JP2013120893A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser which has good productivity and high yield and emits high-power light.SOLUTION: In a semiconductor laser, an active layer, and an n-type clad layer and a p-type clad layer which sandwich the active layer are laminated on a semiconductor substrate composed of InP. At least a part of the n-type clad layer includes layers composed of InP, and layers each having a bandgap wavelength in a range from 0.97 μm to a wavelength shorter than a wavelength of an active part composing the active layer by 0.10 μm and composed of InGaAsP, which are alternately laminated one by one in a layer thickness direction. Because an equivalent refraction factor of the n-type clad layer as a whole is higher than a refraction factor of the p-type clad layer, light occurring in the active layer is distributed with being biased to the n-type clad layer side.

Description

  The present invention relates to a semiconductor laser that emits high output light with good manufacturability and yield.

  Since the optical signal used in the optical communication system is transmitted through an optical fiber laid over a long distance, the characteristics of the semiconductor laser, which is a semiconductor light emitting device used as the light source of this optical signal, are high output and high stability. Degree is required.

[First prior art]
FIG. 7 is a perspective view of the semiconductor laser 10 of the first prior art in consideration of high output characteristics, and FIG. 8 is a schematic cross-sectional view of the main part.

  In FIG. 7, a semiconductor laser 10 includes an n-type cladding layer 12 made of n-type InP and a SCH made of InGaAsP (indium gallium arsenic phosphorus) on a semiconductor substrate 11 made of n-type InP (indium phosphorus). (Separate Confinement Heterostructure optical confinement structure) layer 13, active layer 14 made of InGaAsP, and SCH layer 15 made of InGaAsP are sequentially stacked.

  Note that the n-type cladding layer 12, the SCH layer 13, the active layer 14, and the SCH layer 15 are formed in a mesa shape. A lower buried layer 16 made of p-type InP and an upper buried layer 17 made of n-type InP are formed on both sides of the mesa type.

  A p-type cladding layer 18 made of p-type InP is formed on the upper side of the SCH layer 15 and the upper buried layer 17. A p-type contact layer 19 is formed on the upper surface of the p-type cladding layer 18. Furthermore, a p-electrode 20 is provided on the upper surface of the p-type contact layer 19. An n electrode 21 is provided on the lower surface of the semiconductor substrate 11.

The refractive the p-type and the refractive index of the p-type cladding layer 18 made of InP and n _b, n-type composed of InP n-type cladding layer 12 p-type cladding layer 18 strictly the refractive index by electron plasma effect of the rate n _b smaller than, for simplicity of explanation, here is the refractive index of the n-type cladding layer 12 is also a n _b.

  In the first prior art, in order to obtain good oscillation characteristics, the active layer 14 has a plurality of well layers 14a as shown in FIG. 8 in addition to a bulk structure made of one uniform material. In addition, an MQW (Multiple Quantum Well multi-quantum well) structure in which a plurality of barrier layers 14b located on both sides of each well layer 14a are stacked is employed.

  Note that, as in the case of the well layer 14a constituting the quantum well or the bulk active layer not having the MQW structure, a portion that actually gives a gain as a semiconductor laser is called an active portion.

  Further, the SCH layer 13 positioned below the active layer 14 having the MQW structure is formed into a multilayer structure composed of a plurality of layers 13a, 13b, and 13c. Similarly, the SCH layer 15 positioned above the active layer 14 is A multi-layer structure including a plurality of layers 15a, 15b, and 15c is employed.

  The active layer 14 emits light for each of the n-type cladding layer 12, the SCH layer 13 composed of a plurality of layers, the active layer 14 having an MQW structure, the SCH layer 15 composed of a plurality of layers, and the p-type cladding layer 18. The refractive index n for the light to be set is set so as to have the refractive index characteristics shown in FIG.

  That is, the refractive index of the central active layer 14 is set to be the highest, and the refractive indexes of the clad layers 12 and 18 on both sides are set to be the lowest, and the SCH layers 13 and 15 are also changed in stages. Thus, the characteristics are symmetrical with respect to the active layer 14 as the center.

