WO2014192911A1 - Free-standing gallium nitride substrate, light emitting element, method for producing free-standing gallium nitride substrate, and method for manufacturing light emitting element - Google Patents

Free-standing gallium nitride substrate, light emitting element, method for producing free-standing gallium nitride substrate, and method for manufacturing light emitting element Download PDF

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Publication number
WO2014192911A1
WO2014192911A1 PCT/JP2014/064388 JP2014064388W WO2014192911A1 WO 2014192911 A1 WO2014192911 A1 WO 2014192911A1 JP 2014064388 W JP2014064388 W JP 2014064388W WO 2014192911 A1 WO2014192911 A1 WO 2014192911A1
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gallium nitride
layer
standing substrate
free
single crystal
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PCT/JP2014/064388
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French (fr)
Japanese (ja)
Inventor
守道 渡邊
吉川　潤
七瀧　努
克宏 今井
智彦 杉山
隆史 吉野
武内　幸久
佐藤　圭
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日本碍子株式会社
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Priority to JP2015519956A priority Critical patent/JPWO2014192911A1/en
Priority to US14/499,688 priority patent/US9312446B2/en
Priority to JP2014199217A priority patent/JP5770905B1/en
Priority to EP14195195.4A priority patent/EP2886686B1/en
Priority to EP16204466.3A priority patent/EP3181735B1/en
Publication of WO2014192911A1 publication Critical patent/WO2014192911A1/en
Priority to KR1020177030005A priority patent/KR102132313B1/en
Priority to EP15773888.1A priority patent/EP3128562B1/en
Priority to PCT/JP2015/058752 priority patent/WO2015151902A1/en
Priority to KR1020167007330A priority patent/KR101790458B1/en
Priority to JP2016511554A priority patent/JP6154066B2/en
Priority to CN201580001916.1A priority patent/CN105556685B/en
Priority to CN201810324504.7A priority patent/CN108305923B/en
Priority to JP2015126714A priority patent/JP2016001738A/en
Priority to US15/016,722 priority patent/US9548418B2/en
Priority to US15/072,745 priority patent/US9543473B2/en
Priority to US15/359,813 priority patent/US9768352B2/en
Priority to JP2016241058A priority patent/JP6480398B2/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/005—Processes
    • H01L33/0062—Processes for devices with an active region comprising only III-V compounds
    • H01L33/0075—Processes for devices with an active region comprising only III-V compounds comprising nitride compounds
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
    • C30B29/403—AIII-nitrides
    • C30B29/406—Gallium nitride
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/16—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H01L21/02538—Group 13/15 materials
    • H01L21/0254—Nitrides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/0257—Doping during depositing
    • H01L21/02573—Conductivity type
    • H01L21/02576—N-type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/0257—Doping during depositing
    • H01L21/02573—Conductivity type
    • H01L21/02579—P-type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02612—Formation types
    • H01L21/02617—Deposition types
    • H01L21/0262—Reduction or decomposition of gaseous compounds, e.g. CVD
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/26—Materials of the light emitting region
    • H01L33/30—Materials of the light emitting region containing only elements of group III and group V of the periodic system
    • H01L33/32—Materials of the light emitting region containing only elements of group III and group V of the periodic system containing nitrogen

Definitions

  • the present invention relates to a gallium nitride free-standing substrate, a light emitting device, and a method for manufacturing the same.
  • GaN gallium nitride
  • MQW multi-quantum well layer
  • a gallium nitride crystal multilayer substrate including a sapphire base substrate and a gallium nitride crystal layer formed by crystal growth on the substrate. Yes.
  • GaN gallium nitride
  • Patent Document 2 Japanese Patent Application Laid-Open No. 2010-1325566 discloses a self-supporting n-type gallium nitride single crystal substrate having a thickness of 200 ⁇ m or more.
  • single crystal substrates are generally small in area and expensive.
  • cost reduction of LED manufacturing using a large area substrate has been demanded, but it is not easy to mass-produce a large area single crystal substrate, and the manufacturing cost is further increased. Therefore, an inexpensive material that can be used as a substitute material for a single crystal substrate such as gallium nitride is desired.
  • the present inventors have now obtained the knowledge that a gallium nitride free-standing substrate that is inexpensive and suitable for an increase in area can be produced as an alternative material for a gallium nitride single crystal substrate.
  • an object of the present invention is to provide a gallium nitride free-standing substrate that is inexpensive and suitable for an increase in area and is useful as an alternative material for a gallium nitride single crystal substrate.
  • a gallium nitride free-standing substrate comprising a plate composed of a plurality of gallium nitride-based single crystal particles having a single crystal structure in a substantially normal direction.
  • a gallium nitride free-standing substrate according to the invention, A light emitting functional layer formed on the substrate and having at least one layer composed of a plurality of semiconductor single crystal particles having a single crystal structure in a substantially normal direction; A light-emitting element is provided.
  • a step of preparing an oriented polycrystalline sintered body Forming a seed crystal layer made of gallium nitride on the oriented polycrystalline sintered body so as to have a crystal orientation substantially following the crystal orientation of the oriented polycrystalline sintered body; Forming a layer composed of a gallium nitride-based crystal having a thickness of 20 ⁇ m or more on the seed crystal layer so as to have a crystal orientation substantially following the crystal orientation of the seed crystal layer; Removing the oriented polycrystalline sintered body to obtain a gallium nitride free-standing substrate; A method for manufacturing a gallium nitride free-standing substrate is provided.
  • the gallium nitride free-standing substrate includes at least one layer composed of a plurality of semiconductor single crystal particles having a single crystal structure in a substantially normal direction so as to have a crystal orientation that substantially follows the crystal orientation of the gallium nitride substrate.
  • the gallium nitride substrate of the present invention can have the form of a freestanding substrate.
  • the “self-supporting substrate” means a substrate that can be handled as a solid material without being deformed or damaged by its own weight when handled.
  • the gallium nitride free-standing substrate of the present invention can be used as a substrate for various semiconductor devices such as light-emitting elements, but in addition to this, an electrode (which may be a p-type electrode or an n-type electrode), a p-type layer, an n-type layer It can be used as a member or layer other than the substrate such as.
  • the advantages of the present invention may be described by taking a light emitting element which is one of the main applications as an example. However, similar or similar advantages are not limited to the technical consistency. The same applies to semiconductor devices.
  • the gallium nitride free-standing substrate of the present invention comprises a plate composed of a plurality of gallium nitride-based single crystal particles having a single crystal structure in a substantially normal direction. That is, the gallium nitride free-standing substrate is composed of a plurality of semiconductor single crystal particles that are two-dimensionally connected in the horizontal plane direction, and thus has a single crystal structure in a substantially normal direction. Therefore, although the gallium nitride free-standing substrate is not a single crystal as a whole, the gallium nitride free-standing substrate has a single crystal structure in a local domain unit, and therefore has a sufficiently high crystallinity to ensure device characteristics such as a light emitting function. it can.
  • the gallium nitride free-standing substrate of the present invention is not a single crystal substrate.
  • the single crystal substrate generally has a small area and is expensive.
  • there has been a demand for cost reduction of LED manufacturing using a large area substrate but it is not easy to mass-produce a large area single crystal substrate, and the manufacturing cost is further increased.
  • These drawbacks are eliminated by the gallium nitride free-standing substrate of the present invention. That is, according to the present invention, it is possible to provide a gallium nitride free-standing substrate useful as an alternative material for a gallium nitride single crystal substrate that is inexpensive and suitable for increasing the area.
  • a light-emitting element having a vertical structure can be realized, whereby luminance can be increased.
  • a large-area surface light-emitting element used for surface-emitting illumination or the like can be realized at low cost.
  • the plurality of gallium nitride single crystal particles constituting the self-supporting substrate have crystal orientations substantially aligned in a substantially normal direction.
  • Crystal orientation that is generally aligned in the normal direction is not necessarily a crystal orientation that is perfectly aligned in the normal direction, as long as a device such as a light-emitting element using a self-supporting substrate can ensure desired device characteristics. This means that the crystal orientation may be aligned to some extent in the normal or similar direction.
  • the gallium nitride-based single crystal particles have a structure grown substantially following the crystal orientation of the oriented polycrystalline sintered body used as the base material during the production of the gallium nitride free-standing substrate.
  • the “structure grown substantially following the crystal orientation of the oriented polycrystalline sintered body” means a structure brought about by crystal growth affected by the crystal orientation of the oriented polycrystalline sintered body, and is not necessarily oriented.
  • the crystal of the oriented polycrystalline sintered body is not necessarily a structure that has grown completely following the crystal orientation of the crystalline sintered body, as long as a device such as a light-emitting element using a self-supporting substrate can ensure the desired device characteristics. It may be a structure grown to some extent along the direction. That is, this structure includes a structure that grows in a different crystal orientation from the oriented polycrystalline sintered body.
  • the expression “a structure grown substantially following the crystal orientation” can also be rephrased as “a structure grown substantially derived from the crystal orientation”. This paraphrase and the above meaning are similar to those in this specification. The same applies to expression. Therefore, although such crystal growth is preferably by epitaxial growth, it is not limited to this, and various forms of crystal growth similar thereto may be used. In any case, by growing in this way, the gallium nitride free-standing substrate can have a structure in which crystal orientations are substantially aligned with respect to a substantially normal direction.
  • a gallium nitride free-standing substrate is an aggregate of columnar-structured gallium nitride single crystal particles that are observed as single crystals when viewed in the normal direction and grain boundaries are observed when viewed in the cut plane in the horizontal plane direction. It is also possible to grasp that.
  • the “columnar structure” does not mean only a typical vertically long column shape, but includes various shapes such as a horizontally long shape, a trapezoidal shape, and a shape in which the trapezoid is inverted. Defined as meaning.
  • the gallium nitride free-standing substrate may be a structure having a crystal orientation that is aligned to some extent in the normal or similar direction, and does not necessarily have a columnar structure in a strict sense.
  • the cause of the columnar structure is considered to be that the gallium nitride single crystal particles grow under the influence of the crystal orientation of the oriented polycrystalline sintered body used in the manufacture of the gallium nitride free-standing substrate as described above.
  • the average particle diameter of the cross section of gallium nitride single crystal particles which can be said to be a columnar structure (hereinafter referred to as the average diameter of the cross section), depends not only on the film forming conditions but also on the average particle diameter of the plate surface of the oriented polycrystalline sintered body It is thought to do.
  • the gallium nitride free-standing substrate is used as a part of the light emitting functional layer of the light emitting element, the light transmittance in the cross-sectional direction is poor due to the grain boundary, and the light is scattered or reflected. For this reason, in the case of a light-emitting element having a structure in which light is extracted in the normal direction, an effect of increasing luminance due to scattered light from the grain boundary is also expected.
  • the cross-sectional average diameter of the columnar structure is larger.
  • the cross-sectional average diameter of the semiconductor single crystal particles on the outermost surface of the gallium nitride free-standing substrate is 0.3 ⁇ m or more, more preferably 3 ⁇ m or more.
  • the upper limit of this cross-sectional average diameter is not specifically limited, 1000 micrometers or less are realistic.
  • the sintered particle size on the plate surface of the particles constituting the oriented polycrystalline sintered body used for the production of the gallium nitride free-standing substrate is set to 0.
  • the thickness is desirably 3 ⁇ m to 1000 ⁇ m, and more desirably 3 ⁇ m to 1000 ⁇ m.
  • the gallium nitride single crystal particles constituting the gallium nitride free-standing substrate may not contain a dopant.
  • dopant means that an element added for the purpose of imparting some function or characteristic is not contained, and it is needless to say that inclusion of inevitable impurities is allowed.
  • the gallium nitride-based single crystal particles constituting the gallium nitride free-standing substrate may be doped with an n-type dopant or a p-type dopant.
  • the gallium nitride free-standing substrate is formed by using a p-type electrode, an n-type electrode, p It can be used as a member or layer other than a base material such as a mold layer and an n-type layer.
  • a p-type dopant include one or more selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), and cadmium (Cd). It is done.
  • the n-type dopant include one or more selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), and oxygen (O).
  • the gallium nitride single crystal particles constituting the gallium nitride free-standing substrate may be mixed crystal for controlling the band gap.
  • the gallium nitride single crystal particles may be composed of gallium nitride mixed with at least one crystal selected from the group consisting of AlN and InN, and may be p-type gallium nitride and / or n.
  • the mixed gallium nitride may be doped with a p-type dopant or an n-type dopant.
  • Al x Ga 1-x N which is a mixed crystal of gallium nitride and AlN, is used as a p-type substrate by doping Mg
  • Al x Ga 1-x N is used as an n-type substrate by doping Si. be able to.
  • the band gap is widened by mixing gallium nitride with AlN, and the emission wavelength can be shifted to a higher energy side.
  • gallium nitride may be mixed with InN, whereby the band gap is narrowed and the emission wavelength can be shifted to a lower energy side.
  • the gallium nitride free-standing substrate preferably has a diameter of 50.8 mm (2 inches) or more, more preferably has a diameter of 100 mm (4 inches) or more, and more preferably has a diameter of 200 mm (8 inches) or more.
  • the gallium nitride free-standing substrate is larger, the number of devices that can be manufactured increases, which is preferable from the viewpoint of manufacturing cost. From the viewpoint of a surface light emitting device, the degree of freedom of the device area is increased and the use for surface light emitting lighting is expanded. The upper limit should not be prescribed
  • the gallium nitride free-standing substrate is preferably circular or substantially circular when viewed from above, but is not limited thereto.
  • the area is preferably at 2026Mm 2 or more, more preferably 7850mm 2 or more, further preferably 31400Mm 2 or more.
  • the area may be smaller than the above range, for example, a diameter of 50.8 mm (2 inches) or less, and 2026 mm 2 or less in terms of area.
  • the thickness of the gallium nitride free-standing substrate needs to be capable of imparting self-supporting properties to the substrate, and is preferably 20 ⁇ m or more, more preferably 100 ⁇ m or more, and even more preferably 300 ⁇ m or more. An upper limit should not be defined for the thickness of the gallium nitride free-standing substrate, but 3000 ⁇ m or less is realistic from the viewpoint of manufacturing cost.
  • the gallium nitride free-standing substrate of the present invention is prepared by (1) preparing an oriented polycrystalline sintered body, and (2) arranging a seed crystal layer made of gallium nitride on the oriented polycrystalline sintered body. (3) a layer composed of a gallium nitride-based crystal having a thickness of 20 ⁇ m or more on the seed crystal layer is approximately aligned with the crystal orientation of the seed crystal layer.
  • the gallium nitride free-standing substrate can be manufactured by removing the oriented polycrystalline sintered body by forming it so as to have a crystal orientation that has been copied.
  • An oriented polycrystalline sintered body is prepared as a base substrate for producing a gallium nitride free-standing substrate.
  • the composition of the oriented polycrystalline sintered body is not particularly limited, but is preferably one selected from an oriented polycrystalline alumina sintered body, an oriented polycrystalline zinc oxide sintered body, and an oriented polycrystalline aluminum nitride sintered body.
  • An oriented polycrystalline sintered body can be efficiently manufactured through molding and firing using commercially available plate-like powder, so it can be manufactured at a low cost, but also because it is easy to mold, it can also increase the area. Suitable.
  • a large-area light-emitting element is manufactured at low cost by using an oriented polycrystalline sintered body as a base substrate and growing a plurality of semiconductor single crystal particles thereon. Can be produced. As a result, the gallium nitride free-standing substrate is extremely suitable for manufacturing a large-area light emitting device at low cost.
  • the oriented polycrystalline sintered body is composed of a sintered body including a large number of single crystal particles, and a large number of single crystal particles are oriented to some extent or highly in a certain direction.
  • a highly oriented gallium nitride free-standing substrate when such a highly oriented gallium nitride free-standing substrate is used as a substrate for a light emitting device, a light emitting functional layer can be formed in a state where crystal orientations are substantially aligned in a substantially normal direction. High luminous efficiency equivalent to that when a substrate is used can be realized. Alternatively, even when this highly oriented gallium nitride free-standing substrate is used as a light-emitting functional layer of a light-emitting element, high light emission efficiency equivalent to that when a single crystal substrate is used can be realized. In any case, in order to produce such a highly oriented gallium nitride free-standing substrate, it is necessary to use an oriented polycrystalline sintered body as a base substrate.
  • the oriented polycrystalline sintered body preferably has translucency, but is not limited thereto.
  • translucency a technique such as laser lift-off can be used when removing the oriented polycrystalline plate.
  • a manufacturing method for obtaining an oriented polycrystalline sintered body in addition to a normal atmospheric pressure sintering method using an air furnace, a nitrogen atmosphere furnace, a hydrogen atmosphere furnace, etc., a hot isostatic pressing method (HIP), a hot press method (HP), pressure sintering methods such as spark plasma sintering (SPS), and a combination thereof can be used.
  • HIP hot isostatic pressing method
  • HP hot press method
  • SPS spark plasma sintering
  • the oriented polycrystalline sintered body preferably has a diameter of 50.8 mm (2 inches) or more, more preferably has a diameter of 100 mm (4 inches) or more, and more preferably has a diameter of 200 mm (8 inches) or more. .
  • the gallium nitride free-standing substrate is preferably circular or substantially circular when viewed from above, but is not limited thereto. If not a circular or substantially circular shape, as the area is preferably at 2026Mm 2 or more, more preferably 7850mm 2 or more, further preferably 31400Mm 2 or more. However, for applications that do not require a large area, the area may be smaller than the above range, for example, a diameter of 50.8 mm (2 inches) or less, and 2026 mm 2 or less in terms of area.
  • the thickness of the oriented polycrystalline sintered body is not particularly limited as long as it is self-supporting, but if it is too thick, it is not preferable from the viewpoint of production cost. Accordingly, the thickness is preferably 20 ⁇ m or more, more preferably 100 ⁇ m or more, and further preferably 100 to 1000 ⁇ m.
  • the average particle diameter on the plate surface of the particles constituting the oriented polycrystalline sintered body is preferably 0.3 to 1000 ⁇ m, more preferably 3 to 1000 ⁇ m.
  • the average grain size of the entire oriented polycrystalline sintered body has a correlation with the average grain size of the plate surface, and within these ranges, the sintered body is excellent in mechanical strength and easy to handle.
  • the light-emitting functional layer is also excellent in light emission efficiency.
  • grains in this invention is measured with the following method. That is, the plate surface of the plate-like sintered body is polished and an image is taken with a scanning electron microscope.
  • the visual field range is a visual field range in which a straight line intersecting 10 to 30 particles can be drawn when a straight line is drawn on the diagonal line of the obtained image.
  • a particularly preferred oriented polycrystalline sintered body is an oriented polycrystalline alumina sintered body.
  • Alumina is aluminum oxide (Al 2 O 3 ), which is typically ⁇ -alumina having the same corundum type structure as single crystal sapphire, and the oriented polycrystalline alumina sintered body has innumerable alumina crystal particles oriented. Solids that are bonded together by sintering.
  • the alumina crystal particles are particles composed of alumina, and may include a dopant and inevitable impurities as other elements, or may be composed of alumina and inevitable impurities.
  • the oriented polycrystalline alumina sintered body may contain an additive as a sintering aid as a grain boundary phase.
  • the oriented polycrystalline alumina sintered body may also contain other phases or other elements as described above in addition to the alumina crystal particles, but preferably comprises alumina crystal particles and inevitable impurities.
  • the orientation plane of the oriented polycrystalline alumina sintered body is not particularly limited, and may be a c-plane, a-plane, r-plane, m-plane, or the like.
  • the oriented crystal orientation of the oriented polycrystalline alumina sintered body is not particularly limited and may be a c-plane, a-plane, r-plane, m-plane, etc., from the viewpoint of lattice constant matching with a gallium nitride free-standing substrate. It is preferably oriented in the c-plane.
  • the degree of orientation on the plate surface is preferably 50% or more, more preferably 65% or more, still more preferably 75% or more, particularly preferably 85%, and particularly preferably. 90% or more, and most preferably 95% or more.
  • This degree of orientation is calculated by the following formula by measuring the XRD profile when X-rays are irradiated to the plate surface of plate-like alumina using an XRD apparatus (for example, RINT-TTR III, manufactured by Rigaku Corporation). It is obtained by doing.
  • the crystallinity of the constituent particles of the gallium nitride free-standing substrate tends to be high, and the density of defects such as dislocations can be kept low.
  • the gallium nitride free-standing substrate can even be preferably used as compared with the gallium nitride single crystal substrate in certain applications such as a light emitting device.
  • the functional layer grows substantially following the underlying gallium nitride free-standing substrate and becomes an aggregate of columnar structures.
  • one of the particles constituting the outermost surface of the oriented polycrystalline sintered body serving as a base substrate is used. It is more preferable that all or all of the portions are arranged in a form that is slightly inclined slightly from a certain orientation (for example, a reference orientation such as c-plane or a-plane).
  • the inclined particles may be inclined almost entirely or in a certain amount at a substantially constant angle, or at various angles having a distribution within a certain range (preferably 0.01 to 20 °) and / or various. It may be inclined in any direction.
  • inclined particles and non-inclined particles may be mixed in a desired ratio.
  • the plate surface of the oriented polycrystalline alumina sintered body may be polished obliquely with respect to the reference surface, and the exposed surface of the particles may be inclined in a certain direction, or the surface of the particles on the outermost surface may be processed into a wavy shape or the like. A surface slightly inclined from the reference orientation may be exposed.
  • some or all of the alumina single crystal particles constituting the outermost surface of the oriented polycrystalline alumina sintered body oriented in the reference orientation such as the c-plane, a-plane, etc. have their reference orientation determined by the substrate method. It is preferable to be arranged so as to be inclined so as to deviate within a range of 0.5 to 20 ° from the line direction.
  • An oriented polycrystalline alumina sintered body can be produced by molding and sintering using a plate-like alumina powder as a raw material.
  • Plate-like alumina powder is commercially available and is commercially available.
  • the type and shape of the plate-like alumina powder are not particularly limited as long as a dense oriented polycrystalline alumina sintered body can be obtained, but the average particle diameter may be 0.4 to 15 ⁇ m and the thickness may be 0.05 to 1 ⁇ m. It is good also as what mixed 2 or more types of raw materials of different average particle diameter.
  • the plate-like alumina powder can be oriented by a technique using shearing force to obtain an oriented molded body.
  • the technique using shearing force include tape molding, extrusion molding, doctor blade method, and any combination thereof.
  • the orientation method using the shearing force is made into a slurry by appropriately adding additives such as a binder, a plasticizer, a dispersing agent, and a dispersion medium to the plate-like alumina 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 ⁇ m.
  • the amount of the dispersion medium is preferably such that the slurry viscosity is 5000 to 100,000 cP, more preferably 20000 to 60000 cP.
  • the thickness of the oriented molded body formed into a sheet is preferably 5 to 500 ⁇ m, more preferably 10 to 200 ⁇ m. 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.
  • 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 subjected to hot isostatic pressing (HIP), hot pressing (HP ), A pressure sintering method such as spark plasma sintering (SPS), and a combination thereof, and an alumina sintered body comprising oriented alumina crystal particles is formed.
  • the firing temperature and firing time in the firing vary depending on the firing method, the firing temperature is 1100 to 1900 ° C., preferably 1500 to 1800 ° C., and the firing time is 1 minute to 10 hours, preferably 30 minutes to 5 hours.
  • a first firing step of firing in a hot press at 1500 to 1800 ° C. for 2 to 5 hours under a surface pressure of 100 to 200 kgf / cm 2 and the obtained sintered body is subjected to hot isostatic pressing (HIP) More preferably, it is carried out through a second firing step in which firing is carried out again at 1500 to 1800 ° C. for 30 minutes to 5 hours under a gas pressure of 1000 to 2000 kgf / cm 2 .
  • HIP hot isostatic pressing
  • 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.
  • a method is used in which a high-purity plate-like alumina powder is used as a raw material and calcined at 1100 to 1800 ° C. for 1 minute to 10 hours in an air furnace, hydrogen atmosphere furnace, nitrogen atmosphere furnace or the like Is preferably exemplified.
  • a method of firing the obtained sintered body again at a temperature of 1200 to 1400 ° C. for 30 minutes to 5 hours and a gas pressure of 300 to 2000 kgf / cm 2 by hot isostatic pressing (HIP) is used. May be.
  • the plate-like alumina powder is preferably highly pure, more preferably 98% or more, further preferably 99% or more, particularly preferably 99.9% or more, most preferably Preferably it is 99.99% or more.
  • the firing conditions are not limited to the above.
  • the second firing step by hot isostatic pressing (HIP) may be omitted as long as both densification and high orientation are possible.
  • a very small amount of additives may be added to the raw material as a sintering aid. Although the addition of the sintering aid goes against the reduction of the grain boundary phase, the purpose is to improve the translucency as a result by reducing pores, which is one of the light scattering factors.
  • oxides such as MgO, ZrO 2 , Y 2 O 3 , CaO, SiO 2 , TiO 2 , Fe 2 O 3 , Mn 2 O 3 , fluorides such as MgF 2 and YbF 3 And at least one selected from the above.
  • the amount of additive should be kept to the minimum necessary, and is preferably 1000 ppm or less, more preferably 700 ppm or less.
  • An oriented polycrystalline alumina sintered body can also be produced by molding and sintering using a mixed powder obtained by appropriately adding a plate-like alumina powder to a fine alumina powder and / or a transition alumina powder. it can.
  • a plate-like alumina powder becomes a seed crystal (template)
  • a fine alumina powder and / or a transition alumina powder becomes a matrix
  • the template undergoes a so-called TGG (Tempered Grain Growth) process in which homoepitaxial growth is performed while incorporating the matrix. This causes crystal growth and densification.
  • TGG Tempored Grain Growth
  • the average particle size of the template is 0.5 to 15 ⁇ m
  • the average particle size of the matrix is 0.4 ⁇ m or less. Is preferably 0.2 ⁇ m or less, and more preferably 0.1 ⁇ m or less.
