JP2003092427A - Light emitting diode and epitaxial wafer therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting diode having a good wire bondability and a low driving voltage and an epitaxial wafer for the light emitting diode. SOLUTION: A surface electrode 7 is formed on a portion of a transparent conductive film 6 of 80-100 nm formed on a semiconductor current dispersion layer 5 or a clad layer 4. The portion with the electrode 7 is thinned to 10-75 nm, this allowing the surface electrode 7 to increase its thickness enough to easily wire-bond it, using the known wire bonder. Thinning the transparent conductive layer 6 beneath the surface electrode 7 lowers the electric resistance between the surface electrode 7 and the current dispersion layer 5, resulting in a low forward operating voltage.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light emitting diode and an epitaxial wafer for the light emitting diode.

[0002]

2. Description of the Related Art Conventionally, the light emission color of a light emitting diode (LED) has been mostly GaP green and AlGaAs red. However, recently, a GaN-based or AlGaInP-based crystal layer is subjected to MOVPE (Metal Organic Va).
Pour Phase Epitaxy: metal-organic vapor phase epitaxy) has enabled the production of orange, yellow, and blue LEDs with high brightness.

Epitaxial wafers formed by the MOVPE method have enabled the production of LEDs exhibiting short-wavelength light emission and high brightness, which have never existed before. However, when trying to grow the film of the current spreading layer thickly in order to obtain high brightness,
There has been a problem that the cost of the LED epitaxial wafer increases.

Therefore, as a method of solving this problem, there is a method of using a material having a resistance value as low as possible for the current spreading layer. For example, AlGaInP
In the case of a quaternary system, GaP or AlGa is used as the current spreading layer.
As is used.

[0005]

However, even if these materials having a low resistivity are used, it is necessary to increase the film thickness by 8 μm or more or change the electron mobility in order to improve the current dispersion ratio. To increase the film thickness, it is conceivable to reduce the resistivity of the current spreading layer. Since it is difficult to significantly change the electron mobility, attempts have been made to increase the carrier concentration, but at the present stage, it is not possible to increase the carrier concentration so that the current dispersion layer can be thinned.

As a solution to this problem, a method using a transparent conductive film has been proposed in place of the semiconductor current spreading layer because the carrier concentration is very high and a sufficient current spreading effect can be obtained with a thin film thickness. However, when a transparent conductive film using a metal oxide film is used, the metal electrode formed on the transparent conductive film is peeled off during wire bonding, or the conventional wire bonder takes time and effort for wire bonding, There is a problem that the forward voltage is increased due to the existence of resistance in the portion where the metal electrode is not peeled off.

Therefore, an object of the present invention is to solve the above problems and provide a light emitting diode having a good wire bondability and a low driving voltage, and an epitaxial wafer for a light emitting diode.

[0008]

In order to achieve the above object, a light emitting diode of the present invention comprises a first conductivity type clad layer, an active layer, and a second conductivity type on one surface of a first conductivity type substrate. -Type clad layer, second-conductivity-type current spreading layer, and transparent conductive film composed of a metal oxide film are sequentially stacked, a front surface electrode is partially formed on the transparent conductive film, and a back surface electrode is formed on the other surface of the substrate. In the light emitting diode formed with, the thickness of the transparent conductive film in the portion where the surface electrode is formed is smaller than the thickness of other transparent conductive films.

The light emitting diode of the present invention comprises a transparent conductive film comprising a first conductivity type clad layer, an active layer, a second conductivity type clad layer and a metal oxide film on one surface of a first conductivity type substrate. In the light-emitting diode in which the front surface electrode is partially formed on the transparent conductive film and the back surface electrode is formed on the other surface of the substrate, the thickness of the transparent conductive film in the area where the front surface electrode is formed Is thinner than the other transparent conductive films.

In addition to the above structure, in the light emitting diode of the present invention, the thickness of the transparent conductive film is 80 nm to 1000 nm, and the thickness of the transparent conductive film in the portion where the surface electrode is formed is 10 nm to 75 nm. preferable.

In addition to the above structure, in the light emitting diode of the present invention, it is preferable that the substrate is GaAs and the light emitting portion composed of both clad layers and the active layer is AlGaInP and GaInP.

