Group iii nitride semiconductor epitaxial wafer and device

Abstract

Provided is a group III nitride semiconductor epitaxial wafer in which a group III nitride semiconductor film having a very flat surface is formed on a group III nitride semiconductor doped with high-concentration impurities. The present invention provides a group III nitride semiconductor epitaxial wafer comprising a group III nitride semiconductor substrate that exhibits n-type conductivity and has a carrier concentration of 1020 cm-3 or higher and a group III nitride semiconductor film that includes an epitaxial layer epitaxially grown on the group III nitride semiconductor substrate, wherein: the group III nitride semiconductor film has a thickness of 1 to 30 μm; and the group III nitride semiconductor substrate has an off angle of 0.38° to 0.6° between a normal line of the surface of the group III nitride semiconductor substrate on which the group III nitride semiconductor film is formed and a c axis of the group III nitride semiconductor substrate.

Description

Group III nitride semiconductor epitaxial wafer and device

[0001] The present disclosure relates to a Group III nitride semiconductor epitaxial wafer having a Group III nitride semiconductor substrate and a Group III nitride semiconductor film epitaxially grown thereon, and to a device using the Group III nitride semiconductor epitaxial wafer.

[0002] Group III nitride semiconductors are used in fields such as optical devices such as semiconductor lasers and light-emitting diodes, as well as high-frequency or high-power electronic devices. These semiconductors have attracted particular attention in recent years because they are expected to reduce switching losses during power conversion compared to silicon-based devices. In order to fabricate high-frequency or high-power electronic devices, it is necessary to fabricate the devices on high-quality Group III nitride substrates that can suppress the occurrence of crystal defects in the device layer.

[0003] Methods for producing Group III nitride crystals include, for example, hydride vapor phase epitaxy (hereinafter also referred to as HVPE), ammonothermal, sodium flux, and oxide vapor phase epitaxy (hereinafter also referred to as OVPE).

[0004] In the HVPE method, which is most often used as a substrate manufacturing method, hydrogen halide gas is introduced onto a single Group III element source to generate a halide gas, and the generated Group III element halide gas is used as a source gas for crystal growth. For example, when growing gallium nitride crystals, HCl gas is introduced onto Ga metal to generate gallium chloride (e.g., GaCl ２ By producing a gallium chloride-containing gas as a group III source, high-speed growth of 1 mm / h or more can be achieved. It is known that the HVPE method can obtain group III nitride crystals with N-type conductivity by adding silicon element to the group III nitride crystals.

[0005] In the OVPE method, a high concentration of oxygen is added to a group III nitride crystal by using an oxide source gas to produce the crystal (see, for example, Patent Document 1). In this method, a group III oxide gas is reacted with a nitrogen-containing gas to produce a group III nitride crystal. In the substrate obtained by this method, the dislocation density is 10 ４ cm －２ The dislocation density is low enough that OVPE is one of the means for obtaining high-quality Group III nitride crystals.

[0006] Group III nitride crystals produced by the above-described methods can be processed to obtain Group III nitride substrates. Devices can be fabricated by forming epitaxial films of Group III nitride semiconductors on these substrates. It is known that dislocations, among other crystal defects of the substrate, are inherited by the epitaxial films produced. However, because dislocations are thought to be a cause of leakage during device operation, efforts have been made to develop methods to prevent inheritance of dislocations from the substrate (see, for example, Patent Document 2).

[0007] WO2015 / 053341A1 JP 2010-103353 A

[0008] I. C. Kizilyalli et al. , Microelectron Reliab. 55, 1654 (2015).

[0009] However, in recent years, research has been progressing on reducing the dislocation density of the substrate itself using the aforementioned methods of manufacturing III-nitride crystals, such as the HVPE method, OVPE method, and sodium flux method. Currently, in many cases, by growing thick crystals, it is possible to reduce the dislocation density by 1×10 ６ cm －２ It is possible to obtain a substrate with a dislocation density of about 1000 times or less. Although it is possible to slightly reduce the dislocation density during crystal growth of thin films in device formation, it is becoming more difficult to significantly reduce it compared to the substrate. Therefore, it is becoming unnecessary to use the method described in Patent Document 2.

