JP2960845B2 - Semiconductor laser device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device which is a main component of optical information processing and optical communication and a method of manufacturing the same, and more particularly, to a semiconductor laser having a cross-sectional shape capable of obtaining excellent uniformity characteristics. The present invention relates to an element and a method for manufacturing the same.

[0002]

2. Description of the Related Art Semiconductor lasers for use in the telecommunications industry are required to have characteristics with little variation and excellent uniformity.
In order to supply high quality semiconductor lasers at low cost,
It is necessary to improve the yield. Conventionally, in a practical semiconductor laser device, in order to reduce the threshold current at which laser operation starts and control the oscillation mode, a current confinement layer having a stripe-shaped opening limits the current outside the active region. Known structures are known.

As a laser device having the above-mentioned stripe type structure and excellent characteristics uniformity, there has been proposed a laser device shown in FIG.
266). Hereinafter, the manufacturing process will be described in detail.

First, on an n-type GaAs substrate 10, an n-type G
aAs buffer layer 11, n-type Al _0.45 Ga _0.55 As clad layer 12, non-doped Al _0.15 Ga _0.85 As active layer 1
3, p-type Al _0.45 Ga _0.55 As cladding layer 14, p-type G
an aAs growth promoting layer 15, an n-type Al _0.6 Ga _0.4 As etching stop layer 16, and an n-type GaAs current confinement layer 17;
Metal organic vapor phase epitaxy (hereinafter abbreviated as MOVPE: Metal Organic Vapor Pha)
se Epitaxy) or molecular beam epitaxy (hereinafter abbreviated as MBE: Molecular)
The layers are sequentially stacked by a beam epitaxy (FIG. 6A).

Next, a photoresist (not shown) is applied on the substrate on which the above layers are stacked, and a stripe-shaped opening is formed in the photoresist by ordinary photolithography. Next, using this photoresist as a mask, n of the stripe portion is etched by chemical etching.
After removing the n-type GaAs current confinement layer 17 and the n-type AlGaAs etching stop layer 16, the photoresist is removed (FIG. 6B).

Further, liquid phase epitaxy (hereinafter referred to as LPE)
Abbreviation: Liquid Phase Epitaxy) p-type Al _0.45 Ga _0.55 As cladding layer 2
0, the p-type GaAs contact layer 21 is laminated so as to cover the whole (FIG. 6C). Finally, the n-type GaAs substrate 1
An n-type ohmic electrode 30 is formed on the 0 side and a p-type ohmic electrode 31 is formed on the p-type GaAs contact layer 21 side, thereby completing a semiconductor laser device (FIG. 6D).

In the semiconductor laser device formed by the above process, the current is effectively injected into the central stripe portion by the n-type GaAs current confinement layer 17, so that the oscillation threshold current is as low as 30 mA and the n-type GaAs current is reduced. Narrowing layer 17
As a result, an effective refractive index difference occurs between the stripe portion and the portion other than the stripe due to the light absorption, so that oscillation is performed in a stable fundamental transverse mode up to an optical output of 10 mW.

[0008]

However, the conventional semiconductor laser device having the above structure has a problem that the current confinement layer is easily deformed due to the following two factors. The first factor is that the material forming the upper edge 17-1 of the opening of the n-type GaAs current confinement layer 17 by mass transport in the vapor phase during high-temperature standby for LPE growth is as follows:
This is to move to the lower edge 17-2 of the opening as shown in FIG. The second factor is p-type AlGa
Even when the As clad layer 20 is grown, the material forming the upper edge 17-1 of the opening of the n-type GaAs current confinement layer 17 becomes in the liquid phase due to the melt back in the liquid phase as shown in FIG. It is to melt.

The degree of these deformations differs depending on the location in the wafer, and the reproducibility is poor, so that the stripe width variation after LPE growth becomes large. This appears on the element characteristics as a variation in the radiation angle in the horizontal direction and a variation in the noise characteristics (a minute variation in the effective refractive index difference affects). As a result, the yield at which a desired radiation angle characteristic is obtained is 90%, and the yield at which a desired noise characteristic is obtained is 8%.
This is only 0%, and there is a problem that the overall yield is reduced to about 70%. In view of the above problems, an object of the present invention is to suppress both mass transport in the gas phase and melt back in the liquid phase, to preserve the edge shape of the opening provided in the current confinement layer well, An object of the present invention is to provide a laser element having a structure capable of preventing variations in shape and deformation and manufacturing a laser element having uniform characteristics with high yield, and a method for manufacturing the same.

