LIGHT EMITTING ELEMENT AND MANUFACTURING METHOD THEREOF

A light emitting element includes a group III nitride semiconductor with an emission wavelength of 200 nm or more and 280 nm or less, the light emitting element includes: a semiconductor layer in which an n layer, a light emitting layer, and a p layer are provided in this order; and a p-electrode provided on and in contact with the p layer, and the p-electrode includes a contact layer that is provided in contact with the p layer, has a thickness of 0.5 nm or more and 6 nm or less, and contains Ru or Ni/Au, and a reflection layer that is provided in contact with the contact layer, has a thickness of 50 nm or more, and contains Al or an alloy mainly containing Al.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2023-022147 filed on Feb. 16, 2023.

TECHNICAL FIELD

The present invention relates to a light emitting element and a manufacturing method thereof.

BACKGROUND ART

In recent years, the use of ultraviolet LEDs made of a group III nitride semiconductor with an emission wavelength of UVC (wavelength of 200 nm to 280 nm) for sterilization and disinfection of water, air, and the like is attracting attention, and research and development toward higher efficiency of ultraviolet LEDs are actively conducted.

JP2022-30948A describes a structure in which a p-electrode in a light emitting element made of a group III nitride semiconductor that emits UVC light includes a Rh layer that is in contact with a p-type semiconductor layer and has a thickness of 10 nm or less, and an Al layer that is in contact with the Rh layer and has a thickness of 20 nm or more. It is described that contact resistance can be reduced and a reflectance can be improved by adopting such a structure. In addition, it is described that the Rh layer and the Al layer are mixed by annealing the p-electrode, and the reflectance is improved as compared with a single Rh layer.

SUMMARY OF INVENTION

In the conventional art, a material capable of making ohmic contact with p-AlGaN or p-GaN has a low reflectance for light in the ultraviolet region (particularly UVC). Al has a high reflectance with respect to light in the ultraviolet region, but cannot make ohmic contact with p-AlGaN or p-GaN. Therefore, there has been a demand for a p-electrode that has a high ultraviolet reflectance and is capable of ohmic contact.

In addition, in JP2022-30948A, there is a possibility that the p layer and Al come into contact with each other due to diffusion of Al, and the contact resistance may be deteriorated.

The present invention has been made in view of such a background, and an object thereof is to provide a light emitting element having a p-electrode that has a high ultraviolet reflectance and is capable of ohmic contact, and a manufacturing method of the same.

One aspect of the present invention provides

a light emitting element formed of a group III nitride semiconductor with an emission wavelength of 200 nm or more and 280 nm or less, the light emitting element including:

a semiconductor layer formed by an n layer, a light emitting layer, and a p layer being stacked in this order; and

a p-electrode provided on and in contact with the p layer,

in which the p-electrode includes

a contact layer that is provided in contact with the p layer, has a thickness of 0.5 nm or more and 6 nm or less, and is made of Ru or Ni/Au, and

a reflection layer that is provided in contact with the contact layer, has a thickness of 50 nm or more, and is made of Al or an alloy mainly containing Al.

Another aspect of the present invention provides

a manufacturing method of a light emitting element formed of a group III nitride semiconductor with an emission wavelength of 200 nm or more and 280 nm or less, the manufacturing method including:

a semiconductor layer forming process of forming a semiconductor layer by stacking an n layer, a light emitting layer, and a p layer in this order on a substrate surface;

a contact layer forming process of forming a contact layer of Rh, Ru, or Ni/Au with a thickness of 0.5 nm or more and 6 nm or less in contact with the p layer;

a heat treatment process of performing heat treatment to reduce contact resistance to the p layer; and

a p-electrode forming process of forming, in contact with the contact layer, a reflection layer having a thickness of 50 nm or more and being of Al or an alloy mainly containing Al to form a p-electrode in which the contact layer and the reflection layer are stacked.

In the light emitting element, an ohmic contact with the p layer can be enabled by the contact layer, and ultraviolet rays can also be reflected by the reflection layer.

As described above, according to the above aspect, it is possible to provide a light emitting element having a p-electrode that has a high ultraviolet reflectance and is capable of ohmic contact, and a manufacturing method of the same.

