Light emitting element

Abstract

To provide a light emitting element that emits ultraviolet light with an emission wavelength of less than 300 nm and has a structure that is excellent in resistance to electromigration while maintaining high light extraction efficiency by forming a reflective layer with high reflectance.SOLUTION: A light emitting element 5 that emits ultraviolet light with an emission wavelength of less than 300 nm includes an n-type layer 21 made of an n-type Group III nitride semiconductor, an active layer 22 made of a Group III nitride semiconductor provided on the n-type layer 21, a p-type layer 23 made of a p-type Group III nitride semiconductor provided on the active layer 22, and a p-side electrode 40 including a reflective layer 42 provided on the p-type layer 23 and made of an alloy mainly composed of Al and containing Cu.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a light-emitting device. [Background technology]

[0002] The ultraviolet light emitted by solid-state light-emitting devices using III-nitride semiconductors corresponds to a wavelength band of approximately 210 to 400 nm. In particular, UVC (wavelength 100 to 280 nm) is known to be effective for sterilization and disinfection, and there is an increasing demand for III-nitride semiconductor light-emitting devices that emit ultraviolet light with an emission wavelength corresponding to UVC. Ultraviolet light-emitting devices are configured by forming an AlN layer on a sapphire substrate, and then laminating an n-type layer, an active layer, and a p-type layer made of AlGaN on the AlN layer.

[0003] UV light-emitting elements using III-nitride semiconductors often use a flip-chip type that extracts light from the back side of the substrate. In the flip-chip type, it is thought that the light extraction efficiency can be improved by increasing the reflectivity of the p-side electrode and having the p-side electrode reflect UV light to the light extraction side.

[0004] Patent Document 1 describes the use of a reflective electrode (Ni / Al electrode) in which a Ni film and an Al film are laminated in this order from the p-type contact layer side as the p-side electrode of an ultraviolet light-emitting element using a group III nitride semiconductor.

[0005] Patent Document 2 shows a structure in which a Ni layer and an Mg layer are laminated in this order from the p-type layer side as a p-side electrode of an ultraviolet light-emitting element using a group III nitride semiconductor. The Ni layer is a layer for making good contact with the p-type layer, and the Mg layer is a layer for reflecting ultraviolet light in the UVC band. In the UVC band, Mg has a higher reflectance than Al. Therefore, Patent Document 2 aims to improve the reflectance by using Mg as the reflective layer of the p-side electrode.

[0006] Furthermore, Patent Document 3 describes that a reflective layer used in a light emitting device using a group III nitride semiconductor and emitting light at a wavelength of 470 nm contains one type of alloy selected from the group consisting of Ag-Nd, Ag-Au, Ag-Pt, Ag-Rh, Ag-Cu, Ag-Pd, Ag-Cu-Nd, Ag-Bi-Nd, Ag-Pd, Ag-Cu-Pd, Al-Nd, Al-Au, Al-Pt, Al-Rh, Al-Cu, Al-Pd, Al-Cu-Nd, Al-Bi-Nd, Al-Pd and Al-Cu-Pd.

[0007] Furthermore, Patent Document 4 describes Al, Rh, Ag, or an alloy containing at least one of these elements (e.g., AlCu, ASC (aluminum silicon copper), etc.) as a material for a reflective layer used in a light-emitting element using a group III nitride semiconductor and emitting light with a wavelength of 300 nm to 800 nm.

[0008] Patent Document 5 describes a semiconductor light-emitting device that converts light from a light-emitting layer to emit a desired light, such as white light or warm white light, and that uses a reflective electrode made of a single layer or a laminated film of at least one metal or alloy selected from Al, Rh, and Ag as a material.

