JPH08255950A - Semiconductor laser - Google Patents

Abstract

PURPOSE: To prevent mutual diffusion of Fe in a semiinsulating InP layer and Zn in p-InP layer by a structure wherein a buried part comprises a semiinsulating InP layer and a specific diffusion preventive layer having a band gap higher than that of the InP layer provided between the InP layer and an emission region. CONSTITUTION: A buried part 111 comprises a semiinsulating InP layer 113, and an In1-x-y Gax Aly As diffusion layer 112 (0<=x<=1, 0<=y<=1) having a band gap higher than that of the InP layer 114 provided between the InP layer 113 and an emission region 102. After growing an InGaAsP/InGaAsP quantum well active layer 102 and p-InP clad layer 103 on an n-InP substrate 101, the n-InP layer 111, the InGaAlAs layer 112, the semiinsulating InP layer 113, and the InP layer 114 are formed, as a buried layer, on the side face of a mesa. Mutual diffusion of Zn and Fe can be prevented by setting the band gap of the InGaAlAs layer higher than that of the InP layer.

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 buried type semiconductor laser in which a side surface of a light emitting region is filled with a high resistance layer.

[0002]

2. Description of the Related Art In recent years, as a semiconductor laser for information processing communication which oscillates in a wavelength band of 1.3 to 1.6 .mu.m, a side surface of a mesa forming a light emitting region has a high resistance layer such as semi-insulating InP (S
An embedded semiconductor laser embedded with an (I-InP) layer has been developed. In this type of embedded semiconductor laser, Fe is often added to InP in order to make the InP layer a high resistance layer. However, when InP is actually used as the buried layer of the laser, the SI-InP layer and the p-In are used.
When the P layer is brought into contact, Fe added to the SI-InP layer is acceptor-like, and Zn and Fe cause mutual diffusion, so that the SI-InP layer becomes a p-type conductivity type,
A current flows between the two layers, reducing the resistance of the buried layer. When the resistance of the buried layer is lowered, a driving current flows as a leak current into the buried layer when the laser operation is performed, and the current-light conversion characteristic (IL characteristic) is deteriorated.

This phenomenon is shown in FIG. p-In
When the P layer and the SI-InP layer are directly joined, Zn and Fe diffuse with each other, and a part of the SI-InP layer becomes a p-type conductivity type.

On the other hand, in order to prevent carrier overflow from the SI-InP layer, it has been attempted to form n-InP around the SI-InP layer or at least a part of the periphery (JP-A-1-241886). . In addition, a layer having a large band gap is formed at the interface between the SI-InP layer and the p-InP layer so that the carriers are SI-InP.
Attempts have been made to prevent injection into layers (Japanese Patent Laid-Open No. 63-133587).

However, even with these methods,
Mutual diffusion of Fe and Zn cannot be prevented. Fe and Z
The interdiffusion of n is n between the SI-InP layer and the p-InP layer.
-Since it occurs even if an InP layer or a layer having a large band gap is sandwiched, n-InP is formed around the SI-InP layer or at least a part of the periphery, or SI-InP is formed.
Even if a layer having a large bandgap is formed at the interface between the p-InP layer and the p-InP layer, the resistance of the SI-InP layer decreases due to the mutual diffusion of impurities, and it is difficult to prevent current leakage in the buried layer.

[0006]

As described above, in the conventional buried type semiconductor laser, the F layer is used as the buried layer.
When e-doped semi-insulating InP is formed, Fe and p-I
Zn added to the nP layer causes mutual diffusion, the carrier concentration of the Fe-added burying layer increases, and the resistivity decreases, which makes it difficult to prevent current leakage in the burying layer.

The present invention has been made in consideration of the above circumstances, and an object thereof is to prevent interdiffusion of Fe in a semi-insulating InP layer and Zn in a p-InP layer, It is an object of the present invention to provide an embedded semiconductor laser capable of maintaining a high resistivity of a semi-insulating InP layer, having a small leakage current and capable of operating up to a high output.

[0008]

In order to solve the above problems, the present invention employs the following configurations. That is, the present invention provides a buried type semiconductor laser including a light emitting region including an active layer formed on a substrate and a buried portion filling the side surface of the light emitting region, wherein the buried portion is a semi-insulating InP layer. In having a bandgap larger than that of InP provided between the InP layer and the light emitting region.
_1-xy Ga _x Al _y As diffusion prevention layer (0 ≦ x ≦ 1, 0 ≦
and y ≦ 1) are included.

