JP3505379B2 - Semiconductor laser device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device used as a light source for various optical disc systems, and more particularly to a self-excited oscillation type device which operates with low noise when used as a light source for a recordable / reproducible optical disc system. The present invention relates to a semiconductor laser device.

[0002]

2. Description of the Related Art A conventional semiconductor laser device used in an optical disk system or the like has a problem of so-called "return light noise" in which noise is generated when laser light reflected by a disk or the like is re-incident on the semiconductor laser device. Has become.

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

FIG. 17 shows a sectional structure of the semiconductor laser device described in the above document. This semiconductor laser device
On the n-GaAs substrate 1, the n-AlGaInP lower cladding layer 2, the strained quantum well active layer 3, and the p-AlGaInP first layer.
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 is formed on both side surfaces of the ridge portion.
An n-GaAs current blocking layer 9 is formed so as to fill 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 structure, p-AlGaInP disposed in contact with the upper surface of p-GaInP saturable absorption layer 5 is arranged.
The light guide layer 6 has a function of increasing the optical confinement ratio of the p-GaInP saturable absorption layer 5, and can increase the saturable absorption effect and obtain stable self-sustained pulsation.

Further, in the p-GaInP saturable absorption layer 5, zinc of a concentration of 2 × 10 ¹⁸ cm ^-3 is added as a p-type impurity in order to promote the disappearance of carriers generated by light absorption. When the impurity concentration in the saturable absorption region is high, the lifetime of carriers generated by light absorption is shortened, so that the spontaneous emission light contributes to the rate of change of carrier density with time. Therefore, according to the self-excited oscillation type semiconductor laser device having the above-described structure, the saturable absorption effect is improved, self-excited oscillation is likely to occur, the temperature characteristics and the noise characteristics of the semiconductor laser element are greatly improved, and high temperature It is described in the above document that it has a long life even in continuous operation.

[0009]

However, when the present inventors applied the above-mentioned self-excited oscillation type semiconductor laser device to a recordable / reproducible semiconductor laser device and conducted an experiment, it was found to be suitable for writing on an optical disk. It was found that a sufficient life cannot be obtained at the required high-power operation. Then, the cause was examined, and the following was found.

That is, on the p-GaInP saturable absorption layer 5 or in the vicinity thereof, there are many crystal defects caused by crystal regrowth and the like. Further, the saturable absorption layer 5 inside the ridge not only serves as a passage for the operating current, but also constantly repeats the generation and disappearance of carriers. Therefore, crystal defects are likely to occur. In particular, 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.

Therefore, during high-power operation, these crystal defects and impurities multiply or diffuse and progress to the strained quantum well active layer 3. As a result, the life of the semiconductor laser device during high-power operation deteriorates. In addition, in order to suppress the current spread and reduce the astigmatic difference, the p-AlGaInP first
Since it is necessary to reduce the layer thickness of the upper cladding layer 4, the deterioration of device characteristics becomes 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 it is required for the recording / reproducing semiconductor laser to have both high output operation and low noise maintenance. .

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

[0014]

A semiconductor laser device of the present invention includes a lower clad layer, an active layer, a first upper clad layer, an optical guide layer, an etching stopper layer and a second upper clad 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. And a bandgap of the optical guide layer is smaller than a bandgap of the first upper cladding layer and larger than a bandgap of the etching stopper layer, and the etching stopper layer or the optical guide layer and the etching stopper layer are disposed. Has a saturable absorption effect with respect to the oscillated 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 the saturable absorption layer, and the optical guide layer is disposed below the etching stopper layer near the active layer. There is. This light guide layer not only has the function of increasing the light confinement ratio of the saturable absorber layer, but also has the function of suppressing the propagation of crystal defects in the regrowth interface and the saturable absorber layer to the active layer. There is.

Therefore, according to the above structure, it is possible to prevent the crystal defects from propagating and advancing to the active layer even during high-power operation of the semiconductor laser device, so that the device life of the semiconductor laser device deteriorates. There is nothing to do.

Therefore, according to the present invention, it is possible to realize a highly reliable semiconductor laser device having a long life even during high-power operation.

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 in a range satisfying the following conditions: -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 levels of 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 has a large positive absolute value, the saturable absorption effect in the etching stopper layer is weak and stable self-sustained pulsation cannot be obtained. Therefore, noise is generated even with a small amount of returning light. On the other hand, when λ1-λ2 has a large negative absolute 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 characteristics exhibit a switching operation, and quantum noise due to fluctuations in the light output increases. When 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 the range of −12 nm ≦ λ1−λ2 ≦ 2 nm, both return light noise and quantum noise are generated. It can be reduced. Therefore, stable low noise characteristics can be obtained in a wide light output range.

Further, preferably, the etching strike
The upper layer is made of GaAs-based material and the light guide layer is
Made of AlGaAs material, or the etching
The stopper layer is made of a GaInP-based material and has the optical waveguide.
The conductive layer is made of AlGaInP-based material, and 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 that satisfies the following condition: 0 nm < λ2-λ
The configuration is 3 ≦ 70 nm.

