JPH0715041A - Light emitting element of gallium nitride based compound semiconductor - Google Patents

Abstract

PURPOSE:To make a gallium nitride based compound semiconductor layer emit light uniformly in the surface and improve light emission output, by adjusting the carrier concentration of an N-type gallium nitride based semiconductor layer and/or a P-type gallium nitride based compound semiconductor layer, so as to be small in accordance with the distance nearer form a light emitting layer. CONSTITUTION:The following are laminated on a substrate 1; an N<+> type GaN layer 2 as an N-type gallium nitride based compound semiconductor layer, and an N-type Ga1-YAlYN layer 3 whose carrier concentration is smaller than the N<+> type GaN layer 2. The value of Y is adjusted in the range of 0<=Y<1. An InXGa1-X layer 4 as a light emitting layer is laminated where the value of X is adjusted in the range of 0<X<1. As a P-type gallium nitride based compound semiconductor layer, a P-type Ga1-ZAlZN layer 5 and a P<+> type GaN layer 6 whose carrier concentration is larger than the P-type Ga1-ZAlZN layer 5 are laminated. The value of Z is adjusted in the range of 0<=Z<1. Thereby a current can be made to flow uniformly in the whole part of the active layer, and uniform light emission is realized.

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 using a gallium nitride compound semiconductor, and more particularly to a forward voltage (Vf).
And a gallium nitride-based compound semiconductor light emitting device having a high emission output.

2. Description of the Related Art GaN, GaAlN, InGaN, In
Since gallium nitride-based compound semiconductors such as AlGaN have a direct transition and the bandgap changes from 1.95 eV to 6 eV, they are regarded as promising materials for light emitting devices such as light emitting diodes and laser diodes. At present, a light emitting device using this material is a so-called MIS in which a high-resistance i-type gallium nitride compound semiconductor doped with a p-type dopant is stacked on an n-type gallium nitride compound semiconductor.
Blue light emitting diodes with a structure are known.

As an example of a light emitting device having a MIS structure, in JP-A-3-252176, JP-A-3-252177, and JP-A-3-252178, an n-type gallium nitride-based compound semiconductor layer is formed into an i-layer. A technique of forming a two-layer structure of an n layer having a low carrier concentration and an n ⁺ layer having a high carrier concentration in order from the closest order, and / or the impurity concentration of the i layer is n.
A technique of forming a two-layer structure of an i layer having a low impurity concentration and an i ⁺ layer having a high impurity concentration in the order of being closer to the layer is disclosed. However, these MIS structure light emitting elements have very low light emission intensity and light emission output, and since the i-layer having high resistance is used as the light emitting layer, the forward voltage (Vf) is as high as 20 V or more, and thus the light emitting efficiency is poor, and the light emitting element is put to practical use. Was insufficient to do so.

On the other hand, as an idea of a light emitting device using a gallium nitride-based compound semiconductor having a pn junction, for example, Japanese Patent Laid-Open No. 59-228776 discloses GaAl.
An LED having a double hetero structure having an N layer as a light emitting layer has been proposed, and in Japanese Patent Laid-Open No. 4-209577,
An LED having a double hetero structure, which uses non-doped InGaN as a light emitting layer, has been proposed. In addition to these publications, various structures of double hetero structure light emitting elements using a pn junction have been proposed in the related art. However, these techniques have not been realized because it was difficult to make the gallium nitride-based compound semiconductor layer into p-type.

As a technique for realizing a pn junction light-emitting device having an improved light emission output by changing a high-resistance i-type to a low-resistance p-type, we have proposed in Japanese Patent Application No. 3-357046, i-type. A technique has been proposed in which a gallium nitride-based compound semiconductor layer is annealed at 400 ° C. or higher to make it a low-resistance p-type.

[0005]

SUMMARY OF THE INVENTION We have previously proposed a double heterostructure light emitting device using a pn junction by converting a gallium nitride-based compound semiconductor into a p-type by the above-mentioned technique, and have been conventionally proposed. In the double heterostructure, it was discovered that current does not flow evenly between the n-type layer and the p-type layer, and the gallium nitride-based compound semiconductor does not emit light uniformly in the plane. In addition, according to our experiments, a large difference appears in the light emission output due to factors such as the combination of stacked gallium nitride compound semiconductors and the composition ratio. Moreover, the ohmic property of the electrode formed on the p-type gallium nitride-based compound semiconductor depends on factors such as the crystallinity and type of the p-type layer, and the forward voltage (Vf) with respect to the determined forward current is There is a problem that the light emission efficiency becomes high and the light emission efficiency decreases.

