JPH09326534A - Iii-group nitride semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a III-group nitride semiconductor device, consisting of Alx Gay In1-x-y N crystal, generating no cracks on an Si or 6H-SiC crystal substrate. SOLUTION: In the Alx Gay In1-x-y N layer Nt containing III-group nitride semiconductor device formed on a substrate 1 consisting of the crystal having a thermal expansion coefficient smaller than the thermal expansion coefficient of crystal of Alx Gay In1-x-y N (0<=x, y and 0<=x+y<=1), substrate material and a stress alleviation layer S, consisting of the material having the thermal expansion coefficient larger than the ALGay In1-x-y N crystal, are interposed between the substrate 1 and the above-mentioned Alx Gay In1-x-y N layer. Besides, it is desirable that an oxidation preventing layer T, consisting of Al, Ga, In1-x-y N, is interposed between the stress alleviation layer S and the substrate 1. Silicon crystal or carbonated silicon crystal may be used for the substrate material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to group III nitride semiconductors (Al _x Ga
_{The present} invention relates to a group III nitride semiconductor device such as a laser diode or a light emitting diode using _y In _1-xy N (0 ≤x, y and 0 ≤x + y ≤1).

[0002]

2. Description of the Related Art Direct transition and an optical gap of 1.
Group III nitrides (Al _x Ga _y ) controllable in the range of 9 to 6.2 eV
III-nitride semiconductor devices such as laser diodes and light emitting diodes using In _1-xy N (0 ≦ x, y and 0 ≦ x + y ≦ 1)) have been prototyped. Below, the group III nitride is replaced with Al _x
Abbreviated as Ga _y In _1-xy N or AlGaInN. Group III nitride semiconductor devices have been mainly formed on sapphire substrates due to their good matching of crystal lattice and thermal expansion coefficient.
_{Then, Al x Ga y In 1-} xy composition N (x, y) controlling the optical gap by varying the, Si and magnesium (M
Double heterostructure (MCYoo, KHShim, et al .: P by controlling valence electrons to n-type and p-type by adding g)
roceedings of International Symposium on Blue Lase
r and LightEmitting Diodes, Chiba Univ., Japan, Marc
h 5-7, 1996, p554-557) or quantum well structure (S.Nak
amura, et al, J. Japanese Journal of Applied Physics,
Group III nitride semiconductor devices such as vol35, part2, No 2B (1996), L217 to L220) have been reported.

FIG. 8 shows a conventional group III nitride semiconductor device 1
It is sectional drawing of an example laser diode. sapphire
On the substrate 1 consisting of (c-plane), AlN buffer layer 2, GaN
The contact layer 3 is deposited. Furthermore, n-type AlGaN
The double heterostructure is formed by the clad layer 4, the GaN active layer 5, and the p-type AlGaN clad layer 6. A p-type GaN cap layer 7 is formed thereon, and the double hetero structure and the cap layer 7 are collectively photoetched so that the side surfaces are perpendicular to the substrate surface. Due to the low conductivity of sapphire, the contact layer 3 extends to the outside of the double heterostructure for the electrical leads on the substrate side, on which the first electrode layer 8 of Au / Cr is formed. There is. A second layer of Al / Ti is formed on the cap layer 7.
The electrode layer 9 is formed.

[0004] The organic metal vapor phase growth of _{Al x Ga y In 1-xy} N film
(Hereinafter referred to as MOCVD), the substrate temperature is 1000 ℃
In order to raise the temperature to a certain degree, it is necessary to consider the matching of the thermal expansion coefficient in addition to the matching of the lattice constants when selecting the substrate.
Even if the substrate has a good lattice constant match, the coefficient of thermal expansion is Al
_{If a} substrate material smaller than _x Ga _y In _1-xy N is used, tensile stress may occur in the Al _x Gay _{y 1-xy} N film during cooling after film formation, and the film may crack under some circumstances. Known (A. Kuramata, K. Horino, et al .; Proceedings of
International Symposium on Blue Laser and Light Em
itting Diodes, Chiba Univ., Japan, March 5-7, 1996,
p80-85).

