JPH08167735A - Light emitting element - Google Patents

Abstract

PURPOSE: To enable a light emitting diode composed of nitrogen compound to emit ultraviolet, blue, and green light rays at superhigh luminance by making it possible to grow a high-quality active layer in the diode. CONSTITUTION: After an AlN buffer layer 6 is formed on a sapphire substrate 7, an n-type InGaN current diffusing layer 5, an n-type InGaN clad layer 4, an InGaN active layer 3, a p-type InGaN clad layer 2, and a p-type InGaN current diffusing layer 1 are successively formed on the buffer layer 6. The GaN mixed crystal ratios of the active layer 3 and current diffusing layers 1 and 5 are respectively set at 0.6 and 0.7 so that the mixed crystal ratio difference between the active layer 3 and current diffusing layers 1 and 5 can be controlled to 0.2. When the composition of the current diffusing layers 1 and 5 are brought near to the composition of the active layer 3 in such a way, the quality of the active layer 3 can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device capable of obtaining a good quality active layer, and more particularly to a device suitable for a high output and high brightness light emitting diode capable of emitting light having a wavelength of green to ultraviolet.

[0002]

2. Description of the Related Art A light emitting diode (LED) and a semiconductor laser (LD) using GaN, AlGaN, or InGaN as a light emitting layer can generate light in a wavelength range from green to ultraviolet. Therefore, light-emitting devices that emit such light have been studied for a long time. In recent years, MOCV
1000 using GaN as a light emitting layer by utilizing a buffer layer forming technique by the D growth method and applying a DH structure
High-brightness blue LEDs of mcd class have been developed and commercialized.

However, in order to be used outdoors in the sunlight lit state, ultrahigh brightness of 2000 mcd class is required. The red LED uses AlGaAs and is 300
0mcd class has already been developed and commercialized. Therefore G
Higher brightness is also required for aN blue LEDs.

A green color using InGaN for the active layer has also been studied, and a study for increasing the brightness thereof is under way.
With InGaN, a green color close to blue with a large GaN mixed crystal composition has been realized. InGaN or AlI close to InN
If nN can be realized, pure green can be obtained, but pure green ultra-high brightness LEDs have not yet been realized. Furthermore, if AlGaN is used for the active layer, an ultraviolet light LED can be produced, but this has not been realized.

As described above, I having a mixed crystal composition separated from GaN
Development of an LED using nGaN, AlGaN, or AlInN as an active layer has been awaited.

FIG. 4 shows the structure of a conventional blue LED of a nitrogen compound system which can achieve high brightness. In this LED structure, a GaN or AlN buffer layer 16 is formed on a sapphire substrate 17, an n-type GaN current diffusion layer 15 is grown on the sapphire substrate 17 by several μm, and an In layer to be a light emitting layer is formed thereon.
The GaN active layer 13 is sandwiched between the n-type AlGaN clad layer 14 and the p-type AlGaN clad layer 12, and a double hetero layer is formed so that the n-type AlGaN clad layer 14 is on the lower side, and a p-type GaN current is formed thereon. It has an epitaxial structure in which the diffusion layer 11 is formed.

It is a defect in the active layer that prevents such an LED from achieving ultra-high brightness. Since there is a defect in this active layer, when the thickness of the active layer of a normal LED is about 1 μm, only LEDs with low brightness can be produced. Therefore, conventionally, the InGaN layer is thinned to increase the density of injected carriers and increase the conversion efficiency.

[0008]

However, in order to increase the brightness, as in the conventional method, the InGaN layer is thinned to increase the density of injected carriers and increase the conversion efficiency. There was such a drawback.

(1) In order to confine the injected carriers, it is necessary to increase the band gap energy of the cladding layers on both sides. Therefore, the difference in lattice constant between the active layer and the cladding layer becomes larger, which causes defects.

(2) In order to manufacture an LED that is close to pure green, the composition of GaN mixed crystal of InGaN is reduced.
InGaN cannot be formed.