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

Preferably, the concentration of impurities added to the light guide layer is larger than 1 × 10 ¹⁸ cm ⁻³ and 1 × 1.
The configuration is smaller than 0 ¹⁹ cm ^-3 .

If the concentration of impurities added to the light guide layer is within the above range, excess generated carriers overflow into the light guide layer and disappear in a short time only during high power operation. Further, it is possible to avoid the introduction of crystal defects that deteriorate 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 impurities added to the etching stopper layer is higher than 5 × 10 ¹⁷ cm ^{-3 and} lower than 3 × 10 ¹⁸ cm ^-3 .

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

Further, it is preferable that the band gap of the optical guide layer has a change that is large on the etching stopper layer side and small on the first upper cladding layer side.

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

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

According to this structure, the generated carriers that have overflowed to the optical guide layer are confined in the well layer, so that they do not return to the etching stopper layer side and are likely to disappear by recombination. Therefore, even if excessive carriers are generated by high-power operation, the life of the carriers can be shortened and low noise characteristics can be maintained.

Further, preferably, the impurity concentration of the optical guide layer is changed to be small on the etching stopper layer side and large on the first upper cladding layer side.

According to this structure, the generated carriers overflowing to the optical guide layer are more likely to disappear when they diffuse to the first upper cladding layer side. Therefore, it is possible to maintain the low noise characteristic up to a higher output.

Preferably, the total thickness of the light guide layer is 100 Å or more and 200 Å or less.

When the thickness of the light guide layer is thin, the light confinement ratio in the etching stopper layer is small and the saturable absorption effect cannot be maintained up to high output. On the contrary, when the thickness is thick, the saturable absorption effect is strengthened and the current light output characteristics are switched. It becomes easy to show the target action. Within the above range, the effect of confining light in 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 can be obtained in a wide range, and low noise characteristics can be maintained.

Further, it is preferable that the etching stopper layer is arranged only in the stripe-shaped opening.

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

Further, preferably, the etching stopper layer, in the vicinity of the light emitting end face, a configuration having at least part of which is <br/> removal region.

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

Further, preferably, the etching stopper layer is formed of a material containing no Al.

According to this structure, it is possible to reduce crystal defects such as a regrowth interface due to the oxidation of Al. Therefore, the characteristics and reliability of the device can be further improved.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION 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.

(First Embodiment) FIG. 1 shows a first embodiment of the semiconductor laser device of the present invention. The first embodiment is based on Al
An example applied to a ridge type semiconductor laser device using a GaAs-based material is shown.

The structure of this semiconductor laser device will be described with reference to FIG. First, the n-GaAs substrate 1
01 is set in a growth device (not shown) and the n-G
On the aAs substrate 101, n− was formed by the first crystal growth.
Al _0.5 Ga _0.5 As lower clad layer 102 (carrier concentration 1 × 10 ¹⁸ cm ⁻³ , thickness 1.0 μm), non-doped quantum well active layer 103, p-Al _0.5 Ga _0.5 As first upper clad layer 104 (carrier concentration 1 × 10 ¹⁸ cm ⁻³ , thickness 0.17 μm), p-Al _0.2 Ga _0.8 As optical 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 thickness 0.1 μm) are sequentially grown.

Here, the non-doped quantum well active layer 103
Is an Al _0.14 Ga _0.86 As well layer (thickness 100Å), A
A triple well structure composed of a _0.3 Ga _0.7 As barrier layer (thickness 100 Å) and a guide layer having the same composition (thickness 300 Å).

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

Next, n-G on which the above-mentioned semiconductor layer is formed
The aAs substrate 101 is taken out of the growth apparatus, and the p-GaAs cap layer 1 is formed by using a known photolithography technique.
A stripe-shaped SiO ₂ film is formed on 08. Then, using this SiO ₂ film as an etching mask, a known selective etching technique is used so that the p-AlGaAs etching stopper layer 106 is reached so as to reach the p-AlGaAs etching stopper layer 106.
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
˜4 μm.

After that, the n-GaAs substrate 101 is set in the growth apparatus again, and the n-Al _0.7 Ga _0.3 As current blocking layer 109 (carrier concentration) is formed by the second crystal growth with the SiO ₂ film left. 3 × 10 ¹⁸ cm ⁻³ , thickness 0.6 μm) are laminated. 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 fill both side surfaces of the ridge portion.

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

Then, the n-GaAs substrate 101 is again set 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 , thickness 2.0 μm) are laminated. 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 resonator length is adjusted to 375 μm by the cleavage method.
A reflectance of 15% on the emission side end face and a reflectance of 7 on the opposite side end face.
A 5% coating film is formed. Through the above steps, the ridge type semiconductor laser device of the first embodiment was obtained. The oscillation wavelength λ1 of the semiconductor laser device of the first embodiment was measured and found to be 785 nm.

