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] The device comprises a substrate, a laminated light-emitting semiconductor layer in which a first semiconductor layer, an active layer, and a second semiconductor layer are formed on the substrate in that order, and a light extraction structure formed on the back surface of the substrate. The light extraction structure consists of a waveguide layer formed on the back surface of the substrate and an uneven structure formed on the waveguide layer, wherein the refractive index of the waveguide layer is greater than that of the substrate.

Description

[Technical Field]

[0001] This invention relates to a semiconductor light-emitting element. [Background technology]

[0002] Conventionally, to improve the light extraction efficiency of light-emitting diodes (LEDs), it has been common practice to provide an uneven surface on the light extraction surface.

[0003] For example, Patent Document 1 discloses a periodic uneven structure formed on a light extraction surface and a fine uneven structure formed on the surface of the periodic uneven structure.

[0004] However, in conventional technology, most of the light incident on the uneven structure at an angle greater than the critical angle is reflected, resulting in low light extraction efficiency, and further improvements are needed. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Re-tabled publication No. 2015 / 016150 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention has been made in view of the above-mentioned problems, and provides 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]

[0007] A semiconductor light-emitting device according to one embodiment of the present invention is circuit board and A laminated light-emitting semiconductor layer in which a first semiconductor layer, an active layer, and a second semiconductor layer are formed on the substrate in this order, The substrate has a light extraction structure formed on its back surface, The light extraction structure includes a waveguide layer formed on the back surface of the substrate and a concavo-convex structure formed on the waveguide layer. The refractive index of the waveguide layer is greater than the refractive index of the substrate, which is a characteristic feature.

[0008] A semiconductor light-emitting device according to another embodiment of the present invention includes a substrate, a waveguide layer formed on the substrate, a stacked light-emitting semiconductor layer in which a first semiconductor layer, an active layer, and a second semiconductor layer are formed in this order on the waveguide layer, and a light extraction structure formed on the back surface of the first semiconductor layer. The light extraction structure includes a plurality of recesses formed on the waveguide layer side of the substrate and arranged periodically, and a concavo-convex structure formed by embedding the waveguide layer in the plurality of recesses. The refractive index of the waveguide layer is greater than the refractive index of the substrate, which is a characteristic feature.

[0009] A semiconductor light-emitting device according to another embodiment of the present invention includes a substrate, a stacked light-emitting semiconductor layer in which a first semiconductor layer, an active layer, and a second semiconductor layer are formed in this order on the substrate, and a light extraction structure formed on the second semiconductor layer. The light extraction structure includes a waveguide layer formed on the second semiconductor layer and a concavo-convex structure formed on the waveguide layer. The refractive index of the waveguide layer is greater than the refractive index of the second semiconductor layer, which is a characteristic feature.

Brief Description of the Drawings

[0010] [Figure 1] It 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. [Figure 2] It is a plan view when the semiconductor light-emitting device is viewed from the concavo-convex structure side. [Figure 3]It is a cross-sectional view schematically showing the propagation and diffraction of light in a light extraction structure including a waveguide layer and a concavo-convex structure. [Figure 4A] It is a cross-sectional view schematically showing the waveguide layer and the concavo-convex structure of Example 1 (EX1) of the first embodiment. [Figure 4B] It is a cross-sectional view schematically showing the protrusion of the concavo-convex structure. [Figure 5] It is a cross-sectional view schematically showing the light extraction structure of Comparative Example (CX1) having a concavo-convex structure (protrusion structure) on the substrate surface. [Figure 6] It is a graph showing the integrated transmittance T with respect to the refractive index n of the light extraction structure. [Figure 7] It is a graph showing the simulation result of the integrated transmittance T with respect to the concavo-convex period. [Figure 8] It is a cross-sectional view schematically showing the semiconductor light-emitting device of Example 2 of the first embodiment. [Figure 9] It is a cross-sectional view schematically showing the semiconductor light-emitting device of Example 3 of the first embodiment. [Figure 10] It is a cross-sectional view schematically showing the structure of the semiconductor light-emitting device of the second embodiment.

