WO2023286574A1 - 紫外線発光素子用エピタキシャルウェーハ及びその製造方法 - Google Patents
紫外線発光素子用エピタキシャルウェーハ及びその製造方法 Download PDFInfo
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- WO2023286574A1 WO2023286574A1 PCT/JP2022/025480 JP2022025480W WO2023286574A1 WO 2023286574 A1 WO2023286574 A1 WO 2023286574A1 JP 2022025480 W JP2022025480 W JP 2022025480W WO 2023286574 A1 WO2023286574 A1 WO 2023286574A1
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- layer
- ultraviolet light
- light emitting
- substrate
- epitaxial wafer
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 27
- 238000000034 method Methods 0.000 title abstract description 15
- 239000000758 substrate Substances 0.000 claims abstract description 136
- 239000013078 crystal Substances 0.000 claims abstract description 76
- 229910002704 AlGaN Inorganic materials 0.000 claims abstract description 36
- 229910052594 sapphire Inorganic materials 0.000 claims description 17
- 239000010980 sapphire Substances 0.000 claims description 17
- 229910052757 nitrogen Inorganic materials 0.000 claims description 11
- 239000010453 quartz Substances 0.000 claims description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 7
- 239000000470 constituent Substances 0.000 claims description 5
- 238000001228 spectrum Methods 0.000 claims description 4
- 238000005253 cladding Methods 0.000 abstract description 11
- 238000000605 extraction Methods 0.000 abstract description 8
- 150000004767 nitrides Chemical class 0.000 abstract description 5
- -1 AlN Chemical class 0.000 abstract description 3
- 229910016920 AlzGa1−z Inorganic materials 0.000 abstract 1
- 239000010410 layer Substances 0.000 description 147
- 235000012431 wafers Nutrition 0.000 description 31
- 239000000463 material Substances 0.000 description 18
- 239000007789 gas Substances 0.000 description 15
- 239000002994 raw material Substances 0.000 description 14
- 230000000052 comparative effect Effects 0.000 description 12
- JLTRXTDYQLMHGR-UHFFFAOYSA-N trimethylaluminium Chemical compound C[Al](C)C JLTRXTDYQLMHGR-UHFFFAOYSA-N 0.000 description 12
- XCZXGTMEAKBVPV-UHFFFAOYSA-N trimethylgallium Chemical compound C[Ga](C)C XCZXGTMEAKBVPV-UHFFFAOYSA-N 0.000 description 11
- 239000000919 ceramic Substances 0.000 description 10
- 238000006243 chemical reaction Methods 0.000 description 9
- 239000000203 mixture Substances 0.000 description 9
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 8
- 230000007547 defect Effects 0.000 description 8
- 239000012535 impurity Substances 0.000 description 8
- 239000012790 adhesive layer Substances 0.000 description 7
- 239000001257 hydrogen Substances 0.000 description 7
- 229910052739 hydrogen Inorganic materials 0.000 description 7
- 239000010409 thin film Substances 0.000 description 7
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 6
- 238000004140 cleaning Methods 0.000 description 6
- 230000004888 barrier function Effects 0.000 description 5
- 239000010408 film Substances 0.000 description 5
- 230000001954 sterilising effect Effects 0.000 description 5
- 238000004659 sterilization and disinfection Methods 0.000 description 5
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 4
- 229910004298 SiO 2 Inorganic materials 0.000 description 4
- 239000012159 carrier gas Substances 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 150000002500 ions Chemical class 0.000 description 4
- 238000002488 metal-organic chemical vapour deposition Methods 0.000 description 4
- 239000004065 semiconductor Substances 0.000 description 4
- 230000004913 activation Effects 0.000 description 3
- 230000003746 surface roughness Effects 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 229910021529 ammonia Inorganic materials 0.000 description 2
- 238000000137 annealing Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002248 hydride vapour-phase epitaxy Methods 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- 230000031700 light absorption Effects 0.000 description 2
- QBJCZLXULXFYCK-UHFFFAOYSA-N magnesium;cyclopenta-1,3-diene Chemical compound [Mg+2].C1C=CC=[C-]1.C1C=CC=[C-]1 QBJCZLXULXFYCK-UHFFFAOYSA-N 0.000 description 2
- 230000006798 recombination Effects 0.000 description 2
- 238000005215 recombination Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000000295 emission spectrum Methods 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000005468 ion implantation Methods 0.000 description 1
- 238000003475 lamination Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 238000000992 sputter etching Methods 0.000 description 1
- VCZQFJFZMMALHB-UHFFFAOYSA-N tetraethylsilane Chemical compound CC[Si](CC)(CC)CC VCZQFJFZMMALHB-UHFFFAOYSA-N 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
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- H—ELECTRICITY
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- H01L33/00—Semiconductor devices having potential barriers 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
- H01L33/0066—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound
- H01L33/007—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound comprising nitride compounds
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- 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
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- C30—CRYSTAL GROWTH
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- C30B25/02—Epitaxial-layer growth
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- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
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- C30B25/22—Sandwich processes
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- 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
- C30B29/38—Nitrides
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- 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
- C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
- C30B29/68—Crystals with laminate structure, e.g. "superlattices"
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- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
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- H01L33/06—Semiconductor devices having potential barriers 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 quantum effect structure or superlattice, e.g. tunnel junction within the light emitting region, e.g. quantum confinement structure or tunnel barrier
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Definitions
- the present invention relates to an epitaxial wafer for ultraviolet light emitting devices and a method for manufacturing the same.
- an AlN layer is grown by a hydride vapor phase epitaxy (HVPE) method using a sapphire substrate or an AlN substrate as a base substrate (Patent Document 1).
- HVPE hydride vapor phase epitaxy
- an AlN layer is formed on a material substrate such as sapphire or SiC having different lattice constants, defects due to lattice mismatch occur, which tends to lower the internal quantum efficiency and lower the energy conversion efficiency.
- the effect becomes even more pronounced.
- GaN single-crystal self-supporting substrate with a relatively close lattice constant becomes a light-absorbing substrate due to its bandgap, which reduces the external quantum efficiency.