Table 1 below shows the results of evaluation of the maximum self-excited oscillation output and the aging yield of the semiconductor laser device according to the first embodiment together with Comparative Example 1. The semiconductor laser device of Comparative Example 1 has the same structure as the semiconductor laser device of Embodiment 1 except that the optical guide layer 105 is arranged above the etching stopper layer 106.

[0052]

[Table 1]

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

As can be seen from Table 1, the light guide layer 1
In the semiconductor laser device according to the first embodiment in which 05 is arranged below the etching stopper layer 106, the light guide layer 105 is arranged above the etching stopper layer 106 in Comparative Example 1
The device life is improved as compared with the semiconductor laser device.

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

The optical guide layer 105 is composed of the p-first upper clad layer 104 and the p-second upper clad layer 107 and is made of Al.
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 has not only a function of increasing the light confinement rate of the etching stopper layer 106 that functions as a saturable absorption layer, but also 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 also have both.

In particular, in the semiconductor laser device of the first embodiment, the optical guide layer 105 has no regrowth interface, so that the defect suppressing effect is higher than that of the comparative example. Therefore, in the semiconductor laser device of the first embodiment, the device characteristics do not deteriorate even during high-power operation, and a sufficient life can be obtained.

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

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

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

FIG. 3 shows the relationship between λ1 and λ2 and the reproduction jitter. In the case of an ordinary optical disc system, if the reproduction jitter is 20 nsec or less, there is little possibility of causing a problem in practical use. As can be seen from FIG. 3, the range that satisfies this is −12 nm ≦ λ1−λ2 ≦ 2 nm. 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-sustained pulsation cannot be obtained. Therefore,
It is considered that noise is generated even with a small amount of returning light, fluctuation occurs in the reproduced signal, and jitter is deteriorated.

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 the return light noise can be sufficiently avoided. However, in this case, the optical output-current characteristic exhibits a switching operation at the oscillation threshold, and the quantum noise due to the fluctuation of the optical output increases. It is considered that this quantum noise deteriorated the jitter.

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 optical output range, the laser oscillation wavelength λ1 of the active layer 103 and the etching stopper layer 106 are obtained. It can be seen that the difference λ1−λ2 from the wavelength λ2 corresponding to the bandgap of is within the range of −12 nm ≦ λ1−λ2 ≦ 2 nm.

Although the quantum well layer of the active layer 103 has a three-layer structure in the first embodiment, a so-called multiple quantum well structure having another number of well layers may be used in the first embodiment.
The same effect as can be obtained.

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

(Second Embodiment) The second embodiment has the same structure except that the structures of the light guide layer 105 and the etching stopper layer 106 are different from those of the first embodiment. That is, in the second embodiment, the light guide layer 105 is p-Al _0.13 Ga _0.87 As (carrier concentration 2 × 10 ¹⁸ cm ⁻³ , thickness 150 Å), and the etching stopper layer 106 is p-GaAs (carrier concentration 1 × 1
The difference from the first embodiment is that the thickness is 0 ¹⁸ cm ⁻³ and the thickness is 30 Å).

Since the etching stopper layer 106 in the second embodiment is very thin and the band gap is substantially widened by the quantum effect, it does not have the saturable absorption effect by itself. However, the quantum level of the etching stopper layer 106 is affected by the light guide layer 105 arranged on the lower surface of the etching stopper layer 106, and the light absorption wavelength shifts to the long wavelength side. As a result, the etching stopper layer 106 functions as a saturable absorption layer. The laser oscillation wavelength λ of the active layer was measured by the photoluminescence method.
1 and the difference in wavelength λ2 corresponding to the band gap of the etching stopper layer was λ1−λ2 = −5 nm.

The light guide layer 105 in the second embodiment.
Has a bandgap similar to that of the quantum well active layer, so that the etching stopper layer 10 serving as a saturable absorption layer is formed.
The light guide layer 105 itself also functions as a saturable absorption layer in addition to the function of increasing the light confinement in the light guide layer 6. 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-excited oscillation 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]

From Table 2, the semiconductor laser device according to the second embodiment is different from the semiconductor laser device according to the first embodiment above.
The maximum self-oscillation output is improved. The reason why such a result is 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
Although it recombines and disappears in 06, the etching stopper layer 1
When the band gap difference between 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 its volume is larger than that of, the extinction is promoted by diffusion. Therefore, the carrier life is substantially shorter than that when the generated carriers are consumed only by the etching stopper layer 106. Therefore, saturation of light absorption is less likely to occur, and self-sustained pulsation is maintained even at high output.

