JP2003115640A - Semiconductor laser device and optical disk reproducer/ recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To an Al-free semiconductor laser device which has a high output and high reliability and has 760 to 800 nm by compensating a strain in the active regions of a barrier layer and a quantum well layer, and to provide a reproducer/recorder for an optical disk using the same. SOLUTION: The semiconductor laser device comprises a lower clad layer, a barrier layer, the active region having the quantum well layer and an upper clad layer laminated on the active region, on a GaAs substrate in such a manner that the quantum well layer is made of Inx Ga1-x As1-y Py , and x is 0.69 or more.

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 satisfying the high output and high reliability required for optical discs and the like. The present invention also relates to an optical disk reproducing / recording apparatus using the semiconductor laser device.

[0002]

2. Description of the Related Art A semiconductor laser in the 760 to 800 nm band generally has a structure in which upper and lower cladding layers made of AlGaAs, a guide layer and a quantum well active layer are laminated on a GaAs substrate. However, when a layer containing Al is present, Al
Is likely to be deteriorated because it is easily oxidized, and it is not possible to obtain a semiconductor laser device that meets the requirements for high output and high reliability.

Therefore, some Al-free semiconductor laser devices have been proposed. For example, Japanese Patent Laid-Open No. 10-10
7369 discloses a first clad layer on a GaAs substrate,
Disclosed is a semiconductor laser device including an active layer and a second cladding layer, the active layer being made of InGaAsP containing no Al, and the first and second cladding layers containing Al.
With this structure, generation of a reactive current due to oxidation of Al on the surface of the active layer is suppressed, and the operating current is reduced.

Further, Japanese Patent Laid-Open No. 11-220224 discloses an 800 nm band semiconductor laser device. In this device, the guide layer, barrier layer, and quantum well layer in the active region are made of InGaAsP-based material. The outline of this apparatus is shown in FIG. On the n-GaAs substrate 501,
n-GaAlAs cladding layer 502, n-InGaAs
P optical waveguide layer 503, InGaAsP barrier layer 504, I
nGaAsP quantum well layer 505, InGaAsP barrier layer 506, p-InGaAsP optical waveguide layer 507, p-G
This shows a structure in which an aAlAs clad layer 508 and a p-GaAs contact layer are sequentially stacked. In this structure, the first and second cladding layers have a composition that lattice-matches the GaAs substrate, and the first and second optical waveguide layers also have a composition that lattice-matches the GaAs substrate. This makes InGaAsP
This enables the quantum well active layer to have a tensile strain of 0.3% or less with respect to the GaAs substrate.

76 which can be generally used for optical disks
In order to realize a semiconductor laser of 0 to 800 nm band,
The tensile strain in the quantum well layer (active layer) is 0.3%
It is said that the following is necessary (for example, Japanese Patent Laid-Open No. 11-220224). Here, the amount of strain is (a ₁ −a _GaAs ) / a when the lattice constant of the GaAs substrate is a _GaAs and the lattice constant of the quantum well layer is a _1.
It is represented by _GaAs . A positive value indicates compressive strain, and a negative value indicates tensile strain.

In addition, using an InGaAsP active layer,
When a semiconductor laser in the 60 to 800 nm band is formed, the composition regions in which phase separation occurs due to the relationship between the InGaAsP-based composition ratio and the bandgap are overlapped with each other by compressive strain. It is said that it is difficult to realize an active layer having a large compressive strain. In order to satisfy the above conditions by the InGaAsP active layer, the In composition ratio must be 0.2 or less.

In general, in a semiconductor laser device, it is necessary to increase the bandgap energy (Eg) of the barrier layer in order to improve carrier confinement. However, if it is attempted to form a barrier layer with a lattice-matching system or a composition in the vicinity of the quantum well layer, the barrier layer will fall within the miscibility gap, making its fabrication difficult. Generally, in the crystal growth of the above compound semiconductor mixed crystal, the growth may not be stable in all regions, and there may be a composition region in which a uniform crystal cannot be obtained (which causes spinodal decomposition). It is known (this area is called the “missibility gap”).
It is understood that this region changes with the crystal growth temperature, and the miscibility gap becomes smaller at higher temperatures and larger at lower temperatures.

