JP2013237591A - Gallium oxide melt, gallium oxide single crystal, gallium oxide substrate, and method for producing gallium oxide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a gallium oxide single crystal, by which the disconnection of a gallium oxide melt of a neck part can be suppressed in the production of the gallium oxide single crystal, and the loss of a raw material associated with the evaporation of the gallium oxide melt can be suppressed in a necking step.SOLUTION: A gallium oxide melt 2 having a density larger than a melt not containing an additive is obtained by charging a gallium oxide raw material containing the additive into a crucible 3 and heating the charged raw material, and then a seed crystal 10 is brought into contact with the gallium oxide melt 2. Thereby, a failure of necking is reduced and the evaporation loss of the raw material is reduced. Further, the gallium oxide melt 2 having a density of ≥4.85 g/cc is obtained by adjusting the content of the additive. Thereby, the failure of necking is reduced, and a temperature at which the seed crystal can be brought into contact is raised at least 10°C or more, in comparison with the case when a gallium oxide melt not containing the additive is used, and therefore, a gallium oxide single crystal having a lateral width of ≥2 inches and a straight body length of ≥2 inches can be grown.

Description

  The present invention relates to a gallium oxide melt, a method for producing a gallium oxide single crystal using the gallium oxide melt, a gallium oxide single crystal and a gallium oxide substrate.

  Various semiconductor elements, including light emitting diodes (LEDs: Light Emitting Diodes) and laser diodes (LDs: Laser Diodes), are formed on a substrate made of silicon carbide (SiC) or sapphire (Al2O3). Manufactured by growing a film.

  As a light emitting device using SiC, a light emitting device in which n-type and p-type GaN layers are stacked on a SiC single crystal substrate is known. This light-emitting element is manufactured by forming an n-type GaN layer and a p-type GaN layer on a SiC single crystal substrate and cutting out into a plurality of pieces by dicing using cleavage.

  On the other hand, when fabricating a light emitting device using Al2O3, an n-type GaN layer is formed on an Al2O3 single crystal substrate through a buffer layer, and then a light emitting layer including a GaN layer containing In is formed. .

  In many light emitting devices, nitride semiconductors such as aluminum nitride (AlN) and indium nitride (InN) are used in addition to GaN. Conventionally, a nitride semiconductor film has been grown on a substrate manufactured from SiC or Al2O3, so a lattice constant mismatch (hereinafter referred to as a mismatch) occurs between the substrate material and the nitride semiconductor film. Defects, dislocations, and the like were generated in the nitride semiconductor film fabricated by the above. Therefore, it has been difficult to produce a high-quality nitride semiconductor film.

  Since there is a 16% mismatch between Al2O3 and GaN, it is difficult to grow a GaN layer directly on the substrate, and even if grown, a GaN layer with good crystallinity cannot be obtained.

  On the other hand, the mismatch between SiC and GaN is theoretically said to be 3.4%. However, in SiC, there are many phases such as 3C, 4H, 6H, and 15R, and it is difficult to obtain a single-phase SiC substrate. Further, since SiC has a very high hardness and poor workability, it is difficult to flatten the substrate, and when viewed on an atomic scale, many steps with different phases appear on the substrate surface. When a GaN layer is grown on the substrate, GaN layers having different polycrystallinity and defect density grow. Thus, in the case of SiC, innumerable nuclei of infinite quality grow on one substrate, and as a result, the GaN layer grows in a form where they are combined, so it is extremely difficult to improve the quality of the GaN layer. For these reasons, the actual mismatch between SiC and GaN is small compared to the case of Al2O3 and GaN, but it is still about 6%.

  Since there is a large mismatch between Al2O3 and GaN or between SiC and GaN, a buffer layer called a low-temperature buffer layer composed of AlN or AlGaN is first formed on a substrate made of SiC or Al2O3. And a GaN layer had to be grown on the buffer layer at a high temperature.

  Thus, gallium oxide has been devised as a substrate material to replace SiC and Al2O3 (see, for example, Patent Document 1). By using a gallium oxide single crystal as a substrate material and nitriding the surface of the substrate to form a GaN layer, mismatches can be reduced compared to SiC and Al2O3 substrates.

  Furthermore, the gallium oxide single crystal is a colorless and transparent conductor that transmits light in the visible to ultraviolet wavelength range, so that it can be used in the entire wavelength range of the GaN emission region, particularly in the ultraviolet region. It has the feature that crystals can be manufactured. For example, in the case of 6H—SiC, since the band gap is 3.03 eV, it is opaque in a wavelength range of about 427 nm or less. Considering that the emission region of GaN is about 550 to 380 nm, the wavelength range available for SiC is about 2/3 of that. On the other hand, in the case of β-Ga2O3, since it transmits up to about 260 nm, it can be used in the entire wavelength range of the GaN emission region, particularly in the ultraviolet region.

  In addition, gallium oxide single crystal has a wide band gap of 4.8 eV and is transparent in the visible region, and also exhibits behavior as an n-type semiconductor due to oxygen deficiency in the crystal. It has the possibility of device development different from the Al2O3 substrate.

  In summary, gallium oxide single crystal can be used to produce a bulk single crystal as a blue light emitting device material, and is conductive as described above, has light transmission in the light emitting region, and has a small mismatch with the GaN layer. . Therefore, the gallium oxide single crystal can solve the problems of SiC and Al2O3. It is also possible to obtain a vertical structure type light emitting element.

  As an example of a method for producing such a gallium oxide single crystal, an EFG (Edge-defined Film-fed Growth) method has been devised (see, for example, Patent Document 2). The EFG method is a state in which the lower side of a die having a slit extending in the vertical direction is immersed in the gallium oxide melt in the crucible, and the gallium oxide melt is opened from the lower side opening to the upper side by capillary action. Gallium oxide single crystal (hereinafter referred to as necessary) by pulling up the seed crystal in the vertical direction after bringing the seed crystal into contact with the gallium oxide melt that has been sucked up into the slit and reached the opening on the slit upper side. (Denoted as single crystal). A gallium oxide substrate is produced by cutting the produced plate-like single crystal into a circle or a square.

  The seed crystal is attached to the seed crystal holder so that a predetermined crystal plane of the seed crystal (the crystal plane of the main surface of the gallium oxide substrate to be produced) faces in the thickness direction of the slit (left-right direction in FIG. 1). After the seed crystal is brought into contact with the gallium oxide melt reaching the opening of the slit, when the temperature of the gallium oxide melt is lowered, the gallium oxide melt at the contact portion is crystallized. In this state, when the seed crystal is pulled up in the vertical direction at a constant ascent rate, a gallium oxide single crystal is obtained.

  FIGS. 7A to 7E are schematic process diagrams showing a method for producing a β-Ga2O3 single crystal by the EFG method. First, the seed crystal 100 is attached to the seed crystal holder 101 so that a predetermined crystal plane of the seed crystal 100 (a crystal plane of the main surface of the gallium oxide substrate to be manufactured) faces the thickness direction of the slit. Next, a powder material such as β-Ga2O3 as a raw material is put into the crucible, the crucible upper surface is closed with a lid, and the crucible is mounted on the support base of the single crystal manufacturing apparatus. Next, the crucible is placed at a predetermined position of the single crystal manufacturing apparatus together with the support base.

