JPH06275867A - Method for converting gallium nitride-based compound semiconductor into p-type - Google Patents

Abstract

PURPOSE:To realize a p-n junction by a method wherein a gallium nitride-based compound semiconductor which has been doped with a p-type dopant is etched, uneven parts are formed on its furface and the compound semiconductor is annealed at a specific temperature. CONSTITUTION:A gallium nitride-based compound semiconductor 1 which has been doped with a p-type dopant is etched, uneven parts are formed on its surface, and the gallium nitride-based compound semiconductor is annealed at a temperature of 400 deg.C or higher. Its annealing operation is performed in a nitrogen atmosphere which has been pressurized ay a decomposition pressure or higher of the gallium nitride-based compound semiconductor at its annealing temperature in order to prevent N in the gallium nitride-based compound semiconductor such as GaN, GaAlN or the like from being decomposed and discharged. Thereby, a p-type whose resistance is low is formed, a resistance value is made uniform on the whole wafer irrespective of a film thickness, and a p-n junction can be realized.

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 a p-type having a low resistance.

[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. However, in this method, only the penetration depth of the electron beam, that is, only the extreme surface can be lowered, and since the entire wafer must be irradiated while scanning the electron beam, there is a problem that the resistance cannot be uniformly lowered in the plane. there were. In order to solve this problem, in Japanese Patent Application No. 3-357046, we proposed a technique of annealing a i-type gallium nitride compound semiconductor layer at 400 ° C. or higher to make it a low-resistance p-type.

[0004]

If a gallium nitride-based compound semiconductor doped with a p-type dopant can be made into a p-type having a lower resistance, a high emission output homostructure, double hetero, single hetero, etc. Since it becomes possible to realize a light-emitting element having a heterostructure of, and the light-emitting element can be put into practical use,
That low resistance technology is required

Therefore, an object of the present invention is to make a gallium nitride-based compound semiconductor doped with a p-type dopant into a p-type having a lower resistance and to make the resistance value uniform over the entire wafer regardless of the film thickness. , P-n junction can be realized to provide a p-type method for a gallium nitride-based compound semiconductor.

[0006]

A method for converting a gallium nitride-based compound semiconductor into a p-type according to the present invention is to etch a gallium nitride-based compound semiconductor doped with a p-type dopant,
After the step of forming unevenness on the surface and forming the unevenness,
And a step of annealing the gallium nitride compound semiconductor at a temperature of 400 ° C. or higher.

In the method of the present invention, the gallium nitride-based compound semiconductor doped with a p-type dopant contains a p-type dopant such as Zn, Mg, Cd, Be or Ca.
GaN, GaAlN, InGaN, InAlGaN, etc.,
General formula InXAlYGa1-X-YN (0≤X <1, 0≤Y <
A known gallium nitride-based compound semiconductor represented by 1) may be used. Further, the gallium nitride-based compound semiconductor can be grown by a vapor phase growth method such as a metal organic vapor phase epitaxy method and a molecular beam vapor phase epitaxy method.

Either dry etching or wet etching may be used to etch the gallium nitride compound semiconductor. For example, a reactive ion etching (RIE) apparatus can be used for dry etching, and phosphoric acid is used for wet etching. A mixed acid of sulfuric acid and sulfuric acid can be used. By performing these etchings, unevenness can be formed on the gallium nitride-based compound semiconductor to increase the surface area. The etching depth is not particularly limited, but preferable unevenness can be provided by preferably etching by 0.1 μm or more.

Annealing: Annealing
Can be performed using an annealing device after the etching is completed. Annealing atmosphere is vacuum, N2, H
It is preferable to carry out in an atmosphere of an inert gas such as e, Ne, Ar, or a mixed gas thereof, and most preferably, in a nitrogen atmosphere pressurized at a decomposition pressure of the gallium nitride-based compound semiconductor or more at the annealing temperature. Is preferred. Because by pressurizing as a nitrogen atmosphere,
This is because N has a function of preventing N in the gallium nitride-based compound semiconductor such as GaN or GaAlN from decomposing and flowing out during annealing. For example, in the case of GaN, Ga
The decomposition pressure of N is about 0.01 at 800 ° C., about 1 at 1000 ° C., and about 10 at 1100 ° C. Therefore, when the gallium nitride-based compound semiconductor is annealed at 400 ° C. or higher, the gallium nitride-based compound semiconductor is more or less decomposed, and its crystallinity tends to deteriorate. Therefore, the decomposition can be prevented by pressurizing with nitrogen as described above.

