WO2021240591A1 - Method for producing nitride semiconductor photocatalyst thin film - Google Patents

Method for producing nitride semiconductor photocatalyst thin film Download PDF

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WO2021240591A1
WO2021240591A1 PCT/JP2020/020511 JP2020020511W WO2021240591A1 WO 2021240591 A1 WO2021240591 A1 WO 2021240591A1 JP 2020020511 W JP2020020511 W JP 2020020511W WO 2021240591 A1 WO2021240591 A1 WO 2021240591A1
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thin film
gallium nitride
nitride semiconductor
nitride layer
producing
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French (fr)
Japanese (ja)
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裕也 渦巻
紗弓 里
陽子 小野
武志 小松
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日本電信電話株式会社
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Priority to JP2022527273A priority Critical patent/JP7406167B2/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
    • C23C16/34—Nitrides
    • 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
    • C30B29/38—Nitrides

Definitions

  • the present invention relates to a method for manufacturing a nitride semiconductor photocatalytic thin film.
  • the water decomposition reaction using a photocatalyst consists of a water oxidation reaction and a proton reduction reaction.
  • n-type photocatalyst material When the n-type photocatalyst material is irradiated with light, electrons and holes are generated and separated in the photocatalyst. Holes move to the surface of the photocatalytic material and contribute to the reduction reaction of protons. On the other hand, electrons move to the reduction electrode and contribute to the reduction reaction of protons. Ideally, such a redox reaction proceeds and a water splitting reaction occurs.
  • a conventional water decomposition device has an oxide tank and a reduction tank connected via a proton exchange membrane, and puts an aqueous solution and an oxidation electrode in the oxide tank, and puts an aqueous solution and a reduction electrode in the reduction tank.
  • the oxide electrode and the reduction electrode are electrically connected by a conducting wire.
  • the oxide electrode is, for example, a nitride semiconductor, titanium oxide, or amorphous silicon.
  • the reducing electrode is a metal or a metal compound, for example nickel, iron, gold, platinum, silver, copper, indium, titanium.
  • a water decomposition reaction is caused by irradiating the light source with light having a wavelength that can be absorbed by the material constituting the oxide electrode.
  • the wavelength that can be absorbed is 365 nm or less.
  • the light source is, for example, a xenon lamp, a mercury lamp, a halogen lamp, a pseudo-solar light source, or sunlight, and these may be combined.
  • the water decomposition device as described above has many components and the reaction system is complicated, it is desired to realize a simpler reaction system and downsize the reaction system.
  • the photocatalyst thin film in the aqueous solution is irradiated with light from a light source to cause a water splitting reaction.
  • the photocatalytic thin film like the oxide electrode, is a nitride semiconductor, titanium oxide, or amorphous silicon.
  • a metal co-catalyst that promotes the decomposition reaction of water is supported on the surface of the photocatalyst thin film.
  • the reaction system of the device that produces hydrogen and oxygen by a single photocatalytic thin film is simple, and it is expected that the cost and size of the system will be reduced.
  • the oxide electrode and the photocatalyst thin film are semiconductor thin films, and for example, a gallium nitride thin film grown on a sapphire substrate is used.
  • a gallium nitride thin film grown on a sapphire substrate is used.
  • the gallium nitride thin film holes generated and separated under light irradiation are consumed in the etching reaction of gallium nitride itself at the same time as the oxidation reaction of water. Therefore, there is a problem that the light electrode deteriorates and the light energy conversion efficiency decreases with the light irradiation time.
  • an auxiliary catalyst for oxygen generation nickel oxide
  • the valence band of the gallium nitride semiconductor needs to be at a lower level than the valence band of nickel oxide.
  • the level of the valence band increases as the band gap narrows.
  • the valence band of nickel oxide produced by the conventional method is located at a lower level than the valence band of the visible responsive semiconductor photocatalyst thin film, and a barrier is created in which holes cannot move. Therefore, even if the light absorption rate is improved, there is a problem that holes cannot move due to the generated barrier and the hole does not function as a co-catalyst protective layer.
  • the present invention has been made in view of the above, and an object thereof is to improve efficiency and life in a single nitride semiconductor photocatalytic thin film having a high light absorption rate.
  • the method for producing a nitride semiconductor photocatalyst thin film is a method for producing a nitride semiconductor photocatalyst thin film that exerts a catalytic function by light irradiation and causes an oxidation-reduction reaction, and is an insulating or conductive substrate.
  • the first step of forming an n-type gallium nitride layer on the surface the second step of forming an indium gallium nitride layer on the surface of the n-type gallium nitride layer, and a metal layer on a part of the surface of the indium gallium nitride layer.
  • the third step of forming the indium gallium nitride the fourth step of heat-treating to form an ohmic bond at the interface between the indium gallium nitride layer and the metal layer, and p-type metal oxidation on a part of the surface of the indium gallium nitride layer. It has a fifth step of forming an object and a sixth step of heat-treating the p-type metal oxide.
  • efficiency and life can be improved in a single nitride semiconductor photocatalytic thin film having a high light absorption rate.
  • FIG. 1 is a cross-sectional view showing the configuration of a nitride semiconductor photocatalyst thin film produced by the method for producing a nitride semiconductor photocatalyst thin film of the present embodiment.
  • FIG. 2 is a diagram for explaining a metal layer dispersed and arranged on the surface of a nitride semiconductor photocatalyst thin film and a p-type metal oxide.
  • FIG. 3 is a flowchart showing a method for manufacturing the nitride semiconductor photocatalyst thin film of the present embodiment.
  • FIG. 4 is a diagram showing an outline of an apparatus for performing a redox reaction test.
  • FIG. 1 is a cross-sectional view showing the configuration of a nitride semiconductor photocatalyst thin film produced by the method for producing a nitride semiconductor photocatalyst thin film of the present embodiment.
  • the nitride semiconductor photocatalytic thin film of FIG. 1 is a nitride semiconductor photocatalytic thin film that exerts a catalytic function by irradiation with light in an aqueous solution to cause a redox reaction.
  • the nitride semiconductor photocatalyst thin film 1 shown in FIG. 1 is an insulating or conductive substrate 11, the surface of an n-type gallium nitride (n-GaN) layer 12 and an n-type gallium nitride layer 12 arranged on the surface of the substrate 11.
  • the indium gallium nitride (InGaN) layer 13 arranged above, the metal layer 14 forming an ohmic bond on a part of the surface of the indium gallium nitride layer 13, and the part of the surface of the indium gallium nitride layer 13 are dispersed and arranged.
  • a p-type metal oxide 15 is provided.
  • the holes generated in the indium gallium nitride layer 13 by light irradiation move to the p-type metal oxide 15. become able to.
  • the metal layer 14 and the p-type metal oxide 15 are dispersed and arranged on the indium gallium nitride layer 13. Specifically, as shown in FIG. 2, the metal layer 14 has a disk shape with a diameter of 10 ⁇ m and is dispersedly arranged at intervals of 210 ⁇ m.
  • the p-type metal oxide 15 has a disk shape with a diameter of 10 ⁇ m, and is dispersed and arranged with a space of 100 ⁇ m from the metal layer 14.
  • the n-type gallium nitride layer 12 is formed on the insulating or conductive substrate 11.
  • the n-type gallium nitride layer 12 may be formed by using a metalorganic vapor phase growth method (MOCVD).
  • step S2 the indium gallium nitride layer 13 is formed on the n-type gallium nitride layer 12.
  • the indium gallium nitride layer 13 may be formed by using MOCVD.
  • the metal layer 14 is formed on a part of the surface of the indium gallium nitride layer 13.
  • the metal layer 14 may be formed by a vapor deposition method or a sputtering method using a material having a co-catalytic function with respect to the indium gallium nitride layer 13.
  • step S4 the nitride semiconductor on which the metal layer 14 is formed is heat-treated in order to form an ohmic contact at the interface between the indium gallium nitride layer 13 and the metal layer 14.
  • the p-type metal oxide 15 is formed on a part of the surface of the indium gallium nitride layer 13.
  • the p-type metal oxide 15 may be formed by a vapor deposition method or a sputtering method using p—NiO.
  • step S6 the nitride semiconductor on which the p-type metal oxide 15 is formed is heat-treated.
  • the temperature of the heat treatment is preferably 200 ° C. or higher and 800 ° C. or lower.
  • Examples 1 to 5 are examples of a method for manufacturing a nitride semiconductor photocatalyst thin film in which the heat treatment temperature in step S6 is changed.
  • Examples 6 to 10 and Examples 11 to 15 are examples of a method for producing a nitride semiconductor photocatalytic thin film in Examples 1 to 5 in which the composition ratio of lithium is changed.
  • Example 16 is an example of a method for producing a nitride semiconductor photocatalyst thin film in which the composition ratio of lithium is changed in Example 1.
  • Examples 17 and 18 are examples of a method for producing a nitride semiconductor photocatalytic thin film in which the method for forming the p-type metal oxide 15 in step S5 of Examples 1 and 3 is changed.
  • Examples 19 and 20 are examples of a method for producing a nitride semiconductor photocatalytic thin film in which impurities are changed when producing p—NiO in Example 1.
  • step S5 of Examples 1 and 3 comparative examples 1 and 2 using NiO instead of p-NiO will also be described.
