Nitride semiconductor light-emitting element and method for producing nitride semiconductor light-emitting element

Abstract

This nitride semiconductor light-emitting element comprises an n-type semiconductor layer, a p-type semiconductor layer, and a luminescent layer between the n-type semiconductor layer and the p-type semiconductor layer, wherein the p-type semiconductor layer comprises a p-type contact layer and a p-type clad layer which are made of an Mg-doped nitride semiconductor, the p-type clad layer comprising a first p-type clad layer, which is disposed on the luminescent-layer side, and a second p-type clad layer, which is interposed between the first p-type clad layer and the p-type contact layer. The second p-type clad layer has an average Mg concentration higher than the average Mg concentration of the first p-type clad layer. The p-type clad layer as a whole has a lower average Mg concentration than any other layer of the p-type semiconductor layer.

Description

NITRIDE SEMICONDUCTOR LIGHT EMITTING ELEMENT AND METHOD FOR MANUFACTURING NITRIDE SEMICONDUCTOR LIGHT EMITTING ELEMENT

[0001] The present disclosure relates to a nitride semiconductor light emitting device and a method for manufacturing the nitride semiconductor light emitting device.

[0002] Semiconductor laser devices have been used in a wide range of technical fields due to their excellent features such as compact size, low cost, and high output. For example, high-output semiconductor laser devices are used for processing various materials such as metals, resins, and composite carbon materials (CFRP: Carbon Fiber Reinforced Plastics).

[0003] In recent years, GaN-based semiconductor light-emitting devices that emit light in the blue wavelength range of 405 nm to 540 nm, which has a high absorption rate (low reflectance) in copper materials, have been attracting attention as light sources for processing copper materials, which are widely used in EV motors and other applications.

[0004] GaN-based semiconductor light-emitting devices require high power-to-light conversion efficiency, which indicates the proportion of input power that is converted into laser light. By converting input power into light with high efficiency, it is possible to increase optical output and prevent excess energy from being converted into heat, thereby reducing the reduction in optical output caused by heat generation and the adverse effects on long-term reliability.

[0005] A GaN-based semiconductor light-emitting element includes an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer, all made of GaN-based semiconductors. Generally, the p-type semiconductor layer includes, in order from the light-emitting layer side, a p-type cladding layer and a p-type contact layer. The p-type cladding layer is made of, for example, an AlGaN semiconductor and is doped with Mg as an impurity.

[0006] Patent Document 1 describes a manufacturing method for controlling the Mg concentration in the thickness direction of the p-type cladding layer to a constant value. The technique described in Patent Document 1 makes the carrier distribution in the thickness direction of the p-type cladding layer uniform, thereby reducing the effect on hole injection into the light-emitting layer.

[0007] Furthermore, Patent Document 2 and Non-Patent Document 1 propose a technique in which a p-type electron blocking layer having a higher Mg concentration than the p-type cladding layer is provided at the junction between the p-type cladding layer and the light-emitting layer, and an undoped AlGaN layer is interposed between the p-type electron blocking layer and the light-emitting layer to suppress diffusion of Mg added to the p-type electron blocking layer into the light-emitting layer. According to the techniques described in Patent Document 2 and Non-Patent Document 1, the undoped AlGaN layer prevents deterioration of the light-emitting layer due to diffusion of Mg, so that optical absorption loss is reduced and power-to-light conversion efficiency is improved compared to when the undoped AlGaN layer is not provided.

[0008] JP 2014-63891 A JP 2014-127708 A

[0009] M. Ikeda and S. Uchida, “Blue-Violet Laser Diodes Suitable for Blu-ray Disk”, phys. Stat. sol.(a) 194, no.2407 (2002).

[0010] A nitride semiconductor light-emitting device according to one aspect of the present disclosure is a nitride semiconductor light-emitting device including an n-type semiconductor layer, a p-type semiconductor layer, and a light-emitting layer between the n-type semiconductor layer and the p-type semiconductor layer, wherein the p-type semiconductor layer has a p-type contact layer and a p-type cladding layer made of an Mg-doped nitride semiconductor, the p-type cladding layer has a p-type first cladding layer arranged on the light-emitting layer side, and a p-type second cladding layer arranged between the first p-type cladding layer and the p-type contact layer, the average Mg concentration of the p-type second cladding layer is higher than the average Mg concentration of the first p-type cladding layer, and the average Mg concentration of the entire p-type cladding layer is lower than that of other layers of the p-type semiconductor layer.

[0011] A method for manufacturing a nitride semiconductor light-emitting device according to one aspect of the present disclosure is a method for manufacturing a nitride semiconductor light-emitting device including an n-type semiconductor layer, a p-type semiconductor layer, and a light-emitting layer between the n-type semiconductor layer and the p-type semiconductor layer, wherein the p-type semiconductor layer has a p-type contact layer and a p-type cladding layer made of an Mg-doped nitride semiconductor, and the step of forming the p-type cladding layer includes the steps of forming a p-type first cladding layer on the light-emitting layer side under first growth conditions and forming a p-type second cladding layer between the p-type first cladding layer and the p-type contact layer under second growth conditions, and wherein an Mg supply amount under the second growth conditions is greater than an Mg supply amount under the first growth conditions.

