JP2001036132A - AlGaInP-based light emitting diode and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AlGaInP-based light emitting diode capable of efficiently extracting light emitted from an active layer to the outside of a chip by using an easy process and a general-purpose growth apparatus, and a method of manufacturing the same. SOLUTION: GaAs having a lower electrode 8 provided on the back surface
At least a DBR layer 3 and a cladding layer 4
And an active layer 5 having a composition smaller in bandgap energy than the cladding layer 4, another cladding layer 6 having a composition larger in bandgap energy than the active layer 5, and a current spreading layer 7, which are sequentially laminated. In the AlGaInP-based light emitting diode in which the upper electrode 9 is provided on a part of the surface of the diffusion layer 7 and the manufacturing method thereof,
Another DBR layer 10 having the same shape as the upper electrode 9 and made of an AlGaAs-based material is formed between the upper electrode 9 and the upper electrode 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light emitting diode and a method of manufacturing the same, and more particularly, to an AlGaInP-based light emitting diode having a wavelength range of 650 nm (red) to 550 nm (yellow green) and a method of manufacturing the same.

[0002]

2. Description of the Related Art Recently, demand for high-brightness red and yellow light-emitting diodes manufactured using an AlGaInP-based epitaxial wafer has been greatly increased. Its main demands are traffic lights, car brake lights, fog lights and so on.

FIG. 5 shows AlGaIn having an emission wavelength of 590 nm.
1 shows a typical sectional structure of a P-based light emitting diode chip.

As shown in FIG. 5, a conventional AlGaInP
A system light emitting diode is formed on an n-type GaAs substrate 21 by metal organic chemical vapor deposition (hereinafter, referred to as “MOVPE”).
The n-type GaAs buffer layer 22 and the n-type AlGaInP cladding layer 2 doped with selenium or silicon.
3. An undoped AlGaInP active layer 24, a zinc-doped p-type AlGaInP cladding layer 25, and a zinc-doped p-type GaP current spreading layer 26 (sometimes referred to as a "window layer") are sequentially stacked to form an n-type. The electrode 2 is formed on the entire back surface of the substrate 21 and a part of the surface of the p-type current diffusion layer.
7 and 28 are provided.

[0005]

As shown in FIG. 6, an active layer 24 of a light emitting diode (LED chip) is used.
Is emitted in all directions, up, down, left, and right. Among the materials forming the LED chip, GaAs used for the substrate 21 and the buffer layer 22 and metal generally used for the electrode material are used. Does not transmit light, the light reaching the GaAs layer of the substrate 21, the buffer layer 22, and the electrode 28 is absorbed and cannot be extracted outside the chip. This is a major cause of lowering the light emission luminance of the light emitting diode.

[0006] Regarding the problem of luminance reduction due to light absorption by the substrate, a DBR (distributed Bragg reflector using Bragg reflection between the n-type cladding layer and the substrate) is used.
A technique has been developed in which a distributed Bragg reflector) layer is provided to reflect light emitted downward and upward so that light is not absorbed by the substrate. This technique is disclosed in, for example, JP-A-3-16278 and JP-A-3-163.
No. 882, Patent No. 2778868, etc.
A light emitting diode in which an R layer is inserted is disclosed.

[0007] Regarding the problem of luminance reduction due to light absorption by the electrode, a current confinement layer made of an n-type layer or an insulating layer is provided in a portion of the p-type cladding layer below the electrode. Light emission immediately below is eliminated, the current density in other regions is increased, and light is efficiently extracted to the outside of the LED chip. This technique is disclosed in, for example, Japanese Patent No. 2856374.

However, the method of providing the DBR layer between the n-type cladding layer and the substrate is such that even if light emitted from the active layer is reflected by the underlying DBR layer, a part of the light is emitted from the upper electrode. And the light was absorbed and could not be completely extracted.

The method of providing a current confinement layer in a p-type cladding layer below an electrode has problems in that a complicated process is required to form the current confinement layer and a special growth apparatus is required.

Therefore, an object of the present invention is to provide an AlGaIn which can efficiently extract light emitted from an active layer to the outside of a chip by using an easy process and a general-purpose growth apparatus.
An object of the present invention is to provide a P-based light emitting diode and a method for manufacturing the same.

