Substrate for epitaxial growth

Abstract

The present invention provides a substrate for epitaxial growth which is made of a single crystal represented by general formula RAMO4 (in the formula, R represents trivalent Sc and at least one trivalent element selected from the group consisting of In, Y, and lanthanoid elements, and A represents at least one trivalent element selected from the group consisting of Fe(III), Ga, and Al. Alternatively, R represents at least one trivalent element selected from the group consisting of Sc, In, Y, and lanthanoid elements, and A represents trivalent Al and at least one trivalent element selected from the group consisting of Fe(III) and Ga. M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd. )

Description

Technical Field

[0001] The present invention relates to a substrate for epitaxial growth.

Background Art

[0002] Single crystals represented by the general formula RAMO4 (in the general formula, R represents at least one trivalent element selected from the group consisting of Sc, In, Y and lanthanoid elements, A represents at least one trivalent element selected from the group consisting of Fe(III), Ga and Al, and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn and Cd.) are known. For example, the ScAlMgO4 substrate is used as a substrate for epitaxial growth of nitride semiconductors such as GaN (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

[0005] As described in Patent Document 2, when ScAlMgO4 is used as a substrate for epitaxial growth and GaN is epitaxially grown on the same substrate, the mismatch rate of the lattice constant of the a-axis of GaN is smaller than that of sapphire, and a reduction in threading dislocations can be expected. As reported in Non-Patent Document 3, ScAlMgO4 is a single crystal represented by the general formula RAMO4, in which R represents at least one trivalent element selected from the group consisting of Sc, In, Y and lanthanide elements, A represents at least one trivalent element selected from the group consisting of Fe(III), Ga and Al, and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn and Cd. ScAlMgO4 is a composition that, in order to match the lattice of GaN, uses Sc as R, Al as A, and Mg as M in the general formula, and is combined in such a way that the lattice constant of the a-axis is smallest. As described in Patent Documents 1 and 2, it is suitable as a substrate for epitaxial growth of GaN.

[0006] Generally, if the lattice constant of the epitaxially grown crystal is smaller than that of the substrate, tensile stress is generated at the interface, making cracks more likely to occur. Furthermore, if the lattice mismatch between the epitaxially grown crystal and the substrate is too large, strain will enter the crystal, causing threading dislocations, making it difficult to obtain sufficient luminescence efficiency. For these reasons, it is important to match the lattice constant of the substrate with that of the epitaxially grown crystal.

[0007] Incidentally, in order to fabricate a red light-emitting element made of nitride semiconductors on a ScAlMgO4 substrate, it has been proposed to epitaxially grow indium gallium nitride (InGaN), which has a larger lattice constant than GaN (see Patent Document 3). Here, if we calculate the lattice constant based on the ionic radius according to Vegard's law, the lattice constant mismatch rate between (In,Ga)N and ScAlMgO4 (lattice constant mismatch rate along the a-axis: (InGaN-ScAlMgO4) / InGaN) is zero when the In content is 15-16 mol% relative to the total amount of In and Ga, but increases when the In content exceeds 17 mol%, which is suitable for red light emission.

[0008] Not limited to ScAlMgO4 substrates, conventional heteroepitaxial substrates primarily use single crystals with stoichiometric compositions, resulting in discrete lattice constants for selectable substrates. Therefore, the aforementioned lattice constant mismatch between the substrate crystal and the epitaxially grown crystal affects the quality of the epitaxially grown crystal and the performance of the devices fabricated using it.

[0009] This invention has been made in view of the above circumstances, and aims to provide an epitaxial growth substrate suitable for the epitaxial growth of indium gallium nitride single crystals. [Means for solving the problem]

[0010] One aspect of the present invention includes, for example, the following embodiments. [1] An epitaxial growth substrate made of a single crystal represented by the general formula RAMO4. [In the formula, R represents trivalent Sc and at least one trivalent element selected from the group consisting of In, Y, and lanthanide elements; A represents at least one trivalent element selected from the group consisting of Fe(III), Ga, and Al; and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd.] [2] An epitaxial growth substrate made of a single crystal represented by the general formula RAMO4. [In the formula, R represents at least one trivalent element selected from the group consisting of Sc, In, Y, and lanthanide elements; A represents trivalent Al and at least one trivalent element selected from the group consisting of Fe(III) and Ga; and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd.] [3] The epitaxial growth substrate according to [1] or [2], wherein the a-axis length of the single crystal is 3.25 to 3.52 Å. [4] The epitaxial growth substrate according to [3], wherein the a-axis length of the single crystal is 3.25 to 3.40 Å. [5] The epitaxial growth substrate according to [4], wherein the a-axis length of the single crystal is 3.25 to 3.30 Å. [6] The epitaxial growth substrate according to [1], wherein A is trivalent Al and at least one trivalent element selected from the group consisting of Fe(III) and Ga. [7] An epitaxial growth substrate as described in [6], comprising a single crystal represented by the general formula (Sc,R)(Al,A)MgO4. [In the formula, R represents at least one trivalent element selected from the group consisting of In, Y, Lu, and Yb, and A represents trivalent Ga.] [8] An epitaxial growth substrate as described in [1], comprising a single crystal represented by the general formula (Sc,R)AlMgO4. [In the formula, R represents at least one trivalent element selected from the group consisting of In, Y, Lu, and Yb.] [9] An epitaxial growth substrate as described in [1], comprising a single crystal represented by the general formula (Sc,R)GaMgO4. [In the formula, R represents at least one trivalent element selected from the group consisting of In, Y, Lu, and Yb.]

[10] An epitaxial growth substrate according to any one of [1] to [9], for the epitaxial growth of indium gallium nitride single crystals.

[0011] The present invention relates to a method for manufacturing an epitaxial growth substrate, based on the inventors' discovery that a single crystal with a larger lattice constant can be prepared by, for example, substituting some of the Sc elements in a general formula ScAlMgO4 single crystal with an R element having a larger ionic radius than Sc to form (Sc,R)AlMgO4, or by substituting some of the Al elements in a general formula ScAlMgO4 single crystal with an A element having a larger ionic radius than Al to form Sc(Al,A)MgO4. For example, the lattice constant of a (Sc,R)AlMgO4 substrate can be adjusted by selecting the type of R and the substitution ratio with respect to Sc, or the lattice constant of a Sc(Al,A)MgO4 substrate can be adjusted by selecting the type of A and the substitution ratio with respect to Al. Furthermore, it is also possible to adjust the lattice constant of a (Sc,R)(Al,A)MgO4 substrate by combining these findings. This makes it possible to provide custom-made substrates that are lattice-matched to each crystal, depending on the type of crystal to be epitaxially grown.

