JPH0823124A - Light-emitting element of gallium nitride compound semiconductor - Google Patents

Abstract

PURPOSE:To improve light-emitting efficiency by obtaining uniform light emission from an active layer, improving the luminosity and output of the element and further lowering Vf of the light-emitting element. CONSTITUTION:In a gallium nitride compound semiconductor light-emitting element having a structure in which at least an n-type layer is formed between an active layer and a substrate, said n-type layer contains a first n-type layer 3 formed at the substrate side and also contains a second n-type layer 33 having electron density larger than in the first n-type layer 3 formed at the side of an active layer 5 in contact with the first n-type layer 3.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a laser diode (L
D), gallium nitride-based compound semiconductors (In _a Al _b Ga) used for light emitting devices such as light emitting diodes (LEDs)
_1-ab N, 0 ≦ a, 0 ≦ b, a + b ≦ 1).

[0002]

2. Description of the Related Art Currently, a blue LED having a luminous intensity of 1 cd is put into practical use and is a gallium nitride-based compound semiconductor (In _a Al _b G
a _1-ab N, 0 ≦ a, 0 ≦ b, a + b ≦ 1)
It has the structure shown in. It consists of a substrate 1 made of sapphire, a buffer layer 2 made of GaN, and a Ga layer.
N-type layer 3 made of N, n-type cladding layer 4 made of AlGaN, active layer 5 made of InGaN, and AlGaN
The p-type clad layer 6 made of GaN and the p-type contact layer 7 made of GaN are sequentially stacked to form a double hetero structure. This blue LED has a forward voltage (Vf) of 3.6 V and a peak emission wavelength of 4 at a forward current (If) of 20 mA.
50 nm, luminous intensity 1 cd, emission output 1.2 mW, blue L
ED shows the highest performance ever.

In the LED having the above structure, the substrate 1 can be made of sapphire, ZnO, SiC, GaAs, Si, etc., but sapphire is generally used. The buffer layer 2 is made of GaN, GaAlN, AlN, or the like. n-type contact layer 3 and n-type cladding layer 4
Is Si, Ge, Sn, C for gallium nitride compound semiconductor
It is formed of a gallium nitride-based compound semiconductor doped with an n-type dopant such as. Further, the n-type contact layer 3 and the n-type clad layer 4 do not have to be divided into two layers as described above, but may function as a single n-type layer as a clad layer and a contact layer (that is, either of them). Layers can be omitted). The active layer 5 is made of a gallium nitride-based compound semiconductor containing at least indium, and is non-doped, Zn, M
It is doped with a p-type dopant and / or an n-type dopant such as g, Cd, Be. The p-type cladding layer 6 and the p-type contact layer 7 are made p-type by doping a gallium nitride-based compound semiconductor with a p-type dopant and then annealing at 400 ° C. or higher. The p-type cladding layer 6 and the p-type contact layer 7 are a single p-type layer.
You may make it act as a clad layer and a contact layer (any layer can be abbreviate | omitted like an n layer).

[0004]

In the case of gallium nitride-based compound semiconductor, other GaAs, GaP, AlInGaP
Generally, it has a property that the current hardly spreads uniformly as compared with the III-V group compound semiconductors. Therefore, Figure 1
When an LED element having such a structure is realized, there is a problem in that the flow of electrons supplied from the n layer to the active layer is concentrated in a portion having low resistance. FIG. 2 schematically shows the light emission of the active layer due to the concentration of current. This is because electrons supplied from the negative electrode 8 of the n-type contact layer 3 are transferred to the positive electrode 9 of the p-type contact layer 7 and n as shown by the arrow in FIG.
By flowing through the shortest distance so that the resistance between the negative contact 8 of the mold contact layer 3 becomes low, the active layer 5
Indicates that strong light is emitted locally as indicated by the shaded area. Thus, the electrons are transferred to the n-type contact layer 3
If it does not spread uniformly, there is a drawback that uniform light emission cannot be obtained from the active layer 5.

The LED having the above structure is Vf3.6V.
Then, Vf was decreased by 5 V or more as compared with the blue LED made of the conventional MIS structure gallium nitride-based compound semiconductor. This shows light emission by the pn junction,
There is still room for improvement in Vf, and further Vf
Is expected to decrease.

Therefore, the present invention has been made in view of such circumstances, and an object thereof is to form at least an n-type layer between the active layer and the substrate, such as double hetero and single hetero. In the gallium nitride-based compound semiconductor light emitting device having the above structure, firstly, to obtain uniform light emission from the active layer to improve the luminous intensity and output of the device, and secondly to further reduce Vf, It is to improve the luminous efficiency.