Mode for Carrying Out the Invention

[0011] 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 described with the same reference numerals.

[0012] [First Embodiment] 1. 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. Note that the case where the semiconductor light-emitting device 10 is a deep ultraviolet light-emitting diode (LED) will be described as an example.

[0013] As shown in Figure 1, the semiconductor light-emitting element 10 is formed by epitaxial growth on the surface of a flat substrate 11 made of AlN single crystal, using the substrate 11 as a growth substrate, and sequentially stacking a first semiconductor layer consisting of an n-type semiconductor layer 13, an active layer 14, and a second semiconductor layer consisting of a p-type semiconductor layer 15 and a p-contact layer 16 on the surface of the substrate 11. The second semiconductor layer has the opposite conductivity type to the first semiconductor layer. The second semiconductor layer does not necessarily include a contact layer.

[0014] In the following description, the semiconductor light-emitting element 10 will be described as being made of an AlGaN-based semiconductor layer, but it is not limited to this. That is, the semiconductor light-emitting element 10 is not limited to an ultraviolet light-emitting diode, but may also be a visible light-emitting diode, an infrared light-emitting diode, or the like.

[0015] First, the substrate 11 is not particularly limited, but it is preferable to use one with a low dislocation density. The dislocation density of the substrate 11 is 10 6 cm -2 It is preferable that the following conditions are met, and more preferably 10 4 cm -2 The following is true: By using an AlN substrate with a low dislocation density, the dislocation density of the semiconductor layer stacked on the substrate 11 can also be reduced, and as a result, the luminescence efficiency or light reception efficiency can be improved.

[0016] In this embodiment, the crystal growth surface of the substrate 11 is a C-plane. Alternatively, the crystal growth surface of the 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°.

[0017] The substrate 11 is preferably highly transparent to the light emission of the light-emitting element that will ultimately be formed. 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. -1While 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 5 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 substrate 11.

[0018] Furthermore, the thickness of the substrate 11 used in this embodiment is not particularly limited. If the substrate 11 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 will be difficult to handle and may reduce the yield of the elements. For this reason, the thickness is usually preferably 50 to 1000 μm.

[0019] The crystal growth surface of the substrate 11 is a C-plane (C+ plane), but it is not limited to this. For example, the crystal growth surface of the substrate 11 may be a C-plane (C- plane), an M-plane, or an A-plane.

[0020] Furthermore, a buffer layer may be provided between the 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 a buffer layer from the viewpoint of suppressing lattice relaxation of the n-type semiconductor layer 13 and improving the yield of the crystal growth process.

[0021] Furthermore, the buffer layer is lattice-matched with the single-crystal substrate 11. Here, lattice-matched means that the lattice constant of the a-axis of the substrate 11 is approximately equal to that of the buffer layer, and the lattice relaxation rate is ±5% or less. Furthermore, the substrate 11 can be made of a material with high light transmittance, such as a sapphire substrate.

[0022] The n-type semiconductor layer 13 is a single-crystal AlxGa1-xN (0.5 ≦ x ≦ 1) layer having a bandgap smaller than that of the buffer layer when the buffer layer is provided on the substrate 11. Since the n-type semiconductor layer 13 is lattice-matched with the substrate 11, lattice relaxation accompanied by the generation of dislocations 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 substrate 11. Thus, the dislocation density of the n-type semiconductor layer 13 is preferably 10 6 cm -2 or less, more preferably 10 4 cm -2 or less. Even when the n-type semiconductor layer 13 of the present invention is formed of a plurality of layers, since all of these layers are lattice-matched, the dislocation density of each layer is equivalent. When a sapphire substrate is used for the substrate 11, a buffer layer may be provided on the sapphire substrate. In this case, the dislocation density is larger than that when AlN is used as the substrate.

[0023] 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 may be appropriately determined according to the purpose. Among others, in order to achieve high conductivity, for example, the Si concentration is preferably 1×10 18 cm -3 ~5×10 19 cm -3 . Even when the n-type semiconductor layer 13 is formed of a plurality of layers, the Si concentration of each layer is preferably 1×10 18 cm -3 ~5×10 19 cm -3 . And the Si concentration of each layer may be constant, or the Si concentration of each layer may be different according to device design or the like. Also, the Si concentration can be made relatively high at the interface of each layer.

