JP7090263B2 - Method for manufacturing delafosite type Cu-based composite oxide film - Google Patents

Description

The present invention relates to a method for producing a delafosite-type Cu-based composite oxide film.

In order to improve the performance and reduce the cost of light emitting devices and power devices, inexpensive and high-performance p-type semiconductor materials are required. Nitride-based semiconductors such as GaN and carbide-based semiconductors such as SiC are known as p-type semiconductor materials, but these are expensive materials. Therefore, if a high-performance p-type semiconductor material can be realized with an inexpensive oxide-based material, the merit is great.

As an oxide-based p-type semiconductor, delafosite-type Cu-based composite oxides such as CuAlO ₂ and CuGaO ₂ are known. It is known to be manufactured by the position method) or the like. For example, Non-Patent Document 1 discloses that a p-type CuAlO ₂ thin film is grown on a c-plane sapphire substrate by a radio frequency (RF) magnetron sputtering method, and its structure and optical properties are investigated. Further, Non-Patent Document 2 discloses that a transparent p-type CuGaO ₂ thin film is epitaxially grown on a sapphire (001) substrate by a PLD method (pulse laser deposition method).

On the other hand, the hydrothermal method is known as a method capable of synthesizing high-quality crystals at low cost, and there is an example in which crystals of CuAlO ₂ or CuGaO ₂ are synthesized by the hydrothermal method. For example, Non-Patent Document 3 discloses that CuAlO ₂ nanocrystals are synthesized by a hydrothermal metathesis reaction, and a p-type transparent CuAlO ₂ semiconductor film is produced from the nanocrystals by a spin-on method. Further, Non-Patent Document 4 discloses that a CuGaO ₂ nanoplate having a rhombohedral crystal phase having a diameter of about 10 μm is synthesized by a low-temperature hydrothermal method.

Min Fang et al., "Optical properties of p-type CuAlO2 thin film grown by rf magnetron sputtering", Applied Surface Science, 2011, Vol.257, p.8330-8333 K. Ueda et al., "Epitaxial growth of transparent p-type conducting CuGaO2 thin films on sapphire (001) conveyed by pulsed laser deposition", Journal of Applied Physics, 1 February 2001, Vol.89, No.3, p. 1790-1793 Shanmin Gao et al., "Preparation of CuAlO2 nanocrystalline transparent thin films with high conductivity", Nanotechnology, 2003, Vol.14, p.538-541 Linlin Shi et al., "Photoluminescence and photocatalytic properties of rhombohedral CuGaO2 nanoplates", Scientific Reports 6: 21135 (2016)

WO2015 / 093335A1

However, the conventional delafosite-type Cu-based composite oxide film produced by a sputtering method, a PLD method, or the like as reported in Non-Patent Documents 1 and 2 has insufficient p-type performance. Further, the crystals of CuAlO ₂ and CuGaO ₂ synthesized by the hydrothermal method as reported in Non-Patent Documents 3 and 4 are in the form of powder, and are film-like delafos necessary for producing light emitting devices and power devices. No example of directly synthesizing a site-type Cu-based composite oxide by a hydrothermal method has been reported so far.

The present inventor has recently obtained the finding that a delafosite-type Cu-based composite oxide film having high p-type performance can be produced by forming a seed crystal layer on a substrate and subjecting it to hydrothermal treatment.

Therefore, an object of the present invention is to provide a method capable of producing a delafosite-type Cu-based composite oxide film having high p-type performance.

According to one aspect of the present invention, it is a method for producing a delafosite type Cu-based composite oxide film.
The process of preparing the board and
A step of forming a seed crystal layer of a delafosite-type Cu-based composite oxide on the substrate, and
The seed crystal layer is immersed in a raw material aqueous solution containing Cu ions and ions of at least one element selected from the group consisting of Al, Ga, Fe, Cr and Mn, and subjected to hydrothermal treatment. In the formula, X is a delafosite type Cu-based composite having a composition represented by the general formula of CuXO ₂ (X is at least one element selected from the group consisting of Al, Ga, Fe, Cr and Mn). The process of forming an oxide film and
Methods are provided, including.

