KR102421964B1 - Light emitting device - Google Patents

Abstract

The embodiment relates to a light emitting device in which a driving voltage is reduced by improving step coverage of a transparent electrode layer, comprising a first semiconductor layer, an active layer, and a second semiconductor layer sequentially disposed on a first surface of a substrate light emitting structures; a first electrode electrically connected to the first semiconductor layer; a current blocking layer disposed on the second semiconductor layer; a first transparent conductive pattern completely surrounding the current blocking layer; a second transparent conductive pattern overlapping the first transparent conductive pattern and disposed on an upper surface of the second semiconductor layer; and a second electrode overlapping the second semiconductor layer with the current blocking layer interposed therebetween and electrically connected to the second semiconductor layer.

Description

Light emitting device {LIGHT EMITTING DEVICE}

An embodiment of the present invention relates to a light emitting device having a reduced driving voltage.

A light emitting diode (LED) is one of light emitting devices that emits light when an electric current is applied thereto. Light-emitting diodes can emit high-efficiency light with low voltage, and thus have excellent energy-saving effects. Recently, the luminance problem of light emitting diodes has been greatly improved, and it has been applied to various devices such as a backlight unit of a liquid crystal display device, an electric signboard, a display device, and a home appliance.

The light emitting diode may have a structure in which the first electrode and the second electrode are disposed on one side of the light emitting structure including the first semiconductor layer, the active layer, and the second semiconductor layer. However, in order to easily transfer the carriers of the second electrode to the active layer, a current blocking layer (CBL) may be further disposed between the second electrode and the second semiconductor layer. The current blocking layer is for changing a movement path of carriers injected from the second electrode.

However, due to the thickness of the current blocking layer, a problem in that the step coverage of the transparent electrode layer disposed between the current blocking layer and the second electrode is deteriorated may occur.

1 is a photograph in which a part of a transparent electrode layer is not formed.

As shown in FIG. 1 , when the step applicability of the transparent electrode layer 1 is lowered by the current blocking layer, the transparent electrode layer 10 is not formed (region A) in the region overlapping the current blocking layer. That is, there may be a problem that the transparent electrode layer 1 does not completely cover the current blocking layer. In this case, it becomes difficult to easily inject carriers injected from the second electrode into the second semiconductor layer, and thus the driving voltage may increase.

An object of the present invention is to provide a light emitting device having a reduced driving voltage by improving step coverage of a transparent electrode layer.

The light emitting device according to an embodiment of the present invention includes: a light emitting structure including a first semiconductor layer, an active layer, and a second semiconductor layer sequentially disposed on a first surface of a substrate; a first electrode electrically connected to the first semiconductor layer; a current blocking layer disposed on the second semiconductor layer; a first transparent conductive pattern completely surrounding the current blocking layer; a second transparent conductive pattern overlapping the first transparent conductive pattern and disposed on an upper surface of the second semiconductor layer; and a second electrode overlapping the second semiconductor layer with the current blocking layer interposed therebetween and electrically connected to the second semiconductor layer.

In the light emitting device of the present invention, the transparent electrode layer disposed between the second electrode and the second semiconductor layer is formed in a structure in which the first and second transparent conductive patterns are stacked, so that the step coverage of the transparent electrode layer is reduced. it can be prevented Accordingly, by forming the second transparent conductive pattern to be thin, the amount of light emitted in the direction of the second semiconductor layer increases, so that the driving voltage can be reduced.

1 is a photograph in which a part of a transparent electrode layer is not formed.
2A is a plan view of a light emitting device according to an embodiment of the present invention.
FIG. 2B is a cross-sectional view taken along line I-I' of FIG. 2A.
FIG. 3 is an enlarged view of area B of FIG. 2B .
4 is a cross-sectional view of a light emitting device according to another embodiment of the present invention.
5A to 5D are cross-sectional views of a process of forming the transparent electrode layer of FIG. 2B.

