UV semiconductor light-emitting element

Abstract

The present invention provides a semiconductor light-emitting element that has high efficiency in extracting light to the outside and excellent element characteristics of high efficiency and high output. [Solution] A semiconductor light-emitting element is made of an AlGaN-based multilayer semiconductor layer having an emission wavelength in the ultraviolet wavelength band, in which semiconductor layers including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer are formed on a substrate in this order. It has a mesa portion consisting of a part of the p-type semiconductor layer, the active layer, and the n-type semiconductor layer, and an exposed portion formed in the outer region of the mesa portion where the n-type semiconductor layer is exposed. The exposed portion of the n-type semiconductor layer has a symmetrical structure which is a diffuse reflection structure in a part of the outer region.

Description

[Technical Field]

[0001] This invention relates to an ultraviolet semiconductor light-emitting device, and more particularly to a nitride semiconductor light-emitting device that emits deep ultraviolet light. [Background technology]

[0002] In recent years, AlGaN-based semiconductor light-emitting devices with emission wavelengths in the deep ultraviolet region have attracted attention as light sources that have the effect of inactivating bacteria and viruses and sterilizing them. However, because deep ultraviolet LEDs have a short emission wavelength, most of the light emitted from the active layer is lost without being extracted from the LED.

[0003] For example, Patent Document 1 discloses a semiconductor light-emitting device in which an uneven surface is provided on the contact surface between the n-type gallium nitride layer and the n-electrode. Patent Document 2 also discloses a semiconductor light-emitting device in which a reflective metal layer is provided on the outside of the n-electrode layer.

[0004] However, in cases where the interface between the n-type semiconductor layer and the n-electrode is made into a reflective structure, as described in Patent Document 1, it is necessary to use a metal (for example, Ti or V) which is a material with low reflectivity in order to obtain ohmic contact, and to perform annealing treatment at high temperatures, which leads to the problem that the reflectivity of the electrode itself is lost.

[0005] Furthermore, in the semiconductor light-emitting element described in Patent Document 2, although the reflective metal layer is made Al (aluminum) rich to prevent the reduction of reflectivity due to alloying, the reduction in reflectivity due to alloying itself cannot be avoided, so the reflectivity decreases. In addition, since reflected light from the light extraction surface is incident on the reflective metal layer, the reflected light from the reflective metal layer is again incident on the light extraction surface at an angle greater than the critical angle, so it does not contribute to the light extraction efficiency, and the effect of reflection may be meaningless. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2005-158788 [Patent Document 2] Patent No. 6165602 [Overview of the project] [Problems that the invention aims to solve]

[0007] This invention has been made in view of the above-mentioned problems, and aims to provide a semiconductor light-emitting element that has high light extraction efficiency to the outside and excellent element characteristics of high efficiency and high output. [Means for solving the problem]

[0008] An ultraviolet semiconductor light-emitting device according to one embodiment of the present invention is A semiconductor light-emitting element is formed on a substrate in which semiconductor layers including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer are formed in this order, and the semiconductor light-emitting element is made of an AlGaN-based multilayer semiconductor layer having an emission wavelength in the ultraviolet wavelength band, The mesa portion consists of the p-type semiconductor layer, the active layer, and a part of the n-type semiconductor layer, The outer region of the mesa portion has an exposed portion in which the n-type semiconductor layer is exposed, The exposed portion of the n-type semiconductor layer has a ridged structure that is a diffuse reflection structure in a part of the outer region. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view showing the structure of an ultraviolet LED according to one embodiment of the present invention. [Figure 2] This diagram schematically shows the mesa region and the region outside the mesa region of a semiconductor light-emitting element, as well as the reflection and diffuse reflection of light emitted from the active layer toward the light extraction surface. [Figure 3A] This is a SEM image of a cross-section of a textured structure formed in an n-type semiconductor layer. [Figure 3B] This table shows the diameter a and height h of the base of the conical projections of samples A1-A3 and B1-B3. [Figure 4A]It is a graph showing the received light energy with respect to the detection angle of the light reflected by the diffuse reflection part for Samples A1 to A3. [Figure 4B] It is a graph showing the received light energy with respect to the detection angle of the light reflected by the diffuse reflection part for Samples B1 to B3. [Figure 5] It is a plan view schematically showing the upper surface of the semiconductor light-emitting device which is Example 1 of the first embodiment. [Figure 6] It is a plan view schematically showing the upper surface of the semiconductor light-emitting device which is Example 2 of the first embodiment. [Figure 7] It is a plan view schematically showing the upper surface of the semiconductor light-emitting device which is Example 3 of the first embodiment.