It is an optical microscope image of the surface of the delafosite type Cu-based composite oxide film (CuGaO ₂ layer) produced in Example 1. 6 is a cross-sectional SEM image of a composite material containing a delafosite-type Cu-based composite oxide film (CuGaO ₂ layer) produced in Example 1. 6 is a scanning capacitance microscope (SCM) image showing the p-type intensity of the delafosite-type Cu-based composite oxide film (CuGaO ₂ layer) produced in Example 1. 9 is a scanning capacitance microscope (SCM) image showing the p-type intensity of the CuAlO type ₂ crystal layer according to Example 2 (comparison).

Method for Producing Cu-based Composite Oxide Film The present invention relates to a method for producing a delafosite-type Cu-based composite oxide film. The delafosite-type Cu-based composite oxide film produced by the method of the present invention is CuXO ₂ (in the formula, X is at least one element selected from the group consisting of Al, Ga, Fe, Cr and Mn). It has a composition represented by the general formula of). This composition results in a delafosite-type crystal structure and contributes to the development of p-type performance. Examples of X in the above general formula include Al, Ga, Fe, Cr, Mn and combinations thereof, preferably Al, Ga, Cr and combinations thereof, more preferably Al, Ga and their combinations. Combinations, more preferably Ga. X may be two or more elements, for example a combination of Al and Ga. In this case, two types of delafosite-type crystal phases (for example, CuAlO ₂ phase and CuGaO ₂ phase) may be mixed or may be a mixed crystal.

The method of the present invention comprises (1) a step of preparing a substrate, (2) a step of forming a seed crystal layer of a delafosite-type Cu-based composite oxide on the substrate, and (3) a predetermined composition of the seed crystal layer. The present invention comprises a step of immersing the material in an aqueous solution of the raw material and subjecting it to a hydrothermal treatment to form a delafosite-type Cu-based composite oxide film having a predetermined composition. By forming the seed crystal layer on the substrate and subjecting it to hydrothermal treatment in this way, a delafosite-type Cu-based composite oxide film having high p-type performance can be produced.

As described above, the conventional delafosite-type Cu-based composite oxide film produced by the sputtering method, the PLD method, or the like has insufficient p-type performance, while the conventional CuAlO ₂ or CuGaO synthesized by the hydrothermal method. The _two crystals were in the form of powder and were not film-like crystals required for the production of light emitting devices and power devices. However, according to the method of the present invention, a delafosite-type Cu-based composite oxide having high p-type performance is used. It has the advantage of being able to produce a film.

(1) Preparation of a substrate In the method of the present invention, a substrate is first prepared. The substrate is not particularly limited as long as it can form a seed crystal layer of a delafosite-type Cu-based composite oxide on the substrate, but from the viewpoint of preventing the seed crystal layer from peeling off from the substrate due to heating, the substrate is a substrate. The average coefficient of thermal expansion in the in-plane direction in the temperature range of 25 to 1000 ° C. is preferably 7.0 × 10 ^-6 to 10.0 × 10 ^-6 / K, more preferably 7.5 × 10 ⁻ . It is ⁶ to 9.5 × 10 ^-6 / K. Examples of such a substrate include a sapphire substrate, an oriented polycrystalline alumina substrate, and an _{MgAl 2O4} substrate, with particular preference being a sapphire substrate and an oriented polycrystalline alumina substrate. The average coefficient of thermal expansion of the c-plane sapphire substrate in the temperature range of 25 to 1000 ° C. is 8.3 × 10 ^-6 / K. The average coefficient of thermal expansion of the oriented polycrystalline alumina substrate in the temperature range of 25 to 1000 ° C. is 8.3 × 10 ^-6 / K. The average coefficient of thermal expansion of the substrate in the temperature range of 25 to 1000 ° C. can be measured by the method described in JIS R 1618 using a push rod type expansion meter.

The sapphire substrate may have any azimuth plane such as a plane, c plane, r plane, m plane, etc., and may have a predetermined off angle with respect to these planes. Further, sapphire to which a dopant is added may be used in order to adjust the optical characteristics and the electrical characteristics. Known dopants can be used.