Next, except that the wavelength λ3 corresponding to the band gap of the light guide layer 105 is changed by changing the Al mixed crystal ratio of the light guide layer 105, the structure is the same as that of the semiconductor laser device of the second embodiment. FIG. 4 shows the result of measuring the maximum self-excited oscillation output of the manufactured one. The maximum self-excited oscillation output decreases as the wavelength difference λ2-λ3 corresponding to the band gap between the etching stopper layer 106 and the optical guide layer 105 increases, and the maximum self-excited oscillation output sharply decreases at 70 nm or more. As a result, the etching stopper layer 1
It can be seen that the wavelength difference corresponding to the band gap difference between the etching stopper layer 106 and the optical guide layer 105 is preferably 70 nm or less in order that the excess carriers in 06 overflow to the optical guide layer 105 side. In the case of λ2-λ3 ≦ 0 nm, the light guide layer 105
Since the band gap is smaller than the band gap of the etching stopper layer 106, the saturable absorption effect in the light guide layer 105 becomes remarkable. As a result, defects propagated by laser driving progress to the active layer 3 and the life of the semiconductor laser device is deteriorated.

Further, in the semiconductor laser device of the present invention, carrier overflow does not occur during low light output operation, the generated carriers disappear only in the etching stopper layer 106 having a relatively long life, and the switching operation of current light output characteristics is performed. Hard to happen. As the output becomes high, excess carriers overflow into the light guide layer 105, and the substantial carrier life is shortened.

Next, except that the layer thickness of the light guide layer 105 was changed, a semiconductor laser device having the same structure as that of the semiconductor laser device of the second embodiment was manufactured, and the jump of the optical output at the maximum self-excited oscillation output and the oscillation threshold ( The result of measurement (see FIG. 5) is shown in FIG.
When the thickness of the light guide layer 105 is 100 Å or less, the effect of confining light in the etching stopper layer 106 becomes weak and the maximum self-oscillation output is small. On the other hand, at 200 Å 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 to obtain current light output characteristics with good linearity, the thickness of the light guide layer 105 is 10 mm.
It is preferably 0 Å or more and 200 Å or less.

From Table 2, the semiconductor laser device of the second embodiment has an aging yield equivalent to that of the semiconductor laser device of the first embodiment, although the maximum self-excited oscillation output is improved. I am doing it. Since the etching stopper layer 106 in the second embodiment does not contain Al, the surface is hard to be 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 could be maintained even at a higher output.

In the second embodiment, the thickness of the p-GaAs etching stopper layer 106 is set to 30 Å, but in the quantum well structure, the substantial band gap changes depending on the thickness, so that the above quantum effect can be obtained. It is preferable that the etching stopper layer has a thickness of 100 Å or less. Further, 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 Å or more.

In the second embodiment, the light guide layer 105 itself is configured to act as a saturable absorption layer. However, if λ2-λ3 is within the above range, even a layer that does not absorb laser light can be used in high power operation. Since carrier overflow easily occurs, the same effect can be obtained.

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

From Table 3, the semiconductor laser device according to the third embodiment is different from the semiconductor laser device according to the second embodiment above.
Furthermore, 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 overflowed excess carriers is shortened. As a result, it is considered that the saturation of light absorption became less likely to occur and self-sustained pulsation was maintained even at higher output.

Next, except that the impurity concentration of the optical guide layer 105 was changed, a semiconductor laser device having the same structure as that of the semiconductor laser device of the third embodiment was produced, and the result of evaluation of the maximum self-excited oscillation output and the aging yield is shown. 6 shows. Light guide layer 105
The maximum self-oscillation output sharply increases when the impurity concentration of 1 × 10 ¹⁸ cm ⁻³ or more, but when it exceeds 1 × 10 ¹⁹ cm ⁻³ , crystal defects are likely to occur and the yield sharply decreases. Therefore, in order to maintain self-sustained pulsation and device life up to high output, the impurity concentration of the optical guide layer 105 is 1 × 10 ^18.
cm ^-3 to 1 × is preferably 10 ¹⁹ cm ^-3 or less.

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

Next, with respect to the semiconductor laser device of the third embodiment, FIG. 7 shows the results of evaluating jumps of the maximum self-excited oscillation output and the optical output at the oscillation threshold by changing the impurity concentration of the etching stopper layer 106. 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 it 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 to obtain the current / light output characteristics with good linearity, the etching stopper layer 10 is used.
The impurity concentration of 6 is 5 × 10 ¹⁷ cm ⁻³ or more and 3 × 10 ¹⁸ m ⁻³
The following is preferable.

(Embodiment 4) The semiconductor laser device of Embodiment 4 has the same structure as that of Embodiment 3 except that the Al mixed crystal ratio of the optical 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 Embodiment 4 is 0.14 to 0.
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, the semiconductor laser device of the fourth embodiment is different from the semiconductor laser device of the previous third embodiment in that
Furthermore, the maximum self-excited oscillation output is improved. This is because the generated carriers that have overflowed to the optical guide layer 105 during high light output operation diffuse and disappear in the vicinity of the first upper cladding layer 104 having a low energy level, and do not return to the etching stopper layer 106. Therefore, it is possible to maintain the low noise characteristic up to a higher output.