The annealing temperature can be 400 ° C. or higher, preferably 600 ° C. or higher, and the annealing can be performed for 1 minute or more, preferably 10 minutes or more. Even at 1000 ° C. or higher, decomposition can be prevented by pressurizing with nitrogen as described above.

[0011]

It is presumed that the reason why the high resistance gallium nitride compound semiconductor has a low resistance due to the annealing is as follows. That is, NH ₃ is generally used as the N source in the growth of the gallium nitride-based compound semiconductor layer. NH ₃ is decomposed during growth to form atomic hydrogen, and this atomic hydrogen is doped with M as an acceptor impurity.
It is considered that the bonding with g, Zn and the like prevents the p-type dopant such as Mg and Zn from functioning as an acceptor. Therefore, a gallium nitride-based compound semiconductor doped with a p-type dopant as in the past has a high resistance i-type. However, by performing annealing after the growth, hydrogen bonded in the form of Mg-H, Zn-H, etc. is thermally dissociated, and the hydrogen is released from the i-type gallium nitride-based compound semiconductor layer and normally p Since the type dopant acts as an acceptor, the gallium nitride compound semiconductor has a low resistance and becomes p-type.

Therefore, as in the present invention, the conventional high resistance i
By etching a gallium nitride-based compound semiconductor of the type and providing unevenness on the surface to increase the surface area, it is possible to increase the area through which hydrogen comes out, and it is possible to easily obtain a low resistance p-type.

FIG. 1 is a schematic cross-sectional view showing a cross-sectional shape of irregularities formed on a gallium nitride compound semiconductor 1 doped with a p-type dopant by etching. Also, FIG.
FIG. 2 is a schematic cross-sectional view showing a cross-sectional shape in which the side surface of the gallium nitride-based compound semiconductor 1 is etched in order to further advance the unevenness shown in FIG. That is,
FIG. 1 shows irregularities of the gallium nitride-based compound semiconductor 1 viewed microscopically, and FIG. 2 shows irregularities of the gallium nitride-based compound semiconductor 1 macroscopically observed, both of which are within the scope of the present invention. 2 to 5, reference numeral 2 denotes a material for growing an n-type gallium nitride compound semiconductor, a gallium nitride compound semiconductor doped with a p-type dopant such as a substrate.

Further, as shown in FIG. 3, the recess of FIG. 2 may be further etched so as to penetrate the gallium nitride-based compound semiconductor 1, and the recess is formed by etching so as to penetrate. As a result, the side area of the gallium nitride-based compound semiconductor 1 can be exposed to the maximum. Further, FIG. 4 is a perspective view of FIG. 3, but in the case of etching by penetrating the concave portion as described above, the shape of the convex portion of the gallium nitride-based compound semiconductor 1 is H as shown in FIG.
The shape is particularly preferable when a light emitting element is formed because the electrode can be easily formed on the convex portion and the electrode can be integrally formed. Furthermore, when a light-emitting element is formed using a p-type gallium nitride-based compound semiconductor having a low resistance, the film thickness of the gallium nitride-based compound semiconductor doped with a p-type dopant is usually 2 μm or less and is very thin. ,
Since it is very careful to form the recesses as shown in FIG. 2 by controlling the film thickness while etching, it is more productive to perform the etching for the purpose of penetrating from the beginning as shown in FIG. Is also excellent. It is needless to say that in the case of forming the concavo-convex shape as shown in FIGS. 2 and 3, a protective film made of silica, silicon nitride, or the like is provided in advance on the portion to be the convex portion so as not to be etched together with the concave portion. Absent. Further, when the etching is performed through the through holes, it is preferable that the protrusions are formed with a width of 20 μm or less. By setting the width to 20 μm or less, at least the area of the uppermost end of the convex portion, that is, the area not etched by the protective film can be sufficiently reduced by annealing.

