JP2868081B2 - Gallium nitride based compound semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride-based compound semiconductor light emitting device mainly used for a light emitting device such as a blue light emitting diode and a blue light emitting laser diode.

[0002]

2. Description of the Related Art Practical semiconductor materials used for blue light emitting diodes, blue laser diodes, and the like include gallium nitride (GaN) and indium gallium nitride (InG).
aN), gallium aluminum nitride (GaAlN), indium aluminum gallium nitride (InAlGaN)
Gallium nitride based compound semiconductors such as

For example, a blue light emitting device using GaN is M
An IS (Metal-Insulater-Semiconductor) structure is well known, and this structure will be described with reference to a cross-sectional view of FIG. 1 and a plan view of FIG. This basically has a structure including a buffer layer 2 made of AlN, an n-type GaN layer 3, and a GaN layer 4 doped with a p-type dopant on a sapphire substrate 1 which is a light-transmitting substrate. I have. The GaN layer 4 doped with the p-type dopant is not a low-resistance semiconductor, but is actually a high-resistance semi-insulator (i-type) having a resistivity of 10 ⁶ Ω · cm or more.

Further, for example, Al,
An n-type electrode 6 made of In (in the present specification, all electrodes formed on the n-type gallium nitride-based compound semiconductor are referred to as n-type electrodes) is formed. On the other hand, the i-type GaN layer 4 doped with the p-type dopant is also formed on the p-type electrode 5 made of, for example, Au or In (similarly, in the present specification, formed on the gallium nitride-based compound semiconductor doped with the p-type dopant). All the electrodes are referred to as p-type electrodes). p
The layer connecting the type electrodes is not exactly p-type but i-type Ga
This is the N layer 4. However, since the i-type GaN layer 4 is a GaN layer 4 doped with a p-type dopant, an electrode connected thereto is called a p-type electrode.

In the blue light emitting device having this structure, as shown in the plan view of FIG. 2, an electric field is uniformly spread by forming a p-type electrode 5 on the entire surface of an i-type GaN layer 4 so that the GaN layer 4 emits light over the entire surface. Thus, the light is extracted from the sapphire substrate side 1.

[0006]

In the light emitting diode having this structure, the i-type GaN layer 4 is used as a light emitting layer, and the light emitting layer has a p-type layer.
Form electrode 5 is formed. However, the light emitting diode of this structure has a drawback that the forward voltage is high and the light emission output is low. The forward voltage is high because the i-type GaN layer 4 is almost an insulator. A light-emitting element having such a high-resistance i-type gallium nitride-based compound semiconductor has a high forward voltage and an extremely poor light-emitting output.

Accordingly, the present invention has been developed for the purpose of solving the difficult problem of increasing the light emission output of the conventional blue light emitting device.

[0008]

The present inventor has found that the above problem can be solved by a unique light emitting state which cannot be imagined by the prior art. That is, the gallium nitride-based compound semiconductor light emitting device of the present invention has the following configuration. It has at least an n-type gallium nitride-based compound semiconductor layer and a p-type gallium nitride-based compound semiconductor layer containing hydrogen doped with a p-type dopant on a substrate. An n-type electrode is electrically connected to the n-type gallium nitride-based compound semiconductor layer, and a p-type electrode is connected to the p-type gallium nitride-based compound semiconductor layer doped with a p-type dopant. Further, the p-type electrode is provided so as to extend over substantially the entire surface of the p-type gallium nitride-based compound semiconductor layer, and has fine voids through which hydrogen gas removed from the p-type gallium nitride-based compound semiconductor layer during annealing is transmitted. It has a gas permeable part. The step of annealing the p-type electrode having the gas permeable portion and electrically connecting the p-type electrode to the p-type gallium nitride-based compound semiconductor layer removes hydrogen gas from the p-type gallium nitride-based compound semiconductor layer by transmitting hydrogen gas. That is, hydrogen gas is removed from the p-type gallium nitride-based compound semiconductor layer in the step of annealing and electrically connecting the p-type electrode to the p-type gallium nitride-based compound semiconductor layer. In the p-type gallium nitride-based compound semiconductor layer from which hydrogen has been removed through the gas-permeable portion, the resistance of the portion from which hydrogen has been removed becomes small, and light is emitted strongly.

