Light emitting device

Abstract

To provide an ultraviolet light emitting device having a structure excellent in resistance to electromigration while maintaining high light extraction efficiency by using bonding wires made of a material having high reflectivity.SOLUTION: A light emitting device 1 is configured to include a group III nitride, and includes a light emitting element 5 for emitting ultraviolet light, and a bonding wire 6 that is electrically connected to the light emitting element 5. The bonding wire 6 is configured to include a first layer that is configured to include at least one kind selected from the group consisting of an alloy mainly composed of Al and containing Cu, an alloy mainly composed of Mg and containing Cu, Mg and an alloy containing Mg, or includes Cu or an alloy containing Cu, and a second layer that includes one kind selected from the group consisting of Al, an alloy containing Al, Mg, and an alloy containing Mg.SELECTED DRAWING: Figure 1

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] In a light emitting device in which an ultraviolet light emitting element is mounted on a mounting substrate, electrical connection is sometimes made using a bonding wire. Patent Document 1 describes the use of Al as the bonding wire in an ultraviolet light emitting device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-49949 A Summary of the Invention [Problem to be solved by the invention]

[0005] Since ultraviolet light-emitting elements have a lower light extraction efficiency than visible light-emitting elements, there is a need to improve the light extraction efficiency for ultraviolet light more than for visible light. Depending on the material of the bonding wire used in the light-emitting device, the ultraviolet light emitted by the light-emitting element may be absorbed, which may cause a decrease in the light extraction efficiency. Therefore, in terms of light extraction efficiency, it is preferable to use Al, which has a high reflectivity, as the bonding wire in the light-emitting device.

[0006] However, since Al is prone to electromigration, when Al is used as a bonding wire, there is a possibility that the bonding wire may suffer a break due to electromigration, which poses problems in terms of life span and reliability.

[0007] The present invention has been made in consideration of the above background, and aims to provide an ultraviolet light-emitting device having a structure with excellent resistance to electromigration while maintaining high light extraction efficiency by using bonding wires made of a material with high reflectivity. [Means for solving the problem]

[0008] One aspect of the present invention is a light-emitting element including a group III nitride and emitting ultraviolet light; a bonding wire electrically connected to the light emitting element; The bonding wire is The alloy is composed of at least one selected from the group consisting of an alloy mainly composed of Al and containing Cu, an alloy mainly composed of Mg and containing Cu, Mg, and an alloy containing Mg; Alternatively, the light emitting device includes a first layer made of Cu or an alloy containing Cu, and a second layer made of one material selected from the group consisting of Al, an alloy containing Al, Mg, and an alloy containing Mg. Effect of the Invention

[0009] According to one aspect of the present invention, the bonding wire constituting the light emitting device is composed of at least one selected from the group consisting of an alloy mainly composed of Al and containing Cu, an alloy mainly composed of Mg and containing Cu, and an alloy containing Mg, or is composed of a first layer composed of Cu or an alloy containing Cu and a second layer composed of one selected from the group consisting of Al, an alloy containing Al, Mg, and an alloy containing Mg, thereby obtaining a high reflectance. Therefore, a high light extraction efficiency of ultraviolet light can be obtained. Furthermore, by forming the bonding wire from the above material, it is possible to increase the electromigration resistance and suppress breakage failures, etc., compared to the case of using Al, and as a result, it is possible to improve the life and increase the reliability.

[0010] As described above, according to the above aspect, by using bonding wires made of a material with high reflectivity, it is possible to provide an ultraviolet light emitting device having a structure with excellent resistance to electromigration while maintaining high light extraction efficiency. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing a configuration of a light emitting device according to a first embodiment. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of a light-emitting element constituting the light-emitting device in the first embodiment. [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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] As described above, the light emitting device includes a light emitting element that emits ultraviolet light and is composed of a group III nitride, and a bonding wire that is electrically connected to the light emitting element. The bonding wire is composed of at least one selected from the group consisting of an alloy mainly composed of Al and containing Cu, an alloy mainly composed of Mg and containing Cu, Mg, and an alloy containing Mg, or is composed of a first layer composed of Cu or an alloy containing Cu, and a second layer composed of one selected from the group consisting of Al, an alloy containing Al, Mg, and an alloy containing Mg.