[0012] Fig. 1 is a cross-sectional view of a semiconductor light-emitting element according to an embodiment. Fig. 2 is a diagram showing an example of a concentration profile in the semiconductor light-emitting element according to the embodiment. Fig. 3 is a diagram showing another example of a concentration profile in the semiconductor light-emitting element according to the embodiment. Fig. 4 is a diagram showing another example of a concentration profile in the semiconductor light-emitting element according to the embodiment. Fig. 5 is a diagram showing another example of a concentration profile in the semiconductor light-emitting element according to the embodiment.

[0013] As described in Patent Document 1, when the Mg concentration in the thickness direction of the p-type cladding layer is kept constant, if the Mg concentration that gives the lowest element resistance is set, the optical absorption loss of blue light increases, and there is a risk of a decrease in power-to-light conversion efficiency.

[0014] Furthermore, in the configurations described in Patent Document 2 and Non-Patent Document 1, etc., an undoped AlGaN layer is inserted between the p-type semiconductor layer and the light emitting layer, which increases the device resistance compared to when the undoped AlGaN layer is not provided. Therefore, if the thickness of the undoped AlGaN layer is increased to reduce the light absorption loss, the operating voltage will increase, and there is a risk that the total power-to-light conversion efficiency will decrease.

[0015] An object of the present disclosure is to provide a nitride semiconductor light-emitting device having high power-to-light conversion efficiency and a method for manufacturing the nitride semiconductor light-emitting device.

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0017] In this embodiment, a GaN-based semiconductor light-emitting device capable of emitting blue light with a wavelength of 445 nm will be described as an example of a nitride semiconductor light-emitting device. A nitride semiconductor light-emitting device is typically a semiconductor having layers each of which is represented by the general formula In ｘ Al ｙ Ga １－ｘ－ｙ N (0≦x≦1, 0≦y≦1, 0≦x+y≦1). ｘ Al ｙ Ga １－ｘ－ｙ N (0≦x<1, 0≦y<1, 0≦x+y<1) is called a GaN-based semiconductor light-emitting element.

[0018] Fig. 1 is a cross-sectional view of a GaN-based semiconductor light-emitting device 1 according to an embodiment. Figs. 2 to 5 are diagrams showing examples of concentration profiles in the GaN-based semiconductor light-emitting device 1. The concentration profiles shown in Figs. 2 to 5 were analyzed by secondary ion mass spectrometry (SIMS).

[0019] 1, the GaN-based semiconductor light-emitting device 1 has a layered structure in which an n-type semiconductor layer 20, a light-emitting layer 30, and a p-type semiconductor layer 40 are formed in this order on a substrate 10. The GaN-based semiconductor light-emitting device 1 has a ridge stripe optical waveguide WG. The light-emitting layer 30 is disposed between the n-type semiconductor layer 20 and the p-type semiconductor layer 40.

[0020] In the GaN-based semiconductor light-emitting element 1, the n-type impurity is silicon (Si) and the p-type impurity is magnesium (Mg). In forming the GaN-based semiconductor light-emitting element 1, for example, trimethylgallium (TMG), trimethylindium (TMI), and trimethylaluminum (TMA) are used as Group III raw materials. For example, ammonia (NH ３ The Si source material is, for example, silane (SiH ４ As the Mg raw material, for example, cyclopentadienyl magnesium (Cp ２Mg) is used.

[0021] The configuration of the GaN-based semiconductor light-emitting device 1 described in this embodiment is an example, and the stacked structure of the n-type semiconductor layer 20, the light-emitting layer 30, and the p-type semiconductor layer 40, the film thickness of each layer, the composition ratio of the group III elements forming each layer, etc. can be changed as appropriate.

[0022] The substrate 10 is, for example, an n-type hexagonal GaN substrate having a (0001) plane.

[0023] The n-type semiconductor layer 20 is a cladding layer for confining light in the light emitting layer 30. The n-type semiconductor layer 20 is, for example, a Si-doped Al ｙ Ga １－ｙ The n-type semiconductor layer 20 is composed of Al and N (0<y<1). The Al composition ratio y of the n-type semiconductor layer 20 is, for example, 0.03. The film thickness of the n-type semiconductor layer 20 is, for example, 3 μm. The Si concentration of the n-type semiconductor layer 20 is, for example, 1×10 １８ cm －３ That's about it.

[0024] The light emitting layer 30 is a layer that emits blue light when a current is applied, and includes an n-side light guide layer 31, an active layer 32, and a p-side light guide layer 33 in this order from the substrate 10 side.

[0025] The n-side optical guide layer 31 is a Si-doped In ｘ Ga １－ｘ The n-side optical guiding layer 31 has, for example, a first optical guiding layer made of Si-doped GaN with an In composition ratio x of 0, and a second optical guiding layer made of Si-doped InGaN containing In (not shown).

[0026] The first optical guide layer is formed on the n-type semiconductor layer 20. The thickness of the first optical guide layer is, for example, 250 nm. The Si concentration of the first optical guide layer is, for example, 1×10 １８ cm －３ That's about it.