[0010] In recent years, research has been conducted on the idea that leakage, particularly in vertical power devices, is caused by fluctuations in the surface of each device layer in the thickness direction during formation (see, for example, Non-Patent Document 1). It is believed that leakage occurs due to fluctuations in each device layer and the electrode formation surface, which cause localized electric field concentration. Therefore, this suggests that crystal growth of an epitaxial film with a flat surface may be necessary to reduce leakage in devices.

[0011] Vertical power devices generally have a structure in which current also flows through the substrate. Therefore, in order to reduce the resistance during device operation, it is necessary to reduce the resistance of the substrate as well. Among the aforementioned methods for producing Group III nitride crystals, OVPE makes it easy to dope oxygen atoms, which act as donors in the crystal, at high concentrations, and is known as a method for producing low-resistance substrates.

[0012] The inventors have found that oxygen atoms can be easily added at high concentrations, with the oxygen concentration reaching 4.4 × 10 ２０ atoms・cm －３ We have developed a method for obtaining gallium nitride crystals with oxygen atoms added at a compositional level of 4.4×10 or more. Among group III nitride crystals, for example, the molecular density in gallium nitride crystals is 4.4×10 ２２ cm －３ In gallium nitride, oxygen atoms are said to be incorporated into the crystal by substituting nitrogen atoms, and the oxygen concentration is 4.4 × 10 ２０ atom・cm －３ % at 1 atm. %, which can be said to be an addition at the composition level.

[0013] In semiconductor crystals, impurities are added to the crystal to control the electrical properties, but generally, the amount is limited to at most 10 １９ atoms・cm －３ The reason for this is that adding impurities at a high concentration can lead to a decrease in crystal quality and an increase in the generation of polycrystals due to factors such as impurity segregation, making it difficult to obtain a high-quality thick single crystal.

[0014] Furthermore, there have been few cases in which epitaxial films have been formed using Group III nitride crystals, particularly those containing impurities at the composition level, as substrates. Furthermore, in crystals containing impurities at the composition level, basic physical properties such as the lattice constant of the crystal deviate from their original values. On the other hand, epitaxial films do not contain impurities at the composition level and have physical properties that are relatively close to those of the original material.

[0015] For example, if the lattice constant difference between the epitaxial film and the underlying substrate is large, dislocations are introduced into the epitaxial film due to lattice relaxation, and the substrate may warp during epitaxial film formation. This results in a deterioration of the surface condition of the epitaxial film. In other words, it is generally difficult to maintain crystalline quality when forming an epitaxial film with a low impurity concentration on a substrate with an extremely high impurity concentration.

[0016] An object of the present disclosure is to provide a Group III nitride semiconductor epitaxial wafer in which a Group III nitride semiconductor film with an extremely flat surface is formed on a Group III nitride semiconductor doped with a high concentration of impurities.

[0017] The Group III nitride semiconductor epitaxial wafer according to the present disclosure exhibits n-type conductivity and has a carrier concentration of 10 ２０ cm －３ The present invention comprises a Group III nitride semiconductor substrate as described above, and a Group III nitride semiconductor film including an epitaxial layer epitaxially grown on the Group III nitride semiconductor substrate, wherein the thickness of the Group III nitride semiconductor film is 1 μm or more and 30 μm or less, and the off-angle between a normal to the surface of the Group III nitride semiconductor substrate on which the Group III nitride semiconductor film is formed and a c-axis of the Group III nitride semiconductor substrate is 0.38 degrees or more and 0.6 degrees or less.

[0018] The Group III nitride semiconductor epitaxial wafer according to the present disclosure enables the formation of devices with reduced leakage and low operational loss.

