JPH10294534A - Semiconductor laser device - Google Patents

Abstract

(57) [Problem] To provide a semiconductor laser device capable of obtaining a sufficient life and maintaining low noise characteristics without deteriorating device characteristics even during high-power operation. SOLUTION: On an n-GaAs substrate 101, n-Al
_0.5 Ga _0.5 As clad layer 102, non-doped quantum well active layer 103, p-Al _0.5 Ga _0.5 As first clad layer 104, p-Al _0.2 Ga _0.8 As light guide layer 105, p
-Al _0.14 Ga _0.86 As etching stopper layer 106,
p-Al _0.5 Ga _0.5 As second cladding layer 107 and p-
A GaAs cap layer 108 is sequentially grown and grown, and p-A
The lGaAs second cladding layer 107 and the p-GaAs cap layer 108 are processed into a ridge shape, and n-Al _0.7 Ga
_{A 0.3} As current blocking layer 109 is formed so as to bury both side surfaces of the ridge, a p-GaAs contact layer 110 is laminated, and finally an ohmic electrode is formed.

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 used as a light source for various optical disk systems, and more particularly to a self-oscillation type semiconductor laser device which operates with low noise when used as a light source for a recordable / reproducible optical disk system. The present invention relates to a semiconductor laser device.

[0002]

2. Description of the Related Art In a conventional semiconductor laser device used in an optical disk system or the like, so-called "return light noise" in which laser light reflected by a disk or the like re-enters the semiconductor laser device to generate noise, which is a problem. Has become.

As a means for reducing the return light noise, a method utilizing a self-excited oscillation phenomenon is known. For example, an Applied Physics Letter is used.
s68 (25) p3543-3545 (1996) describes a self-pulsation type semiconductor laser device using a saturable absorption layer in an AlGaInP-based visible light laser.

FIG. 17 shows a sectional structure of a semiconductor laser device described in the above document. This semiconductor laser device
On an n-GaAs substrate 1, an n-AlGaInP lower cladding layer 2, a strained quantum well active layer 3, a p-AlGaInP first
Upper cladding layer 4, p-GaInP saturable absorption layer 5, p-
AlGaInP light guide layer 6, p-AlGaInP second
The upper clad layer 7 and the p-GaInP cap layer 8 are laminated in this order.

Here, the p-AlGaInP second upper cladding layer 7 and the p-GaInP cap layer 8 are etched into a ridge shape, and p-AlGaI
An n-GaAs current blocking layer 9 is formed so as to bury the nP second upper cladding layer 7 and the p-GaInP cap layer 8.

Further, a p-GaAs contact layer 10 is formed on the p-GaInP cap layer 8 and the n-GaAs current blocking layer 9.

In the above configuration, p-AlGaInP disposed in contact with the upper surface of p-GaInP saturable absorption layer 5
The light guide layer 6 has a function of increasing the light confinement rate of the p-GaInP saturable absorption layer 5, and can increase the saturable absorption effect to obtain stable self-excited oscillation.

Furthermore, the p-GaInP saturable absorbing layer 5, zinc concentration of 2 × 10 ¹⁸ cm ^-3 as a p-type impurity in order to accelerate the disappearance of carriers generated by light absorption is added. When the impurity concentration in the saturable absorption region is high, the lifetime of carriers generated by light absorption is shortened, and the contribution of spontaneous emission light to the rate of change in carrier density with time is increased. Therefore, according to the self-sustained pulsation type semiconductor laser device having the above configuration, the saturable absorption effect is improved and self-sustained pulsation is easily generated, and the temperature characteristics and noise characteristics of the semiconductor laser device are greatly improved. It is described in the above-mentioned document that it has a long life even in continuous operation.

[0009]

However, the present inventors conducted an experiment by applying the self-pulsation type semiconductor laser device described above to a recordable / reproducible semiconductor laser device. It was found that a sufficient life could not be obtained at the time of necessary high-output operation. When the cause was examined, the following was found.

That is, on or near the p-GaInP saturable absorption layer 5, there are many crystal defects due to crystal regrowth and the like. In addition, the saturable absorption layer 5 inside the ridge not only serves as a path for the operating current but also constantly generates and disappears carriers. For this reason, crystal defects are likely to occur. Particularly, as in the above conventional example, 2 × 10 ¹⁸ cm
^When impurities are added at a high concentration of ^-3 , this p-Ga
Many crystal defects occur in the InP saturable absorption layer 5.

For this reason, during high-power operation, these crystal defects and impurities multiply or diffuse, and proceed to the strained quantum well active layer 3, so that the life of the semiconductor laser device during high-power operation is deteriorated. In addition, in order to suppress current spreading and reduce astigmatism, p-AlGaInP first
It is necessary to reduce the thickness of the upper cladding layer 4, and the deterioration of device characteristics becomes even more remarkable.

Further, in recent optical disk systems, the rotational speed of the optical disk tends to increase in order to improve the writing speed, and a recording / reproducing semiconductor laser is required to have both high output operation and low noise. .

The present invention has been made in view of such circumstances, and even during high-output operation, the element characteristics are not degraded, a sufficient life can be obtained, and high-output operation and low noise It is an object of the present invention to provide a semiconductor laser device capable of maintaining both.

[0014]

A semiconductor laser device according to the present invention includes a lower cladding layer, an active layer, a first upper cladding layer, a light guide layer, an etching stopper layer, and a second upper cladding layer on a semiconductor substrate. In a semiconductor laser device in which a plurality of semiconductor layers are formed and a current confinement portion having a stripe-shaped opening is formed in the second upper cladding layer, the light guide layer is provided between the etching stopper layer and the active layer. Wherein the band gap of the light guide layer is smaller than the band gap of the first upper cladding layer and larger than the band gap of the etching stopper layer, and the etching stopper layer or the light guiding layer and the etching stopper layer Has a saturable absorption effect on the oscillating laser light, thereby achieving the above object.

In the semiconductor laser device of the present invention having the above structure, the etching stopper layer also has the function of a saturable absorbing layer, and the optical guide layer is disposed below the etching stopper layer close to the active layer. I have. This light guide layer has not only the function of increasing the light confinement rate of the saturable absorption layer, but also the function of suppressing the growth of crystal defects in the regrowth interface and the saturable absorption layer and progressing to the active layer. I have.

Therefore, according to the above configuration, even during high-power operation of the semiconductor laser device, these crystal defects can be prevented from multiplying and proceeding to the active layer, so that the device life of the semiconductor laser device is degraded. Never do.

Therefore, according to the present invention, a semiconductor laser device having a long life and a high reliability even at the time of high output operation can be realized.

Preferably, the difference between the laser oscillation wavelength λ1 of the active layer and the wavelength λ2 corresponding to the band gap of the etching stopper layer is within a range satisfying the following condition: -12 nm ≦ λ1-λ2 ≦ 2 nm And Here, the wavelength corresponding to the band gap is a value obtained by replacing the energy difference due to the quantum level between the valence band and the conduction band with the wavelength when each layer is a quantum well layer as shown in FIG. Define.