Therefore, the present invention has been made for the purpose of solving the above-mentioned problems, and the first object is to provide a structure of a light emitting device having a novel double hetero structure, thereby providing a gallium nitride-based compound. A second object is to make the semiconductor layer emit light uniformly in the plane and improve the light emission output of the light emitting device.
The purpose is to reduce f and improve luminous efficiency.

[0007]

We have further improved a light emitting device having a double hetero structure using a specific gallium nitride compound semiconductor as a light emitting layer, and have an n-type clad layer and / or a p clad layer sandwiching the light emitting layer. It was found that the above problems can be solved by adjusting the carrier concentration. That is, in the gallium nitride-based compound semiconductor light-emitting device of the present invention, the n-type In _X Ga _1-X N is provided between the n-type gallium nitride-based compound semiconductor layer and the p-type gallium nitride-based compound semiconductor layer.
A gallium nitride-based compound semiconductor light-emitting device having a double hetero structure, comprising a (0 <X <1) layer as a light-emitting layer,
The carrier concentration of the n-type gallium nitride-based compound semiconductor layer and / or the p-type gallium nitride-based compound semiconductor layer is adjusted so as to become smaller as it approaches the In _x Ga _{1 -x} N layer. Is characterized by.

FIG. 1 is a schematic cross-sectional view showing the structure of a light emitting device according to an embodiment of the present invention. An n-type gallium nitride compound semiconductor layer (hereinafter referred to as an n-clad layer) is formed on a substrate 1.
As the n ⁺ -type GaN layer 2 and the n _- type Ga _{1 -Y} Al _Y N layer 3 having a carrier concentration smaller than that of the n ⁺ GaN layer 2,
An In _x Ga _1-x N layer 4 is laminated thereon as a light emitting layer, and a p-type gallium nitride-based compound semiconductor layer (hereinafter referred to as a p-clad layer) is formed on the p-type Ga _1-z Al _z N 4 layer. Layer 5
And a p ⁺ -type GaN layer 6 having a carrier concentration higher than that of the p-type Ga _{1 -Z} Al _Z N layer are sequentially stacked to form a double hetero structure.

On the substrate 1, sapphire, SiC, Si, Z
A material such as nO is used, but sapphire is usually used. Further, before growing the n ⁺ GaN layer 2, a buffer layer made of GaN, AlN or the like may be grown on the substrate 1.

In FIG. 1, the n-clad layer has a two-layer structure in which an n ⁺ -type GaN layer 2 and an n-type Ga _{1 -Y} Al _Y N layer 3 are laminated, but this layer is particularly a two-layer structure. No need to
Needless to say, a multi-layer film layer structure in which three or more n-clad layers are laminated may be used as long as the carrier concentration of the n-clad layer is adjusted to be smaller as it approaches the light emitting layer 4. Preferably, the first growth layer is made of n ⁺ -type GaN having the highest carrier concentration, so that the crystallinity is the best, and therefore the n-type Ga _{1 -Y} Al _Y layer grown on the n ⁺ -type GaN layer. The crystallinity of the N layer is also improved, and the light emission output of the light emitting element is improved. The carrier concentration of the n-clad layer is Si, Ge, Se, which is used to dope the gallium nitride-based compound semiconductor.
It can be changed by appropriately changing the doping amount of an n-type dopant such as Te, C, etc., and the carrier concentration is 1 × 10 ¹⁶ / cm 3 to 1 × 10 6 by doping the dopant.
It is preferable to adjust to the range of ²² / cm3.

The light emitting layer 3 is an n-type In _X Ga _1-X N, and if the X value is larger than 0, it is not particularly limited, but 0 <X <0.5.
It is preferable to adjust to the range. As the X value increases, the emission color shifts from the short wavelength side to the long wavelength side, and can be changed to red when the X value is around 1. However, when the X value is 0.5 or more, it becomes difficult to obtain InGaN having excellent crystallinity and it becomes difficult to obtain a light emitting device having excellent light emitting efficiency. Therefore, the X value is preferably less than 0.5.