[0019] 1 is a schematic cross-sectional view showing an example of a nitride semiconductor epitaxial wafer according to the first embodiment; FIG. 2 is a differential interference microscope image of a gallium nitride film surface obtained using a group III nitride semiconductor substrate having different off-angles in an example; FIG. 3 is an atomic force microscope image (AFM image) at a viewing angle of 90 μm in an example; FIG. 4 is a differential interference microscope image of a gallium nitride film surface obtained using a group III nitride semiconductor substrate having different off-angles in a comparative example; FIG. 5 is an atomic force microscope image (AFM image) at a viewing angle of 90 μm in a comparative example; and FIG. 6 is a diagram showing the relationship between surface roughness and the off-angle of the substrate in the examples and the comparative example.

[0020] The Group III nitride semiconductor epitaxial wafer according to the first aspect exhibits n-type conductivity and has a carrier concentration of 10 ２０ cm －３ The present invention comprises a Group III nitride semiconductor substrate as described above, and a Group III nitride semiconductor film including an epitaxial layer epitaxially grown on the Group III nitride semiconductor substrate, wherein the thickness of the Group III nitride semiconductor film is 1 μm or more and 30 μm or less, and the off-angle formed between a normal to the surface of the Group III nitride semiconductor substrate on which the Group III nitride semiconductor film is formed and a c-axis of the Group III nitride semiconductor substrate is 0.38 degrees or more and 0.6 degrees or less.

[0021] A Group III nitride semiconductor epitaxial wafer according to a second aspect is the above-mentioned first aspect, wherein the root mean square roughness (RMS) value of the surface of the Group III nitride semiconductor film within a 50 μm square area may be 10 nm or less.

[0022] A Group III nitride semiconductor epitaxial wafer according to a third aspect is the above-mentioned second aspect, wherein the surface of the Group III nitride semiconductor film has a root mean square roughness (RMS) value of 5 nm or less within a 50 μm square area, and the off-angle formed between a normal to the surface of the Group III nitride semiconductor substrate and a c-axis of the Group III nitride semiconductor substrate is 0.4 degrees or more and 0.55 degrees or less.

[0023] A Group III nitride semiconductor epitaxial wafer according to a fourth aspect is any one of the first to third aspects, wherein the n-type dopant element of the Group III nitride semiconductor substrate is oxygen.

[0024] A Group III nitride semiconductor epitaxial wafer according to a fifth aspect is any one of the first to fourth aspects, wherein the main Group III element of the Group III nitride semiconductor substrate may be gallium.

[0025] A Group III nitride semiconductor epitaxial wafer according to a sixth aspect is the same as that of the fifth aspect, except that the oxygen concentration in the Group III nitride semiconductor substrate is 4.4×10 ２０ atom・cm －３ 6. The Group III nitride semiconductor epitaxial wafer according to claim 5, wherein:

[0026] A Group III nitride semiconductor epitaxial wafer according to a seventh aspect is any one of the first to sixth aspects, wherein the Group III nitride semiconductor film may include an epitaxial layer having a carrier concentration lower than that of the Group III nitride semiconductor substrate.

[0027] A Group III nitride semiconductor epitaxial wafer according to an eighth aspect is the wafer of any one of the first to seventh aspects, wherein the Group III nitride semiconductor film has a carrier concentration of 5×10 １６ cm －３ It may include epitaxial layers such as:

[0028] A Group III nitride semiconductor epitaxial wafer according to a ninth aspect is any one of the first to eighth aspects, wherein the thickness of the Group III nitride semiconductor film is not less than 1 μm and not more than 8 μm.

[0029] A device according to a tenth aspect uses the Group III nitride semiconductor epitaxial wafer according to any one of the first to ninth aspects.

[0030] The method for producing a Group III nitride semiconductor epitaxial wafer according to an eleventh aspect is to produce a Group III nitride semiconductor epitaxial wafer by OVPE, which exhibits n-type conductivity and has a carrier concentration of 10 ２０ cm －３The method includes the steps of: forming the above-mentioned Group III nitride semiconductor substrate; polishing the surface of the obtained Group III nitride semiconductor substrate to obtain a Group III nitride semiconductor substrate having a surface in which an off-angle formed between a normal to the c-axis of the Group III nitride semiconductor substrate is 0.38 degrees or more and 0.6 degrees or less; and epitaxially growing a Group III nitride semiconductor film on the surface of the Group III nitride semiconductor substrate with an off-angle of 0.38 degrees or more and 0.6 degrees or less.

