JPH07162036A - Light emitting diode - Google Patents

Abstract

PURPOSE:To prevent arsine from being produced in air and to protect an AlGaAs window layer against unnecessary etching in a manufacturing process by a method where AlGaAs layers and AlGaInP layer which are both larger than an active layer in energy gap are successively. CONSTITUTION:First AlaGa1-aAs semiconductor layer which meet a formula, 0.4<=a<0.95, are alternately laminated to form a multilayered film reflecting mirror. The semiconductor multilayered film reflecting mirror is formed through such a manner that semiconductor layers of two types different from each other in refractive index are alternately laminated, wherein the one semiconductor layers and the other semiconductor layers are so set in thickness respectively as to satisfy a formula, d=lambda/4n (d:thickness of semiconductor layer lambda: wavelength of emission, n:refractive index of semiconductor layer). 15 to 25 cycles of lamination are adequate so as to make a semiconductor multilayered film reflecting mirror enough in reflection properties. By this setup, arsine is prevented from occurring attendant on oxidation in an element forming process, so that an operator can be protected against danger.

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 formed on a GaAs substrate, and more particularly to a high brightness light emitting diode using AlGaInP for a double hetero structure.

[0002]

2. Description of the Related Art In recent years, high-luminance light emitting diodes using AlGaInP in a light emitting portion in a red to green light emitting region have been actively researched. 1 and 2 show n-type Ga.
An example of the basic structure of a high-brightness light emitting diode manufactured on an As substrate is shown. As a structural means for obtaining high brightness, a reflection layer and an AlGaAs window layer are introduced (Japanese Patent Laid-Open Nos. 59-171116 and 59-1218).
30, JP-A-4-212479, JP-A-3-16388
2, see JP-A-3-163883).

The reflecting layer is also called a semiconductor multilayer film reflecting mirror,
The purpose is to reflect the light emitted toward the rear of the light emitting surface and absorbed by the substrate toward the front of the light emitting surface. The semiconductor multilayer film reflecting mirror has a structure in which two types of semiconductor layers having different refractive indexes are alternately laminated with a layer thickness of λ / 4n (λ: emission wavelength of light emitting portion, n: refractive index of semiconductor layer). By installing this between the board and the double hetero part,
The emission luminance can be increased by a factor of 2 to 3 as compared with the case where it is not provided.

As a material for the semiconductor multilayer film reflecting mirror, Ga is used.
Al that is almost lattice-matched to the As substrate and can have a large difference in refractive index
It is common to use As and AlGaAs to fabricate a reflecting mirror by alternately laminating 15 to 25 pairs of these two layers (Journal of Applied Physics, Autumn 991, No. 1182).
~ 1183 pages, 10A-G1, 10A-G2, 10A-
(See G5).

The AlGaAs window layer is intended to spread the injection current from directly under the electrode to the entire chip to obtain LED light emission on the entire surface of the chip. AlGaInP or Al
In the InP p-type clad layer, it is difficult to obtain a high carrier concentration and the resistance is high, so that the current hardly spreads. However, by introducing an AlGaAs window layer between the p-type cladding layer and the GaAs contact layer, which is easy to have a high p-type carrier concentration and mobility, the injection current is spread over the entire surface of the chip before reaching the p-type cladding layer. It will be possible. In the case where the AlGaAs window layer is not provided, light emission is observed only in the region around the electrode, whereas by introducing the AlGaAs window layer, the light emitting region is spread over the entire surface of the chip and the light emission brightness is also increased.

AlGaAs is generally used for the window layer. This is because the high mobility of the p-type allows easy current diffusion, and the composition can be adjusted to be transparent to the emission wavelength of the active layer.

[0007]

However, there are problems with both the semiconductor multilayer mirror and the AlGaAs window layer. AlAs, which is widely used as a constituent layer of a reflector, easily oxidizes due to oxygen and moisture in the air,
As a product, a toxic gas arsine (AsH ₃ ) is generated. Therefore, there is a high possibility that arsine is generated in the element processing process such as dicing (chip cutting process) and the safety of the operator is significantly impaired.

