Nitride semiconductor light-emitting element

Abstract

To provide a nitride semiconductor light-emitting element having high power-to-light conversion efficiency and high reliability.SOLUTION: A nitride semiconductor light-emitting element according to the present disclosure includes an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer. The light-emitting layer includes an active layer and a p-side optical guide layer disposed in a region adjacent to the p-type semiconductor layer. The p-type semiconductor layer includes a p-type electron blocking layer made of Mg-doped InxAlyGa1-x-yN (0≤x<1, 0<y≤1, 0<x+y≤1) disposed in a region adjacent to the p-side optical guide layer. In profiles of a Mg concentration and an Al composition in a depth direction of the p-side optical guide layer and the p-type electron blocking layer, the Mg concentration peak is located closer to the active layer than the Al composition peak.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to nitride semiconductor light emitting devices. [Background technology]

[0002] Semiconductor laser devices have traditionally 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 a variety of materials, including metals, resins, and composite carbon materials (CFRP: Carbon Fiber Reinforced Plastics).

[0003] In recent years, GaN-based semiconductor light-emitting devices have been attracting attention as light sources for processing copper materials, which are widely used in EV motors, etc. GaN-based semiconductor light-emitting devices emit light in the blue wavelength range of 405 nm to 450 nm, where copper materials have high absorption (low reflectance).

[0004] GaN-based semiconductor light-emitting devices require high power-to-light conversion efficiency. Power-to-light conversion efficiency 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. This in turn reduces the reduction in optical output caused by heat generation and the adverse effects on long-term reliability characteristics of GaN-based semiconductor light-emitting devices.

[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 this 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. The p-type semiconductor layer may also include a p-type electron blocking layer made of a p-type AlGaN semiconductor, which has a larger band gap than the p-type cladding layer, located closer to the active layer than the p-type cladding layer. The p-type electron blocking layer prevents electrons injected from the n-type semiconductor layer side into the active layer from leaking to the p-type semiconductor layer side. Like the p-type cladding layer, the p-type electron blocking layer is doped with Mg as an impurity.

[0006] Patent Document 1 discloses that the depth profiles of the Mg concentration and Al composition in a p-type electron blocking layer are adjusted in order to reduce the operating voltage of a nitride semiconductor light-emitting device. It also describes that in the nitride semiconductor light-emitting device of Patent Document 1, the Mg concentration peak in the depth direction in the p-type electron blocking layer is located closer to the p-type cladding layer than the Al composition peak, i.e., on the opposite side from the light-emitting layer.

[0007] Patent Document 2 also describes providing a p-type electron blocking layer with a higher Mg concentration than the p-type cladding layer at the junction between the p-type cladding layer and the light-emitting layer of a nitride semiconductor light-emitting device, and interposing an undoped AlGaN layer 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. In this nitride semiconductor light-emitting device, the Al composition peak and the Mg concentration peak are located at approximately the same positions in the Al composition and Mg concentration profiles in the depth direction of the p-type electron blocking layer. In the nitride semiconductor light-emitting device of Patent Document 2, the undoped AlGaN layer prevents deterioration of the light-emitting layer due to Mg diffusion. Therefore, optical absorption loss is reduced and power-to-light conversion efficiency is improved compared to when the undoped AlGaN layer is not provided. [Prior art documents] [Patent documents]

[0008] Patent Document 1 Japanese Patent Application Laid-Open No. 2014-127708 Patent Document 2 Japanese Patent No. 5060656 Summary of the Invention<000,0112><000,0113>Problems to be Solved by the Invention<000,0114><000,0115><000,0116><000,0117>However, in the nitride semiconductor devices described in Patent Document 1 and Patent Document 2 above, the electron blocking by the electron blocking layer is not sufficient, and electrons supplied from the n-type semiconductor layer side leak to the p-type semiconductor layer side, resulting in a problem that the light emission efficiency is likely to decrease. In particular, when attempting to form a p-type electron blocking layer doped with Mg by a general method, a doping delay phenomenon due to the properties of Mg is likely to occur. Therefore, the Mg concentration peak tends to shift to the side (p-type cladding layer side) farther from the light emitting layer than the Al composition peak. In this case, in particular, there is a problem that the function as an electron blocking layer deteriorates and the light emission efficiency decreases. <000,0118><000,0119><000,0120>An object of the present disclosure is to provide a nitride semiconductor light emitting device having high power light conversion efficiency and high reliability. <000,0121>Means for Solving the Problems<000,0122><000,0123><000,0124><000,0125>The present disclosure provides a nitride semiconductor light emitting device including an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer, wherein the light emitting layer includes an active layer and a p-side light guide layer disposed in a region adjacent to the p-type semiconductor layer, and the p-type semiconductor layer includes a p-type electron blocking layer made of Mg-doped In 1-x-y , Al y Ga 1-x-y N (0 ≦ x < 1, 0 < y ≦ 1, 0 < x + y ≦ 1), and in the profiles of the Mg concentration and the Al composition in the depth direction of the p-side light guide layer and the p-type electron blocking layer, a nitride semiconductor light emitting device is provided in which the Mg concentration peak is located closer to the active layer side than the Al composition peak. <000,0126>[Effects of the Invention]

