JPH10233528A - Semiconductor light emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively improve the average reflectance of a multilayered light reflecting layer in accordance with an increase in number of pairs without saturating the average reflectance even when the number of pairs is increased by forming the multilayered light reflecting layer of a semiconductor material having a band gap which is larger than that of an active layer. SOLUTION: After a multilayered light reflecting film 12 is formed upon a semiconductor substrate 11, an actively layer 14 is formed on the film 12 with a lower clad layer 13 in between. At the formation of the film 12, a semiconductor material having a band gap which is lager than that of the active layer 14 is used. Then an upper clad layer 15 and a p-type GaP current diffusing layer 16 are successively formed on the active layer 14 and a p-type electrode 17 is formed by vapor-depositing and patterning an Au-Zu film on the layer 16. On the other hand, an n-type electrode 18 composed of another Au-Zn film is formed on the lower surface of the substrate 11 by vapor-depositing the Au-Zn film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor light emitting diode, and more particularly, to a light emitting diode having a light reflecting multilayer film for enhancing the efficiency of extracting light to the outside.

[0002]

2. Description of the Related Art An AlGaInP-based material has the largest direct transition band gap among III-V compound semiconductor materials excluding nitrides, and is used as a light emitting device material having a wavelength of 0.5 to 0.6 μm. Attention has been paid. In particular, a pn-junction light-emitting diode (hereinafter simply referred to as an LED) formed by growing a light-emitting portion (laminated structure including an active layer) of an AlGaInP-based material lattice-matched to GaAs as a substrate is formed on the GaAs substrate. ) Means conventional GaP or AlG
Compared to those using indirect transition type materials such as aAs,
Higher luminance light emission is possible in a wavelength range corresponding to red to green.

Further, in order to form a high-brightness LED, in addition to increasing the luminous efficiency, it is necessary to improve the efficiency of current injection into the light-emitting portion and to efficiently extract light to the outside of the device. is important.

FIG. 16A is a sectional view of a conventional LED 100 having a light emitting portion using an AlGaInP-based material, and FIG. 16B is an enlarged view of a portion A in FIG.
In the LED 100, an n-type GaAs buffer layer 102 is formed on an n-type GaAs substrate 101, and an n-type AlInP layer 103a and an n-type GaInP layer 1 are formed thereon.
03b as one pair, and a large number of pairs (for example, 1
A light reflecting multilayer film (distributed Bragg reflector: hereinafter, referred to as DBR) 103 is formed by laminating 0 pairs).

Here, the n-type AlInP layers 103a and n
The thickness of each of the GaInP layers 103b is, for example, λ / 4 with respect to the emission wavelength λ, assuming that the refractive indices are n ₁ and n ₂ , respectively.
n ₁ , λ / 4n ₂ .

Further, on top of this, n-type AlGaIn
P cladding layer 104, AlGaInP active layer 105, p
An AlGaInP cladding layer 106 and a p-type GaP current diffusion layer 107 are sequentially stacked. Furthermore, p-type Ga
A p-type electrode 108 is formed on the P current diffusion layer 107, and an n-type electrode 109 is formed on the lower surface of the n-type GaAs substrate 101.
Are formed, whereby the LED 100 is configured.

In an LED having no optical semiconductor multilayer film, of the light emitted from the active layer, light traveling downward (toward the GaAs 101 substrate) is absorbed by the GaAs substrate and cannot be extracted to the outside. The above LED10
0, the light reflecting multilayer film 103 is provided, so that light traveling downward from the active layer 105
The light is reflected upward and emitted upward, so that the light extraction efficiency can be improved.

Although the structure is more complicated than that of the embodiment shown in FIG. 16, in order to widen the reflection wavelength range of the light reflecting multilayer film, for example, Japanese Patent Laid-Open No. 5-37017 discloses the following LE.
D has been proposed. FIG. 17A is a cross-sectional view showing the configuration of an LED 200 disclosed in the above-mentioned publication, and FIG.
FIG. 17B is an enlarged view of a portion B in FIG.

In the LED 200, the n-type GaAs substrate 20
1, n-type AlAs 202a and n-type GaAs 20
2b as one pair, and a large number of pairs (for example, 10
A pair of stacked DBRs 202 is formed. Further thereon, a lower cladding layer 203, an active layer 204,
The upper cladding layer 205 forms a double hetero structure. Then, a cap layer 20 is further formed thereon.
6. The p-type electrode 207 is formed, and the n-type GaAs substrate 20 is formed.
An n-type electrode 208 is formed on the lower surface of the LED 1, thereby forming the LED 200.

In this LED 200, as shown in FIG. 18, the layer structure of the DBR 202 is such that the film thickness is gradually increased in a chirped manner by the ratio of DD to the long wavelength and the short wavelength with respect to the film thickness T corresponding to the central reflection wavelength. The configuration has been changed.

