JP2002151733A - Light emitting diode and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting diode which is high in luminous intensity and easily manufactured and to provide a method of manufacturing the same. SOLUTION: A current block layer 3 of the LED is formed on an N-type GaAs substrate 2. A light emitting part 10 composed of an N-type AlGaInP clad layer 4, an AlGaInP active layer 5, and a P-type AlGaInP clad layer 6 is formed thereon, and a P-type AlGaInP current dispersion layer 7 is grown thereon. A surface electrode 9 is formed thereon, and a back electrode 1 is formed on the rear of the N-type GaAs substrate 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode (hereinafter, also referred to as "LED") and a method for manufacturing the same, and more particularly, to a light emitting diode which is easy to manufacture with high luminous intensity and a method for manufacturing the same.

[0002]

2. Description of the Related Art Light emitting diodes (LEDs) are widely used as industrial and consumer display devices. As a high-luminance LED, there is an AlGaAs red LED.
As LEDs having a wavelength shorter than red, GaAsP-based LEDs and Ga
There were P-based LEDs, but only those with low luminosity.
In contrast, metalorganic vapor phase epitaxial growth (MO
Since VPE (metal organic vapor phase epitaxy) method enables epitaxial growth of AlGaInP and GaN, LED with high luminous intensity even at a wavelength shorter than orange
Are being developed and sold.

FIG. 4 shows a conventional AlGaInP-based visible light emitting diode. This light emitting diode has n-type Ga
On an As substrate 2, an n-type AlGaInP cladding layer 4, p-type
A light emitting portion 10 comprising a p-type AlGaInP active layer 5 and a p-type AlGaInP cladding layer 6 is formed, a circular surface electrode 9 is formed at the center of the surface, and a back electrode 1 is formed as a whole electrode on the back. The carrier 21 injected from the front surface electrode 9 is injected into the active layer 5 and the back electrode 1
Recombines with the carriers 22 injected from the substrate and emits light. At this time, when the resistance of the epitaxial layer (hereinafter, abbreviated as “epi layer”) between the surface electrode 9 and the active layer 5 is high, the carriers 21 are injected only into the portion of the active layer 5 immediately below the surface electrode 9. It comes to be. Then, the light emitted at that portion is blocked by the surface electrode 9 and does not come out of the chip, resulting in extremely poor luminous efficiency.

For this reason, it is necessary to distribute the current uniformly over the entire surface of the active layer. To this end, the resistivity of the epi layer between the surface electrode and the active layer is lowered or the epi layer is It is conceivable to increase the film thickness. But MOV
AlGaIn that can be epitaxially grown by PE method
In the p-type cladding layer or window layer of P or GaN,
An epi layer with low resistivity cannot be obtained. Therefore, GaP
(Patent US5008718: HP patent) and AlGaAs
Other semiconductor materials, such as (registered trademark 2139978, US Pat. No. 5,153,889: Toshiba patent), have been used as window layers.

However, in such a method, current can be dispersed, but it is difficult to achieve a really low resistance, and a thicker epitaxial growth is performed by a vapor phase epitaxy (VPE) method. For this reason, the problem of high cost could not be solved. Further, even if the current is dispersed, the current density immediately below the electrode is the highest, and light emitted at that portion cannot be taken out, so that high efficiency cannot be achieved.

Accordingly, a structure using a current spreading layer has been proposed as a method of suppressing light emission immediately below an electrode. Such a conventional light emitting diode is disclosed in, for example,
Japanese Patent Publication No. 229665 and Japanese Patent Publication No. 6-82862.

FIG. 5 shows a light emitting diode disclosed in JP-A-4-229665. This light-emitting diode includes a light-emitting portion 10 made of an InGaAlP-based material and having a double hetero junction structure in which an active layer 35 is sandwiched between an n-type clad layer 34 and a p-type clad layer 36 on an n-type GaAs substrate 32. N-type InGaAs having a size of about the surface electrode 39 from the light-emitting portion 10 side between the semiconductor device 10 and the surface electrode 39.
1P current blocking layer 33 and p-type GaAlAs current spreading layer 3 having a larger band gap than InGaAlP active layer 35
7 is formed. 40 is a p-type InGa
P cap layer, 38 is a p-type GaAs contact layer, 31
Is a back electrode. Light emitting section 10 and light emitting side surface electrode 3
9, the current injection layer 37 and the current blocking layer 33 are provided, so that the current injected from the surface electrode 39 into the active layer 35 can be spread to the outside of the current blocking layer 33, so that the luminous intensity is improved. be able to.

