JPH10107368A - Manufacture of semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor laser, having a P-type current stop layer which is sufficiently thick to display a sufficient current constriction effect and easily formed for high yield, without deteriorating the semiconductor laser in characteristics and reliability. SOLUTION: A semiconductor laser has such a structure that a stripe-like SiO2 film 10 is formed on the surface of an N-type InP substrate 11, a growth film which comprises an active layer 3 is selectively formed using the stripe-like SiO2 film 10 as a mask, then the SiO2 film 10 is removed, the surface of the N-type InP substrate 1 is etched, and a P-type current stop layer and an N-type current stop layer are formed on a region, other than a light-emitting region. Therefore, a current stop layer of superior crystal can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a buried semiconductor laser and a method of manufacturing the same.

[0002]

2. Description of the Related Art A buried semiconductor laser having a PNPN thyristor structure formed on both sides of an active layer and having a current confinement effect is currently widely used in semiconductor laser structures for optical communication applications and the like. However, in order to obtain a sufficient current confinement effect, it is necessary to form the current confinement layers on both sides of the active layer relatively thick. For example, in the device described in JP-A-62-61381 "Semiconductor laser", a P-type dopant is implanted into an N-type substrate by diffusion or ion implantation to form a P-type current blocking layer, and then formed by crystal growth. By forming a thick P-type current blocking layer together with the P-type current blocking layer, the current confinement effect is to be improved.

[0003] The above conventional example will be described in detail with reference to the drawings. Japanese Patent Application Laid-Open No. Sho 62-61381 "Semiconductor Laser" shows two structural examples of the semiconductor laser in FIG.
(A) and (b). The element shown in FIG.
After a P-type dopant is implanted into the N-type InP substrate 1 by diffusion (or ion implantation) to form a P-type diffusion (or ion implantation) layer 5b, the active layer 3 and the P-type InP
The mesa region M composed of the cladding layer 4 and the InGaAsP cap layer 8a is replaced with a P-type diffusion (or ion-implanted) layer 5b.
Are formed on the N-type InP substrate 1 on which the P-type current blocking layer 5a and the N-type current blocking layer 6 are formed on the side surface of the mesa region M and the P-type diffusion (or ion implantation) layer 5b. It has a formed structure.

On the other hand, in the semiconductor laser shown in FIG. 3B, a P-type dopant is diffused (or ion-implanted) into the N-type substrate 1 before the mesa region M is formed.
It has a structure in which a P-type diffusion (or ion implantation) layer 5b is formed. Each element has a structure in which P-type and N-type current blocking layers are formed on a diffusion (or ion implantation) layer.

[0005]

The first problem is that, in the above-described conventional semiconductor laser, as shown in FIGS. 3A and 3B, N-type InP is diffused or ion-implanted.
Since a P-type dopant was implanted into the substrate 1 to form a P-type diffusion (or ion-implanted) layer 5b, and a P-type current blocking layer 5a and an N-type current blocking layer 6 were formed thereon, the device characteristics and This leads to deterioration in reliability.

The reason is that when a P-type dopant is diffused or ion-implanted, point defects and dislocations are unavoidably introduced into the crystal, and the P-type current blocking layer 5a and the N-type current blocking layer formed thereon are inevitable. This is because the crystal quality of No. 6 is deteriorated. For this reason, a leak current occurs via a crystal defect at the PN junction interface between the P-type current blocking layer 5a and the N-type current blocking layer 6, and a sufficient current blocking effect cannot be obtained, leading to deterioration of device characteristics. . In addition, the leak current causes the growth of crystal defects, and further increases the leak current, which leads to deterioration of device reliability.

The second problem is that the P-type diffusion (or ion implantation) layer 5b formed by diffusion or ion implantation is not accurately formed on both sides of the active layer 3, and the current confinement effect is deteriorated. It is to be. For example, when the region not diffused is narrowed in order to improve the current confinement effect, a P-type diffusion (or ion implantation) layer 5b is formed under the active layer 3 so that a current can be effectively transmitted to the active layer 3. Failures that cannot be injected occur frequently. Conversely, if the non-diffused region is formed relatively wide in an attempt to reduce this defect, the thin region of the P-type current blocking layer 5a becomes
This is located on a region where the mold diffusion (or ion implantation) layer 5b is not formed, and a defect occurs in which a sufficient current confinement effect cannot be obtained.