[0031] A twelfth aspect of the present invention relates to a method for producing a Group III nitride semiconductor epitaxial wafer according to the eleventh aspect, and in the step of polishing the Group III nitride semiconductor substrate, the Group III nitride semiconductor substrate may be placed so that a normal to a virtual polished surface, which is a flat surface obtained by polishing, forms an angle of 0.38 degrees or more and 0.6 degrees or less between a c-axis of the Group III nitride semiconductor substrate, and the surface of the Group III nitride semiconductor substrate is polished so that it is parallel to the polished surface, thereby obtaining a Group III nitride semiconductor substrate having an off-angle between the normal to the surface and the c-axis of 0.38 degrees or more and 0.6 degrees or less.

[0032] Hereinafter, Group III nitride semiconductor epitaxial wafers and devices according to embodiments of the present disclosure will be described using examples, although the present disclosure is not limited in any way by the use of numerical values ​​or specific elements used in the following description.

[0033] 1 is a schematic cross-sectional view showing an example of a nitride semiconductor epitaxial wafer according to the present embodiment 1. The group III nitride semiconductor epitaxial wafer according to the present disclosure includes at least two layers, namely, a group III nitride semiconductor substrate and a group III nitride semiconductor film including an epitaxial layer epitaxially grown thereon.

[0034] Each of the components constituting this Group III nitride semiconductor epitaxial wafer will be described below.

[0035] <Group III nitride semiconductor substrate> In order to reduce the on-resistance during operation, the Group III nitride semiconductor substrate is doped with impurities that act as n-type dopants, exhibiting n-type conductivity, and has a carrier concentration of 10 ２０ cm－３ As shown in Fig. 1, the normal to the surface of the Group III nitride semiconductor substrate is preferably tilted at an angle of 0.38 degrees or more and 0.6 degrees or less from the c-axis of the Group III nitride semiconductor crystal having a hexagonal wurtzite crystal structure, and more preferably at an angle of 0.4 degrees or more and 0.55 degrees or less. Hereinafter, this tilt angle may be simply referred to as the "off angle." This makes it easier to maintain the flatness of the surface when a Group III nitride semiconductor film including an epitaxial layer is formed on the Group III nitride semiconductor substrate.

[0036] The n-type dopant element of the Group III nitride semiconductor substrate preferably includes at least one selected from the group consisting of silicon, germanium, and oxygen. The n-type dopant element of the Group III nitride semiconductor substrate more preferably includes oxygen. In this case, oxygen can be easily added to the Group III nitride semiconductor crystal, particularly when producing the Group III nitride semiconductor crystal used for the substrate by OVPE. When oxygen is the main element as the n-type dopant element of the Group III nitride semiconductor substrate, the amount of oxygen is 4.4×10 ２０ atom・cm －３ It is preferable that the carrier concentration of the Group III nitride semiconductor substrate is increased to 10 ２０ cm －３ This makes it easier to achieve the above.

[0037] <Group III Nitride Semiconductor Film> A Group III nitride semiconductor film includes an epitaxial layer epitaxially grown on a Group III nitride semiconductor substrate. Its electrical characteristics are determined by the performance required for the device and are not limited to specific carrier concentrations or polarities such as p-type or n-type. However, in order to reduce leakage current when a device is formed, the surface flatness is such that the root mean square roughness (RMS) measured in a 50 μm square area randomly selected from the surface is preferably 10 nm or less, and more preferably 5 nm or less. The epitaxial layer constituting the Group III nitride semiconductor film may be a single layer or may have a structure of two or more layers.

[0038] The group III nitride semiconductor film has a carrier concentration of 5×10 １６ cm －３ It is preferable that the semiconductor device includes at least one of the following epitaxial layers: By combining a Group III nitride semiconductor film including an epitaxial layer with a low carrier concentration with a substrate with a high carrier concentration, it becomes easy to realize a device with low resistance and high breakdown voltage, which has not been realized before.

