JP5793732B2 - Highly crystalline conductive α-type gallium oxide thin film doped with dopant and method for producing the same - Google Patents

Description

  The present invention relates to a highly crystalline conductive α-type gallium oxide thin film to which a dopant is added and a method for producing the same.

Gallium oxide (Ga ₂ O ₃ ) is a transparent semiconductor that has a wide band gap of 4.8 to 5.3 eV at room temperature and hardly absorbs visible light and ultraviolet light. Therefore, it is a promising material particularly for use in optical / electronic devices and transparent electronics that operate in the deep ultraviolet region.
Recently, a photodetector, a light emitting diode (LED), and a transistor based on gallium oxide (Ga ₂ O ₃ ) have been developed (see Non-Patent Document 1).
Patent Document 1 discloses an ultraviolet photodetector including a gallium oxide single crystal substrate.

Gallium oxide (Ga ₂ O ₃ ) has five crystal structures of α, β, γ, σ, and ε, and a generally stable structure is β-Ga ₂ O ₃ .
Since pure gallium oxide _(Ga 2 _{O 3)} is in the normal state is substantially non-conductive, the realization of optical and electronic devices using gallium oxide _(Ga 2 _{O 3),} gallium oxide _(Ga 2 _{O 3} ) To add conductivity by adding a dopant.

Conductive β-Ga ₂ O ₃ thin films doped with dopants have already been developed.
The β-Ga ₂ O ₃ thin film can be produced by a method such as a sol-gel method, a spray method, or a pulse laser deposition (PLD) method.
Patent Document 2 discloses a highly functional Ga ₂ O ₃ single crystal film characterized by being formed by being laminated on a β-Ga ₂ O ₃ single crystal wafer.
However, although the thin film is crystalline, it takes a crystal system called monoclinic crystal, the vertical axis and the longitudinal axis are oblique, and the horizontal axis is orthogonal to both. Since it is a crystal and is physically anisotropic, it is different from the crystal system that we generally use for electronic materials etc., so when trying to grow other materials on β-Ga ₂ O ₃ , its consistency However, it becomes difficult to grow a thin film with high crystallinity. Therefore, it is difficult to produce a high-quality device, which is not preferable. Further, since the growth of the β-Ga ₂ O ₃ thin film requires a high substrate temperature and a high degree of vacuum, the manufacturing cost also increases.

On the other hand, α-Ga ₂ O ₃ is suitable for use in optical / electronic devices because it has the same crystal structure as a sapphire substrate that has already been sold for general use.
Non-Patent Document 2 discloses that an α-Ga ₂ O ₃ thin film is formed on an α-Al ₂ O ₃ substrate by an ultrasonic spray mist CVD method.
However, the α-Ga ₂ O ₃ thin film of Non-Patent Document 2 does not have conductivity, and this technique alone is not suitable for use in optical / electronic devices.

Recently, α- (Ga _1-X M _X ) ₂ having high crystallinity containing α-Ga ₂ O ₃ on a c-plane sapphire substrate having a moderately low temperature of 500 ° C. at normal pressure by a mist CVD method. It has succeeded in growing an O ₃ alloy (M is a metal material).
Non-Patent Document 3 discloses that an α- (Ga _1-X M _X ) ₂ O ₃ alloy having high crystallinity was manufactured on a sapphire substrate.
In order to use the α- (Ga _1-X M _X ) ₂ O ₃ alloy for an optical / electronic device, the growth of conductive α-Ga ₂ O ₃ is an essential condition. However, the conductivity of the α-Ga ₂ O ₃ contained in the α- (Ga _1-X M _X ) ₂ O ₃ alloy of Non-Patent Document 3 is not added.

Since α-Ga ₂ O ₃ has high crystallinity, it is difficult for dopants such as tin to enter, so that conductivity cannot be added, and it has not yet been applied to optical and electronic devices.

JP 2008-303119 A JP 2009-130012 A

IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 58, NO.5 MAY 2011 Japanese Journal of Applied Physics Vol.47 No.9, 2008, pp.7311-7313 `` Heteroepitaxy of Corundum-Structured α-Ga2O3 Thin Films on α-Al2O3 Substrates by Ultrasonic Mist Chemical Vapor Deposition '' Applied Physics Express 2 (2009) 075501 `` Fabrication of Highly Crystalline Corundum-Structured α- (Ga1-XFex) 2O3 Alloy Thin Films on Sapphire Substrates ''

The present invention has been made to solve the above-described problems, and provides a conductive α-Ga ₂ O ₃ thin film with high crystallinity to which a dopant is added and a method for producing the same.

