KR100716752B1 - Light emitting element and method for manufacturing thereof - Google Patents

Abstract

Disclosed are a light emitting device having an electrode structure for increasing light extraction efficiency and a method of manufacturing the same. The first gallium nitride layer is formed at a first height in the first region of the substrate and is formed at a second height smaller than the first height in the second region. The first electrode is formed over the first gallium nitride layer formed at the second height, and the active layer is formed over the first gallium nitride layer formed at the first height. The second gallium nitride layer is formed over the active layer, the current spreading layer is formed over the second gallium nitride layer, and the second electrode is formed in some region of the current spreading layer. The light extraction enhancement layer has a refractive index larger than that of the current diffusion layer, and is formed in the form of irregularities in the remaining region of the current diffusion layer. Accordingly, by forming the uneven structure of the high refractive index dielectric material on the current spreading layer, the light extraction efficiency can be improved.

Light emitting element, gallium nitride, light extraction, light extraction enhancement layer pattern substrate

Description

LIGHT EMITTING ELEMENT AND METHOD FOR MANUFACTURING THEREOF

1 is a schematic diagram illustrating Snell's law.

2 is a perspective view schematically illustrating a structure of a general gallium nitride based light emitting diode.

3 is a cross-sectional view schematically illustrating a gallium nitride based light emitting diode according to the present invention.

4 is a conceptual diagram illustrating light extraction characteristics of the light emitting diode of FIG. 3.

5A and 5B are a plan view and a cross-sectional view illustrating a gallium nitride based light emitting diode structure according to a first embodiment of the present invention, respectively.

6A to 6D are cross-sectional views illustrating a method of manufacturing the light emitting diode shown in FIG. 3.

<Description of the symbols for the main parts of the drawings>

110 substrate 120 buffer layer

130: n-type gallium nitride layer 140: active layer

150: p-type gallium nitride layer 160: current diffusion layer

170: light extraction enhancement layer 180: p-electrode

190 n-electrode

The present invention relates to a light emitting device and a manufacturing method thereof, and more particularly to a light emitting device having an electrode structure for increasing the extraction efficiency (light extraction efficiency) of the light and a manufacturing method thereof.

In general, a light emitting diode, which is a light emitting device, is spotlighted as a next-generation lighting that replaces an incandescent bulb or a fluorescent lamp. In particular, demand is expected to increase further as it is used for lighting of large area LCDs with long lifespan.

However, most of the light generated by total reflection due to the difference in refractive index between the materials constituting the light emitting diode (sapphire substrate, epi, epoxy, etc.) is trapped. The total reflection occurs when light travels from a material having a relatively high refractive index to a material having a low refractive index at an interface having a different refractive index. The total reflection is determined by Snell'law.

1 is a schematic diagram illustrating Snell's law. Where n1 and n2 are the refractive indices of the first and second media, respectively, and θ1 and θ2 are the incident angle and the exit angle, respectively. Wherein the refractive index of the second medium is greater than the refractive index of the first medium.

Referring to FIG. 1, when light is transmitted from a second medium having a relatively large refractive index to a first medium having a relatively small refractive index, the exit angle θ2 of the transmitted light has an angle greater than the incident angle θ1.

In particular, the sapphire substrate and the gallium nitride (GaN) layer employed in the gallium nitride-based light emitting diode widely used as a blue light source has a refractive index of 1.8 and 2.5, respectively, and thus there is a significant difference from the air layer having a refractive index of 1. This large difference in refractive index causes a large portion of the light generated by the light emitting diode to be trapped inside. For example, the critical angle of the interface between the gallium nitride (GaN) layer and the sapphire substrate is about 46 degrees. Therefore, light having an angle of incidence greater than 46 degrees is trapped inside the gallium nitride (GaN) layer.

In the same manner, the critical angle between the sapphire substrate and the air interface is 33.5 degrees, and the critical angle between the gallium nitride (GaN) layer and the air layer is about 23.6 degrees. Therefore, light having an angle of incidence greater than 33.5 degrees is trapped inside the sapphire substrate, and light having an angle of incidence greater than 23.6 degrees is trapped inside the gallium (GaN) layer.

