KR100690366B1 - Light emitting diode havigng a roughened surface for light extraction and method of fabricating the same - Google Patents

Abstract

Disclosed are a light emitting diode having a roughened surface for light extraction and a method of manufacturing the same. This light emitting diode includes a lower N-type semiconductor layer and a P-type semiconductor layer. An active layer is interposed between the lower N-type semiconductor layer and the P-type semiconductor layer. A high refractive material layer is positioned on the P-type semiconductor layer opposite the active layer. The high refractive material layer has a roughened surface. Accordingly, it is possible to provide a light emitting diode having improved light extraction efficiency.

Light Emitting Diodes, Roughened Surfaces, Light Extraction Efficiency

Description

LIGHT EMITTING DIODE HAVIGNG A ROUGHENED SURFACE FOR LIGHT EXTRACTION AND METHOD OF FABRICATING THE SAME}

1 is a cross-sectional view illustrating a light emitting diode according to an embodiment of the present invention.

2 to 5 are cross-sectional views illustrating a method of manufacturing a light emitting diode according to an embodiment of the present invention.

6 is a cross-sectional view for describing a light emitting diode according to another exemplary embodiment of the present invention.

The present invention relates to a light emitting diode and a method of manufacturing the same, and more particularly, to a light emitting diode having a rough surface for light extraction and a method of manufacturing the same.

Gallium nitride (GaN) series light emitting diodes have been applied and developed for about 10 years. GaN-based LEDs have changed the LED technology considerably and are currently used in a variety of applications, including color LED indicators, LED traffic signals, and white LEDs.

Recently, high-efficiency white LEDs are expected to replace fluorescent lamps. In particular, the efficiency of white LEDs has reached a level similar to that of conventional fluorescent lamps. However, there is a possibility that the LED efficiency is further improved, and thus continuous efficiency improvement is further required.

Two major approaches are being attempted to improve LED efficiency. The first is to increase the internal quantum efficiency, which is determined by the crystal quality and epilayer structure, and the second is to increase the light extraction efficiency.

Internal quantum efficiency is currently 70-80%, so there is not much room for improvement, but light extraction efficiency has much room for improvement. Improvement of light extraction efficiency has become a major problem to remove the internal light loss by internal reflection.

The light emitting diode, which prevents internal reflection and improves light extraction efficiency, is called Fuji, etc. under the title of "Increase in the extraction efficiency of GaN-Based ligth emitting diodes via surface roughening". It was disclosed in Applied physics letters, Vol84, N6, p855-857 by Fujii et al.

The light emitting diode is stacked on an sapphire substrate with an N-type semiconductor layer, an active layer and a P-type semiconductor layer, bonding the semiconductor layers on a submount and using laser lift-off (LLO) technology. After separating the semiconductor layers from the substrate, it is formed by roughening the surface of the N-type semiconductor layer. By roughening the surface of the N-type semiconductor layer, it is possible to improve the extraction efficiency of light emitted to the outside through the N-type semiconductor layer.

However, since the light emitting diodes must bond the semiconductor layers to the submount and separate the semiconductor layers from the substrate using LLO technology, the manufacturing process is complicated and the number of manufacturing processes is increased.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a light emitting diode having a rough surface for improving light extraction efficiency, and to provide a light emitting diode having a simple manufacturing process.

In order to achieve the above technical problem, the present invention provides a light emitting diode having a rough surface for light extraction and a method of manufacturing the same. A light emitting diode according to an aspect of the present invention includes a lower N-type semiconductor layer and a P-type semiconductor layer. An active layer is interposed between the lower N-type semiconductor layer and the P-type semiconductor layer. In addition, a high refractive material layer is disposed on the P-type semiconductor layer opposite the active layer. The high refractive material layer has a roughened surface. As a result, a light emitting diode having improved light extraction efficiency can be provided, and a light emitting diode having a rough surface can be manufactured without using a laser lift-off (LLO) technology, thereby simplifying the manufacturing process.

