Light emitting element and manufacturing method thereof

Abstract

To provide a light emitting element with high light extraction efficiency.SOLUTION: A flip-chip type ultraviolet light-emitting element 1 includes a p-side electrode 17 provided on a p-type layer (p-type contact layer 15), including a layer made of Ru, Rh or an alloy mainly composed of these and in contact with the p-type layer, and set to a thickness that transmits ultraviolet light of the emission wavelength, an etching stop layer 18B provided in a dot shape in contact with a partial region on the p-side electrode 17, and including a conductive material that is resistant to etching, a DBR layer 19 provided in contact with the p-side electrode 17 and the etching stop layer 18B and reflecting ultraviolet light of the emission wavelength, a hole 25 provided in a region of the DBR layer 19 above the etching stop layer 18B, which penetrates the DBR layer 19 and exposes the etching stop layer 18B at the bottom, and a second p-side electrode (p-side pad electrode 22) provided on the DBR layer 19 and connected to the etching stop layer 18B via the hole 25.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a light-emitting device and a method for manufacturing the same. [Background technology]

[0002] The wavelength of ultraviolet light emitted by solid-state light-emitting devices using III-nitride semiconductors corresponds to a wavelength band of approximately 210 to 400 nm. On the other hand, UVC (wavelength 100 to 280 nm) is known to be effective for sterilization and disinfection, and is attracting attention for its use in sterilizing and disinfecting water and air. As a result, there is a growing demand for III-nitride semiconductor light-emitting devices that emit ultraviolet light with an emission wavelength corresponding to UVC, and research and development aimed at improving efficiency is being actively conducted.

[0003] Patent Document 1 describes that in a flip-chip type light-emitting element that emits deep ultraviolet light, a p-side electrode covering layer made of TiN is provided so as to cover the side and top surfaces of a p-side electrode made of Rh, and describes that this p-side electrode covering layer functions as an etching stop layer when a protective layer is dry-etched.

[0004] Patent Document 2 describes a structure in which a Rh layer, an Al layer, a Ti layer, and a TiN layer are laminated in this order from the p-type layer side as a p-side contact electrode in a flip-chip type light-emitting device that emits deep ultraviolet light. It describes that the TiN layer among them functions as an etching stop layer when the protective layer is dry-etched. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-72376 [Patent Document 2] Patent Publication No. 2022-30948 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Documents 1 and 2, the p-type contact electrode is made of Rh to reflect deep ultraviolet light toward the substrate, but the reflectance is not high enough. Therefore, there is a demand for a higher reflectance of deep ultraviolet light and an improvement in the light extraction efficiency.

[0007] The present invention has been made in view of the above background, and aims to provide a light-emitting device having high light extraction efficiency. [Means for solving the problem]

[0008] One aspect of the present invention is In flip-chip type ultraviolet light-emitting devices, 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 provided on the p-type layer, the p-side electrode including a layer made of Ru, Rh, or an alloy containing Ru or Rh as a main component and in contact with the p-type layer, the p-side electrode having a thickness set to transmit ultraviolet light having an emission wavelength; an etching stop layer provided in a dot shape in contact with a partial region of the p-side electrode, the etching stop layer including a conductive material that is resistant to etching; an insulating DBR layer that is provided on and in contact with the p-side electrode and the etching stop layer and that reflects ultraviolet light having an emission wavelength; a hole provided in a region of the DBR layer above the etching stop layer, the hole penetrating the DBR layer and exposing the etching stop layer at a bottom surface thereof; a second p-side electrode provided on the DBR layer and connected to the etching stop layer through the hole; The light emitting device has the following structure.

[0009] Another aspect of the present invention is A method for manufacturing a flip-chip type ultraviolet light-emitting device, comprising the steps of: an n-type layer forming step of forming an n-type layer made of an n-type Group III nitride semiconductor; an active layer forming step of forming an active layer made of a Group III nitride semiconductor on the n-type layer; a p-type layer forming step of forming a p-type layer made of a p-type Group III nitride semiconductor on the active layer; a p-side electrode formation step of forming a p-side electrode on the p-type layer, the p-side electrode including a layer made of Ru, Rh, or an alloy mainly containing ... an etching stop layer forming step of forming an etching stop layer in a dot shape, the etching stop layer including a conductive material that is resistant to etching, so as to be in contact with a partial region on the p-side electrode; a DBR layer formation step of forming an insulating DBR layer that reflects ultraviolet light having an emission wavelength so as to be in contact with the p-side electrode and the etching stop layer; a hole forming step of forming a hole in a region of the DBR layer above the etching stop layer by etching the DBR layer until the etching stop layer is exposed at a bottom surface thereof; a second p-side electrode formation step of forming a second p-side electrode on the DBR layer, the second p-side electrode being connected to the etching stop layer through the hole; The present invention relates to a method for producing a light emitting device having the above structure. Effect of the Invention