In addition to the above structure, in the light emitting diode of the present invention, the front surface electrode has a substantially circular shape, a substantially elliptical shape, a substantially polygonal shape or a shape in which protrusions are provided, and the back surface electrode has a whole surface or a substantially circular shape, and has a substantially circular shape. It may be oval or substantially polygonal.

The light emitting diode epitaxial wafer of the present invention comprises a first conductivity type clad layer, an active layer, a second conductivity type clad layer, and a second conductivity type clad layer on one surface of a first conductivity type substrate. A transparent conductive film consisting of a current spreading layer and a metal oxide film is sequentially stacked, a front surface electrode is partially formed on the transparent conductive film, and a back surface electrode is formed on the other surface of the substrate. In, the thickness of the transparent conductive film in the portion where the surface electrode is formed is thinner than the thickness of other transparent conductive films.

The light emitting diode epitaxial wafer of the present invention comprises a first conductivity type clad layer, an active layer, a second conductivity type clad layer and a metal oxide film on one surface of a first conductivity type substrate. In a light emitting diode epitaxial wafer in which transparent conductive films are sequentially stacked, a front surface electrode is partially formed on the transparent conductive film, and a back surface electrode is formed on the other surface of the substrate, the front surface electrode is formed. The thickness of the transparent conductive film of a part is thinner than the thickness of other transparent conductive films.

In addition to the above structure, in the epitaxial wafer for a light emitting diode of the present invention, the transparent conductive film has a thickness of 80 nm.
The thickness of the transparent conductive film in the portion where the surface electrode is formed is preferably 10 nm to 75 nm.

According to the present invention, the thickness of 80 nm formed on the current spreading layer or the clad layer made of semiconductor is
Since the thickness of the surface electrode can be increased by reducing the thickness of the portion of the transparent conductive film of 1000 nm where the electrode is provided to 10 nm to 75 nm, wire bonding can be easily performed with an existing wire bonder. By reducing the thickness of the transparent conductive film directly under the surface electrode, the value of the electric resistance between the surface electrode and the current spreading layer or the second conductivity type cladding layer becomes small, so that the forward operating voltage becomes low.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an embodiment of a light emitting diode using the light emitting diode epitaxial wafer of the present invention.

This light emitting diode has an n-type cladding layer 2, an active layer 3, and a p-type as a second conductivity type on one surface (upper surface in the figure) of an n-type substrate 1 as a first conductivity type. Clad layer 4, p-type current spreading layer 5, and transparent conductive film 6 made of a metal oxide film are sequentially stacked, and a surface electrode 7 is formed in the center of the transparent conductive film 6, and the other surface of the substrate 1 (see FIG. In the light emitting diode in which the back surface electrode 8 is formed on the lower surface), the thickness of the transparent conductive film 6 is in the range of 80 nm to 1000 nm, and the thickness of the transparent conductive film 6 in the portion where the front surface electrode 7 is formed. Is in the range of 10 nm to 75 nm. The n-type clad layer 2, the active layer 3, and the p-type clad layer 4 constitute a light emitting layer 9.

The thickness of the portion where the surface electrode 7 of the transparent conductive film 6 having a thickness of 80 nm to 1000 nm formed on the current spreading layer 5 made of a semiconductor as described above is 10 nm to
By reducing the thickness to 75 nm, the thickness of the surface electrode 7 can be made thicker than in the conventional case, so that wire bonding can be easily performed with the existing wire bonder.
Further, by reducing the thickness of the transparent conductive film 6 directly below the surface electrode 7, the distance between the surface electrode 6 and the current distribution layer 5 is shortened, so that the resistance value therebetween is reduced, and the forward operating voltage is reduced. Get lower.

FIG. 2 is a sectional view showing another embodiment of a light emitting diode using the light emitting diode epitaxial wafer of the present invention. Hereinafter, common reference numerals are used for the same members as those shown in FIG.

The difference from the embodiment shown in FIG. 1 is that the current spreading layer 5 is not provided.

That is, the light emitting diode shown in FIG.
An n-type clad layer 2, an active layer 3, a p-type clad layer 4 and a transparent conductive film 6 made of a metal oxide film are sequentially laminated on one surface (upper surface in the figure) of the n-type substrate 1 to form a transparent film. A light emitting diode in which a front surface electrode 7 is formed in the center of the conductive film 6 and a back surface electrode 8 is formed on the other surface (the lower surface in the figure) of the substrate 1, and the transparent conductive film 6 has a thickness of 80 nm to 100
It is in the range of 0 nm, and the thickness of the transparent conductive film 6 in the portion where the surface electrode 7 is formed is in the range of 10 nm to 75 nm.

