JPH11220172A - Gallium nitride compound semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve luminous power conversion efficiency by obtaining light emission which is more uniform than an active layer, to improve the luminous intensity and output of an element and to further lower Vf of the light-emitting element. SOLUTION: 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, the n-type layer contains a first n-type layer 3 formed on the substrate side 1 and a second n-type layer 33 shaped on the active layer 5 side, while being brought into contact with the first n-type layer 3 and having electron carrier concentration which is larger than that of the first n-type layer 3, and the second n-type layer 33 is composed of a gallium nitride compound semiconductor (INx Aly Ga1-x-y N, 0<X, 0<=Y, X+Y<=1 so as to contain at least indium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser diode (L)
D), a light emitting diode (LED) gallium nitride is used in the light-emitting element such as a compound semiconductor (In _a Al _b Ga
_1-ab N, 0 ≦ a, 0 ≦ b, a + b ≦ 1).

[0002]

2. Description of the Related Art At present, a blue LED having a luminous intensity of 1 cd is a gallium nitride-based compound semiconductor (In _a AlbG _).
a _1-ab N, 0 ≦ a, 0 ≦ b, a + b ≦ 1), and FIG.
Has the structure shown in FIG. It consists of a buffer layer 2 made of GaN and a Ga layer on a surface of a substrate 1 made of sapphire.
An n-type layer 3 of N, an n-type cladding layer 4 of AlGaN, an active layer 5 of InGaN,
It has a double hetero structure in which a p-type cladding layer 6 made of GaN and a p-type contact layer 7 made of GaN are sequentially stacked. 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 power 1.2 mW, blue L
The ED shows the highest performance ever.

In the LED having the above-mentioned structure, the substrate 1 can be made of a material such as ZnO, SiC, GaAs, or Si, in addition to sapphire. Generally, sapphire is used. The buffer layer 2 is formed of GaAlN, AlN, or the like in addition to GaN. n-type contact layer 3, n-type cladding layer 4
Is a gallium nitride based compound semiconductor with Si, Ge, Sn, C
GaN-based compound semiconductor doped with an n-type dopant such as Further, the n-type contact layer 3 and the n-type cladding layer 4 may function as a cladding layer and a contact layer as a single n-type layer without being divided into two layers as described above (that is, any one 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
A p-type dopant and / or an n-type dopant such as g, Cd, and Be are doped. The p-type cladding layer 6 and the p-type contact layer 7 are made to be p-type by doping a gallium nitride-based compound semiconductor with a p-type dopant and annealing at 400 ° C. or higher. The p-type cladding layer 6 and the p-type contact layer 7 are formed as a single p-type layer.
It may function as a cladding layer and a contact layer (any of the layers can be omitted as in the case of the n-layer).

[0004]

In the case of a gallium nitride based compound semiconductor, other GaAs, GaP, AlInGaP
In general, compared to the group III-V compound semiconductors described above, it has a property that the current is hardly spread uniformly. So Figure 1
When the LED element having such a structure is realized, there is a problem that the flow of electrons supplied from the n-layer to the active layer concentrates on a portion having a low resistance. FIG. 2 schematically shows light emission of the active layer due to current concentration. This is because the electrons supplied from the negative electrode 8 of the n-type contact layer 3 are, as shown by arrows in FIG.
The active layer 5 flows through the closest distance so that the resistance between the negative electrode 8 of the contact layer 3 and the negative electrode 8 decreases.
Indicates that the light is partially intensely emitted as shown by the shaded portion. Thus, the electrons are transferred to the n-type contact layer 3.
If it does not spread uniformly, there is a disadvantage that uniform light emission cannot be obtained from the active layer 5.

The LED having the above structure has a Vf of 3.6 V
Vf is reduced by 5 V or more as compared with a conventional blue LED made of a gallium nitride-based compound semiconductor having a MIS structure. This shows light emission by the pn junction,
There is still room for improvement in Vf, and further Vf
Is desired.