FIG. 7 shows the miscibility gap at 200 to 800 ° C. and plots the composition ratio which causes spinodal decomposition at isothermal temperatures. The resulting curve is shown by the dash-dotted line. This curve is also called a "spinodal curve".

The tensile strain in the InGaAsP quantum well layer (active layer) must be 0.3% or less, preferably zero in order to make it a semiconductor laser device in the 760 to 800 nm band so that it can be used in an optical disk reproducing / recording device. However, for this purpose, the In composition ratio of the InGaAsP-based active layer must be 0.2 or less as described above. However, in the case of using such an active layer, when a barrier layer suitable for this active layer is formed, an attempt is made to obtain a sufficient bandgap energy (Eg) in a lattice-matching system, and the region enters into the miscibility gap region. It will be impossible. For this reason, even if the barrier layer has a tensile strain to some extent, the barrier layer is forced to be adopted, and as a result, the reliability of the semiconductor laser device is reduced.

Further, in order to improve the carrier confinement, the barrier layer is formed of a composition region having tensile strain, and as a result, the quantum well active region as a whole is in a state of receiving large tensile strain. Tends to enter, the crystallinity decreases, and the reliability of the semiconductor laser device decreases.
As a countermeasure, an attempt to use reverse compressive strain is generally adopted for the quantum well layer. However, even if the composition of the lattice-matching system or its vicinity is used and the composition of the region outside the miscibility gap is used, the compressive strain obtained is about 1% at most. When a semiconductor laser device is manufactured by using such a composition, defects existing inside the crystal are proliferated by energization, and the device is apt to be deteriorated, so that the reliability of the device is deteriorated.

[0011]

The present invention solves the above problems, compensates for strain in the active regions of the barrier layer and the quantum well layer, and has a high output and high reliability, 760-80.
Provided is a 0 nm Al-free semiconductor laser device, and an optical disk reproducing / recording device using the same.

[0012]

A semiconductor laser device according to the present invention is a semiconductor laser device in which a lower cladding layer, an active region having a barrier layer and a quantum well layer, and an upper cladding layer are laminated on a GaAs substrate. And the quantum well layer is In _x
It consists of Ga _1-x As _1-y P _y , and x is 0.69 or more. In the semiconductor laser device of the present invention, the lower clad layer and the upper clad layer are AlGaAs layers. Further, the barrier layer may be a GaAs layer. In the semiconductor laser device of the present invention, the compressive strain of the quantum well layer with respect to the substrate is 3.5% or less. The quantum well layer thickness is less than 60Å.

In the semiconductor laser device of the present invention, the barrier layer has tensile strain, and the active region composed of the quantum well layer and the barrier layer has a strain compensation structure. In the semiconductor laser device of the present invention, the oscillation wavelength is 760 nm or more and less than 800 nm. Further, the semiconductor laser device of the present invention is used in an optical disk reproducing / recording device.

In the semiconductor laser device of the present invention, a buffer layer is provided between the substrate and the lower clad layer, a lower guide layer is provided between the lower clad layer and the active region, and an upper guide layer is provided between the active region and the upper clad layer. A protective layer may be laminated subsequent to the guide layer or the second clad layer.

As in the semiconductor laser of the present invention, when the quantum well layer (active layer) is made of InGaAsP system and the In composition ratio is 0.69 or more, a large compressive strain is generated as described in the above prior art. And means that it is far outside the region that has been considered as a precondition for realizing fabrication of a semiconductor laser. That is, it means to adopt a state in which a large compressive strain is considered, which is considered to be difficult to manufacture a semiconductor laser. However, surprisingly,
In the present invention, although a large compressive strain exists in the quantum well layer (active layer), a structure in which a large tensile strain exists in the barrier layer to automatically compensate the strain between the active layer and It was possible to solve the technical problem of. Further, in the present invention, InGa
Since the In composition ratio of the AsP-based active layer is large, it is possible to obtain the effect that crystal defects are hard to grow.

The P composition ratio can be arbitrarily selected from a wide range and is not particularly limited. In the present invention, fabrication of a semiconductor laser device was realized by adopting 0.40 or more as a preferable range.

[0017]

Embodiment 1 FIG. 1 shows an example of the structure of a semiconductor laser device according to the present invention. In this structure, a buffer layer, a first-conductivity-type semiconductor lower clad layer, a quantum well active region, and a second-conductivity-type semiconductor upper clad layer are laminated on the semiconductor substrate surface, and a part of the upper clad layer has a mesa stripe shape. And a semiconductor laser device in which both sides of the stripe are filled with first and second conductivity type semiconductor current block layers.

