JPH07176788A - Light emitting diode - Google Patents

Abstract

PURPOSE:To provide a light emitting diode that can be prepared by one cycle of epitaxial growth, wherein resistance will not be increased and a high quality DBR is obtained even if the DBR is formed between a GaAs substrate and a lower cladding layer, and wherein external projection efficiency will be improved by reducing luminescence under an electrode. CONSTITUTION:A DBR (Distributed Bragg Reflector) 2 is formed on a GaAs substrate 1, and a contact layer 10 of a first conductivity type, a lower cladding layer 3 of the first conductivity type, an undoped active layer 4, an upper cladding layer of a second conductivity type and a contact layer 5 of the second conductivity type, are formed on the DBR 2 in this order. The layers in the DBR 2 are undoped. Or, only several upper layers are of the first conductivity type. The layers above the contact layer 10 of the first conductivity type are formed in a way that the periphery of the contact layer 10 of the first conductivity type is exposed. An electrode 9 of the first conductivity type is formed on the exposed portion.

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 more particularly to a GaAs substrate on which a DBR is formed.
The present invention relates to a light emitting diode in which a light emitting layer is formed of a material whose substrate serves as an absorption substrate, has low resistance, high external emission efficiency, and can be manufactured by one epitaxial growth.

[0002]

2. Description of the Related Art In a light emitting diode having an emission wavelength such that the GaAs substrate serves as an absorption substrate, in order to obtain higher brightness light emission, the light traveling from the light emitting layer toward the GaAs substrate is somehow processed. It is effective to return it to the light emitting layer again.

Generally, in a light emitting diode using an AlGaInP-based material as a light emitting layer, the luminous efficiency decreases as the Al mixed crystal ratio increases. Therefore, as shown in FIG.
A DBR (Distributed Bragg Reglector) 32 is provided between the AlGaInP lower cladding layer 33 and the GaAs substrate 31 to increase the external emission efficiency. still,
In FIG. 7, 34 is an AlGaInP active layer, and 35 is
Is an AlGaInP upper cladding layer, 36 is an AlGaAs current diffusion layer, 37 is a GaAs contact layer, and 38 and 3
Reference numeral 9 represents an electrode.

When the distance from the light emitting layer to the surface layer from which light is emitted is smaller than that in the light emitting region, the light generated under the electrode is prevented from being emitted by the electrode. For this reason, as shown in FIG.
A current blocking layer 50 is formed on the portion above the aInP upper cladding layer 45.
Is provided to reduce the light emission under the electrode 49 and increase the external emission efficiency. In FIG. 8, 41 is a GaAs substrate, 42 is DBR, and 43 is AlG.
aInP lower clad layer, 44 is an AlGaInP active layer,
46 is a current diffusion layer, 47 is a GaAs contact layer, 48
And 49 denote electrodes.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the method of providing the above-mentioned DBR between the lower cladding layer and the GaAs substrate, the DBR is
It is advantageous to use a low refractive index material such as AlAs or AlInP. However, these materials have large bandgap energy and band discontinuity at the heterojunction portion with the GaAs substrate, resulting in a light emitting diode having a higher resistance than in the case where the DBR is not provided. In order to reduce the resistance, it is necessary to increase the impurity doping concentration of the DBR, but in that case, it is difficult to obtain a semiconductor layer with good crystallinity, and a high quality DBR cannot be obtained, so that the characteristics of the light emitting diode are reduced. It causes deterioration.

Further, in the method of providing the above-mentioned current blocking layer in the portion above the upper cladding layer which is below the electrode, it is necessary to stop the growth after growing the current blocking layer. Therefore, it is necessary to grow the semiconductor layer twice, and the device manufacturing process becomes complicated.

The present invention has been made to solve the above-mentioned conventional problems. Even if the DBR is provided between the GaAs substrate and the lower cladding layer, the resistance is not high and the DBR is of high quality.
It is an object of the present invention to provide a light emitting diode that can obtain R, can reduce the light emission under the electrode, can enhance the external emission efficiency, and can be manufactured by a single epitaxial growth.

[0008]

The light emitting diode of the present invention comprises a DBR (Distributed Bragg Reflective) on a GaAs substrate.
and a first conductive type contact layer, a first conductive type lower clad layer, an undoped active layer, a second conductive type upper clad layer, and a second conductive type contact layer are formed on the DBR. In the light-emitting diode laminated in this order, the DBR has a structure composed of a plurality of undoped layers, or only the upper few layers have the first conductivity type and the other layers have an undoped structure. , Each layer above the contact layer of the first conductivity type is formed by exposing a peripheral portion of the contact layer of the first conductivity type, and an electrode of the first conductivity type is formed on the exposed portion of the contact layer of the first conductivity type. Is formed,
Since the second conductivity type electrode is formed on the second conductivity type contact layer, the above object is achieved thereby.