In such a light emitting diode as well, FIG.
The same effect as the light emitting diode shown in FIG.

Next, specific numerical values will be described, but the present invention is not limited thereto.

[0026]

(Example) A case where a light emitting diode having substantially the same structure as the light emitting diode shown in FIG. 1 is manufactured will be described. This light emitting diode uses an epitaxial wafer for a red light emitting diode with an emission wavelength of around 630 nm.

On the n-type GaAs substrate 1, an n-type (Se-doped) GaAs buffer layer, an n-type (Se-doped) (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 2, and an undoped (Al _0.15 ) are formed by MOVPE. Ga _0.85 ) _0.5 In _0.5 P
Active layer 3, p-type (zinc-doped) (Al _0.7 Ga _0.3 ) _0.5
An In _0.5 P cladding layer 4 is grown, and p-type (zinc-doped) (Al _0.7 Ga _0.3 ) _0.5 is grown on the p-type cladding layer 4.
The In _0.5 P layer and the GaP current spreading layer 5 are grown by the MOVPE method to obtain an epitaxial wafer.

On this epitaxial wafer, ITO (I
ndium Tin Oxide) solution was formed by the coating method. This is for forming the surface electrode 7. The ITO film was applied three times to form a three-layer structure. The epitaxial wafer is sintered and further 266 × 10 ⁻⁶ Pa (2 ×
Heat treatment was performed at 500 ° C. in a vacuum of 10 ⁻⁶ Torr).

A resist mask was formed in a matrix on the epitaxial wafer with the ITO film by photolithography. The size of the portion without the resist mask is circular with a diameter of 155 μm.

This epitaxial wafer with a resist mask is etched with an etching solution using hydrochloric acid, nitric acid and pure water to etch the ITO film in the resist-free area, and the thickness of the ITO film in the resist-free area is 10 nm.
I chose Further, the etching time of the ITO film is changed so that the thickness of the ITO film in the part without the resist mask is 50 nm, 7
Those with 5 nm and 100 nm were also manufactured in the same manner.

After etching the ITO film to a predetermined thickness, the resist mask was removed. Then, a circular p-type electrode having a diameter of 135 μm was formed on the upper surface of the epitaxial wafer, and was formed in a matrix by vapor deposition so as to match the center of the circular portion removed by etching. Surface electrode 7
Is formed by depositing gold / zinc, nickel and gold on the p-type electrode in the order of 60 nm, 10 nm and 1000 nm, respectively.

Further, an n-type back electrode 8 is formed on the entire bottom surface of the epitaxial wafer. The n-type electrode is made of gold / germanium, nickel and gold at 60 nm and 10 n, respectively.
m and 500 nm were vapor-deposited in this order, and then alloying for alloying the electrodes was performed in a nitrogen gas atmosphere at 400 ° C. for 5 minutes.

An epitaxial wafer with an ITO film and electrodes is processed by dicing or the like to obtain a chip size of 300 μm.
An m-square light emitting diode chip was produced, and then die bonding and wire bonding were performed to produce a light emitting diode.

As a result, when the thickness of the ITO film directly under the surface electrode 7 is 10, 50, or 75 nm, the wire bonding failure of the light emitting diode chip using GaP and AlGaInP for the current spreading layer 5 is 1%. It was below.

Thus, the wire bondability could be improved without depending on the material of the current spreading layer 5. However, the thickness of the ITO film directly below the surface electrode 7 is 10
At 0 nm, about 40% of defective wire bonding occurred. The thickness of the ITO film directly below the surface electrode 7 is 10,
As a result of examining the light emitting characteristics of the light emitting diode manufactured at 50 and 75 nm, the forward operating voltage (at 20 mA current application) when the current spreading layer 5 is a GaP layer is 1.90 V, and the current spreading layer 5 is
Is the AlGaInP layer, the forward operating voltage (20 mA
(When energized) is 1.89 V, and both light emission outputs are 2.
It was 5 mW.

Here, the necessity of forming two parts (thick part and thin part) having different thicknesses of the transparent conductive film 6 will be described.

