JPS60260163A - Semiconductor element for photochemical reaction - Google Patents

Abstract

PURPOSE:To improve the reactive efficiency of the titled semiconductor element by a method wherein the carrier formed by the irradiation of light is isolated in the planer orientation of a film-like or tabular semiconductor. CONSTITUTION:When a semiconductor A4 and a semiconductor B5 are jointed in a plane surface, a bend of conductive band and valence band is generally generated on the jointed region by a junction electric field. With the above-mentioned junction electric field, electrons and holes are drifted in reverse direction respectively, and these carriers are isolated in the planer orientation on the surface of the semiconductor. Thus, the life of the carrier subjected to drift in the junction region is made longer than that where the junction region is in the flat board state having no junction electric field. To be more precise, the speed of recoupling is reduced. The moving distance of each carrier is made short, the degree of establishment of recoupling of the carrier is reduced, and the reactive efficiency of the semiconductor element can be improved by forming the repetition of junction consisting of the semiconductors 4 and 5 in the semiconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a semiconductor device for photochemical reactions that utilizes light energy to cause chemical reactions.

[Technical background of the invention and its problems]

Technology that converts light energy into chemical energy using photochemical reactions has attracted attention in recent years as a solar energy utilization technology, and research is particularly active on photocatalytic reactions and photoelectrode reactions using semiconductor materials. is in progress.

For example, a typical example is a photochemical reaction in which sunlight is irradiated onto a reaction system in which water as a reaction component and a semiconductor for photochemical reaction coexist to cause photolysis of water as shown in the following formula: be. Semiconductor materials used in such reactions include:
'1''to, , 5rTiO,, GaP + GaAs
, InP, CdS, Si, and other semiconductors have been well studied.

In the semiconductors used in these studies, holes (h+) and electrons (e-
) can be generated by a junction electric field perpendicular to the surface at the interface between the semiconductor and the reaction liquid, as shown in Figure 2 (a), or by laminating a metal 3 on the semiconductor surface as shown in Figure 2 (bl). Separation in the direction perpendicular to the surface was attempted using the junction electric field formed in the direction perpendicular to the surface.

However, if the holes and electrons are simply separated in the vertical direction, the holes and electrons are likely to recombine and disappear, and the reaction components are reaction intermediates such as ions and radicals that are forming products with the holes and electrons. Even at the body stage, there were problems such as the tendency to cause a reverse reaction and return to the original reaction components, which hindered improvement in reaction efficiency.

[Purpose of the invention]

The present invention was made in view of such problems, and provides a semiconductor for photochemical reactions in which reaction efficiency is improved by separating carriers generated by light irradiation in the in-plane direction of a film-like or plate-like semiconductor. The purpose is to

[Summary of the invention]

The present invention separates electrons and holes generated in a semiconductor by light irradiation in the in-plane direction of the semiconductor surface, and furthermore guides these carriers to a specific region within the semiconductor, thereby recombining the carriers with each other. Alternatively, it is intended to make it possible to suppress the reverse reaction of reaction products or intermediates thereof on the semiconductor surface of these carriers.

A detailed explanation will be given below. As shown in Figure 1, semiconductor A
When (4) and semiconductor B (5) are bonded in a plane, the conduction band and valence band generally bend in the bonding region due to the bonding electric field. This junction electric field causes electrons and holes to drift in opposite directions, and these carriers are separated in the in-plane direction of the semiconductor surface. Carriers that undergo drift in the junction region in this manner have a longer lifetime than in a flat band state without a junction electric field. That is, the recombination rate decreases.

Furthermore, by creating repeated junctions in the semiconductor consisting of semiconductor A (4) and semiconductor B (5) as illustrated in FIG. 3, the holes and electrons generated are It is possible to prevent the recombination of carriers by moving them separately to specific regions obtained by the method, and furthermore, it is possible to intentionally control the reaction sites of oxidation and reduction.

Therefore, by creating such a region on a micro scale, the distance traveled by each carrier is shortened, reducing the probability of recombination of the carriers, and furthermore, oxidation or reduction reactions can occur on the surface of the region where carriers of the same type have gathered. By doing so, it is possible to prevent reverse reactions between reaction intermediates and reaction products and to further improve reaction efficiency.

Semiconductor junctions that separate carriers are conventionally known n-n+ type, p-1 type homojunctions, p-n
Homozygous type or p-1-n type, and heterozygous p-n type or nn+1)-p type can be used. Further, even by using a junction between a semiconductor and a metal, it is possible to create the combined electric field that is the object of the present invention.

