JPH0715038A - Semiconductor light emitting element - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] To provide a semiconductor light-emitting device that achieves high brightness. [Structure] InGaAlP composed of a double heterojunction, a single heterojunction or a homojunction on a semiconductor substrate
Forming a light emitting layer 6, a current diffusion layer for adjusting current flow formed on the bonding layer, a first electrode formed on the back surface of the semiconductor substrate, and formed on the current diffusion layer. A semiconductor light emitting device having a second electrode formed by:
The current diffusion layer is made of n-type InGaAlP having a bandgap energy larger than that of the light emitting layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device used as a display light source for, for example, a stop lamp of an automobile, an information plate of a road, an outdoor display device such as a traffic signal and an advertising signboard, and particularly, an InGaAlP-based material. The present invention relates to the semiconductor light emitting device used.

[0002]

2. Description of the Related Art A semiconductor light emitting device made of an InGaAlP-based material emits light of a direct transition type in an emission wavelength range of 550 nm to 690 nm, so that high emission efficiency can be obtained. Further, by further reducing the light absorption inside the element, a light emitting element having higher luminous efficiency can be obtained.

Conventionally, as a semiconductor light emitting element relating to this kind, there is one shown in FIG. 4, for example.

FIG. 4 is a sectional view showing an example of the configuration of a conventional green LED chip.

Crystal growth of this LED chip is performed by metal organic chemical vapor deposition (MO-CVD). In the figure, the Bragg reflection layer 103 is formed on the 15 ° off-angle substrate 101 in the [011] direction from the n-GaAs (100) orientation via the n-GaAs buffer layer 102. The Bragg reflection layer 103 has a different refractive index n.
It has a multilayer structure in which 20 pairs of -GaAs layers and n-InAlP layers are alternately laminated.

On the Bragg reflection layer 103, an InGaAlP layer having a double hetero structure composed of a cladding layer 104, an active layer 105 and a cladding layer 106 is formed.
The active layer 105 is an undoped In layer as a light emitting layer.
N-In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P and p-In _0.5 (which are transparent to the emission wavelength of the active layer 105, and are composed of _0.5 (Ga _0.6 Al _0.4 ) _0.5 P. Ga _0.3 Al _0.7 ) _0.5 P, respectively.

Further, a current block layer 107 and a current diffusion layer 108 are formed on the clad layer 106. Then, p-GaA is formed on the current diffusion layer 108.
A p-type electrode 110 is formed via the s-contact layer 109, and an n-type electrode 111 is formed on the entire back surface of the substrate 101.

Here, the current blocking layer 107 is n-Ga.
It is made of As and is formed immediately below the p-type electrode 110 corresponding to the lateral width thereof as shown in FIG. That is, after forming the n-GaAs layer on the cladding layer 106, the current blocking layer 107 is formed by selectively etching the n-GaAs layer in a size corresponding to the area of the P-type electrode 110. The current spreading layer 108 is made of p-Ga _0.2 Al _0.8.
It is made of As and is provided to improve the current flow from the p-type electrode 110 and increase the light extraction efficiency. The above green LED using the InGaAlP-based material in this way
The chip has a luminous efficiency of 0.7% in the green region of 573 nm and a luminous intensity of 1.5 cd (half-value angle of product 8 °).
That is, the brightness is more than doubled as compared with the conventional green LED chip using the GaP-based material.

[0009]

However, the conventional LED chip having the above structure has the following problems.

(1) FIG. 5 shows G vs. emission wavelength when a quaternary mixed crystal material of InGaAlP is used for the emission layer.
It is a diagram showing the light transmittance of a _1-y Al _y As current spreading layer. The current diffusion layer is 2 × 10 ¹⁸ cm ⁻³ and its thickness is 7 μm.

In the conventional LED chip described above, a p-type Ga _0.2 Al _0.8 As layer is used as a current diffusion layer in order to enhance the light extraction efficiency. When the Al mixed crystal ratio y of the current diffusion layer is set to, for example, 0.7 to 0.8 as in the above-mentioned conventional example, the transmittance is 65% to 83% for the emission wavelength of 570 nm as shown in FIG. To be improved. However, about 20% of this point still absorbs light, and there is room for further improvement. In order to obtain a more pure green light emission, the light absorption becomes even greater when trying to shorten the wavelength. The light transmittance drops sharply. Therefore, LE
There is a problem that the light extraction efficiency to the outside of the D chip is reduced.

