Photocatalytic device and control method therefor

Abstract

To provide a photocatalytic device that allows improvement in efficiency of oxidation-reduction reactions.SOLUTION: A photocatalytic device comprising: a substrate; a plurality of columnar portions provided on the substrate, each columnar portion having a first surface being at least one of a c-plane and a semi-polar plane, and a second surface being an m-plane, the columnar portions including InxGa1-xN (0≤x<1); and a first oxide layer provided on the first surface while avoiding the second surface, the first oxide layer including InyGa1-yOz (0≤y<1, 0<z).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a photocatalytic device and a control method thereof. [Background technology]

[0002] Photocatalysts are known that exhibit catalytic activity when irradiated with light.

[0003] For example, Patent Document 1 describes a visible light responsive photocatalyst consisting of a nanostructure with a core made of InGaN and a shell made of TiO2 that covers the core. When the visible light responsive photocatalyst absorbs light having an energy equal to or greater than the energy corresponding to the band gap, holes and electrons are generated, and the holes are used in a water oxidation reaction to generate oxygen, and the electrons are used in a water reduction reaction to generate hydrogen. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 104072 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-mentioned visible light responsive photocatalyst, it is desired to increase the efficiency of the oxidation-reduction reaction. [Means for solving the problem]

[0006] One aspect of the photocatalytic device according to the present invention is A substrate; a first surface that is at least one of a c-plane and a semi-polar plane and a second surface that is an m-plane, x Ga 1-x a plurality of pillars including N (0≦x<1); provided on the first surface to avoid the second surface, y Ga1-y O z A first oxide layer including (0≦y<1, 0<z), including

[0007] One aspect of the method for manufacturing a photocatalyst device according to the present invention is On a substrate, having a surface that is at least one of a c-plane and a semi-polar plane, and an m-plane, In x Ga 1-x forming a plurality of columnar portions containing N(0≦x<1); immersing the plurality of columnar portions in a strongly basic aqueous solution; irradiating ultraviolet light on the plurality of columnar portions immersed in the strongly basic aqueous solution to oxidize the surface that is at least one of the c-plane and the semi-polar plane, and forming a first oxide layer; including

Brief Description of the Drawings

[0008] [Figure 1] Cross-sectional view schematically showing a photocatalyst device according to the first embodiment. [Figure 2] Planar view schematically showing a photocatalyst device according to the first embodiment. [Figure 3] Diagram for explaining the band structure of GaN. [Figure 4] Diagram for explaining the operation of a photocatalyst device according to the first embodiment. [Figure 5] Flowchart for explaining the manufacturing method of a photocatalyst device according to the first embodiment. [Figure 6] Cross-sectional view schematically showing the manufacturing process of a photocatalyst device according to the first embodiment. [Figure 7] Cross-sectional view schematically showing the manufacturing process of a photocatalyst device according to the first embodiment. [Figure 8] Cross-sectional view schematically showing a photocatalyst device according to a modification of the first embodiment. [Figure 9] Cross-sectional view schematically showing a photocatalyst device according to the second embodiment. [Figure 10] Cross-sectional view schematically showing the manufacturing process of a photocatalyst device according to the second embodiment. [Figure 11]5A to 5C are cross-sectional views schematically showing the manufacturing process of the photocatalytic device according to the second embodiment. [Figure 12] FIG. 10 is a cross-sectional view schematically showing a photocatalytic device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. Note that the embodiments described below do not unduly limit the content of the present invention as defined in the claims. Furthermore, not all of the configurations described below are necessarily essential components of the present invention.

[0010] 1. First embodiment 1.1. Photocatalyst device Configuration First, the photocatalytic device according to the first embodiment will be described with reference to the drawings. Fig. 1 is a cross-sectional view that schematically shows the photocatalytic device 100 according to the first embodiment. Fig. 2 is a plan view that schematically shows the photocatalytic device 100 according to the first embodiment. Fig. 1 is a cross-sectional view taken along line II in Fig. 2.

[0011] 1 and 2, the photocatalytic device includes, for example, a substrate 10, a mask layer 20, a columnar section 30, an oxide layer 40, and a container 50 that contains water W. For convenience, the mask layer 20, the oxide layer 40, and the water W are not shown in FIG.

[0012] As shown in FIG. 1, the substrate 10 includes, for example, a support substrate 12 and a buffer layer 14.

