JPH065969A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a low threshold value and a stable lateral mode in a buried semiconductor laser. CONSTITUTION:An active region made of an optical waveguide layer 3 and a quantum well active layer 4 is buried in a surface A (111) between clad layers 2 and 5 on an n-type GaAs substrate 1 (001) having the surface A (111), a cap layer 6 is provided on the layer 5, and a current block layer 7 is provided on a surface (001) except the surface A (111). Since crystal orientation of a surface for crystal growth are decided to the surfaces (001) and A (111), when growing conditions are decided, crystal growth velocities on the surfaces are hence decided, and a thickness of the film, a width of the active region can be finely controlled. Further, since the active region is formed only on an oblique surface of the surface A (111), recombination of a current diffused in a lateral direction in the upper clad layer of an injected current can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an embedded semiconductor laser device, and more particularly to a V formed on a slope of a (111) A plane of a GaAs substrate or on a (111) B plane and a (001) plane.
The present invention relates to a semiconductor laser device having a structure for confining light and carriers on the bottom of a V-shaped groove.

[0002]

2. Description of the Related Art Conventionally, some structures of buried type semiconductor lasers have been proposed and can be roughly classified into three structures. The first structure is that a ridge is formed by etching after crystal growth including an active layer on a (001) plane substrate, and a buried layer is formed by regrowth on the side surface of the ridge which is an active region. is there. In this structure, the thickness of the active layer, the embedding width, and the refractive index of the embedding crystal can be selected independently, and the degree of freedom in device design is high. In the second structure, a groove, a ridge and the like are formed on a (001) plane substrate by etching, and then crystal growth is performed to bend the active layer on the side surface of the ridge so that the active region on the ridge becomes an upper clad layer. Or the active region at the bottom of the trench is embedded in the lower cladding layer. In the case of this structure, it can be manufactured by one crystal growth. In the third structure, first, crystal growth including the active layer is performed, and then impurities are diffused while leaving a necessary active layer width to mix the active layer and the clad layer to form a mixed crystal in the active region. It is embedded between areas. In the case of this structure as well, it can be manufactured by one-time crystal growth, and since it is a planar type, it is highly versatile.

[0003]

By the way, in the second structure, the active region is buried by the bending of the active layer on the side surface of the ridge or groove, but in the case of normal crystal growth, at the end of the ridge or groove, Since the growth rate on the higher-order surface is different from that on the flat portion, nonuniformity of the thin film occurs. Also,
The thin film on the side surface of the ridge or groove is determined by the angle of the slope, and the width of the active layer and the effective refractive index in the ridge portion vary depending on the shape of the ridge. It is difficult to manufacture a ridge with high accuracy.

Further, since the active layer is formed on the (001) plane other than the ridge, the current diffused in the lateral direction in the upper cladding layer flows into the active layer in the lateral flat portion of the ridge and recombines. Since the light generated here does not contribute to the stimulated emission of the laser in the active region on the ridge, the current diffused in the lateral direction becomes a leakage current, which causes a problem of increasing the threshold value. An object of the present invention is to provide an embedded semiconductor laser device that can obtain a stable lateral mode with a low threshold value.

[0005]

In order to achieve the above object, the present invention provides a stripe-shaped (111) extending in the [011] direction with respect to the crystal orientation of the first conductivity type GaAs substrate.
Grown on a (001) plane substrate having a slope of plane A,
In a semiconductor laser device in which an active layer sandwiched by an optical waveguide layer is provided between a first conductivity type cladding layer and a second conductivity type cladding layer, the optical waveguide layer and an active region sandwiched by the optical waveguide layer are provided. And (111) A of the (001) plane substrate
The structure is embedded on the slope of the surface.

The first conductivity type GaAs substrate is (11
1) Configuration of a semiconductor laser device in which the surface of the (001) surface on one side across the A surface is made the second conductivity type by impurity diffusion and the second conductivity type semiconductor layer is formed on the (001) surface on the other side. It is in.