On the other hand, the oriented polycrystalline alumina substrate is typically composed of an oriented polycrystalline alumina sintered body. Alumina is aluminum oxide (Al ₂ O ₃ ), typically α-alumina having the same corundum type structure as single crystal sapphire, and the oriented polycrystalline alumina sintered body is oriented with innumerable alumina crystal particles. It is a solid that is bonded to each other by sintering in the state. The alumina crystal particles are particles composed of alumina, and may contain a dopant and unavoidable impurities as other elements, or may be composed of alumina and unavoidable impurities. The oriented polycrystalline alumina sintered body may contain an additive as a sintering aid as a grain boundary phase. Further, the oriented polycrystalline alumina sintered body may contain other phases or other elements as described above in addition to the alumina crystal particles, but is preferably composed of alumina crystal particles and unavoidable impurities. Further, the orientation plane of the oriented polycrystalline alumina sintered body on which the single crystal film is produced is not particularly limited, and may be a c-plane, an a-plane, an r-plane, an m-plane, or the like. In any case, the oriented polycrystalline alumina sintered body is composed of an alumina sintered body composed of a large number of alumina single crystal particles, and the large number of single crystal particles are oriented in a certain direction to some extent or highly. be. Polycrystalline alumina sintered bodies oriented in this way are stronger and cheaper than alumina single crystals and therefore provide a much cheaper but larger area substrate than when using single crystal substrates. There is an advantage that it can be done. Such an oriented polycrystalline alumina substrate or an oriented polycrystalline alumina sintered body is already known together with a method for producing the same, and is disclosed in, for example, Patent Document 1 (WO2015 / 093335A1).

(2) Formation of a seed crystal layer Next, a seed crystal layer of a delafosite-type Cu-based composite oxide is formed on the substrate. The seed crystal layer has a composition represented by the general formula of CuX'O ₂ (in the formula, X'is at least one element selected from the group consisting of Al, Ga, Fe, Cr and Mn). Is preferable. The above composition enables the desired formation of a delafosite-type Cu-based composite oxide film on a seed crystal layer, and contributes to the realization of a delafosite-type Cu-based composite oxide film exhibiting high p-type performance. Examples of X'in the above general formula include Al, Ga, Fe, Cr, Mn and combinations thereof, preferably Al, Ga, Cr, and combinations thereof, more preferably Al, Ga, and their combinations. , More preferably Ga. X may be two or more elements, for example a combination of Al and Ga. The seed crystal layer may have the same composition as the delafosite-type Cu-based composite oxide film synthesized by hydrothermal treatment, or may have a different composition.

The seed crystal layer is preferably formed by a vapor phase method such as a sputtering method or a PLD, and more preferably a sputtering method. For example, the seed crystal layer may be formed by a sputtering method on a substrate by a desired method such as high frequency (RF) magnetron sputtering using a sputtering target having a composition of CuX'O ₂ . At this time, it is preferable to use a mixed gas of Ar and O ₂ as the sputtering atmosphere, and the preferable flow rate ratio is Ar: O ₂ = 1:10 to 10: 1, for example, 3: 2.

Since the film formed by a vapor phase method such as sputtering (for example, CuX'O ₂ film) is amorphous, it is desirable to crystallize the film by annealing to form a delafosite-type seed crystal layer. Is done. The preferred annealing temperature is 900-1200 ° C. Annealing may be carried out by holding at a temperature within the above range, preferably for 1 second to 60 minutes. Annealing is preferably carried out by a high speed heat treatment method (RTA), in which case the preferred heating rate to the annealing temperature is 0.1-50 ° C./sec. Further, annealing is preferably performed in vacuum. The temperature drop after annealing is not particularly limited, and may be performed by cooling the furnace.

The seed crystal layer thus formed typically has a polycrystalline structure, and more typically has a plurality of single crystal domains that bind to each other in the film plane direction. Each of the domains preferably has a size of 10 to 150 μm in the film surface direction (hereinafter referred to as a single crystal domain size), more preferably 20 to 130 μm, still more preferably 50 to 130 μm, and particularly preferably 50 to 100 μm. .. The single crystal domain size can be determined by the following procedure by observing the surface of the seed crystal layer with an optical microscope. Specifically, an optical microscope is used to acquire an observable image in which a large number of particles are bonded to each other in the film surface direction. At this time, it can be confirmed that each particle (domain) is a single crystal (the crystal orientation is the same) by separately using a method such as EBSD or Raman spectroscopy. Further, the field of view is set so that when a straight line parallel to the upper and lower ends of the field of view is drawn, a straight line that intersects 5 to 15 particles can be drawn for each straight line. Then, in the three straight lines drawn in parallel, the value obtained by multiplying the average length of the inner line segments of the individual particles by 1.5 is adopted as the domain size for all the particles where the straight lines intersect. be able to.

