JPH08195526A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PURPOSE: To easily manufacture a semiconductor laser which has an InAsP or InGaAsP light confinement layer in which a refractive index is continuously varied. CONSTITUTION: The method for manufacturing a semiconductor laser comprises the steps of forming an InP clad layer 2 on a semiconductor substrate 1, growing an InAsP light confinement layer 3 thereon while gradually varying the flow rate of the raw material of V-group composition or III-group composition, growing an InGaAsP active layer 4 thereon, growing an InAsP light confinement layer 5 thereon while gradually varying the flow rate of the raw material of V-group composition or III-group composition, and forming an InP clad layer 6 thereon. Even if the layers 3, 5 are not lattice-matched to the substrate 1, the confinement layer having excellent crystallinity can be formed similarly to the case of the lattice-matching, thereby obtaining a low threshold current and a high slope efficiency.

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 in an optical communication system and its manufacturing method.

[0002]

2. Description of the Related Art As an optical confinement layer for a semiconductor laser,
Those having a single band gap energy are often used. For example, FIG. 5 shows an example of an InGaAsP / InP semiconductor laser, in which p-type is formed on a p-InP substrate 21.
InP clad layer 22, InGaAsP optical confinement layer 2
3, an InGaAsP active layer 24, an InGaAsP optical confinement layer 25, and an n-InP clad layer 26 are formed. Since such a semiconductor laser has a single bandgap energy as shown in FIG. 6, there is a problem that the light confinement rate is low.

On the other hand, a structure has been proposed in which the mixed crystal composition of the light confining layer is continuously changed to continuously change the refractive index and improve the light confining rate. Further, as a result, the band gap energy can also be inclined, so that improvement of the injection efficiency can be expected. The optical confinement layer having such a structure is called a GRINSCH structure.

Such a structure has a structure of AlGaAs / GaA.
It has already been proposed for the s laser, and Al of AlGaAs
The band gap and the refractive index can be changed by changing the composition. In this case, AlAs and Ga
Since the lattice constant of As is only about 0.16%, AlGaAs of all Al compositions is almost lattice-matched to GaAs. Therefore, the GRINSCH layer can be easily manufactured by continuously changing the Al composition.

Incidentally, T. Fujii et al., AlGaA
A laser having such a GRINSCH layer was manufactured by using an s / GaAs laser, and a low threshold current density (124 A /
cm ² ) (extended abstracts of the 16th
Conf. Solid State Decicesand Materials, Kobe, 1984
pp145-148).

Therefore, such a technique is applied to In _1-x Ga _x
It may be applied to the optical confinement layer of the As _y P _1-y / InP semiconductor laser, and the band gap and the refractive index may be changed by changing the composition x of the group III or the composition y of the group V. Being tried.

[0007]

However, in order to lattice-match such an optical confinement layer with InP,
It is necessary to satisfy the relationship of y = 2.18x. Therefore, in order to manufacture the GRINSCH layer, it is required to change the amounts of both the group III raw material and the group V raw material at the same time.
However, in the usual MOCVD (Metal Organic Chemical Vapor Deposition) method widely used for laser crystal growth, the flow rate of the raw material and the composition of the growing crystal are not necessarily proportional, so that the desired band gap and refraction are obtained, and In order to grow an InGaAsP layer that is lattice-matched to InP, it is necessary to repeat growth and adjustment several times to find an appropriate flow rate of group III and group V raw materials, which requires a great deal of time and labor. It costs. Further, because of this restriction, it is actually difficult to form a layer that continuously changes, and a stepwise energy layer as shown in FIG. 7 is formed, which reduces the effect. There's a problem.

[0008]

OBJECTS OF THE INVENTION It is an object of the present invention to use InGaAs or I
It is an object of the present invention to provide a semiconductor laser having an nGaAsP active layer, which has an optical confinement layer whose refractive index continuously changes, and which can be easily manufactured, and a manufacturing method thereof.

[0009]

The semiconductor laser of the present invention is a semiconductor laser having a structure in which an active layer made of InGaAsP or InGaAs is sandwiched between optical confinement layers made of InAsP layers or InGaAsP layers.
It is characterized in that the light confinement layer is formed as a layer having a layer thickness and a strain amount that does not lattice match with the substrate and does not exceed the critical layer thickness.

For example, in the optical confinement layer, the amount of strain is continuously changed by changing the V group composition in the thickness direction of the layer. Alternatively, the amount of strain is continuously changed by changing the group III composition in the thickness direction of the layer.

