JPH10163561A - Semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce operating current of an active layer with specifying layer thickness total of quantum well layers of a self-excited oscillation type semiconductor laser element, having a multiple quantum-well active layers obtained by alternately laminating pluralities of quantum-well layers and quantum-barrier layers. SOLUTION: An MQW active layer is constituted by growing Al0.33 Ga0.67 As lower quantum-barrier layer 120 (thickness of 50Å), alternately repeatedly growing thereon eight Al0.13 Ga0.87 As quantum-well layers 121 (thickness of 110Å) and seven Al0.33 Ga0.67 As quantum-barrier layers 122 (thickness of 50Å) and further laminating thereon Al0.33 Ga0.67 As upper part quantum-barrier layer 123 (thickness of 50Å). The total thickness of the active layer is 1250Å, and the total of the thickness of the well layer is 800Å. The total of the thickness of the well layer is 700 to 1000Å or less. When the active layer thickness is 800Å, operating current of the element having bulk active layer having equal thickness to the total of the thickness of the well layers is 26mA, and hence the current of about 30% or more can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-pulsation type semiconductor laser device having low noise characteristics and used for an optical disk.

[0002]

2. Description of the Related Art As a semiconductor laser device used for an optical disk, a self-excited oscillation type is used to reduce noise. A self-excited oscillation type semiconductor laser device which achieves low current driving by using a multiple quantum well structure for an active layer and performing light absorption by a current confinement and light absorption layer is disclosed in Japanese Patent Application Laid-Open No. 2-72688 by Tanaka. It is described in the gazette.

FIG. 11 shows a semiconductor laser device described in JP-A-2-72688. n-GaAs substrate 30
1, n-GaAs buffer layer 302, n-Al _x G
a _1-x As clad layer 303, multiple quantum well (MQW:
Multi Quantum Well) active layer 304,
p-Al _x Ga _1-x As clad layer 305, p-GaAs
After the layer 306 is grown and the ridge stripe 307 is formed by etching, the n-GaAs current confinement and light absorption layer 308 is selectively grown on both sides of the ridge stripe 307, and the p-GaAs buried layer 309 is grown on the entire surface.
Electrodes 310 and 311 are formed on the substrate side and on the surface of the growth layer.
Conventionally, the operating current is 35 to 40 mA, and the operating current can be reduced by 30 to 40% as compared with a semiconductor laser device having a double hetero (DH) structure including a normal bulk active layer.

[0004]

Problems to be Solved by the Invention
In the semiconductor laser device described in Japanese Patent Application Laid-Open Publication No. H11-107, low noise is achieved by defining the total thickness of the MQW active layer.

However, in a conventional semiconductor laser device, M
Since the total thickness of the quantum well layers of the QW active layer is not specified, there is a problem described below.

In the semiconductor laser device described in JP-A-2-72688, the total thickness of the quantum well layers is 360 °.
From 440 °. At this time, in order to increase the saturable absorption amount of the quantum well layer outside the ridge stripe to achieve low noise, the light emission distribution is sufficiently expanded outside the ridge stripe, and the light is distributed to the MQW active layer outside the ridge stripe. Need to exude. However, in order to broaden the light emission distribution, the wavefront of light in the MQW active layer outside the ridge stripe is bent, and the beam waist of the emitted light in the direction parallel to the MQW active layer is separated from the laser end face, while the beam of the emitted light in the vertical direction is Since the waist is located at the laser end face, there is a problem that the astigmatic difference of the semiconductor laser element increases.

In addition, the emission distribution in the direction parallel to the MQW active layer is narrowed by the spread of the light emission distribution outside the ridge stripe, and the ellipticity of the emitted light (= radiation angle perpendicular to active layer / radiation angle parallel to active layer) (Radiation angle) increases.

Deterioration of optical characteristics due to an increase in astigmatic difference of the semiconductor laser element or an increase in the ellipticity of the emitted light is caused by the fact that when the semiconductor laser element is used as a light source for an optical disk, the emitted light from the semiconductor laser element is formed into a minute spot by a lens. There has been a problem that it is difficult to condense the light, and it is difficult to effectively use the optical output due to a reduction in the coupling efficiency of the emitted light to the lens.

In a conventional semiconductor laser device, a current confinement and light absorption layer is used as current light confinement means. The light absorption by this light confinement means and the M outside the ridge stripe
Due to the saturable absorption of the quantum well layer in the QW active layer,
There is a problem that the operating current increases due to an excessive increase in light absorption loss inside the semiconductor laser element.