- AlN single-crystal free-standing substrates are promising as very high-quality epitaxial substrates, but they are difficult to manufacture and are very expensive materials. Therefore, there has been a problem in the spread of high-output, high-efficiency deep-ultraviolet light-emitting diodes for sterilization.
- the present invention has been made in view of the above circumstances, and an object of the present invention is to provide an epitaxial wafer for an ultraviolet light emitting device having an epitaxial layer of a high-quality Group III nitride such as AlN, which is inexpensive and has good light extraction efficiency, and a method for producing the same. to be
- the present invention provides a first support substrate transparent to ultraviolet light and heat-resistant, an Al x Ga 1-x N (0.5 ⁇ x ⁇ 1) single crystal seed crystal layer bonded to the first support substrate by bonding; On the seed crystal layer, a first-conductivity-type clad layer containing Al y Ga 1-y N (0.5 ⁇ y ⁇ 1) as a main component, an AlGaN-based active layer, and Al z Ga 1-z N ( Provided is an epitaxial wafer for an ultraviolet light emitting device, characterized by having an epitaxial layer in which a second conductivity type clad layer having 0.5 ⁇ z ⁇ 1) as a main component and a second conductivity type clad layer are sequentially grown.
- the epitaxial wafer of an ultraviolet light emitting device With such an epitaxial wafer for an ultraviolet light emitting device, light can be extracted from the substrate side, so that a high-quality one with improved light extraction efficiency can be obtained.
- the seed crystal layer is bonded by bonding, for example, an expensive nitride semiconductor single crystal seed substrate separated by bonding can be recycled and used, and the material cost of the entire process can be reduced. can be significantly reduced. As a result, the epitaxial wafer of the present invention also becomes inexpensive.
- the main component of the first support substrate may be synthetic quartz or sapphire.
- Ceramics which is used as the material for the first support substrate of the conventional product, is made by molding and sintering powdered raw materials, so it is easy for voids to form on the surface. The voids are filled and polished, but it is difficult to eliminate them completely. There is concern that voids in the ceramics will collapse and the crystallinity of the seed crystal layer will be lost, resulting in defects and a decrease in yield.
- the above-described materials are relatively inexpensive, and more reliably produce wafers that are transparent to ultraviolet light, have less surface roughness, and do not deform, break, or evaporate due to high heat. .
- the epitaxial wafer for an ultraviolet light emitting element can be obtained at a lower cost and with improved crystallinity and higher quality than the conventional product in which the first support substrate is a ceramic substrate and defects are likely to occur.
- the AlGaN-based active layer may be formed with an MQW structure, In may be present as a constituent element other than Al, Ga, and N, and the ratio of In may be less than 1%.
- the peak wavelength ⁇ p of the spectrum emitted from the AlGaN-based active layer at 25° C. and a current injection of 0.2 A/mm 2 may be shorter than 235 nm.
- it If it has such a peak wavelength, it will be an epitaxial wafer for ultraviolet light emitting devices that is particularly useful as a light source for sterilization.
- the bandgap of the seed crystal layer may be larger than the bandgap of the AlGaN-based active layer.
- the seed crystal layer may have a C-plane as an epitaxial growth surface.
- a seed crystal layer is laminated by peeling and transferring Al x Ga 1-x N (0.5 ⁇ X ⁇ 1) single crystal onto a first support substrate transparent to ultraviolet light and heat resistant.
- a step of producing a bonded substrate by On the bonded substrate, a first-conductivity-type clad layer containing Al y Ga 1-y N (0.5 ⁇ y ⁇ 1) as a main component, an AlGaN-based active layer, and Al z Ga 1-z N Provided is a method for producing an epitaxial wafer for an ultraviolet light emitting device, comprising the step of forming an epitaxial layer by sequentially epitaxially growing a second conductivity type clad layer containing 0.5 ⁇ z ⁇ 1) as a main component.
- the first support substrate can be made mainly of synthetic quartz or sapphire.
- the wafer is relatively inexpensive, and more reliably transparent to ultraviolet light, has less surface roughness, and does not deform, break, or evaporate due to high heat. It is possible to obtain a high-quality epitaxial wafer for an ultraviolet light emitting device with improved crystallinity.
- the AlGaN-based active layer can be formed with an MQW structure, In can be included as a constituent element other than Al, Ga, and N, and the ratio of In can be less than 1%.
- the AlGaN-based active layer can be one having a peak wavelength ⁇ p of a spectrum emitted when a current of 0.2 A/mm 2 is injected at 25° C. is shorter than 235 nm.
- the seed crystal layer may have a bandgap larger than that of the AlGaN-based active layer.
- the epitaxial growth surface of the seed crystal layer can be the C-plane.
- the epitaxial wafer for ultraviolet light emitting elements and the method for producing the same according to the present invention it is possible to obtain a high-quality epitaxial wafer for ultraviolet light emitting diodes that is inexpensive and has high light extraction efficiency.
- BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows an example of the epitaxial wafer for ultraviolet light emitting elements of this invention. It is a schematic diagram showing an example of an ultraviolet light emitting element layer. BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart which shows an example of the manufacturing method of the epitaxial wafer for ultraviolet light emitting elements of this invention.
- the inventors have found that high-quality epitaxial wafers with good light extraction efficiency can be provided by the method, and have completed the present invention.
- An epitaxial wafer 100 for an ultraviolet light emitting element of the present invention shown in FIG. 1 has a substrate (bonded substrate 1) produced by bonding and an ultraviolet light emitting element layer 2 made of a nitride semiconductor.
- the bonded substrate 1 has a first support substrate 3, an adhesive layer 4, and a seed crystal layer 5, and is bonded to the first support substrate 3 by bonding a seed crystal (seed crystal layer 5). It is.
- the first supporting substrate 3 and the seed crystal layer 5 are bonded together by the adhesive layer 4 to be produced.
- the material of the first support substrate 3 is not particularly limited as long as it is transparent to ultraviolet light and has heat resistance.
- a substrate having a light transmittance of 70% or more at least at a wavelength of 230 nm and having heat resistance such that it does not melt, peel off, or break during treatment at a high temperature exceeding 1000° C. can be used.
- a substrate containing synthetic quartz or sapphire as a main component can be used.