  When a DC voltage is applied between the p-electrode 20 and the n-electrode 21 of the semiconductor laser 10 having such a refractive index characteristic, light P is generated in the active layer 14, and the generated light P is shown in FIG. The semiconductor laser 10 shown is emitted from the end faces 22a and 22b to the outside.

  In addition, when the refractive index of the active layer 14 is higher than the refractive indexes of the cladding layers 12 and 18, an optical waveguide that prevents the dissipation of the light P generated in the active layer 14 is formed. By interposing the SCH layers 13 and 15 having an intermediate refractive index between the layers 12 and 18, respectively, the injected carriers can be concentrated in the vicinity of the active layer 14, and the carriers and light are simultaneously in the same region. Therefore, luminous efficiency is increased.

  In order to increase the output of the semiconductor laser 10 having such a structure, it is effective to reduce the optical confinement coefficient in the SCH layers 13 and 15 and the active layer 14.

  However, when the optical confinement coefficient in the SCH layers 13 and 15 and the active layer 14 is reduced, the light component passing through both the clad layers 12 and 18 increases, and another problem occurs.

  That is, it is necessary to increase the thickness of both cladding layers 12 and 18 in response to an increase in the components of light passing through both cladding layers 12 and 18, but the p-type cladding layer 18 has a relatively high electrical resistance. Therefore, the increase in the thickness of the p-type cladding layer 18 increases the electrical resistance of the entire device, increasing the amount of heat generated by the device in the high current region, and reducing the light output.

  Moreover, when the light distribution in the p-type cladding layer 18 of both the cladding layers 12 and 18 increases, the amount of light loss due to light absorption between the valence bands increases.

  The amount of light loss due to light absorption between the valence bands can be reduced by reducing the p-type impurity concentration of the p-type cladding layer 18, but if the p-type impurity concentration is reduced in this way, the electrical resistance of the device is reduced. Will increase further, making it impossible to obtain a high output.

[Second prior art]
A configuration for solving the problem of optical loss due to absorption between the valence bands is disclosed in Patent Document 1 as a second conventional technique. The cross-sectional structure of the main part is shown in FIG. Here, an optical field control layer 23 having a refractive index considerably higher than that of the n-type cladding layer 12 and close to the refractive index of the active layer 14 is provided inside the n-type cladding layer 12, and the light distribution is changed to the n-type cladding layer. A technique for shifting to the 12 side and reducing the amount of light distributed in the p-type cladding layer 18 is disclosed. It can be seen from the refractive index distribution of the material used for the optical field control layer 23 shown in FIG. 10 that the equivalent refractive index of the optical field control layer 23 is high.

  However, the provision of the optical field control layer 23 having a refractive index close to that of the active layer 14 in the n-type cladding layer 12 not only complicates the structure but also causes new problems.

  That is, since the optical field control layer 23 as described above has the same structure as the active layer 14, when it is provided at a position far from the SCH layer 13, another optical waveguide is formed and the light distribution has a bimodal characteristic. Become.

  Therefore, the optical field control layer 23 must be provided near the SCH layer 13. However, when the optical field control layer 23 having such a high refractive index is provided near the SCH layer 13, the equivalent refractive index of the entire waveguide is obtained. The rate becomes high, and it becomes easy to shift from the single mode to the lateral high-order mode.

  Further, the transition to the lateral higher-order mode can be prevented by narrowing the width of the region including the active layer 14 and the SCH layers 13 and 15, but the active layer 14 and the SCH layers 13 and 15 are thus included. Narrowing the width of the region causes an increase in the electrical resistance and thermal resistance of the element, and decreases the luminous efficiency.

[Third prior art]
A configuration for solving the above problems is disclosed in Patent Document 2 as a third prior art. FIG. 11 shows the overall configuration of a semiconductor laser 30 to which the third prior art is applied, and FIG. 12 shows the cross-sectional structure of the main part. In the configuration of the semiconductor laser 30, the same parts as those of the semiconductor laser 10 shown in FIG.