The reason is that a step of forming a P-type diffusion (or ion implantation) layer 5b and a mesa region M including an active layer 3 are formed.
Are formed independently of each other, the misalignment of the masks in both the steps significantly shifts the formation positions of the P-type diffusion (or ion-implanted) layer 5b and the mesa region M, and causes the above-described failure. It depends.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor laser capable of forming a P-type current blocking layer having a thickness necessary for obtaining a sufficient current confinement effect with good yield without deteriorating device characteristics and reliability, and manufacturing thereof. It is to provide a method.

[0010]

The semiconductor laser of the present invention In order to achieve the above object, according to the SiO ₂ film formed on the N-type InP substrate surface as a mask, after selectively forming a growth film including an active layer S
The surface of the N-type InP substrate from which the iO ₂ film was removed and the SiO ₂ film was removed was etched, and a P-type current blocking layer and an N-type current It has a structure in which a blocking layer is formed.

Further, the method for manufacturing a semiconductor laser according to the present invention comprises the steps of:
Selectively forming a growth film including an active layer on the surface of the N-type InP substrate by using the SiO ₂ film formed on the surface of the N-type InP substrate as a mask, and so as to make the side surface of the growth film thinner than other regions. After forming the SiO ₂ film on the entire surface, etching the SiO ₂ film to the extent that only the SiO ₂ film on the side of the growth film is removed, applying a resist on the entire surface,
Removing the SiO ₂ film on the surface of the type InP substrate, thereby removing the resist to the extent that it covers the side surface and upper portion of the growth film, and using the resist as a mask,
At least a step of etching the surface of the P substrate and a step of removing the resist and forming a P-type current blocking layer and an N-type current blocking layer using the SiO ₂ film above the mesa region M as a mask are included.

According to the present invention, a mesa-like growth film including an active layer is selectively formed on the surface of an N-type InP substrate, and growth films are formed on both sides of the mesa-like growth film. Then, a P-type current blocking layer and an N-type current blocking layer are formed in a region excluding the upper portion of the mesa growth film including the active layer, including the etched region. Thus, a semiconductor laser having a structure in which a P-type InP layer and a cap layer are formed is obtained.

Further, according to the present invention, a pair of stripe-shaped masks is provided on the surface of the N-type InP substrate, and a mesa-like growth film including an active layer is selectively formed on the surface of the N-type InP substrate, and growth films are formed on both sides thereof. Forming a mask, forming a mask on the mesa growth film and the growth film on both sides thereof, applying a resist on the entire surface, and then removing the mask on the surface of the N-type InP substrate and removing the resist thereon. Etching the surface of the N-type InP substrate using the resist remaining as a mask to cover the mesa-like growth film and the growth films on both sides thereof, and forming a portion other than the upper portion of the mesa-like growth film including the remaining resist and the active layer. Removing the mask that has been removed, forming a P-type current blocking layer and an N-type current blocking layer in a region other than above the mesa-like growth film, and removing the mask above the mesa-like growth film to form a P-type current blocking layer over the entire surface. I Method for manufacturing a semiconductor laser and a step of forming a P layer and the cap layer.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a first embodiment of the present invention will be described.
This will be described in detail with reference to the drawings. First, FIG.
According to (e), the manufacturing method of the semiconductor laser of this embodiment is
explain. As shown in FIG. 1A, an N-type InP substrate 1
SiO on the surface_TwoForm a film and remove it in a stripe
This SiO_TwoN-type I using stripe mask 9a
An N-type InP cladding layer 2, an active layer 3,
P-type InP cladding layer 4, InGaAsP cap layer 8
The mesa region M made of a is selectively formed. Next, FIG.
As shown in FIG. 2B, only the side surface of the mesa region M has another region.
SiO 2_TwoFilm is SiO_TwoStrike
Over the mask 9a and the top and sides of the mesa region M.
After the formation, SiO on the side surface of the mesa region M_TwoAll of the membranes
SiO_Two Etch the film. Next, FIG.
As shown in (c), the resist 11 was applied to the entire surface.
And SiO_TwoBy removing the stripe mask 9a
Therefore, the registration is performed so as to cover the side surface and the upper portion of the mesa region M.
Remove the strike. Next, as shown in FIG.
The resist 11 formed so as to cover the side surface and the upper portion of the region M is masked.
The surface of the N-type InP substrate 1 is etched as a mask. Next
Next, as shown in FIG.
SiO above region M_TwoP-type current blocking using film 10 as a mask
Stop layer 5a, N-type current blocking layer 6, and InGaAsP cap.
Forming layer 8b.