[0013] The support substrate 12 is, for example, a sapphire substrate, a Si substrate, a GaN substrate, a SiC substrate, etc. Although not shown, the substrate 10 may be composed of only the buffer layer 14 without the support substrate 12.

[0014] The buffer layer 14 is provided on the support substrate 12. The buffer layer 14 is provided between the support substrate 12 and the mask layer 20. The buffer layer 14 is made of In u Ga 1-u N (0≦u<1). The material of the buffer layer 14 is, for example, i-type In that is not intentionally doped with impurities. u Ga 1-u N (0≦u<1). The material of the buffer layer 14 may be gallium nitride or indium gallium nitride.

[0015] The mask layer 20 is provided on the buffer layer 14. A plurality of openings 22 are formed in the mask layer 20. The columnar portions 30 are provided in the openings 22. The mask layer 20 is, for example, a titanium layer, a silicon oxide layer, a titanium oxide layer, an aluminum oxide layer, or the like. The mask layer 20 functions as a mask for selectively growing the columnar portions 30.

[0016] The columnar portion 30 is provided on the substrate 10. In the illustrated example, the columnar portion 30 is provided on the buffer layer 14. The columnar portion 30 protrudes upward from the substrate 10. The columnar portion 30 is also called, for example, a nanocolumn, a nanowire, a nanorod, or a nanopillar. The planar shape of the columnar portion 30 is, for example, a polygon such as a hexagon, or a circle. In the example shown in FIG. 2, the planar shape of the columnar portion 30 is a regular hexagon. The diameter of the columnar portion 30 is, for example, 1 nm or more and 1000 nm or less, and preferably 10 nm or more and 500 nm or less.

[0017] A plurality of columnar sections 30 are provided. The columnar sections 30 are spaced apart from one another. The number of columnar sections 30 is not particularly limited. The interval between adjacent columnar sections 30 is, for example, 1 nm or more and 1000 nm or less, and preferably 10 nm or more and 500 nm or less. The columnar sections 30 are arranged at a predetermined pitch in a predetermined direction in a planar view. The columnar sections 30 are arranged, for example, in a triangular lattice pattern or a square lattice pattern. In the example shown in FIG. 2, the columnar sections 30 are arranged in a regular triangular lattice pattern. Note that the columnar sections 30 may be arranged randomly without a predetermined pitch.

[0018] The columnar section 30 is made of, for example, a semiconductor having a wurtzite crystal structure. The material of the columnar section 30 is, for example, a group III nitride semiconductor. x Ga 1-x N (0≦x<1) is included. x is, for example, 0.1 or more and 0.5 or less, and preferably 0.2 or more and 0.4 or less. If x is 0.1 or more, the band gap becomes narrow, and for example, when sunlight is irradiated onto the columnar section 30, visible light other than ultraviolet light can also be absorbed. Therefore, the utilization efficiency of sunlight can be improved. If x is 0.5 or less, it is possible to prevent the band gap from becoming too narrow, preventing the hydrogen ion reduction reaction described below from occurring.

[0019] The material of the columnar portion 30 is, for example, i-type In that is not intentionally doped with impurities. x Ga 1-x The material of the columnar section 30 may be gallium nitride or indium gallium nitride.

[0020] As shown in FIG. 1, the columnar portion 30 has a first surface 32 and a second surface .

[0021] The first surface 32 of the columnar section 30 is at least one of a c-plane and a semi-polar plane. The semi-polar plane is, for example, a facet plane. In the illustrated example, the first surface 32 is a c-plane. The crystal orientation of the c-plane is {0001}. The first surface 32 is, for example, parallel to the upper surface of the substrate 10. In the illustrated example, the first surface 32 is the upper surface of the columnar section 30. The first surface 32 is, for example, a polar plane having polarity.

[0022] The second surface 34 of the columnar section 30 is an m-plane. The crystal orientation of the m-plane is {10-10}. The second surface 34 is connected to the first surface 32. The second surface 34 is, for example, perpendicular to the first surface 32. In the illustrated example, the second surface 34 is a side surface of the columnar section 30. The second surface 34 is, for example, a non-polar surface that does not have polarity.

