KR20090077340A - Gallium nitride light emitting diode and method for manufacturing the same - Google Patents

Abstract

A nitride light emitting device and a manufacturing method thereof are provided to improve optical extraction efficiency by forming transparent electrode layers having continuously varying refractive index. A nitride light emitting device includes a semiconductor substrate(301) and a plurality of transparent electrode layers(401,402,403). A nitride layer(300) is formed in the semiconductor substrate. The plurality of transparent electrode layers are sequentially formed on the nitride layer so as to have different particle size. Upper transparent electrode layer among the plurality of transparent layers is formed to have larger particle size than the adjacent lower transparent layer.

Description

A nitride light emitting device having improved luminous efficiency and a method for manufacturing the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride light emitting device and a method of manufacturing the same, and more particularly, to a nitride light emitting device having improved luminous efficiency and a method of manufacturing the same.

GaN-based light emitting diodes (LEDs) that emit blue, green, and UV light, as well as small and large display boards, are widely used in society such as indicators, backlights of LCD devices, and backlights of mobile phone keypads.

Currently, cyan LEDs are replacing existing traffic lights, various LEDs are used as light sources for automobiles and indirect lighting, and when the LEDs with higher light efficiency are developed, current lamps can be replaced with LEDs.

In order to manufacture LEDs used in various fields, a thin film is conventionally formed on a sapphire substrate or a SiC substrate by a method such as metal organic chemical vapor deposition (MOCVD) to form an LED using GaN material.

1A and 1B are diagrams illustrating a method of manufacturing a light emitting device using the conventional technique. Referring to FIGS. 1A and 1B, a conventional method forms a buffer layer (Un-doped GaN) 12 by MOCVD on a substrate 11 such as sapphire, SiC, GaN, and the like, and then forms N-GaN on the buffer layer 12. A layer 13, an active layer (In _x Ga _1-x N (x = 0 to 1); 14), and a P-GaN layer 15 are sequentially formed (see FIG. 1A (a)).

Thereafter, heat treatment is performed at about 600 ° C. for about 20 minutes to activate impurities in the P-GaN layer 15, and then a portion of the N-GaN layer 13 is exposed to form an N-type electrode. Etching is performed from the GaN layer 15 downward (see (b) of FIG. 1A).

Thereafter, a thin ohmic contact metal (or transparent conductive thin film) 16 is formed on the entire surface of the P-GaN layer 15 (see (c) of FIG. 1A), and a pad for bonding upon assembling the chip thereon. P-type ohmic contact 17 is formed (see (d) of FIG. 1B).

Thereafter, on the etched N-GaN layer 13, an electrode layer 18 which is simultaneously used as ohmic and pad metal is formed to complete the chip (see (e) of FIG. 1B).

The finished LED chip is packaged and molded to form SMD, lamp and high power LED PKG.

On the other hand, the driving process of the LED, when the voltage is applied through the N and P-type electrode, electrons and holes flow into the active layer 14 from the N-GaN layer 13 and P-GaN layer 15, In the active layer 14, electrons and holes are combined to emit light.

The light generated from the active layer 14 travels up and down the active layer 14, and the light propagated upwards is emitted through the transparent electrode formed thinly on the P-GaN layer 15, and a part of the light propagated down is Emitted to the outside of the chip, the rest proceeds to the bottom of the substrate is absorbed by the solder used in the assembly of the LED chip, or reflected and proceeded upward again, some of it is absorbed back into the active layer 14, Some pass through the active layer 14 and out of the chip through the transparent electrode.

In order to realize different wavelengths with this LED chip, when the assembly forms a phosphor, a wavelength converting material, on top of the LED chip to realize multi-color color, it is possible to realize specific wavelengths, mixed wavelengths, and white LEDs with converted wavelengths. Will be.

As described above, in the conventional LED structure, due to the large bandgap energy of the GaN material, in order to realize ohmic contact between the p-GaN layer and the metal, a metal material having a large work function of about 7.5 eV should be used. do.