  Next, the crucible is induction heated by energizing the high frequency coil. The powder material accommodated in the crucible melts based on the temperature rise of the crucible and becomes a gallium oxide melt having a melting point of 1800 ° C. or higher. A part of this gallium oxide melt enters the slit of the die 103 and rises in the slit based on the capillary phenomenon to become the gallium oxide melt 102 on the die top.

  Next, as shown in FIG. 7A, the seed crystal 100 is lowered together with the seed crystal holder 101 in the direction of the arrow, and the seed crystal 100 reaches the surface of the die 103 as shown in FIG. 7B. Contact with the gallium oxide melt 102 on the die top (seed touch).

  Next, as shown in FIG. 7 (c), the temperature of the gallium oxide melt 102 on the die top is lowered while pulling up the seed crystal 100 in the vertical direction to form a neck portion 105 that is thinner than the thickness of the seed crystal 100. .

  Subsequently, when the temperature of the gallium oxide melt 102 on the die top is lowered to near the melting point, the β-Ga2O3 single crystal 104 is centered on the seed crystal 100 in the width direction of the die 103 (see FIG. 7D). The crystal grows while widening in the horizontal direction of the figure.

  Once the β-Ga2O3 single crystal 104 is expanded to the width of the die 103, the width is maintained and the flat β-Ga2O3 single crystal 104 (straight barrel portion) is continuously pulled up (FIG. 7 (e) )reference).

  Next, as shown in FIG. 7 (e), when the β-Ga2O3 single crystal 104 reaches a predetermined pulling length, the crystal pulling speed is increased to separate the β-Ga2O3 single crystal 104 from the gallium oxide melt 102, Thereafter, energization of the high-frequency coil is stopped. Next, after confirming that the temperature of the crucible has dropped sufficiently, the support base, the crucible, the β-Ga2O3 single crystal 104, the seed crystal 100, and the seed crystal holder 101 are moved upward to obtain the β-Ga2O3 single crystal 104. Remove and separate from seed crystal 100 and die 103.

  In each of the above steps, the temperature of the gallium oxide melt 102 brought into contact with the seed crystal 100 in FIG. 7B is set as high as possible, and the neck portion 105 is formed thin in FIG. Non-Patent Document 1 discloses that it is possible to suppress the formation of a polycrystal by mixing a surface (irregular surface) other than the crystal surface of the gallium oxide substrate main surface produced from a gallium oxide single crystal to be crystal-grown. ing.

JP 2004-056098 A JP 2006-312571 A

Hideo AIDA et al. “Growth of β-Ga2O3 Single Crystals by the edge-Defined, Film Fed Growth Method” Japanese Journal of Applied Physics Vol. 47, No. 11, 2008, pp. 8506-8509

但し、ｋは係数で2.0、Tcは融液の臨界温度（沸点：℃）、Tは融液の温度(℃)、dは単結晶の密度、Mは単結晶の分子量を、それぞれ表す。 FIG. 8 shows that in the EFG method, the gallium oxide single crystal to be grown has irregular surfaces depending on the temperature of the gallium oxide melt on the die top during seed touch (seed touch temperature) and the diameter of the neck (neck diameter). It is a graph which represents typically the tendency of the above-mentioned nonpatent literature 1 in which the frequency of mixing changes. In order to obtain a single crystal containing no irregular surface by utilizing this tendency, we would like to try to contact the seed crystal with the gallium oxide melt in the high gallium oxide melt temperature range. As the seed touch temperature becomes higher, the density of the gallium oxide melt decreases, and as a result, the surface tension γ of the gallium oxide melt decreases from the following equation (1).

However, k is a coefficient, 2.0, Tc is the critical temperature (boiling point: ° C) of the melt, T is the temperature of the melt (° C), d is the density of the single crystal, and M is the molecular weight of the single crystal.

  When the surface tension of the gallium oxide melt decreases, the gallium oxide melt hangs down from the neck portion being formed, and necking is interrupted. In this case, the temperature of the gallium oxide melt must be increased again to a predetermined seed touch temperature, and the neck portion must be formed again from the point where the seed crystal and the gallium oxide melt are brought into contact again. Also, gallium oxide has a high vapor pressure above the melting point, so the gallium oxide melt evaporates during the necking (necking) and during the reworking process, and in the production of β-Ga2O3 single crystal for 2-inch substrates, When necking failed once, the raw material loss of about 5-6g had generate | occur | produced. Therefore, if necking fails about 6 times, the raw material loss will be enough to process one 2-inch substrate, and depending on the number of failures, the raw material necessary to pull up a single crystal sufficient to process a 2-inch substrate will be obtained. It was also happening that it did not remain in the crucible.

  Therefore, the present applicant tried to produce a β-Ga2O3 single crystal by setting the gallium oxide melt temperature on the die top at the time of the seed touch to a low value, for example, 1820 ° C., and as a result, the frequency of the necking failure was suppressed. It was found that it can be manufactured. However, when the seed touch temperature is lowered as shown in FIG. 8, the occurrence frequency of irregular surfaces during the growth of β-Ga2O3 single crystal increases. For example, irregularities as shown by hatching in β-Ga2O3 single crystal as shown in FIG. Surfaces were generated and became polycrystalline. Due to the generation of the irregular surface, the lateral width W of the crystal plane coinciding with the main surface of the gallium oxide substrate to be manufactured becomes less than 2 inches. It was found that it was not possible to cut out so as to include only the crystal plane. In other words, there is a trade-off between the quality of the single crystal required for 2-inch substrate processing and the evaporation loss of the raw material, so the fundamental solution for obtaining a single crystal for a 2-inch substrate is just by adjusting the seed touch temperature. I found out that

  The present invention has been made in view of the above circumstances. A gallium oxide melt that suppresses cutting of the gallium oxide melt at the neck portion during the production of a gallium oxide single crystal, and a gallium oxide single crystal using the gallium oxide melt. It is an object of the present invention to provide a crystal manufacturing method and a gallium oxide single crystal and a gallium oxide substrate.

The above object is achieved by the present invention described below. That is,
(1) The gallium oxide melt of the present invention is characterized by containing an additive excluding inevitable impurities and having a higher density than a melt containing no additive.

  (2) In one embodiment of the gallium oxide melt of the present invention, the density is preferably 4.85 g / cc or more.

  (3) In one embodiment of the gallium oxide melt of the present invention, it is preferable that at least one element of Mg, Al, Si, Sn, Ti, Ge is added as the additive.

  (4) In another embodiment of the gallium oxide melt of the present invention, the additive is Si, and the addition amount is 0.001 mol% or more and 0.1 mol% as the content in the composition of the gallium oxide melt. The temperature is preferably 1840 ° C. or higher.

  (5) In another embodiment of the gallium oxide melt of the present invention, the additive is Si, and the addition amount is 0.01 mol% or more and 0.1 mol% as the content in the composition of the gallium oxide melt. The temperature is preferably 1860 ° C. or higher.

