JP4570353B2 - Semiconductor laser element - Google Patents

Description

  The present invention relates to a semiconductor laser device.

  With the development and sophistication of optical communication systems, the characteristics required for semiconductor laser elements used as pumping light sources and signal light sources are becoming more stringent than ever, especially with higher output and temperature characteristics. There is a need for improvement. As temperature characteristics, the temperature dependence of the light output and the threshold current is small, and it is required that a sufficient light output and a low threshold can be obtained even during high temperature operation.

  Here, for high output, reduction of light absorption and suppression of carrier overflow are important, and suppression of carrier overflow is important for improving temperature characteristics.

  InP / GaInAsP-based semiconductor laser elements can use GaInAsP, which is a light emitting material having an oscillation wavelength of 1.3 μm or more, as an active layer, and therefore, as a light emitting element in a long wavelength band, an excitation light source for an optical fiber amplifier, It is used for a signal light source for optical communication, and the improvement of characteristics as described above is particularly important.

  In a semiconductor laser device, the reason why high output and good temperature characteristics are hindered is that carriers that should contribute to light emission in the active layer overflow into the cladding layer when current is injected into the semiconductor laser device. there were. In particular, in semiconductor lasers with a short wavelength, such as the 1.3 μm band, the band gap of the active layer and the band gap of the cladding layer are relatively close, so even if an optical confinement layer is used, the carrier confinement effect Was weak and overflow was a particular problem.

As a method for suppressing carrier overflow, there is a DCH (Decoupled configuration heterostructure) structure in which a carrier block layer is provided between an active layer and an optical confinement layer, as shown in Non-Patent Document 1. A composition wavelength profile of a semiconductor laser having this structure is shown in FIG. This semiconductor laser includes a multiple quantum well active layer 4 composed of a GaInAsP quantum well layer having a composition wavelength of 1.3 μm and a barrier layer having a composition wavelength of 1.03 μm, an n-side GaInAsP light confinement layer 23 having a composition wavelength of 1.15 μm, a composition wavelength of 1 .10 μm p-side GaInAsP optical confinement layer 25, n-type InP clad layer 22 and p-type InP clad layer 27, and between n-type optical confinement layer 23 and n-type InP clad layer A carrier block layer 30 is provided. In this specification, the composition wavelength is used to specify the band gap energy of the material.
S. Hausser, H .; P. Meier, R.A. Germann and Ch. S. Harder, “1.3 um Multiquantum Well Decoupled Heterostructure (MQW-DCH) Laser Dides”, IEEE Journal of Quantum Electronics, Vol. 29, no. 6, June 1993, p. 1596-1600

  Another method for suppressing the overflow of electrons as carriers is to set the doping concentration of the p-type cladding high. In InP / GaInAsP-based materials, Zn is often used as a p-type dopant, but light absorption by Zn contributes to a decrease in light output. That is, if the Zn concentration is increased in order to suppress the overflow of carriers, there is a problem that light absorption by Zn increases and the effect of increasing the output cannot be obtained sufficiently.

  Conventionally, in a semiconductor laser on an InP substrate, the material constituting the cladding layer and the optical confinement layer is usually used only in a composition that lattice-matches with InP constituting the substrate in order to stabilize the crystal structure. It was. That is, a material having a lattice constant close to that of InP has been used as a material for the cladding layer and the optical confinement layer. As a GaInAsP-based material lattice-matched to InP, there is no material having a larger band gap than InP, so that even if a carrier block layer is introduced as in the technique disclosed in Patent Document 1, sufficient effects can be obtained. I could not.