Since the present invention may have various changes and may have various embodiments, specific embodiments will be illustrated and described in the drawings. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

Terms including an ordinal number, such as first, second, etc., may be used to describe various elements, but the elements are not limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the second component may be referred to as the first component, and similarly, the first component may also be referred to as the second component. and/or includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being “connected” or “connected” to another component, it may be directly connected or connected to the other component, but it is understood that other components may exist in between. it should be On the other hand, when it is said that a certain element is "directly connected" or "directly connected" to another element, it should be understood that no other element is present in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It is to be understood that this does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

Hereinafter, the embodiment will be described in detail with reference to the accompanying drawings, but the same or corresponding components are given the same reference numerals regardless of reference numerals, and overlapping descriptions thereof will be omitted.

Hereinafter, the light emitting device of the embodiment will be described in detail with reference to the accompanying drawings.

2A is a plan view of a light emitting device according to an embodiment of the present invention, and FIG. 2B is a cross-sectional view taken along line I-I' of FIG. 2A. And, FIG. 3 is an enlarged view of area B of FIG. 2B .

2a, 2b and 3, the light emitting device of the embodiment of the present invention is disposed on the substrate 100, and includes a first semiconductor layer 110a, an active layer 110b, and a second semiconductor layer 110c. The light emitting structure 110, the first electrode 120 electrically connected to the first semiconductor layer 110a, the current blocking layer 150 and the current blocking layer 150 disposed on the second semiconductor layer 110c The first transparent conductive pattern 140a completely surrounding, the second transparent conductive pattern 140b completely surrounding the first transparent conductive pattern 140a, the first transparent conductive pattern 140a and the second transparent conductive pattern 140b are interposed between and a second electrode 130 overlapping the second semiconductor layer 110c.

The substrate 100 may be formed of a material selected from sapphire (Al ₂ O ₃ ), SiC, GaAs, GaN, ZnO, Si, GaP, InP and Ge, but is not limited thereto. In addition, the concave-convex pattern 100a is formed on the surface of the substrate 100 to disperse light emitted from the light emitting structure 110 disposed on the first surface of the substrate 100 to improve light emitting characteristics. In particular, although the drawing shows that the concave-convex pattern 100a is regular, the concave-convex pattern 100a may be an irregular pattern.

In this case, the reflective pattern 200 may be disposed on the second surface of the substrate 100 opposite to the first surface. The reflective pattern 200 is for reflecting the light incident on the substrate 100, among the light emitted from the active layer 110b, in the direction of the light emitting structure 110 . In this case, the reflective pattern 200 is composed of a Distributed Bragg Reflector Layer (DBR), or includes a metal such as Ag or Al or a metal oxide such as TiO ₂ , Al ₂ O ₃ and ZrO ₂ . You may.

The DBR layer may have a structure in which two materials having different refractive indices are alternately stacked. The DBR layer may be formed by repeating a first layer having a high refractive index and a second layer having a low refractive index. Both the first and second layers may be dielectrics, and the high and low refractive indices of the first and second layers may be relative refractive indices. When the reflective pattern 200 is formed of a DBR layer, light passing through the substrate 100 is reflected by a difference in refractive index between the first layer and the second layer of the reflective pattern 200 and travels in the direction of the light emitting structure 110 . can

In addition, the light emitting structure 110 may be disposed on the first surface of the substrate 100 as described above. Although not shown, a buffer layer may be further formed between the substrate 100 and the light emitting structure 110 . The buffer layer is to increase the stability of the light emitting device by reducing the difference in the lattice constant and the coefficient of thermal expansion between the substrate 100 and the first semiconductor layer 110a. The buffer layer may be formed by growing an undoped nitride semiconductor. When the first semiconductor layer 110a is grown on a buffer layer made of an undoped nitride semiconductor, the crystallinity of the first semiconductor layer 110a may be improved. . In this case, the material of the buffer layer is not limited thereto.

