JP7129633B2 - Method for producing group III nitride crystal - Google Patents

Description

The present invention relates to a method for producing group III nitride crystals, and more particularly to a method for producing group III nitride crystals such as GaN crystals using a _RAMO4 substrate.

In recent years, a single crystal substrate represented by the general formula _RAMO4 has attracted attention as a substrate for growing GaN crystals. wherein R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanides, and A represents the group consisting of Fe(III), Ga, and Al. represents one or more trivalent elements selected from Mg, Mn, Fe(II), Co, Cu, Zn, and Cd. represents a valence element.

In particular, the ScAlMgO ₄ single crystal (also referred to as “SCAM crystal”), which is an example of RAMO ₄ described in Patent Document 1, has a rock salt structure (111) plane ScO ₂ layer and a hexagonal (0001) plane. It has a structure in which typical AlMgO ₂ layers are alternately laminated. The hexagonal (0001) plane two layers are planar compared to the wurtzite structure, and compared to the in-plane bond, the bond between the upper and lower layers is about 0.03 nm longer, and the bond strength is is weak. Therefore, the _ScAlMgO4 single crystal can be cleaved at the (0001) plane.

Further, the a-axis lattice constant of the hexagonal (0001) AlMgO ₂ layer is 3.23 Å (0.323 nm), the a-axis lattice constant of GaN is 3.18 Å (0.318 nm), The lattice mismatch between the two is about 1.5%. On the other hand, since the lattice mismatch between the sapphire single crystal and GaN is 16%, it can be expected that the SCAM crystal can be used as a growth substrate to obtain a higher quality GaN crystal than the sapphire crystal.

Also, the thermal expansion coefficient of ScAlMgO ₄ crystal is 6.6×10 ⁻⁶ /K, which is larger than 5.5×10 ⁻⁶ /K of GaN. Therefore, it is expected that detachment and self-sustaining on the c-plane will be possible by utilizing the c-plane cleavability and the stress difference during thermal contraction in the cooling process after crystal growth.

However, when a thick GaN crystal exceeding 400 μm is grown directly on a cleaved ScAlMgO ₄ single crystal, it has been difficult to reduce the dislocation density as expected from the crystal lattice matching. When forming a GaN crystal on a sapphire substrate, in order to reduce the pit density and defect density of the GaN crystal after crystal growth, it is effective to carve a pattern groove in the sapphire substrate and grow the GaN crystal. It is known.

For example, Patent Document 2 discloses that pit density and defect density can be reduced by forming a GaN crystal on a sapphire substrate having conical or pyramidal projections arranged in a grid pattern on the surface. will be disclosed.

JP 2015-178448 A JP 2016-060659 A

According to the method described above, although the pit density and defect density can be reduced, a large strain still remains at the interface between the sapphire substrate and the group III nitride crystal grown thereon. , cannot solve the essential problem that the stress increases as a whole. Reducing the stress at this interface becomes important when trying to form a thick group III nitride crystal on a heterogeneous substrate. This is because, if the stress at the interface cannot be reduced, the strain caused by the difference in lattice constant between the group III nitride crystal and the heterosubstrate cannot be alleviated, and as the crystal growth proceeds, crystal cracks and This is because it causes quality defects such as the occurrence of cracks.

An object of the present disclosure is to provide a method for manufacturing a group III nitride crystal that can relax the crystal strain of the group III nitride crystal grown on a substrate.

In order to achieve the above object, a method for producing a Group III nitride crystal according to the present disclosure provides a single crystal represented by the general formula _RAMO4 (wherein R represents one or more trivalent elements selected from the group consisting of the elements, A represents one or more trivalent elements selected from the group consisting of Fe(III), Ga, and Al , M represents one or more _divalent elements selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd). When,
forming a III-nitride film on the _RAMO4 substrate;
The surface of the RAMO ₄ substrate on which the group III nitride film is formed is chemically reacted with a chemical solution containing at least sulfuric acid and hydrogen peroxide water to etch the surface, thereby forming unevenness on the surface, and the RAMO _4. A step of leaving a Group III nitride film having a longitudinal direction wider than the longitudinal width of the protrusions on the protrusions of the substrate;
growing a group III nitride crystal on the group III nitride film after forming the unevenness;
have

According to the method for producing a group III nitride crystal according to the present disclosure, a group III nitride crystal can be produced while relaxing stress.

