JP2022072611A - Crystalline oxide film, structure including the same and method for manufacturing crystalline oxide film - Google Patents

Abstract

To provide a perovskite type oxide thin film having high conductivity and including doped rare earth metal.SOLUTION: A crystalline oxide film including an oxide obtained by doping a rare earth element in a perovskite type oxide represented by a composition formula AXBYO3 (where, A and B represent different metal elements; X is 0.95≤X≤1.05; and Y is 0.60≤Y≤1.05.) has 0.25 degree or less of a rocking curve half value width measured on a (004) plane by an X-ray diffraction method. Preferably, A in the composition formula is a group 2 element, especially Sr, and B is a group 14 element, especially, Sn.SELECTED DRAWING: Figure 1

Description

The present invention relates to a crystalline oxide film and a structure having the crystalline oxide film. The present invention also relates to a method for producing a crystalline oxide film.

A material in which strontium tin oxide is doped with lanthanum is useful as an oxide semiconductor or a transparent conductor. Conventionally, oxide semiconductors and transparent conductors made of this material have been formed mainly by a pulsed laser deposition (PLD) method. For example, Patent Document 1 describes that an SrSnO ₃ film containing 3 atomic% of La is deposited on an SrTiO ₃ substrate containing Nb by the PLD method. In the same document, this film is used as a cathode of a photochemical electrode, and hydrogen gas is generated by using a nitrite electrolytic solution containing hydrogen ions, a sulfurous acid electrolytic solution, or a carbonic acid electrolytic solution as a raw material.

Non-Patent Document 1 describes that a La-doped _SrSnO3 thin film is epitaxially grown by a PLD method. It is described in the same document that this thin film is transparent in the wavelength region of 390 nm to 1600 nm.

Non-Patent Document 2 describes that a lanthanum-doped SrSnO ₃ thin film is formed on an MgO substrate by a PLD method and annealed in a vacuum to obtain high conductivity.

Japanese Unexamined Patent Publication No. 2018-24913

Journal of Physics D: Applied Physics 48 (2015) 455106 Appl. Phys. Lett. 116, 022103 (2020)

As described above, the perovskite-type oxide thin film doped with rare earth metals such as SrSnO ₃ doped with La is a useful material in various fields. As described above, the PLD method was adopted for the production of this thin film. However, the PLD method is industrially unsuitable in that it is unsuitable for producing a large-area thin film and that the film formation rate is low. In addition, the thin film formed by the PLD method could not sufficiently increase its conductivity.
Therefore, an object of the present invention is to improve the conductivity of a perovskite-type oxide thin film doped with a rare earth metal.

In the present invention, the composition formula A _X B _{YO 3} (in the formula, A and B represent different metal elements, X is 0.95 ≦ X ≦ 1.05, and Y is 0.60 ≦ Y ≦ 1. It is a crystalline oxide film containing an oxide obtained by doping a perovskite type oxide represented by (0.05) with a rare earth element.
(004) Provided is a crystalline oxide film having a half-value width of a locking curve of an X-ray diffraction method measured with respect to a plane of 0.25 degrees or less.

Further, the present invention has a substrate having a lattice constant of 3.800 Å or more and 4.300 Å or less and containing an oxide, and a crystalline oxide film formed on the substrate.
A structure in which the crystals of the crystalline oxide film are arranged so as to be aligned with the crystal plane of the substrate.
The crystalline oxide film has a composition formula A _X B _{YO 3} (in the formula, A and B represent metal elements different from each other, X is 0.95 ≦ X ≦ 1.05, and Y is 0.60. The perovskite-type oxide represented by (≦ Y ≦ 1.05) contains an oxide doped with a rare earth element, and the locking curve half-value width of the X-ray diffraction method measured with respect to the (004) plane. Provides a structure having a temperature of 0.25 degrees or less.

Further, the present invention is a method for producing a crystalline oxide film in which a dopant-doped crystalline oxide film is formed on a crystalline substrate.
A precursor layer of the crystalline oxide film is formed on the crystalline substrate, and the precursor layer is formed.
Provided is a method for producing a crystalline oxide film, wherein a dopant-containing layer containing the dopant is formed on the precursor layer, and then the precursor layer and the dopant-containing layer are heated to obtain the crystalline oxide film. It is a thing.