[0010]

In order to solve the above problems, the present invention has the following arrangement. That is, the present invention
A semiconductor substrate, a semiconductor multilayer film laminated on the semiconductor substrate and including an active region for laser oscillation, and a current confinement layer having a stripe-shaped opening laminated on the semiconductor multilayer film and reaching the semiconductor multilayer film, and growth. A semiconductor laser device comprising: a suppression layer; and a cladding layer in contact with the semiconductor multilayer film at the opening and interrupted on the growth suppression layer.

Further, the present invention provides a semiconductor substrate, a semiconductor multilayer film laminated on the semiconductor substrate and including an active region for laser oscillation, and a stripe-shaped opening formed on the semiconductor multilayer film and reaching the semiconductor multilayer film. A growth suppression layer having a current constriction function having a portion, a cladding layer that is in contact with the semiconductor multilayer film in the opening and is interrupted on the growth suppression layer,
Is a semiconductor laser device having:

According to the present invention, in the above-mentioned semiconductor laser device, the material of the growth suppressing layer is Al _x Ga _{1 -x} As.
(X ≧ 0.1) or _{(Al y Ga 1-y)} 1-z In z P (y
.Gtoreq.0.1, z to 0.5). Further, in the present invention, in the above-described semiconductor laser device, the material of the growth suppressing layer is Al ₂ O ₃ , SiO ₂ , SiN _w ( _w （4 /
3), any of photoresists.

Further, the present invention provides a step of forming a semiconductor multilayer film including an active region for laser oscillation, a current confinement layer and a growth suppressing layer on a semiconductor substrate, and forming the semiconductor confining layer and the growth suppressing layer on the semiconductor substrate. A step of forming a stripe-shaped opening reaching the multilayer film; and a step of growing a cladding layer in contact with the semiconductor multilayer film at the opening and interrupted on the growth suppressing layer by a liquid phase epitaxial growth method. This is a method for manufacturing a laser element.

The present invention also provides a step of forming a semiconductor multilayer film including an active region for laser oscillation and a growth suppressing layer having a current confinement function on a semiconductor substrate. Forming a stripe-shaped opening that reaches, and a cladding layer that is in contact with the semiconductor multilayer film in the opening and is cut off on the growth suppression layer,
And a step of growing by a liquid phase epitaxial growth method.

[0015]

According to the present invention, in the present invention, the current confinement layer is protected by the growth suppressing layer even during standby at a high temperature in the gas phase, so that mass transport is suppressed and good shape preservation is performed. In addition, since LPE growth occurs intensively in a stripe-shaped opening having no growth suppressing layer, meltback is suppressed and the shape is well preserved.

Further, it is also possible to give the current suppressing function to the growth suppressing layer. It is not so difficult to select a material that is less likely to cause mass transport and has an effect of suppressing LPE growth as a material for the growth suppressing layer. For example, as a material when the growth suppressing layer is formed of a semiconductor layer, Al _x Ga _{1 -x} As (x ≧ 0.
1) or (Al _y Ga _1-y ) _1-z In _z P (x ≧ 0.1,
z to 0.5) are appropriate. Further, when the growth suppressing layer is formed of a dielectric film, the material may be Al ₂ O ₃ or SiO _2.
2 , SiN _w (w〜 / 4/3) and photoresist are suitable.

The mass transport in the gas phase depends on the shape of the n-type GaAs current confinement layer 17 after etching.
Generally, since an acute angle portion has a larger surface energy than an obtuse angle portion, as shown in FIG. 7A, a direction in which the energy decreases, that is, a deformation from an acute angle to an obtuse angle occurs. On the other hand, if the processing is performed at an obtuse angle from the beginning, the effective stripe width increases, and the desired laser characteristics cannot be obtained. Therefore, it is effective to form the acute-angled tip portion with a substance that does not easily cause mass transport.

