JPH09260290A - Iii group nitride semiconductor and manufacture of p-n junction diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a P-conductivity type III group nitride semiconductor film which is easily cleaved and high in carrier density by a method wherein a ZnO film is eqitaxially grown on the surface of a GaAs single crystal substrate, and furthermore a III group nitride semiconductor film is epitaxially grown thereon, where the GaAs single crystalline substrate and the ZnO film are possessed of surfaces prescribed in plane orientation respectively. SOLUTION: An ZnO film 2 whose surface is of (0001) plane is selectively and epitaxially formed on the surface of a GaAs single crystalline substrate 1 whose surface is of (111) plane, and a P-type III group nitride semiconductor film 3 whose surface is of (0001) plane is epitaxially grown the surface of the ZnO film 2. At this point, the ZnO film 2 is formed by an RF magnetron sputtering method to serve as buffer layer. The P-type GaN, GaAlN, or GaInN film 3 is formed on the ZnO buffer layer 2 through an MBE device. The MBE device is composed of two vacuum chambers which communicate with each other, wherein three Knudsen cells are provided in the lower part of one of the vacuum chambers, and a radical beam device is provided in the other vacuum chamber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a group III nitride semiconductor material used for light emitting devices such as ultraviolet light, blue light, green light emitting diodes and lasers, and a method for manufacturing a pn junction diode.

[0002]

2. Description of the Related Art II-VI group semiconductors and III group nitride semiconductors have been studied as materials for devices that emit light of short wavelength such as ultraviolet rays, blue rays and green rays. Group III nitride semiconductors A1N, GaN, and InN other than BN have a wurtzite structure, and a mixed crystal system such as A1GaN and InGaN can be obtained.
The band structure is a direct transition type, and the band gap is I
Since it has a wide range from 1.9 eV for nN to 6.2 eV for AIN, it has been regarded as a promising material for short wavelength light emitting devices.

The synthesis of these group III nitride semiconductors is carried out by metalorganic vapor phase epitaxy (MOVPE) using organic metal and ammonia gas as raw materials and hydrogen as carrier gas.
Is being done in. Sapphire is generally used as the substrate, and the (0001) plane is generally used as the substrate surface, and the substrate temperature during film formation is as high as about 1100 ° C. The synthesized film shows n-type conduction, which is thought to be due to nitrogen deficiency. n
The type conduction control is performed by adding Si or Ge atoms into the film during synthesis. Similarly, the p-type conduction control is performed by adding Mg atoms during the synthesis and further performing activation treatment. A pn junction is obtained by stacking these films. AIGaN and In
By controlling the band gap with a mixed crystal of GaN, a double hetero structure, a quantum well structure, etc. can be manufactured.

As a short-wavelength light emitting device using a group III nitride semiconductor, LEDs of ultraviolet, blue, green, etc. have been manufactured. On the other hand, in the laser diode (LD), it is difficult to form a light resonance surface, and a short wavelength light emitting LD using a group III nitride semiconductor has not been put to practical use. Infrared LD is
The resonance surface is formed by a cleavage plane. The substrate used for this is GaAs, and its (111) plane has very strong cleavage. This cleavage plane is suitable as a resonance plane because it has flatness of atomic order and parallelism.

[0005]

The group III nitride semiconductor is a crystal having a hexagonal wurtzite structure, and a hexagonal sapphire is also used as a substrate for its synthesis. Since the (0001) plane easily grows in the group III nitride semiconductor, the substrate also uses the (0001) plane. However, a hexagonal crystal generally has a weak cleavage property, and in particular (0
It is difficult to cleave the surfaces other than the (001) surface. Sapphire is also less cleavable. Therefore, it is difficult to form the light resonance surface necessary for the LD by the cleavage surface.