As described above, the object of the present invention is achieved by separating carriers in the in-plane direction of the semiconductor surface using a junction electric field. In other words, if it is moved to the front or back surface of the semiconductor, the reaction efficiency can be further improved. For such movement of carriers in a direction perpendicular to the semiconductor surface, a vertical junction electric field formed from the various semiconductor-semiconductor junctions or semiconductor metal junctions described above can be used. That is, for example, if you want to move electrons to the semiconductor surface in a region that is separated in a plane and where electrons gather, you can use a vertical junction that allows electrons to drift toward the surface in this region, as shown in Figure 4. It is sufficient to create an electric field using four semiconductors A' (4) and semiconductor A'' (4).The same applies to holes, and the direction of drift can be roughly controlled by the direction of the junction electric field.

Or carriers moving in the plane inside the semiconductor,
By applying a magnetic field in a direction perpendicular to the moving direction of the carrier in the in-plane direction, the carrier is drifted in a direction perpendicular to both the moving direction and the direction of the magnetic field due to the action of Lorentz force. It is also possible to cause the carriers to drift in the film thickness direction. In addition to applying an external magnetic field, methods for inducing this magnetic field inside the semiconductor film include stacking a semiconductor film on a magnetic film,
Alternatively, this can be achieved by sandwiching the semiconductor film between magnetic films in a direction parallel to the plane. At this time, it is desirable from the standpoint of efficiency that the direction of magnetization in the external magnetic field or in the magnetic film is perpendicular to the junction electric field formed in the semiconductor film. and,
For example, the following two directions can be cited as the direction of the magnetic field. One is as shown in FIG. 5(a), where holes and electrons move in the direction of the 1.8 direction and the direction of the vx force, respectively, due to the junction electric field created in the semiconductor film 14, and move there in the same plane to the above-mentioned -.
By applying magnetic fields -BY and By in the direction perpendicular to X and x, holes and electrons both receive an F2O force perpendicular to the plane of the paper and drift upward perpendicular to the plane of the paper.

On the other hand, by applying the magnetic fields -By and By generated in the semiconductor film 14 as shown in FIG. drifts vertically downwards on the paper.
As examples of magnetic films that can be used to attract such magnetic fields, there are the following two types depending on the direction of the magnetization vector within the film. One is a magnetic material that is easily magnetized in the in-plane direction of the magnetic film 6, as shown in FIG. 6(a), and is herein referred to as a horizontally magnetized film. On the other hand, a magnetic material having an axis of easy magnetization in a direction perpendicular to the film surface of the magnetic film, as shown in FIG. 7 (al), is generally well known as a perpendicular magnetization film.

When horizontally magnetized films are used, a magnetic field can be induced in adjacent semiconductor films by utilizing gaps in the magnetic circuit as shown in FIG. 6(b).

In other words, if a semiconductor film is stacked on a uniform magnetic film, a magnetic field in the opposite direction to that of the underlying magnetic film is induced in the semiconductor, and if a semiconductor film is sandwiched between magnetic films in the in-plane direction, the magnetic field A magnetic field in the same direction is induced in the semiconductor film. This horizontally magnetized film is grown using a strong uniform external magnetic field or a fine magnetic head (Figure (C)).

By magnetizing as shown in (d), the magnetic field according to the present invention can be induced in the semiconductor film.

On the other hand, when a perpendicularly magnetized film is used, an external magnetic field that is horizontal to the film is created between adjacent magnetic regions as shown in Figure 7(b), so it is necessary to control such magnetic domains using a perpendicularly magnetized magnetic head. For example, a magnetic field as shown in (C1 and (d)) in the same figure can be induced in the semiconductor film.

In this case, if a horizontal magnetization film made of a high permeability magnetic material 7, such as permalloy, is further laminated under the vertical magnetization film layer as shown in FIG. This is already well known in research on perpendicular magnetization recording media, and this method can also be used in the present invention.

The magnetic material used here is preferably a material with a large residual magnetic flux density and a large coercive force, and the horizontally magnetized magnetic material is MK steel (Fe-N 1-A1 alloy), which is well known as a permanent magnet material. ), new KS steel (Fe-Co-
N i -Al-'f i alloy), alnico magnet (Fe
-At-Ni-Co-(:'u-Ti alloy),
Examples include Pt-Co alloy, Fe-Cr-Co alloy, ferrite magnet, and rare earth magnet. A typical example of the perpendicularly magnetized magnetic material is a Co--Cr film.