(3) Since the active layer is thin, the temperature rise of the active layer cannot be suppressed and the reliability of the LED is poor.

(4) Since the thickness of the active layer is thin, the change in the emission wavelength with respect to the temperature rise of the energizing current is large.

An object of the present invention is to solve the above-mentioned problems of the prior art by forming a light emitting layer having good crystallinity in a light emitting device of a nitrogen compound type, and to provide a light emitting device having higher brightness. To provide. Another object of the present invention is to provide a high-output, high-luminance light emitting element that can emit light having a wavelength in the green to ultraviolet range.

[0014]

The gist of the present invention is to provide a high-quality active layer by making the composition of the n-type layer and the p-type layer outside the clad layer sandwiching the active layer close to that of the active layer. Is to be able to grow. That is, in the light emitting device of the first invention, a buffer layer of a nitrogen compound semiconductor is formed on a sapphire substrate, and a current spreading layer of an n-type nitrogen compound semiconductor or a nitrogen compound mixed crystal semiconductor is formed thereon. In addition, an active layer of a nitrogen compound semiconductor or a nitrogen compound mixed crystal semiconductor is further formed on the clad layer of an n-type and p-type nitrogen compound semiconductor or a nitrogen compound mixed crystal semiconductor having a larger band gap energy than that. In the light-emitting device, the double hetero layer sandwiched is formed so that the n-type layer is on the lower side, and the current diffusion layer of the p-type nitrogen compound semiconductor or the nitrogen compound mixed crystal semiconductor is formed on the double hetero layer. A current diffusion layer of p-type and n-type nitrogen compound semiconductors or nitrogen compound mixed crystal semiconductors sandwiching the hetero layer, and a nitrogen compound half in the center of the double hetero layer serving as a light emitting layer. Mixed crystal ratio difference between the body or nitrogen compound mixed crystal semiconductor of the active layer, in which was 0.2 or less.

The light emitting device of the second invention is the light emitting device of the first invention in which the p-type and the n-type are reversed.

A light emitting device according to a third invention is the light emitting device according to the first or second invention, wherein any one of GaN, AlN and InN is used as a nitrogen compound semiconductor and AlGaN and InGaN are used as a nitrogen compound mixed crystal semiconductor. , AlI
Any one of nN is used.

In the light emitting device of the fourth invention, a buffer layer of a nitrogen compound semiconductor is formed on a sapphire substrate, an n-type InGaN current spreading layer is formed thereon, and an InGaN active layer is further formed thereon. N-type and p-type InGaN, GaN or Al having a bandgap energy larger than that of
A double hetero layer sandwiched between GaN cladding layers is formed so that the n-type layer is on the lower side, and p-type InGaN is formed on the double hetero layer.
In the light emitting device having the current spreading layer, the difference in mixed crystal ratio between the p-type and n-type InGaN current diffusion layers sandwiching the double hetero layer and the central InGaN active layer of the double hetero layer serving as the light emitting layer is It is set to 0.2 or less.

In the light emitting device of the fifth invention, a buffer layer of a nitrogen compound semiconductor is formed on a sapphire substrate, an n-type AlGaN current diffusion layer is formed thereon, and an AlGaN active layer is formed thereon. A double hetero layer sandwiched between n-type and p-type AlGaN cladding layers having a larger band gap energy than that of the n-type layer,
In a light emitting device having a p-type AlGaN current diffusion layer formed thereon, a p-type and n-type sandwiching the double hetero layer are provided.
Type AlGaN current spreading layer and the difference in the mixed crystal ratio between the central AlGaN active layer of the double hetero layer serving as the light emitting layer is 0.1 or less.

