JPH1070317A - Manufacture of bismuth-antimony-tellurium compound thermoelectric semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably form a thermoelectric semiconductor which has excellent thermoelectric characteristics around room temperature by depositing alloy of a plurality of elements on a substrate electrode by plating method in an inert gas atmosphere and heat-treating the alloy in a hydrogen gas atmosphere. SOLUTION: An airtight glass container 10 having external inserting holes 20 at five areas is used as a plating bath. Aqueous solution containing a suitable quantity of nitric acid is used as solvent, and solution containing Bi(NO3 )3 , SbF3 and TeO2 is used as a plating solution 30 in the plating bath. Then, inert gas, Argon(Ar), is introduced into the solution at approximately 1 litter per minute from a gas introducing capillary 70 for 30 minutes or more, and Ar gas is kept flowing while plating is performed. A three-element alloy compound is obtained on the surface of a substrate 40 by reducing Bi<3+> ions, Sb<3+> ions and HTeO2 <+> ions. The plating film is heat-treated in a hydrogen flow or in the inert gas. Thus, a thermoelectric semiconductor with excellent thermoelectric characteristics is stably formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a BiSbTe compound thermoelectric semiconductor, and more particularly, to a method of forming a compound by using a plating method.

[0002]

2. Description of the Related Art Thermoelectric semiconductors have been considered to be used as power generating elements by utilizing the so-called Seebeck effect, which generates a voltage when a temperature difference is applied. Although there are various uses for power generation elements, those using thermoelectric semiconductors are considered to be advantageous for miniaturization compared to other power generators because of their simple structure, and they are suitable for portable electronic devices such as watches. Applications are drawing attention. Portable electronic devices are generally used near room temperature, and thermoelectric semiconductors having good characteristics at room temperature are effective as power generating elements.

At present, a thermoelectric semiconductor having the best characteristics at around room temperature is a BiTe-based compound, and a ternary BiSbTe is often used as a P-type semiconductor. The basic structures are Bi ₂ Te ₃ and Sb ₂ Te ₃
Solid solution. Incidentally, such a thermoelectric semiconductor is generally obtained by melting and crystallizing a raw material metal. The BiSbTe compound semiconductor manufactured by the melting method has a thermoelectromotive force of 150 to 200 μV / K,
At room temperature it far exceeds other compounds.

However, mechanical processing is required to process a BiSbTe compound produced by a melting method as a power generating element. Since mechanical processing has a limit in miniaturization, a new method for manufacturing thermoelectric semiconductors in a minute size is required. As one of them, it has been proposed that a thermoelectric semiconductor is formed into a thin film by a vapor phase method such as sputtering or vapor deposition, and is miniaturized by etching or the like.

However, the use of the gas phase method requires a very expensive apparatus, which is not preferable for industrial use. Further, it is very difficult to control the composition ratio of the product formed by the vapor phase method, and there is a problem in maintaining stable characteristics. Further, in the vapor phase method, the formation at a thickness of several μm is the limit due to the problem of peeling and cracking due to the influence of film stress and the like, and it is not practical because the element resistance cannot be reduced for application to power generation materials. .

Therefore, a plating method is considered as a method for forming minute thermoelectric semiconductors. The plating method is applied in various places to create minute structures by using in combination with photolithography technology, as represented by electroforming.

[0007]

However, formation of a thermoelectric semiconductor using a plating method has not been studied much, and there are very few reports on the formed product. In particular, there is no example of a ternary compound containing Bi, Sb, and Te which is of interest in the present invention.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to form a BiSbTe thermoelectric semiconductor having good thermoelectric properties at around room temperature stably by a plating method capable of miniaturization and to have good properties. An object of the present invention is to provide a method for manufacturing a thermoelectric semiconductor.

[0009]

In order to achieve the above object, the following method is employed in the method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor according to the present invention.

The method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor according to the present invention comprises the steps of electrochemically reacting bismuth (Bi), antimony (Sb) and tellurium (Te).
An alloy of Bi, Sb, and Te is deposited on the substrate electrode by plating in an inert gas atmosphere using a solution containing
Further, the heat treatment is performed on the alloy in a hydrogen gas atmosphere or an inert gas atmosphere.