A method of manufacturing the semiconductor laser structure will be described with reference to FIGS. N with (100) face
N-GaAs buffer layer 10 on -GaAs substrate 101
2 (layer thickness: 0.5 μm), n-Al _0.5 Ga _0.5 As lower cladding layer 103 (layer thickness: 2.0 μm), n-Al _0.35 G
a _0.65 As Lower guide layer 104 (layer thickness: 300Å), In
_0.75 Ga _0.25 As _0.15 P _0.85 Compressed strain quantum well layer (strain:
2.48%, layer thickness: 54Å, 2 layers) and GaAs _0.72 P
_0.28 tensile strain barrier layer (strain: -1.0%, layer thickness: 50
Å, multiple strained quantum well active layer 105 formed by arranging alternately three _{layers), n-Al 0. 35 Ga} 0.65 As upper guide layer 106
(Layer thickness: 300Å), p-Al _0.5 Ga _0.5 As first upper cladding layer 107 (layer thickness: 0.235 μm), p-GaA
s Etching stop layer 108 (layer thickness: 30Å), p-
Al _0.5 Ga _0.5 As second upper cladding layer 109 (layer thickness:
1.2 μm), GaAs protective layer 110 (layer thickness: 0.75
μm) in order of metalorganic chemical vapor deposition (MOCVD)
Method). Further, a resist mask 111 was formed by a photographic process (photolithography technique) so that the stripe direction had a (011) direction at the portion where the mesa stripe portion was formed (FIG. 2).

Next, the portion other than the resist mask portion 111 is etched to form a mesa stripe portion 121a. The etching was performed in two steps using a mixed aqueous solution of sulfuric acid and hydrogen peroxide and hydrofluoric acid, and was performed right above the etching stop layer 108. GaAs utilizes the fact that the etching rate by hydrofluoric acid is very slow, which makes it possible to flatten the etching surface and control the width of the mesa stripe. The etching depth is 1.95 μm, and the width of the mesa stripe is about 2.5 just above the etching stop layer 108.
μm. After etching, the resist mask 111
Was removed (Fig. 3).

Subsequently, the n-Al _0.7 Ga _0.3 As first block layer 112 (layer thickness: 0.6 μm), the n-GaAs second block layer 113 (layer thickness: 0.3 μm), and the p-GaAs flattening layer 114. (Layer thickness: 1.05 μm) was sequentially grown with an organic metal crystal to form a photo / current constriction region. After that, a resist mask 115 was formed only on both sides 121b of the mesa stripe portion by a photolithography process (FIG. 4).

Subsequently, the block layer on the mesa stripe portion 121a was removed by etching. For this etching, a mixed aqueous solution of ammonia and hydrogen peroxide solution and a mixed aqueous solution of sulfuric acid and hydrogen peroxide solution were used, and etching was performed in two steps. Thereafter, the resist mask 115 is removed, and the p-GaAs cap layer 116 (layer thickness: 2.0 μm
m) were laminated. Thus, the semiconductor laser device having the structure shown in FIG. 1 could be manufactured.

In the present embodiment, the strained quantum well layer
Is In_0.75Ga_0.25As_0.15P _0.85Is due to distortion
Bandgap in bulk considering energy shift
Energy is about 1.553 eV, but quantum well
Therefore, the band gap is larger than that.
Becomes about 1.589 eV and the oscillation wavelength is about 7
It became 80 nm. Composition diagram near the composition of the quantum well layer
Is shown in FIG.

In general, a composition diagram as shown in FIG. 7 is used to determine the composition of each semiconductor layer when a semiconductor laser is manufactured. FIG. 7 shows the equal band gap energy (Eg) line (solid line), the equal strain amount line (dashed line), and the miscibility gap (dashed line) at each growth temperature in bulk in consideration of strain. Show.

The equidistant lines are lattice-matched to the GaAs substrate.
The composition ratio is 0%. As mentioned above, this distortion amount is
Let the lattice constant of the GaAs substrate be a_GaAs, Lattice constant of semiconductor layer
A ₁Then, (a₁-A_GaAs) / A_GaAsIt is represented by.
If this value is positive, it is called compressive strain, and if it is negative, it is called tensile strain.
Be exposed.

