JPH07118015A - Transparent oxide and transparent conductive oxide using the oxide - Google Patents

Abstract

PURPOSE:To obtain a new material transparent to the light of <=250nm and having electric conductivity. CONSTITUTION:This transparent oxide is expressed by Zn(Ga(1-x)Alx)2O4 (where (x) is 0.05 to 0.8) and is a solid soln. having a spinel crystal structure. A carrier is injected into a solid soln. shown by Zn(Ga(1-x)Alx)2O4 (where (x) is 0.05 to 0.8) and having a spinel crystal structure to obtain the transparent conductive oxide. The carrier is injected, for example, at 1X10<18> to 1X10<22>/cm<2>. The transparent conductive oxide is useful as the various displays such as liq. crystal display and EL display, electrode of a solar battery, defogging heater of a refrigerated showcase, heat reflecting glass of the panel of building and automobile, coating material for preventing the electrification of a transparent material and for shielding the electromagnetic wave, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent conductive oxide having transparency in the ultraviolet region and electrical conductivity and a transparent oxide useful as an intermediate thereof. In particular, the invention is
The present invention relates to a transparent conductive oxide having excellent transparency and electric conductivity with respect to light of nm or less. The transparent conductive oxide of the present invention,
Preferred as various displays such as liquid crystal displays and EL displays, solar cell electrodes, anti-fog heaters for freezer showcases, heat ray reflective films for window glass of buildings and automobiles, coating materials for preventing static electricity of transparent substances and shielding electromagnetic waves. Can be used.

[0002]

2. Description of the Related Art So-called transparent conductive materials which are transparent in the visible light region and have electrical conductivity are liquid crystal displays,
Used as various displays such as EL displays and transparent electrodes for solar cells, anti-fog heaters for freezer showcases, heat ray reflection films for window glass of buildings and automobiles, and as a coating for antistatic and electromagnetic shielding of transparent materials. Has been done.

A metal oxide semiconductor is generally used as this type of transparent conductive material. For example, tin oxide (SnO ₂ ), tin-doped indium oxide (IT
O), CdSn ₂ O ₄ , ZnCd ₂ O _4, etc. have been proposed. Among these, ITO is particularly widely used. ITO has an optical absorption edge near 370 nm, and is not only transparent over almost the entire region except the region on the shortest wavelength side of the visible region, but also has a carrier concentration comparable to that of metal and is relatively large as an oxide. It has carrier mobility and high electrical conductivity.

[0004]

Problems to be Solved by the Invention Laser light source and SOR
With the development of light sources, bright light in the ultraviolet region can be used relatively easily. However, such a conductive material that is transparent to the ultraviolet region, particularly light having a wavelength of 250 nm or less, has not existed so far, which has been a technical problem in the application of ultraviolet light. For example, the above-mentioned ITO has an optical absorption edge near 370 nm and is not transparent to light having a shorter wavelength. In addition, the recently reported ZnGa ₂ O ₄ spinel compound has an electric conductivity of 30 / Ω · cm and has an absorption edge at 250 nm (Proceedings of 1993 Annual Meeting of the Ceramic Society of Japan, p. 585). However, it is not transparent to light with a shorter wavelength than this.

Therefore, an object of the present invention is to provide a new material having both transparency to light of 250 nm or less and electrical conductivity.

[0006]

Means for Solving the Problems As a result of investigations aimed at solving such problems, the present inventors have found that an oxide in which Ga sites of ZnGa ₂ O ₄ are partially substituted with Al is in a wavelength range shorter than 250 nm. It was found that the oxide of the present invention exhibits excellent transparency, and that by injecting a carrier into this oxide, an oxide having electric conductivity in addition to the above transparency can be obtained.

That is, the present invention is based on the general formula Zn (Ga _(1-X) A
l _X ) ₂ O ₄ (where X is 0.05 or more and 0.8 or less), and relates to a transparent oxide which is a solid solution having a spinel type crystal structure.

Further, the present invention is the above transparent oxide,
General formula Zn (Ga _(1-X) Al _X ) ₂ O ₄ (where X is 0.05 or more and 0.
8 or less), and a carrier is injected into a solid solution having a spinel type crystal structure.