The first semiconductor layer 110a may be implemented with a compound semiconductor such as Group III-5, Group II-6, or the like, and may be doped with a first conductivity type dopant. For example, the first semiconductor layer 110a may be a semiconductor having a composition formula of InxAlyGa1-x-yN (0≤x≤1, 0≤y≤1, 0≤x+y≤1), Si, Ge , Sn, etc. may be doped with an n-type dopant.

The active layer 110b may generate light by energy generated in the recombination process of electrons and holes, which are carriers provided from the first semiconductor layer 110a and the second semiconductor layer 110c. can The active layer 110b may be a semiconductor compound, for example, a group 3-5 or group 2-6 compound semiconductor, and may have a single well structure, a multi-well structure, a quantum-wire structure, or a quantum dot. (Quantum Dot) structure may be formed.

When the active layer 110b has a quantum well structure, a well layer having a composition formula of InxAlyGa1-x-yN (0≤x≤1, 0≤y≤1, 0≤x+y≤1) and InaAlbGa1-a-bN ( It may have a single or quantum well structure having a barrier layer having a compositional formula of 0≤a≤1, 0≤b≤1, 0≤a+b≤1). The well layer may be a material having a band gap lower than the energy band gap of the barrier layer.

The second semiconductor layer 110c may be implemented with a compound semiconductor such as Group III-5, Group II-6, or the like, and may be doped with a second conductivity type dopant. For example, the second semiconductor layer 110c may be a semiconductor having a composition formula of InxAlyGa1-x-yN (0≤x≤1, 0≤y≤1, 0≤x+y≤1), Mg, Zn , Ca, Sr, Ba, etc. may be doped with p-type dopants.

The light emitting structure 110 as described above may be formed of at least any one of np, pn, npn, and pnp junction structures. It may have a variety of structures including In addition, doping concentrations of impurities in the first semiconductor layer 110a and the second semiconductor layer 110c may be uniformly or non-uniformly formed. That is, the doped structure of the light emitting structure 110 may be formed in various ways, but is not limited thereto.

The first electrode 120 and the second electrode 130 are electrically connected to the first semiconductor layer 110a and the second semiconductor layer 110c, respectively. In particular, a current blocking layer (CBL) 150 may be further disposed between the second electrode 130 and the second semiconductor layer 110c. The current blocking layer 150 is for changing the movement path of carriers injected from the second electrode 130, and may be made of a metal capable of forming a Schottky contact with the second semiconductor layer 110c. have.

For example, the current blocking layer 150 may be formed of at least one of titanium (Ti), zirconium (Zr), chromium (Cr), gold (Au), or tungsten (W) or an alloy including at least one. have. Also, the current blocking layer 150 may be formed of a dielectric material such as SiOx, SiON, SixNy, or the like, but is not limited thereto.

When the current blocking layer 150 further includes a reflective material, light is reflected between the second electrode 130 and the reflective pattern 200 , so that light extraction efficiency may be improved. The reflective material is composed of a Distributed Bragg Reflector Layer (DBR) like the above-described reflective pattern 200, or includes a metal such as Ag or Al or a metal oxide such as TiO ₂ , Al ₂ O ₃ and ZrO ₂ may be, but is not limited thereto.

Furthermore, the transparent electrode layer 140 is disposed between the second electrode 130 and the second semiconductor layer 110c, so that carriers of the second electrode 130 pass through the transparent electrode layer 140 to the second semiconductor layer 110c. It can be smoothly injected into the entire area of However, when the thickness of the current blocking layer 150 is too thick, the step coverage of the transparent electrode layer 140 is deteriorated due to the step difference of the current blocking layer 150 . Accordingly, the transparent electrode layer 140 may not be partially formed in the region overlapping the current blocking layer 150 . In order to prevent this, when the transparent electrode layer 140 is formed thickly, when light is emitted to the upper surface of the light emitting device on which the first and second electrodes 120 and 130 are disposed, light emission efficiency by the transparent electrode layer 140 this is lowered

Accordingly, in the embodiment of the present invention, the transparent electrode layer 140 is formed in a structure in which the first transparent conductive pattern 140a and the second transparent conductive pattern 140b are sequentially stacked.

