JP5803288B2 - Semiconductor material and photocatalyst, photoelectrode and solar cell using the same - Google Patents
Semiconductor material and photocatalyst, photoelectrode and solar cell using the same Download PDFInfo
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- 239000004065 semiconductor Substances 0.000 title claims description 46
- 239000000463 material Substances 0.000 title claims description 31
- 239000011941 photocatalyst Substances 0.000 title claims description 11
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 127
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 125
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 99
- 239000010949 copper Substances 0.000 claims description 77
- 229910052757 nitrogen Inorganic materials 0.000 claims description 56
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 37
- 229910052802 copper Inorganic materials 0.000 claims description 37
- JBQYATWDVHIOAR-UHFFFAOYSA-N tellanylidenegermanium Chemical compound [Te]=[Ge] JBQYATWDVHIOAR-UHFFFAOYSA-N 0.000 claims description 34
- 229910052742 iron Inorganic materials 0.000 claims description 16
- 229910052751 metal Inorganic materials 0.000 claims description 16
- 239000002184 metal Substances 0.000 claims description 15
- 239000013078 crystal Substances 0.000 claims description 10
- LIKBJVNGSGBSGK-UHFFFAOYSA-N iron(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Fe+3].[Fe+3] LIKBJVNGSGBSGK-UHFFFAOYSA-N 0.000 claims description 10
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 9
- 229910052595 hematite Inorganic materials 0.000 claims description 8
- 239000011019 hematite Substances 0.000 claims description 8
- 239000011777 magnesium Substances 0.000 claims description 6
- 238000006243 chemical reaction Methods 0.000 claims description 5
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 3
- 229910052749 magnesium Inorganic materials 0.000 claims description 3
- 229910044991 metal oxide Inorganic materials 0.000 claims description 3
- 150000004706 metal oxides Chemical class 0.000 claims description 3
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 235000013980 iron oxide Nutrition 0.000 description 62
- 230000000052 comparative effect Effects 0.000 description 32
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 28
- 229910021607 Silver chloride Inorganic materials 0.000 description 21
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 description 20
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 18
- 239000010408 film Substances 0.000 description 15
- 239000007789 gas Substances 0.000 description 15
- 238000005259 measurement Methods 0.000 description 15
- 229910052786 argon Inorganic materials 0.000 description 14
- 238000010438 heat treatment Methods 0.000 description 13
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 12
- 239000001301 oxygen Substances 0.000 description 12
- 229910052760 oxygen Inorganic materials 0.000 description 12
- 239000011701 zinc Substances 0.000 description 11
- 239000004332 silver Substances 0.000 description 10
- 229910052709 silver Inorganic materials 0.000 description 9
- 238000004544 sputter deposition Methods 0.000 description 9
- 239000000758 substrate Substances 0.000 description 8
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 7
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 6
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 5
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 5
- 239000001257 hydrogen Substances 0.000 description 5
- 229910052739 hydrogen Inorganic materials 0.000 description 5
- 229910052725 zinc Inorganic materials 0.000 description 5
- 239000007864 aqueous solution Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- OTYBMLCTZGSZBG-UHFFFAOYSA-L potassium sulfate Chemical compound [K+].[K+].[O-]S([O-])(=O)=O OTYBMLCTZGSZBG-UHFFFAOYSA-L 0.000 description 4
- 229910052939 potassium sulfate Inorganic materials 0.000 description 4
- 235000011151 potassium sulphates Nutrition 0.000 description 4
- 230000004044 response Effects 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- ROFVEXUMMXZLPA-UHFFFAOYSA-N Bipyridyl Chemical compound N1=CC=CC=C1C1=CC=CC=N1 ROFVEXUMMXZLPA-UHFFFAOYSA-N 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 230000009471 action Effects 0.000 description 3
- 239000001569 carbon dioxide Substances 0.000 description 3
- 229910002092 carbon dioxide Inorganic materials 0.000 description 3
- 230000031700 light absorption Effects 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 230000001699 photocatalysis Effects 0.000 description 3
- 229910052724 xenon Inorganic materials 0.000 description 3
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 3
- 239000011787 zinc oxide Substances 0.000 description 3
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 description 2
- 229910017486 Cu 50W Inorganic materials 0.000 description 2
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- JZQOJFLIJNRDHK-CMDGGOBGSA-N alpha-irone Chemical compound CC1CC=C(C)C(\C=C\C(C)=O)C1(C)C JZQOJFLIJNRDHK-CMDGGOBGSA-N 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000001747 exhibiting effect Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 229910000859 α-Fe Inorganic materials 0.000 description 2
- 239000005751 Copper oxide Substances 0.000 description 1
- 229910006404 SnO 2 Inorganic materials 0.000 description 1
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 1
- 238000000862 absorption spectrum Methods 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 238000004577 artificial photosynthesis Methods 0.000 description 1
- 238000005513 bias potential Methods 0.000 description 1
- 230000005587 bubbling Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 230000000295 complement effect Effects 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 229910000431 copper oxide Inorganic materials 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000004332 deodorization Methods 0.000 description 1
- 238000002848 electrochemical method Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- VBMVTYDPPZVILR-UHFFFAOYSA-N iron(2+);oxygen(2-) Chemical class [O-2].[Fe+2] VBMVTYDPPZVILR-UHFFFAOYSA-N 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 230000001678 irradiating effect Effects 0.000 description 1
- 238000001755 magnetron sputter deposition Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 230000001443 photoexcitation Effects 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 230000004043 responsiveness Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 230000001954 sterilising effect Effects 0.000 description 1
- 238000004659 sterilization and disinfection Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 1
- 229910001887 tin oxide Inorganic materials 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- AKJVMGQSGCSQBU-UHFFFAOYSA-N zinc azanidylidenezinc Chemical compound [Zn++].[N-]=[Zn].[N-]=[Zn] AKJVMGQSGCSQBU-UHFFFAOYSA-N 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
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- Physical Vapour Deposition (AREA)
- Photovoltaic Devices (AREA)
- Compounds Of Iron (AREA)
Description
本発明は、光を照射することにより起電力又は光触媒作用を発生させることができる半導体材料並びにそれを用いた光触媒体、光電極及び太陽電池に関する。 The present invention relates to a semiconductor material capable of generating an electromotive force or a photocatalytic action by irradiating light, and a photocatalyst body, a photoelectrode, and a solar cell using the semiconductor material.
酸化チタン、酸化スズ、酸化亜鉛等の金属酸化物は紫外光を照射すると光励起により電子や正孔を生じ、強い還元力や酸化力を呈する光触媒体として作用することが知られている。このような光触媒体は、その作用を利用して有害物質の分解・浄化、脱臭、殺菌等に広く用いられている。 It is known that metal oxides such as titanium oxide, tin oxide, and zinc oxide generate electrons and holes by photoexcitation when irradiated with ultraviolet light and act as a photocatalyst exhibiting strong reducing power and oxidizing power. Such a photocatalyst is widely used for decomposition / purification, deodorization, sterilization and the like of harmful substances by utilizing its action.