- a synthetic quartz substrate or a sapphire substrate can be used. These are less expensive than conventional ceramics and have a small surface roughness, so that the crystallinity of the seed crystal layer 5 joined by bonding can be prevented from being impaired. As a result, the quality of the seed crystal layer 5 and further the ultraviolet light emitting element layer 2 can be improved, resulting in an excellent epitaxial wafer for ultraviolet light emitting elements.
- the seed crystal layer 5 made of Al x Ga 1-x N (0.5 ⁇ x ⁇ 1) single crystal is not limited to the method described below, but for example, Al x Ga 1-x N (0.5 ⁇ x ⁇ 1) 1)
- a single crystal free-standing substrate or Al x Ga 1-x N (0.5 ⁇ x ⁇ 1) epitaxial substrate is prepared (seed substrate), ions are implanted into the substrate to form a brittle layer, and a first support is formed. It can be produced on the first support substrate 3 by peeling and transferring the brittle layer after bonding it to the substrate 3 .
- the surface of the self-supporting substrate or the like that is, the seed substrate separated by peeling the seed crystal layer 5) from which the seed crystal layer 5 is bonded is polished to obtain an ion-implanted surface.
- it can be repeatedly used for a seed crystal layer when producing another epitaxial wafer for an ultraviolet light emitting device of the present invention.
- the relatively expensive Al x Ga 1-x N (0.5 ⁇ x ⁇ 1) single crystal substrate can be used repeatedly and effectively, so that the overall cost can be reduced.
- the seed crystal layer 5, and the epitaxial wafer 100 for the ultraviolet light emitting device of the present invention are inexpensive.
- the bandgap of the seed crystal layer 5 is larger than the bandgap of the AlGaN-based active layer, which will be described later. This is because absorption of light in the seed crystal layer 5 can be prevented, and light can be extracted more reliably and efficiently. From the viewpoint of preventing this light absorption, the larger the bandgap of the seed crystal layer 5, the better, and there is no upper limit.
- the seed crystal layer 5 preferably has a C-plane as an epitaxial growth plane. With such a material, crystal growth is easier and a high quality thin film (ultraviolet light emitting element layer 2) can be obtained.
- the adhesive layer 4 joins the first support substrate 3 and the seed crystal layer 5, and can be made of, for example, a layer such as SiO 2 that is transparent to ultraviolet light.
- the bonded substrate 1 is not bonded by such an adhesive layer 4, but the surface of the AlGaN single crystal serving as the seed crystal layer 5 is activated by plasma or argon ion etching to form an amorphous layer, followed by heating. It can also be bonded to the first supporting substrate 3 by applying pressure and heating.
- An ultraviolet light emitting element layer 2 is vapor-grown on the bonded substrate 1 .
- An outline of an example of the ultraviolet light emitting element layer 2 is shown in FIG. The structure of the ultraviolet light emitting element layer will be described in detail below.
- a homoepitaxial layer 6 is epitaxially grown on the bonded substrate 1 .
- a homoepitaxial layer is introduced to improve crystal quality and can be designed with a thickness ranging from 100 nm to 500 nm. The homoepitaxial layer may be omitted depending on the device design.
- the first-conductivity-type cladding layer 7 (mainly composed of Al y Ga 1-y N (0.5 ⁇ y ⁇ 1)) is formed to supply electrons to the AlGaN-based active layer 8.
- the film thickness is not limited, it can be, for example, 2.5 ⁇ m.
- the AlGaN-based active layer 8 has a quantum well structure, in which barrier layers 9 and well layers 10 are alternately laminated (MQW structure).
- MQW structure barrier layers 9 and well layers 10 are alternately laminated
- In may be present as a constituent element other than Al, Ga, and N, and the ratio of In may be more than 0% and less than 1%. Such a material is preferable because the internal quantum efficiency can be improved and light can be emitted more efficiently.
- the AlGaN-based active layer 8 can have a peak wavelength ⁇ p of light emitted when a current of 0.2 A/mm 2 is injected at 25° C. is shorter than 235 nm.
- light in the deep ultraviolet range can be obtained more reliably, and is useful as a light source for sterilization.
- the lower limit of the peak wavelength ⁇ p of the emission spectrum in the deep ultraviolet region can be set to 200 nm, for example.
- the film thickness is not particularly limited, for example, a three-layer lamination of a barrier layer of 6 nm and a well layer of 1.5 nm can be used.
- the second-conductivity-type cladding layer 11 (mainly composed of Al z Ga 1-z N (0.5 ⁇ z ⁇ 1)) is formed to supply holes to the AlGaN-based active layer 8. .
- the film thickness is not particularly limited, it can be set to 30 nm, for example. These layers are laminated in order by epitaxial growth.
- a p-type AlGaN contact layer 12 is formed to reduce the contact resistance with the electrode.
- the film thickness is not particularly limited, it can be set to 60 nm, for example.
- the layer arrangement may be such that P/N is reversed according to the conductivity type of the second conductivity type clad layer 11 .
- FIG. 3 shows an example of a method for producing an epitaxial wafer 100 for ultraviolet light emitting devices according to the present invention.
- the manufacturing process of the bonded substrate 1 will be described.
- An Al x Ga 1-x N (0.5 ⁇ x ⁇ 1) single crystal seed substrate 13 (for example, an AlN substrate) is prepared, and ions are implanted from one surface (ion implantation surface) (step A).
- the ions to be implanted at this time can be, for example, hydrogen ions or rare gas ions.
- a fragile layer (damage layer) 14 that serves as a peeling position is formed in the seed substrate 13 (step B).
- the ion-implanted surface of the seed substrate 13 is bonded to a bonding layer 4 (eg, SiO 2 layer) formed on a separately prepared first support substrate 3 (eg, synthetic quartz substrate) to form a bonding substrate 15 (step C).
- a bonding layer 4 eg, SiO 2 layer
- first support substrate 3 eg, synthetic quartz substrate
- the seed substrate 13 is separated at the brittle layer 14 of the seed substrate 13 in the joint substrate 15 (step D).
- an Al x Ga 1-x N (0.5 ⁇ x ⁇ 1) single crystal film is thinly transferred as a seed crystal layer 5 onto the adhesive layer 4 on the first support substrate 3,
- the first support substrate 3 , the adhesive layer 4 and the seed crystal layer 5 are laminated to form the bonded substrate 1 .
