CN120129999A - Semiconductor laser element - Google Patents

Abstract

Translated fromChinese

本发明提供一种能够使振荡波长的纵模单一化或接近单一的半导体激光元件。半导体激光元件具备氮化物半导体层叠体，该氮化物半导体层叠体具有第一端面、第二端面和光导波路，氮化物半导体层叠体具有第一n侧氮化物半导体层、第二n侧氮化物半导体层、有源层和p侧氮化物半导体层，第一n侧氮化物半导体层具有：衍射光栅部，其设有折射率沿着光导波路的谐振方向周期性地变化的周期结构；以及非衍射光栅部，其位于衍射光栅部与第一端面之间，且未设置周期结构，有源层具有n侧阱层和n侧势垒层，第二n侧氮化物半导体层是具有In和Ga的氮化物半导体层，第二n侧氮化物半导体层的厚度比n侧势垒层的厚度大。

The present invention provides a semiconductor laser element capable of making the longitudinal mode of the oscillation wavelength uniform or close to uniform. The semiconductor laser element comprises a nitride semiconductor stack having a first end face, a second end face and an optical waveguide, the nitride semiconductor stack having a first n-side nitride semiconductor layer, a second n-side nitride semiconductor layer, an active layer and a p-side nitride semiconductor layer, the first n-side nitride semiconductor layer having: a diffraction grating portion having a periodic structure in which the refractive index changes periodically along the resonance direction of the optical waveguide; and a non-diffraction grating portion located between the diffraction grating portion and the first end face and not having a periodic structure, the active layer having an n-side well layer and an n-side barrier layer, the second n-side nitride semiconductor layer being a nitride semiconductor layer having In and Ga, and the thickness of the second n-side nitride semiconductor layer being greater than the thickness of the n-side barrier layer.

Description

Semiconductor laser device

Technical Field

The present invention relates to a semiconductor laser device.

Background

A semiconductor laser element partially provided with a diffraction grating is known. For example, patent document 1 describes an EA (Electro-Absorption) modulator integrated DFB laser device having an oscillator section provided with a diffraction grating layer and a modulator section not provided with a diffraction grating layer. The semiconductor laser device described in patent document 1 has an InGaAsP active layer.

Prior art literature

Patent literature

Patent document 1 (Japanese patent application) JP 2011-151088A

Disclosure of Invention

Technical problem to be solved by the invention

The present disclosure aims to provide a semiconductor laser element having a nitride semiconductor layer, which can unify or nearly unify the longitudinal modes of oscillation wavelengths.

Technical scheme for solving technical problems

The present invention includes the following means.

A semiconductor laser device includes a nitride semiconductor laminate having a first end face, a second end face, and an optical waveguide connecting the first end face and the second end face, wherein the nitride semiconductor laminate has a first n-side nitride semiconductor layer, a second n-side nitride semiconductor layer disposed above the first n-side nitride semiconductor layer, an active layer having one or more well layers and one or more barrier layers disposed above the second n-side nitride semiconductor layer, and a p-side nitride semiconductor layer disposed above the active layer, wherein the first n-side nitride semiconductor layer has a periodic structure In which a refractive index periodically changes along a resonance direction of the optical waveguide, wherein the second n-side nitride semiconductor layer is disposed between the first n-side nitride semiconductor layer and the second n-side nitride semiconductor layer, wherein the active layer has a barrier layer disposed above the second n-side nitride semiconductor layer, wherein the second n-side nitride semiconductor layer has a barrier layer having a thickness larger than that of the first n-side nitride semiconductor layer, and the second n-side nitride semiconductor layer has a barrier layer disposed above the second n-side nitride semiconductor layer.

Effects of the invention

According to the semiconductor laser device described above, the longitudinal mode of the oscillation wavelength can be made single or nearly single.

Drawings

Fig. 1 is a schematic plan view showing a semiconductor laser device according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view of line II-II of fig. 1.

Fig. 3 is a cross-sectional view taken along line III-III of fig. 1.

Fig. 4 is a schematic diagram for explaining the first n-side nitride semiconductor layer.

Fig. 5 is a schematic diagram for explaining the first contact layer and the second contact layer.

Fig. 6 is a graph showing the frequency spectrum of the semiconductor laser device of example 1.

Fig. 7 is a Z-contrast image of a part of the semiconductor laser device of example 1.

Fig. 8 is a graph showing the frequency spectrum of the semiconductor laser device of example 2.

Detailed Description

An embodiment of the present invention will be described below with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals.

Fig. 1 is a schematic plan view showing a semiconductor laser device according to the present embodiment. Fig. 2 is a cross-sectional view of line II-II of fig. 1. Fig. 3 is a cross-sectional view taken along line III-III of fig. 1. Fig. 4 is a schematic diagram for explaining the first n-side nitride semiconductor layer. As shown in fig. 1 to 4, the semiconductor laser device 100 of the present embodiment includes a nitride semiconductor laminate 20. The nitride semiconductor stack 20 has a first end face 20a, a second end face 20b, and an optical waveguide 10 connecting the first end face 20a and the second end face 20 b. The nitride semiconductor stack 20 includes a first n-side nitride semiconductor layer 31, a second n-side nitride semiconductor layer 32 disposed above the first n-side nitride semiconductor layer 31, an active layer 40 including one or more well layers 41 and one or more barrier layers 42 disposed above the second n-side nitride semiconductor layer 32, and a p-side nitride semiconductor layer 50 disposed above the active layer 40. In this embodiment, a direction from the n-side nitride semiconductor layer 30 toward the p-side nitride semiconductor layer 50 will be described as an upward direction. The upper side may not necessarily coincide with the upper side of the light emitting device or the like to which the semiconductor laser element 100 is fixed.

(Substrate 60)

The substrate 60 is, for example, a semiconductor substrate. The substrate 60 is, for example, a nitride semiconductor substrate such as a GaN substrate. For example, a nitride semiconductor substrate can be used as the substrate 60, and the upper surface thereof can be the +c plane (i.e., the (0001) plane). In the present embodiment, the c-plane is not limited to a plane strictly matching the (0001) plane, and includes a plane having an off angle in the range of ±0.03 to 1 degree. The semiconductor laser element 100 may not have the substrate 60. As the upper surface of the substrate, a nonpolar surface (M-surface, a-surface) and a semipolar surface having a deviation angle within a range of ±0.03 to 25 degrees from the nonpolar surface may be used.

(Nitride semiconductor laminate 20)

The nitride semiconductor stack 20 has a plurality of nitride semiconductor layers. The nitride semiconductor constituting the nitride semiconductor stack 20 is, for example, a group III nitride semiconductor. Examples of the group III nitride semiconductor include GaN, inGaN, alGaN, inN, alN and InAlGaN. The nitride semiconductor stack 20 has an n-side nitride semiconductor layer 30, an active layer 40, and a p-side nitride semiconductor layer 50. The active layer 40 is disposed between the n-side nitride semiconductor layer 30 and the p-side nitride semiconductor layer 50. The n-side nitride semiconductor layer 30, the active layer 40, and the p-side nitride semiconductor layer 50 may be in direct contact with each other, or other semiconductor layers may be disposed therebetween. The nitride semiconductor stack 20 has, in order, a first n-side nitride semiconductor layer 31, a second n-side nitride semiconductor layer 32, an active layer 40, and a p-side nitride semiconductor layer 50. The nitride semiconductor stack 20 is epitaxially grown on the substrate 60, for example. The main surface of the nitride semiconductor stack 20 is, for example, a +c plane (i.e., a (0001) plane).

In fig. 1 to 3, the resonance direction is defined as a resonance direction D1, and a direction perpendicular to the resonance direction is defined as a perpendicular direction D2. When the length of the optical waveguide 10 in the vertical direction D2 is set to the width of the optical waveguide 10, the width of the optical waveguide 10 is, for example, 1 μm or more. The width of the optical waveguide 10 is preferably 10 μm or more. This can improve the light output of the semiconductor laser device 100. The width of the optical waveguide 10 is more preferably 50 μm or more, and may be 80 μm or more. The width of the optical waveguide 10 can be set to 400 μm or less, for example. As shown in fig. 1 to 3, in the case where the nitride semiconductor stack 20 has the ridge 20c, the width of the ridge 20c can be regarded as the width of the optical waveguide 10. Alternatively, in the case of having a current narrow structure other than the ridge 20c, the width of the current narrow structure in the vertical direction D2 may be regarded as the width of the optical waveguide 10.

The nitride semiconductor stack 20 has a first end face 20a and a second end face 20b. The first end face 20a and the second end face 20b are faces that are not parallel to the main face of the active layer 40. The first end face 20a and the second end face 20b are faces perpendicular to the main face of the active layer 40, for example. The first end face 20a and the second end face 20b are faces intersecting the resonance direction D1 of the optical waveguide 10, and are faces perpendicular to the resonance direction D1, for example. The first end face 20a is one of a light emitting end face and a light reflecting end face, and the second end face 20b is the other of the light emitting end face and the light reflecting end face.

(N-side nitride semiconductor layer 30)

The n-side nitride semiconductor layer 30 has one or more nitride semiconductor layers containing n-type impurities. Examples of the n-type impurity include Si and Ge. The n-side nitride semiconductor layer 30 may also have an undoped layer that is not intentionally doped with impurities. The n-side nitride semiconductor layer 30 includes a first n-side nitride semiconductor layer 31 and a second n-side nitride semiconductor layer 32. The n-side nitride semiconductor layer 30 may have other layers. The semiconductor laser device 100 shown in fig. 1 to 3 has a third n-side nitride semiconductor layer 33, a fourth n-side nitride semiconductor layer 34, and a fifth n-side nitride semiconductor layer 35. The n-side nitride semiconductor layer 30 may not have all of these layers. The n-side nitride semiconductor layer 30 may have a layer other than these layers.

