KR101617951B1 - Light emitting device and method of fabricating the same - Google Patents

Abstract

A light emitting element is provided. The light emitting device includes a first semiconductor layer of a first conductivity type, an active layer on the first semiconductor layer, a second semiconductor layer of a second conductivity type, disposed on the active layer, and a second semiconductor layer A core portion having a refractive index smaller than that of the second semiconductor layer, and a rod structure having a shell portion covering the core portion and having a refractive index smaller than that of the core portion.

Description

TECHNICAL FIELD The present invention relates to a light emitting device,

The present invention relates to a light emitting device and a manufacturing method thereof, and more particularly to a light emitting device including a core and a rod structure including a shell portion covering the core portion and having a lower refractive index than the core portion, and a method of manufacturing the same.

2. Description of the Related Art A light-emitting diode (LED) is a kind of pn junction diode, which is a semiconductor device using electroluminescence, which is a phenomenon in which a monochromatic light is emitted when a voltage is applied in a forward direction. The wavelength of the emitted light is determined by the bandgap energy (Eg) of the material used. Particularly, in recent years, light emitting devices made of a nitride based semiconductor material are being commercialized.

In order to improve the light extraction efficiency of such a light emitting device, various techniques have been developed. For example, in Korean Patent Laid-Open Publication No. 10-2007-0075592 (Application No. 10-2006-0004013), an upper surface separated from a mother substrate after being grown on a mother substrate having an uneven surface has an inverted phase of the uneven surface of the mother substrate Discloses a technique for fabricating a light emitting diode including an uneven first semiconductor layer to prevent light loss due to internal reflection and to improve light extraction efficiency.

Conventionally, methods for improving the light extraction efficiency of a light emitting device have been proposed in which the critical angle that can escape from the light emitting device is increased to increase the total internal reflection of light generated at the interface between the uppermost layer of the light emitting device and the air internal reflection. However, since there is Fresnel reflection due to a difference in refractive index between the uppermost layer of the light emitting element and air, there is a limit to improvement in light extraction of the light emitting element. In addition, these methods are problematic in that they are complicated, complicated, and expensive in practical application.

Korean Patent Publication No. 10-2007-0075592

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light emitting device having improved luminous efficiency and a method of manufacturing the same.

It is another object of the present invention to provide a light emitting device having improved light extraction efficiency and a method of manufacturing the same.

In order to solve the above technical problem, the present invention provides a light emitting device.

According to one embodiment, the light emitting device includes a first semiconductor layer of a first conductivity type, an active layer on the first semiconductor layer, a second semiconductor layer of a second conductivity type disposed on the active layer, A rod structure disposed on the semiconductor layer and having a refractive index smaller than that of the second semiconductor layer and a shell portion covering the core portion and having a refractive index smaller than that of the core portion, . ≪ / RTI >

According to an embodiment, the refractive index difference between the shell part and the core part may be at least 0.35 or more.

According to one embodiment, the core portion and the shell portion may be formed of different metal oxides.

According to one embodiment, the core portion comprises zinc oxide, and the shell portion may comprise aluminum oxide.

According to one embodiment, the rod structure is provided on the second semiconductor layer in plurality, and the plurality of rod structures may include being spaced from each other.

According to one embodiment, the core portion may include direct contact with the second semiconductor layer.

In order to accomplish the above object, the present invention provides a method of manufacturing a light emitting device.

According to one embodiment, a method of manufacturing a light emitting device includes preparing a structure in which a first semiconductor layer of a first conductivity type, an active layer, and a second semiconductor layer of a second conductivity type are sequentially stacked, Providing the mixed solution on the second semiconductor layer of the structure to produce a core portion formed of a metal oxide on the second semiconductor layer and forming a shell portion covering the core portion, . ≪ / RTI >

According to one embodiment, the shell portion may comprise being formed by atomic layer deposition.

According to one embodiment, the shell portion may have a refractive index smaller than that of the core portion, and the core portion may have a refractive index smaller than that of the second semiconductor layer.

According to one embodiment, the core portion may be formed of zinc oxide, and the shell portion may be formed of aluminum oxide.

The light emitting device according to an embodiment of the present invention may include a rod structure having a first semiconductor layer, an active layer, a second semiconductor layer, and a core portion and a shell portion sequentially stacked. The refractive index of the core portion may be smaller than the refractive index of the second semiconductor layer and the refractive index of the shell portion may be smaller than the refractive index of the core portion. Accordingly, Fresnel reflection of light emitted from the active layer is minimized, and a light emitting device having improved light extraction efficiency can be provided.