Hereinafter, the light emitting device of the present invention will be described with reference to FIG. In this light emitting device, an annealed p-type electrode 5 is connected to a p-type GaN layer 4A doped with a p-type dopant for the purpose of making ohmic contact. The p-type electrode 5 that has been annealed and electrically connected to the p-type GaN layer 4A has a p-type GaN layer 4A
And the contact resistance with the contact is reduced. This is because during annealing, hydrogen contained in the p-type GaN layer 4A is removed, and the resistance decreases. In this state, p-type GaN
When a current is applied to the p-type electrode 5 connected to the layer 4A, the current becomes p
It flows intensively at the peripheral edge of the mold electrode 5 and emits light near the peripheral edge of the p-type electrode 5 more strongly than other portions. That is, the gallium nitride-based compound semiconductor light emitting device of the present invention has the i-type layer G of FIG.
Contrary to the conventional myth that the aN layer 4 emits light uniformly, the overall light emission output is markedly increased by locally emitting light near the periphery of the p-type GaN layer 4A and the p-type electrode 5 having a small contact resistance. Increase it. Although the homojunction LED in FIG. 3 has been described above, for example, in the case of a double heterostructure LED as well, it is possible to emit light strongly near the periphery of the p-type electrode.

For the p-type electrode 5 and the n-type electrode 6, for example, Au, Al, In, Ni, Pt, Cr, Ti or an alloy of these metals can be used. p-type electrode 5
Can be formed in any shape such as a dot, a stripe, or a grid pattern. Further, as shown in FIG. 4, after forming the p-type electrodes 5 independently of each other, it is also possible to overcoat with a conductive material 8 in order to electrically connect these electrodes.

[0011]

The gallium nitride-based compound semiconductor light emitting device of the present invention comprises a step of electrically connecting the p-type electrode to the p-type gallium nitride-based compound semiconductor layer by annealing the p-type electrode. In particular, it is possible to increase the light emission output of a portion that can be effectively used. For example, as shown in FIG. 3, a light emitting element provided with a p-type electrode 5 having a gas-permeable portion has a p-type GaN layer 4A at the gas-permeable portion of the p-type electrode.
Lower the electrical resistance of the That is, p having a gas permeable portion
The light emitting element in which the mold electrode 5 is annealed and is electrically resistive to the p-type GaN layer 4A is formed by p-type Ga by annealing.
The electric resistance of the N layer 4A becomes partially different. The gas permeable portion of the p-type electrode 5 transmits hydrogen gas from the p-type GaN layer 4A in the annealing process. Therefore, p
In the portion corresponding to the gas-permeable portion of the type GaN layer 4A, hydrogen is removed, the electric resistance is reduced, the current easily flows, and the light emission output is increased. When the p-type electrode 5 having the gas permeable portion is annealed and electrically connected to the p-type GaN layer 4A, the hydrogen gas in the p-type GaN layer 4A is permeated and removed. The light emitted from the layer 4A is transmitted. For this reason, the p-type electrode having the gas permeable portion can emit light intensely at a portion where light can be effectively extracted, and can increase the light emission output as a whole.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. However, the following examples illustrate light emitting devices for embodying the technical idea of the present invention, and the light emitting device of the present invention has the following chemical composition of components, the entire structure and arrangement, and the like. It is not something specific. The light emitting device of the present invention can be modified within the scope of the claims.

In the gallium nitride based compound semiconductor light emitting device shown in FIG. 3, a GaN buffer layer 2 is formed on a C-plane of a sapphire substrate 1 which is a light-transmitting substrate by using a MOCVD apparatus.
It is grown with a thickness of 00 Å. GaN
An n-type GaN layer 3 doped with Si is grown on the buffer layer 2 to a thickness of 4 μm. Furthermore, a p-type GaN layer 4A doped with Mg is provided on the n-type GaN layer, a p-type electrode 5 is provided on the p-type GaN layer 4A, and an n-type electrode 6 is provided on the n-type GaN layer. I have.

The light emitting device shown in FIG. 3 has a p-type GaN layer 4A.
And a p-type electrode 5 and an n-type electrode 6 on the n-type GaN layer 3, respectively. The electrodes 5 and 6 are formed as described below. A predetermined pattern is formed with a photoresist on the p-type GaN layer 4A. A part of the p-type GaN layer 4A is etched until the n-type GaN layer 3 is exposed. After the completion of the etching, the resist is peeled off, and the patterns of the electrodes 5 and 6 are formed again with the photoresist. Al is deposited on the n-type GaN layer 3 and the p-type GaN layer 4
A is vapor-deposited with Ni to form an n-type electrode 6 and a p-type electrode 5, respectively. In addition, 15 p-type electrodes are provided on one chip with a stripe width of 30 μm and a stripe interval of 10 μm in order to provide a gas permeable portion with minute voids. After both electrodes are formed, the wafer is annealed at 700.degree. In order to electrically connect the striped p-type electrode 5 provided on the p-type GaN layer 4A, a conductive material 8 such as Au or In is deposited on the p-type electrode 5 as shown in FIG. .