[0023] Here, Figure 3 is a diagram illustrating the band structure of GaN. Utilizing the difference in polarization characteristics between the c-plane and the m-plane, the energy band structure near the contact surface T of GaN that comes into contact with water W is designed. When the contact surface T is a polar c-plane, the GaN energy band can be easily designed to bend upward significantly near the contact surface T, as shown in Figure 3A. On the other hand, when the contact surface T is a non-polar m-plane, the GaN energy band can be easily designed to bend upward slightly near the contact surface S, as shown in Figure 3B.

[0024] The columnar section 30 is designed so that the energy band bends upward significantly near the first surface 32, as shown in FIG. 3A. The energy band of the columnar section 30 is designed so that the energy band bends upward slightly near the second surface 34, as shown in FIG. 3B. The energy band near the first surface 32 bends upward more significantly than the energy band near the second surface 34. For example, depending on the type of conductivity type of the columnar section 30, the type of dopant, the doping concentration, etc., the energy band can be designed so that the energy band bends upward significantly near the first surface 32, and so that the energy band bends upward more slightly near the second surface 34. Although not shown, the energy band of the columnar section 30 may also be designed so that the energy band bends downward near the second surface 34.

[0025] 1, the oxide layer 40 is provided on the first surface 32 of the columnar section 30, avoiding the second surface 34 of the columnar section 30. The oxide layer 40 is in contact with the first surface 32. The oxide layer 40 is not provided on the second surface 34.

[0026] The thickness of the oxide layer 40 is, for example, 5 nm or more and 50 nm or less. If the thickness of the oxide layer 40 is 5 nm or more, the oxide layer 40 can suppress self-oxidation of the first surface 32. If the thickness of the oxide layer 40 is 50 nm or less, the oxide layer 40 can suppress a decrease in the efficiency of the oxidation reaction of water W in the vicinity of the first surface 32. The thickness of the oxide layer 40 is measured, for example, by a scanning electron microscope (SEM).

[0027] The oxide layer 40 contains In y Ga 1-y O z (0 ≦ y < 1, 0 < z). The material of the oxide layer 40 is In y Ga 1-y O z . When the material of the columnar part 30 is gallium nitride, the material of the oxide layer 40 is gallium oxide. When the material of the columnar part 30 is indium gallium nitride, the material of the oxide layer 40 is indium gallium oxide.

[0028] The container 50 contains water W. In the illustrated example, the container 50 is provided on the substrate 10. The bottom of the container 50 is constituted by the substrate 10. The container 50 contains a plurality of columnar parts 30. Although not shown, the bottom of the container 50 may not be constituted by the substrate 10, and the container 50 may contain a plurality of columnar parts 30 and the substrate 10. The material of the container 50 is, for example, resin, metal, or the like.

[0029] The water W contained in the container 50 may be tap water, or may be pure water such as ion-exchanged water, ultrafiltrated water, reverse osmosis water, and distilled water, or may be water containing substances such as carbon dioxide. The columnar part 30 and the oxide layer 40 are in contact with the water W. In the illustrated example, the mask layer 20 is also in contact with the water W.

[0030] In addition, as described below, if oxygen is generated by an oxidation reaction in the vicinity of the first surface 32 and hydrogen is generated by a reduction reaction in the vicinity of the second surface 34, the liquid contained in the container 50 may be a liquid other than the water W.

[0031] 1.1.2. Operation FIG. 4 is a diagram for explaining the operation of the photocatalytic device 100.

[0032] In the photocatalytic device 100, as shown in FIG. 4, when light L is irradiated onto the columnar portion 30, the columnar portion 30 absorbs the light L, and the light L excites electrons E in the valence band to the conduction band, generating holes H in the valence band. The light L may be irradiated onto the columnar portion 30 from above, from an obliquely upward direction, from the side, or from below. When the light L is irradiated from below, the substrate 10 transmits the light L. The light L is light that includes ultraviolet rays. The light L is, for example, sunlight. The light L may also be light irradiated from a light source not shown.

[0033] As described above, the energy band of the columnar section 30 bends upward significantly near the first surface 32 and bends upward slightly near the second surface 34. In this way, the energy band of the columnar section 30 bends differently near the first surface 32 and the second surface 34. This makes it easier for electrons E and holes H to separate, with the holes H moving to the first surface 32 and the electrons E moving to the second surface 34. As a result, an oxidation reaction occurs near the first surface 32 as shown in the following formula (1), and water W is oxidized to generate oxygen. A reduction reaction occurs near the second surface 34 as shown in the following formula (2), and hydrogen ions are reduced to generate hydrogen.