(First n-side nitride semiconductor layer 31)

The first n-side nitride semiconductor layer 31 has a diffraction grating portion 311 provided with a periodic structure in which the refractive index periodically changes along the resonance direction D1, and a non-diffraction grating portion 312 located between the diffraction grating portion 311 and the first end surface 20a and not provided with a periodic structure.

The semiconductor laser device 100 includes the first n-side nitride semiconductor layer 31 having the diffraction grating portion 311, and can unify or nearly unify the longitudinal mode of the oscillation wavelength. If slight natural emission is considered, there is no state of a single longitudinal mode in a strict sense. Therefore, the case where the output of one mode is sufficiently stronger than the output of the other modes is set to a single vertical mode or a nearly single vertical mode. The semiconductor laser element 100 includes not only the diffraction grating portion 311 but also a non-diffraction grating portion 312. Damage, defects, impurities, and the like generated when forming a diffraction grating by etching increase absorption loss. By providing the semiconductor laser element 100 with the non-diffraction grating portion 312, the non-diffraction grating portion 312 does not cause an increase in absorption loss due to the diffraction grating and/or a decrease in optical confinement to the active layer 40. Therefore, the light emission efficiency of the semiconductor laser device 100 can be improved as compared with a semiconductor laser device having a periodic structure provided from the first end surface 20a to the second end surface 20 b.

The diffraction grating portion 311 and the non-diffraction grating portion 312 are arranged so as to be aligned along the resonance direction D1. The diffraction grating portion 311 has a periodic structure immediately below the optical waveguide 10. The refractive index of the periodic structure periodically changes along a direction connecting the first end face 20a and the second end face 20b in the shortest manner. The non-diffraction grating portion 312 is not provided with a periodic structure at least immediately below the optical waveguide 10. The non-diffraction grating portion 312 may be a region where no periodic structure is provided at any position thereof. The non-diffraction grating portion 312 can function as a gain region having no diffraction grating. Therefore, the length of the diffraction grating portion 311 along the resonance direction D1 is preferably smaller than the length of the non-diffraction grating portion 312 along the resonance direction D1. In other words, the length of the non-diffraction grating portion 312 along the resonance direction D1 is preferably longer than the length of the diffraction grating portion 311 along the resonance direction D1. This can improve the light output of the semiconductor laser device 100.

The length of the non-diffraction grating portion 312 in the resonance direction D1 may be, for example, 100 μm or more. The larger the distance from the periodic structure provided in the diffraction grating portion 311 to the active layer 40, the lower the coupling efficiency of the light from the active layer 40 and the periodic structure, and the lower the reflectance at the wavelength corresponding to the periodic structure. By setting the length of the diffraction grating portion 311 in the resonance direction D1 to 100 μm or more, the reflectance corresponding to the periodic structure can be set to a value higher than the degree to which the semiconductor laser element 100 can oscillate. If the diffraction grating portion 311 is made too long, the absorption loss due to regrowth damage increases, and the reflectance due to the resonator structure excessively increases, so that it is difficult to obtain the light output, but by increasing the length of the non-diffraction grating portion 312, the actual gain of the semiconductor laser element 100 increases, and therefore, the decrease in the light output can be suppressed. Therefore, the length of the non-diffraction grating portion 312 in the resonance direction D1 is preferably 500 μm or more. The length of the non-diffraction grating portion 312 in the resonance direction D1 may be 1500 μm or more. The length of the non-diffraction grating portion 312 in the resonance direction D1 can be 4000 μm or less.

In nitride semiconductors, the activation rate of n-type impurities (e.g., si) tends to be higher than that of p-type impurities (e.g., mg). Therefore, the n-type impurity concentration of the n-side nitride semiconductor layer 30 can be made lower than the p-type impurity concentration of the p-side nitride semiconductor layer 50. The periodic structure is formed, for example, by forming a concave-convex structure in one semiconductor layer and then filling the concave-convex structure with another semiconductor layer, but the lower the impurity concentration is, the more easily and densely filled. Therefore, the diffraction grating portion 311 provided with the periodic structure is suitably arranged as a part of the n-side nitride semiconductor layer 30. The periodic structure of the diffraction grating portion 311 of the first n-side nitride semiconductor layer 31 has, for example, an average refractive index higher than that of the fifth n-side nitride semiconductor layer 35. Alternatively, the first n-side nitride semiconductor layer 31 may also serve as an n-side cladding layer.

When the periodic structure is arranged close to the active layer 40, an increase in absorption loss due to a relatively high electric field strength of the p-side nitride semiconductor layer 50 and/or a decrease in optical confinement to the active layer 40 may occur. Thereby, the threshold current at which the semiconductor laser device 100 performs laser oscillation can be raised. Therefore, the first n-side nitride semiconductor layer 31 is provided at a position distant from the active layer 40. For example, as shown in fig. 2, the second n-side nitride semiconductor layer 32 is disposed between the first n-side nitride semiconductor layer 31 and the active layer 40. As a result, the electric field intensity of the p-side nitride semiconductor layer 50 becomes relatively low, and absorption loss can be reduced and/or optical confinement to the active layer 40 can be improved. This can reduce the threshold current of the semiconductor laser device 100. By reducing the threshold current, the current density at the time of laser oscillation can be reduced, and the probability of occurrence of a high mode in the longitudinal mode can be reduced. Further, by making the electric field strength of the p-side nitride semiconductor layer 50 relatively low, absorption loss due to p-type impurities can be suppressed, and the slope efficiency of the semiconductor laser element 100 can be improved.

In the present embodiment, the periodic structure provided in the diffraction grating portion 311 is a diffraction grating. The size of the periodic structure can be appropriately adjusted according to the wavelength of the laser light to be obtained, the composition of the semiconductor to be used, and the like. The cross-sectional shape of the concave-convex portions constituting the periodic structure along the resonance direction D1 of the optical waveguide 10 can be, for example, a saw-tooth shape, a sine wave shape, a rectangular shape, a trapezoid shape, an inverted trapezoid shape, or the like. The cross-sectional shape of the convex portion in the concave-convex portion constituting the periodic structure is rectangular in fig. 2, but the shape is not limited thereto, and may be a trapezoid shape having inclined sides whose width becomes narrower as approaching the active layer 40. By forming the semiconductor layer to have a shape with inclined sides, the semiconductor layer having embedded irregularities can be easily grown, and the thickness of the semiconductor layer can be reduced. Each of the convex portions of the concave-convex can have an upper surface. The upper surface is, for example, a surface parallel to the main surface of the active layer 40. Each concave portion of the concave-convex shown in fig. 2 has a bottom surface. The bottom surface is, for example, a surface parallel to the main surface of the active layer 40. Each concave portion of the concave-convex may have a shape not having a bottom surface such as a U-shape or a V-shape.

The period (pitch) of the irregularities constituting the periodic structure can be determined according to the wavelength of the desired oscillation and the effective refractive index. The pitch of the irregularities (one period of the irregularities) is, for example, 40nm to 140 nm. The width of the convex portion and the width of the concave portion in the direction along the resonance direction D1 of the optical waveguide 10 may be the same or different. In the case of providing a high-mode diffraction structure, the diffraction can be set to 120nm to 420nm in the third diffraction and 400nm to 2000nm in the tenth diffraction. Preferably, one of the width of the convex portion and the width of the concave portion is in the range of 1/2 to 2 times the width of the other.

The height H of the irregularities constituting the periodic structure may be 300nm or less or 200nm or less. By increasing the height of the irregularities Γ_grating, the coupling coefficient k can be increased. Therefore, the height H of the irregularities is preferably 50nm or more. The height of the irregularities constituting the periodic structure is, for example, the shortest distance between a line parallel to the principal surface of the active layer 40 and passing through the portion closest to the active layer 40 among the irregularities and a line parallel to the principal surface of the active layer 40 and passing through the portion farthest from the active layer 40 among the irregularities in a section perpendicular to the principal surface of the active layer 40 and parallel to the resonance direction D1 of the optical waveguide 10. Such a section can be observed by, for example, a transmission electron microscope (Transmission Electron Microscope: TEM). The cross section can also be observed by scanning transmission electron microscopy (Scanning Transmission Electron Microscope: STEM).

The diffraction grating portion 311 has a plurality of first portions and a plurality of second portions having a refractive index higher than that of the first portions. The periodic structure is configured by alternately disposing the plurality of first portions and the plurality of second portions along the resonance direction D1.

In the diffraction grating portion 311 shown in fig. 4, a plurality of first portions are connected to one common portion, and one first semiconductor portion 31a is constituted by the plurality of first portions and the one common portion. Similarly, the plurality of second portions are connected to one common portion, and one second semiconductor portion 31b is constituted by the plurality of second portions and one common portion. In other words, the first semiconductor portion 31a has a plurality of first portions protruding upward from one common portion, and the second semiconductor portion 31b has a plurality of second portions protruding downward from one common portion, and the first portions and the second portions are alternately arranged along the resonance direction D1. A part of the first semiconductor portion 31a and the second semiconductor portion 31b constitutes a diffraction grating portion 311, and the other part constitutes a non-diffraction grating portion 312. The first n-side nitride semiconductor layer 31 may be composed of only the first semiconductor portion 31a and the second semiconductor portion 31b.