[0010] According to the above aspect, since the etch stop layer is provided in a dot shape on a partial region of the p-side electrode, the area of ​​the etch stop layer is sufficiently small relative to the p-side electrode. Therefore, the absorption of ultraviolet light by the etch stop layer is reduced. In addition, the area where the p-side electrode and the DBR layer contact each other is increased, and the area where the DBR layer reflects ultraviolet light can be increased. As a result, a light-emitting device with high light extraction efficiency can be realized. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing the configuration of a light-emitting device in embodiment 1, taken along a direction perpendicular to a main surface of a substrate. [Diagram 2] FIG. 1 is a diagram showing the configuration of a light emitting device in embodiment 1, and is a plan view seen from above the device. [Diagram 3] 2A to 2C are diagrams illustrating a manufacturing process of the light-emitting element according to the first embodiment. [Figure 4] 2A to 2C are diagrams illustrating a manufacturing process of the light-emitting element according to the first embodiment. [Diagram 5] 2A to 2C are diagrams illustrating a manufacturing process of the light-emitting element according to the first embodiment. [Figure 6] 2A to 2C are diagrams illustrating a manufacturing process of the light-emitting element according to the first embodiment. [Figure 7] 2A to 2C are diagrams illustrating a manufacturing process of the light-emitting element according to the first embodiment. [Figure 8] 2A to 2C are diagrams illustrating a manufacturing process of the light-emitting element according to the first embodiment. [Figure 9] 2A to 2C are diagrams illustrating a manufacturing process of the light-emitting element according to the first embodiment. [Figure 10] Graph showing the wavelength dependence of reflectance of DBR and Al. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] a p-type layer made of a p-type Group III nitride semiconductor provided on the active layer; a p-type layer made of a p-type Group III nitride semiconductor provided on the active layer; a p-side electrode provided on the p-type layer, the p-type layer comprising Ru, Rh or an alloy mainly composed of Ru or Rh and in contact with the p-type layer, the p-side electrode having a thickness set to transmit ultraviolet light of an emission wavelength; an etching stop layer provided in a dot shape in contact with a partial region on the p-side electrode, the etching stop layer comprising a conductive material that is resistant to etching; an insulating DBR layer provided in contact with the p-side electrode and the etching stop layer and reflecting ultraviolet light of an emission wavelength;

[0013] The light-emitting device may further include a reflective layer that is provided on and in contact with the DBR layer and is made of Al, Mg, or an alloy containing them as a main component, thereby reducing the incidence angle dependency of the reflectance and further improving the reflectance.

[0014] In the light emitting device, the area of ​​the entire etching stop layer may be 1% to 60% of the area of ​​the p-side electrode, thereby further improving the light extraction efficiency.

[0015] In the light-emitting device, the etching stop layer may be a multi-layer film, and the layer in contact with the p-type layer may be a layer made of Al or an alloy mainly composed of Al. A part of the ultraviolet light transmitted through the p-side electrode is incident on the etching stop layer, but the ultraviolet light can be reflected by the etching stop layer. Therefore, the light extraction efficiency can be further improved.

[0016] In the light-emitting element, the etching stop layer may have a pattern in which a plurality of dots are arranged, or a pattern in which a plurality of arranged dots and an extension part are arranged, thereby improving the in-plane diffusivity of current while improving the light extraction efficiency.

[0017] In the light-emitting element, the diameter of the dots in the etching stop layer may be 1.2 to 1.5 times the diameter of the holes, so that the function of the etching stop layer is not impaired even if the holes are misaligned.

[0018] In the light-emitting element, the distance between adjacent dots may be at least 1 time and at most 6 times the diameter of the hole.

[0019] The etching resistant conductive material may be Ti, TiN, Ni, Al or Pt.

[0020] In the light-emitting device, the emission wavelength may be 210 to 280 nm. The DBR layer can have a high reflectance even for the emission wavelength in this range, and the light extraction efficiency can be improved.

[0021] The above-mentioned light-emitting device can be manufactured as follows: That is, a flip-chip type ultraviolet light-emitting device is manufactured by an n-type layer forming step of forming an n-type layer made of an n-type Group III nitride semiconductor, an active layer forming step of forming an active layer made of a Group III nitride semiconductor on the n-type layer, a p-type layer forming step of forming a p-type layer made of a p-type Group III nitride semiconductor on the active layer, a p-side electrode forming step of forming a p-side electrode on the p-type layer, the p-side electrode including a layer made of Ru, Rh or an alloy mainly composed of Ru or Rh and in contact with the p-type layer, the p-side electrode having a thickness that transmits ultraviolet light of an emission wavelength, and a layer made of Ru, Rh or an alloy mainly composed of Ru or Rh and in contact with a partial region of the p-side electrode, the p-side electrode being etched to a thickness that is in contact with the p-side electrode. the etching stop layer forming step of forming an etching stop layer in a dot pattern, the etching stop layer containing a conductive material that is resistant to ultraviolet light; the DBR layer forming step of forming an insulating DBR layer that reflects ultraviolet light of an emission wavelength so as to be in contact with the p-side electrode and the etching stop layer; the hole forming step of forming a hole in a region of the DBR layer above the etching stop layer by etching the DBR layer until the etching stop layer is exposed at the bottom, penetrating the DBR layer; and the second p-side electrode forming step of forming a second p-side electrode on the DBR layer, the second p-side electrode being connected to the etching stop layer via the hole.

[0022] (Embodiment 1) Fig. 1 is a diagram showing the configuration of a light-emitting element 1 in embodiment 1, and is a cross-sectional view in a direction perpendicular to the main surface of a substrate. Fig. 2 is a diagram showing a planar pattern of the light-emitting element 1 in embodiment 1. The cross section in Fig. 1 corresponds to the cross section taken along line AA in Fig. 2.

[0023] 1, the light-emitting element 1 in the first embodiment includes a substrate 10, an n-type layer 11, an active layer 12, an electron blocking layer 13, a compositionally graded layer 14, a p-type contact layer 15, an n-side electrode 16, a p-side electrode 17, an etching stop layer 18, a DBR (distributed Bragg reflector) layer 19, a protective layer 20, an n-side pad electrode 21, and a p-side pad electrode 22. Hereinafter, the stacked structure from the n-type layer 11 to the p-type contact layer 15 may be referred to as a semiconductor layer.

[0024] The light emitting element 1 in the first embodiment is a flip chip type that extracts light from the rear surface of the substrate 10 (the surface opposite to the n-type layer 11). The emitted light has a predetermined wavelength in the range of 210 to 280 nm, and is in the UVC band (100 to 280 nm).

[0025] 1. Light-emitting element configuration The configuration of each layer of the light-emitting device 1 in embodiment 1 will be described in detail.