[0027] The second optical guide layer is formed by gradually increasing the In composition ratio x from the first optical guide layer side. The thickness of the second optical guide layer is, for example, 150 nm. The second optical guide layer is not intentionally doped with Si. The Si concentration is, for example, 5×10 １５ cm－３ It is about the following.

[0028] In the film formation process of the second optical guide layer, for example, the In composition ratio x can be increased by gradually increasing the supply amount of the In source material (TMI). Alternatively, for example, the supply amount of the Ga source material (TMG) may be gradually decreased while keeping the supply amount of the TMI constant to increase the In composition ratio x of the second optical guide layer. In this case, in order to keep the Si concentration substantially constant, SiH ４ It is preferable to increase the supply rate of the raw material in accordance with the increase in the supply rate of TMG.

[0029] Furthermore, instead of gradually changing the TMI supply rate or the TMG supply rate, the In composition ratio x of the second optical guiding layer may be increased substantially continuously by supplying TMI in a pulsed manner and gradually increasing the duty. Furthermore, since the amount of In taken up increases when the growth temperature is lowered, the In composition ratio x of the second optical guiding layer may be increased by gradually lowering the growth temperature while keeping the TMI supply rate and the TMG supply rate constant. It is preferable that the composition ratio x of the second optical guiding layer does not exceed the composition ratio x of the n-side optical guiding layer to be stacked next, i.e., it increases monotonically.

[0030] The active layer 32 is made of In ｘ Ga １－ｘ The active layer 32 is composed of N layers (0≦x<1). The active layer 32 has, for example, quantum well layers and barrier layers (not shown). The active layer 32 has, for example, a two-period multiple quantum well structure in which quantum well layers and barrier layers are alternately stacked. Specifically, a first barrier layer, a first quantum well layer, a second barrier layer, a second quantum well layer, and a third barrier layer (all not shown) are formed in this order on the n-side optical guide layer 31.

[0031] The first barrier layer has, for example, an In composition ratio x of 0.03 and a thickness of 20 nm. The first quantum well layer has, for example, an In composition ratio x of 0.18 and a thickness of 3.0 nm. The second barrier layer has, for example, an In composition ratio x of 0.08 and a thickness of 10 nm. The second quantum well layer has, for example, an In composition ratio x of 0.18 and a thickness of approximately 3.0 nm. The third barrier layer has, for example, an In composition ratio x of 0.03 and a thickness of 10 nm.

[0032] If the barrier layers are too thick, the internal quantum efficiency will decrease due to radiative recombination in the barrier layers. Therefore, it is preferable to limit the thickness of each barrier layer to approximately 40 nm at most. The thicknesses of the barrier layers (first to third barrier layers) may be set appropriately taking into consideration the uniformity of carrier injection, and may be the same or different.

[0033] The p-side optical guide layer 33 is an undoped In ｘ Al ｙ Ga １－ｘ－ｙ N (0≦x<1, 0≦y<1, 0≦x+y<1). The p-side optical guiding layer 33 is, for example, a layer made of undoped InGaN, undoped GaN, undoped AlGaN, or a combination thereof. The thickness of the p-side optical guiding layer 33 is, for example, 0.2 μm.

[0034] From the viewpoint of the light confinement effect inside the element, the p-side light guide layer 33 is preferably configured so that the refractive index decreases from the active layer 32 side toward the p-type semiconductor layer 40 (p-type cladding layer 42) side. For example, the light confinement effect can be improved by forming the p-side light guide layer 33 by depositing InGaN, GaN, and AlGaN in this order from the active layer 32 side.

[0035] The p-type semiconductor layer 40 includes a p-type electron blocking layer 41 , a p-type cladding layer 42 , and a p-type contact layer 43 .

[0036] The p-type electron blocking layer 41 is made of Mg-doped Al ｙ Ga １－ｙ N (0≦y<1). By providing the p-type electron blocking layer 41, the efficiency of hole injection into the active layer 32 can be improved. The Al composition ratio y of the p-type electron blocking layer 41 is preferably 0.35 or more, and is, for example, 0.35. The film thickness of the p-type electron blocking layer 41 is, for example, 5 nm. The Mg concentration of the p-type electron blocking layer 41 is 1×10 １９ cm －３ It is preferable that this is equal to or greater than this.

[0037] The p-type cladding layer 42 is made of Mg-doped Alｙ Ga １－ｙ N (0≦y<1). The p-type cladding layer 42 is only required to include an Mg-doped AlGaN layer, and may have a superlattice structure in which Mg-doped AlGaN layers and Mg-doped GaN layers are periodically stacked. The Al composition ratio y of the p-type cladding layer 42 is preferably 0.02 to 0.05, and is, for example, 0.03. Here, when the p-type cladding layer 42 is a superlattice composed of AlGaN and GaN, the Al composition ratio means the average Al composition ratio. The total film thickness of the p-type cladding layer 42 is preferably 500 to 800 nm, and is, for example, 650 nm.