The method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor according to the present invention comprises the steps of electrochemically reacting bismuth (Bi), antimony (Sb) and tellurium (Te).
Using a solution containing Bi, Sb and T dissolved in the solution.
When the molar ratio of e is represented by MixSbyTez, z =
When 0.4 ≦ x ≦ 0.6 and 0.5 ≦ y with respect to 1.5, an alloy of Bi, Sb, and Te is deposited on the substrate electrode using a plating method in an inert gas atmosphere, Further, the heat treatment is performed on the alloy in a hydrogen gas atmosphere or an inert gas atmosphere.

The method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor according to the present invention comprises the steps of electrochemically reacting bismuth (Bi), antimony (Sb) and tellurium (Te).
Using a solution containing Bi, Sb and T dissolved in the solution.
When the molar ratio of e is represented by MixSbyTez, z =
For 1.5, 0.4 ≦ x ≦ 0.6 and 0.5 ≦ y, and further −20x + 11.5 ≦ y ≦ −20x + 13.
When the relationship of 5 is satisfied, an alloy of Bi, Sb, and Te is deposited on the substrate electrode using a plating method in an inert gas atmosphere, and the alloy is heat-treated in a hydrogen gas atmosphere or an inert gas atmosphere. It is characterized by the following.

In the method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor according to the present invention, plating is performed in an inert gas atmosphere in which only an inert gas is introduced into a sealed container, so that a stable BiSbTe film is formed. Compound semiconductors can be manufactured. BiSbT manufactured by the melting method
By dissolving a very large amount of Sb in the plating solution and plating compared to the element ratio contained in e, stable BiSbT
e A thermoelectric semiconductor is obtained.

In the method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor according to the present invention, a thermoelectric semiconductor film having extremely high characteristics can be formed by appropriately setting the concentration conditions of Bi, Sb, and Te. .

Further, the coating film obtained by the method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor of the present invention is improved in a good p-type thermoelectric characteristic by performing a heat treatment in a hydrogen gas atmosphere or an inert gas atmosphere. can do.

In the method of manufacturing a bismuth-antimony-tellurium compound thermoelectric semiconductor according to the present invention, since it is formed by plating, it can be used in combination with photolithography technology to obtain high-performance and minute dimensions which have not been obtained before. Can be obtained.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor of the present invention will be described below in detail with reference to the drawings. First, a method for producing a BiSbTe compound thermoelectric semiconductor by a plating method according to the present invention will be described with reference to FIG.
FIG. 1 is a sectional view showing a schematic configuration of a plating apparatus used in an embodiment of the present invention.

As shown in FIG. 1, the plating tank uses a sealed glass container 10 having five external insertion ports 20. Using an aqueous solution obtained by mixing an appropriate amount of nitric acid as a solvent, dissolving Bi (NO ₃ ) ₃ , SbF ₃ and TeO ₂ in a plating tank, and finally adjusting the pH (pH) to 0.9 as a plating solution 30 Use glass container 10 in advance
Put in.

As will be described later, the concentration of TeO ₂ is fixed at 1.5 mmol / l, and the concentration of Bi (NO ₃ ) ₃ is changed from 0.25 mmol / l to 0.75 mmol / l. The SbF ₃ concentration was changed in the range of 0.5 mmol / l to 6 mmol / l, and various plating solutions 30 were used.
Is prepared and a film is formed.

As the substrate 40 to be plated, a glass plate on which Ti is deposited to a thickness of about 1 μm by a vacuum deposition method is used.
A Pt plate is used for the counter electrode 50, and a Pt wire whose surface is sufficiently etched and cleaned using aqua regia is used for the reference electrode 60. Further, a gas introduction capillary 70 and a gas discharge capillary 80 are prepared, and together with the three electrodes described above, the external insertion port 2 is provided.
Insert from 0 into the container. Then, the gap between the external insertion ports 20 is sealed with a sealant 90.

An argon (Ar) gas, which is an inert gas, is introduced into the solution at a flow rate of about 1 liter / minute from the gas introduction capillary 70 for at least 30 minutes, and plating is performed after the dissolved oxygen in the solution is sufficiently removed. During the plating, the Ar gas is kept flowing. Here, the excess gas is discharged from the gas discharge capillary 80. However, the inside of the container is filled with an inert gas during plating because it is not in contact with the outside except for the two points of introduction and discharge. .