Mode for Carrying Out the Invention

[0010] Hereinafter, preferred embodiments of the present invention will be described, but these may be appropriately modified and combined. In the following description and the accompanying drawings, substantially the same or equivalent parts will be denoted by the same reference numerals and described.

[0011] [Structure of Semiconductor Light-Emitting Device] FIG. 1 is a cross-sectional view schematically showing the structure of a semiconductor light-emitting device 10 according to the first embodiment of the present invention. The semiconductor light-emitting device 10 is an ultraviolet light-emitting diode (ultraviolet LED), and is a deep ultraviolet light-emitting device having a peak of the emission wavelength within a range of, for example, 200 nm to 360 nm.

[0012] Further, FIG. 2 is a view schematically showing the mesa portion 18M of the semiconductor light-emitting device 10 and the outer region 18R outside the mesa portion 18M, and the reflection and diffuse reflection of the light radiated from the active layer 14 toward the light extraction surface 11E.

[0013] As shown in FIG. 1, the semiconductor light-emitting device 10 includes a single crystal substrate of AlN (hereinafter referred to as an AlN substrate) 11, and using the AlN substrate 11 as a growth substrate, an n-type semiconductor layer 13, an active layer 14, and a p-type semiconductor layer 15 are sequentially formed by epitaxial growth on the AlN substrate 11.

[0014] In the following, a semiconductor light-emitting device including an AlN layer and an AlGaN layer will be described. However, it may have an AlInGaN layer. In this specification, a semiconductor including AlN, an AlGaN layer, and AlInGaN will be described by referring to it as an AlGaN-based semiconductor.

[0015] First, the AlN substrate 11 is not particularly limited, but it is preferable to use one having a low dislocation density. The dislocation density of the AlN substrate 11 is preferably 4 cm -2 or less, more preferably 4 cm -2 or less. By using the AlN substrate 11 with a low dislocation density, the dislocation density of the semiconductor layer laminated on the AlN substrate 11 can also be lowered. As a result, the light-emitting efficiency or the light-receiving efficiency can be improved. The lower limit of the dislocation density is 0 cm -2 . The dislocation density can be measured by a known method such as measuring the number of dislocations from a transmission electron microscope image or measuring the number of etch pits measured after immersion in a heated acid mixed solution.

[0016] Using an AlN substrate with a lower dislocation density, 6 cm -2 or less, and more preferably 4 cm -2 or less can prevent the reduction of the light-emitting efficiency in the active layer 14 due to dislocations. Furthermore, it can also prevent problems such as the diffusion of impurities through dislocations generated when the ultraviolet light-emitting device is energized and an increase in leakage current.

[0017] In the semiconductor light-emitting device 10 of this embodiment, an AlN substrate having a dislocation density of 4 cm -2 was used.

[0018] In this embodiment, the crystal growth surface of the AlN substrate 11 is the C-plane. Alternatively, the crystal growth surface of the AlN substrate 11 may be a plane that is slightly inclined (off-angled) from the C-plane, in which case the off-angle is preferably 0.1 to 0.5°, and more preferably 0.3 to 0.4°. Furthermore, the direction in which the crystal plane is inclined is not particularly limited, but from the viewpoint of smoothness, it is preferably inclined in the direction of the M-axis. In this embodiment, a C-plane AlN substrate is used as the AlN substrate 11, and the semiconductor layer grown on the AlN substrate 11 also has the same C-plane as the substrate as its crystal growth surface.