Accordingly, an object of the present invention is to provide a semiconductor laser device having low noise characteristics without increasing the operating current and operating voltage, and without increasing astigmatism and ellipticity of emitted light. And

[0011]

In order to solve the above-mentioned problems, a self-pulsation type semiconductor laser device having an MQW active layer according to the present invention is provided on a semiconductor substrate by forming a first conductive type cladding layer and an active layer. A cladding layer of the second conductivity type, the cladding layer of the second conductivity type has a stripe shape, and has current light confinement means on both sides of the stripe shape;
The active layer is a self-pulsation type semiconductor laser device comprising a multiple quantum well active layer in which a plurality of quantum well layers and quantum barrier layers are alternately stacked, and the total thickness of the quantum well layers is 7
It is not less than 00 ° and not more than 1000 °.

The quantum well layer may have a thickness of not less than 60 ° and not more than 120 °, and the quantum barrier layer may have a thickness of not less than 30 ° and not more than 80 °.

In particular, it is preferable that the current light confinement means has a current light confinement layer of the first conductivity type having a larger forbidden band width than the active layer.

The active layer may include a lower quantum barrier layer on the side of the first conductivity type cladding layer, and an upper quantum barrier layer on the side of the second conductivity type cladding layer. A semiconductor laser device in which at least one of the lower quantum barrier layers has a smaller forbidden band width than the other quantum barrier layers is a semiconductor laser device with lower noise and lower operating voltage and current.

Further, the difference Δn (= n1−n2) between the equivalent refractive index n1 of the stripe shape in the layer thickness direction and the equivalent refractive index n2 of the current light confining means in the layer thickness direction is 3 × 1.
It is preferable that 0 ⁻³ ≦ Δn ≦ 7 × 10 ⁻³ .

[0016]

Embodiments of the present invention will be described below. FIG. 1 shows a cross-sectional view of the semiconductor laser device of the first embodiment.

On an n-GaAs substrate 101, n-GaAs
s buffer layer 102 (layer thickness 0.5 μm), n-Al _0.45
Ga _0.55 As first cladding layer 103 (layer thickness 1.3 μm)
m), n-Al _0.5 Ga _0.5 As low refractive index layer 104 (layer thickness 0.2 μm), non-doped MQW active layer 105, p-
Al _0.5 Ga _0.5 As second cladding layer 106 (layer thickness 0.1
5 μm), p-GaAs etching stop layer 107 (layer thickness 0.003 μm), p-Al _0.5 Ga _0.5 As third cladding layer 108 (layer thickness 1.2 μm), p-GaAs cap layer 109 (layer thickness 0.8 μm) ) Are sequentially grown by metal organic chemical vapor deposition (MOCVD).

Here, the MQW active layer is made of Al _0.33 Ga
_{A 0.67} As lower quantum barrier layer 120 (layer thickness: 50 °) is grown, and an Al _0.13 Ga _0.87 As quantum well layer 121 is formed thereon.
(Layer thickness: 100 °) and Al _0.33 Ga _0.67 As quantum barrier layer 1
22 (thickness: 50 °) are alternately and repeatedly grown with eight quantum well layers and seven quantum barrier layers, and further thereon, an Al _0.33 Ga _0.67 As upper quantum barrier layer 123 (layer thickness of 5).
0Å). In the present embodiment, the total thickness of the MQW active layer is 1250 °, and the total thickness of the quantum well layers is 800 °. FIG. 2 shows the distribution of the Al composition ratio in the structure described above.

A photoresist stripe mask is formed on the surface of the p-GaAs cap layer 109, and the etching is stopped on the surface of the p-GaAs etching stop layer 107 by selective etching to form a stripe width of 2.2 μm at the bottom.
The m ridge stripes 114 are formed. N-Al _0.7 Ga is buried on both sides of the ridge stripe 114.
_0.3 As first current confinement layer 110 (layer thickness 0.6 μm)
m), n-GaAs second current / light confinement layer 111 (layer thickness 0.6 μm), p-GaAs planarization layer 112 (layer thickness 0.
7 μm) are sequentially grown by MOCVD. p-G
aAs cap layer 109, p-GaAs planarization layer 112
Embedded in the p-GaAs contact layer 113.
(Thickness: 3 μm) is grown by MOCVD. n-G
aAs substrate 101 surface and p-GaAs contact layer 11
An n-type electrode 115 and a p-type electrode 116 are formed on three surfaces.
The cavity length is adjusted to 100 to 250 μm to form a cavity end face, and the end face reflectivity on the light emission side of the cavity end face is 50% to 50%, and the end face reflectivity on the opposite side is 50% to 95%.
An Al ₂ O ₃ film and a Si film are formed on the end face of the resonator so that