1A to 1D are schematic cross-sectional views showing each step of a method for manufacturing a group III nitride crystal on a _RAMO4 substrate according to Embodiment 1; 1 is a schematic facility diagram for realizing a method for producing a group III nitride crystal according to Embodiment 1. FIG. FIG. 4 is a diagram showing an example of the relationship between etching amount and time when a ScAlMgO ₄ substrate is processed under typical etching conditions. 4 is a schematic cross-sectional view after GaN thin film patterning before wet etching of ScAlMgO ₄ in the method for producing a group III nitride crystal according to Embodiment 1; FIG. 4 is a micrograph of the surface after GaN thin film patterning before wet etching of ScAlMgO ₄ in the method for producing a group III nitride crystal according to Embodiment 1. FIG. 4 is a schematic diagram showing evaluation results of crystal strain in a GaN thin film before wet etching of ScAlMgO ₄ in the method for producing a group III nitride crystal according to Embodiment 1; FIG. 4 is a schematic cross-sectional view after ScAlMgO ₄ wet etching in the method for producing a group III nitride crystal according to Embodiment 1; FIG. 4 is a micrograph of the surface after ScAlMgO ₄ wet etching in the method for producing a group III nitride crystal according to Embodiment 1. FIG. 4 shows the results of evaluation of crystal strain in a GaN thin film after wet etching of ScAlMgO ₄ in the method for producing a group III nitride crystal according to Embodiment 1. FIG. FIG. 4 is a schematic cross-sectional view of an etched groove; FIG. 10 is a schematic cross-sectional view showing a GaN crystal peeling step in the method for manufacturing a group III nitride crystal according to Embodiment 2;

A method for producing a Group III nitride crystal according to the first aspect is a single crystal represented by the general formula RAMO ₄ (wherein R is selected from the group consisting of Sc, In, Y, and lanthanide elements A represents one or more trivalent elements selected from the group consisting of Fe(III), Ga, and Al; M represents Mg, providing a RAMO ₄ substrate consisting of one or more divalent elements selected from the group consisting of Mn, Fe(II), Co, Cu, Zn, and Cd;
forming a III-nitride film on the _RAMO4 substrate;
The surface of the RAMO ₄ substrate on which the group III nitride film is formed is chemically reacted with a chemical solution containing at least sulfuric acid and hydrogen peroxide water to etch the surface, thereby forming unevenness on the surface, and the RAMO _4. A step of leaving a Group III nitride film having a longitudinal direction wider than the longitudinal width of the protrusions on the protrusions of the substrate;
growing a group III nitride crystal on the group III nitride film after forming the unevenness;
have

A method for producing a Group III nitride crystal according to a second aspect is the method according to the first aspect, wherein the temperature of the chemical in the etching is set to a range of 35° C. to 290° C. to form unevenness on the surface of the RAMO ₄ substrate. may be formed.

A third aspect of the method for producing a Group III nitride crystal is the first or second aspect, wherein the chemical solution has a value of (sulfuric acid/hydrogen peroxide solution) in the range of 1 to 10. good too.

A method for manufacturing a Group III nitride crystal according to a fourth aspect is the method according to the third aspect, wherein the etching is performed such that the width of the convex portion in the longitudinal direction is r, and the width of the remaining Group III nitride film in the longitudinal direction is The unevenness may be formed so as to satisfy 30%≦r/R≦70%, where R is the width of R.