It is very important to keep this whole in an inert gas atmosphere. For example, when the container is made in a normal open-type beaker, similarly, deoxidation is performed with Ar for a sufficient time, and even if plating is performed while flowing a gas, a film formed is a very low-density coarse film. It is difficult to use.

In a system in which an active gas such as oxygen can be introduced from the outside, there is a limit even if deoxygenation is performed only in the solution, and the environment is not sufficient for forming a BiTe film by plating. . Therefore, in the present invention, plating is performed by using a plating tank that is as close as possible to a sealed state, and all three electrodes are taken in the same container.

After the dissolved oxygen in the plating solution 30 is sufficiently removed by Ar gas for 30 minutes, the temperature is maintained at 40 ° C. With the plating solution 30 not forcibly agitated, the potential of the Ti-deposited glass as the substrate 40 is set to about-
The voltage is set to 0.65 V, and Bi ^{3 +} ions, Sb ^{3 +} ions, and HTeO ₂ ⁺ ions in the plating solution 30 are reduced to obtain a ternary alloy compound on the surface of the substrate 40.

At this time, the plating current density was 1 mA / cm ²
Before and after, the current density is very small as compared with the ordinary plating method. However, a dense film can be formed by forming at a low current.

For evaluation of electrical characteristics, the film thickness is 2-3 μm.
The BiSbTe compound formed is peeled off from the substrate 40 and the thermoelectromotive force and the specific resistance are measured. Prior to the measurement, the plating film is subjected to a heat treatment in a hydrogen stream or an inert gas.

By the way, the BiSbTe compound was formed by the melting method, and the result showed that the stoichiometric ratio in the film was B
When i: Sb: Te = 1: 1: 3, BiSbTe
It is known that a compound having good characteristics can be obtained as a compound. Therefore, in the present invention, first, the plating solution 3
0 and 1.5 mmol / l of TeO ₂ and Bi (NO ₃ ) ₃
0.5 mmol / l and SbF ₃ 0.5 mmol / l
It was melted and plated.

In the plating of a binary BiTe compound, the element ratio of Bi and Te contained in the film is almost the same as the element ratio in the plating solution, and therefore, it seems that the same applies to the BiSbTe compound. Is common. However, when the film plated at the above ratio was analyzed, Sb was scarcely contained in the film. The film should be a P-type semiconductor if it has a desired composition, but naturally has an N-type characteristic because the amount of Sb is small. This was not improved by heat treatment.

That is, in the ternary plating, the desired composition is not obtained because the precipitation of Sb is suppressed by the precipitation of Bi and Te, and thus the ternary BiSbTe compound plating cannot be easily performed. Therefore, in the present invention, plating is performed by dissolving a considerably large amount of Sb in the solution, which is twice to several times the amount of the element normally considered from the stoichiometric ratio of the compound. Thereby, Sb can be gradually mixed into the film.

FIG. 2 shows that the plating solution 30 contains TeO ₂ .
5 mmol / l and Bi (NO ₃ ) ₃ 0.5 mmol /
was dissolved in l, the SbF ₃ 1mmol / l~5mmol /
1 shows the thermoelectromotive force of a film formed by changing the thickness of the film. FIG.
The symbol a in the figure indicates the thermoelectromotive force of the film immediately after plating.
The thermoelectromotive force is a negative number, which means that the formed film has N-type semiconductor characteristics. In other words, the plating film becomes necessary P if only Sb enters the film.
No mold characteristics can be obtained.

The symbol "b" in FIG. 2 also indicates the thermoelectromotive force of a heat-treated material at 300 ° C. for one hour in a hydrogen stream. As is clear from FIG. 2, the film having the N-type characteristics immediately after plating changes the thermoelectromotive force to a positive number due to the heat treatment, and has the P-type characteristics. Furthermore, Sb
It can be seen that a very high thermoelectromotive force of 150 μV / K or more can be obtained depending on the concentration of Here, the heat treatment is performed in a hydrogen atmosphere, which is a reducing atmosphere, in order to prevent oxidation of the film. This is for the sake of safety. If there are few impurities on the inner wall of the furnace where heat treatment is performed, heat treatment in an inert gas such as argon or nitrogen is sufficient.

FIG. 3 shows that the plating solution 30 contains TeO ₂ .
5 mmol / l and Bi (NO ₃ ) ₃ 0.5 mmol /
and SbF ₃ are dissolved at 3 mmol / l to form a plating,
The analysis result by the X-ray diffraction of the BiSbTe compound film which performed the heat processing is shown.