  (6) In another embodiment of the gallium oxide melt of the present invention, the additive is Si, and the addition amount is 0.05 mol% or more and 0.1 mol% as the content in the composition of the gallium oxide melt. The temperature is preferably 1880 ° C. or higher.

  (7) In addition, the gallium oxide single crystal of the present invention is a gallium oxide single crystal grown from a gallium oxide melt containing an additive excluding inevitable impurities and having a higher density than a melt containing no additive. It is characterized by that.

  (8) Further, in one embodiment of the gallium oxide single crystal of the present invention, the density is 4.85 g / cc or more and the crystal is grown from a gallium oxide melt containing an additive, and the lateral width and the straight body length are 2 inches or more. It is characterized by being.

  (9) In another embodiment of the gallium oxide single crystal of the present invention, it is preferable that at least one element of Mg, Al, Si, Sn, Ti, Ge is contained as the additive.

  (10) In another embodiment of the gallium oxide single crystal of the present invention, the additive is Si, and the content of the additive in the gallium oxide single crystal is 0.001 mol% or more and 0.1 mol% or less. It is preferable.

  (11) In another embodiment of the gallium oxide single crystal of the present invention, the additive is Si, and the content of the additive in the gallium oxide single crystal is 0.01 mol% or more and 0.1 mol% or less. It is preferable.

  (12) In another embodiment of the gallium oxide single crystal of the present invention, the additive is Si, and the content of the additive in the gallium oxide single crystal is 0.05 mol% or more and 0.1 mol% or less. It is preferable.

  (13) In another embodiment of the gallium oxide single crystal of the present invention, the FWHM of the X-ray rocking curve is preferably 200 arcsec or less.

  (14) The gallium oxide substrate of the present invention is made of a gallium oxide single crystal grown from a gallium oxide melt containing an additive excluding inevitable impurities and having a higher density than a melt containing no additive. It is characterized by.

  (15) Further, in one embodiment of the gallium oxide substrate of the present invention, the density is 4.85 g / cc or more, crystal growth is performed from a gallium oxide melt containing an additive, and the lateral width and the straight body length are 2 inches or more. The main surface is made of a single crystal of gallium oxide and has a single crystal plane of 2 inches or more.

  (16) In another embodiment of the gallium oxide substrate of the present invention, the X-ray rocking curve FWHM is preferably 200 arcsec or less.

  (17) In another embodiment of the gallium oxide substrate of the present invention, it is preferable that at least one element of Mg, Al, Si, Sn, Ti, and Ge is contained as the additive.

  (18) In another embodiment of the gallium oxide substrate of the present invention, the additive is Si, and the content of the additive in the gallium oxide substrate is 0.001 mol% or more and 0.1 mol% or less. Is preferred.

  (19) In another embodiment of the gallium oxide substrate of the present invention, the additive is Si, and the content of the additive in the gallium oxide substrate is 0.01 mol% or more and 0.1 mol% or less. Is preferred.

  (20) In another embodiment of the gallium oxide substrate of the present invention, the additive is Si, and the content of the additive in the gallium oxide substrate is 0.05 mol% or more and 0.1 mol% or less. Is preferred.

  (21) In another embodiment of the gallium oxide substrate according to the present invention, a reducing atmosphere is used for crystal growth of the gallium oxide single crystal, the additive is Si, and the additive is contained in the gallium oxide substrate. The amount is preferably 0.01 mol% or more and 0.03 mol% or less.

(22) The method for producing a gallium oxide single crystal of the present invention includes:
Put gallium oxide raw material containing additives into a crucible and heat,
Including an additive excluding inevitable impurities, obtaining a gallium oxide melt having a higher density than the melt containing no additive,
A gallium oxide single crystal is grown from the gallium oxide melt by bringing a seed crystal into contact with the gallium oxide melt,
The temperature of the gallium oxide melt in contact with the seed crystal is set to be higher than the upper limit temperature of the gallium oxide melt not containing the additive that can contact the seed crystal.

(23) Further, an embodiment of the method for producing a gallium oxide single crystal of the present invention is as follows:
The density of the gallium oxide melt containing the additive is 4.85 g / cc or more,
The temperature of the gallium oxide melt in contact with the seed crystal is at least 10 ° C. higher than the upper limit temperature at which the seed crystal can be contacted with the gallium oxide melt not containing the additive.

  (24) In another embodiment of the method for producing a gallium oxide single crystal of the present invention, it is preferable that at least one element of Mg, Al, Si, Sn, Ti, and Ge is added as the additive.

  (25) In another embodiment of the method for producing a gallium oxide single crystal of the present invention, the additive is Si, and the addition amount is 0.001 mol% or more as the content in the composition of the gallium oxide melt. It is preferable that the temperature of the gallium oxide melt in contact with the seed crystal is 1840 ° C. or higher.

  (26) In another embodiment of the method for producing a gallium oxide single crystal of the present invention, the additive is Si, and the addition amount is 0.01 mol% or more as the content in the composition of the gallium oxide melt. It is preferable that the temperature of the gallium oxide melt in contact with the seed crystal is 1860 ° C. or higher.

  (27) In another embodiment of the method for producing a gallium oxide single crystal of the present invention, the additive is Si, and the addition amount is 0.05 mol% or more as the content in the composition of the gallium oxide melt. It is preferable that the temperature of the gallium oxide melt in contact with the seed crystal is 1880 ° C. or higher.

  (28) In another embodiment of the method for producing a gallium oxide single crystal of the present invention, it is preferable to use a reducing atmosphere for crystal growth of the gallium oxide single crystal.

(29) In another embodiment of the method for producing a gallium oxide single crystal of the present invention, the method for growing the gallium oxide single crystal from the gallium oxide melt is an EFG method,
It is preferable to manufacture a plurality of plate-shaped gallium oxide single crystals by arranging a plate-shaped seed crystal in the thickness direction of the slit and pulling up the plurality of gallium oxide single crystals.

  According to the inventions according to claims 1, 7, 14, and 22 of the present invention (that is, the inventions of (1), (7), (14), and (22)), the gallium oxide melt contains the additive. Because it has a higher density than the melt that does not contain, the surface tension of the gallium oxide melt is increased, and the gallium oxide melt can be prevented from being cut at the neck of the gallium oxide single crystal. It is possible to suppress the raw material loss accompanying the evaporation of the melt.

  Furthermore, the inventions according to claims 2 to 6, 8 to 12, 15, 17 to 21, and 23 to 27 (that is, (2) to (6), (8) to (12), (15), ( 17) to (21) and (23) to (27)), the surface tension of the gallium oxide melt increases because the gallium oxide melt is densified to 4.85 g / cc or more. The cutting of the gallium oxide melt at the neck portion of the gallium oxide single crystal can be suppressed, and the raw material loss accompanying the evaporation of the gallium oxide melt during the necking process is reduced to a single crystal used for processing one 2-inch substrate. It becomes possible to make it less than weight.

  Furthermore, according to the invention of claim 22 (that is, the invention of (22) above), the density of the gallium oxide melt becomes higher than that of the melt containing no additive, so that the gallium oxide melt The upper limit temperature at which the seed crystal can be contacted can be made higher than that of the melt containing no additive. Accordingly, by setting the seed touch temperature to a higher temperature, the frequency with which a gallium oxide single crystal of 2 inches or more is obtained increases.

