WO2006022532A1

WO2006022532A1 - Iii-nitride semiconductor light emitting device

Info

Publication number: WO2006022532A1
Application number: PCT/KR2005/002842
Authority: WO
Inventors: Tae Kyung Yoo; Chang Tae Kim; Keuk Kim
Original assignee: Epivalley Co., Ltd.
Priority date: 2004-08-26
Filing date: 2005-08-26
Publication date: 2006-03-02
Also published as: KR100568830B1; KR20060018989A

Abstract

The present invention relates to a III-nitride semiconductor light emitting device comprising a plurality of III-nitride semiconductor layers epitaxially grown on a substrate, in which the exposed surface including a region for breaking of the light emitting device, the exposed surface of the region for breaking of the light emitting device having protrusions which makes the surface rough, the protrusions being formed by etching with an etching mask.

Description

Description m-NITRIDE SEMICONDUCTOR LIGHT EMITTING DEVICE

Technical Field

[1] The present invention relates to a IH-nitride semiconductor light emitting device, and more particularly to a IE-nitride semiconductor light emitting device having a high external quantum efficiency. The IH-nitride compound semiconductor means a semi¬ conductor having a formula of Al(x)In(y)Ga(l-y)N, which may further comprise a semiconductor of elements from other groups such as SiC, SiN and SiCN or the elements per se. Background Art

[2] Various attempts have been made to increase external quantum efficiency of the light emitting device. Among them, there have been disclosed many methods for roughing an exposed surface of the light emitting device.

[3] US PAT NO. 6,504,180 which is directed to a GaAs-based light emitting device discloses a technique to increase the external quantum efficiency by roughing at least a part of the exposed surface of the light emitting device. Since GaAs has material properties which can be readily processed, a desired part of the exposed surface of the GaAs-based light emitting device can be freely roughened. However, a GaN-based light emitting device has a lot of limitations in processing the exposed surface, unlike the GaAs-based light emitting device. Such limitations include that since an n-type layer is deposited on a substrate such as sapphire, it cannot be processed and the growth of a thick p-type GaN layer can cause lattice mismatch, though it should be thickly grown for processing. Therefore, it is difficult to introduce technologies applied to the GaAs-based light emitting device into the GaN-based light emitting device. Thus, in order to increase the external quantum efficiency by roughening the exposed surface of the GaN-based light emitting device, an approach should be made on the basis of the GaN-based light emitting device itself. Further, US PAT NO. 6,504,180 employs polystyrene spheres as a mask to roughen the exposed surface. However, the technology using polystyrene spheres as a mask cannot be applied to the GaN-based light emitting device.

[4] US PAT NO. 6,441,403 is directed to a GaN-based light emitting device, in which the light emitting device comprises a roughened surface formed on a p-type Al(x)Ga(y)In(l-x-y)N layer epitaxially grown on an active layer or an n-type Al(x)Ga(y)In(l-x-y)N layer epitaxially grown on an active layer. From this technology, we can see that it is not easy to form a roughened surface on an n-type Al(x)Ga(y)In(l-x-y)N layer in the conventional light emitting device comprising the n- type Al(x)Ga(y)In(l-x-y)N layer under an active layer.

[5] In order to address and overcome such a problem, Korean Patent Application No.

2003-55907, filed by the present applicant, discloses a IH-nitride semiconductor light emitting device with external quantum efficiency increased by employing a room space for breaking process which is left in the perimeter of a light emitting device to be broken between light emitting devices.

[6] As shown in FlG. 1, Korean Patent Application No. 2003-55907 discloses a

IE-nitride semiconductor light emitting device formed by sequentially epitaxially growing a buffer layer 30, an n-type Al(x)In(y)Ga(l-x-y)N layer 31, an n-type Al(x 1 )In(y I)Ga(I -x 1-y I)N clad layer 32, an active layer 33, a p-type Al(al)In(bl)Ga(l-al-bl)N clad layer 34 and a p-type Al(a)In(b)Ga(l-a-b)N layer 35 on a substrate 20, and forming a p-type electrode 51 and a p-type bonding pad 53 on the p-type Al(a)In(b)Ga(l-a-b)N layer 35 and an n-type electrode 52 on the n-type Al(x)In(y)Ga(l-x-y)N layer 31.

