JP2001352097A - Light-emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting diode of low price, having a simple struc ture and high efficiency. SOLUTION: This light-emitting diode enables suppression of electric current flowing in a light-emitting layer 5 of the lower part of an upper electrode 11 of the side of the upper electrode 11 (light extraction side) and to reflect a radiating light from a lightemitting layer 5 to a light extracting side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a light emitting diode.

[0002]

2. Description of the Related Art Light emitting diodes (hereinafter referred to as "LEDs") are widely used as light sources for various displays.
In particular, it is used as an outdoor display or a traffic light source. This type of LED is required to have high output, high reliability, and low cost. Therefore, Al
In a GaInP-based visible light LED, a thick film (a so-called window layer) having a high transmittance and a low resistance to light emitted from the light emitting layer is provided above the light emitting layer, and a current injected into the upper electrode is provided. Is sufficiently diffused to obtain a high output.

[0003]

By introducing a window layer, the output can be greatly improved as compared with the case where there is no window layer. The absorption by the electrodes hinders the improvement of the external quantum efficiency.

Therefore, for example, a current blocking layer for suppressing the current from flowing into the light emitting layer below the upper electrode is inserted, or a reflective layer is provided immediately below the upper electrode to reduce the influence of absorption at the upper electrode. (Japanese Patent Laid-Open No. 6-974)
Japanese Patent Application Laid-Open No. 98-9898) reduces the light absorption at the upper electrode, but has a problem in that the manufacturing process is complicated.

An object of the present invention is to solve the above-mentioned problems and to provide an inexpensive light-emitting diode having a simple structure, high luminous efficiency and high efficiency.

[0006]

In order to achieve the above object, a light emitting diode according to the present invention comprises a lower electrode, a substrate formed on the lower electrode, and an AlGaInP formed on the substrate.
III-V compounds having different compositions are alternately stacked between the substrate and the light emitting layer in a light emitting diode having a light emitting layer composed of a mixed crystal of and a top electrode formed partially on the light emitting layer. A reflective layer is provided to reflect emitted light of the light-emitting layer to the upper electrode side, and between the light-emitting layer and the upper electrode, has a conductivity type opposite to that of an adjacent semiconductor layer, and prevents current from flowing through the light-emitting layer. A current blocking layer that suppresses and reflects emitted light from the light emitting layer is provided.

[0007] In addition to the above configuration, the area of the current blocking layer of the light emitting diode of the present invention is preferably equal to or larger than the upper electrode.

In addition to the above structure, the current blocking layer of the light emitting diode of the present invention is preferably formed by alternately laminating III-V compounds having different compositions to reflect light emitted from the light emitting layer.

In addition to the above configuration, the upper electrode of the light emitting diode of the present invention may be formed substantially at the center on the light emitting layer.

[0010] In addition to the above configuration, the upper electrode of the light emitting diode of the present invention may be formed in a peripheral portion on the light emitting layer.

In addition to the above structure, the reflection layer of the light emitting diode of the present invention is made of AlGaInP, AlGaAs, GaAs,
It is preferable to include at least one of AlInP.

In addition to the above configuration, the current blocking layer of the light emitting diode of the present invention is made of AlGaInP, AlGaAs, G
It is preferable to include at least one of aAs and AlInP.

In addition to the above configuration, the light emitting diode of the present invention preferably has the same conductivity type as the substrate and the current blocking layer.

In addition to the above structure, the light emitting diode according to the present invention has a structure in which the conductivity type of the substrate and the conductivity type of the current blocking layer are n.
Preferably it is a mold.

[0015] In addition to the above configuration, in the light emitting diode of the present invention, it is preferable that at least one of Si, Se, Te, and Ge is added to the current blocking layer.

According to the present invention, by inserting a current blocking layer composed of a semiconductor multilayer film between the upper electrode and the light emitting layer, current is applied to the light emitting layer below the upper electrode on the upper electrode side (light extraction side). Can be suppressed, and radiated light from the light emitting layer can be reflected to the light extraction side.

Hereinafter, the configuration of the light emitting diode of the present invention will be described.

First, the substrate is not particularly limited as long as it is a GaAs substrate which can make electrical contact with the light emitting region and does not adversely affect the crystal quality of the semiconductor layer constituting the LED. The plane orientation of the substrate is basically 2 ° to 20 ° inclined from the (100) plane from the viewpoint of doping efficiency, but is not particularly limited, and substrates having other plane orientations are also used. Can be used.