Therefore, in the semiconductor laser of the present embodiment, since the P-type current blocking layer 5a and the N-type current blocking layer 6 are not formed at least on the diffusion layer, good crystallinity is obtained without deteriorating the crystallinity. It has a structure that can realize element characteristics and reliability.

In the method of manufacturing a semiconductor laser according to the present embodiment, an N-type I-type semiconductor laser is formed by using the SiO ₂ stripe mask 9a used for forming the mesa region M as shown in FIG.
The resist 11 used as a mask when etching the surface of the nP substrate 1 is removed. Therefore, N-type InP
When the surface of the substrate 1 is etched, the etched region is necessarily a region where the mesa region M is not formed. As a result, the P-type current blocking layer 5a is formed under the mesa region M, which has conventionally occurred, and a defect that a current cannot be effectively injected into the active layer 3 and a partial region of the P-type current blocking layer become thin. It is possible to improve a defect that the PNPN thyristor is turned on and a sufficient current confinement effect cannot be obtained.

It should be noted that the semiconductor laser of the present embodiment
By etching the surface of the nP substrate 1, the P-type current blocking layer 5a can be formed to have a sufficiently large thickness as compared with the case where the nP substrate 1 is not etched. Needless to say, a sufficient current confinement effect can be obtained. In the above embodiment, an example in which the SiO ₂ film is used as a mask has been described, but a nitride film may be used as a mask.

Next, an example of a method of manufacturing a semiconductor laser according to the present embodiment will be described with reference to FIGS. FIG.
As shown in (a), the surface of the N-type InP substrate 1 has a thickness of 20 μm.
A 100 angstrom SiO ₂ film is formed and stripped, and this SiO ₂ stripe mask 9a is formed.
A so-called MQW (multiple quantum well) activity comprising an N-type InP cladding layer 2 having a thickness of 0.3 μm on the surface of an N-type InP substrate 1 and two InGaAsPs having a total thickness of 0.1 μm and different band gaps. Layer 3 and thickness 0.9
μm P-type InP cladding layer 4 and 0.3 μm thick I
A mesa region M made of the nGaAsP cap layer 8a is selectively formed. Next, as shown in FIG.
So that the thickness is 1000 angstroms on the side surface and 2000 angstroms on the other surface.
An SiO ₂ film is formed on the SiO ₂ stripe mask 9a and over the upper and side surfaces of the mesa region M. Then, the SiO ₂ film is etched by about 1200 angstroms so that only the SiO ₂ film on the side surface of the mesa region M is removed. Next, as shown in FIG. 1C, after applying a resist on the entire surface, the SiO ₂ stripe mask 9a is removed, so that the resist is removed so as to cover the side surfaces and the upper portion of the mesa region M. Next, as shown in FIG. 1D, the surface of the N-type InP substrate 1 is wet-etched (or dry-etched) with a depth of 0.5 μm using the resist 11 formed so as to cover the side surface and the upper portion of the mesa region M as a mask. Next, FIG.
As shown in (e), the resist 11 is removed, and the SiO ₂ film 10 above the mesa region M is used as a mask to form a 1 μm thick P
Current blocking layer 5a and 0.8 μm thick N-type current blocking layer 6
Then, an InGaAsP cap layer 8b having a thickness of 0.3 μm is formed.

As described above, the semiconductor laser of this embodiment has
By etching the surface of the nP substrate 1 to a depth of 0.5 μm, the P-type current blocking layer 5a can be doubled from 0.5 μm to 1 μm as compared with the case without etching, so that a sufficient current confinement effect can be obtained. It is possible.