As such, since a large amount of light generated in the light emitting diode is not extracted due to total reflection of the interface, there is a problem that reduces the external quantum efficiency of the entire light emitting diode, thereby reducing the light output of the light emitting diode.

Accordingly, the technical problem of the present invention is to solve such a conventional problem, and an object of the present invention is to provide a gallium nitride-based light emitting device that can increase the extraction efficiency of light to implement a high brightness light emitting device.

Another object of the present invention is to provide a method of manufacturing the above light emitting device.

In order to realize the above object of the present invention, a light emitting device includes: a substrate; A first gallium nitride layer formed at a first height in the first region of the substrate and formed at a second height smaller than the first height in the second region; A first electrode formed on the first gallium nitride layer formed to the second height; An active layer formed on the first gallium nitride layer formed to the first height; A second gallium nitride layer formed on the active layer; A current diffusion layer formed on the second gallium nitride layer; A second electrode formed in a portion of the current spreading layer; And a light extraction enhancement layer having a refractive index greater than that of the current diffusion layer and formed in the concave-convex shape in the remaining region of the current diffusion layer.

In another aspect, a method of manufacturing a light emitting device includes: depositing a current diffusion layer on a first gallium nitride layer, an active layer, and a second gallium nitride layer sequentially grown on a substrate; removing the second gallium nitride layer and the active layer so as to correspond to an n-contact, and removing a portion of the surface of the first gallium nitride layer; Forming a light extraction enhancement layer having a refractive index greater than that of the current diffusion layer on the first region of the current diffusion layer; And removing the surface to deposit a first electrode over the relatively low gallium nitride layer, and depositing a second electrode over the second region of the relatively high current spreading layer.

According to such a light emitting device and a method of manufacturing the same, the extraction efficiency of light can be improved by forming the uneven structure of the dielectric material of high refractive index on the current spreading layer.

Hereinafter, with reference to the accompanying drawings, it will be described in detail the present invention.

2 is a perspective view schematically illustrating a structure of a general gallium nitride based light emitting diode.

Referring to FIG. 2, a general gallium nitride based light emitting diode includes a substrate 11, an n-type gallium nitride layer 13, an active layer 14, a p-type gallium nitride layer 15, and a p-type transparent electrode ( 16), p-electrode 17 and n-electrode 18. In operation, when current flows through the p-electrode 21 and the n-electrode 20, light is emitted while electron-hole recombination occurs in the active layer 12.

In order to grow the gallium nitride layer 11 on the substrate 10, a metal organic chemical vapor deposition (MOCVD) device is usually used. The substrate 10 is a sapphire substrate or a silicon carbide substrate.

First, a buffer layer (not shown) to help grow the gallium nitride layer 13 is formed on the substrate 11, and the n-type gallium nitride layer 13 and the active layer 14 are formed. And the p-type gallium nitride layer 15 are sequentially grown.

In general, a diode forms an electrode on an upper portion of a p-type gallium nitride layer and a lower substrate connected to an n-type gallium nitride layer to flow current through a p-n junction. However, since the sapphire used as the substrate of the gallium nitride-based diode is an insulator, an electrode cannot be formed on the sapphire substrate 11. Therefore, an electrode must be directly formed on the n-type gallium nitride layer 13.

To this end, partial regions of the p-type gallium nitride layer 15, the active layer 14, and the n-type gallium nitride layer 13 of the portion where the electrode is to be formed are removed, and the n-type gallium nitride layer 13 is exposed on the n-type gallium nitride layer 13. -Form the electrode 18. Since the light is emitted from the p-n junction surface, the p-electrode 17 is formed at the corner of the p-type transparent electrode 16 so that the light is not obscured by the electrode.