[0012] According to the present disclosure, a nitride semiconductor light emitting device having high power-to-light conversion efficiency and high reliability can be obtained. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view of a nitride semiconductor light-emitting device according to one embodiment. [Figure 2] FIG. 2 shows profiles of the Mg concentration and Al composition of the p-type first cladding layer, the p-type electron blocking layer, and the p-side optical guide layer of the nitride semiconductor light-emitting device shown in FIG. [Figure 3] FIG. 3 shows profiles of the Mg concentration and Al composition of the entire p-type semiconductor layer and the p-side optical guide layer of the nitride semiconductor light-emitting device shown in FIG. [Figure 4] FIG. 4 shows the Mg concentration and Al composition profiles of a comparative nitride semiconductor light-emitting device. [Figure 5] FIG. 5(a) shows the profile of the Mg concentration and Al composition of the reference example, and FIG. 5(b) shows the profile for simulation. [Figure 6] FIG. 6 is a diagram showing the simulation results. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, one embodiment of the nitride semiconductor light emitting device of the present disclosure will be described in detail with reference to the drawings. In this specification, the term "nitride semiconductor light emitting device" typically refers to a nitride semiconductor light emitting device in which each layer is formed of a nitride semiconductor material represented by the general formula In x Al y Ga 1-x-y N (0≦x≦1, 0≦y≦1, 0≦x+y≦1). Among these, when the active layer contains Ga, that is, when the active layer contains In, x Al y Ga 1-x-yWhen it is composed of N(0≦x<1, 0≦y<1, 0≦x + y<1), it is referred to as a GaN-based semiconductor light-emitting device in this specification. Hereinafter, as an example of a nitride semiconductor light-emitting device, a GaN-based semiconductor light-emitting device capable of emitting blue light with a wavelength of 445 nm will be described. However, the nitride semiconductor light-emitting device of the present disclosure is not limited thereto. Also, the values of the Al and In compositions in each layer of the nitride semiconductor light-emitting device in this specification are those obtained by analyzing the nitride semiconductor light-emitting device itself or a film for evaluation grown under equivalent film-forming conditions by X-ray diffraction method (XRD: X-ray diffraction).

[0015] FIG. 1 is a cross-sectional view of a GaN-based semiconductor light-emitting device 1 according to the present embodiment. As shown in FIG. 1, the GaN-based semiconductor light-emitting device 1 of the present embodiment has a laminated structure in which an n-type semiconductor layer 20, a light-emitting layer 30, and a p-type semiconductor layer 40 are sequentially formed on a substrate 10. Also, the GaN-based semiconductor light-emitting device 1 has a ridge stripe type optical waveguide WG. In the GaN-based semiconductor light-emitting device 1, the n-type impurity is silicon (Si), and the p-type impurity is magnesium (Mg). The configuration of the GaN-based semiconductor light-emitting device 1 described below is an example, and the laminated 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 group III elements forming each layer, etc. can be appropriately changed.

[0016] The substrate 10 of the GaN-based semiconductor light-emitting device 1 is, for example, an n-type hexagonal GaN substrate having a (0001) plane.

[0017] 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, Si-doped Al y Ga 1-y N(where 0 < y < 1), and the Al composition ratio y is, for example, 0.03. The film thickness of the n-type semiconductor layer 20 is, for example, about 3 μm. The Si concentration of the n-type semiconductor layer 20 is, for example, 1×10 18 cm -3 or so.

[0018] The n-type semiconductor layer 20 can be formed by metal organic chemical vapor deposition (MOCVD). For example, trimethylgallium (TMG) or trimethylaluminum (TMA) can be used as a Group III raw material. For example, ammonia (NH3) can be used as a Group V raw material. For example, silane (SiH4) can be used as a Si raw material.