[0026] The substrate 10 is a substrate made of sapphire with a c-plane as the principal surface. The plane orientation of the principal surface of the sapphire may be the a-plane. In addition, the substrate may have an off angle of 0.1 to 2 degrees in the m-axis direction. The back surface of the substrate 10 (the surface opposite to the n-type layer 11) serves as the main light extraction surface. An anti-reflection film may be provided on the back surface of the substrate 10 to improve the light extraction efficiency. In addition, the surface of the substrate 10 may be provided with irregularities to improve the light extraction efficiency. In addition, an AlN substrate or an AlN template substrate in which an AlN layer is formed on a sapphire substrate may be used as the substrate 10.

[0027] The thickness of the substrate 10 is, for example, 1000 μm or less, and preferably 400 μm or more and 700 μm or less, which can suppress light extraction from the side surface of the substrate 10 and improve the on-axis intensity.

[0028] The substrate 10 may be removed by a method such as LLO (laser lift-off), etc. An anti-reflection film may be provided on the back surface of the substrate 10 to improve light extraction efficiency.

[0029] The n-type layer 11 is located on the substrate 10. The n-type layer 11 is made of n-AlGaN. The Al composition (the molar ratio of Al in the whole group III metals) is, for example, 60 to 90%. The n-type impurity is Si, and the Si concentration is, for example, 1×10 18 ~5×10 19 cm -3 The thickness of the n-type layer 11 is, for example, 0.5 to 5 μm. The C concentration of the n-type layer 11 is 1×10 15 ~1×10 19 cm -3 The n-type layer 11 may be composed of a plurality of layers. For example, it may be a superlattice layer in which AlGaN layers having different Al compositions are alternately stacked. Also, an underlayer made of AlN may be provided between the substrate 10 and the n-type layer 11. Also, an element other than Si may be used as the n-type impurity.

[0030] The active layer 12 is located on the n-type layer 11. The active layer 12 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 11 side. The active layer 12 may have an MQW structure. In that case, the number of repetitions is, for example, 2 to 10.

[0031] 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 non-doped and has a thickness of, for example, 0.5 to 5 nm.

[0032] 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 or less, and may be non-doped. The thickness of the barrier layer is, for example, 3 to 30 nm. The barrier layer may be made of AlGaInN, which has a larger band gap energy than the well layer. Furthermore, the layer of the barrier layer in contact with the electron blocking layer 13 preferably has a thickness of 0.5 to 10 nm.

[0033] A hole blocking layer may be provided between the n-type layer 11 and the active layer 12. This can prevent holes injected from the p-side electrode 17 from diffusing beyond the active layer 12 toward the n-type layer 11. The hole blocking layer is made of AlGaN or AlN having a higher Al composition than the barrier layer of the active layer 12. 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.

[0034] The electron blocking layer 13 is located on the active layer 12. The electron blocking layer 13 has a two-layer structure in which a first electron blocking layer and a second electron blocking layer are laminated in this order from the active layer 12 side. The electron blocking layer 13 prevents electrons injected from the n-side electrode 16 from diffusing beyond the active layer 12 toward the composition gradient layer 14 side.

[0035] The electron blocking layer 13 does not necessarily have to have a two-layer structure, and may consist of only a first electron blocking layer.

[0036] The first electron blocking layer is made of AlGaN or AlN having a higher Al composition ratio than the barrier layer of the active layer 12, and the Al composition is, for example, 90 to 100%. The first electron blocking layer may be doped with a p-type impurity or may be undoped. The p-type impurity is, for example, Mg. When doped with Mg, the Mg concentration is, for example, 3×10 20 cm -3 The thickness of the first electron blocking layer is, for example, 1 to 10 nm.

[0037] The second electron blocking layer is made of AlGaN having a lower Al composition than the first electron blocking layer, and the Al composition is, for example, 80 to 99%. By providing the second electron blocking layer, the difference in Al composition with the composition gradient layer 14 is adjusted. If the first electron blocking layer is made of AlN alone, the resistance will be high, and if the first electron blocking layer is made thin, the electron blocking performance will decrease. Therefore, by providing the second electron blocking layer, both low resistance and electron blocking function are achieved. The second electron blocking layer may be doped with p-type impurities or may be undoped. In the case of Mg doping, the Mg concentration is, for example, 3×10 20 cm -3 The second electron blocking layer has a thickness of, for example, 1 to 10 nm.

[0038] The compositionally graded layer 14 is located on the electron blocking layer 13. The compositionally graded layer 14 has a two-layer structure in which a first compositionally graded layer and a second compositionally graded layer are laminated in this order from the electron blocking layer 13 side.

[0039] The compositionally graded layer 14 is a layer that has been made p-type by a method called polarization doping. That is, the compositionally graded layer 14 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 blocking layer 13. It was difficult to increase the hole concentration of AlGaN with a high Al composition by Mg doping, but polarization doping can improve the hole concentration and increase the efficiency of hole injection into the active layer 12. In addition, polarization doping does not require Mg doping, so crystallinity can be improved.

[0040] When the Al composition of the compositionally graded layer 14 is set as described above, polarization due to crystal distortion occurs continuously in the compositionally graded layer 14 in the thickness direction. Holes are generated in the compositionally graded layer 14 to cancel the fixed charges caused by this polarization. The generated holes are distributed in the compositionally graded layer 14. Therefore, the holes are widely distributed in the thickness direction from the electron block layer 13 side in the compositionally graded layer 14, and the layer as a whole becomes p-type. In this p-type region, the hole concentration is 1×10 16 ~1×1020 cm -3 The hole concentration decreases with increasing distance from the electron blocking layer 13. The reason why the number of holes decreases near the interface of the compositionally graded layer 14 with the p-type contact layer 15 is that the Fermi levels attempt to match due to the p-type heterojunction, causing the band to bend.