The method of manufacturing a semiconductor laser according to the present invention comprises the steps of forming an InP clad layer on a semiconductor substrate, and gradually changing the flow rate of the raw material of V group composition or III group composition on the InP cladding layer. InGaAsP
Step of growing optical confinement layer and InGaAs on it
A step of growing a P or InGaAs active layer, a step of growing an InAsP or InGaAsP optical confinement layer on the active layer of the group V composition or a group III composition gradually, and an InP clad layer thereon. And a forming step.

[0012]

By growing the InAsP or InGaAsP optical confinement layer while gradually changing the flow rate of the raw material of the group III or group V composition, it is possible to perform lattice matching with the semiconductor substrate even if the lattice matching is achieved. An optical confinement layer having good crystallinity can be formed. Therefore, carriers can be injected into the active layer by diffusion and electric field,
The carrier injection efficiency is improved, and the refractive index is continuously changed, so that the optical confinement efficiency is improved and the carrier injection efficiency is improved. As a result, a semiconductor laser having a low threshold current and high efficiency can be obtained.

[0013]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the DH of the semiconductor laser of the first embodiment of the present invention.
FIG. 2 is a cross-sectional view of the structure portion, and FIG. 2 is a diagram showing the corresponding energy band, refractive index and strain amount. A clad layer 2 made of p-InP on the p-InP substrate 1 by the MOCVD method.
To grow. Next, TMI and TBP which are raw materials of InP
In addition, TBA, which is a source of As of Group V, is allowed to flow into the reaction chamber to grow the InAs _y P _1-y optical confinement layer 3.

At this time, by gradually increasing the flow rate of TBA from 0, the group V composition is gradually changed from InP to InAs _0.15 P _0.85 , and the strain amount is changed so as to gradually increase in the compression direction. . Along with this, the band gap gradually decreases and the refractive index increases.

Next, the InGaAsP active layer 4 is grown, and then the InAs _y P _1-y optical confinement layer 5 is grown again by TBA. At this time, by gradually decreasing the flow rate of TBA, InAs _0.15 P _0.85 to I
The group V composition is gradually changed up to nP, and an optical confinement layer whose strain amount is reduced from the compression direction is grown. Along with this, the band gap is gradually increased and the refractive index is reduced. After that, an n-InP clad layer is grown. As a result, the DH structure portion of FIG. 1 is formed.

Here, in forming the InAs _y P _1-y optical confinement layers 3 and 5, the strain amount and the layer thickness are set so that the thickness of each layer does not exceed the critical layer thickness for the light wavelength or the refractive index. Set. By performing this setting, the InAs _y
The P _1-y light confinement layers 3 and 5 are formed as light confinement layers having good crystallinity, as in the case of lattice matching.

The semiconductor laser is completed by forming an embedded structure and forming electrodes by the LPE or MOCVD method.

The characteristics of the semiconductor laser of the first embodiment are
When evaluated with a device having a cavity length of 300 μm and both ends cleaved, an oscillation threshold current of 7 mA at 20 ° C. and 0.3
A slope efficiency of 2 W / A was obtained. Incidentally, 20 of the InGaAsP mixed crystal semiconductor lasers shown in FIGS.
The characteristics at 0 ° C. were an oscillation threshold current of 9 mA and a slope efficiency of 0.30 W / A.

As described above, in the semiconductor laser of the first embodiment, InGa having a single composition, which is often used in the past, is used.
Since the optical confinement efficiency and the carrier injection efficiency can be improved as compared with the semiconductor laser having the AsP mixed crystal in the optical confinement layer, a semiconductor laser having a low threshold current and a high slope efficiency can be realized. Further, as compared with a semiconductor laser having an optical confinement layer whose composition is changed stepwise as shown in FIG. 7, it is only necessary to change and control the composition flow rate of a single group, so that there is an advantage that it can be easily manufactured.

FIG. 3 is a sectional view of the DH structure portion of the semiconductor laser of the second embodiment of the present invention, and FIG. 4 is a diagram showing the corresponding energy band, refractive index and strain amount. In this example, first, the cladding layer 12 made of p-InP is grown on the p-InP substrate 11 by the MOCVD method. Next, the flow rate of TMI, which is a group III In raw material, is continuously increased, or the flow rate of TEG, which is a Ga raw material, is continuously decreased, and the In _1-x Ga _x As _0.3 P _0.7 optical confinement layer 13 is formed. To grow.