The n-type In _x Ga ₁ -x n layer 3 has a property of becoming n-type even when it is undoped. However, the n-type dopant described above or the n-type dopant and Zn, Mg, Be or C are used.
It is more preferable to make it n-type by doping with a p-type dopant such as a, Sr, or Ba. FIG. 2 shows that Zn is 1 × 10 ¹⁸
/ Cm ³ doped n-type In0.15Ga0.85N layer and Zn 1 × 10 ¹⁹ / cm ³ and Si 5 × 10 ¹⁹ / cm ³ doped n-type In0.15Ga0.85N layer He-Cd laser FIG. 3 is a diagram showing the photoluminescence (PL) measured at room temperature by irradiating with, and comparing the emission intensities thereof. The spectral intensity of the InGaN layer doped only with Zn is shown by enlarging the actual intensity ten times. As shown in this figure, rather than the PL spectrum (b) of n-type InGaN doped with only Zn, the n-type I doped with Si and Zn was used.
The PL spectrum (a) of nGaN has an emission intensity 10 times or more higher than that of (a), and InG made into n-type by simultaneously doping an n-type dopant and a p-type dopant.
An element using the aN layer as a light emitting layer has the best light emission output. In0.1 doped with Si only at 1 × 10 ¹⁹ / cm 3
The emission spectrum of the 5Ga0.85N layer has an emission peak near 410 nm, and its emission intensity is about half that of (a).
Met.

In FIG. 1, the p-clad layer is p-type Ga.
_{The 1-Z} Al _Z N layer 4 and the p ⁺ -type GaN layer 5 are laminated to form a two-layer structure. However, like the n-clad layer, this layer need not be a two-layer structure. If the carrier concentration is adjusted to be smaller as it gets closer to the light emitting layer 4, a multilayer film layer structure in which three or more p-clad layers are stacked may be used. Preferably, the layer forming the electrode is made of p ⁺ -type GaN having the highest carrier concentration, whereby a preferable ohmic contact with the electrode material can be obtained, Vf of the light emitting element can be lowered, and the light emission efficiency can be improved. . The carrier concentration of the p-clad layer can be changed by appropriately changing the doping amount of the p-type dopant described above, and the carrier concentration is 1 × 10 ¹⁶ / cm 3.
It is preferable to adjust to the range of 1 × 10 ²² / cm 3.

Further, as described above, the p-cladding layer has a lower resistance by annealing at 400 ° C. or higher as disclosed in Japanese Patent Application No. 3-357046 previously filed by us. A p-type can be obtained, and the light emission output of the light emitting element can be improved.

[0015]

The operation of the light emitting device of the present invention will be described with reference to FIG. When the positive electrode 8 and the negative electrode 7 are energized, the current spreads in-plane uniformly in the p ⁺ -type GaN layer 6 having a high carrier concentration. When the current value is increased and an electric field is applied to some extent, p ⁺ type G
The current spread to the aN layer 6 is p-type Ga with a low carrier concentration.
It can evenly spread to the _1-Z Al _Z N layer, and the In _X Ga _1-X N layer 3 can be made to uniformly emit light. there is a similar effect also for n cladding layer, an n-cladding layer n ⁺ -type GaN layer 2
And n-type Ga _{1 -Y} Al _Y N layer 3
_An electric current flows evenly through the _X Ga _{1 -X} N layer 3, uniform light emission is obtained, and the light emission output can be increased.

Further, by limiting the layer having the highest carrier concentration in the n-clad layer to GaN, the crystallinity of the n-type Ga _{1 -Y} Al _Y N layer laminated thereon is improved and the crystallinity is improved. As a result, the light emission output can be increased.

Further, by limiting the layer having the highest carrier concentration in the p-clad layer to GaN, the p ⁺ -type G
The ohmic property with the positive electrode formed on the aN layer is improved, and Vf can be reduced to improve the light emission efficiency.

[0018]

EXAMPLES A method of manufacturing the light emitting device of the present invention by the metal organic chemical vapor deposition method will be described below.

[Example 1] A well-cleaned sapphire substrate was set in a reaction vessel, the inside of the reaction vessel was sufficiently replaced with hydrogen, and then the temperature of the substrate was raised to 1050 ° C while flowing hydrogen to clean the sapphire substrate. I do.