The composition of the common portion of the first semiconductor portion 31a is the same as that of the first portion. The composition of the common portion of the second semiconductor portion 31b is the same as that of the second portion. The same composition means that the composition is not intentionally formed to be different, and may include manufacturing errors. Here, the case where the first semiconductor portion 31a includes a plurality of first portions and the second semiconductor portion 31b includes a plurality of second portions has been described, but the first semiconductor portion 31a may include a plurality of second portions and the second semiconductor portion 31b may include a plurality of first portions.

The first semiconductor portion 31a can be obtained by, for example, forming a first semiconductor layer serving as the first semiconductor portion 31a, and then removing a part of the first semiconductor layer by dry etching or the like. If the first semiconductor portion is removed to the lower surface of the first semiconductor layer when a part thereof is removed, a first semiconductor portion which is composed of only a plurality of first portions without a common portion can be formed. If the removal is performed at a depth that does not reach the lower surface of the first semiconductor layer in consideration of the accuracy of the removal depth, the first semiconductor portion 31a composed of one common portion and a plurality of first portions can be formed.

The second semiconductor portion 31b can be obtained by forming the second semiconductor portion 31b on the first semiconductor portion 31a, for example. The second semiconductor portion 31b is filled between the plurality of first portions of the first semiconductor portion 31 a. The second semiconductor portion 31b can be formed under a growth condition in which lateral growth is promoted as compared with the first semiconductor layer, for example. In the case where the second semiconductor portion 31b is formed in this way, the lower the impurity concentration of the second semiconductor portion 31b is, the lower the possibility of occurrence of a gap between the second semiconductor portion 31b and the first semiconductor portion 31a can be reduced. Therefore, the n-type impurity concentration of the second semiconductor portion 31b is preferably 1×10²⁰/cm³ or less. The n-type impurity concentration of the first semiconductor portion 31a may be 1×10¹⁷/cm³ or more and 1×10²⁰/cm³ or less, or may be equal to or less than the detection limit. The n-type impurity concentration of the first semiconductor portion 31a may be greater than the n-type impurity concentration of the second semiconductor portion 31 b. The concentration of impurities other than the n-type impurities of the second semiconductor portion 31b may be set to be less than the detection limit. In addition, the second semiconductor portion 31b is preferably made of GaN, whereby the possibility of occurrence of a gap between the second semiconductor portion 31b and the first semiconductor portion 31a can be reduced. In fig. 2, the upper surface of the second semiconductor portion 31b is at the same height from the diffraction grating portion 311 to the non-diffraction grating portion 312, but is not limited thereto. For example, the upper surface of the second semiconductor portion 31b of the diffraction grating portion 311 having the concave portion provided in the first semiconductor portion 31a may be lower than the upper surface of the second semiconductor portion 31b of the non-diffraction grating portion 312.

At least one of the two ends in the vertical direction D2 may be located inside the nitride semiconductor stack 20 in any one of the plurality of first portions and the plurality of second portions. Either one of the two ends of the plurality of first portions or the plurality of second portions may be in other words two ends of the periodic structure. In the case of using a method in which the formation area is proportional to the operation time, such as electron beam drawing, in the formation of the periodic structure, the formation time of the periodic structure can be shortened by making the width of the periodic structure smaller than the width of the semiconductor laser element 100.

In fig. 2, the first semiconductor portion 31a has a plurality of concave shapes recessed in a direction away from the active layer 40. The portion of the first semiconductor portion 31a that sandwiches the plurality of concave shapes along the resonance direction D1 is one of the first portion or the second portion. The plurality of concave shapes are buried by the second semiconductor portion 31b, and a portion where the plurality of concave shapes are buried is the other of the first portion or the second portion. The first semiconductor portion 31a may have a plurality of convex shapes protruding toward the active layer 40. In this case, the plurality of convex portions of the first semiconductor portion 31a are one of the first portion and the second portion, and the plurality of convex portions of the second semiconductor portion 31b are the other of the first portion and the second portion, which are sandwiched along the resonance direction D1. It is considered that the concave shape or convex shape is easily and stably formed by at least one of both ends in the vertical direction D2 of the concave shape or convex shape portion of the first semiconductor portion 31a being located inside the nitride semiconductor laminate 20. This is because the narrower the width in the vertical direction D2 of the concave shape or the convex shape is, the higher the strength of the first semiconductor portion 31a can be expected. The concave shape or the convex shape is preferably a shape in which both ends in the vertical direction D2 of the concave shape or the convex shape are located inside the nitride semiconductor stack 20. The width of the concave or convex shape in the vertical direction D2 may be equal to or greater than the width of the optical waveguide 10, or may be greater than the width of the optical waveguide 10. The width in the vertical direction D2 of the concave or convex shape may be a value obtained by adding 5 μm or more on one side and 10 μm or more in total to the width of the optical waveguide 10. The width in the vertical direction D2 of the concave shape or the convex shape may also be smaller than the maximum width in the vertical direction D2 of the p-electrode 82. In the case of forming the periodic structure by using a method in which the formation area is proportional to the operation time, such as electron beam drawing, the formation of the first semiconductor portion 31a having a plurality of concave shapes can shorten the formation time of the periodic structure as compared with the formation of the first semiconductor portion 31a having a plurality of convex shapes. In addition, forming the first semiconductor portion 31a having a plurality of concave shapes can be expected to improve the strength of the first semiconductor portion 31a as compared with forming the first semiconductor portion 31a having a plurality of convex shapes.

For example, the first portion is composed of a nitride semiconductor containing Ga, and the second portion is composed of a nitride semiconductor containing In and Ga. For example, the first portion is made of GaN, and the second portion is made of In_XGa_1-X N (0 < x < 1). The In composition ratio of the second portion was set to 0.001≤X≤0.1. In this case, the n-side clad layer is provided as a layer different from the first n-side nitride semiconductor layer 31, and the first n-side nitride semiconductor layer 31 can be disposed between the n-side clad layer and the active layer 40. This can reduce the threshold current and can improve the light blocking. When the first portion is made of GaN, the first semiconductor portion 31a preferably includes a plurality of second portions, and the second semiconductor portion 31b preferably includes a plurality of first portions. As a result, the irregularities of the first semiconductor portion 31a can be buried by the second semiconductor portion 31b, and therefore the probability of occurrence of a gap between the first portion and the second portion can be reduced. In such a first semiconductor portion 31a and a second semiconductor portion 31b, for example, in a Z contrast image (ZC image) obtained by STEM, a change in contrast at the bottom can be gentle compared with the side surface of the concave portion of the first semiconductor portion 31 a. The Z contrast image is an atomic weight-based contrast image.

As another example of the material of the first portion and the second portion, the first portion may be made of a nitride semiconductor containing Al and Ga, and the second portion may be made of a nitride semiconductor containing Ga. For example, the first portion is composed of Al_YGa_1-Y N (0 < Y < 1), and the second portion is composed of GaN. The Al composition ratio of the first portion is set to 0.001≤Y≤0.2. In the case where the first n-side nitride semiconductor layer 31 includes a nitride semiconductor containing Al and Ga at least in a part thereof, the first n-side nitride semiconductor layer 31 may be a layer functioning as an n-side clad layer.

The average refractive index of the periodic structure provided in the diffraction grating portion 311 may be an average value of refractive indices in the resonance direction D1 of the minimum unit constituting periodic repetition of the periodic structure. For example, when the minimum unit of periodic repetition constituting the periodic structure is one first portion and one second portion, the average refractive index n_ave of the periodic structure provided in the diffraction grating portion 311 is represented by the following formula (1).

n_ave＝{(n₁×t₁)+(n₂×t₂)}/(t₁+t₂) (1)

Here, n₁ is the refractive index of the first portion, n₂ is the refractive index of the second portion, t₁ is the length of one first portion in the resonance direction D1, and t₂ is the length of one second portion in the resonance direction D1. When the lengths of the first portion and the second portion in the resonance direction D1 are different depending on the height, the lengths of the first portion and the second portion at a position half the thickness of the periodic structure may be t₁ and t₂, respectively, to determine the average refractive index of the periodic structure. The refractive index is set to the refractive index at the peak wavelength of the laser light oscillated by the semiconductor laser element 100. The refractive index of each material may be a known refractive index value. The refractive index of the semiconductor can be calculated from the composition ratio of the semiconductor.

The distance from the first n-side nitride semiconductor layer 31 to the well layer 41 is preferably greater than 300nm. This can reduce the threshold current of the semiconductor laser device 100. In addition, the slope efficiency of the semiconductor laser device 100 can be improved. The distance from the first n-side nitride semiconductor layer 31 to the well layer 41 can be, for example, 800nm or less, preferably 500nm or less. Thus, a desired binding efficiency is easily obtained. The distance from the first n-side nitride semiconductor layer 31 to the active layer 40 may be set to a range of values thereof. The distance from the periodic structure of the diffraction grating portion 311 provided in the first n-side nitride semiconductor layer 31 to the well layer 41 may be set to a range of values, or the distance from the periodic structure to the active layer 40 may be set to a range of values. The distance from the periodic structure provided in the diffraction grating portion 311 to the well layer 41 (n-side well layer) may be 320nm or more and 800nm or less, or 400nm or more and 800nm or less.

The thickness of the first n-side nitride semiconductor layer 31 is preferably 50nm or more, more preferably 100nm or more. Thereby, the periodic structure is easily formed in the first n-side nitride semiconductor layer 31. The thickness of the first n-side nitride semiconductor layer 31 may be 1000nm or less or 500nm or less.

The thickness of the periodic structure, i.e., the length in the direction perpendicular to the main surface of the active layer 40 of the periodic structure is the same as or smaller than the thickness of the first n-side nitride semiconductor layer 31. The difference between the thickness of the first n-side nitride semiconductor layer 31 and the thickness of the periodic structure can be set to 0nm or more and 1000nm or less.