  • the mixing ratio of the template and matrix varies depending on the particle size ratio, firing conditions, and the presence or absence of additives. For example, a plate-like alumina powder having an average particle size of 2 ⁇ m is used as the template, and a fine alumina powder having an average particle size of 0.1 ⁇ m is used as the matrix. In such a case, the template / matrix ratio may be 50/50 to 1/99 wt%.
  • a high-quality oriented polycrystalline alumina sintered body can be obtained by a pressure sintering method such as sintering (SPS) or a combination thereof.
  • a pressure sintering method such as sintering (SPS) or a combination thereof.
  • the alumina sintered body thus obtained becomes a polycrystalline alumina sintered body oriented in a desired plane such as the c-plane depending on the kind of the plate-like alumina powder used as the raw material. It is preferable that the oriented polycrystalline alumina sintered body thus obtained is ground with a grindstone to flatten the plate surface, and then the plate surface is smoothed by lapping using diamond abrasive grains to obtain an oriented alumina substrate.
  • a seed crystal layer made of gallium nitride is formed on the oriented polycrystalline sintered body so as to have a crystal orientation that substantially follows the crystal orientation of the oriented polycrystalline sintered body.
  • Forming so as to have a crystal orientation generally following the crystal orientation of the oriented polycrystalline sintered body means that the structure is brought about by crystal growth affected by the crystal orientation of the oriented polycrystalline sintered body. This means that the structure does not necessarily grow completely following the crystal orientation of the oriented polycrystalline sintered body, but also includes a structure that grows in a different crystal orientation from the oriented polycrystalline sintered body.
  • the method for producing the seed crystal layer is not particularly limited, but MOCVD (metal organic vapor phase epitaxy), MBE (molecular beam epitaxy), HVPE (halide vapor phase epitaxy), sputtering and other gas phase methods, Na flux method, Preferred examples include liquid phase methods such as ammonothermal method, hydrothermal method, sol-gel method, powder method utilizing solid phase growth of powder, and combinations thereof.
  • MOCVD metal organic vapor phase epitaxy
  • MBE molecular beam epitaxy
  • HVPE halide vapor phase epitaxy
  • sputtering and other gas phase methods Na flux method
  • Preferred examples include liquid phase methods such as ammonothermal method, hydrothermal method, sol-gel method, powder method utilizing solid phase growth of powder, and combinations thereof.
  • MOCVD metal organic vapor phase epitaxy
  • MBE molecular beam epitaxy
  • HVPE halide vapor phase epitaxy
  • sputtering and other gas phase methods Na flux method
  • a layer composed of a gallium nitride-based crystal having a thickness of 20 ⁇ m or more is formed on the seed crystal layer so as to have a crystal orientation that substantially follows the crystal orientation of the seed crystal layer.
  • the method of forming a layer composed of gallium nitride-based crystals is not particularly limited as long as it has a crystal orientation that substantially follows the crystal orientation of the oriented polycrystalline sintered body and / or the seed crystal layer, and is a gas phase method such as MOCVD or HVPE.
  • Preferred examples include a liquid phase method such as Na flux method, ammonothermal method, hydrothermal method, sol-gel method, powder method utilizing solid phase growth of powder, and combinations thereof, but the Na flux method is used. Is particularly preferred.
  • a thick gallium nitride crystal layer with high crystallinity can be efficiently produced on the seed crystal layer.
  • the formation of the gallium nitride crystal layer by the Na flux method is performed by using a crucible provided with a seed crystal substrate and metal n-type such as metal Ga, metal Na, and optionally a dopant (eg, germanium (Ge), silicon (Si), oxygen (O)).
  • a melt composition containing a dopant or a p-type dopant such as beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), cadmium (Cd), etc.
  • a nitrogen atmosphere Among them, it is preferable to carry out the heating and pressurizing to 830 to 910 ° C. and 3.5 to 4.5 MPa, and then rotating while maintaining the temperature and pressure.
  • the holding time varies depending on the target film thickness, but may be about 10 to 100 hours.
  • the gallium nitride crystal thus obtained by the Na flux method is ground with a grindstone to flatten the plate surface, and then the plate surface is smoothed by lapping using diamond abrasive grains.
  • the oriented polycrystalline sintered body can be removed to obtain a gallium nitride free-standing substrate.
  • the method for removing the oriented polycrystalline sintered body is not particularly limited, but is spontaneous, utilizing grinding, chemical etching, interfacial heating (laser lift-off) by laser irradiation from the oriented sintered body side, and thermal expansion difference during temperature rise Exfoliation and the like.
  • a high-quality light-emitting element can be manufactured using the above-described gallium nitride free-standing substrate according to the present invention.
  • a light-emitting element is manufactured by providing a light-emitting functional layer on a gallium nitride free-standing substrate, and the light-emitting functional layer is formed so that the crystal orientation approximately follows the crystal orientation of the gallium nitride substrate. It is preferable to form one or more layers composed of a plurality of semiconductor single crystal particles having a single crystal structure in the normal direction.
  • a light-emitting element may be manufactured using a gallium nitride free-standing substrate as a member or layer other than a substrate such as an electrode (which may be a p-type electrode or an n-type electrode), a p-type layer, or an n-type layer.
  • the element size is not particularly limited, and may be a small element of 5 mm ⁇ 5 mm or less, or a surface light emitting element of 10 cm ⁇ 10 cm or more.
  • FIG. 1 schematically shows a layer structure of a light-emitting element according to one embodiment of the present invention.
  • a light-emitting element 10 shown in FIG. 1 includes a gallium nitride free-standing substrate 12 and a light-emitting functional layer 14 formed on the substrate.
  • the light emitting functional layer 14 has one or more layers composed of a plurality of semiconductor single crystal particles having a single crystal structure in a substantially normal direction.
  • the light-emitting functional layer 14 emits light based on the principle of a light-emitting element such as an LED by appropriately providing electrodes and applying a voltage.
  • gallium nitride free-standing substrate 12 of the present invention it can be expected to obtain a light-emitting element having a light emission efficiency equivalent to that when a gallium nitride single crystal substrate is used, and a significant cost reduction can be realized.
  • gallium nitride imparted with conductivity by introducing a p-type or n-type dopant as a substrate, a light-emitting element having a vertical structure can be realized, whereby luminance can be increased.
  • a large area surface light emitting device can be realized at low cost.
  • a light emitting functional layer 14 is formed on the substrate 12.
  • the light emitting functional layer 14 may be provided on the entire surface or a part of the substrate 12, or may be provided on the entire surface or a part of the buffer layer when a buffer layer described later is formed on the substrate 12. Good.
  • the light-emitting functional layer 14 has one or more layers composed of a plurality of semiconductor single crystal particles having a single crystal structure in a substantially normal direction, and is appropriately provided with electrodes and / or phosphors to apply a voltage. Therefore, it is possible to adopt various known layer configurations that cause light emission based on the principle of a light emitting element represented by an LED. Therefore, the light emitting functional layer 14 may emit visible light such as blue and red, or may emit ultraviolet light without visible light or with visible light.
  • the light emitting functional layer 14 preferably constitutes at least a part of a light emitting element using a pn junction, and the pn junction includes a p-type layer 14a and an n-type layer 14c as shown in FIG.
  • the active layer 14b may be included in between.
  • a double heterojunction or a single heterojunction (hereinafter collectively referred to as a heterojunction) using a layer having a smaller band gap than the p-type layer and / or the n-type layer as the active layer may be used.
  • a quantum well structure in which the active layer is thin can be adopted as one form of the p-type layer-active layer-n-type layer.
  • the light emitting functional layer 14 preferably includes a pn junction and / or a heterojunction and / or a quantum well junction having a light emitting function.
  • At least one layer constituting the light emitting functional layer 14 is at least selected from the group consisting of an n-type layer doped with an n-type dopant, a p-type layer doped with a p-type dopant, and an active layer.
  • an n-type layer, the p-type layer, and the active layer may be composed of the same material as the main component, or may be composed of materials whose main components are different from each other.
  • each layer constituting the light emitting functional layer 14 is not particularly limited as long as it grows substantially following the crystal orientation of the gallium nitride free-standing substrate and has a light emitting function, but gallium nitride (GaN) based material, zinc oxide ( It is preferably composed of a material mainly composed of at least one selected from a ZnO) -based material and an aluminum nitride (AlN) -based material, and appropriately contains a dopant for controlling p-type or n-type. It may be.
  • a particularly preferable material is a gallium nitride (GaN) -based material, which is the same material as the gallium nitride free-standing substrate.
  • the material constituting the light emitting functional layer 14 may be a mixed crystal in which, for example, AlN, InN or the like is dissolved in GaN in order to control the band gap.
  • the light emitting functional layer 14 may be a heterojunction made of a plurality of types of materials. For example, a gallium nitride (GaN) -based material may be used for the p-type layer, and a zinc oxide (ZnO) -based material may be used for the n-type layer.
  • GaN gallium nitride
  • ZnO zinc oxide
  • a zinc oxide (ZnO) -based material may be used for the p-type layer
  • a gallium nitride (GaN) -based material may be used for the active layer and the n-type layer, and the combination of materials is not particularly limited.
  • Each layer constituting the light emitting functional layer 14 is composed of a plurality of semiconductor single crystal particles having a single crystal structure in a substantially normal direction. That is, each layer is composed of a plurality of semiconductor single crystal particles that are two-dimensionally connected in the horizontal plane direction, and therefore has a single crystal structure in a substantially normal direction. Therefore, each layer of the light emitting functional layer 14 is not a single crystal as a whole, but has a single crystal structure in a local domain unit, and thus can have high crystallinity sufficient to ensure a light emitting function. .
  • the semiconductor single crystal particles constituting each layer of the light emitting functional layer 14 have a structure grown substantially following the crystal orientation of the gallium nitride free-standing substrate which is the substrate 12.
  • a structure grown substantially following the crystal orientation of a gallium nitride free-standing substrate means a structure brought about by crystal growth affected by the crystal orientation of the gallium nitride free-standing substrate, and is not necessarily a crystal of the gallium nitride free-standing substrate.
  • the structure does not necessarily grow perfectly following the orientation, and may be a structure grown somewhat following the crystal orientation of the gallium nitride free-standing substrate as long as a desired light emitting function can be secured. That is, this structure includes a structure that grows in a different crystal orientation from the oriented polycrystalline sintered body. In that sense, the expression “a structure grown substantially following the crystal orientation” can be rephrased as “a structure grown substantially derived from the crystal orientation”.
  • crystal growth is preferably by epitaxial growth, it is not limited to this, and various forms of crystal growth similar thereto may be used.
  • the crystal in the substantially normal direction is also observed in each layer of the light emitting functional layer from the gallium nitride free-standing substrate.
  • a structure in which the orientation is substantially uniform can be obtained, and good light emission characteristics can be obtained. That is, when the light emitting functional layer 14 also grows substantially following the crystal orientation of the gallium nitride free-standing substrate 12, the orientation is substantially constant in the vertical direction of the substrate.
  • the normal direction is the same as that of a single crystal, and when a gallium nitride free-standing substrate to which an n-type dopant is added is used, a light-emitting element having a vertical structure using the gallium nitride free-standing substrate as a cathode can be obtained.
  • a gallium nitride free-standing substrate to which a p-type dopant is added is used, a vertical structure light-emitting element using the gallium nitride free-standing substrate as an anode can be obtained.
  • each layer of the light-emitting functional layer 14 is a single crystal when viewed in the normal direction. It can also be regarded as an aggregate of columnar-structured semiconductor single crystal particles that are observed and viewed from a cut surface in the horizontal plane direction.
  • the “columnar structure” does not mean only a typical vertically long column shape, but includes various shapes such as a horizontally long shape, a trapezoidal shape, and a shape in which the trapezoid is inverted. Defined as meaning.
  • each layer has only to have a structure grown to some extent along the crystal orientation of the gallium nitride free-standing substrate, and does not necessarily have a columnar structure in a strict sense.
  • the cause of the columnar structure is considered to be that the semiconductor single crystal particles grow under the influence of the crystal orientation of the gallium nitride free-standing substrate as the substrate 12 as described above.
  • the average particle diameter of the cross section of the semiconductor single crystal particles which can be said to be a columnar structure (hereinafter referred to as the average cross section diameter) depends not only on the film forming conditions but also on the average particle diameter of the plate surface of the gallium nitride free-standing substrate. Conceivable.
  • the interface of the columnar structure constituting the light emitting functional layer affects the light emission efficiency and the light emission wavelength, but due to the presence of the grain boundary, the light transmittance in the cross-sectional direction is poor, and the light is scattered or reflected. For this reason, in the case of a structure in which light is extracted in the normal direction, an effect of increasing the luminance due to scattered light from the grain boundary is also expected.
  • the cross-sectional average diameter of the columnar structure is larger.
  • the cross-sectional average diameter of the semiconductor single crystal particles on the outermost surface of the light emitting functional layer 14 is 0.3 ⁇ m or more, more preferably 3 ⁇ m or more.
  • the upper limit of this cross-sectional average diameter is not specifically limited, 1000 micrometers or less are realistic.
  • the average cross-sectional diameter of the outermost surface of the gallium nitride-based single crystal particles constituting the gallium nitride free-standing substrate is set to 0.3 ⁇ m to 1000 ⁇ m. Is more desirable, and more desirably 3 ⁇ m or more.
  • a buffer layer for suppressing the reaction is provided between the gallium nitride free-standing substrate 12 and the light emitting functional layer 14. Also good.
  • the main component of such a buffer layer is not particularly limited, but it is preferably composed of a material mainly containing at least one selected from a zinc oxide (ZnO) -based material and an aluminum nitride (AlN) -based material. , A dopant for controlling p-type to n-type may be included as appropriate.
  • Each layer constituting the light emitting functional layer 14 is preferably made of a gallium nitride material.
  • a gallium nitride material For example, an n-type gallium nitride layer and a p-type gallium nitride layer may be grown in order on the gallium nitride free-standing substrate 12, and the stacking order of the p-type gallium nitride layer and the n-type gallium nitride layer may be reversed.
  • the p-type dopant used for the p-type gallium nitride layer include a group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), and cadmium (Cd).
  • n-type dopant used for the n-type gallium nitride layer at least one selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), and oxygen (O) is used.
  • Si silicon
  • Ge germanium
  • Sn tin
  • O oxygen
  • the p-type gallium nitride layer and / or the n-type gallium nitride layer may be made of gallium nitride mixed with one or more kinds of crystals selected from the group consisting of AlN and InN.
  • the mixed gallium nitride may be doped with a p-type dopant or an n-type dopant.
  • a p-type dopant for example, Al x Ga 1-x N, which is a mixed crystal of gallium nitride and AlN, is used as a p-type layer by doping Mg, and Al x Ga 1-x N is used as an n-type layer by doping Si. be able to.
  • gallium nitride is mixed with AlN, the band gap is widened, and the emission wavelength can be shifted to a higher energy side.
  • gallium nitride may be mixed with InN, whereby the band gap is narrowed and the emission wavelength can be shifted to a lower energy side.
  • the p-type gallium nitride layer and the n-type gallium nitride layer it is composed of a mixed crystal of GaN with one or more selected from the group consisting of GaN or AlN and InN having a smaller band gap than both layers.
  • You may have an active layer at least.
  • the active layer has a double heterojunction structure with a p-type layer and an n-type layer, and the thinned structure of the active layer corresponds to a light emitting device having a quantum well structure which is an embodiment of a pn junction, and has a luminous efficiency.
  • the active layer may be made of a mixed crystal of GaN having one or more selected from the group consisting of GaN or AlN and InN having a smaller band gap than either one of the two layers. Even in such a single heterojunction, the luminous efficiency can be further increased.
  • the gallium nitride buffer layer may be made of non-doped GaN, n-type or p-type doped GaN, and selected from the group consisting of AlN, InN, or GaN, AlN, and InN having a close lattice constant. It may be mixed with one or more kinds of crystals.
  • the light emitting functional layer 14 may be composed of a plurality of material systems selected from gallium nitride (GaN) -based materials, zinc oxide (ZnO) -based materials, and aluminum nitride (AlN) -based materials.
  • GaN gallium nitride
  • ZnO zinc oxide
  • AlN aluminum nitride
  • a p-type gallium nitride layer and an n-type zinc oxide layer may be grown on the gallium nitride free-standing substrate 12, and the stacking order of the p-type gallium nitride layer and the n-type zinc oxide layer may be reversed.
  • an n-type or p-type zinc oxide layer may be formed.
  • Preferable examples of the p-type dopant used for the p-type zinc oxide layer include nitrogen (N), phosphorus (P), arsenic (As), carbon (C), lithium (Li), sodium (Na), potassium ( K), one or more selected from the group consisting of silver (Ag) and copper (Cu).
  • Preferred examples of the n-type dopant used for the n-type zinc oxide layer include aluminum (Al), gallium (Ga), indium (In), boron (B), fluorine (F), chlorine (Cl), One or more selected from the group consisting of bromine (Br), iodine (I), and silicon (Si) may be mentioned.
  • the film formation method of the light emitting functional layer 14 and the buffer layer is not particularly limited as long as it grows substantially following the crystal orientation of the gallium nitride free-standing substrate, but a vapor phase method such as MOCVD, MBE, HVPE, sputtering, Na flux, etc.
  • a vapor phase method such as MOCVD, MBE, HVPE, sputtering, Na flux, etc.
  • Preferred examples include a liquid phase method such as a method, an ammonothermal method, a hydrothermal method, a sol-gel method, a powder method utilizing solid phase growth of powder, and a combination thereof.
  • a gas for example, ammonia
  • an organometallic gas for example, trimethyl gallium
  • gallium (Ga) and nitrogen (N) On the substrate as a raw material and grown in a temperature range of about 300 to 1200 ° C. in an atmosphere containing hydrogen, nitrogen, or both.
  • 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
  • n-type and p-type dopants for example, trimethylindium, trimethylaluminum, monosilane, disilane
  • Bis-cyclopentadienylmagnesium may be appropriately introduced to form a film.
  • a seed crystal layer may be formed on the gallium nitride free-standing substrate.
  • any method may be used as long as it promotes crystal growth substantially following the crystal orientation.
  • a zinc oxide-based material is used for a part or all of the light emitting functional layer 14
  • an ultrathin zinc oxide seed crystal is prepared by vapor phase growth methods such as MOCVD, MBE, HVPE, and sputtering. May be.
  • the electrode layer 16 and / or the phosphor layer may be further provided on the light emitting functional layer 14.
  • an electrode layer 18 is provided on the back surface of the gallium nitride free-standing substrate 12 as shown in FIG.
  • the gallium nitride free-standing substrate 12 may be used as the electrode itself. In that case, it is preferable that an n-type dopant is added to the gallium nitride free-standing substrate 12.
  • the electrode layers 16 and 18 may be made of a known electrode material.
  • the electrode layer 16 on the light emitting functional layer 14 is a transparent conductive film such as ITO, or a metal electrode having a high aperture ratio such as a lattice structure, This is preferable in that the extraction efficiency of light generated in the light emitting functional layer 14 can be increased.
  • a phosphor layer for converting ultraviolet light into visible light may be provided outside the electrode layer.
  • the phosphor layer is not particularly limited as long as it includes a known fluorescent component capable of converting ultraviolet light into visible light.
  • a fluorescent component that emits blue light when excited by ultraviolet light, a fluorescent component that emits blue to green light when excited by ultraviolet light, and a fluorescent component that emits red light when excited by ultraviolet light are mixed. It is preferable that the white color is obtained as a mixed color.
  • Preferred combinations of such fluorescent components include (Ca, Sr) 5 (PO 4 ) 3 Cl: Eu, BaMgAl 10 O 17 : Eu, and Mn, Y 2 O 3 S: Eu, and these components Is preferably dispersed in a resin such as a silicone resin to form a phosphor layer.
  • a fluorescent component is not limited to the above-exemplified substances, but may be a combination of other ultraviolet light-excited phosphors such as yttrium aluminum garnet (YAG), silicate phosphors, and oxynitride phosphors. .
  • a phosphor layer for converting blue light into yellow light may be provided outside the electrode layer.
  • the phosphor layer is not particularly limited as long as it includes a known fluorescent component capable of converting blue light into yellow light. For example, it may be combined with a phosphor emitting yellow light such as YAG. By doing in this way, since blue light emission which permeate
  • the phosphor layer includes both a fluorescent component that converts blue light into yellow and a fluorescent component that converts ultraviolet light into visible light, thereby converting ultraviolet light into visible light and blue light yellow. It is good also as a structure which performs both conversion to light.
  • gallium nitride free-standing substrate of the present invention can be preferably used for various applications such as various electronic devices, power devices, light receiving elements, solar cell wafers as well as the above-described light emitting elements.
  • Example 1 Production of c-plane oriented alumina sintered body As a raw material, a plate-like alumina powder (manufactured by Kinsei Matech Co., Ltd., grade 0700) was prepared. 7 parts by weight of binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.) and plasticizer (DOP: di (2-ethylhexyl) phthalate, black metal chemicals 3.5 parts by weight), 2 parts by weight of a dispersant (Rheidol SP-O30, manufactured by Kao Corporation), and a dispersion medium (2-ethylhexanol) were mixed.
  • binder polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.
  • plasticizer DOP: di (2-ethylhexyl) phthalate, black metal chemicals 3.5 parts by weight
  • a dispersant Rosidol SP-O
  • the amount of the dispersion medium was adjusted so that the slurry viscosity was 20000 cP.
  • the slurry prepared as described above was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 20 ⁇ m.
  • the obtained tape was cut into a circular shape having a diameter of 50.8 mm (2 inches), 150 sheets were laminated, placed on an Al plate having a thickness of 10 mm, and then vacuum-packed. This vacuum pack was hydrostatically pressed in warm water at 85 ° C. at a pressure of 100 kgf / cm 2 to obtain a disk-shaped molded body.
  • the obtained molded body was placed in a degreasing furnace and degreased at 600 ° C. for 10 hours.
  • the obtained degreased body was fired in a nitrogen atmosphere at 1600 ° C. for 4 hours under a surface pressure of 200 kgf / cm 2 using a graphite mold.
  • the obtained sintered body was fired again at 1700 ° C. for 2 hours in argon at a gas pressure of 1500 kgf / cm 2 by a hot one-pressure method (HIP).
  • HIP hot one-pressure method
  • the sintered body thus obtained was fixed to a ceramic surface plate and ground to # 2000 using a grindstone to flatten the plate surface.
  • the surface of the plate was smoothed by lapping using diamond abrasive grains, and an oriented alumina sintered body having a diameter of 50.8 mm (2 inches) and a thickness of 1 mm was obtained as an oriented alumina substrate.
  • the flatness was improved while gradually reducing the size of the abrasive grains from 3 ⁇ m to 0.5 ⁇ m.
  • the average roughness Ra after processing was 1 nm.
  • the average particle diameter of the plate surface was measured with the following method.
  • the plate surface of the obtained oriented alumina substrate was polished and subjected to thermal etching at 1550 ° C. for 45 minutes, and then an image was taken with a scanning electron microscope.
  • the visual field range was such that a straight line intersecting 10 to 30 particles could be drawn when a straight line was drawn on the diagonal line of the obtained image.
  • the average particle size of the plate surface was 100 ⁇ m.
  • a seed crystal layer was formed on the processed oriented alumina substrate by MOCVD. Specifically, after depositing a low-temperature GaN layer of 40 nm at 530 ° C., a GaN film having a thickness of 3 ⁇ m was laminated at 1050 ° C. to obtain a seed crystal substrate.
  • the alumina crucible was placed on a table that can rotate the crystal growth furnace.
  • the gallium nitride crystal was grown with stirring by rotating the solution while maintaining the temperature for 50 hours after heating and pressurizing to 870 ° C. and 4.0 MPa in a nitrogen atmosphere. After completion of the crystal growth, it was gradually cooled to room temperature over 3 hours, and the growth vessel was taken out of the crystal growth furnace.
  • the melt composition remaining in the crucible was removed using ethanol, and the sample on which the gallium nitride crystal was grown was collected. In the obtained sample, a Ge-doped gallium nitride crystal was grown on the entire surface of a 50.8 mm (2 inch) seed crystal substrate, and the thickness of the crystal was about 0.5 mm. Cracks were not confirmed.
  • the oriented alumina substrate portion of the sample thus obtained was removed by grinding with a grindstone to obtain a Ge-doped gallium nitride simple substance.
  • the plate surface of the Ge-doped gallium nitride crystal is ground with a # 600 and # 2000 grindstone to flatten the plate surface, and then smoothed by lapping using diamond abrasive grains to form a Ge surface having a thickness of about 300 ⁇ m.
  • a doped gallium nitride free-standing substrate was obtained.
  • the flatness was improved while gradually reducing the size of the abrasive grains from 3 ⁇ m to 0.1 ⁇ m.
  • the average roughness Ra after processing of the surface of the gallium nitride free-standing substrate was 0.2 nm.
  • an n-type semiconductor was formed by doping germanium, but different elements may be doped depending on the application and structure, or non-doped.
  • volume resistivity The in-plane volume resistivity of the gallium nitride free-standing substrate was measured using a Hall effect measuring device. As a result, the volume resistivity was 1 ⁇ 10 ⁇ 2 ⁇ ⁇ cm.
  • the average cross-sectional diameter of the GaN single crystal particles on the outermost surface of the gallium nitride free-standing substrate was used.
  • the average cross-sectional diameter was about 100 ⁇ m.
  • the interface can be clearly discriminated by the scanning microscope image of the surface.
  • the above evaluation may be performed after performing a process of making the interface stand out by thermal etching or chemical etching.
  • the visual field range was such that a straight line intersecting with 10 to 30 columnar structures could be drawn when a straight line was drawn on the diagonal line of the obtained image.
  • Two straight lines are arbitrarily drawn on the diagonal line of the obtained image, and the 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 lines It was set as the cross-sectional average diameter of the single crystal particle in the outermost surface of a light emitting functional layer.
  • the average cross-sectional diameter was about 100 ⁇ m.