[0009] Patent Document 6 describes that the reflective layer used in a light emitting device using a group III nitride semiconductor and emitting light at a wavelength of 455 nm is a single layer or multilayer film made of Ag, Al, Cu or an alloy containing any of these (for example, an AlCu alloy or an AlNd alloy, which also has excellent heat resistance). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2015-216352 A [Patent Document 2] JP 2019-036629 A [Patent Document 3] JP 2006-135026 A [Patent Document 4] JP 2012-222196 A [Patent Document 5] JP 2014-22530 A [Patent Document 6] JP 2017-118031 A Summary of the Invention [Problem to be solved by the invention]

[0011] Since ultraviolet light-emitting elements with an emission wavelength of less than 300 nm have a lower light extraction efficiency than light-emitting elements with an emission wavelength of 300 nm or more, there is a demand for improving the light extraction efficiency for ultraviolet light more than for visible light. In particular, in flip-chip types, it is extremely important to increase the reflectance of the p-side electrode for ultraviolet light in order to increase the light extraction efficiency for ultraviolet light. Therefore, it is preferable to use Al, which has a high reflectance, for the p-side electrode from the viewpoint of light extraction efficiency.

[0012] However, since Al is susceptible to electromigration, when Al is used as a reflective electrode for the p-side electrode of a light-emitting element, there is a possibility that the p-side electrode may suffer a disconnection failure due to electromigration.

[0013] The present invention has been made in view of the above background, and aims to provide an ultraviolet-emitting light-emitting element having an emission wavelength of less than 300 nm and a structure having excellent resistance to electromigration while maintaining high light extraction efficiency by forming a reflective layer having high reflectivity. [Means for solving the problem]

[0014] One aspect of the present invention is a light-emitting element that emits ultraviolet light having an emission wavelength of less than 300 nm, an n-type layer made of an n-type Group III nitride semiconductor; an active layer made of a Group III nitride semiconductor provided on the n-type layer; a p-type layer made of a p-type Group III nitride semiconductor provided on the active layer; a p-side electrode including a reflective layer formed on the p-type layer and made of an alloy mainly composed of Al and containing Cu; The light-emitting device comprises: Effect of the Invention

[0015] According to one aspect of the present invention, the reflective layer constituting the p-side electrode is made of an alloy mainly composed of Al and containing Cu, thereby obtaining a high reflectance. Therefore, a high light extraction efficiency of ultraviolet light can be obtained. Furthermore, by forming the reflective layer from the above material, it is possible to improve the electromigration resistance and suppress breakage failures, etc., compared to the case where Al is used, and as a result, it is possible to improve reliability.

[0016] As described above, according to the above embodiment, a reflective layer having high reflectivity is formed, thereby maintaining high light extraction efficiency, and a light-emitting element having an emission wavelength of less than 300 nm and a structure having excellent resistance to electromigration can be provided. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view showing a configuration of a light emitting device according to a first embodiment. [Diagram 2] 2 is an enlarged cross-sectional view of a light-emitting element that constitutes the light-emitting device of FIG. 1. [Diagram 3] 1 is a graph showing the results of Experiment 1, illustrating the relationship between the emission wavelength and the reflectance of the reflective layer. [Figure 4] 11 is a graph showing the results of Experiment 2, illustrating the relationship between the thickness of the p-side contact electrode (ITO) and the transmittance of ultraviolet light with a wavelength of 280 nm. [Diagram 5] FIG. 11 is a cross-sectional view showing the configuration of a light-emitting element in a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] As described above, the light-emitting device is an ultraviolet light-emitting device having an emission wavelength of less than 300 nm, and includes an n-type layer made of an n-type Group III nitride semiconductor, an active layer made of a Group III nitride semiconductor provided on the n-type layer, a p-type layer made of a p-type Group III nitride semiconductor provided on the active layer, and a p-side electrode including a reflective layer provided on the p-type layer and made of an alloy mainly composed of Al and containing Cu. The alloy mainly composed of Al and containing Cu is preferably at least one selected from the group consisting of AlCu, AlSiCu, and AlCuSn.

[0019] The p-side electrode may further include a cover layer provided on and in contact with the reflective layer and made of at least one material selected from the group consisting of Ti, TiN, Ni, Pt, Au, and Cr. The provision of the cover layer has the effect of enhancing the electromigration resistance of the p-side electrode.

[0020] The cover layer may cover the top surface and the side surfaces of the reflective layer. By configuring the cover layer to cover not only the top surface but also the side surfaces of the reflective layer, it is possible to improve electromigration resistance. The cover layer may cover only the top surface of the reflective layer, and not cover the side surfaces of the reflective layer.

[0021] The light-emitting element may further include a p-side contact electrode provided on the p-type layer and transmitting ultraviolet light of an emission wavelength, and the reflective layer may be provided on the p-side contact electrode, thereby making it possible to obtain good contact between the p-side electrode and the p-type layer.