[0011]

[0006] By the way, FIG.
In each of the embodiments shown in FIG. 17, there are the following problems. First, the embodiment shown in FIG. 16 will be described. The relationship between the number of DBR pairs and the average reflection intensity in the embodiment of FIG. 16 is as shown in FIG. here,
The wavelength was 0.59 μm. The average reflection intensity on the vertical axis indicates the average intensity of how much light is reflected from the reflection surface toward each direction.

As is apparent from FIG. 19, the average reflection intensity increases as the number of pairs increases, but tends to saturate on the way. With 20 pairs or more, the average reflection intensity hardly improves from around 0.47.

FIG. 20 and FIG. 21 show the wavelength dependence of the reflectance in the embodiment shown in FIG. FIGS. 20 and 21 show the characteristics when the central reflection wavelength is set to 0.9 μm and 0.6 μm, respectively.
2 indicates the characteristic of the DBR of a single cycle, and Q1 and Q2 indicate the characteristic of the DBR changed in a chirp shape. The reflectance on the vertical axis in FIGS. 20 and 21 indicates the reflectance in the vertical direction from the reflection surface.

In FIG. 20, a single-period, chirped DBR has high reflectivity, and the chirped shape allows the reflection wavelength region to be widened on both the long wavelength side and the short wavelength side. . However, in FIG.
Even in BR, the reflection intensity is weak, and further, even in the case of a chirp, the wavelength region cannot be extended to the longer wavelength side. That is, the characteristics may be extremely deteriorated depending on the wavelength.

The inventor of the present invention has examined the problems of both structures. As a result, it was found that the layer constituting the DBR absorbs the light from the light emitting layer, which is a common feature of both structures. Found that it is caused by having points.

That is, in the embodiment shown in FIG.
Since the GaInP 103b has a characteristic of absorbing light in the reflection wavelength region, the D
It is considered that the reason is that the reflection of the portion of the BR remote from the light emitting layer hardly contributes to the reflection intensity. Also in the embodiment of FIG. 17, n-type GaAs constituting the DBR 202 is used.
Since the layer 202b has the property of absorbing light, the reflectance is low even in a single cycle, as in the embodiment of FIG. 16, and further, in the chirped DBR, the lower the layer, the longer the distance from the light emitting layer. It is considered that the reflection intensity in the long-wavelength region is low due to the design of reflecting light of the wavelength.

[0017] The above-mentioned problems are caused by other materials LED,
For example, wavelengths 0.7 to
AlGaAs known as a 1.0 μm band light emitting element material
It has been confirmed that it is also found in s-based and AlGaInAs-based LEDs.

In view of the above, an object of the present invention is to provide a D
Even if the number of pairs is increased by preventing the BR from absorbing the light of the light emitting layer, the average reflectance does not saturate, and the average reflectance can be effectively improved in accordance with the increase in the number of pairs. The object of the present invention is to provide a semiconductor light emitting diode that can improve the reflection intensity at the center wavelength while securing a wide reflection wavelength region.

[0019]

According to the present invention, there is provided a semiconductor device comprising: an active layer on a semiconductor substrate; and an active layer disposed between the semiconductor substrate and the active layer in a direction from the active layer to the semiconductor substrate. And a light-reflecting multilayer film that reflects light traveling toward the light-emitting device, wherein the light-reflecting multilayer film is formed of a semiconductor material having a band gap larger than the band gap of the active layer. I do.

As described above, since the material of the light reflecting multilayer film is a semiconductor material having a band gap larger than the band gap of the active layer, light emitted from the active layer as in the conventional structure is generated in the middle of the light reflecting multilayer film. , And even a multilayer film at a position distant from the active layer can contribute to reflection, so that light extraction efficiency can be improved.

Here, the light reflecting multilayer film is characterized in that two kinds of materials having mutually different refractive indexes are alternately laminated.

Further, the light reflecting multilayer film is composed of a pair of two kinds of films having different refractive indices, and a plurality of the pairs are alternately laminated, and the plurality of the pairs reflect the emission wavelength from the active layer. It is characterized by being continuously changed at a fixed ratio from a layer thickness smaller than a layer thickness to be reflected to a larger layer thickness.

The semiconductor substrate comprises a GaAs substrate,
The active layer is made of an AlGaInP-based material, and the light reflection multilayer film is formed by alternately stacking an AlInP-based material and an AlGaInP-based material. here,
The light reflection multilayer film includes a film made of an AlInP-based material and A
It is characterized in that at least 20 pairs or more are laminated with a pair of films made of lGaInP-based material.

Further, the semiconductor substrate is made of a GaAs substrate, and the active layer is made of an AlGaAs-based material.

Further, the semiconductor substrate is made of a GaAs substrate, and the active layer is made of an AlGaInAs-based material.

