JP2026055832A - UV semiconductor light-emitting element - Google Patents

Abstract

[Problem] 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.
[Solution] The semiconductor light-emitting element is made of an AlGaN-based multilayer semiconductor layer having an emission wavelength in the ultraviolet wavelength band, in which a semiconductor layer including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer is 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.
[Selection Diagram] Figure 1

Description

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.

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

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.

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 (e.g., Ti or V) with low reflectivity to obtain ohmic contact, and to perform annealing at high temperatures. This leads to the problem that the reflectivity of the electrode itself is lost.

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 in reflectivity due to alloying, the reduction in reflectivity due to alloying itself cannot be avoided, and therefore the reflectivity decreases. Also, 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, thus not contributing to the light extraction efficiency, and the effect of reflection may be meaningless.

Japanese Patent Publication No. 2005-158788 Patent No. 6165602

This invention has been made in view of the above-mentioned problems, and aims to provide a semiconductor light-emitting element with high efficiency in extracting light to the outside, and excellent element characteristics of high efficiency and high output.

The ultraviolet semiconductor light-emitting device according to one embodiment of the present invention is
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 rippled structure that is a diffuse reflection structure in a part of the outer region.

This is a schematic cross-sectional view showing the structure of an ultraviolet LED according to one embodiment of the present invention. 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. This is a SEM image of a cross-section of a surface irregularity structure formed in an n-type semiconductor layer. This table shows the diameter a and height h of the base of the conical projections of samples A1-A3 and B1-B3. This graph shows the received light energy as a function of the detection angle of light reflected by the diffuse reflector for samples A1 to A3. This graph shows the received light energy as a function of the detection angle of light reflected by the diffuse reflector for samples B1 to B3. This is a schematic plan view showing the upper surface of a semiconductor light-emitting element, which is Example 1 of the first embodiment. This is a schematic plan view showing the upper surface of a semiconductor light-emitting element, which is an embodiment 2 of the first embodiment. This is a schematic plan view showing the upper surface of a semiconductor light-emitting element, which is Example 3 of the first embodiment.

The following describes preferred embodiments of the present invention, which may be modified and combined as appropriate. Furthermore, in the following description and accompanying drawings, substantially identical or equivalent parts are denoted by the same reference numerals.

[Structure of semiconductor light-emitting diodes]
Figure 1 is a schematic cross-sectional view showing the structure of a semiconductor light-emitting element 10 according to a first embodiment of the present invention. The semiconductor light-emitting element 10 is an ultraviolet light-emitting diode (ultraviolet LED), and is a deep ultraviolet light-emitting element having, for example, an emission wavelength peak in the range of 200 nm to 360 nm.

Furthermore, Figure 2 schematically shows the reflection and diffuse reflection of light emitted from the active layer 14 toward the light extraction surface 11E, in relation to the mesa portion 18M and the outer region 18R of the semiconductor light-emitting element 10.

As shown in Figure 1, the semiconductor light-emitting element 10 is formed by sequentially stacking an n-type semiconductor layer 13, an active layer 14, and a p-type semiconductor layer 15 on the AlN substrate 11, using the AlN substrate 11 as a growth substrate, through epitaxial growth.

In the following description, a semiconductor light-emitting element consisting of an AlN layer and an AlGaN layer will be described, but it may also have an AlInGaN layer. In this specification, semiconductors containing AlN, an AlGaN layer, and AlInGaN will be referred to as AlGaN-based semiconductors.

First, while the AlN substrate 11 is not particularly limited, it is preferable to use one with a low dislocation density. The dislocation density of the AlN substrate 11 is preferably ^{10⁶ cm⁻²} or less, and more preferably ^{10⁴ cm⁻²} or less. By using an AlN substrate 11 with a low dislocation density, the dislocation density of the semiconductor layer laminated on the AlN substrate 11 can also be reduced, and as a result, the luminescence efficiency or light reception efficiency can be improved. The lower limit of the dislocation density is 0 ^cm⁻² . The dislocation density can be measured using known methods, such as measuring the number of dislocations from a transmission electron microscope image, or measuring the number of etch pits after immersion in a heated acid mixed solution.

By using an AlN substrate with a lower dislocation density, such as ^{10⁶ cm⁻²} or less, or even ^{10⁴ cm⁻²} , it is possible to prevent a reduction in the luminescence efficiency in the active layer 14 due to dislocations. Furthermore, it is possible to prevent problems such as the diffusion of impurities via dislocations generated when the ultraviolet light-emitting element is energized, and an increase in leakage current.

In this embodiment, the semiconductor light-emitting element 10 uses an AlN substrate with a dislocation density of ^{10⁴ cm⁻²} .