Accordingly, the present invention has been made in view of such circumstances, and an object of the present invention is to form at least an n-type layer between an active layer and a substrate, such as a double hetero or single hetero. In the gallium nitride-based compound semiconductor light-emitting device having the structure described above, 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 luminous efficiency.

[0007]

Means for Solving the Problems 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 a second n-type layer formed on the active layer side in contact with the first n-type layer and having a higher electron carrier concentration than the first n-type layer Gallium nitride based compound semiconductor containing at least indium (In _x Al _Y Ga _{1 -XYN} , 0 <X, 0 ≦
Y, X + Y ≦ 1).

FIG. 3 shows the structure of a light emitting device according to one embodiment of the present invention.
Shown in The basic structure is almost the same as that of the light-emitting element shown in FIG. 1, but is in contact with the n-type contact layer 3 which is the first n-type layer, and is closer to the active layer 5 than the first n-type layer 3 is. 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 cladding layer 4, the active layer 5, the p-type cladding layer 6, the p-type contact layer 7 and the like are formed of a gallium nitride-based compound semiconductor. And the n-type cladding layer 4 may be a single n-type layer, and the p-type cladding 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.
N or AlN is grown and 10 Å to
It is preferable to form it with a thickness of 0.5 μm.

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

Next, the active layer 5 is preferably grown to a thickness of usually 50 Å to 0.5 μm, and is preferably made of InGaN. InGaN can easily change the emission wavelength of the light emitting element from purple to green by utilizing interband emission depending on the mixed crystal ratio of indium, and furthermore, doping n-type and p-type dopants to make the emission center. Is also easy. Further, the mixed crystal ratio of In to Ga (In / Ga) is preferably 0.5 or less. In more than 0.5
Since GaN has poor crystallinity, it tends to be difficult to obtain a practical light emitting device. The most excellent active layer is an n-type dopant which is doped with an n-type dopant and a p-type dopant and has an In mixed crystal ratio of 0.5 or less.
Preferably, nGaN is used as the active layer.

The p-type layer grown on the active layer 5 is also GaN,
AlGaN is preferable, and the p-type cladding layer 6 is formed with a thickness of 50 Å to 1 μm.
Grows with a thickness of 50 Å to 5 μm. However, the p-type cladding layer 6 need not be formed. GaN, Al as the gallium nitride based compound semiconductor
Preferably, GaN is formed. In these, a single-layered film having good crystallinity easily grows easily, and tends to easily become p-type when doped with a p-type dopant and annealed at 400 ° C. or more.

[0013]

FIG. 4 schematically shows a flow of electrons supplied to the active layer 5 from the n-type contact layer 3 which is the first n-type layer in the light emitting device of FIG. This is because the electrons supplied from the n-type contact layer 3 uniformly spread through the second n-type layer 33 having a high electron carrier concentration as shown by the arrows, so that the active layer 5 emits light uniformly. Is shown. Thus, 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, electrons spread uniformly in the second n-type layer 33, so that uniform surface light emission can be obtained from the active layer 5.

The second n-type layer 33 is made of In containing Indium.
_X Al _Y Ga _{1 -XYN} (0 <X, Y ≦ 0) is preferred, and the mixed crystal ratio of In to Ga (In
/ Ga) is preferably 0.5 or less InGaN. The reason is that a gallium nitride-based compound semiconductor containing In is easier to form a layer having a higher electron carrier concentration than a gallium nitride-based compound semiconductor not containing In. Easy to absorb crystal defects. Therefore, when the first n-type layer 3 such as AlGaN or GaN, which is not lattice-matched, is grown on the substrate, crystal defects of the first n-type layer 3 are alleviated by the second n-type layer 33. Is possible.

