JP2002009336A - Light-emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting diode which can be manufactured readily, improve light emission output by restraining cost rise and provide high reliability. SOLUTION: A distribution Bragg reflector 3, which reflects light injected at an angle in a prescribed range, and refracts and emits light injected at an angle out of a prescribed range from a side surface, is provided.

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.
And a light emitting diode having excellent reliability.

[0002]

2. Description of the Related Art Conventionally, light emitting diodes (Light Emitting
Diodes) are widely used as various display light sources. In particular, LEDs used for outdoor displays and light sources for traffic signals are required to have high output, low power consumption, long life, and low price.

[0003] In order to satisfy such demands, for example, in an AlGaInP-based visible light LED, a distributed Bragg reflector is inserted between a substrate and a light emitting layer. High output is realized by increasing the extraction efficiency, inserting a current blocking layer, or attaching a transparent substrate to the light emission from the light emitting layer to improve the light extraction efficiency.

[0004]

However, the conventional light emitting diode has the following problems. (1) When a distributed Bragg reflector is provided, light incident at a predetermined angle out of light directed toward the substrate is reflected, but there is a problem that most of the unreflected light is absorbed by the substrate. (2) When the thickness of the window layer is increased, the external quantum efficiency is improved, but the material of the window layer is GaP and high AlA.
When s-mixed AlGaAs is used, the lattice mismatch with the GaAs substrate becomes large, and as the film becomes thicker, the light-emitting layer is greatly strained, so that a highly reliable element cannot be manufactured. Further, when an AlGaAs layer is used as a window layer, impurities intentionally added to lower the resistance of the AlGaAs layer diffuse to the vicinity of the light emitting layer, and the luminous efficiency is significantly reduced. This phenomenon is remarkable when the film is thickened by long-term crystal growth. (3) In the case where the current block layer is inserted, the crystal growth must be performed a plurality of times, which causes a problem of increasing the manufacturing cost. (4) In the case of bonding a transparent substrate, a complicated process step is required, so that there is a problem that the labor required for manufacturing is increased.

Accordingly, it is an object of the present invention to provide a light emitting diode which is easy to manufacture, can increase the light emission output while suppressing an increase in cost, and is excellent in reliability.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an active region for generating light, a substrate located below the active region, and an active region located above the active region. A window layer that transmits light generated in a region, first and second electrode units that apply a voltage to the active region,
Formed of a material that transmits light generated in the active region,
A distributed Bragg reflector that reflects the light incident at an angle within a predetermined range, refracts the light incident at an angle deviating from the predetermined range, and emits the light from a side surface. .

According to the above-described light emitting diode, light out of the predetermined angle range is emitted and extracted from the side surface by the distributed Bragg reflector located below the active region, so that the loss due to light absorption can be reduced. As a result, the light emission output can be increased.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a light emitting diode according to the present invention will be described in detail with reference to the drawings. In the following embodiment, the emission wavelength range is 550 to 650 nm,
A light-emitting diode using a P-type crystal as a material for a light-emitting region will be described.

FIG. 1 shows a light emitting diode according to a first embodiment, wherein (a) shows a cross section and (b) shows the whole. This light-emitting diode has a Se-doped GaAs buffer layer 2 on a GaAs substrate 1 and a Se-doped (Al _x Ga
_1-x ) _y In _1-y P distributed Bragg reflector 3, Se-doped n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P lower cladding layer 4, and undoped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P A light-emitting layer 5 and Zn-doped p-type (Al _0.7 Ga _0.3 ) _0.5 I
An epitaxial wafer in which an n _0.5 P upper cladding layer 6 and a Zn-doped p-type Al _0.8 Ga _0.2 As window layer 7 transparent to light emission from the light-emitting layer 5 are formed, and a p-type Al _0.8 Ga _0.2 An electrode portion 8 made of an Au-Zn-Ni alloy is provided on the surface of the As window layer 7. Au-Ge-Ni is provided under the GaAs substrate 1.
An electrode portion 9 made of an alloy is provided.

Since the light emitting layer 5 is made of a III-V group crystal, the GaAs substrate 1 is preferably a GaAs single crystal substrate made of a III-V group crystal from the viewpoint of physical properties and lattice matching. The conductivity type of the substrate may be n-type or p-type. The plane orientation of the substrate is basically a plane orientation inclined at about 10 ° to 15 ° from (100) from the viewpoint of doping efficiency, but there is no particular limitation, and a substrate having another plane orientation may be used. It is possible.

The GaAs buffer layer 2 has a thickness of 0.1 to less in order to eliminate the influence of crystal defects from the GaAs substrate 1.
It is formed with a thickness of 1 μm and is doped with Se so as to have the same conductivity as the GaAs substrate 1. However,
GaAs buffer layer 2 with distributed Bragg reflector 3
It is also possible to substitute the role of.