The thickness of the seed crystal layer is not particularly limited, but is preferably 0.001 to 5 μm, more preferably 0.01 to 3 μm, still more preferably 0.1 to 2 μm, and particularly preferably 0.1 to 1 μm.

(3) Hydrothermal treatment Subsequently, the seed crystal layer is immersed in a raw material aqueous solution and subjected to hydrothermal treatment, whereby X is selected from the group consisting of Al, Ga, Fe, Cr and Mn at least in CuXO ₂ (in the formula, X is selected from the group consisting of Al, Ga, Fe, Cr and Mn). A delafosite-type Cu-based composite oxide film having a composition represented by the general formula (which is one kind of element) is formed. The raw material aqueous solution is a solution containing a precursor for producing CuXO ₂ , specifically, Cu ions and at least one element selected from the group consisting of Al, Ga, Fe, Cr and Mn. Contains ions. The ions of these metals are preferably provided in the form of metal salts such as nitrates, sulfates and acetates. Preferred examples of the salt giving Cu ions include copper nitrate, copper sulfate, copper acetate, and hydrates thereof, and particularly preferably copper nitrate or a hydrate thereof. Preferred examples of the salt that gives Al ions include aluminum nitrate, aluminum sulfate, aluminum acetate, and hydrates thereof, and particularly preferably aluminum nitrate or a hydrate thereof. Preferred examples of the salt giving Ga ion include gallium nitrate, gallium sulfate, gallium acetate, and hydrates thereof, and gallium nitrate or a hydrate thereof is particularly preferable. Preferred examples of the salt giving Fe ions include iron nitrate, iron sulfate, iron acetate, and hydrates thereof, and iron nitrate or a hydrate thereof is particularly preferable. Preferred examples of the salt giving Cr ions include chromium nitrate, chromium sulfate, chromium acetate, and hydrates thereof, and particularly preferably chromium nitrate or a hydrate thereof. Preferred examples of the salt giving Mn ion include manganese nitrate, manganese sulfate, manganese acetate, and hydrates thereof, and manganese nitrate or a hydrate thereof is particularly preferable. The pH of the raw material aqueous solution is preferably 6.0 to 11.0, more preferably 7.0 to 10.0, and even more preferably 8.0 to 10.0. The pH of the raw material aqueous solution is preferably adjusted by dropping an alkaline aqueous solution such as a potassium hydroxide aqueous solution. Further, a reducing agent such as ethylene glycol may be added to reduce the metal ion. For example, when divalent Cu ion (Cu ²⁺ ) is used, it can be reduced to monovalent by adding a reducing agent such as ethylene glycol.

The hydrothermal treatment is preferably performed at a temperature of 120 to 250 ° C, more preferably 140 to 240 ° C, and even more preferably 160 to 230 ° C. The holding time at a temperature within the above range (that is, hydroheat treatment time) is preferably 1 hour or longer, more preferably 1 to 100 hours, and further preferably 1 to 50 hours. The hydrothermal treatment is preferably performed in an autoclave (pressure resistant container). For example, it is preferable to place the substrate with the seed crystal layer upright in the autoclave, put the raw material aqueous solution in it, and perform hydrothermal treatment at the above temperature for the above time.

The delafosite-type Cu-based composite oxide film thus obtained by hydrothermal treatment is CuXO ₂ (in the formula, X is at least one element selected from the group consisting of Al, Ga, Fe, Cr and Mn). ) Is a film having a composition represented by the general formula. The delafosite-type Cu-based composite oxide film can exhibit high p-type performance. The reason why the Cu-based composite oxide film exhibits high p-type performance is not clear, but it is presumed that it is due to its high crystallinity.