When λ1-λ2 takes a positive value with a large absolute value, the saturable absorption effect in the etching stopper layer is weak, and stable self-pulsation cannot be obtained. Therefore, noise occurs even with a small amount of return light. On the other hand, when λ1−λ2 takes a large negative value, the saturable absorption effect in the etching stopper layer is strong and return light noise can be sufficiently avoided.
At the oscillation threshold, the current light output characteristic shows a switching operation, and the quantum noise caused by the fluctuation of the light output increases. If the difference between the laser oscillation wavelength λ1 of the active layer and the wavelength λ2 corresponding to the band gap of the etching stopper layer is in the range of −12 nm ≦ λ1−λ2 ≦ 2 nm, both the return light noise and the quantum noise are reduced. Can be reduced. Therefore, stable low noise characteristics can be obtained in a wide light output range.

Preferably, the difference between the wavelength λ2 corresponding to the band gap of the etching stopper layer and the wavelength λ3 corresponding to the band gap of the optical guide layer is within a range satisfying the following condition: 0 nm <λ2 −λ3 ≦ 70 nm

At the start of laser oscillation, if the life of carriers generated by light absorption is short, the switching operation in current light output characteristics becomes remarkable. Therefore, it is desirable that the carrier life be relatively long at low output. On the other hand, as the optical output increases, the photon density increases in the saturable absorption region and the number of generated carriers increases. Therefore, it is necessary to shorten the carrier life in order to maintain self-pulsation. If the band gap difference λ2-λ3 between the etching stopper layer and the optical guide layer is in the range of 0 nm <λ2-λ3 ≦ 70 nm, excessive generation of carriers in the etching stopper layer, which is a saturable absorption region, occurs. It easily overflows to the light guide layer. As a result, the life of the generated carriers can be substantially shortened only at the time of the high output operation, so that both the high output operation and the low noise characteristic can be achieved.

Preferably, the impurity concentration added to the light guide layer is greater than 1 × 10 ¹⁸ cm ^-3 and 1 × 1
The structure is smaller than 0 ¹⁹ cm ⁻³ .

If the concentration of the impurity added to the light guide layer is within the above range, excess generated carriers overflow into the light guide layer only during high-power operation and disappear in a short time. In addition, it is possible to avoid the introduction of crystal defects that lower the reliability of the device. Therefore, the reliability and low noise characteristics of the semiconductor laser device are maintained up to high output.

Preferably, the concentration of the impurity added to the etching stopper layer is greater than 5 × 10 ¹⁷ cm ^{−3 and} less than 3 × 10 ¹⁸ cm ⁻³ .

If the concentration of the impurity added to the etching stopper layer is within the above range, the carrier disappears in the etching stopper layer having a relatively long carrier life at low output with few generated carriers, so that the switching operation of the current light output characteristic is performed. Can be alleviated. Therefore, current light output characteristics with good linearity can be obtained in a wide output range, and the low noise characteristics of the semiconductor laser device can be maintained.

Preferably, the bandgap of the light guide layer has a variation that increases on the etching stopper layer side and decreases on the first upper cladding layer side.

According to this configuration, the generated carriers that have once overflowed into the optical guide layer do not return to the etching stopper layer side, but diffuse into the vicinity of the first upper cladding layer having a low energy level and disappear. Therefore, it is possible to maintain low noise characteristics up to a higher output.

Preferably, the light guide layer has a multiple quantum well structure.

According to this structure, generated carriers overflowing to the light guide layer are confined in the well layer, so that they do not return to the etching stopper layer side and are easily lost by recombination. Therefore, even if carriers are excessively generated by the high-power operation, the lifetime can be shortened and low noise characteristics can be maintained.

[0030] Preferably, the impurity concentration of the light guide layer has a variation that decreases on the etching stopper layer side and increases on the first upper cladding layer side.

According to this configuration, the generated carriers overflowing to the light guide layer are more easily eliminated when they diffuse toward the first upper cladding layer. Therefore, it is possible to maintain low noise characteristics up to a higher output.

Preferably, the total thickness of the light guide layer is not less than 100 ° and not more than 200 °.

When the thickness of the light guide layer is reduced, the light confinement ratio to the etching stopper layer is reduced, and the saturable absorption effect cannot be maintained up to a high output. It becomes easy to show the target action. Within the above range, the effect of confining light to the etching stopper layer can be enhanced and the sharp rise of the current light output characteristics can be suppressed. Therefore, current light output characteristics with good linearity are obtained over a wide range, and low noise characteristics are maintained.

Preferably, the etching stopper layer is arranged only in the stripe-shaped opening.

According to this configuration, the difference in effective refractive index between inside and outside of the stripe can be increased. Therefore, the astigmatic difference can be reduced and the transverse mode can be stabilized.

[0036] Preferably, the etching stopper layer has a region at least partially removed in the vicinity of the light emitting end face.

According to this structure, when the return light from the optical disk or the like re-enters the semiconductor laser end face, it is less likely to cause an interaction with the region having the saturable absorption effect. Therefore, a stable self-excited oscillation operation can be obtained.

[0038] Preferably, the etching stopper layer is formed of a material not containing Al.

According to this structure, crystal defects such as a regrowth interface caused by oxidation of Al can be reduced. Therefore, the characteristics and reliability of the element can be further improved.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings.

In the following, the unit of the layer thickness is μm, but Å is mainly used for the layer thickness of an extremely thin layer having a quantum effect.

(Embodiment 1) FIG. 1 shows Embodiment 1 of the semiconductor laser device of the present invention. In the first embodiment, the primary power source is Al
An example in which the present invention is applied to a ridge-type semiconductor laser device using a GaAs-based material will be described.

Referring to FIG. 1, the structure of the semiconductor laser device will be described together with the manufacturing process. First, the n-GaAs substrate 1
01 in a growth apparatus (not shown).
On the aAs substrate 101, n-
Al _0.5 Ga _0.5 As lower cladding layer 102 (carrier concentration 1 × 10 ¹⁸ cm ^-3, thickness 1.0 .mu.m), a non-doped quantum well active layer _{103, p-Al 0.5 Ga 0.5} As first upper cladding layer 104 (carrier concentration 1 × 10 ¹⁸ cm ⁻³ , thickness 0.17 μm), p-Al _0.2 Ga _0.8 As light guide layer 1
05 (carrier concentration 1 × 10 ¹⁸ cm ⁻³ , thickness 200)
Å), p-Al _0.14 Ga _0.86 As etching stopper layer 106 (carrier concentration 1 × 10 ¹⁸ cm ⁻³ , thickness 100)
Å), p-Al _0.5 Ga _0.5 As second upper cladding layer 107
(Carrier concentration 1 × 10 ¹⁸ cm ⁻³ , thickness 1.2 μm) and p-GaAs cap layer 108 (carrier concentration 1 × 1
0 ¹⁸ cm ^-3 and a thickness of 0.1 μm) are sequentially grown.

Here, the non-doped quantum well active layer 103
_Represents an Al _0.14 Ga _0.86 As well layer (thickness: 100 mm);
It is formed in a triple well structure composed of a l _0.3 Ga _0.7 As barrier layer (thickness of 100 °) and a guide layer of the same composition (thickness of 300 °).

Further, p-Al _0.14 G serving as a saturable absorption layer
a _0.86 As The band gap of the etching stopper layer 106 was measured by a photoluminescence method, and the corresponding wavelength λ2 was 792 nm.