[0022] The p-side contact electrode may be formed to be thinner than the reflective layer, so that the ultraviolet light emitted from the active layer can be efficiently transmitted through the p-side contact electrode and reflected by the reflective layer, thereby improving the light extraction efficiency.

[0023] The p-side contact electrode preferably has a transmittance of 30% or more for ultraviolet light having an emission wavelength, thereby improving the light extraction efficiency.

[0024] The p-side contact electrode may be made of one oxide selected from the group consisting of ITO and IZO, and the thickness of the p-side contact electrode may be 40 nm or less, thereby making it possible to obtain good contact with the p-side layer and improving the light extraction efficiency.

[0025] The p-side contact electrode may be made of one metal selected from the group consisting of Ru, Rh, or an alloy mainly composed of Ru, Rh, NiAu, and Mg, and the thickness of the p-side contact electrode may be 10 nm or less, which allows good contact with the p-side layer and improves light extraction efficiency.

[0026] (Embodiment 1) 1. Configuration of the Light Emitting Device 1 The configuration of the light emitting device 1 of this embodiment will be described with reference to Fig. 1. The light emitting device 1 may be configured as a light emitting device package that houses the light emitting element 5 as a main element, or may be configured as a device that includes a driving circuit and the like in addition to the light emitting element 5.

[0027] The light emitting device 1 includes a mounting substrate 2, a sealing material 3, a submount 4, and a light emitting element 5. The light emitting device 1 may not include the submount 4, and may include a driving circuit (not shown) and the like.

[0028] The mounting substrate 2 has a mounting surface 2a, and is a substrate for mounting components such as a submount 4 and a light emitting element 5 on the mounting surface 2a. The mounting surface 2a of the mounting substrate 2 has an electrode pad on the upper surface. The mounting substrate 2 may have a circuit pattern electrically connected to the electrode pad, for example. In this embodiment, the mounting substrate 2 has a recess 2b formed therein, and has the mounting surface 2a on the bottom surface of the recess 2b. However, the mounting substrate 2 may be a flat substrate without the recess 2b, and one surface of the flat substrate may constitute the mounting surface 2a. The main body of the mounting substrate 2 is formed of ceramics such as AlN, Al2O3, SiC, and Si2N4.

[0029] The sealing material 3 forms an accommodation space 7 between the mounting substrate 2 and the submount 4, the light emitting element 5, etc., and is made of a transparent material that transmits ultraviolet light of the emission wavelength emitted by the light emitting element 5. The sealing material 3 may be made of any material that transmits ultraviolet light of the emission wavelength, for example, quartz, sapphire, etc. In this embodiment, the sealing material 3 is formed in a flat plate shape, and the periphery of one surface is bonded to the mounting substrate 2. The sealing material 3 is not limited to a flat plate shape, and may be formed in a lens shape.

[0030] The submount 4 is mounted on the electrode pads on the mounting surface 2a of the mounting substrate 2 and is electrically connected to the electrode pads on the mounting surface 2a. The submount 4 has an electrode pad on its upper surface. The main body of the submount 4 is formed of ceramics such as AlN, Al2O3, SiC, Si2N4, Si3N4, and Al2O3 / ZrO2. Here, Al2O3 / ZrO2 means that Al2O3 and ZrO2 are laminated in this order from the mounting substrate 2 side.

[0031] The light emitting element 5 contains a group III nitride and emits ultraviolet light with a predetermined emission wavelength. The emission wavelength of the light emitting element 5 is equal to or greater than 200 nm and less than 300 nm. The light emitting element 5 is disposed on the submount 4. That is, the light emitting element 5 is mounted on the mounting surface 2a of the mounting substrate 2 via the submount 4. The light emitting element 5 is placed on the upper surface of the electrode pad of the submount 4 and is electrically connected to the electrode pad of the submount 4.