The base material of the oxide of the present invention is zinc gallium spinel, ZnGa ₂ O ₄ . The spinel structure, which is the crystal structure of ZnGa ₂ O ₄ , is described, for example, in “Crystal Chemistry of Illustrated Fine Ceramics” (FS Galassau, translated by Seiji Kato, Keizo Uematsu, published by Agne Technical Center (198).
4)) and the like, and has the structure described below. The chemical formula of a substance having a spinel structure is generally represented by AB ₂ O ₄ (A and B represent two kinds of cations). The unit cell of the spinel structure is a cubic type, and 32 oxygen ions are contained in one unit cell, and the oxygen ions are closest packed in the <111> direction. The cubic closest packing of oxygen ions creates 64 tetrahedral coordination sites and 32 octahedral coordination sites in one unit lattice, of which 1/8 of the tetrahedral coordination sites Two types of cations occupy 1/2 of the octahedral coordination site, and one unit cell contains eight AB ₂ O ₄ . The spinel structure is classified into the following two types according to the occupancy of the tetrahedral coordination site and the octahedral coordination site by the A and B ions. When the A ion occupies the tetrahedral coordination site and the B ion occupies the octahedral coordination site, it is called a positive spinel. Half of the B ion is the tetrahedral coordination site, and the remaining half of the B ion and A ion is the octahedral coordination site. The case of occupying a site is called reverse spinel.

ZnGa ₂ O ₄ is a positive spinel, Zn ²⁺ ions are located at tetrahedral coordination sites, and Ga ³⁺ ions are located at octahedral coordination sites (JB Good Enough and AL Lobe (JBGood).
enough and ALLoeb), Physical Review (Physic
al Review), Vol. 98-2, 1955, p. 392). Since the octahedra are arranged with their edges shared, the distance between Ga ³⁺ ions is sufficiently short, and the empty Ga 4S orbits overlap each other to form a conduction band, thereby providing electrical conductivity. On the other hand, for example, MgGa ₂ O ₄
Is an inverse spinel, and 1/2 of the octahedral coordination site is Mg ²⁺
Ions are occupied. Therefore, the overlap between Ga4S orbitals is not always formed effectively. Since the electrical conductivity is brought about by the overlap between the 4S orbitals of Ga ³⁺ occupying the octahedral coordination site, it is preferable that the crystal maintain a positive spinel structure when ion-substituting ZnGa ₂ O ₄ .

As described above, ZnGa ₂ O ₄ has an electric conductivity of 30 / Ω · cm, which is a sufficient value as a conductive material. However, the optical absorption edge wavelength is 250 nm,
In order to transmit light with a shorter wavelength than this, it is necessary to shift the absorption edge to the shorter wavelength side. In order to shift the absorption edge wavelength to a shorter wavelength side, it is necessary to widen the energy width of the forbidden band of the substance that defines the absorption edge wavelength, that is, the forbidden band width. Bandwidth and electrical conductivity are both properties that are related to the crystal structure of a material. In the present invention, as described below, various ions of ZnGa ₂ O ₄
Substitution of Zn ²⁺ or Ga ³⁺ was investigated. As a result, the band gap and electrical conductivity can be controlled by partially substituting the Ga ³⁺ site with Al ³⁺ , and a material with a shorter absorption edge wavelength and higher electrical conductivity was successfully obtained.

First, regarding the ions that can be replaced with Zn ²⁺ ,
We studied divalent ions that form Ga ³⁺ and spinel structure. The divalent ions to create a Ga ³⁺ and spinel structure, Mg ^2+,
There are Mn ²⁺ , Ni ²⁺ , Fe ²⁺ , Cu ²⁺ and Cd ²⁺ , of which M
Since g ²⁺ , Mn ²⁺ , Ni ²⁺ , Fe ²⁺ and Cu ^{2+ form an} inverse spinel with Ga ³⁺ , they cannot be used in the present invention. Cd ^{2+ forms a} positive spinel with Ga ³⁺ . However, its forbidden band width is 3.5 eV, which is smaller than 5 eV of ZnGa ₂ O ₄ . Therefore, the substitution with Cd ²⁺ would rather reduce the forbidden band width, and therefore could not be used in the present invention. Therefore, none of these divalent ions has a wide band gap while maintaining the positive spinel structure.