According to the present invention, there is provided a perovskite-type oxide thin film having high conductivity, doped with a rare earth metal, and having element B deficiency and oxygen deficiency.

It is a schematic diagram which shows the apparatus preferably used for manufacturing the crystalline oxide film which concerns on this invention. It is a figure which shows the result of the X-ray diffraction measurement of the crystalline oxide film obtained in Example 1. FIG.

Hereinafter, the present invention will be described based on the preferred embodiment thereof. The present invention relates to a crystalline oxide film. The crystalline oxide film according to the present invention (hereinafter, simply referred to as “oxide film”) has a perovskite-type crystal structure. Specifically, the oxide film according to the present invention contains an oxide obtained by doping a perovskite-type oxide represented by the following composition formula (1) with a rare earth element.
A _X B _Y O ₃ (1)
In the formula, A and B represent different metal elements, X is 0.95 ≦ X ≦ 1.05, and Y is 0.60 ≦ Y ≦ 1.05.
Hereinafter, this oxide film will be described in detail.

As the elements A and B constituting the perovskite-type oxide in the oxide film according to the present invention, various metal ions having different ion sizes and / or valences can be used. Then, by appropriately selecting the combination of the element A and the element B, an oxide film having a desired conductivity can be obtained.
As the element A (that is, the element located at the A site of the perovskite type crystal structure), for example, a group 2 element or a rare earth element can be used. The valence of element A is typically, but not limited to, divalent.
On the other hand, examples of the B element (that is, the element located at the B site of the perovskite type crystal structure) include various transition metal elements. The valence of element B is typically tetravalent, but is not limited to this.

As the element A, it is preferable to use a group 2 element from the viewpoint of improving the conductivity of the oxide film according to the present invention, and a particularly preferable element is Sr.
On the other hand, as the element B, it is preferable to use a group 14 element from the viewpoint of improving the conductivity of the oxide film according to the present invention, and a particularly preferable element is Sn.

In the perovskite-type oxide represented by the composition formula (1), X, which is the molar ratio of element A, is 0.95 or more and 1.05 or less, preferably 0.97 or more and 1.03 or less as described above. It is more preferably 0.98 or more and 1.02 or less. When the perovskite-type oxide contains element A in this range, an appropriate oxygen deficiency occurs in the perovskite-type oxide, and it becomes possible to improve the conductivity of the oxide film according to the present invention.
On the other hand, in the perovskite-type oxide represented by the composition formula (1), Y, which is the molar ratio of element B, is 0.60 or more and 1.05 or less, preferably 0.70 or more and 0. It is 95 or less, more preferably 0.80 or more and 0.90 or less. When the perovskite-type oxide contains element B in this range, appropriate element B deficiency and oxygen deficiency occur in the perovskite-type oxide, and it is possible to improve the conductivity of the oxide film according to the present invention. It becomes.

The perovskite-type oxide represented by the composition formula (1) is doped with a rare earth element. By doping with a rare earth element, it is possible to improve the conductivity of the oxide film according to the present invention. Although not bound by theory, it is preferable that the rare earth element is located at the A site in the perovskite type crystal structure, in other words, it is substituted with a part of the A element from the viewpoint of improving the conductivity.

Examples of the rare earth element include La, Ce, Sc, Y, and Yb. One of these rare earth elements can be used alone, or two or more of them can be used in combination.
Controlling the content of rare earth elements in the perovskite-type oxide represented by the composition formula (1) controls the thickness of the precursor layer and the dopant-containing layer for producing the oxide film according to the present invention. It is achieved by that. Specifically, it is preferably 0.04 or more and 0.5 or less, and more preferably 0.05 or more and 0.2 or less in terms of the ratio of the thickness of the dopant-containing layer to the precursor layer. It is more preferably 0.1 or more and 0.2 or less. By setting the thickness of the dopant-containing layer with respect to the precursor layer in this range, it is possible to improve the conductivity of the oxide film according to the present invention. Details of the precursor layer and the dopant-containing layer will be described later.

The amounts of the elements A and B and the rare earth elements contained in the oxide film according to the present invention can be calculated, for example, by measuring the cross section observed by the cross section TEM by EDS measurement. The amount of oxygen can be measured by, for example, an oxygen / nitrogen analyzer (PS3520U VDD manufactured by Hitachi High-Technologies Corporation).

