JP6783984B2 - Light emitting element - Google Patents

Description

The present invention relates to a light emitting device having a reflective electrode.

The flip-chip type light emitting element is provided with a reflective film (reflecting electrode) that also serves as a p-electrode, which reflects light toward the substrate side to improve light extraction efficiency. As a material for the reflective electrode, Ag or an Ag alloy having high reflectance is widely used.

It is known that Ag is prone to migration (movement of metal ions by electrochemical action). Migration deteriorates various characteristics of the light emitting element such as current leakage.

In order to suppress the migration of Ag, the Ag is sealed with an insulating film or the like to prevent the Ag from coming into contact with water or the like.

Patent Document 1 describes that a reflective metal layer containing Ag is provided so as to cover an end portion of an ohmic electrode made of ITO, and a reflective metal layer containing Ag is embedded in a coated electrode layer made of ITO. There is. With this configuration, since the end of the reflective metal layer is in contact with the p layer, the adhesion is better than that of contact with the ohmic electrode, and the uplift of the end of the reflective metal layer is suppressed. As a result, the reflective metal layer can be reliably coated with the ohmic electrode and the coated electrode layer, and the occurrence of Ag migration is prevented. It is also described that by reducing the oxygen concentration of the coated electrode layer, the generation of silver hydroxide due to the influence of water and oxygen is suppressed, thereby suppressing the generation of migration.

JP 2015-65205

According to the study by the inventors, it was found that even if the reflective electrode is sealed with an insulating film, Ag migrates when used at a high temperature and a high current, and voids are generated in the reflective electrode. This void lowers the reflectance of the reflective electrode and reduces the amount of light of the light emitting element. It also causes a current leak.

Further, in order to improve the reflectance of the reflective electrode, it is necessary to make Ag as thick as possible. However, when the Ag is thick, migration is likely to occur, and even if the structure of Patent Document 1 is adopted, the effect of suppressing migration is not sufficient when the Ag is thick.

Therefore, an object of the present invention is to realize a reflective electrode in which migration is suppressed.

In the present invention, the p-layer, the transparent electrode provided on the p-layer, the DBR layer provided on the transparent electrode, and the transparent electrode provided through the holes provided on the DBR layer and provided in the DBR layer. a light-emitting element having a reflective electrode connected, reflective electrode, Ri Do from Ag or Ag alloy, a reflective film having a thickness of 10 to 100 nm, Ri Do a transparent conductive oxide, the thickness The structure is such that the number of layers of the reflective film is 2 or more by alternately and repeatedly laminating oxide films having a diameter of 1 to 10 nm , and the reflective film is 10 times or more the thickness of the oxide film. It is a light emitting element.

The transparent conductive oxide is a material having translucency and conductivity with respect to light having an emission wavelength of a light emitting element. Indium oxide-based materials, zinc oxide-based materials, tin oxide-based materials, and the like can be used. In particular, ITO (tin-doped indium oxide) or IZO (zinc-doped indium oxide) is preferable because of its high translucency and conductivity. In particular, IZO is preferable because of its high translucency.

The reflective film is preferably 10 times or more the thickness of the oxide film. While enhancing the migration suppressing effect of the reflecting electrode, the reflectance of the reflecting electrode can also be increased. More preferably, it is 15 times or more, and even more preferably 20 times or more.

The total thickness of the reflective film is preferably 100 nm or more. As a result, the reflectance of the reflective electrode can be further improved without impairing the migration suppressing effect.

The thickness of each reflective film is preferably 10 to 100 nm. This is because if it is thinner than 10 nm, the proportion of light that passes through the reflective film increases, the reflectance of the reflecting electrode is not sufficiently improved, and if it is thicker than 100 nm, there is a high possibility that migration will occur.

The thickness of each oxide film is preferably 1 to 10 nm. This is because if it is thinner than 1 nm, the effect of suppressing Ag migration of the reflective film is not sufficient, and if it is thicker than 10 nm, the reflectance and conductivity of the reflective electrode are lowered.

The number of layers of the reflective film is preferably 3 or more. This is to further improve the reflectance of the reflecting electrode while suppressing the migration of the reflecting electrode. Further, it is desirable that the outermost surface layer of the reflective electrode is a reflective film. This is to improve the contact between the outermost layer of the reflective electrode and the metal layer in contact with the metal layer, and to fully exert the function of the reflective electrode as an electrode.