The invention according to claim 1 contains tin, has a full width at half maximum (ωFWHM) (s ⁻¹ ) of 60 to 70 in an X-ray diffraction measurement when the film thickness is 220 to 240 nm , and a carrier density (cm ^{− 3)} is about 8 × ¹⁰ 17 ~1 × ^{10 19} high crystallinity conductivity _alpha-Ga 2 _{O 3} thin film characterized in that a.

The invention according to claim 2 contains tin, has a full width at half maximum (ωFWHM) (s ⁻¹ ) of 60 to 70 in the X-ray diffraction measurement when the film thickness is 220 to 240 nm , and the carrier density (cm ^{− 3} ) relates to a substrate characterized in that a highly crystalline conductive α-Ga ₂ O ₃ thin film of 8 × 10 ¹⁷ to 1 × 10 ¹⁹ is grown on the surface .

The invention according to claim 3 relates to a method for producing a highly crystalline conductive α-Ga ₂ O ₃ thin film comprising the following steps (a) to (d).
(A) Step of preparing a raw material solution by mixing a solution containing water, hydrochloric acid and hydrogen peroxide, a gallium compound, and a tin (II) compound (b) Mistating the raw material solution to prepare a mist-like raw material (C) supplying the mist-like raw material to the film-forming surface of the substrate with a carrier gas; (d) heating the substrate to thermally decompose the mist-like raw material; Of forming a conductive α-Ga ₂ O ₃ thin film to which tin is added

According to the present invention, conductivity can be added to the thin film by adding the dopant to the α-Ga ₂ O ₃ thin film. In addition, a thin film with high crystallinity can be obtained by using an α-type Ga ₂ O ₃ thin film. Thereby, the applicability to an optical / electronic device can be improved.

According to the present invention, by the dopant is high conductivity α-Ga ₂ O ₃ thin film crystal property you being a tetravalent tin, has high conductivity alpha-Ga ₂ O _Three thin films can be obtained. Thereby, the applicability to an optical / electronic device can be improved.

According to the present invention, a highly crystalline conductive α-Ga ₂ O ₃ thin film doped with a dopant is formed on the surface, whereby a highly crystalline conductive α-Ga. _A substrate comprising a ₂ O ₃ thin film can be provided.

According to the present invention, by the dopant is board you being a tetravalent tin, may be a substrate with α-Ga ₂ O ₃ thin film having a high conductivity. Thereby, the applicability to an optical / electronic device can be improved.

According to the present invention, a method for producing an α-Ga ₂ O ₃ thin film is obtained by mixing (a) a solution containing water, hydrochloric acid and hydrogen peroxide, a gallium compound, and a tin (II) compound. A step of preparing, (b) a step of misting the raw material solution to prepare a mist-like raw material, (c) a step of supplying the mist-like raw material to the film-forming surface of the substrate by a carrier gas, and (d) By thermally decomposing the mist-like raw material by heating the substrate, and forming a conductive α-Ga ₂ O ₃ thin film to which tetravalent tin is added on the substrate, A highly conductive α-Ga ₂ O ₃ thin film having high crystallinity and reliably added conductivity can be manufactured safely and with less burden on the environment with a simple configuration.

It is a schematic diagram for explaining a method of generating a high crystallinity conductive α-Ga ₂ O ₃ thin film of the present invention. It is an X-ray diffraction pattern of the α-Ga ₂ O ₃ thin film of Comparative Examples 2 to 5. _{2 is} an X-ray diffraction diagram and an X-ray rocking curve of α-Ga ₂ O ₃ thin films of Examples 2 and 5 and Comparative Example 1. FIG. 6 is a graph showing characteristics of Examples 1 to 5 and Comparative Example 1.

Hereinafter, a highly crystalline conductive α-Ga ₂ O ₃ thin film and a method for producing the same according to the present invention will be described with reference to the drawings.