In the case where the semiconductor laser element 100 has the ridge 20c, the refractive index of the periodic structure provided in the diffraction grating portion 311 periodically changes along the extending direction of the ridge 20 c. The periodic structure is disposed at least immediately below the ridge 20 c.

(Second n-side nitride semiconductor layer 32)

The second n-side nitride semiconductor layer 32 is disposed between the first n-side nitride semiconductor layer 31 and the active layer 40.

The smaller the distance between the periodic structure and the active layer 40, the higher the electric field strength of the p-side nitride semiconductor layer 50 increases and the absorption loss increases, and/or the light blocking to the active layer 40 tends to decrease. By providing the second n-side nitride semiconductor layer 32, the distance between the first n-side nitride semiconductor layer 31, in which the periodic structure is partially provided, and the active layer 40 can be increased as compared with the case where it is not provided. This can reduce the electric field intensity of the p-side nitride semiconductor layer 50 to reduce absorption loss and/or can improve optical confinement to the active layer 40. Therefore, the threshold current of the semiconductor laser device 100 can be reduced.

The second n-side nitride semiconductor layer 32 is preferably a nitride semiconductor layer having In and Ga. The thickness of the second n-side nitride semiconductor layer 32 is preferably greater than the thickness of an n-side barrier layer described later. By providing these structures, absorption loss can be reduced and/or light blocking into the active layer 40 can be improved.

The refractive index of the second n-side nitride semiconductor layer 32 is preferably higher than the average refractive index of the periodic structure of the diffraction grating portion 311. The thickness of the second n-side nitride semiconductor layer 32 is preferably greater than the thickness of the periodic structure of the diffraction grating portion 311. By providing these structures, absorption loss can be reduced and/or light blocking into the active layer 40 can be improved. The refractive index of the material constituting the second n-side nitride semiconductor layer 32 may be higher than the refractive index of the material constituting the periodic structure of the diffraction grating portion 311, and the refractive index of the second n-side nitride semiconductor layer 32 may be higher than the average refractive index of the periodic structure provided in the diffraction grating portion 311. The thickness of the second n-side nitride semiconductor layer 32 is more preferably greater than the thickness of the first n-side nitride semiconductor layer 31.

The refractive index of the second n-side nitride semiconductor layer 32 is preferably higher than that of the n-side barrier layer. The n-side barrier layer has a band gap energy larger than that of the well layer in order to function as a barrier layer, but such an n-side barrier layer tends to have a relatively low refractive index. Therefore, by providing the second n-side nitride semiconductor layer 32 having a higher refractive index than that of the n-side barrier layer, absorption loss can be reduced and/or optical confinement to the active layer 40 can be improved. When the n-side barrier layer is formed of a plurality of layers, the refractive index of the second n-side nitride semiconductor layer 32 is preferably higher than the average refractive index of the n-side barrier layer, or may be higher than the refractive index of any one of the plurality of layers constituting the n-side barrier layer.

The second N-side nitride semiconductor layer 32 is composed of In_ZGa_1-Z N (0 < z < 1), for example. The In composition ratio of the second n-side nitride semiconductor layer 32 is set to 0.001≤Z≤0.2. The second n-side nitride semiconductor layer 32 may also be a constituent inclined layer. The second n-side nitride semiconductor layer 32 can be formed, for example, as a composition inclined layer whose entire is InGaN and whose In composition ratio increases as it approaches the active layer 40. Such a composition inclined layer may be a nitride semiconductor layer having In and Ga. As the composition inclined layer, in the case where a portion farthest from the active layer 40 is GaN, a portion closest to the active layer 40 is InGaN, and a composition ratio of In increases as the active layer 40 is approached, a remaining portion of the composition inclined layer other than the portion farthest from the active layer 40 may be the second n-side nitride semiconductor layer 32.

The thickness of the second n-side nitride semiconductor layer 32 may be 150nm or more, and preferably 200nm or more. This can reduce absorption loss and/or improve light blocking into the active layer 40. The thickness of the second n-side nitride semiconductor layer 32 may be greater than the thickness of the fourth n-side nitride semiconductor layer 34. The thickness of the second n-side nitride semiconductor layer 32 can be 500nm or less. The thickness of the second n-side nitride semiconductor layer 32 may be 170nm or more and 500nm or less, 230nm or more and 500nm or less, or 300nm or more and 500nm or less, depending on the light intensity in the diffraction grating, the light blocking of the well layer 41, and the light leakage into the p-side nitride semiconductor layer 50.

(Third n-side nitride semiconductor layer 33)

The third n-side nitride semiconductor layer 33 is disposed on the opposite side of the first n-side nitride semiconductor layer 31 from the active layer 40. The first n-side nitride semiconductor layer 31 is located between the third n-side nitride semiconductor layer 33 and the active layer 40.

The third n-side nitride semiconductor layer 33 may be disposed between the n-side clad layer and the first n-side nitride semiconductor layer 31. Such a configuration can be adopted so that the distance from the periodic structure of the first n-side nitride semiconductor layer 31 to the active layer 40 is not excessively large. The n-side clad layer is disposed on the opposite side of the first n-side nitride semiconductor layer 31 from the active layer 40. The third n-side nitride semiconductor layer 33 has a refractive index between the refractive index of the n-side cladding layer and the average refractive index of the periodic structure of the diffraction grating portion 311 of the first n-side nitride semiconductor layer 31. For example, the refractive index of the third n-side nitride semiconductor layer 33 is higher than that of the n-side cladding layer and lower than the average refractive index of the periodic structure of the diffraction grating portion 311. By the refractive index of the material constituting the third n-side nitride semiconductor layer 33 being lower than any of the refractive indices of the materials constituting the periodic structure of the diffraction grating portion 311, the refractive index of the third n-side nitride semiconductor layer 33 may be lower than the average refractive index of the periodic structure provided in the diffraction grating portion 311.

In fig. 2, the third n-side nitride semiconductor layer 33 is disposed between the first n-side nitride semiconductor layer 31 and a fifth n-side nitride semiconductor layer 35 described later. The third n-side nitride semiconductor layer 33 may have a refractive index between the refractive index of the fifth n-side nitride semiconductor layer 35 and the average refractive index of the periodic structure of the diffraction grating portion 311 of the first n-side nitride semiconductor layer 31. For example, the fifth n-side nitride semiconductor layer 35 is an n-side clad layer.

By providing the third n-side nitride semiconductor layer 33, light leaking to the substrate 60 or the like located below the third n-side nitride semiconductor layer can be reduced. For example, in the case where the first n-side nitride semiconductor layer 31 has a periodic structure in which GaN and InGaN are periodically arranged, the refractive index of the first n-side nitride semiconductor layer 31 increases as compared with the case where the first n-side nitride semiconductor layer 31 has no periodic structure but is composed of only GaN. In this way, when the refractive index of the first n-side nitride semiconductor layer 31 is relatively high, it is particularly preferable to provide the third n-side nitride semiconductor layer 33 to reduce the leakage of light.

The third n-side nitride semiconductor layer 33 is, for example, an AlGaN layer. The third n-side nitride semiconductor layer 33 may contain an n-type impurity. The thickness of the third n-side nitride semiconductor layer 33 may be 100nm or more and 1000nm or less.

(Fourth n-side nitride semiconductor layer 34)

The fourth n-side nitride semiconductor layer 34 is arranged between the second n-side nitride semiconductor layer 32 and the first n-side nitride semiconductor layer 31. The refractive index of the fourth n-side nitride semiconductor layer 34 may be lower than the refractive index of the second n-side nitride semiconductor layer 32 and higher than the average refractive index of the periodic structure of the diffraction grating portion 311 of the first n-side nitride semiconductor layer 31. By the refractive index of the material constituting the fourth n-side nitride semiconductor layer 34 being lower than any of the refractive indices of the materials constituting the periodic structure of the diffraction grating portion 311, the refractive index of the fourth n-side nitride semiconductor layer 34 may be lower than the average refractive index of the periodic structure provided to the diffraction grating portion 311.

By providing the fourth n-side nitride semiconductor layer 34, light blocking to the active layer 40 can be improved. For example, in the case where the first n-side nitride semiconductor layer 31 has a periodic structure in which AlGaN and GaN are periodically arranged, the refractive index of the first n-side nitride semiconductor layer 31 is reduced as compared with the case where the first n-side nitride semiconductor layer 31 has no periodic structure but is made of only GaN. In this way, when the refractive index of the first n-side nitride semiconductor layer 31 is relatively low, it is particularly preferable to provide the fourth n-side nitride semiconductor layer 34 to improve the optical confinement to the active layer 40. Alternatively, the fourth n-side nitride semiconductor layer 34 may not be provided, and instead, the thickness of the common portion of the second semiconductor portion 31b may be 50nm or more. This can improve the light blocking into the active layer 40. The thickness of the common portion of the second semiconductor portion 31b can be 300nm or less.

The fourth n-side nitride semiconductor layer 34 is, for example, an InGaN layer. The fourth n-side nitride semiconductor layer 34 may contain an n-type impurity. The thickness of the fourth n-side nitride semiconductor layer 34 may be 1nm or more and 500nm or less.

(Fifth n-side nitride semiconductor layer 35)

The fifth n-side nitride semiconductor layer 35 is disposed on the opposite side of the first n-side nitride semiconductor layer 31 from the active layer 40. The fifth n-side nitride semiconductor layer 35 is disposed between the first n-side nitride semiconductor layer 31 and the substrate 60. The fifth n-side nitride semiconductor layer 35 is, for example, an n-side clad layer. The fifth n-side nitride semiconductor layer 35 is, for example, a layer having the largest band gap energy in the n-side nitride semiconductor layer 30. The fifth n-side nitride semiconductor layer 35 is, for example, an AlGaN layer containing an n-type impurity.

