JP2008110911A - Oxide sintered compact, its manufacturing method, transparent electroconductive film, and solar cell obtained using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide sintered compact containing zinc oxide as a main component, aluminum, and gallium and its manufacturing method, a target capable of forming a film continuously for a long time without causing an abnormal discharge in a sputtering method or the like, a transparent electroconductive film of high quality with a low resistance and a high transparency obtained by using it, and a solar cell having a high conversion efficiency. <P>SOLUTION: The oxide sintered compact comprises zinc oxide, aluminum and gallium and is substantially composed of a crystalline phase of a wurtzite structure zinc oxide phase and a spinel structure oxide phase wherein (1) the content of aluminum and gallium is 0.3-6.5 atomic% in terms of an atomic ratio (Al+Ga)/(Zn+Al+Ga) and 30-70 atomic% in terms of an atomic ratio Al/(Al+Ga), and (2) the content of aluminum in the spinel structure oxide phase is 10-90 atomic% in terms of an atomic ratio Al/(Al+Ga). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an oxide sintered body, a method for producing the same, a transparent conductive film, and a solar cell obtained by using the oxide sintered body. A target that can be formed continuously for a long time without any abnormal discharge due to the bonded body and its manufacturing method, sputtering method or ion plating method, and a high-quality transparent conductive film with low resistance and high permeability obtained by using it Furthermore, the present invention relates to a high conversion efficiency solar cell using the same.

Transparent conductive films with high conductivity and high transmittance in the visible light region are used for electrodes of solar cells, liquid crystal display elements, and other various light receiving elements, and in addition, heat ray reflection for automobile windows and buildings. It is also used as a transparent heating element for various types of antifogging, such as a film, an antistatic film, and a frozen showcase.
As the transparent conductive film, tin oxide (SnO ₂ ) -based, zinc oxide (ZnO) -based, and indium oxide (In ₂ O ₃ ) -based thin films are known. As the tin oxide, those containing antimony as a dopant (ATO) and those containing fluorine as a dopant (FTO) are used. As the zinc oxide system, those containing aluminum as a dopant (AZO) and those containing gallium as a dopant (GZO) are used. The transparent conductive film most industrially used is an indium oxide type. Indium oxide containing tin as a dopant is called an ITO (Indium-Tin-Oxide) film, and a low resistance film is particularly easy. It has been widely used so far.

The low-resistance transparent conductive film is suitable for surface elements such as solar cells, liquid crystals, organic electroluminescence, and inorganic electroluminescence, touch panels, and the like. A sputtering method or an ion plating method is often used for producing a transparent conductive film useful for these. In particular, the sputtering method is an effective method when forming a material with a low vapor pressure or when precise film thickness control is required, and since the operation is very simple, it is widely used industrially. ing.
The sputtering method is a film forming method using a sputtering target as a thin film raw material. The target is a solid containing a metal element constituting a thin film to be formed, and a sintered body such as a metal, a metal oxide, a metal nitride, or a metal carbide, or a single crystal depending on the case. In this method, a vacuum apparatus is generally evacuated once and then a rare gas such as argon is introduced. Under a gas pressure of about 10 Pa or less, the substrate is the anode and the sputtering target is the cathode. An argon plasma is generated by causing a discharge, and the argon cations in the plasma collide with the sputtering target of the cathode, and particles of target components that are repelled by this are deposited on the substrate to form a film.

Sputtering methods are classified according to the method of generating argon plasma, those using high-frequency plasma are called high-frequency sputtering methods, and those using DC plasma are called DC sputtering methods.
In general, the direct current sputtering method is widely used industrially because the film forming speed is higher than that of the high frequency sputtering method, the power supply equipment is inexpensive, and the film forming operation is simple. However, in contrast to the high-frequency sputtering method, which can form a film even with an insulating target, in the direct current sputtering method, a conductive target must be used.
The deposition rate when depositing using the sputtering method is closely related to the chemical bonding of the target material. The sputtering method uses a phenomenon in which an argon cation having kinetic energy collides with a target surface, and a substance on the target surface receives energy and is ejected. The weaker the probability of popping out by sputtering increases.

  In the method of forming a transparent conductive film of an oxide such as ITO by sputtering, an alloy target of an element constituting the film (In-Sn alloy in the case of an ITO film) is used in a mixed gas of argon and oxygen. A method of forming an oxide film by the reactive sputtering method and an oxide sintered body target of an element constituting the film (In-Sn-O sintered body in the case of an ITO film) of argon and oxygen There is a method of forming an oxide film by a reactive sputtering method in a mixed gas.

Among these, the method using an alloy target supplies a large amount of oxygen gas during sputtering, but the film formation rate and film characteristics (specific resistance, transmittance) are extremely dependent on the amount of oxygen gas introduced during film formation. It is difficult to stably produce a transparent conductive film having a constant film thickness and desired characteristics. On the other hand, in the method using an oxide target, a part of oxygen supplied to the film is supplied by sputtering from the target, and the remaining deficient oxygen amount is supplied as oxygen gas. Therefore, the dependency of the film formation rate and film characteristics (specific resistance, transmittance) on the amount of oxygen gas introduced during film formation is smaller than when using an alloy target, and the film thickness and characteristics are more stable and constant. Since a transparent conductive film can be produced, a method using an oxide target is employed industrially.
In consideration of productivity and manufacturing cost, the direct current sputtering method is easier to form at high speed than the high frequency sputtering method. That is, when the same power is input to the same target and the film formation rates are compared, the direct current sputtering method is about two to three times faster. The direct current sputtering method is also advantageous in terms of productivity because the film formation rate increases as high direct current power is input. For this reason, a sputtering target that can form a film stably even when high DC power is applied industrially is useful.

  On the other hand, ion plating is a method in which the surface of a target material to be a film is locally heated by arc discharge to be sublimated, ionized, and attached to a negatively charged workpiece to form a film. In any case, a film having good adhesion at a low temperature can be obtained, a very wide variety of substrate properties and film properties can be selected, an alloy or a compound can be formed, and the process is environmentally friendly. Even when an oxide film is formed by ion plating, it is the same as sputtering, and a transparent conductive film having a certain film thickness and characteristics can be manufactured more stably by using an oxide sintered body tablet.

  As described above, indium oxide-based materials such as ITO are widely used industrially, but rare metals indium is expensive, and components having toxicity such that the indium element adversely affects the environment and the human body. In recent years, a non-indium-based transparent conductive film material has been demanded. As described above, zinc oxide materials such as GZO and AZO and tin oxide materials such as FTO and ATO are known as non-indium materials. In particular, zinc oxide-based materials are attracting attention as low-cost materials that are abundantly embedded as resources or as materials that are friendly to the environment and the human body.

Among the zinc oxide-based transparent conductive film materials, a method for manufacturing an AZO transparent conductive film that is C-axis oriented by a direct current magnetron sputtering method using a target in which aluminum oxide is mixed with zinc oxide as a main component is proposed. (See Patent Document 1). Further, a sputtering target made of a zinc oxide sintered body containing an element having a positive trivalent or higher valence having a sintered density of 5 g / cm ³ or higher and a specific resistance of 1 Ω · cm or lower has been proposed (see Patent Document 2). ). In these AZO targets, arc deposition (abnormal discharge) frequently occurs when DC sputtering film formation is performed by increasing the power density applied to the target in order to perform film formation at high speed. When arcing occurs in the production process of a film forming line, a film defect occurs or a film having a predetermined film thickness cannot be obtained, making it impossible to stably manufacture a high-quality transparent conductive film. .

  Regarding GZO, a sputtering target made of a zinc oxide sintered body containing gallium produced by a hot press sintering method has been proposed (see Patent Document 3). When this GZO target is used, it is possible to obtain a low-resistance thin film that is less susceptible to abnormal discharge than AZO, but the GZO film attached to the surface other than the target erosion (the portion dug by sputtering) is easily peeled off. Problems such as easy generation of particles occur. When such a particle is generated in the vacuum chamber during continuous film formation in the film formation mass production process, the particles move in the vacuum chamber and adhere to the substrate by the air flow of the film forming gas. When a film is formed on a substrate to which particles are attached, only a film having a defect such as a pinhole is obtained, and a high-quality transparent conductive film cannot be manufactured. Further, if particles are deposited on the erosion portion, it causes arcing. Therefore, in such a case, there is a problem that the operation of the continuous line must be stopped and the removal operation must be performed, and the productivity of the line is greatly reduced.

For this reason, the present applicant has proposed a sputter target in which abnormal discharge is reduced by adding a third element (Ti, Ge, Al, Mg, In, Sn) (see Patent Document 4). Here, the GZO sintered body is mainly composed of a ZnO phase in which at least one selected from the group consisting of Ga, Ti, Ge, Al, Mg, In, and Sn is dissolved at 2 wt% or more. The other constituent phases are a ZnO phase in which at least one of the above is not dissolved, and an intermediate compound phase represented by ZnGa ₂ O ₄ (spinel phase). In such a GZO target to which a third element such as Al is added, the abnormal discharge can surely be reduced as described in Patent Document 4, but the abnormal discharge cannot be completely eliminated. It was. If abnormal discharge occurs even once in the continuous line of film formation, the product at the time of film formation becomes a defective product and affects the production yield, so that a sputter target that does not substantially generate abnormal discharge can be obtained. A sintered body was desired.
JP-A-62-122011 JP-A-2-14959 JP-A-7-138745 Japanese Patent Laid-Open No. 10-306367

  The object of the present invention is to provide an oxide sintered body containing zinc oxide as a main component and further containing aluminum and gallium, and its production method, sputtering method and ion plating method. It is an object of the present invention to provide a target that can be continuously formed for a long time, a low-resistance and high-transparency high-quality transparent conductive film obtained by using the target, and a high conversion efficiency solar cell using the target.

  In order to solve the above-described conventional problems, the present inventors have made extensive studies, and in an oxide sintered body containing zinc oxide as a main component and further containing aluminum and gallium as additive elements, the inclusion of aluminum and gallium By optimizing the amount and optimally controlling the type and composition of the crystalline phase produced during firing, especially the composition of the spinel crystalline phase, particles are less likely to form even when film formation is performed continuously for a long time with a sputtering device. , It is found that a target oxide sintered body that does not cause any abnormal discharge even when high DC power is applied can be obtained, and if this is used, a high-quality transparent conductive film with low resistance and high permeability can be formed. The present invention has been completed by confirming that it can be applied to the production of solar cells with high conversion efficiency.

  That is, according to the first invention of the present invention, an oxide containing zinc oxide, aluminum and gallium, and being substantially composed of a crystal phase of a wurtzite zinc oxide phase and a spinel oxide phase. (1) The content of aluminum and gallium in the oxide sintered body is 0.3 to 6.5 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio, and The content is 30 to 70 atomic% in terms of Al / (Al + Ga) atomic ratio, and (2) the content of aluminum in the spinel type oxide phase is 10 to 90 atoms in terms of Al / (Al + Ga) atomic ratio. % Of oxide sinter is provided.

According to the second invention of the present invention, in the first invention, aluminum and gallium are all contained in the wurtzite zinc oxide phase and / or the spinel oxide phase, and the aluminum oxide phase and the oxide are oxidized. An oxide sintered body characterized by not containing a gallium phase is provided.
Furthermore, according to the third invention of the present invention, there is provided an oxide sintered body characterized in that the spinel oxide phase of zinc aluminate or zinc gallate is not included in the first or second invention. The

  On the other hand, according to the fourth invention of the present invention, in the first to third inventions, after adding and mixing the gallium oxide powder and the aluminum oxide powder to the zinc oxide powder as the raw material powder, A method for producing an oxide sintered body in which a slurry obtained by blending an aqueous medium is pulverized and mixed, then pulverized and mixed, and then the molded body is fired. Is uniformly ground and mixed under conditions sufficient for the standard deviation of the Al / (Al + Ga) atomic ratio to be 25 atomic% or less.

According to the fifth aspect of the present invention, in the fourth aspect, the gallium oxide powder and the aluminum oxide powder contain 0.3 to 6.5 atomic percent in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio. Thus, the manufacturing method of the oxide sintered compact characterized by adding to zinc oxide powder is provided.
Further, according to the sixth invention of the present invention, in the fourth or fifth invention, zinc oxide at a ratio that the gallium oxide powder and the aluminum oxide powder are 30 to 70 atomic% in Al / (Al + Ga) atomic ratio. A method for producing an oxide sintered body characterized by being added to a powder is provided.
According to a seventh aspect of the present invention, there is provided the method for producing an oxide sintered body according to the fourth aspect, wherein the raw material powder is pulverized and mixed using a bead mill. .
According to an eighth aspect of the present invention, there is provided the method for producing an oxide sintered body according to the fourth or seventh aspect, wherein the raw material powder is preliminarily pulverized and mixed by a ball mill. Provided.
Furthermore, according to the ninth invention of the present invention, in the fourth invention, the sintered compact is characterized in that the compact is fired at a temperature of 1250 to 1350 ° C. for 15 to 25 hours under normal pressure. A method of manufacturing a body is provided.

On the other hand, according to a tenth aspect of the present invention, there is provided a target obtained by processing a zinc oxide-based oxide sintered body containing aluminum and gallium, according to any one of the first to third aspects. .
The eleventh invention of the present invention is related to the tenth invention, and provides a transparent conductive film formed on a substrate by sputtering or ion plating using a target.

According to the twelfth aspect of the present invention, in the eleventh aspect, the content of aluminum and gallium is 0.3 to 6.5 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio. A transparent conductive film is provided.
According to a thirteenth aspect of the present invention, in the eleventh or twelfth aspect, the aluminum content is 30 to 70 atomic% in terms of an Al / (Al + Ga) atomic ratio, A membrane is provided.
According to a fourteenth aspect of the present invention, there is provided the transparent conductive film according to the eleventh aspect, wherein the transparent conductive film is substantially composed of a crystal phase substantially composed of a wurtzite zinc oxide phase.
According to the fifteenth aspect of the present invention, in the eleventh aspect, aluminum and gallium are all contained in the wurtzite zinc oxide phase, and do not contain an aluminum oxide phase and a gallium oxide phase. A transparent conductive film is provided.
According to a sixteenth aspect of the present invention, there is provided the transparent conductive film according to the eleventh aspect, wherein the specific resistance is 9.0 × 10 ⁻⁴ Ωcm or less.
According to a seventeenth aspect of the present invention, there is provided the transparent conductive film according to any one of the first to sixteenth aspects, wherein the transmittance of the film itself at a wavelength of 780 to 1200 nm is 76% or more. Is done.
Furthermore, according to an eighteenth aspect of the present invention, there is provided the transparent conductive film according to the eleventh to seventeenth aspects, wherein the substrate is a transparent substrate made of glass or plastic.

On the other hand, according to the nineteenth aspect of the present invention, there is provided a solar cell using the transparent conductive film as an electrode according to the eleventh to seventeenth aspects.
According to a twentieth aspect of the present invention, there is provided a solar cell according to the nineteenth aspect, wherein the photoelectric conversion element is a thin film solar cell using a silicon-based semiconductor or a compound semiconductor. .
According to a twenty-first aspect of the present invention, in the nineteenth aspect, a p-type semiconductor light absorption layer and an n-type semiconductor are provided on a nonmetallic substrate provided with an electrode layer or a metal substrate having electrode properties. There is provided a solar cell including a structure in which an intermediate layer, a semiconductor window layer, and an electrode layer made of the transparent conductive film are sequentially laminated.
According to a twenty-second aspect of the present invention, in the nineteenth aspect, on the electrode layer made of the transparent conductive film on the transparent substrate, a semiconductor window layer, an n-type semiconductor intermediate layer, A solar cell comprising a structure in which p-type semiconductor light absorption layers are sequentially stacked is provided.
According to the twenty-third aspect of the present invention, in the twenty-first or twenty- _{second aspect} , the light absorption layer is at least one selected from CuInSe ₂ , CuInS ₂ , CuGaSe ₂ , CuGaS ₂ , a solid solution thereof, or CdTe. A solar cell is provided.
According to a twenty-fourth aspect of the present invention, in any one of the twenty-first to twenty-third aspects, the intermediate layer is a solution-deposited CdS layer or (Cd, Zn) S layer. Is provided.
Furthermore, according to a twenty-fifth aspect of the present invention, there is provided a solar cell according to any one of the twenty-first to twenty-fourth aspects, wherein the window layer is ZnO or (Zn, Mg) O.

