WO2016035417A1 - Zinc oxide substrate and method for producing group 13 nitride crystal using same - Google Patents

Abstract

Provided is a zinc oxide substrate which contains 0.1% by weight or more of Mg, and which is used for the purpose of growing a group 13 nitride crystal thereon by an MOCVD method. A zinc oxide substrate according to the present invention enables growth of a group 13 nitride crystal having excellent crystallinity on a substrate by an MOCVD method without forming an insulating layer in advance.

Description

Zinc oxide substrate and method for producing group 13 nitride crystal using the same

The present invention relates to a zinc oxide substrate and a method for producing a group 13 nitride crystal using the same.

As a substrate material for gallium nitride (GaN) -based light-emitting elements, zinc oxide (ZnO) has been attracting attention (see, for example, Patent Document 1 (International Publication No. 2014/092163)). This is because ZnO has a lattice constant close to that of GaN, so that an improvement in crystal quality of GaN grown on a ZnO substrate is expected.

However, since GaN and ZnO are highly reactive, it is desired to suppress the reaction between GaN and ZnO when GaN is formed on a ZnO substrate using MOCVD (metal organic vapor phase epitaxy). For example, Non-Patent Document 1 (Ray-Ming Lin et al., Proc. SPIE, 2010, vol. 7602, pp. 76021L-1-6) and Non-Patent Document 2 (SJ Wang et al., J. Phys. D) : Appl. Phys. 42 (2009) 245302), a buffer layer of AlN or Al ₂ O ₃ is previously formed on a ZnO substrate in order to suppress the reaction between GaN and ZnO to obtain high quality GaN. It is proposed to keep. In this case, since AlN and Al ₂ O ₃ are insulative, it has been impossible to produce a vertical LED structure that is highly efficient and advantageous for downsizing. In addition, it is desirable to omit the formation of such a layer because it leads to an increase in manufacturing cost.

International Publication No. 2014/092163 JP 2007-254206 A

The inventors of the present invention have recently used a zinc oxide substrate containing a predetermined amount of Mg to form a Group 13 nitride crystal having excellent crystallinity by MOCVD without forming an insulating layer in advance. The knowledge that it can be grown on a substrate was obtained.

Accordingly, an object of the present invention is to provide a zinc oxide substrate capable of growing a group 13 nitride crystal having excellent crystallinity on the substrate by MOCVD without forming an insulating layer in advance. There is.

According to one aspect of the present invention, a zinc oxide substrate containing 0.1 wt% or more of Mg, which is used as a substrate for growing a group 13 nitride crystal thereon by MOCVD method A substrate is provided.

According to another aspect of the present invention, a step of preparing a zinc oxide substrate according to the above aspect;
A Group 13 nitride crystal represented by Ga _x Al _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is grown on the zinc oxide substrate by MOCVD. Process,
A method for producing a Group 13 nitride crystal is provided.

FIG. 6 is a schematic diagram showing the configuration of a crystal manufacturing apparatus 20 used in Example 7. It is a figure explaining the scanning method of the slit 37 shown by FIG. It is the image which image | photographed film peeling of the MOCVD-GaN film | membrane observed in Example 7, and an arrow shows a film peeling part.

The zinc oxide substrate according to the present invention is a zinc oxide substrate containing 0.1 wt% or more of Mg. The Mg-containing zinc oxide substrate is used as a substrate for growing a group 13 nitride crystal on the substrate by MOCVD. This makes it possible to grow a Group 13 nitride crystal having excellent crystallinity on the substrate by MOCVD without forming an insulating layer in advance.

That is, as described above, since ZnO has a lattice constant close to that of a group 13 nitride crystal such as GaN, an improvement in crystal quality of GaN grown on a zinc oxide substrate is expected. However, since GaN and ZnO are highly reactive, when depositing GaN on a ZnO substrate using the MOCVD method, in order to suppress the reaction between GaN and ZnO and obtain high quality GaN, AlN or Al It has been desired to form a ₂ O ₃ buffer layer on a ZnO substrate (for example, Non-Patent Documents 1 and 2). However, in this case, since AlN and Al ₂ O ₃ are insulative, it is impossible to produce a vertical LED structure that is highly efficient and advantageous for downsizing. Under such circumstances, the present inventors used a zinc oxide substrate containing 0.1% by weight or more of Mg, so that the MOCVD method did not form an insulating layer in advance. It was found that a group 13 nitride crystal can be grown on a substrate. Although the mechanism of improving the crystallinity of the Group 13 nitride crystal by inclusion of Mg in zinc oxide and the adoption of the MOCVD method is not necessarily clear, the solid solution of Mg in ZnO causes ZnO in the GaN film formation atmosphere in MOCVD. It is presumed that this is because the volatilization of silicon and the reactivity with Group 13 nitrides such as GaN are suppressed.

By the way, the group 13 nitride crystal is not particularly limited as long as it is a crystal having a group 13 element nitride as a main phase, but preferably a gallium nitride (GaN) crystal, an aluminum nitride (AlN) crystal, or indium nitride. An (InN) crystal, particularly preferably a gallium nitride (GaN) crystal. The group 13 element nitride crystal may be a mixed crystal in which, for example, AlN, InN or the like is dissolved in GaN. Therefore, a preferred Group 13 element nitride is expressed as a Group 13 nitride crystal represented by Ga _x Al _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1). More preferably, 0.5 ≦ x ≦ 1, 0 ≦ y ≦ 0.5, still more preferably 0.7 ≦ x ≦ 1, and 0 ≦ y ≦ 0.3. Further, the Group 13 element nitride crystal may be a non-doped material or may appropriately include a dopant for controlling the p-type or n-type.

The zinc oxide substrate according to the present invention contains 0.1% by weight or more of Mg. The effect of improving the crystallinity of the Group 13 nitride crystal can be expected when Mg is dissolved in zinc oxide in a certain amount or more. Therefore, the upper limit of the Mg content is not particularly limited. The Mg content is preferably 0.1 to 5.0% by weight, more preferably 0.5 to 4.5% by weight, still more preferably 1.0 to 4.0% by weight, and particularly preferably 2%. 0.0 to 4.0% by weight. Within such a range, Mg can be sufficiently dissolved in zinc oxide while preventing or suppressing the formation of a different phase MgO phase. As a result, the crystallinity of the group 13 nitride crystal formed on the substrate by MOCVD can be further improved. If a sputtering method is used, a larger amount of Mg (which may exceed the above-mentioned preferable range) can be dissolved in ZnO without generating a different phase (MgO phase) as compared with a normal solid phase reaction. .

Thus, it is preferable that the zinc oxide substrate of the present invention does not contain the MgO phase as a different phase. By not including the MgO phase, the crystallinity of the group 13 nitride crystal formed on the substrate by MOCVD is further improved. Presence or absence of MgO heterogeneous phase on the substrate is determined from 2θ = 20 ° to 80 ° using an XRD apparatus (for example, product name “RINT-TTR III” manufactured by Rigaku Corporation) with the plate surface of the zinc oxide substrate as the sample surface. Thus, it can be evaluated by measuring the XRD profile when the surface of the zinc oxide substrate is irradiated with X-rays. When the maximum value of the peak due to ZnO (including a solid solution of different elements) is m ₁ and the maximum value of the peak due to MgO (including a solid solution of different elements) is m ₂ , m _{When 2} / m ₁ ≦ 0.01, it may be determined that “no MgO different phase” and when m ₂ / m ₁ > 0.01, “MgO different phase exists”.