[0007]

We have found that the above problem can be solved by interposing a layer having a higher carrier concentration in the n-type layer. That is, the gallium nitride-based compound semiconductor light-emitting device of the present invention is a gallium nitride-based compound semiconductor light-emitting device having a structure in which at least an n-type layer is formed between an active layer and a substrate. The formed first n-type layer and the second n-type layer that is formed in contact with the first n-type layer on the active layer side and has an electron carrier concentration higher than that of the first n-type layer. It is characterized by including.

FIG. 3 shows the structure of a light emitting device according to an embodiment of the present invention.
Shown in The basic structure is almost the same as that of the light emitting device shown in FIG. A new second n-type layer 33 having a high electron carrier concentration is formed. The substrate 1, the buffer layer 2, the n-type contact layer 3, the n-type clad layer 4, the active layer 5, the p-type clad layer 6, the p-type contact layer 7, etc. are formed of a gallium nitride-based compound semiconductor, and the n-type contact layer 3 And the n-type clad layer 4 may be a single n-type layer, and the p-type clad layer 6 and the p-type contact layer 7 may be a single p-type layer.

In the light emitting device of the present invention, in order to grow a gallium nitride compound semiconductor layer having excellent crystallinity, sapphire is preferably used for the substrate 1 and Ga is used for the buffer layer 2.
Grow N or AlN and grow to 10 angstrom ~
It is preferably formed with a film thickness of 0.5 μm.

The first n-type layer formed between the active layer 5 and the substrate 1 is usually 1 μm to 5 as the n-type contact layer 3.
When the n-type clad layer 4 is formed on the surface of the film with a film thickness of μm, the film is grown with a film thickness of 50 Å to 1 μm. However, as described above, the n-type cladding layer 4
Need not be formed. The gallium nitride-based compound semiconductor is preferably GaN or AlGaN, and most preferably GaN. This is because GaN and AlGaN easily become n-type by being non-doped or doped with an n-type dopant, and it is easy to control the electron carrier concentration by the dopant. Furthermore, GaN is likely to grow in order to form a thick film having good crystallinity as a single layer rather than AlGaN.
For example, in the case of realizing an element in which an n-type layer and a p-type layer are sequentially stacked using sapphire as a substrate, the p-type layer is removed by etching to form the electrode 8 of the n-type contact layer 3, and the n-type contact layer 3 is removed. Although it is necessary to expose it, if a thick film can be formed by a single layer, there is a degree of freedom in etching depth, which is very convenient for realizing an actual device.

Next, the active layer 5 is preferably grown to have a thickness of 50 angstroms to 0.5 μm and is made of InGaN. InGaN can easily change the emission wavelength of a light emitting device from purple to green by utilizing band-to-band emission due to a mixed crystal ratio of indium, and further be doped with an n-type or p-type dopant to serve as an emission center. Is also easy. Furthermore, the mixed crystal ratio of In to Ga (In / Ga) is preferably 0.5 or less. In greater than 0.5
Since GaN has poor crystallinity, it tends to be difficult to obtain a practical light emitting device. As the most excellent active layer, an n-type dopant and a p-type dopant are doped to be n-type and the In mixed crystal ratio to Ga is I or less.
It is preferable to use nGaN as the active layer.

The p-type layer grown on the active layer 5 is also GaN,
AlGaN is preferable, the p-type clad layer 6 is formed with a film thickness of 50 angstrom to 1 μm, and the p-contact layer 7 is formed.
Grows to a film thickness of 50 Å to 5 μm. However, the p-type cladding layer 6 does not have to be formed. GaN, Al as the gallium nitride-based compound semiconductor
GaN is preferably formed, and a thick film having good crystallinity is easily grown in a single layer, and when doped with a p-type dopant and annealed at 400 ° C. or higher, it tends to be a p-type easily.

[0013]

FIG. 4 schematically shows the flow of electrons supplied from the n-type contact layer 3 which is the first n-type layer in the light emitting device of FIG. 3 to the active layer 5. This is because the electrons supplied from the n-type contact layer 3 spread evenly through the second n-type layer 33 having a high electron carrier concentration as shown by the arrow so that the active layer 5 emits light uniformly. Is shown. In this way, the first n-type layer is in contact with the first n-type layer.
Second n-type layer 33 having a higher electron carrier concentration than the type layer
Is formed on the active layer side, the electrons are uniformly spread in the second n-type layer 33, and uniform surface emission is obtained from the active layer 5.

