JPH06314821A - Formation of p-type gallium nitride compound semiconductor - Google Patents

Abstract

PURPOSE:To acquire a p-type layer of low resistance by realizing a low resistance of a gallium nitride compound semiconductor layer doped with a p-type dopant and by making it uniform in a depth direction by selective formation. CONSTITUTION:After a protective film is selectively formed in a surface of a gallium nitride compound semiconductor layer doped with p-type dopant, the gallium nitride compound semiconductor layer is annealed at 400 deg.C or higher to realize a low resistance, and a difference of resistivity is provided to the same gallium nitride compound semiconductor layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for converting a gallium nitride-based compound semiconductor doped with a p-type dopant into p-type,
In particular, it relates to a method of providing a difference in resistivity within the same gallium nitride-based compound semiconductor layer.

[0002]

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, in a light emitting device using this material, a high-resistance i (insulator) type gallium nitride compound semiconductor laminated with a p-type dopant (p-type impurity) is laminated on an n-type gallium nitride compound semiconductor. A so-called blue light emitting diode having a MIS structure is known.

A light emitting device having a MIS structure generally has a very low light emission output, which is still insufficient for practical use. 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, for example, JP-A-2-257679 and JP-A-3-218 are known.
Japanese Patent No. 325 discloses a technique of irradiating an i-type gallium nitride compound semiconductor layer with an electron beam. Also, in Japanese Patent Application No. 3-357046, we have proposed a technique for making a low resistance p-type by annealing an i-type gallium nitride compound semiconductor layer at 400 ° C. or higher.

[0004]

As described above, there are roughly two types of p-type conversion methods, electron beam irradiation and annealing. In the method using electron beam irradiation, the portion irradiated with the electron beam is selectively selected. However, there is a disadvantage in that the resistance can be reduced only in the depth direction of electron beam irradiation. On the other hand, the anneal has an advantage that the gallium nitride-based compound semiconductor layer doped with a p-type dopant can be made uniform p-type in the depth direction, but it is difficult to selectively make p-type because the whole is made p-type. There is a drawback. If the gallium nitride-based compound semiconductor layer doped with a p-type dopant can be selectively made p-type, for example, a current confinement layer can be formed in the case of a light emitting device, and a laser diode or the like can be realized. Becomes Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to make a gallium nitride-based compound semiconductor layer doped with a p-type dopant have a low resistance and to select it uniformly in the depth direction. To make it p-type.

[0005]

According to the method of making a gallium nitride-based compound semiconductor p-type according to the present invention, a protective film is selectively formed on the surface of a gallium nitride-based compound semiconductor layer doped with a p-type dopant, and then the nitride film is nitrided. The gallium-based compound semiconductor layer is annealed at 400 ° C. or higher to have a low resistance, and the same gallium nitride-based compound semiconductor layer is provided with a difference in resistivity.

In the p-type conversion method of the present invention, the gallium nitride compound semiconductor doped with a p-type dopant is, for example, a general formula InXAlYGa1-X doped with a known p-type dopant such as Zn, Cd, Be, Mg and Ca. -YN (0≤X
A gallium nitride-based compound semiconductor represented by ≦ 1).
This gallium nitride-based compound semiconductor usually exhibits a high resistance i-type when it is doped with a p-type dopant. further,
By annealing this high-resistance gallium nitride-based compound semiconductor at 400 ° C. or higher, the resistance of the gallium nitride-based compound semiconductor is lowered and the p-type characteristics are exhibited.
In Japanese Patent Application No. 3-357046, we provide a cap layer as a protective film on this i-type gallium nitride compound semiconductor layer and anneal it to prevent decomposition of the gallium nitride compound semiconductor and to reduce p-resistance. Although a technique for forming a mold has been disclosed, it has been found that a different p-type characteristic can be obtained by selectively forming the protective film instead of uniformly forming the i-layer. That is, when the protective film is selectively formed so that the i layer is partially exposed, the exposed i layer becomes a p-type having a particularly low resistance, and the resistance of the gallium nitride-based compound semiconductor in the protective film formed portion is increased. Rate and
A difference can be provided between the exposed portion and the resistivity of the gallium nitride-based compound semiconductor.

The protective film is not particularly limited as long as it is a material that decomposes at 400 ° C. or higher, but it is easy to form it on the gallium nitride-based compound semiconductor by a CVD technique such as vapor deposition or sputtering, and the protective film is later etched. As a material that is easy to peel off and withstands temperatures of 400 ° C or higher, silica,
Any of silicon nitride can be preferably used.

The shape of the protective film can be freely changed depending on the position, shape, etc. of the gallium nitride-based compound semiconductor on which the current is to be concentrated. However, it is preferable that the protective film is formed on the gallium nitride-based compound semiconductor to have a width of at least 20 μm or more. Even if the width is less than 20 μm, the same gallium nitride-based compound semiconductor can be provided with a difference in resistivity, but the difference in resistivity between a formed portion and a non-formed portion is small. In this case, the purpose of concentrating and flowing the current in the low resistance portion tends to be insufficient for achieving the purpose.

The annealing time is appropriately changed in consideration of decomposition of the gallium nitride-based compound semiconductor due to the annealing temperature. Although it is possible to suppress decomposition to a certain extent by providing a protective film, if the protective film is provided at a high temperature for a long time, the resistivity of the portion provided with the protective film and the resistivity of the non-provided portion are likely to approach each other. It tends to be insufficient to achieve the purpose.