The oxide film according to the present invention may be composed only of an oxide obtained by doping a perovskite-type oxide represented by the above composition formula (1) with a rare earth element, or in addition to the oxide. It may be composed of other oxides. From the viewpoint of further enhancing the conductivity of the oxide film according to the present invention, the oxide film is composed only of an oxide obtained by doping a perovskite type oxide represented by the composition formula (1) with a rare earth element. It is preferably configured.

Whether or not the oxide film according to the present invention has a perovskite-type crystal structure can be confirmed by, for example, a powder X-ray diffraction method or a surface X-ray diffraction method.

The oxide film according to the present invention is preferably preferentially oriented on the (004) plane. This further improves the conductivity of the oxide film. In order to preferentially orient the oxide film on the (004) plane, for example, according to a suitable manufacturing method for the oxide film described later, on a crystalline substrate having a lattice constant within a predetermined range and preferentially orienting on the (002) plane. An oxide film may be formed on the surface.

As a result of diligent studies by the present inventor of the oxide film according to the present invention, the conductivity of the oxide film is closely related to the full width at half maximum of the locking curve of the X-ray diffraction method (hereinafter, also referred to as "FWHM"). It turned out that there was. Specifically, it was found that the smaller the FWHM value of the oxide film according to the present invention, the higher the conductivity. The reason for this is not clear at present, but as the value of FWHM decreases, the size of the crystal grains of the perovskite-type oxide in the oxide film according to the present invention increases, and the electrical resistance at the grain boundaries decreases. The present inventor thinks that. From this viewpoint, the value of FWHM in the oxide film according to the present invention is set to 0.25 degrees or less, preferably 0.20 or less, and more preferably 0.15 degrees or less. The lower limit of the FWHM is not particularly limited, and the smaller the value, the more preferable. However, if the FWHM value is as small as about 0.05, the intended object of the present invention is achieved.

The value of FWHM is determined by the X-ray diffraction measurement for the oxide film according to the present invention. The value of FWHM is determined based on the diffraction peak of the (004) plane of the oxide film according to the present invention. The reason for selecting the diffraction peak on the (004) plane is that the peak derived from the (004) plane has the highest intensity among the diffraction peaks obtained by the X-ray diffraction measurement for the oxide film according to the present invention. This is due to this (see FIG. 2 described later).

The specific method for measuring the FWHM value is as follows.
2θ (deg) at the intensity value of 1/2 of the diffraction peak of the (004) plane of the oxide film obtained by using the analysis software PDXL2 of the XRD apparatus is calculated.

Next, a suitable method for producing the oxide film according to the present invention will be described. The present production method includes a step of forming a crystalline oxide film doped with a rare earth element as a dopant on a crystalline substrate. In detail, the present manufacturing method is roughly classified into the following steps.
First step: A step of forming a precursor layer of a crystalline oxide film on a crystalline substrate.
Second step: A step of forming a dopant-containing layer containing a rare earth element which is a dopant on the precursor layer.
Third step: The precursor layer and the dopant-containing layer are heated to dope the dopant in the dopant-containing layer, i.e., a rare earth element, into the precursor layer, or simultaneously or separately in the precursor layer. A step of diffusing element B of No. 1 into a layer containing a dopant to obtain a crystalline oxide.
Hereinafter, each step will be described in detail below.

<First step>
In this step, a crystalline substrate is first prepared. The crystalline substrate is used to control the crystallinity of the target oxide film. The crystalline substrate broadly includes those that function as a base for forming a target oxide film, and may be literally a plate-like one or a thin-film one, for example. Considering that the target oxide film contains an oxide having a perovskite-type crystal structure, it is preferable that the crystalline substrate has a cubic crystal structure, and in particular, the lattice constant is 3.800 Å or more 4 It is preferably one having a cubic crystal structure of .300 Å or less. By using a crystalline substrate having a lattice constant in this range, an oxide film having a uniform crystal orientation can be successfully formed on the substrate. From the viewpoint of further enhancing this advantage, the lattice constant of the crystalline substrate is more preferably 3.850 Å or more and 4.200 Å or less, and further preferably 3.900 Å or more and 4.100 Å or less.

The crystalline substrate is preferably configured to contain an oxide. Examples of the oxide include SrTiO ₃ , MgO, KTaO ₃ , NdScO ₃ , NdGaO ₃ , and the like. The crystalline substrate containing these oxides is preferably a single crystal. In particular, the surface index of the surface of the crystalline substrate, that is, the surface on which the precursor layer of the target oxide film is formed is the (002) surface, so that the oxide film having the same crystal orientation can be formed on the substrate. It is preferable because it can be formed successfully.