In addition, the p-type gallium nitride layer 15 has a larger resistance than the n-type gallium nitride layer 13, and thus, it is more difficult for the current to flow uniformly through the p-type gallium nitride layer 15. In order to prevent this, a thin transparent electrode is formed on the entire upper surface of the p-type gallium nitride layer 15 so that current can be transferred to the entire surface of the p-type gallium nitride layer 15.

Meanwhile, a method of texturing a surface is used to reduce light loss due to total reflection of light generated from a gallium nitride based light emitting diode. This is a method of scattering the light generated by the light emitting diode, thereby changing the propagation path of the light in various directions to increase the probability of the light escape from the inside of the light emitting diode.

The texturing method is divided into a method of texturing a surface of a gallium nitride (GaN) layer, a method of texturing a surface of a sapphire substrate, and a method of texturing a surface of a current diffusion layer (or window layer).

In the method of texturing the surface of the gallium nitride (GaN) layer, the surface of the gallium nitride (GaN) layer becomes rough, which adversely affects the p-electrode formation process, thereby deteriorating the electrical characteristics of the light emitting diode as a whole.

The method of texturing the surface of the sapphire substrate is not easy to etch the sapphire substrate itself is not easy manufacturing process. In addition, since the surface of the etched sapphire substrate is rough, there is a big problem in epitaxial growth.

The current spreading layer used in the method of texturing the surface of the current spreading layer is mainly a transparent oxide electrode such as indium tin oxide (ITO) or antimony tin oxide (ATO). Since the p-type gallium nitride layer and the ITO are difficult to make ohmic contact with each other, a tunnel junction is actually formed by introducing a thin super lattice structure (SLS) on the p-type gallium nitride layer.

However, the ITO electrode material is not only easy to etch, but also gives surface roughness to the electrode itself, so that surface scattering occurs when the current is injected, resulting in inferior electrical properties.

3 is a cross-sectional view schematically illustrating a gallium nitride based light emitting diode according to an embodiment of the present invention.

Referring to FIG. 3, a gallium nitride based light emitting diode 100 according to an exemplary embodiment of the present invention may include a substrate 110, a buffer layer 120, an n-type gallium nitride layer 130, and an active layer. 140, a p-type gallium nitride layer 150, a current spreading layer 160, a light extraction enhancement layer 170, a p-electrode 180, and an n-electrode 190. In operation, when a current flows between the p-electrode 180 and the n-electrode 190, light is emitted while electron-hole recombination occurs in the active layer 150.

In order to grow a gallium nitride layer on the substrate 110, a MOCVD (Metal Organic Chemical Vapor Deposition) device is usually used. The substrate 110 is a sapphire substrate or a silicon carbide substrate.

A buffer layer 130 is formed on the substrate 110 to help the growth of the gallium nitride layer.

The n-type gallium nitride layer 130, the active layer 140, and the p-type gallium nitride layer 150 are sequentially grown on the buffer layer 120. In general, a diode forms an electrode on an upper portion of a p-type gallium nitride layer and a lower substrate connected to an n-type gallium nitride layer to flow current through a p-n junction. However, since the sapphire used as the substrate of the gallium nitride-based diode is an insulator, an electrode cannot be formed on the substrate 110. Therefore, an electrode must be formed on the n-type gallium nitride layer 130.

To this end, some regions of the p-type gallium nitride layer 150, the active layer 140, and the n-type gallium nitride layer 130 of the portion where the electrode is to be formed are removed, and the n-type gallium nitride layer 130 is exposed on the n-type gallium nitride layer 130. An electrode 190 is formed. Accordingly, the n-type gallium nitride layer 130 is formed at a first height in the first region of the buffer layer 120 and is formed at a second height smaller than the first height in the second region.

Since the light is emitted from the p-n junction surface, the p-electrode 180 is formed at the edge of the current diffusion layer 160 so that the light is not obscured by the electrode.

When both the p-electrode 180 and the n-electrode 190 are positioned at the top, the p-electrode 180 and the n-electrode 190 have a current distribution compared to a general diode structure located parallel to different planes. Is not uniform.