The thin film of the present invention is a conductive α-Ga ₂ O ₃ thin film with high crystallinity to which a dopant is added.
The dopant is not particularly limited as long as it can add conductivity to the α-Ga ₂ O ₃ thin film, but elements such as Group I, Group II, Group IV, Group V, and Group VII can be used. . Li, Na, K as Group I elements, Zn, Mg, Ti, Fe, Ca as Group II elements, Si, Ge, Ti, Zr, Sn, Group V elements as Group IV elements Cl, F, Br, I, etc. can be used as the elements of N, P, As, Sb, and VII. Among them, Sn (tin) and Zn (zinc) are preferable, and tetravalent tin is preferable. It is particularly preferred. By tetravalent tin is added to the _α-Ga 2 _{O 3} thin film can be an _α-Ga 2 _{O 3} thin film having a high conductivity.

The highly crystalline conductive α-Ga ₂ O ₃ thin film of the present invention can be formed by growing on a substrate surface.
The material of the substrate is not particularly limited as long as α-Ga ₂ O ₃ grows. For example, a crystal substrate, particularly a sapphire (Al ₂ O ₃ ) substrate is preferably used.
Since the α-Ga ₂ O ₃ thin film has a trigonal corundum structure, which is the same crystal structure as sapphire, the α-Ga ₂ O ₃ thin film is easy to grow on the sapphire substrate. Used for.

The highly crystalline conductive α-Ga ₂ O ₃ thin film of the present invention is manufactured by a mist CVD method, and includes (a) a solution containing water, hydrochloric acid and hydrogen peroxide, a gallium compound, a tin (II) compound, Preparing a raw material solution by mixing
(B) misting the raw material solution to prepare a mist-like raw material;
(C) supplying the mist-like raw material to the film formation surface of the substrate with a carrier gas;
(D) by thermally decomposing the mist-like raw material by heating the substrate, and forming a conductive α-Ga ₂ O ₃ thin film to which tetravalent tin is added on the substrate. ing.

FIG. 1 is a schematic diagram for explaining a method for producing a highly crystalline conductive α-Ga ₂ O ₃ thin film according to the present invention.
A raw material solution is prepared in the raw material supply unit (11).
First, a solution containing water, hydrochloric acid and hydrogen peroxide is prepared. The mixing ratio of this solution is not particularly limited, but it is prepared, for example, with water: hydrochloric acid: hydrogen peroxide = 100: 1: 0.5.
Hydrochloric acid and hydrogen peroxide react with a tin (II) compound to be mixed later to convert the tin (II) compound into a tin (IV) compound. Hydrogen peroxide also plays a role in stretching the crystals of the α-Ga ₂ O ₃ thin film that is produced and making it easier for dopants to enter.

Next, this solution, a gallium compound, and a tin (II) compound are mixed to prepare a raw material solution.
The gallium compound is not particularly limited, but gallium acetylacetonate (GaAcac ₃ ) and gallium chloride are preferably used.
As the tin (II) compound, tin (II) chloride is preferably used.

Next, the obtained raw material solution is misted to prepare a mist-like raw material (1).
The means of mist formation is not particularly limited, and for example, general spray methods such as a pressurization method, a rotating disk method, an ultrasonic method, an orifice vibration method, and an electrostatic method can be used. Preferably used. An ultrasonic transducer (5) is preferably used for mist formation using ultrasonic waves. By applying the container containing the raw material solution to the ultrasonic vibrator (5), the raw material solution becomes mist, and a mist-like raw material (1) is prepared.

This mist-like raw material (1) is supplied by the carrier gas (2) to the film formation surface of the substrate (4) installed in the film formation chamber (21).
A carrier gas (2) supply means is provided on the upstream side of the raw material solution, and the mist-like raw material (1) is also moved downstream by sending the carrier gas (2) to the downstream side (deposition chamber (21) side). Sent out.
Although it does not specifically limit as carrier gas (2), Noble gases, such as air and argon, are used suitably.