The oxide sintered body of the present invention contains zinc oxide as a main component, but zinc oxide is abundantly embedded as a resource, is a low-cost material, and is also friendly to the environment and the human body. In addition, when a target obtained by processing the oxide sintered body of the present invention is used, even when performing direct current sputtering by increasing direct current power density in order to increase production efficiency, there is a problem with conventional AZO targets and GZO targets. No arcing occurs. Further, even when used in continuous film formation, particles due to film peeling off the surface of the target and the wall of the film formation chamber are less likely to occur. Therefore, mass production film formation with a high yield with almost no defective products is possible in the continuous film formation process, and productivity is greatly improved.
Moreover, the transparent conductive film obtained by sputtering or the like using the oxide sintered body of the present invention is lower in resistance than the conventional AZO film, and the conventional GZO film is not impaired in visible light transmittance. Compared to, the near infrared light transmittance is high. Since a highly conductive transparent conductive film can be obtained without heating the substrate, a low resistance film can also be obtained on an organic material such as a film substrate having poor heat resistance. Furthermore, when used for a transparent electrode such as a solar cell, high energy conversion efficiency can be obtained because of low resistance and high transparency in a wide region from the visible region to the near infrared region. It is also useful as a transparent electrode for touch panels, flat panel displays (LCD, PDP, EL, etc.) and light emitting devices (LED, LD, etc.).

  Hereinafter, the oxide sintered body of the present invention, the target using the oxide sintered body, the transparent conductive film, and the production methods thereof will be described in detail.

1. Oxide Sintered Body The oxide sintered body of the present invention contains zinc oxide, aluminum and gallium, and is substantially composed of a crystal phase of a wurtzite type zinc oxide phase and a spinel type oxide phase. (1) The content of aluminum and gallium in the oxide sintered body is 0.3 to 6.5 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio, and The aluminum content is 30 to 70 atomic% in terms of Al / (Al + Ga) atomic ratio, and (2) the aluminum content in the spinel oxide phase is 10 to 10 in terms of Al / (Al + Ga) atomic ratio. It is characterized by 90 atomic%.

That is, the oxide sintered body of the present invention is an oxide sintered body containing zinc, aluminum and gallium, and the composition is such that the sum of the contents of aluminum and gallium is (Al + Ga) / (Zn + Al + Ga) atoms. The ratio is 0.3 to 6.5 atomic%.
The composition of the transparent conductive film obtained by sputtering or ion plating using the oxide sintered body of the present invention is almost the same as that of the oxide sintered body, but aluminum and gallium in the oxide sintered body are the same. If the sum total of the contents is within this range, a highly conductive transparent conductive film can be obtained even under a wide range of film formation conditions, particularly at room temperature film formation without heating the substrate. When the total content of aluminum and gallium is less than 0.3 atomic%, the amount of generated carrier free electrons in the film is small, so that high conductivity cannot be obtained. In addition, when the total content of aluminum and gallium exceeds 6.5 atomic%, especially in the case of room temperature film formation, the decrease in carrier free electron mobility accompanying the decrease in crystallinity becomes significant, and the high conductivity. This film cannot be obtained.
In particular, a low-resistance transparent conductive film (for example, a specific resistance of 4.9 × 10 ^{−4 to} 9.0 × 10 ⁻⁴ Ωcm at a film thickness of about 200 nm) is obtained under film formation conditions at room temperature without heating the substrate. For this purpose, the total content of aluminum and gallium needs to be 3.2 to 6.5 atomic%.

Regarding the transmittance of the obtained transparent conductive film, in the oxide sintered body in which the total content of aluminum and gallium is in the range of 0.3 to 6.5 atomic%, in the visible region (wavelength 400 to 800 nm). The transmittance is high, and the transmittance of the film itself defined by {(transmittance including substrate) / (transmittance of substrate only)} × 100 (%) is 87% or more. Referring to the transmittance in the near-infrared region (wavelength 800 to 1200 nm), it is particularly excellent when the total content of aluminum and gallium is 0.3 to 3.2 atomic%, and the film thickness is similarly defined at 200 nm. The film itself exhibits a high transmittance of 91 to 94%, and a low-resistance transparent conductive film sufficient for use in a solar cell (for example, at a film thickness of about 200 nm, 9.0 × 10 ⁻⁴ To 3.0 × 10 ⁻³ Ωcm).

  In the oxide sintered body of the present invention, the ratio of aluminum to gallium is 30 to 70 atomic%, preferably 40 to 60 atomic% in terms of Al / (Al + Ga) atomic ratio. When the Al / (Al + Ga) atomic ratio of the oxide sintered body is less than 30 atomic%, as will be described later, the spinel oxidation in which the Al / (Al + Ga) atomic ratio is less than 10 atomic% in the sintered body. A physical phase is generated, and when such an oxide sintered body is used as a target and sputtering is performed for a long time, particles are likely to be generated. Moreover, when the Al / (Al + Ga) atomic ratio of the oxide sintered body exceeds 70 atomic%, the spinel type in which the Al / (Al + Ga) atomic ratio exceeds 90 atomic% in the sintered body, as will be described later. An oxide phase is generated, and arcing tends to occur when direct current sputtering is performed using such an oxide sintered body as a target to increase direct current input power.

  The oxide sintered body of the present invention is composed of a crystal phase, and the crystal phase is substantially a wurtzite zinc oxide phase and a spinel oxide phase. Aluminum content is 10-90 atomic% in Al / (Al + Ga) atomic ratio. The aluminum element and the gallium element are all contained in the wurtzite zinc oxide phase and / or the spinel oxide phase, and do not contain the aluminum oxide phase and the gallium oxide phase. If an aluminum oxide phase or a gallium oxide phase is contained in the oxide sintered body, these are high resistance or insulating materials, which may cause arcing during sputtering film formation. Therefore, the aluminum element and the gallium element do not exist as an aluminum oxide phase or a gallium oxide phase in the oxide sintered body, but are all contained in the wurtzite zinc oxide phase and / or the spinel oxide phase. Need to be.

  In the present invention, the wurtzite type zinc oxide phase in the oxide sintered body refers to a hexagonal wurtzite structure described in JCPDS card 36-1451, and has a non-stoichiometric composition of oxygen deficiency and zinc deficiency. Are also included. Since the zinc oxide phase takes such a non-stoichiometric composition to generate free electrons and increase conductivity, arcing is unlikely to occur during DC sputtering. Further, the wurtzite zinc oxide phase may contain gallium and / or aluminum in solid solution as described above. It is preferable that these are solid-dissolved in the zinc site because carrier electrons are generated and the conductivity is increased, so that arcing is less likely to occur during DC sputtering.

Furthermore, the spinel type oxide phase in the oxide sintered body of the present invention contains zinc, aluminum, and gallium, and the aluminum and gallium in the spinel type oxide phase have Al / (Al + Ga) atoms. The ratio needs to be 10 to 90 atomic%. Therefore, it is a feature of the present invention that the spinel oxide phase of zinc aluminum gallate and zinc gallate is not included independently, and is a spinel type oxide phase in which aluminum and gallium are solid-solved. This is significantly different from the GZO sintered body containing the spinel oxide phase (ZnGa ₂ O ₄ ) of zinc gallate described in Document 4.

In the present invention, the Zn—Al—Ga—O-based spinel oxide phase contained in the oxide sintered body has a composition represented by Zn (Al, Ga) ₂ O _4-δ (δ ≧ 0). If a spinel oxide phase having an Al / (Al + Ga) atomic ratio of less than 10 atomic% is included, particles are generated during film formation, which is not preferable.
If the spinel phase composition in the target contains a spinel phase having an Al / (Al + Ga) atomic ratio of less than 10 atomic%, particles due to peeling of the film deposited on the target surface increase. This is because, when the Al / (Al + Ga) atomic ratio of the spinel crystal phase is less than 10 atomic%, the difference in thermal expansion coefficient between the spinel phase and the zinc oxide deposited film becomes particularly large, and the deposited film is formed by the above-described thermal history. This is considered to be easy to peel.
Therefore, the oxide sintered body of the present invention should not have a spinel phase having a composition with an Al / (Al + Ga) atomic ratio of less than 10 atomic%, and ZnGa ₂ that is particularly easily formed in the sintered body. There must be no zinc gallate spinel compound represented by the composition O _{4 -δ} (δ ≧ 0). In addition, when a spinel phase having an Al / (Al + Ga) atomic ratio exceeding 90 atomic% is present in the oxide sintered body, arcing is likely to occur.
Therefore, in the oxide sintered body of the present invention, a spinel phase having a composition with an Al / (Al + Ga) atomic number ratio exceeding 90 atomic% should not be present. There must be no zinc aluminate spinel compounds represented by the composition of ₂ O _4-δ (δ ≧ 0).

In addition to zinc, aluminum, gallium, and oxygen, the oxide sintered body of the present invention includes other elements (for example, indium, titanium, tungsten, molybdenum, iridium, ruthenium, rhenium, cerium, magnesium, silicon, fluorine, Etc.) may be included as long as the object of the present invention is not impaired.
The oxide sintered body of the present invention can be used not only as a sputtering target but also as a target for ion beam sputtering or laser ablation, or a tablet for vacuum deposition or ion plating.

2. Method for Producing Oxide Sintered Body The method for producing an oxide sintered body according to the present invention comprises adding and mixing a gallium oxide powder and an aluminum oxide powder to a zinc oxide powder as a raw material powder. A method for producing an oxide sintered body in which a slurry obtained by blending an aqueous medium is pulverized and mixed, then pulverized and mixed, and then the molded body is fired. Is uniformly pulverized and mixed under conditions sufficient for the standard deviation of the Al / (Al + Ga) atomic ratio to be 25 atomic% or less.

  As described above, an oxide sintered body containing zinc, aluminum, and gallium is substantially composed of a crystal phase of a wurtzite type zinc oxide phase and a spinel type oxide phase. , The wurtzite type zinc oxide phase and / or the spinel type oxide phase are all contained, and the spinel type oxide phase contains zinc, aluminum and gallium, and the composition thereof is Al / (Al + Ga). It has characteristics such as a ratio of 10 to 90 atomic% in atomic ratio. In order to manufacture such an oxide sintered body, it is necessary to control manufacturing conditions as described below.

  Oxide sintered bodies containing zinc, aluminum and gallium are made of zinc oxide, aluminum oxide and gallium oxide powders, mixed and molded to form a green compact, which is fired at a high temperature. , Made by reaction and sintering. Each powder of zinc oxide, aluminum oxide, and gallium oxide is not special and may be a conventionally used raw material for oxide sintered bodies. The average particle diameter of the powder used is 1.5 μm or less, preferably 0.1 to 1.1 μm.

In general, as described in Patent Document 4, a ball mill mixing method is used as a method for mixing raw material powders when manufacturing an oxide sintered body. The ball mill is a device for producing a fine mixed powder by grinding and mixing materials by putting a hard ball (ball diameter: 10 to 30 mm) such as ceramic and powder of the material into a container and rotating. Ball mills (grinding media) include steel, stainless steel, and nylon as can bodies, and alumina, magnetic material, natural silica, rubber, urethane, etc. are used as linings. Examples of the balls include alumina balls containing alumina as a main component, natural silica, nylon balls with iron core, and zirconia balls. There are wet and dry pulverization methods, and they are widely used for mixing and pulverizing raw material powders to obtain sintered bodies.
However, in order to obtain the oxide sintered body of the present invention, mixing and pulverization of the raw material powder by the ball mill method is insufficient. In the mixing and pulverization of the raw material powder by the ball mill, σ may exceed 25 atomic% in the above-described uniformity evaluation method, and a highly uniform mixed raw material powder having σ of 25 atomic% or less cannot be obtained. A bead mill method or a jet mill method is effective for obtaining a highly uniform mixed raw material powder having σ of 25 atomic% or less.

In the bead mill method, 70-90% of beads (crushed media, bead diameter: 0.005-3 mm) are filled in a container called a vessel, and the rotation axis at the center of the vessel is set at a peripheral speed of 7-15 m / sec. Giving motion to the beads by rotating. The slurry which mixed the to-be-ground materials, such as raw material powder, with the liquid here is sent with a pump, and it pulverizes and disperses by making a bead collide. In the case of a bead mill, efficiency can be improved by reducing the bead diameter according to the object to be crushed. In general, a bead mill can achieve pulverization and mixing at an acceleration close to 1,000 times that of a ball mill. The bead mill with such a structure is called by various names. For example, sand grinder, aquamizer, attritor, pearl mill, avex mill, ultra visco mill, dyno mill, agitator mill, coball mill, spike mill, SC mill Are known, and any of them can be used in the present invention.
In addition, a jet mill is a method in which an object to be crushed, such as raw material powder, is crushed into fine particles by impact between particles by colliding the particles with high-pressure air or steam jetted from a nozzle at around sonic speed as an ultra-high speed jet. it can.

  When using fine and non-agglomerated raw material powder, the oxide sintered body of the present invention can be obtained by finely pulverizing and mixing only by the bead mill method or the jet mill method. However, after pulverizing and mixing by the ball mill method and then finely pulverizing and mixing by the bead mill method, the oxide sintered body of the present invention can be surely obtained. As described above, the oxide sintered body of the present invention can be preferably manufactured as follows, for example, by a method using both a ball mill and a bead mill.

First, zinc oxide powder, aluminum oxide powder, and gallium oxide powder as raw material powders are put into a ball mill pot at a desired ratio, and mixed powder is prepared by dry or wet mixing.
In order to obtain the oxide sintered body of the present invention, the mixing ratio of the raw material powder is such that the content of aluminum and gallium is 0.3 to 6.5 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio. It is preferable that aluminum and gallium have an Al / (Al + Ga) atomic number ratio of 30 to 70 atomic%.

A slurry is produced by adding water and organic substances such as a dispersing agent and a binder to the powder thus obtained. The viscosity of the slurry is preferably 150 to 5000 cP, more preferably 400 to 3000 cP.
Next, the obtained slurry and beads are placed in a bead mill container and processed. Examples of the bead material include zirconia and alumina. Zirconia is preferable from the viewpoint of wear resistance. The diameter of the beads is preferably 1 to 3 mm from the viewpoint of grinding efficiency. The number of passes may be one, but is preferably two or more, and a sufficient effect can be obtained by five or less. Moreover, as processing time, Preferably it is 10 hours or less, More preferably, it is 4 to 8 hours.
By performing such treatment, the pulverization and mixing of the zinc oxide powder, aluminum oxide powder and gallium oxide powder in the slurry is improved, and the relative uniformity of aluminum and gallium in the slurry before firing is Get higher. The uniformity of the aluminum and gallium needs to be mixed and pulverized until the Al / (Al + Ga) atomic ratio is 25 atomic% or less in standard deviation when the molded body described below is formed. By using such a slurry, homogenization further proceeds during firing, and the oxide sintered body of the present invention can be obtained.

Next, it shape | molds using the slurry processed in this way. As the molding method, either a cast molding method or a press molding method can be employed. When cast molding is performed, the obtained slurry is injected into a casting mold to produce a molded body. The time from the bead mill treatment to casting is preferably within 10 hours. By carrying out like this, it can prevent that the obtained slurry shows thixotropic property. When performing press molding, a binder such as polyvinyl alcohol is added to the obtained slurry, moisture is adjusted as necessary, and then dried with a spray dryer or the like to obtain a powder. After filling the obtained powder into a metal mold of a predetermined size, it is pressed at a pressure of 100 to 300 kg / cm ² using a press machine to obtain a molded body. When the uniformity evaluation of the Al / (Al + Ga) atomic number ratio is performed by the above method using this molded body, uniformity with σ of 25 atomic% or less can be obtained. The thickness of the molded body at this time is set to a thickness at which a sintered body having a thickness of 10 mm or more can be obtained in consideration of shrinkage caused by the subsequent CIP process or firing process.

Next, the molded body thus obtained is subjected to treatment by cold isostatic pressing (CIP) as necessary. At this time, since the pressure of the CIP to obtain a sufficient compaction effect 1 ton / cm ² or more, it is desirable that preferably is 2~5ton / cm ^2. If the molded body produced from the above-mentioned mixed powder is used, the oxide sintered body of the present invention can be obtained by a hot pressing method or a normal pressure sintering method as a firing method. However, it is preferable to produce by a normal pressure sintering method that can produce a large sintered body at a low production cost.