Generally, Ni having a high work function is used as a p-GaN ohmic material, but recently, a p-GaN / transparent conductive oxide (TCO) type using transparent electrode materials capable of ohmic contact with low light absorption is used. A lot of research is being conducted to realize the performance of TCO (ITO, IZO, CIO, ZnO, etc.) materials. Indium tin oxide (ITO) transparent electrodes have excellent electrical conductivity and band-gap of 2.5 eV or more in the visible region. Because of its transparency, it is currently in the spotlight as a transparent electrode material of LED.

As a conventional technology for generating an indium tin oxide (ITO) transparent electrode, a single layer ITO thin film is mainly used. However, the method of forming the transparent electrode layer including the ITO transparent electrode has the following problems.

The transparent electrode has an advantage of light transmittance of about 90%, whereas the transparent electrode formed of a single layer transmits only light having a limited incident angle due to the difference in refractive index between adjacent layers such as the P-GaN layer and the air layer. There is a problem that the light extraction efficiency is lowered.

Specifically, the difference in refractive index at the interface between the p-GaN layer and the transparent electrode layer when light from the active layer of the GaN LED passes through the p-GaN and the transparent electrode (p-GaN layer = 2.4, transparent electrode layer (ITO) = 2.0) has a limitation in that only light of limited incidence angle passes according to Snell's law.

In addition, as shown in FIG. 2, since the refractive index of the transparent electrode layer 16 is about 2.0 uniformly throughout the transparent electrode layer, when light passes through the transparent electrode layer 16 and exits the air (refractive index = 1.0) layer, When the incident angle of light is smaller than the critical angle Θ, it passes outside the transparent electrode layer 16 (1 in FIG. 2), but when it is above the critical angle (2 and 3 in FIG. 2) at the interface between the transparent electrode layer 16 and the air layer. There is a problem that total reflection according to Snell's law occurs and the amount of light extracted is significantly reduced.

Therefore, there is a need for the development of a new transparent electrode layer having a higher transmittance and better film quality than the conventional transparent electrode, and can improve the light extraction efficiency to the air layer.

The problem to be solved by the present invention is to provide a nitride light emitting device and a method of manufacturing the light extraction efficiency is improved than the light emitting device of the prior art.

A nitride light emitting device of the present invention for achieving the above object is a semiconductor substrate having a nitride layer; And a plurality of transparent electrode layers sequentially formed on the nitride layer to have particles of different sizes between each layer.

In addition, the plurality of transparent electrode layers described above may be formed such that the size of the particles of the upper transparent electrode layer is larger than the size of the particles of the lower transparent electrode layer adjacent to the nitride layer.

In addition, the plurality of transparent electrode layers described above may be sequentially formed such that the amount of voids included in the upper transparent electrode layer is greater than the amount of voids included in the lower transparent electrode layer adjacent to the nitride layer.

In addition, the plurality of transparent electrode layers may be formed of an indium tin oxide (ITO) material.

On the other hand, the nitride light emitting device manufacturing method of the present invention for achieving the above technical problem, (a) forming a nitride layer on the substrate; And (b) sequentially forming a plurality of transparent electrode layers having particles of different sizes between the layers in the nitride layer.

In addition, in the step (b) described above, the plurality of transparent electrode layers may be sequentially formed such that the size of the particles of the upper transparent electrode layer is larger than the size of the particles of the lower transparent electrode layer adjacent to the nitride layer.

In addition, in the step (b) described above, the plurality of transparent electrode layers may be sequentially formed such that the amount of voids included in the upper transparent electrode layer is greater than the amount of voids contained in the lower transparent electrode layer adjacent to the nitride layer. have.

In addition, the above step (b) is a step of forming a lower transparent electrode layer by coating and baking the transparent electrode layer solution on the (b1) nitride layer; And (b2) coating and baking the coated transparent electrode layer solution and the transparent electrode layer solution having a different hydrogen ion concentration (pH) on the lower transparent electrode layer to form the lower transparent electrode layer, thereby forming the upper transparent electrode layer. have.

In addition, the above-described method for manufacturing the nitride light emitting device may further include performing the step (b2) by using the upper transparent electrode layer formed in the step (b3) (b2) as the lower electrode layer.

In addition, the method of manufacturing the above-described nitride light emitting device may further include forming a plurality of transparent electrode layers by performing (b3) a plurality of times on the transparent electrode layer formed below.

