Semiconductor laser element

Abstract

Provided is a semiconductor laser element capable of reducing carrier loss. The semiconductor laser element has, in order upward, an n-side semiconductor layer, an active layer, and a p-side semiconductor layer each comprising a nitride semiconductor, the p-side semiconductor layer having a non-doped first portion, an electron barrier layer containing a p-type impurity, and a second portion having one or more p-type semiconductor layers containing a p-type impurity. The first portion has: a first p-side composition inclined layer comprising InxGa1-xN, the In composition ratio x decreasing in a range of 0 or more and less than 1 as the first p-side composition inclined layer faces upward; a second p-side composition inclined layer that is disposed between the first p-side composition inclined layer and the electron barrier layer, is composed of AlyGa1-yN, and increases in an Al composition ratio y in a range of more than 0 and less than 1 as the second p-side composition inclined layer faces upward; and an intermediate layer that is disposed between the first p-side compositional tilt layer and the second p-side compositional tilt layer, is composed of AlzGa1-zN, and has an Al composition ratio z of more than 0 and less than y.

Description

Technical Field

[0001] The present disclosure relates to a semiconductor laser element. Background Art

[0002] Patent Document 1 describes a semiconductor laser element including an undoped p-side composition gradient layer and an undoped p-side intermediate layer between an active layer and an electron barrier layer.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: (Japanese) Patent Publication No. 2020-115539 Summary of the invention

[0006] Technical problem to be solved by the invention

[0007] An object of one embodiment of a semiconductor laser device disclosed herein is to obtain a semiconductor laser device capable of reducing carrier loss.

[0008] Technical solutions for solving technical problems

[0009] In one embodiment of a semiconductor laser element disclosed herein, the semiconductor laser element has an n-side semiconductor layer, an active layer, and a p-side semiconductor layer, each of which is composed of a nitride semiconductor, in order upward, wherein the p-side semiconductor layer has, in order upward, a non-doped first portion, which has one or more semiconductor layers; an electron barrier layer, whose band gap energy is larger than that of the first portion, and contains p-type impurities; a second portion, which has one or more p-type semiconductor layers containing p-type impurities, wherein the first portion has: a first p-side composition inclined layer, which is composed of In x Ga 1-x N, and the In composition ratio x decreases in the range of greater than 0 and less than 1 as it goes upward; a second p-side composition inclined layer is arranged between the first p-side composition inclined layer and the electron barrier layer, and is composed of Al y Ga 1-y N, the Al composition ratio y increases in the range of more than 0 and less than 1 as it goes upward; the intermediate layer is arranged between the first p-side composition gradient layer and the second p-side composition gradient layer, and is composed of Al z Ga 1-z N composition, and the Al composition ratio z exceeds 0 and is less than y.

[0010] Effects of the Invention

[0011] A semiconductor laser element capable of reducing carrier loss can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic cross-sectional view of a semiconductor laser element according to one embodiment of the present invention.

[0013] Figure 2 It is schematically indicated Figure 1 FIG. 1 is a diagram showing an example of a layer structure of a p-side semiconductor layer of a semiconductor laser element.

[0014] Figure 3 It is schematically indicated Figure 1 FIG. 1 is a diagram showing an example of the layer structure of the n-side semiconductor layer of a semiconductor laser element.

[0015] Figure 4 This is a diagram schematically showing another example of the layer structure of the active layer.

[0016] Figure 5 yes Figure 1 A local enlarged view of the first p-side component tilted layer and its vicinity of the semiconductor laser element.

[0017] Figure 6 yes Figure 1 A partial enlarged view of the second p-side component tilted layer and its vicinity of the semiconductor laser element.

[0018] Figure 7 These are the results of SIMS analysis of a wafer on which the same p-side semiconductor layer as in Example 1 was grown.

[0019] Figure 8 Graphs showing I-L characteristics of semiconductor laser elements of Example 1 and Comparative Example 1.

[0020] Fig. 9 Graphs showing I-L characteristics of semiconductor laser elements of Example 2, Example 3, and Comparative Example 2. DETAILED DESCRIPTION

[0021] Hereinafter, the embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments shown below are examples of methods for concretizing the technical ideas of the present invention, and do not specify the present invention as the following embodiments. In addition, in the following description, the same names and reference numerals represent the same or equivalent parts, and detailed description is appropriately omitted.

[0022] Figure 1 1 is a schematic cross-sectional view of the semiconductor laser element 100 according to the present embodiment, and shows a cross section of the semiconductor laser element 100 in a direction perpendicular to the cavity direction. Figure 2 Schematically shows an example of the layer structure of the p-side semiconductor layer 4 of the semiconductor laser element 100. Figure 2 , the relationship between the band gap energies of the various layers is schematically shown. Figure 2The dashed line in is a line indicating the position of the bottom surface of the ridge 4a. The bottom surface of the ridge 4a refers to a surface connecting the lowermost sides of both side surfaces of the ridge 4a.

[0023] like Figure 1 As shown in FIG. 1 , the semiconductor laser element 100 has an n-side semiconductor layer 2, an active layer 3, and a p-side semiconductor layer 4, each of which is made of a nitride semiconductor, in this order. In this specification, the direction from the n-side semiconductor layer 2 toward the p-side semiconductor layer 4 is referred to as up or above, and the opposite direction is referred to as down or below. Such up and down directions may not coincide with the direction of gravity when the semiconductor laser element 100 is used.

[0024] The p-side semiconductor layer 4 has a first portion 41, an electron barrier layer 42, and a second portion 43 in order toward the top. The first portion 41 has one or more semiconductor layers. The first portion 41 is undoped. The electron barrier layer 42 has a band gap energy greater than that of the first portion 41 and contains p-type impurities. The second portion 43 has one or more p-type semiconductor layers containing p-type impurities. It should be noted that in this specification, undoped means not intentionally doped. In the analysis results of secondary ion mass spectrometry (SIMS) and the like, a concentration that does not exceed the detection limit can be referred to as undoped. Alternatively, an impurity concentration less than 1×10 17 / cm 3 For example, the first portion 41 can be considered as non-doped when the concentration of p-type impurities and n-type impurities is below the detection limit. However, if the first portion 41 is in contact with the electron barrier layer 42 with a high p-type impurity concentration, even if the first portion 41 is not intentionally doped with p-type impurities, p-type impurities may be detected in the analysis results. In this case, the concentration of the detected p-type impurities is preferably less than 1×10 18 / cm 3. In addition, in the case where the first part 41 and the like are formed by non-doping, unintentional impurities such as H and C are sometimes contained, but in this case it can also be called non-doping. In addition, in this specification, the thickness of a certain layer or a certain part refers to the shortest distance from the lower surface to the upper surface of the layer or the part. In the case where the lower surface and / or the upper surface have local recesses and / or protrusions such as V-shaped pits, the shortest distance between the flat parts of the lower surface and / or the upper surface without such recesses and / or protrusions can be used as the thickness of the layer or the part. In addition, the distance from a certain layer to other layers refers to the shortest distance from a certain layer to other layers. In the case where the lower surface and / or the upper surface of these layers have local recesses and / or protrusions such as V-shaped pits, the shortest distance between the flat parts of the lower surface and / or the upper surface without such recesses and / or protrusions can be used as the distance between these layers. The magnitude relationship of the band gap energy can be judged based on the composition of the semiconductor of the comparison object. For example, when two layers of comparison object are both composed of AlGaN, the layer having a relatively large Al composition ratio is determined to be a layer having a relatively large band gap energy.

[0025] The first portion 41 includes a first p-side composition gradient layer 411, a second p-side composition gradient layer 412 disposed between the first p-side composition gradient layer 411 and the electron barrier layer 42, and an intermediate layer 413 disposed between the first p-side composition gradient layer 411 and the second p-side composition gradient layer 412. The first p-side composition gradient layer 411 is composed of In x Ga 1-x N, and the In composition ratio x decreases upward within a range of 0 to less than 1. The second p-side composition gradient layer 412 is composed of Al y Ga 1-y N, and the Al composition ratio y increases upward within a range of more than 0 and less than 1. The intermediate layer 413 (first intermediate layer) is composed of Al z Ga 1-z N composition, and the Al composition ratio z exceeds 0 and is less than y.

[0026] By providing the second p-side composition tilted layer 412, the band gap energy can be gradually changed toward the electron barrier layer 42, and the influence of the band peak generated at the heterogeneous interface with a band gap energy difference can be reduced. The influence of the band peak means that electrons are generated in the band peak and holes are relatively reduced, and the loss of carriers increases. x Ga 1-x N, and the second p-side gradient layer 412 is composed of Al y Ga 1-yN composition. Therefore, when growing these layers, the raw material gas is switched in the middle. By growing the intermediate layer 413 between these layers, the raw material gas after switching can be stabilized, and the second p-side composition gradient layer 412 can be well formed. These layers can be formed by, for example, metal organic chemical vapor deposition (MOCVD) method. By well forming the second p-side composition gradient layer 412, the influence of the energy band peak in the p-side semiconductor layer 4 can be reduced, and the loss of carriers can be reduced.

[0027] (Semiconductor laser element 100)

[0028] like Figure 1 As shown, the semiconductor laser element 100 includes a substrate 1, an n-side semiconductor layer 2, an active layer 3, and a p-side semiconductor layer 4 provided on the substrate 1. The semiconductor laser element 100 is an end-emitting laser element having a light emitting end face and a light reflecting end face intersecting the main surface of the semiconductor layer such as the active layer 3.