[0019] The light emitting layer 30 is a layer that emits blue light when a current is applied. In this embodiment, the light emitting layer 30 has 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.

[0020] The n-side optical guide layer 31 is a Si-doped In x Ga 1-x N (0≦x<1), for example, it is composed of a first optical guide layer made of Si-doped GaN with an In composition ratio x of 0, and a second optical guide layer made of Si-doped InGaN containing In (not shown).

[0021] The first optical guide layer is a layer disposed on the n-type semiconductor layer 20 side of the n-side optical guide layer 31, and is made of Si-doped GaN. The film 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.

[0022] The second optical guide layer is a layer disposed on the active layer 32 side of the n-side optical guide layer 31. The second optical guide layer is made of InGaN, and its In composition ratio x gradually increases from the first optical guide layer side. The film thickness of the second optical guide layer is, for example, 150 nm. The second optical guide layer is not intentionally doped with Si, and the Si concentration is, for example, 5×10 15 cm -3 It is about the following.

[0023] The n-side light guide layer 31 (first and second light guide layers) can be formed continuously with the n-type semiconductor layer 20 by metal organic chemical vapor deposition (MOCVD). The same Group III and Group V raw materials and Si raw materials as those described above can be used. Trimethylindium (TMI) can be used as the In raw material.

[0024] During the deposition of the second optical guide layer, the In composition ratio x can be increased, for example, by gradually increasing the supply rate of the In source material (TMI). Alternatively, the In composition ratio x of the second optical guide layer can be increased by gradually decreasing the supply rate of the Ga source material (TMG) while keeping the supply rate of the TMI constant. In this case, it is preferable to increase the supply rate of the SiH4 source material in accordance with the increase in the supply rate of the TMG in order to maintain the Si concentration substantially constant.

[0025] Furthermore, instead of gradually changing the TMI supply rate or TMG supply rate, TMI may be supplied in a pulsed manner and the duty may be gradually increased, thereby substantially continuously increasing the In composition ratio x of the second optical guide layer. Furthermore, since the amount of In taken up increases when the growth temperature is lowered, the In composition ratio x of the second optical guide layer may be increased by gradually lowering the growth temperature while keeping the TMI supply rate and TMG supply rate constant. It is preferable that the composition ratio x of the second optical guide layer increase monotonically.

[0026] The active layer 32 is 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), and one example is a structure having a two-period multiple quantum well structure in which quantum well layers and barrier layers are alternately stacked. In this case, 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 arranged in this order on the n-side optical guide layer 31.

[0027] The first barrier layer is, for example, an In layer having a thickness of 20 nm. x Ga 1-xThe first quantum well layer is, for example, an InN layer (x=0.03) having a thickness of 3.0 nm. x Ga 1-x The second barrier layer is an In layer (x=0.18) with a thickness of 10 nm. x Ga 1-x The second quantum well layer is, for example, an InN layer (x=0.08) having a thickness of about 3.0 nm. x Ga 1-x The third barrier layer is an InN layer (x=0.18) having a thickness of 10 nm. x Ga 1-x N layer (x=0.03).

[0028] If each barrier layer is too thick, the internal quantum efficiency will decrease due to radiative recombination in the barrier layer. 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.

[0029] The active layer 32 (quantum well layer and barrier layer) can be formed continuously with the n-side light guide layer 31 by metal organic chemical vapor deposition (MOCVD). The group III and group V raw materials are the same as those for the other layers.

[0030] The p-side optical guide layer 33 is a layer disposed between the active layer 32 and a p-type electron blocking layer 41 described later, and 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, an undoped InGaN layer, an undoped GaN layer, an undoped AlGaN layer, or a layer made of a combination thereof. The total film thickness of the p-side optical guiding layer 33 is, for example, 0.2 μm.

[0031] From the viewpoint of the light confinement effect inside the device, the p-side light guiding layer 33 preferably has a structure in which the refractive index decreases from the active layer 32 side toward the p-type semiconductor layer 40 (p-type electron blocking layer 41) side. For example, the light confinement effect can be improved by forming the p-side light guiding layer 33 by stacking an InGaN layer, a GaN layer, and an AlGaN layer (none of which are shown) in this order from the active layer 32 side.

[0032] The p-side light guiding layer 33 can be formed continuously with the active layer 32 by metalorganic chemical vapor deposition (MOCVD). The group III and group V raw materials are the same as those for the other layers. As will be described later, the p-side light guiding layer 33 is preferably doped with Mg near the interface between the p-side light guiding layer 33 and the p-type electron blocking layer 41, and the region of the p-side light guiding layer 33 on the p-type electron blocking layer 41 side may also be doped with Mg. The Mg concentration and Al composition profiles of the p-side light guiding layer, and the doping of the p-side light guiding layer with Mg will be described in detail later.