  In the case of obtaining an oxide sintered body by firing by the normal pressure sintering method, the following is performed. The obtained molded body is debindered at a temperature of 300 to 500 ° C. for about 5 to 20 hours, and then fired. The rate of temperature rise is set to 150 ° C./hour or less, preferably 100 ° C./hour or less, and more preferably 80 ° C./hour or less in order to effectively release internal vacancies to the outside. The sintering temperature is 1200 to 1600 ° C, preferably 1200 to 1400 ° C, more preferably 1250 to 1350 ° C, and sintering is performed for 5 to 40 hours, preferably 10 to 30 hours, more preferably 15 to 25 hours. . After sintering, when introducing oxygen, the introduction of oxygen is stopped and the temperature up to 1000 ° C. is 0.1 to 8 ° C./min, preferably 0.2 to 5 ° C./min, particularly preferably 0.2 to 1 ° C./min. It is preferable to lower the temperature at a temperature falling rate within the range. By doing so, the oxide sintered body of the present invention as described above can be obtained.

  In accordance with the process described above, fine raw material powder is used, and sufficient pulverization and mixing using a bead mill is always performed, and if sintering is performed at a sintering temperature sufficient for diffusion to proceed, oxidation A spinel type composition that does not contain an aluminum oxide phase or a gallium oxide phase in the sintered product, and further deviates from a ratio of 10 to 90 atomic% in terms of the number ratio of Al / (Al + Ga) atoms such as zinc aluminate and zinc gallate An oxide sintered body containing no oxide phase (Zn—Al—Ga—O system) can be obtained. That is, the sum of the contents of aluminum and gallium in the oxide sintered body is 0.3 to 6.5 atomic% in terms of the (Al + Ga) / (Zn + Al + Ga) atomic ratio, and the oxide sintered body is a wurtzite type. It is composed of a zinc oxide phase and a spinel oxide phase, and the composition of the spinel oxide phase (Zn—Al—Ga—O system) in the oxide sintered body is 10 in terms of the Al / (Al + Ga) atomic ratio. The oxide sintered body of the present invention having characteristics such as a ratio of ˜90 atomic% can be produced.

During this firing, a wurtzite zinc oxide phase in which aluminum or gallium is dissolved, or a spinel phase having a simple composition such as ZnAl ₂ O _4-δ (δ ≧ 0) or ZnGa ₂ O _4-δ (δ ≧ 0) is immediately obtained. Formed. As the firing time progresses, the composition of each crystal phase is made uniform by diffusion, but a spinel phase having a composition in which the Al / (Al + Ga) atomic ratio deviates from the range of 10 to 90 atomic% is generated. There is. The factors that occur in the sintered body are as follows.
Uniformity due to diffusion during firing in a solid solution is very slow between ions of the same valence. In the case of Zn (Al, Ga) ₂ O _4-δ (δ ≧ 0), the same site is occupied and the valence is mutually increased. The nonuniformity between Al ions and Ga ions having the same number is stable because it does not break the charge balance, and the homogenization by diffusion during firing is very slow.
If the compositional deviation in the mixed raw material powder is too large, homogenization due to diffusion during firing becomes insufficient, and a sintered body with a large compositional variation is obtained. In particular, the uniformity between Al ions and Ga ions having the same valence is likely to be affected by the nonuniformity of Al and Ga in the mixed raw material powder. In other words, due to insufficient mixing, if there is a part in which the aluminum oxide particles are much more than gallium oxide in the green compact before firing, an aluminum oxide phase, ZnAl ₂ O _4-δ (δ ≧ The spinel phase (hereinafter sometimes referred to as ZAO phase) having a large aluminum composition centering on 0) is contained in the sintered body even after firing. On the contrary, if there is a portion with a large amount of gallium oxide powder, a gallium oxide phase or a spinel phase with a large gallium composition centered on ZnGa ₂ O _{4 -δ} (δ ≧ 0) (hereinafter sometimes referred to as a ZGO phase) Will be contained in the sintered body after firing. Al ions and Ga ions are diffused between the ZAO phase and the ZGO phase, but because of the same valence, diffusion for homogenization is slow, reflecting the local bias of aluminum and gallium in the mixed raw material powder. Thus, an oxide sintered body in which the ZAO phase and the ZGO phase are distributed is obtained.

In order to reduce the compositional deviation in the mixed raw material powder, it is important to mix and pulverize the aluminum oxide powder and the gallium oxide powder among the raw material powder. Uniform mixing between gallium is particularly important.
The uniformity of the mixed raw material powder before firing can be evaluated by the following method. Using a mixed raw material powder to produce a compact and observing the fractured surface with a scanning electron microscope, using an attached energy dispersive X-ray analyzer (EDX) to irradiate an electron beam to about 1 μmΦ The composition analysis of the minute region is performed, and the Al / (Al + Ga) atomic ratio in the region is grasped. The Al / (Al + Ga) atomic ratio is measured at an arbitrary 50 points, and the standard deviation σ is obtained. The higher the uniformity, the smaller the σ. In order to obtain the oxide sintered body of the present invention, it is necessary that σ is 25 atomic% or less.

3. Target The oxide sintered body produced by the above method is processed by surface grinding or the like to obtain a predetermined dimension, and then bonded to a backing plate made of oxygen-free copper by using indium solder or the like, thereby sputtering. It can be a target (also referred to as a single target). If necessary, several sintered bodies may be divided into divided shapes to form a large area target.
In the present invention, the target is used when producing a transparent conductive film containing zinc oxide as a main component by a gas phase synthesis method represented by sputtering. By using this target, the input power density is increased and high speed is achieved. Even when DC sputtering film formation is performed, abnormal discharge such as arcing does not occur at all, and even when the film is continuously formed for a long time, particles due to peeling of the film attached to the target surface are hardly generated.

  In the present invention, the target is a processed oxide sintered body containing zinc oxide, aluminum and gallium, and substantially composed of a crystal phase of a wurtzite zinc oxide phase and a spinel oxide phase. The content of aluminum and gallium is 0.3 to 6.5 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio, and the ratio of aluminum to gallium is Al / (Al + Ga) atomic number. The ratio is 30 to 70 atomic%. Aluminum and gallium are all contained in the wurtzite type zinc oxide phase and / or the spinel type oxide phase, and do not contain the aluminum oxide phase and the gallium oxide phase.

Aluminum and gallium are contained in the spinel-type oxide phase at a ratio of Al / (Al + Ga) atomic ratio of 10 to 90 atomic%, including zinc aluminate and zinc gallate spinel oxide phase. Not. The Zn—Al—Ga—O-based spinel oxide phase contained in this oxide sintered body has a composition represented by Zn (Al, Ga) ₂ O _4-δ (δ ≧ 0), When a spinel oxide phase having an Al / (Al + Ga) atomic ratio of less than 10 atomic% is included, particles are generated during film formation, which is not preferable. If particles are generated during film formation, they will adhere to the substrate and cause film defects, or if they are deposited on the erosion portion of the target, arcing will occur.

  Particles generated during film formation occur by the following mechanism. In sputtering film formation, the sputtered particles fly toward the substrate mounted on the opposite side of the target, but some of the sputtered particles collide with the sputter gas particles and return to the target surface. come. The returning sputtered particles are deposited mainly on a non-erosion portion (erosion portion: a portion that can be cut by sputtering) that is not sputtered on the target surface to form a thin film. This deposited film is a crystal film of a zinc oxide phase in which Al and Ga are dissolved when a target of an oxide sintered body of Zn, Al, and Ga is used. The surface of the target sintered body is composed of a zinc oxide crystal phase in which Al and Ga are dissolved, and a Zn—Al—Ga—O spinel crystal phase, on which a thin film is deposited. During film formation, the target surface is heated to receive heat radiation from the plasma, but is cooled when film formation is completed. The target surface and the deposited film undergo thermal expansion and contraction during heating and cooling. The difference in thermal expansion and contraction between the zinc oxide phase in the target and the zinc oxide phase in the deposited film is relatively small because of the same crystal structure, but the spinel crystal phase in the target and the zinc oxide phase in the deposited film are relatively small. The difference in thermal expansion and contraction is relatively large, and the difference greatly depends on the composition of the spinel crystal phase.

In the present invention, if the composition of the spinel phase in the target is less than 10 atomic% in terms of the Al / (Al + Ga) atomic ratio, particles tend to increase due to peeling of the film deposited on the target surface.
This is because when the Al / (Al + Ga) atomic ratio is less than 10 atomic%, the difference in thermal expansion coefficient between the spinel phase and the zinc oxide deposited film becomes particularly large, and the deposited film is easily peeled off due to the above-described thermal history. This is probably because of this. In most cases, during cooling after film formation, the deposited film is subjected to strong stress due to the difference in thermal contraction between the spinel phase and the deposited film, and peels off to become particles. In addition, if the oxide sintered body includes a spinel phase having an Al / (Al + Ga) atomic ratio exceeding 90 atomic%, arcing is likely to occur.
The reason is that a spinel phase with an Al / (Al + Ga) atomic ratio exceeding 90 atomic% has a high resistance. Therefore, using a target of an oxide sintered body in which such a spinel phase exists, a high DC power is used. When the deposited sputtering film is formed, it is considered that the high resistance spinel phase is charged by irradiation with argon ions, causing dielectric breakdown and easily causing arcing.

4). Transparent conductive film and manufacturing method thereof The transparent conductive film of the present invention is formed on a substrate by sputtering or ion plating using the above target in a film forming apparatus. In particular, the direct current (DC) sputtering method is industrially advantageous because it has less thermal influence during film formation and enables high-speed film formation.

  Since the transparent conductive film of the present invention is formed using the oxide sintered body as a raw material, the composition of the oxide sintered body is reflected. That is, a transparent conductive film containing zinc oxide as a main component and further containing aluminum and gallium. (1) The total content of aluminum and gallium is 0.3 in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio. -6.5 atomic%, and aluminum and gallium are 30-70 atomic% in Al / (Al + Ga) atomic ratio, and (2) the transparent conductive film is composed of a crystalline phase. Moreover, it is preferable that the crystal phase of the transparent conductive film of the present invention is substantially composed of a wurtzite zinc oxide phase, and the aluminum element and the gallium element are all contained in the wurtzite zinc oxide phase.

  Further, the obtained wurtzite type zinc oxide phase is c-axis oriented in a direction perpendicular to the substrate such as glass. The better the crystallinity (the larger the crystal grain), the faster the mobility of carrier electrons, and thus the better the conductivity. As the conductivity of the zinc oxide-based transparent conductive film, the higher the film thickness, the higher the conductivity. This is because when the film thickness is large, the crystallinity of the film is improved and the mobility of carrier electrons is increased.

In the present invention, a target obtained from the oxide sintered body is used, and a sputtering condition such as a specific substrate temperature, pressure, oxygen concentration, etc. is adopted, and the substrate is made of zinc oxide containing aluminum and gallium. A transparent conductive film can be formed. The composition of the transparent conductive film obtained by sputtering or ion plating using the oxide sintered body of the present invention is the same as the composition of the oxide sintered body.
The substrate is not particularly limited by the material such as glass, resin, metal, ceramic, and may be transparent or non-transparent, but a transparent substrate is preferable. In the case of a resin, those having various shapes such as a plate shape and a film can be used.

As described above, the composition of the target (oxide sintered body) is such that the total content of aluminum and gallium is 0.3 to 6.5 atomic% in terms of the (Al + Ga) / (Zn + Al + Ga) atomic ratio. In particular, a low-resistance transparent conductive film (for example, a specific resistance of 4.9 × 10 ^{−4 to} 9.0 × 10 ⁻⁴ Ωcm at a film thickness of about 200 nm) is obtained under film formation conditions at room temperature without heating the substrate. For this purpose, the total content of aluminum and gallium needs to be 3.2 to 6.5 atomic%.

Regarding the transmittance of the obtained transparent conductive film, in the oxide sintered body in which the total content of aluminum and gallium is in the range of 0.3 to 6.5 atomic%, in the visible region (wavelength 400 to 800 nm). The transmittance is high, and the transmittance of the film itself defined by {(transmittance including substrate) / (transmittance of substrate only)} × 100 (%) is 87% or more. Referring to the transmittance in the near-infrared region (wavelength 800 to 1200 nm), it is particularly excellent when the total content of aluminum and gallium is 0.3 to 3.2 atomic%, and the film thickness is similarly defined at 200 nm. The film itself exhibits a high transmittance of 91 to 94%, and a low-resistance transparent conductive film sufficient for use in a solar cell (for example, at a film thickness of about 200 nm, 9.0 × 10 ⁻⁴ To 3.0 × 10 ⁻³ Ωcm).

  A transparent conductive film manufactured from such an oxide sintered body containing zinc, aluminum, and gallium by sputtering is composed mainly of zinc oxide in which aluminum ions and gallium ions are substituted into zinc ion sites as dopants. It is a conductive crystalline thin film of type semiconductor. Aluminum ions and gallium ions are positively trivalent, and by replacing these positively divalent zinc ion sites, carrier free electrons in the film can be generated to increase conductivity.

In the present invention, the composition of the target stipulates that the total content of aluminum and gallium is 0.3 to 6.5 atomic% in terms of the (Al + Ga) / (Zn + Al + Ga) atomic ratio. Even under a wide range of film forming conditions, a highly conductive transparent conductive film can be obtained even at room temperature film formation without heating the substrate, and the transmittance in the visible region is also high.
When the total content of aluminum and gallium is less than 0.3 atomic%, the amount of generated carrier free electrons in the film is small, so that high conductivity cannot be obtained. In addition, when the total content of aluminum and gallium exceeds 6.5 atomic%, a highly conductive film cannot be obtained particularly at room temperature.
In the case of room temperature film formation, the amount of dopant is too large to be completely dissolved in the zinc oxide phase, and aluminum and gallium compounds are precipitated at the grain boundaries, resulting in poor crystallinity of the thin film, and the mobility of carrier electrons The deterioration of conductivity due to the decrease is remarkable. If the film is formed while heating the substrate to 400 to 500 ° C., a highly conductive transparent conductive film can be obtained up to the addition of 13 atomic%. However, such high temperature film formation is a special film formation condition. In order to obtain a highly transparent conductive film under a wide range of film formation conditions including room temperature film formation, the sum of the contents of aluminum and gallium is 0.3 to 6.6 in terms of the (Al + Ga) / (Zn + Al + Ga) atomic ratio. It is necessary to use a target that is 5 atomic%.
In particular, a low-resistance transparent conductive film (for example, a specific resistance of 4.9 × 10 ^{−4 to} 9.0 × 10 ⁻⁴ Ωcm at a film thickness of about 200 nm) is obtained under film formation conditions at room temperature without heating the substrate. For this purpose, the total content of aluminum and gallium needs to be 3.2 to 6.5 atomic%.

Regarding the transmittance of the obtained transparent conductive film, in the oxide sintered body in which the total content of aluminum and gallium is in the range of 0.3 to 6.5 atomic%, in the visible region (wavelength 400 to 800 nm). The transmittance is high, and the transmittance of the film itself defined by {(transmittance including substrate) / (transmittance of substrate only)} × 100 (%) is 87% or more.
When the transmittance in the near infrared region (wavelength 800 to 1200 nm) is mentioned, it is particularly excellent when the (Al + Ga) / (Zn + Al + Ga) atomic ratio of the film is 0.3 to 3.2 atomic%, and the film thickness is 200 nm. A transparent conductive film having a low resistance sufficient for use in a solar cell (e.g., 9.0 at a film thickness of about 200 nm) while exhibiting high transmittance of 91 to 94% with the transmittance of the film itself similarly defined in FIG. X10 ^{−4 to} 3.0 × 10 ⁻³ Ωcm).