The first conductivity type GaAs substrate is (11
1) Configuration of a multi-beam type semiconductor laser device having a plurality of stripe-shaped convex portions composed of an A-plane slope and a (001) plane, and an active region being embedded on the plurality of (111) A-plane slopes It is in.

A semiconductor laser device according to still another invention has a second-conductivity-type buried layer and a first-conductivity-type buried layer which are sequentially stacked with a predetermined width left on a first-conductivity-type (001) plane GaAs substrate. Then, a V-shaped groove having a stripe-shaped (111) B surface extending in the [011] direction with respect to the crystal orientation of the GaAs substrate as an inclined surface and a (001) surface as a bottom surface and an upper surface is formed, An active region is embedded on the bottom of the V-shaped groove.

The side surface of the V-shaped groove formed on the GaAs substrate of the first conductivity type (001) surface is more than the optical waveguide layer of the active region buried on the bottom of the V-shaped groove. The semiconductor laser device is composed of a semiconductor layer having a low refractive index.

The first conductivity type (001) plane GaAs substrate has a striped (111) B plane as a slope (001).
It has a plurality of V-shaped groove shapes whose surfaces are a bottom surface and an upper surface,
This is a configuration of a multi-beam type semiconductor laser device in which an active region is embedded on the bottoms of a plurality of V-shaped groove shapes.

[0011]

In the case of a semiconductor laser in which the active region is embedded on the slope of the (111) A plane of the (001) plane substrate, the crystal orientations of the planes on which crystal growth is carried out are always (001) and (111) A. Therefore, if the growth conditions are determined, the crystal growth rate on each surface is determined, and the film thickness can be finely controlled by time. Therefore, since the film thickness can be made uniform on each surface, the width of the active region can be controlled by determining the height of the ridge and the crystal growth rate on each surface. The width of the active region can also be changed by controlling the height of the striped slope. Also,
Since the active region is formed only on the slope of the (111) A plane, it is possible to suppress recombination of the injected current that is laterally diffused in the upper cladding layer.

Further, a first-conductivity-type (001) plane GaAs substrate is provided with a second-conductivity-type buried layer and a first-conductivity-type buried layer, which are sequentially stacked with a predetermined width left, and has a crystal orientation of the GaAs substrate. On the other hand, a V-shaped groove shape having a stripe-shaped (111) B surface extending in the [011] direction as an inclined surface and having a (001) surface as a bottom surface and an upper surface is formed, and the bottom portion of the V-shaped groove shape is formed. In the case of a semiconductor laser in which an active region is embedded above, the width of the active region can be controlled by the V-shaped groove width and the crystal growth rate on the (001) plane. Further, current can be efficiently injected into the active region of the groove.

[0013]

EXAMPLES Examples of the present invention will be described below. FIG. 1 shows a sectional structure showing a first embodiment of a semiconductor laser device according to the present invention. In this embodiment, the n-type is the first conductivity type and the p-type is the second conductivity type. The semiconductor laser device has a (001) plane n-type GaA having a (111) A plane.
The first clad layer 2 sequentially laminated on the substrate 1;
The optical waveguide layer 3 formed on the (111) A plane, the quantum well active layer 4 sandwiched between the optical waveguide layers 3, and the second cladding layer 5.
And a cap layer 6, and the cap layer 6 serves as a current blocking layer with S on the (001) plane excluding the (111) A plane.
The i ₃ N ₄ film 7 is provided, and the Si ₃ N ₄ film 7 and (111) A
P-side electrodes 8 and (00
1) Surface n-side electrode 9 in contact with the bottom surface of the n-type GaAs substrate 1
It is configured to have and.