In the semiconductor laser device of this embodiment, n
When a forward voltage is applied between the pattern electrode 115 and the p-type electrode 116, the oscillation wavelength is 0.78 μm and the oscillation threshold current is 14 m
A, slope efficiency of current-light output characteristics 0.75 W / A,
The operating current at a light output of 3 mW was 18 mA. Since the semiconductor laser device of the present embodiment uses the first current light confinement layer 110 having a bandgap larger than the bandgap of the MQW active layer 105, the semiconductor laser device absorbs light to such an extent that self-sustained pulsation can be achieved by the active layer outside the stripe. Is performed, and light absorption of light emitted by the semiconductor laser element in the first current / light confinement layer 110 can be suppressed.

The operating current of a self-pulsation type semiconductor laser device having a bulk active layer whose active layer thickness is 800 ° equal to the total thickness of the quantum well layers is 26 mA. In the semiconductor laser device having the above, the operating current could be reduced by about 30% or more.

The operating voltage of the semiconductor laser device according to the present embodiment was reduced by about 5% or more as compared with the semiconductor laser device having a bulk active layer of 800.degree.

Examining the change in operating current at an ambient temperature of 70 ° C. and a constant light output of 5 mW, the running time until the operating current increases by 20% from the initial value is 10,000 hours or more.

The astigmatic difference in radiation angle of the semiconductor laser device of this embodiment is 13 μm, which is almost the same as that of the self-pulsation type semiconductor laser device having a bulk active layer.

Further, in the semiconductor laser device of the present invention, the radiation angle in the direction parallel to the MQW active layer is 12 ° and the radiation angle in the vertical direction is 38 °. A value equivalent to that of the oscillation type semiconductor laser device was obtained.

In the semiconductor laser device of the present invention, the active layer 1
The reason why the n-low refractive index layer 104 having a smaller refractive index than the n-first cladding layer 103 is provided between the n-type first cladding layer 05 and the n-first cladding layer 103 is that the total thickness of the MQW active layer is increased. Is to suppress a vertical radiation angle increase due to the above, and obtain a vertical radiation angle equivalent to that of a self-pulsation type semiconductor laser device having a bulk active layer having a thickness of 800 °. This gives n
-It is possible to suppress an increase in vertical radiation angle by about 2 ° as compared with the case where the low refractive index layer 104 is not provided. Note that the n-low refractive index layer 104 is not always required.

When the return light noise of the semiconductor laser device of the present embodiment was measured, a low noise characteristic with a relative noise intensity of −110 dB / Hz or less was obtained from a return light amount of 0.001% to 15%.

Next, FIGS. 3 and 4 show changes in the astigmatic difference and changes in the parallel radiation angle to the active layer when the total thickness of the quantum well layers of the MQW active layer is changed. At this time,
The difference Δn between the equivalent refractive index n1 in the layer thickness direction inside the ridge stripe and the equivalent refractive index n2 in the layer thickness direction on both sides of the ridge stripe so as to obtain low noise characteristics by self-pulsation.
(= N1-n2) is adjusted. FIG. 3 shows that the astigmatic difference increases as the total thickness of the quantum well layers decreases. If the total thickness is less than 700 °,
The astigmatic difference is greater than 20 μm. This is because, when the total layer thickness is small, in order to cause self-pulsation, it is necessary to reduce the difference Δn in the equivalent refractive index to increase the spread of the emitted light outside the ridge stripe. Is caused by an increase in astigmatism.

FIG. 4 shows that the smaller the total quantum well layer thickness is, the smaller the horizontal radiation angle is. Total thickness 7
If less than 00 °, the horizontal radiation angle will be less than 9 °. This is because when the total thickness of the layers is small, it is necessary to reduce the difference Δn in the equivalent refractive index in order to cause self-pulsation and to increase the spread of the light emission distribution outside the stripe. Angle reduction occurs.