[0019] Furthermore, the crystal growth surface of the AlN substrate 11 is preferably smooth from the viewpoint of suppressing the generation of new dislocations at the interface between the AlN substrate and the semiconductor layer. Specifically, 5 × 5 μm 2 The mean square roughness (RMS) in this region is preferably 5 nm or less, more preferably 1 nm or less, and even more preferably 0.5 nm or less. Such a smooth surface can be obtained by known chemical mechanical polishing (CMP polishing) treatment. The lower limit of the RMS is preferably 0 nm, but considering industrial production, it is 0.05 nm with current technology.

[0020] The AlN substrate 11 is preferably highly transparent to light for the ultimately formed light-emitting element. Therefore, the absorption coefficient in the deep ultraviolet region, specifically at wavelengths of 210 nm or higher, should be 25 cm². -1 The following is preferable. Note that the lower limit of the absorption coefficient is 0 cm. -1 While this is preferable, considering industrial production and measurement accuracy, the lower limit of the absorption coefficient at 210 nm is 15 cm². -1 Therefore, the lower limit of the absorption coefficient at wavelengths of 250 nm or more is 1 cm -1 Therefore, by using an AlN substrate with such a low absorption coefficient, it is possible to suppress the degradation of properties due to ultraviolet light absorption in the AlN substrate 11.

[0021] Furthermore, the thickness of the AlN substrate 11 used in this embodiment is not particularly limited. If the AlN substrate is thin, the amount of light absorbed in the substrate can be reduced even if the absorption coefficient is high. However, if it is too thin, it becomes difficult to handle and may reduce the yield of the device. For this reason, the thickness is usually preferably 50 to 1000 μm. The AlN substrate 11 described above can be manufactured, for example, by the sublimation method described in the literature J.Cryst.Growth 312, 58-63 (2009) or the literature Appl.Phys.Express 5,055504 (2011), or by the hydride vapor phase growth method.

[0022] Furthermore, the crystal growth surface of the AlN substrate 11 is not limited to the C-plane (C+ plane), but may also be the M-plane or A-plane, for example.

[0023] A buffer layer may be provided between the AlN substrate 11 and the n-type semiconductor layer 13. While the buffer layer is not essential for the function of the semiconductor light-emitting element, it is preferable to provide one from the viewpoint of suppressing lattice relaxation of the n-type semiconductor layer 13 and improving the yield of the crystal growth process. The thickness of the buffer layer is not particularly limited, but in order to obtain the lattice relaxation suppression effect described above, it is preferable to have a layer thickness of 5 to 1000 nm, and more preferably 30 to 100 nm.

[0024] Furthermore, the buffer layer is lattice-matched with the single-crystal AlN substrate 11. Here, lattice matching means that the lattice constant of the a-axis of the AlN substrate 11 is approximately equal to that of the buffer layer, and the lattice relaxation rate is ±5% or less. The lower limit of the lattice relaxation rate is 0, which means that the lattice constants of the AlN substrate 11 and the semiconductor layer are perfectly matched. This lattice relaxation rate can be measured by X-ray reciprocal lattice mapping.

[0025] The n-type semiconductor layer 13 is an AlN substrate 11, and if a buffer layer is provided, it is a single-crystal AlxGa1-xN (0.5≦x≦1) layer having a band gap smaller than that of the buffer layer. Since the n-type semiconductor layer 13 is lattice-matched with the AlN substrate 11, lattice relaxation accompanied by dislocation generation does not occur in the n-type semiconductor layer 13. Therefore, the dislocation density in the n-type semiconductor layer 13 is equivalent to the dislocation density on the surface of the AlN substrate 11. Thus, the dislocation density of the n-type semiconductor layer 13 is the same as that of the AlN substrate 11, 10 6 cm -2 It is preferable that the following conditions are met, and more preferably 10 4 cm -2 The following applies. Furthermore, even when the n-type semiconductor layer 13 of the present invention is formed from multiple layers, all of these layers are lattice-matched, and therefore the dislocation density is equivalent in each layer.