Next, the n-G on which the above-described semiconductor layer is formed
The aAs substrate 101 is taken out of the growth apparatus, and the p-GaAs cap layer 1 is formed using a known photolithography technique.
A stripe-shaped SiO ₂ film is formed on the substrate 08. Then, using this SiO ₂ film as an etching mask, p-AlGaAs is etched to reach the p-AlGaAs etching stopper layer 106 using a known selective etching technique.
Second upper cladding layer 107 and p-GaAs cap layer 1
08 is processed into a ridge shape.

In the first embodiment, hydrofluoric acid was used as the selective etching solution. The ridge width is p-AlG
1 at the interface with the aAs etching stopper layer 106
４4 μm.

Thereafter, the n-GaAs substrate 101 is set again in the growth apparatus, and the n-Al _0.7 Ga _0.3 As current blocking layer 109 (carrier concentration) is formed by the second crystal growth while leaving the SiO ₂ film. 3 × 10 ¹⁸ cm ⁻³ , thickness 0.6 μm). At this time, AlGaAs is formed on the SiO ₂ film by using a known selective growth technique.
The film does not grow, and the current blocking layer 109 is formed so as to bury both side surfaces of the ridge portion.

Thereafter, the n-GaAs substrate 101 is taken out of the growth apparatus again, and the SiO ₂ film is removed.

Next, the n-GaAs substrate 101 is set again in the growth apparatus, and the p-GaAs contact layer 110 (carrier concentration 5 × 1) is formed by the third crystal growth.
0 ¹⁸ cm ^-3 and a thickness of 2.0 μm). Finally p-
Ohmic electrodes (not shown) are formed on the upper surface of the GaAs contact layer 110 and the lower surface of the n-GaAs substrate 101, and the cavity length is adjusted to 375 μm by a cleavage method.
15% reflectivity on the exit end face, 7 reflectivity on the opposite end face
A 5% coating film is formed. Through the above steps, a ridge-type semiconductor laser device of the first embodiment was obtained. When the oscillation wavelength λ1 of the semiconductor laser device of the first embodiment was measured, it was 785 nm.

Table 1 below shows the result of evaluating the maximum self-excited oscillation output and the aging yield of the semiconductor laser device of Embodiment 1 together with Comparative Example 1. The semiconductor laser device of Comparative Example 1 had the same structure as the semiconductor laser device of Embodiment 1 except that the light guide layer 105 was disposed above the etching stopper layer 106.

[0052]

[Table 1]

In Table 1, the aging yield indicates the rate of increase in drive current within 20% of the initial value after a life test at a temperature of 60 ° C. and an output of 35 mW for 1000 hours.

As understood from Table 1, the light guide layer 1
Comparative Example 1 in which the light guide layer 105 is disposed above the etching stopper layer 106 is the semiconductor laser device of the first embodiment in which the light-transmitting layer 05 is disposed below the etching stopper layer 106.
As compared with the semiconductor laser device of the above, the device life is improved.

The reason why such a result is obtained is considered as follows.

The light guide layer 105 is made of Al from the p-first upper cladding layer 104 and the p-second upper cladding layer 107.
Since the mixed crystal ratio is low, defects are unlikely to occur inside the crystal and at the interface. That is, the light guide layer 105 not only has a function of increasing the light confinement rate of the etching stopper layer 106 serving as a saturable absorption layer, but also has a function of suppressing the growth of crystal defects at the regrowth interface and progressing to the active layer 103. It is considered that they have the same.

In particular, in the semiconductor laser device of the first embodiment, since the light guide layer 105 has no regrowth interface, the effect of suppressing defects is higher than that of the comparative example. Therefore, in the semiconductor laser device of the first embodiment, a sufficient life can be obtained without deteriorating device characteristics even during high-power operation.

Next, the Al of the etching stopper layer 106 is
The etching stopper layer 1 can be formed by changing the mixed crystal ratio.
A semiconductor laser device having the same structure as that of the semiconductor laser device of the first embodiment is manufactured except that the wavelength λ2 corresponding to the band gap of 06 is changed, and the light output and the relative noise intensity (hereinafter referred to as RIN) are obtained.
The result of evaluating the relationship is shown in FIG. Optical path length is 20mm
And the measurement frequency and bandwidth are each 720 kHz · 1
0 kHz. RIN indicates the maximum value when changed at a return light rate of 1 to 15%.

From FIG. 2, the saturable absorption effect increases as the value of λ1-λ2 becomes a negative value having a large absolute value.
It can be seen that self-sustained pulsation continues until high output. As the noise approaches the maximum self-oscillation output, the noise gradually increases.
IN maintains a low noise characteristic of -130 dB / Hz or less. When the output further increases and the self-sustained pulsation stops, the noise rapidly increases. From this, it can be seen that both high output operation and low noise characteristics are realized by increasing the maximum self-excited oscillation output.

Next, these semiconductor laser devices were applied to an optical pickup to measure jitter (fluctuation in the time axis of the reproduced signal).

FIG. 3 shows the relationship between λ1-λ2 and the reproduction jitter. In the case of a normal optical disk system, if the reproduction jitter is 20 nsec or less, there is little possibility that a practical problem will occur. The range that satisfies this is −12 nm ≦ λ1−λ2 ≦ 2 nm, as can be seen from FIG. The reason why this result was obtained is considered as follows.

When λ1-λ2 is larger than 2 nm, the saturable absorption effect in the etching stopper layer 106 is weak (low), and stable self-pulsation cannot be obtained. Therefore,
It is considered that noise occurs even with a small amount of return light, fluctuations occur in the reproduced signal, and jitter deteriorates.

On the other hand, when λ1-λ2 is smaller than -12 nm, the saturable absorption effect in the etching stopper layer 106 is strong (high) and return light noise can be sufficiently avoided. However, in this case, the light output-current characteristic shows a switching operation at the oscillation threshold, and the quantum noise due to the fluctuation of the light output increases. It is considered that the jitter deteriorated due to the quantum noise.

From the above inference results, in order to avoid both return light noise and quantum noise and obtain stable low noise characteristics in a wide light output range, the laser oscillation wavelength λ1 of the active layer 103 and the etching stopper layer 106 It can be seen that the configuration should be such that the difference λ1-λ2 from the wavelength λ2 corresponding to the band gap of is within the range of −12 nm ≦ λ1-λ2 ≦ 2 nm.

In the first embodiment, the quantum well layer of the active layer 103 has a three-layer structure. However, a so-called multiple quantum well structure employing another number of well layers may be used.
The same effect as described above can be obtained.

In the first embodiment, the case where the present invention is applied to a high-output semiconductor laser device has been described. However, the present invention is similarly applied to a low-output semiconductor laser device for reading information. be able to. In this case, there is an advantage that the element life can be further improved.

(Embodiment 2) In Embodiment 2, the structure is the same as that of Embodiment 1 except that the structures of the light guide layer 105 and the etching stopper layer 106 are different from those of Embodiment 1. That is, in Embodiment 2, the light guide layer 105 is made of p-Al _0.13 Ga _0.87 As (carrier concentration 2 × 10 ¹⁸ cm ⁻³ , thickness 150 °), and the etching stopper layer 106 is made of p-GaAs (carrier concentration 1 × 1
0 ¹⁸ cm ^-3 and a thickness of 30 °).