In order to solve the above problems, the present invention sandwiches a quantum well active layer, a light confinement layer in contact with at least one side of the quantum well active layer, and the quantum well active layer and the light confinement layer on a semiconductor substrate. And a resonator formed in parallel to the semiconductor substrate, the semiconductor laser element includes a band gap that is greater than that of the pair of cladding layers. A wide gap layer made of a large material is provided, and the wide gap layer is doped to have the same conductivity type as the clad layer closer to the wide gap layer of the set of clad layers. A semiconductor laser device comprising: a semiconductor laser device, wherein the semiconductor substrate is made of InP, and the wide gap layer is formed of the clad layer of I If made of P is composed of GaInP or GaAs, the cladding layer, if made of GaInAsP that is lattice-matched to InP is to the InP or GaInAsP. In addition, the said wide gap layer is the thickness below a critical film thickness.

  The wide gap layer may be provided in any part of the semiconductor laser element, but is provided in a part of the cladding layer that is in contact with or close to the optical confinement layer. It is particularly preferred.

  Here, the larger the band gap of the material constituting the wide gap layer, the higher the effect of suppressing overflow. However, when the band gap of the wide gap layer is increased, the absolute value of the strain amount is also increased, so that the crystallinity is deteriorated. Therefore, it is necessary to appropriately select the band gap according to the application.

  Further, it is preferable that the wide gap layer is composed of two or more layers having different band gaps from each other because the effect of suppressing carrier overflow is increased.

  For example, when the clad layer is made of InP, the material of the wide gap layer is preferably made of GaInP or GaAs. In addition, when the cladding layer is made of GaInAsP, the wide gap layer can also be a lattice matching system if InP is used. In addition, GaInP can be used to increase the effect of suppressing carrier overflow.

  In addition, it is preferable that the wide gap layer be provided on the p side, because the effective mass is small and it is possible to suppress an overflow of electrons that is disadvantageous in terms of confinement.

  According to the present invention, by having a layer made of a material having a band gap larger than that of the cladding layer, it is possible to obtain a semiconductor laser with suppressed carrier overflow, high output and excellent temperature characteristics.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 shows a semiconductor laser device according to Embodiment 1 of the present invention. FIG. 1 is a cross-sectional view perpendicular to the cavity direction of the semiconductor laser according to the first embodiment. This semiconductor laser element 20 is formed on an n-type InP substrate 1 and an n-type cladding layer 2 made of n-type InP doped to 1 × 10 ¹⁸ cm ⁻³ and having a thickness of 1 μm. An n-side optical confinement layer 3 made of GaInAsP and InP having a thickness of 0.045 μm, a GaInAsP quantum well layer having a composition wavelength of 1.65 μm, and a GaInAsP barrier layer having a composition wavelength of 1.2 μm, having a total thickness of 0.06 μm. 2. active layer 4, 0.045 μm thick upper optical confinement layer 5 made of non-doped GaInAsP and InP, the composition of which is changed stepwise, and a thickness of p-type InP doped to 7 × 10 ¹⁷ cm ⁻³ . A 5 μm p-type cladding layer 7 and a 0.5 μm thick p-type contact layer 8 made of p-type GaInAsP are laminated. In the multiple quantum well active layer 4, it is preferable that the quantum well layer has a compressive strain of about + 1% and the barrier layer has a tensile strain of about -0.02 to -0.8%. In addition, when the n-type doping of about 1 × 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ is applied to the multiple quantum well active layer 4, the device resistance is reduced, so that the thermal resistance of the device can be reduced. And better temperature characteristics can be obtained. Further, the doping to the active layer may be p-type doping instead of n-type doping.

In a portion sandwiched between the p-side optical confinement layer 5 and the p-type cladding layer 7, a p-side wide gap made of p-type GaInP doped with 3 × 10 ¹⁸ cm ⁻³ at a composition wavelength of 0.87 μm is formed. Layer 6b is provided. In the n-side optical confinement layer 3, an n-side wide gap having a thickness of 8 nm made of n-type GaInP doped with a composition wavelength of 0.87 μm and 1 × 10 ¹⁸ cm ⁻³ is formed in a portion in contact with the n-type cladding layer 2. Layer 6a is provided.