In the fourth embodiment, A of the light guide layer 105
Although the l mixed crystal ratio was changed from 0.14 to 0.2, the maximum 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 in the range of <λ2-λ3 ≦ 70 nm.

Although the degree of change in the Al mixed crystal ratio is constant in the layer thickness direction in the fourth embodiment, the same effect can be obtained if the energy level on the first upper cladding layer 104 side is lower. Therefore, the Al mixed crystal ratio change rate may be changed in the layer thickness direction or may be set in multiple stages.

(Embodiment 5) The semiconductor laser device of Embodiment 5 has the same structure as that of Embodiment 3 except that the optical guide layer 105 has a multiple quantum well structure. That is, as shown in FIG. 9, the light guide layer 10 according to the fifth embodiment.
5 is Al _0.12 Ga _0.88 As well layer 3 layers (thickness 50 Å each)
This is different from the third embodiment, which is a multiple quantum well structure in which two Al _0.3 Ga _0.7 As barrier layers (thickness: 30 Å each) are alternately arranged, which is 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]

From Table 5, the semiconductor laser device according to the fifth embodiment is different from the semiconductor laser device according to the third embodiment above in that
Furthermore, the maximum self-excited oscillation output is improved. This is because the generated carriers that have overflowed to the optical 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 the low noise characteristic up to a higher output.

In addition, the fifth embodiment is the same as the A of the fourth embodiment.
When it was applied to an optical guide layer in which the l mixed crystal ratio was changed, the maximum self-pulsation output was further improved.

In the fifth embodiment, the number of wells of the multiple quantum well optical guide layer 105 is set to 3, but the effect of the present invention is the same even if the number of wells is other. Further, the thickness and mixed crystal ratio of the barrier layer may be 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 structure as that of Embodiment 3 except that the impurity concentration of the optical 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 Embodiment 6 is 3 × 10 ¹⁸ cm ^{−3 in the} layer thickness direction.
To 1 × 10 ¹⁹ cm ⁻³ , which is small on the etching stopper layer 106 side and large 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-excited oscillation 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]

From Table 6, the semiconductor laser device of the sixth embodiment is different from the semiconductor laser device of the above-mentioned third embodiment in that
Furthermore, 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 surely shortened even if the carrier overflow increases. As a result, it is considered that the saturation of light absorption became less likely to occur and self-sustained pulsation was maintained even at higher output.

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

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

The structure of this semiconductor laser device will be described with reference to FIGS. However, in FIG.
The same parts as those in are denoted by the same reference numerals.

First, the n-GaAs substrate 101 is set in a growth apparatus (not shown), and the n-GaAs substrate 10 is set.
1 on the top surface of the 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 In _0.49 P first upper cladding layer 104, p- (Al _0.
45 Ga _0.55 ) _0.51 In _0.49 P optical 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
3 is a Ga _0.44 In _0.56 P well layer 4 layers, (Al _0.5 Ga
_0.5 ) _0.51 In _0.49 P three barrier layers are alternately laminated, 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 Å.

Next, n-G having the above-mentioned semiconductor layer is formed.
The aAs substrate 101 is taken out of the growth apparatus, and using a known selective etching technique, n-GaAs is formed 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.

After that, the n-GaAs substrate 101 is set in the growth apparatus again, and p- is formed by the second crystal growth.
(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 stacked. Finally, the p-GaInP contact layer 11
0 and the lower surface of the n-GaAs substrate 101 are each formed with an ohmic electrode (not shown), the cavity length is adjusted to 375 μm by the cleavage method, and the reflectance at the emitting end face is 1
5% and a coating film having a reflectance of 75% was formed on the end face on the opposite side to obtain a semiconductor laser device of the seventh embodiment.

The oscillation wavelength λ1 of the semiconductor laser device according to 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 values of λ1-λ2 are 0 nm. It was

Table 7 below shows, together with Comparative Example 7, the evaluation results of the maximum self-excited oscillation output and aging yield of the semiconductor laser device of the seventh embodiment. The semiconductor laser device of Comparative Example 7 has the same structure as the semiconductor laser device of the seventh embodiment except that the optical guide layer is arranged above the etching stopper layer.

[0113]

[Table 7]

As is clear from a comparison between Table 7 and Table 1 above, the semiconductor laser device of the seventh embodiment also has the same effect as the semiconductor laser device of the first embodiment.

Here, in the self-aligned semiconductor laser device, the current path serves as a regrowth interface.
In the structure (1), the aging yield is lower than that of the ridge type semiconductor laser device, but in the seventh embodiment, the yield is not reduced.

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

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

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

Similar to 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 thereafter, they 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.
Only selectively remove. This etching solution selectively etches an AlGaAs layer having a low Al mixed crystal ratio, and P
By adjusting H, selectivity can be given when the Al mixed crystal ratio is between 0.1 and 0.3. Therefore, the etching is stopped at the p-AlGaAs optical guide layer 105 having a higher Al mixed crystal ratio than the etching stopper layer 106. In addition, p-GaA
Since the s cap layer 108 is covered with the SiO ₂ film, it is not corroded. The subsequent manufacturing process is exactly the same as in the first and second embodiments.