また、酸化鉄(Fe2O3)に亜鉛(Zn)や銅(Cu)をドーピングすることによって、Pt電極に対して−0.25Vだけ負な電位を示し、波長600nm以下の可視光に応答性を有するp型半導体の性質を示すことが知られている(非特許文献1参照)。 Moreover, by doping zinc oxide (Fe 2 O 3 ) with zinc (Zn) or copper (Cu), it shows a negative potential of −0.25 V with respect to the Pt electrode, and responds to visible light with a wavelength of 600 nm or less. It is known to show the properties of p-type semiconductors having a property (see Non-Patent Document 1).
ところで、従来技術では、酸化鉄(Fe2O3)をp型半導体とするために亜鉛(Zn)や銅(Cu)等の金属元素をドーピングしているが、p型としてさらに優れた半導体特性を発現させることが望まれている。また、安価な材料の組み合わせによって酸化鉄(Fe2O3)により優れたp型半導体特性を発現させることができれば、工業レベルの光触媒、太陽電池及び人工光合成を実現するうえで利点がある。 By the way, in the prior art, metal elements such as zinc (Zn) and copper (Cu) are doped to make iron oxide (Fe 2 O 3 ) a p-type semiconductor. Is desired to be expressed. Further, if excellent p-type semiconductor characteristics can be expressed by iron oxide (Fe 2 O 3 ) by combining inexpensive materials, there is an advantage in realizing industrial-level photocatalysts, solar cells, and artificial photosynthesis.
本発明の1つの態様は、ヘマタイト結晶相を含む酸化鉄の結晶中に亜鉛(Zn)、銅(Cu)、ニッケル(Ni)及びマグネシウム(Mg)の少なくとも1つの金属元素と窒素がドーピングされ、p型の半導体特性を示すことを特徴とする半導体材料である。 In one embodiment of the present invention, an iron oxide crystal including a hematite crystal phase is doped with nitrogen and at least one metal element of zinc (Zn), copper (Cu), nickel (Ni), and magnesium (Mg). It is a semiconductor material characterized by exhibiting p-type semiconductor characteristics.
ここで、鉄に対する窒素の原子数比(N/Fe換算)が0を超え0.05以下であり、かつ鉄に対する前記金属元素の原子数比(金属元素/Fe換算)が0を超え0.05以下であることが好適である。 Here, the atomic ratio of nitrogen to iron (N / Fe conversion) is more than 0 and 0.05 or less, and the atomic ratio of the metal element to iron (converted to metal element / Fe) is more than 0 and less than 0.0. It is preferable that it is 05 or less.
また、上記半導体材料の表面に金属助触媒を坦持させることが好適である。また、上記半導体材料の表面に金属酸化物助触媒を坦持させることが好適である。また、上記半導体材料の表面に錯体助触媒を坦持させることが好適である。 In addition, it is preferable to support a metal promoter on the surface of the semiconductor material. In addition, it is preferable to support a metal oxide promoter on the surface of the semiconductor material. In addition, it is preferable to support a complex promoter on the surface of the semiconductor material.
上記半導体材料は、光電極、光触媒体及び太陽電池を構成する材料として用いることができる。 The said semiconductor material can be used as a material which comprises a photoelectrode, a photocatalyst body, and a solar cell.
本発明によれば、安価な材料を用いて光応答性、特に可視光応答性を有する材料を実現することができる。 According to the present invention, a material having photoresponsiveness, particularly visible light responsiveness, can be realized using an inexpensive material.
本発明の実施の形態における半導体材料は、ヘマタイト結晶相を含む酸化鉄に窒素(N)と共に、鉄(Fe)以外の金属元素をドーピングすることによって形成される。 The semiconductor material in the embodiment of the present invention is formed by doping iron oxide containing a hematite crystal phase with nitrogen (N) and a metal element other than iron (Fe).
本実施の形態における半導体材料は、窒素含有ガスのプラズマ中において酸化鉄ターゲットをスパッタリングして基板上に半導体材料の膜を形成し、その膜を熱処理して結晶化させることによって得ることができる。 The semiconductor material in this embodiment can be obtained by sputtering an iron oxide target in a plasma of a nitrogen-containing gas to form a film of the semiconductor material on the substrate, and heat-treating the film to crystallize it.
1つの製造方法の例では、窒素(N2)とアルゴン(Ar)の混合ガスのプラズマを発生させ、酸化鉄及び酸化亜鉛(ZnO)のターゲットをスパッタリングして基板上に膜を形成する。また、別の製造方法の例では、窒素(N2)とアルゴン(Ar)の混合ガスのプラズマを発生させ、酸化鉄及び銅(Cu)のターゲットをスパッタリングして基板上に膜を形成する。このとき、これに限定されるものではないが、RFマグネトロンスパッタリングを適用することが好適である。 In one example of the manufacturing method, plasma of a mixed gas of nitrogen (N 2 ) and argon (Ar) is generated, and a film is formed on a substrate by sputtering a target of iron oxide and zinc oxide (ZnO). In another example of the manufacturing method, plasma of a mixed gas of nitrogen (N 2 ) and argon (Ar) is generated, and a film of iron oxide and copper (Cu) is sputtered to form a film on the substrate. At this time, although not limited to this, it is preferable to apply RF magnetron sputtering.
酸化鉄,酸化亜鉛(ZnO)及び銅(Cu)のターゲットは、例えば、純度4N及び直径4インチとする。また、プラズマへの投入電力は、例えば、直径4インチのターゲットに対して、酸化鉄では600W、酸化亜鉛(ZnO)では70W以下、銅(Cu)では60W以下とする。 The target of iron oxide, zinc oxide (ZnO), and copper (Cu) has a purity of 4N and a diameter of 4 inches, for example. Further, for example, with respect to a target having a diameter of 4 inches, the input power to the plasma is 600 W for iron oxide, 70 W or less for zinc oxide (ZnO), and 60 W or less for copper (Cu).
窒素(N2)とアルゴン(Ar)の混合ガスは、例えば、窒素(N2)分圧で0より大きく30%以下とし、総流量50sccm及び圧力0.5Paとする。 The mixed gas of nitrogen (N 2 ) and argon (Ar) is, for example, a nitrogen (N 2 ) partial pressure greater than 0 and 30% or less, with a total flow rate of 50 sccm and a pressure of 0.5 Pa.