In the light emitting device shown in FIG. 3, the electric resistance of the p-type GaN layer 4A on which the p-type electrode 5 is formed and the electric resistance of the p-type GaN layer 4A located in the gas permeable portion are changed by annealing. As a result, the electric resistance of the lower p-type GaN layer 4A on which the p-type electrode 5 is formed is reduced by the p-type Ga
It is larger than the N layer 4A. In the light-emitting device having this structure, the p-type GaN layer below the p-type electrode 5 formed thereon has a large resistance, so that it is difficult for current to flow. Has a small resistance, so that current easily flows. Therefore, the current flows intensively at the peripheral portion of the p-type electrode 5, and the light emission output at this portion can be increased.

In the light emitting device of the present invention, the resistance of the lower p-type GaN layer 4A on which the p-type electrode 5 is formed by the annealing treatment is increased, and the resistance of the p-type GaN layer 4A in the gas permeable portion is reduced. After the p-type electrode 5 is formed on the p-type GaN layer 4A, hydrogen gas is transmitted through the gas permeable portion of the p-type electrode 5,
This state can be realized. The electric resistance of the p-type GaN layer 4A is increased by hydrogen contained in the p-type GaN layer 4A. When growing the GaN layer, the GaN layer contains hydrogen. It is extremely difficult to completely remove hydrogen when growing a GaN layer. It uses a compound gas containing hydrogen and nitrogen such as ammonia as a nitrogen source during the growth of the GaN layer, and this ammonia is decomposed during growth to form atomic hydrogen, and this hydrogen atom is doped as an acceptor by any means. Dopants (eg, Mg, Z
This is because they combine with n) to inactivate the p-type dopant. Therefore, when atomic hydrogen enters the p-type GaN layer, the hydrogen inactivates the acceptor dopant and increases the resistance of the p-type GaN.

The hydrogen in the p-type GaN layer 4A is, for example, 40
It can be removed by annealing at 0 ° C. or higher. That is, in the GaN layer, only the hydrogen is emitted from the p-type dopant (M) and the hydrogen (H) bonded in the MH state, so that the acceptor dopant is activated and holes are generated. The generation of holes further reduces the resistance of the p-type GaN layer 4A. When annealing is performed at, for example, 700 ° C. in a state where the p-type electrode 5 is formed on the p-type GaN layer 4A,
Hydrogen cannot escape from the portion directly below the type electrode 5 from the crystal, and remains under the p-type electrode 5. Therefore, by forming and annealing the p-type electrode 5, the resistance of the p-type GaN layer 4A on which the p-type electrode 5 is formed can be increased, and the resistance of the portion located in the gas-permeable portion can be reduced. That is, the distribution of the electric resistance of the p-type GaN layer 4A can be adjusted. When performing annealing, it is desirable to perform in an atmosphere containing no hydrogen, ammonia,
When performed in an atmosphere containing hydrogen such as hydrazine, p-type Ga
There is a risk of being reoccluded in the N layer.

When a current is applied to the light emitting device obtained as described above, a large amount of current flows in the peripheral portion of the p-type electrode 5 indicated by the arrow A in FIG. This is because the resistance of the lower p-type GaN layer 4A on which the p-type electrode 5 is formed is large, and the resistance of the gas-permeable portion that is not formed is small. Therefore, current flows intensively at the peripheral portion of the p-type electrode 5 indicated by the arrow A, and this portion emits light with a high light emission output.

Finally, the wafer was cut into chips of 1 × 0.8 mm square and assembled in a light emitting diode to emit light. At a forward current of 20 mA, a forward voltage of 5 V
It emitted light of 30 nm, and the emission output was 10 μW.

FIG. 5 shows a light emitting device of a p-type gallium nitride compound semiconductor having a different structure. This light emitting element also
Using a MOCVD apparatus, G is applied to the C face of the sapphire substrate 1.
The aN buffer layer is grown to a thickness of 200 Å. An n-type GaN layer 3 doped with Si is grown to a thickness of 4 μm on the GaN buffer layer 2, and a p-type or n-type InGaN layer 9 is formed on the n-type GaN layer 3 to a thickness of 100 Å. Grown in thickness, this I
Mg doped p-type GaN layer 4A on nGaN layer 9
And an n-type electrode 6 and a p-type electrode 5 are formed on the n-type GaN layer 3 and the p-type GaN layer 4A.

Also in the light emitting device having this structure, the resistance of the p-type GaN layer 4A in the portion where the p-type electrode 5 is formed is made larger than that in the portion where the p-type electrode 5 is not formed. When a current is applied to the p-type electrode 5 and the n-type electrode 6 in the light emitting element having this structure, InGa
The N layer 9 emits light, and the strong light emission of the InGaN layer 9 near the periphery of the p-type electrode can be observed from the sapphire substrate side. Similarly, when this light-emitting element was a light-emitting diode, it emitted light of 420 nm at a forward voltage of 5 V and a light-emitting output of 300 μW at a forward voltage of 20 mA.