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 slightly inclined (off-angled) from the C-plane, with the off-angle preferably being 0.1 to 0.5°, and more preferably 0.3 to 0.4°. While the direction of the crystal plane inclination is not particularly limited, from the viewpoint of smoothness, inclination in the M-axis direction is preferable. 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.

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, the mean square roughness (RMS) in a 5 × 5 ^μm² 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 a known Chemical Mechanical Polish (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.

The AlN substrate 11 is preferably highly transparent to light for the light-emitting element that will ultimately be formed. Therefore, it is preferable that the absorption coefficient in the deep ultraviolet region, specifically at wavelengths of 210 nm or higher, is 25 ^cm⁻¹ or less. While it is preferable that the lower limit of the absorption coefficient be 0 ^cm⁻¹ , considering industrial production and measurement accuracy, the lower limit of the absorption coefficient at 210 nm is 15 ^cm⁻¹ , and the lower limit of the absorption coefficient at wavelengths of 250 nm or higher is 1 ^cm⁻¹ . By using an AlN substrate with such a low absorption coefficient, it is possible to suppress the deterioration of properties due to ultraviolet light absorption in the AlN substrate 11.

Furthermore, the thickness of the AlN substrate 11 used in this embodiment is not particularly limited. A thinner AlN substrate can reduce the amount of light absorbed within the substrate, 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. Therefore, the thickness is usually preferably 50 to 1000 μm. Such an AlN substrate 11 can be manufactured, for example, by the sublimation method described in J. Cryst. Growth 312, 58-63 (2009) or Appl. Phys. Express 5, 055504 (2011), or by the hydride vapor phase growth method.

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

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 to obtain the aforementioned lattice relaxation suppression effect, a thickness of 5 to 1000 nm is preferred, and a thickness of 30 to 100 nm is more preferable.

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.

The n-type semiconductor layer 13 is a single-crystal AlxGa1-xN (0.5 ≤ x ≤ 1) layer having a band gap smaller than that of the AlN substrate 11 and, if a buffer layer is provided, the band gap of the AlN substrate 11 and 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 preferably ^{10⁶ cm⁻²} or less, and more preferably ^{10⁴ cm⁻²} or less, similar to that of the AlN substrate 11. Even when the n-type semiconductor layer 13 of the present invention is formed from multiple layers, all of these layers are lattice-matched, so the dislocation density of each layer is equivalent.

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, in order to achieve high conductivity, the Si concentration is preferably 1 × ^{10¹⁸ cm⁻³} to 5 × ^{10¹⁹ cm⁻³} . Even when the n-type semiconductor layer 13 is formed from multiple layers, the Si concentration of each layer is preferably 1 × ^{10¹⁸ cm⁻³} to 5 × ^{10¹⁹ cm⁻³} . Furthermore, the Si concentration of each layer may be constant, or it may differ depending on the device design, etc. Also, the Si concentration can be made relatively high at the interfaces of each layer.

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., the direction away from the AlN substrate 11 (towards the active layer 14).

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. It also has a mesa portion 18M consisting of the active layer 14, the p-type semiconductor layer 15, and a part of the n-type semiconductor layer 13. Furthermore, an exposed portion (exposed surface 13S) where the n-type semiconductor layer 13 is exposed is formed in the outer region 18R of the mesa portion 18M.

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, forming an exposed portion of the n-type semiconductor layer 13. Each of these multilayer semiconductor layers is an AlGaN-based semiconductor layer.

First, the structure of the mesa portion 18M will be described below. The active layer 14 consists of an AlGaN layer having a band gap smaller than that of 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. Furthermore, the active layer 14 emits light in the deep ultraviolet region. Note that the structure of the active layer 14 is not limited to this; it may be composed of a single layer or have a single quantum well structure.

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.

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.

The configuration of the p-type semiconductor layer 15 is not limited to this. For example, the electron blocking layer 15A does not need to have a p-type dopant, and the electron blocking layer 15A does not need to be provided at all.

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. In a portion of the outer region 18R, a surface irregularity structure 21 consisting of fine irregularities on the surface of the n-type semiconductor layer 13 is formed (irregularity structure formation region). Here, fine irregularities refer to irregularities with a size approximately equal to the emission wavelength.

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.

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.

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).

The metal reflective layer 23 can be made of a material with high reflectivity to ultraviolet light, such as Al. Alternatively, instead of the metal reflective layer 23, a highly reflective coating film with 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.

Furthermore, while it is preferable that the metal reflective layer 23 is formed over the entire upper surface of the transparent insulating layer 22, it may also be provided on a portion of the upper surface of the transparent insulating layer 22.

Furthermore, while it is preferable that a metal reflective layer 23 is provided on the transparent insulating layer 22, it is not necessary. 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 reflector 24 (Lambertian reflector).

