KR100716646B1 - Light emitting device having a sloped surface for exiting ligth and method of fabricating the same - Google Patents

Abstract

Disclosed are a light emitting device having an inclined light emitting surface and a method of manufacturing the same. The light emitting device includes a first conductive semiconductor layer, a second conductive semiconductor layer, and an active layer interposed between the first and second conductive semiconductor layers. On the other hand, the upper surface of the first conductivity type semiconductor layer has a flat surface and an inclined surface that is closer to the active layer toward the outside from the flat surface. Accordingly, compared with the conventional light emitting device having a flat light emitting surface, light loss due to internal reflection can be reduced, thereby improving light extraction efficiency.

Light emitting devices, light emitting diodes, sloped surfaces, light extraction efficiency

Description

LIGHT EMITTING DEVICE HAVING A SLOPED SURFACE FOR EXITING LIGTH AND METHOD OF FABRICATING THE SAME

1 is a cross-sectional view illustrating a conventional vertical light emitting device.

2 is a cross-sectional view for describing a light emitting device according to an embodiment of the present invention.

3 is a plan view illustrating a light emitting device according to an embodiment of the present invention.

4 to 8 are cross-sectional views illustrating a method of manufacturing a light emitting device according to an embodiment of the present invention.

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

The present invention relates to a light emitting device and a method of manufacturing the same, and more particularly, to a light emitting device and a method of manufacturing the same having an inclined light emitting surface to reduce light loss due to internal reflection.

In general, a light emitting device includes a light emitting diode having a first conductive semiconductor layer, a second conductive semiconductor layer, and an active layer interposed between these semiconductor layers. In the active layer, light is generated by recombination of electrons and holes and emitted to the outside.

Recently, a vertical light emitting device for reducing energy loss in a light emitting diode by shortening the recombination distance between electrons and holes has been disclosed, and FIG. 1 is a cross-sectional view for describing such a vertical light emitting device.

Referring to FIG. 1, a light emitting diode 10 having a first conductive semiconductor layer 5, a second conductive semiconductor layer 9, and an active layer 7 interposed between these conductive semiconductor layers is a conductive substrate. It is located on (15). The reflective layer 13 is interposed between the light emitting diode 10 and the conductive substrate 15. In addition, an ohmic electrode layer 11 may be further interposed between the reflective layer 13 and the light emitting diode 10.

An electrode pad 19 may be formed on the first conductive semiconductor layer 5, and a transparent electrode layer 17 may be formed as necessary.

The vertical light emitting device emits light generated in the active layer 7 by recombination of electrons and holes to the outside through the side surface and the top surface of the first conductive semiconductor layer 5. The reflective layer 13 reflects the light emitted or reflected from the light emitting diode 10 to the conductive substrate 15 to the first conductivity type semiconductor layer 5.

Since the vertical light emitting device adopts a conductive substrate 15, heat generated from the light emitting diode 10 can be easily discharged to the outside, thereby preventing a decrease in luminous efficiency due to an increase in temperature. Compared to the light emitting device, the recombination distance between electrons and holes can be shortened to reduce electric energy loss. In addition, the light emitted from the light emitting diode 10 is refracted at the upper surface so that the viewing angle becomes considerably wider.

However, since the upper surface of the first conductivity type semiconductor layer 5 is made of a flat surface, light reaching the upper surface at an incident angle of more than a critical angle is not emitted to the outside and proceeds toward the active layer 7 by total internal reflection. . In particular, when the first conductivity-type semiconductor layer 5 is a gallium nitride (GaN) -based semiconductor layer, the refractive index is high as about 2.4, the critical angle is small. Therefore, a large part of the light generated by the light emitting diode 10 is not directly emitted to the outside, and the internal reflection is repeated, thereby causing light loss in the light emitting device. This light loss leads to reduced light extraction efficiency.

The present invention has been made in an effort to provide a light emitting device capable of improving light extraction efficiency by preventing light loss due to internal reflection.

Another object of the present invention is to provide a light emitting device manufacturing method capable of improving light extraction efficiency by preventing light loss due to internal reflection.

In order to achieve the above technical problem, an aspect of the present invention provides a light emitting device having an inclined light emitting surface. The light emitting element includes a first conductivity type semiconductor layer having an upper surface and a lower surface. An upper surface of the first conductive semiconductor layer has a flat surface and an inclined surface that is closer to the lower surface toward the outside from the flat surface. On the other hand, a second conductive semiconductor layer is positioned on the lower surface side of the first conductive semiconductor layer, and an active layer is interposed between the first conductive semiconductor layer and the second conductive semiconductor layer. As a result, light loss due to total internal reflection can be prevented compared to the conventional vertical light emitting device, and a light emitting device capable of improving light extraction efficiency can be provided.