In the present invention, it is preferable to use DC sputtering by using an inert gas such as argon as the sputtering gas. For example, after evacuating to 5 × 10 ⁻⁵ Pa or less, pure Ar gas is introduced, and the gas pressure is set to 0.1 to 1 Pa, particularly 0.2 to 0.8 Pa, and 0.55 to 4.7 W / cm ^2. The DC power density (DC input power / target area) can be applied to generate DC plasma and pre-sputtering can be performed. After performing this pre-sputtering for 5 to 30 minutes, it is preferable to perform sputtering after correcting the substrate position if necessary. When the target obtained from the oxide sintered body of the present invention is used, high-speed film formation can be stably performed without causing any abnormal discharge such as arcing even when a high DC power of 4.7 W / cm ² is applied. Can do.

The conductivity of the zinc oxide-based transparent conductive film greatly depends on the substrate heating temperature during film formation. This is because when the substrate heating temperature is high, the crystallinity of the film is improved and the mobility of carrier electrons is increased. In the present invention, a film can be formed without heating the substrate, but the substrate can also be heated to 50 to 300 ° C., particularly 80 to 200 ° C. When the film is formed by heating the substrate, the crystallinity of the obtained transparent conductive film is improved, and excellent conductivity can be realized due to the above-described factors. However, when the substrate has a low melting point such as a resin plate or resin film, it is desirable to form the film without heating.
If the sputtering target produced from the oxide sintered body of the present invention is used, there is less concern about resource depletion, and a ZnO-based transparent conductive film that is inexpensive and excellent in electrical conductivity can be arced by DC sputtering with high input power. It can be stably produced on the substrate without generating, and the production cost can be greatly reduced.

  The transparent conductive film of the present invention has a low resistance compared to a conventional AZO film, and has a higher transmittance in the visible region to the near infrared region than a conventional GZO film. The average transmittance in the visible region (wavelength 400 to 800 nm) including the substrate is 85% or more, and the average transmittance in the near infrared region of the wavelength 800 to 1200 nm including the substrate is 80% or more. That is, when the transmittance of the film itself is defined by {(transmittance including the substrate) / (transmittance of the substrate only)} × 100 (%), the average transmittance of the film itself of the transparent conductive film of the present invention is , 87% or more at a wavelength of 400 to 800 nm, and 88% or more at a wavelength of 800 to 1200 nm. Therefore, it is useful as a transparent electrode of a high-efficiency solar cell that effectively uses solar energy from the visible range to the near-infrared range.

In addition, when a tablet for ion plating (also referred to as a pellet or a target) produced from the oxide sintered body is used, a similar transparent conductive film can be formed. In the ion plating method, when a tablet as an evaporation source is irradiated with heat by an electron beam or arc discharge, the irradiated portion becomes locally high in temperature, and evaporated particles are evaporated and deposited on the substrate. At this time, the evaporated particles are ionized by an electron beam or arc discharge. There are various ionization methods. The high-density plasma-assisted deposition method (HDPE method) using a plasma generator (plasma gun) is suitable for forming a high-quality transparent conductive film. In this method, arc discharge using a plasma gun is used. Arc discharge is maintained between the cathode built in the plasma gun and the crucible (anode) of the evaporation source. Electrons emitted from the cathode are introduced into the crucible by magnetic field deflection, and concentrated and irradiated on the local part of the tablet charged in the crucible. By this electron beam, the evaporated particles are evaporated and deposited on the substrate from the portion where the temperature is locally high. Since vaporized evaporated particles and O ₂ gas introduced as a reaction gas are ionized and activated in the plasma, a high-quality transparent conductive film can be produced.
According to the present invention, a transparent conductive film having a low resistance can be manufactured without impairing visible light transmittance as compared with a conventional AZO film. In addition, since a highly conductive transparent conductive film can be obtained without heating the substrate, a low resistance film can be obtained on an organic substance such as a film substrate having poor heat resistance.

5. Solar cell The solar cell of the present invention is a photoelectric conversion element using the transparent conductive film as an electrode. The structure of the photoelectric conversion element is not particularly limited, and is a PN junction type in which a p-type semiconductor and an n-type semiconductor are stacked, a PIN junction type in which an insulating layer (I layer) is interposed between the p-type semiconductor and the n-type semiconductor, or And a hybrid in which a plurality of these types of joints are stacked.

These photoelectric conversion elements have electrodes formed on both sides. The solar cell of the present invention uses the transparent conductive film of the present invention for at least one of the electrodes on both sides. A transparent electrode is indispensable for the electrode on the side where sunlight enters, and it is effective to use the transparent conductive film of the present invention. Moreover, although the metal electrode may be used for the electrode on the side where sunlight does not enter, it is effective to use the laminated film of the transparent conductive film (photoelectric conversion element side) and the metal film of the present invention. In this case, sunlight passing through the PN or the photoelectric conversion element is confined by the transparent conductive film between the photoelectric conversion element and the metal film, and is photoelectrically converted. If the transparent conductive film of the present invention is used, light loss is caused. It is effective because there are few.
In the case where the photoelectric conversion element is formed as a thin film, the photoelectric conversion element is provided on a substrate such as glass or metal. However, the solar cell of the present invention is not limited to the stacking order of the PN junction and the PIN junction on the substrate. That is, in the solar cell of the present invention, the transparent conductive film of the present invention may be provided between the photoelectric conversion element and the substrate, but may be provided on the surface side of the photoelectric conversion element, or may be provided on both. In some cases, both are valid.

Solar cells are broadly classified according to the type of semiconductor. Solar cells using silicon-based semiconductors such as single crystal silicon, polycrystalline silicon, microcrystalline silicon, and amorphous silicon, and CuInSe and Cu (In, Ga) Se are used. Thin films of compound semiconductors typified by Pt, Ag (In, Ga) Se, CuInS, Cu (In, Ga) S, Ag (In, Ga) S, solid solutions thereof, GaAs, CdTe, and the like Are classified into a compound thin film solar cell using a dye and a dye-sensitized solar cell using an organic dye (also called a Gretzel cell solar cell), but the solar cell of the present invention is included in any case, and High efficiency can be realized by using a transparent conductive film as an electrode.
In particular, in a solar cell or a compound thin film solar cell using amorphous silicon or microcrystalline silicon, a transparent conductive film is indispensable for the electrode on which sunlight is incident (light receiving unit side, front side). By using a transparent conductive film, high conversion efficiency characteristics can be exhibited. A structure in which amorphous silicon photoelectric conversion elements and microcrystalline silicon photoelectric conversion elements are stacked, a structure in which amorphous silicon photoelectric conversion elements and single crystal silicon photoelectric conversion elements are stacked, amorphous silicon photoelectric conversion elements and polycrystals A structure in which a photoelectric conversion element of silicon is laminated, a structure in which a photoelectric conversion element of microcrystalline silicon and a photoelectric conversion element of single crystal silicon are laminated, a photoelectric conversion element of microcrystalline silicon and a photoelectric conversion element of polycrystalline silicon are laminated. A transparent conductive film is indispensable even in a hybrid type such as a structure, and high conversion efficiency can be exhibited by using the transparent conductive film of the present invention.

  When these silicon-based solar cells are outlined, a PN junction solar cell element can use, for example, a monocrystalline or polycrystalline silicon substrate having a thickness of about 0.2 to 0.5 mm and a size of about 180 mm square, Inside the silicon substrate of the element, a PN junction is formed in which a P layer containing a large amount of P-type impurities such as boron and an N layer containing a large amount of N-type impurities such as phosphorus are in contact. Further, a transparent substrate such as a glass plate, a resin plate, or a resin film is also used instead of the silicon substrate. In the present invention, a transparent substrate is preferable. In that case, after forming the transparent conductive film of the present invention as an electrode on a substrate, an amorphous or microcrystalline silicon thin film is laminated. Amorphous or microcrystalline silicon can be formed in a thin film at a relatively low temperature on a substrate such as glass or resin using silane gas.

  In the case of an amorphous or microcrystalline silicon thin film, for example, as shown in FIG. 1, a PIN junction in which an insulating layer (I layer) is interposed between PN junctions. On the glass substrate 1, a front side (light receiving part side) transparent electrode film 2, a p-type amorphous silicon film or hydrogenated amorphous silicon carbide film 3, an amorphous silicon film 4 containing no impurities, and an n-type amorphous silicon film 5 And the back side transparent electrode film (contact improvement layer) 6 and the back side metal electrode, ie, the back surface electrode 7, are laminated | stacked. The p-type amorphous silicon film or hydrogenated amorphous silicon carbide film 3, the amorphous silicon film 4 containing no impurities, and the n-type amorphous silicon film 5 are usually formed by a plasma CVD method.

  Next, the compound thin film solar cell will be described in detail. A solar cell using a compound thin film is usually composed of a heterojunction of a compound semiconductor thin film (n-type semiconductor intermediate layer) having a wide band gap and a compound semiconductor (p-type semiconductor light absorbing layer) having a narrow band gap. ing. As shown in FIG. 2, the general structure is “surface electrode (transparent conductive film) / window layer / intermediate layer / light absorption layer / back electrode (metal or transparent conductive film)”. Specifically, as shown in FIG. 2, the transparent electrode film 11 of the present invention, the ZnO thin film of the window layer 10, the semiconductor intermediate layer 9, the light absorption layer 8 of the p-type semiconductor, The Au film of the back electrode 7 is laminated. FIG. 3 also shows a lower electrode, that is, a back electrode 13, a p-type semiconductor light absorption layer 8, a semiconductor intermediate layer 9, a window layer 10, and a zinc oxide-based material according to the present invention. The transparent electrode film 11 is laminated. In any structure, the transparent electrode film 11 side is the incident direction of sunlight.

As described above, the substrate is not particularly limited by the material such as glass, resin, metal, ceramic, and may be transparent or non-transparent, but a transparent substrate is preferable. In the case of a resin, those having various shapes such as a plate shape and a film can be used. In the case of a metal, examples of the ceramic such as stainless steel and aluminum include alumina, zinc oxide, carbon, silicon nitride, and silicon carbide. As oxides other than alumina and zinc oxide, oxides selected from Ga, Y, In, La, Si, Ti, Ge, Zr, Sn, Nb or Ta may be used. Examples of these oxides include Ga ₂ O ₃ , Y ₂ O ₃ , In ₂ O ₃ , La ₂ O ₃ , SiO ₂ , TiO ₂ , GeO ₂ , ZrO ₂ , SnO ₂ , Nb ₂ O ₅ , Ta. ₂ O ₅ etc. can be mentioned. In the present invention, these glass, resin, and ceramic substrates are referred to as non-metallic substrates. It is desirable that the surface of the substrate is provided with a mountain-shaped unevenness on at least one side, and is roughened by etching or the like so as to easily reflect incident sunlight.

  As the back electrode 13, a conductive electrode material such as Mo, Ag, Au, Al, Ti, Pd, Ni, or an alloy thereof is used, and any of Mo, Ag, Au, or Al is preferable. Usually, the thickness is 0.5 to 5 μm, preferably 1 to 3 μm. Although the formation means is not particularly limited, for example, a direct current magnetron sputtering method, a vacuum deposition method or a CVD method is used.

CuInSe ₂ , CuInS ₂ , CuGaSe ₂ , CuGaS ₂ , AgInSe ₂ , AgInS ₂ , AgGaSe ₂ , AgGaS ₂ and their solid solutions and CdTe can be used as the p-type semiconductor of the light absorption layer 8. The conditions required to obtain higher energy conversion efficiency are the optical optimum design to obtain more photocurrent, high quality heterojunction without carrier recombination at the interface or especially the absorbing layer and It is to make a thin film. Usually, the thickness is 1 to 5 μm, preferably 2 to 3 μm. Although the formation means is not particularly limited, for example, it is formed by a vacuum deposition method or a CVD method. High quality heterointerfaces are closely related to the combination of intermediate layer / absorbing layer, CdS / CdTe system, CdS / CuInSe ₂ system, CdS / Cu (In, Ga) Se ₂ system, CdS / Ag (In, Ga). A heterojunction useful in Se ₂ system and the like can be obtained.

In order to increase the efficiency of the solar cell, a semiconductor having a wider band gap, for example, the intermediate layer 9 is made of CdS, CdZnS, or the like as the semiconductor thin film. As a result, the sensitivity of the short wavelength of sunlight can be improved. Usually, the thickness is 10 to 200 nm, preferably 30 to 100 nm. The means for forming the intermediate layer 9 is not particularly limited. In the case of a CdS thin film, it is formed by a solution deposition method using a mixed solution of CdI ₂ , NH ₄ Cl ₂ , NH ₃ , and thiourea.

Further, on the incident light side of CdS or (Cd, Zn) S, which is the intermediate layer 9, a semiconductor having a larger band gap than those thin films can be disposed as the window layer 10. Thereby, it becomes a high-performance solar cell with high reproducibility. The window layer 10 is a thin film having a conductivity similar to that of a CdS thin film, such as a ZnO or (Zn, Mg) O thin film, and is usually 50 to 300 nm, preferably 100 to 200 nm thick. A method for forming the window layer 10 is not particularly limited, and is formed by a direct current magnetron sputtering method using a target such as ZnO or (Zn, Mg) O and Ar as a sputtering gas.
The solar cell of the present invention is obtained by using the transparent conductive film of the present invention as an electrode on the side (front surface and / or back surface) on which sunlight of such a compound thin film solar cell is incident. Therefore, high conversion efficiency can be realized.

  The above-described compound thin film system can achieve high conversion efficiency when the transparent conductive film of the present invention is used even in the case of a hybrid type solar cell in which photoelectric conversion elements having different compositions are laminated. In particular, a solar cell obtained by laminating light absorption layers having different compositions with different light absorption wavelength ranges can effectively use sunlight in a wide wavelength range, and therefore has high transmittance from visible to near infrared. It is useful to use a transparent conductive film.

  In both types of elements, the bus bar electrode and finger electrode are formed on the light receiving surface (front surface) side and back surface side by screen printing method, etc., and these electrode surfaces are attached with protection and connection tabs. In order to make it easier, the entire surface is solder coated. When the element is a silicon substrate, a transparent protective material such as a glass plate, a resin plate, or a resin film is provided on the light receiving surface side.

  The thickness of the transparent conductive film is not particularly limited and is preferably 50 to 1500 nm, particularly preferably 400 to 1300 nm, although it depends on the composition of the material. The transparent conductive film of the present invention has a low resistance and has a high transmittance of sunlight including visible light to near infrared light having a wavelength of 380 nm to 1200 nm. Therefore, the light energy of sunlight is extremely effectively converted into electric energy. be able to.

  In addition to the solar cell, the transparent conductive film of the present invention is also useful as a transparent electrode of a light detection element, a touch panel, a flat panel display (LCD, PDP, EL, etc.) and a light emitting device (LED, LD, etc.). .

  For example, the light detection element includes a structure in which a glass electrode, a transparent electrode on the light incident side, a light detection material layer such as infrared rays, and a back electrode are laminated. The photo-sensitive material layer for detecting infrared rays is a type using a semiconductor material based on Ge or InGeAs (photodiode (PD) or avalanche photodiode (APD)), sulfide of an alkaline earth metal element or Examples include a material obtained by adding one or more elements selected from Eu, Ce, Mn, and Cu and one or more elements selected from Sm, Bi, and Pb to selenide. In addition, APDs using a laminate of amorphous silicon germanium and amorphous silicon are also known, and any of them can be used.

  Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples. The evaluation method is as follows.

<Uniformity of mixed raw material powder before firing>
Using a mixed raw material powder to produce a compact and observing the fractured surface with a scanning electron microscope, using an attached energy dispersive X-ray analyzer (EDX) to irradiate an electron beam to about 1 μmΦ The composition analysis of the minute region is performed, and the Al / (Al + Ga) atomic ratio in the region is grasped. The Al / (Al + Ga) atomic ratio is measured at an arbitrary 50 points, and the standard deviation σ is obtained. The higher the uniformity, the smaller the σ. In order to obtain the oxide sintered body of the present invention, it is necessary that σ is 25 atomic% or less.

<Evaluation of oxide sintered body>
After cutting the obtained oxide sintered body in the depth direction and mirror-polishing the cut surface, it was thermally corroded to precipitate grain boundaries, and the structure was observed with a scanning electron microscope, and the average The crystal grain size and maximum pore diameter were determined. The sintered density and volume resistivity of the oxide sintered body were measured by a four-probe method on the mirror-polished surface of the cut surface. Moreover, the end material of the obtained oxide sintered body was pulverized and subjected to powder X-ray diffraction measurement to identify the generated phase. The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). EDX composition analysis was performed on 50 spinel crystal phases, and the Al / (Al + Ga) atomic ratio was measured.