基板は、これに限定されるものではないが、ガラス基板、ガラス上に透明導電膜(ATO:Sb−SnO2等)を形成した基板等とすることができる。透明導電膜(ATO)は、例えば、100nmの膜厚で堆積させる。 The substrate is not limited to, a glass substrate, a transparent conductive film on the glass: it is possible to (ATO Sb-SnO 2, etc.) formed by a substrate or the like. The transparent conductive film (ATO) is deposited with a film thickness of 100 nm, for example.
酸素(O2)を流す加熱炉において、基板上に形成された窒素(N)及び鉄(Fe)以外の金属元素をドーピングした酸化鉄をポスト加熱処理する。ポスト加熱処理は、450℃〜600℃の温度範囲で行うことが好適である。 In a heating furnace in which oxygen (O 2 ) flows, iron oxide doped with a metal element other than nitrogen (N) and iron (Fe) formed on the substrate is post-heat treated. The post heat treatment is preferably performed in a temperature range of 450 ° C to 600 ° C.
上記スパッタリング処理及びポスト加熱処理によって基板上にp型半導体特性を有する酸化鉄(Fe2O3:N+金属元素)が形成される。 Iron oxide (Fe 2 O 3 : N + metal element) having p-type semiconductor characteristics is formed on the substrate by the sputtering process and the post-heating process.
[実施例及び比較例]
以下、本発明の実施の形態における実施例及び比較例について説明する。まず、実施例及び比較例における試料の作成について説明した後、実施例及び比較例のそれぞれの特性について説明する。
[Examples and Comparative Examples]
Examples and comparative examples in the embodiment of the present invention will be described below. First, after preparation of the sample in an Example and a comparative example is demonstrated, each characteristic of an Example and a comparative example is demonstrated.
<実施例1>
スパッタリング製膜時の酸化鉄(Fe2O3)のターゲットに対する投入電力を600W、酸化亜鉛(ZnO)のターゲットに対する投入電力45Wの条件で、窒素(N2)とアルゴン(Ar)の混合ガスの流量比7.5/42.5(窒素流量比15%)において、亜鉛(Zn)と窒素(N)をともにドープした酸化鉄(Fe2O3)を200nmの膜厚で製膜した。これを酸素(O2)のフロー中において550℃で2時間熱処理した。
<Example 1>
Under the conditions of an input power of 600 W for an iron oxide (Fe 2 O 3 ) target during sputtering film formation and an input power of 45 W for a zinc oxide (ZnO) target, a mixed gas of nitrogen (N 2 ) and argon (Ar) Iron oxide (Fe 2 O 3 ) doped with zinc (Zn) and nitrogen (N) at a flow rate ratio of 7.5 / 42.5 (nitrogen flow rate ratio of 15%) was formed to a thickness of 200 nm. This was heat-treated at 550 ° C. for 2 hours in a flow of oxygen (O 2 ).
<実施例2>
酸化亜鉛(ZnO)のターゲットに対する投入電力を50Wとした以外は実施例1と同様に亜鉛(Zn)と窒素(N)をともにドープした酸化鉄(Fe2O3)を製膜し、その後熱処理を施した。
<Example 2>
Iron oxide (Fe 2 O 3 ) doped with both zinc (Zn) and nitrogen (N) is formed in the same manner as in Example 1 except that the input power to the target of zinc oxide (ZnO) is 50 W, and then heat treatment is performed. Was given.
<実施例3>
窒素(N2)とアルゴン(Ar)の混合ガスの流量比10/40(窒素流量比20%)とした以外は実施例1と同様に亜鉛(Zn)と窒素(N)をともにドープした酸化鉄(Fe2O3)を製膜し、その後熱処理を施した。
<Example 3>
Oxidation doped with both zinc (Zn) and nitrogen (N) in the same manner as in Example 1 except that the flow rate ratio of the mixed gas of nitrogen (N 2 ) and argon (Ar) was 10/40 (nitrogen flow rate ratio 20%). Iron (Fe 2 O 3 ) was formed and then heat-treated.
<実施例4>
酸化亜鉛(ZnO)のターゲットに対する投入電力を50Wとし、窒素(N2)とアルゴン(Ar)の混合ガスの流量比10/40(窒素流量比20%)とした以外は実施例1と同様に亜鉛(Zn)と窒素(N)をともにドープした酸化鉄(Fe2O3)を製膜し、その後熱処理を施した。
<Example 4>
The same as in Example 1 except that the input power to the target of zinc oxide (ZnO) was 50 W and the flow rate ratio of the mixed gas of nitrogen (N 2 ) and argon (Ar) was 10/40 (nitrogen flow rate ratio 20%). Iron oxide (Fe 2 O 3 ) doped with both zinc (Zn) and nitrogen (N) was formed, and then heat treatment was performed.
<実施例5>
酸化亜鉛(ZnO)のターゲットに対する投入電力を55Wとし、窒素(N2)とアルゴン(Ar)の混合ガスの流量比10/40(窒素流量比20%)とした以外は実施例1と同様に亜鉛(Zn)と窒素(N)をともにドープした酸化鉄(Fe2O3)を製膜し、その後熱処理を施した。
<Example 5>
The same as in Example 1 except that the input power to the target of zinc oxide (ZnO) was 55 W and the flow rate ratio of the mixed gas of nitrogen (N 2 ) and argon (Ar) was 10/40 (nitrogen flow rate ratio 20%). Iron oxide (Fe 2 O 3 ) doped with both zinc (Zn) and nitrogen (N) was formed, and then heat treatment was performed.
<実施例6>
酸化亜鉛(ZnO)の代りに銅(Cu)のターゲットとし、投入電力を45Wとした以外は実施例1と同様に酸化鉄(Fe2O3)を製膜し、その後、酸素(O2)のフロー中において500℃で2時間熱処理した。
<Example 6>
Iron oxide (Fe 2 O 3 ) was formed in the same manner as in Example 1 except that copper (Cu) was used instead of zinc oxide (ZnO) and the input power was 45 W, and then oxygen (O 2 ) Heat treatment at 500 ° C. for 2 hours.
<実施例7>
銅(Cu)のターゲットに対する投入電力を50Wとした以外は実施例6と同様に銅(Cu)と窒素(N)をともにドープした酸化鉄(Fe2O3)を製膜し、その後熱処理を施した。
<Example 7>
Iron oxide (Fe 2 O 3 ) doped with both copper (Cu) and nitrogen (N) is formed in the same manner as in Example 6 except that the input power to the copper (Cu) target is 50 W, and then heat treatment is performed. gave.
<実施例8>
銅(Cu)のターゲットに対する投入電力を55Wとした以外は実施例6と同様に銅(Cu)と窒素(N)をともにドープした酸化鉄(Fe2O3)を製膜し、その後熱処理を施した。
<Example 8>
Iron oxide (Fe 2 O 3 ) doped with both copper (Cu) and nitrogen (N) is formed in the same manner as in Example 6 except that the input power to the copper (Cu) target is 55 W, and then heat treatment is performed. gave.