[0024] Also, in the present embodiment, the n-type semiconductor layer 13 is composed of an AlGaN layer (composition gradient layer) in which the Al composition decreases in the growth direction, that is, the direction away from the substrate 11 (the direction toward the active layer 14).

[0025] The n-type semiconductor layer 13 may be composed of multiple semiconductor layers with different crystal compositions or impurity concentrations. It may also include an undoped layer (or i-layer).

[0026] The semiconductor light-emitting element 10 has an active layer 14 formed on an n-type semiconductor layer 13, a p-type semiconductor layer 15 formed on the active layer 14, and a p-contact layer 16 formed on the p-type semiconductor layer 15. The p-type semiconductor layer 15 functions as a p-type cladding layer.

[0027] 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 (MQW) structure consisting of multiple well layers and a barrier layer. The active layer 14 also emits light in the deep ultraviolet region. The configuration 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.

[0028] 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.

[0029] The p-type semiconductor layer 15 consists of an AlN layer and an AlGaN layer containing, for example, Mg as a p-type dopant. The p-type semiconductor layer 15 may also be composed of multiple semiconductor layers with different crystal compositions or impurity concentrations. Furthermore, it may include an undoped layer (or i-layer). Additionally, an electron blocking layer may be provided between the active layer 14 and the p-type semiconductor layer 15.

[0030] A p-electrode 17 is provided on the p-contact layer 16. The p-electrode 17 is made of, for example, a laminate of a Ni layer and an Au layer. A reflective layer may be provided on the p-electrode 17, and it is preferable that the reflective layer is provided over the entire surface of the p-electrode 17.

[0031] A semiconductor layer (multilayer light-emitting semiconductor layer 19) consisting of an n-type semiconductor layer 13, an active layer 14, a p-type semiconductor layer 15, and a p-contact layer 16 stacked on a substrate 11 in this order is partially removed so that the n-type semiconductor layer 13 is exposed, and an exposed portion (exposed surface 13D) of the n-type semiconductor layer 13 is formed.

[0032] An n-electrode 18 is formed on the exposed surface 13D of the n-type semiconductor layer 13 (n-electrode formation region). The n-electrode 18 consists of an ohmic contact metal layer 18A (e.g., Ti layer, layer thickness: 1 nm) with respect to the n-type semiconductor layer 13, an electrode layer 18B (e.g., Al layer, layer thickness: 250 nm) formed on the ohmic contact metal layer 18A, and a pad electrode 18C (e.g., layer thickness: 1.5 μm) made of Au formed on the electrode layer 18B. By applying a voltage between the p electrode 17 and the n electrode 18, the active layer 14 emits light.

[0033] 2. Light extraction structure for semiconductor light-emitting elements (1) Light extraction structure As shown in Figure 1, a light extraction structure 25 is provided on the back surface 11E of the substrate 11 (the side opposite to the side on which the multilayer light-emitting semiconductor layer 19 is stacked). The light extraction structure 25 consists of a waveguide layer 21 provided on the back surface 11E of the substrate 11 and a bumpy structure 23 provided on the waveguide layer 21. The light emitted from the active layer 14 and extracted from the light extraction structure 25 is emitted to the outside (air) (output light LO).

[0034] Figure 2 is a plan view of the semiconductor light-emitting element 10 as seen from the side of the uneven structure 23. The waveguide layer 21 is flat and has a constant thickness, and the uneven structure 23 consists of a plurality of fine protrusions 23P arranged on the waveguide layer 21. More specifically, in the uneven structure 23, the plurality of protrusions 23P are arranged in a triangular grid arrangement in which each of the protrusions 23P is positioned at a triangular grid point with a period PK. The surface 21S of the waveguide layer 21 is exposed between adjacent protrusions 23P where no protrusions 23P are provided.