Next, regarding the ions that can replace Ga ³⁺ ,
Trivalent ions forming Zn ²⁺ and spinel structure were investigated. Zn
Trivalent ions that form a spinel structure with ²⁺ include V ³⁺ and C
There are r ³⁺ , Fe ³⁺ , Rh ³⁺ , Mn ³⁺ , Co ³⁺ and Al ³⁺ , all of which are positive spinels. However, of these, V ³⁺ , Cr ³⁺ , F
e ³⁺ , Rh ³⁺ , Mn ³⁺ and Co ³⁺ are ions of d metal whose d orbitals are partially filled. Since the radius of the d orbital is small, even if it occupies the octahedral site, it does not sufficiently overlap with the orbits of the ions of the adjacent octahedral sites, and the conduction band width narrows, causing a significant decrease in electrical conductivity. Further, since the band gap does not widen, these d metals could not be used.
Al ³⁺ ions have completely filled 2p orbitals and empty 3s orbitals. This orbital radius is smaller than the radius of the Ga ³⁺ 4s orbital, but larger than the d orbital, and has a sufficient overlap with the orbitals of the ions of the adjacent octahedral sites. Therefore, no significant decrease in electrical conductivity occurs. At the same time, the band gap widens, so that the absorption edge wavelength can be made smaller than 250 nm. Thus, in the present invention, an oxide that can realize sufficient transparency and electrical conductivity was found by partially substituting the Ga ³⁺ site of ZnGa ₂ O ₄ with Al ³⁺ .

In the oxide of the present invention, x is in the range of 0.05 or more and 0.8 or less. When x is less than 0.05, the amount of substitution is not sufficient and the band gap does not widen, so that the absorption edge wavelength does not become 250 nm or less. Further, when x exceeds 0.8, the light transmittance is sufficient, but it becomes difficult to exhibit electric conductivity. That is, in order to obtain a transparent oxide _{Zn (Ga (1-X)} Al X) 2 O 4 to be expressed electrically conductive transparent conductive oxide, it is necessary to inject carriers into the conduction band, x
When exceeds 0.8, carriers cannot be injected. x is preferably in the range of 0.05 to 0.5.

The transparent oxide of the present invention _{Zn (Ga (1-X)} Al X) 2 O 4
Is a sintering method, a thin film method (eg, sputtering method, CV
D method, MBE method, vapor deposition method, etc.). In the sintering method, for example, raw material oxides such as zinc oxide, aluminum oxide, and gallium oxide are mixed so as to have a desired composition and molded into a desired shape, for example, 1400 to 17
It can be performed by sintering at 00 ° C. for 1 to 48 hours. Further, the thin film method, for example, in the case of a sputtering method, using a _{Zn (Ga (1-X)} Al X) sintered body having a composition of ₂ O ₄ or a mixture powder compact or the like as a target, ^10-4 to ^{- 2}
A film can be formed on a transparent substrate such as glass such as quartz or plastic such as PMMA under the condition of heating the substrate at room temperature to 500 ° C. under the pressure of Torr.

The transparent conductive oxide of the present invention can be obtained by injecting electrons as carriers into the above transparent oxide.
The carrier injection amount is 1 × 10 ¹⁸ / cm ² to 1 × 10 ²² / cm ²
Is suitable, and preferably in the range of 1 × 10 ¹⁹ / cm ² to 1 × 10 ²¹ / cm ² . When the injection amount of the carrier is less than the above range, it becomes difficult to obtain electric conductivity, and when the injection amount of the carrier exceeds the above range, plasma vibration reduces transparency in the visible light region. Examples of the carrier injection method include an ion exchange method and an ion injection method. That is, by injecting electrons left in the oxygen vacancies in withdrawal of the oxygen atoms from the crystal _{Zn (Ga (1-X)} Al X) 2 O 4- σ
(Σ is a number of 0 or more), a method of injecting electrons generated by doping an ion having a higher valence than Zn ²⁺ or Ga ³⁺ into each ion site, and the like can be used. σ may be a number of 0 or more, but since the injected carriers are small, it is almost the same as the stoichiometric composition. As a method of extracting oxygen atoms to form oxygen vacancies, a method such as firing in a reducing atmosphere, firing in a pressurized atmosphere or a reduced pressure atmosphere, and firing in an inert gas can be used. However, even if these methods are used, when x exceeds 0.8, electrons in oxygen vacancies are bonded to Zn ²⁺ and cannot be injected into the conduction band.