In this light emitting diode, the band gap energy of the contact layer of the first conductivity type may be larger than the band gap energy of the active layer and smaller than the band gap energy of the lower cladding layer. Further, the impurity concentration of the first conductivity type contact layer may be higher than the impurity concentration of the lower cladding layer. Further, between the second conductive type upper clad layer and the second conductive type contact layer,
A second conductivity type current diffusion layer may be formed.

[0010]

In the present invention, each layer above the contact layer of the first conductivity type is formed by exposing the peripheral portion of the contact layer of the first conductivity type, and the electrode of the first conductivity type is formed on the exposed portion. Are formed. Therefore, no current flows in the heterojunction between the GaAs substrate and the DBR, and the resistance does not increase even if the DBR is provided. Further, since the ratio of the current flowing obliquely downward (the peripheral portion of the chip) from the second conductivity type electrode increases, the ratio of light emission under the electrode can be reduced. Therefore, it is not necessary to provide a current blocking layer, and it can be manufactured by a single epitaxial growth.

Further, since each layer of the DBR is undoped or only some of the upper layers are of the first conductivity type, the crystallinity of each layer of the DBR can be easily improved and a high quality DBR can be obtained. You can

The band gap energy of the first conductivity type contact layer may be larger than the band gap energy of the active layer and smaller than the band gap energy of the lower cladding layer. Alternatively, the impurity concentration of the first conductivity type contact layer may be higher than the impurity concentration of the lower cladding layer. By doing so, good ohmic contact is easily made without light being absorbed by the contact layer.

A second conductivity type current diffusion layer may be formed between the second conductivity type upper clad layer and the second conductivity type contact layer. By doing so, it is possible to reduce light that is blocked by the electrodes and cannot be extracted to the outside.

[0014]

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

(Embodiment 1) FIG. 1 is a sectional view showing a light emitting diode of Embodiment 1, and FIG. 2 is a sectional view for explaining a manufacturing process thereof. This light emitting diode is
A GaInP-based material is used as the light emitting layer.

As shown in FIG. 1, on a GaAs substrate 1,
AlAs / Al _0.7 Ga _0.3 As with each layer undoped
20 pairs are laminated to form DBR2. An n-type (Al _0.45 Ga _0.55 ) _0.5 In _0.5 P contact layer 10 having a thickness of 1 μm and an n-type (Al _0.6 Ga _0.4 ) having a thickness of 1 μm are formed on the contact layer 10.
_0.5 In _0.5 P lower clad layer 3, 0.6 μm thick undoped (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P active layer 4, thickness 2
A p-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P upper cladding layer 5 having a thickness of 7 μm, a p-type Al _0.7 Ga _0.3 As current diffusion layer 6 having a thickness of 7 μm, and a p-type GaAs contact layer 7 having a thickness of 1 μm are laminated. The peripheral portion of each layer above the n-type contact layer 10 is removed to expose the n-type contact layer 10. Ni / on the exposed portion of the n-type contact layer 10.
An n-type electrode 9 made of AuGe / Au is formed, and p made of Au / AuZn / Au is formed on the p-type contact layer 7.
The mold electrode 8 is formed.

This light emitting diode can be manufactured in a single growth step as follows.

First, as shown in FIG. 2, a GaAs substrate 1
AlAs / Al _0.7 Ga with each layer undoped
DBR2 is formed by stacking 20 pairs of _0.3 As, on which n-type contact layer 10, n-type lower clad layer 3, undoped active layer 4, p-type upper clad layer 5, p-type current diffusion layer 6 and p-type are formed. The contact layer 7 is sequentially laminated. In this example, each layer was formed by MOCVD (metal organic chemical vapor deposition).

Thereafter, by photolithography, chemical etching with a sulfuric acid-based etchant and hot phosphoric acid, etc., the peripheral portion of each layer above the n-type contact layer 10 (the portion indicated by the hatched portion 60 in FIG. 2) is removed, The n-type contact layer 10 is exposed. The n-type electrode 9 is formed on the exposed portion of the n-type contact layer 10, and the p-type electrode 8 is formed on the remaining portion of the p-type contact layer 7.

In the light emitting diode of this embodiment thus obtained, no current flows through the heterojunction between the GaAs substrate 1 and the DBR 2, so that the light emitting diode with the conventional DBR (shown in FIG. 7) is used. ) Was able to be low resistance compared with. Since each layer of DBR2 is undoped, a high quality DBR can be obtained, and p-type electrode 8
Since the ratio of the current flowing in the obliquely downward direction is increased, the external emission efficiency can be increased to about 1.5 to 2 times that of the conventional light emitting diode.

(Embodiment 2) FIG. 3 is a sectional view showing a light emitting diode of Embodiment 2, and FIG. 4 is a sectional view for explaining the manufacturing process thereof. This light emitting diode is
A GaInP-based material is used as the light emitting layer.