[0013] Here, the alloy containing Al is not limited to an alloy mainly composed of Al, but includes an alloy containing Al but not mainly composed of Al. The alloy containing Mg is not limited to an alloy mainly composed of Mg, but includes an alloy not mainly composed of Mg but containing Mg. The alloy containing Cu is not limited to an alloy mainly composed of Cu, but includes an alloy not mainly composed of Cu but containing Cu.

[0014] In particular, the wire electrically connected to the p-side electrode of the light-emitting element among the bonding wires may be composed of at least one selected from the group consisting of an alloy mainly composed of Al and containing Cu, an alloy mainly composed of Mg and containing Cu, and an alloy containing Mg, or may be composed of a first layer composed of Cu or an alloy containing Cu and a second layer composed of one selected from the group consisting of Al, an alloy containing Al, Mg, and an alloy containing Mg. Electromigration occurs significantly on the side of the p-side electrode. Therefore, by forming the wire connected to the p-side electrode side from the above material, it is possible to increase the electromigration resistance.

[0015] In the light emitting device, the light emitting element may include an electrode pad, and the bonding wire may be bonded to the electrode pad of the light emitting element. In this case, the bonding wire bonded to the electrode pad of the light emitting element can have high electromigration resistance.

[0016] In this configuration, the light emitting device further includes a mounting substrate having a mounting surface, the light emitting element is mounted on the mounting surface of the mounting substrate, and is a face-up type having the electrode pad on a surface of the mounting substrate opposite the mounting surface, and the bonding wire may be bonded at one end to the electrode pad of the light emitting element and at the other end to the mounting substrate.

[0017] (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.

[0018] The light emitting device 1 includes a mounting substrate 2, a sealing material 3, a submount 4, a light emitting element 5, and a bonding wire 6. The light emitting device 1 may not include the submount 4, and may include a driving circuit (not shown) and the like.

[0019] 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 substrate 2 has a circuit pattern formed thereon, and has substrate electrode pads 2b for bonding bonding wires 6. In this embodiment, the mounting substrate 2 has a recess 2c formed therein, and the mounting substrate 2a is provided on the bottom surface of the recess 2c. However, the mounting substrate 2 may be flat without the recess 2c, with one surface of the flat substrate forming the mounting surface 2a. The main body of the mounting substrate 2 is formed of ceramics such as AlN, Al2O3, SiC, and Si2N4.

[0020] The sealing material 3 forms an accommodation space 7 between the mounting substrate 2 and the sealing material 3, capable of accommodating the submount 4, the light emitting element 5, the bonding wires 6, 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.

[0021] The submount 4 is mounted on the mounting surface 2a of the mounting substrate 2. The main body of the submount 4 is made 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.

[0022] 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 200 nm to 400 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.

[0023] Moreover, the light emitting element 5 is a face-up type element having electrode pads 32, 42 on the surface opposite to the mounting surface 2a of the mounting substrate 2. Therefore, the electrode pads 32, 42 of the light emitting element 5 are located on the surface opposite to the mounting surface 2a of the mounting substrate 2, and are arranged to face the inner surface of the sealing material 3 at a distance. And, an element substrate 10 of the light emitting element 5, which will be described later, is located on the mounting surface 2a side of the mounting substrate 2. That is, the ultraviolet light emitted by the light emitting element 5 is emitted from the electrode pads 32, 42 side, passes through the sealing material 3, and is output to the outside.

[0024] One end of the bonding wire 6 is bonded to the electrode pads 32, 42 of the light emitting element 5, and the other end is bonded to the board electrode pad 2b of the mounting board 2. Therefore, the bonding wire 6 is directly electrically connected to the light emitting element 5.

[0025] The bonding wire 6 may be configured to be made of a single material or to be configured to be made of multiple layers, as described below.

[0026] The bonding wire 6 is formed of a single material and is composed of at least one selected from the group consisting of an alloy mainly made of Al and containing Cu, an alloy mainly made of Mg and containing Cu, Mg, and an alloy containing Mg. Here, the alloy containing Mg is not limited to an alloy mainly made of Mg, but includes an alloy not mainly made of Mg but containing Mg. However, as the alloy containing Mg, an alloy mainly made of Mg is preferable.