Of course, it is also possible to use both the vertical junction electric field and the magnetic field to move holes and electrons in a direction perpendicular to the semiconductor surface.

One of the important features of the present invention is that the reactions of electrons and holes can be limited to specific regions, that is, the site where the ring element reaction occurs and the site where the oxidation reaction occurs. Furthermore, if a substance that acts as a catalyst for the desired reaction is installed, the reaction efficiency will be further improved. Such catalyst materials include Pt, Au, Ru, Os, Rh,
Examples include transition metals such as Fe, Ni, Co, etc., and their oxides.

Further, the semiconductor material used in the present invention is Si.

Ge and InP, GaP, 5ISn3P21
AJtAs, GaAs, CdS.

'1Zns, Cu2S, WS2. CdSe,
Zn5e, WSe, CdTe, ZnTe.

TiO2,5rTi03. Metal phosphides, metal arsenides, metal sulfides, metal selenides, metal tellurides, metal oxides such as ZnQ FetO, and semiconductors in which these semiconductors are combined into ternary or quaternary elements, such as GaA7
As, InGaAs, InGaAsP+ GaA/
AsP, CuIn51. Examples include CuInSe2.

Hereinafter, some of the semiconductors for photochemical reactions according to the present invention will be explained in detail based on Examples.

[Embodiments of the invention]

Example 1 Using a semi-insulating GaAs wafer, a selective ion implantation method was used to form an n region 8 with 3i ions + a p region 10 with Mg ions, and a junction electric field due to a p-1-n junction was applied in a direction parallel to the surface. was formed. The band profile of this semiconductor for photochemical reaction is shown in FIG. 8(a)K. Further, on this wafer, as shown in FIG. 6(b), PT, R, UO, and 8I02 as a window material were deposited as a catalyst material, and a Pi layer 11. Sho.

Layer 12. A photochemical reaction semiconductor device was prepared by providing a uO layer 13.

This semiconductor element for photochemical reaction was immersed in a mixed solution of water and methanol, and under vacuum degassing, the light 1 was 2KWHg.
When the lamp was irradiated for 3 hours, the water decomposition reaction resulted in 0.
5 μmol of hydrogen was generated.

As a comparative example, a semiconductor device for photochemical reaction was fabricated in which a Pt layer and a Ru2O layer were formed in a checkered pattern on the surface of a semi-insulating GaAs wafer. When this semiconductor element for photochemical reaction was immersed in a water-methanol mixed solution and irradiated with a 2 KWHg lamp for 3 hours under vacuum degassing, 0.2 μmol of hydrogen was generated by a water decomposition reaction.

Example 2 Using semi-insulating GaAs uni/・-, selective ion implantation was performed to form n region 8 with Si ions and p region with Mg ions.
A region 10 was formed to form a p-1-n junction electric field in a direction parallel to the surface. At this time, by controlling the implanted current accelerating voltage when forming the n region and the p region and the subsequent annealing process, n+-n-i, p'' are formed from the surface to the inside in each region.
The impurity density was changed so that -p-i, and a junction electric field in the direction perpendicular to the surface was formed. The band profile of this semiconductor is shown in FIG. Furthermore, on the wafer on which this junction electric field was formed, as shown in the same figure (bl), a PT layer 11 is placed on the n-region surface, a Rub layer 1 is placed on the p-region surface,
3. A layer 12 was formed on Si in other regions to form a semiconductor element for photochemical reaction. When such a semiconductor element for a photochemical reaction is irradiated with light, photogenerated electrons and holes are separated in a direction parallel to the surface and transported together to the surface.

When this semiconductor element for photochemical reaction was immersed in a water-methanol mixed solution and irradiated with a 2KwHg lamp for 3 hours under vacuum degassing, it became 1.3μm thick due to water decomposition reaction.
ol hydrogen was generated.

Example 3 Using a non-doped GaAs layer formed on a Si-doped n+ type GaAs wafer by liquid phase epitaxial growth, the n-region 8. Form an n region 1o with Mg ions, and apply a junction electric field due to a p-1-n junction in a direction parallel to the surface of GaA.
It was formed in the s epi layer. By controlling the implanted current, accelerating voltage, and subsequent annealing process when forming the n and n regions, it is possible to form a p-p junction in the direction perpendicular to the surface of the mold in the n region from the surface to the inside. In the n region, the electric field increases from the surface to the inside as n-
A junction electric field was formed in the direction perpendicular to the n-type and the surface connected to the n-type of the wafer. The band profile of this semiconductor is shown in FIG. 10(a). On the front and back surfaces of this semiconductor, as shown in FIG. 2B, a dielectric layer 10 is formed on the n region of the surface, and a layer 10 is formed on the other regions.