[0038] The average Mg concentration throughout the p-type cladding layer 42 is, for example, 3×10 １８ cm －３ ~1 x 10 １９ cm －３ The overall average Mg concentration of the p-type cladding layer 42 is lower than the average Mg concentration of the other layers of the p-type semiconductor layer 40, i.e., the p-type contact layer 43 and the p-type electron blocking layer 41.

[0039] In this embodiment, the p-type cladding layer 42 has a p-type first cladding layer 421 arranged on the light-emitting layer 30 side, and a p-type second cladding layer 422 arranged between the p-type first cladding layer 421 and the p-type contact layer 43. The p-type first cladding layer 421 and the p-type second cladding layer 422 can be distinguished, for example, by their respective Mg concentrations.

[0040] The first p-type cladding layer 421 has a constant Mg concentration C1 in the thickness direction (see FIGS. 2 to 5). The term "constant Mg concentration" means that the variation (deviation) of the Mg concentration in the thickness direction is small and falls within a predetermined concentration range. Typically, the deviation (difference between the maximum and minimum values) is 1×10 １８ cm －３ The following is the result.

[0041] The Mg concentration of the p-type first cladding layer 421, i.e., the first Mg concentration C1, is at least 0.5 to 5×10 １８ cm －３The Mg concentration is preferably controlled to be within the range of 1000 to 15000 at the boundary between the p-type electron blocking layer 41 and the first p-type cladding layer 421 (see FIG. 2). For example, by setting the Mg supply amount in the film formation process of the first p-type cladding layer 421 to 1% or less of the Mg supply amount in the film formation process of the p-type electron blocking layer 41, the Mg concentration can be reduced abruptly, thereby achieving a desired Mg concentration profile.

[0042] The first Mg concentration C1 is 2×10 １８ cm －３ If the first Mg concentration C1 is higher than 1×10, the blue light emitted from the active layer 32 is absorbed by the p-type first cladding layer 421, increasing the optical absorption loss and possibly reducing the power-to-light conversion efficiency. １８ cm －３ If the concentration is lower than this, the element resistance increases, and the power-light conversion efficiency may decrease. １８ cm －３ It is preferable that:

[0043] In a conventional GaN semiconductor light emitting device, as shown in FIG. 2 as a comparative example, the Mg concentration in the p-type cladding layer 42 is 1 to 2×10 throughout the entire p-type cladding layer 42. １９ cm －３ In this case, the device resistance is low, but a high Mg level exists near the light emitting layer 30, so the optical absorption loss is large compared to when the p-type first cladding layer 421 with a low Mg concentration is provided as in this embodiment.

[0044] The p-type second cladding layer 422 has a constant Mg concentration C2 in the thickness direction (see FIGS. 2 to 5). As shown in FIGS. 2 to 5, the second Mg concentration C2 is greater than the first Mg concentration C1. Naturally, the average Mg concentration of the p-type second cladding layer 422 is greater than the average Mg concentration of the p-type first cladding layer 421.

[0045] The Mg concentration of the p-type second cladding layer 422, i.e., the second Mg concentration C2, is at least 0.5×10 １９ cm －３However, the second Mg concentration C2 is controlled to be 2×10 １９ cm －３ If the second Mg concentration C2 is higher than this, the blue light emitted from the active layer 32 may be absorbed by the p-type second cladding layer 422, increasing the optical absorption loss and possibly reducing the power-to-light conversion efficiency. １９ cm －３ It is preferable that:

[0046] The p-type first cladding layer 421 and the p-type second cladding layer 422 can also be distinguished by the inflection point in the Mg concentration profile. An inflection point is a boundary where the rate of change in Mg concentration with depth (the slope of the Mg concentration profile) is larger than the rate of change in Mg concentration in the regions before and after it. There is a difference of at least 10 times between the first Mg concentration C1 of the p-type first cladding layer 421 and the second Mg concentration C2 of the p-type second cladding layer 422, so the Mg concentrations change abruptly at the boundary between them.

[0047] Furthermore, for example, the first p-type cladding layer 421 and the second p-type cladding layer 422 can also be distinguished by their respective growth conditions. That is, when forming the p-type cladding layer 42, the region formed with a first Mg supply rate may be defined as the first p-type cladding layer 421, and the region formed with a second Mg supply rate that is greater than the first Mg supply rate may be defined as the second p-type cladding layer 422.

[0048] In a high-power blue semiconductor laser having a wavelength of 450 nm and having a watt-level optical output per laser used for laser processing, when the thickness of the first p-type cladding layer 421 is 0.3 μm or less, the distribution of laser light intensity is substantially broadened. Furthermore, when the thickness of the first p-type cladding layer 421 is less than 0.2 μm (see FIG. 5 ), the second p-type cladding layer 422 approaches the light-emitting layer 30, which makes it more likely that absorption loss of blue light will occur due to the Mg level in the second p-type cladding layer 422. For this reason, the thickness of the first p-type cladding layer 421 is preferably 0.2 to 0.4 μm, e.g., 0.35 μm.

[0049] The thickness of the p-type second cladding layer 422 is preferably 100 to 600 nm, for example, 300 nm. The total thickness of the p-type cladding layer 42 is preferably 500 to 800 nm, because when the thickness of the p-type first cladding layer 421 is 0.2 to 0.4 μm, the thickness of the p-type second cladding layer 422 falls within the range of 100 to 600 nm.