  The wide gap layers 6a and 6b are more effective in suppressing overflow if they are provided near the active layer 4. However, if the distance is too close, there is a problem that the dopant in the wide gap layer diffuses into the active layer, and light absorption by the dopant in the wide gap layer occurs. Therefore, the distance from the end of the active layer to the wide gap layer (the length of 5 + 5b + 6b / 2 in FIG. 2) is preferably 250 nm or less, and more preferably 50 nm or less. Accordingly, the position of the wide gap layer is not limited to the inside of the cladding layer as shown in the first embodiment, but may be the boundary between the cladding layer and the light confinement layer or the inside of the light confinement layer.

  Here, in the case of the quantum well active layer, the end of the active layer refers to the boundary between the outermost barrier layer and the optical confinement layer (the boundary between 4 and 5 or the boundary between 4 and 3 in FIG. 2). To do. Further, the position of the wide gap layer refers to the center position in the thickness direction of the wide gap layer.

  From the viewpoint of carrier injection into the active layer, the n-side optical confinement layer 3 and the p-side optical confinement layer 5 are designed such that the band gap gradually increases as the active layer approaches the cladding layer. desirable. Therefore, as shown in the first embodiment, it is preferable that the p-side wide gap layer 6 b is provided in a portion in the p-type cladding layer 7 and close to the p-side optical confinement layer 5. . Similarly, the n-side wide gap layer 6 a is preferably provided between the n-side optical confinement layer 3 and the n-type cladding layer 2. However, even if the position of the wide gap layer is not limited to the above position, the effect of suppressing the carrier overflow is exhibited.

  An upper electrode 9 is formed on the upper surface of the p-type contact layer 8, and a lower electrode 10 is formed on the lower surface of the n-type InP substrate 1.

  The semiconductor laser element 20 is manufactured by using an epitaxial growth method such as a metal organic chemical vapor deposition method (MOCVD method). The dopant used for the p-type layer is zinc (Zn), and the dopant used for the n-type layer is selenium (Se) or sulfur (S). In addition, Si may be used as the n-type dopant, and C or Mg may be used as the p-type dopant. Since GaInP has a smaller lattice constant than InP, it has a tensile strain of about -1% on the cladding layer made of InP. However, since the thickness of the wide gap layer is set to 8 nm which is equal to or less than the critical film thickness, there is no problem such as generation of crystal defects due to strain.

  The thicker the wide gap layer, the greater the effect of suppressing carrier overflow. Therefore, it is preferable that the wide gap layer is as thick as possible with a thickness not more than a critical thickness determined according to the amount of strain, for example, not more than about 30 nm.

  FIG. 2 shows a composition wavelength profile in a direction perpendicular to the substrate of this semiconductor laser device. The p-side wide gap layer 6b provided in the p-type cladding layer 7 serves as a carrier block for electrons, and the n-side wide gap layer 6a provided in the n-type cladding layer 2 serves as a carrier block for holes. Play a role.

The p-side wide gap layer 6b is preferably doped p-type as in this embodiment. Similarly, the n-side wide gap layer 6a is preferably doped n-type. As these doping amounts, 1 × 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ is appropriate.

In order to evaluate the influence of the doping amount on the wide gap layer on the carrier overflow suppression effect, a simulation of leakage current reflecting the degree of carrier overflow was performed by Crosslight Software Inc. This was performed using a general-purpose simulation software “PICS3D”. The semiconductor laser structure is as shown in FIG. 1, and the doping amount into the p-side wide gap layer 6b made of GaInP is used as a parameter. The temperature was 300K. The simulation result is shown in FIG. The vertical axis in FIG. 3 is the electron current. However, the electron current is normalized by the value of the electron current in the n-type region. The horizontal axis is the position in the direction perpendicular to the substrate, and the axis is taken so that the position of 1.6 to 1.7 μm corresponds to the active layer. As can be seen from FIG. 3, when the p-side wide gap layer is not doped (non-doped), the normalized electron current in the p-type region is as large as about 0.26, whereas it is 7 × 10 ^17. It becomes 0.05 or less when performing doping cm ^-3, and approximately a zero when performing doping of 5 × ¹⁰ 18 ^{cm -3.} As described above, the higher the doping concentration in the p-side wide gap layer, the smaller the electron current in the p-type cladding layer, that is, the smaller the carrier overflow to the p-type cladding layer. .