A GaAs buffer layer is deposited on the substrate to eliminate the influence of crystal defects from the substrate. The thickness is generally 0.1 μm to 1 μm,
Doping is performed so as to have the same conductivity as the substrate.
Furthermore, in order to reflect light emitted from the light emitting layer, a distributed Bragg reflector using a crystalline material having the same electrical conductivity as the substrate and lattice-matching with the substrate is inserted.

Next, an (Al _x Ga _{1 -x} ) _y In _{1 -y} P double heterostructure is formed. In order to grow a good quality crystal, the conditions of x and y are set as 0 ≦ x ≦ 1, 0.47 ≦ y ≦ 0.57
X and y are selected so that the double hetero structure and the GaAs substrate are lattice-matched. The composition of the light emitting layer is determined from a desired light emission wavelength. The thickness of the light emitting layer is set to such a thickness that non-radiative recombination at the interface with the cladding layer does not become the most dominant factor of carrier recombination. The composition of the cladding layers on both sides of the light emitting layer is selected so as to have a value larger than the band gap of the light emitting layer so that the overflow of the carrier does not cause a decrease in luminous efficiency. The thickness of the cladding layer is selected so that carriers from the light emitting layer do not tunnel. When an LED is formed on an n-type GaAs substrate, the cladding layer (upper cladding layer) above the light emitting layer is doped with Mg or Zn so as to have a sufficiently low resistance. However, in the vicinity of the interface between the light emitting layer and the upper cladding layer, the doping concentration is reduced in order to reduce the effect of non-radiative recombination. An impurity such as Se, Si or Te is added to the lower cladding layer (lower cladding layer) of the light emitting layer. When an LED is formed on a p-type GaAs substrate, an impurity such as Se, Si or Te is added to the upper cladding layer, and Mg or Zn is added to the lower cladding layer. The composition and doping concentration of the upper and lower cladding layers may be changed in the film thickness direction so as to reduce the resistance. Further, instead of the light emitting layer having the double hetero structure, a quantum well structure may be used.

Next, a current block layer is formed on the upper clad layer. In order to realize the characteristic of suppressing the current from flowing to the light emitting layer below the electrode on the light extraction side, the current blocking layer is provided with an electric conductivity opposite to that of the upper cladding layer. Further, in order to have the property of reflecting the emitted light of the light emitting layer, a current blocking layer is formed by a reflective layer that reflects the emitted light of the light emitting layer by alternately stacking group III-V compound layers having different compositions. Due to the distributed Bragg reflector below the light emitting layer and the current blocking layer that reflects the light emitted from the light emitting layer, the light emitted from the light emitting layer is efficiently absorbed without being absorbed by the substrate or the electrode. Will be released.

After forming up to the current block layer by a single crystal growth, a portion other than a part of the current block layer is removed by etching to form a window layer. A contact layer is formed on the window layer as needed.

Electrodes are formed on the substrate side and the upper clad layer side of the LED epitaxial wafer thus formed, and an LED chip is manufactured through dicing.
Implement.

As described above, with a simple structure of two crystal growths and a normal manufacturing process, the luminous efficiency is high and the inexpensive L is used.
ED is obtained.

[0025]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a structural view showing one embodiment of the light emitting diode of the present invention.

In this light emitting diode, a buffer layer 2, a reflection layer 3, a lower cladding layer 4, a light emitting layer 5, an upper cladding layer 6, a current blocking layer 7, a window layer 8, and a contact layer 9 are sequentially formed on a substrate 1. The lower electrode 10 is formed on the lower surface of the substrate 1 and the upper electrode 11 is formed on the contact layer 9.

By inserting a current blocking layer 7 composed of a semiconductor multilayer film between the upper electrode 11 and the light emitting layer 5,
It is possible to suppress a current from flowing to the light emitting layer 5 below the upper electrode 11 and reflect the radiation emitted from the light emitting layer 5 to the light extraction side (upper electrode 11 side). Therefore, it is possible to provide an inexpensive light-emitting diode having a simple configuration, high luminous efficiency, and low cost.

[0029]

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

(Example 1) (Al) was deposited on an n-type GaAs substrate.
An LED having a DH (double hetero) structure having a light emitting layer of _0.1 Ga _0.9 ) _0.5 In _0.5 P was manufactured.