In addition, a method of adding Mg which is a p-type impurity during synthesis is widely used for synthesizing a p-type conductive group III nitride semiconductor. However, hydrogen generated by the decomposition of the organic metal used for synthesis and hydrogen used as a carrier gas enter the film to inactivate the Mg acceptor.
Therefore, the Mg activation process must be performed by irradiating with a low-acceleration electron beam after the growth or by performing heat treatment in a nitrogen atmosphere. In this case, the obtained carrier density is 10 ¹⁸ cm ⁻³ or less, which does not reach the required high carrier density.

It is an object of the present invention to solve the above problems and to provide a group III nitride semiconductor which can be used as a substrate of an LD device emitting short wavelength light and which can be easily cleaved to obtain p-type conduction with high carrier density. It is to provide a manufacturing method. Another object of the present invention is to provide a method for manufacturing a pn junction diode using such a semiconductor.

[0008]

In order to achieve the above object, the method for producing a group III nitride semiconductor material according to the present invention comprises:
A Zn0 film having a (0001) plane as a surface is epitaxially grown on the surface of a GaAs single crystal substrate having a (111) plane as a surface, and a group III nitride film having a (0001) plane as a surface is epitaxially grown on this Zn0 film. I shall. GaAs is an example of a substrate having a very strong cleavage. The (111) plane is a triangular lattice, which is the same as the (0001) plane of the group III nitride semiconductor having a hexagonal wurtzite structure. However, the lattice mismatch is -20 with respect to GaN.
As large as 2%, it is difficult to grow epitaxially. A buffer layer is inserted on the substrate for the purpose of mitigating this lattice mismatch. As the buffer layer, Zn0, which has a small lattice mismatch with GaN of -1.9% and is easily epitaxially grown, is used. The Zn0 film is preferably formed by a magnetron sputtering method using an inert gas and a Zn0 target. The reason why the Zn0 epitaxial film can be formed by the magnetron sputtering method using the inert gas and the Zn0 target is considered to be as follows.
In the Sputterer method, Ar ions collide with a target, and a film is formed by the ejected atomic groups and molecular groups. Zn
Since the 0 target is used, a film is formed by the Zn0 molecular group and the surface of the GaAs substrate is hardly oxidized. An epitaxial film of Zn0 cannot be obtained by a sputtering method using Ar / oxygen mixed gas or a molecular beam epitaxial method using oxygen radicals. From this, it is considered that the oxidation of the GaAs substrate surface hinders the epitaxial growth. The substrate temperature during sputtering is preferably 350 ° C. or lower. When the substrate temperature reaches 400 ° C, X of Zn0 film
Since the line diffraction peak intensity decreases, the temperature is kept at 350 ° C or lower.

Molecular beam epitaxy using a group III nitride film made of a material containing no hydrogen (hereinafter referred to as MBE)
It is better to form. Since MBE does not use hydrogen and the substrate temperature is lower than that of MOVPE, II
When forming a group I nitride semiconductor, a GaAs substrate or ZnO
Less damage to the buffer layer. The lattice mismatch between the group III nitride semiconductor and Zn0 is small as described above, and it is relatively easy to epitaxially grow the group III nitride semiconductor on the Zn0 epitaxial film. By this method, a group III nitride film exhibiting p-type conduction can be formed. It is not clear why the thus-produced Group III nitride semiconductor exhibits p-type conduction with high carrier density, but since hydrogen is not used to inactivate the acceptor, the p-type conductivity can be obtained without performing activation treatment. Conductors can be formed. M
The substrate temperature during BE is preferably 625 ° C. or lower. The X-ray diffraction peak intensity of the formed Group III nitride film is the highest at a substrate temperature of 600 ° C and is 650 ° C.
Becomes about 60%. Therefore, the substrate strength is 62
Keep below 5 ° C. The group III nitride is preferably GaN. Further, it is preferably GaAlN or GaInN.

