JP6483628B2 - Semiconductor photocatalyst - Google Patents
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- JP6483628B2 JP6483628B2 JP2016000393A JP2016000393A JP6483628B2 JP 6483628 B2 JP6483628 B2 JP 6483628B2 JP 2016000393 A JP2016000393 A JP 2016000393A JP 2016000393 A JP2016000393 A JP 2016000393A JP 6483628 B2 JP6483628 B2 JP 6483628B2
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- 239000004065 semiconductor Substances 0.000 title claims description 194
- 239000011941 photocatalyst Substances 0.000 title claims description 49
- 229910052751 metal Inorganic materials 0.000 claims description 86
- 239000002184 metal Substances 0.000 claims description 86
- 239000000758 substrate Substances 0.000 claims description 17
- 150000004767 nitrides Chemical class 0.000 claims description 8
- 230000000052 comparative effect Effects 0.000 description 19
- 239000007864 aqueous solution Substances 0.000 description 17
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 16
- 238000007254 oxidation reaction Methods 0.000 description 15
- 238000006722 reduction reaction Methods 0.000 description 15
- 230000015572 biosynthetic process Effects 0.000 description 13
- 229910002601 GaN Inorganic materials 0.000 description 12
- 230000003647 oxidation Effects 0.000 description 12
- 238000000034 method Methods 0.000 description 10
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- 229910052697 platinum Inorganic materials 0.000 description 8
- 238000006243 chemical reaction Methods 0.000 description 7
- 150000001875 compounds Chemical class 0.000 description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
- 239000000463 material Substances 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 5
- 239000001257 hydrogen Substances 0.000 description 5
- 229910052739 hydrogen Inorganic materials 0.000 description 5
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 4
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 4
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 4
- 239000000956 alloy Substances 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 4
- 229910052738 indium Inorganic materials 0.000 description 4
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 4
- 239000012528 membrane Substances 0.000 description 4
- 230000001699 photocatalysis Effects 0.000 description 4
- 238000013032 photocatalytic reaction Methods 0.000 description 4
- 238000002360 preparation method Methods 0.000 description 4
- 229910052594 sapphire Inorganic materials 0.000 description 4
- 239000010980 sapphire Substances 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
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- 238000010438 heat treatment Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
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- 239000010703 silicon Substances 0.000 description 3
- 239000010936 titanium Substances 0.000 description 3
- 229910052719 titanium Inorganic materials 0.000 description 3
- 229910002704 AlGaN Inorganic materials 0.000 description 2
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- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 229920000557 Nafion® Polymers 0.000 description 2
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 2
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 2
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 2
- UIIMBOGNXHQVGW-UHFFFAOYSA-M Sodium bicarbonate Chemical compound [Na+].OC([O-])=O UIIMBOGNXHQVGW-UHFFFAOYSA-M 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
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- 239000003513 alkali Substances 0.000 description 2
- 229910021529 ammonia Inorganic materials 0.000 description 2
- 229910021417 amorphous silicon Inorganic materials 0.000 description 2
- 239000012298 atmosphere Substances 0.000 description 2
- 229910002092 carbon dioxide Inorganic materials 0.000 description 2
- 238000005229 chemical vapour deposition Methods 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 238000000206 photolithography Methods 0.000 description 2
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- 229910052709 silver Inorganic materials 0.000 description 2
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- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 2
- 229910052724 xenon Inorganic materials 0.000 description 2
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- 229910003902 SiCl 4 Inorganic materials 0.000 description 1
- 239000003570 air Substances 0.000 description 1
- RNQKDQAVIXDKAG-UHFFFAOYSA-N aluminum gallium Chemical compound [Al].[Ga] RNQKDQAVIXDKAG-UHFFFAOYSA-N 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 229910001882 dioxygen Inorganic materials 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- NBVXSUQYWXRMNV-UHFFFAOYSA-N fluoromethane Chemical compound FC NBVXSUQYWXRMNV-UHFFFAOYSA-N 0.000 description 1
- 229910052736 halogen Inorganic materials 0.000 description 1
- 150000002367 halogens Chemical class 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 230000002209 hydrophobic effect Effects 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- 150000002830 nitrogen compounds Chemical class 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- -1 perfluoro side chain Chemical group 0.000 description 1
- 229920001296 polysiloxane Polymers 0.000 description 1
- 235000015497 potassium bicarbonate Nutrition 0.000 description 1
- 229910000028 potassium bicarbonate Inorganic materials 0.000 description 1
- 239000011736 potassium bicarbonate Substances 0.000 description 1
- 239000001103 potassium chloride Substances 0.000 description 1
- 235000011164 potassium chloride Nutrition 0.000 description 1
- TYJJADVDDVDEDZ-UHFFFAOYSA-M potassium hydrogencarbonate Chemical compound [K+].OC([O-])=O TYJJADVDDVDEDZ-UHFFFAOYSA-M 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- 239000012266 salt solution Substances 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 235000017557 sodium bicarbonate Nutrition 0.000 description 1
- 229910000030 sodium bicarbonate Inorganic materials 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 125000000542 sulfonic acid group Chemical group 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
- BFKJFAAPBSQJPD-UHFFFAOYSA-N tetrafluoroethene Chemical group FC(F)=C(F)F BFKJFAAPBSQJPD-UHFFFAOYSA-N 0.000 description 1
- TXEYQDLBPFQVAA-UHFFFAOYSA-N tetrafluoromethane Chemical compound FC(F)(F)F TXEYQDLBPFQVAA-UHFFFAOYSA-N 0.000 description 1
- RGGPNXQUMRMPRA-UHFFFAOYSA-N triethylgallium Chemical compound CC[Ga](CC)CC RGGPNXQUMRMPRA-UHFFFAOYSA-N 0.000 description 1
- OTRPZROOJRIMKW-UHFFFAOYSA-N triethylindigane Chemical compound CC[In](CC)CC OTRPZROOJRIMKW-UHFFFAOYSA-N 0.000 description 1
- JLTRXTDYQLMHGR-UHFFFAOYSA-N trimethylaluminium Chemical compound C[Al](C)C JLTRXTDYQLMHGR-UHFFFAOYSA-N 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- 238000001771 vacuum deposition Methods 0.000 description 1
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Description
本発明は、半導体から構成されて光触媒機能を有する半導体光触媒に関する。 The present invention relates to a semiconductor photocatalyst composed of a semiconductor and having a photocatalytic function.
光触媒を用いた技術が多数開発されている。例えば、酸化電極と還元電極とを用いる技術がある（非特許文献１参照）。例えば、図４に示すように、酸化槽３０１と還元槽３０２と、酸化槽３０１に収容された酸またはアルカリの水溶液３０３と、還元槽３０２に収容された塩の水溶液３０４と、水溶液３０３および水溶液３０４の間でプロトンを移動させるプロトン膜３０５と、水溶液３０３に浸漬された酸化電極３０６と、水溶液３０４に浸漬された還元電極３０７と、酸化電極３０６および還元電極３０７を接続する導線３０８とを用いて水の電気分解を行う。 Many technologies using photocatalysts have been developed. For example, there is a technique using an oxidation electrode and a reduction electrode (see Non-Patent Document 1). For example, as shown in FIG. 4, an oxidation tank 301, a reduction tank 302, an acid or alkali aqueous solution 303 accommodated in the oxidation tank 301, an aqueous salt solution 304 accommodated in the reduction tank 302, an aqueous solution 303 and an aqueous solution. A proton membrane 305 that moves protons between 304, an oxidation electrode 306 immersed in an aqueous solution 303, a reduction electrode 307 immersed in the aqueous solution 304, and a conductive wire 308 that connects the oxidation electrode 306 and the reduction electrode 307 are used. Electrolyze water.
水溶液３０３は、例えば、水酸化ナトリウム水溶液、水酸化カリウム水溶液、塩酸であり、水溶液３０４は、例えば、炭酸水素カリウム水溶液、炭酸水素ナトリウム水溶液、塩化カリウム水溶液、塩化ナトリウム水溶液である。酸化電極３０６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から構成され、還元電極３０７は、例えば、ニッケル、鉄、金、白金、銀、銅、インジウム、チタン、またはこれらの合金や金属化合物から構成されている。 The aqueous solution 303 is, for example, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, and hydrochloric acid, and the aqueous solution 304 is, for example, an aqueous potassium bicarbonate solution, an aqueous sodium bicarbonate solution, an aqueous potassium chloride solution, and an aqueous sodium chloride solution. Oxidizing electrode 306 is, for example, nitrogen compound semiconductor is composed of titanium oxide or amorphous silicon, the reduction electrode 307, for example, nickel, iron, gold, platinum, silver, copper, indium, titanium, or an alloy or a metal, It is composed of compounds.
酸化槽３０１と還元槽３０２との間にプロトン膜３０５が配置され、水溶液３０３で生成したプロトンが、プロトン膜３０５を介して水溶液３０４へ拡散していく。プロトン膜３０５は例えば、ナフィオン（登録商標）である。ナフィオン（登録商標）は、炭素−フッ素からなる疎水性テトラフルオロエチレン骨格とスルホン酸基を持つパーフルオロ側鎖から構成されたパーフルオロカーボン材料である。 A proton membrane 305 is disposed between the oxidation tank 301 and the reduction tank 302, and protons generated in the aqueous solution 303 diffuse into the aqueous solution 304 through the proton membrane 305. The proton membrane 305 is, for example, Nafion (registered trademark). Nafion (registered trademark) is a perfluorocarbon material composed of a hydrophobic tetrafluoroethylene skeleton composed of carbon-fluorine and a perfluoro side chain having a sulfonic acid group.
酸化電極３０６と還元電極３０７とは、導線３０８で電気的に接続されており、酸化電極３０６から還元電極３０７へ電子が移動可能とされている。光源３１０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、太陽光またはこれらの組み合わせである。酸化電極３０６を構成する材料の吸収可能な波長の光が照射される。例えば、窒化ガリウムで構成される酸化電極３０６では、３６５ｎｍ以下の波長の光が吸収可能である。 The oxidation electrode 306 and the reduction electrode 307 are electrically connected by a conducting wire 308, and electrons can move from the oxidation electrode 306 to the reduction electrode 307. The light source 310 is, for example, a xenon lamp, a mercury lamp, a halogen lamp, a pseudo solar light source, sunlight, or a combination thereof. Light having a wavelength that can be absorbed by the material constituting the oxidation electrode 306 is irradiated. For example, the oxidation electrode 306 made of gallium nitride can absorb light having a wavelength of 365 nm or less.
しかしながら、上述した技術では、構成要素が多く、反応系が複雑なことから、より簡易な反応系および小型化が課題である。これに対し、より簡便な構成で小型が可能な技術として、配線構造を必要とせずに１つの光触媒で構成する技術がある（非特許文献２参照）。 However, in the above-described technique, since there are many components and the reaction system is complicated, a simpler reaction system and miniaturization are problems. On the other hand, as a technique that can be reduced in size with a simpler configuration, there is a technique that includes a single photocatalyst without requiring a wiring structure (see Non-Patent Document 2).
例えば、図５に示すように、光触媒槽４０１に収容された酸やアルカリなどの水溶液４０２と、水溶液４０２に浸漬した光触媒４０３とを備える。光触媒４０３は、窒化物半導体、酸化チタン、またはアモルファスシリコンなどから構成されている。なお、光触媒４０３の表面には、例えば水の分解反応を促進する金属助触媒が担持されている。光源４１０からの光が光触媒４０３に照射されると、水素および酸素が生成される。 For example, as shown in FIG. 5, an aqueous solution 402 such as an acid or alkali contained in a photocatalyst tank 401 and a photocatalyst 403 immersed in the aqueous solution 402 are provided. The photocatalyst 403 is made of a nitride semiconductor, titanium oxide, amorphous silicon, or the like. For example, a metal promoter that promotes the decomposition reaction of water is supported on the surface of the photocatalyst 403. When light from the light source 410 is irradiated onto the photocatalyst 403, hydrogen and oxygen are generated.
この構成は、前述した光触媒の反応系に比べて簡易であり、系の低コスト化および小型化が可能である点で期待されている。しかしながら、この反応系では、光エネルギー変換効率が低いという問題がある。 This configuration is simpler than the above-described photocatalytic reaction system, and is expected in that the system can be reduced in cost and size. However, this reaction system has a problem that the light energy conversion efficiency is low.
本発明は、以上のような問題点を解消するためになされたものであり、簡素な構成で光触媒反応の効率をより向上させることを目的とする。 The present invention has been made to solve the above-described problems, and an object thereof is to further improve the efficiency of the photocatalytic reaction with a simple configuration.