In the light emitting device of the sixth invention, a buffer layer of a nitrogen compound semiconductor is formed on a sapphire substrate, an n-type AlInN current diffusion layer is formed thereon, and an AlInN active layer is formed thereon. A double hetero layer sandwiched between n-type and p-type AlInN or AlGaN cladding layers having a larger bandgap energy than that of the n-type layer is formed on the lower side, and a p-type AlInN current diffusion layer is formed thereon. In the formed light emitting device, the difference in mixed crystal ratio between the p-type and n-type AlInN current diffusion layers sandwiching the double hetero layer and the central AlInN active layer of the double hetero layer serving as the light emitting layer is 0.1 or less. It was done.

The light emitting device of the seventh invention is the first to sixth inventions.
The light emitting element of the invention is a LED.

The light emitting element of the eighth invention is the first to sixth embodiments.
A semiconductor laser is used as the light emitting device of the invention.

[0022]

In the epitaxial growth, the most important point for growing a good quality crystal layer on the crystal is that the crystal layer to be grown has a lattice constant which is the same as or close to that crystal at the growth temperature. Is to grow on.

In the structure of a light emitting element of a nitrogen compound type, generally, a current diffusion layer, a clad layer, an active layer, a clad layer and a current diffusion layer are sequentially formed on a buffer layer formed on a sapphire substrate. It is like this. Of these, in order to improve the quality of the active layer, it is preferable to reduce the mixed crystal ratio difference (lattice constant difference) of the cladding layer sandwiching the active layer with respect to the active layer as much as possible.

On the other hand, the current spreading layers sandwiching the clad layer are also related to the active layer. The relationship between the current spreading layer and the active layer has never been studied so far.

In the present invention, the current diffusion layer was also examined, and it was found that the clad layer should be sandwiched between the current diffusion layers having a composition close to that of the active layer in order to obtain high brightness.
This means that, similarly to the clad layer, if the current spreading layer is formed with a lattice constant close to that of the active layer, a good quality active layer can be easily formed. That is,
If a good quality active layer is easily formed, the thickness of the active layer can be increased. Therefore, the injection current density becomes smaller,
It is not necessary to make the bandgap energy of the clad layer sandwiching the active layer much higher than that of the active layer, and the composition of the clad layer, that is, the lattice constant can be made closer to that of the active layer. Therefore, it becomes easy to form a higher quality active layer.

By reducing the mixed crystal ratio difference between the current spreading layer and the active layer sandwiching the cladding layer in this way, an active layer having good crystallinity can be formed, so that high output and high brightness can be obtained. It becomes easy to convert.

Further, it becomes possible to easily grow a good quality mixed crystal layer over a wide range of the mixed crystal composition of the active layer. For example, even with InGaN having a small GaN mixed crystal composition, an epitaxial layer having good crystallinity can be grown. Therefore, if the GaN mixed crystal composition of InGaN is reduced as in the conventional case, InGaN cannot be formed. Such inconvenience is eliminated, and a light emitting element close to pure green can be easily manufactured. Therefore, the wavelength control becomes easy, and a high-intensity or high-power light emitting device capable of emitting light of wavelengths in the green, blue, and ultraviolet regions can be manufactured.

Further, as the quality of the active layer is improved, it becomes possible to increase the thickness of the active layer, so that the temperature rise of the active layer due to the applied current can be suppressed and the change of the emission wavelength can be reduced, and the reliability of the LED can be improved. The property can also be improved.

[0029]

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

Example 1 FIG. 1 shows the structure of a green LED chip using InGaN as a nitrogen compound mixed crystal semiconductor. In the LED structure, an AlN buffer layer 6 is formed on a sapphire substrate 7, and an n-type InGaN current dispersion layer 5 is formed thereon to a thickness of 5 μm. This InGaN current spreading layer 5 is Si-doped and has a GaN mixed crystal composition of 0.6.
Is.

On this, a double hetero layer having a three-layer structure in which the active layer is sandwiched by clad layers is formed. That is, first, the n-type InGaN cladding layer 4 is formed. The InGaN cladding layer 4 is Si-doped and has a Ga content.
The N mixed crystal ratio is 0.7 and the thickness is 200 nm. Next, a Zn-doped InGaN active layer 3 to be a light emitting layer is formed. The GaN mixed crystal ratio of this InGaN active layer 3 is 0.6. The thickness is 500 nm. And p
Type InGaN clad layer 2 is formed. This In
The GaN cladding layer 2 is Mg-doped, has a GaN mixed crystal ratio of 0.7, and has a thickness of 200 nm.