  • step S1 a silicon-doped n-GaN semiconductor thin film was epitaxially grown on a 2-inch sapphire substrate by MOCVD to form an n-type gallium nitride layer 12.
  • a sapphire substrate was used as the substrate 11.
  • Ammonia gas and trimethylgallium were used as growth raw materials.
  • Silane gas was used as the n-type impurity source.
  • Hydrogen was used as the carrier gas sent into the growth furnace.
  • the film thickness of the n-type gallium nitride layer 12 was set to 2 ⁇ m, which is sufficient to absorb light.
  • the carrier density was 3 ⁇ 10 18 cm -3 .
  • step S2 indium gallium nitride (InGaN) having an indium composition ratio of 5% was grown on the n-type gallium nitride layer 12 by MOCVD to form the indium gallium nitride layer 13.
  • Ammonia gas, trimethylgallium, and trimethylindium were used as growth raw materials.
  • Hydrogen was used as the carrier gas sent into the growth furnace.
  • the film thickness of the indium gallium nitride layer 13 was set to 100 nm, which is sufficient to absorb light.
  • step S3 a disk-shaped metal layer 14 having a diameter of 10 ⁇ m was vacuum-deposited on the surface of the indium gallium nitride layer 13 at intervals of 210 ⁇ m.
  • Ti was laminated with a thickness of 25 nm, Al at 50 nm, Ti at 25 nm, and Pt at 100 nm in order from the semiconductor side.
  • step S4 the semiconductor thin film on which the metal layer 14 was formed was heat-treated at 800 ° C. for 30 seconds in a nitrogen atmosphere. By heat treatment, a pseudo ohmic contact was formed at the interface between the indium gallium nitride layer 13 and the metal layer 14.
  • step S5 a disk-shaped p-NiO having a diameter of 10 ⁇ m is vacuum-deposited at a film thickness of 2 nm on the surface of the indium gallium nitride layer 13 at intervals of 100 ⁇ m from the metal layer 14, and the metal layers 14 are deposited at intervals of 100 ⁇ m.
  • the p-type metal oxide 15 was formed so that the p-type metal oxide 15 and the p-type metal oxide 15 were alternately arranged.
  • the weights of the NiO powder and the lithium oxide powder are determined so that the composition ratio of Li becomes a desired value, and the NiO powder and the lithium oxide powder are mixed and electrically charged. It was produced by heat treatment in a furnace.
  • the weights of the NiO powder and the lithium oxide powder were determined so that the Li composition ratio was 1% (Ni composition ratio was 99%).
  • the volume resistivity of the obtained p-NiO powder was about 4 orders of magnitude lower than the volume resistivity of the NiO powder, and it was found that the NiO powder was p-shaped and the conductivity was improved.
  • step S6 the semiconductor thin film obtained in step S5 was heat-treated on a hot plate at 200 ° C. for 1 hour in an air atmosphere.
  • heat treatment may be performed in an electric furnace.
  • Example 1 the nitride semiconductor photocatalyst thin film of Example 1 was obtained.
  • Example 2 In the method for producing a nitride semiconductor photocatalytic thin film of Example 2, the heat treatment temperature was set to 500 ° C. in the heat treatment in step S6. In other respects, it is the same as in Example 1.
  • Example 3 In the method for producing a nitride semiconductor photocatalytic thin film of Example 3, the heat treatment temperature was set to 800 ° C. in the heat treatment in step S6. In other respects, it is the same as in Example 1.
  • Example 4 In the method for producing a nitride semiconductor photocatalytic thin film of Example 4, the heat treatment temperature was set to 100 ° C. in the heat treatment in step S6. In other respects, it is the same as in Example 1.
  • Example 5 In the method for producing a nitride semiconductor photocatalytic thin film of Example 5, the heat treatment temperature was set to 900 ° C. in the heat treatment in step S6. In other respects, it is the same as in Example 1.
  • Example 6 In the method for producing a nitride semiconductor photocatalytic thin film of Example 6, when the p—NiO used in step S5 of Example 1 is produced, the composition ratio of Li is 10% (the ratio of Li to Ni is 1: 9). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 1.
  • Example 7 In the method for producing a nitride semiconductor photocatalytic thin film of Example 7, when the p—NiO used in step S5 of Example 2 is produced, the composition ratio of Li is 10% (the ratio of Li to Ni is 1: 9). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 2.
  • Example 8 In the method for producing a nitride semiconductor photocatalytic thin film of Example 8, when the p—NiO used in step S5 of Example 3 is produced, the composition ratio of Li is 10% (the ratio of Li to Ni is 1: 9). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 3.
  • Example 9 In the method for producing a nitride semiconductor photocatalytic thin film of Example 9, when the p—NiO used in step S5 of Example 4 is produced, the composition ratio of Li is 10% (the ratio of Li to Ni is 1: 9). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 4.
  • Example 10 In the method for producing a nitride semiconductor photocatalytic thin film of Example 10, when the p—NiO used in step S5 of Example 5 is produced, the composition ratio of Li is 10% (the ratio of Li to Ni is 1: 9). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 5.
  • Example 11 In the method for producing a nitride semiconductor photocatalytic thin film of Example 11, when p—NiO used in step S5 of Example 1 is produced, the composition ratio of Li is 40% (the ratio of Li to Ni is 4: 6). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 1.
  • Example 12 In the method for producing a nitride semiconductor photocatalytic thin film of Example 12, when the p—NiO used in step S5 of Example 2 is produced, the composition ratio of Li is 40% (the ratio of Li to Ni is 4: 6). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 2.
  • Example 13 In the method for producing a nitride semiconductor photocatalytic thin film of Example 13, when the p—NiO used in step S5 of Example 3 is produced, the composition ratio of Li is 40% (the ratio of Li to Ni is 4: 6). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 3.
  • Example 14 In the method for producing a nitride semiconductor photocatalytic thin film of Example 14, when the p—NiO used in step S5 of Example 4 is produced, the composition ratio of Li is 40% (the ratio of Li to Ni is 4: 6). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 4.
  • Example 15 In the method for producing a nitride semiconductor photocatalyst thin film of Example 15, when the p—NiO used in step S5 of Example 5 is produced, the composition ratio of Li is 40% (the ratio of Li to Ni is 4: 6). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 5.
  • Example 16 In the method for producing a nitride semiconductor photocatalytic thin film of Example 16, when the p—NiO used in step S5 of Example 1 is produced, the composition ratio of Li is 50% (the ratio of Li to Ni is 5: 5). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 1.
  • Example 17 In the method for producing a nitride semiconductor photocatalytic thin film of Example 17, a target (sintered body) was prepared from p—NiO powder in step S5 of Example 1, and a p-type metal oxide 15 was formed by a sputtering method. In other respects, it is the same as in Example 1.
  • Example 18 In the method for producing a nitride semiconductor photocatalytic thin film of Example 18, a target (sintered body) was prepared from p—NiO powder in step S5 of Example 3, and a p-type metal oxide 15 was formed by a sputtering method. In other respects, it is the same as in Example 3.
  • Example 19 In the method for producing a nitride semiconductor photocatalytic thin film of Example 19, p—NiO prepared by using silver (Ag) as an impurity was vapor-deposited in step S5 of Example 1. In other respects, it is the same as in Example 1.
  • Example 20 In the method for producing a nitride semiconductor photocatalytic thin film of Example 20, p—NiO prepared by using potassium (K) as an impurity was vapor-deposited in step S5 of Example 1. In other respects, it is the same as in Example 1.
  • a reaction cell with a quartz window having an internal capacity of 150 ml was used as the photocatalyst tank 110, and the stirrer 120 and the aqueous solution 130 were placed in the photocatalyst tank 110.
  • As the aqueous solution 130 125 ml of a 1 mol / l potassium hydroxide aqueous solution was used.
  • the semiconductor photocatalytic thin films of Examples 1 to 20 and Comparative Examples 1 and 2 were immersed in the aqueous solution 130 so that the surface of the indium gallium nitride layer 13 forming the metal layer 14 and the p-type metal oxide 15 faces the light source 140. Fixed.
  • Nitrogen gas was bubbled at 200 ml / min for 30 minutes to complete defoaming and replacement with air, and then sealed with silicon Teflon septum.
  • the pressure in the photocatalyst tank 110 was set to atmospheric pressure (1 atm).
  • the light source 140 As the light source 140 , a 300 W high-voltage xenon lamp (wavelength 400 nm or more cut, illuminance 5 mW / cm 2 ) was used. The light from the light source 140 was uniformly applied to the semiconductor photocatalyst thin film from the outside of the quartz window of the photocatalyst tank 110.
  • the light irradiation area of the sample was 1 cm 2, and the aqueous solution 130 was stirred at the center position of the bottom of the photocatalyst tank 110 at a rotation speed of 250 rpm using a stirrer 120 and a stirrer.
  • the gas in the photocatalyst tank 110 was collected from the septum portion with a syringe, and the reaction product was analyzed with a gas chromatograph mass spectrometer. As a result, it was confirmed that hydrogen and oxygen were generated.
  • Table 1 shows the amounts of oxygen and hydrogen gas produced 1 hour and 10 hours after the light irradiation in Examples 1 to 20 and Comparative Examples 1 and 2.
  • the amount of each gas produced is standardized by the surface area of the semiconductor photocatalyst thin film.
  • Example 16 in which the composition ratio of lithium was 50%, it was found that a single phase of NiO could not be obtained, lithium oxide remained as an impurity, and p-NiO could not be obtained.