Here, the light reflection multilayer film is characterized in that at least five pairs or more are laminated.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.
Description will be made with reference to (a) and (b). FIG. 1A shows a semiconductor light emitting diode (LED, hereinafter referred to as LE) according to this embodiment.
D), and FIG. 1B is an enlarged view of a portion C in FIG. 1A.

In the LED 1 of the present embodiment, as shown in FIG. 1A, a light reflection multilayer film (hereinafter, referred to as DBR) 12 is formed on an n-type GaAs substrate 11. Here, FIG. As a material of a film constituting the DBR 12, a material having small light absorption with respect to light emission from the active layer 14 described later is used.

The reason for using such a material is based on the following inventor's consideration of the problems of the conventional structure. That is, in the conventional structure, when the number of pairs constituting the DBR is increased, the average reflectance is saturated with a certain number of pairs or more, and further improvement in the reflectance cannot be expected. This is because the layer constituting the DBR having the structure has a property of absorbing light in the reflection wavelength region, and therefore, reflection of a portion of the DBR that is particularly distant from the light-emitting layer hardly contributes to the reflection intensity. it is conceivable that. Therefore, a feature of the present structure is that a pair of portions away from the light emitting layer is configured to contribute to the reflection intensity.

More specifically, as shown in FIG.
l _0.51 In _0.49 P layer 12a and n-type (Al _x Ga _{1 -x} ) _0.51
A light-reflective multilayer film (hereinafter, referred to as DBR) 12 composed of a large number of pairs (here, 40 pairs) is formed by stacking an In _0.49 P (0 ≦ X ≦ 1) layer 12b as one pair.

Here, the n-type Al _0.5 1In _0.49 P layer 12
a and n-type (Al _x Ga _{1 -x} ) _0.51 In _0.49 P (0 ≦ X ≦
1) The thicknesses d ₁ and d ₂ of each layer of the layer 12b are determined by, for example, the following formula, where the respective refractive indices are n ₁ and n ₂ and the emission wavelength from the active layer is λ.

D ₁ = λ / 4n ₁ formula (1) d ₂ = λ / 4n ₂ formula (2) Then, an n-type (Al _x Ga ₁ -x) _0.51 is placed on the DBR 12.
In _0.49 P (0 ≦ X ≦ 1) Lower cladding layer 13 (for example, X = 1.0, thickness 1.0 μm), (Al _X Ga _1-x ) _0.51
In _0.49 P (0 ≦ X ≦ 1) active layer 14 (for example, X = 0.
3, thickness 0.5 μm), p-type (Al _X Ga _{1 -x} ) _0.51 In
_0.49 P (0 ≦ X ≦ 1) upper cladding layer 15 (for example, X =
1.0 and a thickness of 1.0 μm), and a p-type (Al _x Ga _{1 -x} ) _0.51 In _0.49 P (0 ≦ X ≦ 1) upper cladding layer 15 is further stacked on the upper cladding layer 15. A diffusion layer 16 is formed.

Next, for example, an Au—Zn film is deposited on the p-type GaP current diffusion layer 16 and is patterned into, for example, a circle to form a p-type electrode 17. On the other hand, GaAs
On the lower surface of the substrate 11, an n-type electrode 18 made of, for example, an Au—Zn film is formed by vapor deposition. As described above, the LED 1 of this embodiment is completed.

In the above embodiment, a DBR 12 having a small light absorption coefficient with respect to light emission from the active layer 14 is used. Therefore, as the number of pairs constituting the DBR 12 increases, the average reflectance increases and a desired value is obtained. Average reflectance can be obtained. Regarding this point, the relationship between the number of DBR pairs and the average reflectance according to the present embodiment will be described with reference to the characteristic diagram of FIG.

Compared with the characteristic diagram of FIG. 19 showing the characteristics of the conventional structure of FIG. 16, in FIG. 19, the average reflectance was less than 0.5 even when the number of pairs was 40, but in this embodiment, According to FIG. 2, it can be seen that the average reflectance of the 40 pairs reaches a little over 0.7, as is clear from FIG. Comparing the light emission luminance, it was confirmed that the present example had about 1.3 times the luminance of the conventional structure of FIG.

When the number of pairs is less than 20, the average reflectance is higher in the conventional example, and it can be seen that the structure of the present embodiment is particularly effective for 20 or more pairs. However, as higher brightness is demanded in the future, the present structure, which can achieve an average reflectance which cannot be obtained conventionally by increasing the number of pairs, is extremely useful.

FIG. 3A is a sectional view of an LED according to another embodiment of the present invention, and FIG. 3B is an enlarged view of a portion D in FIG. 3A.