[0041] The maximum value of the Al composition of the first composition gradient layer (the Al composition at the interface with the electron blocking layer 13) is preferably 1 to 20% lower than the Al composition of the electron blocking layer 13. The hole concentration can be further increased by polarization due to strain. For example, the maximum value of the Al composition is 65 to 95%.

[0042] In addition, the minimum value of the Al composition of the first composition gradient layer (the Al composition at the interface with the second composition gradient layer) is preferably 3 to 30% lower than the maximum value of the Al composition of the first composition gradient layer. The hole concentration can be further increased by polarization due to strain. In addition, the Al composition is preferably one having a band energy that does not absorb the emission wavelength.

[0043] The decrease rate of the Al composition of the first composition gradient layer is preferably 0.1 to 0.3% / nm. By setting the decrease rate in this range, the hole concentration of the first composition gradient layer can be further increased. The decrease rate of the Al composition may be constant, that is, may change linearly, or may not be constant.

[0044] The first composition gradient layer is undoped. However, it may be doped with Mg. This is expected to further increase the hole concentration by the p-type impurity. In this case, the Mg concentration is, for example, 1×10 20 cm -3 The following applies.

[0045] The second compositional gradient layer is a layer having a higher Mg concentration than the first compositional gradient layer, and the other portions have the same Al composition as the first compositional gradient layer. That is, the Al composition changes in the thickness direction, and the Al composition decreases with increasing distance from the electron block layer 13. Doping the second compositional gradient layer with Mg enables good connection to the p-type contact layer 15.

[0046] The difference between the maximum value of the Al composition of the second composition gradient layer (the Al composition at the interface with the first composition gradient layer) and the minimum value of the Al composition of the first composition gradient layer is 0 to 5%, and is preferably the same as the minimum value of the Al composition of the first composition gradient layer. In other words, it is preferable that the Al composition is continuous from the first composition gradient layer to the second composition gradient layer.

[0047] Moreover, the minimum value of the Al composition of the second composition gradient layer (the Al composition at the interface with the p-type contact layer 15) is preferably 3 to 30% lower than the maximum value of the Al composition of the second composition gradient layer.

[0048] The decrease rate of the Al composition of the second composition gradient layer is in the same range as the decrease rate of the Al composition of the first composition gradient layer, and may be the same as the decrease rate of the Al composition of the first composition gradient layer.

[0049] The Mg concentration of the second composition gradient layer is arbitrary as long as it is higher than the Mg concentration of the first composition gradient layer. 20 cm -3 It is preferable that the number of the electrodes is less than or equal to 100 in order to suppress the series resistance.

[0050] In the first embodiment, the Al composition of the composition gradient layer 14 decreases continuously, but it may decrease stepwise. However, it is preferable that the region where the Al composition is constant is as small as possible.

[0051] The thickness ratio of the first composition gradient layer to the composition gradient layer 14 is preferably 0.4 to 0.7. This range ensures sufficient improvement in hole concentration by polarization doping while also providing good contact between the composition gradient layer 14 and the p-type contact layer 15. The ratio is more preferably 0.4 to 0.6.

[0052] The composition gradient layer 14 does not necessarily have to have a two-layer structure of the first composition gradient layer and the second composition gradient layer, but may have only the first composition gradient layer. Also, it may have a structure of three or more layers with different Al composition change rates, Mg concentrations, etc.

[0053] The ratio of the thickness of the composition gradient layer 14 to the total thickness of the electron block layer 13, the composition gradient layer 14, and the p-type contact layer 15 is preferably 50% or more and 90% or less. Within this range, the function as a p-type layer can be sufficiently enhanced.

[0054] Instead of the compositionally graded layer 14, a layer made of Mg-doped p-type AlGaN may be provided. In this case, the Mg concentration is, for example, 1×10 17 ~1×10 19 cm -3 The Al composition is, for example, 40 to 80%.

[0055] The p-type contact layer 15 is located on the compositionally graded layer 14. The p-type contact layer 15 is made of Mg-doped p-GaN. It may be p-AlGaN having a lower Al composition than the minimum Al composition of the compositionally graded layer 14, and the Al composition is, for example, 50% or less, preferably 30% or less.

[0056] When the p-type contact layer 15 is made of GaN, the thickness is preferably 1 nm or more and 50 nm or less. GaN absorbs the ultraviolet light emitted from the active layer 12, but can transmit the ultraviolet light by making it sufficiently thin. Therefore, a large decrease in the external quantum efficiency can be avoided. The thickness is preferably 1 nm or more and 10 nm or less. The Mg concentration of the p-type contact layer 15 is, for example, 1×10 20 ~1×10 22 cm -3 It is.

[0057] The p-type contact layer 15 may be composed of multiple layers with different Al compositions and Mg concentrations. When composed of multiple layers, the top layer in contact with the p-side electrode 17 is preferably p-GaN or AlGaN with a low Al composition. This is to reduce the contact resistance of the p-side electrode 17. 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 contact layer 15 is made of 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.

[0058] A hole 23 having a depth reaching the n-type layer 11 is provided in a partial area of ​​the surface of the p-type contact layer 15. This hole 23 is for exposing the n-type layer 11 so that an n-side electrode 16 can be provided therein.

[0059] 2, the holes 23 are dot-shaped and provided in plurality. The dots are arranged in a regular triangular lattice pattern. However, they are not provided near one side of the light-emitting element 1. This is to ensure an area for forming the p-side pad electrode 22, as described below. By arranging the holes 23 in a dot-shaped pattern in this way, the surface area of ​​the p-type contact layer 15 is left as large as possible to increase the light-emitting area, while also maintaining the current diffusion properties within the surface.

[0060] The planar pattern of the holes 23 is a circle. Alternatively, it may be a regular hexagon, a square, an equilateral triangle, etc. For example, it may be a regular hexagonal pattern with m-faces on the side.