  • a Ni / Au film was patterned on the p-type layer as a light-transmitting anode electrode to a thickness of 6 nm and 12 nm, respectively. Thereafter, a heat treatment at 500 ° C. was performed for 30 seconds in a nitrogen atmosphere in order to improve the ohmic contact characteristics. Further, by using a photolithography process and a vacuum deposition method, a Ni / Au film serving as an anode electrode pad is formed to a thickness of 5 nm and 60 nm on a partial region of the upper surface of the Ni / Au film serving as a light-transmitting anode electrode, respectively. Patterned. The wafer thus obtained was cut into chips and further mounted on a lead frame to obtain a light emitting device having a vertical structure.
  • Example 2 (1) Production of Mg-doped gallium nitride free-standing substrate A seed crystal substrate was produced by laminating a GaN film having a thickness of 3 ⁇ m on an oriented alumina substrate in the same manner as in (1) to (3) of Example 1. An Mg-doped GaN film was formed on this seed crystal substrate in the same manner as (3b) of Example 1 except that the melt composition was changed to the following composition. ⁇ Metal Ga: 60g ⁇ Metal Na: 60g ⁇ Metal Mg: 0.02g
  • an Mg-doped gallium nitride crystal was grown on the entire surface of a 50.8 mm (2 inch) seed crystal substrate, and the thickness of the crystal was about 0.5 mm. Cracks were not confirmed. Moreover, Mg density
  • the oriented alumina substrate portion of the sample thus obtained was removed by grinding with a grindstone to obtain a simple Mg-doped gallium nitride.
  • the plate surface of this Mg-doped gallium nitride crystal is ground with a # 600 and # 2000 grindstone to flatten the plate surface, and then smoothed by lapping using diamond abrasive grains, and a Mg surface having a thickness of about 150 ⁇ m.
  • a doped gallium nitride free-standing substrate was obtained.
  • the flatness was improved while gradually reducing the size of the abrasive grains from 3 ⁇ m to 0.1 ⁇ m.
  • the average roughness Ra after processing of the surface of the Mg-doped gallium nitride free-standing substrate was 0.2 nm.
  • the cross-sectional average diameter of the Mg-doped gallium nitride free-standing substrate was measured by the same method as in Example 1 (3b), the cross-sectional average diameter was about 100 ⁇ m.
  • a seed crystal layer made of n-ZnO doped with Al having a thickness of 20 nm was formed while being controlled.
  • a gallium nitride free-standing substrate on which a seed crystal layer was formed was suspended and placed in 1 liter in an aqueous solution for growth.
  • a waterproof ceramic heater and a magnetic stirrer were placed in an aqueous solution, placed in an autoclave and subjected to hydrothermal treatment at 270 ° C. for 3 hours to deposit a ZnO layer on the seed crystal layer.
  • the gallium nitride free-standing substrate on which the ZnO layer was deposited was washed with pure water and then annealed at 500 ° C. in the atmosphere to form an n-ZnO layer doped with Al having a thickness of about 3 ⁇ m.
  • the cross-sectional average diameter of the light emitting functional layer was about 100 ⁇ m.
  • a Ni / Au film having a thickness of 50 nm and 100 nm is formed as an anode electrode on the surface opposite to the p-GaN layer and the n-ZnO layer of the gallium nitride free-standing substrate, respectively. Patterned. Thereafter, a heat treatment at 500 ° C. was performed for 30 seconds in a nitrogen atmosphere in order to improve the ohmic contact characteristics. The wafer thus obtained was cut into chips and further mounted on a lead frame to obtain a light emitting device having a vertical structure.
  • Example 3 (1) Fabrication of light-emitting device using Mg-doped gallium nitride free-standing substrate (1a) Formation of active layer by RS-MBE method Mg-doped gallium nitride free-standing substrate by the same method as (2) in Example 2 And p-GaN was added to the substrate as a p-type layer at a volume of 200 nm. Next, using a RS-MBE (radical source molecular beam growth) apparatus, zinc (Zn) and cadmium (Cd), which are metal materials, were irradiated with a Knudsen cell and supplied onto the p-type layer.
  • RS-MBE radio source molecular beam growth
  • Oxygen (O) which is a gas material, was supplied as oxygen radicals using O 2 gas as a raw material in an RF radical generator.
  • the purity of various raw materials was Zn, Cd 7N, and O 2 6N.
  • the substrate was heated to 700 ° C. using a resistance heater, and an active layer having a thickness of 1.5 nm was formed while controlling the flux of various gas sources so as to be a Cd 0.2 Zn 0.8 O layer.
  • a Ni / Au film having a thickness of 5 nm and 100 nm is formed as an anode electrode on the surface opposite to the p-GaN layer and the n-ZnO layer of the gallium nitride free-standing substrate, respectively. Patterned. Thereafter, a heat treatment at 500 ° C. was performed for 30 seconds in a nitrogen atmosphere in order to improve the ohmic contact characteristics. The wafer thus obtained was cut into chips and further mounted on a lead frame to obtain a light emitting device having a vertical structure.

Abstract

Provided is a free-standing gallium nitride substrate which is formed of a plate that is configured from a plurality of gallium nitride-based single crystal grains having a single crystal structure generally in the normal direction. This free-standing gallium nitride substrate can be produced by a method which comprises: a step for preparing an oriented polycrystalline sintered body; a step for forming a seed crystal layer formed of gallium nitride on the oriented polycrystalline sintered body so that the seed crystal layer has a crystal orientation generally following the crystal orientation of the oriented polycrystalline sintered body; a step for forming a layer, which is configured from a gallium nitride-based crystal and has a thickness of 20 μm or more, on the seed crystal layer so that the layer has a crystal orientation generally following the crystal orientation of the seed crystal layer; and a step for obtaining a free-standing gallium nitride substrate by removing the oriented polycrystalline sintered body. The present invention can provide a low-cost free-standing gallium nitride substrate that is suitable for area increase and is useful as an alternative material for a gallium nitride single crystal substrate.

Description

窒化ガリウム自立基板、発光素子及びそれらの製造方法Gallium nitride free-standing substrate, light emitting device, and manufacturing method thereof
　本発明は、窒化ガリウム自立基板、発光素子及びそれらの製造方法に関する。 The present invention relates to a gallium nitride free-standing substrate, a light emitting device, and a method for manufacturing the same.
　単結晶基板を用いた発光ダイオード（ＬＥＤ）等の発光素子として、サファイア（α－アルミナ単結晶）上に各種窒化ガリウム（ＧａＮ）層を形成したものが知られている。例えば、サファイア基板上に、ｎ型ＧａＮ層、ＩｎＧａＮ層からなる量子井戸層とＧａＮ層からなる障壁層とが交互積層された多重量子井戸層（ＭＱＷ）、及びｐ型ＧａＮ層が順に積層形成された構造を有するものが量産化されている。また、このような用途に適した積層基板も提案されている。例えば、特許文献１（特開２０１２－１８４１４４号公報）には、サファイア下地基板と、該基板上に結晶成長せしめて形成された窒化ガリウム結晶層とを含む、窒化ガリウム結晶積層基板が提案されている。 As a light emitting element such as a light emitting diode (LED) using a single crystal substrate, one in which various gallium nitride (GaN) layers are formed on sapphire (α-alumina single crystal) is known. For example, an n-type GaN layer, a multi-quantum well layer (MQW) in which quantum well layers composed of InGaN layers and barrier layers composed of GaN layers are alternately stacked, and a p-type GaN layer are sequentially stacked on a sapphire substrate. Those with different structures have been mass-produced. A multilayer substrate suitable for such applications has also been proposed. For example, Patent Document 1 (Japanese Patent Laid-Open No. 2012-184144) proposes a gallium nitride crystal multilayer substrate including a sapphire base substrate and a gallium nitride crystal layer formed by crystal growth on the substrate. Yes.
　もっとも、サファイア基板上にＧａＮ層を形成する場合、ＧａＮ層は異種基板であるサファイアとの間で格子定数及び熱膨張率が一致しないため転位を生じやすい。また、サファイアは絶縁性材料であるため、その表面に電極を形成することができず、それ故、素子の表裏に電極を備えた縦型構造の発光素子を構成できない。そこで、窒化ガリウム（ＧａＮ）単結晶上に各種ＧａＮ層を形成したＬＥＤが注目されている。ＧａＮ単結晶基板であれば、ＧａＮ層と同種の材質であることから、格子定数及び熱膨張率が整合しやすく、サファイア基板を用いる場合よりも性能向上が期待できる。例えば、特許文献２（特開２０１０－１３２５５６号公報）には、厚みが２００μｍ以上の自立したｎ型窒化ガリウム単結晶基板が開示されている。 However, when a GaN layer is formed on a sapphire substrate, the GaN layer is prone to dislocation because the lattice constant and the coefficient of thermal expansion do not match with sapphire, which is a different substrate. In addition, since sapphire is an insulating material, electrodes cannot be formed on the surface thereof, and therefore a vertical structure light emitting device having electrodes on the front and back sides of the device cannot be formed. Therefore, attention is paid to LEDs in which various GaN layers are formed on a gallium nitride (GaN) single crystal. Since the GaN single crystal substrate is made of the same material as the GaN layer, the lattice constant and the thermal expansion coefficient are easily matched, and an improvement in performance can be expected as compared with the case of using a sapphire substrate. For example, Patent Document 2 (Japanese Patent Application Laid-Open No. 2010-132556) discloses a self-supporting n-type gallium nitride single crystal substrate having a thickness of 200 μm or more.
特開２０１２－１８４１４４号公報JP 2012-184144 A 特開２０１０－１３２５５６号公報JP 2010-132556 A
　しかしながら、単結晶基板は一般的に面積が小さく且つ高価なものである。特に、大面積基板を用いたＬＥＤ製造の低コスト化が求められてきているが、大面積の単結晶基板を量産することは容易なことではなく、その製造コストはさらに高くなる。そこで、窒化ガリウム等の単結晶基板の代替材料となりうる安価な材料が望まれる。 However, single crystal substrates are generally small in area and expensive. In particular, cost reduction of LED manufacturing using a large area substrate has been demanded, but it is not easy to mass-produce a large area single crystal substrate, and the manufacturing cost is further increased. Therefore, an inexpensive material that can be used as a substitute material for a single crystal substrate such as gallium nitride is desired.
　本発明者らは、今般、窒化ガリウム単結晶基板の代替材料として、安価で且つ大面積化にも適した窒化ガリウム自立基板を作製できるとの知見を得た。 The present inventors have now obtained the knowledge that a gallium nitride free-standing substrate that is inexpensive and suitable for an increase in area can be produced as an alternative material for a gallium nitride single crystal substrate.
　したがって、本発明の目的は、安価で且つ大面積化にも適した、窒化ガリウム単結晶基板の代替材料として有用な窒化ガリウム自立基板を提供することにある。 Therefore, an object of the present invention is to provide a gallium nitride free-standing substrate that is inexpensive and suitable for an increase in area and is useful as an alternative material for a gallium nitride single crystal substrate.
　本発明の一態様によれば、略法線方向に単結晶構造を有する複数の窒化ガリウム系単結晶粒子で構成される板からなる、窒化ガリウム自立基板が提供される。 According to one aspect of the present invention, there is provided a gallium nitride free-standing substrate comprising a plate composed of a plurality of gallium nitride-based single crystal particles having a single crystal structure in a substantially normal direction.
　本発明の他の一態様によれば、本発明による窒化ガリウム自立基板と、
　該基板上に形成され、略法線方向に単結晶構造を有する複数の半導体単結晶粒子で構成される層を一以上有する発光機能層と、
を備えた、発光素子が提供される。 According to another aspect of the invention, a gallium nitride free-standing substrate according to the invention,
A light emitting functional layer formed on the substrate and having at least one layer composed of a plurality of semiconductor single crystal particles having a single crystal structure in a substantially normal direction;
A light-emitting element is provided.
　本発明のさらに他の一態様によれば、配向多結晶焼結体を用意する工程と、
　前記配向多結晶焼結体上に、窒化ガリウムからなる種結晶層を、前記配向多結晶焼結体の結晶方位に概ね倣った結晶方位を有するように形成する工程と、
　前記種結晶層上に、厚さ２０μｍ以上の窒化ガリウム系結晶から構成される層を、前記種結晶層の結晶方位に概ね倣った結晶方位を有するように形成する工程と、
　前記配向多結晶焼結体を除去して、窒化ガリウム自立基板を得る工程と、
を含む、窒化ガリウム自立基板の製造方法が提供される。 According to still another aspect of the present invention, a step of preparing an oriented polycrystalline sintered body;
Forming a seed crystal layer made of gallium nitride on the oriented polycrystalline sintered body so as to have a crystal orientation substantially following the crystal orientation of the oriented polycrystalline sintered body;
Forming a layer composed of a gallium nitride-based crystal having a thickness of 20 μm or more on the seed crystal layer so as to have a crystal orientation substantially following the crystal orientation of the seed crystal layer;
Removing the oriented polycrystalline sintered body to obtain a gallium nitride free-standing substrate;
A method for manufacturing a gallium nitride free-standing substrate is provided.
　本発明のさらに別の一態様によれば、本発明による窒化ガリウム自立基板を用意する、又は本発明の方法により前記窒化ガリウム自立基板を用意する工程と、
　前記窒化ガリウム自立基板に、前記窒化ガリウム基板の結晶方位に概ね倣った結晶方位を有するように、略法線方向に単結晶構造を有する複数の半導体単結晶粒子で構成される層を一つ以上形成して発光機能層を設ける工程と、
を含む、発光素子の製造方法が提供される。 According to yet another aspect of the present invention, providing a gallium nitride free-standing substrate according to the present invention, or preparing the gallium nitride free-standing substrate by the method of the present invention;
The gallium nitride free-standing substrate includes at least one layer composed of a plurality of semiconductor single crystal particles having a single crystal structure in a substantially normal direction so as to have a crystal orientation that substantially follows the crystal orientation of the gallium nitride substrate. Forming and providing a light emitting functional layer;
The manufacturing method of the light emitting element containing this is provided.
本発明の窒化ガリウム自立基板を用いて作製された縦型発光素子の一例を示す模式断面図である。It is a schematic cross-sectional view showing an example of a vertical light-emitting element manufactured using the gallium nitride free-standing substrate of the present invention.
　窒化ガリウム自立基板
　本発明の窒化ガリウム基板は自立基板の形態を有しうる。本発明において「自立基板」とは、取り扱う際に自重で変形又は破損せず、固形物として取り扱うことのできる基板を意味する。本発明の窒化ガリウム自立基板は発光素子等の各種半導体デバイスの基板として使用可能であるが、それ以外にも、電極（ｐ型電極又はｎ型電極でありうる）、ｐ型層、ｎ型層等の基材以外の部材又は層として使用可能なものである。なお、以下の説明においては、主たる用途の一つである発光素子を例に本発明の利点を記述することがあるが、同様ないし類似の利点は技術的整合性を損なわない範囲内で他の半導体デバイスにも当てはまる。 Gallium Nitride Freestanding Substrate The gallium nitride substrate of the present invention can have the form of a freestanding substrate. In the present invention, the “self-supporting substrate” means a substrate that can be handled as a solid material without being deformed or damaged by its own weight when handled. The gallium nitride free-standing substrate of the present invention can be used as a substrate for various semiconductor devices such as light-emitting elements, but in addition to this, an electrode (which may be a p-type electrode or an n-type electrode), a p-type layer, an n-type layer It can be used as a member or layer other than the substrate such as. In the following description, the advantages of the present invention may be described by taking a light emitting element which is one of the main applications as an example. However, similar or similar advantages are not limited to the technical consistency. The same applies to semiconductor devices.
　本発明の窒化ガリウム自立基板は、略法線方向に単結晶構造を有する複数の窒化ガリウム系単結晶粒子で構成される板からなる。すなわち、窒化ガリウム自立基板は、水平面方向に二次元的に連結されてなる複数の半導体単結晶粒子で構成されており、それ故、略法線方向には単結晶構造を有することになる。したがって、窒化ガリウム自立基板は、全体としては単結晶ではないものの、局所的なドメイン単位では単結晶構造を有するため、発光機能等のデバイス特性を確保するのに十分な高い結晶性を有することができる。そうでありながら、本発明の窒化ガリウム自立基板は単結晶基板ではない。前述のとおり、単結晶基板は一般的に面積が小さく且つ高価なものである。特に、近年、大面積基板を用いたＬＥＤ製造の低コスト化が求められてきているが、大面積の単結晶基板を量産することは容易なことではなく、その製造コストはさらに高くなる。これらの欠点が本発明の窒化ガリウム自立基板によれば解消される。すなわち、本発明によれば、安価で且つ大面積化にも適した、窒化ガリウム単結晶基板の代替材料として有用な窒化ガリウム自立基板を提供することができる。また、ｐ型ないしｎ型ドーパントの導入により導電性を持たせた窒化ガリウムを基板とすることで、縦型構造の発光素子を実現することができ、それにより輝度を高めることができる。その上、面発光照明等に用いられる大面積な面発光素子も低コストで実現可能となる。 The gallium nitride free-standing substrate of the present invention comprises a plate composed of a plurality of gallium nitride-based single crystal particles having a single crystal structure in a substantially normal direction. That is, the gallium nitride free-standing substrate is composed of a plurality of semiconductor single crystal particles that are two-dimensionally connected in the horizontal plane direction, and thus has a single crystal structure in a substantially normal direction. Therefore, although the gallium nitride free-standing substrate is not a single crystal as a whole, the gallium nitride free-standing substrate has a single crystal structure in a local domain unit, and therefore has a sufficiently high crystallinity to ensure device characteristics such as a light emitting function. it can. Nevertheless, the gallium nitride free-standing substrate of the present invention is not a single crystal substrate. As described above, the single crystal substrate generally has a small area and is expensive. In particular, in recent years, there has been a demand for cost reduction of LED manufacturing using a large area substrate, but it is not easy to mass-produce a large area single crystal substrate, and the manufacturing cost is further increased. These drawbacks are eliminated by the gallium nitride free-standing substrate of the present invention. That is, according to the present invention, it is possible to provide a gallium nitride free-standing substrate useful as an alternative material for a gallium nitride single crystal substrate that is inexpensive and suitable for increasing the area. In addition, by using gallium nitride imparted with conductivity by introducing a p-type or n-type dopant as a substrate, a light-emitting element having a vertical structure can be realized, whereby luminance can be increased. In addition, a large-area surface light-emitting element used for surface-emitting illumination or the like can be realized at low cost.
　好ましくは、自立基板を構成する複数の窒化ガリウム系単結晶粒子は、略法線方向に概ね揃った結晶方位を有する。「略法線方向に概ね揃った結晶方位」とは、必ずしも法線方向に完全に揃った結晶方位とは限らず、自立基板を用いた発光素子等のデバイスが所望のデバイス特性を確保できるかぎり、法線ないしそれに類する方向にある程度揃った結晶方位であってよいことを意味する。製法由来の表現をすれば、窒化ガリウム系単結晶粒子は、窒化ガリウム自立基板の製造の際時に下地基材として使用した配向多結晶焼結体の結晶方位に概ね倣って成長した構造を有するともいえる。「配向多結晶焼結体の結晶方位に概ね倣って成長した構造」とは、配向多結晶焼結体の結晶方位の影響を受けた結晶成長によりもたらされた構造を意味し、必ずしも配向多結晶焼結体の結晶方位に完全に倣って成長した構造であるとは限らず、自立基板を用いた発光素子等のデバイスが所望のデバイス特性を確保できるかぎり、配向多結晶焼結体の結晶方位にある程度倣って成長した構造であってよい。すなわち、この構造は配向多結晶焼結体と異なる結晶方位に成長する構造も含む。その意味で、「結晶方位に概ね倣って成長した構造」との表現は「結晶方位に概ね由来して成長した構造」と言い換えることもでき、この言い換え及び上記意味は本明細書中の同種の表現に同様に当てはまる。したがって、そのような結晶成長はエピタキシャル成長によるものが好ましいが、これに限定されず、それに類する様々な結晶成長の形態であってもよい。いずれにしても、このように成長することで、窒化ガリウム自立基板は略法線方向に関しては結晶方位が概ね揃った構造とすることができる。 Preferably, the plurality of gallium nitride single crystal particles constituting the self-supporting substrate have crystal orientations substantially aligned in a substantially normal direction. "Crystal orientation that is generally aligned in the normal direction" is not necessarily a crystal orientation that is perfectly aligned in the normal direction, as long as a device such as a light-emitting element using a self-supporting substrate can ensure desired device characteristics. This means that the crystal orientation may be aligned to some extent in the normal or similar direction. In terms of the expression derived from the manufacturing method, the gallium nitride-based single crystal particles have a structure grown substantially following the crystal orientation of the oriented polycrystalline sintered body used as the base material during the production of the gallium nitride free-standing substrate. It can also be said. The “structure grown substantially following the crystal orientation of the oriented polycrystalline sintered body” means a structure brought about by crystal growth affected by the crystal orientation of the oriented polycrystalline sintered body, and is not necessarily oriented. The crystal of the oriented polycrystalline sintered body is not necessarily a structure that has grown completely following the crystal orientation of the crystalline sintered body, as long as a device such as a light-emitting element using a self-supporting substrate can ensure the desired device characteristics. It may be a structure grown to some extent along the direction. That is, this structure includes a structure that grows in a different crystal orientation from the oriented polycrystalline sintered body. In that sense, the expression “a structure grown substantially following the crystal orientation” can also be rephrased as “a structure grown substantially derived from the crystal orientation”. This paraphrase and the above meaning are similar to those in this specification. The same applies to expression. Therefore, although such crystal growth is preferably by epitaxial growth, it is not limited to this, and various forms of crystal growth similar thereto may be used. In any case, by growing in this way, the gallium nitride free-standing substrate can have a structure in which crystal orientations are substantially aligned with respect to a substantially normal direction.
　したがって、窒化ガリウム自立基板は、法線方向に見た場合に単結晶と観察され、水平面方向の切断面で見た場合に粒界が観察される柱状構造の窒化ガリウム系単結晶粒子の集合体であると捉えることも可能である。ここで、「柱状構造」とは、典型的な縦長の柱形状のみを意味するのではなく、横長の形状、台形の形状、及び台形を逆さにしたような形状等、種々の形状を包含する意味として定義される。もっとも、上述のとおり、窒化ガリウム自立基板は法線ないしそれに類する方向にある程度揃った結晶方位を有する構造であればよく、必ずしも厳密な意味で柱状構造である必要はない。柱状構造となる原因は、前述のとおり、窒化ガリウム自立基板の製造に用いられる配向多結晶焼結体の結晶方位の影響を受けて窒化ガリウム単結晶粒子が成長するためと考えられる。このため、柱状構造ともいえる窒化ガリウム単結晶粒子の断面の平均粒径（以下、断面平均径という）は成膜条件だけでなく、配向多結晶焼結体の板面の平均粒径にも依存するものと考えられる。窒化ガリウム自立基板を発光素子の発光機能層の一部として用いる場合、粒界があることにより断面方向の光の透過率が悪く、光が散乱ないし反射する。このため、法線方向に光を取り出す構造の発光素子の場合、粒界からの散乱光により輝度が高まる効果も期待される。 Therefore, a gallium nitride free-standing substrate is an aggregate of columnar-structured gallium nitride single crystal particles that are observed as single crystals when viewed in the normal direction and grain boundaries are observed when viewed in the cut plane in the horizontal plane direction. It is also possible to grasp that. Here, the “columnar structure” does not mean only a typical vertically long column shape, but includes various shapes such as a horizontally long shape, a trapezoidal shape, and a shape in which the trapezoid is inverted. Defined as meaning. However, as described above, the gallium nitride free-standing substrate may be a structure having a crystal orientation that is aligned to some extent in the normal or similar direction, and does not necessarily have a columnar structure in a strict sense. The cause of the columnar structure is considered to be that the gallium nitride single crystal particles grow under the influence of the crystal orientation of the oriented polycrystalline sintered body used in the manufacture of the gallium nitride free-standing substrate as described above. For this reason, the average particle diameter of the cross section of gallium nitride single crystal particles, which can be said to be a columnar structure (hereinafter referred to as the average diameter of the cross section), depends not only on the film forming conditions but also on the average particle diameter of the plate surface of the oriented polycrystalline sintered body It is thought to do. When the gallium nitride free-standing substrate is used as a part of the light emitting functional layer of the light emitting element, the light transmittance in the cross-sectional direction is poor due to the grain boundary, and the light is scattered or reflected. For this reason, in the case of a light-emitting element having a structure in which light is extracted in the normal direction, an effect of increasing luminance due to scattered light from the grain boundary is also expected.
　もっとも、窒化ガリウム自立基板を構成する柱状構造同士の界面は結晶性が低下するため、発光素子の発光機能層として用いる場合、発光効率が低下し、発光波長が変動し、発光波長がブロードになる可能性がある。このため、柱状構造の断面平均径は大きいほうが良い。好ましくは、窒化ガリウム自立基板の最表面における半導体単結晶粒子の断面平均径は０．３μｍ以上であり、より好ましくは３μｍ以上である。この断面平均径の上限は特に限定されないが、１０００μｍ以下が現実的である。また、このような断面平均径の半導体単結晶粒子を作製するには、窒化ガリウム自立基板の製造に用いられる、配向多結晶焼結体を構成する粒子の板面における焼結粒径を０．３μｍ～１０００μｍとするのが望ましく、より望ましくは３μｍ～１０００μｍである。 However, since the crystallinity of the interface between the columnar structures constituting the gallium nitride free-standing substrate is lowered, when used as a light-emitting functional layer of a light-emitting element, the light emission efficiency is lowered, the light emission wavelength varies, and the light emission wavelength becomes broad. there is a possibility. For this reason, it is better that the cross-sectional average diameter of the columnar structure is larger. Preferably, the cross-sectional average diameter of the semiconductor single crystal particles on the outermost surface of the gallium nitride free-standing substrate is 0.3 μm or more, more preferably 3 μm or more. Although the upper limit of this cross-sectional average diameter is not specifically limited, 1000 micrometers or less are realistic. Moreover, in order to produce the semiconductor single crystal particles having such an average cross-sectional diameter, the sintered particle size on the plate surface of the particles constituting the oriented polycrystalline sintered body used for the production of the gallium nitride free-standing substrate is set to 0. The thickness is desirably 3 μm to 1000 μm, and more desirably 3 μm to 1000 μm.