Various thin film forming methods can be adopted to form the precursor layer of the target oxide film on the surface of the crystalline substrate. For example, the PLD method can be adopted as the thin film forming method, but considering that the precursor layer of the oxide film is formed in the first step and the dopant-containing layer is formed in the second step, mist is used as the thin film forming method. It is advantageous to adopt the CVD method (mist chemical vapor deposition method). In the mist CVD method, the raw material solution for forming the precursor layer is transported onto the crystalline substrate in a mist-like state under non-vacuum (generally under atmospheric pressure). At this time, the crystalline substrate is kept in a heated state. The mist-like raw material solution transported onto the crystalline substrate is heated on the surface of the substrate and gradually vaporized, and a target precursor is formed in layers by a chemical reaction.

As the raw material solution for forming the precursor layer, a solution containing elements A and B constituting the target oxide film is used. The raw material solution is obtained by dissolving these element sources in a solvent capable of dissolving the A element source and the B element source. As the solvent, an appropriate solvent is used depending on the type of the element A source and the element B source, and examples thereof include water and various organic solvents such as alcohols, ketones and aromatics.

The concentrations of element A and element B in the raw material solution are appropriately adjusted by the mist CVD method so that the desired precursor layer can be successfully formed. In general, satisfactory results can be obtained by setting the concentrations of element A and element B in the raw material solution independently and preferably preferably 0.01 mol% or more and 50 mol% or less.

The mist-like raw material solution is heated on the substrate and chemically reacts. The temperature of the substrate is appropriately set according to the types of the element A source and the element B source contained in the raw material solution. In general, satisfactory results can be obtained by setting the temperature of the substrate to preferably 300 ° C. or higher and 900 ° C. or lower.

In this way, a precursor layer containing elements A and B is formed on the crystalline substrate. The precursor layer in this state is amorphous. This precursor layer is composed of an oxide containing an element A and an element B. Specifically, the precursor layer has a composition formula A _X B ZO ₃ (in the formula, A and B represent metal elements different from each other, X is 0.95 ≦ X ≦ 1.05, and _Z is 0. It is composed of an oxide represented by (.95 ≦ Z ≦ 1.05). The element A is preferably a group 2 element, and particularly preferably Sr. On the other hand, the element B is preferably a group 14 element, and particularly preferably Sn. Therefore, the precursor layer is preferably composed of an oxide containing Sr and Sn.

<Second step>
In this step, the dopant-containing layer is directly formed on the precursor layer formed in the first step. Various thin film forming methods can be adopted to form the dopant-containing layer. In relation to the advantage of forming the precursor layer described above by the mist CVD method, it is advantageous to form the dopant-containing layer by the mist CVD method as well.

As the raw material solution for forming the dopant-containing layer, a solution containing an element contained as a dopant in the target oxide film is used. The raw material solution is formed by dissolving the dopant element source in a solvent capable of dissolving the dopant element source. As the solvent, an appropriate solvent is used depending on the type of dopant element source, and examples thereof include water and various organic solvents such as alcohols, ketones and aromatics.

The concentration of the dopant in the raw material solution is appropriately adjusted by the mist CVD method so that the desired dopant-containing layer can be successfully formed. In general, satisfactory results can be obtained by setting the concentration of the dopant in the raw material solution to preferably 0.01 mol% or more and 10 mol% or less.

The mist-like raw material solution is heated and chemically reacts on the substrate on which the precursor layer is formed. The temperature of the substrate is appropriately set according to the type of dopant element source contained in the raw material solution. In general, satisfactory results can be obtained by setting the temperature of the substrate to preferably 300 ° C. or higher and 900 ° C. or lower.

In this way, a dopant-containing layer containing a dopant is formed on the precursor layer. The dopant-containing layer in this state is amorphous. This dopant-containing layer is composed of, for example, an oxide containing a dopant. The dopant is preferably a rare earth element, and particularly preferably La.

The precursor layer and the dopant-containing layer are formed so that the ratio of the thickness of the dopant-containing layer to the thickness of the precursor layer is preferably 0.04 or more and 0.5 or less. It is preferable because the membrane can be obtained successfully. From this viewpoint, the ratio of the thickness of the dopant-containing layer to the thickness of the precursor layer is more preferably 0.05 or more and 0.2 or less, and further preferably 0.1 or more and 0.2 or less.