The zinc oxide substrate according to the present invention preferably contains 0.05 to 2% by weight, more preferably 0.1 to 1%, of one or more dopant elements selected from the group consisting of Al, Ga and In. 0.5% by weight, more preferably 0.2 to 1.3% by weight. By adding such a dopant, the crystallinity of the Group 13 nitride crystal formed on the substrate by MOCVD can be further improved. In addition, it is possible to produce a vertical LED structure that imparts conductivity to the substrate and can be highly efficient and downsized. In addition, even if the zinc oxide substrate contains an element other than Mg, Al, Ga and In (which may be an n-type dopant or a p-type dopant) and / or an inevitable impurity within a range that does not impair the spirit of the present invention. Needless to say, it is good.

The zinc oxide substrate according to the present invention preferably has a resistivity of 2 Ω · cm or less, more preferably less than 0.1 Ω · cm, still more preferably less than 2 × 10 ⁻² Ω · cm. The lower the resistivity, the more preferably the zinc oxide substrate can be used as a conductive substrate. Therefore, it is possible to produce a vertical LED structure that imparts conductivity to the substrate and can be highly efficient and downsized.

The zinc oxide substrate according to the present invention may be either a single crystal or a polycrystal, and the polycrystal is a group 13 film formed on the substrate by MOCVD by controlling the grain size. This is preferable in that the crystallinity of the nitride crystal is easily improved. In the case of a polycrystal, the zinc oxide substrate includes zinc oxide crystal particles. The zinc oxide crystal particle is a particle composed of zinc oxide, and Mg and the dopant element (that is, Al, Ga and / or In) are substituted with a hexagonal wurtzite structure Zn site or O site. Alternatively, it may be contained as an additive element that does not constitute a crystal structure, or may exist at a grain boundary.

When the zinc oxide substrate is a polycrystal, the average grain size of the polycrystal (that is, the average grain size of the crystal grains constituting the zinc oxide substrate) is preferably 10 to 200 μm, more preferably 30 to 200 μm, still more preferably. 50 to 200 μm. Thereby, the crystallinity of the group 13 nitride crystal formed on the substrate by the MOCVD method can be further improved. The aspect ratio of the crystal grains constituting the zinc oxide substrate is preferably 2.0 or less, more preferably 1.5 or less, still more preferably 1.4 or less, and particularly preferably 1.0 to 1. 3. This aspect ratio is a length ratio of (direction parallel to the plate surface of the zinc oxide substrate) / (direction perpendicular to the plate surface of the zinc oxide substrate), and if within this range, the aspect ratio is formed on the substrate by the MOCVD method. There is an advantage that the crystallinity of the Group 13 nitride crystal to be formed is further improved.

In the present invention, the average particle diameter and the aspect ratio can be determined as follows. That is, a sample about 10 mm square is cut out from a zinc oxide substrate, a surface perpendicular to the plate surface is polished, etched with nitric acid having a concentration of 0.3 M for 10 seconds, and then an image is taken with a scanning electron microscope. The visual field range is a visual field range in which straight lines intersecting with 10 to 30 particles can be drawn when straight lines parallel and perpendicular to the disk surface are drawn. In three straight lines drawn parallel to the disc surface, for all particles straight lines intersect, the individual values obtained by multiplying 1.5 to that the length of the inner segment and an average particle as a ₁ Similarly, in the three straight lines drawn perpendicular to the disk surface, the value obtained by multiplying the average of the lengths of the inner line segments of each particle by 1.5 for all the particles intersecting each other. Is a ₂ , (a ₁ + a ₂ ) / 2 is the average particle size, and a ₁ / a ₂ is the aspect ratio.

A preferred polycrystalline body is an oriented polycrystalline body. In the oriented polycrystal, crystal grains constituting the zinc oxide substrate are oriented in a certain direction. The plane orientation to be oriented on the plate surface of the oriented polycrystal is not particularly limited, but may be the (002) plane, the (100) plane, the (110) plane, and the like. It may be a surface.

The zinc oxide substrate according to the present invention has an orientation degree of (002) plane, an orientation degree of (100) plane, an orientation degree of (110) plane, or a total orientation degree of (100) plane and (110) plane on the substrate surface. It is preferably 30% or more, more preferably 40% or more, still more preferably 50% or more, even more preferably 60% or more, particularly preferably 70% or more, particularly more preferably 80% or more, and most preferably 90%. % Or more. There is an advantage that the higher the degree of orientation, the higher the light emission efficiency when a light emitting device is manufactured.

In particular, the orientation degree of the (100) plane, the orientation degree of the (110) plane, or the total orientation degree of the (100) plane and the (110) plane on the substrate surface is preferably 30% or more, more preferably 40%. More preferably, it is 50% or more, still more preferably 60% or more, particularly preferably 70% or more, particularly more preferably 80% or more, and most preferably 90% or more. Thus, when a GaN film is formed by MOCVD on a zinc oxide substrate oriented in the m-plane or a-plane, the crystal quality of the MOCVD-GaN film is higher than when a zinc oxide substrate oriented in the c-plane is used. There is an advantage that the film is improved and the film is hardly peeled off. Since peeling of the film becomes a leak source when the LED structure is manufactured, it is preferable that the film peels less. Further, since GaN having high crystallinity with little peeling can be formed on a zinc oxide substrate, growth of GaN by a flux method as described in Patent Document 2 (Japanese Patent Laid-Open No. 2007-254206) can be achieved. It becomes possible. Na flux used for GaN growth by the flux method has high reactivity with zinc oxide, and the zinc oxide substrate dissolves when directly contacted at a high temperature. However, highly crystalline GaN is formed in advance by a vapor phase method. By forming a film, this not only functions as a seed crystal but also functions as a protective layer for suppressing dissolution of the zinc oxide substrate. If the MOCVD GaN film is peeled off, Na flux penetrates from the peeled portion and reacts and dissolves with ZnO. Therefore, it is preferable that the number of peeled portions is small. Since GaN and zinc oxide have close lattice constants and thermal expansion coefficients, it is possible to grow GaN of good quality even in the flux method by using a zinc oxide substrate.

Therefore, the upper limit of the degree of orientation of the (002) plane, the degree of orientation of the (100) plane, the degree of orientation of the (110) plane, or the total degree of orientation of the (100) plane and the (110) plane should not be particularly limited. Ideally 100%. The degree of orientation of the (002) plane, the degree of orientation of the (100) plane, the degree of orientation of the (110) plane, or the total degree of orientation of the (100) plane and the (110) plane is XRD apparatus (product name, manufactured by Rigaku Corporation). Using “RINT-TTR III”), the surface of the disc-shaped zinc oxide substrate can be measured by measuring the XRD profile when X-rays are irradiated.

The degree of orientation of the (002) plane can be calculated by the following formula (however, it can be omitted when I ₀ (102) and I ₀ (110) are negligible levels).

Further, the degree of orientation of the (100) plane can be calculated by the following formula (however, it can be omitted when I ₀ (102) and I ₀ (110) are negligible levels).

Furthermore, the degree of orientation of the (110) plane can be calculated by the following formula (however, it can be omitted when I ₀ (102) is a negligible level).

Furthermore, the total orientation degree of the (100) and (110) planes can be calculated by the following equation (however, it can be omitted when I ₀ (102) is a negligible level).

Method for Producing Group 13 Nitride Crystal As described above, by using the zinc oxide substrate of the present invention, a group 13 nitride crystal having excellent crystallinity can be grown on the substrate by MOCVD. That is, for the production of the Group 13 nitride crystal according to the present invention, the above-described zinc oxide substrate of the present invention is prepared, and Ga _x Al _y In _1-xy N (wherein 0 It is carried out by growing a group 13 nitride crystal represented by ≦ x ≦ 1, 0 ≦ y ≦ 1) by the MOCVD method. The details of the Group 13 nitride crystal are as described above.