<実施例9>
銅(Cu)のターゲットに対する投入電力を50Wとし、窒素(N2)とアルゴン(Ar)の混合ガスの流量比10/40(窒素流量比20%)とした以外は実施例6と同様に銅(Cu)と窒素(N)をともにドープした酸化鉄(Fe2O3)を製膜し、その後熱処理を施した。
<Example 9>
Copper was applied in the same manner as in Example 6 except that the input power to the target of copper (Cu) was 50 W and the flow rate ratio of the mixed gas of nitrogen (N 2 ) and argon (Ar) was 10/40 (nitrogen flow rate ratio 20%). Iron oxide (Fe 2 O 3 ) doped with both (Cu) and nitrogen (N) was formed, and then heat-treated.
<実施例10>
銅(Cu)のターゲットに対する投入電力を55Wとした以外は実施例9と同様に銅(Cu)と窒素(N)をともにドープした酸化鉄(Fe2O3)を製膜し、その後熱処理を施した。
<Example 10>
Iron oxide (Fe 2 O 3 ) doped with both copper (Cu) and nitrogen (N) is formed in the same manner as in Example 9 except that the input power to the copper (Cu) target is 55 W, and then heat treatment is performed. gave.
<実施例11>
銅(Cu)のターゲットに対する投入電力を50Wとし、窒素(N2)とアルゴン(Ar)の混合ガスの流量比12.5/37.5(窒素流量比25%)とした以外は実施例6と同様に銅(Cu)と窒素(N)をともにドープした酸化鉄(Fe2O3)を製膜し、その後熱処理を施した。
<Example 11>
Example 6 except that the input power to the target of copper (Cu) was 50 W and the flow rate ratio of the mixed gas of nitrogen (N 2 ) and argon (Ar) was 12.5 / 37.5 (nitrogen flow rate ratio 25%). In the same manner as above, iron oxide (Fe 2 O 3 ) doped with both copper (Cu) and nitrogen (N) was formed, and then heat treatment was performed.
<比較例1>
スパッタリング製膜時の酸化鉄(Fe2O3)のターゲットに対する投入電力を600W、酸化亜鉛(ZnO)及び銅(Cu)のターゲットに対する投入電力は0の条件で、窒素(N2)を含まないアルゴン(Ar)ガスの流量を50sccmとして、亜鉛(Zn)、銅(Cu)及び窒素(N)がドープされていない酸化鉄(Fe2O3)を200nmの膜厚で製膜した。これを酸素(O2)のフロー中において500℃で2時間熱処理した。以降、図中において比較例1についてN0%と示す。
<Comparative Example 1>
The power input to the target of iron oxide (Fe 2 O 3 ) during sputtering film formation is 600 W, and the power input to the targets of zinc oxide (ZnO) and copper (Cu) is 0, and does not include nitrogen (N 2 ). The flow rate of argon (Ar) gas was 50 sccm, and iron oxide (Fe 2 O 3 ) not doped with zinc (Zn), copper (Cu), and nitrogen (N) was formed to a thickness of 200 nm. This was heat-treated at 500 ° C. for 2 hours in a flow of oxygen (O 2 ). Hereinafter, N0% is shown for Comparative Example 1 in the figure.
<比較例2>
スパッタリング製膜時の酸化鉄(Fe2O3)のターゲットに対する投入電力を600W、酸化亜鉛(ZnO)のターゲットに対する投入電力を35Wとし、窒素(N2)を含まないアルゴン(Ar)ガスの流量を50sccmとして、亜鉛(Zn)のみがドープされた酸化鉄(Fe2O3)を200nmの膜厚で製膜した。これを酸素(O2)のフロー中において500℃で2時間熱処理した。以降、図中において比較例2についてZnO−35Wと示す。
<Comparative Example 2>
The flow rate of argon (Ar) gas not containing nitrogen (N 2 ) is 600 W, the input power to the target of zinc oxide (ZnO) is 35 W, and the input power to the target of iron oxide (Fe 2 O 3 ) during sputtering film formation Was set to 50 sccm, and iron oxide (Fe 2 O 3 ) doped only with zinc (Zn) was formed to a thickness of 200 nm. This was heat-treated at 500 ° C. for 2 hours in a flow of oxygen (O 2 ). Hereinafter, Comparative Example 2 is shown as ZnO-35W in the figure.
<比較例3>
スパッタリング製膜時の酸化鉄(Fe2O3)のターゲットに対する投入電力を600W、酸化亜鉛(ZnO)及び銅(Cu)のターゲットに対する投入電力を0とし、窒素(N2)とアルゴン(Ar)の混合ガスの流量比10/40(窒素流量比20%)として、窒素(N)のみがドープされた酸化鉄(Fe2O3)を200nmの膜厚で製膜した。これを酸素(O2)のフロー中において500℃で2時間熱処理した。以降、図中において比較例3についてN20%と示す。
<Comparative Example 3>
The power input to the target of iron oxide (Fe 2 O 3 ) during sputtering film formation is 600 W, the power input to the targets of zinc oxide (ZnO) and copper (Cu) is 0, and nitrogen (N 2 ) and argon (Ar) As a mixed gas flow ratio of 10/40 (nitrogen flow ratio 20%), iron oxide (Fe 2 O 3 ) doped only with nitrogen (N) was formed to a thickness of 200 nm. This was heat-treated at 500 ° C. for 2 hours in a flow of oxygen (O 2 ). Hereinafter, N20% is indicated for Comparative Example 3 in the figure.
<比較例4>
スパッタリング製膜時の酸化鉄(Fe2O3)のターゲットに対する投入電力を600W、銅(Cu)のターゲットに対する投入電力を50Wとし、窒素(N2)を含まないアルゴン(Ar)ガスの流量を50sccmとして、銅(Cu)のみがドープされた酸化鉄(Fe2O3)を200nmの膜厚で製膜した。これを酸素(O2)のフロー中において500℃で2時間熱処理した。以降、図中において比較例4についてCu−50Wと示す。
<Comparative Example 4>
The power input to the iron oxide (Fe 2 O 3 ) target during sputtering film formation is 600 W, the power input to the copper (Cu) target is 50 W, and the flow rate of argon (Ar) gas not containing nitrogen (N 2 ) is An iron oxide (Fe 2 O 3 ) doped with only copper (Cu) was formed to a film thickness of 200 nm at 50 sccm. This was heat-treated at 500 ° C. for 2 hours in a flow of oxygen (O 2 ). Hereinafter, in the figure, Comparative Example 4 is indicated as Cu-50W.
[測定結果]
以下、上記実施例及び比較例の試料について各種測定を行った結果を示す。
[Measurement result]
The results of various measurements performed on the samples of the above examples and comparative examples are shown below.