The flat surface may be located at the center of the first conductivity type semiconductor layer. Therefore, it is possible to form the inclined surface of the vertical and / or symmetrical structure around the flat surface.

The inclined surface may be variously modified, for example, may be made of small inclined surfaces connected in multiple stages. The small slopes can be connected to vertical and / or horizontal planes. Accordingly, the surface area of the light emitting surface can be increased, so that the light extraction efficiency can be further improved.

On the other hand, a conductive substrate may be located under the second conductive semiconductor layer. In addition, a reflective layer may be interposed between the conductive substrate and the second conductive semiconductor layer. The conductive substrate promotes heat dissipation, thereby preventing a decrease in light efficiency due to an increase in temperature. In addition, the reflective layer reflects the light traveling from the active layer to the conductive substrate to the first conductive semiconductor layer.

In addition, an ohmic electrode layer may be interposed between the reflective layer and the second conductive semiconductor layer. The ohmic electrode layer may be formed as a transparent electrode and is adopted to lower contact resistance between the reflective layer and the first conductive semiconductor layer.

In order to achieve the above another technical problem, another aspect of the present invention provides a method for manufacturing a light emitting device having an inclined light emitting surface. The light emitting device manufacturing method includes forming a first conductive semiconductor layer, an active layer and a second conductive semiconductor layer on a preliminary substrate. Thereafter, a conductive substrate is formed on the second conductive semiconductor layer, and the preliminary substrate is separated to expose the first conductive semiconductor layer. An upper surface of the exposed first conductive semiconductor layer is polished or etched to form an inclined surface that is closer to the active layer toward the outside. According to this method, a light emitting device capable of improving light extraction efficiency by reducing light loss due to total internal reflection by the inclined surface is manufactured.

On the other hand, the inclined surface may be composed of small inclined surfaces connected in multiple stages. Therefore, it is possible to further improve the light extraction efficiency by increasing the surface area of the light emitting surface.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided as examples to ensure that the spirit of the present invention can be fully conveyed to those skilled in the art. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. And, in the drawings, the width, length, thickness, etc. of the components may be exaggerated for convenience. Like numbers refer to like elements throughout.

2 is a cross-sectional view illustrating a light emitting device according to an embodiment of the present invention, and FIGS. 3A and 3B are plan views illustrating a light emitting device according to an embodiment of the present invention.

Referring to FIG. 2, the light emitting diode 30a is positioned on the conductive substrate 35. The light emitting diode 30a includes the first conductive semiconductor layer 25a, the second conductive semiconductor layer 29, and the active layer 27 interposed between the first and second conductive semiconductor layers 25a and 29. It includes.

The first conductivity type semiconductor layer 25a has an upper surface and a lower surface. The upper surface has a flat surface 25b and an inclined surface 25c closer to the lower surface toward the outside from the flat surface. On the other hand, the second conductivity type semiconductor layer 29 is located on the lower surface side of the first conductivity type semiconductor layer 25a.

The first conductive semiconductor layer 25a and the second conductive semiconductor layer 29 are formed of P-type and N-type, or N-type and P-type semiconductors, respectively. In addition, the active layer 27 may be a single quantum well or multiple quantum wells. The first and second conductivity-type semiconductor layers 25a and 29 have a wider bandgap than the active layer 27. The first conductive semiconductor layer 25a, the active layer 27, and the second conductive semiconductor layer 29 may be GaN-based semiconductor layers each formed of (B, Al, Ga, In) N, but are not limited thereto. However, it may be another layer of material, such as ZnO.

The conductive substrate 35 is positioned under the second conductive semiconductor layer 29. The conductive substrate 35 may be a metal or silicon (Si) substrate having excellent thermal conductivity. The reflective layer 33 is interposed between the second conductive semiconductor layer 29 and the conductive substrate 35. The reflective layer 33 may include silver (Ag) and / or aluminum (Al). If the reflective layer 33 does not form an ohmic contact with the second conductive semiconductor layer 29 or has a large contact resistance, the ohmic is formed between the reflective layer 33 and the second conductive semiconductor layer 29. The electrode layer 31 may be interposed. For example, when the second conductivity-type semiconductor layer 29 is a P-type semiconductor, the ohmic electrode layer 31 may include platinum (Pt), nickel (Ni) and / or titanium (Ti) / gold (Au). Can be. In addition, when the second conductivity-type semiconductor layer 29 is an N-type semiconductor, the ohmic electrode layer 31 may include Ti and / or Al.