[0011]

According to a first aspect of the present invention, at least an n-type DBR is provided on a GaAs substrate having a lower electrode provided on the back surface and having n-type conductivity.
Layer, an n-type cladding layer composed of an AlGaInP-based material, an active layer composed of an AlGaInP-based material having a composition having a smaller bandgap energy than the n-type cladding layer, and an AlGaInP-based material having a composition having a larger bandgap energy than the active layer In the AlGaInP-based light emitting diode in which a p-type cladding layer made of and a p-type current diffusion layer made of an AlGaInP-based material are sequentially stacked, and an upper electrode is provided on a part of the surface of the p-type current diffusion layer, Between the current diffusion layer and the upper electrode, a p-type material having the same shape as the upper electrode and made of an AlGaAs-based material is used.
It has a type DBR layer inserted.

According to a second aspect of the present invention, at least a GaAs substrate provided with a lower electrode on a back surface and having p-type conductivity is provided.
a p-type DBR layer, a p-type cladding layer composed of an AlGaInP-based material, an active layer composed of an AlGaInP-based material having a composition having a smaller bandgap energy than the p-type cladding layer, and a composition having a bandgap energy greater than that of the active layer. In an AlGaInP-based light emitting diode in which an n-type cladding layer made of an AlGaInP-based material and an n-type current spreading layer made of an AlGaInP-based material are sequentially stacked, and an upper electrode is provided on a part of the surface of the n-type current spreading layer, Between the n-type current spreading layer and the upper electrode,
An n-type DBR layer having the same shape as the upper electrode and made of an AlGaAs-based material is inserted.

According to a third aspect of the present invention, the current spreading layer is formed of Ga.
It consists of a P layer.

According to a fourth aspect of the present invention, there is provided a GaAs substrate having one conductivity type, a DBR layer having at least the same conductivity type as the substrate, a cladding layer of the same type made of an AlGaInP-based material, and a bandgap formed by the cladding layer. An active layer made of an AlGaInP-based material having a low energy composition, a cladding layer made of an AlGaInP-based material having a composition having a bandgap energy larger than that of the active layer and having the other conductivity type, and the other conductivity type made of an AlGaInP-based material are used. A current diffusion layer having a DBR layer made of an AlGaAs-based material and having the other conductivity type, and further a material serving as an electrode is stacked on the other conductivity type DBR layer;
A patterned protective film layer for obtaining a desired electrode shape is provided thereon, and using the protective film layer as a mask, the non-electrode portion of the electrode material is removed by etching to form an upper electrode, and then the protective film layer or Using the upper electrode itself as a mask, only the other conductive type DBR layer made of an AlGaAs-based material is removed by selective etching, and AlGaIn
In this method, a DBR layer having the same shape as the upper electrode is left between the P-based current diffusion layer and the upper electrode.

According to a fifth aspect of the present invention, the current diffusion layer is formed of Ga
This is a method of forming with P.

That is, according to the present invention, in a standard AlGaInP-based light emitting diode having a GaP current diffusion layer on the upper side, a DBR layer having the same shape as the upper electrode is inserted between the GaP current diffusion layer and the upper electrode. The light emitted from the active layer is reflected by the upper and lower DBR layers so that the light can be efficiently extracted to the outside of the chip. In order to realize this structure, the material of the DBR layer is made of an AlGaAs-based material, Utilizing that the current diffusion layer of the LED is made of an AlGaInP-based material, only the AlGaAs-based DBR layer can be easily processed by using selective etching.

According to the above structure, light emitted from a certain point of the active layer is radiated from that point in the entire circumferential direction and directly or after being reflected by the upper DBR layer or the lower DBR layer. Emitted to the outside of the light emitting diode.

In a conventional DH structure light emitting diode that does not include a DBR layer, the light emitted downward from the active layer is:
It is absorbed by the GaAs layer and cannot be taken out of the LED chip. Further, even light emitted to the side and above the active layer, which reaches the metal of the electrode, is absorbed by the interface or the electrode metal and cannot be taken out of the chip. Therefore, of the light emitted from the active layer, only a part of the light that can be actually extracted to the outside of the LED chip becomes small. Therefore, in order to reflect light emitted downward from the active layer, a method of inserting a DBR layer below the active layer is generally employed.

With this method, the efficiency of extracting light to the outside of the LED chip is greatly increased. However, among the reflected light, the light that reaches the electrode cannot be extracted for the above-described reason. In contrast, when the present invention is used, light emitted from the active layer can be taken out of the LED chip very efficiently.

[0020]

Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view of an AlGaInP-based light emitting diode according to the present invention.