The electron carrier concentration of the second n-type layer 33 is 1
× 10¹⁸/cm^Three~ 1 × 10^{twenty two}/cm^ThreeAdjust to the range of
, And more electron carriers than the second n-type layer 33.
The low concentration first n-type layer is 1 × 10¹⁶/cm^Three~ 1 × 1
0¹⁹/cm^ThreeIt is preferable to adjust the range. these
As described above, the electron carrier concentration in the second n-type layer
Doping with n-type dopants such as i, Ge, Sn, C, etc.
And can be adjusted. The electron cap of the second n-type layer 33
Rear concentration is 1 × 10¹⁸/cm^ThreeIf it is smaller than
And it is difficult to obtain a uniform light emission from the active layer.
1 × 10 ^{twenty two}/cm^ThreeIf it is larger than this, the crystallinity is poor.
And the performance of the light emitting element may be adversely affected.
The electron carrier concentration of the first n-type layer is also 1 × 1.
0¹⁶/cm^ThreeIf it is smaller than this, light emission from the active layer itself will be obtained.
Kuku, again 1 × 10¹⁹/cm^ThreeLarger than 1μm
When a thick film is formed, the crystallinity tends to worsen.
This is because the output of the child may be reduced.

The thickness of the second n-type layer 33 is usually 10 angstrom to 1 μm, and more preferably 50 angstrom to 0.3 μm. If the thickness is less than 10 angstroms, the crystallinity becomes insufficient, so that it is difficult to obtain an effect of spreading electrons, and it is difficult to obtain uniform light emission from the active layer. If the thickness is more than 1 μm, crystal defects are caused by the second n-type layer. Since it is likely to be generated inside and the crystallinity is deteriorated, the performance of the light emitting element may be deteriorated.

Further, the second n-type layer 33 includes In, Ga,
Gallium nitride-based compound semiconductors having different Al composition ratios
It may be a multilayer film in which a plurality of layers are stacked. When forming a multilayer film, the thickness of each layer is also preferably 10 Å to 1 μm, more preferably 50 Å to 0.3 μm. By using the second n-type layer 33 as a multilayer film, crystal defects of the first n-type layer are stopped by the multilayer film layer, and the crystal in the case where a lattice-matched gallium nitride-based compound semiconductor is laminated. Can be relaxed and a semiconductor layer having excellent crystallinity can be grown, so that the output of the light emitting element can be improved.

FIG. 5 is a schematic sectional view showing the structure of a light emitting device according to another embodiment of the present invention. This is because a 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 reduced. Indicates 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 as compared with, for example, FIG. Therefore, Vf of the light emitting element can be reduced. However, when an insulating substrate such as sapphire is used, it is difficult in terms of production technology to stop etching at the second n-type layer 33, and therefore, as shown in FIG. 8, the electron injected from the electrode 8 passes through the second n-type layer 33 having a high carrier concentration, so that Vf can be reduced.

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

[0020]

EXAMPLE 1 A buffer layer 2 of GaN is grown to a thickness of 0.02 μm on the surface of a substrate 1 of sapphire having a diameter of 2 inches by MOVPE. As the first n-type layer on the surface of the buffer layer 2, the electron carrier concentration is doped with Si 5 × ^10/18 cm ³ of n-type Ga
An n-type contact layer 3 of N is grown to a thickness of 1 μm.

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

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

Si is doped on the surface of the n-type contact layer 3 '.
Electron carrier concentration 1 × 10 ¹⁸/cm^ThreeN-type Al
An n-type cladding layer of 0.2Ga0.8N is a 0.1 μm film
And grown on top of it with Si and Zn-doped n-type In0.1
The active layer 5 made of Ga0.9N has a thickness of 0.1 μm,
A p-type cladding layer 6 made of Al0.2Ga0.8N;
A p-type contact layer 7 made of doped GaN is sequentially grown.
And stack.

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

Thereafter, 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. This was a blue light emitting device having a structure. When this light-emitting element was caused to emit light, uniform surface light emission with a main emission wavelength of 450 nm was observed from the active layer 5, and the V.V.
f was 3.3 V and the light emission output was 1.8 mW.