[0026] The n-type semiconductor layer 13 contains, for example, Si as an n-type dopant. The dopant concentration of the n-type semiconductor layer 13 is not particularly limited and can be appropriately determined according to the purpose. In particular, to achieve high conductivity, for example, the Si concentration should be 1 × 10⁻⁶ 18 cm -3 ~5×10 19 cm -3 It is preferable that the n-type semiconductor layer 13 is formed from multiple layers, the Si concentration of each layer is 1 × 10 18 cm -3 ~5×10 19 cm -3 This is preferable. The Si concentration in each layer may be constant, or it may differ depending on the device design. Furthermore, the Si concentration can be relatively high at the interfaces of each layer.

[0027] Furthermore, in this embodiment, the n-type semiconductor layer 13 consists of an AlGaN layer (composition gradient layer) in which the Al composition decreases in the growth direction, i.e., in the direction away from the AlN substrate 11 (towards the active layer 14).

[0028] The semiconductor light-emitting element 10 has an active layer 14 formed on an n-type semiconductor layer 13 and a p-type semiconductor layer 15 formed on the active layer 14. The active layer 14 and the p-type semiconductor layer 15, along with a mesa portion 18M consisting of a part of the n-type semiconductor layer 13, are also included. Furthermore, an exposed portion (exposed surface 13S) is formed in the outer region 18R of the mesa portion 18M, where the n-type semiconductor layer 13 is exposed.

[0029] More specifically, a semiconductor layer (multilayer semiconductor layer) consisting of an n-type semiconductor layer 13, an active layer 14, and a p-type semiconductor layer 15 stacked in this order on an AlN substrate 11 is partially removed so that the n-type semiconductor layer 13 is exposed, thereby forming an exposed portion of the n-type semiconductor layer 13. Each of these multilayer semiconductor layers is an AlGaN-based semiconductor layer.

[0030] First, the structure of the mesa portion 18M will be described below. The active layer 14 consists of an AlGaN layer having a smaller band gap than the n-type semiconductor layer 13. In this embodiment, the active layer 14 has a multiple quantum well structure consisting of multiple well layers and a barrier layer. The active layer 14 also emits light in the deep ultraviolet region. Note that the structure of the active layer 14 is not limited to this, and it may consist of a single layer or have a single quantum well structure.

[0031] The emission wavelength (peak wavelength) of the active layer 14 is preferably in the range of 200 to 360 nm, more preferably 200 to 300 nm, and even more preferably 200 nm to 280 nm.

[0032] The p-type semiconductor layer 15 consists of an AlN layer, an AlGaN layer, or a GaN layer containing, for example, Mg as a p-type dopant. In this embodiment, the p-type semiconductor layer 15 has a structure in which an electron blocking layer 15A made of an AlN layer, a p-type cladding layer 15B made of an AlGaN layer, and a p-type contact layer 15C made of a GaN layer are grown on the active layer 14.

[0033] The configuration of the p-type semiconductor layer 15 is not limited to this. For example, the electron block layer 15A does not have to have a p-type dopant, and the electron block layer 15A does not have to be provided.

[0034] Next, the outer region 18R of the mesa portion 18M will be described below. As shown in Figures 1 and 2, the outer region 18R is the region where the n-type semiconductor layer 13 is exposed, and a surface irregularity structure 21 consisting of fine irregularities on the surface of the n-type semiconductor layer 13 is formed in a part of the outer region 18R (irregularity structure formation region). Here, fine irregularities refer to irregularities with a size approximately equal to the emission wavelength.

[0035] A transparent insulating layer 22, which is transparent to the emission wavelength, is formed on the uneven structure 21. The transparent insulating layer 22 is formed to cover part or all of the uneven structure 21.

[0036] The transparent insulating layer 22 is, for example, a thin film made of SiO2, but is not limited to this; any insulating dielectric layer that is transparent to the emission wavelength can be used. For example, oxides such as SiO2, Al2O3, HfO, ZrO, and MgO, or fluorides can be used. Furthermore, the transparent insulating layer 22 may be composed of multiple dielectric layers (dielectric sublayers) made of different materials.

[0037] In this embodiment, a metal reflective layer 23 made of a metal having a high reflectivity with respect to the emission wavelength may be provided on the transparent insulating layer 22. The uneven structure 21, the transparent insulating layer 22, and the metal reflective layer 23 function as a diffuse reflecting portion 24 (Lambertian reflecting portion).