DETAILED DESCRIPTION OF THE INVENTION

A light emitting element is formed of a group III nitride semiconductor with an emission wavelength of 200 nm or more and 280 nm or less. The light emitting element includes: a semiconductor layer formed by an n layer, a light emitting layer, and a p layer being stacked in this order; and a p-electrode provided on and in contact with the p layer. The p-electrode includes a contact layer that is provided in contact with the player, has a thickness of 0.5 nm or more and 6 nm or less, and is made of Ru or Ni/Au, and a reflection layer that is provided in contact with the contact layer, has a thickness of 50 nm or more, and is made of Al or an alloy mainly containing Al.

In the light emitting element described above, the contact layer is made of Ru, a contact resistivity of the p-electrode is 2×10−3Ω·cm2or less, and a reflectance at the emission wavelength is 55% or more.

In the light emitting element described above, the contact layer is made of Ni/Au, a contact resistivity of the p-electrode is 2×10−3Ω·cm2or less, and a reflectance at the emission wavelength is 40% or more.

In the light emitting element described above, a region where a material for the contact layer and a material for the reflection layer are mixed may not be present at an interface between the contact layer and the reflection layer.

A manufacturing method of a light emitting device is a manufacturing method of a light emitting element formed of a group III nitride semiconductor with an emission wavelength of 200 nm or more and 280 nm or less. The manufacturing method of a light emitting element includes: a semiconductor layer forming process of forming a semiconductor layer by stacking an n layer, a light emitting layer, and a p layer in this order on a substrate surface; a contact layer forming process of forming a contact layer of Rh, Ru, or Ni/Au with a thickness of 0.5 nm or more and 6 nm or less in contact with the p layer; a heat treatment process of performing heat treatment to reduce contact resistance to the p layer; and a p-electrode forming process of forming, in contact with the contact layer, a reflection layer having a thickness of 50 nm or more and being of Al or an alloy mainly containing Al to form a p-electrode in which the contact layer and the reflection layer are stacked.

In the manufacturing method of a light emitting element described above, the contact layer is made of Rh, a contact resistivity of the p-electrode is 2×10−2Ω·cm2or less, and a reflectance at the emission wavelength is 70% or more.

The contact layer may be made of Ru, a contact resistivity of the p-electrode may be 2×10−3Ω·cm2or less, and a reflectance at the emission wavelength may be 55% or more.

The contact layer may be made of Ni/Au, a contact resistivity of the p-electrode may be 2×10−3Ω·cm2or less, and a reflectance at the emission wavelength may be 40% or more.

Embodiment

FIG.1is a diagram showing a configuration of a light emitting element according to the embodiment, and is a cross-sectional view perpendicular to a substrate.FIG.2is a diagram showing a plane pattern of an electrode of the light emitting element according to the embodiment. The light emitting element according to the embodiment is a flip-chip type ultraviolet light emitting element, and has an emission wavelength of UVC, for example, 200 nm to 280 nm.

1. CONFIGURATION OF LIGHT EMITTING ELEMENT

As shown inFIG.1, the light emitting element according to the embodiment includes a substrate10, an n layer11, a light emitting layer12, an electron block layer13, a p layer14, a p-electrode15, n-electrodes16, pn electrodes17A and17B, a protective film18, a reflection film19, a p-pad electrode20, an n-pad electrode21, and an antireflection film22. Hereinafter, each configuration will be described.

The substrate10is a sapphire substrate having a c-plane as a main surface. Other than sapphire, any material may be used as long as the material has a high transmittance with respect to the emission wavelength and can grow a group III nitride semiconductor. A thickness of the substrate10is, for example, 0.4 mm to 1 mm. Within this range, light extraction efficiency can be improved. On the other hand, since the substrate10is thick, heat tends to accumulate inside the light emitting element, which reduces heat dissipation performance and shortens the life of the element. In the embodiment, the heat dissipation performance is improved by forming an electrode pattern as described later.

An antireflection film22is provided on a back surface (a surface opposite to the n layer11, a light extraction side) of the substrate10. By providing the antireflection film22, it is possible to prevent ultraviolet rays from being reflected on the back surface of the substrate10and returning to an element side, thereby improving light extraction.