FIG. 6 shows a light emitting diode disclosed in Japanese Patent Publication No. 6-82862. This light emitting diode
A p-type GaAs current blocking layer 4 is formed on an n-type GaAs substrate 42.
3 is formed on the current blocking layer 43. The n-type AlGaInP cladding layer 44, the p-type AlGaInP active layer 45, and the p-type
The light emitting unit 10 is formed of a type AlGaInP cladding layer 46, the back electrode 41 is formed on the back surface of the n-type GaAs substrate 42, and the surface electrode 49 is formed on the light emitting unit 10. By inserting the current blocking layer 43 immediately below the surface electrode 49 and between the epi layer (44) and the substrate 42, the current injected from the surface electrode 49 into the active layer 45 is:
Since the current is distributed so as to flow around the current blocking layer 43, the current is constricted in the peripheral region, and the current density is significantly increased. Therefore, photons are satisfactorily generated in both side regions of the active layer 45 by recombination, and most of the photons go outside without being blocked by the surface electrode 49, so that the luminous intensity can be improved.

[0009]

However, according to the conventional light emitting diode shown in FIG. 5, although the light emission immediately below the electrode can be suppressed, the current blocking layer is provided closer to the surface electrode than the active layer. It is necessary to use a semiconductor containing Al having a larger band gap energy than that of the active layer as a material of the current blocking layer, which limits the selection range of the material. In addition, when the current blocking layer is processed, the surface is oxidized to make epi growth difficult, or by etching the current blocking layer, an inverted mesa portion is formed and epi growth becomes difficult. Further, since MOVPE growth is performed twice, there is a problem that the cost is increased.

According to the light emitting diode shown in FIG.
When the current blocking layer 43 is smaller than the surface electrode 49, the luminous intensity may not be sufficiently improved, and it is necessary to optimize the size of the current blocking layer 43 with respect to the surface electrode 49.

Accordingly, an object of the present invention is to provide a light emitting diode which can be easily manufactured at a high luminous intensity, and a method for manufacturing the same.

[0012]

In order to achieve the above object, the present invention provides a first conductive type substrate, a first conductive type cladding layer, an active layer and a second conductive type formed sequentially on the substrate.
A light-emitting portion comprising a conductive-type cladding layer; a second-conductivity-type current-dispersion layer formed on the light-emitting portion; a surface electrode formed on a part of the surface of the current-dispersion layer; A back surface electrode formed entirely or partially on the back surface of the substrate, and formed immediately below the front surface electrode and at the interface between the substrate and the light emitting portion, having a predetermined size, a second conductivity type or a high resistance A light-emitting diode first conductivity type substrate comprising: a current blocking layer;
The active layer provides a cladding of the first conductivity type. The current injected into the active layer from the surface electrode is distributed by the current spreading layer and distributed around the current blocking layer, avoiding the current blocking layer. Most of the emitted photons go outside without being blocked by the surface electrode, so that the light extraction efficiency is improved. Further, by forming the current blocking layer at the interface between the substrate and the light emitting portion, the range of material selection is expanded, and growth by LPE with high mass productivity becomes possible.

In order to achieve the above object, the present invention provides a sapphire substrate, an n-type GaN layer formed on the sapphire substrate and having an n-side electrode, and an n-type GaN layer formed on the n-type GaN layer in order. An AlGaN cladding layer, an InGaN active layer and a p-type AlGaN cladding layer;
A p-side electrode formed on the GaN cladding layer, the n-type GaN layer and the n-type AlG just below the p-side electrode.
Provided is a light emitting diode comprising a p-type or high-resistance current blocking layer formed at an interface of an aN cladding layer and having a size equal to or larger than that of the p-side electrode. The size of the p-type or high-resistance current blocking layer provided immediately below the p-side electrode is approximately the same as or larger than that of the p-side electrode. Since most of the photons go outside without being blocked by the p-side electrode, the light extraction efficiency is improved.