[0038] For the metal reflective layer 23, a material having high reflectivity to ultraviolet light, such as Al, can be used. Alternatively, instead of the metal reflective layer 23, a highly reflective coating film having high reflectivity to the emission wavelength, or a DBR (Distributed Bragg Reflector) film in which a thin film with a high refractive index (HfO, ZrO) and a thin film with a low refractive index (SiO2) are alternately laminated at a predetermined optical thickness (λ / 4), can be used as the reflective layer 23.

[0039] Preferably, the metal reflective layer 23 is formed over the entire upper surface of the transparent insulating layer 22, but it may also be provided on a portion of the upper surface of the transparent insulating layer 22.

[0040] Furthermore, while it is preferable that a metal reflective layer 23 is provided on the transparent insulating layer 22, it is not necessary to provide the metal reflective layer 23. That is, if the metal reflective layer 23 is not provided, the fine uneven structure 21 on the surface of the n-type semiconductor layer 13 and the transparent insulating layer 22 function as a diffuse reflecting portion 24 (Lambertian reflecting portion).

[0041] Furthermore, an n-electrode 16 is formed on the exposed surface 13S of the n-type semiconductor layer 13 where the uneven structure 21 is not provided (n-electrode formation region). The n-electrode 16 consists of an ohmic contact metal layer 16A (e.g., Ti layer, layer thickness: 1 nm) with respect to the n-type semiconductor layer 13, an electrode layer 16B (e.g., Al layer, layer thickness: 250 nm) formed on the ohmic contact metal layer 16A, and a pad electrode 16C (e.g., Au, layer thickness: 5 nm) formed on the electrode layer 16B. These layers are alloyed by annealing to form the n-electrode 16.

[0042] A protective film 25 is provided to cover the top and side surfaces of the laminate, which consists of a transparent insulating layer 22 and a metal reflective layer 23, and the exposed surface of the n-type semiconductor layer 13. The protective film 25 is also formed to cover the side surfaces of the mesa portion 18M. At least the top surface of the pad electrode 16C is exposed from the protective film 25. Here, "top surface" refers to the surface opposite to the light extraction surface 11E.

[0043] The electrode layer 16B may be formed in conjunction with the metal reflective layer 23. That is, the electrode layer 16B and the metal reflective layer 23 may be made of the same metal (e.g., Al) and formed, for example, by a simultaneous deposition process.

[0044] A p-electrode 17 is provided on the p-type contact layer 15C of the p-type semiconductor layer 15. The p-electrode 17 is made of, for example, a laminate of a Ni layer and an Au layer. A reflective layer may also be provided on the p-type contact layer 15C, and it is preferable that the reflective layer is provided over the entire upper surface of the p-type contact layer 15C. By applying a voltage between the p-electrode 17 and the n-electrode 16, the active layer 14 emits light.

[0045] [Light extraction structure for semiconductor light-emitting elements]

[0046] (1) Light extraction efficiency The following describes the internal reflection and light extraction of synchrotron radiation from the active layer 14. As shown in Figure 2, synchrotron radiation La emitted from the active layer 14 and incident on the light extraction surface 11E at an angle greater than or equal to the critical angle is reflected by the light extraction surface 11E (reflected light Lr). The reflected light Lr that returns to the interior of the semiconductor light-emitting element 10 is diffusely reflected by the diffuse reflection section 24 (diffuse reflected light Ld). Therefore, the diffuse reflected light Le of the diffuse reflected light Ld that is incident on the light extraction surface 11E at an angle less than the critical angle is extracted from the AlN substrate 11 to the outside, thus increasing the light extraction efficiency.

[0047] (2) Diffuse reflection structure The uneven structure 21 of the diffuse reflecting portion 24 is composed of numerous conical protrusions. Figure 3A is a scanning electron microscope (SEM) image of a cross-section of the uneven structure 21 formed on the n-type semiconductor layer 13. Figure 3B is a table showing the diameter a (nm) and height h (nm) of the base of the conical protrusions for samples A1-A3 and B1-B3. Samples A1-A3 and B1-B3 were obtained from different wafer lots.