[0039] The thickness of the Group III nitride semiconductor film is 1 μm or more and 30 μm or less. The thickness of the Group III nitride semiconductor film is preferably 1 μm or more. If the Group III nitride semiconductor film is thinner than 1 μm, a sufficiently stable surface is not formed when forming an epitaxial layer on the substrate, and the surface is likely to become rough depending on the flatness of the substrate.

[0040] The thickness of the Group III nitride semiconductor film is preferably 30 μm or less. If it exceeds 30 μm, it may be difficult to maintain the flatness of the surface due to the influence of lattice mismatch. If it is 30 μm or less, it is easy to maintain the flatness of the epitaxial layer, and since the substrate of the present disclosure has a very high carrier concentration and is doped with a large amount of impurities, it is possible to maintain the flatness of the surface even though the lattice constant of the crystal deviates from that of a pure Group III nitride semiconductor crystal.

[0041] The thickness of the Group III nitride semiconductor film is more preferably 1 μm or more and 8 μm or less. If the thickness is 1 μm or more and 8 μm or less, a film having a sufficiently stable surface can be formed, and sufficient flatness can be maintained even when the lattice mismatch between the substrate and the epitaxial layer is large.

[0042] This Group III nitride semiconductor epitaxial wafer has a root mean square (RMS) roughness of 10 nm or less when measured over a 50 μm square area, and when used in electronic devices, it can realize devices with low resistance during operation and low leakage current.

[0043] <Method for Manufacturing a Group III Nitride Semiconductor Epitaxial Wafer> The method for manufacturing a Group III nitride semiconductor epitaxial wafer according to the first embodiment includes the following steps: (1) growing a group III nitride semiconductor epitaxial wafer exhibiting n-type conductivity and having a carrier concentration of 10 ２０ cm －３ The above-described Group III nitride semiconductor substrate is formed. Note that the method for manufacturing a Group III nitride semiconductor substrate by OVPE may be performed under normal conditions. (2) The surface of the obtained Group III nitride semiconductor substrate is polished to obtain a Group III nitride semiconductor substrate having a surface in which the off-angle between the normal and the c-axis of the Group III nitride semiconductor substrate is 0.38 degrees or more and 0.6 degrees or less. The process for obtaining a Group III nitride semiconductor substrate having a surface in which the off-angle is 0.38 degrees or more and 0.6 degrees or less will be described later. (3) A Group III nitride semiconductor film is epitaxially grown on the surface of the Group III nitride semiconductor substrate having an off-angle of 0.38 degrees or more and 0.6 degrees or less. The Group III nitride semiconductor film may be epitaxially grown by, for example, metalorganic vapor phase epitaxy (MOVPE). Note that the epitaxial growth method is not limited to metalorganic vapor phase epitaxy (MOVPE). In this manner, a Group III nitride semiconductor epitaxial wafer can be obtained.

[0044] <Regarding the Step of Obtaining a Group III Nitride Semiconductor Substrate Having a Surface with an Off-Angle of 0.38 to 0.6 Degrees> In the step of polishing a Group III nitride semiconductor substrate, the Group III nitride semiconductor substrate is mounted so that the angle between the normal to a virtual polished surface, which is a plane obtained by polishing, and the c-axis of the Group III nitride semiconductor substrate is inclined by 0.38 to 0.6 degrees. The virtual polished surface may be a horizontal plane. Alternatively, it may be a vertical plane. Note that in a typical Group III nitride semiconductor substrate, the c-plane, to which the c-axis is the normal, appears on the surface. Therefore, when the virtual polished surface is horizontal, the c-plane, which is the surface of the mounted Group III nitride semiconductor substrate, is inclined with respect to the horizontal plane. Therefore, the Group III nitride semiconductor substrate may be mounted on a jig whose surface normal is inclined by 0.38 to 0.6 degrees with respect to the vertical direction. Thereafter, the surface of the Group III nitride semiconductor substrate is polished so as to be parallel to the polishing surface, thereby obtaining a Group III nitride semiconductor substrate having an off-angle between the surface normal and the c-axis of 0.38 degrees or more and 0.6 degrees or less.