[7] After the light emitting device has been made, a scribing and breaking process is performed to package the device. For the scribing and breaking process, there has been left a room space of 40 to 6OD between devices. The room space has no specific function and is just for a room for processing.

[8] Korean Patent Application No. 2003-55907 discloses a method for increasing external quantum efficiency by forming protrusions 154 in such a room space, in which the n-type Al(x)In(y)Ga(l-x-y)N layer 31 is dry etched by using the etching residues spontaneously generated upon the etching of the n-type Al(x)In(y)Ga(l-x-y)N layer 31 as a mask pattern to form the protrusions 154.

[9] However, the use of etching residues as a mask pattern has a disadvantage in that the reproducibility is limited by the atmosphere of a vacuum chamber. Disclosure of Invention Technical Problem

[10] Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide a IE-nitride semiconductor light emitting device having a high external quantum efficiency by forming fine protrusions with high density at the outside of the El-nitride semiconductor light emitting device except for a light emitting part of the device. Technical Solution

[11] To accomplish the above objects of the present invention, according to the present invention, there is provided a IE-nitride semiconductor light emitting device comprising a plurality of IH-nitride semiconductor layers epitaxially grown on a substrate, in which the IH-nitride semiconductor layers comprises an active layer for generating protons by recombination of electron and hole, an n-type Al(x)In(y)Ga(l-x-y)N layer epitaxially grown prior to the growth of the active layer, and a pad electrode electrically connected to the n-type Al(x)In(y)Ga(l-x-y)N layer, in which the n-type Al(x)In(y)Ga(l-x-y)N layer has a surface exposed by etching, the exposed surface including a region for breaking of the light emitting device, the exposed surface of the region for breaking of the light emitting device having protrusions which makes the surface rough, the protrusions being formed by etching using an etching mask.

[12] Also, the present invention provides a IE-nitride semiconductor light emitting device comprising an etching mask formed of a material that is able to endure the dry etching for a predetermined period of time. Here, that the etching mask endures the dry etching for a predetermined period of time means that the etching mask controls the etching rate of the nitride semiconductor layer so that protrusions are formed between the region where the etching mask is provided and the region where the etching mask is not provided. Preferably, the etching mask is formed of a metal or metal oxide film. Advantageous Effects

[13] The present invention pays attention to the exposed surface of the n-type

Al(x)In(y)Ga(l-x-y)N layer which has not been noticed in the IH-nitride semi¬ conductor light emitting device and forms a roughened surface in the exposed surface to increase external quantum efficiency of the light emitting device. Brief Description of the Drawings

[14] Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

[15] FIG. 1 is a cross-sectional view for explanation of a conventional El-nitride semi¬ conductor light emitting device;

[16] FIG. 2 is a cross-sectional view for explanation of a El-nitride semiconductor light emitting device according to an embodiment of the present invention;

[17] FTG. 3 is a plane view of HG. 2;

[18] FIG. 4 to FIG. 7 are views for explanation of the method for forming a roughened surface according to a preferred embodiment of the present invention;

[19] FIG. 8 and FIG. 9 are views for explanation of the principle, based on which the external quantum efficiency is increased;

[20] FIG. 10 to FIG. 12 are AFM photographs of the roughened surface formed according to the present invention;

[21] FIG. 13 is a view showing the density of the roughened surface according to the thickness of the ITO film, which is the metal oxide film 70;

[22] FlG. 14 is a graph of applied current over brightness for comparison of the present invention with the conventional example; and

[23] FlG. 15 is a view for explanation of another embodiment according to the present invention. Mode for the Invention

[24] Now, the preferred embodiment of the present invention is described in further detail with reference to the drawings. In the drawings, the same numerical references as those in FlG. 1 represent construction elements performing the same function and thus, repetitive explanation is omitted.

