JP2000261046A - Thermoelectric converting material and manufacture or the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polycrystalline Si system thermoelectric converting materials, having a high Seebeck coefficient contained by a new Si system thermoelectric converting materials in which various kinds of dopant elements are included in Si by 20 atom% or less, which can be easily manufactured without damaging electric conductivity, and which can be easily manufactured in the same method as the method for manufacturing an integrated circuit, and a method for manufacturing this polycrystalline Si system thermoelectric converting materials. SOLUTION: An Si-rich layer using Si as main components and a dopant element rich layer using dopant elements as main components are film-formed and laminated on a required substrate made of silicon or glass, and heat treatment is carried out so that organization in which the dopant element rich layer is distributed to the grain field of the Si rich layer in the laminated direction and/or each layer can be generated. Thus, a Seebeck coefficient can be sharply increased, and thermal conductivity can be reduced, and thermoelectric conversion efficiency can be sharply increased, and Si rich in resources can be used as main components, and environmental contamination can be sharply reduced in this thin film-shaped polycrystalline Si system thermoelectric converting materials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel thermoelectric conversion material containing 20 atomic% or less of various additive elements in Si, wherein Si is mainly formed on a required substrate such as silicon or glass.
A rich layer and an additive element are formed by depositing and laminating a main additive element-rich layer, and further performing a heat treatment to disperse a structure in which a rich phase of the additive element is dispersed in a lamination direction and / or a grain boundary of a Si-rich phase in each layer. By forming it, the Seebeck coefficient is extremely large and the thermal conductivity is low, the thermoelectric conversion efficiency is remarkably increased, and polycrystalline Si in the form of a thin film is characterized by mainly silicon rich in resources and extremely low environmental pollution The present invention relates to a thermoelectric conversion material.

[0002]

2. Description of the Related Art Thermoelectric conversion elements are devices that are expected to be put to practical use from the viewpoint of effective use of thermal energy, which is required in recent industries. For example, thermoelectric conversion elements convert waste heat into electric energy. A very wide range of applications are being studied, such as systems, small portable generators for easily obtaining electricity outdoors, and flame sensors for gas appliances.

[0003] The conversion efficiency from heat energy to electric energy is a function of the figure of merit ZT, and increases as ZT increases. This figure of merit ZT is expressed as in equation (1). ZT = α ² σT / κ (1) where α is the Seebeck coefficient of the thermoelectric material, σ is the electrical conductivity, κ is the thermal conductivity, and T is the high-temperature side (T _H ) and low-temperature side ( It is the absolute temperature represented by the average value of T _L ).

[0004] FeSi, a thermoelectric conversion material known so far,
₂ , silicides such as SiGe are abundant in resources, but the former has a figure of merit (ZT) of 0.2 or less, its conversion efficiency is low and the operating temperature range is very narrow, and the latter contains Ge which is poor in resources. If the amount is not about 20 to 30 at%, no decrease in heat conduction is observed, and Si and Ge have a wide range of liquid-solid and solid-phase lines of totally controlled solid solution, dissolution and ZL method (Zone-Leveling ) Is not widely used because it is difficult to produce a uniform composition and it is difficult to industrialize.

At present, chalcogen-based compounds such as BiTe and PbTe, such as IrSb ₃ having a skutterudite-type crystal structure exhibiting the highest figure of merit, are known to have high-efficiency thermoelectric conversion capabilities. From the viewpoint of environmental protection, it is expected that the use of these heavy metal elements will be regulated in the future.

[0006]

On the other hand, while Si has a high Seebeck coefficient, it has a very high thermal conductivity,
It is not considered suitable for high-efficiency thermoelectric materials, and the study of its thermoelectric properties has been limited to Si with a carrier concentration of 10 ¹⁸ (Mm ³ ) or less.

