JPH06237012A - Semiconductor light emitting element of gallium nitride compound - Google Patents

Abstract

PURPOSE:To increase the light emitting output power of a blue light emitting element by emitting the light from the vicinity of the periphery of a p-type electrode stronger than the other part. CONSTITUTION:At least an n-type gallium-nitride-based compound semiconductor layer and a p-type gallium-nitride-based compound semiconductor layer, wherein P p-type dopand is doped and the resistivity is made to be 1,000OMEGA.cm or less, are provided on a substrate. An n-type electrode 6 and a p-type electrode 5, which undergo annealing and are electrically connected, are formed on the n-type gallium-nitride-based compound semiconductor layer and the p-type gallium-nitride-based compound semiconductor layer, wherein p-type dopant is doped. A current is conducted through the n-type electrode 6 and the p-type electrode 5, and the vicinity of the periphery of the p-type electrode emits the light stronger than the other part. Thus, the light emitting output power of the blue light emitting element can be increased.

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.

In the blue light emitting device having this structure, as shown in the plan view of FIG. 2, a p-type electrode 5 is formed on the entire surface of the i-type GaN layer 4 to uniformly spread the electric field, thereby forming the p-type GaN layer 4. The entire surface is made to emit light and 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 the following configuration. It has at least an n-type gallium nitride-based compound semiconductor layer on a substrate and a p-type gallium nitride-based compound semiconductor layer doped with a p-type dopant and having a resistivity of 1000 Ω · cm or less. An n-type electrode and a p-type electrode that are annealed and electrically connected are formed on the gallium nitride-based compound semiconductor layer and the p-type gallium nitride-based compound semiconductor layer doped with the p-type dopant, It is characterized in that the vicinity of the peripheral edge of the p-type electrode is made to emit light more strongly than other portions by energizing the n-type electrode and the p-type electrode.

The light emitting device of the present invention will be described below with reference to FIG. In this light emitting device, an annealed p-type electrode 5 is connected to the p-type GaN layer 4A doped with a p-type dopant for ohmic contact. The contact resistance with the p-type GaN layer 4 is small in the peripheral portion of the p-type electrode 6 that is annealed and electrically connected to the p-type GaN layer 4A. This is because hydrogen contained in the p-type GaN layer 4A is removed during annealing, and the resistance of the p-type GaN layer 4A is reduced. In this state, when the p-type electrode 6 connected to the p-type GaN layer 4A is energized, the current concentrates on the peripheral portion of the p-type electrode 5,
The vicinity of the peripheral edge of the p-type electrode 5 is made to emit light more strongly than other portions. That is, in the gallium nitride-based compound semiconductor light emitting device of the present invention, contrary to the conventional theory that the i-type GaN layer 4 of FIG. 1 is made to uniformly emit light, the p-type GaN layer 4A and the p-type electrode 5 having a small contact resistance are used. The strong light emission locally in the vicinity of the peripheral edge significantly increases the total light emission output. The homojunction LED of FIG. 3 has been described above.
For example, in the case of a double heterostructure LED, 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 lattices. Further, as shown in FIG. 4, after the p-type electrodes 5 are formed independently of each other, these electrodes are electrically connected. To this end, the conductive material 8 may be overcoated.

[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, the light emitting element provided with the p-type electrode 5 has a p-type GaN layer 4A near the periphery of the electrode 5.
Then, by changing the electric resistance with the p-type GaN layer 4A on which the electrode is not formed, the manner of current flow can be adjusted.
That is, when the electric resistance of the p-type GaN layer 4A near the p-type electrode 5 is increased and the electric resistance of the p-type GaN layer 4A in which the p-type electrode 5 is not formed is decreased, current concentrates on the periphery of the p-type electrode 5. And then it begins to flow. This is because the peripheral edge of the p-type electrode 5 has a smaller contact resistance, so that the electric current concentrates on the peripheral edge of the p-type electrode 5.