On top of that, a p-type InGaN layer current spreading layer 1 is formed.
Is formed. This InGaN current spreading layer 1 is made of Mg
It is doped, the GaN mixed crystal ratio is 0.7, and the thickness is 5
It is 00 nm. P-type InG of this epitaxial wafer
A p-side electrode 8 was formed on the aN current diffusion layer 1. Also,
Part of the p-type InGaN current diffusion layer 1 and the double hetero layer formed as described above is removed by dry etching to expose the n-type InGaN current diffusion layer 5, and the exposed n-type InGaN current diffusion layer 5 is exposed. An n-side electrode 9 is formed on top. Chip size is 600 μm x 600
μm.

The AlN buffer layer 6 of this epitaxial wafer and the InGaN mixed crystal layer formed thereon were grown by the MOCVD method as in the conventional method. Further, the n-type Si and the p-type Mg, which are dopants, and the Zn used in the active layer were controlled in the same manner as in the conventional case.

When the characteristics of this LED were examined, it was a pure green color with a wavelength of 515 nm, and the luminous intensity was 400.
0 mcd was obtained.

First, in order to investigate the influence of the mixed crystal ratio of the cladding layer on the brightness, the active layer 3 (mixed crystal ratio of 0.6) was used.
An LED in which the GaN mixed crystal ratio of the p-type clad layer 2 and the n-type clad layer 4 sandwiching (fixed to) was changed was manufactured, and the brightness thereof was measured. The result is shown in FIG. Than this,
It can be seen that the maximum luminous intensity is obtained when the GaN mixed crystal ratio of the clad layer is 0.7 to 0.8. Incidentally, the mixed crystal ratio of both clad layers in the above embodiment is 0.7.

What can be said from this is that the clad layer has the best GaN mixed crystal ratio difference of about 0.1 to 0.2 with respect to the active layer, and if the GaN mixed crystal ratio difference is larger than that, the luminous intensity decreases. Is to do. Further, when the difference in GaN mixed crystal ratio becomes smaller than that, naturally the luminous intensity becomes low. These facts are also said in the conventional AlGaAs-based DH structure LED, and are not particularly new facts. However, even in InGaN-based LEDs, AlGaAs
It is interesting that the facts about the difference in the mixed crystal ratio of the clad layer to the active layer of the LED system are almost the same.

Next, in order to investigate the influence of the mixed crystal ratio of the current diffusion layer on the brightness, the G of InGaN cladding layers 2 and 4 was examined.
The aN mixed crystal ratio was fixed to be 0.1 higher than the GaN mixed crystal ratio of the InGaN active layer 3. Then, the p-type InGaN current diffusion layer 1 and the n-type InG sandwiching the double hetero layer are provided.
Epitaxial wafers with different GaN mixed crystal ratios with the aN current diffusion layer 5 were grown. An LED was produced from the epitaxial wafer and the luminous intensity was measured. The measurement result is shown in FIG. As shown in the figure, n-type and p-type InG
The luminous intensity is highest when the GaN composition of the aN current diffusion layers 1 and 5 is almost the same as the GaN composition of the InGaN active layer 2.
Whether the GaN mixed crystal composition is higher or lower than that,
The luminous intensity tends to decrease. Therefore, 2000 mc
To obtain d-class ultra-high brightness, the GaN composition difference between the current diffusion layer and the active layer must be about 0.2 or less.

