JPH06196810A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser element conducting self oscillation in small astigmatic difference at a small operating current value. CONSTITUTION:An n-type GaAs substrate 1, and n-type AlGaAs first clad layer 2 formed onto the n-type GaAs substrate 1, an active layer 4 shaped onto the first clad layer 2 and a p-type AlGaAs second clad layer 5 which a striped ridge section formed onto the active layer 4 are provided. An n-type AluGa1-u As first supersaturated optical absorption layer 3 is shaped into the first clad layer 2 while a p-type AluGa1-uAs second supersaturated optical absorption layer 6 is formed onto the p-type third AlGaAs clad layer 5a of the second clad layer 5, and the first and second supersaturated optical absorption layers 3, 6 have band gap energy equal to oscillation wavelength energy.

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 in which noise caused by returning light of output laser light is reduced.

[0002]

2. Description of the Related Art In a conventional semiconductor laser device, when return light of output laser light is re-incident on the semiconductor laser device, noise caused by this return light (hereinafter referred to as return light noise) is present in the output laser light. There was a problem that it occurred. Such return light noise is generated, for example, when the semiconductor laser element is used as a light source of an optical disk device, and the return light of the output laser light due to reflection from the disk surface or the like is re-incident on the semiconductor laser element.

A method of utilizing a self-oscillation phenomenon in order to reduce the return light noise of this semiconductor laser device is known, for example, Japanese Patent Application Laid-Open No. 63-202083 (H01S 3).
/ 18).

In such a semiconductor laser device, AlGaAs
The energy corresponding to the oscillation wavelength (oscillation wavelength energy: h
It is described that self-excited oscillation is caused by using a refractive index layer having a bandgap energy much larger than ν) or a light absorption layer having a bandgap energy much smaller than the oscillation wavelength energy.

[0005]

However, according to the experimental results of the applicant of the present application, in the case of a refractive index layer having a bandgap energy considerably larger than the above oscillation wavelength energy, the astigmatic difference increases, while the oscillation wavelength energy increases. It was found that the operating current value becomes large in the case of the light absorption layer having a much smaller bandgap energy.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor laser device which performs self-sustained pulsation with a small astigmatic difference and a small operating current value.

[0007]

A semiconductor laser device according to the present invention comprises a first conductivity type semiconductor substrate, a first conductivity type first clad layer provided on the semiconductor substrate, and a first clad layer on the first clad layer. And a second conductivity type second clad layer provided on the active layer, wherein the first and second clad layers have a refractive index smaller than that of the active layer and a large bandgap. At least one of the first and second cladding layers has a supersaturated light absorption layer (saturable light absorption layer) having a bandgap of energy substantially equal to the oscillation wavelength energy.

In particular, the first cladding layer is a first AlG layer.
an aAs clad layer and a second AlGaAs clad layer, and the first AlGaAs clad layer and the second AlGaA
an Al _u Ga _1-u As first supersaturated light absorption layer of the first conductivity type between the second cladding layer and the third AlGaAs cladding layer formed on the active layer; And a fourth AlGaAs clad layer forming a striped ridge portion formed on the third AlGaAs clad layer, and forming a second conductivity type Al _u Ga _1-u As second supersaturated light absorption layer on the third AlGaAs clad layer. It is characterized by having done.

[0009]

According to the present invention, since the supersaturated light absorption layer having the bandgap energy substantially equal to the oscillation wavelength energy is provided in at least one of the first and second cladding layers that sandwich the active layer, self-excitation Oscillation occurs with low astigmatic difference, low operating current, and single transverse mode.

In particular, the first cladding layer is a first AlG layer.
an AlAs clad layer and a second AlGaAs clad layer, and has a first conductivity type Al _u Ga _1-u As first saturable light absorption layer between the first and second AlGaAs clad layers, and the second clad layer is A third layer formed on the active layer
AlGaAs clad layer and fourth Al forming a striped ridge portion formed on the third AlGaAs clad layer.
And a second conductivity type Al _u Ga _1-u As second supersaturated light absorption layer formed on the third AlGaAs clad layer, the Al _u Ga _1-u As second supersaturated light 4A in which the absorption layer forms a striped ridge
The third layer formed on the active layer also functions as an etching stop layer when forming the 1 GaAs clad layer.
The layer thickness of the AlGaAs clad layer can be easily formed with high precision.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing an AlGaAs semiconductor laser device of this embodiment.