[0007] However, the inventors have found that adding various elements to Si alone, for example, adding a small amount of a group 3 or 5 element and a small amount of Ge to Si can lower the thermal conductivity. It is possible to find that the Seebeck coefficient is equal to or higher than that of conventionally known Si-Ge and Fe-Si systems, or that it is extremely high at a given carrier concentration, impairing the essential advantages of Si alone. Instead, it was found that the thermoelectric conversion material exhibited a large figure of merit and could be improved in performance.

[0008] The inventors have also added various elements to Si to add P
As a result of investigating the relationship between the amount of addition and the thermoelectric properties, the Seebeck coefficient decreased with the increase of the carrier up to the addition amount, that is, the carrier concentration of 10 ¹⁸ (M / m ³ ). , 10 ¹⁸ to 10 ¹⁹ (M / m ³ ).

[0009] The present invention is based on this novel Si which the inventors have found.
Polycrystalline Si-based thermoelectric conversion material that has a high Seebeck coefficient that the system-based thermoelectric conversion material has and can be easily manufactured without impairing the electrical conductivity and the same method as the integrated circuit manufacturing method And a method of manufacturing the same.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies on the mechanism of obtaining a high Seebeck coefficient in a Si-based thermoelectric conversion material to which various additive elements are added.
As shown in FIG. 3, this novel Si-based material was found to have a structure in which a rich phase of the additive element was formed at the grain boundary of a Si-rich phase mainly composed of Si.

[0011] Further, the inventors have studied the crystal structure, and found that the increase in the Seebeck coefficient is caused by the aggregation of the additional element at the crystal grain boundaries, thereby increasing the carrier conduction.
We found that a high Seebeck coefficient can be obtained in the Si-rich phase in the crystal grains, and as a method of keeping the Seebeck coefficient high and reducing the thermal conductivity, we examined the control of the crystal structure other than the component system. By controlling the cooling rate at the time of dissolving and solidifying the additive-rich phase and the additive element-rich phase, it was found that a structure in which these phases were dispersed in a required arrangement in the material was obtained.

[0012] Therefore, the inventors have such a structure and structure.
As a result of intensive studies on the configuration and manufacturing method that can easily realize a Si-based thermoelectric conversion material, for example, alternately depositing and laminating a Si-rich layer mainly composed of Si or Si and an additional element-rich layer, and then applying a heat treatment By doing so, a structure equivalent to that of FIG. 3 can be obtained in the thickness direction of the laminate or for each layer.Also, an Si-rich layer of Si and the required additive element, and an additive element-rich layer mainly containing the required additive element and also containing Si Alternately,
By laminating, melting, a structure equivalent to the structure obtained by controlling the cooling rate during solidification can be obtained, and the material having the high figure of merit can be obtained by a simple method of forming a film on the substrate. We have found and completed this invention.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the thermoelectric conversion material according to the present invention, in which a rich phase of the additive element is formed at a grain boundary of a Si-rich phase mainly composed of Si, will be described.
For example, when a melt of Si _1-x Ge _x (at%) is produced by arc melting and the cooling after melting is made as rapid cooling, as shown in the schematic diagram of FIG. Si-rich phase mainly composed of Si
A structure in which the additive element segregates at the grain boundary of the Si-rich phase and the additive element-rich phase is obtained.

[0014] Further, when the relationship between the precipitation of added elements of P and B instead of Ge at the crystal grain boundaries and the carrier concentration of n-type and p-type Si was investigated, the correlation between the added amount and the carrier concentration was found to be one. It was confirmed that the additive element was agglomerated at the crystal grain boundary by the structure in which the rich phase of the additional element was formed at the grain boundary of the Si-rich phase, where the carrier conduction was increased and the It was confirmed that a high Seebeck coefficient can be obtained in the Si-rich phase.

Further, the thermal conductivity of this Si-based thermoelectric conversion material is as follows:
It was confirmed that it decreased as the carrier concentration increased. This is considered to be because κ _ph decreased due to scattering of localized phonons of impurities due to the added element in the crystal.