[0029] For example, a ridge 4a protruding upward is provided on the p-side semiconductor layer 4. The ridge 4a is a table structure. The top view shape of the ridge 4a is a shape that is long in the direction connecting the light emitting end face and the light reflecting end face, for example, a rectangle with a short side in a direction parallel to the light reflecting end face and a long side in a direction perpendicular to the light reflecting end face. The portion directly below the ridge 4a in the active layer 3 and its vicinity are the optical waveguide region. An insulating film 5 can be provided on the side surface of the ridge 4a and on the surface of the p-side semiconductor layer 4 continuous from the side surface of the ridge 4a. The substrate 1 is composed of, for example, an n-type semiconductor, and an n-electrode 8 is provided on its lower surface. In addition, a p-electrode 6 is provided in contact with the upper surface of the ridge 4a, and a p-side pad electrode 7 is provided thereon.

[0030] The semiconductor laser element 100 can oscillate visible light laser, for example. The semiconductor laser element 100 can oscillate blue or green laser, for example. The peak wavelength of the laser oscillated by the semiconductor laser element 100 is, for example, 400 nm or more and 600 nm or more, 420 nm or more and 580 nm or more, or 500 nm or more and 580 nm or less. As the wavelength of the laser oscillated by the semiconductor laser element 100 becomes longer, the leakage light from the optical waveguide layer to the outside increases due to the influence of the wavelength dispersion of the refractive index. As a result, the threshold current rises, and the current density during laser oscillation increases. Moreover, the greater the current density, the greater the effective transition interval is through the shielding of the local energy level and the band filling, and the oscillation wavelength shifts to a shorter wavelength. By providing the first p-side composition tilted layer 411, the laser oscillation threshold current density can be reduced, and the effect of suppressing the short wavelength shift can be expected. Therefore, the peak wavelength of the laser oscillated by the semiconductor laser element 100 is preferably 500 nm or more, and can also be 500 nm or more and 580 nm or less.

[0031] (Substrate 1)

[0032] The substrate 1 can use a nitride semiconductor substrate composed of, for example, GaN. As the n-side semiconductor layer 2, active layer 3, and p-side semiconductor layer 4 grown on the substrate 1, for example, semiconductors grown substantially in the c-axis direction can be cited. For example, a GaN substrate with a +c plane ((0001) plane) as the main plane can be used, and each semiconductor layer can be grown on its +c plane. Here, the +c plane as the main plane can include a plane with an offset angle within ±1 degree. By using a substrate with a +c plane as the main plane, the advantage of excellent mass productivity can be obtained.

[0033] (n-side semiconductor layer 2)

[0034] The n-side semiconductor layer 2 may be a multilayer structure composed of nitride semiconductors such as GaN, InGaN, and AlGaN. The n-side semiconductor layer 2 includes one or more n-type semiconductor layers. As the n-type semiconductor layer, a layer composed of a nitride semiconductor containing n-type impurities such as Si and Ge can be cited. The n-side semiconductor layer 2 may have an n-side cladding layer and an n-side photoconductive layer, and may also include layers other than these. The band gap energy of the n-side cladding layer is larger than the band gap energy of the n-side photoconductive layer. Although not a p-type impurity, the n-type impurity also becomes the main cause of light absorption, so the n-side photoconductive layer is preferably undoped or, when containing n-type impurities, has an n-type impurity concentration lower than the n-type impurity concentration of the n-side cladding layer.

[0035] Figure 3 An example of the layer structure of the n-side semiconductor layer 2 is shown. Figure 31 is a diagram schematically showing an example of the layer structure of the n-side semiconductor layer 2 of the semiconductor laser element 100. The n-side semiconductor layer 2 can include an n-side composition gradient layer 21 disposed in contact with the lower surface of the active layer 3, an n-type semiconductor layer 22 disposed below the n-side composition gradient layer 21, and an n-side intermediate portion 23 disposed between the n-side composition gradient layer 21 and the n-type semiconductor layer 22. The n-side composition gradient layer 21 changes the composition so that the band gap energy increases as it goes downward. The n-type semiconductor layer 22 contains n-type impurities and has a band gap energy greater than the band gap energy of any layer constituting the first portion 41 of the p-side semiconductor layer 4. The distance from the n-side composition gradient layer 21 to the n-type semiconductor layer 22 is preferably greater than the distance from the first p-side composition gradient layer 411 to the electron barrier layer 42. As a result, the electric field intensity distribution in the semiconductor laser element 100 can be biased toward the n-side semiconductor layer 2 side, so that the loss caused by light absorption in the electron barrier layer 42 containing p-type impurities and the layer above it can be reduced. The n-side semiconductor layer 2 may include layers other than these.

[0036] The band gap energy of the n-side composition tilted layer 21 decreases as it approaches the active layer 3. The refractive index of the n-side composition tilted layer 21 increases as it approaches the active layer 3. Thus, it is possible to strengthen the light confinement to the active layer 3. The n-side composition tilted layer 21 is, for example, an n-side optical guide layer. The n-side composition tilted layer 21 can be, for example, In a Ga 1-a N, and a layer in which the In composition ratio a increases in the range of greater than 0 and less than 1 as it goes upward. As a criterion for determining the size relationship between the band gap energy and impurity concentration of the composition tilted layer and other layers, the average value of the composition tilted layer can be used. The average value of the composition tilted layer refers to the value obtained by dividing the total value of the product of the band gap energy, etc. and the thickness of each sublayer constituting the composition tilted layer by the total thickness. In the case where the n-side composition tilted layer 21 is a composition tilted layer whose lattice constant increases as it is closer to the active layer 3, it is preferred to add n-type impurities to the composition tilted layer. In other words, it can also be said that the composition tilted layer is composed of a plurality of sublayers with gradually different compositions. Therefore, in the composition tilted layer, even if the composition change rate is reduced, it is difficult to avoid the generation of fixed charges. If n-type impurities are added, the fixed charges can be shielded, and thus the degree of voltage rise caused by the generation of fixed charges can be reduced.

[0037] The n-type semiconductor layer 22 is, for example, an n-type AlGaN layer. The n-type semiconductor layer 22 is, for example, an n-side cladding layer. The n-type semiconductor layer 22 and the n-side intermediate portion 23 may be in contact with each other, or another layer may be disposed between the n-type semiconductor layer 22 and the n-side intermediate portion 23. The distance from the n-side composition inclined layer 21 to the n-type semiconductor layer 22 may be less than 600 nm, or may be less than 400 nm.

[0038] The n-side intermediate portion 23 is a layer having a band gap energy smaller than that of the n-type semiconductor layer 22. The n-type impurity concentration of the n-side intermediate portion 23 may be smaller than that of the n-type semiconductor layer 22. The n-side intermediate portion 23 is, for example, an n-type GaN layer containing n-type impurities.

[0039] The n-side intermediate portion 23 may also include a composition gradient layer 232 whose band gap energy decreases as it approaches the active layer 3. In the composition gradient layer, the band gap energy at its lower end is smaller than the band gap energy of the n-type semiconductor layer 22, and the band gap energy at its upper end is the same as or larger than the band gap energy at the lower end of the n-side composition gradient layer 21. The n-side intermediate portion 23 may include a composition gradient layer 232 and an intermediate layer 233 in order from the n-side composition gradient layer 21 side. The n-side intermediate portion 23 may include an intermediate layer 231, a composition gradient layer 232, and an intermediate layer 233 in order from the n-side composition gradient layer 21 side. The intermediate layer 231 and the intermediate layer 233 are not composition gradient layers, or are composition gradient layers having a composition change rate smaller than that of the composition gradient layer 232. The composition gradient layer 232 is preferably doped with n-type impurities in the same manner as the n-side composition gradient layer 21. Thus, the degree of voltage rise caused by the generation of fixed charges can be reduced. The intermediate layer 231 and the intermediate layer 233 may be undoped, but may contain, for example, n-type impurities. The thickness of the n-side intermediate portion 23 may be greater than 100 nm. Thus, light leakage to the n-type semiconductor layer 22 can be reduced. The thickness of the n-side intermediate portion 23 may be less than 400 nm. Thus, light confinement to the active layer 3 can be improved.

[0040] (Active layer 3)

[0041] The active layer 3 may be a multilayer structure composed of nitride semiconductor layers such as GaN and InGaN. The active layer 3 has a single quantum well structure or a multi-quantum well structure. For example, the active layer 3 has an n-side barrier layer 31, a well layer 32, and a p-side barrier layer 33 in order from the n-side semiconductor layer 2. When the active layer 3 is a multi-quantum well structure, it has a plurality of well layers 32 and an intermediate barrier layer sandwiched by the well layers 32.

[0042] The distance from the well layer 32 closest to the n-side semiconductor layer 2 to the lower surface of the active layer 3 can be set to, for example, 10 nm or less. The distance from the well layer 32 closest to the n-side semiconductor layer 2 to the lower surface of the active layer 3 can also be 0 nm, that is, the lower surface of the well layer 32 is the lower surface of the active layer 3. In the case where the n-side semiconductor layer 2 has an n-side composition tilted layer 21, it is preferred that a layer having a band gap energy greater than the band gap energy of the upper end of the n-side composition tilted layer 21 is configured as at least a part of the n-side barrier layer 31. Thereby, the probability of light recombination in the well layer 32 can be increased. The n-side barrier layer 31 is configured between the well layer 32 closest to the n-side semiconductor layer 2 and the n-side composition tilted layer 21. The distance from the well layer 32 closest to the n-side semiconductor layer 2 to the lower surface of the active layer 3 can be greater than 1 nm, or greater than 1 nm and less than 10 nm.