[0012] Conventionally, epitaxial growth substrates made from single crystals represented by the general formula RAMO4 have been developed primarily with the aim of lattice matching to GaN, and therefore, it was sufficient to use ScAlMgO4, which has the smallest a-axis length, as the composition. In other words, the idea of ​​increasing the a-axis length of the single crystal represented by RAMO4 had not been considered at all. However, while the inventors were experimenting with methods to obtain high-quality InGaN by epitaxial growth, they conceived the idea of ​​adjusting the lattice constant, which had not been sufficiently considered in single crystals represented by RAMO4, as described above, and arrived at a single crystal with a new composition. Of course, the above findings are important in particular for fabricating substrates for epitaxial growth of InGaN, but it can be said that they can also be applied to crystals other than InGaN to the extent that is technically reasonable. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide an epitaxial growth substrate suitable for the epitaxial growth of indium gallium nitride single crystals.

[0014] In other words, according to the present invention, it is possible to provide an epitaxial growth substrate that is lattice-matched with an epitaxially grown (In,Ga)N single crystal. For the quality of the epitaxially grown crystal and the performance of the device fabricated using it, it is desirable to provide a substrate crystal in which the desired lattice constant can be arbitrarily selected. According to the present invention, for example, if the lattice constant of the a-axis is In 0.17 Ga 0.83 InN is a group III nitride that is larger than N and smaller than InN. 0.25 Ga 0.75 By epitaxially growing single crystals of materials such as N on a (Sc,R)AlMgO4 substrate, excellent epitaxial single crystals can be obtained in which the occurrence of cracks and through dislocations is suppressed. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a graph showing the change in the lattice constant due to R in RFe2O4. [Figure 2] Figure 2 is a graph showing the change in the lattice constant due to A in RAMO4. [Figure 3] Figure 3 is a graph showing the lattice constant and emission wavelength of an InxGa1-xN single crystal. [Figure 4] Figure 4 is the powder XRD chart of ScAlMgO4 calcined at 1600°C. [Figure 5] Figure 5 is the powder XRD chart of (Sc0.75,Lu0.25)AlMgO4 calcined at 1600°C. [Figure 6] Figure 6 is the powder XRD chart of (Sc0.5,Lu0.5)AlMgO4 calcined at 1600°C. [Figure 7] Figure 7 is a graph showing the change in the Lu substitution rate and the lattice constant on the a-axis of (Sc,Lu)AlMgO4. [Figure 8] Figure 8 is a graph showing the change in the Y substitution rate and the lattice constant on the a-axis of (Sc,Y)AlMgO4. [Figure 9] Figure 9 is a graph showing the change in the Yb substitution rate and the lattice constant on the a-axis of (Sc,Yb)AlMgO4. [Figure 10] Figure 10 is a graph showing the change in the R substitution rate and the lattice constant on the a-axis of (Sc,R)GaMgO4. [Figure 11] Figure 11 is a graph showing the change in the In substitution rate and the lattice constant on the a-axis of (Sc,In)GaMgO4. [Figure 12] Figure 12 is a graph summarizing the lattice constants along the a-axis of the single crystals grown in each example. [Modes for carrying out the invention]

[0016] Preferred embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

[0017] <Substrate for epitaxial growth> This embodiment primarily relates to the following epitaxial growth substrates I and II.

[0018] An epitaxial growth substrate I made of a single crystal represented by the general formula RAMO4. [In the formula, R represents trivalent Sc and at least one trivalent element selected from the group consisting of In, Y, and lanthanide elements; A represents at least one trivalent element selected from the group consisting of Fe(III), Ga, and Al; and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd.] In the above substrate, in addition to trivalent Sc, at least one trivalent element selected from the group consisting of In, Y, and lanthanide elements, which have a larger ionic radius than Sc, is used as R. This makes it possible to lengthen the a-axis in the single crystal represented by RAMO4.

[0019] Epitaxial growth substrate II, consisting of a single crystal represented by the general formula RAMO4. [In the formula, R represents at least one trivalent element selected from the group consisting of Sc, In, Y, and lanthanide elements; A represents trivalent Al and at least one trivalent element selected from the group consisting of Fe(III) and Ga; and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd.] In the above substrate, in addition to trivalent Al, at least one trivalent element selected from the group consisting of Fe(III) and Ga, which have larger ionic radii than Al, is used as A. This makes it possible to lengthen the a-axis in the single crystal represented by RAMO4.

[0020] From a similar perspective, in the epitaxial growth substrate I, A may represent trivalent Al and at least one trivalent element selected from the group consisting of Fe(III) and Ga.

[0021] Since both epitaxial growth substrates I and II described above allow for a longer a-axis length compared to the ScAlMgO4 substrate, they can be suitably used for the epitaxial growth of indium gallium nitride single crystals. In other words, epitaxial growth substrates I and II can also be described as substrates for the epitaxial growth of indium gallium nitride single crystals.

[0022] Since the a-axis length of an indium gallium nitride single crystal varies depending on its composition, the a-axis length can be adjusted by changing the composition of RAMO4 according to the composition of the target indium gallium nitride single crystal.

[0023] The a-axis length of an indium gallium nitride single crystal ranges from approximately 3.18 Å to approximately 3.55 Å. From the perspective of use as a red light-emitting element, the a-axis length of the indium gallium nitride single crystal can be set to 3.25 to 3.40 Å. From these perspectives, the a-axis length of the single crystal used in epitaxial growth substrates I and II can be 3.25 to 3.52 Å, may be 3.25 to 3.40 Å, or may be 3.25 to 3.30 Å.

[0024] The a-axis length (lattice constant of the a-axis) of a crystal represented by the general formula RAMO4 can be determined based on values ​​calculated by powder X-ray diffraction (XRD) after preparing a sintered body of RAMO4. Alternatively, the a-axis length of a single crystal represented by the general formula RAMO4 can be calculated by fabricating a single crystal of RAMO4 and using the bond method with X-ray diffraction. The c-axis length can be determined in the same manner.

[0025] For example, the epitaxial growth substrate may consist of a single crystal represented by the general formula (Sc,R)(Al,A)MgO4. The parenthetical notation (Sc,R), etc., indicates that the two elements form a solid solution. [In the formula, R represents at least one trivalent element selected from the group consisting of In, Y, Lu, and Yb, and A represents trivalent Ga.] By using at least one element selected from the group consisting of In, Y, Lu, and Yb as R for solid solution with Sc, it is possible to increase the lattice constant of the a-axis. Similarly, by using Ga as A for solid solution with Al, it is possible to increase the lattice constant of the a-axis. In this way, by simultaneously solid-solving "R" and "A", it is possible to obtain a solid solution with a desired lattice constant. For example, if the desired lattice constant cannot be obtained even when the substitution rate of "R" exceeds the suitable range for forming a solid solution, it is possible to obtain a solid solution with the desired lattice constant by further adjusting the substitution rate of "A".