The antireflection film22has a single layer structure or a structure in which materials having different refractive indexes are alternately stacked, and a thickness of each layer is set so that reflections weaken each other due to light interference. The material for the antireflection film22is an insulator having transparency with respect to the UVC. For example, SiO2, HfO2, MgF2, or the like is used.

The n layer11is located on the substrate10via a buffer layer (not shown) interposed therebetween. The n layer11is made of n-AlGaN. The n-type impurity is Si, and the Si concentration is 5×1018/cm3to 5×1019/cm3. The n layer11may include a plurality of layers.

The light emitting layer12is located on the n layer11. The light emitting layer12has an MQW structure in which well layers and barrier layers are alternately and repeatedly stacked. The number of repetitions is, for example, 2 to 5. The well layer is made of AlGaN, and an Al composition thereof is set according to a desired emission wavelength. The barrier layer is made of AlGaN having an Al composition higher than that of the well layer. AlGaInN having a band gap energy larger than that of the well layer may also be used. The light emitting layer12may have an SQW structure.

The electron block layer13is located on the light emitting layer12. The electron block layer13is made of p-AlGaN having an Al composition ratio higher than that of the barrier layer of the light emitting layer12. The electron block layer13prevents electrons injected from the n-electrode16from passing beyond the light emitting layer12and diffusing toward the p layer14.

The p layer14is located on the electron block layer13. The player14is made of p-AlGaN. In the light emitting element according to the embodiment, all semiconductor layers from the n layer11to the p layer14are made of AlGaN, which prevents absorption of ultraviolet rays by the semiconductor layers. The Al composition of the p layer14is, for example, 5% to 80%. The p-type impurity is Mg. The Mg concentration is 1×1019/cm3or more. The p layer14may include a plurality of layers having different Al compositions and Mg concentrations. In this case, a layer in contact with the p-electrode15is made of p-AlGaN having an Al composition of 5% to 80%. The p layer14is not limited to AlGaN, and may be a group III nitride semiconductor containing Al, and may be AlGaInN.

A hole23having a depth reaching the n layer11is formed in a region of a surface of the p layer14. The hole23is dot-shaped, and a plurality of the holes23are arranged in a lattice pattern (seeFIG.2). The hole23is not provided in a region (one corner portion in a rectangular pattern of the element) corresponding to a lower portion of the p-pad electrode20. The n layer11is exposed on a bottom surface of the hole23. The holes23for exposing the n layer11are formed in a dot-shaped arrangement pattern, so that reduction in a light emitting area (the area of the p layer14) due to the holes23is reduced as much as possible while the in-plane light emission is ensured, and the light output is improved.

A plane pattern of each hole23is, for example, a circle. Alternatively, a polygon such as a regular hexagonal shape may be used. In the case of a regular hexagonal shape, a side surface of the hole23is preferably an m-plane. The arrangement pattern of the holes23is, for example, a square lattice, a regular triangular lattice, or a honeycomb pattern.

The p-electrode15(contact layer) is provided on the p layer14. The p-electrode15is provided on the surface of the p layer14except for the vicinity of edges of the p layer14(seeFIG.2), thereby ensuring a wide light emitting area. The p-electrode15is a reflective electrode that increases the light extraction efficiency by reflecting ultraviolet rays emitted from the light emitting layer12toward the substrate10.

A material for the p-electrode15is a material having a low contact with respect to the p layer14and having high UVC reflectance, and is Rh, Ru, or Ni/Au. A thickness of the p-electrode15is 0.5 nm to 6 nm. For Ni/Au, a thickness of a Ni layer may be one atomic layer or more. By setting such a thickness, it is possible to reduce the contact resistance with the p-electrode15, and ultraviolet rays can be transmitted and reflected by the Al layer of the pn electrode17A.

In order to further increase the ultraviolet reflectance while reducing the contact resistance, the thickness of the p-electrode15is preferably 1 nm to 4 nm.

A ratio of the area of the p-electrode15to an area of an element upper surface (a total area of the holes23and the p layer14) is 70% or more. The plane pattern of the holes23and the p-electrode15is set to satisfy the above. For example, a diameter, the number of arrays, and an arrangement interval of the holes23are adjusted. By increasing the area of the p-electrode15, it is possible to increase the reflection of the ultraviolet rays by the p-electrode15and improve the light extraction efficiency. The ratio is more preferably 75% or more.

