JP2003224297A - Light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor light emitting diode in which the light from an active layer can be efficiently emitted. <P>SOLUTION: The light emitting element comprises a semiconductor layer and an ohmic electrode brought into ohmic contact with the semiconductor layer so that the ohmic electrode is a translucent ohmic electrode, and a reflecting structure is formed by covering the ohmic electrode with the reflecting layer via a translucent insulating film. In this element, the reflecting layer is formed of one selected from the group consisting of Al, Ag and Rh. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a nitride semiconductor light emitting device.

[0002]

2. Description of the Related Art In recent years, a light emitting diode (nitride semiconductor light emitting diode) composed of a nitride semiconductor has been widely used mainly as a blue light emitting diode. This nitride semiconductor light emitting diode is
For example, on a sapphire substrate, an n-type nitride semiconductor layer, In
An active layer and a p-type nitride semiconductor layer made of GaN or the like are laminated, and a part of the active layer and the p-type nitride semiconductor layer are removed to expose the exposed n-type nitride semiconductor layer. An electrode is formed, and a p-side ohmic electrode is formed on the p-type nitride semiconductor layer. Further, in this nitride semiconductor light-emitting diode, the p-type nitride semiconductor layer has a higher resistance value than the n-type nitride semiconductor layer, so that the p-side ohmic electrode is formed on almost the entire surface of the p-type nitride semiconductor layer. By forming it, the current is efficiently injected into the entire active layer.

In the nitride semiconductor light emitting diode configured as described above, the light emitted in the active layer can be emitted from the substrate side by utilizing the fact that the sapphire substrate has a light-transmitting property, and the light on the p side can be emitted. The ohmic electrode is made thin so that it has a light-transmitting property.
Alternatively, the light can be emitted through the side ohmic electrode.

[0004]

However, the conventional nitride semiconductor light emitting diode has a problem that the light emitted in the active layer cannot be efficiently emitted to the outside. Therefore, an object of the present invention is to provide a nitride semiconductor light emitting diode capable of efficiently emitting the light emitted in the active layer.

[0005]

To achieve the above object, a light emitting device according to the present invention is a light emitting device having a semiconductor layer and an ohmic electrode in ohmic contact with the semiconductor layer. The reflective structure is configured by using the ohmic electrode as a translucent ohmic electrode and covering the translucent ohmic electrode with a reflective layer via a translucent insulating film, and the reflective layer is made of Al, Ag and Rh. It is characterized by comprising one selected from the group consisting of. The light emitting device according to the present invention configured as described above can reflect light by the reflective layer and efficiently emit the light in a desired direction.

The light emitting device may include a p-type contact layer made of a p-type nitride semiconductor layer as the semiconductor layer, and the translucent ohmic electrode formed on the p-type contact layer.

In order to increase the reflectance, the above-mentioned insulating film is
It is preferably made of SiO ₂ which is a material having a low refractive index.

The thickness of the insulating film is preferably 3 μm or less in order to accurately pattern the insulating film.

The thickness of the reflective layer is 0.05 μm to 1 μm.
It is preferably set in the range of m.

The insulating film may have an opening, and the ohmic electrode and the reflective layer may be electrically connected to each other through the opening. By doing so, the pad electrode can be formed on the surface of the reflective layer. In this case, it is preferable that the pad electrode is located above the opening.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A nitride semiconductor light emitting device according to an embodiment of the present invention will be described below with reference to the drawings. As shown in FIGS. 1 and 2, the nitride semiconductor light emitting device according to the first embodiment of the present invention includes, for example, a substrate 10 made of sapphire and an n-side nitride semiconductor layer 20 via a buffer layer 11. The active layer 30 and the p-side nitride semiconductor layer 40 are sequentially grown to form the n-side and p-side electrodes. Here, in the nitride semiconductor light emitting device of the present embodiment, in particular, the translucent p-side ohmic electrode 53 is formed on substantially the entire surface of the p-side nitride semiconductor layer 40 (p-type contact layer 42), Further, the reflective layer 1 made of Al or Ag is formed on the ohmic electrode 53 so as to cover the ohmic electrode 53 with the insulating film 2 interposed therebetween, whereby the reflectance on the p side can be improved, The extraction efficiency of the light output from the substrate side or the substrate side surface is improved. In the nitride semiconductor light emitting device according to the present embodiment, the n-side electrode is exposed by removing a part of the p-side nitride semiconductor layer 40 and the active layer 30 as in the conventional case. It is formed on the semiconductor layer 20 (n-type contact layer 21).