[0050] The p-type contact layer 43 is made of an Mg-doped GaN layer. The thickness of the p-type contact layer 43 is, for example, 10 nm. The average Mg concentration of the p-type contact layer 43 is set to 1×10 in order to reduce the contact resistance with the p-side electrode 51. ２０ cm －３ It is preferable that this is equal to or greater than this.

[0051] The n-type semiconductor layer 20, the light emitting layer 30, and the p-type semiconductor layer 40 are successively formed by using, for example, a metal organic chemical vapor deposition (MOCVD) method.

[0052] The process of forming the p-type cladding layer 42 includes a first process for forming the p-type first cladding layer 421 and a second process for forming the p-type second cladding layer 422. The first and second processes have different growth conditions, particularly the Mg supply rate. In the first process, an Mg source (TMG) is supplied so that the Mg concentration in the thickness direction of the p-type first cladding layer 421 is constant at a first Mg concentration C1 (first growth condition). In the second process, an Mg source (TMG) is supplied so that the Mg concentration in the thickness direction of the p-type second cladding layer 422 is constant at a second Mg concentration C2 (second growth condition). The Mg supply rate in the second growth condition is set to be larger than the Mg supply rate in the first growth condition.

[0053] The upper surface of the p-type semiconductor layer 40 is processed into a ridge stripe shape, and a p-side electrode 51, a wiring electrode 52, and a pad electrode 53 are arranged in a predetermined pattern. An n-side electrode 54 is arranged on the back surface of the substrate 10. Specifically, each electrode is formed as follows.

[0054] First, a SiO.sub.2 film is deposited on the p-type semiconductor layer 40 (p-type contact layer 43) by using, for example, a thermal CVD method.２ Deposit an insulating film. SiO ２ The insulating film has a thickness of, for example, 0.3 μm. ２ The insulating film is left in stripes with a width of 16 μm, and the other regions are etched away. At this time, the orientation of the stripes is set parallel to the m-axis direction of the hexagonal GaN semiconductor, taking into consideration that the natural cleavage plane (m-plane) of the hexagonal GaN semiconductor is used to form the laser facets.

[0055] Next, SiO ２ The laminated structure on which the insulating film is formed is etched to a depth of, for example, 1.0 μm from the top. A ridge stripe portion that constitutes the optical waveguide WG is formed in the p-type contact layer 43 and the p-type cladding layer 42. Then, SiO ２ The insulating film is removed to expose the p-type contact layer 43 and the p-type cladding layer 42 .

[0056] On the exposed p-type contact layer 43 and p-type cladding layer 42, a SiO.sub.2 layer is again formed by thermal CVD over the entire surface including the ridge stripe portion. ２ Deposit an insulating film. SiO ２ The insulating film has a thickness of, for example, 0.2 μm. ２ The insulating film constitutes the insulating layer 55. SiO ２ A resist pattern having openings corresponding to the ridge stripe portions is formed on the upper surface of the insulating film by lithography.

[0057] Next, for example, trifluoromethane (CHF ３ SiO 2 was etched by reactive ion etching (RIE) using a resist pattern as a mask. ２ The insulating film is etched to expose the p-type contact layer 43 from the top surface of the ridge stripe portion.

[0058] Next, a metal laminate film made of, for example, palladium (Pd) and platinum (Pt) is formed by electron beam (EB) evaporation on at least the p-type contact layer 43 exposed from the upper surface of the ridge stripe portion. For example, the Pd has a thickness of 40 nm, and the Pt has a thickness of 35 nm. The metal laminate film in the region other than the ridge stripe portion is removed by lift-off. A p-side electrode 51 is formed on the upper surface of the p-type contact layer 43 in the ridge stripe portion. The p-side electrode 51 may be made of a transparent oxide such as indium tin oxide or indium oxide.

[0059] Next, SiO ２ The wiring electrode 52 is selectively formed so as to cover the insulating film and the p-side electrode 51. The wiring electrode 52 has, for example, a planar dimension of 750 μm in a direction parallel to the ridge stripe portion and a planar dimension of 150 μm in a direction perpendicular to the ridge stripe portion. The wiring electrode 52 is formed, for example, of a metal laminate film made of titanium (Ti), platinum (Pt), and gold (Au). For example, the thickness of Ti is 50 nm, the thickness of Pt is 200 nm, and the thickness of Au is 100 nm.

[0060] Next, a pad electrode 53 made of an Au layer is formed by electrolytic plating on the upper surface of the wiring electrode 52. The pad electrode 53 has a thickness of, for example, 10 μm. This makes it possible to mount a laser chip by wire bonding and also makes it possible to effectively dissipate heat generated in the active layer 32, thereby improving the reliability of the GaN-based semiconductor light-emitting element 1.

[0061] Next, the back surface of the semiconductor wafer on which the p-side electrode 51, wiring electrode 52, and pad electrode 53 are formed is polished with diamond slurry to thin the substrate 10 to a thickness of approximately 100 μm. Thereafter, an n-side electrode 54 is formed on the back surface of the substrate 10 by, for example, EB evaporation. The n-side electrode 54 is formed of a metal laminate film made of, for example, Ti, Pt, and Au. For example, the Ti has a thickness of 5 nm, the Pt has a thickness of 10 nm, and the Au has a thickness of 1000 nm.