  In this semiconductor laser 30, an n-type cladding layer 32 made of n-type InGaAsP, an SCH layer 13 made of InGaAsP, an active layer 14 made of InGaAsP, and an SCH layer 15 made of InGaAsP are formed on a semiconductor substrate 11 made of n-type InP. They are stacked in order. The n-type cladding layer 32, the SCH layer 13, the active layer 14, and the SCH layer 15 are formed in a mesa type, and a lower buried layer 16 made of p-type InP and an upper buried layer made of n-type InP are formed on both sides of the mesa type. An embedded layer 17 is formed.

  A p-type cladding layer 18 made of p-type InP is formed on the upper side of the SCH layer 15 and the upper buried layer 17. A p-type contact layer 19 is formed on the upper surface of the p-type cladding layer 18. Furthermore, a p-electrode 20 is provided on the upper surface of the p-type contact layer 19. An n electrode 21 is provided on the lower surface of the semiconductor substrate 11.

  As shown in FIG. 12, the active layer 14 has a four-layer MQW (multiple quantum well) structure in which four well layers 14a and five barrier layers 14b located on both sides of each well layer 14a are stacked. It has been adopted. The SCH layer 13 located below the active layer 14 having the four-layer MQW structure has a multi-layer structure composed of a plurality of layers 13a, 13b, and 13c. Similarly, the SCH layer 15 located above the active layer 14 is formed. Has a multilayer structure composed of a plurality of layers 15a, 15b and 15c.

As shown in FIG. 12, the refractive index of the barrier layer 14b in the active layer 14 _n s, a refractive index _n a of the n-type cladding layer 32, the refractive index of the p-type cladding layer 18 and _{n b.}
Further, the refractive indexes and thicknesses of the layers 13a, 13b, and 13c constituting the SCH layer 13 are n ₁ , n ₂ , n ₃ , t ₁ , t ₂ , and t ₃ , respectively, and the SCH layer 15 is similarly configured. The refractive indexes and thicknesses of the respective layers 15a, 15b, and 15c are set to n ₁ , n ₂ , n ₃ , t ₁ , t ₂ , and t ₃ , respectively.

Then, the magnitude of each refractive index, as shown in FIG. 13, is set to be smaller enough away from the active layer 14, and a refractive index _{n a} of the n-type cladding layer 32 made of InGaAsP is made of InP higher than the refractive index _{n b} of the p-type cladding layer 18. That is, n _s > n ₁ > n ₂ > n ₃ > n _a > n _b . Furthermore, in this semiconductor laser 30, as shown in FIG. 13, the refractive index difference between adjacent layers constituting the SCH layers 13 and 15 becomes smaller from the active layer 14 toward the cladding layers 32 and 18. Is set to _{That, n s -n 1> n 1} -n 2> n 2 -n 3> n 3 -n b> n 3 are set such that -n _a. Further, the thicknesses t ₁ , t ₂ and t ₃ of the layers 13a, 13b, 13c, 15a, 15b and 15c constituting the SCH layers 13 and 15 may be the same or different.

  In the semiconductor laser 30 configured as described above, when a DC voltage is applied between the p electrode 20 and the n electrode 21, light P is generated in the active layer 14, and the light P is generated in the semiconductor laser 30 shown in FIG. The light is emitted from the end faces 22a and 22b to the outside.

  In this case, as shown in the refractive index characteristics of FIG. 13, the refractive index difference between adjacent layers constituting the SCH layers 13 and 15 becomes smaller toward the cladding layers 32 and 18 from the active layer 14. Therefore, in the region where the refractive index is high in the region near the active layer 14 in the SCH layers 13 and 15, the refractive index sharply decreases, and in the region where the refractive index is low in the region near both clad layers, The refractive index decreases slowly.

  For this reason, the concentration of light within the optical waveguide can be relaxed, that is, the optical confinement factor can be lowered, and the internal loss is reduced.

The refractive index _{n a} of the n-type cladding layer 32 made of InGaAsP is higher than the refractive index _{n b} of the p-type cladding layer 18 made of InP, as shown in Figure 14, the light distribution, both cladding In contrast to the symmetrical characteristic A ′ in the case of the first prior art in which the layers have the same refractive index, the distribution is biased toward the n-type cladding layer 32 as in the characteristic A.