Specifically, the first transparent conductive pattern 140a and the second transparent conductive pattern 140b are ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), AZO (Aluminum Zinc Oxide), AGZO (Aluminum Gallium Zinc Oxide), IZTO(Indium Zinc Tin Oxide), IAZO(Indium Aluminum Zinc Oxide), IGZO(Indium Gallium Zinc Oxide), IGTO(Indium Gallium Tin Oxide), ATO(Antimony Tin Oxide), GZO(Gallium Zinc Oxide), NitIZON ), ZnO, IrOx, RuOx, and transparent conductive oxides such as NiO.

The first transparent conductive pattern 140a may be disposed between the second transparent conductive pattern 140b and the current blocking layer 150 . The first transparent conductive pattern 140a is used to prevent the second transparent conductive pattern 140b from being partially unformed when the second transparent conductive pattern 140b is directly formed on the current blocking layer 150 . , the first transparent conductive pattern 140a functions to compensate for the step difference between the current blocking layer 150 and the second semiconductor layer 110c.

Accordingly, when the thickness of the first transparent conductive pattern 140a is too thin, the first transparent conductive pattern 140a may be partially unformed due to the thickness of the current blocking layer 150 . In addition, when the thickness of the first transparent conductive pattern 140a is too thick, the second transparent conductive pattern 140b may be partially unformed by the first transparent conductive pattern 140a.

To this end, the thickness of the first transparent conductive pattern 140a satisfies Equation 1 below. In this case, T1 is the thickness of the first transparent conductive pattern, and T _C is the thickness of the current blocking layer.

In addition, in order for the first transparent conductive pattern 140a to compensate for the step difference between the current blocking layer 150 and the second semiconductor layer 110c, the first transparent conductive pattern 140a completely covers the edge of the current blocking layer 150 . It should have a structure in which the edge of the first transparent conductive pattern 140a extends beyond the edge of the current blocking layer 150 . At this time, in consideration of the process margin of the first transparent conductive pattern 140a, the interval d between the edge of the first transparent conductive pattern 140a and the edge of the current blocking layer 150 is 4 μm to 10 μm. desirable.

In addition, a second transparent conductive pattern 140b may be disposed on the second semiconductor layer 110c to completely cover the first transparent conductive pattern 140a. In this case, the second transparent conductive pattern 140b preferably has a thickness smaller than that of the first transparent conductive pattern 140a.

The second transparent conductive pattern 140b is formed to prevent a change in the degree of carrier injection in the second semiconductor layer 110c in the region relatively spaced apart from the second semiconductor layer 110c in the region adjacent to the second electrode 130 . For this purpose, it may be formed to extend from the upper surface of the second semiconductor layer 110c to a region adjacent to the first electrode 120 .

At this time, since the thickness of the second transparent conductive pattern 140b is thinner than that of the first transparent conductive pattern 140a, the light generated in the active layer 110b is partially absorbed by the second transparent conductive pattern 140b. can be prevented In addition, since the transparent electrode layer 140 has a structure in which the first and second transparent conductive patterns 140a and 140b are stacked, the step coverage of the transparent electrode layer 140 is reduced due to the step difference of the current blocking layer 150 . deterioration can be prevented.

The second transparent conductive pattern 140b as described above may have a structure that does not completely cover the first transparent conductive pattern 140a.

4 is a cross-sectional view of a light emitting device according to another embodiment of the present invention.

