KR100867569B1

KR100867569B1 - Light emitting diode with transparent substrate and method for fabricating the same

Info

Publication number: KR100867569B1
Application number: KR1020070056639A
Authority: KR
Inventors: 김창연; 윤여진; 이준희
Original assignee: 서울옵토디바이스주식회사
Priority date: 2007-06-11
Filing date: 2007-06-11
Publication date: 2008-11-10

Abstract

An LED(Light Emitting Diode) with a transparent substrate and a fabricating method thereof are provided to increase the amount of light which is irradiated from concavo-convex patterns without passing through other layers or the interfaces between layers even though a transparent substrate on which the concavo-convex patterns are formed. An LED(Light Emitting Diode) has a transparent substrate(10), first and second conductive semiconductor layers(22,24), which are formed on the upper plane of the transparent substrate, and a single light emitting cell(20) which is placed between the semiconductor layers. The upper plane of the transparent substrate is limited to an interface region, which interface with the single light emitting cell, and an exposure region of the outer portion of the single light emission cell. The exposure region is formed to surround the whole interface region, and a concavo-convex pattern is formed over both the exposure region and the interface region.

Description

LIGHT EMITTING DIODE WITH TRANSPARENT SUBSTRATE AND METHOD FOR FABRICATING THE SAME

1 is a cross-sectional view showing a light emitting diode according to the prior art.

2 is a plan view of a light emitting diode according to an embodiment of the present invention.

3 is a cross-sectional view of the light emitting diode shown in FIG. 2 taken along line A-A.

4A to 4C are views for explaining a light emitting diode manufacturing method according to an embodiment of the present invention.

5A to 5C are views for explaining a light emitting diode manufacturing method according to another embodiment of the present invention.

Figure 6 is a graph showing the light efficiency test results of the light emitting diode according to the embodiment of the present invention and the prior art.

10: transparent substrate 10a: uneven pattern

11: buffer layer 20: light emitting cell

22: first conductive semiconductor layer # 23: active layer

24: second conductive semiconductor layer E: exposed region

I: interface area

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode having a transparent substrate, and more particularly, to an improvement of a light emitting diode including an uneven pattern for improving light extraction efficiency in a transparent substrate.

In general, a light emitting diode (LED) is a device in which electrons and holes meet and emit light by a p-n semiconductor junction. The light emitting diode is configured to emit light by receiving a current from the outside.

Among them, light emitting diodes using III-V compound semiconductors are now widely used. Group III-nitride compound semiconductors are direct transition semiconductors, and have a stable light emission operation at a high temperature compared to devices using other semiconductors, and are widely used in light emitting diodes.

A group III nitride light emitting diode is usually formed by forming an n-type semiconductor layer, an active layer and a p-type semiconductor layer on a substrate using a transparent sapphire (Al ₂ O ₃ ) substrate. The active layer is interposed between the n-type semiconductor layer and the p-type semiconductor layer, and emits light by bonding electrons and holes at the position.

In the light emitting diode field as described above, there have been many studies related to the improvement of light extraction efficiency. As a result of such studies, a light emitting diode having improved total internal reflection characteristics due to an interlayer interface by forming an interface between a transparent substrate and a semiconductor layer formed thereon in an uneven pattern has been developed in the past.

1 is a cross-sectional view showing a conventional light emitting diode. Referring to FIG. 1, a conventional light emitting diode 100 includes a transparent substrate 110, an n-type semiconductor layer 112, an active layer 114, and a p-type semiconductor formed on an upper surface of the transparent substrate 110. Layer 116. In addition, the n-type semiconductor layer 112 includes an n-type electrode pad 112a in a portion of the n-type semiconductor layer 112 that is exposed to the upper side under the active layer 114 and the p-type semiconductor layer 116, and the p-type semiconductor layer 116. The upper surface of the transparent electrode layer 116a and the p-type electrode pad 116b is provided. In addition, the transparent substrate 110 and the n-type semiconductor layer 112 form a boundary as a whole, and a buffer layer 111 is interposed between the transparent substrate 110 and the n-type semiconductor layer 112. In addition, the transparent substrate 110 includes an uneven pattern 110b for improving light extraction efficiency by improving total reflection characteristics at an interface with the buffer layer 111 or the n-type semiconductor layer 112. Reference numeral 110a denotes a lead frame in which the light emitting diodes 100 are mounted, and the lead frame 110a may be made of metal to reflect light upward.