The MOCVD method may be performed by appropriately adopting known procedures and conditions capable of epitaxially growing a group 13 nitride crystal on a zinc oxide substrate. For example, when a Group 13 nitride crystal made of a gallium nitride-based material is manufactured, a gas containing at least an organometallic gas containing at least gallium (Ga) (for example, trimethylgallium) and nitrogen (N) in an MOCVD apparatus (for example, Ammonia) is flowed over the substrate as a raw material, and is preferably grown in a temperature range of 450 to 1200 ° C., more preferably 600 to 1100 ° C. in an atmosphere containing hydrogen, nitrogen, or both. In this case, in order to control the band gap, organometallic gases containing indium (In), aluminum (Al), silicon (Si) and magnesium (Mg) as n-type and p-type dopants (for example, trimethylindium, trimethylaluminum, monosilane, disilane) Bis-cyclopentadienylmagnesium) may be appropriately introduced to form a film.

By using the zinc oxide substrate of the present invention, it is possible to grow a group 13 nitride crystal without forming an insulating layer on the surface of the zinc oxide substrate. Further, the crystal orientation of the group 13 nitride crystal thus grown on the zinc oxide substrate is preferably substantially coincident with the crystal orientation of the zinc oxide particles constituting the zinc oxide substrate, whereby the substrate is formed by MOCVD. There is an advantage that the crystallinity of the Group 13 nitride crystal formed thereon is further improved.

Method for Producing Zinc Oxide Substrate The zinc oxide substrate according to the present invention is not limited to single crystals, polycrystals, and the presence or absence of orientation as long as a zinc oxide substrate containing 0.1 wt% or more of Mg is finally obtained. It may be produced by any method. Therefore, the production of the zinc oxide substrate according to the present invention may be carried out by appropriately adopting known procedures and conditions capable of dissolving Mg in zinc oxide.

For example, an oriented polycrystalline zinc oxide substrate (oriented polycrystalline zinc oxide sintered body), which is a preferred embodiment of a zinc oxide substrate, is molded and sintered using a plate-like zinc oxide powder as a raw material as described below. It can be manufactured by doing.

(1) Preparation of plate-like zinc oxide powder The plate-like zinc oxide powder used as a raw material was produced by any method as long as an oriented sintered body (oriented polycrystalline body) was obtained by the molding and firing steps described later. There may be.

For example, in order to obtain a (002) plane oriented sintered body, a plate-like zinc oxide powder produced by the following production method may be used as a raw material. The plate-like zinc oxide powder includes a step of producing zinc oxide precursor plate-like particles by a solution method using a zinc ion-containing raw material solution, and calcining the precursor plate-like particles at a heating rate of 150 ° C./h or less. And calcining by raising the temperature to a temperature and producing a zinc oxide powder composed of a plurality of zinc oxide plate-like particles.

In the method for producing a plate-like zinc oxide powder for obtaining a (002) plane-oriented sintered body, first, zinc oxide precursor plate-like particles are produced by a solution method using a zinc ion-containing raw material solution. Examples of the zinc ion supply source include organic acid salts such as zinc sulfate, zinc nitrate, zinc chloride, and zinc acetate, zinc alkoxide, and the like, but zinc sulfate is preferable because sulfate ions described later can also be supplied. The production method of the zinc oxide precursor plate-like particles by the solution method is not particularly limited, and can be performed according to a known method.

The raw material solution preferably contains a water-soluble organic substance and sulfate ions because it is porous and can increase the specific surface area. Examples of water-soluble organic substances include alcohols, polyols, ketones, polyethers, esters, carboxylic acids, polycarboxylic acids, celluloses, saccharides, sulfonic acids, amino acids, and amines, and more Specifically, aliphatic alcohols such as methanol, ethanol, propanol, butanol, pentanol and hexanol, aliphatic polyhydric alcohols such as ethylene glycol, propanediol, butanediol, glycerol, polyethylene glycol and polypropylene glycol, phenol and catechol , Aromatic alcohols such as cresol, alcohols having a heterocyclic ring such as furfuryl alcohol, ketones such as acetone, methyl ethyl ketone, acetylacetone, ethyl ether, tetrahydrofuran, dioxane, poly Ethers or polyethers such as xylalkylene ether, ethylene oxide adduct, propylene oxide adduct, esters such as ethyl acetate, ethyl acetoacetate, glycine ethyl ester, formic acid, acetic acid, propionic acid, butanoic acid, butyric acid, succinic acid, Malonic acid, citric acid, tartaric acid, gluconic acid, salicylic acid, benzoic acid, acrylic acid, maleic acid, glyceric acid, eleostearic acid, polyacrylic acid, polymaleic acid, carboxylic acid such as acrylic acid-maleic acid copolymer, polycarboxylic acid Acids or hydroxycarboxylic acids and salts thereof, carboxymethylcelluloses, monosaccharides such as glucose and galactose, polysaccharides such as sucrose, lactose, amylose, chitin and cellulose, alkylbenzenesulfonic acid, paratoluenesulfonic acid, alcohol Kill sulfonic acid, α-olefin sulfonic acid, polyoxyethylene alkyl sulfonic acid, lignin sulfonic acid, naphthalene sulfonic acid and other sulfonic acids and their salts, glycine, glutamic acid, aspartic acid, alanine and other amino acids, monoethanolamine, diethanolamine, Examples thereof include hydroxyamines such as ethanolamine and butanolamine, trimethylaminoethylalkylamide, alkylpyridinium sulfate, alkyltrimethylammonium halide, alkylbetaine, and alkyldiethylenetriaminoacetic acid. Among these water-soluble organic substances, those having at least one functional group among hydroxyl group, carboxyl group, and amino group are preferable, hydroxycarboxylic acid having a hydroxyl group and a carboxyl group and salts thereof are particularly preferable, for example, sodium gluconate, Examples include tartaric acid. The water-soluble organic substance is preferably allowed to coexist in a raw material solution to which ammonia water described later is added in a range of about 0.001 wt% to about 10 wt%. A preferred sulfate ion source is zinc sulfate as described above. The raw material solution may further contain an additive substance such as the dopant described above.

At this time, the raw material solution is preferably heated to a precursor reaction temperature of 70 to 100 ° C., more preferably 80 to 100 ° C. Further, it is preferable that ammonia water is added to the raw material solution after or during this heating, and the raw material solution to which the ammonia water is added is preferably held at 70 to 100 ° C. for 0.5 to 10 hours, more preferably. Is 80 to 100 ° C. for 2 to 8 hours.

Next, the precursor plate-like particles are heated to the calcination temperature at a heating rate of 150 ° C./h or less and calcined to generate zinc oxide powder composed of a plurality of zinc oxide plate-like particles. By slowing the heating rate to 150 ° C / h or less, the crystal surface of the precursor is easily transferred to zinc oxide when changing from precursor to zinc oxide, and the degree of orientation of plate-like particles in the compact is improved. It is thought to do. It is also considered that the connectivity between the primary particles increases and the plate-like particles are less likely to collapse. A preferable temperature increase rate is 120 ° C./h or less, more preferably 100 ° C./h or less, further preferably 50 ° C./h or less, particularly preferably 30 ° C./h or less, and most preferably 15 It is below ℃ / h. Prior to calcination, the zinc oxide precursor particles are preferably washed, filtered and dried. The calcination temperature is not particularly limited as long as the precursor compound such as zinc hydroxide can be changed to zinc oxide, but is preferably 800 to 1100 ° C, more preferably 850 to 1000 ° C. The precursor plate-like particles are preferably held for 0 to 3 hours, more preferably 0 to 1 hour. Under such temperature holding conditions, a precursor compound such as zinc hydroxide can be reliably changed by zinc oxide. By such a calcination step, the precursor plate-like particles are changed to plate-like zinc oxide particles having many pores. In addition to the method described above, a known method (for example, see Non-Patent Document 3 (Gui Han et. Al., EJ. Surf. Sci. Nanotech. Vol. 7 (2009) 354-357)) is also applicable. .