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., a Ti layer, thickness: 1 nm) with respect to the n-type semiconductor layer 13, an electrode layer 16B (e.g., an Al layer, thickness: 250 nm) formed on the ohmic contact metal layer 16A, and a pad electrode 16C (e.g., thickness: 5 nm) made of Au formed on the electrode layer 16B. These layers are alloyed by annealing to form the n-electrode 16.

A protective film 25 is provided covering 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.

Furthermore, 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 vapor deposition process.

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, for example, made of 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 this reflective layer extends across 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.

[Light extraction structure for semiconductor light-emitting elements]

(1) Light extraction efficiency The internal reflection and light extraction of synchrotron radiation from the active layer 14 will be described below. 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 inside 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.

(2) Diffuse Reflection Structure The uneven structure 21 of the diffuse reflection 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 of samples A1 to A3 and B1 to B3. Samples A1 to A3 and samples B1 to B3 were obtained from different wafer lots.

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.

As shown in Figures 4A and 4B, in the diffuse reflectance section 24 of samples A1-A3 and B1-B3, which have conical protrusions with 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 ideal Lambertian reflection.

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 height h in the diffuse reflection portion 24.

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 reflection sections]
As described above, if the diffuse reflection 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 reflection portion 24 will be explained below with reference to an example.

(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.

The semiconductor light-emitting element 40 has a rectangular columnar shape, and multiple rectangular columnar mesa portions 18M are provided on its upper surface. That is, each of the multiple mesa portions 18M has a rectangular shape when viewed from above. More specifically, in the semiconductor light-emitting element 40, multiple rectangular columnar mesa portions 18M extending in one direction (x-direction) are formed parallel to each other. A p-electrode 17 is provided across the entire upper surface of the mesa portion 18M. Directly emitted light 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 with reflective function.

Furthermore, in a top view, the mesa portion 18M has a rectangular shape, and multiple parallel n-electrodes 16 extending 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.

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

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). The reflected light Lr reflected by the light extraction surface 11E is diffusely reflected by the rectangular ring-shaped diffuse reflecting portion 24 (diffuse reflected light Ld). Therefore, the diffuse reflected light Le 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.

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

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

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). Furthermore, 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. Note that, as in Example 1, a p electrode 17 having a reflective layer is provided across the entire upper surface of the mesa portions 18M.

In this embodiment 2, a first diffuse reflection portion 24A (first uneven structure portion) is provided between the mesa portion 18M and the n-electrode 16, and a second diffuse reflection portion 24B (second uneven structure portion) is provided in the outer regions of the multiple mesa portions 18M and the multiple n-electrode 16.

In this embodiment 2, the first diffuse reflection section 24A and the second diffuse reflection section 24B diffusely reflect the reflected light and multiple reflected light within the element that are emitted from the active layer 14 of the mesa section 18M, which is located at a distance from the element, and totally reflected by the light extraction surface 11E. Since the diffuse reflected light Le below the critical angle of the light extraction surface 11E is extracted to the outside, a semiconductor light-emitting element with improved light extraction efficiency can be provided.

Although the case with multiple mesa portions 18M and multiple n-electrodes 16 has been described, it is sufficient to have at least one mesa portion 18M and at least one n-electrode 16. Essentially, the diffuse reflection portion 24 should be 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).

Furthermore, the first diffuse reflecting portion 24A, provided between the mesa portion 18M and the n-electrode 16, and the second diffuse reflecting portion 24B, provided in the outer region of the mesa portion 18M and the n-electrode 16, only need to be provided at least once each.

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

The above-described embodiments 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 circumference in embodiment 1 may be combined with the first diffuse reflecting portion 24A provided between the mesa portion 18M and the n electrode 16 in embodiment 2 to form the diffuse reflecting portion 29.

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.

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. Therefore, a semiconductor light-emitting element with further improved light extraction efficiency can be provided.

As described in detail above, this disclosure provides a semiconductor light-emitting element with high efficiency for external light extraction and excellent element characteristics of high efficiency and high output.

10, 40, 50: Semiconductor light-emitting element 11: Substrate 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 region 18R: Outer region 21: Uneven structure 22: Transparent insulating layer 23: Metal reflective layer 24: Diffuse reflective region 24A: First diffuse reflective region 24B: Second diffuse reflective region 25: Protective film 29: Diffuse reflective region La: Synchrotron radiation Ld: Diffuse reflected light Lr: Reflected light

Claims (11)

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. 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. The ultraviolet semiconductor light-emitting element according to claim 1, comprising 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. The ultraviolet semiconductor light-emitting element according to claim 3, wherein the dielectric layer comprises a plurality of dielectric sublayers made of different materials. The ultraviolet semiconductor light-emitting element according to claim 3, comprising 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. 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. 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. 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. 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. 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. 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.