Manufacturing of the semiconductor laser device will be described with reference to FIG. In this production, MOCVD is used for crystal growth.
Used the method. First, (00) having a (111) A plane
1) A thickness of 1 μm composed of Se-doped A1 _0.6 Ga _0.4 As under growth conditions for growing isotropically on a plane n-type GaAs substrate 1.
m first clad layer 2 is grown (FIG. 2A). After that, under the growth condition that the growth rate becomes faster on the (111) A plane, the undoped A1 _0.3 Ga _0.7 As optical waveguide layer 3, the undoped GaAs quantum well active layer 4, and the undoped A1 _0.3
The Ga _0.7 As optical waveguide layer 3 is grown (FIG. 2B).

Next, under the growth condition of isotropic growth, the second cladding layer 5 made of Mg-doped Al _0.6 Ga _0.4 As and having a thickness of 1 μm, and the thickness of 0.1 μm made of Mg-doped GaAs.
The cap layer 6 is sequentially grown (FIG. 2C). In the ordinary MOCVD method, the V / III ratio is 60,
The growth temperature on the substrate is 700 to 800 ° C.,
Under this growth condition, the growth rate is isotropic or (00
1) The surface is fast. Further, when growing the optical waveguide layer and the quantum well active layer, the growth rate on the (111) A plane is (001) by setting the V / III ratio to 60 and the growth temperature on the substrate to 600 ° C. ) Three times as much as on the surface.

Therefore, assuming that the thickness of the optical waveguide layer on the (111) A plane is 0.1 μm and the thickness of the quantum well active layer is 100Å, the thickness of the optical waveguide layer on the (001) plane is Is 0.03 μm, and the thickness of the quantum well active layer is 30 Å. Then, due to the difference in thickness, (00
The energy gap in the well of the quantum well active layer on the 1) plane is about 1 than that of the quantum well active layer on the (111) A plane.
Since it becomes larger by 00 meV, the injected carriers are (1
11) Confined in the quantum well active layer on the A surface.

Further, the optical waveguide layer on the (001) plane is thin, and the optical waveguide layer is bent between the (111) A plane and the (001) plane, and the optical waveguide layer on the (111) A plane is formed. Is laterally embedded by the cladding layer on the (001) plane, so that the light is confined in the waveguide layer on the (111) A plane. After crystal growth, Si ₃ is formed on the entire surface as a current blocking layer.
The N ₄ film 7 is deposited to a thickness of 0.1 μm, and the Si ₃ N ₄ film 7 on the (111) A plane which becomes the current injection region is formed by photolithography.
Are removed by etching (FIG. 3D). After that, the p-side electrode 8 and the n-side electrode 9 are vapor-deposited (see FIG. 3).
(E)). As described above, the embedded laser can be easily manufactured by the substrate having the inclined surface and the selective growth.

4 and 5 show the steps of an improved method of manufacturing the semiconductor laser of the first embodiment. First, a Si ₃ N ₄ film 7 is deposited on the n-type GaAs substrate 1 and a window is opened by photolithography. Using this Si ₃ N ₄ film 7 as a mask, 0.5
.mu.m to form a Zn diffusion region 11 (FIG. 4).
(A)). After removing the Si ₃ N ₄ film 7, the Se-doped GaAs layer 12 having a thickness of 2 μm and the thickness of 0.1 is formed by the MOCVD method.
A 1 μm Mg-doped GaAs layer 13 is sequentially grown (FIG. 4B). Then, after depositing the Si ₃ N ₄ film 7 again, a window is opened by photolithography (FIG. 4).
(C)).

Then, H ₂ SO ₄ : H ₂ O ₂ : H ₂ O = 1:
Etching is performed until the Zn diffusion region 11 is reached by an 8:80 etchant to form a slope of the (111) A plane (FIG. 5D). After removing the Si ₃ N ₄ film 7 used as a mask, the same crystal growth as in the first embodiment is performed (FIG. 5E). Thereby, the Zn diffusion region 11 and the Mg
Since an npn structure is formed between the upper and lower layers of the doped GaAs layer 13, the current flow is suppressed. Therefore, the current is squeezed on the n-side as compared with the first embodiment, so that a low threshold semiconductor laser with less leakage current is obtained.