(Progress leading to the present invention)
First, the technique of forming high-quality GaN on a _ScAlMgO4 substrate, which is a kind of _RAMO4 substrate, and spontaneously self-supporting and exfoliating will be described below. The ScAlMgO ₄ single crystal has a structure in which rock salt structure (111) face ScO ₂ layers and hexagonal (0001) face AlMgO ₂ layers are alternately laminated. The hexagonal (0001) plane two layers are planar compared to the wurtzite structure, and compared to the in-plane bond, the bond between the upper and lower layers is about 0.03 nm longer, and the bond strength is is weak. Therefore, the ScAlMgO ₄ single crystal can be cleaved on the (0001) plane.

A hexagonal (0001) AlMgO ₂ plane appears on the exfoliated surface, and its a-axis lattice constant is 0.323 nm (3.23 Å). is 0.318 nm (3.18 Å). The a-axis lattice constants of both are very close, and it is possible to grow a GaN crystal on the peeled surface of the ScAlMgO ₄ substrate.

The lattice mismatch between the ScAlMgO ₄ crystal and the GaN crystal is about 1.5%, and the lattice mismatch between the sapphire single crystal and the GaN crystal is 16%. Comparing the respective lattice mismatches, it can be seen that the ScAlMgO ₄ crystal is more suitable as a substrate for growth than the sapphire crystal. Actually, when GaN crystals with a thickness of about 10 μm were grown on each crystal, the dislocation density in the crystal was about 5×10 8 cm −2 on the sapphire substrate, whereas it was about 5×10 ⁸ cm ⁻² on the ScAlMgO ₄ substrate. In , it was greatly reduced to 8×10 ⁷ cm ⁻² .

For this reason, the selective epitaxial technique, which has conventionally been performed for the purpose of reducing the dislocation density on the sapphire substrate, is not necessary for the purpose of reducing dislocations in the GaN crystal on the ScAlMgO ₄ substrate. However, the structure that realizes the reduction of the internal stress of the GaN crystal on ScAlMgO ₄ for pit suppression and the intra-crystal stress distribution at the GaN crystal/ScAlMgO ₄ crystal interface in the ScAlMgO ₄ substrate plane that promotes spontaneous detachment is necessary.

Therefore, the present inventors formed island-shaped seed crystals of GaN separated from each other on a _ScAlMgO4 substrate, and chemically reacted with a chemical solution containing sulfuric acid and hydrogen peroxide while the surface of the _ScAlMgO4 substrate was exposed. By etching to form unevenness on the surface of the ScAlMgO ₄ substrate, and leaving GaN on the projections of the ScAlMgO ₄ substrate, the longitudinal direction of which is wider than the width of the projections in the longitudinal direction. It has been found that hollow regions can be formed sequentially from the periphery to the center of the region.
Since the GaN crystal on ScAlMgO ₄ having such a structure is in a completely free state, the internal stress of the crystal is reduced, and the occurrence of crystal breakage and cracks can be suppressed, which led to the present invention. It is.

Hereinafter, a method for producing a Group III nitride crystal according to an embodiment will be described with reference to the accompanying drawings. In addition, the same code|symbol is attached|subjected about the substantially same member in drawing.

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing each step of a method for producing a Group III nitride crystal (2) on a _RAMO4 substrate (1) according to Embodiment 1. FIG. FIG. 2A is a schematic facility diagram for realizing the method for producing a group III nitride crystal according to Embodiment 1. FIG. FIG. 2B is a diagram showing an example of the relationship between etching amount and time when a ScAlMgO ₄ substrate is processed under typical etching conditions.