  • the amount of hydrogen / oxygen produced 10 hours after the light irradiation of Examples 1, 2, 3, 6, 7, 8, 11, 12, 13, 17, and 18 having a heat treatment temperature of 200 ° C. to 800 ° C. is the other implementation. It was found to be 20 times higher than the amount produced after 10 hours in the example.
  • the heat treatment conditions for forming the p-type metal oxide 15 that can be expected to extend the service life are a temperature of 200 ° C. or higher and 800 ° C. or lower.
  • the amount of oxygen and hydrogen produced 1 hour and 10 hours after the light irradiation of Examples 17 and 18 and Examples 1 and 3 was about the same, and even if the p-type metal oxide 15 was formed by the sputtering method, it was vapor-deposited. It was found that the same effect as that for forming the p-type metal oxide 15 can be obtained by the method.
  • Comparative Target Examples 1 and 2 the amount of hydrogen and oxygen produced was low both 1 hour and 10 hours after the light irradiation. This is considered to be due to the fact that holes cannot move through the barrier at the InGaN interface in the case of NiO.
  • the heat treatment conditions for forming the p-type metal oxide 15 in step S6 are set to 200 ° C. or higher and 800 ° C. or lower, and the composition of Li for producing the p—NiO powder used for forming the p-type metal oxide 15 in step S5.
  • the ratio is set to 40% or less with respect to Ni, it was possible to improve the efficiency of the water splitting reaction (light energy conversion efficiency) and extend the service life.
  • the formation of the p-type metal oxide 15 is not limited to the vapor deposition method, but the sputtering method is also effective, and it is also effective to use Ag or K as an impurity when producing p—NiO, not limited to Li. all right.
  • the method for manufacturing the nitride semiconductor photocatalyst thin film of the present embodiment includes a step of forming the n-type gallium nitride layer 12 on the insulating or conductive substrate 11 and a step of forming the n-type gallium nitride layer 12 on the n-type gallium nitride layer 12.
  • It has a step of heat-treating, a step of forming a p-type metal oxide 15 on a part of the surface of the indium gallium nitride layer 13, and a step of heat-treating a semiconductor thin film on which the p-type metal oxide 15 is formed.
  • a p-type metal oxide 15 exhibiting characteristics as a p-type semiconductor is formed on the indium gallium nitride layer 13 as an auxiliary catalyst for an oxidation reaction, and a metal layer 14 is provided on the same surface of the indium gallium nitride layer 13 as an auxiliary catalyst for a reduction reaction.
  • the target product is hydrogen
  • the metal on the surface of the metal layer 14 which is the auxiliary catalyst for the reduction reaction is, for example, Ni, Fe, Au, Pt, Ag, Cu, In, Ti, Co.
  • the aqueous solution 130 used in the redox reaction test may be an aqueous solution in which an electrolyte for ion transfer such as potassium hydroxide aqueous solution or hydrochloric acid is dissolved, in addition to sodium hydroxide.
  • an electrolyte for ion transfer such as potassium hydroxide aqueous solution or hydrochloric acid is dissolved, in addition to sodium hydroxide.
  • GaN is preferably an alkaline aqueous solution.
  • Nitride semiconductor photocatalyst thin film 11 Nitride semiconductor photocatalyst thin film 11 .
  • Substrate 12 n-type gallium nitride layer 13 .
  • Indium gallium nitride layer 14 ...
  • Metal layer 15 P-type metal oxide

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Abstract

A method for producing a nitride semiconductor photocatalyst thin film 1 that causes an oxidation-reduction reaction by exerting a catalytic function upon irradiation of light, wherein: an n-type gallium nitride layer 12 is formed on the surface of an insulating or conductive substrate 11; an indium gallium nitride layer 13 is formed in the surface of the n-type gallium nitride layer 12; a metal layer 14 is formed in a part of the surface of the indium gallium nitride layer 13; a heat treatment is carried out so as to form an ohmic junction at the interface between the indium gallium nitride layer 13 and the metal layer 14; a p-type metal oxide 15 is formed in a part of the surface of the indium gallium nitride layer 13; and the p-type metal oxide 15 is subjected to a heat treatment.

Description

窒化物半導体光触媒薄膜の製造方法Method for manufacturing nitride semiconductor photocatalytic thin film
　本発明は、窒化物半導体光触媒薄膜の製造方法に関する。 The present invention relates to a method for manufacturing a nitride semiconductor photocatalytic thin film.
　光触媒を用いた水の分解反応は、水の酸化反応とプロトンの還元反応からなる。 The water decomposition reaction using a photocatalyst consists of a water oxidation reaction and a proton reduction reaction.
　酸化反応：２Ｈ2Ｏ＋４ｈ+→Ｏ2＋４Ｈ+
　還元反応：４Ｈ+＋４ｅ-→２Ｈ2 Oxidation reaction: 2H 2 O + 4h + → O 2 + 4H +
Reduction reaction: 4H + + 4e - → 2H 2
　ｎ型の光触媒材料に光を照射した場合、光触媒中で電子と正孔が生成分離する。正孔は光触媒材料の表面に移動し、プロトンの還元反応に寄与する。一方、電子は還元電極に移動し、プロトンの還元反応に寄与する。理想的には、このような酸化還元反応が進行し、水分解反応が生じる。 When the n-type photocatalyst material is irradiated with light, electrons and holes are generated and separated in the photocatalyst. Holes move to the surface of the photocatalytic material and contribute to the reduction reaction of protons. On the other hand, electrons move to the reduction electrode and contribute to the reduction reaction of protons. Ideally, such a redox reaction proceeds and a water splitting reaction occurs.
　従来の水の分解装置は、プロトン交換膜を介して繋がっている酸化槽と還元槽を有し、酸化槽に水溶液と酸化電極を入れ、還元槽に水溶液と還元電極を入れる。酸化電極と還元電極とは導線で電気的に接続される。酸化電極は、例えば、窒化物半導体、酸化チタン、またはアモルファスシリコンである。還元電極は、金属または金属化合物であり、例えば、ニッケル、鉄、金、白金、銀、銅、インジウム、チタンである。光源から酸化電極を構成する材料が吸収可能な波長の光を照射して水分解反応を生じさせる。例えば、酸化電極が窒化ガリウムで構成される場合、吸収可能な波長は３６５ｎｍ以下の波長である。光源は、例えば、キセノンランプ、水銀ランプ、ハロゲンランプ、疑似太陽光源、または太陽光であり、これらを組み合わせてもよい。 A conventional water decomposition device has an oxide tank and a reduction tank connected via a proton exchange membrane, and puts an aqueous solution and an oxidation electrode in the oxide tank, and puts an aqueous solution and a reduction electrode in the reduction tank. The oxide electrode and the reduction electrode are electrically connected by a conducting wire. The oxide electrode is, for example, a nitride semiconductor, titanium oxide, or amorphous silicon. The reducing electrode is a metal or a metal compound, for example nickel, iron, gold, platinum, silver, copper, indium, titanium. A water decomposition reaction is caused by irradiating the light source with light having a wavelength that can be absorbed by the material constituting the oxide electrode. For example, when the oxide electrode is made of gallium nitride, the wavelength that can be absorbed is 365 nm or less. The light source is, for example, a xenon lamp, a mercury lamp, a halogen lamp, a pseudo-solar light source, or sunlight, and these may be combined.
　上記のような水の分解装置は構成要素が多く、反応系が複雑なことから、より簡易な反応系の実現および反応系の小型化が望まれている。例えば、光触媒槽内に光触媒薄膜と水溶液を入れた構成の装置を用い、水溶液中の光触媒薄膜に光源から光を照射して水分解反応を生じさせる。光触媒薄膜は、酸化電極と同様に、窒化物半導体、酸化チタン、またはアモルファスシリコンである。光触媒薄膜の表面には、水の分解反応を促進する金属助触媒が担持されている。単一の光触媒薄膜により水素および酸素を生成する装置の反応系は簡易であり、系の低コスト化および小型化が期待されている。 Since the water decomposition device as described above has many components and the reaction system is complicated, it is desired to realize a simpler reaction system and downsize the reaction system. For example, using a device having a photocatalyst thin film and an aqueous solution in a photocatalyst tank, the photocatalyst thin film in the aqueous solution is irradiated with light from a light source to cause a water splitting reaction. The photocatalytic thin film, like the oxide electrode, is a nitride semiconductor, titanium oxide, or amorphous silicon. A metal co-catalyst that promotes the decomposition reaction of water is supported on the surface of the photocatalyst thin film. The reaction system of the device that produces hydrogen and oxygen by a single photocatalytic thin film is simple, and it is expected that the cost and size of the system will be reduced.
　しかしながら、シンプルな構成の装置においても、光触媒薄膜の光エネルギー変換効率が光照射時間と共に低下する問題があった。 However, even in a device having a simple structure, there is a problem that the light energy conversion efficiency of the photocatalyst thin film decreases with the light irradiation time.
