Light emitting element

Abstract

To provide a light emitting element capable of reducing absorption of an ultraviolet light by an electrode and increasing a luminous efficiency while securing conduction between the electrode and a semiconductor.SOLUTION: A light emitting element (1) comprises: a semiconductor structure body (100) that includes an n-side layer (20), a p-side layer (40), and an active layer (30) that is positioned between the layers, and emits an ultraviolet light; an n-side electrode (50) that is electrically connected to the n-side layer; and a p-side electrode (60) that is electrically connected to the p-side layer. The n-side layer includes: an undoped first layer (21); and a second layer (22) that is positioned between the active layer and the first layer, and contains an n-type impurity. The n-side electrode includes a first electrode (51) and a second electrode (52) that are in contact with the second layer and not in contact with the first layer. A reflection ratio to a peak wavelength of light emitted by the active layer of the first electrode is higher than that to the peak wavelength of light emitted by the active layer of the second electrode, and a contact resistance between the second electrode and the second layer is lower than that of the first electrode and the second layer.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The invention according to the present disclosure relates to a light-emitting element.

Background Art

[0002] As a light-emitting element that emits ultraviolet light, for example, Patent Document 1 discloses a group III nitride semiconductor light-emitting element having an emission peak wavelength of 200 to 350 nm.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present disclosure is to provide a light-emitting element capable of reducing the absorption of ultraviolet light by an electrode while ensuring conduction between the electrode and the semiconductor, thereby increasing the light-emitting efficiency.

Means for Solving the Problems

[0005] The light-emitting element according to the present disclosure includes a semiconductor structure including an n-side layer, a p-side layer, and an active layer located between the n-side layer and the p-side layer, each of which is made of a nitride semiconductor and emits ultraviolet light, an n-side electrode electrically connected to the n-side layer, a p-side electrode electrically connected to the p-side layer, the n-side layer has an undoped first layer and a second layer located between the active layer and the first layer and containing an n-type impurity, the n-side electrode includes a first electrode and a second electrode that are in contact with the second layer and not in contact with the first layer, the reflectance of the first electrode with respect to the peak wavelength of the light emitted by the active layer is higher than the reflectance of the second electrode with respect to the peak wavelength of the light emitted by the active layer, The contact resistance between the second electrode and the second layer is lower than the contact resistance between the first electrode and the second layer. It is a light-emitting element.

Effect of the Invention

[0006] The light-emitting element of the present disclosure can reduce the absorption of ultraviolet light by the electrode while ensuring the conduction between the electrode and the semiconductor, thereby increasing the light-emitting efficiency.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Embodiments for Carrying Out the Invention

[0008] (Embodiment 1) Embodiment 1 of the light-emitting element of the present disclosure is shown in a plan view or a cross-sectional view in each of FIGS. 1 to 2. FIG. 1 is a plan view of the light-emitting element 1 of this embodiment. FIG. 3 is a plan view schematically showing the arrangement of the n-side layer and the p-side layer constituting the light-emitting element 1. FIG. 4 is a plan view schematically showing the arrangement of the n-side electrode 50 and the p-side electrode 60 of the light-emitting element 1. The hatched area indicates the area where each member is arranged in a plan view and does not show a cross-section. FIG. 5 is a cross-sectional view schematically showing a part of the light-emitting element 1 along the line I-I of FIG. 1 of the n-side electrode 50 in FIG. 1. FIG. 2 is a cross-sectional view schematically showing the light-emitting element 1 along the line II-II of FIG. 1.

[0009] As shown in these figures, the light-emitting element 1 of this embodiment has a substrate 10 and a semiconductor structure 100 disposed on the substrate 10. As shown in FIGS. 2 and 5, the semiconductor structure 100 has an n-side layer 20, a p-side layer 40, and an active layer 30 located between the n-side layer 20 and the p-side layer 40, each of which is made of a nitride semiconductor and emits ultraviolet light. The n-side layer 20 has an undoped first layer 21 and a second layer 22 containing an n-type impurity located between the active layer 30 and the first layer 21. The light-emitting element 1 includes an n-side electrode 50 electrically connected to the n-side layer 20 and a p-side electrode 60 electrically connected to the p-side layer 40. Further, the light-emitting element 1 has an insulating layer 70, an n-side pad electrode 80, and a p-side pad electrode 90. The n-side pad electrode 80 is electrically connected to the n-side electrode 50 through a first opening 71 formed in the insulating layer 70, and the p-side pad electrode 90 is electrically connected to the p-side electrode 60 through a second opening 72 formed in the insulating layer 70. The semiconductor structure 100 is formed on the substrate 10. In Embodiment 1, the ultraviolet light emitted by the active layer 30 is mainly extracted from the side of the substrate 10.

[0010] As shown in FIGS. 4 and 5, the n-side electrode 50 includes a first electrode 51 and a second electrode 52. Both the first electrode 51 and the second electrode 52 are in contact with the second layer 22 and not in contact with the first layer 21. The reflectance of the first electrode 51 with respect to the peak wavelength of the light emitted by the active layer 30 is higher than the reflectance of the second electrode 52 with respect to the peak wavelength of the light emitted by the active layer 30. Also, the contact resistance of the second electrode 52 with the second layer 22 is lower than the contact resistance of the first electrode 51 with the second layer 22.

[0011] Metals with high reflectance to ultraviolet light tend to have high contact resistance with the n-side layer 20. Also, when annealed to reduce the contact resistance between the n-side layer 20 and the metal disposed on the n-side layer 20, the metal disposed on the n-side layer 20 tends to have a reduced reflectance. On the other hand, metals with low reflectance to ultraviolet light tend to have low contact resistance with the n-side layer 20. In the present embodiment, when a current flows through the light-emitting element 1, the first electrode 51 reflects the light emitted by the active layer 30 while playing a role of moving electrons, and the second electrode 52 serves to supply electrons to the n-side layer 20. Therefore, according to the present embodiment, as shown in FIG. 1, when the n-side electrode 50 is disposed in a relatively wide range for current dispersion, it is possible to reduce the absorption of ultraviolet light by the n-side electrode 50 while reducing the unevenness of light emission by dispersing the current, and improve the light emission efficiency.

[0012] In this embodiment, as shown in FIG. 5, both the first electrode 51 and the second electrode 52 are in contact with the second layer 22 containing n-type impurities and are not in contact with the undoped first layer 21. That is, in the exposed region 22a of the n-side layer 20 where the n-side electrode 50 is disposed, the first layer 21 is not exposed from the second layer 22. Since the undoped first layer 21 tends to have a large contact resistance with a metal, both the first electrode 51 and the second electrode 52 are in contact with the second layer 22 containing n-type impurities and are not in contact with the undoped first layer 21, thereby reducing the increase in the forward voltage Vf. Further, in the n-side layer 20, the undoped first layer 21 is a portion where the electrical resistance is large and it is difficult to function as a current path, and the second layer 22 is a portion where the electrical resistance is small and it is easy to function as a current path because it contains n-type impurities. In this embodiment, since the exposed region 22a of the n-side layer 20 where the n-side electrode 50 is disposed does not expose the first layer 21, the variation in current in the n-side layer 20 can be reduced, and as a result, the unevenness of light emission in the light-emitting element 1 can be reduced.

[0013] Here, the undoped layer is a layer that is not intentionally doped with n-type impurities or p-type impurities. When the undoped layer is adjacent to a layer that is intentionally doped with at least one of n-type impurities and p-type impurities, at least one of n-type impurities and p-type impurities may be contained in the undoped layer due to diffusion from the adjacent layer or the like. Even if the undoped first layer 21 contains n-type impurities, it contains them at a concentration lower than 1×10 17 / cm 3 The second layer 22 contains n-type impurities at a concentration of, for example, 5×10 18 / cm 3 or more and 1×10 20 / cm 3 or less.