Although the light transmittance itself is improved by increasing the Al mixed crystal ratio y as described above, on the other hand, the resistivity is sharply increased and the current flow is rather deteriorated. Therefore, the position in the case of using a p-type Ga _0.2 Al _{0. 8} As layer as a current spreading layer specific resistance becomes 0.5 .OMEGA · cm longitudinal, spaced 30μm order of the electrode end as in the conventional LED chip configured as described above However, there was a problem that the light intensity was reduced to 1/2, and the LED could not emit light more uniformly over the entire surface.

(2) A part of the light emitted from the active layer 105 and a part of the light reflected by the Bragg reflection layer 103 are absorbed by the current blocking layer 107, so that sufficient light extraction efficiency cannot be obtained. there were.

From the above points, it has been difficult to further increase the brightness of the LED chip having the conventional structure.

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a semiconductor light emitting device which realizes a high brightness.

[0016]

In order to achieve the above-mentioned object, a feature of the first invention is that it is constituted by a double heterojunction, a single heterojunction or a homojunction on a semiconductor substrate.
A bonding layer having nGaAlP as a light emitting layer, a current diffusion layer for current flow adjustment formed on the bonding layer, a first electrode formed on the back surface of the semiconductor substrate, and formed on the current diffusion layer. In the semiconductor light emitting device including the second electrode, the current diffusion layer is made of n-type InGaAlP having a bandgap energy larger than that of the light emitting layer.

According to a second aspect of the present invention, a junction layer having a double heterojunction, a single heterojunction or a homojunction on the semiconductor substrate and having InGaAlP as a light emitting layer, and a current flow adjusting layer formed on the junction layer. The current diffusion layer, the first electrode formed on the back surface of the semiconductor substrate, the second electrode formed on the current diffusion layer, and the second electrode corresponding to the shapes of the second electrode. In the semiconductor light emitting device including a current block for blocking current formed under the electrode, the current blocking layer is configured to have a reflection structure for light emitted from the active layer.

[0018]

According to the above-mentioned structure, the first aspect of the present invention reduces the light absorption and lowers the specific resistance in the short wavelength region of, for example, 580 nm or less, and thus improves the efficiency of extracting light to the outside. Therefore, more uniform light emission is realized on the entire surface of the device.

In the second invention, the current blocking layer reflects the light emitted from the active layer. That is, the light absorbed by the conventional current blocking layer is reflected, and the light extraction efficiency is improved.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a cross-sectional view of a semiconductor light emitting device (green LED) according to a first embodiment of the present invention.

In FIG. 1, M is placed on the substrate 1 tilted in the 15 ° [011] direction from the p-GaAs (100) orientation.
The following layers are formed by the O-CVD method.

The MOCVD method is one of vapor phase growth methods and utilizes thermal decomposition of an organometallic compound.
In the case of a group compound, a group III (Al, Ga, In) organic metal and a group V (P, As) hydrogen compound are reacted at a high temperature to obtain many kinds of compounds and mixed crystals thereof. According to this MOCVD method, a uniform thin film can be obtained.

In the present embodiment, in the above MOCVD method, as the source source, trimethylindium (TMI) and trimethylgallium (TM) are used for the group III element.
G) and trimethyl aluminum (TMA),
For group V elements, phosphine (PH3) and arsine (AsH3) are used. Furthermore, dimethyl zinc (DMZ) and silane (S) are used as dopants.
iH4) for p-type and n-type, respectively. The reaction system is H
Using 2 as a carrier gas, the source and the dopant of each layer are supplied and grown on the substrate 1 heated to a constant temperature under reduced pressure. That is, the substrate 1 placed in the reaction chamber is depressurized (3
After maintaining at 800 ° C. under 0 to 100 Torr), a large amount of H 2 gas is caused to flow into the reaction chamber at a proper ratio of the above source source and dopant, and chemically reacted,
Deposit each layer on the substrate.

According to this MOCVD method, first, p-G
On the aAs substrate 1, p-GaAs buffer layer 2 (5 × 10 5
¹⁷ cm ⁻³ , 0.5 μm) and then p-GaA
A total of 20 pairs of s and p-In _0.5 Al _0.5 P are alternately laminated to grow the light reflecting layer 3. The light reflection layer 3 has a wavelength of about 1/2 (about 86n) of the emission wavelength in order to reflect light efficiently.
m) with a stacking period (Zn-doped, 5 × 10 ¹⁸
cm ^-3 ).