Example 2 First surface of the buffer layer 2
Electron carrier concentration of 1 × 10¹⁸/cm ^ThreeG
The n-type contact layer 3 made of e-doped GaN is
It grows with a film thickness and the electron carrier concentration is 5 × 10²⁰
/cm^ThreeSecond n made of Ge-doped In0.2Ga0.8N
The mold layer is grown at a film pressure of 0.01 μm. Then the second n
An electron carrier concentration of 1 × 10¹⁸/
cm^ThreeN-type contact layer made of Ge-doped n-type GaN
3 ′ is 2 μm and the electron carrier concentration is 5 × 10²⁰/cm^Threeof
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 × 10¹⁸
/cm^ThreeGe-doped n-type GaN layer in order of 1 μm thickness.
To grow.

Thereafter, 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 obtain 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 light emission was observed from the active layer 5 as in Example 1, and If20m
In A, the Vf was 3.2 V and the light emission output was 2.0 mW.

Example 3 First surface of the buffer layer 2
Electron carrier concentration of 1 × 10¹⁸/cm ^ThreeS
n-type contact layer 3 made of i-doped Al0.1Ga0.9N
Is grown to a thickness of 3 μm. Next, an electronic key is placed on the surface.
Carrier concentration 1 × 10²⁰/cm^ThreeSi-doped In0.2Ga0.
8N to 0.01 μm, electron carrier concentration 1 × 10²⁰/ C
m^ThreeOf Si-doped Al0.05Ga0.95N to 0.01 μm
N-type layers 33 in which five layers are alternately laminated, respectively.
Grow.

Next, on the surface of the second n-type layer 33, Si and Z
The active layer 5 made of n-doped n-type In0.1Ga0.9N has a thickness of 0.1 mm.
1 μm, a p-type cladding layer 6 made of Mg-doped Al0.2Ga0.8N, 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 the first embodiment is not grown. Thereafter, etching is performed in the same manner as in Example 1, and FIG.
A light emitting device having the structure shown in FIG. When this light emitting device was caused to emit light, uniform surface light emission was similarly obtained from the active layer 5, and at If mA of 20 mA, Vf was 3.5 V and 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 thickness of 4 μm without growing the mold layer 33. As shown in FIG. 2, the active layer of the light emitting device emitted strong light between the positive electrode 9 and the negative electrode 8, and could not obtain uniform light emission. At If 20 mA, Vf is 3.6 V, and light emission output is 1.V.
It was 2 mW.

[0031]

As described above, all of the light-emitting devices of the present invention can obtain uniform surface light emission from the active layer and can realize a device with improved light-emission output. 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 clearly reduced. Example 3
Is Vf because there is no second n-type layer between the substrate and the negative electrode.
Has little effect on the decrease, but since the second n-type layer is a multilayer film, crystal defects in the active layer, the p-type cladding layer, and the p-type contact layer are reduced, and the light emission output is improved. As described above, the light-emitting element of the present invention has a uniform surface emission and a light-emission output because the second n-type layer having a high carrier concentration is formed on the active layer side in contact with the first n-type layer. Can be realized.

[Brief description of the drawings]

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

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

FIG. 3 is a schematic cross-sectional view illustrating a structure of a light-emitting element according to one embodiment of the present invention.

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

FIG. 5 is a schematic sectional view showing a light emitting state of a light emitting device according to another embodiment of the present invention.

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

[Explanation of symbols]

1 ... substrate 2 ... buffer layer 4 ... n-type cladding layer 5 ... active layer 6 ... p-type cladding layer 7 ... p ... Negative electrode 9... Positive electrode 3, 3 ′, 3 ″... First n-type layer (n-type contact layer) 33, 33 ′. ..Second n-type layer

Claims (2)

[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 on the active layer side in contact with the first n-type layer and having a higher electron carrier concentration than the first n-type layer. Is a gallium nitride-based compound semiconductor containing at least indium (In
_A gallium nitride-based compound semiconductor light emitting device comprising: _X Al _Y Ga _1-XY N, 0 <X, 0 ≦ Y, X + Y ≦ 1). 2. The gallium nitride-based compound semiconductor according to claim 1, wherein the second n-type layer comprises a multilayer film in which two or more gallium nitride-based compound semiconductor layers having different compositions are stacked. Light emitting element.