[0014] Hereinafter, this embodiment will be described in more detail. <Substrate> As the material of the substrate 10, for example, sapphire, silicon (Si), gallium nitride (GaN), aluminum nitride (AlN), etc. can be used. The substrate 10 made of sapphire is preferable because it has high translucency to ultraviolet rays from the active layer 30. The semiconductor structure 100 can be disposed, for example, on the c-plane of the sapphire substrate, and is preferably disposed on a plane inclined in the range of 0.2° or more and 2° or less in the a-axis direction or the m-axis direction of the sapphire substrate from the c-plane of the sapphire substrate. The thickness of the substrate 10 can be, for example, 150 μm or more and 800 μm or less. The light-emitting element 1 may not have the substrate 10.

[0015] The planar shape of the substrate 10 is, for example, rectangular. When the planar shape of the substrate 10 is rectangular, the length of one side can be about 500 μm or more and 2000 μm or less. The upper surface of the substrate 10 has a first substrate region 10a where the semiconductor structure 100 is disposed and a second substrate region 10b where the semiconductor structure 100 is not disposed. In a plan view, the first substrate region 10a is surrounded by the second substrate region 10b. The boundary between the first substrate region 10a and the second substrate region 10b is located, for example, in the range of 10 μm or more and 30 μm or less from the outer edge of the substrate 10. Here, as shown in FIG. 1, the direction parallel to one side of the substrate 10 is defined as the first direction D1, and the direction orthogonal to the first direction D1 is defined as the second direction D2.

[0016] <Semiconductor structure> The semiconductor structure 100 is a laminate in which a plurality of semiconductor layers made of a nitride semiconductor are laminated. The nitride semiconductor includes semiconductors of all compositions in which the composition ratios x and y are changed within their respective ranges in the chemical formula of In x Al y Ga 1-x-y N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1).

[0017] The semiconductor structure 100 has an n-side layer 20, an active layer 30, and a p-side layer 40. The active layer 30 is disposed between the n-side layer 20 and the p-side layer 40.

[0018] The n-side layer 20 includes one or more n-type semiconductor layers, and as described above, includes the undoped first layer 21 and the second layer containing n-type impurities. Examples of the n-type impurity include silicon (Si), germanium (Ge), and the like. The n-type semiconductor layer is, for example, an AlGaN layer containing aluminum (Al), gallium (Ga), and nitrogen (N), and may contain indium (In).

[0019] The n-side layer 20 may include, for example, in order from the substrate 10 side, a third layer 23 as a superlattice layer, an undoped first layer 21 as an underlying layer, and a second layer 22 containing n-type impurities as an n-contact layer.

[0020] The third layer 23 has a multilayer structure in which a semiconductor layer A and a semiconductor layer B having a lattice constant different from that of the semiconductor layer A are alternately laminated. The third layer 23 has a function of relaxing the stress generated in the semiconductor layer disposed above the third layer 23. The third layer 23 can have, for example, a multilayer structure in which an AlN layer and an aluminum gallium nitride (AlGaN) layer are alternately laminated. In the third layer 23, the number of pairs of the first semiconductor layer and the second semiconductor layer can be 20 pairs or more and 50 pairs or less. The total thickness of the third layer 23 can be, for example, 300 nm or more and 3000 nm or less, particularly 600 nm or more and 1600 nm or less. Further, the third layer 23 can be an undoped layer.

[0021] For the first layer 21, an undoped AlGaN layer can be used, for example. When the first layer 21 as the underlying layer is an AlGaN layer, the Al composition ratio of the AlGaN layer can be, for example, 50% or more. The thickness of the first layer 21 can be, for example, 200 nm or more and 1000 nm or less, particularly 400 nm or more and 600 nm or less.

[0022] For the second layer 22, a layer made of AlGaN containing an n-type impurity can be used, for example. When the second layer as the n-contact layer is an AlGaN layer, the Al composition ratio of the AlGaN layer can be, for example, 50% or more. In this specification, for example, an AlGaN layer having an Al composition ratio of 50% means Al X Ga1-X In the chemical formula consisting of N, it means an AlGaN layer where the composition ratio x is 0.5. The n-type impurity concentration of the second layer 22 is, for example, 5×10 18 / cm 3 or more and 1×10 20 / cm 3 or less. The thickness of the second layer 22 may be, for example, 1000 nm or more and 3000 nm or less, particularly 1500 nm or more and 2500 nm or less.

[0023] As shown in FIG. 3, the second layer 22, which is an n-contact layer, has an exposed region 22a that is exposed from the p-side layer 40 and the active layer 30. As shown in FIG. 4, the n-side electrode 50 is disposed on a part of the exposed region 22a. Here, when x is exposed from y, or y exposes x, it means that a part of x is covered by y while another part of x is not covered by y, and it is allowed that the part not covered by y is further covered by another element or member.

[0024] As shown in FIG. 3, in plan view, the exposed region 22a has a first region 22a1 extending in a first direction D1 and a second region 22a2 extending from the first region 22a1 in a second direction D2 orthogonal to the first direction D1 and located between the p-side layers 40 in the first direction D1. A plurality of the second regions 22a2 are arranged. When a plurality of the second regions 22a2 are arranged, it is preferable that the second regions 22a2 are arranged at substantially equal intervals in the first direction D1. With this arrangement, the variation in the current density distribution can be reduced. Here, "substantially equal intervals" means that a deviation in interval of 1 μm or less is allowed.

[0025] In FIG. 3, the region located at the outer edge of the substrate 10 indicated by reference numeral 10a is a first substrate region where the substrate 10 is exposed from the semiconductor structure 100. Neither the n-side electrode 50 nor the p-side electrode 60 is disposed in the first substrate region 10a. The width of the first substrate region 10a may be, for example, 940 μm or more and 970 μm or less.

[0026] The shape configurations of the first region 22a1 and the second region 22a2 may be, for example, as follows. Length of the first region 22a1 in the first direction D1: 70% or more and 85% or less of the length of the substrate in the first direction D1 Length of the first region 22a1 in the second direction D2: 5% or more and 20% or less of the length of the substrate in the second direction D2 Number of the second regions 22a2: 3 or more and 6 or less Length of the second region 22a2 in the first direction D1: 5% or more and 20% or less of the length of the substrate in the first direction D1 Length of the second region 22a2 in the second direction D2: 70% or more and 85% or less of the length of the substrate in the second direction D2 Interval of the second regions 22a2 in the first direction D1 (distance between the center lines of the second regions in the second direction D2): 5% or more and 20% or less of the length of the substrate in the Y direction

[0027] The p-side layer 40 includes one or more p-type semiconductor layers. The p-type semiconductor layer is, for example, a semiconductor layer containing a p-type impurity such as magnesium (Mg). The p-side layer may include a plurality of layers having different p-type impurity concentrations and / or Al composition ratios. The concentration of the p-type impurity is, for example, 1×10 19 / cm 3 or more and 1×10 21 / cm 3 or less.

[0028] When the p-side layer 40 includes three p-type semiconductor layers, from the side closer to the substrate 10, a lower layer with an Al composition ratio of 60% or more and 70% or less, a middle layer with an Al composition ratio of 30% or more and 60% or less, and an upper layer with an Al composition ratio of 3% or less may be arranged in this order. When the p-side layer 40 has these three layers, a part of the upper layer may be removed to expose the middle layer, and the p-side electrode 60 may be arranged to contact the exposed regions of the upper layer and the middle layer. This arrangement can reduce the absorption of light from the active layer 30 by the upper layer with a large Al composition ratio and thus easily absorb ultraviolet light, while efficiently reflecting the light from the active layer 30 at the interface between the p-side electrode and the middle layer. Also, by arranging the p-side electrode 60 to contact not only the middle layer but also the upper layer, the contact resistance between the p-side electrode 60 and the p-side layer 40 can be made smaller compared to the case where it is arranged to contact only the middle layer. Furthermore, since the p-side electrode 60 contacts the surfaces of the middle layer and the upper layer, the adhesion between the p-side electrode 60 and the p-side layer 40 can be improved compared to the case where the p-side electrode 60 contacts only the surface of the upper layer.