[0032] Moreover, the light emitting element 5 is a flip chip type element having electrode pads 33, 45 on the surface on the submount 4 side. Therefore, the electrode pads 33, 45 of the light emitting element 5 are located on the mounting surface 2a side of the mounting substrate 2 (the upper surface side of the submount 4) and are electrically connected to the electrode pads of the submount 4. Then, an element substrate 10 of the light emitting element 5, which will be described later, is located on the opposite side of the mounting surface 2a of the mounting substrate 2 and is disposed so as to face the inner surface of the sealing material 3 at a distance. In other words, the ultraviolet light emitted by the light emitting element 5 is emitted from the back side of the element substrate 10, passes through the sealing material 3, and is output to the outside.

[0033] In this embodiment, the accommodation space 7 formed by the mounting substrate 2 and the sealing material 3 constitutes an air layer. Alternatively, the accommodation space 7 may contain an inactive compound that is liquid at room temperature and normal pressure. The entire accommodation space 7 may be filled with a liquid inactive compound, or an inactive compound may be placed only in a partial region of the accommodation space 7 including the opposing region of the light emitting element 5 and the sealing material 3, with the remaining region being an air layer. An example of the inactive compound is a fluoride resin.

[0034] In this embodiment, the light emitting device 1 includes the submount 4, but as described above, the light emitting device 1 may not include the submount 4. In this case, the light emitting element 5 is directly mounted on the mounting surface 2a of the mounting substrate 2.

[0035] 2. Configuration of flip-chip type light-emitting element 5 The configuration of the flip-chip type light emitting element 5 will be described with reference to Fig. 2. Fig. 2 is a diagram showing the configuration of the light emitting element 5, and is a cross-sectional view in a direction perpendicular to the main surface of the substrate.

[0036] The light-emitting element 5 includes an element substrate 10, a semiconductor layer 20, an n-side electrode 30, a p-side electrode 40, a protective layer 50, and an antireflection layer 60. The light-emitting element 5 is of a flip-chip type, that is, has a structure in which light is extracted from the surface on the element substrate 10 side (the lower surface in FIG. 2). The light-emitting element 5 is an ultraviolet light-emitting element having an emission wavelength of 200 nm or more and less than 300 nm, and in particular is a deep ultraviolet light-emitting element having an emission wavelength of 200 nm to 280 nm (UVC band).

[0037] The element substrate 10 is, for example, a substrate made of sapphire. The plane orientation of the main surface of the element substrate 10 is, for example, the a-plane or the c-plane. The element substrate 10 may have an off-angle of 0.1 to 2 degrees in the m-axis direction. The element substrate 10 may be made of any material other than sapphire as long as it has high transmittance for the emission wavelength and can grow a crystal of a group III nitride semiconductor. For example, the element substrate 10 may be an AlN substrate or an AlN template substrate in which an AlN layer is formed on a sapphire substrate.

[0038] The semiconductor layer 20 is formed by crystal growth on the main surface of the element substrate 10. The semiconductor layer 20 includes a group III nitride semiconductor. The semiconductor layer 20 has at least an n-type layer 21, an active layer 22, and a p-type layer 23. The semiconductor layer 20 is configured by laminating the n-type layer 21, the active layer 22, and the p-type layer 23 in this order from the element substrate 10 side.

[0039] The n-type layer 21 is provided on the element substrate 10. The n-type layer 21 is formed of an n-type Group III nitride semiconductor. The n-type layer 21 is formed of, for example, n-AlGaN. The Al composition (the molar ratio of Al in the entire Group III metals) in the n-type layer 21 is, for example, 60 to 90%. The n-type impurity in the n-type layer 21 is Si, and the Si concentration is, for example, 1×10 18 ~5×10 19 cm -3The thickness of the n-type layer 21 is, for example, 0.5 to 5 μm. The C concentration of the n-type layer 21 is 1×10 15 ~1×10 19 cm -3 The n-type layer 21 may be composed of a plurality of layers. For example, the n-type layer 21 may be a superlattice layer in which AlGaN layers having different Al compositions are alternately stacked. Also, a base layer made of AlN may be provided between the element substrate 10 and the n-type layer 21. Also, an element other than Si may be used as the n-type impurity.

[0040] The active layer 22 is provided on the n-type layer 21. The active layer 22 is made of a group III nitride semiconductor. The active layer 22 has an SQW structure in which a barrier layer, a well layer, and a barrier layer are stacked in this order from the n-type layer 21 side. The active layer 22 may have an MQW structure. In this case, the number of repetitions of the MQW structure is, for example, 2 to 10.