[0027] In the above, the alloy containing Cu and mainly containing Al may be at least one selected from the group consisting of AlCu, AlSiCu, and AlCuSn. The alloy containing Mg may be at least one selected from the group consisting of AlZnMg, AlMgSi, and AlMg. In other words, the alloy containing Mg may contain Al.

[0028] In addition, when the bonding wire 6 is configured to be formed of multiple layers, it has two or more layers formed of different materials. The bonding wire 6 is configured to be formed of multiple layers, and includes a first layer made of Cu or an alloy containing Cu, and a second layer made of one selected from the group consisting of Al, an alloy containing Al, Mg, and an alloy containing Mg. The first layer may be configured to form the central part of the bonding wire 6, or may be formed on the surface layer of the base material that forms the central part. It is preferable that the second layer forms a coating layer that coats the outer circumferential surface of the first layer. In this case, it is preferable that the cross-sectional area of ​​the transverse section (radial cross section) of the first layer is larger than the cross-sectional area of ​​the transverse section of the second layer.

[0029] The Cu-containing alloy constituting the first layer is not limited to an alloy mainly composed of Cu, but includes an alloy not mainly composed of Cu but containing Cu. However, the Cu-containing alloy is preferably an alloy mainly composed of Cu. The Cu-containing alloy is preferably at least one selected from the group consisting of AlCu, AlSiCu, and AlCuSn.

[0030] The alloy containing Al constituting the second layer is not limited to an alloy mainly composed of Al, but includes an alloy containing Al but not mainly composed of Al. However, the alloy containing Al is preferably an alloy mainly composed of Al. The alloy containing Al may be at least one selected from the group consisting of AlCu, AlSiCu, and AlCuSn. The alloy containing Mg constituting the second layer is not limited to an alloy mainly composed of Mg, but includes an alloy containing Mg but not mainly composed of Mg. However, the alloy containing Mg is preferably an alloy mainly composed of Mg. The alloy containing Mg may be at least one selected from the group consisting of AlZnMg, AlMgSi, and AlMg.

[0031] By forming the bonding wires 6 from the above materials, it is possible to improve resistance to electromigration.

[0032] In particular, among the bonding wires 6, the wire connected to the p-side electrode 40 (described later) of the light-emitting element 5 should be made of the above material. Electromigration occurs significantly on the side of the p-side electrode 40. Therefore, by forming the bonding wire 6 connected to the p-side electrode 40 from the above material, it is possible to improve resistance to electromigration. In this case, the bonding wire 6 connected to the n-side electrode 30 may be made of the same material as the bonding wire 6 connected to the p-side electrode 40, or may be made of a different material.

[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 face-up type light-emitting element 5 The configuration of the face-up 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 a reflective layer 60. The light-emitting element 5 is of a face-up type, that is, has a structure in which light is extracted from the surface opposite to the element substrate 10 (the upper surface in FIG. 2). The light-emitting element 5 is an ultraviolet light-emitting element having an emission wavelength of 200 nm to 400 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 -3 The 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 and an n-side electrode pad 32 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 mounting surface side. 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 n-type layer 21 side. The thickness of the n-side contact electrode 31 is 100 to 300 nm.

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

[0052] 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 and a p-side electrode pad .

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] The p-side electrode pad 42 is provided on and in contact with the p-side contact electrode 41. The p-side electrode pad 42 is made of Ti / Ni / Au / Al, Ti / Pt / Au / Al, or the like. The thickness of the p-side electrode pad 42 is 300 to 600 nm. The p-side electrode pad 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 p-side electrode pad 42. The p-side electrode pad 42 can be formed simultaneously with the n-side electrode pad 32.

[0060] The protective layer 50 is provided so as to cover the upper surface side of the light-emitting element 5 except for a part of the n-side electrode pad 32 and a part of the p-side electrode pad 42. The protective layer 50 is formed of an insulating material, such as SiO2, SiN, or the like.