[0029] When the p-side layer 40 includes the above three layers, it is preferable that the thickness of the lower layer is greater than that of either the middle layer or the upper layer. The thickness of the lower layer may be, for example, 20 nm or more and 40 nm or less. The thickness of the middle layer may be, for example, 3 nm or more and 20 nm or less, particularly 3 nm or more and 15 nm or less. The thickness of the upper layer may be, for example, 3 nm or more and 20 nm or less, particularly 3 nm or more and 15 nm or less. Also, the p-side layer 40 may further include another layer between the lower layer and the active layer 30.

[0030] As shown in FIG. 3, the p-side layer 40 has a base portion 40a extending in the first direction D1 and a plurality of extending portions 40b extending in the second direction D2. In a plan view, all the sides of the second region 22a2 parallel to the second direction D2 face the extending portions 40b. With this arrangement, all the sides of the second region 22a2 extending in the second direction D2 will face the p-side layer 40. Also, the extending portions 40b located at both ends in the first direction D1 are longer in the second direction D2 than the other extending portions 40b so as to face the ends of the first region 22a1 in the first direction D1.

[0031] The length of the base 40a of the p-side layer 40 in the second direction D2 is determined by, for example, the lengths of the first region 22a1 and the second region 22a2. The length of the extension 40b in the first direction D1 is determined by the length and the interval of the second region 22a2 in the first direction D1. The length of the extension 40b in the second direction D2 is determined by the length of the second region 22a2 in the second direction D2 and has substantially the same length as the length of the second region 22a2 in the second direction D2.

[0032] The active layer 30 has a well layer containing Al and a barrier layer containing Al. The active layer 30 has, for example, a multiple quantum well structure including a plurality of well layers and a plurality of barrier layers. The Al composition ratio of the barrier layer is larger than that of the well layer. That is, the bandgap energy of the barrier layer is larger than that of the well layer. Light having an emission wavelength corresponding to the bandgap energy of the well layer is emitted from the well layer containing Al. Note that the active layer 30 is not limited to a multiple quantum well structure including a plurality of well layers and may be a single quantum well structure. At least a part of the well layer and the barrier layer may contain at least one of an n-type impurity and a p-type impurity.

[0033] For the well layer, a layer made of, for example, AlGaN can be used. The Al composition ratio of the well layer can be, for example, 30% or more and 50% or less. For example, when the emission peak wavelength of light from the well layer is about 280 nm, an AlGaN layer having an Al composition ratio of about 42% can be used for the well layer. The peak wavelength of the ultraviolet light emitted from the well layer may be 100 nm or more and 280 nm or less (C wave), or may be 280 nm or more and 315 nm or less (B wave), or may be 315 nm or more and 405 nm or less (A wave). For the barrier layer, a layer made of, for example, AlGaN can be used. The Al composition ratio of the barrier layer can be, for example, 30% or more and 60% or less.

[0034] The thickness of the well layer can be, for example, 3 nm or more and 6 nm or less. The thickness of the barrier layer is, for example, 2 nm or more and 4 nm or less.

[0035] The active layer 30, together with the p-side layer 40, exposes the second layer 22 which is the second layer of the n-side layer 20. Therefore, the shape and dimensions of the active layer 30 in plan view are substantially the same as those of the p-side layer 40.

[0036] A buffer layer (not shown) may be disposed between the substrate 10 and the semiconductor structure 100. For the buffer layer, for example, a layer made of AlN can be used. The buffer layer has a function of relaxing the lattice mismatch between the substrate 10 and the nitride semiconductor layer disposed on the buffer layer. The thickness of the buffer layer can be, for example, 1.5 μm or more and 4 μm or less. It can be.

[0037] <n-side electrode> The n-side electrode 50 is disposed in the exposed region 22a and has a first electrode 51 and a second electrode 52. As shown in FIG. 4, the first electrode 51 has a shape that is substantially similar to the exposed region 22a in plan view. As shown in FIG. 5, in cross-sectional view, the first electrode 51 is located between the second electrodes 52, at least a part of two side surfaces of the first electrode 51 is in contact with the second electrode 52, and the bottom surface of the first electrode 51 and the bottom surface of the second electrode 52 are both in contact only with the second layer 22. According to this arrangement, the current path between the second electrode 52 and the p-side electrode 60 can be shortened, and an increase in Vf can be reduced.

[0038] The reflectance of the first electrode 51 with respect to the peak wavelength of the light emitted by the active layer 30 is higher than the reflectance of the second electrode 52 with respect to the peak wavelength of the light emitted by the active layer 30. Also, the contact resistance between the second electrode 52 and the exposed region 22a (i.e., the second layer 22) is lower than the contact resistance between the first electrode 51 and the second region 22a2.

[0039] The first electrode 51 may be made of a material containing at least one metal selected from Au, Ag, Al, Ni, Pd, Ge, Si, Sn, Ti, Rh, Pt, Mo, Ta, Ru, and W. For example, it may be made of an alloy containing one or more of these metals as components. It is preferable that the surface of the first electrode 51 in contact with the second layer 22 has a reflectivity of 60% or more, particularly 85% or more, with respect to the peak wavelength of ultraviolet light from the active layer 30. Metals that reflect ultraviolet light with a high reflectivity are, for example, Al, Mg, and Ru. The contact surface of the first electrode 51 with the second layer 22 preferably contains at least one selected from these metals. For example, when the contact surface of the first electrode 51 with the second layer 22 is made of an alloy of Al and another metal, the proportion of Al is preferably 70 atomic% or more. The metal that forms an alloy with Al may be, for example, Si, Cu, or Ti. The first electrode 51 may have a laminated structure having a plurality of layers. The first electrode 51 having a laminated structure may be, for example, a structure in which an Al-Cu alloy layer, a Ti layer, and a Ru layer are laminated in this order from the side closer to the second layer 22.

[0040] The second electrode 52 may be made of a material containing at least one metal selected from Au, Ag, Al, Ni, Pd, Ge, Si, Sn, Ti, Rh, Pt, Mo, Ta, Ru, and W. For example, it may be made of an alloy containing one or more of these metals as components. The second electrode 52 may be subjected to an annealing treatment to improve the ohmic contact with the n-side layer 20, and the reflectivity of the metal after the annealing treatment is generally lower than the reflectivity before the annealing. Therefore, even when the first electrode 51 and the second electrode 52 are made of the same metal, the relationship between the reflectivity and the contact resistance may be satisfied. The second electrode 52 may have a laminated structure having a plurality of layers. The first electrode 51 having a laminated structure may be, for example, a structure in which a Ti-Al-Si alloy layer, a Ta layer, and a Ru layer are laminated in this order from the side closer to the second layer 22.

[0041] The first electrode 51 functions as a path for transporting electrons supplied from the n-side pad electrode 80, and can reflect the ultraviolet light emitted from the active layer 30 with a high reflectivity, thereby improving the light emission efficiency of the light emitting element 1. In the present embodiment, although the area where the second electrode 52 having a lower contact resistance with the second layer 22 contacts the second layer 22 is smaller than the case where the entire n-side electrode 50 is the second electrode 52, as shown in FIG. 5, the second electrode 52 is arranged so as to cover the side surface of the first electrode 51 and contact the second layer 22. Therefore, while reducing the variation in the current density distribution, electrons are supplied to the active layer 30, and in combination with the reflection of ultraviolet light by the first electrode 51, the light emission efficiency of the entire light emitting element 1 is improved.