Next, a second embodiment of the present invention will be described in detail with reference to the drawings. First, FIGS. 2A to 2E
The manufacturing method of the semiconductor laser according to the present embodiment will be described below. As shown in FIG. 2 (a), disconnect them in stripes to form a 2000 Å thick of SiO ₂ film in the N-type InP substrate 1, a pair of SiO ₂ stripe masks 9b, these SiO ₂ stripe Mask 9
A so-called MQW (multiple quantum well) activity comprising an N-type InP cladding layer 2 having a thickness of 0.2 μm and two InGaAsPs having a total thickness of 0.1 μm and having different band gaps on the surface of the N-type InP substrate 1 other than b. Layer 3 and thickness 0.3
A mesa region M composed of a P-type InP cladding layer 4 of μm is selectively formed. In this case, as shown in FIG. 2A, the structure has a mesa region M at the center and a mesa growth film left outside the mesa region M. Next, as shown in FIG. 2B, the surface of the side surface of the mesa region M and the surface of the side surface of the growth film formed outside the SiO ₂ stripe mask 9b have a thickness of 1000 Å and the other regions have a thickness of 2,000 Å. The SiO ₂ film 10 is formed such that And
To the extent that only the SiO ₂ film formed on the side surfaces of the mesa region M and the growth film formed outside the SiO ₂ stripe mask 9b is removed, the entire surface of the SiO ₂ film is etched by about 1200 Å. Next, as shown in FIG. 2C, a resist is applied to the entire surface, and then the SiO ₂ stripe mask 9b is removed to cover the side surfaces and the upper portion of the growth film formed outside and the side surfaces and the upper portion of the mesa region M. The resist is removed in the remaining area. Next, FIG.
As shown in (d), the resist 11 is used as a mask to form N-type In.
The surface of the P substrate 1 is wet-etched (or dry-etched) with a depth of 0.5 μm. Next, as shown in FIG. 2E, the resist 11 is removed, and the SiO 2 on the mesa region M is removed.
₂ N-type InP substrate 1 in a region subjected to wet etching (or dry etching) using film 10 as a mask.
P-type current blocking layer 5a having a thickness of 1 μm
To form Then, a thickness of 0.8 is formed on the P-type current blocking layer 5a.
A μm N-type current blocking layer 6 is formed. Next, the SiO ₂ film 10 above the mesa region M is removed, and a P-type InP layer 7 having a thickness of 2 μm and a P-type InGa
An AsP cap layer 8a is formed. Thus, a semiconductor laser having a double channel planar buried heterostructure (DCPBH structure) is completed.

Therefore, in the semiconductor laser of this embodiment, since the P-type current blocking layer 5a and the N-type current blocking layer 6 are not formed at least on the diffusion layer, good crystallinity is not caused. It has a structure that can realize element characteristics and reliability.

In the method of manufacturing a semiconductor laser according to the present embodiment, the resist 11 is removed by using the SiO ₂ stripe mask 9b used for forming the mesa region M as shown in FIG. . And this resist 11 is N-type I
It is used as a mask when etching the surface of the nP substrate 1. Therefore, when the surface of the N-type InP substrate 1 is etched, the etched region is necessarily a region where the mesa region M is not formed. As a result, the P-type current blocking layer 5a is formed below the mesa region M, which has conventionally occurred, and
It is possible to improve a defect that a current cannot be effectively injected into the active layer 3 and a defect that a sufficient current confinement effect cannot be obtained because only a part of the P-type current blocking layer 5a is thinned.

It should be noted that the semiconductor laser of the present embodiment
By etching the surface of the nP substrate 1 to a depth of 0.5 μm, the P-type current blocking layer 5a can be doubled from 0.5 μm to 1 μm as compared with the case without etching, so that a sufficient current confinement effect can be obtained. Made possible.

The semiconductor laser according to the second embodiment has a D
Since the semiconductor laser has the CPBH structure, the turn-on of the PNPN thyristor in the buried region is less likely to occur than in the semiconductor laser according to the first embodiment, so that there is an advantage that the current can be effectively blocked.

[0025]

The first effect of the present invention described above is that a P-type current blocking layer and an N-type current blocking layer are formed on both sides of a mesa region to be a light emitting region in a growth film including an active layer. Since the crystallinity is not deteriorated unlike a conventional semiconductor laser, a semiconductor laser having good device characteristics and reliability can be realized.

The reason is that the semiconductor laser of the present invention does not form the P-type current blocking layer and the N-type current blocking layer on the diffusion layer as in the conventional case, but removes the surface of the N-type InP substrate by etching. Since the P-type current blocking layer and the N-type current blocking layer have a structure formed thereon, the P-type current blocking layer and the N-type current blocking layer have enormous amounts as in the conventional semiconductor laser. This is because a current blocking layer made of a high-quality crystal can be formed without a fear of introducing a crystal defect.

The second effect is that a defect such as the formation of a P-type current blocking layer below the mesa region as in a conventional semiconductor laser, or a region where the P-type current blocking layer is thin is formed by P-type diffusion (or It is possible to improve a defect in which a sufficient current confinement effect cannot be obtained due to being located on a region where the (ion-implanted) layer is not formed.