In addition, the p-type gallium nitride layer 160 has a larger resistance than the n-type gallium nitride layer 130, and thus, it is more difficult for a current to flow uniformly through the p-type gallium nitride layer 160.

In order to prevent this, the current diffusion layer 180, which is a thin transparent electrode, is formed on the entire upper surface of the p-type gallium nitride layer 160 to transmit current to the entire surface of the p-type gallium nitride layer 160.

A light extraction enhancement layer 170 having a predetermined pattern is formed on the current diffusion layer 160. The light extraction enhancement layer 170 has a concave-convex structure that covers a portion of the current diffusion layer 160 and exposes the remaining region. The light extraction enhancement layer 170 preferably has a refractive index larger than that of the current diffusion layer 160. In general, since the refractive index of ITO used as the current diffusion layer 160 is 2.0, the light extraction enhancement layer 170 may have a minimum refractive index of 2.0 or more, no absorption in the visible light region, and easy etching. For example, SiNx, TiO2, Ta2O5, ZrO2 and the like can be used. Easily etched SiNx or TiO2, SixTi (1-x) O2 are suitable.

4 is a conceptual diagram illustrating light extraction characteristics of the light emitting diode of FIG. 3.

Referring to FIG. 4, the light passing through the interface between the current diffusion layer 160 and the light extraction enhancement layer 170 is refracted without total reflection and enters the light extraction enhancement layer 170. Because, as you can see from Snell's law, total reflection may occur when light passes from a high refractive index medium to a low refractive index medium, but when light passes from a low refractive index to a high refractive index, total reflection does not occur and all light is refracted Because it becomes.

5A and 5B are a plan view and a cross-sectional view illustrating a gallium nitride based light emitting diode structure according to a first embodiment of the present invention, respectively. In particular, a hemispherical light extraction enhancement layer is shown. For convenience of description, only the light extraction enhancement layer formed on the current diffusion layer is shown.

5A and 5B, the light emitting diode 200 according to the first embodiment of the present invention includes a current spreading layer 210 and a light extraction enhancement layer 220 formed in a hemispherical shape on the current spreading layer 210. Include. Although the light extraction enhancement layer 170 illustrated in FIG. 3 is disposed closely to each other so that the areas of the current diffusion layer 160 exposed are minimized, in the first embodiment of the present invention, the light extraction enhancement layer 220 is disposed. The arrangement is shown at regular intervals.

The light extraction enhancement layer 220 has a substantial height of 1 to 5 μm, a substantial radius of 1 to 5 μm, and a substantial interval of 1 to 10 μm. The light extraction enhancement layer is formed of a material having a refractive index larger than that of the current diffusion layer.

In FIG. 5A, although the diameters of the light extraction enhancement layers 220 formed in the hemispherical shape are the same, they may be formed to have diameters of various sizes. Although the height of the light extraction enhancement layer 220 is shown in FIG. 5B, the light extraction enhancement layer 220 may be formed to have various heights, and the distance between the light extraction enhancement layers 220 is uniform. It may be formed. In addition, although the radius of curvature of the light extraction enhancement layer 220 is shown to be uniform, it may be formed to have various radius of curvature. In addition, although the formation frequency of the light extraction enhancement layer 220 is uniform in one region, it may be formed densely in an arbitrary region and may be slightly formed in another region.

A light extraction enhancement layer having an uneven structure is formed on the current diffusion layer 160 of the gallium nitride-based light emitting diode according to the present invention to increase light extraction efficiency, and is formed of a material having a refractive index greater than that of the current diffusion layer.

Then, the light extraction efficiency of the light emitting devices was observed using a ray tracing simulator. In particular, in order to determine the optimized patterns of the light extraction enhancement layer, when the pattern processing is not performed, the light extraction efficiency of the light extraction enhancement layer was calculated corresponding to the radius, height, and spacing between the hemispheres. The calculation results are shown in Table 1 below.