Further, the present invention is suitable for a light emitting device made of a group III nitride semiconductor. Light emitting devices made of group III nitride semiconductors are widely used for lighting and are driven by a large current. Even when used at such a large current, the light emitting element of the present invention can effectively suppress the migration of the reflecting electrode.

According to the present invention, it is possible to realize a reflective electrode having a high effect of suppressing migration, and it is possible to suppress a decrease in the amount of light of the light emitting element.

The cross-sectional view which showed the structure of the light emitting element of Example 1. FIG. The plan view which saw the light emitting element of Example 1 from above. The figure which showed the structure of the reflection electrode 17. A graph showing the relationship between luminosity and drive time.

Hereinafter, specific examples of the present invention will be described with reference to the drawings, but the present invention is not limited to the examples.

FIG. 1 is a cross-sectional view showing the configuration of the flip-chip type light emitting element of the first embodiment. Further, FIG. 2 is a plan view showing a plan pattern of the light emitting element of the first embodiment. The light emitting element of Example 1 is a rectangle of 1 mm × 1.35 mm in a plan view, and has a light emitting wavelength of 450 nm. As shown in FIG. 1, the light emitting element of the first embodiment has a substrate 10 made of sapphire. The surface of the substrate 10 is subjected to uneven processing to improve the light extraction efficiency. The n layer 11, the light emitting layer 12, and the p layer 13 are laminated in this order on the surface of the substrate 10 on the uneven processing side via a buffer layer (not shown) made of AlN. Any conventionally known configuration can be adopted for the n layer 11, the light emitting layer 12, and the p layer 13.

On the surface of the p layer 13, a plurality of dot-shaped holes having a depth reaching the n layer 11 are provided. Dot-shaped n-dot electrodes 14 are provided on the n-layer 11 exposed on the bottom surface of each hole. The n-dot electrode 14 is made of Ti / AlNd / Ta. Here, the symbol "/" means lamination, and A / B means a laminated structure in which A is formed and then B is formed. In the following, "/" is used in the same meaning in the description of materials.

A transparent electrode 15 is provided on the p-layer 13. The transparent electrode 15 is made of IZO (zinc-doped indium oxide). In addition, ITO (tin-doped indium oxide), ICO (cerium-doped indium oxide) and the like can be used. Further, the DBR layer 16 is provided so as to cover the entire element (excluding the n-dot electrode 14) including the transparent electrode 15. The DBR layer 16 has a structure in which Nb ₂ O ₅ (niobium pentoxide) and SiO ₂ are alternately and repeatedly laminated. The thickness of each layer of the DBR layer 16 is set so as to have a high reflectance at the emission wavelength. The light emitted from the light emitting layer 12 is reflected by the DBR layer 16 toward the substrate 10 to improve the light extraction efficiency.

The DBR layer 16 is provided with a plurality of holes 25 having a depth that penetrates the DBR layer 16 and reaches the transparent electrode 15. Further, the reflective electrode 17 is continuously provided on the DBR layer 16 in the form of a film. In the region of the hole 25, the reflective electrode 17 is provided in a film shape along the side surface and the bottom surface of the hole 25. Then, the transparent electrode 15 and the reflective electrode 17 are connected to each other through the holes 25 formed in the DBR layer 16. The reflective electrode 17 has the following two functions. One is a function as a reflective film that reflects the light radiated from the light emitting layer 12 toward the substrate 10 to improve the light extraction efficiency. The other is a function as a wiring electrode that electrically connects the transparent electrodes 15 exposed on the bottom surface of each hole 25 of the DBR layer 16 in parallel. A more detailed configuration of the reflective electrode 17 will be described later.

A cover metal layer 18 is provided on the reflective electrode 17 so as to cover the reflective electrode 17. The surface and side surfaces of the reflective electrode 17 are in contact with the cover metal layer 18. The cover metal layer 18 is made of Ti / Pt / Au / Ta. By covering the reflective electrode 17 with the cover metal layer 18, the reflective electrode 17 is prevented from coming into contact with water or oxygen, the migration of the reflective electrode 17 is suppressed, and the reflective electrode 17 is formed from the p-side bonding layer 23 described later. It prevents the atoms from diffusing to the side.