As described above, in the conventional light emitting diode 100, the transparent substrate 110 has the uneven pattern 110b between the buffer layer 111 or the n-type semiconductor layer 112, even though the transparent substrate 110 has the uneven pattern 110b. 110, the buffer layer 111 and the n-type semiconductor layer 112 are generally present on the upper side, so that the amount of light loss due to the absorption of light in the layers 111 and 112 and the total internal reflection due to the large interlayer interface area There is a problem that the amount of loss is large. Such a problem is caused by internal absorption and / or total internal reflection when light travels in the same direction as indicated by the arrow in FIG. 1 and passes through the buffer layer 111, the n-type semiconductor layer 112, and the interfaces of the layers. Caused by a lot of light loss.

Accordingly, a technical object of the present invention is to provide a light emitting diode having a transparent substrate on which an uneven pattern is formed, and having an increased amount of light emitted directly from the uneven pattern without passing through an interface between other layers or layers, and a method of manufacturing the same. Shall be.

The light emitting diode according to the present invention comprises a transparent substrate having a plurality of uneven patterns on the upper surface, formed on the upper surface of the transparent substrate, and having an active layer between the first and second conductive semiconductor layers and the semiconductor layers. The light emitting cell includes a light emitting cell, and an upper surface of the transparent substrate is defined by an interface region forming an interface with the light emitting cell and an exposed region outside the light emitting cell, and the uneven pattern is present over the interface region and the exposed region.

Preferably, the light emitting cell includes a first conductive semiconductor layer located above the interface region, an active layer formed on an upper surface of the first conductive semiconductor layer, and a second conductive semiconductor formed on an upper surface of the active layer. A first electrode pad is formed on an exposed portion of the first conductive semiconductor layer formed by removing the second conductive semiconductor layer and a portion of the active layer, and a transparent electrode layer and a second upper surface of the second conductive semiconductor layer. An electrode pad is formed. A buffer layer is formed on the upper surface of the transparent substrate, confined to the interface region.

According to another aspect of the invention, preparing a transparent substrate having a plurality of uneven patterns on the upper surface, and sequentially forming a first conductive semiconductor layer, an active layer and a second conductive semiconductor layer on the upper surface of the transparent substrate And partially etching away the first conductive semiconductor layer, the active layer, and the second conductive semiconductor layer to expose a portion of the uneven pattern of the transparent substrate.

According to still another aspect of the present invention, there is provided a method of manufacturing a transparent substrate having a plurality of uneven patterns on an upper surface, covering a portion of an upper surface of the transparent substrate having the uneven pattern with a mask, and covering the mask with the mask. Forming a light emitting cell by sequentially forming a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer on an upper surface of the transparent substrate, removing the mask, and exposing a portion of the uneven pattern of the transparent substrate upward. There is provided a light emitting diode manufacturing method comprising the step of.

Other objects and advantages of the invention will be fully understood from the following description of the examples. 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 plan view illustrating a light emitting diode according to an embodiment of the present invention, and FIG. 3 is a cross-sectional view taken along the line A-A of FIG. 2.

2 and 3, the light emitting diode 1 of the present embodiment includes a transparent substrate 10 and a light emitting cell 20 formed on an upper surface of the transparent substrate 10. The transparent substrate 10 is preferably a sapphire substrate having a refractive index of approximately 1.7. The light emitting cell 20 is preferably made of GaN-based semiconductor layers.

As shown in FIG. 3, the light emitting cell 20 includes a first conductive semiconductor layer 22 and a second conductive semiconductor layer 24, and an active layer interposed between the semiconductor layers 22 and 24. 23). In the present embodiment, the first conductive semiconductor layer 22 is an n-type semiconductor layer 22, and the second conductive semiconductor layer 24 is a p-type semiconductor layer 24.

A buffer layer 11 for alleviating lattice mismatch is interposed between the transparent substrate 10 and the n-type semiconductor layer 22 of the light emitting cell 20. In addition, the p-type semiconductor layer 24 and a portion of the active layer 23 thereunder are removed, and a portion of the n-type semiconductor layer 22 below the removed portion is exposed upward. In this case, a portion of the n-type semiconductor layer 22 may be further removed in the depth direction. An n-type first electrode pad 22a is formed on an exposed portion of the n-type semiconductor layer 22, and a transparent electrode layer 24a and a p-type second electrode are formed on an upper surface of the p-type semiconductor layer 24. The pad 24b is formed. In the drawing, reference numeral 10b denotes a lead frame to which the light emitting diodes 1 are attached and mounted in a package process. In this embodiment, the lead frame 10b serves to apply an electric current to the light emitting diodes 1 in addition to the active layer 23. It serves to reflect the light toward the downward direction of the upward direction.