According to the present invention, there is provided a first method for achieving the above object.
A current blocking layer of a second conductivity type or a high resistance having a predetermined size is formed on a substrate of a conductivity type, and a cladding layer of a first conductivity type, an active layer, and a second conductivity type are formed on the current blocking layer. A light emitting portion is formed by sequentially forming a cladding layer, a second conductive type current spreading layer is formed on the light emitting portion, and a part of the surface of the current spreading layer immediately above the current blocking layer. A method for manufacturing a light-emitting diode, comprising: forming a front surface electrode; and forming a back surface electrode on the entire back surface or a part of the back surface of the substrate.

[0015]

FIG. 1 shows an LED according to a first embodiment of the present invention. This LED includes an n-type GaAs substrate 2 and a p-type GaAs formed on the n-type GaAs substrate 2.
s current blocking layer 3 and n-type A formed on current blocking layer 3
lGaInP cladding layer 4, 0.5 μm thick p-type Al
GaInP active layer 5 and carrier concentration of 5 × 10 ¹⁷
a light emitting unit 10 composed of a p-type AlGaInP cladding layer 6 having a thickness of 0.5μm in cm ^-3, the carrier concentration is formed on the light emitting portion 10 is thick 4μm at 2 × 10 ¹⁸ cm ^-3 p-type A
an lGaInP current spreading layer 7, a p-type GaAs contact layer 8 formed on the current spreading layer 7, a surface electrode 9 having a diameter of 130 μm formed at the center of the surface of the contact layer 8,
a back electrode 1 formed on the entire back surface of the n-type GaAs substrate 2 and having a chip size of 300 μm square.

The p-type GaAs current blocking layer 3 has a surface electrode 9
It has a larger size and may have any shape such as a circle, a shape close to a circle, a square, a shape close to a square, and the like. The current blocking layer 3 may have the same size as the n-type GaAs substrate 2 or a smaller size, and may have a ring-shaped hole therein. In this embodiment, the diameter 2
Use a 00 μm circular one. The current blocking layer 3
Has a carrier concentration of 2 × 10 ¹⁸ cm ⁻³ and a thickness of 1 μm. The current blocking layer 3 is manufactured by processing an epitaxial wafer having a plurality of current blocking portions arranged in an array.

The n-type AlGaInP cladding layer 4 preferably has a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or less and a thickness of 5 μm or less. In the present embodiment, the carrier concentration is 1 × 10
^{It is 17} cm ^-3 and has a thickness of 0.5 μm.

Next, the LED according to the first embodiment will be described.
Will be described. First, a p-type GaAs layer is formed on an n-type GaAs substrate 2 by liquid phase epitaxy (LPE).
taxy). In addition, you may grow by a metal vapor phase epitaxial growth (MOVPE) method. This epitaxial wafer (hereinafter abbreviated as “epi wafer”) is processed by a photolithography process and etching to form a current blocking layer 3 having a diameter of 200 μm. An n-type AlGaI is formed on the current blocking layer 3 by MOVPE.
nP cladding layer 4, AlGaInP active layer 5, and p
A light emitting section 10 composed of the AlGaInP cladding layer 6 is grown, and a p-type AlGaInP current spreading layer 7 is grown thereon. A back electrode 1 is formed on the n-type GaAs substrate 2, which is the back surface of the epi-wafer, by vapor deposition and alloy processing. next,
A p-type GaAs contact layer 8 is formed on the surface of the epi-wafer, and AuZn / Ni / Au
Electrodes are formed by vapor deposition and alloy processing. After that, a circular surface electrode 9 having a diameter of 130 μm is formed by a photolithography process and etching.
The As contact layer is also removed. When the surface electrode 9 is formed, the position of the surface electrode 9 is adjusted by using the current blocking layer 3 provided at the ungrown portion of MOVPE provided at the end of the epi-wafer. The epiwafer is formed into chips by dicing, mounted on a stem by die bonding and wire bonding, and resin molded to produce an LED.