The ratio of the thickness of the dopant-containing layer to the thickness of the precursor layer is preferably as described above, whereas the thickness of the precursor layer itself is preferably 50 nm or more and 150 nm or less, and the thickness of the dopant-containing layer itself. The precursor is preferably 1 nm or more and 50 nm or less. The thickness of each of the precursor layer and the dopant-containing layer can be measured by a step meter.

When the second step is completed, the crystalline substrate and the composition formula _{AX BZO 3} (in the formula, A and B represent metal elements different from each other, and _X is 0.95 ≤ X ≤ 1.05). There is, Z is 0.95 ≦ Z ≦ 1.05), and an amorphous precursor layer (first layer) made of an oxide and an amorphous material made of an oxide of a rare earth element. A multilayer structure is obtained in which the dopant-containing layer (second layer) of the above is laminated in this order. This multilayer laminate is industrially useful as a precursor structure for producing the oxide film of the present invention.

<Third step>
In this step, the precursor layer and the dopant-containing layer in the above-mentioned multilayer structure are heated. By heating, the constituent elements of the precursor layer and / or the constituent elements of the dopant-containing layer are thermally diffused and crystallization occurs. By appropriately adjusting the heating temperature and heating time, at least a part of the dopant is thermally diffused from the dopant-containing layer to at least a part of the precursor layer to perform doping. Alternatively, at least a part of the element B contained in the precursor layer is thermally diffused to at least a part of the dopant-containing layer. Depending on the heating conditions, a small amount of oxides of element B and rare earth elements may be generated at the interface between the precursor layer and the dopant-containing layer. For example, when the element B is Sn and the dopant is La, La ₂ Sn ₂ O ₇ may be generated. In any case, it is preferable to heat the precursor layer and the dopant-containing layer so that the target oxide film has a perovskite-type crystal structure. As a result, a structure in which the target crystalline oxide film is formed on the crystalline substrate can be obtained.
When at least a part of the element B diffuses into the dopant-containing layer, oxygen deficiency occurs in the precursor layer for charge compensation.

It is preferable that the crystals of the oxide film formed by heating are aligned with the crystal plane of the crystalline substrate from the viewpoint of further enhancing the conductivity of the oxide film. In particular, it is preferable that the (004) plane of the oxide film is aligned with the (002) plane of the crystalline substrate from the viewpoint of further enhancing the conductivity of the oxide film.

In order to obtain the structure having the desired oxide film by using the multilayer structure obtained in the second step, the heating is carried out under an inert gas atmosphere or a vacuum. As the inert gas, nitrogen and a rare gas can be used. When heating under vacuum, it is preferable to set the pressure in the system to 1.0 Pa or less.
Setting the heating temperature to 900 ° C. or higher successfully diffuses the thermal diffusion of the dopant from the dopant-containing layer, successfully crystallization of the precursor layer, and oxidation caused by crystallization of the precursor layer. It is preferable because the FWHM value of the material film can be set to the above-mentioned value. From this point of view, the heating temperature is preferably set to 950 ° C. or higher, particularly 1000 ° C. or higher.
The present inventor has confirmed that the FWHM value of the oxide film gradually decreases as the heating temperature rises. However, the present inventor has also confirmed that when the heating temperature is excessively increased, the value of FWHM, which has been decreasing until then, starts to increase. From this point of view, the upper limit of the heating temperature is preferably set to 1100 ° C. or lower, more preferably 1075 ° C. or lower, and even more preferably 1050 ° C. or lower.
The heating time is preferably set to 2 hours or more and 10 hours or less, more preferably 3 hours or more and 7 hours or less, and even more preferably 4 hours or more 6 on condition that the heating temperature is within the above-mentioned range. It's less than an hour.

By the above method, a structure having a crystalline substrate and a crystalline oxide film formed on the substrate can be obtained. Due to the fact that this structure is obtained by the mist CVD method described above, it is easy to increase the area of the surface of the oxide film opposite to the surface in contact with the substrate (that is, the exposed surface). Is. For example, it is possible to easily form an oxide film having an exposed surface area of preferably 25 mm ² or more, more preferably 50 mm ² or more, and even more preferably 100 mm ² or more. The thickness of the crystalline oxide film is preferably 90 nm or more and 180 nm or less from the viewpoint of ensuring conductivity and manufacturability.