(Active layer 40)

The active layer 40 is disposed between the n-side nitride semiconductor layer 30 and the p-side nitride semiconductor layer 50. The active layer 40 can be provided in a multiple quantum well structure or a single quantum well structure. The active layer 40 has one or more well layers 41 and one or more barrier layers 42.

The active layer 40 has an n-side well layer located closest to the second n-side nitride semiconductor layer 32 among the one or more well layers 41, and an n-side barrier layer located between the second n-side nitride semiconductor layer 32 and the n-side well layer among the one or more barrier layers 42.

The active layer 40 is preferably disposed from above the diffraction grating portion 311 to above the non-diffraction grating portion 312. Further, it is preferable that each layer above the first n-side nitride semiconductor layer 31 including the active layer 40 is provided from above the diffraction grating portion 311 to above the non-diffraction grating portion 312. As a method of forming the diffraction grating portion and the non-diffraction grating portion, for example, there is a method of forming a first epitaxial structure including the non-diffraction grating portion and the active layer, removing a part thereof to expose an end surface of the active layer, and thereafter, regrowing a second epitaxial structure including the diffraction grating portion and the active layer. In such a method, impurities are introduced at the interface between the exposed end face and the regrown second epitaxial structure during regrowth, and there is a concern that the light absorption loss due to impurities increases and carrier traps increase. In the semiconductor laser device 100 shown in fig. 2, a diffraction grating portion 311 and a non-diffraction grating portion 312 are formed in the first n-side nitride semiconductor layer 31. This makes it possible to make the semiconductor laser device 100 have a structure in which the regrowth interface is located only in the first n-side nitride semiconductor layer 31. Since the electric field intensity of the first n-side nitride semiconductor layer 31 at the time of driving the semiconductor laser element 100 is smaller than that of the active layer 40, the influence of impurities introduced at the time of regrowth due to such arrangement can be reduced.

By providing the periodic structure of the diffraction grating portion 311, the upper surface of the first n-side nitride semiconductor layer 31 may have the diffraction grating portion 311 lower than the non-diffraction grating portion 312. In this way, in the case where there is a level difference in the upper surface of the first n-side nitride semiconductor layer 31, if the thickness of the layer provided thereon is smaller than the level difference, the level difference may be cut off, but such a state may be referred to as a state provided from above the diffraction grating portion 311 toward above the non-diffraction grating portion 312.

In the case where a plurality of semiconductor layers are present between the n-side well layer and the second n-side nitride semiconductor layer 32, the thickness of the second n-side nitride semiconductor layer 32 is preferably larger than the thickness of the layer having the largest thickness. This can reduce absorption loss and/or improve light blocking into the active layer 40. Further, it is preferable that the thickness of the second n-side nitride semiconductor layer 32 is larger than the total thickness of the plurality of semiconductor layers located between the n-side well layer and the second n-side nitride semiconductor layer 32. This can further reduce absorption loss and/or improve light blocking into the active layer 40.

The active layer 40 can be formed with a composition capable of emitting light having a wavelength of 400nm or more and 600nm or less, for example. The one or more well layers 41 are made of InGaN, for example. The In composition ratio of InGaN constituting one or more well layers 41 may be, for example, 0.05 or more and 0.50 or less. The In composition ratio of InGaN constituting one or more well layers 41 may be 0.15 or more.

(P-side nitride semiconductor layer 50)

The p-side nitride semiconductor layer 50 has one or more nitride semiconductor layers containing p-type impurities. Examples of the p-type impurity include Mg. The p-side nitride semiconductor layer 50 may also have an undoped layer that is not intentionally doped with impurities. The p-side nitride semiconductor layer 50 may have a contact layer. The p-side nitride semiconductor layer 50 may have one or more of a p-side light guide layer, an electron blocking layer, and a p-side clad layer. The p-side nitride semiconductor layer 50 may have all of these layers or may have other layers than these layers.

In the nitride semiconductor, the activation rate of the p-type impurity is lower than that of the n-type impurity. Therefore, the p-type impurity concentration of the p-side nitride semiconductor layer 50 tends to be higher than the n-type impurity concentration of the n-side nitride semiconductor layer 30. For example, the highest value of the p-type impurity concentration in the p-side nitride semiconductor layer 50 is larger than the highest value of the n-type impurity concentration in the n-side nitride semiconductor layer 30.

(N electrode 81)

The semiconductor laser element 100 has an n-electrode 81. The n-electrode 81 is provided on the lower surface of the substrate 60. Examples of the material of the n-electrode 81 include a single-layer film or a multilayer film of a conductive oxide including at least one selected from metals such as Ni, rh, cr, au, W, pt, ti, al, alloys thereof, zn, in, and Sn. Examples of the conductive Oxide include ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide: indium Zinc Oxide), GZO (Gallium-doped Zinc Oxide), and the like.

(P-electrode 82)

The semiconductor laser element 100 has a p-electrode 82. The p-electrode 82 is provided in contact with a part of the p-side nitride semiconductor layer 50. The p-electrode 82 is provided in contact with the upper surface of the ridge 20c, for example. The p-electrode 82 of the semiconductor laser element 100 can have a pad electrode. Examples of the material of the p-electrode 82 include a single-layer film or a multilayer film of a conductive oxide including at least one selected from metals such as Ni, rh, cr, au, W, pt, ti, al, alloys thereof, zn, in, and Sn. As the conductive oxide, ITO, IZO, GZO and the like can be mentioned.

As shown in fig. 1, the semiconductor laser element 100 can have a first p electrode 821 and a second p electrode 822 as the p electrode 82. The first p electrode 821 is provided on the upper surface of the p-side nitride semiconductor layer 50 and above the diffraction grating portion 311. The second p electrode 822 is provided on the upper surface of the p-side nitride semiconductor layer 50 and above the non-diffraction grating portion 312 so as to be separated from the first p electrode 821. By providing the first p-electrode 821 and the second p-electrode 822 as described above, the diffraction grating portion 311 and the non-diffraction grating portion 312 can be independently controlled in current, and a current having an appropriate magnitude can be supplied. For example, the current flowing through the non-diffraction grating portion 312 is a magnitude corresponding to the desired light output, and the current flowing through the diffraction grating portion 311 is a magnitude of the degree of decrease in light absorption in the diffraction grating portion 311. When no current flows through the diffraction grating 311, the well layer 41 is a highly absorbing layer, and a standing bend occurs, but this can be suppressed by flowing current through the diffraction grating 311. The current flowing through the diffraction grating portion 311 may be smaller than the current flowing through the non-diffraction grating portion 312. The wavelength may be tuned by changing the magnitude of the current flowing through the diffraction grating portion 311. The first p-electrode 821 is disposed separately from the second p-electrode 822.

Fig. 5 is a schematic diagram for explaining the first contact layer 511 and the second contact layer 512. In the case where the first p electrode 821 and the second p electrode 822 are provided, as shown in fig. 5, the p-side nitride semiconductor layer 50 may have, as contact layers, a first contact layer 511 in contact with the lower surface of the first p electrode 821 and a second contact layer 512 in contact with the lower surface of the second p electrode 822. This enables the diffraction grating portion 311 and the non-diffraction grating portion 312 to be controlled independently with greater reliability. The first contact layer 511 is disposed separately from the second contact layer 512.

The first p-electrode 821 may have a first conductive oxide film 823 provided on the upper surface of the p-side nitride semiconductor layer 50 and a first metal film 824 disposed above the first conductive oxide film 823. The second p-electrode 822 may have a second conductive oxide film 825 provided on the upper surface of the p-side nitride semiconductor layer 50 and a second metal film 826 disposed above the second conductive oxide film 825. One or both of the light-emitting side end of the first conductive oxide film 823 and the light-reflecting side end of the second conductive oxide film 825 are preferably located between the light-emitting side end of the first metal film 824 and the light-reflecting side end of the second metal film 826 in a plan view. One or both of the end portion of the first conductive oxide film 823 on the first end surface 20a side and the end portion of the second conductive oxide film 825 on the second end surface 20b side are preferably located between the end portion of the first metal film 824 on the first end surface 20a side and the end portion of the second metal film 826 on the second end surface 20b side in plan view. Thus, the distance from the first p electrode 821 to the second p electrode 822 can be reduced as compared with the case where the first p electrode 821 and the second p electrode 822 are formed only of metal. Among the films constituting the first p-electrode 821 and the second p-electrode 822, one end of the optical waveguide near the first end face 20a is an end on the first end face 20a side, and the end near the second end face 20b is an end on the second end face 20b side. The end on the first end face 20a side is an end on the light emission side, and the end on the second end face 20b side is an end on the light reflection side. Alternatively, the end on the first end surface 20a side may be an end on the light reflection side, and the end on the second end surface 20b side may be an end on the light emission side. More preferably, both the end of the first conductive oxide film 823 on the first end face 20a side and the end of the second conductive oxide film 825 on the second end face 20b side are located between the end of the first metal film 824 on the first end face 20a side and the end of the second metal film 826 on the second end face 20b side. More preferably, both the light-emitting-side end of the first conductive oxide film 823 and the light-reflecting-side end of the second conductive oxide film 825 are located between the light-emitting-side end of the first metal film 824 and the light-reflecting-side end of the second metal film 826. No current is injected between the first p-electrode 821 and the second p-electrode 822, and the light absorption increases as the distance therebetween increases. By using the first conductive oxide film 823 and the second conductive oxide film 825, a region where current is not injected can be reduced, and thus light absorption can be reduced. The distance from the first conductive oxide film 823 to the second conductive oxide film 825 can be, for example, 1 μm or more and 30 μm or less.