As described above, carrier overflow can be suppressed by providing a wide gap layer or doping the wide gap layer. This method is advantageous for the following reason as compared with the case where the doping concentration of the cladding layer is increased to suppress the overflow of carriers. In the present invention, the effect of suppressing the overflow of carriers can be carried out by the wide gap layer, and even if the doping concentration of the p-cladding layer that causes light absorption is lowered, the overflow of carriers hardly occurs. That is, it is preferable because the doping concentration of the p-type cladding layer can be lowered as compared with the conventional structure having no wide gap layer. However, regarding this point, if the doping concentration of the p-type cladding layer is lowered too much, problems such as an increase in device resistance will occur, so the doping concentration of the p-type cladding layer is approximately 7 × 10 ¹⁶ cm ⁻³ to 1. It is desirable that it is about × 10 ¹⁸ cm ⁻³ , more preferably about 1 × 10 ¹⁷ cm ^{−3 to} 5 × 10 ¹⁷ cm ⁻³ . In addition, the higher the doping concentration of the wide gap layer, the higher the effect of suppressing overflow. However, if the doping concentration is too high, light absorption in the wide gap layer becomes a problem, and non-ionized Zn diffuses into the active layer. This is not preferable because it is too high.

  In the semiconductor laser device of the first embodiment, the p-type dopant to the p-type cladding layer 7 is usually used Zn. This Zn is easily diffused from the p-type cladding layer 7 during epitaxial growth, and Zn is taken into the multiple quantum well active layer 4. Since Zn has the property of easily absorbing light during the operation of the laser, it is disadvantageous for high output. Here, as shown in the first embodiment, by providing the p-side wide gap layer 6b made of GaInP in the p-side optical confinement layer 5, the p-side wide gap layer 6b is separated from the p-type cladding layer 7 of Zn. It can also serve to block the movement to the multiple quantum well active layer 4. In order to make this effect clearer, it is important that the layer 5b adjacent to the p-side wide gap layer 6b made of GaInP is made of InP among the layers constituting the p-type cladding layer 7.

  Further, as already described, the wide gap layer made of GaInP has tensile strain on InP, and thus has a function of suppressing Auger absorption, which is advantageous for increasing the output of the semiconductor laser.

  As described above, in the first embodiment, since the wide gap layer having a larger band gap than the adjacent cladding layer is provided in the optical confinement layer, a semiconductor laser having high output and excellent temperature characteristics can be obtained.

  FIG. 4 shows optical output-current characteristics measured for the semiconductor laser device according to the first embodiment and the conventional semiconductor laser device. Both of these semiconductor laser elements have a resonator length of 1500 μm, and a low-reflection film is coated on the emission side end face, and a light reflection film is coated on the reflection side end face. In addition, a buried heterostructure is adopted as a current confinement structure. The light output-current characteristics were measured using a semiconductor laser element in a chip state and a pulse current. The stage temperature during measurement was 20 ° C.

  As can be seen from FIG. 4, the semiconductor laser device according to the first embodiment has a higher output than the conventional semiconductor laser device, and can achieve an optical output of 500 mW or more.

  In the first embodiment, the wide gap layer is provided on both the p side and the n side. However, even if the wide gap layer is provided only on the p side, the carrier overflow suppressing effect can be obtained. This is due to the following reason. That is, since electrons have a smaller effective mass than holes, carrier overflows when electrons are injected into the semiconductor laser device are more problematic for electrons than for holes. In particular, in an InP-based material, the conduction band is more likely to occur than the hole overflow because the conduction band has a smaller energy difference between the quantum well layer and the barrier layer in the active layer than the valence band. Therefore, if the wide gap layer is provided at least on the p side, a certain effect of suppressing the carrier overflow effect can be obtained.