  Furthermore, according to the invention of claim 23 (that is, the invention of the above (23)), after ensuring a melt density of 4.85 g / cc or more, the upper limit temperature at which the seed crystal of the gallium oxide melt can be contacted, It can be at least 10 ° C. higher than the melt containing no additives. Therefore, by setting the seed touch temperature to a high temperature of 10 ° C. or higher, the frequency with which a gallium oxide single crystal of 2 inches or more is obtained increases.

  Furthermore, according to the invention of claims 25 to 27 (that is, the invention of the above (25) to (27)), the temperature of the gallium oxide melt contacting the seed crystal is set to a high temperature range of 1840 ° C. or higher. It becomes possible. Furthermore, in that temperature range, a gallium oxide melt having a surface tension corresponding to a density of 4.85 g / cc or more can be obtained. Therefore, the surface tension is increased by increasing the density of the gallium oxide melt, and the gallium oxide melt is less likely to be cut during the necking process, so the seed touch temperature can be set to a high temperature range of 1840 ° C or higher. It becomes. This makes it possible to obtain a high-quality gallium oxide single crystal that is large and has a small mosaic property. Therefore, as described in the invention according to claim 8 of the present invention (that is, the invention of (8)), a gallium oxide single crystal having a lateral width (the width W) and a straight body length of 2 inches or more is manufactured. I can do it. Further, since mixing of irregular surfaces over 2 inches or more is suppressed and a high-quality gallium oxide single crystal with a small mosaic property is realized, the invention according to claim 13 of the present invention (that is, the above (13) As described in (1), it is possible to realize a gallium oxide single crystal having a width of 2 inches or more and a straight body length of FWHM of an X-ray rocking curve of 200 arcsec or less.

  Further, according to the inventions of claims 4 and 25 of the present invention (that is, the inventions of (4) and (25)), the frequency of occurrence of irregular surfaces in the temperature range of the gallium oxide melt of 1840 ° C. or higher. Can be reduced.

  Further, according to the inventions according to claims 5 and 26 of the present invention (that is, the inventions of (5) and (26)), the occurrence frequency of irregular surfaces in the temperature range of the gallium oxide melt of 1860 ° C. or higher. Can be reduced.

  Further, according to the inventions according to claims 6 and 27 of the present invention (that is, the inventions of (6) and (27)), the occurrence frequency of irregular surfaces in the temperature range of the gallium oxide melt of 1880 ° C. or higher. Can be reduced.

  Further, since a gallium oxide single crystal having a width of 2 inches or more and a straight body length is realized, as described in the invention of claim 15 (that is, the invention of (15)), its oxidation A gallium oxide substrate having a main surface of 2 inches or more can be obtained from a gallium single crystal. Furthermore, by being composed of a high quality single crystal face with a small mosaic property, as described in the invention of claim 16 (that is, the invention of the above (16)), an X of 200 arcsec or less A 2 inch gallium oxide substrate with a FWHM of line rocking curve is realized.

  Further, according to the inventions according to claims 21 and 28 of the present invention (that is, the inventions of the above (21) and (28)), a gallium oxide single crystal or gallium oxide can be obtained by performing crystal growth using a reducing atmosphere. Variations in the specific resistance of the substrate can be suppressed.

  Furthermore, according to the invention of claim 29 of the present invention (that is, the invention of (29)), the contact area between the gallium oxide melt and the seed crystal can be reduced, so that the neck portion is narrowed. Therefore, the generation of irregular surfaces of the gallium oxide single crystal can be suppressed, and the crystal quality can be kept high. Therefore, the yield of the gallium oxide single crystal can be improved.

  Further, it becomes possible to simultaneously manufacture a plurality of gallium oxide single crystals from a single seed crystal, which improves mass productivity. Furthermore, a plurality of gallium oxide single crystals can be manufactured with one seed crystal, and the manufacturing cost of a single gallium oxide single crystal can be reduced. In addition, by using a seed crystal as a single crystal material, the direction of the crystal axes of a plurality of gallium oxide single crystals can be aligned, and a plurality of gallium oxide single crystals with little variation in quality can be manufactured simultaneously. .

(a) A schematic cross-sectional view illustrating a growth furnace as an example of a method for producing a gallium oxide single crystal by an EFG method. (b) It is the elements on larger scale which show the seed crystal of FIG. 1 (a), the gallium oxide single crystal, and the gallium oxide melt part on a die top. It is explanatory drawing of the manufacturing method of an example of the gallium oxide single crystal by EFG method. It is a perspective view showing an example of a gallium oxide substrate concerning this embodiment. It is explanatory drawing which shows the positional relationship of the seed crystal substrate and die | dye in an example of this embodiment. It is explanatory drawing which shows a mode that a part of seed crystal substrate is fuse | melted in other embodiment. It is explanatory drawing which showed a mode that the neck part in embodiment of FIG. 5 grew. It is a schematic process drawing which shows the manufacturing method of the β-Ga2O3 single crystal by the EFG method. 5 is a graph schematically showing a relationship between a seed touch temperature (° C.) and a neck diameter (mm) in the EFG method. It is a graph which represents typically the relationship between the gallium oxide melt density (g / cc) and the seed touch temperature (degreeC) of a gallium oxide melt for every additive Si content. FIG. 5 is an explanatory diagram schematically showing a β-Ga2O3 single crystal produced by an EFG method and having an increased probability of occurrence of irregular surfaces.

  Hereinafter, a gallium oxide melt, a gallium oxide single crystal, a gallium oxide substrate, and a method for producing a gallium oxide single crystal according to the present invention will be described in detail. An example of the method for producing a gallium oxide single crystal of the present invention is the EFG method. Hereinafter, a method for producing a gallium oxide single crystal will be described with reference to FIGS. 1 to 7 and 9 by taking the EFG method as an example. FIG. 1A is a schematic cross-sectional view showing the structure of a gallium oxide single crystal manufacturing apparatus used in the EFG method.

  The method for producing a gallium oxide single crystal is not particularly limited as long as the gallium oxide single crystal is grown from the gallium oxide melt by bringing the seed crystal into contact with the molten gallium oxide melt. Specific methods include CZ (Czochralski) method and FZ (Floating Zone) method. However, the EFG method is preferable to other crystal growth methods in that crystal growth on an arbitrary main surface and single crystal growth with high composition uniformity are possible.

  As shown in FIG. 1, a crucible 3 for receiving a gallium oxide melt 2 (hereinafter referred to as “melt” as appropriate) as a raw material for a gallium oxide single crystal is provided in a gallium oxide single crystal growth furnace 1. Has been placed. As a raw material of the melt 2, it is essential that at least gallium (Ga) is contained and a melt containing gallium oxide is obtained when the raw material is melted in the melting step.

  Furthermore, in the present invention, an element other than gallium or a compound containing the element is added to the raw material as an additive. The additive is at least one element of Mg, Al, Si, Sn, Ti, and Ge.