The second n-type layer 33 is In containing indium.
_X Al _Y Ga _1-XY N (0 <X, Y ≦ 0) is preferable, and a mixed crystal ratio of In to Ga (In) is particularly preferable.
/ Ga) is preferably 0.5 or less. This is because a gallium nitride-based compound semiconductor containing In is more likely to form a layer having a higher electron carrier concentration than one not containing it, and a crystal containing In is softer than a crystal not containing In, and a crystal such as dislocation Easy to absorb crystal defects. Therefore, when the first n-type layer 3 which is not lattice-matched, such as AlGaN or GaN, is grown on the substrate, the crystal defects of the first n-type layer 3 are relaxed by the second n-type layer 33. Because it is possible.

The electron carrier concentration of the second n-type layer 33 is 1
× 10¹⁸/cm³~ 1 × 10^{twenty two}/cm³Adjust to the range of
Is preferable, and electron carriers are more preferable than the second n-type layer 33.
The first n-type layer having a low concentration is 1 × 10¹⁶/cm³~ 1 x 1
0¹⁹/cm³It is preferable to adjust to the range. these
The electron carrier concentration is S in the second n-type layer as described above.
Dope an n-type dopant such as i, Ge, Sn, or C.
It can be adjusted by and. The electronic carrier of the second n-type layer 33.
Rear concentration is 1 × 10¹⁸/cm³Less than, spread the electrons
It becomes difficult to obtain the effect of the red light, and uniform emission of the active layer is obtained.
Difficult to get 1 x 10 ^{twenty two}/cm³Crystallinity is worse than
And the performance of the light emitting device may be adversely affected.
The electron carrier concentration of the first n-type layer is also 1 × 1.
0¹⁶/cm³If it is smaller than that, light emission from the active layer itself cannot be obtained.
Kuku, again 1 × 10¹⁹/cm³Greater than 1 μm or more
The crystallinity tends to deteriorate when a thick film of
This is because the output of the child may be reduced.

The thickness of the second n-type layer 33 is usually 10 Å to 1 μm, more preferably 50 Å to 0.3 μm. If the thickness is less than 10 angstroms, the crystallinity is insufficient, so that it is difficult to obtain the action of spreading electrons, and it is difficult to obtain uniform light emission from the active layer. If the thickness is more than 1 μm, the crystal defect is the second n-type layer. Since it is likely to occur in the inside and the crystallinity is deteriorated, the performance of the light emitting element may be deteriorated.

Further, the second n-type layer 33 is made of In, Ga,
2 gallium nitride-based compound semiconductors with different Al composition ratios
It may be a multilayer film in which more than one layer is laminated. When forming the multilayer film, the thickness of each layer is preferably 10 angstrom to 1 μm, more preferably 50 angstrom to 0.3 μm. By forming the second n-type layer 33 as a multi-layer film, crystal defects in the first n-type layer are stopped in the multi-layer film layer, and in the crystal when a gallium nitride-based compound semiconductor that is not lattice-matched is laminated. Since the strain can be relaxed and a semiconductor layer having excellent crystallinity can be grown, the output of the light emitting element can be improved.

Next, FIG. 5 is a schematic sectional view showing the structure of a light emitting device of another embodiment of the present invention. This is because the second n-type layer 33 is formed between the negative electrode 8 formed on the first n-type layer 3 and the substrate 1, and the distance between the second n-type layer 33 and the negative electrode 8 is It indicates that they are approaching. Originally, if the electrode 8 can be formed on the surface of the second n-type layer 33 having a high carrier concentration, electrons flow through the second n-type layer 33 having a high carrier concentration, for example, as compared with FIG. Therefore, Vf of the light emitting element can be reduced. However, when an insulating substrate such as sapphire is used, it is difficult to stop etching at the second n-type layer 33 in terms of production technology. Therefore, as shown in FIG. Vf can be reduced by shortening the distance from the electrode 8 and allowing the electrons injected from the electrode 8 to pass through the second n-type layer 33 having a high carrier concentration.