本発明に係る半導体光触媒は、基板の主表面上に形成され、Ｇａを含む窒化物半導体からなり、主表面を（０００１）面とした第１半導体層と、第１半導体層の主表面上に接触して形成され、基板平面方向の格子定数が第１半導体層より小さいＧａを含む窒化物半導体からなり、主表面を（０００１）面とした第２半導体層と、第２半導体層の主表面上にショットキー接合して形成された第１金属層と、第２半導体層の主表面上に第１金属層とは分離してオーミック接合して形成され、第１半導体層と電気的に接続された第２金属層とを備える。 The semiconductor photocatalyst of the present invention is formed on the main surface of the substrate, Ri Do a nitride semiconductor containing Ga, a main surface (0001) plane and the first semiconductor layer, on a main surface of the first semiconductor layer contacts are formed on the lattice constant of the substrate planar direction is a nitride semiconductor containing Ga have smaller than the first semiconductor layer, a second semiconductor layer in which the major surface and the (0001) plane, of the second semiconductor layer The first metal layer formed by Schottky junction on the main surface and the first metal layer formed separately from the first metal layer on the main surface of the second semiconductor layer are formed by ohmic junction, and is electrically connected to the first semiconductor layer. And a second metal layer connected to.
上記半導体光触媒において、第１半導体層は、ｎ型とされているとよい。 In the semiconductor photocatalyst, the first semiconductor layer may be n-type.
上記半導体光触媒において、第２半導体層、第１金属層、第２金属層、および第２半導体層と第１金属層との接触領域は、露出する部分を備える。 In the semiconductor photocatalyst, the second semiconductor layer, the first metal layer, the second metal layer, and the contact region between the second semiconductor layer and the first metal layer include an exposed portion.
上記半導体光触媒において、島状とされた複数の第１金属層および島状とされた複数の第２金属層が、第２半導体層の主表面上に形成されているようにすればよい。 In the semiconductor photocatalyst, the plurality of island-shaped first metal layers and the plurality of island-shaped second metal layers may be formed on the main surface of the second semiconductor layer.
以上説明したように、本発明によれば、化合物半導体からなる第１半導体層の主表面上に接触して化合物半導体からなる第２半導体層を形成し、第２半導体層は第１半導体層より小さい格子定数としたので、簡素な構成で光触媒反応の効率がより向上するという優れた効果が得られる。 As described above, according to the present invention, the second semiconductor layer made of the compound semiconductor is formed in contact with the main surface of the first semiconductor layer made of the compound semiconductor, and the second semiconductor layer is formed from the first semiconductor layer. Since the lattice constant is small, an excellent effect is obtained in that the efficiency of the photocatalytic reaction is further improved with a simple configuration.
以下、本発明の実施の形態について図１および図２を参照して説明する。図１は、本発明の実施の形態における半導体光触媒の構成を示す断面図である。また、図２は、実施の形態における半導体光触媒の一部構成を示す平面図である。 Hereinafter, embodiments of the present invention will be described with reference to FIG. 1 and FIG. FIG. 1 is a cross-sectional view showing a configuration of a semiconductor photocatalyst according to an embodiment of the present invention. FIG. 2 is a plan view showing a partial configuration of the semiconductor photocatalyst according to the embodiment.
この半導体光触媒は、第１半導体層１０１、および第１半導体層１０１の主表面上に接触して形成された第２半導体層１０２を備える。第１半導体層１０１および第２半導体層１０２は、化合物半導体から構成されている。また、第２半導体層１０２は、第１半導体層１０１より小さな格子定数とされている。 The semiconductor photocatalyst includes a first semiconductor layer 101 and a second semiconductor layer 102 formed in contact with the main surface of the first semiconductor layer 101. The first semiconductor layer 101 and the second semiconductor layer 102 are made of a compound semiconductor. The second semiconductor layer 102 has a smaller lattice constant than the first semiconductor layer 101.
また、第２半導体層１０２の主表面上にショットキー接合（接触）して形成された第１金属層１０３、および第２半導体層１０２の主表面上にオーミック接合（接触）して形成され、第１半導体層１０１と電気的に接続された第２金属層１０４を備える。例えば、第２金属層１０４を構成する金属が拡散して形成された合金領域１４１により、第２金属層１０４が半導体層１０１に電気的に接続している。第１金属層１０３と第２金属層１０４とは、電気的に分離されている。なお、第２金属層１０４、第２半導体層１０２、第１金属層１０３、および第２半導体層１０２と第１金属層１０３との接触領域は、露出する部分を備えていることが重要となる。 The first metal layer 103 formed by Schottky junction (contact) on the main surface of the second semiconductor layer 102 and the ohmic junction (contact) formed on the main surface of the second semiconductor layer 102, A second metal layer 104 electrically connected to the first semiconductor layer 101 is provided. For example, the second metal layer 104 is electrically connected to the semiconductor layer 101 by an alloy region 141 formed by diffusing the metal constituting the second metal layer 104. The first metal layer 103 and the second metal layer 104 are electrically separated. Note that it is important that the second metal layer 104, the second semiconductor layer 102, the first metal layer 103, and the contact region between the second semiconductor layer 102 and the first metal layer 103 have an exposed portion. .
例えば、第２半導体層１０２の主表面上に、島状とされた複数の第１金属層１０３が形成されている。同様に、第２半導体層１０２の主表面上に、島状とされた複数の第２金属層１０４が形成されている。例えば、図２の平面図に示すように、平面視で直径１０μｍの円形とされた複数の第１金属層１０３、および平面視で直径１０μｍの円形とされた複数の第２金属層１０４が、各々１つおきに正方配列された状態とすればよい。隣り合う島部分の中心間の距離は１１０μｍとすればよい。 For example, a plurality of first metal layers 103 having an island shape are formed on the main surface of the second semiconductor layer 102. Similarly, a plurality of second metal layers 104 having an island shape are formed on the main surface of the second semiconductor layer 102. For example, as shown in the plan view of FIG. 2, a plurality of first metal layers 103 having a diameter of 10 μm in a plan view and a plurality of second metal layers 104 having a diameter of 10 μm in a plan view, What is necessary is just to set it as the state where every other square arrangement. The distance between the centers of adjacent island portions may be 110 μm.
このように構成することで、第２半導体層１０２、第１金属層１０３、および第２半導体層１０２と第１金属層１０３との接触領域を、より広い面積で露出させることができる。また、各々の島状の部分（第２金属層１０４）を規則的に配列させることで、局所的な正孔の捕集による、例えば材料を劣化させる目的外の反応が抑制できるようになる。 With this configuration, the second semiconductor layer 102, the first metal layer 103, and the contact region between the second semiconductor layer 102 and the first metal layer 103 can be exposed in a wider area. Further, by regularly arranging the island-like portions (second metal layer 104), an unintended reaction that degrades the material, for example, due to local hole collection can be suppressed.