[25] The following example is presented to help the understanding of the disclosure of the present invention and thus, those having the ordinary knowledge in the art can make changes in the technical spirit of the present invention. Therefore, it should not be construed that the present invention is limited to this example.

[26] FlG. 2 is a cross-sectional view for explanation of a IH-nitride semiconductor light emitting device according to an embodiment of the present invention and FlG. 3 is a plane view of FlG. 2.

[27] Referring to FlGs. 2 and 3, a light emitting device is shown to have a substrate 20, a buffer layer 30 epitaxially grown on the substrate 20, an n-type Al(x)In(y)Ga(l-x-y)N layer 31 epitaxially grown on the buffer layer 30, an active layer 33 epitaxially grown on the n-type Al(x)In(y)Ga(l-x-y)N layer 31, a p-type Al(a)In(b)Ga(l-a-b)N layer 35 epitaxially grown on the active layer 33, a p-side electrode 51 and an p-side bonding pad 53 electrically connected to the p-type Al(a)In(b)Ga(l-a-b)N layer 35, and a pad electrode 52 electrically connected to the n-type Al(x)In(y)Ga(l-x-y)N layer 31. Also, on the exposed surface of the n-type Al(x)In(y)Ga(l-x-y)N layer 31, protrusions 54 are formed to make the surface rough.

[28] The present invention can be applied to the light emitting devices having various types of epitaxial structures. In FlG. 2, the light emitting device is shown to have an epitaxial structure comprising an n-type Al(xl)In(yl)Ga(l-xl-yl)N clad layer 32 disposed between the n-type Al(x)In(y)Ga(l-x-y)N layer 31 and the active layer 33 and a p-type Al(al)In(bl)Ga(l-al-bl)N clad layer 34 disposed between the active layer 33 and the p-type Al(a)In(b)Ga(l-a-b)N layer 35.

[29] The present invention is not limited to these epitaxial structures and can be applied to any IH-nitride semiconductor light emitting devices having the n-type Al(x)In(y)Ga(l-x-y)N layer 31 disposed under an active layer and serving as an electrical contact layer of the pad electrode 52. For example, an n-type compound semiconductor layer or a super lattice layer thereof may be disposed between the p- side electrode 51 and the p-type Al(a)In(b)Ga(l-a-b)N layer 35. The n-type Al(x)In(y)Ga(l-x-y)N layer 31 is preferably made of GaN and may be composde of a multi-layered or super lattice structured n-type contact layer composed of Al(a2)In(b2)Ga(l-a2-b2)N/Al(a3)In(b3)Ga(l-a3-b3)N.

[30] Now, the method for forming the protrusions 54 on the exposed surface of the n- type Al(x)In(y)Ga(l-x-y)N layer 31 using dry etching according to a preferred embodiment of the present invention is described.

[31] 1. Growth of epi-layers 30, 31, 32, 33, 34 and 35

[32] Firstly, the buffer layer 30, the n-type Al(x)In(y)Ga( 1 -x-y)N layer 31 , the n-type

Al(x 1 )In(y I)Ga(I -x 1-y I)N clad layer 32, the active layer 33, the p-type Al(al)In(bl)Ga(l-al-bl)N clad layer 34 and the p-type Al(a)In(b)Ga(l-a-b)N layer 35 are sequentially epitaxially grown on the sapphire substrate 20. When ITO is used as the p-side electrode 51, the n-type semiconductor layer is preferably provided on the p- type Al(a)In(b)Ga(l-a-b)N layer 35.

[33] 2. Formation of etching mask

[34] Next, the epitaxially grown wafer is dipped in HCl:DI(Deionized Water) = 3:1 solution for 5 minutes and rinsed with DI for 5 minutes. As shown in FIG. 4, a metal film or metal oxide film 70 is deposited on the region where the roughened surface will be formed (corresponding to the exposed surface 60 where protrusions 54 will be formed after etching), using photolithography process. In this example, the region where the metal film or metal oxide film 70 will be formed is the entire region except for a region 90 where the light emitting part will be formed and a region 100 where the pad electrode 52 will be formed.