When light is irradiated from the front side of a semiconductor element, photo-generated holes move to the front side, and photo-generated electrons move to the back side.

This semiconductor for photochemical reaction was immersed in a water-methanol mixed solution and irradiated with a 2 KWHg lamp for 3 hours under vacuum degassing, and 1.1 μmol of hydrogen was generated by a water decomposition reaction.

Example 4 A 50° Fe film with a thickness of about 1 μm was formed on a glass substrate by sputtering Fe, O, and a target in an Ar atmosphere, and this was further oxidized in the atmosphere to form a γ-Fe20s film. Formed. %Ga on this magnetic film
A GaAs film with a thickness of 0.5 μm was formed by sputtering an As target in an Ar atmosphere.

As shown in FIG. 11, n-region 8 and n-region 1o were formed on this GaAs by selective ion implantation to form a junction electric field in the semiconductor film. Si was used to form the n region, and Mg was used to form the n region. This n area and n
A magnetic head is used to apply periodic alternating magnetic fields in the magnetic film in a direction parallel to the repeating structure of the regions, with opposite directions in the same region and the same direction K at the region interfaces, as shown by the arrows. was formed. This applies an upward force to the plane of the paper on all carriers.

Furthermore, Pt was electron beam evaporated on the n region using a resist, and l'Lu01 was formed on the n region by reactive sputtering.

This was used as a semiconductor element for photochemical reaction, and was immersed in a 1:1 mixed solution of water and methanol, and irradiated with a 2 KW Hg lamp from the semiconductor film side for 3 hours under vacuum degassing. of hydrogen was generated.

Example 5 In the same manner as in Example 4, γ was deposited to form a magnetic film on a glass substrate.
-Fe, 0. After forming the film, a P layer with a thickness of about 0.3 cm is applied on top of this film.
The t-film was formed by electron beam evaporation.

Furthermore, a GaAs film was formed thereon in the same manner as in Example 4. After this, as shown in FIG. 12, an n region 8 and an n region 10 are formed in the direction parallel to the repeated structure of the n region and the n region, as shown by the arrow, the same region name is in the opposite direction. In addition, the magnetic film was magnetized so that the directions were opposite even at the region interface. As a result, a force acts on each carrier so that holes entering the n region move upward in the paper, and electrons entering the n region move downward in the paper, that is, into the PT layer.

Finally, a Rub layer is placed on the n region, and a Sin layer is placed on the n region.
.

formed a layer. This is used as a semiconductor element for photochemical reactions.
When light was irradiated under the same conditions as in Example 4, 1.0 μmol of hydrogen was generated due to water decomposition.

In addition, in semiconductor elements for photochemical reactions having the same configuration as those used in Examples 4 and 5, when the magnetic film is used without special magnetization, hydrogen generation is 0 under the same irradiation conditions.
．． They were 7 μmol and 0.5 μmol.

Example 6 Kumuloy (F) was deposited on a glass substrate by the ivy method.
A Co--Cr perpendicular magnetization film was formed thereon using the vine method. On top of this, a GaAs film was formed in the same manner as in Examples 4 and 5, and the n-region 8 was formed by ion implantation as shown in FIG.
and n region 10 was formed. In the direction parallel to this repeating structure of n-region and n-region, as shown by the arrow in Fig. 13,
A periodic alternating magnetic field having opposite directions in the same region and the same direction at the region interface was induced by magnetizing the perpendicular magnetic film using a perpendicular magnetization magnetic head. This G
A PT film is placed on the n region on the aAs, and a Rub film is placed on the n region.
, formed a film. When this was used as a semiconductor element for photochemical reaction and irradiated with light under the same conditions as in Examples 4 and 5, 1
．． 4 μmol of hydrogen was generated.

Furthermore, when the semiconductor element for photochemical reaction produced in Example 6 is used without special magnetization, the
μmol of hydrogen was generated.

〔Effect of the invention〕

As is clear from the above description, the semiconductor device for photochemical reactions according to the present invention forms a junction electric field in the direction parallel to the semiconductor surface inside, and separates electrons and holes generated by light irradiation in the in-plane direction. By guiding these carriers to a specific area in a planar manner, the recombination of carriers,
Alternatively, by suppressing the reverse reaction of reaction products or intermediates thereof on the semiconductor surface, it has become possible to greatly improve the reaction efficiency for photochemical reactions.

[Brief explanation of the drawing]

FIGS. 1 and 3 are schematic diagrams showing carrier separation in the photochemical reaction semiconductor element ≠≠# according to the present invention, and FIG. 2 (aL
(b) is a schematic diagram showing carrier separation in a semiconductor in the prior art; Figure 4 is a junction band profile diagram that transports carriers in a direction perpendicular to the semiconductor surface; Figure 5 is a diagram showing the relationship between the carrier motion direction and the magnetic field direction. Depending on how they are combined, (a) a schematic diagram showing carriers drifting to one surface, (b) a schematic diagram showing carriers drifting to separate surfaces, and Figure 6 (a) shows a horizontally magnetized film. Representing a shaman figure, (b), (
C), (d) is a schematic diagram showing the direction of the magnetic field in a semiconductor film induced using a horizontally magnetized film, Figure 7 (a) is a schematic diagram showing a vertically magnetized film, (b), (
C1, (d) is a schematic diagram showing the content of the magnetic field in the semiconductor film induced using a perpendicular magnetization film, and (e) is a schematic diagram showing the content of the magnetic field in the semiconductor film induced using a perpendicular magnetization film and a horizontal magnetization film. Figure 8 (a) is a junction profile diagram showing carrier separation in a semiconductor with a junction electric field parallel to the semiconductor surface, and Figure 8 (b) is a diagram showing a structure using a catalytic material. Schematic diagram, Figure 9 (al is a junction showing carrier separation in which a junction electric field is formed perpendicular to the semiconductor surface along with a junction electric field parallel to the semiconductor surface, and both electrons and holes move to the semiconductor surface) Figure 10(a) is a schematic diagram showing a structure using a substance, a junction profile diagram showing carrier generation that moves holes to the surface and electrons to the back surface, and a schematic diagram showing a structure using a covering medium. Figure 11 is a schematic diagram showing the magnetization state of the magnetic film and the arrangement of n+n regions when carrying both carriers on one side of the semiconductor, and Figure 12 is a schematic diagram showing the magnetic film when carriers are separated on both sides of the semiconductor. Figure 13 is a schematic diagram showing the magnetization state and the arrangement of the nvp region when a perpendicular magnetization film is used to transport both carriers to one side of the semiconductor.1 ...Light 2...Semiconductor 3...Metal 4...Semiconductor A 4'...Semiconductor 4"...Semiconductor A"5
...Semiconductor B 6...Magnetic film 7...High magnetic permeability magnetic body 8...N region 9...N region 10...N region 11・PT layer 12・Sin, layer 13-Rub ,
Layer 14...Semiconductor film agent Patent attorney Noriyuki Chika (and 1 other person) Figure 4 Figure 5 <a) tb) Figure 6 (b) (C) Fig. 8 Fig. 9 3 1 fL/'7 V Fig. 10 298 Fig. 13

Claims (1)

[Scope of Claims] (1) A semiconductor element for a photochemical reaction using a semiconductor that causes a redox reaction by light irradiation in the coexistence with a reaction component, wherein the semiconductor is in the form of a film or a plate, and A semiconductor element for photochemical reactions, characterized in that it has a junction electric field that separates photogenerated electrons and holes into a region that causes a reduction reaction and a region that causes an oxidation reaction in the in-plane direction of the semiconductor. (2) The semiconductor for photochemical reactions according to claim 1, wherein the semiconductor has a vertical junction electric field that moves the electrons and holes in a direction perpendicular to the surface of the semiconductor. element. (8) A semiconductor for photochemical reactions according to claim 1, further comprising means for inducing a magnetic field in an in-plane direction perpendicular to the direction in which the electrons and holes are separated by the junction electric field. element. (4) The semiconductor device for photochemical reaction according to claim 3, characterized in that a magnetic material is provided adjacent to the semiconductor as means for inducing the magnetic field. (5) The semiconductor device for photochemical reaction according to any one of claims 1 to 4, wherein a reduction reaction catalyst substance is supported on a portion of the semiconductor that causes a reduction reaction. (6) The semiconductor device for photochemical reactions according to any one of claims 1 to 4, wherein an oxidation reaction catalyst substance is supported on a portion of the semiconductor that causes an oxidation reaction.