[0033] 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 .

[0034] The p-type electron blocking layer 41 is a layer disposed adjacent to the p-side optical guide layer 33, and is made of Mg-doped In. x Al y Ga 1-x-yIt is composed of N(0≦x<1, 0<y≦1, 0<x + y≦1). For example, it may be a Mg-doped AlGaN layer or a Mg-doped InAlGaN layer. The p-type electron blocking layer 41 is a layer for improving the hole injection efficiency into the active layer 32. Here, the Al composition ratio y of the p-type electron blocking layer 41 is preferably 0.35 or more, for example, 0.35. The film thickness of the p-type electron blocking layer 41 is preferably 2 nm or more and 7 nm or less, more preferably 3 nm or more and 6 nm or less, for example, 5 nm. The film thickness is measured using, for example, the transmission electron microscopy (TEM) method. The p-type electron blocking layer 41 satisfies specific requirements in terms of the profiles of the Mg concentration and the Al composition. The profiles of the Mg concentration and the Al composition will be described in detail later.

[0035] The film formation of the p-type electron blocking layer 41 can be carried out continuously with the film formation of the p-side optical guide layer 33 and can be formed by the metalorganic chemical vapor deposition (MOCVD) method. The group III raw materials and group V raw materials are the same as those of other layers. For the Mg raw material, for example, cyclopentadienyl magnesium (Cp2Mg) can be used. By adjusting the doping timing of Mg during the film formation of the p-type electron blocking layer 41, a p-type electron blocking layer 41 having the Mg concentration profile described later can be obtained. For example, by starting the doping of Mg immediately before the end of the growth of the p-side optical guide layer 33 and not performing the doping of Mg (stopping the supply of the Mg raw material) in the latter half of the growth of the p-type electron blocking layer 41, the desired p-type electron blocking layer 41 can be obtained.

[0036] The p-type cladding layer 42 is, for example, Mg-doped Al y Ga 1-yN (0≦y<1). The p-type cladding layer 42 may have a superlattice structure in which Mg-doped AlGaN layers and Mg-doped GaN layers are periodically stacked. In this case, 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. When the p-type cladding layer 42 has a superlattice structure made of AlGaN and GaN, the Al composition ratio means the average Al composition ratio. The entire thickness of the p-type cladding layer 42 is preferably 500 to 800 nm, and is, for example, 620 nm. In this case, the average Mg concentration of the entire p-type cladding layer 42 is, for example, 3×10 18 cm -3 ~1×10 19 cm -3 The overall average Mg concentration of the p-type cladding layer 42 is set to be lower than the average Mg concentration of the other layers of the p-type semiconductor layer 40, namely the p-type contact layer 43 and the p-type electron blocking layer 41.

[0037] Alternatively, the p-type cladding layer 42 may be composed of a first p-type cladding layer 421 and a second p-type cladding layer 422 having a higher Mg concentration than the first p-type cladding layer 421. The first p-type cladding layer and the second p-type cladding layer 422 preferably have a constant Mg concentration in the thickness direction. "Constant Mg concentration" means that the variation (deviation) in the Mg concentration in the thickness direction is small and falls within a predetermined concentration range, and typically the deviation (difference between the maximum and minimum values) is 1×10 18 cm -3 The first p-type cladding layer 421 and the second p-type cladding layer 422 can be distinguished by, for example, their respective Mg concentrations.

[0038] 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 greater than the first Mg supply rate may be defined as the second p-type cladding layer 422. The Mg concentration in the p-type cladding layer 42 (the first p-type cladding layer 421 and the second p-type cladding layer 422) will be described in detail later.

[0039] When the p-type cladding layer 42 includes the first p-type cladding layer 421 and the second p-type cladding layer 422, the thickness of the first p-type cladding layer 421 is preferably 0.2 to 0.4 μm, for example, 0.35 μm. In particular, for a high-power blue semiconductor laser with a wavelength of 450 nm and a watt-level optical output per laser used for laser processing, the thickness is preferably 0.3 μm or less, from the viewpoint of substantially widening the distribution of laser light intensity. On the other hand, if the thickness of the first p-type cladding layer 421 is 0.2 μm or more, the second p-type cladding layer 422 is farther from the light-emitting layer 30, and absorption loss of blue light due to the Mg level of the second p-type cladding layer 422 is less likely to occur.