Since the crystalline oxide film in the structure thus obtained is adjusted so that the FWHM has the above-mentioned value, the oxide film has high conductivity. Specifically, the crystalline oxide film in the structure has a high conductivity of preferably 5.0 S / cm or more, more preferably 100 S / cm or more, and even more preferably 300 S / cm. That is all. The higher the value of the conductivity, the more desirable it is, but the upper limit is generally 7000 S / cm.

In relation to the above-mentioned conductivity, the crystalline oxide film in the above structure has a high mobility of preferably 1.0 cm ² / V / s or more, and more preferably 5.0 cm ² / s. It is V / s or more, more preferably 20 cm ² / V / s or more. The higher the mobility, the more desirable it is, but the upper limit is generally 100 cm ² / V / s.
Further, the crystalline oxide film in the above structure has a carrier density of preferably 1.0 × 10 ¹⁴ cm ^-3 or more, more preferably 1.0 × 10 ¹⁹ cm ^-3 or more. Yes, more preferably 1.0 × 10 ²⁰ cm ^-3 or more. The higher the carrier density is, the more desirable it is, but the upper limit is generally 1.0 × 10 ²² cm ^-3 .

Methods for measuring the conductivity, mobility and carrier density of the crystalline oxide film will be described in Examples described later.

Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the invention is not limited to such examples. Unless otherwise specified, "%" means "mass%".

[Example 1]
(1) Film formation of SrSnO ₃ film (1-1) Film formation device The mist CVD device 1 used in this embodiment will be described with reference to FIG. 1. The mist CVD device 1 includes a carrier gas source 2 for supplying a carrier gas, a flow rate control valve 3 for adjusting the flow rate of the carrier gas sent out from the carrier gas source 2, and a mist generation source 4 in which the raw material solution 4a is housed. A container 5 containing water 5a, an ultrasonic transducer 6 attached to the bottom surface of the container 5, a film forming chamber 7, and a supply pipe 9 connecting the mist generation source 4 to the film forming chamber 7. It is provided with a hot plate 8 installed in the membrane chamber 7. On the hot plate 8, a substrate 10 made of a single crystal SrTiO ₃ (cubic crystal, lattice constant: 3.905 Å) having a diameter of □ 15 mm is installed. On the surface of the substrate 10, the (002) surface of the single crystal SrTiO ₃ was exposed.

(1-2) Preparation for film formation The raw material solution 4a in which the Sr compound and the Sn compound were dissolved in the solvent was housed in the mist generation source 4. Next, the substrate 10 placed on the hot plate 8 was heated by operating the hot plate 8. Subsequently, the flow rate control valve 3 was opened to supply the carrier gas from the carrier gas source 2 to the film forming chamber 7, and the atmosphere of the film forming chamber 7 was sufficiently replaced with the carrier gas. Nitrogen was used as the carrier gas.

(1-3) Formation of SrSnO ₃ film The ultrasonic transducer 6 is vibrated at 2.4 MHz, and the vibration is propagated to the raw material solution 4a through water 5a to atomize the raw material solution 4a and mist 4b. Generated. The mist 4b was transported by the carrier gas, passed through the supply pipe 9, and was introduced into the film forming chamber 7. Under atmospheric pressure, the mist thermally reacted on the heated substrate 10 to form an SrSnO ₃ film on the substrate 10. The obtained _SrSnO3 film was amorphous.

(2) Formation of LaO _x film The LaO _x film was formed on the SrSnO ₃ film obtained in (1-3) in the same manner as in (1) except that the raw material solution in which the La compound was dissolved in the solvent was used. Formed. The obtained LaO _x film was amorphous. In this way, a multilayer structure composed of a substrate made of single crystal SrTiO ₃ , an amorphous SrSnO ₃ film, and an amorphous LaO _x film was obtained. The ratio of the thickness of the LaO _x film to the thickness of the SrSnO ₃ film was as shown in Table 1 below.