[0034] 2H2O → O2+ 4H + + 4e - ···(1) 4H + + 4e - → 2H2···(2)

[0035] In this way, in the photocatalytic device 100, the electrons E and holes H can be separated and moved by the electric field between the first surface 32 and the second surface 34 of the columnar section 30, thereby generating hydrogen and oxygen. The photocatalytic device 100 can realize artificial photosynthesis.

[0036] 1.1.3. Effects The photocatalytic device 100 includes a substrate 10, a first surface 32 provided on the substrate 10 and being at least one of a c-plane and a semi-polar plane, and a second surface 34 that is an m-plane. x Ga 1-xA plurality of columnar portions 30 including N(0≦x<1), provided on the first surface 32 while avoiding the second surface 34, In y Ga 1-y O z and an oxide layer 40 as a first oxide layer including (0≦y<1, 0<z).

[0037] Therefore, in the photocatalytic device 100, the oxide layer 40 can suppress the self-oxidation of the columnar portions 30 on the first surface 32. If no oxide layer is provided on the first surface, the columnar portions are self-oxidized as shown in the following formula (3). When the columnar portions are self-oxidized, the efficiency of the oxygen generation reaction near the first surface decreases.

[0038] 2GaN → 2Ga 3+ + N2+ 6e - ···(3)

[0039] Furthermore, in the photocatalytic device 100, since the oxide layer 40 is provided while avoiding the second surface 34, the reduction reaction near the second surface 34 is not inhibited by the oxide layer 40.

[0040] Therefore, in the photocatalytic device 100, the efficiency of the redox reaction can be increased.

[0041] In the photocatalytic device 100, the first surface 32 is a c-plane. Therefore, compared with the case where the first surface is a semi-polar surface, the energy band of the columnar portions 30 can be bent upward significantly near the first surface 32 due to polarity. Thereby, when the columnar portions 30 are irradiated with light L, holes H and electrons E can be easily separated and moved.

[0042] In the photocatalytic device 100, the plurality of columnar portions 30 are irradiated with light L. Therefore, in the photocatalytic device 100, electrons E can be excited in the columnar portions 30 to generate holes H.

[0043] 1.2. Method for manufacturing a photocatalytic device Next, a method for manufacturing the photocatalytic device 100 according to the first embodiment will be described with reference to the drawings. Fig. 5 is a flowchart for explaining the method for manufacturing the photocatalytic device 100 according to the first embodiment. Fig. 6 and Fig. 7 are cross-sectional views schematically showing the manufacturing process of the photocatalytic device 100 according to the first embodiment.

[0044] 5 and 6, a buffer layer 14 is formed on a support substrate 12 by epitaxial growth (step S1). Examples of epitaxial growth include MOCVD (Metal Organic Chemical Vapor Deposition) and MBE (Molecular Beam Epitaxy). This process forms a substrate 10.

[0045] Next, a mask layer 20 is formed on the substrate 10 (step S2). The mask layer 20 is formed by, for example, electron beam evaporation or sputtering. Next, the mask layer 20 is patterned to form a plurality of openings 22. The patterning is performed by, for example, EB (Electron Beam) exposure and etching.

[0046] Next, using the mask layer 20 as a mask, a plurality of columnar sections 30 are formed on the substrate 10 by epitaxial growth (step S3). Examples of epitaxial growth include MOCVD and MBE. The epitaxial growth is performed under conditions such that the columnar sections 30 have a surface 32a that is at least one of a c-plane and a semi-polar plane, and a second surface 34 that is an m-plane. In the illustrated example, the surface 32a is a c-plane, and hereinafter will also be referred to as the "c-plane 32a."

[0047] 6, the plurality of columns 30, the mask layer 20, and the substrate 10 are immersed in a strongly basic aqueous solution R (step S4). The strongly basic aqueous solution R is alkaline, for example, with a pH of 11 or higher, preferably a pH of 12 or higher. The strongly basic aqueous solution R is, for example, a sodium hydroxide (NaOH) aqueous solution or a potassium hydroxide (KOH) aqueous solution. The strongly basic aqueous solution R is contained in a container 2.