[35] Here, the usable metal includes, for example, Ni, Cr, W, La, Au, Pt, Ti, Ta, Pd, Ru,

V, Ir, In, Sn, Ga and Al or an alloy of two or more thereof and the usable metal oxide film includes, for example, Ni O , Cr O , W O , La O , Ti O , Ta O , Ru O , Mg O , x y x y x y x y x y x y x y x y

Ru O , V O , In O , Sn O , Ga O , Al O or two or more thereof (provided that x and y x y x y x y x y x y x y is an integer which is greater than or equal to 1 and less than or equal to 10). In this example, ITO (Indium Tin Oxide: In Sn O ) is used. x y z

[36] 3. Formation of p-side electrode 51

[37] Next, as shown in FIG. 5, the p-side electrode 51 is formed in a predetermined pattern, on the wafer with the epi-layers 30, 31, 32, 33, 34 and 35. The p-side electrode 51 is subjected to thermal treatment (600°C, 1 minutes) for ohmic contact with the p- type Al(a)In(b)Ga(l-a-b)N layer 35 which is provided thereunder and the metal film or metal oxide film 70 is also thermally treated. That is, according to a preferred embodiment of the present invention, without a separate thermal treatment for the metal film or metal oxide film 70, the metal film or metal oxide film 70 can be converted to an etching mask by the thermal treatment of the p-side electrode 51. However, the thermal treatment for converting the metal film or metal oxide film 70 to an etching mask can be a separate procedure.

[38] It is clear to those skilled in the art that the temperature at the thermal treatment is performed and the thickness of the metal film or metal oxide film 70 can vary according to various conditions such as materials of the p-side electrode 51 and the metal film or metal oxide film 70, the density of the roughened surface, etching conditions and the like.

[39] By the thermal treatment, the metal film or metal oxide film 70 is converted to an etching mask 80 for forming the roughened surface, as shown in FlG. 6. When the metal film or metal oxide film 70 having a small thickness on the surface of the gallium nitride semiconductor is thermally treated, it conglomerates to form fine particles 80. Upon dry etching, these particles 80 serve as an etching mask and the other part without particles is etched. The particles 80 are preferably of material having sufficient resistance to a gas used in the dry etching.

[40] 4. Dry etching

[41] Next, the dry etching is performed on the region except for the region 90 using the photolithography. Here, the fine particles 80 serve as an etching mask. As the etching is performed, the area to be etched is narrowed. As the etching mask is removed, protrusions 54 in the form of a cone or a pyramid are formed as shown in FlG. 2.

[42] Here, since the region 100 where the pad electrode 52 will be formed is etched si¬ multaneously, there is no need of a separate mesa-etching process for forming the pad electrode 52. As shown in FlG. 7, since the etching mask of the fine particles 80 is not formed in the region 100, there is not formed protrusions in the region 100 after etching.

[43] Here, the dry etching is usually performed using plasma, in which the plasma forming gas is based on chlorine. The chlorine based gas may be one of Cl , BCl , CCl and HCl or a mixture of two or more thereof. The conditions for dry etching used in this example include Cl =20sccm, process pressure of 1.5mTorr, RF Power of 200W (for ICP source), 45W (for RF bias), and the time of 5 minutes. The etching conditions can vary according to the used etching equipment and gas.

[44] As shown in FlG. 8, among the lights generated at the active layer of the light emitting device, the lights entering at an incident angle less than the critical angle (θ ) are extinguished within the device. The structure having an external quantum efficiency of 1 is a sphere or a cone as shown in FlG. 9. According to the present invention, the protrusions can be formed in the form of a cone or pyramid to maximize the external quantum efficiency of the light emitting device. [45] 5. Formation of p-side bonding pad 53 and pad electrode 52

[46] Next, the p-side bonding pad 53 is formed on the p-side electrode 51 using pho- tolithography process and the pad electrode 52 is deposited on the region 100. Finally, the light emitting as shown in FIG. 3 is formed.