- the surface can be polished, for example, if necessary (step E).
- the remaining part of the separated seed substrate 13 can be reused for the seed crystal layer when producing yet another bonded substrate by polishing the surface again to form an ion-implanted surface. .
- step F the manufacturing process of the ultraviolet light emitting element layer 2 (epitaxial layer particularly suitable for light emitting diodes in the deep ultraviolet region) is shown (step F).
- step F Introduction into Reaction Furnace
- the bonded substrate stack 1 is introduced into the reaction furnace of the MOVPE apparatus. Before the bonded substrate stack 1 is introduced into the reactor, it is cleaned with a chemical. After the bonded substrate stack 1 is introduced into the reactor, the reactor is filled with a high-purity inert gas such as nitrogen, and the gas in the reactor is exhausted.
- a high-purity inert gas such as nitrogen
- Step of Cleaning the Surface of the Bonded Substrate in a Furnace The bonded substrate 1 is heated in a reaction furnace to clean the surface of the substrate.
- the temperature for cleaning can be determined between 1000° C. and 1200° C. in terms of temperature of the surface of the bonded substrate, and cleaning at 1050° C. in particular can provide a clean surface.
- Cleaning is carried out after the pressure in the furnace has been reduced and the pressure in the furnace can be between 200 mbar and 30 mbar.
- the inside of the furnace is cleaned for about 10 minutes, for example, in a state in which a mixture of hydrogen, nitrogen, ammonia, and the like is supplied. These conditions are examples and are not particularly limited.
- a step of growing a homoepitaxial layer In this step, Al is grown on the bonded substrate 1 by introducing a gas that serves as a source of Al, Ga, and N, which are raw materials, at a specified furnace pressure and substrate temperature.
- x Ga 1-x N (0.5 ⁇ x ⁇ 1) is epitaxially grown (homoepitaxial layer 6).
- the growth can be performed at a furnace pressure of 50 mbar and a substrate temperature of 1120° C., for example.
- Trimethylaluminum (TMAl) can be used as the Al source
- trimethylgallium (TMGa) can be used as the Ga source
- NH 3 ammonia
- the material efficiency of the source gas is taken into consideration, and the ratio of the source materials TMAl and TMGa is adjusted so that the Al/Ga ratio taken into the thin film becomes a set ratio.
- AlN can be grown at a flow rate of 0.24 L/min (240 sccm) of TMAl and a flow rate of NH 3 of 2.0 L/min (2000 sccm) under standard conditions.
- the carrier gas of TMAl, TMGa, NH3 can be hydrogen, for example. These conditions are examples and are not particularly limited.
- Step of Growing a First-Conductivity-Type Cladding Layer This step is a step of growing a first-conductivity-type clad layer 7 on the homoepitaxial layer 6 .
- this step after the inside of the reaction furnace is maintained at a specified furnace pressure and substrate temperature, raw materials TMAl, TMGa, and NH 3 , and an impurity gas for n-type conductivity are supplied into the furnace.
- a clad layer 7 of one conductivity type is grown.
- the first-conductivity-type cladding layer 7 can be freely produced with a composition whose main component is Al y Ga 1-y N (0.5 ⁇ y ⁇ 1). It can be 0.05N .
- a plurality of layers may be formed by changing the composition.
- the furnace pressure in this process can be, for example, 75 mbar and the substrate temperature can be 1100.degree.
- the flow rates of the source materials TMAl and TMGa are adjusted so that the Al/Ga ratio taken into the thin film is a set ratio, taking into consideration the material efficiency of the source gases. set.
- Monosilane (SiH 4 ) can be used as an impurity gas for n-type conductivity.
- Hydrogen can be used as a carrier gas for transporting the raw material gas. Note that tetraethylsilane may be used as the impurity gas.
- Step of Growing an AlGaN-Based Active Layer This step is a step of growing an AlGaN-based active layer 8 on the clad layer 7 of the first conductivity type.
- raw materials TMAl, TMGa and NH 3 are supplied into the furnace to grow the AlGaN-based active layer 8 .
- the AlGaN-based active layer 8 may be, for example, a barrier layer 9 of Al 0.75 Ga 0.25 N and a well layer 10 of Al 0.6 Ga 0.4 N.
- the furnace pressure in this process can be, for example, 75 mbar, and the substrate temperature can be 1100.degree.
- the raw material TMAl and TMGa are mixed so that the Al/Ga ratio taken into the thin film becomes a set ratio in consideration of the material efficiency of the raw material gas.
- Set the flow rate are examples and are not particularly limited.
- Step of Growing Second-Conductivity-Type Cladding Layer This step is a step of growing a second-conductivity-type clad layer 11 on the AlGaN-based active layer 8 .
- this step after the inside of the reaction furnace is maintained at a specified furnace pressure and substrate temperature, raw materials TMAl, TMGa, and NH 3 and impurity raw materials for making p-type conductivity are supplied into the furnace.
- a two-conductivity type clad layer 11 is grown.
- the second-conductivity-type cladding layer 11 can be freely manufactured with a composition represented by Al z Ga 1-z N (0.5 ⁇ z ⁇ 1), and an example is Al 0.95 Ga 0.05 . can be N.
- a plurality of layers may be formed by changing the composition.
- the furnace pressure in this process can be, for example, 75 mbar and the substrate temperature can be 1100.degree.
- the flow rates of the source materials TMAl and TMGa are adjusted so that the Al/Ga ratio taken into the thin film is a set ratio, taking into consideration the material efficiency of the source gases. set.
- These values are examples and are not particularly limited.
- Biscyclopentadienylmagnesium (Cp 2 Mg) can be used as an impurity material for providing p-type conductivity.
- hydrogen can be used as a carrier gas for transporting the raw material gas.
- Step of growing p-type AlGaN contact layer This step is a step of growing the p-type AlGaN contact layer 12 on the second-conductivity-type cladding layer 11 .
- raw materials TMAl, TMGa, and NH 3 and impurity raw materials for making p-type conductivity are supplied into the furnace and p-type conductivity is obtained.
- a type AlGaN contact layer 12 is grown.