Sapphire has been used as a substrate material for depositing Al _x Ga _y In _1-xy N. Sapphire substrate is Al
Lattice matching with _x Ga _y In _1-xy N crystal is good, and the coefficient of thermal expansion of sapphire, α (sapphire) is 7.5 × 10 ^-6
A / K (hereinafter, alpha (substance name) represents a thermal expansion coefficient of the material), the _{Al x Ga y In 1-xy} N α (Al x Ga y In 1-xy
N) = 5.6 × 10 ⁻⁶ / K, so cracks do not occur.

However, the sapphire substrate has the following drawbacks. 1. Since there is no cleavage, an optical resonator in a laser diode cannot be formed by simple cleavage. 2.
The conductivity is low and the electrode cannot be taken from the substrate surface.

[0007]

On the other hand, Si crystal or 6H
-Using a SiC crystal substrate solves the above two drawbacks, but the coefficient of thermal expansion is α (Si) = 3.59 × 10 ^-6 / K, α (6
Since H-SiC) = less than 4.2 × 10 ^-6 / K and _{Al x Ga y In 1-xy} N -based coefficient of thermal expansion (e.g., α (GaN) = 5.6 × 10 -6 / K),
The film shrinks more than the substrate when it is cooled from the deposition temperature (about 1000 ° C) to room temperature after deposition, but since the substrate is thicker than the film, tensile stress occurs on the film side. . As a result, the film may crack. Therefore, a semiconductor device cannot be manufactured. FIG. 9 is a diagram showing a crystal state of a surface of an Al _x Ga _y In _1-xy N film formed directly on a Si crystal substrate, which is observed by a scanning electron microscope. It can be seen that there are cracks.

In view of the above problems, the object of the present invention is to provide Si
Al _x Ga without cracks on crystalline or 6H-SiC crystalline substrate
_An object is to provide a group III nitride semiconductor device made of _y In _1-xy N crystal.

[0009]

In order to achieve the above object, Al _x Ga _y In _1-xy N (0 ≤ x, y and 0 ≤ x + y ≤ 1)
Including an Al _x Ga _y In _1-xy N layer formed on a substrate consisting of a crystal with a thermal expansion coefficient smaller than that of the crystal II
In the group I nitride semiconductor device, the substrate and the Al _x Ga
Substrate material and Al _x Ga _y In between _y In _1-xy N layer
_A stress relaxation layer made of a material having a coefficient of thermal expansion larger than that of the _1-xy N crystal is interposed, and Al _x Ga _y In
_The stress generated in _1-xy N will be relaxed.

The substrate material is preferably silicon (Si) crystal or carbonized silicon (SiC) crystal. The stress relaxation layer is made of at least one of zinc oxide (ZnO), magnesium oxide (MgO), sapphire (α-Al ₂ O ₃ ), spinel (MgAl ₂ O ₄ ), or neodymium gallate (NdGaO ₃ ). good.

Al _x Ga _y is formed between the stress relaxation layer and the substrate.
In _1-xy N (0 ≤ x, y and 0 ≤ x + y ≤ 1) intervening the anti-oxidation layer and formed on the stress relaxation layer and on it
It is preferable to prevent deterioration of the crystallinity of the Al _x Ga _y In _1-xy N film. The group III nitride semiconductor device is preferably a light emitting diode or a laser diode.

[0012]

1 is a cross-sectional view of the layer structure of a group III nitride semiconductor device according to the present invention. Antioxidation layer T, stress relaxation layer S, and then Al _x Ga _y In _1-xy N layer Nt on substrate 1.
Are laminated. The surface of the substrate 1 is the (1,1,1) plane of Si crystal or the (0,0,0,1) plane of SiC crystal. Al _x Ga _y In
_{The 1-xy} N layer Nt consists of multiple layers with different compositions (x, y) and doping. For example, in the case of a diode having a double hetero structure, it is the same as buffer layer 2 to cap layer 7 in FIG. Other semiconductor layers or electrode layers are further laminated depending on the application.