<X線回折測定>
実施例1〜11及び比較例1〜4の試料についてX線回折測定を行った。X線回折測定は、Cu(Kα)線を用いたθ−2θ法を適用した。
<X-ray diffraction measurement>
X-ray diffraction measurement was performed on the samples of Examples 1 to 11 and Comparative Examples 1 to 4. For the X-ray diffraction measurement, the θ-2θ method using Cu (Kα) ray was applied.
いずれの試料もα―酸化鉄(Fe2O3:ヘマタイト)の(110)回折線と、非常に弱い(104)回折線を示した。また、亜鉛(Zn)、酸化亜鉛(ZnO)、銅(Cu)、酸化銅(Cu2O,CuO)、亜鉛(Zn)の窒化物及び銅(Cu)の窒化物に由来する回折線は観察されなかった。 All the samples showed (110) diffraction lines of α-iron oxide (Fe 2 O 3 : hematite) and very weak (104) diffraction lines. In addition, diffraction lines derived from zinc (Zn), zinc oxide (ZnO), copper (Cu), copper oxide (Cu 2 O, CuO), nitride of zinc (Zn) and nitride of copper (Cu) are observed. Was not.
<光吸収特性>
実施例1〜11について紫外―可視光線領域における光吸収スペクトルを計測した。その結果、いずれの試料においても光の吸収端はすべて、ごくわずかに短波長側にシフトしている傾向を示すが、ドープなしのα―酸化鉄(Fe2O3:ヘマタイト)と同じく光の吸収端が波長600nm以下であった。このことから、バンドギャップは約2.1eVであることが明らかとなった。
<Light absorption characteristics>
For Examples 1 to 11, light absorption spectra in the ultraviolet-visible light region were measured. As a result, in all samples, the absorption edge of light tends to be shifted slightly to the short wavelength side, but the light absorption is similar to that of undoped α-iron oxide (Fe 2 O 3 : hematite). The absorption edge was 600 nm or less. From this, it became clear that the band gap was about 2.1 eV.
<光応答電圧−電流測定>
実施例1〜11及び比較例1〜4の試料について伝導特性を調べるために、作製した試料の光電気化学的な光応答電圧−電流測定を、ポテンショスタットを使用して測定した。ポテンショスタットを用いて濃度0.2モル(M)の硫酸カリウム(K2SO4)水溶液中で参照電極に対するバイアス電位を変化させながら光応答電圧−電流特性を測定した。参照電極には銀/塩化銀(Ag/AgCl)を、対電極には白金(Pt)を使用した。照射光源には500Wキセノンランプ(ウシオ電機製)を使用した。またキセノンランプの直接照射による紫外線+可視光線条件下の実験だけではなく、照射光を短波長カットフィルタ(シグマ光機製、型番42L)に透過させ、波長410nm以上(短波長側のカット率99.99%)の可視光のみの照射実験もあわせて実施した。
<Optical response voltage-current measurement>
In order to examine the conduction characteristics of the samples of Examples 1 to 11 and Comparative Examples 1 to 4, photoelectrochemical photoresponse voltage-current measurements of the prepared samples were measured using a potentiostat. Using a potentiostat, photoresponse voltage-current characteristics were measured in a potassium sulfate (K 2 SO 4 ) aqueous solution having a concentration of 0.2 mol (M) while changing the bias potential with respect to the reference electrode. Silver / silver chloride (Ag / AgCl) was used for the reference electrode, and platinum (Pt) was used for the counter electrode. A 500 W xenon lamp (USHIO Inc.) was used as the irradiation light source. In addition to the experiment under the condition of ultraviolet ray + visible ray by direct irradiation with a xenon lamp, the irradiation light is transmitted through a short wavelength cut filter (manufactured by Sigma Kogyo, model number 42L), and the wavelength is 410 nm or more (cut rate 99.99 on the short wavelength side). (99%) was also subjected to an irradiation experiment using only visible light.
図1〜図4に比較例1〜4の光電流プロファイル及び図5〜図7に実施例1,4及び10の光電流プロファイルを示す。硫酸カリウム(K2SO4)水溶液中に酸素(O2)ガスでバブリングを行った条件下で計測を行っており、主として溶存酸素に電子を渡す電流(O2+e-→O2 -)を検出している。光照射は、キセノンランプ全波長域の光を、チョッパで連続的にオン/オフを繰り返して電位を挿引しながら電気化学測定を行った。測定された材料は、いずれもターゲットへの投入電力、スパッタ時の窒素(N2)分圧や熱処理温度は、それらの材料系で最も高い光電流を示すときの作製条件である。 1 to 4 show the photocurrent profiles of Comparative Examples 1 to 4, and FIGS. 5 to 7 show the photocurrent profiles of Examples 1, 4 and 10. FIG. Measurement is performed under the condition that bubbling with oxygen (O 2 ) gas is carried out in an aqueous solution of potassium sulfate (K 2 SO 4 ), and the current (O 2 + e − → O 2 − ) is mainly used to transfer electrons to dissolved oxygen. Detected. For light irradiation, electrochemical measurement was performed while light in the entire wavelength region of the xenon lamp was continuously turned on / off with a chopper and the potential was inserted. For the measured materials, the power applied to the target, the nitrogen (N 2 ) partial pressure at the time of sputtering, and the heat treatment temperature are the production conditions when the highest photocurrent is exhibited in those material systems.
<比較例1>
比較例1(N0%と記載)では、光のオン/オフに応答しないカソード的(cathodic)電流が観察された。一方、それよりも正の電位においては、光のオン/オフに伴いスパイク状の電流とともに、オン時は正の電流が、オフ時には負の電流が生じたが、それらの成分を伴い光照射で正の電位側でアノード的(anodic)電流の生じるn型半導体であった。
<Comparative Example 1>
In Comparative Example 1 (described as N0%), a cathodic current that does not respond to light on / off was observed. On the other hand, at a positive potential, a positive current was generated when the light was turned on, and a negative current was generated when the light was turned off. It was an n-type semiconductor in which an anodic current was generated on the positive potential side.