In the figure, 1 is an n-type GaAs substrate,
On the n-type GaAs substrate 1, a first n-type film having a layer thickness of 1 to 2 μm is formed.
Al _xa Ga _1-xa As (AlGaAs) cladding layer (typically composition ratio xa = 0.51) 2a, n-type A with layer thickness S ₁
l _u Ga _1-u As first saturable light absorbing layer (composition ratio u of 0.1
2 ≦ u ≦ 0.14, carrier concentration 2 × 10 ^{17 to} 5 × 10
¹⁷ cm ⁻³ ) 3, and an n-type second layer having a layer thickness t ₁ of 0.3 μm
An Al _xb Ga _1-xb As (AlGaAs) clad layer (typically composition xb = 0.51) 2b is formed in this order, and the clad layers 2a and 2b constitute the first clad layer 2. There is. That is, the first clad layer 2 has a first
The supersaturated light absorption layer 3 is formed.

A layer thickness of 0.08 is formed on the first cladding layer 2.
μm undoped Al _q Ga _1-q As (composition ratio q = 0.
13) The active layer 4 is formed.

A layer thickness t ₂ of 0.3 μm is formed on the active layer 4.
p-type third Al _ya Ga _1-ya As (AlGaA
s) Cladding layer (typically composition ratio ya = 0.51) 5
a, p-type Al _u Ga _{1 -u} As second supersaturated light absorption layer having a layer thickness S ₂ (composition ratio u is 0.12 ≦ u ≦ 0.14, carrier concentration 4 × 10 ¹⁷ to 2 × 10 ¹⁸ cm ^{− 3} ) 6, and height is 0.5
P-type fourth Al _yb Ga ₁ -yb As (AlG) forming a striped ridge having a stripe lower surface width W of 4 μm.
aAs) clad layer (typically composition ratio yb = 0.5
1) 5b are formed in this order, and the cladding layer 5
The second cladding layer 5 having a striped ridge portion is constituted by a and 5b.

A p-type GaAs cap layer 7 having a layer thickness of 0.3 μm is formed on the upper surface of the ridge portion of the fourth AlGaAs clad layer 5b, and the side surface of the p-type GaAs cap layer 7 and the fourth AlGaAs clad layer are formed. N-type GaAs current blocking layers 8 having a layer thickness of 0.8 μm are formed on the side surface of 5b and on the second supersaturated light absorption layer 6. A p-type GaAs contact layer 9 having a thickness of 4 μm is formed on the n-type GaAs current blocking layers 8 and 8 and the p-type GaAs cap layer 7.
Are formed.

Although not shown, a p-type ohmic electrode made of Au-Cr is formed on the p-type GaAs contact layer 9, and Au-Sn-Cr is formed on the lower surface of the n-type GaAs substrate 1.
The n-type ohmic electrode made of is formed.

In such a semiconductor laser device, the n-type Al _u Ga _1-u As first supersaturated light absorption layer 3 and the p-type Al _{u are used.}
The composition ratio u (here, both are the same composition ratio) and the layer thickness (here, the same layer thickness: S ₁ = S ₂ ) of the Ga _{1 -u} As second supersaturated light absorption layer 6 are changed, and the γ value ( Visibility), astigmatic difference, and operating current value at optical output of 3 mW were examined. Incidentally, here, as an example, an example in which an element having a laser cavity length of 250 μm is not coated with an end face is shown.

Here, the γ value indicates the degree of self-sustained pulsation (interference between longitudinal modes). When γ = 1, self-sustained pulsation is not performed, and as γ approaches 0, the self-sustained pulsation becomes higher. Get stronger.
According to the experimental results of the inventor of the present application, when the semiconductor laser device is mounted on the optical disk device, a good C / N value is obtained when the γ value is 0.7 or less, and a particularly good C / N value is obtained when the γ value is 0.6 or less. It has been found that the above-mentioned astigmatic difference is 17 in the optical system used in a general disc device.
With a small value of μm or less, sufficient laser light can be collected and a good C / N value can be obtained, and particularly with a value of 15 μm or less, good laser light can be collected and a better C / N value can be obtained. It turns out that

First, FIG. 2 shows that the composition ratio u of the Al _u Ga _1-u As first and second supersaturated light absorption layers 3 and 6 is 0.12 to 0.12.
The relationship between the γ value and the layer thickness of the first and second supersaturated light absorption layers 3 and 6 in the range of 0.14 is shown.

