JPH07170013A - Semiconductor laser element and its manufacture - Google Patents

Abstract

PURPOSE:To restrain mass transport in vapor phase and melt back in liquid phase, surely preserve the edge shape of an aperture part formed in a current constriction layer, prevent the irregularity and the deformation of a stripe shape, and manufacture a laser element having uniform characteristics with high yield. CONSTITUTION:A semiconductor laser element is provided with the following; a semiconductor multilayered film which is formed on a semiconductor substrate 10 and contains an active region 13 for laser oscillation, a current constriction layer 17 and a growth restriction layer 18 which are laminated on the semiconductor multilayered film and have a stripe type aperture part reaching the semiconductor multilayered film, and a clad layer 20 which is in contact with the semiconductor multilayered film in the aperture part, and cut out on the growth restriction layer 18.

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 manufacturing method thereof.

[0002]

2. Description of the Related Art Semiconductor lasers for the telecommunications industry are required to have excellent uniformity with little variation in characteristics.
Also, in order to supply a good quality semiconductor laser at low cost,
Yield needs to be improved. Conventionally, in a practical semiconductor laser device, a current confinement layer having a stripe-shaped opening restricts a current other than an active region in order to reduce a threshold current at which laser operation is started and control an oscillation mode. The structure is known.

As a laser device having the above-mentioned stripe type structure and excellent in uniformity of characteristics, a laser device having a cross section in the order of steps shown in FIG. 6 has been proposed (Japanese Patent: 1534).
No. 266). The manufacturing process will be described in detail below.

First, an n-type G is formed on an n-type GaAs substrate 10.
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 clad 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 Pha (hereinafter abbreviated as MOVPE: Metal Organic Vapor Pha)
se epitaxy growth method or molecular beam epitaxial (hereinafter abbreviated as MBE: Molecular)
The layers are sequentially stacked by the beam epitaxy (FIG. 6A).

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

Furthermore, liquid phase epitaxial (hereinafter, LPE
Abbreviated as: p-type Al _0.45 Ga _0.55 As clad layer 2 by a liquid phase epitaxy) growth method.
0 and a p-type GaAs contact layer 21 are laminated so as to cover the whole (FIG. 6C). Finally, 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 to complete a semiconductor laser device (FIG. 6D).

In the semiconductor laser device formed by the above process, since the current is effectively injected into the central stripe portion by the n-type GaAs current confinement layer 17, the oscillation threshold current is as low as 30 mA, and the n-type GaAs current is reduced. Constriction layer 17
Due to the absorption of light, the effective refractive index difference is generated between the stripe portion and the portion other than the stripe, 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 constriction layer is easily deformed due to the following two factors. The first factor is that when the LPE growth is in a high temperature standby state, the substance constituting the upper edge 17-1 of the opening of the n-type GaAs current confinement layer 17 is caused by the mass transport in the gas phase.
To move to the lower edge 17-2 of the opening as shown in FIG. The second factor is p-type AlGa.
Due to the meltback in the liquid phase even during the growth of the As clad layer 20, the substance forming the upper edge 17-1 of the opening of the n-type GaAs current confinement layer 17 becomes in the liquid phase as shown in FIG. 7B. It is to melt.

The degree of these deformations differs depending on the location within the wafer, and the reproducibility is poor, so that the variation in stripe width after LPE growth becomes large. This appears as a variation in the radiation angle in the horizontal direction and a variation in the noise characteristic (which is affected by a minute variation in the effective refractive index difference) on the element characteristics. As a result, the yield yielding the desired radiation angle characteristic is 90%, and the yield yielding the desired noise characteristic is 8%.
There is a problem in that the total yield is only 0% and the total 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 meltback in the liquid phase, to favorably preserve the edge shape of the opening provided in the current constriction layer, and stripe. It is an object of the present invention to provide a laser device having a structure capable of manufacturing a laser device having uniform characteristics with a good yield while preventing variations in shape and deformation.