[0042] As shown in FIG. 5, in a cross-sectional view, when the first electrode 51 and the second electrode 52 are arranged side by side in contact with the exposed region 22a, the area of the first electrode 51 in contact with the exposed region 22a and the area of the second electrode 52 in contact with the exposed region 22a may be either larger. When the area of the first electrode 51 in contact with the exposed region 22a is larger than the area of the second electrode 52 in contact with the exposed region 22a, the effect of improving the light emission efficiency due to the reflection of ultraviolet light tends to be greater. When the area of the second electrode 52 in contact with the exposed region 22a is larger than the area of the first electrode 51 in contact with the exposed region 22a, the contact resistance between the entire n-side electrode 50 and the exposed region 22a (i.e., the second layer 22) becomes lower, and Vf tends to be lower.

[0043] In FIG. 4, the first electrode 51 is arranged over substantially the entire length of the second direction D2 of the second region 22a2 and substantially the entire length of the first direction D1 of the first region 22a1. The first electrode 51 does not necessarily have to be arranged over substantially the entire length of the second direction D2 of the second region 22a2. Also, the first electrode 51 does not necessarily have to be arranged over substantially the entire length of the first direction D1 of the first region 22a1. Further, the first electrode 51 may not be arranged in each of the first regions 22a1, but may be arranged only in part.

[0044] In any case of arranging the first electrode 51, in plan view, the total area where the first electrode 51 contacts the exposed region 22a is preferably 35% or more and 70% or less, particularly 45% or more and 55% or less, of the ratio of the total area where the entire n-side electrode 50 contacts the exposed region 22a. When the ratio of the total area where the first electrode 51 contacts the exposed region 22a is small, the effect of improving the light emission efficiency due to the reflection of ultraviolet light tends to be small. When it is large, the ratio of the area where the second electrode 52 contacts the exposed region 22a becomes small, and Vf tends to increase.

[0045] In FIG. 5, the first electrode 51 is disposed in a recess defined by the side surface of the second electrode 52 and the upper surface of the second layer 22. As shown in FIG. 5, the first electrode 51 may be in contact with the upper surface of the second electrode 52. By arranging the first electrode 51 in this way, the adhesion with the second electrode 52 can be improved. A part of the first electrode 51 does not necessarily have to be in contact with the upper surface of the second electrode.

[0046] The arrangement of the first electrode 51 and the second electrode 52 is not limited to that shown in FIGS. 4 and 5. The arrangement of the first electrode 51 and the second electrode 52 may be, for example, an arrangement opposite to that shown in FIG. 5. Specifically, the second electrode 52 may be disposed in a recess defined by the side surface of the first electrode 51 and the upper surface of the second layer 22. Alternatively, only one side surface of the first electrode 51 may be in contact with the second electrode 52, one side surface of the n-side electrode 50 may be the side surface of the first electrode 51, and the other side surface may be the side surface of the second electrode 52. However, it is preferable that the entire outer edge of the first electrode 51 is surrounded by the outer edge of the second electrode 52. By the second electrode 52 surrounding the outer edge of the first electrode, in plan view, at the boundary between the p-side layer 40 and the n-side layer 20, the p-side layer 40 and the p-side electrode 60 face the second electrode 52, and current easily flows between the n-side electrode 50 and the p-side electrode 60, so the variation in the current density distribution is reduced.

[0047] In plan view, it is preferable that 70% or more of the outer edge of the n-side electrode 50 faces the p-side layer 40. With such a shape and arrangement of the n-side electrode 50, current more easily flows between the n-side electrode 50 and the p-side electrode 60, and variations in the current density distribution are further reduced. The outer edge of the n-side electrode 50 facing the p-side layer 40 is more preferably the outer edge of the second electrode 52. According to this arrangement, as described above, the p-side layer 40 and the p-side electrode 60 face the second electrode 52, and current more easily flows between the n-side electrode 50 and the p-side electrode 60, so variations in the current density distribution are further reduced.

[0048] The thickness of the first electrode 51 may be, for example, 0.1 μm or more and 1 μm or less, particularly 0.5 μm or more and 0.8 μm or less. The thickness of the first electrode 51 refers to the shortest distance among the distances between the surface of the first electrode 51 that forms a boundary with the exposed region 22a and the surface of the first electrode 51 facing said surface and parallel to the semiconductor structure 100 forming surface of the substrate 10, and corresponds to the distance indicated by t1 in FIG. 5. When the thickness of the first electrode 51 is within the above range, while reducing the resistance of the first electrode 51, the n-side pad electrode 80 can be easily formed.

[0049] The thickness of the second electrode 52 may be, for example, 0.5 μm or more and 1.5 μm or more, particularly 0.7 μm or more and 1 μm or less. The thickness of the second electrode 52, similar to the thickness of the first electrode 51, refers to the shortest distance among the distances between the surface of the second electrode 52 that forms a boundary with the exposed region 22a and the surface of the second electrode 52 facing said surface and parallel to the semiconductor structure 100 forming surface of the substrate 10, and corresponds to the distance indicated by t2 in FIG. 5. When the thickness of the second electrode 52 is within the above range, while reducing the resistance of the second electrode 52, the n-side pad electrode 80 can be easily formed.

[0050] <p-side electrode> The p-side electrode 60 is disposed substantially over the entire upper surface of the p-side layer 40. The p-side electrode 60 may be made of a metal that reflects the ultraviolet light emitted by the active layer 30 to the n-side layer 20. It is preferable to use a metal having a reflectivity of 50% or more, preferably 60% or more, with respect to the peak wavelength of the ultraviolet light for the p-side electrode 60. For example, it is preferable to use a metal such as Rh or Ru as the p-side electrode 60. The p-side electrode 60 may have a laminated structure in which a plurality of metal layers are laminated. For example, the p-side electrode 60 may have a laminated structure in which a Ru layer, a Ni layer, and an Au layer are laminated in this order from the semiconductor structure 100 side. Further, for example, the p-side electrode 60 may have a laminated structure in which a Ti layer, a Rh layer, and a Ti layer are laminated in this order from the semiconductor structure 100 side. The thickness of the p-side electrode 60 may be, for example, 300 nm or more and 1500 nm or less.

[0051] <Insulating layer> The light-emitting element 1 of the present embodiment has a configuration in which an n-side pad electrode 80 and a p-side pad electrode 90 are disposed on the same surface side of the semiconductor structure 100. In the present embodiment, the insulating layer 70 is used to ensure electrical insulation between the n-side electrode 50 and the p-side electrode 60 and electrical connection between these electrodes and the n-side pad electrode 80 and the p-side pad electrode 90 so that the n-side pad electrode 80 and the p-side pad electrode 90 can be disposed on the right side and the left side of FIG. 1, respectively. In FIG. 1, the insulating layer 70 covers the semiconductor structure 100, the n-side electrode 50, and the p-side electrode, and a first opening 71 that exposes a part of the surface of the n-side electrode 50 and a second opening 72 that exposes a part of the surface of the p-side electrode 60 are disposed in the insulating layer 70.

[0052] A material selected from SiO2, SiN, SiON, etc. can be used for the insulating layer 70. The thickness of the insulating layer 70 may be 1 μm or more and 2 μm or less. The insulating layer 70 may be a multilayer film composed of two or more layers.

[0053] <Pad electrode> The n-side pad electrode 80 and the p-side pad electrode 90 are portions that are electrically connected to an external power source. The n-side pad electrode 80 is electrically connected to the n-side electrode 50 at the first opening 71 of the insulating layer 70, and the p-side pad electrode 90 is electrically connected to the p-side electrode 60 at the second opening 72 of the insulating layer 70.

[0054] The n-side pad electrode 80 and the p-side pad electrode 90 are shown by solid lines in FIG. 1 in a plan view. In the plan view, the area of the n-side pad electrode 80 and the area of the p-side pad electrode 90 are each, for example, 20% or more and 40% or less of the area of the light-emitting element 1 in the plan view.