　窒化ガリウム自立基板を構成する窒化ガリウム系単結晶粒子は、ドーパントを含まないものであってもよい。ここで、「ドーパントを含まない」とは何らかの機能ないし特性の付与を意図して添加された元素を含まないことを意味し、不可避不純物の含有が許容されるのはいうまでもない。あるいは、窒化ガリウム自立基板を構成する窒化ガリウム系単結晶粒子は、ｎ型ドーパント又はｐ型ドーパントでドープされていてもよく、この場合、窒化ガリウム自立基板を、ｐ型電極、ｎ型電極、ｐ型層、ｎ型層等の基材以外の部材又は層として使用することができる。ｐ型ドーパントの好ましい例としては、ベリリウム（Ｂｅ）、マグネシウム（Ｍｇ）、カルシウム（Ｃａ）、ストロンチウム（Ｓｒ）、亜鉛（Ｚｎ）及びカドミウム（Ｃｄ）からなる群から選択される１種以上が挙げられる。ｎ型ドーパントの好ましい例としては、シリコン（Ｓｉ）、ゲルマニウム（Ｇｅ）、スズ（Ｓｎ）及び酸素（Ｏ）からなる群から選択される１種以上が挙げられる。 The gallium nitride single crystal particles constituting the gallium nitride free-standing substrate may not contain a dopant. Here, “does not contain dopant” means that an element added for the purpose of imparting some function or characteristic is not contained, and it is needless to say that inclusion of inevitable impurities is allowed. Alternatively, the gallium nitride-based single crystal particles constituting the gallium nitride free-standing substrate may be doped with an n-type dopant or a p-type dopant. In this case, the gallium nitride free-standing substrate is formed by using a p-type electrode, an n-type electrode, p It can be used as a member or layer other than a base material such as a mold layer and an n-type layer. Preferable examples of the p-type dopant include one or more selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), and cadmium (Cd). It is done. Preferable examples of the n-type dopant include one or more selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), and oxygen (O).
　窒化ガリウム自立基板を構成する窒化ガリウム系単結晶粒子は、バンドギャップの制御のため混晶化されていてもよい。好ましくは、窒化ガリウム単結晶粒子は、ＡｌＮ及びＩｎＮからなる群から選択される１種以上の結晶と混晶化された窒化ガリウムからなるものであってもよく、ｐ型窒化ガリウム及び／又はｎ型窒化ガリウム単結晶粒子はこの混晶化された窒化ガリウムにｐ型ドーパント又はｎ型ドーパントがドープされていてもよい。例えば、窒化ガリウムとＡｌＮの混晶であるＡｌｘＧａ１－ｘＮにＭｇをドーピングすることでｐ型基板、ＡｌｘＧａ１－ｘＮにＳｉをドーピングすることでとしてｎ型基板として使用することができる。自立基板を発光素子の発光機能層として用いる場合、窒化ガリウムをＡｌＮと混晶化することでバンドギャップが広がり、発光波長を高エネルギー側にシフトさせることができる。また、窒化ガリウムをＩｎＮとの混晶としてもよく、これによりバンドギャップが狭まり、発光波長を低エネルギー側にシフトさせることができる。 The gallium nitride single crystal particles constituting the gallium nitride free-standing substrate may be mixed crystal for controlling the band gap. Preferably, the gallium nitride single crystal particles may be composed of gallium nitride mixed with at least one crystal selected from the group consisting of AlN and InN, and may be p-type gallium nitride and / or n. In the type gallium nitride single crystal particles, the mixed gallium nitride may be doped with a p-type dopant or an n-type dopant. For example, Al x Ga 1-x N, which is a mixed crystal of gallium nitride and AlN, is used as a p-type substrate by doping Mg, and Al x Ga 1-x N is used as an n-type substrate by doping Si. be able to. When a self-supporting substrate is used as a light emitting functional layer of a light emitting element, the band gap is widened by mixing gallium nitride with AlN, and the emission wavelength can be shifted to a higher energy side. In addition, gallium nitride may be mixed with InN, whereby the band gap is narrowed and the emission wavelength can be shifted to a lower energy side.
　窒化ガリウム自立基板は直径５０．８ｍｍ（２インチ）以上の大きさを有するのが好ましく、より好ましくは直径１００ｍｍ（４インチ）以上であり、さらに好ましくは直径２００ｍｍ（８インチ）以上である。窒化ガリウム自立基板は大きければ大きいほど作製可能な素子の個数が増えるため、製造コストの観点で好ましく、面発光素子用との観点でも素子面積の自由度が増え面発光照明等への用途が広がる点で好ましく、その面積ないし大きさに上限は規定されるべきではない。なお、窒化ガリウム自立基板は上面視で円形状あるいは実質的に円形状であることが好ましいが、これに限定されない。円形状あるいは実質的に円形状ではない場合、面積として、２０２６ｍｍ２以上であることが好ましく、より好ましくは７８５０ｍｍ２以上であり、さらに好ましくは３１４００ｍｍ２以上である。もっとも、大面積を要しない用途については、上記範囲よりも小さい面積、例えば直径５０．８ｍｍ（２インチ）以下、面積換算で２０２６ｍｍ２以下としてもよい。窒化ガリウム自立基板の厚さは基板に自立性を付与できる必要があり、２０μｍ以上が好ましく、より好ましくは１００μｍ以上であり、さらに好ましくは３００μｍ以上である。窒化ガリウム自立基板の厚さに上限は規定されるべきではないが、製造コストの観点では３０００μｍ以下が現実的である。 The gallium nitride free-standing substrate preferably has a diameter of 50.8 mm (2 inches) or more, more preferably has a diameter of 100 mm (4 inches) or more, and more preferably has a diameter of 200 mm (8 inches) or more. As the gallium nitride free-standing substrate is larger, the number of devices that can be manufactured increases, which is preferable from the viewpoint of manufacturing cost. From the viewpoint of a surface light emitting device, the degree of freedom of the device area is increased and the use for surface light emitting lighting is expanded. The upper limit should not be prescribed | regulated at the point and the area thru | or magnitude | size. The gallium nitride free-standing substrate is preferably circular or substantially circular when viewed from above, but is not limited thereto. If not a circular or substantially circular shape, as the area is preferably at 2026Mm 2 or more, more preferably 7850mm 2 or more, further preferably 31400Mm 2 or more. However, for applications that do not require a large area, the area may be smaller than the above range, for example, a diameter of 50.8 mm (2 inches) or less, and 2026 mm 2 or less in terms of area. The thickness of the gallium nitride free-standing substrate needs to be capable of imparting self-supporting properties to the substrate, and is preferably 20 μm or more, more preferably 100 μm or more, and even more preferably 300 μm or more. An upper limit should not be defined for the thickness of the gallium nitride free-standing substrate, but 3000 μm or less is realistic from the viewpoint of manufacturing cost.
　製造方法
　本発明の窒化ガリウム自立基板は、（１）配向多結晶焼結体を用意し、（２）配向多結晶焼結体上に、窒化ガリウムからなる種結晶層を、配向多結晶焼結体の結晶方位に概ね倣った結晶方位を有するように形成し、（３）種結晶層上に、厚さ２０μｍ以上の窒化ガリウム系結晶から構成される層を、種結晶層の結晶方位に概ね倣った結晶方位を有するように形成し、（４）配向多結晶焼結体を除去して、窒化ガリウム自立基板を得ることにより製造することができる。 Manufacturing Method The gallium nitride free-standing substrate of the present invention is prepared by (1) preparing an oriented polycrystalline sintered body, and (2) arranging a seed crystal layer made of gallium nitride on the oriented polycrystalline sintered body. (3) a layer composed of a gallium nitride-based crystal having a thickness of 20 μm or more on the seed crystal layer is approximately aligned with the crystal orientation of the seed crystal layer. The gallium nitride free-standing substrate can be manufactured by removing the oriented polycrystalline sintered body by forming it so as to have a crystal orientation that has been copied.
（１）配向多結晶焼結体
　窒化ガリウム自立基板を作製するための下地基板として、配向多結晶焼結体を用意する。配向多結晶焼結体の組成は特に限定されないが、配向多結晶アルミナ焼結体、配向多結晶酸化亜鉛焼結体、配向多結晶窒化アルミニウム焼結体から選ばれる１種であるのが好ましい。配向多結晶焼結体は、商業的に入手可能な板状粉末を用いて成形及び焼成を経て効率的に製造できるため、低コストで製造できるだけでなく、成形しやすいが故に大面積化にも適する。そして、本発明者らの知見によれば、配向多結晶焼結体を下地基板として用い、その上に複数の半導体単結晶粒子を成長させることで、大面積の発光素子を低コストで製造するのに適した窒化ガリウム自立基板を製造できる。その結果、窒化ガリウム自立基板は、大面積の発光素子を低コストで製造するのに極めて適するものとなる。 (1) Oriented polycrystalline sintered body An oriented polycrystalline sintered body is prepared as a base substrate for producing a gallium nitride free-standing substrate. The composition of the oriented polycrystalline sintered body is not particularly limited, but is preferably one selected from an oriented polycrystalline alumina sintered body, an oriented polycrystalline zinc oxide sintered body, and an oriented polycrystalline aluminum nitride sintered body. An oriented polycrystalline sintered body can be efficiently manufactured through molding and firing using commercially available plate-like powder, so it can be manufactured at a low cost, but also because it is easy to mold, it can also increase the area. Suitable. According to the knowledge of the present inventors, a large-area light-emitting element is manufactured at low cost by using an oriented polycrystalline sintered body as a base substrate and growing a plurality of semiconductor single crystal particles thereon. Can be produced. As a result, the gallium nitride free-standing substrate is extremely suitable for manufacturing a large-area light emitting device at low cost.
　配向多結晶焼結体は、多数の単結晶粒子を含んで構成される焼結体からなり、多数の単結晶粒子が一定の方向にある程度又は高度に配向したものである。このように配向された多結晶焼結体を用いることで略法線方向に概ね揃った結晶方位を有する窒化ガリウム自立基板を作製可能であり、窒化ガリウム自立基板上に窒化ガリウム系材料をエピタキシャル成長又はこれに類する結晶成長により形成した場合、略法線方向に結晶方位が概ね揃った状態が実現される。このため、そのような配向性の高い窒化ガリウム自立基板を発光素子用基板として用いれば、発光機能層を同様に略法線方向に結晶方位が概ね揃った状態で形成することができ、単結晶基板を用いた場合と同等の高い発光効率を実現できる。あるいは、この配向性の高い窒化ガリウム自立基板を発光素子の発光機能層として用いた場合であっても、単結晶基板を用いた場合と同等の高い発光効率を実現できる。いずれにしても、このような配向性が高い窒化ガリウム自立基板を作製するには配向多結晶焼結体を下地基板として用いる必要がある。配向多結晶焼結体は、透光性を有しているほうが好ましいが、この限りではない。透光性を有する場合、配向多結晶板を除去する際に、レーザーリフトオフ等の手法を用いることができる。配向多結晶焼結体を得る製法としては、大気炉、窒素雰囲気炉、水素雰囲気炉等を用いた通常の常圧焼結法に加え、熱間等方圧加圧法（ＨＩＰ）、ホットプレス法（ＨＰ）、放電プラズマ焼結（ＳＰＳ）等の加圧焼結法、及びこれらを組み合わせた方法を用いることができる。 The oriented polycrystalline sintered body is composed of a sintered body including a large number of single crystal particles, and a large number of single crystal particles are oriented to some extent or highly in a certain direction. By using a polycrystalline sintered body oriented in this way, a gallium nitride free-standing substrate having a crystal orientation substantially aligned in a substantially normal direction can be produced, and a gallium nitride-based material is epitaxially grown or grown on the gallium nitride free-standing substrate. When formed by crystal growth similar to this, a state in which crystal orientations are substantially aligned in a substantially normal direction is realized. For this reason, when such a highly oriented gallium nitride free-standing substrate is used as a substrate for a light emitting device, a light emitting functional layer can be formed in a state where crystal orientations are substantially aligned in a substantially normal direction. High luminous efficiency equivalent to that when a substrate is used can be realized. Alternatively, even when this highly oriented gallium nitride free-standing substrate is used as a light-emitting functional layer of a light-emitting element, high light emission efficiency equivalent to that when a single crystal substrate is used can be realized. In any case, in order to produce such a highly oriented gallium nitride free-standing substrate, it is necessary to use an oriented polycrystalline sintered body as a base substrate. The oriented polycrystalline sintered body preferably has translucency, but is not limited thereto. In the case of translucency, a technique such as laser lift-off can be used when removing the oriented polycrystalline plate. As a manufacturing method for obtaining an oriented polycrystalline sintered body, in addition to a normal atmospheric pressure sintering method using an air furnace, a nitrogen atmosphere furnace, a hydrogen atmosphere furnace, etc., a hot isostatic pressing method (HIP), a hot press method (HP), pressure sintering methods such as spark plasma sintering (SPS), and a combination thereof can be used.
　配向多結晶焼結体は直径５０．８ｍｍ（２インチ）以上の大きさを有するのが好ましく、より好ましくは直径１００ｍｍ（４インチ）以上であり、さらに好ましくは直径２００ｍｍ（８インチ）以上である。配向多結晶焼結体は大きければ大きいほど作製可能な窒化ガリウム自立基板の面積が増え、それにより作製可能な発光素子の個数が増えるため、製造コストの観点で好ましい。また、面発光素子用との観点でも素子面積の自由度が増え面発光照明等への用途が広がる点で好ましく、その面積ないし大きさに上限は規定されるべきではない。なお、窒化ガリウム自立基板は上面視で円形状あるいは実質的に円形状であることが好ましいが、これに限定されない。円形状あるいは実質的に円形状ではない場合、面積として、２０２６ｍｍ２以上であることが好ましく、より好ましくは７８５０ｍｍ２以上であり、さらに好ましくは３１４００ｍｍ２以上である。もっとも、大面積を要しない用途については、上記範囲よりも小さい面積、例えば例えば直径５０．８ｍｍ（２インチ）以下、面積換算で２０２６ｍｍ２以下としてもよい。配向多結晶焼結体の厚さは自立する限り特に限定はないが、厚すぎると製造コストの観点では好ましくない。従って、２０μｍ以上が好ましく、より好ましくは１００μｍ以上であり、さらに好ましくは１００～１０００μｍである。 The oriented polycrystalline sintered body preferably has a diameter of 50.8 mm (2 inches) or more, more preferably has a diameter of 100 mm (4 inches) or more, and more preferably has a diameter of 200 mm (8 inches) or more. . The larger the oriented polycrystalline sintered body is, the larger the area of the gallium nitride free-standing substrate that can be produced, which increases the number of light-emitting elements that can be produced, which is preferable from the viewpoint of production cost. Also, from the viewpoint of the surface light emitting device, it is preferable from the viewpoint that the degree of freedom of the device area is increased and the application to surface light emitting lighting is widened, and the upper limit should not be defined for the area or size. The gallium nitride free-standing substrate is preferably circular or substantially circular when viewed from above, but is not limited thereto. If not a circular or substantially circular shape, as the area is preferably at 2026Mm 2 or more, more preferably 7850mm 2 or more, further preferably 31400Mm 2 or more. However, for applications that do not require a large area, the area may be smaller than the above range, for example, a diameter of 50.8 mm (2 inches) or less, and 2026 mm 2 or less in terms of area. The thickness of the oriented polycrystalline sintered body is not particularly limited as long as it is self-supporting, but if it is too thick, it is not preferable from the viewpoint of production cost. Accordingly, the thickness is preferably 20 μm or more, more preferably 100 μm or more, and further preferably 100 to 1000 μm.
　配向多結晶焼結体を構成する粒子の板面における平均粒径は、０．３～１０００μｍであるのが好ましく、より好ましくは３～１０００μｍである。配向多結晶焼結体全体の平均粒径は板面の平均粒径と相関があり、これらの範囲内であると焼結体の機械強度の点で優れ、ハンドリングが容易である。また、配向多結晶焼結体を用いて作製した窒化ガリウム自立基板の上部及び／又は内部に発光機能層を形成して発光素子を作製した場合、発光機能層の発光効率の点でも優れる。なお、本発明における焼結体粒子の板面における平均粒径は以下の方法により測定されるものである。すなわち、板状焼結体の板面を研磨し、走査電子顕微鏡にて画像を撮影する。視野範囲は、得られる画像の対角線に直線を引いた場合に、いずれの直線も１０個から３０個の粒子と交わるような直線が引けるような視野範囲とする。得られた画像の対角線に２本の直線を引いて、直線が交わる全ての粒子に対し、個々の粒子の内側の線分の長さを平均したものに１．５を乗じた値を板面の平均粒径とする。なお、板面の走査顕微鏡像で明瞭に焼結体粒子の界面を判別できない場合は、サーマルエッチング（例えば１５５０℃で４５分間）やケミカルエッチングによって界面を際立たせる処理を施した後に上記の評価を行ってもよい。 The average particle diameter on the plate surface of the particles constituting the oriented polycrystalline sintered body is preferably 0.3 to 1000 μm, more preferably 3 to 1000 μm. The average grain size of the entire oriented polycrystalline sintered body has a correlation with the average grain size of the plate surface, and within these ranges, the sintered body is excellent in mechanical strength and easy to handle. In addition, when a light-emitting element is manufactured by forming a light-emitting functional layer on and / or inside a gallium nitride free-standing substrate manufactured using an oriented polycrystalline sintered body, the light-emitting functional layer is also excellent in light emission efficiency. In addition, the average particle diameter in the plate | board surface of the sintered compact particle | grains in this invention is measured with the following method. That is, the plate surface of the plate-like sintered body is polished and an image is taken with a scanning electron microscope. The visual field range is a visual field range in which a straight line intersecting 10 to 30 particles can be drawn when a straight line is drawn on the diagonal line of the obtained image. Two straight lines are drawn on the diagonal line of the obtained image, and the value obtained by multiplying the average of the length of the inner line segment of each particle by 1.5 for all the particles that intersect the line The average particle size of In addition, when the interface of the sintered body particles cannot be clearly discriminated from the scanning microscope image of the plate surface, the above evaluation is performed after performing the process of making the interface stand out by thermal etching (for example, 1550 ° C. for 45 minutes) or chemical etching. You may go.
　特に好ましい配向多結晶焼結体として、配向多結晶アルミナ焼結体が挙げられる。アルミナは酸化アルミニウム（Ａｌ２Ｏ３）であり、典型的には単結晶サファイアと同じコランダム型構造を有するα－アルミナであり、配向多結晶アルミナ焼結体は無数のアルミナ結晶粒子が配向された状態で焼結により互いに結合されてなる固体である。アルミナ結晶粒子はアルミナを含んで構成される粒子であり、他の元素として、ドーパント及び不可避不純物を含んでいてもよいし、アルミナ及び不可避不純物からなるものであってもよい。配向多結晶アルミナ焼結体は焼結助剤としての添加物を粒界相として含んでいてもよい。また、配向多結晶アルミナ焼結体も、アルミナ結晶粒子以外に他の相又は上述したような他の元素を含んでいてもよいが、好ましくはアルミナ結晶粒子及び不可避不純物からなる。また、配向多結晶アルミナ焼結体の配向面は特に限定がなく、ｃ面、ａ面、ｒ面又はｍ面等であってもよい。 A particularly preferred oriented polycrystalline sintered body is an oriented polycrystalline alumina sintered body. Alumina is aluminum oxide (Al 2 O 3 ), which is typically α-alumina having the same corundum type structure as single crystal sapphire, and the oriented polycrystalline alumina sintered body has innumerable alumina crystal particles oriented. Solids that are bonded together by sintering. The alumina crystal particles are particles composed of alumina, and may include a dopant and inevitable impurities as other elements, or may be composed of alumina and inevitable impurities. The oriented polycrystalline alumina sintered body may contain an additive as a sintering aid as a grain boundary phase. The oriented polycrystalline alumina sintered body may also contain other phases or other elements as described above in addition to the alumina crystal particles, but preferably comprises alumina crystal particles and inevitable impurities. The orientation plane of the oriented polycrystalline alumina sintered body is not particularly limited, and may be a c-plane, a-plane, r-plane, m-plane, or the like.
　配向多結晶アルミナ焼結体の配向結晶方位は特に限定されるものではなく、ｃ面、ａ面、ｒ面又はｍ面等であってもよく、窒化ガリウム自立基板との格子定数マッチングの観点でｃ面に配向しているのが好ましい。配向度については、例えば、板面における配向度が５０％以上であるのが好ましく、より好ましくは６５％以上、さらに好ましくは７５％以上であり、特に好ましくは８５％であり、特により好ましくは９０％以上であり、最も好ましくは９５％以上である。この配向度は、ＸＲＤ装置（例えば、株式会社リガク製、ＲＩＮＴ－ＴＴＲ　ＩＩＩ）を用い、板状アルミナの板面に対してＸ線を照射したときのＸＲＤプロファイルを測定し、以下の式により算出することにより得られるものである。 The oriented crystal orientation of the oriented polycrystalline alumina sintered body is not particularly limited and may be a c-plane, a-plane, r-plane, m-plane, etc., from the viewpoint of lattice constant matching with a gallium nitride free-standing substrate. It is preferably oriented in the c-plane. Regarding the degree of orientation, for example, the degree of orientation on the plate surface is preferably 50% or more, more preferably 65% or more, still more preferably 75% or more, particularly preferably 85%, and particularly preferably. 90% or more, and most preferably 95% or more. This degree of orientation is calculated by the following formula by measuring the XRD profile when X-rays are irradiated to the plate surface of plate-like alumina using an XRD apparatus (for example, RINT-TTR III, manufactured by Rigaku Corporation). It is obtained by doing.
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　なお、窒化ガリウム自立基板の構成粒子の結晶性は高くなる傾向があり、転位等の欠陥の密度を低く抑えることができる。このため、発光デバイス等のある種の用途においては、窒化ガリウム自立基板を窒化ガリウム単結晶基板に比べて好ましく用いることすら可能になるものと考えられる。例えば、エピタキシャル成長により窒化ガリウム自立基板上に機能層を作製する場合、機能層は下地の窒化ガリウム自立基板に概ね倣って成長し、柱状構造の集合体となる。エピタキシャル成長では下地の結晶品質を引き継ぐため、機能層を構成する柱状構造の各ドメイン単位では高い結晶品質を得ることができる。窒化ガリウム自立基板を構成する結晶粒子の欠陥密度が低い理由は定かではないが、窒化ガリウム自立基板の作製初期で生じた格子欠陥のうち水平方向に傾いて発展するものが成長に伴って粒界に吸収されて消滅するためと推測される。 Note that the crystallinity of the constituent particles of the gallium nitride free-standing substrate tends to be high, and the density of defects such as dislocations can be kept low. For this reason, it is considered that the gallium nitride free-standing substrate can even be preferably used as compared with the gallium nitride single crystal substrate in certain applications such as a light emitting device. For example, when a functional layer is formed on a gallium nitride free-standing substrate by epitaxial growth, the functional layer grows substantially following the underlying gallium nitride free-standing substrate and becomes an aggregate of columnar structures. In epitaxial growth, since the underlying crystal quality is inherited, a high crystal quality can be obtained in each domain unit of the columnar structure constituting the functional layer. The reason why the defect density of the crystal grains constituting the gallium nitride free-standing substrate is low is not clear, but among the lattice defects generated at the initial stage of the gallium nitride free-standing substrate, the one that grows in the horizontal direction is the grain boundary as it grows. This is presumed to be absorbed and disappear.
　窒化ガリウム自立基板中に含まれる転位等の欠陥の密度を下げるという観点においては、窒化ガリウム自立基板を作製する場合に、下地基板となる配向多結晶焼結体の最表面を構成する粒子の一部乃至全てが一定の方位（例えば、ｃ面、ａ面等の基準方位）よりランダムに若干傾斜した形で配置されたものとするのが、より好ましい。傾斜する粒子はその略全部又は一定量が略一定の角度で傾斜していてもよいし、あるいは一定範囲内（好ましくは０．０１～２０°）で分布を有する様々な角度で及び／又は様々な方向で傾斜していてもよい。また、傾斜する粒子と傾斜していない粒子が所望の比率で混在していてもよい。あるいは、配向多結晶アルミナ焼結体の板面を、基準面に対し斜めに研磨し、一定方向に粒子の露出面を傾斜させてもよいし、波状等に加工することにより最表面の粒子の基準方位から若干傾斜した面を露出させてもよい。上記いずれの場合においても、ｃ面、ａ面等の基準方位に配向した配向多結晶アルミナ焼結体の最表面を構成するアルミナ単結晶粒子の一部乃至全てが、それらの基準方位が基板法線方向より０．５～２０°の範囲内でずれるように傾斜して配置されるのが好ましい。 From the viewpoint of reducing the density of defects such as dislocations contained in the gallium nitride free-standing substrate, when producing a gallium nitride free-standing substrate, one of the particles constituting the outermost surface of the oriented polycrystalline sintered body serving as a base substrate is used. It is more preferable that all or all of the portions are arranged in a form that is slightly inclined slightly from a certain orientation (for example, a reference orientation such as c-plane or a-plane). The inclined particles may be inclined almost entirely or in a certain amount at a substantially constant angle, or at various angles having a distribution within a certain range (preferably 0.01 to 20 °) and / or various. It may be inclined in any direction. Further, inclined particles and non-inclined particles may be mixed in a desired ratio. Alternatively, the plate surface of the oriented polycrystalline alumina sintered body may be polished obliquely with respect to the reference surface, and the exposed surface of the particles may be inclined in a certain direction, or the surface of the particles on the outermost surface may be processed into a wavy shape or the like. A surface slightly inclined from the reference orientation may be exposed. In any of the above cases, some or all of the alumina single crystal particles constituting the outermost surface of the oriented polycrystalline alumina sintered body oriented in the reference orientation such as the c-plane, a-plane, etc. have their reference orientation determined by the substrate method. It is preferable to be arranged so as to be inclined so as to deviate within a range of 0.5 to 20 ° from the line direction.