Then, the temperature is lowered to 510 ° C., hydrogen is used as a carrier gas, and ammonia and TMG are used as a source gas.
(Trimethylgallium), a buffer layer made of GaN is grown on the sapphire substrate to a thickness of about 200 Å.

After the growth of the buffer layer, only TMG is stopped and the temperature is raised to 1030.degree. When the temperature reaches 1030 ° C., similarly, TMG and ammonia gas are used as source gases, and silane gas is used as a dopant gas, and an Si ⁺ -doped n ⁺ -type GaN layer is grown to 3.5 μm. The carrier concentration of this Si-doped n ⁺ GaN layer was 1 × 10 ¹⁹ / cm 3.

Subsequently, the flow rate of silane gas is reduced,
0.5 n-type GaN layer with a carrier concentration of 1 × 10 ¹⁸ / cm 3
Grow μm. Thus, the n-clad layer has a two-layer structure having different carrier concentrations.

After the growth of the n-type GaN layer, the source gas and the dopant gas are stopped, the temperature is set to 800 ° C., the carrier gas is switched to nitrogen, TMG, TMI (trimethylindium) and ammonia are used as the source gases, and DEZ ( Diethyl zinc) and silane gas, Z
An n-type In0.15Ga0.85N layer doped with n and Si is grown to 100 angstroms.

Then, the raw material gas and the dopant gas are stopped,
The temperature is again raised to 1020 ° C. and T
MG and ammonia, Cp2Mg as dopant gas
(Cyclopentadienyl magnesium) and Mg
A p-type GaN layer doped with is grown to 0.2 μm.

Subsequently, the flow rate of Cp2Mg gas was increased,
P ⁺ type GaN in which Mg is more heavily doped than the p type GaN layer
The layer is grown 0.3 μm. In this way, the p-clad layer has a two-layer structure with different carrier concentrations.

After the growth of the p ⁺ -type GaN layer, the substrate was taken out from the reaction vessel and was annealed at 70 in a nitrogen atmosphere.
Annealing is performed at 0 ° C. for 20 minutes to further reduce the resistance of the p-type GaN layer and the p ⁺ -type GaN layer. The carrier concentration of the p-type GaN layer is 1 × 10 ¹⁶ / cm 3, p ⁺ GaN
The carrier concentration of the layer was 1 × 10 ¹⁷ / cm 3.

The p-clad layer, the n-type In0.15Ga0.85N layer, and the n-type Ga of the wafer thus obtained were obtained.
Part of the N layer is removed by etching to remove n ⁺ -type GaN
The layer was exposed, and ohmic electrodes were provided on the p ⁺ -type GaN layer and the n ⁺ -type GaN layer, and after cutting into chips of 500 μm square, a light emitting diode was formed according to a conventional method. The entire surface was observed from the sapphire substrate surface. Uniform light emission is obtained, and
At 0 mA, Vf4.0V, emission output 700 μW, emission wavelength 490 nm, and brightness 1.1 cd were obtained.

[Embodiment 2] In Embodiment 1, the n-type Ga is used.
When growing the N layer, TMA (trimethylaluminum) is newly added to the source gas, and the carrier concentration is 1 × 10.
¹⁸ / cm ³ of Si-doped n-type Ga0.9Al0.1N layer with 3.5
Grow μm.

Further, when growing the p-type GaN layer, TMA (trimethylaluminum) is newly added to the source gas, and a Mg-doped p-type Ga0.9Al0.1N layer having a carrier concentration of 1 × 10 ¹⁶ / cm ³ is also added. Grow to 2 μm.

When a blue light emitting diode was obtained in the same manner as in Example 1 except for the above, uniform uniform overall light emission was obtained, Vf 4.0 V at 20 mA, and light emission output 700 μ.
W, emission wavelength was 490 nm, and brightness was 1.1 cd.

[Embodiment 3] A blue light emitting diode is obtained in the same manner as in Embodiment 1, except that the n-clad layer is one Si-doped n-type GaN layer having a carrier concentration of 1 × ¹⁸ / cm 3 and a film thickness of 4 μm. As a result, the same uniform overall light emission was obtained, Vf4.2V at 20 mA, and light emission output of 500 μ.
W, emission wavelength was 490 nm, and brightness was 1 cd.