In this embodiment, the first-conductivity-type GaAs substrate is n-type and Zn and Mg are used as impurities.
Be or C, which is a type dopant, may be used. When the first conductivity type GaAs substrate is p-type, the impurity to be diffused is S
An n-type dopant such as i, Ge, Se or S is used. In this embodiment, thermal diffusion is used as the impurity introducing method, but the impurity can be introduced also by ion implantation.

Next, a second embodiment of the present invention will be described. FIG. 6 shows a sectional structure of a multi-beam semiconductor laser device to which the present invention is applied. The multi-beam semiconductor laser device includes a first clad layer 2 sequentially laminated on an n-type GaAs substrate 1 on which a plurality of striped ridges composed of (111) A plane and (001) plane are formed, and ( 11
1) An optical waveguide layer 3 formed on the A surface, a quantum well active layer 4 sandwiched between the optical waveguide layers 3, a second cladding layer 5, and a cap layer 6 are provided, and the cap layer 6 has a current As a block layer, Si ₃ N _{4 is formed on the} (001) plane except the (111) A plane.
The film 7 is provided, and the insulating region 10 is formed between each film and the (111) A plane, and the Si ₃ N ₄ film 7 and (1
11) It has a structure having a p-side electrode 8 in contact with the cap layer 6 on the A surface and an n-side electrode 9 in contact with the bottom surface of the (001) surface n-type GaAs substrate 1.

The manufacture of the multi-beam type semiconductor laser device will be described. After depositing a SiO ₂ film of 0.1 μm on the n-type GaAs substrate 1, a plurality of windows are opened in the SiO ₂ film by photolithography. On this substrate, as described in the first embodiment, (001) was formed by the MOCVD method.
S growth of 1.5 μm under the growth condition that the growth rate on the surface is fast.
By selectively growing the e-doped GaAs layer or selectively etching the GaAs substrate using a sulfuric acid-based etchant, the (111) A plane and the (00) plane are formed.
1) Form a plurality of striped ridges each having a surface. Here, the distance between (111) A planes is set to 3 μm or more so that the beams do not optically interact with each other.

By performing crystal growth on this substrate in the same manner as in the first embodiment, active regions are formed on a plurality of (111) A planes. After crystal growth, protons are injected into the active region to a depth of 1.2 μm to provide the insulating region 10. Then-deposit a the Si ₃ N ₄ film 7 on the entire surface the Si ₃ N ₄ film 7 on by photolithography (111) A plane is removed by etching. After that, after the p-side electrode 8 is deposited, the p-side electrode 8 between the active regions is removed by etching or lift-off, and the n-side electrode 9 is deposited. This produces a multi-beam semiconductor laser that can be individually addressed on a single chip.

Since the active layer is a quantum well,
Since the TE mode is dominant in the emitted light, and the adjacent active regions have opposite inclinations with respect to the substrate, the polarization planes of the light emitted from the adjacent active regions are different. Next, a third embodiment of the present invention will be described. FIG. 7 shows a sectional structure of an embedded semiconductor laser to which the present invention is applied. The layers having the same functions as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

The semiconductor laser device has a first conductivity type (00
1) A plane-type GaAs substrate 1 has a first-conductivity-type buried layer 22 and a second-conductivity-type buried layer 23, which are sequentially stacked with a predetermined width left, and has a crystal orientation [0
[11] B plane extending in the [11] direction is a slope, and a V-shaped groove shape 24 having a (001) plane as a bottom surface and an upper surface is provided and embedded on the bottom of this V-shaped groove shape. It is configured to have an active region 20 that is formed. The manufacture of the semiconductor laser device will be described with reference to FIG. In this production, the MOCVD method was used for crystal growth.