　酸化電極および光触媒薄膜は半導体薄膜であり、例えば、サファイア基板上に成長した窒化ガリウム薄膜が用いられる。窒化ガリウム薄膜は、光照射下にて生成・分離した正孔が水の酸化反応と同時に、窒化ガリウム自身のエッチング反応に消費される。そのため、光電極が劣化し、光エネルギー変換効率が光照射時間と共に低下する問題がある。このような劣化の抑制を目的として、酸素発生用の助触媒（酸化ニッケル）を保護層として形成し、寿命向上した例が報告されている。 The oxide electrode and the photocatalyst thin film are semiconductor thin films, and for example, a gallium nitride thin film grown on a sapphire substrate is used. In the gallium nitride thin film, holes generated and separated under light irradiation are consumed in the etching reaction of gallium nitride itself at the same time as the oxidation reaction of water. Therefore, there is a problem that the light electrode deteriorates and the light energy conversion efficiency decreases with the light irradiation time. For the purpose of suppressing such deterioration, an example has been reported in which an auxiliary catalyst for oxygen generation (nickel oxide) is formed as a protective layer to improve the life.
　窒化ガリウム薄膜で生じた正孔は窒化ガリウム薄膜中から酸化ニッケルへ移動し、酸化ニッケル表面で水の酸化反応が進行する。正孔がスムーズに移動するためには、窒化ガリウム半導体の価電子帯が酸化ニッケルの価電子帯よりも低い準位にある必要がある。しかしながら、例えば、窒化インジウムガリウムのように光吸収率向上に期待できる可視応答化半導体光触媒薄膜の場合、バンドギャップが狭くなるに従い、価電子帯の準位が高くなる。従来の手法で作製された酸化ニッケルの価電子帯は、可視応答化半導体光触媒薄膜の価電子帯よりも低い準位に位置してしまい、正孔が移動できない障壁が生成される。そのため、光吸収率を向上しても、生成する障壁により正孔が移動できず、助触媒保護層としての機能を果たさないという問題があった。 Holes generated in the gallium nitride thin film move from the gallium nitride thin film to nickel oxide, and the oxidation reaction of water proceeds on the surface of the nickel oxide. In order for holes to move smoothly, the valence band of the gallium nitride semiconductor needs to be at a lower level than the valence band of nickel oxide. However, in the case of a visible responsive semiconductor photocatalytic thin film that can be expected to improve the light absorption rate, for example, indium gallium nitride, the level of the valence band increases as the band gap narrows. The valence band of nickel oxide produced by the conventional method is located at a lower level than the valence band of the visible responsive semiconductor photocatalyst thin film, and a barrier is created in which holes cannot move. Therefore, even if the light absorption rate is improved, there is a problem that holes cannot move due to the generated barrier and the hole does not function as a co-catalyst protective layer.
　本発明は、上記に鑑みてなされたものであり、光吸収率が高い単一の窒化物半導体光触媒薄膜において効率および寿命を向上することを目的とする。 The present invention has been made in view of the above, and an object thereof is to improve efficiency and life in a single nitride semiconductor photocatalytic thin film having a high light absorption rate.
　本発明の一態様の窒化物半導体光触媒薄膜の製造方法は、光照射により触媒機能を発揮して酸化還元反応を生じる窒化物半導体光触媒薄膜の製造方法であって、絶縁性または導電性の基板の表面上にｎ型窒化ガリウム層を形成する第１工程と、前記ｎ型窒化ガリウム層の表面に窒化インジウムガリウム層を形成する第２工程と、前記窒化インジウムガリウム層の表面の一部に金属層を形成する第３工程と、前記窒化インジウムガリウム層と前記金属層との界面でオーミック接合を形成するために熱処理する第４工程と、前記窒化インジウムガリウム層の表面の一部にｐ型金属酸化物を形成する第５工程と、前記ｐ型金属酸化物を熱処理する第６工程を有する。 The method for producing a nitride semiconductor photocatalyst thin film according to one aspect of the present invention is a method for producing a nitride semiconductor photocatalyst thin film that exerts a catalytic function by light irradiation and causes an oxidation-reduction reaction, and is an insulating or conductive substrate. The first step of forming an n-type gallium nitride layer on the surface, the second step of forming an indium gallium nitride layer on the surface of the n-type gallium nitride layer, and a metal layer on a part of the surface of the indium gallium nitride layer. The third step of forming the indium gallium nitride, the fourth step of heat-treating to form an ohmic bond at the interface between the indium gallium nitride layer and the metal layer, and p-type metal oxidation on a part of the surface of the indium gallium nitride layer. It has a fifth step of forming an object and a sixth step of heat-treating the p-type metal oxide.
　本発明によれば、光吸収率が高い単一の窒化物半導体光触媒薄膜において効率および寿命を向上できる。 According to the present invention, efficiency and life can be improved in a single nitride semiconductor photocatalytic thin film having a high light absorption rate.
図１は、本実施形態の窒化物半導体光触媒薄膜の製造方法により作製される窒化物半導体光触媒薄膜の構成を示す断面図である。FIG. 1 is a cross-sectional view showing the configuration of a nitride semiconductor photocatalyst thin film produced by the method for producing a nitride semiconductor photocatalyst thin film of the present embodiment. 図２は、窒化物半導体光触媒薄膜の表面に分散配置された金属層とｐ型金属酸化物を説明するための図である。FIG. 2 is a diagram for explaining a metal layer dispersed and arranged on the surface of a nitride semiconductor photocatalyst thin film and a p-type metal oxide. 図３は、本実施形態の窒化物半導体光触媒薄膜の製造方法を示すフローチャートである。FIG. 3 is a flowchart showing a method for manufacturing the nitride semiconductor photocatalyst thin film of the present embodiment. 図４は、酸化還元反応試験を行う装置の概要を示す図である。FIG. 4 is a diagram showing an outline of an apparatus for performing a redox reaction test.
　以下、本発明の実施の形態について図面を用いて説明する。なお、本発明は以下で説明する実施の形態に限定されるものではなく、本発明の趣旨を逸脱しない範囲内において変更を加えても構わない。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and modifications may be made without departing from the spirit of the present invention.
　［窒化物半導体光触媒薄膜の構成］
　図１は、本実施形態の窒化物半導体光触媒薄膜の製造方法により作製される窒化物半導体光触媒薄膜の構成を示す断面図である。図１の窒化物半導体光触媒薄膜は、水溶液中での光照射により触媒機能を発揮して酸化還元反応を生じる窒化物半導体光触媒薄膜である。 [Construction of nitride semiconductor photocatalyst thin film]
FIG. 1 is a cross-sectional view showing the configuration of a nitride semiconductor photocatalyst thin film produced by the method for producing a nitride semiconductor photocatalyst thin film of the present embodiment. The nitride semiconductor photocatalytic thin film of FIG. 1 is a nitride semiconductor photocatalytic thin film that exerts a catalytic function by irradiation with light in an aqueous solution to cause a redox reaction.
　図１に示す窒化物半導体光触媒薄膜１は、絶縁性または導電性の基板１１、基板１１の表面上に配置されたｎ型窒化ガリウム（ｎ－ＧａＮ）層１２、ｎ型窒化ガリウム層１２の表面上に配置された窒化インジウムガリウム（ＩｎＧａＮ）層１３、窒化インジウムガリウム層１３の表面の一部にオーミック接合を形成する金属層１４、および窒化インジウムガリウム層１３の表面の一部に分散配置されたｐ型金属酸化物１５を備える。窒化インジウムガリウム層１３上にｐ型金属酸化物１５を形成した窒化物半導体光触媒薄膜１を製造することで、光照射によって窒化インジウムガリウム層１３中で生じる正孔がｐ型金属酸化物１５へ移動できるようになる。 The nitride semiconductor photocatalyst thin film 1 shown in FIG. 1 is an insulating or conductive substrate 11, the surface of an n-type gallium nitride (n-GaN) layer 12 and an n-type gallium nitride layer 12 arranged on the surface of the substrate 11. The indium gallium nitride (InGaN) layer 13 arranged above, the metal layer 14 forming an ohmic bond on a part of the surface of the indium gallium nitride layer 13, and the part of the surface of the indium gallium nitride layer 13 are dispersed and arranged. A p-type metal oxide 15 is provided. By manufacturing the nitride semiconductor photocatalyst thin film 1 in which the p-type metal oxide 15 is formed on the indium gallium nitride layer 13, the holes generated in the indium gallium nitride layer 13 by light irradiation move to the p-type metal oxide 15. become able to.
　金属層１４とｐ型金属酸化物１５は、窒化インジウムガリウム層１３上に分散配置される。具体的には、図２に示すように、金属層１４は、直径１０μｍの円盤形状であり、２１０μｍ間隔で分散配置される。ｐ型金属酸化物１５は、直径１０μｍの円盤形状であり、金属層１４との間に１００μｍの間隔を持たせて分散配置される。 The metal layer 14 and the p-type metal oxide 15 are dispersed and arranged on the indium gallium nitride layer 13. Specifically, as shown in FIG. 2, the metal layer 14 has a disk shape with a diameter of 10 μm and is dispersedly arranged at intervals of 210 μm. The p-type metal oxide 15 has a disk shape with a diameter of 10 μm, and is dispersed and arranged with a space of 100 μm from the metal layer 14.
　［窒化物半導体光触媒薄膜の製造方法］
　図３を参照し、本実施形態の窒化物半導体光触媒薄膜の製造方法について説明する。 [Manufacturing method of nitride semiconductor photocatalytic thin film]
A method for manufacturing the nitride semiconductor photocatalyst thin film of the present embodiment will be described with reference to FIG.