The high refractive material layer has a refractive index greater than that of the P-type semiconductor layer. Accordingly, since the light generated in the active layer is incident on the high refractive material layer without total reflection at the interface between the P-type semiconductor layer and the high refractive material layer, internal light loss due to total reflection can be prevented.

The high refractive material layer may have an opening that exposes the P-type semiconductor layer. P-type ohmic metal is formed in the opening and bonded to the exposed P-type semiconductor layer. Accordingly, the junction resistance of the P-type semiconductor layer can be lowered.

A light emitting diode manufacturing method according to another aspect of the present invention includes forming a lower N-type semiconductor layer, an active layer, and a P-type semiconductor layer in sequence on a substrate. A high refractive material layer is formed on the P-type semiconductor layer. Thereafter, the high refractive material layer is etched to form a roughened surface. The light emitting diode manufacturing method according to the present embodiment does not need to separate the semiconductor layers from the substrate using the LLO technique as in the prior art, so that the manufacturing process is simple.

In addition, the high refractive material layer may be etched to form an opening exposing the P-type semiconductor layer. P-type ohmic metal is formed in the opening. The P-type ohmic metal is bonded to the P-type semiconductor layer to reduce the bonding resistance of the P-type semiconductor layer.

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.

1 is a cross-sectional view illustrating a light emitting diode according to an embodiment of the present invention.

Referring to FIG. 1, the lower N-type semiconductor layer 25 is positioned on the substrate 21. The substrate 21 may be an insulating substrate such as a conductive substrate or sapphire. The buffer layer 23 may be interposed between the lower N-type semiconductor layer 25 and the substrate 21.

The P-type semiconductor layer 29 is positioned on the lower N-type semiconductor layer 25, and an active layer 27 is interposed between the lower N-type semiconductor layer 25 and the P-type semiconductor layer 29. The active layer 27 may be a single quantum well or multiple quantum wells. The lower N-type semiconductor layer 25 and the P-type semiconductor layer 29 have a wider bandgap than the active layer 27.

The high refractive material layer 31a is positioned on the P-type semiconductor layer 29. The high refractive material layer 31a has a larger refractive index than the P-type semiconductor layer 29. In addition, the high refractive material layer 31a has a roughened surface. The roughened surface may be of various shapes. For example, the roughened surface may be made of cones, as shown, and the cones may be hexagonal in cross section. Alternatively, the roughened surface may consist of pillars.

The lower N-type semiconductor layer, the active layer, and the P-type semiconductor layer may be GaN-based semiconductor layers formed of (B, Al, Ga, In) N, respectively. In addition, the high refractive material layer 31a may be a GaN-based semiconductor layer formed of (B, Al, Ga, In) N, and may be an N-type or P-type semiconductor layer. However, the semiconductor layers are not limited to GaN-based semiconductor layers, and may be other material layers such as ZnO. In addition, the high refractive material layer 31a is not limited to the semiconductor layer, and may be a transparent or translucent material layer of a conductive layer or a non-conductive layer.

The high refractive material layer 31a is formed of a material layer having a refractive index larger than that of the P-type semiconductor layer 29. Accordingly, the light emitted from the active layer may be incident on the high refractive material layer 31a without being totally reflected at the interface between the P-type semiconductor layer 29 and the high refractive material layer 31a.

Meanwhile, the high refractive material layer 31a may have an opening that exposes the P-type semiconductor layer 29. The opening may be composed of a single contact hole or a plurality of contact holes arranged in a matrix. Alternatively, the opening may consist of a plurality of trenches arranged in a single trench or matrix.

P-type ohmic metal 33 is formed in the opening. The P-type ohmic metal is ohmic-bonded to the P-type semiconductor layer 29 to reduce the bonding resistance of the P-type semiconductor layer. When the high refractive material layer 31a is a P-type or N-type semiconductor layer, current dispersion in the P-type ohmic metal 33 may be realized by the high refractive material layer 31a. Accordingly, it is possible to minimize the voltage rise due to the adoption of the P-type ohmic metal 33.