As shown in FIG. 1, a red LED chip having a light emission wavelength of about 620 nm according to the present invention has an Se type of 1.times. On an n-type GaAs substrate 1 provided with a lower electrode 8 on the back surface.
N-type GaAs buffer layer 2 doped at a concentration of 10 ¹⁸ cm ^-3 and Se-doped (Al _0.85 Ga _0.15 ) _0.5
As _0.5 : 48.45 nm / GaAs: 40.98 nm
Is an n-type DBR layer 3 in which 20 pairs are stacked, and Se is 8 × 1
N type doped with a concentration of 0 ¹⁷ cm ^-3 (Al _0.7 Ga
_0.3 ) _0.5 In _0.5 P clad layer 4 and an undoped (Al _0.15 Ga _0.85 ) _0.5 In _0.5 P active layer 5 having a composition whose band gap energy is smaller than that of the n-type clad layer 4.
A p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 6 having a composition larger in band gap energy than the active layer 5 and doped with Zn at a concentration of 5 × 10 ¹⁷ cm ⁻³ ; P-type G doped at a concentration of × 10 ¹⁸
An epitaxial wafer is formed by sequentially laminating the p-type current diffusion layer 7 made of aP. The upper electrode 9 is provided on a part of the surface of the p-type current diffusion layer 7.

Further, between the p-type current diffusion layer 7 and the upper electrode 9, the same shape as that of the upper electrode 9 and doped with Zn (Al _0.85 Ga _0.15 ) _0.5 As _0.5 : 48.45 nm
/ GaAs: A p-type DBR layer 10 in which 10 pairs of 40.98 nm are stacked is inserted.

The size of this LED chip is 300 μm square as shown in FIG. 2, and the shape of the upper electrode 9 and the p-type DBR layer is such that the diameter is the length of one side of the current diffusion layer 7. Of about 150 μm, which is about half the length of

The p-type GaP current diffusion layer 7 is formed to a thickness of 10 μm.

The lower electrode 8 is made of gold germanium, nickel and gold, each having a thickness of 60 nm,
nm, formed by vapor deposition with a thickness of 500 nm,
The upper electrode 9 is made of gold zinc, nickel, and gold in order from the current diffusion layer 7 side at 60 nm, 10 nm, and 1000 nm, respectively.
It is formed by vapor deposition with a thickness of nm.

Next, a method for manufacturing this light emitting diode will be described.

In manufacturing an epitaxial wafer of a light emitting diode, the epitaxial wafer is grown by MOVPE.

In MOVPE growth, the growth temperature is 700 ° C., the growth pressure is 50 Torr, and the growth rate of each of the layers 2 to 6 is 0.3 to
It is grown at a V / III ratio of 300 to 600 at 1.0 nm / s. GaP to be the current diffusion layer 7 is grown at a V / III ratio of 100 and a growth rate of 1 nm / s.

After growing the current diffusion layer 7,
On the current diffusion layer 7, another DBR layer 10 is grown, and as described above, gold germanium, nickel, and gold are sequentially deposited, and an electrode material layer serving as the upper electrode 9 is laminated.

Then, a protective film layer (resist film) which has been subjected to patterning to obtain a desired electrode shape is provided on the electrode material layer by using a photolithography technique.
Using the protective film layer as a mask, the upper electrode 9 is formed by removing the metal of the portion of the electrode that is not covered with the resist film with an iodine-based etchant.

Thereafter, using the protective film layer or the upper electrode 9 itself as a mask, sulfuric acid: hydrogen peroxide solution: water = 3:
Only a portion of the p-type AlGaAs DBR layer that is not covered with the resist film is removed (selective etching) with a 1: 1 etchant to form a p-type DBR layer 10 having the same shape as the upper electrode 9.

Finally, the resist film on the upper electrode 9 is removed by using a commercially available resist stripper to manufacture a light emitting diode.

It should be noted that the AlGaInP-based material is
As an etching solution for selectively etching only the aAs-based material, a mixture of sulfuric acid, hydrogen peroxide solution, and water is well known. For example, sulfuric acid: hydrogen peroxide solution: water = 3: Selective etching can be easily performed by using an etchant mixed at a mixing ratio of 1: 1. For this reason, the DBR on the side to be selectively etched
The material of the layer 10 was an AlGaAs-based material. The etchant is not particularly limited because other types of etchants can be selectively etched.

Next, the operation will be described with reference to FIG.

FIG. 3 is a schematic view showing a path through which light emitted from the active layer of the light emitting diode passes.