[0040] Furthermore, the p-type second cladding layer 422 is processed into a ridge stripe shape, and the thickness of the ridge stripe portion of the p-type second cladding layer 422 is preferably 100 to 600 nm, for example, 300 nm. The thickness of the entire p-type cladding layer 42 is preferably 500 to 800 nm, and when the thickness of the p-type first cladding layer 421 is 200 to 400 nm, the thickness of the p-type second cladding layer 422 is preferably in the range of 100 to 600 nm.

[0041] The p-type cladding layer can be formed continuously with the p-type electron blocking layer 41, and can be formed by metal organic chemical vapor deposition (MOCVD). The materials are the same as those for the other layers. When forming the p-type first cladding layer 421 and the p-type second cladding layer 422 as the p-type cladding layer 42, these layers can be formed by varying the amount of Mg raw material (TMG).

[0042] The p-type contact layer 43 is a layer disposed on the ridge-stripe-shaped p-type second cladding layer 422, and 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 1×10 20 cm -3 It is preferable that this is equal to or greater than this.

[0043] In the GaN-based semiconductor light-emitting device 1 of this embodiment, 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 above the p-type semiconductor layer 40. In addition, an n-side electrode 54 is arranged on the back surface of the substrate 10. These can be formed by, for example, performing the following steps after forming a stack of the substrate 10 / n-type semiconductor layer 20 / light-emitting layer 30 / p-type semiconductor layer 40.

[0044] An SiO2 insulating film is formed on the p-type semiconductor layer 40 (p-type contact layer 43) by, for example, thermal CVD. The thickness of the SiO2 insulating film is, for example, 0.3 μm. By photolithography and etching using hydrofluoric acid, the SiO2 insulating film is left in stripes with a width of, for example, 16 μm, and other regions are etched. At this time, taking into consideration that the natural cleavage plane (m-plane) of the hexagonal GaN-based semiconductor is used to form the laser facets, the stripes are oriented parallel to the m-axis direction of the hexagonal GaN-based semiconductor.

[0045] Next, the stacked structure on which the SiO2 insulating film has been formed is etched to a depth of, for example, 1.0 μm by an inductively coupled plasma (ICP) etching method. As a result, a ridge stripe portion constituting the optical waveguide WG is formed in the p-type contact layer 43 and the p-type cladding layer 42. Thereafter, the SiO2 insulating film is removed using hydrofluoric acid to expose the p-type contact layer 43 and the p-type cladding layer 42.

[0046] An SiO2 insulating film is again formed by thermal CVD over the entire surface, including the ridge stripe portion, on the exposed p-type contact layer 43 and p-type cladding layer 42. The thickness of the SiO2 insulating film is, for example, 0.2 μm. This SiO2 insulating film constitutes the insulating layer 55. A resist pattern having an opening corresponding to the ridge stripe portion is formed on the upper surface of the SiO2 insulating film by lithography.

[0047] Next, the SiO2 insulating film is etched using the resist pattern as a mask by reactive ion etching (RIE) using, for example, methane trifluoride (CHF3) gas, to expose the p-type contact layer 43 from the top surface of the ridge stripe portion.

[0048] 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 thickness of Pd is 40 nm, and the thickness of Pt is 35 nm. The metal laminate film in the region other than the ridge stripe portion is removed by lift-off. As a result, 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.

[0049] Next, a wiring electrode 52 is selectively formed by lithography and lift-off so as to cover the SiO2 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, from 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.

[0050] Next, a pad electrode 53 made of an Au layer is formed on the upper surface of the wiring electrode 52 by electrolytic plating. 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.

[0051] 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 about 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.

[0052] 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. 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 surface on which the front coat film is disposed becomes an emission end surface from which the laser light is emitted, and the other end surface on which the rear coat film is disposed becomes a reflection end surface that reflects the laser light.

[0053] The front coat film and rear coat film are formed by, for example, electron cyclotron resonance (ECR) sputtering. The front coat film is made of a dielectric film such as a single layer of SiO2. The rear coat film is made of a dielectric film such as a ZrO2 / SiO2 laminated film.

[0054] 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.

[0055] The laminated structure with the front and rear coating films 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.