  Specific examples of gallium oxide as a starting material may include industrial gallium oxide, gallium salts such as gallium carbonate, hydrates, or a mixture thereof. In the case of using the latter, gallium oxide is obtained by firing them. In addition, the step of obtaining the gallium oxide by baking or the like may be performed immediately before crystal growth inside the growth furnace, or may be performed in advance outside the growth furnace. Further, the additive may be included in advance in any of the starting materials, or may be separately prepared and mixed with the starting materials. The form of the raw material may be any form such as powder, a sintered body, and a crushed material obtained by roughly crushing the sintered body.

  The raw material of the melt containing the additive for growing the gallium oxide single crystal by the above method contains impurities inevitable in production. For example, as an example of the highest-purity starting material, gallium oxide having a purity of about 6N is used as industrial gallium oxide, but this contains impurities of less than 0.0001 mol%. Even if it does not, it contains less than 0.0001 mol% of any element of the additive. In the present invention, an element having a total content of less than 0.0001 mol% at the stage of the gallium oxide melt 2 is defined as an inevitable impurity, and the impurity is excluded from the additive.

  The gallium oxide single crystal 13 and the gallium oxide substrate 16 obtained from the gallium oxide single crystal 13 are most preferably β-Ga2O3 single crystals. Since the β-Ga2O3 single crystal has conductivity, a light emitting element (LED) having a vertical electrode structure can be manufactured. As a result, current can flow through the entire light-emitting element, so that the current density can be reduced. Therefore, the lifetime of the light emitting element can be extended.

  Furthermore, the β-Ga2O3 single crystal does not show a large lattice constant mismatch with GaN. Further, from the viewpoint of the band gap, the β-Ga2O3 single crystal transmits up to about 260 nm, so that it can be used in the entire wavelength range of the GaN emission region, particularly in the ultraviolet region.

  The crucible 3 is formed in a bottomed cylindrical shape and is placed on a support base 4, and the temperature of the bottom surface is measured by a thermocouple 7. The crucible 3 is made of a heat-resistant material so as to receive the melt 2, and is formed of, for example, iridium (Ir), and a necessary amount of raw material is charged into the crucible 3 by a raw material charging unit (not shown).

  Furthermore, a die 5 is disposed in the crucible 3. The die 5 is formed in a substantially rectangular parallelepiped shape, for example, and is provided with one or more slits 5A extending from the lower end to the upper end (opening 5B). For example, in FIG. 1, the die 5 is provided with one slit 5A at the center in the thickness direction.

  The slit 5A is provided over almost the entire width of the die 5. When a plurality of slits 5A are provided, they are provided at predetermined intervals in the thickness direction of the die 5. The slit 5A serves to raise the melt 2 from the lower end of the die 5 to the opening 5B of the slit 5A by capillary action.

  Further, a lid 6 is disposed on the upper surface of the crucible 3. The lid 6 is formed in a shape that closes the upper surface of the crucible 3 except for the die 5. For this reason, in the state where the lid 6 is disposed on the upper surface of the crucible 3, the upper surface of the crucible 3 except the opening 5B of the slit 5A is closed (see FIG. 2). In this way, the lid 6 prevents the high-temperature melt 2 from evaporating from the crucible 3, and further suppresses the vapor of the melt 2 from adhering to other than the upper surface of the slit 5A.

  Moreover, the heater part 9 which consists of a high frequency coil, for example is arrange | positioned around the heat insulating material 8 provided so that the crucible 3 may be surrounded. The crucible 3 is heated to a predetermined temperature by the heater unit 9, and the raw material in the crucible 3 is melted to obtain the melt 2 (melting step). Furthermore, the heat insulating material 8 is disposed so as to have a predetermined distance from the crucible 3, and has a role of improving the heat retaining property around the crucible 3 heated by the heater unit 9.

  The raw material accommodated in the crucible 3 is melted (raw material melt) based on the temperature rise of the crucible 3 to become the melt 2. A part of the melt 2 enters the slit 5A of the die 5, and as described above, rises in the slit 5A based on the capillary phenomenon and is exposed from the opening 5B to become the melt 2A on the die top. (See FIG. 1 (b)).

  A seed crystal holder 11 that holds the seed crystal 10 is disposed above the slit 5A. The seed crystal holder 11 is connected to a shaft 12 that supports the seed crystal holder 11 and the seed crystal 10 so as to be movable up and down. Then, the seed crystal holder 11 is lowered by the shaft 12 (see FIG. 7A), and the seed crystal 10 is brought into contact (seed touch) with the melt 2A having a temperature sufficiently higher than the melting point exposed from the opening 5B. (Refer to FIG. 7 (b)) After that, the temperature of the melt 2A is lowered, so that the melt in the contact portion is crystallized and the crystal growth of the gallium oxide single crystal 13 is started.

  Subsequently, the seed crystal holder 11 is pulled up at a predetermined ascent rate. Specifically, first, the temperature of the melt 2A is lowered while the seed crystal holder 11 is raised at a predetermined speed by the shaft 12 to produce (necking) the thin neck portion 17 (see FIG. 7C). Next, the temperature of the melt 2A on the die top is lowered to the vicinity of the melting point, and the gallium oxide single crystal 13 is grown in the width direction of the die 5 around the seed crystal 10 (spreading, FIG. 7). (See (d)). When the gallium oxide single crystal 13 is widened to the full width of the die 5 (full spread), thereafter, a flat gallium oxide single crystal 13 having the same width as the full width of the die 5 is grown and grown (straight cylinder process, (See FIG. 7 (e)).

  Subsequently, the plate-like gallium oxide single crystal 13 having the same width as the entire width of the die 5 is pulled up to an appropriate length (straight cylinder length). The straight body length is preferably 2 inches or more. Further, by setting the total width of the die 5 to 2 inches or more, the lateral width of the gallium oxide single crystal 13 is also set to 2 inches or more.

  Next, the shaft 12 is controlled to increase the ascent speed of the seed crystal holder 11, the gallium oxide single crystal 13 is separated from the melt 2 A, and the heater 9 is controlled to lower the temperature of the crucible 3 for heating. finish. Thereby, a gallium oxide single crystal 13 having a predetermined size is manufactured.

  After confirming that the temperature of the gallium oxide single crystal 13 has sufficiently decreased, for example, an electrodeposition diamond core drill or the like is used to cut a flat circular gallium oxide substrate 16 as shown in FIG. Next, an orientation flat (orientation flat) 14 is formed for each gallium oxide substrate 16 by a slicing machine or the like as necessary, and the gallium oxide substrate 16 is manufactured.

  Further, one side of the produced gallium oxide substrate 16 is used as the main surface 15, and at least one side thereof is subjected to polishing or the like to flatten the main surface 15.

  The thus obtained gallium oxide substrate 16 (shown in FIG. 3 shows a substrate that has been subjected to circle processing from the gallium oxide single crystal 13) is used, for example, as a substrate for epitaxial growth of a light-emitting element, as well as a new gallium oxide single crystal. It can be used as a seed crystal for growing crystals.

  As described above, the additive and the gallium sintered body containing the additive are added to the starting material. Therefore, at least one element of Mg, Al, Si, Sn, Ti, and Ge is added to the melt 2. As a result of the study, the inventors have added at least one element of Mg, Al, Si, Sn, Ti, and Ge to the melt 2. It has been found that the melt during necking becomes difficult to cut.