When the astigmatism is increased to 20 μm or more, when the emitted light is focused by a lens, the size of the focused spot increases, and it is difficult to use the system in a system such as an optical disk. When the parallel radiation angle is reduced to 9 ° or less,
Since the ellipticity of emitted light (= vertical emission angle / parallel emission angle) increases, the coupling efficiency with the lens decreases, and it becomes difficult to use the system in a system such as an optical disk. Thus, in order to prevent the deterioration of the optical characteristics of the semiconductor laser device,
It is important to make the total thickness of the quantum well layers of the MQW active layer larger than 700 °.

FIGS. 5 and 6 show a change in operating current and a change in operating voltage at an optical output of 3 mW when the total thickness of the quantum well layers is changed. Total thickness 1000
Above Å, the operating current increases above 25 mA. This is because the current value required for the oscillation of the semiconductor laser element increases with an increase in the total layer thickness. When the total thickness exceeds 1000 °, the operating voltage becomes 2.0V.
It increases above. This is because the carrier injection into the MQW active layer into the quantum well layer becomes non-uniform, and the rise voltage and the device resistance increase. As described above, in order to prevent an increase in the operating current and the operating voltage, the total thickness of the quantum well layers needs to be smaller than 1000 °.

If the thickness of the quantum well layer is less than 60 °, the number of wells becomes too large, so that carrier injection is not performed uniformly and the operating voltage is increased. On the other hand, when the thickness of the quantum well layer is larger than 120 °, the quantum effect is reduced, so that it is difficult to reduce the operating current. Therefore, the quantum well layer should be at least
Å The following is appropriate.

When the thickness of the quantum barrier layer is smaller than 30 °, it is difficult to obtain a designed quantum barrier layer due to the influence of the interface of the growth layer. On the other hand, if the thickness of the quantum barrier layer is more than 80 °, carrier injection between quantum wells is hindered, and it becomes difficult to uniformly inject carriers into all quantum well layers. Therefore, it is appropriate that the quantum barrier layer has a thickness of 30 ° or more and 80 ° or less.

Here, in order to uniformly inject carriers into all the quantum well layers of the quantum well active layer and to suppress an increase in the device resistance which causes an increase in the operating current, the p-type impurity concentration Np To 5 × 10 ¹⁶ cm ⁻³ ≦ Np ≦ 2 × 10 ¹⁸ c
By setting m ⁻³ , an increase in operating voltage caused by uneven injection of carriers can be suppressed. Np is 2 × 10
^If it is larger than ¹⁸ cm ^-3, the diffusion of the p-type impurity increases during the formation of the stacked film, and a mixed crystal occurs in the quantum well layer in the MQW active layer, the quantum effect of the MQW active layer decreases, and the operating current increases. There is a problem that increases. When Np is less than 5 × 10 ¹⁶ cm ⁻³ , the effect of adding impurities is almost eliminated,
The operating voltage increases.

Further, in the semiconductor laser device of the present invention,
Since light is not absorbed by the current light confinement layer, the equivalent refractive index difference Δn between the inside and the outside of the ridge stripe can be set to a relatively large value of 4 × 10 ⁻³ or more to suppress the spread of the light emission distribution outside the ridge stripe. . The equivalent refractive index difference (Δn (= n1-n) in the thickness direction of the layer inside and outside the ridge stripe
When 2)) is small, excessive saturable absorption of the active layer outside the ridge stripe occurs, so that the optical characteristics deteriorate and the operating current increases. Equivalent refractive index difference Δn is 7 × 10
^{If the value} is larger than ^{-3, the} saturable absorption of the active layer outside the ridge stripe decreases, so that self-sustained pulsation hardly occurs and noise increases. Therefore, the refractive index difference is 4 ×
It is appropriate to set 10 ⁻³ ≦ Δn ≦ 7 × 10 ⁻³ .

The width of the bottom of the ridge stripe (W
When s) becomes narrow, excessive saturable absorption occurs in the active layer outside the ridge stripe, so that the optical characteristics deteriorate and the operating current increases. When the width of the ridge stripe is increased, saturable absorption of the active layer outside the ridge stripe is reduced, so that self-sustained pulsation is less likely to occur and noise increases. Therefore, the ridge stripe width is 1 μm ≦ W
It is appropriate to set s ≦ 4 μm.