　ステップＳ１にて、絶縁性または導電性の基板１１上にｎ型窒化ガリウム層１２を形成する。ｎ型窒化ガリウム層１２は、有機金属気相成長法（ＭＯＣＶＤ）を用いて形成してよい。 In step S1, the n-type gallium nitride layer 12 is formed on the insulating or conductive substrate 11. The n-type gallium nitride layer 12 may be formed by using a metalorganic vapor phase growth method (MOCVD).
　ステップＳ２にて、ｎ型窒化ガリウム層１２上に窒化インジウムガリウム層１３を形成する。窒化インジウムガリウム層１３は、ＭＯＣＶＤを用いて形成してよい。 In step S2, the indium gallium nitride layer 13 is formed on the n-type gallium nitride layer 12. The indium gallium nitride layer 13 may be formed by using MOCVD.
　ステップＳ３にて、窒化インジウムガリウム層１３の表面の一部に金属層１４を形成する。金属層１４は、窒化インジウムガリウム層１３に対して助触媒機能を有する材料を用い、蒸着法またはスパッタリング法により形成してよい。 In step S3, the metal layer 14 is formed on a part of the surface of the indium gallium nitride layer 13. The metal layer 14 may be formed by a vapor deposition method or a sputtering method using a material having a co-catalytic function with respect to the indium gallium nitride layer 13.
　ステップＳ４にて、窒化インジウムガリウム層１３と金属層１４との界面でオーミック接合を形成するために、金属層１４を形成した窒化物半導体を熱処理する。 In step S4, the nitride semiconductor on which the metal layer 14 is formed is heat-treated in order to form an ohmic contact at the interface between the indium gallium nitride layer 13 and the metal layer 14.
　ステップＳ５にて、窒化インジウムガリウム層１３の表面の一部にｐ型金属酸化物１５を形成する。ｐ型金属酸化物１５は、ｐ－ＮｉＯを用い、蒸着法またはスパッタリング法により形成してよい。 In step S5, the p-type metal oxide 15 is formed on a part of the surface of the indium gallium nitride layer 13. The p-type metal oxide 15 may be formed by a vapor deposition method or a sputtering method using p—NiO.
　ステップＳ６にて、ｐ型金属酸化物１５を形成した窒化物半導体を熱処理する。熱処理の温度は２００℃以上８００℃以下が好ましい。 In step S6, the nitride semiconductor on which the p-type metal oxide 15 is formed is heat-treated. The temperature of the heat treatment is preferably 200 ° C. or higher and 800 ° C. or lower.
　［窒化物半導体光触媒薄膜の実施例］
　次に、ステップＳ６の熱処理温度、ステップＳ５で使用するｐ－ＮｉＯの組成比を変えて作製した実施例１～２０について説明する。 [Examples of Nitride Semiconductor Photocatalytic Thin Film]
Next, Examples 1 to 20 produced by changing the heat treatment temperature in step S6 and the composition ratio of p—NiO used in step S5 will be described.
　実施例１～５は、ステップＳ６の熱処理温度を変えた窒化物半導体光触媒薄膜の製造方法の実施例である。実施例６～１０および実施例１１～１５は、実施例１～５においてリチウムの組成比を変えた窒化物半導体光触媒薄膜の製造方法の実施例である。実施例１６は、実施例１においてリチウムの組成比を変えた窒化物半導体光触媒薄膜の製造方法の実施例である。実施例１７，１８は、実施例１，３のステップＳ５のｐ型金属酸化物１５の形成方法を変えた窒化物半導体光触媒薄膜の製造方法の実施例である。実施例１９，２０は、実施例１においてｐ－ＮｉＯを作製する際の不純物を変えた窒化物半導体光触媒薄膜の製造方法の実施例である。 Examples 1 to 5 are examples of a method for manufacturing a nitride semiconductor photocatalyst thin film in which the heat treatment temperature in step S6 is changed. Examples 6 to 10 and Examples 11 to 15 are examples of a method for producing a nitride semiconductor photocatalytic thin film in Examples 1 to 5 in which the composition ratio of lithium is changed. Example 16 is an example of a method for producing a nitride semiconductor photocatalyst thin film in which the composition ratio of lithium is changed in Example 1. Examples 17 and 18 are examples of a method for producing a nitride semiconductor photocatalytic thin film in which the method for forming the p-type metal oxide 15 in step S5 of Examples 1 and 3 is changed. Examples 19 and 20 are examples of a method for producing a nitride semiconductor photocatalytic thin film in which impurities are changed when producing p—NiO in Example 1.
　また、実施例１，３のステップＳ５において、ｐ－ＮｉＯではなく、ＮｉＯを用いた比較対象例１，２についても説明する。 Further, in step S5 of Examples 1 and 3, comparative examples 1 and 2 using NiO instead of p-NiO will also be described.
　＜実施例１＞
　ステップＳ１にて、２インチのサファイア基板上に、シリコンをドープしたｎ－ＧａＮ半導体薄膜をＭＯＣＶＤによりエピタキシャル成長させてｎ型窒化ガリウム層１２を形成した。基板１１としてサファイア基板を用いた。成長原料には、アンモニアガス、トリメチルガリウムを用いた。ｎ型不純物源にはシランガスを用いた。成長炉内に送るキャリアガスには水素を用いた。ｎ型窒化ガリウム層１２の膜厚は、光を吸収するに十分足る２μｍとした。キャリア密度は３×１０18ｃｍ-3であった。 <Example 1>
In step S1, a silicon-doped n-GaN semiconductor thin film was epitaxially grown on a 2-inch sapphire substrate by MOCVD to form an n-type gallium nitride layer 12. A sapphire substrate was used as the substrate 11. Ammonia gas and trimethylgallium were used as growth raw materials. Silane gas was used as the n-type impurity source. Hydrogen was used as the carrier gas sent into the growth furnace. The film thickness of the n-type gallium nitride layer 12 was set to 2 μm, which is sufficient to absorb light. The carrier density was 3 × 10 18 cm -3 .
　ステップＳ２にて、ｎ型窒化ガリウム層１２上に、インジウムの組成比を５％とした窒化インジウムガリウム（ＩｎＧａＮ）をＭＯＣＶＤにより成長させて窒化インジウムガリウム層１３を形成した。成長原料には、アンモニアガス、トリメチルガリウム、トリメチルインジウムを用いた。成長炉内に送るキャリアガスには水素を用いた。窒化インジウムガリウム層１３の膜厚は、光を十分に吸収するに足る１００ｎｍとした。 In step S2, indium gallium nitride (InGaN) having an indium composition ratio of 5% was grown on the n-type gallium nitride layer 12 by MOCVD to form the indium gallium nitride layer 13. Ammonia gas, trimethylgallium, and trimethylindium were used as growth raw materials. Hydrogen was used as the carrier gas sent into the growth furnace. The film thickness of the indium gallium nitride layer 13 was set to 100 nm, which is sufficient to absorb light.
　ステップＳ３にて、窒化インジウムガリウム層１３の表面に、直径１０μｍの円盤形状の金属層１４を２１０μｍ間隔で真空蒸着した。ここでは、半導体側から順に、Ｔｉを２５ｎｍ、Ａｌを５０ｎｍ、Ｔｉを２５ｎｍ、Ｐｔを１００ｎｍの厚さで積層した。 In step S3, a disk-shaped metal layer 14 having a diameter of 10 μm was vacuum-deposited on the surface of the indium gallium nitride layer 13 at intervals of 210 μm. Here, Ti was laminated with a thickness of 25 nm, Al at 50 nm, Ti at 25 nm, and Pt at 100 nm in order from the semiconductor side.
　ステップＳ４にて、金属層１４を形成した半導体薄膜を窒素雰囲気下で、８００℃で３０秒間熱処理を行った。熱処理により、窒化インジウムガリウム層１３と金属層１４の界面において疑似的なオーミック接合を形成した。 In step S4, the semiconductor thin film on which the metal layer 14 was formed was heat-treated at 800 ° C. for 30 seconds in a nitrogen atmosphere. By heat treatment, a pseudo ohmic contact was formed at the interface between the indium gallium nitride layer 13 and the metal layer 14.
　ステップＳ５にて、窒化インジウムガリウム層１３の表面に、金属層１４と１００μｍの間隔を持たせて、直径１０μｍの円盤形状のｐ－ＮｉＯを膜厚２ｎｍで真空蒸着し、１００μｍ間隔で金属層１４とｐ型金属酸化物１５とが交互に並ぶようにｐ型金属酸化物１５を形成した。 In step S5, a disk-shaped p-NiO having a diameter of 10 μm is vacuum-deposited at a film thickness of 2 nm on the surface of the indium gallium nitride layer 13 at intervals of 100 μm from the metal layer 14, and the metal layers 14 are deposited at intervals of 100 μm. The p-type metal oxide 15 was formed so that the p-type metal oxide 15 and the p-type metal oxide 15 were alternately arranged.