Generally, the equal Eg line is obtained by plotting the composition ratio of the band gap energies in the bulk calculated from the composition ratio. However, regarding the Eg line that has been obtained conventionally, some are based on different calculation examples,
It wasn't very clear. Further, although the iso-Eg line varies depending on the amount of strain, the iso-Eg line considering this influence has not been obtained either. Therefore, the present inventors diligently studied the experimental results so far, and independently derived a calculation formula to create an equal Eg line. Further, an equal Eg line in which the amount of variation of Eg due to the amount of strain is taken into consideration can be obtained.

Further, as described above, in the crystal growth of such a compound semiconductor mixed crystal, not all the composition regions are stable, and uniform crystals cannot be obtained (spinodal decomposition occurs). There is a miscibility gap). This region changes depending on the crystal growth temperature. The higher the temperature, the smaller the miscibility gap, and the lower the temperature, the larger the gap. In FIG. 7, the miscibility gap at 200 to 800 ° C. is shown, and the composition ratio that causes spinodal decomposition at an equal temperature is plotted (spinodal curve, alternate long and short dash line).

When the semiconductor laser device obtained in this embodiment was subjected to a reliability test, it was confirmed that the semiconductor laser device could operate stably for more than 5000 hours even at 85 ° C. and 200 mW. This means that even if defects are present inside the crystal, the defects are unlikely to propagate because the In composition ratio is large when the semiconductor laser is energized, and the effect of extending the life and reliability of the semiconductor laser device is obtained. Presumed to be. When the In composition ratio was 0.69 or more, this effect was more prominent. For this reason, the conventional window structure has been used to increase the output of the laser, but in the case of the present invention, the effect of high output and high reliability was obtained without using the window structure. This means that a low-cost and highly reliable semiconductor laser device is realized.

In consideration of the strain of the strained quantum well layer, if the composition ratio is changed with the Eg in the bulk being the same value to increase the strain amount, in the region where the strain amount exceeds 3.5%, the prototype semiconductor laser device is manufactured. There was a tendency for reliability to deteriorate. Therefore, in order to manufacture a semiconductor laser device with a stable film thickness, the quantum well layer preferably has a strain amount of 3.5% or less.

Regarding the crystal growth of the above strained quantum well layer composition, the temperature at which spinodal decomposition occurs is about 50.
It is 0 ° C. Therefore, 600 to 750 that is normally used
A homogeneous film can be obtained at a growth temperature of ° C. It was also confirmed that diffusion of impurities can be prevented if the temperature does not exceed 750 ° C. Furthermore, In
If the composition ratio of is 0.69 or more, the growth temperature is 75
At 0 ° C., since it is outside the miscibility gap, it is possible to grow at a normal growth temperature of 600 to 750 ° C.

The layer thickness of the strained quantum well layer was 54Å. Further, by increasing the layer thickness, it is possible to oscillate light having a longer wavelength. However, in the case of the present embodiment in which the strain amount of the quantum well layer is 2.48%, there is a tendency that the reliability decreases when the quantum well layer is 60 Å or more.
Therefore, to make a laser with stable film quality, 60 Å
It has been found suitable to be less than.

The differential gain of the compressive strain quantum well layer depends on the layer thickness, and has a peak at a layer thickness of 40Å. The larger the differential gain, the more rapidly the semiconductor laser device is compatible with high-speed modulation.
It is preferably about Å.

In this embodiment, since the quantum well layer has a large amount of compressive strain and the tensile strain is applied to the barrier layer to compensate for the strain, it is more reliable than when the barrier layer has no tensile strain. A semiconductor laser device having excellent characteristics was obtained.

In the present embodiment, the semiconductor laser device has a ridge structure (in the laminated structure of semiconductor lasers, the upper cladding layer has a mesa stripe shape, and the light / current confinement layers are provided on both sides of the mesa stripe. Construction)
BH structure (buried hetero structure. In the laminated structure of a semiconductor laser, a part of the lower clad has a mesa stripe shape, and a light / current confinement layer is provided on both sides of the mesa stripe). Even if it has, the same effect can be obtained.