(3) Heat treatment The multilayer structure obtained in the previous section (2) was heat-treated under a nitrogen atmosphere. The heat treatment conditions were as shown in Table 1 below. In this way, a structure in which a crystalline oxide film was formed on a substrate made of single crystal SrTiO ₃ was obtained. The area of the exposed surface of the crystalline oxide film in this structure was 225 mm ² .
As a result of X-ray diffraction measurement, this oxide film is SrSnO ₃ having a perovskite type crystal structure, and the (004) plane of the oxide film is aligned with the (002) plane of the substrate made of single crystal SrTiO ₃ . Was confirmed. The X-ray diffraction measurement result is shown in FIG. From the results of elemental analysis, it was confirmed that this oxide film was doped with La.

[Examples 2 to 4]
A structure in which a crystalline oxide film is formed on a substrate made of single crystal SrTiO ₃ in the same manner as in Example 1 except that the thickness of the LaO _x film and the temperature of the heat treatment are changed as shown in Table 1. Got As a result of X-ray diffraction measurement, this oxide film is SrSnO ₃ having a perovskite type crystal structure, and the (004) plane of the oxide film is aligned with the (002) plane of the substrate made of single crystal SrTiO ₃ . Was confirmed.
As a result of analyzing the structure of Example 2 by EDS, the ratio of the number of moles of La to the total number of moles of Sr and La was 0.210.

[Comparative Examples 1 to 3]
A structure in which a crystalline oxide film is formed on a substrate made of single crystal SrTiO ₃ in the same manner as in Example 1 except that the thickness of the LaOx film and the temperature of the heat treatment are changed as shown in Table 1. Obtained.

〔evaluation〕
For the crystalline oxide film in the structures obtained in Examples and Comparative Examples, the value of FWHM of the (004) plane was determined by the above-mentioned method. Furthermore, the conductivity, mobility and carrier density were measured by the following methods. The results are shown in Table 1 below.

〔conductivity〕
It was calculated from the following formula using a Hall effect measuring device (HL5500PC manufactured by Nanometrics Japan Co., Ltd.).
ρ = ( _πt / _ln2 ) (VM / IS)
ρ: Volume resistance (Ω ・ cm)
t: Sample thickness (cm)
VM: _Measured voltage (V)
_IS : Current applied (A)

[Mobility]
It was calculated from the following formula using a Hall effect measuring device (HL5500PC manufactured by Nanometrics Japan Co., Ltd.).
μ = -R _HS / ρ _S =-( _VH / ( _IS / B)) / (ρ / t)
μ: Electron mobility (cm ² / V · s)
_RHS : Seat hole coefficient (m ² / C)
ρ _S : Sheet resistance (Ω / Sq.)
V _H : Measured Hall voltage (V)
_IS : Current applied (A)
B: Applied magnetic field (T)
ρ: Volume resistance (Ω ・ cm)
t: Sample thickness (cm)

[Carrier density]
It was calculated from the following formula using a Hall effect measuring device (HL5500PC manufactured by Nanometrics Japan Co., Ltd.).
N = (1 / q ・ t ・ R _HS ) = _{IS ・ B / (q ・ t ・ V H )}
N: Carrier density (cm ^-3 )
_RHS : Seat hole coefficient (m ² / C)
V _H : Measured Hall voltage (V)
_IS : Current applied (A)
B: Applied magnetic field (T)
t: Sample thickness (cm)
q: Charge (C)

As is clear from the results shown in Table 1, it can be seen that the oxide film in the structure obtained in each example has high conductivity, mobility and carrier density. Since the oxide film in the structure of the comparative example was an insulator, measured values of conductivity, mobility and carrier density could not be obtained.

1 Mist CVD device 2 Carrier gas source 3 Flow control valve 4 Mist generation source 4a Raw material solution 4b Mist 5 Container 5a Water 6 Ultrasonic oscillator 7 Film formation chamber 8 Hot plate 9 Supply pipe 10 Substrate

Claims (24)