[0061] The reflective layer 60 is provided on the back surface of the element substrate 10 (the lower surface in FIG. 2, the surface opposite to the light extraction side). However, the reflective layer 60 is not essential. The reflective layer 60 reflects the ultraviolet light emitted by the active layer 22 in the light extraction direction. The reflective layer 60 may have a single-layer structure or a multi-layer structure.

[0062] 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 the bonding wire 6 was formed on the main surface of a sapphire substrate, and specimen 2 in which a layer made of Al corresponding to the bonding wire 6 was formed on the main surface of a sapphire substrate as a comparative example. Note that in specimen 1, Cu was 0.5 wt%.

[0063] 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 bonding wire 6, it is possible to obtain a reflectance approximately the same as that of Al.

[0064] (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.

[0065] 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.

[0066] 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.

[0067] 4.Effects According to the light emitting device 1 of this embodiment, the bonding wire 6 is formed only from an alloy containing Cu and mainly made of Al, thereby obtaining a reflectance as high as that of Al. Therefore, a high light extraction efficiency of ultraviolet light can be obtained. Furthermore, by forming the bonding wire 6 from the above material, it is possible to improve electromigration resistance and suppress breakage failures, etc., compared to the case where Al is used, and as a result, it is possible to improve the life and reliability. In this case, the bonding wire 6 may be configured to include an alloy containing Cu and mainly made of Al, and may be configured to include a layer made of another material.

[0068] The same effect can be obtained when the following materials are used as the bonding wire 6 in addition to the alloy mainly containing Al and Cu. That is, the same effect can be obtained when the bonding wire 6 is made of at least one selected from the group consisting of an alloy mainly containing Mg and containing Cu, Mg, and an alloy containing Mg. In this case, the bonding wire 6 may be configured to include the above metal and a layer made of another material.

[0069] The same effect can be obtained when the bonding wire 6 includes a first layer made of Cu or an alloy containing Cu and a second layer made of one selected from the group consisting of Al, an alloy containing Al, Mg, and an alloy containing Mg. In this case, the bonding wire 6 may be made of only the first and second layers, or may include a layer made of another material in addition to the first and second layers.

[0070] Therefore, the light emitting device 1 has a structure that is excellent in resistance to electromigration while maintaining high light extraction efficiency by using the bonding wires 6 made of a material with high reflectivity. [Explanation of symbols]

[0071] 1 Light emitting device 2. Mounting Board 2a Mounting surface 4 Submount 5 Light emitting element 6 Bonding Wire 10 Element substrate 20 Semiconductor layer 21 n-type layer 22 Active layer 23 p-type layer 30 n side electrode 40 p side electrode 41 p-side contact electrode 42 p-side electrode pad

Claims

1. a light emitting device that contains a group III nitride and emits ultraviolet light; a bonding wire electrically connected to the light emitting element; The bonding wire is The alloy is composed of at least one selected from the group consisting of an alloy mainly composed of Al and containing Cu, an alloy mainly composed of Mg and containing Cu, Mg, and an alloy containing Mg; Alternatively, a light emitting device comprising a first layer made of Cu or an alloy containing Cu, and a second layer made of one material selected from the group consisting of Al, an alloy containing Al, Mg, and an alloy containing Mg.

2. Among the bonding wires, a wire electrically connected to a p-side electrode of the light emitting element is The alloy is composed of at least one selected from the group consisting of an alloy mainly composed of Al and containing Cu, an alloy mainly composed of Mg and containing Cu, Mg, and an alloy containing Mg; Alternatively, the light-emitting device according to claim 1, comprising a first layer made of Cu or an alloy containing Cu, and a second layer made of one type selected from the group consisting of Al, an alloy containing Al, Mg, and an alloy containing Mg.

3. The light emitting element includes an electrode pad, The light emitting device according to claim 1 , wherein the bonding wire is bonded to the electrode pad of the light emitting element.

4. Further, a mounting substrate having a mounting surface is provided, the light-emitting element is a face-up type that is mounted on the mounting surface of the mounting substrate and has the electrode pad on a surface of the mounting substrate opposite to the mounting surface, The light emitting device according to claim 3 , wherein one end of the bonding wire is bonded to the electrode pad of the light emitting element, and the other end is bonded to the mounting substrate.

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