  For this reason, it is possible to suppress an increase in optical loss due to light absorption between the valence bands in the p-type cladding layer 18 due to the reduction of the optical confinement coefficient in the active layer 14 and the SCH layers 13 and 15, and high-power laser light Can be obtained.

  Further, since the refractive index difference between the active layer 14 and the n-type cladding layer 32 is smaller than that of the conventional one, the maximum active layer width capable of suppressing the lateral higher-order mode can be increased, and the laser output can be increased. Further advantageous.

  Further, as described above, the structure is simpler than that in which the optical field layer having a high refractive index is provided in the n-type cladding layer, and the width of the active layer 13 can be increased. Can also be prevented.

  However, in the third prior art, when the refractive index of the n-type cladding layer 32 is considerably larger than the refractive index of the p-type cladding layer 18 made of p-InP, n is the same as in the second prior art shown in FIG. The mold clad layer 32 becomes an optical waveguide, and bimodal light is emitted.

  In other words, in the third prior art, the refractive index of the n-type cladding layer 32 needs to be made slightly higher than the refractive index of the p-type cladding layer 18 made of p-InP. As a specific configuration described in Patent Document 2, the band gap wavelength of InGaAsP constituting the n-type cladding layer 32 is set to 0.97 μm or less, and the thickness of the n-type cladding layer 32 is as thick as several microns. It has come to grow.

  However, it is quite difficult to crystallize InGaAsP having a composition close to InP (that is, a band gap wavelength) on the semiconductor substrate made of InP uniformly by several microns from the viewpoint of crystal defects and requires advanced techniques. In the normal manufacturing method, the white turbidity of the crystal surface is generated with high probability, or the quality of the active layer 14 is deteriorated. For this reason, not only a lot of know-how is required for production, but also there is a risk that the yield is significantly deteriorated from the viewpoint of the quality of the active layer.

JP 2000-174394 A Japanese Patent No. 3525257

  As described above, the prior art has a problem that high-power light cannot be obtained, or even if high-power light can be emitted, crystal growth is very difficult.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a semiconductor laser capable of emitting high-power light with a configuration that facilitates crystal growth.

  In order to solve the above problems, a semiconductor laser according to claim 1 of the present invention is provided with an active layer, an n-type cladding layer and a p-type cladding layer sandwiching the active layer on a semiconductor substrate made of InP. In the semiconductor laser, the n-type cladding layer includes at least a part made of InP, and an InGaAsP having a band gap wavelength from 0.97 μm to a wavelength shorter by 0.10 μm than the wavelength of the active portion constituting the active layer. And a layer having a thickness equivalent to that of the n-type cladding layer, and an equivalent refractive index of the n-type cladding layer as a whole is higher than that of the p-type cladding layer. Yes.

  The semiconductor laser according to claim 2 of the present invention is the semiconductor laser according to claim 1, wherein the band gap wavelength of InGaAsP constituting the n-type cladding layer is 1.1 to 1.35 μm. It is said.

  According to a third aspect of the present invention, there is provided the semiconductor laser according to the third aspect, wherein an active layer, an n-type cladding layer sandwiching the active layer, and a p-type cladding layer are provided on a semiconductor substrate made of InP. The layer includes at least a layer made of InP and a layer made of InAlAs or InGaAlAs from a band gap wavelength of 0.97 μm to a wavelength shorter by 0.10 μm than the wavelength of the active part constituting the active layer. The n-type cladding layer is configured so that the equivalent refractive index of the n-type cladding layer as a whole is higher than the refractive index of the p-type cladding layer.

  The semiconductor laser according to claim 4 of the present invention is the semiconductor laser according to claim 3, wherein the band gap wavelength of InAlAs or InGaAlAs constituting the n-type cladding layer is 1.1 to 1.35 μm. It is characterized by.

  The semiconductor laser according to claim 5 of the present invention is the semiconductor laser according to claim 1 or 2, wherein the thickness of the InP layer constituting the n-type cladding layer is equal to that of the InGaAsP layer constituting the n-type cladding layer. It is characterized by being thicker than the thickness.