[0017]

EXAMPLES Next, the present invention will be described in more detail by way of examples. Examples 1 to 6 and Comparative Examples 1 to 4 ZnO (high purity chemistry, purity 99.9%), Al ₂ O ₃ (high purity chemistry, purity 99.99%) and Ga ₂ O ₃ (high purity chemistry, purity). Each of the powders was weighed at a ratio of 10 kinds shown in Table 1 and wet-mixed using a nylon ball and a nylon pot. Ethanol was used as the dispersion medium. Each mixed powder was calcined in an alumina crucible at 1000 ° C. for 5 hours in the air, and then crushed into a fine powder in a mortar. Powder X-ray analysis was carried out using an X-ray diffractometer RADIIB manufactured by Rigaku Denki Co., Ltd., and it was confirmed that all the powders were a mixed phase of ZnGa ₂ O ₄ and ZnAl ₂ O ₄ . Each calcined powder was uniaxially pressed (100 kg / cm ² ) into a disk shape with a diameter of 20 mm, and
A sintered body was obtained by firing at 00 ° C to 1700 ° C for 2 to 24 hours. To obtain a dense sintered body having a relative density of 95% or more, x
The higher the temperature, the higher the temperature and the time required for firing. As a result of X-ray analysis of the sintered body using the above equipment, Zn (Ga
Was confirmed _(1-X) to Al _X) of the ₂ O ₄ solid solutions were formed.
In Examples 1 to 6, the transparent oxide of the present invention was obtained.

Next, for each sintered body, the surface of the dense sintered body was lapped to prepare two kinds of samples, a disk-shaped sample having a thickness of about 500 μm and a thin piece sample having a thickness of about 30 μm. 1 to 600 ° C. to 800 ° C. in a hydrogen atmosphere
The carrier was injected after reduction for 2 hours to obtain a transparent conductive oxide of the present invention (carrier injection amount: 1 × 10 ²⁰ / c).
m ² ). The light transmittance and electric conductivity of these transparent conductive oxides were measured. In measuring the light transmittance, the thickness is about 3
The light transmittance of a 0 μm thin piece sample was measured using a Hitachi Electric Model 330 self-recording spectrophotometer, and the wavelength at which the absorptance was 50% was taken as the absorption edge wavelength. The electrical conductivity was measured as follows. Gold was vapor-deposited in a 1 mm square shape at four locations on the circumference of the disk-shaped sample to form electrodes. Silver paste (Kamakura Kasei Co., Ltd., DOTITE, D55
0) was used. After measuring the electric resistance by the van der Pauw method, the surface layer was lapped, electrodes were formed again, and the electric resistance was measured. By repeating this, the relationship between the polishing thickness and the electric resistance was obtained, and the electric conductivity was calculated. Absorption edge wavelength measured as described above, 24
Table 1 shows the values of the transmittance and the electric conductivity at 0 nm.

[0019]

[Table 1]

In the oxides in which x is 0 and 0.01 (Comparative Examples 1 and 2), the absorption edge wavelengths are 250 nm and 24, respectively.
It was 9 nm, and the transmittance at 240 nm was 0%. The oxide of the present invention in which x is 0.05 or more (Example 1
In ~ 6), the absorption edge shifts to 245 nm or more, and
The transmission at 0 nm increased from 18% to 91%. The transmittance shows a maximum value of 91% when x is 0.7 and 0.8, and this transmittance can be brought close to 100% by improving the compactness of the sintered body. Moreover, when x was made larger than 0.8 (Comparative Examples 3 and 4), the electrical conductivity was lost.

[0021]

The transparent oxide of the present invention is excellent in transparency to ultraviolet light, and the transparent conductive oxide of the present invention obtained by injecting a carrier into this oxide is excellent in transparency to ultraviolet light, and It is an excellent transparent conductive oxide having a sufficient electric conductivity. This transparent conductive oxide of the present invention,
Useful as various displays such as liquid crystal displays and EL displays, solar cell electrodes, anti-fog heaters for freezer showcases, heat ray reflection films for window glass of buildings and automobiles, coating materials for antistatic and electromagnetic shielding of transparent substances. Is.

Claims (3)

[Claims] 1. A general formula _{Zn (Ga (1-X)} Al X) 2 O 4 ( where, X
Is 0.05 or more and 0.8 or less) and is a solid solution having a spinel type crystal structure. 2. A general formula _{Zn (Ga (1-X)} Al X) 2 O 4 ( where, X
Is 0.05 or more and 0.8 or less), and a carrier is injected into a solid solution having a spinel type crystal structure. 3. The carrier injection amount is 1 × 10 ¹⁸ / cm ² to
The transparent conductive oxide according to claim ² , which has a concentration in the range of 1 × 10 ²² / cm ² .