According to the method of manufacturing a pn junction diode of the present invention, a Zn0 film having a (0001) plane as a surface is selectively epitaxially grown on a surface of a GaAs single crystal substrate having a (111) plane as a surface, and this Zn0 film is grown. Above (000
1) A p-type group III nitride semiconductor film whose surface is the surface is epitaxially grown, and an n-type group III nitride semiconductor film whose surface is the (0001) surface is epitaxially grown on the exposed GaAs surface. A GaAs single crystal substrate surface on which a Zn0 buffer layer is not formed by utilizing the fact that the p-type Group III nitride semiconductor film is formed on the Zn0 buffer layer by the method for manufacturing a Group III nitride semiconductor and a pn junction diode described above. Adjacent to the n-type group III nitride film directly epitaxially grown on the pn perpendicular to the substrate surface
A diode having a junction surface can be easily manufactured.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An RF magnetron sputtering method is used for forming a Zn0 film as a buffer layer.
P-type GaN, GaAlN, Ga on the Zn0 buffer layer
The MBE apparatus shown in FIG. 2 is used for forming the InN film.
This device consists of two vacuum chambers 21 and 22 in communication with each other.
At the bottom of the vacuum chamber 21, three Knudsen cells 31, 32,
33 is provided. A radical beam device 34 is provided below the vacuum chamber 22. Ga in Knudsen cell 31
41, Al51 in the Knudsen cell 32 and In61 in the Knudsen cell 33 are heated and evaporated, respectively.
An a atomic beam 42, an Al atomic beam 52, and an In atomic beam 62 are created. In the radical beam device 34, the nitrogen gas 71 introduced from the outside is activated in the plasma formed by the RF coil 35 to generate a nitrogen radical beam 72. The atomic beams 42, 52 made in this way,
Using some of 62 and the nitrogen radical beam 72 as raw materials, GaN is formed on the substrate 8 heated by the heater 81.
A film can be deposited. In order to confirm the crystallinity of the deposited GaN, a high-speed reflection + diffraction method (RHEED) by irradiating the substrate 8 with an electron beam 92 emitted from an electron gun 91 to form a diffraction pattern on the fluorescent plate 93. It can be carried out.

Example: A single crystal substrate has a specific resistance of 1 × 1.
GaAs having a (111) surface as the surface and having a resistance of 0 ⁷ Ωcm or more was used. Typical film forming conditions of the Zn0 buffer layer by the RF magnetron sputtering method are as follows. Target: Zn0 (diameter 150 mm) Raw material gas: Ar gas pressure: 1 Pa Substrate temperature: 300 ° C. High frequency output: 50 W Zn0 was deposited to a thickness of about 100 nm. As measured by the X-ray diffraction method, the (111) plane of GaAs and the (0) of Zn0
Only the diffraction peak from the (001) plane was observed. Zn0
The (0002) plane spacing was 0.259 nm, which was half the lattice constant of Zn0 in the c-axis direction. From this, it was found that the formed film was Zn0 and its (0001) plane was parallel to the (111) plane of the GaAs substrate. Also,
According to RHEED measurement, the Zn0 film was a single crystal with 6-fold symmetry, and its electron beam diffraction pattern interval was a.
It corresponded to the lattice constant in the axial direction. The crystal orientation relationship with the GaAs substrate is [1-10] direction of the GaAs substrate and Zn
It can be seen that the [11-20] direction of 0 is parallel and the Zn0 film is epitaxially grown on the GaAs substrate. GaAs (100) substrate, GaAs (1
10) A Zn0 film was formed on the substrate, but the Zn0 film was polycrystalline.

For comparison, a Zn target and an Ar / oxygen mixed gas were used to form a film by the sputtering method under the same conditions. However, although this film is (0001) oriented,
It was polycrystalline. MBE using oxygen radicals
The same applies to the film formed by the method. FIG. 3 shows the relationship between the substrate temperature and the X-ray diffraction peak intensity at the time of forming the Zn0 film.
As described above, when the substrate temperature rises to 400 ° C., the strength sharply decreases, and it is appropriate to set the substrate temperature to 300 ° C.