From FIG. 2, the γ value is 0.7 or less when the layer thickness of the supersaturated light absorbing layers 3 and 6 is 0.01 μm or more, and the γ value is 0.6 or less when 0.02 μm or more. I understand.

Next, referring to FIG. 3, the first and second supersaturated light absorption layers 3 and 6 in the composition ratio u of the first and second supersaturated light absorption layers 3 and 6 are in the range of 0.12 to 0.14. The relation between the layer thickness and the astigmatic difference is shown.

From FIG. 3, when the layer thickness of the first and second supersaturated light absorption layers 3 and 6 is 0.01 μm or more, and the composition ratio u is 0.13 or less, the astigmatic difference is 17 μm or less. It can be seen that when 0.02 μm or more, an astigmatic difference of 17 μm or less is obtained when the composition ratio u is 0.14 or less.

Subsequently, in FIG. 4, the first and second supersaturated light absorption layers 3 and 6 in the composition ratio u of the first and second supersaturated light absorption layers 3 and 6 are in the range of 0.12 to 0.14. Shows the relationship between the layer thickness and the operating current when the light output is 3 mW.

From FIG. 4, when the composition ratio is 0.12 or more, the layer thickness of the first and second supersaturated light absorption layers 3 and 6 is 0.0.
32 μm or less, when the composition ratio is 0.13 or more, the layer thickness is 0.041 μm or less, and when the composition ratio is 0.14 or more, the layer thickness is 0.043 μm or less, and the operating current is 80 mA or less, which is practically no problem. It turns out that it becomes a small value of.

As can be seen from FIGS. 2 to 4, the n-type Al _u Ga _{1 -u} As first supersaturated light absorption layer 3 and the p-type Al _u.
The Ga _{1 -u} As second supersaturated light absorption layer 6 is made of Al _q Ga _{1 -q.}
The difference in the Al composition ratio from the As active layer 4 is -0.01 to 0.0.
1 (that is, q-0.01≤u≤q + 0.01; 0≤u <
In the range of 1), it is a single transverse mode and γ
The values, the astigmatic difference, and the operating current value can be within good ranges. Such a good effect is
The band gap energy of the first and second supersaturated light absorption layers 3 and 6 is 0.0 in terms of an absolute value difference from the band gap energy of the active layer 3, that is, the oscillation wavelength energy.
This is because the values are 125 eV or less and are substantially equal to each other, so that a good supersaturated state is achieved.

Further, the composition ratio q of the Al _q Ga _1-q As active layer 4 is not limited to 0.13, and Al _u Ga _1-u is selected even when selected from the range of 0 ≦ q <1. As composition ratio u of the first and second supersaturated light absorption layers 3 and 6 (0 ≦ u <
1) and the values S ₁ and S ₂ of the respective layer thicknesses, if selected from the range shown by the hatched portion in FIG.
Both the astigmatic difference and the operating current value are better than those of the conventional one.

In the above description, the layer thickness t ₁ of the second AlGaAs clad layer 2b and the third AlGaAs clad layer 5a are set.
The layer thickness t _{2 of each} is 0.3 μm, but the layer thicknesses t ₁ , t
_By changing both ₂ to the layer thickness t, the γ value (visibility),
The astigmatic difference and the operating current value when the light output was 3 mW were examined. still,
Here, the composition ratio u and the layer thickness of the Al _u Ga _1-u As first and second supersaturated light absorption layers 3 and 6 are both u = 0.13 and 0.0.
3 μm, and the composition ratio q of the Al _q Ga _{1 -q} As active layer 4 is 0.13.