On the other hand, in order to obtain a (100) plane oriented sintered body, a plate-like zinc oxide powder produced by the following production method may be used as a raw material. The plate-like zinc oxide powder is prepared by adding an aqueous alkaline salt solution to an aqueous zinc salt solution and stirring at 60 to 95 ° C. for 2 to 10 hours to precipitate a precipitate, washing and drying the precipitate, and further pulverizing the precipitate. Obtainable. The aqueous zinc salt solution may be an aqueous solution containing zinc ions, and is preferably an aqueous solution of a zinc salt such as zinc nitrate, zinc chloride, or zinc acetate. The alkaline aqueous solution is preferably an aqueous solution of sodium hydroxide, potassium hydroxide or the like. The concentration and mixing ratio of the zinc salt aqueous solution and the alkaline aqueous solution are not particularly limited, but it is preferable to mix the zinc salt aqueous solution and the alkaline aqueous solution having the same molar concentration in the same volume ratio. It is preferable to wash the precipitate with ion exchange water a plurality of times. The washed precipitate is preferably dried at 100 to 300 ° C. Since the dried precipitate is a spherical secondary particle in which plate-like zinc oxide primary particles are aggregated, it is preferably subjected to a pulverization step. This pulverization is preferably carried out by adding a solvent such as ethanol to the washed precipitate in a ball mill for 1 to 10 hours. By this pulverization, plate-like zinc oxide powder as primary particles is obtained. The plate-like zinc oxide powder thus obtained preferably has a volume-based D50 average particle diameter of 0.1 to 1.0 μm, more preferably 0.3 to 0.8 μm. This volume standard D50 average particle diameter can be measured by a laser diffraction particle size distribution measuring apparatus.

By the way, prior to the production of the oriented molded body, which is a subsequent process, Mg and a dopant element selected from the group consisting of Al, Ga, and In as required are added to the zinc oxide powder, or Mg and optionally It is preferable that the dopant element is previously contained in the zinc oxide powder. These dopant elements may be added to the zinc oxide powder in the form of compounds or ions containing these elements. The addition method of the additive substance is not particularly limited, but in order to spread the additive substance even inside the fine pores of the zinc oxide powder, (1) a method of adding the additive substance to the zinc oxide powder in the form of fine powder such as nanoparticles (2) A method of adding the zinc oxide powder after dissolving the additive substance in the solvent and drying the solution is preferably exemplified. The additive substance containing Mg (for example, magnesium oxide) has a Mg content of 0.1 wt% or more, preferably 0.1 to 5.0 wt%, more preferably 0.1 wt% in the finally obtained zinc oxide substrate. It may be added in an amount of ˜4.5% by weight, more preferably 1.0 to 4.0% by weight, particularly preferably 2.0 to 4.0% by weight. When an additive substance containing one or more dopant elements selected from the group consisting of Al, Ga and In is added, the dopant element content in the finally obtained zinc oxide substrate is 0.05 to 2% by weight. More preferably, it may be added in an amount such that it is 0.1 to 1.5% by weight, more preferably 0.2 to 1.3% by weight.

(2) Molding and firing step The plate-like zinc oxide powder produced by the above method is oriented by a technique using shearing force to obtain an oriented molded body. At this time, another element or component such as a metal oxide powder for dopant (for example, α-Al ₂ O ₃ powder) may be added to the plate-like zinc oxide powder. Preferable examples of the technique using shearing force include tape molding, extrusion molding, doctor blade method, and any combination thereof. In any of the methods exemplified above, the orientation method using the shearing force is made into a slurry by appropriately adding additives such as a binder, a plasticizer, a dispersant, and a dispersion medium to the plate-like zinc oxide powder. It is preferable to discharge and form the sheet on the substrate by passing through a thin discharge port. The slit width of the discharge port is preferably 10 to 400 μm. The amount of the dispersion medium is preferably such that the slurry viscosity is 5000 to 100,000 cP, more preferably 8000 to 60000 cP. The thickness of the oriented molded body formed into a sheet is preferably 5 to 300 μm, more preferably 10 to 200 μm. It is preferable to stack a large number of oriented molded bodies formed in this sheet shape to form a precursor laminate having a desired thickness, and press-mold the precursor laminate. This press molding can be preferably performed by isostatic pressing at a pressure of 10 to 2000 kgf / cm ^{2 in} warm water at 50 to 95 ° C. by packaging the precursor laminate with a vacuum pack or the like. In addition, when using extrusion molding, the sheet-shaped molded body is integrated and laminated in the mold after passing through a narrow discharge port in the mold due to the design of the flow path in the mold. The molded body may be discharged. The obtained molded body is preferably degreased according to known conditions.

The oriented molded body obtained as described above is fired at a firing temperature of 1000 to 1500 ° C., preferably 1100 to 1400 ° C., to form a zinc oxide sintered body comprising oriented zinc oxide crystal particles. . The firing time at the above-mentioned firing temperature is not particularly limited, but is preferably 1 to 10 hours, and more preferably 2 to 5 hours. The zinc oxide sintered body thus obtained is an oriented sintered body oriented in the (100) plane, (002) plane, etc., depending on the type of plate-like zinc oxide powder used as the raw material, that is, an oriented polycrystalline zinc oxide substrate and Become. The degree of orientation is high, preferably 50% or more on the substrate surface, preferably 60% or more, more preferably 70% or more, still more preferably 80% or more, particularly preferably 90% or more. is there.

The present invention will be described more specifically by the following examples.

Example 1
(1) Preparation of zinc oxide substrate 99.5 parts by weight of commercially available high-purity ZnO powder (specific surface area 9.4 m ² / g) and 0.5 parts by weight of commercially available high-purity MgO powder (specific surface area 23 m ² / g) Were mixed in a ball mill using ethanol as a solvent for 4 hours. The obtained slurry was dried with a rotary evaporator to obtain a mixed powder. With respect to 100 parts by weight of the obtained mixed powder, 15 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), a plasticizer (DOP: di (2-ethylhexyl) phthalate, black gold chemical stock) 6.2 parts by weight of a company), 3 parts by weight of a dispersant (product name: Leodol SP-O30, manufactured by Kao Corporation), and a dispersion medium (2-ethylhexanol) were mixed. The amount of the dispersion medium was adjusted so that the slurry viscosity was 10,000 cP. The slurry thus prepared was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 100 μm. The obtained tape was cut and laminated, placed on an aluminum plate having a thickness of 10 mm, and then vacuum packed. This vacuum pack was hydrostatically pressed in warm water of 85 ° C. at a pressure of 100 kgf / cm ² to produce a disk-shaped molded body having a diameter of about 65 mm and a thickness of about 1.5 mm. The obtained molded body was placed in a degreasing furnace and degreased at 600 ° C. The obtained degreased body was fired in the atmosphere at 1200 ° C. for 5 hours under normal pressure to obtain a disk-shaped ZnO-based sintered body. The obtained sintered body was subjected to HIP treatment under conditions of an atmospheric pressure of 150 MPa and 1300 ° C. for 2 hours using Ar gas as a pressure medium. The periphery of the obtained sintered body was processed, the surface was mirror-polished with a diamond slurry, and then subjected to CMP treatment using colloidal silica to obtain a zinc oxide substrate having a diameter of about 50 mm and a thickness of about 0.6 mm.

(2) Evaluation of Zinc Oxide Substrate Various evaluations shown below were performed on the zinc oxide substrate thus prepared. The results were as shown in Table 1.

<Quantitative analysis>
The Mg content and 3B group element content of the substrate were measured by ICP (inductively coupled plasma) emission spectroscopy.