　ｐ型金属酸化物１５の形成に使用したｐ－ＮｉＯは、Ｌｉの組成比が所望の値となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定め、ＮｉＯ粉末と酸化リチウム粉末を混合し、電気炉内で熱処理して作製した。実施例１では、Ｌｉの組成比が１％（Ｎｉの組成比は９９％）となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定めた。得られたｐ－ＮｉＯ粉末の体積抵抗率は、ＮｉＯ粉末の体積抵抗率に比べて、およそ４桁低く、ＮｉＯ粉末はｐ型化し導電率が向上していることが分かった。 For p-NiO used for forming the p-type metal oxide 15, the weights of the NiO powder and the lithium oxide powder are determined so that the composition ratio of Li becomes a desired value, and the NiO powder and the lithium oxide powder are mixed and electrically charged. It was produced by heat treatment in a furnace. In Example 1, the weights of the NiO powder and the lithium oxide powder were determined so that the Li composition ratio was 1% (Ni composition ratio was 99%). The volume resistivity of the obtained p-NiO powder was about 4 orders of magnitude lower than the volume resistivity of the NiO powder, and it was found that the NiO powder was p-shaped and the conductivity was improved.
　ステップＳ６にて、ステップＳ５で得られた半導体薄膜をホットプレート上で、空気雰囲気中、２００℃、１時間熱処理した。なお、ステップＳ６は、電気炉で熱処理してもよい。 In step S6, the semiconductor thin film obtained in step S5 was heat-treated on a hot plate at 200 ° C. for 1 hour in an air atmosphere. In step S6, heat treatment may be performed in an electric furnace.
　以上の工程により、実施例１の窒化物半導体光触媒薄膜を得た。 Through the above steps, the nitride semiconductor photocatalyst thin film of Example 1 was obtained.
　＜実施例２＞
　実施例２の窒化物半導体光触媒薄膜の製造方法では、ステップＳ６の熱処理において、熱処理温度を５００℃とした。その他の点においては実施例１と同様である。 <Example 2>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 2, the heat treatment temperature was set to 500 ° C. in the heat treatment in step S6. In other respects, it is the same as in Example 1.
　＜実施例３＞
　実施例３の窒化物半導体光触媒薄膜の製造方法では、ステップＳ６の熱処理において、熱処理温度を８００℃とした。その他の点においては実施例１と同様である。 <Example 3>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 3, the heat treatment temperature was set to 800 ° C. in the heat treatment in step S6. In other respects, it is the same as in Example 1.
　＜実施例４＞
　実施例４の窒化物半導体光触媒薄膜の製造方法では、ステップＳ６の熱処理において、熱処理温度を１００℃とした。その他の点においては実施例１と同様である。 <Example 4>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 4, the heat treatment temperature was set to 100 ° C. in the heat treatment in step S6. In other respects, it is the same as in Example 1.
　＜実施例５＞
　実施例５の窒化物半導体光触媒薄膜の製造方法では、ステップＳ６の熱処理において、熱処理温度を９００℃とした。その他の点においては実施例１と同様である。 <Example 5>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 5, the heat treatment temperature was set to 900 ° C. in the heat treatment in step S6. In other respects, it is the same as in Example 1.
　＜実施例６＞
　実施例６の窒化物半導体光触媒薄膜の製造方法では、実施例１のステップＳ５で使用するｐ－ＮｉＯを作製する際、Ｌｉの組成比が１０％（ＬｉとＮｉの比が１：９）となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定めた。その他の点においては実施例１と同様である。 <Example 6>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 6, when the p—NiO used in step S5 of Example 1 is produced, the composition ratio of Li is 10% (the ratio of Li to Ni is 1: 9). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 1.
　＜実施例７＞
　実施例７の窒化物半導体光触媒薄膜の製造方法では、実施例２のステップＳ５で使用するｐ－ＮｉＯを作製する際、Ｌｉの組成比が１０％（ＬｉとＮｉの比が１：９）となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定めた。その他の点においては実施例２と同様である。 <Example 7>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 7, when the p—NiO used in step S5 of Example 2 is produced, the composition ratio of Li is 10% (the ratio of Li to Ni is 1: 9). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 2.
　＜実施例８＞
　実施例８の窒化物半導体光触媒薄膜の製造方法では、実施例３のステップＳ５で使用するｐ－ＮｉＯを作製する際、Ｌｉの組成比が１０％（ＬｉとＮｉの比が１：９）となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定めた。その他の点においては実施例３と同様である。 <Example 8>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 8, when the p—NiO used in step S5 of Example 3 is produced, the composition ratio of Li is 10% (the ratio of Li to Ni is 1: 9). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 3.
　＜実施例９＞
　実施例９の窒化物半導体光触媒薄膜の製造方法では、実施例４のステップＳ５で使用するｐ－ＮｉＯを作製する際、Ｌｉの組成比が１０％（ＬｉとＮｉの比が１：９）となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定めた。その他の点においては実施例４と同様である。 <Example 9>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 9, when the p—NiO used in step S5 of Example 4 is produced, the composition ratio of Li is 10% (the ratio of Li to Ni is 1: 9). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 4.
　＜実施例１０＞
　実施例１０の窒化物半導体光触媒薄膜の製造方法では、実施例５のステップＳ５で使用するｐ－ＮｉＯを作製する際、Ｌｉの組成比が１０％（ＬｉとＮｉの比が１：９）となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定めた。その他の点においては実施例５と同様である。 <Example 10>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 10, when the p—NiO used in step S5 of Example 5 is produced, the composition ratio of Li is 10% (the ratio of Li to Ni is 1: 9). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 5.
　＜実施例１１＞
　実施例１１の窒化物半導体光触媒薄膜の製造方法では、実施例１のステップＳ５で使用するｐ－ＮｉＯを作製する際、Ｌｉの組成比が４０％（ＬｉとＮｉの比が４：６）となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定めた。その他の点においては実施例１と同様である。 <Example 11>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 11, when p—NiO used in step S5 of Example 1 is produced, the composition ratio of Li is 40% (the ratio of Li to Ni is 4: 6). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 1.
　＜実施例１２＞
　実施例１２の窒化物半導体光触媒薄膜の製造方法では、実施例２のステップＳ５で使用するｐ－ＮｉＯを作製する際、Ｌｉの組成比が４０％（ＬｉとＮｉの比が４：６）となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定めた。その他の点においては実施例２と同様である。 <Example 12>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 12, when the p—NiO used in step S5 of Example 2 is produced, the composition ratio of Li is 40% (the ratio of Li to Ni is 4: 6). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 2.
　＜実施例１３＞
　実施例１３の窒化物半導体光触媒薄膜の製造方法では、実施例３のステップＳ５で使用するｐ－ＮｉＯを作製する際、Ｌｉの組成比が４０％（ＬｉとＮｉの比が４：６）となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定めた。その他の点においては実施例３と同様である。 <Example 13>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 13, when the p—NiO used in step S5 of Example 3 is produced, the composition ratio of Li is 40% (the ratio of Li to Ni is 4: 6). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 3.
　＜実施例１４＞
　実施例１４の窒化物半導体光触媒薄膜の製造方法では、実施例４のステップＳ５で使用するｐ－ＮｉＯを作製する際、Ｌｉの組成比が４０％（ＬｉとＮｉの比が４：６）となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定めた。その他の点においては実施例４と同様である。 <Example 14>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 14, when the p—NiO used in step S5 of Example 4 is produced, the composition ratio of Li is 40% (the ratio of Li to Ni is 4: 6). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 4.
　＜実施例１５＞
　実施例１５の窒化物半導体光触媒薄膜の製造方法では、実施例５のステップＳ５で使用するｐ－ＮｉＯを作製する際、Ｌｉの組成比が４０％（ＬｉとＮｉの比が４：６）となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定めた。その他の点においては実施例５と同様である。 <Example 15>
In the method for producing a nitride semiconductor photocatalyst thin film of Example 15, when the p—NiO used in step S5 of Example 5 is produced, the composition ratio of Li is 40% (the ratio of Li to Ni is 4: 6). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 5.
　＜実施例１６＞
　実施例１６の窒化物半導体光触媒薄膜の製造方法では、実施例１のステップＳ５で使用するｐ－ＮｉＯを作製する際、Ｌｉの組成比が５０％（ＬｉとＮｉの比が５：５）となるようにＮｉＯ粉末と酸化リチウム粉末の重量を定めた。その他の点においては実施例１と同様である。 <Example 16>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 16, when the p—NiO used in step S5 of Example 1 is produced, the composition ratio of Li is 50% (the ratio of Li to Ni is 5: 5). The weights of the NiO powder and the lithium oxide powder were determined so as to be. In other respects, it is the same as in Example 1.
　＜実施例１７＞
　実施例１７の窒化物半導体光触媒薄膜の製造方法では、実施例１のステップＳ５において、ｐ－ＮｉＯ粉末からターゲット（焼結体）を作製し、スパッタリング法によってｐ型金属酸化物１５を形成した。その他の点においては実施例１と同様である。 <Example 17>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 17, a target (sintered body) was prepared from p—NiO powder in step S5 of Example 1, and a p-type metal oxide 15 was formed by a sputtering method. In other respects, it is the same as in Example 1.
　＜実施例１８＞
　実施例１８の窒化物半導体光触媒薄膜の製造方法では、実施例３のステップＳ５において、ｐ－ＮｉＯ粉末からターゲット（焼結体）を作製し、スパッタリング法によってｐ型金属酸化物１５を形成した。その他の点においては実施例３と同様である。 <Example 18>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 18, a target (sintered body) was prepared from p—NiO powder in step S5 of Example 3, and a p-type metal oxide 15 was formed by a sputtering method. In other respects, it is the same as in Example 3.