Melt back in the liquid phase is also caused by the fact that the melting rate in the liquid phase is higher than the rate of crystal precipitation from the liquid phase at the acute angle portion. It can be prevented by increasing the (deposition rate). However, there is a limit to the degree of supersaturation when growing over the entire surface of the wafer. This is because, even if the melt temperature is excessively lowered so as to increase the degree of supersaturation, microcrystals are precipitated in the melt and the degree of supersaturation is rather lowered. For this purpose, the most effective means is to provide a window for the growth suppressing layer on the growth surface, limit the growth region to a part of the wafer without the growth suppressing layer, and concentrate the supersaturation degree of the melt on the part. Becomes

[0019]

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing the structure of a first embodiment of the semiconductor laser device according to the present invention. The semiconductor laser device of the first embodiment includes an n-type GaAs substrate 10, an n-type Ga
As buffer layer 11, n-type Al _0.45 Ga _0.55 As cladding layer 12, non-doped Al _0.15 Ga _0.85 As active layer 1
3, p-type Al _0.45 Ga _0.55 As cladding layer 14, p-type G
aAs growth promotion layer 15, n-type Al _0.6 Ga _0.4 As etching stop layer 16, n-type GaAs current confinement layer 17, n
-Type Al _x Ga _{1 -x} As (x = 0.5) growth inhibiting layer 18, p
Al _0.45 Ga _0.55 As clad layer 20, p-type GaAs
It comprises a contact layer 21, an n-type ohmic electrode 30, and a p-type ohmic electrode 31.

FIG. 2 is a process sectional view showing the manufacturing process of the first embodiment. First, as shown in FIG. 2A, an n-type GaAs buffer layer 11 is formed on an n-type GaAs substrate 10.
n-type Al _0.45 Ga _0.55 As clad layer 12, non-doped Al _0.15 Ga _0.85 As active layer 13, p-type Al _0.45 Ga
_0.55 As clad layer 14, p-type GaAs growth promoting layer 1
5. n-type Al _0.6 Ga _0.4 As etching stop layer 1
6, n-type GaAs current confinement layer 17, n-type Al _x Ga _{1 -x} A
The s (x = 0.5) growth suppressing layer 18 is laminated by MOVPE growth method or MBE growth method.

Next, a photoresist (not shown) is applied, and a stripe-shaped opening is formed in the photoresist by ordinary photolithography. Using this photoresist as a mask, n-type AlGaAs is grown in the stripe by chemical etching. Suppression layer 18, n-type GaAs current confinement layer 17, n-type AlGaAs etching stop layer 1
6 is removed, and the photoresist is continuously removed.

Thereafter, as shown in FIG.
The p-type Al _0.45 Ga _0.55 As clad layer 2
0, a p-type GaAs contact layer 21 is laminated. Furthermore,
An n-type ohmic electrode 30 is formed on the n-type GaAs substrate 10 side and a p-type ohmic electrode 31 is formed on the p-type GaAs contact layer 21 side, thereby completing the semiconductor laser device shown in FIG.

During the high-temperature standby for LPE growth, Al in the crystal
Is an element hardly released in the gas phase,
Almost no mass transport occurs in the s growth suppression layer 18, and the n-type GaAs current confinement layer 17 also has n-type AlG
Deformation due to mass transport is suppressed by being protected by the aAs growth suppression layer 18.

On the other hand, n-type AlGaAs
Al in the s growth inhibition layer 18 is oxidized in the air, and n-type A
Since a thin oxide film is formed on the surface of the lGaAs growth suppression layer 18, LPE growth on the n-type AlGaAs growth suppression layer 18 is suppressed. Therefore, since the growth of the p-type AlGaAs cladding layer 20 is concentrated on the stripe portion, the effective degree of supersaturation is very large, and almost no meltback in the liquid phase of the n-type GaAs current confinement layer 17 is observed. Further, since the n-type AlGaAs growth suppressing layer 18 itself is a substance that is unlikely to melt back, it also functions as a protective film for the n-type GaAs current confinement layer 17 with respect to the melt back.