The structure and manufacturing method of the nitride semiconductor light emitting device of this embodiment will be described in detail below. In the present embodiment, the semiconductor laminated structure of the nitride semiconductor light emitting device is configured as follows. That is, on the sapphire substrate 10, the AlGaN layer 11, which is a low temperature buffer layer,
An n-type contact layer 21 (for example, a thickness of about 2 μm) made of Si-doped GaN and having an n-electrode formed thereon, n-type Al
N-type cladding layer 22 made of GaN, non-doped In
A light emitting layer 30 having a single or multiple quantum well structure including a GaN well layer (for example, a thickness of about 30Å), a p-type clad layer 41 made of p-type AlGaN, and a p-type contact layer 42 made of GaN doped with Mg ( For example, about 1200
Å) is formed in sequence.

The electrode structure is constructed as follows.
In the nitride semiconductor light emitting device of the present embodiment, the n-side ohmic electrode 51 has the same structure as the conventional one, and the n-side nitride exposed by removing a part of the p-side nitride semiconductor layer 40 and the active layer 30. It is formed on the semiconductor layer 20 (n-type contact layer 21). In the nitride semiconductor light emitting device of the present embodiment, as shown in FIG. 1, at one corner of the rectangular nitride semiconductor light emitting device, the p-side nitride semiconductor layer 40 is fan-shaped.
And the active layer 30 is removed by etching so that the surface of the n-type contact layer 21 is exposed, and the exposed n
N-type ohmic electrode 51 on the surface of the mold contact layer 21.
And the pad electrode 52 is formed thereon. Further, the n-side ohmic electrode 51 is composed of two layers of a Ti layer having a thickness of 100 Å and an Al layer having a thickness of 5000 Å, so that the n-type contact layer 21 made of an n-type nitride semiconductor is formed.
And good ohmic contact can be obtained. Also, n
On the side ohmic electrode 51, a W layer may be formed instead of the Ti layer.

In the nitride semiconductor light emitting device of the present embodiment, the p-side ohmic electrode 53 is formed so as to have a light-transmitting property over substantially the entire surface of the p-type contact layer 42. The p-side ohmic electrode 53 has, for example, a thickness of 100Å
Of the Ni layer and the Au layer having a thickness of 100 Å, and with such a structure, it is possible to make ohmic contact with the p-type contact layer 42 and to have a light-transmitting property.
The ohmic electrode 53 on the side can be formed. Further, as the p-side ohmic electrode 53 capable of making ohmic contact with the p-type contact layer 42 and having a light-transmitting property, in addition to the above Ni-Au electrode, a Ni-Pt electrode, Co-A.
A u electrode can also be used.

The transparent insulating film 2 is formed so as to cover the entire nitride semiconductor light emitting device, has an opening 2a on the n-side ohmic electrode 51, and is opposed to the n-side ohmic electrode 51. P-side ohmic electrode 5 at the corner
3 has an opening 2b. This translucent insulating film 2
Is transparent to at least the emission wavelength, and is, for example, SiO ₂ , Al ₂ O ₃ , SiN, or TiO 2.
₂ , ZrO _{2 and the} like. Further, as a material of the translucent insulating film 2, particularly preferable one is SiO.
₂ and TiO ₂ because the reflectance can be particularly high among the materials exemplified above. Even more preferred is SiO ₂ . The reason is not only that the reflectance can be the highest, but also because the stability is excellent, the reliability can be enhanced. The thickness of the translucent insulating film 2 is preferably set in the range of emission wavelength or more and 3 μm or less, and by setting it to the emission wavelength or more, high reflection can be realized at the boundary with the reflective layer, and By setting the thickness to 3 μm or less, it becomes easy to form the translucent insulating film by lift-off, and the yield can be improved.