The thicker the transparent conductive film 6, the lower the resistance and the better the current dispersion. However, if the transparent conductive film is thick in the portion where the electrode is formed, the wire bondability is poor.
In other words, in order to improve wire bondability,
It can be said that it is better to make the transparent conductive film thinner to increase the current dispersibility and the light emission output.

Therefore, only the transparent conductive film in the electrode portion (wire bonding portion, that is, the surface electrode) is thinned to improve wire bondability, and the transparent conductive film other than the electrode portion (wire bonding portion) is thickened to increase the current. The dispersibility is improved to improve the light emission output. That is, the wire bondability and the light emission output can be improved by forming the two portions having different thicknesses of the transparent conductive film.

Further, since the transparent conductive film becomes thin,
The current dispersion effect in the transparent conductive film does not weaken. It is the thick film that needs current distribution. The thin film part is
There is not much need for current distribution.

Further, the wire bondability changes depending on the hardness of the layer directly under the electrode and the hardness of the electrode itself, and the softer the wire bondability, the better. The hardness of the film is determined by the material and thickness of the film. If the material of the film is the same, the thinner the film is, the softer it is (the thinner glass and ceramic can be bent). From this, if the material is the same (transparent conductive film), the thinner the thickness, the softer. That is, if the materials are the same, the thinner the thickness, the better the wire bondability.

FIG. 3 is a diagram showing the film thickness of the ITO film directly under the electrode of the light emitting diode of the present invention and the defect rate at the time of wire bonding. The horizontal axis is the ITO film thickness axis directly under the electrode, and the vertical axis is the wire bonding. This is the defect rate axis.

From the figure, the ITO film thickness is 10 nm to 75 n.
It can be seen that it is preferable to be within the range of m. (Comparative Example) FIG. 4 is a sectional view of a light emitting diode using a conventional epitaxial wafer for a light emitting diode.

An epitaxial wafer for a red light emitting diode having an emission wavelength of about 630 nm having the structure shown in FIG. 4 was produced. The epitaxial growth method, the epitaxial structure, etc. were basically the same as those in the examples, and the ITO film forming method, the electrode forming method, and the electrode shape were also basically the same as the examples. Further, the process processing and wire bonding process were the same as in the example.

On the upper surface of the transparent conductive film 6a of the epitaxial wafer with the ITO film, circular p-type surface electrodes 7a having a diameter of 135 μm were formed in a matrix by vapor deposition. The surface electrode 7a is made of gold, zinc, nickel, and gold each of 60n.
m, 10 nm, and 1000 nm were deposited in this order. Further, an n-type back electrode 8 was formed on the entire bottom surface of the epitaxial wafer. The back surface electrode 8 is made of gold, germanium, nickel and gold of 60 nm, 10 nm and 500 nm, respectively.
Then, the alloy that is the alloying of the electrodes is deposited.
It was performed at 400 ° C. for 5 minutes in a nitrogen gas atmosphere.

An epitaxial wafer with an ITO film and electrodes is processed by dicing and the like, and the chip size is 300 μm.
A square light emitting diode chip was manufactured, and further die bonding and wire bonding were performed to manufacture a light emitting diode.

As a result, in both the light emitting diode using AlGaInP for the current spreading layer and the light emitting diode chip using GaP for the current spreading layer, the wire bonding failure was 60% or more. In addition, as a result of examining the light emitting characteristics of the light emitting diode chip that can be wire-bonded, the light emitting output of both the light emitting diode chip using AlGaInP for the current spreading layer and the light emitting diode chip using GaP for the current spreading layer 5 is 2. 5mW, forward operating voltage (20
The current was 1.9 V (when energized at mA).

From the above, the ITO in the portion where the electrode is formed
It can be said that if the film is too thick, the wire bondability deteriorates.

In the above embodiment, the first conductivity type is n-type and the second conductivity type is p-type. However, the present invention is not limited to this. May be p-type and the second conductivity type may be n-type.

In the above, by manufacturing a light emitting diode using the present light emitting diode epitaxial wafer, the ITO film can be used as a current distribution layer for an LED. As a result, the film thickness of the LED epitaxial layer can be reduced from ⅕ to tens of minutes. This is because the thickness of the current spreading layer is the largest among the epitaxial layers forming the LED.
As a result, the cost of the epitaxial wafer can be significantly reduced. Further, although the wire bonding failure frequently occurred and the yield was poor, the yield can be improved while maintaining the brightness.