[0055] The n-side pad electrode 80 and the p-side pad electrode 90 may be made of a material containing at least one metal selected from, for example, Au, Ag, Pt, Ti, Ni, Ge, Rh, and Ru, and may be made of an alloy containing one or more of these metals as components, particularly a eutectic. Examples of the eutectic used for the n-side pad electrode 80 and the p-side pad electrode 90 are Au-Sn eutectic and Ag-Sn eutectic. The thicknesses of the n-side pad electrode 80 and the p-side pad electrode 90 may each be 720 nm or more and 1080 nm or less.

[0056] (Embodiment 2) Next, Embodiment 2 will be described. In the following description and FIGS. 6 to 8, members described using the same reference numerals as those in Embodiment 1 are the same members as those described in Embodiment 1, and the description regarding Embodiment 1 applies except for the parts different from Embodiment 1. FIG. 6 shows an example in which the first electrode 51 of the n-side electrode 50 is disposed over substantially the entire length of the second region 22a2 of the exposed region 22a of the second layer 22 shown in FIG. 3. In FIG. 6, only the second electrode 52 is disposed in the first region 22a1 shown in FIG. 3. FIG. 7 is a cross-sectional view schematically showing a part of the light-emitting element 102 along line I-I in FIG. 6, and FIG. 8 is a cross-sectional view schematically showing a part of the light-emitting element 102 along line II-II in FIG. 6.

[0057] In a plan view, each of the second regions 22a2 is sandwiched by the p-side layer 40 and is a portion where the second electrode 52 and the p-side electrode 60 form a short current path. Therefore, the active layer 30 located near the second region 22a2 has a large emission amount and is likely to have a high luminance. In the present embodiment, by disposing the first electrode 51 only near the portion where the emission amount is likely to be large, ultraviolet light can be efficiently reflected. Further, by disposing only the second electrode 52 having a lower contact resistance with the second layer 22 in the first region 22a1, an increase in Vf caused by the disposition of the first electrode 51 can be further reduced.

[0058] The first electrode 51 does not have to be disposed over substantially the entire length of the second region 22a2 in the second direction D2. Further, the first electrode 51 does not have to be disposed on all of the plurality of second regions 22a2 and may be disposed only on a part thereof. For example, the first electrode 51 may not be disposed on two second regions 22a2 located at both ends in the first direction D1 among the plurality of second regions 22a2, and the first electrode 51 may be disposed on the second region 22a2 sandwiched by the two second regions 22a2 located at both ends in the first direction D1. By disposing the first electrode 51 in this manner, the emission intensity near the center of the light-emitting element 1 can be increased, and the light distribution control can be easily performed. In the present embodiment, in any case of disposing the first electrode 51, in a plan view, the total area where the first electrode 51 contacts the second region 22a2 is preferably 10% or more and 80% or less of the ratio of the area where the entire n-side electrode 50 contacts the second region 22a2, and may particularly be 30% or more and 60% or less.

[0059] (Embodiment 3) Next, Embodiment 3 will be described. In the following description and FIGS. 9 to 11, members described using the same reference numerals as those in Embodiment 1 are the same members as those described in Embodiment 1, and the description regarding Embodiment 1 applies except for the portions different from Embodiment 1.

[0060] FIG. 9 shows an example in which the first electrode 51 of the n-side electrode 50 is disposed in the first region 22a1 of the exposed region 22a of the second layer 22 shown in FIG. 3. In FIG. 9, only the second electrode 52 is disposed in the second region 22a2 shown in FIG. 3. FIG. 10 is a cross-sectional view schematically showing a part of the light-emitting element 1 along the line I-I in FIG. 9, and FIG. 11 is a cross-sectional view schematically showing a part of the light-emitting element 103 along the line II-II in FIG. 9.

[0061] According to this arrangement, the reflection of ultraviolet light by the first electrode 51 is performed in the first region 22a1, and in the second region 22a2, the second electrode 52 is in good electrical contact with the second layer 22. According to this configuration, the supply of electrons from the n-side electrode 50 to the n-side layer 20 in the second region 22a2 where current is likely to concentrate is smoothed, and an increase in the Vf of the entire light-emitting element 1 due to the arrangement of the first electrode 51 can be reduced. Moreover, since ultraviolet light is reflected in the first region 22a1, the luminous efficiency can be improved. According to Embodiment 3, the reliability of the light-emitting element 1 can be increased. That is, the vicinity of the second region 22a2 is likely to generate heat due to the concentration of current. Such heat generation may cause a failure of the light-emitting element 1. According to the present embodiment, by disposing the second electrode 52 having a relatively small contact resistance with the second layer 22 in a region where current is likely to concentrate, heat generation in the vicinity of the second region 22a2 can be reduced, and as a result, the reliability of the light-emitting element 1 can be increased.

[0062] (Embodiment 4) Next, Embodiment 4 will be described. In the following description and FIGS. 12 to 14, members described using the same reference numerals as those in Embodiment 1 are the same members as those described in Embodiment 1, and the description regarding Embodiment 1 applies except for the parts different from Embodiment 1.

[0063] In this embodiment, the upper surface of the exposed region 22a of the second layer 22 has a recess 24 corresponding to the position where the first electrode 51 is disposed, and a part of the first electrode 51 is located within the recess 24. The shape of the recess 24 in plan view is shown in FIG. 12, and a partial cross-sectional view of the light-emitting element 104 showing a cross-section of the n-side electrode 50 with a part of the first electrode 51 located within the recess 24 is shown in FIG. 13.

[0064] Since a part of the first electrode 51 is located within the recess 24, the area where the first electrode 51 contacts the second layer 22, that is, the area that reflects the ultraviolet light emitted by the active layer 30, increases, and the luminous efficiency can be further improved.

[0065] The area of the recess 24 in plan view may be, for example, 10% or more and 70% or less, particularly 30% or more and 50% or less of the area of the exposed region 22a in plan view. In the second region 22a2, the length in the first direction D1 of the recess 24 may be 30 μm or more and 50 μm or less, and in the first region a1, the length in the second direction D2 of the recess 24 may be 30 μm or more and 80 μm or less.

[0066] The bottom surface of the recess 24 does not reach the undoped first layer 21. As described above, the first layer 21 is a portion with a large electrical resistance and is not easily functional as a current path. Therefore, since the bottom surface of the recess 24 does not reach the first layer 21, the second layer 22 can be positioned below the recess 24, making it easier to diffuse the current. The depth of the recess 24 is preferably 0.1 μm or more and 5 μm or less, and more preferably 0.5 μm or more and 3 μm or less. By setting the depth of the recess 24 within such a range, while sufficiently obtaining the effect of improving the luminous efficiency due to the increase in the contact area between the first electrode 51 and the second layer 22, the thickness of the second layer 22 located below the recess 24 can be maintained, and the current can be easily diffused.

[0067] As shown in Fig. 13, when the side surface defining the concave portion 24 is inclined in a cross-sectional view, the angle θ formed by the bottom surface defining the concave portion 24 and the side surface defining the concave portion 24 is preferably 100° or more and 140° or less, and more preferably 110° or more and 130° or less. When the inclination angle is within these ranges, the first electrode 51 and the second layer 22 can be satisfactorily adhered to each other. Also, when the angle θ is within these ranges, the luminous efficiency is further improved. This is considered to be because the concave portion 24 serves to reduce the total internal reflection of the light reflected by the first electrode 51 within the semiconductor structure 100, and the total internal reflection is further reduced because the angle formed by the bottom surface defining the concave portion 24 and the side surface defining the concave portion 24 is within these ranges.