- the furnace pressure in this process can be, for example, 75 mbar and the substrate temperature can be 1100.degree. These values are examples and are not particularly limited.
- Biscyclopentadienylmagnesium (Cp 2 Mg) can be used as an impurity material for providing p-type conductivity.
- hydrogen can be used as a carrier gas for transporting the raw material gas.
- Activation Annealing Step the wafer is annealed at a predetermined temperature and time in a heating furnace to activate the p-type impurities in the second conductivity type cladding layer 11 and the p-type AlGaN contact layer 12. .
- Activation in a heating furnace can be, for example, 750° C. for 10 minutes.
- the manufacturing method of the present invention By producing the epitaxial wafer 100 for light-emitting diodes in the ultraviolet region (especially in the deep ultraviolet region) by the manufacturing method of the present invention, it is possible to obtain a substrate with few defects due to voids with a simple epitaxial layer. productivity can be improved. Further, by recovering the AlN single crystal substrate or the AlGaN single crystal substrate from which the seed crystal layer has been peeled off and transferred and re-polished, an expensive compound semiconductor single crystal substrate can be reused as a seed substrate to form the seed crystal layer. can be newly peeled off and transferred, an epitaxial substrate for a light emitting diode in the ultraviolet range can be manufactured at low cost.
- Epitaxial wafers for deep ultraviolet light emitting diodes as shown in FIGS. 1 and 2 were manufactured by the manufacturing method of the present invention as shown in FIG. That is, it was manufactured by manufacturing processes AE of the bonded substrate and manufacturing process F of the ultraviolet light emitting element layer (processes [1] to [8] described above).
- An adhesive layer (flattening layer) made of SiO 2 was grown to a thickness of 2 ⁇ m on the sapphire substrate, and the surface was subjected to CMP processing for planarization.
- a substrate (bonded substrate) was prepared by bonding a seed crystal (seed substrate) made of an AlN single crystal to the above sapphire substrate at normal temperature and peeling and transferring the same.
- Al 0.95 Ga 0.05 N was grown to 100 nm on the bonded substrate by the MOVPE method, and n-type Al 0.95 Ga 0.05 N was grown thereon to 2.5 ⁇ m.
- a quantum well structure consisting of three layers of barrier layers: Al 0.75 Ga 0.25 N and well layers: Al 0.6 Ga 0.4 N was formed thereon. After that, a p-type Al 0.95 Ga 0.05 N layer and a p-type GaN contact layer were formed.
- Example 2 In the epitaxial substrate produced in Example, defects were remarkably reduced as compared with Comparative Example 1 described later, and the defect density was reduced to 0.32/cm 2 .
- Comparative Example 1 a step of removing the ceramic substrate was required, but in Example, since ultraviolet light could be extracted from the substrate side, the light extraction efficiency was good and the manufacturing cost could be reduced.
- Comparative Example 2 a device with a low threading dislocation density and good luminous efficiency was obtained.
- a 2 ⁇ m thick planarizing layer made of SiO 2 is grown on a substrate made of AlN ceramics, and a seed crystal made of Al 0.95 Ga 0.05 N single crystal is attached to the substrate (bonded substrate). ) was prepared.
- Al 0.95 Ga 0.05 N was grown to 100 nm on the bonded substrate by the MOVPE method, and n-type Al 0.95 Ga 0.05 N was grown thereon to 2.5 ⁇ m.
- a quantum well structure consisting of three layers of barrier layers: Al 0.75 Ga 0.25 N and well layers: Al 0.6 Ga 0.4 N was formed thereon. After that, a p-type Al 0.95 Ga 0.05 N layer and a p-type GaN contact layer were formed.
- An epitaxial substrate for a light-emitting diode in the deep ultraviolet region using a sapphire substrate was manufactured in the following manner. [1] Introduction into Reactor The sapphire substrate was introduced into the reactor of the MOVPE apparatus. Before the sapphire substrate was introduced into the reactor, it was cleaned with chemicals. After introducing the sapphire substrate into the reactor, the reactor was filled with a high-purity inert gas such as nitrogen, and the gas in the reactor was exhausted.
- a high-purity inert gas such as nitrogen
- Step of cleaning the sapphire substrate in the furnace The sapphire substrate was heated in the reaction furnace to clean the surface of the substrate. Cleaning was performed at a temperature of 1030°C. Further, the pressure in the furnace was set to 150 mbar. The furnace was cleaned for 10 minutes while hydrogen or nitrogen was supplied.
- a step of growing a buffer layer In this step, a crystal of an epitaxial layer is grown on a sapphire substrate by introducing a gas that serves as a source of Al, Ga, and N as raw materials at a specified furnace pressure and substrate temperature. Grow a buffer layer to improve the properties. By adjusting the nucleation layer on the substrate and the growth conditions, a layer that reduces dislocations was formed by repeating a low-speed growth layer and a high-speed growth layer. In order to obtain a substrate suitable for an ultraviolet LED, a buffer layer was grown to a thickness of 3 ⁇ m.
- Table 1 shows the results of XRD rocking curve measurement of the epitaxial substrates for deep ultraviolet light emitting diodes produced in Examples and Comparative Examples 1 and 2.
- the FWHM of the XRD rocking curve of AlN (0002) of the epitaxial substrate for deep ultraviolet light emitting diodes of Example was 43 arcsec, whereas that of Comparative Example 2 was 43 arcsec.
- the FWHM was 541 arcsec, and an epitaxial wafer with better crystallinity than Comparative Example 2 could be obtained.
- a high-quality epitaxial wafer with higher crystallinity can be obtained.
- the present invention is not limited to the above embodiments.
- the above embodiment is an example, and any device that has substantially the same configuration as the technical idea described in the claims of the present invention and produces similar effects is the present invention. It is included in the technical scope of the invention.