1 is a perspective view illustrating a light emitting device according to an embodiment of the present invention.
2 is a cross-sectional view illustrating a light emitting device according to an embodiment of the present invention.
3 is a flowchart illustrating a method of manufacturing a light emitting device according to an embodiment of the present invention.
4 is a SEM photograph of a rod structure included in a light emitting device according to an embodiment of the present invention.
5 is a graph illustrating the light emission intensity of the light emitting device according to the embodiment of the present invention.
FIG. 6 is a graph illustrating a difference in refractive index between a core portion and a shell portion included in a light emitting device according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the technical spirit of the present invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments disclosed herein are provided so that the disclosure can be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

In this specification, when an element is referred to as being on another element, it may be directly formed on another element, or a third element may be interposed therebetween. Further, in the drawings, the thicknesses of the films and regions are exaggerated for an effective explanation of the technical content.

Also, while the terms first, second, third, etc. in the various embodiments of the present disclosure are used to describe various components, these components should not be limited by these terms. These terms have only been used to distinguish one component from another. Thus, what is referred to as a first component in any one embodiment may be referred to as a second component in another embodiment. Each embodiment described and exemplified herein also includes its complementary embodiment. Also, in this specification, 'and / or' are used to include at least one of the front and rear components.

The singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. It is also to be understood that the terms such as " comprises "or" having "are intended to specify the presence of stated features, integers, Should not be understood to exclude the presence or addition of one or more other elements, elements, or combinations thereof. Also, in this specification, the term "connection " is used to include both indirectly connecting and directly connecting a plurality of components.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

FIG. 1 is a perspective view illustrating a light emitting device according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view illustrating a light emitting device according to an embodiment of the present invention.

1 and 2, a light emitting device according to an embodiment of the present invention includes a substrate 100, a first semiconductor layer 110 on the substrate 100, an active layer 115 on the first semiconductor layer 110, ), A second semiconductor layer 120 on the active layer 115, and a plurality of rod structures (NR) on the second semiconductor layer 120. Although not shown in FIGS. 1 and 2, a first electrode connected to the first semiconductor layer 110 and a second electrode connected to the second semiconductor layer 120 may be further provided.

The substrate 100 may be formed of any one of sapphire (Al ₂ O ₃ ), GaN, SiC, Si, ZnO, GaAs, InP, Ge, Ga ₂ O ₃ , ZrB ₂ or GaP. According to one embodiment, the substrate 100 may be flexible.

The first semiconductor layer 110 may be doped with a dopant of the first conductivity type. According to one embodiment, the first semiconductor layer 110 may be an N-type semiconductor layer doped with an N-type dopant. For example, the N-type dopant may include at least one of silicon (Si), germanium (Ge), tin (Sn), tellurium (Te), and selenium (Se) ) May include at least one of GaN, AlN, AlGaN, InGaN, InN, InAlGaN, and AlInN doped with the N-type dopant.

Although not shown in FIGS. 1 and 2, an undoped semiconductor layer may be further disposed between the first semiconductor layer 110 of the first conductivity type and the substrate 100. In this case, the first semiconductor layer 110 may be formed by an epitaxial process using the undoped semiconductor layer as a seed layer. According to one embodiment, the undoped semiconductor layer may be formed of an undoped GaN layer (undoped-GaN, U-GaN). For example, the undoped semiconductor layer may be formed using a liquid phase epitaxy (LPE), a vapor phase epitaxy (VPE), a molecular beam epitaxy (MBE) A metal organic chemical vapor deposition (MOCVD) method, or the like.

Further, although not shown in FIGS. 1 and 2, a buffer layer may be further disposed between the undoped semiconductor layer and the substrate 100. For example, the buffer layer may be formed of GaN, InN, AlN, InGaN, AlGaN, InAlGaN, or AlInN (AlN) Or the like.