The etching stopper layer 106 according to the second embodiment has a very small thickness and a substantial band gap is widened due to a quantum effect, and therefore has no saturable absorption effect by itself. However, the quantum level of the etching stopper layer 106 is affected by the light guide layer 105 disposed on the lower surface of the etching stopper layer 106, and the light absorption wavelength shifts to a longer wavelength side. Thereby, the etching stopper layer 106 functions as a saturable absorption layer. The laser emission wavelength λ of the active layer was measured by the photoluminescence method.
The difference between 1 and the wavelength λ2 corresponding to the band gap of the etching stopper layer was λ1−λ2 = −5 nm.

Light Guide Layer 105 in Second Embodiment
Has a band gap similar to that of the quantum well active layer, and thus has an etching stopper layer 10 serving as a saturable absorption layer.
6, the light guide layer 105 itself also functions as a saturable absorption layer. However, the saturable absorption effect is weaker than that of the etching stopper layer 106. When measured by the photoluminescence method, the difference between the wavelength λ2 corresponding to the band gap of the etching stopper layer 106 and the wavelength λ3 corresponding to the band gap of the optical guide layer 105 was λ2−λ3 = 20 nm.

Table 2 below shows the evaluation results of the maximum self-sustained pulsation output and the aging yield of the semiconductor laser device of the second embodiment. The aging conditions are the same as in the first embodiment.

[0071]

[Table 2]

According to Table 2, the semiconductor laser device of the second embodiment is different from the semiconductor laser device of the first embodiment in that
The maximum self-oscillation output has been improved. The reason why such a result was obtained is considered as follows.

As the light output of the semiconductor laser device increases, the light intensity in the etching stopper layer 106 also increases, and the carriers generated by the saturable absorption effect increase. These generated carriers are the etching stopper layer 1
Recombine and disappear in step 06, but the etching stopper layer 1
When the band gap difference between the light guide layer 06 and the light guide layer 105 is small, excess carriers that cannot be completely eliminated by the etching stopper layer 106 overflow to the light guide layer 105 side. The light guide layer 105 is an etching stopper layer 106
Since the volume is larger than that of, extinction is promoted by diffusion. Therefore, the carrier lifetime is substantially shorter than when the generated carriers are consumed only by the etching stopper layer 106. Therefore, saturation of light absorption hardly occurs, and self-excited oscillation is maintained even at high output.

Next, except that the wavelength λ3 corresponding to the band gap of the light guide layer 105 was changed by changing the Al composition ratio of the light guide layer 105, the same structure as the semiconductor laser device of the second embodiment was adopted. FIG. 4 shows the result of measuring the maximum self-excited oscillation output of the fabricated device. As the wavelength difference λ2-λ3 corresponding to the band gap between the etching stopper layer 106 and the light guide layer 105 increases, the maximum self-oscillation output decreases, and when the wavelength is 70 nm or more, the maximum self-oscillation output sharply decreases. Thus, the etching stopper layer 1
In order for excess carriers at 06 to overflow to the light guide layer 105 side, it is understood that the wavelength difference corresponding to the band gap difference between the etching stopper layer 106 and the light guide layer 105 is preferably 70 nm or less. When λ2−λ3 ≦ 0 nm, the light guide layer 105
Is smaller than the band gap of the etching stopper layer 106, so that the saturable absorption effect in the light guide layer 105 becomes significant. As a result, defects that multiply due to laser driving progress to the active layer 3, and the life of the semiconductor laser element is degraded.

Further, in the semiconductor laser device of the present invention, the carrier overflow does not occur during the low light output operation, the generated carriers disappear only by the etching stopper layer 106 having a relatively long life, and the switching operation of the current light output characteristic is performed. Less likely. As the output becomes higher, excess carriers overflow into the light guide layer 105, and the effective carrier life is shortened.

Next, a semiconductor laser device having the same structure as that of the semiconductor laser device of the second embodiment is manufactured except that the thickness of the light guide layer 105 is changed. FIG. 5 shows the result of the measurement.
When the thickness of the light guide layer 105 is 100 ° or less, the effect of confining light in the etching stopper layer 106 is weakened, and the maximum self-excited oscillation output is small. On the other hand, at 200 ° or more, the substantial carrier life becomes extremely short, and the switching operation of the current light output characteristics becomes remarkable. Therefore, in order to maintain self-sustained pulsation in a wide output range and obtain current light output characteristics with good linearity, the thickness of the light guide layer 105 is 10
It is preferable to set the angle between 0 ° and 200 °.

As can be seen from Table 2, the semiconductor laser device according to the second embodiment has the same aging yield as the semiconductor laser device according to the first embodiment, although the maximum self-excited oscillation output is improved. I have. Since the etching stopper layer 106 in Embodiment 2 does not contain Al, the surface is hardly oxidized. Therefore, it is considered that the defects at the regrowth interface were reduced as compared with the semiconductor laser device of Embodiment 1, and the reliability was maintained even at a higher output.

In the second embodiment, the thickness of the p-GaAs etching stopper layer 106 is set to 30 °. However, in the quantum well structure, the substantial band gap changes depending on the thickness. The thickness of the etching stopper layer is preferably 100 ° or less. In order to have a sufficient etching stop function for an etching solution such as hydrofluoric acid, the thickness of the etching stopper layer is preferably 10 ° or more.

In the second embodiment, the light guide layer 105 itself also functions as a saturable absorbing layer. However, if λ2−λ3 is within the above range, even if the layer does not absorb laser light, it can be used for high output operation. Since the carrier overflow easily occurs, the same effect can be obtained.

(Embodiment 3) The semiconductor laser device of Embodiment 3 is different from that of Embodiment 2 in that the impurity concentration of the light guide layer 105 is different from that of the light guide layer 105 of Embodiment 2.
It has a similar configuration. That is, the impurity concentration of the light guide layer 105 in the third embodiment is 5 × 10 ¹⁸ cm ^−3, which is different from the second embodiment in which the impurity concentration is 2 × 10 ¹⁸ cm ⁻³ .

Table 3 below shows the evaluation results of the maximum self-pulsation output and the aging yield of the semiconductor laser device of the third embodiment. The aging conditions are the same as in the first embodiment.

[0082]

[Table 3]

According to Table 3, the semiconductor laser device of the third embodiment is different from the semiconductor laser device of the second embodiment in that
Further, the maximum self-excited oscillation output is improved. This is because the impurity concentration of the light guide layer 105 is higher than that of the second embodiment, and the life of the overflowed excess carriers is shortened. As a result, it is considered that the saturation of the light absorption hardly occurs, and the self-sustained pulsation was maintained even at a higher output.

Next, a semiconductor laser device having the same structure as that of the third embodiment except that the impurity concentration of the light guide layer 105 was changed was fabricated, and the results of evaluating the maximum self-excited oscillation output and the aging yield were shown. 6 is shown. Light guide layer 105
When the impurity concentration is 1 × 10 ¹⁸ cm ⁻³ or more, the maximum self-sustained pulsation output sharply increases. However, when the impurity concentration is 1 × 10 ¹⁹ cm ⁻³ or more, crystal defects easily occur and the yield sharply decreases. Therefore, in order to maintain the self-sustained pulsation and the element life up to a high output, the impurity concentration of the light guide layer 105 must be 1 × 10 ¹⁸
It is preferable that it is not less than cm ^{−3 and not} more than 1 × 10 ¹⁹ cm ⁻³ .