In addition, in the above-described method of manufacturing a nitride light emitting device, it is preferable that the transparent electrode layer solution used for forming the upper transparent electrode layer has a lower hydrogen ion concentration (pH) than the transparent electrode layer solution used for forming the lower transparent electrode layer.

In addition, the above-described transparent electrode layer may be formed of indium tin oxide (ITO).

As described above, the present invention, when forming the transparent electrode layer of the nitride light emitting device, by using the Sol-Gel method to reduce the light extraction efficiency generated when the light emitted from the active layer through the transparent electrode layer is emitted into the air As a result, the effect of improving the light extraction efficiency appears.

Specifically, the refractive index of the transparent electrode layer formed of a material of ITO as a conventional single layer has a large difference in refractive index with air that is constantly maintained in the entire transparent electrode layer at about 2.0, so that total reflection occurs at the interface, thereby reducing light extraction efficiency. There is this.

However, the present invention forms a plurality of transparent electrode layers from the p-GaN layer to the air layer when forming the transparent electrode layer, and by adjusting the size of the particles contained in each transparent electrode layer, the closer to the air layer to each transparent electrode layer The refractive index of each transparent electrode layer is gradually decreased by gradually increasing the amount of voids included, and finally, the refractive index of the transparent electrode layer in contact with the air layer is adjusted to be close to the refractive index of the air layer, whereby light generated in the active layer is separated from the transparent electrode layer and the air layer. By minimizing the amount totally reflected at the interface there is an effect to significantly improve the light extraction efficiency.

In particular, the present invention can finely control the size of the particles forming the transparent electrode layer by adjusting the hydrogen ion concentration (pH) of the solution of the transparent electrode layer forming material used to form the transparent electrode layer, so that the refractive index is continuously changed By forming the transparent electrode layer, there is an effect that can improve the light extraction efficiency.

 In addition, the present invention, by using the Sol-Gel method instead of the sputtering method or e-beam deposition method used to form the conventional ITO transparent electrode, it is transparent by the synthesis / coating method instead of the conventional deposition method An electrode layer can be formed. Therefore, since the transparent electrode layer is formed at a relatively low temperature, the impact of the p-GaN layer is reduced when forming the transparent electrode layer, thereby reducing the defects at the interface between the p-GaN layer and the transparent electrode layer.

In addition, the Sol-Gel method has a simple manufacturing process compared to the conventional "e-beam deposition" or "Sputtering" method and has the effect of reducing the manufacturing cost.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

3 is a view showing the structure of a light emitting device according to a preferred embodiment of the present invention. Referring to FIG. 3, FIG. 3 (a) shows an overall cross section of the light emitting device of the present invention, and FIG. 3 (b) shows an enlarged cross section of the electrode layer 400 shown in FIG. Shown.

As shown in FIG. 3 (a), the nitride light emitting device of the present invention includes a buffer layer 302, an N-GaN layer 303, an active layer 304, and a P- on a substrate 301 such as sapphire or silicon. The GaN layer 305 is sequentially formed to form the nitride layer 300. The process of forming the nitride layer 300 may be formed in the same manner as the conventional method.

On the other hand, the electrode layer 400 is formed on the nitride layer 300, as shown in Figure 3 (b), the electrode layer 400 is composed of two or more transparent electrode layers. For convenience of description, the electrode layer 400 is illustrated as being composed of three transparent electrode layers 401, 402, and 403 in FIG. 3B, but may further include more transparent electrode layers.

Referring to (b) of FIG. 3, each of the plurality of transparent electrode layers is composed of particles of a predetermined size, and the size of such particles is the same in the same transparent electrode layer, but the sizes of the different transparent electrode layers are different from each other. . In addition, the transparent electrode layer adjacent to the nitride layer has a smaller particle size, so that the amount of voids is smaller. The larger the transparent electrode layer is remote from the nitride layer, the larger the particle size is, the larger the amount of voids.

In this case, when the particles of each transparent electrode layer are regularly and regularly arranged, the amount of voids will be the same regardless of the size of the particles, but in reality, the particles of each layer are arranged irregularly, so that the larger the particle size is, It can be seen experimentally that the amount of pores included increases, and the smaller the particle size, the smaller the amount of pores included in the transparent electrode layer.