The stress relaxation layer S will be described below. Since the thermal expansion coefficient of the substrate material is smaller than that of the AlGaInN crystal, the deposition temperature (approximately 1000 ° C) after the deposition of AlGaInN
When cooled from room temperature to room temperature, the AlGaInN film shrinks more than the substrate, but since the substrate is thicker than the AlGaInN film, tensile stress occurs on the AlGaInN film side. As a result, cracks may occur in the AlGaInN film. But,
If a layer of material with a coefficient of thermal expansion greater than those of these two materials is inserted between the substrate and the AlGaInN film, this insertion layer will try to shrink the substrate more, ie Since the coefficient of thermal expansion is increased to approach that of the AlGaInN film, the tensile force on the AlGaInN film is relaxed and cracks are prevented in the AlGaInN film. Therefore, this insertion layer is called a stress relaxation layer.

A material suitable for the stress relaxation layer is also required to have a small lattice mismatch rate. Table 1 lists such materials. Table 1 shows the thermal expansion coefficient of materials suitable for the stress relaxation layer.
The lattice mismatch rate with respect to a GaN crystal is shown.

[0015]

【table 1 】 However, since all of these stress relaxation layer materials are oxides, there is concern about oxidation of the Si or SiC surface during film formation.
If the surface of the substrate is oxidized, an amorphous layer is often formed at the interface between the substrate and the oxide material, and the crystallinity of the film formed thereon deteriorates. Therefore, as an anti-oxidation layer T for suppressing oxidation on the substrate, Al _x Ga _y In
_1-xy N is formed extremely thin (about 10 nm), and the stress relaxation layer S is formed on it. _{Finally, Al x Ga y In 1-} xy N
A multilayer AlGaInN layer Nt for a target semiconductor device such as a double hetero structure or a quantum well structure is formed. Molecular beam epitaxy (MBE) or metalorganic vapor phase epitaxy can be applied as a film forming method. Example 1 First, a thickness of 100 n was directly formed on a (1,1,1) plane substrate of a Si single crystal.
A ZnO layer of m 2 was formed. As the sputtering conditions, the substrate temperature was 250 ° C., the sputtering gas was Ar, and the pressure was 1 Pa.
And A ZnO sintered body containing 2 wt% Al was used as the target. The addition of Al is to make the stress relaxation layer conductive.

From the X-ray diffraction pattern, it was confirmed that the obtained ZnO film was c-axis oriented. Figure 2 shows a reflection high-energy electron diffraction (RHEED) image of a ZnO film directly formed on a Si substrate. (A) is a pattern diagram when the electron beam is incident in the (1, -1,1) direction, (B) is a diagram of a case in which the electron beam is incident in the (1,0,0) direction and is rotated by 30 ° in the c-plane with respect to (a). From Fig. 2, it can be seen that the single crystal pattern (only high brightness (large white spots) in (b)) and low brightness (light white spots) in the c-plane of the ZnO film are misaligned. It was found to be a polycrystalline film whose a-axis was rotated.

FIG. 3 is a diagram showing the result of elemental analysis in the depth direction by Auger electron spectroscopy of a ZnO film directly formed on a Si substrate. A large amount of oxygen was detected in the Si substrate area,
It can be seen that the surface of the Si substrate is oxidized. Therefore, Zn
It can be assumed that the polycrystallization of O 2 is caused by the oxidation of the Si surface when forming ZnO. On this ZnO film, a multilayer Al _x Ga _y In _1-xy N film was formed by molecular beam epitaxy (MBE) using nitrogen radicals. The layer structure is the first buffer layer of AlN, the second buffer layer of GaN on it, the cladding layer of n-type AlGaN, the active layer of GaN,
A double heterostructure consisting of a p-type AlGaN cladding layer was used, but no cracks were observed and the effect of the ZnO stress relaxation layer was confirmed.