[0048] 7, the plurality of columnar sections 30 immersed in the strongly basic aqueous solution R are irradiated with ultraviolet light UV to cause the c-faces 32a of the columnar sections 30 to self-oxidize, thereby forming an oxide layer 40 (step S5). Because the reduction reaction occurs on the second faces 34 of the columnar sections 30 as described above, the oxide layer 40 is not formed on the second faces 34. This allows the oxide layer 40 to be formed on the first faces 32, avoiding the second faces 34.

[0049] The photocatalytic device 100 can be manufactured through the above steps.

[0050] In the method for manufacturing the photocatalytic device 100, the substrate 10 has a surface 32a which is at least one of a c-plane and a semi-polar plane, and a second surface 34 which is an m-plane, and In x Ga 1-x The method includes the steps of forming a plurality of pillars 30 containing N (0≦x<1), immersing the plurality of pillars 30 in a strongly basic aqueous solution R, and irradiating the plurality of pillars 30 immersed in the strongly basic aqueous solution R with ultraviolet light UV to oxidize the surface 32a, which is at least one of the c-plane and the semi-polar plane, thereby forming an oxide layer 40.

[0051] Therefore, in the method for manufacturing the photocatalytic device 100, the oxide layer 40 can be selectively formed on the first surface 32. Therefore, it is possible to manufacture a photocatalytic device 100 that can increase the efficiency of the oxidation-reduction reaction.

[0052] Furthermore, the manufacturing method of the photocatalytic device 100 can reduce damage to the columnar portion 30 compared to forming an oxide layer by, for example, sputtering, CVD (Chemical Vapor Deposition), ALD (Atomic Layer Deposition), etc. Furthermore, it can reduce the incorporation of unintended impurities into the columnar portion 30. If the columnar portion is damaged or if impurities are incorporated, an interface state is formed, and electrons and holes generated by photoexcitation recombine, making it difficult for the oxidation-reduction reaction to proceed.

[0053] Furthermore, in the manufacturing method of the photocatalytic device 100, even if the surface of the columnar section 30 is uneven, the oxide layer 40 can be formed with good uniformity.

[0054] In the method for manufacturing the photocatalytic device 100, the strongly basic aqueous solution is a sodium hydroxide aqueous solution. Therefore, in the method for manufacturing the photocatalytic device 100, the oxide layer 40 can be selectively formed on the first surface 32 of the columnar section 30.

[0055] 1.3. Modified photocatalytic device Next, a photocatalytic device according to a modified example of the first embodiment will be described with reference to the drawings. Fig. 8 is a cross-sectional view showing a photocatalytic device 110 according to a modified example of the first embodiment. Hereinafter, in the photocatalytic device 110 according to the modified example of the first embodiment, components having the same functions as the components of the photocatalytic device 100 described above will be given the same reference numerals, and detailed description thereof will be omitted.

[0056] As shown in FIG. 8, the photocatalytic device 110 differs from the above-described photocatalytic device 100 in that it includes a first promoter 60 and a second promoter 62.

[0057] The first promoter 60 is provided on the oxide layer 40. The first promoter 60 is provided on the side of the oxide layer 40 opposite the columnar section 30. The oxide layer 40 is provided between the first promoter 60 and the columnar section 30. The first promoter 60 is in contact with water W. The first promoter 60 is, for example, in a layer shape.

[0058] The material of the first promoter 60 is different from the material of the oxide layer 40. The material of the first promoter 60 is, for example, nickel oxide (NiO x ), nickel iron oxide (NiFeO x ), iridium oxide (IrO x ), magnesium oxide (MnO x ), cobalt oxide (CoO x The first promoter 60 is preferably a metal oxide such as ruthenium oxide (RuO2), or ruthenium oxide (RuO2). The material of the first promoter 60 is not limited to these. The first promoter 60 has a function of assisting the oxidation reaction that occurs near the first surface 32 of the columnar section 30.

[0059] The second promoter 62 is provided on the second surface 34 of the columnar section 30. In a plan view, the second promoter 62, for example, surrounds the columnar section 30. The second promoter 62 is in contact with the water W. The second promoter 62 is, for example, in a layer shape.