In FIG. 6, when a gallium nitride-based compound semiconductor doped with a p-type dopant is annealed, the horizontal axis indicates the annealing temperature (° C.) and the vertical axis indicates the resistivity (Ω · Ω) of the gallium nitride-based compound semiconductor at that temperature. (cm) is taken and it is a figure which compares and shows the change of the resistivity of what was etched (a) and what is not etched (b). For the gallium nitride-based compound semiconductor doped with the p-type dopant, a GaN buffer layer was grown on a sapphire substrate, and Mg-doped Ga was deposited on the buffer layer.
N was grown to a thickness of 4 μm, and etching was performed with a stripe shape as shown in the sectional shape of FIG.
Etching was performed at a depth of 0.5 μm with a pitch of 10 μm, and irregularities were formed.

As shown in this figure, both are annealed at a temperature of 400.degree.
The resistivity of aN sharply decreases. However, comparing the etched product (a) with the unetched product (b), the final resistivity value of the etched product (a) is lower by one digit, and (a) shows At the annealing temperature of 600 ° C., the resistivity value of (b) has already been reached. As described above, by etching the gallium nitride-based compound semiconductor doped with the p-type dopant to increase the surface area, the effect of annealing is further enhanced.

[0017]

The present invention will be described in detail with reference to the following examples. Example 1 A sapphire substrate was placed in a reaction vessel, and after cleaning the sapphire substrate, the growth temperature was set to 5
The temperature is set to 10 ° C., hydrogen is used as a carrier gas, ammonia and TMG (trimethylgallium) are used as source gases, and a GaN buffer layer of about 200 is formed on a sapphire substrate.
It is grown to a film thickness of angstrom.

After the growth of the buffer layer, only TMG is stopped and the temperature is raised to 1030.degree. When the temperature reached 1030 ° C, TMG and ammonia gas were used as the source gas, and cyclopentadienyl magnesium (Cp2
Mg) is used to grow a Mg-doped GaN layer to 4 μm.

After the growth, the wafer is taken out of the reaction vessel, and about 0.5 μm Mg-doped GaN layer is etched by RIE.

After the etching is completed, the substrate is placed in an annealing apparatus and annealed by holding it at 700 ° C. for 20 minutes in a nitrogen atmosphere at atmospheric pressure.

As a result of hole measurement of the p-type GaN layer obtained as described above, excellent p-type characteristics such as a resistivity of 1 Ω · cm and a hole carrier concentration of 2 × 10 ¹⁸ / cm ³ were exhibited.

[Embodiment 2] In Embodiment 1, in the step of growing the Mg-doped GaN layer, TMA (trimethylaluminum) is newly added to the source gas to form a Mg-doped Ga0.9Al0.1N layer having a thickness of 4 μm. Example 1 was carried out in the same manner as in Example 1 except that the p-type was formed.
Similarly, the resistivity is 1Ω · cm, hole carrier concentration is 2 × 1
It exhibited an excellent p-type characteristic of 0 ¹⁸ / cm ³ .

[Embodiment 3] In Embodiment 1, after the Mg-doped GaN layer is grown, stripes of 4 μm pitch are formed on the entire surface with photoresist. After forming the photoresist, a silica film having a thickness of 0.2 μm is formed on the photoresist. After forming the silica film, the wafer is dipped in a solvent and the photoresist is peeled off.
A wafer in which stripes of a silica film having a width of 10 μm and a pitch of 10 μm are formed on the doped GaN layer is obtained.

After etching the Mg-doped GaN layer of this wafer with a mixed acid of phosphoric acid and sulfuric acid to a depth of about 1 μm, the wafer is immersed in hydrofluoric acid to remove the silica film.

The wafer having the unevenness as shown in FIG. 2 obtained by the above steps was annealed in the same manner as in Example 1. The resistivity was 0.5 Ω · cm and the hole carrier concentration was 8 × 10 ¹⁸ / cm ³ and excellent p-type characteristics.