As shown in FIG. 3, AlAs / Al _0.7 Ga _0.3 with each layer undoped on the GaAs substrate 11.
20 pairs of As are stacked to form the DBR 12. On top of that, p-type (Al _0.45 Ga _0.55 ) _0.5 In _0.5 with a thickness of 2 μm
P contact layer 20, 2 μm thick p-type (Al _0.6 Ga
_0.4 ) _0.5 In _0.5 P Lower cladding layer 13, thickness 0.6 μm
Undoped (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P active layer 1
4, n-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P with a thickness of 7 μm
An upper clad layer 15 and an n-type GaAs contact layer 17 having a thickness of 1 μm are laminated. The peripheral portion of each layer above the p-type contact layer 20 is removed, and the p-type contact layer 20 is exposed. On the exposed part of the p-type contact layer 20, a p-type electrode 19 made of Au / AuZn / Au is formed.
Are formed, and Ni / Au is formed on the n-type contact layer 17.
An n-type electrode 18 made of Ge / Au is formed.

This light emitting diode can be manufactured in one growth step as follows.

First, as shown in FIG. 4, a GaAs substrate 1
1 on top of which AlAs / Al _0.7 G with each layer undoped
20 pairs of a _0.3 As are laminated to form the DBR 12, on which the p-type contact layer 20, the p-type lower clad layer 13, the undoped active layer 14, the n-type upper clad layer 15 and the n-type contact layer 17 are sequentially laminated. Form. In this example, each layer was formed by MOCVD.

Thereafter, by photolithography, chemical etching with sulfuric acid-based etchant and hot phosphoric acid, and the like, peripheral portions of each layer above the p-type contact layer 20 (portions indicated by hatched portions 70 in FIG. 4) are removed, The p-type contact layer 20 is exposed. A p-type electrode 19 is formed on the exposed portion of the p-type contact layer 20, and the n-type contact layer 17 is formed.
An n-type electrode 18 is formed on the remaining portion of the.

[0026] In the light emitting diode of the present embodiment thus obtained is, n-type _{(Al 0. 6 Ga 0.4) 0.5} In
The resistivity of the _0.5 P upper cladding layer 15 is p-type (Al _0.6 Ga).
_0.4) about 1/40 of _{0. 5} In _0.5 P lower cladding layer 13, about the same as the p-type Al _0.7 Ga _0.3 As layer. Therefore, by making the n-type upper cladding layer 15 as thick as 7 μm, it can function as a current diffusion layer.

Further, since no current flows through the heterojunction between the GaAs substrate 11 and the DBR 12, the resistance can be made lower than that of the conventional light emitting diode having the DBR (shown in FIG. 7). Since each layer of the DBR 12 is undoped, a high-quality DBR can be obtained, and since the proportion of the current flowing diagonally downward from the n-type electrode 18 is large, it is about 2 to 2.5 times that of the conventional light emitting diode. The external emission efficiency could be increased.

Example 3 FIG. 5 is a sectional view showing a light emitting diode of Example 3, and FIG. 6 is a sectional view for explaining the manufacturing process thereof. This light emitting diode is
The GaAs material is used as the light emitting layer.

As shown in FIG. 5, AlAs / Al _0.5 Ga _0.5 with each layer undoped on the GaAs substrate 21.
20 pairs of As are stacked to form a DBR 22. Moreover n-type Al _0.5 Ga _0.5 As contact layer 30 having a thickness of 1 [mu] m, the thickness 1 [mu] m n-type Al _{0. 7} Ga _0.3 As lower cladding layer 23, the thickness 0.6μm undoped (Al _0.35 Ga _0.
65 As active layer 24, 7 μm thick p-type Al _0.7 Ga _0.3 A
An upper cladding layer 25 and a p-type GaAs contact layer 27 having a thickness of 1 μm are laminated. The peripheral portion of each layer above the n-type contact layer 30 is removed to expose the n-type contact layer 30. An n-type electrode 2 made of Ni / AuGe / Au is formed on the exposed portion of the n-type contact layer 30.
9 is formed, and Au / A is formed on the p-type contact layer 27.
A p-type electrode 28 made of uZn / Au is formed.

This light emitting diode can be manufactured in one growth step as follows.

First, as shown in FIG. 6, the GaAs substrate 2
1 on top of which AlAs / Al _0.5 G with each layer undoped
20 pairs of a _0.5 As are laminated to form the DBR 22, and the n-type contact layer 30, the n-type lower clad layer 23, the undoped active layer 24, the p-type upper clad layer 25 and the p-type contact layer 27 are sequentially laminated thereon. Form. In this example, each layer was formed by MOCVD.