In the LED 2 of this embodiment, as shown in FIG. 3A, a light reflection multilayer film (hereinafter referred to as DBR) 22 is formed on an n-type GaAs substrate 21. Here, As a material of a film constituting the DBR 22, a material having small light absorption with respect to light emission from the active layer 24 described later is used.

More specifically, as shown in FIG.
l _0.51 In _0.49 P layer 22a and n-type (Al _x Ga _{1 -x} ) _0.51
In _0.49 P (0 ≦ _X ≦ 1) layer 22b (for example, _X = 0.3
5) as one pair, and a plurality of DBRs 22 (here, 40 pairs) are stacked. The DBR 22 in this embodiment is a chirped DBR whose layer thickness gradually changes from the lower layer to the upper layer. The DBR 22 has an n-type Al _0.51 In _0.49 P layer 22a and an n-type (Al _X G
a _1−X ) _0.51 In _0.49 The thickness of the P (0 ≦ _X ≦ 1) layer 22b is as follows, assuming that the respective refractive indices are n ₁ and n ₂ and the emission wavelength from the active layer 24 is λ. Designed to.

That is, as shown in FIG. 4, n-type Al _0.51 I
Regarding the n _0.49 P layer 22a, the layer thicknesses of the lowermost layer and the uppermost layer are (λ / 4n ₁ ) × (1 + DD ₁ ) and (λ / 4n
₁ ) × (1-DD ₂ ), and similarly, an n-type (Al _X G
a _1−X ) _0.51 In _0.49 The layer thickness of the lowermost layer and the uppermost layer of the P (0 ≦ _X ≦ 1) layer 22 b is (λ / 4n ₂ ) × (1 + D
D ₁ ), (λ / 4n ₂ ) × (1−DD ₂ ), and the layer thickness is determined so that the layers between the lowermost layer and the uppermost layer are equally spaced.

Then, an n-type (Al _x
Ga _1-x ) _0.51 In _0.49 P (0 ≦ _X ≦ 1) Lower cladding layer 23 (for example, X = 1.0, thickness 1.0 μm), n-type (A
l _x Ga _1-x ) _0.51 In _0.49 P (0 ≦ _X ≦ 1) active layer 24
(For example, X = 0.3, thickness 0.5 μm), p-type (Al _X
Ga _1−X ) _0.51 In _0.49 P (0 ≦ _X ≦ 1) Upper cladding layer 25 (for example, X = 1.3, thickness 1.0 μm) is sequentially laminated, and further thereon a p-type GaP current diffusion layer 26 is formed. To form

Next, on the p-type current diffusion layer 26, for example, A
A p-type electrode 27 is formed by depositing a u-Zn film and patterning it into a circular shape, for example. On the other hand, the GaAs substrate 2
1, an n-type electrode 2 made of, for example, an Au—Zn film
8 is formed by vapor deposition. Thus, the LED 2 is completed.

FIG. 5 is a diagram showing the reflection spectrum of the DBR 22 in the LED 2 (the characteristics of the present embodiment are indicated by R in the drawing). FIG. 5 shows, for comparison, the reflection spectrum of a DBR fabricated using Ga _0.51 In _0.49 P and Al _0.51 In _0.49 P as the material constituting the DBR and having the same layer thickness as LED2. In the figure, indicated by S).

As can be seen from FIG. 5, the characteristic of S has a lower reflection intensity on the long wavelength side than the characteristic of Example R. This is because Ga _0.51
Since In _0.49 P has an absorption characteristic with respect to light from the active layer, light does not reach the lower DBR layer,
As a result, the lower DBR layer cannot contribute to the reflection characteristics. In the layer thickness configuration as shown in the LED 2, the lower the DBR, the longer wavelength light is reflected. Therefore, the reflection intensity of the DBR with the characteristic E is lower on the longer wavelength side.

On the other hand, the DBR 22 of the LED 2 is
Since a material that does not absorb the light from the active layer 24 is used for the material, the lower DBR layer can also contribute to the reflection intensity, and a high reflection intensity can be secured even on the long wavelength side.
Good reflection characteristics as shown in FIG. 5 are obtained.

As described above, even when a chirped DBR is formed, the reflection wavelength region of the DBR can be broadened by using a material having a small light absorption for light from the active layer as a material for forming the DBR. Thereby, the LED 2 of the present embodiment is about 1.1 compared to the LED 200 of the conventional structure.
Double emission luminance can be obtained.

In this embodiment, the DBR has a layer thickness structure which becomes thinner toward the upper layer, but the DBR which has a layer thickness structure which becomes thicker toward the upper layer also has a relation between the long wavelength and the short wavelength. Is reversed, there is an effect of similarly widening the reflection wavelength region, and substantially the same improvement in light emission luminance is possible.

Also, in this embodiment, as in the embodiment of FIG. 1, when the total number of the DBRs is 20 or more, a remarkable reflection intensity not obtained in the conventional structure can be obtained.