First, S is formed on a (001) plane GaAs substrate 1.
A stripe 21 having a width of 3 μm was formed by depositing 1000 liters of an iO ₂ film and extending in the [011] direction by photolithography.
Are formed (FIG. 8A). A 0.1 μm thick first burying layer 22 made of Mg-doped GaAs and a second burying layer 1.2 μm thick made of Se-doped Al _0.4 Ga _0.6 As were formed on this substrate by using a stripe-shaped SiO ₂ film as a mask. Grow 23. In the MOCVD method, the growth rate has anisotropy, and under normal growth conditions for growing on the (001) plane, it does not grow on the (111) B plane.
₂ Growth in the (111) direction on the film 11 does not occur, and Si
A V-shaped groove shape is obtained in which the both ends of the O ₂ film are the starting points of the slope and the (111) B plane is the slope (FIG. 8B).

After the SiO ₂ film extending in a stripe shape is removed by etching, the cladding layer 2 made of Se-doped Al _0.6 Ga _0.4 As and having a thickness of 1 μm is grown under the growth condition of growing only on the (001) plane. , Undoped Al _0.3
An optical waveguide layer 3 made of Ga _0.7 As and having a thickness of 0.1 μm, a quantum well active layer 4 made of undoped GaAs and having a thickness of 0.01 μm, and an optical waveguide layer 3 made of undoped Al _0.3 Ga _0.4 As and having a thickness of 0.1 μm. , Mg-doped Al _0.6 Ga _0.4 A
1 μm thick clad layer 5 made of s, Mg-doped Ga
A cap layer 6 made of As and having a thickness of 0.1 μm is sequentially laminated (FIG. 8C). In this case as well, the growth in the (111) direction is not performed on the (111) B surface, but the growth is performed in the (001) direction on the (001) surface, so that the V-shaped groove 24 is filled with the active region.

In the structure described here, the second buried layer 2
Since the AlAs mixed crystal ratio of No. 3 is higher than the AlAs mixed crystal ratio of the optical waveguide layer 3, the refractive index of the second buried layer 23 is low, and the light propagating in the optical waveguide in the groove is also confined laterally. It is a refractive index guiding structure that can be used. A Si ₃ N ₄ film 7 is formed on this sample.
And deposit Si _{3 on the} groove by photolithography.
After removing the N ₄ film, the p-side electrode 8 and the n-side electrode 9 are vapor-deposited.

According to the present embodiment, the current injected from the cap layer 6 in the groove is a component of the effective current flowing into the active region 20 and the leakage current flowing in the second buried layer 23 on the side surface of the V-shaped groove. However, since the AlAs mixed crystal ratio of the n-type second buried layer 23 and the p-type clad layer 2 is high and the turn-on voltage is higher than that of the active region 20, the n-type buried layer and the p-type clad layer are formed. Due to the formed pn junction, it becomes difficult for the current to flow into the second buried layer 23, and the current is efficiently injected into the active region 20. Further, because of the npn structure between the buried layers 22 and 23 and the substrate, the current passing through other than the groove is suppressed.

Next, a fourth embodiment of the present invention will be described. FIG. 9 shows a sectional structure of a multi-beam semiconductor laser to which the present invention is applied. 1 SiO ₂ film on n-type GaAs substrate
000Å deposit and photolithography [01
1] direction, a plurality of stripes with a width of 3 μm
It is formed at m intervals. After that, crystal growth similar to that of the third embodiment is performed to form a plurality of V-shaped grooves 24a and 24a.
The active region 20 is embedded in b. Next, Si ₃ N _{4 on the} entire surface
The film is deposited and the Si of the groove is formed by photolithography.
_{The 3} N ₄ film is removed. After that, the p-side electrode is vapor-deposited, the electrodes between the active regions are removed by etching or lift-off, and the n-side electrode is vapor-deposited. Thus, individually addressable multi-beam semiconductor lasers are manufactured on one semiconductor laser chip.