According to the above-described first embodiment, light emission in the active layer 5 immediately below the surface electrode 9 can be eliminated as compared with a light emitting diode not using a current confinement layer, so that high efficiency can be obtained. Can be. In addition, since the current can be dispersed without growing a thick current distribution layer as compared with the conventional light emitting diode, the total thickness of the epi layer can be significantly reduced, and as a result, the cost of MOVPE growth can be significantly reduced. it can. In addition, the following effects are obtained as compared with a conventional light emitting diode in which a current blocking layer is provided in a window layer or a current distribution layer. That is, the current blocking layer is made of LP with high mass productivity.
Since the growth by E is possible, the epi layer including the active layer can be completed by one MOVPE growth, so that the price of the epi wafer can be greatly reduced. Further, since it is not necessary to use a semiconductor having a larger band gap energy than the active layer as the current blocking layer, the material selection range is widened, and there is no need to use an Al-containing material that is easily oxidized. As a result, the epitaxy of the current blocking layer after the processing is facilitated, and the epitaxy of good quality is possible. Also, when the luminous intensity of this LED was measured, it was 1.5 times that of the case where the current blocking layer was not formed. In addition, commercially available GaP and A
It was possible to obtain a luminous intensity about 1.8 times that of an AlGaInP-based LED having a current dispersion layer of lGaAs.

The back electrode 1 may be partially formed on the back surface of the substrate 2. The p-type AlGaInP active layer 5 has the same conductivity type as the substrate 2 and a carrier concentration of 1 × 10
^It may be ¹⁷ cm ^-3 or less.

FIG. 2 shows an LED according to a second embodiment of the present invention. This LED is formed by embedding the current blocking layer 3 in the substrate 2 in the first embodiment, and the other configuration is the same as that of the first embodiment. That is, the epitaxial wafer portion and the electrodes formed by the MOVPE method are the same as in the first embodiment. The reason for this structure is that
In the case where the current blocking layer 3 is formed by the process as described in the first embodiment, if the current blocking layer 3 is thick during the etching process, the reverse mesa portion becomes a problem during epitaxial growth. In order to make the current blocking layer 3 thin, the current blocking layer 3
However, the dopant of the current blocking layer 3 diffuses into the active layer 5 and has an effect such as a decrease in luminous intensity. Further, it is conceivable to use another semiconductor material for the current blocking layer 3. However, it is easier to form a high quality light emitting layer by using a material having the same lattice constant as the current blocking layer 3. Therefore, when a GaAs crystal is used as a substrate, it is easily expected that the current blocking layer should be made of GaAs as much as possible and the carrier concentration should be as low as possible. Further, when performing MOVPE growth, it is easy to consider that epitaxial growth on a substrate as flat as possible will form a high quality light emitting portion.

Next, the LED according to the second embodiment will be described.
Will be described. First, concave portions 2a having a diameter of 200 μm and a depth of 2 μm are formed on the GaAs substrate 2 by photolithography and etching so as to be periodically arranged. Next, p-type GaAs is formed on the substrate 2 by the LPE method.
Grow the layer. When growing this, at a relatively high temperature,
When epi growth is performed with a low degree of supersaturation, a p-type GaAs layer grows only in the concave portion 2a. This is a growth method utilizing the characteristics of the LPE method. Since there is a variation in the film thickness, the growth cannot be stopped at the time when the substrate is almost flat. The surface of the epi-wafer is etched to form a recess 2
The p-type GaAs layers other than a are removed. This surface etching is performed so that the unevenness formed on the surface becomes flat. Of course, when making this epiwafer,
A part of the epiwafer where LPE has not been grown is left for positioning at the time of surface electrode formation. Using this epi-wafer, processes such as MOVPE growth, electrode formation, and mounting are performed to manufacture a resin mold LED. The method is the same as in the first embodiment.