[0026] The epitaxial growth substrate may be made of a single crystal represented by the general formula (Sc,R)AlMgO4. [In the formula, R represents at least one trivalent element selected from the group consisting of In, Y, Lu, and Yb.] By using at least one element selected from the group consisting of In, Y, Lu, and Yb as R to form a solid solution with Sc, it is possible to increase the lattice constant of the a-axis. Furthermore, by using Al alone, it is possible to increase the lattice constant of the a-axis from 3.24 Å in ScAlMgO4 without significantly changing the lattice constant of the c-axis.

[0027] The epitaxial growth substrate may be made of a single crystal represented by the general formula (Sc,R)GaMgO4. [In the formula, R represents at least one trivalent element selected from the group consisting of In, Y, Lu, and Yb.] By using at least one element selected from the group consisting of In, Y, Lu, and Yb as R to form a solid solution with Sc, it is possible to increase the lattice constant of the a-axis. Furthermore, by using Ga alone instead of Al, it is possible to increase the lattice constant of the a-axis from 3.27 Å for ScGaMgO4. By using Ga alone, the substitution rate of R can be reduced compared to when Al is used alone, and the lattice constant of the c-axis can be increased.

[0028] The epitaxial growth substrate may also be made of a single crystal represented by ScGaMgO4.

[0029] The epitaxial growth substrate described above is a compound of general formula RAMO4 that takes on a YbFe2O4 crystal structure, as described in Non-Patent Document 3, where R is a trivalent metal element occupying an octahedral oxygen hexa-coordinate site in the YbFe2O4 crystal structure, A is a trivalent metal element occupying a bipyramidal triangular oxygen penta-coordinate site, and M is a divalent metal element occupying a bipyramidal triangular oxygen penta-coordinate site, and both A and M are metal elements occupying bipyramidal triangular oxygen penta-coordinate sites in the YbFe2O4 crystal structure. At least one of R and A is a solid solution of two or more independent elements. Here, "independent" means that the solid solution of A in R and the solid solution of R in A are not included in the two elements.

[0030] Hereinafter, the ionic radius of the present invention will be explained using the Crystal Radii described in Non-Patent Document 4. Here, the average ionic radius is calculated as follows when multiple ions coexist in solid solution at a specific oxygen coordination site represented by R, A, M, etc. in the general formula. When a specific ion site is composed of ion species X1, X2, ..., Xi, the average ionic radius = y1 × z1 + y2 × z2 + ... + yi × zi can be calculated from the crystal radii values ​​y1, y2, ..., yi of each ion and their constituent ratios z1, z2, ..., zi. In compounds of the general formula RAMO4, the average ionic radius of R, which consists of two or more elements, is r ≤ 1.041 Å, and compounds of the general formula RAMO4 are crystals where the average ionic radii r, a, and m of R, A, and M satisfy 3.2 < (2 × r) / (a ​​× m) < 4.0. Furthermore, in compounds of the general formula RAMO4, the average ionic radius of A, which consists of two or more elements, is a ≤ 0.72 Å, and compounds of the general formula RAMO4 are crystals in which the average ionic radii r, a, and m of R, A, and M satisfy 3.2 < (2 × r) / (a ​​× m) < 4.0. For example, in the case of ScAlMgO4, since each element is an element of 1, we can use the ionic radius of that element, and calculate (2 × 0.885) / (0.80 × 0.62) = 3.6, which satisfies the above relationship. Incidentally, among the compounds of RAMO4, the crystal with the longest a-axis length that satisfies the above relationship is YFe2O4, and its a-axis lattice constant has been reported to be 3.511 Å ((2 × 1.04) / (0.72 × 0.78) = 3.7).

[0031] A substrate crystal with the desired a-axis lattice constant a0 is prepared by the following procedure. First, for a RAMO4 compound (XS) with a lattice constant a1 smaller than the desired a0 and a RAMO4 compound (XL) with a lattice constant a2 larger than the desired a0, solid solution compositions are designed by applying Vegard's rule, and crystals are fabricated. Next, the crystal structure and a-axis lattice constant of the prototypes are measured by X-ray diffraction. If the measurement results differ from the design values ​​by exceeding the allowable deviation, the solid solution composition is redesigned based on the measured values, and crystals are fabricated again. It is necessary to repeat the design and fabrication of the solid solution composition until the a-axis lattice constant of the fabricated crystals is below the allowable deviation. Specifically, this is done as follows. The desired a0 of the present invention is a value assumed when 3.28 Å suitable for the underlying layer (host layer) of red-light-emitting InGaN is taken as the design value. This desired value a0 depends on the design concept of the device and is not actually limited to the value of the present invention. Generally, the lattice mismatch rate is considered to be acceptable within 0.1%. When a0 is 3.28 Å, the allowable deviation range is 3.25 Å to 3.36 Å. As the RAMO4 compound (XS) having a lattice constant a1 smaller than the desired a0, ScAlMgO4 is selected. As the RAMO4 compound (XL) having a lattice constant a2 larger than the desired a0, in addition to LuAlMgO4, YAlMgO4, YbAlMgO4, InAlMgO4, one or more are selected from ScAlGaO4, LuAlGaO4, YAlGaO4, YbAlGaO4, InAlGaO4 to design a solid solution. In the case of a RAMO4 compound (XL) having a lattice constant a2 that does not satisfy the relational expression of 3.2 < (2×r) / (a×m) < 4.0, the Vegard's law is not applicable to the RAMO4 compound (XS) having a small lattice constant a1 and the RAMO4 compound (XL) having a large lattice constant a2. In that case, a RAMO4 compound (XM) powder sample having a solid solution composition predicted to have a lattice constant a3 larger than a0 is prepared. Next, the Vegard's law is applied to the RAMO4 compound (XS) having a lattice constant a1 smaller than a0 and the RAMO4 compound (XM) having a solid solution composition predicted to have a lattice constant a3 larger than a0, and after obtaining the substitution rate of the solid solution that gives the desired a0, the growth of a single crystal can be demonstrated.