[0056] (Mg concentration and Al composition profile) The Mg concentration and Al composition profiles of the p-side light guiding layer 33 and the p-type electron blocking layer 41 will be described below. Fig. 2 shows the Mg concentration and Al composition profiles in the depth direction of the p-side light guiding layer 33, the p-type electron blocking layer 41, and the first p-type cladding layer 421 of the above-mentioned GaN-based semiconductor light-emitting device 1. In this specification, the term "Mg concentration and Al composition profile" refers to both the Mg concentration profile in the depth direction and the Al composition profile in the depth direction, and in this application, both are shown in a single graph, for example, as shown in Fig. 2. Unless otherwise specified, the Mg concentration profile and the Al composition profile were obtained by analyzing each layer by secondary ion mass spectrometry (SIMS).

[0057] In Figure 2, the solid line indicates the Mg concentration profile C21, and the dashed line indicates the Al composition profile C22. Both are measurements obtained by SIMS analysis. In the SIMS analysis, the interval between adjacent measurement points is approximately 1.5 nm. The Mg concentration profile C21 was quantitatively analyzed in the SIMS analysis. The Al composition profile C22 is the signal intensity in the SIMS analysis, and is not quantified as an absolute value of the composition in the SIMS analysis.

[0058] 2, in the GaN-based semiconductor light-emitting device 1 of this embodiment, in the profiles of the Mg concentration and Al composition in the depth direction of the p-side light guiding layer 33 and the p-type electron blocking layer 41, the Mg concentration peak M21 is located closer to the active layer 32 than the Al composition peak A22. As described above, the Mg concentration profile C21 can be realized by, for example, starting Mg doping immediately before the end of growth of the p-side light guiding layer 33 and not performing Mg doping (stopping the supply of Mg raw material) during the first half or the second half of the growth of the p-type electron blocking layer 41.

[0059] FIG. 4 shows the Mg concentration and Al composition profiles in the depth direction of the p-side light guide layer 33 and the p-type electron blocking layer 41 when a semiconductor light-emitting device (comparative example) having a configuration similar to that of the GaN-based semiconductor light-emitting device 1 described above is fabricated by a known method. The solid line indicates the Mg concentration profile C41, and the dashed line indicates the Al composition profile C42. In the GaN-based semiconductor light-emitting device 1, Mg doping is performed simultaneously with the formation of the p-type electron blocking layer 41. If Mg is doped simultaneously with the start of the formation of the p-type electron blocking layer 41, a doping delay occurs in the Mg, and the Mg concentration peak M41 is located closer to the p-type first cladding layer 421 than the Al composition peak A42. In this case, since there is a certain distance between the Mg and the light-emitting layer 30 (laser light), optical absorption loss due to the Mg level is unlikely to occur. However, leakage current is likely to increase significantly, reducing overall efficiency.

[0060] To prevent the leakage current, it is possible to dope the p-type electron blocking layer 41 with an excessive amount of Mg. However, an increase in the amount of Mg in the p-type electron blocking layer 41 increases the light absorption loss of the semiconductor light-emitting element 1, resulting in a decrease in the power-to-light conversion efficiency. Furthermore, excess Mg diffuses into the light-emitting layer during crystal growth of the element structure, resulting in a decrease in the reliability of the semiconductor light-emitting element 1. Therefore, such an excessive addition of Mg is not desirable.

[0061] The increase in the leakage current occurs when positive charges are generated on the p-type electron blocking layer 41 side due to strain generated at the interface between the p-type electron blocking layer 41 and the p-side light guiding layer 33. When positive charges are generated on the p-type electron blocking layer 41 side, the potential at the p-side light guiding layer interface decreases, and the electron barrier of the p-type electron blocking layer 41 also decreases, reducing its electron blocking function.

[0062] In contrast, when the Mg concentration peak M21 of the Mg concentration profile C21 is located closer to the p-side light guide layer 33 than the Al composition peak A22 of the Al composition profile C22, as in this embodiment, the depleted Mg acceptors cancel out the positive charges generated at the interface between the p-type electron blocking layer 41 and the p-side light guide layer. This suppresses a decrease in the potential of the p-type electron blocking layer 41. In other words, to fully utilize the effects of the p-type electron blocking layer 41, it is sufficient to perform Mg doping near the interface between the p-type electron blocking layer 41 and the p-side light guide layer to cancel out the positive charges generated at the interface. By achieving this Mg concentration profile C21, electrons injected into the light-emitting device from the n-side are effectively blocked by the p-type electron blocking layer 41, reducing leakage current and improving internal quantum efficiency. Improving internal quantum efficiency reduces the rate of conversion to heat within the light-emitting device, suppressing the generation of new defects and significantly improving device reliability.