[Embodiment 4] Description will be given with reference to the sectional view of FIG. An n-type GaN layer doped with Si by growing a buffer layer 12 made of GaN on the sapphire substrate 11 in the same manner as in Example 1 and using TMA, ammonia as a raw material gas and silane gas as a dopant gas on the buffer layer 12. 13 is grown to a film thickness of 4 μm. Mg-doped GaN 15 is grown thereon to a film thickness of 1 μm in the same manner as in Example 1 to obtain a homojunction light emitting device wafer.

On the Mg-doped GaN layer of the wafer, a silica film is formed in a stripe shape having a width of 10 μm and a pitch of 10 μm in the same manner as in the third embodiment. In addition, this shape has the Mg-doped GaN layer 1 between the stripes as shown in FIG.
The shape connected in 5.

After forming the silica protective film, it is etched by RIE in the same manner as in Example 1 to a depth of about 1 μm. As a result of this etching, as shown in FIG.
The layer is almost penetrated and partly etched to the n-type GaN layer 13, but this does not have any adverse effect on the light emission characteristics. After that, the silica film is removed with hydrofluoric acid in the same manner as in Example 3.

After removing the silica film, the Mg-doped GaN layer 14
After depositing the electrode 15 on substantially the entire surface of the convex portion of the above and a predetermined position of the Si-doped n-type GaN layer 13, the electrode 15 is placed in an annealing apparatus and annealed in the same manner as in Example 1.

The wafer obtained as described above was processed into chips, and light was emitted as a homo-structured light emitting diode. The forward current was 20 mA and the forward voltage was 5 mA.
V, the light emission output was 70 μW.

[0031]

As described above, according to the method of the present invention, a gallium nitride-based compound semiconductor, which has a high resistance even when doped with a p-type dopant, is changed into a low-resistance p-type by annealing at 400 ° C. or higher. Therefore, it is possible to manufacture devices having various structures. Furthermore, the surface of the gallium nitride-based compound semiconductor doped with the p-type dopant is etched to form irregularities so that the surface area can be increased and the resistance can be further reduced to the p-type. Further, the conventional method using electron beam irradiation can reduce the resistance of only the uppermost pole surface, but in the present invention, the gallium nitride-based compound semiconductor layer doped with p-type impurities by annealing can be made to be p-type as a whole. The p-type layer can be formed uniformly in the plane and even in the depth direction, and the p-type layer can be formed on any layer.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an uneven shape of a gallium nitride-based compound semiconductor according to an example of the present invention.

FIG. 2 is a sectional view showing an uneven shape of a gallium nitride-based compound semiconductor according to an embodiment of the present invention.

FIG. 3 is a sectional view showing an uneven shape of a gallium nitride-based compound semiconductor according to an example of the present invention.

FIG. 4 is a perspective view of FIG.

FIG. 5 is a cross-sectional view showing a structure of a light emitting device having a p-type gallium nitride based compound semiconductor whose resistance is reduced according to an embodiment of the present invention.

FIG. 6 is a diagram showing the relationship between the annealing temperature and the resistivity of a gallium nitride-based compound semiconductor doped with a p-type dopant.

[Explanation of symbols]

1 --- Gallium nitride-based compound semiconductor doped with p-type dopant 11 --- Sapphire substrate 12 --- GaN buffer layer 13 --- Si-doped n-type GaN layer 14 --- Mg-doped GaN layer 15 ... Electrode

Claims (2)

[Claims] 1. A step of etching a gallium nitride-based compound semiconductor doped with a p-type dopant to form irregularities on the surface thereof, and after the irregularities are formed, the gallium nitride-based compound semiconductor is heated at a temperature of 400 ° C. or higher. And a step of annealing the compound gallium nitride-based compound semiconductor to p-type. 2. The p-type of the gallium nitride-based compound semiconductor according to claim 1, wherein the recesses and depressions are formed so that the recesses penetrate the gallium nitride-based compound semiconductor doped with the p-type dopant. Method.