[0010]

In order to solve the above problems, the present invention has the following constitution. That is, the present invention is
A semiconductor substrate, a semiconductor multilayer film laminated on the semiconductor substrate and including an active region for laser oscillation, 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 clad layer that is in contact with the semiconductor multilayer film in the opening and is interrupted on the growth suppression layer.

Further, according to the present invention, a semiconductor substrate, a semiconductor multilayer film which is laminated on the semiconductor substrate and includes an active region for laser oscillation, and a stripe-shaped opening which is formed on the semiconductor multilayer film and reaches the semiconductor multilayer film. A growth suppressing layer having a current confinement function, a clad layer that is in contact with the semiconductor multilayer film in the opening and is interrupted on the growth suppressing layer,
It is a semiconductor laser device having.

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

According to the present invention, a step of forming a semiconductor multilayer film including an active region for laser oscillation, a current confinement layer and a growth inhibiting layer on a semiconductor substrate, and the current confinement layer and the growth inhibiting layer having the semiconductor Semiconductor having a step of forming a stripe-shaped opening reaching the multilayer film and a step of growing a clad layer in contact with the semiconductor multilayer film in the opening and interrupted on the growth suppressing layer by a liquid phase epitaxial growth method It is a method of manufacturing a laser element.

According to the present invention, a step of forming, on a semiconductor substrate, a semiconductor multilayer film including an active region for laser oscillation and a growth inhibiting layer having a current constriction function, and the growth inhibiting layer including the semiconductor multilayer film. A step of forming a stripe-shaped opening that reaches, and a clad layer that is in contact with the semiconductor multilayer film in the opening and is interrupted on the growth suppressing layer,
And a step of growing by a liquid phase epitaxial growth method.

[0015]

With the above structure, in the present invention, the current confinement layer is protected by the growth inhibiting layer even during high temperature standby in the vapor phase, so that mass transport is suppressed and good shape preservation is performed. Further, since LPE growth occurs concentratedly in the stripe-shaped opening having no growth suppressing layer, meltback is suppressed and the shape is well preserved.

It is also possible to provide the growth restraining layer with a current constriction function. It is not so difficult to select, as the material of the growth suppressing layer, a substance that is less likely to cause mass transport and has an effect of suppressing LPE growth. For example, as a material for forming the growth suppressing layer by 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 ~ 0.5) is suitable. Further, as a material for forming the growth suppressing layer by a dielectric film, Al ₂ O ₃ and SiO are used.
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.
In general, since the acute angle portion has a larger surface energy than the obtuse angle portion, as shown in FIG. 7A, the energy decreases, that is, the deformation from the acute angle to the obtuse angle occurs. However, if an obtuse angle is processed from the beginning, the effective stripe width will be widened and desired laser characteristics cannot be obtained. Therefore, it is effective to form the acute-angled tip portion from a material that does not easily cause mass transport.

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

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 is a cross-sectional view showing the structure of a first embodiment of a semiconductor laser device according to the present invention. The semiconductor laser device of the first embodiment comprises an n-type GaAs substrate 10 and an n-type Ga.
As 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 clad layer 14, p-type G
aAs growth promoting 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
Type Al _0.45 Ga _0.55 As clad layer 20, p-type GaAs
The contact layer 21, the n-type ohmic electrode 30, and the p-type ohmic electrode 31 are included.

2A to 2D are cross-sectional views in order of the processes, 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, undoped 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 inhibiting layer 18 is laminated by MOVPE growth method or MBE growth method.

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

After that, as shown in FIG.
The p-type Al _0.45 Ga _0.55 As clad layer 2 was grown by the growth method.
0, p-type GaAs contact layer 21 is laminated. Furthermore,
The n-type ohmic electrode 30 is formed on the n-type GaAs substrate 10 side, and the p-type ohmic electrode 31 is formed on the p-type GaAs contact layer 21 side to complete the semiconductor laser device shown in FIG.