[0035] Furthermore, it is preferable that the multiple protrusions 23P are arranged periodically, such as in a triangular lattice arrangement, a square lattice arrangement, or a hexagonal lattice arrangement, and it is most preferable that they be arranged in a triangular lattice arrangement, which maximizes the filling factor. However, the multiple protrusions 23P do not have to be arranged periodically and may be arranged randomly.

[0036] The waveguide layer 21 is made of a material with a higher refractive index than the substrate 11. If the substrate 11 is an AlN substrate (refractive index 2.3), then the waveguide layer 21 can be made of a material with a higher refractive index than AlN, for example, ZrO2 with a refractive index of 2.6.

[0037] Furthermore, when a sapphire substrate (refractive index 1.8) is used as the substrate 11, the waveguide layer 21 can be made of, for example, SiN, HfO2 with a refractive index of 2.3, or ZrO2 with a refractive index of 2.6.

[0038] The waveguide layer 21 and the multiple fine protrusions 23P constituting the uneven structure 23 may be made of the same material, or they may be made of a material having a different refractive index than the waveguide layer 21.

[0039] (2) Method for manufacturing a light extraction structure The optical extraction structure 25, consisting of a waveguide layer 21 and a textured structure 23, can be fabricated by well-known methods. For example, high refractive index layers such as ZrO2 and HfO2 can be deposited using ALD (Atomic Layer Deposition), sputtering, or CVD equipment. For the textured structure 23, methods such as electron beam lithography, photolithography, and nanoimprint lithography can be applied.

[0040] Furthermore, etching methods such as inductively coupled plasma (ICP) etching, reactive ion etching (RIE), and other dry etching techniques, or wet etching using acidic or alkaline solutions as etching solutions, can be applied. In this case, dry etching is preferable to form a highly periodic pattern.

[0041] (3) Optical extraction structure consisting of a waveguide layer and an uneven structure Figure 3 is a schematic cross-sectional view showing the propagation and diffraction of light in the optical extraction structure 25, which consists of a waveguide layer 21 and an uneven structure 23.

[0042] The incident light Li, which is incident on the back surface 11E of the substrate 11, which is the interface between the substrate 11 and the waveguide layer 21, at an incident angle θi, propagates within the waveguide layer 21 (incident light La). Note that although the trajectory of the light is illustrated with arrows, this does not mean that it can be approximated by geometrical optics; it merely illustrates the direction perpendicular to the wavefront WF of the light.

[0043] The incident light La propagating within the waveguide layer 21 is diffracted and scattered by the uneven structure 23, generating diffracted light in multiple directions. Here, the diffracted light reflected towards the substrate 11 is referred to as reflected diffracted light Lb, and the diffracted light emitted to the outside (into the air) is referred to as transmitted diffracted light Lt.

[0044] A portion of the reflected diffracted light Lb is totally reflected at the interface between the substrate 11 (AlN) and the waveguide layer 21 (i.e., the back surface 11E of the substrate 11), and the totally reflected propagated light Lc propagates within the waveguide layer 21. This propagated light Lc is again incident on the uneven structure 23, and a portion of it is radiated to the outside as transmitted diffracted light Lt. Therefore, the transmittance of the incident light Li to the light extraction structure 25 to the outside (into the air) can be improved, and the light extraction efficiency can be improved.

[0045] Figure 4A is a schematic cross-sectional view showing the waveguide layer 21 and the uneven structure 23 of Example 1 (EX1) of the first embodiment, and Figure 4B is a schematic cross-sectional view showing the protrusions 23P of the uneven structure 23. The simulation results performed based on the structures shown in Figures 4A and 4B will be described below.

[0046] Specifically, the uneven structure 23 has multiple conical protrusions 23P. The inclination angle of the sides of the conical protrusions 23P is, for example, 60°. The substrate 11 (AlN) has a refractive index n0 = 2.3, and the waveguide layer 21 and the multiple protrusions 23P of the uneven structure 23 are formed of ZrO2 with a refractive index n1 = n2 = 2.6. The layer thickness t of the waveguide layer 21 is 127 nm. The multiple protrusions 23P are arranged at triangular lattice point positions with a period PK = 600 nm. Each protrusion 23P is a conical protrusion, and the simulation was performed with a base diameter DP = 500 nm and a height HP = 433 nm.