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Abstract
Description
また、250nmより短波長の場合、その影響がさらに著しくなる。
しかしながら、AlNセラミックス基板が不透明なため、基板側から光を取り出すことが困難であった。
該第一支持基板上に、貼り合わせにより接合されたAlxGa1-xN(0.5<x≦1)単結晶の種結晶層と、
該種結晶層上に、AlyGa1-yN(0.5<y≦1)を主成分とする第一導電型クラッド層と、AlGaN系活性層と、AlzGa1-zN(0.5<z≦1)を主成分とする第二導電型クラッド層とが順に積層成長されたエピタキシャル層を有することを特徴とする紫外線発光素子用エピタキシャルウェーハを提供する。
また、種結晶層が貼り合わせにより接合されたものであるので、例えば、貼り合わせで分離した高価な窒化物半導体単結晶の種基板を再生して使用することができ、工程全体の材料コストを著しく低下させることができる。その結果、本発明のエピタキシャルウェーハも安価なものとなる。
該貼り合わせ基板上に、AlyGa1-yN(0.5<y≦1)を主成分とする第一導電型クラッド層と、AlGaN系活性層と、AlzGa1-zN(0.5<z≦1)を主成分とする第二導電型クラッド層とを順にエピタキシャル成長させたエピタキシャル層を形成する工程を含む紫外線発光素子用エピタキシャルウェーハの製造方法を提供する。
上述のように、紫外線領域(特には深紫外線領域(UVC:200~290nm))の発光ダイオード用に好適な、安価で高品質なエピタキシャルウェーハが求められていた。
発明者らは、鋭意検討を重ねた結果、紫外光に透明で耐熱性のある第一支持基板と、該第一支持基板上に、貼り合わせにより接合されたAlxGa1-xN(0.5<x≦1)単結晶の種結晶層と、該種結晶層上に、AlyGa1-yN(0.5<y≦1)を主成分とする第一導電型クラッド層と、AlGaN系活性層と、AlzGa1-zN(0.5<z≦1)を主成分とする第二導電型クラッド層とが順に積層成長されたエピタキシャル層を有するエピタキシャルウェーハにより、安価で光取り出し効率の良い高品質なエピタキシャルウェーハを提供することができることを見出し、この発明を完成させた。
図1に示す本発明の紫外線発光素子用エピタキシャルウェーハ100は、貼り合わせによって作製された基板(貼り合わせ基板1)と、窒化物半導体からなる紫外線発光素子層2を有する。
貼り合せ基板1は、第一支持基板3と接着層4と種結晶層5とを有しており、第一支持基板3上に、種結晶(種結晶層5)を貼り合わせて接合されたものである。ここでは、第一支持基板3と種結晶層5とが接着層4により接合されて作製されたものである。
種結晶層5がこのような貼り合わせによるものであるため、貼り合わせ元の上記の自立基板等(すなわち、種結晶層5の剥離で分離された種基板)を、表面研磨してイオン注入面とすることによって、更に別の本発明の紫外線発光素子用エピタキシャルウェーハを作製する際の種結晶層のために繰り返し利用することができる。このように、比較的高価なAlxGa1-xN(0.5<x≦1)単結晶の基板を繰り返し有効に使うことができるため、全体としてコストを抑制することができ、その結果、種結晶層5、さらには本発明の紫外線発光素子用エピタキシャルウェーハ100は安価なものとなる。
あるいは、貼り合わせ基板1がこのような接着層4で接合されたものではなく、種結晶層5となるAlGaN単結晶の表面をプラズマやアルゴンイオンエッチングによって、活性化してアモルファス層を形成し、加圧、加熱する方法で第一支持基板3と貼り合わせて接合されたものとすることもできる。
貼り合わせ基板1上にホモエピタキシャル層6がエピタキシャル成長されている。ホモエピタキシャル層は、結晶品質を向上させるために導入され、厚さ100nm~500nmの範囲で設計することができる。ホモエピタキシャル層は、デバイスの設計により省略することもできる。
AlGaN系活性層8は、量子井戸構造を有しており、障壁層9と井戸層10が交互に積層されている(MQW構造)。なお、例えば、Al、Ga、N以外の構成元素としてInが存在し、該Inの割合が0%より大きく1%未満であるものとすることができる。このようなものであれば、内部量子効率が向上され、より効率良く発光させることができるので好ましい。また、AlGaN系活性層8は、25℃、0.2A/mm2の電流注入時に発光するスペクトルのピーク波長λpが235nmより短波長であるものとすることができ、このようなものであれば特には深紫外線領域の光をより確実に得ることができ、殺菌用光源として有用である。この深紫外線領域の発光スペクトルのピーク波長λpの下限としては、例えば200nmとすることができる。特に膜厚は限定されないが、例えば障壁層6nm、井戸層1.5nmで3層積層とすることができる。
第二導電型クラッド層11(AlzGa1-zN(0.5<z≦1)が主成分)は、AlGaN系活性層8へ正孔を供給するために形成されているものである。特に膜厚は限定されないが、例えば30nmとすることができる。
これらの層が順にエピタキシャル成長により積層されている。
まず、貼り合わせ基板1の製造工程について説明する。
AlxGa1-xN(0.5<x≦1)単結晶の種基板13(例えばAlN基板)を用意して一つの面(イオン注入面)からイオン注入を行う(工程A)。このとき注入するイオンは、例えば、水素イオンや希ガスイオンなどとすることができる。これにより、種基板13内に、剥離位置となる脆弱層(ダメージ層)14を形成する(工程B)。
次に、種基板13のイオン注入面を、別途用意した第一支持基板3(例えば合成石英基板)上に形成した接着層4(例えばSiO2層)と接合して接合基板15とする(工程C)。
一方、分離された種基板13の残部は、再びこの表面を研磨してイオン注入面とすることによって、更に別の貼り合わせ基板を作製する際の種結晶層のために繰り返し利用することができる。
[1]反応炉への導入
貼り合わせ基板1をMOVPE装置の反応炉内に導入する。貼り合わせ基板1を反応炉に導入する前に、薬品によりクリーニングを行う。貼り合わせ基板1を反応炉内に導入後、窒素などの高純度不活性ガスで炉内を満たして、炉内のガスを排気する。