During high temperature standby for LPE growth, Al in the crystal
Is an element that is difficult to release in the gas phase, so n-type AlGaA
The mass transport of the s growth restraining layer 18 hardly occurs, and the n-type GaAs current confinement layer 17 also has n-type AlG.
By being protected by the aAs growth inhibiting layer 18, the deformation due to mass transport is suppressed.

On the other hand, during etching, n-type AlGaA
Al in the growth-inhibiting layer 18 is oxidized in the air, and n-type A
Since a thin oxide film is formed on the surface of the 1GaAs growth inhibiting layer 18, the LPE growth on the n-type AlGaAs growth inhibiting layer 18 is suppressed. For this reason, since the growth of the p-type AlGaAs cladding layer 20 is concentrated in the stripe portion, the effective degree of supersaturation is very large, and the meltback of the n-type GaAs current confinement layer 17 in the liquid phase is hardly seen. Furthermore, since the n-type AlGaAs growth suppressing layer 18 itself is a substance that is unlikely to cause meltback, it also functions as a protective film for the n-type GaAs current constriction layer 17 with respect to meltback.

Although the growth of the p-type AlGaAs cladding layer 20 is limited to the stripe and its peripheral portion, the p-type G
The aAs contact layer 21 can be grown on the entire surface of the wafer by increasing the growth time. n
Regarding the composition of the type Al _x Ga _1-x As growth inhibiting layer 18,
The larger the Al composition ratio x, the greater the effect of suppressing deformation,
The effect is confirmed when x ≧ 0.1.

The present invention is not limited to AlGaAs-based materials, but a GaInP-based material is shown as a second embodiment. The second embodiment is the same in structure as the first embodiment of FIG. The constituent material of each layer of the second embodiment is the n-type GaAs substrate 10 and the n-type GaAs buffer layer 1.
1, n-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 1
2, non-doped Ga _0.5 In _0.5 P active layer 13, p-type (A
l _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 ) _z In _1-z P The effect of Al in the growth-inhibiting layer 18 suppresses the deformation of the n-type Ga _0.5 In _0.5 P current confinement layer 17 due to mass transport and meltback. It is similar to the embodiment of. For composition y ≧
The effect could be confirmed at 0.1 and z to 0.5.

Next, FIG. 3 shows a sectional view of 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, but the growth time of the p-type GaAs contact layer 21 is shorter than that of the first embodiment. Will not be reached and will be partial. p-type GaAs contact layer 2
Whether the growth of No. 1 is whole surface or partial growth does not particularly affect the device characteristics.

Next, FIG. 4 shows a sectional view of a fourth embodiment of the semiconductor laser device according to the present invention. In this embodiment, the composition of layers other than the growth inhibiting layer 18 is the same as that of the first embodiment. The growth restraining layer 18 is formed of a dielectric film of Al ₂ O _3, SiO _2, SiN _w (w˜4 / 3) or photoresist. In the case of a photoresist, it is not necessary to provide a step of forming a growth inhibiting layer, and in the conventional semiconductor laser manufacturing process, after the stripe-shaped etching processing of the n-type GaAs current confinement layer 17 and the n-type AlGaAs etching stop layer 16. The photoresist of the etching mask may be used as it is as the growth inhibiting layer 18 without removing the photoresist. The growth inhibiting effect of the dielectric film is larger, and the p-type GaAs contact layer 21 does not grow on the entire surface of the wafer regardless of the growth time.

Next, FIG. 5 shows a sectional view of a fifth embodiment of the semiconductor laser device according to the present invention. In this embodiment, since the growth inhibiting layer 18 also has the current confinement function, there is no current constriction 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 (w-
4/3) or a dielectric film of photoresist. Therefore, the p-type GaAs contact layer 21
The fact that the growth is partial is similar to 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 inhibiting layer having a current constriction function, and p-type AlGa at this time is used.
The shapes of the As clad layer 20 and the p-type GaAs contact layer 21 are similar to those in FIG. 1 or 2.