As shown in FIG. 3, light emitted from the active layer 5 to the upper side is directly emitted from a portion where the p-type DBR layer 10 is not formed upward, and the p-type DBR layer 10 is formed. The part is reflected downward. Light emitted from the active layer 5 to the lower side is reflected by the n-type DBR layer 3 formed on the substrate 1 and the buffer layer 2, and finally the p-type DBR layer 10 is formed above. Not released from the part.

As a result, the light emitted from the active layer 5 is not absorbed by the substrate 1, the buffer layer 2, or the upper electrode 9, so that the present invention emits light with high output.

Further, in order to prevent the electrode from acting as a light absorber and preventing the light emitted from the active layer from being emitted to the outside of the chip, the current spreading layer is preferably as thick as possible. . For example, in the following paper, the light extraction efficiency is increased by stacking several tens of μm of a GaP layer.

"Twofold efficiency improvement in hi
gh performance AlGaInP light-emitting diodes in th
e 555-620nm spectral region using a thick GaP "App
l.Phys.Lett.61 (9), 31 August 1992 pp.1045-1047 However, in order to grow the current spreading layer thickly by the MOVPE method, a large amount of growth time and materials are consumed.
In order to avoid this, as described in the above-mentioned article, it is troublesome to stack only the GaP layer by another growth method with a high growth rate.

According to the present invention, from the active layer 5 to the upper electrode 9
Is also reflected and can be finally taken out of the chip. Therefore, the current spreading layer 7 can be formed to have a thickness of several μm which is sufficient to perform the original current spreading function. it can. As a result, the epi for LED can be made thinner, the production becomes very easy, the cost can be reduced, and the device can be downsized.

As described above, according to the present invention, since the light absorbed by the electrodes does not matter, it is possible to provide an electrode having a larger area than before, and as a result,
The thickness of the GaP layer required for current diffusion can also be made smaller than before.

Next, a modified example of this embodiment will be described.

The light emitting diode chip shown in FIG.
An epi-wafer for an LED in which the thickness of the P current diffusion layer 7 is 5 μm is manufactured, and the upper electrode 11 and the p-type AlGaAs-based DB are formed.
This is a modification of the shape of the R layer.

As shown in FIG. 4, the shape of the upper electrode 11 and the p-type AlGaAs-based DBR layer is such that two electrodes are formed on the circular electrode 11a so as to extend toward the corner of the current diffusion layer 7. It is formed by crossing the linear electrodes 11b in a cross shape.

This light emitting diode is manufactured by a method similar to the method described in the present embodiment.

As described above, the upper electrode 11 and the p-type AlG
By extending the shape of the aAs-based DBR layer toward the corners of the chip, a current can be made to flow widely throughout the current diffusion layer 7, so that the current diffusion layer 7 can be formed thin. The light emitting diode chip can be further thinned.

As another modified example, the structure is p
It is also conceivable to apply the present invention to a light-emitting diode having a structure called n-side up in which the type and the n-type are reversed. Even with such a configuration, as described above, light emitted from the active layer can be efficiently extracted to the outside of the chip.

Next, the light emission characteristics of the present invention and the prior art will be compared.

First, the light emitting diode chip shown in FIG. 1 was produced as Example 1, the light emitting diode chip shown in FIG. 4 was produced as Example 2, and the light emitting diode having the structure shown in FIG. 5 was produced as Comparative Example. The light emitting diode of the comparative example is manufactured by the same method as that described in the present embodiment.

The LED chips of Example 1, Example 2, and Comparative Example were assembled into a stem, and the light emission characteristics were examined.

As a result, the light emission output of the comparative example was 0.8 mW
In contrast, the emission output of Example 1 was 1.1 mW,
Regarding the light emission output of Comparative Example 2, a value that was the same as 1.1 mW was obtained even though the thickness of the current diffusion layer was formed to be half that of Example 1. That is, according to the present invention, the light emission output was improved to about 1.4 times that of the related art.

The shape of the upper electrode of the present invention may be variously modified in addition to the shapes shown in FIGS. In particular, according to the present invention, since the absorption of light at the electrodes can be greatly reduced, the degree of freedom in designing the electrode shape increases, and the complicated electrode shape formation for the purpose of assisting current diffusion in the current diffusion layer can be achieved. Will be possible.

Further, in this embodiment, the n-type DBR layer on the substrate side is formed of an AlGaAs-based material, but the material may be AlGaInP-based.

[0055]

As described above, according to the present invention, it is possible to obtain a light-emitting diode having a higher light-emission output than a conventional one by a simple method using a general-purpose growth apparatus.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an AlGaInP-based light emitting diode according to the present invention.