[0010]

[Function] A protective film made of SiO ₂ is selectively formed on the Zn-doped GaN layer, the Zn-doped GaN layer is annealed, and then the SiO ₂ film is removed to form the protective film and the protective film. FIG. 1 shows the results of measuring the resistivity of the Zn-doped GaN layer depending on the annealing temperature by attaching two electrodes to the non-formed portion and each electrode. In this figure, (a) is a portion where a protective film is not formed,
(B) shows the resistivity of the Zn-doped GaN layer in the portion where the protective film is formed. As shown in this figure, the resistivity of the Zn-doped GaN layer sharply decreases by annealing at 400 ° C. or higher, but the Zn-doped GaN layer has the same Zn-doping in the portion where the protective film is formed and the portion where the protective film is not formed. Ga
It can be seen that a difference in resistivity appears in the N layer. Therefore, this p-type Ga has a low resistance due to annealing.
When an electrode is formed on the N layer and electricity is applied, the current concentrates in the region (a) having a lower resistance. Therefore, for example, when a laser element is realized, the current confinement layer can be formed here.

The reason why the p-type gallium nitride-based compound semiconductor layer having a low resistance can be obtained by annealing is as follows. When a gallium nitride-based compound semiconductor is grown by a vapor phase growth method, ammonia is used as an N source, hydrogen such as hydrogen or a compound containing hydrogen is used as a carrier gas. It is considered that this hydrogen binds with the p-type dopant in the form of MH in the gallium nitride-based compound semiconductor doped with the p-type dopant (M) and prevents it from functioning as a normal p-type dopant. Therefore, by thermally dissociating H from the p-type dopant bonded in the form of MH by annealing, the p-type dopant normally acts as an acceptor and the resistivity is reduced. When the protective film is selectively formed as in the present invention, the gallium nitride compound semiconductor under the protective film is prevented from being decomposed by heating, and hydrogen is released to reduce the resistivity. On the other hand, the surface of the gallium nitride-based compound semiconductor without the protective film is decomposed to some extent, but since it is exposed to the outside, the amount of hydrogen released is predominantly large, and it is considered that a difference in resistivity appears. However, when the width of the protective film is narrowed, hydrogen under the protective film moves to some extent and escapes, so that it is considered that the difference in resistivity between the portion where the protective film is formed and the portion where the protective film is not formed becomes small.

[0012]

【Example】

[Example 1] 500 μm grown on a sapphire substrate
On both sides of the Mg-doped GaAlN layer 2 at the corners, a protective film 1 made of SiO ₂ having a width of 240 μm is formed by vapor deposition to have a thickness of 2 μm as shown in FIGS.

After forming the protective film, annealing is performed at 700 ° C. for 2 minutes in a nitrogen atmosphere with an annealing device. After annealing, the SiO ₂ film was removed with hydrofluoric acid, and two electrodes were formed in each of the portion where the protective film was formed and the portion where the protective film was not formed, and the resistivity was measured. As a result, the protective film was formed. The area was 100 Ω · cm, whereas the area without the protective film was 2 Ω · cm.

[Example 2] A GaN buffer layer and a Si-doped n-type Ga are formed on a sapphire substrate by MOCVD.
N layer, Si-doped n-type InGaN layer, Mg-doped G
A wafer having a light emitting element structure is prepared by sequentially laminating an aN layer.

Next, on the Mg-doped GaN layer which is the uppermost layer of the wafer, a protective film made of silicon nitride was formed on a chip of 500 μm square as in Example 1, and then the annealing time was set to 5 minutes. Was annealed in the same manner as in Example 1.

After that, the wafer was cut on a chip according to a conventional method, electrodes were formed on the n-type GaN layer and the p-type GaN layer to emit light as a light emitting diode, and the entire surface was made p-type without forming a protective film. The forward voltage is 1 compared to
It was reduced to / 3 or less, and the light emission output was more than doubled.

[0017]

As described above, according to the method of the present invention, a high resistance gallium nitride compound semiconductor doped with a p-type dopant is made to have a low resistance, and the resistivity of the same gallium nitride compound semiconductor layer is increased. A difference can be made. Therefore, when a particularly low resistance portion is provided in the p-type layer of the light emitting device using the method of the present invention as shown in Example 2,
The current concentrates in this low resistance portion, the current density increases, and the injected carriers concentrate. As a result, the forward voltage of the light emitting element is lowered, and the light emission output can be increased.

[0018]

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an annealing temperature and a resistivity of a gallium nitride-based compound semiconductor doped with a p-type dopant.

FIG. 2 is a schematic cross-sectional view showing the structure of a gallium nitride-based compound semiconductor having a protective film according to an embodiment of the present invention.

3 is a perspective view showing the structure of the gallium nitride-based compound semiconductor of FIG.

[Explanation of symbols]

1 ... Protective film 2 ... Gallium nitride-based compound semiconductor doped with p-type dopant

Claims (3)

[Claims] 1. A low resistance is obtained by selectively forming a protective film on the surface of a gallium nitride-based compound semiconductor layer doped with a p-type dopant and then annealing the gallium nitride-based compound semiconductor layer at 400 ° C. or higher. A method for making a gallium nitride-based compound semiconductor p-type, wherein the same gallium nitride-based compound semiconductor layer is provided with a difference in resistivity. 2. The method for converting a gallium nitride-based compound semiconductor to a p-type according to claim 1, wherein the protective film is made of silica or silicon nitride. 3. The method for converting a gallium nitride-based compound semiconductor to a p-type according to claim 1, wherein the protective film has a width of at least 20 μm or more.