[0050]

In summary, according to the present invention, the following excellent effects are exhibited.

It is possible to provide a light emitting diode having a good wire bondability and a low driving voltage and an epitaxial wafer for a light emitting diode.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a light emitting diode using the light emitting diode epitaxial wafer of the present invention.

FIG. 2 is a cross-sectional view showing another embodiment of a light emitting diode using the light emitting diode epitaxial wafer of the present invention.

FIG. 3 is a diagram showing a film thickness of an ITO film directly under an electrode of a light emitting diode of the present invention and a defective rate at the time of wire bonding.

FIG. 4 is a cross-sectional view of a light emitting diode using a conventional light emitting diode epitaxial wafer.

[Explanation of symbols]

1 substrate 2 n-type (first conductivity type) clad layer 3 Active layer 4 p-type (second conductivity type) clad layer 5 Current distribution layer 6 Transparent conductive film 7 Surface electrode 8 Back electrode 9 Light-emitting layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenji Shibata             Hitachi, 1-1 Hidaka-cho, Hitachi City, Ibaraki Prefecture             Electric Wire Co., Ltd. Hidaka Factory F term (reference) 5F041 AA24 AA41 CA34 CA82 CA84                       CA88

Claims (8)

[Claims] 1. A first-conductivity-type clad layer, an active layer, a second-conductivity-type clad layer, a second-conductivity-type current spreading layer, and a metal oxide film on one surface of a first-conductivity-type substrate. In the light emitting diode in which the transparent conductive film is sequentially laminated, the front surface electrode is partially formed on the transparent conductive film, and the back surface electrode is formed on the other surface of the substrate, the surface electrode is formed. 2. The light emitting diode, wherein the thickness of the transparent conductive film is thinner than the thickness of other transparent conductive films. 2. A transparent conductive film comprising a first conductivity type clad layer, an active layer, a second conductivity type clad layer and a metal oxide film is sequentially laminated on one surface of a first conductivity type substrate, In a light emitting diode in which a front surface electrode is partially formed on the transparent conductive film and a back surface electrode is formed on the other surface of the substrate, the thickness of the transparent conductive film at the portion where the front surface electrode is formed is different. A light-emitting diode characterized by being thinner than the transparent conductive film. 3. The transparent conductive film has a thickness of 80 nm to 10
The light emitting diode according to claim 1 or 2, wherein the thickness of the transparent conductive film in the portion where the surface electrode is formed is 10 nm to 75 nm. 4. The substrate is GaAs, and the light emitting portion composed of the both clad layers and the active layer is AlGaInP.
And the light emitting diode according to claim 1, which is GaInP. 5. The surface electrode has a substantially circular shape, a substantially elliptical shape, a substantially polygonal shape, or a shape in which protrusions are provided in these shapes,
The light emitting diode according to any one of claims 1 to 4, wherein the back electrode is the entire surface, or is substantially circular, substantially elliptical, or substantially polygonal. 6. A clad layer of a first conductivity type, an active layer, a clad layer of a second conductivity type, a current diffusion layer of a second conductivity type and a metal oxide film on one surface of a substrate of the first conductivity type. In a light emitting diode epitaxial in which transparent conductive films are sequentially laminated, a front surface electrode is partially formed on the transparent conductive film, and a back surface electrode is formed on the other surface of the substrate, the front surface electrode is An epitaxial wafer for a light-emitting diode, characterized in that the thickness of the transparent conductive film in the formed portion is smaller than the thickness of other transparent conductive films. 7. A transparent conductive film comprising a first conductivity type clad layer, an active layer, a second conductivity type clad layer and a metal oxide film is sequentially laminated on one surface of a first conductivity type substrate, In a light emitting diode epitaxial wafer in which a front surface electrode is partially formed on the transparent conductive film and a back surface electrode is formed on the other surface of the substrate, the transparent conductive film in the portion where the front surface electrode is formed. An epitaxial wafer for a light-emitting diode, characterized in that its thickness is smaller than the thickness of other transparent conductive films. 8. The transparent conductive film has a thickness of 80 nm to 10 nm.
The epitaxial wafer for a light emitting diode according to claim 6 or 7, wherein the thickness of the transparent conductive film in the portion where the surface electrode is formed is 10 nm to 75 nm.