FIG. 2 is a top view of the AlGaInP-based light emitting diode of FIG.

FIG. 3 is a schematic diagram showing a path through which light emitted from an active layer passes in the AlGaInP-based light emitting diode of FIG.

FIG. 4 is a top view of an AlGaInP-based light emitting diode in which the upper electrode of FIG. 1 is modified.

FIG. 5 is a cross-sectional view of an AlGaInP-based light emitting diode according to the related art.

FIG. 6 is a schematic view showing a path through which light emitted from an active layer passes in an AlGaInP-based light-emitting diode according to the related art.

[Explanation of symbols]

 1,21n-type GaAs substrate 2,22 n-type GaAs buffer layer 3 n-type DBR layer 4,23 n-type cladding layer 5,24 active layer 6,25 p-type cladding layer 7,26 p-type current diffusion layer 8,27 lower part Electrodes 9, 28 Upper electrode 10 p-type AlGaAs-based DBR layer 11 Upper electrode

Continued on the front page (72) Inventor Naoki Kaneda 3550 Kida Yomachi, Tsuchiura-shi, Ibaraki Hitachi Cable Advanced Research Center Co., Ltd. (72) Inventor Kenji Shibata 5-1-1 Hidaka-cho, Hitachi-shi, Ibaraki Hitachi Cable F term in Hidaka factory Co., Ltd. (reference) 5F041 AA03 AA04 CA12 CA34 CA35 CA36 CA37 CA65 CA74 CA93 CB15

Claims (5)

[Claims] At least an n-type DBR layer is provided on a GaAs substrate provided with a lower electrode on a back surface and having n-type conductivity;
An n-type cladding layer made of an AlGaInP-based material;
An active layer composed of an AlGaInP-based material having a composition smaller in band gap energy than the mold cladding layer, and an AlGa composition having a composition larger in band gap energy than the active layer.
A p-type cladding layer made of an InP-based material;
An p-type current diffusion layer made of a P-based material is sequentially laminated, and an upper electrode is provided on a part of the surface of the p-type current diffusion layer.
In the GaInP-based light emitting diode, a p-type DBR layer having the same shape as the upper electrode and made of an AlGaAs-based material is inserted between the p-type current diffusion layer and the upper electrode. Light emitting diode. 2. A p-type DBR layer on a GaAs substrate provided with a lower electrode on a back surface and having p-type conductivity;
A p-type cladding layer made of an AlGaInP-based material;
An active layer composed of an AlGaInP-based material having a composition smaller in band gap energy than the mold cladding layer, and an AlGa composition having a composition larger in band gap energy than the active layer.
An n-type cladding layer made of an InP-based material;
An n-type current diffusion layer made of a P-based material is sequentially stacked, and an upper electrode is provided on a part of the surface of the n-type current diffusion layer.
In the GaInP-based light emitting diode, an n-type DBR layer having the same shape as the upper electrode and made of an AlGaAs-based material is inserted between the n-type current diffusion layer and the upper electrode. Light emitting diode. 3. The AlGaInP-based light-emitting diode according to claim 1, wherein said current diffusion layer comprises a GaP layer. 4. A DBR layer having at least the same conductivity as that of the substrate and a cladding layer of the same type made of an AlGaInP-based material on a GaAs substrate having one conductivity type.
An active layer made of an AlGaInP-based material having a composition smaller in bandgap energy than the clad layer, a clad layer made of an AlGaInP-based material having a composition larger in bandgap energy than the active layer and having the other conductivity type, and an AlGaInP-based material. A current diffusion layer having the other conductivity type and a DBR layer made of an AlGaAs-based material and having the other conductivity type are stacked, and a material serving as an electrode is further stacked on the other conductivity type DBR layer. After providing a patterned protective film layer for obtaining a desired electrode shape, using the protective film layer as a mask, removing the non-electrode portion of the electrode material by etching to form an upper electrode, and then forming the protective film layer or the upper electrode itself Is used as a mask and only the other conductive type DBR layer made of an AlGaAs-based material is selectively etched. Removed, between the AlGaInP-based current diffusion layer and the upper electrode, the manufacturing method of the AlGaInP-based light-emitting diode, characterized in that to leave the DBR layer of the upper electrode and the same shape. 5. The method for manufacturing an AlGaInP-based light emitting diode according to claim 4, wherein said current diffusion layer is formed of GaP.