Embodiment 2 FIG. 5 shows an example of the structure of a semiconductor laser device according to the present invention. In this structure, a buffer layer, a first conductivity type semiconductor lower clad layer, a quantum well active region, and a second conductivity type semiconductor upper clad layer are laminated on a semiconductor substrate surface, and the layer structure has a mesa stripe shape, A semiconductor laser device in which both sides of a stripe are filled with a current block layer, a cladding layer and a cap layer are laminated on the structure surface, and a metal electrode is arranged on the cap layer.

A method of manufacturing the semiconductor laser structure will be described. First, an n-GaAs buffer layer 202 (layer thickness: 0.5 μm) is formed on an n-GaAs substrate 201 having a (100) plane.
m), n-Al _0.5 Ga _0.5 As lower cladding layer 203 (layer thickness: 1.5 μm), In _0.15 Ga _0.85 As _0.60 P _0.40 lower guide layer 204 (layer thickness: 400 Å), In _{0.7 1} Ga _0.2
9 As _0.18 P _0.82 Compressed strain quantum well layer (strain: 2.29%,
Layer thickness: 52Å, 3 layers) and In _0.15 Ga _0.85 As _0.60 P
_0.40 tensile strain barrier layer (strain: -0.34%, layer thickness: 8
0 Å multi-strained quantum well active layer 205 in which two layers are alternately arranged, In _0.15 Ga _0.85 As _0.60 P _0.40 upper guide layer 206 (layer thickness: 400 Å), p-Al _0.5 Ga _0.5 As upper clad layer 207 (Layer thickness: 1.5 μm) and GaAs protective layer 208 (layer thickness: 200 Å) were sequentially grown by metal organic vapor phase epitaxy (MOCVD method).

Further, a SiO ₂ insulating film was laminated, and a resist mask was formed by a photographic process so that the stripe direction had the (011) direction at the portion where the mesa stripe portion was formed. After that, the insulating film other than the resist mask was removed, and the resist mask was further removed to obtain a striped insulating film mask.

Next, the portion other than the insulating film mask portion was etched to form an inverted mesa stripe portion 221a.
The etching was performed halfway through the lower clad layer 203 using a mixed aqueous solution of hydrogen bromide water and hydrogen peroxide water. The etching depth was about 2.0 μm, and the width of the mesa stripe was about 1.5 μm in the quantum well active region. Then, the side surface of the stripe portion 221a and both sides 2 of the mesa stripe portion
21b was subjected to a surface cleaning treatment with buffered hydrofluoric acid (a mixed solution of hydrogen fluoride and ammonium fluoride).

Next, using the insulating film mask as a selective growth mask, a p-Al _0.5 Ga _0.5 As block layer 209 (layer thickness: 1.0 μm) and an n-Al _0.5 Ga _0.5 As block layer 210 (layer thickness: 1 0.0 μm) was sequentially grown to form a photo / current confinement region on both sides 221b of the mesa stripe portion. After that, the insulating film mask is removed, and p-
Al _0.5 Ga _0.5 As clad layer 211 (layer thickness: 1.0 μ
m), p-GaAs cap layer 212 (layer thickness: 2.0 μm
m) were sequentially laminated. Thus, the semiconductor laser device having the structure shown in FIG. 5 could be manufactured.

In the present embodiment, the strained quantum well layer
Is In_0.71Ga_0.29As_0.18P _0.82Consider the distortion
Bandgap energy in bulk is about 1.5
It is 53 eV, but since it is a quantum well,
The bandgap becomes larger, about 1.589 eV
And the oscillation wavelength became about 780 nm. The amount
FIG. 7 shows a composition diagram around the composition of the child well layer.

In the present embodiment, the In composition ratio of the strained quantum well layer is 0.71, but the effect of this is the same as that of the first embodiment. Although the strain amount of the strain quantum well layer was 2.48%, the effect of this strain amount was similar to that of the first embodiment. Further, the layer thickness of the strained quantum well layer was 52Å, but the effect of this layer thickness was similar to that of the first embodiment. Further, the barrier layer had tensile strain, and the effect obtained from this was similar to that of the first embodiment.

In the present embodiment, the semiconductor laser device has a BH structure, but the same effect can be obtained even if it has a ridge structure. Further, in the BH structure, a regrowth interface exists on the side surface of the quantum well active region and crystal defects are likely to occur, but since the composition ratio is large in In, the effect of suppressing defects on the regrowth interface on the side surface can be obtained. It is valid. Further, not only the well layer but also the barrier layer and the guide layer are made of In
The above effects are obtained due to the composition containing the.