　配向多結晶アルミナ焼結体は、板状アルミナ粉末を原料として用いて成形及び焼結を行うことにより製造することができる。板状アルミナ粉末は市販されており、商業的に入手可能である。板状アルミナ粉末の種類及び形状は緻密な配向多結晶アルミナ焼結体が得られる限り特に限定されないが、平均粒径が０．４～１５μｍ、厚み０．０５～１μｍとしてもよく、この範囲内で異なる平均粒径の原料を２種類以上混ぜたものとしてもよい。好ましくは、板状アルミナ粉末を、せん断力を用いた手法により配向させ、配向成形体とすることができる。せん断力を用いた手法の好ましい例としては、テープ成形、押出し成形、ドクターブレード法、及びこれらの任意の組合せが挙げられる。せん断力を用いた配向手法は、上記例示したいずれの手法においても、板状アルミナ粉末にバインダー、可塑剤、分散剤、分散媒等の添加物を適宜加えてスラリー化し、このスラリーをスリット状の細い吐出口を通過させることにより、基板上にシート状に吐出及び成形するのが好ましい。吐出口のスリット幅は１０～４００μｍとするのが好ましい。なお、分散媒の量はスラリー粘度が５０００～１０００００ｃＰとなるような量にするのが好ましく、より好ましくは２００００～６００００ｃＰである。シート状に成形した配向成形体の厚さは５～５００μｍであるのが好ましく、より好ましくは１０～２００μｍである。このシート状に成形した配向成形体を多数枚積み重ねて、所望の厚さを有する前駆積層体とし、この前駆積層体にプレス成形を施すのが好ましい。このプレス成形は前駆積層体を真空パック等で包装して、５０～９５℃の温水中で１０～２０００ｋｇｆ／ｃｍ２の圧力で静水圧プレスにより好ましく行うことができる。また、シート状に成形した配向成形体、もしくは前駆積層体をロールプレス法（例えば加熱ロールプレスやカレンダーロールなど）による処理を施してもよい。また、押出し成形を用いる場合には、金型内の流路の設計により、金型内で細い吐出口を通過した後、シート状の成形体が金型内で一体化され、積層された状態で成形体が排出されるようにしてもよい。得られた成形体には公知の条件に従い脱脂を施すのが好ましい。上記のようにして得られた配向成形体を大気炉、窒素雰囲気炉、水素雰囲気炉等を用いた通常の常圧焼成に加え、熱間等方圧加圧法（ＨＩＰ）、ホットプレス法（ＨＰ）、放電プラズマ焼結（ＳＰＳ）等の加圧焼結法、及びこれらを組み合わせた方法にて焼成し、アルミナ結晶粒子を配向して含んでなるアルミナ焼結体を形成する。上記焼成での焼成温度や焼成時間は焼成方法によって異なるが、焼成温度は１１００～１９００℃、好ましくは１５００～１８００℃、焼成時間は１分間～１０時間、好ましくは３０分間～５時間である。ホットプレスにて１５００～１８００℃で２～５時間、面圧１００～２００ｋｇｆ／ｃｍ２の条件で焼成する第一の焼成工程と、得られた焼結体を熱間等方圧加圧法（ＨＩＰ）にて１５００～１８００℃で３０分間～５時間、ガス圧１０００～２０００ｋｇｆ／ｃｍ２の条件で再度焼成する第二の焼成工程を経て行われるのがより好ましい。上記焼成温度での焼成時間は特に限定されないが、好ましくは１～１０時間であり、より好ましくは２～５時間である。なお、透光性を付与する場合は、高純度な板状アルミナ粉末を原料として使用し、大気炉、水素雰囲気炉、窒素雰囲気炉等にて１１００～１８００℃で１分間～１０時間焼成する方法が好ましく例示される。得られた焼結体に対し、熱間等方圧加圧法（ＨＩＰ）にて１２００～１４００℃にて３０分間～５時間、ガス圧３００～２０００ｋｇｆ／ｃｍ２の条件で再度焼成する方法を用いてもよい。粒界相は少ない方が良いため、板状アルミナ粉末は高純度である方が好ましく、より好ましくは純度９８％以上であり、さらに好ましくは９９％以上、特に好ましくは９９．９％以上、最も好ましくは９９．９９％以上である。なお、焼成条件は上記に限定されるものではなく、緻密化と高配向の両立が可能であれば、例えば熱間等方圧加圧法（ＨＩＰ）による第二の焼成工程は省略してもよい。また、極少量の添加物を焼結助剤として原料中に加えてもよい。焼結助剤の添加は粒界相の減量と逆行するが、光の散乱因子の一つである気孔を減らすことで、結果的に透光性が向上することを目的としたものである。このような焼結助剤として、ＭｇＯ、ＺｒＯ２、Ｙ２Ｏ３、ＣａＯ、ＳｉＯ２、ＴｉＯ２、Ｆｅ２Ｏ３、Ｍｎ２Ｏ３等の酸化物、ＭｇＦ２、ＹｂＦ３等のフッ化物などから選ばれる少なくとも１種以上が挙げられる。しかし、透光性の観点では添加物の量は必要最小限に留めるべきであり、好ましくは１０００ｐｐｍ以下、より好ましくは７００ｐｐｍ以下である。 An oriented polycrystalline alumina sintered body can be produced by molding and sintering using a plate-like alumina powder as a raw material. Plate-like alumina powder is commercially available and is commercially available. The type and shape of the plate-like alumina powder are not particularly limited as long as a dense oriented polycrystalline alumina sintered body can be obtained, but the average particle diameter may be 0.4 to 15 μm and the thickness may be 0.05 to 1 μm. It is good also as what mixed 2 or more types of raw materials of different average particle diameter. Preferably, the plate-like alumina powder can be oriented by a technique using shearing force to obtain an oriented molded body. 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 dispersing agent, and a dispersion medium to the plate-like alumina 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 20000 to 60000 cP. The thickness of the oriented molded body formed into a sheet is preferably 5 to 500 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. Moreover, you may give the process by the roll press method (for example, a heating roll press, a calender roll, etc.) to the orientation molded object shape | molded in the sheet form, or a precursor laminated body. 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. In addition to normal atmospheric firing using an atmospheric furnace, nitrogen atmosphere furnace, hydrogen atmosphere furnace or the like, the oriented molded body obtained as described above is subjected to hot isostatic pressing (HIP), hot pressing (HP ), A pressure sintering method such as spark plasma sintering (SPS), and a combination thereof, and an alumina sintered body comprising oriented alumina crystal particles is formed. Although the firing temperature and firing time in the firing vary depending on the firing method, the firing temperature is 1100 to 1900 ° C., preferably 1500 to 1800 ° C., and the firing time is 1 minute to 10 hours, preferably 30 minutes to 5 hours. A first firing step of firing in a hot press at 1500 to 1800 ° C. for 2 to 5 hours under a surface pressure of 100 to 200 kgf / cm 2 , and the obtained sintered body is subjected to hot isostatic pressing (HIP) More preferably, it is carried out through a second firing step in which firing is carried out again at 1500 to 1800 ° C. for 30 minutes to 5 hours under a gas pressure of 1000 to 2000 kgf / cm 2 . 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. In the case of imparting translucency, a method is used in which a high-purity plate-like alumina powder is used as a raw material and calcined at 1100 to 1800 ° C. for 1 minute to 10 hours in an air furnace, hydrogen atmosphere furnace, nitrogen atmosphere furnace or the like Is preferably exemplified. A method of firing the obtained sintered body again at a temperature of 1200 to 1400 ° C. for 30 minutes to 5 hours and a gas pressure of 300 to 2000 kgf / cm 2 by hot isostatic pressing (HIP) is used. May be. Since it is better that the grain boundary phase is smaller, the plate-like alumina powder is preferably highly pure, more preferably 98% or more, further preferably 99% or more, particularly preferably 99.9% or more, most preferably Preferably it is 99.99% or more. The firing conditions are not limited to the above. For example, the second firing step by hot isostatic pressing (HIP) may be omitted as long as both densification and high orientation are possible. . Also, a very small amount of additives may be added to the raw material as a sintering aid. Although the addition of the sintering aid goes against the reduction of the grain boundary phase, the purpose is to improve the translucency as a result by reducing pores, which is one of the light scattering factors. As such sintering aids, oxides such as MgO, ZrO 2 , Y 2 O 3 , CaO, SiO 2 , TiO 2 , Fe 2 O 3 , Mn 2 O 3 , fluorides such as MgF 2 and YbF 3 And at least one selected from the above. However, from the viewpoint of translucency, the amount of additive should be kept to the minimum necessary, and is preferably 1000 ppm or less, more preferably 700 ppm or less.
　また、配向多結晶アルミナ焼結体は、微細なアルミナ粉末及び／又は遷移アルミナ粉末に板状アルミナ粉末を適宜加えた混合粉末を原料として用いて成形及び焼結を行うことによっても製造することができる。この製法では板状アルミナ粉末が種結晶（テンプレート）となり、微細アルミナ粉末及び／又は遷移アルミナ粉末がマトリックスとなって、テンプレートがマトリックスを取り込みながらホモエピタキシャル成長する、所謂ＴＧＧ（Ｔｅｍｐｌａｔｅｄ　Ｇｒａｉｎ　Ｇｒｏｗｔｈ）過程を経ることで結晶成長と緻密化が生じる。テンプレートとなる板状アルミナ粒子とマトリックスの粒径はその粒径比が大きい方が粒成長しやすく、例えばテンプレートの平均粒径が０．５～１５μｍのとき、マトリックスの平均粒径０．４μｍ以下が好ましく、より好ましくは０．２μｍ以下であり、さらに好ましくは０．１μｍ以下である。テンプレートとマトリックスの混合比は粒径比や焼成条件、添加物の有無によっても異なるが、例えばテンプレートに平均粒径２μｍの板状アルミナ粉末、マトリックスに平均粒径０．１μｍの微細アルミナ粉末を用いた場合、テンプレート／マトリックス比が５０／５０～１／９９ｗｔ％となるようにしてもよい。このような手法においても前述した大気炉、窒素雰囲気炉、水素雰囲気炉等を用いた通常の常圧焼成に加え、熱間等方圧加圧法（ＨＩＰ）、ホットプレス法（ＨＰ）、放電プラズマ焼結（ＳＰＳ）等の加圧焼結法、及びこれらを組み合わせた方法で良質な配向多結晶アルミナ焼結体を得ることができる。 An oriented polycrystalline alumina sintered body can also be produced by molding and sintering using a mixed powder obtained by appropriately adding a plate-like alumina powder to a fine alumina powder and / or a transition alumina powder. it can. In this manufacturing method, a plate-like alumina powder becomes a seed crystal (template), a fine alumina powder and / or a transition alumina powder becomes a matrix, and the template undergoes a so-called TGG (Tempered Grain Growth) process in which homoepitaxial growth is performed while incorporating the matrix. This causes crystal growth and densification. The larger the particle size ratio of the plate-like alumina particles and the matrix used as the template, the easier the particle growth. For example, when the average particle size of the template is 0.5 to 15 μm, the average particle size of the matrix is 0.4 μm or less. Is preferably 0.2 μm or less, and more preferably 0.1 μm or less. The mixing ratio of the template and matrix varies depending on the particle size ratio, firing conditions, and the presence or absence of additives. For example, a plate-like alumina powder having an average particle size of 2 μm is used as the template, and a fine alumina powder having an average particle size of 0.1 μm is used as the matrix. In such a case, the template / matrix ratio may be 50/50 to 1/99 wt%. In such a method, in addition to the normal atmospheric firing using the above-mentioned atmospheric furnace, nitrogen atmosphere furnace, hydrogen atmosphere furnace, etc., hot isostatic pressing (HIP), hot press (HP), discharge plasma A high-quality oriented polycrystalline alumina sintered body can be obtained by a pressure sintering method such as sintering (SPS) or a combination thereof.
　こうして得られたアルミナ焼結体は、前述した原料となる板状アルミナ粉末の種類によりｃ面等の所望の面に配向した多結晶アルミナ焼結体となる。こうして得られた配向多結晶アルミナ焼結体を砥石で研削して板面を平坦にした後、ダイヤモンド砥粒を用いたラップ加工により板面を平滑化して配向アルミナ基板とするのが好ましい。 The alumina sintered body thus obtained becomes a polycrystalline alumina sintered body oriented in a desired plane such as the c-plane depending on the kind of the plate-like alumina powder used as the raw material. It is preferable that the oriented polycrystalline alumina sintered body thus obtained is ground with a grindstone to flatten the plate surface, and then the plate surface is smoothed by lapping using diamond abrasive grains to obtain an oriented alumina substrate.
（２）種結晶層の形成
　配向多結晶焼結体上に、窒化ガリウムからなる種結晶層を、配向多結晶焼結体の結晶方位に概ね倣った結晶方位を有するように形成する。なお、「配向多結晶焼結体の結晶方位に概ね倣った結晶方位を有するように形成する」とは、配向多結晶焼結体の結晶方位の影響を受けた結晶成長によりもたらされた構造を意味し、必ずしも配向多結晶焼結体の結晶方位に完全に倣って成長した構造であるとは限らず、配向多結晶焼結体と異なる結晶方位に成長する構造も含む。種結晶層の作製方法は特に限定されないが、ＭＯＣＶＤ（有機金属気相成長法）、ＭＢＥ（分子線エピタキシー法）、ＨＶＰＥ（ハライド気相成長法）、スパッタリング等の気相法、Ｎａフラックス法、アモノサーマル法、水熱法、ゾルゲル法等の液相法、粉末の固相成長を利用した粉末法、及びこれらの組み合わせが好ましく例示される。例えば、ＭＯＣＶＤ法による種結晶層の形成は、４５０～５５０℃にて低温ＧａＮ層を２０～５０ｎｍ堆積させた後に、１０００～１２００℃にて厚さ２～４μｍのＧａＮ膜を積層させることにより行うのが好ましい。 (2) Formation of seed crystal layer A seed crystal layer made of gallium nitride is formed on the oriented polycrystalline sintered body so as to have a crystal orientation that substantially follows the crystal orientation of the oriented polycrystalline sintered body. “Forming so as to have a crystal orientation generally following the crystal orientation of the oriented polycrystalline sintered body” means that the structure is brought about by crystal growth affected by the crystal orientation of the oriented polycrystalline sintered body. This means that the structure does not necessarily grow completely following the crystal orientation of the oriented polycrystalline sintered body, but also includes a structure that grows in a different crystal orientation from the oriented polycrystalline sintered body. The method for producing the seed crystal layer is not particularly limited, but MOCVD (metal organic vapor phase epitaxy), MBE (molecular beam epitaxy), HVPE (halide vapor phase epitaxy), sputtering and other gas phase methods, Na flux method, Preferred examples include liquid phase methods such as ammonothermal method, hydrothermal method, sol-gel method, powder method utilizing solid phase growth of powder, and combinations thereof. For example, the formation of a seed crystal layer by MOCVD is performed by depositing a 20 to 50 nm low-temperature GaN layer at 450 to 550 ° C. and then laminating a GaN film having a thickness of 2 to 4 μm at 1000 to 1200 ° C. Is preferred.
（３）窒化ガリウム系結晶層の形成
　種結晶層上に、厚さ２０μｍ以上の窒化ガリウム系結晶から構成される層を、種結晶層の結晶方位に概ね倣った結晶方位を有するように形成する。窒化ガリウム系結晶から構成される層の形成方法は配向多結晶焼結体及び／又は種結晶層の結晶方位に概ね倣った結晶方位を有する限り特に限定がなく、ＭＯＣＶＤ、ＨＶＰＥ等の気相法、Ｎａフラックス法、アモノサーマル法、水熱法、ゾルゲル法等の液相法、粉末の固相成長を利用した粉末法、及びこれらの組み合わせが好ましく例示されるが、Ｎａフラックス法により行われるのが特に好ましい。Ｎａフラックス法によれば結晶性の高い厚肉の窒化ガリウム結晶層を種結晶層上に効率良く作製できる。Ｎａフラックス法による窒化ガリウム系結晶層の形成は、種結晶基板を設置した坩堝に金属Ｇａ、金属Ｎａ及び所望によりドーパント（例えばゲルマニウム（Ｇｅ）、シリコン（Ｓｉ）、酸素（Ｏ）等のｎ型ドーパント、又はベリリウム（Ｂｅ）、マグネシウム（Ｍｇ）、カルシウム（Ｃａ）、ストロンチウム（Ｓｒ）、亜鉛（Ｚｎ）、カドミウム（Ｃｄ）等のｐ型ドーパント）を含む融液組成物を充填し、窒素雰囲気中で８３０～９１０℃、３．５～４．５ＭＰａまで昇温加圧した後、温度及び圧力を保持しつつ回転することにより行うのが好ましい。保持時間は目的の膜厚によって異なるが、１０～１００時間程度としてもよい。また、こうしてＮａフラックス法により得られた窒化ガリウム結晶を砥石で研削して板面を平坦にした後、ダイヤモンド砥粒を用いたラップ加工により板面を平滑化するのが好ましい。 (3) Formation of gallium nitride-based crystal layer A layer composed of a gallium nitride-based crystal having a thickness of 20 μm or more is formed on the seed crystal layer so as to have a crystal orientation that substantially follows the crystal orientation of the seed crystal layer. . The method of forming a layer composed of gallium nitride-based crystals is not particularly limited as long as it has a crystal orientation that substantially follows the crystal orientation of the oriented polycrystalline sintered body and / or the seed crystal layer, and is a gas phase method such as MOCVD or HVPE. Preferred examples include a liquid phase method such as Na flux method, ammonothermal method, hydrothermal method, sol-gel method, powder method utilizing solid phase growth of powder, and combinations thereof, but the Na flux method is used. Is particularly preferred. According to the Na flux method, a thick gallium nitride crystal layer with high crystallinity can be efficiently produced on the seed crystal layer. The formation of the gallium nitride crystal layer by the Na flux method is performed by using a crucible provided with a seed crystal substrate and metal n-type such as metal Ga, metal Na, and optionally a dopant (eg, germanium (Ge), silicon (Si), oxygen (O)). Filled with a melt composition containing a dopant or a p-type dopant such as beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), cadmium (Cd), etc., and a nitrogen atmosphere Among them, it is preferable to carry out the heating and pressurizing to 830 to 910 ° C. and 3.5 to 4.5 MPa, and then rotating while maintaining the temperature and pressure. The holding time varies depending on the target film thickness, but may be about 10 to 100 hours. Further, it is preferable that the gallium nitride crystal thus obtained by the Na flux method is ground with a grindstone to flatten the plate surface, and then the plate surface is smoothed by lapping using diamond abrasive grains.
（４）配向多結晶焼結体の除去
　配向多結晶焼結体を除去して、窒化ガリウム自立基板を得ることができる。配向多結晶焼結体を除去する方法は、特に限定されないが、研削加工、ケミカルエッチング、配向焼結体側からのレーザー照射による界面加熱（レーザーリフトオフ）、昇温時の熱膨張差を利用した自発剥離等が挙げられる。 (4) Removal of oriented polycrystalline sintered body The oriented polycrystalline sintered body can be removed to obtain a gallium nitride free-standing substrate. The method for removing the oriented polycrystalline sintered body is not particularly limited, but is spontaneous, utilizing grinding, chemical etching, interfacial heating (laser lift-off) by laser irradiation from the oriented sintered body side, and thermal expansion difference during temperature rise Exfoliation and the like.
　発光素子及びその製造方法
　上述した本発明による窒化ガリウム自立基板を用いて高品質の発光素子を作製することができる。本発明の窒化ガリウム自立基板を用いた発光素子の構造やその作製方法は特に限定されるものではない。典型的には、発光素子は、窒化ガリウム自立基板に発光機能層を設けることにより作製され、この発光機能層の形成は、窒化ガリウム基板の結晶方位に概ね倣った結晶方位を有するように、略法線方向に単結晶構造を有する複数の半導体単結晶粒子で構成される層を一つ以上形成することに行われるのが好ましい。もっとも、窒化ガリウム自立基板を電極（ｐ型電極又はｎ型電極でありうる）、ｐ型層、ｎ型層等の基材以外の部材又は層として利用して発光素子を作製してもよい。素子サイズに特に規定はなく、５ｍｍ×５ｍｍ以下の小素子としてもよいし、１０ｃｍ×１０ｃｍ以上の面発光素子としてもよい。 Light-Emitting Element and Manufacturing Method Thereof A high-quality light-emitting element can be manufactured using the above-described gallium nitride free-standing substrate according to the present invention. There is no particular limitation on the structure of the light-emitting element using the gallium nitride free-standing substrate of the present invention and the manufacturing method thereof. Typically, a light-emitting element is manufactured by providing a light-emitting functional layer on a gallium nitride free-standing substrate, and the light-emitting functional layer is formed so that the crystal orientation approximately follows the crystal orientation of the gallium nitride substrate. It is preferable to form one or more layers composed of a plurality of semiconductor single crystal particles having a single crystal structure in the normal direction. However, a light-emitting element may be manufactured using a gallium nitride free-standing substrate as a member or layer other than a substrate such as an electrode (which may be a p-type electrode or an n-type electrode), a p-type layer, or an n-type layer. The element size is not particularly limited, and may be a small element of 5 mm × 5 mm or less, or a surface light emitting element of 10 cm × 10 cm or more.
　図１に、本発明の一態様による発光素子の層構成を模式的に示す。図１に示される発光素子１０は、窒化ガリウム自立基板１２と、この基板上に形成される発光機能層１４とを備えてなる。発光機能層１４は、略法線方向に単結晶構造を有する複数の半導体単結晶粒子で構成される層を一以上有してなる。この発光機能層１４は、電極等を適宜設けて電圧を印加することによりＬＥＤ等の発光素子の原理に基づき発光をもたらすものである。特に、本発明の窒化ガリウム自立基板１２を用いることで、窒化ガリウム単結晶基板を用いた場合と同等の発光効率を有する発光素子を得ることも期待でき、大幅な低コスト化が実現できる。また、ｐ型ないしｎ型ドーパントの導入により導電性を持たせた窒化ガリウムを基板とすることで、縦型構造の発光素子を実現することができ、それにより輝度を高めることができる。その上、大面積な面発光素子も低コストで実現可能となる。 FIG. 1 schematically shows a layer structure of a light-emitting element according to one embodiment of the present invention. A light-emitting element 10 shown in FIG. 1 includes a gallium nitride free-standing substrate 12 and a light-emitting functional layer 14 formed on the substrate. The light emitting functional layer 14 has one or more layers composed of a plurality of semiconductor single crystal particles having a single crystal structure in a substantially normal direction. The light-emitting functional layer 14 emits light based on the principle of a light-emitting element such as an LED by appropriately providing electrodes and applying a voltage. In particular, by using the gallium nitride free-standing substrate 12 of the present invention, it can be expected to obtain a light-emitting element having a light emission efficiency equivalent to that when a gallium nitride single crystal substrate is used, and a significant cost reduction can be realized. In addition, by using gallium nitride imparted with conductivity by introducing a p-type or n-type dopant as a substrate, a light-emitting element having a vertical structure can be realized, whereby luminance can be increased. In addition, a large area surface light emitting device can be realized at low cost.
　発光機能層１４が基板１２上に形成される。発光機能層１４は、基板１２上の全面又は一部に設けられてもよいし、後述するバッファ層が基板１２上に形成される場合にはバッファ層上の全面又は一部に設けられてもよい。発光機能層１４は、略法線方向に単結晶構造を有する複数の半導体単結晶粒子で構成される層を一以上有してなり、電極及び／又は蛍光体を適宜設けて電圧を印加することによりＬＥＤに代表される発光素子の原理に基づき発光をもたらす公知の様々な層構成を採りうる。したがって、発光機能層１４は青色、赤色等の可視光を放出するものであってもよいし、可視光を伴わずに又は可視光と共に紫外光を発光するものであってもよい。発光機能層１４は、ｐ－ｎ接合を利用した発光素子の少なくとも一部を構成するのが好ましく、このｐ－ｎ接合は、図１に示されるように、ｐ型層１４ａとｎ型層１４ｃの間に活性層１４ｂを含んでいてもよい。このとき、活性層としてｐ型層及び／又はｎ型層よりもバンドギャップが小さい層を用いたダブルへテロ接合又はシングルへテロ接合（以下、ヘテロ接合と総称する）としてもよい。また、ｐ型層－活性層－ｎ型層の一形態として、活性層の厚みを薄くした量子井戸構造を採りうる。量子井戸を得るためには活性層のバンドギャップがｐ型層及びｎ型層よりも小さくしたダブルへテロ接合が採用されるべきことは言うまでもない。また、これらの量子井戸構造を多数積層した多重量子井戸構造（ＭＱＷ）としてもよい。これらの構造をとることで、ｐ－ｎ接合と比べて発光効率を高めることができる。このように、発光機能層１４は、発光機能を有するｐ－ｎ接合及び／又はへテロ接合及び／又は量子井戸接合を備えたものであるのが好ましい。 A light emitting functional layer 14 is formed on the substrate 12. The light emitting functional layer 14 may be provided on the entire surface or a part of the substrate 12, or may be provided on the entire surface or a part of the buffer layer when a buffer layer described later is formed on the substrate 12. Good. The light-emitting functional layer 14 has one or more layers composed of a plurality of semiconductor single crystal particles having a single crystal structure in a substantially normal direction, and is appropriately provided with electrodes and / or phosphors to apply a voltage. Therefore, it is possible to adopt various known layer configurations that cause light emission based on the principle of a light emitting element represented by an LED. Therefore, the light emitting functional layer 14 may emit visible light such as blue and red, or may emit ultraviolet light without visible light or with visible light. The light emitting functional layer 14 preferably constitutes at least a part of a light emitting element using a pn junction, and the pn junction includes a p-type layer 14a and an n-type layer 14c as shown in FIG. The active layer 14b may be included in between. At this time, a double heterojunction or a single heterojunction (hereinafter collectively referred to as a heterojunction) using a layer having a smaller band gap than the p-type layer and / or the n-type layer as the active layer may be used. Further, as one form of the p-type layer-active layer-n-type layer, a quantum well structure in which the active layer is thin can be adopted. In order to obtain a quantum well, it goes without saying that a double heterojunction in which the band gap of the active layer is smaller than that of the p-type layer and the n-type layer should be adopted. Moreover, it is good also as a multiple quantum well structure (MQW) which laminated | stacked many of these quantum well structures. By adopting these structures, the luminous efficiency can be increased as compared with the pn junction. Thus, the light emitting functional layer 14 preferably includes a pn junction and / or a heterojunction and / or a quantum well junction having a light emitting function.