[0061] In the first embodiment, the holes 23 are arranged in a regular triangular lattice pattern, but may be arranged in a square lattice pattern, a honeycomb pattern, or the like.

[0062] The diameter of the holes 23 and the center-to-center distance between adjacent holes 23 are preferably within the following ranges. This allows for an increase in the light-emitting area and improved in-plane current diffusion. The diameter of the holes 23 is preferably 30 to 60 μm. In addition, the center-to-center distance between adjacent holes 23 is preferably 100 to 250 μm.

[0063] The n-side electrode 16 is provided in contact with the n-type layer 11 exposed at the bottom of the hole 23. The material of the n-side electrode 16 is Ti / Al, V / Al, etc. Here, A / B means that A and B are laminated in order from the n-type layer 11 side. As shown in Fig. 2, the n-side electrode 16 is formed in a dot-like shape and has a planar pattern in which multiple dots are arranged, thereby preventing a reduction in the light-emitting area and diffusing the current in the plane.

[0064] The p-side electrode 17 is provided on the p-type contact layer 15 in contact therewith, covering the entire surface except for the end portion. The material of the p-side electrode 17 is Ru, Rh, or an alloy mainly composed of these. These materials can provide good contact with the p-type contact layer 15. The p-side electrode 17 may be composed of multiple layers. In that case, the layer in contact with the p-type contact layer 15 may be Ru, Rh, or an alloy mainly composed of these. For example, the p-side electrode 17 may have a structure in which a transparent electrode layer such as ITO or IZO is laminated on a Ru layer or an Rh layer.

[0065] The thickness of the p-side electrode 17 is set so as to transmit ultraviolet light of the emission wavelength. Since the p-side electrode 17 is made of Ru, Rh, or an alloy mainly composed of these, the reflectance of deep ultraviolet light is relatively high, but this is not sufficient for improving the light extraction efficiency of the light-emitting element 1. Therefore, by providing the DBR layer 19 and thinning the p-side electrode 17, the ultraviolet light from the active layer 12 can be transmitted through the p-side electrode 17, and the ultraviolet light can be efficiently reflected by the DBR layer 19.

[0066] The thickness of the p-side electrode 17 is preferably 1 to 50 nm. Within this range, the ultraviolet light transmitted through the p-side electrode 17 can be efficiently reflected by the DBR layer 19 while maintaining good contact with the p-type contact layer 15. The thickness is more preferably 1 to 30 nm, and further preferably 1 to 20 nm.

[0067] As described later, in the first embodiment, a DBR layer 19 is used on the p-side electrode 17 instead of the conventional Al. Since the DBR layer 19 has a higher UVC reflectance than Al, it can better reflect the ultraviolet light transmitted through the p-side electrode 17.

[0068] If an Al layer is formed instead of the DBR layer 19, thinning the p-side electrode 17 may expose the p-type contact layer 15 in some regions, and the Al layer may come into contact with the p-type contact layer 15, causing a deterioration in contact resistance. However, in the first embodiment, the DBR layer 19 is provided instead of the Al layer, and the DBR layer 19 is an insulator. Therefore, even if the p-side electrode 17 is thin and the DBR layer 19 comes into contact with the p-type contact layer 15, the contact resistance does not deteriorate and good contact can be maintained.

[0069] The etching stop layer 18 is provided in a predetermined region on the n-side electrode 16 and the p-side electrode 17. Hereinafter, the etching stop layer 18 on the n-side electrode 16 is referred to as an etching stop layer 18A, and the etching stop layer 18 on the p-side electrode 17 is referred to as an etching stop layer 18B. The etching stop layer 18 is a layer that functions as a stopper when holes 24 and 25 described below are formed in the DBR layer 19 and the protective layer 20.

[0070] The etching stop layer 18A is provided over the entire surface except for the vicinity of the end of the n-side electrode 16. Therefore, the pattern of the etching stop layer 18A is the same as that of the n-side electrode 16.

[0071] The etching stop layer 18B is dot-shaped. It may be a combination of dot-shaped and extended (wire-shaped) shapes. The etching stop layer 18B is provided according to the positions of holes 25, which will be described later. In addition, the holes 25 are set to be inside the etching stop layer 18B in a plan view.

[0072] As described above, the etching stop layer 18B is provided in a limited area on the p-side electrode 17. The reason is as follows. If the etching stop layer 18B is formed entirely on the p-side electrode 17, most of the ultraviolet light transmitted through the p-side electrode 17 enters the etching stop layer 18, and some of the ultraviolet light is absorbed by the etching stop layer 18B. Therefore, even if the DBR layer 19 is provided, the reflectance is not sufficiently improved. Therefore, the etching stop layer 18B is limited to the area where the hole 25 is provided, and the absorption of ultraviolet light by the etching stop layer 18B is suppressed.

[0073] The material of the etching stop layer 18 is a conductive material that is resistant to dry etching of the DBR layer 19 and the protective layer 20. For example, it is a conductive material that is resistant to dry etching using a fluorine-based gas. Specifically, it is Ti, TiN, Ni, Pt, Al, etc. Also, it may be a multilayer film containing these materials.

[0074] When the etching stop layer 18B is a multilayer film, the first layer in contact with the p-side electrode 17 is preferably an Al layer or a metal layer mainly composed of Al. The ultraviolet light that passes through the p-side electrode 17 and enters the etching stop layer 18B can be reflected, and the light extraction efficiency can be further improved. In this case, the thickness of the Al layer is preferably 10 to 500 nm, and more preferably 80 to 200 nm. When the etching stop layer 18B is a multilayer film, for example, Al / Ti / Ni / Ti / Al or Al / Ti / Pt / Ti / Al can be used.