第１半導体層１０１および第２半導体層１０２は、ＩＩＩ−Ｖ族化合物半導体から構成すればよい。例えば、第１半導体層１０１は、ｎ型のＧａＮから構成し、第２半導体層１０２は、ＡｌＧａＮから構成すればよい。この場合、主表面の面方位を（０００１）面としたサファイアからなる基板１１１の上に、例えば公知の有機金属気相成長法により、シリコンをドープしてｎ型としたＧａＮをエピタキシャル成長させて第１半導体層１０１とすればよい。また、有機金属気相成長法によりＡｌ0.05Ｇａ0.95Ｎをエピタキシャル成長させて第２半導体層１０２とすればよい。 The first semiconductor layer 101 and the second semiconductor layer 102 may be made of a III-V group compound semiconductor. For example, the first semiconductor layer 101 may be composed of n-type GaN, and the second semiconductor layer 102 may be composed of AlGaN. In this case, n-type GaN doped with silicon is epitaxially grown on a substrate 111 made of sapphire having a (0001) plane orientation of the main surface by, for example, a known metal organic chemical vapor deposition method. One semiconductor layer 101 may be used. Alternatively, Al 0.05 Ga 0.95 N may be epitaxially grown by metal organic vapor phase epitaxy to form the second semiconductor layer 102.
上述した実施の形態における半導体光触媒によれば、第２半導体層１０２を第１半導体層１０１より小さな格子定数としていることによるピエゾ電界により、光を受けたことにより発生した正孔は、第２半導体層１０２の主表面側に移動し、ショットキー接合する第１金属層１０３に到達して捕集される。また、光を受けたことによりで発生した電子は、第１半導体層１０１の側に移動し、第１半導体層１０１に電気的に接続する第２金属層１０４に到達して捕集される。 According to the semiconductor photocatalyst in the above-described embodiment, holes generated by receiving light by a piezo electric field due to the second semiconductor layer 102 having a lattice constant smaller than that of the first semiconductor layer 101 are generated by the second semiconductor. It moves to the main surface side of the layer 102 and reaches the first metal layer 103 where Schottky junction is reached and is collected. In addition, electrons generated by receiving light move to the first semiconductor layer 101 side, reach the second metal layer 104 electrically connected to the first semiconductor layer 101, and are collected.
上述した状態において、図３に示すように、実施の形態における半導体光触媒１００が、光触媒槽２０１に収容された電解質の水溶液２０２中に配置（浸漬）されていれば、正孔が捕集された第１金属層１０３において、酸化反応が発生し、電子が捕集されている第２金属層１０４で還元反応が発生する。この結果、水が電気分解できる（水の酸化反応による酸素生成、水の酸化により生じたプロトンの還元による水素生成）。 In the state described above, as shown in FIG. 3, if the semiconductor photocatalyst 100 according to the embodiment is disposed (immersed) in the aqueous solution 202 of the electrolyte accommodated in the photocatalyst tank 201, holes are collected. An oxidation reaction occurs in the first metal layer 103, and a reduction reaction occurs in the second metal layer 104 where the electrons are collected. As a result, water can be electrolyzed (oxygen generation by water oxidation reaction, hydrogen generation by reduction of protons generated by water oxidation).
第１金属層１０３、第２半導体層１０２、第２金属層１０４、および第２半導体層１０２と第１金属層１０３との接触領域は、露出する部分を備えているので、これらは水溶液２０２に接触することになり、上述した反応が起こる状態とされている。なお、光は、光が透過する光触媒槽２０１の外部に配置した光源２０４から照射すればよい。 Since the first metal layer 103, the second semiconductor layer 102, the second metal layer 104, and the contact region between the second semiconductor layer 102 and the first metal layer 103 include exposed portions, these are in the aqueous solution 202. It is in a state where the above-described reaction occurs. Note that light may be emitted from a light source 204 disposed outside the photocatalyst tank 201 through which light passes.
また、第１金属層１０３の金属種や、光触媒槽２０１内部の雰囲気を変えることで、二酸化炭素の還元反応による一酸化炭素、ギ散、メタノール、メタンの炭化水素類の生成、または、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 addition, by changing the metal species of the first metal layer 103 and the atmosphere inside the photocatalyst tank 201, the generation of hydrocarbons such as carbon monoxide, mist, methanol, and methane by the reduction reaction of carbon dioxide, or nitrogen It is also possible to produce ammonia by a reduction reaction.
実施の形態によれば、第１半導体層１０１と、第１半導体層１０１より小さな格子定数の第２半導体層１０２とを積層することで、光反応により生成した電子および正孔を分離させ、ショットキー接合する第１金属層１０３で分離した正孔を捕集するようにした。電子は、第１半導体層１０１に電気的に接続する第２金属層１０４で捕集する。この結果、上述した触媒反応の効率をより向上させることができる。また、実施の形態によれば、１つの溶液、１つの半導体光触媒で構成できるので、複雑な構成とする必要がない。 According to the embodiment, by stacking the first semiconductor layer 101 and the second semiconductor layer 102 having a lattice constant smaller than that of the first semiconductor layer 101, electrons and holes generated by the photoreaction are separated, and shot Holes separated by the first metal layer 103 to be key-joined are collected. The electrons are collected by the second metal layer 104 that is electrically connected to the first semiconductor layer 101. As a result, the above-described catalytic reaction efficiency can be further improved. In addition, according to the embodiment, since it can be configured with one solution and one semiconductor photocatalyst, it is not necessary to have a complicated configuration.
また、第１半導体層１０１をｎ型とすることで、上述した電子および正孔の移動をより効率的に起こさせることができるようになる。また、主表面を（０００１）面とした窒化物半導体から各半導体層を構成することで、各半導体層において発生する自然分極により電界が発生した状態となり、上述した電子および正孔の移動を、更に効率的に起こさせることができる。 In addition, by making the first semiconductor layer 101 n-type, the above-described movement of electrons and holes can be caused more efficiently. In addition, by configuring each semiconductor layer from a nitride semiconductor having a (0001) plane as the main surface, an electric field is generated due to natural polarization generated in each semiconductor layer, and the above-described movement of electrons and holes is performed. Furthermore, it can be made to occur efficiently.
例えば、ｎ型のＧａＮなどの窒化物半導体から構成した第１半導体層１０１の主表面をＶ族極性（Ｎ極性）とし、ＡｌＧａＮなどの窒化物半導体から構成した第２半導体層１０２の主表面はＩＩＩ族極性（Ｇａ極性）とすることで、各半導体層において発生する自然分極による電界で、第１半導体層１０１と第２半導体層１０２との界面側に発生した電子を移動させ、第２半導体層１０２においては、主表面側に発生した正孔を移動させることができる。 For example, the main surface of the first semiconductor layer 101 composed of a nitride semiconductor such as n-type GaN has a group V polarity (N polarity), and the main surface of the second semiconductor layer 102 composed of a nitride semiconductor such as AlGaN is By adopting the group III polarity (Ga polarity), electrons generated on the interface side between the first semiconductor layer 101 and the second semiconductor layer 102 are moved by an electric field due to natural polarization generated in each semiconductor layer, and the second semiconductor is moved. In the layer 102, holes generated on the main surface side can be moved.