  However, if a wide gap layer made of GaInP is provided only on the p side, the following inconvenience may occur. That is, since GaInP has a higher refractive index than InP constituting the cladding layer, if a wide gap layer made of GaInP is provided only on the p side, the light intensity distribution is biased toward the p side. As a result, light absorption by Zn added to the p-type cladding layer as a dopant increases, which hinders high output. Therefore, the wide gap layer is preferably provided in both the p-side and n-side optical confinement layers as shown in the first embodiment. On the other hand, when the wide gap layer is provided only on the p side, the refractive index distribution is made symmetrical by increasing the thickness of the optical confinement layer in contact with the n-type cladding layer, or biased toward the n side. It is effective to generate

  In the first embodiment, the wide gap layer is made of GaInP, but may be made of GaAs having a larger band gap. In this case, the carrier overflow suppressing effect is further improved.

  [Embodiment 2] In Embodiment 1, a semiconductor laser element in which a single wide gap layer is provided in an optical confinement layer is shown. However, in Embodiment 2, the wide gap layer is composed of a plurality of layers having different band gaps. A semiconductor laser device is shown.

  A semiconductor laser device according to the second embodiment is shown in FIG. FIG. 5 is a cross-sectional view perpendicular to the cavity direction of the semiconductor laser according to the second embodiment. The structure of the semiconductor laser device according to the second embodiment is the same as that shown in the first embodiment except for the p-side wide gap layer. The p-side wide gap layer 6b is composed of wide gap layers 6b1, 6b2, and 6b3 made of GaInP having composition wavelengths of 0.89 μm, 0.87 μm, and 0.85 μm, respectively. Moreover, the composition wavelength profile of this vicinity is shown in FIG. As described above, the wide gap layer 6b is composed of a plurality of layers such that the band gap increases as the distance from the active layer 4 increases, so that the entire band of the wide gap layers 6b1, 6b2, 6b3 and the p-side optical confinement layer 5 is formed. The profile can be made close to a gentle state, and carrier injection into the active layer 4 becomes smooth.

  As described above, the plurality of layers constituting the wide gap layer 6b preferably have a larger band gap as the distance from the active layer increases. However, the present invention is not limited to this. For example, as shown in FIG. The band gap of 6b2 may be maximized, or the band gap of the layer 6b1 close to the multiple quantum well active layer 4 may be maximized as shown in FIG.

  Further, as shown in FIG. 9, the p-side wide gap layer 6b is provided between the p-side optical confinement layer 5 and the p-type cladding layer 7, and the p-side optical confinement layer 5 and the p-side wide gap layer 6b are It is more preferable to show a linear composition wavelength profile as a whole.

In the second embodiment, the case where the p-side wide gap layer is composed of a plurality of layers having different band gaps has been described. Needless to say, this may be applied to the n-side wide gap layer.
[Embodiment 3] Embodiments 1 and 2 have described the case where a wide gap layer made of GaInP is introduced in a semiconductor laser whose cladding layer is InP. However, in Embodiment 3, the cladding layer is made GaInAsP. A case where a wide gap layer made of InP is introduced will be described. This combination of the clad layer and wide gap layer materials is particularly effective when using a refractive index asymmetric clad layer in order to suppress light absorption in the Zn-doped p-type clad layer. When GaInAsP with a composition wavelength of about 0.95 μm, which has a higher refractive index than InP, is used as the n-type cladding layer, the band gap of the n-type cladding layer is smaller than when InP is used, which is disadvantageous in confining carriers. Therefore, it is effective to provide an n-side wide gap layer in the n-side optical confinement layer. In this case, InP can be used as the material for the n-side wide gap layer.