  First, it was found that when the additive having a content of 0.0001 mol% or more is contained in the melt 2A, the melt during necking is hardly cut.

  Further, the present inventors have further studied, and when at least one element of Mg, Al, Si, Sn, Ti, and Ge is added to the melt 2 in an amount of 0.001 mol% or more, the melt 2A is 4.85 even if the melt temperature is 1820 ° C. or more. It has been found that by maintaining a density of g / cc or more and ensuring a surface tension corresponding to the melt density, the melt during necking becomes more difficult to break. Thereby, the single crystal can be manufactured with a high yield without the raw material evaporation loss due to the necking failure exceeding the weight of the single crystal subjected to the 2-inch substrate processing.

  Therefore, by adding 0.001 mol% or more of the additive to the melt, the material evaporation loss due to necking failure does not exceed the weight of the single crystal used for 2-inch substrate processing, and the seed touch temperature depends on the amount added. Thus, a conclusion was reached that the frequency of setting to a higher temperature and the frequency of obtaining a single crystal was increased, and the present invention was completed.

  Furthermore, in order to obtain a high-quality gallium oxide single crystal 13, it is necessary to set the seed touch temperature to a high temperature range, and a melt density of 4.85 g / cc or higher can be realized at a melt temperature of 1840 ° C. or higher. I derived what I need to do. Therefore, the temperature of the melt 2A at the time of seed touch is set to 1840 ° C. or higher. Based on the above requirements, it is necessary to set the amount of the additive to be in the range of at least 0.001 mol% or more in order to realize a melt density of 4.85 g / cc or more at a melt temperature of 1840 ° C. or more. The inventors have derived.

  In addition, since the seed-touch can be performed at a high temperature of 1840 ° C. or higher, the probability that an irregular surface is mixed into the gallium oxide single crystal 13 can be suppressed. As a result, a gallium oxide single crystal 13 in which both the lateral width (the width W) and the straight body length of a single crystal plane necessary for substrate production are 2 inches or more can be manufactured. In addition, it is possible to obtain a high-quality gallium oxide single crystal with a small mosaic property, and a single crystal having a width of FWHM of 2 inches or more and a straight body length having a FWHM of an X-ray rocking curve of 200 arcsec or less. It becomes possible to realize a gallium oxide single crystal composed of surfaces.

  If the seed touch temperature is set above 1960 ° C., depending on the design of the crystal growth apparatus, a part of the crucible 3 may reach the melting point of the crucible material, and the crucible 3 may be destroyed. In order to protect the crucible 3, the upper limit of the seed touch temperature is preferably set to 1960 ° C. or lower.

  Further, from the viewpoint of increasing the frequency with which a gallium oxide single crystal can be obtained, the seed touch temperature should be at least 10 ° C. higher than the upper limit temperature for contact with a seed crystal of a gallium oxide melt not containing the additive. Is preferred.

  When the additive having a content of 0.0001 mol% or more is contained in the melt 2A, the melt during necking is less likely to break, and evaporation loss of the raw material can be reduced. From FIG. 9, it is possible to realize a melt density of 4.85 g / cc or more at a melt temperature of 1840 ° C. or more and 1960 ° C. or less, and from the viewpoint of reducing the occurrence frequency of irregular surfaces, The content in 2A is set to 0.001 mol% or more and 0.1 mol% or less. Furthermore, by increasing the density to 4.85 g / cc or more, the surface tension of the melts 2 and 2A increases, and the cutting of the melt 2A at the neck portion of the gallium oxide single crystal 13 is suppressed, and the necking is repeated. The raw material loss due to evaporation from the melts 2 and 2A can be reduced. Note that the addition amount in the gallium oxide single crystal 13 and the gallium oxide substrate 16 is also set to 0.001 mol% or more and 0.1 mol% or less. The content of the additive in the crystal 13 and the gallium oxide substrate 16 is defined.

  Furthermore, from FIG. 9, it is possible to achieve a melt density of 4.85 g / cc or higher at a melt temperature of 1860 ° C. or higher and 1960 ° C. or lower, which is a higher melt temperature range, and to reduce the frequency of irregular surfaces. In view of the above, it is more preferable to set the content in the composition of the melts 2 and 2A to 0.01 mol% or more and 0.1 mol% or less. Note that, in the gallium oxide single crystal 13 and the gallium oxide substrate 16, the addition amount is set to 0.01 mol% or more and 0.1 mol% or less.

  Furthermore, from FIG. 9, it is possible to realize a melt density of 4.85 g / cc or higher at a melt temperature of 1880 ° C. or higher and 1960 ° C. or lower, which is an even higher melt temperature range, and further reduce the occurrence frequency of irregular surfaces. From the viewpoint of being possible, it is more preferable to set the content in the composition of the melts 2 and 2A to 0.05 mol% or more and 0.1 mol% or less. In addition, also in the gallium oxide single crystal 13 and the gallium oxide substrate 16, the addition amount is set to 0.05 mol% or more and 0.1 mol% or less.

  Further, by using a reducing atmosphere for crystal growth of the gallium oxide single crystal 13, fluctuations in the specific resistance of the gallium oxide single crystal 13 can be suppressed. Furthermore, when producing the gallium oxide substrate 16 using a reducing atmosphere, the additive is Si, and the content of the additive in the gallium oxide substrate 16 is set to 0.01 mol% or more and 0.03 mol% or less. This is preferable from the viewpoint of suppressing fluctuations in the specific resistance of the gallium substrate 16.

  When the EFG method is used as the method for growing the gallium oxide single crystal 13 from the melt 2, a plurality of gallium oxide single crystals 13 are pulled up by arranging a plate-shaped seed crystal in the thickness direction of the slit. Thus, a plurality of plate-shaped gallium oxide single crystals 13 may be manufactured.

  4 and 5 are schematic configuration diagrams of a growth furnace for simultaneously producing a plurality of flat plate-shaped gallium oxide single crystals (hereinafter referred to as “single crystals”) 13 by the EFG method. 4 and 5, a plurality of dies 5 are provided, and a plate-like substrate 34 (hereinafter referred to as “seed crystal substrate 34”) made of gallium oxide single crystal is used as a seed crystal. In addition, the same number is attached | subjected to the same location as the growth furnace 1 of FIG.1 and FIG.2, and the overlapping description is abbreviate | omitted suitably and demonstrated.

  The crucible 3 is filled with the melt 2, and the melt 2 is raised from the lower end of the die 5 to the opening 5B of the slit 5A by capillary action. The plurality of dies 5 have the same shape and are arranged in parallel to each other. The upper part of the die 5 is an inclined surface, and the inclined surfaces are arranged facing each other to form a liquid pool (melt 2A) of the melt 2 that has passed through the slit 5A (see FIG. 5 (a)).