Next, n-In _0.5 which becomes the current block layer 4 is formed.
Al _0.5 P layer (Si-doped, 5 × 10 ¹⁷ m ⁻³ , 0.2 μ
m), then take out the substrate 1 from the reaction chamber and match the shape of the n-side electrode 10 to be formed later (so that the area is equal to or larger than the area of the electrode), that is, The n-InAlP layer in the unnecessary region is removed by etching using the resist film formed by the usual photoresist method as a mask so as to leave it just below the n-side electrode 10.

Further, again by the MOCVD method, a double hetero structure, that is, p-In _0.5 (Ga _0.3 Al _0.7 ) is formed.
_0.5 P cladding layer 5 (Zn-doped, 4 × 10 ¹⁷ m ⁻³ ,
0.6 μm), undoped In _0.5 (Ga _0.55 Al)
_0.45 ) _0.5 P active layer 6 (Zn-doped, 4 × 10
¹⁷ m ^-3 , 0.6 μm), n-In _0.5 (Ga _0.3 Al
_0.7 ) _0.5 P cladding layer 7 (Si-doped, 5 × 10 ¹⁷
m ⁻³ , 0.6 μm) are successively grown. The cladding layer 5, the active layer 6, and the cladding layer 7 forming the double heterojunction structure have small-large-small refractive indexes, and have a structure in which light and carriers are confined in the central active layer 6. With the above composition, the difference in bandgap energy between the active layer 6 and the cladding layers 5 and 7 is 0.1 ev, and the carrier confinement effect is sufficient.

Then, in order to improve the current flow, n
_{-In 0.5 (Ga 0.3 Al 0.7)} 0. 5 P of the current diffusion layer 8
(Si-doped, 1 × 10 ¹⁸ cm ⁻³ , 5 μm) is laminated. Here, the current diffusion layer 8 has a bandgap energy larger than that of the active layer 6. As a result, the current diffusion layer 8 becomes a highly transparent film. The correlation between the film thickness of the current diffusion layer 8 and the luminous efficiency is 0.5% at 1 μm, 2
It is 1% in μm, and the higher the thickness, the higher the efficiency.
When it is m or more, a stable value is obtained at around 1.5%.

After that, in order to facilitate the formation of the ohmic electrode, an n-GaAs contact layer 9 (Si-doped,
1 × 10 ¹⁸ cm ⁻³ , 0.1 μm), and the n-side electrode 1
0 is Au-Ge alloy, and p-side electrode 11 is Au-
Each Be alloy is vacuum-deposited by 0.5 μm and heat-treated in an Ar atmosphere at a temperature of 480 ° C. for 10 minutes to obtain an ohmic contact.

Further, a pure gold electrode having a thickness of about 1 μm is vacuum-deposited on the n-side surface, and then an n-side electrode 10 is formed by using a normal photoresist method. Further, a region of the contact layer 9 other than under the n-electrode 10 is formed. Since it causes light absorption, it is removed by etching. Then, each element is diced by a blade dicing method to obtain a green LED of about 0.3 mm square as shown in FIG.

In the above embodiment, In is used as the current spreading layer.
_{Since 0.5} (Ga _0.3 Al _0.7 ) _0.5 P is used, as shown in FIG. 2, the light transmittance of the current diffusion layer is clearly improved as compared with the case of using the conventional Ga _0.2 Al _0.8 As. As a result, a luminous efficiency of 1.5% (0.7% in the past) is obtained at an emission wavelength of 570 nm, and the luminous intensity is 3 cd.
(The half-value angle of the product is 8 °), which is 2 compared to the conventional structure.
About double the brightness is achieved. That is, there is no light absorption even in the pure green emission region around 560 nm, and the specific resistance is 0.1
Since it can be reduced to about Ω · cm, which is about 1/5 of that in the conventional case, more uniform light emission can be realized on the entire surface of the LED chip.

In the above embodiment, n-InGaAl is used.
Although the P layer has a two-layer structure of the clad 7 and the current diffusion layer 8, the film thickness, carrier concentration, and Al composition can be arbitrarily selected within a range where light absorption can be ignored.
Further, the present invention is applicable not only to the double heterojunction but also to a single heterojunction or a homojunction. Further, even in the case of the yellow LED, the structure equivalent to that of the above-mentioned embodiment is 4.0% (590 nm), which is the conventional value (3.0%).
The brightness is 1.3 times higher.