The light emitting device shown in FIGS. 3 and 5 is a p-type GaN
As shown in FIG. 6, a striped p-type electrode 5 having a gas permeable portion with fine voids is provided on the layer 4A.
The p-type electrode 5 shown in this figure is provided so as to extend over almost the entire surface of the p-type gallium nitride-based compound semiconductor layer. The p-type electrode 5 is formed on almost the entire surface as shown in FIGS. The p-type electrode 5 shown in FIG. 7 is formed in a grid pattern, and a number of fine gas-permeable portions are provided in gaps in the grid. The p-type electrode 5 shown in FIG. 8 is formed in a point shape, and a gas permeable portion is provided between the points. The p-type electrode 5 shown in FIG. 9 is formed in a concentric linear shape, and a gas permeable portion is provided in a gap between the lines. That is, the shape of the p-type electrode 5 is not particularly limited.

[0023]

According to the gallium nitride-based compound semiconductor light emitting device of the present invention, a p-type electrode is provided uniformly over substantially the entire surface of the p-type gallium nitride-based compound semiconductor layer, and hydrogen gas can be transmitted through the p-type electrode. A gas permeable portion having fine voids is provided. The p-type electrode including the gas permeable portion is electrically connected to the p-type gallium nitride-based compound semiconductor layer by performing an annealing process. The gallium nitride-based compound semiconductor light emitting device having this structure can be provided over a wide area on the surface of the p-type gallium nitride-based compound semiconductor layer to provide a p-type electrode having a gas permeable portion. P having a gas permeable portion with fine voids
The type electrode can also be provided so as to extend over the entire surface of the p-type gallium nitride-based compound semiconductor layer. This is because the gas transmitting portion transmits light. A p-type electrode without a gas-permeable portion for transmitting light cannot be provided on the entire surface of the p-type gallium nitride-based compound semiconductor layer. This is because light emission from the p-type gallium nitride-based compound semiconductor layer is blocked by the p-type electrode and cannot be extracted. In the light emitting device of the present invention, the p-type electrode is provided with a gas permeable portion having fine voids, so that the p-type electrode can be provided on the entire surface of the p-type gallium nitride-based compound semiconductor layer. In the annealing for electrically connecting the p-type electrode to the p-type gallium nitride-based compound semiconductor layer, the gas permeable portion of the p-type electrode removes hydrogen from the p-type gallium nitride-based compound semiconductor layer and emits light when emitting light. The light emitted by passing through is effectively extracted. In particular, since the p-type gallium nitride-based compound semiconductor layer has a property of strongly emitting light at a portion from which hydrogen is removed, the gas-permeable portion of the p-type electrode is formed by annealing the p-type gallium nitride-based compound semiconductor layer. When the compound semiconductor layer is made to emit light intensely, furthermore, when light is emitted, an ideal feature of effectively extracting this light emission to the outside is realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a conventional light-emitting element.

FIG. 2 is a plan view of the light-emitting element shown in FIG.

FIG. 3 is a cross-sectional view of a light-emitting element showing one embodiment of the present invention.

FIG. 4 is a sectional view showing a state in which a conductive material is overcoated on the p-type electrode shown in FIG. 3;

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

FIG. 6 is a plan view showing another specific example of the shape of the p-type electrode.

FIG. 7 is a plan view showing another specific example of the shape of the p-type electrode.

FIG. 8 is a plan view showing another specific example of the shape of the p-type electrode.

FIG. 9 is a plan view showing another specific example of the shape of the p-type electrode.

[Explanation of symbols]

 1. Sapphire substrate 2. Buffer layer 3. n-type GaN layer 4. i-type GaN layer 4A p-type GaN layer 5. p-type electrode 6. n-type electrode 8. conductive material 9.・ InGaN layer

Claims (1)

(57) [Claims] A substrate comprising at least an n-type gallium nitride-based compound semiconductor layer and a p-type gallium nitride-based compound semiconductor layer doped with a p-type dopant and containing hydrogen;
An n-type electrode is provided on the n-type gallium nitride-based compound semiconductor layer,
In the gallium nitride-based compound semiconductor light emitting device in which a p-type electrode is connected to the p-type gallium nitride-based compound semiconductor layer, the p-type electrode is provided on substantially the entire surface of the p-type gallium nitride-based compound semiconductor layer and is annealed. A gas permeable portion having fine voids through which hydrogen gas is sometimes removed from the p-type gallium nitride-based compound semiconductor layer is provided, and the p-type electrode is annealed to be electrically connected to the p-type gallium nitride-based compound semiconductor layer. A gallium nitride-based compound semiconductor light emitting device, which is connected.