As is clear from FIG. 3, the plating film has sufficient crystallinity, and when its diffraction angle is viewed, for example, the peak of (110) is Bi ₂ Te obtained from the literature value.
₃ is located in the middle of the single peak and Sb ₂ Te ₃ single peak, films can be seen that is a solid solution of Bi ₂ Te ₃ and Sb ₂ Te _3.

The d value of the strongest (110) diffraction peak is d = 1.160, and d = 2.192 of the Bi ₂ Te ₃ single peak obtained from the literature value and Sb ₂ Te.
Calculating from d = 2.130 of the peak of ₃ alone, it can be seen that Bi ₂ Te ₃ and Sb ₂ Te ₃ are contained in the film at about 50% each. That is, this corresponds to the element ratio B in the plating film.
i: Sb: Te = 1: 1: 3,
That is, the intended stoichiometric ratio is obtained.

Next, FIG. 4 shows that the plating solution 30 contains TeO.
₂ was dissolved at 1.5 mmol / l, and Bi (NO ₃ )
₃ shows the electrical characteristics of various BiSbTe compound films formed by plating while changing the ₃ concentration and the SbF ₃ concentration to each other. In FIG. 4, the vertical axis is the electrical figure of merit. The electrical figure of merit is a number obtained by dividing the square of the thermoelectromotive force by the specific resistance, and is more effective than the thermoelectromotive force alone in expressing the performance of the thermoelectric material. Naturally, the larger the electrical figure of merit, the better the material.

The electrical figure of merit represents the power generated from the formula, and when a thermoelectric material is used as the power generating element, its value must exceed at least 5 × 10 ⁻⁴ W / mK ^2. it is conceivable that.

In FIG. 4, the horizontal axis represents S in the plating solution.
The curves a, b, c, d, and e show the Bi concentrations of 0.25 mmol / l and 0.4 mmol /
l, 0.5 mmol / l, 0.6 mmol / l and 0.7
The figure shows the electrical performance index for various Sb concentrations at 5 mmol / l.

First, as is clear from the graph of FIG. 4, when the Bi concentration in the plating solution is low (0.25 mm
1 / l) or high (0.75 mmol / l) the electrical figure of merit is very low. On the other hand, when the Bi concentration is from 0.4 mmol / l to 0.6 mmol / l, it is clearly understood that the Bi concentration shows a very high value. At this time, if the Sb concentration is 0.5 mmol / l or more, an electric performance index of 5 × 10 ⁻⁴ W / mK ² or more can always be obtained.

Further, according to the graph of FIG. 4, the Bi concentration in the plating solution was 0.4 mmol / l to 0.6 mmol / l.
In the case of, it can be seen that the electrical figure of merit changes with a certain maximum value. The Sb concentration in the plating solution having the maximum value is 1 with respect to the Bi concentrations of 0.4 mmol / l, 0.5 mmol / l and 0.6 mmol / l.
It becomes mmol / l, 3 mmol / l, and 5 mmol / l, and both have a correlation.

When this is represented by an equation, y = −20x + 13. At this time, x is the concentration of Bi in the plating solution and y
Is the Sb concentration in the plating solution. This is the limitation of the Sb concentration only at the maximum value, but the Sb concentration has a certain spread and the electric figure of merit is good. That is, S to obtain the maximum value
b concentration of -1.5 mmol / l to +0.5 mmol /
In l, it can be seen that if successfully set the Bi concentration and Sb concentration always 5 × 10 ^-4 W / mK ² or more high performance can be obtained.

That is, the Te concentration in the plating solution is 1.5 mm
ol / l, Bi concentration (x) is 0.4 ≦ x ≦ 0.6
Then, the Sb concentration (y) is −20x + 11.5 ≦ y ≦ −
If plating is performed at 20x + 13.5, a BiSbTe compound film with high characteristics can always be obtained.

In the present invention, Bi and Sb in the plating solution
The plating is performed by adjusting the concentrations of Te and Te all in the order of mmol / l, because the lower the concentration, the easier the dissolution. What is important here is not the absolute value of the concentration but the ratio of each concentration. For example, in order to change the plating speed, it is not possible to perform plating by increasing or decreasing the absolute value of the concentration with the concentration ratio obtained in the present invention. No problem.