　＜実施例１９＞
　実施例１９の窒化物半導体光触媒薄膜の製造方法では、実施例１のステップＳ５において、不純物に銀（Ａｇ）を用いて作製したｐ－ＮｉＯを蒸着した。その他の点においては実施例１と同様である。 <Example 19>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 19, p—NiO prepared by using silver (Ag) as an impurity was vapor-deposited in step S5 of Example 1. In other respects, it is the same as in Example 1.
　＜実施例２０＞
　実施例２０の窒化物半導体光触媒薄膜の製造方法では、実施例１のステップＳ５において、不純物にカリウム（Ｋ）を用いて作製したｐ－ＮｉＯを蒸着した。その他の点においては実施例１と同様である。 <Example 20>
In the method for producing a nitride semiconductor photocatalytic thin film of Example 20, p—NiO prepared by using potassium (K) as an impurity was vapor-deposited in step S5 of Example 1. In other respects, it is the same as in Example 1.
　＜比較対象例１＞
　比較対象例１の窒化物半導体光触媒薄膜の製造方法では、実施例１のステップＳ５において、ｐ－ＮｉＯではなく、ＮｉＯを蒸着した。その他の点においては実施例１と同様である。 <Comparison target example 1>
In the method for producing a nitride semiconductor photocatalyst thin film of Comparative Example 1, NiO was vapor-deposited instead of p—NiO in step S5 of Example 1. In other respects, it is the same as in Example 1.
　＜比較対象例２＞
　比較対象例１の窒化物半導体光触媒薄膜の製造方法では、実施例３のステップＳ５において、ｐ－ＮｉＯではなく、ＮｉＯを蒸着した。その他の点においては実施例３と同様である。 <Comparison target example 2>
In the method for producing a nitride semiconductor photocatalyst thin film of Comparative Example 1, NiO was vapor-deposited instead of p—NiO in step S5 of Example 3. In other respects, it is the same as in Example 3.
　［酸化還元反応試験］
　実施例１～２０と比較対象例１～２について図４の装置を用いて酸化還元反応試験を行った。 [Redox reaction test]
Redox reaction tests were performed on Examples 1 to 20 and Comparative Examples 1 and 2 using the apparatus shown in FIG.
　内容量１５０ｍｌの石英窓付き反応セルを光触媒槽１１０として用い、光触媒槽１１０内に撹拌子１２０と水溶液１３０を入れた。水溶液１３０には、１ｍｏｌ／ｌの水酸化カリウム水溶液１２５ｍｌを用いた。 A reaction cell with a quartz window having an internal capacity of 150 ml was used as the photocatalyst tank 110, and the stirrer 120 and the aqueous solution 130 were placed in the photocatalyst tank 110. As the aqueous solution 130, 125 ml of a 1 mol / l potassium hydroxide aqueous solution was used.
　実施例１～２０および比較対象例１～２の半導体光触媒薄膜を水溶液１３０中に浸し、金属層１４とｐ型金属酸化物１５を形成した窒化インジウムガリウム層１３の面が光源１４０を向くように固定した。 The semiconductor photocatalytic thin films of Examples 1 to 20 and Comparative Examples 1 and 2 were immersed in the aqueous solution 130 so that the surface of the indium gallium nitride layer 13 forming the metal layer 14 and the p-type metal oxide 15 faces the light source 140. Fixed.
　窒素ガスを２００ｍｌ／ｍｉｎで３０分間バブリングして脱泡および空気との置換を終えた後、シリコンテフロンセプタムで密閉した。光触媒槽１１０内の圧力は大気圧（１気圧）とした。 Nitrogen gas was bubbled at 200 ml / min for 30 minutes to complete defoaming and replacement with air, and then sealed with silicon Teflon septum. The pressure in the photocatalyst tank 110 was set to atmospheric pressure (1 atm).
　光源１４０には、３００Ｗの高圧キセノンランプ（波長４００ｎｍ以上をカット、照度５ｍＷ／ｃｍ2）を用いた。光源１４０の光を、光触媒槽１１０の石英窓の外側から、半導体光触媒薄膜に均一に照射した。 As the light source 140, a 300 W high-voltage xenon lamp (wavelength 400 nm or more cut, illuminance 5 mW / cm 2 ) was used. The light from the light source 140 was uniformly applied to the semiconductor photocatalyst thin film from the outside of the quartz window of the photocatalyst tank 110.
　サンプルの光照射面積を１ｃｍ2とし、撹拌子１２０とスターラーを用い、光触媒槽１１０の底の中心位置で２５０ｒｐｍの回転速度で水溶液１３０を撹拌した。 The light irradiation area of the sample was 1 cm 2, and the aqueous solution 130 was stirred at the center position of the bottom of the photocatalyst tank 110 at a rotation speed of 250 rpm using a stirrer 120 and a stirrer.
　光照射後任意の時間に、光触媒槽１１０のガスをセプタム部分からシリンジで採取し、ガスクロマトグラフ質量分析計にて反応生成物を分析した。その結果、水素と酸素が生成していることを確認した。 At an arbitrary time after light irradiation, the gas in the photocatalyst tank 110 was collected from the septum portion with a syringe, and the reaction product was analyzed with a gas chromatograph mass spectrometer. As a result, it was confirmed that hydrogen and oxygen were generated.
　［試験結果］
　実施例１～２０および比較対象例１～２における、光照射から１時間後および１０時間後の酸素・水素ガスの生成量を表１に示す。各ガスの生成量は、半導体光触媒薄膜の表面積で規格化して示した。 [Test results]
Table 1 shows the amounts of oxygen and hydrogen gas produced 1 hour and 10 hours after the light irradiation in Examples 1 to 20 and Comparative Examples 1 and 2. The amount of each gas produced is standardized by the surface area of the semiconductor photocatalyst thin film.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　実施例１～１５，１７，１８の光照射から１時間後の水素・酸素生成量に大きな差異は見られなかった。なお、リチウムの組成比を５０％とした実施例１６では、ＮｉＯの単相は得られず、不純物として酸化リチウムが残存し、ｐ－ＮｉＯが得られないことがわかった。 No significant difference was observed in the amount of hydrogen / oxygen produced 1 hour after the light irradiation of Examples 1 to 15, 17, and 18. In Example 16 in which the composition ratio of lithium was 50%, it was found that a single phase of NiO could not be obtained, lithium oxide remained as an impurity, and p-NiO could not be obtained.
　熱処理温度が２００℃から８００℃の実施例１，２，３，６，７，８，１１，１２，１３，１７，１８の光照射から１０時間後の水素・酸素生成量は、その他の実施例の１０時間後の生成量に比べて２０倍であることがわかった。 The amount of hydrogen / oxygen produced 10 hours after the light irradiation of Examples 1, 2, 3, 6, 7, 8, 11, 12, 13, 17, and 18 having a heat treatment temperature of 200 ° C. to 800 ° C. is the other implementation. It was found to be 20 times higher than the amount produced after 10 hours in the example.
　熱処理温度を１００℃とした実施例４，９，１４では、１０時間後の水素・酸素生成量は、１時間後の水素・酸素生成量から大きく低下した。熱処理温度が１００℃の場合では、ｐ－ＮｉＯとＩｎＧａＮ界面の接合が弱く、光触媒薄膜との界面に空隙が生成されたことで、空隙を起点とした電極性能劣化が進行し、１０時間後にはおおよそ触媒として失活したためと考えられる。 In Examples 4, 9 and 14 in which the heat treatment temperature was 100 ° C., the amount of hydrogen / oxygen produced after 10 hours was significantly lower than the amount of hydrogen / oxygen produced after 1 hour. When the heat treatment temperature is 100 ° C., the bond between the p—NiO and the InGaN interface is weak, and voids are generated at the interface with the photocatalyst thin film, so that the electrode performance deteriorates starting from the voids, and after 10 hours, It is thought that it was deactivated as a catalyst.
　熱処理温度を９００℃とした実施例５，１０，１５では、１０時間後の水素・酸素生成量は、１時間後の水素・酸素生成量から大きく低下した。熱処理温度が９００℃の場合では、窒化インジウムガリウム層１３の結晶性が悪くなり、光照射とともに進行するエッチング反応により、生成した電子－正孔が再結合する確率が高まったことで、光照射から１０時間後には反応に必要な電荷を取り出せなくなったためと考えられる。 In Examples 5, 10 and 15 at a heat treatment temperature of 900 ° C., the amount of hydrogen / oxygen produced after 10 hours was significantly lower than the amount of hydrogen / oxygen produced after 1 hour. When the heat treatment temperature is 900 ° C., the crystallinity of the indium gallium nitride layer 13 deteriorates, and the probability of recombination of generated electrons-holes increases due to the etching reaction that proceeds with light irradiation. It is considered that the charge required for the reaction could not be taken out after 10 hours.
　これらの結果より、長寿命化に期待できるｐ型金属酸化物１５形成の熱処理条件は、温度が２００℃以上８００℃以下ということを抽出した。 From these results, it was extracted that the heat treatment conditions for forming the p-type metal oxide 15 that can be expected to extend the service life are a temperature of 200 ° C. or higher and 800 ° C. or lower.