FIG. 6A is a sectional view of an LED according to still another embodiment of the present invention, and FIG. 6B is an enlarged view of a portion E in FIG. 6A. In this embodiment, the present invention is applied to an LED made of an AlGaAs-based material.

As shown in FIG. 6, the LED 3 is an n-type GaAs
On the s substrate 31, an n-type AlAs 32a and an n-type Al _x G
a _1-x As (0 ≦ x ≦ 1) 32b (for example, x = 0.1)
Are stacked, and a light reflection multilayer (DBR) 32 composed of a large number of pairs (for example, 20 pairs) is laminated.

Here, n-type AlAs 32a and n-type AlG
The thicknesses d ₁ and d ₂ of aAs (0 ≦ x ≦ 1) 32b are designed based on, for example, the following equation, where n ₁ and n ₂ are the refractive indexes and λ is the emission wavelength from the active layer. .

D ₁ = λ / 4n ₁ (1) d ₂ = λ / 4n ₂ (2) Then, n-type Al _x Ga _{1 -x} As (0
≦ x ≦ 1) Lower cladding layer 33 (for example, x = 0.7, thickness 1.0 μm), Al _x Ga _1-x As (0 ≦ x ≦ 1) active layer 34 (for example, x = 0, thickness 0) .5 μm), p-type Al _x
A Ga _1-x As (0 ≦ x ≦ 1) upper cladding layer 35 (for example, x = 0.7, thickness 1.0 μm) is sequentially laminated, and a p-type GaAs contact layer 36 is further formed thereon.

Next, for example, an Au—Be film is deposited on the p-type GaAs contact layer 36, and this is patterned into, for example, a circle to form a p-type electrode 37. On the other hand, Ga
On the lower surface of the As substrate 31, an n-type electrode 38 made of, for example, an Au—Zn film is formed by vapor deposition to complete the LED1.

FIG. 7 is a view showing the number of pairs of the average reflection intensity of the DBR 32 according to the present embodiment. In a conventional LED using a material having a large light absorption dependence on light emission from an active layer as a material of a layer constituting a DBR, as the number of pairs of DBRs increases, the average reflection intensity increases but tends to saturate. There is. On the other hand, in this embodiment, since the material constituting the DBR has a small light absorption coefficient with respect to the emission from the active layer, the average reflection intensity can be increased as the number of pairs is increased, and the reflection is reduced. The rate can approach 100%. According to the present embodiment, L
Emission luminance approximately 1.3 times as high as that of the ED was obtained.

FIG. 8A is a sectional view of an LED according to still another embodiment of the present invention, and FIG. 8B is an enlarged view of a portion F in FIG. 8A. As shown in FIG. 8, the LED 4 of this embodiment
On the n-type GaAs substrate 41, an n-type AlAs layer 42a and an n-type In _x Ga _1-x As layer (0 ≦ x ≦ 1) 42b (for example, x = 0.0) are paired in a large number (for example, 20 pairs). )
Is laminated.
n-type AlAs layer 42a and the n-type In _x Ga _1-x As layer 42
The thickness b is determined by the same method as in the embodiment of FIG.

Next, an n-type Al _x G
a _1-x As (0 ≦ x ≦ 1) Lower cladding layer 43 (for example, x = 0.0, thickness 1.0 μm), (Al _x Ga _1-x ) _y I
n _1-y As (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) active layer 44 (for example, x = 0.0, y = 0.8 and thickness 100 °), p-type Al _x Ga _1-x As ( 0 ≦ x ≦ 1) Upper cladding layer 45
(For example, x = 0.0 and a thickness of 1.0 μm) are sequentially laminated, and a p-type GaAs contact layer 46 is further formed thereon.

Next, for example, an Au—Be film is vapor-deposited on the p-type GaAs contact layer 46, and this is patterned into, for example, a circle to form a p-type electrode 47. On the other hand, Ga
On the lower surface of the As substrate 41, an n-type electrode 48 made of, for example, an Au—Zn film is formed by vapor deposition to complete the LED 4.

FIG. 9 is a graph showing the dependence of the average reflection intensity of the DBR on the number of pairs in the LED 4 formed as described above. The LED 4 according to the present embodiment also uses a material having a small light absorption coefficient with respect to light emission from the active layer as a material of a layer constituting the DBR, similarly to the embodiment of FIG.
As the number of pairs increases, the average reflection intensity can be increased, and the reflectance can be made close to 100%. Also according to the present embodiment, it was possible to obtain about 1.3 times the emission luminance as compared with the LED according to the prior art.