Further, in the method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor of the present invention, a nitric acid aqueous solution is used as a solution when plating is performed. In addition, a Bi compound as a solute such as a sulfuric acid aqueous solution or a hydrochloric acid aqueous solution is used. Other solutions may be used as long as they can dissolve the Sb compound and the Te compound.

[0044] In yet explained above bismuth antimony telluride method of manufacturing a thermoelectric semiconductor of the present invention, with Bi (NO3) 3 as a Bi source, SbF ₃ used as Sb source, using a Te02 as Te source I have. However, other compounds such as Bi2O3 and Bi
Cl3, Bi (OH) 3, SbCl 3, Sb 2 O 3, T
Other soluble compounds such as eBr4 and TeCl4 can be used.

Further, the plating method in the method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor according to the present invention uses a three-electrode method, but two electrodes can be used if voltage conditions are adjusted. In addition, although Ti-deposited glass is used for the substrate 40, a Ti plate may be used without any problem, and another metal plate or a metal-deposited substrate may be used.

[0046]

As is apparent from the above description, the method for producing a BiSbTe compound thermoelectric semiconductor using the plating method of the present invention can easily and stably produce a film-form BiSbTe compound thermoelectric semiconductor. Further, the obtained film is heat-treated in a hydrogen gas atmosphere or an inert gas atmosphere to improve the P-type thermoelectric properties.

By appropriately setting the concentration ratio of Bi, Sb, and Te, a thermoelectric semiconductor film having very high characteristics can be formed. Since the BiSbTe compound thermoelectric semiconductor of the present invention is formed by plating, it is advantageous for miniaturization, and by using photolithography technology, it can be applied to the manufacture of a small and high-output thermoelectric power generation element that could not be achieved conventionally. can do.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a plating apparatus for manufacturing a BiSbTe compound semiconductor used in an embodiment of the present invention.

FIG. 2 is a graph showing a thermoelectromotive force of a BiSbTe compound thermoelectric semiconductor manufactured by using a plating method according to an embodiment of the present invention before and after a heat treatment.

FIG. 3 is a graph showing an X-ray diffraction pattern of a BiSbTe compound thermoelectric semiconductor manufactured according to an embodiment of the present invention.

FIG. 4 shows the electrical performance index of the BiSbTe compound thermoelectric semiconductor manufactured according to the embodiment of the present invention and B in the plating solution.
It is a graph which shows the relationship between i density and Sb density.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Glass container 20 External insertion port 30 Plating solution 40 Substrate 50 Counter electrode 60 Reference electrode 70 Capillary for gas introduction 80 Capillary for gas discharge

Claims (3)

[Claims] 1. Bismuth (Bi) electrochemically reacting
An alloy of Bi, Sb, and Te is deposited on a substrate electrode by a plating method in an inert gas atmosphere using a solution containing Al, antimony (Sb), and tellurium (Te), and the alloy is further placed in a hydrogen gas atmosphere or A method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor, comprising performing heat treatment in an inert gas atmosphere. 2. Bismuth (Bi) electrochemically reacting
And a solution containing antimony (Sb) and tellurium (Te), and the molar ratio of Bi, Sb, and Te dissolved in the solution is represented by B
When expressed as ixSbyTez, 0.4 ≦ x ≦ 0.6 and 0.5 ≦ y for z = 1.5
In this case, an alloy of Bi, Sb, and Te is deposited on the substrate electrode using a plating method in an inert gas atmosphere, and the alloy is heat-treated in a hydrogen gas atmosphere or an inert gas atmosphere. A method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor. 3. Bismuth (Bi) electrochemically reacting
And a solution containing antimony (Sb) and tellurium (Te), and the molar ratio of Bi, Sb, and Te dissolved in the solution is represented by B
When expressed as ixSbyTez, 0.4 ≦ x ≦ 0.6 and 0.5 ≦ y for z = 1.5
And -20x + 11.5 ≦ y ≦ −20x + 1
When the relationship of 3.5 is satisfied, an alloy of Bi, Sb, and Te is deposited on the substrate electrode using a plating method in an inert gas atmosphere, and the alloy is heat-treated in a hydrogen gas atmosphere or an inert gas atmosphere. A method for producing a bismuth-antimony-tellurium compound thermoelectric semiconductor, comprising: