JPH09129931A - Gan compd. semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the light emitting output. SOLUTION: A GaN compd. semiconductor light emitting element comprises an n-type GaN compd. semiconductor layer 3 on a substrate and p-type dopant doped p-type Ga compd. semiconductor layer 4A thereon. To this layer 4A p-type electrodes 5 are electrically connected by the annealing by which the electrodes 5 make weak the emission of light emitting parts facing at the positions of the electrodes 5 located at a part difficult to remove H from the semiconductor layer 4A and intense the emission of light emitting parts facing at the electrodes 5 located at a part easy to remove H.

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 light emitting devices such as blue light emitting diodes and blue light emitting laser diodes.

[0002]

2. Description of the Related Art Gallium nitride (GaN) and indium gallium nitride (InG) are practical semiconductor materials used for blue light emitting diodes, blue laser diodes and the like.
aN), gallium aluminum nitride (GaAlN), indium aluminum gallium nitride (InAlGaN)
The gallium nitride-based compound semiconductors such as the above have attracted attention.

For example, a blue light emitting element using GaN is M
An IS (Metal-Insulator-Semiconductor) structure is well known, and this structure will be described with reference to the sectional view of FIG. 1 and the 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 transparent substrate. There is. The p-type dopant-doped GaN layer 4 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 the n-type GaN layer 3, for example, Al,
An n-type electrode 6 made of In (in this specification, all electrodes formed on an n-type gallium nitride compound semiconductor are referred to as n-type electrodes) is formed. On the other hand, in the i-type GaN layer 4 doped with the p-type dopant, the p-type electrode 5 made of, for example, Au or In (similarly, in the present specification, it is formed in the gallium nitride-based compound semiconductor doped with the p-type dopant. All electrodes are referred to as p-type electrodes). p
The layer connecting the mold electrodes is not exactly p-type but i-type Ga.
It is the N layer 4. However, since this i-type GaN layer 4 is a GaN layer 4 doped with a p-type dopant, the electrode connected thereto is called a p-type electrode.

As shown in the plan view of FIG. 2, in the blue light emitting device having this structure, the p-type electrode 5 is formed on the entire surface of the i-type GaN layer 4 to uniformly spread the electric field, and the GaN layer 4 is entirely illuminated. 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 p-type light emitting layer is used as the light emitting layer.
The mold electrode 5 is formed. However, the light emitting diode having 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 device having such a high-resistance i-type gallium nitride compound semiconductor has a high forward voltage, and the light emission output is extremely poor.

Therefore, the present invention was developed for the purpose of solving the difficult problem of increasing the light emission output of the conventional blue light emitting element.

[0008]

The inventor of the present invention has found that the above problems can be solved by a peculiar light emitting state that cannot be imagined by the prior art. That is, the gallium nitride-based compound semiconductor light-emitting device of the present invention has at least an n-type gallium nitride-based compound semiconductor layer and a p-type gallium nitride-based compound semiconductor layer containing hydrogen by doping with a p-type dopant on a substrate. Growing up. The p-type gallium nitride-based compound semiconductor layer is annealed to electrically connect the p-type electrode. Furthermore, the gallium nitride-based compound semiconductor light-emitting device of the present invention is a p-type gallium nitride-based compound semiconductor light-emitting device that is subjected to an annealing treatment for electrically connecting a p-type electrode with a p-type gallium nitride-based compound electrically connected to the surface of a p-type gallium nitride-based compound semiconductor layer. The light emission of the light emitting portion corresponding to the position of the p-type electrode in the portion where hydrogen is hardly removed from the compound semiconductor layer is weakened so that the light emission of the light emitting portion corresponding to the position of the p-type electrode in the portion where hydrogen is easily removed is emitted. I'm getting stronger.