貼り合わせ基板1を反応炉内で加熱して、基板の表面をクリーニングする。クリーニングを行う温度は、貼り合わせ基板表面の温度で1000℃から1200℃の間で決めることができるが、特に1050℃でクリーニングを行うことで清浄な表面を得ることができる。
クリーニングは、炉内の圧力が減圧された後に実施し、炉内圧力は200mbarから30mbarの間で決めることができる。炉内には、水素、窒素、アンモニアなどからなる混合カスを供給した状態で、例えば10分間程度クリーニングを行う。これらの条件は一例であり、特に限定されるものではない。
この工程では、規定の炉内圧力および基板温度において、原料であるAl,Ga,N源となるガスを導入することによって、貼り合わせ基板1上に、AlxGa1-xN(0.5<x≦1)をエピタキシャル成長させる(ホモエピタキシャル層6)。
この工程では、例えば炉内圧力は50mbar、基板温度1120℃で成長を行うことができる。Al源としてはトリメチルアルミニウム(TMAl),Ga源としてはトリメチルガリウム(TMGa),N源としてはアンモニア(NH3)を用いることができる。また、所望のAl組成の混晶を得るために、原料ガスの材料効率を考慮して、薄膜中に取り込まれるAl/Ga比が設定している比率になるように、原料のTMAl,TMGaの流量を設定する。この工程では、TMAlの流量を標準状態で例えば0.24L/min(240sccm),NH3の流量は例えば2.0L/min(2000sccm)でAlNの成長を行うことができる。TMAl,TMGa,NH3のキャリアガスは例えば水素を使用することができる。これらの条件は一例であり、特に限定されるものではない。
この工程は、ホモエピタキシャル層6の上に第一導電型クラッド層7を成長する工程である。
この工程では、反応炉内を規定の炉内圧力、基板温度に保持した後、原料のTMAl,TMGa,NH3,およびn型導電性にするための不純物ガスを、炉内に供給して第一導電型クラッド層7を成長する。第一導電型クラッド層7は、主成分がAlyGa1-yN(0.5<y≦1)で表される組成で自由に作製することができるが、一例としてAl0.95Ga0.05Nとすることができる。組成を変えて複数層形成してもよい。
この工程の炉内圧力は例えば75mbar,基板温度は1100℃とすることができる。所望のAl組成の混晶を得るために、原料ガスの材料効率を考慮して、薄膜中に取り込まれるAl/Ga比が設定している比率になるように、原料のTMAl,TMGaの流量を設定する。これらの値は、一例であり特に限定されるものではない。
n型導電性にするための不純物ガスは、モノシラン(SiH4)を用いることができる。原料ガスを輸送するためのキャリアガスは、水素を用いることができる。なお、不純物ガスとして、テトラエチルシランを用いてもよい。
この工程は、第一導電型クラッド層7の上にAlGaN系活性層8を成長する工程である。この工程では、反応炉内を規定の炉内圧力、基板温度に保持した後、原料のTMAl,TMGa,NH3を炉内に供給してAlGaN系活性層8を成長する。AlGaN系活性層8は、一例として障壁層9:Al0.75Ga0.25N,井戸層10:Al0.6Ga0.4Nとすることができる。また、この工程の炉内圧力は例えば75mbar,基板温度は1100℃とすることができる。各層で所望のAl組成の混晶を得るために、原料ガスの材料効率を考慮して、薄膜中に取り込まれるAl/Ga比が設定している比率になるように、原料のTMAl,TMGaの流量を設定する。これらの値は、一例であり特に限定されるものではない。
この工程は、AlGaN系活性層8の上に第二導電型クラッド層11を成長する工程である。この工程では、反応炉内を規定の炉内圧力、基板温度に保持した後、原料のTMAl,TMGa,NH3,およびp型導電性にするための不純物原料を、炉内に供給して第二導電型クラッド層11を成長する。第二導電型クラッド層11は、AlzGa1-zN(0.5<z≦1)で表される組成で自由に作製することができるが、一例としてAl0.95Ga0.05Nとすることができる。組成を変えて複数層形成してもよい。
この工程の炉内圧力は例えば75mbar,基板温度は1100℃とすることができる。所望のAl組成の混晶を得るために、原料ガスの材料効率を考慮して、薄膜中に取り込まれるAl/Ga比が設定している比率になるように、原料のTMAl,TMGaの流量を設定する。これらの値は、一例であり特に限定されるものではない。
p型導電性にするための不純物原料は、ビスシクロペンタジエニルマグネシウム(Cp2Mg)を用いることができる。また、原料ガスを輸送するためのキャリアガスは、水素を用いることができる。
この工程は、第二導電型クラッド層11の上にp型AlGaNコンタクト層12を成長する工程である。この工程では、反応炉内を規定の炉内圧力、基板温度に保持した後、原料のTMAl,TMGa,NH3,およびp型導電性にするための不純物原料を、炉内に供給してp型AlGaNコンタクト層12を成長する。この工程の炉内圧力は例えば75mbar,基板温度は1100℃とすることができる。これらの値は、一例であり特に限定されるものではない。
p型導電性にするための不純物原料は、ビスシクロペンタジエニルマグネシウム(Cp2Mg)を用いることができる。また、原料ガスを輸送するためのキャリアガスは、水素を用いることができる。
この工程では、加熱炉内で所定の温度、時間でウェーハをアニールすることで、第二導電型クラッド層11、p型AlGaNコンタクト層12のp型不純物を活性化させる。加熱炉内での活性化は、例えば750℃で10分とすることができる。
また、種結晶層の剥離転写をした後のAlN単結晶基板やAlGaN単結晶基板を回収して、再研磨することにより、高価な化合物半導体単結晶基板を種基板として再利用して種結晶層を新たに剥離転写できるので、紫外線領域の発光ダイオード用エピタキシャル基板を安価に製造することができる。
(実施例)
図1、2に示すような深紫外線発光ダイオード用エピタキシャルウェーハを、図3のような本発明の製造方法により製造した。すなわち、貼り合わせ基板の製造工程A-Eと、紫外線発光素子層の製造工程F(前述した工程[1]-[8])により製造した。