FIG. 2 is an explanatory view of one embodiment of the epitaxial wafer used for the light emitting diode of the present invention. FIG. 2 (a) shows a state before etching of a current blocking film, and FIG. 2 (b) shows a completed state. The state of the epitaxial wafer after is shown.

As the substrate 1 shown in FIG. 2A, a Si-doped n-type single crystal was used. The carrier concentration of the substrate 1 is 2
× 10 ¹⁸ cm ^-3 , and the plane orientation was (100) 15 degrees off. An epitaxial layer was deposited on the substrate 1 by MOVPE. As materials for the epitaxial layer, TMAl (trimethylaluminum), TEGa
(Triethylgallium), TMIn (trimethylindium), DEZn (diethylzinc), arsine, phosphine, monosilane, using a gas mixing ratio and flow rate,
By changing the growth temperature, the composition of the crystal was changed.

First, a buffer layer 2 made of n-GaAs was grown on a substrate 1.

The buffer layer 2 is doped with Si, has a carrier concentration of 1 × 10 ¹⁸ cm ^-3 and a thickness of about 0.5 μm. On the buffer layer 2, a reflective layer 3 made of a distributed Bragg reflector (DBR) for reflecting the light emitted from the light emitting layer 5 was formed on the buffer layer 2, which had n-type conductivity with Si doping.
The distributed Bragg reflector has an Al _0.85 Ga thickness of about 44 nm.
It is composed of 12 pairs of _0.15 As and GaAs having a thickness of about 39 nm.

Next, an (Al _x Ga _{1 -x} ) _y In _{1 -y} P double heterostructure was formed. The lower cladding layer 4 was made of Si-doped n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P with a mixed crystal ratio of x = 0.7 and y = 0.5. The carrier concentration of the lower cladding layer 4 was 8 × 10 ¹⁷ cm ⁻³ , and the thickness was 0.5 μm.

The light emitting layer 5 has a mixed crystal ratio of x = 0.1, y =
0.5 and undoped (Al _0.1 Ga _0.9 ) _0.5 I
n _0.5 P. The carrier concentration of the light emitting layer 5 is 1 × 10 ¹⁶
cm ⁻³ and a thickness of about 0.6 μm.

The mixed crystal ratio of the upper cladding layer 6 is x = 0.7,
y = 0.5, Zn-doped p-type (Al _0.7 G
a _0.3 ) _0.5 In _0.5 P The carrier concentration of the upper cladding layer 6 was 5 × 10 ¹⁷ cm ⁻³ , and the thickness was about 1 μm.

The current blocking film 7a is formed on the upper cladding layer 6.
Was formed. The current blocking film 7a was made of Si-doped n-type, and was constituted by six pairs of Al _0.85 Ga _0.15 As having a thickness of about 44 nm and GaAs having a thickness of about 39 nm. The carrier concentration of the current blocking film 7a was set to 1 × 10 ¹⁸ cm ⁻³ .

In this way, the layers from the buffer layer 2 to the current block film 7a were formed on the substrate 1 by a single crystal growth, and were removed by selective etching so that a part of the current block film 7a remained. The mixed solution of sulfuric acid, hydrogen peroxide and water dissolves the current blocking film 7a at an etching rate of about 1 μm / min and hardly dissolves the upper cladding layer 6, so that selective etching can be easily performed.

After the current block film 7a was selectively etched to remove a part thereof to form a current block layer 7, a window layer 8 was formed so as to cover the upper clad layer 6 and the current block layer 7. The crystal material is Al _0.85 Ga
_0.15 As, and doping with Zn to increase the carrier concentration (from 1 to
20) × 10 ¹⁸ cm ⁻³ . About 0.03 μm of Zn-GaAs is formed on the window layer 8 as the contact layer 9a.
The LED shown in FIG.
An epitaxial wafer was obtained.

An LED chip as shown in FIG. 1 was manufactured from the thus obtained LED epitaxial wafer.

The LED chip is provided on the lower electrode 10 with n
A substrate 1 made of -GaAs, a buffer layer 2 made of n-GaAs, a reflective layer 3 made of DBR, and n- (Al _0.7 G
a _0.3 ) Lower cladding layer 4 made of _0.5 In _0.5 P;
A light-emitting layer 5 made of (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P, an upper clad layer 6 made of p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, a current blocking layer 7, p-AlGaAs
A window layer 8 made of S, a contact layer 9 made of p-GaAs, and an upper electrode 11 are sequentially laminated.