[0032] From the experiment of the powder sample, when Lu is selected as R from the single crystal represented by the general formula (Sc, R)AlMgO4, when the amount ratio of Sc and R is defined as the substitution rate x, the range of 0 < x ≦ 0.5 is suitable according to the Vegard's law. When the desired a0 is 3.28 Å suitable for the underlying layer of red-light-emitting InGaN, it is approximately x = 0.32. From the experiment of the powder sample, when Y is selected as R from the single crystal represented by the general formula (Sc, R)AlMgO4, when the amount ratio of Sc and R is defined as the substitution rate x, the range of 0 < x ≦ 0.25 is suitable according to the Vegard's law. From the experiments on powder samples, when Yb is selected as R from single crystals represented by the general formula (Sc,R)AlMgO4, when the amount ratio of Sc to R is defined as the substitution rate x, the range of 0 < x ≤ 0.5 is suitable according to Vegard's law. When the desired a0 is 3.28 Å suitable for the underlying layer of red-emitting InGaN, it is approximately x = 0.25. From the experiments on powder samples, when Lu is selected as R from single crystals represented by the general formula (Sc,R)GaMgO4, when the amount ratio of Sc to R is defined as the substitution rate x, the range of 0 < x ≤ 0.25 is suitable according to Vegard's law. When the desired a0 is 3.28 Å suitable for the underlying layer of red-emitting InGaN, it is approximately x = 0.09. It is possible to make x smaller than the case of (Sc,R)AlMgO4. From the experiments on powder samples, when Yb is selected as R from single crystals represented by the general formula (Sc,R)GaMgO4, when the amount ratio of Sc to R is defined as the substitution rate x, the range of 0 < x ≤ 0.25 is suitable according to Vegard's law. When the desired a0 is 3.28 Å suitable for the underlying layer of red-emitting InGaN, it is approximately x = 0.06. It is possible to make x smaller than the case of (Sc,R)AlMgO4. From the experiments on powder samples, when In is selected as R from single crystals represented by the general formula (Sc,R)GaMgO4, when the amount ratio of Sc to R is defined as the substitution rate x, the range of 0 < x ≤ 0.75 is suitable according to Vegard's law. When the desired a0 is 3.28 Å suitable for the underlying layer of red-emitting InGaN, it is approximately x = 0.39. In the growth of single crystals, the general formula is (Sc,R)(Al,A)MgO4, and the amount ratio of Sc to R is the substitution rate x, and the amount ratio of Al to A is y. In the results of single crystal growth, when R is Lu, attempts were made to grow crystals with x = 0.32 and y = 0 and y = 0.1, and it was confirmed that single crystal formation occurred. When R is Yb, attempts were made to grow crystals with x = 0.25 and y = 0.1, and it was confirmed that single crystal formation occurred.

[0033] Figure 1 is a graph showing the change in the lattice constant due to "R" in RFe2O4. As shown in Figure 1, the a-axis length of the RFe2O4 crystal is proportional to the ionic radius of R according to Vegard's law. Figure 2 is a graph showing the change in the lattice constant due to "A" in RAMO4. As shown in Figure 2, in the case of InAMgO4 and ScAMgO4, the length of the a-axis is proportional to the ionic radius of A according to Vegard's law.

[0034] Figure 3 shows In x Ga 1-x This graph shows the lattice constant and emission wavelength of an N single crystal. The figure shows the relationship between the lattice constant and bandgap energy of a group III nitride semiconductor (Al, Ga, In)N disclosed in Non-Patent Literature 2 (see Figure 1 in the document).

[0035] GaN and InN form a perfect solid solution, allowing for any possible composition ratio. The energy gap is determined by the GaN-InN composition ratio, and the emission wavelength can be selected from ultraviolet light (energy gap 3.42 eV: wavelength 363 nm) of GaN to infrared light (energy gap 0.77 eV: wavelength 1610 nm) of InN. The approximate GaN-InN composition ratio required for red emission can be read from Figure 3. Figure 3 shows that the a-axis lattice constants of GaN and InN are 3.19 Å and 3.55 Å, respectively. Generally, in red and green LEDs, in order to create a quantum well structure for the light-emitting layer, the underlying host layer must be an InGaN layer with a composition that emits a wavelength shorter than the light-emitting layer. In addition, to alleviate stress that causes a decrease in luminous efficiency, it is necessary to stack multiple InGaN layers with intermediate lattice constants (InGaN layers with a lower In substitution rate than the light-emitting layer) as host layers from the substrate up to the light-emitting layer. In other words, to realize LEDs with long wavelengths, it is necessary to form multiple InGaN layers with large lattice constants, and in order to accommodate various InGaN layer designs, a growth substrate with a lattice constant of 3.25 to 3.52 Å, which is larger than the lattice number of conventional ScAlMgO4, is required. Note that this lattice constant may be smaller than the lattice constant of the InGaN composition that emits light at the desired wavelength. As a host layer serving as a base for a red light-emitting layer that emits red light, for example, In 0.25 Ga 0.75 When using an N crystal, the lattice constant of the a-axis of the crystal is estimated to be approximately 3.28 Å by interpolating from the end components GaN (3.19 Å) and InN (3.55 Å) according to Vegard's law.

[0036] In RAMO4, when the ionic radius of the substitution element R is larger than Sc (0.745 Å), for example, Lu (1.001 Å), Y (1.040 Å), Yb (1.008 Å), or when the ionic radius of the substitution element A is larger than Al (0.62 Å), such as Ga (0.69 Å), the lattice constant of the a-axis becomes larger than that of ScAlMgO4 (3.245 Å). Therefore, (Sc, R)AMO4, R(Al, A)MO4, or (Sc, R)(Al, A)MO4 is expected to be lattice-matched with a host layer serving as a base for a red light-emitting layer having a lattice constant with an In substitution rate in InGaN (InN composition ratio (molar ratio) to GaN) greater than 0.17 due to R and / or A being substituted by the above elements to form a solid solution.

[0037] Sc 3+ 、Lu 3+ 、Y 3+ 、Yb 3+ etc. are known to enter the 6-coordination position because they are significantly larger than the ionic radius of Al 3+ , and Mg 2+ , Al 3+ etc. enter the 4-coordination position. By adjusting the ratios of Sc to Lu, Y, Yb and the ratio of Al to Ga within the solid solubility range, a substrate having a lattice constant lattice-matched with, for example, In 0.25 Ga 0.75 N can be realized.

[0038] While single crystals represented by the general formula RAMO4 are known, without knowledge of the elemental ratios when multiple elements are used as R and A, it is not possible to strictly match them to the lattice constant of an (In,Ga)N single crystal with an arbitrary InGa ratio. In this embodiment, the Sc and Al at the R and A sites of RAMO4 are partially substituted with other elements in appropriate ratios for a specific purpose to form a solid solution, and a substrate with a lattice constant that matches to an (In,Ga)N single crystal with an arbitrary lattice constant can be provided. It is also possible to match the lattice to reduce threading dislocations, or to introduce strain and apply an electric field by intentionally creating a slight mismatch.

[0039] A powder having the composition of general formula RAMO4 can be obtained, for example, by preparing a molded body from mixed raw materials, firing it, and then grinding it.

[0040] A single crystal having the composition of general formula RAMO4 can be obtained, for example, by preparing a calcined powder from mixed raw materials, melting it, and using a single crystal growth furnace to obtain it by the pulling method. However, the method of growing the single crystal is not limited to this, and other methods such as the TSSG method, EFG method, and Bridgman method may also be used. The obtained single crystal can be cleaved, or cut into c-plate crystals using a wire saw, outer blade, inner blade, or other simple cutting machine, thereby producing a single crystal body represented by the general formula RAMO4 that can be used as a substrate for epitaxial growth. [Examples]

[0041] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples.