The semiconductor laser devices of the above-mentioned first to fifth embodiments were prepared, and the characteristics were measured. As a result, the yields of non-defective products satisfying the predetermined radiation angle characteristics and noise characteristics were both 99%.
And was very expensive. Further, as the active layer in all of the above-mentioned embodiments, the quantum well structure (Q
W: Quantum Well), strained quantum well structure (Strained QW), separate confinement heterostructure (SCH: Separate Confinement)
It goes without saying that it is also effective when the Heterostructure) is adopted. Further, although the semiconductor laser device having one stripe has been described in the above embodiment, the present invention can be applied to a semiconductor laser device having a plurality of stripes depending on the application of the semiconductor laser device. It is also clear that the process is not limited to the number of stripes.

[0033]

As described above, according to the present invention,
Since both mass transport in the gas phase and meltback in the liquid phase are suppressed and the stripe shape is well preserved, variations in laser characteristics due to variations in stripe shape, especially variations in horizontal radiation angle, noise characteristics Variation is reduced, a semiconductor laser element having excellent uniformity of characteristics can be obtained, and a semiconductor laser element having excellent uniformity of characteristics can be manufactured with high yield.

[Brief description of drawings]

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

2A to 2C are cross-sectional views in order of the processes, showing the manufacturing process of the semiconductor laser device according to 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 a structure of a semiconductor laser device according to a fourth embodiment of 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.

6A to 6C are sectional views in order of the processes, showing the manufacturing process of a conventional semiconductor laser device.

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

[Explanation of symbols]

 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 constriction layer 18 growth inhibiting layer 20 clad layer 21 contact layer 30 n-type ohmic electrode 31 p-type ohmic electrode

Claims (6)

[Claims] 1. A semiconductor substrate, a semiconductor multilayer film which is laminated on the semiconductor substrate and includes an active region for laser oscillation, and a stripe-shaped opening which is laminated on the semiconductor multilayer film and reaches the semiconductor multilayer film. A semiconductor laser device comprising: a current confinement layer and a growth inhibiting layer; and a clad layer that is in contact with the semiconductor multilayer film in the opening and is interrupted on the growth inhibiting layer. 2. A semiconductor substrate, a semiconductor multilayer film which is laminated on the semiconductor substrate and includes an active region for laser oscillation, and a stripe-shaped opening which is formed on the semiconductor multilayer film and reaches the semiconductor multilayer film. A semiconductor laser device comprising: a growth suppressing layer having a current constriction function; and a clad layer that is in contact with the semiconductor multilayer film in the opening and is interrupted on the growth suppressing layer. 3. The growth inhibiting layer comprises Al _x Ga _1-x As (x ≧ 3
0.1) or (Al _y Ga _1-y ) _1-z In _z P (y ≧ 0.
1, z to 0.5), and the semiconductor laser device according to claim 1 or 2. 4. The growth inhibiting layer comprises Al ₂ O ₃ , SiO ₂ and S.
3. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is made of either iNw ( _w- 4 / 3) or photoresist. 5. A step of forming, on a semiconductor substrate, a semiconductor multilayer film including an active region for laser oscillation, a current confinement layer and a growth inhibiting layer, and the current confinement layer and the growth inhibiting layer including the semiconductor multilayer film. A step of forming a stripe-shaped opening reaching the opening, and a step of growing a clad layer that is in contact with the semiconductor multilayer film in the opening and is interrupted on the growth suppressing layer by a liquid phase epitaxial growth method. Method for manufacturing semiconductor laser device. 6. A step of forming, on a semiconductor substrate, a semiconductor multilayer film including an active region for laser oscillation and a growth inhibiting layer having a current confinement function, and a stripe shape reaching the growth inhibiting layer to the semiconductor multilayer film. And a step of growing a clad layer that is in contact with the semiconductor multilayer film in the opening and is interrupted on the growth inhibiting layer by a liquid phase epitaxial growth method. Device manufacturing method.