In the third embodiment, although the maximum self-oscillation output is improved as compared with the second embodiment,
No decrease in aging yield is observed. This is because the generated carrier is consumed by the light guide layer 105 during a high light output operation, so that the impurity concentration of the etching stopper layer that easily causes crystal defects due to a high cycle of self-excited vibration can be set low.

Next, FIG. 7 shows the results of evaluating the maximum self-excited oscillation output and the jump of the optical output at the oscillation threshold value by changing the impurity concentration of the etching stopper layer 106 for the semiconductor laser device of the third embodiment. When the impurity concentration of the etching stopper layer 106 is 5 × 10 ¹⁷ cm ⁻³ or less, self-sustained pulsation hardly occurs, and when the impurity concentration is 3 × 10 ¹⁸ cm ⁻³ or more, the switching operation becomes remarkable. Therefore, in order to maintain the self-sustained pulsation in a wide output range and obtain a current light output characteristic with good linearity, it is necessary to use the etching stopper layer 10.
6 has an impurity concentration of 5 × 10 ¹⁷ cm ⁻³ or more and 3 × 10 ¹⁸ m ⁻³
The following is preferred.

(Embodiment 4) The semiconductor laser device of Embodiment 4 has the same configuration as that of Embodiment 3 except that the Al mixed crystal ratio of the light guide layer 105 changes in the layer thickness direction. That is, as shown in FIG. 8, the Al mixed crystal ratio of the light guide layer 105 of the fourth embodiment is 0.14 to 0.1 in the layer thickness direction.
2, the band gap is large on the etching stopper layer 106 side and small on the first upper cladding layer 104 side. This is different from the third embodiment in which the Al mixed crystal ratio of the light guide layer 105 is constant in the layer thickness direction.

Table 4 below shows the evaluation results of the maximum self-excited oscillation output and the aging yield of the semiconductor laser device of the fourth embodiment. The aging conditions are the same as in the first embodiment.

[0089]

[Table 4]

From Table 4, it can be seen that the semiconductor laser device of the fourth embodiment is different from the semiconductor laser device of the third embodiment.
Further, the maximum self-excited oscillation output is improved. This is because generated carriers overflowing to the light guide layer 105 during high light output operation are diffused near the first upper cladding layer 104 having a low energy level and disappear, so that they do not return to the etching stopper layer 106. Therefore, it is possible to maintain low noise characteristics up to a higher output.

In the fourth embodiment, the light guide layer 105
Although the l-mixed crystal ratio was changed from 0.14 to 0.2, the maximum value of the difference between the wavelength λ2 corresponding to the band gap of the etching stopper layer 106 and the wavelength λ3 corresponding to the band gap of the optical guide layer 105 was 0 nm. The effect of the present invention is effective within the range of <λ2−λ3 ≦ 70 nm.

In the fourth embodiment, the degree of change in the Al mixed crystal ratio is constant in the layer thickness direction. However, the same effect can be obtained if the first upper cladding layer 104 has a lower energy level. Therefore, the change rate of the Al mixed crystal ratio may be changed in the layer thickness direction, or may be multi-stepped.

Embodiment 5 The semiconductor laser device of Embodiment 5 has the same configuration as that of Embodiment 3 except that the light guide layer 105 has a multiple quantum well structure. That is, as shown in FIG.
5 is three Al _0.12 Ga _0.88 As well layers (each 50 Å in thickness)
And a multiple quantum well structure in which two Al _0.3 Ga _0.7 As barrier layers (each having a thickness of 30 °) are alternately arranged, which is different from the third embodiment having a single quantum well structure.

Table 5 below shows the evaluation results of the maximum self-excited oscillation output and the aging yield of the semiconductor laser device of this embodiment. The aging conditions are the same as in the first embodiment.

[0095]

[Table 5]

Table 5 shows that the semiconductor laser device of the fifth embodiment is different from the semiconductor laser device of the third embodiment.
Further, the maximum self-excited oscillation output is improved. This is because generated carriers overflowing to the light guide layer 105 during high light output operation are confined in the well layer surrounded by the barrier layer and disappear, and do not return to the etching stopper layer 106. Therefore, it is possible to maintain low noise characteristics up to a higher output.

Further, the present embodiment 5 is replaced by A
When applied to an optical guide layer in which the l-crystal ratio was changed, the maximum self-sustained pulsation output was further improved.

In the fifth embodiment, the number of wells in the multiple quantum well light guide layer 105 is set to 3. However, the effect of the present invention is the same even if the number of wells is other. Further, the thickness and the mixed crystal ratio of the barrier layer may have any structure as long as carriers are confined in the well layer without returning to the etching stopper layer.

Embodiment 6 The semiconductor laser device of Embodiment 6 has the same configuration as that of Embodiment 3 except that the impurity concentration of the light guide layer 105 changes in the layer thickness direction. That is, as shown in FIG. 10, the impurity concentration of the light guide layer 105 of the sixth embodiment is 3 × 10 ¹⁸ cm ^{−3 in the} layer thickness direction.
To 1 × 10 ¹⁹ cm ⁻³ , which is smaller on the etching stopper layer 106 side and larger on the first upper cladding layer 104 side. This is different from the third embodiment in which the impurity concentration of the light guide layer 105 is constant in the layer thickness direction.

Table 6 below shows the evaluation results of the maximum self-sustained pulsation output and the aging yield of the semiconductor laser device of the sixth embodiment. The aging conditions are the same as in the first embodiment.

[0101]

[Table 6]

Table 6 shows that the semiconductor laser device of the sixth embodiment is different from the semiconductor laser device of the third embodiment in that
Further, the maximum self-excited oscillation output is improved. By providing a gradient in the impurity concentration of the light guide layer 105 as in the present embodiment, the carrier life can be reliably shortened even if the carrier overflow increases. As a result, it is considered that the saturation of the light absorption hardly occurs, and the self-sustained pulsation was maintained even at a higher output.

When the impurity concentration profile of Embodiment 6 was applied to the light guide layers of Embodiments 4 and 5, the maximum self-pulsation oscillation output was further improved in any of the embodiments.

(Embodiment 7) FIG. 11 shows a semiconductor laser device according to Embodiment 7 of the present invention. Embodiment 7 shows an example in which the present invention is applied to a self-aligned red semiconductor laser device using an AlGaInP-based material.

Referring to FIG. 11, the structure of the semiconductor laser device will be described together with the manufacturing steps. However, in FIG.
The same reference numerals are given to the same parts as.

First, the n-GaAs substrate 101 is set in a growth apparatus (not shown), and the n-GaAs substrate 10
On the first crystal growth, a thickness of n- (Al _0.7
Ga _0.3 ) _0.51 In _0.49 P lower cladding layer 102, non-doped strained quantum well active layer 103, p- (Al _0.7 Ga _0.3 )
_0.51 an In _0.49 P first upper cladding layer 104, p- (Al _0.
45 Ga _0.55 ) _0.51 In _0.49 P light guide layer 105, p-G
a _0.44 In _0.56 P etching stopper layer 106 and n-
A GaAs current blocking layer 109 is sequentially grown.