The thermoelectric conversion material according to the present invention can be used for forming a thermoelectric conversion element, for example, on a single crystal or polycrystalline silicon substrate, a glass or ceramic substrate, a resin substrate, or a resin film, or another film. Any known substrate,
A film can also be used, such a substrate, a Si layer or a Si-rich layer mainly composed of Si, and an additive element-rich layer mainly composed of one or more additional elements for forming Si into a P-type semiconductor or an N-type semiconductor. Are laminated, that is, a Si layer or
It is characterized in that a stacked body of a Si-rich layer and an additive element-rich layer is formed.

For example, in the configuration example shown in FIG. 1A, the crystal plane is (111)
Or, on a (100) single crystal silicon substrate, first, a Ge + P thin film layer is formed to a required thickness as an additive element rich layer, and then
A thin film layer of only Si is formed to a required thickness as a Si rich layer,
Further, the above Ge + P thin film layers and Si thin film layers are alternately laminated.

After the lamination, for example, when heat treatment is performed at 873 K for 1 hour in a vacuum, as shown in FIG. 1B, diffusion occurs between the thin film layers, and the Ge + P + ΔSi thin film layer in which Si is diffused, And a thin film layer of Si + ΔP + ΔGe in which P is diffused is alternately stacked. In FIG. 1A, when the Si-rich layer is a Si + P thin film layer, the Si + P layer becomes a Si + ΔGe + P thin film layer after the heat treatment.

As shown in FIG. 2, a Ge + P + Si thin film layer mainly containing Ge and P and containing Si is formed to a required thickness as an additive element rich layer, and then a Si + Ge A thin film layer of the required thickness is formed, and the thin film layer of Ge + P + Si and the thin film layer of Si + Ge are alternately stacked to realize the stacked state after the heat treatment of FIG.1B. Is possible.

FIG. 1B shows a film formed and laminated on a single crystal silicon substrate.
Alternatively, the laminate shown in FIG. 2 has a Si-rich phase mainly composed of Si shown in FIG.
It is equivalent to embodying a structure in which an additive element-rich phase in which the additive element segregates at the grain boundary of the i-rich phase is formed,
When the diffusion heat treatment is performed, a similar structure is formed even when viewed in the plane of each thin film layer.
A thermoelectric conversion material having a structure equivalent to that of FIG. 3 obtained by rapidly cooling a Si-based molten metal containing

Therefore, the thickness of the above-described Si layer or the Si-rich layer and the additive element-rich layer and the stacking thickness ratio thereof are determined so that these are appropriately dispersed according to the composition of the target Si-based thermoelectric conversion material. It is necessary to select the composition and thickness of the rich layer and the additive element-rich layer, and change the composition of the Si-rich layer and the additive element-rich layer for each lamination, Any laminating means can be adopted as long as at least the structure shown in FIG. 3 can be embodied in the laminating direction, such as a combination of various compositions.

As described above, the thermoelectric conversion material formed and laminated on the substrate is appropriately selected so that the entire laminate has a composition described later, and forms the structure shown in FIG. 3 in the lamination direction. Therefore, a P-type semiconductor, an S-type semiconductor, an electrode film, etc. of the Si-based thermoelectric conversion material are formed in an appropriate pattern such that the temperature gradient direction of the target thermoelectric conversion element is the above-described stacking direction, By stacking, a thermoelectric conversion element can be easily obtained.

The film forming and laminating methods include any of known growth and film forming methods such as a known vapor deposition method such as vapor deposition, sputtering, and CVD, a discharge plasma processing method, and a plasma processing method using a gas containing an additive element. Can be adopted. In addition, as described later, any of the additional elements can be added, and therefore, various cases such as limitations are assumed from a case where the means adopted can be selected depending on the type of the element. Since the processing conditions of the means selected vary depending on the elements to be combined, it is necessary to appropriately select the above means and conditions according to the desired composition. As the heat treatment method, any temperature condition, atmosphere, and heating method can be adopted as long as the conditions cause diffusion between the respective layers.