Next, using the MBE apparatus shown in FIG.
A p-type GaN film was formed on the GaAs substrate 8 on which the buffer layer was formed. Knudsen cell is Ga Knudsen cell 41
Only was used. Typical film forming conditions are as follows. Pressure: 1 × 10 ⁻³ Pa Substrate temperature: 600 ° C. Raw metal: Ga tractor cell temperature: 930 ° C. N ₂ gas flow rate: 1 sccm RF output: 500 W GaN was deposited to a thickness of about 500 nm. Impurities such as Mg and Si were not added during the GaN film formation. As measured by X-ray diffraction, the (111) plane of GaAs and Ga
Only the diffraction peak from the (0001) plane of N was observed.
The diffraction peak from the (0001) plane of Zn0 could not be observed because it overlaps with the diffraction peak from the (0001) plane of GaN. The (0002) plane spacing of GaN was 0.259 nm, which was half the lattice constant of GaN in the c-axis direction.
From this, the formed film is GaN and its (000
The (1) plane is the (111) plane of the GaAs substrate or the (00) plane of Zn0.
It was found to be parallel to the (01) plane. Also, the electron gun 9
1 and the RHEED measurement using the fluorescent plate 92,
The GaN film was a 6-fold symmetric single crystal, and its electron beam diffraction pattern interval corresponded to the lattice constant of GaN in the a-axis direction. The crystal orientation is [11-2 of the Zn0 buffer layer].
It can be seen that the [0] direction and the [11-20] direction of the GaN film are parallel, and the GaN film is epitaxially grown on the Zn0 buffer layer. FIG. 4 shows the photoluminescence spectrum of this film. An emission peak was observed at about 367 nm near the band gap of 3.4 eV of GaN. As a result of hole measurement, p-type conduction and carrier density of 2 ×
The mobility was 10 ²⁰ cm ^-3 and the mobility was 18 cm ² / Vs. The conductivity type was confirmed using the Seebeck effect. Prior to these measurements, no heat treatment or low-speed electron beam treatment was performed. No peak due to Zn impurities was observed in the spectrum of FIG. Elemental analysis in the thickness direction was performed by Auger analysis, but Zn was not diffused in the GaN film. From the above, it is considered that the acceptor is not Zn. The reason for showing p-type conduction is not clear. When a sapphire substrate or GaAs substrate is used, the grown Ga
The N film showed n-type conduction.

Al _0.05 Ga _0.95 N and In
It was confirmed that, for the mixed crystal film of _0.05 Ga _0.95 N, the Knudsen cell 32 or 33 of the apparatus shown in FIG. FIG. 5 shows the relationship between the X-ray diffraction peak intensity of the (0002) plane of deposited GaN and the substrate temperature during deposition. As shown in the figure, when the substrate temperature rises to 650 ° C., the strength becomes very small. Further, at a substrate temperature of 800 ° C., separation between the substrate and the Zn0 buffer layer occurred. Therefore, it can be seen that the substrate temperature of 600 ° C. under the above film forming conditions is appropriate.

FIG. 1 shows a sectional structure of a pn junction diode using the GaN single crystal film thus formed.
As shown in the figure, a Zn0 buffer layer 2 was formed by masking a part of the (111) plane of the GaAs substrate 1. G in MBE
When the aN single crystal was formed, the p-type GaN film 3 was formed on the Zn0 buffer layer as described above, and the n-type GaN film 4 was formed on the surface of the GaAs substrate 1 without the Zn0 buffer layer. An Au film and n-type GaN are formed on the p-type GaN film 3.
An Al film is formed on the film 4 by a vacuum vapor deposition method, each of which is about 2
Formed to a thickness of 00 nm and trimmed to Au electrode 5, A
The L electrode 6 was formed. In this way, a diode having a pn junction perpendicular to the surface of the substrate 1 was produced, and the voltage / current characteristics thereof showed rectification.