  Next, the seed crystal substrate 34 is lowered while being held in the thickness direction of the slit 5A (see FIGS. 4 and 5), and is brought into contact with the melt 2A in the liquid reservoir portion (see FIG. 5B). By arranging the positional relationship between the slit 5A and the seed crystal substrate 34 in directions perpendicular to each other, the contact area between the melt 2A in the liquid reservoir portion and the seed crystal substrate 34 can be reduced. Therefore, the contact portion of the seed crystal substrate 34 becomes compatible with the melt 2A, and crystal defects are less likely to occur in the gallium oxide single crystal to be crystal-grown. Furthermore, since it is possible to reduce the contact area between the melt 2A in the liquid pool portion and the seed crystal substrate 34, the neck portion can be formed narrowly, and the irregular surface of the gallium oxide single crystal 13 is generated. It is possible to suppress the crystal quality and keep it high. Therefore, the yield of the gallium oxide single crystal 13 can be improved.

  A part of the seed crystal substrate 34 may be melted when the seed crystal substrate 34 is brought into contact with the melt 2A of the liquid reservoir portion. By melting a part of the seed crystal substrate 34, the temperature difference from the melt 2A can be quickly eliminated, and the probability of occurrence of crystal defects in the gallium oxide single crystal can be further suppressed.

  Next, as shown in FIG. 6, the seed crystal substrate 34 starts to be pulled up, and after forming the neck portion, as described above, a plurality of plate-like gallium oxide single crystals 13 are pulled and grown through the spreading and straight body processes. Is done.

  In this way, by using a plurality of dies 5 and arranging a seed crystal substrate 34 in the thickness direction of the slit 5A and pulling and growing the gallium oxide single crystal 13, a plurality of oxides are produced from one seed crystal substrate 34. The gallium single crystal 13 can be manufactured at the same time, and the mass productivity is improved. Furthermore, a plurality of gallium oxide single crystals 13 can be manufactured on one seed crystal substrate 34, and the manufacturing cost of the gallium oxide single crystal 13 per sheet can be reduced. Also, by using the seed crystal substrate 34 as a single crystal material, the direction of the crystal axes of a plurality of gallium oxide single crystals 13 can be aligned, and a plurality of gallium oxide single crystals 13 with little variation in quality can be manufactured simultaneously. Is possible.

  From the melts 2 and 2A, a gallium oxide single crystal having a width of 2 inches or more and a straight body length is realized. Therefore, the gallium oxide single crystal is composed of a single crystal plane with a main surface of 2 inches or more. A gallium oxide substrate 16 is obtained. Further, the gallium oxide substrate 16 can be configured with a FWHM of an X-ray rocking curve of 200 arcsec or less by being composed of a single crystal surface with a small mosaic property.

  Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the following examples.

(Examples 1-5 and Comparative Example 1)
The EFG method was used for the production methods of the gallium oxide single crystals of Examples 1 to 5 and Comparative Example 1, and a reducing atmosphere containing 100% argon gas was used as the condensing atmosphere. In Examples 1 to 5, the additive was Si, and a β-Ga2O3 single crystal for producing a (101) plane substrate was produced from a gallium oxide melt to which Si was added. On the other hand, in Comparative Example 1, a β-Ga2O3 single crystal was produced from a gallium oxide melt containing no additive. The seed touch temperatures of Examples 1 to 5 and Comparative Example 1 were set to 1820 ° C. to 1960 ° C.

  The lateral width and the straight body length of the β-Ga2O3 single crystal were 2 inches or more in both Examples 1 to 5 and Comparative Example 1. The main surface of each of the β-Ga2O3 substrates of Examples 1 to 5 and Comparative Example 1 was 2 inches.

  Table 1 below shows the success rate (%) of necking at each seed touch temperature (1820 ° C., 1830 ° C., 1840 ° C., 1860 ° C., 1880 ° C., and 1960 ° C.) in each of Examples 1 to 5 and Comparative Example 1. Indicates the number of failures. The neck diameter was as narrow as possible within the range that would not hinder the handling of the grown crystals, and necking was performed with a target of approximately 0.3 mm. The success rate represents the probability that a neck can be formed without cutting the gallium oxide melt after starting necking at the seed touch temperature. Also, the average number of times of failure and redo before necking succeeded was defined as the number of failures.

  From Table 1, if the necking success rate is 20% or more, that is, if the number of failures is within 4 times, the loss of evaporation of the raw material during necking is less than the crystal weight corresponding to one substrate. Of course, no single crystal was obtained under the condition of a success rate of 0%.

  In Table 1, the conditions for crystal growth at the maximum seed touch temperature for each Si addition amount were extracted from the conditions that resulted in a necking success rate of 20% or more. Table 2 shows the evaluation results of the FWHM of the curve and the yield when producing a 2-inch gallium oxide substrate.

  From the results of Comparative Example 1 in Tables 1 and 2, in the growth of β-Ga2O3 single crystals from Si-free gallium oxide melt, a thin neck can be formed by seed-touching at 1820 ° C, but necking was successful. Since the rate is less than 20%, the evaporation loss of raw materials during necking exceeds the weight of a single crystal that can process one 2-inch substrate, and the generation of irregular surfaces in a β-Ga2O3 single crystal is suppressed. I couldn't. On the other hand, it was found that as the Si addition amount was increased from Examples 1 to 5, β-Ga2O3 single crystal growth at a higher seed touch temperature became possible, and the occurrence frequency of irregular surfaces was suppressed. . It was also found that the yield of the β-Ga2O3 substrate having a main surface of 2 inches was improved as the occurrence frequency of irregular surfaces was suppressed. Furthermore, by setting the Si addition amount to at least 0.05 mol%, even if the number of trials of β-Ga2O3 single crystal growth is increased (5 to 8 times), the frequency of occurrence of irregular surfaces can be suppressed to 0 times. It was also found that the yield can be made 100%. The FWHM of the X-ray rocking curve of the 2-inch β-Ga 2 O 3 substrate obtained in each of Examples 1 to 5 was 200 arcsec, but in Comparative Example 1, it was a multi-peak.

(Examples 6 to 10 and Comparative Example 2)
Next, Examples 6 to 10 and Comparative Example 2 will be described with reference to Table 3 below. In addition, description is abbreviate | omitted about the manufacturing process and technical content same as the said Examples 1-5 and the comparative example 1, and it shall mainly explain a difference.

  Also in Examples 6 to 10 and Comparative Example 2, the EFG method was used, and a reducing atmosphere of 100% argon gas was used as the atmosphere. In Examples 6 to 10, the additive was Si, and a β-Ga2O3 single crystal for producing a (101) plane substrate was produced from a gallium oxide melt to which Si was added. On the other hand, in Comparative Example 2, a gallium oxide melt containing no additive was used. In Examples 6 to 10 and Comparative Example 2, single crystals were grown in the same manner as in Examples 1 to 5 and Comparative Example 1, respectively. Moreover, the failure of necking during each crystal growth was within 4 times, and the raw material evaporation loss could be suppressed.

  Table 3 below shows the Si content of β-Ga2O3 single crystals in Examples 6 to 10 and Comparative Example 2, and the specific resistance value for each Si content. The specific resistance value is the specific resistance in the in-plane direction of the main surface of the β-Ga2O3 substrate produced from each β-Ga2O3 single crystal of Examples 6 to 10 and Comparative Example 2. In addition, since the single crystal was not obtained in Comparative Example 2, the single crystal portion of 2 inches or less was cut out to make the substrate. However, the specific resistance is uniform on the substrate surface, which is particularly important when compared with other substrates. There is no hindrance.