[0068] As shown in Fig. 14, the concave portion 24 may be disposed only in the second region 22a2 of the exposed region 22a of the second layer 22. As described above, since the active layer 30 located in the vicinity of the second region 22a2 is likely to have a large light emission amount, the first electrode 51 disposed in the concave portion 24 located in the second region 22a2 can efficiently reflect light. On the other hand, by not disposing the concave portion 24 in the first region 22a1, the thickness of the second layer 22 in the first region 22a1 can be increased, and an increase in Vf can be reduced. The arrangement of the concave portion 24 shown in Fig. 14 is preferably combined with the arrangement of the first electrode 51 in Embodiment 2.

[0069] In FIGS. 13 and 12, the recess 24 may be disposed only in a part of the second region 22a2. The recess 24 may be disposed only in a part of the first region 22a1. For example, the recess 24 may not be disposed in two second regions 22a2 located at both ends in the first direction D1 among a plurality of second regions 22a2, and the recess 24 may be disposed in a second region 22a2 sandwiched between two second regions 22a2 located at both ends in the first direction D1. By disposing the recess 24 in this way, the light emission intensity near the center of the light emitting element 1 is increased, and the light distribution control becomes easier. In FIGS. 13 and 12, the recess 24 may, for example, extend only partially in the second region 22a2 and not over the entire length of the first electrode 51 in the second direction D2. In FIG. 13, the recess 24 may, for example, extend only partially in the first region 22a1 and not over the entire length of the first electrode 51 in the first direction D1.

[0070] (Embodiment 5) Next, Embodiment 5 will be described. In the following description and FIGS. 15 to 17, members described using the same reference numerals as those in Embodiment 1 are the same members as those described in Embodiment 1, and the description regarding Embodiment 1 applies except for the parts different from Embodiment 1.

[0071] In the present embodiment, the first region 22a1 and the second region 22a2 of the exposed region 22a of the second layer 22 each have a plurality of recesses 24. FIG. 15 shows a form in which the first region 22a1 and the second region 22a2 each have a plurality of circular recesses 24 in a plan view. FIG. 16 is a partial cross-sectional view of the light emitting element 105 showing a state in which the first electrode 51 is continuously disposed in a plurality of recesses 24 along the line I-I of FIG. 15. Each recess 24 is defined by a bottom surface and an inclined side surface, similar to the recess 24 shown in Embodiment 4, and its three-dimensional shape is a frustum of a cone. Since the first electrode 51 is continuously disposed across a plurality of recesses, the contact area between the first electrode 51 and the second layer 22 is further increased, so the amount of ultraviolet light reflected is further increased, and the light emission efficiency is further increased.

[0072] The preferred depth of each recess 24 and the preferred inclination angle of the side wall shown in FIG. 15 are as described in Embodiment 4 above. In FIG. 15, the planar shape of each recess 24 is circular, but the planar shape of each recess 24 is not limited to this, and may be a polygon such as a triangle and a quadrilateral, and an ellipse or the like.

[0073] In a plan view, the area of the exposed region 22a of each recess 24 is, for example, 50000 μm 2 or more and 200000 μm 2 or less, particularly 100000 μm 2 or more and 150000 μm 2 or less. Further, the density of the recesses 24, that is, the ratio of the recesses 24 in the exposed region 22a may be, for example, 10% or more and 50% or less, particularly 30% or more and 40% or less. If the density of the recesses 24 is too small, the interval between the recesses 24 becomes large, and the effect of arranging a plurality of recesses 24 may not be sufficiently obtained. If the density of the recesses 24 is too large, it may be difficult to form the recesses 24 in the exposed region 22a. If the area of each recess 24 is small, the effect of forming the recess 24 may not be sufficiently obtained. If the area of each recess 24 is large, the number of recesses 24 in which the first electrode 51 is continuously formed decreases, and the effect of arranging a plurality of recesses 24 may not be obtained.

[0074] As shown in FIG. 17, the density of the recesses 24 arranged in the second region 22a2 may be made larger than the density of the recesses 24 arranged in the first region 22a1. The second region 22a2 faces the p-side layer 40 over the entire length in the second direction D2 and is close to the active layer 30. Therefore, by arranging the recesses 24 at a high density in the second region 22a2 and arranging the first electrode 51 continuously in a plurality of recesses 24, the amount of ultraviolet light reflected by the first electrode 51 can be made larger and the light emission efficiency can be further improved. The density difference of the recesses 24 may be arranged such that, for example, the ratio of the recesses 24 in the surface of the second region 22a2 is 20% or more and 70% or less, particularly 40% or more and 60% or less, and the ratio of the recesses 24 in the surface of the first region 22a1 is 20% or more and 70% or less, particularly 40% or more and 60% or less. The arrangement of the recess 24 shown in FIG. 17 is preferably combined with the arrangement of the first electrode 51 in Embodiment 2. Further, when adopting the arrangement of the first electrode in Embodiment 3, the density of the recesses 24 arranged in the first region 22a1 may be made larger than the density of the recesses 24 arranged in the second region 22a2.

[0075] (Embodiment 6) Next, Embodiment 6 will be described. In the following description and FIGS. 18 to 21, members described using the same reference numerals as those in Embodiment 1 are the same members as those described in Embodiment 1, and the description regarding Embodiment 1 applies except for the parts different from Embodiment 1.

[0076] FIG. 18 is a plan view of the light-emitting element 106 of the present embodiment, and FIG. 19 is a cross-sectional view taken along line II in FIG. 18. In the present embodiment, the n-side layer 20 has, in plan view, a first portion 201, a second portion 202 located on the outer periphery of the first portion 201, and a plurality of third portions 203 surrounded by the first portion. The active layer 30 and the p-side layer 40 are arranged on the first portion 201. A first insulating film 700 is arranged on the semiconductor structure 100. The first insulating film 700 has a plurality of first openings h1 arranged on the third portion 203 and a plurality of second openings h2 arranged in the p-side layer 40. The n-side electrode 50 is arranged on the first insulating film 700, and the first insulating film 700 electrically insulates the n-side electrode 50 and the p-side electrode 60. The n-side electrode 50 is electrically connected to the n-side layer 20 through the first opening h1. The n-side electrode 50 is electrically connected to an n-side pad electrode 80 arranged in the second portion 202. The n-side pad electrode 80 has a shape corresponding to the second portion 202 in plan view.

[0077] The second opening h2 disposed on the p-side layer 40 exposes the p-side electrode 60 electrically connected to the p-side layer 40. A second insulating film 702 is disposed on the first insulating film 700, and the second insulating film 702 has a plurality of third openings h3 disposed at positions overlapping the second opening h2. The p-side electrode 60 is electrically connected to the p-side pad electrode 90 disposed on the second insulating film 702 through the second opening h2 and the third opening h3. The second insulating film 702 electrically insulates the n-side electrode 50 from the p-side pad electrode 90 and also electrically insulates the n-side pad electrode 80 from the p-side pad electrode 90. The p-side pad electrode 90 has a substantially octagonal planar shape corresponding to the first portion 201, is disposed over a relatively large area, and contributes to improving heat dissipation.

[0078] The stacked structure of the n-side layer 20 is the same as that in the first embodiment, and includes a third layer 23, an undoped first layer 21 as a base layer, and a second layer 22 containing n-type impurities as a contact layer. The second portion 202 and the third portion 203 correspond to the portions where the n-side layer 20 is exposed from the p-side layer 40 and the active layer 30, and the second layer 22 containing n-type impurities is exposed.

[0079] The n-side electrode 50 has an n-side conduction portion 501 and an n-side wiring portion 502. The n-side conduction portion 501 is electrically connected to the n-side layer 20 through the first opening h1, and the n-side wiring portion 502 electrically connects the n-side conduction portion 501 and the n-side pad electrode 80. The n-side conduction portion 501a disposed in the first opening h1 includes a first electrode 51 and a second electrode 52. The first electrode 51 and the second electrode 52 are in contact with the second layer 22 and not in contact with the first layer 21. In plan view, the first electrode 51 is circular, and the second electrode 52 surrounds the first electrode 51. In cross-sectional view, the side surface of the first electrode 51 is in contact with the second electrode 52. Note that the first electrode 51 and the second electrode 52 of the n-side electrode 50 may be disposed in the second portion 202 instead of or together with the first portion 201.