[0062] The wafer-state laminated structure thus fabricated is cleaved (primary cleavage) along the m-plane. The length in the m-axis direction is, for example, 1200 μm. A front coat film (not shown) capable of emitting laser light is disposed on one cleavage surface in the cavity length direction of the optical waveguide WG. Furthermore, a rear coat film for reflecting the laser light is disposed on the other cleavage surface in the cavity length direction of the optical waveguide WG. One end face on which the front coat film is disposed becomes an emission end face from which the laser light is emitted, and the other end face on which the rear coat film is formed becomes a reflection end face that reflects the laser light.

[0063] The front coat film and the rear coat film are formed by, for example, an electron cyclotron resonance (ECR) sputtering method. The front coat film is formed of, for example, SiO ２ The rear coat film is made of a dielectric film such as a single layer film. ２ / SiO ２ It is composed of a dielectric film such as a laminated film.

[0064] The reflectance of the light-emitting end face on which the front coating film is disposed is, for example, 6%, and the reflectance of the light-emitting end face on which the rear coating film is disposed is, for example, 95%. This makes it possible to realize a highly efficient GaN-based semiconductor light-emitting element 1.

[0065] The laminated structure with the front coat film and rear coat film formed thereon is cleaved (secondary cleavage) along the a-plane between the optical waveguides WG formed at a pitch of, for example, 200 μm, thereby producing a GaN-based semiconductor light-emitting element 1 for a semiconductor laser device.

[0066] 2, the Mg concentration changes sharply at the boundary between the p-type electron blocking layer 41 and the first p-type cladding layer 421. On the other hand, when the p-type electron blocking layer 41 and the first p-type cladding layer 421 are formed by MOCVD, the Mg raw material Cp ２ There are cases where Mg is taken into the p-type first cladding layer 421 in an amount greater than the set amount due to the memory effect, or where Mg diffuses from the p-type electron blocking layer 41 into the p-type first cladding layer 421 in a solid phase.

[0067] 3 to 5 , the p-type third cladding layer 423 is interposed between the p-type first cladding layer 421 and the p-type electron blocking layer 41. The p-type third cladding layer 423 is not an intentionally formed layer, but rather a transition layer that is formed as a result of forming the p-type first cladding layer 421 on the p-type electron blocking layer 41. In other words, the growth conditions for the p-type third cladding layer 423 are typically the same as the growth conditions for the p-type first cladding layer 421. Note that the growth conditions for the p-type third cladding layer 423 may be set to be different from the growth conditions for the p-type first cladding layer 421.

[0068] When clearly distinguishing it from the p-type first cladding layer 421, the p-type third cladding layer 423 can be defined as a layer in which the Mg concentration monotonically increases from the p-type first cladding layer 421 toward the p-type electron blocking layer 41. The Mg concentration C3 of the p-type third cladding layer 423 is higher than the Mg concentration C1 of the p-type first cladding layer 421, for example, 2×10 １８ cm －３ Exceeds.

[0069] 4, when the thickness of the p-type third cladding layer 423 is 0.2 μm or less, the effect of providing the p-type first cladding layer 421 can be obtained, that is, the effect of suppressing light absorption loss due to the Mg level in the p-type second cladding layer 422. In other words, when the thickness of the p-type third cladding layer 423 exceeds 0.2 μm, the absorption loss of blue light due to the Mg level in the p-type third cladding layer 423 becomes significant, and deterioration of the device characteristics cannot be ignored.

[0070] Therefore, the thickness of the p-type third cladding layer 423 must be 0.2 μm or less, and preferably 0.1 μm or less. The thickness of the p-type third cladding layer 423 can be controlled by appropriately adjusting the growth conditions of the p-type electron blocking layer 41 and the growth conditions of the p-type first cladding layer 421 in the initial stage of growth.

[0071] For example, by setting the growth temperature in the initial stage of growth of the p-type electron blocking layer 41 and the p-type cladding layer 42 to a low temperature (e.g., 850°C) similar to that of the active layer 32 and the p-side light guiding layer 33 and adjusting the growth rate appropriately, it is possible to suppress diffusion of Mg from the p-type electron blocking layer 41 into the p-type cladding layer 42 (p-type third cladding layer 423).

[0072] When the growth temperature in the initial stage of growth of the p-type electron blocking layer 41 and the p-type cladding layer 42 is low, carbon (C) is incorporated into the initial growth regions of the p-type electron blocking layer 41 and the p-type cladding layer 42, as shown in Fig. 2. C atoms are incorporated into both C lattice sites and Ga lattice sites in the GaN crystal lattice, and have the property of compensating for impurities. By appropriately controlling the concentration of C atoms in the p-type electron blocking layer 41, pairing occurs so that Mg atoms are compensated by C atoms, and diffusion of Mg can be suppressed.