Example 2 AlGaN was used in place of InGaN which is a nitrogen compound mixed crystal semiconductor of Example 1.
In that case, AlGa sandwiching the outside of the cladding layer
The GaN mixed crystal ratio composition of the N current diffusion layer was changed, and Example 1 was used.
The luminous intensity was examined in the same manner as in. As a result, it was found that a high-brightness LED can be obtained with a composition difference of the GaN mixed crystal ratio of 0.1 or less. At that time, the wavelength was 400 nm ultraviolet light, and an emission output of 8 mW was obtained.

Example 3 AlInN was used instead of InGaN which is a nitrogen compound mixed crystal semiconductor of Example 1.
In that case, AlIn sandwiching the outside of the cladding layer
The AlN mixed crystal ratio composition of the N current diffusion layer was changed, and Example 1 was used.
The luminous intensity was examined in the same manner as in. As a result, it was found that a high-brightness LED can be obtained with a composition difference of the GaN mixed crystal ratio of 0.1 or less. At that time, the wavelength was 420 nm, which was green, and the emission luminous intensity was 3500 mcd.

(Effect of Example) As described above, it has become possible to manufacture LEDs of 2000 mcd or more in blue and green in addition to red. Therefore, a high-luminance full-color display can be manufactured by combining three colors. It can also be used in places where blue and high brightness are required, such as traffic signals.

[0041]

According to the first aspect of the present invention, by reducing the mixed crystal ratio difference between the current spreading layer and the active layer sandwiching the cladding layer, it is possible to easily form an active layer which becomes a high quality light emitting layer. It is possible to increase the brightness by further growing.

According to the second aspect of the invention, the above effect can be obtained even if p and n are reversed.

According to the third aspect of the invention, GaN, AlN and InN are used as the nitrogen compound semiconductor and AlGaN, InGaN and AlI are used as the nitrogen compound mixed crystal semiconductor.
Since each nN is used, wavelength control is facilitated, and a high-luminance or high-power light emitting device capable of emitting light of wavelengths in the green, blue, and ultraviolet regions can be manufactured. .

According to the invention of claim 4, InGa
The mixed crystal ratio difference between the N current diffusion layer and the InGaN active layer was set to 0.
By setting the ratio to 2 or less, I having a small GaN mixed crystal ratio composition
Even with nGaN, an InGaN epitaxial layer having good crystallinity can be grown, so that a light emitting element having a color close to pure green can be easily manufactured.

According to the light emitting device of the fifth aspect, Al
By setting the mixed crystal ratio difference between the GaN current spreading layer and the AlGaN active layer to be 0.1 or less, a good quality AlGaN active layer can be formed.

According to the light emitting device of the sixth aspect, Al
Since the mixed crystal ratio difference between the InN current diffusion layer and the AlInN active layer is 0.1 or less, a good quality AlInN active layer can be formed.

According to the light emitting device of the seventh aspect, since the light emitting device is an LED, high brightness or high output LED light capable of emitting light of wavelengths of ultraviolet, blue and green is obtained.

According to the light emitting device of the eighth aspect, since the light emitting device is a semiconductor laser, high-intensity or high-power laser light capable of emitting light of ultraviolet, blue, and green wavelengths can be obtained.

[Brief description of drawings]

FIG. 1 is a graph for explaining an embodiment of a light emitting device of the present invention.
Sectional drawing of an nGaN green LED chip.

FIG. 2 is a diagram showing the GaN mixed crystal ratio dependence of the luminous intensity of the InGaN green LED according to this example.

FIG. 3 is a diagram showing the GaN mixed crystal ratio dependence of the luminous intensity of the InGaN green LED according to this example in the InGaN current diffusion layer.

FIG. 4 is a sectional view of a conventional nitrogen compound-based blue LED chip.