The second semiconductor layer 120 may be doped with a dopant of a second conductivity type different from the first conductivity type. According to one embodiment, the second semiconductor layer 120 may be a P-type semiconductor layer doped with a P-type dopant. For example, the P-type dopant may include at least one of magnesium (Mg), zinc (Zn), barium (Ba), and calcium (Ca), and the second semiconductor layer 120 may include at least one of GaN, AlN, AlGaN, InGaN, InN, InAlGaN, or AlInN doped with the P-type dopant. The second semiconductor layer 140 may be formed by any one of a liquid crystal growth method, a vapor phase growth method, a molecular beam growth method, and an organic metal chemical vapor deposition method.

The active layer 115 combines electrons supplied from the first semiconductor layer 110 and holes supplied from the second semiconductor layer 120 to generate excitons, and the energy state of the excitons is changed to emit light can do. The active layer 115 may have a multi-quantum well (MQW) structure, a quantum dot structure, or the like. For example, the active layer 130 may be an InGaN film, an InGaN film doped with zinc (Zn), or silicon (Si). For example, the active layer 130 may be formed using any one of a liquid growth method, a vapor phase growth method, a molecular beam growth method, and an organic metal chemical vapor deposition method.

The plurality of rod structures NR may be randomly disposed on the second semiconductor layer 120. [ According to one embodiment, the plurality of load structures NR may be spaced from each other. Accordingly, external air may be disposed between the plurality of rod structures NR. The light generated in the active layer 115 may be emitted from the outer surface of the plurality of rod structures NR in contact with the outside air. A plurality of rod structures NR spaced apart from each other can increase a light emitting surface of light generated in the active layer 115 and provide a light emitting device with improved light extraction efficiency.

The rod structure NR may include a core portion (CP) and a shell portion (SP). The core portion CP may be in direct contact with the second semiconductor layer 120. The refractive index of the core portion CP may be smaller than the refractive index of the second semiconductor layer 120. For example, when the second semiconductor layer 120 is formed of P-type gallium nitride (refractive index: 2.5), the core portion CP may be formed of zinc oxide (refractive index: 2.08).

According to one embodiment, the core CP may be in the form of a rod extending in a direction perpendicular to the upper surface of the substrate 100. Alternatively, according to another embodiment, the core portion CP may be a sphere-shaped particle, unlike the one shown in Figs.

The shell part SP may conformally cover the core part CP. The shell part SP may be provided in a manufacturing process different from the core part CP. For example, the shell part SP may be formed on the second semiconductor layer 120 after the core part CP is formed on the second semiconductor layer 120 by atomic layer deposition (ALD), chemical vapor deposition (CVD), or physical vapor deposition (PVD)), or the like, may be provided on the core portion (CP). The refractive index of the shell portion SP may be smaller than the refractive index of the second semiconductor layer 120 and may be smaller than the refractive index of the core portion CP. For example, when the second semiconductor layer 120 is formed of P-type gallium nitride and the core portion CP is formed of zinc oxide, the shell portion SP may be formed of aluminum oxide. According to one embodiment, the refractive index of the shell portion SP may be at least 0.35 or less than the refractive index of the core portion CP.

The core portion CP and the shell portion SP are formed of metal oxide and may be formed of different materials. According to one embodiment, the core portion CP is formed of zinc oxide (for example, ZnO), and the shell portion SP may be formed of aluminum oxide (for example, Al ₂ O ₃ ).

According to the embodiment of the present invention, the light emitted from the active layer 115 is transmitted through the second semiconductor layer 120, the core portion CP, and the shell portion SP in turn, have. That is, as the refractive indexes of the second semiconductor layer 120, the core part CP, and the shell part SP through which light is transmitted are sequentially reduced, the light emitted from the active layer 115 is efficiently emitted to the outside Can be released. Accordingly, a light emitting device having improved light extraction efficiency can be provided.

If the rod structure NR having the core part CP and the shell part SP is omitted on the second semiconductor layer 120 so that the light emitted from the active layer 115 is incident on the second semiconductor layer 120, (For example, when the second semiconductor layer 120 is formed of a gallium nitride film), the refractive index difference between the second semiconductor layer 120 and the external air A part of the light emitted from the active layer 115 is totally totally internally reflected and a part of the light not totally internally reflecting according to the Snell's law due to the Fresnel reflection (Fresnel reflection), so that the light emitted from the active layer 115 can not be efficiently emitted to the outside.

However, as described above, according to the embodiment of the present invention, the light emitted from the active layer 115 is incident on the second semiconductor layer 120, the core portion CP, And the shell part SP in this order, the Fresnel reflection is reduced, and the light extraction efficiency is improved by the scattering effect by the rod structure NR.