Further, a plurality of p-dot electrodes 19 on the dots are provided on the cover metal layer 18. The p-dot electrode 19 is made of Ti / Pt / Au / Ta. A first insulating film 20 made of SiO ₂ is provided so as to cover the entire element except for the p-dot electrode 19.

A hole 26 penetrating the first insulating film 20 is provided at a position of the first insulating film 20 that overlaps with the n-dot electrode 14 in a plan view, and the surface of the n-dot electrode 14 is exposed. Further, an n wiring electrode 21 made of Ti / Pt / Au / Ta is provided on the first insulating film 20. The n-wiring electrode 21 is connected to a plurality of n-dot electrodes 14 via a plurality of holes 26 formed in the first insulating film 20.

A second insulating film 22 made of SiO ₂ is provided so as to cover the entire element including the n wiring electrode 21, the first insulating film 20, and the p-dot electrode 19. A hole 27 penetrating the second insulating film 22 is provided at a position of the second insulating film 22 that overlaps with the p-dot electrode 19 in a plan view, and the surface of the p-dot electrode 19 is exposed. Further, a p-side bonding layer 23 is provided on the second insulating film 22. The p-side bonding layer 23 is connected to a plurality of p-dot electrodes 19 via a plurality of holes 27 provided in the second insulating film 22.

Further, a plurality of holes 28 penetrating the second insulating film 22 are provided at positions of the second insulating film 22 that overlap with the n wiring electrodes 21 in a plan view, and the n wiring electrodes 21 are exposed. Further, an n-side bonding layer 24 is provided on the second insulating film 22 at a position separated from the p-side bonding layer 23. The n-side bonding layer 24 is connected to the n-wiring electrode 21 via a plurality of holes 28 provided in the second insulating film 22.

Next, a more detailed configuration of the reflective electrode 17 will be described. As shown in FIG. 3, the reflective electrode 17 has a multilayer structure in which a reflective film 17A made of Ag and an oxide film 17B made of IZO (zinc-doped indium oxide) are alternately and repeatedly laminated. Two pairs of the reflective film 17A and the oxide film 17B are laminated as one pair, and the reflective film 17A is further laminated on the oxide film 17B. The first layer (the layer on the 16th side of the DBR layer) and the final layer (the layer on the 18th side of the cover metal layer and the outermost layer on which the surface is exposed) are the reflective film 17A. The reflective film 17A is 50 nm, and the oxide film 17B is 2 nm. The total thickness of the reflective film 17A is 150 nm, and the total film thickness of the reflective electrode 17 is 154 nm.

An IZO film (not shown) is formed between the reflective electrode 17 and the DBR layer 16. As a result, the adhesion between the DBR layer 16 and the reflective electrode 17 is improved, and the contact between the transparent electrode 15 and the reflective electrode 17 is improved. Further, a Ta film (not shown) is provided between the reflective electrode 17 and the cover metal layer 18 in order to prevent thermal diffusion of atoms from the cover metal layer 18 side.

Further, the end faces of the reflection films 17A and the oxide films 17B are exposed on the end faces of the reflection electrodes 17. Then, the cover metal layer 18 covering the reflective electrode 17 is in contact with the upper surface and the end surface of the reflective electrode 17. In this way, the end face of the reflective film 17A is covered with the cover metal layer 18, so that the migration of the reflective film 17A is further suppressed.

Although Ag is used as the material of the reflective film 17A in Example 1, an Ag alloy mainly composed of Ag may be used, or a plurality of materials may be laminated. The Ag alloy is, for example, AgPdCu. By using such an Ag alloy, it is possible to improve the antioxidative property and the corrosiveness while maintaining the same reflectance as Ag. Further, in the first embodiment, the reflective films 17A are made of the same material in terms of ease of manufacture and the like, but different materials may be used.

Further, the reflective film 17A is preferably a material having a reflectance of 80% or more of light having an emission wavelength at a thickness of 150 nm. It is more preferably 85% or more, still more preferably 90% or more. The electric conductivity of the reflective film 17A is preferably more materials 30 × 10 ⁶ S / m. It is more preferably 40 × 10 ⁶ S / m or more, and further preferably 50 × 10 ⁶ S / m or more.