The mist-like raw material (1) sent to the downstream side by the carrier gas (2) is introduced into the film forming chamber (21) through the raw material supply pipe (12).
Hereinafter, although the structure of the film-forming chamber (21) will be described in detail, the structure of the film-forming chamber (21) of the present invention is not limited to the following.
The film forming chamber (21) includes a rectifying space (22) into which the mist-like raw material (1) conveyed from the raw-material supply pipe (12) is introduced and rectified, and a mist-like raw material rectified in the rectifying space (22) ( 1) is transported and a reaction space (23) in which a thermal decomposition reaction is performed to form a film on a substrate (4), and a reaction space (23) and a substrate (4) installed in the reaction space (23) are heated. And a heater (6).
The mist-like raw material (1) conveyed from the raw material supply pipe (12) is introduced into a rectifying space (22) having a wide space. The introduced mist-like raw material (1) is rectified here and conveyed to the reaction space (23).

The reaction space (23) has a flat shape (fine channel structure) so that the flow path is narrowed from the rectifying space (22). The height is preferably 0.5 to 3.0 mm. A substrate (4) is placed on the lower surface of the reaction space (23). Below the reaction space (23), a heater (6) for heating the substrate (4) and the reaction space (23) is provided. The mist-like raw material (1) introduced into the reaction space (23) is heated by the heater (6), undergoes thermal decomposition, and generates an α-Ga ₂ O ₃ thin film on the substrate (4).

The mist-like raw material (1) introduced into the reaction space (23) passes through a rapidly narrowed flow path, so that its kinetic energy decreases due to the pressure drop of the fluid, and the mist-like raw material (1) loses speed. Sinks in the direction of gravity. For this reason, it can form into a film on a board | substrate (4) reliably by the press effect to the board | substrate (4) of a raw material.
Further, since the reaction space (23) is very narrow, the introduced mist-like raw material (1) is efficiently heated by the heater (6) and reaches the reaction temperature. Therefore, high reaction efficiency can be achieved.
Furthermore, a uniform thin film having a low surface roughness from the center to the end can be formed on the substrate surface. Further, the present invention can be applied to film formation on a large substrate.

Tin (II) compounds react with hydrogen peroxide and hydrochloric acid in solution and are converted to tin (IV) chloride. Tetravalent tin (Sn (IV)) of the converted tin (IV) compound is added as a dopant to the α-Ga ₂ O ₃ thin film.

It is a feature of the method for producing an α-Ga ₂ O ₃ thin film according to the present invention that a divalent tin (II) compound is used as a dopant starting material and tetravalent tin (IV) is added.
This is based on the following reaction formula (1) (when the tin (II) compound is tin (II) chloride).
(Formula 1) SnCl ₂ + H ₂ O ₂ + 2HCl → SnCl ₄ + 2H ₂ O

The inventors of the present application have tried to add tin several times so far, and even if tin is added to the α-Ga ₂ O ₃ thin film using SnCl ₂ , high conductivity cannot be added to the thin film. However, it was found that when Sn is added to the α-Ga ₂ O ₃ thin film using SnCl ₄ , conductivity can be added to the thin film.
However, SnCl ₄ is a liquid at normal temperature and reacts with moisture in the air to produce white smoke of hydrogen chloride. In addition, when a large amount of water is added, it is violently hydrolyzed to generate heat and generate fumes, which is very dangerous in the thin film production method of the present invention.
On the other hand, SnCl ₂ is solid and stable at room temperature.
Therefore, by utilizing the safe reaction of the above (formula 1), a tin (II) compound such as SnCl ₂ is converted into a tin (IV) compound such as SnCl ₄ , and Sn (IV) is converted into an α-Ga ₂ O ₃ thin film. By adding to the α-Ga ₂ O ₃ thin film, it is possible to add conductivity to the α-Ga ₂ O ₃ thin film.

In the following examples, the temperature in the film forming chamber (21) and the substrate (4) is preferably 350 to 500 ° C. If it is less than 350 ° C., the energy required for the reaction is insufficient, and a conductive α-Ga ₂ O ₃ thin film cannot be produced, which is not preferable. Exceeding 500 ° C. is not preferable because the load on the substrate increases. However, the temperature conditions also change depending on the conditions such as the film forming apparatus, the precursor material (solute) and the solvent, and the method of applying external energy such as an electric field and plasma. The temperature of 4) is not limited to the above temperature.

Be described in more detail with reference to the following examples, crystalline high conductivity α-Ga ₂ O ₃ thin film and the generation method of the present invention is not limited thereto.