<Evaluation of transparent conductive film>
The film thickness of the obtained transparent conductive film was measured with a surface roughness meter (manufactured by Tencor). The specific resistance of the film was calculated from the product of the surface resistance and the film thickness measured by the four probe method. The optical properties of the film were measured with a spectrophotometer (manufactured by Hitachi, Ltd.). The formation phase of the film was identified by X-ray diffraction measurement (manufactured by PANalytical). The film composition was measured by ICP emission spectroscopy. The product phase of the film was identified by X-ray diffraction measurement.

<Evaluation of discharge characteristics and particles>
Number of occurrences of arcing (abnormal discharge) per 10 minutes after increasing the DC input power only to 850 W (input DC power density: 4.7 W / cm ² ) and performing pre-sputtering for about 10 minutes. Was measured. Moreover, after applying DC power 200W continuously and supplying electric power to 4 kWh, the target surface was observed.

(Example 1)
<Preparation of sintered oxide>
An oxide sintered body containing zinc, aluminum and gallium was prepared as follows. Zinc oxide powder having an average particle size of 1 μm or less, aluminum oxide powder having an average particle size of 1 μm or less, and gallium oxide powder having an average particle size of 1 μm or less are used as starting materials, and the mixing ratio of the materials is Al / (Al + Ga) It mix | blended so that it might be set to 55 atomic% by atomic ratio, and 5.2 atomic% by (Al + Ga) / (Zn + Al + Ga) atomic ratio. The raw material powder was put into a resin pot together with water and mixed by a wet ball mill. At this time, hard ZrO ₂ balls were used and the mixing time was 18 hours. After ball mill mixing, this slurry was taken out, and a dispersant and a binder of polyvinyl alcohol were added. This slurry was placed in a bead mill containing beads having a diameter of 3 mm made of zirconia and subjected to two passes. The total processing time was 6 hours. This slurry was filtered, dried and granulated. The granulated product was molded by applying a pressure of 3 ton / cm ² with a cold isostatic press.
The uniformity of the mixed raw material powder was evaluated using the green body thus produced. While observing the fractured surface of the molded body with a scanning electron microscope, composition analysis was performed on a minute region of about 1 μmΦ irradiated with an electron beam using the attached energy dispersive X-ray analyzer (EDX). The Al / (Al + Ga) atomic ratio was measured. When the Al / (Al + Ga) atomic ratio was measured at an arbitrary 50 locations on the fracture surface and the standard deviation σ was calculated, it was 15 atomic%, and it was found that the above mixing and grinding were sufficiently performed. It was.
Next, the compact was sintered as follows. The temperature in the sintering furnace was raised to 1000 ° C. at a rate of temperature rise of 0.5 ° C./min with the atmosphere as air. After reaching 1000 ° C., oxygen was introduced into the atmosphere in the sintering furnace at a rate of 5 liters / minute per 0.1 m ^{3 of} the furnace volume, and kept at 1000 ° C. for 3 hours. Subsequently, the temperature was raised again to a sintering temperature of 1250 ° C. at a heating rate of 0.5 ° C./min. When cooling after sintering, the introduction of oxygen was stopped, and the temperature was lowered to 1000 ° C. at 0.5 ° C./min to produce an oxide sintered body containing zinc, aluminum and gallium. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 5.3 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same, including the atomic ratio.
After cutting the obtained oxide sintered body in the depth direction and mirror-polishing the cut surface, it was thermally corroded to precipitate grain boundaries, and the structure was observed with a scanning electron microscope, and the average The crystal grain size and maximum pore diameter were determined. The sintered density and volume resistivity of the oxide sintered body were measured by a four-probe method on the mirror-polished surface of the cut surface. As a result, the volume resistivity of the oxide sintered body was 0.007 Ωcm, the density was 5.1 g / cm ³ , the average crystal grain size was 7 μm, and the maximum pore size was 1 μm. In addition, when the milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified, the zinc oxide crystal phase and the spinel type having a hexagonal wurtzite structure A diffraction peak attributed to the crystalline phase of the structure was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed from electron diffraction that the spinel crystal phase of 1 to 5 μm was dispersed in the mother phase having a wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel crystal phase was a Zn—Al—Ga—O phase. When EDX composition analysis was performed on 50 spinel crystal phases and the Al / (Al + Ga) atomic ratio was measured, it was 44 to 67 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was no spinel phase outside the range.
<Preparation of transparent conductive film>
Such an oxide sintered body was bonded to a backing plate made of oxygen-free copper using metallic indium to obtain a sputtering target. The diameter was 152 mm and the thickness was 5 mm, and the sputtering surface was polished with a cup grindstone so that the maximum height Rz was 3.0 μm or less. Using this as a sputtering target, film formation by direct current sputtering was performed. A sputtering target was attached to a cathode for a non-magnetic target of a DC magnetron sputtering apparatus equipped with a DC power supply without an arcing suppression function. As the substrate, an alkali-free glass substrate (Corning # 7059, thickness 1.1 mmt) was used, and the target-substrate distance was fixed to 60 mm. After evacuating to 5 × 10 ⁻⁵ Pa or less, pure Ar gas was introduced, the gas pressure was set to 0.3 Pa, DC power was applied at 200 W to generate DC plasma, and pre-sputtering was performed. After sufficient pre-sputtering, the substrate was placed immediately above the center (non-erosion part) of the sputtering target, and sputtering was performed without heating to form a transparent conductive film having a thickness of 200 nm.
The film thickness of the obtained transparent conductive film was measured with a surface roughness meter (manufactured by Tencor). The specific resistance of the film was calculated from the product of the surface resistance and the film thickness measured by the four probe method. The optical properties of the film were measured with a spectrophotometer (manufactured by Hitachi, Ltd.). The formation phase of the film was identified by X-ray diffraction measurement (manufactured by PANalytical). The film composition was measured by ICP emission spectroscopy. It was confirmed that the composition of the obtained transparent conductive film was almost the same as that of the target. When the formation phase of the film was identified by X-ray diffraction measurement, it was composed only of a zinc oxide phase having a hexagonal wurtzite structure. The diffraction peak of the zinc oxide phase having a hexagonal wurtzite structure was observed only due to c-plane (002) reflection, and was a c-axis oriented thin film. When the specific resistance of the film was measured, it was 5.5 × 10 ⁻⁴ Ωcm, the visible region including the substrate (wavelength 400 to 800 nm) had a transmittance of 85%, and the wavelength including the substrate was about 800 to 1200 nm. The transmittance in the infrared region was 83%. When the transmittance of the film itself is defined as {(transmittance including substrate) / (transmittance of substrate only)} × 100 (%), the transmittance of the transparent conductive film of the present invention is 87% in the visible region. It was 90% in the near infrared region.
Therefore, a transparent electrode film having a high transmittance in the near infrared region as well as in the visible region and having a low resistance can be obtained by using a surface transparent electrode film (2) and / or Or if it uses for the transparent electrode film (6) of the back side of a pin junction part, the solar energy of an infrared region can be effectively converted into an electrical energy. Such a highly conductive transparent conductive film could be stably obtained even when the DC input power to the target was increased to 850 W.
In the above film forming conditions, only DC input power is increased to 850 W (input DC power density: 4.7 W / cm ² ), pre-sputtering is performed for about 10 minutes, and then arcing (abnormal discharge) per 10 minutes is performed. The number of occurrences was measured. However, arcing did not occur at all and the discharge was stably performed, and the characteristics of the obtained film were the same as those obtained by forming at 200 W. Moreover, although the target surface was observed after supplying electric power continuously to 4 kWh, the particle | grains by peeling of the thin film of a non-erosion part did not generate | occur | produce. These results are shown in Table 1.

(Example 2)
An oxide sintered body containing zinc, aluminum, and gallium was manufactured under the same method and conditions as in Example 1 except that the raw powder was not mixed and pulverized by a ball mill but only a bead mill process was performed. That is, the type and blending ratio of the raw material powder, the bead mill conditions, the production conditions of the molded body, and the firing conditions are the same methods and conditions as in Example 1.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the molded body before firing in the same manner as in Example 1, the standard deviation σ was 25 atomic%. It had high uniformity.
The oxide sintered body obtained after firing was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 5.2 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.006 Ωcm, the density was 5.0 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 1 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic number ratio was measured. There was no spinel phase out of range.
When a sputtering target was produced under the same method and conditions as in Example 1 and a film was formed under the same conditions, the transmittance including the substrate with a specific resistance of 5.4 × 10 ⁻⁴ Ωcm was 85% in the visible region. Thus, 83% of a transparent conductive film could be obtained in the near infrared region. The transmittance of the film itself was 87% in the visible region and 90% in the near infrared region. Therefore, a transparent electrode film having a high transmittance in the near infrared region as well as in the visible region and having a low resistance is used, for example, the surface transparent electrode film (2) on the light receiving portion side of the solar cell as shown in FIG. When used for the transparent electrode film (6) on the back side of the PIN junction, solar energy in the infrared region can be effectively converted into electrical energy.
Such a highly conductive transparent conductive film can be stably obtained even when the direct current input power to the target is increased to 850 W, and can be formed at high speed. The characteristics of the obtained film were equivalent to those of the film formed at 200W. Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. However, no arcing occurred and no particles were generated. These results are shown in Table 1.

(Comparative Example 1)
An oxide sintered body containing zinc, aluminum, and gallium was produced under the same method and conditions as in Example 1 except that the raw powder was not mixed and pulverized by a bead mill but only a ball mill process was performed. That is, the types and blending ratios of the raw material powders, the ball mill conditions, the production conditions of the molded body, and the firing conditions are the same methods and conditions as in Example 1.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the molded body before firing in the same manner as in Example 1, the standard deviation σ was 35 atomic%. The uniformity between Al and Ga was inferior to the examples.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. The (Al + Ga) / (Zn + Al + Ga) atomic ratio was 5.5 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.01 Ωcm, the density was 5.1 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 1 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. When EDX composition analysis was performed on 50 spinel phases and the Al / (Al + Ga) atomic ratio was measured, it was 15 to 92 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. Out of range, there was a spinel phase.
When a sputtering target was prepared under the same method and conditions as in Example 1 and film formation was performed under the same conditions, the visible transmittance including the substrate with a specific resistance of 7.9 × 10 ⁻⁴ Ωcm was 85% or more. A transparent conductive film could be obtained. Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. No particles were generated. However, arcing occurred 5 times in 10 minutes. Such an oxide sintered body cannot be used as a target for mass production of a transparent conductive film. The specific resistance is higher than the films prepared from Examples 1 and 2 that are the same raw material compounding ratio and the oxide sintered body of the present invention because the film contains defects due to arcing during film formation. It is. When a film was formed in the same manner by increasing the DC input power to the target to 850 W, a transparent conductive film having high conductivity and high transmittance as described above could not be obtained. This is due to arcing that occurs during film formation, and only a defective film is obtained due to film damage, and the structure as in the example does not form a dense and high-quality film. Therefore, it cannot be used as a transparent electrode of a highly efficient solar cell. These results are shown in Table 1.

(Example 3)
Implementation was carried out except that the mixing ratio of zinc oxide, aluminum oxide and gallium oxide in the raw material powder was 31 atomic% in the Al / (Al + Ga) atomic ratio and 5.2 atomic% in the (Al + Ga) / (Zn + Al + Ga) atomic ratio. A mixed and pulverized treatment using a ball mill and a bead mill was performed under the same procedure and conditions as in Example 1, followed by molding and firing to produce an oxide sintered body.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the molded body before firing in the same manner as in Example 1, the standard deviation σ was 18 atomic%. It had high uniformity.
The oxide sintered body obtained after firing was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 5.4 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same as the composition, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.008 Ωcm, the density was 5.2 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 1 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic ratio was measured. As a result, it was 17 to 44 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was no spinel phase out of range.
When a sputtering target was produced under the same method and conditions as in Example 1 and a film was formed under the same conditions, the transmittance including the substrate with a specific resistance of 4.9 × 10 ⁻⁴ Ωcm was 85% in the visible region. Thus, an 80% transparent conductive film was obtained in the near infrared region (the transmittance of the film itself was 87% in the visible region and 87% in the near infrared region). Such a transparent conductive film with high conductivity and high transmittance could be stably obtained even when the direct current input power to the target was increased to 850 W. Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. However, no arcing occurred and no particles were generated.
These results are shown in Table 1.

Example 4
Implementation was performed except that the mixing ratio of zinc oxide, aluminum oxide and gallium oxide in the raw material powder was 68 atomic% in terms of Al / (Al + Ga) atomic ratio and 5.2 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio. A mixed and pulverized treatment using a ball mill and a bead mill was performed under the same procedure and conditions as in Example 1, followed by molding and firing to produce an oxide sintered body.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the green body before firing as in Example 1, the standard deviation σ was 16 atomic%. It had high uniformity.
The oxide sintered body obtained after firing was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 5.3 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.004 Ωcm, the density was 5.3 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 0.8 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic ratio was measured. As a result, it was 54 to 85 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was no spinel phase out of range.
When a sputtering target was produced under the same method and conditions as in Example 1 and a film was formed under the same conditions, the transmittance including the substrate with a specific resistance of 6.1 × 10 ⁻⁴ Ωcm was 85% in the visible region. Thus, a transparent conductive film of 84% was obtained in the near infrared region (the transmittance of the film itself was 87% or more in the visible region and 92% in the near infrared region).
Therefore, a transparent electrode film having a high transmittance in the near-infrared region as well as such a visible region and a low resistance can be obtained by, for example, the surface transparent electrode film (2) on the light-receiving part side of the solar cell as shown in FIG. Or if it uses for the transparent electrode film (6) of the back side of a PIN junction part, the solar energy of an infrared region can be effectively converted into an electrical energy.
Such a highly conductive transparent conductive film could be stably obtained even when the DC input power to the target was increased to 850 W. Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. However, no arcing occurred and no particles were generated.
These results are shown in Table 1.

(Comparative Example 2)
Compared except that the mixing ratio of zinc oxide, aluminum oxide and gallium oxide in the raw material powder was 31 atomic% in terms of Al / (Al + Ga) atomic ratio and 5.2 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio. A mixed and pulverized treatment using a ball mill was performed under the same procedure and conditions as in Example 1, followed by forming and firing to produce an oxide sintered body. That is, in the mixing and pulverization of the raw material powder, the treatment with the ball mill was carried out without the treatment with the bead mill.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the molded body before firing in the same manner as in Example 1, the standard deviation σ was 35 atomic%. The uniformity between Al and Ga was inferior to the examples.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 5.4 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same as the composition, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.01 Ωcm, the density was 5.1 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 1 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. The EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic ratio was measured. As a result, it was 7 to 57 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was a spinel phase out of range.
When a sputtering target was prepared under the same method and conditions as in Example 1 and film formation was performed under the same conditions, the visible transmittance including the substrate was 85% or more with a specific resistance of 5.9 × 10 ⁻⁴ Ωcm. A transparent conductive film could be obtained. Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. The specific resistance of the film of Comparative Example 2 is higher than that of the film produced from the oxide sintered body of Example 3 of the present invention having the same raw material blending ratio because arcing occurred during film formation and defects were included. This is because it is a film. When continuous sputtering was performed, many particles were generated, and arcing occurred twice in 10 minutes. The generation of particles seems to be because a large number of spinel phases having an Al / (Al + Ga) atomic ratio of 10 atomic% or less in the oxide sintered body were included. The arcing factor seems to be due to particles.
Such an oxide sintered body cannot be used as a target for mass production of a transparent conductive film.
When the film was formed in the same manner by increasing the DC input power to the target to 850 W, a transparent conductive film having high conductivity and high transmittance as described above could not be obtained. This is due to arcing that occurs during film formation, and only a defective film is obtained due to film damage, and the structure as in the example does not form a dense and high-quality film. Therefore, it cannot be used as a transparent electrode of a highly efficient solar cell. These results are shown in Table 1.