Table 8 below shows the results of evaluation of the astigmatic difference at the output of 5 mW of the semiconductor laser device of the eighth embodiment. Further, as a comparative example, the results of the same evaluation performed on the semiconductor laser device of Embodiment 2 are also shown.

[0121]

[Table 8]

As can be seen from Table 8, the semiconductor laser device of 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 of the second embodiment. Compared with, the astigmatic difference is reduced and the optical characteristics are improved. The reason is,
This is because, according to the above structure, the difference in effective refractive index inside and outside 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. The ninth embodiment shows an example in which the present invention is applied to a ridge type semiconductor laser device similar to the second embodiment. However, the ninth embodiment is exactly the same as the second embodiment except that the p-GaAs etching stopper layer 106 is removed only in the outer region of the ridge stripe of 30 μm from the light emitting end face (see FIG. 13A). It is structured.

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

Similar to the eighth embodiment, the p-GaAs etching stopper layer 1 exposed outside the ridge stripe.
When only 06 is selectively removed, a resist film is applied on 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. Then, the resist film is peeled off.

After that, a semiconductor laser device is manufactured by the same process as in the second embodiment, but when the end facet of the semiconductor laser device is finally cleaved, 30 μm from the laser beam emitting end facet.
The semiconductor laser device of the ninth embodiment was obtained by dividing the above region so as to become the above etching stopper layer removed portion.

When the maximum self-excited oscillation 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 above were obtained.

Next, when the semiconductor laser device of the ninth embodiment was applied to the light source of the optical disc, stable self-excited oscillation occurred regardless of the fluctuation of the returning light amount. Table 9 below shows the results of measuring the number of read errors before error correction of the optical disc, with the semiconductor laser device of this structure being manufactured by changing the distance from the light emitting end face to the removal region of the etching stopper layer.

[0130]

[Table 9]

Here, in the case of a disc for a CD (compact disc) or the like, normally, if the number of errors is 200 or less per second, the error correction function is unlikely to cause a problem, but practically 1 second. An error of 100 or less is 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, and the desired characteristic is obtained. It can be seen that is obtained.

The reason is that the etching stopper layer 10 having a saturable absorption effect when the returning light enters the light emitting end face.
It is considered that the output of the semiconductor laser element is stable and the reading error is reduced because the effect of being absorbed by 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 insufficient and the error increases, and when it is smaller than 3 μm. It is considered that the return light is absorbed by the etching stopper layer 106 and causes the output of the semiconductor laser element to fluctuate, thus increasing the error.

In the ninth embodiment, the etching stopper layer removal region is formed only on one side of the optical resonator end face. However, when return light from the remaining end face exists, stripes on both light emitting end faces are formed. The same effect can be obtained even with a structure in which the removal region of the etching stopper layer 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-GaA region 30 μm away from the light emitting end face.
The semiconductor laser device is the same as that of the ninth embodiment except that the s etching stopper layer 106 is entirely removed. The structure will be described below together with the manufacturing process.

First, the n-GaAs substrate 101 is set in a growth apparatus (not shown), and the n-GaAs substrate 10 is set.
1, the n-AlGaAs lower cladding layer 102, the non-doped quantum well active layer 103, and
p-AlGaAs first upper cladding layer 104, p-AlG
An aAs light guide layer 105 and a p-GaAs etching stopper layer 106 are sequentially grown.

Next, the n-GaAs substrate 101 is taken out from 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 cavity direction by using a known photolithography technique. , 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 peeled off.

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

Next, when the semiconductor laser device of the tenth embodiment was applied to an optical disk, stable self-excited oscillation occurred regardless of fluctuations in the amount of returned light. Table 10 below shows the results of measuring the number of read errors before error correction of the optical disc, with the semiconductor laser device of this structure being manufactured by changing the distance from the light emitting end face to the removal region of the etching stopper layer.

[0141]

[Table 10]

In the semiconductor laser device of the tenth embodiment,
Since the saturable absorption region inside the stripe having the strongest return light intensity is also removed at the light emitting end face, it is clear from comparing Table 10 and Table 9 that the semiconductor laser device of the ninth embodiment is clear. It can be seen that the number of optical disc reading errors is further reduced, and a more stable self-excited oscillation operation occurs as compared with the above.

(Embodiment 11) FIG. 15 shows Embodiment 11 of the semiconductor laser device of the present invention. The eleventh embodiment 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 p-Ga _0.44 In semiconductor laser device according to the seventh embodiment.
_{The 0.56} P etching stopper layer 106 is _replaced with p-Ga _0.51 In
The structure is the same as that of the semiconductor laser device according to the seventh embodiment except that the _0.49 P etching stopper layer is formed on the n-GaAs current blocking layer 109 outside the stripe.