次に、実施例を用いてより詳細に説明する。 Next, it demonstrates in detail using an Example.
［実施例１］
はじめに、実施例１における半導体光触媒の作製について説明する。まず、主表面を（０００１）面としたサファイア基板を用意する。次に、サファイア基板の上に、よく知られた有機金属気相成長法によりシリコンをドープしたＧａＮをエピタキシャル成長させ、引き続いて、Ａｌ0.05Ｇａ0.95Ｎをエピタキシャル成長させる。例えば、アンモニアを窒素原料とし、トリエチルガリウムをＧａ原料とし、トリメチルアルミニウムをＡｌ原料とすればよい。また、ｎ型とするためのシリコンは、ＳｉＣｌ4を原料とすればよい。
[Example 1]
First, production of a semiconductor photocatalyst in Example 1 will be described. First, a sapphire substrate having a main surface of (0001) plane is prepared. Next, GaN doped with silicon is epitaxially grown on the sapphire substrate by a well-known metal organic chemical vapor deposition method, and subsequently Al 0.05 Ga 0.95 N is epitaxially grown. For example, ammonia may be used as a nitrogen material, triethylgallium as a Ga material, and trimethylaluminum as an Al material. Further, silicon for n-type may be made from SiCl 4 as a raw material.
以上のことにより、サファイア基板の上に、厚さ２μｍのｎ−ＧａＮからなる第１半導体層を形成し、第１半導体層の上に、厚さ１００ｎｍのＡｌ0.05Ｇａ0.95Ｎからなる第２半導体層を形成した。第１半導体層は、キャリア密度を３×１０18ｃｍ-3とした。第２半導体層の層厚１００ｎｍは、第２半導体層における主表面方向からの、第２半導体層で吸収される波長の光の侵入長さと同程度となる。なお、第２半導体層で吸収されない波長の光が第１半導体層で効率よく吸収されるように、第１半導体層の層厚を２μｍとしている。 As described above, the first semiconductor layer made of n-GaN having a thickness of 2 μm is formed on the sapphire substrate, and the second semiconductor made of Al 0.05 Ga 0.95 N having a thickness of 100 nm is formed on the first semiconductor layer. A layer was formed. The first semiconductor layer had a carrier density of 3 × 10 18 cm −3 . The layer thickness of 100 nm of the second semiconductor layer is approximately the same as the penetration length of light having a wavelength absorbed by the second semiconductor layer from the main surface direction in the second semiconductor layer. The thickness of the first semiconductor layer is set to 2 μm so that light having a wavelength that is not absorbed by the second semiconductor layer is efficiently absorbed by the first semiconductor layer.
なお、ｎ−ＧａＮからなる第１半導体層は、基板平面方向の格子定数が０．３１８９ｎｍである。また、Ａｌ0.05Ｇａ0.95Ｎからなる第２半導体層は、基板平面方向の格子定数が０．３１８５ｎｍである。この場合、第２半導体層は、第１半導体層より格子定数が小さいものとなる。 Note that the first semiconductor layer made of n-GaN has a lattice constant of 0.3189 nm in the substrate plane direction. The second semiconductor layer made of Al 0.05 Ga 0.95 N has a lattice constant of 0.3185 nm in the substrate plane direction. In this case, the second semiconductor layer has a smaller lattice constant than the first semiconductor layer.
次に、第２半導体層の主表面上に、第２金属層を形成した。例えば、公知のフォトリソグラフィ技術により島部に開口部を有するレジストパターンを形成し、このレジストパターンの上から真空蒸着法により以下に示す各金属を堆積する。例えば、まず、厚さ２５ｎｍのチタン層を堆積し、続いて厚さ５０ｎｍのアルミニウム層を堆積し、続いて厚さ２５ｎｍのチタン層を堆積し、続いて厚さ１００ｎｍの白金層を堆積した。最表面は白金層となる。なお、白金の代わりに、金、銀、銅、ニッケル、タングステン、タンタル、パラジウム、ルテニウムを用いてもよい。 Next, a second metal layer was formed on the main surface of the second semiconductor layer. For example, a resist pattern having an opening on the island is formed by a known photolithography technique, and the following metals are deposited on the resist pattern by vacuum deposition. For example, a 25 nm thick titanium layer was first deposited, followed by a 50 nm thick aluminum layer, followed by a 25 nm thick titanium layer, followed by a 100 nm thick platinum layer. The outermost surface is a platinum layer. Note that gold, silver, copper, nickel, tungsten, tantalum, palladium, or ruthenium may be used instead of platinum.
この後、レジストパターンを除去（リフトオフ）することで、開口部に堆積された白金が残り、島状の第２金属層となる。各々の第２金属層は、直径１０μｍの平面視円形とし、また、基板平面方向における各々の第２金属層の中心間の距離は、２２０μｍとした。また、複数の第２金属層は、正方配列させた。 Thereafter, the resist pattern is removed (lifted off), so that the platinum deposited in the opening remains and becomes an island-shaped second metal layer. Each second metal layer was circular in plan view with a diameter of 10 μm, and the distance between the centers of the respective second metal layers in the substrate plane direction was 220 μm. The plurality of second metal layers were arranged in a square.
以上のようにして、第２半導体層の主表面上に島状とした複数の第２金属層を形成した後、窒素雰囲気において、８００℃・３０秒の条件で加熱処理を実施し、第２金属層と第２半導体層（第１半導体層）との間にオーミック接合を形成させた。加熱処理により、第２金属層を構成する金属が半導体層中に拡散して合金領域を形成する。この合金領域が第１半導体層に到達することで、第２金属層と第１半導体層とが電気的に接続した状態とすることができる。なお、この熱処理は、各半導体層の組成が変化しない条件であれば、大気，不活性ガス，酸素ガス，水素ガス，真空減圧下などの雰囲気で実施してもよい。 As described above, after forming a plurality of second metal layer and islands on the main surface of the second semiconductor layer, in a nitrogen atmosphere, it was carried out heat treatment under conditions of 800 ° C. · 30 sec, a second An ohmic junction was formed between the metal layer and the second semiconductor layer (first semiconductor layer). By the heat treatment, the metal constituting the second metal layer diffuses into the semiconductor layer to form an alloy region. When the alloy region reaches the first semiconductor layer, the second metal layer and the first semiconductor layer can be electrically connected. Note that this heat treatment may be performed in an atmosphere such as air, inert gas, oxygen gas, hydrogen gas, or vacuum under reduced pressure as long as the composition of each semiconductor layer does not change.
