JPH01187891A - Semiconductor laser and its manufacture - Google Patents

Abstract

PURPOSE:To absorb damages of a semiconductor crystal caused by dry-etching for forming a ridge form and a stress caused by the difference in thermal expan sion coefficient between the semiconductor crystal and a surface protective film and realize the long life of a semiconductor laser with the ridge form by providing a semiconductor layer between a cladding layer and a surface insulating film. CONSTITUTION:A protective semiconductor layer 16 made of P-type GaAs is formed on a clad layer 13. The thickness of the semiconductor layer 16 is 0.3mum. The thickness is approximately uniform over the whole width. The semiconductor layer 16 is formed after the cladding layer 13 and an electrode contact layer 6 are partially removed by dry-etching. The layer 16 has an effect of absorbing crystal damages of the clad layer 13 caused by etching and improves the life because of the following two points: (1) defects existing in the recesses (thin parts) 15 of the cladding layer 13 are reduced by the growth of the protective semiconductor layer 16 and the long life can be realized, (2) a stress caused by the difference in thermal expansion coefficient between an insulating film (Si3N4 film) 7 and the clad layer 13 is absorbed so that the long life can be assured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser used as a light source for optical communication, optical recording, etc.

[Conventional technology] The basic structure of a semiconductor laser is shown in FIG.

The structure of the semiconductor laser shown in FIG. 4 will be explained according to its manufacturing process.

This laser uses a liquid phase growth method (I) on an n-GaAs substrate 1.
The laser structure is formed using methods such as the JP method, the MOCVD method, the MBE method, and the like. Here, we will discuss the case of creating using the MBE method. A buffer layer 2 made of n-GaAs doped with Si on this n-GaAs substrate 1
is formed to a thickness of approximately 0.5 μm. Furthermore, n-8l was also doped with Si. A crand layer 3 made of 3Gao and 78S is formed to a thickness of about 1.5 μm. On this layer, an active layer 4 made of a non-doped layer of GaAs is typically formed. I
1. Be (beryllium)-doped P-8l grows to about tm and becomes a cladding layer (light confinement layer).
o, aGao, 78 S layer 5 is formed to a thickness of 1.5 μm.

This P-^i0.3Gao, 78S layer 5 and n-Alo
The 3Gaa, , As layer 3 has the effect of confining carriers and light in the GaAs non-doped layer 4, which is an active layer.

The electrode contact layer 6 is made of P-G doped with Be.
Since it is made of aAs, the film thickness is 0.5 μm. The insulating layer 7 is a Si3N4 film, and the film thickness is 2000 mm. The P-type electrode 8 has a stacked structure of ^U/Cr, and the n-type electrode IO has a
It consists of Au/Ni.

When using such a semiconductor laser, the most important thing is the stability of the light emitting section 11, which is usually controlled in the "transverse mode".
It is important that the transverse mode is single. The current 12 is injected through the electrode opening 9 and reaches the light emitting section 11 . Whether there is a single light emitting section 11 or a plurality of light emitting sections 11 depends on the size of the electrode opening 9 and the horizontal spread of the current 12.

A ridge type semiconductor laser is an example of an improved laser created to solve this problem.

FIG. 5 is a sectional view showing the structure of an example of a ridge type semiconductor laser.

n-GaAs as a buffer layer on the n-GaAs substrate 1.
An s-layer 2 is formed, on top of which an n-layer. ,,Gao7As
A cladding layer 3 consisting of the following is formed. Non-dope G
The thickness of the active layer 4 made of aAs is 0.1 μm.

The structure of this ridge type laser differs from that in Figure 4 in that P
-At0. , Gao, , As, the thickness of the cladding layer 13 is partially different to form a ridge structure, and the thickness of the ridge portion 14 is the same as the conventional one.
5 μm, and the thickness of the four parts 15 is approximately 0.2 μm.

Reference number 6 is an electrode contact layer (made of P-GaAs). The ridge is formed by uniformly forming up to the electrode contact layer 6, and then dry etching using Cfl2 (for example, using Herr gas) or wet etching (ll2S04).
:ll□02:lI□O=1:I:1.0) using an etching jig or the like. With this configuration,
The spread of the current 12 can be restricted, the light emitting section 11 can also be made smaller, and it becomes possible to operate in a single transverse mode. This ridge structure is easy to form, has good characteristics, and is an excellent structure.