[0043] The distance from the well layer 32 closest to the p-side semiconductor layer 4 to the upper surface of the active layer 3 can be set to, for example, less than 5 nm. As at least a part of the p-side barrier layer 33, it is preferred to configure a layer having a band gap energy greater than the band gap energy of the lower end of the first p-side composition inclined layer 411. Thus, the probability of light recombination in the well layer 32 can be increased. The p-side barrier layer 33 is arranged between the well layer 32 closest to the p-side semiconductor layer 4 and the p-side semiconductor layer 4. The distance from the well layer 32 closest to the p-side semiconductor layer 4 to the upper surface of the active layer 3 can be greater than 1 nm, or greater than 1 nm and less than 5 nm. The active layer 3 is preferably formed without adding p-type impurities. Thus, light absorption losses caused by the addition of p-type impurities can be suppressed. Each layer of the active layer 3 is, for example, a non-doped layer.

[0044] The well layer 32 is, for example, In x Ga 1-x N well layer. In when used as a semiconductor laser element with an oscillation wavelength of 500 nm or more x Ga 1-x The In composition ratio x of the N well layer increases or decreases depending on the layer structure other than the active layer 3, and is, for example, 0.23 or more. The upper limit of the In composition ratio x of the well layer 32 is, for example, 0.50 or less. In this case, the oscillation wavelength of the semiconductor laser element is considered to be about 600 nm or less.

[0045] Figure 4 Another example of the active layer is shown. Figure 4 This is a diagram schematically showing another example of the layer structure of the active layer. Figure 4The active layer 3A shown has an n-side barrier layer 31, a plurality of well layers 32, an intermediate barrier layer 34 and a p-side barrier layer 33. The plurality of well layers 32 are located between the n-side barrier layer 31 and the p-side barrier layer 33. The plurality of well layers 32 include a first well layer and a second well layer. The first well layer and the second well layer are located between the n-side barrier layer 31 and the p-side barrier layer 33. The intermediate barrier layer 34 is a layer sandwiched between the two well layers 32. The intermediate barrier layer 34 is located between the first well layer and the second well layer. The number of well layers 32 is multiple, for example, two. The band gap energy of the n-side barrier layer 31, the intermediate barrier layer 34 and the p-side barrier layer 33 is larger than the band gap energy of the well layer 32. The thickness of the plurality of well layers 32 can be, for example, greater than 1 nm and less than 4 nm. The thickness of the plurality of well layers 32 can be the same.

[0046] It is observed that the smaller the thickness of the intermediate barrier layer 34 is, the lower the driving voltage of the semiconductor laser element 100 tends to be. On the other hand, as for the p-side barrier layer 33, as the base layer before laminating the p-side semiconductor layer 4, in order to restore the crystallinity, it is preferred to have a certain degree of thickness. Therefore, the thickness of the intermediate barrier layer 34 is preferably less than the thickness of the p-side barrier layer 33. Thus, it is possible to take into account both the reduction in the driving voltage of the semiconductor laser element 100 and the improvement in the crystallinity of the p-side semiconductor layer 4. Crystallinity can be evaluated, for example, by dislocation density. It should be noted that the thickness of each layer refers to the thickness in the lamination direction. The intermediate barrier layer 34 is, for example, an undoped GaN layer. The thickness of the intermediate barrier layer 34 is preferably less than 3nm, and more preferably less than 2.5nm. Thus, the injection efficiency of electrons into the well layer 32 can be improved. The thickness of the intermediate barrier layer 34 can be more than 1nm, preferably more than 1.5nm, and more preferably more than 2nm. By making the thickness of the intermediate barrier layer 34 greater than or equal to 1.5 nm, it is possible to suppress a decrease in the carrier confinement efficiency, and it is possible to suppress a decrease in the output of the semiconductor laser element 100. The thickness of the intermediate barrier layer 34 can be set to be greater than or equal to 1 nm and less than or equal to 3 nm, preferably greater than or equal to 1.5 nm and less than or equal to 3 nm, and more preferably greater than or equal to 1.5 nm and less than or equal to 2.5 nm. The thickness of the intermediate barrier layer 34 can be greater than or equal to 2 nm and less than or equal to 2.5 nm.

[0047] The thickness of the p-side barrier layer 33 may also be greater than the thickness of one well layer 32. The thickness of the p-side barrier layer 33 is preferably greater than 2.5 nm. Thus, the crystallinity of the p-side semiconductor layer 4 can be more effectively improved. It is observed that when the thickness of the p-side barrier layer 33 increases to a certain extent, the driving voltage of the semiconductor laser element 100 increases. The thickness of the p-side barrier layer 33 is preferably less than 7 nm. Thus, the increase in the driving voltage of the semiconductor laser element 100 can be suppressed. The thickness of the p-side barrier layer 33 is preferably greater than 2.5 nm and less than 7 nm. The thickness of the p-side barrier layer 33 may be greater than 2.5 nm. The thickness of the p-side barrier layer 33 may be greater than 2.5 nm and less than 7 nm. The p-side barrier layer 33 is preferably a GaN layer, and more preferably a non-doped GaN layer. Thus, the crystallinity of the p-side semiconductor layer 4 can be more effectively improved.

[0048] The semiconductor laser element 100 having the active layer 3A may also be a semiconductor laser element 100 that has, in order upward, an n-side semiconductor layer 2, an active layer 3, and a p-side semiconductor layer 4 each made of a nitride semiconductor, wherein the active layer 3A has an n-side barrier layer 31, a p-side barrier layer 33, a plurality of well layers 32 including a first well layer and a second well layer located between the n-side barrier layer 31 and the p-side barrier layer 33, and an intermediate barrier layer 34 located between the first well layer and the second well layer, wherein the thickness of the intermediate barrier layer 34 may be smaller than that of the p-side barrier layer 33. In this case, the p-side semiconductor layer 4 may have, in order upward, a non-doped first portion 41 having one or more semiconductor layers; an electron barrier layer 42 having a larger band gap energy than the first portion 41 and containing a p-type impurity; and a second portion 43 having one or more p-type semiconductor layers containing a p-type impurity. In this case, the p-side semiconductor layer 4 may also have a first p-side composition gradient layer 411. In this case, the p-side semiconductor layer 4 may not include the second p-side composition gradient layer 412 and the intermediate layer 413 .

[0049] (p-side semiconductor layer 4)

[0050] The p-side semiconductor layer 4 can be a multilayer structure composed of nitride semiconductors such as GaN, InGaN, and AlGaN. The p-side semiconductor layer 4 can have a p-side cladding layer and a p-side photoconductive layer, and can also include layers other than these. In the case of providing a transparent conductive film as the p-electrode 6, it can function as a cladding layer, so the cladding layer may not be provided in the p-side semiconductor layer 4. The p-side semiconductor layer 4 includes one or more p-type semiconductor layers. As the p-type semiconductor layer, a layer composed of a nitride semiconductor containing p-type impurities such as Mg can be cited. Since the activation rate of p-type impurities is lower than that of n-type impurities such as Si, in order to obtain sufficient hole injection in the p-type semiconductor layer, it is necessary to dope the p-type impurities at a higher concentration, and the free carrier absorption loss caused by the p-type impurities increases.

[0051] (Part 1 41)

[0052] The first portion 41 is a portion of the p-side semiconductor layer 4 that connects the active layer 3 to the p-type impurity containing layer. The first portion 41 can be arranged in contact with the upper surface of the active layer 3. The first portion 41 is a portion that does not contain a p-type semiconductor layer. As long as the p-type impurity concentration and thickness do not affect the free carrier absorption loss, a layer containing p-type impurities can be included in a portion of the first portion 41. However, if Mg is doped for p-type conversion, 1×10 18 / cm 3 The p-type impurities above the above level, in this case, the possibility of increased free carrier absorption loss is high. Therefore, the first part 41 is preferably a part that does not contain a p-type semiconductor layer. It is preferred that the first part 41 has a p-type impurity concentration as low as the detection limit of the p-type impurity concentration based on SIMS and other analysis in its entirety. For example, the first part 41 is formed without intentionally adding p-type impurities in its entirety during manufacture. The first part 41 can be formed in a non-doped manner throughout its entirety. Since the thicker the thickness of the first part 41, the more it can reduce the leakage of light to the second part 43, the thickness of the first part 41 is preferably 400nm or more. The upper limit of the thickness of the first part 41 can be set to a degree that does not hinder the supply of holes from the second part 43. In addition, there is a tendency that the thicker the thickness of the first part 41, the more the overflowed electrons increase, so from this point of view, it can be said that the thinner the thickness of the first part 41, the lower the probability of electron overflow. From this point of view, the thickness of the first part 41 can be set to 660nm or less, for example. The band gap difference between the first portion 41 and the electron barrier layer 42 can reduce the probability of electron overflow. Therefore, the layer in the first portion 41 that is in contact with the electron barrier layer 42 preferably has a band gap energy smaller than that of the electron barrier layer 42 .