  From Table 3, it is recognized that the specific resistance of β-Ga2O3 single crystal or β-Ga2O3 substrate is 0.02Ωcm regardless of Si addition by crystal growth using reducing atmosphere, and Si addition does not affect the specific resistance. It was.

1, 35 Growth furnace 2, 2A Melt containing gallium oxide 3 Crucible 4 Support base 5 Die
5A slit
5B Opening 6 Lid 7 Thermocouple 8 Insulation 9 Heater
10 seed crystals
11 Seed crystal holder
12 shaft
13 Gallium oxide single crystal
14 Orientation flat
15 Main surface
16 Gallium oxide substrate
17 The narrowest part of the neck
34 Seed crystal substrate

Claims (29)

  A gallium oxide melt containing an additive excluding inevitable impurities and having a higher density than a melt containing no additive.   The gallium oxide melt according to claim 1, wherein the density is 4.85 g / cc or more.   The gallium oxide melt according to claim 1, wherein at least one element of Mg, Al, Si, Sn, Ti, and Ge is added as the additive.   The additive is Si, and the addition amount in the composition of the gallium oxide melt is 0.001 mol% or more and 0.1 mol% or less, and the temperature is 1840 ° C or more, The gallium oxide melt according to any one of 1 to 3.   The additive is Si, the addition amount is 0.01 mol% or more and 0.1 mol% or less as a content in the composition of the gallium oxide melt, and the temperature is 1860 ° C or more, The gallium oxide melt according to any one of 1 to 4.   The additive is Si, and the addition amount is 0.05 mol% or more and 0.1 mol% or less as a content in the composition of the gallium oxide melt, and the temperature is 1880 ° C or more. The gallium oxide melt according to any one of 1 to 5.   A gallium oxide single crystal grown from a gallium oxide melt containing an additive excluding inevitable impurities and having a higher density than a melt containing no additive.   The gallium oxide single crystal according to claim 7, wherein the gallium oxide single crystal has a density of 4.85 g / cc or more and is grown from a gallium oxide melt containing an additive and has a lateral width and a straight body length of 2 inches or more.   The gallium oxide single crystal according to claim 7 or 8, wherein the additive contains at least one element of Mg, Al, Si, Sn, Ti, and Ge.   The oxidation according to any one of claims 7 to 9, wherein the additive is Si, and the content of the additive in the gallium oxide single crystal is 0.001 mol% or more and 0.1 mol% or less. Gallium single crystal.   The oxidation according to any one of claims 7 to 10, wherein the additive is Si, and the content of the additive in the gallium oxide single crystal is 0.01 mol% or more and 0.1 mol% or less. Gallium single crystal.   The oxidation according to any one of claims 7 to 11, wherein the additive is Si, and the content of the additive in the gallium oxide single crystal is 0.05 mol% or more and 0.1 mol% or less. Gallium single crystal.   The gallium oxide single crystal according to any one of claims 7 to 12, wherein the X-ray rocking curve has a FWHM of 200 arcsec or less.   A gallium oxide substrate made of a gallium oxide single crystal grown from a gallium oxide melt containing an additive excluding inevitable impurities and having a higher density than a melt containing no additive.   Crystal growth from a gallium oxide melt with an additive of 4.85 g / cc or more and containing an additive, made from a gallium oxide single crystal with a width and straight body length of 2 inches or more, and a main surface of 2 inches or more The gallium oxide substrate according to claim 14.   The gallium oxide substrate according to claim 14 or 15, wherein FWHM of an X-ray rocking curve is 200 arcsec or less.   The gallium oxide substrate according to claim 14, wherein the additive contains at least one element of Mg, Al, Si, Sn, Ti, and Ge.   The gallium oxide according to any one of claims 14 to 17, wherein the additive is Si, and the content of the additive in the gallium oxide substrate is 0.001 mol% or more and 0.1 mol% or less. substrate.   The gallium oxide according to any one of claims 14 to 18, wherein the additive is Si, and the content of the additive in the gallium oxide substrate is 0.01 mol% or more and 0.1 mol% or less. substrate.   The gallium oxide according to any one of claims 14 to 19, wherein the additive is Si, and the content of the additive in the gallium oxide substrate is 0.05 mol% or more and 0.1 mol% or less. substrate.   A reducing atmosphere is used for crystal growth of the gallium oxide single crystal, the additive is Si, and the content of the additive in the gallium oxide substrate is 0.01 mol% or more and 0.03 mol% or less, The gallium oxide substrate according to claim 14. Put gallium oxide raw material containing additives into a crucible and heat,
Including an additive excluding inevitable impurities, obtaining a gallium oxide melt having a higher density than the melt containing no additive,
A gallium oxide single crystal is grown from the gallium oxide melt by bringing a seed crystal into contact with the gallium oxide melt,
A method for producing a gallium oxide single crystal, wherein the temperature of the gallium oxide melt in contact with the seed crystal is higher than the upper limit temperature of the gallium oxide melt not containing the additive that can contact the seed crystal. The density of the gallium oxide melt containing the additive is 4.85 g / cc or more,
23. The gallium oxide according to claim 22, wherein the temperature of the gallium oxide melt in contact with the seed crystal is at least 10 ° C. higher than the upper limit temperature at which the seed crystal can be contacted with the gallium oxide melt not containing the additive. A method for producing a single crystal.   The method for producing a gallium oxide single crystal according to claim 22 or 23, wherein at least one element of Mg, Al, Si, Sn, Ti, and Ge is added as the additive. The additive is Si, and the addition amount is the content in the composition of the gallium oxide melt,
25. The gallium oxide unit according to claim 22, wherein the gallium oxide melt is in a range of 0.001 mol% to 0.1 mol% and the temperature of the gallium oxide melt contacting the seed crystal is 1840 ° C. or higher. Crystal production method.   The additive is Si, and the addition amount in the composition of the gallium oxide melt is 0.01 mol% or more and 0.1 mol% or less, and the temperature of the gallium oxide melt in contact with the seed crystal is 1860. 26. The method for producing a gallium oxide single crystal according to any one of claims 22 to 25, wherein the temperature is higher than or equal to ° C. The additive is Si, and the addition amount is 0.05 mol% or more and 0.1 mol% or less as the content in the composition of the gallium oxide melt, and the temperature of the gallium oxide melt in contact with the seed crystal is 1880. 27. The method for producing a gallium oxide single crystal according to any one of claims 22 to 26, wherein the gallium oxide single crystal is at or above a temperature.   The method for producing a gallium oxide single crystal according to any one of claims 22 to 27, wherein a reducing atmosphere is used for crystal growth of the gallium oxide single crystal.   The method of growing the gallium oxide single crystal from the gallium oxide melt is the EFG method, and by arranging the plate-shaped seed crystal in the thickness direction of the slit and pulling up the plurality of gallium oxide single crystals. The method for producing a gallium oxide single crystal according to any one of claims 22 to 28, wherein a plurality of the plate-shaped gallium oxide single crystals are produced.

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