When the substrate 21 is a conductive substrate, an N-type electrode pad (not shown) may be formed under the substrate 21. In contrast, when the substrate 21 is an insulated substrate, the lower N-type semiconductor layer 25 may extend toward the side and an N-type electrode pad may be formed in the extension portion. In addition, a P-type electrode pad (not shown) may be formed on the high refractive material layer 31a. The P-type electrode pad is electrically connected to the P-type ohmic metal directly or through the high refractive material layer 31a.

According to the present embodiment, there is provided a light emitting diode having a roughened surface of the high refractive material layer 31a formed on the P-type semiconductor layer 29 to improve the light extraction efficiency. Thus, a laser lift-off (LLO) technique or the like can be used to provide a light emitting diode having a roughened surface without the need to separate the semiconductor layers from the substrate 21.

Hereinafter, a method of manufacturing a light emitting diode according to an embodiment of the present invention will be described with reference to FIGS. 2 to 5.

Referring to FIG. 2, a lower N-type semiconductor layer 25 is formed on the substrate 21. The substrate 21 may be an insulating substrate such as sapphire, insulating SiC or a conductive substrate such as SiC, GaN or ZnO substrate. The lower N-type semiconductor layer 25 may be, for example, a GaN-based semiconductor layer, that is, a GaN-based semiconductor layer formed of (B, Al, Ga, In) N. Si may be doped into the GaN-based semiconductor layer to form an N-type semiconductor layer.

Before forming the lower N-type semiconductor layer 25, the buffer layer 23 may be formed. The buffer layer 23 mitigates lattice mismatch between the semiconductor layers to be formed thereon and the substrate 21 to reduce the occurrence of dislocations. The buffer layer 23 may be a GaN-based N-type semiconductor layer or a semi-insulating semiconductor layer, depending on the required light emitting diode structure.

An active layer 27 is formed on the lower N-type semiconductor layer 25. The active layer 27 may have a single layer of (B, Al, Ga, In) N or a multilayer structure in which (B, Al, Ga, In) N layers having different band gaps are alternately stacked.

The P-type semiconductor layer 29 is formed on the active layer 27. The P-type semiconductor layer may also be a GaN-based semiconductor layer of (B, Al, Ga, In) N, and may be doped with Mg to form a P-type semiconductor layer.

The lower N-type semiconductor layer 25, the active layer 27, and the P-type semiconductor layer 29 each include metalorganic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE). , Molecular beam epitaxy (MBE) technology, or the like.

The high refractive material layer 31 is formed on the P-type semiconductor layer 29. The high refractive material layer 31 may be, for example, a GaN-based semiconductor layer or a ZnO-based semiconductor layer, but is not limited thereto and may be a transparent or translucent conductive or non-conductive material layer. The high refractive material layer 31 may be formed using various deposition techniques, such as MOCVD, HVPE, MBE technology, depending on the type of material to be deposited. The high refractive material layer 31 is formed of a material having a refractive index larger than that of the P-type semiconductor layer 29. When the high refractive material layer 31 is a GaN-based semiconductor layer, the refractive index of the high refractive material layer 31 may be adjusted according to the amount of dopant or the relative composition ratio of Ga.

The semiconductor layers are sequentially grown and stacked, and the dopants required by the dopant source may be doped during the growth.

Referring to FIG. 3, the surface of the high refractive material layer 31 is partially etched to form a high refractive material layer 31 a having a roughened surface. The etching process may be performed using a dry etching using an etching mask or a photoelectrochemical (PEC) etching technique.