FIG. 6 shows the layer thickness t and the γ value (visibility).
Shows the relationship. From this figure, the layer thickness t is 0.27 μm or more, the γ value is 0.7 or less, and the layer thickness is 0.28 μm.
From the above, it can be seen that the γ value becomes 0.6 or less.

FIG. 7 shows the relationship between the layer thickness t and the astigmatic difference. It can be seen from this figure that the astigmatic difference is 17 μm or less when the layer thickness t is 0.33 μm or less, and the astigmatic difference is 15 μm or less when the layer thickness t is 0.32 μm or less.

FIG. 8 shows the relationship between the layer thickness t and the operating current. From this figure, it can be seen that the layer thickness t has a particularly good value in the range of 0.33 μm or less and a remarkably good value in the range of 0.32 μm or less.

Therefore, the layer thickness t of the second AlGaAs clad layer 2b and the third AlGaAs clad layer 5a can be selected within the range of 0.27 μm or more and 0.33 μm or less, and preferably within the range of 0.28 μm or more and 0.32 μm or less. You can select with. The second AlGaAs cladding layer 2b and the third AlGaAs cladding layer 5a have a layer thickness t.
Although (0.27 μm ≦ t ≦ 0.33 μm), the same effect can be obtained when the layer thicknesses t ₁ and t ₂ are selected in the range of 0.27 μm or more and 0.33 μm or less, and in particular 0.28 μm
A more desirable effect can be obtained by selecting in the range of m or more and 0.32 μm or less.

When the composition ratios of the Al _u Ga _1-u As first and second supersaturated light absorption layers 3 and 6 and the active layer 4 and the layer thicknesses are changed, the second AlGaAs cladding layer 2b and the second AlGaAs cladding layer 2b are also changed. A preferable effect can be obtained by optimizing the layer thickness of the 3AlGaAs cladding layer 5a.

A method of manufacturing such a semiconductor laser device will be described with reference to FIG.

First, as shown in FIG. 9A, the n-type first AlGaAs cladding is formed on the n-type GaAs substrate 1 by the metal organic chemical vapor deposition method (MOCVD method) or the molecular beam epitaxial growth method (MBE method). Layer 2a, n-type Al _u G
a _1-u As first supersaturated light absorption layer 3, n-type second AlGa
As clad layer 2b, undoped Al _q Ga _1-q As active layer 4, p-type third AlGaAs clad layer 5a, p-type Al _u Ga _1-u As second supersaturated light absorption layer 6, p-type fourth A
The 1GaAs clad layer 5b and the p-type GaAs cap layer 7 are continuously grown in this order.

Next, as shown in FIG. 9B, a stripe-shaped SiO 2 layer having a thickness of 0.2 μm is formed on the p-type GaAs cap layer 7 by using an ordinary photolithography technique or the like.
_{2 The} mask layer 10 is formed. Using the phosphoric acid-based etchant with the SiO ₂ mask layer 10 as a mask, the p-type GaAs cap layer 7 and the p-type fourth AlGaAs are left so that the p-type fourth AlGaAs cladding layer 5b remains to a thickness of 0.1 to 0.3 μm. After the cladding layer 5b is etched, the remaining cladding layer 5b is etched with a hydrochloric acid etching solution.
Are removed by etching to form a striped ridge portion. Here, in the hydrochloric acid etching solution, Al _t Ga _1-t As having a small Al composition ratio is changed to Al _s Ga having a large Al composition ratio.
_Since the etching rate is smaller than that of _1-s As (t <s), the p-type Al _u Ga _1-u As second supersaturated light absorption layer 6 is used.
Also has a function as a so-called etching stop layer. Therefore, the etching can be stopped with good controllability by the second supersaturated light absorption layer 6.

After that, as shown in FIG.
On the second supersaturated light absorption layer 6 and on the side surfaces of the p-type GaAs cap layer 7 and the p-type fourth AlGaAs cladding layer 5b in the shape of a ridge by MOCVD or MBE with the iO ₂ mask layer 10 interposed. The n-type GaAs current blocking layers 8 and 8 are formed.