[0041] The well layer is made of AlGaN, and the Al composition is set according to the desired emission wavelength. The Si concentration in the well layer is, for example, 1×10 18 cm -3 The well layer may be undoped. The well layer has a thickness of, for example, 0.5 to 5 nm.

[0042] The barrier layer is made of AlGaN having a larger Al composition than the well layer, and the Al composition is, for example, 50 to 100%. The Si concentration of the barrier layer is, for example, 2×10 19 cm -3 The barrier layer may be undoped. The thickness of the barrier layer is, for example, 3 to 30 nm. The barrier layer may be made of AlGaInN having a band gap energy larger than that of the well layer.

[0043] A hole blocking layer may be provided between the n-type layer 21 and the active layer 22. The hole blocking layer can prevent holes injected from the p-side electrode 40 from diffusing beyond the active layer 22 toward the n-type layer 21. The hole blocking layer is made of AlGaN or AlN having a higher Al composition than the barrier layer of the active layer 22. The thickness of the hole blocking layer is, for example, one molecular layer to 2 nm. In the case of AlN, one molecular layer is approximately 0.26 nm.

[0044] The p-type layer 23 is provided on the active layer 22. The p-type layer 23 is formed of a group III nitride semiconductor. The p-type layer 23 is also called a p-type contact layer because it constitutes a layer in contact with an electrode. The p-type layer 23 may be made of Mg-doped p-GaN or p-AlGaN. When the p-type layer 23 is made of p-AlGaN, the Al composition is, for example, 50% or less, preferably 30% or less.

[0045] When the p-type layer 23 is made of GaN, the thickness of the p-type layer 23 is preferably 1 nm or more and 50 nm or less. GaN may absorb the ultraviolet light emitted from the active layer 22, but by making the layer sufficiently thin, the ultraviolet light can be transmitted. Therefore, a large decrease in the external quantum efficiency can be avoided. The thickness of the p-type layer 23 is preferably 1 nm or more and 10 nm or less. The Mg concentration of the p-type layer 23 is, for example, 1×10 20 ~1×10 22 cm -3 It is.

[0046] The p-type layer 23 may be composed of multiple layers with different Al compositions or Mg concentrations. When the p-type layer 23 is composed of multiple layers, the top layer (p-type contact layer) in contact with the p-side contact electrode 41 is preferably p-GaN or AlGaN with a low Al composition. This is to reduce the contact resistance with the p-side contact electrode 41. In this case, the AlGaN with a low Al composition has an Al composition of 50% or less, preferably 30% or less. When the p-type layer 23 is AlGaN with an Al composition of 50% or less, the thickness is preferably 20 nm or less. By making it sufficiently thin, ultraviolet light can be transmitted.

[0047] A groove 23a is formed in a partial area of ​​the surface of the p-type layer 23, the depth of which reaches the n-type layer 21. This groove 23a is for exposing the n-type layer 21 so that an n-side electrode 30 can be provided thereon.

[0048] An electron blocking layer may be provided between the active layer 22 and the p-type layer 23. The electron blocking layer can prevent electrons injected from the n-side electrode 30 from diffusing beyond the active layer 22 toward the p-type layer 23. The electron blocking layer is made of a group III nitride semiconductor. The electron blocking layer is made of AlGaN or AlN having a higher Al composition ratio than the barrier layer of the active layer 22. The electron blocking layer may be doped with a p-type impurity such as Mg, or may be non-doped. The electron blocking layer has a thickness of, for example, 1 to 20 nm.

[0049] A compositionally graded layer may be provided between the electron block layer and the p-type layer 23. The compositionally graded layer is made of a group III nitride semiconductor. The compositionally graded layer is a layer that has been made p-type by a method called polarization doping. That is, the compositionally graded layer is a layer in which the Al composition changes in the thickness direction, and is set so that the Al composition decreases with increasing distance from the electron block layer. The Al composition of the p-type layer 23 is set to be lower than the minimum Al composition of the compositionally graded layer. It was difficult to increase the hole concentration of AlGaN with a high Al composition by Mg doping, but the hole concentration can be improved by polarization doping, and the hole injection efficiency into the active layer 22 can be increased. In addition, since polarization doping does not require doping with Mg, the crystallinity can be improved.