次に、第２半導体層の主表面上に、白金から構成した複数の島状の第１金属層を形成した。例えば、公知のフォトリソグラフィ技術により島部に開口部を有するレジストパターンを形成し、このレジストパターンの上から真空蒸着法により白金を堆積する。厚さ１００ｎｍ程度に形成する。この後、レジストパターンをリフトオフすることで、開口部に堆積された白金が残り、複数の島状の第１金属層となる。第１金属層は、第２半導体層にショットキー接合した状態となる。第１金属層は、直径１０μｍの平面視円形とした。また、基板平面方向における各第１金属層の中心間の距離は、２２０μｍとした。また、複数の島状の第１金属層は、複数の島状の第２金属層と、各々１つおきに配列されている状態とした。 Next, a plurality of island-shaped first metal layers made of platinum were formed on the main surface of the second semiconductor layer. For example, a resist pattern having an opening on the island is formed by a known photolithography technique, and platinum is deposited on the resist pattern by vacuum evaporation. It is formed to a thickness of about 100 nm. Thereafter, the resist pattern is lifted off, whereby platinum deposited in the opening remains and becomes a plurality of island-shaped first metal layers. The first metal layer is in a Schottky junction with the second semiconductor layer. The first metal layer was circular in plan view with a diameter of 10 μm. The distance between the centers of the first metal layers in the substrate plane direction was 220 μm. In addition, the plurality of island-shaped first metal layers are in a state of being arranged with every other island-shaped second metal layer.
次に、上述したことにより作製した積層構造を切断することで半導体光触媒チップ（試料１）を形成した。チップは、光触媒機能が発現される実効的な面積が１ｃｍ2となるサイズに形成した。 Next, the semiconductor photocatalyst chip (sample 1) was formed by cutting the laminated structure produced as described above. The chip was formed in such a size that the effective area where the photocatalytic function is expressed is 1 cm 2 .
［実施例２］
次に、実施例２における半導体光触媒の作製について説明する。実施例２では、第１半導体層をインジウムの組成比を５％としたｎ型の窒化インジウムガリウム（Ｉｎ0.05Ｇａ0.95Ｎ）から構成し、第２半導体層をＧａＮから構成した。Ｉｎ0.05Ｇａ0.95Ｎの成長では、トリエチルインジウムをＩｎ原料とすればよい。第１半導体層は厚さ２μｍとし、第２半導体層は厚さ１００ｎｍとした。なお、ｎ−Ｉｎ0.05Ｇａ0.95Ｎからなる第１半導体層は、基板平面方向の格子定数が０．３２０７ｎｍである。この場合、第２半導体層は、第１半導体層より格子定数が小さいものとなる。
[Example 2]
Next, production of a semiconductor photocatalyst in Example 2 will be described. In Example 2, the first semiconductor layer was made of n-type indium gallium nitride (In 0.05 Ga 0.95 N) with an indium composition ratio of 5%, and the second semiconductor layer was made of GaN. In the growth of In 0.05 Ga 0.95 N, triethylindium may be used as the In raw material. The first semiconductor layer was 2 μm thick, and the second semiconductor layer was 100 nm thick. Note that the first semiconductor layer made of n-In 0.05 Ga 0.95 N has a lattice constant of 0.3207 nm in the substrate plane direction. In this case, the second semiconductor layer has a smaller lattice constant than the first semiconductor layer.
なお、各半導体層の形成（成長）および各金属層の形成は、実施例１と同様にした。また、上述したことにより作製した積層構造を実施例１と同様にしてチップとすることで、試料２とした。 The formation (growth) of each semiconductor layer and the formation of each metal layer were the same as in Example 1. Further, Sample 2 was obtained by using the laminated structure produced as described above as a chip in the same manner as in Example 1.
［実施例３］
次に、実施例３における半導体光触媒の作製について説明する。実施例３では、第１半導体層をｎ型のＩｎ0.05Ｇａ0.95Ｎから構成し、第２半導体層をアルミニウムの組成比を５％とした窒化アルミニウムガリウム（Ａｌ0.05Ｇａ0.95Ｎ）から構成した。第１半導体層は厚さ２μｍとし、第２半導体層は厚さ１００ｎｍとした。なお、Ａｌ0.05Ｇａ0.95Ｎからなる第２半導体層は、基板平面方向の格子定数が０．３１８５ｎｍである。この場合、第２半導体層は、第１半導体層より格子定数が小さいものとなる。
[Example 3]
Next, preparation of the semiconductor photocatalyst in Example 3 will be described. In Example 3, the first semiconductor layer was composed of n-type In 0.05 Ga 0.95 N, and the second semiconductor layer was composed of aluminum gallium nitride (Al 0.05 Ga 0.95 N) with an aluminum composition ratio of 5%. The first semiconductor layer was 2 μm thick, and the second semiconductor layer was 100 nm thick. Note that the second semiconductor layer made of Al 0.05 Ga 0.95 N has a lattice constant of 0.3185 nm in the substrate plane direction. In this case, the second semiconductor layer has a smaller lattice constant than the first semiconductor layer.
なお、各半導体層の形成（成長）および各金属層の形成は、実施例１，２と同様にした。また、上述したことにより作製した積層構造を実施例１と同様にしてチップとすることで、試料３とした。 The formation (growth) of each semiconductor layer and the formation of each metal layer were the same as in Examples 1 and 2. Further, Sample 3 was obtained by using the laminated structure manufactured as described above as a chip in the same manner as in Example 1.
［実施例４］
次に、実施例４における半導体光触媒の作製について説明する。実施例４では、第１半導体層をｎ型のＩｎ0.05Ｇａ0.95Ｎから構成し、第２半導体層をインジウムの組成比を１％としたｎ型のＩｎ0.01Ｇａ0.99Ｎから構成した。第１半導体層は厚さ２μｍとし、第２半導体層は厚さ１００ｎｍとした。なお、Ｉｎ0.01Ｇａ0.99Ｎからなる第２半導体層は、基板平面方向の格子定数が０．３１９３ｎｍである。この場合、第２半導体層は、第１半導体層より格子定数が小さいものとなる。
[Example 4]
Next, production of a semiconductor photocatalyst in Example 4 will be described. In Example 4, the first semiconductor layer was composed of n-type In 0.05 Ga 0.95 N, and the second semiconductor layer was composed of n-type In 0.01 Ga 0.99 N with an indium composition ratio of 1%. The first semiconductor layer was 2 μm thick, and the second semiconductor layer was 100 nm thick. Note that the second semiconductor layer made of In 0.01 Ga 0.99 N has a lattice constant of 0.3193 nm in the substrate plane direction. In this case, the second semiconductor layer has a smaller lattice constant than the first semiconductor layer.