As a first embodiment of the present disclosure, process steps in a method for manufacturing a group III nitride crystal for forming a GaN crystal as a group III nitride crystal on a _ScAlMgO4 substrate as a _RAMO4 substrate are shown in FIGS. ). Details of the process are described below.
(a) A GaN thin film crystal (2) is deposited on a _ScAlMgO4 substrate (1) by MOCVD, for example (Fig. 1(a)). This GaN thin film (2) is used not only as a seed crystal, but also as a mask material for the ScAlMgO ₄ crystal. Therefore, if the thickness of the GaN thin film (2) is too thick, patterning will be difficult. On the other hand, if the thickness of the GaN thin film (2) is too thin, a film having a uniform thickness cannot be formed even if the MOCVD method is used, so that quality as a seed crystal is not obtained. Therefore, it is preferable to set the appropriate film thickness range to, for example, about 1 μm to 5 μm.

(b) Subsequently, in step (b), a resist mask (3) is formed on the GaN thin film (2) and patterned by exposure (FIG. 1(b): GaN thin film patterning process). The resist mask (3) is used to pattern the GaN thin film (2). For example, it can be easily implemented using a technique such as a dry etching process using chlorine gas. The resist mask (3) is preferably removed after patterning the GaN thin film (2). It is possible to form a patterned GaN thin film (2) through such a process.

(c) Next, with the patterned GaN thin film (2) formed on the ScAlMgO substrate (1), sulfuric acid represented by the chemical formula H ₂ SO ₄ and H ₂ O ₂ represented by the chemical _formula chemical reaction with ScAlMgO ₄ crystals in a chemical solution containing at least hydrogen peroxide water (FIG. 1(c): etching process of ScAlMgO ₄ substrate). As for the temperature of this chemical, it is possible to etch the ScAlMgO ₄ substrate at a practically acceptable etching rate by etching in a high temperature state of 35° C. or higher. Also, the ScAlMgO ₄ substrate (1) is etched by being immersed in a chemical solution in which at least sulfuric acid and hydrogen peroxide are mixed. Since the temperature rises to nearly 100° C. due to reaction heat immediately after mixing sulfuric acid and peroxide water, etching may be performed with such a chemical solution. Alternatively, for example, the quartz container (12) is set in the constant temperature bath (13) shown in FIG. 2A. In this quartz vessel (12), the temperature of the chemical solution (11), which is a mixture of sulfuric acid and hydrogen peroxide water at a ratio of 3:1, is adjusted to 75°C. The ScAlMgO ₄ substrate (10) having the patterned hard mask described above may be immersed in this chemical solution (11). As a result, it is possible to process the substrate to form grooves at the etching rate shown in FIG. 2B. Here, the temperature of the chemical solution is desirably set in the range of 35°C to 290°C, more preferably in the range of 50°C to 150°C. The higher the temperature, the faster the etching rate, but if the temperature exceeds 290° C., which is the boiling point of sulfuric acid, it becomes difficult to keep the mixing ratio of the chemicals constant, and the U-shaped groove (4) in FIG. It becomes difficult to control the shape of (pattern groove). Industrially, it is preferable to set the chemical liquid temperature to about 50° C. to 150° C., which is inexpensive and has good temperature controllability.