In order to suppress the oxidation of the surface of the Si substrate, an n-type GaN film having a thickness of 10 nm was formed on the Si substrate as an antioxidant layer. A ZnO stress relaxation layer was formed on it to a thickness of 100 nm. Figure 4 shows the Si substrate
FIG. 6 is a diagram showing the results of elemental analysis in the depth direction by Auger electron spectroscopy of a ZnO 2 film on which a GaN film is formed. As compared with FIG. 3, it can be confirmed from FIG. 4 that the GaN film prevents the oxidation of Si.

FIG. 5 shows Zn formed on the GaN film on the Si substrate.
The RHEED image of the O 2 film is shown, (a) shows (1, -1, -1,
1) Pattern diagram in the case of direction, (b) shows electron beam incidence
It is a figure of a pattern in the case of (1,0,0) direction (it rotated by 30 degrees in c surface with respect to (a)). Unlike the case where no antioxidant layer is formed (Fig. 2), the pattern does not have a double structure, and rotation of the a-axis in the c-plane of ZnO is not observed. From this, it was found that by introducing the GaN layer for suppressing the oxidation, the oxidation of the Si substrate was suppressed, and ZnO was epitaxially grown (single crystal growth).

On this ZnO film, a multi-layer Al _x Ga _y In _1-xy N double heterostructure having the same layer structure as described above is formed,
Further, a cap layer was formed. Figure 6 shows GaN on Si substrate
FIG. 3 is a diagram showing a crystal state of an Al _x Ga _y In _1-xy N film on a double layer of a film and a ZnO 2 film, observed by an electron microscope. From the figure,
It can be seen that the surface is smooth and no cracks are formed. By using the AlGaInN film in this state, a group III nitride semiconductor device such as a photodiode that does not require a particularly fine structure is established.

II of a layer structure including the above-mentioned double hetero structure
A laser diode was manufactured as an example of a group I nitride semiconductor device. FIG. 7 is a sectional view of a laser diode according to the present invention, taken along a plane perpendicular to the cleavage plane. Substrate 1 is the (1,1,1) plane
It is made of Si, and the antioxidant layer 11 and the stress relaxation layer 12 are sequentially laminated. A first buffer layer 2 of AlN having a thickness of 50 nm is formed, and a second buffer layer of GaN having a thickness of 0.5 μm is formed on the first buffer layer 2.
150 nm thick n-type AlGaN cladding layer 4, 50 nm thick GaN
Active layer 5 and p-type AlGaN cladding layer 6 with a thickness of 150 nm
A double heterostructure consisting of 100 nm thick
A p-type GaN cap layer 7 is formed. Substrate 1 electrode 8a
Is Al and the electrode 9 of the cap layer 7 is Au / Cr.

By cleaving the Si substrate 1, the (1, -1,0,0) plane of the group III nitride semiconductor layer becomes a cleavage plane, and an optical resonator can be formed. A pulse current was passed through this laser diode, and laser oscillation was possible at a current density of about 10 kA / cm ² or more. In addition, as an antioxidant layer, Ga _1-x Al _x N
(0 <x ≤ 1) was also carried out, but similarly, there was an effect of preventing oxidation, the stress relaxation layer was a single crystal, and the Group III nitride semiconductor layer could be formed well. Example 2 A (1,1,1) plane of Si single crystal was used as a substrate, and sapphire (α−) formed by magnetron sputtering as a stress relaxation layer.
Al ₂ O ₃ ) was used. The substrate temperature was 500 ° C., the target was a sintered body of Al ₂ O ₃ , the sputtering gas was Ar, the pressure was 1 Pa, and the film thickness was 120 nm.