[0075] The total area of ​​the etching stop layer 18B is preferably 60% or less of the area of ​​the p-side electrode 17. This is to make the area of ​​the etching stop layer 18B, which absorbs ultraviolet light of the emission wavelength, as small as possible and to increase the contact area between the p-side electrode 17 and the DBR layer 19 as large as possible to further improve the light extraction efficiency. It is more preferably 50% or less, and further preferably 25% or less. In addition, the total area of ​​the etching stop layer 18B is preferably 3% or more of the area of ​​the p-side electrode 17. This means that the area is greater than or equal to the area when the etching stop layer is disposed only directly under the hole 25 connecting the p-side electrode 17 and the p-side pad electrode 22.

[0076] The diameter of the dots of the etching stop layer 18B is set according to the diameter of the holes 25. The diameter of the dots of the etching stop layer 18B is preferably 1.2 times or more the diameter of the holes 25. If it is 1.2 times or more, even if the position of the holes 25 is shifted or the diameter of the holes 25 is erroneous, the holes 25 can be positioned inside the outer circumference of the etching stop layer 18B in a plan view, and the function of the etching stop layer 18B can be prevented from being impaired. In addition, the diameter of the dots of the etching stop layer 18B is preferably 1.5 times or less the diameter of the holes 25. If it is 1.5 times or less, the absorption of ultraviolet light by the etching stop layer 18B can be sufficiently reduced. In addition, the distance between the dots of the etching stop layer 18B is preferably 1 to 6 times the diameter of the holes 25.

[0077] The DBR layer 19 is provided so as to cover the side surfaces of the p-side electrode 17, the etching stop layer 18, the holes 23, and the semiconductor layers (the stacked structure from the n-type layer 11 to the p-type contact layer 15) exposed on the peripheral side surfaces of the element. Hereinafter, the DBR layer 19 is in contact with the p-side electrode 17 except for the region where the etching stop layer 18B is provided. The DBR layer 19 is a layer provided to reflect ultraviolet light that passes through the p-side electrode 17. The DBR layer 19 also reflects ultraviolet light directed toward the peripheral portion of the element and the holes 23.

[0078] If an Al layer were provided instead of the DBR layer 19, the Al layer would not be able to cover the side surfaces of the semiconductor layer (the side surfaces of the outer periphery of the element and the side surfaces of the holes 23) because the Al layer is a conductor. However, the DBR layer 19 is an insulator and can cover the side surfaces of the outer periphery of the element and the side and bottom surfaces of the holes 23. Therefore, the area that reflects ultraviolet light is wider than when an Al layer is used, and the light extraction efficiency can be improved.

[0079] The DBR layer 19 has a structure in which low refractive index layers and high refractive index layers with a higher refractive index than the low refractive index layers are alternately laminated, and the thickness of each layer is set so as to increase the reflectance of ultraviolet light of the emission wavelength. Each layer may be made of an insulating material that transmits ultraviolet light of the emission wavelength, and the high refractive index layers may be made of HfO2, ZrO2, etc., while the low refractive index layers may be made of SiO2, Al2O3, MgF2, etc. In particular, HfO2 has high durability against deep ultraviolet light and is suitable as a material for the DBR layer 19.

[0080] In the first embodiment, the area of ​​the etching stop layer 18 on the p-side electrode 17 is small, so that the contact area between the p-side electrode 17 and the DBR layer 19 is large. Therefore, most of the ultraviolet light emitted from the active layer 12 toward the p-side electrode 17 and transmitted through the p-side electrode 17 enters the DBR layer 19 and can be reflected by the DBR layer 19 toward the substrate 10. In other words, the reduction in light extraction efficiency caused by providing the etching stop layer 18 can be suppressed.

[0081] The material, thickness, and number of layers of DBR layer 19 are preferably set so that the reflectance of DBR layer 19 is 95% or more. The reflectance here is the reflectance when ultraviolet light of the emission wavelength is incident perpendicularly on the main surface of DBR layer 19. The reflectance is more preferably 97% or more, and even more preferably 99% or more.

[0082] Furthermore, it is preferable that the incidence angle dependency of the reflectance of DBR layer 19 is set so that the reflectance is 90% or more at any incidence angle in the range of -60 to 60 degrees. The incidence angle dependency of the reflectance of DBR layer 19 can be set by the refractive index, thickness, and number of layers of DBR layer 19.

[0083] The protective layer 20 is provided so as to cover the DBR layer 19. The material of the protective layer 20 is SiO2 or the like. A plurality of holes 24, 25 penetrating the protective layer 20 and the DBR layer 19 are provided in predetermined regions of the protective layer 20 and the DBR layer 19. The hole 24 is a hole for connecting the etching stop layer 18A and the n-side pad electrode 21. The hole 25 is a hole for connecting the etching stop layer 18B and the p-side pad electrode 22.

[0084] The holes 24 are provided in a region corresponding to the upper part of the etching stop layer 18A. Therefore, the arrangement pattern of the holes 24 is the same as that of the etching stop layer 18A. The holes 24 are provided so as to be inside the outer circumferential circle of the etching stop layer 18A in a plan view. For example, the diameter of the holes 24 is 0.5 to 0.9 times the diameter of the etching stop layer 18A. The planar pattern of the holes 24 is a circle, like the etching stop layer 18A. Alternatively, the shape may be a regular hexagon, a square, or an equilateral triangle.

[0085] The holes 25 are provided in a region corresponding to the upper part of the etching stop layer 18B. The holes 25 are dot-shaped and have a circular planar pattern. As shown in Fig. 2, a plurality of holes 25 are arranged along one side of the light-emitting element 1 near the side where the holes 23 are not provided. The holes 25 are provided inside the outer circumferential circle of the etching stop layer 18B in plan view.

[0086] The diameter of the holes 25 is preferably 60 μm or less. By reducing the diameter of the holes 25, the diameter of the etching stop layer 18B can also be reduced, and the light extraction efficiency can be improved. The diameter is more preferably 50 μm or less, and further preferably 40 μm or less. The diameter of the holes 25 is preferably 10 μm or more. This is to ensure good conduction between the p-side electrode 17 and the p-side pad electrode 22. The diameter is more preferably 20 μm or more.