[0050] The n-side electrode 30 is provided in contact with the n-type layer 21 exposed at the bottom of the groove 23a. The n-side electrode 30 has an n-side contact electrode 31, a first n-side electrode pad 32, and a second n-side electrode pad 33 in a direction perpendicular to the main surface of the element substrate 10. The n-side contact electrode 31 is provided in contact with the n-type layer 21 exposed at the bottom of the groove 23a. The n-side contact electrode 31 is formed of V / Al / Ti, Ti / Al, V / Al, or the like. Here, A / B means that A and B are laminated in this order from the side of the surface to be placed. For example, when the n-side contact electrode 31 is formed of V / Al / Ti, V, Al, and Ti are laminated in this order from the side of the n-type layer 21. The thickness of the n-side contact electrode 31 is 100 to 300 nm.

[0051] The first n-side electrode pad 32 is provided on and in contact with the n-side contact electrode 31. The first n-side electrode pad 32 is made of Ti / Ni / Au / Al, Ti / Pt / Au / Al, etc. The first n-side electrode pad 32 has a thickness of 300 to 600 nm.

[0052] The second n-side electrode pad 33 is provided on the protective layer 50. A portion of the second n-side electrode pad 33 is provided on and in contact with the first n-side electrode pad 32 through a hole in the protective layer 50. Therefore, the second n-side electrode pad 33 is electrically connected to the first n-side electrode pad 32.

[0053] The p-side electrode 40 is provided on and in contact with the p-type layer 23. The p-side electrode 40 includes a p-side contact electrode 41, a reflective layer 42, a cover layer 43, a first p-side electrode pad 44, and a second p-side electrode pad 45.

[0054] The p-side contact electrode 41 is provided on and in contact with the p-type layer 23. The p-side contact electrode 41 is provided on the entire area of ​​the element substrate 10 except for the periphery and the groove 23a. The p-side contact electrode 41 is set to transmit ultraviolet light of the emission wavelength. The p-side contact electrode 41 is formed of one type of oxide selected from the group consisting of ITO and IZO, or one type of metal selected from the group consisting of Ru, Rh, or an alloy mainly composed of these, NiAu, and Mg. These materials can make good contact with the p-type layer 23.

[0055] When the p-side contact electrode 41 is an oxide such as ITO or IZO, the thickness of the p-side contact electrode 41 is 40 nm or less, and preferably 20 nm or less. By making the thickness of the p-side contact electrode 41 as described above, the transmittance of ultraviolet light can be increased. Furthermore, the thickness of the p-side contact electrode 41 is 1 nm or more, and preferably 3 nm or more. By making the thickness of the p-side contact electrode 41 as described above, good contact with the p-type layer 23 can be achieved.

[0056] Furthermore, when the p-side contact electrode 41 is made of Ru, Rh, or an alloy mainly composed of these metals, NiAu, Mg, or the like, the thickness of the p-side contact electrode 41 is 10 nm or less, and preferably 4 nm or less. By making the thickness of the p-side contact electrode 41 as described above, the transmittance of ultraviolet light can be increased. Furthermore, the thickness of the p-side contact electrode 41 is 1 nm or more, and preferably 3 nm or more. By making the thickness of the p-side contact electrode 41 as described above, good contact with the p-type layer 23 can be obtained.

[0057] Moreover, it is preferable that the p-side contact electrode 41 is configured so that the transmittance of ultraviolet light of a predetermined emission wavelength is 30% or more, preferably 50% or more. For example, the p-side contact electrode 41 may be configured so that the transmittance of ultraviolet light of a wavelength of 280 nm is 30% or more, preferably 50% or more.

[0058] As described above, when the p-side contact electrode 41 is an oxide such as ITO or IZO, the transmittance of ultraviolet light with a wavelength of 280 nm can be made 30% or more by making the thickness of the p-side contact electrode 41 40 nm or less. Also, the transmittance of ultraviolet light with a wavelength of 280 nm can be made 50% or more by making the thickness of the p-side contact electrode 41 20 nm or less.