In the case of the sapphire stress relaxation layer, as in the case of the ZnO stress relaxation layer, Si (1,1,1,
1) Growth on the substrate was c-axis oriented, but rotation in the a-axis direction was observed within the c-plane. However, by introducing the antioxidant layer, both sapphire and the double heterostructure formed thereon were epitaxially grown and no crack was observed. Example 3 A (1,1,1) plane of Si single crystal was used as a substrate, and a stress relaxation layer was formed by magnetron sputtering.
(MgO) was used. The substrate temperature was 400 ° C., the target was a MgO 2 sintered body, the sputtering gas was Ar, the pressure was 1 Pa, and the film thickness was 100 nm. In the case of MgO as well, in the absence of the antioxidant layer, rotation in the a-axis direction within the c-plane was observed, although it was c-axis oriented on the Si (1,1,1) substrate. However,
By introducing the antioxidant layer, both MgO and the double heterostructure formed on it grew epitaxially and no crack was observed. Example 4 A (1,1,1) plane of Si single crystal was used as a substrate, and a spinel formed by magnetron sputtering as a stress relaxation layer.
(MgAl ₂ O ₄ ) was used. The substrate temperature was 600 ° C, the target was MgAl ₂ O ₄ sintered body, and the sputtering gas was Ar.
The pressure was 1 Pa and the film thickness was 120 nm. In the case of spinel, if there is no anti-oxidation layer, c on Si (1,1,1) substrate
Although it was axially oriented, rotation in the a-axis direction within the c-plane was observed. However, by introducing the antioxidant layer, both the spinel and the double hetero structure formed thereon were epitaxially grown, and no crack was observed. Example 5 A (1,1,1) plane of Si single crystal was used as a substrate, and neodigalate (NdGaO ₃ ) formed by magnetron sputtering was used as a stress relaxation layer. The substrate temperature was 700 ° C, NdGaO ₃ sintered body was used as the target, and Ar gas was used as the sputtering gas.
The pressure was 1 Pa and the film thickness was 120 nm. Also in the case of neo digallate, rotation in the a-axis direction within the c-plane was observed in the absence of the antioxidant layer, although it was c-axis oriented on the Si (1,1,1) substrate. However, by introducing the antioxidant layer, both neodigallate and the double hetero structure formed thereon were epitaxially grown, and no crack was observed. Example 6 Further, using a 6H-SiC substrate, an experiment was conducted in which ZnO was used as a stress relaxation layer and a GaN antioxidation layer as in the case of Example 1. The effect of layers was confirmed.

[0024]

According to the present invention, Al _x Ga _y In _1-xy N (0
≤ x, y and 0 ≤ x + y ≤ 1) Al _x formed on a substrate made of a crystal having a coefficient of thermal expansion smaller than that of the crystal
In group III nitride semiconductor device including a Ga _y In _1-xy N layer, the substrate material and _{Al x Ga y In 1-xy} N crystal between the substrate and _{Al x Ga y In 1-xy} N layer The stress generated in Al _x Ga _y In _1-xy N was relaxed by interposing a stress relaxation layer made of a material having a thermal expansion coefficient larger than that of Al _x Ga _y In _1-xy N. no cracks in the III-nitride semiconductor device having a multilayer film composed of _{Al x Ga y in 1-xy} N on a substrate smaller than the film, also individualized by utilizing the cleavage property can be easy.

Further, between the stress relaxation layer and the substrate, Al _{x
Ga y In 1-xy N (} 0 ≦ x, y and 0 ≦ x + y ≦ 1) is interposed antioxidant layer made of, Al _x Ga is formed stress relieving layer and thereon _y In _1-xy N Since the deterioration of the crystallinity of the film is prevented, a light emitting diode or a laser diode having a fine layer structure can be formed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a layer structure of a group III nitride semiconductor device according to the present invention.

FIG. 2 shows a reflection high-energy electron diffraction (RHEED) image of a ZnO film directly formed on a Si substrate.
-1,1) direction pattern, (b) is the case where the electron beam is incident in (1,0,0) direction.
Illustration of pattern when rotated

FIG. 3 is a diagram showing the results of elemental analysis in the depth direction of a ZnO film directly formed on a Si substrate by Auger electron spectroscopy.

FIG. 4 is a diagram showing the results of elemental analysis in the depth direction of a ZnO film having a GaN film formed on a Si substrate by Auger electron spectroscopy.