　したがって、発光機能層１４を構成する一以上の層は、ｎ型ドーパントがドープされているｎ型層、ｐ型ドーパントがドープされているｐ型層、及び活性層からなる群から選択される少なくとも一以上を含むものであることができる。ｎ型層、ｐ型層及び（存在する場合には）活性層は、主成分が同じ材料で構成されてもよいし、互いに主成分が異なる材料で構成されてもよい。 Accordingly, at least one layer constituting the light emitting functional layer 14 is at least selected from the group consisting of an n-type layer doped with an n-type dopant, a p-type layer doped with a p-type dopant, and an active layer. One or more can be included. The n-type layer, the p-type layer, and the active layer (if present) may be composed of the same material as the main component, or may be composed of materials whose main components are different from each other.
　発光機能層１４を構成する各層の材質は、窒化ガリウム自立基板の結晶方位に概ね倣って成長し且つ発光機能を有するものであれば特に限定されないが、窒化ガリウム（ＧａＮ）系材料、酸化亜鉛（ＺｎＯ）系材料及び窒化アルミニウム（ＡｌＮ）系材料から選択される少なくとも１種以上を主成分とする材料で構成されるのが好ましく、ｐ型ないしｎ型に制御するためのドーパントを適宜含むものであってよい。特に好ましい材料は、窒化ガリウム自立基板と同種の材料である、窒化ガリウム（ＧａＮ）系材料である。また、発光機能層１４を構成する材料は、そのバンドギャップを制御するため、例えばＧａＮにＡｌＮ、ＩｎＮ等を固溶させた混晶としてもよい。また、直前の段落で述べたとおり、発光機能層１４は複数種の材料系からなるヘテロ接合としてもよい。例えば、ｐ型層に窒化ガリウム（ＧａＮ）系材料、ｎ型層に酸化亜鉛（ＺｎＯ）系材料を用いてもよい。また、ｐ型層に酸化亜鉛（ＺｎＯ）系材料、活性層とｎ型層に窒化ガリウム（ＧａＮ）系材料を用いてもよく、材料の組み合わせに特に限定はない。 The material of each layer constituting the light emitting functional layer 14 is not particularly limited as long as it grows substantially following the crystal orientation of the gallium nitride free-standing substrate and has a light emitting function, but gallium nitride (GaN) based material, zinc oxide ( It is preferably composed of a material mainly composed of at least one selected from a ZnO) -based material and an aluminum nitride (AlN) -based material, and appropriately contains a dopant for controlling p-type or n-type. It may be. A particularly preferable material is a gallium nitride (GaN) -based material, which is the same material as the gallium nitride free-standing substrate. Further, the material constituting the light emitting functional layer 14 may be a mixed crystal in which, for example, AlN, InN or the like is dissolved in GaN in order to control the band gap. Further, as described in the immediately preceding paragraph, the light emitting functional layer 14 may be a heterojunction made of a plurality of types of materials. For example, a gallium nitride (GaN) -based material may be used for the p-type layer, and a zinc oxide (ZnO) -based material may be used for the n-type layer. Further, a zinc oxide (ZnO) -based material may be used for the p-type layer, and a gallium nitride (GaN) -based material may be used for the active layer and the n-type layer, and the combination of materials is not particularly limited.
　発光機能層１４を構成する各層は、略法線方向に単結晶構造を有する複数の半導体単結晶粒子で構成される。すなわち、各層は、水平面方向に二次元的に連結されてなる複数の半導体単結晶粒子で構成されており、それ故、略法線方向には単結晶構造を有することになる。したがって、発光機能層１４の各層は、層全体としては単結晶ではないものの、局所的なドメイン単位では単結晶構造を有するため、発光機能を確保するのに十分な高い結晶性を有することができる。好ましくは、発光機能層１４の各層を構成する半導体単結晶粒子は、基板１２である窒化ガリウム自立基板の結晶方位に概ね倣って成長した構造を有する。「窒化ガリウム自立基板の結晶方位に概ね倣って成長した構造」とは、窒化ガリウム自立基板の結晶方位の影響を受けた結晶成長によりもたらされた構造を意味し、必ずしも窒化ガリウム自立基板の結晶方位に完全に倣って成長した構造であるとは限らず、所望の発光機能を確保できるかぎり、窒化ガリウム自立基板の結晶方位にある程度倣って成長した構造であってよい。すなわち、この構造は配向多結晶焼結体と異なる結晶方位に成長する構造も含む。その意味で、「結晶方位に概ね倣って成長した構造」との表現は「結晶方位に概ね由来して成長した構造」と言い換えることもできる。したがって、そのような結晶成長はエピタキシャル成長によるものが好ましいが、これに限定されず、それに類する様々な結晶成長の形態であってもよい。特にｎ型層、活性層、ｐ型層等を構成する各層が窒化ガリウム自立基板と同じ結晶方位に成長する場合は、窒化ガリウム自立基板から発光機能層の各層間でも略法線方向に関しては結晶方位が概ね揃った構造となり、良好な発光特性を得ることができる。すなわち、発光機能層１４も窒化ガリウム自立基板１２の結晶方位に概ね倣って成長する場合は、基板の垂直方向では方位が概ね一定になる。このため、法線方向は単結晶と同等の状態であり、ｎ型ドーパントを添加した窒化ガリウム自立基板を用いた場合、窒化ガリウム自立基板をカソードとした縦型構造の発光素子とすることができ、ｐ型ドーパントを添加した窒化ガリウム自立基板を用いた場合、窒化ガリウム自立基板をアノードとした縦型構造の発光素子とすることができる。 Each layer constituting the light emitting functional layer 14 is composed of a plurality of semiconductor single crystal particles having a single crystal structure in a substantially normal direction. That is, each layer is composed of a plurality of semiconductor single crystal particles that are two-dimensionally connected in the horizontal plane direction, and therefore has a single crystal structure in a substantially normal direction. Therefore, each layer of the light emitting functional layer 14 is not a single crystal as a whole, but has a single crystal structure in a local domain unit, and thus can have high crystallinity sufficient to ensure a light emitting function. . Preferably, the semiconductor single crystal particles constituting each layer of the light emitting functional layer 14 have a structure grown substantially following the crystal orientation of the gallium nitride free-standing substrate which is the substrate 12. “A structure grown substantially following the crystal orientation of a gallium nitride free-standing substrate” means a structure brought about by crystal growth affected by the crystal orientation of the gallium nitride free-standing substrate, and is not necessarily a crystal of the gallium nitride free-standing substrate. The structure does not necessarily grow perfectly following the orientation, and may be a structure grown somewhat following the crystal orientation of the gallium nitride free-standing substrate as long as a desired light emitting function can be secured. That is, this structure includes a structure that grows in a different crystal orientation from the oriented polycrystalline sintered body. In that sense, the expression “a structure grown substantially following the crystal orientation” can be rephrased as “a structure grown substantially derived from the crystal orientation”. Therefore, although such crystal growth is preferably by epitaxial growth, it is not limited to this, and various forms of crystal growth similar thereto may be used. In particular, when each layer constituting the n-type layer, the active layer, the p-type layer, etc. grows in the same crystal orientation as the gallium nitride free-standing substrate, the crystal in the substantially normal direction is also observed in each layer of the light emitting functional layer from the gallium nitride free-standing substrate. A structure in which the orientation is substantially uniform can be obtained, and good light emission characteristics can be obtained. That is, when the light emitting functional layer 14 also grows substantially following the crystal orientation of the gallium nitride free-standing substrate 12, the orientation is substantially constant in the vertical direction of the substrate. Therefore, the normal direction is the same as that of a single crystal, and when a gallium nitride free-standing substrate to which an n-type dopant is added is used, a light-emitting element having a vertical structure using the gallium nitride free-standing substrate as a cathode can be obtained. When a gallium nitride free-standing substrate to which a p-type dopant is added is used, a vertical structure light-emitting element using the gallium nitride free-standing substrate as an anode can be obtained.
　少なくとも発光機能層１４を構成するｎ型層、活性層、ｐ型層等の各層が同じ結晶方位に成長する場合は、発光機能層１４の各層は、法線方向に見た場合に単結晶と観察され、水平面方向の切断面で見た場合に粒界が観察される柱状構造の半導体単結晶粒子の集合体であると捉えることも可能である。ここで、「柱状構造」とは、典型的な縦長の柱形状のみを意味するのではなく、横長の形状、台形の形状、及び台形を逆さにしたような形状等、種々の形状を包含する意味として定義される。もっとも、上述のとおり、各層は窒化ガリウム自立基板の結晶方位にある程度倣って成長した構造であればよく、必ずしも厳密な意味で柱状構造である必要はない。柱状構造となる原因は、前述のとおり、基板１２である窒化ガリウム自立基板の結晶方位の影響を受けて半導体単結晶粒子が成長するためと考えられる。このため、柱状構造ともいえる半導体単結晶粒子の断面の平均粒径（以下、断面平均径という）は成膜条件だけでなく、窒化ガリウム自立基板の板面の平均粒径にも依存するものと考えられる。発光機能層を構成する柱状構造の界面は発光効率や発光波長に影響を与えるが、粒界があることにより断面方向の光の透過率が悪く、光が散乱ないし反射する。このため、法線方向に光を取り出す構造の場合、粒界からの散乱光により輝度が高まる効果も期待される。 When at least the layers such as the n-type layer, the active layer, and the p-type layer constituting the light-emitting functional layer 14 grow in the same crystal orientation, each layer of the light-emitting functional layer 14 is a single crystal when viewed in the normal direction. It can also be regarded as an aggregate of columnar-structured semiconductor single crystal particles that are observed and viewed from a cut surface in the horizontal plane direction. Here, the “columnar structure” does not mean only a typical vertically long column shape, but includes various shapes such as a horizontally long shape, a trapezoidal shape, and a shape in which the trapezoid is inverted. Defined as meaning. However, as described above, each layer has only to have a structure grown to some extent along the crystal orientation of the gallium nitride free-standing substrate, and does not necessarily have a columnar structure in a strict sense. The cause of the columnar structure is considered to be that the semiconductor single crystal particles grow under the influence of the crystal orientation of the gallium nitride free-standing substrate as the substrate 12 as described above. For this reason, the average particle diameter of the cross section of the semiconductor single crystal particles, which can be said to be a columnar structure (hereinafter referred to as the average cross section diameter) depends not only on the film forming conditions but also on the average particle diameter of the plate surface of the gallium nitride free-standing substrate. Conceivable. The interface of the columnar structure constituting the light emitting functional layer affects the light emission efficiency and the light emission wavelength, but due to the presence of the grain boundary, the light transmittance in the cross-sectional direction is poor, and the light is scattered or reflected. For this reason, in the case of a structure in which light is extracted in the normal direction, an effect of increasing the luminance due to scattered light from the grain boundary is also expected.
　もっとも、発光機能層１４を構成する柱状構造同士の界面は結晶性が低下するため、発光効率が低下し、発光波長が変動し、発光波長がブロードになる可能性がある。このため、柱状構造の断面平均径は大きいほうが良い。好ましくは、発光機能層１４の最表面における半導体単結晶粒子の断面平均径は０．３μｍ以上であり、より好ましくは３μｍ以上である。この断面平均径の上限は特に限定されないが、１０００μｍ以下が現実的である。また、このような断面平均径の半導体単結晶粒子を作製するには、窒化ガリウム自立基板を構成する窒化ガリウム系単結晶粒子の基板の最表面における断面平均径を０．３μｍ～１０００μｍとするのが望ましく、より望ましくは３μｍ以上である。 However, since the crystallinity of the interface between the columnar structures constituting the light emitting functional layer 14 is lowered, the light emission efficiency is lowered, the light emission wavelength is changed, and the light emission wavelength may be broad. For this reason, it is better that the cross-sectional average diameter of the columnar structure is larger. Preferably, the cross-sectional average diameter of the semiconductor single crystal particles on the outermost surface of the light emitting functional layer 14 is 0.3 μm or more, more preferably 3 μm or more. Although the upper limit of this cross-sectional average diameter is not specifically limited, 1000 micrometers or less are realistic. In order to produce semiconductor single crystal particles having such an average cross-sectional diameter, the average cross-sectional diameter of the outermost surface of the gallium nitride-based single crystal particles constituting the gallium nitride free-standing substrate is set to 0.3 μm to 1000 μm. Is more desirable, and more desirably 3 μm or more.
　発光機能層１４の一部又は全てに窒化ガリウム（ＧａＮ）系以外の材料が用いられる場合には、窒化ガリウム自立基板１２と発光機能層１４の間に反応を抑制するためのバッファ層を設けてもよい。このようなバッファ層の主成分は特に限定されないが、酸化亜鉛（ＺｎＯ）系材料及び窒化アルミニウム（ＡｌＮ）系材料から選択される少なくとも１種以上を主成分とする材料で構成されるのが好ましく、ｐ型ないしｎ型に制御するためのドーパントを適宜含むものであってよい。 When a material other than gallium nitride (GaN) is used for part or all of the light emitting functional layer 14, a buffer layer for suppressing the reaction is provided between the gallium nitride free-standing substrate 12 and the light emitting functional layer 14. Also good. The main component of such a buffer layer is not particularly limited, but it is preferably composed of a material mainly containing at least one selected from a zinc oxide (ZnO) -based material and an aluminum nitride (AlN) -based material. , A dopant for controlling p-type to n-type may be included as appropriate.
　発光機能層１４を構成する各層が窒化ガリウム系材料で構成されるのが好ましい。例えば、窒化ガリウム自立基板１２上にｎ型窒化ガリウム層及びｐ型窒化ガリウム層を順に成長させてもよく、ｐ型窒化ガリウム層とｎ型窒化ガリウム層の積層順序は逆であってもよい。ｐ型窒化ガリウム層に使用されるｐ型ドーパントの好ましい例としては、ベリリウム（Ｂｅ）、マグネシウム（Ｍｇ）、カルシウム（Ｃａ）、ストロンチウム（Ｓｒ）、亜鉛（Ｚｎ）及びカドミウム（Ｃｄ）からなる群から選択される１種以上が挙げられる。また、ｎ型窒化ガリウム層に使用されるｎ型ドーパントの好ましい例としては、シリコン（Ｓｉ）、ゲルマニウム（Ｇｅ）、スズ（Ｓｎ）及び酸素（Ｏ）からなる群から選択される１種以上が挙げられる。また、ｐ型窒化ガリウム層及び／又はｎ型窒化ガリウム層は、ＡｌＮ及びＩｎＮからなる群から選択される１種以上の結晶と混晶化された窒化ガリウムからなるものであってもよく、ｐ型層及び／又はｎ型層はこの混晶化された窒化ガリウムにｐ型ドーパント又はｎ型ドーパントがドープされていてもよい。例えば、窒化ガリウムとＡｌＮの混晶であるＡｌｘＧａ１－ｘＮにＭｇをドーピングすることでｐ型層、ＡｌｘＧａ１－ｘＮにＳｉをドーピングすることでとしてｎ型層として使用することができる。窒化ガリウムをＡｌＮと混晶化することでバンドギャップが広がり、発光波長を高エネルギー側にシフトさせることができる。また、窒化ガリウムをＩｎＮとの混晶としてもよく、これによりバンドギャップが狭まり、発光波長を低エネルギー側にシフトさせることができる。ｐ型窒化ガリウム層とｎ型窒化ガリウム層との間に、両層のいずれよりもバンドギャップが小さいＧａＮ、又はＡｌＮ及びＩｎＮからなる群から選択される１種以上とＧａＮとの混晶からなる活性層を少なくとも有してもよい。活性層はｐ型層及びｎ型層とダブルへテロ接合された構造であり、この活性層を薄くした構成はｐ－ｎ接合の一態様である量子井戸構造の発光素子に相当し、発光効率をより一層高めることができる。また、活性層は両層のいずれか一方よりもバンドギャップが小さくＧａＮ、又はＡｌＮ及びＩｎＮからなる群から選択される１種以上とＧａＮとの混晶からなるものとしてもよい。このようなシングルヘテロ接合にても発光効率をより一層高めることができる。窒化ガリウム系バッファ層は、ノンドープのＧａＮ、又はｎ型若しくはｐ型ドーピングされたＧａＮからなるものであってもよいし、格子定数が近いＡｌＮ、ＩｎＮ、或いはＧａＮとＡｌＮ及びＩｎＮからなる群から選択される１種以上の結晶と混晶化されたものであってもよい。 Each layer constituting the light emitting functional layer 14 is preferably made of a gallium nitride material. For example, an n-type gallium nitride layer and a p-type gallium nitride layer may be grown in order on the gallium nitride free-standing substrate 12, and the stacking order of the p-type gallium nitride layer and the n-type gallium nitride layer may be reversed. Preferable examples of the p-type dopant used for the p-type gallium nitride layer include a group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), and cadmium (Cd). 1 or more types selected from are mentioned. Moreover, as a preferable example of the n-type dopant used for the n-type gallium nitride layer, at least one selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), and oxygen (O) is used. Can be mentioned. The p-type gallium nitride layer and / or the n-type gallium nitride layer may be made of gallium nitride mixed with one or more kinds of crystals selected from the group consisting of AlN and InN. In the type layer and / or the n-type layer, the mixed gallium nitride may be doped with a p-type dopant or an n-type dopant. For example, Al x Ga 1-x N, which is a mixed crystal of gallium nitride and AlN, is used as a p-type layer by doping Mg, and Al x Ga 1-x N is used as an n-type layer by doping Si. be able to. When gallium nitride is mixed with AlN, the band gap is widened, and the emission wavelength can be shifted to a higher energy side. In addition, gallium nitride may be mixed with InN, whereby the band gap is narrowed and the emission wavelength can be shifted to a lower energy side. Between the p-type gallium nitride layer and the n-type gallium nitride layer, it is composed of a mixed crystal of GaN with one or more selected from the group consisting of GaN or AlN and InN having a smaller band gap than both layers. You may have an active layer at least. The active layer has a double heterojunction structure with a p-type layer and an n-type layer, and the thinned structure of the active layer corresponds to a light emitting device having a quantum well structure which is an embodiment of a pn junction, and has a luminous efficiency. Can be further increased. The active layer may be made of a mixed crystal of GaN having one or more selected from the group consisting of GaN or AlN and InN having a smaller band gap than either one of the two layers. Even in such a single heterojunction, the luminous efficiency can be further increased. The gallium nitride buffer layer may be made of non-doped GaN, n-type or p-type doped GaN, and selected from the group consisting of AlN, InN, or GaN, AlN, and InN having a close lattice constant. It may be mixed with one or more kinds of crystals.
　もっとも、発光機能層１４は窒化ガリウム（ＧａＮ）系材料、酸化亜鉛（ＺｎＯ）系材料、窒化アルミニウム（ＡｌＮ）系材料から選ばれる複数の材料系で構成してもよい。例えば窒化ガリウム自立基板１２上にｐ型窒化ガリウム層、ｎ型酸化亜鉛層を成長させてもよく、ｐ型窒化ガリウム層とｎ型酸化亜鉛層の積層順序は逆であってもよい。窒化ガリウム自立基板１２を発光機能層１４の一部として用いる場合は、ｎ型又はｐ型の酸化亜鉛層を形成してもよい。ｐ型酸化亜鉛層に使用されるｐ型ドーパントの好ましい例としては、窒素（Ｎ）、リン（Ｐ）、砒素（Ａｓ）、カーボン（Ｃ）、リチウム（Ｌｉ）、ナトリウム（Ｎａ）、カリウム（Ｋ）、銀（Ａｇ）及び銅（Ｃｕ）からなる群から選択される１種以上が挙げられる。また、ｎ型酸化亜鉛層に使用されるｎ型ドーパントの好ましい例としては、アルミニウム（Ａｌ）、ガリウム（Ｇａ）、インジウム（Ｉｎ）、硼素（Ｂ）、フッ素（Ｆ）、塩素（Ｃｌ）、臭素（Ｂｒ）、ヨウ素（Ｉ）及びシリコン（Ｓｉ）からなる群から選択される１種以上が挙げられる。 However, the light emitting functional layer 14 may be composed of a plurality of material systems selected from gallium nitride (GaN) -based materials, zinc oxide (ZnO) -based materials, and aluminum nitride (AlN) -based materials. For example, a p-type gallium nitride layer and an n-type zinc oxide layer may be grown on the gallium nitride free-standing substrate 12, and the stacking order of the p-type gallium nitride layer and the n-type zinc oxide layer may be reversed. When the gallium nitride free-standing substrate 12 is used as a part of the light emitting functional layer 14, an n-type or p-type zinc oxide layer may be formed. Preferable examples of the p-type dopant used for the p-type zinc oxide layer include nitrogen (N), phosphorus (P), arsenic (As), carbon (C), lithium (Li), sodium (Na), potassium ( K), one or more selected from the group consisting of silver (Ag) and copper (Cu). Preferred examples of the n-type dopant used for the n-type zinc oxide layer include aluminum (Al), gallium (Ga), indium (In), boron (B), fluorine (F), chlorine (Cl), One or more selected from the group consisting of bromine (Br), iodine (I), and silicon (Si) may be mentioned.
　発光機能層１４及びバッファ層の成膜方法は、窒化ガリウム自立基板の結晶方位に概ね倣って成長する方法であれば特に限定されないが、ＭＯＣＶＤ、ＭＢＥ、ＨＶＰＥ、スパッタリング等の気相法、Ｎａフラックス法、アモノサーマル法、水熱法、ゾルゲル法等の液相法、粉末の固相成長を利用した粉末法、及びこれらの組み合わせが好ましく例示される。例えばＭＯＣＶＤ法を用いて窒化ガリウム系材料からなる発光機能層１４を作製する場合においては、少なくともガリウム（Ｇａ）を含む有機金属ガス（例えばトリメチルガリウム）と窒素（Ｎ）を少なくとも含むガス（例えばアンモニア）を原料として基板上にフローさせ、水素、窒素又はその両方を含む雰囲気等において３００～１２００℃程度の温度範囲で成長させてもよい。この場合、バンドギャップ制御のためインジウム（Ｉｎ）、アルミニウム（Ａｌ）、ｎ型及びｐ型ドーパントとしてシリコン（Ｓｉ）及びマグネシウム（Ｍｇ）を含む有機金属ガス（例えばトリメチルインジウム、トリメチルアルミニウム、モノシラン、ジシラン、ビス－シクロペンタジエニルマグネシウム）を適宜導入して成膜を行ってもよい。 The film formation method of the light emitting functional layer 14 and the buffer layer is not particularly limited as long as it grows substantially following the crystal orientation of the gallium nitride free-standing substrate, but a vapor phase method such as MOCVD, MBE, HVPE, sputtering, Na flux, etc. Preferred examples include a liquid phase method such as a method, an ammonothermal method, a hydrothermal method, a sol-gel method, a powder method utilizing solid phase growth of powder, and a combination thereof. For example, in the case where the light emitting functional layer 14 made of a gallium nitride-based material is manufactured using the MOCVD method, a gas (for example, ammonia) containing at least an organometallic gas (for example, trimethyl gallium) containing gallium (Ga) and nitrogen (N). ) On the substrate as a raw material and grown in a temperature range of about 300 to 1200 ° 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.
　また、発光機能層１４及びバッファ層に窒化ガリウム系以外の材料を用いる場合は、窒化ガリウム自立基板上に種結晶層を成膜してもよい。種結晶層の成膜方法や材質に限定は無いが、結晶方位に概ね倣った結晶成長を促すものであればよい。例えば、酸化亜鉛系材料を発光機能層１４の一部又は全てに用いる場合、ＭＯＣＶＤ法、ＭＢＥ法、ＨＶＰＥ法、スパッタリング法等の気相成長法を用いて極薄い酸化亜鉛の種結晶を作製してもよい。 Further, when a material other than gallium nitride is used for the light emitting functional layer 14 and the buffer layer, a seed crystal layer may be formed on the gallium nitride free-standing substrate. There are no limitations on the method and material for forming the seed crystal layer, but any method may be used as long as it promotes crystal growth substantially following the crystal orientation. For example, when a zinc oxide-based material is used for a part or all of the light emitting functional layer 14, an ultrathin zinc oxide seed crystal is prepared by vapor phase growth methods such as MOCVD, MBE, HVPE, and sputtering. May be.
　発光機能層１４の上に電極層１６及び／又は蛍光体層をさらに備えていてもよい。上述のとおり、導電性を有する窒化ガリウム自立基板１２を用いた発光素子は縦型構造を採ることができるため、図１に示されるように窒化ガリウム自立基板１２の裏面にも電極層１８を設けることができるが、窒化ガリウム自立基板１２を電極そのものとして使用してもよく、その場合には窒化ガリウム自立基板１２にはｎ型ドーパントを添加されているのが好ましい。電極層１６，１８は公知の電極材料で構成すればよいが、発光機能層１４上の電極層１６は、ＩＴＯ等の透明導電膜、又は格子構造等の開口率が高い金属電極とすれば、発光機能層１４で発生した光の取り出し効率を上げられる点で好ましい。 The electrode layer 16 and / or the phosphor layer may be further provided on the light emitting functional layer 14. As described above, since the light-emitting element using the conductive gallium nitride free-standing substrate 12 can have a vertical structure, an electrode layer 18 is provided on the back surface of the gallium nitride free-standing substrate 12 as shown in FIG. However, the gallium nitride free-standing substrate 12 may be used as the electrode itself. In that case, it is preferable that an n-type dopant is added to the gallium nitride free-standing substrate 12. The electrode layers 16 and 18 may be made of a known electrode material. However, if the electrode layer 16 on the light emitting functional layer 14 is a transparent conductive film such as ITO, or a metal electrode having a high aperture ratio such as a lattice structure, This is preferable in that the extraction efficiency of light generated in the light emitting functional layer 14 can be increased.