The n-electrode16is provided on the n layer11exposed on the bottom surface of each hole23. Therefore, the n-electrodes16also have a dot-shaped arrangement pattern (seeFIG.2). A material for the n-electrode16is a heat-treated V/Al/Ti structure. Other materials such as Ti/Al/Ti can also be used. Specifically, the heat-treated V/Al/Ti structure has a structure in which a layer made of AlNx, a layer made of a metal mainly containing Al and containing V and Ti, and a layer made of Ti are stacked in this order.

The layer made of AlNxhas a thickness of 1 nm to 3 nm. x is, for example, 0.4 to 0.7. Further, x may decrease as a distance from the n layer11increases in a thickness direction. In this case, an average of x in the thickness direction is 0.4 to 0.7. Ga may be diffused from the n layer11side, and in this case, AlyGa1-yNx(0.4≤x≤0.7) having an Al composition ratio higher than that of the n layer11is used. When the Al composition ratio of the n layer11is a, a<y≤1. y is, for example, 0.7 or more. In this case, x may also decrease as the distance from the n layer11increases in the thickness direction, and y may increase as the distance from the n layer11increases in the thickness direction.

The layer made of a metal mainly containing Al and containing V and Ti has a thickness of 50 nm to 500 nm. The ratio of Al, V, and Ti is, for example, 50 mol % to 85 mol % for Al, 5 mol % to 20 mol % for V, and 10 mol % to 30 mol % for Ti.

In the n-electrode16having the above structure, the contact resistance with respect to the n layer11is reduced. For example, the contact resistivity of the n-electrode16with respect to the n layer11is 4×10−4Ω·cm2or less. The reason for this is considered to be, firstly, that the layer made of AlNxfunctions as a good contact layer for the n layer11. Secondly, it is considered that nitrogen vacancies are generated on a surface of the n layer11, and the contact resistance is reduced because it becomes n-type.

The layer made of Ti is provided as a cover to prevent Al in the n-electrode16from evaporating during alloying. TiN, Ni, Pt, Au, or the like may be used, other than Ti.

The pn electrodes17A and17B are provided on the p-electrode15and the n-electrode16, respectively. The plane pattern of the pn electrode17A is the same as the plane pattern of the p-electrode15. The plane pattern of the pn electrode17B is the same as the plane pattern of the n-electrode16, and is a pattern in which a plurality of dots are arranged.

A material for the pn electrodes17A and17B is Al/Ti/Ni/Au/Al. An Al layer, which is the first layer of the pn electrodes17A and17B, is in contact with the p-electrode15and the n-electrode16, respectively. The Al layer is a reflection layer that reflects ultraviolet rays. The pn electrode17A is formed after the p-electrode15is heat-treated, so that no atomic diffusion occurs between the p-electrode15and the Al layer, and an interface between the p-electrode15and the Al layer does not include a layer in which the material for the p-electrode and Al are mixed. Therefore, the ultraviolet rays can be reflected by the Al layer without impairing the effect of reducing the contact resistance by the p-electrode15. That is, it is possible to both reduce a forward voltage Vf and improve the light extraction efficiency.

For example, in the case of Rh/Al, the contact resistivity can be 2×10−2Ω·cm2or less and the ultraviolet reflectance in the UVC can be 70% or more. Further, for example, in the case of Ru/Al, the contact resistivity can be 3×10−3Ω·cm2or less and the ultraviolet reflectance in the UVC can be 55% or more. Further, for example, in the case of Ni/Au/Al, the contact resistivity can be 2×10−3Ω·cm2or less and the ultraviolet reflectance in the UVC can be 40% or more.

A thickness of the Al layer in the pn electrodes17A and17B is 10 nm to 500 nm. Within this range, the ultraviolet reflectance can be sufficiently increased. The ultraviolet reflectance of the Al layer increases as the thickness of the Al layer increases to about 50 nm, and becomes saturated at 50 nm or more. Therefore, considering the variation in the thickness of the Al layer, the thickness is preferably 80 nm or more. Further, in consideration of reflectance saturation, material cost, film formation time and the like, the thickness is preferably 200 nm or less.