FIG. 3 is a sectional view of a semiconductor light emitting device (green LED) according to a second embodiment of the present invention.

By this MOCVD method, the n-GaAs buffer layer 22 and the n-In are formed on the n-GaAs substrate 21.
Light-reflecting layer 23 comprising alternating layers of AlP / n-GaAs
And a cladding layer 24 of n-In _0.5 (Ga _1-x Al _x ) _0.5 P and undoped In _0.5 (Ga _1-y Al _y ).
_0.5 P active layer 25 and p-In _0.5 (Ga _{1 -z} A
1 _z ) _0.5 P cladding layer 26 and current blocking layer 27
And n-InAlP / n-GaAs alternating laminated layers are sequentially laminated. In addition, A of the active layer 25 and the both clad layers 24 and 26 constituting the double heterojunction layer of InGaAlP.
l composition x, y, z is such that y ≦, so that a high composition is obtained.
x and y ≦ z.

Then, the substrate 21 is taken out from the reaction chamber,
In accordance with the shape of the p-side electrode 30 to be formed later (so as to have an area equal to or larger than the area of the electrode), the alternate stack for the current block layer 27 is selectively etched to selectively remove the current block layer 27. To form.

Then, again by the MOCVD method, p-
Ga _1-x1 Al _x1 As current diffusion layer 28 and p-GaAs
The contact layers 29 are sequentially laminated. Where GaAl
The Al composition x1 of the As current diffusion layer 28 is set so that a sufficient window effect can be obtained with respect to the emission wavelength of the active layer. Then, a p-side electrode material is vapor-deposited on the contact layer 29 side and an n-side electrode material is vapor-deposited on the back surface side of the substrate 21, respectively, and a p-side electrode 30 and an n-type electrode 31 are formed by photolithography. From the above, the element structure shown in FIG. 3 is obtained.

As described above, in the present embodiment, the current blocking layer is composed of alternating layers of n-InAlP / n-GaAs, so that the light absorbed by the conventional current blocking layer is reflected, The light extraction efficiency is improved.

[0037]

As described above, according to the first invention, the current diffusion layer is made of n-type InGaAlP having a bandgap energy larger than that of the light emitting layer, so that the efficiency of extracting light to the outside is improved. In addition, more uniform light emission is possible on the entire surface of the device, and higher brightness can be realized as compared with the conventional technique. This makes G
aAlAs red LED (~ 3 cd) and InGaAlP
It is possible to provide a display light source that achieves high brightness equivalent to that of an orange / yellow LED (3 to 5 cd) and that has improved visibility in the green to red visible light region.

According to the second invention, the current blocking layer comprises
Since the active layer is structured so as to reflect the light emitted, the light absorption in the current blocking layer can be improved and the light extraction efficiency can be improved. As a result, a light emitting device with higher brightness can be realized.

[Brief description of drawings]

FIG. 1 is a chip cross-sectional view of a semiconductor light emitting device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an effect of the first embodiment.

FIG. 3 is a chip cross-sectional view of a semiconductor light emitting device according to a second embodiment of the present invention.

FIG. 4 is a chip cross-sectional view of a conventional semiconductor light emitting device.

FIG. 5 is a diagram for explaining a conventional problem.

[Explanation of symbols]

 1, 21 Substrate 4, 27 Current blocking layer 5, 24, 26 Clad layer 6, 7, 25 Active layer Active layer 8, 28 Current diffusion layer 10, 31 n-side electrode 11, 30 p-side electrode

Claims (2)

[Claims] 1. InGaAl formed on a semiconductor substrate by a double heterojunction, a single heterojunction or a homojunction.
A bonding layer having P as a light emitting layer, a current diffusion layer for current flow adjustment formed on the bonding layer, a first electrode formed on the back surface of the semiconductor substrate, and formed on the current diffusion layer. In the semiconductor light emitting device, the current spreading layer is made of n-type InGaAlP having a bandgap energy larger than that of the light emitting layer. 2. InGaA composed of a double heterojunction, a single heterojunction or a homojunction on a semiconductor substrate.
A bonding layer having IP as a light emitting layer, a current diffusion layer for current flow adjustment formed on the bonding layer, a first electrode formed on the back surface of the semiconductor substrate, and formed on the current diffusion layer. In the semiconductor light emitting device, the current blocking layer is provided with a current blocking current block formed under the second electrode corresponding to the shape of the second electrode. A semiconductor light emitting device, which is configured to have a reflection structure for light emitted from the active layer.