A plurality of uneven patterns 10a are formed on the entire upper surface of the transparent substrate 10. The light emitting cell 20 is formed to be limited to a portion of the upper surface of the transparent substrate 10. As a result, an upper surface of the transparent substrate 10 is an interface region I bordering the light emitting cell 20 and an exposed region E positioned outside the light emitting cell 20 and exposed upward. The concave-convex pattern 10a is present throughout the interface region I and the exposure region E. In addition, the above-described buffer layer 11 is locally formed on the interface region I on the upper surface of the transparent substrate 10, and the buffer layer 11 is exposed in the exposed region E of the transparent substrate 10. ) Does not exist. Therefore, in the exposed region E, the uneven pattern 10a of the transparent substrate 10 is exposed to the outside as it is.

Due to the structure of the light emitting diode 1 described above, many regions above the uneven pattern 10a are directly exposed to the outside without forming an interface with the semiconductor layers. And the total area of the interlayer interfaces mainly causing light loss due to total internal reflection is greatly reduced. In this case, in particular, the buffer layer 11, which is formed of an internal absorption and total internal reflection of light unnecessarily, is removed above the exposed region E, thereby contributing to reducing the loss of light.

For example, the light reflected by the lead frame 10b in the direction of the arrow in FIG. 2 is located in the exposed area E on the transparent substrate 10 without passing through the n-type semiconductor layer 22 and the buffer layer 11. It immediately exits through the uneven pattern 10a. Therefore, the light emitted from the exposed region E does not have a loss generated when passing through the n-type semiconductor layer 22 and the buffer layer 11. In addition, since the surface critical angle is reduced by the uneven pattern 10a, it contributes to greatly reducing the loss of light due to total internal reflection in the exposed area E. In this case, the uneven pattern 10a is preferably a stripe type or a hemisphere type, but may have various shapes to reduce the surface critical angle.

First, a transparent substrate 10 made of sapphire material as shown in FIG. 4A is prepared. The transparent substrate 10 is prepared to have the uneven pattern 10a on one surface, and the uneven pattern 10a may be formed by, for example, a partial etching process using a photographic technique.

Next, as shown in FIG. 4B, a buffer layer 11, an n-type semiconductor layer 22, an active layer 23, and a p-type semiconductor are formed on an upper surface of the transparent substrate 10, that is, the uneven pattern 10a. Layer 24 is formed in turn. The transparent electrode layer 24a may be formed on the p-type semiconductor layer 24. In this case, the buffer layer 11 and the semiconductor layers 22, 23, and 24 thereon entirely cover the uneven pattern 10a. In this case, the n-type semiconductor layer 22, the active layer 23 and the p-type semiconductor layer 24, respectively, metalorganic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE) ), Molecular beam epitaxy (MBE) technology, or the like.

Next, as shown in FIG. 4C, the p-type semiconductor layer 24, the active layer 23, and the n-type semiconductor layer 22 and the buffer layers 11 are partially left, and the layers 24, 23, 22, 11) Etch them in the depth direction. If the transparent electrode layer 24a is formed on the p-type semiconductor layer 24, a part of the transparent electrode layer 24a is also removed. By the etching removal process, a portion of the uneven pattern 10a of the upper surface of the transparent substrate 10 is exposed, and the exposed portion becomes the exposure area E. FIG. The light emitting cell 20 including the p-type semiconductor layer 24, the active layer 23, and the n-type semiconductor layer 22, the light emitting cell 20, and the transparent cell 20 are not disposed on the unexposed interface region I. The buffer layer 11 interposed between the substrates 10 is positioned.

Next, a light emitting diode 1 having a structure as shown in FIG. 3 is formed. For this purpose, a part of the p-type semiconductor layer 24 on which the transparent electrode layer 24a is formed and the p-type semiconductor layer 24 are formed. An etching process of removing a portion of the lower active layer 23 to expose a portion of the n-type semiconductor layer 22 upward, and an n-type first electrode pad 22a at an exposed portion of the n-type semiconductor layer 22. ) And forming a p-type second electrode pad 24b on the transparent electrode layer 24a.

By the above-described light emitting diode manufacturing method, the transparent substrate 10 is limited to the interface region I and the exposure region E, and the uneven pattern 10a is formed over the interface region I and the exposure region E. The existing light emitting diode 1 can be manufactured.

5A to 5C illustrate a method of manufacturing a light emitting diode according to another embodiment of the present invention. In describing the present embodiment, description of the same process as in the previous embodiment is omitted to avoid duplication.