[0080] Rather than separately forming the n-side conduction part 501 and the n-side wiring part 502, for example, after forming the first electrode 51 at a position corresponding to the first opening h1 and further forming the first insulating film 700, the second electrode 52 and the n-side wiring part 502 may be integrally formed of the same material. In that case, the second electrode 52 and the n-side wiring part 502 are integrated, and there is no boundary line between the n-side conduction part 501 and the n-side wiring part 502 as shown in FIG. 19.

[0081] The third portion 203 where the first opening h1 is disposed is surrounded by the p-side layer 40 and the active layer 30, shortening the current path between the n-side electrode 50 and the p-side electrode 60. In the vicinity of the third portion 203, the luminance is high and the light emission amount tends to be larger. Therefore, by disposing the first electrode 51 having a high reflectance on the third portion 203, ultraviolet light can be efficiently reflected in a portion where ultraviolet light emission is likely to be concentrated, and the light emission efficiency can be improved.

[0082] Plan views of the n-side conduction part 501 and the n-side wiring part 502 of the n-side electrode 50 are shown in FIGS. 20 and 21, respectively. The n-side conduction parts 501 are arranged at substantially equal intervals, diffusing current and thus improving the uniformity of the light emission intensity distribution. The opening 502a of the n-side wiring part 502 corresponds to the second opening h2 and the third opening h3 of the first insulating film 700 and the second insulating film 702, exposing the p-side electrode 60 together with the second opening h2 and the third opening h3 so that the p-side pad electrode 90 and the p-side electrode 60 are electrically connected.

Example

[0083] (Examples 1 to 6) The light-emitting element 1 having the configuration shown in FIGS. 1 to 2, in which the concave portions 24 having the shapes shown in FIGS. 12 to 13 are arranged on the surface of the second layer 22, was fabricated as Examples 1 and 2. Specifically, the substrate 10 was a square with a side length of 1 mm in plan view. In the n-side layer 20, a third layer 23 (thickness: 945 nm), which is a superlattice layer in which an AlN layer and an AlGaN layer with an Al composition ratio of 60% are alternately laminated 30 times, a first layer 21 (thickness: 480 nm) as an underlying layer made of an undoped AlGaN layer with an Al composition ratio of 60%, and a second layer 22 (thickness: 2220 nm) as an n-contact layer containing Si as an n-type impurity at a concentration of about 9.5×10 18 / cm 3 . The active layer 30 had a multiple quantum well structure in which an AlGaN layer (thickness: 4.4 nm) with an Al composition ratio of 42% was a well layer and an AlGaN layer (thickness: 2.5 nm) with an Al composition ratio of 52% was a barrier layer, and the total thickness of the active layer 30 was 11.3 nm. The p-side layer 40 had Mg as a p-type impurity at a concentration of 1×10 19 / cm 3 , and had a laminated structure in which an AlGaN layer with an Al composition ratio of 40% and a thickness of 10 nm and a GaN layer with a thickness of 10 nm were arranged thereon.

[0084] An etching process was performed on the semiconductor structure 100 formed up to the p-side layer 40 to remove the p-side layer 40 and the active layer 30, and the n-side layer 20 was exposed. As shown in FIG. 3, the exposed region 22a had a first region 22a1 in which the n-side layer 20 extended in the first direction D1 and a second region 22a2 extending from the first region 22a1 perpendicular to the first direction D1. The exposed region 22a had an area of 450934 μm 2 in plan view. The length (width) in the second direction D2 and the length in the first direction D1 of the first region 22a1 were 106 μm and 814 μm, respectively, and the length (width) in the first direction D1 and the length in the second direction D2 of the second region 22a2 were 62 μm and 794 μm, respectively. Five second regions 22a2 were arranged along the first direction D1 at intervals of 126 μm.

[0085] On the surface of the exposed region 22a, a recess 24 having the shape shown in FIG. 12 was formed in plan view. The width of the recess 24 formed in the second region 22a2 in the first direction D1 was 20 μm, and the width of the recess 24 formed in the first region 22a1 in the second direction D2 was 60 μm. In plan view, the area of the recess 24 was 123144 μm 2 had an area of. In Examples 1 to 6, the combination of the depth of the recess 24 and the inclination angle of the recess 24 was made as shown in Table 1, respectively, so that the configuration of the recess was different for each example.

[0086]

Table 1

[0087] A Ti-Al-Si alloy layer, a Ta layer, and Ru were laminated in this order on the first region 22a1 and the second region 22a2, and a part of them was removed by etching to form a first electrode 51 having a cross-sectional shape as shown in FIG. 5. On the upper surface of the p-side layer 40, a Ti layer, a Rh layer, and a Ti layer were laminated in this order to form a p-side electrode 60. After forming the second electrode 52 and the p-side electrode 60, the semiconductor structure and these electrodes were subjected to an annealing treatment. After the annealing treatment, an Al-Cu alloy layer, a Ti layer, and a Ru layer were laminated in this order to form the first electrode 51. As shown in FIG. 5, the second electrode 52 was disposed in the recess formed by the second electrode 52 in cross-sectional view and a part of it extended to the upper surface of the first electrode 51. The n-side electrode 50 composed of the first electrode 51 and the second electrode 52 had an area of 248732 μm 2 in plan view.

[0088] An insulating layer 70 was formed to have a first opening 71 that partially exposed the surface of the n-side electrode 50 and a second opening 72 that partially exposed the surface of the p-side electrode 60. The first opening 71 and the second opening 72 were formed by dry etching. The insulating layer 70 was made of SiO2 and had a thickness of 1.3 μm.

[0089] The n-side pad electrode 80 and the p-side pad electrode 90 were formed to have the shapes shown in FIG. 1 in plan view. The n-side pad electrode 80 and the p-side pad electrode 90 were composed of a stack of Ti, Pt, and Au and had a thickness of 900 nm.

[0090] (Comparative Example) A comparative example was prepared which had the same shape and configuration as the above-described embodiment, but did not have the concave portion 24, did not have the first electrode 51, and the n-side electrode 50 was composed only of the second electrode 52.

[0091] A current of 350 mA was passed through the light-emitting elements of Examples 1 to 6 and the comparative example to measure the light-emitting output, and the ratio of the light-emitting output of each example to the light-emitting output of the comparative example was determined with the light-emitting output of the light-emitting element of the comparative example taken as 1. The results are shown in FIG. 22.

[0092] All of the examples showed a higher light-emitting output than the comparative example, and it was confirmed that the light-emitting efficiency of the light-emitting element 1 was improved by the arrangement of the first electrode 51.