The light emitting device of the present invention will be described below with reference to FIG. This light emitting device is provided on the sapphire substrate 1.
A buffer layer 2, an n-type GaN layer 3, and a p-type GaN layer 4A doped with a p-type dopant are stacked, and an annealed p-type electrode 5 is connected to the p-type GaN layer 4A for ohmic contact. ing. Upon annealing, hydrogen contained in the p-type GaN layer 4A is removed, and the resistance of the p-type GaN layer 4A decreases. However, p-type GaN
Hydrogen is not uniformly removed from the entire layer 4A. p-type Ga
When the p-type electrode 5 is formed on the N layer 4A and annealed, hydrogen cannot escape from the crystal right under the p-type electrode 5 and becomes a part where hydrogen is difficult to be removed.
It remains under the mold electrode 5. Therefore, by forming the p-type electrode 5 and annealing, the resistance of the p-type GaN layer 4A in which the p-type electrode 5 is formed can be increased, and the resistance of a portion of the p-type GaN layer 4A where hydrogen is not easily formed can be reduced. That is, the distribution of the electric resistance of the p-type GaN layer 4A can be adjusted. In this state, when the p-type electrode 5 connected to the p-type GaN layer 4A is energized, a current concentrates on the peripheral portion of the p-type electrode 5 and emits light in the vicinity of the peripheral portion of the p-type electrode 5 more strongly than other portions. Let That is, the gallium nitride-based compound semiconductor light-emitting device of the present invention is different from the conventional light-emitting device in which the i-type GaN layer 4 of FIG.
By locally and strongly emitting light in the vicinity of the periphery of the layer 4A and the p-type electrode 5 having a small contact resistance, the overall light emission output is significantly increased. Above, the homozygous LE of FIG.
Although D has been described, for example, a double heterostructure LED
In this case, similarly, strong light can be emitted 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 alloys of these metals can be used. p-type electrode 5
Can be formed in any shape such as dots, stripes, and checkerboard grids. Alternatively, as shown in FIG. 4, after the p-type electrodes 5 are formed independently of each other, they may be overcoated with a conductive material 8 in order to electrically connect these electrodes.

[0011]

In the gallium nitride-based compound semiconductor light-emitting device of the present invention, the current is concentrated and flows near the periphery of the p-type electrode 5 on the p-type GaN layer 4A, so that the emission output of this portion can be increased. For example, as shown in FIG. 3, a light emitting device provided with a p-type electrode 5 is provided with a p-type GaN layer 4A by the electrode 5.
The current flow can be adjusted by changing the electric resistance of the. That is, p-type GaN on which the p-type electrode 5 is formed
The electrical resistance of the layer is changed by annealing. As a result, the electric resistance of the p-type GaN layer 4A, which is the portion below the p-type electrode 5 where hydrogen is hard to be removed by the p-type electrode 5, is reduced by the hydrogen which is not formed by the p-type electrode 5. It is made larger than the p-type GaN layer 4A, which is easy. In the light emitting device having this structure, since the p-type GaN layer, which is a portion directly below the p-type electrode 5 and is hard to remove hydrogen, has a large resistance, it is difficult for current to flow, and the p-type electrode 5 has a lower peripheral portion. Since the p-type GaN layer has a small resistance, a current easily flows. Therefore, the electric current tends to concentrate on the peripheral portion of the p-type electrode 5,
The light emission output of the light emitting portion corresponding to this portion can be increased.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. However, the examples shown below exemplify a light emitting device 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, overall structure and arrangement, etc. It is not specific to one. 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 the C surface of a sapphire substrate 1 which is a transparent substrate by using a MOCVD device.
It is grown to a film thickness of 00 angstrom. GaN
An n-type GaN layer 3 doped with Si is grown on the buffer layer 2 to a film thickness of 4 μm. Further, a Mg-doped p-type GaN layer 4A 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. There is.

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 are provided on the n-type GaN layer 3, respectively. The electrodes 5 and 6 are formed as follows. 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 etching is completed, the resist is peeled off, and the pattern of the electrodes 5 and 6 is formed again with the photoresist. Al is deposited on the n-type GaN layer 3 and the p-type GaN layer 4
Ni is vapor-deposited on A to form an n-type electrode 6 and a p-type electrode 5, respectively. The p-type electrode is a stripe having a width of 30 μm, and the stripe interval is 10 μm, and 15 pieces are provided on one chip. After forming both electrodes, the wafer is annealed at 700 ° C. In order to electrically connect the stripe-shaped 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 electrical resistances of the p-type GaN layer 4A on which the p-type electrode 5 is formed and the p-type GaN layer 4A not formed are changed by annealing to adjust the electric resistance. As a result, the electric resistance of the lower p-type GaN layer 4A in which the p-type electrode 5 is formed, which is a portion where hydrogen is difficult to be removed in the annealing process, is changed to the p-type GaN where the p-type electrode, which is a portion where hydrogen is easily removed, is not formed. It is made larger than the layer 4A. In the light emitting device having this structure, since the p-type GaN layer below the p-type electrode 5 has a large resistance, it is difficult for current to flow, and the p-type GaN layer below the peripheral edge of the p-type electrode 5 is difficult.
Since the resistance of the layer 4A is small, the current easily flows. Therefore, the electric current concentrates on the peripheral portion of the p-type electrode 5, and the light emission output of this portion can be increased.