(Comparative Example 3)
Compared except that the mixing ratio of zinc oxide, aluminum oxide and gallium oxide in the raw material powder is 68 atomic% in terms of Al / (Al + Ga) atomic ratio and 5.2 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio A mixed and pulverized treatment using a ball mill was performed under the same procedure and conditions as in Example 1, followed by forming and firing to produce an oxide sintered body. That is, in the mixing and pulverization of the raw material powder, the treatment with the ball mill was carried out without the treatment with the bead mill.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the molded body before firing in the same manner as in Example 1, the standard deviation σ was 32 atomic%. The uniformity between Al and Ga was inferior to the examples.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 5.3 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.02 Ωcm, the density was 5.0 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 1 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic number ratio was measured to be 42 to 98 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was a spinel phase out of range.
When a sputtering target was prepared under the same method and conditions as in Example 1 and film formation was performed under the same conditions, the visible transmittance including the substrate was 85% or more with a specific resistance of 6.9 × 10 ⁻⁴ Ωcm. A transparent conductive film could be obtained.
Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. When continuous sputtering was performed, no particles were generated. However, arcing occurred 11 times in 10 minutes. The specific resistance of the film of Comparative Example 3 is higher than that of the film obtained from the oxide sintered body of Example 4 in which the raw material blending ratio is the same. This is because arcing occurs during film formation and the film is damaged. Because. The cause of arcing seems to be that the Al / (Al + Ga) atomic ratio of the spinel phase in the oxide sintered body deviates from 10 to 90 atomic% and has high resistance. When a film was formed in the same manner by increasing the DC input power to the target to 850 W, a transparent conductive film having high conductivity and high transmittance as described above could not be obtained. This is due to arcing that occurs during film formation, and only a defective film is obtained due to film damage, and the structure as in the example does not form a dense and high-quality film. Therefore, it cannot be used as a transparent electrode of a highly efficient solar cell. Such an oxide sintered body cannot be used as a target for mass production of a transparent conductive film. These results are shown in Table 1.

(Example 5)
The mixing ratio of zinc oxide, aluminum oxide, and gallium oxide in the raw material powder is 55 atomic% in the Al / (Al + Ga) atomic ratio, and 6.3 atomic% in the (Al + Ga) / (Zn + Al + Ga) atomic ratio, An oxide sintered body containing zinc, aluminum, and gallium was produced under the same method and conditions as in Example 1 except that only the bead mill treatment was performed without performing the mixing / pulverization treatment by the ball mill. That is, the bead mill conditions, the molded body production conditions, and the firing conditions are the same methods and conditions as in Example 1.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the molded body before firing in the same manner as in Example 1, the standard deviation σ was 23 atomic%. It had high uniformity.
The oxide sintered body obtained after firing was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 6.5 atomic%, and Al / (Al + Ga). ) It was confirmed that the composition was almost the same, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.008 Ωcm, the density was 5.2 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 0.9 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic ratio was measured. As a result, it was 35 to 82 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was no spinel phase out of range.
When a sputtering target was produced under the same method and conditions as in Example 1 and a film was formed under the same conditions, the transmittance including the substrate with a specific resistance of 8.5 × 10 ⁻⁴ Ωcm was 85% in the visible region. Thus, an 80% transparent conductive film was obtained in the near infrared region (the transmittance of the film itself was 87% in the visible region and 88% in the near infrared region). Therefore, a transparent electrode film having a high transmittance in the near infrared region as well as in the visible region and having a low resistance is used, for example, the surface transparent electrode film (2) on the light receiving portion side of the solar cell as shown in FIG. When used for the transparent electrode film (6) on the back side of the PIN junction, solar energy in the infrared region can be effectively converted into electrical energy.
Such a highly conductive transparent conductive film could be stably obtained even when the DC input power to the target was increased to 850 W. Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. However, no arcing occurred and no particles were generated. These results are shown in Table 1.

(Example 6)
The mixing ratio of zinc oxide, aluminum oxide, and gallium oxide in the raw material powder is 55 atomic% in the Al / (Al + Ga) atomic ratio, and 4.5 atomic% in the (Al + Ga) / (Zn + Al + Ga) atomic ratio. An oxide sintered body containing zinc, aluminum, and gallium was produced under the same method and conditions as in Example 1 except that only the bead mill treatment was performed without performing the mixing / pulverization treatment by the ball mill. That is, the bead mill conditions, the molded body production conditions, and the firing conditions are the same methods and conditions as in Example 1.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the compact before firing in the same manner as in Example 1, the standard deviation σ was 21 atomic%. It had high uniformity.
The oxide sintered body obtained after firing was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. The (Al + Ga) / (Zn + Al + Ga) atomic ratio was 4.4 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same as the composition, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.006 Ωcm, the density was 5.1 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 0.8 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic ratio was measured. As a result, it was 32 to 80 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was no spinel phase out of range.
When a sputtering target was prepared under the same method and conditions as in Example 1 and film formation was performed under the same conditions, the transmittance including the substrate with a specific resistance of 6.6 × 10 ⁻⁴ Ωcm was 85% in the visible region. Thus, a transparent conductive film of 82% was obtained in the near infrared region (the transmittance of the film itself was 87% in the visible region and 89% in the near infrared region). Therefore, a transparent electrode film having a high transmittance in the near infrared region as well as in the visible region and having a low resistance is used, for example, the surface transparent electrode film (2) on the light receiving portion side of the solar cell as shown in FIG. When used for the transparent electrode film (6) on the back side of the PIN junction, solar energy in the infrared region can be effectively converted into electrical energy.
Such a highly conductive transparent conductive film could be stably obtained even when the DC input power to the target was increased to 850 W. Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. However, no arcing occurred and no particles were generated. These results are shown in Table 1.

(Example 7)
The mixing ratio of zinc oxide, aluminum oxide, and gallium oxide in the raw material powder is 55 atomic% in the Al / (Al + Ga) atomic ratio, and 3.4 atomic% in the (Al + Ga) / (Zn + Al + Ga) atomic ratio, An oxide sintered body containing zinc, aluminum, and gallium was produced under the same method and conditions as in Example 1 except that only the bead mill treatment was performed without performing the mixing / pulverization treatment by the ball mill. That is, the bead mill conditions, the molded body production conditions, and the firing conditions are the same methods and conditions as in Example 1.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the green body before firing as in Example 1, the standard deviation σ was 24 atomic%. It had high uniformity.
The oxide sintered body obtained after firing was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. When the milled end material of the obtained oxide sintered body was pulverized and the composition was analyzed by ICP emission spectroscopy, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 3.2 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same as the composition, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.008 Ωcm, the density was 5.2 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 1 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic ratio was measured. As a result, it was 30 to 83 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was no spinel phase out of range.
When a sputtering target was prepared under the same method and conditions as in Example 1 and film formation was performed under the same conditions, the transmittance including the substrate with a specific resistance of 9.0 × 10 ⁻⁴ Ωcm was 86% in the visible region. Thus, 83% transparent conductive film was obtained in the near infrared region (the transmittance of the film itself was 88% in the visible region and 90% in the near infrared region). Therefore, a transparent electrode film having a high transmittance in the near infrared region as well as in the visible region and having a low resistance is used, for example, the surface transparent electrode film (2) on the light receiving portion side of the solar cell as shown in FIG. When used for the transparent electrode film (6) on the back side of the PIN junction, solar energy in the infrared region can be effectively converted into electrical energy.
Such a highly conductive transparent conductive film could be stably obtained even when the DC input power to the target was increased to 850 W. Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. However, no arcing occurred and no particles were generated. These results are shown in Table 1.

(Example 8)
Implementation was carried out except that the mixing ratio of zinc oxide, aluminum oxide and gallium oxide in the raw material powder was 55 atomic% in the Al / (Al + Ga) atomic ratio and 2.8 atomic% in the (Al + Ga) / (Zn + Al + Ga) atomic ratio. A mixed and pulverized treatment using a ball mill and a bead mill was performed under the same procedure and conditions as in Example 1, followed by molding and firing to produce an oxide sintered body.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the molded body before firing in the same manner as in Example 1, the standard deviation σ was 18 atomic%. The uniformity between Al and Ga was good.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. When the milled end of the obtained oxide sintered body was pulverized and analyzed for the composition by ICP emission spectroscopy, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 2.9 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.02 Ωcm, the density was 5.0 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 1 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. When EDX composition analysis was performed on 50 spinel phases and the Al / (Al + Ga) atomic ratio was measured, it was 41 to 64 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was no spinel phase out of range.
A sputtering target was produced under the same method and conditions as in Example 1, and the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions, but no arcing occurred and no particles were generated.
Further, when film formation was performed under the same conditions as in Example 1, the obtained film had a visible transmittance of 85% including the substrate, and the specific resistance was 1.4 × 10 ⁻³ Ωcm. However, the transmittance in the near infrared region is 84% (92% for the film itself) including the substrate, and it was found that the transparent conductive film has a particularly high transmittance in the near infrared region.

Example 9
Implementation was carried out except that the mixing ratio of zinc oxide, aluminum oxide and gallium oxide in the raw material powder was 55 atomic% in the Al / (Al + Ga) atomic ratio and 0.3 atomic% in the (Al + Ga) / (Zn + Al + Ga) atomic ratio. A mixed and pulverized treatment using a ball mill and a bead mill was performed under the same procedure and conditions as in Example 1, followed by molding and firing to produce an oxide sintered body.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the compact before firing in the same manner as in Example 1, the standard deviation σ was 17 atomic%. The uniformity between Al and Ga was good.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. The (Al + Ga) / (Zn + Al + Ga) atomic ratio was 0.3 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was the same, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.03 Ωcm, the density was 5.0 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 1 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic number ratio was measured to be 42 to 66 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was no spinel phase out of range.
A sputtering target was produced under the same method and conditions as in Example 1, and the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions, but no arcing occurred and no particles were generated.
Further, when film formation was performed under the same conditions as in Example 1, the obtained film had a visible transmittance of 85% including the substrate, and the specific resistance was 2.9 × 10 ⁻³ Ωcm. However, the transmittance in the near-infrared region is 86% including the substrate (94% for the film itself), indicating that the transparent conductive film has a particularly high transmittance in the near-infrared region.

(Comparative Example 4)
Implementation was performed except that the mixing ratio of zinc oxide, aluminum oxide and gallium oxide in the raw material powder was 55 atomic% in the Al / (Al + Ga) atomic ratio and 0.15 atomic% in the (Al + Ga) / (Zn + Al + Ga) atomic ratio. A mixed and pulverized treatment using a ball mill and a bead mill was performed under the same procedure and conditions as in Example 1, followed by molding and firing to produce an oxide sintered body.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the molded body before firing in the same manner as in Example 1, the standard deviation σ was 18 atomic%. The uniformity between Al and Ga was good.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 0.16 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same as the composition, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.02 Ωcm, the density was 5.0 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 1 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic ratio was measured. As a result, it was 40 to 69 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was no spinel phase out of range.
A sputtering target was produced under the same method and conditions as in Example 1, and the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions, but no arcing occurred and no particles were generated.
Further, when film formation was performed under the same conditions as in Example 1, the obtained film had a visible transmittance of 85% or more including the substrate and a high transmittance in the near infrared region, but the specific resistance was A high resistance of 6.8 × 10 ⁻³ Ωcm and a low resistance transparent conductive film could not be obtained. This is because the amount of aluminum and gallium in the oxide sintered body is too small (0.15 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic number), and these dopants contribute to lowering the resistance of the film. It seems that there was a shortage. If such a high-resistance transparent conductive film is used for a transparent electrode of a solar cell, high efficiency cannot be realized.

(Comparative Example 5)
Implementation was carried out except that the mixing ratio of zinc oxide, aluminum oxide and gallium oxide in the raw material powder was 55 atomic% in the Al / (Al + Ga) atomic ratio and 6.8 atomic% in the (Al + Ga) / (Zn + Al + Ga) atomic ratio. A mixed and pulverized treatment using a ball mill and a bead mill was performed under the same procedure and conditions as in Example 1, followed by molding and firing to produce an oxide sintered body.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the green body before firing as in Example 1, the standard deviation σ was 16 atomic%. The uniformity between Al and Ga was good.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. The milled end material of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 6.9 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same as the composition, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.02 Ωcm, the density was 5.0 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 1 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. The EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic ratio was measured. As a result, it was 43 to 65 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was no spinel phase out of range.
A sputtering target was produced under the same method and conditions as in Example 1, and the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions, but no arcing occurred and no particles were generated. Further, when film formation was performed under the same conditions as in Example 1, the obtained film had a visible transmittance of 85% including the substrate, but the specific resistance was as high as 5.5 × 10 ⁻³ Ωcm. A low-resistance transparent conductive film could not be obtained. This is because the amount of aluminum and gallium in the oxide sintered body is too large (6.9% by atomic ratio of (Al + Ga) / (Zn + Al + Ga)), and these dopants contribute to the reduction in resistance of the film. It seems that there were too many. The transmittance in the near infrared region including the substrate was 62% (67% in the transmittance of the film itself), which was lower than that of the transparent conductive film of the present invention. If such a high-resistance transparent conductive film is used for a transparent electrode of a solar cell, high efficiency cannot be realized. These results are shown in Table 1.

(Comparative Example 6)
As raw material powder, gallium oxide is not used but zinc oxide and aluminum oxide are used, and the compounding ratio is 5.1 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio (ie, Al / (Zn + Al) atomic ratio). A conventional oxide sintered body (AZO) was manufactured by performing mixing and pulverizing treatment with a ball mill and a bead mill under the same procedures and conditions as in Example 1, except that the molding and firing were performed.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. When the milled chip of the obtained oxide sintered body was pulverized and the composition was analyzed by ICP emission spectroscopy, the (Al + Ga) / (Zn + Al + Ga) atomic ratio (that is, Al / (Zn + Al) atomic ratio) was 5. .2 atomic%, confirming that it was almost the same as the composition. The volume resistivity of the oxide sintered body was 0.04 Ωcm, the density was 5.2 g / cm ³ , the average crystal grain size was 10 μm, and the maximum pore size was 1 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum, and the spinel phase was a Zn—Al—O phase. When the EDX composition analysis was performed on 50 spinel phases, the compositions were all close to ZnAl ₂ O ₃ . That is, the composition of the spinel phase defined in the present invention is a spinel phase in which the Al / (Al + Ga) atomic ratio is outside the range of 10 to 90 atomic%.
A sputtering target was prepared under the same method and conditions as in Example 1, and the occurrence of arcing and the generation of particles were evaluated under the same method and conditions. No particles were generated, but arcing occurred 230 times in 10 minutes. Therefore, such a target cannot perform high-speed film formation with high input power and is not suitable for mass production.
Furthermore, when film formation was performed under the same conditions as in Example 1, the obtained film had a transmittance including the substrate of 85% in the visible region and 84% in the near infrared region (the transmittance of the film itself is It was 87% in the visible region and 92% in the near infrared region), but the specific resistance was 1.5 × 10 ⁻³ Ωcm. However, the specific resistance of the transparent conductive film obtained in a state where arcing occurred at 850 W was as high as 8.1 × 10 ⁻³ Ωcm.

(Comparative Example 7)
As the raw material powder, zinc oxide and gallium oxide are used without using aluminum oxide, and the compounding ratio is 5.3 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio (that is, Ga / (Zn + Ga) atomic ratio). A conventional oxide sintered body (GZO) was manufactured by performing mixing and pulverization treatment with a ball mill and a bead mill under the same procedures and conditions as in Example 1, except that the molding and firing were performed.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. When the milled end of the obtained oxide sintered body was pulverized and the composition was analyzed by ICP emission spectroscopy, the (Al + Ga) / (Zn + Al + Ga) atomic ratio (that is, Ga / (Zn + Ga) atomic ratio) was 5. .3 atomic%, confirming that it was almost the same as the composition. The volume resistivity of the oxide sintered body was 0.01 Ωcm, the density was 4.8 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 2 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum, and the spinel phase was a Zn—Ga—O phase. When the EDX composition analysis was performed on 50 spinel phases, the compositions were all close to ZnGa ₂ O ₃ . That is, the composition of the spinel phase defined in the present invention is a spinel phase in which the Al / (Al + Ga) atomic ratio is outside the range of 10 to 90 atomic%.
When film formation was performed under the same conditions as in Example 1, the obtained film had a transmittance including the substrate of 85% in the visible region (87% as the transmittance of the film itself), and a specific resistance of 4 A transparent conductive film having a low resistance of 5 × 10 ⁻⁴ Ωcm could be obtained, but it was 79% in the near infrared region (86% in the transmittance of the film itself), and the transmittance in the near infrared region was It was lower than the transparent conductive film of the invention. If such a transparent conductive film is used as a transparent electrode of a solar cell, a solar cell with high efficiency cannot be realized because solar energy in the near infrared region cannot be effectively used. Further, a sputtering target was produced under the same method and conditions as in Example 1, and the occurrence of arcing and the generation of particles were evaluated under the same method and conditions. When continuous sputtering was performed, many particles were generated, and arcing occurred about 12 times in 10 minutes. The cause of the generation of particles seems to be that the oxide sintered body contained a spinel phase having a composition close to that of ZnGa ₂ O ₃ . The cause of arcing is probably due to particles. Such an oxide sintered body cannot be used as a target for mass production of a transparent conductive film.
When the film was formed in the same manner by increasing the DC input power to the target to 850 W, a transparent conductive film having high conductivity and high transmittance as described above could not be obtained. The specific resistance of the transparent conductive film obtained in the state where arcing occurred was as high as 5.7 × 10 ⁻³ Ωcm. This is due to arcing that occurs during film formation, and only a defective film is obtained due to film damage, and the structure as in the example does not form a dense and high-quality film. Therefore, it cannot be used as a transparent electrode of a highly efficient solar cell. These results are shown in Table 1.