[0073] Here, Mg is known to supply holes at a concentration of about 1 / 10 of the atomic concentration. １９ cm －３ When the hole concentration is about 1×10 １８ cm －３ On the other hand, the C concentration, which has the potential to compensate for holes, is preferably 10% or less of the Mg concentration. If the C concentration is too low, the effect of suppressing the diffusion of Mg atoms decreases. Therefore, the C concentration of the p-type electron blocking layer 41 is set to 5×10 １６ ~1 x 10 １７ cm －３ It is preferable that:

[0074] As described above, the GaN-based semiconductor light-emitting device 1 according to the embodiment has the following characteristics either singly or in appropriate combination.

[0075] That is, the GaN-based semiconductor light-emitting element 1 (nitride semiconductor light-emitting element) is a GaN-based semiconductor element including an n-type semiconductor layer 20, a p-type semiconductor layer 40, and a light-emitting layer 30 between the n-type semiconductor layer 20 and the p-type semiconductor layer 40, in which the p-type semiconductor layer 40 has a p-type contact layer 43 and a p-type cladding layer 42 made of an Mg-doped nitride semiconductor, and the p-type cladding layer 42 has a p-type first cladding layer 421 arranged on the light-emitting layer 30 side, and a p-type second cladding layer 422 arranged between the p-type first cladding layer 421 and the p-type contact layer 43. The average Mg concentration of the p-type second cladding layer 422 is higher than the average Mg concentration of the p-type first cladding layer 421, and the average Mg concentration of the entire p-type cladding layer 42 is lower than that of other layers of the p-type semiconductor layer 40 (e.g., the p-type contact layer 43).

[0076] The method for manufacturing a GaN-based semiconductor light-emitting element 1 (nitride semiconductor light-emitting element) is a method for manufacturing a GaN-based semiconductor light-emitting element 1 including an n-type semiconductor layer 20, a p-type semiconductor layer, and a light-emitting layer 30 between the n-type semiconductor layer and the p-type semiconductor layer, wherein the p-type semiconductor layer 40 has a p-type contact layer 43 and a p-type cladding layer 42 made of an Mg-doped nitride semiconductor, and the step of forming the p-type cladding layer 42 includes a step of forming a p-type first cladding layer 421 on the light-emitting layer 30 side under first growth conditions, and a step of forming a p-type second cladding layer 422 between the p-type first cladding layer 421 and the p-type contact layer 43 under second growth conditions, and the Mg supply amount under the second growth conditions is larger than the Mg supply amount under the first growth conditions.

[0077] According to the GaN-based semiconductor light-emitting element 1 and the manufacturing method thereof according to the embodiment, the p-type second cladding layer 422 with a high Mg concentration ensures low element resistance, while the p-type first cladding layer 421 with a low Mg concentration can reduce the optical absorption loss of blue light due to the Mg level of the p-type second cladding layer 422, thereby increasing the total power-to-light conversion efficiency (the product of current and voltage).

[0078] In the GaN-based semiconductor light-emitting element 1, the p-type semiconductor layer 40 preferably has a p-type electron blocking layer 41 made of an Mg-doped nitride semiconductor at the portion where it is bonded to the light-emitting layer 30. By providing the p-type electron blocking layer 41, the efficiency of hole injection into the active layer 32 can be improved.

[0079] In the GaN-based semiconductor light-emitting device 1, it is preferable that the Mg concentration in the thickness direction of the first p-type cladding layer 421 is constant at a first Mg concentration C1, and the Mg concentration in the thickness direction of the second p-type cladding layer 422 is constant at a second Mg concentration C2 that is higher than the first Mg concentration C1. This makes it possible to easily control the average Mg concentrations of the first p-type cladding layer 421 and the second p-type cladding layer 422, and to make the average Mg concentration of the second p-type cladding layer 422 higher than the average Mg concentration of the first p-type cladding layer 421.

[0080] In the GaN-based semiconductor light-emitting device 1, the first Mg concentration C1 is 1 to 2×10 １８ cm －３ This makes it possible to reduce the device resistance while suppressing the optical absorption loss of blue light due to the Mg level of the p-type first cladding layer 421, and effectively improve the power-to-light conversion efficiency of the GaN-based semiconductor device 1.

[0081] In the GaN-based semiconductor light-emitting device 1, the second Mg concentration is 5×10 １８ cm －３ This makes it possible to effectively reduce the element resistance and improve the power-to-light conversion efficiency of the GaN-based semiconductor element 1.

[0082] In the GaN-based semiconductor light-emitting device 1, the film thickness of the p-type first cladding layer 421 is preferably 0.2 to 0.3 μm, which has the effect of suppressing optical absorption loss of blue light due to Mg levels in the p-type second cladding layer 422, and also substantially widens the distribution of laser light intensity.

[0083] In the GaN-based semiconductor device 1, the p-type cladding layer 42 may have, between the p-type first cladding layer 421 and the p-type electron blocking layer 41, a p-type third cladding layer 423 in which the Mg concentration monotonically increases from the p-type first cladding layer 421 toward the p-type electron blocking layer 41. This allows some diffusion of Mg from the p-type electron blocking layer 41 to the p-type cladding layer 42, making it possible to easily control the Mg concentration in the p-type cladding layer 42.