Example 1
<Preparation of raw material solution>
Water, hydrochloric acid and hydrogen peroxide were mixed at a weight ratio of 100: 1: 0.5 to obtain a solution. To this solution, gallium acetylacetonate (GaAcac ₃ ) (manufactured by Sigma-Aldrich) was added to 0.020 mol / L, and tin (II) chloride was added as a dopant to 0, 2, 4, 6, 8, 10 The raw material solution was prepared in a container. These are referred to as Comparative Example 1, Examples 1, 2, 3, 4, and 5, respectively. Comparative Examples 2 to 5 were those to which hydrochloric acid, hydrogen peroxide and tin (II) chloride were not added.

<Preparation of mist-like raw material>
The raw material solution obtained in the above step is subjected to an ultrasonic vibrator HM-2412 (manufactured by Honda Electronics Co., Ltd.) under the conditions of 2.4 MHz, 24 V · 0.625 A, 3 (frequency, power, number), The solution was misted to prepare a mist-like raw material in the space in the container.

<Supply to the deposition surface of the substrate>
Next, compressed air was supplied as a carrier gas into the container at a flow rate of 2.0 L / min, and the mist-like raw material in the space was conveyed to the raw material supply pipe. Furthermore, compressed air was supplied as a dilution gas to the raw material supply pipe at a flow rate of 4.5 L / min, and the mist-like raw material was conveyed to a film forming chamber having a fine channel structure of a reaction space having a height of 1 mm while being diluted.

<Film formation>
A c-plane sapphire (c-Al ₂ O ₃ ) substrate was placed in the reaction space in the deposition chamber. The substrate temperature was adjusted with heaters so that the raw materials of Examples 1 to 5 and Comparative Example 1 containing hydrochloric acid, hydrogen peroxide and tin (II) 0, 2, 4, 6, 8, and 10% were 400 ° C. The substrate temperature of the raw material which did not contain hydrochloric acid, hydrogen peroxide, and tin (II) chloride was heated to 350, 400, 450, and 500 ° C. with a heater, and Comparative Examples 2 to 5 were used. A thin film was formed on the substrate with a growth time of 10 minutes.

An α-Ga ₂ O ₃ thin film was obtained by the method described above. Table 1 shows the raw materials, substrate temperature, and tin doping concentration of Examples 1 to 5 and Comparative Examples 1 to 5. The following evaluation was performed with respect to the obtained α-Ga ₂ O ₃ thin film.

<X-ray diffraction measurement>
X-ray diffraction measurement was performed on the α-Ga ₂ O ₃ thin film using an X-ray diffractometer (manufactured by Rigaku Corporation, ATX-G, CuKα ₁ line 1.540561４０) to evaluate crystallinity. Comparative Examples 2 to 5 _alpha-Ga 2 _{O 3} 2 X-ray diffraction measurement of a thin film, Examples 2, 5 and Comparative Example 1 of _alpha-Ga 2 _{O 3} FIG results of X-ray diffraction measurement of the thin film 3 ( a) The X-ray rocking curve is shown in FIG.

From FIG. 2, peak A, which is the diffraction line of the (0006) plane of the α-Ga ₂ O ₃ crystal, and peak B, which is the diffraction line of the (0006) plane of the α-Al ₂ O ₃ of the substrate, were observed. It can be seen that the α-Al ₂ O ₃ thin film is formed in the temperature range of 350 to 450 ° C.

From FIG. 3, peak C, which is the diffraction line of the (0006) plane of the α-Ga ₂ O ₃ crystal, and peak D, which is the diffraction line of the (0006) plane of α-Al ₂ O ₃ of the substrate, were observed. It can be seen that α-Al ₂ O ₃ thin films are formed at tin doping concentrations of 0%, 4%, and 10%.
It can be seen that even at a high tin doping concentration of 10%, the peak is clear and high crystallinity can be achieved.
The peak having a diffraction line of (0006) plane of _α-Ga 2 _{O 3} crystal, and Examples 1 to 5 and Comparative Example 1, but are offset when compared with Comparative Example 2-5, which is over It is presumed that the crystals are expanded and contracted by hydrogen oxide, and the dopant (tin) is likely to enter.

<Characteristics of α-Ga ₂ O ₃ thin film>
The thickness (nm), full width at half maximum (ωFWHM) (s ⁻¹ ), resistivity (Ωcm), carrier concentration (cm ⁻³ ) of each of the α-Ga ₂ O ₃ thin films of Examples 1 to 5 and Comparative Example 1 Mobility (cm ² / Vs) was measured. For the measurement, a Hall measuring device HL5500PC (manufactured by Accent) was used. The results are shown in FIG.
The resistivity is a resistance value per unit thickness obtained by dividing the resistance value of the thin film by the film thickness. The resistance of the α-Ga ₂ O ₃ thin film having a tin doping concentration of 0% was too large to exceed the measurement limit, and thus could not be measured. Similarly, the carrier concentration and mobility of the α-Ga ₂ O ₃ thin film having a tin doping concentration of 0% exceeded the measurement limit and could not be measured. The resistance was 10 ² Ωcm or less at a tin doping concentration of 2 to 10%, and the lowest resistivity was ² Ωcm at a tin doping concentration of 4%.
It was proved that conductivity was added to the α-Ga ₂ O ₃ thin film by the thin film production method of the present invention.

The thickness is calculated from Laue interference fringes appearing in the 2θ / ω plot of X-ray diffraction. The thickness of the α-Ga ₂ O ₃ thin film to which tin is added is 220 to 240 nm.
The full width at half maximum (ωFWHM) of the α-Ga ₂ O ₃ thin film to which tin was added was 60 to 70 s ⁻¹ . Since the β-Ga ₂ O ₃ thin film is about 200 s ⁻¹ , it can be seen that the crystallinity is very high.
The carrier concentration of the α-Ga ₂ O ₃ thin film to which tin was added was 8 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , and the highest was α-Ga ₂ O ₃ having a tin doping concentration of 4%. It was a thin film. The α-Ga ₂ O ₃ thin film having a tin doping concentration of 2,4% exhibits n-type conductivity. On the other hand, α-Ga ₂ O ₃ thin films with tin doping concentrations of 6, 8, and 10% did not show characteristics that determine n-type or p-type.

From the above results, it was confirmed that the dopant could be added to the α-Ga ₂ O ₃ thin film by the thin film formation method of the present invention, thereby producing a conductive α-Ga ₂ O ₃ thin film. Recognize. It can also be seen that high crystallinity can be maintained even when a dopant is added.

  The present invention is suitably used for optical / electronic devices such as photodetectors, light emitting diodes (LEDs), and transistors.

DESCRIPTION OF SYMBOLS 1 Mist-form raw material 2 Carrier gas 3 Dilution gas 4 Substrate 5 Ultrasonic vibrator 6 Heater 11 Raw material supply unit 12 Raw material supply pipe 21 Deposition chamber 22 Rectification space 23 Reaction space

Claims (3)

The full width at half maximum (ωFWHM) (s ⁻¹ ) in X-ray diffraction measurement when tin is contained and the film thickness is 220 to 240 nm is 60 to 70, and the carrier density (cm ⁻³ ) is 8 × 10 ¹⁷ to A conductive α-Ga ₂ O ₃ thin film having high crystallinity, which is 1 × 10 ¹⁹ . The full width at half maximum (ωFWHM) (s ⁻¹ ) in X-ray diffraction measurement when tin is contained and the film thickness is 220 to 240 nm is 60 to 70, and the carrier density (cm ⁻³ ) is 8 × 10 ¹⁷ to A substrate characterized in that a conductive α-Ga ₂ O ₃ thin film having high crystallinity of 1 × 10 ¹⁹ is grown on the surface. A method for producing a highly crystalline conductive α-Ga ₂ O ₃ thin film comprising the following steps (a) to (d):
(A) Step of preparing a raw material solution by mixing a solution containing water, hydrochloric acid and hydrogen peroxide, a gallium compound, and a tin (II) compound (b) Mistating the raw material solution to prepare a mist-like raw material (C) supplying the mist-like raw material to the film-forming surface of the substrate with a carrier gas; (d) heating the substrate to thermally decompose the mist-like raw material; Forming a conductive α-Ga ₂ O ₃ thin film to which tin is added.