In the embodiment, Al/Ti/Ni/Au/Al is used for the pn electrodes17A and17B, but other materials may be used as long as the first layer in contact with the p-electrode15is made of Al. Instead of Al, an alloy mainly containing Al may be used.

The protective film18is provided to cover the entire element upper surface. That is, the protective film18is provided continuously on side surfaces and surfaces of the p-electrode15, the n-electrode16, and the pn electrodes17A and17B, the surface and a side surface of the semiconductor layer (the n layer11, the light emitting layer12, the electron block layer13, and the p layer14), a side surface of an element isolation groove26, and the inside of the holes23. A material for the protective film18is SiO2or the like.

The protective film18includes two layers, a first protective film18A and a second protective film18B, and the reflection film19made of Al is provided between the first protective film18A and the second protective film18B. The reflection film19is entirely provided except for regions where holes24and25, which will be described later, are present. Light is reflected toward the substrate10by the reflection film19to improve the light extraction efficiency. In addition, by embedding the reflection film19in the protective film18, the heat dissipation performance of the protective film18is improved, and migration of the reflection film19is prevented.

A material for the reflection film19is not limited to Al, and may be any material that has a high reflectance in the emission wavelength. An alloy containing mainly Al may be used. The reflection film19may be provided not between the first protective film18A and the second protective film18B but in the first protective film18A or in the second protective film18B. When a plurality of reflection films19are provided, the plane pattern may be changed. The first protective film18A and the second protective film18B may be made of the same material or different materials.

The p-pad electrode20and the n-pad electrode21are spaced apart from each other on the protective film18. The p-pad electrode20is connected to the pn electrode17A through a hole24formed in the protective film18. The n-pad electrode21is connected to each pn electrode17B via holes25formed in the protective film18. The material for the p-pad electrode20and the n-pad electrode21is, for example, Ti/Pt/Au/AuSn.

For the plane pattern of the p-pad electrode20and the n-pad electrode21, as shown inFIG.2, a rectangular pattern slightly inside the rectangular pattern of the element is divided into two by a linear region with a width W along a straight line L forming an angle of 45° with respect to the sides of the rectangle at a corner of the rectangle, one part forming a right isosceles triangle pattern is the p-pad electrode20, and the other part (a pentagon with the corner of the rectangle cut off) is the n-pad electrode21. No n-electrode16is located under the p-pad electrode20, and all the n-electrodes16are located under the n-pad electrode21and connected to the n-pad electrode21.

The angle of the linear region is not limited to 45°, but is preferably close to 45°, for example, 30° to 60°, and more preferably 40° to 50° in order to reduce the area of the linear region and increase a sum of the areas of the p-pad electrode20and the n-pad electrode21as much as possible.

The position and width W of the linear region is preferably set such that the sum of the areas of the p-pad electrode20and the n-pad electrode21is 90% or more with respect to a light emitting area (the area of the p-electrode15). Of course, the width W is set to such a width that no short circuit occurs between the p-pad electrode20and the n-pad electrode21. For example, the width W is 100 μm or more. Further, the p-pad electrode20has a size that allows good bonding to the sub-mount. This is to increase the heat dissipation performance by widening a heat dissipation area (an area of the region of the p-electrode15in contact with the sub-mount in plan view).

By setting the plane pattern of the p-pad electrode20and the n-pad electrode21as described above, the sum of the area of the p-pad electrode20and the area of the n-pad electrode21can be increased, and the heat dissipation area can be increased, so that the heat dissipation performance of the light emitting element can be increased. In particular, in the UVC light emitting element, although it is necessary to increase the thickness of the substrate10to improve light extraction efficiency, the heat dissipation performance is deteriorated. However, since the heat dissipation performance can be improved as described above, sufficient heat dissipation performance can be ensured even when the substrate is made thick.

As described above, in the light emitting element according to the embodiment, Rh, Ru, or Ni/Au with a thickness of 0.5 nm to 6 nm is used as the p-electrode15, and the Al layer is used as the first layer of the pn electrode17A, so that the ultraviolet reflectance can be improved while enables the ohmic contact with the p layer14. As a result, the light emitting element in the embodiment can both reduce the forward voltage Vf and improve the light extraction efficiency.