[0047] (a) Transmission diffraction due to uneven structure Figure 5 is a schematic cross-sectional view showing the light extraction structure of a comparative example (CX1) having an uneven surface (protrusion structure) on the substrate surface.

[0048] More specifically, the surface of the substrate 11 (AlN) is provided with a textured structure 103. Unlike the light extraction structure 25 of this embodiment, there is no waveguide layer 21 between the substrate 11 and the textured structure 103. That is, the surface of the substrate 11 simply has fine irregularities, and the protrusions 103P of the textured structure 103 are made of the same AlN as the substrate 11.

[0049] The shape, size, and arrangement of projection 103P are the same as those of projection 23P in Example 1 (EX1).

[0050] The diffraction angles of all diffracted light diffracted by the uneven structure 103 of comparative example (CX1) can be determined by the following equation (1).

[0051]

number

[0052] Under the above conditions, simulations were performed using the three-dimensional finite difference time-domain method (FDTD) for reflected and transmitted diffracted light. The incident angle θi was fixed at 60° during the simulation.

[0053] The uneven structure 103 causes diffraction and scattering, allowing some light to pass through to the air. Simulation results showed that the energy of the light propagating into the air was approximately 10.8% of the total incident energy. The majority of the remaining energy is reflected and propagated to the substrate 11 (AlN). If this reflected light (reflected diffracted light and reflected scattered light) can be effectively utilized, it is possible to improve the transmittance.

[0054] On the other hand, when a similar simulation was performed on the light extraction structure 25 of Example 1 (EX1), the energy of the light propagated into the air was approximately 13.8% of the total incident energy. In other words, an improvement of approximately 1.28 times was obtained compared to the 10.8% of Comparative Example (CX1).

[0055] As explained with reference to Figure 3, the propagating light Lc reflected by the uneven structure 23 towards the substrate 11 and totally reflected at the interface between the substrate 11 (AlN) and the waveguide layer 21 is then incident on the uneven structure 23 again, and a portion of it is radiated into the air as transmitted diffracted light Lt, thereby improving the light extraction efficiency. In other words, by totally reflecting the diffracted and scattered light generated by the uneven structure 23 at the interface with the substrate 11 and causing multiple reflections within the waveguide layer 21, the amount of transmitted diffracted light from the uneven structure 23 is increased, improving the transmittance from the substrate 11 to the air and improving the light extraction efficiency.

[0056] (b) Refractive index of the light extraction structure The light emitted from the active layer 14 is radiated in various directions in three-dimensional space. Therefore, it is important to improve the integrated value obtained by accumulating the transmittance of all incident light incident on the light extraction structure 25 in the range of incident angle θ from 0 to 90° and azimuth angle φ from 0 to 360°. In this specification, this integrated value will be referred to as the integrated transmittance T. The integrated transmittance T is calculated by the following equation (2).

[0057]

number

[0058] Figure 6 shows the integral transmittance T calculated for the optical extraction structure 25, which consists of a waveguide layer 21 and an uneven structure 23 as shown in Figures 4A and 4B, by varying the refractive index n of the waveguide layer 21 and the uneven structure 23 (i.e., the optical extraction structure 25) by 1.0 in the range of n = 2.3 to 2.8. The integral transmittance T for flat AlN and air was 0.07.

[0059] From these simulation results, it can be seen that a high integral transmittance T can be obtained when the refractive index n of the waveguide layer 21 is greater than the refractive index of the substrate 11 (AlN, refractive index = 2.3). It is preferable that the refractive index n of the light extraction structure 25 be in the range of 2.4 to 2.75, which is 0.1 to 0.45 greater than the refractive index of the substrate 11, and more preferably in the range of 2.5 to 2.7, which is 0.2 to 0.3 greater than the refractive index of the substrate 11.

[0060] The waveguide layer 21 may be formed as a single layer of a material with a refractive index greater than that of the substrate 11, or as a multilayer thin film including a layer with a refractive index greater than that of the substrate 11.