Hereinafter, a method of manufacturing a light emitting device according to an embodiment of the present invention described with reference to FIGS. 1 and 2 will be described with reference to FIG.

3 is a flowchart illustrating a method of manufacturing a light emitting device according to an embodiment of the present invention.

Referring to FIG. 3, a structure in which a first semiconductor layer of a first conductivity type, an active layer, and a second semiconductor layer of a second conductivity type are sequentially stacked is prepared (S110). The structure may be formed on a substrate.

A mixed liquid containing metal and oxygen is prepared (S120). When the metal includes zinc, the mixed solution may be a mixture of ZNH (zinc nitrate hexahydrate), HMT (hexamethylene tetramine), and DI water.

3, the step of preparing the structure in which the first semiconductor layer, the active layer, and the second semiconductor layer are stacked in order may be performed after performing the step of preparing the mixed solution. That is, steps S110 and S120 described in FIG. 3 are not limited to the order.

The mixed liquid is provided on the second semiconductor layer so that a core portion formed of a metal oxide on the second semiconductor layer can be manufactured (S130). The step of providing the mixed liquid on the second semiconductor layer may include dipping the structure having the second semiconductor layer in the mixed liquid for a predetermined time. After the mixed solution is provided on the second semiconductor layer to manufacture the core part on the second semiconductor layer, a step of providing gas (for example, nitrogen gas or the like) to the second semiconductor layer and drying .

Stirring the mixed solution for a predetermined period of time before the mixed solution is provided on the second semiconductor layer, filtering the mixed solution using a filter, and heat treating the mixed solution, A step of allowing the mixed liquid to have a growth temperature suitable for being produced can be further performed.

After the core portion is formed, a shell portion covering the core portion may be formed (S140). For example, the shell portion can be formed by various methods such as atomic layer deposition (ALD), chemical vapor deposition (CVD), or physical vapor deposition (PVD). The step of forming the shell portion may be performed in a separate process from the step of forming the core portion.

Hereinafter, the light extraction efficiency of the light emitting device including the rod structure according to the embodiment of the present invention will be described.

4 is a SEM photograph of a rod structure of a light emitting device according to an embodiment of the present invention.

4, in order to form a ZnO core part having a refractive index lower than the refractive index of gallium nitride on the P-type GaN film of the gallium nitride based diode, a zinc nitrate hexahydrate (ZNH) HMT (hexamethylene tetramine) was placed in 200 ml of DI water to prepare a mixed solution having zinc and oxygen. The mixture was steered for 1 hour, filtered through a stirrer, and heat-treated at 95 ° C.

A core portion formed of ZnO was grown on the P-type gallium nitride film while keeping the gallium nitride diode in the mixed solution at 95 캜 for 6 hours. Thereafter, it was dried with nitrogen to prepare a core portion formed of ZnO on the P-type gallium nitride film.

After producing the ZnO core portion, for producing ZnO core portion than Al ₂ O ₃ shell part having a low refractive index, by atomic layer deposition, to form an Al ₂ O ₃ on the ZnO core, ZnO / Al ₂ O _{A three-} core-shell rod structure was prepared. As shown in Fig. 4, it can be seen that a plurality of rod structures extending in one direction are formed.

5 is a graph illustrating the light emission intensity of the light emitting device according to the embodiment of the present invention.

Referring to FIG. 5, as a first comparative example of the embodiment of the present invention, a gallium nitride diode in which a ZnO core portion and an Al ₂ O ₃ shell portion are omitted, and a ZnO core portion on a P-type gallium nitride film in a second comparative example And the light emitting intensity of the GaN-based diode in which the Al ₂ O ₃ shell was excluded was measured. In the first embodiment of the present invention, a GaN core portion and a GaN layer having an Al ₂ O ₃ shell portion with a thickness of 20 nm And a luminescent intensity of a gallium nitride diode having a ZnO core portion and a 40 nm thick Al ₂ O ₃ shell portion on a P-type gallium nitride film was measured in the second embodiment.