As for the concentration ratio of the chemical solution, the ratio of sulfuric acid to hydrogen peroxide solution (sulfuric acid/hydrogen peroxide solution) is preferably in the range of 1-10. The ScAlMgO ₄ crystal is hardly etched with only sulfuric acid. The present inventors discovered that ScAlMgO ₄ crystals are well soluble in a mixed solution of sulfuric acid and hydrogen peroxide mixed with an appropriate amount of hydrogen peroxide. It is believed that the mixed solution of sulfuric acid and hydrogen peroxide water advances the etching process on the ScAlMgO ₄ substrate by the chemical reaction described below. By supplying oxygen radicals with a hydrogen peroxide solution, strong bonds such as Mg—O having a short bond distance in the AlMgO ₂ layer are cut. When the Mg--O bond is broken, Al is dissolved by sulfuric acid to form aluminum sulfate. If the AlMgO ₂ layer dissolves, then the ScO ₂ layer dissolves while reacting with sulfuric acid to form scandium sulfate. By repeating this process, the ScAlMgO ₄ crystals are dissolved in the chemical solution. The main role of the hydrogen peroxide solution is to cut the Mg—O bond, and the dissolution of the ScAlMgO ₄ crystals is mainly due to sulfuric acid. Therefore, 10% of the ratio of hydrogen peroxide solution to sulfuric acid is sufficient. However, if the mixing ratio is lower than 10%, the generation of reaction heat is suppressed, so there is an aspect that it is difficult to practically use it as a chemical solution. Therefore, as the lower limit of the ratio of the hydrogen peroxide solution, it is preferable to use a chemical solution that contains about 10% of the composition ratio of the sulfuric acid solution. In addition, hydrogen peroxide water is treated as a 35% aqueous solution due to practical safety restrictions. Therefore, even if the ratio of sulfuric acid and hydrogen peroxide solution is 1:1, the concentration of the mixed solution is diluted to about half by the water contained in the hydrogen peroxide solution. If it is diluted further than this, the etching rate will be reduced to half or less, which makes it impractical. Therefore, it is preferable to set the ratio of sulfuric acid to hydrogen peroxide within the above range of 1 to 10.

As shown in FIG. 1(c), the GaN thin film (2) is substantially unetched after such processing, while the ScAlMgO ₄ substrate (1) is U-shaped. It becomes possible to form grooves (4). In particular, since the etching of the ScAlMgO ₄ crystal progresses from the periphery of the island of the GaN thin film (2), a cavity is formed below the periphery of the island of the GaN thin film (2). That is, the surface of a _ScAlMgO4 substrate (1), which is an example of a _RAMO4 substrate, on which a GaN thin film (2), which is an example of a Group III nitride film, is formed is chemically treated with a chemical solution containing at least sulfuric acid and hydrogen peroxide. By reacting and etching, unevenness such as U-shaped grooves (4) is formed on the surface. At this time, a III-nitride film (37) wider than the protrusion can be left on the _ScAlMgO4 support (38), which is an example of the protrusion of the _RAMO4 substrate (FIG. 4D). In this case, the III-nitride film (37) has a longitudinal width R that is greater than the in-plane longitudinal width r of the top of the underlying ScAlMgO ₄ pillars (38). Specifically, the III-nitride film (37) is wide in any direction in the plane of the top of the ScAlMgO ₄ pillars (38). In addition, the unevenness is not limited to the U-shaped groove, and may be another pattern groove.

(d) Finally, the substrate is cleaned to allow crystal growth. By forming a thick film using the GaN thin film (2) thus patterned as a seed crystal, a high-quality GaN crystal (FIG. 1(d): (5)) can be finally obtained.

At this time, since the ScAlMgO ₄ crystal located directly under the outer peripheral portion of the GaN thin film (2) is also partially etched, the ScAlMgO ₄ crystal is only etched in the region offset from the outer peripheral side of the GaN thin film (2) to the inner peripheral side. GaN crystal is connected. That is, at the interface between the GaN crystal (5) and the _ScAlMgO4 substrate (1), voids, which are spatial regions, are formed, and the crystal strain is relaxed in this portion, so the internal stress of the obtained GaN crystal (5) is reduced. It is possible to realize a GaN crystal free from cracks and substrate breakage.

3A, 3B, and 3C are respectively a schematic cross-sectional view showing the cross-sectional structure after removing the mask in the step (b), a micrograph seen from the surface, and a crystal strain in the region (26) in FIG. 3B. It is the schematic which shows the evaluated result. 4A, 4B, 4C, and 4D are a schematic cross-sectional view showing the cross-sectional structure of the ScAlMgO ₄ substrate (1) after wet etching in the step (c), a micrograph seen from the surface, and a GaN substrate. FIG. 10 is a schematic diagram showing the results of evaluating the distribution of intra-crystal strain in a crystal.