Although GaN as a group III nitride semiconductor is manufactured in the above-mentioned embodiment, Al _0.05 Ga _0.95 N or In _{0.90 is} obtained by using Al Knudsen cell 32 or In Knudsen cell 33 together _{. 05} Ga _0.95
It was confirmed that the mixed crystal film of N was epitaxially grown under the above film forming conditions.

[0018]

According to the present invention, the cleavage is strong (111).
By using a GaAs single crystal substrate whose surface is the surface and interposing a buffer layer made of Zn0 that relaxes the lattice mismatch, the cleavage of the group III nitride is strong (0001) without requiring special activation treatment. It was possible to epitaxially grow the semiconductor film having the surface as the surface. This film surface can be effectively used as a resonance surface of an LD element generating a short wavelength.
In addition, a p-type group III nitride film is epitaxially grown on the Zn0 buffer layer, but n is formed directly on the GaAs substrate surface.
The epitaxial growth of the type III nitride film makes it possible to manufacture the pn junction diode very easily.

[Brief description of drawings]

FIG. 1 is a sectional view of a pn junction diode manufactured according to an embodiment of the present invention.

FIG. 2 is a sectional view of an MBE device used in an embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the X-ray diffraction intensity and the substrate temperature of a Zn0 film in one example of the present invention.

FIG. 4 is a photoluminescence spectrum diagram of a GaN film obtained according to an example of the present invention.

FIG. 5: X of a GaN film obtained according to an embodiment of the present invention
Diagram of the relationship between line diffraction intensity and substrate temperature

[Explanation of symbols]

1 GaAs substrate 2 Zn0 buffer layer 3 p-GaN film 4 n-GaN film 5 Au electrode 6 Al electrode 21, 22 vacuum chamber 31, 32, 33 Knudsen cell 34 radical beam device 41 Ga 51 Al 61 In 71 N ₂ 8 substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shoji Kitamura Shoji Kitamura 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. No. 1 inside Fuji Electric Co., Ltd.

Claims (9)

[Claims] 1. A Zn0 film having a (0001) plane as a surface is epitaxially grown on a surface of a GaAs single crystal substrate having a (111) plane as a surface, and a (0001) plane is formed on this Zn0 film.
A method for producing a group III nitride semiconductor material, which comprises epitaxially growing a group III nitride film having a surface as a surface. 2. The method for producing a group III nitride semiconductor material according to claim 1, wherein the Zn0 film is formed by a magnetron sputtering method using an inert gas and a Zn0 target. 3. The method for producing a Group III nitride semiconductor material according to claim 2, wherein the substrate temperature during sputtering is 350 ° C. or lower. 4. The method for producing a group III nitride semiconductor material according to claim 1, wherein the group III nitride film is formed by a molecular beam epitaxial method using a material containing no hydrogen as a raw material. 5. The method for producing a Group III nitride semiconductor material according to claim 1, wherein a Group III nitride film exhibiting p-type conduction is formed. 6. The method for producing a group III nitride semiconductor material according to claim 4, wherein the substrate temperature during the molecular beam epitaxial method is 625 ° C. or lower. 7. The method for producing a Group III nitride semiconductor material according to claim 1, wherein the Group III nitride is GaN. 8. A group III nitride is GaAlN or GaI.
7. The method for producing a group III nitride semiconductor material according to claim 1, wherein the group III nitride semiconductor material is nN. 9. A Z having a (0001) plane as a surface selectively on a surface of a GaAs single crystal substrate having a (111) plane as a surface.
The n0 film is epitaxially grown, and the Zn0 film (0
A p-type group III nitride semiconductor film having a (001) surface as a surface is epitaxially grown, and (000) is formed on the exposed GaAs surface.
1) A method for manufacturing a pn junction diode, which comprises epitaxially growing an n-type group III nitride semiconductor film having a surface as a surface.