FIG. 10 (a) is a sectional view of an LED according to still another embodiment of the present invention, and FIG. 10 (b) is an enlarged view of a portion G in FIG. 10 (a). As shown in FIG. 10, the LED 5
On an n-type GaAs substrate 51, an n-type AlAs layer 52a and n
Type Al _x Ga _{1 -x} As layer (0 ≦ x ≦ 1) 52b (for example, x
= 0.1) as a pair, and a light reflection multilayer film (DBR) 52 composed of many pairs (for example, 40 pairs) is laminated. The DBR 52 in this embodiment is a chirped DBR whose film thickness gradually changes from the lower layer to the upper layer, and includes an n-type AlAs layer 52a and an n-type Al _x Ga _1-x
The thickness of the As layer (0 ≦ x ≦ 1) 52b is designed as follows, for example, assuming that the respective refractive indexes are n ₁ and n ₂ and the emission wavelength from the active layer is λ.

As shown in FIG. 11 by taking the layer thickness of the n-type AlAs layer 52a as an example, the layer thickness of the lowermost layer and the uppermost layer of the n-type AlAs 52a is (λ / 4n ₁ ) × (1 + DD ₁ ), respectively. (Λ / 4n ₁ ) × (1
−DD ₂ ), and similarly, an n-type Al _x Ga ₁ -xAs layer (0 ≦ x ≦ 1)
The thicknesses of the lowermost layer and the uppermost layer of 52b are (λ / 4n ₂ ) × (1 + DD ₁ ) and (λ / 4n ₂ ) × (1
−DD ₂ ), and the layer thickness is determined so that all the layers between the lowermost layer and the uppermost layer are equally spaced.

Next, on the DBR 52, an n-type Al _x G
a _1-x As (0 ≦ x ≦ 1) Lower cladding layer 53 (for example, x = 0.7 and thickness 1.0 μm), Al _x Ga _1-x As
(0 ≦ x ≦ 1) Active layer 54 (for example, x = 0.0 and thickness 0.5 μm), p-type Al _x Ga _1-x As (0 ≦ x ≦ 1) upper cladding layer 55 (for example, x = 0) 0.7 and thickness 1.0μ
m) are sequentially laminated, and a p-type GaAs contact layer 56 is further formed thereon.

Next, for example, an Au—Be film is vapor-deposited on the p-type GaAs contact layer 56, and this is patterned into, for example, a circle to form a p-type electrode 57. On the other hand, Ga
An LED 5 is obtained by forming an n-type electrode 58 made of, for example, an Au—Zn film on the lower surface of the As substrate 51 by vapor deposition.

FIG. 12 is a diagram showing a reflection spectrum of the DBR in the LED 5. In FIG. 12, for comparison, AlAs and G
DB created with the same layer thickness configuration as LED5 using aAs
9 shows the reflection spectrum of R (the characteristics of this comparative example are indicated by S ′ in the figure). As is apparent from FIG. 12, the reflection intensity on the long wavelength side is lower than the characteristics of the example R ′.

This is because, in the DBR of Comparative Example S, GaAs
Has the absorption characteristic with respect to the light from the active layer, so that the lower DBR layer cannot contribute to the reflection characteristic. In the layer configuration of the LED 5, the lower side of the DBR reflects longer wavelength light.
The reflection intensity on the long wavelength side is low.

On the other hand, since a material that does not absorb light from the active layer is used as the material of the DBR of this embodiment, the lower DBR can also contribute to the reflection intensity. As a result, high reflection intensity is maintained even on the long wavelength side, and good reflection characteristics are obtained.

In the case of forming a chirped DBR as described above, a material having a small light absorption for light emission from the active layer is used as a material for forming the DBR.
Can be broadened. Thus, according to the present embodiment, about 1.1 compared to the LED of the prior art.
It was possible to obtain four times the emission luminance.

Although the present embodiment has a DBR structure in which the layer thickness becomes smaller as the upper layer becomes thinner, the relationship between the long wavelength and the short wavelength is reversed for a DBR having a layer thickness that becomes thicker as the upper layer. Alone has the effect of broadening the reflection wavelength region as well,
Almost the same improvement in light emission luminance is possible.

FIG. 13A is a sectional view of an LED according to still another embodiment of the present invention, and FIGS.
It is an H section enlarged view of (a).

As shown in FIG. 13, the LED 6 is an n-type G
An n-type AlAs layer 62a and an n-type In
_x Ga _1-x As layer (0 ≦ x ≦ 1) 62 b (for example, x = 0.
The light reflecting multilayer film (DBR) 62 composed of a large number of pairs (for example, 40 pairs) is formed by setting the pair of the light reflection multilayer films (0) as a pair. The DBR 62 in this embodiment is a chirped DBR whose thickness gradually changes from the lower layer to the upper layer, and includes an n-type AlAs layer 62a and an n-type In _x Ga _{1 -x} As layer (0 ≦ x ≦ 1) The thickness of 62b is such that each refractive index is n ₁ ,
Assuming that n ₂ and the wavelength of light emitted from the active layer are λ, for example, it is designed as follows.