Here, the amount of strain is gradually changed from In _0.8 Ga _0.2 As _0.3 P _0.7 to In _0.86 Ga _0.14 As _0.3 P _0.7 by gradually increasing the flow rate of the Group III raw material. Next, the InGaAsP active layer 14 is grown,
After that, this time, by gradually decreasing the TMI flow rate continuously or increasing the TEG flow rate,
_0.86 Ga _0.14 As _0.3 P _0.7 to In _0.8 Ga _0.2 As
An optical confinement layer 15 whose group III composition gradually changes to _0.3 P _0.7 is grown. Then, the n-InP clad layer 1
By growing 6, the DH structure of FIG. 3 is produced.

Also in the second embodiment, by setting the strain amount and layer thickness so that the layer thickness of the light confinement layers 13 and 15 does not exceed the critical film thickness, the crystal is crystallized as in the case of lattice matching. It is possible to produce a light confinement layer having good properties. It has been confirmed that the oscillation threshold current and slope efficiency can be obtained also in the second embodiment, as in the first embodiment.

In each of the above-mentioned embodiments, the present invention is called p-I.
Although the example in which the semiconductor laser is configured on the nP substrate has been described, the invention can be similarly applied to the n-InP substrate to configure the semiconductor laser. Also,
For the active layer, InGaAsP or InGaAs
It is needless to say again that the bulk structure or the quantum well structure may be used without limitation. Further, the present invention is an InGaAsP formed on a GaAs substrate.
It can also be applied to a laser.

[0024]

As described above, according to the present invention, InAsP or InGaAsP provided so as to sandwich the active layer is provided.
As the light confinement layer, it is formed as a layer having a layer thickness and a strain amount that does not lattice match with the substrate and does not exceed the critical layer thickness. A light confinement layer having good crystallinity can be formed, the light confinement efficiency can be increased, the carrier injection efficiency can be improved, and a low threshold current and a high slope efficiency can be obtained.

In the present invention, InAsP or InG is used.
When the aAsP light confinement layer is grown, the growth is performed while gradually changing the flow rate of the raw material of the group V composition or the group III composition. Therefore, the light confinement layer can be produced only by changing the flow rate of a single composition. Therefore, the optical confinement layer having the required characteristics can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a sectional view of a DH structure portion of a first embodiment of a semiconductor laser of the present invention.

FIG. 2 is a diagram showing an energy band, a refractive index, and a strain amount of the first embodiment.

FIG. 3 is a sectional view of a DH structure portion of a second embodiment of the semiconductor laser of the present invention.

FIG. 4 is a diagram showing an energy band, a refractive index, and a strain amount of a second embodiment.

FIG. 5 is a sectional view of a DH structure portion of a conventional semiconductor laser.

FIG. 6 is an energy band diagram of the semiconductor laser of FIG.

FIG. 7 is an energy band diagram of the improved semiconductor laser.

[Explanation of symbols]

 1, 11 substrate 2, 12 clad layer 3, 5 InAsP optical confinement layer 4, 14 active layer 6, 16 clad layer 13, 15 InGaAsP optical confinement layer

Claims (4)

[Claims] 1. In a semiconductor laser having a structure in which an active layer made of InGaAsP or InGaAs is sandwiched between optical confinement layers made of InAsP layers or InGaAsP layers, the optical confinement layers do not lattice match with a substrate and exceed a critical layer thickness. A semiconductor laser characterized in that it is formed as a layer having no layer thickness and strain amount. 2. The semiconductor laser according to claim 1, wherein the optical confinement layer has a strain amount continuously changed by changing the V group composition in the thickness direction of the layer. 3. The semiconductor laser according to claim 1, wherein the optical confinement layer has a strain amount continuously changed by changing the group III composition in the thickness direction of the layer. 4. A step of forming an InP clad layer on a semiconductor substrate, and InAsP or InG while gradually changing the flow rate of the raw material of the group V composition or the group III composition thereon.
Step of growing an aAsP optical confinement layer and In
InAsP or InGaAsP while growing the active layer of GaAsP or InGaAs and gradually changing the flow rate of the raw material of V group composition or III group composition
A method of manufacturing a semiconductor laser, comprising: a step of growing an optical confinement layer; and a step of forming an InP clad layer thereon.