The Cu-based composite oxide film preferably contains H atoms (hydrogen atoms) at a concentration of 1 × 10 ¹⁸ atoms / cm ³ or more, more preferably 1 × 10 ¹⁸ to 1 × 10 ²² atoms / cm ³ , and further. It is preferably 3 × 10 ¹⁸ to 3 × 10 ²¹ atoms / cm ³ , and particularly preferably 1 × 10 ¹⁹ to 1 × 10 ²¹ atoms / cm ³ . The inclusion of H atoms in such a concentration range contributes to the improvement of p-type performance. Further, the Cu-based composite oxide film preferably contains C atoms (carbon atoms) at a concentration of 1 × 10 ¹⁸ atoms / cm ³ or more, and more preferably 1 × 10 ¹⁸ to 1 × 10 ²² atoms / cm ³ . , More preferably 3 × 10 ¹⁸ to 3 × 10 ²¹ atoms / cm ³ , and particularly preferably 1 × 10 ¹⁹ to 1 × 10 ²¹ atoms / cm ³ . The inclusion of C atoms in such a concentration range contributes to further improvement of p-type performance. Further, in the Cu-based composite oxide film, the C atom contained in the film has the same concentration as or lower than the H atom contained in the film (atoms / cm ³ ), which is the p-type performance. It is preferable from the viewpoint of further improvement.

The Cu-based composite oxide film typically has a polycrystalline structure, and more typically has a plurality of single crystal domains that are bonded to each other in the film surface direction. In this case, from the viewpoint of isotropic conductivity, it is preferable that each of the single crystal domains has a size of 10 to 150 μm in the film surface direction (hereinafter referred to as a single crystal domain size), and more preferably 20 to 130 μm. It is more preferably 50 to 130 μm, and particularly preferably 50 to 100 μm. The determination of the single crystal domain size can be performed in the same manner as described above for the seed crystal layer.

The thickness of the Cu-based composite oxide film is not particularly limited, but is preferably 0.01 to 10 μm, more preferably 0.01 to 5 μm, still more preferably 0.1, from the viewpoint of the balance between conductivity and translucency. It is ~ 5 μm, particularly preferably 0.1 ~ 2 μm.

According to the production method of the present invention, the Cu-based composite oxide film is obtained in a form accompanied by a seed crystal layer and a substrate as an initial form, but a seed crystal layer and / or a substrate is obtained by a subsequent treatment or processing. It may be in the removed form. That is, the Cu-based composite oxide film may be in the form of a self-standing film by itself, in the form of a seed crystal layer, or in the form of a seed crystal layer and a substrate. For example, the Cu-based composite oxide film may be separated from the substrate and the seed crystal layer, or the composite layer of the Cu-based composite oxide film and the seed crystal layer may be separated from the substrate. Separation of the Cu-based composite oxide film may be performed by a known method and is not particularly limited. For example, a method of applying a mechanical impact to separate the film, a method of applying heat to separate the film using thermal stress, a method of applying vibration such as ultrasonic waves to separate the film, and etching unnecessary parts. Examples include a method of separating the film, a method of separating the film by laser lift-off, and a method of separating by mechanical processing such as cutting and polishing. By such a separation method, a Cu-based composite oxide film can be obtained as a self-supporting film. Further, when the composite layer of the Cu-based composite oxide film and the seed crystal layer is separated from the substrate, the composite layer may be separated according to the above method.

The present invention will be described in more detail with reference to the following examples.

Example 1
(1) Formation of Seed Crystal Layer on the Substrate A CuAlO ₂ layer having a thickness of 500 nm was formed on a c-plane sapphire substrate (manufactured by Namiki Precision Jewel Co., Ltd.) having a diameter of 2 inches (5.08 cm) by sputtering.
<Sputtering conditions>
・ Target: CuAlO ₂ (manufactured by Toshima Manufacturing Co., Ltd., purity 4N)
・ Sputtering method: RF magnetron ・ Pressure during film formation: 1.0 Pa
-Introduced gas type at the time of film formation: Ar + O ₂ (flow rate ratio Ar: O ₂ = 3: 2)
・ Substrate temperature: No heating

Although the formed CuAlO ₂ layer was amorphous, it was crystallized by annealing by a high-speed heat treatment method (RTA) to form a delafosite-type CuAlO ₂ layer as a seed crystal layer. This annealing by RTA was carried out by raising the temperature of the CuAlO ₂ layer at 50 ° C./sec, holding it in vacuum at 1050 ° C. for 2 minutes, and lowering the temperature through furnace cooling. The CuAlO _two -layered sapphire substrate thus obtained was cut into 10 mm squares.