FIG. 3A is a schematic cross-sectional view after removing the mask 3 after the step (b). As shown in Figure 3A, a GaN thin film is patterned on a _ScAlMgO4 substrate (22). In other words, the patterned GaN thin film (21) in FIG. 3A has an island shape, and the surface of the ScAlMgO ₄ substrate (22) is exposed in the region (23) between them. FIG. 3B is a surface micrograph showing the island-like GaN film (24) and the regions (25) of the _ScAlMgO4 substrate between the islands. FIG. 3C is a schematic diagram showing the results of evaluating the crystal strain in the region (26) (50.13 μm long×50.19 μm wide) in FIG. 3B. As shown in FIG. 3C, before wet etching of ScAlMgO ₄ , compressive stress is generated in the GaN thin film crystal at the center of the island.

FIG. 4A is a schematic cross-sectional view after the step (c). As shown in FIG. 4A, the GaN thin film (31) on the ScAlMgO ₄ substrate (32) is used as a mask to form etching grooves (33) in the ScAlMgO ₄ crystal (32). From FIG. 4A, it can be seen that an etching groove (33) is formed so as to penetrate into the lower end surface of the GaN thin film (31), and the area of the interface between the GaN thin film (31) and the _ScAlMgO4 substrate (32) is reduced. Recognize. That is, an etching groove (33) is formed so as to cover the end of the etching groove (33), which is an example of a pattern groove, with a GaN thin film (31), which is an example of a group III nitride film. FIG. 4B is a surface micrograph showing islands of the GaN film (34) and etched regions (35) between the islands. FIG. 4C is a schematic diagram showing the results of evaluating the crystal strain in the region (36) (50.13 μm long×50.19 μm wide) in FIG. 4B. As shown in FIG. 4C, after the ScAlMgO ₄ wet etch, the compressive stress is suppressed in the GaN thin crystal at the center of the island compared to the case of FIG. 3C.

In order to achieve the effect of reducing the stress in the GaN thin film, there is a preferable range for the area ratio of the etching grooves (35) under the GaN thin film. FIG. 4D is a schematic cross-sectional view depicting this etching groove (35) in more detail. There are GaN island regions (37) and ScAlMgO ₄ pillars (38) supporting the islands. A hollow region (39) sandwiched between the GaN thin film and the _ScAlMgO4 substrate (40) has a structure that relaxes the stress generated in the GaN crystal. The stress generated in the GaN island region (37) is highly dependent on the ratio of the width (R) of the GaN thin film island to the width (r) of the supporting ScAlMgO ₄ pillars (32). The ScAlMgO ₄ strut (32) has a trapezoidal shape, and the width (r) here indicates the length of the upper base side located on the diameter-reducing side in the cross section in the thickness direction. The GaN crystal on the hollow region (39) sandwiched between the ScAlMgO ₄ and the GaN crystal is in a substantially free state, so no strain occurs. On the other hand, the GaN crystal on the ScAlMgO ₄ pillars (38) has an interface with the ScAlMgO ₄ crystal and strain occurs. However, the smaller the value of r/R, which is the inverse ratio of the width (R) of the GaN islands to the width of the supporting ScAlMgO ₄ pillars (32), the smaller the strain in the crystal. On the other hand, as the value of r/R approaches 1, the strain at the interface increases. Here, the width (R) of the GaN island indicates the length of the longest side in the section in the thickness direction.

When the value of r/R is less than 30%, the dislocation density in the GaN crystal decreases as crystal growth progresses. As a result, the generated crystal strain cannot be endured, and part of the ScAlMgO ₄ struts (32) is peeled off, making it difficult to maintain the crystal orientation and degrading the crystal quality. When the value of r/R is 30% or more, such problems do not occur and stable crystal growth can be achieved.

Conversely, when the value of r/R exceeds 70%, cracks and pits are generated inside the GaN crystal due to strain generated at the interface between the ScAlMgO ₄ crystal and the GaN crystal. In the worst case, cracks occur in the GaN crystal.