<Average particle size>
The average particle size of the substrate is about 10 mm square cut out from the substrate, the surface perpendicular to the plate surface is polished, etched with nitric acid with a concentration of 0.3 M for 10 seconds, and then imaged with a scanning electron microscope. I took a picture. The visual field range was such that when straight lines parallel to and perpendicular to the plate surface were drawn, straight lines intersecting 10 to 30 particles could be drawn. In three straight lines drawn parallel to the plate surface, a value obtained by multiplying the average length of the line segments inside the individual particles by 1.5 for all the particles intersecting the straight line is a ₁ , Similarly, in three straight lines drawn perpendicularly to the plate surface, a value obtained by multiplying the average length of the inner line segment of each particle by 1.5 for all the particles intersecting with each other is a ₂ and (a ₁ + a ₂ ) / 2 was defined as the average particle size.

<Resistivity>
The resistivity of the substrate was measured by a four-probe method using a resistivity meter (Made by Mitsubishi Chemical, Loresta GP MCP-T610 type).

<Presence / absence of MgO heterogeneous phase>
Presence or absence of MgO heterogeneous phase on the substrate was determined in the range of 2θ = 20 ° -80 ° using an XRD apparatus (product name “RINT-TTR III” manufactured by Rigaku Corporation) with the plate surface of the zinc oxide substrate as the sample surface. Evaluation was made by measuring the XRD profile when the surface of the zinc oxide substrate was irradiated with X-rays. When the maximum value of the peak due to ZnO (including a solid solution of different elements) is m ₁ and the maximum value of the peak due to MgO (including a solid solution of different elements) is m ₂ , m _{When 2} / m ₁ ≦ 0.01, it was determined that “no MgO different phase” and when m ₂ / m ₁ > 0.01, “MgO different phase existed”.

(3) MOCVD-GaN film formation Using MOCVD, TMG (trimethylgallium) and NH ₃ (ammonia) are used as source gases and N ₂ is used as a carrier gas on a ZnO substrate at a substrate temperature of 800 ° C. About 4 μm of GaN was deposited.

(4) Evaluation of GaN crystallinity Using a microscopic Raman spectroscope (ARAMIS manufactured by Horiba, Ltd.), the half width of the Raman peak due to GaN E2 phonons near 568 cm ⁻¹ was measured with a laser beam having a wavelength of 532 nm. The full width at half maximum was as small as 32 cm ⁻¹ , indicating good crystallinity.

Example 2
The raw material mixing ratio of the zinc oxide substrate was 92.0 parts by weight of a commercially available high purity ZnO powder (specific surface area 9.4 m ² / g) and a commercially available high purity MgO powder (specific surface area 23 m ² / g) 8.0 weight. A zinc oxide substrate was prepared and evaluated in the same manner as in Example 1 except that it was made a part. The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was as small as 35 cm ⁻¹ , indicating good crystallinity.

Example 3 (Comparison)
The raw material mixing ratio of the zinc oxide substrate was 99.95 parts by weight of a commercially available high purity ZnO powder (specific surface area 9.4 m ² / g) and a commercially available high purity MgO powder (specific surface area 23 m ² / g) 0.05 weight. A zinc oxide substrate was prepared and evaluated in the same manner as in Example 1 except that it was made a part. The results are as shown in Table 1. A clear Raman peak due to GaN E2 phonons was not observed, and the crystallinity of GaN was low.

Example 4
The raw material mixing ratio of the zinc oxide substrate was 85.8 parts by weight of a commercially available high purity ZnO powder (specific surface area 9.4 m ² / g) and a commercially available high purity MgO powder (specific surface area 23 m ² / g) 14.2 weights. A zinc oxide substrate was prepared and evaluated in the same manner as in Example 1 except that it was made a part. The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was 82 cm ⁻¹ , indicating good crystallinity.

Example 5
The raw material mixing ratio of the zinc oxide substrate is 94.8 parts by weight of commercially available high purity ZnO powder (specific surface area 9.4 m ² / g) and commercially available high purity MgO powder (specific surface area 23 m ² / g) 5.2 weight. The zinc oxide substrate was prepared and evaluated in the same manner as in Example 1 except that the temperature of the HIP treatment was 1400 ° C. The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was as small as 28 cm ⁻¹ , indicating good crystallinity.

Example 6
A zinc oxide substrate was produced and evaluated in the same manner as in Example 5 except that the temperature of the HIP treatment was 1200 ° C. The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was as small as 42 cm ⁻¹ , indicating good crystallinity.

Example 7
94.8 parts by weight of commercially available high-purity ZnO powder (specific surface area 9.4 m ² / g) and 5.2 parts by weight of commercially available high-purity MgO powder (specific surface area 23 m ² / g) were ball milled using ethanol as a solvent. For 4 hours. The mixture was dried and then heat treated at 1400 ° C. for 5 hours. The resulting powder was coarsely pulverized in a mortar, and pulverized to a volume reference D ₅₀ average particle size 1μm by a ball mill using alumina balls.

Using the powder obtained above, a zinc oxide single crystal substrate (10 mm × 10 mm square, c plate) was used as a seed substrate, and an MgO solid solution zinc oxide single crystal was manufactured by the crystal manufacturing apparatus 20 shown in FIG. This apparatus is an apparatus for producing crystals by an aerosol deposition (AD) method in which the temperature in the chamber corresponds to 1200 ° C. The crystal manufacturing apparatus 20 includes an aerosol generating unit 22 that generates an aerosol of a raw material powder containing a raw material component, and a crystal that injects the raw material powder onto a seed substrate 21 to form a film containing the raw material component and crystallizes the film. And a generation unit 30. The aerosol generation unit 22 includes an aerosol generation chamber 23 that stores raw material powder and receives aerosol from a carrier gas (not shown) to generate aerosol, and a raw material supply pipe 24 that supplies the generated aerosol to the crystal generation unit 30. I have. A preheater heater 26 for preheating the aerosol is disposed on the crystal supply unit 30 side of the raw material supply pipe 24, and the preheated aerosol is supplied to the crystal generation unit 30. The crystal generation unit 30 fixes the seed substrate 21 by being disposed inside the vacuum chamber 31 for injecting the aerosol onto the seed substrate 21, the room-like heat insulating material 32 provided in the vacuum chamber 31, and the heat insulating material 32. A substrate holder 34 and an XY stage 33 that moves the substrate holder 34 in the X-axis-Y-axis directions are provided. The crystal generation unit 30 includes a heating unit 35 that is disposed inside the heat insulating material 32 and heats the seed substrate 21, a spray nozzle 36 that has a slit 37 formed at the tip thereof and sprays aerosol onto the seed substrate 21, and a vacuum chamber And a vacuum pump 38 for depressurizing 31. In the crystal manufacturing apparatus 20, each is configured using a member such as quartz glass or ceramics so that the heat treatment can be performed at a temperature at which the raw material powder is single-crystallized in the vacuum chamber 31.

In this apparatus, aerosol was injected using a ceramic nozzle 36 in which He was used as a carrier gas and a pressure adjusting gas, and a slit 37 having a long side of 5 mm and a short side of 0.4 mm was formed. At that time, the nozzle 36 was scanned at a scanning speed of 0.5 mm / s. As shown in FIG. 2, this scan is moved 10 mm in the direction perpendicular to the long side of the slit 37 (first film formation region 21 a) and moved 5 mm in the long side direction of the slit 37. The cycle of moving 10 mm in the direction perpendicular to the long side and returning in the direction of returning (second film formation region 21 b) and moving 5 mm in the long side direction and the initial position direction of the slit 37 was repeated 200 times. In one cycle of film formation at room temperature, the set pressure of the carrier gas was adjusted to 0.06 MPa, the flow rate was adjusted to 6 L / min, and the pressure in the chamber was adjusted to 100 Pa or less. As a crystal growth condition, the temperature of the chamber film forming chamber, which is a temperature at which a single crystal grows, was 1200 ° C. The thickness of the obtained single crystal substrate was 0.5 mm.