Referring to FIG. 3, an upper surface of the first conductivity type semiconductor layer 25a has a flat surface 25b and an inclined surface 25c. The flat surface 25b may be located at the center of the first conductivity type semiconductor layer 25a. Accordingly, as illustrated, the inclined surface 25c which is symmetrical to the left and right and up and down about the flat surface 25b may be formed. Accordingly, the first conductivity type semiconductor layer 25a has a square pyramid shape. Since the first conductive semiconductor layer 25a has left and right symmetrical structures, light emitted through the first conductive semiconductor layer 25a is also emitted in left and right symmetrical directions.

On the other hand, the flat surface 25b and the inclined surface 25c may be deformed in various forms, for example, the flat surface 25b may be a disk, and the inclined surface 25c may be a surface inclined radially about the disk. have. In this case, the first conductivity-type semiconductor layer 25a has a truncated conical shape.

According to the present embodiment, since the upper surface of the first conductivity-type semiconductor layer 25a has a flat surface 25b and an inclined surface 25c, the internal surface reflection is higher than that of the light emitting device having the upper surface made of the conventional flat surface. Can reduce the light loss.

4 to 8 are cross-sectional views illustrating a method of manufacturing a light emitting device according to an embodiment of the present invention.

Referring to FIG. 4, the first conductive semiconductor layer 25, the active layer 27, and the second conductive semiconductor layer 29 are formed on the preliminary substrate 21. The preliminary substrate 21 may be, for example, a sapphire substrate. The first conductive semiconductor layer 25, the active layer 27, and the second conductive semiconductor layer 29 may be formed using metal organic chemical vapor deposition (MOCVD). The first and second conductive semiconductor layers 25 and 29 and the active layer 27 may be formed of (B, Al, Ga, In) N, but are not limited thereto, and may be formed of another material such as ZnO. Can be formed. Meanwhile, GaN-based P-type semiconductors and N-type semiconductors may be formed by doping magnesium (Mg) and silicon (Si), respectively. The first conductive semiconductor layer 25, the active layer 27, and the second conductive semiconductor layer 29 constitute a light emitting diode 30.

Meanwhile, the buffer layer 23 may be formed before the first conductive semiconductor layer 25 is formed. The buffer layer 23 may also be formed of a GaN-based semiconductor using MOCVD.

Referring to FIG. 5, a conductive substrate 35 is formed on the second conductive semiconductor layer 29. The conductive substrate 35 may be formed using, for example, a plating technique, a physical vapor deposition technique or a chemical vapor deposition technique, or may be formed by bonding a metal substrate or a silicon substrate.

Meanwhile, before forming the conductive substrate 35, the reflective layer 33 may be formed on the second conductive semiconductor layer 29. The reflective layer 33 may be formed of, for example, Ag and / or Al. In addition, before forming the reflective layer 33, an ohmic electrode layer 31 may be formed to make ohmic contact with the second conductivity-type semiconductor layer 29. The ohmic electrode layer 31 may include, for example, Pt, Ni, or Ti / Au.

Referring to FIG. 6, after the conductive substrate 35 is formed, the preliminary substrate 21 is separated. The preliminary substrate 21 may be separated using, for example, a laser, or using a polishing, dry etching, or wet etching technique.

In the case of using a laser, the preliminary substrate 21 is preferably a translucent substrate that transmits laser light, such as a sapphire substrate. The preliminary substrate 21 is irradiated with a laser, and the laser may be, for example, a KrF (248 nm) laser. Since the preliminary substrate 21 is a light transmissive substrate, the laser penetrates the preliminary substrate 21 and is absorbed by the buffer layer 23. As a result, the buffer layer 23 is decomposed by the absorbed radiation energy at the interface between the buffer layer 23 and the preliminary substrate 21, thereby separating the preliminary substrate 21. After the preliminary substrate 21 is separated, the remaining buffer layer 23 is removed using an etching technique or a polishing technique. As a result, the first conductivity-type semiconductor layer 25 is exposed.