2. MANUFACTURING PROCESS OF LIGHT EMITTING ELEMENT

A manufacturing process of the light emitting element according to the embodiment will be described with reference to the drawings.

First, the substrate10made of sapphire is prepared. Then, the n layer11, the light emitting layer12, the electron block layer13, and the p layer14are sequentially formed on the substrate10by the MOCVD method (seeFIG.3).

Next, predetermined regions of the p layer14is dry etched to form a plurality of holes23having a depth reaching the n layer11(seeFIG.4).

Next, the p-electrode15is formed on the p layer14by sputtering or vapor deposition (seeFIG.5). Next, a V layer, an Al layer, and a Ti layer are sequentially stacked on the n layer11exposed on the bottom surface of the hole23by sputtering or vapor deposition to form the n-electrode16(seeFIG.6). Although the n-electrode16may be formed before the p-electrode15, in the embodiment, the p-electrode15is formed first because it is desired to form the p-electrode15with the surface of the p layer14as clean as possible.

Next, heat treatment is performed at a temperature of 500° C. to 650° C. for 1 to 10 minutes. The atmosphere is, for example, an inert gas atmosphere such as nitrogen. The heat treatment is preferably carried out under reduced pressure, for example, 1×102Pa to 1×104Pa. The heat treatment temperature is preferably 500° ° C. to 600° C. When Ni/Au is used as the p-electrode15, heat treatment is carried out in an atmosphere containing oxygen.

This heat treatment also serves both to activate Mg in the p layer14and to reduce the contact resistance of the p-electrode15and n-electrode16.

In the embodiment, by using V/Al/Ti as the n-electrode16, the heat treatment temperature is lowered, and the Mg activation treatment of the p layer14and the reduction of the contact resistance of the p-electrode15and the n-electrode16are shared and performed at the same time, thereby reducing the number of heat treatments. As a result of lowering the heat treatment temperature and reducing the number of heat treatments, deterioration of electrical characteristics of the light emitting element can be prevented.

In this regard, the n-electrode16changes to the following structure by the heat treatment. Of V/Al/Ti that is the n-electrode16, V diffuses into Al and does not diffuse into the n layer11or Ti. As a result of this diffusion, the V layer disappears. In addition, Al in V/Al/Ti reacts with N in the n layer11, and AlNxis formed at an interface between the n layer11and the Al layer. V is considered to act as a catalyst that promotes the reaction between Al and N. As a result of this heat treatment, the structure of the n-electrode16changes to a three-layer structure including a layer made of AlNx, a layer made of metal mainly containing Al and containing V and Ti, and a layer made of Ti.

By changing the n-electrode16to such a structure, the contact resistance of the n-electrode16with respect to the n layer11is reduced. The reason is as described above. That is, firstly, it is considered that the layer made of AlNxfunctions as a good contact layer with respect to the n layer11, and secondly, it is considered that the conversion of the n layer11into an n-type is further promoted due to the generation of nitrogen vacancies in the n layer11from the formation of AlNx.

Next, pn electrodes17A and17B are formed on the p-electrode15and the n-electrode16respectively by sputtering or vapor deposition (seeFIG.7). The pn electrodes17A and17B are made of Al/Ni/Au/Al, and the Al layer, which is the first layer, is in contact with the p-electrode15.

In this regard, the pn electrode17A is formed after the heat treatment of the p-electrode15, and no heat treatment is performed after the formation of the pn electrode17A. Therefore, no diffusion of atoms occurs between the p-electrode15and the Al layer as the first layer of the pn electrode17A, and a region where atoms of the p-electrode15and Al are mixed is not formed at the interface between the p-electrode15and the Al layer. As a result, it is possible to improve the ultraviolet reflectance by the Al layer without impairing good contact of the p-electrode15with the p layer14.

Next, the element isolation groove26is formed. The element isolation groove26has a depth such that the substrate10is exposed. Next, the first protective film18A covering the entire element upper surface is formed (seeFIG.8). The first protective film18A is formed by CVD, sputtering, vapor deposition, ALD, or the like. Sputtering, CVD, and ALD are preferred from the viewpoint of film density.

Next, the reflection film19made of Al is formed on the first protective film18A in a region excluding the regions where the holes24and25are to be formed later (seeFIG.9). The reflection film19is formed by vapor deposition or sputtering, and patterned by wet etching.