[0063] This effect is demonstrated by the following simulation results. FIG. 5(a) shows a Mg concentration profile C51 and an Al composition profile C52 of a GaN semiconductor light-emitting device (reference example) in which the Mg concentration peak and the Al composition peak are at approximately the same position (depth). FIG. 5(b) shows a Mg concentration profile C53 and an Al composition profile C54 when the film thickness at the Mg concentration peak in FIG. 5(a) is added by a distance L55 toward the p-side light guide layer 33. FIG. 6 shows the calculation results of the leakage electron current and the optical absorption loss when the length L55 in FIG. 5(b) is changed from 0 to 10 nm. FIG. 6 also shows the leakage electron current and the optical absorption loss when the rising position of the Mg concentration peak on the active layer 32 side is shifted by 5 μm toward the p-type first cladding layer 421 while keeping the position of the Mg concentration peak fixed as in FIG. 5(a) (in FIG. 6, the values ​​are shown as when the "additional film thickness is -5 nm"). Furthermore, in Figure 6, there are two peak values ​​of Mg concentration (1.0 × 10 19 cm -3 , and 1.6 × 10 19 cm -3 ) The calculation results are shown below.

[0064] As shown in FIG. 6, as the film thickness of the Mg concentration peak was increased on the p-side optical guiding layer 33 side, the leakage current decreased and saturated. This result shows that the leakage current can be decreased by moving the Mg concentration peak position toward the p-side optical guiding layer 33 side. Furthermore, the optical absorption loss increased as the Mg concentration peak value increased, and also increased as the additional film thickness to the p-side optical guiding layer 33 increased. This is because the optical absorption due to the Mg level increases as Mg approaches the light-emitting layer 30 (laser light). On the other hand, when the additional film thickness is negative, the optical absorption loss decreases slightly, but the leakage current increases, which is undesirable. In view of these results, it is recommended that the Mg concentration peak be 1.0×10 19 cm -3 In this case, adding a few nm to the p-side guide layer reduces the leakage current to 0.15 kA / cm 2 and the optical absorption loss is reduced to 3cm -1Therefore, according to the present disclosure, it is possible to achieve a desired Mg profile, reduce optical absorption loss due to the Mg level, and suppress leakage current of electrons injected into the light-emitting device to the p-layer side, thereby improving internal quantum efficiency and thereby improving reliability.

[0065] The position (depth) of the Mg concentration peak M21 in the Mg concentration profile C21 may be closer to the active layer 32 than the Al composition peak A21, and may be, for example, in the p-side light guide layer 33 or in the p-type electron blocking layer 41. However, as can be seen from the above calculation results, it is preferable that the Mg concentration peak M21 be located in the p-type electron blocking layer 41 in order to suppress light absorption loss. Furthermore, the Mg concentration peak M21 may be located on the p-side light guide layer 33 side (first half side) of the p-type electron blocking layer 41 or on the p-type cladding layer 42 side (second half side). It is particularly effective to locate the Mg concentration peak M21 in the range (position) where the slope of the Al composition profile C22 is maximum, closer to the active layer 32 than the Al composition peak A21 of the Al composition profile C22.

[0066] Furthermore, the half width of the Mg concentration peak C21 and the half width of the Al composition peak A21 may be approximately equal, but in the p-type electron blocking layer 41, the balance between the reduction in light absorption loss and the increase in carrier injection efficiency due to the reduction in leakage current is particularly good when the half width of the Mg concentration peak C21 is smaller than the half width of the Al composition peak A21.

[0067] As mentioned above, Mg doped more than necessary into the p-type electron blocking layer 41 absorbs the blue laser emitted from the light emitting layer, causing optical absorption loss. Therefore, as shown in FIG. 2, the value of the Mg concentration peak M21 is 0.8×10 19 cm -3 or greater than 1.2×10 19 cm -3By setting the content in this range, not only is it possible to obtain an acceptor concentration sufficient to cancel out the positive charge generated at the interface, but also, since Mg is not excessively doped, solid-phase diffusion to the light-emitting layer 30 side is less likely to occur, and a decrease in reliability due to deterioration of the light-emitting layer 30 is suppressed.

[0068] Next, Figure 3 shows the Mg concentration profile C31 (solid line) and Al composition profile C32 (dashed line) in the depth direction of the p-side light guiding layer 33 and the entire p-type semiconductor layer 40, and also explains the Mg concentration profile other than the p-type electron blocking layer 41 of the p-type semiconductor layer 40.