Embodiment 3 FIG. 6 shows an example of the structure of a semiconductor laser device according to the present invention. In this structure, a buffer layer, a first-conductivity-type semiconductor lower clad layer, a quantum well active region, and a second-conductivity-type semiconductor upper clad layer are laminated on the semiconductor substrate surface, and a part of the upper clad layer has a mesa stripe shape. And a semiconductor laser device in which both sides of the stripe are filled with first and second conductivity type semiconductor current block layers.

A method of manufacturing the semiconductor laser structure will be described.
It N on an n-GaAs substrate 301 having a (100) plane
-GaAs buffer layer 302 (layer thickness: 0.5 μm), n
-Al_0.5Ga_0.5As lower clad layer 303 (layer thickness: 2.
0 μm), n-Al_0.35Ga _0.65As lower guide layer 304
(Layer thickness: 300Å), In_0.69Ga_0.31As_0.57P_{0. 43}
Compressive strain quantum well layer (strain: 3.47%, layer thickness: 34Å, 2
Layer) and In_0.03Ga_{0. 97}As_0.68P_0.32Tensile strain burr
A layer (strain: -0.93%, layer thickness: 100Å, 3 layers)
Multi-strained quantum well active layers 305, n-A arranged with each other
l_0.35Ga_0.65As upper guide layer 306 (layer thickness: 300
Å), p-Al_0.5Ga_0.5As first upper clad layer 307
(Layer thickness: 0.235 μm), p-GaAs etching layer
Top layer 308 (layer thickness: 30Å), p-Al_0.5Ga_0.5
As second upper clad layer 309 (layer thickness: 1.2 μm), G
The aAs protective layer 310 (layer thickness: 0.75 μm) is sequentially formed as an organic layer.
Crystal growth was performed by metal chemical vapor deposition (MOCVD method).
Let In addition, at the part where the mesa stripe part is formed,
The stripe direction of the mask has a (011) direction.
It was prepared by a photographic process.

Next, a portion other than the resist mask portion was etched to form a mesa stripe portion 321a.
Etching is performed in two steps using a mixed aqueous solution of sulfuric acid and hydrogen peroxide and hydrofluoric acid, and etching stop layer 308
I went right above. GaAs utilizes the fact that the etching rate by hydrofluoric acid is very slow, which makes it possible to flatten the etching surface and control the width of the mesa stripe. The etching depth is 1.95 μm, and the width of the mesa stripe is about 2.5 μm just above the etching stop layer 308.
Met. After etching, the resist mask was removed.

Subsequently, the n-Al _0.7 Ga _0.3 As first block layer 312 (layer thickness: 0.6 μm), the n-GaAs second block layer 313 (layer thickness: 0.3 μm), and the p-GaAs flattening layer 314. (Layer thickness: 1.05 μm) is sequentially grown with an organic metal crystal to form a photo / current constriction region. After that, a resist mask was formed only on both sides 321b of the mesa stripe portion by a photolithography process.

Subsequently, the block layer on the mesa stripe portion 321a was removed by etching. For this etching, a mixed aqueous solution of ammonia and hydrogen peroxide solution and a mixed aqueous solution of sulfuric acid and hydrogen peroxide solution were used, and etching was performed in two steps. After that, the resist mask is removed,
A p-GaAs cap layer 316 (layer thickness: 2.0 μm) was laminated. In this way, the semiconductor laser device having the structure shown in FIG. 6 could be manufactured.

In the present embodiment, the strained quantum well layer In _0.69 Ga _0.31 As _0.0.57 P _0.43 has a bandgap energy of about 1.268 eV in bulk in consideration of energy shift due to strain. Since it is a quantum well, the bandgap becomes larger than that, and the oscillation wavelength becomes approximately 1.393 eV and the oscillation wavelength becomes approximately 890 nm. FIG. 7 shows a composition diagram around the composition of the quantum well layer.

The In composition ratio of the strained quantum well layer was 0.69, and the effect of this was similar to that of the first embodiment. The strain amount of the strain quantum well layer was 3.47%, but the effect of this strain amount was the same as that of the first embodiment.