[Problem to be solved by the invention]

However, in the conventional example described above, P-Alo3G
About 0.2 μm of the cladding layer 13 made of ao, 7AS remains in the recess 15, and if the layer formed by wet etching or dry etching is removed, the remaining film is likely to be damaged. Damage to the layer will affect the lifespan of the semiconductor laser. Forming a ridge using wet etching, which causes the least damage, has the disadvantage that the slope of the ridge becomes gentle, reducing the current confinement effect.

Furthermore, tri-etching is better in terms of controllability, and P
-A.I. , , , Gao, , The film thickness in the concave portion of As 13 can be controlled with a grain size of ±0.1 μm. Therefore, if dry etching is used, the problem is that the remaining film is likely to be damaged. Furthermore, when the film thickness in the recess is 0.2 μm, it is 0.1 μm to 0.3 μm due to the controllability of etching.
It varies by m. If the film thickness is as thick as 0.3 μm, there will be less damage to the active layer, and the lifespan will be extended (several hundred thousand hours, -25°C, 5 mW), but this is important when using a semiconductor laser. The astigmatism becomes larger,
Furthermore, the threshold current increases and the initial performance deteriorates. On the other hand, when it becomes 0.1 μm, the astigmatism becomes small, the threshold current becomes small, and the initial characteristics are that it may not be possible to make an excellent semiconductor laser, but the damage due to dry etching will increase, and the lifetime will be shortened (several thousand hours). , 25"C, 5mW).

[Means to solve the problem]

The semiconductor laser of the present invention is a semiconductor laser in which a ridge shape is formed, and a semiconductor layer is provided between a cladding layer and a surface insulating film.

Further, the method of manufacturing a semiconductor laser having a ridge shape according to the present invention includes the steps of forming a cladding layer on the active layer, selectively etching a part of the cladding layer to form a ridge shape, and forming a semiconductor layer on the surface exposed by etching.

[Effect]

Damage to the semiconductor crystal caused by dry etching to form the ridge shape is absorbed by growing a semiconductor layer on the semiconductor crystal.

Further, this semiconductor layer absorbs stress due to the difference in thermal expansion coefficient between the semiconductor crystal and the surface protective film. Therefore, the life of the laser can be extended.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

Figure 1 is a sectional view of a first embodiment of the semiconductor laser of the present invention.

The difference between this embodiment and the conventional example is that the cladding layer IL
1 m is provided with a protective semiconductor layer 16 made of P-GaAs. The thickness of this protective semiconductor layer 16 is 0.3 μm, and this thickness is substantially uniform over the entire width. This protective semiconductor layer 16 includes the cladding layer 13
and is formed after partially dry etching the electrode contact layer 6. The protective semiconductor layer 16 has the effect of absorbing the crystal damage to the cladding layer 13 caused by etching, and the life span is improved in the following two ways.

(1) The defects existing in the recesses (thin parts) of the cladding layer 13 are reduced by the growth of the protective semiconductor layer,
Longer life can be achieved.

(2) Stress caused by the difference in thermal expansion coefficient between the insulating film (Si3N, film) and the cladding layer 13 is absorbed, thereby extending the life.

In addition, in this example, the current spread is larger than in the conventional ridge type semiconductor laser, and there is a risk that the confinement effect will be reduced, but this problem can be prevented by paying attention to the following points. .

(1) When forming a ridge shape by etching, the ridge width at the time of etching is made narrower than in the conventional example, taking into consideration the expansion of the ridge width due to the presence of the protective semiconductor layer 16. For example, when the ridge width is set to 3 μm or less, current spread can be sufficiently suppressed.

(2) The resistance value of the protective semiconductor layer 16 is made slightly larger than that of the conventional example, and the carrier concentration thereof is, for example, 5X for GaAs.
1017 cm"" or less, IX for AlGaAs
It is desirable to keep it at 1018 cl” or less.

When the semiconductor laser configured as described above was driven by applying voltage from the power supply 20, the initial characteristics (
low threshold current, etc.), and a long lifespan was also achieved.

The descendant's side FIG. 2 is a sectional view of a second embodiment of the invention.