Here, the non-doped strained quantum well active layer 10
Reference _numeral 3 denotes four Ga _0.44 In _0.56 P well layers, and (Al _0.5 Ga
_0.5 ) _0.51 In _0.49 P barrier layers are alternately stacked, and guide layers having the same composition as the barrier layers are formed above and below the barrier layers.

The p-Ga _0.44 In _0.56 P etching stopper layer 106 was a single quantum well layer having a thickness of 30 °.

Next, the n-G on which the above-described semiconductor layer is formed
The aAs substrate 101 is taken out of the growth apparatus, and n-GaAs is reached by a known selective etching technique so as to reach the p-Ga _0.44 In _0.56 P etching stopper layer 106.
A stripe-shaped groove 111 is formed in the current blocking layer 109.

Then, the n-GaAs substrate 101 is set again in the growth apparatus, and the p-type
(Al _0.7 Ga _0.3 ) _0.51 In _0.49 P second cladding layer 10
7 and p-Ga _0.51 In _0.49 P contact layer 110 are sequentially laminated. Finally, the p-GaInP contact layer 11
Ohmic electrodes (not shown) are formed on the upper surface of the semiconductor substrate 101 and the lower surface of the n-GaAs substrate 101, respectively, and the cavity length is adjusted to 375 μm by a cleavage method.
A coating film having a reflectivity of 75% was formed on the opposite end face at 5% to obtain a semiconductor laser device of the seventh embodiment.

The oscillation wavelength λ1 of the semiconductor laser device of the seventh embodiment and the wavelength λ2 corresponding to the band gap of the etching stopper layer 106 serving as the saturable absorption layer are both 658 nm, and the value of λ1-λ2 is 0 nm. Was.

Table 7 below shows the evaluation results of the maximum self-excited oscillation output and the aging yield of the semiconductor laser device of the seventh embodiment together with Comparative Example 7. The semiconductor laser device of Comparative Example 7 had the same structure as the semiconductor laser device of Embodiment 7 except that the light guide layer was disposed above the etching stopper layer.

[0113]

[Table 7]

As is apparent from a comparison between Table 7 and Table 1, the same effect as that of the semiconductor laser device of the first embodiment can be obtained in the semiconductor laser device of the seventh embodiment.

Here, in the self-aligned type semiconductor laser device, since the current path is a regrowth interface, the semiconductor laser device of Comparative Example 7 was used.
Although the aging yield is lower than that of the ridge-type semiconductor laser device in the structure of No. 7, the yield is not reduced in the seventh embodiment.

From this, it can be seen that the present invention does not depend on the material or manufacturing method of the semiconductor laser device, and that a sufficient effect can be obtained if the light guide layer is arranged on the side close to the active layer.

(Eighth Embodiment) FIG. 12 shows an eighth embodiment of the semiconductor laser device of the present invention. Embodiment 8 shows an example in which the present invention is applied to a ridge-type semiconductor laser device similar to Embodiment 2 described above. However, in Embodiment 8, p-
The GaAs etching stopper layer 106 is formed only inside the ridge stripe, and is different from the semiconductor laser device of the second embodiment in this point.

The semiconductor laser device according to the eighth embodiment is manufactured in exactly the same manner as in the second embodiment. The main manufacturing steps will be described below with reference to FIG.

As in the first and second embodiments, the p-AlGaAs second upper cladding layer 107 and the p-GaAs cap layer 108 are processed into a ridge shape by using a known selective etching technique, and then are treated with citric acid. Using a mixed solution of hydrogen oxide as an etching solution, the p-GaAs etching stopper layer 106 exposed outside the ridge stripe is used.
Only selective removal. This etching solution selectively etches the AlGaAs layer having a low Al mixed crystal ratio,
By adjusting H, selectivity can be given when the Al mixed crystal ratio is between 0.1 and 0.3. Accordingly, the etching stops at the p-AlGaAs optical guide layer 105 having an Al mixed crystal ratio higher than that of the etching stopper layer 106. In addition, p-GaAs
Since the s cap layer 108 is covered with the SiO ₂ film, it is not eroded. Subsequent fabrication steps are exactly the same as in the first and second embodiments.

Table 8 below shows the results of evaluating the astigmatic difference at an output of 5 mW of the semiconductor laser device of the eighth embodiment. As a comparative example, a result of the same evaluation performed on the semiconductor laser device of the second embodiment is also shown.

[0121]

[Table 8]

As understood from Table 8, the semiconductor laser device according to the eighth embodiment in which the etching stopper layer 106 having the saturable absorption function is formed only inside the ridge stripe is the semiconductor laser device according to the second embodiment. The astigmatic difference is reduced and the optical characteristics are improved. The reason is,
This is because according to the above structure, the effective refractive index difference between the inside and outside of the ridge stripe is larger than that in the second embodiment.

As described above, in the semiconductor laser device of the present invention in which the light guide layer is formed below the etching stopper layer, the optical characteristics can be easily improved.

(Embodiment 9) FIG. 13 shows Embodiment 9 of the semiconductor laser device of the present invention. Embodiment 9 shows an example in which the present invention is applied to a ridge-type semiconductor laser device similar to Embodiment 2 described above. However, in the ninth embodiment, the p-GaAs etching stopper layer 106 is removed only from the light emitting end face in the outer region of the ridge stripe of 30 μm (see FIG. 13A). It has a structure.

The main manufacturing steps of the semiconductor laser device according to the ninth embodiment will be described below with reference to FIG.

As in the eighth embodiment, the p-GaAs etching stopper layer 1 exposed outside the ridge stripe
When selectively removing only 06, a resist film is applied to the entire surface, and a groove having a width of 30 μm is formed perpendicularly to the resonator direction by using a photolithography technique. Using a mixed solution of citric acid and hydrogen peroxide as an etching solution, only the p-GaAs etching stopper layer 106 exposed inside the groove is etched. Next, the resist film is removed.

Thereafter, a semiconductor laser device is manufactured by the same process as in the second embodiment, but when the end face of the semiconductor laser element is cleaved at last, the semiconductor laser device is 30 μm from the laser light emitting end face.
The semiconductor laser device according to the ninth embodiment was obtained by dividing the region so as to be the portion where the etching stopper layer was removed.

When the maximum self-sustained pulsation output and the aging yield of the semiconductor laser device of the ninth embodiment were evaluated, the same results as those of the semiconductor laser device of the second embodiment shown in Table 2 were obtained.

Next, when the semiconductor laser device of the ninth embodiment was applied to a light source of an optical disk, stable self-sustained pulsation occurred irrespective of a change in the amount of return light. Table 9 below shows the results of measuring the number of read errors before error correction of an optical disk by fabricating a semiconductor laser device having this structure while changing the distance from the light emitting end face to the region where the etching stopper layer is removed.

[0130]

[Table 9]

Here, in the case of a disc for a CD (compact disc) or the like, if the number of errors is 200 or less per second, there is little possibility that a problem will occur due to the error correction function. Less than 100 errors are desired. In the ninth embodiment, as shown in Table 9, when the distance from the light emitting end face to the etching stopper layer 106 is in the range of 3 μm to 100 μm, the number of errors is 100 or less per second. It can be seen that is obtained.

The reason is that when the return light enters the light emitting end face, the etching stopper layer 10 having a saturable absorption effect is formed.
It is considered that the output of the semiconductor laser device is stabilized and the reading error is reduced because the effect absorbed by the laser beam 6 is small.