[0031]

According to the present invention, since the width of the active region and the thickness of the active layer in the ridge and the groove can be precisely controlled, it is possible to obtain a stable lateral mode with a low threshold value. You can In addition, since the active layer is not formed in regions other than the active region or there is no current path to the active layer in regions other than the active region, leakage current that does not contribute to stimulated emission of laser can be suppressed.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the manufacturing procedure of the semiconductor laser device of the first embodiment.

FIG. 3 is a cross-sectional view showing the manufacturing procedure following FIG.

FIG. 4 is a cross-sectional view showing another manufacturing procedure of the semiconductor laser device of the first embodiment.

FIG. 5 is a cross-sectional view showing the manufacturing procedure following FIG.

FIG. 6 is a sectional view of a multi-beam semiconductor laser device according to a second embodiment of the present invention.

FIG. 7 is a sectional view of a semiconductor laser device according to a third embodiment of the present invention.

FIG. 8 is a cross-sectional view showing the manufacturing procedure of the semiconductor laser device according to the third embodiment.

FIG. 9 is a sectional view of a multi-beam semiconductor laser according to a fourth embodiment of the present invention.

[Explanation of symbols]

1 n-type GaAs substrate, 2 n-type Se-doped AI _0.6 G
a _0.4 As clad layer, 3 undoped AI _0.3 Ga _0.4
As optical waveguide layer, 4 undoped GaAs quantum well active layer, 5 p-type Mg-doped AI _0.6 Ga _0.4 As clad layer, 6 p-type Mg-doped GaAs cap layer, 7 Si
₃ N ₄ film, 8 p-side electrode, 9 n-side electrode, 10 proton injection region, 11 Zn diffusion region, 20 active region, 21
SiO ₂ film 22 Mg-doped GaAs (second buried layer), 23
Se doped Al _0.4 Ga _{0 .6} As buried layer (second buried layer)

Claims (6)

[Claims] 1. A stripe-shaped (111) extending in the [011] direction with respect to the crystal orientation of the first conductivity type GaAs substrate.
Grown on a (001) plane substrate having a slope of plane A,
In a semiconductor laser device having an active layer sandwiched between optical waveguide layers between a first conductivity type cladding layer and a second conductivity type cladding layer, the optical waveguide layer and an active region sandwiched between the optical waveguide layers. Are embedded on the slope of the (111) A plane of the (001) plane substrate. 2. The first conductivity type GaAs substrate is (111) A.
7. A surface of a (001) surface on one side of the surface is made to have a second conductivity type by impurity diffusion, and a second conductivity type semiconductor layer is formed on the (001) surface of the other side. 1. The semiconductor laser device according to 1. 3. The first conductivity type GaAs substrate is (111) A.
2. The active region is embedded on the plurality of (111) A plane slopes, which has a plurality of stripe-shaped convex portions composed of a surface slope and a (001) plane. Semiconductor laser device. 4. A first conductivity type (001) plane GaAs substrate having a second conductivity type buried layer and a first conductivity type buried layer, which are sequentially stacked with a predetermined width left, and a crystal orientation of the GaAs substrate. On the other hand, a stripe-shaped (111) B surface extending in the [011] direction is a slope, and a V-shaped groove shape having a (001) surface as a bottom surface and an upper surface is formed. A semiconductor laser device having an active region embedded on the bottom. 5. An active layer embedded on the bottom of a V-shaped groove formed on a GaAs substrate of the first conductivity type (001) surface, wherein the side surface of the V-shaped groove has the side surface. 5. The semiconductor laser device according to claim 4, wherein the semiconductor laser device comprises a semiconductor layer having a refractive index lower than that of the optical waveguide layer in the active region. 6. A first-conductivity-type (001) -plane GaAs substrate has a plurality of V-shaped groove shapes in which a striped (111) B plane is a slope and a (001) plane is a bottom surface and an upper surface. The semiconductor laser device according to claim 4, wherein an active region is embedded on the bottoms of the plurality of V-shaped grooves.