(2) Hydrothermal treatment Gallium nitrate octahydrate (manufactured by Kishida Chemical Co., Ltd.) 2.460 g, copper nitrate 2.5 hydrate (manufactured by Sigma Aldrich) 1.450 g, milli-Q water 36 mL, ethylene glycol (Kishida) (Chemical Co., Ltd.) 30 mL was placed in a beaker and stirred with a magnet stirrer for 10 minutes to prepare a raw material solution. A separately prepared 0.5 M KOH aqueous solution was added dropwise to the raw material solution to adjust the pH to 8.8. Then, the raw material solution was kept agitated for 30 minutes. The 10 mm square CuAlO _two -layered sapphire substrate produced in (1) above was inserted into a silicone tube having an inner diameter of 10 mm and a length of about 10 mm, and the substrate was placed upright. This was set in an autoclave having an internal volume of 50 mL, 35 mL of the above pH-adjusted raw material solution was put therein, and hydrothermal heat treatment was performed at 190 ° C. for 24 hours to form a hydrothermal synthetic film. After cooling to room temperature, the substrate was removed from the autoclave and washed with milli-Q water. In this way, a composite material provided with a seed crystal layer (thickness 500 nm) and a hydrothermal synthetic film (thickness 0.2 μm) on the substrate was obtained.

(3) Evaluation The following various evaluations were performed on the hydrothermal synthetic film on the seed crystal layer of the composite material after the hydrothermal treatment.

<Qualitative analysis by X-ray analysis>
When the hydrothermal synthetic membrane was subjected to qualitative analysis of the membrane using an X-ray diffractometer (D8 ADVANCE, manufactured by Bruker AXS), delafosite-type CuAlO ₂ and CuGaO ₂ were detected. CuAlO ₂ has a composition derived from the seed crystal layer, and CuGaO ₂ has a composition derived from the hydrothermal synthesis film.

<Measurement of single crystal domain size>
The surface of the hydrothermal synthesis membrane was observed with an optical microscope to obtain the image shown in FIG. The single crystal domain size was measured by the following procedure based on the obtained optical microscope image. From the optical microscope image, it is observed that a large number of particles are bonded to each other in the film surface direction. It can be confirmed that each particle (domain) is a single crystal (the crystal orientation is the same) by separately using a method such as EBSD or Raman spectroscopy. The field of view was set so that when a straight line parallel to the upper and lower ends of the field of view was drawn, a straight line could be drawn so that each straight line intersected with 5 to 15 particles. In the three straight lines drawn in parallel, the value obtained by multiplying the average length of the inner line segments of the individual particles by 1.5 for all the particles where the straight lines intersect was defined as the domain size. The domain size in this example was 72 μm. In addition, the single crystal domain size of the seed crystal layer was about the same.

<Cross-section observation and measurement of H concentration and C concentration>
The cross section of the composite material after the hydrothermal treatment was observed by SEM, and the cross section SEM image shown in FIG. 2 was obtained. As shown in FIG. 2, a CuAlO type 2 crystal layer formed by sputtering and a CuGaO ₂ layer formed on the CuAlO type ₂ crystal layer by hydrothermal treatment were confirmed. For this film, the impurity concentration of the CuGaO ₂ layer portion was measured by TOF-SIMS. This measurement was performed under the conditions of etching ion species: Cs ⁺ , etching ion acceleration voltage: 2 kV, primary ion species: Bi ⁺ , primary ion acceleration voltage: 25 kV, and secondary ion polarity: Negative. As a result, H was detected at a concentration of 5 × 10 ²⁰ atoms / cm ³ and C was detected at a concentration of 3 × 10 ²⁰ atoms / cm ³ in the CuGaO ₂ layer.

<P-type strength by SCM>
The p-type strength of the hydrothermal synthetic membrane was measured on the surface of the hydrothermal synthetic membrane using a scanning capacitance microscope (SCM) (NanoScope IV, manufactured by Bruker AEX). This measurement was performed using a PtIr-coated silicon cantilever as a probe at a modulation voltage of 8.0 V and a DC bias voltage of 0 V. As a result, the SCM image shown in FIG. 3 was obtained. As shown in the SCM image shown in FIG. 3, a strong p-type dC / dV signal was detected.