[0042] <Preparation of powder samples> Powders of Sc2O3, Lu2O3, Y2O3, Yb2O3, In2O3, MgO, Al2O3, and Ga2O3 were weighed so that the molar ratios of each element (Sc, Lu, Y, Yb, In, Al, Mg, and Ga) matched the values ​​in Table 1. The mixtures were then mixed using a mixer and a mortar and pestle, solidified using a cold isostatic press, and then calcined at 1600°C for 100 hours. The calcined material was then pulverized and mixed to prepare powder samples. Here, "substitution rate" refers to the molar ratio of the element that substitutes for R or A in RAMO4. For example, the Lu substitution rate refers to the molar ratio of Lu when the total amount of Sc and Lu is set to 1.

[0043] [Table 1]

[0044] <Measurement of lattice constant of powder samples> As described above, the obtained powder samples were mixed with Si standard samples, ground and mixed using a mortar and pestle, and then analyzed and measured using a powder XRD instrument. RAMO4 was identified, and the a-axis length for each sample was determined using Bragg's equation from the 2θ of the (110) diffraction peak of RAMO4 corrected for Si's (111).

[0045] The unit cell length along the c axis of ScAlMgO4 is 25.160 Å, and the unit cell length along the a axis is 3.245 Å. Typically, a GaN layer or Ga layer is placed on top of the c plate of ScAlMgO4. 1-x In x Since the N layer is grown epitaxially, the lattice constant of the a-axis becomes important.

[0046] (Example 1; Preparation of Lu-partially substituted ScAlMgO4 powder sample) Sc2O3: 42.9g, Al2O3: 31.7g, and MgO: 25.4g were weighed and placed in a plastic bottle, then mixed for 4 hours in a Synmaru Enterprises Turbra shaker mixer. After removing the mixture from the plastic bottle, it was placed in a platinum crucible and calcined in air at 1600°C for 100 hours (Table 1 Composition (1)). Additionally, 123.8g of Lu2O3, 31.7g of Al2O3, and 25.4g of MgO were weighed and placed in a plastic bottle, then mixed for 4 hours using a Synmaru Enterprises Turbra shaker mixer. After removing the mixture from the plastic bottle, it was placed in an aluminium and calcined in air at 1600°C for 100 hours. After finely grinding each calcined powder using a mortar and pestle, 5g was taken from a mixture of Sc2O3:42.94g, Al2O3:31.7g, and MgO:25.4g, and 9g from a mixture of Lu2O3:123.8g, Al2O3:31.7g, and MgO:25.4g. These were then ground and mixed using a mortar and pestle, pressed, and calcined in air at 1600°C for 100 hours (Table 1 Composition (3)). Similarly, the above mixed calcined material was weighed to achieve the composition (2) shown in Table 1, crushed and mixed in a mortar and pestle, then pressed and calcined in air at 1600°C for 100 hours.

[0047] Figure 4 is the powder XRD chart of ScAlMgO4 calcined at 1600°C.

[0048] Figure 5 shows the results of firing at 1600°C (Sc 0.75 Lu 0.25 This is an XRD chart of AlMgO4 powder.

[0049] Figure 6 shows the results of firing at 1600°C (Sc 0.5 Lu 0.5 This is an XRD chart of AlMgO4 powder.

[0050] Figure 7 is a graph showing the change in the Lu substitution rate and the lattice constant on the a-axis of (Sc,Lu)AlMgO4.

[0051] According to Non-Patent Document 1, the a-axis lattice mismatch rate of ScAlMgO4 with respect to GaN is 1.8%, and the misfit dislocation density is 5.9 × 10⁻⁶. 11 / cm 2(ScAlMgO4) is calculated. On the other hand, according to Non-Patent Literature 1, the a-axis lattice mismatch rate of sapphire with respect to GaN is approximately 14.0%, which is an order of magnitude larger than that of ScAlMgO4, and the misfit dislocation density of sapphire is 4.0 × 10 13 / cm 2 (Sapphire) is calculated to be the result shown. In other words, compared to ScAlMgO4, the misfit dislocation density in sapphire is two orders of magnitude larger. ScAlMgO4, with its low misfit dislocation density, is said to be able to reduce the threading dislocation density of InGaN originating from misfit dislocations. On the other hand, ScAlMgO4 and In 0.25 Ga 0.75 The lattice mismatch rate of N is approximately 1%, and by using the present invention, it is possible to prepare a substrate in which the lattice mismatch rate can be further reduced by an order of magnitude to within 0.1%, and it is expected that the threading dislocation density can be further reduced. From the results of compositions (2) and (3), as shown in Figure 7, if the substitution rate x is around 0.30 to 0.35, In used in red and green LEDs, etc. 0.25 Ga 0.75 An a-axis length can be obtained in which the mismatch with the a-axis length (lattice length 3.28 Å) of the N crystal material is approximately within 0.1%, and In 0.25 Ga 0.75 It can be seen that a lattice-matched epitaxial growth substrate can be obtained with N-crystal material.

[0052] (Example 2; Preparation of Yb-partially substituted ScAlMgO4 powder sample) A mixed calcined product was prepared in the same manner as described above, except that the raw materials were changed. The mixed calcined product was weighed and mixed to have compositions (6) and (7) as shown in Table 1, pressed, and calcined at 1600°C for 100 hours.

[0053] Figure 9 is a graph showing the relationship between the Yb substitution rate and the lattice constant of the a-axis in (Sc,Yb)AlMgO4. Figure 9 shows the relationship between the a-axis length and the Yb substitution rate in (Sc,Yb)AlMgO4 in which Yb, which has an ionic radius greater than Sc, is dissolved. From the results of compositions (6) and (7), Figure 9 shows that if the substitution rate x is around 0.23 to 0.27, then the In used in red and green LEDs, etc. 0.25 Ga0.75 An a-axis length can be obtained in which the mismatch with the a-axis length (lattice length 3.28 Å) of the N crystal material is approximately within 0.1%, and In 0.25 Ga 0.75 It can be seen that a lattice-matched epitaxial growth substrate can be obtained with N-crystal material.