[0053] It should be noted that, when the first portion 41 is not an undoped portion but a low-concentration doped portion, it is preferable that the p-type impurity concentration of the entire portion is lower than the p-type impurity concentration of the electron barrier layer 42, and it is more preferable that the p-type impurity concentration is lower than the p-type impurity concentration of either the electron barrier layer 42 or the second portion 43. In addition, the n-type impurity concentration of the first portion 41 may be less than 2×10 18 / cm 3 Preferably, the first portion 41 has an n-type impurity concentration that is low enough that no n-type impurities are detected by SIMS analysis (ie, a background level). In other words, preferably, the first portion 41 does not substantially contain n-type impurities.

[0054] The lower end of the ridge 4a is preferably located in the first portion 41. This allows the lower end of the ridge 4a to be close to the active layer 3. For example, the ridge 4a is composed of a part of the first portion 41, the electron barrier layer 42, and the second portion 43.

[0055] (First p-side composition inclined layer 411)

[0056] The first p-side composition tilted layer 411 is a layer whose band gap energy increases as it goes upward. By having such a structure, light confinement to the active layer 3 can be strengthened. The first p-side composition tilted layer 411 can be in contact with the active layer 3. By configuring the first p-side composition tilted layer 411 near the active layer 3 in this way, the light confinement effect brought by the first p-side composition tilted layer 411 can be improved. The first p-side composition tilted layer 411 can be in contact with the second p-side composition tilted layer 412. The distance from the first p-side composition tilted layer 411 to the electron barrier layer can be more than 150nm. The distance from the first p-side composition tilted layer 411 to the electron barrier layer can be less than 600nm. By strengthening the light confinement to the active layer 3 using the first p-side composition tilted layer 411, the laser oscillation threshold current density can be reduced. As a result, the shielding of the local energy level can be suppressed, and the short wavelength shift of the oscillation wavelength accompanied by the increase of current injection can be suppressed, which is conducive to the long wavelength of the oscillation wavelength.

[0057] The first p-side composition gradient layer 411 has an upper surface and a lower surface, and its band gap energy increases from the lower surface toward the upper surface. The band gap energy of the lower surface side of the first p-side composition gradient layer 411 is smaller than the band gap energy of the upper surface side. Figure 2In the figure, the first p-side composition inclined layer 411 is represented as a slope, but as described later, it can be said that the composition inclined layer is an aggregate of multiple sublayers with different compositions. Therefore, it can be said that in the first p-side composition inclined layer 411, the band gap energy increases stepwise from the lower surface to the upper surface. An n-side composition inclined layer 21 that is paired with the first p-side composition inclined layer 411 can also be provided in the n-side semiconductor layer 2. For example, as a band gap energy structure, the first p-side composition inclined layer 411 and the n-side composition inclined portion can be formed symmetrically across the active layer 3.

[0058] The first p-side composition inclined layer 411 functions as a p-side photoconductive layer, for example. The thickness of the first p-side composition inclined layer 411 is thicker than the thickness of the well layer of the active layer 3, and in addition, when the p-side barrier layer 33 is present, it is thicker than the thickness of the p-side barrier layer 33. In order to improve the light confinement effect, the thickness of the first p-side composition inclined layer 411 is preferably greater than 100 nm. The thickness of the first p-side composition inclined layer 411 may be less than 500 nm. The thickness of the first p-side composition inclined layer 411 may be less than 200 nm. In the case of providing the p-side barrier layer 33, the band gap energy of the lower end of the first p-side composition inclined layer 411 is preferably less than the band gap energy of the p-side barrier layer 33. The band gap energy of the upper end of the first p-side composition inclined layer 411 may be equal to or greater than the band gap energy of the p-side barrier layer 33.

[0059] The first p-side composition inclined layer 411 is a structure in which the refractive index decreases from the active layer 3 side to the electron barrier layer 42 side and the band gap energy increases from the active layer 3 side to the electron barrier layer 42 side. As a result, light can be brought close to the active layer 3 and the overflow of electrons can be suppressed. The first p-side composition inclined layer 411 changes the composition at a first rate of change so that the band gap energy increases as it moves upward. The first rate of change is the rate of change of the band gap energy, which can be calculated based on the rate of change of the In composition ratio x. For example, the In content of the first p-side composition inclined layer 411 obtained by analysis such as SIMS can be plotted in a table, and its slope can be used as the rate of change of the In composition ratio x. The In content obtained by analysis can also be plotted in a table with a linear scale, and a linear approximate curve can be made based on the table, and the slope of the approximate curve can be used as the rate of change of the In composition ratio x.

[0060] like Figure 5 As shown, it can also be said that the first p-side composition gradient layer 411 is composed of a plurality of sub-layers 411 a , 411 b , 411 c , 411 y , and 411 z having different compositions. Figure 5 This is a partial enlarged view of the first p-side composition gradient layer 411 and its vicinity. In addition to these, there are multiple sub-layers between the sub-layer 411c and the sub-layer 411y. x Ga 1-xWhen N constitutes the first p-side composition gradient layer 411, the In composition ratio x of the lowermost sublayer 411a of the first p-side composition gradient layer 411 is a The In composition ratio x of the uppermost sublayer 411z is z The relationship is 0≤x z <x a The In composition ratio x of the sublayer 411a constituting the lower end of the first p-side composition gradient layer 411 is a The upper limit of is, for example, 0.25. If the suppression of crystallinity degradation is considered, the In composition ratio x a It is preferably 0.1 or less.

[0061] It is preferred that the difference in lattice constants between adjacent sublayers is small. Thus, deformation can be reduced. Therefore, it is preferred that the first p-side composition inclined layer 411 changes the composition little by little with a thinner thickness. Specifically, the first p-side composition inclined layer 411 preferably has a reduced In composition ratio x for every 25 nm or less thickness from the bottom surface to the top surface. That is, the thickness of each sublayer 411a, 411b, 411c, 411y, 411z is preferably 25 nm or less. The thickness of each sublayer 411a, 411b, 411c, 411y, 411z is more preferably 20 nm or less, and may be 10 nm or less, or 5 nm or less. The lower limit of the thickness of each sublayer 411a, 411b, 411c, 411y, 411z is, for example, about 1 atomic layer (about 0.25 nm). In addition, the difference in In composition ratio x between adjacent sublayers (e.g., sublayer 411a and sublayer 411b) is preferably 0.005 or less, and more preferably 0.001 or less. The lower limit of the difference in In composition ratio x between adjacent sublayers is, for example, about 0.00007. Such a range preferably covers the entire first p-side composition gradient layer 411. That is, all sublayers are preferably within such a range. In the first p-side composition gradient layer 411, the number of composition changes, that is, the number of sublayers of the first p-side composition gradient layer 411, is preferably 90 or more.

[0062] When the n-side composition gradient layer 21 is provided, the preferred ranges of its composition, composition change rate, and thickness can be the same as those of the first p-side composition gradient layer 411 .

[0063] (Second p-side composition inclined layer 412)

[0064] The second p-side composition inclined layer 412 is arranged between the first p-side composition inclined layer 411 and the electron barrier layer 42. The second p-side composition inclined layer 412 has an upper surface and a lower surface, and its band gap energy increases from the lower surface toward the upper surface. The band gap energy of the lower surface side of the second p-side composition inclined layer 412 is smaller than the band gap energy of the upper surface side. Similar to the first p-side composition inclined layer 411, it can be said that the composition inclined layer is an aggregate of a plurality of sublayers having different compositions, and therefore, in the second p-side composition inclined layer 412, it can be said that the band gap energy increases in a step-like manner from the lower surface to the upper surface.

[0065] The thickness of the second p-side composition inclined layer 412 may be greater than 2 nm. Thus, the energy band peak can be effectively reduced. The thickness of the second p-side composition inclined layer 412 may be greater than 10 nm, or may be greater than 50 nm. Thus, light leakage to the electron barrier layer 42 and the second portion 43 can be reduced, and light absorption loss can be reduced. The thickness of the second p-side composition inclined layer 412 may be thicker than the thickness of the well layer of the active layer 3. In the presence of the p-side barrier layer 33, the thickness of the second p-side composition inclined layer 412 may be thicker than the thickness of the p-side barrier layer 33. The thickness of the second p-side composition inclined layer 412 is preferably less than 250 nm, may be less than 200 nm, or may be less than 100 nm. The thickness of the second p-side composition inclined layer 412 may be greater than 2 nm and less than 250 nm, or may be greater than 10 nm and less than 250 nm.

[0066] The band gap energy of the lower end of the second p-side composition inclined layer 412 is greater than the band gap energy of the upper end of the first p-side composition inclined layer 411. The band gap energy of the upper end of the second p-side composition inclined layer 412 is less than the band gap energy of the electron barrier layer 42. The band gap energy of the upper end of the second p-side composition inclined layer 412 can be greater than the band gap energy of the layer constituting the lower end of the second part 43. The Al composition ratio y of the lower end of the second p-side composition inclined layer 412 is preferably greater than the Al composition ratio z of the intermediate layer 413 and is 0.05 or less. Thus, it is easy to stably form the second p-side composition inclined layer 412 composed of AlGaN. The Al composition ratio y of the upper end of the second p-side composition inclined layer 412 is preferably less than 0.1. Thus, it is easy to reduce the influence of the energy band spike.