Thereafter, by photolithography, chemical etching with a sulfuric acid-based etchant and hot phosphoric acid, etc., the peripheral portion of each layer above the n-type contact layer 30 (the portion indicated by the shaded portion 80 in FIG. 6) is removed, The n-type contact layer 30 is exposed. An n-type electrode 29 is formed on the exposed portion of the n-type contact layer 30, and the p-type contact layer 27 is formed.
A p-type electrode 28 is formed on the remaining portion of the.

In the light emitting diode of this embodiment thus obtained, the p-type Al _0.7 Ga _0.3 As upper cladding layer 25 can be made to function as a current diffusion layer by forming a thick film of 7 μm.

Further, since no current flows through the heterojunction between the GaAs substrate 21 and the DBR 22, the resistance can be made lower than that of the conventional light emitting diode having a DBR (shown in FIG. 7). Since each layer of the DBR 22 is undoped, a high-quality DBR can be obtained, and since the proportion of the current flowing obliquely downward from the p-type electrode 28 is large, it is about 1.5 to 2 times that of the conventional light emitting diode. The external emission efficiency could be increased.

In the above embodiment, DBRs 2, 12,
Although each layer of 22 is undoped, only the upper few layers may be of the first conductivity type.

The contact layers 10 and 2 of the first conductivity type are also provided.
The band gap energies of 0 and 30 are set to the active layers 4 and 1,
Although the band gap energy of the first and second clad layers 4 and 24 is smaller than that of the lower cladding layers 3, 13, and 23, the contact layer 1 of the first conductivity type
The impurity concentration 20 of 0, 20, 30 is set to the lower cladding layer 3, 1,
It may be higher than the impurity concentrations of 3 and 23.

As the material of the light emitting layer, any material can be used as long as it is a material that uses a GaAs substrate as an absorption substrate, and the mixed crystal ratio of the growth layer can be appropriately selected.

As the growth method, in addition to the MOCVD method, LPE is used.
A growth method such as a (liquid phase growth) method or an MBE (molecular beam growth) method may be used.

[0039]

As is apparent from the above description, according to the present invention, a high quality DBR is used in a light emitting diode having a light emitting layer made of a material having a GaAs substrate as an absorption substrate.
Can be obtained, and low resistance can be achieved even if the DBR is provided. Further, it is possible to reduce the light emission under the electrode to increase the external emission efficiency, and further, it is possible to easily manufacture the film in one growth step.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a light emitting diode of Example 1.

FIG. 2 is a cross-sectional view showing a manufacturing process of the light emitting diode of Example 1.

FIG. 3 is a cross-sectional view showing a light emitting diode of Example 2.

FIG. 4 is a cross-sectional view showing the manufacturing process of the light-emitting diode of Example 2.

5 is a sectional view showing a light emitting diode of Example 3. FIG.

FIG. 6 is a cross-sectional view showing the manufacturing process of the light-emitting diode of Example 3.

FIG. 7 is a cross-sectional view showing a conventional light emitting diode.

FIG. 8 is a cross-sectional view showing a conventional light emitting diode.

[Explanation of symbols]

1, 11, 21, 31, 41 GaAs substrate 2, 12, 22, 32, 42 DBR 3, 13, 23, 33, 43 First conductivity type lower cladding layer 4, 14, 24, 34, 44 Undoped active layer 5, 15, 25, 35, 45 Second conductive type upper clad layer 6, 36, 46 Current spreading layer 7, 17, 27, 37, 47 Second conductive type contact layer 8, 18, 28, 38, 48 Second conductivity type electrode 9, 19, 29, 39, 49 First conductivity type electrode 50 Current blocking layer 60, 70, 80 Removed portion 10, 20, 30 First conductivity type contact layer

Claims (4)

[Claims] 1. A DBR (Distributed) on a GaAs substrate.
Bragg Reflector) is formed, and the first
In a light emitting diode in which a conductivity type contact layer, a first conductivity type lower clad layer, an undoped active layer, a second conductivity type upper clad layer, and a second conductivity type contact layer are stacked in this order, the DBR is , A structure composed of a plurality of undoped layers, or a structure in which only the upper few layers are of the first conductivity type and the other layers are undoped, and each layer above the contact layer of the first conductivity type is A first conductive type electrode is formed on the exposed part of the first conductive type contact layer, and a second conductive type contact is formed on the exposed part of the first conductive type contact layer. A light emitting diode in which an electrode of the second conductivity type is formed on the layer. 2. The light emitting diode according to claim 1, wherein a bandgap energy of the first conductivity type contact layer is larger than a bandgap energy of the active layer and smaller than a bandgap energy of the lower cladding layer. . 3. The light emitting diode according to claim 1, wherein the impurity concentration of the first conductivity type contact layer is higher than the impurity concentration of the lower cladding layer. 4. The light emitting diode according to claim 1, wherein a second conductivity type current spreading layer is formed between the second conductivity type upper clad layer and the second conductivity type contact layer.