The growth of the p-type AlGaAs cladding layer 20 is limited to the stripe and its peripheral portion.
The aAs contact layer 21 can be grown over the entire surface of the wafer by increasing the growth time. n
The composition of the Al _x Ga _{1 -x} As growth suppression layer 18 is as follows.
Although the effect of suppressing deformation is greater as the Al composition ratio x is larger,
The effect has been confirmed at x ≧ 0.1.

The present invention is not limited to an AlGaAs-based material, but shows a second embodiment using a GaInP-based material. The second embodiment is the same in structure as the first embodiment of FIG. The constituent materials of each layer of the second embodiment are an n-type GaAs substrate 10, an n-type GaAs buffer layer 1
1. n-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P cladding layer 1
2, non-doped Ga _0.5 In _0.5 P active layer 13, p-type (A
1 _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 14, p-type Ga
_0.5 In _0.5 P growth promoting layer 15, n-type (Al _0.8 Ga _0.2 )
_0.5 In _0.5 P etching stop layer 16, n-type Ga _0.5
In _0.5 P current confinement layer 17, n-type (Al _y Ga _{1 -y} ) _z In
_1-z P (y = 0.5, z = 0.5) growth inhibiting layer 18, p
A type Al _0.8 Ga _0.2 As clad layer 20 and a p-type GaAs contact layer 21.

Also in the second embodiment, the n-type (Al _y G
a _1-y ) The deformation of the n-type Ga _0.5 In _0.5 P current confinement layer 17 due to mass transport and meltback due to the effect of Al in the _z In _{1 -z} P growth suppression layer 18 is first. This is the same as the embodiment. For the composition, y ≧
The effect was able to be confirmed at 0.1 and z to 0.5.

FIG. 3 is a sectional view showing a third embodiment of the semiconductor laser device according to the present invention. In this embodiment, the composition of each layer is the same as that of the first embodiment. However, the growth time of the p-type GaAs contact layer 21 is shorter than that of the first embodiment. And it is partial. p-type GaAs contact layer 2
Whether the growth of 1 is all or partial does not particularly affect the element characteristics.

FIG. 4 is a sectional view of a fourth embodiment of the semiconductor laser device according to the present invention. In the present embodiment, the composition of the layers other than the growth suppressing layer 18 is the same as in the first embodiment. The growth suppressing layer 18 is formed of a dielectric film of Al ₂ O _3, SiO _2, SiN _w (w〜 / 4) or a photoresist. In the case of a photoresist, it is not necessary to provide a step of forming a growth inhibition layer. In a conventional semiconductor laser manufacturing process, after the n-type GaAs current confinement layer 17 and the n-type AlGaAs etching stop layer 16 have been subjected to the striped etching process. The photoresist of the etching mask may be used as it is as the growth suppressing layer 18 without removing the photoresist. The effect of suppressing the growth of the dielectric film is greater, and the p-type GaAs contact layer 21 does not grow over the entire surface of the wafer regardless of the growth time.

FIG. 5 is a sectional view showing a fifth embodiment of the semiconductor laser device according to the present invention. In the present embodiment, since the growth suppressing layer 18 also has a current confining function, there is no current confining layer and no etching stop layer is required. The composition of the other layers is the same as in the first embodiment. The growth suppressing layer 18 is made of Al ₂ O ₃ or SiO ₂ or SiN _w (wｗ
4/3) or a dielectric film of a photoresist. Therefore, the p-type GaAs contact layer 21
Is similar to that of the fourth embodiment.

Further, n-type Al _x Ga _{1 -x} As (x ≧ 0.
1) or n-type _{(Al y Ga 1-y)} 1-z In z P (y ≧ 0.
1, z to 0.5) can be adopted as a growth suppressing layer having a current confinement function.
The shapes of the As cladding layer 20 and the p-type GaAs contact layer 21 are the same as those in FIG. 1 or FIG.