[0048] Furthermore, Figures 4A and 4B are graphs showing the received light energy as a function of the detection angle for light (wavelength 265 nm) reflected by the diffuse reflector 24 for samples A1-A3 and B1-B3, respectively. In other words, Figures 4A and 4B show the reflectance of the diffuse reflector 24 as a function of the incident angle θ. Note that in the figures, samples REF2 and REF1 are samples in which the n-type semiconductor layer 13 does not have conical protrusions and the surface of the n-type semiconductor layer 13 is flat.

[0049] As shown in Figures 4A and 4B, in the diffuse reflectance section 24 of samples A1-A3 and B1-B3, which have conical protrusions of different diameters a (nm) and heights h, it can be seen that a mixed reflection of specular reflection and Lambertian reflection is obtained, rather than an ideal Lambertian reflection.

[0050] The structure of sample A2 is closest to Lambertian reflection, while the structure of sample B3 has the highest reflectivity as a mixed reflection structure. From this data, it is preferable that the diameter a of the base of the conical projection is 30 nm or more, and the height h is 25 nm or more. Furthermore, it is preferable that both the diameter a and height h are less than or equal to the emission wavelength. Note that the conical projection may have random diameters a and heights h in the diffuse reflection portion 24.

[0051] Furthermore, in this specification, "conical projection" is not limited to cases where the projection has a perfect conical shape, but also includes cases where it has a shape similar to a cone, a pointed shape, or a tabular shape. For example, "conical projection" includes elongated conical projections, frustoconical projections or elongated frustoconical projections with a missing apex, and conical projections with curved sides. It also includes cases where multiple shapes of conical projections are randomly included. Note that the diameter a of the base of the conical projection refers to the major axis at the base. [Examples of diffuse reflecting surfaces] As described above, if the diffuse reflecting portion 24 is provided in the outer region 18R of the mesa portion 18M, it contributes to improving the light extraction efficiency. The arrangement of the formation regions of the mesa portion 18M, the n electrode 16, and the diffuse reflecting portion 24 will be explained below with reference to an example.

[0052] (1) Example 1 Figure 5 is a schematic plan view showing the top surface (the surface opposite to the light extraction surface 11E) of the semiconductor light-emitting element 40, which is Example 1 of the first embodiment. For clarity, the formation areas of the mesa portion 18M, n electrode 16, and diffuse reflection portion 24 are shown with hatching.

[0053] The semiconductor light-emitting element 40 has a rectangular columnar shape, and a plurality of rectangular columnar mesa portions 18M are provided on its upper surface. That is, each of the plurality of mesa portions 18M has a rectangular shape when viewed from above. More specifically, in the semiconductor light-emitting element 40, a plurality of rectangular columnar mesa portions 18M extending in one direction (x direction) are formed parallel to each other. A p electrode 17 is provided over the entire upper surface of the mesa portion 18M. Direct light emitted from the active layer 14 provided within the mesa portion 18M and reflected light from the p electrode 17 are radiated toward the light extraction surface 11E (back surface of the element). The p electrode 17 may be a reflective layer having a reflective function.

[0054] Furthermore, a plurality of parallel n electrodes 16, which have a rectangular shape when viewed from above and extend along the extension direction (x direction) of the mesa portion 18M, are provided between adjacent mesa portions 18M and on the outside of the mesa portions 18M. As described above, each of the n electrodes 16 is provided on the exposed surface 13S of the n-type semiconductor layer 13 in ohmic contact with the n-type semiconductor layer 13.

[0055] The diffuse reflecting portion 24 is formed in a rectangular ring-shaped region that surrounds the entire area (i.e., the periphery) where the multiple mesa portions 18M and multiple n electrodes 16 are formed. In other words, the diffuse reflecting portion 24 is formed in a rectangular ring shape on the outer periphery of the semiconductor light-emitting element 40 when viewed from above.