Referring to FIG. 7, the top surface of the exposed first conductivity-type semiconductor layer 25 is polished or etched to form an inclined surface 25c closer to the active layer 27 toward the outside as illustrated. . For example, the inclined surface 25c may be formed by dry etching using a photoresist pattern formed by changing a thickness as an etching mask. As a result, a first conductive semiconductor layer 25a having a flat surface 25b and an inclined surface 25c connected to the flat surface 25b is formed, and the first conductive semiconductor layer 25a and the second conductive type are formed. A light emitting diode 30a including a semiconductor layer 29 and an active layer 27 interposed between the first and second conductivity type semiconductor layers 25a and 29 is formed.

Referring to FIG. 8, an electrode pad 39 is formed on the first conductivity type semiconductor layer 25a. The electrode pad 39 is a pad for bonding a wire to the light emitting diode 30a and is in ohmic contact with the first conductive semiconductor layer 25a.

Meanwhile, before forming the electrode pad 39, a transparent electrode 37 may be formed on the first conductive semiconductor layer 25a. The transparent electrode 37 is formed to disperse current in the first conductive semiconductor layer 25a and is in ohmic contact with the first conductive semiconductor layer 25a. For example, the transparent electrode 37 may be indium tin oxide (ITO) or Ni / Au.

According to the present embodiment, the inclined surface 25a is formed on the upper surface of the first conductivity type semiconductor layer 25a, and the light due to the difference in refractive index between the first conductivity type semiconductor layer 25a and its surroundings (air) A light emitting device capable of reducing total internal reflection can be manufactured. As a result, it is possible to reduce the light loss due to internal reflection in the light emitting device, thereby providing a light emitting device having improved light extraction efficiency. On the other hand, the light emitting device according to the present embodiment can adjust the viewing angle of the light emitted by adjusting the inclination of the inclined surface.

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

Referring to FIG. 9, as described with reference to FIG. 2, the light emitting diode 50a is positioned on the conductive substrate 35, and the reflective layer 33 is disposed between the light emitting diode 50a and the conductive substrate 35. And an ohmic electrode layer 31 may be interposed. In addition, as described with reference to FIG. 2, the light emitting diode 50a includes a first conductive semiconductor layer 55a, an active layer 27, and a second conductive semiconductor layer 29. The conductive semiconductor layer 55a has a flat surface 55b and an inclined surface 55c.

However, the inclined surface 55c of the light emitting device according to the present embodiment includes small inclined surfaces 55d connected in multiple stages. That is, the small inclined surfaces 55d are connected by the vertical surfaces as shown to form the inclined surfaces 55c. The inclined surfaces 55d may be formed by dry etching using a photoresist pattern corresponding to the inclined surfaces 55d as an etching mask. Alternatively, the first conductive semiconductor layer may be formed to be inclined several times. Accordingly, in addition to increasing the light extraction efficiency by the inclined surfaces 55d, the light extraction efficiency is increased by increasing the surface area of the light emitting surface.

According to embodiments of the present invention, it is possible to provide a light emitting device and a light emitting device manufacturing method which can improve light extraction efficiency by reducing light loss due to internal reflection. In addition, the light emitting surface area is increased by the small inclined surface formed in the first conductivity-type semiconductor layer to increase the light extraction efficiency.

Claims (7)

A first conductivity type semiconductor layer having an upper surface and a lower surface, the upper surface having a flat surface and an inclined surface closer to the lower surface toward the outside from the flat surface; A second conductivity type semiconductor layer positioned on a lower surface side of the first conductivity type semiconductor layer; An active layer interposed between the first conductive semiconductor layer and the second conductive semiconductor layer; A conductive substrate positioned under the second conductive semiconductor layer; And And a reflective layer interposed between the conductive substrate and the second conductive semiconductor layer. The method according to claim 1, The flat surface is a light emitting device located in the center of the first conductivity type semiconductor layer. The method according to claim 1, The inclined surface is a light emitting device consisting of small inclined surfaces connected in multiple stages. delete The method according to claim 1, And a ohmic electrode layer interposed between the reflective layer and the second conductive semiconductor layer. Forming a first conductive semiconductor layer, an active layer and a second conductive semiconductor layer on the preliminary substrate, Forming a conductive substrate on the second conductivity-type semiconductor layer, Separating the preliminary substrate to expose the first conductivity type semiconductor layer, And polishing or etching the exposed upper surface of the first conductive semiconductor layer to form an inclined surface that is closer to the active layer toward the outside. The method according to claim 6, The inclined surface is a light emitting device manufacturing method consisting of small inclined surfaces connected in multiple stages.

Images