On the other hand, the AlGaAs window layer also has a problem during the element processing process. The GaAs contact layer for obtaining a good ohmic electrode needs to be removed by etching after forming the electrode because it serves as an absorption layer for the emission wavelength. However, at this time, most of the AlGaAs window layer immediately below the GaAs contact layer is also etched together with the GaAs contact layer. For this reason, the injected current cannot spread sufficiently in the AlGaAs window layer, and the light emitting region is limited to the periphery of the electrode on the chip, resulting in difficulty in obtaining a light emitting diode with high brightness.

Therefore, according to the present invention, a semiconductor multi-layered film reflecting mirror that does not generate arsine in the air is provided without reducing the reflection efficiency of the reflecting portion, and unnecessary etching of the AlGaAs window layer is performed when the GaAs contact layer is etched. It is an object of the present invention to provide a high-brightness LED which is safe and capable of emitting light on the entire surface of the chip by the two points of preventing the above.

[0010]

In order to achieve the above-mentioned object, the light emitting diode of the present invention does not use AlAs as a constituent semiconductor layer of a semiconductor multilayer film reflector, but uses Al _a Ga _1-a.
As (0.4 ≦ a <0.95) and Al _b Ga _1-b As
(0.95 ≦ b <1) is adopted. In addition, an AlGaInP layer is provided between the current diffusion layer and the GaAs contact layer to prevent etching of the AlGaAs window layer (hereinafter, referred to as
Function as an "etching stop layer"). FIG. 3 shows the structure of an LED according to the present invention. In the present invention, a GaAs substrate tilted in the range of 0 to 4 degrees from the (100) plane in the [011] direction is used. AlGaIn
This is because both P and AlGaAs are lattice-matched to the GaAs substrate, and those having good crystallinity can be easily obtained.

For the multilayer film reflecting mirror, 0.4 ≦ a <0.
A first Al _a Ga _1-a As semiconductor layer satisfying 95;
Second Al _b Ga _1-b As semiconductor layers satisfying 0.95 ≦ b <1 are alternately formed. As described above, in the semiconductor multilayer film reflecting mirror, the thicknesses of the two semiconductor layers having different refractive indexes are respectively d = λ / 4n (d: layer thickness of semiconductor layer, λ: emission wavelength of light emitting portion, n: semiconductor layer). It is configured by alternately stacking layers having a layer thickness calculated by (refractive index). In order to obtain a sufficient reflection characteristic, it is suitable that the lamination cycle is 15 to 25 times. The reason for setting a within the range of 0.4 ≦ a <0.95 is to have a composition that does not serve as an absorption layer of light having a target wavelength, and the reason for setting b to 0.95 ≦ b <1 is in the air. In the range that does not generate arsine, the first Al _a Ga _1-a
This is because the As semiconductor layer has a composition having a large difference in refractive index.

The contents of the experiment for confirming the presence or absence of arsine generation on the reflecting mirror are shown below. As a semiconductor layer of the reflecting mirror, AlA
and a reflecting mirror using Al _0.4 Ga _0.6 As (hereinafter referred to as “reflecting mirror A”), Al _0.95 Ga _0.05 As and Al _0.4
A reflecting mirror using Ga _0.6 As (hereinafter referred to as “reflecting mirror B”) was produced on a GaAs substrate by stacking 25 pairs. Then, as a result of measuring the arsine concentration at the position immediately above after adding the crushing water in the mortar so that the reflection mirror A and the reflection mirror B are in a situation similar to the dicing process of element processing, A limited amount of 0.05
Although the arsine concentration exceeding ppm was detected and the oxidation reaction of AlAs was confirmed, the detection of arsine was not confirmed from the reflecting mirror B. The measurement has a detection sensitivity of 0.001
A potentiostatic meter with ppm was used. Moreover, as a result of measuring the reflectance of the reflecting mirror B, it has a reflectance of 90% or more,
It was confirmed that it has comparable characteristics to the reflecting mirror A using AlAs. FIG. 4 shows the reflectance measurement result of the reflecting mirror B.