On the other hand, the larger the amount of voids in the plurality of transparent electrode layers, the smaller the difference in refractive index with the phosphor material surrounding the outside of the air layer or the light emitting device. Therefore, since the amount of voids increases toward the upper transparent electrode layer of the electrode layer 400, the refractive index decreases, so that the difference in refractive index between the uppermost transparent electrode layer of the electrode layer 400 and air or an external phosphor becomes very small, and thus, the electrode layer 400. The total reflection at the interface between the air layer and the air layer can be significantly reduced.

FIG. 3 (c) is a diagram illustrating the light extraction efficiency at the interface between the electrode layer 400 and the air layer. As shown in FIG. 3 (c), the electrode layer 400 of the present invention gradually goes from bottom to top. Since the refractive index decreases, the difference between the refractive index of the electrode layer and the refractive index of the air layer becomes very small at the interface with the air layer, so that the critical angle at which total reflection occurs is very large. Therefore, it can be seen that most of the light introduced into the electrode layer 400 is leaked to the outside of the electrode layer 400 without causing total reflection to improve the light extraction efficiency.

4A to 4C illustrate a process of manufacturing a nitride light emitting device according to a preferred embodiment of the present invention. Hereinafter, a process of manufacturing a nitride light emitting device according to a preferred embodiment of the present invention will be described with reference to FIGS. 4A to 4C. However, the present invention is characterized by the structure of the electrode layer formed on the P-GaN layer and the method of forming the same, and the process of manufacturing other light emitting elements is similar to the above-described prior art. Therefore, the present invention will be described with a focus on the process of forming the electrode layer on the P-GaN layer.

First, referring further to FIG. 4A, a nitride layer 310 as shown in FIG. 3 is formed on a substrate 301 such as sapphire, SiC, GaN, etc. to manufacture the light emitting device of the present invention. ), An N-GaN layer 312, an active layer 313, and a P-GaN layer 314 are formed in this order to form a semiconductor substrate 300. However, in this step, in order to form an N-type electrode, etching may be performed from the P-GaN layer 314 downward so that a part of the N-GaN layer 312 is exposed, and then the following process may be performed.

Thereafter, a solution containing a material forming a transparent electrode layer on the P-GaN layer 314 formed in the semiconductor substrate 300 (hereinafter abbreviated as "semiconductor substrate" only) (hereinafter referred to as "transparent electrode layer solution"). ) Spin-coating or dip-coating in a Sol-Gel method to a thickness of 10 ~ 800nm, baking at a temperature of about 100 to 150 ℃ to evaporate the solvent to evaporate the transparent electrode layer (401 ).

In this case, as a material for forming the transparent electrode layer 401, all materials used to form the transparent electrode layer in the prior art may be used, but the preferred embodiment of the present invention forms a transparent electrode layer using an ITO material, Hereinafter, it will be exemplarily described that the transparent electrode layer is formed of an ITO material.

The transparent electrode layer solution is produced by mixing an indium source and a tin source in a solvent such as ethanol, and adding a basic reagent such as NH ₄ OH or NH ₃ having different molar concentrations in the process. At this time, the hydrogen ion concentration (pH) of the transparent electrode layer solution is adjusted by adjusting the concentration of the basic reagent, and the hydrogen ion concentration of the transparent electrode layer solution determines the size of the particles of the transparent electrode layer.

Specifically, the higher the hydrogen ion concentration (pH), the smaller the particle size of the transparent electrode layer formed in the baking process and the smaller the amount of pores of the transparent electrode layer, and thus the refractive index is increased. In addition, the lower the hydrogen ion concentration (pH), the larger the particle size of the transparent electrode layer formed in the baking process, the larger the amount of voids, the smaller the refractive index.