The (Al _x Ga _{1 -x} ) _y In _{1 -y} P distributed Bragg reflector 3 has an AlP composition that does not cause absorption when the emission wavelength is 550 to 650 nm, and a composition doped with Se. Are formed by a multilayer structure of two different types of AlGaInP. The crystal material used for the distributed Bragg reflector is not particularly limited as long as it satisfies the condition of being transparent with respect to the emission wavelength. ) Can be used.

Hereinafter, a method of manufacturing the light emitting diode according to the first embodiment will be described.

As the GaAs substrate 1, a Si-doped n-type GaAs having a carrier concentration of 1.0 × 10 ¹⁸ cm ^-3 is used.
Use a single crystal. The plane orientation is (100) 15 degrees off. An epitaxial layer is deposited and formed on the substrate by the MOVPE method. TMAl, TEG as raw materials
a, TMIn, DEZn, arsine, phosphine, hydrogen selenide are used, and the composition of the crystal to be grown is changed by changing the gas mixing ratio, flow rate, and growth temperature.

First, the GaAs substrate 1 is keyed with Se doping.
Carrier concentration is 1.0 × 10¹⁸cm- ^Three0.5μ thick
A m GaAs buffer layer 2 is grown.

Next, a mixed crystal ratio x =
1, two layers of y = 0.5 and two layers of x = 0.7 and y = 0.5 are doped with Se, and are made of n-type Al _0.5 In _0.5 P with a thickness of 51 nm and n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P is a pair structure having a thickness of 45 nm, and a total of 100 pairs of (Al _x G
a _1-x ) _y In _1-y P distributed Bragg reflector 3 is grown. The film thickness of the distributed Bragg reflector 3 is 9.6 μm.

Next, on the distributed Bragg reflector 3, the mixed crystal ratio is x = 0.7, y = 0.5, and the carrier concentration is 1.0 ×
Se-doped n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P lower cladding layer 4 having a thickness of 10 ¹⁸ cm ⁻³ and a thickness of 0.5 μm
Grow.

Next, a mixed crystal ratio of x
= 0, y = 0.5, and the carrier concentration is 1.0 × 10¹⁶c
m-^ThreeUndoped (Al) having a thickness of 0.6 μm_0.1
Ga _0.9)_0.5In_0.5The P light emitting layer 5 is grown.

Next, a mixed crystal ratio of x = 0.
7, y = 0.5 and carrier concentration of 4 × 10¹⁷cm^-3, Thickness
Zn-doped p-type (Al_0.7Ga
_0.3)_{0. Five}In_0.5The upper cladding layer 6 is grown.

Next, a Zn-doped layer is formed on the upper cladding layer 6.
And 4μm thick p-type Al_0.8Ga_{0 .2}As window layer
7 was grown into an LED epitaxial wafer.

Next, an LED chip is manufactured from the above-described LED epitaxial wafer. Tip size is L ₁
300 × L ₂ 300 μm, the Au-epitaxial wafer covers the entire lower surface of the chip corresponding to the GaAs substrate 1 side with Au-
An electrode portion 9 made of a Ge—Ni alloy is provided, and a diameter L ₃ made of an Au—Zn—Ni alloy is 150 on the window layer 7 side.
A circular electrode part 8 of μm is formed.

FIG. 2 shows the light transmission state of the distributed Bragg reflector 3, wherein the constituent layers of the distributed Bragg reflector 3, which are generally made of a semiconductor material, are 1 / l light emission from the light emitting layer 5.
Although the film thickness is about four optical path lengths, the film thickness of each of the constituent layers is intentionally shifted from the quarter optical path length, or the refractive index difference of each constituent layer of the distributed Bragg reflector 3 is intended. If the overall thickness is increased by reducing the thickness, the light A and the light B incident within a predetermined incident angle range of the light emission from the light emitting layer 5 are reflected, and the light C incident outside the range is reflected. In this case, most of the transmitted light is gradually refracted in a direction that is not horizontal to the film thickness direction based on the difference in the refractive index at the interface of the reflective film constituent layer, and is emitted from the side surface. The light D entering the window layer 7 is reflected on the side surface, refracted at the interface of the upper surface portion, and emitted.

FIG. 3 shows the state when the LED chip is energized.
Showing the relationship between the light emission output and the LED chip on the stem
The light emission characteristics were examined using an integrating sphere and a DC power supply.
As a result, the light emission output at the time of applying a current of 20 mA was 59a. u. And
(Al_xGa_1-x)_yIn_1-yNo P distribution Bragg reflector 3
Ku-type Al_0.8Ga_0.2As window layer 7 having a thickness of 8 μm
37a. u. About 60% increase in output compared to
Has been added. After applying electricity at 25 ° C and 100mA for 100h
Output drop is 3% or less, and p-type Al_0.8Ga_{0 .2}As
It was better than the case where the window layer 7 was thick.

In the light emitting diode described above, (Al _x G
a _1-x ) _y In _{1 -y} P When forming a double heterostructure,
0 ≦ x ≦ 1, 0.45 ≦ y to grow good quality crystals
It is preferable to set ≦ 0.55 and select x and y so as to lattice-match with the GaAs substrate. The composition of the light emitting layer 5 is determined from a desired light emission wavelength. The thickness of the light-emitting layer 5 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 lower cladding layer 4 and the upper cladding layer 6 on both sides of the light emitting layer 5 is as follows:
The value is set to be 100 meV or more larger than the band gap of the light emitting layer 5 so that the overflow of the carrier does not cause a decrease in the light emission efficiency. It is desirable that the thicknesses of the lower cladding layer 4 and the upper cladding layer 6 be selected so that carriers from the light emitting layer 5 do not tunnel. Further, the light emitting layer 5 may have a quantum well structure. Window layer 7
In the light emitting region described above, GaP or the like can be used in addition to AlGaAs. The thickness is set to a thickness that does not deteriorate the light emitting layer 5.

According to the light emitting diode of the first embodiment, the manufacturing cost can be reduced by one crystal growth and ordinary process steps, the luminous output can be increased, and the lattice mismatch is suppressed and the reliability is improved. Performance can be improved.

FIG. 4 shows a light emitting die according to the second embodiment.
FIG. 3A shows a cross section, and FIG. 3B shows the whole. This
Is a Se-doped GaAs substrate 10
GaAs buffer layer 11 and Se-doped Al_pG
a_1-pAs distributed Bragg reflector 12 and Se-doped n
Type (Al_0.7Ga_0.3)_0.5In_0.5P lower cladding layer 13
And undoped (Al_xGa₁-_y)_yIn₁-_yP multiple weight
A light emitting layer 14 having a sub-well structure and a Zn-doped p-type
(Al_0.7Ga_0.3)_0.5In_0.5P upper cladding layer 15
And Zn-doped p transparent to light emission from the light-emitting layer 14.
Type Al_0.8Ga_0.2As window layer 16
Forming a epitaxial wafer, p-type Al _0.8Ga
_0.2Au-Zn-Ni alloy is applied to the surface of the As window layer 7.
An electrode portion 17 made of gold is provided. GaA
The lower part of the s-substrate 10 is made of an Au-Ge-Ni alloy.
A pole 18 is provided.

The light emitting layer 14 is made of undoped (Al _0.5 G
a _0.5 ) _0.5 In _0.5 P and undoped Ga _0.5 In _0.5
It has a multilayer structure of P, a carrier concentration of 1.0 × 10 ¹⁶ cm ⁻³ , and the number of Ga _0.5 In _0.5 P layers is 40.
It is.

Hereinafter, a method of manufacturing the light emitting diode according to the second embodiment will be described.

As the GaAs substrate 10, a Si-doped n-type GaAs having a carrier concentration of 1.0 × 10 ¹⁸ cm ^-3 is used.
Use a single crystal. The plane orientation is (100) 15 degrees off. An epitaxial layer is deposited and formed on the substrate by the MOVPE method. TMAl, TEG as raw materials
a, TMIn, DEZn, arsine, phosphine, hydrogen selenide are used, and the composition of the crystal to be grown is changed by changing the gas mixing ratio, flow rate, and growth temperature.

First, a GaAs substrate 10 is doped with Se so that the carrier concentration is 1.0 × 10 ¹⁸ cm ⁻³ and the thickness is 0.5
A μm GaAs buffer layer 11 is grown.

Next, the mixed crystal ratio x
= 1, y = 0.5, and x = 0.7, y = 0.5
The layers are doped with Se, n-type Al _0.9 Ga _0.1 P having a thickness of 44 nm, and n-type Al _0.75 Ga _0.25 As having a thickness of 41.
A total of 75 pairs of Al _p Ga _1-p As Bragg reflectors 12 are grown with a pair structure of nm. This Bragg reflector 12
Is 6.375 μm.

Next, on the Bragg reflector 12, the mixed crystal ratio is x = 0.7, y = 0.5, and the carrier concentration is 1.0 × l.
0 ¹⁸ cm- ³ , Se-doped n having a thickness of 0.5 μm
Mold (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Lower cladding layer 13
Grow.

Next, on the lower cladding layer 13, the mixed crystal ratio is x = 0.5, y = 0.5 and undoped (Al _0.5 G
a _0.5 ) _0.5 In _0.5 P and a mixed crystal ratio of x = 0, y = 0.5
Then, the light emitting layer 14 having a multilayer structure of undoped Ga _0.5 In _0.5 P is grown. The carrier concentration is 1.0 × 10
^{At 16} cm- ³ , the number of Ga _0.5 In _0.5 P layers is 40.