[0061] (c) Periodicity of the uneven structure When the lattice period in a pitted structure (protruding structure) exceeds the coherence length CL in a vacuum, the coherence of light is lost and diffracted light is no longer generated. Here, the coherence length CL is given by CL = (λ) when the wavelength is λ and the full width at half maximum of the wavelength spectrum is Δλ. 2 It is defined as ( / Δλ). For example, in the case of a deep ultraviolet light-emitting diode, when the wavelength λ = 265 nm and Δλ = 11 nm, CL = 6.3 μm.

[0062] The relationship between the lattice period and the surface irregularity period (arrangement period) within the plane changes depending on the arrangement of the periodic surface irregularity structure. However, since the lattice period is considered to be less than or equal to the surface irregularity period, it is desirable that the surface irregularity period be less than or equal to the coherence length CL in a vacuum. Furthermore, in the case of deep ultraviolet light-emitting diodes, it is preferable that it be 6.3 μm or less.

[0063] Furthermore, if the period of the uneven structure becomes too small, diffracted light will no longer be generated according to equation (1).

[0064] Figure 7 is a graph showing the simulation results of the integral transmittance T against the period (arrangement period) PK of the uneven structure shown in Figures 4A and 4B. However, the simulation was performed with the diameter DP = PK × 0.83 and the height HP = PK × 0.7 of the base of the conical protrusion 23P.

[0065] As shown in Figure 7, diffracted light satisfying equation (1) is generated when the period PK of the surface irregularities is around 50 nm, and the effect becomes more pronounced when the period PK is 100 nm or higher. In this case, the optical wavelength (wavelength within the medium) is approximately 102 nm (= 265 nm / 2.6). From the simulation results, it can be seen that the period PK of the surface irregularities is preferably greater than 0.5 times the optical wavelength, and more preferably greater than 1 time.

[0066] Furthermore, the diameter DP and height HP of the bottom surface of the projection 23P are preferably greater than 0.5 times the wavelength in the medium, and more preferably greater than 1 time. In addition, the diameter DP and height HP are preferably less than or equal to the coherence length CL in a vacuum.

[0067] (4) Other examples and modifications (a) Example 2 Figure 8 is a schematic cross-sectional view of the semiconductor light-emitting element 40 of Example 2 of the first embodiment. In the semiconductor light-emitting element 40 of Example 2, the light extraction structure 45 provided on the back surface of the substrate 11 consists of a waveguide layer 41 and an uneven structure 43 formed on the waveguide layer 41. It differs from the semiconductor light-emitting element 10 of Example 1 in that materials with different refractive indices are used for the waveguide layer 41 and the protrusions 43P of the uneven structure 43.

[0068] For example, ZrO2 (refractive index: 2.6) can be used for the waveguide layer 41, and for example, SiO2, Al2O3, SiN, HfO2, etc. can be used for the uneven structure 43. It is sufficient that the waveguide layer 41 uses a material with a refractive index greater than that of the substrate 11. In the semiconductor light-emitting element 40 of Example 2, the light that has been diffracted and scattered by the uneven structure 43 and then totally reflected at the interface between the waveguide layer 41 and the substrate 11 and returned to the uneven structure 43 is diffracted and scattered again by the uneven structure 43, thus improving the light extraction efficiency.

[0069] (b) Example 3 Figure 9 is a schematic cross-sectional view showing the semiconductor light-emitting element 50 of Example 3 of the first embodiment. In the semiconductor light-emitting element 50 of Example 3, a sapphire substrate is used as the substrate 51, and a light extraction structure 55 is provided on the substrate 51.

[0070] More specifically, the surface of the substrate 51 has a plurality of recesses periodically arranged at lattice positions. A layer with a refractive index greater than that of the substrate 51 (sapphire), such as an AlGaN layer, is formed on the surface of the substrate 51 where the plurality of recesses are formed. The plurality of recesses of the substrate 51 are, for example, cylindrical and of the same size. Therefore, the AlGaN embedded in the plurality of recesses of the substrate 51 constitutes a bumpy structure 52 consisting of a plurality of cylindrical protrusions 52P arranged at lattice positions, and the AlGaN layer on the substrate 51 constitutes a waveguide layer 53. In other words, the semiconductor light-emitting element 50 has a light extraction structure 55 consisting of the bumpy structure 52 and the waveguide layer 53. Note that the shape of the plurality of protrusions 52P is not limited to a cylindrical shape.