[0037] Subsequently, as shown in FIG. 1, the SiO ₂
The mask layer 10 is removed with a hydrofluoric acid-based etching solution to remove the p
After the type GaAs cap layer 7 is exposed, a p type GaAs contact layer 9 is formed on the exposed p type GaAs cap layer 7 and the n type GaAs current blocking layers 8 and 8 by MOCVD or MBE. Then, the upper surface of the p-type GaAs contact layer 9 and the n-type GaAs substrate 1
A p-type side ohmic electrode made of Au—Cr and an n-type side ohmic electrode made of Au—Sn—Cr are formed on the lower surfaces of the two.

As described above, the p-type Al _u Ga _1-u As
Second saturable light absorbing layer 6, because it has a substantially equal band gap energy and the oscillation wavelength energy (Al _t G
a _1-t As has a larger band gap and a smaller refractive index as the composition ratio t thereof increases, and the fourth Al _yb Ga
_The Al composition ratio is smaller than that of the _1-yb As clad layer 5b (u <yb), the etching rate is slower than that of the clad layer 5b, and excessive light absorption is not performed, so a sufficient layer thickness is selected. it can. As a result, the second supersaturated light absorption layer 6 sufficiently functions as an etching stop layer during the mesa etching, and thus the third AlG on the active layer 4 is formed.
The layer thickness of the aAs clad layer 5a can be made highly accurate.

In the above embodiment, Al _q G is used as the active layer 4.
Although the a _1-q As (0 ≦ q <1) layer is used, a quantum well structure may of course be used. Also in this case, if each composition ratio u is selected so that the bandgap energy of the first and second supersaturated light absorption layers 3 and 6 is substantially equal to the oscillation wavelength energy, a low astigmatic difference at a low operating current is obtained. Good self-sustained pulsation occurs in the single transverse mode, and the second supersaturated light absorption layer 6 is more Al than the fourth AlGaAs cladding layer 5b.
The composition ratio is considerably small, and it functions as an etching stop layer. The first and second AlGaAs cladding layers 2a,
2b, third and fourth AlGaAs cladding layers 5a and 5b
(0 <xa, xb, ya, yb <1) has a smaller refractive index and a larger bandgap than the active layer 4 similarly to the above embodiment, that is, light and carriers having an oscillation wavelength can be sufficiently confined. Each layer thickness or each composition ratio is optimized to the extent possible.

Further, the second supersaturated light absorption layer 6 is not limited to the above position, but the third and fourth AlGaAs clad layers 5a and 5b.
May be provided at an appropriate position in the layer 5a or the layer 5b by appropriately changing the layer thickness. Further, the absolute value difference from the oscillation wavelength energy is 0.0125 eV or less, and the band gap energies are substantially equal. The supersaturated light absorption layer has the same effect if it is provided on either one of the clad layers sandwiching the active layer with an appropriate distance from the active layer, and is not limited to, for example, the ridge type semiconductor laser device of the present embodiment, It is also effective when used in a semiconductor laser device having another structure such as a self-aligned type. However, it is preferable to provide the supersaturated light absorption layers on both sides of the active layer because the spot shape of the output laser light becomes symmetric when the supersaturated light absorption layer is provided only on one side.

Further, although the AlGaAs semiconductor laser device has been described above, other materials such as AlGaInP may be provided with a saturable light absorption layer having a bandgap energy substantially equal to the oscillation wavelength energy in at least one cladding layer. Similar effects such as low astigmatic difference at low operating current and good self-sustained pulsation in single transverse mode can be obtained.

The term "having a supersaturated light absorption layer in the clad layer" as used in the present invention also includes those provided on the upper surface or the lower surface of the clad layer.

[0043]

According to the present invention, a supersaturated light absorption layer having a bandgap energy substantially equal to the oscillation wavelength energy is provided in at least one of the first and second cladding layers. At sufficiently small operating current, good self-sustained pulsation occurs in single transverse mode with astigmatic difference sufficiently smaller than in the past. As a result, a return light noise can be reduced, an optical system is easy, and a highly reliable semiconductor laser device can be obtained.

