KR20060072391A - Led having roughness surface by etching - Google Patents

Abstract

The present invention relates to a light emitting diode having an anti-reflective transparent electrode layer, and more particularly, to an external quantum efficiency (EQE) for escaping photons formed inside the light emitting diode to the outside by forming a micro-sized roughness on the transparent electrode layer. The present invention relates to a light emitting diode having an anti-reflective transparent electrode layer having an increased a).

To this end, in the present invention, an N-type region layer, an active layer that emits light, a P-type region layer, and a transparent electrode are sequentially deposited on a substrate, and the N-type region layer and the P-type region are applied to external power. In the light emitting diode in which each electrode is disposed in the layer, the transparent electrode is etched to form an antireflection surface in order to minimize total reflection of light generated therein.

Total reflection, transparent electrode, external quantum efficiency, non-reflective surface

Description

Light Emitting Diode Having Anti-Reflective Transparent Electrode Layer {LED Having Roughness Surface by Etching}

1 is a cross-sectional view showing the structure of a general nitride-based light emitting diode.

2 is a graph showing light emission luminance values according to a forward current of a general nitride based light emitting diode.

3 is a cross-sectional view of a light emitting diode according to the present invention.

4A is a plan view of a light emitting diode according to the present invention;

4B is an enlarged view of a portion A of FIG. 4A.

4C is an enlarged view of a portion B of FIG. 4B.

Figure 5a is a structure of the formation of the non-reflective surface according to an embodiment of the present invention.

Figure 5b is a formation structure of the non-reflective surface according to an embodiment of the present invention.

Figure 6 is a graph showing the additional luminous efficiency due to the formation of the non-reflective surface compared to the vertex angle of the cone-shaped non-reflective surface according to an embodiment of the present invention.

Figure 7 is a graph showing the light emission luminance value of the forward current according to an embodiment of the present invention.

<Description of Symbols for Main Parts of Drawing>

10 substrate 20 N-type region layer

30: active layer 40: P-type region layer

50: transparent electrode 60: N-type electrode

70: P-type electrode 80: antireflective surface

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode having an antireflective transparent electrode, and more particularly to a light emitting diode having an antireflective treatment region on a transparent electrode layer to improve light extraction characteristics.

Recently, with the rapid development of information technology and mobile communication technology, the development of the display device that can visually display information is also progressing rapidly. The display device is a projection type, a direct view type, a virtual image type, a hologram, etc. according to its driving type. In addition, the direct-type display is classified into a non-emission type that can emit light by other external factors than a self-emission type display in which the material itself emits light.

In recent years, development trends such as LCD (Lyquid Crystal Display), PDP (Plasma Display Pannel), and organic EL (LED) have been developed to satisfy various requirements such as high brightness, high-speed response characteristics, high luminous intensity, and overall manufacturing process. Organic electroluminescent scents and light emitting diodes (LEDs) are rapidly replacing the existing display device market.

Among them, light emitting diodes (LEDs) are particularly widely used as light sources for displays having small size, low power consumption, high reliability, and the like. AlGaAs, GaAlP, GaP, InGaAlP, etc. Group 3-5 compound semiconductors using As and P as Group 5 elements are used for emitting red, orange, yellow, and green light, and GaN compound semiconductors are used for green, blue, and ultraviolet region. Thus, a light emitting diode having high light emission intensity has been realized.

Such a stacked structure of a gallium nitride-based light emitting diode device as shown in FIG. 1 includes an N-type region layer (GaN layer) 20, an active layer 30, and a P-type region layer on a sapphire substrate 10. (GaN layer) 40 is crystal-grown in sequence, and a portion is etched up to the N-type region layer 20 to form the N-type electrode 60, and the transparent electrode 50 on the front of the P-type region layer 40 Is deposited by depositing the N-type electrode 60 and the P-type electrode 80.

In the past, gallium nitride-based light emitting diode devices have a P-type region layer in which ohmic contact using a thin Ni / Au metal is a main method, and the absorption of light under a blue wavelength due to the use of Au metal is relatively large. Recently, a transparent electrode (TCO: Transparent Conductive Oxide) such as an Indium Thin Oxide (hereinafter referred to as "ITO") having a light transmittance superior to Ni / Au is used.

In such a general gallium nitride-based light emitting diode device, when a current is injected into the semiconductor light emitting diode via a voltage applied to a lead frame (not shown), the injected current is extended by a transparent electrode having high conductivity, and N It is injected into a type GaN layer and a P type GaN layer. The generation of energy hυ (h: Frank's constant, ν = c / λ, c: luminous flux, λ: wavelength) generated by the PN junction is emitted to the outside of the light emitting diode light emitting element.

In addition, the efficiency of light generated in the light emitting diode device is divided into internal quantum efficiency and external quantum efficiency. The internal quantum efficiency is determined by the design and quality of the active layer, and in the case of external quantum efficiency, the light generated in the active layer emits light. It is determined according to the degree of coming out of the diode light emitting device, and the external quantum efficiency may be determined by the refractive index and the critical angle.

That is, in the case of external quantum efficiency, GaN (gallium nitride) material having a constant refractive index or sapphire should not exceed a critical angle in order to emit light into the air having a refractive index of 1, and light is emitted between the GaN and the air having different refractive indices. The critical angle of the escaped escape angle is represented by θ _C = sin ⁻¹ (N ₁ / N ₂ ), and the critical angle when light propagates from the gallium nitride (GaN) into the air having a refractive index of 1 is about 24.6 °.