The semiconductor laser devices of the first to fifth embodiments were fabricated and their characteristics were measured. As a result, the yield of non-defective products satisfying predetermined radiation angle characteristics and noise characteristics was 99%.
And it was very expensive. Further, the active layer in all the above embodiments is not a single composition layer but a quantum well structure (Q
W: Quantum Well, strained quantum well structure (Strained QW), isolated confinement heterostructure (SCH: Separate Confinement)
It is needless to say that the case where Heterostructure is adopted is also effective. Further, in the above embodiment, the semiconductor laser device having one stripe has been described. However, depending on the application of the semiconductor laser device, the present invention is applicable to a device having a plurality of stripes. It is clear from the fact that the process is not limited to the number of stripes.

[0033]

As described above, according to the present invention,
Both mass transport in the gas phase and melt back in the liquid phase are suppressed, and the stripe shape is well preserved. Therefore, variations in the laser characteristics due to variations in the stripe shape, especially variations in the horizontal radiation angle, noise characteristics Is reduced, a semiconductor laser device having excellent uniformity of characteristics can be obtained, and a semiconductor laser device having excellent uniformity of characteristics can be manufactured with good yield.

[Brief description of the drawings]

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

FIG. 2 is a process order sectional view showing a manufacturing process of the semiconductor laser device of the first embodiment.

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

FIG. 4 is a sectional view showing the structure of a fourth embodiment of the semiconductor laser device according to the present invention.

FIG. 5 is a sectional view showing the structure of a fifth embodiment of the semiconductor laser device according to the present invention.

FIG. 6 is a process order sectional view showing a manufacturing process of a conventional semiconductor laser device.

FIG. 7 is a cross-sectional view illustrating a state of deformation of a current confinement layer of a conventional semiconductor laser.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 semiconductor substrate 11 buffer layer 12 clad layer 13 active layer 14 clad layer 15 growth promoting layer 16 etching stop layer 17 current confinement layer 18 growth suppression layer 20 clad layer 21 contact layer 30 n-type ohmic electrode 31 p-type ohmic electrode

Claims (6)

(57) [Claims] A semiconductor substrate, a semiconductor multilayer film laminated on the semiconductor substrate and including an active region for laser oscillation, and a stripe-shaped opening laminated on the semiconductor multilayer film and reaching the semiconductor multilayer film. A semiconductor laser device comprising: a current confinement layer and a growth suppressing layer; and a cladding layer that is in contact with the semiconductor multilayer film at the opening and is interrupted on the growth suppressing layer. 2. A semiconductor substrate comprising: a semiconductor substrate; a semiconductor multilayer film laminated on the semiconductor substrate and including an active region for laser oscillation; and a stripe-shaped opening formed on the semiconductor multilayer film and reaching the semiconductor multilayer film. A semiconductor laser device comprising: a growth suppression layer having a current constriction function; and a cladding layer that is in contact with the semiconductor multilayer film at the opening and is interrupted on the growth suppression layer. 3. The growth suppressing layer is made of Al _x Ga _{1 -x} As (x ≧
0.1) or _{(Al y Ga 1-y)} 1-z In z P (y ≧ 0.
3. The semiconductor laser device according to claim 1, wherein the semiconductor laser device comprises: 1, z to 0.5). 4. The growth inhibiting layer is made of Al ₂ O ₃ , SiO ₂ , S
3. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is made of one of iN _w (w〜4 / 3) and a photoresist. 4. 5. A step of forming a semiconductor multilayer film including an active region for laser oscillation and a current confinement layer and a growth suppression layer on a semiconductor substrate; and forming the current confinement layer and the growth suppression layer up to the semiconductor multilayer film. A step of forming a stripe-shaped opening reaching, and a step of growing a cladding layer in contact with the semiconductor multilayer film at the opening and interrupted on the growth suppressing layer by a liquid phase epitaxial growth method. Manufacturing method of a semiconductor laser device. 6. A step of forming a semiconductor multilayer film including an active region for laser oscillation and a growth suppressing layer having a current confinement function on a semiconductor substrate, wherein the growth suppressing layer has a stripe shape reaching the semiconductor multilayer film. Forming an opening, and a step of growing, by a liquid phase epitaxial growth method, a cladding layer in contact with the semiconductor multilayer film at the opening and interrupted on the growth suppressing layer by a liquid phase epitaxial growth method. Device manufacturing method.