[0067] The second p-side composition inclined layer 412 is a structure in which the refractive index decreases from the active layer 3 side to the electron barrier layer 42 side and the band gap energy increases from the active layer 3 side to the electron barrier layer 42 side. The second p-side composition inclined layer 412 changes the composition at a second rate of change that is smaller than the first rate of change so that the band gap energy increases as it moves upward. As a result, it is easy to reduce the influence of the energy band peak. The second rate of change can be obtained by the same method as the first rate of change. That is, the second rate of change is the rate of change of the band gap energy, which can be calculated based on the rate of change of the Al composition ratio y. The Al content of the second p-side composition inclined layer 412 obtained by analysis such as SIMS is plotted in a table, and its slope is used as the rate of change of the Al composition ratio y. The Al content obtained by analysis can also be plotted in a table of linear scales, and a linear approximate curve is made based on the table, and the slope of the approximate curve is used as the rate of change of the Al composition ratio y. Even when at least one of the In content of the first p-side composition gradient layer 411 and the Al content of the second p-side composition gradient layer 412 changes nonlinearly within the layer, by creating these linear approximate curves, the magnitude relationship between the first change rate and the second change rate can be compared.

[0068] like Figure 6 As shown, it can also be said that the second p-side composition gradient layer 412 is composed of a plurality of sub-layers 412a, 412b, 412c, 412y, and 412z having different compositions. Figure 6 This is a partial enlarged view of the second p-side composition inclined layer 412 and its vicinity. In addition to these, there are multiple sub-layers between the sub-layer 412c and the sub-layer 412y. y Ga 1-y When N constitutes the second p-side composition gradient layer 412, the Al composition ratio y of the lowermost sublayer 412a of the second p-side composition gradient layer 412 is a The Al composition ratio y of the uppermost sublayer 412z is z The relationship is y a <y z The Al composition ratio y of the sublayer 412a constituting the lower end of the second p-side composition gradient layer 412 is a Can satisfy z<y a ≤0.05. z is the Al composition ratio of the intermediate layer 413. The Al composition ratio y of the sublayer 412z constituting the upper end of the second p-side composition gradient layer 412 is z Can satisfy y a <y z ≤0.1.

[0069] The second p-side composition inclined layer 412 preferably has an Al composition ratio y that increases for every thickness of 25 nm or less from the bottom surface to the top surface. That is, the thickness of each sublayer 412a, 412b, 412c, 412y, and 412z is preferably 25 nm or less. In this way, the deformation generated between adjacent sublayers can be reduced. The thickness of each sublayer 412a, 412b, 412c, 412y, and 412z is more preferably 20 nm or less, and can be 10 nm or less, or 5 nm or less. The lower limit of the thickness of each sublayer 412a, 412b, 412c, 412y, and 412z is, for example, about 1 atomic layer (about 0.25 nm). In addition, the difference in the Al composition ratio y of adjacent sublayers (for example, sublayer 412a and sublayer 412b) is preferably 0.005 or less, and more preferably 0.001 or less. The lower limit of the difference in Al composition ratio y between adjacent sublayers is, for example, about 0.00007. Such a range is preferably spread over the entire second p-side composition gradient layer 412. That is, all sublayers are preferably within such a range. In the second p-side composition gradient layer 412, the number of composition changes, that is, the number of sublayers of the second p-side composition gradient layer 412 is preferably 10 or more, and more preferably 30 or more.

[0070] When the composition gradient layer 232 is provided in the n-side intermediate portion 23 , the preferred ranges of its composition, composition change rate, and thickness can be the same as those of the second p-side composition gradient layer 412 .

[0071] (Middle layer 413)

[0072] The intermediate layer 413 is disposed between the first p-side composition gradient layer 411 and the second p-side composition gradient layer 412. The intermediate layer 413 is in contact with the second p-side composition gradient layer 412. The intermediate layer 413 may be in contact with the first p-side composition gradient layer 411.

[0073] The middle layer 413 is made of Al z Ga 1-zN composition. The Al composition ratio z of the intermediate layer 413 is smaller than the Al composition ratio y of the second p-side composition gradient layer 412. The Al composition ratio y of the second p-side composition gradient layer 412 is not constant, but the Al composition ratio z of the intermediate layer 413 is smaller than any value thereof. Since the smallest Al composition ratio y in the second p-side composition gradient layer 412 is the Al composition ratio y at the lower end, the Al composition ratio y at the lower end of the second p-side composition gradient layer 412 can also be compared with the Al composition ratio z of the intermediate layer 413. The Al composition ratio z of the intermediate layer 413 can exceed 0 and be less than 0.01. In order to stably form the second p-side composition gradient layer 412, such a smaller Al composition ratio z is suitable. The Al composition ratio z of the intermediate layer 413 can be greater than 0 and less than 0.01, or greater than 0 and less than 0.005. The intermediate layer 413 is not a composition gradient layer, or is a composition gradient layer having a composition change rate smaller than the composition change rate of the second p-side composition gradient layer 412. The change in Al composition per 1 nm of the intermediate layer 413 may be 0.0001 or less, for example. When the composition of the intermediate layer 413 is not constant, the central value thereof is defined as the Al composition ratio z.

[0074] The thickness of the intermediate layer 413 may be greater than 2 nm, greater than 10 nm, or greater than 50 nm. Thus, the second p-side composition inclined layer 412 is easily and stably formed. The thickness of the intermediate layer 413 may be less than 250 nm, less than 200 nm, or less than 100 nm. Thus, the first portion 41 including the intermediate layer 413 can be efficiently formed. The thickness of the intermediate layer 413 may be greater than 0.5 times and less than 1.5 times the thickness of the second p-side composition inclined layer 412.

[0075] When the intermediate layer 231 is provided in the n-side intermediate portion 23 , the preferred ranges of its composition, composition change rate, and thickness can be the same as those of the intermediate layer 413 .

[0076] (Middle layer 414)

[0077] The second p-side composition inclination layer 412 may be in contact with the electron barrier layer 42, but an intermediate layer 414 may be disposed between the second p-side composition inclination layer 412 and the electron barrier layer 42. The intermediate layer 413 and the intermediate layer 414 may be referred to as a first intermediate layer and a second intermediate layer, respectively. The intermediate layer 414 may be in contact with the second p-side composition inclination layer 412 and the electron barrier layer 42.

[0078] The band gap energy of the intermediate layer 414 is the same value as the band gap energy of the upper end of the second p-side composition inclined layer 412, or a value between the band gap energy of the upper end of the second p-side composition inclined layer 412 and the band gap energy of the electron barrier layer 42. By providing such an intermediate layer 414, light confinement to the active layer 3 can be improved. In addition, by providing the intermediate layer 414, the electron barrier layer 42 and the second portion 43 containing p-type impurities can be further away from the active layer 3, so that the absorption loss of light can be reduced. By reducing the absorption loss of light, the efficiency of the semiconductor laser element 100 can be improved. As the efficiency of the semiconductor laser element 100, the slope in the characteristic curve diagram of the current and the light output at the current value above the threshold current, that is, the slope efficiency, can be listed.

[0079] The intermediate layer 414 is not a compositionally inclined layer, or is a compositionally inclined layer having a composition variation rate smaller than that of the second p-side compositionally inclined layer 412. The change in the Al composition of the intermediate layer 414, for example, per 1 nm, can be 0.001 or less. In the case where the composition of the intermediate layer 414 is not constant, its central value can be used as the composition of the intermediate layer 414 to compare the size of the band gap energy of other layers. The lower end of the ridge 4a is preferably located in the intermediate layer 414. Thus, compared with the case where the lower end of the ridge 4a is located in the compositionally inclined layer, the change in the effective refractive index difference between the inside and the outside of the ridge 4a accompanying the change in the depth of the ridge 4a can be reduced.

[0080] For example, the intermediate layer 414 is composed of AlGaN. When the lower surface of the intermediate layer 414 is in contact with the upper surface of the second p-side composition inclined layer 412, the lattice constant of the lower end of the intermediate layer 414 is preferably the same as the lattice constant of the upper end of the second p-side composition inclined layer 412. The smaller the difference between the lattice constant of the intermediate layer 414 and the lattice constant of the upper end of the second p-side composition inclined layer 412, the more the influence of the band peak can be reduced. In the case where the intermediate layer 414 is composed of AlGaN, the difference between the maximum Al composition ratio in the intermediate layer 414 and the Al composition ratio y at the upper end of the second p-side composition inclined layer 412 is preferably less than 0.02, and more preferably less than 0.01. Thereby, the influence of the band peak can be reduced.

[0081] The thickness of the intermediate layer 414 is thicker than the sublayer constituting the second p-side composition gradient layer 412. The thickness of the intermediate layer 414 may be thicker than 25 nm or may be greater than 50 nm. The thickness of the intermediate layer 414 may be less than 600 nm or less than 250 nm.