[0060] The material of the second promoter 62 is different from the material of the first promoter 60. Examples of materials for the second promoter 62 include platinum (Pt), gold (Au), silver (Ag), and rhodium (Rh). However, the material of the second promoter 62 is not limited to these. The second promoter 62 may be composed of a core made of Rh and a shell made of chromium oxide (Cr2O3). The second promoter 62 has the function of assisting the reduction reaction that occurs near the second surface 34 of the columnar section 30. The promoters 60 and 62 are formed by, for example, vacuum deposition, sputtering, CVD, ALD, or photoelectrodeposition.

[0061] The photocatalytic device 110 includes a first promoter 60 provided on the side of the oxide layer 40 opposite to the multiple columnar portions 30. Therefore, the photocatalytic device 110 can promote the oxidation reaction that occurs near the first surfaces 32 of the columnar portions 30.

[0062] The photocatalytic device 110 includes a second promoter 62 provided on the second surface 34. Therefore, in the photocatalytic device 110, the reduction reaction occurring in the vicinity of the second surface 34 of the columnar section 30 can be promoted.

[0063] 2. Second embodiment 2.1. Photocatalyst device Next, a photocatalytic device 200 according to a second embodiment will be described with reference to the drawings. Fig. 9 is a cross-sectional view schematically showing the photocatalytic device 200 according to the second embodiment. Hereinafter, in the photocatalytic device 200 according to the second embodiment, components having the same functions as the components of the photocatalytic device 100 described above will be given the same reference numerals, and detailed description thereof will be omitted.

[0064] In the above-described photocatalytic device 100, the mask layer 20 was provided on the substrate 10 as shown in FIG.

[0065] In contrast, in the photocatalyst device 200, as shown in FIG. 9, no mask layer 20 is provided on the substrate 10, and an oxide layer 42 is provided.

[0066] In the photocatalyst device 200, the buffer layer 14 of the substrate 10 has a third surface 16. The third surface 16 is a c-plane.

[0067] The oxide layer 42 is provided on the third surface 16. The oxide layer 42 is in contact with the third surface 16. The thickness of the oxide layer 42 is, for example, 5 nm or more and 50 nm or less. If the thickness of the oxide layer 42 is 5 nm or more, self-oxidation of the third surface 16 can be suppressed by the oxide layer 42. If the thickness of the oxide layer 42 is 50 nm or less, it is possible to suppress a decrease in the efficiency of the oxidation reaction of water W in the vicinity of the third surface 16 due to the oxide layer 42. The thickness of the oxide layer 42 is measured, for example, by SEM.

[0068] The oxide layer 42 contains In v Ga 1-v O w (0 ≦ v < 1, 0 < w). The material of the oxide layer 42 is In v Ga 1-v O w . When the material of the buffer layer 14 is gallium nitride, the material of the oxide layer 42 is gallium oxide. When the material of the buffer layer 14 is indium gallium nitride, the material of the oxide layer 42 is indium gallium oxide.

[0069] A plurality of openings 44 are formed in the oxide layer 42. Columnar portions 30 are provided in the openings 44.

[0070] In the photocatalyst device 200, it is provided on the third surface 16 which is the c-plane of the substrate 10, and In v Ga 1-v O wIt includes an oxide layer 42 as a second oxide layer including (0≦v<1, 0<w), and a plurality of openings 44 are formed in the oxide layer 42. The plurality of columnar portions 30 are provided in the plurality of openings 44, and the substrate 10 is In u Ga 1-u N(0≦u<1). Therefore, in the photocatalytic device 200, when the substrate 10 is irradiated with light L, water W can be oxidized in the vicinity of the third surface 16. Therefore, for example, the area where the oxidation reaction of water W occurs can be increased compared to the photocatalytic device 100.

[0071] Although not shown, a first cocatalyst 60 may be provided on the first surface 32, a second cocatalyst 62 may be provided on the second surface 34, and a third cocatalyst may be provided on the third surface 16. The material of the third cocatalyst may be the same as the material of the first cocatalyst 60.

[0072] 2.2. Manufacturing method of photocatalytic device Next, the manufacturing method of the photocatalytic device 200 according to the second embodiment will be described with reference to the drawings. FIGS. 10 and 11 are cross-sectional views schematically showing the manufacturing process of the photocatalytic device 200 according to the second embodiment.

[0073] In the manufacturing method of the photocatalytic device 200, a plurality of columnar portions 30 are formed on the substrate 10 in the same manner as the manufacturing method of the photocatalytic device 100 described above.