Radius (μm) Height (㎛) Thickness (㎛) Extraction efficiency (%) Remarks - - - 33.8 - 3 1.5 6 53.09 Refractive index of the light extraction enhancement layer = 2.2 3 1.5 8 47.93 Same as above 3 1.5 10 44.18 Same as above 3 1.5 12 41.69 Same as above 3 0.5 6 43.30 Same as above 3 One 6 50.31 Same as above 3 2 6 53.75 Same as above

As can be seen in Table 1, it can be seen that the narrower the hemisphere and the hemisphere, the higher the hemisphere, the higher the light extraction efficiency. The light extraction efficiency of the light emitting diode having a radius of 3 mu m, a height of 2 mu m on a plane, and a thickness of 6 mu m between hemispheres was 53.75%. In contrast, in the absence of the dielectric layer, the light extraction efficiency was observed to be about 33.8%. As can be seen from the above results, more light is extracted as the area where the light extraction enhancement layer is formed is relatively large.

6A to 6D are cross-sectional views illustrating a method of manufacturing the light emitting diode shown in FIG. 3.

Referring to FIG. 6A, a light extraction enhancement layer 202 is coated on a substrate to be sequentially formed up to a current spreading layer 160. The current diffusion layer 160 is a material in ohmic contact with the p-type gallium nitride layer, and mainly Ni / Au, Pd / Au, Pt / Au, or the like may be used. The current spreading layer 160 is deposited within 10 nm by an evaporation method.

The light extraction enhancement layer 202 is a dielectric material having a refractive index equal to or greater than that of the current diffusion layer 160. In general, since the refractive index of ITO, which is a current diffusion layer, is 2.0, the refractive index is at least 2.0, and there is no absorption in the visible light region, and it is possible to improve the extraction layer if the material is easy to etch. For example, SiNx, TiO2, Ta2O5, ZrO2, SixTi (1-x) O2, or the like may be used as the light extraction enhancement layer 160.

In the present embodiment, TiO 2 having a refractive index of about 2.4 will be described as the light extraction enhancement layer 160. TiO 2 is deposited to a thickness of about 1-3 μm on the current spreading layer 160 using a sputtering method. For convenience of explanation, a part of the light emitting diode shown in FIG. 3 is shown and given the same reference numeral. A p-type gallium nitride layer 150 is formed below the current diffusion layer 160, and an active layer 140, an n-type gallium nitride layer 130, and a buffer layer 120 formed under the p-type gallium nitride layer 150. The illustration of the substrate 110 is omitted. As the deposition method, a plasma enhanced chemical vapor deposition (PECVD) method, a low pressure CVD (LPCVD) method, a sputtering method, or the like can be used. However, PECVD methods are preferred for process convenience.

Referring to FIG. 6B, after the photoresist (PR) 204 is coated on the resultant of FIG. 6A, patterning is performed by a photolithography method. The pattern may have various shapes. The shape of the pattern according to the present embodiment has a constant interval, to form a cylindrical photoresist (PR) pattern having a hexagonal arrangement. The radius of the cylinder is preferably 1-5 탆, the interval is 1-5 탆, and the height is 1-3 탆. If there is no difficulty in the process, it is preferable to form a narrow gap and a high height.

Referring to FIG. 6C, the photoresist PR pattern is reflowed to form a hemispherical photoresist pattern 205. Specifically, baking for about 3 to 10 minutes at a temperature of 140 to 160 degrees Celsius in a hot plate or oven (oven). By appropriately adjusting the baking time, the hemispherical photoresist pattern 205 is completed. At this time, the hemispherical ends may be attached to each other by overflowing. If possible, the hemispherical shape is preferably distributed throughout the entire surface.

Referring to FIG. 6D, a Reactive Ion Etching (RIE) method or an Inductive Coupled Plasma RIE (ICP-RIE) method is performed to transfer the photoresist pattern 205 to TiO 2 as it is. The etching conditions are most preferably etched PR and TiO2 having the same etching ratio. It is appropriate if the PR / TiO2 etching ratio is a value between 1 and 2. The etching gas uses CF4 and O2. It is desirable to add trace amounts of Ar gas for stable plasma. Instead of CF4, fluorine-based gases such as CHF3 and SF6 can be used. Adjust the ratio of CF4 and O2 to select the appropriate PR and TiO2 etch selectivity. The etching time is until the upper PR is completely gone.

In the above, the method of forming the TiO 2 uneven pattern on the current diffusion layer 160 has been described. After the TiO 2 uneven pattern is formed, a light emitting diode is manufactured by a conventional manufacturing method. That is, after mesa etching a portion to be an n-contact, Ti / Al / Ti / Au or Cr / Ni / Au are sequentially deposited to form an n-electrode, and finally, Cr / Ni / Au To form a p-electrode to produce a gallium nitride-based light emitting diode.

As described above, a dielectric material having a high refractive index is deposited on the current diffusion layer of the gallium nitride (GaN) -based light emitting diode, and a three-dimensional pattern is formed by photolithography to produce a diode having high light extraction efficiency. By forming a texturing pattern using a dielectric on the current diffusion layer, it is possible to fabricate a high brightness light emitting diode without increasing the p-contact resistance.

In addition, it is possible to reduce the total reflection of the light generated in the active layer of the light emitting device can be produced a light emitting device with high light extraction efficiency.

In addition, since the manufacturing process of the concave-convex structure is similar to the general silicon process, the fabrication is easy, and thus the reliability and mass productivity of the process can be improved.

Although described above with reference to the embodiments, those skilled in the art can be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below. I can understand.

Claims (11)

Board; A first gallium nitride layer formed at a first height in the first region of the substrate and formed at a second height smaller than the first height in the second region; A first electrode formed on the first gallium nitride layer formed to the second height; An active layer formed on the first gallium nitride layer formed to the first height; A second gallium nitride layer formed on the active layer; A current diffusion layer formed on the second gallium nitride layer; A second electrode formed in a portion of the current spreading layer; And And a light extraction enhancement layer having a refractive index greater than that of the current diffusion layer and formed in a hemispherical shape in the remaining region of the current diffusion layer. The method of claim 1, wherein the first gallium nitride layer is doped with an n-type or p-type, and the second gallium nitride layer is doped with a polarity opposite to the first gallium nitride layer to form a pn junction surface. Light emitting device. The light emitting device of claim 1, wherein the light extraction enhancement layer is formed of any one of SiNx, TiO2, Ta2O5, ZrO2, and SixTi (1-x) O2. The light emitting device according to claim 3, wherein the refractive index of the light extraction enhancement layer is 2.0 or more. delete The light emitting device according to claim 1, wherein the hemispherical radius is 1 to 5 mu m, an interval is 1 to 5 mu m, and a height is 1 to 3 mu m. The light emitting device according to claim 1, wherein the light extraction enhancement layer is arranged in a hexagonal shape. Depositing a current diffusion layer on the first gallium nitride layer, the active layer, and the second gallium nitride layer sequentially grown on the substrate; removing the second gallium nitride layer and the active layer so as to correspond to an n-contact, and removing a portion of the surface of the first gallium nitride layer; Forming a light extraction enhancement layer having a refractive index greater than that of the current diffusion layer on the first region of the current diffusion layer; And A method of manufacturing a light emitting device comprising removing a surface to deposit a first electrode on a relatively low gallium nitride layer, and depositing a second electrode on a second region of the relatively high current spreading layer. Forming the light extraction enhancement layer, Depositing a light extraction enhancement layer on the current spreading layer; Coating a photoresist and patterning the photoresist; Reflowing the patterned photoresist pattern; And And transferring the reflowed photoresist pattern to the light extraction enhancement layer, and etching the light extraction enhancement layer. delete The method of claim 8, wherein the light extraction enhancement layer is formed of any one of SiN x, TiO 2, Ta 2 O 5, ZrO 2, and SixTi (1-x) O 2. The method of claim 8, wherein the refractive index of the light extraction enhancement layer is equal to or larger than that of the current diffusion layer.

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