As shown in Table 1, when the distance from the light emitting end face to the etching stopper layer 106 is larger than 100 μm, the saturable absorption effect is not sufficient and the error increases. It is considered that the return light is absorbed by the etching stopper layer 106 and causes the output of the semiconductor laser device to fluctuate, thereby increasing the error.

In the ninth embodiment, the removal region of the etching stopper layer is formed only on one side of the end face of the optical resonator. However, when return light from the remaining end face exists, the stripes on both light emission end faces are used. The same effect can be obtained even in a structure in which a region where the etching stopper layer is removed is formed outside.

(Embodiment 10) FIG. 14 shows Embodiment 10 of the semiconductor laser device of the present invention. The semiconductor laser device of the tenth embodiment has a p-GaAs of 30 μm from the light emitting end face.
The semiconductor laser device is the same as the semiconductor laser device of the ninth embodiment except that the s etching stopper layer 106 is entirely removed. Hereinafter, the structure will be described together with the manufacturing process.

First, the n-GaAs substrate 101 is set in a growth apparatus (not shown), and the n-GaAs substrate
On the first crystal growth, an n-AlGaAs lower cladding layer 102, a non-doped quantum well active layer 103,
p-AlGaAs first upper cladding layer 104, p-AlG
The aAs light guide layer 105 and the p-GaAs etching stopper layer 106 are sequentially grown.

Next, the n-GaAs substrate 101 is taken out of the growth apparatus, a resist film is applied on the entire surface of the n-GaAs substrate 101, and a groove having a width of 30 μm is formed perpendicularly to the resonator direction using a known photolithography technique. And p-G
The aAs etching stopper layer 106 is exposed. Then, the exposed portion of the p-GaAs etching stopper layer 106 is etched using a mixed solution of citric acid and hydrogen peroxide as an etching solution, and then the resist film is stripped.

Then, the n-GaAs substrate 101 is set again in the growth apparatus, and the p-type is grown by the second crystal growth.
-AlGaAs second upper cladding layer 107 and p-GaAs
The s cap layer 108 is sequentially grown. Thereafter, a semiconductor laser device is manufactured by the same process as that of the second embodiment, but when the device end face is cleaved at last, the semiconductor laser element is divided so that a region of 30 μm from the laser light emitting end face becomes a portion where the saturable absorption layer is removed. Thus, a semiconductor laser device of the tenth embodiment was obtained.

When the maximum self-excited oscillation output and the aging yield of the semiconductor laser device of the tenth embodiment were evaluated, the same results as those of the semiconductor laser device of the second embodiment shown in Table 2 were obtained.

Next, when the semiconductor laser device of the tenth embodiment was applied to an optical disk, stable self-sustained pulsation occurred irrespective of the fluctuation of the return light amount. Table 10 below shows the results of measuring the number of read errors before error correction of an optical disk by fabricating a semiconductor laser device having this structure while changing the distance from the light emitting end face to the region where the etching stopper layer is removed.

[0141]

[Table 10]

In the semiconductor laser device of the tenth embodiment,
Since the saturable absorption region inside the stripe having the highest return light intensity at the light emitting end face is also removed, it is clear from comparison between Tables 10 and 9 that the semiconductor laser device of Embodiment 9 is clear. It can be seen that the number of optical disk reading errors is further reduced as compared with that of FIG.

(Embodiment 11) FIG. 15 shows an embodiment 11 of a semiconductor laser device of the present invention. Embodiment 11 shows an example in which the present invention is applied to a self-aligned red semiconductor laser device using an AlGaInP-based material.

The semiconductor laser device according to the eleventh embodiment is the same as the semiconductor laser device according to the seventh embodiment _{except that the} p-Ga _0.44 In
_0.56 P etching stopper layer 106 is made of p-Ga _0.51 In
The structure is the same as that of the semiconductor laser device of the seventh embodiment, except that the etching stopper layer is formed on the n-GaAs current blocking layer 109 outside the stripes as a _0.49 P etching stopper layer.

In the semiconductor laser device according to the eleventh embodiment, the p-G
The aInP etching stopper layer alone does not have a saturable absorption effect, but has a saturable absorption effect only in a stripe that is a junction region with the p-AlGaInP light guide layer. Therefore, as in the semiconductor laser device of the eighth embodiment, the effective refractive index difference inside and outside the stripe is larger than that outside the ridge stripe, so that the astigmatic difference is reduced and the transverse mode is stabilized.

Table 11 below shows the results of evaluating the astigmatic difference at the output of 5 mW of the semiconductor laser device of the eleventh embodiment.

[0147]

[Table 11]

As will be understood by comparing Table 11 and Table 8, the self-aligned semiconductor laser device of Embodiment 11 also improves the astigmatic difference similarly to the semiconductor laser device of Embodiment 8. It turns out that there is an effect to do.

(Other Embodiments) Various embodiments of the present invention have been described above. However, the embodiments to which the present invention is applied are not limited to the above-described first to eleventh embodiments. The following various changes are possible.

As an example, the ridge type AlGaAs-based semiconductor laser device and the self-aligned AlGaInP-based semiconductor laser device are shown, but the same effect can be obtained by changing the combination of the material and the device structure. . Further, other material systems, for example, ZnSe system, GaN
A similar effect can be obtained with a semiconductor laser device using a system material or the like.

Although only the quantum well active layer is shown as the active layer, the same effect can be obtained in a bulk structure having no quantum effect as long as it does not contradict the gist of the present invention.

Further, even if the oscillation wavelength of the active layer, the absorption coefficient of the saturable absorber layer, or the resonator length or the end face reflectivity are changed, the effects of the present invention are not impaired.

[0153]

As described above, according to the semiconductor laser device of the present invention, since the light guide layer is disposed below the etching stopper layer having the saturable absorption effect, the growth of crystal defects is suppressed. Even at the time of high-output operation, sufficient device life can be obtained without deterioration of device characteristics.

In particular, according to the semiconductor laser device of the second aspect, the laser oscillation wavelength λ1 of the active layer and the wavelength λ2 corresponding to the band gap of the etching stopper layer are in the range of −12 nm ≦ λ1−λ2 ≦ 2 nm. Therefore, both return light noise and quantum noise can be avoided. Therefore, stable low noise characteristics can be obtained in a wide light output range.

According to the semiconductor laser device of the third aspect, the difference between the wavelength λ2 corresponding to the band gap of the etching stopper layer and the wavelength λ3 corresponding to the band gap of the optical guide layer is 0 nm <λ2- Since the configuration is in the range of λ3 ≦ 70 nm, excess carriers generated by saturable absorption overflow and the carrier life can be substantially shortened. Therefore, both high output operation and low noise characteristics can be achieved.

According to the semiconductor laser device of the fourth aspect, the impurity concentration added to the light guide layer is 1 ×.
Since the configuration is larger than 10 ¹⁸ cm ^{−3 and} smaller than 1 × 10 ¹⁹ cm ⁻³ , crystal defects can be suppressed and self-excited oscillation output can be improved. Therefore, the reliability and low noise characteristics of the device are maintained up to high output.