サファイヤ基板上に、SiO2からなる接着層(平坦化層)を2μm成長し、平坦化のため表面にCMP加工を行った。その後、上記のサファイヤ基板にAlN単結晶からなる種結晶(種基板)を常温接合で貼り合わせて剥離転写した基板(貼り合わせ基板)を準備した。
貼り合わせ基板上に、MOVPE法でAl0.95Ga0.05Nを100nm成長し、その上にn型Al0.95Ga0.05Nを2.5μm成長した。その上に、3層の障壁層:Al0.75Ga0.25N、井戸層:Al0.6Ga0.4Nからなる量子井戸構造を形成した。その後、p型Al0.95Ga0.05N層とp型GaNコンタクト層を形成した。
AlNのセラミックスで作製された基板上に、SiO2からなる平坦化層を2μm成長し、Al0.95Ga0.05N単結晶からなる種結晶を貼り合わせて剥離転写した基板(貼り合わせ基板)を準備した。
貼り合わせ基板上に、MOVPE法でAl0.95Ga0.05Nを100nm成長し、その上にn型Al0.95Ga0.05Nを2.5μm成長した。その上に、3層の障壁層:Al0.75Ga0.25N,井戸層:Al0.6Ga0.4Nからなる量子井戸構造を形成した。その後、p型Al0.95Ga0.05N層とp型GaNコンタクト層を形成した。
より具体的には、実施例が8%、比較例1は4%以下で多くは3%程度であった。
以下のようにして、サファイヤ基板を用いた深紫外線領域の発光ダイオード用エピタキシャル基板を製造した。
[1]反応炉への導入
サファイヤ基板をMOVPE装置の反応炉内に導入した。サファイヤ基板を反応炉に導入する前に、薬品によりクリーニングを行った。サファイヤ基板を反応炉内に導入後、窒素などの高純度不活性ガスで炉内を満たして、炉内のガスを排気した。
サファイヤ基板を反応炉内で加熱して、基板の表面のクリーニングを行った。クリーニングは1030℃の温度で行った。また、炉内圧力は150mbarとした。炉内には、水素あるいは窒素を供給した状態で10分間クリーニングを行った。
この工程では、規定の炉内圧力および基板温度において、原料であるAl,Ga,N源となるガスを導入することによって、サファイヤ基板上に、エピタキシャル層の結晶性を改善するためのバッファー層を成長する。基板上の核形成層と成長条件を調整し、低速で成長する低速成長層と高速成長層を繰り返すことにより転位を低減する層を形成した。紫外LEDとして好適な基板を得るために、バッファー層を3μm成長した。
特に実施例と比較例2の結果を比較してみたところ、実施例の深紫外線発光ダイオード用エピタキシャル基板のAlN(0002)のXRDロッキングカーブのFWHMが43arcsecであるのに対して、比較例2のFWHMは541arcsecであり、実施例は比較例2に比べて結晶性の良いエピタキシャルウェーハを得ることができた。
このように、本発明のように貼り合わせにより形成した種結晶層の上でエピタキシャル成長することによって、より結晶性の高い高品質なエピタキシャルウェーハを得られる。
Claims (12)
- 紫外光に透明で耐熱性のある第一支持基板と、
該第一支持基板上に、貼り合わせにより接合されたAlxGa1-xN(0.5<x≦1)単結晶の種結晶層と、
該種結晶層上に、AlyGa1-yN(0.5<y≦1)を主成分とする第一導電型クラッド層と、AlGaN系活性層と、AlzGa1-zN(0.5<z≦1)を主成分とする第二導電型クラッド層とが順に積層成長されたエピタキシャル層を有することを特徴とする紫外線発光素子用エピタキシャルウェーハ。 - 前記第一支持基板の主成分が、合成石英またはサファイヤであることを特徴とする請求項1に記載の紫外線発光素子用エピタキシャルウェーハ。
- 前記AlGaN系活性層がMQW構造で形成されており、Al、Ga、N以外の構成元素としてInが存在し、該Inの割合が1%未満であることを特徴とする請求項1または請求項2に記載の紫外線発光素子用エピタキシャルウェーハ。
- 前記AlGaN系活性層が、25℃、0.2A/mm2の電流注入時に発光するスペクトルのピーク波長λpが235nmより短波長であることを特徴とする請求項1から請求項3のいずれか一項に記載の紫外線発光素子用エピタキシャルウェーハ。
- 前記種結晶層のバンドギャップが、前記AlGaN系活性層のバンドギャップよりも大きいものであることを特徴とする請求項1から請求項4のいずれか一項に記載の紫外線発光素子用エピタキシャルウェーハ。
- 前記種結晶層は、エピタキシャル成長面がC面であることを特徴とする請求項1から請求項5のいずれか一項に記載の紫外線発光素子用エピタキシャルウェーハ。
- 紫外光に透明で耐熱性のある第一支持基板上に、AlxGa1-xN(0.5<X≦1)単結晶より剥離転写して種結晶層を貼り合わせて貼り合わせ基板を作製する工程と、
該貼り合わせ基板上に、AlyGa1-yN(0.5<y≦1)を主成分とする第一導電型クラッド層と、AlGaN系活性層と、AlzGa1-zN(0.5<z≦1)を主成分とする第二導電型クラッド層とを順にエピタキシャル成長させたエピタキシャル層を形成する工程を含む紫外線発光素子用エピタキシャルウェーハの製造方法。 - 前記第一支持基板を、合成石英またはサファイヤが主成分のものとすることを特徴とする請求項7に記載の紫外線発光素子用エピタキシャルウェーハの製造方法。
- 前記AlGaN系活性層をMQW構造で形成し、Al、Ga、N以外の構成元素としてInを含め、該Inの割合を1%未満とすることを特徴とする請求項7または請求項8に記載の紫外線発光素子用エピタキシャルウェーハの製造方法。
- 前記AlGaN系活性層を、25℃、0.2A/mm2の電流注入時に発光するスペクトルのピーク波長λpが235nmより短波長のものとすることを特徴とする請求項7から請求項9のいずれか一項に記載の紫外線発光素子用エピタキシャルウェーハの製造方法。
- 前記種結晶層を、バンドギャップが前記AlGaN系活性層のバンドギャップよりも大きいものとすることを特徴とする請求項7から請求項10のいずれか一項に記載の紫外線発光素子用エピタキシャルウェーハの製造方法。
- 前記種結晶層のエピタキシャル成長面をC面とすることを特徴とする請求項7から請求項11のいずれか一項に記載の紫外線発光素子用エピタキシャルウェーハの製造方法。
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