[0024] The thermoelectric conversion material according to the present invention is capable of adjusting the carrier concentration by adding various impurities to a polycrystalline Si semiconductor having a diamond-type crystal structure, without impairing the inherent advantages of Si alone. This is a highly efficient Si-based thermoelectric conversion material of P-type and N-type semiconductors whose electrical index has been lowered and the Seebeck coefficient has been improved to dramatically improve the figure of merit.

Here, considering the application of the thermoelectric conversion material, the Seebeck coefficient, electric conductivity, thermal conductivity, etc., vary depending on the application such as the heat source, the place of use and form, the current to be handled, and the magnitude of the voltage. Although it is necessary to place emphasis on any of the characteristics, in the thermoelectric conversion material of the present invention, the carrier concentration can be selected by the addition amount of the selected element.

[0026] For example, it contains 0.001 atomic% to 0.5 atomic% of elements added element α of the foregoing alone or combined to give P-type semiconductor carrier concentration is ^{10 17 ~10 20 (M / m} 3) is And
A P-type semiconductor having a carrier concentration of 10 ¹⁹ to 10 ²¹ (M / m ³ ) containing 0.5 to 5.0 atomic% of the additional element α is obtained.

Similarly, an N-type semiconductor containing 0.001 atomic% to 0.5 atomic% of the above-mentioned additive element β alone or in combination and having a carrier concentration of 10 ¹⁷ to 10 ²⁰ (M / m ³ ) Obtained and also
An N-type semiconductor containing 0.5 to 10 atomic% of the additive element β and having a carrier concentration of 10 ¹⁹ to 10 ²¹ (M / m ³ ) is obtained.

When the additive element α or the additive element β is contained and 0.5 to 5.0 atomic% is added so that the carrier concentration becomes 10 ¹⁹ to 10 ²¹ (M / m ³ ), a highly efficient thermoelectric Although the conversion element is obtained and has excellent thermoelectric conversion efficiency, its thermal conductivity is about 50 to 150 W / mK at room temperature, and if the thermal conductivity can be reduced, the figure of merit ZT is further improved. I can expect that.

In general, the thermal conductivity of a solid is given by the sum of phonon conduction and carrier conduction. In the case of a Si-based semiconductor thermoelectric conversion material, phonon conduction is dominant because the carrier concentration is low. Therefore, in order to reduce the thermal conductivity, it is necessary to increase the absorption or scattering of phonons. In order to increase the absorption or scattering of phonons, it is effective to disturb the regularity of the crystal grain size and the crystal structure.

Therefore, as a result of various studies on the elements to be added to Si, at least one of a Group 3 element and a Group 5 element was added to Si, and the carrier concentration was 10 ¹⁹ to 10 ²¹ (M / m ³ ), It is possible to disturb the crystal structure without changing the carrier concentration in Si, and to reduce the thermal conductivity by 30 to 90%.
It was found that the temperature can be reduced to 150 W / m · K or less at room temperature, and a highly efficient thermoelectric conversion material can be obtained.

In the thermoelectric conversion material having the above structure, a P-type semiconductor is obtained when the Group 3 element is contained in an amount of 0.3 to 5 atomic% more than the Group 5 element, and the Group 5 element is contained in an amount of 0.3 to 5 atomic% than the Group 3 element. If a large amount is contained, an N-type semiconductor can be obtained.

Further, it was examined whether a reduction in thermal conductivity could be achieved with elements other than the group 3 element and the group 5 element, and it was found that adding a group 3-5 compound semiconductor or a group 2-6 compound semiconductor to Si further
By adding at least one of a Group 3 element or a Group 5 element and controlling the carrier concentration to 10 ¹⁹ to 10 ²¹ (M / m ³ ),
The crystal structure can be disturbed without changing the carrier concentration in Si, the thermal conductivity can be reduced to 150 W / mK or less at room temperature, and a highly efficient thermoelectric conversion material can be obtained.