[0082] The sum of the thickness of the second p-side composition inclined layer 412 and the thickness of the intermediate layer 414 is preferably 100 nm or more. Thus, light leakage to the electron barrier layer 42 and the second portion 43 can be reduced, and light absorption loss can be reduced. The sum of the thickness of the second p-side composition inclined layer 412 and the thickness of the intermediate layer 414 is preferably 500 nm or less. Thus, the electron barrier layer 42 can be arranged at a position not too far from the active layer 3, so the total amount of electron overflow to the second portion 43 can be suppressed. The ratio of the thickness of the second p-side composition inclined layer 412 to the sum of the thickness of the second p-side composition inclined layer 412 and the thickness of the intermediate layer 414 is preferably 0.5 or less. Since the average value of the band gap energy of the second p-side composition inclined layer 412 is smaller than the band gap energy of the intermediate layer 414, the greater the thickness of the second p-side composition inclined layer 412, the lower the light confinement to the active layer 3. Therefore, by making the thickness of the second p-side composition inclined layer 412 relatively thin, the light confinement to the active layer 3 can be improved. This can be expected to reduce the oscillation threshold current of the semiconductor laser element 100. In addition, since the amount of light reaching the second portion 43 can be reduced, light absorption loss can be reduced, and light output can be increased.

[0083] When the intermediate layer 233 is provided in the n-side intermediate portion 23 , the preferred ranges of its composition, composition change rate, and thickness can be the same as those of the intermediate layer 414 .

[0084] (Electron barrier layer 42)

[0085] The electron barrier layer 42 contains p-type impurities such as Mg. The electron barrier layer 42 can be arranged in contact with the upper surface of the first part 41. The band gap energy of the electron barrier layer 42 is greater than the band gap energy of the first part 41. When the first part 41 is a multilayer structure as described above, the electron barrier layer 42 is set to a layer with a band gap energy greater than the band gap energy of any layer constituting the first part 41. By making the electron barrier layer 42 a layer with such a large band gap energy, the electron barrier layer 42 can act as a barrier to electrons overflowing from the active layer 3. The electron barrier layer 42 preferably has a band gap energy difference of 0.1eV or more with the uppermost layer of the first part 41. These band gap energy differences can be set to 1eV or less, for example. The electron barrier layer 42 is, for example, a layer with the highest band gap energy in the p-side semiconductor layer 4. The electron barrier layer 42 can also be a layer with a thickness smaller than the first p-side composition inclined layer 411.

[0086] The electron barrier layer 42 may be a multilayer structure. In this case, one or more layers constituting the electron barrier layer 42 have a band gap energy greater than the band gap energy of any layer constituting the first portion 41. The electron barrier layer 42 may also be a composition tilted layer. The electron barrier layer 42 may, for example, be a composition tilted layer whose composition changes in a manner in which the band gap energy decreases as it moves upward. In the case where the first portion 41 or the electron barrier layer 42 has a superlattice layer, the average band gap energy of the superlattice layer is used instead of the band gap energy of each layer constituting the superlattice layer to compare the size relationship. The electron barrier layer 42 is, for example, composed of AlGaN. In the case where the electron barrier layer 42 is AlGaN, its Al composition ratio may be set to be greater than 0.08 and less than 0.5. The thickness of the electron barrier layer 42 may, for example, be set to be greater than 4 nm and may be set to be less than 100 nm.

[0087] (Part 2 43)

[0088] The second portion 43 has one or more p-type semiconductor layers containing p-type impurities. The second portion 43 may be arranged in contact with the upper surface of the electron barrier layer. The concentration of the p-type impurities in the p-type semiconductor layer of the second portion 43 may be, for example, 1×10 18 / cm 3 Above, and can be set to 1×10 22 / cm 3 As described above, since the driving voltage can be reduced by thinning the thickness of the second portion 43, the thickness of the second portion 43 is preferably less than 260 nm. The thickness of the second portion 43 can be more than 10 nm. The second portion 43 may also include an undoped layer. The second portion 43 preferably contains p-type impurities throughout. Thus, the resistance of the second portion 43 can be reduced compared to the case where the undoped layer is included. In the case of a superlattice layer, its average p-type impurity concentration can be regarded as the p-type impurity concentration of the superlattice layer, so when the second portion 43 has a superlattice layer, the superlattice layer can have a stacked structure of an undoped layer and a p-type impurity containing layer.

[0089] The thickness of the second portion 43 may be smaller than that of the first portion 41. By making the first portion 41 relatively thick, the peak of the light intensity can be kept away from the p-type impurity containing layer, and the loss caused by the free carrier absorption in the p-type impurity containing layer can be reduced. Therefore, the efficiency of the semiconductor laser element 100, such as the slope efficiency, can be improved. In addition, by making the second portion 43 relatively thin, the driving voltage of the semiconductor laser element 100 can be reduced, and the efficiency can be improved. The reason why the voltage is reduced by reducing the thickness of the portion containing the p-type impurity is that in nitride semiconductors, the activation rate of p-type impurities such as Mg is lower than that of n-type impurities such as Si, and the p-type impurity containing layer has a relatively high resistance. The first portion 41 is non-doped, but because it is located between the electron barrier layer 42 and the active layer 3, it is more likely to show a tendency of n-type conductivity rather than being completely insulating due to electron overflow. Therefore, it is believed that by reducing the thickness of the second portion 43 containing the p-type impurity as a higher resistance, the effect of reducing the driving voltage and suppressing the increase in the driving voltage caused by the thickness of the non-doped first portion 41 being thicker can be obtained. Since the first portion 41 is relatively thick, the lower end of the ridge 4a is preferably provided at the first portion 41. Thus, lateral light confinement can be enhanced.

[0090] The second portion 43 may also include a lower p-type semiconductor layer and an upper p-type semiconductor layer. The upper p-type semiconductor layer constitutes the upper surface of the ridge 4a. That is, the upper p-type semiconductor layer is the uppermost layer of the second portion 43. The upper p-type semiconductor layer functions as a p-side contact layer. The lower p-type semiconductor layer is disposed between the upper p-type semiconductor layer and the electron barrier layer 42, and has a band gap energy greater than the band gap energy of the upper p-type semiconductor layer.

[0091] The lower p-type semiconductor layer is composed of, for example, AlGaN. The upper p-type semiconductor layer is composed of, for example, GaN. The lower p-type semiconductor layer can also function as a p-side cladding layer. The lower p-type semiconductor layer can also be a p-type GaN layer, thereby further reducing the resistance of the second portion 43. In this case, it is preferred that the p-electrode is formed of a material such as ITO that functions as a cladding layer. The thickness of the upper p-type semiconductor layer can be, for example, set to be greater than 5 nm and less than 30 nm. The thickness of the lower p-type semiconductor layer can be, for example, set to be greater than 1 nm and less than 260 nm. For example, the thickness of the lower p-type semiconductor layer is greater than the thickness of the electron barrier layer 42. In this case, in order to reduce free carrier absorption losses, it is preferred that the p-type impurity concentration of the lower p-type semiconductor layer is lower than the p-type impurity concentration of the electron barrier layer 42.

[0092] (Insulating film 5, n-electrode 8, p-electrode 6, p-side pad electrode 7)

[0093] The insulating film 5 can be formed of, for example, a single-layer film or a multilayer film of an oxide or nitride of Si, Al, Zr, Ti, Nb, Ta, etc. The n-electrode 8 is provided, for example, on the substantially entire area of ​​the lower surface of the n-type substrate 1. The p-electrode 6 is provided on the upper surface of the ridge 4a. When the width of the p-electrode 6 is narrow, a p-side pad electrode 7 having a width wider than the p-electrode 6 is provided on the p-electrode 6, and a wire or the like is connected to the p-side pad electrode 7. The material of each electrode can be, for example, a single-layer film or a multilayer film containing a conductive oxide selected from metals or alloys such as Ni, Rh, Cr, Au, W, Pt, Ti, Al, Zn, In, Sn, etc., or at least one kind thereof. Examples of conductive oxides include ITO (Indium Tin Oxide: Indium Tin Oxide), IZO (Indium Zinc Oxide: Indium Zinc Oxide), GZO (Gallium-doped Zinc Oxide: Gallium-doped Zinc Oxide), etc. The thickness of the electrode can generally be any thickness that can function as an electrode of a semiconductor element. For example, it is about 0.05 μm to 2 μm.

[0094] The p-electrode 6 is preferably a transparent conductive film having a refractive index smaller than that of the active layer 3. Thus, it can function as a cladding layer. Furthermore, the p-electrode 6 is preferably a transparent conductive film having a refractive index smaller than that of the second portion 43. Thus, a light confinement effect can be further obtained. In addition, in the case where a p-side cladding layer is provided in the second portion 43, for example, an AlGaN layer having a relatively high Al composition ratio and doped with p-type impurities is provided as the p-side cladding layer, but the higher the Al composition ratio, the more likely the resistance becomes higher. If the p-electrode 6 is made to function as a cladding layer, the p-side cladding layer may not be provided in the second portion 43, or even in the case where a p-side cladding layer is provided, its Al composition ratio may be reduced. Therefore, the resistance can be reduced, and the driving voltage of the semiconductor laser element 100 can be reduced. The p-electrode 6 that functions as a cladding layer may, for example, be a p-electrode 6 composed of ITO.

[0095] (Manufacturing method)

[0096] The manufacturing method of the semiconductor laser element 100 of the embodiment includes, for example, the following first to fifth steps. The first step is a step of forming an n-side semiconductor layer 2 on a substrate 1. The second step is a step of forming an active layer 3 on the n-side semiconductor layer 2. The third step is a step of forming a first portion 41 having one or more semiconductor layers on the upper surface of the active layer 3 without doping. The fourth step is a step of forming an electron barrier layer 42 by doping a p-type impurity on the upper surface of the first portion 41. The fifth step is a step of forming a second portion 43 having one or more p-type semiconductor layers formed by doping a p-type impurity on the upper surface of the electron barrier layer 42. In the third step, the layers constituting the first portion 41 are formed sequentially from bottom to top. The manufacturing method of the semiconductor laser element 100 may further include a sixth step of forming a ridge 4a protruding upward by removing a portion of the p-side semiconductor layer 4 including the first portion 41, the electron barrier layer 42, and the second portion 43. The effects, preferred configurations, etc. of the layers obtained by the various steps are as described above.