[Explanation of symbols]

 1 p-type InGaN current diffusion layer 2 p-type InGaN clad layer 3 InGaN active layer 4 n-type InGaN clad layer 5 n-type InGaN current diffusion layer 6 AlN buffer layer 7 sapphire substrate 8 p-side electrode 9 n-side electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ken Takahashi, 3550 Kidayomachi, Tsuchiura City, Ibaraki Prefecture, Hitachi Cable Ltd. Advanced Research Center (72) Shoji Kuma, 3550, Kidayomachi, Tsuchiura City, Ibaraki Hitachi Cable Shares Company Advance Research Center

Claims (8)

[Claims] 1. A buffer layer of a nitrogen compound semiconductor is formed on a sapphire substrate, a current spreading layer of an n-type nitrogen compound semiconductor or a nitrogen compound mixed crystal semiconductor is formed on the buffer layer, and a nitrogen layer is further formed thereon. A double hetero layer is formed by sandwiching an active layer of an element compound semiconductor or a nitrogen compound mixed crystal semiconductor with a clad layer of an n-type and a p-type nitrogen compound semiconductor or a nitrogen compound mixed crystal semiconductor having a larger band gap energy than that. In a light emitting device in which the n-type layer is formed downward, and the current spreading layer of a p-type nitrogen compound semiconductor or a nitrogen compound mixed crystal semiconductor is formed thereon, the double hetero layer is sandwiched. Current diffusion layers of p-type and n-type nitrogen compound semiconductors or nitrogen compound mixed crystal semiconductors, and nitrogen compound semiconductors or nitrogen compounds in the center of the double hetero layer serving as the light emitting layer Mixed crystal ratio difference between the active layer of the crystal semiconductor light-emitting element, characterized in that not more than 0.2. 2. The light emitting device according to claim 1, wherein the p-type and the n-type are opposite to each other. 3. The light emitting device according to claim 1, wherein the nitrogen compound semiconductor is GaN, AlN, or I.
A light-emitting device characterized by using any one of nN and AlGaN, InGaN, or AlInN as a nitrogen compound mixed crystal semiconductor. 4. A buffer layer of a nitrogen compound semiconductor is formed on a sapphire substrate, an n-type InGaN current spreading layer is formed on the buffer layer, and an InGaN active layer having a band gap energy larger than that is formed thereon. n-type and p-type I
In the light-emitting device, a double hetero layer sandwiched between nGaN, GaN, or AlGaN cladding layers is formed so that the n-type layer is lower, and a p-type InGaN current spreading layer is formed on the double hetero layer. The difference in the mixed crystal ratio between the p-type and n-type InGaN current diffusion layers sandwiching the gap and the InGaN active layer at the center of the double hetero layer serving as the light emitting layer is 0.
A light emitting device having a number of 2 or less. 5. A buffer layer made of a nitrogen compound semiconductor is formed on a sapphire substrate, an n-type AlGaN current diffusion layer is formed on the buffer layer, and an AlGaN active layer is further formed on the sapphire substrate. n-type and p-type A
A double hetero layer sandwiched between lGaN cladding layers is formed so that the n-type layer is on the lower side, and p-type AlGaN is formed on the double hetero layer.
In the light emitting device having the current diffusion layer formed, the difference in mixed crystal ratio between the p-type and n-type AlGaN current diffusion layers sandwiching the double hetero layer and the central AlGaN active layer of the double hetero layer serving as the light emitting layer is A light emitting device having a ratio of 0.1 or less. 6. A buffer layer made of a nitrogen compound semiconductor is formed on a sapphire substrate, an n-type AlInN current diffusion layer is formed on the buffer layer, and an AlInN active layer having a band gap energy larger than that is formed thereon. n-type and p-type A
In a light-emitting device, a double hetero layer sandwiched between lInN or AlGaN cladding layers is formed so that the n-type layer is on the lower side, and a p-type AlInN current diffusion layer is formed on the double hetero layer. p-type and n-type AlIn
A light-emitting device characterized by having a mixed crystal ratio difference of 0.1 or less between an N current diffusion layer and an AlInN active layer at the center of a double hetero layer serving as a light-emitting layer. 7. The light emitting device according to claim 1, wherein the light emitting device is a light emitting diode. 8. The light emitting device according to claim 1, wherein the light emitting device is a semiconductor laser.