[0056] As described above, light emitted from the active layer 14 is incident on the light extraction surface 11E at an angle greater than or equal to the critical angle (synchrotron radiation La), and the reflected light Lr reflected by the light extraction surface 11E is diffusely reflected by the rectangular ring-shaped diffuse reflector 24 (diffuse reflected light Ld). Therefore, the diffuse reflected light Le of the diffuse reflected light Ld with an incident angle less than the critical angle is extracted from the AlN substrate 11 to the outside, resulting in a semiconductor light-emitting element with improved light extraction efficiency.

[0057] Although the case in which multiple mesa sections 18M are provided has been described, it is sufficient to provide at least one mesa section 18M. Furthermore, although the case in which an n-electrode 16 extending along the direction of extension of the mesa section 18M is provided has been described, the shape and arrangement of the n-electrode 16 are not limited thereto and can be appropriately modified and provided according to the configuration (shape, size, etc.) of the mesa section 18M.

[0058] (2) Example 2 Figure 6 is a schematic plan view showing the top surface of the semiconductor light-emitting element 50, which is an embodiment 2 of the first embodiment.

[0059] The semiconductor light-emitting element 50 has a rectangular shape when viewed from above and has a plurality of parallel mesa portions 18M and a plurality of n electrodes 16 extending in one direction (x direction). In addition, the n electrodes 16 extending along the direction of extension of the mesa portions 18M are provided between adjacent mesa portions 18M and on the outside of the mesa portions 18M. As in Example 1, a p electrode 17 having a reflective layer is provided over the entire upper surface of the mesa portions 18M.

[0060] In this embodiment 2, a first diffuse reflecting portion 24A (first uneven structure portion) is provided between the mesa portion 18M and the n electrode 16, and a second diffuse reflecting portion 24B (second uneven structure portion) is provided in the outer region of the multiple mesa portions 18M and the multiple n electrodes 16.

[0061] The first diffuse reflecting portion 24A and the second diffuse reflecting portion 24B of this embodiment 2 diffusely reflect the reflected light and multiple reflected light within the element that are emitted from the active layer 14 of the mesa portion 18M located at a distance from each other and totally reflected by the light extraction surface 11E. Since the diffuse reflected light Le of the diffuse reflected light Ld that is below the critical angle of the light extraction surface 11E is extracted to the outside, it is possible to provide a semiconductor light-emitting element with improved light extraction efficiency.

[0062] Although the case in which multiple mesa portions 18M and multiple n electrodes 16 are provided has been described, it is sufficient if at least one mesa portion 18M and at least one n electrode 16 are provided. In short, it is sufficient if the diffuse reflector portion 24 is provided in the regions on both sides of the n electrode 16, that is, in the inner region between the mesa portion 18M and the n electrode 16 and in the outer region of the n electrode 16 (the region opposite to the mesa portion 18M).

[0063] Furthermore, it is sufficient to have at least one first diffuse reflecting portion 24A provided between the mesa portion 18M and the n electrode 16, and at least one second diffuse reflecting portion 24B provided in the outer region of the mesa portion 18M and the n electrode 16.

[0064] (3) Example 3 Figure 7 is a schematic plan view showing the top surface of the semiconductor light-emitting element 50, which is Example 3 of the first embodiment.

[0065] The above-described examples 1 and 2 may be modified or combined as appropriate. For example, as shown in Figure 7, the rectangular ring-shaped diffuse reflecting portion 24 provided on the outer periphery in Example 1 may be combined with the first diffuse reflecting portion 24A provided between the mesa portion 18M and the n electrode 16 in Example 2 to form a diffuse reflecting portion 29.

[0066] In this case, it is preferable that the diffuse reflecting portion 29 is formed by connecting the diffuse reflecting portion 24 provided on the outer periphery and the first diffuse reflecting portion 24A provided between the mesa portion 18M and the n electrode 16 (Figure 7), but they may be formed separately, or they may be formed in combination.

[0067] According to the semiconductor light-emitting element 50 of Example 3, the reflected light emitted from the active layer 14 of the multiple mesa portions 18M and totally reflected by the light extraction surface 11E, as well as the multiple reflected light within the element, are efficiently diffusely reflected, thus providing a semiconductor light-emitting element with further improved light extraction efficiency.