Therefore, from the viewpoint of stress relaxation, the etching according to the present disclosure is such that the width of the pillars (32) of _ScAlMgO4 , which is an example of the protrusion, is r, and the left GaN island region (37), which is an example of the group III nitride film, is ) is R, the unevenness is preferably formed so that the ratio value r/R satisfies 30%≦r/R≦70%.

(Embodiment 2)
FIG. 5 is a schematic cross-sectional view showing a step of peeling off a GaN crystal in a method for manufacturing a group III nitride crystal according to the second embodiment.
In contrast to the method for producing a group III nitride crystal according to the first embodiment, the method for producing a group III nitride crystal according to the second embodiment differs from the method for producing a group III nitride crystal according to the first embodiment in that the step of separating the GaN crystal from the _RAMO4 substrate (FIG. 5(b) ). According to the method described in Embodiment 1, the hollow region can be formed under the island due to the isotropic nature of wet etching. Since the method for producing a group III nitride crystal according to the second embodiment further includes a peeling step, it is possible to realize a structure in which the peeling is further facilitated.
_In other words, if the crystal growth can be completed with the structure shown in FIG. The stress that prompts progresses. As a result, more concentrated stress is applied to the island region, and as shown in FIG. 5(b), it becomes possible to develop the peeling of the ScAlMgO ₄ substrate (42) more easily.
As a result, it is possible to obtain a single GaN crystal, which is a Group III nitride crystal with suppressed crystal strain.

It should be noted that the present disclosure includes appropriate combinations of any of the various embodiments and / or examples described above, and each embodiment and / or The effects of the embodiment can be obtained.

1 ScAlMgO ₄ substrate 2 GaN thin film 3 patterned mask 4 patterned U-groove formed on ScAlMgO ₄ substrate 5 epi region on ScAlMgO ₄ substrate 6 ScAlMgO ₄ substrate patterned with U-groove 10 with patterned hard mask. _ScAlMgO4 substrate 11 etching chemical solution 12 quartz bath 13 constant temperature bath 21 GaN thin film 22 _ScAlMgO4 substrate 23 GaN inter-island region 24 GaN island region 25 GaN inter-island region 26 GaN middle strain evaluation region 31 GaN thin film 32 _ScAlMgO4 substrate 33 _ScAlMgO4 Intermediate etching region 34 GaN island region 35 GaN inter-island region 36 GaN intermediate strain evaluation region 41 GaN thick film crystal region 42 ScAlMgO ₄ substrate patterned with U grooves

Claims (4)

A single crystal represented by the general formula RAMO ₄ (wherein R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanide elements, and A represents , Fe(III), Ga, and Al, and M represents one or more trivalent elements selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd. providing a _RAMO4 substrate consisting of one or more divalent elements selected from the group consisting of
forming a III-nitride film on the _RAMO4 substrate;
The surface of the RAMO ₄ substrate on which the group III nitride film is formed is chemically reacted with a chemical solution containing at least sulfuric acid and hydrogen peroxide water to etch the surface, thereby forming unevenness on the surface, and the RAMO _4. A step of leaving a Group III nitride film having a longitudinal direction wider than the longitudinal width of the protrusions on the protrusions of the substrate;
growing a group III nitride crystal on the group III nitride film after forming the unevenness;
A method for producing a group III nitride crystal having 2. The method for producing a Group III nitride crystal according to claim ₁ , wherein the temperature of said chemical in said etching is set within a range of 35.degree. C. to 290.degree. 3. The method for producing group III nitride crystals according to claim 1, wherein the chemical solution has a value of (sulfuric acid/hydrogen peroxide solution) in the range of 1 to 10. The etching is performed so as to satisfy 30%≦r/R≦70%, where r is the width of the protrusion in the longitudinal direction and R is the width of the remaining group III nitride film in the longitudinal direction. 4. The method for producing a Group III nitride crystal according to claim 3, wherein the unevenness is formed.

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