Further, as a result of various studies on other additional elements to Si, it was found that Si contained a Group 4 element of Ge, C, and Sn in an amount of 0.1 to 5 atomic%,
By substituting a part of the element i with a group 4 element with a different atomic weight, the scattering of phonons in the crystal increases,
Reduces the thermal conductivity of semiconductors by 20 to 90%, 150 W / mK at room temperature
It is possible to make
A thermoelectric conversion material containing a P-type semiconductor by containing 5.05.0 at% and a N-type semiconductor containing a Group V element by 0.1 to 10 at% can be obtained.

[0034] In the thermoelectric conversion material of the present invention, it was investigated whether elements other than the above-mentioned Group 3 elements and Group 5 elements can be similarly added to Si. For example, although there is no particular limitation, if an element having a very different ionic radius is added, most of the element is precipitated in the grain boundary phase. As an additive element α for forming, and as an additional element β for forming an N-type semiconductor,
It has been confirmed that the single or combined addition of the following groups of elements is particularly effective.

As the additional element α, the additional element A (Be, Mg, Ca, Sr,
Ba, Zn, Cd, Hg, B, Al, Ga, In, Tl), transition metal element M ₁ (M ₁ ; Y, M
o, Zr), and the additive element β is the additive element B
(N, P, As, Sb, Bi, O, S, Se, Te), transition metal element M ₂ (M ₂ ; Ti, V, C
r, Mn, Fe, Co, Ni, Cu, Nb, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, P
t, Au, where Fe is 10 atomic% or less), rare earth element RE (RE; La, Ce,
Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu).

Further, the additive element α for forming a P-type semiconductor and the additional element β for forming an N-type semiconductor are contained in a total amount of at least one from each group in a total amount of 0.002 to 20 atomic%. In order to obtain a P-type semiconductor, the combination of each group can be arbitrarily selected as long as the total amount of the additional element α exceeds that of the additional element β and is contained in a necessary amount to become a P-type semiconductor.

[0037]

EXAMPLE 1 A Si (111) wafer was inserted into a vacuum chamber of 10 ^-6 Torr, and the elements shown in Table 1 were alternately changed into A and B layers by electron beam heating at the thicknesses shown in Table 1 respectively. Was deposited and laminated 50 times.

[0038] The sample on the obtained Si wafer was 5 × 15 mm, 10 × 1
The workpiece was cut into a shape having a diameter of 0 mm and an outer diameter of 10 mm, and the Seebeck coefficient, the Hall coefficient (including the carrier concentration and the electrical conductivity), and the thermal conductivity were measured together with the Si wafer. Table 2 shows the measured values at 1100 K and the figure of merit (ZT = S ² T / ρκ).

The Seebeck coefficient is set as a value obtained by setting the temperature difference between the high temperature part and the low temperature part to about 6K while increasing the temperature, measuring the thermoelectromotive force of the sample with a digital multimeter, and dividing by the temperature difference. I asked. The Hall coefficient was measured by an AC method, and the electrical resistance was measured by a four-terminal method simultaneously with the carrier concentration. The thermal conductivity was measured by a laser flash method.

Example 2 A Si (111) wafer substrate was inserted into a vacuum chamber of 10 ^-2 Torr, and the elements shown in Table 3 were alternately sputtered into layers A and B at the thicknesses shown in Table 1, respectively, by sputtering. Film formation and lamination were repeated.

The sample on the obtained Si wafer was 5 × 15 mm, 10 × 1
The workpiece was cut into a shape having a diameter of 0 mm and an outer diameter of 10 mm, and the Seebeck coefficient, the Hall coefficient (including the carrier concentration and the electrical conductivity), and the thermal conductivity were measured together with the Si wafer. Table 4 shows the measured values at 1100K and the figure of merit (ZT = S ² T / ρκ).

[0042]

【table 1】

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

The thermoelectric conversion material according to the present invention comprises
Si is excellent in terms of global environment, earth resources and safety, and it is very convenient as a thermoelectric conversion element for automobiles because of its low specific gravity and light.Si has excellent corrosion resistance, There is an advantage that processing and the like are unnecessary.