The following are preferred embodiments of the present invention. (1) The substrate is InP. (2) The light emitting region forms a stripe-shaped mesa. (3) The light emitting region includes the p-InP layer. (4) Between the InGaAlAs layer and the mesa portion of the light emitting region,
A p-InP layer is provided. (5) The light emitting region has a double hetero structure in which the active layer is sandwiched by the cladding layers, and the InGaAlAs diffusion prevention layer in the buried portion has a band gap larger than that of the cladding layer. (6) The composition of the InGaAlAs diffusion prevention layer should have a band gap corresponding to at least twice the oscillation wavelength. (7) The InGaAlAs diffusion prevention layer has a thickness of 5 nm or more and the lattice mismatch with InP is less than the critical film thickness. In particular, when it is difficult to control the lattice matching condition by forming it in the buried layer, the grown film thickness at the (100) flat portion is 40
be less than or equal to nm. (8) The active layer should have a quantum well structure.

[0010]

In the semiconductor laser of the present invention, p-InP is used.
InG between the layer and the semi-insulating InP (SI-InP) layer.
An aAlAs diffusion prevention layer is provided. Where p-
The InP layer may be included in the light emitting region,
It may be a layer in the buried layer.

According to the earnest studies by the present inventors, as shown in FIG. 4, the InGaAlAs layer is Zn in the p-InP layer.
And also acts as a diffusion suppressing layer for Fe in the SI-InP layer. Therefore, Zn and Fe generated in InP
Mutual diffusion with and can be prevented. Therefore, the Fe-added semi-insulating InP layer exhibits a p-type conductivity type and reduces the resistance, and prevents Fe from spreading to a layer other than a predetermined value, thereby deteriorating the optical characteristics of the device. This can be prevented and the laser characteristics can be improved.

Further, since the bandgap of the InGaAlAs layer is made larger than that of InP, a carrier blocking effect is produced, so that the effect of preventing mutual diffusion of Zn and Fe and keeping the resistance of the semi-insulating layer high is more effective. Get to work. Further, by making the band gap of the InGaAlAs layer larger than that of the InGaAlAs layer used for the clad, it is possible to prevent carriers from leaking into the buried layer due to carrier confinement of the InGaAlAs clad layer, and the buried type laser of the InGaAlAs clad layer can be prevented. Will be realized. In particular, by making the band gap of InGaAlAs of at least a part of the clad layer at least twice the energy of the oscillation wavelength, the current blocking effect can be produced even for the overflow of the current due to the Auger effect generated in the active layer. Therefore, the IL characteristics and temperature characteristics of the laser can be greatly improved.

Here, in order to prevent the diffusion of Zn and Fe, it is extremely effective to set the thickness of the InGaAlAs layer to 5 nm or more. Further, when the growth film thickness in the (100) flat portion is 40 nm or less, it is relatively easy to control the lattice mismatch between InGaAlAs and InP even when it is difficult to control the amount of lattice mismatch when embedding on the side surface of the mesa. The thickness can be kept below the critical film thickness.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a sectional view showing an element structure of a semiconductor laser according to a first embodiment of the present invention. 101 in the figure
Is an n-InP substrate with a plane orientation of (100), and 102 is InGaAsP / InGaAs that oscillates at a wavelength of 1.55 μm.
P quantum well active layer, 103 p-InP first cladding layer, 104 p-InP second cladding layer, 105 p-
It is an InGaAs contact layer. Also, 111 is p-
InP buried layer, 112 is InGa for preventing diffusion
AlAs embedded layer, 113 is Fe-added semi-insulating In
The P buried layer 114 is an n-InP buried layer. Here, the Al composition of the InGaAlAs layer 112 is 0.6,
The Ga composition was 0, and the thickness was 10 nm on the (100) plane.

As a manufacturing method, an n-InP substrate 101 is used.
InGaAsP / InGaAsP quantum well active layer 1 on top
02 and p-InP clad layer 103 are grown, etching is performed leaving a stripe-shaped mesa, and then p-InP layers 111 and InG as buried layers are formed on the side surfaces of the mesa.
aAlAs layer 112, semi-insulating InP layer 113 and n-
The InP layer 114 is grown. Then, the structure of FIG. 1 is obtained by growing the p-InP cladding layer 104 and the InGaAs contact layer 105. As an electrode for supplying a current, an n-side electrode may be formed on the lower surface of the substrate 101 and a p-side electrode may be formed on the contact layer 105.

When the temperature dependence of the differential quantum efficiency η of the laser of this example was investigated, it was found that η (75 ° C.) / Η (25 ° C.)
0.75, which is the conventional η (75 ° C) / η (25 ° C) ~
It was a great improvement compared with 0.65. This is the semi-insulating InP layer 113 in the semiconductor laser of this embodiment.
Surrounds the n-InP layer 114 and the InGaAlAs layer 1.
12, the high resistance can be maintained, and the band gap of the InGaAlAs layer 112 is about 1.8 eV, which has a carrier blocking effect on both electrons and holes. Therefore, the semi-insulating InP layer 11
This is because the carriers that overflowed 3 could be suppressed.