(Comparative Example 8)
As raw material powder, gallium oxide is not used but zinc oxide and aluminum oxide are used, and the compounding ratio is 0.3 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio (ie, Al / (Zn + Al) atomic ratio). A conventional oxide sintered body (AZO) was manufactured by performing mixing and pulverizing treatment with a ball mill and a bead mill under the same procedures and conditions as in Example 1, except that the molding and firing were performed.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. When the milled chip of the obtained oxide sintered body was pulverized and the composition was analyzed by ICP emission spectrometry, the (Al + Ga) / (Zn + Al + Ga) atomic ratio (that is, Al / (Zn + Al) atomic ratio) was 0. .3 atomic%, confirming that it was almost the same as the composition. The volume resistivity of the oxide sintered body was 0.08 Ωcm, the density was 5.0 g / cm ³ , the average crystal grain size was 10 μm, and the maximum pore size was 1 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum, and the spinel phase was a Zn—Al—O phase. When the EDX composition analysis was performed on 50 spinel phases, the compositions were all close to ZnAl ₂ O ₃ . That is, the composition of the spinel phase defined in the present invention is a spinel phase in which the Al / (Al + Ga) atomic ratio is outside the range of 10 to 90 atomic%.
A sputtering target was prepared under the same method and conditions as in Example 1, and the occurrence of arcing and the generation of particles were evaluated under the same method and conditions. No particles were generated, but arcing occurred 120 times in 10 minutes. Therefore, such a target cannot perform high-speed film formation with high input power and is not suitable for mass production.
Further, when film formation was performed under the same conditions as in Example 1, the obtained film had a transmittance including the substrate of 85% in the visible region and 86% in the near infrared region (the transmittance of the film itself was The specific resistance was as high as 8.5 × 10 ⁻³ Ωcm, but 87% in the visible region and 94% in the near infrared region. In particular, the specific resistance of the transparent conductive film obtained in the state where arcing occurred at 850 W was as high as 1.3 × 10 ⁻² Ωcm.

(Comparative Example 9)
As the raw material powder, zinc oxide and gallium oxide are used without using aluminum oxide, and the compounding ratio is 0.3 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic number ratio (that is, Ga / (Zn + Ga) atomic number ratio). A conventional oxide sintered body (GZO) was manufactured by performing mixing and pulverization treatment with a ball mill and a bead mill under the same procedures and conditions as in Example 1, except that the molding and firing were performed.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. A diffraction peak attributed to the crystal phase was confirmed, and a diffraction peak attributed to the aluminum oxide phase or the gallium oxide phase was not detected. When the milled chip of the obtained oxide sintered body was pulverized and the composition was analyzed by ICP emission spectroscopy, the (Al + Ga) / (Zn + Al + Ga) atomic ratio (that is, Ga / (Zn + Ga) atomic ratio) was 0. .3 atomic%, confirming that it was almost the same as the composition. The volume resistivity of the oxide sintered body was 0.03 Ωcm, the density was 4.7 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 2 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum, and the spinel phase was a Zn—Ga—O phase. When the EDX composition analysis was performed on 50 spinel phases, the compositions were all close to ZnGa ₂ O ₃ . That is, the composition of the spinel phase defined in the present invention is a spinel phase in which the Al / (Al + Ga) atomic ratio is outside the range of 10 to 90 atomic%.
When film formation was performed under the same conditions as in Example 1, the obtained film had a transmittance including the substrate of 85% in the visible region (87% as the transmittance of the film itself), and a specific resistance of 2 A transparent conductive film having a low resistance of 5 × 10 ⁻³ Ωcm could be obtained. The transmittance in the near infrared region including the substrate was 84% (the transmittance of the film itself was 92%).
Further, a sputtering target was produced under the same method and conditions as in Example 1, and the occurrence of arcing and the generation of particles were evaluated under the same method and conditions. When continuous sputtering was performed, many particles were generated, and arcing occurred about 3 times in 10 minutes. The cause of the generation of particles seems to be that the oxide sintered body contained a spinel phase having a composition close to that of ZnGa ₂ O ₃ . The cause of arcing is probably due to particles. The specific resistance of the transparent conductive film obtained in the state where arcing occurred was as high as 1.7 × 10 ⁻² Ωcm. Such an oxide sintered body cannot be used as a target for mass production of a transparent conductive film.

(Comparative Example 10)
The same method and conditions as in Example 1 except that a raw material powder of aluminum oxide having a particle size of 10 μm was used, and only the ball mill treatment was performed without mixing the bead mill treatment for the raw material powder mixing and pulverization treatment. An oxide sintered body containing gallium was manufactured. That is, the types of zinc oxide powder and gallium oxide powder, the blending ratio of the raw material powder, the ball mill conditions, the forming conditions of the molded body, and the firing conditions are the same methods and conditions as in Example 1.
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the molded body before firing in the same manner as in Example 1, the standard deviation σ was 45 atomic%. The uniformity between Al and Ga was inferior to the examples. The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. In addition to the diffraction peak attributed to the crystal phase, a diffraction peak attributed to the aluminum oxide crystal phase was also confirmed. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 5.3 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.3 Ωcm, the density was 4.4 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 3 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic number ratio was measured to be 26 to 100 atomic%, and the Al / (Al + Ga) atomic number ratio was 10 to 90 atomic%. Out of range, there was a spinel phase. In particular, the presence of a spinel phase close to the composition of ZnAl ₂ O ₄ was also observed.
When a sputtering target was prepared under the same method and conditions as in Example 1 and film formation was performed under the same conditions, the visible transmittance including the substrate was 85% or more with a specific resistance of 8.5 × 10 ⁻⁴ Ωcm. A transparent conductive film could be obtained.
Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. No particles were generated, but arcing occurred 520 times in 10 minutes. The cause of arcing is that an insulating aluminum oxide phase contained in the oxide sintered body and a high resistance spinel phase having an Al / (Al + Ga) atomic ratio of 90 atomic% or more were contained. Thus, the oxide sintered compact which is easy to generate | occur | produce arcing by supplying high direct-current power cannot be used as a target for mass production of a transparent conductive film.
When the film was formed in the same manner by increasing the DC input power to the target to 850 W, a transparent conductive film having high conductivity and high transmittance as described above could not be obtained. This is due to arcing that occurs during film formation, and only a defective film is obtained due to film damage, and the structure as in the example does not form a dense and high-quality film. Therefore, it cannot be used as a transparent electrode of a highly efficient solar cell.

(Comparative Example 11)
The same method and conditions as in Example 1 except that a gallium oxide raw material powder having a particle size of 10 μm was used, and the raw material powder was mixed and pulverized without performing the bead mill treatment, and the same method and conditions as in Example 1. An oxide sintered body containing gallium was manufactured. That is, the types of zinc oxide powder and aluminum oxide powder, the blending ratio of the raw material powders, the ball mill conditions, the production conditions of the compact, and the firing conditions are the same methods and conditions as in Example 1. When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the molded body before firing in the same manner as in Example 1, the standard deviation σ was 42 atomic%. The uniformity between Al and Ga was inferior to the examples.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. In addition to the diffraction peak attributed to the crystal phase, a diffraction peak attributed to the gallium oxide crystal phase was also confirmed. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 5.3 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same, including the atomic ratio. The volume resistivity of the oxide sintered body was 0.09 Ωcm, the density was 5.0 g / cm ³ , the average crystal grain size was 6 μm, and the maximum pore size was 2 μm.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic ratio was measured. As a result, it was 0 to 75 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. Out of range, there was a spinel phase. In particular, the presence of a spinel phase close to the composition of ZnGa ₂ O ₄ was also observed.
When a sputtering target was prepared under the same method and conditions as in Example 1 and film formation was performed under the same conditions, the visible transmittance including the substrate was 85% or more with a specific resistance of 6.9 × 10 ⁻⁴ Ωcm. A transparent conductive film could be obtained.
Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. No particles were generated. However, arcing occurred 260 times in 10 minutes. The cause of arcing is due to the insulating gallium oxide phase and particles contained in the oxide sintered body. The generation of particles seems to be due to the inclusion of a high resistance spinel phase with an Al / (Al + Ga) atomic ratio of 10 atomic% or less. In this way, arcing is likely to occur by applying high DC power, and particles are likely to be generated during continuous sputtering film formation.
When a film was formed in the same manner by increasing the DC input power to the target to 850 W, a transparent conductive film having high conductivity and high transmittance as described above could not be obtained. This is due to arcing that occurs during film formation, and only a defective film is obtained due to film damage, and the structure as in the example does not form a dense and high-quality film. Therefore, it cannot be used as a transparent electrode of a highly efficient solar cell.
Such an oxide sintered body cannot be used as a target for mass production of a transparent conductive film.

(Comparative Example 12)
Zinc oxide powder, aluminum oxide powder, and gallium oxide powder having an average particle size of 1 μm or less were used. The mixing ratio of these materials was 26.9 atomic% in terms of the Al / (Al + Ga) atomic ratio, (Al + Ga). ) / (Zn + Al + Ga) atomic ratio was 6.1 atomic%, and the mixture was placed in a resin pot and wet mixed by a ball mill. In this wet ball mill mixing, hard zirconia balls were used, and 1% by weight of polyvinyl alcohol was added as a binder to the total amount of raw material powder and mixed for 18 hours. The mixed slurry was taken out, dried and granulated. The granulated product was molded with a cold isostatic press at a pressure of 3 ton / cm ² .
When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the compact before firing in the same manner as in Example 1, the standard deviation σ was 46 atomic%. The uniformity between Al and Ga was inferior to the examples.
Next, the molded body was fired by the following procedure. The temperature was raised to 1000 ° C. at a rate of 1 ° C./min and 1000 to 1400 ° C. at a rate of 3 ° C./min in an air atmosphere, and the sintering temperature was held at 1400 ° C. for 5 hours for sintering.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. In addition to the diffraction peak attributed to the crystal phase, a diffraction peak attributed to the gallium oxide crystal phase was also confirmed. The milled end of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 6.0 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same, including the atomic ratio.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. The EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic ratio was measured to be 3 to 61 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. Out of range, there was a spinel phase. In particular, the presence of a spinel phase close to the composition of ZnGa ₂ O ₄ was also observed.
When a sputtering target was prepared under the same method and conditions as in Example 1 and film formation was performed under the same conditions, the visible transmittance including the substrate was 85% or more with a specific resistance of 8.5 × 10 ⁻⁴ Ωcm. A transparent conductive film could be obtained.
Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. Particles were easily generated and arcing occurred twice in 10 minutes. The generation of particles is considered to be due to the inclusion of a high resistance spinel phase having an Al / (Al + Ga) atomic ratio of 10 atomic% or less, and it is considered that arcing occurred due to the particles. In this way, arcing is likely to occur by applying high DC power, and particles are likely to be generated during continuous sputtering film formation. When a film was formed in the same manner by increasing the DC input power to the target to 850 W, a transparent conductive film having high conductivity and high transmittance as described above could not be obtained. This is because arcing that occurs during film formation is the cause, and only defective films can be obtained. Therefore, a fine film having a dense structure as in the example cannot be obtained, and it cannot be used as a transparent electrode of a highly efficient solar cell. In addition, such an oxide sintered body cannot be used as a target for mass production of a transparent conductive film.

(Comparative Example 13)
A zinc oxide powder, an aluminum oxide powder, or a gallium oxide powder having an average particle size of 1 μm or less was used. The mixing ratio of these materials was 52.5 atomic% in terms of the Al / (Al + Ga) atomic ratio, (Al + Ga). ) / (Zn + Al + Ga) atomic ratio was 6.2 atomic%, and the mixture was placed in a resin pot and wet mixed by a ball mill. In this wet ball mill mixing, hard zirconia balls were used, and 1% by weight of polyvinyl alcohol was added as a binder to the total amount of raw material powder and mixed for 18 hours. The mixed slurry was taken out, dried and granulated. The granulated product was molded with a cold isostatic press at a pressure of 3 ton / cm ² . When the uniformity of the Al / (Al + Ga) atomic number ratio of the mixed raw material powder was evaluated using the molded body before firing in the same manner as in Example 1, the standard deviation σ was 43 atomic%. The uniformity between Al and Ga was inferior to the examples.
Next, the molded body was fired by the following procedure. The temperature was raised to 1000 ° C. at a rate of 1 ° C./min and 1000 to 1400 ° C. at a rate of 3 ° C./min in an air atmosphere, and the sintering temperature was held at 1400 ° C. for 5 hours for sintering.
The obtained oxide sintered body was evaluated in the same manner as in Example 1. The milled end of the obtained oxide sintered body was pulverized, powder X-ray diffraction measurement was performed, and the formation phase was identified. As a result, a zinc oxide crystal phase having a hexagonal wurtzite structure and a spinel structure were obtained. In addition to the diffraction peak attributed to the crystal phase, a diffraction peak attributed to the gallium oxide crystal phase was also confirmed. The milled end material of the obtained oxide sintered body was pulverized and analyzed for composition by ICP emission spectroscopy. As a result, the (Al + Ga) / (Zn + Al + Ga) atomic ratio was 6.2 atomic%, and Al / (Al + Ga) ) It was confirmed that the composition was almost the same as the composition, including the atomic ratio.
The end material of the oxide sintered body was sliced by FIB processing and observed with a transmission electron microscope (TEM) mounted on an energy dispersive X-ray fluorescence spectrometer (EDX). In the oxide sintered body, it was confirmed by electron beam diffraction that the spinel crystal phase was dispersed in the parent phase of the wurtzite structure. When local composition analysis was performed by EDX, it was found that the parent phase of the wurtzite structure was zinc oxide containing aluminum and gallium, and the spinel phase was a Zn—Al—Ga—O phase. EDX composition analysis was performed on 50 spinel phases, and the Al / (Al + Ga) atomic ratio was measured. As a result, it was 6 to 85 atomic%, and the Al / (Al + Ga) atomic ratio was 10 to 90 atomic%. There was a spinel phase out of range. In particular, the presence of a spinel phase close to the composition of ZnGa ₂ O ₄ was also observed.
When a sputtering target was prepared under the same method and conditions as in Example 1 and film formation was performed under the same conditions, the visible transmittance including the substrate with a specific resistance of 9.8 × 10 ⁻⁴ Ωcm was 85% or more. A transparent conductive film could be obtained.
Further, the occurrence of arcing and the occurrence of particles were evaluated under the same method and conditions as in Example 1. Particles were easily generated and arcing occurred twice in 10 minutes. The generation of particles is considered to be due to the inclusion of a high resistance spinel phase having an Al / (Al + Ga) atomic ratio of 10 atomic% or less, and it is considered that arcing occurred due to the particles. In this way, arcing is likely to occur when high DC power is applied, and particles are likely to be generated during continuous sputtering film formation. When a film was formed in the same manner by increasing the DC input power to the target to 850 W, a transparent conductive film having high conductivity and high transmittance as described above could not be obtained. This is due to arcing that occurs during film formation, and only a defective film is obtained due to film damage, and the structure as in the example does not form a dense and high-quality film. Therefore, it cannot be used as a transparent electrode of a highly efficient solar cell. Therefore, such an oxide sintered body cannot be used as a target for mass production of a transparent conductive film.