  The semiconductor laser according to Embodiment 3 is the same as that shown in Embodiment 1 except for the n-type cladding layer and the n-side optical confinement layer.

  FIG. 10 shows a composition wavelength profile near the n-side optical confinement layer of the semiconductor laser according to the third embodiment. An n-side wide gap layer 6 a made of InP is provided between the n-type cladding layer 2 ′ made of GaInAsP with a composition wavelength of 0.95 μm and the n-side optical confinement layer 3. The semiconductor laser according to Embodiment 3 can suppress the carrier overflow with a material having a band gap larger than that of the cladding layer while using only a lattice matching material while causing the light intensity to be biased toward the n side. A semiconductor laser with high output and excellent temperature characteristics.

  In the third embodiment, the wide gap layer may be made of GaInP.

  It is also possible to provide a distributed feedback semiconductor laser (DFB laser) or the like by providing a diffraction grating layer in the structure of the semiconductor laser element described in the first to third embodiments. In that case, the positional relationship between the diffraction grating layer and the wide gap layer does not matter.

  In the examples shown in Embodiments 1 and 2, the refractive index of GaInP, which is a wide gap layer, is higher than that of InP, which is a cladding layer. In such a case, a diffraction grating is formed in the wide gap layer itself. Thus, the wide gap layer may be a diffraction grating layer. Such a structure is advantageous from the following points. Generally, when a diffraction grating layer is provided to form a diffraction grating, the diffraction grating layer is required to have a higher refractive index than the cladding layer. In InP / GaInAsP-based lasers, the band gap becomes smaller as the refractive index of the composition increases, so that the diffraction grating layer obstructs the carrier blocking effect and is weak against carrier overflow. Therefore, by providing the wide gap layer or forming the diffraction grating layer itself with the wide gap layer, an excellent effect is exhibited against carrier overflow, which has been a particular problem in the DFB laser.

  The present invention is not limited to the structure described in the above embodiment. For example, the present invention can also be applied to a semiconductor laser element using a material such as GaAs other than InP as a semiconductor substrate. Furthermore, the present invention can be applied regardless of the waveguide structure of the semiconductor laser as long as it has a resonator parallel to the substrate. For example, a buried hetero structure, a ridge structure, a self-aligned structure, or the like may be used. Further, it is preferable to apply a low reflection film / high reflection film coating to the light emitting end face of the laser.

It is sectional drawing of the semiconductor laser element which concerns on Embodiment 1 of this invention. It is a composition wavelength profile of the semiconductor laser element which concerns on Embodiment 1 of this invention. It is a graph showing the simulation result of the leakage current in the semiconductor laser element which concerns on Embodiment 1 of this invention. It is a graph which shows the optical output-current characteristic in the semiconductor laser element concerning Embodiment 1 of this invention. It is sectional drawing of the semiconductor laser element which concerns on Embodiment 2 of this invention. It is a composition wavelength profile of the semiconductor laser element which concerns on Embodiment 2 of this invention. It is a composition wavelength profile which shows the other form example which concerns on Embodiment 2 of this invention. It is a composition wavelength profile which shows the other form example which concerns on Embodiment 2 of this invention. It is a composition wavelength profile which shows the other form example which concerns on Embodiment 2 of this invention. It is a composition wavelength profile of the semiconductor laser element which concerns on Embodiment 3 of this invention. It is a composition wavelength profile of the semiconductor laser element of the conventional DCH structure.