As described above, according to this embodiment, carrier overflow including the Auger effect can be suppressed in the semiconductor laser of wavelength 1.55 μm band used for communication or information processing. Therefore, it becomes possible to realize a semiconductor laser having good characteristics with small temperature dependence. In addition, the semi-insulating InP layer 113 is used as a buried layer.
Closer to the p-InP layer 111 than the InGaAlAs layer 112 having a large band gap and a small carrier transfer rate.
Therefore, the embedded portion capacitance can be reduced, and a semiconductor laser capable of high-speed operation can be realized. (Embodiment 2) FIG. 2 is a sectional view showing an element structure of a semiconductor laser according to a second embodiment of the present invention. 201 in the figure
Is a p-InP substrate and 202 is InGa with a wavelength of 1.3 μm.
As / InGaAsP strained quantum well active layer, 203 is n-
The InP first clad layer, 204 is an n-InP second clad layer, and 205 is an InGaAsP contact layer. Further, 211 is a p-InP buried layer, 212 is an InGaAlAs buried layer for preventing diffusion, 213 is a semi-insulating InP buried layer, and 215 is InG for preventing diffusion.
The aAlAs embedded layer and 214 are n-InP embedded layers.

The manufacturing method is basically the same as that of the first embodiment, and the active layer 202 and the cladding layer 20 are formed on the substrate 201.
3 is formed, then a mesa is formed by etching, and each layer 211, 212, 21 as a buried layer is formed on the side surface of the mesa.
3,215,214 are grown, and the cladding layer 20 is further grown.
4. By growing the contact layer 205, the structure shown in FIG. 2 is obtained.

When the high-speed modulation characteristics of the semiconductor laser of this example were examined, it was possible to operate up to 20 GHz. This is because the current blocking layer serving as the buried layer is the p-InP layer 2
11, InGaAlAs layer 212, semi-insulating InP layer 2
13, InGaAlAs layer 215, n-InP layer 214
This is because the capacitance of the pn junction is small and the parasitic capacitance around the active layer can be made extremely small.

Further, in this embodiment, InG is grown by the second growth.
Since the surface of the aAlAs layer 215 is covered with the n-InP layer 214, the InGaAlAs layer 215 was not oxidized and the device could be stably manufactured.

In particular, when the (110) direction is used when forming the mesa structure as in this embodiment, the side surface of the mesa of the buried layer becomes the (111) A plane, and the impurity of Zn can be added at a high concentration. For the p-InP layer 211, the higher the doping concentration is, the p / n with the n-InP clad layer 203 is increased.
Since the rising voltage at the junction increases, the active layer 202
The efficiency of current injection into the device is increased and higher output is possible. However, in this case, there was a problem that Zn diffusion also increased. Therefore, the present embodiment using the InGaAlAs layer 212 was more effective. (Embodiment 3) FIG. 3 is a sectional view showing the device structure of a semiconductor laser according to a third embodiment of the present invention. 301 in the figure
Is a p-InP substrate and 306 is a p- lattice-matched to InP.
InAlAs clad layer, 306 'is p- _In0.4Al
0.6 As high band gap layer, 302 is InGaAs
/ InGaAlAs quantum well active layer, 307 'is n-I
n _0.4 Al _0.6 As high band gap layer, 307 is n
-InAlAs cladding layer, 305 is n-InGaAs
It is a contact layer. Further, 312 is an In _0.35 Al _0.65 As embedded layer for preventing diffusion, and 313 is a semi-insulating layer I.
nP buried layer, 315 is InGaA for diffusion prevention
The 1As buried layer 316 is a p-InP buried layer (reverse bias layer).

As the manufacturing method, p
-Type cladding layer 306, p-type high band gap layer 30
6 ', active layer 302, n-type high band gap layer 30
After growing a double heterostructure consisting of 7 ', n-type cladding layer 307 and further growing a contact layer 305 thereon, mesas are formed by etching to reach the substrate 301, and each layer 312 as a buried layer is formed on the side surface of the mesa. , 31
By growing 3,315,316, the structure shown in FIG. 3 is obtained.

When the high-speed modulation characteristics of the semiconductor laser of this example were examined, it was possible to operate up to 30 GHz. This is because the active layer 302 can operate at high speed with InGaAs / I.
It is formed of nGaAlAs quantum wells and is p-In
_0.4 Al _0.6 As high band gap layer 306 'and n-
The In _0.4 Al _0.6 As high band gap layer 307 ′ prevents carriers from overflowing into the cladding layers 306 and 307 due to Auger excitation, and has a larger band gap than the high band gap layers 306 ′ and 307 ′. In _0.35 Al _0.65 As layer This is because the leakage of carriers to the buried layer can be prevented by 312, so that the current injection efficiency is high and the differential quantum efficiency is high.