Using the MOCVD method on the obtained single crystal substrate (MgO solid solution zinc oxide single crystal growth surface), using TMG (trimethylgallium) and NH ₃ (ammonia) as source gases and N ₂ as a carrier gas, the substrate About 4 μm of GaN was deposited at a temperature of 800 ° C. The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was as small as 50 cm ⁻¹ , indicating good crystallinity.

Example 8
The raw material mixing ratio of the zinc oxide substrate is 94.8 parts by weight of commercially available high purity ZnO powder (specific surface area 9.4 m ² / g) and commercially available high purity MgO powder (specific surface area 23 m ² / g) 5.2 weight. A zinc oxide substrate was prepared and evaluated in the same manner as in Example 1, except that the content was 2.0 parts by weight and 2.0 parts by weight of commercially available high-purity θ-Al ₂ O ₃ powder (specific surface area 82 m ² / g). The results are as shown in Table 1, and the Raman peak half-value width indicating GaN crystallinity was as small as 26 cm ⁻¹ , indicating good crystallinity.

Example 9
The raw material mixing ratio of the zinc oxide substrate is 94.8 parts by weight of commercially available high purity ZnO powder (specific surface area 9.4 m ² / g) and commercially available high purity MgO powder (specific surface area 23 m ² / g) 5.2 weight. A zinc oxide substrate was prepared and evaluated in the same manner as in Example 1 except that the content was 0.1 parts by weight and 0.1 parts by weight of commercially available high-purity Ga ₂ O ₃ powder (specific surface area 5.3 m ² / g). The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was as small as 28 cm ⁻¹ , indicating good crystallinity.

Example 10
The raw material mixing ratio of the zinc oxide substrate is 94.8 parts by weight of commercially available high purity ZnO powder (specific surface area 9.4 m ² / g) and commercially available high purity MgO powder (specific surface area 23 m ² / g) 5.2 weight. A zinc oxide substrate was prepared and evaluated in the same manner as in Example 1 except that 0.3 parts by weight and 0.3 parts by weight of commercially available high-purity In ₂ O ₃ powder (specific surface area 4.2 m ² / g) were used. The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was as small as 25 cm ⁻¹ , indicating good crystallinity.

Example 11
A zinc oxide substrate was prepared and evaluated in the same manner as in Example 5 except that the MOCVD film formation temperature was 700 ° C. The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was as small as 39 cm ⁻¹ , indicating good crystallinity.

Example 12
A zinc oxide substrate was prepared and evaluated in the same manner as in Example 5 except that the MOCVD film formation temperature was 900 ° C. The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was as small as 22 cm ⁻¹ , indicating good crystallinity.

Example 13
1730 g of zinc sulfate heptahydrate (manufactured by Kojundo Chemical Laboratory) and 4.5 g of sodium gluconate (manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in 3000 g of ion-exchanged water. This solution was placed in a beaker and heated to 90 ° C. while stirring with a magnetic stirrer. While this solution was maintained at 90 ° C. and stirred, 490 g of 25% aqueous ammonium was added dropwise with a microtube pump. After completion of dropping, the mixture was kept at 90 ° C. with stirring for 4 hours and then allowed to stand. The precipitate was separated by filtration, further washed with ion-exchanged water three times, and dried to obtain a white powdered zinc oxide precursor. The obtained zinc oxide precursor was placed on a zirconia setter and calcined in the air in an electric furnace to obtain a plate-like porous zinc oxide powder. The temperature schedule at the time of calcination was raised from room temperature to 900 ° C. at a rate of temperature increase of 100 ° C./h, and then kept at 900 ° C. for 30 minutes to allow natural cooling. The obtained plate-like zinc oxide powder was pulverized to a mean particle size of 1.0 μm with a ball mill using ZrO ₂ balls.

4.8 parts by weight of zinc oxide plate-like particles obtained by the above method, 90.0 parts by weight of commercially available high purity ZnO powder (specific surface area 9.4 m ² / g), and commercially available high purity MgO powder (specific surface area) 23 parts by weight (23 m ² / g) and 0.6 parts by weight of commercially available high-purity θ-Al ₂ O ₃ powder (specific surface area 82 m ² / g) were mixed in a ball mill for 4 hours using ethanol as a solvent. With respect to 100 parts by weight of the mixed powder thus obtained, 15 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), a plasticizer (DOP: di (2-ethylhexyl) phthalate, black metal conversion) 6.2 parts by weight (manufactured by Co., Ltd.), 3 parts by weight of a dispersant (product name: Leodol SP-O30, manufactured by Kao Corporation), and a dispersion medium (2-ethylhexanol) were mixed. The amount of the dispersion medium was adjusted so that the slurry viscosity was 10,000 cP. The slurry thus prepared was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 100 μm. The obtained tape was cut and laminated, placed on an aluminum plate having a thickness of 10 mm, and then vacuum packed. This vacuum pack was hydrostatically pressed in warm water of 85 ° C. at a pressure of 100 kgf / cm ² to produce a disk-shaped molded body having a diameter of about 65 mm and a thickness of about 1.5 mm. The obtained molded body was placed in a degreasing furnace and degreased at 600 ° C. The obtained degreased body was fired in the atmosphere at 1200 ° C. for 5 hours under normal pressure to obtain a disk-shaped ZnO-based sintered body. The obtained sintered body was subjected to HIP treatment under conditions of an atmospheric pressure of 150 MPa and 1300 ° C. for 2 hours using Ar gas as a pressure medium. The periphery of the obtained sintered body was processed, the surface was mirror-polished with a diamond slurry, and then subjected to CMP treatment using colloidal silica to obtain a zinc oxide substrate having a diameter of about 50 mm and a thickness of about 0.6 mm.

The zinc oxide substrate thus obtained was evaluated in the same manner as in Example 1, and the degree of orientation and aspect ratio were also evaluated as follows. The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was as small as 29 cm ⁻¹ , indicating good crystallinity. The aspect ratio of the particles constituting the zinc oxide substrate was as small as 1.1.

<(002) Degree of orientation>
The degree of orientation of the substrate was determined by measuring the orientation degree of the (002) plane by XRD with the plate surface of the zinc oxide substrate as the sample surface. This measurement was performed using an XRD apparatus (product name “RINT-TTR III” manufactured by Rigaku Corporation) and measuring the XRD profile when the surface of the zinc oxide substrate was irradiated with X-rays. The degree of (002) orientation was calculated by the following formula (however, in this example, I ₀ (102) and I ₀ (110) can be omitted as negligible levels).

<Aspect ratio>
With _{a 1} and _{a 2} obtained to a mean particle diameter measuring time of the _substrate, was a 1 / _{a 2} and aspect ratio.

Example 14
A zinc (NO ₃ ) ₂ aqueous solution with a concentration of 0.1 M was prepared using zinc nitrate hexahydrate (manufactured by Kanto Chemical Co., Inc.). In addition, a 0.1 M NaOH aqueous solution was prepared using sodium hydroxide (manufactured by Sigma-Aldrich). A Zn (NO ₃ ) ₂ aqueous solution was mixed with the NaOH aqueous solution at a volume ratio of 1: 1, and the mixture was held at 80 ° C. for 6 hours with stirring to obtain a precipitate. The precipitate was washed with ion-exchanged water three times and then dried to obtain spherical secondary particles in which plate-like zinc oxide primary particles were aggregated. Subsequently, using ZrO ₂ balls having a diameter of 2 mm, ethanol as a solvent, by performing the ball milling process 3 hours, the zinc oxide secondary particle to volume basis D ₅₀ average particle size 0.6μm of the plate-like primary particles And crushed.