Meanwhile, after the transparent electrode layer is formed on the semiconductor substrate 300, as shown in FIG. 4B, the transparent electrode layer solution is coated and baked in the same manner as described above on the transparent electrode layer 401 to form another transparent electrode layer 402. ). At this time, the hydrogen ion concentration (pH) of the transparent electrode layer solution coated on the transparent electrode layer 401 is lower than the hydrogen ion concentration (pH) of the coated transparent electrode layer solution when the lower transparent electrode layer 401 is formed. As a result, in the baking process, particles larger than the particles of the lower transparent electrode layer 401 are formed in the transparent electrode layer 401 and the amount of voids is increased, so that the overall refractive index of the transparent electrode layer smaller than the transparent electrode layer 401 is lower. 402 is formed.

In addition, a new upper transparent electrode layer 403 is formed on the newly formed transparent electrode layer 402 by coating and baking a transparent electrode layer solution having a lower hydrogen ion concentration than the transparent electrode layer solution used to form the lower transparent electrode layer 402. According to the number of transparent electrode layers to be formed, the above-described process is repeated to form a plurality of transparent electrode layers as shown in FIG. 4B, and finally annealed at a temperature of about 300 to 600 ° C. to form the electrode layer 400. To complete.

Thereafter, as shown in FIG. 4C, the semiconductor substrate 300 is etched until the N-GaN layer is exposed from the electrode layer 400, and the ohmic contact is exposed to the upper portion of the electrode layer 400 by etching. To form a light emitting device.

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

1A and 1B illustrate a method of manufacturing a light emitting device according to the prior art.

2 is a diagram illustrating a problem of light extraction efficiency occurring according to the prior art.

3 is a view for explaining the structure and the luminous efficiency of the electrode layer of the light emitting device produced according to the preferred embodiment of the present invention.

4A to 4C illustrate a process of generating a nitride light emitting device according to a preferred embodiment of the present invention.

Claims (12)

A semiconductor substrate having a nitride layer formed thereon; And And a plurality of transparent electrode layers sequentially formed on the nitride layer to have particles of different sizes between each layer. The method of claim 1, wherein the plurality of transparent electrode layer And a particle size of the upper transparent electrode layer larger than a particle size of the lower transparent electrode layer adjacent to the nitride layer. The method of claim 1, wherein the plurality of transparent electrode layer The nitride light emitting device, characterized in that formed in order so that the amount of pores contained in the upper transparent electrode layer is larger than the amount of pores contained in the lower transparent electrode layer closer to the nitride layer. The method according to any one of claims 1 to 3, The plurality of transparent electrode layer is nitride light emitting device, characterized in that formed of indium tin oxide (ITO) material. (a) forming a nitride layer on the substrate; And (b) sequentially forming a plurality of transparent electrode layers having particles of different sizes between the layers in the nitride layer. The method of claim 5, wherein step (b) And forming the plurality of transparent electrode layers sequentially so that the size of the particles of the upper transparent electrode layer is larger than the size of the particles of the lower transparent electrode layer adjacent to the nitride layer. The method of claim 5, wherein step (b) And forming the plurality of transparent electrode layers sequentially so that the amount of voids included in the upper transparent electrode layer is greater than the amount of voids included in the lower transparent electrode layer adjacent to the nitride layer. . The method of claim 5, wherein step (b) (b1) forming a lower transparent electrode layer by coating and baking the transparent electrode layer solution on the nitride layer; And (b2) forming an upper transparent electrode layer by coating and baking a transparent electrode layer solution having a different hydrogen ion concentration (pH) on the lower transparent electrode layer and baking the coated transparent electrode layer solution to form the lower transparent electrode layer; A nitride light emitting device manufacturing method characterized in that. The method of claim 8, and (b3) performing the step (b2) by using the upper transparent electrode layer formed in the step (b2) as the lower electrode layer. The method of claim 9, And performing the step (b3) a plurality of times with respect to the transparent electrode layer formed below, to form the plurality of transparent electrode layers. The method according to any one of claims 8 to 10, The transparent electrode layer solution used to form the upper transparent electrode layer is a method of manufacturing a nitride light emitting device, characterized in that the hydrogen ion concentration (pH) is lower than the transparent electrode layer solution used to form the lower transparent electrode layer. The method according to any one of claims 5 to 10, The transparent electrode layer is a nitride light emitting device manufacturing method, characterized in that formed of indium tin oxide (ITO).

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