<比較例2>
比較例2(ZnO−35Wと記載)では、ドープなし酸化鉄(Fe2O3)の場合と同様に負の電位位置において光照射しない暗条件下においてもカソード的電流が生じた。ただし、その開始位置は、ドープなし酸化鉄(Fe2O3)の場合と比べてより負側にシフトしており、その値はおよそ−0.4V(対銀/塩化銀(Ag/AgCl))であった。光照射した場合、+0.9V(対銀/塩化銀(Ag/AgCl))付近から負の電位領域において、光照射に応答した負電流すなわちカソード的電流が流れ、また光照射時の電流はバイアス電位が負に大きくなるのに伴いそのカソード的電流値が大きくなる。このことから、本発明のように酸化鉄(Fe2O3)へ亜鉛(Zn)をドープすることによりp型半導体となり、光応答するカソード的電流が発現したと考えられる。このとき0.0V(対銀/塩化銀(Ag/AgCl))におけるカソード的電流の値は平均で−51.9μAであった。
<Comparative Example 2>
In Comparative Example 2 (described as ZnO-35W), a cathodic current was generated even under dark conditions where no light was irradiated at a negative potential position, as in the case of undoped iron oxide (Fe 2 O 3 ). However, the starting position is shifted to the negative side compared with the case of undoped iron oxide (Fe 2 O 3 ), and the value is about −0.4 V (against silver / silver chloride (Ag / AgCl)). )Met. In the case of light irradiation, a negative current in response to light irradiation, that is, a cathodic current flows in the negative potential region from around +0.9 V (vs. silver / silver chloride (Ag / AgCl)). As the potential increases negatively, the cathodic current value increases. From this, it can be considered that by doping zinc oxide (Fe 2 O 3 ) with zinc (Zn) as in the present invention, a p-type semiconductor is formed, and a cathodic current that responds to light is developed. At this time, the value of the cathodic current at 0.0 V (vs. silver / silver chloride (Ag / AgCl)) was -51.9 μA on average.
<比較例3>
比較例3(N20%と記載)では、その光電流挙動は亜鉛(Zn)をドープした酸化鉄(Fe2O3)と同様であった。光照射した場合、+0.9V(対銀/塩化銀(Ag/AgCl))付近から負の電位領域において、光照射に応答した負電流すなわちカソード的電流が流れ、また光照射時の電流はバイアス電位が負に大きくなるのに伴いそのカソード的電流の値が大きくなった。このことから、本発明のように酸化鉄(Fe2O3)に窒素(N)をドープすることによりp型半導体となり、光応答するカソード的電流が発現したと考えられる。このとき0.0V(対銀/塩化銀(Ag/AgCl))におけるカソード的電流の値は平均で−20.5μAであった。
<Comparative Example 3>
In Comparative Example 3 (described as N20%), the photocurrent behavior was the same as that of iron oxide (Fe 2 O 3 ) doped with zinc (Zn). In the case of light irradiation, a negative current in response to light irradiation, that is, a cathodic current flows in the negative potential region from around +0.9 V (vs. silver / silver chloride (Ag / AgCl)). As the potential increased negatively, the value of the cathodic current increased. From this, it is considered that the iron oxide (Fe 2 O 3 ) is doped with nitrogen (N) as in the present invention to form a p-type semiconductor, and a cathodic current that responds to light is developed. At this time, the value of the cathodic current at 0.0 V (vs. silver / silver chloride (Ag / AgCl)) was −20.5 μA on average.
<比較例4>
比較例4(Cu−50Wと記載)では、その光電流挙動は亜鉛(Zn)ドープした酸化鉄(Fe2O3)と同様である。光照射しない暗条件下においてもカソード的電流が生じた。ただし、その開始位置は、亜鉛(Zn)をドープした酸化鉄(Fe2O3)あるいは窒素(N)をドープした酸化鉄(Fe2O3)の場合と比べてより正側にシフトしており、その値はおよそ−0.3V(対銀/塩化銀(Ag/AgCl))であった。光照射した場合、+0.6V(対銀/塩化銀(Ag/AgCl))付近から負の電位領域において、光照射に応答した負電流すなわちカソード的電流が流れ、また光照射時の電流はバイアス電位が負に大きくなるのに伴いそのカソード的電流の値が大きくなった。このことから、本発明のように酸化鉄(Fe2O3)へ銅(Cu)をドープすることによりp型半導体となり、光応答するカソード電流が発現したと考えられる。このとき、0.0V(対銀/塩化銀(Ag/AgCl))におけるカソード的電流の値は平均で−45.3μAであった。
<Comparative Example 4>
In Comparative Example 4 (described as Cu-50W), the photocurrent behavior is the same as that of zinc (Zn) -doped iron oxide (Fe 2 O 3 ). Cathodic current was generated even under dark conditions without light irradiation. However, the starting position is shifted to the positive side compared to the case of iron oxide (Fe 2 O 3 ) doped with zinc (Zn) or iron oxide (Fe 2 O 3 ) doped with nitrogen (N). The value was about -0.3 V (vs. silver / silver chloride (Ag / AgCl)). In the case of light irradiation, a negative current in response to light irradiation, that is, a cathodic current flows in the negative potential region from around +0.6 V (against silver / silver chloride (Ag / AgCl)). As the potential increased negatively, the value of the cathodic current increased. From this, it is considered that iron oxide (Fe 2 O 3 ) is doped with copper (Cu) as in the present invention to form a p-type semiconductor, and a cathode current that responds to light is developed. At this time, the value of the cathodic current at 0.0 V (vs. silver / silver chloride (Ag / AgCl)) averaged −45.3 μA.
<実施例1,4及び10>
図5に実施例1、図6に実施例4及び図7に実施例10の光電圧−電流特性を示す。いずれも、負のバイアス電圧領域で負のカソード電流を示し、p型半導体であった。また、光照射しない暗条件下におけるカソード的電流の開始位置は、亜鉛(Zn)、銅(Cu)や窒素(N)を単独でドープした酸化鉄(Fe2O3)の場合と比べてより負側にシフトしており、その値はおよそ−0.7V(対銀/塩化銀(Ag/AgCl))であった。
<Examples 1, 4 and 10>
FIG. 5 shows the photovoltage-current characteristics of Example 1, FIG. 6 shows Example 4 and FIG. All of these were negative cathode currents in the negative bias voltage region, and were p-type semiconductors. Moreover, the starting position of the cathodic current under dark conditions without light irradiation is more than in the case of iron oxide (Fe 2 O 3 ) doped solely with zinc (Zn), copper (Cu) or nitrogen (N). The value was shifted to the negative side, and the value was about −0.7 V (vs. silver / silver chloride (Ag / AgCl)).