If the light generated at an angle above the critical angle is returned to the inside of the chip, the result is trapped inside the chip, and the absorption of light in the gallium nitride and the sapphire wafer, the substrate, reduces the external quantum efficiency.

For these reasons, even with the use of high quality semiconductor materials, the ratio of photons generated inside the light emitting diodes and finally emitted to the atmosphere still has a small limit.

The present invention has been invented to solve the above problems, by forming a micro-sized antireflection surface (roughness) in the transparent electrode layer (antireflective treatment to increase the external quantum efficiency (EQE) to escape the photons formed inside the light emitting diode to the outside) It is an object to provide a light emitting diode having a transparent electrode layer.

The present invention has the following features to achieve the above object.

According to the present invention, an N-type region layer, an active layer that emits light, a P-type region layer, and a transparent electrode are sequentially deposited on a substrate, and an N-type region layer and a P-type region layer are applied to an external power source. In the light emitting diode in which each electrode is disposed, the transparent electrode is etched to form an antireflection surface in order to minimize total reflection of light generated therein.

Hereinafter, one preferred embodiment according to the present invention will be described in detail with reference to the accompanying drawings. First, like reference numerals designate functionally identical or similar parts throughout the drawings.

3 is a cross-sectional view of a light emitting diode according to an embodiment of the present invention, FIG. 4A is a plan view according to FIG. 3, FIG. 4B is an enlarged view of a portion A of FIG. 4A, and FIG. 4C is an enlarged view of a B portion of FIG. 4B. 5A is a structural diagram of an antireflection surface according to an embodiment of the present invention, and FIG. 5B is a structural diagram of an antireflection surface according to another embodiment of the present invention.

Referring to the drawings, an N-type region layer 20, an active layer 30 for emitting light, a P-type region layer 40, and a transparent electrode 50 are sequentially deposited on the substrate 10. The electrodes 60 and 70 are disposed in the N-type region layer 20 and the P-type region layer 30 so that external power is applied.

Here, an antireflection surface 80 is formed on the transparent electrode 50 to minimize the total reflection of photons generated therein.

The non-reflective surface 80 is a surface that is made of irregularities about the length of the light wavelength emitted to the outside, and transmits most of the light regardless of the incident angle according to Fresnel's law.

The total thickness of the transparent electrode 50 on which the anti-reflective surface 80 is formed is deposited to about 1000 kPa to 5000 kPa, wherein the anti-reflective surface 80 is formed to a thickness of about 2000 kPa when the thickness of the transparent electrode is 4000 kPa.

The transparent electrode 50 is deposited on the P-type region layer for smooth current flow in the P-type region layer, and is generally indium oxide (InO), cadmium oxide (CdO), tin oxide (SnO ₂ ), and zinc oxide. It is deposited using (ZnO) or the like, and preferably indium oxide having high light transmittance is used.

The formation structure of the anti-reflective surface 80 formed according to this is shown as etched along the GRAIN of the transparent electrode before etching.

As in the embodiment of the present invention, it may have a shape similar to a cone, but may have the same shape as other embodiments, and may be represented by various forming structures different from the above shape.

In addition, in order to form the anti-reflective surface 80, the roughness metal may be deposited on the transparent electrode 50, heat treated at a high temperature, and then formed by physical and chemical operations using an etching solution.

In addition, by treating the bonding density differently in the deposition step of the transparent electrode 50 can be formed by using the difference in the degree of chemical reaction according to the etching.

As such, the method and the structure of the formation of the non-reflective surface 80 may be various, and the present invention is not limited thereto.

Figure 2 is a graph showing the light emission luminance value according to the forward current of a conventional nitride-based light emitting diode, Figure 6 shows the additional luminous efficiency due to the formation of the non-reflective surface compared to the vertex angle of the cone-reflective surface according to an embodiment of the present invention 7 is a graph showing the luminance value of the forward current versus the luminance according to an embodiment of the present invention.

Referring to the drawings, the light emission luminance value of the general nitride-based light emitting diode and the light emission luminance value according to an embodiment of the present invention increases as the current value increases, and the cone tip angle is increased when the non-reflective surface 80 has a cone structure. The smaller the value, the higher the luminous efficiency.

Preferred cone angle is 5 ° ~ 50 ° and the highest luminous efficiency appears at this time.

According to the present invention, the transparent electrode layer is finely controlled and etched to form an anti-reflective surface having a micro size, thereby minimizing total reflection of photons generated therein, and appropriately reducing a large difference in refractive index between the P-type region layer and air.

As a result, the external quantum efficiency of escaping photons formed inside the light emitting diode to the outside is increased by twice as much as when using a flat transparent electrode.

Claims (3)

The N-type region layer 20, the active layer 30 emitting light, the P-type region layer 40, and the transparent electrode 50 are sequentially deposited on the substrate 10, and external power is applied. In the light emitting diode in which the electrodes 60 and 70 are disposed in the N-type region layer 20 and the P-type region layer 30, A light emitting diode having an anti-reflective transparent electrode layer, characterized in that to form a non-reflective surface (80) by etching the transparent electrode 50 to minimize the total reflection of the light generated therein. The method of claim 1, The light emitting diode having the anti-reflective transparent electrode layer, characterized in that the vertex angle of the anti-reflective surface (80) having a conical structure of the anti-reflective surface (80) is 5 ° ~ 50 °. The method of claim 1, The thickness of the transparent electrode 50 is a light emitting diode having an anti-reflective transparent electrode layer, characterized in that 1000 ~ 5000Å.

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