4 , the second transparent conductive pattern 140b may expose a portion of the upper surface of the first transparent conductive pattern 140a. The drawing illustrates that the second transparent conductive pattern 140b overlaps the first transparent conductive pattern 140a of the region disposed on the upper surface of the second semiconductor layer 110c. In this case, the upper surface of the first transparent conductive pattern 140a may be directly connected to the second electrode 130 .

Hereinafter, a method of manufacturing the transparent electrode layer 140 according to an embodiment of the present invention will be described in detail.

5A to 5D are cross-sectional views of a process of forming the transparent electrode layer of FIG. 2B.

As shown in FIG. 5A , a photoresist pattern 300 exposing the current blocking layer 150 is formed on the second semiconductor layer 110c. In this case, the photoresist pattern 300 has a structure in which the upper surface protrudes from the lower surface than the lower surface at the edge.

Accordingly, as shown in FIG. 5B , when the transparent conductive material 400 is formed on the entire surface of the second semiconductor layer 110c including the photoresist pattern 300 , the transparent conductive material 400 is formed at the edge of the photoresist pattern 300 . may be separated, and accordingly, the transparent conductive material 400 formed on the photoresist pattern 300 and the transparent conductive material 400 surrounding the current blocking layer 150 may be separated from each other.

Then, as shown in FIG. 5C , the first transparent conductive pattern 140a surrounding the current blocking layer 150 may be formed, and the photoresist pattern 300 may be removed. Meanwhile, the first transparent conductive pattern 140a may be formed using a general photolithography process. That is, the transparent conductive material 400 is formed on the entire surface of the second semiconductor layer 110c including the current blocking layer 150, and the transparent conductive material 400 is formed only in the region surrounding the current blocking layer 150 using a photoresist pattern ( The transparent conductive material 400 may be partially removed so that 400 ) remains.

Next, as shown in FIG. 5D , a second transparent conductive pattern 140b is formed on the first transparent conductive pattern 140a. The second transparent conductive pattern 140b may be formed of the same material as the first transparent conductive pattern 140a. The second transparent conductive pattern 140b may be formed by forming a transparent conductive material on the entire surface of the second semiconductor layer 110c to cover the first transparent conductive pattern 140a and patterning the same. In this case, the second transparent conductive pattern 140b may have a thickness smaller than that of the first transparent conductive pattern 140a, but is not limited thereto.

Although the drawing shows that the second transparent conductive pattern 140b completely surrounds the first transparent conductive pattern 140a, the second transparent conductive pattern 140b exposes a portion of the upper surface of the first transparent conductive pattern 140a. It may be formed to do so.

Table 1 below is a table comparing the performance of a general light emitting device in which a single transparent electrode layer is disposed on a current blocking layer and the performance of the light emitting device of the embodiment of the present invention. A typical light emitting device arranges a transparent electrode layer having a thickness of 20 nm on a current blocking layer, and the embodiment of the present invention has a first transparent conductive pattern having a thickness of 50 nm and a second transparent conductive pattern having a thickness of 20 nm on the current blocking layer The patterns were stacked one after the other.

At this time, as shown in Table 1, when the general light emitting device and the light emitting device according to the embodiment of the present invention have the same light output, the driving voltage of the light emitting device according to the embodiment of the present invention may be lower than that of the general light emitting device.

Driving voltage (VF) Light output (Po) common light emitting device 3.08 (100%) 32.89 (100%) Light emitting device of embodiment of the present invention 3.07 (99.9%) 32.89 (100%)

In this case, when the transparent electrode layer is thinly formed in order to improve the light emission efficiency of a general light emitting device, the step coverage of the transparent electrode layer is lowered, so that the carrier is transferred from the second electrode to the second semiconductor layer. Injection is not smooth. Conversely, when the transparent electrode layer is thickly formed, it is possible to prevent deterioration of the step applicability of the transparent electrode layer, but the light extraction efficiency is reduced, and thus the driving voltage is increased.