[0071] A semiconductor layer 56 made of AlN is formed on the light extraction structure 55, and an n-type semiconductor layer 13, an active layer 14, a p-type semiconductor layer 15, and a p-contact layer 16 are stacked on the semiconductor layer 56 in this order (stacked light-emitting semiconductor layer 19).

[0072] In the semiconductor light-emitting element 50 of Example 3, light that propagates within the waveguide layer 53, is diffracted by the uneven structure 52, and then totally reflected by the semiconductor layer 56 and returns to the uneven structure 52 is diffracted again by the uneven structure 52, thus improving the light extraction efficiency.

[0073] (c) Modified example (i) In the above-described embodiment, the case in which the multiple protrusions of the uneven structure have a conical or cylindrical shape has been explained, but the embodiment is not limited to this. The multiple protrusions may have shapes such as columnar, conical, or frustoconical. For example, they may have various shapes such as cones, frustocones, cylinders, hemispheres, triangular pyramids, triangular prisms, frustoconical pyramids, hexagonal pyramids, hexagonal prisms, and frustoconical pyramids. Furthermore, these multiple shapes of protrusions may be included randomly.

[0074] In this specification, "conical projection" is not limited to projections having a perfect conical shape, but also includes conical projections with a substantially conical surface on their sides. Furthermore, the terms cone, cylinder, frustum of a cone, and hemisphere include elliptical cone, elliptical cylinder, frustum of an ellipse, and elliptical sphere. In addition, conical and frustum-shaped projections may have curved sides, for example, a rounded shape that bulges outward from the conical surface. The diameter a of the base of the conical projection refers to the major axis at the base.

[0075] (ii) In the above-described embodiment, when an AlN substrate is used as the substrate, the waveguide layer may be a layer containing at least one of ZrO2, AlGaN, and diamond.

[0076] Furthermore, when a sapphire substrate is used as the substrate, the waveguide layer can be a layer containing at least one of the following: HfO2, SiN, AlN, ZrO2, AlGaN, and diamond.

[0077] [Second Embodiment] Figure 10 is a schematic cross-sectional view showing the structure of a semiconductor light-emitting element 70 according to a second embodiment of the present invention.

[0078] In the semiconductor light-emitting element 70 of the second embodiment, a light extraction structure 75 is provided on the side opposite to the substrate 11. Specifically, the light extraction structure 75, which consists of a waveguide layer 71 and an uneven structure 73 having a plurality of protrusions 73P, is formed on the second semiconductor layer 15A. Note that the second semiconductor layer 15A does not necessarily include a p-contact layer 16.

[0079] More specifically, a p-electrode 17 is formed on a portion of the p-contact layer 16, and a light extraction structure 75 is formed in the region outside the area where the p-electrode 17 is formed. The waveguide layer 71 is made of a material with a higher refractive index than the p-contact layer 16 or the second semiconductor layer 15A.

[0080] Furthermore, in this embodiment, a light-reflecting layer 77 is provided on the back surface of the substrate 11. The light-reflecting layer 77 is made of a metal layer or the like that has a high reflectivity to the light emitted from the active layer 14. Therefore, the light emitted from the active layer 14 is emitted to the outside (air) from the light extraction structure 75 (output light LO).

[0081] Although the example shows the optical extraction structure 75 formed on the p-contact layer 16, if the optical loss of the p-contact layer 16 is large, the p-contact layer 16 may be partially removed and the optical extraction structure 75 may be formed on the p-type semiconductor layer 15.

[0082] Alternatively, a transparent electrode made of a transparent conductor such as ITO (indium tin oxide) may be provided on the second semiconductor layer 15A, and a light extraction structure 75 may be formed on the transparent electrode. In this case, the waveguide layer 71 has a higher refractive index than the transparent electrode. Therefore, light that propagates within the waveguide layer 71, is diffracted by the uneven structure 73, and then totally reflected by the p-contact layer 16 and returns to the uneven structure 73 is diffracted again by the uneven structure 73, thus improving the light extraction efficiency.