This embodiment has a structure that takes into consideration the case where the etching becomes deep and reaches the active layer. That is, when the etched region reaches the active layer 4 as a result of dry etching as shown in FIG.
A semiconductor HJta (thickness: 2000 nm) made of GaO, 3Gao, and tAs is formed, and then a P-GaAs protective semiconductor layer 16 is formed. After this, as described in Example 1, the surface protection Si3N4 film 7 and the P-type electrode 8 are
(Au/cr), and Au-Ge/Ni//lu
An n-type electrode IO is formed.

P-A10.3Ga6. The role of the tAs semiconductor layer 18 is to make the energy barrier between the recessed portion of the cladding layer 13 and the active layer 4 almost equal to the energy barrier between the ridge portion of the cladding layer 13 and the active layer 4 . The protective semiconductor layer 16 made of P-GaAs serves not only as an electrode contact layer but also as a light absorption layer in the recessed region, and has the effect of confining light near the active layer.

Conventionally, the lifespan of a laser that cuts into the active layer 4 is 5 m at room temperature.
The time taken by W was about several hundred hours, but according to this example, the time was reduced to just one. In addition, in the present invention, the active layer includes:
Non-doped (liaAs is used, but MQW structure or SQW structure is also suitable for the active layer.Also, in the present invention, an n-substrate is used, but the same effect can be expected with a p-substrate.In that case, , if the polarities of P and n in the above-mentioned embodiments are reversed, an example using a P substrate can be obtained.

husband five side 1 FIG. 3 is a sectional view of a third embodiment of the invention.

The features of this embodiment are as follows: (1) The structure of the active layer 4 is a multiple quantum well structure (MQW); (2) After the formation of the protective semiconductor layer 16 made of silicon-doped n-GaAs, the ridge portion is removed. Then, the main surface of the electrode contact layer 6 is exposed, and then a P-type electrode (Gr/Au) is formed.
8 was formed. In this example, n-GaA
s protective semiconductor layer 16 and P-Al. , 5Gao5As
The voltage applied to the cladding layer 13 is reverse biased, and the current confinement effect is improved. The composition of the MQW active layer 4 is, for example, 4 layers of Alo, 5Gao, 7AS (100 people) and 5 layers of AIo, Gao, , , As (60 people).

Incidentally, the crystal growth method used in this embodiment is a molecular beam epitaxy method (MBE method), and the substrate temperature is 500 DEG C., and the ratio of S molecules to Ga molecules is As/Ga.about.2. However, when performing crystal growth, these conditions are not always necessary, and the substrate temperature is usually 400°C to 800°C, As/
The crystal used in this example can be produced if the Ga molecular ratio is 5 or less.

(Effects of the invention) As explained above, by forming several thousand thin films on the ridge, compared to the conventional ridge, stress due to the difference in thermal expansion coefficient is reduced and defects on the etched surface are reduced. The lifespan, which was previously less than several thousand hours, has now been reduced.
In addition to having a lifespan longer than the drinking time, it has become possible to have a degree of freedom in the etching technique, which requires the most controllability.

In this example, the GaAs/81Ga s system was described, but the problem of defects during regrowth can be seen in other AlGa1nP.
.

The same problem occurs in AlGa1nAs-based materials, and the present invention is also effective for these materials.

[Brief explanation of the drawing]

1 is a cross-sectional view of a first embodiment of the present invention, FIG. 2 is a cross-sectional view of a second embodiment of the present invention, FIG. 3 is a cross-sectional view of a third embodiment of the present invention, and FIG. The figure is a sectional view of one conventional example, and FIG. 5 is a sectional view of another conventional example. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Buffer layer, 3... Clad layer, 4... Active layer, 7... Insulating film, 8... P-type electrode, 10--n-type electrode, 13 -... cladding layer, 14-... ridge portion, 15-... recessed portion, 16... protective semiconductor layer. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] 1. A semiconductor laser having a ridge shape, characterized in that a semiconductor layer is provided between a cladding layer and a surface insulating film. 2. A method for manufacturing a semiconductor laser having a ridge shape, comprising: forming a cladding layer on an active layer; selectively etching a part of the cladding layer to form a ridge shape; forming a semiconductor layer on the surface of the semiconductor laser.