[0084] In the GaN-based semiconductor device 1, the thickness of the p-type third cladding layer 423 is preferably 0.2 μm or less, which makes it possible to suppress light absorption loss due to Mg levels in the p-type third cladding layer 423.

[0085] In the GaN-based semiconductor light-emitting device 1, the carbon concentration in the p-type electron blocking layer 41 and the p-type third cladding layer 423 is 0.5 to 1×10 １７ cm －３ This makes it possible to suppress the diffusion of Mg from the p-type electron blocking layer 41 to the p-type cladding layer 42, and to suppress the light absorption loss due to the Mg level in the p-type third cladding layer 423.

[0086] The invention made by the inventor has been specifically described above based on an embodiment, but the present invention is not limited to the above embodiment and can be modified within the scope of the gist thereof.

[0087] For example, the GaN-based semiconductor light-emitting device 1 described in the embodiment has a p-type electron blocking layer 41 at the junction between the p-type semiconductor layer 40 and the light-emitting layer 30, but the p-type electron blocking layer 41 may be omitted.

[0088] Furthermore, for example, in the embodiment, a GaN-based semiconductor light-emitting element having a single optical waveguide WG has been described, but the same effects can also be obtained by applying the present disclosure to a GaN-based semiconductor light-emitting element (a so-called bar laser) in which multiple optical waveguides are formed in an array.

[0089] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0090] According to the present disclosure, it is possible to improve the power-to-light conversion efficiency of a nitride semiconductor light-emitting element.

[0091] INDUSTRIAL APPLICABILITY The nitride semiconductor light-emitting element and manufacturing method according to the present disclosure are useful as a blue laser light source suitable for laser processing machines for cutting, welding, and the like, copper materials that are often used in EV motors and the like.

[0092] REFERENCE SIGNS LIST 1 GaN-based semiconductor light-emitting element (nitride semiconductor light-emitting element) 10 Substrate 20 n-type semiconductor layer 30 Light-emitting layer 32 Active layer 40 P-type semiconductor layer 41 P-type electron blocking layer 42 P-type cladding layer 43 P-type contact layer 421 P-type first cladding layer 422 P-type second cladding layer 423 P-type third cladding layer

Claims

1. A nitride semiconductor light-emitting element comprising: an n-type semiconductor layer; a p-type semiconductor layer; and a light-emitting layer between the n-type semiconductor layer and the p-type semiconductor layer, the p-type semiconductor layer having a p-type contact layer and a p-type cladding layer made of an Mg-doped nitride semiconductor, the p-type cladding layer having a p-type first cladding layer arranged on the light-emitting layer side, and a p-type second cladding layer arranged between the first p-type cladding layer and the p-type contact layer, the average Mg concentration of the p-type second cladding layer being higher than the average Mg concentration of the p-type first cladding layer, and the overall average Mg concentration of the p-type cladding layer being lower than other layers of the p-type semiconductor layer.

2. The nitride semiconductor light-emitting element according to claim 1, wherein the p-type semiconductor layer has a p-type electron blocking layer made of an Mg-doped nitride semiconductor at a portion where the p-type semiconductor layer is in contact with the light-emitting layer.

3. The nitride semiconductor light-emitting element according to claim 1 or 2, wherein the first p-type cladding layer has a constant Mg concentration in the thickness direction at a first Mg concentration, and the second p-type cladding layer has a constant Mg concentration in the thickness direction at a second Mg concentration higher than the first Mg concentration.

4. The first Mg concentration is 1 to 2×10 １８ cm －３ The nitride semiconductor light emitting device according to claim 3 , 5. The second Mg concentration is 5×10 １８ cm －３ The nitride semiconductor light emitting device according to claim 3 .

6. The nitride semiconductor light emitting device according to claim 1, wherein the first p-type cladding layer has a thickness of 0.2 to 0.4 μm.

7. The nitride semiconductor light-emitting element according to claim 2, wherein the p-type cladding layer has a p-type third cladding layer between the p-type first cladding layer and the p-type electron blocking layer, the Mg concentration of which monotonically increases from the p-type first cladding layer toward the p-type electron blocking layer.

8. The nitride semiconductor light emitting device according to claim 7, wherein the p-type third cladding layer has a thickness of 0.2 μm or less.

9. The carbon concentration in the p-type electron blocking layer and the p-type third cladding layer is 0.5 to 1×10 １７ cm －３ The nitride semiconductor light emitting device according to claim 7 , 10. A method for manufacturing a nitride semiconductor light-emitting device comprising an n-type semiconductor layer, a p-type semiconductor layer, and a light-emitting layer between the n-type semiconductor layer and the p-type semiconductor layer, wherein the p-type semiconductor layer has a p-type contact layer and a p-type cladding layer made of an Mg-doped nitride semiconductor, and the step of forming the p-type cladding layer comprises the steps of forming a p-type first cladding layer under first growth conditions on the light-emitting layer side, and forming a p-type second cladding layer under second growth conditions between the p-type first cladding layer and the p-type contact layer, and a Mg supply amount under the second growth conditions is greater than a Mg supply amount under the first growth conditions.

Images