However, in the embodiment of the present invention, since the transparent electrode layer 140 is formed by stacking the first and second transparent conductive patterns 140a and 140b, the second transparent conductive pattern surrounding the upper surface of the second semiconductor layer 110c ( 140b) may be formed thinner than the first transparent conductive pattern 140a. Accordingly, the step applicability of the transparent electrode layer 140 can be improved and light output from being reduced can be prevented. That is, the present invention can reduce the driving voltage.

The light emitting device according to the embodiment of the present invention as described above may further include an optical member such as a light guide plate, a prism sheet, and a diffusion sheet to function as a backlight unit. In addition, the light emitting device of the embodiment may be further applied to a display device, a lighting device, and an indicator device.

In this case, the display device may include a bottom cover, a reflector, a light emitting module, a light guide plate, an optical sheet, a display panel, an image signal output circuit, and a color filter. The bottom cover, the reflector, the light emitting module, the light guide plate, and the optical sheet may form a backlight unit.

The reflector is disposed on the bottom cover, and the light emitting module emits light. The light guide plate is disposed in front of the reflection plate to guide the light emitted from the light emitting device forward, and the optical sheet includes a prism sheet and the like, and is disposed in front of the light guide plate. A display panel is disposed in front of the optical sheet, an image signal output circuit supplies an image signal to the display panel, and a color filter is disposed in front of the display panel.

In addition, the lighting device may include a light source module including a substrate and the light emitting device of the embodiment, a heat dissipation unit for dissipating heat of the light source module, and a power supply unit for processing or converting an electrical signal provided from the outside and providing it to the light source module. . Furthermore, the lighting device may include a lamp, a head lamp, or a street lamp.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and it is conventional in the art to which the present invention pertains that various substitutions, modifications and changes are possible within the scope without departing from the technical spirit of the embodiments. It will be clear to those who have knowledge.

100: substrate 100a: uneven pattern
110: light emitting structure 110a: first semiconductor layer
110b: active layer 110c: second semiconductor layer
120: first electrode 130: second electrode
140: transparent electrode layer 140a: first transparent conductive pattern
140b: second transparent conductive pattern 150: current blocking layer
200: reflection pattern 300: photoresist pattern
400: transparent conductive material

Claims (12)

a light emitting structure including a first semiconductor layer, an active layer, and a second semiconductor layer sequentially disposed on a first surface of a substrate;
a first electrode electrically connected to the first semiconductor layer;
a current blocking layer disposed on the second semiconductor layer;
a first transparent conductive pattern completely surrounding the current blocking layer;
a second transparent conductive pattern overlapping the first transparent conductive pattern and disposed on an upper surface of the second semiconductor layer; and
and a second electrode overlapping the second semiconductor layer with the current blocking layer interposed therebetween and electrically connected to the second semiconductor layer,
A light emitting device in which the first and second transparent conductive patterns are made of the same material. The method of claim 1,
The second transparent conductive pattern completely surrounds the first transparent conductive pattern, the second electrode is in direct contact with the second transparent conductive pattern, the second electrode is the current blocking layer, the first transparent conductive pattern and A light emitting device electrically connected to the second semiconductor layer through the second transparent conductive pattern. The method of claim 1,
A light emitting device in which the second transparent conductive pattern overlaps an edge of the first transparent conductive pattern to expose an upper surface of the first transparent conductive pattern, and the second electrode is in direct contact with the first transparent conductive pattern. The method of claim 1,
Further comprising a reflection pattern comprising a DBR layer (Distributed Bragg Reflector Layer) disposed on a second surface opposite to the first surface of the substrate,
The reflective pattern is a light emitting device including a metal including Ag or Al, or a metal oxide including TiO ₂ , Al ₂ O ₃ and ZrO ₂ . The method of claim 1,
A thickness of the current blocking layer and the first transparent conductive pattern satisfies Equation 1 below.
[Equation 1]

(T1 is the thickness of the first transparent conductive pattern, T _C is the thickness of the current blocking layer)

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