<Discharge current-discharge voltage characteristics experiment>
Using the oxide sintered compact targets of Examples 1 and 2 and Comparative Examples 1, 6, and 7, the current-voltage during discharge under constant sputtering conditions was examined. The target-substrate distance was fixed to 60 mm with respect to the target produced from said oxide sintered compact of diameter 152mm (PHI). After evacuating to 5 × 10 ⁻⁵ Pa or less, pure Ar gas was introduced, the gas pressure was set to 0.6 Pa, and direct current power 500 W was applied to generate direct current plasma. The results of measuring the discharge voltage and discharge current at that time are shown in Table 2.

  As shown in Table 2, when the oxide sintered bodies of Examples 1 and 2 were used, compared to when the oxide sintered bodies of Comparative Examples 1, 6, and 7 were used, the same DC power was applied. The discharge voltage is low and the discharge current is high. That is, when the oxide sintered bodies of Examples 1 and 2 are used, the discharge impedance is low, and electrons are easily emitted from the surface of the oxide sintered bodies of Examples 1 and 2. This is due to the difference in the composition of the spinel phase in the oxide sintered body, and in the Zn-Al-Ga-O-based spinel phase rather than the zinc aluminate spinel phase and the zinc gallate spinel phase. It is considered that the conductivity is high and electrons are likely to be emitted during discharge, thereby reducing the impedance. From comparison between Examples 1 and 2 and Comparative Example 1, it can be said that the better the uniformity of the Zn-Al-Ga-O spinel phase Al and Ga, the lower the impedance. Needless to say, arcing is unlikely to occur when the discharge voltage is low.

In addition, when magnetron sputtering film formation is performed using a zinc oxide-based oxide target, the shadow of oxygen in the sintered body generated from the erosion part of the target surface (where the target surface is irradiated with a lot of Ar ions). Ions are accelerated by the discharge voltage and collide with the thin film on the substrate. The higher the discharge voltage, the greater the impact and damage the thin film. On the other hand, the center of the target is a non-erosion portion, and the thin film on the substrate disposed immediately above the target is hardly damaged by the impact of oxygen anions. The specific resistance (ρ _s ) of the film deposited immediately above the non-erosion portion at the center of the target and the specific resistance (ρ _e ) of the film deposited immediately above the center of the erosion portion are measured, and the rate of change (ρ _e / ρ _s ) was examined. The results are shown in Table 2. The rate of change (ρ _e / ρ _s ) was smaller when the oxide sintered bodies of Examples 1 and 2 having a low discharge voltage were used.

  When a transparent conductive film is formed on a large substrate during mass production, the substrate is often formed while the substrate passes and moves on the target so that a uniform film can be formed on the entire substrate. At that time, a film formed immediately above the non-erosion portion and a film formed immediately above the erosion portion are laminated. Therefore, the specific resistance of the film deposited immediately above the erosion part should be as low as possible. The target produced from the oxide sintered body of the present invention has a lower discharge voltage than the conventional one, and the resistivity of the high resistance film deposited from the erosion part is relatively low. can do. Therefore, the oxide sintered body of the present invention can provide an industrially useful target capable of obtaining a low resistance film even in pass film formation during mass production.

(Example 10)
A solar cell having a structure as shown in FIG. 2, which is an example of the present invention, was produced by the following procedure. On the glass substrate (12), the transparent electrode film (11) of Example 1 was formed to a thickness of about 500 nm under the same film forming conditions as in Example 1 by direct current magnetron sputtering.
A ZnO target was used thereon, a ZnO target was used, Ar was used as the sputtering gas, and a ZnO thin film having a thickness of about 150 nm was formed as the window layer (10). In order to form a hetero pn junction thereon, a CdS thin film is deposited as a semiconductor intermediate layer (9) by a solution deposition method, and a mixed solution of CdI ₂ , NH ₄ Cl ₂ , NH ₃ , and thiourea is used. Formed. A CuInSe ₂ thin film was formed thereon as a p-type semiconductor light absorption layer (8) to a thickness of 2 to 3 μm by vacuum evaporation. An Au film was formed thereon as a back metal electrode (7) to a thickness of about 1 μm by vacuum deposition.
When the characteristics of this solar cell were examined by irradiating irradiation light of AM1.5 (100 mW / cm ² ) from the transparent electrode film side, the conversion efficiency was 14%.

(Example 11)
A solar cell having the structure shown in FIG. 2 was produced by the same procedure and the same method as in Example 10 except that the film of Example 4 was used as the transparent electrode film. When the characteristics of the solar cell with respect to the irradiation light of AM 1.5 (100 mW / cm ² ) were examined under the same conditions and in the same manner as in Example 10, the conversion efficiency was 13.5%.

(Example 12)
In Example 10 and Example 11, the example which investigated the characteristic of the solar cell using the film | membrane of Example 1 and Example 4 was shown, However, The other film | membrane of Examples 2, 3, 5-9 was used. The produced solar cell having the structure shown in FIG. 2 also had a high conversion efficiency of 12% or more.

(Comparative Example 14)
A solar cell having the structure shown in FIG. 2 was produced under the same conditions and procedures as in Example 8 except that an ITO film was used as the transparent electrode film. The ITO film was fixed at a target-substrate distance of 60 mm by using an ITO sintered body target (10 wt% SnO ₂ added product) having a diameter of 152 mm and a thickness of 5 mm. After evacuating to 5 × 10 ⁻⁵ Pa or less, pure Ar gas mixed with 5% O ₂ gas is introduced, the gas pressure is set to 0.3 Pa, and DC power is applied to generate DC plasma. DC sputtering film formation was performed without heating.
When the characteristics of the solar cell were examined under the same conditions, the conversion efficiency was 5%, which was extremely low as compared with the solar cells of Examples 10 to 12 of the present invention. In addition, when an ITO film having the same composition produced by changing the amount of oxygen in the sputtering gas during film formation from 0 to 10% was used as a transparent electrode film, the characteristics were examined in the same manner, and the conversion efficiency was 7% or less. Met.

(Comparative Example 15)
A solar cell having the structure of FIG. 2 was produced under the same conditions and procedure as in Example 10 except that the gallium-doped zinc oxide film of Comparative Example 7 was used as the transparent electrode film.
When the characteristics were examined under the same conditions, the conversion efficiency was 7%, which was lower than that of the solar cells of Examples 8 to 10 of the present invention. Further, using a gallium-doped zinc oxide film having the same composition as that of Comparative Example 7 produced by changing the amount of oxygen in the sputtering gas during film formation from 0 to 10%, the characteristics were similarly examined. As a result, the conversion efficiency was 7.5% or less, and a conversion efficiency higher than that of Examples 8 to 10 of the present invention was not obtained.

(Example 13)
A solar cell having a structure as shown in FIG. 3, which is an example of the present invention, was produced by the following procedure. A Mo electrode as a lower electrode (13) was formed on a glass substrate (12) to a thickness of 1 to 2 μm by a direct current magnetron sputtering method. Thereafter, a CuInSe ₂ thin film was formed in a predetermined region as a p-type semiconductor light absorption layer (8) to a thickness of 2 to 3 μm by vacuum deposition. In order to form a hetero pn junction thereon, a CdS thin film, which is a semiconductor intermediate layer (9), is deposited by solution deposition using a mixed solution of CdI ₂ , NH ₄ Cl ₂ , NH ₃ , and thiourea to a thickness of 50 nm. It was formed to a thickness of about. On top of this, a ZnO target is formed by DC magnetron sputtering, Ar is used as the sputtering gas, and a ZnO thin film having a conductivity similar to that of the CdS thin film is formed as the window layer (10) to a thickness of about 150 nm. did. Further, a zinc oxide-based transparent electrode film (11) of Example 1 (the present invention) was formed to a thickness of about 500 nm under the same conditions as in Example 1 by the same DC magnetron sputtering method.
When the characteristics were examined by irradiating the solar cell with irradiation light of AM1.5 (100 mW / cm ² ) from the glass substrate side, the conversion efficiency was 14.5%.

(Example 14)
The solar cell of the present invention having the structure of FIG. 3 was prepared under the same conditions and procedures as in Example 10 except that the zinc oxide-based transparent electrode film of Example 4 was used as the transparent electrode film. As a result, the conversion efficiency was 14%.

(Example 15)
In Example 13 and Example 14, an example was shown in which the characteristics of the solar cell having the structure of FIG. 3 were examined using the films of Example 1 and Example 4, but other than Examples 2, 3, and 5-9. Similarly, the solar cell produced using this film had a high conversion efficiency of 13% or more.

(Comparative Example 16)
A solar cell having the structure of FIG. 3 was produced under the same conditions and procedure as in Example 13 except that a conventional ITO film was used as the transparent electrode film, and the characteristics of the solar cell were examined under the same conditions. The composition of the ITO film and the film forming conditions are the same as in Comparative Example 14.
Similarly, as a result of examining the solar cell characteristics, the conversion efficiency was 6%, which was extremely low as compared with the solar cells of Examples 13 to 15 of the present invention. Moreover, when the ITO film of the same composition produced on the same conditions except having changed the amount of oxygen in the sputtering gas at the time of film-forming to 0-10% was used for the transparent electrode film, the characteristic was investigated similarly, and conversion was carried out. The efficiency was 8.5% or less.

(Comparative Example 17)
A solar cell having the structure of FIG. 3 was produced under the same conditions and procedures as in Example 13 except that the gallium-doped zinc oxide film of Comparative Example 7 was used as the transparent electrode film.
When the characteristics were examined under the same conditions, the conversion efficiency was 8%, which was lower than that of the solar cells of Examples 13 to 15 of the present invention. Further, using a gallium-doped zinc oxide film having the same composition as that of Comparative Example 7 produced by changing the amount of oxygen in the sputtering gas during film formation from 0 to 10%, the characteristics were similarly examined. It was. As a result, all had a conversion efficiency of 8% or less, which was lower than those of Examples 13 to 15 of the present invention.

Examples 10 to 15, an example of a solar cell using the CuInSe ₂ thin film in the light-absorbing layer, CuInS ₂ in the light-absorbing _{layer, CuGaSe 2, Cu (In,} Ga) Se 2, Cu (In, Ga ) (S, Se) ₂ , using CdTe thin film is the same result, and the use of the transparent electrode film of the present invention clearly shows higher conversion efficiency than the case of using the conventional transparent electrode film. It has been found that solar cells can be manufactured.

  As described above, the characteristics of the solar cell obtained in this example are far superior to the characteristics of the solar cell obtained with the conventional configuration. This is considered to be because the transparent electrode film of the present invention has high transmittance of not only visible light but also infrared rays, and thus solar energy can be converted into electric energy with high efficiency.

It is explanatory drawing which shows schematic structure of the silicon-type solar cell using the oxide transparent electrode film of this invention. It is explanatory drawing which shows schematic structure of the compound thin film type solar cell which used the oxide transparent electrode film of this invention for the glass substrate side. It is explanatory drawing which shows schematic structure of the compound thin film type solar cell which used the oxide transparent electrode film of this invention on the opposite side to a glass substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Front side (light-receiving part side) Transparent electrode film 3 P-type amorphous silicon film 4 Amorphous silicon film not containing impurities 5 N-type amorphous silicon film 6 Back side transparent electrode film 7 Back side metal electrode 8 Light absorbing layer 9 Semiconductor intermediate Layer 10 Window layer 11 Oxide transparent electrode film 12 Glass substrate 13 Lower electrode

Claims (25)

An oxide sintered body containing zinc oxide, aluminum and gallium, and substantially composed of a crystal phase of a wurtzite zinc oxide phase and a spinel oxide phase,
(1) The content of aluminum and gallium in the oxide sintered body is 0.3 to 6.5 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio, and the aluminum content is Al / ( Al + Ga) atomic ratio is 30-70 atomic%,
(2) The oxide sintered body, wherein the content of aluminum in the spinel type oxide phase is 10 to 90 atomic% in terms of Al / (Al + Ga) atomic ratio.   2. The oxide firing according to claim 1, wherein aluminum and gallium are all contained in the wurtzite zinc oxide phase and / or the spinel oxide phase, and do not contain the aluminum oxide phase and the gallium oxide phase. Union.   3. The oxide sintered body according to claim 1, wherein the oxide sintered body does not contain a zinc oxide or zinc gallate spinel type oxide phase. 4. After adding and mixing gallium oxide powder and aluminum oxide powder to the zinc oxide powder as the raw material powder, the slurry obtained by mixing the raw material powder with the aqueous medium is then pulverized and mixed, and then pulverized and mixed. A method for producing an oxide sintered body in which a mixture is molded and then the molded body is fired,
The raw material powder in the slurry is uniformly pulverized and mixed under conditions sufficient for the standard deviation of the Al / (Al + Ga) atomic ratio to be 25 atomic% or less. The manufacturing method of oxide sinter described in 2.   The gallium oxide powder and the aluminum oxide powder are added to the zinc oxide powder so as to contain 0.3 to 6.5 atomic percent in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio. A method for producing an oxide sintered body.   6. The oxide firing according to claim 4, wherein the gallium oxide powder and the aluminum oxide powder are added to the zinc oxide powder at a ratio of 30 to 70 atomic% in terms of an Al / (Al + Ga) atomic ratio. A method for producing a knot.   The method for producing an oxide sintered body according to claim 4, wherein the raw material powder is pulverized and mixed using a bead mill.   The method for producing an oxide sintered body according to claim 4 or 7, wherein the raw material powder is preliminarily pulverized and mixed in a ball mill.   5. The method for producing an oxide sintered body according to claim 4, wherein the compact is fired at normal pressure at a temperature of 1250 to 1350 ° C. for 15 to 25 hours.   The target obtained by processing the zinc oxide type oxide sintered compact containing aluminum and gallium in any one of Claims 1-3.   A transparent conductive film formed on a substrate by sputtering or ion plating using the target according to claim 10.   The transparent conductive film according to claim 11, wherein the content of aluminum and gallium is 0.3 to 6.5 atomic% in terms of (Al + Ga) / (Zn + Al + Ga) atomic ratio.   13. The transparent conductive film according to claim 11, wherein the aluminum content is 30 to 70 atomic% in terms of an Al / (Al + Ga) atomic ratio.   The transparent conductive film according to claim 11, wherein the transparent conductive film is composed of a crystal phase substantially consisting of a wurtzite zinc oxide phase.   The transparent conductive film according to claim 11, wherein aluminum and gallium are all contained in the wurtzite zinc oxide phase and do not contain an aluminum oxide phase and a gallium oxide phase. The specific resistance is 9.0 * 10 < ^-4 > (omega | ohm) cm or less, The transparent conductive film in any one of Claims 11-15 characterized by the above-mentioned.   The transparent conductive film according to claim 11, wherein the transmittance of the film itself at a wavelength of 780 to 1200 nm is 76% or more.   The transparent conductive film according to claim 11, wherein the substrate is a transparent substrate made of glass or plastic.   The solar cell which uses the transparent conductive film in any one of Claims 11-17 as an electrode.   The solar cell according to claim 19, wherein the photovoltaic cell is a thin-film solar cell using a silicon-based semiconductor or a compound semiconductor.   An electrode layer made of a p-type semiconductor light absorption layer, an n-type semiconductor intermediate layer, a semiconductor window layer, and a transparent conductive film is formed on a non-metallic substrate provided with an electrode layer or a metal substrate having electrode properties. The solar cell according to claim 19, comprising a sequentially stacked structure.   It includes a structure in which a semiconductor window layer, an n-type semiconductor intermediate layer, and a p-type semiconductor light absorption layer are sequentially stacked on an electrode layer made of a transparent conductive film on a transparent substrate. The solar cell according to claim 19. Light absorbing _{layer, CuInSe 2, CuInS 2, CuGaSe} 2, CuGaS 2, solar cell according to claim 21 or 22, characterized in that at least one selected from a solid solution thereof, or CdTe.   The solar cell according to any one of claims 21 to 23, wherein the intermediate layer is a CdS layer or a (Cd, Zn) S layer.   The solar cell according to any one of claims 21 to 24, wherein the window layer is ZnO or (Zn, Mg) O.

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