JP2006196660A - Semiconductor laser - Google Patents

Abstract

A semiconductor laser capable of high temperature operation and high output operation is provided.
A semiconductor laser 1 comprising a substrate 10 and a semiconductor layer provided on the substrate 10 including at least an n-type cladding layer 11, an active layer 13 and a p-type cladding layer 15 in this order. The mold cladding layer 15 includes at least two impurity diffusion prevention layers (a first impurity diffusion prevention layer 16A and a second impurity diffusion prevention layer 16B) having a composition different from that of the p-type cladding layer 15 therein. The impurity diffusion preventing layers 16 </ b> A and 16 </ b> B are for preventing the p-type impurities doped when the p-type cladding layer 15 is epitaxially grown on the active layer 13 from diffusing into the active layer 13.
[Selection] Figure 1

Description

  The present invention relates to a semiconductor laser used for an optical disc or optical communication.

  In recent years, write-once DVD (Digital Versatile Disk) devices are rapidly spreading. For reading / writing of this DVD device, a red semiconductor LD (Laser Diode) in which an AlGaInP-based semiconductor is stacked on a GaAs substrate is used. The red semiconductor LD has, for example, a quantum well structure in which an n-type cladding layer made of AlInP, a lower guide layer made of AlGaInP, a well layer made of GaInP, and a barrier layer made of AlGaInP are alternately stacked on a GaAs substrate. , An upper guide layer made of AlGaInP, a first p-type cladding layer made of AlInP, an etching stop layer made of GaInP, and a second p-type cladding layer made of AlInP are stacked in this order.

  By the way, this red semiconductor LD is not very suitable for high-temperature operation and high-power operation because its temperature characteristics are very poor compared to an LD used in a CD (Compact Disc) device or the like. Thus, as a method for overcoming such a problem, for example, a method of increasing the carrier concentration of the p-type cladding layer and reducing the resistance of the p-type cladding layer while suppressing carrier overflow in the p-type cladding layer is conceivable. . However, the p-type impurity Zn (zinc) used in the MOCVD (Metal Organic Chemical Vapor Deposition) method generally used when epitaxially growing an AlGaInP-based semiconductor on a GaAs substrate is an active layer. Diffuse to occur easily. Therefore, if Zn diffuses into the active layer, the quantum well structure of the active layer is destroyed by Zn, so it is not appropriate to increase the carrier concentration in the region near the active layer in the p-type cladding layer. Absent.

  Thus, for example, the following two methods can be considered in order to suppress diffusion into the active layer. The first method is a method using Mg (magnesium) as a p-type doping material having a low diffusion rate instead of Zn, and the second method is undoped between the upper guide layer and the first p-type cladding layer. This is a method of providing a spacer layer (Patent Document 1).

JP 2000-286507 A

  However, in the first method, even if the diffusion rate is low, the diffusion to the active layer is not actively controlled, so the same problem as in the case of using Zn as the p-type doping material. May occur. In the second method, the thickness of the upper guide layer and the first p-type cladding layer is determined based on optical specifications and cannot be arbitrarily changed. The distance between the active layer and the active layer cannot be arbitrarily changed. Therefore, when the distance between the spacer layer and the active layer is too close, the p-type impurity diffuses to the active layer through the upper guide layer regardless of the presence of the spacer layer. The well structure will be destroyed. Therefore, it is difficult to realize a high temperature operation or a high output operation by any of these methods.

  The present invention has been made in view of such problems, and an object thereof is to provide a semiconductor laser capable of high-temperature operation and high-power operation.

  A semiconductor laser according to the present invention includes a substrate and a semiconductor layer provided on the substrate so as to include at least a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer in this order. The two-conductivity-type clad layer includes at least two impurity diffusion prevention layers having a composition different from that of the second-conductivity-type clad layer.