Further, using sapphire as a substrate, at least an n-type layer, an active layer, and a p-type layer are formed on the surface of the sapphire substrate.
In a light emitting device having a structure in which a p-type layer is sequentially laminated and an electrode is formed on the surface of the n-type layer exposed by etching the p-type layer and the active layer, the second n-type layer 33 is used. , N
Vf can be effectively reduced by forming it between the electrode forming surface of the mold layer and the substrate. Because Si
If the light emitting device has a structure in which a gallium nitride compound semiconductor is grown on the surface of a conductive substrate such as C, ZnO, or Si, then n
The electrodes of the mold layer can be formed on the substrate side, and the electrons on the n layer side are supplied perpendicularly to the active layer. On the other hand, the element having the sapphire substrate as described above is supplied in parallel to the active layer. The distance that electrons supplied vertically move through the n-type layer is several μm at the most, whereas the distance that electrons supplied in parallel travel several tens to several hundreds μm. Therefore, in an element in which electrons are supplied in parallel, by increasing the carrier concentration of the second n-type layer in which electrons are supplied in parallel, the electrons easily move and Vf can be reduced.

[0020]

【Example】

Example 1 A buffer layer 2 made of GaN is grown to a thickness of 0.02 μm on the surface of a substrate 1 made of sapphire having a diameter of 2 inches by MOVPE method. This surface of the buffer layer 2 as the first n-type layer, the n-type contact layer 3 made of n-type GaN electron carrier concentration of 5 × ^10/18 cm ³ doped with Si is grown to the thickness of 1 [mu] m.

Next, a second n-type is formed on the surface of the n-type contact layer 3.
Si layer-doped electron carrier concentration of 1 × 1
An 0 ²⁰ / cm ³ n-type In0.1Ga0.9N layer is grown to a thickness of 0.05 μm.

Next, an n-type contact layer 3'made of GaN similarly doped with Si and having an electron carrier concentration of 5 × 10 ¹⁸ / cm ³ is grown to a film thickness of 3 μm.

Si is deposited on the surface of the n-type contact layer 3 '.
Electron carrier concentration 1 × 10 ¹⁸/cm³N-type Al
N-type clad layer consisting of 0.2 Ga 0.8 N with a thickness of 0.1 μm
It is grown thick, and Si and Zn-doped n-type In0.1 is grown on it.
The active layer 5 made of Ga0.9N has a thickness of 0.1 μm and Mg
P-type cladding layer 6 made of Al0.2Ga0.8N and Mg
A p-type contact layer 7 made of doped GaN is grown in order.
And stack.

The wafer obtained as described above is put into an annealing apparatus and annealed at 700 ° C. to make the p-type cladding layer 6 and the p-type contact layer 7 into a p-type having a lower resistance, and then the p-type contact layer. A mask having a predetermined shape is formed on the surface of 7, and etching is performed from the p-type contact layer side to expose the n-type contact layer 3 '.

After that, according to a conventional method, a positive electrode 9 is formed on the p-type contact layer 7 and a negative electrode 8 is formed on the exposed n-type contact layer 3 ', and then separated into chips, as shown in FIG. A blue light emitting device having a structure was used. When light was emitted from this light emitting element, uniform surface emission with a main emission wavelength of 450 nm was observed from the active layer 5, and V was measured at a forward current (If) of 20 mA.
f was 3.3 V, and the light emission output was 1.8 mW.

[Example 2] On the surface of the buffer layer 2, the first
Electron concentration of 1 × 10 as n-type layer of¹⁸/cm ³G
The n-type contact layer 3 made of e-doped GaN having a thickness of 1 μm
It grows to a film thickness, and the electron carrier concentration is 5 × 10 on the surface.²⁰
/cm³A second n of Ge-doped In0.2Ga0.8N of
The mold layer is grown with a film thickness of 0.01 μm. Then the second n
The surface of the mold layer 33 also has an electron carrier concentration of 1 × 10¹⁸/
cm³N-type contact layer made of Ge-doped n-type GaN
3'is 2 μm and the electron carrier concentration is 5 × 10²⁰/cm³of
Second n-type layer made of Ge-doped n-type In0.2Ga0.8N
33 'is 0.01 μm and the electron carrier concentration is 1 × 10.¹⁸
/cm³Ge-doped n-type GaN layer with a thickness of 1 μm
Grow to.

After that, the n-type cladding layer 4, the active layer 5, the p-type cladding layer 6 and the p-type contact layer 7 are formed in the same manner as in the first embodiment.
Were laminated to form a blue light emitting device having a structure as shown in FIG. However, as shown in FIG. 6, the etching depth from the p-type contact layer 7 was up to the n-type contact layer 3 ′, and the negative electrode 8 was formed on the surface of the n-type contact layer 3 ′. Then, when this light emitting device was caused to emit light, uniform surface emission was observed from the active layer 5 as in Example 1, and If 20 m
In A, Vf was 3.2 V and the emission output was 2.0 mW.