[Embodiment 4] In Embodiment 1, the p-clad layer is formed of M having a carrier concentration of 1 × ¹⁷ / cm 3 and a film thickness of 0.5 μm.
A blue light emitting diode was obtained in the same manner except that the g-doped p ⁺ -type GaN layer was formed as a single layer. As a result, uniform uniform light emission was obtained, and Vf4.2V at 20 mA and light emission output 5
The emission was 00 μW, the emission wavelength was 490 nm, and the brightness was 1 cd.

[Embodiment 5] In the embodiment 1, the p-cladding layer has a carrier concentration of 1 × 10 ¹⁶ / cm ³ and a film thickness of 0.2 μm.
A blue light emitting diode was obtained in the same manner except that the Mg-doped p-type Ga0.9Al0.1N layer was used as a single layer, and the same uniform overall light emission was obtained. At 20 mA, Vf10V, light emission output 500 μW, light emission wavelength 490 nm, and brightness were obtained. It was 1 cd. Vf increased because the p-clad layer was made of GaAl.
This is because the ohmic property deteriorates because of N.

[0034]

As described above, since the gallium nitride compound semiconductor light emitting device of the present invention has the double hetero structure of the pn junction having n-type InGaN as the light emitting layer, it emits light of the conventional MIS structure. The luminous efficiency and the luminous output are remarkably increased as compared with the device. Also preferably n-type InG
If the aN layer is n-type doped with a p-type dopant and an n-type dopant, the emission output is further increased.

Further, in the light emitting device of the present invention, the carrier concentration of the n-clad layer and / or the p-clad layer sandwiching the InGaN layer is made smaller so as to approach InGaN which is the active layer, so that the entire active layer is made uniform. A current flows and uniform light emission is obtained. In order to maximize the light emission output of the light emitting device, it is preferable that both the n-clad layer and the p-clad layer have the above structure, but either one may be used. By changing the clad layer in this way, the light emission output of the light emitting element can be significantly improved. Further, by preferably forming the p + GaN layer as the electrode forming layer of the p-clad layer, the ohmic property with the electrode is improved, Vf can be lowered, and the luminous efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a gallium nitride-based compound semiconductor light emitting device of one embodiment of the present invention.

FIG. 2 is a diagram showing a comparison of photoluminescence intensities of n-type InGaN layers due to differences in dopants.

[Explanation of symbols]

1 ... substrate 2 ... n
⁺ -Type GaN layer 3 ... N-type Ga _1-Y Al _Y N layer 4 ...
Type In _X Ga _1-X N layer 5 ... P-type Ga _1-Z Al _Z N layer 6 ...
⁺ Type GaN layer 7, 8 ... Electrode

Claims (5)

[Claims] 1. An n-type gallium nitride-based compound semiconductor layer,
n-type In _X between the p-type gallium nitride-based compound semiconductor layer
A gallium nitride-based compound semiconductor light-emitting device having a double hetero structure, which comprises a Ga _1-X N (0 <X <1) layer as a light-emitting layer, wherein the n-type gallium nitride-based compound semiconductor layer and / or the p-type A gallium nitride-based compound semiconductor light-emitting device, wherein the carrier concentration of the type gallium nitride-based compound semiconductor layer is adjusted so as to become smaller as it approaches the In _x Ga _1-x N layer. 2. The n-type gallium nitride-based compound semiconductor layer comprises an n ⁺ -type GaN layer having a high carrier concentration and an n ⁺ -type Ga.
N _- type Ga _{1 -Y} Al _Y N with carrier concentration smaller than that of N layer
2. A layer comprising (0 ≦ Y <1) layers.
2. A gallium nitride-based compound semiconductor light emitting device according to. 3. The p-type gallium nitride compound semiconductor layer comprises a p ⁺ -type GaN layer having a high carrier concentration and a p ⁺ -type Ga.
P-type Ga _1-Z Al _Z N having a carrier concentration smaller than that of the N layer
2. A (0 ≦ Z <1) layer.
2. A gallium nitride-based compound semiconductor light emitting device according to. 4. The gallium nitride-based material according to claim 1, wherein the n-type In _x Ga _{1 -x} N layer is n-type by being doped with an n-type dopant and a p-type dopant. Compound semiconductor light emitting device. 5. The gallium nitride-based compound semiconductor light emission according to claim 1, wherein the p-type gallium nitride-based compound semiconductor layer is annealed at 400 ° C. or higher to reduce the resistance. element.