[47] FIGs. 10 to 12 are AFM photographs of the roughened surface formed according to the present invention. In FIG. 10, the metal oxide film 70 of ITO is formed to 2OA, in FTG. 11, the metal oxide film 70 of ITO is formed to 50A and in FTG. 12, the metal oxide film 70 of ITO is formed to 10OA. The protrusions have roughly a circular cone or pyramid shape and has a width of the bottom of about ID or less and a height of ID or less.

[48] FTG. 13 is a view showing the density of the roughened surface according to the thickness of the ITO film, which is the metal oxide film 70. When the ITO film has a thickness of about 5OA, the protrusions 54 are formed at a density of about 8.8x10 /cm

2

[49] FTG. 14 is a graph of applied current over brightness for comparison of the present invention with the conventional example. The example according to the present invention showed 30 to 50% increase in brightness compared to the conventional example, though there was a little difference according to the size and shape of the protrusions 54.

[50] A metal film or metal oxide film 170 according to the present invention can be formed only in the outer room space of the light emitting device, as shown in FTG. 15. In this case, the light emitting device can be formed by the above-described method. However, protrusions 54 are not formed in the part surrounding the region 100.

[51] While the method for forming the roughened surface by a preferred example of the present invention, it should be understood that the used procedures and conditions for the process is for illustration and the present invention is not limited thereto.

Claims

[1] A IE-nitride semiconductor light emitting device comprising a plurality of

El-nitride semiconductor layers epitaxially grown on a substrate, in which the m-nitride semiconductor layers comprises an active layer for generating protons by recombination of electron and hole, an n-type Al(x)In(y)Ga(l-x-y)N layer epitaxially grown prior to the growth of the active layer, and a pad electrode electrically connected to the n-type Al(x)In(y)Ga(l-x-y)N layer, in which the n- type Al(x)In(y)Ga(l-x-y)N layer has a surface exposed by etching, the exposed surface including a region for breaking of the light emitting device, the exposed surface of the region for breaking of the light emitting device having protrusions which makes the surface rough, the protrusions being formed by etching with an etching mask.

[2] The El-nitride semiconductor light emitting device of claim 1, in which the etching is dry etching.

[3] The El-nitride semiconductor light emitting device of claim 2, in which the etching mask is formed of a material that is able to endure the dry etching for a predetermined period of time.

[4] The El-nitride semiconductor light emitting device of claim 1, in which the etching mask is formed of a metal or metal oxide film.

[5] The El-nitride semiconductor light emitting device of claim 4, in which the etching mask is formed of at least one selected from the group consisting of Ni, Cr, W, La, Au, Pt, Ti, Ta, Pd, Ru, V, Ir, In, Sn, Ga and Al.

[6] The El-nitride semiconductor light emitting device of claim 4, in which the etching mask is formed of at least one selected from the group consisting of Ni O

, Cr O , W O , La O , Ti O , Ta O , Ru O , Mg O , Ru O , V O , In O , Sn O , y x y x y x y * y * y * y * y x y x y x y * y

Ga x O y and Al x O y .

[7] The El-nitride semiconductor light emitting device of claim 1, in which the protrusions are in the form of a pyramid.

[8] The El-nitride semiconductor light emitting device of claim 1, in which the exposed surface further comprises a region for contact with the pad electrode, and the exposed surface having protrusions formed thereon and the exposed surface of the region for contact with the pad electrode are simultaneously formed by the etching.

[9] The El-nitride semiconductor light emitting device of claim 1, in which the exposed surface further comprises a region for contact with the pad electrode and an additional exposed surface for surrounding the region for contact with the pad electrode, and the additional exposed surface has protrusions on the surface.