[0097] (Example 1)

[0098] As Example 1, a semiconductor laser element 100 was produced. An MOCVD device was used to produce an epitaxial wafer to be the semiconductor laser element 100. In addition, trimethylgallium (TMG), triethylgallium (TEG), trimethylaluminum (TMA), trimethylindium (TMI), ammonia (NH3), silane gas, and bis(cyclopentadienyl)magnesium (Cp2Mg) were used as raw materials as appropriate.

[0099] An n-side semiconductor layer 2 , an active layer 3 , and a p-side semiconductor layer 4 are grown in this order on an n-type GaN substrate (substrate 1 ) having a +c-plane as the upper surface.

[0100] The n-side semiconductor layer 2 has, in order from the n-type GaN substrate side: Al doped with Si, 0.016 Ga 0.984 N layer, In layer with Si added, thickness 150nm 0.05 Ga 0.95 N layer, Al layer with Si added and thickness of 900nm 0.072 Ga 0.928 N layer (n-type semiconductor layer 22), GaN layer with a thickness of 3500 nm to which Si is added (n-side intermediate portion 23), and GaN layer with a thickness of 200 nm to which Si is added and In 0.05 Ga 0.95 The n-side composition gradient layer 21 is formed by growing the In composition with N as the termination substantially monotonically increasing.

[0101] The active layer 3 is formed by sequentially including a GaN layer to which Si is added, a non-doped In composition gradient layer, and a non-doped In layer from the n-type GaN substrate side. 0.2 Ga 0.8 N layer, undoped GaN layer.

[0102] The p-side semiconductor layer 4 is formed to have, in order from the n-type GaN substrate side, a non-doped first p-side composition inclined layer 411 with a thickness of 200 nm, a non-doped intermediate layer 413 with a thickness of 50 nm, a non-doped second p-side composition inclined layer 412 with a thickness of 70 nm, a non-doped Al layer with a thickness of 130 nm, and a non-doped intermediate layer 413 with a thickness of 50 nm. 0.045 Ga 0.955 The first p-side composition gradient layer 411 has a growth start point of In. 0.05 Ga 0.95 N, and the end point of growth is GaN. The second p-side composition gradient layer 412 starts growth at AlGaN with an Al composition ratio of 1% or less, and ends growth at Al 0.045 Ga 0.955 N.

[0103] Then, the epitaxial wafer formed with the above layers is taken out by MOCVD device, and the ridge 4a, insulating film 5, p-electrode 6, p-side pad electrode 7, and n-electrode 8 are formed. Reflective films are formed on the light emitting end face and the light reflecting end face, respectively, and the semiconductor laser element 100 is obtained by single-chip. The depth of the ridge 4a is about 270nm. That is, the ridge 4a is formed in such a way that its lower end is located on the second p-side constituting the inclined layer 412. In addition, as the p-electrode 6, an ITO film with a thickness of 200nm is formed. The peak wavelength of the laser light emitted by the semiconductor laser element 100 of Example 1 is about 455nm.

[0104] (SIMS analysis)

[0105] exist Figure 7 2 shows the results of SIMS analysis of a wafer in which the p-side semiconductor layer 4 was grown in the same manner as in Example 1 and stopped before the ridge 4a etc. were formed. Figure 7 In FIG. 1 , the dotted line represents the detected amount of In, and the solid line represents the detected amount of Al. Figure 7 The vertical and horizontal axes are linear scales. Figure 7 It can be confirmed that the intermediate layer 414 is formed between the first p-side composition gradient layer 411 and the second p-side composition gradient layer 412. Figure 7In the figure, at the lower end (right end in the figure) of the intermediate layer 414 , the line indicating the detected amount of In intersects the line indicating the detected amount of Al, and Al is detected in more than half of the intermediate layer 414 .

[0106] (Example 2)

[0107] An n-side semiconductor layer 2 , an active layer 3 , and a p-side semiconductor layer 4 are grown in this order on an n-type GaN substrate (substrate 1 ) having a +c-plane as the upper surface.

[0108] The n-side semiconductor layer 2 is formed to have, in order from the n-type GaN substrate side: Al doped with Si, with a thickness of 1.25 μm; 0.018 Ga 0.982 N layer, Al with a thickness of 250nm with Si added 0.08 Ga 0.92 N layer, In layer with Si added, thickness 150nm 0.04 Ga 0.96 N layer, GaN layer with Si added and thickness of 10nm, Al layer with Si added and thickness of 650nm 0.08 Ga 0.92 N layer (n-type semiconductor layer 22), GaN layer with a thickness of 200 nm to which Si is added (n-side intermediate portion 23), and non-doped In layer with a thickness of 230 nm 0.03 Ga 0.97 N layers.

[0109] The active layer 3 is formed by sequentially including a GaN layer to which Si is added, an In layer to which Si is added, and 0.05 Ga 0.95 N layer, GaN layer with Si added, undoped In 0.25 Ga 0.75 N layer, undoped GaN layer, undoped In 0.25 Ga 0.75 N layer, undoped GaN layer.

[0110] The p-side semiconductor layer 4 is formed to have, in order from the n-type GaN substrate side, a non-doped first p-side composition inclined layer 411 with a thickness of 180 nm, a non-doped intermediate layer 413 with a thickness of 50 nm, a non-doped second p-side composition inclined layer 412 with a thickness of 100 nm, a non-doped Al layer with a thickness of 200 nm, and a non-doped intermediate layer 414 with a thickness of 50 nm. 0.04 Ga 0.96 The first p-side composition gradient layer 411 has a growth start point of In.0.05 Ga 0.95 N, and the end point of growth is GaN. The second p-side composition gradient layer 412 starts growth at AlGaN with an Al composition ratio of 1% or less, and ends growth at Al 0.04 Ga 0.96 N.

[0111] Then, the epitaxial wafer formed with the above layers is taken out by MOCVD device, and the ridge 4a, insulating film 5, p-electrode 6, p-side pad electrode 7, and n-electrode 8 are formed, and reflective films are formed on the light emitting end face and the light reflecting end face, respectively, and the semiconductor laser element 100 is obtained by single-chip. The depth of the ridge 4a is about 270nm. That is, the ridge 4a is formed so that its lower end is located in the intermediate layer 414. In addition, as the p-electrode 6, an ITO film with a thickness of 200nm is formed. The peak wavelength of the laser light emitted by the semiconductor laser element 100 of Example 2 is about 527nm.

[0112] (Example 3)

[0113] The semiconductor laser element 100 of Example 3 was manufactured in the same manner as Example 2 except for the following points. The last two layers of the n-side semiconductor layer 2 were a 250 nm thick GaN layer (n-side intermediate portion 23) doped with Si and a 180 nm thick non-doped In layer. 0.03 Ga 0.97 N layer. In the p-side semiconductor layer 4, the thickness of the second p-side composition inclined layer 412 is set to 300nm, and there is no intermediate layer 414. The non-doped intermediate layer 413 with a thickness of 50nm remains as it is. The depth of the ridge 4a is maintained at about 270nm. That is, the ridge 4a is formed in such a way that its lower end is located in the second p-side composition inclined layer 412. The peak wavelength of the laser light emitted by the semiconductor laser element 100 of Example 3 is 527nm.

[0114] (Comparative Example 1)

[0115] The semiconductor laser element of Comparative Example 1 was manufactured in the same manner as the semiconductor laser element 100 of Example 1, except that the intermediate layer 413 and the second p-side composition inclined layer 412 were not formed, and a non-doped GaN layer with a thickness of 120 nm was formed in their place. The depth of the ridge 4a was maintained at about 270 nm. That is, the ridge 4a was formed in such a way that its lower end was located in the non-doped GaN layer with a thickness of 120 nm. The peak wavelength of the laser light emitted by the semiconductor laser element of Comparative Example 1 was 455 nm.

[0116] (Comparative Example 2)

[0117] The semiconductor laser device of Comparative Example 2 was produced in the same manner as in Example 2 except for the following points. The last two layers of the n-side semiconductor layer 2 were a 250 nm thick GaN layer doped with Si and a 180 nm thick non-doped In layer. 0.03 Ga 0.97 N layer. In the p-side semiconductor layer 4, the second p-side composition gradient layer 412 is not formed, and a non-doped GaN layer with a thickness of 150 nm is formed in its place. The peak wavelength of the laser light emitted by the semiconductor laser element of Comparative Example 2 is 527 nm.

[0118] (I-L characteristics)

[0119] The I-L characteristics of the semiconductor laser elements of Example 1 and Comparative Example 1 are shown in FIG. Figure 8 .exist Figure 8 In the graph, the horizontal axis represents the current and the vertical axis represents the light output. Figure 8 In FIG. 1 , the solid line represents Example 1, and the dotted line represents Comparative Example 1. The I-L characteristics of the semiconductor laser elements of Example 2, Example 3, and Comparative Example 2 are shown in FIG. Fig. 9 .exist Fig. 9 In the graph, the horizontal axis represents the current and the vertical axis represents the light output. Fig. 9 In the figure, the solid line represents Example 2, the dashed line represents Example 3, and the dotted line represents Comparative Example 2. Figure 8 and Fig. 9 As shown, it was confirmed that the slope efficiency was improved and the light output was improved by providing the first p-side composition gradient layer 411, the intermediate layer 413, and the second p-side composition gradient layer 412. This is believed to be due to the effect of reducing the loss of carriers in the p-side semiconductor layer 4.