  In the semiconductor laser of the present invention, at least two impurity diffusion prevention layers having a composition different from that of the second conductivity type cladding layer are included in the second conductivity type cladding layer. Here, the impurity diffusion preventing layer prevents the impurity of the second conductivity type doped when the semiconductor layer including the second conductivity type cladding layer is epitaxially grown on the active layer from diffusing into the active layer. Is for. However, the impurity diffusion prevention layer may have a role other than this. For example, a layer farther from the active layer among the plurality of impurity diffusion prevention layers is used when forming the ridge. It may have a role as an etching stop layer. Further, it is not necessary that all impurity diffusion preventing layers have the same composition or thickness.

  According to the semiconductor laser of the present invention, at least two impurity diffusion prevention layers having a composition different from that of the second conductivity type cladding layer are included in the second conductivity type cladding layer, so that high temperature operation and high output operation are realized. can do.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a cross-sectional structure of an AlGaInP-based semiconductor laser 1 according to an embodiment of the present invention. The AlGaInP-based semiconductor laser 1 includes an n-type cladding layer 11, a lower guide layer 12, an active layer 13, an upper guide layer 14, a first p-type cladding layer 15 A made of an AlGaInP-based compound semiconductor material. The first impurity diffusion preventing layer 16A, the second p-type cladding layer 15B, the second impurity diffusion preventing layer 16B, the third p-type cladding layer 15C and the p-side contact layer 17 are laminated in this order. Here, the third p-type cladding layer 15C and a part of the p-side contact layer 17 are formed up to the third p-type cladding layer 15C, and then selectively etched, whereby the laser light is emitted in the axial direction. An extending stripe-shaped ridge portion (projection portion) 18 is formed. An insulating film 19 is formed so as to cover both side surfaces of the ridge portion 18. Hereinafter, a direction in which the semiconductor layers are stacked is referred to as a vertical direction, and an axial direction and a direction perpendicular to the vertical direction are referred to as a horizontal direction.

The substrate 10 is made of, for example, n-type GaAs having a thickness in the vertical direction (hereinafter simply referred to as thickness) of 100 μm. Here, examples of the n-type impurity include silicon (Si) and selenium (Se). The n-type cladding layer 11 is made of, for example, an n-type Al _a Ga _1-ab In _b P mixed crystal (0 <a <1, 0 <b <1) having _a thickness of 1 μm. The lower guide layer 12 is made of, for example, an n-type Al _c Ga _{1 -cb} In _b P mixed crystal (0 <c <a, 0 <b <1) having a thickness of 50 nm. The reason why the Al composition of the lower guide layer 12 is smaller than that of the n-type cladding layer 11 is to confine carriers in the active layer 13.

The active layer 13 has a thickness of about 5 nm, for example, and is composed of an undoped Ga _d In _1-d P mixed crystal (0 <d <1). In the active layer 13, a region facing the ridge portion 18 is a current injection region into which current is injected, and this current injection region functions as a light emitting region.

The upper guide layer 14 is made of, for example, a p-type Al _e Ga _1-eb In _b P mixed crystal (0 <e <f (described later), 0 <b <1) having a thickness of 50 nm. Here, examples of the p-type impurity include zinc (Zn) and magnesium (Mg). The first p-type cladding layer 15A, the second p-type cladding layer 15B, and the third p-type cladding layer 15C are composed of a p-type Al _f Ga _{1 -fb} In _b P mixed crystal (0 <f <1, 0 <b <1). The respective thicknesses are, for example, 0.1 μm, 0.1 μm, and 0.8 μm. The reason why the Al composition of the upper guide layer 14 is smaller than that of the first p-type cladding layer 15A, the second p-type cladding layer 15B, and the third p-type cladding layer 15C is to confine carriers in the active layer 13.

  In the present embodiment, the lower guide layer 12, the n-type cladding layer 11, the upper guide layer 14, the first p-type cladding layer 15A, the second p-type cladding layer 15B, and the third p-type cladding layer 15C have the same In composition. However, this is simply to simplify the explanation by associating the Al composition with the band structure, and appropriately combining the Al composition, the Ga composition, and the In composition with the band structure in the present embodiment. You may make it become the same structure.

The first impurity diffusion preventing layer 16A is made of, for example, an undoped Al _g Ga _1-gh In _h P mixed crystal (0 ≦ g <1, 0 <h <1) having a thickness of 20 nm, and the second impurity diffusion preventing layer 16A. The layer 16B is made of, for example, a p-type Al _i Ga _1-ik In _k P mixed crystal (0 ≦ i <1, 0 <k <1) having a thickness of 20 nm. However, since the diffusion rate of impurities can be suppressed when the Al composition is smaller, the Al composition of the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B is desirably small and more preferably zero. desirable.

  Further, the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B have an energy gap such that light emitted from the active layer 13 is not absorbed, that is, energy corresponding to the wavelength of light emitted from the active layer 13. It is desirable to have a large energy gap. Therefore, in the present embodiment, the first impurity diffusion preventing layer 16A and the second impurity diffusion are utilized by utilizing the property that when a crystal having a lattice constant different from that of the substrate 10 is grown, distortion is generated inside and the band structure changes. These compositions are set so that the energy gap of the prevention layer 16B is larger than the energy corresponding to the wavelength of the light emitted from the active layer 13. However, since the Al composition is desirably zero as described above, it is desirable to set the composition of Ga and In after making the Al composition zero. By adjusting the composition of the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B in this way, the first impurity diffusion prevention layer 16A and the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B are suppressed while suppressing the diffusion of impurities into the active layer 13. The band structure of the two impurity diffusion preventing layer 16B can be controlled.

  Note that the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B have the first p-type cladding layer 15A, the second p-type cladding layer 15B, and the third p-type cladding layer 15C as one p-type cladding layer 15. It can be understood that it is provided inside the p-type cladding layer 15. However, the second impurity diffusion preventing layer 16B also serves as an etching stop layer when forming the ridge portion 18, and the shape of the ridge portion 18 according to the position of the second impurity diffusion preventing layer 16B, that is, Since the degree of light confinement in the lateral direction of the laser is determined, the second impurity diffusion preventing layer 16B cannot be disposed at an arbitrary position in the p-type cladding layer 15. On the other hand, since the first impurity diffusion preventing layer 16A has no such restriction, the first impurity diffusion preventing layer 16A can be freely moved between the upper guide layer 14 and the second impurity diffusion preventing layer 16B. . A plurality of first impurity diffusion preventing layers 16A may be provided between the upper guide layer 14 and the second impurity diffusion preventing layer 16B.

The p-side contact layer 17 is made of, for example, a p-type GaAs mixed crystal having a thickness of 0.5 μm. The third p-type cladding layer 15 and the p-side contact layer 17 are provided in a ridge portion 18 having a lateral width of 50 μm. The insulating film 19 is made of, for example, SiO _{2 having a} thickness of 0.2 μm. The ridge portion 18 limits the current injection region of the active layer 13 and stably controls the optical mode in the lateral direction to the fundamental (0th order) mode and guides it in the axial direction.

  The AlGaInP semiconductor laser 1 has an n-side electrode 21 on the back surface of the substrate 10. The n-side electrode 21 has, for example, a structure in which an alloy layer of gold and germanium (Ge), a nickel (Ni) layer, and a gold (Au) layer are sequentially stacked from the substrate 10 side. And electrically connected to the n-type semiconductor layer. On the other hand, a p-side electrode 20 is provided on the p-side contact layer 17. The p-side electrode 20 is formed, for example, by sequentially laminating a titanium (Ti) layer, a platinum (Pt) layer, and a gold layer from the p-side contact layer 17 side, and is electrically connected to the p-type semiconductor layer. .

Further, the AlGaInP semiconductor laser 1 has a pair of side surfaces in the axial direction serving as resonator end surfaces, and a reflecting mirror film (not shown) is formed on each of the resonator end surfaces. One reflecting mirror film (main emission side) is made of, for example, aluminum oxide (Al ₂ O ₃ ) and is adjusted to have a low reflectance. On the other hand, the other reflecting mirror film is formed by alternately laminating aluminum oxide layers and amorphous silicon (amorphous silicon) layers, for example, and is adjusted to have a high reflectance. Thereby, the light generated in the active layer 13 is amplified by reciprocating between the pair of reflecting mirror films, and is emitted as a laser beam from the reflecting mirror film on the low reflectance side.

In the present embodiment, as described above, the band structures of the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B set the composition of Ga and In after setting the Al composition to zero. The method for setting the Ga and In composition will be described below with reference to FIG. Incidentally, FIG. 2 is equal to the band gap of Ga _1-x In the composition ratio x of In in the first impurity diffusion prevention layer 16A and the second impurity diffusion preventing layer 16B made of _x P, Ga _x In _1-x P It represents the relationship with the wavelength of light (absorption edge wavelength) corresponding to the magnitude energy.

From FIG. 2, it can be confirmed that the tensile strain increases as the In composition x in Ga _1-x In _x P decreases. In general, since the energy gap of a crystal having tensile strain becomes narrower than the original energy gap, the transparent region (region where light is not absorbed) shifts to the longer wavelength side as the In composition x increases. On the contrary, it can be confirmed that as the composition x of In in Ga _1-x In _x P increases, the compressive strain increases and the energy gap widens. This transparent region corresponds to the upper region of the graph in FIG. Therefore, in order to prevent the light emitted from the active layer 13 from being absorbed by the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B, it is only necessary to be in the upper region of the graph in FIG. Specifically, the In composition x may be reduced so that the band gap is larger than the energy corresponding to the emission wavelength.

  For example, when the PL wavelength of the active layer 13 is 610 nm (in this case, the wavelength of light emitted as a laser is 640 nm), the In composition ratio x is 0.40 or less, and the PL wavelength of the active layer 13 is 625 nm. In this case (in this case, the wavelength of light emitted as a laser is 655 nm), it is understood that the In composition ratio x should be 0.45 or less.

  However, when increasing the amount of strain introduced into the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B, the film thickness should be set to a thickness equal to or less than the critical film thickness to prevent the occurrence of lattice defects. Can be considered. However, if the thickness is too thin, the effect of preventing the diffusion of impurities is diminished. Therefore, it is desirable to set the film thickness to a certain level or more, and preferably about 5 nm to 15 nm or more. The critical film thickness refers to a limit thickness at which lattice defects do not occur at a certain strain amount.

  Note that although the Ga composition may be zero depending on the combination of a to c, e to i, and k, this embodiment does not exclude the case where the Ga composition is zero.

  The AlGaInP semiconductor laser 1 having such a configuration can be manufactured, for example, as follows.

3 to 5 show the manufacturing method in the order of steps. In order to manufacture the AlGaInP semiconductor laser 1, the compound semiconductor layer on the substrate 10 is formed by, for example, MOCVD (Metal Organic Chemical Vapor Deposition) method. At this time, for example, trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMIn), or phosphine (PH ₃ ) is used as a raw material for a III-V group compound semiconductor. , H ₂ Se, and dimethyl zinc (DMZ), for example, is used as the acceptor impurity material.

  Specifically, first, as shown in FIG. 3, an n-type cladding layer 11, a lower guide layer 12, an active layer 13, an upper guide layer 14, a first p-type cladding layer 15A, and a first impurity are formed on a substrate 10. The diffusion prevention layer 16A, the second p-type cladding layer 15B, the second impurity diffusion prevention layer 16B, the third p-type cladding layer 15C, and the p-side contact layer 17 are laminated in this order.

  At this time, the flow rate of TMIn is adjusted so that the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B have a predetermined lattice mismatch with respect to the substrate 10, and each layer has a predetermined Al composition. Adjust the flow rate of TMA so that After the first impurity diffusion preventing layer 16A is provided, the second p-type cladding layer 15B is epitaxially grown and doped with p-type impurities, and then the second impurity diffusion preventing layer 16B is provided, and then the third p The type cladding layer 15C is epitaxially grown and doped with p-type impurities.

  Next, as shown in FIG. 4, for example, a mask layer (not shown) is formed on the p-side contact layer 17, and the p-side contact layer is formed by reactive ion etching (RIE). 17 and the third p-type cladding layer 15C are selectively removed. Thereby, a stripe-shaped ridge portion 18 extending in the axial direction is formed in part of the p-side contact layer 17 and the third p-type cladding layer 15C corresponding to the current injection region of the active layer 13.

Subsequently, an insulating film 19 made of SiO ₂ is formed using the mask layer so as to cover the side surface of the ridge portion 19. Thereafter, the mask layer is removed. Further, for example, the other surface side of the substrate 10 is lapped so that the thickness of the substrate 10 is 100 μm, and the n-type contact layer 21 and the n-side electrode 21 are sequentially formed on the other surface side. A p-side electrode 20 is formed on the p-side contact layer 17 and the insulating film 19. Thereafter, a reflecting mirror film (not shown) is formed on the pair of side surfaces in the axial direction. Thereby, the AlGaInP semiconductor laser 1 shown in FIG. 1 is formed.

  Next, the operation of the AlGaInP semiconductor laser 1 of the present embodiment will be described.

  That is, in the AlGaInP semiconductor laser 1, when a predetermined voltage is applied between the n-side electrode 21 and the p-side electrode 20, current is confined by the ridge portion 18, and current is injected into the current injection region of the active layer 13. As a result, light emission is caused by recombination of electrons and holes. This light is reflected by a pair of reflecting mirror films (not shown), causes laser oscillation at a wavelength at which the phase change when it reciprocates once in the element is an integral multiple of 2π, and is emitted to the outside as a laser beam. The

  Here, the effect of the semiconductor laser 1 of the present embodiment will be described in comparison with a comparative example.

  In the semiconductor laser 1 of the present embodiment, as described above, the first impurity impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B are provided in the cladding layer 15, and the semiconductor laser of the comparative example is provided. In this case, the second impurity diffusion preventing layer is provided as an etching stop layer, but the first impurity diffusion preventing layer is not provided as a layer for preventing impurity diffusion. 5A shows the distribution of the Al composition of the semiconductor laser, and FIG. 5B shows the concentration distribution of the p-type impurity of the semiconductor laser. ) And (B), the solid line A represents the Al composition distribution or concentration distribution of the semiconductor laser 1 of the present embodiment, and the broken line B represents the Al composition distribution or concentration distribution of the semiconductor laser of the comparative example. ing.

  As described above, in the semiconductor laser 1 of the present embodiment, after providing the first impurity diffusion prevention layer 16A having an Al composition smaller than that of the cladding layer 15, the second p-type cladding layer 15B is epitaxially grown and the p-type impurity is grown. Then, after providing the second impurity diffusion preventing layer 16B, the third p-type cladding layer 15C is epitaxially grown and doped with p-type impurities, as shown in FIG. In addition, the pile-up due to the very low diffusion rate in the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B as compared with the cladding layer 15 causes the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer. It occurs in the vicinity of 16B. Thus, not only can the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B be doped with high-concentration p-type impurities, but also the first impurity diffusion prevention layer 16A can be diffused into the active layer 13 through the first impurity diffusion prevention layer 16A. The amount of p-type impurities to be drastically reduced can be suppressed.

  On the other hand, in the semiconductor laser of the comparative example, after the second impurity diffusion prevention layer having an Al composition smaller than that of the cladding layer was provided, the third p-type cladding layer was epitaxially grown and the p-type impurity was doped. However, since there is no first impurity diffusion preventing layer in the vicinity of the active layer as in the present embodiment, the amount of p-type impurity diffused into the active layer 13 cannot be suppressed. As a result, if the cladding layer is doped with a high-concentration p-type impurity as in this embodiment, the high-concentration p-type impurity reaches the active layer as shown in FIG. 5B. .

  For these reasons, according to the semiconductor laser 1 of the present embodiment, the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B are provided inside the p-type cladding layer 15. The concentration distribution of the p-type impurity inside the layer 15 can be positively controlled. Thereby, not only can the p-type cladding layer 15 be doped with high-concentration p-type impurities, but also when the first impurity diffusion prevention layer 16A is disposed in the vicinity of the active layer 13, the p-type cladding layer 15 can reach the vicinity of the active layer 13. A concentration of p-type impurities can be doped.

  As a result, it is possible to reduce the resistance of the p-type cladding layer 15 while suppressing carrier overflow in the p-type cladding layer 15, and to realize a high temperature operation and a high output operation. In addition, the lifetime of the device can be extended.

  Although the present invention has been described with reference to one embodiment, the present invention is not limited to the above-described embodiment, and various modifications can be made.

  For example, the semiconductor laser 1 of the present embodiment is composed of an AlGaInP-based compound semiconductor, but may be composed of, for example, an AlGaAs-based or GaN-based compound semiconductor.

Specifically, in a semiconductor laser composed of an AlGaAs compound semiconductor, the p-type cladding layer 15 is an Al _m Ga _1-m As (0 <m <0) mixed crystal, and the impurity diffusion prevention layer 16A is an Al _n Ga. _{The 1-n} As (0 <n <k <0) mixed crystal, and the impurity diffusion preventing layer 16B are composed of Al _p Ga _1-p As (0 <p <k <0) mixed crystal. However, since the diffusion rate of impurities can be suppressed when the Al composition is smaller, the Al composition of the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B is desirably small. However, if the Al composition is reduced to zero, it becomes GaAs and the composition ratio cannot be adjusted. Therefore, the band structures of the first impurity diffusion preventing layer 16A and the second impurity diffusion preventing layer 16B can be adjusted. It is desirable to have an Al composition as much as possible. For example, when the Al composition m of the cladding layer 15 is 0.45 to 0.60 and the PL wavelength of the active layer is 780 to 810 nm, the Al compositions n and p are preferably 0.2 to 0.3, for example. .

  In this embodiment, the current ridge is provided by providing the ridge portion 18, but the current may be confined by another method. In that case, the first impurity diffusion prevention layer 16A and the second impurity diffusion prevention layer 16B may further have some function in addition to the impurity diffusion prevention function described in detail above.

It is a section lineblock diagram of a semiconductor laser in one embodiment of the present invention. It is a characteristic view showing the relationship between In composition of an impurity diffusion prevention layer, a wavelength, and a lattice mismatch. FIG. 7 is a cross-sectional view for explaining a manufacturing step of the semiconductor laser of FIG. 1. FIG. 4 is a cross-sectional view for explaining a step following the step in FIG. 3. FIG. 2 is a diagram showing the Al composition and impurity concentration distribution of the semiconductor laser of FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 10 ... Board | substrate, 11 ... N-type cladding layer, 12 ... Lower guide layer, 13 ... Active layer, 14 ... Upper guide layer, 15 ... P-type cladding layer, 15A ... 1st p-type cladding layer, 15B ... Second p-type cladding layer, 15C ... third p-type cladding layer, 16A ... first impurity diffusion preventing layer, 16B ... second impurity diffusion preventing layer, 17 ... p-side contact layer, 18 ... ridge portion, 19 ... insulating film, 20 ... p-side electrode, 21 ... n-side electrode

Claims (6)

A semiconductor laser comprising: a substrate; and a semiconductor layer provided on the substrate by including at least a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer in this order,
The semiconductor laser according to claim 1, wherein the second conductivity type cladding layer includes at least two impurity diffusion prevention layers having a composition different from that of the second conductivity type cladding layer. 2. The semiconductor laser according to claim 1, wherein the impurity diffusion preventing layer is formed of a mixed crystal having an Al composition less than that of the second conductivity type cladding layer. The second conductivity type cladding layer is Al _s Ga _1-st In _t P (0 <s <1, 0 <t <1),
The impurity diffusion preventing _{layer, Al u Ga 1-uv In} v P (0 <u <s, 0 <v <1) The semiconductor laser according to claim 2, characterized in that a. The second conductivity type cladding layer is Al _w Ga _1-w As (0 <w <1),
3. The semiconductor laser according to claim 2, wherein the layer on the active layer side of the impurity diffusion preventing layer is Al _x Ga _1-x As (0 <x <w <1). The semiconductor laser according to claim 2, wherein the impurity diffusion preventing layer is a mixed crystal having an Al composition of zero. The second conductivity type cladding layer is Al _s Ga _1-st In _t P (0 <s <1, 0 <t <1),
The semiconductor laser according to claim 5, wherein the impurity diffusion preventing layer is Ga _1-y In _y P (0 <y <1).

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