Explanation of symbols

1 n-type InP substrate 2 n-type cladding layer 3 n-side optical confinement layer 4 multiple quantum well active layer 5 p-side optical confinement layer 6a n-side wide gap layer 6b p-side wide gap layer 7 p-type cladding layer 8 p-type contact layer 9 Upper electrode 10 Lower electrode 20 Semiconductor laser element

Claims (16)

A semiconductor substrate has a quantum well active layer, a light confinement layer in contact with at least one side of the quantum well active layer, and a pair of cladding layers provided with the quantum well active layer and the light confinement layer interposed therebetween. ,
In the semiconductor laser device having a resonator formed in parallel to the semiconductor substrate, the semiconductor laser device is provided with a wide gap layer made of a material having a larger band gap than the pair of clad layers. ,
The wide gap layer has a layer doped so as to have the same conductivity type as the clad layer closer to the wide gap layer of the set of clad layers,
The semiconductor substrate is made of InP, the wide-gap layer is made of GaInP, the closer the cladding layer of InP Ri Tona,
The wide-gap layer, a semiconductor laser device characterized critical film thickness or less thick der Rukoto. A semiconductor substrate has a quantum well active layer, a light confinement layer in contact with at least one side of the quantum well active layer, and a pair of cladding layers provided with the quantum well active layer and the light confinement layer interposed therebetween. ,
In the semiconductor laser device having a resonator formed in parallel to the semiconductor substrate, the semiconductor laser device is provided with a wide gap layer made of a material having a larger band gap than the pair of clad layers. ,
The wide gap layer has a layer doped so as to have the same conductivity type as the clad layer closer to the wide gap layer of the set of clad layers,
The semiconductor substrate is made of InP, the wide-gap layer is made of InP, or GaInP, the closer cladding layer of Ri GaInAsP Tona that is lattice-matched to InP,
The wide-gap layer, a semiconductor laser device characterized critical film thickness or less thick der Rukoto. A semiconductor substrate has a quantum well active layer, a light confinement layer in contact with at least one side of the quantum well active layer, and a pair of cladding layers provided with the quantum well active layer and the light confinement layer interposed therebetween. ,
In the semiconductor laser device having a resonator formed in parallel to the semiconductor substrate, the semiconductor laser device is provided with a wide gap layer made of a material having a larger band gap than the pair of clad layers. ,
The wide gap layer has a layer doped so as to have the same conductivity type as the clad layer closer to the wide gap layer of the set of clad layers,
The semiconductor substrate is made of InP, the wide-gap layer is made of GaAs, the closer the cladding layer of Ri InP Tona,
The wide-gap layer, a semiconductor laser device characterized critical film thickness or less thick der Rukoto.   The semiconductor laser device according to claim 1, wherein the quantum well active layer is made of GaInAsP.   5. The semiconductor laser device according to claim 1, wherein the optical confinement layer is made of InP and GaInAsP. 6.   6. The semiconductor laser device according to claim 1, wherein a doping concentration of the wide gap layer is higher than a doping concentration of the closer cladding layer.   7. The semiconductor laser device according to claim 1, wherein the wide gap layer is provided in at least one of the pair of clad layers.   The semiconductor laser device according to claim 1, wherein the wide gap layer is provided in proximity to the optical confinement layer.   9. The semiconductor laser device according to claim 1, wherein the wide gap layer is provided at a position of 250 nm or less from an end of the quantum well active layer. 10.   9. The semiconductor laser device according to claim 1, wherein the wide gap layer is provided at a position of 50 nm or less from an end of the quantum well active layer. 10.   11. The semiconductor laser device according to claim 1, wherein the wide gap layer includes two or more layers having different band gaps. 11.   The wide gap layer is provided in at least a p-type clad layer or in contact with a p-type clad layer of the set of clad layers. The semiconductor laser device described.   The wide gap layer is provided in an optical confinement layer in contact with at least a p-type clad layer of the set of clad layers. Semiconductor laser element.   The distributed semiconductor laser element according to claim 1, wherein the semiconductor laser element includes a diffraction grating.   2. The semiconductor laser device according to claim 1, wherein the wide gap layer is formed as a diffraction grating.   16. The semiconductor laser device according to claim 1, wherein an oscillation wavelength of the semiconductor laser is 1.3 μm or more and 1.64 μm or less.

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