Further, in the nitride semiconductor light emitting device of this embodiment, the reflective layer 1 is made of Al, Ag or Rh,
It is formed so as to cover the p-side ohmic electrode 53 with the translucent insulating film 2 interposed therebetween. Here, the reflective layer 1 has an opening 2b.
At, is electrically connected to the p-side ohmic electrode 53. The thickness of the reflective layer 1 is preferably set in the range of 0.05 μm to 1 μm, more preferably 0.1 μm.
It is set in the range of μm to 0.3 μm. Even if the film thickness of the reflective layer 1 is thicker than 0.3 or 1 μm, the effect on reflection does not change, but the manufacturing cost increases. Also, the reflective layer 1
This is because if the film thickness is less than 0.05 μm, the reflectance becomes low, and if it is 0.1 μm or more, better reflection characteristics can be obtained.

The n-side pad electrode 52 and the p-side pad electrode 54 are made of a common material, for example, by forming a Ni layer to a thickness of 1000 Å and an Au layer to a thickness of 6000 Å. Can be configured. Where n
The side pad electrode 52 is formed immediately above the n-side ohmic electrode 51 so as to be electrically connected to the n-side ohmic electrode 51 through the opening 2a, and the p-side pad electrode 54 is formed.
Is formed on the surface of the reflective film 1 so as to be located above the opening 2b.

In the nitride semiconductor light emitting device configured as described above, the translucent ohmic electrode 53, the translucent insulating film 2 and the reflective layer 1 constitute a reflective structure having a high reflectance as described later. Therefore, for example, light can be efficiently extracted in a desired direction such as the substrate side or the side surface of the light emitting element.

Next, a method of manufacturing the nitride semiconductor light emitting device of this embodiment will be described. Step 1. In this method, first, on a sapphire substrate (sapphire wafer) 10, a low-temperature buffer layer 11, an n-type contact layer 21, an n-type cladding layer 22, a light-emitting layer 30, a p-type cladding layer 41, and a p-type, which are each made of a nitride semiconductor. The contact layer 42 is sequentially formed, and the mask 5 is formed for each element except for a portion exposing the surface of the n-type contact layer 21.
5 is formed (FIG. 3). Step 2. Next, the surface of the n-type contact layer 21 is exposed for each element by etching the part where the mask 55 is not formed up to the middle of the n-type contact layer 21 (FIG. 4), and then the mask is formed. 55 is removed (FIG. 5).

Step 3. Next, for example, thickness 100Å
The p-type contact is formed by forming an electrode film 53a consisting of two layers of a Ni layer and a 100 Å thick Au layer (FIG. 6) and patterning by etching using a mask 56 (FIGS. 7 and 8). A p-side ohmic electrode 53 that makes ohmic contact with the layer 42 is formed on substantially the entire surface of each p-type contact layer 42. Step 4. Then, an n-side ohmic electrode 51 is formed on the surface of the n-type contact layer 21 exposed corresponding to each element (FIG. 9), and S is formed so as to cover the entire element.
A transparent insulating film 2 made of iO2 is formed (FIG. 10).

Step 5. Next, in the translucent insulating film 2, an opening 2a is formed on the n-side ohmic electrode 51, and an opening 2b is formed at a corner diagonal to the n-side ohmic electrode 51 of each element. The translucent insulating film 2 is connected to the ohmic electrode 53 on the p-side in the opening 2b.
The reflection layer 1 is formed so as to cover the p-side ohmic electrode 53 through (FIG. 11). Step 6. Next, a Ni layer is formed to a thickness of 1000 Å, an Au layer is formed thereon to a thickness of 6000 Å, and patterning is performed so that the pad electrode 52 on the n-side is formed on the n-side through the opening 2a. The p-side pad electrode 54 is formed on the surface of the reflective film 1 so as to be located above the opening 2b so as to be electrically connected to the ohmic electrode 51. As described above, a nitride semiconductor light emitting device having a reflective structure in which the translucent ohmic electrode 53, the translucent insulating film 2 and the reflective layer 2 are laminated on the p side can be manufactured.