As shown in FIG. 14 by way of example of the layer thickness of the n-type AlAs layer 62a, the layer thicknesses of the lowermost layer and the uppermost layer of the n-type AlAs 62a are (λ / 4n ₁ ) × (1 + DD ₁ ), respectively. (Λ / 4n ₁ ) × (1
−DD ₂ ), and similarly, an n-type In _x Ga ₁ -xAs layer (0 ≦ x ≦ 1)
The layer thicknesses of the lowermost layer and the uppermost layer of 62b are (λ / 4n ₂ ) × (1 + DD ₁ ) and (λ / 4n ₂ ) × (1
−DD ₂ ), and the layer thickness is determined so that all layers between the lowermost layer and the uppermost layer are equally spaced.

Next, on the DBR 62, an n-type Al _x G
a _1-x As (0 ≦ x ≦ 1) lower cladding layer 63 (for example, x = 0.7 and thickness 1.0 μm), (Al _x Ga _1-x ) _y
In _1-y As (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) Active Layer 64
(Eg x = 0.0, y = 0.8 and thickness 100 °),
p-type Al _x Ga _{1 -x} As (0 ≦ x ≦ 1) upper cladding layer 6
5 (for example, x = 0.7 and a thickness of 1.0 μm) are sequentially laminated, and a p-type GaAs contact layer 66 is further formed thereon.

Next, for example, an Au—Be film is deposited on the p-type GaAs contact layer 66, and this is patterned into a circular shape, for example, to form a p-type electrode 67. On the other hand, Ga
On the lower surface of the As substrate 61, for example, an Au—Zn film, for example, A
An LED 6 is obtained by forming an n-type electrode 68 made of a u-Zn film by vapor deposition.

FIG. 15 is a diagram showing the reflection spectrum of the DBR at the LED 6. In FIG. 15, for the purpose of comparison, AlAs and I
shows n _x Ga reflection spectrum of the DBR created with the same thickness structure and LED6 using _{1-x As (x = 0.25} ) ( figure characteristics of this comparative example, indicated by S "). FIG.
As is clear from the graph, the reflection intensity on the long wavelength side is lower than the characteristics of the embodiment R ″.

FIG. 10 shows such characteristics.
For the same reason as described in the embodiment. That is, in the DBR of Comparative Example S ″, since GaAs has absorption characteristics with respect to light from the active layer, the layer of the lower DBR cannot contribute to the reflection characteristics. LED
In the layer configuration of No. 6, since the lower side of the DBR is configured to reflect light of a longer wavelength, the reflection intensity on the longer wavelength side is lower.

On the other hand, since a material that does not absorb light from the active layer is used as the material of the DBR of this embodiment, the lower DBR can also contribute to the reflection intensity. As a result, high reflection intensity is maintained even on the long wavelength side, and good reflection characteristics are obtained.

In the case of forming a chirped DBR as described above, a material having a small light absorption with respect to light emission from the active layer is used as a material for forming the DBR.
Can be broadened. Thus, according to the present embodiment, about 1.1 compared to the LED of the prior art.
It was possible to obtain four times the emission luminance.

Although the present embodiment has a DBR structure in which the layer thickness becomes smaller as the upper layer becomes smaller, the relationship between the long wavelength and the shorter wavelength is reversed for a DBR having a layer thickness that becomes larger as the upper layer becomes smaller. In this case, the reflection wavelength region is similarly widened, and substantially the same improvement in light emission luminance can be achieved.

In the embodiments of the present invention described above, a DBR having a single-period structure and a DBR having a chirp-like structure have been described. The present invention can be applied to any multi-layer reflective film regardless of the layer thickness configuration.

[0079]

As described above, in the semiconductor light emitting diode according to the present invention, a semiconductor having a band gap larger than the band gap of the active layer is used as a material of the light reflecting multilayer film. Little absorption of light emitted from the part. Therefore, the reflection intensity of the DBR can be increased, and the chirped DBR
In this case, the reflection wavelength region can be widened, whereby the efficiency of extracting light emitted from the active layer to the outside can be increased, and the luminance of the light emitting diode can be improved.

[Brief description of the drawings]

FIGS. 1A and 1B are a cross-sectional view of a semiconductor light emitting diode according to an embodiment of the present invention and C in FIG.
Part enlarged view.

FIG. 2 is a characteristic diagram showing a relationship between the number of layers of a light reflecting multilayer film of the semiconductor light emitting diode of FIG. 1 and an average reflectance.

3A and 3B are a cross-sectional view of a semiconductor light emitting diode according to another embodiment of the present invention and an enlarged view of a portion D in FIG.