なお、各半導体層の形成（成長）および各金属層の形成は、実施例１，２と同様にした。また、上述したことにより作製した積層構造を実施例１と同様にしてチップとすることで、試料４とした。 The formation (growth) of each semiconductor layer and the formation of each metal layer were the same as in Examples 1 and 2. Further, a sample 4 was obtained by using the laminated structure manufactured as described above as a chip in the same manner as in Example 1.
［実施例５］
次に、実施例５における半導体光触媒の作製について説明する。実施例５では、第１半導体層を、アルミニウムの組成比を５％としたｎ型のＡｌ0.05Ｇａ0.95Ｎから構成し、第２半導体層をアルミニウムの組成比を１０％としたｎ型のＡｌ0.1Ｇａ0.9Ｎから構成した。第１半導体層は厚さ２μｍとし、第２半導体層は厚さ１００ｎｍとした。なお、ｎ型のＡｌ0.05Ｇａ0.95Ｎからなる第１半導体層は、基板平面方向の格子定数が０．３１８５ｎｍである。また、Ａｌ0.1Ｇａ0.9Ｎからなる第２半導体層は、基板平面方向の格子定数が０．３１８３ｎｍである。この場合においても、第２半導体層は、第１半導体層より格子定数が小さいものとなる。
[Example 5]
Next, preparation of the semiconductor photocatalyst in Example 5 will be described. In Example 5, the first semiconductor layer is made of n-type Al 0.05 Ga 0.95 N with an aluminum composition ratio of 5%, and the second semiconductor layer is an n-type Al with an aluminum composition ratio of 10%. It was composed of 0.1 Ga 0.9 N. The first semiconductor layer was 2 μm thick, and the second semiconductor layer was 100 nm thick. Note that the first semiconductor layer made of n-type Al 0.05 Ga 0.95 N has a lattice constant of 0.3185 nm in the substrate plane direction. The second semiconductor layer made of Al 0.1 Ga 0.9 N has a lattice constant of 0.3183 nm in the substrate plane direction. Also in this case, the second semiconductor layer has a smaller lattice constant than the first semiconductor layer.
なお、各半導体層の形成（成長）および各金属層の形成は、実施例１と同様にした。また、上述したことにより作製した積層構造を実施例１と同様にしてチップとすることで、試料５とした。 The formation (growth) of each semiconductor layer and the formation of each metal layer were the same as in Example 1. Further, a sample 5 was obtained by using the laminated structure produced as described above as a chip in the same manner as in Example 1.
［比較例１］
次に、比較例１における半導体光触媒の作製について説明する。比較例１では、実施例１における第２半導体層を形成しない構成とした。比較例１では、第１金属層および第２金属層を、第１半導体層の主表面上に形成した。各々島状とし、実施例１と同様に正方配列させた複数の第１金属層および複数の第２金属層を形成した。
[Comparative Example 1]
Next, preparation of the semiconductor photocatalyst in Comparative Example 1 will be described. In Comparative Example 1, the second semiconductor layer in Example 1 was not formed. In Comparative Example 1, the first metal layer and the second metal layer were formed on the main surface of the first semiconductor layer. A plurality of first metal layers and a plurality of second metal layers each having an island shape and arranged in a square manner as in Example 1 were formed.
なお、半導体層の形成（成長）および各金属層の形成は、実施例１と同様にした。また、上述したことにより作製した積層構造を実施例１と同様にしてチップとすることで、比較試料１とした。 The formation (growth) of the semiconductor layer and the formation of each metal layer were the same as in Example 1. Further, a comparative sample 1 was obtained by using the laminated structure produced as described above as a chip in the same manner as in Example 1.
［比較例２］
次に、比較例２における半導体光触媒の作製について説明する。比較例２では、実施例１における第２半導体層をアンドープのＧａＮから構成した。この構成は、第１半導体層と第２半導体層とが同じ格子定数となる。比較例２でも、実施例１と同様に、第１金属層および第２金属層を、第２半導体層の主表面上に形成した。
[Comparative Example 2]
Next, preparation of the semiconductor photocatalyst in Comparative Example 2 will be described. In Comparative Example 2, the second semiconductor layer in Example 1 was composed of undoped GaN. In this configuration, the first semiconductor layer and the second semiconductor layer have the same lattice constant. In Comparative Example 2, similarly to Example 1, the first metal layer and the second metal layer were formed on the main surface of the second semiconductor layer.
なお、半導体層の形成（成長）および各金属層の形成は、実施例１と同様にした。また、上述したことにより作製した積層構造を実施例１と同様にしてチップとすることで、比較試料２とした。 The formation (growth) of the semiconductor layer and the formation of each metal layer were the same as in Example 1. In addition, a comparative sample 2 was obtained by using the laminated structure manufactured as described above as a chip in the same manner as in Example 1.
［酸化還元反応試験］
次に、試料１，試料２，試料３，試料４，試料５，比較試料１，比較試料２を用いた酸化還元反応試験の結果について説明する。この試験では、図３を用いて説明した光触媒槽２０１をセルとして用い、水溶液２０２として濃度１ｍｏｌ／リットルの水酸化カリウム水溶液（１２５ｍリットル）を用いた。半導体光触媒１００として試料１，試料２，試料３，試料４，試料５，比較試料１，比較試料２を用いた。
[Redox reaction test]
Next, the results of the oxidation-reduction reaction test using Sample 1, Sample 2, Sample 3, Sample 4, Sample 5, Comparative Sample 1, and Comparative Sample 2 will be described. In this test, the photocatalyst tank 201 described with reference to FIG. 3 was used as a cell, and a 1 mol / liter potassium hydroxide aqueous solution (125 ml) was used as the aqueous solution 202. As the semiconductor photocatalyst 100, Sample 1, Sample 2, Sample 3, Sample 4, Sample 5, Comparative Sample 1, and Comparative Sample 2 were used.