[0059] Furthermore, when the p-side contact electrode 41 is made of Ru, Rh, an alloy mainly composed of these, NiAu, Mg, or other metal, the transmittance of ultraviolet light with a wavelength of 280 nm can be made 30% or more by making the thickness of the p-side contact electrode 41 10 nm or less. Furthermore, the transmittance of ultraviolet light with a wavelength of 280 nm can be made 50% or more by making the thickness of the p-side contact electrode 41 4 nm or less.

[0060] The reflective layer 42 is provided on and in contact with the p-side contact electrode 41. The reflective layer 42 is made of a material having electrical conductivity, and reflects ultraviolet light of the emission wavelength. In other words, the reflective layer 42 reflects ultraviolet light transmitted through the p-side contact electrode 41. The reflective layer 42 is made of an alloy mainly composed of Al and containing Cu. The alloy mainly composed of Al and containing Cu is at least one selected from the group consisting of AlCu, AlSiCu, and AlCuSn.

[0061] The thickness of the reflective layer 42 is not less than 50 nm and not more than 300 nm. In particular, the reflective layer 42 is formed to be thicker than the p-side contact electrode 41. In other words, the p-side contact electrode 41 is formed to be thinner than the reflective layer 42. This allows the ultraviolet light emitted from the active layer 22 to be efficiently transmitted by the p-side contact electrode 41 and reflected by the reflective layer 42. As a result, the light extraction efficiency can be improved.

[0062] The cover layer 43 is provided on and in contact with the reflective layer 42, and is configured to cover the reflective layer 42. In this embodiment, the cover layer 43 is provided in contact only with the upper surface of the reflective layer 42, and is provided in contact with the entire upper surface of the reflective layer 42. The cover layer 43 is made of at least one material selected from the group consisting of Ti, TiN, Ni, Pt, Au, and Cr. The cover layer 43 has the effect of increasing electromigration resistance.

[0063] The first p-side electrode pad 44 is provided on and in contact with the cover layer 43. The first p-side electrode pad 44 is formed of Ti / Ni / Au / Al, Ti / Pt / Au / Al, or the like. The first n-side electrode pad 32 has a thickness of 300 to 600 nm. The first p-side electrode pad 44 can be formed simultaneously with the first n-side electrode pad 32.

[0064] The second p-side electrode pad 45 is provided on the protective layer 50. A portion of the second p-side electrode pad 45 is provided on and in contact with the first p-side electrode pad 44 through a hole in the protective layer 50. Therefore, the second p-side electrode pad 45 is electrically connected to the first p-side electrode pad 44.

[0065] The protective layer 50 is provided so as to cover the upper surface side of the light-emitting element 5 except for the second n-side electrode pad 33 and the second p-side electrode pad 45. The protective layer 50 is formed of an insulating material, for example, SiO2, SiN, or the like.

[0066] The antireflection layer 60 is provided on the back surface (the lower surface in FIG. 2, the surface on the light extraction side) of the element substrate 10. However, the antireflection layer 60 may be omitted.

[0067] 3. Experiment (Experiment 1) In experiment 1, the reflectance of ultraviolet light having an emission wavelength of 200 nm to 400 nm was measured using specimen 1 in which a layer made of AlCu corresponding to reflective layer 42 was formed on the main surface of a sapphire substrate, and specimen 2 in which a layer made of Al corresponding to reflective layer 42 was formed on the main surface of a sapphire substrate as a comparative example. Note that in specimen 1, Cu was 0.5 wt %.

[0068] In Fig. 3, the reflectance of specimen 2 at an emission wavelength of 280 nm is taken as 100%. As shown in Fig. 3, the reflectance of specimen 1 is inferior to that of specimen 2 in the emission wavelength range of 200 nm to 400 nm, but is approximately the same. In particular, the reflectance of specimen 1 is closer to that of specimen 2 in the emission wavelength range of 260 nm to 400 nm. This shows that by using AlCu as the reflective layer 42, it is possible to obtain a reflectance approximately the same as that of Al.

[0069] (Experiment 2) In experiment 2, the transmittance of ultraviolet light with a wavelength of 280 nm was measured using specimen 3 in which ITO corresponding to p-side contact electrode 41 was formed on the main surface of a sapphire substrate. For specimen 3, five types of ITO thicknesses were used: 16 nm, 18 nm, 32 nm, 42 nm, and 105 nm.

[0070] The transmittance was 56%, 54%, 42%, 36%, and 12% for ITO thicknesses of 16 nm, 18 nm, 32 nm, 42 nm, and 105 nm, respectively.

[0071] As shown in Figure 4, the results of Experiment 2 show that an ITO transmittance of 35% or more can be achieved by setting the ITO thickness to 40 nm or less. Furthermore, an ITO transmittance of 50% or more can be achieved by setting the ITO thickness to 20 nm or less.

[0072] 4.Effects According to the light emitting device 1 of this embodiment, the reflective layer 42 constituting the p-side electrode 40 is made of an alloy mainly composed of Al and containing Cu, so that a high reflectance equivalent to that of Al can be obtained. Therefore, a high light extraction efficiency of ultraviolet light can be obtained. Furthermore, by forming the reflective layer 42 from the above material, it is possible to improve the electromigration resistance and suppress breakage failures, etc., compared to the case where Al is used, and as a result, it is possible to improve reliability.

[0073] Therefore, the light emitting device 1 has a structure that is excellent in resistance to electromigration while maintaining high light extraction efficiency by forming the reflective layer 42 with high reflectance.

[0074] (Embodiment 2) The light emitting device 1 of this embodiment will be described with reference to Fig. 5. In this embodiment, the same components as those of the light emitting device 1 of embodiment 1 are denoted by the same reference numerals. As shown in Fig. 5, the light emitting device 1 of this embodiment is different from the light emitting device 1 in the cover layer 143 of the p-side electrode 140 in the light emitting element 105 constituting the light emitting device 1, but the other components are the same.

[0075] The cover layer 43 in the first embodiment is provided in contact only with the upper surface of the reflective layer 42. The cover layer 143 constituting the p-side electrode 140 in the second embodiment is provided in contact with the side surface of the reflective layer 42 as well as the upper surface of the reflective layer 42. In other words, the cover layer 143 is configured to cover the upper surface and the side surface of the reflective layer 42. With this configuration, the electromigration resistance provided by the cover layer 143 can be further improved. [Explanation of symbols]

[0076] 1 Light emitting device 2. Mounting Board 2a Mounting surface 4 Submount 5, 105 Light emitting element 10 Element substrate 20 Semiconductor layer 21 n-type layer 22 Active layer 23 p-type layer 30 n-side electrode 40, 140 p side electrode 41 p-side contact electrode 42 Reflective layer 43, 143 Cover layer 44, 45 p-side electrode pad

Claims

1. In a light-emitting element that emits ultraviolet light with an emission wavelength of less than 300 nm, an n-type layer made of an n-type Group III nitride semiconductor; an active layer made of a Group III nitride semiconductor provided on the n-type layer; a p-type layer made of a p-type Group III nitride semiconductor provided on the active layer; a p-side electrode including a reflective layer formed on the p-type layer and made of an alloy mainly composed of Al and containing Cu; A light-emitting element comprising:

2. The p-side electrode further comprises:

2. The light-emitting device according to claim 1, further comprising a cover layer provided on and in contact with the reflective layer and made of at least one material selected from the group consisting of Ti, TiN, Ni, Pt, Au, and Cr.

3. The light-emitting device according to claim 2 , wherein the cover layer covers an upper surface and a side surface of the reflective layer.

4. a p-side contact electrode provided on and in contact with the p-type layer and transmitting ultraviolet light having an emission wavelength; 4. The light-emitting device according to claim 1, wherein the reflective layer is provided on the p-side contact electrode.

5. The light-emitting element according to claim 4 , wherein the p-side contact electrode is formed thinner than the reflective layer.

6. The light emitting device according to claim 4 , wherein the p-side contact electrode has a transmittance of 30% or more for ultraviolet light having an emission wavelength.

7. the p-side contact electrode is made of one oxide selected from the group consisting of ITO and IZO, The light-emitting device according to claim 4 , wherein the p-side contact electrode has a thickness of 40 nm or less.

8. the p-side contact electrode is made of one metal selected from the group consisting of Ru, Rh, or an alloy containing Ru or Rh as a main component, NiAu, and Mg; The light-emitting device according to claim 4 , wherein the p-side contact electrode has a thickness of 10 nm or less.

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