Further, in Example 1, IZO is used as the material of the oxide film 17B, but if it is an oxide (transparent conductive oxide film) that is transparent to the emission wavelength of the light emitting element and has conductivity. Any material other than IZO may be used, and a plurality of materials may be laminated. For example, indium oxide-based materials, zinc oxide-based materials, tin oxide-based materials, and the like can be used. Further, in Example 1, each oxide film 17B is made of the same material from the viewpoint of ease of production, but different materials may be used. Similarly, from the viewpoint of ease of production, it is preferable that the transparent electrode 15 and the oxide film 17B are made of the same material as in Example 1.

The indium oxide-based material is In ₂ O ₃ (indium oxide) or a material obtained by adding various elements to indium oxide, such as ITO (tin-doped indium oxide), ICO (cerium-doped indium oxide), and IZO.

The zinc oxide-based material is ZnO (zinc oxide) or a material obtained by adding various elements to zinc oxide, and is, for example, AZO (aluminum-doped zinc oxide), GZO (gallium-doped zinc oxide), and the like.

The tin oxide-based material is SnO ₂ (tin oxide), or a material obtained by adding various elements to tin oxide, such as FTO (fluorine-doped tin oxide).

It is desirable to use IZO or ITO as the oxide film 17B because of its high conductivity and transmittance. In particular, it is desirable to use IZO as in Example 1 because of its high transmittance.

Further, the electric conductivity of the oxide film 17B is preferably 1 × 10 ⁴ S / m or more. It is more preferably 10 × 10 ⁴ S / m or more, and further preferably 20 × 10 ⁴ S / m or more. Further, the internal transmittance of light having an emission wavelength at a thickness of 100 nm of the oxide film 17B is preferably 50% or more. It is more preferably 60% or more, still more preferably 70% or more.

Further, in Example 1, the thickness of the reflective film 17A is 50 nm and the thickness of the oxide film 17B is 2 nm, but any thickness may be used as long as the thickness of the reflective film 17A is larger than the thickness of the oxide film 17B. .. By setting the thicknesses of the reflective film 17A and the oxide film 17B in this way, it is possible to suppress the migration of Ag of the reflective film 17A while ensuring the conductivity and reflectance as the reflective electrode. It is desirable that the thickness of the reflective film 17A is 10 times or more the thickness of the oxide film 17B in order to sufficiently increase the reflectance of the reflective electrode 17 and sufficiently suppress the migration. More preferably, it is 15 times or more, and even more preferably 20 times or more. However, if the reflective film 17A becomes too thick, the possibility of migration will increase. Therefore, it is desirable that the thickness of the reflective film 17A is 100 times or less the thickness of the oxide film 17B. More preferably 80 times or less, and even more preferably 50 times or less.

Further, it is desirable that the thickness of each reflective film 17A is 10 to 100 nm. If it is thinner than 10 nm, the proportion of light transmitted through the reflective film 17A increases, and the reflectance of the reflective electrode 17 is not sufficiently improved. On the other hand, if it is thicker than 100 nm, there is a high possibility that migration will occur. It is more preferably 10 to 50 nm, and even more preferably 10 to 20 nm. The thinner the oxide film 17B, the thinner the reflective film 17A can be.

The thickness of each reflective film 17A does not have to be equal, but it is desirable that the total thickness of the reflective film 17A is 100 nm or more. As a result, the reflectance of the reflective electrode 17 can be further improved. As the total thickness of each reflective film 17A increases, the effect of improving the reflectance becomes saturated. Therefore, it is desirable that the total thickness of each reflective film 17A is 300 nm or less.

The thickness of each oxide film 17B is preferably 1 to 10 nm. If it is thinner than 1 nm, the effect of suppressing migration of Ag of the reflective film 17A is not sufficient, and it is not easy to form the reflective film 17A because the thickness varies. Further, if it is thicker than 10 nm, the reflectance and conductivity of the reflective electrode 17 are lowered, which is not desirable. It is more preferably 1 to 5 nm, and even more preferably 1 to 2 nm. The thickness of each oxide film 17B may be different. However, the thickness of the thickest oxide film 17B among the oxide films 17B is thinner than that of the reflective film 17A (when the thickness of each reflective film 17A is different, the thinnest reflective film 17A among them).