Example 2 (comparison)
This example is an example in which the CuAlO _two -layered sapphire substrate (the one on which the hydrothermal synthesis film is not formed) produced in Example 1 is evaluated, and the formation of the hydrothermal synthesis film by hydrothermal treatment is performed. It corresponds to a comparative example in which the same manufacturing procedure as in Example 1 was performed except that the above was not performed. When the impurity concentration in the CuAlO type ₂ crystal layer was measured by TOF-SIMS for the sapphire substrate with CuAlO ₂ layer prepared in Example 1, both the H concentration and the C concentration were below the detection limit. Further, when the CuAlO type ₂ crystal layer was evaluated using a scanning capacitance microscope (SCM) (NanoScope IV manufactured by Bruker AEX Co., Ltd.), the SCM image shown in FIG. 4 was obtained. As shown in FIG. 4, a weak p-type dC / dV signal was detected.

Example 3
A hydrothermal synthetic film was prepared and evaluated in the same manner as in Example 1 except that the CuGaO ₂ target was used as the sputtering target in the formation of the seed crystal layer. The results are as shown in Table 1, and a strong p-type dC / dV signal was detected in the SCM image.

Example 4
A hydrothermal synthetic film was prepared and evaluated in the same manner as in Example 1 except that the annealing conditions were set at 1050 ° C. for 15 seconds in the formation of the seed crystal layer. The results are as shown in Table 1, and although the single crystal domain size was slightly smaller, a strong p-type dC / dV signal was detected in the SCM image.

Example 5
A hydrothermal synthetic film was prepared and evaluated in the same manner as in Example 1 except that the annealing condition was set to 1150 ° C. for 2 minutes in the formation of the seed crystal layer. The results are as shown in Table 1, and although the single crystal domain size was slightly larger, a strong p-type dC / dV signal was detected in the SCM image.

Example 6
A hydrothermal synthetic film was prepared and evaluated in the same manner as in Example 1 except that the pH of the raw material solution in the hydrothermal treatment was 6.5. The results are as shown in Table 1, and a strong p-type dC / dV signal was detected in the SCM image.

Example 7
The hydrothermal synthetic membrane was prepared and evaluated in the same manner as in Example 1 except that the temperature of the hydrothermal treatment was 120 ° C. The results are as shown in Table 1, and a strong p-type dC / dV signal was detected in the SCM image.

Example 8
The hydrothermal synthetic membrane was prepared and evaluated in the same manner as in Example 1 except that the temperature of the hydrothermal treatment was set to 220 ° C. The results are as shown in Table 1, and a strong p-type dC / dV signal was detected in the SCM image.

Example 9
A hydrothermal synthetic film was prepared and evaluated in the same manner as in Example 1 except that the pH of the raw material solution in the hydrothermal treatment was set to 10.5. The results are as shown in Table 1, and a strong p-type dC / dV signal was detected in the SCM image.

Example 10
The hydrothermal synthesis film was prepared and evaluated in the same manner as in Example 1 except that the oriented polycrystalline alumina substrate prepared by the procedure shown below was used instead of the c-plane sapphire substrate. The results are as shown in Table 1, and a strong p-type dC / dV signal was detected in the SCM image.

<Preparation of oriented polycrystalline alumina substrate>
(1) Preparation of plate-shaped alumina particles 96 parts by weight of high-purity γ-alumina powder (TM-300D, manufactured by Taimei Chemicals Co., Ltd.) and 4 parts by weight of high-purity AlF ₃ powder (manufactured by Kanto Chemical Co., Ltd., special grade deer) And 0.17 parts by weight of high-purity α-alumina powder (TM-DAR, manufactured by Taimei Chemicals Co., Ltd., D50: 1 μm) as a seed crystal, together with IPA (isopropyl alcohol) as a solvent, alumina having a diameter of 2 mm. The mixture was mixed in a pot mill for 5 hours using a ball. After mixing in the pot mill, IPA was distilled off with an evaporator to obtain a mixed powder. 300 g of the obtained mixed powder is placed in a sheath made of high-purity alumina (purity 99.5% by weight, volume 750 cm ³ ), covered with a lid made of high-purity alumina (purity 99.5% by weight), and air flowed in an electric furnace. Medium, heat-treated at 900 ° C. for 3 hours. The air flow rate was 25000 cc / min. The heat-treated powder is annealed in the air at 1150 ° C. for 42.5 hours and then pulverized using an alumina ball having a diameter of 2 mm for 4 hours to form a plate having an average particle size of 2 μm, a thickness of 0.3 μm, and an aspect ratio of about 7. A powder composed of like alumina particles was obtained.