In the light emitting device of the present invention, the resistance of the lower p-type GaN layer 4A having the p-type electrode 5 formed by annealing is increased, and the resistance of the p-type GaN layer 4A not formed is decreased. After forming the p-type electrode 5 on the p-type GaN layer 4A,
This state can be realized by removing hydrogen contained in the p-type GaN layer in which the p-type electrode 5 is not formed. p-type GaN
The electric resistance of the layer 4A is increased by the hydrogen contained in the p-type GaN layer 4A. Hydrogen is included in the GaN layer when the GaN layer is grown. It is extremely difficult to completely remove hydrogen when growing a GaN layer. That is Ga
A p-type dopant in which a compound gas containing hydrogen and nitrogen such as ammonia is used as a nitrogen source during the growth of the N layer, the ammonia is decomposed during the growth to form atomic hydrogen, and this hydrogen atom is inevitably doped as an acceptor. This is because the p-type dopant is inactivated by combining with (for example, Mg, Zn). 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 hydrogen is released from the p-type dopant (M) and hydrogen (H) that are bonded in the MH state, so that the acceptor dopant is activated and holes are formed. The generation of holes further reduces the resistance of the p-type GaN layer 4A. When p-type electrode 5 is formed on p-type GaN layer 4A and annealed at 700 ° C., for example, p
Directly below the die electrode 5 is a portion where hydrogen is difficult to be removed, and hydrogen cannot escape from the crystal from this portion, and remains under the p-type electrode 5. Therefore,
By forming the p-type electrode 5 and annealing,
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 a portion where it is not formed can be decreased. That is,
The distribution of the electric resistance of the p-type GaN layer 4A can be adjusted. As described above, the p-type electrode 5 is the p-type GaN layer 4A.
Suppress the removal of hydrogen from the. p-type GaN layer 4A
The hydrogen is rapidly removed in the portion without the p-type electrode, but the removal of hydrogen is hindered by the p-type electrode 4A in the portion covered with the p-type electrode 4A. Therefore, p-type GaN
In a gallium nitride-based compound semiconductor light-emitting device in which a p-type electrode is laminated on a layer, when the p-type electrode is annealed to make an electrical connection, the p-type electrode causes the p-type GaN layer to be separated from hydrogen and a portion where hydrogen is easily removed. The part that is difficult to remove. When annealing is performed, it is desirable to perform it in an atmosphere containing no hydrogen, and if it is performed in an atmosphere containing hydrogen such as ammonia and hydrazine, there is a possibility that the p-type GaN layer will occlude it again.

When the light emitting device obtained as described above is energized, a large amount of current flows in the peripheral portion of the p-type electrode 5 shown by the arrow A in FIG. This is because the lower p-type GaN layer 4A on which the p-type electrode 5 is formed has a large resistance, and the portion not formed has a small resistance. Therefore, a current flows concentratedly on 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, when the wafer was cut into 1 × 0.8 mm square chips and incorporated in a light emitting diode to emit light, a forward current of 20 mA was applied, and a forward voltage of 5 V was applied.
It emitted light of 30 nm and had a light emission output of 10 μW.