FIG. 4 is a characteristic diagram showing a relationship between a layer thickness and a layer position of a light reflecting multilayer film of the semiconductor light emitting diode of FIG. 3;

FIG. 5 is a characteristic diagram showing a relationship between the wavelength and the reflectance of the semiconductor light emitting diode of FIG. 3;

FIGS. 6A and 6B are a cross-sectional view of a semiconductor light-emitting diode according to still another embodiment of the present invention and an enlarged view of a portion E of FIG. 6A.

FIG. 7 is a characteristic diagram showing a relationship between the number of layers of the light reflecting multilayer film of the semiconductor light emitting diode of FIG. 6 and the average reflectance.

8A and 8B are a cross-sectional view of a semiconductor light emitting diode according to still another embodiment of the present invention and an enlarged view of a portion F of FIG. 8A.

9 is a characteristic diagram showing a relationship between a layer thickness and a layer position of a light reflecting multilayer film of the semiconductor light emitting diode of FIG.

FIGS. 10A and 10B are a cross-sectional view of a semiconductor light-emitting diode according to still another embodiment of the present invention and an enlarged view of a G part of FIG.

11 is a characteristic diagram showing a relationship between a layer thickness and a layer position of a light reflection multilayer film of the semiconductor light emitting diode of FIG.

FIG. 12 is a characteristic diagram showing a relationship between the wavelength and the reflectance of the semiconductor light emitting diode of FIG. 10;

13A and 13B are a cross-sectional view of a semiconductor light-emitting diode according to still another embodiment of the present invention and an enlarged view of a portion H of FIG.

FIG. 14 is a characteristic diagram showing a relationship between a layer thickness and a layer position of a light reflecting multilayer film of the semiconductor light emitting diode of FIG.

FIG. 15 is a characteristic diagram showing a relationship between the wavelength and the reflectance of the semiconductor light emitting diode of FIG.

16A and 16B are a cross-sectional view of a semiconductor light emitting diode according to a conventional example and an enlarged view of a portion A in FIG.

17A and 17B are a cross-sectional view of a semiconductor light emitting diode according to another conventional example and an enlarged view of a portion B of FIG. 17A, respectively.

18 is a characteristic diagram showing a relationship between a layer thickness and a layer position of a light reflection multilayer film of the semiconductor light emitting diode of FIG.

FIG. 19 is a characteristic diagram showing a relationship between the number of layers of the light reflecting multilayer film of the semiconductor light emitting diode of FIG. 16 and the average reflectance.

FIG. 20 is a characteristic diagram showing the relationship between the wavelength and the reflectance of the semiconductor light emitting diode of FIG. 17;

FIG. 21 is another characteristic diagram showing the relationship between the wavelength and the reflectance of the semiconductor light emitting diode of FIG. 17;

[Explanation of symbols]

 1, 2 semiconductor light emitting diode 11, 21 semiconductor substrate 12, 22 light reflecting multilayer film 14, 24 active layer

Claims (8)

[Claims] 1. A semiconductor having, on a semiconductor substrate, at least an active layer and a light-reflective multilayer film disposed between the semiconductor substrate and the active layer and reflecting light traveling from the active layer toward the semiconductor substrate. 2. A light emitting diode according to claim 1, wherein said light reflecting multilayer film is formed of a semiconductor material having a band gap larger than a band gap of said active layer. 2. The semiconductor light emitting diode according to claim 1, wherein the light reflecting multilayer film is formed by alternately laminating two types of materials having mutually different refractive indexes. 3. The light-reflecting multilayer film includes a pair of two types of films having different refractive indexes, and a plurality of the pairs are stacked, and the plurality of pairs reflect an emission wavelength from an active layer. 3. The semiconductor light-emitting diode according to claim 2, wherein the semiconductor light-emitting diodes are continuously changed at a constant rate from a layer thickness smaller than a layer thickness to a large layer thickness. 4. The semiconductor substrate comprises a GaAs substrate, the active layer comprises an AlGaInP-based material, and the light reflection multilayer film comprises an AlInP-based material and AlGaInP.
The semiconductor light-emitting diode according to any one of claims 1 to 3, wherein the semiconductor light-emitting diode is formed by alternately laminating a base material. 5. The semiconductor according to claim 4, wherein the light reflection multilayer film is formed by stacking at least 20 pairs of a film made of an AlInP material and a film made of an AlGaInP material. Light emitting diode. 6. The semiconductor light emitting diode according to claim 1, wherein said semiconductor substrate is made of a GaAs substrate, and said active layer is made of an AlGaAs-based material. 7. The semiconductor light emitting diode according to claim 1, wherein said semiconductor substrate is made of a GaAs substrate, and said active layer is made of an AlGaInAs-based material. 8. The semiconductor light emitting diode according to claim 6, wherein at least five pairs of said light reflecting multilayer films are laminated.