The dry etching may form a roughened surface made of cones or a roughened surface made of pillars, and the PEC etching may form a roughened surface made of cones. As an example of such dry etching, US Patent Publication No. 2005/0145864 discloses a dry etching technique using a copolymer. On the other hand, an example of PEC etching is described in the paper of Fuji et al. Described in the prior art. Here, PEC etching using a KOH solution as an electrolyte and an Xe lamp as a light source is introduced. Meanwhile, an Hg lamp may be used as the light source.

Referring to FIG. 4, the high refractive material layer 31a is etched to form an opening exposing the P-type semiconductor layer 29. The opening may be formed using a photo and etching process. The opening may be composed of contact hole (s) or trench (es).

P-type ohmic metal 33 is formed in the opening. The p-type ohmic metal may be, for example, Ni / Au. The P-type ohmic metal 33 may be formed using a lift-off technique, and heat treatment may be performed for ohmic bonding.

Here, the P-type ohmic metal 33 is formed after the formation of the high refractive material layer 31a having the roughened surface, but before the formation of the high refractive material layer 31a having the roughened surface of FIG. 3. P-type ohmic metal 33 may be formed.

Referring to FIG. 5, a portion of the high refractive material layer 31a, the P-type semiconductor layer 29, and the active layer 27 are sequentially etched to expose the lower N-type semiconductor layer 25. Thereafter, an N-type bonding pad 35 is formed on the exposed lower N-type semiconductor layer 25. In addition, a P-type bonding pad (not shown) is formed on a predetermined region of the high refractive material layer 31a.

Accordingly, the light emitting diode may be driven by supplying power through the N-type bonding pad 35 and the P-type bonding pad. As power is supplied, light is generated in the active layer 27, and the generated light passes through the P-type semiconductor layer 29 and is incident to the high refractive material layer 31a. Since the high refractive material layer 31a has a refractive index larger than that of the P-type semiconductor layer 29, light is incident on the high refractive material layer 31a without total reflection. Meanwhile, the light incident on the high refractive material layer 31a is emitted out of the surface of the high refractive material layer 31a by the rough surface structure. Accordingly, the light loss generated from the inside due to total reflection can be reduced compared to the light emitting diode having the flat surface, thereby improving the light extraction efficiency.

Meanwhile, when the substrate 21 is a conductive substrate, as shown in FIG. 6, an N-type bonding pad 55 may be formed under the substrate 21. At this time, the buffer layer 23 is conductive. According to this embodiment, a larger area of the active layer 27 can be secured, thereby increasing the light output emitted from a single chip.

According to embodiments of the present invention, a light emitting diode having a roughened surface for improving light extraction efficiency may be provided, and a light emitting diode having a simple manufacturing process and a method of manufacturing the same may be provided.

Claims (6)

Lower N-type semiconductor layer; P-type semiconductor layer; An active layer interposed between the lower N-type semiconductor layer and the P-type semiconductor layer; And And a high refractive material layer disposed on the P-type semiconductor layer opposite the active layer and having a refractive index greater than that of the P-type semiconductor layer and having a roughened surface. The method according to claim 1, The high refractive material layer has an opening that exposes the P-type semiconductor layer, And a P-type ohmic metal formed in the opening and bonded to the exposed P-type semiconductor layer. The method according to claim 1, The lower N-type semiconductor layer, the active layer, the P-type semiconductor layer and the high refractive material layer are each formed of (B, Al, Ga, In) N. Forming a lower N-type semiconductor layer, an active layer, and a P-type semiconductor layer on the substrate, Forming a high refractive index material layer having a refractive index greater than that of the P-type semiconductor layer on the P-type semiconductor layer, And partially etching the high refractive material layer to form a roughened surface. The method according to claim 4, Etching the high refractive material layer to form an opening exposing the P-type semiconductor layer, The method of manufacturing a light emitting diode further comprising forming a P-type ohmic metal in the opening. The method according to claim 4, The roughened surface is a light emitting diode manufacturing method is formed using a dry etching or PEC etching technology.

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