First, as shown in FIG. 5A, a process of covering a portion of the upper surface of the transparent substrate 10 having the uneven pattern 10a with a mask M is performed. Next, as shown in FIG. 5B, an n-type semiconductor layer 22, an active layer 23, and a p-type semiconductor layer 24 are sequentially formed on an upper surface of the transparent substrate 10 covered with the mask M. FIG. Thus, one light emitting cell 20 is formed. In this case, the transparent electrode layer 24a may be formed on the p-type semiconductor layer 24. Next, as shown in FIG. 5C, the mask M is removed from the upper surface of the transparent substrate 10. At this time, a part of the uneven pattern 10a covered by the mask M is exposed to the outside, so that the upper surface of the transparent substrate 10 is limited to the exposed area E and the interface area I. do. In addition, the uneven pattern 10a is present throughout the exposed area E and the interface area I. Subsequent processes are substantially the same as those of the foregoing embodiment, and thus description thereof is omitted.

6 is a comparative test of the light efficiency of the light emitting diode (ie, B type LED) of the present embodiment shown in FIGS. 2 and 3 and the conventional light emitting diode (ie, A type LED) shown in FIG. It is a graph showing the results. In the graph of FIG. 6, the horizontal axis represents the chip number, that is, the test number of the present embodiment and the conventional light emitting diode used in the comparison test, and the vertical axis represents the light intensity of the light emitting diode. Referring to FIG. 6, it can be seen that the light emitting diode (ie, B type LED) of the present embodiment has a higher light intensity and a higher light efficiency than a conventional light emitting diode (ie, A type LED) under the same conditions. Specifically, it was confirmed that the light emitting diode of the present embodiment has an optical efficiency improvement of approximately 17% compared to the conventional light emitting diode.

In the above, the light emitting diode in which one light emitting cell is formed on the transparent substrate is mainly described. However, forming a plurality of light emitting cells on the transparent substrate may be considered.

The present invention improves the light extraction efficiency degradation caused by the uneven pattern formed on the transparent substrate being entirely covered by the semiconductor layers thereon. According to the present invention, the interface between the uneven patterns and other layers or layers may be reduced. The amount of light emitted immediately without going through is increased, thereby greatly improving the light extraction efficiency.

Claims

A light emitting diode comprising a transparent substrate and a single light emitting cell formed on an upper surface of the transparent substrate and having first and second conductive semiconductor layers and an active layer between the semiconductor layers.

An upper surface of the transparent substrate is limited to an interface region forming an interface with the single light emitting cell and an exposed area outside the single light emitting cell,

The exposed area is formed to completely surround the interface area,

A light emitting diode, characterized in that the uneven pattern is formed over the exposed area and the entire interface area.

The light emitting diode of claim 1, wherein the transparent substrate is a sapphire substrate.

The method of claim 1, wherein the single light emitting cell, the first conductive semiconductor layer positioned above the interface region, the active layer formed on the upper surface of the first conductive semiconductor layer, and the second surface formed on the upper surface of the active layer A first electrode pad is formed on an exposed portion of the first conductive semiconductor layer formed by removing the second conductive semiconductor layer and a part of the active layer, and a transparent electrode layer on an upper surface of the second conductive semiconductor layer; A light emitting diode, characterized in that the second electrode pad is formed.

The light emitting diode of claim 1, wherein a buffer layer is formed on an upper surface of the transparent substrate so as to be limited to the interface region.

Preparing a transparent substrate having an uneven pattern on the entire upper surface thereof;

Forming semiconductor layers including a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer sequentially from an upper surface of the transparent substrate;

Etching away one region of the semiconductor layers to form a single light emitting cell;

The method of manufacturing a light emitting diode according to claim 1, wherein the upper surface of the transparent substrate is exposed with an uneven pattern surrounding the single light emitting cell as a whole.

Covering a portion of the upper surface of the transparent substrate with a mask;

Forming a single light emitting cell by sequentially forming a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer on an upper surface of the transparent substrate covered with the mask;

Removing the mask to expose a portion of the uneven pattern of the transparent substrate upward;

After removing the mask, the upper surface of the transparent substrate is a light emitting diode manufacturing method, characterized in that the uneven pattern surrounding the single light emitting cell as a whole.

The method of claim 5, wherein the transparent substrate is a sapphire substrate.

7. The light emitting diode manufacturing method according to claim 5 or 6, wherein a buffer layer is formed on an upper surface of the transparent substrate, only at an interface between the first conductive semiconductor layer and the transparent substrate.