4.8 parts by weight of zinc oxide plate-like particles obtained by the above method, 90.0 parts by weight of commercially available high purity ZnO powder (specific surface area 9.4 m ² / g), and commercially available high purity MgO powder (specific surface area) 23 m ² / g) and 5.2 parts by weight of commercially available high-purity θ-Al ₂ O ₃ powder (specific surface area of 82 m ² / g) were mixed for 4 hours in a ball mill using ethanol as a solvent. With respect to 100 parts by weight of the mixed powder thus obtained, 15 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), a plasticizer (DOP: di (2-ethylhexyl) phthalate, black metal conversion) 6.2 parts by weight (manufactured by Co., Ltd.), 3 parts by weight of a dispersant (product name: Leodol SP-O30, manufactured by Kao Corporation), and a dispersion medium (2-ethylhexanol) were mixed. The amount of the dispersion medium was adjusted so that the slurry viscosity was 10,000 cP. The slurry thus prepared was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 100 μm. The obtained tape was cut and laminated, placed on an aluminum plate having a thickness of 10 mm, and then vacuum packed. This vacuum pack was hydrostatically pressed in warm water of 85 ° C. at a pressure of 100 kgf / cm ² to produce a disk-shaped molded body having a diameter of about 65 mm and a thickness of about 1.5 mm. The obtained molded body was placed in a degreasing furnace and degreased at 600 ° C. The obtained degreased body was fired in the atmosphere at 1200 ° C. for 5 hours under normal pressure to obtain a disk-shaped ZnO-based sintered body. The obtained sintered body was subjected to HIP treatment under conditions of an atmospheric pressure of 150 MPa and 1300 ° C. for 2 hours using Ar gas as a pressure medium. The periphery of the obtained sintered body was processed, the surface was mirror-polished with a diamond slurry, and then subjected to CMP treatment using colloidal silica to obtain a zinc oxide substrate having a diameter of about 50 mm and a thickness of about 0.6 mm.

The zinc oxide substrate thus obtained was evaluated in the same manner as in Example 1, and the particle aspect ratio was measured in the same manner as in Example 13. In addition, the degree of orientation was evaluated as follows. The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was as small as 31 cm ⁻¹ , indicating good crystallinity. The particle aspect ratio was as small as 1.3.

<(100) degree of orientation>
The degree of orientation of the substrate was determined by measuring the degree of orientation of the (100) plane by XRD using the plate surface of the zinc oxide substrate as the sample surface. This measurement was performed using an XRD apparatus (product name “RINT-TTR III” manufactured by Rigaku Corporation) and measuring the XRD profile when the surface of the zinc oxide substrate was irradiated with X-rays. The degree of (100) orientation was calculated by the following formula (however, in this example, I ₀ (102) and I ₀ (110) can be omitted as negligible levels).

Example 15
The raw material mixing ratio of the zinc oxide substrate is 94.8 parts by weight of commercially available high purity ZnO powder (specific surface area 9.4 m ² / g) and commercially available high purity MgO powder (specific surface area 23 m ² / g) 5.2 weight. The zinc oxide substrate was prepared and evaluated in the same manner as in Example 1 except that the temperature of the HIP treatment was 1450 ° C. The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was as small as 24 cm ⁻¹ , indicating good crystallinity.

Example 16
1730 g of zinc sulfate heptahydrate (manufactured by Kojundo Chemical Laboratory) and 4.5 g of sodium gluconate (manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in 3000 g of ion-exchanged water. This solution was placed in a beaker and heated to 90 ° C. while stirring with a magnetic stirrer. While this solution was maintained at 90 ° C. and stirred, 490 g of 25% aqueous ammonium was added dropwise with a microtube pump. After completion of dropping, the mixture was kept at 90 ° C. with stirring for 4 hours and then allowed to stand. The precipitate was separated by filtration, further washed with ion-exchanged water three times, and dried to obtain a white powdered zinc oxide precursor. 100 g of the obtained zinc oxide precursor was placed on a zirconia setter and calcined in the air in an electric furnace to obtain 65 g of a plate-like porous zinc oxide powder. The temperature schedule at the time of calcination was raised from room temperature to 900 ° C. at a rate of temperature increase of 100 ° C./h, and then kept at 900 ° C. for 30 minutes to allow natural cooling. The obtained plate-like zinc oxide powder was pulverized to a mean particle size of 0.5 μm with a ball mill using ZrO ₂ balls.

4.8 parts by weight of zinc oxide plate-like particles obtained by the above method, 90.0 parts by weight of commercially available high purity ZnO powder (specific surface area 9.4 m ² / g), and commercially available high purity MgO powder (specific surface area) 23 m ² / g) 5.2 parts by weight and commercially available high-purity θ-Al ₂ O ₃ powder (specific surface area 82 m ² / g) 0.6 parts by weight were mixed for ⁴ hours in a ball mill using ethanol as a solvent. The obtained slurry was dried with a rotary evaporator to obtain a mixed powder. With respect to 100 parts by weight of the obtained mixed powder, 15 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), a plasticizer (DOP: di (2-ethylhexyl) phthalate, black gold chemical stock) 6.2 parts by weight of a company), 3 parts by weight of a dispersant (product name: Leodol SP-O30, manufactured by Kao Corporation), and a dispersion medium (2-ethylhexanol) were mixed. The amount of the dispersion medium was adjusted so that the slurry viscosity was 10,000 cP. The slurry thus prepared was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 3 μm. The obtained sheet-like molded body was placed in a degreasing furnace and degreased at 600 ° C. The obtained degreased body was fired in the atmosphere at 1200 ° C. for 5 hours under normal pressure to obtain a sheet-like ZnO-based sintered body. This was pulverized by a pot mill to obtain a plate-like powder having a thickness of 2.0 μm and a size in the plate surface direction of about 7 μm.

With respect to 100 parts by weight of the plate powder thus obtained, 15 parts by weight of binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), plasticizer (DOP: di (2-ethylhexyl) phthalate, black gold 6.2 parts by weight of Kasei Co., Ltd., 3 parts by weight of a dispersant (product name: Leodol SP-O30, manufactured by Kao Corporation), and a dispersion medium (2-ethylhexanol) were mixed. The amount of the dispersion medium was adjusted so that the slurry viscosity was 10,000 cP. The slurry thus prepared was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 100 μm. The obtained tape was cut and laminated, placed on an aluminum plate having a thickness of 10 mm, and then vacuum packed. This vacuum pack was hydrostatically pressed in warm water of 85 ° C. at a pressure of 100 kgf / cm ² to produce a disk-shaped molded body having a diameter of about 65 mm and a thickness of about 1.5 mm. The obtained molded body was placed in a degreasing furnace and degreased at 600 ° C. The obtained degreased body was fired in the atmosphere at 1200 ° C. for 5 hours under normal pressure to obtain a disk-shaped ZnO-based sintered body. The obtained sintered body was subjected to HIP treatment using Ar gas as a pressure medium at an atmospheric pressure of 150 MPa and 1400 ° C. for 2 hours. The periphery of the obtained sintered body was processed, the surface was mirror-polished with a diamond slurry, and then subjected to CMP treatment using colloidal silica to obtain a zinc oxide substrate having a diameter of about 50 mm and a thickness of about 0.6 mm.

The zinc oxide substrate thus obtained was evaluated in the same manner as in Examples 1 and 13. The results are as shown in Table 1, and the aspect ratio of the particles constituting the zinc oxide substrate was as large as 3.0. The value of the half-width of the Raman peak indicating GaN crystallinity was as small as 40 cm ⁻¹ , indicating good crystallinity, but the crystallinity was lower than that of the zinc oxide substrates of Examples 13 and 14 having a particle aspect ratio as small as 2.0 or less. It was inferior.

The reason why the crystallinity of GaN is improved when the particle aspect ratio of the zinc oxide substrate is small is not clear, but when the aspect ratio of the ZnO particles is small, stress is not easily accumulated in the ZnO particles, and the GaN grown on the ZnO particles has a smaller aspect ratio. It is thought that distortion is reduced.