Next, a mixed crystal ratio of x = 0.
7, y = 0.5 and carrier concentration of 4 × 10¹⁷cm^-3, Thickness
Zn-doped p-type (Al_0.7Ga
_0.3) _0.5In_0.5The upper cladding layer 15 is grown.

Next, a p-type Al _0.8 Ga _0.2 As window layer 16 having a thickness of 4 μm and doped with Zn was grown on the upper cladding layer 15 to obtain an LED epitaxial wafer.

Next, an LED chip is manufactured from the above-described LED epitaxial wafer. Tip size is L ₁
300 × L ₂ 300 μm, the entire surface of the chip under the LED epitaxial wafer on the GaAs substrate 10 side is Au
An electrode portion 17 made of a Ge—Ni alloy is provided, and a circular electrode portion 17 made of an Au—Zn—Ni alloy and having a diameter L ₃ of 150 μm is formed on the window layer 16 side.

The above-mentioned LED chips were evaluated for reliability during energization. As a result of assembling the LED chip on the stem and examining the light emission characteristics using an integrating sphere and a DC power supply, as shown in FIG. u. 37a in the case where the Al _x Ga _{1 -x} As Bragg reflector 12 is not provided and the p-type Al _0.8 Ga _0.2 As window layer 7 is 8 μm thick. u. The output is increased by about 70% as compared with. Further, the output reduction after applying electricity at 25 ° C. and 100 mA for 100 hours was 3% or less, and a better result was obtained than when the p-type Al _0.8 Ga _0.2 As window layer 7 was 8 μm and the light emitting layer 14 was bulk.

According to the light emitting diode of the second embodiment, by providing the light emitting layer 14 having the multiple quantum well structure, the light emitting output can be increased and the lattice mismatch is suppressed, thereby improving the reliability. be able to.

In the above-described first and second embodiments, the substrate made of GaAs is used. However, as long as electrical contact with the light emitting region is obtained and the crystal quality of the LED constituent layer is not adversely affected. There is no particular limitation.

[0040]

As described above, according to the light emitting diode of the present invention, light incident on the distributed Bragg reflector at an angle within a predetermined range is reflected, and light incident at an angle deviating from the angle within the predetermined range. Since the light is refracted and emitted from the side surface, manufacturing is easy, the increase in cost can be suppressed, the light emission output can be increased, and excellent reliability can be provided.

[Brief description of the drawings]

FIG. 1A is a sectional view of a light emitting diode according to a first embodiment of the present invention. FIG. 1B is a perspective view of the light emitting diode according to the first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a light transmission state of a distributed Bragg reflector 3;

FIG. 3 is an explanatory diagram showing a relationship between an energizing time of a LED chip and a light output

FIG. 4A is a sectional view of a light emitting diode according to a second embodiment of the present invention, and FIG. 4B is a perspective view of a light emitting diode according to the second embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 GaAs substrate 2 GaAs buffer layer 3 (Al _x Ga _{1 -x} ) _y In _{1 -y} P distributed Bragg reflector 4 (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P lower cladding layer 5 (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P light emitting layer _{6 (Al 0.7 Ga 0.3) 0.5} In 0.5 P upper cladding layer 7 Al _0.8 Ga _0.2 As window layer 8 electrode portion 9 the electrode portion 10 GaAs substrate 11 GaAs buffer layer 12 Al _p Ga _1-p As distributed Bragg reflector 13 (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Lower Cladding Layer 14 Light Emitting Layer 15 (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Upper Cladding Layer 16 Al _0.8 Ga _0.2 As Window Layer 17 Electrode 18 Electrode

Claims (5)

[Claims] An active region for generating light; a substrate positioned below the active region; a window layer positioned on the active region and transmitting light generated in the active region; First and second electrode portions for applying a voltage to the active region, and a material that transmits light generated in the active region;
A distributed Bragg reflector that reflects the light incident at an angle within a predetermined range, refracts the light incident at an angle deviating from the predetermined range, and emits the light from a side surface. diode. 2. The light emitting diode according to claim 1, wherein said active region is composed of AlGaInP in a composition region having a band gap in a visible light region. 3. The light emitting diode according to claim 1, wherein said active region is made of AlGaInN having a band gap ranging from an ultraviolet region to a visible light region. 4. The distributed Bragg reflector comprises AlGaI.
nP or at least one of AlGaAs,
2. The structure according to claim 1, wherein at least one impurity of i, Se, Te, C, Mg, Be, or Zn is added.
A light-emitting diode according to the item. 5. The light emitting diode according to claim 1, wherein said active region has a quantum well structure.