[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 is formed.
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 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 electrical resistances of the p-type GaN layer 4A having the p-type electrode 5 formed thereon and the p-type GaN layer 4A not having the p-type electrode 5 are adjusted by annealing. As a result, the lower p-type Ga on which the p-type electrode 5 is formed is
The electric resistance of the N layer 4A is not formed and the p-type GaN layer 4A is not formed.
It is larger than. The light emitting device of this structure has p
The lower p-type GaN layer on which the type electrode 5 is formed has a large resistance, and thus it is difficult for a current to flow.
Therefore, the current flows concentratedly on the peripheral portion of the p-type electrode 5,
The light emission output of this portion can be increased.

The light emitting device of the present invention does not specify a method for increasing the resistance of the p-type GaN layer 4A below the p-type electrode 5 and decreasing the resistance of the p-type GaN layer 4A not formed. After forming the p-type electrode 5 on the GaN layer 4A, p
This state can be realized by removing hydrogen contained in the p-type GaN layer in which the mold electrode 5 is not formed. The electric resistance of the p-type GaN layer 4A is increased by the hydrogen contained in the p-type GaN layer 4A. When growing a GaN layer,
Hydrogen is contained in the GaN layer. 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 a GaN layer, and this ammonia decomposes 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 the dopant (eg, 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
Hydrogen cannot escape from the crystal directly under the mold electrode 5, 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 in which the p-type electrode 5 is formed can be increased, and the resistance of a portion not formed can be decreased. 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 it in an atmosphere containing no hydrogen, and if it is performed in an atmosphere containing hydrogen such as ammonia or hydrazine, there is a possibility that it will be occluded in the p-type GaN layer 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 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 is not particularly limited, and the longer the peripheral edge, the larger the light emitting area,
Luminous efficiency can be increased.

[0023]

The gallium nitride-based compound semiconductor light-emitting device of the present invention has a conventional structure in which the vicinity of the periphery of the p-type electrode formed in the p-type gallium nitride-based compound semiconductor layer is made to emit light at a higher output than other portions. The product can have an outstanding light emission output. Incidentally, the light emitting diode using the light emitting device shown in FIG. 3 according to the embodiment of the present invention has a light emission output of 10 μm at a forward voltage of 4 V and a forward current of 20 mA.
It became W. Further, in the light emitting diode using the light emitting element having the double hetero structure according to the embodiment of the present invention shown in FIG. 5, the light emission output was dramatically improved to 300 μW under the same conditions. The light emitting diode using the conventional MIS structure light emitting element shown in FIG. 1 has a light emission output of only 1 μW at a forward voltage of 15 V and a forward current of 10 mA.
When a forward current of 20 mA was applied, it was thermally destroyed and no light was emitted. This is because the resistivity of the i-type GaN layer is 106 Ω · cm.
This is because, since it is extremely high as described above, the Joule heat rapidly increases and the temperature of the light emitting element rises when the current is increased.

As described above, the light emitting device of the present invention strongly emits light at the peripheral portion of the p-type electrode.
By providing long thin linear p-type electrodes or by providing a lot of dot-like p-type electrodes, it is possible to lengthen the low resistance portion of the p-type layer and increase the light emission output. Further, since light is emitted near the periphery of the p-type electrode, light can be concentrated locally as a dot-shaped p-type electrode, and by using a linear p-type electrode, the light-emitting portion is concentrated linearly. It is also possible.

[Brief description of 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]

DESCRIPTION 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 ... In
GaN layer

Claims (1)

[Claims] 1. A substrate having at least an n-type gallium nitride compound semiconductor layer and a p-type gallium nitride compound semiconductor layer having a resistivity adjusted to 1000 Ω · cm or less by doping with a p-type dopant. The n-type gallium nitride-based compound semiconductor layer and the p-type gallium nitride-based compound semiconductor layer doped with the p-type dopant are each annealed to be electrically connected to the n-type electrode and p.
A gallium nitride system characterized in that a type electrode is formed, and when the n-type electrode and the p-type electrode are energized, the vicinity of the peripheral edge of the p-type electrode is made to emit light more strongly than other portions. Compound semiconductor light emitting device.