[0054] (Example 3; Preparation of (Sc,R)GaMgO4 powder sample) A mixed calcined product was prepared in the same manner as described above, except that the raw materials were changed. The mixed calcined product was weighed and mixed to have compositions (8), (9), and (10) as shown in Table 1, pressed, and calcined at 1600°C for 100 hours. Figure 10 is a graph showing the relationship between the R substitution rate and the lattice constant of the a-axis in (Sc,R)GaMgO4. Figure 10 shows the relationship between the a-axis length and the R substitution rate x of (Sc,R)GaMgO4 in which Ga with an ionic radius greater than Al is dissolved. From the results of compositions (8), (9), and (10), Figure 10 shows that if X = 0.06 to 0.13 for (Sc,Lu)GaMgO4 and x = 0.04 to 0.10 for (Sc,Y)GaMgO4, then In used in red and green LEDs, etc. 0.25 Ga 0.75 An a-axis length can be obtained in which the mismatch with the a-axis length (lattice length 3.28 Å) of the N crystal material is approximately within 0.1%, and In 0.25 Ga 0.75 It can be seen that a lattice-matched epitaxial growth substrate can be obtained with N-crystal material.

[0055] (Example 4; Preparation of Y-substituted ScAlMgO4 powder sample) A mixed calcined product was prepared in the same manner as described above, except that the raw materials were changed. The mixed calcined product was weighed and mixed to have compositions (4) and (5) as shown in Table 1, pressed, and calcined at 1600°C for 100 hours.

[0056] Figure 8 is a graph showing the relationship between the Y substitution rate and the lattice constant of the a-axis in (Sc,Y)AlMgO4. Figure 8 shows the relationship between the a-axis length and the Y substitution rate in (Sc,Y)AlMgO4 in which Y, which has a larger ionic radius than Sc, is dissolved. It can be seen that the lattice constant is larger than that of ScAlMgO4 (3.245 Å).

[0057] As shown in Example 3, the a-axis length can be further extended by substituting Al with Ga while keeping the Y substitution rate below 0.25. In other words, in a ScAlMgO4 single crystal, by substituting Al with Ga and partially substituting some of Sc with Y, etc., it is possible to manufacture a substrate with a similar lattice constant while reducing the amount of expensive Lu and Sc. In the RAMO4 material system, Vegard's law holds independently or mutually between the ionic radius of the element partially substituting the trivalent "R" and the ionic radius of the trivalent "A" element. Even if a different phase occurs with each element individually, it is thought that a single phase of RAMO4 with a large lattice constant can exist by adjusting the ratio of each element. In other words, even if the substitution rate of "R" exceeds the suitable range for a solid solution, if the desired lattice constant cannot be obtained, it is possible to create a solid solution with the desired lattice constant by adjusting the substitution rate of "A".

[0058] (Example 5; Preparation of In-partially substituted ScGaMgO4 powder sample) A mixed calcined product was prepared in the same manner as described above, except that the raw materials were changed. The mixed calcined product was weighed and mixed to have compositions (11) and (12) as shown in Table 1, pressed, and calcined at 1600°C for 100 hours.

[0059] Figure 11 is a graph showing the relationship between the In substitution rate and the lattice constant of the a-axis in (Sc,In)GaMgO4. Figure 11 shows the relationship between the a-axis length and the R substitution rate x of (Sc,In)GaMgO4 in which Ga, which has an ionic radius greater than Al, is dissolved. Although there is no linear relationship between the a-axis length and the substitution rate, from the results of (11) and (12), even in the case of (Sc,In)GaMgO4, when the substitution rate x is in the range of 0.31 to 0.37, In used in red and green LEDs, etc. 0.25 Ga 0.75 An a-axis length can be obtained in which the mismatch with the a-axis length (lattice length 3.28 Å) of the N crystal material is approximately within 0.1%, and In 0.25 Ga 0.75 It can be seen that a lattice-matched epitaxial growth substrate can be obtained with N-crystal material.

[0060] <Growing single crystals> (Example 6; Growth of Lu-partially substituted ScAlMgO4 single crystal 1) Scandium oxide (Sc2O3), magnesium oxide (MgO), aluminum oxide (Al2O3), and lutetium oxide (Lu2O3) powders were weighed and mixed to prepare a partially substituted Lu ScAlMgO4 calcined powder with a Lu substitution rate of x = 0.32. The resulting powder was placed in a platinum crucible, calcined at 1600°C, cooled, and then placed in an iron crucible in a single crystal growth furnace. A Lu substitution rate of x = 0.32 corresponds to a substitution rate of 3.28 Å obtained using Vegard's law for powder samples. An iron crucible was heated using high-frequency induction heating, and the calcined powder was melted in nitrogen containing trace amounts of oxygen. A seed was then brought into contact with the molten material and solidified to pull up a single crystal. After separating the grown single crystal from the molten material and cooling, it was removed from the furnace. As described above, a Lu-partially substituted ScAlMgO4 single crystal was obtained.

[0061] (Measurement of lattice constant of single crystal) The obtained Lu-substituted ScAlMgO4 single crystal was cleaved or cut with a wire saw to obtain a 1 mm thick c plate. This c plate was placed in a Rigaku ATX X-ray diffractometer, and the lattice constant was obtained by the bond method. In the bond method, the lattice plane spacing d was first obtained from the 2θ value, which is the (0024) peak. 0024 The c-axis length of 25.1226 Å was calculated from equation (1). Next, from the 2θ value, which is the peak in (2014), d 2014 The c-axis length was measured and calculated, and using this length, the a-axis length of 3.2703 Å was determined, confirming that the lattice constant of the a-axis was larger than that of the ScAlMgO4 grown as a comparative example.

number

[0062] (Example 7; Growth of Lu-partially substituted ScAlMgO4 single crystal 2) Subsequently, after growing a Lu-partially substituted ScAlMgO4 single crystal (1), a Lu-partially substituted ScAlMgO4 calcined powder with a substitution rate of x=0.32 was weighed to the same weight as the crystal grown in Lu-partially substituted ScAlMgO4 single crystal growth (1) and placed in the Ir crucible inside the single crystal growth furnace as an additional charge composition. An iron crucible was heated using high-frequency induction heating, and the calcined powder was melted in nitrogen containing trace amounts of oxygen. A seed was then brought into contact with the molten material and solidified to pull up a single crystal. After separating the grown single crystal from the molten material and cooling, it was removed from the furnace. As described above, a Lu-partially substituted ScAlMgO4 single crystal was obtained.

[0063] (Measurement of lattice constant of single crystal) The obtained Lu-substituted ScAlMgO4 single crystal was cleaved or cut with a wire saw to obtain a 1 mm thick c plate. This c plate was placed in a Rigaku ATX X-ray diffractometer, and the lattice constant was obtained by the bond method. In the bond method, the lattice plane spacing d was first obtained from the 2θ value, which is the (0024) peak. 0024 The c-axis length was measured, and a value of 25.1043 Å was calculated from equation (1). Next, from the 2θ value, which is the peak in (2014), d 2014 The c-axis length was measured and calculated, and using this length, the a-axis length of 3.27241 Å was determined, confirming that the lattice constant of the a-axis was larger than that of the ScAlMgO4 grown as a comparative example.