[0083] 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]

[0084] 10, 40, 50, 70: Semiconductor light-emitting element 11,51: Circuit board 11E: Back side (interface) 13: n-type semiconductor layer (first semiconductor layer) 13D: Exposed surface 14:Active layer 15: p-type semiconductor layer 15A: Second semiconductor layer 16:p contact layer 21,41,53,71: Waveguide layer 23,43,52,73: Uneven structure 23P, 43P, 52P, 73P: Protrusion (convex part) 25, 45, 55, 75: Light extraction structure PK: Array period

Claims

1. circuit board and A stacked light-emitting semiconductor layer in which a first semiconductor layer, an active layer, and a second semiconductor layer are formed on the substrate in this order, The substrate has a light extraction structure formed on its back surface, The light extraction structure comprises a waveguide layer formed on the back surface of the substrate and an uneven structure formed on the waveguide layer. The refractive index of the waveguide layer is greater than the refractive index of the substrate. Semiconductor light-emitting element.

2. The semiconductor light-emitting element according to claim 1, wherein the uneven structure comprises a plurality of protrusions periodically arranged on the waveguide layer.

3. The semiconductor light-emitting element according to claim 2, wherein the arrangement period of the plurality of protrusions is greater than 0.5 times the wavelength in the medium and less than or equal to the coherence length in a vacuum.

4. The semiconductor light-emitting element according to claim 2, wherein the protrusions of the uneven structure have at least one shape from among a cone, a frustum of a cone, a cylinder, a hemisphere, a triangular pyramid, a triangular prism, a frustum of a triangular pyramid, a hexagonal pyramid, a hexagonal prism, and a hexagonal pyramid.

5. The semiconductor light-emitting element according to claim 1, wherein the uneven structure is formed of a material different from the waveguide layer.

6. The light emitted from the active layer has a peak wavelength in the range of 200 to 360 nm. The substrate is AlN, The waveguide layer is ZrO ２ , consisting of a layer containing at least one of AlGaN and diamond, The semiconductor light-emitting element according to claim 1.

7. circuit board and A waveguide layer formed on the substrate, A laminated light-emitting semiconductor layer is formed on the waveguide layer in the order of a first semiconductor layer, an active layer, and a second semiconductor layer, The first semiconductor layer has a light extraction structure formed on its back surface, The aforementioned light extraction structure is, The substrate comprises a plurality of periodically arranged recesses formed on the waveguide layer side, and a surface with unevenness formed by the waveguide layer being embedded in the plurality of recesses. The refractive index of the waveguide layer is greater than the refractive index of the substrate. Semiconductor light-emitting element.

8. The aforementioned stacked light-emitting semiconductor layer is made of an AlGaN-based semiconductor, The first semiconductor layer includes an AlN layer formed on the waveguide layer, The semiconductor light-emitting element according to claim 7, wherein the substrate is made of sapphire and the waveguide layer is made of AlGaN.

9. circuit board and A stacked light-emitting semiconductor layer in which a first semiconductor layer, an active layer, and a second semiconductor layer are formed on the substrate in this order, The present invention has a light extraction structure formed on the second semiconductor layer, The light extraction structure comprises a waveguide layer formed on the second semiconductor layer and an uneven structure formed on the waveguide layer. The refractive index of the waveguide layer is greater than the refractive index of the second semiconductor layer. Semiconductor light-emitting element.

10. The semiconductor light-emitting element according to claim 9, wherein the uneven structure comprises a plurality of protrusions periodically arranged on the waveguide layer.

11. The semiconductor light-emitting element according to claim 10, wherein the arrangement period of the plurality of protrusions is greater than 0.5 times the wavelength in the medium and less than or equal to the coherence length in a vacuum.

12. The transparent electrode formed on the second semiconductor layer is The waveguide layer has a higher refractive index than the transparent electrode and is formed on the transparent electrode. The semiconductor light-emitting element according to claim 9.

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