　発光機能層１４が紫外光を放出可能なものである場合には、紫外光を可視光に変換するための蛍光体層を電極層の外側に設けてもよい。蛍光体層は紫外線を可視光に変換可能な公知の蛍光成分を含む層であればよく特に限定されない。例えば、紫外光により励起されて青色光を発光する蛍光成分と、紫外光により励起されて青～緑色光を発光する蛍光成分と、紫外光により励起されて赤色光を発光する蛍光成分とを混在させて、混合色として白色光を得るような構成とするのが好ましい。そのような蛍光成分の好ましい組み合わせとしては、（Ｃａ，Ｓｒ）５（ＰＯ４）３Ｃｌ：Ｅｕ、ＢａＭｇＡｌ１０Ｏ１７：Ｅｕ、及びＭｎ、Ｙ２Ｏ３Ｓ：Ｅｕが挙げられ、これらの成分をシリコーン樹脂等の樹脂中に分散させて蛍光体層を形成するのが好ましい。このような蛍光成分は上記例示物質に限定されるものではなく、他の紫外光励起蛍光体、例えばイットリウム・アルミニウム・ガーネット（ＹＡＧ）やシリケート系蛍光体、酸窒化物系蛍光体等の組み合わせでもよい。 When the light emitting functional layer 14 can emit ultraviolet light, a phosphor layer for converting ultraviolet light into visible light may be provided outside the electrode layer. The phosphor layer is not particularly limited as long as it includes a known fluorescent component capable of converting ultraviolet light into visible light. For example, a fluorescent component that emits blue light when excited by ultraviolet light, a fluorescent component that emits blue to green light when excited by ultraviolet light, and a fluorescent component that emits red light when excited by ultraviolet light are mixed. It is preferable that the white color is obtained as a mixed color. Preferred combinations of such fluorescent components include (Ca, Sr) 5 (PO 4 ) 3 Cl: Eu, BaMgAl 10 O 17 : Eu, and Mn, Y 2 O 3 S: Eu, and these components Is preferably dispersed in a resin such as a silicone resin to form a phosphor layer. Such a fluorescent component is not limited to the above-exemplified substances, but may be a combination of other ultraviolet light-excited phosphors such as yttrium aluminum garnet (YAG), silicate phosphors, and oxynitride phosphors. .
　一方、発光機能層１４が青色光を放出可能なものである場合には、青色光を黄色光に変換するための蛍光体層を電極層の外側に設けてもよい。蛍光体層は青色光を黄色光に変換可能な公知の蛍光成分を含む層であればよく特に限定されない。例えばＹＡＧ等の黄色発光する蛍光体との組み合わせたものとしてもよい。このようにすることで、蛍光体層を透過した青色発光と蛍光体からの黄色発光は補色関係にあるため、擬似的な白色光源とすることができる。なお、蛍光体層は、青色を黄色に変換する蛍光成分と、紫外光を可視光に変換するための蛍光成分との両方を備えることで、紫外光の可視光への変換と青色光の黄色光への変換との両方を行う構成としてもよい。 On the other hand, when the light emitting functional layer 14 is capable of emitting blue light, a phosphor layer for converting blue light into yellow light may be provided outside the electrode layer. The phosphor layer is not particularly limited as long as it includes a known fluorescent component capable of converting blue light into yellow light. For example, it may be combined with a phosphor emitting yellow light such as YAG. By doing in this way, since blue light emission which permeate | transmitted the fluorescent substance layer and yellow light emission from a fluorescent substance have a complementary color relationship, it can be set as a pseudo white light source. The phosphor layer includes both a fluorescent component that converts blue light into yellow and a fluorescent component that converts ultraviolet light into visible light, thereby converting ultraviolet light into visible light and blue light yellow. It is good also as a structure which performs both conversion to light.
　用途
　本発明の窒化ガリウム自立基板は、上述した発光素子のみならず、各種電子デバイス、パワーデバイス、受光素子、太陽電池用ウェハー等の種々の用途に好ましく利用することができる。 Applications The gallium nitride free-standing substrate of the present invention can be preferably used for various applications such as various electronic devices, power devices, light receiving elements, solar cell wafers as well as the above-described light emitting elements.
　本発明を以下の例によってさらに具体的に説明する。 The present invention will be described more specifically with reference to the following examples.
　例１
（１）ｃ面配向アルミナ焼結体の作製
　原料として、板状アルミナ粉末（キンセイマテック株式会社製、グレード００６１０）を用意した。板状アルミナ粒子１００重量部に対し、バインダー（ポリビニルブチラール：品番ＢＭ－２、積水化学工業株式会社製）７重量部と、可塑剤（ＤＯＰ：ジ（２－エチルヘキシル）フタレート、黒金化成株式会社製）３．５重量部と、分散剤（レオドールＳＰ－Ｏ３０、花王株式会社製）２重量部と、分散媒（２－エチルヘキサノール）を混合した。分散媒の量は、スラリー粘度が２００００ｃＰとなるように調整した。上記のようにして調製されたスラリーを、ドクターブレード法によって、ＰＥＴフィルムの上に、乾燥後の厚さが２０μｍとなるように、シート状に成形した。得られたテープを口径５０．８ｍｍ（２インチ）の円形に切断した後１５０枚積層し、厚さ１０ｍｍのＡｌ板の上に載置した後、真空パックを行った。この真空パックを８５℃の温水中で、１００ｋｇｆ／ｃｍ２の圧力にて静水圧プレスを行い、円盤状の成形体を得た。 Example 1
(1) Production of c-plane oriented alumina sintered body As a raw material, a plate-like alumina powder (manufactured by Kinsei Matech Co., Ltd., grade 0700) was prepared. 7 parts by weight of binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.) and plasticizer (DOP: di (2-ethylhexyl) phthalate, black metal chemicals 3.5 parts by weight), 2 parts by weight of a dispersant (Rheidol 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 20000 cP. The slurry prepared as described above was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 20 μm. The obtained tape was cut into a circular shape having a diameter of 50.8 mm (2 inches), 150 sheets were laminated, placed on an Al plate having a thickness of 10 mm, and then vacuum-packed. This vacuum pack was hydrostatically pressed in warm water at 85 ° C. at a pressure of 100 kgf / cm 2 to obtain a disk-shaped molded body.
　得られた成形体を脱脂炉中に配置し、６００℃で１０時間の条件で脱脂を行った。得られた脱脂体を黒鉛製の型を用い、ホットプレスにて窒素中１６００℃で４時間、面圧２００ｋｇｆ／ｃｍ２の条件で焼成した。得られた焼結体を熱間当方圧加圧法（ＨＩＰ）にてアルゴン中１７００℃で２時間、ガス圧１５００ｋｇｆ／ｃｍ２の条件で再度焼成した。 The obtained molded body was placed in a degreasing furnace and degreased at 600 ° C. for 10 hours. The obtained degreased body was fired in a nitrogen atmosphere at 1600 ° C. for 4 hours under a surface pressure of 200 kgf / cm 2 using a graphite mold. The obtained sintered body was fired again at 1700 ° C. for 2 hours in argon at a gas pressure of 1500 kgf / cm 2 by a hot one-pressure method (HIP).
　このようにして得た焼結体をセラミックスの定盤に固定し、砥石を用いて＃２０００まで研削して板面を平坦にした。次いで、ダイヤモンド砥粒を用いたラップ加工により、板面を平滑化し、口径５０．８ｍｍ（２インチ）、厚さ１ｍｍの配向アルミナ焼結体を配向アルミナ基板として得た。砥粒のサイズを３μｍから０．５μｍまで段階的に小さくしつつ、平坦性を高めた。加工後の平均粗さＲａは１ｎｍであった。 The sintered body thus obtained was fixed to a ceramic surface plate and ground to # 2000 using a grindstone to flatten the plate surface. Next, the surface of the plate was smoothed by lapping using diamond abrasive grains, and an oriented alumina sintered body having a diameter of 50.8 mm (2 inches) and a thickness of 1 mm was obtained as an oriented alumina substrate. The flatness was improved while gradually reducing the size of the abrasive grains from 3 μm to 0.5 μm. The average roughness Ra after processing was 1 nm.
（２）配向アルミナ基板の評価
（配向度の評価）
　得られた配向アルミナ基板の配向度を確認するため、ＸＲＤにより本実験例における測定対象とする結晶面であるｃ面の配向度を測定した。ＸＲＤ装置（株式会社リガク製、ＲＩＮＴ－ＴＴＲ　ＩＩＩ）を用い、配向アルミナ基板の板面に対してＸ線を照射したときの２θ＝２０～７０°の範囲でＸＲＤプロファイルを測定した。ｃ面配向度は、以下の式により算出した。この結果、本実験例におけるｃ面配向度の値は９７％であった。
Figure JPOXMLDOC01-appb-M000002
 (2) Evaluation of oriented alumina substrate (Evaluation of degree of orientation)
In order to confirm the degree of orientation of the obtained oriented alumina substrate, the degree of orientation of the c-plane, which is the crystal plane to be measured in this experimental example, was measured by XRD. Using an XRD apparatus (RINT-TTR III, manufactured by Rigaku Corporation), the XRD profile was measured in the range of 2θ = 20 to 70 ° when X-ray was irradiated onto the plate surface of the oriented alumina substrate. The c-plane orientation degree was calculated by the following formula. As a result, the value of the c-plane orientation degree in this experimental example was 97%.
Figure JPOXMLDOC01-appb-M000002
（焼結体粒子の粒径評価）
　配向アルミナ基板の焼結体粒子について、板面の平均粒径を以下の方法により測定した。得られた配向アルミナ基板の板面を研磨し、１５５０℃で４５分間サーマルエッチングを行った後、走査電子顕微鏡にて画像を撮影した。視野範囲は、得られる画像の対角線に直線を引いた場合に、いずれの直線も１０個から３０個の粒子と交わるような直線が引けるような視野範囲とした。得られた画像の対角線に引いた２本の直線において、直線が交わる全ての粒子に対し、個々の粒子の内側の線分の長さを平均したものに１．５を乗じた値を板面の平均粒径とした。この結果、板面の平均粒径は１００μｍであった。 (Evaluation of sintered particle size)
About the sintered compact particle | grains of the orientation alumina substrate, the average particle diameter of the plate surface was measured with the following method. The plate surface of the obtained oriented alumina substrate was polished and subjected to thermal etching at 1550 ° C. for 45 minutes, and then an image was taken with a scanning electron microscope. The visual field range was such that a straight line intersecting 10 to 30 particles could be drawn when a straight line was drawn on the diagonal line of the obtained image. In the two straight lines drawn on the diagonal line of the obtained image, the value obtained by multiplying the average of the length of the inner line segment of each particle by 1.5 for all the particles intersecting the straight line Average particle diameter. As a result, the average particle size of the plate surface was 100 μm.
（３）Ｇｅドープ窒化ガリウム自立基板の作製
（３ａ）種結晶層の成膜
　次に、加工した配向アルミナ基板の上に、ＭＯＣＶＤ法を用いて種結晶層を形成した。具体的には、５３０℃にて低温ＧａＮ層を４０ｎｍ堆積させた後に、１０５０℃にて厚さ３μｍのＧａＮ膜を積層させて種結晶基板を得た。 (3) Production of Ge-doped gallium nitride free-standing substrate (3a) Formation of seed crystal layer Next, a seed crystal layer was formed on the processed oriented alumina substrate by MOCVD. Specifically, after depositing a low-temperature GaN layer of 40 nm at 530 ° C., a GaN film having a thickness of 3 μm was laminated at 1050 ° C. to obtain a seed crystal substrate.
（３ｂ）Ｎａフラックス法によるＧｅドープＧａＮ層の成膜
　上記工程で作製した種結晶基板を、内径８０ｍｍ、高さ４５ｍｍの円筒平底のアルミナ坩堝の底部分に設置し、次いで融液組成物をグローブボックス内で坩堝内に充填した。融液組成物の組成は以下のとおりである。
・金属Ｇａ：６０ｇ
・金属Ｎａ：６０ｇ
・四塩化ゲルマニウム：１．８５ｇ (3b) Formation of Ge-doped GaN layer by Na flux method The seed crystal substrate prepared in the above step is placed on the bottom of a cylindrical flat bottom alumina crucible having an inner diameter of 80 mm and a height of 45 mm, and then the melt composition is gloved The crucible was filled in the box. The composition of the melt composition is as follows.
・ Metal Ga: 60g
・ Metal Na: 60g
・ Germanium tetrachloride: 1.85 g
　このアルミナ坩堝を耐熱金属製の容器に入れて密閉した後、結晶育成炉の回転が可能な台上に設置した。窒素雰囲気中で８７０℃、４．０ＭＰａまで昇温加圧後、５０時間保持しつつ溶液を回転することで、撹拌しながら窒化ガリウム結晶を成長させた。結晶成長終了後、３時間かけて室温まで徐冷し、結晶育成炉から育成容器を取り出した。エタノールを用いて、坩堝内に残った融液組成物を除去し、窒化ガリウム結晶が成長した試料を回収した。得られた試料は、５０．８ｍｍ（２インチ）の種結晶基板の全面上にＧｅドープ窒化ガリウム結晶が成長しており、結晶の厚さは約０．５ｍｍであった。クラックは確認されなかった。 After placing this alumina crucible in a refractory metal container and sealing it, the alumina crucible was placed on a table that can rotate the crystal growth furnace. The gallium nitride crystal was grown with stirring by rotating the solution while maintaining the temperature for 50 hours after heating and pressurizing to 870 ° C. and 4.0 MPa in a nitrogen atmosphere. After completion of the crystal growth, it was gradually cooled to room temperature over 3 hours, and the growth vessel was taken out of the crystal growth furnace. The melt composition remaining in the crucible was removed using ethanol, and the sample on which the gallium nitride crystal was grown was collected. In the obtained sample, a Ge-doped gallium nitride crystal was grown on the entire surface of a 50.8 mm (2 inch) seed crystal substrate, and the thickness of the crystal was about 0.5 mm. Cracks were not confirmed.
　こうして得られた試料の配向アルミナ基板部を砥石による研削加工により除去して、Ｇｅドープ窒化ガリウムの単体を得た。このＧｅドープ窒化ガリウム結晶の板面を＃６００及び＃２０００の砥石によって研削して板面を平坦にし、次いでダイヤモンド砥粒を用いたラップ加工により、板面を平滑化し、厚さ約３００μｍのＧｅドープ窒化ガリウム自立基板を得た。なお、平滑化加工においては、砥粒のサイズを３μｍから０．１μｍまで段階的に小さくしつつ、平坦性を高めた。窒化ガリウム自立基板表面の加工後の平均粗さＲａは０．２ｎｍであった。 The oriented alumina substrate portion of the sample thus obtained was removed by grinding with a grindstone to obtain a Ge-doped gallium nitride simple substance. The plate surface of the Ge-doped gallium nitride crystal is ground with a # 600 and # 2000 grindstone to flatten the plate surface, and then smoothed by lapping using diamond abrasive grains to form a Ge surface having a thickness of about 300 μm. A doped gallium nitride free-standing substrate was obtained. In the smoothing process, the flatness was improved while gradually reducing the size of the abrasive grains from 3 μm to 0.1 μm. The average roughness Ra after processing of the surface of the gallium nitride free-standing substrate was 0.2 nm.
　なお、本例では、ゲルマニウムドーピングしてｎ型半導体としたものを作製したが、用途、構造によっては異なる元素をドーピングしてもよく、ノンドープとしてもよい。 In this example, an n-type semiconductor was formed by doping germanium, but different elements may be doped depending on the application and structure, or non-doped.
（体積抵抗率の評価）
　ホール効果測定装置を用い、窒化ガリウム自立基板の面内の体積抵抗率を測定した。その結果、体積抵抗率は１×１０－２Ω・ｃｍであった。 (Evaluation of volume resistivity)
The in-plane volume resistivity of the gallium nitride free-standing substrate was measured using a Hall effect measuring device. As a result, the volume resistivity was 1 × 10 −2 Ω · cm.
（窒化ガリウム自立基板の断面平均径の評価）
　窒化ガリウム自立基板の最表面におけるＧａＮ単結晶粒子の断面平均径を測定するため、自立基板の表面を走査電子顕微鏡にて画像を撮影した。視野範囲は、得られる画像の対角線に直線を引いた場合に、１０個から３０個の柱状組織と交わるような直線が引けるような視野範囲とした。得られた画像の対角線に２本の直線を任意に引き、直線が交わる全ての粒子に対し、個々の粒子の内側の線分の長さを平均したものに１．５を乗じた値を、窒化ガリウム自立基板の最表面におけるＧａＮ単結晶粒子の断面平均径とした。この結果、断面平均径は約１００μｍであった。なお、本例では表面の走査顕微鏡像で明瞭に界面を判別できたが、サーマルエッチングやケミカルエッチングによって界面を際立たせる処理を施した後に上記の評価を行ってもよい。 (Evaluation of average cross-sectional diameter of gallium nitride free-standing substrate)
In order to measure the cross-sectional average diameter of the GaN single crystal particles on the outermost surface of the gallium nitride free-standing substrate, an image of the surface of the free-standing substrate was taken with a scanning electron microscope. The visual field range was such that a straight line intersecting with 10 to 30 columnar structures could be drawn when a straight line was drawn on the diagonal line of the obtained image. Two straight lines are arbitrarily drawn on the diagonal line of the obtained image, and the 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 lines, The average cross-sectional diameter of the GaN single crystal particles on the outermost surface of the gallium nitride free-standing substrate was used. As a result, the average cross-sectional diameter was about 100 μm. In this example, the interface can be clearly discriminated by the scanning microscope image of the surface. However, the above evaluation may be performed after performing a process of making the interface stand out by thermal etching or chemical etching.
（４）Ｇｅドープ窒化ガリウム自立基板を用いた発光素子の作製
（４ａ）ＭＯＣＶＤ法による発光機能層の成膜
　ＭＯＣＶＤ法を用いて、窒化ガリウム自立基板上にｎ型層として１０５０℃でＳｉ原子濃度が５×１０１８／ｃｍ３になるようにドーピングしたｎ－ＧａＮ層を１μｍ堆積した。次に発光層として７５０℃で多重量子井戸層を堆積した。具体的にはＩｎＧａＮによる２．５ｎｍの井戸層を５層、ＧａＮによる１０ｎｍの障壁層を６層にて交互に積層した。次にｐ型層として９５０℃でＭｇ原子濃度が１×１０１９／ｃｍ３になるようにドーピングしたｐ－ＧａＮを２００ｎｍ堆積した。その後、ＭＯＣＶＤ装置から取り出し、ｐ型層のＭｇイオンの活性化処理として、窒素雰囲気中で８００℃の熱処理を１０分間行った。発光機能層の再表面における単結晶粒子の断面平均径を測定するため、発光機能層の表面を走査電子顕微鏡にて画像を撮影した。視野範囲は、得られる画像の対角線に直線を引いた場合に、１０個から３０個の柱状組織と交わるような直線が引けるような視野範囲とした。得られた画像の対角線に２本の直線を任意に引き、直線が交わる全ての粒子に対し、個々の粒子の内側の線分の長さを平均したものに１．５を乗じた値を、発光機能層の最表面における単結晶粒子の断面平均径とした。この結果、断面平均径は約１００μｍであった。 (4) Fabrication of light-emitting element using Ge-doped gallium nitride free-standing substrate (4a) Formation of light-emitting functional layer by MOCVD method Si atom concentration at 1050 ° C. as an n-type layer on a gallium nitride free-standing substrate using MOCVD method An n-GaN layer doped to have a thickness of 5 × 10 18 / cm 3 was deposited by 1 μm. Next, a multiple quantum well layer was deposited at 750 ° C. as a light emitting layer. Specifically, five 2.5 nm well layers made of InGaN and six 10 nm barrier layers made of GaN were alternately stacked. Next, 200 nm of p-GaN doped so that the Mg atom concentration becomes 1 × 10 19 / cm 3 at 950 ° C. was deposited as a p-type layer. After that, it was taken out from the MOCVD apparatus and subjected to a heat treatment at 800 ° C. for 10 minutes in a nitrogen atmosphere as an activation process for Mg ions in the p-type layer. In order to measure the cross-sectional average diameter of the single crystal particles on the resurface of the light emitting functional layer, an image of the surface of the light emitting functional layer was taken with a scanning electron microscope. The visual field range was such that a straight line intersecting with 10 to 30 columnar structures could be drawn when a straight line was drawn on the diagonal line of the obtained image. Two straight lines are arbitrarily drawn on the diagonal line of the obtained image, and the 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 lines It was set as the cross-sectional average diameter of the single crystal particle in the outermost surface of a light emitting functional layer. As a result, the average cross-sectional diameter was about 100 μm.
（４ｂ）発光素子の作製
　フォトリソグラフィープロセスと真空蒸着法とを用いて、窒化ガリウム自立基板のｎ－ＧａＮ層及びｐ－ＧａＮ層とは反対側の面にカソード電極としてのＴｉ／Ａｌ／Ｎｉ／Ａｕ膜をそれぞれ１５ｎｍ、７０ｎｍ、１２ｎｍ、６０ｎｍの厚みでパターニングした。その後、オーム性接触特性を良好なものとするために、窒素雰囲気中での７００℃の熱処理を３０秒間行った。さらに、フォトリソグラフィープロセスと真空蒸着法とを用いて、ｐ型層に透光性アノード電極としてＮｉ／Ａｕ膜をそれぞれ６ｎｍ、１２ｎｍの厚みにパターニングした。その後、オーム性接触特性を良好なものとするために窒素雰囲気中で５００℃の熱処理を３０秒間行った。さらに、フォトリソグラフィープロセスと真空蒸着法とを用いて、透光性アノード電極としてのＮｉ／Ａｕ膜の上面の一部領域に、アノード電極パッドとなるＮｉ／Ａｕ膜をそれぞれ５ｎｍ、６０ｎｍの厚みにパターニングした。こうして得られたウェハーを切断してチップ化し、さらにリードフレームに実装して、縦型構造の発光素子を得た。 (4b) Fabrication of light-emitting element Using a photolithography process and a vacuum deposition method, Ti / Al / Ni / as a cathode electrode is formed on the surface of the gallium nitride free-standing substrate opposite to the n-GaN layer and the p-GaN layer. The Au film was patterned with a thickness of 15 nm, 70 nm, 12 nm, and 60 nm, respectively. Thereafter, a heat treatment at 700 ° C. in a nitrogen atmosphere was performed for 30 seconds in order to improve the ohmic contact characteristics. Furthermore, using a photolithography process and a vacuum deposition method, a Ni / Au film was patterned on the p-type layer as a light-transmitting anode electrode to a thickness of 6 nm and 12 nm, respectively. Thereafter, a heat treatment at 500 ° C. was performed for 30 seconds in a nitrogen atmosphere in order to improve the ohmic contact characteristics. Further, by using a photolithography process and a vacuum deposition method, a Ni / Au film serving as an anode electrode pad is formed to a thickness of 5 nm and 60 nm on a partial region of the upper surface of the Ni / Au film serving as a light-transmitting anode electrode, respectively. Patterned. The wafer thus obtained was cut into chips and further mounted on a lead frame to obtain a light emitting device having a vertical structure.
（４ｃ）発光素子の評価
　カソード電極とアノード電極間に通電し、Ｉ－Ｖ測定を行ったところ、整流性が確認された。また、順方向の電流を流したところ、波長４５０ｎｍの発光が確認された。 (4c) Evaluation of Light-Emitting Element When conducting current measurement between the cathode electrode and the anode electrode and performing IV measurement, rectification was confirmed. Further, when a forward current was passed, light emission with a wavelength of 450 nm was confirmed.
　例２
（１）Ｍｇドープ窒化ガリウム自立基板の作製
　例１の（１）～（３）と同様の方法で配向アルミナ基板の上に厚さ３μｍのＧａＮ膜を積層させた種結晶基板を作製した。この種結晶基板上に、融液組成物を下記組成としたこと以外は例１の（３ｂ）と同様にしてＭｇドープＧａＮ膜を成膜した。
・金属Ｇａ：６０ｇ
・金属Ｎａ：６０ｇ
・金属Ｍｇ：０．０２ｇ Example 2
(1) Production of Mg-doped gallium nitride free-standing substrate A seed crystal substrate was produced by laminating a GaN film having a thickness of 3 μm on an oriented alumina substrate in the same manner as in (1) to (3) of Example 1. An Mg-doped GaN film was formed on this seed crystal substrate in the same manner as (3b) of Example 1 except that the melt composition was changed to the following composition.