[0064] (Example 8; Growth of Lu-partially substituted ScAlMgO4 single crystal 3) Subsequently, after growing a Lu-partially substituted ScAlMgO4 single crystal (step 2), as an additional charge composition, a Lu-partially substituted ScAlMgO4 calcined powder with a Lu substitution rate of x = 0.32 was weighed to the same weight as the crystal grown in Lu-partially substituted ScAlMgO4 single crystal growth step 1 and placed in the Ir crucible inside the single crystal growth furnace. An iron crucible was heated using high-frequency induction heating, and the calcined powder was melted in nitrogen containing trace amounts of oxygen. A seed was then brought into contact with the molten material and solidified to pull up a single crystal. After separating the grown single crystal from the molten material and cooling, it was removed from the furnace. As described above, a Lu-partially substituted ScAlMgO4 single crystal was obtained.

[0065] (Measurement of lattice constant of single crystal) The obtained Lu-substituted ScAlMgO4 single crystal was cleaved or cut with a wire saw to obtain a 1 mm thick c plate. This c plate was placed in a Rigaku ATX X-ray diffractometer, and the lattice constant was obtained by the bond method. In the bond method, the lattice plane spacing d was first obtained from the 2θ value, which is the (0024) peak. 0024 The c-axis length of 25.1118 Å was calculated from equation (1). Next, from the 2θ value, which is the peak in (2014), d 2014 The c-axis length was measured and calculated, and using this length, the a-axis length of 3.26936 Å was determined, confirming that the lattice constant of the a-axis was larger than that of the ScAlMgO4 grown as a comparative example.

[0066] (Example 9; Growth of Lu-partially substituted ScAlMgO4 single crystal 4) Next, after growing the Lu-partially substituted ScAlMgO4 single crystal 3, as an additional charge composition, a Lu-partially substituted ScAlMgO4 calcined powder with a Lu substitution rate of x=0.50 was weighed to the same weight as the crystal grown in Lu-partially substituted ScAlMgO4 single crystal growth 1 and placed in the Ir crucible inside the single crystal growth furnace. An iron crucible was heated using high-frequency induction heating, and the calcined powder was melted in nitrogen containing trace amounts of oxygen. A seed was then brought into contact with the molten material and solidified to pull up a single crystal. After separating the grown single crystal from the molten material and cooling, it was removed from the furnace. As described above, a Lu-partially substituted ScAlMgO4 single crystal was obtained.

[0067] (Measurement of lattice constant of single crystal) The obtained Lu-substituted ScAlMgO4 single crystal was cleaved or cut with a wire saw to obtain a 1 mm thick c plate. This c plate was placed in a Rigaku ATX X-ray diffractometer, and the lattice constant was obtained by the bond method. In the bond method, the lattice plane spacing d was first obtained from the 2θ value, which is the (0024) peak. 0024 The c-axis length was measured, and a value of 25.089 Å was calculated from equation (1). Next, from the 2θ value, which is the peak in (2014), d 2014 The c-axis length was measured and calculated, and using this length, the a-axis length of 3.27352 Å was determined, confirming that the lattice constant of the a-axis was larger than that of the ScAlMgO4 grown as a comparative example.

[0068] (Example 10; Growth of Lu, Ga partially substituted ScAlMgO4 single crystals) Scandium oxide (Sc2O3), magnesium oxide (MgO), aluminum oxide (Al2O3), lutetium oxide (Lu2O3), and gallium oxide (Ga2O3) powders were weighed and mixed to prepare calcined ScAlMgO4 powders with partial Lu substitution (Lu substitution rate x=0.32) and partial Ga substitution (Ga substitution rate y=0.10). The resulting powders were placed in a platinum crucible, calcined at 1600°C, cooled, and then placed in an iron crucible in a single crystal growth furnace. An iron crucible was heated using high-frequency induction heating, and the calcined powder was melted in nitrogen containing trace amounts of oxygen. A seed was then brought into contact with the molten material and solidified to pull up a single crystal. After separating the grown single crystal from the molten material and cooling, it was removed from the furnace. As described above, a Lu,Ga partially substituted ScAlMgO4 single crystal was obtained.

[0069] (Measurement of lattice constant of single crystal) The obtained Lu,Ga partially substituted ScAlMgO4 single crystal was cut by cleavage or wire sawing to obtain a 1 mm thick c plate. This c plate was placed in a Rigaku ATX X-ray diffractometer, and the lattice constant was obtained by the bond method. In the bond method, the lattice plane spacing d was first obtained from the 2θ value, which is the (0024) peak. 0024 The c-axis length of 25.1828 Å was calculated from equation (1). Next, from the 2θ value, which is the peak in (2014), d 2014The c-axis length was measured, and using the calculated c-axis length, the a-axis length of 3.27311 Å was calculated, confirming that the lattice constant of the a-axis was larger than that of the ScAlMgO4 grown as a comparative example.

[0070] (Example 11; Growth of Yb, Ga partially substituted ScAlMgO4 single crystals) Scandium oxide (Sc2O3), magnesium oxide (MgO), aluminum oxide (Al2O3), ytterbium oxide (Yb2O3), and gallium oxide (Ga2O3) powders were weighed and mixed to prepare calcined ScAlMgO4 powders with Yb partial substitution (Yb substitution rate x=0.25) and Ga partial substitution (Ga substitution rate y=0.10). The resulting powders were placed in a platinum crucible, calcined at 1600°C, cooled, and then placed in an iron crucible in a single crystal growth furnace. An iron crucible was heated using high-frequency induction heating, and the calcined powder was melted in nitrogen containing trace amounts of oxygen. A seed was then brought into contact with the molten material and solidified to pull up a single crystal. After separating the grown single crystal from the molten material and cooling, it was removed from the furnace. As described above, a Yb,Ga partially substituted ScAlMgO4 single crystal was obtained.

[0071] (Measurement of lattice constant of single crystal) The obtained Yb,Ga partially substituted ScAlMgO4 single crystal was cleaved or cut with a wire saw to obtain a 1 mm thick c plate. This c plate was placed in a Rigaku ATX X-ray diffractometer, and the lattice constant was obtained by the bond method. In the bond method, the lattice plane spacing d was first obtained from the 2θ value, which is the (0024) peak. 0024 The c-axis length of 25.1877 Å was calculated from equation (1). Next, from the 2θ value, which is the peak in (2014), d 2014 The c-axis length was measured, and using the calculated c-axis length, the a-axis length of 3.26606 Å was calculated, confirming that the lattice constant of the a-axis was larger than that of the ScAlMgO4 grown as a comparative example.