[0120] In this specification, the following technical matters are disclosed through the contents described so far.

[0121] (Item 1) A semiconductor laser element comprising, in this order upward, an n-side semiconductor layer, an active layer, and a p-side semiconductor layer, each of which is made of a nitride semiconductor,

[0122] The p-side semiconductor layer has the following components in order:

[0123] an undoped first portion having more than one semiconductor layer;

[0124] an electron barrier layer having a band gap energy greater than that of the first portion and containing p-type impurities;

[0125] The second part has one or more p-type semiconductor layers containing p-type impurities,

[0126] The first part has:

[0127] The first p-side constitutes the tilted layer, which is composed of In x Ga 1-x N composition, the In composition ratio x decreases in the range of greater than 0 and less than 1 as it goes upward;

[0128] The second p-side composition inclined layer is disposed between the first p-side composition inclined layer and the electron barrier layer and is composed of Al y Ga 1-y N composition, the Al composition ratio y increases in the range of more than 0 and less than 1 as it goes upward;

[0129] The intermediate layer is disposed between the first p-side component inclined layer and the second p-side component inclined layer, and is composed of Al z Ga 1- z N composition, and the Al composition ratio z exceeds 0 and is less than y.

[0130] (Item 2) The semiconductor laser device according to Item 1, wherein the first p-side composition gradient layer changes composition at a first rate of change so that band gap energy increases upward.

[0131] The second p-side composition gradient layer changes composition at a second change rate that is smaller than the first change rate so that the band gap energy increases upward.

[0132] (Item 3) The semiconductor laser device according to Item 1 or 2, wherein the Al composition ratio y at the upper end of the second p-side composition gradient layer is 0.1 or less.

[0133] (Item 4) The semiconductor laser device according to any one of Items 1 to 3, wherein the thickness of the second p-side composition gradient layer is 2 nm or more.

[0134] (Item 5) The semiconductor laser device according to any one of Items 1 to 4, wherein an Al composition ratio z of the intermediate layer exceeds 0 and is 0.01 or less.

[0135] (Item 6) The semiconductor laser device according to any one of Items 1 to 5, wherein the Al composition ratio y at the lower end of the second p-side composition gradient layer exceeds the Al composition ratio z of the intermediate layer and is 0.05 or less.

[0136] (Item 7) The semiconductor laser device according to any one of Items 1 to 6, wherein the intermediate layer is a first intermediate layer.

[0137] The first part has a second intermediate layer, which is arranged between the second p-side composition tilted layer and the electron barrier layer and has a band gap energy that is the same as or between the upper end of the second p-side composition tilted layer and the electron barrier layer.

[0138] (Item 8) The semiconductor laser element according to Item 7, wherein a ratio of a thickness of the second p-side composition gradient layer to a sum of a thickness of the second p-side composition gradient layer and a thickness of the second intermediate layer is 0.5 or less.

[0139] (Item 9) The semiconductor laser device according to any one of Items 1 to 8, wherein the n-side semiconductor layer has:

[0140] An n-side composition gradient layer is arranged in contact with the lower surface of the active layer and has a composition that changes in such a way that the band gap energy increases as it goes downward;

[0141] An n-type semiconductor layer, which is arranged below the n-side composition gradient layer, has a band gap energy larger than a band gap energy of any layer constituting the first portion of the p-side semiconductor layer, and contains n-type impurities;

[0142] an n-side intermediate portion disposed between the n-side composition gradient layer and the n-type semiconductor layer,

[0143] A distance from the n-side composition gradient layer to the n-type semiconductor layer is greater than a distance from the first p-side composition gradient layer to the electron barrier layer.

[0144] (Item 10) The semiconductor laser device according to any one of Items 1 to 9, wherein:

[0145] The active layer has:

[0146] n-side barrier layer;

[0147] p-side barrier layer;

[0148] a plurality of well layers, comprising a first well layer and a second well layer located between the n-side barrier layer and the p-side barrier layer;

[0149] an intermediate barrier layer, which is located between the first well layer and the second well layer,

[0150] The thickness of the intermediate barrier layer is smaller than the thickness of the p-side barrier layer.

[0151] Description of Reference Numerals

[0152] 100: Semiconductor laser element

[0153] 1: Substrate

[0154] 2: n-side semiconductor layer

[0155] 21: n-side constitutes an inclined layer

[0156] 22: n-type semiconductor layer

[0157] 23: middle part of n side

[0158] 231: Middle layer

[0159] 232: Composition of tilted layers

[0160] 233: Middle layer

[0161] 3. 3A: Active layer

[0162] 31: n-side barrier layer

[0163] 32: Well layer

[0164] 33: p-side barrier layer

[0165] 34: Intermediate barrier layer

[0166] 4: p-side semiconductor layer

[0167] 41: Part 1

[0168] 411: The first p-side constitutes the inclined layer

[0169] 411a, 411b, 411c, 411y, 411z: sublayer

[0170] 412: The second p-side constitutes an inclined layer

[0171] 412a, 412b, 412c, 412y, 412z: sublayer

[0172] 413: Middle layer

[0173] 414: Middle layer

[0174] 42: Electron barrier layer

[0175] 43: Part 2

[0176] 4a: Ridge

[0177] 5: Insulation film

[0178] 6: p-electrode

[0179] 7: p-side pad electrode

[0180] 8: n-electrode

Claims

1. A semiconductor laser element, comprising an n-side semiconductor layer, an active layer, and a p-side semiconductor layer each consisting of a nitride semiconductor in this order upward, characterized in that: The p-side semiconductor layer has the following components in order: an undoped first portion having more than one semiconductor layer; an electron barrier layer having a band gap energy greater than that of the first portion and containing p-type impurities; The second part has one or more p-type semiconductor layers containing p-type impurities, The first part has: The first p-side constitutes the tilted layer, which is composed of In x Ga 1-x N composition, the In composition ratio x decreases in the range of greater than 0 and less than 1 as it goes upward; The second p-side composition inclined layer is disposed between the first p-side composition inclined layer and the electron barrier layer and is composed of Al y Ga 1-y N composition, the Al composition ratio y increases in the range of more than 0 and less than 1 as it goes upward; The intermediate layer is disposed between the first p-side composition inclined layer and the second p-side composition inclined layer, and is composed of Al z Ga 1-z N composition, and the Al composition ratio z exceeds 0 and is less than y.

2. The semiconductor laser element according to claim 1, wherein The first p-side composition gradient layer changes its composition at a first change rate so that the band gap energy increases upward. The second p-side composition gradient layer changes composition at a second change rate that is smaller than the first change rate so that the band gap energy increases upward.

3. The semiconductor laser element according to claim 1 or 2, wherein: The Al composition ratio y at the upper end of the second p-side composition gradient layer is 0.1 or less.

4. The semiconductor laser device according to any one of claims 1 to 3, wherein The thickness of the second p-side composition gradient layer is greater than or equal to 2 nm.

5. The semiconductor laser device according to any one of claims 1 to 4, wherein The Al composition ratio z of the intermediate layer exceeds 0 and is 0.01 or less.

6. The semiconductor laser device according to any one of claims 1 to 5, wherein The Al composition ratio y at the lower end of the second p-side composition gradient layer exceeds the Al composition ratio z of the intermediate layer and is 0.05 or less.

7. The semiconductor laser device according to any one of claims 1 to 6, wherein The intermediate layer is a first intermediate layer, The first part has a second intermediate layer, which is arranged between the second p-side composition tilted layer and the electron barrier layer and has a band gap energy that is the same as or between the upper end of the second p-side composition tilted layer and the electron barrier layer.

8. The semiconductor laser element according to claim 7, wherein A ratio of the thickness of the second p-side composition gradient layer to the sum of the thickness of the second p-side composition gradient layer and the thickness of the second intermediate layer is 0.5 or less.

9. The semiconductor laser device according to any one of claims 1 to 8, wherein The n-side semiconductor layer has: An n-side composition gradient layer is arranged in contact with the lower surface of the active layer and has a composition that changes in such a way that the band gap energy increases as it goes downward; An n-type semiconductor layer, which is arranged below the n-side composition gradient layer, has a band gap energy greater than a band gap energy of any layer constituting the first portion of the p-side semiconductor layer, and contains n-type impurities; an n-side intermediate portion disposed between the n-side composition gradient layer and the n-type semiconductor layer, A distance from the n-side composition gradient layer to the n-type semiconductor layer is greater than a distance from the first p-side composition gradient layer to the electron barrier layer.

10. The semiconductor laser device according to any one of claims 1 to 9, wherein The active layer has: n-side barrier layer; p-side barrier layer; a plurality of well layers, comprising a first well layer and a second well layer located between the n-side barrier layer and the p-side barrier layer; an intermediate barrier layer, which is located between the first well layer and the second well layer, The thickness of the intermediate barrier layer is smaller than the thickness of the p-side barrier layer.

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