FIG. 5 shows a p-type gallium nitride-based compound semiconductor light emitting device having a different structure. This light emitting element also
Using a MOCVD device, G
The aN buffer layer is grown to a film thickness of 200 Å. A Si-doped n-type GaN layer 3 having a thickness of 4 μm is grown on the GaN buffer layer 2, and a p-type or n-type InGaN layer 9 having a thickness of 100 Å is further formed on the n-type GaN layer 3. This thick I
Mg-doped p-type GaN layer 4A on the nGaN layer 9
And the n-type electrode 6 and the 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 higher than that in the portion where it is not formed. In the light emitting device having this structure, when the p-type electrode 5 and the n-type electrode 6 are energized, InGa
The N layer 9 emits light, and strong 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 used as a light emitting diode, it emitted light of 420 nm at a forward voltage of 5 V at a forward voltage of 20 mA and an emission output of 300 μW.

The light emitting device shown in FIGS. 3 and 5 is a p-type GaN.
Striped p-type electrodes 5 are provided on the layer 4A as shown in FIG. The p-type electrode shown in this figure is provided on almost the entire surface of the p-type gallium nitride compound semiconductor. p
The mold electrode 5 can also be formed as shown in FIGS. The p-type electrode 5 shown in FIG. 7 is formed in a grid pattern, the p-type electrode 5 shown in FIG. 8 is formed in a dot shape, and the p-type electrode 5 shown in FIG. 9 is formed in a concentric linear shape. That is, the shape of the p-type electrode 5 does not matter.

[0023]

In the gallium nitride compound semiconductor light emitting device of the present invention, the p-type gallium nitride compound semiconductor layer is subjected to an annealing treatment for electrically connecting the p-type electrode to weaken the light emission in the portion where hydrogen is difficult to be removed. , The light emission of the part where hydrogen is easily removed is increased. P by annealing process
The p-type electrode in which a part of the type gallium nitride-based compound semiconductor layer is a part from which hydrogen is difficult to be removed makes it difficult to transmit light. In other words, the p-type electrode that covers the p-type gallium nitride-based compound semiconductor layer and does not allow light to easily pass through makes it difficult for hydrogen to pass through during the annealing process. This is because it is difficult for the p-type electrode covering the p-type gallium nitride based compound semiconductor layer to pass hydrogen that is removed from the p-type gallium nitride based compound semiconductor layer even in the annealing treatment, in a state where light is not transmitted through. . The gallium nitride-based compound semiconductor light-emitting device of the present invention weakens the light emission of a portion where hydrogen is difficult to be removed, that is, reduces the light emission of a portion where light is difficult to pass, and allows the portion where hydrogen is easily removed, that is, light is transmitted. Increase the light emission in the easy areas. For this reason, it is possible to increase the overall light emission output by strongly emitting the portion where the light emission can be effectively taken out as an output.

In the gallium nitride-based compound semiconductor light-emitting device of the present invention, hydrogen is expelled from the p-type GaN layer by annealing and the resistance is reduced. The part whose resistance is lowered is
It depends on the p-type electrode formed on the surface of the p-type GaN layer. p
Hydrogen easily escapes from the p-type GaN layer in the portion where the p-type electrode is not formed, and hydrogen does not easily escape from the p-type GaN layer in the portion where the p-type electrode is formed. Therefore, for example, a current easily flows in the peripheral portion of the electrode, and the peripheral portion emits light stronger than the central portion of the electrode. Therefore, a thin linear p
By providing a long mold electrode or providing a large number of dot-shaped p-type electrodes, it is possible to increase the low-resistance portion of the p-type layer and increase the light emission output.

[Brief description of the drawings]

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

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

FIG. 3 is a sectional view of a light emitting device showing an embodiment of the present invention.

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

FIG. 5 is a cross-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)

[Claims] 1. A n-type gallium nitride compound semiconductor layer and at least a p-type gallium nitride compound semiconductor layer containing hydrogen doped with a p-type dopant are grown on a substrate. The p-type electrode is electrically connected to the gallium-based compound semiconductor layer by an annealing process, and further, the p-type electrode is electrically connected by an annealing process.
By the p-type electrode electrically connected to the surface of the p-type gallium nitride compound semiconductor layer, the light emission of the light emitting portion corresponding to the position of the p-type electrode in the portion where hydrogen is hardly removed from the p-type gallium nitride compound semiconductor layer is generated. A gallium nitride-based compound semiconductor light-emitting device characterized by weakening and strengthening the light emission of the light emitting portion corresponding to the position of the p-type electrode in the portion where hydrogen is easily removed.