[0074] Next, in the manufacturing method of the photocatalytic device 200, the mask layer 20 is removed. The mask layer 20 is removed, for example, by etching. As a result, as shown in FIG. 10, the c-plane 16a of the substrate 10 is exposed. Next, the plurality of columnar portions 30 and the substrate 10 are immersed in a strongly basic aqueous solution R.

[0075] As shown in FIG. 11, ultraviolet rays UV are irradiated onto the plurality of columnar portions 30 and the substrate 10 immersed in the strongly basic aqueous solution R. Then, the c-plane 32a of the columnar portion 30 is self-oxidized to form an oxide layer 40, and the c-plane 16a of the substrate 10 is self-oxidized to form an oxide layer 42.

[0076] The photocatalytic device 200 can be manufactured through the above steps.

[0077] 3. Third embodiment 3.1. Photocatalytic device Next, a photocatalytic device 300 according to a third embodiment will be described with reference to the drawings. Fig. 12 is a cross-sectional view schematically showing the photocatalytic device 300 according to the third embodiment. Hereinafter, in the photocatalytic device 300 according to the third embodiment, components having the same functions as the components of the photocatalytic devices 100 and 200 described above will be given the same reference numerals, and detailed description thereof will be omitted.

[0078] In the photocatalyst device 200 described above, as shown in FIG. 9, the first surface 32 of the columnar portion 30 was the c-plane.

[0079] In contrast to this, in the photocatalytic device 300, as shown in FIG. 12, the first surface 32 of the columnar section 30 is a semi-polar surface.

[0080] In the photocatalytic device 300, the first surface 32 of the columnar section 30 is inclined with respect to the third surface 16 of the substrate 10. The energy band near the semipolar plane bends upward more than the energy band near the m-plane and bends upward less than the energy band near the c-plane.

[0081] Although not shown, as in the photocatalytic device 110 described above, a first promoter 60 may be provided on the first surface 32 of the columnar section 30, and a second promoter 62 may be provided on the second surface 34 of the columnar section 30. A third promoter may be provided on the third surface 16 of the substrate 10. A mask layer 20 may be provided between adjacent columnar sections 30, as in the photocatalytic device 100 described above. Although not shown, the first surface 32 may be both a c-plane and a semi-polar plane. That is, the first surface 32 may be composed of a c-plane and a semi-polar plane.

[0082] 3.2. Photocatalytic device manufacturing method Next, a method for manufacturing the photocatalyst device 300 according to the third embodiment will be described while referring to the drawings.

[0083] In the method for manufacturing the photocatalyst device 300, as shown in FIG. 12, a columnar portion 30 having a semi-polar plane is formed. For example, in the epitaxial growth of the columnar portion 30, a columnar portion 30 having a 0 plane can be formed by adjusting the growth temperature, growth rate, composition of the material, and the like.

[0084] Except for the above, the method for manufacturing the photocatalyst device 300 is basically the same as the method for manufacturing the photocatalyst device 200 described above.

[0085] The above-described embodiments and modifications are merely examples and are not limited thereto. For example, it is also possible to appropriately combine each embodiment and each modification with each other.

[0086] The present invention includes configurations that are substantially the same as the configurations described in the embodiments, for example, configurations having the same functions, methods, and results, or configurations having the same objectives and effects. The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. The present invention also includes configurations that exhibit the same operational effects as the configurations described in the embodiments or configurations that can achieve the same objectives. The present invention also includes configurations in which known technologies are added to the configurations described in the embodiments.

[0087] The following content is derived from the above-described embodiments and modifications.

[0088] One aspect of the photocatalyst device is a substrate, provided on the substrate, having a first surface that is at least one of a c-plane and a semi-polar plane, and a second surface that is an m-plane, and having a plurality of columnar portions containing In x Ga 1-x N (0 ≦ x < 1), provided on the first surface while avoiding the second surface, and having a first oxide layer containing In y Ga 1-y O z (0 ≦ y < 1, 0 < z). It includes.

[0089] According to this photocatalytic device, the efficiency of the redox reaction can be increased.

[0090] In one aspect of the photocatalytic device, It may include a first cocatalyst provided on the side opposite to the plurality of columnar portions of the first oxide layer.