FIG. 5: RHEE of ZnO film formed on GaN film on Si substrate
D image, (a) shows the pattern when the electron beam is incident in the (1, -1,1) direction, and (b) shows the pattern when the electron beam is incident in the (1,0,0) direction ((a () Rotated by 30 ° in the c-plane))

FIG. 6 Al _x on a double layer of GaN film and ZnO film on Si substrate
Diagram showing the crystal state of the Ga _y In _1-xy N film observed by electron microscopy

FIG. 7 is a sectional view of a laser diode according to the present invention in a plane perpendicular to the cleavage plane.

FIG. 8 is a cross-sectional view of a laser diode which is an example of a conventional group III nitride semiconductor device.

FIG. 9: Al _x Ga _y In _1-xy formed directly on a Si crystal substrate
Diagram showing the state of the crystal observed by scanning electron microscopy on the surface of the N film

[Explanation of symbols]

 1 substrate 2 buffer layer 2a first buffer layer 2b second buffer layer 3 contact layer 4 clad layer 5 active layer 6 clad layer 7 cap layer 8 first electrode layer 8a first electrode layer 9 second electrode layer S stress relaxation layer T oxidation prevention layer Nt AlGaInN layer

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 9, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2 shows a reflection high-energy electron diffraction (RHEED) image of a ZnO film directly formed on a Si substrate.
A photograph of the crystal structure in the (1,1) direction, (b) is the case where the electron beam incidence is in the (1, 0, 0) direction, and is 30 in the c-plane with respect to (a).
Photograph of the crystal structure when rotated by °

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Fig. 5

[Correction method] Change

[Correction contents]

FIG. 5 shows a reflection high-energy electron diffraction (RHEED) image of a ZnO film formed on a GaN film on a Si substrate. (A) shows the case where the electron beam incidence is in the (1, -1,1) direction. Photograph of the crystal structure, (b) shows that the electron beam incident is in the (1, 0, 0) direction (30 ° in the c-plane with respect to ((a)).
Photograph of crystal structure when rotated)

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] Fig. 6

[Correction method] Change

[Correction contents]

FIG. 6 Al _x Ga on a double layer of GaN film and ZnO film on Si substrate
Micrograph showing the crystal state of the _y In _1-xy N film observed by electron microscopy

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] Figure 9

[Correction method] Change

[Correction contents]

FIG. 9: Al _x Ga _y In formed directly on a Si crystal substrate
Micrograph showing the crystal state of the surface of the _1-xy N film observed by scanning electron microscopy.

Continued Front Page (72) Inventor Hiroshi Kamijo 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Fuji Electric Co., Ltd.

Claims (5)

[Claims] 1. Al _x Ga _y In _1-xy N (0≤x, y and 0≤x +
y ≤ 1) In the group III nitride semiconductor device including an Al _x Ga _y In _1-xy N layer formed on a substrate made of a crystal having a thermal expansion coefficient smaller than that of the crystal, the substrate and the
_{Al x Ga y In 1-xy} N layer substrate material and Al _x Ga _y between the
A stress relaxation layer made of a material having a coefficient of thermal expansion larger than that of the In _1-xy N crystal is interposed to form an Al _x Ga _y In
Characterized by relaxing the stress generated in _1-xy N III
Group nitride semiconductor device. 2. The group III nitride semiconductor device according to claim 1, wherein the substrate material is a silicon (Si) crystal or a carbonized silicon (SiC) crystal. 3. The stress relaxation layer comprises zinc oxide (ZnO), magnesium oxide (MgO), sapphire (α-Al ₂ O ₃ ), spinel.
_{3. The} group III nitride semiconductor device according to claim 1, comprising at least one of (MgAl ₂ O ₄ ) and neodymium gallate (NdGaO ₃ ). 4. An Al _x Ga _y layer between the stress relaxation layer and the substrate.
In _1-xy N (0 ≤ x, y and 0 ≤ x + y ≤ 1) intervening the antioxidant layer, and formed on the stress relaxation layer and above
Al _x Ga _y In III-nitride semiconductor device according to 3 claims 1, characterized in that to prevent deterioration of the crystalline _1-xy N film. 5. The group III nitride semiconductor device according to claim 1, which is a light emitting diode or a laser diode.