表1に、窒素(N)と亜鉛(Zn)をドープした酸化鉄(Fe2O3)の光電流を示す。実施例1〜5はすべて、比較例1〜3のドープなし、あるいは亜鉛(Zn)又は窒素(N)を単独でドープした酸化鉄(Fe2O3)よりも高い光カソード電流を示し、ヘマタイト結晶相を有する酸化鉄(Fe2O3)の結晶中に窒素(N)とともに亜鉛(Zn)がドーピングされることによるより優れたp型半導体特性が得られた。
表2に、窒素(N)と銅(Cu)をドープした酸化鉄(Fe2O3)の光電流を示す。実施例6〜11はすべて、比較例1,3,4のドープなし、あるいは窒素(N)又は銅(Cu)を単独でドープした酸化鉄(Fe2O3)よりも高い光カソード電流を示し、ヘマタイト結晶相を有する酸化鉄(Fe2O3)の結晶中に窒素(N)とともに銅(Cu)がドーピングされることによるより優れたp型半導体特性が得られた。
このように、亜鉛(Zn)又は銅(Cu)を窒素(N)とともに酸化鉄(Fe2O3)中にドープすることにより、亜鉛(Zn)、銅(Cu)又は窒素(N)を単独でドープする場合よりも大きな光電流が得られる。このときの亜鉛(Zn)および窒素(N)の組成比の例を表3に示す。
組成の測定は、p型半導体特性と判定された実施例の酸化鉄(Fe2O3)膜に対してX線光電子分光測定(XPS)による窒素(N)及び亜鉛(Zn)の含有量の測定を行った。装置は、ULVAC PHI社製「Quantera SXM」を、X線源にはAl Kαを使用した。また、試料表面の汚染の影響を避けるため、Arイオンで1分間、加速電圧3kVでエッチングしてから測定を行った。この結果、いずれのサンプルも399.5eV付近にピークを示し、また一部のサンプルでは403.5eV付近にもピークを示した。p型半導体に特徴的な光カソード電流を示す実施例のみ、396.5eV±0.5Vの位置にもピークを示した。これらのN1s殻スペクトルを計算によりピーク分離し、本発明のp型半導体となる実施例のみにおいて特徴的にみられる396.5eVピークの窒素(N)の組成比を算出した。また、亜鉛(Zn)については、1021.5eV付近のピークから組成比を算出した。 The composition was measured by measuring the content of nitrogen (N) and zinc (Zn) by X-ray photoelectron spectroscopy (XPS) with respect to the iron oxide (Fe 2 O 3 ) film of the example determined to be p-type semiconductor characteristics. Measurements were made. The apparatus used was “Quantera SXM” manufactured by ULVAC PHI, and Al Kα was used as the X-ray source. In order to avoid the influence of contamination on the sample surface, measurement was performed after etching with Ar ions for 1 minute at an acceleration voltage of 3 kV. As a result, all the samples showed a peak around 399.5 eV, and some of the samples also showed a peak around 403.5 eV. Only the example showing the photocathode current characteristic of the p-type semiconductor also showed a peak at a position of 396.5 eV ± 0.5 V. These N1s shell spectra were peak-separated by calculation, and the composition ratio of nitrogen (N) of the 396.5 eV peak, which is characteristic only in the example of the p-type semiconductor of the present invention, was calculated. For zinc (Zn), the composition ratio was calculated from the peak near 1021.5 eV.
比較例2である亜鉛(Zn)をドープした酸化鉄(Fe2O3)における亜鉛/鉄(Zn/Fe)比は0.131、また比較例3の窒素(N)をドープした酸化鉄(Fe2O3)における窒素/鉄(N/Fe)比は0.021であった。これに対して、光電流のより大きな実施例1における亜鉛/鉄(Zn/Fe)比および窒素/鉄(N/Fe)比は各々0.002及び0.013であった。また実施例4における亜鉛/鉄(Zn/Fe)比および窒素/鉄(N/Fe)比は各々0.003及び0.015であった。 The zinc / iron (Zn / Fe) ratio in the iron oxide (Fe 2 O 3 ) doped with zinc (Zn), which is Comparative Example 2, is 0.131, and the iron oxide doped with nitrogen (N) in Comparative Example 3 ( The nitrogen / iron (N / Fe) ratio in Fe 2 O 3 was 0.021. On the other hand, the zinc / iron (Zn / Fe) ratio and the nitrogen / iron (N / Fe) ratio in Example 1 with higher photocurrent were 0.002 and 0.013, respectively. Moreover, the zinc / iron (Zn / Fe) ratio and the nitrogen / iron (N / Fe) ratio in Example 4 were 0.003 and 0.015, respectively.
以上の結果から、本発明でドープされた亜鉛(Zn)と窒素(N)の量は、それぞれが単独でドープされ最適なp型特性を発現させる時のドープ量よりも少ない量でより高い光電流値を発現することが明らかである。窒素(N)ともに亜鉛(Zn)がドープされた場合、それらが相補してさらに高い光電流を発現するものと考えられる。このときのドープ量は亜鉛/鉄(Zn/Fe)比が0を超え0.050以下、かつ窒素/鉄(N/Fe)比が0を超え0.050以下が好ましい。より好ましくは亜鉛(Zn)のドープ量は亜鉛/鉄(Zn/Fe)比が0.001を超え0.010以下、かつ窒素/鉄(N/Fe)比が0.005を超え0.025以下である。この傾向は、窒素(N)とともに銅(Cu)がドープされた酸化鉄(Fe2O3)においても同様であった。 From the above results, the amount of zinc (Zn) and nitrogen (N) doped in the present invention is higher than the amount of doping when each of them is doped alone to develop the optimum p-type characteristics. It is clear that the current value is developed. When nitrogen (N) is doped with zinc (Zn), it is considered that they complement each other and develop a higher photocurrent. The amount of doping at this time is preferably such that the zinc / iron (Zn / Fe) ratio is more than 0 and not more than 0.050, and the nitrogen / iron (N / Fe) ratio is more than 0 and not more than 0.050. More preferably, the doping amount of zinc (Zn) is such that the zinc / iron (Zn / Fe) ratio exceeds 0.001 and is 0.010 or less, and the nitrogen / iron (N / Fe) ratio exceeds 0.005 and 0.025. It is as follows. This tendency was the same in iron oxide (Fe 2 O 3 ) doped with copper (Cu) together with nitrogen (N).
これらの窒素(N)と亜鉛(Zn)又は窒素(N)と銅(Cu)を共にドープした酸化鉄(Fe2O3)10を図8に示すように酸素(O2)の代りにアルゴン(Ar)を硫酸カリウム(K2SO4)水溶液12中にバブリングした水素生成系反応に用いた場合、その表面に白金(Pt)助触媒を担持すると光電流が増大することから、水溶液中のプロトンを還元し水素を生成する速度が向上した。またその表面に[Ru(bpy)2(CO)2]2+や[Ru(C3−pyroyl−bpy)2(CO)2Cl2](ここでbpyはbipyridine)などの錯体触媒を担持すると、二酸化炭素(CO2)を光還元する能力が大きく向上した。
The iron oxide (Fe 2 O 3 ) 10 doped with both nitrogen (N) and zinc (Zn) or nitrogen (N) and copper (Cu) is replaced with argon instead of oxygen (O 2 ) as shown in FIG. When (Ar) is used in a hydrogen generation system reaction in which an
なお、上述した熱処理温度のうち、本発明の対象となるp型半導体に特有の光カソード電流の値が最も大きくなる値は、窒素(N)と銅(Cu)を共にドープした酸化鉄(Fe2O3)では500℃、一方窒素(N)と亜鉛(Zn)を共にドープした酸化鉄(Fe2O3)では550℃であった。 Of the heat treatment temperatures described above, the value of the maximum photocathode current characteristic of the p-type semiconductor that is the subject of the present invention is the iron oxide (Fe) doped with both nitrogen (N) and copper (Cu). It was 500 ° C. for 2 O 3 ), whereas it was 550 ° C. for iron oxide (Fe 2 O 3 ) doped with both nitrogen (N) and zinc (Zn).