[0069] The first p-type cladding layer 421 preferably has a constant Mg concentration (first Mg concentration) M32 in the thickness direction. The Mg concentration M32 of the first p-type cladding layer 421 is preferably 0.5 to 5×10 18 cm -3 It is preferable that the Mg concentration changes sharply at the boundary between the p-type electron blocking layer 41 and the first p-type cladding layer 421. Such a sharp change in the Mg concentration can be achieved, for example, by setting the amount of Mg supplied in the process of forming the first p-type cladding layer 421 to 1% or less of the amount of Mg supplied in the process of forming the p-type electron blocking layer 41.

[0070] The first Mg concentration M32 is 2 × 10 18 cm -3 If the first Mg concentration M32 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 decreasing 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. Therefore, the first Mg concentration M32 is set to 1 to 2 × 10 18 cm -3 It is preferable that:

[0071] In a conventional GaN semiconductor light emitting device, the Mg concentration in the p-type cladding layer 42 is 1 to 3×1019 cm -3 In this case, the device resistance is low, but a high Mg concentration exists near the light-emitting layer. Therefore, by providing the p-type first cladding layer 421 with a low Mg concentration as in this embodiment, it is possible to reduce the optical absorption loss.

[0072] Furthermore, it is preferable that the Mg concentration (second Mg concentration) M33 of the p-type second cladding layer 422 is constant in the thickness direction, and the second Mg concentration M33 should be greater than the first Mg concentration M32. 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. From the viewpoint of reducing resistance, the Mg concentration of the p-type second cladding layer 422, i.e., the second Mg concentration M33, should be at least 0.5×10 19 cm -3 However, it is preferable to control the second Mg concentration M33 to be 2×10 or more. 19 cm -3 If the second Mg concentration M33 is higher than this, the blue light emitted from the active layer 32 is absorbed by the p-type second cladding layer 422, increasing the optical absorption loss and decreasing the power-to-light conversion efficiency. 19 cm -3 It is preferable that:

[0073] The first p-type cladding layer 421 and the second p-type 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 greater than the rate of change in Mg concentration in the regions before and after it. There is a difference of at least three times between the first Mg concentration M32 in the first p-type cladding layer 421 and the second Mg concentration M33 in the second p-type cladding layer 422, so the Mg concentrations change abruptly at their boundary.

[0074] Although the invention made by the inventor has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments and can be modified within the scope of the gist thereof.

[0075] 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 be obtained by applying the present disclosure to a GaN-based semiconductor light-emitting element (so-called bar laser) in which multiple optical waveguides are formed in an array.

[0076] 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. [Industrial Applicability]

[0077] INDUSTRIAL APPLICABILITY The nitride semiconductor light-emitting element and manufacturing method according to the present disclosure are useful as blue laser light sources suitable for laser processing machines for cutting, welding, and the like, copper materials that are often used in EV motors and the like. [Explanation of symbols]

[0078] 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

Claims

1. A nitride semiconductor light emitting device including an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer, the light emitting layer includes an active layer and a p-side optical guide layer disposed in a region adjacent to the p-type semiconductor layer, The p-type semiconductor layer is an Mg-doped In layer disposed in a region adjacent to the p-side optical guide layer. ｘ Al ｙ Ga １－ｘ－ｙ N (0≦x<1, 0<y≦1, 0<x+y≦1), In the profiles of Mg concentration and Al composition in the depth direction of the p-side light guiding layer and the p-type electron blocking layer, an Mg concentration peak is located closer to the active layer than an Al composition peak. Nitride semiconductor light emitting device.

2. the Mg concentration peak is located on the active layer side of the Al composition peak, in a region where the gradient of the Al composition profile is maximum; The nitride semiconductor light emitting device according to claim 1 .

3. The Mg concentration at the Mg concentration peak is 0.8×10 １９ cm －３ or greater than 1.2 x 10 １９ cm －３ Below is the The nitride semiconductor light-emitting device according to claim 1 or 2.

4. the half width of the Mg concentration peak is smaller than the half width of the Al composition peak; The nitride semiconductor light-emitting device according to claim 1 or 2.

5. the p-type semiconductor layer includes a p-type first cladding layer disposed adjacent to a surface of the p-type electron blocking layer opposite to the p-side optical guiding layer, The Mg concentration of the p-type first cladding layer is 1×10 １８ cm －３ Greater than or equal to 2 x 10 １８ cm －３ is as follows: the thickness of the p-type first cladding layer is 0.2 μm or more and 0.4 μm or less; The nitride semiconductor light-emitting device according to claim 1 or 2.

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