Example 17
In the same manner as in Example 13, plate-like zinc oxide particles were produced. And zinc oxide-shaped particles 4.8 parts by weight, commercially available high purity ZnO powder (specific surface area 9.4m ² /g)90.0 parts, commercially available high-purity MgO powder (specific surface area ^23m 2 / g) 5.2 parts by weight and 0.6 parts by weight of commercially available high-purity θ-Al ₂ O ₃ powder (specific surface area 82 m ² / g) were mixed in a ball mill using ethanol as a solvent for 4 hours. With respect to 100 parts by weight of the mixed powder thus obtained, 15 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), a plasticizer (DOP: di (2-ethylhexyl) phthalate, black metal conversion) 6.2 parts by weight (manufactured by Co., Ltd.), 3 parts by weight of a dispersant (product name: Leodol SP-O30, manufactured by Kao Corporation), and a dispersion medium (2-ethylhexanol) were mixed. The amount of the dispersion medium was adjusted so that the slurry viscosity was 10,000 cP. The slurry thus prepared was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 100 μm. Many of the obtained tapes were cut into strips of 8 mm × 65 mm, and about 650 sheets were laminated and vacuum packed. This vacuum pack was hydrostatically pressed at a pressure of 100 kgf / cm ² in 85 ° C. warm water to produce a molded body of 65 mm × 8 mm × 65 mm. The obtained molded body was placed in a degreasing furnace and degreased at 600 ° C. The obtained degreased body was fired at atmospheric pressure at 1200 ° C. for 5 hours under normal pressure to obtain a square plate-like ZnO-based sintered body. The obtained sintered body was subjected to HIP treatment under conditions of an atmospheric pressure of 150 MPa and 1300 ° C. for 2 hours using Ar gas as a pressure medium. The obtained sintered body was sliced in the thickness direction, the periphery was processed, the surface was mirror-polished with diamond slurry, and then subjected to CMP treatment using colloidal silica. The diameter was about 50 mm × thickness was about 0.6 mm. A zinc oxide substrate was obtained.

<(100) and (110) total orientation degree>
For the substrate of Example 17, the plate surface of the zinc oxide substrate was used as the sample surface, and the total orientation degree of the (100) plane and the (110) plane was measured by XRD. This measurement was performed using an XRD apparatus (product name “RINT-TTR III” manufactured by Rigaku Corporation) and measuring the XRD profile when the surface of the zinc oxide substrate was irradiated with X-rays. The total orientation degree of the (100) plane and the (110) plane was calculated by the following formula.

The zinc oxide substrate thus obtained was evaluated in the same manner as in Example 1. The results are as shown in the table. The Raman peak half-value width indicating GaN crystallinity was as small as 28 cm ⁻¹ , indicating good crystallinity.

Example 18
A zinc oxide substrate was prepared and evaluated in the same manner as in Example 17 except that the plate-like zinc oxide was ground to an average particle size of 0.1 μm with a ball mill. The results are as shown in Table 1. The Raman peak half-value width indicating GaN crystallinity was as small as 35 cm ⁻¹ , indicating good crystallinity.

In evaluation examples 7, 13, 14, 17 and 18 of the MOCVD-GaN film peeling site, the surface of the sample in which the GaN layer was formed on the zinc oxide substrate by MOCVD was observed with an optical microscope in 5 fields with a 1 mm square field. Observation was made to determine the average number of film peeling points.

In Example 7 relating to the single crystal substrate, film peeling as indicated by arrows in FIG. 3 was observed. The average film peeling location in 5 fields was 9 locations. On the other hand, in Example 13 relating to the (002) plane-oriented polycrystalline substrate, the average film peeling location was 4 locations. Moreover, in Example 14, Example 17, and Example 18 related to the (100) plane oriented or (100) and (110) plane oriented polycrystalline substrates, no film peeling was observed. Although the reason is not clear, the stress applied to the film is reduced in the polycrystal as compared with the single crystal, and the (100) plane orientation, or the (100) and (110) plane orientations, rather than the (002) plane orientation. This is presumed that the adhesion between the particles and the film was increased, and the film was less likely to peel off. Since peeling of the film becomes a leak source when the LED structure is manufactured, it is preferable that the film peels less. Further, since GaN having high crystallinity with little peeling can be formed on a zinc oxide substrate, growth of GaN by a flux method as described in Patent Document 2 (Japanese Patent Laid-Open No. 2007-254206) can be achieved. It becomes possible. Na flux used for GaN growth by the flux method has high reactivity with zinc oxide, and the zinc oxide substrate dissolves when directly contacted at a high temperature. However, highly crystalline GaN is formed in advance by a vapor phase method. By forming a film, this not only functions as a seed crystal but also functions as a protective layer for suppressing dissolution of the zinc oxide substrate. If the MOCVD GaN film is peeled off, Na flux penetrates from the peeled portion and reacts and dissolves with ZnO. Therefore, it is preferable that the number of peeled portions is small. Since GaN and zinc oxide have close lattice constants and thermal expansion coefficients, it is possible to grow GaN of good quality even in the flux method by using a zinc oxide substrate.

In crystal orientation evaluation examples 1 to 18 by EBSD, the cross section of the sample after the GaN film formation was confirmed by EBSD (electron beam backscatter diffraction apparatus). As a result, in all examples except Example 3, it was confirmed that the crystal orientation of GaN substantially coincided with the crystal orientation of the underlying ZnO particles.

Claims (14)

1. A zinc oxide substrate containing 0.1% by weight or more of Mg, which is used as a substrate for growing a group 13 nitride crystal by MOCVD.
2. The zinc oxide substrate according to claim 1, having a resistivity of 2 Ω · cm or less.
3. The zinc oxide substrate according to claim 1 or 2, which is a polycrystal having an average particle diameter of 10 to 200 µm.
4. The zinc oxide substrate according to any one of claims 1 to 3, which does not contain an MgO phase as a different phase.
5. The zinc oxide substrate according to any one of claims 1 to 4, comprising 0.05 to 2% by weight of one or more dopant elements selected from the group consisting of Al, Ga and In.
6. The zinc oxide substrate according to any one of claims 1 to 5, which has a resistivity of 0.1 Ω · cm or less.
7. The orientation degree of the (002) plane, the orientation degree of the (100) plane, the orientation degree of the (110) plane, or the total orientation degree of the (100) plane and (110) on the substrate surface is 30% or more. The zinc oxide substrate according to any one of 1 to 6.
8. 7. The degree of orientation of the (100) plane, the degree of orientation of the (110) plane, or the total degree of orientation of the (100) plane and the (110) plane on the substrate surface is 40% or more. A zinc oxide substrate according to 1.
9. 7. The degree of orientation of the (100) plane, the degree of orientation of the (110) plane, or the total degree of orientation of the (100) plane and the (110) plane on the substrate surface is 70% or more. A zinc oxide substrate according to 1.
10. The zinc oxide substrate according to any one of claims 1 to 9, wherein an aspect ratio of crystal grains constituting the zinc oxide substrate is 2.0 or less.
11. The zinc oxide substrate according to any one of claims 1 to 10, wherein the Mg content is 0.1 to 5.0 wt%.
12. Preparing the zinc oxide substrate according to any one of claims 1 to 11,
    A Group 13 nitride crystal represented by Ga _x Al _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is grown on the zinc oxide substrate by MOCVD. Process,
    A method for producing a Group 13 nitride crystal.
13. The method according to claim 12, wherein a crystal orientation of the group 13 nitride crystal grown on the zinc oxide substrate is substantially coincident with a crystal orientation of zinc oxide particles constituting the zinc oxide substrate.
14. The method according to claim 12 or 13, wherein the group 13 nitride crystal is grown on the surface of the zinc oxide substrate without forming an insulating layer.
    
    
    

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