Since the semiconductor laser device of this embodiment is a self-excited oscillation type real refractive index guided semiconductor laser device, the saturable absorption effect in the MQW active layer outside the stripe is used. In a normal semiconductor laser device having a bulk active layer, the TM polarization mode is less susceptible to saturable absorption than the TE polarization mode. Oscillation was observed. On the other hand, in the device of the present embodiment, the effect of increasing the TE polarization mode of the semiconductor laser device oscillation gain can be used because the quantum well structure is used for the active layer, and the TE having a sufficiently high mode selection ratio can be used.
Single mode oscillation by the polarization mode is obtained.

A semiconductor laser device having a single polarization mode like the device of this embodiment is suitable for use as a light source for a disk.

(Embodiment 2) As Embodiment 2, the structure of the semiconductor laser device shown in FIG.
FIG. 7 shows the distribution of the Al composition ratio of the semiconductor laser device different only in the W active layer.

Al _x Ga _{1 -x} As lower quantum barrier layer 130
(Layer thickness: 50 °), and Al _0.13 Ga _0.87
As quantum well layer 131 (layer thickness 100 Å) and Al _0.33 Ga
_0.67 As quantum barrier layers 132 (layer thickness: 50 °) are alternately and repeatedly grown to form eight quantum well layers and seven quantum barrier layers, and further thereon, an Al _x Ga _{1 -x} As upper quantum barrier layer 133. (Layer thickness of 50 °). Also in this embodiment, the total thickness of the MQW active layer is 125
0 °, and the total thickness of the quantum well layers was 800 °.

FIGS. 8 and 9 show A of the lower and upper quantum barrier layers.
4 shows the correlation between the 1 composition ratio and the relative noise intensity or operating current of a semiconductor laser.

The relative noise intensity is the noise due to the return light from the optical disk when the semiconductor laser element is used for the optical disk, and is at least the relative noise intensity minus 110 dB in practical use.
/ Hz or less, preferably -120 dB / Hz or less. According to FIG. 8, when the Al composition ratio of the lower and upper quantum barrier layers becomes smaller than the Al composition ratio of the quantum barrier layer, the relative noise intensity decreases, and according to FIG. 9, the operating current increases. In the case where the Al composition ratio of the quantum barrier layer is 0.33, 0.1 is used.
The Al composition ratio was reduced by 10% to 30% compared to the other quantum barrier layers so that the characteristics of the semiconductor laser device having the lower and upper quantum barrier layers having an Al composition ratio of 23 ≦ x ≦ 0.3 were good. It is preferred to have lower and upper quantum barrier layers.
The reason is that, when the Al composition ratio of the lower and upper quantum barrier layers is smaller than the Al composition ratio of the quantum barrier layer, the bandgap of the lower and upper quantum barrier layers becomes smaller. Increases the amount of saturable absorption in the entire active layer, thereby increasing the self-sustained pulsation and decreasing the relative noise intensity. To increase the saturable absorption outside the ridge stripe as in this embodiment, the Al composition ratio of the lower and upper quantum barrier layers is adjusted, and the forbidden band width of the lower and upper quantum barrier layers is changed to other quantum barrier layers. This can be achieved by making the barrier layer smaller than the barrier layer.

In this embodiment, the case where the Al composition ratio of the quantum barrier layer 132 is small in both the Al composition ratio of the lower and upper quantum barrier layers has been described. However, the same effect can be obtained when only one of them is smaller.

Third Embodiment FIG. 10 is a sectional view of a GaInP-based semiconductor laser device according to a third embodiment.

On an n-GaAs substrate 201, n-Ga
_0.5 In _0.5 P buffer layer 202, n- (Al _0.7 G
a _0.3 ) _0.5 In _0.5 P first cladding layer 203 (layer thickness 1.
5 μm), p-doped multiple quantum well active layer 204, p-
(Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second cladding layer 205
(Layer thickness 1.5 μm) and p-Ga _0.5 In _0.5 P cap layer 206 (Layer thickness 0.3 μm) are sequentially grown by molecular beam epitaxy (MBE) and etched to form p- (Al _0.7 Ga _0.3 ). _The etching is stopped so that the remaining thickness of the flat portion of the _0.5 In _0.5 P second cladding layer becomes 0.3 μm, and the ridge stripe 20 having a width of 2.5 μm is formed.
7 is formed. Although the MQW active layer is not shown,
(Al _0.5 Ga _0.5 ) _0.5 In _0.5 P lower quantum barrier layer (layer thickness 200 Å), GaInP quantum well layer (layer thickness 80 Å) and (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P quantum barrier layer (layer thickness 40)
Å) are alternately and repeatedly grown, and nine quantum well layers and eight quantum barrier layers are laminated to form (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P
It is constituted by laminating an upper quantum barrier layer (layer thickness 200 Å) thereon. In this embodiment, the total thickness of the MQW active layer is 1440 °, the total thickness of the quantum well layers is 720 °, and the number of quantum well layers is nine.