[0087] The center-to-center distance between adjacent holes 25 is preferably 50 to 250 μm. Within this range, it is possible to sufficiently achieve both current diffusion properties and improved light extraction efficiency. Since each dot of the etching stop layer 18B is provided corresponding to a hole 25, it is also preferable that the center-to-center distance between adjacent dots for each dot of the etching stop layer 18B is in the same range as the center-to-center distance between adjacent holes 25.

[0088] The planar pattern of the holes 25 does not have to be a circle, but may be an equilateral triangle, a square, a regular hexagon, or the like.

[0089] The number of holes 25 and dots of the etching stop layer 18B may be one or more. However, in order to diffuse the current in the plane, it is preferable to provide a plurality of holes 25 and etching stop layer 18B as dots as in the first embodiment. When providing a plurality of holes, they may be arranged in a straight line as in the first embodiment, but may also be arranged two-dimensionally. For example, they may be arranged in a regular triangular lattice, a square lattice, a honeycomb, or the like. In addition, in order to improve the diffusion of the current in the plane, the dot shape and the extension shape may be combined. For example, a pattern in which wiring extending in the opposite direction is connected to the arranged dots may be used.

[0090] A reflective layer made of Al, Mg or an alloy mainly composed of these may be provided between the DBR layer 19 and the protective layer 20 in contact with the DBR layer 19. However, no reflective layer is provided in the areas where the holes 24 and 25 are formed. Since the reflectance of the DBR layer 19 depends on the incidence angle, ultraviolet light incident at a large angle to the DBR layer 19 may not be reflected sufficiently. For example, when the number of layers of the DBR layer 19 is reduced, the incidence angle dependency becomes significant. On the other hand, since the reflective layer is made of metal, it has little incidence angle dependency. Therefore, by providing a reflective layer in contact with the DBR layer 19, ultraviolet light with a large incidence angle can be reflected, and the angle dependency of the reflectance of the DBR layer 19 can be compensated for. The thickness of the reflective layer is, for example, 30 to 200 nm. Within this range, the reflectance can be sufficiently increased.

[0091] The n-side pad electrode 21 is provided on the protective layer 20 in a region corresponding to the upper part of each hole 24. The etching stop layer 18A and the n-side pad electrode 21 are connected via each hole 24. As a result, the n-side pad electrode 21 and the n-side electrode 16 are electrically connected to each other.

[0092] The p-side pad electrode 22 is provided on the protective layer 20 in a region corresponding to the upper part of each hole 25. The etching stop layer 18B and the p-side pad electrode 22 are connected via each hole 25. This electrically connects the p-side pad electrode 22 and the p-side electrode 17. In this way, by connecting the p-side pad electrode 22 and the p-side electrode 17 with dots through the holes 25, the contact area between the p-side electrode 17 and the DBR layer 19 can be made large, and the area for reflecting ultraviolet light can be made large.

[0093] As described above, in the light-emitting element 1 of the first embodiment, the etching stop layer 18B is provided in a dot pattern, and the area where the p-side electrode 17 and the DBR layer 19 contact each other is large. Therefore, the ultraviolet light transmitted through the p-side electrode 17 can be efficiently reflected by the DBR layer 19. As a result, the light extraction efficiency of the light-emitting element 1 can be improved.

[0094] 2. Light-emitting device manufacturing method Next, a method for manufacturing the light-emitting device 1 in the first embodiment will be described with reference to the drawings.

[0095] First, an n-type layer 11, an active layer 12, an electron blocking layer 13, a compositionally graded layer 14, and a p-type contact layer 15 are laminated in this order on a substrate 10 via a buffer layer by MOCVD (see FIG. 3).

[0096] Next, a predetermined region of the p-type contact layer 15 is dry-etched until it reaches the n-type layer 11, thereby forming a hole 23 (see FIG. 4).

[0097] Next, the p-side electrode 17 is formed on the p-type contact layer 15 by sputtering or vapor deposition (see FIG. 5).

[0098] Next, the n-side electrode 16 is formed by sputtering or vapor deposition on the n-type layer 11 exposed at the bottom of the hole 23. Then, a heat treatment is performed to reduce the contact resistance of the n-side electrode 16 and to activate the p-type impurity. Next, etching stop layers 18A and 18B are formed in predetermined regions on the n-side electrode 16 and the p-side electrode 17 (see FIG. 6).

[0099] Next, the DBR layer 19 is formed so as to cover the p-side electrode 17, the etching stop layers 18A and 18B, the hole 23, and the outer peripheral side surface of the element (see FIG. 7). The DBR layer 19 is formed by a method such as sputtering, vapor deposition, or ALD.

[0100] Next, the protective layer 20 is formed by CVD, sputtering, deposition or the like so as to cover the DBR layer 19 (see FIG. 8).

[0101] Next, holes 24, 25 penetrating the protective layer 20 and the DBR layer 19 are formed by dry etching. Since the etching stop layers 18A, 18B are formed, the formation of the holes 24, 25 stops when the etching stop layers 18A, 18B are exposed. Therefore, the holes 24, 25 can be formed with high precision.

[0102] Next, an n-side pad electrode 21 and a p-side pad electrode 22 are formed in predetermined regions on the protective layer 20. As a result, the etching stop layer 18 on the n-side electrode 16 and the n-side pad electrode 21 are connected through the hole 24, and the etching stop layer 18 on the p-side electrode 17 and the p-side pad electrode 22 are connected through the hole 25. In this manner, the light-emitting element 1 of the embodiment 1 shown in FIG.