[0157] According particularly to a semiconductor laser device according to claim 5, since the impurity concentration added to the etching stopper layer 5 × 10 ¹⁷ cm ^-3 take greater than 3 × 10 ¹⁸ cm ^-3 smaller configuration In addition, it is possible to improve the self-excited oscillation output by suppressing the switching operation. Therefore, current light output characteristics with good linearity can be obtained in a wide output range, and the low noise characteristics of the element are maintained.

According to the semiconductor laser device of the sixth aspect, the bandgap of the optical guide layer has a change in which the band gap is large on the etching stopper layer side and small on the first upper cladding layer side. Even if carriers are generated, the extinction can be promoted. For this reason,
Low noise characteristics can be maintained even in high output operation.

According to the semiconductor laser device of the present invention, since the light guide layer has a multiple quantum well structure, carrier annihilation can be promoted and the substantial carrier life can be shortened. For this reason, it is possible to maintain low noise characteristics up to a higher output.

According to the semiconductor laser device of the present invention, the optical guide layer has a structure in which the impurity concentration is small on the etching stopper layer side and large on the first upper cladding layer side. And the effective carrier life can be shortened. For this reason, it is possible to maintain low noise characteristics up to a higher output.

Further, according to the semiconductor laser device of the ninth aspect, the total thickness of the light guide layer is 100 ° or more and 200 ° or more.
る の で Since the following configuration is adopted, the effect of confining light to the etching stopper layer can be enhanced, and the switching operation can be suppressed. Therefore, current light output characteristics with good linearity can be obtained over a wide range, and low noise characteristics are maintained.

According to the semiconductor laser device of the tenth aspect, since the etching stopper layer is disposed only in the stripe-shaped opening, the effective refractive index difference inside and outside the stripe can be increased. Therefore, the astigmatic difference can be reduced and the transverse mode can be stabilized.

According to the semiconductor laser device of the eleventh aspect, since the etching stopper layer has a region removed near the light emitting end face, the return light interacts with the saturable absorption region. Hard to cause. Therefore, a stable self-excited oscillation operation can be obtained.

According to the semiconductor laser device of the twelfth aspect, since the etching stopper layer is formed of a material containing no Al, crystal defects at the regrowth interface can be reduced. Therefore, the characteristics and reliability of the device can be further improved.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a relationship between optical output and relative noise intensity in the ridge-type semiconductor laser device of the first embodiment.

FIG. 3 is a graph showing a relationship between λ1-λ2 and reproduction jitter in the ridge-type semiconductor laser device of the first embodiment.

FIG. 4 is a graph showing a relationship between λ2-λ3 and a maximum self-excited oscillation output in the ridge-type semiconductor laser device of the second embodiment.

FIG. 5A shows a ridge-type semiconductor laser device according to a second embodiment, in which FIG.
(B) is a graph which shows the relationship of the jump of an optical output, respectively.

FIG. 6 is a graph showing the relationship between the impurity concentration of the light guide layer, the maximum self-sustained pulsation output, and the aging yield in the ridge-type semiconductor laser device of the third embodiment.

FIG. 7 is a graph showing the relationship between the impurity concentration of an etching stopper layer and the jump of the maximum self-excited oscillation output and the optical output in the ridge-type semiconductor laser device of the third embodiment.

FIG. 8 is a structural diagram of a light guide layer and an etching stopper layer, showing Embodiment 4 of the present invention.

FIG. 9 is a structural diagram of an optical guide layer and an etching stopper layer, showing Embodiment 5 of the present invention.

FIG. 10 is a structural diagram of an optical guide layer and an etching stopper layer and a graph of impurity concentration distribution, showing Embodiment 6 of the present invention.

FIG. 11 is a cross-sectional view of a self-aligned semiconductor laser device according to a seventh embodiment of the present invention.

FIG. 12 is a sectional view of a ridge-type semiconductor laser device according to an eighth embodiment of the present invention.

FIG. 13 shows a ninth embodiment of the present invention, in which (a) is a sectional view of a light emitting end face of a ridge type semiconductor laser device,
(B) is a cross-sectional view taken along the line AA 'of (a), and (c) is a cross-sectional view of the non-emission end face.

FIG. 14 is a cross-sectional view of a light emitting end face of a ridge-type semiconductor laser device according to a tenth embodiment of the present invention.

FIG. 15 is a cross-sectional view of a self-aligned semiconductor laser device according to an eleventh embodiment of the present invention.

FIG. 16 is a band structure diagram showing a definition of a band gap in the present invention.

FIG. 17 is a sectional view of a conventional self-pulsation type semiconductor laser device.

DESCRIPTION OF SYMBOLS 101 n-GaAs substrate 102 n-lower cladding layer 103 quantum well active layer 104 p-first upper cladding layer 105 p-light guide layer 106 p-etching stopper layer 107 p-second upper cladding layer 108 p-cap layer 109 n-current blocking layer 110 p-contact layer 111 striped groove

Claims (12)

[Claims] A plurality of semiconductor layers including a lower cladding layer, an active layer, a first upper cladding layer, a light guide layer, an etching stopper layer, and a second upper cladding layer formed on a semiconductor substrate; In a semiconductor laser device in which a current confinement portion having a stripe-shaped opening is formed in a cladding layer, the light guide layer is disposed between the etching stopper layer and the active layer, and a band gap of the light guide layer is The lamination structure of the etching stopper layer or the optical guide layer and the etching stopper layer is smaller than the band gap of the first upper cladding layer and larger than the band gap of the etching stopper layer. A semiconductor laser device having a saturation absorption effect. 2. The difference between the laser oscillation wavelength λ1 of the active layer and the wavelength λ2 corresponding to the band gap of the etching stopper layer is within a range satisfying the following condition: −12 nm ≦ λ1−λ2 ≦ 2 nm. 2. The semiconductor laser device according to 1. 3. The difference between the wavelength λ2 corresponding to the band gap of the etching stopper layer and the wavelength λ3 corresponding to the band gap of the light guide layer is within a range satisfying the following condition: 0 nm <λ2-λ3 ≦ The semiconductor laser device according to claim 1 or 2. 4. The semiconductor laser device according to claim 1, wherein an impurity concentration added to said light guide layer is higher than 1 × 10 ¹⁸ cm ^{−3 and} lower than 1 × 10 ¹⁹ cm ^−3. . 5. An impurity concentration added to the etching stopper layer is greater than 5 × 10 ¹⁷ cm ^-3 and 3 × 10 ¹⁸ c.
The semiconductor laser device according to claim 1, wherein m is smaller than m ⁻³ . 6. The semiconductor laser device according to claim 1, wherein a band gap of said light guide layer has a variation that is larger on said etching stopper layer side and smaller on said first upper cladding layer side. . 7. The semiconductor laser device according to claim 1, wherein said light guide layer has a multiple quantum well structure. 8. The semiconductor laser device according to claim 1, wherein the impurity concentration of the light guide layer has a variation that decreases on the etching stopper layer side and increases on the first upper cladding layer side. . 9. The semiconductor laser device according to claim 1, wherein a total thickness of the light guide layer is 100 ° or more and 200 ° or less. 10. The semiconductor laser device according to claim 1, wherein said etching stopper layer is disposed only in said stripe-shaped opening. 11. The semiconductor laser device according to claim 1, wherein said etching stopper layer has a region at least partially removed near a light emitting end face. 12. The semiconductor laser device according to claim 1, wherein said etching stopper layer is formed of a material not containing Al.