Further, the differential quantum efficiency η of the laser of this embodiment
The temperature dependence of η (75 ° C) / η (25
C.) to 0.85, and η (7 of the conventional InP-based laser
5 ° C./η (25 ° C.) to 0.65, which was a significant improvement. Also in the semiconductor laser of this embodiment, p
-In _0.4 Al _0.6 As the high bandgap layer 306 '
And n-In _0.4 Al _0.6 As high band gap layer 30
The cladding layers 306 and 30 by Auger excitation by 7 '
This is because the overflow of carriers into No. 7 can be prevented, and further, the leakage of carriers into the buried layer can be prevented by the In _0.35 Al _0.65 As layer 312 having a band gap larger than that of the high band gap layers 306 ′ and 307 ′.

The present invention is not limited to the above embodiments. The composition of the diffusion prevention layer is not limited to the composition described in the embodiments, but may be represented by the general formula In _1-xy Ga _x A
It may be a composition as defined in _{l y As (0 ≦ x ≦} 1,0 ≦ y ≦ 1). Further, in the embodiment, Fe-doped InP is used for the high resistance semi-insulating InP layer.
r, V, Mn, Co, Ti or a combination thereof may be used as an additive to the high resistance layer. Also, p-I
Although Zn is used as the impurity for the nP layer, Cd, Mg, or a combination thereof may be used as the p-type impurity in addition to Zn.

In this embodiment, InGaAs is used as the active layer.
P / InGaAsP, InGaAs / InGaAsP,
Although the InGaAs / InGaAlAsP quantum well structure is used, the quantum well structure is not limited to these, and it is needless to say that a quantum well structure of a structure other than these may be used, a bulk active layer, or the like.

In this embodiment, InP was used as the substrate, but the same effect could be obtained when GaAs was used as the substrate. In addition to this, as a substrate, GaP or In
Not to mention III-V group compound semiconductors such as As, Si and S
A group IV semiconductor such as iGe or a group II-VI compound semiconductor may be used. Further, in the embodiment, the light emitting region including the active layer is formed in a mesa type, and the buried layer is formed on the side surface of the mesa portion. However, not limited to this, a groove is formed in at least one of the light emitting regions and The structure may be such that a buried layer is formed. In addition, various modifications can be made without departing from the scope of the present invention.

[0028]

As described above in detail, according to the present invention, a semi-insulating InP layer and an InP provided between the InP layer and the light emitting region are used as a buried portion for embedding the side surface of the light emitting region. Has a large band gap, InGaAlAs
Since the diffusion prevention layer is used, the F in the semi-insulating InP layer is
It is possible to prevent the interdiffusion of Zn in the e and p-InP layers, keep the resistivity of the semi-insulating InP layer high, and realize a buried semiconductor laser that has a small leakage current and can operate up to a high output. Becomes

[Brief description of drawings]

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

FIG. 2 is a sectional view showing a device structure of a semiconductor laser according to a second embodiment.

FIG. 3 is a sectional view showing a device structure of a semiconductor laser according to a third embodiment.

FIG. 4 is a p-InP layer and semi-insulating InP according to the present invention.
The figure which shows the mutual diffusion between layers.

FIG. 5 is a p-InP layer and a semi-insulating InP in the conventional example.
The figure which shows the mutual diffusion between layers.

[Explanation of symbols]

101, 201 ... n-InP substrate 102 ... InGaAsP / InGaAsP quantum well active layer 103, 203 ... p-InP first clad layer 104, 204 ... p-InP second clad layer 105 ... p-InGaAs contact layer 111, 211 ... p-InP buried layer 112,212,215,315 ... InGaAlAs buried layer 113,213,313 ... Fe-added semi-insulating InP buried layer 114,214 ... n-InP buried layer 202 ... InGaAs / InGaAsP strained quantum well active layer 205 ... InGaAsP contact layer 301 ... p-InP substrate 302 ... InGaAs / InGaAlAs quantum well active layer 305 ... n-InGaAs contact layer 306 ... p-InAlAs clad layer 307 ... n-InAlAs clad layer 306 _{'... p-In 0.4 Al 0.6} As the high bandgap layer _{307' ... n-In 0.4 Al} 0.6 As the high bandgap layer 312 ... In _0.35 Al _0.65 As buried layer 316 ... p-InP buried layer (reverse bias layer)

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshihiro Kokubun No. 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki City, Kanagawa Prefecture Corporate Research & Development Center

Claims (1)

[Claims] 1. A light emitting region including an active layer formed on a substrate, and a buried portion filling a side surface of the light emitting region. The buried portion includes a semi-insulating InP layer and the InP layer. An In _1-xy Ga _x Al _y As diffusion prevention layer (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) having a bandgap larger than that of InP provided between the layer and the light emitting region. Characteristic semiconductor laser.