Also in the semiconductor laser device of the eleventh embodiment, as in the semiconductor laser device of the seventh embodiment, p-G
The aInP etching stopper layer alone does not have the saturable absorption effect, but has the saturable absorption effect only in the stripe which is the 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 when the output of the semiconductor laser device of the eleventh embodiment was 5 mW.

[0147]

[Table 11]

As can be understood by comparing Table 11 with Table 8 above, also in the self-aligned semiconductor laser device of the eleventh embodiment, the astigmatic difference is improved as in the semiconductor laser device of the eighth embodiment. It turns out that there is an effect.

(Other Embodiments) Although various embodiments of the present invention have been described above, the embodiments to which the present invention is applied are not limited to those of the above-mentioned first to eleventh embodiments. Various modifications shown below are possible.

As an example, only the ridge type structure is shown for the AlGaAs type semiconductor laser device and the self-alignment type structure is shown for the AlGaInP type semiconductor laser device, but the same effect can be obtained by changing the combination of the material and the element structure. . Also, other material systems such as ZnSe system and GaN
The same effect can be obtained with a semiconductor laser element using a system material or the like.

Further, the active layer is shown only in the case of the quantum well active layer, but the same effect can be obtained even in the case of a bulk structure having no quantum effect unless it goes against the gist of the present invention.

The effect of the present invention is not impaired even if the oscillation wavelength of the active layer, the absorption coefficient of the saturable absorption layer, the cavity length or the end face reflectance is changed.

[0153]

As described above, according to the semiconductor laser device of the present invention, since the optical guide layer is arranged below the etching stopper layer having the saturable absorption effect, the growth of crystal defects is suppressed. The element characteristics do not deteriorate even during high-power operation, and a sufficient element life can be obtained.

According to the semiconductor laser device of one embodiment , the laser oscillation wavelength λ1 of the active layer and the wavelength λ2 corresponding to the band gap of the etching stopper layer are −12.
Since the configuration is in the range of nm ≦ λ1−λ2 ≦ 2 nm, 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 one embodiment , the etching stopper layer is made of a GaAs material.
And the light guide layer is made of an AlGaAs material.
Or the etching stopper layer is a GaInP type
Made of a material and the light guide layer is an AlGaInP-based material
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-λ3 ≦ 70 nm.
Therefore, the carrier lifetime can be substantially shortened by overflowing excess carriers generated by saturable absorption. Therefore, it is possible to achieve both high output operation and low noise characteristics.

Further, according to the semiconductor laser device of the embodiment , the impurity concentration of the optical guide layer is 1 × 10 5.
Since the structure is larger than ¹⁸ cm ^{−3 and} smaller than 1 × 10 ¹⁹ cm ⁻³ , it is possible to suppress crystal defects and improve the self-oscillation output. Therefore, the reliability and low noise characteristics of the device are maintained up to high output.

In addition, according to the semiconductor laser device of one embodiment , the impurity concentration added to the etching stopper layer is higher than 5 × 10 ¹⁷ cm ^{−3 and} lower than 3 × 10 ¹⁸ cm ^−3, and thus switching is performed. It is possible to suppress the operation and improve the self-excited oscillation output. Therefore, current light output characteristics with good linearity can be obtained in a wide output range, and low noise characteristics of the device can be maintained.

Further, according to the semiconductor laser device of the present invention , since the band gap of the optical guide layer is changed so as to be large on the etching stopper layer side and small on the first upper cladding layer side, excessive carriers are generated. Even if it is created, its extinction can be promoted. Therefore, the low noise characteristic can be maintained even in the high output operation.

Further, according to the semiconductor laser device of one embodiment , the optical guide layer has a multiple quantum well structure, so that carrier annihilation can be promoted and the substantial carrier life can be shortened. For this reason, it is possible to maintain the low noise characteristic up to a higher output.

Further, according to the semiconductor laser device of one embodiment , since the impurity concentration of the optical guide layer is changed to be small on the etching stopper layer side and large on the first upper cladding layer side, carrier disappearance is promoted. The actual carrier life can be shortened. For this reason, it is possible to maintain the low noise characteristic up to a higher output.

Further, according to the semiconductor laser device of one embodiment , since the total thickness of the light guide layer is 100 Å or more and 200 Å or less, the effect of confining light in the etching stopper layer is enhanced and the switching operation is performed. Can be suppressed. Therefore, the current-light output characteristic having good linearity can be obtained in a wide range, and the low noise characteristic is maintained.

According to the semiconductor laser device of one embodiment , since the etching stopper layer is arranged 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.

[0163] Further, according to the semiconductor laser element of one embodiment, the etching stopper layer, in the vicinity of the light emitting end face, since a configuration with at least a portion has been removed region, and the returned light saturable absorption region Difficult to cause the interaction of. Therefore, stable self-excited oscillation operation can be obtained.