[0093] (Supplementary Note 1) A semiconductor structure including an n-side layer, a p-side layer, and an active layer located between the n-side layer and the p-side layer, each of which is made of a nitride semiconductor and emits ultraviolet light. An n-side electrode electrically connected to the n-side layer. A p-side electrode electrically connected to the p-side layer. The n-side layer has an undoped first layer and a second layer located between the active layer and the first layer and containing an n-type impurity. The n-side electrode includes a first electrode and a second electrode that are in contact with the second layer and not in contact with the first layer. The reflectance of the first electrode with respect to the peak wavelength of the light emitted by the active layer is higher than the reflectance of the second electrode with respect to the peak wavelength of the light emitted by the active layer. The contact resistance between the second electrode and the second layer is lower than the contact resistance between the first electrode and the second layer. Light-emitting element. (Supplementary Note 2) The second layer has an exposed region exposed from the p-side layer and the active layer. The exposed region has a first region extending in a first direction, and a second region extending from the first region in a second direction orthogonal to the first direction and located between the p-side layers in the first direction. The n-side electrode is disposed continuously with the first region and the second region. The first electrode and the second electrode are disposed in the second region. The light-emitting element according to Supplementary Note 1, wherein only the second electrode is disposed in the first region. (Supplementary Note 3) The second layer has an exposed region exposed from the p-side layer and the active layer. The exposed region has a first region extending in a first direction, and a second region extending from the first region in a second direction orthogonal to the first direction and located between the p-side layers in the first direction. The n-side electrode is disposed continuously with the first region and the second region. The first electrode and the second electrode are disposed in the first region. The light-emitting element according to Supplementary Note 1, wherein only the second electrode is disposed in the second region. (Supplementary Note 4) A part of the first electrode is located between the second electrodes in a cross-sectional view, and at least a part of two side surfaces of the first electrode is in contact with the second electrodes respectively. The light-emitting element according to any one of Supplementary Notes 1 to 3. (Supplementary Note 5) The second layer has a recess. A part of the first electrode is located in the recess. The light-emitting element according to any one of Supplementary Notes 1 to 4. (Supplementary Note 6) The second layer has a plurality of the recesses. The first electrode is disposed continuously in the plurality of the recesses. The light-emitting element according to Supplementary Note 5. (Supplementary Note 7) The plurality of the recesses are disposed in the first region and the second region respectively. The density of the plurality of recesses disposed in the second region is higher than the density of the plurality of recesses disposed in the first region. The light-emitting element according to any one of claims 5 to 6, which cites appended note 2. (Appended note 8) The light-emitting element according to any one of appended notes 5 to 7, wherein the depth of the recess is 0.1 μm or more and 5 μm or less. (Appended note 9) The light-emitting element according to any one of appended notes 5 to 8, wherein the angle formed by the bottom surface defining the recess and the side surface defining the recess is 100° or more and 140° or less. (Appended note 10) The outer edge of the second electrode surrounds the outer edge of the first electrode in plan view. The light-emitting element according to any one of appended notes 1 to 9. (Appended note 11) The n-side layer has, in plan view, a first portion, a second portion located on the outer periphery of the first portion, and a plurality of third portions surrounded by the first portion. The active layer and the p-side layer are disposed on the first portion. A first insulating film having a plurality of first openings disposed on the third portions and a plurality of second openings disposed in the p-side layer to expose the p-side electrode is disposed on the semiconductor structure. The n-side electrode is disposed on the first insulating film and is electrically connected to the n-side layer through the plurality of first openings. An n-side pad electrode electrically connected to the n-side electrode is disposed in the second portion. The first electrode and the second electrode are disposed in one or more of the plurality of first openings. The light-emitting element according to appended note 1. (Appended note 12) The n-side electrode has a plurality of n-side conduction portions and an n-side wiring portion. The n-side conduction portions are in contact with the n-side layer through the first openings. The n-side wiring portion electrically connects the n-side conduction portions and the n-side pad electrode. One or more of the plurality of n-side conduction portions are constituted by the first electrode and the second electrode. The light-emitting element described in Supplementary Note 11.

Industrial Applicability

[0094] The light-emitting element of the present disclosure can be used, for example, as a light source for resin curing, a lamp for sterilization and disinfection, an industrial exposure machine, etc., as it efficiently emits ultraviolet light.

Explanation of Reference Numerals

[0095] 1, 102, 103, 106 Light-emitting element 10 Substrate 10a First substrate region 10b Second substrate region 100 Semiconductor structure 20 n-side layer 21 First layer (underlayer) 22 Second layer (n-contact layer) 23 Third layer (superlattice layer) 24 Concave portion 30 Active layer 40 p-side layer 40a Base portion 40b Extension portion 40b 50 n-side electrode 51 First electrode 52 Second electrode 60 p-side electrode 70 Insulating layer 71 First opening 72 Second opening 80 n-side pad electrode 90 p-side pad electrode 201 First portion 202 Second portion 203 Third portion 501 n-side conduction portion 502 n-side wiring portion 700 First insulating film 702 Second insulating film h1 First opening h2 Second opening h3 Third opening

Claims

1. A semiconductor structure including an n-side layer, a p-side layer, and an active layer located between the n-side layer and the p-side layer, each made of a nitride semiconductor and emitting ultraviolet light; An n-side electrode electrically connected to the n-side layer; A p-side electrode electrically connected to the p-side layer; The n-side layer has an undoped first layer and a second layer located between the active layer and the first layer and containing an n-type impurity; The n-side electrode includes a first electrode and a second electrode that are in contact with the second layer and not in contact with the first layer; The reflectivity of the first electrode with respect to the peak wavelength of the light emitted by the active layer is higher than the reflectivity of the second electrode with respect to the peak wavelength of the light emitted by the active layer; The contact resistance between the second electrode and the second layer is lower than the contact resistance between the first electrode and the second layer; A light-emitting element.

2. The second layer has an exposed region exposed from the p-side layer and the active layer; The exposed region has a first region extending in a first direction and a second region extending from the first region in a second direction orthogonal to the first direction and located between the p-side layers in the first direction; The n-side electrode is continuously disposed in the first region and the second region; The first electrode and the second electrode are disposed in the second region; The light-emitting element according to claim 1, wherein only the second electrode is disposed in the first region.

3. The second layer has an exposed region exposed from the p-side layer and the active layer; The exposed region has a first region extending in a first direction and a second region extending from the first region in a second direction orthogonal to the first direction and located between the p-side layers in the first direction; The n-side electrode is continuously disposed in the first region and the second region; The first electrode and the second electrode are disposed in the first region; The light-emitting element according to claim 1, wherein only the second electrode is disposed in the second region.

4. The light-emitting element according to any one of claims 1 to 3, wherein a part of the first electrode is located between the second electrodes in a cross-sectional view, and at least a part of two side surfaces of the first electrode is in contact with the second electrode respectively.

5. The second layer has a recess; The light-emitting element according to any one of claims 1 to 3, wherein a part of the first electrode is located in the recess.

6. The second layer has a plurality of recesses; The light-emitting element according to claim 5, wherein the first electrode is continuously disposed in the plurality of recesses.

7. A plurality of the concave portions are disposed in each of the first region and the second region. The light-emitting element according to claim 5, which cites claim 2, wherein the density of the plurality of concave portions disposed in the second region is higher than the density of the plurality of concave portions disposed in the first region.

8. The light-emitting element according to claim 7, wherein the depth of the concave portion is 0.1 μm or more and 5 μm or less.

9. The light-emitting element according to claim 7, wherein an angle formed by a bottom surface defining the concave portion and a side surface defining the concave portion is 100° or more and 140° or less.

10. An outer edge of the second electrode surrounds an outer edge of the first electrode in a plan view. The light-emitting element according to any one of claims 1 to 3.

11. In a plan view, the n-side layer has a first portion, a second portion located on an outer periphery of the first portion, and a plurality of third portions surrounded by the first portion. The active layer and the p-side layer are disposed on the first portion. A first insulating film having a plurality of first openings disposed on the third portions and a plurality of second openings disposed in the p-side layer to expose the p-side electrode is disposed on the semiconductor structure. The n-side electrode is disposed on the first insulating film and is electrically connected to the n-side layer through the plurality of first openings. An n-side pad electrode electrically connected to the n-side electrode is disposed in the second portion. The first electrode and the second electrode are disposed in one or more of the plurality of first openings. The light-emitting element according to claim 1.

12. The n-side electrode has a plurality of n-side conduction portions and an n-side wiring portion. The n-side conduction portions are in contact with the n-side layer through the first openings. The n-side wiring portion electrically connects the n-side conduction portions and the n-side pad electrode. One or more of the plurality of n-side conduction portions are constituted by the first electrode and the second electrode. The light-emitting element according to claim 11.

Images