The LED chip has a size of 300 μm square, a lower electrode 10 made of an Au—Ge—Ni alloy is formed on the entire lower surface of the chip on the substrate 1 side of the epitaxial wafer, and an Au—Zn— A circular upper electrode 11 made of a Ni alloy and having a diameter of 150 μm is formed. This LED chip was placed on the stem, and the light emission characteristics of the LED were measured using an integrating sphere photometer and a DC power supply. u. And
30a. Of the luminous output of the LED having the structure without the current blocking layer 7 having the characteristic of reflecting the radiated light of the luminescent layer 5 u. The output was increased by 67% as compared with.

Example 2 An LED having a quantum well light emitting layer on an n-type GaAs substrate was manufactured.

FIG. 3 is an explanatory view of another embodiment of the epitaxial wafer used for the light emitting diode of the present invention.
(A) shows a state before etching of the current blocking film,
(B) shows the state of the completed epitaxial wafer.

As the substrate 20 shown in FIG. 3A, a Si-doped n-type GaAs single crystal was used. The carrier concentration of the substrate 20 is 2 × 10 ¹⁸ cm ⁻³ and the plane orientation is (100).
Turned off 15 degrees. An epitaxial layer was deposited on the substrate 20 by MOVPE. As a raw material, TMA
Using I, TEGa, TMIn, DEZn, arsine, phosphine, and monosilane, the composition of the crystal to be grown was changed by changing the gas mixing ratio, flow rate, and growth temperature.

First, a buffer layer 21 made of n-GaAs was grown on a substrate 20.

The buffer layer 21 was doped with Si to have a carrier concentration of 1 × 10 ¹⁸ cm ^-3 and a thickness of about 0.5 μm. On the buffer layer 21, a DB for reflecting n-type conductivity by doping with Si and reflecting light emitted from the light emitting layer 24 is provided.
A reflection layer 22 made of R was formed. The distributed Bragg reflector has a thickness of 44 nm of Al _0.85 Ga _0.15 As and a thickness of 39 n.
It is composed of 12 pairs with m GaAs.

Next, the lower cladding layer 23 and the light emitting layer 24
Was formed. The lower cladding layer 23 has a mixed crystal ratio of x = 0.
7, y = 0.5, and Si-doped n-type (Al _0.7 Ga
_0.3 ) _0.5 In _0.5 P. The carrier concentration of the lower cladding layer 23 is set to 8 × 10 ¹⁷ cm ⁻³ and the thickness is set to about 0.5 μm.
m.

The light emitting layer 24 is made of (Al _0.5 Ga _0.5 ) _0.5
And an In _0.5 P, and a Ga _0.5 an In _0.5 undoped multi-quantum well made of a P (MQW) structure.

The upper cladding layer 25 has a mixed crystal ratio of x = 0.
7, y = 0.5 and Zn-doped p-type (Al _0.7 Ga
_0.3 ) _0.5 In _0.5 P. The carrier concentration of the upper cladding layer 25 was 5 × 10 ¹⁷ cm ⁻³ , and the thickness was about 1 μm.

The current blocking film 2 is formed on the upper cladding layer 25.
6a was formed.

The current blocking film 26a is made of Si-doped n
It is a mold and is composed of eight pairs of Al _0.5 In _0.5 P having a thickness of about 43 nm and (Al _0.35 Ga _0.65 ) _0.5 In _0.5 P having a thickness of about 49 nm. The carrier concentration of the current block film 26a was set to 1 × 10 ¹⁸ cm ⁻³ .

Thus, the buffer layer 2 is formed on the substrate 20.
1 to the current blocking layer 26a are formed by a single crystal growth, and the current blocking layer 2a is formed using a hydrochloric acid-based etchant.
The current blocking layer 26 was formed by removing a part of the current blocking layer 6a. The current blocking layer 26 and the upper cladding layer 25
The LED epitaxial wafer as shown in FIG. 3B was obtained by forming the window layer 27 so as to cover the LED epitaxial wafer. The window layer 27 is made of GaP, doped with Zn, and has a carrier concentration of (1 to 20) × 1.
0 ¹⁸ cm ⁻³ .