Further, according to the semiconductor laser device of the one embodiment , the etching stopper layer is formed of a material not containing Al, so that crystal defects at the regrowth interface can be reduced.
Therefore, the characteristics and reliability of the device can be further improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a ridge type semiconductor laser device showing a first embodiment of the present invention.

FIG. 2 is a graph showing the 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 and λ2 and reproduction jitter in the ridge type semiconductor laser device of the first embodiment.

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

FIG. 5 (a) shows the optical guide layer thickness and the maximum self-oscillation output in the ridge type semiconductor laser device of Embodiment 2.
(B) is a graph which shows the jump relation of optical output, respectively.

FIG. 6 is a graph showing the relationship between the impurity concentration of the optical guide layer, the maximum self-excited oscillation 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 the etching stopper layer and the jump of the maximum self-excited oscillation output and 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 a fourth embodiment of the present invention.

FIG. 9 is a structural diagram of a light guide layer and an etching stopper layer, showing a fifth embodiment 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 sectional view of a self-aligning type semiconductor laser device showing a seventh embodiment of the present invention.

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

FIG. 13 is a sectional view of a light emitting end face of a ridge type semiconductor laser device, showing a ninth embodiment of the present invention;
(B) is sectional drawing by the AA 'line of (a), (c) is sectional drawing in the non-exiting end surface.

FIG. 14 is a sectional view showing 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 sectional view of a self-aligned semiconductor laser device showing an eleventh embodiment of the present invention.

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

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

[Explanation of symbols]

101 n-GaAs substrate 102 n-lower clad 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

Continuation of the front page (56) Reference JP-A-7-22695 (JP, A) JP-A-6-196810 (JP, A) JP-A-7-263794 (JP, A) JP-A-5-3367 (JP , A) JP 7-106695 (JP, A) JP 7-321395 (JP, A) JP 9-83064 (JP, A) JP 10-321946 (JP, A) JP 9-283840 (JP, A) Special Table 10-505960 (JP, A) International Publication 96/030977 (WO, A1) Technical Report of IEICE, Vol. 96 No. 290, p. 7-12 (LQ E96-78) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 G11B 7/125

Claims (5)

(57) [Claims] 1. A plurality of semiconductor layers including a lower clad layer, an active layer, a first upper clad layer, a light guide layer, an etching stopper layer and a second upper clad layer are formed on a semiconductor substrate, and the second upper clad layer is formed. In a semiconductor laser device in which a current constriction portion having a stripe-shaped opening is formed in the clad layer,
The light guide layer is disposed between the etching stopper layer and the active layer, and the band gap of the light guide layer is smaller than the band gap of the first upper cladding layer and the band gap of the etching stopper layer. larger, layered structure of the etching stopper layer or the light guide layer and the etching stopper layer, have a saturable absorption effect for oscillating a laser beam, the band gap of the light guide layer, the etching stopper layer side And a semiconductor laser device having a change that becomes larger at the side of the first upper cladding layer. 2. The etching stopper layer is a GaAs type
Made of a material and the light guide layer is an AlGaAs-based material
Or the etching stopper layer is made of GaI
The light guide layer is made of nP-based material, and the light guide layer is AlGaIn.
The difference between the wavelength λ2 made of a P-based material and 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 conditions: 0
nm <λ2-λ3 ≦ 70 nm The semiconductor laser device according to claim 1 . 3. A plurality of semiconductor layers including a lower clad layer, an active layer, a first upper clad layer, a light guide layer, an etching stopper layer and a second upper clad layer are formed on a semiconductor substrate, and the second upper layer is formed. In a semiconductor laser device in which a current constriction portion having a stripe-shaped opening is formed in the clad layer,
The light guide layer is disposed between the etching stopper layer and the active layer, and the band gap of the light guide layer is smaller than the band gap of the first upper cladding layer and the band gap of the etching stopper layer. larger, layered structure of the etching stopper layer or the light guide layer and the etching stopper layer, have a saturable absorption effect for oscillating laser light, the impurity concentration of the light guide layer, the etching stopper layer side And a semiconductor laser device having a change in which becomes smaller at the side of the first upper cladding layer. 4. The semiconductor laser device according to claim 3 , wherein the light guide layer has a multiple quantum well structure. 5. A plurality of semiconductor layers including a lower clad layer, an active layer, a first upper clad layer, an optical guide layer, an etching stopper layer and a second upper clad layer are formed on a semiconductor substrate, and the second upper layer is formed. In a semiconductor laser device in which a current constriction portion having a stripe-shaped opening is formed in the clad layer,
The light guide layer is disposed between the etching stopper layer and the active layer, and the band gap of the light guide layer is smaller than the band gap of the first upper cladding layer and the band gap of the etching stopper layer. larger, layered structure of the etching stopper layer or the light guide layer and the etching stopper layer, have a saturable absorption effect for oscillating a laser beam, the etching stopper layer, in the vicinity of the light emitting end face, at least a A semiconductor laser device having a region where a portion is removed.