[0072] (Example 12; Growth of Ga-substituted ScAlMgO4 single crystal) Scandium oxide (Sc2O3), magnesium oxide (MgO), aluminum oxide (Al2O3), and gallium oxide (Ga2O3) powders were weighed and mixed to prepare a partially Ga-substituted ScAlMgO4 calcined powder with a Ga substitution rate of y = 0.1. The resulting powder was placed in a platinum crucible, calcined at 1600°C, cooled, and then placed in an iron crucible in a single crystal growth furnace. An iron crucible was heated using high-frequency induction heating, and the calcined powder was melted in nitrogen containing trace amounts of oxygen. A seed was then brought into contact with the molten material and solidified to pull up a single crystal. After separating the grown single crystal from the molten material and cooling, it was removed from the furnace. As described above, a Ga-partially substituted ScAlMgO4 single crystal was obtained.

[0073] (Measurement of lattice constant of single crystal) The obtained Ga-substituted ScAlMgO4 single crystal was cleaved or cut with a wire saw to obtain a 1 mm thick c plate. This c plate was placed in a Rigaku ATX X-ray diffractometer, and the lattice constant was obtained by the bond method. In the bond method, the lattice plane spacing d was first obtained from the 2θ value, which is the (0024) peak. 0024 The c-axis length was measured, and a value of 25.2252 Å was calculated from equation (1). Next, from the 2θ value, which is the peak in (2014), d 2014 The c-axis length was measured, and using the calculated c-axis length, the a-axis length of 3.2520 Å was calculated, confirming that the lattice constant of the a-axis was larger than that of the ScAlMgO4 grown as a comparative example.

[0074] (Comparative Example 1; Preparation of ScAlMgO4 powder sample) 42.9 g of Sc2O3, 31.7 g of Al2O3, and 25.4 g of MgO were weighed and placed in a plastic bottle. They were mixed for 4 hours in a Synmaru Enterprises Turbra shaker mixer. After removing the mixture from the plastic bottle, it was placed in a platinum crucible and calcined in air at 1600°C for 100 hours (Table 1 Composition (1)). The a-axis length was 3.246 Å.

[0075] (Comparative Example 2: Growth of ScAlMgO4 single crystals) Scandium oxide (Sc2O3), magnesium oxide (MgO), and aluminum oxide (Al2O3) powders were weighed and mixed as raw materials to obtain a mixed powder. The resulting mixed powder was placed in a platinum crucible, calcined at 1600°C, and then cooled. After that, the calcined powder was placed in an Ir crucible inside a single crystal growth furnace. An iron crucible was heated using high-frequency induction heating, and the calcined powder was melted in nitrogen containing trace amounts of oxygen. A seed was then brought into contact with the molten material and solidified to pull up a single crystal. After separating the grown single crystal from the molten material and cooling, it was removed from the furnace. As described above, a single crystal of ScAlMgO4 was obtained.

[0076] (Measurement of lattice constant of single crystal) The obtained ScAlMgO4 single crystal was cleaved or cut with a wire saw to obtain a 1 mm thick c plate. This c plate was placed in a Rigaku ATX X-ray diffractometer, and the lattice constant was obtained by the bond method. In the bond method, the lattice plane spacing d was first obtained from the 2θ value, which is the (0024) peak. 0024 The c-axis length of 25.1324 Å was calculated from equation (1). Next, from the 2θ value, which is the peak in (2014), d 2014 The c-axis length was measured, and using the calculated c-axis length, the a-axis length of 3.2468 Å was calculated.

[0077] Figure 12 is a graph summarizing the lattice constants along the a-axis of the single crystals grown in each example.

[0078] As described in the above examples, according to the present invention, in a single crystal represented by the general formula RAMO4, the number of lattice elements in the resulting single crystal can be set to a desired value by using two or more elements with different ionic radii (Sc and an element with a larger ionic radius than Sc) in the R portion and / or using two or more elements with different ionic radii (Al and an element with a larger ionic radius than Al) in the A portion, and by appropriately selecting the ionic radii and composition ratio of the elements in the R portion and the A portion. For example, in a crystal substrate for epitaxial growth such as a ScAlMgO4 single crystal, by partially substituting a portion of Sc with elements with large ionic radii such as In, Y, Yb, and Lu, it becomes possible to use In as a host layer for the red light-emitting layer of a red LED, which was difficult with conventional ScAlMgO4 single crystals (a-axis length 3.245 Å). 0.25 Ga 0.75 A crystal substrate for epitaxial growth can be obtained with lattice matching to a N a-axis length of approximately 3.28 Å. [Industrial applicability]

[0079] By using the single crystal represented by the general formula RAMO4 according to this disclosure as a crystal substrate for epitaxial growth, strain stress and threading dislocations due to lattice mismatch can be reduced when epitaxially growing (In,Ga)N single crystals on the substrate. Therefore, nitride semiconductors such as (In,Ga)N with low defect density can be formed on a crystal substrate for epitaxial growth using the single crystal represented by the general formula RAMO4.

Claims

1. General formula RAMO ４ It consists of a single crystal represented by An epitaxial growth substrate in which the a-axis length of the single crystal is 3.25 to 3.52 Å. [In the formula, R represents trivalent Sc partially substituted with at least one trivalent element selected from the group consisting of In, Y, and lanthanide elements; A represents at least one trivalent element selected from the group consisting of Fe(III), Ga, and Al; and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd.]

2. General formula RAMO ４ It consists of a single crystal represented by An epitaxial growth substrate in which the a-axis length of the single crystal is 3.25 to 3.52 Å. [In the formula, R represents at least one trivalent element selected from the group consisting of Sc, In, Y, and lanthanide elements; A represents trivalent Al partially substituted with at least one trivalent element selected from the group consisting of Fe(III) and Ga; and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd.]

3. The epitaxial growth substrate according to claim 1 or 2, wherein the a-axis length of the single crystal is 3.25 to 3.40 Å.

4. The epitaxial growth substrate according to claim 1 or 2, wherein the a-axis length of the single crystal is 3.25 to 3.30 Å.

5. The epitaxial growth substrate according to claim 1, wherein A represents trivalent Al partially substituted with at least one trivalent element selected from the group consisting of Fe(III) and Ga.

6. General formula (Sc,R)(Al,A)MgO ４ The epitaxial growth substrate according to claim 5, comprising a single crystal represented by [the specified formula]. [In the formula, R represents at least one trivalent element selected from the group consisting of In, Y, Lu, and Yb, and A represents trivalent Ga.]

7. General formula (Sc,R)AlMgO ４ The epitaxial growth substrate according to claim 1, comprising a single crystal represented by [the specified formula]. [In the formula, R represents at least one trivalent element selected from the group consisting of In, Y, Lu, and Yb.]

8. General formula (Sc,R)GaMgO ４ The epitaxial growth substrate according to claim 1, comprising a single crystal represented by [the specified formula]. [In the formula, R represents at least one trivalent element selected from the group consisting of In, Y, Lu, and Yb.]

9. An epitaxial growth substrate according to claim 1 or 2, for the epitaxial growth of indium gallium nitride single crystals.

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