　実施例１７，１８と実施例１，３の光照射から１時間後および１０時間後の酸素・水素生成量は同じ程度であり、スパッタリング法によりｐ型金属酸化物１５を形成しても、蒸着法によりｐ型金属酸化物１５を形成したものと同様の効果が得られることがわかった。 The amount of oxygen and hydrogen produced 1 hour and 10 hours after the light irradiation of Examples 17 and 18 and Examples 1 and 3 was about the same, and even if the p-type metal oxide 15 was formed by the sputtering method, it was vapor-deposited. It was found that the same effect as that for forming the p-type metal oxide 15 can be obtained by the method.
　実施例１９，２０では、不純物としてＡｇおよびＫを用いて作製したｐ－ＮｉＯでも同様の効果が得られることがわかった。 In Examples 19 and 20, it was found that the same effect can be obtained with p-NiO prepared using Ag and K as impurities.
　比較対象例１，２では、光照射から１時間後および１０時間後のいずれにおいても水素・酸素の生成量が低かった。これは、ＮｉＯの場合、ＩｎＧａＮ界面の障壁を正孔が移動できないことが影響していると考えられる。 In Comparative Target Examples 1 and 2, the amount of hydrogen and oxygen produced was low both 1 hour and 10 hours after the light irradiation. This is considered to be due to the fact that holes cannot move through the barrier at the InGaN interface in the case of NiO.
　以上から、ステップＳ６のｐ型金属酸化物１５形成の熱処理条件を２００℃以上８００℃以下とし、ステップＳ５においてｐ型金属酸化物１５の形成に用いるｐ－ＮｉＯ粉末を作製するためのＬｉの組成比をＮｉに対して４０％以下とすることで、水分解反応（光エネルギー変換効率）の高効率化および長寿命化を図ることができた。また、ｐ型金属酸化物１５の形成は蒸着法に限らずスパッタリング法も有効であり、ｐ－ＮｉＯを作製する際にＬｉに限らずＡｇまたはＫを不純物として使用することも有効であることがわかった。 From the above, the heat treatment conditions for forming the p-type metal oxide 15 in step S6 are set to 200 ° C. or higher and 800 ° C. or lower, and the composition of Li for producing the p—NiO powder used for forming the p-type metal oxide 15 in step S5. By setting the ratio to 40% or less with respect to Ni, it was possible to improve the efficiency of the water splitting reaction (light energy conversion efficiency) and extend the service life. Further, the formation of the p-type metal oxide 15 is not limited to the vapor deposition method, but the sputtering method is also effective, and it is also effective to use Ag or K as an impurity when producing p—NiO, not limited to Li. all right.
　以上説明したように、本実施形態の窒化物半導体光触媒薄膜の製造方法は、絶縁性または導電性の基板１１上にｎ型窒化ガリウム層１２を形成する工程と、ｎ型窒化ガリウム層１２上に窒化インジウムガリウム層１３を形成する工程と、窒化インジウムガリウム層１３の表面の一部に金属層１４を形成する工程と、窒化インジウムガリウム層１３と金属層１４との界面でオーミック接合を形成するための熱処理する工程と、窒化インジウムガリウム層１３の表面の一部にｐ型金属酸化物１５を形成する工程と、ｐ型金属酸化物１５を形成した半導体薄膜を熱処理する工程を有する。窒化インジウムガリウム層１３上にｐ型の半導体としての特性を示すｐ型金属酸化物１５を酸化反応用助触媒として形成し、窒化インジウムガリウム層１３の同一表面上に金属層１４を還元反応用助触媒として形成することで、光吸収率が高い単一の窒化物半導体光触媒薄膜１において効率および寿命を向上できる。 As described above, the method for manufacturing the nitride semiconductor photocatalyst thin film of the present embodiment includes a step of forming the n-type gallium nitride layer 12 on the insulating or conductive substrate 11 and a step of forming the n-type gallium nitride layer 12 on the n-type gallium nitride layer 12. To form an ohmic junction at the interface between the indium gallium nitride layer 13 and the metal layer 14, the step of forming the metal layer 14 on a part of the surface of the indium gallium nitride layer 13, and the step of forming the metal layer 14 on a part of the surface of the indium gallium nitride layer 13. It has a step of heat-treating, a step of forming a p-type metal oxide 15 on a part of the surface of the indium gallium nitride layer 13, and a step of heat-treating a semiconductor thin film on which the p-type metal oxide 15 is formed. A p-type metal oxide 15 exhibiting characteristics as a p-type semiconductor is formed on the indium gallium nitride layer 13 as an auxiliary catalyst for an oxidation reaction, and a metal layer 14 is provided on the same surface of the indium gallium nitride layer 13 as an auxiliary catalyst for a reduction reaction. By forming it as a catalyst, the efficiency and life of a single nitride semiconductor photocatalyst thin film 1 having a high light absorption rate can be improved.
　なお、本実施形態では目的生成物を水素としたが、還元反応用助触媒である金属層１４の再表面の金属を例えば、Ｎｉ，Ｆｅ，Ａｕ，Ｐｔ，Ａｇ，Ｃｕ，Ｉｎ，Ｔｉ，Ｃｏ，Ｒｕに変えたり、セル内の雰囲気を変えることで、二酸化炭素の還元反応による炭素化合物の生成、窒素の還元反応によるアンモニアの生成も可能である。 In this embodiment, the target product is hydrogen, but the metal on the surface of the metal layer 14 which is the auxiliary catalyst for the reduction reaction is, for example, Ni, Fe, Au, Pt, Ag, Cu, In, Ti, Co. By changing to Ru or changing the atmosphere in the cell, it is possible to generate a carbon compound by a carbon dioxide reduction reaction and to produce ammonia by a nitrogen reduction reaction.
　酸化還元反応試験に用いる水溶液１３０は、水酸化ナトリウム以外に、水酸化カリウム水溶液、塩酸のようなイオン移動させる電解質を溶解させた水溶液でも構わない。特に、ＧａＮはアルカリ性水溶液が好ましい。 The aqueous solution 130 used in the redox reaction test may be an aqueous solution in which an electrolyte for ion transfer such as potassium hydroxide aqueous solution or hydrochloric acid is dissolved, in addition to sodium hydroxide. In particular, GaN is preferably an alkaline aqueous solution.
　１…窒化物半導体光触媒薄膜
　１１…基板
　１２…ｎ型窒化ガリウム層
　１３…窒化インジウムガリウム層
　１４…金属層
　１５…ｐ型金属酸化物 1 ... Nitride semiconductor photocatalyst thin film 11 ... Substrate 12 ... n-type gallium nitride layer 13 ... Indium gallium nitride layer 14 ... Metal layer 15 ... P-type metal oxide

Claims (4)

  1. 　光照射により触媒機能を発揮して酸化還元反応を生じる窒化物半導体光触媒薄膜の製造方法であって、
    　絶縁性または導電性の基板の表面上にｎ型窒化ガリウム層を形成する第１工程と、
    　前記ｎ型窒化ガリウム層の表面に窒化インジウムガリウム層を形成する第２工程と、
    　前記窒化インジウムガリウム層の表面の一部に金属層を形成する第３工程と、
    　前記窒化インジウムガリウム層と前記金属層との界面でオーミック接合を形成するために熱処理する第４工程と、
    　前記窒化インジウムガリウム層の表面の一部にｐ型金属酸化物を形成する第５工程と、
    　前記ｐ型金属酸化物を熱処理する第６工程を有する
    　窒化物半導体光触媒薄膜の製造方法。     It is a method for manufacturing a nitride semiconductor photocatalytic thin film that exerts a catalytic function by light irradiation and causes a redox reaction.
    The first step of forming an n-type gallium nitride layer on the surface of an insulating or conductive substrate, and
    The second step of forming the indium gallium nitride layer on the surface of the n-type gallium nitride layer, and
    A third step of forming a metal layer on a part of the surface of the indium gallium nitride layer,
    The fourth step of heat-treating to form an ohmic contact at the interface between the indium gallium nitride layer and the metal layer,
    The fifth step of forming a p-type metal oxide on a part of the surface of the indium gallium nitride layer, and
    A method for producing a nitride semiconductor photocatalytic thin film, which comprises a sixth step of heat-treating the p-type metal oxide.
  2. 　請求項１に記載の窒化物半導体光触媒薄膜の製造方法であって、
    　前記第１工程および前記第２工程では、有機金属気相成長法を用いる
    　窒化物半導体光触媒薄膜の製造方法。     The method for manufacturing a nitride semiconductor photocatalytic thin film according to claim 1.
    In the first step and the second step, a method for producing a nitride semiconductor photocatalytic thin film using an organic metal vapor phase growth method.
  3. 　請求項１または２に記載の窒化物半導体光触媒薄膜の製造方法であって、
    　前記第３工程および前記第５工程では、蒸着法またはスパッタリング法を用いる
    　窒化物半導体光触媒薄膜の製造方法。     The method for producing a nitride semiconductor photocatalytic thin film according to claim 1 or 2.
    In the third step and the fifth step, a method for manufacturing a nitride semiconductor photocatalytic thin film using a thin film deposition method or a sputtering method.
  4. 　請求項１ないし３のいずれかに記載の窒化物半導体光触媒薄膜の製造方法であって、
    　前記第６工程では、２００℃以上８００℃以下の温度で熱処理する
    　窒化物半導体光触媒薄膜の製造方法。     The method for producing a nitride semiconductor photocatalytic thin film according to any one of claims 1 to 3.
    In the sixth step, a method for producing a nitride semiconductor photocatalytic thin film, which is heat-treated at a temperature of 200 ° C. or higher and 800 ° C. or lower.
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