Although the strained quantum well layer has a layer thickness of 34Å, the effect of this layer thickness was similar to that of the first embodiment. Further, the barrier layer had tensile strain, and the effect obtained from this was similar to that of the first embodiment.

Although the semiconductor laser device has a ridge structure, the same effect can be obtained even if it has a BH structure.
In the above first to third embodiments, the growth method for forming each semiconductor layer is shown as an example, but the present invention is not limited to those shown in each of these embodiments, and other than these, for example, a gas source. Alternatively, a molecular beam epitaxy method (MBE) using an organic metal source can be used.

Further, the layer thickness and the number of layers of the quantum well layer are not limited to those shown in the first to third embodiments, and the same may be applied to those other than those shown in the first embodiment. The effect can be obtained. Further, the semiconductor laser device is not limited to the ridge structure and the BH structure shown in each of the embodiments, but may be a broad area structure semiconductor laser device. Further, the current blocking layer shown in each of the embodiments is not limited to the pn reverse junction semiconductor buried structure, and may be, for example, a high resistance layer buried or an insulator film buried.

Embodiment 4 FIG. 8 shows an example of the structure of an optical disk recording / reproducing apparatus according to the present invention. This is for writing data on the optical disc 401 and reproducing the written data. As a light emitting element used at that time,
The semiconductor laser device 4 according to the first embodiment of the present invention described above.
It is equipped with 02.

The optical disk recording / reproducing apparatus will be described in more detail. When writing, the signal light emitted from the semiconductor laser device 402 is collimated by the collimator lens 403.
Is converted into parallel light by means of a light beam, transmitted through the beam splitter 404, adjusted in polarization state by the λ / 4 polarizing plate 405, condensed by the objective lens 406, and irradiated onto the optical disc 401.
At the time of reading, the laser beam having no data signal is applied to the optical disc 401 along the same path as that at the time of writing. This laser light is reflected on the surface of the optical disc 401 on which data is recorded, passes through the laser light irradiation objective lens 406 and the λ / 4 polarizing plate 405, is reflected by the beam splitter 404, and is changed by 90 °, and then reproduced. The light is collected by the light objective lens 407 and is received by the light receiving element 408 for signal detection.
Incident on. The data signal recorded by the intensity of the laser light incident in the signal detecting light-receiving element is converted into an electric signal and reproduced by the signal light reproducing circuit 409 to the original signal.

Since the optical disk device of the present embodiment uses the semiconductor laser device which operates at a higher optical output than the conventional one, it is possible to read / write data even if the rotational speed of the disk is made faster than the conventional one. Therefore, the access time to the disk, which has been a problem especially at the time of writing, is remarkably shorter than that of the apparatus using the conventional semiconductor laser device, and it is possible to provide an optical disk apparatus which can be operated more comfortably.

Here, an example in which the semiconductor laser device of the present invention is applied to a recording / reproducing optical disk device has been described, but the present invention is not limited to this, and the same wavelength 78 is used.
It can also be applied to an optical disk recording device and an optical disk reproducing device using the 0 nm band.

[0056]

According to the present invention, in a semiconductor laser device manufactured on a GaAs substrate, Al-free InG is used.
By setting the In composition ratio in the aAsP strained quantum well layer to 0.69 or more, high compressive strain can be obtained, and generation and multiplication of crystal defects due to In deficiency can be prevented, and a highly reliable semiconductor laser can be obtained. The device can be made. Further, by setting the strain amount of the strained quantum well layer to 3.5% or less, a highly reliable semiconductor laser device having a well layer of stable film quality can be manufactured. Further, by setting the layer thickness of the strained quantum well layer to less than 60 Å, preferably 20 Å or more and less than 60 Å, a highly reliable semiconductor laser device having a quantum well layer with stable film quality can be manufactured.

Further, according to the present invention, with the composition of the strained quantum well layer, the quantum well layer can be grown at a growth temperature of 750 ° C. or lower, phase diffusion does not occur, and diffusion of impurities can be prevented. A reliable semiconductor laser can be manufactured. Further, by providing the strain compensation structure in the quantum well active region, crystal defects are reduced, and a semiconductor laser device with higher reliability can be manufactured.

Further, according to the present invention, it is possible to provide a higher speed optical disk reproducing / recording apparatus using the semiconductor laser device according to the present invention.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a semiconductor laser device according to a first embodiment of the present invention after completion of a first crystal growth mask process.