Since the nitride semiconductor light emitting device of the embodiment configured as described above has the reflection structure configured as described above, for example, the extraction efficiency when light is output from the substrate side. Can be raised. FIG. 13 is a graph showing the wavelength dependence of the reflection characteristic of the reflection structure according to the present invention.
In FIG. 13, L1 to L3 each represent the reflection characteristic at the interface between the SiO2 film and the reflection film in the reflection structure according to the present invention, and L1 represents the reflection structure R1 configured by using Al as the reflection layer. L2 is the reflection characteristic of the reflection structure R2 formed by using Ag as the reflection layer, and L3 is the reflection characteristic of the reflection structure R3 formed by using Rh as the reflection layer. Further, L4 of FIG. 13 is shown for comparison, and in the conventional electrode structure constituted by forming only the conventional ohmic electrode made of Ni / Au on the p-type nitride semiconductor layer, The reflectance at the interface between the p-type nitride semiconductor layer and the ohmic electrode is shown.

From the results shown in FIG. 13, the following can be seen. First, as shown in FIG. 13, a wavelength of about 350 nm
In the range of 530 nm, the reflective structure according to the present invention can have a higher reflectance than the electrode structure of the conventional example, and thus emits yellow to blue light having a relatively short wavelength composed of a nitride semiconductor. It is particularly suitable as a reflective structure in a light emitting diode which can be. Further, as shown in FIG. 13, the reflective structure R1 according to the present invention configured by using Al as the reflective layer has a wavelength longer than that of the reflective structures R2, R3 according to the present invention using Ag and Rh as the reflective layer. About 350n
Since the reflectance can be increased in the range of m to 430 nm, it is particularly suitable as a reflecting structure of a light emitting diode configured to use nitride semiconductor to emit light of ultraviolet light to blue light having a shorter wavelength. Further, as shown in FIG. 13, the reflective structure R2 according to the present invention configured by using Ag as the reflective layer is
Compared with the reflective structures R1 and R3 according to the present invention using Al and Rh as the reflective layer, the reflectance can be increased at a wavelength of about 430 nm or more, and therefore, as a reflective structure of a light emitting diode that emits blue to yellow light, Are suitable.

14 to 16 show the reflection characteristics of the reflecting structures R1, R2 and R3 when the incident angle of light is changed. Here, L11, L21, and L31 in FIGS. 14 to 16 are reflection characteristics when the incident angle is 20 degrees, and L11, L21, and L22 in FIGS.
L32 is the reflection characteristic when the incident angle is 40 degrees, and is shown in FIG.
L13, L23, and L33 in FIG. 16 are reflection characteristics when the incident angle is 60 degrees. Further, FIG. 17 shows a case where the incident angle is 20 degrees (L41), the incident angle is 40 degrees (L42), and the incident angle is 60 degrees (L4) in the conventional electrode structure.
3) shows the respective reflection characteristics. It can be seen from FIGS. 14 to 16 that the reflective structure according to the present invention hardly depends on the incident angle. In this study, the p-side ohmic electrode has a thickness of 0.02 μm, the SiO 2 film 2 has a thickness of 0.5 μm, and the reflective layer 1 has a thickness of 0.2 μm.
m.

[0025]

As described above in detail, the light emitting device according to the present invention is a light emitting device having a semiconductor layer and an ohmic electrode in ohmic contact with the semiconductor layer.
A reflective structure is formed by covering the translucent ohmic electrode with a reflective layer via a translucent insulating film, and the reflective layer is formed of one selected from the group consisting of Al, Ag and Rh. Since it is configured, the light can be efficiently emitted in a desired direction by reflecting the light by the reflective layer, and the emitted light can be efficiently emitted.