AlGaInP is adopted as the light emitting material,
It has a double hetero structure in which the active layer is sandwiched between upper and lower cladding layers. This is because it is easy to obtain high luminous efficiency at the emission wavelength of 580 to 650 nm. The mixed crystal ratio is (Al _X
Ga _1-X ) _Y In _1-Y P is 580,
The mixed crystal ratio of the active layer with respect to the emission wavelength of 650 nm is X = 0.4 or 0 and Y = 0.5, respectively, and the mixed crystal ratio of the cladding layer at this time is 0.7 ≦ X ≦ 1, Y = 0. 0.5 is suitable. The thickness of each layer is 0.8 μm or more for the clad layer and 0.1 to 1 μm for the active layer so that the effect of light confinement is sufficiently exerted.
It is desirable to set it in the range of m.

The carrier concentration of each layer is as follows. The n-type cladding layer is 1 × 10 ¹⁸ cm ⁻³ to 2 × 10 ¹⁸
cm ^-3 . The active layer is undoped. The p-type cladding layer has a thickness of 1 × 10 ¹⁷ cm ^{−3 to} 3 × 10 ¹⁷ cm ⁻³ . The carrier concentration of the clad layer is both of the fact that when the concentration is too high, the crystallinity is deteriorated due to lattice defects and the absorption coefficient increases with respect to the emission wavelength, and when the concentration is too low, the element resistance increases. Considering the above, it is optimal to set in the above range.

The composition of the AlGaAs window layer is a crystal composition having an energy gap larger than the energy gap of the active layer so that absorption at the emission wavelength of the active layer does not occur. More preferably, the energy gap difference is 0.
It is better to be able to obtain more than 05eV. Therefore, when the mixed crystal ratio of the active layer is X = 0.1 or 0.4 and Y = 0.5, Al
_In the notation _Z Ga _1-Z As, Z = 0.6 or 0.
It should be 95. When the thickness is 3 to 4 μm, a sufficient current spreading effect can be obtained.

The role of the etching stop layer formed of AlGaInP is that G formed by the etchant in the device forming process.
When etching the aAs contact layer, AlGaAs
It is to prevent the window layer from being removed. GaA
The s contact layer is an indispensable layer for obtaining a good ohmic electrode, but the energy gap is as small as 1.4 eV and it becomes an absorption layer for the emission wavelength. There is a need to. At this time, directly under the GaAs contact layer, AlGaA
If there is an s window layer, both of them are As-based substances, so that they are etched by the etchant. Therefore, the resistance to the etchant is sufficiently higher than that of the As-based layer P
A system layer is provided as an etching stop layer between the GaAs contact layer and the AlGaAs window layer, and etching is performed
Stop at the aAs contact layer. At this time, the composition has an energy gap larger than the energy gap of the active layer so that the etching stop layer does not become an absorption layer for the emission wavelength. Layer thickness is AlGaA
It suffices that it is effective for suppressing the etching of the s current diffusion layer, and 0.01 to 0.05 μm is appropriate.

The contents of the experiment for confirming the effect of using AlGaInP for the etching stop layer are shown below. n-type Ga
On the As substrate, p-type AlGaAs window layer 3 μm via n-type GaAs buffer layer 0.5 μm, p-type AlGaInP having the same composition as the p-type clad layer as an etching stop layer 0.05 μm, p-type GaAs contact layer 0. 3μ
a sample (hereinafter referred to as “Sample C”) in which m are sequentially stacked,
A sample (hereinafter referred to as “Sample D”) having a structure in which the p-type AlGaInP etching stop layer was removed from Sample C was prepared, and electrodes were formed on both samples. Went with a water etchant. As a result of observing the shape under the electrode after the etching treatment with an electron microscope, in sample D, AlG under the electrode was observed.
While most of the aAs window layer is etched,
In Sample C, no etching was observed in the AlGaAs window layer, and it was confirmed that etching was suppressed in the etching stop layer. FIG. 5 schematically shows the shape of each sample.