[0045] <Electronic Devices> The above-described Group III nitride semiconductor epitaxial wafer may be used in electronic devices, thereby realizing devices with low resistance and low leakage current during operation.

[0046] In this example, a gallium nitride substrate manufactured by OVPE was used as a group III nitride semiconductor substrate, and a gallium nitride film, which is a group III nitride semiconductor film, was formed by metal organic vapor phase epitaxy (MOVPE). The gallium nitride substrate had an oxygen concentration of 1×10 ２１ atom・cm －３ and the carrier concentration is 2×10 ２０ cm －３ The thickness was 400 μm. The off-angle was changed from 0.383 to 0.584 degrees. The gallium nitride film was doped with silicon as a dopant element, and was n-type with a carrier concentration of 2×10 １６ cm －３After the gallium nitride film was formed, the surface condition was evaluated with an atomic force microscope (AFM), and the RMS value of a 50 μm square area was measured.

[0047] 2(a) to (f) are differential interference microscope images of the gallium nitride film surface obtained using a Group III nitride semiconductor substrate having different off angles in this example, and FIGS. 3(a) to (f) are atomic force microscope images (AFM images) with a field of view of 90 μm in this example. In the differential interference microscope image of FIG. 2, it can be seen that the surface is flat when the off angle is (c) 0.415 degrees, (d) 0.473 degrees, and (e) 0.514 degrees. Also, in the atomic force microscope image of FIG. 3, it can be seen that the surface is flat with relatively little difference in brightness when the off angle is (c) 0.415 degrees, (d) 0.473 degrees, and (e) 0.514 degrees. 2 and 3, it was confirmed that when the off-angle is 0.4 degrees or more and 0.5 degrees or less, the surface after the formation of the epitaxial film is relatively flat in the differential interference microscope image, and furthermore, from the atomic force microscope image (AFM image), it was possible to form a flat film with RMS suppressed to 5 nm or less.

[0048] Comparative Example In the comparative example, a gallium nitride substrate manufactured by the HVPE method was used as the group III nitride semiconductor substrate, and a gallium nitride film was formed by the MOVPE method in the same manner as in the example. The gallium nitride substrate was n-type and had a carrier concentration of 2×10 １８ cm －３ The thickness was 400 μm. The off-angle was changed from 0.355 degrees to 0.611 degrees. The gallium nitride film was doped with silicon as a dopant element, and was n-type with a carrier concentration of 2×10 １６ cm －３ After the gallium nitride film was formed, the surface condition was evaluated with an atomic force microscope (AFM) and the RMS value of a 50 μm square area was measured in the same manner as in the example.

[0049] Figures 4(a) to (e) are differential interference microscope images of the surface of a gallium nitride film obtained using a Group III nitride semiconductor substrate having different off-angles in a comparative example, and Figures 5(a) to (e) are atomic force microscope images (AFM images) at a field of view of 90 μm in a comparative example. From Figures 4 and 5, it can be seen that the Group III nitride film formed on a substrate with a low impurity concentration is relatively flat in the differential interference microscope images of the surface at any off-angle, and furthermore, it can be confirmed from the atomic force microscope images (AFM images) that a flat film with an RMS suppressed to 5 nm or less can be formed over a wide range of off-angles of 0.4 degrees or more.

[0050] Figure 6 shows the relationship between surface roughness and the substrate off-angle in the examples and comparative examples. As shown in Figure 6, in the comparative example, it was confirmed that an off-angle of 0.4 degrees or more is sufficient to achieve an RMS value of 5 nm or less. On the other hand, in the examples, it was confirmed that an RMS value of 10 nm or less is achieved when the off-angle is in the range of 0.38 to 0.6 degrees, and that in order to achieve an RMS value of 5 nm or less, the off-angle must be limited to a narrow range of 0.4 to 0.55 degrees. It was confirmed that in substrates with high impurity concentrations, the off-angle has a significant effect on improving flatness in a limited, narrow region.