[Brief description of drawings]

FIG. 1 is a plan view showing a configuration of a nitride semiconductor light emitting device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the line A-A ′ in FIG.

FIG. 3 is a cross-sectional view before etching for exposing the surface of the n-type contact layer 21 in the manufacturing method according to the embodiment.

FIG. 4 is a cross-sectional view after etching to expose the surface of n-type contact layer 21 in the manufacturing method according to the embodiment.

5 is a cross-sectional view after removing the mask 55 after the etching of FIG.

FIG. 6 is a cross-sectional view after forming an electrode film 53a for forming a p-side ohmic electrode.

FIG. 7 is a cross-sectional view after a mask 56 is formed on the electrode film 53a.

FIG. 8 is a cross-sectional view after etching using the mask 56 (after forming the p-side ohmic electrode 53 on substantially the entire surface of each p-type contact layer 42).

FIG. 9 is a cross-sectional view after an n-side ohmic electrode 51 is formed on the surface of the n-type contact layer 21.

FIG. 10 is a cross-sectional view after a translucent insulating film 2 made of SiO 2 is formed so as to cover the entire elements.

FIG. 11 is a cross-sectional view after forming a reflective layer 1.

FIG. 12 is a cross-sectional view after forming an n-side pad electrode 52 and a p-side pad electrode 54.

FIG. 13 is a graph showing the wavelength dependence of the reflection characteristics of the reflection structure according to the present invention.

FIG. 14 is a graph showing reflection characteristics when the incident angle of light is changed in the reflection structure R1 according to the present invention.

FIG. 15 is a graph showing reflection characteristics when the incident angle of light is changed in the reflection structure R2 according to the present invention.

FIG. 16 is a graph showing reflection characteristics when the incident angle of light is changed in the reflection structure R3 according to the present invention.

FIG. 17 is a graph showing reflection characteristics in a conventional electrode structure.

[Explanation of symbols]

1 ... Reflective layer, 2 ... Insulating film, 2a ... opening, 2b ... opening, 10 ... substrate, 11 ... buffer layer, 20 ... N-side nitride semiconductor layer, 21 ... n-type contact layer, 22 ... n-type cladding layer, 30 ... Active layer, 40 ... p-side nitride semiconductor layer, 41 ... p-type cladding layer, 42 ... p-type contact layer, 51 ... n-side ohmic electrode, 52, 54 ... Pad electrodes 53 ... p-side ohmic electrode, 53a ... Electrode film, 55, 56 ... Mask.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shuji Shioji             100, 491, Oka, Kaminaka-cho, Anan City, Tokushima Prefecture             Gaku Kogyo Co., Ltd. F-term (reference) 5F041 AA03 CA05 CA13 CA40 CA46                       CA82 CA88 CA92 CB15

Claims (7)

[Claims] 1. A light emitting device comprising a semiconductor layer and an ohmic electrode in ohmic contact with the semiconductor layer, comprising a reflective structure, wherein the reflective structure uses the ohmic electrode as a translucent ohmic electrode. A light emitting device, characterized in that the electrode is covered with a reflective layer via a translucent insulating film, and the reflective layer is composed of one selected from the group consisting of Al, Ag and Rh. 2. The light emitting device according to claim 1, wherein the semiconductor layer includes a p-type contact layer made of a p-type nitride semiconductor layer, and the translucent ohmic electrode is formed on the p-type contact layer. 3. The insulating film is made of SiO _2.
Alternatively, the nitride semiconductor light emitting device according to item 2. 4. The light emitting device according to claim 1, wherein the insulating film has a thickness of 3 μm or less. 5. The reflective layer has a thickness of 0.05 μm to 1
The light emitting device according to claim 1, wherein the light emitting device is set in a range of μm. 6. The insulating film according to claim 1, wherein the insulating film has an opening, and the ohmic electrode and the reflective layer are electrically connected through the opening. The light emitting device described. 7. The light emitting device according to claim 6, wherein a pad electrode is formed on a portion of the surface of the reflective layer located above the opening.