An LED chip was fabricated from the thus obtained LED epitaxial wafer.

FIG. 4 is a sectional view of a light emitting diode using the epitaxial wafer shown in FIGS. 3 (a) and 3 (b).

The LED chip is provided on the lower electrode 28 with n
-GaAs substrate 20, n-GaAs buffer layer 21, DBR reflective layer 22, n- (Al
_0.7 Ga _0.3 ) _0.5 In _0.5 P lower cladding layer 23, MQW light emitting layer 24, p- (Al _0.7 Ga
_0.3 ) An upper cladding layer 25 made of _0.5 In _0.5 P, a current blocking layer 26, a window layer made of p-GaP, and an upper electrode 29 are sequentially laminated.

The size of the LED chip is 300 μm square, and the lower electrode 28 made of an Au—Ge—Ni alloy is formed on the entire lower surface of the chip on the substrate 20 side of the epitaxial wafer.
Is formed, and on the window layer 27 side, Au—Zn—Ni
A circular upper electrode 29 made of an alloy and having a diameter of 150 μm is formed. Place this LED chip on the stem,
As a result of measuring the light emission characteristics of the LED using an integrating sphere photometer and a DC power supply, the light emission output when a current of 20 mA was supplied was 55a. u. And the light emission output of the LED having the structure without the current blocking layer 26 having the characteristic of reflecting the emitted light of the light emitting layer 24 is 30.
a. u. The luminous output increased by 83% as compared with.

[0059]

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

It is possible to provide an inexpensive light emitting diode having a simple structure, high luminous efficiency, and low cost.

[Brief description of the drawings]

FIG. 1 is a structural view showing one embodiment of a light emitting diode of the present invention.

FIGS. 2A and 2B are explanatory views of an embodiment of an epitaxial wafer used for the light emitting diode of the present invention, wherein FIG. 2A shows a state before etching of a current blocking film, and FIG. Is shown.

3A and 3B are explanatory views of another embodiment of the epitaxial wafer used for the light emitting diode of the present invention, wherein FIG. 3A shows a state before etching of a current blocking film, and FIG. Indicates the status.

FIG. 4 is a sectional view of a light emitting diode using the epitaxial wafer shown in FIGS. 3 (a) and 3 (b).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 3 Reflective layer 4 Lower clad layer 5 Light emitting layer 6 Upper clad layer 7 Current block layer 8 Window layer 9 Contact layer 10 Lower electrode 11 Upper electrode

Claims (10)

[Claims] 1. A lower electrode, a substrate formed on the lower electrode, a light emitting layer formed on the substrate and made of a mixed crystal of AlGaInP, and an upper electrode formed on a part of the light emitting layer. In the light-emitting diode, a III-V compound having a different composition is alternately stacked between the substrate and the light-emitting layer, and a reflection layer is provided for reflecting the emitted light of the light-emitting layer toward the upper electrode. A current block that has an opposite conductivity type to the adjacent semiconductor layer between the light emitting layer and the upper electrode, suppresses current from flowing through the light emitting layer, and reflects emitted light from the light emitting layer A light-emitting diode comprising a layer. 2. The light emitting diode according to claim 1, wherein an area of the current blocking layer is equal to or larger than the upper electrode. 3. The current blocking layer according to claim 1, wherein said current blocking layers have different compositions.
The light emitting diode according to claim 1, wherein the group IV compounds are alternately stacked to reflect light emitted from the light emitting layer. 4. The light emitting diode according to claim 1, wherein the upper electrode is formed substantially at the center on the light emitting layer. 5. The light emitting diode according to claim 1, wherein the upper electrode is formed in a peripheral portion on the light emitting layer. 6. The reflective layer is made of AlGaInP, AlG
4. The light emitting diode according to claim 1, comprising at least one of aAs, GaAs, and AlInP. 7. The current blocking layer is made of AlGaIn.
4. The light emitting diode according to claim 1, comprising at least one of P, AlGaAs, GaAs, and AlInP. 8. The light emitting diode according to claim 1, wherein the conductivity type of the substrate is the same as the conductivity type of the current blocking layer. 9. The light emitting diode according to claim 8, wherein the conductivity type of the substrate and the conductivity type of the current blocking layer are n-type. 10. The method according to claim 1, wherein the current blocking layer includes Si, Se,
The light emitting diode according to claim 8, wherein at least one of Te and Ge is added.