また、本発明において窒素(N)とともに酸化鉄にドープする金属の種類については、実施例に挙げた亜鉛(Zn)又は銅(Cu)に限られず、Fe3+に対してイオン価数の少ないニッケル(Ni)やマグネシウム(Mg)など、それらが単独でドーピングされても酸化鉄にp型特性を発現させる金属であればよい。また表面に担持する助触媒についても、上述された金属や錯体に限られず、反応を促進するものであればよい。 In the present invention, the type of metal doped into iron oxide together with nitrogen (N) is not limited to zinc (Zn) or copper (Cu) mentioned in the examples, and has a smaller ionic valence than Fe 3+ . Even if they are doped singly, such as nickel (Ni) or magnesium (Mg), any metal that exhibits p-type characteristics in iron oxide may be used. The cocatalyst supported on the surface is not limited to the above-described metals and complexes, and any promoter that promotes the reaction may be used.
[効果]
ヘマタイト結晶相を有する酸化鉄は、紫外線及び波長600nm以下の可視光を吸収して光励起電子を生じる。また、本発明のp型半導体は、伝導帯の最下部のポテンシャルが−0.6V(対NHE(標準水素電極電位))となり、通常のn型酸化鉄よりも約0.8Vだけ卑な電位位置(あるいは真空準位に近い位置)に存在することから、光励起された電子を他の物質に渡す能力が高い。従って、本発明の材料を光触媒として用いた場合には、物質を効率よく還元することができる。また本発明の材料を太陽電池のp型層として用いた場合には、解放電圧が大きくなる利点がある。
[effect]
Iron oxide having a hematite crystal phase absorbs ultraviolet light and visible light having a wavelength of 600 nm or less to generate photoexcited electrons. In the p-type semiconductor of the present invention, the lowest potential of the conduction band is −0.6 V (vs NHE (standard hydrogen electrode potential)), which is a lower potential by about 0.8 V than normal n-type iron oxide. Since it exists at a position (or a position close to a vacuum level), the ability to pass photoexcited electrons to another substance is high. Therefore, when the material of the present invention is used as a photocatalyst, the substance can be reduced efficiently. Further, when the material of the present invention is used as a p-type layer of a solar cell, there is an advantage that the release voltage is increased.
[原理]
窒素(N)及び鉄以外の金属元素をドーピングすることによってヘマタイト構造を有する酸化鉄がp型半導体特性を向上させる理由については明確ではないが、これまで報告されている酸化物半導体へのドーピングによるp型半導体特性の発現の事例から以下のように推測される。
[principle]
The reason why iron oxide having a hematite structure improves p-type semiconductor characteristics by doping a metal element other than nitrogen (N) and iron is not clear, but it has been reported so far by doping into an oxide semiconductor. It is inferred from the example of the manifestation of p-type semiconductor characteristics as follows.
図9に示すとおり、酸化鉄の価電子帯は酸素のO2p軌道などによって形成される。そのためドープした窒素(N)がN3-である場合には、酸素のO2p軌道などから形成される価電子帯の最上端部よりやや卑な位置(真空準位に近い位置)にアクセプタ準位を形成するためにp型半導体となる。ここに亜鉛(Zn)や銅(Cu)がZn2+やCu2+として共にドープされた場合、これらも窒素(N)と同様に酸化鉄をp型半導体にする効果があるため、その相乗効果があると考えられる。 As shown in FIG. 9, the valence band of iron oxide is formed by oxygen O 2p orbitals and the like. Therefore, when the doped nitrogen (N) is N 3− , the acceptor level is slightly lower than the uppermost end of the valence band formed from the O 2p orbit of oxygen (position close to the vacuum level). A p-type semiconductor is formed to form a position. Here, when zinc (Zn) or copper (Cu) is doped together as Zn 2+ or Cu 2+ , these also have the effect of making iron oxide into a p-type semiconductor in the same way as nitrogen (N). It is considered effective.
またこの結果、酸化鉄のバンドポテンシャルが全体に卑な電位方向にシフトする結果、図10に示すように伝導帯の最下部のポテンシャルECBMがn型の酸化鉄の場合の+0.2V(対NHE(標準水素電極電位))から、NHEに対して卑の位置である−0.7V(対NHE)にまでシフトする。従って、電気的なバイアス無しでも光照射のみによって光励起電子をプロトン(H+)に渡し、光触媒的な水素発生が可能となる。またその上、ポテンシャルECBMが−0.6V(対NHE)であることから、二酸化炭素(CO2)を還元するのに適した助触媒との組合せによって、二酸化炭素(CO2)へ電子を渡して多電子還元し有用物質に変換する能力を発揮できる。 As a result, the band potential of the iron oxide is shifted in the direction of the base potential as a whole. As a result, as shown in FIG. 10, the lowest potential E CBM of the conduction band is + 0.2V (vs. NHE (standard hydrogen electrode potential)) shifts to −0.7 V (vs NHE), which is a base position with respect to NHE. Accordingly, photoexcited electrons are transferred to protons (H + ) only by light irradiation without an electrical bias, and photocatalytic hydrogen generation becomes possible. Further thereon, since the potential E CBM is -0.6 V (vs. NHE), by a combination with a suitable cocatalyst for the reduction of carbon dioxide (CO 2), the electrons to carbon dioxide (CO 2) The ability to convert to useful substances can be demonstrated by multi-electron reduction.
10 半導体材料(酸化鉄)、12 硫酸カリウム(K2SO4)水溶液。 10 Semiconductor material (iron oxide), 12 Potassium sulfate (K 2 SO 4 ) aqueous solution.
Claims (8)
鉄に対する窒素の原子数比(N/Fe換算)が0を超え0.05以下であり、かつ鉄に対する前記金属元素の原子数比(金属元素/Fe換算)が0を超え0.05以下であることを特徴とする半導体材料。 The semiconductor material according to claim 1,
The atomic ratio of nitrogen to iron (N / Fe conversion) is more than 0 and 0.05 or less, and the atomic ratio of the metal element to iron (metal element / Fe conversion) is more than 0 and 0.05 or less. A semiconductor material characterized by being.
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