Further, in Example 1, the reflective film 17A and the oxide film 17B are alternately laminated so that the first layer and the final layer form the reflective film 17A, but at least one of the first layer and the final layer becomes the oxide film 17B. It may be laminated alternately as described above. However, it is desirable that the final layers are alternately laminated so as to form the reflective film 17A. This is to realize good contact with the cover metal layer 18 and to fully exert the function of the reflective electrode 17 as an electrode.

Further, in Example 1, the reflective film 17A and the oxide film 17B are alternately and repeatedly laminated to set the number of layers of the reflective film 17A to 3, but if the number of layers of the reflective film 17A is 2 or more, an arbitrary number of layers can be obtained. It's fine. However, it is desirable that the number of layers of the reflective film 17A is 3 or more as in Example 1. This is to further improve the reflectance of the reflective electrode 17 while suppressing the migration of the reflective electrode 17.

The reflective electrode 17 is produced by alternately laminating the reflective film 17A and the oxide film 17B on the DBR layer 16 by using a sputtering method. The reflective film 17A is formed using, for example, a pure Ag target. The oxide film 17B is formed using, for example, an IZO target as a target.

Of course, the reflective electrode 17 may be produced by a method other than the sputtering method, and may be produced by, for example, a vapor deposition method. However, it is preferable to use the sputtering method in terms of film thickness, uniformity of composition, productivity and the like. Further, as the sputtering method, various methods such as DC sputtering, RF sputtering, magnetron sputtering, and ECR sputtering can be used.

The reflective electrode 17 of Example 1 has a structure in which a reflective film 17A made of Ag and an oxide film 17B made of IZO are alternately laminated, the number of layers of the reflective film 17A is 2 or more, and the thickness of the reflective film 17A is oxidized. It is made larger than the thickness of the film 17B. With such a structure, migration of Ag in the reflective film 17A can be suppressed. As a result, it is possible to suppress the generation of voids due to migration in the reflective electrode 17 and the decrease in reflectance. Further, if the reflective electrode 17 has such a structure, the conductivity and reflectance of the reflective electrode 17 are not impaired, and the function of the reflective electrode 17 as an electrode and the function as a reflective film are secured.

The reason why migration is suppressed by having the reflective electrode 17 having the above structure is not clear, but it is presumed as follows.

First, in the structure of the reflective electrode 17, the Ag layer in the reflective electrode 17 is divided into the respective reflective films 17A by sandwiching the oxide film 17B between the Ag layers. Therefore, the thickness of each reflective film 17A is thinner than that when the reflective electrode 17 is composed of one Ag layer. Generally, the thicker the Ag layer, the easier it is for migration to occur. Therefore, it is considered that migration is less likely to occur because the Ag layer is divided into each reflective film 17A and becomes thin. Further, for the above reason, it is necessary that the Ag layer is divided into two or more layers, that is, the reflective film 17A has two or more layers.

Second, the reflective electrode 17 has a structure in which the reflective film 17A and the oxide film 17B are in contact with each other. Further, the oxide film 17B is IZO, and has acquired conductivity due to oxygen defects. Due to the presence of oxygen defects in the oxide film 17B and the structure in which the reflective film 17A and the oxide film are in contact with each other, water and oxygen diffused in the reflective electrode 17 are in contact with the reflective film 17A rather than the reflective film 17A. Reacts preferentially. In particular, since the structure is such that the reflective film 17A and the oxide film 17B are alternately and repeatedly laminated, the contact area between the reflective film 17A and the oxide film 17B is widened. As a result, it is considered that the reflective film 17A is less affected by water and oxygen, and migration is suppressed.

If the oxide film 17B takes in oxygen in preference to the reflective film 17A, it is considered that the conductivity of the oxide film 17B is deteriorated instead of suppressing the migration of the reflective film 17A. This is because it is considered that the oxygen defects in the oxide film 17B are reduced. However, in reality, the conductivity of the reflective electrode 17 as a whole is hardly deteriorated. Since the oxide film 17B is very thin, it is considered that even if the conductivity of the oxide film 17B deteriorates, its influence is small.