[Example 3] On the surface of the buffer layer 2, the first
Electron concentration of 1 × 10 as n-type layer of¹⁸/cm ³Of S
n-type contact layer 3 made of i-doped Al0.1Ga0.9N
Are grown to a film thickness of 3 μm. Next, the electronic key
Carrier concentration 1 × 10²⁰/cm³Si-doped In0.2Ga0.
8N 0.01μm, electron carrier concentration 1 × 10²⁰/ C
m³Si-doped Al0.05Ga0.95N of 0.01 μm
A second n-type layer 33 in which five layers are alternately laminated.
Grow.

Next, Si and Z are formed on the surface of the second n-type layer 33.
The active layer 5 made of n-doped n-type In0.1Ga0.9N is formed into a thin film.
1 μm, a p-type clad layer 6 made of Mg-doped Al 0.2 Ga 0.8 N, and a p-type contact layer 7 made of Mg-doped GaN are sequentially grown and laminated. That is, the active layer 5, the p-type cladding layer 6, and the p-type contact layer 7 are grown in the same manner except that the n-type cladding layer 4 of Example 1 is not grown. After that, etching is performed in the same manner as in Example 1, and
A light emitting device having a structure as shown in FIG. When this light emitting device was made to emit light, uniform surface emission was similarly obtained from the active layer 5, and Vf was 3.5 V at If 20 mA, and the light emission output was 2.2 mW.

Comparative Example 1 In Example 1, the second n
A light emitting device having a structure as shown in FIG. 1 was obtained in the same manner except that the GaN contact layer was continuously grown to a film thickness of 4 μm without growing the mold layer 33. As shown in FIG. 2, the active layer of this light emitting element emitted strong light between the positive electrode 9 and the negative electrode 8, and uniform light emission could not be obtained. Also, at If 20 mA, Vf is 3.6 V and the light emission output is 1.
It was 2 mW.

[0031]

As described above, the light emitting device of the present invention can realize a device having improved emission output by obtaining uniform surface emission from the active layer. Further, in the light emitting element in which the second n-type layer 33 is formed between the negative electrode 8 and the substrate 1 as in Examples 1 and 2, Vf is obviously lowered. Example 3
Vf because the second n-type layer is not between the substrate and the negative electrode.
However, since the second n-type layer is a multilayer film, the number of crystal defects in the active layer, the p-type cladding layer, and the p-type contact layer is small, and the light emission output is improved. As described above, in the light emitting device of the present invention, since the second n-type layer having a high carrier concentration is formed in contact with the first n-type layer on the active layer side, uniform surface emission is obtained, and the light emission output is obtained. It is possible to realize an element having improved

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a conventional light emitting element.

FIG. 2 is a schematic cross-sectional view showing a light emitting state of the light emitting element of FIG.

FIG. 3 is a schematic cross-sectional view showing the structure of a light emitting device according to an embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view showing a light emitting state of the light emitting element of FIG.

FIG. 5 is a schematic cross-sectional view showing a light emitting state of a light emitting element of another embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view showing the structure of a light emitting device of another embodiment of the present invention.

[Explanation of symbols]

1 ... Substrate 2 ... Buffer layer 4 ... N-type clad layer 5 ... Active layer 6 ... P-type clad layer 7 ... P -Type contact layer 8 ... Negative electrode 9 ... Positive electrode 3, 3 ', 3 "... First n-type layer (n-type contact layer) 33, 33' ... ..Second n-type layer

Claims (3)

[Claims] 1. A gallium nitride-based compound semiconductor light-emitting device having a structure in which at least an n-type layer is formed between an active layer and a substrate, wherein the n-type layer is a first n-type layer formed on the substrate side. And a second n-type layer formed in contact with the first n-type layer on the active layer side and having an electron carrier concentration higher than that of the first n-type layer. Compound semiconductor light emitting device. 2. A gallium nitride-based compound semiconductor (In _x Al _y Ga) in which the second n-type layer contains at least indium.
_The gallium nitride-based compound semiconductor light-emitting device according to claim 1, wherein _1-XY N, 0 <X, 0 ≦ Y, X + Y ≦ 1). 3. The first n-type layer comprises a multi-layer film in which two or more gallium nitride-based compound semiconductor layers having different compositions are stacked.
2. A gallium nitride-based compound semiconductor light emitting device according to.