Next, the second protective film18B is formed on the first protective film18A and the reflection film19. The second protective film18B is formed by CVD, sputtering, vapor deposition, ALD, or the like. Sputtering is preferred from the viewpoint of film density. Thus, the protective film18having a structure in which the first protective film18A and the second protective film18B are sequentially stacked and the reflection film19is formed therebetween is formed (seeFIG.10)

It is preferable that the protective film18is not formed on the bottom surface of the element isolation groove26and the protective film18is separated for each element. This is to prevent a force from being applied to the protective film18or a change in stress of the protective film18when the protective film18is divided for each element.

Next, a predetermined region of the protective film18is dry-etched to form holes24and25reaching the pn electrodes17A and17B. The p-pad electrode20and the n-pad electrode21are formed on the protective film18, the p-pad electrode20is connected to the pn electrode17A through the hole24, and the n-pad electrode21is connected to the pn electrode17B through the hole25. The patterns of the p-pad electrode20and the n-pad electrode21are as shown inFIG.2. The p-pad electrode20and the n-pad electrode21are formed by vapor deposition or sputtering, and patterned by lift-off.

Next, the back surface of the substrate10is polished to make the substrate10ahave a predetermined thickness, and then the antireflection film22is formed on the back surface of the substrate10. Then, the substrate10is divided into individual elements. Thus, the light emitting element according to the embodiment shown inFIG.1is manufactured.

3. EXPERIMENTAL RESULTS

Various experimental results according to the embodiment will be described.

Experimental Example 1

After forming Ni/Au on a sapphire substrate and performing heat treatment, an Al layer was formed on the Au layer, and the reflectance was measured by emitting ultraviolet rays with a wavelength of 275 nm from a side of the sapphire substrate. Further, for comparison, the reflectance was similarly measured in the case of only Ni/Au.

FIG.11is a graph showing the reflectance of samples a to e. The samples a to e differ in the thickness of Ni/Au and in the presence or absence of an Al layer. The thicknesses of the Ni/Au layer and the Al layer in each sample a to e are shown in Table 1 below. In Table 1, in the column of Ni/Au, in addition to an overall thickness, the thicknesses of the Ni layer and the Au layer are listed in parentheses.

As shown inFIG.11, in the Ni/Au/Al structure, it was found that the thinner the Ni/Au, the better the reflectance. In particular, it has been found that when the thickness of Ni/Au is 6 nm or less, the reflectance can be improved more than when using a structure of only Ni/Au, and the reflectance can be increased to 35% or more. Therefore, it has been found that by setting the thickness of Ni/Au to 6 nm or less in the Ni/Au/Al structure, it is possible to improve the ultraviolet reflectance while enabling ohmic contact with the p layer14.

Experimental Example 2

After forming an Rh layer on a sapphire substrate and performing heat treatment, an Al layer was formed, and the reflectance was measured in the same manner as in Experimental Example 1. Further, for comparison, the reflectance was similarly measured in the case where only Rh was used.

FIG.12is a graph showing the reflectance of each sample f and g. Sample f has a Rh single layer with a thickness of 150 nm, and sample g has a Rh/Al structure with a Rh layer of 4 nm and an Al layer of 150 nm.

As shown inFIG.12, it was found that the reflectance of Rh/Al was higher than that of the Rh single layer, and that the reflectance was increased to 70% or more. As a result, it has been found that the Rh/Al structure enables ohmic contact and improves ultraviolet reflectance.

Experimental Example 3

After forming a Ru layer on a sapphire substrate and performing heat treatment, an Al layer was formed, and the reflectance was measured in the same manner as in Experimental Example 1. Further, for comparison, the reflectance was similarly measured in the case where only Ru was used.

FIG.13is a graph showing the reflectance of each sample h and i. Sample h has a Ru single layer with a thickness of 150 nm, and sample i has a Ru/Al structure with a Ru layer of 4 nm and an Al layer of 150 nm.

As shown inFIG.13, it was found that the reflectance of Ru/Al was higher than that of the Ru single layer, and that the reflectance was increased to 55% or more. As a result, it has been found that the Ru/Al structure enables ohmic contact and improves ultraviolet reflectance.

REFERENCE SIGNS LIST