・ Metal Ga: 60g
・ Metal Na: 60g
・ Metal Mg: 0.02g
　得られた試料は、５０．８ｍｍ（２インチ）の種結晶基板の全面上にＭｇドープ窒化ガリウム結晶が成長しており、結晶の厚さは約０．５ｍｍであった。クラックは確認されなかった。また、得られた窒化ガリウム中のＭｇ濃度は４×１０１９／ｃｍ３であり、ホール効果測定装置を用いて測定したホール濃度は１×１０１８／ｃｍ３であった。こうして得られた試料の配向アルミナ基板部を砥石による研削加工により除去して、Ｍｇドープ窒化ガリウムの単体を得た。このＭｇドープ窒化ガリウム結晶の板面を＃６００及び＃２０００の砥石によって研削して板面を平坦にし、次いでダイヤモンド砥粒を用いたラップ加工により、板面を平滑化し、厚さ約１５０μｍのＭｇドープ窒化ガリウム自立基板を得た。なお、平滑化加工においては、砥粒のサイズを３μｍから０．１μｍまで段階的に小さくしつつ、平坦性を高めた。Ｍｇドープ窒化ガリウム自立基板表面の加工後の平均粗さＲａは０．２ｎｍであった。なお、例１の（３ｂ）と同様の方法でＭｇドープ窒化ガリウム自立基板の断面平均径を測定したところ、断面平均径は約１００μｍであった。 In the obtained sample, an Mg-doped gallium nitride crystal was grown on the entire surface of a 50.8 mm (2 inch) seed crystal substrate, and the thickness of the crystal was about 0.5 mm. Cracks were not confirmed. Moreover, Mg density | concentration in the obtained gallium nitride was 4 * 10 < 19 > / cm < 3 >, and the hole density | concentration measured using the Hall effect measuring apparatus was 1 * 10 < 18 > / cm < 3 >. The oriented alumina substrate portion of the sample thus obtained was removed by grinding with a grindstone to obtain a simple Mg-doped gallium nitride. The plate surface of this Mg-doped gallium nitride crystal is ground with a # 600 and # 2000 grindstone to flatten the plate surface, and then smoothed by lapping using diamond abrasive grains, and a Mg surface having a thickness of about 150 μm. A doped gallium nitride free-standing substrate was obtained. In the smoothing process, the flatness was improved while gradually reducing the size of the abrasive grains from 3 μm to 0.1 μm. The average roughness Ra after processing of the surface of the Mg-doped gallium nitride free-standing substrate was 0.2 nm. In addition, when the cross-sectional average diameter of the Mg-doped gallium nitride free-standing substrate was measured by the same method as in Example 1 (3b), the cross-sectional average diameter was about 100 μm.
（２）Ｍｇドープ窒化ガリウム自立基板を用いた発光素子の作製
（２ａ）ＭＯＣＶＤ法によるｐ型層の成膜
　ＭＯＣＶＤ法を用いて、基板上にｐ型層として９５０℃でＭｇ原子濃度が１×１０１９／ｃｍ３になるようにドーピングしたｐ－ＧａＮを２００ｎｍ堆積した。その後、ＭＯＣＶＤ装置から取り出し、ｐ型層のＭｇイオンの活性化処理として、窒素雰囲気中で８００℃の熱処理を１０分間行った。 (2) Fabrication of light-emitting element using Mg-doped gallium nitride free-standing substrate (2a) Formation of p-type layer by MOCVD method Using MOCVD method, Mg atom concentration is 1 × as a p-type layer on a substrate at 950 ° C. 200 nm of p-GaN doped so as to be 10 19 / cm 3 was deposited. After that, it was taken out from the MOCVD apparatus and subjected to a heat treatment at 800 ° C. for 10 minutes in a nitrogen atmosphere as an activation process for Mg ions in the p-type layer.
（２ｂ）ＲＳ－ＭＢＥ法及び水熱法によるｎ型層の成膜
（２ｂ－１）ＲＳ－ＭＢＥ法による種結晶層の成膜
　ＲＳ－ＭＢＥ（ラジカルソース分子線成長）装置にて、金属材料である亜鉛（Ｚｎ）とアルミニウム（Ａｌ）をクヌーセンセルで照射し、ｐ型層上に供給した。ガス材料である酸素（Ｏ）は、ＲＦラジカル発生装置にてそれぞれＯ２ガスを原料とし、酸素ラジカルとして供給した。各種原料の純度はＺｎが７Ｎ、Ｏ２が６Ｎのものを用いた。基板は抵抗加熱ヒーターを用いて７００℃に加熱し、膜中のＡｌ濃度が２×１０１８／ｃｍ３となり、ＺｎとＯ原子濃度の比が１対１となるように各種ガスソースのフラックスを制御しながら厚さ２０ｎｍのＡｌがドープされたｎ－ＺｎＯからなる種結晶層を成膜した。 (2b) Formation of n-type layer by RS-MBE method and hydrothermal method (2b-1) Formation of seed crystal layer by RS-MBE method Metal material with RS-MBE (radical source molecular beam growth) apparatus Zinc (Zn) and aluminum (Al) were irradiated by a Knudsen cell and supplied onto the p-type layer. Oxygen (O), which is a gas material, was supplied as oxygen radicals using O 2 gas as a raw material in an RF radical generator. The purity of various raw materials was 7N for Zn and 6N for O 2 . The substrate is heated to 700 ° C. using a resistance heater, and the flux of various gas sources is adjusted so that the Al concentration in the film is 2 × 10 18 / cm 3 and the ratio of Zn and O atom concentration is 1: 1. A seed crystal layer made of n-ZnO doped with Al having a thickness of 20 nm was formed while being controlled.
（２ｂ－２）水熱法によるｎ型層の成膜
　硝酸亜鉛を純水中に０．１Ｍとなるように溶解させて溶液Ａとした。次に１Ｍのアンモニア水を準備し、溶液Ｂとした。次に硫酸アルミニウムを純水中に０．１Ｍとなるように溶解させて溶液Ｃとした。これらの溶液を容積比で、溶液Ａ：溶液Ｂ：溶液Ｃ＝１：１：０．０１となるように混合及び撹拌して、育成用水溶液を得た。 (2b-2) Formation of n-type layer by hydrothermal method Zinc nitrate was dissolved in pure water to a concentration of 0.1 M to obtain a solution A. Next, 1M ammonia water was prepared to prepare a solution B. Next, aluminum sulfate was dissolved in pure water to a concentration of 0.1 M to obtain a solution C. These solutions were mixed and stirred at a volume ratio of solution A: solution B: solution C = 1: 1: 0.01 to obtain a growing aqueous solution.
　種結晶層を成膜した窒化ガリウム自立基板を懸垂させて育成用水溶液中１リットル中に設置した。次に、防水加工を施したセラミックス製ヒーターとマグネチックスターラーを水溶液中に設置し、オートクレーブに入れて２７０℃で３時間の水熱処理を行い、種結晶層上にＺｎＯ層を析出させた。ＺｎＯ層が析出した窒化ガリウム自立基板を純水洗浄した後、大気中５００℃でアニール処理を行い、厚さ約３μｍのＡｌがドープされたｎ－ＺｎＯ層を形成した。試料中に気孔やクラックは検出されず、テスターにてＺｎＯ層の導電性が確認された。また、例１の（４ａ）と同様の方法を用いて発光機能層の断面平均径を評価した結果、発光機能層の最表面における単結晶粒子の断面平均径は約１００μｍであった。 A gallium nitride free-standing substrate on which a seed crystal layer was formed was suspended and placed in 1 liter in an aqueous solution for growth. Next, a waterproof ceramic heater and a magnetic stirrer were placed in an aqueous solution, placed in an autoclave and subjected to hydrothermal treatment at 270 ° C. for 3 hours to deposit a ZnO layer on the seed crystal layer. The gallium nitride free-standing substrate on which the ZnO layer was deposited was washed with pure water and then annealed at 500 ° C. in the atmosphere to form an n-ZnO layer doped with Al having a thickness of about 3 μm. No pores or cracks were detected in the sample, and the conductivity of the ZnO layer was confirmed by a tester. Moreover, as a result of evaluating the cross-sectional average diameter of the light emitting functional layer using the same method as in (4a) of Example 1, the cross-sectional average diameter of the single crystal particles on the outermost surface of the light emitting functional layer was about 100 μm.
（２ｃ）発光素子の作製
　フォトリソグラフィープロセスと真空蒸着法とを用いて、ｎ型層にカソード電極としてＴｉ／Ａｌ／Ｎｉ／Ａｕ膜をそれぞれ１５ｎｍ、７０ｎｍ、１２ｎｍ、６０ｎｍの厚みでパターニングした。カソード電極のパターンは、電極が形成されていない箇所から光が取り出せるように開口部を有する形状とした。その後、オーム性接触特性を良好なものとするために、窒素雰囲気中での７００℃の熱処理を３０秒間行った。さらに、フォトリソグラフィープロセスと真空蒸着法とを用いて、窒化ガリウム自立基板のｐ－ＧａＮ層及びｎ－ＺｎＯ層とは反対側の面にアノード電極として、Ｎｉ／Ａｕ膜をそれぞれ５０ｎｍ、１００ｎｍの厚みにパターニングした。その後、オーム性接触特性を良好なものとするために窒素雰囲気中で５００℃の熱処理を３０秒間行った。こうして得られたウェハーを切断してチップ化し、さらにリードフレームに実装して、縦型構造の発光素子を得た。 (2c) Fabrication of light emitting device Using a photolithography process and a vacuum deposition method, a Ti / Al / Ni / Au film as a cathode electrode was patterned on the n-type layer with a thickness of 15 nm, 70 nm, 12 nm, and 60 nm, respectively. The cathode electrode pattern was shaped to have an opening so that light could be extracted from a location where no electrode was formed. Thereafter, a heat treatment at 700 ° C. in a nitrogen atmosphere was performed for 30 seconds in order to improve the ohmic contact characteristics. Further, by using a photolithography process and a vacuum deposition method, a Ni / Au film having a thickness of 50 nm and 100 nm is formed as an anode electrode on the surface opposite to the p-GaN layer and the n-ZnO layer of the gallium nitride free-standing substrate, respectively. Patterned. Thereafter, a heat treatment at 500 ° C. was performed for 30 seconds in a nitrogen atmosphere in order to improve the ohmic contact characteristics. The wafer thus obtained was cut into chips and further mounted on a lead frame to obtain a light emitting device having a vertical structure.
（２ｄ）発光素子の評価
　カソード電極とアノード電極間に通電し、Ｉ－Ｖ測定を行ったところ、整流性が確認された。また、順方向の電流を流したところ、波長約３８０ｎｍの発光が確認された。 (2d) Evaluation of Light Emitting Element When conducting current measurement between the cathode electrode and the anode electrode and performing IV measurement, rectification was confirmed. Further, when a forward current was passed, light emission with a wavelength of about 380 nm was confirmed.
　例３
（１）Ｍｇドープ窒化ガリウム自立基板を用いた発光素子の作製
（１ａ）ＲＳ－ＭＢＥ法による活性層の成膜
　例２の（１）及び（２ａ）と同様の方法でＭｇドープ窒化ガリウム自立基板を作製し、基板上にｐ型層としてｐ－ＧａＮを２００ｎｍ体積した。次にＲＳ－ＭＢＥ（ラジカルソース分子線成長）装置にて、金属材料である亜鉛（Ｚｎ）、カドミウム（Ｃｄ）をクヌーセンセルで照射し、ｐ型層上に供給した。ガス材料である酸素（Ｏ）は、ＲＦラジカル発生装置にてそれぞれＯ２ガスを原料とし、酸素ラジカルとして供給した。各種原料の純度はＺｎ、Ｃｄが７Ｎ、Ｏ２が６Ｎのものを用いた。基板は抵抗加熱ヒーターを用いて７００℃に加熱し、Ｃｄ０．２Ｚｎ０．８Ｏ層となるように各種ガスソースのフラックスを制御しながら厚さ１．５ｎｍの活性層を成膜した。 Example 3
(1) Fabrication of light-emitting device using Mg-doped gallium nitride free-standing substrate (1a) Formation of active layer by RS-MBE method Mg-doped gallium nitride free-standing substrate by the same method as (2) in Example 2 And p-GaN was added to the substrate as a p-type layer at a volume of 200 nm. Next, using a RS-MBE (radical source molecular beam growth) apparatus, zinc (Zn) and cadmium (Cd), which are metal materials, were irradiated with a Knudsen cell and supplied onto the p-type layer. Oxygen (O), which is a gas material, was supplied as oxygen radicals using O 2 gas as a raw material in an RF radical generator. The purity of various raw materials was Zn, Cd 7N, and O 2 6N. The substrate was heated to 700 ° C. using a resistance heater, and an active layer having a thickness of 1.5 nm was formed while controlling the flux of various gas sources so as to be a Cd 0.2 Zn 0.8 O layer.
（１ｂ）スパッタリングによるｎ型層の成膜
　次にＲＦマグネトロンスパッタ法を用いて、活性層上にｎ型ＺｎＯ層を５００ｎｍ成膜した。成膜にはＡｌが２重量部添加されたＺｎＯターゲットを使用し、成膜条件は純Ａｒ雰囲気、圧力０．５Ｐａ、投入電力１５０Ｗ、成膜時間５分間とした。また、例１の（４ａ）と同様の方法を用いて発光機能層の断面平均径を評価した結果、発光機能層の板面の平均粒径は約１００μｍであった。 (1b) Formation of n-type layer by sputtering Next, an RF magnetron sputtering method was used to form an n-type ZnO layer having a thickness of 500 nm on the active layer. A ZnO target added with 2 parts by weight of Al was used for the film formation, and the film formation conditions were a pure Ar atmosphere, a pressure of 0.5 Pa, an input power of 150 W, and a film formation time of 5 minutes. Moreover, as a result of evaluating the cross-sectional average diameter of the light emitting functional layer using the same method as in (4a) of Example 1, the average particle diameter of the plate surface of the light emitting functional layer was about 100 μm.
（１ｃ）発光素子の作製
　フォトリソグラフィープロセスと真空蒸着法とを用いて、ｎ型層にカソード電極としてＴｉ／Ａｌ／Ｎｉ／Ａｕ膜をそれぞれ１５ｎｍ、７０ｎｍ、１２ｎｍ、６０ｎｍの厚みでパターニングした。カソード電極のパターンは、電極が形成されていない箇所から光が取り出せるように開口部を有する形状とした。その後、オーム性接触特性を良好なものとするために、窒素雰囲気中での７００℃の熱処理を３０秒間行った。さらに、フォトリソグラフィープロセスと真空蒸着法とを用いて、窒化ガリウム自立基板のｐ－ＧａＮ層及びｎ－ＺｎＯ層とは反対側の面にアノード電極として、Ｎｉ／Ａｕ膜をそれぞれ５ｎｍ、１００ｎｍの厚みにパターニングした。その後、オーム性接触特性を良好なものとするために窒素雰囲気中で５００℃の熱処理を３０秒間行った。こうして得られたウェハーを切断してチップ化し、さらにリードフレームに実装して、縦型構造の発光素子を得た。 (1c) Production of Light Emitting Element Using a photolithography process and a vacuum deposition method, a Ti / Al / Ni / Au film as a cathode electrode was patterned on the n-type layer with a thickness of 15 nm, 70 nm, 12 nm, and 60 nm, respectively. The cathode electrode pattern was shaped to have an opening so that light could be extracted from a location where no electrode was formed. Thereafter, a heat treatment at 700 ° C. in a nitrogen atmosphere was performed for 30 seconds in order to improve the ohmic contact characteristics. Further, using a photolithography process and a vacuum deposition method, a Ni / Au film having a thickness of 5 nm and 100 nm is formed as an anode electrode on the surface opposite to the p-GaN layer and the n-ZnO layer of the gallium nitride free-standing substrate, respectively. Patterned. Thereafter, a heat treatment at 500 ° C. was performed for 30 seconds in a nitrogen atmosphere in order to improve the ohmic contact characteristics. The wafer thus obtained was cut into chips and further mounted on a lead frame to obtain a light emitting device having a vertical structure.
（１ｄ）発光素子の評価
　カソード電極とアノード電極間に通電し、Ｉ－Ｖ測定を行ったところ、整流性が確認された。また、順方向の電流を流したところ、波長約４００ｎｍの発光が確認された。 (1d) Evaluation of Light Emitting Element When conducting current measurement between the cathode electrode and the anode electrode and performing IV measurement, rectification was confirmed. Further, when a forward current was passed, light emission with a wavelength of about 400 nm was confirmed.

Claims (21)

  1. 　略法線方向に単結晶構造を有する複数の窒化ガリウム系単結晶粒子で構成される板からなる、窒化ガリウム自立基板。 A gallium nitride free-standing substrate composed of a plate composed of a plurality of gallium nitride single crystal particles having a single crystal structure in a substantially normal direction.
  2. 　前記基板の最表面における前記窒化ガリウム系単結晶粒子の断面平均径が０．３μｍ以上である、請求項１に記載の窒化ガリウム自立基板。 The gallium nitride free-standing substrate according to claim 1, wherein an average cross-sectional diameter of the gallium nitride-based single crystal particles on the outermost surface of the substrate is 0.3 µm or more.
  3. 　前記断面平均径が３μｍ以上である、請求項２に記載の窒化ガリウム自立基板。 The gallium nitride free-standing substrate according to claim 2, wherein the cross-sectional average diameter is 3 μm or more.
  4. 　２０μｍ以上の厚さを有する、請求項１～３のいずれか一項に記載の窒化ガリウム自立基板。 The gallium nitride free-standing substrate according to any one of claims 1 to 3, having a thickness of 20 µm or more.
  5. 　直径１００ｍｍ以上の大きさを有する、請求項１～４のいずれか一項に記載の窒化ガリウム自立基板。 The gallium nitride free-standing substrate according to any one of claims 1 to 4, which has a diameter of 100 mm or more.
  6. 　前記窒化ガリウム系単結晶粒子が、略法線方向に概ね揃った結晶方位を有する、請求項１～５のいずれか一項に記載の窒化ガリウム自立基板。 The gallium nitride free-standing substrate according to any one of claims 1 to 5, wherein the gallium nitride-based single crystal particles have a crystal orientation substantially aligned in a substantially normal direction.
  7. 　前記窒化ガリウム系単結晶粒子がｎ型ドーパント又はｐ型ドーパントでドープされている、請求項１～６のいずれか一項に記載の窒化ガリウム自立基板。 The gallium nitride free-standing substrate according to any one of claims 1 to 6, wherein the gallium nitride single crystal particles are doped with an n-type dopant or a p-type dopant.
  8. 　前記窒化ガリウム系単結晶粒子がドーパントを含まない、請求項１～６のいずれか一項に記載の窒化ガリウム自立基板。 The gallium nitride free-standing substrate according to any one of claims 1 to 6, wherein the gallium nitride-based single crystal particles do not contain a dopant.
  9. 　前記窒化ガリウム系単結晶粒子が混晶化されている、請求項１～８のいずれか一項に記載の窒化ガリウム自立基板。 The gallium nitride free-standing substrate according to any one of claims 1 to 8, wherein the gallium nitride single crystal particles are mixed.
  10. 　請求項１～９のいずれか一項に記載の窒化ガリウム自立基板と、
    　該基板上に形成され、略法線方向に単結晶構造を有する複数の半導体単結晶粒子で構成される層を一以上有する発光機能層と、
    を備えた、発光素子。     A gallium nitride free-standing substrate according to any one of claims 1 to 9,
    A light emitting functional layer formed on the substrate and having at least one layer composed of a plurality of semiconductor single crystal particles having a single crystal structure in a substantially normal direction;
    A light emitting device comprising:
  11. 　前記発光機能層の最表面における前記半導体単結晶粒子の断面平均径が０．３μｍ以上である、請求項１０に記載の自立した発光素子。 The self-supporting light-emitting device according to claim 10, wherein an average cross-sectional diameter of the semiconductor single crystal particles on the outermost surface of the light-emitting functional layer is 0.3 μm or more.
  12. 　前記断面平均径が３μｍ以上である、請求項１１に記載の発光素子。 The light emitting device according to claim 11, wherein the cross-sectional average diameter is 3 μm or more.
  13. 　前記半導体単結晶粒子が、前記窒化ガリウム自立基板の結晶方位に概ね倣って成長した構造を有する、請求項１０～１２のいずれか一項に記載の発光素子。 The light-emitting element according to any one of claims 10 to 12, wherein the semiconductor single crystal particles have a structure grown substantially following the crystal orientation of the gallium nitride free-standing substrate.
  14. 　前記発光機能層が窒化ガリウム系材料で構成される、請求項１０～１３のいずれか一項に記載の発光素子。 The light-emitting element according to any one of claims 10 to 13, wherein the light-emitting functional layer is made of a gallium nitride-based material.
  15. 　配向多結晶焼結体を用意する工程と、
    　前記配向多結晶焼結体上に、窒化ガリウムからなる種結晶層を、前記配向多結晶焼結体の結晶方位に概ね倣った結晶方位を有するように形成する工程と、
    　前記種結晶層上に、厚さ２０μｍ以上の窒化ガリウム系結晶から構成される層を、前記種結晶層の結晶方位に概ね倣った結晶方位を有するように形成する工程と、
    　前記配向多結晶焼結体を除去して、窒化ガリウム自立基板を得る工程と、
    を含む、窒化ガリウム自立基板の製造方法。     Preparing an oriented polycrystalline sintered body;
    Forming a seed crystal layer made of gallium nitride on the oriented polycrystalline sintered body so as to have a crystal orientation substantially following the crystal orientation of the oriented polycrystalline sintered body;
    Forming a layer composed of a gallium nitride-based crystal having a thickness of 20 μm or more on the seed crystal layer so as to have a crystal orientation substantially following the crystal orientation of the seed crystal layer;
    Removing the oriented polycrystalline sintered body to obtain a gallium nitride free-standing substrate;
    A method for manufacturing a gallium nitride free-standing substrate.
  16. 　前記配向多結晶焼結体が配向多結晶アルミナ焼結体である、請求項１５に記載の方法。 The method according to claim 15, wherein the oriented polycrystalline sintered body is an oriented polycrystalline alumina sintered body.
  17. 　前記配向多結晶焼結体を構成する粒子の板面における平均粒径が０．３～１０００μｍである、請求項１５又は１６に記載の方法。 The method according to claim 15 or 16, wherein an average particle diameter on the plate surface of particles constituting the oriented polycrystalline sintered body is 0.3 to 1000 µm.
  18. 　前記窒化ガリウム系結晶から構成される層の形成がＮａフラックス法により行われる、請求項１５～１７のいずれか一項に記載の方法。 The method according to any one of claims 15 to 17, wherein the layer composed of the gallium nitride-based crystal is formed by a Na flux method.
  19. 　前記配向多結晶焼結体が透光性を有する、請求項１５～１８のいずれか一項に記載の方法。 The method according to any one of claims 15 to 18, wherein the oriented polycrystalline sintered body has translucency.
  20. 　請求項１～９のいずれか一項に記載の窒化ガリウム自立基板を用意する、又は請求項１５～１９のいずれか一項に記載の方法により前記窒化ガリウム自立基板を用意する工程と、
    　前記窒化ガリウム自立基板に、前記窒化ガリウム基板の結晶方位に概ね倣った結晶方位を有するように、略法線方向に単結晶構造を有する複数の半導体単結晶粒子で構成される層を一つ以上形成して発光機能層を設ける工程と、
    を含む、発光素子の製造方法。     Preparing the gallium nitride free-standing substrate according to any one of claims 1 to 9, or providing the gallium nitride free-standing substrate by the method according to any one of claims 15 to 19;
    The gallium nitride free-standing substrate includes at least one layer composed of a plurality of semiconductor single crystal particles having a single crystal structure in a substantially normal direction so as to have a crystal orientation that substantially follows the crystal orientation of the gallium nitride substrate. Forming and providing a light emitting functional layer;
    A method for manufacturing a light emitting device, comprising:
  21. 　前記発光機能層が窒化ガリウム系材料で構成される、請求項２０に記載の方法。
          The method according to claim 20, wherein the light emitting functional layer is made of a gallium nitride-based material.
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WO2016051890A1 (en) * 2014-09-29 2016-04-07 日本碍子株式会社 Gallium nitride self-supporting substrate, light-emitting element, and production methods therefor
WO2016121853A1 (en) * 2015-01-29 2016-08-04 日本碍子株式会社 Free-standing substrate, function element and method for producing same
JP2017152665A (en) * 2016-02-25 2017-08-31 日本碍子株式会社 Surface emitting element, external resonator type vertical surface emitting laser, and manufacturing method for surface emitting element
US20170250519A1 (en) * 2016-02-25 2017-08-31 Ngk Insulators, Ltd. Surface-Emitting Device, Vertical External-Cavity Surface-Emitting Laser, and Method for Manufacturing Surface-Emitting Device
JP2018078232A (en) * 2016-11-11 2018-05-17 日本碍子株式会社 Broad wavelength band light-emitting element and manufacturing method thereof
JP2020055697A (en) * 2018-09-28 2020-04-09 国立大学法人 名古屋工業大学 METHOD FOR MANUFACTURING DELAFOSSITE TYPE Cu BASED COMPOSITE OXIDE FILM
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WO2016051890A1 (en) * 2014-09-29 2016-04-07 日本碍子株式会社 Gallium nitride self-supporting substrate, light-emitting element, and production methods therefor
WO2016121853A1 (en) * 2015-01-29 2016-08-04 日本碍子株式会社 Free-standing substrate, function element and method for producing same
JPWO2016121853A1 (en) * 2015-01-29 2017-11-30 日本碍子株式会社 Self-standing substrate, functional element, and manufacturing method thereof
US10249494B2 (en) 2015-01-29 2019-04-02 Ngk Insulators, Ltd. Free-standing substrate, function element and method for producing same
JP2017152665A (en) * 2016-02-25 2017-08-31 日本碍子株式会社 Surface emitting element, external resonator type vertical surface emitting laser, and manufacturing method for surface emitting element
US20170250519A1 (en) * 2016-02-25 2017-08-31 Ngk Insulators, Ltd. Surface-Emitting Device, Vertical External-Cavity Surface-Emitting Laser, and Method for Manufacturing Surface-Emitting Device
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JP2018078232A (en) * 2016-11-11 2018-05-17 日本碍子株式会社 Broad wavelength band light-emitting element and manufacturing method thereof
CN111699419A (en) * 2018-02-19 2020-09-22 日本碍子株式会社 Optical member and lighting device
CN111699419B (en) * 2018-02-19 2022-09-09 日本碍子株式会社 Optical member and lighting device
JP2020055697A (en) * 2018-09-28 2020-04-09 国立大学法人 名古屋工業大学 METHOD FOR MANUFACTURING DELAFOSSITE TYPE Cu BASED COMPOSITE OXIDE FILM
JP7090263B2 (en) 2018-09-28 2022-06-24 国立大学法人 名古屋工業大学 Method for manufacturing delafosite type Cu-based composite oxide film

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