The n-Al _0.5 Ga _0.5 P first current light confinement layer 2 is buried outside the ridge stripe 207.
08 (layer thickness 0.3 μm) and an n-GaAs second current / light confinement layer 209 (layer thickness 1.2 μm) are sequentially grown by MBE. The surfaces of the p-Ga _0.5 In _0.5 P cap layer 206 and the n-GaAs second current / light confinement layer 209 are p-
A GaAs contact layer 210 is grown by MBE.

The surface of the n-GaAs substrate 201 and the p-GaAs
An n-type electrode 211 and a p-type electrode 212 are formed on the surface of the s-contact layer 210. Resonator length 300 ~ by cleavage method
The resonator end face is formed by adjusting the thickness to 700 μm, and the Al ₂ O ₃ film and the Si are formed so that the reflectance of the light emission side end face of the resonator end face becomes 30 to 50% and the reflectance of the rear side becomes 70 to 95%. Form a film.

In the device of the present embodiment, when a forward voltage is applied between the n-type electrode 211 and the p-type electrode 212, the oscillation wavelength is 0.65 μm, the oscillation threshold current is 20 mA, and the slope efficiency of the current-light output characteristics is obtained. The operating current at 0.75 W / A and light output of 3 mW is 24 mA. The device of the present embodiment is a self-pulsation type semiconductor laser device having a bandgap larger than the bandgap of the active layer in the first current light confinement layer,
Since there is no excessive light absorption, it can be driven with a low operating current.

Since the operating current of a self-pulsation type semiconductor laser device having a bulk active layer with a thickness of 720 ° is 34 mA, the operating current can be reduced by about 30% or more in the semiconductor laser device of this embodiment. It became.

The operating voltage of the device of this embodiment was reduced by about 5% or more as compared with a semiconductor laser device having a bulk active layer having a thickness of 720 ° due to a reduction in operating current. When the change in operating current at an ambient temperature of 70 ° C. and a constant light output of 5 mW is examined, the operating current is 20
The running time to increase by% is 5000 hours or more.

The astigmatic difference of the radiation angle of the device of this embodiment was 15 μm, which was almost the same as that of the self-pulsation type semiconductor laser device having a bulk active layer. Further, in this semiconductor laser device, the radiation angle in the direction parallel to the MQW active layer is 10 degrees and the radiation angle in the vertical direction is 30 degrees, and the ellipticity of the emitted light is a self-pulsation type having the bulk active layer active layer. A value equivalent to that of the semiconductor laser device of No. 1 was obtained.

When the return light noise of the semiconductor laser device of the present embodiment was measured, a low noise characteristic with a relative noise intensity of -110 dB / Hz or less was obtained from a return light amount of 0.001% to 15%.

As described above, the semiconductor laser device of the present embodiment was able to realize a self-pulsation type semiconductor laser device with good optical characteristics and low current and low voltage driving.

It should be noted that the present invention is not limited to the above-described embodiment, and the layer thickness, Al
The composition ratio and the carrier concentration are applicable as long as the effects of the present invention are obtained. In the embodiment, the current light confinement structure has been described with respect to a structure having a ridge stripe near the second cladding layer. However, a structure having a trench filling near the second cladding layer also has the effect of the present invention. As long as it is applicable.

As for the growth method, in addition to the MOCVD method and the MBE method, LPE method, gas source MBE method, A
The present invention is applicable to the LE (atomic beam epitaxy) method as long as the effects of the present invention are obtained.

[0056]

According to the present invention, in order to solve the above-mentioned problems, M
A self-excited oscillation type semiconductor laser device having a QW active layer
By increasing the total thickness of the quantum well layer of the MQW active layer to more than 700 °, the saturable absorption effect of the quantum well layer outside the stripe is increased, and the spread of the light emission distribution outside the stripe is suppressed. Can be. As a result, an increase in the astigmatic difference and an increase in the ellipticity of the emitted light of the semiconductor laser device can be suppressed. Further, by making the total thickness of the quantum well layers less than 1000 °, it is possible to suppress an increase in operating current due to an increase in the saturable absorption effect of the quantum well layers outside the stripe, and to make carrier injection into all quantum well layers non-uniform. , The increase in the operating voltage associated with the operation can be suppressed.