FIG. 2 is a cross-sectional view of the semiconductor laser device according to the first embodiment of the present invention after completion of a mesa stripe forming etching process.

FIG. 3 is a cross-sectional view of the semiconductor laser device according to the first embodiment of the present invention after completion of the block layer buried crystal growth process.

FIG. 4 is a sectional view of the semiconductor laser device according to the first embodiment of the present invention.

FIG. 5 is a sectional view of a semiconductor laser device according to a second embodiment of the present invention.

FIG. 6 is a sectional view of a semiconductor laser device according to a third embodiment of the present invention.

FIG. 7 shows G in the In _1-x Ga _x As _1-y P _y composition diagram.
3 is a graph showing an equal strain amount line for an aAs substrate, an equal band gap energy curve in a bulk in which strain is taken into consideration, and a spinodal decomposition curve.

FIG. 8 is a schematic diagram of an optical disc recording / reproducing apparatus according to a fourth embodiment of the present invention.

FIG. 9 is a sectional view of a conventional semiconductor laser device.

[Explanation of symbols]

101 substrate 102 buffer layer 103 Lower clad layer 104 Lower guide layer 105 Multi-strained quantum well active layer 106 Upper guide layer 107 first upper clad layer 108 Etching stop layer 109 Second upper clad layer 110 protective layer 111 resist mask 112 First Block Layer 113 Second block layer 114 Planarization layer 115 resist mask 116 cap layer 121a Mesa stripe part 121b Mesa stripe part both sides 201 substrate 202 buffer layer 203 Lower clad layer 204 Lower guide layer 205 Multi-strained quantum well active layer 206 Upper guide layer 207 Upper clad layer 208 protective layer 209 block layer 210 block layer 211 Clad layer 212 cap layer 221a stripe part 221b Mesa stripe part both sides 301 substrate 302 buffer layer 303 Lower clad layer 304 Lower guide layer 305 Multi-strained quantum well active layer 306 Upper guide layer 307 First upper clad layer 308 Etching stop layer 309 Second upper clad layer 310 Protective layer 312 First block layer 313 Second block layer 314 Planarization layer 316 Cap layer 321a Mesa stripe part 321b Mesa stripe part both sides 401 optical disk 402 semiconductor laser device 403 Collimating lens 404 beam splitter 405 Polarizer 406 Objective lens for laser light irradiation 407 Reproduction light objective lens 408 Photodetector for signal detection 409 Signal light regeneration circuit 501 substrate 502 clad layer 503 light guide layer 504 barrier layer 505 Quantum well active layer 506 barrier layer 507 Light guide layer 508 clad layer

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5D119 AA42 BA01 FA05 FA17                 5D789 AA42 BA01 FA05 FA17                 5F073 AA45 AA74 BA06 CA12 CB02                       DA22 EA15 EA28

Claims (11)

[Claims] 1. A semiconductor laser device in which a lower clad layer, an active region having a barrier layer and a quantum well layer, and an upper clad layer are laminated on a GaAs substrate, wherein the quantum well layer is In _x Ga _{1 -x} As _1-y P _y , where x is 0.69
The semiconductor laser device as described above. 2. The semiconductor laser device according to claim 1, wherein y is 0.40 or more. 3. The semiconductor laser device according to claim 1, wherein the lower clad layer and the upper clad layer contain Al. 4. The semiconductor laser device according to claim 1, wherein the lower clad layer and the upper clad layer are AlGaAs layers. 5. The semiconductor laser device according to claim 1, wherein the barrier layer is a GaAs layer. 6. The semiconductor laser device according to claim 1, wherein the compressive strain of the quantum well layer with respect to the substrate is 3.5% or less. 7. The semiconductor laser device according to claim 1, wherein the quantum well layer thickness is less than 60Å. 8. The semiconductor laser device according to claim 1, wherein the quantum well layer thickness is 20 Å or more and less than 60 Å. 9. The semiconductor laser device according to claim 1, wherein the barrier layer has tensile strain, and the active region including the quantum well layer and the barrier layer has a strain compensation structure. 10. The oscillation wavelength is 760 nm or more and 800 nm.
The semiconductor laser device according to claim 1, which is less than 10. 11. An optical disk reproducing / recording apparatus using the semiconductor laser device according to claim 1.