In particular, the first cladding layer is a first AlG layer.
an AlAs clad layer and a second AlGaAs clad layer, and has a first conductivity type Al _u Ga _1-u As first saturable light absorption layer between the first and second AlGaAs clad layers, and the second clad layer is A third layer formed on the active layer
An AlGaAs clad layer and a fourth ridge forming a striped ridge portion formed on the third AlGaAs clad layer.
consists of a lGaAs cladding layer, when forming the second conductivity type Al _u Ga _1-u As second saturable light absorbing layer on the 3AlGaAs cladding layer, the Al _u Ga _1-u As second saturable light absorbing layer Is a striped ridge-shaped fourth AlG
Since it also functions as an etching stop layer when forming the aAs clad layer, there is an effect that the layer thickness of the third AlGaAs clad layer on the active layer can be made highly accurate.
As a result, it is possible to easily form a semiconductor laser device that is strong against return light noise, has an easy optical system, and is highly reliable, with a high yield.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between a composition ratio u and a layer thickness of a supersaturated light absorption layer and a γ value in the above example.

FIG. 3 is a diagram showing the relationship between the composition ratio u and the layer thickness of the supersaturated light absorption layer of the above-described example and the astigmatic difference.

FIG. 4 is a diagram showing a relationship between a composition ratio u and a layer thickness of a supersaturated light absorption layer of the above-described example and an operating current.

FIG. 5 is a diagram showing the relationship between the composition ratio u and the layer thickness of the supersaturated light absorption layer of the above-described example, and good characteristics.

FIG. 6 is a diagram showing the relationship between the layer thickness t and the γ value of the second and third AlGaAs cladding layers in the above-mentioned embodiment.

FIG. 7 is a diagram showing the relationship between the layer thickness t and the astigmatic difference of the second and third AlGaAs clad layers in the above-mentioned embodiment.

FIG. 8 is a diagram showing the relationship between the layer thickness t of the second and third AlGaAs cladding layers and the operating current in the above-mentioned embodiment.

FIG. 9 is a diagram showing a manufacturing process of the semiconductor laser device according to the embodiment.

[Explanation of symbols]

1 n-type GaAs substrate (semiconductor substrate) 2 first clad layer 2a n-type first AlGaAs clad layer 2b n-type second AlGaAs clad layer 3 n-type Al _u Ga _1-u As first supersaturated light absorption layer 4 active layer 5 second Clad layer 5a n-type first AlGaAs clad layer 5b n-type second AlGaAs clad layer (ridge portion) 6 p-type Al _u Ga _1-u As second supersaturated light absorption layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kotaro Furusawa, 2-18, Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Inventor, Atsushi Tajiri 2--18, Keihan Hondori, Moriguchi City, Osaka Sanyo Denki (72) Inventor Toru Ishikawa 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (72) Inventor Kenichi Matsukawa 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. ( 72) Inventor Teruaki Miyake 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (72) Inventor Soken Goto 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. A semiconductor substrate of a first conductivity type, a first conductivity type first clad layer provided on the semiconductor substrate, an active layer provided on the first clad layer, and an active layer on the active layer. Second provided
A second clad layer of conductivity type, wherein the first and second clad layers have a refractive index and a larger bandgap smaller than that of the active layer, and at least one of the first and second clad layers is provided. A semiconductor laser device having a supersaturated light absorption layer having a bandgap having an energy substantially equal to an oscillation wavelength energy. 2. The first cladding layer is a first AlGaA layer.
s clad layer and a second AlGaAs clad layer, the first AlGaAs clad layer and the second AlGaAs
The first conductivity type Al _u Ga _1-u As (0
≦ u <1) A third AlGaAs having a first supersaturated light absorption layer and the second cladding layer formed on the active layer.
It is composed of a clad layer and a fourth AlGaAs clad layer forming a striped ridge portion formed on the third AlGaAs clad layer, and has a second conductivity type Al _u Ga _1-u As (0 ≦ u) on the third AlGaAs clad layer. <1) The semiconductor laser device according to claim 1, wherein a second supersaturated light absorption layer is formed. 3. The active layer comprises Al _q Ga _1-q As (0 ≦ q
3. The semiconductor according to claim 2, wherein the semiconductor is composed of a <1) layer, and the composition ratio u of each of the first and second supersaturated light absorption layers is selected from the range of q-0.01 ≦ u ≦ q + 0.01. Laser device.