[0091] According to this photocatalytic device, the oxidation reaction occurring near the first surface of the columnar portion can be promoted.

[0092] In one aspect of the photocatalytic device, It may include a second cocatalyst provided on the second surface and having a different material from the first cocatalyst.

[0093] According to this photocatalytic device, the reduction reaction occurring near the second surface of the columnar portion can be promoted.

[0094] In one aspect of the photocatalytic device, The first surface may be a c-plane.

[0095] According to this photocatalytic device, when the columnar portion is irradiated with light, holes and electrons are easily separated and moved.

[0096] In one aspect of the photocatalytic device, It is provided on the third surface which is the c-plane of the substrate, and contains a second oxide layer including In v Ga 1-v O w (0≦v<1, 0<w), A plurality of openings are formed in the second oxide layer, The plurality of columnar portions are provided in the plurality of openings, The substrate may contain In u Ga 1-u N(0≦u<1).

[0097] According to this photocatalytic device, the area where the oxidation reaction occurs can be increased.

[0098] In one embodiment of the photocatalytic device, The plurality of columnar portions may be irradiated with light.

[0099] According to this photocatalytic device, electrons can be excited in the columnar portions to generate holes.

[0100] One aspect of the method for manufacturing a photocatalytic device is: The substrate has a surface that is at least one of a c-plane and a semipolar plane, and an m-plane, and x Ga 1-x forming a plurality of pillars, including N (0≦x<1); immersing the plurality of pillars in a strongly basic aqueous solution; irradiating the plurality of pillars immersed in the strongly basic aqueous solution with ultraviolet light to oxidize at least one of the c-plane and the semi-polar plane, thereby forming an oxide layer; Includes.

[0101] According to this method for manufacturing a photocatalytic device, it is possible to manufacture a photocatalytic device that can increase the efficiency of the oxidation-reduction reaction.

[0102] In one embodiment of the method for producing a photocatalytic device, The strongly basic aqueous solution may be an aqueous sodium hydroxide solution.

[0103] According to this method for manufacturing a photocatalytic device, an oxide layer can be selectively formed on the first surface of the columnar portion. [Explanation of symbols]

[0104] 2...container, 10...substrate, 12...support substrate, 14...buffer layer, 16...third surface, 16a...c-surface, 20...mask layer, 22...opening, 30...columnar portion, 32...first surface, 32a...c-surface, 34...second surface, 40, 42...oxide layer, 44...opening, 50...container, 60...first co-catalyst, 62...second co-catalyst, 100, 110, 200, 300...photocatalytic device

Claims

1. A substrate; a first surface that is at least one of a c-plane and a semi-polar plane and a second surface that is an m-plane, ｘ Ga １－ｘ a plurality of pillars including N (0≦x<1); provided on the first surface while avoiding the second surface, ｙ Ga １－ｙ O ｚ a first oxide layer including (0≦y<1, 0<z); A photocatalytic device comprising:

2. In claim 1, A photocatalytic device comprising a first promoter provided on the side of the first oxide layer opposite to the plurality of columnar portions.

3. In claim 2, A photocatalytic device comprising a second promoter provided on the second surface and made of a material different from that of the first promoter.

4. In claim 1, A photocatalytic device, wherein the first surface is a c-plane.

5. In claim 1, provided on a third surface, which is the c-plane of the substrate; ｖ Ga １－ｖ O ｗ a second oxide layer comprising (0≦v<1, 0<w); a plurality of openings are formed in the second oxide layer; the plurality of columnar portions are provided in the plurality of openings, The substrate is In ｕ Ga １－ｕ N (0≦u<1).

6. In claim 1, A photocatalytic device in which light is irradiated onto the plurality of columnar portions.

7. The substrate has a surface that is at least one of a c-plane and a semipolar plane, and an m-plane, and ｘ Ga １－ｘ forming a plurality of pillars including N (0≦x<1); immersing the plurality of pillars in a strongly basic aqueous solution; irradiating the plurality of pillars immersed in the strongly basic aqueous solution with ultraviolet light to oxidize at least one of the c-plane and the semi-polar plane, thereby forming an oxide layer; A method for manufacturing a photocatalytic device, comprising:

8. In claim 7, The method for manufacturing a photocatalytic device, wherein the strongly basic aqueous solution is a sodium hydroxide aqueous solution.

Images