According to the second embodiment, as in the first embodiment, the manufacturing is easy at a high luminous intensity, so that the cost can be greatly reduced. When the luminous intensity of this LED was measured, it was found that GaP or A
The emission luminous intensity was about twice as high as that of the LED of the current dispersion layer of lGaAs. In addition, the variation in the luminous intensity was about 2.5 times smaller than that in the first embodiment.

FIG. 3 shows an LED according to a third embodiment of the present invention. This LED is an AlGaInN-based LE
D, the sapphire substrate 12 and the sapphire substrate 12
An n-type GaN layer 20 formed thereon and an n-type GaN layer 20
A high resistance GaN current blocking layer 13 formed thereon and an n-type AlGaN cladding layer 1 formed on the current blocking layer 13
4, a light emitting unit 10 including an InGaN active layer 15 and a p-type AlGaN cladding layer 16, an n-side electrode 11 formed on an n-type GaN layer 20, and a p-side electrode formed on a p-type AlGaN cladding layer 16. 19 is provided. The current blocking layer 13 has the same or larger shape than the p-side electrode 19. The n-type cladding layer 16 preferably has a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or less.

According to the third embodiment, the current blocking layer 13 provided immediately below the p-side electrode 19 is made larger in size than the p-side electrode 19, so that the active layer 15 directly below the p-side electrode 19 is formed. Since most of the photons generated in the peripheral region other than the region go outside without being blocked by the p-side electrode 19, the light extraction efficiency is improved. Therefore, not only when the electrode is in the center of the chip, but also when the AlGaIn
Similar effects can be obtained when the electrodes are located at the corners of the chip as in the case of N-type LEDs. Note that the current blocking layer 13 may be a p-type current blocking layer.

The present invention is not limited to the above embodiment, but can be variously modified. For example, in the first and second embodiments, a light reflection film made of a semiconductor multilayer film may be provided between the substrate and the current blocking layer and the cladding layer. This allows the light generated on the substrate side to be reflected by the light reflecting film, so that the light extraction efficiency is further improved.

[0027]

As described above, according to the present invention, the current injected from the surface electrode into the active layer is dispersed by the current spreading layer and further distributed so as to flow around the current blocking layer avoiding the current blocking layer. Therefore, the light extraction efficiency is improved and a high luminous intensity is obtained. In addition, by forming the current blocking layer at the interface between the substrate and the light emitting portion, the range of material selection can be expanded, and the current blocking layer can be grown by LPE with high mass productivity. Can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a light emitting diode according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a light emitting diode according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a light emitting diode according to a third embodiment of the present invention.

FIG. 4 shows a conventional light emitting diode.

FIG. 5 shows a conventional light emitting diode.

FIG. 6 is a diagram showing a conventional light emitting diode.

[Explanation of symbols]

 Reference Signs List 1 back electrode 2 n-type GaAs substrate 3 p-type GaAs current blocking layer 4 n-type AlGaInP cladding layer 5 p-type AlGaInP active layer 6 p-type AlGaInP cladding layer 7 p-type AlGaInP current dispersion layer 8 p-type GaAs contact layer 9 front surface electrode 10 Light-emitting section 11 n-side electrode 12 sapphire substrate 13 high-resistance GaN current blocking layer 14 n-type AlGaN cladding layer 15 InGaN active layer 16 p-type AlGaN cladding layer 19 p-side electrode 20 n-type GaN layer 31 back electrode 32 n-type GaAs substrate 33 n-type InGaAlP current blocking layer 34 n-type InGaAlP cladding layer 35 InGaAlP active layer 36 p-type InGaAlP cladding layer 37 p-type GaAlAs current dispersion layer 38 p-type GaAs contact layer 39 surface electrode 40 p-type InGaP cap layer 41 Surface electrode 42 n-type GaAs substrate 43 p-type GaAs current blocking layer 44 n-type AlGaInP cladding layer 45 p-type AlGaInP active layer 46 p-type AlGaInP cladding layer 49 surface electrode

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenji Shibata 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture F-term in the Hidaka Factory of Hitachi Cable Co., Ltd. 5F041 AA03 CA05 CA34 CA37 CA40 CA58 CA63 CA65 CB03 CB04