[0103] 3. Various Experimental Examples Related to the First Embodiment A DBR was fabricated so as to have a high reflectance against deep ultraviolet light, and the wavelength dependency of the reflectance of the DBR was measured. The reflectance was also measured in the same manner when Al was formed in contact with the DBR. For comparison, the wavelength dependency of the reflectance of Al was also measured. Figure 10 is a graph showing the wavelength dependency of the reflectance of the DBR, DBR / Al, and Al. The DBR has a structure in which HfO2 and SiO2 are alternately laminated, and is paired with a simulated film thickness so that the reflectance is 97% or more at a wavelength of 270 to 280 nm. The thickness of the Al layer was set to 1000 nm. The reflectance was measured by irradiating light at an incident angle of 10° on the main surface of the DBR and Al.

[0104] As shown in Figure 10, in the UVC band with wavelengths of 280 nm or less, it was found that the reflectance of DBR and DBR / Al can be made higher than that of Al. It was also found that DBR / Al can improve the reflectance even more than DBR alone. At a wavelength of 280 nm, the reflectance of Al was 91.3%, while the reflectance of DBR was 98.1%, and the reflectance of DBR / Al was approximately 99.3%. From this result, it was found that the Ru / DBR or Rh / DBR structure can improve the reflectance more than the Ru / Al or Rh / Al structure.

[0105] 4. Various Modifications of the First Embodiment An intermediate electrode having a wiring pattern may be provided between the n-side pad electrode 21 and the etching stop layer 18A, and between the p-side pad electrode 22 and the etching stop layer 18B, via an insulating film, and this intermediate electrode may connect each etching stop layer 18A to the n-side pad electrode 21, and each etching stop layer 18B to the p-side pad electrode.

[0106] In the first embodiment, it was not possible to arrange the dots of the n-side electrode 16 over the entire surface in order to secure an area for forming the p-side pad electrode 22, but by providing the intermediate electrode, the arrangement of the dots of the n-side electrode 16 can be freely determined, so that the dots of the n-side electrode 16 can be arranged over the entire surface. As a result, the in-plane uniformity of light emission can be improved, and the light-emitting area can be enlarged. In addition, by providing the intermediate electrode, the planar patterns of the n-side pad electrode 21 and the p-side pad electrode 22 can be freely set. [Explanation of symbols]

[0107] 10: Substrate 11:n-type layer 12:Active layer 13: Electron block layer 14: Composition gradient layer 15: p-type contact layer 16:n side electrode 17:p side electrode 18, 18A, 18B: Etching stop layer 19:DBR layer 20:Protective layer 21: n-side pad electrode 22: p-side pad electrode 23~25: Hole

Claims

1. In flip-chip type ultraviolet light-emitting devices, 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 provided on the p-type layer, the p-side electrode including a layer made of Ru, Rh, or an alloy containing Ru or Rh as a main component and in contact with the p-type layer, the p-side electrode having a thickness set to transmit ultraviolet light having an emission wavelength; an etching stop layer provided in a dot shape in contact with a partial region of the p-side electrode, the etching stop layer including a conductive material that is resistant to etching; an insulating DBR layer provided on and in contact with the p-side electrode and the etching stop layer, the DBR layer reflecting ultraviolet light having an emission wavelength; a hole provided in a region of the DBR layer above the etching stop layer, the hole penetrating the DBR layer and exposing the etching stop layer at a bottom surface thereof; a second p-side electrode provided on the DBR layer and connected to the etching stop layer through the hole; A light-emitting element having the following structure.

2. 2. The light-emitting device according to claim 1, further comprising a reflective layer made of Al, Mg or an alloy containing Al or Mg as a main component, the reflective layer being provided on and in contact with the DBR layer.

3. The light-emitting element according to claim 1 , wherein the total area of ​​said etching stop layer is 1% to 60% of the area of ​​said p-side electrode.

4. 3. The light-emitting device according to claim 1, wherein the etching stop layer is a multi-layer film, and a layer in contact with the p-type layer is a layer made of Al or an alloy containing Al as a main component.

5. 3. The light-emitting element according to claim 1, wherein the etching stop layer has a pattern in which a plurality of dots are arranged, or a pattern having a plurality of arranged dots and an extension portion.

6. The light-emitting device according to claim 5 , wherein the diameter of the dot of the etching stop layer is 1.2 to 1.5 times the diameter of the hole.

7. The light-emitting element according to claim 5 , wherein the distance between adjacent dots is from 1 to 6 times the diameter of the hole.

8. 3. The light-emitting element according to claim 1, wherein the conductive material exhibiting resistance to etching is Ti, TiN, Ni, Al or Pt.

9. 3. The light-emitting device according to claim 1, wherein the emission wavelength is 210 to 280 nm.

10. A method for manufacturing a flip-chip type ultraviolet light-emitting device, comprising the steps of: an n-type layer forming step of forming an n-type layer made of an n-type Group III nitride semiconductor; an active layer forming step of forming an active layer made of a Group III nitride semiconductor on the n-type layer; a p-type layer forming step of forming a p-type layer made of a p-type Group III nitride semiconductor on the active layer; a p-side electrode formation step of forming a p-side electrode on the p-type layer, the p-side electrode including a layer made of Ru, Rh, or an alloy mainly containing ... an etching stop layer forming step of forming an etching stop layer in a dot shape, the etching stop layer including a conductive material that is resistant to etching, so as to be in contact with a partial region on the p-side electrode; a DBR layer forming step of forming an insulating DBR layer that reflects ultraviolet light having an emission wavelength so as to be in contact with the p-side electrode and the etching stop layer; a hole forming step of forming a hole in a region of the DBR layer above the etching stop layer by etching the DBR layer until the etching stop layer is exposed at a bottom surface thereof; a second p-side electrode forming step of forming a second p-side electrode on the DBR layer, the second p-side electrode being connected to the etching stop layer through the hole; A method for manufacturing a light-emitting device having the above structure.

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