As described above, the semiconductor laser device of the present invention
The total thickness of the quantum well layers is greater than 700 °
By making it smaller than 00 °, deterioration of optical characteristics due to increase of astigmatism and increase of ellipticity can be prevented, and increase in operating current and operating voltage can be suppressed. A type MQW semiconductor laser device can be realized.

In the semiconductor laser device of the present invention, a current light confinement layer having a larger forbidden band width than the active layer and less absorption of light from the semiconductor laser device is used for the current light confinement means. Accordingly, light absorption is mainly performed by saturable absorption outside the stripe, so that gain saturation in the MQW active layer hardly occurs, an increase in operating current can be suppressed, and low current operation can be realized.

Further, by making the lower and upper quantum well layers of the present invention smaller than the forbidden band of the other quantum barrier layers, the light absorption efficiency in the active layer is increased, and the intensity of self-excited oscillation is further increased to lower the quantum efficiency. A noise effect can be realized.

Further, by setting the equivalent refractive index difference between the outside and the inside of the stripe structure to a predetermined value, it is possible to further improve optical characteristics and achieve both low noise.

[Brief description of the drawings]

FIG. 1 is a diagram showing a semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an Al composition of an active layer of the semiconductor laser device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between astigmatic difference and the total thickness of quantum well layers.

FIG. 4 is a diagram showing the relationship between the parallel radiation angle and the total thickness of the quantum well layer.

FIG. 5 is a diagram showing the relationship between the operating current and the total thickness of the quantum well layer.

FIG. 6 is a diagram showing a relationship between an operating voltage and a total thickness of a quantum well layer.

FIG. 7 is a diagram showing a semiconductor laser device according to a second embodiment of the present invention.

FIG. 8 is a diagram showing a relationship between relative noise intensity and Al composition ratio.

FIG. 9 is a diagram showing a relationship between an operating current and an Al composition ratio.

FIG. 10 is a diagram showing the Al composition of the active layer of the semiconductor laser device according to the second embodiment of the present invention.

FIG. 11 is a view showing a conventional semiconductor laser device.

[Explanation of symbols]

 101, 201 n-GaAs substrate 102, 202 n-GaAs buffer layer 103, 203 n-first cladding layer 104 n-low refractive index layer 105, 204 MQW active layer 106, 205 p-second cladding layer 107 p-GaAs Etching stop layer 108 p-third cladding layer 109,206 p-cap layer 114,207 ridge stripe 110,208 n-first current light confinement layer 111,209 n-second current light confinement layer 112 p-planarization layer 113, 210 p-contact layer 115, 116, 211, 212 electrode

Claims (5)

[Claims] A first conductive type clad layer, an active layer, and a second conductive type clad layer on a semiconductor substrate, wherein the second conductive type clad layer has a stripe shape; A self-pulsation type semiconductor laser device comprising a multiple quantum well active layer in which a plurality of quantum well layers and quantum barrier layers are alternately stacked, wherein the active layer has current light confinement means on both sides of the stripe shape; The total thickness of the quantum well layers is 700 to 1000
A semiconductor laser device characterized by the following. 2. The quantum well layer according to claim 1, wherein said quantum well layer has a thickness of not less than 60 ° and not more than 12 °.
0 ° or less, and the thickness of the quantum barrier layer is 30 ° or more and 8
2. The semiconductor laser device according to claim 1, wherein the angle is 0 [deg.] Or less. 3. The semiconductor laser device according to claim 1, wherein said current light confinement means has a first conductivity type current light confinement layer having a larger forbidden band width than said active layer. 4. The active layer includes a lower quantum barrier layer on the side of the first conductivity type clad layer, an upper quantum barrier layer on the side of the second conductivity type clad layer, 4. The semiconductor laser device according to claim 1, wherein at least one of the lower quantum barrier layers has a smaller forbidden band width than the other quantum barrier layers. 5. 5. The difference Δn (= n1−n2) between the equivalent refractive index n1 of the stripe shape in the layer thickness direction and the equivalent refractive index n2 of the current light confining means in the layer thickness direction is 3 × 10 ^−3. 5. The semiconductor laser device according to claim 1, wherein ≦ Δn ≦ 7 × 10 ⁻³ .