Since the thermoelectric conversion material according to the present invention mainly uses Si, it is less expensive than a Si-Ge material containing a large amount of expensive Ge, and a higher figure of merit can be obtained than an Fe-Si material. . Further, Si used in the present invention has a much lower purity than for semiconductor devices, so the raw materials can be obtained relatively inexpensively, and can be produced by a simple method of simply forming and laminating,
An inexpensive thermoelectric material with good productivity and stable quality can be obtained.

The thermoelectric conversion material according to the present invention makes use of the characteristics of Si having a large Seebeck coefficient and a small electric resistance where the carrier concentration is high, and significantly reduces defects having a large thermal conductivity, and has a large figure of merit. Is an effective way to get Further, there is an advantage that the physical property value can be controlled by the type and amount of the added element.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a laminated state of a thermoelectric conversion material according to the present invention, wherein A shows a state after lamination and B shows a state after heat treatment.

FIG. 2 is an explanatory diagram showing another laminated state of the thermoelectric conversion material according to the present invention.

FIG. 3 is a schematic explanatory view showing a crystal structure of a thermoelectric conversion material according to the present invention.

Claims (8)

[Claims] Claims 1. A substrate or a film, comprising a Si layer or a Si-rich layer mainly composed of Si, and an additive element-rich layer mainly composed of one or more additional elements for forming Si into a P-type semiconductor or an N-type semiconductor. A thermoelectric conversion material comprising a laminate formed by laminating layers, and having a total composition of Si containing the additive element in an amount of 0.001 atomic% to 20 atomic%. 2. The thermoelectric conversion material according to claim 1, wherein the heat treatment is performed on the laminate. 3. The method according to claim 1, wherein the additional element (additional element α) for forming a P-type semiconductor and the additional element (additional element β) for forming an N-type semiconductor are at least
0.002 atomic% to 20 atomic% in total in each case, and additional element α
Or a thermoelectric conversion material containing only a necessary amount of β to form a P-type semiconductor or an N-type semiconductor exceeding that of the corresponding additive element β or α. 4. The semiconductor device according to claim 1, wherein the semiconductor device is a P-type semiconductor.
The additive element (additive element α) of the additive element A (Be, Mg, Ca, Sr, B
a, Zn, Cd, Hg, B, Al, Ga, In, Tl), transition metal element M₁(M₁; Y, Mo,
Zr) is one or more selected from each group, and is an N-type semiconductor.
The additive element (additive element β) for forming the body is an additive element B (N,
P, As, Sb, Bi, O, S, Se, Te), transition metal element M _Two(M_Two; Ti, V, Cr, M
n, Fe, Co, Ni, Cu, Nb, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, A
u, where Fe is 10 atomic% or less), rare earth element RE (RE; La, Ce, Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu)
One or more thermoelectric conversion materials. 5. The method according to claim 1, wherein 1 to 10 atomic% of a Group 3-5 compound semiconductor or a Group 2-6 compound semiconductor is further added, and an additional element A (Be, Mg, Ca, Sr, Ba, Zn, Cd, Hg , B, Al, Ga, In, Tl) or additional element B (N, P, As, Sb, Bi, O, S, Se, Te)
Thermoelectric conversion material containing up to 10 atomic%. 6. The method according to claim 1, wherein at least one of Ge, C, and Sn is selected.
0.1 to 5 atomic% of the seed and the additive element A (Be, Mg, Ca, Sr, Ba, Zn, Cd,
Hg, B, Al, Ga, In, Tl) or additive element B (N, P, As, Sb, Bi, O, S,
A thermoelectric conversion material that is contained singly or in combination from the respective additive element groups of (Se, Te). 7. An Si-rich layer mainly composed of a Si layer or Si, and an additive element rich mainly composed of one or more additional elements for forming Si into a P-type semiconductor or an N-type semiconductor on a substrate or a film. A method for producing a thermoelectric conversion material in which a layered structure is formed, and the entire composition of the formed laminate is a Si-based material containing 0.001 atomic% to 20 atomic% of the additive element. 8. The method for producing a thermoelectric conversion material according to claim 1, wherein a heat treatment is performed on the laminated body after lamination.