An end portion of the first conductive oxide film 823 on the first end surface 20a side protrudes from an end portion of the first metal film 824 on the first end surface 20a side toward the second p-electrode 822 in a plan view. The end portion on the light emission side of the first conductive oxide film 823 protrudes from the end portion on the light emission side of the first metal film 824 toward the second p-electrode 822 in a plan view. The distance from the first end face 20a to the first conductive oxide film 823 is smaller than the distance from the first end face 20a to the first metal film 824 in plan view. An end portion of the second conductive oxide film 825 on the second end surface 20b side protrudes from an end portion of the second metal film 826 on the second end surface 20b side toward the first p-electrode 821 in a plan view. The end portion on the light reflection side of the second conductive oxide film 825 protrudes from the end portion on the light reflection side of the second metal film 826 toward the first p-electrode 821 in a plan view. The distance from the second end face 20b to the second conductive oxide film 825 is smaller than the distance from the second end face 20b to the second metal film 826 in plan view. The first conductive oxide film 823 and the second conductive oxide film 825 have at least a portion overlapping the optical waveguide in a plan view. In fig. 1, the first conductive oxide film 823 and the second conductive oxide film 825 have at least portions overlapping the ridge 20 c. Portions of the first conductive oxide film 823 and the second conductive oxide film 825 protruding from the first metal film 824 and the second metal film 826 overlap with the optical waveguide in a plan view. In fig. 1, both the first p-electrode 821 and the second p-electrode 822 have a conductive oxide film, but only one of them may have a conductive oxide film.

(First protective film 71, second protective film 72)

The semiconductor laser element 100 may also have a first protective film 71 and a second protective film 72. The first protective film 71 is provided on the first end surface 20a of the nitride semiconductor stack 20. The second protective film 72 is provided on the second end face 20b of the nitride semiconductor stack 20. One or both of the first protective film 71 and the second protective film 72 may not be provided. Each of the first protective film 71 and the second protective film 72 may have one or more dielectric films.

When the first end face 20a, which is the end face on the side where the non-diffraction grating portion 312 is located, is the light-emitting end face, the reflectance of the first protective film 71 can be set to, for example, 0.1% or more, and preferably 5% or more. Thus, the threshold current can be reduced as compared with the case where the first protective film 71 is an AR (non-reflective) coating. By setting the first end surface 20a as the light emission end surface, the diffraction grating portion 311 can be set as a part of the reflection film on the light reflection side, and the reflectance on the light reflection side can be increased, so that the light output can be increased.

In the case where the increase in the threshold current is to be further suppressed, the reflectance of the first protective film 71 may be 18% or more, and more preferably 30% or more. When the semiconductor laser element 100 is an element that emits laser light having a peak wavelength of 500nm or more, the gain inside the resonator tends to be lower than that of an element that emits laser light having a peak wavelength of less than 500 nm. Therefore, in the case of the semiconductor laser device 100 which emits laser light having a peak wavelength of 500nm or more, the reflectance of the first protective film 71 is preferably 30% or more and less than the reflectance of the second protective film 72. This can reduce the threshold current. When the nitride semiconductor stack 20 is provided with a periodic structure, and the longitudinal mode of the oscillation wavelength is made single or nearly single by the periodic structure, the sealing coefficient of the laser oscillation is reduced compared with the case where this is not the case. The higher the reflectance of the first protective film 71 is, the higher the blocking coefficient can be raised. The reflectance of the first protective film 71 may be 60% or more, or 80% or more. The upper limit of the reflectance of the first protective film 71 can be set smaller than that of the second protective film 72.

The second protective film 72 has a higher reflectance than the first protective film 71. The reflectance of the second protective film 72 may be, for example, 95% or more, or 98% or more. The reflectance of the second protective film 72 can be set to, for example, 100% or less. The reflectivity of the second protective film 72 may be 100%. The reflectance of the first protective film 71 and the reflectance of the second protective film 72 refer to the reflectance at the peak wavelength of the laser light oscillated by the semiconductor laser element 100.

The second end surface 20b, which is the end surface on the side of the diffraction grating portion 311, may be used as the light emitting end surface. In this case, the reflectance of the second protective film 72 is made lower than that of the first protective film 71. The reflectance of the first protective film 71 may be 85% or more, or 90% or more, for example. The reflectance of the first protective film 71 can be set to, for example, 100% or less. The second protective film 72 may also be an AR coating. The reflectance of the second protective film 72 may be 0.1% or more, or may be 5% or more. The second protective film 72 may not be provided. By setting the second end surface 20b as the light-emitting end surface, the second protective film 72 can be dispensed with. By setting the second end surface 20b as the light-emitting end surface, the light output can be stabilized. This is because an effective refractive index difference is generated between the concave portion and the convex portion of the diffraction grating portion 311, and an effective reflectance of the laser diode can be obtained. By forming the diffraction grating portion 311 having a length of 100 μm or more in the resonance direction D1, the reflectance required for laser oscillation can be sufficiently obtained even without the second protective film 72.

(Insulating film 73)

The semiconductor laser element 100 may have an insulating film 73 provided on a part of the surface of the p-side nitride semiconductor layer 50. The insulating film 73 is a single-layer film or a multilayer film of an oxide or nitride such as Si, al, zr, ti, nb, ta, for example.

Example 1

As example 1, a semiconductor laser device 100 shown below was produced. A MOCVD apparatus is used for manufacturing an epitaxial wafer serving as the semiconductor laser device 100. Further, trimethylgallium (TMG), triethylgallium (TEG), trimethylaluminum (TMA), trimethylindium (TMI), ammonia gas (NH₃), silane gas, bis (cyclopentadienyl) magnesium (Cp₂ Mg) are suitably used as the raw materials.

On the c-plane GaN substrate (substrate 60), an Al_0.016Ga_0.984 N layer containing Si was grown at a thickness of 1.8. Mu.m.

Next, an Al_0.08Ga_0.92 N layer containing Si was grown to a thickness of 200 nm.

Next, an In_0.04Ga_0.96 N layer containing Si was grown at a thickness of 150 nm.

Subsequently, an Al_0.08Ga_0.92 N layer (N-side clad layer) containing Si was grown at a thickness of 650 nm.

Next, a GaN layer containing Si was grown at a thickness of 100 nm.

Next, an In_0.03Ga_0.97 N layer containing Si (the first semiconductor layer to be the first semiconductor portion 31 a) was grown at a thickness of 150 nm.

The epitaxial wafer on which the above layers were formed was taken out by an MOCVD apparatus, and periodic uneven shapes (periodic structures) were produced by using an electron beam drawing apparatus, reactive Ion Etching (RIE), and sputtering. The depth of the concave portion was 83nm, the width of the concave portion was 39nm, and the diffraction grating period Λ (one period of the concave-convex) was 112nm. The periodic structure is formed only in the diffraction grating portion 311. The length of the diffraction grating portion 311 along the resonance direction D1 is 300 μm, and the length of the non-diffraction grating portion 312 along the resonance direction D1 is 500 μm.

After the concave-convex shape was formed, a GaN layer (second semiconductor portion 31 b) containing Si was grown to a thickness of 150nm by an MOCVD apparatus. 150nm is the thickness from the uppermost part of the convex portion of the concave-convex shape to the upper surface of the Si-containing GaN layer (second semiconductor portion 31 b).

Next, an undoped In_0.03Ga_0.97 N layer (second N-side nitride semiconductor layer 32) was grown at a thickness of 240 nm. The N-side nitride semiconductor layer 30 is from the Si-containing Al_0.016Ga_0.984 N layer to this layer.

Next, an active layer 40 was grown, and the active layer 40 sequentially included an N-side barrier layer (barrier layer 42) composed of three layers of a Si-doped GaN layer having a thickness of 1nm, an In_0.05Ga_0.95 N layer having a thickness of 8nm, a Si-doped GaN layer having a thickness of 1nm, an undoped In_0.25Ga_0.75 N layer having a thickness of 2.1nm (well layer 41), an undoped GaN layer having a thickness of 3.3nm (barrier layer 42), an undoped In_0.25Ga_0.75 N layer having a thickness of 2.1nm (well layer 41), and an undoped GaN layer having a thickness of 2.3nm (barrier layer 42).

Next, undoped compositionally tilted layers were grown at a thickness of 150 nm. The composition of the inclined layer was changed to In_0.05Ga_0.95 N at the start of growth, gaN at the end of growth, and the In composition was grown so as to be substantially monotonously reduced so that the composition of the inclined layer was substantially linear.

Next, an Al_0.10Ga_0.90 N layer and an Al_0.16Ga_0.84 N layer containing Mg were grown to a thickness of 3nm and 7nm, respectively.

Next, an undoped Al_0.015Ga_0.985 N layer was grown at a thickness of 125 nm.

Next, an Al_0.015Ga_0.985 N layer containing Mg was grown at a thickness of 325 nm.

Next, a GaN layer containing Mg was grown at a thickness of 15 nm. The undoped composition inclined layer to this layer is the p-side nitride semiconductor layer 50.

Then, the epitaxial wafer on which the above layers are formed is taken out by an MOCVD apparatus, and the ridge 20c, the p electrode 82, the n electrode 81, and the like are formed by photolithography, RIE, and sputtering. As shown in fig. 1 and 2, a first conductive oxide film 823, a first metal film 824, a second conductive oxide film 825, and a second metal film 826 are formed as the p-electrode 82. As shown in fig. 4, the p-side nitride semiconductor layer 50 has a structure of a first contact layer 511 and a second contact layer 512 for using photolithography and RIE.

Then, the semiconductor laser device 100 is obtained by dicing, forming the first protective film 71 on the first end face 20a, and forming the second protective film 72 on the second end face 20 b. The reflectance of the first protective film 71 was 90%, and the reflectance of the second protective film 72 was 97%. That is, in the semiconductor laser element 100 of embodiment 1, the first end face 20a is a light-emitting end face. The semiconductor laser element 100 has a ridge width of 2 μm, a resonator length of 800 μm, and an element width of 200 μm.

In the semiconductor laser device 100 of example 1, a voltage was applied between the n-electrode 81 and the second metal film 826 provided over the non-diffraction grating portion 312, and a current of 500mA was injected, so that the semiconductor laser device 100 of example 1 oscillated laser light having a peak wavelength of about 528 nm. No voltage is applied between the n-electrode 81 and the first metal film 824 provided on the diffraction grating portion 311. Fig. 6 shows a spectrum of the semiconductor laser device 100 of example 1. The horizontal axis of fig. 6 is wavelength. The vertical axis of fig. 6 represents light intensity in intensity ratio (unit dB), and the Side Mode Suppression Ratio (SMSR) was estimated with the maximum peak value set to 0dB. The side mode suppression ratio of the semiconductor laser element 100 of embodiment 1 is greater than 20dB. The spectral width of the semiconductor laser device 100 of example 1 was about 3pm. The resolution of the spectrum analyzer used was about 3pm, and thus it can be said that an extremely narrow spectrum width was obtained. The interval between adjacent longitudinal modes calculated from the effective refractive index and the resonator length is about 0.06nm to 0.07nm, but a large peak value considered to be caused by the adjacent longitudinal modes is not observed, and the side mode suppression ratio is at least more than 20dB, so it can be said that the semiconductor laser element 100 of embodiment 1 oscillates in a single longitudinal mode.

Fig. 7 shows a Z-contrast image of a part of the semiconductor laser device of example 1 obtained by STEM. Fig. 7 is a Z-contrast image of a cross section of a portion including the first semiconductor portion 31a and the second semiconductor portion 31b in the diffraction grating portion 311. Fig. 7 is a cross section along the direction of the resonance direction D1. In the Z-contrast image, the difference in composition can be observed as the difference in display density in the image. In fig. 7, a portion having a concave portion recessed downward is a first semiconductor portion 31a, and a portion provided above the concave portion to fill the concave portion is a second semiconductor portion 31b. In fig. 7, the first semiconductor portion 31a and the second semiconductor portion 31b are shown with different display densities, and it is understood that they have different compositions.

Example 2

As example 2, a semiconductor laser device similar to example 1 was fabricated, except that the second protective film 72 was not provided, and the reflectance of the first protective film 71 was set to 90%. That is, in the semiconductor laser device of embodiment 2, the second end face 20b is a light emitting end face.

In the semiconductor laser device of example 2, a voltage is applied between the n-electrode 81 and the second metal film 826 provided on the non-diffraction grating portion 312 to inject 500mA of current, and a voltage is also applied between the n-electrode 81 and the first metal film 824 provided on the diffraction grating portion 311 to inject 100mA to 300mA of current. Fig. 8 shows the spectrum of the semiconductor laser device of example 2. The horizontal axis of fig. 8 is wavelength. The vertical axis of fig. 8 represents light intensity in intensity ratio (unit dB), and the Side Mode Suppression Ratio (SMSR) was estimated with the maximum peak value set to 0dB. The five peaks in fig. 8 are spectra when the current flowing between the n-electrode 81 and the first metal film 824 is set to 100mA, 150mA, 200mA, 250mA, 300mA in order from the left side. The side mode suppression ratio of the semiconductor laser element of example 2 is greater than 20dB. The semiconductor laser device 100 of example 2 oscillates a laser beam having a peak wavelength of about 528.5nm by injecting a current of 100mA between the n-electrode 81 and the first metal film 824. The semiconductor laser device 100 of example 2 oscillates laser light having a peak wavelength of about 530nm by injecting a current of 300mA between the n-electrode 81 and the first metal film 824. It can be said that the semiconductor laser device of example 2 oscillates in a single longitudinal mode, and further, the wavelength can be controlled by changing the injection current.

In the present specification, the following technical matters are disclosed in the content described so far.

(Item 1)

A semiconductor laser device is provided, which comprises a semiconductor laser,

The nitride semiconductor multilayer body has a first end face, a second end face, and an optical waveguide connecting the first end face and the second end face,

The nitride semiconductor laminate has:

a first n-side nitride semiconductor layer;

a second n-side nitride semiconductor layer disposed above the first n-side nitride semiconductor layer;

An active layer having one or more well layers and one or more barrier layers arranged above the second n-side nitride semiconductor layer, and

A p-side nitride semiconductor layer disposed above the active layer,

The first n-side nitride semiconductor layer has a diffraction grating portion provided with a periodic structure whose refractive index varies periodically along the resonance direction of the optical waveguide, and a non-diffraction grating portion which is located between the diffraction grating portion and the first end face and is not provided with the periodic structure,

The active layer has an n-side well layer located closest to the second n-side nitride semiconductor layer among the one or more well layers, and an n-side barrier layer located between the n-side well layer and the second n-side nitride semiconductor layer among the one or more barrier layers,

The second n-side nitride semiconductor layer is a nitride semiconductor layer having In and Ga,

The second n-side nitride semiconductor layer has a thickness greater than that of the n-side barrier layer.

(Item 2)

The semiconductor laser element according to item 1, wherein,

The length of the diffraction grating portion along the resonance direction is smaller than the length of the non-diffraction grating portion along the resonance direction.

(Item 3)

The semiconductor laser device according to item 1 or 2, comprising:

a first p electrode provided on the upper surface of the p-side nitride semiconductor layer and above the diffraction grating portion, and

And a second p electrode provided on the upper surface of the p-side nitride semiconductor layer and located above the non-diffraction grating portion at a position distant from the first p electrode.

(Item 4)

The semiconductor laser element according to item 3, wherein,

The first p-electrode has a first conductive oxide film provided on the upper surface of the p-side nitride semiconductor layer, and a first metal film provided above the first conductive oxide film,

The second p-electrode has a second conductive oxide film provided on the upper surface of the p-side nitride semiconductor layer, and a second metal film provided above the second conductive oxide film,

One or both of the first end face side end portion of the first conductive oxide film and the second end face side end portion of the second conductive oxide film are located between the first end face side end portion of the first metal film and the second end face side end portion of the second metal film in a plan view.

(Item 5)

The semiconductor laser device according to any one of the above 1 to 4, wherein,

The refractive index of the second n-side nitride semiconductor layer is higher than the average refractive index of the periodic structure of the diffraction grating portion of the first n-side nitride semiconductor layer,

The second n-side nitride semiconductor layer has a thickness greater than that of the periodic structure of the diffraction grating portion of the first n-side nitride semiconductor layer.

(Item 6)

The semiconductor laser device according to any one of claims 1 to 5, wherein,

The distance from the first n-side nitride semiconductor layer to the well layer is greater than 300nm.

(Item 7)

The semiconductor laser device according to any one of claims 1 to 6, wherein,

The first n-side nitride semiconductor layer has a plurality of first portions composed of nitride semiconductors containing Ga and a plurality of second portions composed of nitride semiconductors containing In and Ga,

The periodic structure of the diffraction grating portion is configured by alternately disposing the plurality of first portions and the plurality of second portions along the resonance direction.

(Item 8)

The semiconductor laser device according to any one of claims 1 to 7, wherein the nitride semiconductor laminate has:

An n-side cladding layer disposed on the opposite side of the first n-side nitride semiconductor layer from the active layer, and

And a third n-side nitride semiconductor layer disposed between the n-side cladding layer and the first n-side nitride semiconductor layer, the third n-side nitride semiconductor layer having a refractive index between a refractive index of the n-side cladding layer and an average refractive index of the periodic structure of the diffraction grating portion of the first n-side nitride semiconductor layer.

(Item 9)

The semiconductor laser element according to item 8, wherein,

The nitride semiconductor laminate has a fourth n-side nitride semiconductor layer disposed between the second n-side nitride semiconductor layer and the first n-side nitride semiconductor layer,

The refractive index of the fourth n-side nitride semiconductor layer is lower than the refractive index of the second n-side nitride semiconductor layer, and is higher than the average refractive index of the periodic structure of the diffraction grating portion of the first n-side nitride semiconductor layer.

(Item 10)

A semiconductor laser device is provided with:

A nitride semiconductor laminate having a first end face, a second end face, and an optical waveguide connecting the first end face and the second end face;

a first p-electrode, and

A second p-electrode is provided for the purpose of forming a second p-electrode,

The nitride semiconductor laminate has:

a first n-side nitride semiconductor layer;

a second n-side nitride semiconductor layer disposed above the first n-side nitride semiconductor layer;

An active layer having one or more well layers and one or more barrier layers arranged above the second n-side nitride semiconductor layer, and

A p-side nitride semiconductor layer disposed above the active layer,

The first n-side nitride semiconductor layer has a diffraction grating portion provided with a periodic structure whose refractive index varies periodically along the resonance direction of the optical waveguide, and a non-diffraction grating portion which is located between the diffraction grating portion and the first end face and is not provided with the periodic structure,

The first p-electrode has a first conductive oxide film provided on the upper surface of the p-side nitride semiconductor layer and above the diffraction grating portion, and a first metal film provided above the first conductive oxide film,

The second p-electrode includes a second conductive oxide film provided on the upper surface of the p-side nitride semiconductor layer and above the non-diffraction grating portion, the second conductive oxide film being separated from the first conductive oxide film, and a second metal film provided above the second conductive oxide film,

One or both of the first end face side end portion of the first conductive oxide film and the second end face side end portion of the second conductive oxide film are located between the first metal film and the second metal film in a plan view.

Description of the reference numerals

10. Optical waveguide

20. Nitride semiconductor laminate

20A first end face

20B second end face

20C ridge

30N side nitride semiconductor layer

31. First n-side nitride semiconductor layer

31A first semiconductor portion

31B second semiconductor portion

311. Diffraction grating part

312. Non-diffraction grating part

32. Second n-side nitride semiconductor layer

33. Third n-side nitride semiconductor layer

34. Fourth n-side nitride semiconductor layer

35. Fifth n-side nitride semiconductor layer

40. Active layer

41. Well layer

42. Barrier layer

50 P-side nitride semiconductor layer

511. First contact layer

512. Second contact layer

60. Substrate board

71. First protective film

72. Second protective film

73. Insulating film

81N electrode

82P electrode

821. First p-electrode

822. Second p-electrode

823. First conductive oxide film

824. First metal film

825. Second conductive oxide film

826. Second metal film

100. A semiconductor laser device.

Claims (9)

Translated fromChinese

1.一种半导体激光元件，具备氮化物半导体层叠体，所述氮化物半导体层叠体具有第一端面、第二端面、以及将所述第一端面与所述第二端面连接的光导波路，1. A semiconductor laser element comprising a nitride semiconductor stack, wherein the nitride semiconductor stack has a first end face, a second end face, and an optical waveguide connecting the first end face and the second end face,所述氮化物半导体层叠体具有：The nitride semiconductor stack has:第一n侧氮化物半导体层；a first n-side nitride semiconductor layer;第二n侧氮化物半导体层，其配置于所述第一n侧氮化物半导体层的上方；a second n-side nitride semiconductor layer disposed above the first n-side nitride semiconductor layer;有源层，其具有在所述第二n侧氮化物半导体层的上方配置的一个以上的阱层及一个以上的势垒层；以及an active layer having one or more well layers and one or more barrier layers arranged above the second n-side nitride semiconductor layer; andp侧氮化物半导体层，其配置于所述有源层的上方，a p-side nitride semiconductor layer disposed above the active layer,所述第一n侧氮化物半导体层具有：衍射光栅部，其设有折射率沿着所述光导波路的谐振方向周期性地变化的周期结构；以及非衍射光栅部，其位于所述衍射光栅部与所述第一端面之间，且未设置所述周期结构，The first n-side nitride semiconductor layer has: a diffraction grating portion having a periodic structure in which a refractive index periodically changes along a resonance direction of the optical waveguide; and a non-diffraction grating portion located between the diffraction grating portion and the first end face and not having the periodic structure.所述有源层具有：n侧阱层，其位于所述一个以上的阱层中的最靠近所述第二n侧氮化物半导体层的位置；以及n侧势垒层，其位于所述一个以上的势垒层中的所述n侧阱层与所述第二n侧氮化物半导体层之间，The active layer comprises: an n-side well layer located at a position closest to the second n-side nitride semiconductor layer among the one or more well layers; and an n-side barrier layer located between the n-side well layer among the one or more barrier layers and the second n-side nitride semiconductor layer,所述第二n侧氮化物半导体层是具有In和Ga的氮化物半导体层，The second n-side nitride semiconductor layer is a nitride semiconductor layer containing In and Ga,所述第二n侧氮化物半导体层的厚度比所述n侧势垒层的厚度大。The thickness of the second n-side nitride semiconductor layer is greater than the thickness of the n-side barrier layer.2.根据权利要求1所述的半导体激光元件，其中，2. The semiconductor laser element according to claim 1, wherein所述衍射光栅部的沿着谐振方向的长度比所述非衍射光栅部的沿着谐振方向的长度小。The length of the diffraction grating portion along the resonance direction is smaller than the length of the non-diffraction grating portion along the resonance direction.3.根据权利要求1或2所述的半导体激光元件，其中，具备：3. The semiconductor laser element according to claim 1 or 2, comprising:第一p电极，其设于所述p侧氮化物半导体层的上表面且所述衍射光栅部的上方；以及A first p-electrode provided on an upper surface of the p-side nitride semiconductor layer and above the diffraction grating portion; and第二p电极，其设于所述p侧氮化物半导体层的上表面且在所述非衍射光栅部的上方远离所述第一p电极的位置。A second p-electrode is provided on the upper surface of the p-side nitride semiconductor layer and above the non-diffraction grating portion at a position away from the first p-electrode.4.根据权利要求3所述的半导体激光元件，其中，4. The semiconductor laser element according to claim 3, wherein所述第一p电极具有：第一导电性氧化物膜，其设于所述p侧氮化物半导体层的上表面；以及第一金属膜，其配置于所述第一导电性氧化物膜的上方，The first p-electrode includes: a first conductive oxide film provided on the upper surface of the p-side nitride semiconductor layer; and a first metal film disposed above the first conductive oxide film.所述第二p电极具有：第二导电性氧化物膜，其设于所述p侧氮化物半导体层的上表面；以及第二金属膜，其配置于所述第二导电性氧化物膜的上方，The second p-electrode includes: a second conductive oxide film provided on the upper surface of the p-side nitride semiconductor layer; and a second metal film disposed above the second conductive oxide film.在俯视时，所述第一导电性氧化物膜的第一端面侧的端部及所述第二导电性氧化物膜的第二端面侧的端部中的一方或双方位于所述第一金属膜的第一端面侧的端部与所述第二金属膜的第二端面侧的端部之间。In a plan view, one or both of an end of the first conductive oxide film on the first end surface side and an end of the second conductive oxide film on the second end surface side are located between an end of the first metal film on the first end surface side and an end of the second metal film on the second end surface side.5.根据权利要求1至4中任一项所述的半导体激光元件，其中，5. The semiconductor laser element according to any one of claims 1 to 4, wherein所述第二n侧氮化物半导体层的折射率比所述第一n侧氮化物半导体层的所述衍射光栅部的所述周期结构的平均折射率高，The refractive index of the second n-side nitride semiconductor layer is higher than the average refractive index of the periodic structure of the diffraction grating portion of the first n-side nitride semiconductor layer,所述第二n侧氮化物半导体层的厚度比所述第一n侧氮化物半导体层的所述衍射光栅部的所述周期结构的厚度大。The thickness of the second n-side nitride semiconductor layer is greater than the thickness of the periodic structure of the diffraction grating portion of the first n-side nitride semiconductor layer.6.根据权利要求1至5中任一项所述的半导体激光元件，其中，6. The semiconductor laser element according to any one of claims 1 to 5, wherein:从所述第一n侧氮化物半导体层到所述阱层的距离大于300nm。A distance from the first n-side nitride semiconductor layer to the well layer is greater than 300 nm.7.根据权利要求1至6中任一项所述的半导体激光元件，其中，7. The semiconductor laser element according to any one of claims 1 to 6, wherein:所述第一n侧氮化物半导体层具有由包含Ga的氮化物半导体构成的多个第一部分、以及由包含In和Ga的氮化物半导体构成的多个第二部分，The first n-side nitride semiconductor layer has a plurality of first portions composed of a nitride semiconductor containing Ga, and a plurality of second portions composed of a nitride semiconductor containing In and Ga.所述衍射光栅部的所述周期结构通过所述多个第一部分和所述多个第二部分沿着所述谐振方向交替地配置而构成。The periodic structure of the diffraction grating portion is formed by alternately arranging the plurality of first portions and the plurality of second portions along the resonance direction.8.根据权利要求1至7中任一项所述的半导体激光元件，其中，8. The semiconductor laser device according to any one of claims 1 to 7, wherein:所述氮化物半导体层叠体具有：The nitride semiconductor stack has:n侧包覆层，其配置在所述第一n侧氮化物半导体层的与所述有源层相反的一侧；以及An n-side cladding layer is disposed on a side of the first n-side nitride semiconductor layer opposite to the active layer; and第三n侧氮化物半导体层，其配置在所述n侧包覆层与所述第一n侧氮化物半导体层之间，具有所述n侧包覆层的折射率与所述第一n侧氮化物半导体层的所述衍射光栅部的所述周期结构的平均折射率之间的折射率。A third n-side nitride semiconductor layer is arranged between the n-side cladding layer and the first n-side nitride semiconductor layer, and has a refractive index between the refractive index of the n-side cladding layer and the average refractive index of the periodic structure of the diffraction grating portion of the first n-side nitride semiconductor layer.9.根据权利要求8所述的半导体激光元件，其中，9. The semiconductor laser element according to claim 8, wherein所述氮化物半导体层叠体具有在所述第二n侧氮化物半导体层与所述第一n侧氮化物半导体层之间配置的第四n侧氮化物半导体层，The nitride semiconductor stack includes a fourth n-side nitride semiconductor layer disposed between the second n-side nitride semiconductor layer and the first n-side nitride semiconductor layer.所述第四n侧氮化物半导体层的折射率比所述第二n侧氮化物半导体层的折射率低，并且，比所述第一n侧氮化物半导体层的所述衍射光栅部的所述周期结构的平均折射率高。The refractive index of the fourth n-side nitride semiconductor layer is lower than the refractive index of the second n-side nitride semiconductor layer, and is higher than the average refractive index of the periodic structure of the diffraction grating portion of the first n-side nitride semiconductor layer.