The reason is that the semiconductor laser of the present invention uses the SiO ₂ stripe mask used for forming the mesa region and removes the resist 11 used as a mask when etching the surface of the N-type InP substrate. I have. The step of forming the mesa region and the step of etching the surface of the N-type InP substrate are not independent as in a conventional semiconductor laser, but are performed through the same SiO ₂ mask. As a result, it is possible to improve a defect in which a current cannot be effectively injected into the active layer and a defect in which a sufficient current confinement effect cannot be obtained because only a part of the P-type current blocking layer 5a is thinned. it can.

As a third effect, the semiconductor laser of the present invention has a structure in which a sufficiently thick P-type current blocking layer is formed without the current injected into the mesa region leaking to the P-type current blocking layer. It has a sufficient current confinement effect.

The reason is that in the semiconductor laser of the present invention, even if the growth film in the mesa region is formed thin,
By etching the p-type InP substrate, the p-type current blocking layer can be formed without forming the p-type current blocking layer above the active layer.
This is because a sufficiently thick P-type current blocking layer can be formed without increasing the contact area between the P-cladding layer and the P-type current blocking layer, that is, without leaking the injected current to the P-type current blocking layer.

[Brief description of the drawings]

FIGS. 1A to 1E show a first example of a semiconductor laser according to the present invention.
It is sectional drawing which shows the manufacturing process and structure of 2nd Embodiment.

FIGS. 2A to 2E show a second example of the semiconductor laser of the present invention.
It is sectional drawing which shows the manufacturing process and structure of 2nd Embodiment.

FIGS. 3A and 3B are cross-sectional views showing a conventional semiconductor laser.

[Explanation of symbols]

Reference Signs List 1 N-type InP substrate 2 N-type InP cladding layer 3 Active layer 4 P-type InP cladding layer 5 a P-type current confinement layer 5 b P-type diffusion layer 6 N-type current confinement layer 7 P-type InP layer 8 a P-type InGaAsP layer cap layer 8 b P-type InGaAsP layer cap layer 9a SiO ₂ stripe mask 9b 1 pair of SiO ₂ stripe masks 10 SiO ₂ film 11 resist 12 diffusion layer mask

Claims (4)

[Claims] 1. A mesa-like growth film including an active layer is selectively formed on a surface of an n-type InP substrate, and the surface of the n-type InP substrate other than the mesa-like growth film is etched. A semiconductor laser having a structure in which a P-type current blocking layer and an N-type current blocking layer are formed in a region excluding the mesa-shaped growth film. 2. A step of providing a stripe-shaped mask on the surface of an N-type InP substrate, selectively forming a mesa-like growth film including an active layer on the surface of the N-type InP substrate, and forming a mask on the mesa-like growth film. Forming, applying a resist on the entire surface, removing the mask on the surface of the N-type InP substrate and removing the resist applied thereon, and using the resist remaining over the mesa growth film as a mask, Etching the surface of the N-type InP substrate, and removing the resist to form a P-type current blocking layer and an N-type current blocking layer on the side surface of the mesa growth film and the N-type InP substrate surface. Manufacturing method of a semiconductor laser. 3. A mesa-like growth film selectively including an active layer on a surface of an N-type InP substrate and growth films formed on both sides thereof.
N-type InP between the mesa growth film and the growth films on both sides
The surface of the substrate is etched, and a P-type current blocking layer and an N-type current blocking layer are formed in a region excluding the upper portion of the mesa growth film including the active layer, including the etched region. A semiconductor laser having a structure in which a layer and a cap layer are formed. 4. A step of providing a pair of stripe-shaped masks on the surface of the N-type InP substrate and selectively forming a mesa-like growth film including an active layer on the surface of the N-type InP substrate and growth films on both sides thereof; Forming a mask on the mesa growth film and the growth film on both sides thereof, applying a resist on the entire surface, removing the mask on the surface of the N-type InP substrate and removing the resist thereon, Etching the surface of the N-type InP substrate using the resist remaining as a mask covering the film and the growth film on both sides thereof, and removing the mask formed on the mesa-like growth film including the remaining resist and the active layer, except for the upper portion. Forming a P-type current blocking layer and an N-type current blocking layer in a region other than the upper portion of the mesa growth film;
The mask above the mesa-like growth film is removed, and P-type In
A method of manufacturing a semiconductor laser, comprising: forming a P layer and a cap layer.