Claims (18)

[Claims] A light emitting unit comprising a first conductivity type substrate, a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer formed sequentially on the substrate; A second-conductivity-type current spreading layer formed thereon, a front surface electrode formed on a part of the front surface side of the current spreading layer, and a back surface electrode formed on the whole or part of the back surface of the substrate; A light emitting diode formed immediately below the surface electrode and at an interface between the substrate and the light emitting portion, having a predetermined size and a current blocking layer of a second conductivity type or a high resistance. . 2. The light emitting diode according to claim 1, wherein said substrate is made of GaAs, and said light emitting part is made of AlGaInP. 3. The light emitting diode according to claim 1, wherein said current blocking layer is manufactured by processing an epitaxial wafer having a plurality of current blocking portions arranged in an array. 4. The light emitting diode according to claim 1, wherein the substrate has a concave portion on a surface of the substrate, and the current blocking layer is formed in the concave portion. 5. The current blocking layer according to claim 1, wherein the current blocking layer has a circular shape, a shape close to a circle, a square shape, or a shape close to a square shape, and the diameter thereof is larger than the diameter of the surface electrode. Light emitting diode. 6. The light emitting diode according to claim 1, wherein the current blocking layer has the same size as the substrate or a size smaller than the substrate, and has a ring-shaped hole therein. 7. The light emitting diode according to claim 1, wherein said first conductivity type cladding layer has a thickness of 5 μm or less. 8. The light emitting diode according to claim 1, wherein the first conductivity type cladding layer has a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or less. 9. The active layer has a conductivity type different from that of the substrate, or has the same conductivity type and a carrier concentration of 1 × 10 5.
The light-emitting diode according to claim 1, wherein the light-emitting diode is ⁷ cm ^-3 or less. 10. The light emitting diode according to claim 1, wherein said active layer has a quantum well structure. 11. The light emitting diode according to claim 1, further comprising a light reflection film made of a semiconductor multilayer film between said substrate and said current blocking layer and said first conductivity type cladding layer. 12. A sapphire substrate, and n formed on the sapphire substrate and having an n-side electrode.
A GaN layer, an n-type AlGaN cladding layer, an InGaN active layer and a p-type AlGaN cladding layer sequentially formed on the n-type GaN layer, a p-side electrode formed on the p-type AlGaN cladding layer, Immediately below the p-side electrode, the n-type GaN layer and the n-type GaN layer
A light emitting diode, comprising: a p-type or high-resistance current blocking layer formed at the interface of a p-type AlGaN cladding layer and having the same or larger size as the p-side electrode. 13. The light emitting diode according to claim 12, wherein the n-type AlGaN cladding layer has a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or less. 14. A second conductive type or high resistance current blocking layer having a predetermined size is formed on a substrate of a first conductive type, and a first conductive type cladding layer and an active layer are formed on the current blocking layer. Forming a light emitting portion by sequentially forming a layer and a cladding layer of the second conductivity type; forming a current spreading layer of the second conductivity type on the light emitting portion; A method for manufacturing a light emitting diode, comprising: forming a front surface electrode on a part of the surface of a layer; and forming a back surface electrode on the whole or part of the back surface of the substrate. 15. The method according to claim 15, wherein the current blocking layer is grown by a metal vapor phase epitaxial growth method or a liquid phase epitaxial method, and the light emitting portion and the current diffusion layer are grown by a metal vapor phase epitaxial growth method. 1
5. The method for manufacturing a light emitting diode according to item 4. 16. The method of manufacturing a light emitting diode according to claim 15, wherein said light emitting portion has an ungrown portion when growing by said metal vapor phase epitaxial growth method. 17. The method of forming a current blocking layer according to claim 16, wherein a concave portion and a convex portion are formed on the substrate by a photolithographic process, and a current blocking layer of a conductivity type different from that of the substrate is grown in the concave portion or etched after the growth. The method according to claim 15, wherein the current blocking layer is formed by performing the following. 18. The method for manufacturing a light emitting diode according to claim 17, wherein said current blocking layer is formed at a portion where no epitaxial growth portion is formed.