[0051] As described above, the Group III nitride semiconductor epitaxial wafer according to the present disclosure enables the formation of a flat Group III nitride semiconductor epitaxial film, which is expected to reduce leakage current in low on-resistance electronic devices and improve reliability.

Claims

1. It exhibits n-type conductivity and has a carrier concentration of 10 ２０ cm －３ a Group III nitride semiconductor film including an epitaxial layer epitaxially grown on the Group III nitride semiconductor substrate, wherein the thickness of the Group III nitride semiconductor film is 1 μm or more and 30 μm or less, and the off angle between a normal to a surface of the Group III nitride semiconductor substrate on which the Group III nitride semiconductor film is formed and a c-axis of the Group III nitride semiconductor substrate is 0.38 degrees or more and 0.6 degrees or less.

2. The Group III nitride semiconductor epitaxial wafer according to claim 1, wherein the root mean square roughness (RMS) value of the surface of said Group III nitride semiconductor film over a 50 μm square area is 10 nm or less.

3. The Group III nitride semiconductor epitaxial wafer according to claim 2, wherein a root mean square roughness (RMS) value in an area of ​​50 μm square of a surface of said Group III nitride semiconductor film is 5 nm or less, and said off-angle between a normal to a surface of said Group III nitride semiconductor substrate and a c-axis of said Group III nitride semiconductor substrate is 0.4 degrees or more and 0.55 degrees or less.

4. The Group III nitride semiconductor epitaxial wafer according to any one of claims 1 to 3, wherein the n-type dopant element of said Group III nitride semiconductor substrate is oxygen.

5. A Group III nitride semiconductor epitaxial wafer according to any one of claims 1 to 3, wherein a main Group III element in said Group III nitride semiconductor substrate is gallium.

6. The oxygen concentration in the Group III nitride semiconductor substrate is 4.4×10 ２０ atoms・cm －３ 6. The Group III nitride semiconductor epitaxial wafer according to claim 5 .

7. A Group III nitride semiconductor epitaxial wafer according to any one of claims 1 to 3, wherein said Group III nitride semiconductor film includes an epitaxial layer having a carrier concentration lower than that of said Group III nitride semiconductor substrate.

8. The Group III nitride semiconductor film has a carrier concentration of 5×10 １６ cm －３ 4. The Group III nitride semiconductor epitaxial wafer according to claim 1, comprising the following epitaxial layer:

9. The Group III nitride semiconductor epitaxial wafer according to any one of claims 1 to 3, wherein the thickness of said Group III nitride semiconductor film is not less than 1 μm and not more than 8 μm.

10. A device using the Group III nitride semiconductor epitaxial wafer according to any one of claims 1 to 3.

11. By OVPE, n-type conductivity and carrier concentration of 10 ２０ cm －３ forming the above Group III nitride semiconductor substrate; polishing a surface of the obtained Group III nitride semiconductor substrate to obtain a Group III nitride semiconductor substrate having a surface in which an off-angle between a normal to a c-axis of the Group III nitride semiconductor substrate is 0.38 degrees or more and 0.6 degrees or less; and epitaxially growing a Group III nitride semiconductor film on the surface of the Group III nitride semiconductor substrate having an off-angle of 0.38 degrees or more and 0.6 degrees or less.

12. A method for producing a Group III nitride semiconductor epitaxial wafer as set forth in claim 11, wherein in the step of polishing the Group III nitride semiconductor substrate, the Group III nitride semiconductor substrate is placed so that an angle between a normal to a virtual polishing surface, which is a flat surface obtained by polishing, and a c-axis of the Group III nitride semiconductor substrate has a tilt of 0.38 degrees or more and 0.6 degrees or less, and a surface of the Group III nitride semiconductor substrate is polished so as to be parallel to the polishing surface, thereby obtaining a Group III nitride semiconductor substrate having an off-angle between the normal to the surface and the c-axis of 0.38 degrees or more and 0.6 degrees or less.

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