FIG. 4 is a graph showing the time change of the luminous intensity of the light emitting device of the first embodiment. For comparison, a time change in luminosity was also examined for a light emitting element (light emitting element of Comparative Example) having the same configuration as the light emitting element of Example 1 except that the reflective electrode was made of one layer of Ag. The horizontal axis is the elapsed time from the start of driving, and the vertical axis is a relative value with the luminous intensity at the start of driving of the light emitting element of Example 1 as 1. The light emitting elements of Examples 1 and Comparative Examples were driven at an IF (forward current) of 2200 mA and a Tj (junction temperature) of 150 ° C.

As shown in FIG. 4, until the driving time of 500 hours passed, both the light emitting element of Example 1 and the light emitting element of Comparative Example had a similar decrease in luminous intensity. However, when it exceeds 500 hours, the luminous intensity gradually differs between the light emitting element of Example 1 and the light emitting element of Comparative Example, and the light emitting element of Example 1 has a lower luminous intensity than the light emitting element of Comparative Example. Was small. When the driving time was 2000 hours, the luminous intensity of the light emitting element of the comparative example was reduced to about 0.94. On the other hand, it was found that the luminous intensity of the light emitting element of Example 1 decreased to about 0.97, and the decrease of luminous intensity was slower than that of the light emitting element of Comparative Example. From this result, it was found that the structure of the reflective electrode 17 of Example 1 suppressed the migration of Ag and suppressed the generation of voids in the reflective electrode as compared with the case of using the Ag single layer.

As described above, in the light emitting element of the first embodiment, the reflective electrode 17 has a structure in which the reflective film 17A made of Ag and the oxide film 17B made of IZO are alternately and repeatedly laminated, and the reflective film 17A has two or more layers. The migration of Ag is suppressed, and the decrease in reflectance is suppressed. Further, since the reflective film 17A is thicker than the oxide film 17B, the migration suppressing effect can be enhanced without impairing the function of the reflective electrode 17 as an electrode and the function as a reflective film.

The light emitting element of Example 1 was a flip chip type, but the present invention is not limited to this, and can be applied to a light emitting element having an arbitrary structure having a reflecting electrode. Further, although the first embodiment is a light emitting device made of a group III nitride semiconductor, it can be applied to any light emitting device. For example, the present invention can be applied not only to LEDs and LDs, but also to organic EL elements and inorganic EL elements. Further, the present invention is suitable for a light emitting element for lighting. In lighting applications, the light emitting element is driven by a large current and becomes hot, but according to the present invention, the migration of the reflecting electrode can be effectively suppressed even in such a situation, and the reflectance of the reflecting electrode is lowered. It is possible to suppress the decrease in luminous intensity. In particular, it is suitable for a light emitting device made of a group III nitride semiconductor.

The light emitting element of the present invention can be used as a light source for lighting or a backlight.

10: Substrate 11: n layer 12: Light emitting layer 13: p layer 14: Transparent electrode 15: n dot electrode 16: DBR layer 17: Reflective electrode 17A: Reflective film 17B: Oxidation film 18: Cover metal layer 19: p dot electrode 23: p-side bonding layer 24: n-side bonding layer

Claims (7)

The transparent electrode is provided through a p-layer, a transparent electrode provided on the p-layer, a DBR layer provided on the transparent electrode, and a hole provided on the DBR layer and provided in the DBR layer. A light emitting element having a reflective electrode connected to the
The reflective electrode is made of Ag or an Ag alloy and has a reflective film having a thickness of 10 to 100 nm and a transparent conductive oxide having an oxide film having a thickness of 1 to 10 nm. It has a structure in which the number of film layers is 2 or more.
The reflective film is 10 times or more the thickness of the oxide film.
A light emitting element characterized by this. The light emitting element according to claim 1, wherein the total thickness of the reflective film is 100 nm or more. The light emitting element according to claim 1 or 2, wherein the number of layers of the reflective film is 3 or more. The light emitting device according to any one of claims 1 to 3, wherein the oxide film is made of IZO or ITO. The light emitting element according to any one of claims 1 to 4, wherein the reflective electrode has the outermost surface layer of the reflective film. The light emitting device according to any one of claims 1 to 5, wherein the light emitting device is made of a group III nitride semiconductor. The light emitting device according to any one of claims 1 to 6, wherein an IZO film is further provided between the DBR layer and the reflective electrode.

Images