[0068] As described in detail above, this disclosure makes it possible to provide a semiconductor light-emitting element with high efficiency and high output, and excellent element characteristics. [Explanation of Symbols]

[0069] 10,40,50: Semiconductor light-emitting element 11: Circuit board 11E: Light extraction surface 13: n-type semiconductor layer 13S: Exposed surface 14:Active layer 15: p-type semiconductor layer 15A: Electron Blocking Layer 15B: p-type cladding layer 15C: p-type contact layer 16:n electrode 16A: Ohmic contact metal layer 16B: Electrode layer 16C: Pad electrode 17:p electrode 18M: Mesa section 18R:Outer area 21: Uneven structure 22: Transparent insulating layer 23: Metal reflective layer 24: Diffuse reflector 24A: First diffuse reflector 24B: Second diffuse reflector 25:Protective film 29: Diffuse reflector La: Synchrotron radiation Ld: diffuse reflected light Lr:Reflected light

Claims

1. A semiconductor light-emitting element is made of an AlGaN-based multilayer semiconductor layer having an emission wavelength in the ultraviolet wavelength band, wherein semiconductor layers including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer are formed on a substrate in this order, The mesa portion consists of the p-type semiconductor layer, the active layer, and a part of the n-type semiconductor layer, The outer region of the mesa portion has an exposed portion in which the n-type semiconductor layer is exposed, The exposed portion of the n-type semiconductor layer has a symmetrical structure that is a diffuse reflection structure in a part of the outer region. Ultraviolet semiconductor light-emitting device.

2. The emission wavelength of the active layer is in the range of 200 to 360 nm. The ultraviolet semiconductor light-emitting element according to claim 1, wherein the uneven structure includes a plurality of conical protrusions, the diameter of the base of the plurality of conical protrusions is 30 nm or more, the height is 25 nm or more, and the diameter and height are less than or equal to the emission wavelength.

3. The ultraviolet semiconductor light-emitting element according to claim 1, having a dielectric layer made of a dielectric material transparent to the emission wavelength of the active layer and covering at least a portion of the upper surface of the uneven structure.

4. The ultraviolet semiconductor light-emitting element according to claim 3, wherein the dielectric layer comprises a plurality of dielectric sublayers made of different materials.

5. The ultraviolet semiconductor light-emitting element according to claim 3, which has a metallic reflective layer covering at least a portion of the upper surface of the dielectric layer and having a high reflectivity with respect to the emission wavelength.

6. Each of the mesa portions has a rectangular columnar shape and extends in one direction, Between adjacent mesa portions, there is provided at least one n-electrode that extends along the direction of extension of the mesa portion and is in ohmic contact with the n-type semiconductor layer at the exposed portion, The ultraviolet semiconductor light-emitting element according to claim 1, wherein the uneven structure has a ring shape surrounding the plurality of mesa portions and at least one n electrode when viewed from above.

7. The ultraviolet semiconductor light-emitting element according to claim 6, further comprising n electrodes provided on both outer sides of the plurality of mesa portions.

8. Each of the mesa portions has a rectangular columnar shape and extends in one direction, Between adjacent mesa portions, there is provided at least one n-electrode that extends along the direction of extension of the mesa portion and is in ohmic contact with the n-type semiconductor layer at the exposed portion, The ultraviolet semiconductor light-emitting element according to claim 1, wherein the uneven structure is provided in a top view, extending in one direction between the mesa portion and the n electrode.

9. Each of the mesa portions has a rectangular columnar shape and extends in one direction, Between adjacent mesa portions, there is provided at least one n-electrode that extends along the direction of extension of the mesa portion and is in ohmic contact with the n-type semiconductor layer at the exposed portion, The ultraviolet semiconductor light-emitting element according to claim 1, wherein the uneven structure comprises, in a top view, a first uneven structure portion extending in one direction between the mesa portion and the n electrode, and a second uneven structure portion having an annular shape surrounding the plurality of mesa portions and at least one n electrode.

10. The ultraviolet semiconductor light-emitting element according to claim 9, wherein the first uneven structure and the second uneven structure are connected and formed in a top view.

11. The ultraviolet semiconductor light-emitting element according to claim 6 or 9, wherein the uneven structure has a rectangular ring shape when viewed from above.

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