試験においては、水溶液２０２に窒素ガスを２００ｍリットル／ｍｉｎで３０分間バブリングして脱泡・置換した後、光触媒槽２０１を、シリコーンとフッ素樹脂との２層構造のセプタムで密閉した。光触媒槽２０１内の圧力は大気圧とした。また、光源２０４として、３００Ｗの高圧キセノンランプ（４００ｎｍ以上をカット、照度５ｍＷ／ｃｍ2）を用いた。光源２０４からの光は、光触媒槽２０１の外側から、半導体光触媒１００に均一に照射した。光源２０４からの光が、第１金属層、第２金属層の形成面に照射される状態とした。また、水溶液２０２の攪拌は、光触媒槽２０１の底部中心に配置した攪拌子２０５を、図示しないスターラを用いて２５０ｒｐｍの回転速度で回転させて実施した。 In the test, nitrogen gas was bubbled through the aqueous solution 202 at 200 ml / min for 30 minutes to defoam and replace, and then the photocatalyst tank 201 was sealed with a two-layered septum of silicone and fluororesin. The pressure in the photocatalyst tank 201 was atmospheric pressure. As the light source 204, a 300 W high-pressure xenon lamp (400 nm or more cut, illuminance 5 mW / cm 2 ) was used. The light from the light source 204 was uniformly applied to the semiconductor photocatalyst 100 from the outside of the photocatalyst tank 201. The light from the light source 204 was irradiated on the formation surface of the first metal layer and the second metal layer. The aqueous solution 202 was stirred by rotating the stirring bar 205 disposed at the center of the bottom of the photocatalyst tank 201 at a rotational speed of 250 rpm using a stirrer (not shown).
任意の時間が経過した時点で、光触媒槽２０１内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。この分析では、水素と酸素が生成していることが確認された。 When an arbitrary time passed, the gas in the photocatalyst tank 201 was collected from the septum portion with a syringe, and the reaction product was analyzed with a gas chromatograph mass spectrometer. This analysis confirmed the generation of hydrogen and oxygen.
また、試料１，試料２，試料３，試料４，試料５，比較試料１，比較試料２における、光照射時間に対する水素ガスの生成量を以下の表１に示す。水素ガスの生成量は、チップの面積で規格化して示した。 Table 1 below shows the amount of hydrogen gas generated with respect to the light irradiation time in Sample 1, Sample 2, Sample 3, Sample 4, Sample 5, Comparative Sample 1, and Comparative Sample 2. The amount of hydrogen gas produced is shown normalized by the chip area.
表１に示すように、いずれの試料も、光照射時間の経過とともにセル内の水素量が増加した。一方、実施例１〜５における試料１〜５は、比較試料１，２に比較して、水素生成量が多いことが確認された。第２半導体層を用いていない比較試料１、ならびに、第１半導体層と第２半導体層との格子定数が等しい比較試料２に比較し、試料１〜５は、約５〜６倍の生成量が示された。これらの結果は、半導体光触媒の半導体表面から光の侵入領域において生成した電子と正孔の分離が、格子定数の歪みに起因して生じるピエゾ電界によって促進され、近傍の第１金属層および第２金属層にて、還元反応および酸化反応が生じているためと考えられる。 As shown in Table 1, in all the samples, the amount of hydrogen in the cell increased with the passage of light irradiation time. On the other hand, it was confirmed that Samples 1 to 5 in Examples 1 to 5 had a larger amount of hydrogen generation than Comparative Samples 1 and 2. Compared to the comparative sample 1 that does not use the second semiconductor layer and the comparative sample 2 in which the lattice constants of the first semiconductor layer and the second semiconductor layer are equal, samples 1 to 5 are about 5 to 6 times as large It has been shown. These results indicate that the separation of electrons and holes generated in the light intrusion region from the semiconductor surface of the semiconductor photocatalyst is promoted by the piezoelectric field generated due to distortion of the lattice constant, and the first metal layer and the second This is probably because a reduction reaction and an oxidation reaction occur in the metal layer.
以上に説明したように、本発明によれば、化合物半導体からなる第１半導体層の主表面上に接触して化合物半導体からなる第２半導体層を形成し、第２半導体層は第１半導体層より小さい格子定数としたので、簡素な構成で光触媒反応の効率をより向上させることができるようになる。 As described above, according to the present invention, the second semiconductor layer made of the compound semiconductor is formed in contact with the main surface of the first semiconductor layer made of the compound semiconductor, and the second semiconductor layer is the first semiconductor layer. Since the lattice constant is smaller, the efficiency of the photocatalytic reaction can be further improved with a simple configuration.
なお、本発明は以上に説明した実施の形態に限定されるものではなく、本発明の技術的思想内で、当分野において通常の知識を有する者により、多くの変形および組み合わせが実施可能であることは明白である。 The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.
１０１…第１半導体層、１０２…第２半導体層、１０３…第１金属層、１０４…第２金属層。 DESCRIPTION OF SYMBOLS 101 ... 1st semiconductor layer, 102 ... 2nd semiconductor layer, 103 ... 1st metal layer, 104 ... 2nd metal layer.
Claims (4)
前記第１半導体層の主表面上に接触して形成され、基板平面方向の格子定数が前記第１半導体層より小さいＧａを含む窒化物半導体からなり、主表面を（０００１）面とした第２半導体層と、
前記第２半導体層の主表面上にショットキー接合して形成された第１金属層と、
前記第２半導体層の主表面上に前記第１金属層とは分離してオーミック接合して形成され、前記第１半導体層と電気的に接続された第２金属層と
を備えることを特徴とする半導体光触媒。 Is formed on the main surface of the substrate, a first semiconductor layer Do Ri, a main surface and the (0001) plane of a nitride semiconductor containing Ga,
Wherein formed in contact on the main surface of the first semiconductor layer, the lattice constant of the substrate planar direction is set to the first a nitride semiconductor containing Ga have smaller than the semiconductor layer, the main surface (0001) plane Two semiconductor layers;
A first metal layer formed on the main surface of the second semiconductor layer by a Schottky junction;
And a second metal layer formed on the main surface of the second semiconductor layer so as to be in ohmic contact with the first metal layer and electrically connected to the first semiconductor layer. A semiconductor photocatalyst.
前記第１半導体層は、ｎ型とされていることを特徴とする半導体光触媒。 The semiconductor photocatalyst according to claim 1,
The semiconductor photocatalyst, wherein the first semiconductor layer is an n-type.
前記第２半導体層、前記第１金属層、前記第２金属層、および前記第２半導体層と前記第１金属層との接触領域は、露出する部分を備えることを特徴とする半導体光触媒。 The semiconductor photocatalyst according to claim 1 or 2,
The semiconductor photocatalyst comprising the exposed portion of the second semiconductor layer, the first metal layer, the second metal layer, and a contact region between the second semiconductor layer and the first metal layer.
島状とされた複数の前記第１金属層および島状とされた複数の前記第２金属層が、前記第２半導体層の主表面上に形成されていることを特徴とする半導体光触媒。 The semiconductor photocatalyst according to claim 3,
A semiconductor photocatalyst comprising: a plurality of island-shaped first metal layers and a plurality of island-shaped second metal layers formed on a main surface of the second semiconductor layer.
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