5, the luminous efficiency of the light emitting device having the ZnO core part and the Al ₂ O ₃ shell part according to the first and second embodiments is higher than that of the ZnO core part and the Al ₂ O ₃ shell part It can be confirmed that the ZnO core part is provided and the light emitting efficiency of the light emitting device in which the Al ₂ O ₃ shell part is omitted is measured higher than the light emitting efficiency of the omitted light emitting device and the second comparative example. That is, a ZnO core portion having a refractive index smaller than that of the P-type gallium nitride film and an Al ₂ O ₃ shell portion having a refractive index lower than that of the ZnO core portion are formed on the P-type gallium nitride film and the light generated in the active layer gradually has a refractive index As passing through the reduced media, Fresnel reflection is minimized and the light extraction efficiency is improved.

FIG. 6 is a graph illustrating a difference in refractive index between a core portion and a shell portion included in a light emitting device according to an embodiment of the present invention.

Referring to FIG. 6, in order to confirm the light extraction efficiency according to the refractive index difference between the core portion and the shell portion, the intensity of light emitted while varying the refractive indexes of the core portion and the shell portion on the LED was measured. Specifically, the core portion was formed of materials having different refractive indexes based on the shell portion formed of Al ₂ O ₃ having a refractive index of 1.65, and the intensity of the emitted light was measured. When the core portion and the shell portion were omitted on the light emitting diode, the intensity of light emitted was measured to be 7000 (au).

When the refractive indexes of the core portions are 1.7, 1.8, and 1.9, that is, the difference between the refractive indices of the core portion and the shell portion is 0.05, 0.15. 0.25, it can be confirmed that the intensity of light emitted is lower than that in the case where the core portion and the shell portion are omitted on the light emitting diode. On the other hand, when the refractive indices of the core portions are 2.0, 2.1, 2.2, and 2.3, that is, the refractive index difference between the core portion and the shell portion is 0.35, 0.45, 0.55, and 0.65, the core portion and the shell portion are omitted It can be confirmed that the intensity of the emitted light is higher than in the case where the light is emitted. That is, it can be confirmed that when the refractive index of the core portion is at least 0.35 or more than the refractive index of the shell portion, that is, the refractive index of the shell portion is at least 0.35 or more smaller than the refractive index of the core portion, the light extraction efficiency of light emitted onto the light- .

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the present invention is not limited to the disclosed exemplary embodiments. It will also be appreciated that many modifications and variations will be apparent to those skilled in the art without departing from the scope of the invention.

100: substrate
110: first? Conductor layer
115:
120: second semiconductor layer
NR: load structure
CP: core part
SP: shell part

Claims (10)

A first semiconductor layer of a first conductivity type;
An active layer on the first semiconductor layer;
A second semiconductor layer of a second conductivity type disposed on the active layer; And
A core portion having a refractive index smaller than that of the second semiconductor layer and disposed directly in contact with the second semiconductor layer and a shell portion covering the core portion and having a refractive index smaller than that of the core portion, a rod structure having a first portion and a second portion,
Wherein the light emitted from the active layer sequentially passes through the second semiconductor layer, the core portion, and the shell portion and is emitted to the outside.
The method according to claim 1,
Wherein a difference in refractive index between the shell portion and the core portion is at least 0.35.
The method according to claim 1,
Wherein the core portion and the shell portion are formed of different metal oxides.
The method according to claim 1,
Wherein the core portion comprises zinc oxide,
Wherein the shell portion comprises aluminum oxide.
The method according to claim 1,
Wherein the rod structure is provided in plurality on the second semiconductor layer,
Wherein the plurality of rod structures are spaced apart from each other.
The method according to claim 1,
Wherein the shell portion is made of aluminum oxide, the core portion is made of zinc oxide, and the refractive index difference between the shell portion and the core portion is at least 0.35 or more.
Preparing a structure in which a first semiconductor layer of a first conductivity type, an active layer, and a second semiconductor layer of a second conductivity type are sequentially stacked;
Preparing a mixed liquid containing metal and oxygen;
Providing the mixed liquid on the second semiconductor layer of the structure to produce a core portion formed of a metal oxide so as to be in direct contact with the second semiconductor layer and having a refractive index smaller than that of the second semiconductor layer; And
Forming a shell portion covering the core portion and having a refractive index smaller than that of the core portion,
And the light emitted from the active layer is sequentially transmitted through the second semiconductor layer, the core portion, and the shell portion to be emitted to the outside.
8. The method of claim 7,
Wherein the shell portion is formed by an atomic layer deposition method.
delete 8. The method of claim 7,
Wherein the core portion is formed of zinc oxide,
Wherein the shell portion is formed of aluminum oxide.

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