Composition formula A _X B _{YO 3} (In the formula, A and B represent different metal elements, X is 0.95 ≦ X ≦ 1.05, and Y is 0.60 ≦ Y ≦ 1.05. A crystalline oxide film containing an oxide obtained by doping a perovskite-type oxide represented by) with a rare earth element.
(004) A crystalline oxide film having a half-value width of the locking curve of the X-ray diffraction method measured with respect to the plane of 0.25 degrees or less. The crystalline oxide film according to claim 1, wherein A is a Group 2 element and B is a Group 14 element in the composition formula. The crystalline oxide film according to claim 2, wherein A is Sr and B is Sn in the composition formula. The crystalline oxide film according to any one of claims 1 to 3, wherein the rare earth element is La. The crystalline oxide film according to any one of claims 1 to 4, wherein the conductivity is 5.0 S / cm or more and 7000 S / cm or less. The crystalline oxide film according to any one of claims 1 to 5, wherein the mobility is 1.0 cm ² / V / S or more and 100 cm ² / V / S or less. The crystalline oxide film according to any one of claims 1 to 6, wherein the carrier density is 1.0 × 10 ¹⁴ cm ^-3 or more and 1.0 × 10 ²² cm ^-3 or less. It has a substrate having a lattice constant of 3.800 Å or more and 4.300 Å or less and containing an oxide, and a crystalline oxide film formed on the substrate.
A structure in which the crystals of the crystalline oxide film are arranged so as to be aligned with the crystal plane of the substrate.
The crystalline oxide film has a composition formula A _X B _{YO 3} (in the formula, A and B represent metal elements different from each other, X is 0.95 ≦ X ≦ 1.05, and Y is 0.60. The perovskite-type oxide represented by (≦ Y ≦ 1.05) contains an oxide doped with a rare earth element, and the locking curve half-value width of the X-ray diffraction method measured with respect to the (004) plane. A structure having a temperature of 0.25 degrees or less. The structure according to claim 8, wherein the (004) plane of the crystalline oxide film is aligned with the (002) plane of the substrate. The structure according to claim 8 or 9, wherein A is a Group 2 element and B is a Group 14 element in the composition formula. The structure according to claim 10, wherein A is Sr and B is Sn in the composition formula. The structure according to any one of claims 8 to 11, wherein the rare earth element is La. The crystalline oxide film has an area of 25 mm ² or more on the surface opposite to the surface in contact with the substrate.
The structure according to any one of claims 8 to 12, wherein the crystalline oxide film has a thickness of 90 nm or more and 180 nm or less. A method for producing a crystalline oxide film in which a crystalline oxide film doped with a dopant is formed on a crystalline substrate.
A precursor layer of the crystalline oxide film is formed on the crystalline substrate, and the precursor layer is formed.
A method for producing a crystalline oxide film, wherein a dopant-containing layer containing the dopant is formed on the precursor layer, and then the precursor layer and the dopant-containing layer are heated to obtain the crystalline oxide film. The production method according to claim 14, wherein the amorphous precursor layer is formed. The production method according to claim 14 or 15, wherein the precursor layer containing a Group 2 element is formed. The production method according to claim 16, wherein the precursor layer further containing a Group 14 element is formed. The production method according to any one of claims 14 to 17, wherein the crystalline oxide film is heated so as to have a perovskite-type crystal structure. The production method according to any one of claims 14 to 18, wherein the dopant-containing layer containing a rare earth element is formed. The invention according to any one of claims 14 to 19, wherein the layer is formed so that the ratio of the thickness of the dopant-containing layer to the thickness of the precursor layer is 0.04 or more and 0.5 or less. Production method. A crystalline substrate having a lattice constant of 3.800 Å or more and 4.300 Å or less and containing an oxide.
Composition formula A _X B ZO ₃ (In the formula, A and B represent different metal elements, X is 0.95 ≦ X ≦ 1.05, and _Z is 0.95 ≦ Z ≦ 1.05. The first amorphous layer of oxides represented by.)
A multi-layer structure in which a second amorphous layer made of an oxide of a rare earth element is laminated in this order. The multilayer structure according to claim 21 is heated in an inert gas atmosphere to diffuse the rare earth elements contained in the second layer into the first layer, and the composition formula _{AX BYO 3} ( In the formula, A and B represent different metal elements, X is 0.95 ≦ X ≦ 1.05, and Y is 0.60 ≦ Y ≦ 1.05). A method for producing a structure, which forms a crystalline oxide film containing an oxide obtained by doping a substance with a rare earth element. By heating at 900 ° C. or higher, the rare earth element contained in the second layer is diffused into the first layer, and the (004) surface of the crystalline oxide film is changed to the (002) surface of the crystalline substrate. The manufacturing method according to claim 22. By heating at 900 ° C. or higher, the element B contained in the first layer is diffused into the second layer, and the (004) surface of the crystalline oxide film is changed to the (002) surface of the crystalline substrate. 23. The manufacturing method according to claim 23.

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