(2) Tape molding 1.5 parts by weight of the plate-shaped alumina particles produced in (1) above and fine alumina particles (TM-DAR, average particle size 0.1 μm) having an average particle size smaller than the thickness of the plate-shaped alumina particles. , Taimei Chemicals Co., Ltd.) 98.5 parts by weight was mixed. For 100 parts by weight of this mixed alumina powder, 0.025 parts by weight of magnesium oxide (500A, manufactured by Ube Materials Co., Ltd.) and 7.8 weights of polyvinyl butyral (product number BM-2, manufactured by Sekisui Chemical Industry Co., Ltd.) as a binder. 3.9 parts by weight of di (2-ethylhexyl) phthalate (manufactured by Kurokin Kasei Co., Ltd.) as a plasticizer, and 2 parts by weight of sorbitan trioleate (Leodor SP-O30, manufactured by Kao Co., Ltd.) as a dispersant. , 2-Ethylhexanol was added as a dispersion medium and mixed. The amount of the dispersion medium was adjusted so that the slurry viscosity was 20000 cP. The slurry thus prepared was formed into a sheet on a PET film by a doctor blade method so that the thickness after drying was 20 μm. The obtained sheet (tape) was cut into circular sheet pieces having a diameter of 50.8 mm (2 inches), and then 150 sheet pieces were laminated. The obtained laminate was placed on an Al plate having a thickness of 10 mm, and then placed in a package to evacuate the inside to form a vacuum pack. This vacuum pack was subjected to hydrostatic pressure pressing at a pressure of 100 kgf / cm ² in warm water at 85 ° C. to obtain a disk-shaped molded product.

(3) Firing The obtained molded product was placed in a degreasing furnace and degreased at 600 ° C. for 10 hours. The obtained degreased body was calcined in nitrogen at 1975 ° C. for 4 hours under the condition of a surface pressure of 200 kgf / cm ² by hot pressing using a graphite mold, and then the temperature was lowered. When the temperature was lowered, the surface pressure was released when the temperature reached 1200 ° C. to obtain an alumina sintered body having a diameter of 50.8 mm.

(4) Surface polishing Both the front and back surfaces of the obtained alumina sintered body were mirror-polished with diamond abrasive grains to obtain a thickness of 0.5 mm. The sintered body (sample) thus polished was washed with acetone, ethanol, and ion-exchanged water in this order for 10 minutes each to complete an oriented polycrystalline alumina substrate.

Example 11
A hydrothermal synthetic membrane was prepared and evaluated in the same manner as in Example 1 except that 0.520 g of chromium nitrate nine hydrate was further added at the time of preparing the raw material solution in the hydrothermal treatment. The results are as shown in Table 1, and a strong p-type dC / dV signal was detected in the SCM image.

Claims (3)

A method for producing a delafosite-type Cu-based composite oxide film.
The process of preparing a substrate that is a sapphire substrate or an oriented polycrystalline alumina substrate, and
Dela having a composition represented by the general formula of CuX'O ₂ (in the formula, X'is at least one element selected from the group consisting of Al, Ga, Fe, Cr and Mn) on the substrate. A step of forming a seed crystal layer of a fosite-type Cu-based composite oxide, and
The seed crystal layer is immersed in a raw material aqueous solution having a pH of 6.0 to 11.0 containing Cu ions and ions of at least one element selected from the group consisting of Al, Ga, Fe, Cr and Mn. Then, hydrothermal treatment is performed in an autoclave at a temperature of 120 to 250 ° C. , whereby X is at least one element selected from the group consisting of CuXO ₂ (in the formula, X is Al, Ga, Fe, Cr and Mn). A step of forming a delafosite-type Cu-based composite oxide film having a composition represented by the general formula of (a), and
Including, how. The method according to claim 1, wherein the hydrothermal treatment is performed at a temperature of 150 to 250 ° C. The method according to claim 1 or 2 , wherein the substrate has an average coefficient of thermal expansion of 7.0 × 10 ^-6 to 10.0 × 10 ^-6 / K in a temperature range of 25 to 1000 ° C.

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