In this epitaxial wafer, the same material as the p-type clad layer was used as the material for the etching stop layer, but the Al composition may be reduced as long as it does not cause absorption at the emission wavelength. Furthermore, Ga _U In _1-U P having a composition that does not cause absorption at the emission wavelength
It is also possible to adopt (0.6 <U). When GaInP having a composition that does not cause absorption is used, lattice mismatch with the GaAs substrate occurs, but the layer thickness is 0.01 to 0.05 μm.
Since it is m, there is no problem in device characteristics. Rather, since the material does not contain Al, the effect of protecting the element from oxidation of Al can be obtained.

[0019]

According to the present invention, it is possible to ensure the safety of the operator during the processing of the element by producing a multilayer film reflecting mirror having a composition that does not generate arsine gas due to the oxidation reaction in the air, and also to secure AlGaInP. The layers are AlGaAs window layer and Ga
By providing between the As contact layers, the AlGaAs window layer can be protected during the etching process, and as a result, a high-brightness light emitting diode in which the entire surface of the chip serves as a light emitting region can be manufactured.

[0020]

EXAMPLES The present invention will be specifically described with reference to examples.
An epitaxial wafer having a structure as shown in FIG. 3 was produced. That is, Al _0.95 Ga _0.05 As is formed on an n-type GaAs substrate having a carrier concentration of 2 × 10 ¹⁸ cm ⁻³ via an n-type GaAs buffer layer (carrier concentration 1 × 10 ¹⁸ cm ⁻³ ).
490 Å and Al _0.4 Ga _{0.6 As} 420
An n-type semiconductor multilayer film reflecting mirror consisting of 25 pairs of angstroms (carrier concentration is 1 × 10 ¹⁸ cm ^{−3 in each case} ) was prepared as an n-type cladding layer (Al _0.7 Ga _0.3 ).
_0.5 In _0.5 P (carrier concentration 1 × 10 ¹⁸ cm ⁻³ ), undoped (Al _0.2 Ga _0.8 ) _0.5 In as an active layer
_0.5 P, as p-type cladding layer (Al _0.7 Ga _0.3 )
_0.5 In _0.5 P (carrier concentration 1 × 10 ¹⁷ cm ⁻³ ) is sequentially stacked to form a light emitting portion having a double hetero structure.
Type AlGaAs window layer (carrier concentration 7 × 10 ¹⁷ c
m ^-3 ), as a p-type AlGaInP etching stop layer (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P (carrier concentration 1 × 10 ¹⁷ cm ^-3 ), p-type GaAs contact layer (carrier concentration 2 × 10 ¹⁸ cm ^-3 ). Were laminated. Layer thickness is n-type G
aAs buffer layer 0.5 μm, n-type semiconductor multilayer film reflecting mirror 2.4 μm, n-type clad layer 1.0 μm, undoped active layer 0.5 μm, p-type clad layer 1.0 μm, p-type Al
The GaAs window layer is 4.0 μm, the p-type AlGaInP etching stop layer is 0.05 μm, and the p-type GaAs contact layer is 0.3 μm. In the light emitting diode manufactured from this wafer, the area of the light emitting region is 90% of the portion excluding the electrode part from the chip surface, which is increased compared to 20% of the light emitting diode manufactured from the wafer without the p-type AlGaInP etching stop layer. did. Along with this, a 10-fold increase in device brightness was obtained. Further, generation of arsine from the semiconductor multilayer film reflecting mirror portion was not found during the process of manufacturing the light emitting diode of the present invention.