  A semiconductor laser according to a sixth aspect of the present invention is the semiconductor laser according to any one of the first to fifth aspects, wherein an SCH layer is formed above and below the active layer, and the entire n-type cladding layer is formed. The equivalent refractive index of the SCH layer is smaller than the refractive index of the SCH layer in contact with the n-type cladding layer.

  According to the present invention, as a clad layer located on the side close to the semiconductor substrate, a material having good manufacturability and a refractive index higher than that of other clad layers above the active layer, and the same material as the semiconductor substrate are used. By combining the semiconductor material with good manufacturability in this way, the equivalent refractive index of the entire cladding layer on the side close to the semiconductor substrate is made higher than the refractive index of the other cladding layers above the active layer. Since the structure is made slightly higher, a cladding layer having a thickness of several microns can be easily grown on the semiconductor substrate side. Further, it is possible to realize a semiconductor laser that emits high-output light without causing unnecessary crystal distortion due to crystal growth in the active layer.

Sectional view of the main part of the semiconductor laser of the present invention The figure which shows the refractive index distribution of the principal part of the semiconductor laser of this invention The elements on larger scale of the figure which shows the refractive index distribution of the principal part of the semiconductor laser of this invention The figure which shows the characteristic of the semiconductor laser of this invention The figure which shows distribution of the light radiate | emitted from the semiconductor laser of this invention The figure which shows the light output of the semiconductor laser of this invention, and the semiconductor laser of a prior art 1 is a perspective view of a first prior art semiconductor laser. Sectional view of the principal part of the first conventional semiconductor laser The figure which shows the refractive index distribution of the principal part of the semiconductor laser of 1st prior art. The figure which shows the refractive index distribution of the principal part of the semiconductor laser of the 2nd prior art. 3 is a perspective view of a third conventional semiconductor laser. Sectional view of the principal part of a third conventional semiconductor laser The figure which shows the refractive index distribution of the principal part of the semiconductor laser of the 3rd prior art The figure which shows distribution of the light radiate | emitted from the semiconductor laser of the 1st and 3rd prior art

  Hereinafter, embodiments of the present invention will be described. However, since the same numbers as those of the conventional embodiments shown in FIGS. 7 to 14 correspond to the same function units, the description of the function units having the same numbers is omitted here. To do.

[Embodiment]
FIG. 1 shows a cross-sectional view of the main part of the embodiment of the present invention. The structure other than the n-type cladding layer 40 is the same as that of the third prior art shown in FIGS. A portion that is configured with an MQW structure and that actually produces a gain as a semiconductor laser including the well layer 14a forms an active portion of the active layer. An important point in the present invention is the structure of the n-type cladding 40, which will be discussed below.

  The n-type cladding 40 is configured by alternately laminating InGaAsP layers 35 having a predetermined thickness and InP layers 36 having a predetermined thickness in the layer thickness direction.

For the InGaAsP layer 35, n-type InGaAsP having a band gap wavelength of 0.97 μm or more, for example, 1.1 μm or 1.15 μm, which allows easy crystal growth on InP, is used. The InP layer 36 uses InP made of the same material as that of the n-type semiconductor substrate 11 (not shown). It has been confirmed that the n-type InGaAsP layer 35 has a band gap wavelength in the range of 1.1 to 1.3 μm, which is particularly suitable for realizing the effects of the present invention. FIG. 2 shows a refractive index distribution in this configuration. Here, an enlarged view of the refractive index distribution of the n-type cladding layer 40 is shown in FIG. Here, _{n c} is the refractive index of the n-type InGaAsP layer 35. W _ci (i = 1, 2,..., N) is the thickness of the n-type InGaAsP layer 35, and H _ci (i = 1, 2,..., N−1) is the n-type InP layer 36. Thickness. The thicknesses W _ci (i = 1, 2,..., n) of the n-type InGaAsP layer 35 may be the same or different. Similarly, the thicknesses H _ci (i = 1, 2,..., N−1) of the n-type InP layer 36 may be the same or different from each other.

In order to explain the principle of the present invention, it is assumed in FIG. 4 that W _ci (i = 1, 2,..., N) are all the same, and H _ci (i = 1, 2,. , N-1) are the same, and the equivalent refractive index of the n-type cladding layer 40 as a whole is shown when W _c1 / H _c1 is a variable. In the figure, the refractive index of the n-type InGaAsP clad layer 32 when the band gap wavelength is 0.96 μm in FIG. 12 is indicated by a dotted line. In the present invention, the band gap wavelength of the n-type InGaAsP layer 35 is set to 1.15 μm (value is an example).

As can be seen from FIG. 4, by appropriately setting the ratio of W _c1 / H _c1, an n-type InGaAsP having a bandgap wavelength as short as 0.96 μm or 0.95 μm and a refractive index slightly higher than InP. It can be seen that the n-type cladding layer 40 having a refractive index equivalent to that of the cladding layer can be formed. In other words, an n-type InGaAsP layer 35 having a high refractive index and an n-type InP layer 36 having a low refractive index are alternately combined in the layer thickness direction, so that the n-type InGaAsP used in the third prior art is used. It can be said that a refractive index equivalent to that of the cladding layer was easily realized.

  The n-type InGaAsP layer 35 having a band gap wavelength of 1.15 μm is easier to grow on InP than the n-type InGaAsP layer 32 having a band gap wavelength of 0.96 μm used in the third prior art. In the configuration, since this layer thickness is as thin as 10 nm to 500 nm, there is no problem with respect to the crystal growth. Further, by using the n-type InP layer 36 having the same composition as that of the n-type semiconductor substrate 11 and having an effect of removing crystal distortion generated at the time of crystal growth, together with the n-type InGaAsP layer 35. The n-type cladding layer 40 having a refractive index equivalent to that of the n-type InGaAsP layer having a band gap wavelength of 0.96 μm can be easily grown to a thickness of several microns with a high yield.

In general, as an equivalent refractive index of the entire n-type cladding layer 40 in which the n-type InGaAsP layer 35 and the n-type InP layer 36 are combined, the band gap wavelength used in the third prior art is 0.97 μm or less. Since it is preferable that the value be equal to that of n-type InGaAsP, H _ci (i = 1, 2,..., N−1)> W _ci (i = 1, 2,..., N) It is preferable to do this. However, H _ci (i = 1, 2,..., N−1) <W _ci (i = 1, 2,..., N) or H _ci (i = 1, 2,..., N Needless to say, even if it is configured as −1) = W _ci (i = 1, 2,..., N), it belongs to the present invention.

  FIG. 5 shows the light distribution characteristic G in the present embodiment. Similarly to FIG. 14 shown in the third prior art, the light distribution is like a characteristic G with respect to the symmetrical characteristic A ′ in the case of the first prior art in which both cladding layers have the same refractive index. Distribution is biased toward the n-type cladding layer 40 side. For this reason, it is possible to suppress an increase in optical loss due to light absorption between the valence bands in the p-type cladding layer 18 due to the reduction of the optical confinement coefficient in the active layer 14 and the SCH layers 13 and 15, and high-power laser light Can be obtained.

  FIG. 6 shows the light output when the variable is the injection current. As can be seen from the figure, the light output F of the third prior art is improved over the light output F ′ of the first prior art, but the light output G is further improved in the present invention. This is because the crystal strain generated when the n-type cladding layer is formed by several microns is formed between an n-type InGaAsP layer having a band gap wavelength of 1.15 μm and an n-type InP layer having the same composition as that of the semiconductor substrate 11. Since the combination is suppressed to be smaller than the n-type InGaAsP layer having a band gap wavelength of 0.96 μm or 0.95 μm used in the third prior art, the quality of the crystal quality of the active layer 14 to be formed thereafter Means it is better.

  By adopting this configuration, crystal turbidity did not occur during crystal growth, and an extremely excellent yield could be realized. In particular, the longer the band gap wavelength of the n-type InGaAsP layer 35 is, the more suitable it is 0.97 μm, and InGaAsP having a band gap wavelength of 1.1 to 1.35 μm is particularly suitable from the viewpoint of crystal growth controllability and yield. .

  For example, when the band gap wavelength of the active layer 14 (the band gap wavelength of the active portion) is 1.55 μm, the light absorption loss increases unless the band gap wavelength of the n-type InGaAsP layer 35 is shorter than 1.45 μm. It was experimentally confirmed that the threshold value was increased. If there is no difference of 0.10 μm or more between the band gap wavelength of the active layer and the band gap wavelength of the n-type cladding, the light absorption loss increases. For example, the band gap wavelength of the active layer is other than 1.55 μm. It has been experimentally confirmed that it can be established at various other wavelengths such as 1.48 μm, 1.3 μm, and 1.6 μm.

In the above description, the SCH layers 13 and 15 are sandwiched above and below the active layer 14, but the SCH layers 13 and 15 are not essential in the present invention. The relationship between the refractive index n _b of the n-type cladding layer 40 of refractive index n _c> p-type cladding layer 18 need only be satisfied.

  Further, the n-type InGaAsP layer 35 and the n-type InP layer 36 may not be alternately stacked over the entire thickness of the n-type cladding layer 40. What is necessary is just to laminate | stack alternately by the predetermined thickness used as the distribution biased to the n-type clad layer side as shown to the characteristic G of FIG.

[Various embodiments]
In the above description, the n-type cladding layer 40 in the present invention is configured by a combination of an n-type InGaAsP layer and an n-type InP layer, but is configured by a combination of an n-type InAlAs layer (or InGaAlAs layer) and an n-type InP layer. May be. Further, although the case where the semiconductor substrate is n-type has been described, it is also applicable to a p-type semiconductor substrate. In this case, the n-type and the p-type are interchanged in the above description. Furthermore, the present invention can be applied not only to an InP substrate but also to a GaAs substrate.

DESCRIPTION OF SYMBOLS 10, 30 ... Semiconductor laser 11 ... Semiconductor substrate 12, 32, 40 ... n-type clad layer 13, 15 ... SCH layer 14 ... Active layer 16, 17 ... Embedded layer 18 ... p-type clad layer 19 ... p-type contact layer 20 ... p-electrode 35 ... n-type InGaAsP layer 36 ... n-type InP layer 21 ... n-electrode 22a, 22b ... end face

Claims (6)

In a semiconductor laser in which an active layer, an n-type cladding layer and a p-type cladding layer sandwiching the active layer are provided on a semiconductor substrate made of InP,
The n-type cladding layer includes at least a layer made of InP and a layer made of InGaAsP having a band gap wavelength of 0.97 μm to a wavelength shorter by 0.10 μm than the wavelength of the active portion constituting the active layer. Are stacked alternately in the layer thickness direction, and the n-type cladding layer as a whole has an equivalent refractive index higher than the refractive index of the p-type cladding layer.   2. The semiconductor laser according to claim 1, wherein a band gap wavelength of InGaAsP constituting the n-type cladding layer is 1.1 to 1.35 [mu] m. In a semiconductor laser in which an active layer, an n-type cladding layer and a p-type cladding layer sandwiching the active layer are provided on a semiconductor substrate made of InP,
The n-type cladding layer is at least partially composed of InP, and is composed of InAlAs or InGaAlAs having a band gap wavelength of 0.97 μm to a wavelength shorter by 0.10 μm than the wavelength of the active portion constituting the active layer. The semiconductor is characterized in that the layers are alternately stacked in the layer thickness direction, and the equivalent refractive index of the n-type cladding layer as a whole is higher than the refractive index of the p-type cladding layer. laser.   4. The semiconductor laser according to claim 3, wherein the band gap wavelength of InAlAs or InGaAlAs constituting the n-type cladding layer is 1.1 to 1.35 [mu] m.   3. The semiconductor laser according to claim 1, wherein a thickness of the InP layer constituting the n-type cladding layer is larger than a thickness of the InGaAsP layer constituting the n-type cladding layer. SCH layers are formed above and below the active layer, and an equivalent refractive index of the entire n-type cladding layer is smaller than a refractive index of the SCH layer in contact with the n-type cladding layer. The semiconductor laser according to claim 1.

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