, Eg24) increases in order with increasing distance from the p-type cladding layer (37). 9. Band offset (ΔEc) on the conduction band side
9. The semiconductor laser according to claim 7, wherein is composed of a material having a band offset (ΔEv) on the valence band side. 10. The band offset (ΔE) of the valence band
9. The semiconductor laser according to claim 8, wherein v) is made of a material having a larger band offset (ΔEc) on the conduction band side. 11. The semiconductor according to claim 6, wherein GaAs is used as the substrate (1) and the multiple quantum well active layer (5) is made of an AlGaAs-based material. laser. 12. The semiconductor according to claim 6, wherein InP is used as the substrate (21) and the multiple quantum well active layer (25) is made of an AlInGaAs-based material. laser. 13. The substrate (31) is made of InP, and the multi-quantum well active layer (35) is made of an InGaAsP-based material.
The semiconductor laser according to any one of 1. 14. A semiconductor laser comprising a GaAs substrate (1), an n-type cladding layer (3), a p-type cladding layer (7), and a multiple quantum well active layer (5) having two or more wells, The n-type clad layer (3) and the p-type clad layer (7)
And the multiple quantum well active layer (5) is made of an AlGaAs-based material, and the energy band gap (E) of the barrier layer (50) forming the multiple quantum well active layer (5) is
A semiconductor laser characterized in that g1, Eg2, Eg3, Eg4) increase in order with increasing distance from the n-type cladding layer (3). 15. An InP substrate (21), an n-type cladding layer (23), a p-type cladding layer (27), and a well number of 2
In the semiconductor laser including the multiple quantum well active layer (25) described above, the n-type cladding layer (23) and the p-type cladding layer (2
7) is InP or AlInGaAs type material,
The multiple quantum well active layer (25) is composed of an AlInGaAs-based material, and the multiple quantum well active layer (2)
The energy band gap (Eg11, Eg12, Eg13, Eg14) of the barrier layer (60) constituting 5) is n.
A semiconductor laser characterized in that the distance increases from the mold cladding layer (23) in order. 16. An InP substrate (31), an n-type cladding layer (33), a p-type cladding layer (37), and a well number of 2
In the semiconductor laser including the multiple quantum well active layer (35), the n-type cladding layer (33) and the p-type cladding layer (3
7) and the multiple quantum well active layer (35) is InGaAs
The energy band gap (Eg21, Eg22, Eg23, Eg24) of the barrier layer (70) that is made of a P-based material and that constitutes the multiple quantum well active layer (35).
Of the semiconductor laser increases in order with increasing distance from the p-type cladding layer (37). 17. A semiconductor laser including an n-type cladding layer (3), a p-type cladding layer (7), and a multiple quantum well active layer (5) having two or more wells, wherein a band offset (on the conduction band side) The thickness (t31, t32, t33) of the barrier layer (80) constituting the multiple quantum well active layer (5) is made of a material system in which ΔEc) is larger than the band offset (ΔEv) on the valence band side. , T3
4) increases in order as the distance from the n-type cladding layer (3) increases, and the energy band gaps (Eg31, Eg32, Eg33,
A semiconductor laser characterized in that Eg34) increases in order with distance from the n-type cladding layer (3). 18. A semiconductor laser including an n-type cladding layer (33), a p-type cladding layer (37), and a multiple quantum well active layer (35) having two or more wells, wherein a band offset on the valence band side is obtained. The thickness (t51, t52, t53) of the barrier layer (100) constituting the multiple quantum well active layer (35) is made of a material system in which (ΔEv) is larger than the band offset (ΔEc) on the conduction band side. ，
t54) increases in order as the distance from the p-type cladding layer (37) increases, and the barrier layer (100) increases.
Energy band gap (Eg51, Eg52, E
A semiconductor laser characterized in that g53, Eg54) increase in order with distance from the p-type cladding layer (37). 19. A semiconductor laser comprising a GaAs substrate (1), an n-type cladding layer (3), a p-type cladding layer (7), and a multiple quantum well active layer (5) having two or more wells, The n-type clad layer (3) and the p-type clad layer (7)
And the multiple quantum well active layer (5) is composed of an AlGaAs-based material, and the thickness (t31, t32, t3) of the barrier layer (80) forming the multiple quantum well active layer (5).
3, t34) become thicker in order as the distance from the n-type cladding layer (3) increases, and the energy band gaps (Eg31, Eg32, Eg33,
A semiconductor laser characterized in that Eg34) increases in order with distance from the n-type cladding layer (3). 20. An InP substrate (21), an n-type cladding layer (23), a p-type cladding layer (27), and a well number of 2
In the semiconductor laser including the multiple quantum well active layer (25) described above, the n-type cladding layer (23) and the p-type cladding layer (2
7) is InP or AlInGaAs type material,
The multiple quantum well active layer (25) is composed of an AlInGaAs-based material, and the multiple quantum well active layer (2)
5) thickness of the barrier layer (90) (t41, t4)
2, t43, t44) become thicker as the distance from the n-type cladding layer (23) increases, and the barrier layer (9
0) energy band gap (Eg41, Eg4
2, Eg43, Eg44) are sequentially increased with increasing distance from the n-type cladding layer (23). 21. An InP substrate (31), an n-type cladding layer (33), a p-type cladding layer (37), and a well number of 2
In the semiconductor laser including the multiple quantum well active layer (35), the n-type cladding layer (33) and the p-type cladding layer (3
7) and the multiple quantum well active layer (35) is InGaAs
The barrier layer (100) made of a P-based material and constituting the multiple quantum well active layer (35) has a thickness (t51,
t52, t53, t54) become thicker in order as the distance from the p-type cladding layer (37) increases, and the energy band gap (Eg51, Eg) of the barrier layer (100) is increased.
g52, Eg53, Eg54) are p-type cladding layers (3
A semiconductor laser characterized by increasing in size with increasing distance from 7). 22. The number of wells in the multiple quantum well active layer is 5.
22. The semiconductor laser according to claim 1, wherein the semiconductor laser is as described above. 23. The semiconductor laser according to claim 1, wherein a stripe width of a light emitting region in the semiconductor active layer is 100 μm or more.