[0021]

As described above, in the light emitting diode using the double hetero structure of AlGaInP-based material, not AlAs but Al as the constituent layer of the semiconductor multilayer film reflecting mirror.
_{By using b} Ga _1-b As (0.95 ≦ b <1), it is possible to prevent the generation of arsine accompanying the oxidation reaction during the element processing process, and to secure the safety of the operator. Also, AlG
By introducing an aInP etching stop layer, unnecessary etching to the AlGaAs window layer is prevented,
It becomes possible to fabricate a high-brightness light emitting diode having the entire surface of the chip as a light emitting region.

[Brief description of drawings]

FIG. 1 is a diagram showing a structural example of a high-brightness light emitting diode including a semiconductor multilayer film reflecting mirror.

FIG. 2 is a diagram showing a structural example of a high-brightness light emitting diode having an AlGaAs window layer.

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

FIG. 4 is a diagram showing reflectance characteristics of a reflecting mirror of an example.

FIG. 5 is a schematic diagram illustrating the effect of an AlGaInP etching stop layer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 electrode 2 p-type GaAs contact layer 3 p-type AlGaAs window layer 4 double hetero light emitting part 5 semiconductor multilayer film reflecting mirror 6 n-type GaAs buffer layer 7 n-type GaAs substrate 8 electrode 9 p-type cladding layer 10 active layer 11 n-type cladding Layer 12 p-type AlGaInP etching stop layer 13 n-type Al _0.4 Ga _0.6 As layer 14 n-type Al _0.95 Ga _0.05 As layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Hosokawa 1505 Shimokagemori, Chichibu, Saitama Prefecture, Chichibu Research Institute, Showa Denko KK (72) Shigemasa Nakamura 1505 Shimokagemori, Chichibu, Saitama Showaden Chichibu Research Institute Co., Ltd.

Claims (3)

[Claims] 1. A light emitting diode having a light emitting portion of a double hetero structure made of an AlGaInP-based material on a GaAs substrate, wherein an energy gap larger than the energy gap of the active layer is present on the double hetero structure portion A.
A light emitting diode comprising an lGaAs layer and an AlGaInP layer successively. 2. A light emitting diode having a double heterostructure light emitting part made of an AlGaInP-based material on a GaAs substrate, wherein 0.4 ≦ a <0.95 ≦ between the double heterostructure part and the substrate. First Al satisfying b <1
A light emitting diode comprising a semiconductor multi-layered reflective layer formed by alternately stacking _a Ga _1-a As semiconductor layer and a second Al _b Ga _1-b As semiconductor layer. 3. A 0 to 0 in the [011] direction from the (100) plane.
On an n-type GaAs substrate tilted in the range of 4 degrees, 0.4 ≦
First Al _a Ga _1-a A satisfying a <0.95 ≦ b <1
s semiconductor layers and second Al _b Ga _1-b As semiconductor layers are alternately laminated to form a semiconductor multilayer reflective layer, and the n-type clad layer has a crystal composition of (Al _x Ga _{1 -X} )
_{It is represented by Y} In _{1 -Y} P (0.7 ≦ X ≦ 1.0, Y = 0.5), and its carrier concentration is 1 × 10 ¹⁸ to 2 × 10 ¹⁸ cm.
^-3 , and the crystal composition of the active layer is (Al _x Ga
_1-X ) _Y In _1-Y P (0.1 ≦ X ≦ 0.4, Y = 0.
5) and the crystal composition of the p-type cladding layer is (Al _x G
a _1-X ) _Y In _1-Y P (0.7 ≦ X ≦ 1.0, Y = 0.
5) and the carrier concentration is 1 × 10 ^{17 to} 3 × 1.
Loading a double heterostructure within the range of 0 ¹⁷ cm ^-3 ,
In addition, AlGaAs having a crystal composition having an energy gap larger than that of the active layer
A light emitting diode comprising a layer and an AlGaInP layer stacked in this order.